GB2036222A

GB2036222A - Hydraulic motor-vehicle brake system

Info

Publication number: GB2036222A
Application number: GB7940599A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1978-11-25
Filing date: 1979-11-23
Publication date: 1980-06-25
Also published as: GB2036222B; DE2851134A1; JPS5576732A; JPS643698B2

Abstract

A hydraulic braking system has an accumulator 35 connected in parallel with anti-skid control valves 22, 23, so that if these valves are closed when movement of the master cylinder pistons starts, there will be no substantial build-up of pressure in the master cylinder until the master cylinder piston seals have cleared the recuperation ports 6, 7. <IMAGE>

Description

SPECIFICATION An hydraulic motor-vehicle brake system This invention concerns an hydraulic motorvehicle brake system.

A brake system is known from German Offenlegungsschrift No. 2705467 in which the master cylinder is in communication with the wheel brake cylinders and is provided with a fluid reservoir feeding fluid to the master cylinder through an auxiliary port. In hydraulic brake systems in which an auxiliary port serves as a controlling means, because of the marked inflexibility of the brake system, that is, its small capacity, the problem arises that, on braking, a system pressure builds up before the rear of the fluid seal overruns the auxiliary port. Consequently, the fluid seal may be damaged.

In brake systems provided with anti-locking devices, this problem is further increased in two ways. On the one hand, owing to the intrinsic throttling effect of the anti-locking device, on rapid application of the brakes a substantial pressure is generated, notwithstanding the shortness of the piston stroke in the master cylinder, and, on the other hand, when the anti-locking system comes into operation, the frictional coefficients being low, the master cylinder piston is urged back towards its original position, whereby the shoulder of the primary fluid seal is moved back to a position opposite the dangerous rim of the auxiliary port. Consequently, failure of the primary fluid seal repeatedly occurs, particularly in cases where there is limited flexibility between the anti-locking device and the master cylinder.

According to the present there is provided a hydraulic brake system for motor-vehicles comprising an hydraulic master cylinder having a fluid reserve and an auxiliary port, hydraulic wheel brake cylinders to which fluid is applied from the master cylinder, and an anti-locking device, means being provided where by the intrinsic throttling effect of the anti-locking device may be by-passed, such that between the master cylinder and the wheel brake cylinders there is achieved an unthrottled displacement of fluid in the region where a primary fluid seal of the master cylinder passes over the auxiliary port in the master cylinder, there being provided a corresponding storage of fluid when the anti-locking system is in operation.

The brake system according to the present invention has the advantage that by by-passing of the intrinsic throttling effect of the antilocking device, damage to the primary fluid seal due to the use of an anti-locking device is prevented. Moreover when the anti-locking device comes into operation, the storage capacity of the brakes is not returned completely to the master cylinder, but is stored in the region of the return pump.

The invention will now be described further by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a circuit diagram of a dualcircuit brake system, showing two methods of construction of the by-pass system for bypassing the intrinsic throttling effect of the anti-locking system; Figure 2 shows an auxiliary storage device associated with the return pump; Figure 3 is a graph of the embodiment of Fig. 2; Figure 4 is a graph of a combination of the auxiliary storage device and a damper; Figure 5 shows an auxiliary storage device on the low-pressure side of the return pump; and Figure 6 is a graph of the embodiment of Fig. 5.

An hydraulic motor-vehicle brake system has a dual-circuit tandem master cylinder 1 comprising two reservoir fluid tanks 2 and 3, which are combined in a common housing, each tank being connected via a respective replenishment bore 4, 5 and auxiliary port 6, 7 to a corresponding primary and secondary chamber in the master cylinder 1. The master cylinder 1 is connected by brake circuits I and II to respective pairs of wheel cylinder 8, 9 and 10, 11. In each brake circuit I, II there is provided a respective anti-locking device 12, 13, in which the brake circuits I and II are subdivided into individual brake lines 14, 15, 1 6 and 1 7 for each respective wheel cylinder 8, 9, 10 and 11.Furthermore, each antilocking device 12, 1 3 has a storage reservoir 18, 19 and a storage reservoir 20, 21, which, if desired, may be in the form of auxiliary storage devices. It is not essential that every storage reservoir 18 to 21 is provided with an auxiliary storage device, but the reservoirs 18, 1 9 and 20 may be fitted with such an auxiliary storage device. Each anti-locking device 12, 1 3 also has two solenoid valves 22, 23 and 24, 25 respectively, a suction valve 26, 27, a pressure valve 28, 29, and two return pumps 30, 31, which are driven by a common motor 32.

Furthermore, in one of the two brake circuits, I, II, or, alternatively, in both brake circuits, there is provided a by-pass line 33, which is arranged between the master cylinder 1 and and the wheel cylinders, and via which the anti-locking devices 1 2 and 1 3 may be by-passed. In the by-pass iine 33 there is provided an auxiliary storage device 35, comprising substantially a piston 39, which is displaceceable in a housing 37 against the force of a spring 38. The auxiliary storage device 35 is necessary for the brake-applying process. The use of an auxiliary storage device 35 in both brake circuit I and II is advantageous but not essential, for example in certain brake systems the use of a storage device in both circuits will ensure that the vehicle does not pull to one side when the brakes are applied.

The auxiliary storage devices, which, if desired, may be integral with the storage reser voirs 1 8 and 19, are combined with the storage chambers of the return pump, which storage chambers are necessary for the anti locking device. Fig. 5 shows such an auxiliary storage device provided with a piston 40, which, during its working stroke, is at first subjected only to the force of a spring 41. A second spring 42, having a predetermined initial loading, comes into operation only after further displacement of the piston 40. In a preferred embodiment illustrated in Fig. 1 the pressure characteristic of reservoir 1 9 in Fig.

1 corresponds to the graph shown in Fig. 3, that of reservoir 1 8 corresponds to the graph shown in Fig. 6 and that of reservoir 20 corresponds to the graph shown in Fig. 4.

Thus the auxiliary storage device at the reservoirs 19, 20 corresponds to the type shown in Fig. 2. The auxiliary storage device at the reservoir 1 8 corresponds to the type shown in Fig. 5. These are only preferred constructions and alternative arrangements are envisaged.

The storage reservoir 21 is as illustrated in Fig. 1 preferably a conventional reservoir without a special mechanism. Such a mechanism can be omitted there, because the two brake circuits in the master cylinder 1 influence each other reciprocally, i.e. the floating piston of circuit I influences, because of its support the rod-type piston of the brake circuit II.

A damper or throttle incorporated in the circuit and associated with one or both of the reservoirs 20, 21 modifies the characteristics of the device illustrated in Fig. 2.

An auxiliary storage chamber 43 is connected via the valve 26, 27 to a respective pump 30, 31, and via a non-return valve 44, 44', to a respective branch line 48, 48' leading back to the master cylinder 1. On the initiation of the anti-locking action, the auxiliary storage chambers 18, 1 9 are connected via the respective solenoid valves 22 and 23, 24 and 25 to the wheel cylinders 8 and 9, 10 and 11.

The auxiliary storage chamber which is integral with the respective storage reservoir 20, is connected to the pump 30, 31 via the pump outlet valve 28, 29, or, if necessary, via a non-return valve 49 to the branch line 48, 48' leading back to the master cylinder 1.

Optionally the reservoir 21 may have an auxiliary storage device. The auxiliary storage devices in the storage reservoir 20 (and in the storage reservoir 21 when present) are illustrated more clearly in Fig. 2 and are idential in construction to the auxiliary storage device 35. They comprise a piston, which, in its neutral state, is held by pre-loaded spring against the stop, and which has a pre-determined working stroke.

Between the low-pressure side and the high-pressure side there is shown a further pipeline 50, incorporating a non-return valve 51, which line 50 may be selectively used whenever pressure compensation is desired because of differences in temperature.

The method of operation is as follows: On normal braking, brake fluid is forced from the foot-operated master cylinder 1 through the open solenoid valves 22, 23, 24 and 25 of the anti-locking devices 1 2 and 1 3 to the wheel cylinders 10, 11, 12 and 13, and as a result the brakes are applied. if the foot pressure is relaxed, the fluid, relieved of pressure, flows back to the master cylinder 1.

During this process, the shoulders of the two primary fluid seals in the master cylinder 1 overrun the auxiliary ports 6 and 7 without damage to the fluid seals, since the applied pressure in the brake system is not particularly high in the critical region of the piston stroke.

However, should panic braking be necessary, the driver depresses the brake pedal completely and particularly in a brake system whose flexibility is limited, a substantial pressure is very quickly generated, which, when the auxiliary ports 6 and 7 are overrun, particularly the auxiliary port 7 of the brake circuit I, remote from the pedal, is already of such a magnitude that the shoulder of the fluid seal may be damaged.

According to the present invention, however, on panic braking the auxiliary storage device 35 provided in the by-pass line 33 of one or both circuits enters into operation, piston 39 being displaced against the force of the spring 38. The intrinsic effect of the antilocking device is thereby avoided, a corresonding volume of fluid being displaced directly into the respective brake cylinders 8 and 9, 10 and 11, without an excessive increase in the system pressure in the critical fluid seal region of the stroke.

If, during such a braking process, or other braking occasion, locking of one or more wheels should occur, the respective anti-locking device 12, 1 3 starts to operate, whereby brake fluid is removed from the wheel cylinders 8, 9, 10 and 11 and pumped by the return pump 30, 31 back to the master cylinder 1. In known systems, the shoulders of the primary fluid seals in the master cylinder 1 are thereby moved back again to the region of the auxiliary ports 6 and 7, and, since this takes place when the pressure in the pipeline is high (since the brake pedal is still being operated), in such a case also the fluid seals may be damaged.

According to the present invention, in one case this is prevented by virtue of the fact that the return pump 30, 31 does not return the fluid directly to the master cylinder 1, but to the respective auxiliary storage device 20, 21.

Thus, on the compression side of the pump 30, 31, isolated from the master cylinder 1 by the non-return valve 49, there is created a storage capacity corresponding in volume' to such a displacement of the master-cylinder piston as is necessary to remove the fluid seal shoulder from the region of the auxiliary ports 6 and 7, that is, a volume of between 1 and 2 cm3. Discharge of the stored fluid from the auxiliary storage devices 20 and 21 to the master cylinder 1 takes place only when the pressure in the master cylinder 1 is reduced to zero; only then does the non-return valve 49 open.

Fig. 4 shows a graph of an alternative embodiment of a storage device in combination with a damping device.

Alternatively, however, for the same purpose, it is possible to provide a similar device on the input side of the pump, instead of on the output side. For this purpose there is created in the auxiliary storage devices 1 8 and 1 9 a storage capacity which absorbs the necessary quantity of fluid within a pressure range which is smaller than that of the opening pressure of the pump inlet valve 26, 27.

Thus, during the anti-locking process, that is, on the drop in pressure in the wheel cylinder, first of all no return of fluid takes place until the auxiliary storage capacity has been filled and the pressure then further increases. In such a device also, the discharge of the auxiliary storage capacity to the master cylinder is effected via an additional non-return valve when the pressure in the master cylinder has fallen to such a level that its packing rings have moved away from the region of the auxiliary ports in a direction to release the brakes.

Claims

1. An hydraulic brake system for motorvehicles comprising an hydraulic master cylinder having a fluid reserve and an auxiliary port, hydraulic wheel brake cylinders to which fluid is supplied from the master cylinder, and an anti-locking device, means being provided whereby the intrinsic throttling effect of the anti-locking device may be by-passed, such that between the master cylinder and the wheel brake cylinders there is achieved an unthrottled displacement of fluid in the region where a primary fluid seal of the master cylinder passes over the auxiliary port in the master cylinder, there being provided a corresponding storage of fluid when the anti-locking system is in operation.

2. A brake system as claimed in claim 1 in which the means are a connectible and disconnectible auxiliary storage device for a proportion of the hydraulic brake fluid, and that the volume of fluid storable by the auxiliary storage devices corresponds at least to the volume displaceable in said region of the master cylinder piston.

3. A brake system as claimed in claim 2, in which a return pump removes brake fluid from the wheel cylinders during the anti locking control phase, and in which the auxiliary storage device is arranged in the region of the return pump a non-return valve being provided so that the fluid stored in the auxiliary storage device may be isolated from the master cylinder, which fluid is dischargeable into the master cylinder only when the master cylinder is at zero pressure.

4. A brake system as claimed in claim 3, in which the auxiliary storage device is arranged on the compression side of the return pump.

5. A brake system as claimed in claim 3, in which the auxiliary storage device is arranged on the suction side of the return pump.

6. A brake system as claimed in claim 5, in which the non-return valve is preset to a lower opening pressure than the opening pressure of a pump inlet valve of the return pump.

7. A brake system as claimed in claim 5, in which the fluid is stored in the auxiliary storage device at a pressure lower than the opening pressure of the inlet valve to the return pump.

8. A brake system as claimed in any of claims 1 to 7, in which parallel with the brake line incorprating the anti-locking device there is provided a by-pass line which connects the master cylinder to the brake cylinders and in which the auxiliary storage device is inserted.

9. A brake system as claimed in claim 8, in which the auxiliary storage device comprises a piston which is able to perform a stroke corresponding to a displacement of between 1 and 2 cm3.

1 0. A brake system constructed and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

CLAIMS (26/2/80)

1. An hydraulic brake system for motorvehicles comprising an hydraulic master cylinder having a fluid reserve and an auxiliary port, hydraulic wheel brake cylinders to which fluid is supplied from the master cylinder, and an anti-locking device, means being provided whereby an unthrottled displacement of fluid or, in the case of the anti-locking system being in operation, a corresponding storage of fluid is achieved between the master cylinder and the wheel brake cylinders with the intrinsic throttling effect of the anti-locking device being by-passed, for the region in which a primary fluid seal of the master cylinder passes over the auxiliary pprt in the master cylinder.