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.

Document <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.

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:.

When the temporary override valve is in the inactive position, the immobiliser may be operable to move both to the brake release position, in which the spring brake control valve is operable to cause the flow of pressurised fluid into the spring brake or to vent the spring brake chamber, and to the immobilise position, in which the spring brake control valve is not operable.

The trailer braking system may include a shunt valve. The shunt valve may have an activated position and a deactivated position. When the shunt valve is in the activated position, the trailer reservoir may be connected directly or indirectly to the spring brake control valve. When the shunt valve is in the deactivated position, the supply line may be connected to directly or indirectly to the spring brake control valve. Optionally, the shunt valve may be moved to its deactivated position when the supply line is connected to a source of pressurised fluid.

The trailer braking system may include a control line for connection to a source of pressurised fluid when there is a braking demand.

Movement of the temporary override valve to its inactive position may be directly or indirectly controlled by pressure in the control line, for example by the delivery of a modulator valve signalled by the control line. The temporary override valve may be manually operable to its override position. Movement of the temporary override valve to its override position may be controlled by a fluid pressure controlled actuator. The fluid pressure controlled actuator may include a latch to hold the temporary override valve in the override position without a continuous fluid pressure being present. Movement of the temporary override valve to its inactive position may be controlled by a second fluid pressure controlled actuator. Alternatively, the temporary override valve may be biased to its inactive position.

The temporary override valve may include a first port, a second port and a third port. The first port may be connected to the supply line and the third port may be connected to the immobiliser.

When the temporary override valve is in the override position, the first port may be connected to the third port. When the temporary override valve is in the inactive position, the second port may be connected to the third port.

The second port may be connected to a or the control line, or a modulator valve signalled by the control line, or the second port may be a vent.

The trailer braking system may include a park valve. The park valve may have a first position in which the immobiliser and / or spring brake control valve is connected to the supply line and a second position in which the supply line is blocked and the immobiliser and / or spring brake control are vented. The park valve may be operable to move automatically to the second position when the pressure in the supply line is below a threshold. The park valve may be connected to the supply line via the shunt valve.

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

The spring brake control valve may include a biasing element to bias the valve to a first position, in which the outlet may be connected to the exhaust, and 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 may be connected to the outlet.

The immobiliser may include an inlet, an outlet and a control port, wherein 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 and, optionally the outlet may be connected to an exhaust, and 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 may be 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, and the outlet may be connected to the control ports of the immobiliser and 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.

In order that the present invention may be more readily understood, preferable embodiments thereof 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 (also referred to as an activated position) and automatically moves back to its first position (also referred to as an inactive position) when the supply line <NUM> is reconnected to a supply of pressure.

In other words, when the shunt valve <NUM> is in the activated position, the trailer reservoir <NUM> is connected directly or indirectly to the spring brake control valve <NUM>. In embodiments where an immobiliser <NUM> is present (discussed further below), the shunt valve <NUM> may connect to the SBCV <NUM> via the immobiliser <NUM>. When the shunt valve <NUM> is in the deactivated position, the supply line <NUM> is connected to directly or indirectly to the spring brake control valve <NUM> (again potentially through the immobiliser <NUM> if there is one present).

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 "immobilised" 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. These states / positions which positions control the flow of pressurised fluid to the spring brake control valve <NUM>. 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>. However, when the supply line <NUM> is connected to a low pressure region, the immobiliser <NUM> automatically moves to its immobilise position in which the spring brake control valve <NUM> is not operable.

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.

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. 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.

In some embodiments, the port <NUM> (connected to the control port <NUM>' or the check valve <NUM>) is connected to the delivery port 70b of the service braking valve assembly / modulator <NUM>.

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 or embarking or alighting a boat / ferry) 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.

As mentioned above, a shunt valve <NUM> may be provided. As discussed above, the shunt valve <NUM> is manually operable to move it to its second position to connect the trailer reservoir <NUM> to the park line <NUM> / the immobiliser <NUM> (or if no immobiliser <NUM> is present, the SBCV <NUM>). However, there is an issue with this operation if the operators completing the shunt operations do not or are unable to manually activate the shunt valve <NUM>. In such a case, the trailer may be dragged without releasing the spring brake (and, thus, damage to the braking system is possible). The present invention provides a temporary override valve <NUM> that can be activated by a driver or other operator before or when the trailer is disconnected from a towing vehicle / parked in an initial drop off location. The temporary override valve <NUM> allows (fluid in) the supply line to be connected to the spring brake control valve <NUM> automatically when the supply line <NUM> is connected to a source of pressurised fluid. This provides an alternative shunt functionality that preserves the health of the braking system if the trailer is moved with only a connection to the supply line <NUM>. The temporary override valve <NUM> is discussed in more detail below.

As shown in <FIG>, a trailer braking system including a temporary override valve <NUM> is shown. The temporary override valve <NUM> has an override position and an inactive position. When the temporary override valve <NUM> is in the override position, the immobiliser <NUM> remains in the immobilise position and the spring brake remains in the apply position when the supply line <NUM> is unpressured (i.e. unconnected to a supply of fluid). However, on connection to a supply, the immobiliser <NUM> is moved to its brake release position and the supply line <NUM> is connected to the spring brake control valve <NUM> automatically (i.e. when the supply line <NUM> is connected to a source of fluid). In other words, both the actions of the immobiliser <NUM> and the SBCV <NUM> are automatic on pressurisation from a connection to the supply line <NUM>. Thus, the spring brake 58b is moved to the release position automatically.

In embodiments, when the temporary override valve <NUM> is in the inactive position, the immobiliser <NUM> is operable to move both to the brake release position (i.e. the position in which the spring brake control valve <NUM> is operable normally to cause the flow of pressurised fluid into the spring brake 58b or to vent the spring brake chamber 58b as necessary depending on the system and pressure in the braking system) and to the immobilise position (i.e. the position in which the spring brake control valve <NUM> is not operable irrespective of the whether the supply line <NUM> is pressurised / the supply line <NUM> is connected to a source of fluid). In other words, when the temporary override valve <NUM> is inactive, the remaining braking system components operate as they normally would as none of the connections from the temporary override valve <NUM> (in the inactive state) causes changes to the normal operation. Thus, the immobiliser <NUM>, the SBCV <NUM>, the emergency braking override vale <NUM>, etc. all operate between their respective states with no interference from the temporary override valve <NUM>. This is discussed further below where the use of the system is outlined.

In some embodiments, the temporary override valve <NUM> includes a first port 200a, a second port 200b and a third port 200c. In some embodiments, the first port 200a is connected to the supply line <NUM> (via park line <NUM> and a first override line <NUM>) and the third port 200c connects to second override line <NUM>. second override line <NUM> connects to the immobiliser <NUM>. The third port 200c connects to the control port <NUM>' of the immobiliser <NUM> (see <FIG>).

When the temporary override valve <NUM> is in the override position (as shown in <FIG> and <FIG>), the first port 200a is connected to the third port 200c. In other words, the temporary override valve <NUM> connects the park line <NUM> (and, thus, the supply line <NUM>) to the control port <NUM>' of the immobiliser <NUM>. Thus, when the supply line <NUM> is pressured, the immobiliser <NUM> is automatically moved to its brake release position.

In embodiments, the second port 200b connects to the delivery port 70b of the service brake valve assembly <NUM> (which is only pressurised when there is a service braking demand generated by either the brake pedal in the towing vehicle or the trailer EBS generating its own service brake demand via the brake apply valve <NUM>). It should be appreciated that the second port 200b could be connected to the control line <NUM>. In more general terms, the temporary override valve <NUM> is connected to the service brake demand pressure.

When the temporary override valve <NUM> is in the inactive position, the second port 200b is connected to the third port 200c. In other words, the control of the immobiliser <NUM> is from the service brake demand (and usually unpressured) - meaning the immobiliser <NUM> is in its immobilise position. Thus, if the supply line <NUM> is connected to a supply of pressure, the immobiliser <NUM> must be released before fluid can reach the spring brake control valve <NUM> (and release the spring brakes).

In some embodiments, movement of the temporary override valve <NUM> to its inactive position is controlled by a fluid pressure controlled actuator <NUM>. In some embodiments (see <FIG> and <FIG>), movement of the temporary override valve <NUM> to its inactive position is controlled by pressure in the delivery port 70b of the service brake modulator <NUM> or the control line <NUM>. In this case, when the delivery port 70b / control line <NUM> is pressurised, the temporary override valve <NUM> is forced to its inactive position. Thus, the delivery port 70b or control line <NUM> is connected to the immobiliser <NUM> (at the control port <NUM>').

In some embodiments, the temporary override valve <NUM> is manually operable to its override position. In other words, a button or handle <NUM> is provided and a user/driver/operator can move the temporary override valve <NUM> to its override position.

Alternatively (see <FIG>), the movement of the temporary override valve <NUM> to its override position is controlled by either an electrical signal or a fluid pressure controlled / pneumaticsignal (an actuator is shown by references <NUM> and <NUM>). This signal may be generated by a signal from the EBS control unit or other control directly from an operator elsewhere. For example, a driver may cause the signal to be sent when the vehicle is parked up, prior to uncoupling the tractor ready for loading of the trailer onto a ship by pressing a button in the cab or elsewhere.

The temporary override valve <NUM> illustrated in <FIG> and <FIG>, include two such actuators that operate the valve <NUM> in both directions. In other words, the valve <NUM> can be moved to either position by an electric or pneumatic actuator.

In some embodiments, the fluid pressure controlled actuator <NUM> includes a latch to hold the temporary override valve <NUM> in the override position without a continuous signal being provided (i.e. a consistent fluid pressure or constant power for an electrical signal is not required). In such a configuration, the temporary override valve <NUM> may be biased to its inactive position (by biasing element <NUM>). Thus, when the latch is deactivated, the temporary override valve <NUM> is moved to its inactive position automatically.

In some embodiments, the second port 200b is a vent, so when the temporary override valve <NUM> is in its inactive position, then line <NUM> is connected to a vent port (see <FIG> and <FIG>). This allows for an immobiliser <NUM> that is only activated by an electric signal (i.e. only the EBS can move it to its brake release position in "normal" operation) - this is discussed more below.

The manner in which the system operates will now be discussed.

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 (also as illustrated in <FIG>). 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.

The same state can be achieved without disconnecting the towing vehicle, by manually actuating the park valve <NUM>, <NUM>'. The button is manually pulled outwards and the park valve <NUM> 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.

In embodiments of the system that include a park valve <NUM>', the park valve <NUM>' will also automatically move to its second position and vent the connection to the immobiliser <NUM> and the SBCV <NUM> when pressure is lost in the supply line <NUM>. In this example (see <FIG>), 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>'.

However, it should be appreciated that this system is safe even without a park valve <NUM>', <NUM> (i.e. the trailer will not roll away and the spring brakes remain on even with use of the temporary override valve <NUM> until a supply of pressure is supplied on the supply line <NUM>).

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 when the supply line <NUM> is not connected to the trailer. This shunt functionality of facilitated by the trailer's own reservoir <NUM>. 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 activated 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 deactivated position.

It should be appreciated that the shunt valve <NUM> does not assist in a situation in which the trailer will be connected to a supply line <NUM> source of pressure before being moved (as is often the case in ports when the trailer is positioned on a boat). The temporary override valve <NUM> allows an operator to set a temporary state in which the trailer can be connected by a normal supply line from another towing vehicle for the purposes of these small movements when they know that such a movement will be necessary (e.g. on arrival at a port). However, the temporary override valve <NUM> can be left inactive when a trailer is left. In such a situation the immobiliser <NUM> will operate in the normal way to prevent the spring brakes from being pressurised and the trailer being movable when it is unsafe to do so.

In other words, in some facilities (e.g. ports), the trailers must be moved but the manual shunt valve <NUM> is not used. The present invention provides a mechanism to allow this while still maintaining a safe system.

When the trailer is dropped at such a facility, the driver / operator activates the temporary override valve <NUM>. This connects the supply line <NUM> to the immobiliser <NUM> (at the control port <NUM>'). While the trailer is unconnected from any supply of pressurised fluid, the immobiliser <NUM> and SBCV <NUM> will maintained their biased states (e.g. immobilised and brake applied respectively) and the spring brake remains applied (and the trailer doesn't roll away).

When the port operator wants to move the trailer, the supply line <NUM> is connected to a supply of fluid. As the temporary override valve <NUM> is active, the pressurised fluid flows to the control port <NUM>' of the immobiliser <NUM> (and the immobiliser <NUM> is released). Further, the pressurised fluid flows to the SBCV <NUM> (control port 10d and inlet 10a), so that the spring brakes are released. Thus, the trailer can be moved without the spring brake applied and wheels and brakes are not damaged by dragging the trailer.

As discussed above, there are multiple alternatives provided for moving the temporary override valve <NUM> to its inactive state. These are provided so that the trailer braking system will return to "normal" as soon as a towing vehicle is connected / the trailer is being prepared for a normal journey (i.e. being towed on roads rather than being loaded onto a boat or the like).

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 temporary override valve <NUM> may be moved to its inactive position automatically by a signal from the EBS. Or, a service brake demand (present at the delivery port 70b or control line <NUM>) may change the positions of the temporary override valve <NUM>. This depends on the actuation mechanism of the temporary override valve <NUM> (as discussed above).

The supply line <NUM> is now connected to the immobiliser control port <NUM>', so the immobiliser <NUM> stays in its brake release position ready for onward travel.

Alternatively, if the temporary override valve <NUM> is not connected to the service brake demand signal, then the EBS is in control of its position. If the temporary override valve <NUM> is maintained in the active position then the supply line <NUM> connects to the control port <NUM>' of the immobiliser <NUM> and the immobiliser <NUM> is released as above. However, if the temporary override valve <NUM> is switched to inactive prior to supply line <NUM> connection then the immobiliser <NUM> must be released in the "normal manner". In other words, 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.

Claim 1:
A trailer braking system including:
a supply line (<NUM>) for connection to a continuous source of pressurised fluid;
a trailer reservoir (<NUM>) for storing a volume of pressurised fluid;
a spring brake, which has an apply position and a release position, and the spring brake 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;
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 temporary override valve (<NUM>) having an override position and an inactive position, and being operable to move between positions independently of the pressure in the supply line (<NUM>); wherein when the temporary override valve (<NUM>) is in the override position, the immobiliser (<NUM>) remains in the immobilise position and the spring brake remains in the apply position when the supply line (<NUM>) is unpressured and, the immobiliser (<NUM>) is moved to its brake release position and the supply line (<NUM>) is connected to the spring brake control valve (<NUM>) automatically when the supply line (<NUM>) is connected to a source of fluid, such that the spring brake is moved to the release position.