This invention relates to antiloc modulators.

Antilock modulators, for example of the type used in vehicle anti-lock braking systems as disclosed in British Patent Application GB 2 174 775A, comprise a cylinder body having a plunger slidably located therein, sai plunger being arranged to control a ball valve which in turn controls flow of fluid from a brake master cylinder to one or more wheel cylinders. Typically, movement of the plunger is controlled by a vacuum actuator in which, a flexible diaphragm is connected between the outer periphery of a piston and a casing to define two fluid tight chambers. The piston abuts one end of the plunger and spring means is provided to urge the piston and plunger towards the ball valve. The chamber on the side of the piston from which the spring means acts is connected to vacuum and the other chamber is selectively connected to vacuum or to atmosphere, by for example a solenoid valve. The pressure differential across the piston may thus be controlled by the solenoid valve to control movement of the piston.

When servo devices of this type are used in anti-lock systems, problems can be encountered because the ball valve

when open must permit a sufficiently high rate of flow to initially allow the brakes to be applied rapidly. This flow rate may however be too high when coming out of an anti-lock cycle, so that opening of the ball valve will merely induce a further skid situation.

The present invention provides an antilock modulator in which the rate of flow of fluid is controlled depending upon the pressure differential across the valve.

According to one aspect of the present invention an antilock modulator comprises a valve body defining a cylinder; a plunger slidably mounted within the cylinder and sealed with respect to the cylinder towards one end thereof; an inlet and an outlet opening at axially spaced locations into said cylinder, adjacent the other end thereof; a valve assembly mounted co-axially of the plunger between the inlet and the outlet, said valve assembly having a first valve member arranged to control flow of fluid from inlet to outlet characterised in that, the valve assembly defines two fluid flow paths between the inlet and first valve member, a second valve member being provided to control flow of fluid through one of said paths, the plunger being adapted to control movement of the first and second valve members sequentially upon axial movement relative to the cylinder, said second valve

member being arranged such that a pressure differential between the inlet and the outlet will oppose a force applied by the plunger to open said second valve member; and means being provided to selectively move said plunger relative to said cylinder.

An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a sectional elevation of an antilock modulator used in the anti-lock braking system disclosed in British Patent Application GB 2 174 775A; and

Figure 2 is a sectional elevation of the valve assembly of an antilock modulator according to the present invention.

An antilock modulator 10 illustrated in figure 1 comprises a valve body 11 having a cylindrical bore 12 with inlet port 13 and outlet port 14 opening into the bore 12 at axially spaced locations. A valve seat member 15 is secured in the bore 12 and has a control port 16 which can be closed by ball 17. A control plunger 18 is slidable in bore 12 and in the position illustrated in the figure is operative to unseat the ball 17 against a light compression spring 19, thereby opening communication between the inlet

port 13 and outlet port 14. A cylindrical portion 20 of the valve body 11 is mounted through a closure member 25 of a dish shaped casing 26, so that it projects co-axially into the casing 26. A piston 27 has a central supporting - portion 28 with a cylindrical bore which is slidingly located on the cylindrical portion 20 of valve body 11, tite end of support portion 28 engaging the end of plunger 13K._ A pair of helical compression springs 29 and 30 act between the end wall of the casing 26 and the piston 27 to urge the piston 27 towards the closure member 25 and thus the plunger 18 towards the ball 17. An annular elastomeric diaphragm 31 is secured at its inner periphery to the piston 27 in groove 32, and at its outer periphery between the closure member 25 and casing 26 in a groove 33 in the outer periphery of the closure member 25, thereby separating the casing 26 into two separate chambers 34 and 35. A solenoid valve 40 is arranged to selectively connect chamber 35 to atmosphere or via line 41 to a source of vacuum. Chamber 34 is also connected via line 41 to the source of vacuum.

In use, the antilock modulator 10 is connected in the brake circuit with inlet port 13 connected to the hydraulic master cylinder and outlet port 14 connected to one or more wheel cylinders. With chamber 35 connected via solenoid valve 40 to vacuum, the springs 29 and 30 will urge piston

27 towards the closure member 25 and thus the plunger 18 will unseat the ball 17 as illustrated in figure 1. In this condition, if the brakes are applied, fluid from the master cylinder will flow through inlet port 13 past the control port 16 and via the outlet port 14 to the wheel cylinders, thereby to apply the brakes. If however during a braking operation, solenoid valve 40 is switched to connect chamber 35 to atmosphere, the pressure differential across diaphragm 31 will cause piston 27 to move away from the closure member 25 and movement of plunger 18 with the piston 25 will permit ball 17 to close control port 16 thereby isolating the wheel cylinders from the master cylinder. Continued movement of the plunger 18 away from the ball 17 will then permit the fluid in the wheel cylinders to flow back into cylinder 12, thereby reducing the braking effort. Re-application of the brakes may then be achieved by switching solenoid valve 40 to re-connect chamber 35 to vacuum so that the springs 29 and 30 will return the piston 27 and plunger 18 to re-open the control port 16.

In an anti-lock system, switching of the solenoid valve 40 may be controlled by sensors associated with one or more of the wheels, these sensors giving an indication of the deceleration of the wheel, so that when road conditions are such that skidding of the wheel is liable to occur, the

solenoid valve 40 may be switched to connect chamber 35 to atmosphere and thereby reduce the braking effort and the risk of skidding. When road conditions improve, the solenoid valve may be switched to re-connect chamber 35 to vacuum, so that maximum braking effort may be re-applied.

However, during the anti-lock cycle, it is possible that there would be a considerable differential between the pressure of fluid in the master cylinder and the pressure in the wheel cylinders. For example, in an emergency stopping manoeuvre, the driver will have pressed the brake pedal hard down and will continue to apply pressure even though the antilock modulator 10 has been actuated to reduce the braking effort. The flow area through the control port .16 is designed to cope with initial application of the brake, where a high flow rate is required, so that clearances between the elements of the brake may be taken up and the brakes applied quickly. With the high pressure differential at the end of an anti-lock cycle, this flow area will allow a too rapid increase of pressure at the wheel cylinders, inducing further skid conditions or, where adhesion- between the wheels and the road is non-uniform, an undesirable yawing movement of the vehicle.

In the valve illustrated in figure 2, the valve body 11 is

formed in two parts, a cylindrical portion 20 and a valve assembly housing 50, which are secured together and sealed by means of O-ring 51. A further O-ring 52 is provided on the external diameter of the cylindrical portion 20 sealing against the closure member 25 (as shown in figure 1).

The plunger 18 is slidably located in a stepped cylindrical bore and is sealed towards the open end thereof by means of O-ring 53. A bearing ring 54 is located in a circumferential groove 55 adjacent the other end of plunger 18 and bears against the cylindrical bore 12 to provide support for the plunger at that end. Axial grooves are provided on the internal diameter of ring 54 to permit passage of fluid.

The valve assembly housing 50 has an inlet port 13 and an outlet port 14. A valve seat member 56 is located within the housing 50 and is sealed with respect thereto by means of O-ring 57, the seat member 56 being retained in position by abutment with the cylindrical portion 20. The seat member 56 has a stepped axial bore 58 which is coaxial with the cylindrical bore 12, the portion 59 adjacent the cylindrical portion 20 of valve body 11 being of reduced diameter and being separated from an enlarged diameter portion 60 by an axially extending annular seat formation

61. A passage 62 is provided in the seat member 56 to provide connection between the cylindrical bore 12 and

outlet 14 .

A tubular valve member 65 is located in the bore 58 of seat member 56, the end portion 66 of valve member 65 being slidably sealed within portion 59 of bore 58. An enlarged external diameter portion 67 of valve member 65 is provided with radially spaced axial grooves in its outer periphery and locates within the enlarged diameter portion 60 of bore 58. A clearance is provided between the outer periphery of portion 67 and the opposed wall of bore 58, while the portion 67 overlaps the seat formation 61 on a radius positioned inwardly of the grooved outer periphery. A compression spring 68 - acts between an end face 69 of housing 50 and the opposed face of portion 67, to urge the valve member 65 and portion 67 thereof towards the seat formation 61.

The axial bore 70 of member 65 is stepped, the portion 71 at end 66 being of reduced diameter to define a valve seat 72. The opposite end of bore 70 is partially closed by a restrictor 73, said restrictor 73 defining a relatively small orifice 74. A ball 75 is located within the larger diameter portion 76 of bore 70 between the restrictor 73 and seat 72 and is urged towards the seat 72 by means of a compression spring 77. One or more radial bores 78 are provided through the wall of valve member 65, at an axial location intermediate of the portion 67 and the seat 72.

The valve member 65 is dimensioned such that when plunger 18 is at the extremity of its travel to the left (as illustrated in figure 2), the end portion 66 will abut the head 79 of plunger 18 and portion 67 of member 65 will be held clear of the seat formation 61. The end portion 66 of member 65 is notched and head 79 of plunger 18 is chamfered, so as to permit passage of fluid therebetween, even when they are in abutment as illustrated in figure 2.

A small diameter extension 80 of plunger 18 passes through portion 71 of bore 70 to engage ball 75. The extension 80 is longer than portion 71, so that in the ^* position illustrated in figure 2, it will hold ball 75 clear of seat 72. A clearance is provided between the extension 80 and bore 70 so that fluid may flow therebetween.

With the valve disclosed above, in the open position illustrated in figure 2, fluid may flow from the inlet 13 to bore 70 of member 65 through the restricted orifice 74 and also through the annular gap between portion 67 of member 65 and the wall of portion 60 of bore 58 and then through radial bores 78. The fluid in bore 70 will then flow past ball 75 and through the annular gap between extension 80 and the wall of bore 70 into the cylindrical bore 12 and from thence via passage 62 to the outlet 14. When plunger 18 is moved to the right (as illustrated in figure 2) valve member 65 will first move with the plunger

18 under the influence of spring 68 until portion 67 seats against the seat formation 61. Continued movement of plunger 18 will then permit ball 75 to seat against the seat 72. The outlet 14 ^* will then be isolated from inlet 13. Continued movement of plunger 18 will then permit fluid to flow back into the cylindrical bore 12 from the outlet 14 to reduce the pressure at outlet 14 as described with reference to figure 1.

Upon re-application by. movement of plunger 18 to the left (as illustrated in figure 2), the extension 80 will first engage and unseat the ball 75, thus permitting flow of fluid from inlet 13 through the restrictor orifice 74 into bore 70, past ball 75 and through the angular gap between extention 80 and the wall of bore 70 into the cylindrical bore 12 and thus via passage 62 to the outlet 14. However, pressure differential across the valve member 65 will oppose further movement of the plunger 18 and consequently no flow will occur passed the seat formation 61. The rate of flow of fluid through the valve is consequently reduced until the pressure differential between inlet 13 and outlet 14 is ^" reduced to such an extent that the force urging plunger 18 to the left is sufficient to overcome the pressure differential across ^" valve member 65, when the valve member 65 will be unseated thus permitting fluid to flow through the annular gap between portion 67 and the

wall of bore 58 and the radial bores 78, thus restoring flow through the valve to its original value.

This valve arrangement if used in an anti-lock braking system of the type disclosed with reference to figure 1, would consequently permit initial re-applica ion of the brakes at a relatively slow rate until the pressure differential between the master cylinder and the wheel cylinders had been reduced, thus avoiding the problems described above with reference to the conventional antilock modulator illustrated in figure 1.

Various modifications may be made without departing from the invention. For example, while in the above embodiment movement of the plunger 18 is controlled by a vacuum servo of conventional construction, other forms of actuator may be used, for example an air servo or solenoid actuator. Also while this valve is suitable for vehicle anti-lock braking systems it may be used in other applications.