Patent Description:
Heavy goods vehicle made up of a towing vehicle and a trailer are well known. It is extremely important that when such a vehicle is parked and /or a trailer is left without a towing vehicle, the vehicle / trailer are held stationary to reduce the risk of injuries and / or death to persons in the immediately vicinity. Park brakes achieve this to some extent as the spring brakes can be manually applied by a button present on the trailer side, which prevents any unwanted movement of the trailer.

<CIT> discloses a vehicle braking system comprising a spring brake actuator having a spring brake chamber, a spring brake control assembly and an immobiliser valve which is movable between a brake release position in which the spring brake control assembly is operable to cause the flow of pressurised fluid into the spring brake chamber or to vent the spring brake chamber to a low pressure region, and an immobilise position in which the spring brake control assembly is operable to connect the spring brake chamber to a low pressure region but cannot be operated to cause the flow of pressurised fluid into the spring brake chamber.

Embodiments of the present invention aim to alleviate one or more of problems or drawbacks of known trailer systems.

According to an aspect of the invention we provide a trailer braking system including:.

In at least one embodiment, the immobiliser may have a control port which is a fluid pressure operated actuator, such that when the fluid pressure at the control port is at or above a threshold the immobiliser moves to its brake release position.

The shunt valve assembly may include a shunt release valve having a first position which directly or indirectly connects a trailer reservoir to a control port of the immobiliser, and a second position which connects the control port of the immobiliser to atmosphere. Alternatively, the second position may connect the control port of the immobiliser to a line or port which pressurises on brake demand. Optionally the line which pressurises on brake demand is a control line or a delivery line or port from a service brake valve / modulator.

The position of the shunt release valve may be controlled by the presence of pressurised fluid in the supply line such that when the pressure in the supply line is at or above a threshold, the shunt release valve moves to its second position and, when the pressure in the supply line is below the threshold, the shunt release valve moves to its first position.

The shunt valve assembly may include a shunt valve which is operable to move between the shunt-enabled position and the shunt-disabled position, and is optionally manually operable.

The shunt valve may only operable to move to its shunt-enabled position when the supply line is disconnected and / or the fluid pressure in the supply line is below a threshold.

The trailer braking system may further include a trailer reservoir for holding a limited supply of pressurised fluid. When the shunt valve is moved to its shunt-enabled position, the trailer reservoir may be connected to the spring brake control valve.

The trailer braking system may further include a park valve which may be operable to move automatically to a parked position when the pressure in the supply line is below a threshold. The park valve may be connected via the shunt valve to the supply line.

The shunt valve may include a first inlet, a second inlet, an outlet, a manually operable button and a control port. The first inlet may be connected to the supply line. The second inlet may be connected to a or the trailer reservoir. The outlet may be connected to the immobiliser and the spring brake control valve. The control port may be connected to the supply line.

The spring brake control valve may include an inlet, an outlet, an exhaust and a control port. The inlet may be connected to the supply line and the outlet may be connected to the spring brake and the control port may be connected to the supply line via the immobiliser.

The spring brake control valve may include a biasing element to bias the valve to a first position, in which the outlet is connected to the exhaust. The control port may be fluid pressure actuated so that when the required pressure is present at the control port the valve is urged to a second position in which the inlet is connected to the outlet.

The immobiliser may include an inlet, an outlet and a control port. The inlet may be connected to the supply line and the outlet may be connected to the control port of the immobiliser and the control port of the spring brake control valve.

The immobiliser may include a biasing element to bias the immobiliser to a first position, in which an internal check valve prevents fluid flowing to the outlet. The outlet may also be connected to an exhaust. The control port may be fluid pressure actuated so that when the required pressure is present at the control port the valve is urged to a second position in which the inlet is connected to the outlet.

The trailer braking system may include an emergency braking override valve. The emergency braking override valve may include a first inlet and a second inlet, an outlet. The first inlet may be connected to the outlet of the immobiliser and the second inlet may be connected to the supply line, optionally via a trailer reservoir. The outlet may be connected to the control ports of the immobiliser and / or the spring brake control valve.

The emergency braking override valve may include a biasing element to bias the valve to a first position, in which the first inlet connects to the outlet. The emergency braking override valve may be electrically operable to urge the valve against the biasing element to a second position, in which the second inlet may be connected to the outlet.

Preferable embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:.

A braking system for a trailer vehicle is illustrated in <FIG>. A brake actuator <NUM> is illustrated and has a spring brake chamber 58a and a service brake chamber 58b (both chambers are capable of imparting braking force on a connected wheel end). The spring brake (the braking force controlled by the spring brake chamber 58a) is applied when the fluid pressure (in this case, air) drops below a threshold and is released when the air pressure is at or above the threshold. In other words, the spring brake is on when there is low or no pressure in the chamber 58a and the spring brake is released (applying no braking force) when there is pressure present in the chamber 58a. The spring brake includes a resilient biasing element by means of which the braking force is applied when the pressure in the spring brake chamber 58a is below the predetermined level.

The service brake (the braking force controlled by the service brake chamber 58b) is applied according to the pressure present in the chamber 58b and is released when the air pressure is below a threshold. In other words, the service braking force developed is proportional to the pressure present in the chamber 58b.

The service brake is activated / released in accordance with driver (or electronic braking system (EBS)) demand. A control line <NUM> is connectable to the tractor and provides a fluid line to the driver's brake pedal. When the control line <NUM> is pressured (i.e. the driver has pressure applied to the brake pedal), a control valve assembly <NUM> (includes at least a modulator) operates to impart the desired pressure to the service brake chamber 58b (and, thus, the desired braking force is developed). The modulator has three configurations - a build state, a hold state and an exhaust state.

The build state is configured to increase the pressure delivered to the service brake chamber 58b. The hold state is configured to maintain a consistent pressure delivered. And, the exhaust state is configured to vent the pressure developed to atmosphere (and the delivered pressure to the chamber 58b drops to zero).

The modulator has a control port 70a for receipt of a fluid pressure braking demand signal (connected to the control line <NUM>), a supply port (not shown) which is connected to a source of pressurised fluid, a delivery port 70b which is connected to the service brake chamber 58b, and an exhaust port (not shown) which vents to a low pressure region / atmosphere.

In the build state, the supply port is connected to the delivery port 70b whilst the exhaust port is closed (i.e. the pressure increases due to the connection to the supply port). In the hold state, the exhaust port and the supply ports are closed (i.e. the pressure is held stable with no additional pressure coming from the supply port). In the exhaust state, the delivery port 70b is connected to the exhaust port whilst the supply port is closed (i.e. the pressure will drop as all the air is vented).

Either the EBS or the driver (via the control line <NUM>) can provide the control pressure at control port 70a of the control valve assembly <NUM> (along a service brake line <NUM>). A brake apply valve <NUM> operates to connect either the control line <NUM> to the control valve assembly <NUM> or connects a constant supply of pressure from reservoir <NUM> to the control valve assembly <NUM>. In this embodiment, the brake apply valve <NUM> is an electrically operated solenoid valve) and, in this example, is biased to connect the control line <NUM> to the control valve assembly <NUM>). The brake apply valve <NUM> includes a first inlet 74a, an outlet 74b, a second inlet 74c and a control solenoid 74d. The control line <NUM> is connected to the first inlet 74a and the second inlet 74c is connected to the reservoir <NUM> via trailer reservoir supply line <NUM>. The outlet 74b is connected to the control valve assembly <NUM>.

The brake apply valve <NUM> is movable between a first position in which the first inlet 74a is connected to the outlet 74b, whilst the second inlet 74c is closed, and a second position in which the first inlet 74a is closed and the second inlet 74c is connected to the outlet 74b. The brake apply valve <NUM> 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 <NUM> into the first position. Movement of the brake apply valve <NUM> from the first position to the second position is achieved by the supply of an electrical current to the solenoid 74d.

Thus, the driver demand pressure along the control line <NUM> is the default pressure delivered to the control valve assembly <NUM>. However, the EBS can control the signal at port 74d in order to connect the trailer reservoir <NUM> the control valve assembly <NUM>. This results in the EBS being operable to control the pressure going to the control valve assembly <NUM> - this is necessary so that the trailer can provide stability control automatically and independently of the driver demand for braking, for example.

The outlet 70b of the modulator <NUM> and an outlet from the spring brake control valve <NUM> are also connected to an anti-compounding valve <NUM>. This is a two-way check valve which acts to connect whichever of the outlet of a spring brake control valve <NUM> (discussed below) or the outlet 70b of the modulator <NUM> is carrying the highest pressure to the spring brake chamber 58a. Such anti-compounding valves prevent the brakes being damaged by the simultaneous application of a braking force from the spring brake and service brake.

In embodiments, the spring brake control assembly includes a spring brake control valve <NUM>. The spring brake control assembly may also include one or more of a park valve <NUM>, a shunt valve <NUM> and an emergency braking override valve <NUM>.

The spring brake control valve (SBCV) <NUM> operates to control the air pressure permitted to the spring brake chamber 58a. The SBCV <NUM> has an inlet 10a, an outlet 10b, an exhaust port 10c and a control port 10d. The inlet 10a connects to a source of pressurised fluid (coming via a shunt park assembly <NUM>), the outlet 10b connects to the spring brake chamber 58a (via a spring brake line <NUM>), and the exhaust port 10c is connected to a low pressure region (e.g. atmosphere).

The spring brake control valve <NUM> is movable between a first position where the inlet 10a is connected to the outlet 10b whilst the exhaust port 10c is closed, and a second position in which the outlet 10b is connected to the exhaust port 10c whilst the inlet 10a is closed.

The control port 10d is a fluid pressure operated actuator. The fluid pressure operated actuator being configured such that the supply of pressurised fluid to the control port 10d causes the spring brake control valve <NUM> to move to its first position. The spring brake control valve <NUM> also has a resilient biasing element <NUM> (e.g. a spring) which acts to urge the spring brake control valve <NUM> into its second position. When the fluid pressure at the control port 10d exceeds a pre-determined level / threshold, the spring brake control valve <NUM> moves positions, against the biasing force of the resilient biasing element <NUM>, from the second position to the first position.

The inlet 10a is connected to the supply line <NUM>. In this example, the inlet 10a of the spring brake control valve <NUM> is also connected to the pressurised fluid reservoir <NUM> and the supply line <NUM> (via connector <NUM>) which connects to pressurised fluid supply from a tractor / towing vehicle. The inlet 10a of the spring brake control valve <NUM> is connected to the connector <NUM> via a supply line <NUM> which extends from the connector <NUM> through the shunt valve <NUM> to an emergency apply line <NUM> and a park line <NUM>.

The emergency apply line <NUM> extends to the inlet 10a of the spring brake control valve <NUM>, whilst the park line <NUM> extends through a park valve <NUM> (in the example in <FIG>, the park valve <NUM> is manually operable but other park valve examples may have automatic or partially automatic operation) and an electrically operable emergency braking override valve <NUM> to the control port 10d.

Two one-way check valves are provided in the emergency apply line <NUM>, both being oriented to allow flow of fluid from the shunt valve <NUM> to the spring brake control valve <NUM> but to prevent flow of fluid in the other direction along the emergency apply line <NUM>, i.e. away from the spring brake control valve <NUM>.

A trailer reservoir supply line <NUM> extends from the emergency apply line <NUM> in between the two one-way check valves to a pressurised fluid reservoir <NUM> mounted on the trailer. An outlet from the trailer reservoir <NUM> is connected to the shunt valve <NUM>.

The shunt valve <NUM> includes a first inlet 46a, a second inlet 46c, an outlet 46b. The first inlet 46a is connected to the supply line <NUM>, the second inlet 46c is connected to the reservoir <NUM> and the outlet 46b is connected to the inlet 10a of the SBCV <NUM>. The shunt valve <NUM> has a first position in which the first inlet 46a is connected to the outlet 46b whilst the second inlet 46c is closed, and a second position in which the first inlet 46a is closed and the second inlet 46c is connected to the outlet 46b. In this example, the shunt valve <NUM> is adapted to be moved manually to the second position and automatically moves back to its first position when the supply line <NUM> is reconnected to a supply of pressure.

The park valve <NUM> includes an inlet 52a, an outlet 52b and an exhaust. The inlet 52a connects to the supply line <NUM> (in this embodiment, connects after the shunt valve <NUM>, to emergency apply line <NUM>). The outlet 52b connects to the control port 10d of the SBCV <NUM> via an immobiliser <NUM> and the emergency braking override valve <NUM> (both described in more detail below). The park valve <NUM> has a first position in which the inlet 52a is connected to the outlet 52b and a second position in which the inlet 52a is closed and the outlet 52b vents to a low pressure region (e.g. atmosphere). In this example, the park valve <NUM> is adapted to be moved manually between the first and second positions.

The emergency braking override valve <NUM> also has a first and second inlet 54a, 54c, and an outlet 54b. The first inlet 54a is connected to the park valve <NUM> (specifically, the outlet 52b). The second inlet 54c is connected to the emergency apply line <NUM> between the two one-way check valves. The outlet 54b is connected to the control port 10d of the spring brake control valve <NUM>.

The emergency braking override valve <NUM> has a first position in which the inlet 54a is connected to the second port 54b, and the third port 54c is closed, and a second position in which the second inlet 54c is connected to the outlet 54b whilst the first inlet 54a is closed.

The emergency braking override valve <NUM> is electrically operable, in this example, by means of a solenoid 54d. Mechanical biasing means (in this example a spring) is provided to urge the emergency braking override valve <NUM> into the first position. In other words, the emergency braking override valve <NUM> is biased to its first position when there is no signal provided at the solenoid 54d. Movement of the emergency braking override valve <NUM> from the first position to the second position is achieved by the supply of an electrical current to the solenoid 54d.

The supply of electrical power to the emergency braking override valve <NUM> and the brake apply valve <NUM> is provided by a control unit (e.g. the trailer EBS control unit).

The immobiliser <NUM> is configured to prevent the trailer from rolling when it is disconnected from a towing vehicle. In general terms, the immobiliser <NUM> operates to move to an immobilise position automatically when pressure in the supply line <NUM> is lost (and the rest of the system vents, including the SBCV <NUM>). Thus, the spring brake moves to a brake applied position and the immobiliser <NUM> also moves to the <IMG>immobilised<IMG> state when the pressure is lost in the supply line <NUM>.

In more detail, the immobiliser <NUM> includes / is provided by an immobiliser valve <NUM>. The immobiliser valve <NUM> has an inlet 84a, an outlet 84b and a control port <NUM>. A resilient biasing element <NUM> (e.g. a spring) is provided to urge the immobiliser valve <NUM> to a default position when the control port <NUM> is not in use. The inlet 84a is connected to the supply line <NUM> via the shunt and park valves <NUM>, <NUM>. The outlet 84b is connected to the control port 10d of the SBCV <NUM> via the emergency braking override valve <NUM>. The control port <NUM> is a fluid pressure operated actuator. The outlet 84b is also connected to the control port <NUM> via the emergency braking override valve <NUM>.

The immobiliser <NUM> has two states - a brake apply / active immobilisation state and a brake release / inactive state. The state illustrated in <FIG> is the inactive state in which the immobiliser <NUM> does not interfere or change the normal operation of the SBCV <NUM>. The inlet 84a is connected to the outlet 84b - and thus, the supply line <NUM> pressure is permitted to flow to the control port 10d of the SBCV <NUM>.

In the second state (the immobilisation state), the inlet 84a is connected to the outlet 84b via an internal check-valve. This prevents pressure on the supply line <NUM> from reaching the control port 10d of the SBCV <NUM> (and, thus, the spring brake cannot function to allow pressure through to the spring brake chamber 58a because the SBCV <NUM> is biased to vent by default). Furthermore, the biasing element <NUM> urges the immobiliser <NUM> to its immobilisation state, so once there is no fluid on the outlet 84b side of the valve, the immobiliser <NUM> cannot be repressurised merely by connecting the supply line <NUM> to a source of fluid.

In some embodiments, the line connected to the control port <NUM> of the immobiliser valve <NUM> includes a two-way check-valve <NUM>. The check-valve <NUM> has two inlets and a single outlet, which operates automatically to allow the inlet with the larger pressure present to pass the pressure on to the outlet. One inlet is connected to the outlet 84b of the immobiliser valve <NUM> (as discussed above) and the other is connected to a port <NUM>. Port <NUM> can be connected to an external source of fluid pressure - thus, a manual external input could be used to pressure the immobiliser valve <NUM> to its released state. Alternatively (as is the case illustrated in <FIG>), the port <NUM> is connected to the delivery of the control valve assembly / modulator <NUM> for the service braking delivery (outlet / delivery port 70b).

An alternative immobiliser <NUM> is illustrated in <FIG>. The difference in this system is there is no double check valve connecting to the control <NUM> of the immobiliser valve <NUM>. Instead, the immobiliser valve <NUM> is provided with two fluid pressure operated actuators <NUM>,<NUM>'. The first fluid pressure operated actuator <NUM> is connected as before (to the outlet 84b of the immobiliser valve <NUM> and, thus, to the control port 10d of the spring brake control valve <NUM>) and operates in exactly the same way as above. In other words, it pushes the immobiliser valve <NUM> against the biasing force of the spring <NUM> into its brake release position when pressure is present at the control port 10d of the SBCV <NUM> / outlet 54b of the emergency braking override valve <NUM>.

The second fluid pressure operated actuator <NUM>' is connected to an alternative source of pressurised fluid via port <NUM> in the same way as is the second inlet of the two-way check valve <NUM> in system discussed above. Thus (as discussed above), the port <NUM>' may be connected to the pressure delivered to the service brakes (i.e. from delivery port 70b). The second fluid pressure operated actuator <NUM>' is configured to move the immobiliser valve <NUM> against the biasing force of the spring <NUM> into its brake release position when the pressure of fluid from the alternative source of pressurised fluid exceeds a pre-determined amount.

It should be appreciated that the system illustrated in <FIG> includes the same system components as discussed in relation to <FIG> (apart from the check-valve as discussed) but are not shown explicitly in <FIG>.

It should also be appreciated that the immobiliser valve <NUM> may include an exhaust port attached to the check-valve 84c provided between the inlet 84a and the outlet 84b. Thus, when the immobiliser <NUM> moves to the active immobilisation state, the pressure on the outlet 84b side of the immobiliser valve <NUM> may automatically vent (and not be able to repressurise until the immobiliser <NUM> is operated to change states again). This is shown in <FIG>.

The ability to shunt a trailer when it is disconnected from a towing vehicle may be particularly important. Shunting a trailer involves moving it only a small distance (e.g. across a warehouse or trailer yard) and is often used to repark a trailer in a desired position in a yard after a towing vehicle has delivered a trailer to a different position in the yard and departed. The system illustrated on <FIG> does not allow a proper shunt operation because the immobiliser <NUM> cannot be released without power and / or a supply of fluid. <FIG> and <FIG> illustrate a solution to this problem.

<FIG> illustrates part of the braking system with a shunt release valve <NUM> and <FIG> shows additional components to show where the shunt release valve <NUM> is positioned within the wider braking system. It should be appreciated that the other components discussed above (such as the SBCV <NUM> and brake chamber <NUM>) are present but not illustrated.

Essentially, the braking system includes a shunt valve assembly which provides a shunt-enabled configuration and a shunt-disabled configuration. When the shunt valve assembly is in the shunt-disabled configuration, the immobiliser <NUM> is operable to move both to the brake release position, in which the spring brake control valve <NUM> is operable to cause the flow of pressurised fluid into the spring brake <NUM> or to vent the spring brake, and to the immobilise position, in which the spring brake control valve <NUM> is not operable. In other words, the immobiliser <NUM> is free to operate normally. Further, when the shunt valve assembly is in the shunt-enabled configuration, the immobiliser <NUM> is moved to the brake release position and the spring brake control valve <NUM> permits pressurised fluid to the spring brake 58a such that the spring brake is moved to the release position. In other words, the immobiliser <NUM> is held in the brake release position despite there being no proper connection to a towing vehicle (on the supply line <NUM>).

The shunt valve assembly includes the shunt valve <NUM> and the shunt release valve <NUM>. As illustrated, the shunt valve <NUM> is also part of the park shunt assembly <NUM>, alongside the park valve <NUM>'. The park valve <NUM>' has the same ports and is configured to provide the same positions as discussed above but the actuation is different (thus the reference number is provided with a prime symbol (') to indicate this difference). The park valve <NUM>' provides an automatic parking functionality - the positions of the park valve <NUM>' is controlled by pressure in the supply line (between the shunt valve <NUM> and the park valve <NUM>'). A spring actuator <NUM> is provided (which is connected to the output of the shunt valve <NUM>) which acts to move the park valve <NUM>' depending on the pressure present. When the pressure is below a threshold, the actuator <NUM> moves the park valve <NUM>' to its second position, which prevents pressure moving towards the immobiliser <NUM> and vents the immobiliser <NUM> (via the park line <NUM>).

In other words, the park valve <NUM>' will only maintain its first position if there is pressure in the supply line <NUM>. The park valve <NUM>' includes a manually operable button to manually move the valve <NUM>'.

The shunt release valve <NUM> is configured to allow the trailer to shunt (as normal using the (manually operable) shunt valve <NUM>) and release the immobiliser valve <NUM> (and, thus, allow the spring brakes to be released while the trailer is repositioned). In other words, the shunt release valve <NUM> has a first position which directly or indirectly connects the trailer reservoir <NUM> to the control port <NUM> of the immobiliser, and a second position which connects the control port <NUM> of the immobiliser to the delivery port 70b of the service brake modulator <NUM> (see <FIG>) or to a low pressure region (see <FIG>). In reality, both these options provide similar results because the delivery port 70b is not pressured unless service braking demand is present, so is often a low pressure line.

In embodiments (see <FIG> and <FIG>), the shunt release valve <NUM> includes a first port 110a, a second port 110b, a third port 110c and a fluid pressure operated control port 110d. The first port 110a is connected to the park line <NUM> between the park valve <NUM> and the immobiliser <NUM> (shown as line <NUM>). The second port 110b is connected to port <NUM>' of the immobiliser valve <NUM> (shown as line <NUM> on <FIG>). The third port 110c is connected to the delivery port 70b for the service brake demand (and, thus, a controlled low pressure region). The fluid pressure operated control port 110d is connected to the supply line <NUM> (prior to both the shunt valve <NUM> and the park valve <NUM>') via line <NUM>. The shunt release valve <NUM> also includes a mechanical biasing element <NUM>.

As mentioned above, the shunt release valve <NUM> has two positions. In the first position, the first port 110a is connected to the second port 110b and the third port 110c is closed. In the second position, the second port 110b is connected to the third port 110c.

The biasing element <NUM> is configured to urge the shunt release valve <NUM> to its first position. In other words, when the trailer is not connected at the supply line <NUM> to a towing vehicle and the shunt valve <NUM> is activated, the pressure from the reservoir <NUM> is permitted to flow through to the control port <NUM>' of the immobiliser valve <NUM> (thus, pressure is able to get through the immobiliser <NUM> to the SBCV <NUM> and, thus, to the spring brake chamber 58a). In other words, the position of the shunt release valve <NUM> is controlled by the presence of pressurised fluid in the supply line <NUM> such that when the pressure in the supply line <NUM> is at or above a threshold, the shunt release valve <NUM> moves to its second position and, when the pressure in the supply line <NUM> is below the threshold, the shunt release valve <NUM> moves to its first position. When pressure is present at the port 110d (i.e. when the supply line <NUM> is connected to a towing vehicle), the shunt release valve <NUM> is pressured (against the biasing element <NUM>) to its second position. This causes the pressure at the control port <NUM>' of the immobiliser valve <NUM> to vent to a low pressure region (e.g. atmosphere) and the immobiliser <NUM> must be released using the emergency braking override valve <NUM> (normal EBS release is discussed below).

It should be appreciated that the shunt valve <NUM> is moved to the shunt position manually. Further, the park valve <NUM>' is also moved manually to the unparked position once the reservoir <NUM> pressure is permitted between the shunt valve <NUM> and park valve <NUM>' (and reservoir pressure acts on the actuator <NUM> to maintain the park valve <NUM>' in its first position).

Thus, the shunt release valve <NUM> permits the shunt valve <NUM> to control the immobiliser <NUM> as well as the spring brake control valve <NUM>.

<FIG> and <FIG> illustrate an alternative solution including an integrated shunt release valve <NUM>'. In these figures, the standard components from the earlier braking system have the same reference numbers and the description relating to features of the integrated shunt release valve <NUM>' have the same numbers but an additional prime to indicate they are part of the system in <FIG> and <FIG>.

In this example, the shunt release valve <NUM>' is integrated within the shunt park assembly <NUM>'. The shunt release valve <NUM>' includes a first port 110a', a second port 110b', an exhaust / vent, and a fluid pressure operated control port 110d'. The first port 110a' is connected directly to the pressure from the fluid reservoir <NUM> (shown as line <NUM>' on <FIG>). The second port 110b' is connected to port <NUM>' of the immobiliser valve <NUM>.

In some embodiments, the second port 110b' is connected to the immobiliser <NUM> via a two-way check-valve <NUM>' (shown as line <NUM>' on <FIG>). The check-valve <NUM>' includes two inlets - one is connected to the shunt release valve <NUM>' as discussed and the other is connected to the control line <NUM>. Whichever inlet has the higher pressure is passed on to the control port <NUM>' of the immobiliser valve <NUM>.

The exhaust vents to a low pressure region / atmosphere. The fluid pressure operated control port 110d' is connected to the supply line <NUM> (prior to both the shunt valve <NUM> and the park valve <NUM>) via line <NUM>'. The shunt release valve <NUM>' also includes a mechanical biasing element <NUM>'.

The shunt release valve <NUM>' has two positions. In its first position, the first port 110a' is closed and the second port 110b' is connected to the exhaust (illustrated in <FIG> and <FIG>). In its second position, the first port 110a' is connected to the second port 110b' and the exhaust is closed.

The biasing element <NUM>' is configured to urge the shunt release valve <NUM>' to its second position. In other words, when the trailer is not connected at the supply line <NUM> to a towing vehicle, the shunt release valve <NUM>' is in its second position. When the shunt valve <NUM> is activated, the pressure from the reservoir <NUM> is permitted to flow through to the control port <NUM>' of the immobiliser valve <NUM> (thus, pressure is able to get through the immobiliser <NUM> to the SBCV <NUM> and, thus, to the spring brake chamber 58a). If the two-way check-valve <NUM>' is present, the pressure from the reservoir <NUM> is passed to the two-way check-valve <NUM>', which in turn is delivered to the control port <NUM>' (otherwise, the reservoir <NUM> is connected directly to the control port <NUM>').

When pressure is present at the port 110d (i.e. when the supply line <NUM> is connected to a towing vehicle), the shunt release valve <NUM>' is pressured (against the biasing element <NUM>') to its first position. This causes the immobiliser valve <NUM> to vent to a low pressure region (e.g. atmosphere) and the immobiliser <NUM> must be released using the emergency braking override valve <NUM> (normal EBS release is discussed in more detail below).

The system operates in the following manner.

Under normal driving conditions, the connector <NUM> is pressurised by virtue of its connection to "the red line", i.e. the tractor based supply of pressurised fluid, and the shunt valve <NUM>, park valve <NUM> and emergency braking override valve <NUM> are all in their first positions, as illustrated in the <FIG>. The immobiliser <NUM> is in its brake release position. As a result, the control port 10d is connected to the connector <NUM> and is therefore pressurised, and, the spring brake control valve <NUM> is also in its first position. Pressurised fluid can therefore flow from the source of pressurised fluid <NUM>, along the emergency apply line <NUM>, and into the spring brake chamber 58a to release the spring brakes.

When the trailer is left without a towing vehicle, the connector <NUM> is disconnected from the external source of pressurised fluid and the supply line <NUM> thus exhausted to atmosphere. In the absence of pressurised fluid at the control port 10d of the spring brake control valve <NUM>, the spring brake control valve <NUM> moves to its second (default / unpressurised) position. As a result, the inlet 10a is closed, and the outlet 10b is connected to the exhaust port 10c. The spring brake chamber 58a is thus vented to atmosphere via the exhaust port 10c, and the spring brake applied.

Further, when the connector <NUM> is disconnected from the supply of fluid from the towing vehicle, pressure is also lost at the control port <NUM> of the immobiliser valve <NUM> and the immobiliser <NUM> automatically moves to its active / immobilisation state. Thus, the trailer is automatically immobilised with the spring brakes applied.

Further, the park valve <NUM>' will also automatically move to its second position and vent the connections to the immobiliser <NUM> and the SBCV <NUM> when pressure is lost in the supply line <NUM>.

The same state may be be achieved without disconnecting the towing vehicle, by manually actuating the park valve <NUM>. The button is manually pulled outwards and the park valve moves to its second position in which the park line <NUM> is connected to atmosphere. The park line <NUM> vents and the pressure is lost and resulting in the both the control port 10d of the SBCV <NUM> and the control port <NUM> of the immobiliser valve <NUM> losing pressure and moving to their default / biased positions.

Once the trailer is parked and disconnected (i.e. when the trailer is in a yard or the like without a towing vehicle), a shunt operation can be used to move the trailer short distances. The shunt functionality is designed to allow the spring brakes to be released while the trailer is moved but once left again the trailer will default back to its parked (and in this example, immobilised state). The shunt valve <NUM> is manually operable to provide a "shunt state" in the trailer. The manually operable button is pushed inwards to move the shunt valve <NUM> to its second position where the trailer reservoir <NUM> is connected to the park line <NUM>. It should be appreciated that, in this example, the shunt valve <NUM> is only operable to move to its shunt-enabled position when the supply line <NUM> is disconnected and / or the fluid pressure in the supply line <NUM> is below a threshold. Once pressure is in the supply line <NUM>, the shunt valve <NUM> is forced back to its shunt-disabled position.

Thus, when the shunt valve <NUM> is actuated and the park valve <NUM>' actuated to its unparked position, pressure from the trailer reservoir <NUM> is permitted to travel towards the immobiliser <NUM>. The shunt release valve <NUM>, <NUM>' is in its second position as there is no pressure from the supply line <NUM> and due to the biasing of element <NUM>, <NUM>'. In this position, the shunt release valve <NUM>, <NUM>' is operable to allow pressure to the control port <NUM>' of the immobiliser valve <NUM>.

The shunt release valve <NUM>, <NUM>' is connected to the control port of the immobiliser valve <NUM>'. Thus, the immobiliser <NUM> is moved to its released / not immobilised position. In turn, this permits pressure to the spring brake control valve <NUM> (specifically to the control port 10d), which moves the SBCV <NUM> and to its second position in which pressure is permitted to the spring brake chamber 58a. The spring brakes are thus released and the trailer can be moved a short distance without any proper connections to a towing vehicle (i.e. without connection to the supply line <NUM> or the control line <NUM>).

When the movement is complete, the shunt valve <NUM> is moved back to its original first position (i.e. disconnecting the trailer reservoir <NUM> from the park line <NUM>, etc). The pressure is lost in the spring brake control valve <NUM> and in the immobiliser <NUM> and both return to their biased positions - i.e. the SBCV <NUM> vents the spring brake chamber 58a and the immobiliser <NUM> automatically moves to its immobilise position. The shunt valve <NUM> is also configured to move to its shunt-disabled position automatically when there is pressure in the supply line <NUM> (i.e. once a towing vehicle has been connected).

As soon as the supply line <NUM> is connected to a towing vehicle (and is pressurised), the shunt release valve <NUM>, <NUM>' is moved to its second position. Thus, it will no longer connect any source of fluid to the control port <NUM>' of the immobiliser valve <NUM>.

Both alternative embodiments of the shut release valve <NUM>, <NUM>' are configured to provide similar functionality. However, the connections between the valve <NUM>, <NUM>' are different, so there is slightly different operation within the general functionality provided.

In the embodiment in <FIG> and <FIG>, the shunt release valve <NUM> directs fluid from the park line <NUM> to the control port <NUM>' of the immobiliser valve <NUM>. Further, the pressure from the service brake modulator <NUM> may also be connected to the control port <NUM>' (as discussed above, from delivery port 70b).

On reconnection to a towing vehicle, the following occurs to prepare the trailer for departure. Both the supply and control lines <NUM>, <NUM> are connected to the towing vehicle - thus, the supply line <NUM> becomes pressurised. The shunt release valve <NUM> moves to its second position (which connects the delivery port 70b to the control port <NUM>' of the immobiliser <NUM>). As mentioned above, the pressure in the delivery port 70b will be low unless there is service braking demand, so the control port <NUM>' is effectively connected to a low pressure region. However, the driver could depress the brake pedal in the towing vehicle to develop a service brake demand, which would result in pressure building at the control port <NUM>' of the immobiliser <NUM> and connecting the supply line <NUM> to the SBCV <NUM>.

Alternatively, once the tractor / trailer is ready to release the immobiliser <NUM>, the control unit of the EBS provides a signal to the emergency braking override valve <NUM> (specifically a pulse to the solenoid 54d). The emergency braking override valve <NUM> connects the trailer reservoir <NUM> to the control port <NUM> of the immobiliser valve <NUM> (and the control port 10d of the SBCV <NUM>). This allows both the immobiliser <NUM> and the SBCV <NUM> to move to their respective brake release positions and the supply line <NUM> pressure is permitted through to the SBCV <NUM> (and the spring brake chamber 58a) and the spring brakes are released.

The system could be modified to prevent the driver being able to use the brake pedal to release the immobiliser <NUM>. In this case, the shunt release valve <NUM> includes a vent (and does not connect to the delivery port 70b). The immobiliser <NUM> can only be released by the above described action of the EBS (e.g. an electric release) and not by the service brake demand pressure. Thus, the system provides an "electric only" immobiliser release.

In the embodiment in <FIG> and <FIG>, the shunt release valve <NUM>' directs fluid directly from the trailer reservoir <NUM> to the control port <NUM>' of the immobiliser <NUM>. If there is no two-way check-valve, the shunt release <NUM>' works similarly to the "electric only" as the shunt release valve <NUM>' either connects the reservoir to the control port <NUM>' or the control port <NUM>' is vented.

If a two-way check-valve <NUM>' is present, the control line <NUM> may also connect to the control port <NUM>' of the immobiliser <NUM>. However, the control line <NUM> is only pressurised when braking demand is required (i.e. by pressure on the brake pedal in the towing vehicle), so does not influence the shunt functionality (because the control line <NUM> isn't connected to any towing vehicle).

Thus, the same functionality is provided as above with both an electric actuated immobiliser <NUM> release and pneumatic service brake demand actuated immobiliser <NUM> release. On reconnection to a towing vehicle, again both the supply and control lines <NUM>, <NUM> are connected to the towing vehicle - thus, the supply line <NUM> becomes pressurised. The shunt release valve <NUM>' moves to its second position (which connects the control line <NUM> to the control port <NUM>' of the immobiliser <NUM>).

Effectively, if the shunt release valve <NUM>, <NUM>' includes a connection to the delivery port 70b (or to the control line <NUM>), the immobiliser <NUM> is releasable by a pneumatic service brake signal (the brake pedal being depressed). If there is no such connection, then the immobiliser <NUM> is only releasable by an electric signal from the EBS (to the emergency override valve <NUM>).

Embodiments are advantageous because they combine the ability of a trailer to be shunted while maintaining an increased safety when the trailer is being connected to a towing vehicle. The shunt valve assembly allows the immobiliser <NUM> to be overridden only when the trailer is being moved in a shunt operation.

The (condition / state of the) shunt release valve <NUM>, <NUM>' is controlled by the supply line <NUM>. If the supply line <NUM> is pressurised, the shunt release valve is inactive in terms of its effect on the immobiliser <NUM>. If the supply line <NUM> is unpressurised, the shunt release valve <NUM>, <NUM>' is "active" and permits the immobiliser <NUM> to be released outside of the normal requirements for releasing it (i.e. the shunt overrides the park brake and the immobiliser to allow the springs to be released).

Claim 1:
A trailer braking system including:
a supply line (<NUM>) for connection to a continuous source of pressurised fluid;
a spring brake (<NUM>), which has an apply position and a release position, and the spring brake (<NUM>) moves to the release position when pressurised fluid is provided at or above a threshold;
a spring brake control valve (<NUM>), which controls the flow of fluid to the spring brake (<NUM>);
an immobiliser (<NUM>) having a brake release position and an immobilise position, which control the flow of pressurised fluid to the spring brake control valve (<NUM>),
a shunt valve assembly having a shunt-enabled configuration and a shunt-disabled configuration, further characterised by
in the shunt-disabled configuration, the immobiliser (<NUM>) is operable to move both to the brake release position, in which the spring brake control valve (<NUM>) is operable to cause the flow of pressurised fluid into the spring brake (<NUM>) or to vent the spring brake chamber (58a), and to the immobilise position, in which the spring brake control valve (<NUM>) is not operable, and
in the shunt-enabled configuration, the immobiliser (<NUM>) is moved to the brake release position and the spring brake control valve (<NUM>) permits pressurised fluid to the spring brake (<NUM>) such that the spring brake (<NUM>) is moved to the release position.