GB2374391A

GB2374391A - Transmission including a clutch and a safety valve

Info

Publication number: GB2374391A
Application number: GB0216959A
Authority: GB
Inventors: Oswald Friedmann; Bernhard Walter; Manfred Homm; Michael Reuschel
Original assignee: LuK Getriebe Systeme GmbH
Current assignee: LuK Getriebe Systeme GmbH
Priority date: 1997-07-14
Filing date: 1998-07-10
Publication date: 2002-10-16
Anticipated expiration: 2018-07-10
Also published as: GB0216959D0; GB2373829B; GB2374392B; GB0216044D0; GB2374392A; GB2374391B; GB0216962D0; GB2373829A

Abstract

A transmission comprises at least one source of pressurised fluid, and at least one fluid-operated clutch 201, 202 including a cylinder and a piston 201b, 202b movable within the cylinder. An adjustable pressure regulating valve 206 is provided in a conduit means, and an adjustable safety valve 230 is located in the conduit means between the pressure regulating valve and the cylinder. Means for adjusting the safety valve are also provided, including at least one pilot valve 240. Preferably the safety valve comprises a slide valve having a housing 230a and a spool 231 movable in the housing by the pilot valve. The pilot valve may provide the pressure regulating valve with a plurality of different pressures, including a minimum, median and maximum pressure. Two clutches may be provided, with a selecting valve 210 provided between the safety valve and the cylinders, arranged so that the selecting valve allows fluid to flow to only one of the clutches.

Description

:, 237439 1

TRANSMISSION

The present invention relates to improvements in transmissions which can be employed with advantage in the 5 power trains of motor vehicles to transmit torque from a prime mover (such as an internal combustion engine) to the wheels. More particularly, the invention relates to improvements in transmissions which comprise clutches, actuators, torque sensors, pulleys, belts or chains and/or 10 other parts controlled by systems of pumps, valves and other fluid flow initiating and regulating devices.

It is often necessary to convey a fluid (e.g., oil or another hydraulic fluid) between parts which must move 15 with and/or relative to each other, e.g., between a stationary component and a rotary component or between two components which can or must or should rotate at different speeds an/or in different directions. Transmissions wherein a conduit, a pipe, a hose or an analogous fluid 20 conveying component must confine a stream of a fluid to flow between two spaced-apart components which can or should move relative to each other are well known in the art of power trains for motor vehicles.

25 It is also known to mount the fluid conveying component (hereinafter called conduit for short) in such a way that it can further serve as a means for compensating for manufacturing tolerances and/or for improper centring of one of the two spaced-apart components relative to the 30 other component (and/or vice versa) and/or for pronounced or unanticipated or normal wear upon the spaced-apart components. In accordance with a presently known proposal, part on t a small diameter conduit is introduced into a bore of one of two spaced-apart components, and the 35 other end portion of such conduit is confined in a bore of the other of the two spaced-apart components. Each end

1' 1 2 - portion is surrounded by a split-ring piston packing which is intended to seal the end portion of the respective bore. Each such packing is further intended to act as a constituent of a universal joint which enables the 5 respective component to perform at least some stray movements (i.e., movements other than strictly angular movements) relative to the other component. Such stray movements might be necessary to account or to compensate for certain manufacturing tolerances and/or for wear 10 and/or for lack of accurate centring of the end portions of the conduit in the bores of the respective components.

As a rule, the ability of the end portions of the conduit and of the split-ring piston packings to act as parts of a universal joint is enhanced by enlarging those portions of 15 the bores which receive the packings.

A drawback of such connections for the end portions of the conduit is that the universal joints permit pronounced and often excessive leakage of the conveyed fluid. This can 20 entail a penetration of a coolant or a lubricant or a force transmitting fluid agent into certain parts of a power train which should not be lubricated and/or cooled and/or wetted. Furthermore, the escaping fluid must be replaced at frequent intervals, or the reservoir(s) for 25 such fluid must be designed to confine large quantities of oil or another fluid medium.

According to a first aspect of the invention, there is provided a transmission for use in a power train of a 30 motor vehicle, comprising at least one fluid-operated engageable and disengageable clutch including a cylinder and a piston movable in said cylinder, at least one source of pressurisea fluid, conduct,-, eans connect ng said stucco with said cylinder, an adjustable pressure regulating 35 valve in said conduit means and an adjustable safety valve in said conduit means between said pressure regulating

- 3 - valve and said cylinder, and means for adjusting at least said safety valve, including at least one pilot valve.

The safety valve may include a slide valve having a 5 housing and a spool movable in said housing of said safety valve by said at least one pilot valve. The spool can be movable to a first position in which the safety valve establishes communication between a chamber of the cylinder and the pressure regulating valve and to a second 10 position in which the safety valve prevents the flow of fluid between the chamber and the pressure regulating valve and connects the chamber with a sump to thus reduce the pressure of fluid in the chamber.

15 The pilot valve can be arranged to adjust the safety valve and the pressure regulating valve and can be arranged to furnish to the pressure regulating valve and to the safety valve fluid at a plurality of different pressures including an elevated pressure to thereby change the 20 condition of the safety valve, a low pressure at which the condition of the pressure regulating valve remains unchanged, and a median pressure to thus change the condition of the pressure regulating valve.

25 According to a second aspect of the invention, there is provided a transmission for use in a power train of a motor vehicle, comprising first and second fluid-operated engageable and disengageable clutches, each of said clutches including a cylinder and a piston movable in the 30 respective cylinder, at least one source of pressurized fluid, conduit means cv....=ctin said at least one source with said cylinders, a pressure regulating valve in said conduit means, an adjustable safety valve in said conduit means between said pressure regulating valve and said

- 4 - cylinders, means for adjusting said safety valve, including at least one pilot valve, and a selecting valve in said conduit means between said safety valve and said cylinders, said selecting valve being arranged to assume a 5 first condition in which said conduit means can supply fluid only to the cylinder of said first clutch and a second condition in which said conduit means can supply fluid only to the cylinder of said second clutch.

10 The transmission may also include at least one fluid pressure monitoring device installed in the conduit means upstream of the selecting valve, as seen in the direction of fluid flow toward the cylinders.

15 One of the clutches can be a forward drive clutch and one of the clutches can be a reverse drive clutch.

The features which are considered as characteristic of the invention are set forth in particular in the appended 20 claims. The transmission itself, however, both as to its construction and the mode of assembling, adjusting and operating the same, together with numerous additional important novel and advantageous features thereof, will be best understood upon perusal of the following detailed 25 description of certain presently preferred specific

embodiments with reference to the accompanying drawings.

Figure 1 is a fragmentary axial sectional view of a detail in a transmission wherein 30 two fluid conveying components which rotate at different speeds are co'.nect d to each other by a conduit;

- 5 - Figure 2 is an end elevational view of the conduit as seen from the left-hand side of Figure 1; 5 Figure 3 is an end elevational view of the conduit as seen from the right-hand side of Figure 1; Figure 4 is a schematic partly sectional view 10 of a starting clutch which can be utilised in an automated transmission in the power train of a motor vehicle and embodies the features shown in Figures 1 to 3 as well as a hydraulic 15 operating system for the starting clutch; Figure 4a is an axial sectional view of certain parts of a transmission which embodies 20 the starting clutch of Figure 4; Figure 5 shows a coordinate system wherein the curves represent the relationships between pilot pressures and clutch 25 pressures of a hydraulic fluid; Figure 6 shows a coordinate system wherein the curve represents changes of current strength for the regulation of a valve 30 as a function of changes of the pilot pressure; Figure 7 is a schematic partly sectional view of two fluid-operated clutches for use 35 in a transmission and of a hydraulic clutch operating system;

Figure 8 is a fragmentary axial sectional view of a continuously variable transmission and of a hydraulic 5 operating system for the clutch and for several actuators in the transmission; Figure 9 is a block diagram showing various 10 stages of a computerized clutch operating system for use in a transmission embodying one form of the invention; 15 Figure 10 is a different block diagram; and Figure 11 is a view similar to that of Figure 7 but showing a different hydraulic operating system for two clutches of a 20 transmission for use in the power train of a motor vehicle.

Referring first to Figure 1, there is shown a structure which can be utilised with advantage in a starting clutch 25 (such as the starting clutch 20 shown in Figures 4 and 4a) of a transmission (such as the transmission 99 shown in Figure 4a). The structure of Figure 1 comprises a first component 1 (e.g., a hollow rotary cylindrical shaft corresponding to the part 98 shown in Figure 4a), a second 30 component 2 which may but need not be stationary (i.e., which may but need not rotate when the transmission 99 embodying the structure of Figure 1 or 4a is in use), and an coot ad c l ndrical tithe or conduit 3 between the components 1 and 2 (this conduit can correspond to the 35 part 25 shown in Figures 4 and 4a). In the embodiment of Figure 1, the first component l is rotatable about the

- 7 - central longitudinal axis X-X of the conduit 3, and such axis coincides with the axis of the second component 2.

The first component 1 is provided with a socket 4 in the 5 form of the end portion of an axial bore which serves to supply a fluid (e.g., oil or another hydraulic fluid) into the left-hand end portion of the conduit 3. This end portion is adjacent the end face 10 of the conduit 3 and has a wall thickness 12 (as measured radially of the axis 10 X-X) which exceeds the wall thickness 13 of the major portion (including the right-hand end portion at the end face 11) of the conduit. The cylindrical external surface of the relatively thick left-hand end portion of the conduit 3 is a rather snug fit in the socket 4 and has a 15 circumferentially complete annular groove 8 for a first sealing element 9 here shown as a split-ring piston packing. The sealing element 9 can be deformed to increase or 20 reduce its diameter because it has two end portions which are movable toward or away from each other (as seen in the circumferential direction of the left-hand end portion of the conduit 3).

25 The right-hand end portion of the conduit 3 has a cylindrical external surface provided with a circumferentially complete groove 6 for a second sealing element 7 in the form of a resiliently deformable O-ring made of a suitable elastomeric material and being received 30 in the groove 6 in deformed condition so that it establishes a fluid tight seal between the right-hand end portion of the conduit 3 and the second component 2 when =, . =h-_h,= end port.io of the conduit 3 is received in a bore or socket 5 of the second component 2.

- 8 - In accordance with a highly advantageous feature of this embodiment of the invention, the frictional engagement between the deformed sealing element 7 on the one hand, and the second component 2 and the conduit 3 on the other 5 hand, is sufficiently pronounced to ensure that the conduit 3 is compelled to share all angular movements (including zero angular movement) of the second component 2 and/or vice versa.

10 The end face 11 of the conduit 3 is shown at a certain axial distance from an internal stop or abutment 14 (shown in the form of a ring-shaped shoulder provided in the surface bounding the socket 5 and confronting the conduit 3). When the conduit 3 is compelled to move axially (in a 15 direction to the right, as viewed in Figure 1) under the action of a pressurised fluid which flows in the first component 1 and acts upon the end face 10, the extent of axial movement of the conduit 3 against the resistance of the sealing elements 9 and 7 is determined by the internal 20 shoulder 14 which is engaged by the end face 11 to prevent any further axial displacement of the conduit 3 in the direction of the axis X-X and to the right, as viewed in Figure 1.

25 The split-ring piston packing (first sealing element) 9 can be made of a metallic or any other suitable (e.g., plastic) material. The illustrated sealing element 9 has a polygonal (preferably square or rectangular) cross-sectional outline. In addition to being deformable 30 in a sense to increase or reduce its diameter, the sealing element 9 is also deformable for can be deformable) in the axial direction of the conduit 3, i.e., its end portions Hi.....v-v-= = =- "l Aft l fir! r 1 at ice to each other in the direction of the axis X-X. The dimensions of the sealing 35 element 9 can be selected in such a way that its end, portions are not in actual contact with (but preferably

r 9 _ close to) each other when this sealing element is received in the groove 8 and the left-hand end portion of the conduit 3 is received in the socket 4 of the first component 1. It is further preferred to insert the sealing 5 element 9 in a radially stressed condition so that, when the left-hand end portion of the conduit 3 is received in the socket 4, the sealing element 9 tends to expand and bears upon the internal surface surrounding the socket 4.

10 If the first component 1 is a hollow shaft which is rotated about the axis X-X at a speed n1 and serves to supply a stream of a hydraulic fluid into the second component 2 by way of the axial bore or hole in the conduit 3, the rotational speed n2 of the second component 15 2 can be less than n1 (e.g., zero if the component 2 is a stationary housing or case, or a stationary part of a housing or case). As already mentioned above, the frictional engagement between the resilient sealing element 7 on the one hand, and the second component 2 and 20 conduit 3 on the other hand, can be such that the conduit 3 does not rotate if the component 2 does not rotate, or that the conduit 3 rotates relative to the first component 1 and at the exact speed of the second component 2 if the latter is caused to rotate relative to the first component 25 1. The area of the end face 10 of the conduit 3 which is shown in Figures 1 to 3 is greater than the area of the end face 11 because the outer diameter of the (thicker) 30 left-hand end portion of the conduit 3 is greater than the outer diameter of the (thinner) right-hand end portion and because the inner diameters of the two end faces 10, 11 "L^C at leas' GUESS nti ll ' dents CAT The relatively large area of the end face 10 is often desirable because this 35 further ensures that the fluid flowing from the component 1 into the component 2 causes the conduit 3 to assume a

- 10 predetermined axial position in which the end face 11 abuts the stop or shoulder 14.

The structure of Figures 1 to 3 can be put to use in the 5 following way: It is assumed that the first component 1 is a hollow shaft which is rotated at a speed n1. It is further assumed that the second component 2 is rotated at a speed n2. The O-ring 10 7 is deformed to such an extent that it compels the conduit 3 to share all angular movements (if any) of the second component 2 and to thus compel the first component l to rotate relative to the parts 2, 3 if the speed n departs from the speed n2 and/or if the components 1, 2 are 15 caused to rotate in opposite directions.

The tendency of the conduit 3 to share all angular movements of the second component 2 (i.e., not to rotate with the first component 1 if the latter rotates relative 20 to the component 2 and/or vice versa) is further enhanced by the force-locking (frictional) engagement between the end face 11 and the shoulder 14. The finish of the end face 11 and/or shoulder 14 can be selected in such a way that it also enhances the tendency of the conduit 3 to 25 share all angular movements of the second component 2 or to effectively resist any rotation with the first component 1 if and/or when the component 2 does not rotate. 30 As a rule, the relationships of rotational speeds n1 (first component 1), n2 (second component 2) and n3 (conduit 3) are as follows: 1. n1 > n2 = n3, or 35 2. n1 n2 = n3, or 3. n1 > n2 = n3 - 0

It is clear that the positions of the sealing elements 7 and 9 can be reversed (or that the conduit 3 can be installed in inverted position) if the conduit is to 5 rotate (including a rotation at zero speed) with the component 1 relative to the component 2. The diameters of the sockets 4 and 5 are then changed accordingly. All that counts is to employ between one of the two components and one end portion of the conduit a sealing element which lo performs the function of the split-ring piston packing 9, and to install between the other component and the other end portion of the conduit a sealing element which performs the function of the O-ring 7. It is immaterial whether the one and/or the other component rotates, 15 whether the one or the other component does not rotate, or whether one of the components rotates at a speed greater than that of the other component or vice versa.

An additional advantage of the combination of the 20 components l, 2, conduit 3 and sealing elements 7, 9 is that the rate of leakage is relatively low because the escape of fluid, if any, is limited to the region of the packing 9.

25 Furthermore, the sealing action of the O-ring 8 remains unchanged for long periods of time because the O-ring and the adjacent portions of the component 2 and conduit 3 do not turn relative to each other. The wear upon the packing 9 and the adjacent portions of the component 1 and conduit 30 3 is relatively low because the conveyed fluid (such as oil) can adequately lubricate the surfaces which can turn relative to each other.

The provision of the shoulder 14 not only establishes a 35 direct frictional engagement between the component 2 and the conduit 3 (to thus even further reduce the likelihood

- 12 of rotation between the conduit and the component 2) but the shoulder 14 also serves as a means for locating and maintaining the conduit in a predetermined (optimal) axial position relative to the component 2 (as well as relative 5 to the component 1 if the components 1 and 2 are maintained at a fixed axial distance from each other). As already explained hereinbefore, the fluid which flows from the component 1 into the conduit 3 and bears upon the end face 10 causes the end face 11 to abut the shoulder 14 10 whereby the shoulder 14 ensures that, from then on, the axial position of the conduit 3 relative to the component 2 remains unchanged.

The component 1 can constitute a hollow shaft of a 15 transmission (such as a CVT), and the component 2 can constitute a housing or case (or a portion of a housing or case, or a part which is attached to the housing or case) of a transmission.

20 Figures 4 and 4a illustrate certain details of hydraulic controls for the starting clutch 20 in the automated transmission 99 for use in the power train of a motor vehicle, e.g., to receive torque from a friction clutch or any other suitable torque transmitting system (e.g., a 25 torque converter) which can receive torque from the internal combustion engine or another suitable prime mover of the vehicle) and to drive the wheels of the vehicle by way of a differential or the like. The structure of Figure 1 can be utilised to admit a pressurized hydraulic fluid 30 to a chamber 23 of a cylinder or housing 24 of the starting clutch 20.

^'te a' i r l 'r, C1llFCh T,qh h.m nH.ies 0 is combined with a novel structure of the type shown in Figure 1 can be 35 utilized in or in conjunction with an arrangement which is designed to change the direction of rotation (when

necessary), e.g., with a reversing gear. Basically, the structure of Figure 1 can be utilised with advantage in any system wherein a conduit is to convey a fluid medium from a suitable source through a first component to a 5 second component and one of the two components can or should rotate relative to the other component (or vice versa) or the two components can rotate with or relative to each other in the same direction or in opposite directions. As a rule (or at least in many instances), a starting clutch in an automated or automatic transmission comprises a package of lamellae or discs (shown at 21 in Figures 4 and 4a) which can be pressed against each other by an 15 apply piston (221 in response to the application of fluid pressure against the apply piston. The first, third, fifth, etc. discs of the package 21 are compelled to rotate with one of the two components, and the second, fourth, etc. discs are connected with a second component 20 so that, when the neighbouring discs are urged against each other, the first component can transmit torque to the second component or vice versa. The magnitude of the torque which the clutch can transmit depends upon the magnitude of the force which the piston applies to the 25 nearest disc.

When the magnitude of the torque being transmitted by the starting clutch 20 is to decrease, the hydraulic fluid must be free or must be caused to rapidly flow from the 30 chamber 23 next to the apply piston 22 toward and into a reservoir, e.g., into a sump which supplies fluid to a pump or another suitable source of pressurized fluid. To -in's one, he starting clutch normally comprises a suitable spring (particularly a diaphragm spring shown 35 schematically at 29 in each of Figures 4 and 4a) which is installed in such a way that it can push the apply piston

- 14 22 away from the package 21 of clutch discs as soon as the fluid pressure in the chamber 23 at the other side of the piston 22 is reduced to an extent which enables the spring 29 to shift the piston axially and to thus expel fluid 5 from the chamber 23.

Since the starting clutch must be disengaged (at times) while the apply piston 22 rotates, the diaphragm spring 29 must overcome the resistance which the piston 22 offers to 10 axial movement in a direction away from the clutch discs (i.e., away from the package 21 of such clutch discs) as well as the centrifugal force which tends to move the circulating body of hydraulic fluid in the chamber 23 radially outwardly and to thus exert an additional force 15 upon the radially outer portion of the piston 22 in a direction toward the package 21 and the diaphragm spring 29. In other words, the diaphragm spring 29 must overcome that portion of the force being applied (by fluid) against the piston 22 which is due to the pressure of fluid in the 20 conduit 25 supplying pressurized fluid; to the chamber 23 as well as that portion of the force which is attributable to the action of centrifugal force tending to density the fluid in the radially outer portion of the chamber 23.

25 The just discussed problem in connection with rapid evacuation of fluid from the chamber 23 for the purpose of disengaging the starting clutch 20, or of reducing the magnitude of the torque being transmitted by such clutch, can be overcome by utilising a diaphragm spring 29 which 30 stores a substantial amount of energy while the clutch 20 is engaged. This, in turn, necessitates the utilization of a highly pressurized fluid in order to maintain the i:i ^ ' Ad' - And, Id, Ah, aft c n mn berall.Ce slack condition can be established and maintained by filling the 35 chamber 23 with a hydraulic fluid at a pressure which suffices to prevent a displacement of the piston 22 in a

- 15 direction to the right, as viewed in Figure 4, namely to permit at least some angular displacements of the two sets of clutch discs relative to each other. This necessitates a corresponding pressure intensification or multiplication 5 at the valve or valves which control the flow of fluid into and from the chamber 23.

The need for a high or very high pressure of fluid in the chamber 23 for the purpose of maintaining the clutch 20 in lo the engaged condition, together with the appurtenant need for pressure multiplication at the valve(s), creates a number of problems. For example, the operation of the clutch cannot be regulated as reliably and as rapidly when the fluid pressure in the chamber 23 must be very high 15 while the clutch is fully engaged. Moreover, the clutch cannot be regulated as reliably and as accurately as when the fluid pressure is low in order to compensate for certain disturbances and other undesirable phenomena.

20 It is customary, for the reasons of safety, to install in the conduit 25, which supplies pressurized fluid from a source (such as the pump 60 shown in Figure 4) to the chamber 23, a manually operated slide valve (selecting valve) 30 which selects the desired ratio (such as 25 neutral, parking, reverse or forward) of the automated transmission. The purpose of the slide valve 30 is to ensure that the hydraulic fluid can be expelled from the chamber 23 when the transmission is shifted into neutral or parking. Such disengagement of the starting clutch 20 30 (when the transmission has been shifted into neutral or parking gear) is desirable in order to ensure that the motor vehicle cannot be set in motion while the -'nsm'ss on S n such (parking or neutral) gear.

35 The purpose of the various hydraulic controls which are shown in Figures 4 and 4a is to ensure that each

- 16 engagement of the starting clutch 20 involves an optimal utilization of the full range of adjustments of the valve or valves (e.g., a magnetically operated valve) serving to regulate the preliminary fluid pressure, namely that the 5 full range of adjustments can be used optimally for a regulation of the torque being transmitted by the starting clutch. An advantage of such mode of operation is that a pressure reducing slide valve 40 in the control system of Figure 4 can be readily operated in such a way that its 10 axially reciprocable valving element or spool 41 can be reliably biased by a valve spring (such as a coil spring 42) to a position in which the minimal fluid pressure in the chamber 23 of the starting clutch 20 corresponds to the initial stressing of the spring 42.

When the motor vehicle is in use, the fluid pressure in the chamber 23 is preferably reduced only to a value (the so-called creep point) at which the starting clutch 20 can cause the vehicle to crawl or creep. The aforementioned 20 manually operated selecting slide valve 30 is installed in a composite conduit (62, 31, 25) between the pump 60 and the chamber 23 in such a way that it is located downstream of the pressure reducing slide valve 40, i.e., between the valve 40 and the starting clutch 20. As already mentioned 25 above, the manually operated slide valve 30 ensures that the pressure of fluid in the chamber 23 drops rapidly when the transmission is shifted into neutral gear or into parking. 30 Another advantage of the hydraulic control system of Figure 4 is that the pressure multiplication or intensification at the slide valve 30 need not be very _,... ',,,h, ah 1= turn; simplifies the regulation of operation of the starting clutch 20 without affecting the 35 accuracy, versatility and/or reliability of the regulation.

- 17 -

The coordinate system of Figure 5 shows the relationship between the pilot pressure established by the pressure reducing valve 40 and the pressure in the chamber 23 of 5 the starting clutch 20. The coordinate system of Figure 6 shows the manner in which the pilot pressure depends upon the strength of the electric current being supplied to an electromagnetic valve of the control system shown in Figures 4 and 4a.

Referring again to Figures 4 and 4a, the starting clutch 20 comprises the package 21 of clutch discs which can" be pressed against each other with a variable force by the apply piston 22 in dependency upon the pressure of 15 hydraulic fluid in the chamber 23 of the cylinder or housing 24. The prestressed diaphragm spring 29 tends to move the piston 22 in a direction away from the package 21 of clutch discs, i.e., in a direction to expel fluid from the chamber 23. The volume of the chamber 23 (i.e., the 20 quantity of hydraulic fluid in the cylinder 24) rises to a maximum value when the clutch 20 is fully engaged. At such time, the diaphragm spring 29 stores a maximum amount of energy. 25 Figure 4 further shows frictionlinings 26 which flank the package 21, and a counterpressure plate 27. The diaphragm spring 29 is shown only schematically; as can be seen in Figure 4a, this diaphragm spring can act upon the piston 22 radially inwardly of the package 21 of clutch discs.

30 The conduit 25 connects the chamber 23 with the manually operable slide valve 30 which, in turn, is connected with the pressure reducing valve 40 by the aforementioned conduit 31. The conduit 59 connects the outlet of the pump 60 with the valve 40.

The valve 40 is designed to ensure abrupt evacuation of fluid from the chamber 23 when the transmission 99 is set in neutral (A) or park (P). This enhances the safety of operation of the power train including the transmission 99 5 because the motor vehicle cannot be set in motion due to rapid disengagement of the clutch 20 in response to shifting of the transmission into neutral gear or into parking. 10 When the valving element or spool of the valve 30 is shifted to D, the conduit 25 communicates with the conduit 31, i.e., the conduit 25 can receive fluid at a pressure determined by the valve 40. The latter has a first inlet (e. g., a port) E1 for the admission of fluid at a control 15 or pilot pressure determined by an electromagnetic pilot or control valve 50, and a second inlet E2 in the form of a port for reception (from the pump 60) of hydraulic fluid at the full system pressure (namely by way of the conduit 62). A third inlet E3 in the form of a port can receive 20 fluid from an outlet A (e.g., a port) by way of a feedback conduit 45 and admits such fluid into a chamber or compartment 4Ob of the valve housing or body 4Oa. The outlet A supplies fluid to the inlet of the conduit 31 and transmits fluid at the pressure which is to prevail in the 25 chamber 23.

The transmission 99 of Figure 4a comprises a rotary input shaft 98 which is rotatable within the transmission housing or case 98a in antifriction ball bearings 97. The 30 starting clutch 20 spacedly surrounds the input shaft 98 and, in addition to the aforementioned parts, comprises a radially inner carrier or holder 95 for one set of clutch d'. TICS 'n the package 21. A radially outer carrier or holder 94 non-rotatably supports the other set of clutch 35 discs, and such discs alternate with the I discs of the one set. A plate 96 non-rotatably secures the holder 95 to

- / - 19 the input shaft 98. The other carrier or holder 94 is nonrotatably connected with an output element 93 (such as a spur gear) of the transmission 99. Thus, when the starting clutch 20 is engaged, the flow of power is from 5 the shaft 98, through the holder 95, the discs of the package 21, the holder 94, and on to the gear 93.

The energy storing device (diaphragm spring) 29 acts upon the apply piston 22 in a direction to disengage the 10 starting clutch 20. Figure 4a further shows the conduit 25 (e.g., corresponding to the conduit 3 of Figure 1) having a first end portion which is received in a socket of the rotary input shaft 98 (corresponding to the first component 1 of Figure 1) and a second end portion 15 non-rotatably mounted in a socket 89 of the transmission case 98a. The axial passage of the conduit 25 delivers pressurized fluid to the chamber 23 in the cylinder 24 of the starting clutch 20.

20 Referring again to Figure 4, the inlet E1 is connected with the outlet of the control valve 50 (e.g., an electromagnetic valve) by a conduit 51. The valve 50 receives signals from an electronic control unit (schematically shown at 50A) which controls the current 25 flowing in the electromagnet of the valve 50. This ensures that the conduit 51 supplies to the inlet El of the pressure reducing valve 40 a supply of fluid at the pilot pressure. The pressure of fluid which is supplied by the pump into a conduit 61 is reduced in a pressure 30 reducing valve 70 which is connected with the conduit 51 by a further conduit 63. The valve 70 is set up to supply to the conduit 63 fluid at a constant pressure (e.g., 5 . \,, The Bivalve 50 changes such pressure in accordance with signals from the control unit 50A so that the conduit 35 51 delivers to the inlet E1 a hydraulic fluid at the pilot pressure. For example, the pressure (5 bar) of fluid in

- 20 the conduit 63 can be modified by the electromagnetic control valve 50 to a pilot pressure (e.g., between Obar and 5 bar), depending on the current which is selected by the control unit 50A. The control unit 50A can comprise 5 suitable software and selects the current for the electromagnet(s) of the control valve 50 as a function of one or more parameters, e.g., the position (inclination) of the flap forming part of the throttle valve for the engine in the power train of the motor vehicle wherein the 10 power train further includes the transmission 99. For example, the valve 50 can lower the constant pressure of fluid which is supplied by the conduit 63 in that it discharges a predetermined quantity of such fluid into a sump 52. The valve 50 can comprise a reciprocable valving 15 element or spool, and the axial position of such spool determines the rate of evacuation of fluid from the conduit 63 into the sump 52. This ensures that the pressure of fluid in the conduit 51 and at the inlet E1 matches the pilot pressure selected by the control unit 20 50A, e.g., a pilot pressure which is less than the constant pressure of the fluid in the conduit 63.

The spool 41 of the pressure reducing valve 40 is biased by the coil spring 42 which reacts against the housing or 25 cylinder of the valve 40. It is clear that the coil spring 42 can be replaced with other suitable biasing means. The spring 42 bears against the adjacent end face S1 of the spool 41. The arrangement is such that, before it reaches its right- hand end position, a shoulder 44 of the spool 41 30 establishes communication between the inlet E2 (i.e., the discharge end of the conduit 62) and the outlet A so that the outlet A discharges fluid at full system pressure, and SUC'i1 4' U d ' ^';.S in the feedback conduit 45 to the inlet E3 to exert a pressure against a shoulder S2 of the spool 35 41. Thus, the full system pressure acting upon the shoulder S2 opposes the bias of the coil spring 42. This

- 21 causes the spool 41 to move in a direction to the left (as viewed in Figure 4) until the shoulder 44 interrupts the communication between the inlet E2 and the outlet A (and conduit 45). At such time, the pressure of fluid in the 5 chamber 23 of the starting clutch 20 matches the pilot or control pressure at the inlet E1 plus the bias of the spring 42.

The operation of the transmission 99 is as follows; The fluid pressure during initial filling of the chamber 23 of the starting clutch 20 (or during emptying of such chamber) need not be regulated with a high degree of accuracy. The reason is that, at such time, the clutch 20 15 is not called upon to transmit any torque. The spool 41 in the housing or body 40a of the pressure reducing valve 40 is biased only by the coil spring 42 to a position in which the (minimal) pressure of fluid in the chamber 23 of the starting clutch 20 is dependent upon the bias of the 20 diaphragm spring 29 which acts upon the piston 22 in a sense to move the piston axially away from the counterpressure plate 27, i.e., to expel fluid from the chamber 23. The pilot pressure which is established by the electromagnetic control valve 50 is zero.

When the motor vehicle is in use, the control unit BOA receives and transmits signals which cause the control valve 50 to initiate an engagement of the starting clutch 20. Thus, the pilot pressure at the inlet E1 of the valve 30 40 is caused to rise from zero pressure whereby the fluid which is supplied by the conduit 51 acts upon the shoulder S1 of the spool 41 and causes the latter to move in a direct) on to the ri ght Has viewed in Figure 4) so that the conduit 31 receives (from the conduit 62) a stream of 35 fluid at a rate determined by the bias of the spring 42 plus the (pilot) pressure of fluid upon the shoulder S1 of

- 22 the spool 41. When the desired pressure in the chamber 23 is reached, the fluid (supplied by the conduit 45) acts upon the shoulder S2 of the spool 41 so that the flow of pressurized fluid from the inlet E1 to the outlet A is 5 interrupted. At such time, the pilot pressure can be utilized immediately for the transmission of torque. In other words, and in contrast to presently known teachings, no time is lost to first fill the chamber 23 with fluid when the operator of the motor vehicle decides to depress 10 the gas pedal and/or to shift the transmission 99 into reverse or into a forward gear.

In normal operation of the motor vehicle, the fluid pressure in the chamber 23 of the starting clutch 20 can 15 only be reduced to a value which is still sufficient to cause the vehicle to creep or crawl because such creeping takes place while the diaphragm spring 29 assumes a prestressed condition. This is attributable to the bias of the spring 42 upon the spool 41 of the pressure reducing 20 valve 40.

In the coordinate system of Figure 5, the pilot pressure (control valve 50) is measured along the abscissa, and the pressure in the chamber 23 of the starting clutch 20 is 25 measured along the ordinate. The curve AA indicates the pronounced rise of fluid pressure (this must be effected by a valve corresponding to the valve 40 in Figure 4) in accordance with prior proposals (because the initial pilot pressure is zero). The curve BB indicates the much more 30 gradual rise of fluid pressure in the transmission 99 of the present invention; the reason is that the initial pilot pressure is above zero. Thus, the spring 42 cove_ - 'tee t.:ith the contr - 1 irate 50 to maintain the spool 41 in an axial position which ensures that the initial 35 fluid pressure in the chamber 23 (see the line CC) is well above zero. The entire pilot pressure range (normally

- 23 between O bar and 5 bar) can be utilised for the transmission of torque.

Regardless of the momentary axial position of the spool 41 5 (i.e., the position determined by the bias of the spring 42 plus the (pilot) pressure of fluid upon the shoulder S1, the fluid system pressure upon the shoulder S2, and the difference between the areas of the shoulders S1 and S2), it applies that the pressures of fluid acting upon 10 the shoulders S1 and S2 balance or neutralize each other if the communication between the outlet A and the inlet E2 of the housing of the valve 40 is to be interrupted.

Figure 6 shows the dependency of the pilot pressure 15 (measured along the ordinate) upon the strength of the current being supplied by the electromagnet(s) of the pilot valve or control valve 50.

Figure 7 shows a fluid-operated actuating arrangement for 20 a composite starting clutch 200 in an automated transmission. The composite starting clutch 200 comprises a reverse drive disc clutch 201 and a forward drive disc clutch 202. The clutches 201 and 202 are operated hydraulically by way of a manually manipulatable selecting 25 valve 210 having a reciprocable valving element or spool 211 in a suitable housing or body (not referenced). The selected axial position of the spool 211 determines the selection of the clutch 201 or 202, i.e., whether a first conduit 224 supplies hydraulic fluid to a chamber 201a of 30 the clutch 201 or a second conduit 225 supplies hydraulic fluid to a chamber 202a of the clutch 202 The exact pressure of hydraulic fluid which is being supplied to the cvndu' O2^ C- 2 5 'S Set echoed b,r a" pressure regulating valve 206 which receives fluid at system pressure from a 35 pump 203 by way of a conduit leading to an inlet 207.

- 24 The construction of the selecting valve 210 (here shown as a slide valve) is such that, when the valving element or spool 211 assumes a position in which the conduit 224 supplies fluid to the clutch 201, the clutch 202 cannot 5 receive pressurized fluid, and only the conduit 225 receives fluid when the clutch 202 is to be engaged. In other words, the clutch 201 can be engaged only when the clutch 202 is disengaged, and vice versa.

10 The pump 203 draws hydraulic fluid from a source 204 (e.g., a sump or another reservoir), and such fluid must pass through a filter 205 on its way toward the inlet port 207 of the housing or body of the adjustable pressure regulating valve 206. An outlet port 208 of the adjustable 15 valve 206 can admit fluid into a conduit 222 leading to one inlet port of an adjustable safety valve 230 which, in turn, controls the flow of fluid in a conduit 223 on to the manually operated transmission ratio selecting slide valve 210.

The axial position of the spool 209 of the pressure regulating valve 206 is determined by an adjustable control (pilot) valve 220 which determines the establishment and the interruption of communication 25 between the ports 207 and 208. The control valve 220 determines the fluid pressure at the outlet port 208 of the valve 206, i.e., the pressure of fluid to be conveyed to the disc clutch 201 or 202, depending on the axial position of the spool 211. This, in turn, determines the 30 extent of engagement of the clutch 201 or 202, i.e., the magnitude of the torque which the selected clutch 201 or 202 can transmit.

Under normal circumstances, the safety valve 230 35 determines whether or not the fluid supplied by the conduit 222 can enter the conduit 223 and(by way of the

- 25 valve 210) the conduit 224 or 225 to the plenum chamber 201a or 202a, respectively. On the other hand, the valve 206 cooperates with the control or pilot valve 220 to select the pressure of fluid in the conduit 222, i.e., the 5 extent of engagement of the clutch 201 or 202. The engaged clutch 201 or 202 cannot be disengaged in the event of a malfunctioning of the pressure regulating valve 206.

The operation of the safety valve 230 is controlled by a 10 pilot valve or control valve 240 which determines the pilot pressure in a conduit 234 and hence in a chamber 233 at the left-hand end of the spool 231 in the housing or body 230a of the valve 230. The operation of the control valve 240 is regulated by an electronic control unit 250 15 which also controls the operation of the control valve 220. The control unit 250 has several inputs for signals from various monitoring means, e.g., from sensors which monitor selected parameters of the engine and/or motor vehicle. The spool 231 of the safety valve 230 is biased by an energy storing device 232, e.g., a coil spring, which opposes axial movements of the spool 231 in response to admission of pressurized fluid into the chamber 233. In 25 Figure 7, the spool 231 is maintained in an axial position in which it permits a fluid (e.g., oil) to flow from the conduit 222 into the conduit 223. It the pilot pressure of fluid in the conduit 234 and chamber 233 is increased, the spring 232 yields and permits the spool 231 to assume an 30 axial position (to the right of the position shown in Figure 7) in which the path for the flow of fluid from the conduit 222 into the conduit 223 is interrupted At the same time; the spool 231 establishes a connection between the conduit 223 and the sump (at 235) so that the 35 previously engaged clutch 201 or 202 becomes disengaged.

- 26 The clutches 201, 202 respectively comprise housings 201d, 202d for reciprocable pistons 201b, 202b and packages 201c, 202c of clutch discs with pairs of friction linings 201e, 202e. When the clutch 201 or 202 is engaged, the 5 respective package (201c or 202c) of clutch discs is urged against the adjacent counterpressure plate 201f or 202f so that the discs of the package 201c or 202c cannot rotate relative to each other or can slip relative to each other only to the extent determined by the desired 10 extent. of engagement of the clutch 201 or 202.

The pressure of fluid in the conduit 223 is monitored by a suitable sensor (e.g., a pressure gauge) 260.

15 The conduit 290 of Figure 7 serves to convey fluid at system pressure (i.e., from the outlet of the pump 203) to the hydraulic controls of a transmission, e.g., a continuously variable transmission (CVT) of the type shown in Figure 8. The conduit 317 and the pump 308 of 20 Figure 8 respectively correspond to the conduit 209 and pump 203 of Figure 7. The conduit 317 of Figure 8 serves to supply pressurized fluid which is utilised to adjust the sheave or pulley 301 or 302 in the continuously variable transmission of Figure 8.

If the forward drive clutch 202 of Figure 7 is engaged, the spool 211 of the valve 210 permits hydraulic fluid to flow through the conduit 225 and into the chamber 202a to shift the piston 202b against the adjacent friction 30 lining 202e with a force which is required to enable the clutch 202 to transmit torque of a selected magnitude (as determined by the pressure regulating valve 206).

If the pressure regulating valve 206 is damaged or fails 35 to function properly for any other reason, the pressure of fluid in the conduit 222 no longer corresponds to that

- 27 pressure which is required to enable or cause the clutch 201 or 202 to transmit torque of a desired magnitude. This could result in damage to the prime mover or could cause an accident. At such time, the control valve 240 causes 5 the fluid pressure in the conduit 234 and in the chamber 233 of the safety valve 230 to rise so that the conduit 223 communicates with the sump 235 and the clutch 201 or 202 is automatically disengaged.

10 The aforementioned inputs (shown but not referenced) of the control circuit 250 can receive one, two, three or many more signals from suitable sensors and/or electronic circuits. For example, the control unit 250 can receive signals from a sensor which monitors the speed of the 15 motor vehicle (e.g., by monitoring the RPM of one of the wheels), the RPM of a flywheel forming part of a clutch which drives the input shaft A (Figure 8) of the continuously variable transmission, the RPM of the output shaft of such transmission, the position of the gas pedal, 20 the extent of application of the brake(s), the position (such as the inclination) of the flap of the throttle valve in the engine, and/or others. The sensor 260 of Figure 7 can also be set up to transmit to an input of the control unit 250 signals denoting the pressure of fluid in 25 the conduit 223, i.e., the pressure of fluid in the chamber 201a or 202a (depending on the position of the spool 211 in the body or housing of the selecting valve 210). 30 The safety valve 230 of Figure 7 is installed down-stream of the pressure regulating valve 206 and upstream of the selecting valve 210 (as seen in the direction of fluid flow from the source 203 of pressurized fluid to the clutch 201 or 202). However, it is also possible to 35 employ two safety valves one of which can influence the fluid pressure in the conduit 224 and the other of which

--N - 28 can influence the fluid pressure in the conduit 225. The arrangement of Figure 7 (which employs a single safety valve 230) is preferred at this time because it entails savings in space and material and is considered to be just 5 as effective as two discrete safety valves, one for each of the conduits 224 and 225.

Referring now to Figure 8, the continuously variable transmission comprises the two adjustable pulleys 301, 302 10 and an endless flexible element 303 (e.g., a belt or a chain) which is trained over the two pulleys. The pulley 301 rotates with the input shaft A, and the pulley 302 rotates with the output shaft B. The pulley 301 has an axially fixed flange 301b and an axially movable flange 15 301a. Analogously, the pulley 302 has an axially movable flange 302a and an axially fixed flange 302b.

An actuator 304 is provided to adjust the axial position of the flange 301a relative to the axially fixed flange 20 301b, and a second actuator 305 serves to select the axial position of the axially adjustable flange 302a relative to the axially fixed flange 302b. Each of the actuators 304, 305 preferably comprises a fluid-operated motor, e.g., a single-acting or double-acting cylinder and piston 25 assembly. The actuators 304, 305 can serve to urge the respective axially movable flanges 301a, 302a against the adjacent portions of the endless flexible element 303 (e.g., a chain).

30 The actuator 304 operates in parallel with a third actuator 306 (here shown as a third cylinder and piston assembly), and the actuator 30S operates in parallel with a fourth actuator 307 (also shown in the form of a cylinder and piston assembly). The purpose of the 35 actuators 306, 307 is to select the ratio of the continuously variable transmission; these actuators

- 29 respectively comprise plenum chambers 306a, 307a for supplies of a hydraulic fluid (such as oil). The plenum chambers 306a, 307a can receive fluid from the pump 308, or they can discharge fluid into an evacuating conduit 309 5 leading to a sump. The ratio of the transmission is changed by admitting pressurized fluid into one of the chambers 306a, 307a to increase its volume while, at the same time, permitting a corresponding quantity of fluid to escape from the other chamber. The flow of fluid into and 10 from the chambers 306a, 307a is controlled by a regulating valve 310, such as a slide valve having an axially movable valving element or spool 344 biased by a coil spring 343 and being adjacent a chamber 341.

15 The transmission of Figure 8 further comprises a hydromechanical torque sensor 311 serving to generate a pressure which is dependent at least upon the magnitude of the transmitted torque. This torque sensor 311 is mounted in such a way that the entire torque supplied by the input 20 shaft A is transmitted to the first pulley 301. As shown, the torque sensor 311 comprises an axially fixed cam disc 312 which has limited freedom of rotation relative to the input shaft A, and a second cam disc 313 which is movable in the axial direction of but cannot rotate relative to 25 the shaft A. The cam discs 312, 313 have confronting ramps (not referenced) abutting one or more spreading or expanding elements 314 in the form of spheres.

In order to guarantee the establishment of a modulated 30 pressure which is a function at least of the transmitted torque and which is required to adequately tension the continuously variable transmission, the pump 308 is ----cited.,i h a plenum chamber 315 of the torque sensor 311 by conduits 318 and 319. Furthermore, the outlet of 35 the pump 308 is connected, by way of a conduit 321 which

- 30 branches off the conduit 320, with the plenum chamber 307a of the actuator 307 at the second pulley 302.

The chamber 315 of the torque sensor 311 is permanently 5 connected with the plenum chamber 304a of the actuator 304 by one or more channels. The input shaft A is provided with at least one axially extending fluid discharging channel (e.g., a bore) which communicates or which can be communicatively connected with the chamber 315. The fluid 10 which leaves the chamber 315 of the torque sensor 311 by way of a flow restrictor 323 and port 322 can be utilised as coolant and/or lubricant for certain component parts of the power train employing the transmission of Figure 8.

15 The cam disc 313 of the torque sensor 311, which is movable axially of the input shaft A, has a radially inner portion which can regulate the outflow of fluid via port 322 in dependency at least on the magnitude of transmitted torque. In other words, the radially inner portion of the 20 cam disc 313 can be said to form part of a valve or a flow restrictor for the fluid which is to enter the port 322.

The extent to which the inlet of the port 322 is exposed for admission of fluid depends on the axial position of the cam disc 313, i.e., at least upon the magnitude of the 25 torque being transmitted between the cam discs 312 and 313. This ensures that the pressure of fluid which is supplied by the pump 308 and fills the chamber 315 of the torque sensor 311 is indicative, at the very least, of the magnitude of transmitted torque, namely of the torque 30 being supplied by the shaft A to the torque sensor 311 and being transmitted by the torque sensor to the pulley 301.

Hence the chamber 315 communicates with the chamber 304a (by way of the conduits 320, 321) and also with the 35 chamber 305a, the pressure of fluid in the chambers 304a, 305a at least approximates that in the chamber 315. Due to

the fact that the actuators 304, 305 operate in parallel with the respective actuators (cylinder and piston assemblies) 306, 307, the forces which act upon the axially movable flanges 301a, 302a of the pulleys 301, 302 5 in response to a rise of fluid pressure in the chamber 315 are added to the forces acting upon the flanges 301a, 302a in response to fluid pressure prevailing in the chambers 306a, 307a and serving to select or alter the ratio of the transmission. The pressures of fluid in the chambers 315 and 316 are being applied in parallel, and such fluids can communicate with or can be sealed from each other, depending upon the selected ratio or change of ratio of the transmission. The 15 establishment or lack of communication between the chambers 315 and 316 depends upon the axial position of the flange 301a relative to the shaft A. In other words, the flange 301a can act as a valving element which controls the flow of fluid into and from passages in the 20 form of channels machined into the shaft A. It is desirable to ensure that the entire range of shifting the transmission for operation with a decreasing ratio (shifting into lower gear) merely involves the presence of pressurized fluid only in the chamber 315.

The establishment of communication between the chambers 315, 316 can take place at least approximately simultaneously with the transition into the "rapid" stage of the range of the transmission. For example, it can be 30 of advantage to select the timing of the establishment or interruption of communication between the chambers 315, 316 to coincide, at least substantially, with the setting _ a t =nsmis='on ratio of one-to-one. Thus, the torque sensor 311 can ensure the establishment of a transmission 35 ratio-dependent pressure modulation which is superimposed upon a torque-dependent pressure modulation. In actual

- 32 practice, this amounts to the achievement of a two-stage transmission ratio-dependent modulation of the pressure or pressure level.

5 Based on the preceding description of the construction and

mode of operation of the transmission, one can arrive at the conclusion that, within the entire stage of the

transmission range in which the transmission shifts to lower-speed operation (underdrive), the axial force which 10 develops at the ramps of the cam discs 312, 313 is taken up exclusively, or at least primarily, by the axially effective surface in the plenum chamber 315. On the other hand, when the transmission operates within that portion or stage of its range of operation in which the 15 transmission effects an acceleration (overdrive), the axial force which develops at the ramps and acts upon the disc 313 is taken up by the axially effective surfaces in the chambers 315, 316. Thus, and assuming that the input torque is the same, a shifting into operation at a lower 20 speed entails that the pressure generated by the torque sensor 311 is higher than that which the torque sensor generates while the transmission shifts into operation at a higher speed. In accordance with a presently preferred embodiment, the transmission can be set up in such a way 25 that the shifting or switching point at which the chambers 315, 316 begin or cease to communicate with each other is at a transmission ratio of approximately one-to-one.

As concerns further structural and operational features of 30 a continuously variable transmission which employs two adjustable pulleys or sheaves and a chain or belt trained over such pulleys or sheaves, as well as a torque sensor, =-Ere=Ce ma he had to published German patent application No. 44 43 332.8 which describes and shows 35 several embodiments of such transmissions and torque sensors. It is also possible to employ other types of

- 33 presently known torque sensors. For example, the efficiency of the transmission can be enhanced if one employs a torque sensor which caneffect a two-stage, three-stage or even infinitely variable modulation of the 5 pressure in dependency upon the transmission ratio or upon changes of the transmission ratio.

As can be seen in Figure 8, the actuators 304, 305 and 306, 307 and the torque sensor 311 receive fluid from a 10 common source, i.e., from a single source (namely the pump 308). The pump 308 iS followed by an optional volumetric flow control valve 324. For example, the valve 324 can be omitted if the pump 308 is a variable volume pump the output of which varies in dependency upon changing fluid 15 requirements.

The valve 324 is followed by the aforementioned regulating valve 310 which can be operated to change the ratio of the continuously variable transmission, and the valve 310 20 cooperates with the pressure regulating valve 325. As already explained hereinbefore, the valve 325 is connected between the conduits 318, 319 (upstream) and 320 (downstream); this valve 325 regulates the fluid pressure in the conduit 319 (i.e., upstream of the valve 310) in 25 such a way that the pressure in the conduit 319 (and at the corresponding inlet of the housing or body of the valve 310) is higher than the required higher pressure of the two working pressures in the conduits 326, 327 leading from the valve 310 to the respective actuators 306 and 30 307.

The conduit 320 connects the pressure regulating valve 325 ,a,, Ah the torque sensor 311 and, by way of this torque sensor, with the actuator 304. However, it is not always 35 necessary that the flow of fluid from the valve 325 to the actuator 304 take place by way of the torque sensor 311.

- 34 The pressure of fluid in the conduits 320, 321 and in the chambers 304a, 305a is dependent upon the pressure and the torque furnished by the torque sensor 311. In order to ensure a satisfactory operation of the transmission, the 5 pressure of fluid upstream of the regulating valve 310 (i.e., in the conduits 318, 319) is higher than the higher pressure which is required in the conduits 326, 327 and chambers 306a, 307a in order to shift the transmission into a different gear. The pressure which is required to 10 change the ratio of the transmission can exceed the pressure which is furnished by the torque sensor 311. In other words, it could happen that (under certain circumstances of use of the motor vehicle and/or under certain operating conditions) the pressure which is 15 established by the torque sensor 311 would be too low to ensure a rapid shifting of the transmission into a different ratio, such as is required or desirable for a satisfactory operation of the transmission and the entire power train.

For example, a critical situation can develop during braking of the motor vehicle while the engine torque is low or minimal. This entails a rapid deceleration of the vehicle and requires a rapid change of the transmission 25 ratio. If the torque being transmitted by the torque sensor 311 is too low, the pressure of fluid leaving the torque sensor is too low, i.e., too low to ensure a required rapid change of the transmission ratio. In order to ensure that, even under the just outlined or analogous 30 critical circumstances, the pressure in the conduits 318, 319 (i.e., upstream of the regulating valve 310), and hence also in at least one of the conduits 326, 327, will be surricien 'y- high whenever he need Hi see; the pressure regulating (increasing) valve 325 is installed 35 between the torque sensor 311 (i.e., between the conduits 320, 321) and the valve 310 (i.e., the conduit 319). The

- 35 thus installed valve 325 can ensure that the pressure in the conduit 319 and at the valve 310 exceeds (e.g., by a preselected value) the pressures in the conduits 326 and 327. For the just outlined purpose, the pressure regulating valve 325 is associated with or embodies a control means 328 which ensures that, when the operating conditions warrant it, the valve 325 performs at least one flow 10 restricting or throttling operation upon the fluid flowing from the conduit 319 into the conduit 320. In the embodiment of Figure 8, the control means 328 can be influenced or actuated by a feedback of pressures prevailing in the conduits 326 and 327.

A direct feedback takes place by way of the conduits 329, 330 which, on the one hand, communicate with the conduits 326, 327, respectively, and, on the other hand, are connected with a hydraulic OR-gate constituted by the 20 control means 328. The valve 325 and the control means 328 respectively comprise discrete valving elements or spools 331 and 332 which are reciprocable in the respective valve housings or bodies and each of which can move axially independently of the other spool. A pin- shaped distancing 25 element 333 is installed between the spools 331, 332, and the spool 332 is disposed between two chambers 334, 335 which communicate with the conduits 329, 330, respectively. The chamber 325 is located between the spools 331, 332 and receives the distancing element 333.

When the pressure in the conduit 327 (and hence also in the conduit 330) is higher than in the conduit 326, such pressure also prevails L11 the chap.. he r 3 3 C and art S Upon the spool 331 of the pressure regulating valve 325. On the 35 other hand, if the pressure in the conduit 326 (and hence also in the conduit 329) is higher than in the conduit

- 36 327, the pressure in the chamber 334 causes the spool 332 to move in a direction to the left, as viewed in Figure 8; this causes the distancing element 333 to shift the spool 331 in the same (closing) direction. It will be seen that 5 the control means 328 and its spool 332 act as an OR-gate, i.e., the force acting upon the spool 331 of the valve 325 is always indicative of the pressure in that one of the conduits 326, 327 in which the fluid pressure is higher.

10 The group of parts including the pressure regulating valve 325 and the control means 328 further comprises an energy storing device 336 in the form of a coil spring which is installed in a prestressed condition. This spring 336 reacts against a dished retainer 337 in the body or 15 housing of the valve 325 (or in the body or housing of the control means 328) and bears upon the spool 331. The distancing element 333 is surrounded by the convolutions of the spring 336. The bias of this spring is selected in such a way that the pressure of fluid in the conduit 319 20 (and hence in the regulating valve 310) cannot drop below a preselected value. In other words, the pressure of fluid upstream of the valve 310 cannot drop below a certain threshold value.

25 A further chamber 338 in the housing or body of the valve 325 to the left of the spool 331 communicates with a conduit 339 leading to the conduit 318 and containing fluid under pressure matching that in the conduits 318, 319. In other words, fluid in the chamber 338 of the valve 30 325 applies a certain pressure against the left-hand end face of the spool 331, and such pressure opposes the bias of the spring 336. The conduit 339 and the chamber 338 ensure that 0.- 42c. 'I on can be established to the conduits 320, 321 as well as to the torque sensor 311.

35 since the spool 331 is acted upon by fluid pressure at both end faces, it serves as a means for comparing the two

- 37 pressures and for establishing or ascertaining a difference between the maximum pressures prevailing in the conduits 326 and 327 on the one hand, and the pressure prevailing in the conduits 318, 319 (i.e., upstream of the 5 valve 310) on the other hand. In other words, the coil spring 333 (actually the valve 325 and the control means 328) can ascertain the maximum pressure in the conduits 318, 319 (upstream of the valve 310) as well as the desired differential between the maximum pressure 10 prevailing in the conduit 326 or 327 and the pressure upstream of the valve 310.

The valve 310 is actuated by a control or pilot valve 340, and-more particularly by the fluid pressure which is 15 selected by the valve 340. To this end, the housing or body of the valve 310 is provided with the chamber 341 which is connected with the valve 340 by a conduit 342.

The housing of the valve 310 further contains a restoring coil spring 343 acting upon that end face of the spool 344 20 of the valve 310 which is remote from the chamber 341.

When the pressure in the chamber 341 is zero, the spring 343 is free to maintain the spool 344 in an axial position in which the valve 310 establishes communication between the conduit 327 and the conduit 309 leading to the sump, 25 as well as a connection between the conduit 326 and the conduit 319 or 318. At such time, the fluid pressure in the conduit 327 is at least close to zero (due to communication with the sump via conduit 309) but the fluid in the conduit 326 is maintained at the full operating 30 pressure established by the pump 308; this effects a shifting of the transmission in a direction toward overdrive. The admission of pressurized fluid from the valve 340, via 35 conduit 342, and into the chamber 341 of the valve 310 causes the spool 344 to move against the bias of the coil

- 38 spring 343 ( in a direction to the right, as viewed in Figure 8) so that (and depending upon the pressure of fluid in the chamber 341) the spool 344 can assume any one of several positions. Thus, if the chamber 341 receives 5 fluid at a maximum pressure, the spool 344 establishes communication between the conduit 327 and the conduit 318 (or 319) while at the same time connecting the conduit 326 with the outlet conduit 309, i e., with the sump. Thus, the conduit 327 receives fluid at the full system pressure lo but the pressure in the conduit 326 is practically nil.

This results in the selection of an underdrive.

If the pressure in the conduit 342 is changed (by the control valve 340), the conduit 326 can receive fluid at 15 full system pressure and the pressure in the conduit 327 then at least approximates zero.

The pressures of fluid in the conduits 326, 327 can be varied to ensure the selection of a desired ratio for the 20 continuously variable transmission. All this is accomplished by the control valve 340 which receives signals from a suitable electronic control unit 340A. Such control unit has several inputs for signals denoting certain parameters, for example, the RPM of the input 25 shaft A, the RPM of the output shaft B. and/or certain others. The circuitry of the control unit 340A compares and/or otherwise evaluates or processes the incoming signals and 30 selects the pressure of the fluid in the conduit 342 (and in the chamber 341) accordingly. For example, in addition to and/or in lieu of signals denoting the RPM of the shaft A anajor A, the cvn 'v' Unit Acne Can receive signals denoting the position (the extent of depression) of the 35 gas pedal in the motor vehicle, another mode of indicating the rate of fuel flow to and/or fuel consumption by the

- 39 engine, the subatmospheric pressure in the suction manifold of the engine, the load upon the engine, and/or others. 5 The valve 310 can constitute a directional control valve, e.g., a 4/3 valve having a spool with four control edges in the form of shoulders or the like. Furthermore, the illustrated hydraulic regulating valve 310 can be replaced with an electrically or pneumatically operated valve. It 10 is also possible, and often preferred, to utilise a regulating valve which is an electromagnetically actuated directional control valve, and such valve can also employ resilient resetting means (e.g., one or more coil springs or other types of springs).

Similar observations apply as concerns the construction and mode of operation of one or more other valves in the controls for the transmission of Figure 8. For example, the valve 324 or 325 and/or the control means 32 3 (which 20 also constitutes or acts as a valve) can be replaced with different valves and/or control means. Furthermore, two or more valves of those numbered 310, 324, 325 and 328 can be combined into composite valves without departing from the spirit of the invention. By the same token, at least one 25 of the valves 310, 324, 325 and 328 can be replaced with a set of two or more valves which jointly perform the functions of one of the illustrated valves. By way of example only, the valve 310 can be replaced with two valves one of which can connect the conduit 31 3 (319) with 30 the conduit 326, and the other of which can connect the conduit 318 (319) with the conduit 327. As already mentioned above, the illustrated valve 310 constitutes or acts as a directional control va'-v-c.

35 Referring again to Figure 4, the pressure reducing valve 40 in the hydraulic circuit of the starting clutch 20 can

-in - 40 also constitute an electromagnetically operated proportional directional control valve, and this also applies for the electromagnetic control valve 50 of Figure 4. For example, the valve 50 can comprise an electromagnet 5 which receives current at a rate determined by the control unit 50A to select the characteristics of the fluid in the conduit 51. The current is utilised to select the position of a spool in the valve 50 in a manner to ensure that the valve 50 can control the operation of the pressure 10 reducing valve 40 in a manner as already described with reference to Figure 4.

Similar observations are valid for the valves 206, 230 and the associated valves 220 and 240 in the hydraulic 15 circuitry of Figure 7.

Different or excessive tolerances in connection with the making of various constituents of the hydraulic circuits and other parts shown in Figures 4-4a, 7 and 8 (such as 20 the pump 60, 203 or 308, the starting clutch 20, 201 or 202, and/or the torque sensor 311) can entail that, if one relies on characteristic fields or curves (e.g.,. in

connection with the selection of appropriate current by the control unit 50A or 340A for the valve 50 or 340) for 25 predictable changes in torque transmission by a starting clutch, the utilization of identical currents in the electromagnets of different types of motor vehicles will result in the transmission of different clutch torques and/or in different clutch pressures. This lends 30 additional importance to the pressure sensor (such as the sensor 260 in Figure 7) which renders it possible to accurately ascertain the actual clutch pressure (namely the press''r.^. rhich i S required to maintain the clutch in a desired condition of engagement) and thus permits a 35 continuous or sporadic detection of any or excessive departure of the measured value from the desired (rated)

- 41 value of the clutch pressure. The thus detected deviations or departures can be used for an adaption or correction of the characteristic curves. This renders it possible to ensure that a current which has been selected on the basis 5 of a characteristic curve will actually cause the application of an optimal clutch pressure, i.e., a proper engagement of the starting clutch.

The characteristic curve or curves which is or are stored 10 in the microcontroller of the memory in a control unit can be adapted to ensure an accurate adjustment of various valves which control the fluid pressure in a starting clutch. The adaption ensures that, in a quasi stationary condition, the difference between the desired fluid 15 pressure and the actual fluid pressure is at least close to zero. In other words, a pressure monitoring sensor (such as 260) renders it possible to carry out a correction of characteristic curves based on the characteristics of the vehicle in which the transmission 20 employing one or more starting clutches is put to use.

The block diagram of Figure 9 is representative of an adaption of characteristic curves in accordance with a feature of the present invention. The block 401 denotes 25 the step of determining a desired clutch torque 401a by resorting to a control unit and a control process which is implemented therein. The torque 401a is the torque which is to be transmitted by a starting clutch. The block 402 is representative of a calculation of a desired clutch 30 pressure 402a by resorting to an inverse characteristic curve of the clutch. The next block 403 denotes a determination of a desired current value (strength) 403a on the basis of an inverse characteristic value curve, i.e., a conversion of the clutch pressure 402a into a 35 desired current value 403a.

- 42 -

The block 404 denotes a conversion of the desired current value into an actual current value 404a by resorting to suitable current regulator means, such as a PI- or PID current regulator. The signal 404a is fed back at 405 to a 5 subtracting circuit 406 and thence to 404. The block 407 denotes the supplying of current (404a) to a main slide valve (block 408) to select the actual clutch pressure. A wet clutch (block 409), such as a friction clutch immersed in oil or another fluid, selects a torque which can be 10 transmitted by the clutch.

The just described adaption of characteristic curves pertaining to the valves renders it possible to correct the curve or curves which was or were memorized, in the 15 course of a regulating procedure. Thus, the desired torque of the process and an inverse characteristic curve of the clutch (such inverse characteristic curve is stored separately for the reverse and forward drive clutches if the transmission employs two clutches, such as the 20 clutches 201, 202 of Figure 7) are employed jointly with an inverse characteristic curve for the valve to ascertain the corresponding desired or required current for the clutch regulating valve (such as an electromagnetic pilot or control valve). An actual current is generated with 25 resort to a suitable current generator, such as a PI regulator. The actual current ensures the establishment (in a hydraulic system employing at least one slide valve) of an appropriate (corresponding) pressure which can be transmitted by the clutch and which causes the clutch to 30 generate a corresponding friction torque. If the actual pressure departs from the pressure which is desired for the application to the friction clutch, the actual pressure in unloved to correct the inverse characteristic curve of the valve in such a way that the characteristic 35 curve of the valve (such curve has been memorized in the

- 43 course of the regulating operation) departs from the actual (existing) characteristic curve of the valve.

An adaption of the characteristic curve exhibits the 5 important advantage that the reproducible characteristics which are typical of the system (such as, for example, tolerances of the valves and/or of the clutch) can be memorized and corrected as parameters which are characteristic of the system. As compared with regulation, 10 an adaption exhibits the advantage that it is not necessary to await the development of a deviation or departure (of an actual value from a desired or required or optimum value) which is necessary to cause a regulator to react in order to carry out a correction.

Referring to Figure 10, there is shown a diagram 500 wherein the blocks denote the steps or stages of an adaption of a characteristic curve (such as the characteristic curve of a valve). The block 501 is 20 representative of the step of applying a desired clutch pressure (in bar) in order to ascertain a corresponding current strength (in ma). The next block 502 denotes the ascertainment of an additive correction for the characteristic curve, the current strength being measured 25 in mA and the pressure being measured in bar. The step denoted by the block 502 represents the determination of an additive current constant, and the corresponding signal is transmitted to a junction (signal comparing stage) 503 which further receives a signal denoting the summand 30 (addend) from 502. The junction 503 furnishes a signal 504 denoting the corrected current and constituting a sum of the signals from 501 and 502. The corrected current (504) I ''I 'lo sea for regulation of the corresponding valve, i.e., a valve which serves to select the torque to be 35 transmitted by a starting clutch (such as 20 or 201 or 202).

- 44 The ascertainment of the correction value or values preferably takes place in a quasi stationary condition, namely a condition in which the timely gradient of the 5 desired clutch pressure is below a preselectable lower threshold value, e.g., one bar per second. Once such a condition has been reached (namely when the change of the desired clutch pressure as a function of time is less than the lower threshold value), it is proposed to await the 10 expiration of a given interval of time (e.g., between 500 and 1000 milliseconds, preferably about 200 milliseconds) prior to carrying out of an averaging of the desired actual pressures. For example, the averaging step can involve the utilization of a time window of ten 15 milliseconds or a low multiple of ten milliseconds. In the event of a monitoring in the ten-millisecond range, this can result in a number of measurements or samplings in the range 5 of ten (or close to ten) samplings. The next step involves a determination of the difference between the 20 averaged desired pressure and the actual pressure.

Once such difference has been ascertained, the control unit compares the difference between the averaged desired pressure and the actual pressure with threshold values. If 25 the departure from a first lower threshold value is less than 0.01 to 0.05 bar (particularly 0.02 bar), the characteristic curve need not be corrected. If the extent of departure is between a lower threshold value of between 0.01 and 0.05 bar and an upper threshold value (e.g., 30 between 0.1 and 0.5 bar, especially 0.25 bar), one can resort to a fixed current correction value of, for example, 1-5 ma. If the difference exceeds the upper = ash^'d valise; the extent of the additive correction is ascertained or calculated in dependency upon the 35 differences between the averaged values, and the difference can be amplified with a weighing factor. For

- 45 example, one can resort to a correction in accordance with the equation Ekorr = (Pknoll PkIst) X factor wherein Ekorr is the correction value for current adaption, PkSoll is the desired pressure, and PkISt is the actual pressure. 10 Figure 11 shows a hydraulic regulating arrangement constituting a modification of the arrangement which is shown in Figure 7. Those constituents of the arrangement shown in Figure 11 which are identical with or clearly analogous to the corresponding constituents of the 15 arrangement of FIG 7 are denoted by the same reference characters. The pump 203 which is shown in Figure 11 draws a fluid (such as oil) from a sump 204 by way of a filter 650, and 20 the outlet of this pump supplies fluid at system pressure to a conduit 291. Such pressurized fluid is utilised for a regulation of the operation of one or more starting disc clutches (201, 202) and/or for a regulation (selection) of the transmission ratio and/or for the initiation and the 25 carrying out of the movements of axially adjustable flanges (such as 301a, 302a in Figure 8) of pulleys (such as 301, 302) forming part of a continuously variable transmission (CVT). The conduit (outlet) 290 branches off the conduit 291 and serves to supply pressurized fluid to 30 the actuators of a continuously variable transmission (see the actuators 304, 305 and 306, 307 in the transmission of Figure 8), i.e., such fluid can be used to urge the fl aches of the Pulleys against the adjacent portions of an endless chain or belt in a continuously variable 35 transmission with a desired force to prevent any slip or to regulate the extent of slip.

- 46 further conduit 292 serves to supply fluid from the actuators and/or a cooler (heat exchanger) Cola and/or the clutch or clutches back to the sump 203. The illustrated 5 conduit 292 has two branches 293 and 294. The branch 294 serves as a bypass and contains a flow restrictor 295 (e.g., a standard throttle) which supplies fluid to a suction type jet pump 600. The flow of fluid which is supplied to the pump 600 by the conduit 294 enables this 10 pump to draw additional fluid from the sump 204 and to supply the thus increased quantity of fluid to the cooling system 601a by way of a conduit 601. The cooled fluid can be used to cool the starting clutch(es) of the transmission and/or the clutch between the engine and the 15 input shaft of the transmission. The exact manner in which the fluid which is being supplied by the conduit 601 and is being cooled in one or more heat exchangers of the cooling system 601a is utilised to cool one or more clutches or the like forms no part of the present 20 invention. The coolant is or can be used primarily to cool the clutch(es) in the region of the friction surfaces.

The flow restrictor 295 in the bypass conduit 294 serves to enhance a predetermined (predictable) rate of fluid 25 flow to the intake of the jet pump 600 and to thus ensure a highly predictable cooling of friction surfaces in the clutch(es) receiving cooled fluid from the cooling system 601a downstream of the conduit 601; this holds true if the jet pump 600 is utilised in the hydraulic circuit of a 30 continuously variable transmission or any other type of transmission in the power train of a motor vehicle.

The valve 61n of Figure 11 serves to regulate the return flow of fluid through the conduit 292; the valving element 35 or spool 611 in the housing or body 610a of the valve 610 can assume a position in which the conduit 293 supplies

- 47 fluid to the pump 203 by way of a valve 620, as well as a position in which the conduit 293 delivers fluid to a conduit 296, i.e., to the jet pump 600.

5 The valve 620 serves to regulate the quantities of fluid flowing from the valve 610 back to the pump 203; this valve 620 is a pressure limiting valve, and more specifically a valve which prevents the pressure of fluid in a conduit 640 from dropping below a selected minimum 10 acceptable pressure, e.g., in the range of a few bar not necessarily exceeding five bar. The valve 620 establishes a path for the flow of fluid from the conduit 640 to a conduit 641 and thence to the intake of the pump 203 when the pressure in the conduit 640 matches or exceeds the 15 selected minimum acceptable pressure. Such adjustment or mode of operation of the valve 620 ensures that, when the valve 620 is set to establish communication from the conduit 293 to the conduit 640, fluid will flow from the conduit 640 and to the intake of the pump 203 (i.e., 20 through the conduit 641) only when the pressure in the conduits 293, 294 is above a predetermined minimum pressure. The spool 611 in the housing 610a of the valve 610 is 25 shiftable axially under or against the bias of a suitable valve spring 612, e.g., a coil spring. When the spring 612 is free to dissipate energy, the spool 611 moves in a direction to the left (as viewed in Figure 11) and reduces the volume of the chamber 613 in the housing 610a of the 30 valve 610. The pressure of fluid in the chamber 613 is regulated by a pilot or control valve 630 which regulates such pressure by way of the conduits 234 and 614. The =l re 630 receives signals from an electronic control unit (not shown) corresponding to the control unit 340A for the 35 valve 340 (shown in Figure 8) or the control unit 50A for the valve 50 Shown in Figure 4). The control valve 630

- 48 further serves to regulate the fluid pressure in a chamber to the left of the spool 231 in the housing or body 230a of the safety valve 230; this spool 231 is biased by a valve spring 232 and controls the flow of fluid between 5 the conduits 222, 223 (and on to the conduits 224, 225) in a manner as already described with reference to Figure 7.

Thus, the valve 630 of Figure 11 controls the valve 610 (i.e., the fluid pressure in the chamber 613) as well as the safety valve 230 (by controlling the fluid pressure in 10 the chamber of the housing 230a to the left of the spool 231). If the pressure of fluid in the conduit 234 of Figure 11 is zero or close to zero, the control valve 630 does not 15 influence the clutches 201, 202 because the axial position of the spool 231 is determined solely by the valve spring 232; this enables the valve 206 to regulate the pressure of fluid in the conduit 223 (and hence thepressures of fluid in the chambers of the clutches 201, 202) by way of 20 the safety valve 230. The valve 206 is controlled by a control or pilot valve 220. If the pressure of fluid in the conduit 234 is low, the pressure of fluid in the conduit 614 is also low so that the spool 611 of the valve 610 can be shifted by the valve spring 612 to expel fluid 25 from the chamber 613. This ensures that all or nearly all of the fluid flowing in the conduit 292 into the conduit 293 can flow back to the intake of the pump 203 (via conduit 640, valve 620 and conduit 641). At the same time, a certain percentage of the fluid medium flowing from the 30 conduit 292 toward the conduit 293 can enter the bypass conduit 294 to pass through the flow restrictor 295 and to flow to the intake of the jet pump 600.

If the control valve 630 receives one or more signals 35 indicating that the fluid pressure in the conduits 293 and 614 should be increased to a median value, the condition

of the safety valve 230 remains unchanged (because the increased pressure of fluid in the chamber of the valve 230 does not suffice to shift the spool 231 against the opposition of the spring 232). However, the just mentioned rise of fluid pressure in the conduit 614 to a median value suffices to cause the fluid in the chamber 613 of the valve 610 to move the spool 611 against the bias of the spring 612; the spool 611 then assumes a position in which the fluid being supplied by the conduit 293 cannot 10 enter the conduit 640 (i.e., it cannot flow back to the pump 203 via valve 620 and conduit 641) but flows to the intake of the jet pump 600 by way of the conduit 296.

If the control valve 630 causes the fluid pressure in the 15 conduits 234 and 614 to rise to a maximum value, the condition of the valve 610 remains unchanged (the fluid continues to flow from the conduit 293 into the conduit 296 and on to the jet pump 600); however, the fluid flowing from the conduit 234 into the chamber which is 20 located to the left of the spool 231 in the housing 230a of the safety valve 231 induces the spring 232 to store energy (or additional energy) so that the clutches 201, 202 are disengaged because the conduit 223 is free to discharge into the sump 235.

It will be seen that the hydraulic circuit of Figure 11 renders it possible to employ a single pilot or control valve (630) to adjust the safety valve 230 as well as the valve 610 by the simple expedient of varying the fluid 30 pressure in the conduits 234 and 614 between different values (such as the aforementioned low, median and maximum pressures). The valve 610 reacts to the minimal and maxi ma' eS=U. as of he flood in the conduits 234. 614 to direct the returning fluid to the intake of the pump 203 35 or to the intake of the jet pump 600 (i.e., to the cooling system 601a). On the other hand, the safety valve 230

-A - 50 reacts to an increase of fluid pressure in the conduit 234 to a maximum value to thus disengage the clutches 201, 202 as well as to ensure an intensive cooling of such clutches because the jet pump 600 delivers fluid into the conduit 5 601 (i.e., to the cooling system or systems 601a) at a maximum rate.

The pilot or control valve 630 renders it possible to shift (by way of the valve 610) to a cooling of the clutch 10 or clutches by way of the fluid which is supplied by the jet pump 600, as well as to actuate the safety or relief valve 230 when it becomes necessary to disengage the clutches 201 and 202.

15 The valve 620 acts as a pressure regulating means to ensure that the pressure of fluid in the conduit 640 must match or exceed a preselected threshold value before the valve 620 prevents the fluid from flowing through the conduit 640 and on to the intake of the pump 203 by way of 20 the conduit 641. Thus, the valve 620 seals the conduit 640 from the conduit 641 until the pressure of fluid in the conduit 640 matches or exceeds the preselected value. As already explained hereinbefore, this ensures that the pressure of fluid in the conduit 294 cannot drop to any 25 value when the valve 610 prevents the flow of fluid from the conduit 293 into the conduit 640, i.e., to the intake of the pump 203.

The hydraulic system of Figure 11 can be utilized with 30 advantage in combination with a continuously variable transmission (e.g., a transmission of the type shown in Figure 4, 7 or 8) with at least one starting clutch, e.g., with two cluccnes GUi, GUS each v '.vrhi-h nc] Ides Z cylinder and piston unit (201a, 201b and 202a, 202b), with 35 actuators (such as 304, 305 and 306, 307) shown in Figure 8) which change the ratio of the continuously variable

- 51 transmission, with at least one pump (such as 203) for supplying a suitable fluid at system pressure, and with valves (such as 610, 206, 230 and 210 shown in Figure 11) for supplying pressurized fluid to the consumers and for 5 permitting the fluid to flow back to the sump. Such valves can serve to supply a fluid as well as to ensure that the fluid is maintained at a requisite pressure. Thus, the valve 630 can control the operation of the valve 610 (by changing the position of the spool 611) so that the fluid 10 can flow from the actuators for the transmission to the conduit 292, or the valves can co-operate in a manner as described with reference to Figure 8, or the valves can co-operate in a manner to supply fluid to several pumps (such as 203 and 600) for the purposes of supplying fluid 15 at system pressure as well as of cooling the fluid preparatory to circulation through the clutch(es) and/or other parts which should be cooled at all times or only under certain circumstances (e.g., when the friction clutch(es) operates or operate with slip. The illustrated 20 pump 600 is a suction type jet pump.

The features of various embodiments of the invention actually shown in the drawings and/or of any and all other embodiments which are disclosed in this specification can

25 be combined with and/or substituted for and/or modified in view of each other in a number of ways without departing from the spirit of the present invention. Furthermore, through the various improvements embodying the present invention are shown as being incorporated into or 30 assembled with a transmission for use in the power train of a motor vehicle, such improvements (e.g., that described with reference to Figures 1 to 3) can be utiii ed with ecus'. similar advantage under numerous circumstances in fields other than the field of

35 automobiles or other types of vehicles. Thus, and referring again to Figures l to 3, the fields of possible

r - 52 and advantageous utilization of the combination of a conduit with two components which may (but need not always) turn relative to each other are too numerous to mention and/or to be illustrated herein; all such fields

5 will readily occur to those skilled in the relevant art or arts upon perusal of the preceding description in

conjunction with the accompanying drawings.

Continuously variable transmissions which can be improved 10 in a number of ways upon incorporation of one or more features of the present invention are disclosed, for example, in commonly owned U.S. patents Nos. 5,046,991 (granted September 10, 1991 to Friedmann for "CONTINUOUSLY VARIABLE SPEED TRANSMISSION"), 5,169,365 (granted December 15 8, 1992 to Friedmann for "POWER TRAIN"), 5, 217,412 (granted June 8, 1993 to Indlekofer et al. for "CONTINUOUSLY VARIABLE SPEED TRANSMISSION"), 5,295, 915

(granted March 22, 1994 to Friedmann for "CONTINUOUSLY VARIABLE SPEED TRANSMISSION"), 5,667,448 (granted 20 September 16, 1997 to Friedmann for "POWER TRAIN"), and 5,711,730 (granted January 27, 1998 to Friedmann et al. for "TORQUE MONITORING APPARATUS"). The disclosures of all

of the above-enumerated U.S. patents, as well as the disclosure of the aforementioned German application, are

25 incorporated herein by reference.

Claims

- 53 CLAIMS

1. A transmission for use in a power train of a motor vehicle, the combination of: at least one fluid-operated engageable and disengageable clutch including a cylinder and a piston movable in said cylinder; 10 at least one source of pressurized fluid; conduit means connecting said source with said cylinder; an adjustable pressure regulating valve in said conduit is means and an adjustable safety valve in said conduit means between said pressure regulating valve and said cylinder; and means for adjusting at least said safety valve, including 20 at least one pilot valve.

2. A transmission as claimed in Claim 1, wherein said

safety valve includes a slide valve having a housing and a spool movable in said housing of said safety valve by said 25 at least one pilot valve.

3. A transmission as claimed in Claim 2, wherein said spool is movable to a position in which said safety valve establishes communication between a chamber of said 30 cylinder and said pressure regulating valve.

4. A transmission as claimed in Claim 3, wherein said spool is further movable to a second position in which said safety valve prevents the flow of fluid between said

- 54 chamber of said cylinder and said pressure regulating valve and connects said chamber with a sump to thus reduce the pressure of fluid in said chamber.

5 5. A transmission as claimed in any preceding claim, wherein said pilot valve is arranged to adjust said safety valve and said pressure regulating valve.

6. A transmission as claimed in Claim 5, wherein said 10 pilot valve is arranged to furnish to said pressure regulating valve and to said safety valve fluid at a plurality of different pressures including an elevated pressure to thereby change the condition of said safety valve, a low pressure at which the condition of said 15 pressure regulating valve remains unchanged, and a median pressure to thus change the condition of said pressure regulating valve.

7. A transmission for use in a power train of a motor 20 vehicle, comprising: first and second fluid-operated engageable and disengageable clutches, each of said clutches including a cylinder and a piston movable in the respective cylinder; at least one source of pressurized fluid; conduit means connecting said at least one source with said cylinders; a pressure regulating valve in se'' condo. -ns; an adjustable safety valve in said conduit means between said pressure regulating valve and said cylinders;

- 55 means for adjusting said safety valve, including at least one pilot valve; and 5 a selecting valve in said conduit means between said safety valve and said cylinders, said selecting valve being arranged to assume a first condition in which said conduit means can supply fluid only to the cylinder of said first clutch and a second condition in which said 10 conduit means can supply fluid only to the cylinder of said second clutch.

8. A transmission as claimed in Claim 7, further comprising at least one fluid pressure monitoring device 15 installed in said conduit meansupstream of said selecting valve, as seen in the direction of fluid flow toward said cylinders.

9. A transmission as claimed in Claim 7 or Claim 8, 20 wherein one of said clutches is a forward drive clutch.

1O. A transmission as claimed in any one of Claims 7 to 9, wherein one of said clutches is a reverse drive clutch.