GB2044869A

GB2044869A - Hydraulic brake boosters

Info

Publication number: GB2044869A
Application number: GB8006568A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-03-01
Filing date: 1980-02-27
Publication date: 1980-10-22
Also published as: GB2044869B; JPS55119552A

Abstract

A hydraulic power brake valve 6 controls the supply of fluid from an accumulator 58 via chamber 75 and line 76 to working chambers 52, 53 behind master cylinder pistons 23, 43. Excessive movement of the valve spool 36 is prevented by a blocking arrangement 81. This comprises a piston 72 which is moved to the left by pressure (e.g. 100 bar) in chamber 75, so raising ball 71 to obstruct the spool 36. On failure of the pressure source, this movement is not obstructed, and the pedal 51 can move to the left to operate the pistons 23, 43 without power assistance. Loss of accumulator pressure results in piston 28 moving to the right, holding valve 62 closed so creating a hydraulic lock in chamber 63, so that the piston 43 moves with the input rod 42. <IMAGE>

Description

SPECIFICATION Improvements in or relating to hydraulic brake boosters The present invention relates to hydraulic brake boosters for braking systems for vehicles.

A variety of brake boosters are already known. A distinction is made between socalled power operated brake boosters and servo assisted brake boosters. In the case of power operated brake boosters, brake valves are used which introduce pressure into the brake system in proportion to the applied pedal force. These brake valves are generally used in a tandem or twin arrangement, in order to comply with the legal requirements with respect to genuine two-circuit brake systems. The most commonly used brake boosters are so-called power assisted boosters in which the booster unit is connected in tandem with a master brake cylinder.

Pneumatic boosters are widely used. However, increasing use has been made of hydraulic boosters in recent times. Furthermore, in recent times, boosters have been developed which take into account the special requirements of anti-lock systems and provide an integrated solution to the problem. In these constructions, certain functions of the brake force booster are jointly used for the anti-lock system. By way of example, the pistons of the master brake cylinders are used both for boosting the pressure and for the purpose of regulating the pressures for the anti-lock system. An additional aim of these boosters is to improve some hitherto disadvantageous properties of the boosters. By way of example, it is desirable that the travel of the brake pedal should not increase if a brake circuit should fail.A so-called step-up transient should then be taken into account which, compared with the conventional boosters (tandem arrangements), renders it possible to produce the same pressure with smaller pedal forces in the event of failure of the servo assisting power.

As a result of these requirements, including the requirements of the anti-lock system, these types of boosters normally act as power supply systems when the hydraulic energy supply is functioning, and as power-assisted systems if the servo assiting power should fail. This means that a pressure introduced by way of the control valve in proportion to the pedal force acts upon displacement pistons which then produce pressure on the secondary side in the brake system.

These types of brake boosters have changeover valve whose switching states relate to the function of the hydraulic power supply. These valves can be controlled by the accumulator pressure. A disadvantage of this solution resides in the fact that the valves are in each case switched to a second switching state only when the accumulator pressure falls below the minimum limit. Therefore, a demand exists for a hydraulic brake booster to be constructed such that a minimum number of parts should normally be in their rest position, that is to say, they should not become effective only in the event of a fault in the brake system.

According to the present invention there is provided a hydraulic brake booster for a vehicle brake system having a pressure source comprising essentially a pump and accumulator, which comprises an accumulator switch piston subjected to the accumulator pressure when in use, a control valve which controls a connector between the pressure source and master cylinder and a connection between the master cylinder and a pressure relief point, a separate arrangement for actuation of pistons in the master cylinder in the event of failure of the pressure source, and a hydraulic switching arrangement responsive to hydraulic pressure introduced by operation of the control valve for rendering said secured arrangement operable in the absence of said introduced hydraulic pressure.

A brake force booster embodying the present invention can have the following advantages: The hydraulic switching arrangement is controlled by the pressure introduced by the control valve. It is thereby ensured that the switching arrangement is actuated every time the brakes are fully applied. This condition can then indicate to the driver a fault in the actuating device in good time. Furthermore, a booster combined with an anti-lock system can be designed such that the entire arrangement can be constructed more advantageously by the use of electro magnetically operated valves. By way of example, by using master brake cylinder pistons located parallel to one another, it is conceivable to design the brake booster such that the stroke of the pistons only determines the brake pressure in the absence of accumulator pressure (servo power).In this case, a lower pressure, determined by the foot force applied by the driver, can be produced in the brake system. On the other hand, when the servo power is available, the required pressure is substantially higher in order, for example, to ensure maximum retardation of a heavily laden vehicle with smaller applied foot force. With the inclusion of the above-mentioned control valve, additional pressure medium could be fed to a secondary circuit to contribute to the increase in the brake pressure independently of, for example, servo power signals (a limit switch on the master brake cylinder piston) and pressure switches (controlled by the control valve).

Taking these facts into account, the proposed brake booster can be considerably shorter and thus of space-saving and weight-saving construction. Owing to the fact that a travel simulator determines the brake pedal force versus travel characteristic when the power supply is intact, and that the brake booster operates with relatively short pedal travels, the saving of space can be utilised to increase the usable passenger space. These advantages occur particularly when the transmission device is combined with the hydraulic brake force booster for the purpose of matching the actuating characteristic of the coupling to the brake pedal characteristic, optionally including a booster function.

The invention will be further described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic part sectional illustration of a hydraulic brake booster embodying a hydraulic switching arrangement according to one embodiment of the invention integrated with the brake booster, and Figure 2 is a diagrammatic part sectional illustration of part of a hydraulic brake booster and a hydraulic switching arrangement according to a second embodiment of the invention and disposed separately from the booster.

A hydraulic brake booster 1 has a housing 2 which incorporates three adjacently disposed multi-stepped bores 3, 4, and 5 for a control valve 6 and two master cylinders 7 and 8. A topping-up reservoir 9 is mounted on the housing 2 and has three chambers 10, 11 and 1 2. The chamber 10 is connected to the control valve 6 by way of a passage 13, the chamber 11 communicates with the master cylinder 8 by way of a passage 14, and the chamber 1 2 is connected by way of a passage 1 5 to a chamber 1 6 which is located at one end of the brake booster 1 and into which the bores 3 and 4 open and which is externally sealed by an end cover 1 7.

The cover 1 7 carries four pressure-operable switches 18, 18' and 19, 19' (illustrated only diagrammatically), the switch 1 8 being disposed on a level with the upper master cylinder 8, and the switch 1 9 being disposed on a level with the control valve 6. The switch 18 is actuated by a piston 20 forming the end wall of a cylinder 21 to which the passage 14 is connected and into which one end 22 of a piston 23 of the master cylinder 8 can enter in a sealed manner. A return spring 24 for the piston 23 is disposed in a spring chamber 25 which is connected to a brake circuit II by way of an outlet 26.

The switch 1 9 is actuated by the end of a piston rod 27 which is connected to an accumulator control piston 28. The piston 28 is disposed coaxially of the control valve 6 and is movable under accumulator pressure against the force of a spring 29. An accumulator pressure working cylinder is designated 30. The piston 28 carries a push rod 31 which extends into a chamber 32. The chamber 32 is on the one hand connected to the passage 13, and on the other hand can be connected to an auxiliary cylinder 63 in the master cylinder 7 by way of a spring-loaded non-return valve 62 closable by means of a push rod 61. A hydraulic switching arrangement 81 serves to restrict the travel of a valve spool 37 of the control valve 6 and comprises a stop device formed by a spherical stop member 71 co-operating with a sloping surface 70 on a piston rod 72 of an actuating piston 73.The piston 73 and the piston rod 72 are axially bored, so that a chamber 74 downstream of the piston 73 is subjected to the same pressure as a chamber 75 into which an end 36 of the valve spool 37 extends. The brake pressure introduced by the control valve 6 is fed to the chamber 75 by way of a line 76. Thus, the chamber 75 is a pressure-change chamber.

The other end of the valve spool 37 extends out of the housing 2 and carries a rubber spring 38 at this location. The rubber spring 38 is interposed between one end of a yoke 39 and a diaphragm 40 secured to the yoke.

The centre of the yoke 39 carries the auyS'iary piston 42 which constitutes the movable wall of the auxiliary cylinder 63. The rear of the auxiliary piston 42 is supported relative to the housing 2 by means of a disc spring 42'. The auxiliary cylinder 63 is disposed in a secondary piston 64 which is arranged coaxially with a piston 43 of the second master cylinder 7.

The piston 43 is movable in the master cylinder 7 against the force of a spring 44. A spring chamber 45 is connected to a brake circuit I by way of an outlet 46. A piston rod 47 passes through the spring chamber 45 and can enter an annular seal 48, the end of the piston rod 47 being guided by a head 49 which allows fluid to flow towards and away from the chamber 16.

The yoke 39 abuts against the housing 2 by way of a spring 41. An extension 50 of the master cylinder piston 23 is located opposite the other end of the yoke 39 with axial clearance therebetween. Furthermore, a brake pedal 51 acts approximately centrally upon the yoke 39. Chambers 52 and 53 are located downstream of the pistons 23 and 43 and are separately or commonly connectible to the pressure-change chamber 75 of the control valve 6 by way of an anti-lock adjusting member 66.

A suction line 55 is connected to the passage 1 3 connected to the topping-up reservoir chamber 10 and leads both to the adjusting member 66 and to a pump 56. A pressure line 57 commences from the pump 56 and leads to an accumulator 58 and, by way of a branch 59, into the accumulator pressure working cylinder 30. The pump 56 and the accumulator 58 form a pressure producer 56/58 of the brake booster 1. The pressure line branch 59 is connected to the control valve 6 by way of a longitudinal passage 60.

The apparatus described operates as fol lows:- When the pedal 51 is actuated, the yoke 39 and the spool 37 move to the left until the control valve 6 has changed over. Pressure medium from the pressure supply 56, 58 is introduced into the chambers 52 and 53, and the two pistons 23 and 43 move to the left in advance of the movement of the pedal. The two brake circuits I and II are supplied with pressure medium by way of the outlets 26 and 46 and by way of the anti-lock regulating device 66. The brakes are applied.

The end 36 of the valve spool 37 enters the pressure-change chamber 75. When the chamber 75 is pressurised, that is to say, when brake pressure is introduced, the piston 73 moves to the left from a pressure of approximately 100 bar, and the stop member 71 prevents further movement of the control valve 6 by virtue of the fact that the stop member 71 is lifted by the sloping surface 70 to block the spool 37. The spring 38 is then compressed upon further movement of the pedal 51, and the driver senses the effective brake force by way of the spring 38. The switch 1 8 gauges the brake pressure and the switch 1 9 senses the accumulator pressure.

The switch 19' is actuated by an extension 77 of the piston rod 72 and indicates the operation of the stop device 70/71. The switch 18' finally indicates too large a movement of the yoke 39, since the switch 18' is connected to the yoke by way of a rod 78.

The switch 18' thus indicates failure of the servo power.

If the accumulator pressure drops below a predetermined value, a connection has to be established between the yoke 39 and the two pistons 23 and 43, that is to say, the stop device 70/71 for the valve spool 37 has to remain inoperative. This is effected by the deficiency of brake pressure in the pressurechange chamber 75 and thus in the chamber 74. Consequently, the valve spool 37 can move further into the housing 2.

The push rod 61 closes the valve 62 in the event of failure of the reservoir pressure. The hydraulic charge in the auxiliary cylinder 63 then forms an incompressible support for the auxiliary piston 42. After the illustrated axial play has been covered, an arrangement for mechanical to hydraulic through control is then established in the master cylinders 7 and 8. The brakes are then actuated without booster action. Alternatively, the arrangement can be pureiy mechanical or purely hydraulic.

In this manner, relatively small travels of the pedal are rendered possible at full brake pressure, and the travel of the pedal is independent on the state of pressure relief of the brake system. When there is the risk of wheel lock, the regulating device 66 ensures corresponding pressure relief in the brake lines leading to these wheels which are suspected of locking.

Fig. 2 shows a brake force booster embodying some components of indentical construction to those illustrated in Fig. 1. Therefore, the same reference numerals are used for corresponding parts. Furthermore, a number of control valves are shown which, for the most part, are required for the anti-locking function. These control valves are the valves VI and VII (three port, two position valves) located at the primary side (p). The two port, two position valves Vla and Vlb for the brake circuit I, and the two port, two position valves Vlla and Vllb for the brake circuit II are shown at the secondary side (s) of the master brake cylinder pistons 23 and 43.A three port, two position control valve V is illustrated at the primary side of the brake circuit II and, when in its starting position (no pressure in the line PB,), provides a connection between the secondary side of the master brake cylinder piston 43 for the brake circuit I and the primary side of the master brake cylinder piston 23 for the brake circuit 11.

In the event of failure of the servo power supply a control pressure is not produced in the primary circuit acted upon by the control valve 6, with the result that the two master brake cylinder pistons 23 and 43 are connected in series by way of the valve V with respect to their efficacy and the production of pressure. When the servo power supply is intact, the brake pressure (PB,) switches the valve V to its second position, thus isolating the two master brake cylinder pistons from one another.

It will be seen that, in the embodiment of Fig. 2, the three port, two position valve V consitutes a hydraulic actuating device which is actuable by the pressure introduced by the control valve 6.

An additional two port, two position valve V, is shown and its purpose is to introduce additional pressure medium into the secondary circuit in the event of the switch 1 8 being actuated by the master cylinder piston 23. A signal corresponding to actuation of the switch 1 8 designated SBr is additionally logically combined in an electronic control circuit 80 with signal designated Sp which is supplied by the pressure swiched 19' when it is actuated by the piston 73. A pre-requisite for actuation of the valve V, is that the signal Sp appears before the signal SB,. If the signals arrive in the reverese sequence, the brake circuit is leaking or some other fault exists such as failure of circuit I or II.In this case also, the pilot valve Vx is actuated for a short period of time in order to fill the brake circuit.

In this case, however, a warning lamp 79 is activated to indicate a fault. The control valves can be actuated electro-magnetically by, for example, corresponding control by the electronic control circuit by way of a solenoid coil or by way of the central control of a multiposition valve.

The brake booster 1 is constructed such that, together with the size and stroke of the master cylinder pistons 23 and 43, it can reliably maintain emergency operation if the accumulator pressure should fail. The strokes of the master cylinder pistons 23 and 43 then correspond to their actuating travel imparted to the brake pedal 51.

The same pressure medium is used for the entire brake system. Alternatively, however, it is possible to use for boosting on the primary side a pressure medium different from that used in the brake circuits.

Preferably, the valves V1, V", Via, Vib, Villa Vllb and Va can be actuated electro-magnetically and can be combined as a central control in the multiple adjusting member 66 in a single housing as illustrated in Fig. 1.

Claims

1. A hydraulic brake booster for a vehicle brake system having a pressure source comprising essentially a pump and accumulator, which comprises an accumulator switch piston subjected to the accumulator pressure when in use, a control valve which controls a connection between the pressure source and master cylinders and a connection between the master cylinders and a pressure relief point, a separate arrangement for actuation of pistons in the master cylinder in the event of failure of the pressure source, and a hydraulic switching arrangement responsive to hydraulic pressure introduced by operation of the control valve for rendering said separate arrangement operable in the absence of said introduced hydrau lic pressure.

2. A hydraulic brake booster as claimed in claim 1, in which the switching arrangement comprises a stop device which when in use is brought into the path of movement of the control valve when the pressure introduced by the control valve, exceeds a predetermined value.

3. A hydraulic brake booster as claimed in claim 2, in which the stop device comprises a sloping surface on a piston rod of an actuat ing piston and a spherical stop member which rides on the sloping surface, and the stop member is movable along a path substantially at right angles to the axis of the actuating piston by the sloping surface during a control valve stopping operation.

4. A hydraulic brake booster as claimed in claim 1, 2 or 3, in which the hydraulic switching arrangement is combined with a wheel anti-lock system.

5. A hydraulic brake booster as claimed in any of claims 1 to 5, in which the hydraulic switching arrangement during its movement causes actuation of an electrical pressure switch whose response value lies at approxi mately 100 bar.

6. A hydraulic brake booster as claimed in claim 1, in which hydraulic switching arrangement is a three port, two position valve which is fitted in the primary side of that one of the master cylinders which when in use supplies a second brake circuit and by way of which the primary side can be connectible either to the secondary side of that one of the master cylinders which when in use supplies a first brake circuit or to the primary side thereof.

7. A hydraulic brake booster as claimed in claim 6, including a two port, two position solenoid valve responsive through an electronic control circuit to a switching signal indicative of a drop in the accumulator pressure and/or of a drop in the brake pressure, whereby the first and second brake circuit can be replenished by the accumulator.

8. A hydraulic brake booster as claimed in any of claims 1 to 7, in which the size and stroke of the pistons in the master cylinder pistons of the booster are designed for emergency piston operation in the event of failure of the accumulator pressure, the piston stroke corresponding to the actuating travel of the brake pedal.

9. A hydraulic brake booster as claimed in any of claims 1 to 8, in which the same pressure medium is used for the entire brake system.

10. A hydraulic brake booster as claimed in any of claims 1 to 8, in which the pressure medium used in the brake system for boosting is different from that used for operating the brakes.

11. A hydraulic brake booster as claimed in any of claims 1 to 10, in which additional brake pressure regulating valves primarily for anti-lock purposes are electro-magnetically actuated and are combined in a multiple adjusting member in a single housing.

1 2. A hydraulic brake booster for a vehicle brake system, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 1 or Fig. 2 of the accompanying drawings.