The present invention relates to a trailer and in particular a trailer having a drive unit or units and means for determining an amount of torque to be applied by the drive unit to a wheel or wheels of the trailer.

In some circumstances it is desirable for a trailer to incorporate its own drive system to complement the drive provided by a towing vehicle.

Typically, however, trailers that incorporate their own drive systems require information from a towing vehicle as to the required power output of the drive system, thereby allowing the torque that is being applied to the wheels of the trailer by a drive unit of the drive system to be modulated according to the speed of the towing vehicle. Clearly, incompatibility between the speed of the towing vehicle and the torque being applied to the wheels of the trailer can result in wasted energy. For example, an increase in wear upon the towing vehicles brakes could occur if a drive unit of the trailer were to continue to apply positive torque to the trailers wheels while the towing vehicle was braking. Additionally, incompatibility between the drive of a trailer and its towing vehicle can lead to more serious problems such as jack knifing and/or the trailer could become more difficult to control under braking .

Although a communication interface can be used between a towing vehicle and a trailer for allowing data to be transmitted from a towing vehicle to the trailer, it cannot be guaranteed that a communication interface used on one vehicle will be compatible with a communication interface used on another vehicle. Accordingly, there is a need for greater compatibility between self powered trailers and different towing vehicles.

Further, if information is provided by a towing vehicle to a self powered trailer it will typically only relate to longitudinal data, for example longitudinal acceleration. This can result in additional wear on the trailer and would not allow a towing vehicle to identify the possible risk of jack knifing of a towed vehicle and adjust torque accordingly. Accordingly, there is a need to provide a trailer that has a drive unit with information relating to the forces that are being placed on the trailer in more than one axis.

It is desirable to improve this situation.

In accordance with an aspect of the present invention there is provided a trailer according to the accompanying claims .

This provides the advantage of allowing a trailer drive system to be controlled independently of the vehicle that is towing the trailer. Additionally, by determining how to share torque between different wheels tyre wear can be reduced and the dynamic behaviour of the trailer can be improved.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 illustrates a perspective view of a trailer according to an embodiment of the present invention;

Figure 2 illustrates a side view of a trailer according to an embodiment of the present invention. Figure 1 illustrates a trailer 100 having a frame, which for purposes of illustration includes a pair of longitudinal extending side members 101 and a plurality of transverse cross members 102 interconnecting and attached to the side members 101. Attached to a forward transverse cross member 102 is an extending forward member 103 to which is fixed a coupling joint 104 for releasable mounting the trailer 100 to a towing vehicle (not shown) , any suitable coupling joint 104 may be used. Typically, mounted on the frame will be a load carrying structure 105, as shown in figure 2. However, as would be appreciated by a person skilled in the art any form of trailer can be used.

Coupled to each longitudinal extending side member 101 are two wheels 106 upon which are fitted tyres 107. Each wheel 106 has an electric motor (not shown) associated with it, where any suitable type of electric motor could be used, for example an electric motor having a set of coils being part of a stator for attachment to one of the trailers longitudinal extending side members as described in WO

PCT/GB2007/002651. The electric motor will typically include built-in electronics and bearings that act as a motor wheel hub. Alternatively instead of each wheel having an electric motor associated with it a single motor, or a series gang of motors acting like one motor on a common shaft, could be used to drive into a differential for each wheel 106.

The electric motor electronics may include a controller (not shown) for controlling the operation of the electric motor, for example determining the amount of torque that the electric motor should provide. Alternatively, a central controller can be used that is arranged to control the operation of each of the electric motors, which for the purposes of the present embodiment would include four electric motors, one incorporated within each wheel 106. Having a separate electric motor for each wheel 106 of the trailer 100 can have a number of advantages, for example each wheel 106 of the trailer 100 can apply driving or braking torque independently of the other wheels 106, thereby increasing the flexibility in the handling of traction control. As would be appreciated by a person skilled in the art each electric motor has an associated battery (not shown) for powering the respective electric motor. A single battery could be used for powering all of the electric motors or individual batteries could be associated with each electric motor or any combination, for example one battery pack per pair of motors/wheels, however in this case for safety and redundancy reasons the battery is best connected to diagonal opposite motors.

In general, torque is applied by the electric motors to the wheels 106 proportional to the weight distribution, which changes dynamically. For example, during braking greater weight is applied to the front wheels, thereby allowing greater torque to be applied to the front wheels, during acceleration greater weight is applied to the rear wheels, thereby allowing greater torque to be applied to the rear wheels and during cornering greater weight is applied to the outer wheels, thereby allowing greater torque to be applied to the outer wheels.

To allow the total torque requirements for the trailer 100 to be determined it is necessary to determine the force required to move the trailer 100 with the same speed and acceleration as the towing vehicle. To allow this determination to be made sensors are mounted on the trailer which measure characteristics of the trailer that allows this determination to be made.

For example, in one embodiment there is mounted on, or near, the coupling joint 104 of the trailer 100 a sensor arrangement 108 that includes two load cells at substantially 90 degrees to each other and at substantially 45 degrees to the trailers longitudinal axis to provide an indication of a load in the longitudinal direction of the trailer 100 and a load in the lateral direction of the trailer, where the load cells can be used to determine a force on the trailer 100 or the mass of the trailer 100.

By using two sensors it is possible to not only determine longitudinal acceleration of the trailer 100 but also lateral acceleration, thereby allowing the total torque requirements for the trailer 100 to be optimally distributed to all the wheels 106 of the trailer 100 under all driving conditions, for example, as stated above, cornering conditions in addition to forward acceleration and deceleration. Indeed, during a cornering manoeuvre not only is a greater weight applied to the outer wheels but the outer wheels will be rotating at a greater speed to those of the inner wheels and the electric motors can be controlled to accommodate this speed differential to optimise the tyre and road speed, thereby further minimising tyre wear by minimising the scuffing of the tyres 107.

The sensor arrangement 108 is arranged to generate an electrical signal or signals that represent the longitudinal and lateral loads measured by the two load cells. The generated electrical signal is provided to the controller or controllers associated with the electric motors, where the controller or controllers are arranged to determine an appropriate torque that is to be applied by a drive unit to a wheel 106.

Although, the above embodiment describes the use of a sensor arrangement 108 having two load cells that is located on or near the coupling joint 103 of the trailer 100, the sensor arrangement 108 can be located in other locations and the types and number of sensors can be changed, where any form of sensor that can provide acceleration or force information can be used. For example, speed/acceleration sensors associated with the wheels 106 of the trailer 100 can be used to indicate longitudinal and lateral acceleration of the trailer 100. Additional load cells (not shown) can also be located on the trailer 100, for example at each corner and/or each wheel 106 to enhance the ability to determine the roll and load characteristics of the trailer 100 in a number of axes.

By placing a sensor close to a wheel 106 it is possible to determine more accurate information relating to forces being applied to that specific wheel and as such based on information provided from sensors associated with each wheel 106 of the trailer 100 allow an improved torque distribution determination to be made for the trailer 100 as a whole.

As would be appreciated by a person skilled in the art, the trailer 100 may have any number of wheels 106, where all or some of the wheels 106 incorporate an electric motor for providing drive to the respective wheel. Indeed, in one embodiment more than one wheel 106 may be mounted on the same side and axle of the trailer 100, where each wheel 106 has an associated electric motor. By determining accurate longitudinal and lateral acceleration values for the trailer 100, for example by having a number of different sensors placed on the trailer 100 in different positions, it can be possible to determine different torque and speed values to the applied to the two wheels mounted next to each other on the same axle, thereby further reducing tyre wear.

The longitudinal and lateral acceleration values generated by the sensor arrangement 108 allow the controller or controllers to determine a torque distribution that is to be applied by the electric motors to the wheels 106 of the trailer 100 where a determination can be made as to the torque to be applied to individual wheels 106 to compensate for the dynamic changes in weight distribution of the trailer 100 in both longitudinal and lateral directions. To allow this determination to be made either a central controller can be used that receives the longitudinal and lateral acceleration values or force values, dependent upon the type of sensors being used, from the sensor arrangement 108 and determines an appropriate torque value to be applied to each wheel 106 based upon the weight distribution of the trailer 100. Alternatively individual controllers associated with each electric motor can be used that are arranged to communicate with each other to determine an appropriate torque value to be applied by their respective electric motor based on a determined weight distribution for the trailer 100. If the torque values are based on absolute values, for example a specific torque is applied by an electric motor to a wheel 106 for a specific determined weight, the determination can be made independent of the other controllers. If, however, torque values are based on relative values, a controller would need to make a determination based on different torque values being applied by other electric motors, as such each controller would be required to receive torque information from the other controllers .

To ease movement of the trailer 100 a switch (not shown) can also be incorporated on the trailer 100 that is operated by hand to allow the trailer 100 to be moved by an operator without a towing vehicle, where the electric motors are used to power the movement of the trailer 100.

Preferably the switch is coupled to the sensor arrangement 108 to allow an operator to control the signal input into the controller or controllers to allow a torque distribution to be determined based on the operators need to move the trailer. Alternatively, the switch can include a mechanism for providing control signal directly to the electric motors for controlling the operation of the electric motors. Preferably the battery or batteries associated with the electric motors are rechargeable, where regenerative braking can be used to recharge the battery or batteries. Accordingly, when regenerative braking is applied each electric motor functions as a generator that is used to apply charge to the battery or batteries.

The torque values determined by the controller or controllers based on the force/acceleration information provided by the sensor arrangement 108 can be modified based upon the charge level of a battery or batteries. As such, a controller can be configured to ensure that a torque value control signal provided by the controller to an electric motor does not exceed the power output capability of a battery. Accordingly, if the charge level of a battery associated with one electric motor is not capable of supplying the power requirements to allow the electric motor to generate a determined torque value a reduced torque signal is provided to the electric motor. To ensure that a determined torque distribution for a trailer is maintained the torque value signals for the other electric motors are similarly reduced to maintain the same torque distribution ratio between the different wheels 106 of the trailer 100.

The torque values determined by the controller or controllers can also be modified to ensure that the fuel efficiency map of the towing vehicle's engine is optimized. For example, a controller can include a table for an efficiency map for an engine, where typically the fuel efficiency of an engine will vary depending on engine speed and load. Accordingly, the controller or controllers can be configured to modify determined torque values that are to be applied by the trailers electric motors such that the load upon the towing vehicles engine is adjusted so that fuel efficiency is optimized. To optimize battery use the electric motors can be used to generate torque for the trailer wheels, thereby supplementing the power generated by the towing vehicle, when the efficiency gains associated with the use of the electric motors is greatest (e.g. when the towing vehicles engine is operating relatively inefficiently) . Conversely, regenerative charging of the electric motor batteries can be performed when the towing vehicle engine is operating at its most efficient (e.g. at high speed and low torque) or when the towing vehicle is braking. In such a configuration typically, based upon available battery power levels, the electric motors can be used to assist the trailer at low speed and/or when the towing vehicles engine is operating near to its torque or power limit (e.g. at 80% or more of it's maximum) .

Ideally, to allow a controller to determine relevant towing vehicle information, and hence determine the optimum use of the electric motors, the controller (s) would preferably be provided the following towing vehicle information : the towing vehicle's mass; the maximum engine torque for the towing vehicle; the maximum engine power for the towing vehicle; the power line efficiency of the towing vehicle; the speed of the towing vehicle.

Additionally, the controller would ideally also need the following trailer information: the trailer gross mass; the electric motor battery charge levels.

Alternatively, it would also be possible to use an engine efficiency map and power-line efficiency to determine the towing vehicles efficiency at any given time, thereby allowing the trailers electric motors to be used to generate torque when the towing vehicles engine efficiency is below a given threshold and perform regenerative braking when the towing vehicles efficiency is above a predetermined threshold.

Clearly, although the present invention describes an autonomous trailer that is able to determine a torque value independent of towing vehicle information, the determined torque values can be supplemented by efficiency information determined from information provided by the towing vehicle (e.g. the towing vehicle information listed above) . Further the torque applied by the trailers electric motors can be determined solely based upon efficiency information determined independently of the load-cell information (e.g. via information provided by the towing vehicle and information preloaded in the controller (s) ) . As such, in one embodiment the trailer load cell information may not be used to determine torque values to be applied by the electric motors .

Conversely, if no towing vehicle information is available efficiency information can be determined based upon load cell information and trailer wheel speed sensor information .

It will be apparent to those skilled in the art that the disclosed subject matter may be modified in numerous ways and may assume embodiments other than the preferred forms specifically set out as described above, for example even though the embodiment describes the use of an electric motor any form of drive unit could be used, for example a petrol or diesel engine.