FR2780455A1 - Master/slave hydraulic actuator for friction clutches in motor vehicles - Google Patents

Abstract

The master actuator (1) contains a second piston (16) coaxially separated from the first piston (3) but joined by a common rod (17) and a valve (29) lodged in the cylinder (2) of the master actuator (1). This valve is actuated by the second piston (16) when the two pistons (3,16) have displaced a given displacement (Cf) when the two end chambers (C2,C3) of the actuator (1) are then joined by a communicating channel (33) thus maintaining a constant pressure at the outlet of the master actuator.

Description

The present invention relates to a device for exercising a

  remote thrust by displacement of a pressurized liquid from a jack

  hydraulic transmitter to a hydraulic receiver cylinder.

  This device applies in particular to

  friction clutches for motor vehicles.

  According to such a known device, the hydraulic transmitter cylinder is connected by means of a pipe or pipe to the hydraulic receiver cylinder, the hydraulic transmitter cylinder comprising a piston delimiting in the cylinder of this cylinder two chambers at atmospheric pressure in the position of rest of the piston and, when this piston moves under the effect of the thrust applied to the rod of this piston connected to the clutch pedal by means of a push rod, a pressure of liquid develops in the chamber working and is transmitted, via the connecting pipe, to the receiving cylinder, the piston of which is moved to actuate, via its piston rod, the

  friction clutch release clutch.

  According to the device known above, the displacement of the piston of the receiving cylinder is directly proportional to the controlled movement of the piston of the transmitting cylinder, if the flexibility of the assembly constituted by the transmitting cylinder, the connection pipe and the receiving cylinder is considered null. This known design therefore does not make it possible to control the stroke of the piston of the receiving cylinder without perfectly controlling

  that of the piston of the emitting cylinder.

  The object of the present invention is to eliminate the above drawback of the known device by proposing a device, the hydraulic emitting cylinder of which is designed so as to maintain, from a determined distance of displacement of the piston of this cylinder, a constant hydraulic pressure in the circuit which connects this jack to the receiving hydraulic jack, while avoiding the displacement of the piston of the latter despite the actuation of the piston of the sending jack. In this way, the stroke of the piston of the receiving cylinder becomes

  independent of the stroke of the piston of the emitting cylinder

  beyond a given position of the latter's piston.

  To this end, the device according to the invention, making it possible to exert a thrust at a distance by displacement of liquid under pressure from a hydraulic jack cylinder to a hydraulic jack cylinder whose inlet for pressurized liquid is connected to the outlet pressurized liquid from the hydraulic emitting cylinder via a pipe, the hydraulic emitting cylinder comprising at least one piston delimiting in the cylinder of this cylinder at least two chambers at atmospheric pressure in the piston rest position and allowing the exit of pressurized liquid from the sending cylinder to the receiving hydraulic cylinder when the piston moves over a determined distance to move the piston of the receiving hydraulic cylinder, is characterized in that it comprises a second piston coaxially separated from the first piston by being integral with the latter by a rod of common piston so as to delimit in the cylinder of the hydraulic actuating cylinder a three isth chamber also at atmospheric pressure in the rest position of the two pistons and a valve member housed in the cylinder of the emitting hydraulic cylinder opposite the rod of the first piston and actuated by the second piston when the two pistons have been moved over the distance determined so as to put the two extreme chambers of the transmitting hydraulic cylinder into communication and to maintain a constant hydraulic pressure at the output of the transmitting hydraulic cylinder for any movement of the two pistons beyond the determined distance up to a

  position of extreme displacement of these.

  Preferably, the valve member comprises an annular seal mounted on an axially movable ring so as to close the communication passage between the two end chambers of the emitting cylinder during the displacement of the two pistons of this cylinder until the determined distance at which the movable ring is moved to a position where the annular seal opens this passage to put these two chambers in communication through the axial bore of the movable ring which is resiliently supported on one face of an integral annular wall transversely of the cylinder of the emitting cylinder and whose axial drilling allows the flow of liquid under pressure at the outlet of

this jack.

  The second piston includes a cylindrical end piece which can come to bear, through the annular support wall of the movable ring, to move the latter axially to the open position, by the annular seal, of the communication passage between the

two extreme rooms.

  The second piston further comprises a flange which can come to bear on the other face of the annular wall to delimit the distance of extreme movement or maximum stroke of the two pistons in the

master cylinder.

  The communication passage between the two extreme chambers comprises, made in the cylinder of the emitting cylinder, an axial channel parallel to the longitudinal axis of the cylinder opening through a radial orifice in the extreme chamber opposite to the third chamber and an opposite radial channel opening downstream of the annular bearing wall of the movable ring at the level of the annular seal so that this seal closes or releases the radial channel according to its relative axial position. The annular seal of the movable ring has two lips located on either side of the radial channel from the rest position of the two pistons to their position corresponding to the displacement distance

determined above.

  The movable ring comprises at least one radial orifice opening into its axial piercing and allowing the flow of liquid under pressure when the end piece of the second piston is in contact with the movable ring so that the liquid can circulate from the third chamber to the opposite extreme chamber through the aforementioned passage when the two pistons have moved beyond the

determined distance.

  The intermediate chamber of the emitting cylinder is permanently connected to a tank of liquid at atmospheric pressure by means of a connection tube and can communicate with the extreme chamber opposite to the third chamber by a channel formed in the cylinder parallel to its longitudinal axis opening into the cylinder through two axially opposite radial orifices and the two pistons each carry an annular lip seal so that in the rest position of the two pistons, the intermediate chamber and the extreme chamber communicate with each other via the axial channel and the radial orifices and the intermediate chamber and the third chamber communicate with each other by a cylinder orifice closed by the annular lip seal of the second piston as soon as the latter has moved to pressurize the liquid in the third chamber while the other two chambers remain at atmospheric pressure. The annular lip seal of the first piston is downstream of the radial orifice of the abovementioned axial channel shortly before the second piston comes into contact with its end piece with the movable ring so as to interrupt the communication between the intermediate chamber and the extreme chamber by the axial channel to create a vacuum in this extreme chamber which fills with liquid by the effect of one-way valve of the lip of the annular seal of the first piston thus authorizing the transfer of liquid from the intermediate chamber to the

extreme room.

  An annular lip seal integral with the cylinder of the emitting cylinder is also provided to ensure

  the tightness of the rod of the first piston of this jack.

  The diameter of the first piston of the emitting cylinder is greater than the diameter of the second piston of the latter. In the application to friction clutches, the rod of the first piston of the emitting cylinder is connected to an external push rod actuated by the clutch pedal of the friction clutch of the motor vehicle and the piston rod of the receiving cylinder is connected to a clutch release clutch. The invention will be better understood and other aims, characteristics, details and advantages thereof

  will appear more clearly in the description

  Explanatory which will follow made with reference to the accompanying schematic drawings given solely by way of example illustrating an embodiment of the invention and in which: - Figure 1 shows a hydraulic actuator in longitudinal section according to the invention, connected to a controlled receiving hydraulic cylinder; and - Figures 2 to 5 show the hydraulic transmitter cylinder of Figure 1 and whose two pistons occupy several working positions from

  from their rest position in Figure 1.

  The device according to the invention will be described in the application to friction clutches of motor vehicles, but it is understood that it can also have any other application like this.

  will emerge clearly from the description which follows.

  Referring first to FIG. 1, the device shown comprises a hydraulic emitting cylinder 1 in the cylinder 2 from which a piston 3 can slide axially, the piston rod 4 of which is suitably connected to an external push rod 5 itself connected articulated at its end opposite the piston rod 4 to a clutch pedal (not shown) of the friction clutch of the motor vehicle. The piston 3 delimits in the cylinder 2 two chambers C1 and C2 containing a liquid (oil) at atmospheric pressure in the rest position of the piston 3 shown in FIG. 1. The chamber C1 located downstream of the piston 3 relative to FIG. 1 is connected to a tank of liquid at atmospheric pressure (not shown) via a tube or pipette

connection 6.

  The cylinder 2 of the jack 1 comprises at its end opposite the piston 3 an outlet tube or pipette 7 connected to the liquid inlet orifice of a receiving hydraulic jack 8, schematically represented in dashed lines, by means of d '' a conduct or

  line 9 symbolized in phantom.

  The receiving cylinder 8 comprises a piston 10 mounted axially sliding in the cylinder 11 of the cylinder 8 under the action of the pressurized liquid coming from the emitting cylinder 1 so as to control the pivoting of a clutch release fork 12 of the friction clutch articulated connection, for example by a spherical ball 13, at the end of the rod 14 of the piston 10. By way of example, the jack 8 is shown as being of the type according to which the piston 10 is returned to its rest position by a helical spring 15 interposed between the piston 10 and the end wall of the cylinder 11 opposite the entry port for fluid under pressure in the

  cylinder 11 working chamber of cylinder 8.

  According to the invention, the emitting cylinder 1 comprises a second piston 16 coaxially separated from the first piston 3 by being integral with the latter by a piston rod

  common 17 coaxial with the piston rod 4.

  The second piston 16 delimits in the cylinder 2 of the cylinder 1 a third chamber C3 situated downstream of the piston 16 and in which the pressure rise of the liquid exerting the pushing force of the piston 10 of the receiving cylinder 8 during the depressing the clutch pedal. The first piston 3 carries an annular seal 18 with lip 19 elastically contacting the internal surface of the side wall of the cylinder 2 defining the chambers C1 and C2 so as to seal the fluid between the two chambers C1 and C2. The latter can communicate with each other by an axial channel 20 produced in the side wall of the cylinder 2 parallel to the longitudinal axis of this cylinder and two radial orifices 21 and 22 formed at the ends of the channel 20 and opening into the cylinder 2, more particularly respectively in the two chambers C1 and C2 in particular

in the piston rest position 3.

  The second piston 16 carries an annular seal 23 with a lip 24 which can resiliently contact the internal surface of the side wall of the cylinder 2 defining the chamber C3 so as to seal the liquid between the chamber C3 and the intermediate chamber C1. FIG. 1 shows that in the rest position of the second piston 16, the chambers C1 and C3 communicate with each other by a passage 25 produced in the side wall portion of the cylinder 2 situated at the level of the connection wall portion of the tubing 6 to the side wall of this cylinder. This passage 25 is located above the part

  corresponding upper lip 25.

  The emitter cylinder 1 further comprises a ring 26 which can slide axially in the cylinder 2 against the return force of an elastic member 27, such as a helical spring, interposed between the ring 26 and the wall of end of the cylinder 2 opposite the piston 3 so as to allow fluid communication between the chamber C3 and the chamber C2 as will be seen later. The ring 26 is held in abutment, by the elastic member 27, on a corresponding face of an annular wall 28 of the cylinder 2 transverse to the longitudinal axis of the latter. The axial bore 26a of the ring 26 and the circular orifice 28a of the annular wall 28 are coaxial and allow the passage of liquid under pressure to thereby form the chamber C3 on either side of the ring 26. The movable ring 26 carries an annular seal 29 with two lips 30 and 31 contacting the internal surface of the side wall of the cylinder 2 forming the chamber C3. FIG. 1 shows that the two lower lip parts 30, 31 are located on either side of a radial channel 32 produced in the side wall of the cylinder 2 and which can open into the chamber C3 downstream of the wall 28. This radial channel 32 is extended by an axial channel 33 also produced in the side wall of the cylinder 2 parallel to its longitudinal axis and opening at its opposite end into the chamber C2 by a radial orifice 34. The seal 29 constitutes a valve member

  as will emerge from the description relating to

operation of the device.

  The second piston 16 comprises a cylindrical end piece 16a which can come into contact with the ring 26 through the circular orifice 28a of the wall 28 to move the ring 26 against the restoring force of the member elastic 27. The ring 26 also includes one or more radial holes 26b opening into the axial bore 26a and allowing the passage of

  liquid when the nozzle 16a is in contact with the ring 26.

  The piston 16 further comprises a flange 16b which can come to bear on the face of the wall 28 opposite to that serving as a support for the ring 26 so as to define the maximum stroke of the two pistons 3, 16 in the cylinder 2. The piston 3 has a diameter greater than that of piston 16. An annular seal 35 with a lip 36 is fixed in the end wall of the cylinder 2 opposite the ring 26 so that the lip 36 contacts the piston rod 4 to ensure the sealing of the chamber C2 relative to the outside. The operation of the device described above will

now be detailed.

  In the rest position of Figure 1, the piston 3 is supported on the corresponding end wall of the cylinder 2 of the cylinder 1 due to a tensile force

  exerted by the clutch pedal connected to the rod-

  push-button 5. Because the three chambers C1-C3 communicate with each other through the channels 20-22 and the passage 25, the liquid which fills these three chambers is at atmospheric pressure. The ring 26 for guiding the seal 29 is held in abutment on the annular abutment wall 28 by the elastic member 27 so that the radial channel

32 is closed by the seal 29.

  As soon as the piston 3 is moved during an action exerted on the clutch pedal, the lip 24 of the seal 23 of the piston 16 moves downstream of the passage 25 so as to interrupt any communication between the two chambers C1 and C3 as shown in FIG. 2. At the same time, the chamber C2 fills with liquid via the channel 20. The working sections of the seals 23, 18 and 35 are defined in such a way that the volume of liquid displaced in the chamber C3 is equal to the volume of liquid drawn into chamber C2: there is therefore a transfer of liquid from chamber Cl to chamber C2. Thus, chambers C1 and C2 are always at atmospheric pressure while the pressure of the liquid in chamber C3 rises

  in order to actuate the receiving cylinder 8.

  From a given stroke of the two pistons 3 and 16, the seal 18 of the piston 3 passes beyond the radial orifice 21, that is to say downstream of the latter as shown in FIG. 3. Under these conditions, the chambers C1 and C2 no longer communicate via the channel 20. The displacement of the piston 3 puts under pressure the chamber C2 which fills with liquid thanks to the one-way valve effect of the seal 18 with lip 19 which authorizes the liquid transfer only from chamber C1 to the

  chamber C2 to balance the pressures.

  Then, as shown in Figure 4, the end piece 16a of the piston 16 comes into contact with the guide ring 26 of the seal 29 and the liquid flows through the radial orifices 26b, the pistons 16 and 3 and the ring 26 moving simultaneously, so as to continue to actuate the jack

receiver 8.

  Figure 5 shows that from a stroke fixed by construction of the emitting cylinder 1, called Cf, the cylindrical endpiece 16a of the piston 16 has displaced the movable ring 26 to a position such that the annular seal 29 releases the radial bore 32 which thus opens into chamber C3. In this way, the two chambers C2 and C3 communicate with each other through the axial channel 33 and the liquid in these two chambers is at the same pressure. The chamber C2 remains sealed thanks to the annular seals 18 and 35 and the chamber C1 is always at atmospheric pressure. As the two pistons 3 and 16 move, the volume of liquid in the chamber C3 is transferred into the chamber C2 by the channel 33, which has the effect of keeping the chamber C3 at constant pressure and prevent any displacement of the piston 10 of the receiving cylinder 8 until the collar forming the stop 16b of the piston 16 comes into contact with the annular wall 28. When the collar 16b is in contact with the annular wall 28, the total stroke of the pistons 16 and 3 of the emitting cylinder 1 is called Ct as shown in

figure 1.

  When the action on the clutch pedal is released, the ring 26 and the annular seal 29 follow the movement of the piston 16 in the opposite direction to that indicated previously by the action of the restoring force.

  exerted by the elastic member 27 on the ring 26.

  When the seal 29 again closes the radial channel 32, the pressure of the liquid in the chamber C2 rises but the seal 29 immediately acts as a one-way valve thus allowing the liquid in the chamber C2 to be

  transferred to chamber C3 (Figure 4).

  The movable ring 26 will move until it abuts on the annular wall 28 (FIG. 3). When the seal 18 passes beyond the radial orifice 21, the chambers C1 and C2 communicate again through the channel 20 and the liquid in these two chambers is again at atmospheric pressure (FIG. 2). The seal 29 of the ring 26 no longer plays the role of a valve since the liquid pressure in the chamber C3 is greater than that of the liquid in the chamber C2. The liquid is

  driven back from chamber C2 to chamber C1.

  When the piston 3 is in abutment on the end wall of the cylinder 2 opposite to the ring 26, the passage 25 is open to allow the balance of the pressures of the liquid between the chambers C1-C3 so

  that the device is then reset.

  The sending hydraulic cylinder 1 with controlled stroke of the pistons 3, 16 makes it possible to perfectly control the stroke of the piston 10 of the receiving hydraulic cylinder 8 which it controls, from the moment when the movement of the

  pistons 3, 16 of the emitting cylinder is at least equal to Cf.

  Thus, the stroke tolerance interval Ct-Cf of the pistons 3, 16 of the sending cylinder 1 has no consequence on the stroke of the piston 10 of the receiving jack 8. In addition, if the stroke of the pistons 3, 16 of the sending jack 1 is always equal to Ct, the emitter cylinder with controlled stroke makes it possible to produce an additional clearance equal to Ct-Cf between a given position of the pistons 3, 16 of the cylinder 1 and

their final extreme position.

  In the context of the application of the device of the invention to friction clutches of motor vehicles, with the controlled stroke of the pistons of the emitting cylinder, there is no fatigue of the clutch and therefore premature wear of the latter. this is avoided by removing the overtravel of the pistons of the

transmitter cylinder.

Claims (12)

  1. Device making it possible to exert a thrust at a distance by displacement of liquid under pressure from a transmitting hydraulic cylinder (1) to a receiving hydraulic cylinder (8) whose inlet for pressurized liquid is connected to the outlet for liquid under pressure of the hydraulic transmitter cylinder (1) via a pipe (9), the hydraulic transmitter cylinder (1) comprising at least one piston (3) delimiting in the cylinder (2) of the cylinder (1) at least two chambers (C1, C2 ) at atmospheric pressure in the piston rest position (3) and allowing the exit of pressurized liquid from the emitting cylinder (1) to the receiving hydraulic cylinder (8) when the piston (3) moves over a determined distance (Cf) for moving the piston (10) of the receiving cylinder (8), characterized in that it comprises a second piston (16) coaxially separated from the first piston (3) by being integral with the latter by a common piston rod (17) so as to delimit in the cylinder (2) the hydraulic transmitter cylinder (1) a third chamber (C3) also at atmospheric pressure in the rest position of the two pistons (3, 16) and a valve member (29) housed in the cylinder (2) of the hydraulic transmitter cylinder (1 ) opposite the rod (4) of the first piston (3) and actuated by the second piston (16) when the two pistons (3, 16) have been moved over the determined distance so as to put the two in communication extreme chambers (Cl, C3) of the hydraulic transmitter cylinder (1) and to maintain a constant hydraulic pressure at the output of the hydraulic transmitter cylinder (1) for any movement of the two pistons (3, 16) beyond the determined distance (Cf )   to a position of extreme displacement of these.   2. Device according to claim 1, characterized in that the aforementioned valve member comprises an annular seal (29) mounted on the ring (26) so as to close the communication passage (33) between the two chambers extremes (C2, C3) of the emitter cylinder (1) during the movement of the two pistons (3, 16) of this cylinder (1) up to the determined distance (Cf) at which the movable ring (26) is moved at a position o the annular seal (29) of the ring (26) opens the passage (33) to connect the two chambers (C2, C3) through the axial bore (26a) of the movable ring (26) which is held resiliently supported on one face of an annular wall (28) transversely integral with the cylinder (2) of the emitting cylinder (1) and whose axial bore (26a) allows the flow of   pressurized liquid at the outlet of this jack (1).   3. Device according to claim 2, characterized in that the second piston (16) comprises a cylindrical end piece (16a) which can come to bear, through the annular wall (28) for supporting the movable ring ( 26), to move the latter axially to the open position, by the annular seal (29), of the communication passage (33) between the two chambers extremes (C2, C3).   4. Device according to claim 2 or 3, characterized in that the second piston (16) further comprises a flange (16b) which can come to bear on the other face of the annular wall (28) to delimit the distance of movement extreme or maximum stroke of the two pistons (3, 16) in the cylinder (2) of the cylinder transmitter (1).   5. Device according to one of claims 2 to 4,   characterized in that the communication passage (33) between the two end chambers (C2, C3) comprises, made in the cylinder (2) of the emitting cylinder (1), an axial channel (33) parallel to the longitudinal axis of the cylinder (2) opening through a radial orifice (34) in the end chamber (C2) opposite the third chamber (C3) and an opposite radial channel (32) opening downstream of the annular wall (28) for supporting the movable ring (26) at the annular seal (29) so that this seal closes or clears the radial channel (32)   according to its relative axial position.   6. Device according to claim 5, characterized in that the annular seal (29) has two lips (30, 31) located on either side of the radial channel (32) of the rest position of the two pistons (3, 16) of the jack (1) to their position corresponding to the distance of movement determined above (Cf).   7. Device according to one of claims 3 to 6,   characterized in that the movable ring (26) comprises at least one radial orifice (26b) opening into its axial bore (26a) and allowing the flow of liquid under pressure when the end piece (16a) of the second piston (16) is resting on the movable ring (26) so that the liquid can circulate from the third chamber (C3) to the opposite extreme chamber (C2) through the corresponding passage (33) when the two pistons (3, 16) of the jack (1)   are moved beyond the determined distance (Cf).   8. Device according to one of claims   above, characterized in that the intermediate chamber (C1) of the emitting cylinder (1) is permanently connected to a tank of liquid at atmospheric pressure by means of a connection tube (6) and can communicate with the extreme chamber (C2) opposite the third chamber (C3) by a channel (20) produced in the cylinder (2) parallel to its longitudinal axis and opening into the cylinder through two axially opposite radial orifices (21, 22) and in that the two pistons (3, 16) each carry an annular seal (18, 23) with lip (19, 24) so that in the rest position of the two pistons (3, 16), the intermediate chamber (C1) and the chamber end (C2) communicate with each other through the axial channel (20) and the radial orifices (21, 22) and the intermediate chamber (C1) and the third chamber (C3) communicate with each other by a passage (25) of the cylinder (2 ) closed by the annular seal (23) with lip (24) of the second piston (16) as soon as q ue it moved to pressurize the liquid in the third chamber (C3) while the other two chambers (C1, C2) remain at atmospheric pressure. 9. Device according to claim 8, characterized in that the annular seal (18) with lip (19) of the first piston (3) is downstream of the radial orifice (21) of the axial channel (20) shortly before the second piston (16) comes into contact through its end cap (16a) with the movable ring (26) so as to interrupt the communication between the intermediate chamber (C1) and the extreme chamber (C2) via the axial channel (20 ) to create a depression in the extreme chamber (C2) which fills with liquid by the unidirectional valve effect of the lip (19) of the annular seal (18) of the first piston (3) thus authorizing the transfer of liquid from the intermediate chamber (C1) to the extreme chamber (C2).   10. Device according to one of claims   previous, characterized in that it comprises an annular seal (35) with lip (36) integral with the cylinder (2) of the emitting cylinder (1) and ensuring the tightness of the rod   (4) of the first piston (3) of this cylinder.   11. Device according to one of claims   above, characterized in that the diameter of the first piston (3) is greater than the diameter of the second piston (16).   12. Device according to one of claims   previous, characterized in that the rod (4) of the first   piston (3) of the emitting cylinder (1) is connected to a rod-   external pusher (5) actuated by a clutch pedal of a friction clutch of a motor vehicle and the rod (14) of the piston (10) of the receiving cylinder (8) is connected to a clutch fork (12) of the friction clutch.