GB2331562A - Anti-lock braking system - Google Patents

Abstract

In an anti-lock braking system, actuation of drivers control 23 activates valve 20 to supply air from source 10 to a control chamber 58 via electrically operable hold and exhaust valves 60, 59, which results in piston 55 of a relay valve 13 depressing valve member 50 to supply air to two wheel brake actuators 15a, 15b. The system includes two electrically operable anti-lock hold valves 38 each associated with a respective wheel brake actuator. When one of the wheels is tending to skid, exhaust valve 59 is energised to vent chamber 58 and the actuator of the skidding wheel via port 54, and, simultaneously, the anti-lock hold valve 38 of the non-skidding wheel is energised to close exhaust 45 and open chamber 36 to air supply 44, thus diaphragm 34 engages seat 33 to hold or maintain the pressure at the associated wheel brake actuator.

Description

2331562

PATENTS ACT 1977 JNUA91 1 OGB Title: Braking System Description of Invention

This invention relates to an electronically controlled braking system for a vehicle and in particular a vehicle provided with an anti-lock bralcing system (ABS), in which incipient locking of one or more braked wheels is detected and the braking level controlled to avoid such locking.

Accordingly, an electronically controlled braking system comprises means operable by a driver of a vehicle and having means for providing an electrical brake demand signal; electronic control means responsive to said braking demand signal, and brake valve means responsive to a instructing signal supplied to the brake valve means by the electronic control means in response to said electrical braking demand signal and said brake valve means being arranged to control supply of fluid under pressure from a source thereof to at least one actuator means for brake application.

Hitherto the brakes on opposite sides of an axle have either been commonly controlled by a single control valve having anti-lock modudating means (ABS) or a separate ABS valve has been used for each wheel to provide what is known as independent anti-lock control so as to provide differing pressures across an axle during anti-lock control.

It is preferred to provide the ABS valve as a relay valve which may comprise a brake pressure chamber in which brake pressure supplied from said source to said at least one brake actuator means is controlled by a main valve means operated by a relay piston means responsive to fluid control pressure in a control chamber.

Preferably the pressure of control fluid in the control chamber may be caused to increase, be held, or be reduced, with a corresponding change in pressure in the brake chamber.

An object of the present invention is to provide a more economical means of providing electronic control of the pressure supplied to said brake 2 actuator means together with independent across axle anti-lock control.

According to one aspect of the present invention we provide a relay valve comprising a brake pressure chamber in which brake pressure for supply from said source to said at least one brake actuator means is controlled by a main valve means operated by a relay piston means responsive to fluid control pressure in a control chamber wherein the relay valve is adapted to supply brake pressure from said brake pressure chamber to at least two brake actuator means and wherein fluid control pressure is supplied to the control chamber through an electrically operable control valve means and two electrically operable anti-lock hold valves, one for each of said brake actuators.

The control valve means may comprise an electrically operable hold valve and an exhaust valve.

1 1 E Accordingly the hold and exhaust valves are used in normal brake operation to modulate fluid from said supply in accordance with said instructing signal to provide a common brake pressure for both actuators. In anti-lock control an appropriate anti-lock hold valve is energised to provide a pressure hold phase for a non-skidding wheel and the exhaust valve is energised to reduce the pressure in the brake chamber and thus reduce the pressure in the skidding wheel. A combination of intermittent hold solenoid energisation and de-energisation may permit a controlled pressure rise phase to be provided for each brake actuator respectively.

In order to meet brake system response times and provide driver controlled braking to an axle or axles it is necessaiy to utilise only one ABS relay valve for each independently controlled axle. Where two ABS relay valves are used both of the ABS relay valves operate similarly in response to driver demand. The only time that the ABS relay valves will operate in an independent mode is during anti-lock braking control, in particular under split-friction conditions when different pressures are generated on opposite sides of the axle. The value of having two ABS relay valves is therefore unwarranted when only the ability to produce and or maintain different pressures across an axle is required.

3 As mentioned above in electronic control of the brakes, an ability to produce a pressure rise, hold or reduction relative to driver demand is achieved by utilising an electrical braking demand signal which is processed by the electronic control means to provide said instructing signal. To achieve this function requires the provision of an exhaust valve to reduce pressure as well as a hold valve to hold and increase pressure. In order to have the ability to provide across axle independent anti-lock control it has hitherto been necessary to duplicate the complete brake control valve. With electronic brake control the valves used are solenoid valves of a relative high performance in terms of response and durability compared with conventional solenoid valves used in a conventional anti-lock braking system and are therefore of higher cost. The present invention avoids the need to provide two such relay valves. The present invention requires the provision of a single relay valve, having a single exhaust solenoid and a single hold solenoid, which is provided with the above described anti-lock hold solenoid valves.

Each anti-lock hold solenoid valve may supply fluid to control a finiher valve provided to control flow of brake pressure from said brake chamber to an associated brake actuator.

The further valve may comprise a valve member moveable into and out of engagement with a seat under the influence of fluid pressure, said fluid pressure being controlled by a respective hold solenoid.

The flUld pressure may be supplied from an auxiliary source of fluid pressure.

According to a second aspect of the present invention we provide an electronically controlled braking system for a vehicle comprising an electronically controlled bralcing system comprising means operable by a driver of a vehicle and having means for providing an electrical brake demand signal; electronic control means responsive to said braking demand signal, brake valve means responsive to an instructing signal supplied to the brake valve means by the electronic control means in response to said electrical braking demand signal and said brake valve means being arranged to control supply of fluid under pressure from a source 4 thereof to at least one actuator means for brake application wherein said brake valve means is arranged to control supply of said fluid under pressure to at least two actuator means for brake application and said brake valve means comprises a relay valve according to the first aspect of the invention.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which Figure 1 is a diagrammatic illustration of an electronically controlled braking system embodying the invention, and i Figure 2 is a graphical representation showing how solenoid valves are energised, how wheel speed varies and brake pressure varies.

Referring to Figure 1, fluid under pressure, in this case compressed air, is fed from a source, in the form of a reservoir 10, on a line 11 to an inlet port 12 of a relay valve 13. The air thus supplied from the reservoir is modulated by the relay valve 13 to provide brake pressure which is fed by a pair of lines 14a, 14b to actuators 15a., 15b to operate brakes 16a, 16b for wheels 17a, 17b provided on opposite sides of an axle 18. Of course,if desired, each line 14g, 14b may provide brake pressure to more than one wheel on an associated side of more than one axle if desired.

Control air is fed from the reservoir 10 or, if desired a separate reservoir, by a line 19 via a brake apply valve 20 to a control inlet port 21 of the relay valve 13. The or each reservoir is charged by a suitable engine driven compressor on a line 22 in known manner.

The brake system has a driver operable control 23 which provides an electrical braking demand signal on line 24 to an electronic control means 25. The electronic control means provides an instructing signal on lines 26a.' 26b to the relay valve 13. The wheels 17g, 17b are provided with wheel speed sensors 271 27b respectively which provide wheel speed signals to the electronic control means 25 on appropriate lines 28ga, 28b. The electronic control means 25 provides ABS control in conventional manner on the basis of the wheel speed signals provided on the lines 28.

The relay valve 13 comprises an inlet chamber 30 in communication with the port 12 and an outlet or brake chamber 31 in communication with the lines 141 14b. In the Figure the line 14a is connected to an outlet 32 of the brake chamber 3 1. It should be appreciated that the relay valve has a second outlet which is connected to the line 14b but which is not shown. The second outlet is connected in the same manner and to similar components to those to be described below in connection with the outlet 32.

The outlet 32 is connected to a valve seat 33 which is controlled by a diaphragm 34 normally biased by a compression spring 35 into sealing engagement with the seat 33. The diaphragm 34 separates the seat 33 and the brake operating chamber 31 from a secondary chamber 36 which is connected by a passage 37 to a respective anti-lock hold solenoid 38. The hold solenoid 38 has a valve member 39 which is biased by a compression spring 40 into sealing engagement with a second valve seat 41 which is connected by a passage 42 and a line 43 to an auxiliary reservoir 44 which may be at the same pressure as the reservoir 10.

The anti-lock hold solenoid 38 has a second, exhaust, seat 45 which is controlled by the valve member 39 and which, in the normal de-energised, condition of the valve is open whilst the valve seat 41 is closed. Signals are supplied to each anti-lock hold solenoid independently on lines 46a, 46b, the line 46a being connected to the illustrated solenoid 38.

The inlet chamber 30 is separated from the brake chamber 31 by a valve member 50 which is engageable with a valve seat 51 and which is normally spring biased into sealing engagement therewith by a coil compression spring 52.

The valve member 50 is provided with a passage 53 for communication between the brake chamber 31 and an exhaust port 54. A relay piston 55 is slidable in a chamber 56 and carries a valve seat part 57 which is moveable into sealing engagement with the valve member 50. A control chamber 58 is defined above the relay piston 55 and is connected via a solenoid exhaust valve 59 and a solenoid hold valve 60 to the inlet port 2 1. A one way valve 61 is provided between the port 21 and the control chamber 58 to enable flow of air in the direction from the 6 control chamber 58 to the port 21 when an appropriate pressure diffierential exists therebetween.

The hold solenoid 60 has a valve member 62 which is normally spring biased so as to open a hold valve seat 63 and which can be energised to close the valve seat and hence prevent passage of air from the chamber 21 to the control chamber 58.

The exhaust solenoid 59 has a valve member 64 which is normally spring biased by a spring 64a to close an exhaust valve seat 65 and open a flow valve seat 66.

In use, when a driver demands braking he operates the control 23 and a transducer provides an appropriate electronic control signal on line 24 to the controller 25 which provides an appropriate instruction on lines 26a=, 26b to the exhaust and hold solenoids 59, 60 and on line 20g the brake apply solenoid valve 20 so as to cause it to open.

Air then flows firom the inlet 21 past the hold solenoid 60 and since the exhaust solenoid 59 remains de-energised air enters the control chamber 58 from the inlet 21 and cause piston 55 to move downwardly in to engagement with the valve member 50. Further movement then causes the valve member 50 to be moved downwardly so that air is fed from the reservoir 10 via the inlet 12 into the brake chamber 31 and is then fed on the lines 14a and 14b to each of the brake actuators 15a, 15b to apply the brakes.

When driver demand requires the brake pressure to be held, the hold solenoid 60 is energised so as to close the hold seat 63 so that pressure is then held in the control chamber 58 and, as a result the pressure in the brake operating chamber 31 below the piston 55 is similarly held, as a result of the balancing of the pressures on opposite sides of the piston 55, and so the pressure is held in actuators 15a=, 15b.

When it is desired to reduce the brake pressure the solenoid 59 is energised to open the exhaust seat 65 and allow pressure in the control chamber 58 to pass to atmosphere via the exhaust port 54, with resultant upward movement of 7 the piston 55 to the position shown in Figure 1 where the valve member 50 is in engagement with the seat 51 and the brake operating chamber 31 is connected to the exhaust port 54 so that the pressure in the actuators 15A, 15b passes to atmosphere.

At this stage air can flow past the valve seat 33 into and out of the actuator 151 15a without significant hindrance because the coil spring 35 is fight and because at this stage the solenoid 39 is de-energised so that the passage 37 and the auxiliary chamber 36 above the diaphragrn 34 is connected to atmosphere via the exhaust port 35 and hence pressure in either the port 32 or the chamber 31 will easily lift the diaphragm 34 out of engagement with the seat 33.

When anti-skid operation takes place the controller 25 will detect that one wheel is the first to reach a detection threshold as a result of deceleration as an incipient skid approaches. Accordingly, the controller 25 causes the anti-skid hold solenoid 38 which is associated with the nonskidding wheel to be energised so as to close the exhaust port 25 and place the auxiliary reservoir 44 in communication, via the seat 41, with the auxiliary chamber 36 so that the diaphragrn 34 is pressed by reservoir pressure against the valve seat 33. Accordingly, a non-skidding wheel has the pressure in its actuator held. In this example the non- skidding wheel is assumed to be the wheel having the actuator 15a. Simultaneously the exhaust solenoid 59 is energised which allows air from above the relay piston 55 to be exhausted via the port 54 and is continued to be energised until the pressure acting in the actuator 15b of the decelerating ie. skidding wheel is correspondingly reduced to a level where the wheel is no longer decelerating.

At this point the hold solenoid, not shown, of the same wheel ie. the decelerating wheel, is energised to retain whatever pressure is obtaining in its associated actuator 15b.

This is followed by de-energisation of the exhaust solenoid 59 which then allows pressure to be increased above the relay piston thereby opening the main inlet valve as described herein before and thereby re- pressurising the brake operating chamber 31 below the relay piston 55.

1 8 The non-skidding wheel hold solenoid 38 is now de-energised to allow pressure in the associated brake actuator 15a to continue to increase either until maximum pressure is supplied or further anti-lock action is required.

The above described control logic may be summarised as follows:1 Energise anti-skid hold solenoid of non decelerating wheel 2 - Energise common exhaust solenoid to reduce brake pressure at decelerating wheel.

3 - When decelerating wheel ceases to decelerate energise anti-skid hold solenoid for that wheel.

4 - De-energise common exhaust solenoid to re-pressurise relay control chamber and open inlet valve.

- Either de-energise anti-skid hold solenoid of non decelerating wheel and allow pressure to rise uncontrolled or repeatedly de-energise antiskid hold solenoid to provide controlled pressure rise.

6 - When the low wheel (defined in 2 and 3 above) has accelerated to a calculated speed repeatedly de-energise hold solenoid to provide a controlled pressure rise.

7 - Repeat cycle until whenever either the left or right wheel on an axle tends to decelerate towards lock.

This sequence, in one example, is illustrated in Figure 2 wherein the lines identified by reference numbers 1 - 7 represent the following:

Line 1 - Energisation of exhaust solenoid Line 2 - Energisation of left anti-skid hold solenoid Line 3 - Energisation of right hold solenoid Line 4 - Speed of left wheel Line 5 - Speed of right wheel Line 6 - Pressure of brake actuator of left wheel Line 7 - Pressure in brake actuator of right wheel.

The features disclosed in the foregoing description, or the following

9 claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed flmction, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof

Claims (1)

1. CLAIMS:

   1. A relay valve comprising a brake pressure chamber in which brake pressure for supply of fluid under pressure from a source thereof to at least one brake actuator means is controlled by a main valve means operated by a relay piston means responsive to fluid control pressure in a control chamber wherein the relay valve is adapted to supply brake pressure from said brake pressure chamber to at least two brake actuator means and wherein fluid control pressure is supplied to the control chamber through an electrically operable control valve means and two electrically operable anti-lock hold valves, one for each of said brake actuators.

   2. A relay valve according to claim 1 wherein the control valve means comprises an electrically operable hold valve and an exhaust valve.

   3. A relay valve according to claim 2 wherein the hold and exhaust valves are operable to modulate fluid from said supply in accordance with an instructing signal to provide a common brake pressure for both actuators.

   4. A relay valve according to claim 2 or claim 3 wherein in anti-lock control an appropriate anti-lock hold valve is operable to provide a pressure hold phase in the brake chamber of a non-skidding wheel and the exhaust valve is operable to reduce the pressure in the brake chamber of the skidding wheel.

   5. A relay valve according to any one of claims 1 to 4 wherein the antilock hold valves are intermittently operable to permit a controlled pressure rise phase to be provided for each brake actuator respectively.

   11 6. A relay valve according to any one of claims 1 to 5 wherein each antilock hold valve is operable to supply fluid to control a further valve provided to control flow of brake pressure from said brake chamber to an associated brake actuator.

   7. A relay valve according to claim 6 wherein the further valve comprises a valve member moveable into and out of engagement with a seat under the influence of fluid pressure, said fluid pressure being controlled by a respective antilock hold valve.

   8. A relay valve according to claim 7 wherein the fluid pressure is supplied firom, an auxiliary source of fluid pressure, 9. A relay valve as described herein with reference to the accompanying drawings.

   10. An electronically controlled braking system for a vehicle comprising an electronically controlled braking system comprising means operable by a driver of a vehicle and having means for providing an electrical brake demand signal; electronic control means responsive to said braking demand signal, brake valve means responsive to an instructing signal supplied to the brake valve means by the electronic control means in response to said electrical braking demand signal and said brake valve means being arranged to control supply of fluid under pressure from a source thereof to at least one actuator means for brake application wherein said brake valve means is arranged to control supply of said fluid under pressure to at least two actuator means for brake application and said brake valve means comprises a relay valve according to any one of claims 1 to 8.

   11. An electronically controlled braking system as described herein with reference to the accompanying drawings.

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