FR2864504A1 - Pneumatic assistance servomotor for motor vehicle`s braking system, has thrust device with support part having plane support surface to be in support against front surface of reaction disk - Google Patents

Abstract

The servomotor has a thrust device to transmit forces between a reaction disk (11) and master cylinder of brakes. The device has a support part (20) with plane support surface to be in support against a front surface (S11a) of the disk and a central opening (23) in which a plunger (10) slides. A push rod (22) traverses the opening such that the rod is supported by its convex shaped rear end surface on the front surface. An independent claim is also included for a method of adjusting kick-off of an assistance servomotor.

Description

The invention relates to a servomotor for braking assistance and its

  adjustment process. It finds application particularly in braking systems of motor vehicles equipped with brakes

assisted.

  A braking assistance booster essentially comprises an enclosure comprising two chambers (the front chamber and the rear chamber) separated by a movable membrane or piston. A control rod can move toward the front of the vehicle when the driver of the vehicle actuates the brake pedal. This displacement of the control rod is transmitted to a plunger which actuates assistance means and the piston. Generally, these assistance means comprise a three-way valve whose actuation makes it possible to interrupt the communication between the front chamber and the rear chamber of the servomotor and to put the latter chamber in the ambient atmosphere. Since the front chamber is normally under vacuum, and because of the pressure difference between the two chambers, an assisting force is exerted on the piston which separates the two chambers. The piston then moves forwards by acting on a push rod serving to actuate the master cylinder of the braking circuit.

  Usually, the piston for transmitting the assistance force to the push rod acts on the latter through a reaction disc made of a deformable material such as an elastomer.

  At rest, there is little clearance between the front end of the plunger and the reaction disc. When the driver of the vehicle begins to operate the brake pedal, this low clearance allows the diver to immediately move forward to control the means of assistance and ensure immediate response of the brakes.

  When the assistance force exceeds a certain threshold, the game initially existing at rest between the reaction disc and the front face of the plunger is caught, so that the plunger is in contact with the reaction disc and the latter returns to the brake pedal a reaction force representative of the braking force applied to the brakes of the vehicle. This well known arrangement allows the driver to dose the braking force it exerts on the pedal according to the resistance it encounters, which increases with this effort. It follows from the foregoing explanation that the reaction to the pedal begins to appear only when the assisting force generated by the actuation of the brake pedal exceeds a certain threshold. This threshold is called the "jump" of the servomotor. It is an important feature of the servomotor. Indeed, if the existence of the jump is imposed for an immediate response of the brakes when the pedal is actuated, the motor vehicle manufacturers generally wish that the value of this jump remains within certain limits so that the assistance does not occur. does not reach too high a value without increasing the reaction to the pedal.

  However, especially in view of manufacturing tolerances of the various parts constituting the servomotor, there may be significant differences in the value of the jump, from one servomotor to another. In addition, there is currently no way to control or adjust the value of this jump, so the previously mentioned requirements are not always met.

  The subject of the invention is a braking assistance servomotor, in which the value of the jump can be easily adjusted in a simple and economical manner.

  The invention therefore relates to a brake booster comprising: E A control rod for controlling a three-way valve, E A plunger movable axially under the control of the control rod and having an end bearing face A pneumatic piston movable also axially under the effect of a pressure difference induced by the three-way valve, having a hole surrounded by an annular bearing face and in which said plunger slides, É A reaction disc in elastically deformable material having a rear face applied to the annular support surface of the pneumatic piston and intended to receive the forces applied by this annular face and the end support face of the plunger, É A thrust device of which a first end is supported against a front face of the reaction disc opposite the rear face and a second end is supported against a body ommander, so as to transmit a force of the reaction disc to the organ to be controlled.

  According to the invention, the thrust device comprises a bearing piece having a flat bearing surface intended to bear against the front face of the reaction disk and having a central opening located in a zone corresponding substantially to said piston hole. , and a thrust rod passing through the opening of the support piece so as to press a rear end face on the front face of the reaction disc, this rod being secured to the support piece.

  According to one embodiment of the invention, the thrust device comprises a hollow part integral with said support piece whose hollow portion corresponds to the opening of the support piece and whose axis is substantially perpendicular to the front face of the reaction disk, the push rod being placed this hollow portion and passing through the opening of the support piece.

  It can be advantageously provided that the rear end face of the push rod is of convex shape to prevent it does not deteriorate the reaction disc.

  According to one embodiment it is provided that the hollow part is crimped or is welded to the push rod.

  The hollow part and the push rod may preferably be cylindrical. The support piece comprises a flat piece having said bearing surface and provided with lateral flanks for gripping the reaction disk.

  According to the invention, the position of the support rod in the hollow part and in the opening of the support piece is adjusted so that it presses and possibly deforms the reaction disk.

  The invention also relates to a method for adjusting the jump of a braking assistance servomotor. This actuator comprises, as indicated above, a force transmission system comprising: E a control rod for controlling a three-way valve, E a plunger movable axially under the control of the control rod and having a bearing face end, É a pneumatic piston axially movable under the effect of a pressure difference induced by the three-way valve, having an axial hole surrounded on the front face of an annular support face and in which said plunger slides, A reaction disk of elastically deformable material having a rear face applied to the annular support surface of the pneumatic piston and intended to receive the forces applied by this annular face and by the end support face of the plunger, bearing piece having a flat abutment surface intended to bear against the front face of the reaction disk and a thrust rod axially controlled by the a support piece so as to transmit a force of the reaction disk to a body to be controlled.

  The method according to the invention comprises the following steps: E establishment of the push rod in a hole axially through the support piece so that the push rod is supported by a rear end face on the front face of the reaction disc, E adjustment of the distance between the rear face of the reaction disc and the front face of the plunger by axial displacement of the push rod relative to the front face of the reaction disc, E fixing of the push rod to the support piece.

  The various aspects and characteristics of the invention will appear more clearly in the description which follows and in the appended figures which represent: FIG. 1, a general view of an exemplary embodiment of the system of the invention; FIGS. 2a and 2b, detailed views of an exemplary embodiment of the system of the invention, FIG. 3, a curve illustrating the operation of the invention.

  The invention relates to an improvement made to the pneumatic brake booster servomotors of which FIG. 1 illustrates an example according to the invention. However, since the general constitution and operation of the servomotors are well known to those skilled in the art, they will be briefly recalled here only to allow an understanding of the system of the invention. Schematically, a servomotor comprises a rigid casing 1 separated into two chambers 2 and 3, sealingly in operation, by a membrane 4 secured to a movable piston 5 inside the casing.

  the envelope. In the following description we

  will consider that the front of the device is located on the left in the figure and the back of the device is located on the right. Room 3 is the front room and room 2 is the rear room. The front chamber 3 is, in operation, permanently connected to a vacuum source (not shown) through a connection 6.

  The pressure in the rear chamber 2 is controlled by a valve 7 controlled by a control rod 8, which is connected to the brake pedal. When the control rod 8 is in the rest position, in this case pulled to the right, the valve 7 establishes a communication between the two chambers 2 and 3 of the booster. The rear chamber 2 is then subjected to the same depression as the front chamber 3, the piston 5 is pushed to the right, in the rest position, by a spring 9. The actuation of the control rod to the left has the effect in a first step, to move the valve 7 so that it isolates the chambers 2 and 3 from each other and then, in a second step, to move the valve so that it opens the rear chamber 2 at atmospheric pressure. The pressure difference between the two chambers then felt by the membrane 4 exerts on the piston 5 a thrust that tends to move it to the left by compressing the spring 9. The braking force exerted through the intermediary of a plunger 10, the control rod 8 intended for the master cylinder, and the braking assistance force resulting from the thrust of the piston 5, are applied to the rear face (right) of a reaction disc 11 of which the front face (left) retransmits these forces to the push rod 12, which has the function of actuating the master cylinder itself.

  In fact, the assistance force exerted by the piston 5 appears only after a non-zero axial displacement of the control rod 8 and takes, when it appears a minimum non-zero value, called "jump", that the invention proposes to regulate in a simple and effective manner.

  The invention relates to a thrust device, as shown in FIGS. 2a and 2b, which makes it possible to retransmit the forces of the plunger 10 and the piston 5, via the reaction disc 11, to a controlled member, in the occurrence to the master cylinder. The plunger 10 has an axial end face Sla which constitutes a first front support surface, while the piston 5 has an axial annular surface S2a which surrounds the face Sla of the plunger and which constitutes a second bearing surface. before. The reaction disc 11 has a rear face S11b and a front face S11a. The rear face Sllb is intended to receive the forces applied by the first and second bearing surfaces before Sla and S2a.

  Referring to Figure 2a, we will describe an exemplary embodiment of the thrust device according to the invention for retransmitting the forces of the reaction disc 11 to the master cylinder. This thrust device comprises a support piece 20 (or base) intended to be supported by a rear face 20b on the front face Sila of the reaction disk 11. This support piece has an opening 23 located in a substantially corresponding zone. in the center of the axial annular surface S2a. A hollow part 21 (or tube) is fixed to the front face of the support piece 20. The position of this hollow part is such that it has an axis which is substantially aligned with the axis of the plunger 10 and that it is located substantially in the center of the axial annular surface S2a. Note however that the hollow part 21 and the support part 20 can be made in one piece.

  The hollow part 21 contains a push rod 22. This push rod 22 is located along the axis of the hollow part 21. It passes through the opening 23 of the support piece 20 so as to be in contact with the face before the reaction disc in an area substantially in the center of the axial annular surface S2a.

  The hollow part 21 is fixed to the push rod 22 for example by one or more crimps 24. However without departing from the scope of the invention, the fixing of the hollow part on the push rod 22 can be done by any other means such as, for example, by welding.

  The front end 22a of the push rod 22 opposite the end located in the opening 23 comprises a master cylinder control device not shown in the figure. This device can take the form, for example, of a part 30 screwed on the push rod 22 and for retransmitting the forces of the push rod towards the master cylinder. Due to the screwed mounting of the workpiece 30 on the push rod, an axial adjustment of the workpiece 30 can be performed to match the length of the push rod assembly 22 / workpiece 30 to the servomotor / master cylinder distance.

  Preferably the push rod 22 and the hollow part 21 are cylindrical. The inside diameter of the hollow part substantially corresponds to the diameter of the push rod so as to allow the mounting of the thrust piece in the hollow part.

  The opening 23 of the support piece 20 is cylindrical and its diameter allows the passage of the push rod 22.

  As shown in FIG. 2a, the support piece 20 may be in the form of a cup having a rim making it possible to hold the reaction disc, but this is not compulsory, the reaction disc could be attached to the support piece 20 or to the axial annular surface S2a by any other means.

  Preferably, the rear end 22b of the push rod 22 which is in contact with the reaction disc 11 has a convex surface so that it does not damage the surface Slla of the reaction disc. For example, the height of the rounding may be a few tenths of a millimeter.

  According to an alternative embodiment of the invention, the hollow part 21 and the support piece 20 can be made in one piece.

  Referring to Figure 2a, we will now describe the adjustment of the position of the push rod 22 in the hollow part 21 and in particular its position relative to the reaction disk 11. The interest of this push rod fixed in the hollow part 21 supported by means of the support piece 20 will appear in the description of this adjustment process. Indeed, by making the push rod protrude more or less from the front face 20b of the support piece 11, the push rod will press on the reaction disk and force it to deform in the zone located in the center of the axial annular surface S2a and approaching the face Sla of the plunger 10 as amplified in Figure 2b.

  Depending on the importance of the prestress thus exerted on the central part of the reaction disc 11 it is possible to adjust with precision the clearance existing between this front face Sla of the plunger and the reaction disk.

  If a force is applied to the input of the servomotor on the control rod 8, a force is transmitted by the servomotor and is transmitted by the push rod 22 to the output of the servomotor.

  The operation of the servomotor will now be described with reference to the curve of FIG.

  When the servomotor is installed on a vehicle, the front chamber 3 communicates permanently with a source of vacuum. At first, the actuation of the brake pedal by the driver has the effect of making up the original dead stroke initially between the valve 7 and the valve seat formed on the piston 5. The front chambers 3 and rear 2c of the servomotor are then isolated from each other. In this first phase of actuation of the booster, which corresponds to the segment OA in Figure 3, the force exerted on the control rod 8 engenders no force on the push rod 22 at the output of the booster.

  In a second phase of the actuation of the brake corresponding to the segment AB in FIG. 3, the plunger 10 is displaced sufficiently forwards so that the valve 7 is in sealing contact with the seat 50a of the piston and spaced from the seat 18a of the diver. In these conditions. The rear chamber 2 of the servomotor now communicates with the atmosphere. An assistance force is therefore generated, which tends to move the piston 5 forward. This movement is transmitted to the push rod 22 by the reaction disk 11. During this second phase of actuation of the brakes. The assisting force exerted by the piston 5 does not sufficiently deform the reaction disk 11 so that the latter completely fills the space corresponding to the clearance J which initially separates it from the plunger 10. Therefore, the output force FS applied to the the master cylinder by the push rod 8 increases sharply up to the value corresponding to the point B in Figure 3, while the force exerted on the control rod 22 remains unchanged, which characterizes the jump. The point B in FIG. 3 corresponds to the threshold for which the assistance force generated in the servomotor and exerted on the reaction disc 11 by the piston 5 becomes sufficient for the central part of the reaction disk to come into contact with the face. before Sla of the diver 10, that is to say when the game J is caught. In FIG. 3, the length of segment AB corresponds to the jump of the servomotor. According to the invention, it is possible to control and adjust this jump by pressing the reaction disk 11 with the push rod before fixing it inside the hollow part 21 so as to give the game J The desired value.

  In a third phase of the actuation of the brake, which corresponds to the segment BC in FIG. 3, any increase in the force exerted by the driver on the control rod 8 causes an increase in the assistance force exerted on the piston. , which results in an increase in the reaction to the pedal exerted by the disc 11 on the plunger 10, then in contact with one another. Beyond the point C in Figure 3, the pressure in the rear chamber 2 of the booster is equal to the atmospheric pressure and an increase in the boost pressure is no longer possible. The increase in the output force exerted by the push rod 22 on the master cylinder is then substantially equal to the increase in the force exerted by the driver on the brake pedal.

  The value of the jump being capable, in known manner, of being modified by modifying the distance between the face Sla of the plunger and the rear upstream face S11b of the reaction disk 11 under the equilibrium conditions illustrated in FIG. The invention therefore provides by construction to give this distance between the face Sla of the plunger 10 and the face S11b of the reaction disc 11 a value less than that for which the jump takes the desired final value. It suffices then, when mounting the booster, to press with the push rod 22 on the reaction disk 11 and to fix the push rod inside the hollow part when the support piece 20 is pressed against the reaction disk. This operation is done when the jump reaches its desired final value.

Claims (9)

  1. Braking assistance booster comprising: E A control rod for controlling a three-way valve, É A plunger (10) axially movable under the control of the control rod (8) and having a bearing face of end (Sla), é A pneumatic piston (5) also movable axially under the effect of a pressure difference induced by the three-way valve, having a hole surrounded by an annular bearing face (S2a) and in which slides said plunger (10), É A reaction disk (11) of elastically deformable material having a rear face (Sllb) applied to the annular support face (S2a) of the pneumatic piston and intended to receive the forces applied by this face annular and by the end support face (Sla) of the plunger (10), É A thrust device (20, 22), a first end of which bears against a front face (Slla) of the reaction disk (11). ) opposite to the rear face (Sllb) and one of which end is in abutment against a member to be controlled, so as to transmit a force of the reaction disk (11) to the organ to be controlled, characterized in that the thrust device comprises: E a support piece (20) having a planar bearing surface (20b) intended to bear against the front face (S11a) of the reaction disc (11) and having a central opening (23) located in a zone substantially corresponding to said piston hole, push rod (22) passing through the opening of the support piece (20) so as to press by a rear end face on the front face of the reaction disc (11), this rod being secured to the workpiece support (20).   2. Boosting servomotor according to claim 1, characterized in that the thrust device comprises a hollow part (21) integral with said support piece (20) whose hollow portion corresponds to the opening of the workpiece bearing (20) and whose axis is substantially perpendicular to the front face of the reaction disc (11), the push rod (22) being placed in this hollow portion and passing through the opening of the support piece (20).   Braking assistance booster according to Claim 1, characterized in that the rear end face of the push rod (22) is of convex shape.   4. Boosting servomotor according to claim 2 characterized in that the hollow part (21) is crimped on the push rod (22).   5. Boosting servomotor according to claim 2 characterized in that the hollow part (21) is welded to the push rod (22).   6. Boosting servomotor according to claim 5 characterized in that the hollow part (21) and the push rod (22) are cylindrical.   7. Boosting servomotor according to claim 5 characterized in that the bearing piece (20) comprises a flat piece having said bearing surface and provided with lateral flanks for gripping the reaction disc (11).   Braking assistance booster according to Claim 5, characterized in that the position of the support rod in the hollow part (21) and in the opening of the support piece (20) is adjusted in such a way that it presses and possibly deforms the reaction disk (11).   A method of adjusting the jump of a brake booster servomotor, which servomotor comprises a force transmission system comprising: a control rod for controlling a three-way valve, and a plunger (10) axially movable under the control of the control rod (8) and having an end bearing face (Sla), É a pneumatic piston (5) axially movable under the effect of a pressure difference induced by the three-way valve , having an axial hole surrounded on the front face of an annular bearing face (S2a) and in which said plunger (10) slides, E a reaction disk (11) of elastically deformable material having a rear face (S11b) applied to the annular bearing surface (S2a) of the pneumatic piston and intended to receive the forces applied by this annular face and by the end bearing face (Sla) of the plunger (10), É a bearing piece ( 20) having a planar bearing surface (20b) for e to bear against the front face (S11a) of the reaction disc (11) and a thrust rod (22) axially controlled by the support piece so as to transmit a force of the reaction disk (11) towards a organ to be controlled, characterized. in that it comprises the following steps: E establishment of the push rod in a hole axially through the support piece (20) so that the push rod is supported by a rear end face (22b) on the front face (Sula) of the reaction disk (11), E adjusting the distance between the rear face (S11b) of the reaction disk and the front face (Sla) of the plunger (10) by axial displacement of the piston rod; pushing with respect to the front face (S11a) of the reaction disc (11), E attaching the push rod to the support piece.