Patent Description:
Many vehicles are provided with attached trailers for the transportation of goods and materials. For large-scale use such trailers may be provided with braking systems to allow for safe control of the trailer, and to prevent jack-knifing or skidding of the trailer when braking. Typically, the brake system on the trailer is coupled to an output from a trailer brake control system forming part of the towing vehicle brake system and which provides a fluid pressure signal for actuating the brakes on the trailer.

Vehicles used mainly on roads, such as heavy goods vehicles including trucks, often employ electronic brake control systems. In such systems, the fluid pressure forwarded to the brakes of both the towing vehicle and the trailer is not determined solely in response to pressure applied to a brake pedal. Rather, the pressure forwarded to the brakes is adjusted by an electronic control unit (ECU). This is advantageous as the ECU can be programmed to regulate the applied brake force taking into account inputs provided by various sensors which are indicative of the operative conditions of the vehicle and trailer and other factors. Electronic trailer brake control systems are especially advantageous in avoiding jack-knifing. With a conventional fluid only activated trailer brake control system, when a vehicle towing a trailer is subject to engine braking in which it is decelerated by internal resistance in the vehicle (from the engine, transmission or other components) rather than the application of a service or parking brake, the trailer brakes are not activated and the trailer may tend to skid. To avoid this, an electronic trailer brake control system can be configured to activate the brakes on the trailer when a potential jack-knifing situation is detected.

In addition, trucks are usually equipped with dual service brake systems wherein two separate circuits are activated independently when the brake pedal is depressed. A first circuit may thereby act on e.g. the right front wheel and the left rear wheel (or the left wheels of tandem rear axle) while a second circuit acts the left front wheel and the right rear wheel (or the right wheels of tandem rear axle). If one of the circuits fail, the other circuit can still provide sufficient brake force to the safely decelerate the vehicle.

With trucks often travelling at high speeds on roads, dual service brake systems and electronic trailer brake control systems have become a worldwide standard for these types of vehicles. Whilst such system uses components that are expensive, the relatively high production figures for vehicles of this type enable the costs to be kept at an acceptable level.

Electronic trailer brake control systems are less commonly used on agricultural vehicles, such as tractors, for a number of reasons:.

In view of the issues discussed above, customers for agricultural vehicles such as tractors are demanding greater choice in specifying the type of brake system they require in order to perfectly meet their needs at reasonable costs, subject to legal constraints.

There is need, therefore, for a vehicle brake system which can be more easily adapted to provide different functionality at reasonable costs.

In particular, it is an objective of the invention to provide a vehicle brake system incorporating a trailer brake control system which can be easily adapted to provide electronic trailer braking at reasonable costs.

<CIT> discloses a system for actuating the brakes on a trailer when a towing vehicle with a hydrostatic drive is decelerated. A piloting means is mechanically coupled to a trailer brake valve on the towing vehicle. The piloting means is operative to actuate the valve and apply the trailer brakes in response to a pressure differential between an accumulator and a working line to a controller C for a pump of the hydrostat transmission, the pressure differential being indicative that the towing vehicle is being engine braked.

<CIT> discloses a system for electronically controlling the brakes on a trailer. The system determines an optimum target value of braking for the trailer and controls the trailer brakes accordingly.

<CIT> discloses an electronic system for controlling the brakes on a trailer which employs a electrohydraulic control module to enable independent adjustment of the brakes on the trailer and the towing vehicle.

In accordance with an aspect of the invention, there is provided a vehicle brake system comprising:.

wherein the brake system comprises an electronic trailer brake control system including a control valve operative when activated to fluidly connect the source of pressurised hydraulic fluid with the brake demand input port, the electronic trailer brake control system being operative in use to selectively supply pressurised hydraulic fluid indicative of a service brake demand for the trailer to the brake demand input port.

In a vehicle brake system in accordance with the invention, the electronic trailer brake control system is able to control actuation of a hydraulic service brake function on a trailer towed by the vehicle. Actuation of the electronic trailer brake control system generates a hydraulic fluid pressure at the brake demand input port of the trailer valve. This results in a related hydraulic fluid pressure at the trailer brake control output port which is forwarded as a service brake demand to the hydraulic brake system on the trailer. Advantageously, the electronic trailer brake control system can be used to reduce the risk of jack-knifing, for example.

The term "trailer" as used herein should be understood as encompassing any suitable unpowered vehicle or implement with a suitable braking system which can be controlled through the brake system of the towing vehicle when suitably coupled.

In an embodiment, the electronic trailer brake control system comprises an electronic control system with an electronic control unit (ECU), the ECU being configured in use to actuate the electronic trailer brake control system in order to supply pressurised hydraulic fluid indicative of a service brake demand for the trailer to said brake demand input port in dependence on one or more operational conditions of the vehicle and/or a trailer towed by the vehicle being met. The ECU may be configured in use to actuate the electronic trailer brake control system in order to supply pressurised hydraulic fluid indicative of a service brake demand for the trailer to said brake demand input port in dependence on one or more operational conditions of the vehicle and/or a trailer towed by the vehicle indicative of a PUSH condition being met.

The brake demand input port may be a service brake demand input port which is operatively connectable to the service brake circuit and an output from the electronic trailer brake control system by a shuttle valve.

The control valve may comprise a solenoid valve actuatable under control of the electronic control system and operative to cause a pressurised hydraulic fluid indicative of a service brake demand for the trailer to be forwarded to the brake demand input port. The valve may have an inlet fluidly connected with the source of pressurised hydraulic fluid and a fluid outlet, the control valve being movable between an inoperative position in which the inlet and outlet are disconnected so that fluid is unable to flow from the inlet through the outlet and at least one operative position in which the inlet and outlet are fluidly connected and fluid is able to flow from the inlet through the outlet. The outlet of the control valve may be fluidly connected with the brake demand input port (through a shuttle valve in some cases). In this case, the fluid pressure through the valve when the valve is in an operative position may felt at the brake demand inlet port. Alternatively, the control valve is a pilot valve, the outlet of the control valve being connected to a control port of a piloted valve, the piloted valve being operative to selectively connect the brake demand input port to a source of pressurised hydraulic fluid (through a shuttle valve in some cases).

The electronic trailer brake control system may be configured to supply fluid to said brake demand input port at a pressure which is below the maximum pressure of the at least one service brake circuit.

In an embodiment, a pressure limiting valve is provided in the line between the source of pressurised hydraulic fluid and the control valve to limit the fluid pressure level through the control valve.

In an embodiment, the system comprises a pressure sensor for monitoring the pressure of the fluid output from the trailer brake demand output port, the ECU being configured to control operation of the electronic trailer brake control system in dependence on an output from the pressure sensor in order to maintain the pressure of the fluid supplied to said brake demand input port at a predetermined level.

The control valve may be a proportional valve.

Where an outlet of the control valve is fluidly connected with the brake demand input port (through a shuttle valve in some cases), a pressure discharge valve may be operatively connected in a fluid line between the control valve and the brake demand input port, the discharge valve being operative in a first position to depressurise the fluid line. Alternatively, where the control valve is a pilot valve, the outlet of the control valve being connected to a control port of a piloted valve, a pressure discharge valve may be operatively connected in a fluid line between the control valve and the piloted valve, the discharge valve being operative in a first position to depressurise the fluid line. The electronic trailer brake control system may be configured to connect the pressure discharge valve to ambient and depressurise the fluid line when the control valve is in an inoperative position.

In an embodiment, the service brake system has a first service brake circuit and a second service brake circuit , each service brake circuit for forwarding fluid pressure indicative of a service brake demand of an operator, the trailer brake valve having a first service brake demand inlet port and a second service brake demand input port, the pressure output at trailer brake demand output port being dependent on the pressure applied at the first service brake demand input port and/or on the pressure applied at the second service brake demand input port, wherein one of the first and second service brake demand ports constitutes said brake demand input port and is operatively connected with its respective service brake circuit and an output from the electronic trailer brake control system through a shuttle valve.

In an embodiment, the service brake system has a first service brake circuit and a second service brake circuit , each service brake circuit for forwarding fluid pressure indicative of a service brake demand of an operator, the trailer brake valve having a first service brake demand inlet port and a second service brake demand input port, the pressure output at trailer brake demand output port being dependent on the pressure applied at the first service brake demand input port and/or on the pressure applied at the second service brake demand input port, wherein one of the first and second service brake circuits is connected with one of the first and second service demand input ports, the other of the first and second service brake demand input ports being connected with an output from the electronic trailer brake control system.

The electronic trailer brake control system may be connected with the source of hydraulic fluid under pressure through the trailer brake valve. In an embodiment, the trailer brake valve has a fluid supply input port fluidly connected with the source hydraulic fluid under pressure, the trailer brake valve having a fluid supply output port operatively connected with the fluid supply input port, the electronic trailer brake control system valve being fluidly connected with said fluid supply output port by a control system supply line. The control system supply line may be connected with an inlet side of the control valve. Where present, an inlet side of the piloted valve may be connected with the control system supply line. The source of pressurised hydraulic fluid may be a hydraulic pump.

In accordance with a further aspect of the invention, there is provided an agricultural vehicle comprising a vehicle brake system according to the above aspects of the invention. The agricultural vehicle may be a tractor.

The invention will now be described, by way of example only, with reference to the following drawings, in which:.

The term "circuit" as used herein is not limited to a closed loop arrangement of lines and may refer to arrangements as simple as a single line linking two components or consumers.

In the following, the same reference numerals will be used to denote the same features or features that perform substantially the same function in the various embodiments.

<FIG> shows a representation of an agricultural vehicle <NUM>, in the form of a tractor. The tractor <NUM> comprises a chassis <NUM>, a cab <NUM>, a front axle <NUM>, and a rear axle <NUM> and is adapted to tow a range of different trailers. The tractor <NUM> has a brake system <NUM> which is connectable to a brake system on a trailer to control the trailer brakes.

<FIG> illustrates a first embodiment of a brake system <NUM> in accordance with the invention installed on the tractor <NUM> and which comprises electronic control unit ECU <NUM>.

The brake system <NUM> is a hydraulic brake system which includes a hydraulic fluid supply system for supplying hydraulic fluid under pressure, indicated generally at <NUM>. The hydraulic fluid supply system <NUM> includes a hydraulic pump <NUM> and a hydraulic fluid tank <NUM>. The pump <NUM> supplies pressurised hydraulic fluid to various hydraulic consumers on the vehicle, and to a trailer when coupled to the vehicle, as well as the brake system <NUM> in a manner well known in the art. The tank provides a reservoir of hydraulic fluid at ambient pressure.

The brake system <NUM> includes a service brake system indicated generally at <NUM>. The service brake system <NUM> includes a service brake circuit <NUM> with a brake master cylinder <NUM> operated by a brake pedal <NUM> depressed by the foot of an operator to generate a fluid pressure in the service brake circuit <NUM>. The fluid pressure generated in the service brake circuit <NUM> is dependent on the pressure applied by the operator to brake pedal and is indicative of a brake demand by the operator. This fluid pressure will, therefore, be referred to as a Service Brake Demand Signal (SBDS). As is common practice in agricultural machines such as tractors, in order to increase brake actuation force, the service brake circuit <NUM> may include brake boosters supplied with hydraulic fluid under pressure by the pump <NUM> so that the hydraulic pressure applied at the brake actuators is higher than that produced by the operator pressing on the brake pedal. In this embodiment, there is a single service brake circuit <NUM> but as illustrated in relation to further embodiments, there may be more than one service brake circuit in a brake system <NUM> according to the invention.

References herein to a "brake demand" or "brake demand signal" in relation to a hydraulic line or circuit should be understood as referring to a pressure of the fluid in the line or circuit which is indicative of a required braking force.

The vehicle also has a park brake system indicated generally at <NUM>. The park brake system includes an actuator <NUM>, in this case in the form of a park brake lever, which is used by the operator to apply and release the park brakes. The park brake system <NUM> is a mechanical system in which the park brake lever is mechanically coupled, for example by means of a cable, with one or more park brake actuators <NUM> on the vehicle. As such mechanical park brake systems are well known, it will not be described in detail. The park brake system <NUM> does not form part of the present invention and it should be understood that a brake system <NUM> in accordance with the present invention can be adopted on a tractor or other agricultural vehicle or machine having alternative park brake systems, including hydraulic or pneumatic park brake systems.

The brake system <NUM> includes a trailer brake control system <NUM> operatively connected to a trailer when coupled to the tractor <NUM>. The trailer brake control system is provided with a trailer brake valve <NUM> to control application of the brakes on a trailer in dependence on the service brake demand signal SBDS received from the service brake system <NUM>. The trailer brake valve <NUM> is an electronically controlled valve and is operatively connected with the ECU.

When the vehicle <NUM> is towing a trailer, the hydraulic system of the trailer (not shown) is connected with the hydraulic system of the vehicle via standardized trailer couplings <NUM>, <NUM>. These include a supplementary trailer coupling <NUM> and a trailer brake control coupling <NUM>. The supplementary trailer coupling <NUM> provides fluid supply to the trailer park brake system. The trailer brake control coupling <NUM> is provided to forward a trailer service brake demand signal TSBDS to the trailer brake system to provide a service brake functionality on the trailer.

In a common arrangement, the brake system on the trailer may have combined brake units which have a first service brake actuator responsive to hydraulic fluid pressure to apply a braking force to provide a service brake function and a second park brake actuator which is spring biased to apply a braking force to provide a park brake function. The park brake actuator is held in a brake released position by hydraulic fluid pressure when the park brakes are deactivated. If the fluid pressure drops, the spring load applies the full brake force. The supplementary trailer coupling <NUM> is normally connected to the park brake system on the trailer via a brake valve on the trailer. The trailer brake control coupling <NUM> is also connected to the brake valve on the trailer. The trailer service brake demand pressure signal TSBDS provided through the brake control coupling <NUM> pilot-controls the brake valve of the trailer to generate a controlled brake pressure forwarded to the service brake actuators of the combined brake units, which apply a corresponding service brake force to the wheels of the trailer.

Operation of the trailer brake valve <NUM> is now be explained in detail.

The trailer brake valve has eight ports 401a to <NUM>.

The hydraulic pump <NUM> is connected to a fluid supply input port 410a of the trailer valve via a supply line <NUM>. A fluid return port 410b is connected with the hydraulic fluid tank <NUM> through a return line <NUM> to enable hydraulic fluid to be returned to the tank <NUM>, say when a part of the hydraulic system is to be returned to ambient.

Hydraulic fluid supplied by the pump <NUM> through the fluid supply input port 410a can be directed to various hydraulic consumers on the tractor <NUM>, or a trailer when coupled to the tractor, through a consumer supply output port 410c.

A fourth port 410d is connected to the supplementary trailer coupling <NUM> to supply hydraulic fluid for the park brake function on the trailer. In this embodiment where the tractor park brake is mechanical, a micro switch <NUM> is operatively connected to the park brake lever <NUM> and provides an input to the ECU. When an operator applies the park brake on the vehicle using the lever <NUM>, the switch <NUM> provides a park brake on signal to the ECU. In response, the ECU actuates the trailer brake valve <NUM> so that the fluid pressure provided to the trailer park brake through the supplementary coupling <NUM> is reduced to ambient. This causes the spring biased park brake actuators on the trailer to apply the trailer brakes. When the operator releases the park brakes using the lever <NUM>, the switch <NUM> provides a park brake off signal to the ECU. The ECU in response actuates the trailer brake valve <NUM> so that the fluid pressure provided to the trailer park brake through the supplementary coupling <NUM> is increased to release the park brake actuators on the trailer.

A fifth port 410e of the trailer brake valve is operatively connected to the service brake circuit via a service brake demand input line <NUM>. This port receives the service brake demand signal (fluid pressure) SBDS from the service brake circuit <NUM>. The service brake demand signal SBDS controls an internal relay of valve <NUM> (not shown in detail) which generates a trailer service brake demand signal (fluid pressure) TSBDS which is forwarded to the trailer brake control coupling <NUM> through a sixth port 410f to control the service brake functionality of the trailer. The sixth port 410f will be referred to as the trailer brake demand output port. The TSBDS is proportional to the SBDS applied at the port 410e.

The trailer valve <NUM> also has a load sensing port <NUM> which is used to enable adjustment of the supply from the main hydraulic pump <NUM> based on the demand of the hydraulic consumers and/or the trailer brake. Such arrangements are known in the art and will not be described in detail.

The trailer brake valve <NUM> may have provision for responding to critical driving situations in case of breakaway at trailer couplings <NUM>,<NUM>. Furthermore, the trailer brake valve <NUM> may have provision to adjust the advancement of the trailer brake so that when the service brake on the vehicle is activated only slightly, a slightly higher pressure is applied to the trailer to ensure that the trailer brakes are operated prior to the service brake of the tractor. This reduces the risk of the trailer pushing the tractor which could lead to jack-knifing. In known arrangements, the degree of advancement can be set manually at the trailer brake valve <NUM>.

Trailer brake valves <NUM> of the type described which produce a fluid pressure output at the trailer brake demand output port which is dependent on the fluid pressure applied at a brake demand input port are well known in the art and details of the valve will not be described further.

The vehicle brake system as so far described comprising the service brake system <NUM>, the park brake system <NUM>, and the trailer brake control system <NUM> is known in the art. In such known brake systems, control of the service brake function on the trailer is dependent on actuation of the service brake <NUM> on the vehicle. A brake system comprising these components can be adopted if electronically controlled actuation of the service brakes on the trailer is not required. As discussed above, such a brake system may be sufficient for some type of implements or vehicles which do not exceed a certain maximum speed and can be offered at relatively low cost. However, and in accordance with the invention, the brake system <NUM> can be modified to provide electronic trailer service brake functionality as discussed below.

According the invention, the vehicle brake system <NUM> is additionally provided with an electronic pilot trailer brake control system <NUM>. The electronic trailer brake control system <NUM> in this embodiment has a fluid circuit including a control valve <NUM>, a piloted relay valve <NUM>, and a shuttle valve <NUM>. The electronic trailer brake control system <NUM> has an electronic control system including an ECU <NUM> which controls operation of various valves in the fluid circuit. The control valve <NUM> controls actuation of the piloted relay valve <NUM> in order to selectively open or close a fluid connection between a source of pressurised hydraulic fluid (e.g. pump <NUM>) and a service brake pilot line <NUM>. In a convenient arrangement, the control valve <NUM> and the piloted relay valve <NUM> are connected to a supply of pressurised hydraulic fluid from the pump <NUM> through a control system supply line <NUM> which is connected to an output port <NUM> of the trailer brake valve <NUM>. The trailer brake valve <NUM> is operative to transfer some of the hydraulic fluid supplied by the pump <NUM> through the fluid supply inlet port 410a to the output port <NUM>. This provides a very convenient way of connecting the electronic trailer brake control system <NUM> to the hydraulic system of the vehicle. It reduces the number of fluid connections required to incorporate the electronic trailer brake control system <NUM> and so makes it easier to integrate the electronic trailer brake control system into the hydraulic system of an existing tractor design using a suitable trailer brake valve <NUM>. However, it will be appreciated that the electronic trailer brake control system <NUM> could be connected to the hydraulic pump in other ways.

An accumulator <NUM> and a pressure sensor <NUM> may be connected to the electronic trailer brake control system supply line <NUM>. The pressure sensor <NUM> is connected with the ECU and used to monitor hydraulic pressure in the supply line <NUM> and the accumulator <NUM> maintains a relatively constant pressure in the line <NUM>, which might otherwise fluctuate in response to changes in demand on the pump <NUM>.

The piloted valve <NUM> is biased by a spring to a first position 512a, as shown in <FIG>, in which the service brake pilot line <NUM> is disconnected from the control system supply line <NUM> and so is not pressurised. In this position, the piloted valve connects the service brake pilot line <NUM> to the hydraulic tank <NUM> via a control system return line <NUM>, <NUM> so that the service brake pilot line is at ambient pressure. When the piloted valve <NUM> is activated by supplying pressurised hydraulic fluid to a control port 512c, the piloted valve is moved to a second position 512b in which the service brake pilot line <NUM> is connected to the control system supply line <NUM> so that the service brake pilot line <NUM> is pressurised.

Actuation of the piloted relay valve is controlled by the control valve <NUM>. The control valve <NUM> is connected to the control system supply line <NUM> at an inlet port and has an outlet port which is connected via a control valve pilot line <NUM> to the control port 512c of the piloted valve. Control valve <NUM> is a solenoid valve and is biased by a spring to a first position 510a, as shown in <FIG>, in which the control valve pilot line <NUM> is disconnected from the control system supply line <NUM> and so is not pressurised. When energized, the control valve <NUM> moves to a second position 510b in which it connects the control valve pilot line <NUM>, and hence the control port 512c on the piloted relay valve <NUM>, to the control system supply line <NUM>. This applies a fluid pressure to the control port 512c to actuate the piloted relay valve <NUM> moving it to its second position so that the service brake pilot line <NUM> is pressurised.

The service brake pilot line <NUM> is connected at a first input of the shuttle valve <NUM>. A second input to the second shuttle valve <NUM> is connected to the service brake circuit <NUM>. The output side of the shuttle valve <NUM> is connected to the service brake demand input port 401e of the trailer brake valve <NUM> via the service brake demand input line <NUM>. Shuttle valve <NUM> provides a hydraulic OR functionality (i.e., logic control) to forward either the pressure in service brake circuit <NUM> or the pressure in service brake pilot line <NUM> (whichever is at the highest pressure) to the the service brake demand input port 410e of the trailer brake valve. The application of fluid pressure at the service brake demand input port 401e, whether from the service brake circuit <NUM> or the service brake pilot line <NUM>, will result in a corresponding fluid pressure (TSBDS) being output at the trailer brake demand output port 410f. This is forwarded to the trailer brake system via the trailer brake control coupling <NUM> to actuate the service brakes on the trailer.

The electronic trailer brake control system <NUM> is operative to apply the service brake function of the trailer in certain circumstances when the service brake circuit <NUM> of the towing vehicle is either not pressurised or only pressurised to a limited amount. The electronic trailer brake control system <NUM> is operative in particular to selectively apply the service brake function of the trailer to reduce the risk of jack-knifing, for example when the towing vehicle is under engine braking as described in further detail below.

Jack-knifing occurs when the trailer pushes the towing vehicle (known as PUSH mode or condition) rather than the towing vehicle pulling the trailer (PULL mode or condition). In general terms, a PUSH condition exists if the torque input to the vehicle wheels driven by the inertia of the trailer is greater than the nominal torque supplied by the engine or other prime mover (in certain conditions). This condition may be detected by monitoring one or more parameters available on the vehicle and or trailer. A known parameter used to detect PUSH condition in trucks is the difference of the set engine speed and the current engine speed. When going downhill, the trailer pushes the truck tractor and thereby wheels begin to rotate faster so the setting of the engine speed (depending on the desired speed) and the speed of the engine (transmitted via wheels) would show a deviation. Alternative approaches, include comparing torque supply by the engine with the torque transmitted via the wheels. <CIT> and <CIT> disclose arrangements for determining when an agricultural vehicle such as a tractor is in a PUSH condition. A further known system for detecting PUSH condition in a tractor is described in Applicant's unpublished patent application <CIT>. In this system, the vehicle has a continuously-variable hydrostatic transmission. The vehicle transmission includes a first pressure sensor arranged to measure a fluid pressure at a predetermined point within the transmission, and a rotation sensor arranged to determine a rotation direction of a predetermined component in a driveline of the vehicle. When the vehicle is towing a trailer, an ECU unit coupled to the first pressure sensor and rotation sensor determines when a PUSH condition exists based on a particular combination of pressure and rotational direction and applies the trailer brakes to reduce the risk of jack-knifing.

Input from a PUSH condition detection system or sensors for use in detecting a PUSH condition is provided to the ECU <NUM> as indicated at <NUM>. If a PUSH condition is detected, the electronic trailer brake control system <NUM> is utilized to avoid Jack-knifing. In response to a determination that a PUSH condition exists, the ECU energizes the two-position control valve <NUM> moving it to the second position 510b. This actuates the piloted relay valve <NUM> moving it to the second position 512b and so pressurises the service brake pilot line <NUM> and (via second shuttle valve <NUM>) the service brake demand input line <NUM> to port 410e of the trailer brake valve <NUM>. The trailer brake valve <NUM> provides a corresponding trailer service brake demand signal TSBDS output at the port 410f, which is forwarded to trailer via the trailer brake control coupling <NUM> so that the service brake function of the trailer is engaged.

Whilst it is particularly advantageous that the ECU is configured to apply the service brakes on the trailer to avoid a potential jack-knife situation, the ECU can be configured to apply the service brakes on a trailer being towed by the vehicle in dependence on one or more operational conditions of the vehicle and/or trailer other than a PUSH condition being met if appropriate.

The system can be configured such the electronic trailer brake control system <NUM> does not initiate a full braking of the trailer, which could result in a dangerous driving condition. For example, the pressure fed to port 401e of the trailer brake valve may be limited. Alternatively, a further pressure sensor <NUM> may be provided in the hydraulic line between the trailer brake demand output port 410f and the trailer control coupling <NUM> and coupled to the ECU to provide a single indicative of the pressure in the line. The ECU may be configured to regulate actuation of the electronic trailer brake control system so that the fluid pressure forwarded through the trailer brake control coupling <NUM> dos not exceed a predetermined value to ensure the service brakes on the trailer are not fully applied.

As noted above, when the piloted relay valve <NUM> is in its first position 512a, the service brake pilot line <NUM> is connected to the hydraulic fluid tank <NUM> through the control system return line <NUM>. This prevents pressurised hydraulic fluid being trapped in the service brake pilot line <NUM> and the first service brake input line <NUM> when the control valve <NUM> and the piloted valve <NUM> are moved back to their first positions 510a, 512a. As a further precaution, a discharge valve <NUM> may be connected to the control valve pilot line <NUM>. The discharge valve <NUM> is a solenoid valve and is operative to vent the control valve pilot line <NUM> to the hydraulic fluid tank <NUM> through the control system return line <NUM>, <NUM> when in a first position 540a to which it is biased by a spring. The discharge valve is energized by the ECU to move to a second position 540b in which the control valve pilot line <NUM> is not vented to the tank when the control valve <NUM> is energized to the second position 510b to actuate the piloted relay valve <NUM> and connect the service brake pilot line <NUM> to the control system supply line <NUM>. Discharge valve <NUM> provides additional safety feature as pressurised fluid trapped in lines <NUM>, <NUM>, <NUM> could result in actuation of the trailer brakes even if control valve <NUM> is in it non activated first position 510a. The presence of pressurised fluid trapped in lines <NUM>, <NUM>, <NUM> may harm functionality of the service brake input to trailer brake valve <NUM>. To avoid this, the discharge valve <NUM> and the piloted relay valve <NUM> always connect the control valve pilot line <NUM> and the service brake pilot line <NUM> with the tank <NUM> to discharge fluid pressure completely when control valve <NUM> is in its first position 510a. Since the control valve <NUM>, the piloted valve, and the discharge valve <NUM> are all spring biased to their first positions, this provides a fail-safe system in which the control valve pilot line <NUM> and the service brake pilot line <NUM> will be depressurised in the event of a failure to the electric current supply to these valves.

The electronic control functions of the electronic trailer brake system <NUM> may be provided by a vehicle ECU or by separate ECU dedicated to the system <NUM>. Use of a dedicated ECU would avoid the need to provide electrical interfaces in a vehicle ECU for this optional feature. In this case, the vehicle ECU and the electronic trailer brake system <NUM> ECU would communicate via a CAN BUS interface. The ECU may be programmable and comprise a processor and memory as is well known in the art.

It should also be noted that whilst the valves <NUM>, <NUM>, <NUM>, and <NUM> are described as separate elements they may be included in a valve manifold.

The use of a piloted relay valve <NUM> to connect the service brake pilot line <NUM> to the hydraulic fluid source <NUM>, <NUM> may be particularly beneficial where the volume of fluid which must be provided to the service brake pilot line <NUM> to actuate the service brakes on the trailer is relatively high, as the piloted relay valve <NUM> can be operated using a smaller volume of fluid. However, where the volume of fluid required is not overly large, as will often be the case in a hydraulic brake system, the piloted valve <NUM> can be omitted and the control valve <NUM> itself can be used connect the service brake pilot line <NUM> to the source of pressurised hydraulic fluid <NUM>. Such an arrangement is illustrated in <FIG>.

The brake system <NUM>' as shown in <FIG> is substantially the same as that shown in <FIG> and described above. Accordingly, only the differences between the brake system <NUM>' in <FIG> and that of <FIG> will be described in detail.

In the brake system <NUM>' there is no piloted relay valve <NUM>. Rather, the service brake pilot line <NUM> is connected directly to an outlet port of the control valve <NUM> so that when the valve is activated and moved to its second position 510b, the service brake pilot line <NUM> is connected with the control system supply line <NUM> through the control valve <NUM>, and hence is pressurised by the supply of pressurised hydraulic fluid from the pump <NUM>. In this embodiment, the control valve <NUM> has an additional outlet port through which the service brake pilot line <NUM> is connected to the hydraulic fluid tank <NUM> (ambient) via the control system return line <NUM> when the valve is in its first position 510a. In a further modification, the discharge valve is connected with the service brake pilot line <NUM>. This ensures that the service brake pilot line <NUM> and the service brake input line <NUM> are fully depressurised when the control valve <NUM> and discharge valves are in their first positions. The electronic trailer brake control system <NUM> otherwise operates as described above with reference to <FIG> under control of the ECU to actuate the service brakes on the trailer when required.

<FIG> illustrates a further embodiment of a brake system <NUM>" according to the invention. In this embodiment, the trailer brake valve <NUM>" has an additional service brake demand input port 410i. The trailer brake valve <NUM>" is configured such that a service brake demand signal SBDS applied to either of the service brake demand ports 410e or 410i will generate a trailer service brake demand signal (fluid pressure) TSBDS which is forwarded to the trailer brake control coupling <NUM> through the trailer brake demand output port 410f.

The service brake system <NUM> has two separate service brake circuits <NUM>, <NUM>, each operatively connected with a separate brake master cylinder 210a, 210b which are actuated from a single brake pedal <NUM>. This provides for redundancy in case one of the circuits fails. In a dual circuit service brake system, the first service brake circuit <NUM> may be hydraulically connected to the brake actuators on the rear axle <NUM> while the second service brake circuit <NUM> is hydraulically connected to the brake actuators of the front axle <NUM>. In case of failure of one of service brake circuits <NUM>, <NUM>, e.g. should a hydraulic line break, the other circuit <NUM>, <NUM> can still be pressurised to provide braking capability. However, the assignment of the service brake circuits <NUM>, <NUM> to respective vehicle wheels or axles may vary. For example, an alternative configuration may have a diagonal assignment so that brakes on the front left wheel and rear right wheel may be actuated by a first service brake circuit <NUM> while those on the front right wheel and rear left wheel may be actuated by a second service brake circuit <NUM>. In a further alternative, the circuits may be arranged to actuate the brakes on opposite sides of the tractor, which may be required to provide a brake steering functionality. The fluid pressures in first and second service brake circuits <NUM>, <NUM> represent service brake demand signals SBDS1, SBDS2 generated by the driver and which are forwarded to other components.

As illustrated in <FIG>, whist the trailer brake valve <NUM>" has two service brake demand input ports 410e or 410i, the brake system <NUM>" is arranged so that only one of the service brake circuits <NUM>, <NUM> is connected to the trailer brake valve <NUM>. In this case, the first service brake circuit <NUM> is connected through service brake demand input line <NUM> to a first one of the service brake demand input ports 410e, which receives the service brake demand signal SBDS1. This enables the service brake pilot line <NUM> to be connected to the other of the service brake demand input ports 410i without the need for a shuttle valve.

As with the previous embodiment, the pilot trailer brake control system <NUM> as shown in <FIG> does not have a piloted relay valve <NUM> but uses the control valve <NUM> itself to connect the service brake pilot line <NUM> and the service brake demand input port 410i to control system supply line <NUM> when the valve is actuated to move to its second position, in a manner similar to that discussed above in relation to <FIG>. However, the brake system could be modified to use a piloted relay valve <NUM> if required. In this case, the electronic trailer brake control system <NUM> would be configured as shown in <FIG>, except that the service brake pilot line <NUM> is connected to the second service brake demand input port 410i without the need for a shuttle valve.

The brake system <NUM>" of <FIG> is reliant on one of the service brake circuits <NUM> to provide a SBDS to the trailer brake valve <NUM>" to actuate the service brake function on the trailer during normal driving. Whilst this is perfectly acceptable, in the event the first service brake circuit <NUM> were to fail, no service brake demand would be forwarded to the trailer from the second service brake circuit. Alternatively, as illustrated in <FIG>, each of the service brake circuits may be connected with a respective one of the service brake demand input ports 410e, 410i. To allow for electronic control of the service brake function on the trailer, the service brake pilot line <NUM> and one of the service brake circuits <NUM> are connected to one of the service brake demand input ports 410i through a shuttle valve <NUM> and a service brake demand input line 445a. Shuttle valve <NUM> provides a hydraulic OR functionality (i.e., logic control) to forward either the pressure in service brake circuit <NUM> or the pressure in service brake pilot line <NUM> (whichever is at the highest pressure) to the service brake demand input line 445a and to the service brake demand input port 410i of the trailer brake valve. It will be appreciated that the service brake pilot line <NUM> could alternatively be connected together with the first service brake circuit <NUM> to the other service brake demand input port 410e though a shuttle valve <NUM>.

As with the previous embodiment, the electronic trailer brake control system <NUM> as shown in <FIG> does not have a piloted relay valve <NUM> but uses the control valve <NUM> to connect the service brake pilot line <NUM> and the service brake demand input port 410i to the control system supply line <NUM> and hence the pressurised hydraulic fluid from the pump <NUM> when the valve is activated. However, the brake system <NUM>‴, could be modified to use a piloted relay valve <NUM> if required.

The brake system according to the invention and the embodiments described above provides electronic trailer braking function which can be easily incorporated into existing brake systems that currently only provide a fully hydraulic trailer brake control system.

Claim 1:
A vehicle brake system (<NUM>; <NUM>'; <NUM>"; <NUM>"') comprising:
a) a source of pressurised hydraulic fluid (<NUM>, <NUM>);
b) a hydraulic service brake system (<NUM>) having at least one service brake fluid circuit <NUM>, <NUM>) configured to forward a service brake demand of an operator;
c) a trailer brake control system (<NUM>) for connection to a trailer drawn by said vehicle, the trailer brake control system having a trailer brake valve (<NUM>) which comprises:
i) a brake demand input port (410e, 410i) for receiving a hydraulic pressure indicative of a brake demand; and
ii) a trailer brake demand output port (410f) for connection to a trailer brake control coupling (<NUM>), the trailer brake valve configured to generate a hydraulic fluid pressure output at the trailer brake demand output port which is dependent on the hydraulic pressure applied at the brake demand input port;
characterised in that the brake system comprises an electronic trailer brake control system (<NUM>) including a control valve (<NUM>) operative to fluidly connect the source of pressurised hydraulic fluid (<NUM>, <NUM>) with the brake demand input port, the electronic trailer brake control system being operative in use to selectively supply pressurised hydraulic fluid indicative of a brake demand for the trailer to the brake demand input port (410e, 410i).