GB2160284A

GB2160284A - Servo power boosting apparatus

Info

Publication number: GB2160284A
Application number: GB08514140A
Authority: GB
Inventors: Hans-Dieter Reinartz; Helmut Steffes
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1984-06-14
Filing date: 1985-06-05
Publication date: 1985-12-18
Also published as: DE3422153A1; FR2566062A1; FR2566062B1; GB8514140D0; GB2160284B

Abstract

A servo power boosting apparatus for a clutch is furnished with a travel generating element (11) and with a servo control valve (12) linked to a pressure source (13) and to a reservoir. The servo control valve controls the pressure supplied by the pressure source (13) to a slave piston-and-cylinder arrangement (15) according to the travel accomplished by the travel generating element (11). The servo control valve comprises a stepped-piston slide element (17) which is slidably accommodated in a stepped cylinder (18) dimensioned accordingly. The controlled pressure depends on the position of the stepped-piston slide element (17) within the cylinder (18), movement of the piston element (17) causing opening and closing respectively of two ball valves (20) and (21). A hydraulic circuit is disclosed employing a second stepped piston and stepped cylinder having the same size ratio as the element (17) for controlling and limiting the stroke of the clutch pedal (11). <IMAGE>

Description

SPECIFICATION Servo power boosting apparatus This invention relates to a servo power boosting apparatus with a travel generating element movable according to the power to be generated and a servo control valve linked to a pressure source for hydraulic pressure medium and to a reservoir, said servo control valve bringing to bear a controlled pressure supplied by the pressure source on a slave piston-and-cylinder arrangement according to the travel accomplished by the travel generating element.

The inventive servo power boosting apparatus is, in particular, intended to be retrofitted in already existing generating cylinder-slave cylinder units of a clutch which as such remain unchanged and are only to be supplemented by the installation of a power booster.

It is, therefore, an object of the present invention to create a servo power boosting apparatus of the kind mentioned in the beginning by means of which a boosted power allows to be generated in a slave piston-andcylinder arrangement, an already existing generating cylinder-slave cylinder unit working smoothly also without power booster intended to be supplemented only by the installation of a power booster.

According to the present invention there is provided a servo power boosting apparatus with a travel generating element movable according to the power to be generated and a servo control valve linked to a pressure source for hydraulic pressure medium and to a reservoir, said servo control valve bringing to bear a controlled pressure supplied by the pressure source on a slave piston-and-cylinder arrangement according to the travel accomplished by the travel generating element, characterised in that the said servo control valve comprises a cylinder of an internally stepped configuration containing a correspondingly stepped-piston slide element which is preloaded toward its position of rest by a return spring and is subjected to the controlled pressure with its smaller surface, and the controlled pressure is determined by the position of the said piston slide element within the said cylinder, and in that the said travel generating element applies pressure to a generating piston-and-cylinder arrangement whose pressure is brought to bear on the larger surface of the said steppedpiston slide element, causing the latter to slide according to the amount of pressure existing in the said generating piston-and-cylinder arrangement.

The ratio of the surfaces of the steppedpiston slide element is a parameter for the amount of pressure boosting achieved. The stepped-piston slide element is always in equilibrium, which means that the output pressure directly depends on the input pressure. In principle, the inventive servo control valve is comprised of two two-way valves, one of which, being normally closed, leads to the pressure source and the other, being normally open, is linked to the reservoir.

The power booster can be inserted between an already existing generating piston-and-cylinder arrangement and a slave piston-andcylinder arrangement.

An advantageous constructional embodiment of the invention is configured in a manner that the piston slide element acts upon two ball valves, one of which is open when the stepped-piston slide element is in its position of rest thereby opening up a link between the slave piston-and-cylinder arrangement and the reservoir and closing the link as soon as the piston slide element is shifted out of its position of rest, and the other ball valve being positioned between the pressure source and the slave piston-and-cylinder arrangement and opening only after the stepped-piston slide element has closed the one ball valve, with the other ball valve closing again as soon as the power exerted by the controlled pressure on the smaller surface of the steppedpiston slide element and by the return spring is in equilibrium with the power exerted by the input pressure on the larger surface.

A particularly compact constructional arrangement is created when the two ball valves are positioned parallel to each other in the end of the cylinder opposite the smaller surface of the stepped-piston slide element.

Since the inventive servo control valve consumes only a very small volume when actuated by the generating piston-and-cylinder arrangement, it is envisaged according to a particularly preferred embodiment of the invention that a travel simulator is arranged parallel to the servo control valve. This travel simulator is, in particular, to be embodied in such a way that the generating piston-andcylinder arrangement applies pressure to a volume consumer, which accommodates an additional volume of hydraulic pressure medium exactly corresponding to the pressure generated by the generating piston-and-cylinder arrangement.

A particularly compact and nevertheless highly sensitive arrangement allows to be created in that the volume consumer comprises a stepped cylinder with stepped piston located therein, on the larger surface of which latter the pressure of the generating pistonand-cylinder arrangement is exerted and whose smaller surface and whose sliding travel act on a travel-controllable pressure limiting valve arrangement in such a manner that the travel accomplished by the stepped piston is converted into a pressure acting on the smaller surface of the stepped piston.

That means that the basic idea of the travel simulator is to convert a determined travel of a stepped piston by means of pressure boost ing into a counterpressure which limits the consumption of volume on the side of the larger surface of the stepped piston to such a value as is required for a desired travel of the travel generating element, for example of a pedal.

In detail, it is envisaged according to the invention that the pressure limiting valve arrangement comprises a pressure limiting valve which is subjected to the pressure of the smaller surface of the stepped piston and is linked to the reservoir, and which has a travel control inlet being controlled by the travel of the stepped piston.

It is expedient in this context when a nonreturn valve which opens in the event of overpressure in the generating piston-and-cylinder arrangement is inserted between a branching from the generating piston-and-cylinder arrangement to the volume consumer, on one hand, and the servo control valve, on the other hand.

The forementioned features are expedient for a sensitive pressure build-up in the slave piston-and-cylinder arrangement. In order also to safeguard a regular pressure relief upon actuation of the pedal, it is envisaged according to a further advantageous embodiment of the invention that the pressure limiting valve arrangement comprises a pressure limiting valve which is subjected to the pressure at the inlet of the servo control valve and is linked to the reservoir, and which has a travel control inlet being controlled by the travel of the stepped piston. In this configuration, the controlled pressure outlet of the servo control valve is expediently linked, through a nonreturn valve opening in the event of over pressure at the controlled pressure outlet, to the pressure chamber of the stepped cylinder which is subjected to the pressure applied by the smaller surface.Furthermore, a non-return valve opening in the event of overpressure at the pressure inlet of the pressure limiting valve is to be inserted in this configuration between the pressure inlet of the pressure limiting valve subjected to the pressure ap plied by the stepped piston, on one hand, and the generating piston-and-cylinder arrange ment, on the other hand.

Preferably, the non-return valves open at a pressure differential of approximately 0.5 bar.

An embodiment of the invention will be described with reference to the accompanying drawings, in which: Figure 1 is a side view, partly in crosssection, of a servo control valve adapted to be utilised in the servo power boosting apparatus according to the present invention, and Figure 2 is a schematic representation, simi lar to a circuit diagram, of an inventive servo power boosting apparatus.

According to Figure 1, in a servo control valve 1 2 a stepped cylinder 1 8 whose larger diameter region is tightly closed by an axial plug 40 is arranged. Within the cylinder 18, a correspondingly configured stepped-piston slide element 1 7 is slidably accommodated.

Via an inlet 41 and a non-return valve 36, the larger surface 1 9 of the stepped-piston slide element 1 7 is subjected to the pressure generated by a generating piston-and-cylinder arrangement 16 which is, for example, controlled by a pedal 11.

The pressure chamber 42 of the stepped cylinder 18, being juxtaposed to the smaller surface 23 of the stepped piston 17, is linked to a connection 43 leading to a slave pistonand-cylinder arrangement 1 5 and linked to two ball valves 20, 21 which are accommodated parallel to each other in the end of the cylinder 1 8 opposite the smaller surface 23.

The ball valve 20 is juxtaposed to a connection 44 which leads to a pressure source 1 3 constituted, for example, by a pump 45 and an accumulator 46.

The ball valve 20 opens when the ball 47 is opened against the pressure supplied by the pressure source 1 3. To accomplish that opening action, a push rod 50 is provided at the smaller surface 23 of the stepped-piston slide element 17, said push rod 50 being spaced apart from the ball 47 in the position of rest shown in Figure 1, so that the ball valve 20 is closed.

A further ball valve 21 is provided which is located parallel to the ball valve 20 and whose ball 51 interacts with a seat 52 and is coupled to a slide element 53 which through a stop 54, catches behind a counterstop 55 of the stepped-piston slide element 1 7 and which is forced into the position shown in Figure 1 by means of a helical compression spring 10 surrounding the slide element 53 and being active between the slide element 53 and the piston slide element 17, in which position the stop 54 is in abutment against the counterstop 55 and the ball 51 is lifted off from the seat 52. In this way, the pressure chamber 42 is linked to a connection 57 leading to a reservoir 14.A gap 56 between the stop 54 and the material of the stepped piston slide element 1 7 safeguards a sufficient play of motion for the stepped-piston slide element 1 7 upon the closure of the ball valve 21. A return spring 22 retains the stepped piston slide element 1 7 in the position of rest shown in Figure 1 when no pressure is being applied to it.

When upon depression of the pedal 11, a pressure is exerted on the larger surface 1 9 of the stepped-piston slide element 1 7 by the generating piston-and-cylinder arrangement 1 6 upon opening of the non-return valve 36 at a pressure of 0.5 bar, the stepped-piston slide element 1 7 will move to the left as viewed in Figure 1 against the relatively slight force of the return spring 22, whereupon the stepped-piston slide element 1 7 will shift the ball 51 through the helical compression spring 10 and the slide element 53 until the ball 51 comes to be seated on the seat 52 and interrupts the link between the pressure chamber 42 and the reservoir 14.If and when the stepped-piston slide element 1 7 contiues to move to the left, the stop 54 will lift off from the counterstop 55, so moving into the gap 56, with the helical compression spring 10 being compressed. In addition, the push rod 50 will finally touch the ball 47 of the ball valve 20 and will lift it off its seat 49.

At this moment, the pressure supplied by the pressure source 1 3 will be conveyed through the opened ball valve 20 via the connection 43 to the slave piston-and-cylinder arrangement 1 5 whose piston will be shifted accordingly. As soon as an amount of pressure will have built up in the pressure chamber 42 which jointly with the restoring force of the return spring 22 is in equilibrium with the pressure exerted on the larger surface 19, then the ball valve 20 will be closed again under the action of the spring 48. The controlled pressure at the connection 43 is, thus, proportional to the input pressure existing at the connection 41. The amount of power boosting is determined by the ratio between the smaller surface 23 and the larger surface 1 9 of the stepped-piston slide element 1 7.

In Figure 2, identical reference numerals designate corresponding elements to those shown in Figure 1.

In Figure 2, it is illustrated, in addition, that the piston 16' of the generating piston-andcylinder arrangement 1 6 is restorable into the position of rest by a return spring 58. The servo control valve 1 2 of Figure 1 is shown only schematically as a block in Figure 2.

In addition to the embodiment according to Figure 1, a travel simulator 24 is arranged parallel to the servo control valve 1 2.

From a branching-off point 35 in the line going from the generating piston-and-cylinder arrangement 1 6 to the non-return valve 36, a hydraulic line 59 branches off which leads to a volume consumer 25 being configured in the shape of a stepped cylinder 26 with stepped piston 27 accommodated therein.

The hydraulic line 59 is connected to thepressure chamber 28' which acts upon the larger surface 28 of the stepped piston 27. The smaller surface 29 of the stepped piston 27 acts upon a pressure chamber 39 provided at the opposite end of the stepped cylinder 26, from which pressure chamber 39 a hydraulic line 60 leads to a pressure limiting valve 32 of a pressure limiting valve arrangement 30 and another hydraulic line 61 via a non-return valve 37 to an hydraulic line 62 which links the connection 43 with the slave piston-andcylinder arrangement 1 5. A piston rod 63 coupled to the stepped piston 27 acts through a crossbar 64 on the travel control inlet 34 of the pressure limiting valve 32.The crossbar 64 acts, furthermore, on the travel control inlet 33 of a further pressure limiting valve 31 of the pressure limiting valve arrangement 30, which pressure limiting valve 31 is linked through a hydraulic line 65, 66 to the connection 41 of the servo control valve 12.

The line 65 is connected, in addition, through a non-return valve 38 with the hydraulic line 59.

Both pressure limiting valves 31, 32 are, moreover, linked to the reservoir 14.

The dimensioning of the individual components results from the following functional description: When the clutch pedal 11 is actuated, the non-return valve 36 will open and generate a corresponding pressure at the connection 41 of the servo control valve 1 2. Simultaneously, a determined volume of pressure medium will enter the stepped cylinder 26, causing the stepped piston 27 to slide to the left as viewed in Figure 2. A hydraulic pressure boosted in accordance with the ratio of the surfaces 28, 29 will so come about in the pressure chamber 39. The limit pressure adjusted in the pressure limiting valves 31, 32 corresponds to the position of the stepped piston 27 which is transmitted by the piston rod 63 to the travel control inlets 33, 34.The farther the stepped piston 27 is forced in the forward direction, the higher will be the pressure at which the pressure limiting valves 31, 32 will open in order then to establish a link to the reservoir 1 4. The consequence of this is that the larger is the stroke of the stepped piston 27, the higher will become the pressure forming in the pressure chamber 39. As a result, the desired finite travel of the pedal 11 will so be rendered a limited one.

The pressure adjusted by the pressure limiting valve 32 less the pressure transmission ratio of the stepped cylinder 26 and the pressure drop at the non-return valve 36 will now exist at the connection 41, that is to say, at the inlet of the servo control valve 1 2. The servo control valve 1 2 will now adjust, with an identical transmission ratio, the pressure at the connection 43, that is at its outlet, which is applied to the slave piston-and-cylinder arrangement 1 5. As is obvious from the foregoing, it will be of particular importance that the ratio of the sizes of the surfaces 1 9, 23 of the servo control valve 1 2 is identical to that of the surfaces 28, 29 of the volume consumer 25.For the practical case of a generating cylinder-slave cylinder unit of the clutch, this ratio of surfaces corresponds to the desired amount of boosting.

The non-return valves 36, 37, 38, all of them opening at approximately 0.5 bar, divide the function of pressure boost control already described so far from that of pressure relief control which still remains to be desribed. Since, according to the teachings of the invention, the pressure limiting valves 31 and 32 are arranged at the same pressure level and since a slight pressure gradient comes about through the non-return valve 36, no volume can get lost through the pressure limiting valve 32 because thanks to the branching-off point 35 being arranged upstream of the non-return valve 36, the pressure limiting valve 32 is set to a pressure which is slightly higher than the pressure existing at the connection 41 of the servo control valve 1 2.

Therefore, the pressure boost control of the servo control valve 1 2 takes place by the pressure level at the pressure inlet of the stepped cylinder 26 less the slight pressure differential which is caused by the non-return valve 36. That pressure level is adjusted, on its part, by the pressure limiting valve 32 whose setting is determined by the position of the stepped piston 27 of the stepped cylinder 26.

Now, when the pressure in the slave pistonand-cyiinder arrangement 1 5 is to be reduced, first of all the pedal 11 will be relieved, as a result whereof the piston of the generating piston-and-cylinder arrangement 1 6 will be restored under the effect of the return spring 58. This will result in a pressure relief in the hydraulic line 59, causing the stepped piston 1 7 of the stepped cylinder 26 to be restored.

As a result of this, the control power at the travel control inlet 33 of the pressure limiting valve 31 will decrease and, thus, also the pressure at the inlet of the servo control valve 12, which pressure is relieved through the connection 41, the hydraulic lines 66, 65, the pressure limiting valve 31, forth toward the reservoir. As a consequence and due to the ball valve 21 in the servo control valve 1 2 being opened, also the pressure at the connection 43 of the servo control valve 1 2 will decrease. The pressure level in the slave cylinder will be reduced. Part of the volume will flow through the non-return valve into the stepped cylinder. The rest will be relieved through the servo control valve.The pressure at the connection 43 of the servo control valve 1 2 will be applied, through the nonreturn valve 37 which opens. to the pressure chamber 39 of the stepped cylinder 26 and will restore the stepped piston 27 until equilibrium conditions are re-established. Since the pressure of the servo control valve being reduced by the pressure limiting valve 31 is reduced still futher by the pressure gradient at the non-return valve 37, no volume can get lost through the pressure limiting valve 32 because the latter is adjusted too high for this to be possible.

By the describd arrangement, a sensitive boost control and relief control of the pressure in the slave piston-and-cylinder arrangement 1 5 is, thus, possible, even though with a certain hysteresis resulting from the pressure gradiants of the non-return valves 36, 37, 38.

The pressure limiting valves 31, 32 are non-return valves with a more elevated preload whose opening power is varied through the travel control inlets 33, 34 depending on the position of the stepped piston 27. Thanks to the use of non-return valves, the unit has a very compact set-up as compared to a design with force accumulatin4 springs as a travel simulator. The inventive arrangement allows to be given a considerably more compact configuration than a unit relying on force accumulating springs because the springs may be designed much smaller and easier to command, whereas the travel simulation properly speaking is accomplished by way of a hydraulic step-up and step-down transmission, respectively. On the whole, a higher sensitivity and a higher precision are, thus, attained in spite of the substantial savings of space and notwithstanding the lower weight.

Claims

1. A a servo power boosting apparatus with a travel generating element movable according to the power to be generated and a servo control valve linked to a pressure source for hydraulic pressure medium and to a reservoir, said servo control valve bringing to bear a controlled pressure supplied by the pressure source on a slave piston-and-cylinder arrangement according to the travel accomplished by the travel generating element, characterised in that the said servo control valve (12) comprises a cylinder (18) of an internally stepped configuration containing a correspondingly stepped-piston slide element (17) which is preloaded toward its position of rest by a return spring (22) and is subjected to the controlled pressure with its smaller surface (23), and the controlled pressure is determined by the position of the said piston slide element (1 7) within the said cylinder (18), and in that the said travel generating element (11) applies pressure to a generating pistonand-cylinder arrangement (1 6) whose pressure is brought to bear on the larger surface (19) of the said stepped-piston slide element (17), causing the latter to slide according to the amount of pressure existing in the said generating piston-and-cylinder arrangement (16).

2. An apparatus as claimed in claim 1, characterised in that the said piston slide element (17) acts upon two ball valves (20, 21), one of which (21) is open when the said stepped-piston slide element (17) is in its position of rest thereby opening up a link between the said slave piston-and-cylinder arrangement (15) and the said reservoir (14) and serves to close the link as soon as the said piston slide element (17) is shifted out of its position of rest, and the other said ball valve (20) being positioned between the said pressure source (13) and the said slave pistonand-cylinder arrangement (15) and opening only after the said stepped-piston slide element (17) has closed the said one ball valve (21), with the other said ball valve (20) closing again as soon as the power exerted by the controlled pressure on the said smaller surface (23) of said stepped-piston slide element (17) and by the said return spring (22) is in equilibrium with the power exerted by the input pressure on the said larger surface (19).

3. An apparatus as claimed in claim 2, characterised in that the said two ball valves (20, 21) are positioned parallel to each other in the end of the said cylinder (1 8) opposite the said smaller surface (23) of said steppedpiston slide element (17).

4. An apparatus as claimed in any one of the preceding claims, characterised in that a travel simulator (24) is arranged parallel to the said servo control valve (12).

5. An apparatus as claimed in claim 4, characterised in that the said generating piston-and-cylinder arrangement (16) applies pressure to a volume consumer (25) in the travel simulator (24), which consumer accommodates an additional volume of hydraulic pressure medium, said applied pressure exactly corresponding to the pressure generated by the said generating piston-and-cylinder arrangement (16).

6. An apparatus as claimed in claim 5, characterised in that the said volume consumer (25) comprises a stepped cylinder (26) with stepped piston (27) located therein, on the larger surface (28) of which latter the pressure of the said generating piston-andcylinder arrangement (16) is exerted and whose smaller surface (29) and whose sliding travel act on a travel-controllable pressure limiting valve arrangement (30) in such a manner that the travel accomplished by the said stepped piston (27) is converted into a pressure acting on the said smaller surface (29) of said stepped piston (27).

7. An apparatus as claimed in claim 6, characterised in that the said pressure limiting valve arrangement (30) comprises a pressure limiting valve (32) which is subjected to the pressure of the said smaller surface (29) of said stepped piston (27) and is linked to the said reservoir (14), and which has a travel control inlet (34) being controlled by the travel of the said stepped piston (27).

8. An apparatus as claimed in any one of claims 4 to 7, characterised in that a nonreturn valve (36) which opens in the event of overpressure in the said generating pistonand-cylinder arrangement (16) is inserted between a branching (35) from the said generating piston-and-cylinder arrangement (1 6) to the said volume consumer (25), on one hand, and the said servo control valve (12), on the other hand.

9. An apparatus as claimed in any one of claims 6 to 8, characterised in that the said pressure limiting valve arrangement (30) comprises a presure limiting valve (31) which is subjected to the pressure at the inlet of the said servo control valve (12) and is linked to the said reservoir (14), and which has a travel control inlet (33) being controlled by the travel of the said stepped piston (27).

1 0. An apparatus as claimed in claim 9, charcterised in that the controlled pressure outlet of the said servo control valve (12) is linked, through a non-return valve (37) open ing in the event of overpressure at the said controlled pressure outlet, to the pressure chamber (39) of the said stepped cylinder (26) which is subjected to the pressure ap plied by the said smaller surface (29).

11. An apparatus as claimed in claim 9 or in claim 10, charcterised in that a non-return valve (38) opening in the event of overpressure at the pressure inlet of the said pressure limiting valve (31) is inserted between the pressure inlet of the said pressure limiting valve (31) subjected to the pressure applied by the said stepped piston (27), on one hand, and the said generating piston-and-cylinder arrangement (16), on the other hand.

1 2. An apparatus as claimed in any one of claims 8 to 11, characterised in that the said non-return valves (36, 37, 38) open at a pressure differential of approximately 0.5 bar.

1 3. A servo power booster apparatus sub stantially as herein described with reference to Figure 1 or Figures 1 and 2 of the accom panying drawings.