GB2247059A

GB2247059A - A hydraulic regulator for brake systems

Info

Publication number: GB2247059A
Application number: GB9116006A
Authority: GB
Inventors: Frank Stemmer; Wolfgang Reeb
Original assignee: Fatec Fahrzeugtechnik GmbH
Current assignee: Fatec Fahrzeugtechnik GmbH
Priority date: 1990-08-14
Filing date: 1991-07-24
Publication date: 1992-02-19
Anticipated expiration: 2011-07-24
Also published as: DE4025679A1; GB2247059B; GB9116006D0; FR2665870A1

Abstract

A hydraulic regulator for adjusting the pressure in anti-lock and/or drive-slip control brake systems for motor vehicles comprises a piston 3 dividing the regulator into two chambers respectively connected to the brake 7 and containing a biassing spring 4 and the master cylinder 1 pressure is applied to both chambers while the piston 3 is displaceable by an external force F which is electronically adjustable. In a second embodiment the piston 3 and the spring 4 biassing it upwards are disposed in separate cylinders with a lever transmitting the action between them, the lever also receiving the external force. In a third embodiment for drive slip control a pressure-controlled valve can connect the brake to the chamber containing the spring 4 instead of to the upper chamber, this making available a pressure above that of the master cylinder. <IMAGE>

Description

A Hvdraulic Requlator This invention relates to a hydraulic regulator for

adjusting the pressure in anti-lock brake systems and/or in drive wheel-slip regulating systems in motor vehicles, at least one pressure modulator being disposed between the main cylinder and the wheel brake cylinders and a piston in the pressure modulator being movable against the pressure of the main cylinder by an external force the value of which is electronically adjustable.

DE-OS 36 08 573 discloses a pressure modulator in which a laminated spring acting via a lever system prestresses the plunger into the upper piston position. The spring is given a prestress such that, even at the maximum possible locking pressure of the vehicle wheels, the compressive forces acting on the piston cannot push it against the force of the spring. In order to modulate the brake pressure, an additional force is introduced at the lever system and pulls the piston downwards against the force of the spring and thus releases an additional volume of hydraulic brake fluid in the brake circuit and lowers the pressure. The pressure build-up in the brake system occurs only via the laminated spring.

In each case, the additional force needed for modulation is the maximum spring force minus the compressive force on the spring. It has been f ound that the drive is very heavily loaded as a result. Attempts have therefore been made to reduce to a minimum the power k required during adjustment of the anti-locking system (see DE-OS 38 10 445). The spring in this construction is replaced by a piston acted upon by the main cylinder pressure. The piston acts via a lever system on the antilocking system regulating piston. The aim is to designthe lever system so as to limit the drive power for modulating the brake pressure to the power necessary for overcoming the internal friction of the mechanical components. This, however, is possible only in the theoretical ideal case. In practice the pressure-volume characteristic of the brake system can be widely varied by ageing or temperature, or the driver may alter the pedal pressure and thus alter the pressure supplied during adjustment of the anti-locking system. These changes in the boundary conditions, as compared with the ideal state, result in considerable additional forces which have to be applied by the drive of the system. There is therefore no guarantee that the drive will have to overcome only frictional forces. Ultimately this brings into question the usefulness of the proposed lever system, which is designed precisely to reduce the drive forces to a minimum.

There are other disadvantages which may be critical to safety, as follows:

1. The anti-locking system adjusting piston does not have a restoring spring capable, in the pressureless state, of restoring the initial position, i.e., with the plunger in the top piston position and the valve open. Since the drive is not reversible, the result in the worst case (if 1 h 1 1, - 3 the driver releases the brake during an adjustment of the anti- locking system) will be to put the anti-locking system permanently out of action.

2. The following is another imaginable case. If, for example, there is an abrupt change in the road surface from high,m to lowp and the plunger piston is overdriven (which is quite possible in view of the inertia of the wheels), it may happen that a part of the volume of hydraulic brake fluid introduced into the brake system will be discharged into the compensator reservoir owing to the complete compression of the main cylinder piston. This will result in a deficient volume of hydraulic brake fluid in the brake system, which in the extreme case may cause the entire brake system to fail.

The aim of the present invention therefore is to avoid the aforementioned disadvantages and, using simple means, to provide a reliable hydraulic regulator for adjusting the pressure in anti-lock brake systems and/or drive wheel slip regulators.

According to the invention, the solution to this problem is to provide a construction wherein the main cylinder pressure is introduced into two pressure chambers, and the pressure container which contains a non-return spring acts on the plunger piston, either directly or e.g. via a lever system, and the external force engages the piston or lever system.

The energy store for the pressure build-up is the main cylinder and, consequently, the muscular force of driving, the benefits being as follows (a) A smaller overall modulator; (b) Feedback from the pedal during adjustment of the_ anti-locking system, thus warning the driver; (c) A small number of individual parts; (d) The drive power needed for adjusting an antilocking system is reduced to a minimum; (e) An ASR function can be incorporated without considerable expense; and (f) Emergency operation is unrestricted, i.e., if the anti-locking system fails, there is unrestricted operation of the normal brake system.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagram of a hydraulic regulator for anti-lock brake systems according to the invention; Figure 2 is a diagram of a hydraulic regulator and lever system; and Figure 3 is a diagram of a hydraulic regulator for anti-lock brake systems with drive wheel slip adjustment.

Figure 1 shows a modulating piston 3 which is held in the starting position by a spring element 4. In the starting position, the non-return valve 2 is held open by a pin in the piston 3, leaving an open passage from the main cylinder 1 to the wheel brake cylinder 7.

The spring element 4 is dimensioned so that it can move the modulating piston 3 into its upwardly defined i J r 1 i 1 - 5 starting position when the pressure is relaxed. As a result, if the anti-lock brake is prematurely taken off by the driver during a regulating cycle, the piston is moved to its initial position for subsequent anti-locking braking and, consequently, the brake system operates normally. This applies even if there is a defect in the anti- locking system modulator or regulator. The top and bottom surface of the piston are in the starting position, i.e., actuated by pressure from the main cylinder without anti-locking modulation. The two piston surfaces are of equal size. In order to modulate the pressure in the antilocking system, force is applied so as tb move piston 3 in the direction of the spring element 4.

The force for moving the piston can be produced in various ways, as will now be explained.

The motion of the piston initially unblocks a path so that the non-return valve 2 closes and separates the main cylinder from the wheel brake cylinder. During the subsequent notion of the piston, the enclosed volume of hydraulic brake fluid is increased so that the wheel brake cylinder pressure decreases. The force required for moving depends only on the actual pressure between the main cylinder and the wheel brake cylinder. If the additional force is withdrawn, the piston 3, as a result of the balance of forces, will return upwards, thus reducing the enclosed volume and increasing the wheel base cylinder pressure. However, the wheel base cylinder pressure can never be made greater than the main cylinder pressure.

This is an essential safely requirement.

If the piston 3 is overdriven, e.g., if u jumps from high to low as a result of the inertia of the vehicle wheels, the non-return valve 5 ensures that the pressure in the wheel brake cylinder can never fall below the pressure in the compensator reservoir 6, and consequently no air can be sucked through the packing or seal. The second purpose served by the non-return valve 5 is to maintain the volume of brake fluid inside the enclosed brake circuit. This is of critical importance regarding the efficiency of the brake system if, during the overdrive as described, a part of the volume is delivered through the main cylinder central valves to the compensator reservoir 11. Consequently, a volume deficit can never occur in the brake system. If not all ducts are overdriven in phase it may happen, in the proposed arrangement, that the originally enclosed volume of hydraulic brake fluid is increased by subsequent suction as described. The result will be that at the end of the antiblocking system control cycle the central valves of the main cylinder will open at a certain preliminary pressure, but this is not critical if the device is suitably designed. There is no ef fect on the efficiency of the anti- locking system and the operation of the brake system.

In Figure 2 the modulator piston 3 is divided into two pistons coupled by a lever. of course, the compensator reservoirs 6 and 11 may alternatively constitute a single reservoir.

1 1 Figure 3 shows a hydraulic regulator with ASR integration. When a flow occurs through valve 9, a solenoid valve 8 and a switching valve 9 can produce and modulate a pressure above the main cylinder pressure. After the flow through the solenoid valve 2, force is applied at the modulator piston 3 so as to raise the pressure at its spring end, thus connecting the valve 9. An additional increase in force will only increase the pressure in the wheel brake cylinder, thus slowing down the wheel when it is about to race.

8 claims 1. A hydraulic regulator for adjusting the pressure in anti-lock brake systems and/or in drive wheel-slip regulating systems in motor vehicles, at least one pressure modulator being disposed between the main cylinder and the wheel brake cylinders and a piston in the pressure modulator being movable against the pressure of the main cylinder by 'an external force the value of which is electronically adjustable, wherein the main cylinder pressure is introduced into two pressure chambers, and the pressure container which contains a non-return spring acts on the plunger piston, either directly or e.g. via a lever system, and the external force engages the piston or lever system.

2. A hydraulic regulator according to claim 1, wherein both pressure chambers are connected to the wheel brake cylinder by conduits which can alternatively be blocked by magnetically and/or hydraulically actuated onoff valves.

3. A hydraulic regulator according to claim 1 or claim 2, wherein the pressure chamber containing the non-return spring is connected to the main cylinder via a normally open non-return valve.

4. A hydraulic regulator according to any one of claims 1-3, wherein brake fluid can be subsequently sucked from the compensator reservoir through the non-return valve into the wheel brake cylinder pressure chamber.

5. A hydraulic regulator according to claim 1 i 1 1 1 j i I 1 1 i i j I i 1 substantially as described herein with reference to Figure 1, Figure 2 or Figure 3 of the accompanying drawings.

6. An anti-lock brake system or a wheel-slip regulating system for motor vehicles incorporating a hydraulic regulator as claimed in any preceding claim.

a 1992 at The Patent (Alit c Concept House. Cardiff Road. Newport- Gwent NP9 I M Further copies niav be obtained fron, Sales Branch. Unii 6. Nine Mile Point. Owrnfelinfach. Cross Keys. Newport. NPI 7HZ- Printed by Multiplex techniques ltd St Mary- Cray. Kent