GB2175660A

GB2175660A - Braking pressure generator

Info

Publication number: GB2175660A
Application number: GB08612028A
Authority: GB
Inventors: Juan Belart
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1985-05-22
Filing date: 1986-05-16
Publication date: 1986-12-03
Also published as: FR2582275B1; GB2175660B; FR2582275A1; DE3518288C2; DE3518288A1; GB8612028D0

Abstract

In a vacuum brake booster and master cylinder (34) assembly a push rod (14) coupled to a movable wall (2) of the brake booster displaces a first piston (33) in a stepped bore (29) of a housing (34,34a), the said first piston (33), via a pressure fluid column enclosed in an annular chamber (37) displaces a second smaller diameter piston (31) faster into a pressure chamber (40) which is in communication with a wheel brake. On vacuum failure, a compression spring (48) displaces a flexible diaphragm (44) disposed in an inner chamber of the first piston (33) to, in turn, via plungers (49,49'), opens valves (50,51,50',51'), via which the pressure fluid in the annular chamber (37) can flow back into a hydraulic reservoir. The first piston (33), via an extension (38) with a shoulder (41) engages the second piston (31) causing an equally rapid displacement of the second piston (31). As the effective hydraulic cross-sectional surfaces (F-f and F'-f, respectively) of the two pistons (33,31) are of different sizes, normally - with the brake force booster intact - the second piston (31) is displaced faster than the first one. <IMAGE>

Description

SPECIFICATION Braking pressure generator This invention relates to a braking pressure generator comprising a vacuum-operated brake force booster and a master cylinder, wherein a push rod coupled to a movable wall of the brake force booster is coupled to a first piston displaceably disposed in a bore of a housing of the master cylinder which is connected to a vacuum housing, with the said first piston acting on a second piston and with the bore of the master cylinder housing being of a stepped-bore configuration.

Brake systems of the type under consideration are known in the art wherein, with the brake applied, in case of a failure of the vacuum-operated brake force booster, a piston rod pivoted to a brake pedal will force a valve piston of a double-valve in a control housing against a reaction means, then forcing the latter by entraining the control housing and the movable wall against the push rod co-operating with a push rod piston such that a braking pressure can be built up in a pressure chamber of the master cylinder.However, this conventional system involves the disadvantage that the brake pedal in the event of a failure of the vacuum brake force booster is required to be displaced by a comparatively extended distance before build-up of a braking pressure, with the pedal force to be applied to overcome the lost travel, moreover, being relatively high as the efficient cross-section of the piston of the master cylinder remains unchanged in size and is now required to be displaced without any supporting force by the pedal force alone.

Moreover, a tandem master cylinder for a hydraulic brake system is also known in the art (West German DAS 24 60 529), a primary piston of which is adjustable by a driven member of a pedal operated brake force booster having a movable wall, through which a fluid pressure difference can be generated, comprising a means which in the event of a failure of the operating pressure of the brake force booster automatically reduces the pedalactuating efforts and for this purpose comprises a valve preloaded into the open position and by the operating pressure of the brake force booster forced into the closed position, which valve controls the connection between a fluid reservoir and a pressure chamber.For this purpose, the said means includes an auxiliary piston of a larger diameter than that of the primary piston, with the auxiliary piston being disposed between the driven member of the brake force booster and the primary piston of the master cylinder, and with the pressure chamber being formed by a control pressure chamber between the auxiliary piston and the primary piston, i.e. a chamber separated from the primary pressure chamber and the secondary pressure chamber of the master cylinder. However, the said conventional tandem master cylinder of this type involves the disadvantage that in the event of a failure of the vacuum, the pedal will sag through by a comparatively large distance corresponding to the primary piston and the auxiliary piston mating and being jointly displaceable as a mechanical unit.

The present invention thus aims to overcome the disadvantages involved with the prioar art brake force booster including a master cylinder, and to provide a brake system which permits, at the available operating pressure, a reduced pedal travel of the booster and which, upon failure of the operating pressure, will switch over the master cylinder to a smaller efficient piston surface thereby permitting an abrupt change in ratio.

According to the present invention there is provided a braking pressure generator comprising a vacuum-operated brake force booster and a master cylinder, wherein a push rod coupled to a movable wall of the brake force booster is coupled to a first piston displaceably disposed in a bore of a housing of the master cylinder connected to a vacuum housing, with the said first piston acting upon a second piston, wherein the bore of the master cylinder housing is of a stepped-bore configuration, characterised in that the first or actuating piston comprises an interior chamber subdivided by a bellows or flexible diaphragm into two chambers, of which one chamber, via channels provided in the bottom of the first piston, is in communication with a vacuum chamber of the brake force booster, and the second chamber is in communication either with the atmosphere or with a chamber a head of the first piston, which second chamber is filled with pressure fluid and is under atmospheric pressure, with the first piston being displaceable in a large diameter portion of the bore of a stepped-bore configuration of the master cylinder housing, and being provided with a longitudinally extending projection plunging into a blind-end bore of the second or push rod piston, with the blind-end bore, on the one hand, being in communication with a compensating or pressure fluid reservoir in use of the generator and, on the other hand, via channels or a longitudinal bore in the projection and, via a valve actuated by the flexible diaphragm, being in communication with an annular chamber confined by the projection, the first and second pistons and the bore in the master cylinder housing.

Preferably, on the one hand, pressure is applied by a compression spring to the diaphragm subdividing the cavity in the first piston into two chambers and, on the other hand, the diaphragm acts, directly or via plungers, on the valve member of the valve inserted into the pressure fluid passage from the longitudinal bore of the projection to the annular chamber.

The projection of the first piston, moreover, comprises a stop, a flange or a shoulder which, in the initial position of the piston, is in abutting relationship with the second piston.

In the practice of the invention, the annular surface of the second piston to which the pressure fluid from the annular chamber disposed between the first and second pistons is applied, is smaller dimenioned than the effective cross-sectional area of the first piston.

Advantageously, the projection of the first piston comprises a further projection, a nose or shoulder on which is supported a spring applying pressure to the closure member of the valve in the closing sense.

Feasibly, the longitudinal bore of the projection terminates into a further chamber which, via bores, is in communication with the annular chamber and which, through a wall or bottom portion is separated from the second chamber ahead of the flexible diaphragm, with bores being provided in the wall and in the bottom portion, respectively, accommodating plungers respectively with the booster-sided ends thereof being in abutting relationship with the flexible diaphragm and respectively with the master cylinder-sided ends thereof being connected to closure members, sealing cones or sealing bulges controlling the pressure fluid passage through bores establishing a connection between the annular chamber and the further chamber.

The first piston moved by the push rod of the brake force booster is furnished with a bottom portion which, at the master cylindersided interior surface thereof, comprises a stem in abutment with the flexible diaphragm if vacuum is applied to the vacuum chamber of the booster.

In a preferred form of embodiment, the second chamber on the side of the flexible diaphragm facing the master cylinder, via a bore, communicates with a recess or groove in the inner wall of the bore for the first piston, with the recess or groove, in turn, via a channel, being in communication with the atmosphere.

Embodiments of the invention will now be decribed with reference to the accompanying drawings, in which: Figure 1 is a sectional view of one embodiment of a brake force booster along with an associated master cylinder, and Figure 2 is a partial sectional view of a brake force booster with a master cylinder according to another embodiment.

The brake force booster according to Figure 1 includes a vacuum housing 1 subdivided by an axially movable wal! 2 into a working chamber 3 and a vacuum chamber 4. The axially movable wall 2 consists of a diaphragm plate 5 of deep-drawn sheet and a flexible diaphragm 6 in abutment therewith to form a rolling diaphragm serving as a seal between the outer circumference of the diaphragm plate 5 and the vacuum housing 1.

A control valve 9 actuated by the piston rod 8 includes a control valve piston 10 connected to the piston rod 8 which, in the control valve housing 11, will release valve ports such that the working chamber 3 in the nonoperated position as shown is in communication with the vacuum chamber 4 via air ducting channels extending laterally in the control valve housing 11 and terminating frontsidedly (the left hand end as shown) circumferentially of the control valve housing 11.

Upon operating the control valves 9, i.e. on an axial displacement of the piston rod 8, the connection between the vacuum chamber 4 and the working chamber 3 will be interrupted, and the working chamber 3 will be brought into communication with the atmosphere such that the movable wall 2 moves toward the vacuum chamber 4.

The brake force, via a rubber-elastic (resilient) reaction plate 13 accommodated in a front-sided depression of the control valve housing 11 (the left hand end as shown) and via a push rod 14 comprising a head flange 15, is transferred to a driving piston 33 of a master cylinder 34 of a brake system which, at the vacuum-sided end of the brake force booster is provided on a front wall 7.

A compression spring 16 supported on the front wall 7 of the vacuum housing 1 and on the diaphragm plate 5, maintains the movable wall 2 in the initial position as shown.

A plate-shaped member 21 locks the head flange 15 of the push rod 14 in a recess 25 of the control valve housing 11.

When actuating the brake pedal, the piston rod 8 with the valve piston 10 is displaced to the left against the force of springs 17, 17', with spring 17 of a poppet valve 23 forcing the latter to the left onto a seat 22 in the control housing 11 thereby closing the air ducting channel 12. During continued movement, valve piston 10 moves away from the poppet valve 23 thereby opening the passageway to the atmosphere. Now, the way is clear for the outdoor (atmospheric) air to pass through a control bore 26 in the control housing 11 to the right of the valve piston 10 thereby reducing the vacuum in the working chamber 3. The force resulting from the pressure difference prevailing on the right and on the left of the movable wall 2 will displace same against the force of the compression spring 16 as well as the push rod 14 and the first cylinder 33 in the master cylinder 34 to the left. The pressure built up in an annular chamber 37 of the master cylinder 34 after traversing of a compensating port and an intake channel 52, respectively, by a cup seal 36, via the push rod 14, will apply a reaction force to the reaction disc 13 in accordance with the transmission ratio. The reaction pressure, also, is transferred to the valve piston 10 thereby displacing same to the right to be mounted with seat 18 thereof sealingly on poppet valve 23; thus, the air ducting channel 12 and the outdoor air passage 26 are closed. Valve piston 10, hence, has taken its so-called ready-for-operation position.

With the brake fully applied, the outdoor air passageway will be permanently opened thereby adjusting the maximum attainable pressure difference on the movable wall 2 and, hence, the maximum supporting pressure.

The control pressure of the device has thus been attained. No higher pressure in the master cylinder 34 can now be attained unless additional force is applied to the piston rod 8 by the driver's pedal force. With the brake pedal completely released, the valve piston 10 will return into its initial position, with the outdoor air passageway 26 being closed and the vacuum passageway 12,27,28 being permanently opened.

As a result of the vacuum compensation on the movable wall 2 automatically involved therewith, no force will any longer be applied thereto, and the restoring force of spring 16 will be adequate to return the same into its released position. Also piston 33 of master cylinder 34 will, hence, return into its released position.

As shown in Figure 1, the master cylinder 34, in addition to a larger-sized diameter bore 29 comprises a bore 30 of smaller diameter receiving a longitudinally displaceable second piston 31 (push rod piston). The second piston 31 is provided with a blind-end bore 32 in which is guided a projection 38 of the first piston 33 (driving piston). The second piston 31 is provided with a sealing cup 39 and acts upon the pressure fluid provided in the piston chamber 40 (brake circuit 1), which pressure fluid, via the connecting port 71, is in communication with a wheel brake. The projection 38 of the first piston 33 is furnished with a shoulder 41 which in the initial position is in abutment with the second piston 31.

The cup-shaped part of piston 33 which is moved by push rod 14, comprises a cavity which, at the booster-sided end, is closed by a bottom portion 43. Disposed in the cavity is a diaphragm 44, the marginal bulge 45 of which is clamped between the bottom portion 43 and the inner wall of the first piston 33 to separate a chamber 42 from a space 46 which, via channels 47,47' provided in the bottom portion 43, is in communication with the vacuum chamber 4. Provided between the bottom portion 43 and the diaphragm 44 is a compression spring 48 forcing the diaphragm 44 against a plurality of plungers 49,49' guided through bores 50,50' disposed in the bottom portion of the first piston 33. Plungers 49,49' are supported on a ring 19 surrounding the projection 38 and to which pressure is applied by a spring 20 which, in its turn, is supported on a shoulder 24 of the projection 38.Plungers 49,49', respectively at the ends thereof being in abutment with ring 19, comprise cone-shaped portions or sealing bulges 51,51' that seal bores 50,50' in a pressuretight manner in the event that the plungers 49,49' are displaced toward the push rod 14 of the booster. The annular chamber 37 enclosing the projection 38, via the compensating bore or an intake channel 52 extending in the wall of the master cylinder housing 34, is in communication with a port 53 to which is connected a pressure fluid reservoir or a compensating tank (not shown). The connecting port 53, moreover, via a bore 54, is in communication with an annular chamber 55 surrounding the second piston 31, which annular chamber 55, in its turn, via a radial bore 56, is connected to the blind-end bore 32 of the second piston 31.Piston chamber 40 ahead of the second piston 31, via a breather bore 57 is in communication with the connecting port 53 and, via a connecting port 58 and a connecting bore 71, respectively, is in communication with a wheel brake (not shown).

The example of embodiment according to Figure 2 is distinguished from the one according to Figure 1 in that the longitudinal bore 59a of the projection of the first piston 33a terminates into a chamber 60 which, admittedly, via bores 50a,50a', is in communication with the annular chamber 37a but is not confined by diaphragm 44. Diaphragm 44 is separated by a wall 61 or by a bottom portion 68 from the chamber 60, with bores 67,67' including seals, being provided in the wall 61 through which are guided the plungers 49,49' in sealing manner which respectively with the one ends thereof are in abutment with the diaphragm 44 and with the other ends thereof are in abutment with the ring 19.The chamber 42a at the master cylinder 34a side of the diaphragm 44, via a bore 62, is in communication with a groove or recss 63 longitudinally extending in the wall of the bore 29a of the master cylinder 34a which groove or recess in its turn, via a channel 64, is in communication with the atmosphere such that the chamber 42a in case of a longitudinal displacement of the first piston 33a is always under atmospheric pressure.

The operation of the braking pressure generator composed of master cylinder 34 and brake force booster 1 is as follows: While the engine of the motor vehicle is running, a vacuum prevails both in the vacuum chamber 4 and in the chamber 46 of the first piston 33 as the bottom portion 43 includes channels 47,47' interconnecting the two chambers. As a result of the vacuum also prevailing in the chamber 46, the diaphragm 44 is drawn, against the force of the compression spring 48, to the right toward the anvil or stem 65, with plungers 49,49' along with the ring 19 being displaced to the right by spring 20 until the cone-shaped sealing bulges 51,51' close the bores 50,50' thereby separ ating the annular chamber 37 from the chamber 42.As the connecting port 53 of the master cylinder 34 is in permanent communication with a pressure fluid reservoir (not shown), pressure fluid is contained in the annular piston chamber 55, the blind-end bore 32, the longitudinal bore 59 of the projection 38, the chamber 42 and also in the annular chamber 37, with the communication between the connecting port 53 and the annular piston chamber 55 being established by a radial bore 54, and the communication between the annular piston chamber 55 and the blind-end bore 32 being established via a radial bore 56.If upon initiation of a braking operation, the brake pedal (not shown) is pressed down, the piston rod 8 is dipslaced to the left thereby actuating the control valve 9 to allow outdoor (atmospheric) air to flow into the working chamber 3 and cause the movable wall 2 along with the push rod 14 to move to the left thereby moving, at the same time, also the first piston 33, as the push rod 14 with the master-cylinder-sided end thereof-in clearance-free manner-is in abutment with the bottom portion 43 of the first piston 33.

During displacement of the first piston 33, in the direction of actuation (viewed in the arrow A direction), first, cup seal 36 will traverse the intake channel 52 terminating in the annular chamber 37 to subsequently build up an excess pressure in the annular chamber 37 which now acts upon the rear-sided annular surface 66 of the second piston 31 of the master cylinder 34 thereby displacing the same to the left (viewed in the arrow A direction). However, as the effective cross-sectional area F-f of first piston 33 is larger than the efficient cross-sectional area F'-f of the second piston 31, the second piston 31 precedes the first piston 33 (abrupt change in ratio) building up the braking pressure in the piston chanmber 40 which propagates via the connecting port 58 and the connecting bore 71, respectively, toward the wheel brake (not shown).

In the event of a failure of the brake force booster, i.e. if no vacuum is available in the vacuum chamber 4, the compression spring 48 will push the diaphragm 44 to the left so as to enable the plungers 49,49' with the sealing bulges 51,51' and the ring 19 thereof to open bores 50,50' at the front-sided wall of the first piston 33. If the push rod 14, via the control valve piston 10 and the reaction disc 13, is now displaced by the piston rod 8 connected to the brake pedal in the actuating sense, then also the first piston 33 will move in the arrow A direction; however, in that case, no pressure can build up in the annular chamber 37 as there is a permanent communication between the annular chamber 37 and the connecting port 53.The shoulder 41 of the projection 38 will get into abutment with the rear-sided annular face 66 of the second piston 31 such that the two pistons 33 and 31 displace uniformly (together) (the second piston, hence, in that case, does not precede the first piston 33 in the sense of an abrupt change in ratio).

The operation of the embodiment according to Figure 2 is distinguished from the one according to Figure 1 in that the chamber 42a is always under atmospheric presure as, via bore 62, recess 63 and channel 64, it is in communication with the outdoor (atmospheric) air.

Plungers 49,49', in the event of a failure of the vacuum in the vacuum chamber 4 and, hence, in chamber 46a, are displaced to the left (arrow A (Figure 1) direction) such that the sealing bulges 51,51' open the bores 50a,50a, interconnecting the annular chamber 37a and the chamber 60. For that purpose, plungers 49,49' are held and guided in corresponding bores 67,67' in the bottom 68 of the first piston 33a, with the plungers, by means of seals (not identified in any closer detail) being sealed against the bottom and the wall 61, respectively such that the diaphragm 44a will not get into contact with the pressure fluid contained in the master cylinder 34a and chamber 60, respectively. Exactly as in the form of embodiment according to Figure 1, all pistons 33a,31 of the master cylinder 34a move at a uniform rate in the event of a failure of the vacuum, with no abrupt change in ratio occurring.

Claims

1. A braking pressure generator comprising a vacuum-operated brake force booster and a master cylinder (34,34a), wherein a push rod (14) coupled to a movable wall (2) of the brake force booster is coupled to a first piston (33,33a) displaceably disposed in a bore (29,29a) of a housing (34,34a) of the master cylinder connected to a vacuum housing (7), with the said first piston (33,33a) acting upon a second piston (31), wherein the bore (29,29a) of the master cylinder housing (34,34a) is of a stepped-bore configuration, characterised in that the first or actuating piston (33,33a) comprises an interior chamber subdivided by a bellows or flexible diaphragm (44) into two chambers (42,42a, 46,46a), of which one chamber (46,46a), via channels (47,47') provided in the bottom (43) of the first piston (33,33a), is in communication with a vacuum chamber (4) of the brake force booster, and the second chamber (42,42a) is in communication either with the atmosphere or with a chamber (32) ahead of the first piston (33,33a), which second chamber is filled with pressure fluid and is under atmospheric pressure, with the first piston (33,33a) being displaceable in a large diameter portion of the bore (29,29a) of a stepped-bore configuration of the master cylinder housing (34,34a), and being provided with a longitudinally extending projection (38,38a) plunging into a blind-end bore (32) of the second or push rod piston (31), with the blind-end bore (32), on the one hand, being in communication with a compensating or pressure fluid reservoir in use of the generator and, on the other hand, via channels or a longitudinal bore (59,59a) in the projection (38,38a) and, via a valve (50,51 ,50',5 1 ',50a,50a') actuated by the flexible diaphragm (44), being in communication with an annular chamber (37,37a) confined by the projection (38,38a), the first and second pistons (31,33 and 31,33a, respectively) and the bore (29,29a) in the master cylinder housing (34,34a).

2. A braking pressure generator according to claim 1, characterised in that the diaphragm (44) subdividing the interior chamber of the firt piston (33,33a) into two chambers (42,46 and 42a,46a, respectively), on the one hand, is subjected to a pressure application by a compression spring (48) and, on the other hand, acts directly or via plungers (49,49') on valve member of the valve (50,50',51,51' and 50a,50a', respectively) provided in the pressure fluid passageway from the longitudinal bore (59,59a) of the projection (38,38a) to the annular chamber (37,37a).

3. A braking pressure generator according to claim 1 or claim 2, characterised in that the projection (38,38a) of the first piston (33,33a) comprises a stop, a flange or a shoulder (41,41a) which, in the initial position of the two series-arranged first and second pistons (31,33 and 31,33a, respectively) is in abutting relationship with the second piston (31).

4. A braking pressure generator according to any one of claims 1 to 3, characterised in that an annular surface (66) of the second piston (31) disposed between the first piston (33, 33a) and the second piston (31) and to which pressure fluid is applied is smaller dimensioned than the effective cross-sectional area (F-f) of the first piston (33,33a).

5. A braking pressure generator according to any one of the preceding claims, characterised in that the projection (38,38a) of the first piston (33,33a) comprises a further projection a nose or a shoulder (24,24a) supported on which is a spring (20) applying pressure to the valve (50,50',51,51', 50a,50a') in the closing sense.

6. A braking pressure generator according to any one of the preceding claims, characterised in that the longitudinal bore (59a) of the projection (38a) terminates into a further chamber (60) which, via bores (50a,50a'), is in communication with the annular chamber (37a) and, by a wall or a bottom portion (68), is separated from the second chamber (42a) ahead of the flexible diaphragm (44), with bores (67,67') being provided in the wall and in the bottom portion (68), in which bores are disposed plungers (49,49') which respectively with the booster-sided ends thereof are in abutting relationship with the flexible diaphragm (44) and which respectively with the master cylinder-sided ends thereof are connected to closure members or sealing bulges (51,51') controlling the passage of pressure fluid through bores (50a,50a') establishing a connection between the annular chamber (37a) and the further chamber (60).

7. A braking pressure generator according to any one of the preceding claims, characterised in that the first piston (33,33a) moved by the push rod (14) of the brake force booster is provided with a bottom portion (43) which, on the master cyinder-sided interior surface thereof comprises an anvil or pin (65) with which the flexible diaphragm (44) gets into abutment if vacuum is applied to the vacuum chamber (4) of the booster.

8. A braking pressure generator according to any one of the preceding claims, characterised in that the second chamber (42a) on the side of the flexible diaphragm (44) facing the master cylinder (34a), via a bore (62), communicates with a recess or groove (63) in the interior wall of the bore (29) for the first piston (33a), with the recess or groove (63), provided with a channel (64), being in communication with the atmosphere.

9. A braking presure generator according to any one of the preceding claims, characterised in that the second piston (31) of the master cylinder (34,34a) circumferentially thereof comprises a recess or groove which, on the one hand, via an orifice or bore (56) in the second piston (31), is in communication with the blind-end bore (32) for receiving the projection (38,38a) of the first piston (33,33a) and, on the other hand, via a channel or bore (54) disposed in the wall of the master cylinder housing (34,34a), is in use in communication with the compensating or pressure fluid reservoir.

10. A braking pressure generator according to any one of the preceding claims, characterised in that a seal (69) is provided between the projection (38) plunging into the blind-end bore (32) of the second piston (31) and the second piston (31).

11. A braking pressure generator according to any one of the preceding claims, characterised by a sliding member or ring (19) enclosing the projection (38,38a) of the first piston (33,33a) and to which pressure is applied by a spring (20), which ring (19) co-operates with one or several valve members of said valve, for example, sealing bulges (51,51') which, either directly or via plungers (49,49') are displaceable by the flexible diaphragm (44), with the plungers (49,49') being passed through bores (50,50' and 50a,50a', respectively) in the wall portion of the first piston (33,33a) facing the annular chamber (37,37a).

12. A braking pressure generator according to any one of the preceding claims, characterised in that the master cylinder housing (34,34a) comprises a bore (29,29a) of a two step type configuration in which are disposed three pistons (33, 33a and 31 and 70, respectively) in a series arranged manner and longitudinally displaceable, of which the first piston (driving piston 33,33a) adjacent the vacuum housing (1) and actuated by the push rod (14) is disposed in the large-sized step of the bore (29,29a) and the second piston (push rod piston 31) and the third piston (intermediate piston 70) are disposed in the small-sized step of the bore (29,29a), with the second piston (push rod piston 31), at the end thereof facing the vacuum housing (1) comprising the blind-end bore (32) in which is guided the projection (38,38a) connected to the first piston (driving piston 33,33a) in a sealing and longitudinally displaceable manner such that the annular chamber (37,37a) foWcned between the projection (38,38a), the first and second pistons (driving piston 33,33a and push rod piston 31, respectively) and the interior wall of the bore (29,29a) and filled with pressure fluid transfers, by forming a hydraulic rod linkage, the movement of the first piston (driving piston 33,33a) to the second piston (push rod piston 31)

13. A braking pressure generator substantially as herein described with reference to and as illustrated in Figure 1 or Figure 2 of the accompanying drawings.