GB2194009A

GB2194009A - Hydraulic power booster

Info

Publication number: GB2194009A
Application number: GB08718772A
Authority: GB
Inventors: Hajo Pickel
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1986-08-16
Filing date: 1987-08-07
Publication date: 1988-02-24
Anticipated expiration: 2007-08-07
Also published as: GB8718772D0; FR2602835A1; DE3627902A1; GB2194009B; FR2602835B1

Abstract

In an hydraulic power booster (1), in particular for a motor vehicle brake system with anti-lock control, a housing (4) accommodates a pressure chamber (48) which is connectible with a pressure fluid source (11) via an inlet chamber (8) that is confined by a circumferential portion of the booster piston (5), the housing (4) and two annular seals (9, 10), via an axial bore (19) communicating with the inlet chamber (8) and via a supply valve (22), and is connectible with a supply reservoir (17) via a discharge valve (24). Both valves (22,24) are designed as seat valves in the booster piston (5) and are actuatable in dependence upon the position of an actuating piston (20). To accomplish reduction of its response and actuating force, the booster piston (5) is designed as a two-step piston whose small piston step (7) confines the inlet chamber (8), with the supply valve and the discharge valve (22,24) being arranged one behind the other coaxially relative to the two piston axes and with the pressure chamber (48) being interposed between the large piston step (6) and the inlet chamber (8). <IMAGE>

Description

SPECIFICATION Hydraulic power booster This invention relates to an hydraulic power booster, in particular for a motor vehicle brake system, and in particular with anti-lock control, wherein a housing accommodates a pressure chamber which is arranged between a booster piston and a coaxial actuating piston and which is connectible with a pressure fluid source via an inlet chamber that is confined by a circumferential portion of the booster piston, the housing and two annular seals, via an axial bore communicating with the inlet chamber and via a supply valve, and is connectible with a supply reservoir via a discharge valve, both valves being designed as seat valves in the booster piston and being actuatable in dependence upon the position of the actuating piston.

In a known power booster of this type (West German printed and published patent application 2909685), the inlet chamber for the pressure fluid is arranged on the booster piston circumference with the largest diameter.

In this case, both seals of the inlet chamber are continuously pressurised by the high inlet pressure so that they produce a correspondingly high friction force requiring a correspondingly higher actuating force.

In order to reduce this actuating force, it is known to arrange a pressure reducing valve between the pressure fluid source and the power booster (West German printed and published patent application 3218194), which valve reduces the inlet pressure down to the required minimum value. However, this pressure reducing valve is an accessory unit which is not absolutely required for the functioning of the power booster but increases the costs and the susceptance to failure of the power booster.

It is an object of the present invention to create a power booster of the aforementioned type, wherein the friction of the seals acted upon by the inlet pressure is reduced but ad ditionai costs are avoided.

According to the present invention there is provided an hydraulic power booster wherein a housing accommodates a pressure chamber which is arranged between a booster piston and a coaxial actuating piston and which is connectible with a pressure fluid source via an inlet chamber that is confined by a circumferential portion of the booster piston, the housing and two annular seals, via an axial bore communicating with the inlet chamber and via a supply valve, and is connectible with a supply reservoir via a discharge valve, both valves being designed as seat valves in the booster piston and being actuatable in dependence upon -the position of the actuating piston, characterised in that the booster piston is designed as a two-step piston whose small piston step with the small outside diameter confines the inlet chamber, in that the supply valve and the discharge valve are arranged one behind the other coaxially relative to the piston axes, and in that the pressure chamber is interposed between the large piston step with the large diameter and the inlet chamber.

In this arrangement, a pressure reducing valve is omitted on the inlet side. Yet, the force of pressure acting upon the seals sealing the inlet chamber is lower due to the smaller diameter of the small piston step so that the friction of the seals is correspondingly lower when the booster piston is displaced. The series connection of the supply valve and the discharge valve facilitates not only the formation of a piston step with a smaller outside diameter but ensures, in addition, that the booster piston is not actuated eccentrically by the actuating piston via those valves, as is the case with the aforementioned power booster, so that the power booster has no canting tendency which would again increase the actuating force.

Preferably, it is provided that an outlet chamber, communicating with the supply reservoir over a full piston stroke, is defined by the circumference of the small piston step at the end of the inlet chamber which is remote from the large piston step, said outlet chamber being sealed by means of one of the two annular seals and by a third annular seal. In this manner, the leakage of the inlet chamber seal directed away from the larger piston step is drained off towards the supply reservoir allowing, at the same time, the discharge of the pressure-controlled pressure fluid over a full working stroke up to the closing of the discharge valve.

In a power booster for a motor vehicle brake system with anti-lock control (also called ABS = anti-locking system or slip control), wherein an end face of the booster piston directed away from the pressure chamber bears against a coaxial working piston of a master cylinder of the brake system, which working piston acts upon a working chamber, the working piston being sealed relative to the housing and confining, in co-operation with the housing and said end face of the booster piston, a second outlet chamber communicating with the supply reservoir, a pressure-sensitively actuatable blocking valve can be arranged in a connecting line between the second outlet chamber and the supply reservoir, and the pressure chamber of the power booster can be connected with a control inlet of the blocking valve via a slip-sensitively actuatable main valve, and with the second outlet chamber after part of the working piston's stroke has been performed. As long as no slip occurs, the pressure fluid is, in this arrangement, forced out of the second outlet chamber towards the supply reservoir via the open blocking valve on actuating the booster piston, and the working piston is entrained by the booster piston's feed. On the other hand, on releasing the booster piston, the pressure fluid can also escape freely out of the second outlet chamber into the supply reservoir via the open blocking valve. However, as soon as a slip occurs and the booster piston is actuated, the main valve which has been closed beforehand is opened and the blocking valve is controlled by the outlet pressure of the main valve so as to assume its closed position.Due to the closed blocking valve, the pressure fluid can then no longer be discharged out of the second outlet chamber, so that a further displacement of the working piston by the booster piston and thus a brake pressure increase is impossible. If, however, the working piston has already performed the short partial stroke before a slip occurs and the main valve is opened, the pressure fluid can directly flow out of the working chamber of the power booster into the second outlet chamber and can reset the power booster piston, the second outlet chamber acting, at the same time, as a resetting chamber and a re newed normal braking operation being pos sible immediately after the slip has disap peared.In spite of the unpressurised follow-up stroke required for the booster piston in order to enable an unpressurised discharge of the leakage fluid entering the first outlet chamber out of the inlet chamber, a.relatively short overall length of the power booster is achieved in this manner.

In this connection, a throttling fluid inlet bore in the housing communicating, on the inlet side, with a pressure outlet of the main valve can, in particular, be connected, on the outlet side, with the second outlet chamber after having been covered by the working piston when the partial stroke has been performed. In this manner, a connection between the outlet side of the main valve and the sec ond outlet chamber is already established upon completion of the partial stroke of the working piston and before the occurrence of a slip. When a slip occurs, the reset of the booster piston after the opening of the main valve can thus take place without an abrupt pressure build-up being generated in the second outlet chamber as long as the blocking valve is closed by means of the outlet pressure of the main valve.

In order to lock the working chamber of the working piston relative to the supply reservoir communicating with the working chamber via the main valve in the event of an actuation of the booster piston as long as the fluid inlet bore has not been covered by the working piston and/or its seal, a non-return valve is arranged between the outlet of the main valve and the fluid inlet bore, which non-return valve permits a pressure fluid flow in the opposite direction towards the second outlet chamber when the anti-lock control responds.

Instead of the provision of a non-return valve, the fluid inlet bore may also extend into an annular chamber when the working piston is in its unactuated position, said annular chamber being confined by the working piston and the housing as well as by two annular seals arranged between the working piston and the housing.

If the booster piston bears against the working piston through the intermediary of a coaxial bolt, said bolt may have a mushroomshaped head. Said mushroomshaped head ensures a coaxial power transmission from the booster piston to the working piston so that the working piston is not loaded eccentrically and will not cant. This will contribute to a reduction of the actuating force.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a motor vehicle brake system, with anti-lock control, equipped with an hydraulic power booster according to the invention; and Figure 2 shows a section through a variant of a part of the brake system according to Figure 1.

According to Figure 1, an hydraulic power booster 1 acts upon a master cylinder 2 of a motor vehicle brake system with anti-lock control. The hydraulic power booster 1 comprises in a stepped bore 3 of an axially subdivided two-part housing 4 a stepped booster piston 5 with a large piston step 6 and a small piston step 7, the diameter of the piston step 6 exceeding that of the piston step 7.

The small piston step 7 confines, in cooperation with the housing 4, an inlet chamber 8 surrounding the small piston step 7, which inlet chamber is, in addition, axially sealed by means of two annular seals 9 and 10 arranged between the housing 4 and the piston step 7. Pressure fluid is conducted from a pressure fluid source 11, comprising a pump 13 with a non-return valve 14 located downstream thereof and, in parallel to that, a pressure accumulator 15, said pump 13 being driven by a motor 12 and the suction side of said pump 13 being connected with the supply reservoir 17 via a filter 16, into the annular chamber 8 via a supply line 41 and an inlet aperture 18 formed in the housing 4. The small piston step 7 includes a coaxially stepped bore 19, wherein an actuating piston 20 is axially displaceably Located, and which communicates with the inlet chamber 8 via a radial bore 21. In the bore 19, a supply valve 22 is coaxially disposed, and in a coaxial bore 23 of the actuating piston 20, a discharge valve 24 is disposed. Both valves 22 and 24 are seat valves.

The supply valve 22 is provided with a ballshaped spring-loaded closure member 25.

which is urged against an annular valve seat member 26 by means of the spring force and the pressure fluid supplied via the radial bore 21. The discharge valve 24 comprises also a spring-loaded valve closure member 27 with a ball. The valve closure member 27 is urged against an annular valve seat member 28 by means of the spring force and the pressure fluid supplied via the supply valve 22 into the bore 23. The valve closure member 27 is coaxially bolted to a tappet 29 which pushes the supply valve 22 open in dependence upon an actuation of the actuating piston 26.

The actuating piston 20 is sealed relative to the bore 19 in the small piston step 7 by means of two annular seals 30 and 31. The annular seals 30, 31 ensure, at the same time, an axial sealing of an annular chamber 33 between the circumference of the actuating piston 20 and the bore 19, which annular chamber 33 communicates with the bore 23 via a radial bore 32. The annular chamber 33 is connected with an outlet chamber 35 via a radial bore 34 in the housing 4, said outlet chamber 35 surrounding the small piston step 7 and being confined by the latter in cooperation with the housing 4.The outlet chamber 35 is sealed in axial direction by means of the annular seal 10 and another annular seal 36, the annular seal 36 being only subjected to the low outlet pressure since the outlet chamber 35 conmmunicates with the unpressurised supply reservoir 17 via a bore 37, a connection aperture 38 and a return line 39. The return line 39 communicates, in addition, via a pressure relief valve 40 with the supply line 41 leading from the outlet of the pressure fluid source 11 to the inlet aperture 18.

The actuating piston 20 is axially secured in the bore 19 by means of a circiip 42 and is actuated by means of a brake pedal 43 via an actuating rod 44.

The annular seal 36 is axially secured by means of a circlip 45 which, in its turn, is axially secured by means of the radial flange of a sleeve 46 which bears against the chassis of the motor vehicle (not shown) via a pressure spring 47.

The large piston step 6 confines a pressure chamber 48 on the side of the small piston step 7, which pressure chamber is connected with a chamber 51 arranged between the two valves 22 and 24 in the bore 19 via a bore 49 running radially through the small piston step 7 and via a bore 50 which is located parallel to the axis. !n addition, the pressure chamber 48 is connected with an inlet of an electromagnetically actuatable main valve 54 via a radial bore 52 and a line 53. The main valve 54 is a three-way/two-position valve which is operated by means of a slip monitoring circuitry, which is not illustrated, in the event of a vehicle wheel slip occurring, i.e. it is switched from the depicted closed position into an open position.

The face of the large piston step 6 of the booster piston 5 confines, on the one hand, a second outlet chamber 55 in the bore 3 and abuts, on the other hand, on a first working piston 56 of the master cylinder 2 through the intermediary of intermediate discs, said master cylinder being sealed relative to the bore 3 of the housing 4 by means of an annular seal 57. A guide pin 58 protrudes into coaxial blind-end bores arranged in the face of the large piston step 6 of the booster piston 5, on the one hand, and in the back of the working piston 56, on the other hand.

The working piston 56 confines with its face a working chamber 59 in the bore 3 of the housing 4 on one side, which working chamber is confined on the other side by the back of a "floating" second working piston 60. A pressure spring 61 is arranged between the ends of the two working pistons 56 and 60, which ends are directed towards each other.

The second working piston 60 is provided with a circumferential groove 62 confining an annular chamber 63 in cooperation with the housing 4. The annular chamber 63 communicates with the working chamber 59 via a radial bore 64, an axial bore 65 and a central valve 66 in the working piston 60. The closure member 67 of the central valve 66 is coupled with the working piston 56 by means of a cap screw 68 so as to be displaceable relative to the working piston, but it can be entrained by the working piston 56. The working chamber 59 is sealed relative to the annular chamber 63 by means of a sealing cup 69.

The second working piston 60 confines with its end face a second working chamber 70 on one end, which working chamber is confined on the other end by a valve seat member 71 of a central valve 72, the valve seat member 71 being sealed relative to the bore 3 by means of a sealing cup 73. The valve closure member 74 of the central valve 72 is axially displaceably guided in the valve seat member 71 and connected with the second working piston 60 by means of a cap screw 75, the cap screw 75 again being axially displaceable in the working piston and the valve closure member 74 being entrainable by the working piston 60 via the cap screw 75.

The working chamber 70 is sealed relative to a third outlet chamber 76 by means of the sealing cup 73 and relative to the annular chamber 63 by means of a sealing cup 77 encompassing the working piston 60. A pressure spring 78 between the end face of the working piston 60 and the valve seat member 71 urges the latter and the working piston 60 apart.

The outlet chamber 76 communicates with the supply reservoir 17 via a bore 79, a connection aperture 80 and a line 81.

The central valve 72 blocks the connection of the working chamber 70 towards the outlet chamber 76.

The annular chamber 63 communicates, in addition, with the supply reservoir 17 via a radial housing bore 82, a line 83, the main valve 54, a line 84, a housing bore 85, a connection aperture 86 and a line 87.

The outlet chamber 55 communicates with the line 84 via a housing bore 88, a line 89, a pressure-actuatable blocking valve 90 in the form of a two-way/two-position valve and a line 91. The outlet side of the main valve 54 is, furthermore, connected with the control inlet of the blocking valve 90 by means of a line 92 branching off the line 83, on the one hand, and with the working chamber 59 via a non-return valve 93 as well as a fluid inlet bore 94 having a throttling effect, on the other hand. The fluid inlet bore 94 extends into the working chamber 59 in a place where the distance to the end face of the working piston 56, when the latter is in its unactuated position, is small.

The pressure chamber 48 is, furthermore, connected with the rear wheel brakes 97, 98 via the line 53 and an electromagnetically actuatable two-way/two-position valve 95 which is normally open, as well as via a line 96.

The working chamber 59 is connected with a front wheel brake 103 via a housing bore 99, a line 100, an electromagnetically actuatable two-way/two-position valve 101 and a line 102. In the same manner, the working chamber 70 is connected with another front wheel brake 108 via a housing bore 104, a line 105, an electromagnetically actuatable two-way/two-position valve 106 and a line 107. The directional control valves 101 and 106 are of the same form as the directional control valve 95 and are also actuated by means of the slip monitoring circuitry in the event of a slip occurring.

In addition, the lines 96, 102 and 107 are connectible with the; return line 84 via an electromagnetically actuatable, normally blocked (closed) two-way/two-position valve 109, 110 and 111, respectively, and are actuatable by means of the slip monitoring circuitry.

If a braking operation is initiated by applying an actuating force F onto the- brake pedal 43, at first the valve seat 28 is urged against the valve closure member 27 by means of the actuating piston 20 and the discharge valve 24 is closed, and then, after a short additional travel of the piston 20, the supply valve 22 is pushed open by means of the tappet 29 thus allowing pressure fluid to flow from the pressure fluid source 11 via the inlet chamber 8 and the supply valve 22, which is now open, via the chamber 51, the axial bore 50 and the radial bore 49 into the pressure chamber 48.

The pressure which is being built up in the pressure chamber 48 causes a displacement of the booster piston 5, which has, so far, been held back by means of the friction force of the annular seals 9, 10 and. 36, in the direction of the actuating piston 20 until the supply valve 22 is closed again so that a pressure which is proportional to the brake force F is being built up in the pressure chamber 48 and acts on the rear wheel brakes 97 and 98 via the two-way/two-position valve 95. Due to the displacement to the left of the booster piston 5, the pressure fluid is pressed out of the outlet chamber 55 to the supply reservoir 17 via the open blocking valve 90, and the working piston 56 is displaced simultaneously, the valve 66 thus being closed and the pressure in the working chamber 59 being increased.The non-return valve 93 prevents a discharge of the pressure fluid out of the working chamber 59 via the fluid inlet bore 94 until the fluid inlet bore 94 has been covered by the annular seal 57 of the working piston 56. The pressure increase in the working chamber 59 causes not only an actuation of the front wheel brake 103 through the intermediary of the open two-way/two-position valve 101 but also a displacement of the second working piston 60 and, simultaneously, a closing of the valve 72 and a pressure increase in the working chamber 70 so that the same pressure which acts upon the front wheel brake 103 also acts upon the other front wheel brake 108 via the open twoway/two-position valve 106. On releasing the brake pedal 43, the pistons 5, 56 and 60 are reset by means of the pressure springs 61 and 78.

If, during an actuation of the brake pedal 43, an inadmissibly high slip value is reached on one or several vehicle wheels and a locking tendency occurs, for example, on the front wheel with the front wheel brake 103, the slip monitoring circuitry transmits actuating signals to the two-way/two-position valves 101 and 110 which, as a result, change their switching state so that the connection between the working chamber 59 of the master cylinder 2 and the wheel brake 103 is interrupted and a connection is established between the wheel brake 103 and the common return line 84 via the valve 110 now providing a free passage.

When the valves 101, 110 assume such a position, pressure fluid is drawn from the wheel brake 103 and transmitted to the supply reservoir 17 so that the wheel cylinder pressure in the wheel brake 103 decreases.

The directional control valves 95, 109 and/or 106, 111 are actuated correspondingly when the slip monitoring circuitry detects a critical slip value on the associated wheels.

As soon as the slip monitoring circuitry sets in, the electromagnetic main valve 54 is switched over, the connection between the annular chamber 63 and the return line 84 thus being interrupted, the connection between the pressure chamber 48 and the line 83, however, being switched through. The outlet pressure of the main valve 54 causes, on the one hand, a blocking of the blocking valve 90 and, on the other hand, a pressurisa tion of the outlet chamber 55 now acting as a resetting chamber via the non-return valve 93 and the fluid inlet bore 94 as long as the annular seal 57 is situated on the left-hand side of the fluid inlet bore 94. The booster piston 5 is now reset by means of the pressure which is being built up in the outlet chamber 55.At the same time, the working pistons 56 and 60 are reset until the annular seal 57 covers the fluid inlet bore 94 again, whereby the pressure fluid in the outlet chamber 55 is enclosed and a displacement of the booster piston 5 is prevented. When the slip has disappeared, the full actuating stroke is immediately available again.

Due to the pressure fluid supply from the source 11 via the small piston step 7 of the booster piston 5, the annular seals 9 and 10 are subjected to a lower radial pressurisation than is the case in the event of a design of the inlet chamber on the circumference of the large piston step so that a lower friction force occurs between the annular seals 9 and 10 and the booster piston, which results in a correspondingly lower response force. In this case, an unpressurised follow-up of the booster piston 5 over the full working stroke is required in order to drain the leakage of the rear annular seal 10 towards the supply reservoir 17 and to ensure the discharge of the pressure-controlled pressure fluid. The elongation of the power booster by a full stroke length which is due to this follow-up is, however, avoided by a reduction of the overall length of the resetting unit.This reduction is achieved in that the working piston 56 must only effect a partial stroke until it covers the fluid inlet bore 94 so that on occurrance of a slip, the pressure fluid can flow into the resetting chamber 55 and can force the booster piston 5 back to the partial stroke position.

Another advantage of this power booster consists in that it is now provided with only one unpressurised external seal, the annular seal 36, the leakage of which is practically unimportant.

Figure 2 shows a modified part of the brake system according to Figure 1, like parts having been marked alike. In this variant, a second annular seal 57a has been provided on the circumference of the working piston 56' instead of the non-return valve 93 according to Figure 1 and has been arranged such that the fluid inlet bore 94 extends into an annular chamber 112 between the two annular seals 57 and 57a on the circumference of the working piston 56' when the working piston 56' assumes its unactuated position.

Due to the replacement of the non-return valve 93 by the annular seal 57a, the mode of operation of the brake system is not changed.

In addition, the guide pin 58 according to Figure 1 has been replaced in the embodiment according to Figure 2 by a bolt 113 with a mushroom-shaped head 114 which bears against the bottom of a blind-end bore 115 in the large piston step 6 of the booster piston 5 and ensures a better concentric transmission of the pressure force of the booster piston 5 to the working piston 56'.

Claims

1. An hydraulic power booster wherein a housing accommodates a pressure chamber which is arranged between a booster piston and a coaxial actuating piston and which is connectible with a pressure fluid source via an inlet chamber that is confined by a circumferential portion of the booster piston, the housing and two annular seals, via an axial bore communicating with the inlet chamber and via a supply valve, and is connectible with a supply reservoir via a discharge valve, both valves being designed as seat valves in the booster piston and being actuatable in dependence upon the position of the actuating piston, characterised in that the booster piston (5) is designed as a two-step piston whose small piston step (7) with the small outside diameter confines the inlet chamber (8), in that the supply valve and the discharge valve (22, 24) are arranged one behind the other coaxially relative to the piston axes, and in that the pressure chamber (48) is interposed between the large piston step (6) with the large diameter and the inlet chamber (8).

2. A booster according to claim 1, characterised in that an outlet chamber (35), communicating with the supply reservoir (17) over a full piston stroke, is defined by the circumference of the small piston step (7) at the end of the inlet chamber (8) which is remote from the large piston step (6), said outlet chamber being sealed by means of one (10) of the two annular seals (9,10) and by a third annular seal (36).

3. A booster according to claim 1 for a motor vehicle brake system With anti-lock control, wherein an end face of the booster piston (5), which end face is directed away from the pressure chamber (48), bears against a coaxial working piston (56,56') of a master cylinder (2) of the brake system, which working piston acts upon a working chamber (59), the working piston (56,56') being sealed relative to the housing (4) and confining, in cooperation with the housing (4) and said end face of the booster piston (5), a second outlet chamber (55) communicating with the supply reservoir (17), characterised in that a pressuresensitively actuatable blocking valve (90) is arranged in a connecting line (84-91) between the second outlet chamber (55) and the supply reservoir (17), and in that the pressure chamber (48) of the power booster (1) is connectible with a control inlet of the blocking valve (90) via a slip-sensitively actuatable main valve (54) and with the second outlet chamber (55) after part of the working piston's stroke has been performed.

4. A booster according to claim 3, characterised in that a throttling fluid inlet bore (94) in the housing (4) communicating, on the inlet side, with a pressure outlet of the main valve (54) is connectible, on the outlet side, with the second outlet chamber (55) after having been covered by the working piston (56,56') when the partial stroke has been performed.

5. A booster according to claim 4, characterised in that the connection between the control inlet of the block valving (90) and the fluid inlet bore (94) accommodates a non-return valve (93).

6. A booster according to claim 4, characterised in that the fluid inlet bore (94) extends into an annular chamber (112) when the working piston (56') is in its unactuated position, said annular- chamber being confined by the working piston (56') and the housing (4) as well as by two annular seals (57,57a) arranged between the working piston (56') and the housing (4).

7. A booster according to any one of claims 3 to 6, wherein the booster piston (5) bears against the working piston (56') via a coaxial bolt (113), characterised in that the bolt (113) has a mushroom-shaped head (114).

8. An hydraulic power booster for a motor vehicle brake system with anti-lock control substantially as herein described with reference to and as illustrated in Figure 1 or Figure 2 of the accompanying drawings.