This invention relates generally to power conversion apparatus and more specifically, although not exclusively, to power conversion apparatus for powering a refrigeration unit such as those which are towed by vehicles, for example trucks or lorries.

Such refrigeration units require a reliable and/or consistent amount of power in order to ensure their proper functionality. It is known to use a standalone diesel engine which drives the compressor of such a unit. The engine starts and stops based on the load requirements of the refrigeration unit. These refrigeration units also include a power cable for connection into a mains power supply of, say, 400V at 50Hz when the vehicle is parked.

Electrical generators known as alternators are generally coupled to and driven by an automobile engine by means of a flexible belt, whereby a portion of the mechanical power is converted into electrical power. This electrical power is then used to feed a battery. The battery powers ancillary equipment, for example electric windows and/or a fuel management system or the like, which require a direct current power supply.

The variable speed of the automobile engine causes variations in the power and/or frequency generated by the alternator. This issue is mitigated through the use of a battery, which regulates such fluctuations. However, standard alternators and batteries do not generate and/or store sufficient electrical power to drive a refrigeration unit, nor are they able to supply an alternating current to such a unit.

US6662586 discloses a vehicle with a refrigeration unit powered by the vehicle's own engine in place of a standalone system. The vehicle includes a pump, whose stroke volume can be regulated and which is mechanically connected to the vehicle engine, a motor to which fluid is supplied from the pump, a generator mechanically connected to the motor and a control device. The control device allegedly regulates the stroke volume of the hydraulic pump such that the magnitude of flow remains substantially constant.

WO20091 1668 also discloses a vehicle with a refrigeration unit powered by the vehicle's own engine, which further includes a control valve between the pump and the motor to reduce fluctuations, including sharp variations, in pressure and/or flow that result from the aforementioned arrangement. It is a general non-exclusive object of the present invention to provide an improved power conversion apparatus. It is a further non-exclusive object of the invention to provide a power conversion apparatus which is able to draw power from a vehicle's engine more efficiently. It is a yet further non-exclusive object of the invention to supply this power to an existing refrigeration unit without the need to modify the unit or at least to minimise the extent of such a modification.

One aspect of the invention provides a power conversion apparatus for powering automotive ancillary equipment that requires a substantially constant voltage and frequency, the apparatus comprising a variable displacement pump connectable to an automobile engine, a motor fluidly connected to the pump, a generator operatively connected to the motor and a controller with an input configured to receive, in use, a signal indicative of a speed of an automobile engine to which the pump is connected, wherein the pump is configured to induce a flow to drive the motor when the pump is driven by the engine thereby causing the motor to drive the generator, the controller being operable to control the displacement of the pump based on the signal received in order to regulate the pressure and/or flow of fluid supplied to the motor from the pump to cause the generator to supply a predetermined alternating current frequency and voltage.

The magnitude of the aforementioned sharp variations in pressure and/or flow is at least exacerbated by the delay between a change in engine speed occurring, the change being detected by the prior art systems and the ability of the controller to react to the changes. Controlling the displacement of the pump based on the speed of the engine pre-empts these variations and allows the controller to control more effectively the pump flow in order to minimise their magnitude.

A second aspect of the invention provides a controller for use in an apparatus as described above, the controller comprising an input means for receiving a speed signal from a sensor indicative of the speed of an engine to which the apparatus is connected in use and an output means for sending a command signal to the pump, wherein the controller is operable or specifically adapted to generate a command signal arranged to maintain a substantially constant flow rate or motor speed in response to a speed signal received from the input means.

Preferably, the signal comprises a first signal, e.g. the controller also being configured to receive a second signal indicative of a speed of the motor and/or of a speed of the generator and/or of a frequency supplied by the generator, wherein the controller is more preferably operable to control the displacement of the pump based on the first and second control signals.

Thus, a closed loop control system is provided in which a change in engine speed is pre-empted and the controller is able to ensure that the correction made has the desired effect, i.e. maintaining a constant flow rate and generator output frequency.

It will be appreciated that the first signal need not consist of a measured speed of the engine itself and/or the second signal need not consist of a measured electrical frequency.

The first signal may, for example, comprise a signal indicative of the speed of a shaft of the pump, e.g. wherein the apparatus further comprises a speed sensor for measuring the speed of the pump shaft, which may be equal to or proportional to the speed of the engine. Additionally or alternatively, the controller may be operatively connected to the vehicle's onboard computer, wherein the first signal may be received directly from the computer.

The second signal may comprise a signal indicative of the speed of a shaft of the motor or of the generator, e.g. wherein the apparatus further comprises a second speed sensor for measuring the speed of the motor or generator shaft, which may be proportional to the frequency supplied by the generator. Additionally or alternatively, the apparatus may comprise a frequency sensing means or measuring device, wherein the output frequency supplied by the generator may be measured directly to provide the second signal.

The controller may be configured or operable to vary the displacement of the pump, for example the stroke volume thereof, based on the first signal e.g. to provide a coarse control of the flow and/or pressure of fluid supplied to the motor, and/or based on the second signal e.g. to provide a fine control of the flow and/or pressure of the fluid supplied to the motor.

The controller may be operable to vary, for example adjustably vary, in use, the load drawn from the automobile engine based on a required load. Preferably, the controller is operable to supply a constant predetermined alternating current frequency and voltage, for example regardless of the load supplied by the generator. The apparatus may further comprise a load sensing device, for example to measure a demand of the ancillary equipment, which load sensing device may be self powered, e.g. to enable the pump to be set to minimum or zero flow when substantially no or a zero load is required or demanded by the ancillary equipment.

A third aspect of the invention provides a load sensing device, for example to measure a demand of the ancillary equipment, which load sensing device may be self powered, e.g. to enable the pump to be set to minimum or zero flow when substantially no or a zero load is required or demanded by the ancillary equipment.

The load sensing device may comprise a supply or supply circuit, for example a 3 phase supply or supply circuit, which may be configured to provide a load voltage, e.g. 400V or 480V, and/or a relatively low or low or very low current, for example a milliamp current or a current in the order of one or tens or hundreds of milliamps, e.g. when substantially no or a zero load is required or demanded by the ancillary equipment. This arrangement may be provided where the ancillary equipment requires a continuous supply, e.g. for maintaining the continuous supply, for example when substantially no or a zero load is required or demanded by the ancillary equipment.

The load sensing device is preferably operatively connected, e.g. electrically connected, to the ancillary equipment and/or to the controller. The load sensing device may be configured to measure, in use, a demand of the ancillary equipment and/or to send a demand signal to the controller corresponding to the demand. The load sensing device may further comprise a current detector for detecting a demand from the ancillary equipment and/or an output for sending a demand signal to the controller. The load sensing device is preferably configured to generate, e.g. and send, in use, a demand signal to the controller on detection of a demand from the ancillary equipment, for example to cause the controller to adjust the displacement of the pump to regulate the pressure and/or flow of fluid supplied to the motor from the pump to cause the generator to supply a predetermined alternating current frequency and voltage.

The apparatus or load sensing device may further comprise switching means, e.g. for selectively switching the supply to the ancillary equipment from the supply circuit of the load sensing device to the generator supply, for example in response to a demand sensed from the ancillary equipment by the load sensing device. The controller may comprise the load sensing device and/or the switching means and/or may comprise a hydraulic and/or electrical and/or electronic circuit. The pump may comprise an axial piston pump, which pump may be operatively connected or connectable to the engine by a belt or a keyed or geared or splined drive means. Preferably, the pump is connected or connectable directly to the engine such as via a power take off of the engine, e.g. in order for the pump to be driven by the engine.

The pump preferably comprises a swash plate for regulating hydraulic fluid pressure and/or flow. The swash plate may be arranged or operable to cause the pump to supply a predetermined, for example a substantially constant, hydraulic pressure and/or flow. The apparatus or controller may comprise a pressure and/or flow sensor or sensors, for example hydraulic pressure and/or flow sensor or sensors, which may be arranged to measure the hydraulic pressure and/or flow returned to the pump and/or supplied to the motor and/or through the hydraulic circuit. The pressure and/or flow sensor may be hydraulically or fluidly connected to or adjacent the inlet or outlet of the pump or the motor inlet or outlet and/or the hydraulic circuit. The pump may comprise a valve, for example a pump control valve such as a solenoid valve, e.g. an electric proportional solenoid, which valve may be mounted on the pump and/or configured to control proportionately the displacement of the pump.

The motor, e.g. hydraulic motor is preferably operatively coupled, e.g. close coupled, to the generator and/or may be arranged or operable to turn the generator at a predetermined, for example a substantially constant, rotational speed.

The controller preferably comprises a control unit, for example a microprocessor, microcomputer or programmable logic controller. In one embodiment, the controller comprises a control loop feedback controller, for example a proportional-integral- derivative controller, which may be configured to correct a deviation between the second signal and a desired value. The control unit is preferably arranged or programmed or programmable or operable to control the pump control valve, e.g. for regulating the displacement thereof to supply, in use, a predetermined, e.g. a substantially constant or maximum, fluid flow rate to the motor or output frequency of the generator. Thus, the stroke volume of the pump may be used to compensate for any variation in the rotational speed of the engine and/or in the flow rate supplied to the motor.

The pressure and/or flow sensor or sensors may be operatively connected to the controller. The apparatus may further comprise a load sensor which may be operatively connected to the controller. The load sensor may comprise a pressure sensor and/or may be connected between the pump and the motor, e.g. to detect a change in hydraulic pressure. Alternatively, the load sensor may be arranged to detect a relay contact, for example which is representative of a demand from the refrigeration unit or ancillary equipment for power. The controller may be arranged or programmed or programmable or operable to receive a signal from the load sensor and to control the pump in response to the signal.

Additionally or alternatively, the controller may be arranged or programmed or operable to adjustably vary, in use, the fluid pressure supplied by the pump, for example based on the measured and/or determined load, e.g. current, required or drawn by the refrigeration unit. The controller may be arranged or programmed or operable to calculate or determine the required stroke volume and/or valve position for the generator to generate the load required by the refrigeration unit and/or the load measured or determined, in use, by the load sensor and/or a predetermined load, for example substantially constant load.

A fourth aspect of the invention provides a kit, for example a retrofit kit, which kit may comprise one or more of the aforementioned elements and/or additional elements, e.g. for retrofitting the aforementioned apparatus onto an existing vehicle. Preferably, the apparatus and/or retrofit kit comprises a housing within which may be located at least one of the motor, the generator and/or the controller.

A further aspect of the invention provides an apparatus as described above with a refrigeration unit having a power cable electrically connected to the generator.

A yet further aspect of the invention provides an automobile comprising an apparatus as described above, wherein the pump is operatively connected or coupled to the engine of the automobile.

The automobile may be a truck or lorry. The refrigeration unit may be connected or secured to or mounted on the automobile or truck or lorry.

Another aspect of the invention provides a method of converting power, e.g. using a power conversion apparatus as described above, the method comprising converting mechanical power from an automobile engine into electrical power by controlling the displacement of the pump in response to a signal indicative of the speed of an engine to which the pump is connected, thereby to regulate the pressure and/or flow of fluid supplied to the motor from the pump to cause the generator to supply a predetermined alternating current frequency and voltage.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a partial perspective view of an apparatus according to the invention installed in a lorry; and

Figure 2 is a schematic view of the apparatus of Figure 1 .

Referring to Figures 1 and 2, there is shown an apparatus 1 according to the invention installed in a lorry 2 having an engine 3 to which the apparatus 1 is operatively connected and a refrigeration unit 4 electrically connected to the apparatus 1 by a power cable 40 (shown in Figure 2).

The apparatus 1 includes a pump 5, a controller 6, a motor 7, a generator 8, which is an alternator in this embodiment, and a load sensing device 9 for measuring a demand of the refrigeration unit 4. The pump 5 is of the variable displacement type with a swash plate (not shown) for varying the stroke volume according to load requirements and is coupled to the engine 3 by an endless drive belt 50 of the type known in the art. The pump 5 includes a solenoid control valve (not shown), an inlet conduit 51 , an outlet conduit 52, both of which feed into the controller 6.

The motor 7 is coupled to the alternator 8 by an endless drive belt 70 of the type known in the art and includes an outlet conduit 71 and an inlet conduit 72, both of which feed into the controller 6. The alternator 8 supplies power, in use, to the refrigeration unit 4 through a supply cable 80 via the load sensing device 9 and through the power cable 40. The alternator 8 is configured to provide a constant 3 phase, 400V supply when in operation.

In this embodiment, the maximum pump displacement is 80 cubic centimetres and the motor displacement is 32 cubic centimetres. Accordingly, at full pump displacement, this provides a maximum theoretical 0.4 speed step-up, for example a generator speed of 1 ,500rpm at an engine speed of 600rpm. The controller 6 includes a control unit 60 in the form of a programmable logic control (PLC) unit 60 in this embodiment. The controller 6 also includes a pressure sensor 62a, first, second and third feedback cables 66a, 66b, 67 and a control cable 64.

The first feedback cable 66a connects the pressure sensor 62a to the control unit 60 for transmitting a pump pressure output signal thereto. The second feedback cable 66b connects the generator 8 to the control unit 60 for transmitting a generator output frequency signal thereto. The third feedback cable 67 connects the cam bus system (not shown) of the vehicle 2 to the control unit 60 for transmitting an engine speed signal (and demands of the engine) thereto. The control cable 64 connects the control unit 60 to the pump 5 for transmitting a command signal to the solenoid control valve (not shown) to control the position of the swash plate (not shown), thereby controlling the displacement of the pump 5. The controller 6 therefore monitors the engine speed, the generator frequency and the hydraulic pressure supplied by the pump 5.

The outlet conduit 52 of the pump 5 is fluidly connected to the inlet conduit 72 of the hydraulic motor 7 via the pressure sensor 62a and the outlet conduit 71 of the hydraulic motor 7 is fluidly connected to the inlet conduit 51 of the pump 5.

In use and as the speed of the engine 3 increases, so too does the speed of the pump 5, which would normally increase the flow rate, thereby increasing the speed at which the motor 7 and the generator 8 are driven. However, the controller 6 detects the change in the speed of the engine 3 through the third feedback cable 67 and adjusts the position of the swash plate (not shown) and consequently the displacement of the pump 5 to compensate for this change. This is used as a coarse control means for adjusting the flow rate. Fine adjustment is achieved by measuring the actual output frequency of the generator 8 and, if this starts to deviate from the desired frequency, the displacement of the pump 5 is adjusted further.

Similarly, if there is a sudden increase in the required load, this is also sensed by a variation in the output frequency as this is indicative of the speed of the generator 8 and motor 7. In such a case, the displacement of the pump 5 is adjusted as described above in relation to a variation in engine speed.

In some embodiments, the hydraulic pressure measured by the pressure sensor 62a functions as a load sensor by permitting the control unit 60 to detect an increase in demand from the generator 8 which causes an increase in resistance within the motor 7, thereby increasing the pressure measured by the pressure sensor 62a. Additionally or alternatively, the pressure sensor 62a may be used to protect the hydraulic system from a sudden overload or be omitted altogether.

In this embodiment, the refrigeration unit 4 requires a substantially constant voltage (400V) and frequency (50Hz). The control unit 60 is arranged to regulate the frequency supplied by the alternator 8 by varying the position of the swash plate (not shown) to vary the stroke volume of the pump 5 in response to any variation in the engine speed and/or in response to load requirements sensed by the pressure sensor 62a. The controller 6 is programmed to ensure that a predetermined flow rate is supplied to the motor 7, thereby resulting in a predetermined rotational speed, in the case of this embodiment 1500rpm. This predetermined rotational speed results in the generator 8 supplying electrical power at the aforementioned 50Hz frequency.

It will be appreciated that an increase or decrease in the load drawn by the refrigeration unit 4, and therefore by the generator 8, will cause the position of the swash plate (not shown) and of the control valve 61 to change. Thus, the magnitude of the mechanical power transferred from the engine 3 by the apparatus is automatically regulated to match the load required by the refrigeration unit 4.

The apparatus is therefore able to supply a constant voltage and frequency at any engine speed, for example when the engine 3 is idling (e.g. 500rpm) or running at full speed (e.g. 2500rpm).

In this embodiment, the refrigeration unit 4 also requires the substantially constant voltage (400V) and frequency (50Hz) continuously, whether there is a demand for power or not. For this reason, the load sensing device 9 incorporates a supply circuit (not shown) configured to provide the requisite load voltage with a milliamp current when a zero load is required by the refrigeration unit 4 to satisfy its requirement for a continuous supply. This arrangement enables the pump 5 to be set to zero flow when a zero load is required or demanded by the refrigeration unit 4.

The load sensing device 9 is electrically connected to the control unit 60 and supplies the refrigeration unit 4 via the power cable 40. The load sensing device 9 includes a current detector (not shown) for detecting a demand from the refrigeration unit 4 and is configured to generate and send, in use, a demand signal to the control unit 60 on detection of a demand from the refrigeration unit 4. The load sensing device 9 also includes switching means (not shown) for switching the supply to the refrigeration unit 4 from the supply circuit of the load sensing device 9 to the generator supply in response to the detected demand. The control unit 60 responds to the demand signal by adjusting the displacement of the pump 5 to set the pressure and/or flow of fluid supplied to the motor 7 from the pump 5 to cause the alternator 8 to supply the aforementioned supply frequency and voltage.

Tests have shown that this arrangement greatly reduces the overall fuel consumption and noise generation as compared to the aforementioned arrangement which utilises a standalone diesel engine. In addition, the reduction in moving parts results in the system being simpler and easier to maintain.

It will be appreciated by those skilled in the art that several variations to the specific embodiment disclosed herein are envisaged without departing from the scope of the invention. For example, the apparatus disclosed herein may be used for powering other ancillary equipment including, but not limited to, cranes, tanker heaters and/or automobile transportation equipment. The PLC controller may comprise a proportional-integral- derivative (PID) controller, a micro controller or any other suitable control means. Also, the pump 5 may advantageously be coupled to a power take off (not shown) of the engine, for example an engine dry power take off.

The alternator 8 or other type of generator 8 and/or the load sensing device 9 may be configured to provide a different voltage and/or frequency, for example a constant 480V and frequency of 60Hz.

Additionally or alternatively, the controller 6 may include a flow meter fluidly connected to the inlet conduit 72 of the hydraulic motor 7.

It will be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.