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. <CIT> discloses an example of an electronic trailer brake control system.

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.

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 to selectively connect the trailer brake control coupling with the source of pressurised fluid, the electronic trailer brake control system being operative in use to selectively supply pressurised fluid indicative of a service brake demand for the trailer to the trailer brake control coupling.

In a vehicle brake system in accordance with the invention, the electronic trailer brake control system is able to control actuation of the service brake function on a trailer towed by the vehicle. Actuation of the electronic trailer brake control system generates a fluid pressure at the trailer control coupling which is forwarded as a service brake demand to the 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 including an electronic control unit (ECU) or controller, the ECU being configured in use to actuate the control valve in order to supply pressurised fluid indicative of a service brake demand for the trailer to the trailer brake control coupling 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 control valve in order to supply pressurised fluid indicative of a service brake demand for the trailer to the trailer brake control coupling 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 control valve may comprise a solenoid valve actuatable under control of the electronic control system and operative to cause a pressurised fluid indicative of a service brake demand for the trailer to be forwarded to the trailer brake control coupling.

The control valve may have an inlet fluidly connected with the source of pressurised fluid and a fluid outlet, the control valve being movable between an in-operative 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 trailer brake control coupling through a shuttle valve. 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 trailer brake control coupling to a source of pressurised fluid when activated by the control valve. In this embodiment, the piloted valve may be connected in a fluid line between the source of pressurised fluid and the trailer brake control coupling, the piloted valve be biased to an inoperative position in which the trailer brake control coupling is not connected with the source of pressurised fluid and moveable to at least one operative position in which the trailer brake control coupling is connected with the source of pressurised fluid. The trailer brake demand outlet port and the piloted valve may be connected with the trailer brake control coupling through a shuttle valve. The piloted valve may be a proportional valve such that the pressure of the fluid directed to the trailer brake control coupling is dependent on the fluid pressure applied at a control port of the piloted valve from the control valve.

The electronic trailer brake control system may be configured such that the pressure of the fluid supplied to the trailer brake control coupling is insufficient to cause the service brakes on the trailer to be fully applied.

In an embodiment, a pressure limiting valve is provided in the line between the source of pressurised 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 provided to the trailer brake control coupling, 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.

A pressure discharge valve may be connected in a control system pilot fluid line between the control valve and the piloted valve to connect said line to ambient when the discharge valve is in a first position. The electronic trailer brake control system may be configured such that the discharge valve is placed in said first position when the control valve is in an inoperative position. The discharge valve may be a solenoid valve biased to the first position but which can be activated to move the valve to a second position in which the control system pilot fluid line is not connected with ambient.

The service brake system may be hydraulic and the source of pressurised fluid may be a source of pressurised air. The service brake system may have a service brake circuit connected with the brake demand input port of the trailer brake valve, the trailer brake valve being configured to connect the trailer brake demand output port to the source of pressurised air such that the pressure of air emitted through the trailer brake demand output port is dependent on the pressure of hydraulic fluid at the brake demand input port.

The service brake system may be pneumatic and the source of pressurised fluid may be a source of pressurised air. The service brake system may have a service brake line connected with the brake demand input port of the trailer brake valve, the trailer brake valve being configured to connect the trailer brake demand output port to the source of pressurised air such that the pressure of air emitted through the trailer brake demand output port is dependent on the pneumatic pressure fluid at the brake demand input port.

The trailer valve may further have a park brake demand input port fluidly connected with a pneumatic park brake circuit, the fluid pressure output at the trailer brake demand output port being dependent on the fluid pressure applied at the brake demand input port and/or the fluid pressure applied park brake demand input port. The fluid pressure output at the trailer brake demand output port may be inversely proportional to the fluid pressure applied at the park brake demand input port.

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

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.

Whilst an embodiment of the invention is described below with reference to a combined hydraulic and pneumatic brake system, the principles disclosed herein can be adapted for use with purely hydraulic or purely pneumatic vehicle brake systems.

<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>. In the brake system <NUM> the vehicle service brakes are actuated hydraulically whilst the the brakes on the trailer are pneumatic. In this embodiment, the park brakes on the vehicle are mechanically actuated.

The brake system <NUM> includes an air supply system, indicated generally with dotted lines <NUM>, which supplies compressed air to various consumers on the vehicle and its trailer or other towed implement when connected. The principal consumers of interest shown in <FIG> are a park brake system <NUM>, a trailer brake control system <NUM>, and an electronically controlled pilot trailer brake control system <NUM>.

The air supply system <NUM> comprises an air compressor <NUM>, an air drier unit <NUM> and a prioritisation valve arrangement <NUM>. The air compressor <NUM> driven by the combustion engine of the vehicle (or any prime mover such as an electric motor) supplies air into the air drier unit <NUM>, which includes a reservoir to store compressed air and a granule cartridge to extract water from the air. From the air drier unit <NUM>, compressed air is passed through the prioritisation valve arrangement <NUM> which is configured to prioritise supply to primary consumers of the vehicle over the supply to secondary consumers. Primary consumers include safety critical systems such as the park brake system <NUM>, the trailer brake control system <NUM>, and the electronic trailer brake system <NUM>. Secondary consumers, indicated generally at <NUM>, are not shown for clarity reasons but might include a tyre pressure control system (TPCS) or a cleaning system for an engine air filter, for example. The prioritisation valve arrangement <NUM> is operative to maintain the integrity of the primary consumers in the event that the air supply is not capable of meeting all demands.

The various primary consumers shown in <FIG> are supplied via a reservoir <NUM> and a pressure relief valve <NUM> to limit the pressure level to protect the components of the system. For use with components common in pneumatic brake systems, the pressure relief valve may be set to limit the pressure to around <NUM> bar, for example. The reservoir <NUM> and first pressure relief valve <NUM> are assigned to a joint supply line <NUM>. The joint supply line <NUM> supplies compressed air to the park brake system <NUM>, the trailer brake control system <NUM>, and the electronic trailer brake control system <NUM>. The pressure in the reservoir <NUM> may be monitored by a pressure sensor (not shown). If the pressure drops below a minimum value, say <NUM> bar, the compressor <NUM> is switched on (or adjusted to higher delivery) to refill the reservoir <NUM>. Thereby the park brake system, the trailer brake control system and the electronic pilot trailer brake control system <NUM> are kept responsive.

The tractor air supply system <NUM> as shown in <FIG> is an illustrative example only and could be replaced by any other suitable air supply system. For example, an air supply system such as that described in the Applicant's published patent application <CIT>, which comprises an additional higher flow rate compressor could be adopted.

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 a hydraulic pump (not shown) so that the hydraulic pressure applied at the brake actuators is higher than that produced by the operator pressing on the brake pedal.

Whilst <FIG> shows a single service brake circuit <NUM>, there may be more than one service brake circuit in a brake system <NUM> according to the invention. For example, the service brake system <NUM> could have two separate service brake circuits <NUM> each operatively connected with a separate brake master cylinder 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, a first service brake circuit may be hydraulically connected to the brake actuators on the rear axle <NUM> while a second service brake circuit is hydraulically connected to the brake actuators of the front axle <NUM>. In case of failure of one of service brake circuits, e.g. should a hydraulic line break, the other circuit can still be pressurised to provide braking capability. However, the assignment of the service brake circuits 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 while those on the front right wheel and rear left wheel may be actuated by a second service brake circuit. 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. Where dual service brake circuits are provided, the fluid pressures in the first and second service brake circuits represent service brake demand signals SBDS1, SBDS2 generated by the driver.

The park brakes on the vehicle are actuated mechanically. The park brake system <NUM> includes a park brake actuator in the form of a park brake lever <NUM> which is mechanically linked to the park brakes on the vehicle (indicated at <NUM>), for example by means of a cable. <FIG> shows the park brake lever in a park brake off position in which the lever is lowered. To actuate the park brakes, the driver moves the park brake lever <NUM> upwardly to a park brake on position. This movement is mechanically transmitted to the park brake actuators on the vehicle to apply the park brakes in a well-known manner.

The park brake system <NUM> as illustrated is actuated mechanically by the park brake lever. However, alternative park brake systems could be employed. For example, a pneumatic park brake system which allows for electronic control of the park brake such as that described in the applicant's published patent <CIT> could be used.

The brakes on the trailer are pneumatic. In order that the driver can control the brakes on the trailer using the park brake lever <NUM>, the lever is operatively connected with a park brake valve <NUM>. The park brake valve <NUM> is connected to joint supply line <NUM> and is configured to selectively connect or disconnect the joint supply line <NUM> with a park brake circuit <NUM>. The park brake circuit <NUM> provides a park brake demand signal PBDS for actuating the brakes on the trailer as will be described in detail below.

References herein to a "brake demand" or "brake demand signal" in relation to a pneumatic or 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 trailer brake control system <NUM> is provided with a trailer brake valve <NUM> to control application of the brakes on a trailer in dependence on brake demand signal SBDS or PBDS received from the service brake system <NUM> and/or the park brake circuit <NUM>. Trailer brake valve <NUM> also forwards compressed air to the air supply of the trailer. When the vehicle is towing a trailer, the pneumatic system of the trailer (not shown) is connected via standardized trailer couplings <NUM>, <NUM>. These include a trailer supply coupling <NUM> and a trailer brake control coupling <NUM>. The trailer supply coupling <NUM> is usually colour coded red and provides general air supply to the trailer including its brake system and any other consumers. The trailer brake control coupling <NUM> is usually colour coded yellow and is provided to forward a trailer service brake demand signal TSBDS to the trailer brake system.

In a common arrangement, the brake system on the trailer may have combined brake units which have a first, service brake actuator responsive to applied air 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 air pressure from the internal air supply reservoir on the trailer when the park brakes are deactivated. If the internal air supply reservoir on the trailer is discharged, the spring load applies the full brake force. The trailer supply coupling <NUM> is normally connected to the internal air supply reservoir on the trailer via a brake valve on the trailer. The pressure applied to the brake valve on the trailer through the trailer supply coupling <NUM> provides the park brake functionality on the trailer. If the pressure forwarded to the trailer brake valve through the supply coupling <NUM> drops below a certain value, the spring biased park brake actuators apply the brakes on the trailer. This would typically happen if the trailer is decoupled from the tractor or if a failure on the pneumatic connection occurs. The trailer brake control coupling <NUM> is also connected to the brake valve on the trailer. The trailer service brake demand fluid 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 six ports 401a to 401f.

The trailer brake valve <NUM> is connected to the air supply system <NUM> via joint supply line <NUM> of the supply system <NUM> at a first port 410a, which will be referred to as a fluid supply inlet port. The air supply is then forwarded via a second port 410b to the trailer supply coupling <NUM> and thereby the trailer (not shown). The second port 410b will be referred to as a fluid supply outlet port.

The third port 410c is operatively connected to first service brake circuit <NUM> via first service brake input line <NUM>. This port receives the service brake demand signal (hydraulic fluid pressure) SBDS from the service brake circuit <NUM> and will be referred to as a service brake demand input port.

The fourth port 410d is operatively connected to the park brake circuit <NUM> via park brake demand input line <NUM> and a first shuttle valve <NUM> to receive a park brake demand signal (air pressure) PBDS from the park brake circuit <NUM>. The fourth port 410d will be referred to as a park brake demand input port.

As mentioned above, the park brake valve <NUM> is operatively connected with the park brake lever <NUM> and is configured to selectively connect or disconnect the joint supply line <NUM> with the park brake circuit <NUM> in response to actuation of the park brake lever <NUM>. The park brake valve <NUM> is movable between a first position 320a as shown in <FIG> in which the park brake circuit <NUM> is connected with the joint supply line <NUM> and so is pressurised. If the park brake lever <NUM> is moved to a park brake on position, this moves the park brake valve to a second position 320b in which the park brake circuit <NUM> is vented to ambient and so depressurised. The pressure in the park brake circuit is forward to the park brake demand input port 410d as a park brake demand signal PBDS through the first shuttle valve <NUM> and the park brake demand input line <NUM>. The park brake valve <NUM> is biased to the first position 320a so that the park brake circuit <NUM> and the park brake demand input line <NUM> are pressurised in the event that the connection between the park brake leaver and the valve fails. This ensures that the service brakes on the trailer are not unintentionally applied in these circumstances.

The service brake demand signal SBDS and the park brake demand signal PBDS control an internal relay of valve <NUM> (not shown in detail) which generates a trailer service brake demand signal (air pressure) TSBDS which is forwarded to the trailer brake control coupling <NUM> through the fifth port 410e to control the service brake functionality of the trailer. The fifth port 410e will be referred to as the trailer service brake demand output port.

The park brake demand signal PBDS provided at port 410d is inverted by the internal relay valve for onward transmission as a TSBDS through port 410e to enable the service brake actuators on the trailer to be used to apply a braking force in response to actuation of the park brakes on the towing vehicle. In normal use, when a driver applies the park brakes on the vehicle using the park brake lever <NUM>, the park brake valve <NUM> is moved to its second position 320b and the pressure PBDS applied at the park brake demand input port 410d is reduced to zero. Since the trailer brake valve <NUM> provides a TSBDS output at port 410e which is inversely proportional to the air pressure at port 410d, this will result in a high pressure TSBDS at the port 410e which is forwarded to the brake valve on the trailer so that the service brake actuators on the trailer are actuated to apply a high braking force. Accordingly, the service brake actuators are activated to provide a braking force when the park brakes are applied on the towing vehicle, provided the trailer remains pneumatically coupled to the towing vehicle.

The ability to generate a TSBDS through port 410e by use of the park brake system <NUM> on the vehicle is beneficial in providing an emergency braking arrangement in the event the service brakes on the vehicle should fail. In these circumstances, the driver can attempt to slow the vehicle by applying the park brakes on the towing vehicle using the lever <NUM>. This moves the park brake valve <NUM> to a position in between first position 320a and second position 320b to manually reduce the air pressure in the park brake circuit <NUM>. The trailer brake valve <NUM> provides a TSBDS output at port 410e which is inversely proportional to the reducing air pressure in the park brake circuit <NUM> so that the service brake actuators on the trailer are actuated in a controlled manner to provide a braking force.

A sixth port 410f is used to provide a pre-pressurisation function. The hydraulic service brake circuit <NUM> works with relative low volumes of fluid in comparison with the pneumatic brake systems. To compensate for this, a pre-pressurisation system <NUM> is operative to provide a basic level of air pressurisation to the trailer service brake demand output port 410e when the brake pedal is depressed, prior to the hydraulic pressure in the service brake circuit <NUM> building up. The pre-pressurisation port 410f is connected with the joint supply line <NUM> though a pre-pressurisation valve <NUM> and a pre-pressurisation pressure relief valve <NUM>. The valve <NUM> is a solenoid valve which is biased to a first position 610a, as shown in <FIG>, in which a pre-pressurisation line <NUM> to the pre-pressurisation port is not connected with the joint supply line. When activated, the pre-presurisation valve <NUM> is moved to a second position in which the pre-pressurisation line <NUM> is connected with the joint supply line. This pressurises the pre-pressurisation line <NUM> and the fluid pressured applied at port 410f controls an internal relay of valve <NUM> (not shown in detail) which generates pre-pressurisation trailer service brake demand signal (air pressure) at the trailer service brake demand outlet port 410e. Actuation of the pre-presurisation valve <NUM> is controlled by the ECU in response to a signal from a brake pedal switch <NUM>. When the brake pedal <NUM> is depressed, the switch <NUM> sends a signal to the ECU to indicate that a service brake demand is being generated. In response, the ECU <NUM> actuates the pre-presurisation valve <NUM> to pre-pressurise the service brakes on the trailer. When the brake pedal <NUM> is released and the switch <NUM> is no longer indicating that a service brake is being demanded, the pre-pressurisation valve <NUM> is deactivated and moves back to its first position. The pre-pressurisation pressure relief valve <NUM> is included to limit the pressure applied at the pre-pressurisation port when the valve <NUM> is open.

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 and 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.

In order to comply with the vehicle braking requirements (RVBR) of the "EU Mother Regulation", the trailer brake control system <NUM> is provided with an additional control circuit <NUM> operative to inhibit operation of the trailer brakes when activated. This is provided so that the driver is able to test whether the towing vehicle is capable of holding the trailer using only the brakes on the towing vehicle. During the test, the vehicle is not allowed to move.

The additional control circuit <NUM>, referred to as "EU test control circuit", comprises a test valve <NUM> connected to the air supply system via the joint supply line <NUM> and to a first inlet of the first shuttle valve <NUM> by a test control line <NUM>. A second inlet to the first shuttle valve <NUM> is connected to the park brake circuit <NUM>. The output side of the first shuttle valve <NUM> is connected to port 410d of the trailer brake valve <NUM> via the park brake demand (PBDS) input line <NUM>. The first shuttle valve <NUM> provides a pneumatic OR functionality (i.e., logic control) to forward either of the pressure in the park brake circuit <NUM> or the pressure in control line <NUM>, whichever is at greater pressure. The test valve <NUM> is solenoid controlled and connected to the ECU. The valve is biased by a spring to a first position 471a (as shown in <FIG>) in which the test control line <NUM> is discharged to ambient. In this configuration, the first shuttle valve <NUM> blocks test control line <NUM> (as shown in <FIG>) so that only the pressure (PBDS) coming from park brake circuit <NUM> is forwarded to park brake demand input line <NUM> and thereby the park brake demand input port 410d of trailer brake valve <NUM>. When the test is to be carried out, the test valve <NUM> is energized to move to the second position 471b in which the control line <NUM> is connected to joint supply line <NUM>. This pressurises the test control line <NUM>, causing the first shuttle valve to be switched so that the park brake demand input line <NUM> and the park brake demand input port 410d are also pressurised while the connection to the park brake circuit <NUM> is blocked. In this configuration, the pressure applied at the park brake demand input port 410d remains high even if the park brakes are applied on the vehicle and the pressure in the park brake circuit <NUM> reduced to zero. This inhibits actuation of the service brake function of the trailer brakes when the park brakes on the vehicle are applied so that the test can be performed as required.

The vehicle brake system <NUM> as so far described comprising the service brake system <NUM>, the park brake system <NUM>, the trailer brake control system <NUM> and the EU control circuit <NUM> is known in the art and actuation of the trailer brakes is dependent on the operator initiating a brake demand using either the service brake system <NUM> or the park brake system <NUM>. A brake system comprising these components, optionally excluding the EU control circuit where not required, can be adopted if electronic trailer brake control functionality 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 brake functionality if required as discussed below.

According the invention, the vehicle brake system <NUM> is additionally provided with an electronic trailer brake control system <NUM>. The electronic trailer brake control system <NUM> comprises a fluid circuit having a control valve <NUM>, a piloted relay valve <NUM>, a second shuttle valve <NUM>, and an electronic control system including an ECU <NUM>. The electronic trailer brake control system <NUM> is operative under control of the ECU to selectively open or close a fluid connection between the joint supply line <NUM> and the trailer brake control coupling <NUM>.

The trailer control coupling <NUM> is connected to an outlet of the second shuttle valve <NUM> by a trailer service brake demand fluid line <NUM>. The trailer service brake demand output port 410e is connected to a first inlet of the second shuttle valve <NUM> by a trailer service brake demand output port line <NUM>. The other inlet to the second shuttle valve <NUM> is fluidly connectable to the joint supply line <NUM> by the piloted relay valve <NUM> via an electronic trailer brake control system output line <NUM>. The second shuttle valve <NUM> provides a pneumatic OR functionality (i.e., logic control) to forward either the pressure in the trailer service brake demand output port line <NUM> or the pressure in the electronic trailer brake control system output line <NUM> (whichever is at the highest pressure) to the trailer brake control coupling <NUM>.

The piloted relay valve <NUM> is biased to a first position, as shown in <FIG>, in which the electronic trailer brake control system output line <NUM>, and hence the second inlet to the shuttle valve is not connected to the joint supply line <NUM> and is vented to ambient. With the piloted relay valve <NUM> in this position, if a TSBDS (fluid pressure) is felt in the trailer service brake demand output port line <NUM>, this will be forward by the shuttle valve to the trailer control coupling <NUM> and the shuttle valve inlet to the piloted relay valve blocked. The piloted relay valve <NUM> can be moved to a second open position in which the electronic trailer brake control system output line <NUM>, and hence the second inlet to the shuttle valve <NUM>, is connected to the joint supply line <NUM> and pressurised. With the piloted relay valve <NUM> opened, the fluid pressure in the electronic trailer brake control system output line <NUM> will be forwarded by the shuttle valve to the trailer brake control coupling <NUM> and the first inlet of the shuttle valve coupled to the trailer service brake demand output port 410e blocked (assuming that there is no TSBDS felt in the trailer service brake demand output port line <NUM> or that if there is, it is at a lower pressure than the pressure in the electronic trailer brake control system output line <NUM>). The fluid pressure forwarded to the trailer brake control coupling <NUM> will be forwarded from the coupling to the brake valve on the trailer as a service brake demand signal and will result in the service brakes on the trailer being actuated. The piloted relay valve <NUM> is a proportional valve capable of being activated to vary the pressure applied in the electronic trailer brake control system output line <NUM>.

Actuation of the piloted relay valve <NUM> is regulated by the control valve <NUM>, which is operative to selectively apply fluid pressure at a control port 512a of the piloted valve to move the piloted valve from its first position to its second position. The control valve <NUM> has an outlet port connected to the control port 512a of the piloted relay valve <NUM> by a pilot line <NUM> and an inlet port connected to the joint supply line <NUM>. The control valve is a solenoid valve and is biased by a spring to a first position 510a, as shown in <FIG>, in which the pilot line is disconnected from joint supply line <NUM> and so is not pressurised. With the control valve <NUM> in this first position, no fluid pressure is applied at the control port 512a of the piloted relay valve which is biased to its first position. When energized, the control valve <NUM> moves to a second position 510b in which it connects the pilot line <NUM> to the joint supply line <NUM> so that the pilot line <NUM> is pressurised. The fluid pressure in the pilot line <NUM> is applied to the piloted relay valve control port 512a to open the relay valve <NUM> and hence connect the second shuttle valve <NUM> and the trailer brake coupling <NUM> to the joint supply line <NUM>. As illustrated, a pressure relief valve <NUM> may be provided to limit the pressure applied by the control valve to the control port 512a of the relay valve. The pressure relief valve <NUM> may limit the pressure applied by the control valve to the control port 512a to around <NUM> bar, for example.

To prevent pressurised air being trapped in pilot line <NUM> and the relay valve being held open when the control valve <NUM> is moved back to the first position 510a from the second position 510b, a discharge valve <NUM> may be connected to pilot line <NUM>. The discharge valve <NUM> is a solenoid valve and is operative to vent the pilot line <NUM> to atmosphere 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 pilot line <NUM> is not vented to atmosphere when the control valve <NUM> is energized to the second position 510b to connect the pilot line <NUM> to the joint supply line and hence air supply <NUM>. The discharge valve provides additional safety as pressurised air trapped in pilot line <NUM> could hold the relay valve open and result in actuation of the trailer service brakes when not intended, even if control valve <NUM> is in the first position 510a. The control valve <NUM> and the discharge valve <NUM> are controlled by the ECU so that both are moved to their first positions and the pilot line <NUM> vented when the ECU is not operative to apply the service brakes on the trailer and to move to their second positions to allow the pilot line <NUM> to be pressurised when the service brakes on the trailer are to be applied. As both valves <NUM>, <NUM> are biased to their first positions, this provides a fail-safe system which ensures the pilot line <NUM> is vented and the relay valve <NUM> returned to its first position so that the service brakes on the trailer are not applied if the electrical supply to the control and discharge valves <NUM>, <NUM> fails. Alternatively, or in addition, the control valve <NUM> may be configure to vent the pilot line to ambient when in its first position 510a.

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 system <NUM> is operative in particular to 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 as indicated at <NUM>. If a PUSH condition is detected, the electronic pilot trailer brake system <NUM> is utilized to avoid Jack-knifing. In response to a determination that a PUSH condition exists, the ECU energizes the control valve <NUM> and the discharge valve <NUM> moving them to their second positions 510b, 540b. This pressurises the pilot line <NUM> causing the piloted relay valve <NUM> to open so that the pressurised air is forwarded through the electronic trailer brake control system output line <NUM>, the second shuttle valve <NUM>, the trailer service brake demand fluid line <NUM>, and the trailer brake control coupling <NUM> to the brake valve on the trailer to actuate the service brake function on the trailer.

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 that the trailer service brake demand signal output from the electronic trailer brake control system <NUM> fed to the trailer control coupling <NUM> is limited to a pressure below the general maximum pressure limit in the brake system described above so that the electronic trailer brake control system <NUM> does not initiate a full braking of the trailer, which could result in unsafe driving conditions. The pressure may be limited to <NUM> to <NUM> bar, more especially <NUM> bar, for example. This can be achieved in a number of ways. In one embodiment, a pressure sensor <NUM> is installed in the trailer service brake demand fluid line <NUM> from the second shuttle valve <NUM> to trailer brake control coupling <NUM> for determining the fluid pressure (TSBDS) applied to the trailer. The pressure sensor <NUM> provides an input to the ECU and forms part of a closed-loop control for the brake pressure signal TSBDS enabling the ECU to regulate control valve <NUM> and hence piloted relay valve <NUM> to limit the pressure provided to the trailer control coupling <NUM>. Where the piloted relay valve <NUM> is a proportional valve, it can be controlled to set the pressure forwarded to the trailer service brake demand fluid line <NUM>. If the electronic connection fails (say due to cable brake), the ECU can be configured to de-energize the control valve <NUM> and discharge valve <NUM> so that the electronic trailer brake function is deactivated and the vehicle is in a safe state.

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 pilot 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 pneumatic valves <NUM>, <NUM>, <NUM> and <NUM> are described as separate elements they may be included in a valve manifold.

In an alternative embodiment, the service brakes <NUM> on the towing vehicle are pneumatic rather than hydraulic. In this case, the trailer brake valve <NUM> is configured to receive a pneumatic service brake demand signal SBDS at the service brake demand inlet port 410c. The pneumatic service brake demand signal SBDS is received from a line of the pneumatic service brake system, the pressure of the pneumatic service brake demand signal SBDS being indicative of a brake demand from the driver. In this case, the trailer brake valve <NUM> is configured to generate a pneumatic trailer service brake demand signal TSBDS at the trailer service brake demand output port 410e which is proportional to, or at least dependent on, the pneumatic pressure applied at the service brake demand inlet port 410c. In other respects the brake system may be essentially the same as the embodiments described above and incorporate an electronic trailer brake control system <NUM> constructed and operated as described above. Accordingly, the electronic trailer brake system <NUM> as described above can also be incorporated in a vehicle braking system where the service brakes on the towing vehicle are actuated pneumatically.

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 operator controlled actuation of the trailer brakes.

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