GB2543037A

GB2543037A - Vehicle braking system and valve assembly for controlling a vehicle braking system

Info

Publication number: GB2543037A
Application number: GB1517353.7A
Authority: GB
Inventors: Robert Mellings Carl; John Harrison Dudley
Original assignee: Haldex Brake Products Ltd
Current assignee: Haldex Brake Products Ltd
Priority date: 2015-10-01
Filing date: 2015-10-01
Publication date: 2017-04-12
Anticipated expiration: 2035-10-01
Also published as: GB2543037B; GB201517353D0

Abstract

A braking system 10 includes: a supply line 12 which is adapted to be connected to a source of pressurised fluid; and a parking/service brake actuation assembly 23 including a brake actuator 23a, 23b, the parking/service brake actuator assembly 23 being operable such that the supply of pressurised fluid to the parking/service brake actuation assembly 23 causes the brake actuator 23a, 23b to move to a brake release position and the release of pressurised fluid from the parking/service brake actuation assembly 23 causes the brake actuator 23a, 23b to move to a brake apply position. The braking system further includes an emergency apply valve 20 which has a first inlet 20a which is connected to the supply line 12, a second inlet 20e which is connected to the service braking actuation assembly, an exhaust port which vents to a low pressure region, and an outlet 20a which is connected to the parking/service brake actuator assembly 23. The emergency apply valve 20 is movable between a first position in which the first inlet 20a is connected to the outlet 20b whilst the second inlet 20e is closed, a second position in which the outlet 20b is connected to the exhaust port whilst the first inlet 20a and second inlet 20e are closed, and a third position in which the second inlet 20e is connected to the outlet 20b whilst the first inlet 20a is closed.

Description

Title: Vehicle Braking System and Valve Assembly for Controlling a 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, and a valve assembly for the control of such a braking system.

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, and examples of such a prior art systems are illustrated in our co-pending patent applications GB2490925 and GB2492124. In these systems, a pilot operated emergency brake apply valve is provided in the line connecting a spring brake chamber of a brake actuator to the red line. When the red line is pressurised, this valve connects the red line to the spring brake chamber to hold the spring brake off, but when pilot pressure is lost, because the red line is disconnected and therefore depressurised, the emergency brake apply valve moves to an exhaust position in which it vents the spring brake chamber so that the spring brake is applied. In both cases, the pressurised fluid from the spring brake chamber is vented at the emergency brake apply valve. GB2490925 and GB2492124 both disclose alternative methods of over-riding this automatic application of the spring brake in the event that the red line is disconnected. EP2190706 discloses a further alternative trailer braking system including a pilot operated emergency brake apply valve. In this case, however, spring chamber is not vented at the emergency brake apply valve when the red line is depressurised. Instead, when the emergency brake apply valve moves to its exhaust position, the emergency brake apply valve connects the spring brake chamber to the outlet of a service brake control valve. Thus, the spring brake can be held off, and emergency braking achieved using the service brakes, by the supply of pressurised fluid to the service actuators. Alternatively, the emergency braking can be achieved using the spring brakes by venting the pressurised fluid from the spring brake chamber at the service brake control valve.

The present invention relates to a further alternative configuration of braking system.

According to a first aspect of the invention we provide a vehicle braking system including a supply line which is adapted to be connected to a supply of pressurised fluid, a parking brake actuation assembly including a brake actuator, the parking brake actuator assembly being operable such that the supply of pressurised fluid to the parking brake actuation assembly causes the brake actuator to move to a brake release position and the release of pressurised fluid from the parking brake actuation assembly causes the brake actuator to move a brake apply position, and a service brake actuation assembly including a brake actuator, the service brake actuation assembly being operable such that the supply of pressurised fluid to the service brake actuation assembly causes the brake actuator to move to a brake apply position, and release of pressurised fluid from the service brake actuation assemble causes the brake actuator to release the brake, the braking system further including an emergency apply valve which has a first inlet which is connected to the supply line, a second inlet which is connected to the service braking actuation assembly, an exhaust port which vents to a low pressure region, and an outlet which is connected to the parking brake actuator assembly, characterised in that the emergency apply valve is movable between a first position in which the first inlet is connected to the outlet whilst the second inlet is closed, a second position in which the outlet is connected to the exhaust port whilst the first inlet and second inlet are closed, and a third position in which the second inlet is connected to the outlet whilst the first inlet is closed.

In one embodiment, the emergency apply valve is also provided with a first fluid pressure operated actuator having a first control inlet, and being configured to move the emergency apply valve to its first position on the supply of pressurised fluid to the first control inlet. In this case, preferably the first control inlet is connected to the supply line. Advantageously, the first control inlet of the emergency apply valve is connected to the supply line via a park valve, the park valve having an inlet which is connected to the supply line and an outlet which is connected to the first control inlet, and being movable between a first position in which its inlet is connected to its outlet and a second position in which its outlet vents to a low pressure region.

The emergency apply valve may also have a second fluid pressure operated actuator having a second control inlet and being configured to move the emergency apply valve to its third position on the supply of pressurised fluid to the second control inlet, in the absence of fluid pressure at the first control inlet. In this case, preferably the second control inlet is connected to the service brake actuator assembly.

The emergency apply valve may include resilient biasing means which moves the emergency apply valve into its second position in the absence of fluid pressure at the first control inlet and second control inlet.

Advantageously, the supply line is provided with a connector for connection to an external supply of pressurised fluid.

The first inlet may be connected to a compressed air reservoir. In this case, the compressed air reservoir may be located in a line connecting the supply line to the first inlet of the emergency apply valve.

Advantageously, the service brake actuation assembly includes an EBS control valve assembly. In one embodiment, the second inlet, and (where provided) the second control inlet are connected to a line between the EBS control valve assembly and the brake actuator.

The braking system may further be provided with an electrically operated brake apply valve which has a first inlet which is connected to a control line, a second inlet which is connected to a compressed air reservoir, and an outlet which is connected to the EBS control valve assembly, and which is movable between a first position in which the first inlet is connected to the outlet whilst the second inlet is closed, and a second position in which the second inlet is connected to the outlet whilst the first inlet is closed. In this case, preferably the brake apply valve is provided with a resilient biasing element which urges the brake apply valve to the first position, and an electrically operated actuator which, when energised, moves the brake apply valve to its second position.

In one embodiment, the emergency apply valve includes a non-return valve which acts to prevent flow of fluid from the outlet of the emergency apply valve towards the supply line via the first inlet of the emergency apply valve.

According to a second aspect of the invention we provide a valve assembly for controlling a vehicle braking system, the valve assembly having a first inlet which is adapted to be connected to the supply line, a second inlet which is adapted to be connected to a service braking actuation assembly, an exhaust port which vents to a low pressure region, and an outlet which is adapted to be connected to a parking brake actuator assembly, characterised in that the valve is movable between a first position in which the first inlet is connected to the outlet whilst the second inlet is closed, a second position in which the outlet is connected to the exhaust port whilst the first inlet and second inlet are closed, and a third position in which the second inlet is connected to the outlet whilst the first inlet is closed.

The valve assembly may have any of the features or combination of features of the emergency apply valve of the braking system according to the first aspect of the invention.

Embodiments of the invention will be now be described with reference to the accompanying drawings of which FIGURE 1 is a schematic illustration of a vehicle braking system according to the first aspect of the invention with the emergency apply valve in its first position, FIGURE 2 is a schematic illustration of the vehicle braking system illustrated in Figure 1 with the emergency apply valve in the second position, FIGURE 3 is a schematic illustration of the vehicle braking system illustrated in Figure 1 with the emergency apply valve in the third position, FIGURE 4 is a schematic illustration of an valve assembly according to the second aspect of the invention, and suitable for use as the emergency apply valve in the braking system illustrated in Figures 1-3, the valve assembly being in its first position, FIGURE 5 is a schematic illustration of the valve assembly illustrated in Figure 4 in its second position, FIGURE 6 is a schematic illustration of the valve assembly illustrated in Figure 4 in its third position, FIGURE 7 is a schematic illustration of an alternative embodiment of vehicle braking system according to the first aspect of the invention, FIGURE 8 is a schematic illustration of a further alternative embodiment of vehicle braking system according to the first aspect of the invention, FIGURE 9 is a schematic illustration of a yet further alternative embodiment of vehicle braking system according to the first aspect of the invention.

Referring now to figures 1 - 3, 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 to 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 a first inlet 20a of an emergency apply valve 20 via a reservoir of pressurised fluid 28 (in this example, compressed air), whilst the park line 18 extends to an inlet 22a of a park valve 22. The spring 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. The emergency apply valve 20 is also provided with a first control inlet 20c which is connected to an outlet 22b of the park valve 22, and a second control inlet 20d, and second inlet 20e, which are both connected to a delivery line 31 of the service braking system.

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, the 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 the 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 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 whilst the second inlet 20e is closed, a second position (illustrated in Figure 2) in which the first inlet 20a and second inlet 20e are closed and the outlet 20b vents to a low pressure region (typically to atmosphere), and a third position (illustrated in Figure 3) in which the first inlet 20a is closed, whilst the outlet 20b is connected to the second inlet 20e. 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 first control inlet 20c at sufficient pressure to overcome the force of the biasing means, whilst movement of the emergency apply valve 20 from the second position to the third position is achieved by the absence of pressure at the first control inlet 20c and sufficient pressure at the second control inlet 20d to overcome the force of the biasing means. A suitable construction of emergency apply valve 20 which could be used to achieve this will be described below.

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 & 2) 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 3) 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 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 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 first 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 first 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. 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.

When the vehicle is parked, the spring brake can be applied by moving the park valve 22 from its first position to its second position. This causes fluid pressure at the first 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 inlets 20a, 20e are 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 2. 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 its inlets 20a, 20e are 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.

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. If there is no warning mechanism, the automatic application of the spring brakes can be overridden, and the service brakes immediately applied autonomously using brake apply valve 32 as described below.

This is achieved by the supply of electrical power to the brake apply valve 32. This causes the brake apply valve 32 to move to its second position, as illustrated in Figure 3, in which the service braking line 27 is connected to the trailer reservoir 28. The EBS valve assembly 25 operates to pressurise the delivery line 31, and the resulting fluid pressure at the second control inlet 20d of the emergency apply valve 20 will cause the emergency apply valve 20 to move to its third position in which its spring outlet 20b is connected to the second inlet 20e, as illustrated in Figure 3. Pressurised fluid therefore flows from the delivery line 31 to the spring brake chamber 23a of the brake actuator 23 via 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.

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.

It will be appreciated, therefore that by providing the emergency apply valve 20 with the third position in which the service brake delivery line 31 is connected to the spring brake chamber 23a of the brake actuator, and configuring the emergency apply valve 20 so that it moves to the third position in response to fluid pressure in the delivery line 31, the emergency apply valve 20 also provides the anti-compounding function provided in the prior art braking systems mentioned above by a separate anti-compounding valve.

This means, of course, that if the EBS control valve assembly 25 carries out normal anti-lock braking functions while the brake apply valve 32 is energised, the emergency exhausting of the delivery pressure which occurs during antilock braking functions will 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. Thus, carrying out the anti-lock brake functions will be ineffective in changing the braking force applied by the actuator 23, as any decrease in service brake pressure will be matched by a corresponding decrease in pressure acting against the spring brake actuating spring.

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 is 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.

Referring now to Figures 4-6, there is shown an example of an emergency brake apply valve 20 suitable for use in a braking system 10 according to the invention. The valve 20 includes a housing cylinder 60 which encloses a first piston 62, and a second piston 64. The first control inlet 20c is provided in a first end 60a of the housing, whilst the second control inlet 20d and an exhaust port 20f are provided in a second, opposite end 60b of the housing 60. The first inlet 20a and the outlet 20b are provided in the housing 60 between the first end 60a and second end 60b, the outlet 20b being closer to the second end 60b than the first inlet 20a. Both pistons 62, 64 are movable within the housing 60 to control the flow of fluid between the first inlet 20a, the second inlet 20e, the outlet 20b and the exhaust port 20f.

The first piston 62 is mounted at or adjacent to the first end 60a of the housing 60, and has a first end provided with a first seal 62a which provides a fluid tight seal between the first piston 62 and the housing 60 between the first control inlet 20c and the first inlet 20a. As a result, there is a substantially fluid tight control chamber 66 formed between the first end 60a of the housing 60 and the first end of the first piston 62, and pressurised fluid in this control chamber 66 acts on the first piston 62 to push it towards the second end 60b of the housing 60.

The first piston 62 is also provided with a second seal 62b and a third seal 62c, the second seal 62b being located between the first seal 62a and the third seal 62c. The functions of these seals 62b, 62c will be described in more detail below. The third seal 62c is mounted on the exterior surface of a tubular second end portion 62d of the first piston, there being at least one aperture 62e provided in the tubular second end portion 62d between the second seal 62b and the third seal 62c. There is a partition separating the tubular second end portion 62d of the first piston 62 from its first end, and the aperture 62e connects the volume enclosed by the tubular second end portion 62d to the space outside the tubular second end portion 62d.

The second piston 64 is located at the second end 60b of the housing 60, a first end portion of the second piston 64 being enclosed by the tubular second end portion 62d of the first piston 62. The first end portion of the second piston 64 has an end cap and a tubular body, and a first seal 64a and a second seal 64b are mounted on the exterior surface of the tubular body to engage with the interior surface of the tubular second end portion 62d of the first piston 62. The first and second seals 64a, 64b thus form a substantially fluid tight chamber 68 between the tubular second end portion 62d of the first piston 62 and the second piston 64.

At least one aperture 20e is provided in the tubular first end portion of the second piston 64 to connect the interior volume enclosed by first end portion of the second piston 64 with the space around the second piston 64. This aperture 20e is located between the first seal 64a and the second seal 64b, and therefore connects the chamber 68 with the volume enclosed by end cap and tubular body of the first end portion of the second piston 64.

The second piston 64 also has a tubular second end portion, which has a larger diameter than the first end portion. The interior volumes enclosed by the tubular second end portion and tubular first end portion of the second piston 64 are connected. A third seal 64c is mounted on the exterior surface of the second end portion.

There is a helical compression spring 72 extending between the two pistons 62 and 64. The spring 72 extends from the end cap of the first end portion of the second piston 64 to the partition of the tubular second end portion 62 of the first piston 62, and is therefore located in the volume enclosed by the second tubular end portion 62d of the first piston 62.

As mentioned above, the exhaust port 20f and second control inlet 20d are provided in the second end 60b of the housing 60. In this example, both are provided in an end face of the housing 60, there being a sealing tube 74 which extends from around the second control inlet 20d into the interior of the housing 60. A seal 70 is mounted on the sealing tube 74 and engages with the tubular second end portion of the second piston 64 to provide a fluid tight seal between the sealing tube 74 and the second piston 64, whilst allowing the second piston 64 to move up and down the sealing tube 74 away from and towards the second end 60b of the housing 60. As a consequence, the sealing tube 74 and second piston 64 cooperate to provide a substantially fluid tight conduit between the chamber 68 and the second control inlet 20d.

The exhaust port 20f connects to a volume in the housing around the exterior surface of the second piston 64.

The emergency apply valve 20 operates as follows.

When there is a supply of pressurised fluid to the first control inlet 20c, the emergency apply valve 20 moves to its first position, as illustrated in Figures 1 and 4. The pressurised fluid at the first control inlet 20c flows into the control chamber 66 and pushes the first piston 62 towards the second end 60b of the housing 60. This brings the third seal 62c into engagement with the housing 60 at a position between the outlet 20b and the second end 60b of the housing 60, whilst the second seal 62b of the first piston 62 is spaced from the housing 60. The first piston 62 also pushes the second piston 64 towards the second end 60b of the housing 60 (via the spring 72), until the second tubular end portion of the second piston 64 buts against the end face of the second end 60b of the housing 60. At this point, the third seal 64c of the second piston 64 is also spaced from the housing 60.

The interior of the housing 60 around the pistons is therefore divided into three volumes - the control chamber 66 between the first end 60a of the housing 60 and the first piston 62, a delivery chamber 76 around the first piston 62 between the first seal 62a and the third seal 62c, and an exhaust chamber 78 around the second piston 64 between the third seal 62c of the first piston 62 and the second end 60b of the housing 60. The first control inlet 20c is, of course, connected to the control chamber 66, the exhaust port 20f to the exhaust chamber 78, and both the first inlet 20a and the outlet 20b to the delivery chamber 76. Fluid may therefore flow from the first inlet 20a to the outlet 20b.

The engagement of the first and second seals 64a, 64b of the second piston 64 with the tubular second end portion of the first piston 62 contains the fluid pressure at the second control port 20d.

If the first control port 20c is vented, the emergency apply valve 20 moves to the second position illustrated in Figures 2 and 5. The spring 72 pushes the first piston 62 away from the second piston 64. The first piston 62 therefore moves towards the first end 60a of the housing 60 until it engages with a stop provided at the first end 60a of the housing 60, thus reducing the volume of the control chamber 66, as illustrated in Figure 5. The housing 60 is shaped such that this movement causes the second seal 62b of the first piston 62 to engage with the housing 60 between the first inlet 20a and the outlet 20b, whilst the housing 60 is spaced from third seal 62c of the first piston 62, and from the third seal 64c of the second piston 64.

The interior of the housing 60 around the pistons 62, 64 is therefore now divided in a different way. The control chamber 66 remains (albeit with a smaller volume), but the first inlet 20a is now connected to the volume between the first and second seals 62a, 62b of the first piston 62, whilst the outlet 20b and exhaust port 20f are now both connected to the volume between the second seal 62b of the first piston 62 and the second end 60b of the housing 60. Fluid may therefore flow from the outlet 20b to the exhaust port 20f, whilst the first inlet 20a is closed.

If, when the first control port 20c is vented, there is supply of pressurised fluid to the second control port 20d, the emergency apply valve 20 moves to the third position illustrated in Figures 3 and 6. The pressurised fluid at the second control port 20d acts on the end cap of the first end portion of the second piston 64, urging the second piston 64 towards the first end 60a of the housing 60. If the pressure at the second control port 20d is sufficiently high to overcome the biasing force of the spring 72, the second piston 64 will move towards the first piston, compressing the spring 72. The housing 60 is configured such that this movement of the second piston 64 brings the third seal 64c of the second piston 64 into engagement with the housing 60 between the outlet 20b and the exhaust port 20f.

The interior of the housing 60 around the pistons 62, 64 is therefore now divided in yet a different way. The control chamber 66 remains, and the first inlet 20a is still connected to the volume between the first and second seals 62a, 62b of the first piston 62 (and therefore remains closed), but the outlet 20b is now connected to the volume between the second seal 62b of the first piston 62 and the third seal 64c of the second piston 64, whilst the exhaust port 20f is now connected to the volume between the third seal 64c of the second piston and the second end 60b of the housing 60.

The movement of the second piston 64 also moves the volume between the first and second seals 64a, 64b of the second piston 64 into communication with the aperture 62e in the tubular second end portion of the first piston 62. This means that the second control inlet 20d is connected to the outlet 20b via the sealing tube 74, the interior of the second piston 64, the aperture 20e, the volume around the second piston 64 between the first seal 64a and second seal 64b, the aperture 62e and the volume around the first piston 62 between the second seal 62b and third seal 62c.

Whilst the second check valve 24b may be provided as a separate part, in this example, it is incorporated in the emergency apply valve 20 as a sealing lip which is mounted around the first piston 62 between the first seal 62a and second seal 62b. The sealing lip extends between the first piston 62 and the housing 60 and is configured to open to allow flow of fluid between the housing 60 and the first piston 62 from the first inlet 20a to the outlet 20b, but to seal the space between the housing 60 and the first piston 62 to prevent flow of fluid in the reverse direction.

The inventive emergency brake apply valve may also be incorporated into the braking system described in our co-pending patent application GB 2492124, as illustrated in Figure 7. In this case, the braking system is also provided with an electrically operable emergency braking override valve 50 located in the line between the first control inlet 20c of the emergency apply valve 20 and the outlet 22b of the park valve 22. The emergency braking override valve 50 has a first port 50a which is connected to the outlet 22b of the park valve 22, an outlet 50b which is connected to the first control inlet 20c of the emergency apply valve 20, a second inlet 50c which is connected to the pressurised fluid reservoir 28, and a solenoid operated actuator 50d.

The emergency braking override valve 50 is movable between a first position (illustrated in Figure 7) in which its first inlet 50a is connected to its outlet 50b, whilst its second inlet 50c is closed, and a second position in which its second inlet 50c is connected to its outlet 50b whilst its first inlet 50a is closed. The passage of fluid from the supply line 12 to the first control inlet 20c of the emergency apply valve 20 via the park valve 22 is therefore not affected by the emergency braking override valve 50 when the emergency braking override valve 50 is in its first position. The emergency braking override valve 50 is electrically operable, in this example, by means of a solenoid 50d. Mechanical biasing means (in this example a spring) is provided to urge the emergency braking override valve 50 into its first position. Movement of the emergency braking override valve 50 from the first position to the second position is achieved by the supply of an electrical current to the solenoid 50d.

The emergency braking override valve 50 may be used as described in GB2492124 if it is not desirable to allow emergency application of the vehicle spring brakes to take place. If there is no problem with the electrical power supply to the system 10, the emergency braking override valve 50 can be operated to prevent the emergency application of the brakes, specifically by the supply of electrical power to the solenoid 50d. This causes the emergency braking override valve 50 to move to its second position wherein the first control inlet 20c of the emergency apply valve 20 is connected to the reservoir 28. Pressurised fluid thus flows from the reservoir 28 to the first control inlet 20c of the emergency apply valve 20, maintaining it in or returning it to its first position. Pressurised fluid can then also flow from the reservoir 28 to the spring brake chamber 23a via the emergency apply valve 20, to release the spring brake.

Emergency braking can then, if desired, be effected using the service brake by the supply of electrical power to the solenoid of the brake apply valve 32. Just as described above in relation to Figure 3, 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 its outlet 32b. Pressurised fluid thus passes from the reservoir 28 to the EBS control valve assembly 25 via the brake apply valve 32 and on to the service braking chamber 23b of the brake actuator 23 via the service brake line 27 to effect service braking. As with conventional service braking, the EBS valve assembly can use conventional ABS control algorithms to modify the emergency braking in accordance with standard antilock control procedures if wheel slip is detected. A pressure transducer may be provided in the line between the emergency braking override valve 50 and the park valve 22 and 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 emergency override valve 50 to override the emergency application of the spring brake whenever a sudden drop in the pressure is detected, or whenever the pressure detected by this pressure transducer falls below a predetermined level. The ECU may alternatively be programmed to energise the emergency braking override valve 50 to override the emergency application of the spring brake when a sudden drop in the pressure is detected, or when the detected pressure 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.

Whilst the ECU may also be programmed always to activate the brake apply valve 32 when the emergency braking override valve 50 is activated (i.e. to effect emergency service braking when the emergency application of the spring brake is prevented) this need not be the case. The ECU may be 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 which case, an electrical braking demand signal is transmitted directly to the brake valve assembly 25 via a CAN bus to effect service braking.

The ECU may further be programmed such that, once the vehicle has come to a halt, it operates the EBS control valve assembly 25 to hold the pressure in the service brake chamber 23b of the brake actuator 23, whilst the emergency braking override valve 50 is deenergised. This causes the first control inlet 20c of the emergency brake apply valve 20 to be vented to atmosphere, allowing the emergency apply valve 20 to move to its second position, and venting the spring brake line 21 and spring brake chamber 23a. Once the pressure in the spring brake chamber 23a is exhausted, the spring brake is applied, and the EBS control valve assembly 25 may be operated to exhaust the service brake chamber 23b.

The invention may also be incorporated into the braking system described in our co-pending application GB1511974.6 as illustrated in Figure 8. In this case, instead of an emergency braking override valve 50, a double check valve -hereinafter referred to as the override shuttle valve 80 is located in the line between the first control inlet 20c of the emergency apply valve 20 and the park valve 22. The override shuttle valve 80 which has a brake-side inlet 80a, which is connected to the outlet 22b of the park valve 22, and a suspension-side inlet 80b, which is connected to an alternative source of pressurised fluid such as a suspension system of the vehicle (as discussed in more detail in GB1511974.6), and an outlet 80c, which is connected to the first control inlet 20c of the emergency apply valve 20.

The override shuttle valve 80 has a valve member which is movable between a first position in which flow of fluid from the suspension-side inlet 80b to the outlet 80c is substantially prevented whilst flow of fluid from the brake-side inlet 80a to the outlet 80c is permitted, and a second position in which flow of fluid from the suspension-side inlet 80b to the outlet 80c is permitted, but flow of fluid from the brake-side inlet 80a to the outlet 80c is substantially prevented. The override shuttle valve 80 is also configured such that it adopts the second position if the fluid pressure at the suspension side inlet 80b exceeds the fluid pressure at the brake-side inlet 80a by an amount which greater than a predetermined level, and adopts the first position if the fluid pressure at the suspension side inlet 80b does not exceed the fluid pressure at the brake-side inlet 80a 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 80b exceeds the fluid pressure at the brake-side inlet 80a by an amount which is sufficient to overcome the force of the spring.

In this embodiment of the invention, if it is desired to override the emergency application of the brakes, the alternative source of pressurised fluid is activated to supply pressurised fluid to the suspension-side inlet 80b of the over-ride shuttle valve 80. The resulting fluid pressure at the suspension-side inlet 80b pushes the valve member to the second position, and connects the trailer reservoir 28 to the first 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. A further alternative embodiment of braking system according to the invention is illustrated in Figure 9. This embodiment differs from the embodiment illustrated in Figures 1 - 3 in relation to the arrangement of the connections to the park valve 22 and the location of the first one-way check valve 24a. Specifically, in this embodiment, the first one-way check valve 24a is located in the line between the outlet 14b of the shunt valve 14 and the inlet 22a of the park valve 22, and the reservoir 28 is connected directly to the inlet 22a without any intervening valves. The second inlet 14c of the shunt valve is connected to the line 16 downstream of the first one-way check valve 24a, ie. between the inlet 22a of the park valve 22 and the first one-way check valve 24a. A pressure transducer 38 is located in the line between the outlet 22b of the park valve 22 and the first control inlet 20c of the emergency apply valve 20. Moving the first one-way check valve 24a so that the reservoir 28 is connected directly to the inlet 22a of the park valve 22 means that, when the park valve 22 is in its first position, the pressure transducer 38 provides a measure of the pressure in the reservoir 28.

The new position of the first one-way check valve 24a means, however, that when the supply line 12 is disconnected from its source of pressurised fluid, the first one-way check valve 24a would prevent the venting of the first control port 20c of the emergency apply valve 20 required for the emergency application of the spring brake. To facilitate this, the park valve 22 is also provided with a pilot operated actuator 19 which is mechanically connected to the park valve 22, and also fluidly connected to the outlet 14b of the shunt valve 14 by means of a pilot line. The pilot operated actuator 19 is configured to move the park valve 22 from its first position to its second position on the release of pressurised fluid from the pilot line. Once this has occurred, the park valve 22 must be moved manually to return it to its first position, but the pilot operated actuator 20 is configured to allow this only when the pilot control line 18 is pressurised.

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 including a supply line which is adapted to be connected to a supply of pressurised fluid, a parking brake actuation assembly including a brake actuator, the parking brake actuator assembly being operable such that the supply of pressurised fluid to the parking brake actuation assembly causes the brake actuator to move to a brake release position and the release of pressurised fluid from the parking brake actuation assembly causes the brake actuator to move a brake apply position, and a service brake actuation assembly including a brake actuator, the service brake actuation assembly being operable such that the supply of pressurised fluid to the service brake actuation assembly causes the brake actuator to move to a brake apply position, and release of pressurised fluid from the service brake actuation assemble causes the brake actuator to release the brake, the braking system further including an emergency apply valve which has a first inlet which is connected to the supply line, a second inlet which is connected to the service braking actuation assembly, an exhaust port which vents to a low pressure region, and an outlet which is connected to the parking brake actuator assembly, characterised in that the emergency apply valve is movable between a first position in which the first inlet is connected to the outlet whilst the second inlet is closed, a second position in which the outlet is connected to the exhaust port whilst the first inlet and second inlet are closed, and a third position in which the second inlet is connected to the outlet whilst the first inlet is closed.

2. A vehicle braking system according to claim 1 wherein the emergency apply valve is also provided with a first fluid pressure operated actuator having a first control inlet, and being configured to move the emergency apply valve to its first position on the supply of pressurised fluid to the first control inlet.

3. A vehicle braking system according to claim 2 wherein the first control inlet is connected to the supply line.

4. A vehicle braking system according to claim 3 wherein the first control inlet of the emergency apply valve is connected to the supply line via a park valve, the park valve having an inlet which is connected to the supply line and an outlet which is connected to the first control inlet, and being movable between a first position in which its inlet is connected to its outlet and a second position in which its outlet vents to a low pressure region.

5. A vehicle braking system according to any preceding claim wherein the emergency apply valve also has a second fluid pressure operated actuator having a second control inlet and being configured to move the emergency apply valve to its third position on the supply of pressurised fluid to the second control inlet, in the absence of fluid pressure at the first control inlet.

6. A vehicle braking system according to claim 5 wherein the second control inlet is connected to the service brake actuator assembly.

7. A vehicle braking system according to any preceding claim wherein the emergency apply valve includes a resilient biasing element which moves the emergency apply valve into its second position in the absence of fluid pressure at the first control inlet and second control inlet.

8. A vehicle braking system according to any preceding claim wherein the supply line is provided with a connector for connection to an external supply of pressurised fluid.

9. A vehicle braking system according to any preceding claim wherein the first inlet is connected to a compressed air reservoir.

10. A vehicle braking system according to claim 9 wherein the compressed air reservoir is located in a line connecting the supply line to the first inlet of the emergency apply valve.

11. A vehicle braking system according to any preceding claim wherein the service brake actuation assembly includes an EBS control valve assembly.

12. A vehicle braking system according to claim 11 wherein the second inlet, and (where provided) the second control inlet is/are connected to a line between the EBS control valve assembly and the brake actuator.

13. A vehicle braking system according to claim 11 or 12 wherein the braking system is further provided with an electrically operated brake apply valve which has a first inlet which is connected to a control line, a second inlet which is connected to a compressed air reservoir, and an outlet which is connected to the EBS control valve assembly, and which is movable between a first position in which the first inlet is connected to the outlet whilst the second inlet is closed, and a second position in which the second inlet is connected to the outlet whilst the first inlet is closed.

14. A vehicle braking system according to claim 13 wherein the brake apply valve is provided with a resilient biasing element which urges the brake apply valve to the first position, and an electrically operated actuator which, when energised, moves the brake apply valve to its second position.

15. A vehicle braking system according to any preceding claim wherein the emergency apply valve includes a non-return valve which acts to prevent flow of fluid from the outlet of the emergency apply valve towards the supply line via the first inlet of the emergency apply valve.

16. A valve assembly for controlling a vehicle braking system, the valve assembly having a first inlet which is adapted to be connected to the supply line, a second inlet which is adapted to be connected to a service braking actuation assembly, an exhaust port which vents to a low pressure region, and an outlet which is adapted to be connected to a parking brake actuator assembly, characterised in that the emergency apply valve is movable between a first position in which the first inlet is connected to the outlet whilst the second inlet is closed, a second position in which the outlet is connected to the exhaust port whilst the first inlet and second inlet are closed, and a third position in which the second inlet is connected to the outlet whilst the first inlet is closed.

17. A valve assembly according to claim 16 having any of the features or combination of features of the emergency apply valve of the braking system according to any one of claims 1 to 15.

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

19. A valve assembly substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

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