FR2629033A1 - Hydraulic brake servomotor with remote control from pedal - has master cylinder providing auxiliary circuit which opens servo control valve to initiate braking assistance - Google Patents

Abstract

The braking system has a master cylinder (12) transmitting hydraulic pressure (42a,42b) in a dual circuit to wheel cylinders (18a,18b), a brake servomotor (14), and a reservoir (16). The servomotor is mounted separately, and the driver's pedal (10) is connected directly to the master cylinder's piston rod (58). When the pedal is pressed, piston (24b) movement allows a reservoir supply valve (46) to close as pressure is communicated (72) to the back of a head on the servo-motor's actuating rod (112). This moves forward, admitting air to the servo motor diaphragm rear so that the rod drives a spring-loaded piston ahead of it. Piston movement communicates (80) pressure from the master cylinder to the back of the piston assembly on the master cylinder's rod. Pressure already exerted by the driver's foot is thus augmented, and the brakes are applied accordingly. ADVANTAGE - Auxiliary hydraulic circuit permits remote control of brake servomotor thus simplifying location and installation in certain right-hand drive vehicles. (26pp dwg.No.1/3)

Description

() FRENCH REPUBLIC Publication no .: 2,629,033 (to be used only

  for NATIONAL INSTITUTE reproduction orders)

INDUSTRIAL PROPERTY ^^^

  INDUSTRIAL PROPERTY N national registration: 88 039 12 PARIS

(Int CI ': B 60T 13/54, 13/10.

  A1 PATENT APPLICATION

  ) Date of filing: March 25, 1988. Applicant (s): Société anonyme known as BENDIX France.

-FR. Priority

  @ Inventor (s): Jean-Pierre Gautier.

  ) Date of public availability of the

  application: BOPI "Patents" n 39 of September 29, 1989.

  - References to other national documents appearing

rented: (rt Holder (s):

  ) Agent (s): Christian Lejet. Bendix France.

  _ Hydraulic assisted braking system, and booster and master cylinder adapted to such a system.

  (In an assisted hydraulic braking system, designed in particular for use on vehicles with a right-hand drive, the brake pedal 10 acts directly on a rod / actuation 58 of a master cylinder 12. The pressure thus generated is transmitted to an assistance booster 14 by a first hydraulic circuit 72. so as to actuate this booster remotely. The assistance force generated in the latter is in turn transmitted to the master cylinder 12 by a second hydraulic circuit 80, so that the

  master cylinder operates the wheel brakes 18a. 18b.

  <Y N Ve ULU D Sale of booklets to rl'MPRIMERIE NATIONALE, 27. rue de 18 Convention --75732 PARIS CEDEX 15 Hydraulic assisted braking system, and booster and master cylinder adapted to such a system.

DESCRIPTION

  The invention relates to an assisted hydraulic braking system designed in particular for use on a right-hand drive motor vehicle, as well as a brake booster and a master cylinder designed for use in a

such system.

  On vehicles equipped with an assisted hydraulic braking system, this system usually includes an assistance booster and a master cylinder arranged end to end. More

  precise, the brake pedal acts on a control rod

  of the servomotor, which has the effect of actuating inside the latter of the assistance means moving a push rod which in turn actuates at least one actuating piston equipping the master cylinder. This compact arrangement is advantageous because it makes it possible to give the actuator-master cylinder assembly a relatively structure.

simple.

  There are however cases in which it is not possible to place the servomotor directly between the brake pedal and the master cylinder. This situation arises in particular on certain vehicles with right-hand drive. Indeed, the diametrical size of the actuator can then make it impossible to install it directly between

  the brake pedal and the master cylinder.

  The invention specifically relates to an assisted hydraulic braking system whose particular design allows its installation on motor vehicles of all types and in particular

  on right-hand drive vehicles.

  The subject of the invention is also a servomotor and a master cylinder designed to be used in

such a braking system.

  Thus, in its most general definition, the invention relates to a hydraulic braking system

  assisted with a brake pedal, a master cylinder

  dre, a brake booster and at least one wheel brake, the master cylinder comprising a body provided with a bore in which slides sealingly at least one piston for actuating the wheel brake, and the servomotor comprising a control rod actuating assistance means acting

  on a push rod actuating the master piston

  cylinder, characterized in that the brake pedal acts on an actuating rod of the master cylinder, a first hydraulic circuit making communicate a control chamber of the master cylinder formed between the actuating rod and the actuating piston with a servomotor control chamber, partially delimited by the control rod, so that an actuation of the brake pedal causes a displacement of the control rod in the direction of actuation of the assistance means, and a second hydraulic circuit communicating an actuating chamber of the servomotor delimited in part by the push rod with an actuating chamber of the master cylinder delimited in part by the actuating piston, so that a displacement of the push rod controlled by the assistance means causes a displacement of the piston

  in the direction of brake application.

  In a braking system thus designed, the brake pedal is placed in the extension of the barrel-cylinder, while the servomotor can be

  placed anywhere under the hood of the vehicle

  cule. The rise in pressure resulting from the actuation of the brake pedal is transmitted to the booster by the first hydraulic circuit and the assistance force produced by this booster is in turn transmitted to the master cylinder by the second hydraulic circuit. , whatever the position occupied

  by the servomotor relative to the master cylinder.

  In accordance with another aspect of the invention

  tion, a brake booster designed to be used in such a braking system comprises a control rod actuating means

  assistance acting on a push rod, characteristic

  laughed at by the fact that the push rod slides in a bore formed in a body of the actuator and comprises a tubular rear part in which slides a sealed front part forming a piston of the control rod, a servomotor control chamber being formed in said tubular rear part, at the rear of said front part forming a piston, and an actuation chamber being formed in the body of the booster, at the front of the push rod, a first return means interposed between the body of the actuator and the push rod normally maintaining the latter in a rear position of rest, and a second interposed return means

  between the push rod and the control rod now

  normally the latter in a rear position

  re rest, in which the assistance means are not actuated, the second return means exerting a lower return force than the first

means of recall.

  Preferably, the actuator body comprises

  carries an inlet orifice which communicates with the control chamber through an annular space formed between the body of the booster and the push rod, and at least one passage formed in the tubular rear part of the latter, the actuator body also having an outlet opening which opens out

  directly in the actuation chamber.

  According to yet another aspect of the invention, a master cylinder designed for use in the braking system defined above comprises a body provided with a bore in which slides in leaktight manner at least one brake actuating piston, characterized by the fact that it further comprises an actuating rod including a front part forming a piston

  slides tightly in a tubular rear part

  the area of the actuating piston, a control chamber being formed in said tubular rear part, at the front of the front part forming a piston, and an annular actuating chamber being formed in

  the bore, around the actuating rod and at the rear

  of the tubular rear part, a first means

  rappeL, interposed between the body and the piston

  actuation, normally maintaining the latter in a rear position of rest, and a second return means, interposed between the actuating piston and the actuating rod, normally maintaining the latter in a rear position of rest, the second return means exerting a lower restoring force

as the first means of recall.

  Preferably, the master cylinder body has an inlet port which opens directly into the annular actuation chamber, and an outlet port which communicates with the control chamber through an annular space formed between the body of the master cylinder and actuating piston and at least one passage formed in the tubular rear part

of the last.

  A preferred embodiment of the invention will now be described, by way of nonlimiting example, with reference to the accompanying drawings in which: - Figure 1 schematically shows an assisted hydraulic braking system according to the invention ;

  - Figure 2 is a longitudi sectional view-

  nale representing on a larger scale the maltre-cylin-

  dre of the braking system of figure 1; and

  - Figure 3 is a longitudi sectional view-

  nale representing on a larger scale the central part

  braking assistance servo motor system

  of hydraulic braking of figure 1.

  In Figure 1, there is shown very schematically

  a hydraulic assisted braking system which mainly comprises a brake pedal 10,

  a tandem master cylinder 12, an assist servo

  braking force 14, a double reservoir of brake fluid 16 and two sets of wheel brakes 18a and 18b.

  In the following description of the master-

  cylinder 12 and the servomotor 14, we will call by

  convention "rear" the end towards which moves

  cent the moving parts of the master cylinder or servo

  engine when these parts return to their position

  of rest and "before" the end towards which moves

  cent moving parts when activated.

  The rear ends of the maltre-cyLindre and the servo

  tor are oriented to the right in the figures

1 to 3.

  As illustrated more particularly in FIG. 2, the master cylinder 12 comprises a body 20 in which a blind bore 22 opening out is formed

  at the rear end of the body 20. Two pistons

  24a and 24b are arranged end to end

  so that it can slide tightly, independently

  one of the other, inside the bore 22. The sealing of the sliding of the actuating piston 24a closest to the bottom of the bore 22 inside this bore is provided by two

  annular seals 26a supported by each of the ends

tees of this piston.

  The sliding of the second actuating piston 24b inside the bore 22 is sealed also by two annular seals 26b mounted

  on each end of the piston 24b.

  A compression spring 30 supported

  on the facing faces of the pistons 24a and 24b main-

  normally keeps them at rest in a posi-

  tion of maximum spacing determined by the abutment of the head of a rod 32 fixed on the front face of the piston 24b, coaxially with the bore 22, with a

  cup 34 mounted on the rear face of the piston 24a.

  A second compression spring 36 is supported by each of its ends respectively on the front face of the piston 24a and in the bottom of the bore 22. This compression spring 36 constitutes a return means exerting on the piston 24a a force

  return force lower than the force exerted between the

  tones 24a and 24b by the spring 30. Consequently, in the absence of any actuation of the brake, the spring

  36 moves the pistons 24a and 24b in unison so that

  as long as the maximum spacing imposed by the spring 30 is maintained between them. Under the action of the spring

  36, the pistons 24a and 24b are thus now

  naked in a rear rest position. This position is determined by the abutment of the piston 24b against a rear stop constituted by an elastic washer 38 mounted in a groove formed nearby.

  of the rear end of bore 22.

  Two orifices 40a and 40b are formed in the body 20 of the master cylinder, to open into the bore 22 respectively at the front of the piston 24a and between the pistons 24a and 24b, whatever the position occupied by each of these pistons. inside the bore. Referring to FIG. 1, it can be seen that the orifice 40a is connected by a first circuit 42a to the set of wheel brakes 18a and that the orifice 40b is connected by a second circuit 42b to the set of brakes

wheel 18b.

  Two other orifices 44a and 44b are formed in the body 20 of the master cylinder and communicate respectively with each of the tanks 16a and 16b

  (Figure 1) of the double tank 16. The orifice 44a opens out

  che permanently between the two seals 26a of the piston

  24a, in an annular space 46a delimited between the

  sage 22 and the outer peripheral surface of the piston 24a, whatever the position occupied by the latter inside the bore. The orifice 44a also opens out at the front of the piston 24a when the latter

  is in its rear rest position.

  Inside the orifice 44b is placed a valve 46 comprising a valve 48 able to come into leaktight support on a seat 50 under the action of a spring 52. For this purpose, the valve 48 is mounted on a rod tilting 54 and The spring 52 bears simultaneously on the rod 54 and on a shoulder formed inside the orifice 44b. One end of the rod 54 protrudes inside the bore 22, in the space

  annular 46b delimited between the piston 24b and the

wise 22.

  The part of the orifice 44b placed inside

  laughing body 20 relative to the valve 46 standard chamber 57. This chamber 57 opens permanently between the seals 26b carried by the piston 24b, in an annular space 46b formed between the outer peripheral surface of the piston 24b and l bore 22, whatever the position occupied by the piston 24b. Thanks to this arrangement, when the piston 24b occupies its rear position of rest illustrated on

  FIG. 2, a shoulder formed on the piston and delimits

  mitting the front end of the annular space 46b is in abutment on the end of the rod 54 and rocks the latter against the action of the spring 52, so that the valve 46 is held in

  open position. The closing of the valve 46 is ensured

  automatically set by spring 52 from the start

  the forward movement of the piston 24b.

  According to the invention, a blind bore 56 is formed coaxially in the piston 24b and opens on the rear face thereof, so as to give

  at the rear part of this piston a tubular shape.

  The front part forming a piston of an actuating rod 58 slides in leaktight manner in the bore 56, by means of an annular seal 60 received in a groove formed near the end

front of rod 58.

  The axial stroke of the actuating rod

  58 in the bore 56 is defined by two oblong slots-

  gues 62 formed in the tubular rear part 'of the piston 24b and in which are received the ends of a pin 64 passing radially through the rod 58

  at the front of the seal 60. A compression spring

  pressure 66 whose ends are in respective support

  vement in the bottom of the bore 56 and on the front end of the actuating rod 58, constitutes a return member normally maintaining the actuating rod 58 in a rear rest position illustrated on

  Figure 2 and in which The ends of the gou-

  piLle 64 are supported on the rear ends

slots 62.

  As schematically illustrated in FIGS. 1 and 2, the brake pedal 10 acts directly on the rear end of the actuating rod 58

of the master cylinder.

  The volume defined in the bore 56 between the bottom of this bore and the front end of the rod 58 constitutes a control chamber 68. This control chamber 68 communicates permanently with the chamber 57 by the oblong slots 62 and the chamber annular 46b, whatever the position occupied by the actuating rod 58 inside the bore 56. A

  outlet 70 formed in the body 20 of the master

  cylinder opens into the chamber 57, so that this outlet orifice 70 communicates permanently with the chamber 68. As shown in FIG. 1, a hydraulic circuit 72 communicates the outlet orifice 70 of the master cylinder with the servomotor 14, to control the latter in a manner

which will be described later.

  In its part located behind the piston 24b, the actuating rod 58 slides in leaktight manner in the rear part of the bore 22 formed in the

  master cylinder body. For this purpose, a seal

  annular ring 74 is mounted in bore 22, at

  near the open rear end of this bore.

  The volume defined between the seal 74 and the rear end of the piston 24b around the rod 58 constitutes an annular actuation chamber 76 into which an inlet port 78 formed in the body of the master cylinder opens. As illustrated in FIG. 1, this orifice 78 communicates with the servomotor 14 by

  a hydraulic circuit 80 through which the servo

  tor controls the actuation of the cylinder

  manner which will be described later.

  The servomotor 14 used in the hydraulic braking system of FIG. 1 will now

  be described in detail with reference to Figure 3.

  In a manner which is in itself conventional, the booster 14 comprises an outer casing 82

  shell-shaped, presenting a symmetry of revolution-

  tion around the axis of the servomotor. The rear part of the casing 82 is crossed at its center by an annular piston 84 able to move along the axis of the booster. The seal between the piston 84 and the casing 82 is ensured by a seal

  annular 86 and by a deformable sleeve 88.

  A waterproof and deformable membrane 90 connects the front end of the piston 84 to the outer peripheral edge (not shown) of the casing 82, so as to delimit a chamber inside the latter.

  front 92 and a rear chamber 94.

  The front chamber 92 is normally connected to a vacuum source (not shown) by means of a nozzle 96. Passages 98 formed in the piston 84 and controlled by a valve 100 allow the rear chamber 94 to communicate alternately, either

  with the front room 92, or with the outside atmosphere

  better. The valve 100 for this purpose comprises a valve

  102 mounted inside the annular piston 84 and biased

  cited elastically forwards by a spring 104 towards two concentric valve seats 106 and 108 formed respectively on the piston 84 and on a probe secured to a control rod 112 arranged at

  inside the piston 84, along the axis of the booster.

  One or more compression springs 114 interposed between the front part of the envelope

  82 and the front face of the piston 84 maintain normal-

  the latter in its rear position of illus-

  shown in FIG. 3, in which the piston 84 and the membrane 90 are in abutment against the rear part of the casing 82. In a manner also known, the piston 84 carries on its front face and in its central part a reaction disk 116 made of elastomeric material, on which is supported the rear end of a push rod 118 serving to transmit to the cylinder

  The assistance force generated in the servomotor 14.

  In accordance with the invention, the booster 14 further comprises a body 120 tightly fixed to the front part of the casing 82 and in which

  is formed a bore 122 oriented along the axis of the servo

  tor and opening into the front room 92. The part

  front of push rod 118 slides tightly

  che in this bore 122, in particular thanks to two O-rings 124 placed in grooves formed in the rear part of the bore 122. In addition, the rod 118 has a front part 118a in the form of a piston carrying an annular seal. 126 that slides

  tightly in bore 122.

  A compression spring 128 is interposed between a plug 130 closing the front end of the bore 122 and the front face of the part 118a of the push rod 118, so as to exert on the latter a restoring force which is now permanently the rear end of the rod 118 bearing against

the reaction disc 116.

  An orifice 132 formed in the body 120 of the booster opens between the seal 126 and the closest seal 124, in an annular space 134 formed in the bore 122, at the periphery of the piston-shaped front part 118a of the rod. 118, whatever the position occupied by the latter. Port 132 also opens at the front of Part 118a

  of rod 118, when the latter occupies its posi-

  rear rest tion. As illustrated in FIG. 1, this orifice 132 communicates with the reservoir 16b. In its rear part, the push rod 118 has a stepped bore 136 which gives this

  rear part a tubular shape and in which

  smoothly sealingly the front end of the control rod 112. More specifically, the control rod 112 has a front part 112a, in the form of a piston, which slides in a sealed manner in a part

  front of larger diameter of bore 136 by the in-

  through a seal 138.

  A compression spring 140 is interposed between an elastic ring 113 mounted in the bore 136 and the front face of the control rod 112, so as to exert on the latter a restoring force tending to move it towards a rear position of rest shown in Figure 3. In this rear position of rest, the seat 108 of the probe 110 is supported on the valve 102 and the latter is spaced from the seat 106 formed on the piston 84. The chambers 92 and 94 of the booster then communicate between they at

  through passages 98, i.e. they are-

  both in vacuum. The piston 84 is then held

  in its rear position of rest by the springs 114.

  An O-ring 142 is placed in a groove formed near the front end of a rear part of smaller diameter of the bore 136 and cooperates in a sealed manner with the rod 112. The seals 138 and 142 delimit thus inside the larger diameter portion of the bore 136 an annular control chamber 144 of the booster. A hydraulic fluid inlet orifice 146 is formed in the body 120 of the servomotor and opens into an annular space formed between the seals 124 around the rod 118, in the bore 122. The annular space 148 communicates with the chamber. 144 by passages 150 formed in the tubular rear part of the rod 118. The hydraulic circuit 72 previously described

  referring to figure 1 is connected to this orifi-

  this inlet 146, so that the control chamber

  command 68 of the master cylinder communicates permanently

  with the actuator control chamber 144.

  Furthermore, the space formed between the plug

  and the front face of the push rod 118 inside

  laughing hole 122 defines an action chamber

  ment 152. An outlet port 154 is formed in the

  body 120 of the servomotor so as to lead permanently

  nence in chamber 152. The hydraulic circuit 80 described above with reference to FIG. 1 is connected to the outlet port 154, so that the actuation chamber 76 of the master cylinder communicates permanently with the chamber d actuation

152 of the servomotor.

  Braking system operation

  assisted hydraulics which have just been described with reference to

  rant in Figures 1 to 3 is as follows.

  When the brake pedal 10 is not actuated, the various parts of the cylinder

  12 and the servomotor 14 occupy the positions illus-

shown in Figures 2 and 3.

  When the driver of the vehicle actuates the brake pedal 10, the actuating rod 58 moves forward. The restoring forces exerted by the springs 66 and 36 are such that this displacement

  of the actuating rod 58 is accompanied by a displacement

  ment towards the front of the pistons 24a and 24b sufficient to cause the valve 46 to close. The chamber 68 of the master cylinder is therefore isolated from the reservoir 16b. The return force exerted by the spring 36 is however sufficient for the forward movement of the actuating rod 58 to be accompanied

  compression of the spring 66. Consequently, the-

  volume of the chamber 68 of the maltre-cylinder decreases and part of the hydraulic fluid which it contains is expelled by the outlet port 70, the circuit 72, and the inlet port 146 of the servomotor in the

room 144 of the latter.

  The return force exerted by the spring being substantially less than the return force

  exerted by the spring 128 in the actuator, the aug-

  volume statement in chamber 144 therefore results in a forward displacement of the rod

  actuator command 112. Under the effect of this displacement-

  ment, the seat 108 formed on the feeler 110 stecart from the valve 102 and the latter comes to bear sealingly on the seat 106 formed on the piston 84. Consequently,

  the communication between rooms 92 and 94 of the servomo-

  tor is interrupted and the rear chamber 94 is placed in communication with the outside atmosphere. Since the front chamber 92 is still under vacuum, an assisting force tending to move the piston

  84 forward is thus generated.

  This assistance force is transmitted from the piston 84 to the push rod 118 through the reaction disc 116. It results in a forward movement of the piston 84 and the push rod -118. Under the effect of this displacement, the volume

  of chamber 152 of the servomotor decreases significantly

  aunt. The hydraulic fluid thus expelled from the chamber 152 of the booster is transferred to the chamber 76 of the master cylinder through the outlet port 154, the hydraulic circuit 80 and the inlet port 78. The assistance force generated in the booster is thus transmitted to the master cylinder and applied to the piston 24b of the latter. IT is then transmitted to the piston 24a by the spring 30 interposed between the two pistons and by the pressure of the chamber between the pistons 24a and 24b. In this way, assisted braking of the two sets of brakes 18a and 18b is ensured.

  In accordance with the invention, an assisted hydraulic braking system is therefore proposed in which the brake pedal acts directly on an actuating rod of the master cylinder while the brake booster can be placed.

  anywhere under the hood of the vehicle.

  Such a hydraulic assisted braking system is designed in particular to be used on right-hand drive vehicles, in which it is generally not

  it is not possible to place the actuator in the usual way

  miter between the brake pedal and the master cylinder.

  It can however be used in other cases, as soon as the usual installation of the servomotor poses

congestion issues.

  Of course, the invention is not limited to the embodiment which has just been described by way of

  example, but covers all variants.

  Thus, although the master cylinder described is a tandem master cylinder equipped with a reservoir

  double, it is clear that the invention also applies

  ment in the case of a simple master cylinder.

  In addition, the structure of the servomotor

  may be different from the one described, including

  ment with regard to the location of the control chamber 144 inside the push rod 118. Indeed, instead of acting by traction on the plunger 110, the rod 112 can act by pushing on

  the latter, Chamber 144 then being formed at the rear

  re of the plunger, between the piston 84 and a rear face

of the rod 112.

Claims (13)

  1. Hydraulic assisted braking system comprising a brake pedal (10), a brake-cylinder (12), a brake booster (14) and at least one wheel brake (18a, 18b), the master- cylinder comprising a body (20) provided with a bore (22) in which slides at least one actuating piston (24a, 24b) of the wheel brake, and the actuator comprising an actuating control rod (112) assistance means (84,100) acting on a push rod (118) actuating the piston (24a, 24b) of the master cylinder, characterized in that the brake pedal (10) acts on an actuation rod ( 58) of the master cylinder, a first hydraulic circuit (72) communicating a control chamber (68) of the master cylinder formed between the actuating rod and the actuating piston with a control chamber (144) of the servomotor , partly delimited by the control rod, so that actuation of the brake pedal causes displacement nt of the control rod in the direction of actuation of the assistance means, and a second hydraulic circuit (80) communicating an actuation chamber (152) of the servomotor delimited in part by the push rod with a actuation chamber (76) of the master cylinder delimited in part by the actuation piston, so that a displacement of the push rod controlled by the assistance means causes a displacement of the actuation piston in the direction of brake actuation.   2. Braking system according to claim 1, characterized in that the booster comprises a body (120) provided with a bore (122) in which slides the push rod (118), the latter comprising a tubular rear part in Which slides in sealed manner a front part forming a piston (112a) of the control rod (112), the control chamber (144) of the booster being formed in said tubular rear part, at the rear of said front part forming a piston, and the actuation chamber (152) of the booster being formed in the bore (122) formed in the body of the booster, at the front of the push rod, a first return means (128), interposed between the body of the actuator and the push rod, normally keeping the latter in a rear position of rest, and a second return means (140), interposed between the push rod and the control rod, normally maintaining the latter in a rear position of rest in the the assistance means are not actuated, the second return means (140) exerting a return force less than the first means of rapping (128).   3. braking system according to claim 2, characterized in that the first and second hydraulic circuits (72,80) are connected respectively to an inlet orifice (146) and an outlet orifice (154) formed in the body of the servomotor, the inlet orifice (146) communicating with the control chamber (144) of the servomotor through an annular space (148) formed between the body of the servomotor and the push rod, and at least a passage (150) formed in the tubular rear part of the latter, and the outlet orifice (154) opening directly into the chamber   actuator (152).   4. Braking system according to any one   of the preceding claims, characterized by   fact that the actuating piston (24b) of the barrel-cylinder has a tubular rear part in which slides in leaktight manner a front part forming a piston of the actuating rod (58), the control chamber (68) of the maltre- cylinder being formed in the tubular rear part of the actuating piston, at the front of the piston-forming front part of the actuating rod, and the actuating chamber (76) of the master cylinder being an annular chamber formed in the bore (22) of the master cylinder body, around the actuating rod, a first return means (36), interposed between the actuator body and the actuating piston, normally maintaining the latter in a position rear rest, and a second return means (66), interposed between the actuating piston and the actuating rod, normally maintaining the latter in a rear rest position, the second return means (66) exerting a force less reminder   That the first means of recall (36) of the master cylinder.   5. Braking system according to claim 4, characterized in that the first and second hydraulic circuits (72,80) are connected respectively to an outlet orifice (70) and an inlet orifice (78) formed in the body of the master cylinder, the inlet (78) opening directly into the actuation chamber (76) of the master cylinder, and the outlet (70) communicating with the control chamber (68) of the master cylinder through an annular space (46b) formed between the body of the master cylinder and the actuating piston, and through at least one passage (62) formed   in the tubular rear part of the latter.   6. Braking system according to claim, characterized in that the front part forming the piston of the actuating rod (58) carries a pin pin (64) whose ends slide in two oblong slots (62) formed in the rear part tubular of the actuating piston and constituting said passage formed in this last part.   7. Braking system according to any one   of claims 5 and 6, characterized in that.   that it further comprises a reservoir (16) communicating with said annular space (46b) of the master cylinder by a third orifice (44b) formed in the body of the master cylinder, this third orifice (44b) being controlled by a valve (46) provided with a valve (48) sensitive to the position of the actuating piston (24b) in the body of the master cylinder, said valve being normally open when the actuating piston   occupies its rear position of rest and self-closing   materially under the effect of a forward movement of the actuating piston.   8. Brake booster comprising a control rod (112) actuating assistance means (84,100) acting on a push rod (118), characterized in that the push rod (118) slides in a bore (122) formed in a body (120) of the actuator, and comprises a tubular rear part in which slides in sealed manner a front part forming a piston (112a) of the control rod (112). a control chamber (144) of the servomotor being formed in said tubular rear part, at the rear of said front part forming a piston, and an actuation chamber (152) of brakes being formed in the body of the servomotor, at the before the push rod, a first return means (128) interposed between the body (120) of the actuator and the push rod (118) normally maintaining the latter in a rear position of rest, and a second return means ( 140) interposed between the push rod (118) and the control rod (112) normally maintaining the latter in a rear position of rest, in which the assistance means are not actuated, The second rappeL means (140) exerting a lower restoring force   than the first recall means (128).   9. Booster according to claim 8, characterized in that the body (120) of the booster has an inlet orifice (146) which communicates with the control chamber (144) through an annular space (148) formed between the body of the booster and the push rod, and at least one passage (150) formed in the tubular rear part of the latter, the body of the booster also comprising an outlet orifice (154) which opens directly into the chamber brake actuation (152). 10. Master cylinder comprising a body (20) provided with a bore (22) in which slides in leaktight manner at least one brake actuation piston (24a, 24b), characterized in that it further comprises an actuating rod (58) of which a front part forming a piston slides in leaktight manner in a tubular rear part of the actuating piston, a control chamber (68) being formed in said tubular rear part, at the front of the front part forming a piston, and an annular actuating chamber (76) being formed in the bore, around the actuating rod and behind the tubular rear part, a first return means (36), interposed between the body and the actuating piston, normally maintaining the latter in a rear position of rest, and a second return means (66), interposed between the actuating piston and the actuating rod, normally maintaining the latter in a rear position of rest, the second means of ra ppel (66) exerting a lower restoring force than the first means of reminder (36).   11. Master cylinder according to claim, characterized in that the body (20) of the maltre-cylinder has an inlet orifice (78) which opens directly into the annular actuation chamber (76), and an orifice of outlet (70) which communicates with the control chamber (68) through an annular space (46b) formed between the body of the master cylinder and the actuating piston, and at least one passage (62) formed in the back part tubular of the latter.   12. Master cylinder according to claim 11, characterized in that the front part forming the piston of the actuating rod (58) carries a pin (64) whose ends slide in two oblong slots (62) formed in the part tubular rear of the actuating piston and constituting said passage formed in this last part.   13. Master cylinder according to any one   of claims 11 and 12, characterized in that   that a third orifice (44b) is formed in the body of the barrel-cylinder and opens into said annular space (46b), this third orifice being controlled by a valve (46) provided with a valve (48) sensitive to the position of the actuating piston (24b) in the body of the master cylinder, said valve being normally open when the actuating piston occupies its rear rest position and closing automatically under the effect of a forward movement of the actuating piston. oeo10 L'91Ji otp 00 /, 1: v / 9'Pq Eú06Z9- % 0 o N - 919 OlpI..CLMF: 01, 0   Zl /. 0.9 OAqz OZt 9 i <tZ 9Z 0) g sç 'iz 1Dg b 9 86X11 / 8 92.90 FIG. 3 4 14 84.4 132? 15 8 1I o 1 ,,. 84. 00 10 1982 15 18 t 14 _10   e, 146 143 144 1 A4._. 0 0 f 1,184 | s - 82