Electric brake booster

Abstract

An electric brake booster (100) controls a master cylinder (101) from the brake pedal (103), which acts on the control pin (102) and the plunger piston (8) for emergency braking, to act directly on the reaction disk (72) and the pushrod (7). The auxiliary piston (6) is normally driven by the actuating piston (4), which in turn is driven by the electric motor via racks (3, 3') and pinions (2, 2'). The auxiliary piston (6) can move freely forward relative to the actuating piston (4) by means of an intermediate sleeve (5) and the insertion of an intermediate spring (53), which exclusively ensures the return of the pushrod (7) after brake application, without initially having to push the return spring (41). If the emergency braking effect on the brake pedal (103) continues, the force only needs to overcome the force built up by the return spring (41) after the compression of the spring (53).

Description

Field of invention

[0001] The present invention relates to an electric brake booster that controls a brake circuit master cylinder connected to a control pin actuated by the brake pedal, comprising the following: - a brake booster body that accommodates an actuating piston which is translationally driven by an electric motor and pushes the piston of the master cylinder through the thrust piston by means of an auxiliary piston, - a plunger piston that slides in the auxiliary piston and is connected to the control pin, which in turn is connected to the brake pedal, - wherein, at the beginning of a normal brake application, the plunger moves freely forward over a short distance against the counterforce of an attack spring without touching the push pin, and in the case of a very fast and forceful application of the brake pedal or in the event of failure of the electric brake booster, pushes the push pin directly, - wherein the attack spring returns the plunger piston to the position of the relieved brake pedal at the end of a brake actuation by pushing it back relative to the auxiliary piston. State of the art

[0002] Such an electric servo brake 100A ( Fig. 3A, Fig. 3B), which is formed from a body 1A connected to a master brake cylinder and, via an actuating pin 102A, to a brake pedal, wherein the assembly is aligned with the axis XX and the master cylinder is connected to the wheel brake circuit, is known. The body 1A is equipped with an electric motor that drives two coupled straight pinions 2A, 2'A, each of which engages with a rack 3A, 3'A, which is supported by an actuating piston 4 sliding in the cylindrical receiving seat 11A of the body 1A of the brake booster. The actuating piston 4A receives an auxiliary piston 6A, which receives the pushrod 7A that acts on the master cylinder. The head 71A of the pushrod 7A is located in a cavity 61A in front of the auxiliary piston 6A and carries a reaction disk 72A on its rear surface. The auxiliary piston 6A pushes the push pin 7A by resting on the reaction disk 72A.The auxiliary piston 6A slides within the actuating piston 4A and in turn receives a plunger piston 8A, which is movable along the axis and whose front end 81A rests on an intermediate piston 82A located opposite the part of the reaction disk 72A adjacent to the axis XX. The plunger piston 8A is returned to its rearward position by an attack spring 9A, which rests on the bottom of the rear cavity 62A of the auxiliary piston 6A. The auxiliary piston 6A has a ring 63A located in front of the actuating piston 4A and rests on the return spring 41A of the auxiliary piston.

[0003] Under normal operating conditions ( Fig. 3A) Actuation of the brake pedal is converted into a forward movement (arrow F1) of the control pin 102A, which is detected by a displacement sensor (not shown) that actuates the electric brake booster 100A. This booster, via racks 3A and 3'A, drives the actuating piston 4A, which, by bearing on the ring 63A, drives the auxiliary piston 6A. This auxiliary piston, via the reaction disk 72A, pushes the thrust pin 7A and thus the master cylinder. This movement occurs under compression of the return spring 41A.

[0004] Under exceptional operating conditions in emergency mode ( Fig. 3B) It is assumed that the electric brake booster 100A has failed and therefore remains immobile, such that only a mechanical action exerted via the brake pedal enables emergency braking under the following conditions: The control pin 102A moves forward and pushes the plunger piston 8A against the reaction disk 72A, which thus pushes the pusher pin 7A, which actuates the master brake cylinder to build up pressure in the brake fluid of the brake circuits.

[0005] The rear end 83A of the plunger 8A rests on the auxiliary piston 6A, which must necessarily compress the return spring 41A. For this emergency braking movement, the force applied to the brake pedal must therefore overcome the force applied by the support spring 41A in order to move the push pin 7A forward.

[0006] EP 2 559 601 A1 shows an electro-hydraulic dynamic braking system and an associated control method. Object of the invention

[0007] The present invention aims to develop an electric brake booster that improves the functionality of the brake booster in emergency mode and in the event of a failure of the electric brake booster, in order to reduce the force that must be exerted to perform emergency braking independently of the brake booster. Explanation and advantages of the invention

[0008] For this purpose, the invention relates to an electric brake booster of the type defined above, characterized in that it comprises the following: - a support sleeve inserted between the return spring of the actuating piston and the piston, wherein this sleeve provides support for a spring which also acts against the front surface of the rear end of the push pin to push it back towards the bottom of the front cavity of the auxiliary piston, - wherein the auxiliary piston is connected to the actuating piston via a drive connection of the auxiliary piston through the actuating piston in the direction of actuation of the brake booster, but in the initial actuation phase of the plunger piston can still move freely forward through the control pin without being connected to the return spring.

[0009] This brake booster has the advantage of separating the force necessary to return the power transmission to its rest position from the resistance force that counteracts the effect of the driver pressing the pedal in the event of a failure of the electric brake booster motor.

[0010] In the event of a brake booster failure or if emergency braking needs to be performed extremely quickly, the thrust exerted by the control pin 102 on the sliding piston 8 is transmitted directly to the reaction disk 72 and thus to the end 71 of the control pin. This movement simply compresses the intermediate spring 53 during the first phase of the pusher pin's forward movement, without having to overcome the relatively large force generated by the return spring 41 during this initial phase. Under normal operating conditions and after a braking phase, this return spring must return the mechanical elements of the brake booster to their rest or initial position. This includes not only the actuating piston but also, due to the rack and pinion system, the mechanical power transmission to the motor.

[0011] Since the initial force is thus relatively reduced, it can be applied quickly, allowing for a very rapid start to braking. This emergency function, made possible by the brake booster according to the invention, provides an additional safety feature and also reduces driver fatigue and allows for easy emergency intervention even for a person who would not be able to quickly and forcefully exert the necessary force for the immediate compression of the return spring.

[0012] According to another advantageous feature, the intermediate sleeve comprises a rear ring that is inserted between the return spring and the actuating piston, and a front ring that serves as a support for the intermediate spring.

[0013] This embodiment of the intermediate sleeve is advantageous because it does not require a complete modification of the structure of the electric brake booster.

[0014] According to another advantageous feature, the intermediate sleeve includes a stop that limits the compression of the spring by the push pin.

[0015] In particular, the stop is a sleeve that is supported by the front ring of the intermediate sleeve and forms a circumferential receiving seat that accommodates the intermediate spring.

[0016] This stop protects the intermediate spring, preventing it from being extended by the force exerted on the push pin to push the return spring in the second functional phase. Drawings

[0017] The present invention is described in more detail below with the aid of an electric brake booster, which is shown very schematically in the accompanying drawings and by comparison with a known electric brake booster, which is also shown very schematically.

[0018] Thus, they show: - Fig. 1. The brake booster according to the invention in the rest position, - Fig. 2A the brake booster at the beginning of the emergency operation and - Fig. 2B the brake booster in the highlighted phase of emergency braking, - Fig. 3A a known electric brake booster in the rest position and - Fig. 3B the known brake booster in the emergency operating position. Description of an embodiment of the invention

[0019] The invention relates to an electric brake force amplifier 100, which is formed from a body 1 which is connected to a brake master cylinder 101 (not shown in detail) and to the brake pedal 103 via an actuating pin 102.

[0020] The entire assembly is aligned with axis XX. The master cylinder 101 is connected to the brake circuits of the wheels.

[0021] Body 1 carries an electric motor which, via a (not shown) mechanical power transmission, drives two coupled straight pinions 2, 2', each of which engages with a rack 3, 3' supported by an actuating piston 4 that slides in the cylindrical receiving seat 11 of the brake booster body 1. This assembly is movable along the axis XX of the system formed by the electric brake booster 100, the master cylinder 101, and the control pin 102. By convention, the front AV of the brake booster is located on the side of the master cylinder 101, and the rear AR is located on the side of the brake pedal 103.

[0022] The brake booster acts along the arrow FAV to control the piston of the master cylinder 101, which supplies pressurized hydraulic fluid to the vehicle's wheel brake circuits. The movement FAR in the opposite direction is that of the components of the brake booster 100 and the control pin 102 to their rest position or the "relieved of the brake pedal" position 103.

[0023] Starting from this rest position, i.e., from the position relieved by the brake pedal 103, the pedal 103, when actuated again for brake application, moves the control pin 102. This movement is detected by a sensor, which controls the forward movement of the actuating piston 4 to act on the piston of the master cylinder 101, as described later. The plunger piston 8, which is connected to the control pin 102, moves forward under the action of the brake pedal 103 without the plunger piston 8 being in contact with the reaction disk 72.

[0024] The clear path from the beginning of a brake application, when the pedal 103 actuates the control pin 102, until the actuation of the electric brake booster 100, is called the "attack path".

[0025] The actuating piston 4 is subject to the action of a return spring 41, which is supported against the front wall 12 of the body 1.

[0026] The actuating piston 4 is formed by a component with a cylindrical shape, which slides in the cylindrical receiving seat 11 of the body 1 and carries two racks 3, 3' parallel to the axis XX at two diametrically opposite positions, each of which engages with one of the pinions 2, 2', as described above.

[0027] The actuating piston 4 receives an auxiliary piston 6, which receives the thrust pin 7. This pin acts on the piston of the main cylinder 101 along the axis XX of the system and is connected to it via a drive stop (not shown) that is active in the direction of thrust. The thrust pin 7 has a head 71 that slides in a cylindrical cavity 61 in front of the auxiliary piston 6 and carries a reaction disk 72 on its rear surface. The auxiliary piston 6 presses on the thrust pin 7 by bearing against the reaction disk 72A. The auxiliary piston 6, which slides in the actuating piston 4, in turn receives a plunger piston 8 that is movable along the axis XX and whose front end 81 bears against an intermediate piston 82 opposite that part of the reaction disk 72 that is adjacent to the axis XX.

[0028] The rear end 83 of the plunger piston 8, shown enlarged, is connected to the front end of the control pin 102 via a universal joint. This enlarged end 83 is pushed rearward by an attack spring 9, which is supported, among other things, by the bottom 621 of the rear cavity 62 of the auxiliary piston 6. In the Fig. In the rest position shown in Figure 1, the auxiliary piston 6 rests on the base 13 of the receiving seat 11 of the body 1, as does the rear end 83 of the diving piston 8.

[0029] A support sleeve 5 is inserted between the return spring 41 and the actuating piston 4. This support sleeve 5 comprises a rear ring 51, which rests against the actuating piston 4 and serves as a support for the rear end of the return spring 41, and a front ring 52, which serves as a support for an intermediate spring 53.

[0030] The intermediate spring 53 is supported at its other end against the front of the head 71 of the push pin 7. The intermediate spring 53 generates a force that is smaller than that of the return spring 41, such that in the event of a failure of the brake booster 100 and / or during rapid and forceful actuation of the brake pedal 103, the plunger piston 8 compresses the attack spring 9 and is supported against the reaction disk 72 via the intermediate piston 82, which thus pushes the push pin 7 and thereby compresses the intermediate spring 53 over its entire available travel in the support sleeve 5. This travel is limited by an internal stop 54 of the support sleeve, for example in the form of a recess or a sleeve surrounding the push pin 7, in order to prevent the extension of the spring 53. This sleeve is, for example, firmly connected to the front ring of the intermediate sleeve and forms a circumferential receiving seat inside the intermediate sleeve and accommodates the intermediate spring 53.This track generates a specific brake fluid pressure in the brake circuit through the main cylinder 101 when the spring 53 is compressed (. Fig. 2A). During this movement, the return spring 41 is not subjected to any stress.

[0031] If the pressure on the brake pedal 103 continues and exceeds the force built up by the return spring 41, this force is compressed by the forward movement of the rear ring 51 of the sleeve 5, which is pushed by the support of the head 72 of the push pin 7 on the support sleeve 5, resulting in a stronger braking effect ( Fig. 2B).

[0032] A push pin (7) within the meaning of this application can also be understood as an output element of a brake force amplifier. Likewise, a control pin can be understood as an input element of the brake force amplifier. REFERENCE MARK LIST 100 electric brake boosters 101 Master cylinder 102 Control pin 103 Brake pedal 1 Body of the electric brake force amplifier 11 cylindrical mounting seat 12 front wall 13 Floor 2, 2' coupled pinions 3, 3' racks 4 actuating pistons 41 Return spring 5 support sleeve 51 rear wreath 52 front wreath 53 Intermediate spring 54 inner stop 6 auxiliary pistons 61 front cylindrical cavity 62 rear cylindrical cavity 621 Floor 70 Push pin 71 heads 72 reaction disk 8 diving pistons 81 front end 82 Intermediate pistons 83 rear end 9 Attack spring 100A electric brake booster 101A Master Cylinder 102A Control pin 103A Brake pedal 1A Body of the electric brake booster 11A cylindrical mounting seat 12A front wall 13A Ground 2, 2'A coupled pinions 3, 3'A rack and pinion 4A Actuating piston 41A Return spring 6A Auxiliary piston 61A front cylindrical cavity 62A rear cylindrical cavity 7A Push pin 71A Head 72A Reaction disk 8A Piston 81A front end 82A Intermediate piston 83A rear end 9A Attack spring

Claims

[1] Electric brake booster (100) controlling a brake circuit master cylinder (101) connected to a control pin (102) actuated by the brake pedal (103), comprising: - a brake booster body (1) which accommodates an actuating piston (4) which is translationally driven by an electric motor and pushes the master cylinder piston by means of an auxiliary piston (6) which acts on the push pin (70) connected to the piston of the master cylinder (101), - a plunger piston (8) which is slidably housed in the auxiliary piston (6) and is connected to the control pin (102), which in turn is connected to the brake pedal (103), - wherein the plunger (8) moves freely forward over a short distance at the beginning of a brake actuation against the action of an attack spring (9) without touching the push pin (70), and directly pushes the push pin (70) in the case of a very fast and forceful actuation of the brake pedal (103) or in the case of a failure of the electric brake booster (100), - wherein the attack spring (9) returns the plunger piston (8) to the unloaded pedal position at the end of a brake actuation by being pushed back relative to the auxiliary piston (6), wherein the electric brake booster (100) characterized by is that it includes the following: - a support sleeve (5) inserted between the return spring (41) of the actuating piston (4) and the piston (4), wherein this sleeve (5) forms the support (52) for a spring (53) which also acts against the front surface of the rear end (71) of the push pin (7) to push it back to the bottom of the front cavity (61) of the auxiliary piston (6), - wherein the auxiliary piston (6) is connected to the actuating piston (4) by a drive connection of the auxiliary piston (6) through the actuating piston (4) in the direction of actuation (FAV) of the brake booster (100), but remains free to move forward in the initial phase of actuation of the plunger piston (8) by the control pin (102) without being connected to the return spring (41). [2] Electric brake booster (100) according to claim 1, characterized by, that the intermediate sleeve (5) comprises a rear ring (51) which is inserted between the support spring (41) and the actuating piston (4), and a front ring (52) which serves as a support for the intermediate spring (53). [3] Electric brake booster (100) according to claim 1, characterized by , that the intermediate sleeve (5) includes a stop (54) which limits the compression of the spring (53) by the push pin (7). [4] Electric brake booster (100) according to claim 3, characterized by , that the stop (54) is a re-entry sleeve which is supported by the front ring (52) of the intermediate sleeve (5) and forms a circumferential receiving seat which receives the intermediate spring (53).

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