FR2516179A1 - Fluid pressure servomotor for clutch operation - has pressure reducer in piston to control piston thrust on lever - Google Patents

Abstract

The fluid pressure servomotor is for assisted control of a moving rotating part, such as a clutch lever. In the assisting cylinder is a piston placed under fluid pressure from a self regulated pressure reducer in the piston. The connection between the actuating device (2) and the piston is a rod (6) inside the piston (18) and it acts as the thrust part of the pressure reducer. The rod contacts a stop (43) on a surface (46) of the piston when the reducer valve (33) is fully open. The piston then presses on a clutch lever (8) to turn it.

Description

PRESSURE FLUID SERVOMOTOR
The present invention applies to a pressurized fluid booster which can be used in particular for actuating the declutching lever of a motor vehicle in direct control from the vehicle's clutch pedal.

 The clutches of motor vehicles are still, for the vast majority of road vehicles, controlled by the driver of the vehicle who brings them, by pressing a clutch pedal, in the disengaged position during the change from one gear to the other and before starting the vehicle. This last operation requires a progressive and well-damped re-engagement to avoid starting shock or stalling the vehicle engine. The important work that the driver's foot and leg must accomplish to perform a declutching operation is due to the relatively large stroke of the clutch bearing against the full reaction force of the (case of the diaphragm spring) or clutch plate clamping springs. For heavy road vehicles, the clutch release force is generally reduced with an oil-pneumatic assistance device which ensures rapid disengagement respectively by the action of a pneumatic pressure controlled by a pressure hydraulic follower emitted from a hydraulic master cylinder and its progressive re-engagement and well damped by expansion of the pneumatic assistance pressure and discharge of the column of the hydraulic follower fluid.

 The hydropneumatic clutch control systems used on heavy road vehicles give satisfaction to users but have a relatively high cost of establishment and maintenance because they require the installation of a relatively large hydraulic transmitter and receiver. race and subjects leaking after prolonged use. To remedy these cost and usage shortcomings, it has already been proposed for medium-tonnage industrial road vehicles, to provide assistance for the clutch control by only pneumatic means with a mechanical control by cable from the pedal. One of the embodiments of these mechanical-pneumatic assistance systems comprises an assistance cylinder articulated to the clutch housing and the movable assistance piston of which is connected to a source of compressed air and comprises a compressed air regulator self-regulated by a reaction piston and connected, through the piston, to the cylinder chamber delimited by the piston. The self-regulating regulator is actuated by a pusher, the central rod of which passes through the exhaust of the regulator and is connected to the clutch control cable. Such an assistance cylinder provides good control sensitivity to the driver of the vehicle because the regulator rod follows the stroke of the piston and of the control cable while being subjected to the reaction force exerted by the assistance pressure on the reaction piston and directly proportional to the force of friction assistance near the seals of the assistance and reaction pistons.

 Experimentation with assistance cylinders with purely pneumatic actuation and of the type which has just been described has highlighted certain difficulties of installation for guiding the oscillating movement of the cylinder and problems of reliability since the clutch housing is the seat of intense vibrations which tend to degrade the piston guide seats, which did not happen with the hydraulic actuating rods immersed in the control oil. In addition, the effort of rapid declutching and progressive and damped re-clutching which was easily obtained with the oil-pneumatic control, often seems to be reversed, in particular with modern clutches with diaphragm spring and ball thrust.

 The present invention specifically aims to overcome these difficulties of insertion, reliability and damping of compressed air or low pressure oil assistance cylinders for controlling the clutches of road vehicles, in particular industrial vehicles of range average.

 To this end, the pressurized fluid servomotor, usable for the assisted control of a movable rotary member such as a clutch lever, of the type comprising in an assistance cylinder body: an assistance piston acting on said member and capable of being subjected to the pressure of the pressurized fluid delivered by a self-regulating assistance regulator included in the assistance piston, the connection between a pedal or a manual actuation lever of the booster and the piston assistance consisting of an assistance rod mounted inside the assistance piston and constituting the actuator for actuating the assistance regulator, is characterized in that the assistance rod, movable inside the piston assistance under the action of the pedal is likely to come to bear unilaterally by a stop collar on a corresponding bearing surface formed in the assistance piston, when the valve of the assistance regulator is in the position of pl eine opening, to follow in its race the assistance piston which comes to bear by an external bearing surface on the abutment surface of the clutch lever and is liable during the rotation of this lever to struggle with a large angle inside the cylinder while being protected from external pollution by connecting means such as a sealed elastic bellows interposed between the piston rod and the cylinder body secured to the clutch housing.

 According to a common embodiment of the invention, the assistance regulator is supplied with pressurized fluid via a flexible supply duct which is connected to one face of the piston and which is able to follow all the displacements of the piston and the exhaust of the expansion valve takes place inside the breathing chamber of the assistance cylinder delimited by the sealed connection means constituted by the elastic bellows and connected to the exhaust or to the discharge so to better protect the breathing chamber from external pollution. In a manner known per se, the exhaust bellows can carry and / or be traversed by the exhaust pipe and / or the supply pipe of the pressure reducer.

According to another embodiment, the supply passage which connects the regulator to the pressure chamber of the cylinder delimited by the assistance piston has less pressure drops than the exhaust passage which connects the regulator to the chamber breathing the cylinder so as to allow a quick disengagement and a slower and well damped re-engagement
For clutches with a ball or roller release bearing, the release lever can advantageously remain in contact with this stop to better absorb the vibrations of the balls or rollers during normal vehicle operation and for this, the piston assistance is constantly pushed back in contact with the clutch lever stopper by a spring interposed between it and the bottom of the cylinder and whose reaction force is less than that caused on the lever by the return spring of this lever and / or by the clutch spring.

 Other objects, advantages and characteristics of the invention will appear on reading the description of an embodiment of the invention made with reference to the attached drawing in which the single figure represents in schematic section the clutch control system. provided with a declutching assistance servomotor according to the invention.

 The clutch control system shown in the figure is interposed between a clutch housing 1, fixed to the engine of a vehicle, and a clutch pedal 2, articulated on an axis 3 inside the driver's cabin of the vehicle. The pedal 2 has a mushroom or plate-shaped head on which the driver presses with the foot to cause a pressure force P which makes the pedal 2 pivot around its axis 3 by pulling in traction a cable 4 which is housed in a flexible sheath 5 blocked at its two ends and which is connected to an actuation and assistance rod 6 which can come to apply an actuation range 7 on a disengaging lever 8 articulated at 9 on the clutch housing to come to bear on a clutch release bearing 10, shown in dotted lines in the figure and which is capable of pushing the main spring of the clutch into the disengaged position for which the friction plates, not shown, of the clutch are no longer subjected to elastic pressure capable of generating significant clutch torque.

 According to the invention, an assistance cylinder 11 is fixed to the clutch housing 1 by a one-piece body 12 and by any means such as a fixing lug 13 bolted respectively to the outlet flange 14 of the cylinder body 12 produced. for example in stamped thin sheet metal and on the casing of the gearbox 15 adjacent to the clutch body 1.

 The lever 8 has a lower part 16 in the form of a fork overlapping the rod 6 in contact with the stop 7 - and is returned to the disengaged position by a spiral spring 17 wound around the axis 9.

 An assistance piston 18 which carries the rod 6 is mounted in the cylinder body 12 and is connected by an inlet nozzle 19 and a flexible conduit 20 to a reservoir of pressurized fluid 21 generally constituted by an air reservoir compressed air powered by an air compressor not shown.

 The actuator assembly constituted by the assistance piston 18 is slidably mounted in the bore 22 of the cylinder body 12, in contact with which its sealing is ensured by an annular seal 23 cooperating with a friction ring 24. The rod 25 of piston 18 is not guided at the left end of cylinder 12 and can therefore sway or struggle at a large angle inside the cylinder. The rod 25 is elastically connected to the collar 14 by an elastomer bellows 26 which, with the annular buffer space between the external surface of the rod 25 and the bore 22, a breathing chamber 27 connected to the external atmosphere by any means such as an open tube 27a which is integral with the sheath 26 or attached and oriented downward to limit the accidental entry of dust or polluting drops into the chamber 27.

 The breathing chamber 27 is connected to the exhaust chamber 28 of the valve of the booster by a pipe 29 throttled at 30.

 The assistance piston 18 preferably made of a block of light metal, comprises, to produce the valve of the booster, various cavities closed by plugs. A cavity traversed by the rod 6 forms with a plug 32 and a double valve 33 a supply chamber 34 connected by a conduit 35 to the supply hose 20. Another cavity delimited by a reaction piston 37 movable in a bore 38 forms a regulator chamber 36 connected by a conduit 31 which passes through the assistance piston 18, to an assistance chamber 39 formed between the bottom of the bore 22 of the cylinder 11 and the top of the assistance piston 18 sealed by the lining 23.An annular wall 40 separates the supply chambers 34 and regulator 36 and carries the inlet sealing seat on which the elastomeric lining of the double movable valve 33 is applied which is pushed back into contact with this seat by a spring and can slide inside the inlet chamber 34 guided by a sealed bearing provided on the plug 32. The rod 6 is rigidly connected by a stop collar and a nut 41 to the reaction piston 37 which carries a ring plunger 42 capable of coming to bear on the elastomeric lining of the valve 33 to close the communication of the regulator chamber 36 with the chamber 28 connected to the exhaust. The body of the double valve 33 is hollow and crossed by the rod 6 which has at its part opposite the nut 41 a collar 43 capable of coming to bear on a closing washer 44 made tightly integral with the rod 25 of the piston 18 and which comprises sealing and guiding means 45 of this rod 6 The washer 44 has an inner bearing surface 46 for the flange 43 and an outer bearing surface constituted by the outer bearing 7 for the fork 16 of the clutch lever 8.

 In the rest position, the reaction piston 37 is pushed back by a return spring disposed between the bottom of the reaction piston 37 and the annular wall 40, bearing on a tight plug 48 for closing the space surrounding the nut 41 This space is connected to the atmosphere by a balancing passage 50 passing through the reaction piston 37. A return spring 49 is interposed between the plug 48 and the bottom of the cylinder body 12 to push the assistance piston 18 to the left of the figure so as to constantly maintain the seat 7 in contact with the fork 16.

 The operation of the embodiment of the invention which has just been described will now be explained with reference to the figure. In the rest position, of the booster as shown in the figure, the vehicle engine is engaged on the transmission and the powerful clutch tightening spring pushes, by the stop 10, the fork 16 to the right of the figure in contact with the bearing surface 7 and against the return spring 49 of the assistance piston 18. The return spring of the pedal 2, not shown, releases the cable 4 in the position of the figure and releases the rod 6 which is recalled to the right of the figure by the return spring of the reaction piston 37. The assistance chamber 39 is thus connected to the atmosphere via the conduit 31, the regulator chamber 36, the conduit 29, the chamber 27 and the tube 27a open downwards.

 When the driver of the vehicle wishes to disengage, he presses on the pedal 2 according to the arrow P and thus pulls the cable 4 and the rod 6 to the left of the figure. The reaction piston 37 also moves to the left because the seat 7 is in relatively rigid abutment on the fork 16 of the lever 8.

By moving to the left, the annular plunger 42 of the piston 37 comes to bear on the elastomer lining of the double valve 33 and isolates the regulator 36 and assistance 39 chambers from the atmosphere. The displacement of the piston 37 continuing to the left, the pressure of the plunger 42 takes off the elastomeric lining of the double valve 33 of the intake seat formed on the wall 40 and the compressed air from the reservoir 21 flows via the flexible 20 , the conduit 35, the intake chamber 34, the annular passage between the valve 33 open and the seat of the wall 40, the regulator chamber 36, the conduit 31, as far as in the assistance chamber 39 to push back the piston assistance 18 to the left in contact with the fork 16 to rotate the clutch release lever 8 about its axis 9 and push the clutch release bearing 10 to its end position. During the entire stroke of the piston 18 to the left, the driver receives information on the assistance pressure p & the reaction force exerted by the assistance pressure on the reaction piston 37.

 If the driver partially releases his force P on the pedal 2, the traction exerted to the left on the rod 6 decreases and is no longer able to balance the reaction force exerted by the assistance pressure on the piston of reaction 37 which then moves slightly to the right until allowing the double valve 33 to again close the open annular passage between its elastonwre packing and the intake seat of the wall 40. The rise in pneumatic pressure in the assistance chamber 39 then stops and if the driver releases even more of his force P on the pedal 2, for example to control a progressive re-engagement operation, the piston 37 moves even more to the right and the annular seat of escapement 42 is detached from the elastomeric lining of the double valve 33. The chamber 39 is then connected to the exhaust as described previously and represented in the figure. The exhaust of the compressed air contained in the assistance chamber 39 occurs gradually because the constriction 30 interposed on the pipe 29 limits the air flow to the atmosphere and prevents the breathing pressure prevailing in the chamber 27 does not reach significant values which would risk loosening the sheath 26 whose resistance to pressure is limited.

 The rod 25 has in any case a significantly smaller section than the assistance piston 18 and as soon as the pressure prevailing in the assistance chamber 39 has dropped to a low value, the piston 18 moves to the right of the figure . It should be noted that the tube 27a has a significantly larger passage section than the constriction 30 which is however capable of refueling the breathing chamber 27 at a sufficiently rapid speed to prevent that during the displacement of the piston 18 to the right According to the most common applications of the booster according to the invention, in clutch servo systems, the mechanical force exerted by the 'cable 4 on the rod 6 represents a non-negligible part of the lever actuation force 8, generally between 1/4 and 1/7 of the total force, this part being determined by the ratio between the sections of the reaction piston 37 and the assistance piston 18. The total relaxation of the force P of the driver on the pedal 2, in the case of a sudden re-engagement after the passage of a gear for example, produces a rapid reduction of a significant part of the disengagement effort exerted on the lever 8 followed of a rise in p recession of the breathing chamber 27, which allows a relatively quick re-engagement.

 When the driver wishes to proceed with a progressive re-engagement of the vehicle, for example when starting it, in particular on a hill, he gradually releases not the force P which is difficult to dose but the stroke of the pedal 2. It s then a series of exhaust vents from the regulator chamber 36 followed each time by a relative rise in pressure of the breathing chamber 27 and a relaxation of this pressure by the tube 27a.

Each time the pressure in the assistance chamber 39 is relieved, the assistance piston 18 is pushed back by the lever 8 a little more to the right of the figure and the pressure of the main clutch spring on the clutch plates increases which makes it possible to obtain a gradual increase in the torque exerted by the wheels of the vehicle when it starts up.

 In the event that vibrations, particularly of relaxation, appear in the clutch - for example as a result of the clutch linings grazing on their friction surfaces, these vibrations are difficult to transmit to the actuator due to the various existing friction reactions on the reaction and assistance pistons and on the pneumatic damping caused by the pressure losses of the connection circuits between the various pneumatic chambers of the booster.

 In the case where there is a relatively resistant sheath 26, the constriction 30 can no longer be placed on the pipe 29 but on the tube 27a or more simply it can be provided that the tube 27a produces a more pressure drop important that the circuit connecting the breathing chamber 27 to the assistance chamber 39 when the regulator is in the exhaust. In such an arrangement, the breathing chamber rises to relatively greater pressures during the escape from the chamber 39 but the return of the assistance piston 18 in the engaged position is only slightly delayed because the equalization of the pressure between breathing chambers 27 and assist chambers 39 occurs quickly.

 Of course, the present invention is not limited to the embodiments described and shown and it is capable of numerous variants accessible to those skilled in the art, without departing from the spirit of the invention. 'invention.

 Thus, it should be understood that on vehicles where there is no source of compressed air but only a source of low pressure oil such as that provided by the steering assistance pump, it is possible to connect the hose 20 to this source of pressurized oil and the tube 27a on the return to the tarpaulin or the oil tank. In the arrangement according to the figure, the servomotor is fixed on the side of the gearbox 15 and a leakage of assistance oil would not risk producing harmful effects on the clutch because this leakage would flow directly onto the vehicle raceway without entering the clutch.

 In another order of idea, the assistance rod 6 is shown in the figure arranged concentrically with the piston 18 but it can be envisaged for various constructive reasons to place the rod 6 and the regulator offset relative to the assistance piston 18 which it would act in a manner substantially centered on the lever 8 which moves in rotation around the axis 9.

Claims (7)

 1. Pressurized fluid booster, usable in particular for assisted control of a movable rotary member such as a clutch lever, of the type comprising in an assistance cylinder body an assistance piston acting on said member and capable of being subjected to the pressure of the pressurized fluid supplied by a self-regulating assistance regulator included in the assistance piston, the connection between a pedal or a manual actuation lever of the servomotor and the assistance piston being constituted by an assistance rod mounted inside the assistance piston and constituting the actuator for actuating the assistance regulator, characterized in that the assistance rod (6), movable inside the piston d assistance (18) under the action of the pedal (2) is capable of coming to bear unilateral by a stop collar (43) on a corresponding bearing surface (46) formed in the assistance piston (18) when the valve (33) of the assist regulator it is in the fully open position, in order to follow in its race the assistance piston (18) which comes to bear on a clutch lever (8) and is liable during the rotation of this lever (8) to debate at a large angle inside the cylinder (11) while being protected from external pollution by sealed connection means (26) interposed between the rod (25) of the piston (18) and the body (12) of the cylinder secured to the clutch housing (1).  2. Booster according to claim 1, characterized in that the assistance piston (18) bears unilaterally on the abutment surface (16) of the clutch lever (8) via a abutment surface exterior (7)  3. Booster according to one of claims 1 or 2, characterized in that the sealed connection means between the rod (25) of the piston (18) and the body (12) of the cylinder (11) are constituted by an elastic bellows (26).  4. Booster according to one of claims 1 to 3, characterized in that the assistance regulator is supplied with pressurized fluid via a flexible supply duct (20) which is connected to one face of the piston (18) and which is able to follow all the movements of this piston (18) and in that the exhaust of the regulator takes place inside the breathing chamber (27) of the assistance cylinder delimited by the sealed connection means constituted by the elastic bellows (26) and connected to the exhaust (27a) or to the discharge so as to better protect the breathing chamber (27) from external pollution.  5. Booster according to claim 4, characterized in that, in a manner known per se, the exhaust bellows (26) carries and / or is traversed by the exhaust pipe (27a) and / or the supply pipe (20) of the pressure regulator.  6. Booster according to claim 4 or 5, characterized in that the supply passage (31) which connects the pressure reducer to the pressure chamber (39) of the cylinder (11) delimited by the assistance piston (18) present less pressure drop than the exhaust passage (29) which connects the regulator to the breathing chamber (27) of the cylinder (11) so as to allow a quick disengagement and a slower and well-damped re-engagement.  7. Booster according to any one of claims 1 to 6, characterized in that the assistance piston (18) is constantly pushed back in contact with the stop (16) of the clutch lever (8) by a spring (49 ) interposed between this piston (18) and the bottom of the cylinder (11) and whose reaction force is less than that caused on the lever (8) by the return spring (17) of this lever and / or by the clutch spring.