GB2540346A

GB2540346A - Vehicle braking system

Info

Publication number: GB2540346A
Application number: GB1511974.6A
Authority: GB
Inventors: John Harrison Dudley
Original assignee: Haldex Brake Products Ltd
Current assignee: Haldex Brake Products Ltd
Priority date: 2015-07-08
Filing date: 2015-07-08
Publication date: 2017-01-18
Anticipated expiration: 2035-07-08
Also published as: GB201511974D0; GB2540346B

Abstract

A vehicle braking system has a brake actuator 23 sprung into a brake apply position and released by a supply of pressurised fluid from a supply line 12, an emergency apply valve 20 with a control port 20c that connects the brake actuator to a low pressure region when pressure at the control port falls below a predetermined level, and an override shuttle valve 40 which provides fluid to the control port 20c from the supply line 12 or from an alternative source of fluid when that source has a pressure greater than by a predetermined amount. The vehicle a tractor and trailer combination with an electrical control 32,25 of service braking; and the alternative source can be an air suspension system via electrically actuated valve 42(42, fig 6) which may control trailer body raising and lowering, actuated when a transducer 50 detects low pressure. A shunt valve 14 and park valve 22 are also provided. Thus an emergency application can be maintained even after exhausting of brake reservoir pressure by anti-lock braking.

Description

Title: Vehicle Braking System Description of Invention

The present invention relates to a braking system, particularly, but not exclusively to a braking system for a trailer of a road vehicle comprising a tractor and trailer combination.

Large commercial trailers are typically fitted with two types of brake actuator -a service actuator in which air pressure on a piston or diaphragm pushes a rod which applies mechanical turning force to the input shaft of the brake, and a service/spring actuator which includes, in addition to a service actuator, a spring actuator comprising an internal coil spring which acts on the pushrod, which can be compressed when a second chamber is pressurised. The brakes can be applied therefore by either increasing pressure supplied to the service actuator as normal, and/or by a reducing the pressure supplied to the spring actuator. A common configuration, for example, is a semi-trailer with three axles, the front of which has service actuators and the middle and rear of which has service/spring actuators. Other combinations are possible, however.

In the normal driving condition the spring actuators are pressurised from the compressed air supply line (or trailer reservoir) to hold them off. Graduated braking in response to driving demand for braking is effected via the service actuators.

If the compressed air supply (or trailer reservoir) pressure falls, the pressure to the service actuators falls with it, reducing the applied force to the brake. At the same time, however, the pressure in the spring actuators is reducing by the same amount, which results in substantially the same braking force being maintained until and including when the supply line or reservoir is completely empty. Normally a park valve is also included in the supply line, which allows the pressure in the spring actuators to be exhausted in order to positively park the trailer.

It is also normal practice to include an emergency apply function to a trailer brake system. This acts when the pneumatic supply line (‘red line’) to the trailer is disconnected, exhausted or severed (thereby preventing the trailer reservoir from being replenished with compressed air). The emergency apply function acts on either the service actuators or the spring actuators, and can be required due to a fault when the vehicle is moving.

Usually a shunt valve is also included to divert air from the trailer reservoir to defeat the emergency apply function in order to allow the trailer to be moved (‘shunted’) without connection to a towing vehicle with a compressed air supply. This may be required, for instance, at a distribution depot or ferry terminal.

Emergency braking by the supply of pressurised fluid to the service actuators (i.e. via the service brake line) has an advantage in that this flow of fluid is normally controlled by the electronic braking system (EBS) or anti-lock braking system (ABS) of the trailer. The vehicle can either be immediately brought to a safe stop with the benefit of the anti-lock function, or the emergency brake application can be held off whilst the driver is warned of the situation. The driver may then bring the vehicle to a safe stop at the side of the road using normal service braking.

Emergency braking using the spring actuators, i.e. by the release of fluid from the spring line, can be less complex, but has disadvantages in that it is not normally possible to provide an anti-lock function without additional components which then makes the solution more complex than the service solution. One solution to this problem is presented in DE3522183C1. In the system proposed in this document an electrically operated valve is provided to control the release of pressurised fluid from the spring brake, and, if necessary to direct fluid from a trailer mounted reservoir to the spring brake chamber. If wheel-lock is detected, this valve may be operated as an ABS valve to stop, momentarily, release of fluid from the spring brake.

In an alternative proposal, disclosed in EP1538054, the braking system is provided with a means for preventing the emergency application of the spring brake in the event of loss of pressure in the spring brake circuit, and the service braking circuit downstream of the or each modulator associated with brake actuators on one side of the vehicle is connected to the spring brake line via a shuttle valve. The shuttle valve is configured such that pressurised fluid is supplied to the spring brake line from this portion of the service braking circuit when the fluid pressure in the spring brake line is lower than the pressure in the service brake circuit. Thus fluid from one half of the service braking circuit is used to prevent the application of the spring brake. The service braking circuit may then be used to apply the brakes to bring the vehicle to a halt. The ABS is disabled on the one side of the vehicle, however, to avoid chattering of the spring brake during an ABS intervention, but can be operated as normal on the other side of the vehicle. A further alternative proposal, disclosed in WO2011/003491, is alleged to be an improvement over the system disclosed in EP1538054. In this proposal, if wheel lock is detected during the emergency application of the spring brakes resulting from loss of pressure in the spring brake circuit, the system acts to direct pressurised fluid from the service circuit to the spring brake circuit to release the spring brakes, whilst at the same time applying the service brakes. Once the pressure in the spring brake chambers is high enough, a “spring store neutralising valve” is operated to isolate the spring brake chambers. The EBS modulator may then use conventional ABS algorithms to modify the braking force applied by the service brakes on both sides of the vehicle without affecting the spring brake.

Our co-pending patent application GB2492124 shows a further alternative configuration of braking system which provides for emergency braking using the spring brake, and which includes an electrically operable emergency braking override valve which is operable to suppress the automatic application of the spring brake in the event of a loss of pressure in the compressed air supply to the trailer. This system includes an emergency brake apply valve which has a control port which is connected to the compressed air supply line, the emergency brake apply valve being configured automatically to connect the spring brake chamber to a low pressure region when the pressure at the control port falls below a predetermined level. The electrically operable emergency braking override valve has a first port which is connected to the supply line and a second port which is connected to the control port of the emergency brake apply valve and, when supplied with sufficient electrical power, acts to prevent loss of fluid pressure at the control port of the emergency brake apply valve. A yet further alternative solution is illustrated in GB2490925. This document discloses a trailer braking system in which a signal from a brake apply solenoid is used to override the emergency brake apply valve. The brake apply solenoid is provided in the control line to the service braking system, and is electrically operable to connect the service brakes to a local source of pressurised fluid in order to apply the trailer brakes in the absence of a driver generated braking demand signal. The system also includes a shuttle valve with a first inlet which is connected to the emergency brake apply valve and a second inlet which is connected to the brake apply valve, and an outlet which is connected to the spring brake. The shuttle valve either the first inlet or the second inlet to the outlet - whichever carries the highest pressure, so pressure from the brake apply valve only acts on the spring brakes when pressure in the spring brake circuit is lost. It is possible that there is insufficient flow through the brake apply valve to effect a timely re-pressurisation of the spring brakes, and so this system can also include a pressure sensor which detects the emergency condition (falling supply line pressure) in an effort to apply the override before significant pressure is lost in the spring brakes.

It is an object of the present invention to provide an alternative method of emergency trailer braking.

According to a first aspect of the invention we provide a vehicle braking system comprising a brake actuator which is operable to adopt a brake apply position in which the actuator may apply a braking force to a vehicle wheel and a brake release position in which the actuator may release any braking force applied to a vehicle wheel, the brake actuator having a spring brake chamber and a spring and being configured such that supply of pressurised fluid to the spring brake chamber causes the brake actuator to move against the biasing force of the spring to the brake release position and release of pressurised fluid from the spring brake chamber causes the brake actuator to move under the action of the spring to the brake apply position, the system further including a supply line whereby the spring brake chamber is, in use, connected to an external source of pressurised fluid, and an emergency apply valve which has a control port and which is configured automatically to connect the spring brake chamber to a low pressure region when the pressure at the control port falls below a predetermined level, wherein the system further includes an override shuttle valve which has a first inlet which is connected to the supply line and a second inlet which is adapted to be connected to an alternative source of pressurised fluid and an outlet which is connected to the control port of the emergency brake apply valve and which has a valve member which is movable between a first position in which flow of fluid from the second inlet to the outlet is substantially prevented whilst flow of fluid from the first inlet to the outlet is permitted, and a second position in which flow of fluid from the second inlet to the outlet is permitted, but flow of fluid from the first inlet to the outlet is substantially prevented, and adopts the second position if the fluid pressure at the second inlet exceeds the fluid pressure at the first inlet by an amount which greater than a predetermined level, and adopts the first position if the fluid pressure at the second inlet does not exceed the fluid pressure at the first inlet by an amount which is greater than the predetermined level.

The override shuttle valve may be provided with a resilient biasing element which biases the valve member to the first position.

The second inlet of the override shuttle valve may be connected to an outlet of an electrically operable suspension valve, the suspension valve having an inlet which is connected to a source of pressurised fluid, and an exhaust port which is connected a low pressure region, the suspension valve also being adapted to be connected to a suspension control system which is operable to control the operation of a suspension system provided on the vehicle, the suspension valve being movable between a first configuration in which the outlet is connected to the exhaust port, and a second position in which the inlet is connected to the outlet.

The suspension valve may be provided with an electrically operated actuator which is operable to move the suspension valve between the first position and the second position.

The suspension valve may be provided with a resilient biasing element which urges the suspension valve into its first position, and is movable from the first position to the second position by the supply of electrical power to the electrically operated actuator.

The outlet of the suspension valve may be connected to at least one suspension bellows. Alternatively, the outlet of the suspension valve may be connected to a control port of a fluid pressure operated valve actuator, the fluid pressure operated actuator operating a valve which controls the flow of pressurised fluid to or from at least one suspension bellows.

Alternatively, the inlet of the suspension valve may be connected to the outlet of a suspension fill valve, the suspension fill valve having an inlet connected to a source of pressurised fluid, and its outlet also being connected to at least one suspension bellows.

The emergency apply valve preferably has an inlet which is connected to the supply line and an outlet which is connected to the spring brake chamber via a spring brake line, and is movable between a first position in which the inlet is connected to the outlet and a second position in which the inlet is closed and the outlet vents to a low pressure region. A mechanical biasing element may be provided to urge the emergency apply valve into the second position, movement of the emergency apply valve from the second position to the first position being achieved by the supply of pressurised fluid to the control input at sufficient pressure to overcome the force of the biasing element.

Advantageously, the brake actuator further includes a service brake chamber, wherein supply of pressurised fluid to the service brake chamber causes the brake actuator to move to the brake apply position. In this case, the system further includes a control line which in use connects a source of a fluid pressure braking demand signal to the service brake chamber via a braking control valve assembly. The braking control valve assembly preferably comprises at least one modulator which has a control port which is connected to the control line for receipt of a fluid pressure braking demand signal, a supply port which is connected to a source of pressurised fluid, a delivery port which is connected to the service brake chamber via a delivery line, and an exhaust port which vents to a low pressure region, the modulator being operable to move between a build configuration in which the supply port is connected to the delivery port whilst the exhaust port is closed, a hold configuration in which the exhaust port and the supply ports are closed and an exhaust configuration in which the delivery port is connected to the exhaust port whilst the supply port is closed.

The vehicle braking system may further comprise a brake apply valve, and a trailer supply line which connects the supply line to the control line via the brake apply valve. In this case, the brake apply valve may be movable between a first configuration in which the brake apply valve substantially prevents flow of fluid from the pressurised fluid reservoir to the control line, and a second in which the brake apply valve allows flow of fluid from the pressurised fluid reservoir to the control line.

The emergency apply valve may be connected to the spring brake chamber via a spring brake line in which is provided an anti-compounding shuttle valve which has a spring-side inlet which is connected to emergency apply valve via a first portion of the spring brake line, a second inlet which is connected to a cross-over line which extends to the delivery line, and an outlet which is connected the spring brake chamber by a second portion of the spring brake line, the anti-compounding shuttle valve being movable between a first configuration in which flow of fluid from the second inlet to the outlet is substantially prevented whilst flow of fluid from the first inlet to the outlet is permitted, and a second configuration in which flow of fluid between the second inlet and the outlet is permitted whilst flow of fluid from the first inlet to the outlet is substantially prevented.

The anti-compounding shuttle valve may be configured such that it adopts the first configuration if the fluid pressure in the supply line is greater than the fluid pressure in the delivery line, and adopts the second configuration if the fluid pressure in the delivery line exceeds the fluid pressure in the supply line.

The anti-compounding shuttle valve may be provided with a resilient biasing element or spring which biases the valve into the first configuration, the valve moving to the second configuration if the fluid pressure in the delivery line exceeds the fluid pressure in the supply line by more than a predetermined amount.

The system may further comprise a pressurised fluid reservoir which is provided in the supply line between the emergency apply valve and a connector for connecting the supply line to an external source of pressurised fluid. In this case, the second inlet of the over-ride shuttle valve may be connected to the pressurised fluid reservoir via a control valve. The control valve may be the suspension valve, and the pressurised fluid reservoir connected to the inlet of the suspension valve.

The trailer supply line to the brake apply valve may extend from the supply line between the pressurised fluid reservoir and the emergency apply valve.

An embodiment of the invention will now be described, with reference to the accompanying drawings of which: FIGURE 1 is a schematic illustration of a trailer braking system according to the invention, in the normal drive configuration, FIGURE 2 is a schematic illustration of the trailer braking system shown in Figure 1 with service braking using the brake apply valve, FIGURE 3 is a schematic illustration of the trailer braking system shown in Figure 1 with emergency application of the spring brake resulting from a loss of fluid pressure in the supply line, FIGURE 4 is a schematic illustration of the trailer braking system shown in Figure 1 with the emergency application of the spring brake over-ridden by the activation of the brake apply valve, FIGURE 5 is a schematic illustration of the trailer braking system shown in Figure 1 with the emergency application of the spring brake over-ridden by the activation of the suspension valve, and FIGURE 6 is a schematic illustration of an alternative configuration of braking system according to the invention.

Referring now to Figure 1 there is shown a braking system 10 for a trailer of a vehicle comprising a tractor and a trailer or semi-trailer. The braking system comprises a main supply line 12 which is adapted to be connected to a source of pressurised fluid, typically compressed air, on a tractor to which the trailer is coupled. The supply line 12 extends first inlet 14a of a shunt valve 14, the outlet 14b of the shunt valve 14 being connected to a junction between an emergency apply line 16 and a park line 18. The emergency apply line 16 extends to an inlet 20a of an emergency apply valve 20 via a reservoir of pressurised fluid (in this example, compressed air), whilst the park line 18 extends to an inlet 22a of a park valve 22. The outlet 20b of the emergency apply valve 20 is connected to the spring brake chamber 23a of a service / spring brake actuator 23 via a spring brake line 21, and an anti-compounding shuttle valve 36. The emergency apply valve 20 is also provided with a control inlet 20c which is connected to an outlet 22b of the park valve 22.

Two one-way check valves 24a, 24b are provided in the emergency apply line 16, both being oriented to allow flow of fluid from the shunt valve 14 to the emergency apply valve 20 but to prevent flow of fluid in the other direction along the emergency apply line 16, i.e. away from the emergency apply valve 20. In this example, a pressurised fluid reservoir 28 (hereinafter referred to as the trailer reservoir 28) is located in the emergency apply line 16 between the two check valves 24a, 24b. A trailer reservoir supply line 26 extends from the emergency apply line 16 between the first check valve 24a and the pressurised fluid reservoir 28 to a second inlet 14c of the shunt valve 14. A further pressurised fluid reservoir may be provided, and this could be connected to the emergency apply line 16 between the first pressurised fluid reservoir 28 and the second check valve 24b.

There is also provided a control line 30 which is adapted to be coupled to a braking control line on a tractor to which the trailer is coupled, the braking control line 30 carrying a fluid pressure braking demand signal generated when a driver of the vehicle operates a brake pedal or the like to indicate a need for braking. The control line 30 is connected to a first inlet 32a of a brake apply valve 32, an outlet 32b of the brake apply valve 32 being connected to control inlet of a conventional electrical braking system (EBS) control valve assembly 25 via a service brake line 27. The EBS control valve assembly 25 typically comprises at least a modulator and is connected to the service brake chamber 23b of the brake actuator 23. The modulator has a control port which is connected to the control line for receipt of the fluid pressure braking demand signal, a supply port which is connected to a source of pressurised fluid, a delivery port which is connected to the service brake chamber 23b via a delivery line 31, and an exhaust port which vents to a low pressure region, and is operable to move between a build configuration in which the supply port is connected to the delivery port whilst the exhaust port is closed, a hold configuration in which the exhaust port and the supply ports are closed and an exhaust configuration in which the delivery port is connected to the exhaust port whilst the supply port is closed. Various configurations of modulator are well known to those skilled in the art. The EBS control valve assembly 25 is operable to provide anti-lock braking control. A second inlet 32c of the brake apply valve 32 is connected to the pressurised fluid reservoir 28 via a trailer supply line 29.

The spring brake line 21 is divided into first 21a and second 21b portions by a double check valve 36, the first portion 21a extending from a spring-side inlet 36a of the anti-compounding shuttle valve 36 to the emergency apply valve 20 and the second portion 21b extending from an outlet 36c of the anticompounding shuttle valve 36 to the spring chamber 23a of the brake actuator 23. A service-side inlet 36b of the anti-compounding shuttle valve 36 is connected to the delivery line 31 via a cross-over line 34. The anti-compounding shuttle valve 36 has a valve member which is movable between a first position in which flow of fluid from the service-side inlet 36b to the outlet 36c is substantially prevented whilst flow of fluid from the spring-side inlet 36a is permitted, and a second position in which flow of fluid from the service-side inlet 36b to the outlet 36 is permitted, but flow of fluid from the spring inlet 36a to the outlet 36c is substantially prevented.

The anti-compounding shuttle valve 36 is also configured such that it adopts the first position if the fluid pressure in the spring brake line 21a is greater than the fluid pressure in the delivery line 31, and adopts the second position if the fluid pressure in the delivery line 31 exceeds the fluid pressure in the spring brake line 21a. In this example, the double check valve is provided with a resilient biasing element or spring which biases the valve member to the first position. As such, the valve member will not move from the first position to the second position until the fluid pressure in the delivery line 31 exceeds the fluid pressure in the spring brake line 21a by an amount which is sufficient to overcome the biasing force of the spring.

It should be appreciated, however, that the anti-compounding shuttle valve 36 need not be provided with a biasing element, and the valve member may move between the first and second positions when there is any pressure differential between the delivery line 31 and the spring brake line 21a.

The shunt valve 14 is movable between a first position (illustrated in the Figures) in which the first inlet 14a is connected to the outlet 14b whilst the second inlet 14c is closed, and a second position in which the first inlet 14a is closed and the second inlet 14c is connected to the outlet 14b. In this example, the shunt valve 14 is adapted to be moved manually between the first and second positions.

The emergency apply valve 20 is movable between a first position (illustrated in Figure 1) in which the first inlet 20a is connected to the outlet 20b and a second position (illustrated in Figure 2) in which the first inlet 20a is closed and the outlet 20b vents to a low pressure region (typically to atmosphere). Mechanical biasing means (in this example a spring) is provided to urge the emergency apply valve 20 into the second position. Movement of the emergency apply valve 20 from the second position to the first position is achieved by the supply of pressurised fluid to the control inlet 20c at sufficient pressure to overcome the force of the biasing means.

The park valve 22 is movable between a first position (illustrated in the Figures) in which the inlet 22a is connected to the outlet 22b and a second position in which the inlet 22a is closed and the outlet 22b vents to a low pressure region (typically to atmosphere). In this example, the park valve 22 is adapted to be moved manually between the first and second positions.

The brake apply valve 32 is movable between a first position (illustrated in Figures 1 & 3) in which the first inlet 32a is connected to the outlet 32b, whilst the second inlet 32c is closed, and a second position (illustrated in Figure 2) in which the first inlet 32a is closed and the third inlet 32c is connected to the outlet 32b. The brake apply valve 32 is electrically operable, in this example, by means of a solenoid. Mechanical biasing means (in this example a spring) is provided to urge the brake apply valve 32 into the first position. Movement of the brake apply valve 32 from the first position to the second position is achieved by the supply of an electrical current to the solenoid 32d.

The system also includes an override shuttle valve 40 which has a brake-side inlet 40a, which is connected to the outlet 22b of the park valve 22, and a suspension-side inlet 40b, which is connected to the a suspension system of the trailer, as will be described in more detail below, and an outlet 40c, which is connected to the control inlet 20c of the emergency apply valve 20. The override shuttle valve 40 has a valve member which is movable between a first position in which flow of fluid from the suspension-side inlet 40b to the outlet 40c is substantially prevented whilst flow of fluid from the brake-side inlet 40a to the outlet 40c is permitted, and a second position in which flow of fluid from the suspension-side inlet 40b to the outlet 40c is permitted, but flow of fluid from the brake-side inlet 40a to the outlet 40c is substantially prevented. The override shuttle valve 40 is also configured such that it adopts the second position if the fluid pressure at the suspension side inlet 40b exceeds the fluid pressure at the brake-side inlet 40a by an amount which greater than a predetermined level, and adopts the first position if the fluid pressure at the suspension side inlet 40b does not exceed the fluid pressure at the brake-side inlet 40a by an amount which is greater than the predetermined level. Although not essential, in this example, the override shuttle valve is provided with a resilient biasing element or spring which biases the valve member to the first position. As such, the valve member will not move from the first position to the second position until the fluid pressure at the suspension-side inlet 40b exceeds the fluid pressure at the brake-side inlet 40a by an amount which is sufficient to overcome the force of the spring.

Also shown in the figures is a solenoid operated suspension valve 42 which is part of the trailer’s air suspension system. In this example, the suspension valve 42 is a solenoid operated valve which has an inlet 42a which is connected to the trailer supply line 29, and outlet 42b which is connected to the suspension-side inlet 40b of the over-ride shuttle valve 40, and to the trailer suspension bellows, and an exhaust port 42c which vents to the atmosphere. The suspension valve 42 is movable between an exhaust position in which the outlet 42b is connected to the exhaust port 42c while the inlet is closed, and a fill position in which the inlet 42a is connected to the outlet 42b whilst the exhaust portion 42c is closed. In this example, a resilient biasing element (typically a spring) is provided to urge the valve 42 into the exhaust position, and the valve 42 is moved from the exhaust position to the fill position by the supply of electrical power to the solenoid.

The suspension valve 42 may, for example, correspond to the fill valve 132 shown in Figure 19 of EP 2 757 006. In this case, the suspension valve 42 is electrically operable, typically by means of a solenoid, to either connect suspension bellows of the trailer’s suspension system with a source of pressurised fluid to raise the trailer body relative to its chassis, or to vent the suspension bellows to the atmosphere in order to lower the trailer body relative to its chassis. Where used in this invention, an outlet of the suspension valve 42 is connected to both the suspension bellows (possible via an isolation valve such as valve 133 shown in Figure 19 of EP 2 757 006, and a manually operable levelling valve) and to the suspension-side inlet 40b of the over-ride shuttle valve 40. As such, when the suspension valve 42 is operated to connect the trailer suspension bellows to the source of pressurised fluid, pressurised fluid is also supplied to the suspension-side inlet 40a of the override valve 40.

The suspension valve 42, may, alternatively, correspond to the solenoid valve 15 of the suspension system described in EP 0 520 147. This valve is electrically operably to provide a pilot pressure signal to the reset-to-drive valve 51 in EP 0 520 147. It too has an inlet which is connected to a reservoir of pressurised fluid, and an exhaust port which vents to the atmosphere, but in this case, the outlet is connected to a control port of the reset-to-drive valve 51, and the valve is operable to reset the reset-to-drive valve by the supply pressurised fluid to its control port of the reset-to-drive valve, or to vent the control port to atmosphere. Where used as the suspension valve in this invention, the outlet is connected to both the control port of the reset-to-drive valve and the suspension side inlet 40b of the over-ride shuttle valve 40. As such, when the suspension valve 42 is operated to reset the reset-to-drive valve, pressurised fluid is also supplied to the suspension-side inlet 40a of the over-ride valve 40.

The inlet port 42a of the suspension valve 42 may be connected to the trailer reservoir 28, or to an entirely separate source of pressurised fluid.

The braking system is operated as follows.

When the trailer is coupled to a tractor, and the combination in motion, the braking system is configured as shown in Figure 1. The suspension valve 42 is in its exhaust position, and hence the over-ride shuttle valve 40 is in its first position. The shunt valve 14 and park valve 22 are set to their first positions, and there is no supply of electrical current to the brake apply valve 32. The supply line 12 is connected to a source of pressurised fluid on the tractor, and pressurised fluid passes to the control input 20c of the emergency apply valve 20 via the park line 18 and the park valve 22. The presence of pressurised fluid at its control input 20c causes the emergency apply valve 20 to move to its first position whereby the first input 20a is connected to the output 20b. As a result, pressurised fluid passes from reservoir 28 to the spring brake chamber 23a of the brake actuator 23 via the emergency apply valve 20 and spring brake line 21. The fluid pressure in the spring brake chamber 23a overcomes the biasing force of the spring and the actuator acts to release the brake. Pressurised fluid also passes from the tractor to the trailer reservoir 28 so that the trailer reservoir 28 is charged with pressurised fluid.

The control line 30 is connected to the service brake line 27, and so normal service braking can be provided when demanded by the driver. When a driver of the vehicle generates a fluid pressure braking demand signal, this passes along the control line 30 and the service brake line 27 to the EBS valve assembly 25, resulting in the supply of fluid pressure to the service braking chamber 23b of the brake actuator 23, and the gradual application of brake pressure in line with driver demand for braking. A conventional anti-lock function may be provided by means of modulating valves in the EBS valve assembly 25. The second check valve 24b acts to prevent the release of the fluid pressure from the spring brake chamber 23a due to transient air consumption in the trailer reservoir 28 due to service braking modulation in an anti-lock control procedure.

The system 10 may be operated to provide service braking even when there is no fluid pressure braking demand signal by the supply of an electrical current to the brake apply valve 32. This causes the brake apply valve 32 to move to its second position in which the first inlet 32a is closed and the second inlet 32c is connected to the outlet 32b, as illustrated in Figure 2. Pressurised fluid then passes from the supply line 12 through the shunt valve 14 to the emergency apply line, through the first one way check valve 24a in the trailer supply line 29 to the reservoir 28, along the trailer supply line 29 and then on to the EBS control valve assembly 25 via the brake apply valve 32. The service brake chamber 23b of the actuator 23 may therefore be pressurised autonomously, i.e. without driver initiated braking demand, or with a higher pressure than provided by the fluid pressure braking demand signal. Such autonomous service braking may be required in an automatic stability control system.

As the spring-side inlet 36a of the anti-compounding shuttle valve 36 is exposed to the full pressure from the reservoir 28, whereas the service-side inlet 36b is exposed only to delivery pressure, the pressure at the service-side inlet 36b is likely to be lower than the pressure at the spring-side inlet 36a, and certainly cannot exceed the pressure at the spring-side inlet 36a. As such, the resilient biasing means of the anti-compounding valve 36 ensures that it is be maintained in its first position, and so there is no flow of fluid from the crossover line 34 to the spring brake chamber 23a.

When the vehicle is parked, the spring brake can be applied by moving the park valve from its first position to its second position. This causes fluid pressure at the control input 20c of the emergency apply valve 20 to be vented to atmosphere at the park valve 22, and the emergency apply valve 20 to move under the action of its biasing means to its second position in which its outlet 20b vents to atmosphere, and its inlet 20a is closed. Pressure is therefore released from the spring brake chamber 23a of the brake actuator 23 at the emergency apply valve 20 and the actuator 23 moves in response to the spring force to apply the brake.

If the supply line 12 is disconnected from its supply of pressurised fluid, and there is no supply of electrical current to the brake apply valve 32, the braking system adopts the configuration shown in Figure 3. The release of pressure from the supply line 12 and the park line 18 causes the emergency apply valve 20 to move under the action of the biasing means to its second position in which the outlet 20b is exhausted to atmosphere and the inlet 20a is closed. Fluid pressure is therefore released from the spring brake chamber 23a of the brake actuator 23 and vented to atmosphere at the emergency apply valve 20, and the actuator 23 moves in response to the spring force to apply the brake.

If the supply line 12 is disconnected from its source of pressurised fluid (resulting in the venting of the spring brake chamber 23a as described above in relation to Figure 3), and electrical current supplied to the brake apply valve 32, the service braking line 27 is connected to the trailer reservoir 28 as shown in Figure 4. As the fluid pressure in the spring brake line 21 decreases, the fluid pressure in the delivery line 31 will, at some point, exceed the pressure in the spring brake line 21 by an amount which is sufficient to move the valve member of the anti-compounding shuttle valve 36 from its first position to its second position. At that point there will be flow of fluid from the delivery line 31 to the spring brake chamber 23a of the brake actuator 23 via the cross-over line 34 and the second portion 21b of the spring brake line 21. Exhaustion of the spring brake chamber 23a is therefore prevented, and the spring brake is not applied. In other words, by energising the brake apply valve 32, the emergency application of the spring brake can overridden.

It will be appreciated, however, that energising the brake apply valve 32 also results in flow of pressurised fluid to the service brake chamber 32a, and therefore the simultaneous application of the service brake. Thus, where the supply line 12 is disconnected, even if there is no emergency application of the spring brake, a braking force is still applied to the vehicle, albeit via the service brake. This means that the normal anti-lock braking functions can be applied during the emergency braking by energising the brake apply valve 32. The exhausting of the delivery pressure which occurs during anti-lock braking functions will, however, result in the application of the spring brakes, as the loss of pressure in the delivery line 31 causes a corresponding reduction in the pressure in the spring brake chamber 23a. As such, over-riding the emergency application of the spring brake in this way is not ideal.

The over-ride shuttle valve 40 provides an alternative means of over-riding the automatic application of the spring brakes resulting from a loss of pressure in the supply line 12. This can be achieved by the supply of electrical power to the solenoid of the suspension valve 42 to move the suspension valve 42 to the fill position in which the inlet 42a is connected to its outlet 42b. Pressurised fluid thus flows from the trailer reservoir 28 along the line 29 through the suspension valve 42 to the suspension-side inlet 40b of the override shuttle valve 40. This is illustrated in Figure 5. The resulting fluid pressure at the suspension-side inlet 40b pushes the valve member to the second position, and connects the trailer reservoir 28 to the control port 20c of the emergency apply valve 20, thus maintaining the emergency apply valve 20 in its first position. The spring brake chamber 23a is thus supplied with pressurised fluid from the trailer reservoir 28 to hold the spring brakes off.

The ECU is preferably programmed to activate a signal warning a driver of the vehicle that the supply of pressurised fluid to the supply line 12 has been broken via a CAN bus connection to the driver’s cab. The signal may be visual - a warning light or the like, or audible - a buzzer, bell or the like, or preferably both. The driver may then make a decision to activate the brakes himself. In this case, as the braking is normal service braking, the anti-lock functions will operated correctly, without any application of the spring brake. If there is no warning mechanism the service brakes can be immediately applied autonomously using brake apply valve 32 as described above.

As the over-ride function in the inventive system is provided by a valve 42 which also has a function in the operation of the trailer suspension system, the interaction of these functions must be considered.

Considering first the case in which the suspension valve 42 provides the pilot to the reset-to-drive valve illustrated in EP 0 520 147, this valve 42 is activated to reset the reset-to-drive valve to return the vehicle suspension to a level appropriate for when the vehicle is in motion. This is generally done when the spring brake is already released, i.e. whilst there is supply of pressurised fluid to the spring brake chamber 23a via the supply line 12, and the emergency apply valve 20 is pushed to its first position, and so the activation of the suspension valve 42 will not have any effect on the braking system. Equally, activation of the suspension valve 42 for the purpose of over-riding the emergency application of the spring brake should not have any effect on the suspension system, as the reset-to-drive valve should already have been reset as the vehicle started moving.

Where the suspension valve 42 is the fill valve illustrated in EP 2 757 006, the isolation valve 133 can be used to ensure that the activation of suspension valve 42 to perform the above over-ride function does not also result in the supply of pressurised fluid to the air bellows of the suspension system. The activation of the suspension valve 42 for the purpose of the supply of pressurised fluid to the air bellows to raise the trailer body requires more consideration, however, as it is possible that this could be required when release of the spring brakes would be undesirable.

Activation of the suspension valve 42 to raise the trailer can generally be permitted when the trailer is in motion, provided the system is provided with a pressure transducer 50 in the park line 18 which can detect loss of supply pressure and/or there is an IS011992 connection to the tractor, as the spring brake is, of course, already released, i.e. there is already a supply of pressurised fluid to the spring brake chamber 23a via the supply line 12, and the emergency apply valve 20 is pushed to its first position. The activation of the suspension valve 42 under these circumstances will not have any effect on the braking system. Activation of the suspension valve 42 to raise the suspension may, however, be prevented if there is no such pressure transducer 50 and there is no ISO 11992 connection, or the pressure in the trailer reservoir 28 is low. This is done because it is a European regulatory requirement that the automatic braking function may be suppressed if IS011992 is present as long as there is sufficient pressure in the service reservoir to meet a defined minimum braking performance.

If the trailer is not in motion, but is “parked on air”, i.e. braked by the supply of pressurised fluid to the service brake chamber 23b, and the reservoir pressure is high enough to provide sufficient braking force to hold the trailer, the suspension valve 42 can also be activated to raise the suspension as the trailer will be held stationary by the service brake during the resulting release of the parking brake. If, however, the reservoir pressure is so low that the service braking force could not hold the trailer, or if the trailer is braked only with the spring brake (i.e. there is no supply of pressurised fluid to the service brake chamber 23b), activation of the suspension valve 42 to raise the suspension cannot be permitted, as this would lead to the trailer being unbraked. In this latter case, the suspension could be raised after the brake apply valve 32 has been activated to apply the service brake. This would not be permitted if the reservoir pressure is low, to avoid wasting the pressurised fluid in the trailer reservoir 28.

The braking system 10 may include a pressure sensor 50 in the park line 18 between the outlet 22b of the park valve 22 and the over-ride shuttle valve 40.

If this pressure sensor 44 is connected to an electronic control unit (ECU not shown) which controls operation of the electrically operated valves in the braking system (including the brake apply valve 32 and the electrically operated valves in the EBS control valve assembly 25), the ECU can be programmed always to energise the suspension valve 42 to override the emergency application of the spring brake whenever a sudden drop in the pressure in the park line 18 is detected, or whenever the pressure in the park line 18 falls below a predetermined level. The ECU may alternatively be programmed to energise the suspension valve 42 to override the emergency application of the spring brake when a sudden drop in the pressure in the park line 18 is detected, or when the pressure in the park line 18 falls below a predetermined level, but only if certain other predetermined criteria are met - if the vehicle speed exceeds a predetermined level, or if the fluid pressure in the trailer reservoir 28 exceeds a predetermined level, for example.

If, when the spring brake chamber 23a is exhausted to atmosphere as described above in relation to Figures 3 and 4, the driver generates a braking demand signal, the pressure in the service brake line 27 may be sufficient to overcome the force of the biasing element in the anti-compounding valve 36 and so there may be flow of fluid into the spring brake chamber 23a from the service braking line 27 via the cross-over line 34 and the second portion 21b of the spring brake line 21b. This could result in the partial release of the spring brake. This would, however, be countered by the simultaneous application of the service brake, and so there need not be any overall loss of braking force.

For completeness, it should be appreciated that the shunt valve 14 may be operated to release the parking brake without the need for electrical power, for example if the trailer is disconnected from a tractor but needs to be moved around a depot or the like. This can be done by moving the park valve 22 to its first position, and moving the shunt valve 14 to its second position. Pressurised fluid flows from the trailer reservoir 28 to the control inlet 20c of the emergency apply valve 20 via the line 26, park line 18 and the park valve 22. The pressure at the control inlet 20c moves the emergency apply valve 20 to its first position and the trailer reservoir 28 are thus connected to the spring brake chamber 23a via the emergency apply valve 20 and the spring brake line 21. The resulting flow of pressurised fluid to the spring brake chamber 23a results in the release of the spring brake. The spring brake can be reapplied by returning the shunt valve 14 to its first position.

An alternative embodiment of braking system according to the invention is illustrated in Figure 6. This embodiment differs only from the embodiment illustrated in Figures 1 - 5, only in respect of the configuration of an connections to the suspension valve 42’. All other aspects of the system are exactly as described in relation to Figures 1-5. In this case, the suspension valve 42’ is has a fluid pressure operated actuator rather than an electrically operated actuator, and is intended for use in conjunction with the type of suspension system disclosed in EP 2 757 006. It has an inlet 42a’ which is connected to the outlet of the fill valve labelled 132 in Figure 19 of EP 2 757 006, an outlet 42b’ which is connected to the suspension-side port 40b of the over-ride shuttle valve 40, an exhaust port 42c’ which vents to atmosphere, and a control port 42d’ which is connected to the output of the isolation valve labelled 133 in Figure 19 of EP 2 757 006. It is movable between a first position in which the inlet is connected to the outlet, and the exhaust port closed, and an exhaust position in which the inlet is closed and the outlet connected to the exhaust port. There is a resilient biasing element which urges the valve 42’ to the first position, suspension valve 42’ being moved to the exhaust position by the supply of pressurised fluid to its control port. The fill valve is a solenoid operated valve which has an inlet connected to a pressurised fluid reservoir, and outlet which is connected to the inlet of the isolation valve, and an exhaust port which is connected to a low pressure region - typically atmosphere. The fill valve is movable between an exhaust position in which the outlet is connected to the exhaust port whilst the inlet is closed, and a fill position in which the inlet is connected to the outlet whilst the exhaust port is closed. There is a resilient biasing element which urges the fill valve into the exhaust position, and the fill valve is movable to the fill position by the supply of electrical power to its solenoid.

The isolation valve is also a solenoid operated valve which has an inlet connected to the outlet of the fill valve, and an outlet connected to at least one suspension bellows (possibly via a manual level adjustment valve). It is movable between a fill position in which the inlet is connected to the outlet, and a stop position in which the inlet and outlet are closed. There is a resilient biasing element which urges the isolation valve into the stop position, and the isolation valve is movable to the fill position by the supply of electrical power to its solenoid.

The pressurised fluid reservoir to which the inlet of the fill valve is connected may be the trailer reservoir 28, or it may be an entirely separate reservoir.

In this case, over-ride of the emergency application of the spring brake resulting from a loss of pressure in the supply line 12 may be achieved by the supply of electrical power to the fill valve but not to the isolation valve. The suspension valve 42’ is thus maintained in its first position by its resilient biasing element, and connected to the reservoir of pressurised fluid via the fill valve. To release the supply of pressurised fluid to the control port 20c of the emergency apply valve, the supply of electrical power to the fill valve is shut off so that the fill valve returns to its exhaust position. As such the pressurised fluid at the suspension-side inlet 40b of the over-ride shuttle valve 40 is exhausted at the fill valve. If the isolation valve is activated to connect the suspension bellows to the source of pressurised fluid via the fill valve, i.e. to raise the suspension, the suspension valve 42’ moves to its exhaust position as a result of the supply of pressurised fluid to the control port 42d’ of the suspension valve 42’. The suspension-side inlet 40b of the override shuttle valve is therefore vented to atmosphere at the suspension valve 42’ and the suspension valve 42’ cannot, under these circumstances be used to release the spring brakes.

The pressurised fluid used in the invention is preferably compressed air, but any other fluid may be used instead, and the invention could equally be employed in a hydraulic braking system.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, 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. A vehicle braking system comprising a brake actuator which is operable to adopt a brake apply position in which the actuator may apply a braking force to a vehicle wheel and a brake release position in which the actuator may release any braking force applied to a vehicle wheel, the brake actuator having a spring brake chamber and a spring and being configured such that supply of pressurised fluid to the spring brake chamber causes the brake actuator to move against the biasing force of the spring to the brake release position and release of pressurised fluid from the spring brake chamber causes the brake actuator to move under the action of the spring to the brake apply position, the system further including a supply line whereby the spring brake chamber is, in use, connected to a source of pressurised fluid, and an emergency apply valve which has a control port and which is configured automatically to connect the spring brake chamber to a low pressure region when the pressure at the control port falls below a predetermined level, wherein the system further includes an override shuttle valve which has a first inlet which is connected to the supply line and a second inlet which is adapted to be connected to an alternative source of pressurised fluid and an outlet which is connected to the control port of the emergency brake apply valve and which has a valve member which is movable between a first position in which flow of fluid from the second inlet to the outlet is substantially prevented whilst flow of fluid from the first inlet to the outlet is permitted, and a second position in which flow of fluid from the second inlet to the outlet is permitted, but flow of fluid from the first inlet to the outlet is substantially prevented, and adopts the second position if the fluid pressure at the second inlet exceeds the fluid pressure at the first inlet by an amount which greater than a predetermined level, and adopts the first position if the fluid pressure at the second inlet does not exceed the fluid pressure at the first inlet by an amount which is greater than the predetermined level.

2. A vehicle braking system according to claim 1 wherein the override shuttle valve is provided with a resilient biasing element which biases the valve member to the first position.

3. A vehicle braking system according to claim 1 or 2 wherein the second inlet of the override shuttle valve is connected to an outlet of a suspension valve, the suspension valve having an inlet which is connected to a source of pressurised fluid, and an exhaust port which is connected a low pressure region, the suspension valve also being adapted to be connected to a suspension control system which is operable to control the operation of a suspension system provided on the vehicle, the suspension valve being movable between a first configuration in which the outlet is connected to the exhaust port, and a second position in which the inlet is connected to the outlet.

4. A vehicle braking system according to claim 3 wherein the suspension valve is provided with an electrically operated actuator which is operable to move the suspension valve between the first position and the second position.

5. A vehicle braking system according to claim 4 wherein the suspension valve is provided with a resilient biasing element which urges the suspension valve into its first position, and is movable from the first position to the second position by the supply of electrical power to the electrically operated actuator.

6. A vehicle braking system according to any preceding claim wherein the outlet of the suspension valve is connected to at least one suspension bellows.

7. A vehicle braking system according to any one of claims 1 to 5 wherein the outlet of the suspension valve is connected to a control port of a fluid pressure operated valve actuator, the fluid pressure operated actuator operating a valve which controls the flow of pressurised fluid to or from at least one suspension bellows.

8. A vehicle braking system according to any preceding claim wherein the emergency apply valve has an inlet which is connected to the supply line and an outlet which is connected to the spring brake chamber via a spring brake line, and is movable between a first position in which the inlet is connected to the outlet and a second position in which the inlet is closed and the outlet vents to a low pressure region.

9. A vehicle braking system according to any preceding claim wherein mechanical biasing element is provided to urge the emergency apply valve into the second position, and movement of the emergency apply valve from the second position to the first position is achieved by the supply of pressurised fluid to the control input at sufficient pressure to overcome the force of the biasing element.

10. A vehicle braking system according to any preceding claim wherein the brake actuator further includes a service brake chamber, wherein supply of pressurised fluid to the service brake chamber causes the brake actuator to move to the brake apply position.

11. A vehicle braking system according to claim 10 further including a control line which in use connects a source of a fluid pressure braking demand signal to the service brake chamber via a braking control valve assembly.

12. A vehicle braking system according to claim 11 wherein the braking control valve assembly comprises at least one modulator which has a control port which is connected to the control line for receipt of a fluid pressure braking demand signal, a supply port which is connected to a source of pressurised fluid, a delivery port which is connected to the service brake chamber via a delivery line, and an exhaust port which vents to a low pressure region, the modulator being operable to move between a build configuration in which the supply port is connected to the delivery port whilst the exhaust port is closed, a hold configuration in which the exhaust port and the supply ports are closed and an exhaust configuration in which the delivery port is connected to the exhaust port whilst the supply port is closed.

13. A vehicle braking system according to claim 11 or 12 wherein the vehicle braking system further comprises a brake apply valve and a trailer supply line which connects the supply line to the control line via the brake apply valve.

14. A vehicle braking system according to claim 13 wherein the brake apply valve is movable between a first configuration in which the brake apply valve substantially prevents flow of fluid from the supply line to the control line, and a second in which the brake apply valve allows flow of fluid from the supply line to the control line.

15. A vehicle braking system according to claim 12 wherein the emergency apply valve is connected to the spring brake chamber via a spring brake line in which is provided an anti-compounding shuttle valve which has a spring-side inlet which is connected to emergency apply valve via a first portion of the spring brake line, a second inlet which is connected to a cross-over line which extends to the delivery line, and an outlet which is connected the spring brake chamber by a second portion of the spring brake line, the anticompounding shuttle valve being movable between a first configuration in which flow of fluid from the second inlet to the outlet is substantially prevented whilst flow of fluid from the first inlet to the outlet is permitted, and a second configuration in which flow of fluid between the second inlet and the outlet is permitted whilst flow of fluid from the first inlet to the outlet is substantially prevented.

16. A vehicle braking system according to claim 15 wherein the anticompounding shuttle valve is configured such it adopts the second configuration if the fluid pressure in the delivery line exceeds the fluid pressure in the supply line by an amount which is greater than a predetermined level, and adopts the first configuration if the fluid pressure in the delivery line does not exceed the fluid pressure in the supply line by an amount which is greater than the predetermined level.

17. A vehicle braking system according to claim 16 wherein the anticompounding shuttle valve is provided with a resilient biasing element or spring which biases the valve into the first configuration.

18. A vehicle braking system according to any preceding claim wherein the system further comprises a pressurised fluid reservoir which is provided in the supply line between the emergency apply valve and a connector for connecting the supply line to the external source of pressurised fluid.

19. A vehicle braking system according to claim 2 and claim 18 wherein the second inlet of the over-ride shuttle valve is connected to the pressurised fluid reservoir via a control valve.

20. A vehicle braking system according to claim 3 and claim 19 where wherein the control valve is the suspension valve, and the pressurised fluid reservoir is connected to the inlet of the suspension valve.

21. A vehicle suspension system according to claim 13 and claim 18 wherein the trailer supply line to the brake apply valve extends from the supply line between the pressurised fluid reservoir and the emergency apply valve.

22. A vehicle braking system substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

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