GB1591143A

GB1591143A - Control valve assemblies

Info

Publication number: GB1591143A
Application number: GB2142077A
Authority: GB
Original assignee: Girling Ltd
Current assignee: Girling Ltd
Priority date: 1978-05-17
Filing date: 1978-05-17
Publication date: 1981-06-17

Description

(54) CONTROL VALVE ASSEMBLIES (71) We, GIRLING LIMITED, a British Company, of Kings Road, Tyseley, Birmingham 11, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to control valve assemblies for use in vehicle braking systems.

Control valve assemblies are usually positioned in the brake pressure line between the pressure source, for example a master cylinder, and the rear wheel brakes to reduce or limit the pressure applied to the rear brakes relative to the full pressure applied to the front brakes. The valve may have a valve member which is subjected to a pre-load in dependence upon vehicle loading so that the "cut-in" point of the valve, i.e. the inlet pressure at which the valve operates, is varied in dependence upon the vehicle loading.

In a previously proposed control valve assembly the pre-load is applied by a torsion spring having one end acting on the valve member and the other end connected to the rear axle. The spring is subjected to vehicle suspension deflections and has a spring rate determined by the pre-loads required to operate the control valve in both the laden and unladen cases. The resulting pre-load applied to the valve member varies in a generally non-linear relationship with the vehicle suspension deflections caused by changes in vehicle loading.

Furthermore, in certain conditions the brakes may be applied when the vehicle suspension is bottomed (at full bump deflection) and with the previously proposed valve this would result in extremely high loads being applied to the control valve member due to the high spring rate.

In accordance with the present invention, there is provided a control valve assembly for a vehicle braking system, comprising a valve having a valve element which is axially movable to control communication between an inlet and an outlet, for connection in a brake pressure circuit, resilient means for applying a force to the valve element in a sense to urge the valve open, and force-varying means intermediate the resilient means and the valve element, the force-varying means comprising a force-transferring member co-operating with an inclined surface, the inclination of which is in use variable in dependence upon vehicle loading, the arrangement being such that the force applied to the valve element varies substantially linearly with the variation in the inclination of the inclined surface.

Preferably, the force-transferring member is a roller which engages the inclined surface and which is connected to both the valve element and the resilient means. The force of the resilient means acts in a direction which is at an angle, preferably 90 , to the direction of axial movement of the valve element.

The force applied by the resilient means is preferably substantially constant and independent of vehicle loading and preferably comprises a caged coil compression spring.

A control valve assembly in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an axial cross-section of the control valve assembly, Figure 2 is a graph of output pressure versus input pressure showing the ideal curves and the curves obtained by the control valve assembly of Figure 1, and Figure 3 is a graph of cut-in pressure versus the angle of inclination of an inclined surface.

The control valve assembly comprises a housing 1 having bores 2 and 3 arranged substantially at right angles. Bore 2 contains a valve 4 which controls communication between an inlet 5 and an outlet 6 which in use are connected in a vehicle brake pressure line, usually the line to the rear brakes. The valve 4 comprises a valve element in the form of a differential control piston 7 and a valve seat 8. The valve seat is co-operable with a valve closure member in the form of a ball 9. A stem 11 protrudes from an end closure 12 through the valve seat 8 and is engageable with the ball.

The control piston is subjected to a force applied by a coil compression spring 13 housed in bore 3 and engaging at opposed ends a fixed seat 14 and a movable seat 15. The force of the spring 13 is transmitted to the piston 7 by a force-varying arrangement which comprises load transmitting members 16, 17 engaging respectively the piston 7 and the movable spring seat 15. The members 16, 17 are connected to an axle 18 of a roller 19 which engages a surface 20 formed on a rotary member 21 connected to an arm 22. The arm 22 is movable angularly between fully unladen and fully laden vehicle conditions illustrated.

The axle 18 is located on the axis of the control piston 7. In normal operation when the vehicle is in motion, transient movements of the arm 22 cause the surface 20 to rotate around the roller 19 and the valve parts remain in the rest position, the spring 13 being caged. Thus the inclined surface 20 is not loaded. When the brakes are applied pressure is supplied through the inlet 5 and, when the force applied by the spring 13 to the control piston 7 is overcome, the valve closes and further increase in inlet pressure successively opens and closes to meter pressure from the inlet to the outlet in a known manner.

When the inlet pressure is reduced, the control piston forces the foller 19 up the inclined surface 20 to expand the brake volume, i.e. the volume on the outlet side of the valve, and reduce the outlet pressure until the inlet pressure falls below the outlet pressure, at which time the ball valve opens and allows the control piston 7 to return to its original position with the ball valve held fully open.

The spring force acting on the control piston 7 is varied by varying the angle of the arm 22, and thus the inclined surface 20.

When brake pressure is applied, the control pistion 7 urges the roller 19 up the surface 20 against the force of the control spring. At the "cut-in" point, i.e. when the valve first closes, the pressure force on the piston, PA = S tan 0 where P = cut-in pressure A = the minor area of the control piston S = the spring force H = the angle of inclination of the surface to the axis of the control piston In a typical example, the spring force S = 250 lb and the control piston area A = .08 in.2 In the unladen condition 8 = 4" .070 and P = 250 x = 219 p.s.i.

.08 In the laden condition fl = 25 .466 and P = 250 x = 1460 p.s.i.

.08 The angle of inclination H is determined by the movement of the arm 22 due to the relative travel of the axle and chassis of the vehicle and includes the reverse rotation which occurs due to weight transfer during braking.

It will be noted that the rate of spring 13 does not substantially affect the cut-in pressure.

For example, if the control piston moves .02 in. to close the valve, the spring moves only .02 x .070 = .0014 in. when unladen and .02 x .466 = .00932 in. when laden. Thus if the spring rate is 500 Ibs/in, the unladen error is 500 x 8'4 = 8.75 p.s.i. (an error of 4% )and when laden the error is 500 x m32 = 58.5 p.s.i. (an error of 4%).

In this way, the cut-in pressure varies substantially linearly with the angle of inclination of the surface 20, as illustrated in Figure 3. Furthermore, the output/input pressure curves obtained using the valve of Figure 1 follow reasonably closely the curves for ideal braking, as illustrated in Figure 2.

It will be appreciated that the control spring 13 provides a relatively simple overtravel mechanism and the spring will compress if the pressure forces are too great, thereby avoiding jamming of the brakes. Furthermore, the load of the control spring is independent of vehicle loading and the characteristics of the valve can therefore readily be determined independently of the vehicle to which the valve assembly is to be attached. The valve assembly also has a low hysteresis, since the spring rate can be relatively low and relatively few sliding seals are used.

It will be appreciated that during normal travel the arm 22 will oscillate due to transient changes in loading of the vehicle, but since the spring 13 is caged, the inclined surface 20 will merely rotate about the roller 19 and the axle 18 will not be subjected to loads dependent upon the vehicle loading.

Many modifications of the valve assembly are possible, for example, the arm 22 and, therefore, the inclined surface 20 may be biased by an external torsion spring (not shown) to either the unladen case, with the inclined surface 20 substantially horizontal, or to the fully laden case with the inclined surface having an inclination of, say, 25 or more, so that if the linkage (not shown) between the arm and the vehicle should fail, the arm 22 will adopt its desired position. The choice of which failed position the arm adopts can be left to the vehicle manufacturer.

The spring 13 and the force-varying arrangement could be used to control two valves for a vehicle having a dual circuit braking system.

The above-described valve can be modified to suit any vehicle by suitable alterations to the parameters controlling the characteristics of the valve, namely the rate of spring 13, the length of the external arm 22, and changes in the differential areas of the control piston 7.

Although described above as incorporating a pressure reducing valve, in which after "cut-in" the outlet pressure is reduced as compared to the inlet pressure, the valve assembly could incorporate other forms of valve, for example a pressure limiting valve in which the outlet pressure does not increase after "cut-in".

The valve may operate with air or liquid.

WHAT WE CLAIM IS: 1. A control valve assembly for a vehicle braking system, comprising a valve having a valve element which is axially movable to control communication between an inlet and an outlet, for connection in a brake pressure circuit, resilient means for applying a force to the valve element in a sense to urge the valve open, and force-varying means intermediate the resilient means and the valve element, the force-varying means comprising a forcetransferring member co-operating with an inclined surface, the inclination of which is in use variable in dependence upon vehicle loading, the arrangement being such that the force applied to the valve element varies substantially linearly with the variation in the inclination of the inclined surface.

2. An assembly according to claim 1, wherein the force-transferring member comprises a roller which engages the inclined surface and which is connected to both the valve element and the resilient means.

3. An assembly according to claim 1 or 2, wherein the force of the resilient means acts substantially perpendicularly to the direction of movement of the valve element.

4. An assembly according to any of claims 1 to 3, wherein the force of the resilient means is preferebly constant and independent of vehicle loading.

5. An assembly according to any of claims 1 to 4, wherein the resilient means comprises a caged coil compression spring.

6. An assembly according to any of claims 1 to 5, wherein the inclined surface is formed on a rotatable member connected to a movable arm which in use moves in dependence upon vehicle loading.

7. An assembly according to claim 6, wherein the arm is biased towards one of two extreme positions which represent fully laden and unladen vehicle conditions.

8. An assembly according to any of claims 1 to 7, including another such valve having an inlet and outlet for connection in another brake pressure circuit, the resilient means applying a force also to the valve element of said other valve.

9. A control valve assembly for a vehicle braking system substantially as herein described with reference to Figure 1 of the accompanying drawings.

10. A vehicle braking system incorporating a valve assembly according to any of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. will merely rotate about the roller 19 and the axle 18 will not be subjected to loads dependent upon the vehicle loading. Many modifications of the valve assembly are possible, for example, the arm 22 and, therefore, the inclined surface 20 may be biased by an external torsion spring (not shown) to either the unladen case, with the inclined surface 20 substantially horizontal, or to the fully laden case with the inclined surface having an inclination of, say, 25 or more, so that if the linkage (not shown) between the arm and the vehicle should fail, the arm 22 will adopt its desired position. The choice of which failed position the arm adopts can be left to the vehicle manufacturer. The spring 13 and the force-varying arrangement could be used to control two valves for a vehicle having a dual circuit braking system. The above-described valve can be modified to suit any vehicle by suitable alterations to the parameters controlling the characteristics of the valve, namely the rate of spring 13, the length of the external arm 22, and changes in the differential areas of the control piston 7. Although described above as incorporating a pressure reducing valve, in which after "cut-in" the outlet pressure is reduced as compared to the inlet pressure, the valve assembly could incorporate other forms of valve, for example a pressure limiting valve in which the outlet pressure does not increase after "cut-in". The valve may operate with air or liquid. WHAT WE CLAIM IS:

1. A control valve assembly for a vehicle braking system, comprising a valve having a valve element which is axially movable to control communication between an inlet and an outlet, for connection in a brake pressure circuit, resilient means for applying a force to the valve element in a sense to urge the valve open, and force-varying means intermediate the resilient means and the valve element, the force-varying means comprising a forcetransferring member co-operating with an inclined surface, the inclination of which is in use variable in dependence upon vehicle loading, the arrangement being such that the force applied to the valve element varies substantially linearly with the variation in the inclination of the inclined surface.