GB2130323A - Vehicle deceleration responsive braking pressure control device - Google Patents

Abstract

A braking pressure control device to be inserted in the connection between a master cylinder and wheel cylinders of the rear axle of an automotive vehicle, includes a first stepped piston (8) slidable in a first stepped bore (2) in opposition to a first spring (15) and having a first passage (16, 17) closable by a vehicle deceleration-sensitive valve (19, 21) controllable by an inert mass (19) and is open below a predeterminable deceleration value, thus providing a communication between the end faces (9, 10) of the first stepped piston (8). A proportioning valve comprises a second stepped bore (3), a second stepped piston (22) slidable therein against a second spring (25) and with a second valve passage (32, 33) including a valve (37, 41) for the control of the connection between the master cylinder and the wheel cylinders. The valve element (37) has an extension (38) engaging the end face 10 of the first piston so that the valve closure travel of the second piston (22) depends on the axial position of the first piston (8). <IMAGE>

Description

SPECIFICATION Braking pressure control device This invention relates to a braking pressure control device to be inserted in the connection between a master cylinder and wheel cylinders of the rear axle of an automotive vehicle, of the kind wherein a first stepped piston is axially slidably guided in a first stepped bore in opposition to a first pressure spring and has a first valve passage, which is controllable in dependence upon the vehicle deceleration by an inert mass, the first valve passage being open below a predetermined deceleration value and providing a communication between the end faces of the first stepped piston.

A device of this kind is, for instance, known from US Patent Specification 22 42 297.

This describes a braking pressure control device, wherein a stepped piston is axially sliably guided in a stepped bore of a housing in opposition to the force of a spring, the smaller end face of the stepped piston being acted upon by the pressure of a master cylinder.

The chamber, which is confined by the larger end face of the stepped piston, is hydraulically connected to wheel brakes on the rear axle of an automotive vehicle. The stepped piston is provided with an axial pressure fluid channel which is closable by means of a ball, acting as a closure member, when the vehicle deceleration exceeds a certain value. For,that purpose, the known braking pressure control device is mounted on the vehicle with a certain inclination, the axis of the stepped piston being aligned according to the longitudinal axis of the vehicle.

Due to the inclined installation position of this known braking pressure control device, the ball clears the valve passage between the master cylinder and the wheel brakes and/or between both end faces of the stepped piston as long as there are no acceleration forces acting upon said ball or as long as the acceleration forces are positive. When the vehicle deceleration exceeds a certain value, the valve ball will roll on a surface towards a valve seat and will interrupt, upon abutment on the valve seat, the connection between the end faces of the stepped piston, thus interrupting the hydraulic connection between the master cylinder and the wheel brakes.When the pressure in the master cylinder is increased even further, the stepped piston will now be displaced, due to a pressurisation of its smaller end faces, in the stepped bore of the housing, in opposition to the force of the pressure spring, as a result whereof a pressure will be produced in the chamber confined by the larger end face of the stepped piston, this pressure being reduced in proportion to the effective surfaces of the stepped piston.

The braking pressure control device just described is to be considered as disadvantageous in that the braking pressure is controlled exclusively in dependence upon the deceleration and in that the absolute braking pressure has no influence on the change-over point. This is disadvantageous in that, with the vehicle loaded, a higher wheel cylinder pressure on the rear axle is easily allowable before a wheel lock occurs.

It is, therefore, an object of the present invention to create a constructionally simple device of the kind initially referred to, wherein a valve passage between the master cylinder and the wheel brakes of the rear axle of an automotive vehicle is deceleration-sensitively and braking pressure-sensitively operable.

According to the invention in its broadest aspect, a braking pressure control device of the kind referred to is characterised in that in a second stepped bore a second stepped piston containing a second valve passage for the control of the connection between the master cylinder and the wheel cylinders is axially slidably guided in opposition to a second pressure spring, and in that the second valve passage is pressure-sensitively operable and in that the closure travel of the second valve passage is adjustable due to the axial position of the first stepped piston. An advantageous result of this measure consists in that the change-over point of the braking pressure control device will be determined, on the one hand, in dependence upon the vehicle deceleration and, in addition, upon the pressure in the wheel brakes.At a given vehicle deceleration, the first stepped piston will displace the closure member of the second valve passage which is, in principle, controlled by the second stepped piston. With the automotive vehicle unloaded, the vehicle deceleration required for the closure of the first valve passage will be already attained at a lower braking pressure. The first stepped piston will, therefore, only be displaced by a relatively small distance in the first stepped bore. In contrast thereto, with the vehicle loaded, it is allowable that the regulation of the wheel cylinder bridge on the rear axle will start at a higher braking pressure only, since the danger of wheel lock due to a higher axle load is less great. In addition, the change-over point of the braking pressure control device can be influenced favourably by the fact that the preload of the second pressure spring is adjustable.

An advantageous embodiment of the present patent application will be achieved in that the first stepped piston and the second stepped piston are coaxially arranged in a housing. Furthermore, it has become apparent that it will be favourable to allocate a 2:1 ratio of the effective surfaces to the second stepped piston.

A constructionally simple and favourable solution will be achieved in that the second stepped piston carries a valve seat made of a rubber-elastic material, this valve seat constituting together with a closure member, which is in mechanical contact with the first stepped piston, the second valve passage. The closure member of the second valve passage is urged by a third pressure spring against the first stepped piston in the direction of closure of the second valve passage so that the closure member is held in a defined initial position as against the second valve seat.

An embodiment of the present invention will now be described by way of example with reference to the sectional view depicted in the accompanying drawing.

In the drawing, 1 designates a housing, wherein are arranged two coaxial stepped bores 2, 3. The stepped bore 2 has a largerdiameter bore section 4 and a smaller-diameter bore portion 5. In addition, the stepped bore 3 has a larger-diameter portion 6 and a smaller-diameter portion 7. A stepped piston 8, which has a larger effective surface 9 and a smaller effective surface 10, is guided in the stepped bore 2. The stepped piston 8 has at its lateral surfaces peripheral grooves 11, 12, wherein sealing rings 13, 14 are positioned.

The stepped piston 8 is pre-loaded by means of a pressure spring 1 5 against the left-hand confining surface of the stepped bore 2, as shown in the drawing.

The effective surfaces 9, 10 of the stepped piston 8 are hydraulically interconnected via pressure fluid channels 16, 1 7 and a chamber 1 8 within the stepped piston 2.

Within the chamber 18 is a valve ball 1 9 which abuts against a perforated disc 20 in the inoperative position (shown) of the braking pressure control device and which is movable into abutment with a valve seat 21 of the stepped piston 8 when corresponding forces are applied.

In the stepped bore 3, a second stepped piston 22 is axially slidably guided, whose right-hand end, as shown in the drawing, protrudes into the smaller-diameter bore portion 24 by the intermediary of a sealing ring 23, and is loaded by a pressure spring 25.

The pressure spring 25, in turn, bears against a spring casing 26, which is connected to the housing 1 in a form-fit fashion. Furthermore, the second stepped piston 22 has an annular groove 28 in the bone portion 27 of the larger-diameter stepped bore 3, the annular groove carrying a sealing ring 29. The second stepped piston 22 confines within the bore portion 27 of the stepped bore 3 two annular chambers 30, 31, which are normally hydrau lically interconnected through an axial bore 32, an axial channel 33 and a radial channel 34.The annular chamber 30 of the braking pressure control device is in communication with a braking pressure generator (not shown) via a housing connection 35, whereas from the annular chamber 31, a housing connection 36 branches off, the latter being hydraulically connected to the wheel brakes on the rear axle of an automotive vehicle.

Within the axial bore 32 of the second stepped piston 22 is arranged a valve closure member 37 which protrudes with an extension 38 through a connecting bore 39 between the stepped bores 2, 3 and which bears against the smaller effective surface 10 of the stepped piston 8. The valve closure member 37 is pre-loaded by a pressure spring 40 in the direction of the first stepped piston 8.

The left-hand end of the axial bore 32, as shown in the drawing, has a valve seat 41 made of a rubber-elastic material, the valve seat constituting together with the valve closure member 37 a valve passage. The valve passage 37, 41 is closable when the second stepped piston 22 is moved towards the righthand side, as shown in the drawing.

The mode of function of the braking pressure control device will now be explained in more detail.

At first, it is assumed that the braking pressure generator connected to the housing connection 35 is unpressurised so that all movable parts of the braking pressure control device are in the positions illustrated in the drawing. The position of the first stepped piston 8 is produced by the pressure spring 1 5. The second stepped piston 22 is held by the pressure spring 25 in a left-hand end position, as shown in the drawing, whereas the valve closure member 37 with the extension 38 is held into abutment with the first stepped piston 8 by the pressure spring 40.

In this position, the valve closure member 37 has been removed from its valve seat 41, thus providing a hydraulic communication between the annular chambers 30, 31 and/or between the braking pressure generator and the wheel brakes.

A pressure introduced into the housing connection 35 will be transmitted via the annular chamber 30, the radial channel 34, the axial bore 32, the annular chamber 31 to the housing connection 36 so that the pressure from the braking pressure generator will flow directly to the wheel brakes. The pressure prevailing in the annular chamber 31 will, furthermore, be transmitted via the connecting bore to a chamber confined by the smaller end face 10 of the first stepped piston 2, wherefrom it will be transmitted via the pressure fluid channel 1 7 and the perforated disc 20 to the chamber 18 within the first stepped piston 8. A pressure fluid will be transmitted from the chamber 1 8 via the pressure fluid channel 16 to the larger end face 9 of the first stepped piston 2. Due to the varying effective surfaces 9, 10 of the first stepped piston 8, the latter will be displaced in the stepped bore 2 to the right, as shown in the drawing, as a result whereof the displacement travel will be transmitted via the extension 38 to the valve closure member 37 which will move away from the valve seat by a corresponding travel. The pressurisation of the second stepped piston 22 will result also, due to the varying effective surfaces, in a displacement of the stepped piston 22 to the right, the effective surface of the stepped piston in the smaller-diameter bore portion 24 being unpressurised.

The braking pressure control device described will be mounted on the vehicle in such a way that, in the event of a deceleration, forces will act upon the valve ball 1 9 which will finally move the valve ball 1 9 into abutment with the valve seat 21 and will thus interrupt the hydraulic communication between the effective surfaces 9, 10 of the first stepped piston 8. When the valve ball 1 9 abuts against the valve seat 21, a further displacement of the first stepped piston 8 will be impossible so that the position of the valve closure member 37 will also be maintained.

When the pressure at the housing connection 35 is increased even further, only the second stepped piston 22 will be displaced to the right, as shown in the drawing, until the valve seat 41 finally abuts against the valve closure member 37 and interrupts the communication between the housing connections 35, 36, the pressure in the annular chamber 31 and/or in the wheel brakes connected to the housing connection 36 thus being maintained constant on the whole or increasing by at least a less steep gradient.

When the brakes are released, the pressure at the housing connection 35 will drop, as a result whereof the displacement operations described are reversed until the inoperative position depicted in the drawing is re-estab lished.

Claims (7)

1 + A braking pressure control device to be inserted in the connection between a master cylinder and wheel cylinders of the rear axle of an automotive vehicle, of the kind wherein a first stepped piston is axially slidably guided in a first stepped bore in opposition to a first pressure spring and has a first valve pasage, which is controllable in dependence upon the vehicle deceleration by an inert mass, the first valve passage being open below a predeterminable deceleration value and providing a communication between the end faces of the first stepped piston, characterised in that in a second stepped bore (3), a second stepped piston (22) containing a second valve passage (37, 41) for the control of the connection between the master cylinder and the wheel cylinder is axially slidably guided in opposition to a second pressure spring (25), and in that the second valve passage (37, 41) is pressuresensitively operable and in that the closure travel of the second valve passage (37, 41) is adjustable due to the axial position of the first stepped piston (8).

2. A braking pressure control device as claimed in claim 1, characterised in that the preload of the second pressure spring (25) is adjustable.

3. A braking pressure control device as claimed in claim 1, characterised in that the first stepped piston (8) and the second stepped piston (22) are coaxially arranged in a housing (1).

4. A braking pressure control device as claimed in in claim 1, characterised in that the ratio of the effective surfaces allocated to the second stepped piston is 2:1.

5. A braking pressure control device as claimed in claim 1, characterised in that the second stepped piston (22) carries a valve seat (41) made of a rubber-elastic material, this valve seat constituting together with a closure member (37), which is in mechanical contact with the first stepped piston (8), the second valve passage.

6. A braking pressure control device as claimed in claim 5, characterised in that the closure member (37) is urged by a third pressure spring (40) against the first stepped piston (8) in the direction of closure of the second valve passage (37, 41).

7. A braking pressure control device substantially as described with reference to the accompanying drawings.