GB2128279A

GB2128279A - Hydraulic brake master cylinder and booster arrangement

Info

Publication number: GB2128279A
Application number: GB08326202A
Authority: GB
Inventors: Heinz Leiber
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1982-10-02
Filing date: 1983-09-30
Publication date: 1984-04-26
Also published as: FR2533874A1; GB8326202D0; DE3236582A1; JPS5984652A

Abstract

Pedal-actuated plunger 2 actuates a control valve arrangement 3 by way of an interposed travel simulator spring 4 for the purpose of introducing a primary pressure from auxiliary pressure supply 5 into chamber 14 which acts both upon the primary piston 7 of tandem master brake cylinder and upon the plunger 2. Closed brake circuits 11, 12 are connected to the two pressure chambers of the tandem master brake cylinder. In the event of failure of supply 5, plunger 2 acts by means of plate 2a directly on piston 7. A monitoring device comprising position sensors 2b, 7a and 8a, gives an indication when the supply fails. <IMAGE>

Description

SPECIFICATION Hydraulic brake pressure generator The invention relates to a hydraulic brake force generator for vehicle brake systems, containing a dual-circuit tandem master brake cylinder and a pedal-actuated plunger which actuates by way of an interposed travel simulator a control-valve arrangement to cause a primary pressure to act on a piston of said tandem master brake cylinder and on said pedal-actuated plunger.

A brake pressure generator of this kind is known from German Offenlegungsschrift No.

2 531 264.5 in which the control-valve arrangement, actuated by way of the brake pedal, is accommodated in the primary piston. The pressure of the pressure source (pump and accumulator) is normally effective in the pressure chamber located upstream of the primary piston.

The control-valve arrangement produces from this pressure a pressure which reacts upon the pedalactuated plunger, serves directly as the brake pressure for a brake circuit, and acts as a control pressure upon the second piston of the master brake cylinder. In this instance, the primary piston is only displaced in the event of pressure failure and the second piston is then also displaced by way of the primary piston, that is to say, it is only then that a tandem master brake cylinder arrangement exists. In this instance, only one brake circuit is intact in the event of failure of the pressure source. Moreover, the brake force intensifying means fails in the event of a leak in the open brake circuit.

In contrast to this, the hydraulic brake pressure generator constructed in accordance with the present invention has the advantage that the brake force intensifying means remains intact in the event of failure of a brake circuit.

According to the present invention there is provided a hydraulic brake force generator for vehicle brake systems, containing a dual-circuit tandem master brake cylinder and a pedalactuated plunger, which actuates by way of an interposed travel simulator, a control-valve arrangement to cause a primary pressure to act upon a piston of said tandem master brake cylinder and the pedal-actuated plunger, characterised in that a separate closed brake circuit is connected to each of two pressure chambers located respectively upstream of each of the pistons of the tandem master brake cylinder, that the primary pressure acts upon the primary piston of the tandem master brake cylinder in addition to acting upon the pedalactuated plunger, and that the control valve arrangement is disposed parallel to the tandem master brake cylinder.

Preferably the pedal-actuated plunger is constructed and/or disposed such that it engages with and actuates the primary piston in the event of failure of the primary pressure supply. The axis of the pedal-actuated plunger preferably coincides at least approximately with the axis of the control valve arrangement.

The tandem master brake cylinder is preferably of stepped construction, the primary piston having a larger diameter than the other piston of said brake cylinder.

When the two brake circuits are split up in a conventional manner (front and rear axles), the requirements with respect to the pressure level for the two brake circuits differ to a considerable extent, chiefly in the event of a fault. If the brake circuit for the front axle should fail, the smaller dynamic relief of the rear axle necessitates for the rear axial brake circuit the application of a considerably higher pressure level for locking the wheels than that required for the other brake circuit when the brake circuits are intact.Since in the construction of the present invention the primary pressure supply does not fail with failure of the said brake circuit, the pressure force of the piston associated with the brake circuit of the front axle is sufficient to generate sufficient pressure in the rear axle brake circuit by transmitting the pressure force to the associated piston of the master brake cylinder. Since the differences are approximately 30%, the pressure supply in this arrangement can be based on a pressure level reduced by approximately 30%. A so-called step-up transient is possible in this arrangement by corresponding dimensioning of the pistons of the master brake cylinders.

Compared with conventional intensifier arrangements, higher brake pressures can then be obtained with the same pedal force in the event of failure of the pressure supply.

The arrangement of the brake valve device parallel to the master brake cylinder has the advantage that the overall arrangement is not too long.

The invention and advantages thereof are further illustrated by reference to the accompanying drawings, in which: Fig. 1 shows one embodiment of the invention, and Fig. 2 is a force/travel characteristic curve.

Referring to Fig. 1, a brake pedal is designated 1, an actuating plunger is designated 2, and slide valve, actuatable by the plunger 2 by way of a travel-simulating spring 4, is designated 3. A pressure source 5 is connected to the slide valve 3 by way of an inlet line 5a and a return line 5b.

Furthermore, the slide valve 3 is connected to a pressure chamber 14.

A tandem master brake cylinder comprises a housing 6 in which two double pistons 7 and 8 are mounted so as to be displaceable against the forces of springs 9 and 10. The pressure chambers located upstream of the pistons 7 and 8 are connected to the brakes by way of ports 11 (for the front axle brakes) and 1 2 (for the rear axle brakes). Furthermore, the pressure chambers communicate with a reservoir 13 when in the starting position, i.e. with no force being applied to the brake pedal. The pistons 7 and 8 have different diameters.

The plunger 2 is substantially coaxial to the slide valve 3 and carries an actuating plate 2a for actuation of the pistons 7 and 8 during emergency operation. An axially displaceable pin 1 5 is mounted on the plate 2a. A spring 1 6 is interposed between the actuating plate 2a and a widened portion 1 5a of the pin.

The pistons 7 and 8 and the plunger 2 have associated position sensors 7a, 8a or 2b which are actuated by way of sloping surfaces on the pistons 7 and 8 and a sloping surface on a pin 1 7 connected to the plunger 2, and which supply corresponding signals to a monitoring arrangement (not illustrated).

The system which has been described operates as follows: The slide valve 3 is displaced by way of the plunger 2 and the travel-simulating spring 4 when the pedal 1 is actuated. Pressure is built up in the pressure chamber 14 after the return line 5b has been shut off and the inlet line 5a has been opened. The pressure reacts on the plunger 2 and on the piston 7 and also upon the piston 8 by way of the spring 9 upon displacement of the piston 7.

Pressure is built up at the brakes. In the construction, in accordance with the invention, with two closed brake circuits, the diameters of the pistons and cylinders can be smaller than those in, for example, vacuum boosters, since the displaced volumes required for braking can be produced over a correspondingly longer path.

In the event of failure of the pressure supply, the pistons are actuated directly by way of the plunger 2 and plate 2a. By virtue of using the prestressed spring 16, the latter is additionally effective after a specific travel of the plunger 2 at which the slide valve 3 is then fully open and hence it would no longer be possible for the pressure in the chamber 1 4 to increase. Fig. 2 shows the curve of the characteristic between the travel S and the force F to be applied to the pedal 1, the spring 1 6 becoming effective from the amount of travel S1 onwards.

When the system is intact, specific displacements of the pistons 7 and 8 correspond to a specific displacement of the plunger 1 7. This predetermined relationship is checked in the monitoring device and, if it does not exist, this fact is indicated by the monitoring device. It is conceivable to produce analog signals in the sensors 2b, 7a and 8a or, alternatively, to actuate switches after predetermined amounts of travel. If the predetermined relationship does not exist, there is at least a leak or possibly even failure of a circuit.

Claims

1. A hydraulic brake force generator for vehicle brake systems, containing a dual-circuit tandem master brake cylinder and a pedal-actuated plunger, which actuates by way of an interposed travel simulator a control-valve arrangement to cause a primary pressure to act upon a piston of said tandem master brake cylinder and the pedalactuated plunger, characterised in that a separate closed brake circuit is connected to each of two pressure chambers located respectively upstream of each of the pistons of the tandem master brake cylinder, that the primary pressure acts upon the primary piston of the tandem master brake cylinder in addition to acting upon the pedalactuated plunger, and that the control valve arrangement is disposed parallel to the tandem master brake cylinder.

2. A brake pressure generator as claimed in claim 1, characterised in that the pedal-actuated plunger is constructed and/or disposed such that it engages with and actuates the primary piston in the event of failure of the pressure supply.

3. A brake pressure generator as claimed in claim 1 or 2, characterised in that the axis of the pedal-actuated plunger coincides at least approximately with the axis of the control valve arrangement.

4. A brake force generator as claimed in any one of claims 1 to 3, characterised in that the tandem master brake cylinder is of stepped construction such that the primary piston has a larger diameter.

5. A brake force generator as claimed in any one of claims 1 to 4, characterised in that both the plunger and at least one of the pistons has an associated sensor which monitors the amount of displacement thereof, and that a monitoring arrangement is provided to which the signals of the sensors are fed and which monitors the at least one piston with respect to its actual position.

6. A brake force generator as claimed in any one of the claims 1 to 6, characterised in that a prestressed spring is provided which, after a predetermined amount of displacement of the pedal-actuated plunger at which the brakepressure control valve is fully open, operates to reduce the axial movement of said pedal-actuated plunger for a given increase in the force applied to the said pedal.

7. A brake force generator as claimed in claim 1, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.