GB2153932A - Creep inhibiting device - Google Patents

Abstract

A creep-inhibiting device for use in an automotive vehicle equipped with an engine and a transmission mechanism coupled in series to a fluid coupling and having a frictionally engaging element C1. The device includes engine load sensor means for producing a signal fluid having a pressure Pt representative of engine load, control means 50 interposed between the frictionally engaging element and an operating fluid source, and a fluid line 92, 91, 90 for delivering the signal fluid from the engine load sensor means to the control means. The control means is adapted to control the power transmission capacity of the frictionally engaging element within a range from substantially zero to a predetermined value in dependence on the signal fluid pressure supplied thereto, to inhibit creeping of the vehicle when the engine is in a no-load state. Selector valve means 75 is arranged in the fluid line and adapted to assume a first position (as shown) wherein it allows the signal fluid to flow in both directions from the engine load sensor means to the control means and vice versa when the pressure of the signal fluid is lower than a predetermined value, and to assume a second position wherein it allows the signal fluid to flow in a sole direction from the engine load sensor means to the control means when the pressure of the signal fluid is higher than the predetermined value. <IMAGE>

Description

SPECIFICATION Creep-inhibiting device for an automotive vehicle equipped with an automatic transmission This invention relates to a creep-inhibiting device for use in an automotive vehicle equipped with an automatic transmission, and more particularly to a device of this kind which can be rendered operative or inoperative without causing a shock to a frictionally engaging element of the clutch, and with required responsiveness depending on the stepping action of the accelerator pedal.

In an automotive vehicle equipped with an automatic transmission having a fluid coupling such as a torque converter, the phenomenon can occur that, due to dragging torque of the torque converter, the vehicle moves forward or creeps against the driver's will when the vehicle stands with the shift lever shifted to a drive range (forward) position, creating a load on the engine. Such load on the engine, if applied at engine idle, causes a drop in the rotational speed of the engine, even resulting in engine stall. To avoid this disadvantage, the driver has to step on the accelerator pedal by an amount corresponding to the drag torque so as to prevent a drop in the rotational speed of the engine at idle. However, this is not desirable from the viewpoint of fuel curtailment.Therefore, it is desired that when the engine is at idle, the transmission is automatically brought into a neutral state to interrupt power transmission between the engine and the driving wheels, so that the driver is not required to step on the accelerator pedal by a large amount, for economy of fuel consumption. It is known that a creep-inhibiting device manufactured for this purpose can also provide an advantage that vibrations of the vehicle body are reduced during idling operation of the engine, which is particularly effective when the device is applied to front wheeldriven vehicles.

Although creeping of the vehicle can be avoided by reducing the torque transmission capacity of a frictionally engaging element used for starting of the vehicle, i.e. a firstspeed clutch, to substantially zero upon stoppage of the vehicle, the torque transmission capacity has to soon be recovered in response to the engine load, i.e. the stepping amount of the accelerator pedal, in order to start the vehicle. Particularly when the driver is required to move his vehicle in a narrow space, for instance, to park his vehicle in a space between vehicles parked in line with the street, it is desired to maintain the clutch in a slip-permitting state so that a desired small level of power transmission capacity may be obtained through the clutch, which is proportionate to a fine stepping amount of the accelerator pedal.On the other hand, when the vehicle is started with no other vehicle running ahead, it is required to shorten the slip-permitting period to a minimum possible value, so as to promptly establish complete engagement of the clutch. Otherwise the clutch becomes engaged only after the engine speed has risen to a high level, resulting in a uncomfortable shock and early wear of the clutch.

In a vehicle equipped with a conventional creep-inhibiting device, if the accelerator pedal is stepped on and then immediately restored to the idle position, the creep-inhibiting device will be promptly operated so that the whole engine and transmission system is abruptly relieved of torque which has largely twisted mounting rubber members supporting same to suddenly release torsional energy from the mounting rubber members, etc., thus causing an uncomfortable shock. To avoid this, the creep inhibiting function of the creep-inhibiting device has to be exhibited with a time delay by a short period of time until the engine speed is sufficiently decreased, even after the accelerator pedal has been released.

Further, as is known, to increase the internal pressure of the first-speed clutch in good response to the stepping-on of the accelerator pedal, desirably the pressure within the clutch should not be reduced to zero even while the creep-inhibiting device is operating, but should be controlled in advance to a value as close as possible to and at the same time smaller than a pressure value above which the clutch becomes engaged against the force of a return spring provided in the clutch, i.e. the engaging pressure Pe.However, if the pressure within the clutch is thus increased to such value close to the engaging pressure in advance, such increased pressure can act as a residual pressure at subsequent shifting of the shift lever to the neutral position or to the reverse position, thus degrading the responsiveness of the clutch to a gear shifting action by the driver, particularly in cold weather.

It is an object of the invention to provide a creep-inhibiting device for use in an automotive vehicle, which is simple in construction and is capable of controlling the power transmission capacity of a frictionally engaging element used for starting the vehicle, in exact response to a parameter representative of the engine load, such as the stepping amount of the accelerator pedal, to thereby avoid an uncomfortable shock given by the frictionally engaging element upon sudden release of the accelerator pedal and promptly bring about a creep-permitting state when the accelerator pedal is suddenly stepped on.

It is another object of the invention to provide a creep-inhibiting device for use in an automotive vehicle equipped with an automatic transmission, which can provide the automatic transmission with high responsiven ess to shifting of the shift lever by the driver to a neutral position or to a reverse position even in cold weather.

Viewed from one aspect the invention provides a creep-inhibiting device for use in an automotive vehicle equipped with an engine, a fluid coupling, a transmission mechanism coupled in series to the fluid coupling and having a frictionally engaging element, and an operating fluid source for supplying an operating fluid to the frictionally engaging element.

The creep-inhibiting device includes engine load sensor means for producing a signal fluid having a pressure representative of load applied on the engine, control means interposed between the frictionally engaging element and the operating fluid source, and a fluid line for delivering the signal fluid from the engine load sensor means to the control means, wherein the control means is adapted to control the power transmission capacity of the frictionally engaging element within a range from substantially zero to a predetermined value in dependence on the pressure of the signal fluid supplied thereto, to thereby inhibit creeping of the vehicle when the engine is in a no-load state.Selector valve means is arranged in the fluid line, and adapted to assume a first position wherein it allows the signal fluid to flow in both directions from the engine load sensor means to the control means and vice versa when the pressure of the signal fluid is lower than a predetermined value, and to assume a second position wherein it allows the signal fluid to flow in a sole direction from the engine load sensor means to the control means when the pressure of the signal fluid is higher than the predetermined value.

Preferably, the selector valve means includes retarding means for reducing the speed of a shifting motion thereof from the second position to the first position, which takes place when the pressure of the signal fluid decreases, to a value lower than the speed of a shifting motion thereof from the second position to the first position, which takes place when the pressure of the signal fluid increases.

The control means, in a first preferred form, comprises an input fluid line connected to the operating fluid source, an output fluid line connected to the frictionally engaging element, a valve body disposed to selectively connect and disconnect the input fluid line to and from the output fluid line and having first and second end faces, a first pressure chamber defined in part by the first end face of the valve body and disposed to be supplied with an operating fluid pressure in the output fluid line, a second pressure chamber defined in part by the second end face of the valve body and disposed to be supplied with the pressure of the signal fluid, a third fluid line having a restriction and disposed to always deliver the operating fluid pressure in the output fluid line to the second pressure chamber, resilient means urging the valve body in a direction of connecting the input fluid line to the output fluid line, and a drain line disposed to escape the operating fluid pressure in the output fluid line to a zone under a lower pressure when the valve body is biased in a direction of disconnecting the input fluid line from the output fluid line due to a difference in fluid pressure between the first pressure chamber and the second pressure chamber, by an amount corresponding to the amount by which the valve body is biased.

Preferably, the creep-inhibiting device further includes a first one-way valve arranged in the first-mentioned fluid line extending between the control means and the selector valve means, and disposed to allow the fluid to flow in a sole direction from the selector valve means to the control means, and a second one-way valve arranged in the firstmentioned fluid line in parallel with the first one-way valve and disposed to allow the fluid to flow in a sole direction from the control means to the selector valve means, and wherein the second one-way valve is adapted to open when the pressure of fluid upstream thereof is higher than the pressure of fluid downstream thereof by an amount exceeding a predetermined value, Also preferably, the vehicle has a braking device, and the second one-way valve comprises an electromagnetic valve.The creepinhibiting device further includes brake sensor means for detecting whether or not the braking device is operative, and a driving circuit adapted to open the electromagnetic valve when the braking device is detected to be operative by the brake sensor means, whereby the power transmission capacity of the frictionally engaging element is set to different values in dependence on whether the braking device is operative or inoperative.

The control means, in a second preferred form, comprises an input fluid line connected to the operating fluid source, an output fluid line connected to the frictionally engaging element, a valve body disposed to selectively connect and disconnect the input fluid line to and from the output fluid line and having first and second end faces, a first pressure chamber defined in part by the first end face of the valve body and disposed to be supplied with an operating fluid pressure in the output fluid line, a second pressure chamber defined in part by the second end face of the valve body and disposed to be supplied with the pressure of the signal fluid, a third fluid line having a restriction and disposed to always connect the input fluid line to the output fluid line, resilient means urging the valve body in a direction of connecting the input fluid line to the output fluid line, and a drain line disposed to escape the operating fluid pressure in the output fluid line to a zone under a lower pressure when the valve body is biased in a direction of disconnecting the input fluid line from the output fluid line by a difference in fluid pressure between the first pressure chamber and the second pressure chamber, by an amount corresponding to the amount by which the valve body is biased.

Preferably, the creep-inhibiting device further includes shut-off valve means adapted to block the drain line when the braking device is detected to be operative by the brake sensor means.

The control means according to the first and second preferred forms further includes adjusting means for adjusting the magnitude of the operating fluid pressure in the output fluid line, preferably the resilient force of the resilient means, so that the power transmission capacity of the frictionally engaging element is substantially zero.

Still preferably, the control means further includes a bypass fluid line bypassing the control means and connecting the frictionally engaging element to the operating fluid source, and a one-way valve arranged in the bypass fluid line and disposed to allow the fluid to flow in a sole direction from the frictionally engaging element to the operating fluid source.

Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 is a schematic view of an automatic transmission for automotive vehicles, to which is applied a creep-inhibiting device according to the invention; Fig. 2 is a circuit diagram illustrating a hydraulic control system employed in the automatic transmission of Fig. 1, in which is incorporated the creep-inhibiting device according to a first embodiment of the invention; Fig. 3 is a graph showing an operating oil pressure characteristic of the creep-inhibiting device appearing in Fig. 2; Fig. 4 is a circuit diagram similar to Fig. 2, illustrating a hydraulic control system in which is incorporated the creep-inhibiting device according to a second embodiment of the invention;; Fig. 5 is a fragmentary circuit diagram of the hydraulic control system of Fig. 4, showing a creep-inhibiting valve in a position wherein the creeping of the vehicle is inhibited; and Fig. 6 is a fragmentary circuit diagram of the hydraulic control system of Fig. 4, showing a selector valve having a shifting speed retarding function, in a second position which is assumed when a throttle pressure Pt increases above a predetermined value.

The invention will now be described in detail with reference to the drawings illustrating embodiments thereof.

Referring first to Fig. 1, there is schematically illustrated an automatic transmission for automotive vehicles having four forward speed reduction gears and one reverse gear, to which the invention is applied. Output from an engine E is transmitted to driving wheels W and W' for driving same through a crankshaft 1 of the engine, a torque converter T as a fluid coupling, an auxiliary transmission M, and a differential Df in the mentioned order.

The torque converter T comprises a pump 2 coupled to the crankshaft 1, a turbine 3 coupled to an input shaft 5 of the auxiliary transmission M, and a stator 4 coupled, via a one-way clutch 7, to a stator shaft 4a which in turn is supported on the input shaft 5 for rotation relative thereto. Torque is transmitted from the crankshaft 1 to the pump 2, and then to the turbine 3 in a hydrodynamic manner. When amplification of torque takes place while torque is transmitted from the pump 2 to the turbine 3, the resulting reaction force is borne by the stator 4, as is already known.

A pump driving gear 8 is arranged on a right end of the pump 2 as viewed in Fig. 1, for driving an oil hydraulic pump P appearing in Fig. 2. A stator arm 4b is secured to a right end of the stator shaft 4a for controlling a regulator valve Vr appearing in Fig. 2.

The auxiliary transmission M has an output shaft 6 extending parallel with the input shaft 5, and is provided with a first-speed gear train G1, a second-speed gear train G2, a thirdspeed gear train G3, a fourth-speed gear train G4, and a reverse gear train Gr, all arranged in juxtaposition between the input and output shafts 5, 6.The first-speed gear train G1 comprises a driving gear 1 7 connectible to the input shaft 5 through a first-speed clutch C1, and a driven gear 18 connectible to the output shaft 6 through a one-way clutch CO and engaging with the driving gear 1 7. The second-speed gear train G2 comprises a driving gear 1 9 connectible to the input shaft 5 through a second-speed clutch C2, and a driven gear 20 secured to the output shaft 6 and engaging with the driving gear 19, while the third-speed gear train G3 comprises a driving gear 21 secured to the input shaft 5, and a driven gear 22 connectible to the output shaft 6 through a third-speed clutch C3 and engaging with the driving gear 21.

The fourth-speed gear train G4 comprises a driving gear 23 connectible to the input shaft 5 through a fourth-speed clutch C4, and a driven gear 24 connectible to the output shaft 6 through a selector clutch Cs and engaging with the driving gear 23. On the other hand, the reverse gear train Gr comprises a driving gear 25 formed integrally with the driving gear 23 of the fourth-speed gear train G4, a driven gear 27 connectible to the output shaft 6 through the selector clutch Cs, and an idle gear 26 engaging with the gears 25, 27. The selector clutch Cs is arranged between the driven gears 24 and 27, and has a selector sleeve S which is shiftable between a left or forward position and a right or reverse position as viewed in Fig. 1, to selectively connect the driven gear 24 or 27 to the output shaft 6.The one-way clutch CO permits the driving torque from the engine E alone to be transmitted to the driving wheels W, W', while prohibiting transmission of torque from the driving wheels W, W' to the engine E.

If the first-speed clutch C1 alone is engaged while the selector sleeve S is held in the forward position as illustrated in Fig. 1, the driving gear 1 7 is connected to the input shaft 5 to establish the first-speed gear train G1, thereby allowing transmission of torque from the input shaft 5 to the output shaft 6 therethrough. Then, if the second-speed clutch C2 is engaged with the first-speed clutch C1 maintained in its engaged state, the driving gear 1 9 is connected to the input shaft 5 to establish the second-speed gear train G2 through which torque can be transmitted from the input shaft 5 to the output shaft 6.That is, even while the firstspeed clutch C1 is engaged, the second-speed gear train G2, the third-speed gear train G3 or the fourth-speed gear train G4 can be established by the action of the one-way clutch CO, rendering the first-speed gear train G1 substantially inoperative. If the second-speed clutch C2 is disengaged and the third-speed clutch C3 is engaged instead, the driven gear 22 is connected to the output shaft 6 to establish the third-speed gear train G3, while if the third-speed clutch C3 is disengaged and the fourth-speed clutch C4 is engaged instead, the driving gear 23 is connected to the input shaft 5 to thereby establish the fourthspeed gear train G4.On the other hand, if the fourth-speed clutch C4 alone is engaged while the selector sleeve S of the selector clutch Cs is shifted to the right or reverse position, the driving gear 25 and the driven gear 27 are connected, respectively, to the input shaft 5 and the output shaft 6 to establish the reverse gear train Gr, thereby allowing transmission of torque from the input shaft 5 to the output shaft 6 through the reverse gear train Gr.

The torque transmitted to the output shaft 6 is then transmitted through an output gear 28 mounted on one end of the output shaft 6 to an enlarged gear Dg of the differential Df.

Referring now to Fig. 2 illustrating a creepinhibiting device according to a first embodiment of the invention, the oil hydraulic pump P sucks operating oil from an oil tank R for pressure delivery of same to fluid lines 29 and 94. The pressurized oil from the pump P has its pressure regulated to a predetermined value (hereinafter called "the line pressure P1") by the regulator valve Vr, and is then delivered to a manual shift valve Vm, a throt tle opening-responsive valve Vt, and a governor valve Vg.

Having been regulated to a predetermined pressure value by the regulator valve Vr, the pressurized oil is delivered in part to the interior of the torque converter T through an inlet fluid line 34 provided with a restriction 33, to increase the internal pressure of the torque converter T for prevention of cavitation therein.

If the present creep-inhibiting device is to be applied to a gasoline engine, the throttle opening-responsive valve Vt generates as a parameter representative of the output of the engine E a throttle pressure Pt corresponding to the stepping amount of an accelerator pedal, not shown, of the engine E, i.e. the valve opening of a throttle valve, not shown, arranged in the intake system of the engine E, and supplies same to a pilot fluid line 48. On the other hand, the governor valve Vg is rotatively driven by the output shaft 6 of the auxiliary transmission M or the enlarged gear Dg of the differential Df, to generate a governor pressure Pg variable in response to the vehicle speed and supply same to a pilot fluid line 49.

The manual shift valve Vm is arranged between a fluid line 39 branching off from the fluid line 94 and a fluid line 40, and shiftable between a neutral position, drive range positions such as D3 and D4 positions, and a reverse position. When the manual shift valve Vm assumes one of the drive range positions, the fluid lines 39, 40 become communicated with each other, while when the manual shift valve Vm is in the neutral position or the reverse position, the fluid line 40 is communicated with a drain line 39' to drain the pressurized oil in the fluid line 40 to the oil tank R. A fluid line 41 branches off from the fluid line 40 and has a creep-inhibiting valve 50 arranged therein, hereinafter referred to, and it is connected to a hydraulically operating portion of the first-speed clutch C1 as a frictionally engaging element for starting of the vehicle. The pressurized oil in the fluid line 40 is supplied not only to the first-speed clutch C1 via the creep-inhibiting valve 50, but also to hydraulically operating portions of the second-speed, third-speed and fourthspeed clutches C2, C3 and C4 in a selective manner depending upon the switching actions of a 1-2 shift valve VI, a 2-3 shift valve V2, and a 3-4 shift valve V3, as hereinafter de scribed.

The shift valves V1-V3 each have a spool having one end face acted upon by the combined force of the throttle pressure Pt and a spring, not shown, and the other end by the governor pressure Pg, respectively, and are adapted to shift from a left or first position to a right or second position when the governor pressure Pg exceeds the combined force of the throttle pressure Pt and the spring with an increase in the the governor pressure Pg, i.e.

an increase in the vehicle speed. The forces of the springs of the shift valves V1-V3 are set at respective different values. To be specific, the 1-2 shift valve V1, which is arranged between the fluid line 40 and a fluid line 42 provided with a restriction 43, is adapted to assume the first position as illustrated when the vehicle speed is low, to thereby disconnect the fluid line 42 from the fluid line 40.

With the 1-2 shift valve V1 held in this position, the first-speed clutch C1 alone is engageable to establish the first-speed reduction ratio, so long as the creep-inhibiting valve 50 is open.

As the vehicle speed increases, the 1-2 shift valve V1 is shifted to the right or second position to communicate the fluid lines 40, 42 with each other. On this occasion, the 2-3 shift valve V2 is in the first position as illustrated, to communicate the fluid line 42 with a fluid line 44 connected to the hydraulically operating portion of the second-speed clutch C2. Although both the first-speed and secondspeed clutches C1 and C2 are engaged on this occasion, the second-speed gear train G2 alone is established to provide the secondspeed reduction ratio, while the first-speed gear train G1 is rendered substantially inoperative with the first-speed clutch C1 maintained in an engaged state, by the action of the oneway clutch CO in Fig. 1.Likewise, when the third-speed or fourth-speed clutch C3, C4 is engaged, the third-speed or fourth-speed gear train G3, G4 alone is established while the first-speed gear train G1 is rendered substantially inoperative with the first-speed clutch C1 maintained in an engaged state.

When the vehicle speed further increases, the 2-3 shift valve V2 is shifted to the right or second position to communicate the fluid line 42 with a fluid line 45. On this occasion, the 3-4 shift valve V3 still assumes the left or first position as illustrated, to communicate the fluid line 45 with a fluid line 46 connected to the hydraulically operating portion of the third-speed clutch C3, whereby the thirdspeed clutch C3 becomes engaged to establish the third-speed reduction ratio.

The 3-4 shift valve V3 is shifted to the right or second position with a further increase in the vehicle speed, and the fluid line 45 is communicated with a fluid line 47 connected to the hydraulically operating portion 5 of the fourth-speed clutch C4 so that the fourthspeed clutch C4 becomes engaged to establish the fourth-speed reduction ratio. The arrangement of the automatic transmission described above is known in the art.

The creep-inhibiting valve 50, which is arranged in the fluid line 41, has an inlet port 51 connected via the fluid line 41 to the fluid line 40, and an outlet port 52 connected to the hydraulically operating portion of the firstspeed clutch C1. A spool 55 of the valve 50 has one end face 55a formed larger in diameter than its other end face 55b, and the pressure-receiving area of the former is larger than that of the latter. The end face 55a of the spool 55 has a central portion thereof formed with a large-sized hole 56 and a smallsized hole 57 smaller in diameter than the hole 56 and arranged adjacent thereto, while the other end face 55b has its central portion formed with a hole 58.An annular groove 59 is formed in the outer peripheral surface of the spool 55, and disposed to communicate the inlet port 51 with the outlet port 52 when the spool 55 assumes a first position as illustrated. The annular groove 59 communicates with the holes 57 and 58, respectively, via small holes (hereinafter called "the restrictions") 60 and 61.

A one-way valve 62 is arranged in the hole 57 to allow the pressurized oil to flow in a sole direction from the hole 57 to the hole 56.

A pressure chamber 65 is defined between the end face 55a of the spool 55 and an opposed end face of an end block 63, and a through hole (hereinafter called "the port") 63a is formed in the end block 63 and opens into the pressure chamber 65. A spring 64 is arranged in the hole 56 of the spool 55 and urges at its one end the end face of the hole 56 and at its other end the opposed end face of the end block 63, respectively. The ports 51, 52 are disposed to be communicated with each other via a fluid line 67 arranged in parallel with the creepinhibiting valve 50 and provided therein with a one-way valve 68 which allows the pressurized oil to flow in a sole direction from the outlet port 52 to the inlet port 51.The fluid line 67 and the oneway valve 68 act to return the pressurized oil in the first-speed clutch C1 to a zone under a lower pressure when the manual shift valve Vm is shifted from the forward position to the neutral position or to the reverse position, to promptly decrease the internal pressure of the clutch C1 for prompt interruption of the engagement of same. This arrangement is particularly advantageous when the viscosity of the operating oil is low, such as in cold weather.

An electromagnetic valve 70 is mounted on an end of the creep-inhibiting valve 50 closer to the end block 63. A valve body 71 of the valve 70 is disposed to be displaced by the urging force of a spring 72 to close the port 63a when a solenoid 73 is deenergized, and be attracted against the force of the spring 72 to open the port 63a when the solenoid 73 is energized, to thereby communicate the pressure chamber 65 with a port 53. The electromagnetic valve 70 is formed of a poppet valve in which the valve body 71 is urged by the spring 72 to close the port 63a, and the force of the spring 72 and the diameter d of the port 63a are set at respective appropriate values so that when the solenoid 73 is deenergized, the pressure in the pressure chamber 65 is maintained at a predetermined pressure hereinafter referred to.By thus setting the spring force and the port diameter, even when the solenoid 73 is deenergized, the electromagnetic valve 70 can open when the pressure in the pressure chamber 65 exceeds the predetermined pressure value, to a degree corresponding to the difference between the predetermined pressure and the pressure in the pressure chamber 65, thereby communicating the pressure chamber 65 with the port 53 through the port 63a. The pressure chamber 65 can communicate with the port 53 also through a bypass fluid line 54 in which a one-way valve 66 is arranged to allow the pressurized oil to flow in a sole direction from the port 53 to the pressure chamber 65.

A pilot fluid line 90 branches off from the pilot fluid line 48 and is connected to a port 75a of a selector valve 75 hereinafter referred to, via a shut off valve 74 provided on the manual shift valve Vm and disposed to open when the manual shift valve Vm is in one of the drive range positions. The selector valve 75 has a port 75b connected to the port 53 of the creep-inhibiting valve 50 via a pilot fluid line 91. Another pilot fluid line 92 branches off from the pilot fluid line 48 and is connected to the pilot fluid line 91 extending between the port 53 and the selector valve 75. A one-way valve 82 is arranged in the pilot fluid line 92 to allow the pressurized oil to flow in a sole direction from the pilot fluid line 48 to the one-way valve 82.The selector valve 75 has a spool 76, a pressure chamber 78 defined in part by a left end face of the spool 76 as viewed in Fig. 2, and a spring 77 urging the spool 76 toward the pressure chamber 78. The pressure chamber 78 is disposed to be communicated with the pilot fluid line 90 via a one-way valve 79 which allows the pressurized oil to flow in a sole direction from the pilot fluid line 90 to the pressure chamber 78, and also communicated with the pilot fluid line 92 through a restriction 80.

An annular groove 76a is formed in the outer peripheral surface of the spool 76 of the selector valve 75, which is disposed to communicate the ports 75a, 75b with each other when the spool 76 is in a first position as illustrated. The spool 76 is urged by the force of the spring 77 toward the first position.

When the pressure in the pressure chamber 78 exceeds a reference pressure Ps determined by the force of the spring 77, the spool 76 is displaced rightward as viewed in Fig. 2, into a second position to disconnect the ports 75a, 75b from each other, thereby closing the selector valve 75 to block the communication between the pilot fluid lines 90, 91.

The selector valve 75 has a shift-retarding function exhibited when it shifts from a closed position to an open position, which is imparted by the one-way valve 79 and the restriction 80. More specifically, when the throttle pressure Pt increases, it is introduced into the pressure chamber 78 through both the one-way valve 79 and the restriction 80, whereby the selector valve 75 is promptly closed without delay to disconnect the pilot fluid line 90 from the pilot fluid line 91. On the other hand, when the throttle pressure Pt decreases, the pressurized oil in the pressure chamber 78 flows out solely through the restriction 80, at a lower flow rate. Consequently, after the throttle pressure Pt has dropped below the reference pressure Ps due to sudden closing of the throttle valve, the selector valve 75 temporarily remains in a closed state, thus achieving the shiftretarding function.As noted above, the one-way valve 79, the restriction 80 and the selector valve 75 cooperate to function as a retarding valve 81, and the one-way valve 79 and the restriction 80 are formed integrally with the selector valve 75.

According to this arrangement, the creepinhibiting valve 50 and the selector valve 75 are connected with each other via the single pilot fluid line 91 alone. Therefore, the selector valve 75 and the creep-inhibiting valve 50 which is provided with a solenoid and an adjusting mechanism can individually be arranged at different places, for instance, in the interior of the transmission and on the outer peripheral surface of same, respectively, simplifying the construction of the whole creepinhibiting device.

A brake sensor 100 is provided for determining whether or not a brake pedal, not shown, of the vehicle is stepped on, and it generates a signal having a high level when the brake pedal is stepped on. For instance, a switch for turning on and off the stop lamps may be used as the brake sensor 1 00.

An engine rotational speed sensor 101 is provided, which detects the engine speed Ne by counting the interval of time between adjacent pulses of an ignition signal for instance, and generates a signal having a high level when the detected engine speed Ne is lower then a predetermined speed Ns which is slightly higher than a reference speed, e.g. an idling speed.

The brake sensor 100 and the engine speed sensor 101 are connected to respective input terminals of an AND circuit 103 of a solenoid driving circuit 102. The AND circuit 103 has its output terminal connected to the base of a transistor Tr which has its emitter grounded and is connected at its collector to one end of the solenoid 73 of the electromagnetic valve 70 via a line 1 04. The other end of the solenoid 73 is connected via a line 105 to a predetermined power supply source, not shown.

The operation of the creep-inhibiting valve 50 and the retarding valve 81 will now be described.

While the vehicle is running, the output signals of the brake sensor 100 and the engine speed sensor 101 have a low level to keep the transistor Tr off to deenergize the solenoid 73 of the electromagnetic valve 70.

On this occasion, an oil pressure or throttle pressure Pt corresponding to the stepping amount of the accelerator pedal, not shown, is supplied to the pilot fluid lines 90, 92. When the throttle pressure Pt is higher than the reference pressure Ps, the retarding valve 81 is closed with its spool 76 displaced rightward as viewed in Fig. 2, to disconnect the pilot fluid line 91 from the pilot fluid line 90.

Consequently, the throttle pressure Pt can then be freely supplied to the pressure chamber 65 of the creep-inhibiting valve 50 through the pilot fluid line 92, the one-way valve 82 and the pilot fluid line 91, but the pressurized oil in the pressure chamber 65 finds no way for flowing out of same. On this occasion, the line pressure Pl in the fluid line 41 has been supplied in part through the restrictions 60, 61 of the creep-inhibiting valve 50 to the opposite end faces 55a, 55b of the spool 55. Therefore, the spool 55 is displaced downward into the first position as illustrated due to the difference in pressurereceiving area between the end faces 55a and 55b as well as due to the force of the spring 64, thereby communicating the port 51 with the port 52 through the annular groove 59.

Consequently, the line pressure Pl is supplied through the valve 50 to the hydraulically operating portion of the first-speed clutch C1 to positively engage same.

If the accelerator pedal is released from the stepped-on state and at the same time the brake pedal is stepped on so as to stop the vehicle, the throttle pressure Pt decreases with a decrease in the stepping amount of the accelerator pedal. However, the retarding valve 81 temporarily remains in a closed state due to its shift-retarding function, thereby avoiding shocks caused upon abrupt release of the accelerator pedal. When the engine speed Ne drops below the reference speed Ns, the output of the engine speed sensor Ne is inverted to a high level. On this occasion, the output of the brake sensor 100 has already been inverted to a high level since the brake pedal was stepped on. Therefore, the AND circuit 103 generates a signal having a high level to hold the transistor Tr in a conducted or on state, whereby the electromagnetic valve 70 is energized to open the port 63a.

By this time, the retarding valve 81 has been shifted to the first position as illustrated to communicate the pilot fluid line 91 with the pilot fluid line 90, whereby the pressurized oil in the pressure chamber 65 of the creep-inhibiting valve 50 escapes to the lower pressure zone through the port 63a then opened, and the pilot fluid lines 91, 92 to decrease the pressure in the pressure chamber 65. Consequently, the spool 55 is displaced in the direction of disconnecting the ports 51, 52 from each other, i.e. upward as viewed in Fig. 2, by the oil pressure acting upon the end face 55b of the spool 55, to communicate the port 52 with a drain port 69 connected to the oil tank R, thereby decreasing the oil pressure in the fluid line 41 at the port 52, i.e. the oil pressure (clutch pressure) supplied to the hydraulically operating portion of the first-speed clutch C1.The force acting upon the spool 55 to lift same upward as viewed in Fig. 2, i.e. the clutch pressure then applied to the first-speed clutch C1, is controlled to a pressure Po determined by the force of the spring 64. The pressure Po is set at a value almost equal to and slightly smaller than an engaging pressure Pe above which the first-speed clutch C1 is engaged to cause creeping of the vehicle and which is determined by the force of a return spring, not shown, provided in the first-speed clutch C1.

Therefore, the first-speed clutch C1 is maintained in a completely disengaged state, preventing creeping of the vehicle when the vehicle stands.

Then, if the brake pedal is restored to its initial position to start the vehicle, the output of the brake sensor 100 is inverted to the low level. Accordingly, the output of the AND circuit 103 goes low to turn the transistor Tr off, whereby the electromagnetic valve 70 is deenergized to allow its valve body 71 to be displaced by the force of the spring 72 to close the port 63a.If, on this occasion, the accelerator pedal is not stepped on, the valve body 71 starts to be displaced upward by the oil pressure present in the pressure chamber 65 when the same oil pressure becomes higher than the set pressure Po by a predetermined pressure ssP, so that the oil pressure in the pressure chamber 65 is escaped to the lower pressure zone through the port 63a, the pilot fluid line 91, the retarding vlave 81 then opened, and the pilot fluid line 90, thereby controlling the oil pressure in the chamber 65 to a predetermined pressure Po + 8P. This means that the force of the spring 64 of the creep-inhibiting valve 50 is substantially increased by a value corresponding to the predetermined pressure ssP, and accordingly the internal pressure of the first-speed clutch C1 acting upon its hydraulically operating portion is increased from the set pressure Po to the predetermined pressure Po + ssP. By virtue of this increase in the oil pressure by the predetermined pressure bP, there can occur no ineffective stroke of the hydraulically operating portion of the first-speed clutch C1. This predetermined pressure ssP may be small.By thus removing the ineffective stroke, the clutch C1 can positively be kept in a state wherein creeping of the vehicle can take place. Further, a shock caused upon restoring action of the brake pedal can be reduced to a minimum level due to the small pressure difference SP.

The clutch pressure P then present in the firstspeed clutch C1 is indicated by the chain line I in Fig. 3. In the same figure, the broken line represents the engaging pressure Pe at which the force of the return spring for returning a piston of the hydraulically operating portion of the first-speed clutch C1 is equilibrated with the internal pressure of the clutch C1. As stated before, when the internal pressure of the clutch C1 is higher than the engaging pressure Pe, the vehicle is allowed to creep, while when the former is smaller than the latter, the vehicle will not creep.

If the accelerator pedal is then stepped on, a throttle pressure Pt corresponding to the stepping amount of the accelerator pedal is supplied to the fluid line 91 through the pilot fluid line 90 and the retarding valve 81 as well as through the pilot fluid line 92 and the one-way valve 82, and then to the pressure chamber 65 of the creep-inhibiting valve 50 via the one-way valve 66, whereby the spool 55 is urged downward as viewed in Fig. 2.

When the throttle pressure Pt is smaller than the reference pressure Ps and accordingly the retarding valve 81 is in an open state, the spool 55 is displaced downward with an increase in the throttle pressure Pt, so that the outlet port 52 is disconnected from the drain port 69 and communicates with the inlet port 51 alone. Accordingly, the clutch pressure P of the first-speed clutch C1 gradually increases as indicated by the solid line Il in Fig.

3. The creep-inhibiting valve 50 is usually shifted to the creep-permitting position with such increase in the throttle pressure Pt.

When the throttle valve opening is increased above a predetermined opening go so that the throttle pressure Pt exceeds the reference pressure Ps, as shown in Fig. 3, the retarding valve 81 closes to disconnect the pilot fluid line 91 from the pilot fluid line 90.

Therefore, the pressures acting upon the opposite end faces 55a, 55b of the spool 55 of the creep-inhibiting valve 50 become equal to each other, whereby the spool 55 is displaced downward into the first position due to the difference in pressure-receiving area between the end faces 55a and 55b, and the urging force of the spring 64, thereby fully communicating the port 52 with the port 51. Accordingly, the line pressure Pl in the fluid line 41 is supplied to the hydraulically operating portion of the first-speed clutch C1 to increase the clutch pressure P to a level equal to the line pressure Pl, as indicated by the solid line Ill in Fig. 3, thereby increasing the torque transmission capacity of the first-speed clutch C1 to a maximum level to ensure positive engagement of the clutch C1.

When the brake pedal is maintained in a stepped-on state, the electromagnetic valve 70 remains in an open position so long as the engine speed Ne is lower than the predetermined speed Ns. Therefore, the clutch pressure P is then maintained at the pressure Po as indicated by the solid line IV in Fig. 3. If on this occasion the accelerator pedal is stepped on, the clutch pressure P is then varied as indicated by the solid line 11, as the accelerator pedal is further stepped on to supply the increased oil pressure Pt from the pilot fluid line 91 to the pressure chamber 65 via the port 63a and the one-way valve 66.

The retarding valve 81 performs the shiftretarding function only when it is opened, as stated before. Therefore, when the shift lever is shifted to the drive range (D4) position for instance, from the neutral (N) position wherein the throttle valve is normally closed and accordingly the throttle pressure Pt is zero, the retarding valve 81 is then in an open state so that the spool 55 of the creep-inhibiting valve 50 is promptly biased to block the fluid line 41 extending between the first-speed clutch C1 and the operating oil source, to thereby prevent the clutch C1 from becoming suddenly engaged, avoiding the gear shifting shock.

Incidentally, if the shut off valve 74 arranged in the pilot fluid line 90 is constructed such that it opens only when the shift lever is in the drive range (D4) position and closes when the shift lever is in a position other than the drive range (D4) position, the creeping of the vehicle can be prevented only when the shift lever is in the drive range (D4) position.

Fig. 4 illustrates a creep-inhibiting device according to a second embodiment of the invention, wherein like reference characters designate corresponding parts and elements having substantially the same functions to those in Fig. 3, and explanation thereof is therefore omitted.

A fluid line 1 45 branches off from the fluid line 40 connected to the manual shift valve Vm at its output side, and is connected via a creep-inhibiting valve 1 52 which is different in construction from the valve 50 in Fig. 2, to a fluid line 114 connected to the first-speed clutch C1. A valve body 1 53 of the creepinhibiting valve 1 52 has an upper end face with a pressure-receiving area larger than that of a lower end face thereof. An axially central portion of the spool 1 53 has its outer peripheral surface formed with an annular groove 1 62 in communication through a small hole 1 55 with a lower pressure chamber 1 61 defined in part by the lower end face of the spool 1 53. The upper end face of the spool 1 53 defines part of an upper pressure chamber 1 60 in which is arranged a spring 1 58 permanently urging the valve body 1 53 downward as viewed in Fig. 4. The spring 1 58 abuts at its upper end against an adjusting screw 1 65 so that by axially displacing the screw 165, the force of the spring 1 58 can be set at a desired value. Reference numeral 1 65a denotes a lock nut for fixing the adjusting screw 1 58 in a desired position, and 1 65b a cover which is removable from the valve 1 52 and provided for protecting the adjusting screw 165.

A bypass fluid line 1 69 branches off from the input fluid line 145 of the creep-inhibiting valve 1 52 and permanently communicates with the output fluid line 114 of the same valve 1 52 through a filter 1 64 and a restriction 1 54. The upper pressure chamber 1 60 of the creep-inhibiting valve 1 52 permanently communicates with an output fluid line 1 59 which in turn is connected to a port 1 80a of a selector valve 1 70 hereinafter referred to.A feedback fluid line 1 67 branches off from the output fluid line 114 and is disposed to be communicated with a drain line 1 63 of the creep-inhibiting valve 1 52 via an electromagnetic valve 1 56 and a fluid line 1 66. The communication between the feedback fluid line 1 67 and the drain line 1 63 is selectively established and blocked by the valve body 153 of the creep-inhibiting valve 152.

The electromagnetic valve 1 56 is electrically connected to a solenoid driving circuit 102'. The brake sensor 100, a vehicle speed sensor 1 82 and an engine cooling water temperature sensor 1 83 are connected to respective input terminals of an AND circuit 103' of the solenoid driving circuit 102'. These sensors 1 00, 1 82 and 1 83 set predetermined conditions for initiating and terminating exhibition of the creep-inhibiting function, like the sensors appearing in Fig. 2.The vehicle speed sensor 1 82 is adapted to generate a signal having a high level when the vehicle speed is smaller than a reference value, and comprises a magnet which may be driven by a speedometer cable, and a reed switch for instance, while the engine cooling water temperature sensor 1 83 is adapted to generate a signal having a high level when the temperature of the engine cooling water is higher than a reference value which may be set at a value equal to or lower than 0 C, and comprises a member formed of a thermoferrite material, and a reed switch for instance.

When the vehicle speed is lower than the reference value and at the same time the engine cooling water temperature is higher than its reference value while the brake pedal is stepped on, the output of the AND circuit 103' goes high to cause the transistor Tr to conduct, whereby the electromagnetic valve 1 56 is energized to displace its valve body 1 57 to an upper or open position as illustrated. When any one of the aforementioned conditions is not fulfilled, the electromagnetic valve 1 56 is deenergized and accordingly its valve body 1 57 assumes a lower or closed position.

The selector valve 1 70 has its valve body 1 71 always biased leftward as viewed in Fig.

4, by a spring 172. A spring chamber 1 77 is defined in part by a right end face of the valve body 171 and connected to a drain line 178, while a pressure chamber 1 76 is defined in part by a left end face of the valve body 171 and connected via a parallel circuit formed by a check valve 1 74 and a restriction 173, to a fluid line 146 which delivers the throttle pressure Pt. An axially central portion of the valve body 171 has its outer peripheral surface formed with an annular groove 1 71 a which is disposed to communicate the port 180a with a port 1 80b when the valve body 171 is in a first position as illustrated.The fluid line 146 branching off from the pilot fluid line 48 is connected to the port 180b, and a fluid line 1 79 branching off from the fluid line 1 46 is connected to a port 1 80c which permanently communicates with the port 180a. A one-way valve 1 75 is arranged in the fluid line 1 79 to allow the pressurized oil to flow in a sole direction from the fluid line 1 46 to the port 180c. The valve 1 70 further includes a port 1 80d which is connected to the fluid line 145 and disposed to be communicated with the port 1 80a via the annular groove 1 71 a when the valve body 171 assumes a right or second position shown in Fig. 6.According to this embodiment, the one-way valve 174, the restriction 1 73 and the selector valve 1 70 cooperate to function as a retarding valve 81', like the valve 81 appearing in Fig. 2.

The retarding valve 81' and the creepinhibiting valve 1 52 according to the second embodiment of the invention operate as follows: When the vehicle speed is lower than its reference value and the engine cooling water temperature is higher than its reference value while the brake pedal is stepped on, that is, when the vehicle is in a condition wherein creeping should be inhibited, the electromagnetic valve 1 56 is in an energized state with its valve body 1 57 biased to the upper or open position.If, on this occasion, the throttle pressure Pt in the fluid line 146 is substantially zero, the valve body 1 71 of the selector valve 1 70 is maintained in the left position by the urging force of the spring 1 72, to fully communicate the fluid line 1 46 with the fluid line 159 through the annular groove 171a.

Accordingly, the pressure in the upper pressure chamber 1 60 of the creep-inhibiting valve 1 52 is low. On the other hand, the line pressure Pl is introduced from the fluid line 145 directly and/or through the fluid line 169 provided with the restriction 154, to the lower pressure chamber to act upon the lower end face of the valve body 153, whereby the valve body 1 53 is displaced upward.When the valve body 1 53 is displaced upward through a certain stroke, the fluid line 1 66 connected to the fluid line 11 4 becomes communicated with the drain line 163, and the input fluid line 1 45 is blocked by the valve body 1 53. Since the line pressure Pl acting upon the lower end face of the valve body 1 53 is supplied there solely through the restriction 1 54 of the fluid line 169, the annular groove 1 62 and the small hole 155, the valve body 1 53 is held at an equilibrated position shown in Fig. 5, wherein the pressures acting upon the opposite end faces of the valve body are equilibrated.More specifically, if the valve body 1 53 moves upward from the Fig. 5 position, the operating oil in the annular groove 1 62 escapes through the fluid lines 167, 166 and the drain line 163 to decrease the oil pressure in the annular groove 1 62 and the lower pressure chamber 161. Accordingly, the valve body 153 is displaced downward to resume the equilibrated position shown in Fig. 5.On the other hand, when the valve body 1 53 assumes a position downward of the Fig. 5 position, the line pressure Pl is directly supplied from the fluid line 145 to the annular groove 162 to promptly increase the pressure in the annular groove 1 62 and the lower pressure chamber 1 61, whereby the valve body 1 53 is again brought into the equilibrated position shown in Fig. 5. The clutch pressure P in the fluid line 114 is thus maintained at the pressure Po by the valve 152, which is not high enough to cause engagement of the first-speed clutch Ci. Therefore, the clutch C1 is maintained in a disengaged state to prevent creeping of the vehicle.

This set pressure value Po is determined by the pressure-receiving area of the lower end face of the valve body 153, the cross-sectional area of the restriction 154, the line pressure PI, the force of the spring 158, etc., and can be adjusted to a higher value by axially inwardly displacing the adjusting screw 1 65 to further compress the spring 158, and to a lower value by axially outwardly displacing the screw 1 65 to reduce the urging force of the spring 1 58.

When the throttle valve is opened to increase the throttle pressure Pt in the fluid line 146 above a reference pressure Ps', the throttle pressure Pt thus increased is introduced into the pressure chamber 1 76 of the selector valve 1 70 through the check valve 174, so that the valve body 1 71 is shifted rightward to the second position shown in Fig. 6, against the force of the spring 1 72. Therefore, the line pressure Pl in the fluid line 145 is now supplied to the fluid line 1 59 through the annular groove 1 71 a of the selector valve 1 70. The line pressure Pl supplied from the fluid line 145 is higher than the throttle pressure Pt supplied from the fluid line 146 and accordingly the check valve 1 75 is closed by the line pressure PI, whereby the throttle pressure Pt in the fluid line 146 is prohibited from being supplied to the fluid line 1 59 through the check valve 1 75 of the fluid line 1 79. Thus, the pilot pressure Pl is supplied to the fluid line 1 59 in lieu of the throttle pressure Pt, with almost no waste of the throttle pressure Pt.

That is, the selector valve 1 70 operates in response to the throttle pressure Pt supplied as a pilot signal from the fluid line 1 46 to output the line pressure Pl to the fluid line 1 59 when the throttle pressure Pt exceeds the predetermined pressure Ps'.The line pressure Pl thus supplied to the fluid line 1 59 is then introduced into the upper pressure chamber 1 60 via the port 168 so that the valve body 1 53 is promptly displaced downward due to the difference in pressure-receiving area between the upper and lower end faces of the valve body 153, as well as the force of the spring 1 58, to thereby fully communicate the input fluid line 145 with the output fluid line 114 to bring the first-speed clutch Cl into a creep-permitting state.

Now, let it be assumed that the electromagnetic valve 1 56 is deenergized with its valve body 1 57 shifted to the lower or closed position.

When the throttle pressure Pt in the fluid line 146 is substantially zero and accordingly the pressure in the fluid line 1 59 is low, the line pressure Pl in the input fluid line 145 is supplied directly and/or through the bypass fluid line 1 69 to the creep-inhibiting valve 1 52, and then introduced into the lower pressure chamber 1 61 through the annular groove 162 and the small hole 155, so that the line pressure Pl acts upon the valve body 1 53 at its lower end face to bias same upward to the second or Fig. 5 position.With the valve body 1 53 held in this position, the input fluid line 145 is blocked by the valve body 1 53 and therefore the line pressure Pl is supplied to the lower pressure chamber 161 solely through the restriction 1 54 of the bypass fluid line 169, the annular groove 1 62 and the small hole 1 55. However, since the pressurized oil in the fluid line 114 cannot be drained through the fluid line 167 which is then blocked by the valve body 157, the firstspeed clutch C1 is supplied with the line pressure Pl higher than the engaging pressure Pe and thereby brought into a creep-permitting state.

When the throttle pressure Pt in the fluid line 146 increases above the reference pressure, the line pressure Pl is now supplied through the fluid line 1 59 and the port 1 68 to the upper pressure chamber 1 60 as sated before. Accordingly, the valve body 1 53 is promptly displaced downward due to the difference in pressure-receiving area between the upper and lower end faces of the valve body 153, as well as the force of the spring 1 58.

On this occasion, the input fluid line 1 45 still communicates with the output fluid line 114 to continually hold the first-speed clutch C1 in the creep-permitting state.

When the brake pedal is released from its stepped-on position while the first-speed clutch C1 is maintained in a creep-inhibiting state, the creep-permitting state of the clutch C1 is recovered in the following manner: While the clutch C1 is in a creep-inhibiting state, the valve body 1 53 of the creep-inhibiting valve 1 52 assumes the second position shown in Fig. 5.If, on this occasion, the brake pedal is released from its stepped-on position and accordingly the electromagnetic valve 1 56 is deenergized to block the feedback fluid line 1 67 with its valve body 1 57, the line pressure Pl is supplied to the fluid line 11 4 through the restriction 1 54 of the bypass fluid line 1 69 so that the clutch pressure P in the fluid line 114 is gradually increased above the engaging pressure Pe without causing downward displacement of the valve body 1 53. In this manner, the creep-permitting state of the first-speed clutch C1 is gradually recovered.

However, if the accelerator pedal is then stepped on, the line pressure Pl is promptly introduced into the pressure chamber 1 60 through the selector valve 1 70 and the port 1 68 as stated before, so that the valve body 1 53 promptly moves downward in response to the stepping-on speed of the accelerator pedal, to thereby promptly increase the pressure in the fluid line 114.

On the other hand, let it now be assumed that the accelerator pedal is stepped on while the electromagnetic valve 1 56 is maintained in an energized state, for instance, the throttle pressure Pt increases by an amount corresponding to the stepping amount of the accelerator pedal upon starting of the vehicle on an ascending slope.In this event, at an initial stage when the accelerator pedal is being stepped on, due to the action of the retarding valve 81', the pressure in the upper pressure chamber 1 60 of the creep-inhibiting valve 1 52 is increased in proportion to an increase in the valve opening of the throttle valve to gradually increase the clutch pressure P of the first-speed clutch C1, and then finally increased to a value equal to the line pressure PI, whereby smooth starting of the vehicle is ensured.On the other hand, when the throttle valve is suddenly opened for rapid starting the vehicle, the line pressure Pl directly acts upon the valve body 1 53 of the creep-inhibiting valve 1 52 to displace same downward, whereby the first-speed clutch C1 promptly recovers a creep-permitting state, ensuring good responsiveness of the creep-inhibiting device to prompt vehicle starting operation by the driver.

On the other hand, when the accelerator pedal is suddenly released from its stepped-on position and accordingly the throttle pressure Pt in the fluid line 1 46 is suddenly decreased, the oil pressure in the pressure chamber 1 76 of the selector valve 1 70 is gradually drained via the restriction 1 73 alone, so as to allow the valve body 1 71 to be gradually displaced leftward in a manner identical with the valve 81 in Fig. 2, until finally the communication between the fluid lines 1 45 and 1 59 is blocked by the valve body 171, thereby preventing a shock from taking place upon abrupt closing of the throttle valve, through the action of the retarding valve 81'.

Incidentally, the retarding valve 81 used in the first embodiment shown in Fig. 2 may be directly employed in the second embodiment in place of the valve 81, in Fig. 4, or, reversely, the retarding valve 81' used in the second embodiment shown in Fig. 4 may be employed in the first embodiment in place of the valve 81 in Fig. 2. In the former case, the throttle pressure Pt alone will be supplied to the upper pressure chamber 1 60 of the creepinhibiting valve 152, while in the latter case, the line pressure Pl will be supplied to the pressure chamber 65 of the creep-inhibiting valve 50 in lieu of the throttle pressure Pt when the throttle pressure Pt exceeds the reference pressure Ps.

Although in the foregoing embodiments, creeping of the vehicle is inhibited by blocking the communication between the firstspeed clutch C1 and the operating oil source by means of the creep-inhibiting valve, the creep-inhibiting valve according to the invention may alternatively be applied to an arrangement in which the pressurized oil to be supplied to the hydraulically operating portion of the first-speed clutch C1 can be drained to the oil tank to inhibit creeping of the vehicle.

It is to be clearly understood that there are no particular features of the appended claims which are at present regarded as being essential to the performance of the present invention, and that any one or more of such features of combinations thereof may therefore by omitted from any of the claims if and when amended during the prosecution of the application or in the filing or prosecution of any divisional application based thereon.

Claims (11)

1. In a creep-inhibiting device for use in an automotive vehicle equipped with an engine, a fluid coupling, a transmission mechanism coupled in series to said fluid coupling and having a frictionally engaging element, and an operating fluid source for supplying an operating fluid to said frictionally engaging element, said device including engine load sensor means for producing a signal fluid having a pressure representative of load applied on said engine, control means interposed between said frictionally engaging element and said operating fluid source, and a fluid line for delivering said signal fluid from said engine load sensor means to said control means, wherein said control means is adapted to control the power transmission capacity of said frictionally engaging element within a range from substantially zero to a predetermined value in dependence on the pressure of said signal fluid supplied thereto, to inhibit creeping of said vehicle when said engine is in a no-load state, the improvement comprising selector valve means arranged in said fluid line, said selector valve means being adapted to assume a first position wherein it allows said signal fluid to flow in both directions from said engine load sensor means to said control means and vice verso when the pressure of said signal fluid is lower than a predetermined value, and to assume a second position wherein it allows said signal fluid to flow in a sole direction from said engine load sensor means to said control means when the pressure of said signal fluid is higher than said predetermined value.

2. A creep-inhibiting device as claimed in claim 1, wherein said selector valve means includes retarding means for reducing the speed of a shifting motion thereof from said second position to said first position, which takes place when the pressure of said signal fluid decreases, to a value lower than the speed of a shifting motion thereof from said second position to said first position, which takes place when the pressure of said signal fluid increases.

3. A creep-inhibiting device as claimed in claim 1 or 2, including a second fluid line for delivering said operating fluid from said operating fluid source to said selector valve means, and wherein said selector valve means is adapted to supply said operating fluid in lieu of said signal fluid to said control means through the first-mentioned fluid line when said selector valve means is shifted to said second position.

4. A creep-inhibiting device as claimed in any of claims 1 to 3, wherein said control means comprises an input fluid line connected to said operating fluid source, an output fluid line connected to said frictionally engaging element, a valve body disposed to selectively connect and disconnect said input fluid line to and from said output fluid line and having first and second end faces, a first pressure chamber defined in part by said first end face of said valve body and disposed to be supplied with an operating fluid pressure in said output fluid line, a second pressure chamber defined in part by said second end face of said valve body and disposed to be supplied with the pressure of said signal fluid, a third fluid line having a restriction and disposed to always deliver said operating fluid pressure in said output fluid line to said second pressure chamber, resilient means urging said valve body in a direction of connecting said input fluid line to said output fluid line, and a drain line disposed to escape said operating fluid pressure in said output fluid line to a zone under a lower pressure when said valve body is biased in a direction of disconnecting said input fluid line from said output fluid line due to a difference in fluid pressure between said first pressure chamber and said second pressure chamber, by an amount corresponding to the amount by which said valve body is biased.

5. A creep-inhibiting device as claimed in claim 4, wherein said third fluid line is formed in said valve body.

6. A creep-inhibiting device as claimed in claim 4, further including a first one-way valve arranged in the first-mentioned fluid line extending between said control means and said selector valve means, and disposed to allow the fluid to flow in a sole direction from said selector valve means to said control means, and a second one-way valve arranged in the first-mentioned fluid line in parallel with said first one-way valve and disposed to allow the fluid to flow in a sole direction from said control means to said selector valve means, and wherein said second one-way valve is adapted to open when the pressure of fluid upstream thereof is higher than the pressure of fluid downstream thereof by an amount exceeding a predetermined value.

7. A creep-inhibiting device as claimed in claim 6, wherein said vehicle has a braking device, and said second one-way valve comprises an electromagnetic valve, said creepinhibiting device further including brake sensor means for detecting whether or not said braking device is operative, and a driving circuit adapted to open said electromagnetic valve when said braking device is detected to be operative by said brake sensor means, whereby the power transmission capacity of said frictionally engaging element is set to different values in dependence on whether said braking device is operative or inoperative.

8. A creep-inhibiting device as claimed in any of claims 1 to 3, wherein said control means comprises an input fluid line connected to said operating fluid source, an output fluid line connected to said frictionally engaging element, a valve body disposed to selectively connect and disconnect said input fluid line to and from said output fluid line and having first and second end faces, a first pressure chamber defined in part by said first end face of said valve body and disposed to be supplied with an operating fluid pressure in said output fluid line, a second pressure chamber defined in part by said second end face of said valve body and disposed to be supplied with the pressure of said signal fluid, a third fluid line having a restriction and disposed to always connect said input fluid line to said output fluid line, resilient means urging said valve body in a direction of connecting said input fluid line to said output fluid line, and a drain line disposed to escape said operating fluid pressure in said output fluid line to a zone under a lower pressure when said valve body is biased in a direction of disconnecting said input fluid line from said output fluid line due to a difference in fluid pressure between said first pressure chamber and said second pressure chamber, by the amount corresponding to an amount by which said valve body is biased.

9. A creep-inhibiting device as claimed in claim 8, wherein said vehicle has a braking device, said creep-inhibiting device further including brake sensor means for detecting whether or not said braking device is operative, and shut-off valve means adapted to block said drain line when said braking device is detected to be operative by said brake sensor means.

1 0. A creep-inhibiting device as claimed in claim 8 or 9, wherein said control means further includes adjusting means for adjusting the magnitude of said operating fluid pressure in said output fluid line so that the power transmission capacity of said frictionally engaging element is substantially zero.

11. A creep-inhibiting device as claimed in claim 10, wherein said adjusting means is adapted to adjust the resilient force of said resilient member.

1 2. A creep-inhibiting device as claimed in claim 1, wherein said control means further includes a bypass fluid line bypassing said control means and connecting said frictionally engaging element to said operating fluid source, and a one-way valve arranged in said bypass fluid line and disposed to allow the fluid to flow in a sole direction from said frictionally engaging element to said operating fluid source.