GB2179108A - Multiple-circuit hydraulic brake system - Google Patents

Abstract

In a multiple-circuit hydraulic brake system, in particular for automotive vehicles, with a servo-assisted brake-actuating device supplied with servo pressure from supply system (2) (1) and containing several pressurisable working chambers (29, 34, 35), for pressurisation of wheel-brake cylinders (4, 5, 6, 7) and with a fast-fill cylinder (38) inserted into a brake circuit (37), one end compartment (54) of the fast-fill cylinder is connected via pressure lines (57, 69) to one pressure chamber (29) of the brake-actuating device (1) and the other end compartment (51) of the fast-fill cylinder is connected by line (68) to a brake line (37) leading from the brake-actuating device (1) to at least one wheel cylinder (6, 7), and a normally- open controlled non-return valve (53) is arranged in the pressure line (69) which valve (53) closes its pressure-fluid passage upon failure of the servo supply system pressure acting in line 75 and/or upon a sufficient rise of the pressure in the one working chamber (29) and thus hydraulically locks the stepped piston (50) of the fast-fill cylinder (38) preventing displacement of the piston (50). Fig. 2 shows an embodiment of the value (53). <IMAGE>

Description

SPECIFICATION Multiple-circuit hydraulic brake system This invention relates to a multiple-circuit hydraulic brake system, in particular for automotive vehicles, the brake system comprising a brake-actuating device including several pressurisable working chambers, wheel brake cylinders, an auxiliary-energy supply system for pressurisation of the wheel brake cylinders, and a fast-fill cylinder inserted into a brake circuit, one compartment of the fast-fiil cylinder communicating via pressure lines to one working chamber of the brake-actuating device, while another compartment of the fast-fill cylinder is connected to the brake line, which leads from the brake-actuating device to at least one wheel cylinder.

In an older brake system of this type (West German patent application P 35 08 709.9), a booster piston plunges into an annular chamber arranged between a master cylinder and a brake power booster, which chamber is connected to a pressure chamber of a fast-fill cylinder, on the one hand, and with a supply reservoir, on the other hand. The pressure fluid conduit from the annular chamber to the supply resevoir contains a valve actuatable by the pressure in the booster chamber, which valve in one switch position closes the pressure-fluid passage to the supply reservoir and thus permits pressure fluid to flow from the annular chamber into the pressure chamber of the fast-fill cylinder during braking and which, in its other switch position, connects the annular chamber to the supply reservoir.It is the shortcoming of this older brake system that the brake-actuating device has a comparatively large overall length, since beside the working chambers of the master cylinder and that of the power brake booster arranged in series, another working chamber (the annular chamber) must be arranged in series therewith.

It is an object of the present invention to create a brake system which can be connected with a brake-slip monitoring and controlling electronics, which, on booster failure, operates with a reduced brake master cylinder surface and the brake-actuating device of which is of particularly short overall length.

According to the present invention there is provided a multiple-circuit hydraulic brake system, in particular for automotive vehicles, the brake system comprising a brake-actuating device including several pressurisable working chambers, wheel brake cylinders, an auxiliaryenergy supply system for pressurisation of the wheel brake cylinders and a fast-fill cylinder inserted into a brake circuit, one compartment of the fast-fill cylinder communicating via pressure lines to one working chamber of the brake-actuating device, while another compartment of the fast-fill cylinder is connected to the brake circuit, which leads from the brakeactuating device to at least one wheel cylinder, characterised in that a valve is interposed into the pressure line connecting the one compartment of the fast-fill cylinder with the one working chamber of the brake-actuating device, which valve closes its pressure-fluid passage on failure of the auxiliary-energy supply system and/or upon rise of the pressure in the one working chamber and hence hydraulically locks a stepped piston of the fast-fill cylinder.

Preferably, the valve inserted into the pressure line connecting the one compartment of the fast-fill cylinder with the one working chamber, for instance a booster chamber, is designed as a controllable non-return valve, a valve member controlling the pressure-fluid passage of the non-return valve being movable by a valve piston in the opening sense, the said valve piston being applied by the pressure of the auxiliary-energy supply system, for instance an accumulator, on the one hand, and by the pressure in the one compartment of the connected fast-fill cylinder, on the other hand.

Advantageously, the valve piston is designed as a stepped piston, the end surface of a small stage of the valve piston being acted upon by the accumulator pressure, while the end surface of the large stage that is close to the valve member is acted upon by the pressure in the one compartment of the fast-fill cylinder, and wherein the valve piston has on one end a nose or a tappet which cooperates with the valve member.

Expediently, the valve member controlling the pressure-fluid passage is applied by the pressure in the one working chamber, for instance the booster chamber, in the sense of closing, while it is movable by the valve piston in the sense of opening.

The multiple-circuit hydraulic brake system according to the present invention bears the advantage that, on failure of the brake power booster, deceleration of the vehicle is possible without considerable variation of the pedal force and the pedal travel. Besides, the braking pressure generator has a particularly small overall length, since the necessary valve may be arranged outside the braking pressure generator itself.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is the circuit configuration of a multiple-circuit hydraulic brake system, substantially composed of wheel brakes, a fast-fill cylinder, an actuating device with a tandem master cylinder, a modulator, a controllable nonreturn valve, an auxiliary-energy supply system and a supply reservoir for pressure fluid, and Figure 2 is a cross-sectional view of the controllable non-return valve which is shown only schematically in Figure 1.

The illustrated brake system (with slip con trol) destined for an automotive vehicle substantially comprises an actuating device, that is a hydraulic unit 1, with an auxiliary-energy supply system 2 and a valve block or modulator 3 in which electromagnetic pressure-increasing and pressure-reducing valves allocated to a wheel or an axle, respectively, are provided, a fast-fill cylinder 38 and a controllable non-return valve 53. In the embodiment of multiple-circuit brake system shown herein, the two front wheels or wheel brake cylinders 6, 7, respectively, and the two wheels and wheel brake cylinders 4, 5, respectively, of the rear axle are controlled in pairs.

The sensors which are also required for such systems for the purpose of measuring the wheel speeds as well as the electronics for generating the control signals for the valves of the modulator 3 are not illustrated.

The actuating device 1 is substantially composed of a brake valve 14, a tandem master cylinder 15 and two main valves 16, 17 with an associated prechamber 18.

In the embodiment described herein, the brake valve 14 is designed as a compact hydraulic brake power booster. Upon depression of the brake pedal 19, the pedal force F will be transmitted via a push rod 20 and a pushrod piston 21 onto an arrangement consisting of two levers 22, 23 articulated by way of a bolt 24, and from there onto the control piston 25 of the brake valve. As the force required for displacement of the booster piston 40 of the brake valve 14 is considerably higher than that required for displacement of the control piston 25, the control piston 25 will be shifted to the left at first, that is when the lever 22 is turned about bolt 24 by application of the force F. Thereby, the auxiliaryenergy source 2 will be connected with the booster chamber 29 through the inlet 27 and the inner bores 28 in the control piston 25.

Shortly before this the opening 30, through which the booster chamber 29 was in communication with a pressure-compensating and supply reservoir 31 with the brake not applied, was closed. The pressure developing in the pressure chamber 29 likewise acts on the booster piston 40 and displaces it to the left.

The pistons 32 and 33 of the tandem master cylinder will now be displaced also so that braking pressure develops in the associated pressure (working) chambers 34, 35 as well as in the static brake circuits 36, 37 connected thereto and pertaining to the two rear wheels 4, 5 and the two front wheels 6 and 7, respectively.

An intermediate member 39 connecting the booster piston 40 with the tandem master cylinder pistons 32, 33 and forming a unit together with the master cylinder piston 32 carries a positioning piston or a positioning sleeve 41 which, in a known manner, prevents that the tandem master cylinder pistons will displace too far to the left upon commencement of the control and prevents that the working chambers 34, 35 will become 'empty by control'.

In the event of response of the brake slip control due to an imminent locked condition at one or more of the wheels, the solenoid valves 16, 17, that is the so-termed main valves, will be energised, whereby simultaneously the connecting line 58 leading to the supply reservoir 31 under atmospheric pressure will be closed and the flow path 108 from the booster chamber 29 into the prechamber 18 will be opened. The hydraulic medium which is under increased pressure due to the auxiliary-energy supply flows out of the prechamber 18 through the connecting channels 42, 43 to the secondary sides of the two master cylinder pistons 32, 33 and from there via the pistons and through the supply bores 44, 45 with the adjoining sealing lips 46, 47 serving as non-return valves into the pertinent working chambers 34, 35.The positioning piston 41, which is floating, i.e. which is in an intermediate position, prior to commencement of control, will be displaced to the right until it abuts a stop, said displacement taking place in opposition to the direction of the pedal force F and in consequence of the now increased pressure in the compartment 48 at the secondary side of the piston 32.

Signals are generated by means of a control unit (not illustrated) in dependence upon the rotational behaviour of the individual wheels 4, 5, 6, 7 which is determined by means of sensors (not shown), the said signals serving to operate the electromagnetic pressure-increasing and pressure-reducing valves in the modulator 3. The main valves 16 and 17 which modulate the dynamic fluid flow into the static brake circuits 36, 37 as well as the pressure in the prechamber 18 will also be excited and switched over on commencement of brake slip control.

In order to reduce the braking pressure in the two brake circuits (that is the front-wheel brake circuit 37 and the rear-wheel brake circuit 36 in the embodiment described herein) upon an imminent locked condition of a wheel, valves 59, 60, 61, 62 in the modulator 3 will serve which, after their excitation, establish via the return line 63 a connection between the wheel brake cylinders 4, 5 and 6, 7, respectively, and the supply reservoir 31 under atmospheric pressure, and thereby decrease braking pressure. In a similar manner, the pressure in the prechamber 18 will be reduced through the main valve 16 and the line 58 as soon as this valve becomes deenergised. When the main valve 17 is deenergised, the dynamic fluid flow into the prechamber 18 is interrupted.

Suitably, the main valves 16 and 17 are arranged electrically in parallel or in series so that both can always be switched over simultaneously, the switch condition "open/closed" of the two main valves 16, 17 being always the opposed one, though.

Vehicles having a high admissible total weight require a high boosting factor in order to keep the pedal force and the pedal travel within desirable limits. On booster failure, this has as a result undesirably or even inadmissibly great pedal forces and short pedal travels. Therefore, the brake system illustrated will operate on booster failure with a reduced brake master cylinder surface, since a fast-fill cylinder 38 connected via a branch line 68 to the brake line 37 of the front-wheel brakes 6, 7 remains ineffective.To this end, the fast-fill cylinder 38 contains a stepped bore 49 in which a stepped piston 50 is longitudinally displaceably accommodated, the compartment 51 in front of the small stage 52 being connected via the branch line 68 to the brake line 37 and the compartment 54 in front of the large stage 56 being connectible to the flow path 108 for the prechamber 18 via the pressure line 57 via a controllable non-return valve 53 and the pressure line 69.

When the brake system is intact, in the event of a braking action, the controllable nonreturn valve 53 will open the pressure fluid passage from the pressure line 69 to the pressure line 57 and to the compartment 54 so that the pressure fluid prevailing in the compartment 51 will be urged into the brake circuit 37 via the branch line 68.

The controllable non-return valve 53 is illustrated in more detail in Figure 2. It is composed of a valve piston 72 which is sealingly guided in a valve housing 71, one end surface thereof is acted upon by the pressure of the accumulator 70 that is in communication with the port 74 via the pressure line 75. A port 76 of the valve 53 communicates via a line 81 with the supply reservoir 31. The end surface of the valve piston 72 close to valve member 78 is acted upon by the controlled pressure which propagates up to the booster chamber 29 via a port 79 and the pressure line 69. Finally, a port 80 of the valve 53 is connected with the compartment 54 of the fast-fill cylinder 38 via the pressure line 57.

When the pressure in compartment 82 of the valve 53 corresponds to a predetermined accumulator pressure (e.g. 180 bar), the valve piston will be in its opened position (displaced to the right, when viewing in the drawing), in which it lifts, through its tappet 83, the valve member 78 off its valve seat 84 so that the presusre fluid is allowed to enter from the port 80 through valve chamber 85, annular chamber 86, the port 79 and the pressure line 57 into the compartment 54 of the fast-fill cylinder 38. The increased pressure in the compartment 54 will now displace the stepped piston 50 in opposition to the force of the piston spring 87 (to the left) and deliver the pressure fluid disposd in the compartment 51 into the brake circuit 37 of the front wheels (that means the wheel cylinders 6, 7, respectively).In the event of failure of the auxiliary-energy supply system 2 or, respectively, drop of the pressure in the accumulator 70 below a specific pressure level, then the valve piston 72 will return to its initial position displayed in Figure 2, and the pressure fluid passage from the valve chamber 85 into the annular chamber 86 stays closed so that the stepped piston 50 remains in that position which it had just adopted.

The pressure fluid still prevailing in the compartment 54 and, respectively, in the line 57 is not permitted to flow back in consequence of the closed position of the valve so that the pressure fluid displaced exclusively by pedal force via the cylinder pistons 32, 33 serves entirely for pressure build-up in the brake circuit 37. The effective surfaces of the stepped piston 50 and of the controllable non-return valve 53 are suitably conformed to each other such that the valve 52 closes when the controlled pressure (in the flow path 108) amounts to approximately 70 percent of the pressure in the accumulator 70.

When the pressure in the booster chamber 29 reaches the pressure of the accumulator 70, the valve piston 72 will return to its initial position, whereby the piston 50 of the fast-fill cylinder 38 is locked.

Claims (5)

1. A multiple-circuit hydraulic brake system, in particular for automotive vehicles, the brake system comprising a brake-actuating device (1) including several pressurisable working chambers (29, 34, 35), wheel brake cylinders 4, 5, 6, 7), an auxiliary-energy supply system (2) for pressurisation of the wheel brake cylinders (4, 5, 6, 7), and a fast-fill cylinder (38) inserted into a brake circuit (37), one compartment (54) of the fast-fill cylinder communicating via pressure lines (69, 63, 55) to one working chamber (29) of the brake-actuating device (1), while another compartment (51) of the fast-fill cylinder is connected to the brake circuit (37), which leads from the brake-actuating device (1) to at least one wheel cylinder (6, 7), characterised in that a valve (53) is interposed into the pressure line (69) connecting the one compartment (54) of the fast-fill cylinder (38) with the one working chamber (29) of the brake-actuating device (1), which valve closes its pressure-fluid passage on failure of the auxiliary-energy supply system (2) and/or upon rise of the pressure in the one working chamber (29) and hence hydraulically locks a stepped piston (50) of the fast-fill cylinder (38).

2. A multiple-circuit hydraulic brake system as claimed in claim 1, characterised in that the valve (53) inserted into the pressure line (69) connecting the one compartment (54) of the fast-fill cylinder (38) with the one working chamber, for instance a booster chamber (29) of the brake-actuating device (1), is designed as a controllable non-return valve (53), a valve member (78) controlling the pressure-fluid passage of the non-return valve being movable by a valve piston (72) in the opening sense, the said valve piston being applied by the pressure of the auxiliary-energy supply system (2), for instance an accumulator (70), on the one hand, and by the pressure in the one compartment (54) of the connected fast-fill cylinder (38), on the other hand.

3. A multiple-circuit hydraulic brake system as claimed in claim 2, characterised in that the valve piston (72) is designed as a stepped piston, the end surface of a small stage of the valve piston (72) being acted upon by the accumulator pressure, while the end surface of the large stage close to the valve member (78) is acted upon by the pressure in the one compartment (54) of the fast-fill cylinder (38), and wherein the valve piston (72) has on one end a nose or a tappet (83) which co-operates with the valve member (78).

4. A multiple-circuit hydraulic brake system as claimed in claim 2 or claim 3, characterised in that the valve member (78) controlling the pressure-fluid passage is applied in the sense of closing by the pressure in the one working chamber, for instance the booster chamber (29), while it is movable in the sense of opening by the valve piston (72).

5. A multiple-circuit hydraulic brake system substantially as herein described with reference to and as illustrated in the accompanying drawings.