GB2066396A - Hydraulic Two-circuit External Force Brake Systems - Google Patents

Abstract

A hydraulic two-circuit external force brake is proposed which has a brake valve (7) having two separate plunger actuated valves (8, 9), one for each brake circuit, and the two plungers (17, 18) are inter-connected by way of compensating lever or balance beam (14) and the two plungers (17, 18) have an effective pressure surface (20, 21) which is subjected in use to pressure introduced by the respective separate valve (8, 9), and the pressure surfaces of the plungers (17, 18) are of different size, to provide pressure ratio control between the two brake circuits. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Hydraulic Twocircuit External Force Brake Systems The present invention relates to hydraulic twocircuit external force brake systems, primarily for vehicles.

One form of hydraulic two-circuit external force brake system is disclosed in German Offenlegungsschrift 2,335,424.

In vehicle brake systems, it is necessary to match the brake forces acting upon the front axle and upon the rear axle, particularly within a type of vehicle design having variable wheel bases (centre distance) or heights of centre of gravity.

Such matching can be achieved by using brake cylinders of different sizes on the front axle and on the rear axle, or by using master cylinders of different diameters, such as is described in, for example, United States Patent Specification No.

2,131,459. An equivalent method resides in using a pressure-ratio valve on the front axle, by means of which a correlation p Ra PFa= i can be obtained instead of PFa=PRa, where PFa and PAS denote respectively front axle and rear axle brake pressures.

However, different size wheel brake cylinders or master cylinders, and the use of a separate pressure-ratio valve, are complicated and expensive.

According to the present invention there is provided a hydraulic two-circuit external force brake system for a vehicle in which a brake valve has two separate plunger actuated valves, one for each brake circuit, and the plungers of the two valves are interconnected by way of a compensating lever, and the two plungers each have a pressure surface which is subjected in use to pressure introduced by the respective separate valve, and the pressure surfaces of the plungers are of different size.

A hydraulic two-circuited external force brake system embody the present invention can have the advantage that an existing hydraulic external force brake valve can be provided with a pressureratio control in a simple manner merely by varying the sizes of the outlet valve plungers. The additional costs of a construction of this kind are so small that a considerable saving of costs can be achieved relative to a construction having a separate pressure-ratio valve.

The operational reliability of the brake system embodying the present invention can be increased, since, compared with a separate construction, fewer seals, fewer parts and fewer screw pipe connections are needed.

The invention will be further described by way of example with reference to the accompanying drawing in which one embodiment of the invention is illustrated.

A hydraulic two-circuit external force brake system for a vehicle comprises a pressure-supply arrangement 50 including a pump 1 , two nonreturn valves 2 and 3, and two accumulators 4 and 5, one for each brake circuit I and II. A pressure relief valve 6 ensures a predetermined maximum pressure level in the accumulators 4 and 5.

Two separate valves 8 and 9 disposed parallel to one another are arranged in a two-circuit brake valve 7 which is connected to the pressure supply arrangement 50 and which is actuatable by way of a pedal 10 and an interposed travel-extending spring unit 11. The travel-extending spring unit 11 has a thrust protrusion 12 against which a central projection 1 3 of a compensating lever 14 abuts. Two ends of the compensating lever 14 are in contact with two valve plungers 1 7 and 1 8 which are parts of the separate valves 8 and 9.

The ends of the plungers 17 and 18 and the compensating lever 14 are disposed in a chamber 1 9 which has a relief port at 1 5. The two plungers 17 and 18 have different parameters and two annular pressure surfaces 20 and 21 which move across radially disposed housing passages 22 and 23 in a slide-valve-like manner. The passages 22 and 23 are connected to the chamber 19 by way of a common passage 24, so that respective outlet side valves 20, 22 and 21,23 are formed.

The two pressure surfaces 20 and 21 define in part respective valve chambers 25 and 26 which are connected by way of respective passages 27 and 28 to respective brake lines 29 and 30 of the brake circuits I and II which lead to respective wheel brake cylinders 31 and 32 of the front and rear axles respectively.

Respective valve springs 33 and 34 and respective valve plunger extensions 35 and 36 are disposed in the respective valve chambers 25 and 26. The respective extensions 35 and 36 are intended for co-operation with respective spherical valve closure members 37 and 38 of respective inlet seat valves 39 and 40 which are urged against respective valve seats 43 and 44 by respective valve springs 41 and 42. The respective valve springs 41 and 42 are disposed in respective inlet chambers 45 and 46 which are connected to respective pressure lines 47 and 48 which lead from the pressure supply arrangement 50.

The method of operation of the system described and illustrated is as follows: When the brakes are released i.e. when the pedai 10 is released, the pressure supply arrangement 50 is shut off and the wheel brake cylinders 31 and 32 are connected to the relief port 15 by way of the open outlet slide valves 20, 22 and 21,23.

When the brakes are to be applied, the pedal 10 is depressed and exerts a force upon the compensating lever 14 by way of the travelextending spring unit 11. The compensating lever acts as a balance beam having two lever arms of equal length and urges the plungers 17 and 18 to the left as seen in the drawing, so that the two outlet slide valves 20, 22 and 21, 23 are closed.

The extensions 35 and 36 of the plungers then open the two inlet seat valves 39 and 40, so that hydraulic pressure from-the pressure supply arrangement 50 can enter the valve chambers 25 and 26 from the inlet chambers 45 and 46. On the one hand, the pressure acts in the valve chambers 25 and 26 upon the plungers 17 and 18 and, on the other hand, it acts in the brake cylinders 31, 32 by way of the brake lines 29, 30; the brakes are applied.

By virtue of the fact that the plungers 1 7 and 18 have different diameters, the brake pressures at the front wheel brake and at the rear wheel brake differ. The pressures in the two brake lines 29 and 30 are in inverse ratio to the associated surface areas of the associated plungers.

It will be seen that only slight additional costs are involved by integrating the pressure-ratio control in the brake valve 7. Thus, there can be a considerable saving of costs compared with a construction having a separate pressure-ratio valve. Moreover, the operational reliability is improved, since fewer seals, fewer parts and fewer pipe screw connections are required.

Claims (4)

Claims

1. A hydraulic two-circuit external force brake system for a vehicle, in which a brake valve has two separate plunger actuated valves, one for each brake circuit, and the plungers of the two valves are operatively interconnected by way of a compensating lever, and the two plungers each have a pressure surface which is subjected in use to pressure introduced by the respective separate valve and the pressure surfaces of the plungers are of different size.

2. A hydraulic two-circuit external force brake system as claimed in claim 1, in which each of the separate valves has an outlet slide valve and an inlet seat valve, and the pressure surfaces on the respective plungers co-operate with the same control surface of the outlet slide valves.

3. A hydraulic two-circuit external force brake system as claimed in claim 1 or 2, in which the compensating lever, is a balance lever whereby, when in operation, two different brake pressures which are introduced by the separate valves can be counterbalanced relative to one another by way of the balance beam and the different size pressure surfaces of the plunger.

4. A hydraulic two-circuit external force brake system having a brake valve constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in the accompanying drawing.