GB2127506A - Deceleration sensitive brake control valve - Google Patents

Abstract

The valve features a stepped piston (3), displaceable in a bore (2) of a housing against a spring force and having a through bore (15), and a valve closure member in the form of a ball (26) co-operating with the stepped piston. Upon braking, ball (26) movable by inertia will determine the opening condition of the valve. The associated valve seat (16) is formed at the piston front face (5) facing the ball (26) and exposed to the inlet pressure (P1). Between the front face (5) and the ball (26), an abutment flange (18) having radial slots is arranged which is displaceable by the piston (3) to a greater extent than the latter and which leaves open a fluid pressure. This occurs under high inlet pressure/low deceleration conditions symptomatic of braking a heavily- loaded vehicle and the piston displaces the abutment flange before the ball can engage the valve seat (16). Full inlet pressure is thereby transmitted to the brake actuators. <IMAGE>

Description

SPECIFICATION Braking pressure reducer This invention relates to a brake deceleration sensitive braking pressure reducer for a vehicular brake system of the kind comprising a valve having a stepped piston, which is displaceable against a spring force in a bore of a housing and provided with a bore for the passage of the pressure fluid, and a valve closure member cooperating with the stepped piston, and with a ball which upon braking, due to its inertia, is movable along a path inclined contrary to the driving direction and whose position determines the opening condition of the valve, the larger pressure surface of the stepped piston being acted upon by the outlet pressure and the smaller pressure surface being acted upon by the inlet pressure and facing the ball.

In a known braking pressure reducer (French Laid-open Print = FR-OS No. 2 431 401) the ball is accommodated in a second bore running transversely in respect of the bore of the housing and having an axis which is slightly inclined towards the horizontal line, with the ball being in its rest position in the deepest point of the second bore in the path of movement of the stepped piston, which path of movement runs vertically in respect of the second bore, the ball thus keeping the stepped piston in the open position of the valve. Upon braking, the ball will roll out of the path of movement of the stepped piston, the latter thus throttling the flow of the pressure fluid together with a valve closure member surrounding the stepped piston and kept in a stationary position.

It is an object of this invention to provide a braking pressure reducer of this kind but featuring a simpler and more compact design.

According to the invention in its broadest aspect, a braking pressure reducer for a vehicular brake system of the kind referred to is characterised in that the bore of the housing extends approximately in the direction of the path of the movement of the ball, in that the ball forms the valve closure member, and in that the associated valve seat is formed at the piston's front face facing the ball and exposed to the inlet pressure, and in that between the front face and the ball an abutment is arranged for the ball, the abutment being displaceable by the piston to a greater extent than the latter and leaving open a fluid passage.

In an embodiment the ball has a double function, thus rendering a separate valve closure member superfluous. Thus, a second bore also becomes superfluous. The design is correspondingly simple and compact. The displaceability of the abutment, provided for the ball by the piston will ensure that, in dependence on the braking pressure determined by the load of the vehicle, the inertia of the ball will cause the latter to move either so far as to adopt the closed position of the valve in which the valve will effect a pressure reduction, or to move into a position in which the valve is not yet closed, the valve thus being ineffective and the braking pressure being fully transmitted to the brake.

Preferably, it will be provided that the abutment will be formed by the inner edge of a radial flange which is held fast at its outer edge so as to be flexible and which overlaps the circumferential edge of the front face of the piston. This embodiment results in a simple type of displacement transmission between the velocities of the piston and the abutment when the piston is pressed against the abutment.

Radial slots may subdivide the flange into segments which, on the one hand, ensures a fluid passage and which, on the other hand, facilitates the displacement of the radially inner edge of the flange by means of the piston.

It will be advantageous if the flange is arranged at the free end of a cup surrounding the ball and having at least one orifice for the pressure fluid. By correspondingly selecting the number, size and position of the orifice(s) it will be possible to influence at least one characteristic of the flow behaviour, such as the dynamic pressure and/or a turbulence, and hence to influence the kinetic behaviour of the ball.

An axial fluid passage may be formed between the ball and the cup wall. Thus, the ball will be guided axially in the cup. Yet the fluid will be able to flow along the ball.

Then, the cup may be pressed towards the smaller piston front face by a spring whose force is considerably less than the spring force acting on the piston. This weak spring will ensure that, under the outlet side pressure, upon removal of the inlet side braking pressure, the piston will displace the cup together with the ball, the valve thus opening at only a slight differential pressure in order to effect a relief of the outlet side pressure.

The spring may be a coiled spring surrounding the cup and supported by a radially outwardly projecting bead formed by a bend of the flange.

This will provide an axially short and simple design of cup and spring.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is an axial section through a braking pressure reducer, and Figure 2 is an enlarged detail of Figure 1.

The braking pressure reducer shown lies between the master brake cylinder and the rear wheel brake cylinder of a vehicular hydraulic brake system. It has a housing 1 with a stepped through bore 2. The centre line of the bore 2 is inclined in respect of the horizontal line, contrary to the direction of driving. Thus, referring to Figure 1, on the right side it lies slightly more downwards than on the left side. In the bore 2, a stepped piston 3 is received axially displaceably. The stepped piston 3 has a larger front face 4 and a smaller front face 5.

A gasket 7 seals the larger diameter piston section 6 against the bore 2. A gasket 9 seals the smaller diameter piston section 8 against a ring 1 0. The ring 10, on its part, is sealed against the bore 2 by means of a gasket 11 and rests at a shoulder 12 of the bore 2. A coiled spring 13 surrounds the piston section 8. The spring 13, on the one hand, presses against the ring 10 and, on the other hand, against the shoulder of the piston section 6.

A sleeve 14 surrounding the spring 1 3 with play and secured against axial displacement, preferably by means of caulking, rests at the inside of the bore 2 between the ring 10 and the shoulder of the piston section 6, acting as a stop for the shoulder of the piston section 6.

Furthermore, the piston 3 has an axial through bore 1 5 whose opening lying in the smaller front face 5 has a valve seat 1 6.

In the bore 2 a cup 17 of elastic material is arranged in an axially displaceable manner on the side of the smaller front face 5. At its free edge, a flange 1 8 is shaped, running at first radially outwards and then radially inwards. Thus a bead 1 9 is formed. A coiled spring 20 surrounding the cup 1 7 is supported by one of its ends at the bead 19, resting with its other end at a shoulder 21 of the bore 2.

The bottom of the cup 1 7 has orifices 22, 23.

At the inside of the wall 24 the cup 1 7 has axial ribs 25 forming an axial fluid passage between the cup wall 24 and a ball 26 arranged in the cup 17.

The outside diameter of the bead 1 9 is larger than that of the front face 5, thus the flange 1 8 radially overlaps the circumferential edge of the front face 5. Further radial slots (not shown) subdivide the flange 1 8 into segments forming a fluid passage.

At the end lying next to the cup 17, the bore 2 forms a tapped opening 27 for the connection of a connecting line leading to the delivery side of the master brake cylinder At the end lying next to the piston section 6, the bore 2 likewise forms a tapped opening 28 into which a cap 29 is screwed up to a shoulder 30 of the bore 2. Further, the cap 29 has an internal thread 31 for the connection of a connecting line leading to the rear wheel brake cylinder.

Figure 1 represents the rest position of the bail 26 before braking. In this position, the spring 1 3 presses the piston 3 against the cap 29, the spring 20 pressing the cup 1 7 with its flange 1 8 against the ring 10. In this position, there remains a first gap between the cup 17 and the shoulder 21, a second gap remaining between the sleeve 14 and the shoulder of the piston section 6. The first gap slightly exceeds the second gap in size. A third gap remains between the front face 5 and the flange 1 8, the third gap being slightly smaller than the second gap.

The pressure fluid supplied, upon braking, from the master brake cylinder in the direction of the arrow which at the same time approximately indicates the direction of driving of the motor vehicle, under an at first only weak pressure P1 as required for the braking of an empty motor vehicle or of a motor vehicle loaded up to but a fraction of x%, will therefore at first flow through the cup 17, along the ball 26, into the front side opening of the bore 15 of the piston 3, and thence through the bore 1 5 and the cap 29 to the rear wheel brake cylinder. In doing so, the braking pressure P2 on the outlet side of the braking pressure reducer will increase in the same degree as the braking pressure P1 on the inlet side.The result of the braking action thus ensuing will be that the ball 26 in the cup 17, due to its inertia, as well as because of the flow pressure, will roll or slide in the direction of driving up to the radially inner edge of the flange 1 8 without, however, interrupting the flow of the pressure fluid through the braking pressure reducer. A further increase of the pressure P1 and hence of the pressure P2 will finally result in a force acting on the front face 4 of the piston 3 which will exceed the total of the forces exerted by the pressure P1 on the front face 5 and by the spring 13 on the piston 3. The piston 3 will thus be displaced towards the ball 26 until the flow between the latter and the valve seat will be throttled so far that there will be a balance of forces on both sides of the piston 3.Upon a further increase of the pressure P1, the pressure P2 thus will no longer increase in the same degree as pressure P1, yet reduced, the ratio of increase being A2-A3 m= A1-A3 where A is the area of the surface with the diameter D1. A2 is the area of the surface with the diameter D2, and A3 is the area of the surface with the diameter D3.

The motor vehicle now being loaded by more than x%, right from the beginning, a considerably higher pressure P1 must be applied in order to brake the vehicle in the same manner. In consequence, the pressure P2 will also increase very rapidly and, even before the bail 26 will be able to come out of its rest position and reach the flange 1 8 and approach the valve seat 16, the pressure P2 will already have displaced the piston 3 so far (to the right in the drawing) that the piston 3 will have moved the flange 1 8 out of the rest position A into position B according to Figure 2 in which the ball will be kept at a greter distance in respect of the valve seat 1 6 than required for the performance of a throttling action. Thus the pressure P1 will continue to be transmitted, unreduced, to the outlet side of the braking pressure reducer, the rear wheel being permanently braked with the maximum pressure as is permissible in a vehicle loaded by more than x% without the danger of a lock of the rear wheel(s).

The pressure P1 being removed, the piston 3 will displace the cup 1 7 together with the ball 26 against the force of the spring 20 to the right until the piston section 6 abuts with its shoulder at the sleeve 14. The spring 20 is rated so weakly that an opening of the valve formed by ball 26 and valve seat 1 6 will be achieved even if pressure P is only slightly less than pressure P2.

Claims (8)

1. A brake deceleration sensitive braking pressure reducer for a vehicular brake system of the kind comprising a valve having a stepped piston, which is displaceable against a spring force in a bore of a housing and provided with a bore for the passage of the pressure fluid, and a valve closure member co-operating with the stepped piston, and with a ball which upon braking, due to its inertia, is movable along a path inclined contrary to the driving direction and whose position determines the opening condition of the valve, the larger pressure surface of the stepped piston being acted upon by the outlet pressure and the smaller pressure surface being acted upon by the inlet pressure and facing the ball, characterised in that the bore (2) of the housing extends approximately in the direction of the path of movement of the ball (26), in that the ball (26) forms the valve closure member, and in that the associated valve seat (16) is formed at the piston's (3) front face (5) facing the ball (26) and exposed to the inlet pressure (P,), and in that between the front face (5) and the ball (26) an abutment is arranged for the ball (26), the abutment being displaceable by the piston (3) to a greater extent than the latter and leaving open a fluid passage.

2. A braking pressure reducer as claimed in claim 1 , characterised in that the abutment is formed by the inner edge of a radial flange (1 8) which is held fast at its outer edge so as to be flexible and which overlaps the circumferential edge of the front face (5) of the piston.

3. A braking pressure reducer as claimed in claim 2, characterised in that radial slots subdivide the flange (18) into segments.

4. A braking pressure reducer as claimed in claim 2 or 3, characterised in that the flange (1 8) is arranged at the free end of a cup (17) surrounding the ball (26) and having at least one orifice (22, 23) for the pressure fluid.

5. A braking pressure reducer as claimed in claim 4, characterised in that an axial fluid passage (25) is formed between the ball (26) and the cup wall (24).

6. A braking pressure reducer as claimed in claim 4 or 5, characterised in that the cup (17) is pressed towards the stepped piston (3) by a spring (20) whose force is considerably less than the spring force acting on the piston.

7. A braking pressure reducer as claimed in claim 6, characterised in that the spring (20) is a coiled spring surrounding the cup (17) and is supported by a radially outwardly projecting bead (19) formed by a bend of the flange (18).

8. A braking pressure reducer for a vehicle brake system substantially as described with reference to the accompanying drawings.