WO1991008934A1

WO1991008934A1 - Vehicle braking systems

Info

Publication number: WO1991008934A1
Application number: PCT/GB1990/001923
Authority: WO
Inventors: Martin Murphy
Original assignee: Grau Limited
Priority date: 1989-12-12
Filing date: 1990-12-10
Publication date: 1991-06-27
Also published as: GB8928035D0

Abstract

A breaking system comprising a source of brake actuating fluid under pressure (S), a brake actuator (B), a relay valve (8) operative between the source (S) and the actuator (B), a manually operable control valve (M) to provide a fluid pressure control signal and a control device (9) to operate on the control signal to control the relay valve (8) in a first mode in which application of the brake actuating fluid from the source (S) to the brake actuator (B) is controlled manually or in a second mode in which the application of brake actuating fluid from the source (S) to the brake actuator (B) is controlled by an anti-lock brake controller (C) wherein means (47, 51) are provided to apply the control signal to the relay valve (8) (a) when the control device (9) is in the first mode; through a supply line (48) having a first volume, and (b) when the control device (9) is in the second mode; through a supply line (48) (60) having a second volume which is significantly larger than the first volume.

Description

Title: "Vehicle braking systems"

This invention is concerned with improvements relating to vehicle braking systems, and in particular to a system of the kind (hereinafter referred to as being of the kind specified) comprising a source of brake actuating fluid under pressure, a brake actuator, a relay valve operative between the source and the actuator, a manually operable control valve to provide a fluid pressure control signal and a control device to operate on the control signal to control the relay valve in a first mode in which application of the brake actuating fluid from the source to the brake actuator is controlled manually or in a second mode in which the application of brake actuating fluid from the source to the brake actuator is controlled by an anti- lock brake controller.

During operation of a system of the kind specified, the control device will normally be in its first mode, in which the brake is applied manually, e.g. by manual operation of a brake pedal, to slow rotation of a wheel and hence to retard the vehicle, the pressure of the brake actuating fluid applied to the brake actuator being controlled by the relay valve in accordance with the pressure applied to the brake pedal by a driver. If the wheel skids, sensing means is operative to provide an input signal to the anti-lock brake controller which operates on the control signal to cause the relay valve to release the brake until the skid signal is removed, whereupon the brake is re-applied, the pressure of the brake actuating fluid being controlled by the anti-lock brake controller to provide a stepped rise in control signal pressure so as to achieve a corresponding stepped rise in brake actuating fluid pressure and so provide a more precisely controlled brake application towards the skid point.

It is well known to apply the control signal pressure to the relay valve through a restrictor so that change in the pressure of the brake actuating fluid more closely follows the change in the pressure of the control signal. Such an arrangement has been used for many years in the MCR type of valve manufactured and sold by the applicants and is also known from, for example, US-A- 4025127.

However, this is disadvantageous where the vehicle is braked other than in the second mode.

According to this invention there is provided a braking system of the kind specified wherein means are provided to apply the control signal to the relay valve a) when the control device is in the first mode; through a supply line having a first volume, and b) when the control device is in the second mode; through a supply line having a second volume which is significantly larger than the first volume.

Thus, when the control device is in the second mode the rate of increase of pressure of the control signal in the supply line is significantly reduced compared with the rate of increase in pressure in the first mode, and hence the rise in brake actuator pressure more closely follows a rise in control signal pressure: conversely, when the control device is in the first mode, the rate of increase in the pressure of the control signal in the supply line is not so reduced, providing a maximum response rate of the relay valve to braking demand as signalled by the control signal.

Two supply lines may be provided, one operative to apply the control signal to the relay valve when the control device is in the first mode, the other, of significantly larger volume than the volume of the one line, being operative to apply the control signal to the relay valve when the control device is in the second, anti- lock, braking mode.

Preferably, however, a single supply line and an expansion chamber of significantly larger volume than the volume of the supply line, is provided, there being means effective when the control device is in the first mode to isolate the expansion chamber from the supply line and when the control device is in the second mode, to bring the expansion chamber into communication with the supply line.

By the term "significantly larger" as used herein we mean at least twice as large, and preferably between two and five times larger.

If desired the chamber may be adjustable in volume, whereby a desired response profile may be selected.

The expansion chamber may be provided by a cavity, into which a closure member is adjustably mounted to vary the operative volume of the expansion chamber, or by a plurality of expansion sub-chambers, which may be selectively connected to the supply line for the provision of a desired expansion volume.

Thus, a single module of valve may be provided, allowing the volume of the expansion chamber to be determined in accordance with the system into which the valve is fitted.

The control device may comprise a first solenoid operated valve and a second solenoid operated valve, the first valve being operable to control passage of the control signal to or from the relay valve, the second valve being operable to control passage of the control signal to or from the relay valve and to control exhaust of control signal from the relay valve.

The first valve may be operative to isolate the expansion chamber from the supply line when the first valve permits of flow of control signal to or from the relay valve and to bring the expansion chamber into communication with the supply line when the first valve prevents flow of control signal to or from the relay valve.

The first valve may comprise a valve member having a first seat portion to control passage of control signal to or from the relay valve and a second seat portion to control passage of control signal into the expansion chamber. The second valve may comprise a valve member having a first seat portion to control passage of control signal to or from the relay valve and a second seat portion to permit or prevent exhaust of the control signal from the relay valve and of control signal pressure from the expansion chamber.

The first and second solenoid valves may be connected in series in the supply line for the control signal to the relay valve with the first solenoid valve being disposed upstream of the second solenoid valve in said line.

There will now be given a detailed description to be read with reference to the accompanying drawing, of a braking system which is the preferred embodiment of this invention, having been selected for the purposes of illustrating the invention by way of example.

In the accompanying drawings:

FIGURE 1 is a schematic view of part of a control unit of the preferred embodiment; and

FIGURE 2 is a view showing the relationship between brake actuator pressure PI and control signal pressure P2 by utilisation of the control unit shown in Figure 1.

The braking system which is the preferred embodiment of this invention comprises a control unit 7 providing a relay valve mechanism 8 and a control device 9. The unit 7 comprises a valve body 10. The relay valve mechanism 8 is provided by an inlet chamber 12 and in communication therewith, a chamber 14, an inlet passage 16 for brake actuating fluid extending from a source S of fluid under pressure (such as air) to the inlet chamber 12 whilst an outlet passage 18 for brake actuating fluid extends from the chamber 14 to a brake actuator B.

Mounted in the inlet chamber 12 is a seating member 24 having a hollow stem 26 slidably mounted in a relief passage 28 extending from the inlet chamber. Mounted in the chamber 14 is a piston comprising a head 20 and a hollow stem 22 providing a pressure relief passage 23. The volume of the chamber 14 above the head 20 constitutes a control chamber 14a, whilst that below constitutes a delivery chamber 14b.

The seating member 24 is urged by spring means 27 into a first position, shown in Figure 1 of the drawings, in which it engages a circular lip seal 30, effectively closing the inlet passage 16 from the chamber 14b.

The control device 9 is provided by a first chamber 46 in which a first solenoid valve 47 is located, a passage 48 extending from the chamber 46 to a second chamber 50 in which a second solenoid valve 51 is located. Connected to an inlet 44 for control device 9 is a manually operable control valve comprising a brake pedal M which is supplied with air under pressure from a reservoir R and which provides a fluid pressure control signal to the inlet 44. The pressure of the control signal varies in accordance with the extent of operation of the valve M.

A first outlet passage 52 extends from the chamber 50 to the control chamber 14a, whilst a second passage 54 extends from the chamber 50 to a central portion of the piston head 21, so as to be in communication with the pressure relief passage 23 therein.

An expansion chamber 60 is connected to the chamber 46 by passage 62, and to the chamber 50 by a passage 64, the passages 62 and 64 are closed by their respective solenoid valves 47, when in their "zero" or rest positions. The expansion chamber 60 has a volume which is significantly larger than the volume of the supply line provided by the passage 45, chamber 46, passage 48, chamber 50 and passage 52 and control chamber 14a.

Advantageously the expansion chamber increases said volume by a factor of at least two, preferably between two and five, and may if desired by variable, such that the volume of the expansion chamber may be selected in accordance with the braking system into which the control chamber is designed to be installed. The volume of the expansion chamber 60 may be rendered variable by means of a closure member 65 which is adjustable to vary the volume of the chamber 60. Alternatively a plurality of expansion sub-chambers may be provided which may be selectively connected to the supply line.

The two solenoid valves 47 and 51 have valve members with seat portions at opposite ends and are spring- urged into their "0" positions (shown in Figure 1) but may be moved to their "1" positions by energisation of their respective magnets by a conventional anti-skid brake controller C which receives wheel speed signals from sensors .

With the control device 9 in a first mode (i.e. the braking system operating under normal manual control) upon the application of pressure to the vehicle brake pedal M, fluid under pressure is applied to the control port 44. With the solenoids 47 and 51 respectively in their "0" positions, as shown, flow of control signal through passage

45, a first seat portion 66 of the valve 47, the chamber

46, passage 48, a first seat portion 67 of the valve 51, chamber 50 and passage 52 takes place to depress the control piston 20 of the relay valve. This causes the stem 22 to engage the seating member 24 and depressing it against the action of its control spring, allowing fluid under pressure to flow from the reservoir through the inlet passage 16 via the outlet passage 18 to the brake actuator B, for the application of vehicle braking.

On release of the brake pedal M, pressure in the control chamber 14a reduces, and the piston 20 moves upwardly within the control chamber 14a, the seating member 24 following movement of the piston until it contacts the circumferential lip seal 30, sealing off the inlet passage 16. Continued upward movement of the control piston 20 allows pressure within the delivery passage 18 to be vented through the hollow interior of the seating member 24 through exhaust passage 28. On application of fluid under pressure through the control port 44 when the control device is operating in the first mode, the expansion chamber 60 remains isolated from flow of fluid pressure to the control chamber 14a.

In the event, whilst there is a manual application of the brake pedal, and hence control signal fluid under pressure at the inlet port 44, a skid situation is detected by the controller C, the control device 9 adopts a second mode, comprising the following stages:

(a) in a first stage the first solenoid valve 47 is energised to move it to the •l' position, to cause the first seat portion 66 to close the passage 45 and prevent the further application of control signal from the control port 44 into the chamber 46. The second solenoid valve 51 is simultaneously energised, allowing pressure in the control chamber 14a to flow through passage 52, a second seat portion 68 of the valve 51, passage 54 and passage 23 to exhaust. The pressure within the chamber 14b causes the control piston 20 to rise, to relieve the pressure applied to the brake actuator through the hollow interior of sealing member 24 (Point A Figure 2) .

(b) This relief of braking pressure continues until the controller C detects a termination of the skid signal and then a second stage is initiated in which the second solenoid valve 51 is de- energised, allowing the valve to return to its 0 position, whilst the first valve 47 remains energised, in the *1' position. This terminates the dumping of the pressure from the control chamber 14a, whilst the subsisting pressure is maintained (point B) .

(c) After a predetermined time interval the controller indicates a third stage (Point C) in which the first solenoid valve 47 is de-energised δ in pulses for brief periods of time, such as 5 milliseconds.

This allows the application of control signal fluid under pressure through the control port 44, passages 45, 48 and 52 into the control chamber 14a, causing a stepwise rise in the pressure of the control chamber 14a.

During each re-energisation of the first solenoid valve 47, fluid under pressure flows from the passage 48 via a second seat portion 69 of the valve 47 and the chamber 46 additionally into the expansion chamber 60,causing the pressure rise in the chamber 14a for each period of de- energisation of the first solenoid valve 47 to be significantly reduced. In this manner, the stepwise increase in pressure as applied to the brake actuator B through the passage 18 is under significantly greater control, and hence the reapplication of braking pressure towards the originally-detected skid point may be effected significantly more accurately.

It will be appreciated that the reduced application of pressure to the control chamber 14a is proportional to the increase in volume effected by bringing the expansion chamber 60 into communication with the supply line and associated passages 62 and 64, compared with the volume of the supply line. i.e. the passages 45, 48 and 52, together with the free volumes of the chambers 46 and 50 as much as the volume of the control chamber 14a. (d) On movement towards the "skid point" (Point D) , the first solenoid valve 47 is maintained continuously energised, to close off the control port 44, and the second solenoid valve 51 is energised, allowing pressure within the expansion chamber and control chamber 14a to be vented through passage 23.

The sequence can then be repeated if necessary.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in the terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS :

1. A braking system comprising a source of brake actuating fluid under pressure, a brake actuator, a relay valve operative between the source and the actuator, a manually operable control valve to provide a fluid pressure control signal and a control device to operate on the control signal to control the relay valve in a first mode in which application of the brake actuating fluid from the source to the brake actuator is controlled manually or in a second mode in which the application of brake actuating fluid from the source to the brake actuator is controlled by an anti-lock brake controller wherein means are provided to apply the control signal to the relay valve a) when the control device is in the first mode; through a supply line having a first volume, and b) when the control device is in the second mode; through a supply line having a second volume which is significantly larger than the first volume.

2. A braking system according to Claim 1 wherein two supply lines are provided, one operative to apply the control signal to the relay valve when the control device is in the first mode, the other, of significantly larger volume than the volume of the one line, being operative to apply the control signal to the relay valve when the control device is in the second, anti-lock, braking mode.

3. A braking system according to Claim 1 wherein a single supply line and an expansion chamber of significantly larger volume than the volume of the supply line, is provided, there being means effective when the control device is in the first mode to isolate the expansion chamber from the supply line and when the control device is in the second mode, to bring the expansion chamber into communication with the supply line.

4. A braking system according to Claim 3 wherein the expansion chamber is adjustable in volume.

5. A braking system according to Claim 4 wherein the expansion chamber is provided by a cavity, into which a closure member is adjustably mounted to vary the operative volume of the expansion chamber.

6. A braking system according to Claim 4 wherein the expansion chamber comprises a plurality of expansion sub- chambers, which may be selectively connected to the supply line for the provision of a desired expansion volume.

7. A braking system according to any one of Claims 2 to 6 wherein the control device comprises a first solenoid operated valve and a second solenoid operated valve, the first valve being operable to control passage of the control signal to or from the relay valve, the second valve being operable to control passage of the control signal to or from the relay valve and to control exhaust of control signal from the relay valve.

8. A braking system according to Claim 7 wherein the first valve is operative to isolate the expansion chamber from the supply line when the first valve permits of flow of control signal to or from the relay valve and to bring the expansion chamber into communication with the supply line when the first valve prevents flow of control signal to or from the relay valve.

9. A braking system according to Claim 8 wherein the first valve comprises a valve member having a first seat portion to control passage of control signal to or from the relay valve and a second seat portion to control passage of control signal into the expansion chamber.

10. A braking system according to Claim 8 or Claim 9 wherein the second valve comprises a valve member having a first seat portion to control passage of control signal to or from the relay valve and a second seat portion to permit or prevent exhaust of the control signal from the relay valve and of control signal pressure from the expansion chamber.

11. A braking system according to any one of Claims 7 to 10 wherein the first and second solenoid valves are connected in series in the supply line for the control signal to the relay valve with the first solenoid valve being disposed upstream of the second solenoid valve in said line.

12. A braking system substantially as hereinbefore described with reference to the accompanying drawings.

13. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.