GB2545642A

GB2545642A - Traction battery charging method and apparatus

Info

Publication number: GB2545642A
Application number: GB1522063.5A
Authority: GB
Inventors: Greenwood Jeremy; Clarke Chris
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2015-12-15
Filing date: 2015-12-15
Publication date: 2017-06-28
Anticipated expiration: 2035-12-15
Also published as: GB2545642B; GB201522063D0

Abstract

The present disclosure relates to a vehicle 1 having an electric traction machine 2; a traction battery 6 for storing energy; and an inverter 12 for electrically connecting the electric traction machine 2 to the traction battery 6. The vehicle 1 includes an internal combustion engine 3 operable to charge the traction battery 6 depending on the speed of the vehicle. The internal combustion engine 3 having an electric starter motor 8 which is selectively energized by the traction battery 6. A controller 12 includes at least one processor 13 and a memory device 14. The at least one processor 13 is configured to control charging of the traction battery 6 by the electric traction machine 2 while an external driving force is applied to propel the vehicle 1. The at least one processor 13 is configured to control an electrical load on the electric traction machine 2 in dependence on a determined vehicle speed. The present disclosure also relates to a controller 12 for charging a traction battery 6; and to a method of charging a traction battery 6 also dependent on vehicle speed.

Description

TRACTION BATTERY CHARGING METHOD AND APPARATUS TECHNICAL FIELD

The present disclosure relates to a traction battery charging method and apparatus. More particularly, but not exclusively, the method and apparatus are applicable in a range extended electric vehicle.

BACKGROUND A typical range extended electric vehicle (REEV) comprises an electrical traction motor and a range extender internal combustion engine. A traction battery is provided to power the electrical traction motor. The traction battery may also be used to power the starter-generator to start the range extender internal combustion engine. This is done as it is less costly to run the generator in reverse instead of using a separate motor and battery, such as a 12V battery. A problem then arises if the traction battery is flattened without the range extender running, for example due to storage or lack of fuel for the internal combustion engine. If there is no mains supply for a charger, the internal combustion engine cannot be started and the vehicle is disabled. To recover a vehicle from this situation, it would be necessary to apply an external charger or to over-discharge the battery.

It is against this backdrop that the present invention has been conceived. At least in certain embodiments, the present invention seeks to overcome the deficiencies associated with the prior art arrangements.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a vehicle having a controller for controlling charging of a traction battery; to a controller; and to a method as claimed in the appended claims.

According to a further aspect of the present invention there is provided a vehicle comprising: an electric traction machine; a traction battery for storing energy; an inverter for electrically connecting the electric traction machine to the traction battery; an internal combustion engine operable to charge the traction battery, the internal combustion engine having an electric starter motor which is selectively energized by the traction battery; and a controller comprising at least one processor and a memory device; the at least one processor being configured to control charging of the traction battery by the electric traction machine while an external driving force is applied to propel the vehicle; wherein the at least one processor is configured to control an electrical load on the electric traction machine in dependence on a determined vehicle speed. The electric traction machine is connected to the drive wheels of the vehicle. The internal combustion engine is a range extender unit which is operated to re-charge the traction battery and is not mechanically coupled to the drive wheels of the vehicle. Thus, applying an external drive force to propel the vehicle, for example by pushing or towing the vehicle, does not crank the internal combustion engine. It is, therefore, not possible to start the internal combustion engine by pushing or towing the vehicle. By controlling the electrical load applied to the electric traction machine, the input torque required to rotate the electric traction machine may be controlled. The external drive force required to propel the vehicle may thereby be controlled. The at least one processor may be configured to implement a regeneration start mode in which charging of the traction battery is controlled while an external driving force is applied to propel the vehicle.

The electric traction machine may comprise a permanent magnet (PM) motor, a reluctance motor or an induction motor.

The external driving force may comprise: a manually generated force applied by one or more individuals pushing or pulling the vehicle; and/or a gravitational force applied by the vehicle travelling down a hill; and/or a towing force applied by a tow vehicle.

The changes in the electrical load may be proportional to vehicle speed. The at least one processor may be configured to control the electrical load in proportion to the vehicle speed. The electrical load may be reduced or removed from the electric traction machine at low speeds or when the vehicle is stationary. Conversely, the electrical load may be increased as the vehicle speed increases.

The at least one processor may be configured to increase the electrical load in conjunction with an increase in the determined vehicle speed. The vehicle speed may be determined with reference to one or more wheel sensor. Alternatively, the vehicle speed may be determined in dependence on a measured rotational speed of the electric traction machine.

The at least one processor may be configured at least substantially to remove the electrical load on the electric traction machine when the determined vehicle speed is less than or equal to a first vehicle speed threshold. The charging of the traction battery may be inhibited below the first vehicle speed threshold. The first vehicle speed threshold may be predetermined.

The vehicle may comprise one or more contactor for connecting the electric traction machine to the traction battery. This arrangement may, for example, be implemented when the electric traction machine comprises a permanent magnet (PM) motor. The one or more contactor may electrically isolate the electric traction machine and/or the inverter when open. Conversely, the one or more contactor may electrically connect the electric traction machine and/or the inverter when closed. The one or more contactor may be incorporated into the electric traction machine. Alternatively, the one or more contactor may be separate from the inverter, either on a primary side or a secondary side of the inverter. The at least one processor may be configured to close the one or more contactor when the determined vehicle speed is greater than the first vehicle speed threshold and to open the one or more contactor when the determined vehicle speed is less than the first vehicle speed threshold. The controller may apply hysteresis to control operation of said one or more contactor. The hysteresis may be implemented to inhibit operation of the one or more contactor in dependence on relatively small changes in the determined vehicle speed. This may avoid a scenario in which the vehicle speed may fluctuate around the first vehicle speed threshold due to changes in the external drive force as said one or more contactor open and close.

The one or more contactor may be closed automatically when the determined vehicle speed exceeds the first vehicle speed threshold. Alternatively, or in addition, the one or more contactor may be closed in dependence on a driver prompt or request.

In certain embodiments the electric traction machine may comprise a reluctance motor or an induction motor. The at least one processor may be configured to control the inverter to vary the electrical load on the electric traction machine in dependence on the vehicle speed. When the vehicle speed is below the first threshold speed, the inverter may reduce the torque demand, for example the torque demand may be set to zero. The torque demand is increased when the vehicle speed is above the first threshold speed.

The controller may be configured to control the electric traction machine to provide regenerative braking in dependence on a brake request signal. The electrical load may be maintained on the electric traction machine if a brake request signal is received irrespective of the determined vehicle speed. Thus, the electrical load may be applied at speeds below the first vehicle speed threshold when the driver requests vehicle braking. The electric traction machine may thereby provide regenerative braking.

The at least one processor may be configured to increase the electrical load on the electric traction machine to perform fast re-charging of the traction battery when the determined vehicle speed is greater than or equal to a second vehicle speed threshold. The second vehicle speed threshold may be predetermined.

The at least one processor may be configured to increase the electrical load on the electric traction machine by performing a direct starting operation when the determined vehicle speed is greater than or equal to a third vehicle speed threshold.

The at least one processor may be configured to inhibit the supply of electrical energy from the traction battery to the electric traction machine.

The vehicle may comprise means for monitoring the traction battery. The at least one processor may be configured to output an engine start signal when the traction battery has sufficient energy to start the internal combustion engine. The engine start signal may be relayed to the driver, for example as an audible or visible notification. Alternatively, the engine start signal may be output to an electronic control unit for controlling operation of the internal combustion engine. The electronic control unit may be configured automatically to start the internal combustion engine in dependence on said engine start signal.

The at least one processor may be configured to control the electrical load in dependence on the determined vehicle speed only when the traction battery charge is below a predefined minimum operating threshold. The regeneration start mode may be inhibited about the minimum operating threshold. The minimum operating threshold could, for example, correspond to a predetermined charge level required to start the internal combustion engine.

According to a further aspect of the present invention there is provided a controller for use in a vehicle to control charging of a traction battery by an electric traction machine while an external driving force is applied to propel the vehicle; the controller comprising at least one processor and a memory device; the at least one processor being configured to control an electrical load on the electric traction machine in dependence on a determined vehicle speed. The controller may receive a vehicle speed signal, for example derived from one or more wheel speed sensors.

Alternatively, the vehicle speed may be determined in dependence on a rotational speed of the electric traction machine.

The at least one processor may be configured at least substantially to remove the electrical load on the electric traction machine when the determined vehicle speed is less than or equal to a first vehicle speed threshold.

The at least one processor may be configured to close one or more contactor when the determined vehicle speed is greater than the first vehicle speed threshold and to open the one or more contactor when the determined vehicle speed is less than the first vehicle speed threshold.

The at least one processor may be configured to control an inverter to vary the electrical load on the electric traction machine in dependence on the vehicle speed.

The controller may be configured to control an electric traction machine to provide regenerative braking in dependence on a brake request signal.

The at least one processor may be configured to increase the electrical load on the electric traction machine to perform faster re-charging of the traction battery when the determined vehicle speed is greater than or equal to a second vehicle speed threshold.

The at least one processor may be configured to output an engine start signal when the traction battery has sufficient energy to start the internal combustion engine.

According to a still further aspect of the present invention there is provided a method of controlling charging of a traction battery by an electric traction machine while an external driving force is applied to propel a vehicle; the method comprising controlling an electrical load on the electric traction machine in dependence on a determined vehicle speed.

The method may comprise removing the electrical load from the electric traction machine when the determined vehicle speed is less than or equal to a first vehicle speed threshold.

The method may comprise connecting the electrical load to the electric traction machine when the determined vehicle speed is greater than the first vehicle speed threshold; and disconnecting the electrical load from the electric traction machine when the determined vehicle speed is less than the first vehicle speed threshold.

The method may comprise providing regenerative braking in dependence on a brake request signal.

The method may comprise increasing the electrical load on the electric traction machine to perform faster re-charging of the traction battery when the determined vehicle speed is greater than or equal to a second vehicle speed threshold.

The method may comprise increasing the electrical load on the electric traction machine by performing a direct starting operation when the determined vehicle speed is greater than or equal to a third vehicle speed threshold.

The method may comprise comprising inhibiting the supply of electrical energy from the traction battery to the electric traction machine.

The method may comprise starting an internal combustion engine when the traction battery has sufficient energy.

Any controller or controllers described herein may suitably comprise a control unit or computational device having one or more electronic processors. Thus the system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term “controller ” or “control unit” will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide any stated control functionality. To configure a controller, a suitable set of instructions may be provided which, when executed, cause said control unit or computational device to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said controller to be executed on said computational device. A first controller may be implemented in software run on one or more processors. One or more other controllers may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller. Other suitable arrangements may also be used.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment may be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

Figure 1 shows a schematic representation of a vehicle incorporating a controller for controlling charging of a traction battery in accordance with an aspect of the present invention; and

Figure 2 shows a graph representing the electrical loads applied to the electric traction machine during charging.

DETAILED DESCRIPTION A vehicle 1 in accordance with an embodiment of the present invention will now be described with reference to Figures 1 and 2.

As shown in Figure 1, the vehicle 1 comprises an electric traction machine 2 and an internal combustion engine 3. The electric traction machine 2 comprises a rotor 4 and a stator 5. In the present embodiment the electric traction machine 2 comprises a permanent magnet (PM) motor. In alternate embodiments the electric traction machine 2 may comprise a reluctance motor or an induction motor. The electric traction machine 2 is connected to the vehicle powertrain and, in use, delivers a traction force to a pair of drive wheels WD for propelling the vehicle 1. The electric traction machine 2 is connected to a traction battery 6 comprising a plurality of battery cells 7. In a variant, the vehicle 1 may comprise more than one electric traction machine 2. The internal combustion engine 3 is a range extender unit and is not drivingly connected to the vehicle drivetrain. The internal combustion engine 3 does not output a traction force to the drive wheels WD of the vehicle 1. Rather, the internal combustion engine 3 is drivingly connected to an electric starter-generator 8 by a continuous drive belt 9. An electronic control unit 10 is provided to control operation of the internal combustion engine 3. When running, the internal combustion engine 3 outputs an input torque which rotates the starter-generator 8 and generates an electric current for charging the traction battery 6. The starter-generator 8 is also operable to apply a cranking torque to start the internal combustion engine 3. An electric current is supplied to the starter-generator 8 from the traction battery 6 to start the internal combustion engine 3 in conventional manner. The starter-generator 8 may have a wired connection to the traction battery 6. However, the starter-generator 8 may operate at a lower voltage than the traction battery 6, so there may be an inverter to supply electrical energy from the traction battery 6 to the starter-generator 8 when starting the internal combustion engine 3.

An inverter 11 is connected to the traction battery 6 to supply electrical energy to the electric traction machine 2 for propulsion. The inverter 11 may be an inverter/converter which is operable also to change the voltage of the power source. A controller 12 is provided to control operation of the inverter 11. The controller 12 comprises at least one electronic processor 13 and a memory device 14. The electronic processor 13 is configured to execute a set of non-transient computational instructions stored on the memory device 14. The inverter 11 converts direct current (DC) from the traction battery 6 to alternating current (AC) to power the electric traction machine 2. The inverter 11 comprises one or more contactor 15 (or one or more switch/relay) operable to electrically isolate the electric traction machine 2 from the traction battery 6. An electromagnet (not shown) may be provided for opening and closing the contactor 15. When the electric traction machine 2 is operating as a generator, the input torque required to rotate the rotor 4 is dependent on the electrical load applied to the electric traction machine 2. The contactor 15 may be operated to change the electrical load. In particular, the contactor 15 is opened to remove the electrical load from the electric traction machine 2; and closed to apply the electrical load to the electric traction machine 2. The inverter 11 may be configured to provide additional control of the electrical load. As outlined above, the electric traction machine 2 may comprise a reluctance motor or an induction motor. In these arrangements, the contactor 15 may be omitted and the controller 12 configured to control the inverter 11 to modify the electrical load applied to the electric traction machine 2.

In the event that the traction battery 6 is discharged, the internal combustion engine 3 cannot readily be re-started. Although there is typically sufficient power available to control the inverter 11, there may not be enough power to energise the starter-generator 8 and crank the internal combustion engine 3. To overcome this problem, the controller 12 is configured to control operation of the inverter 11 to implement a regeneration start mode. When operating in the regeneration start mode, the controller 12 configures the electric traction machine 2 to operate as a generator suitable for generating an electrical current to charge the traction battery 6. The controller 12 also controls the electrical load applied to the electric traction machine 2 in dependence on vehicle speed Vs, as determined by one or more speed sensor 16 in conventional manner. The controller 12 controls operation of the one or more contactor 15 to control the electrical load applied to the electric traction machine 2 in dependence on the vehicle speed Vs. In embodiments comprising a reluctance motor or an induction motor, the controller 12 is configured to control the inverter 11 to modify the electrical load in dependence on the determined vehicle speed Vs. The electrical load is controlled in direct proportion to the vehicle speed Vs such that a higher electrical load is applied at higher vehicle speed Vs. By controlling the electrical load, the input torque required to rotate the rotor may be adjusted to enable the vehicle 1 to be propelled by an external driving force. The external driving force can, for example, be applied by one or more individuals manually pushing the vehicle 1, referred to herein as a push start; or by towing the vehicle 1 behind another vehicle (not shown), referred to herein as a tow start. The controller 12 is configured to activate the regeneration start mode to charge the traction battery 6 when the external driving force is applied. In the present embodiment, the regeneration start mode is configured to charge the traction battery 6 in either a tow start mode or a push start mode. A user can specify whether a push start or a tow start will be performed on the vehicle 1 and the controller 12 activates the corresponding mode to control application of the electrical load to the electric traction machine 2. In other embodiments, the controller 12 may be configured to implement a combined mode which is performed irrespective of whether a tow start or a push start is implemented. In a further embodiment, the controller 12 may be configured to modify the electrical load so as to transition from a push start mode to a tow start mode in dependence on vehicle speed Vs.

As the vehicle 1 is propelled by the external driving force, the drive wheels WD apply an input torque to the rotor 4. The controller 12 is configured to control the inverter 11 to remove the electrical load from the electric traction machine 2 when the vehicle speed Vs is below a predefined threshold speed. As outlined above, the regeneration start mode comprises a tow start mode and a push start mode. The operation of the controller 12 in each of these modes will now be described.

When the push start mode is selected, the controller 12 is configured to control the inverter 11 to remove the electrical load from the electric traction machine 2 when the vehicle speed Vs is below a first threshold speed VSTi, for example 2 km/h. In the present embodiment in which the electric traction machine 2 comprises a permanent magnet (PM) motor, the controller 12 controls the inverter 11 to open said one or more contactor 15 when the vehicle speed Vs is below the first threshold speed VSn. In the case of a switched reluctance motor or an induction motor, the controller 12 would be configured to control the inverter 11 to set the torque demand to zero when the vehicle speed Vs is below the first threshold speed VSti- In the absence of an electrical load, the electric traction machine 2 does not generate a regeneration current. When the vehicle speed Vs increases above the first threshold speed VSTi, the controller 12 controls the inverter 11 to close the one or more contactor 15 thereby connecting the traction battery 6 to the electric traction machine 2. A first electrical load is thereby applied to the electric traction machine 2. The first electrical load may increase progressively, for example in conjunction with vehicle speed Vs, to a first maximum load value such that a first maximum input torque required to rotate the rotor 4 remains substantially uniform above a predetermined vehicle speed Vs. The first maximum input torque (Nm) may, for example, be reached when the vehicle speed Vs is approximately 10km/h.

When the tow start mode is selected, the controller 12 is configured to control the inverter 11 to remove the electrical load from the electric traction machine 2 when the vehicle speed Vs is below a second threshold speed VST2, for example 10 km/h. The second threshold speed VST2 is higher than the first threshold speed VSn and is intended to be applied when the vehicle 1 is being towed, for example by another vehicle. The controller 12 controls the inverter 11 to open said one or more contactor 15 when the vehicle speed Vs is below the second threshold speed VSt2· In the absence of an electrical load, the electric traction machine 2 does not generate a regeneration current. When the vehicle speed Vs increases above the second threshold speed VSt2, the controller 12 controls the inverter 11 to close the one or more contactor 15 thereby connecting the traction battery 6 to the electric traction machine 2. A second electrical load is thereby applied to the electric traction machine 2. The second electrical load may increase progressively, for example in conjunction with vehicle speed Vs, to a second maximum load value such that a second maximum input torque required to rotate the rotor 4 remains substantially uniform above a predetermined vehicle speed Vs. The second maximum input torque (Nm) may, for example, be reached when the vehicle speed Vs is approximately 40km/h. The second maximum load value may be greater than the first maximum load value.

When the electrical load is applied to the electric traction machine 2, the rotation of the rotor 4 generates a regeneration current which re-charges the traction battery 6. The electric traction machine 2 operates as a generator to re-charge the traction battery 6. The application of an electrical load to the electric traction machine 2 allows an increase in the input torque (Nm) required to rotate the rotor 4. In the case of a reluctance motor or an induction motor, the value of the input torque (Nm) required to rotate the rotor 4 may be set by the inverter 11. Since the vehicle 1 is moving when the electrical load is applied, the vehicle 1 may continue to be propelled by the external driving force while charging the traction battery 6.

An input torque (Nm) required to rotate the rotor 4 and the regeneration current (Amperes) generated by the electric traction machine 2 are illustrated with reference to the vehicle speed Vs in a graph 100 shown in Figure 2. The input torque and the regeneration current for a push start are represented by first and second plots 101, 102 respectively; and the input torque and the regeneration current for a tow start are represented by third and fourth plots 103, 104 respectively. When the one or more contactor 15 is open, or in the case of a nonpermanent magnet (PM) motor the torque demand is set to zero, there is no electrical load on the electric traction machine 2, so the input torque (Nm) and the regeneration current are substantially zero. This facilitates pushing or towing of the vehicle 1 since it can accelerate from rest with relative ease. When the push start mode is selected, the controller 12 determines that the vehicle speed Vs is greater than or equal to the first threshold speed VSti, the one or more contactor 15 is closed and an electrical load is applied to the electric traction machine 2. When the tow start mode is selected, the controller 12 determines that the vehicle speed Vs is greater than or equal to the second threshold speed VST2, the one or more contactor 15 is closed and an electrical load is applied to the electric traction machine 2. The input torque (Nm) and the regeneration current thereafter increase in proportion to the vehicle speed Vs. The input torque (Nm) increases rapidly to improve low speed regeneration of energy. The input torque (Nm) is limited to facilitate acceleration of the vehicle 1 when it is being pushed or towed. The maximum input torque (Nm) may, for example, be reached when the vehicle speed Vs is approximately 10km/h. The maximum regeneration current may, for example, be reached when the speed Vs is approximately 40km/h. It will be appreciated that the graph 100 is provided by way of example only to illustrate operation of one embodiment of the present invention.

The first threshold speed VSti may be predefined as a relatively low value to enable the vehicle 1 to be manually pushed by one or more individuals (a push start). The controller 12 may optionally be configured to vary the electrical load in dependence on one or more additional threshold speed VSt- An alternate charging strategy, for example a fast-charge strategy, could be implemented when the vehicle speed Vs is greater than or equal to the second threshold speed VST2- It will be understood that a third threshold speed (not shown) could also be defined with a corresponding third electrical load applied when the vehicle speed Vs exceeds the third threshold speed. The third threshold speed may be higher than the second threshold speed VST2. The third threshold speed can, for example, be 30 km/h.

The vehicle 1 may comprise means for monitoring the charge of the traction battery 6. For example, a sensor 17 may be provided to measure a current/voltage of the traction battery 6. The sensor 17 may output a measurement signal S1 to the controller 12 to enable estimation of a charge level of the traction battery 6, for example to estimate a state of charge (SOH). When the controller 12 determines that the traction battery 6 has sufficient charge to start the internal combustion engine 3, an engine start signal S2 may be output. The engine start signal S2 may be output to a driver of the vehicle 1, for example in the form of a visual or audio prompt. Alternatively, the engine start signal S2 may be output to the electronic control unit 10 to affect an automated start-up of the internal combustion engine 3.

The controller 12 is operable to implement the regeneration start mode, for example in dependence on a user prompt. In use, the user activates the regeneration start mode. With the regeneration start mode activated, the controller 12 may increase low speed regeneration to enable charging of the traction battery 6 more quickly when the vehicle 1 is being towed. In certain instances this may remove the need for towing the vehicle 1 at high speed. The controller 12 configures the inverter 11 and the electric traction machine 2 to operate in a regenerative mode to re-charge the traction battery 6. The controller 12 configures the inverter 11 to inhibit any drive operation when the regeneration start mode is implemented (and also to avoid the risk of over-discharge of the traction battery 6). The vehicle 1 may be pushed or towed to provide regenerative power to re-charge the traction battery 6 to a sufficient level to allow the internal combustion engine 3 to be started. The internal combustion engine 3 may thereafter be used to re-charge the traction battery 6 in conventional manner.

Additionally, the regeneration and speed characteristic may be optimised depending on whether the vehicle is being push-started (i.e. manually pushed by one or more individuals) or tow started by another vehicle. For example, if push starting, it is desirable to inhibit recharging of the traction battery 6 until the vehicle speed Vs is greater than the first threshold speed VSn, for example 2 km/h, to facilitate accelerating the vehicle 1 from rest. If the vehicle 1 will be towed by another vehicle, the regeneration could be performed at a higher level and may also increase rapidly, for example when the vehicle speed Vs is greater than the second threshold speed VST2, for example 10 km/h, to enable fast re-charging or a direct starting operation at a moderate speed.

The controller 12 may be configured to determine when the traction battery 6 has a minimum energy required to start the internal combustion engine 3. The controller 12 may indicate to the driver when sufficient energy has been accumulated. The driver may then stop the vehicle 1 and start the internal combustion engine 3; or the controller 12 may automatically start the internal combustion engine.

If the battery is at 0% charge, it will usually be able to provide the required voltage to run the inverter 11 and to enable regeneration to recharge the traction battery 6. However, it may not be appropriate to take any significant charge while waiting for the regeneration to being when an external driving force is applied to propel the vehicle. When the regeneration start mode is implemented, the controller 12 may inhibit closing of the one or more contactor 15 until movement is detected or a prompt is received from the driver.

As outlined above, the first threshold speed VSTi is predefined in the present embodiment. In a variant, the first threshold speed VSn could be adjusted manually, for example to increase/decrease the first threshold speed Vsn· The controller 12 could be configured to control the electrical load to control the vehicle speed Vs, for example to maintain a substantially constant vehicle speed Vs if the vehicle 1 is travelling down a gradient. When operating in said regeneration start mode, the controller 12 could optionally also be configured to control the electrical load applied to the electric traction machine 2 to perform regenerative braking, for example in dependence on a braking signal. In a further variant, a user could select when to apply and/or to remove the electrical load to the electric traction machine 2.

The electronic processor 13 may be configured to increase the electrical load on the electric traction machine by performing a direct starting operation when the determined vehicle speed Vs is greater than or equal to a fourth vehicle speed threshold VST4-

Claims

CLAIMS:

1. A vehicle comprising: an electric traction machine; a traction battery for storing energy; an inverter for electrically connecting the electric traction machine to the traction battery; an internal combustion engine operable to charge the traction battery, the internal combustion engine having an electric starter motor which is selectively energized by the traction battery; and a controller comprising at least one processor and a memory device; the at least one processor being configured to control charging of the traction battery by the electric traction machine while an external driving force is applied to propel the vehicle; wherein the at least one processor is configured to control an electrical load on the electric traction machine in dependence on a determined vehicle speed (Vs).

2. A vehicle as claimed in claim 1, wherein the at least one processor is configured to control the electrical load in proportion to the vehicle speed (Vs).

3. A vehicle as claimed in claim 2, wherein the at least one processor is configured to increase the electrical load in conjunction with an increase in the determined vehicle speed (Vs).

4. A vehicle as claimed in any one of claims 1, 2 or 3, wherein the at least one processor is configured at least substantially to remove the electrical load on the electric traction machine when the determined vehicle speed (Vs) is less than or equal to a first vehicle speed threshold (VST1).

5. A vehicle as claimed in claim 4 comprising one or more contactor for connecting the electric traction machine to the traction battery, the at least one processor being configured to close the one or more contactor when the determined vehicle speed (Vs) is greater than the first vehicle speed threshold (VST1) and to open the one or more contactor when the determined vehicle speed is less than the first vehicle speed threshold (VSn).

6. A vehicle as claimed in any one of claims 1 to 4, wherein the at least one processor is configured to control the inverter to vary the electrical load on the electric traction machine in dependence on the vehicle speed (Vs).

7. A vehicle as claimed in any one of the preceding claims, wherein the at least one processor is configured to increase the electrical load on the electric traction machine to perform fast re-charging of the traction battery when the determined vehicle speed (Vs) is greater than or equal to a second vehicle speed threshold (VST2)·

8. A vehicle as claimed in any one of the preceding claims, wherein the at least one processor is configured to increase the electrical load on the electric traction machine by performing a direct starting operation when the determined vehicle speed (Vs) is greater than or equal to a third vehicle speed threshold (VST3).

9. A vehicle as claimed in any one of the preceding claims, wherein the at least one processor is configured to inhibit the supply of electrical energy from the traction battery to the electric traction machine.

10. A vehicle as claimed in any one of the preceding claims comprising means for monitoring the traction battery, wherein the at least one processor is configured to output an engine start signal when the traction battery has sufficient energy to start the internal combustion engine.

11. A vehicle as claimed in claim 10 comprising an electronic control unit for controlling operation of the internal combustion engine, wherein an electronic control unit is configured automatically to start the internal combustion engine in dependence on said engine start signal.

12. A controller for use in a vehicle to control charging of a traction battery by an electric traction machine while an external driving force is applied to propel the vehicle; the controller comprising at least one processor and a memory device; the at least one processor being configured to control an electrical load on the electric traction machine in dependence on a determined vehicle speed (Vs).

13. A controller as claimed in claim 12, wherein the at least one processor is configured at least substantially to remove the electrical load on the electric traction machine when the determined vehicle speed is less than or equal to a first vehicle speed threshold (VST1).

14. A controller as claimed in claim 13, wherein the at least one processor is configured to close one or more contactor when the determined vehicle speed (Vs) is greater than the first vehicle speed threshold (VSn) and to open the one or more contactor when the determined vehicle speed is less than the first vehicle speed threshold (VSt2).

15. A vehicle as claimed in claim 12 or claim 13, wherein the at least one processor is configured to control an inverter to vary the electrical load on the electric traction machine in dependence on the vehicle speed (Vs).

16. A controller as claimed in any one of claims 12 to 15, wherein the at least one processor is configured to increase the electrical load on the electric traction machine to perform faster re-charging of the traction battery when the determined vehicle speed (Vs) is greater than or equal to a second vehicle speed threshold (VSti)-

17. A controller as claimed in any one of claims 12 to 16, wherein the at least one processor is configured to increase the electrical load on the electric traction machine by performing a direct starting operation when the determined vehicle speed (Vs) is greater than or equal to a third vehicle speed threshold (VST1).

18. A controller as claimed in any one of claims 12 to 17, wherein the at least one processor is configured to inhibit the supply of electrical energy from the traction battery to the electric traction machine.

19. A controller as claimed in any one of claims 12 to 18, wherein the at least one processor is configured to output an engine start signal when the traction battery has sufficient energy to start the internal combustion engine.

20. A method of controlling charging of a traction battery by an electric traction machine while an external driving force is applied to propel a vehicle; the method comprising controlling an electrical load on the electric traction machine in dependence on a determined vehicle speed (Vs).

21. A method as claimed in claim 20 comprising removing the electrical load from the electric traction machine when the determined vehicle speed (Vs) is less than or equal to a first vehicle speed threshold (VST1).

22. A method as claimed in claim 21 comprising connecting the electrical load to the electric traction machine when the determined vehicle speed (Vs) is greater than the first vehicle speed threshold (VSn); and disconnecting the electrical load from the electric traction machine when the determined vehicle speed (Vs) is less than the first vehicle speed threshold (VSn).

23. A method as claimed in any one of claims 20, 21 or 22 comprising providing regenerative braking in dependence on a brake request signal.

24. A method as claimed in any one of claims 20 to 23 comprising increasing the electrical load on the electric traction machine to perform faster re-charging of the traction battery when the determined vehicle speed (Vs) is greater than or equal to a second vehicle speed threshold (VST2).

25. A method as claimed in any one of claims 20 to 24 comprising increasing the electrical load on the electric traction machine by performing a direct starting operation when the determined vehicle speed (Vs) is greater than or equal to a third vehicle speed threshold (VsT3)·

26. A method as claimed in any one of claims 20 to 25 comprising inhibiting the supply of electrical energy from the traction battery to the electric traction machine.

27. A method as claimed in any one of claims 20 to 26 comprising starting an internal combustion engine when the traction battery has sufficient energy.

28. A vehicle substantially as herein described with reference to the accompanying figures.

29. A controller substantially as herein described with reference to the accompanying figures.

30. A method substantially as herein described with reference to the accompanying figures.