GB2502804A

GB2502804A - A controller that reduces NVH in a hybrid vehicle

Info

Publication number: GB2502804A
Application number: GB1210068.1A
Authority: GB
Inventors: Martin Ranson
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2012-06-07
Filing date: 2012-06-07
Publication date: 2013-12-11
Also published as: GB2504821B; GB2504821A; GB201210068D0; GB201310156D0; WO2013182694A1

Abstract

A controller 140 operates a powertrain of a hybrid vehicle 100 so as to avoid one or more undesirable combinations of values of generator 123 torque load, driveline speed parameter and driveline ratio parameter. The driveline speed corresponds to a speed Wtx of an output portion 124S of a transmission 124 and the driveline ratio parameter corresponds to a gear ratio TG selected in the transmission 124. Controller 123 uses Wtx and TG in a look-up table to produce an upper limit of allowable CIMG 123 charging torque TQ(maxcharge). If CIMG 123 torque exceeds TQ(maxcharge) the controller 140 commands the CIMG 123 to deliver a value of torque corresponding to TQ(maxcharge). In some embodiments the controller 140 is configured to force the transmission 124 to change gear whenever a value of CIMG 123 torque exceeds or is at risk of exceeding TQ(maxcharge). Reference is also made to a method of controlling a hybrid vehicle and to a hybrid vehicle.

Description

HYBRID ELECTRIC VEHICLE LOAD ADJUSTMENT

FIELD OF THE INVENTION

The present invention relates to a controller for a hybrid electric vehicle and to a method of control of a hybrid vehicle. In particular but not exclusively the invention relates to a controller adapted to reduce noise, vibration and/or harshness (NVH) in a hybrid vehicle.

BACKGROUND

It is known to provide a hybrid electric vehicle having an electric machine operable to provide propulsion for the vehicle fuel burning actuator operable to power a generator for recharging a battery of the vehicle. In some vehicles such as parallel hybrid vehicles the fuel burning actuator is also operable to deliver motive torque to wheels of the vehicle.

STATEMENT OF THE INVENTION

Embodiments of the invention may be understood by reference to the appended claims.

Aspects of the invention provide control means, a hybrid electric vehicle and a method.

In a further aspect of the invention for which protection is sought there is provided control means for a hybrid electric vehicle operable to control a powertrain of the vehicle to avoid operation of the vehicle at a prescribed one or more undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter, wherein the driveline speed parameter corresponds to a speed of an output portion of a transmission of the vehicle and the driveline ratio parameter corresponds to a gear ratio between an output portion of the engine and one or more driven wheels of the vehicle.

The term control means" is to be interpreted herein as including, without limitation, a controller, such as an electronic controller.

Embodiments of the invention have the advantage that vehicle noise, vibration and harshness (NVH) associated with operation of a hybrid electric vehicle in a particular mode or configuration (such as operation in a parallel recharge mode) at a particular vehicle speed and with the transmission operating in a particular gear can be substantially reduced or eliminated by controlling the vehicle to avoid operation at the prescribed one or more undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter. It is to be understood that vibrations may be induced in a vehicle due to oscillations induced in a driveline corresponding to a natural frequency of oscillation under certain combinations of driveline ratio parameter, driveline speed parameter and generator torque load. Under a given set of vehicle operating conditions (e.g. driveline ratio parameter and driveline speed parameter), a change in the generator torque load can be sufficient to cause such vibrations to be induced. It is to be understood that the value of generator torque loading may in some embodiments affect the value of the natural frequency of the driveline, with the risk that a particular value or range of values of generator torque loading applied to the driveline may shift the natural frequency of the driveline such that the driveline is excited at its natural frequency or a harmonic thereof, resulting in increased vehicle NVH.

In some embodiments the driveline speed parameter may be selected to be the speed of any portion of the driveline that is in a substantially fixed ratio with respect to the output of the transmission, independently of the selected gear ratio of the transmission. Thus in some embodiments the selected portion of the driveline may be an output shaft of the transmission. The output speed of the transmission is typically in a substantially fixed ratio with respect to that of one or more wheels of the vehicle. In some embodiments the driveline speed may be determined by reference to an engine speed and the value of driveline ratio parameter.

Advantageously the control means may be operable to command a change to the driveline ratio parameter responsive to values of generator torque load, driveline speed parameter and driveline ratio parameter thereby to avoid operation at the prescribed undesirable combinations of values of generator torque, driveline speed parameter and driveline ratio parameter.

For example the control means may be operable to command a change to the driveline ratio parameter by commanding the transmission to change a gear ratio between an input shaft thereof and an output shaft thereof.

The control means may be operable to command an increase in a driveline ratio parameter responsive to values of generator torque load, driveline speed parameter and driveline ratio parameter.

The increase may correspond to a downshift' in gear whereby a gear number is decreased in order to increase the driveline ratio parameter, for example a shift from second gear to first gear in the case of a transmission having substantially fixed gear ratios.

Alternatively or in addition the control means may be operable to command a decrease in a driveline ratio parameter responsive to values of generator torque load, driveline speed parameter and driveline ratio parameter.

The decrease may correspond to an upshift' whereby a gear number is increased to decrease the driveline ratio parameter, for example a shift from second gear to third gear.

The control means may be provided with data indicating whether an upshift or downshift should be commanded for each of the one or more undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter for which a gear shift is required.

The control means may be operable prior to commanding a change in driveline ratio parameter to determine a future value of each of a driveline speed parameter, driveline ratio parameter and generator torque load that would be assumed by the vehicle following the commanded change, the control means being configured to determine whether to command a given change in driveline ratio responsive to a determination whether the future values correspond to one of said one or more undesirable combinations of values.

Optionally the control means may be operable to command a change to an amount of generator torque load imposed on the engine by the generator means thereby to avoid operation at one of the one or more undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter.

The control means may be operable to command a decrease in generator torque loading responsive to values of generator torque load, driveline speed parameter and driveline ratio parameter thereby to avoid operation at one of the one or more undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter.

Alternatively or in addition the control means is operable to command an increase in generator torque loading responsive to values of generator torque load, driveline speed parameter and driveline ratio parameter thereby to avoid operation at one of the one or more undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter.

The control means may be operable to determine in advance a future value of driveline speed parameter, driveline ratio parameter and generator torque that would be assumed by the vehicle following a given change in generator torque load, the control means being configured to determine whether to command a given change in generator torque load responsive to a determination whether the future values correspond to one of said prescribed undesirable combinations of values of generator torque, driveline speed parameter and driveline ratio parameter.

The control means may be operable to determine the prescribed undesirable conibinations of values of generator torque load, driveline speed parameter and driveline ratio parameter by reference to a database.

The control means may for example be configured to consult a database configured as a look-up table. Other arrangements are also useful.

The control means may be configured to limit a value of generator toique load imposed on the engine by the generator means such that it does not exceed a prescribed limit value, the limit value being responsive to values of driveline speed parameter and driveline ratio parameter, thereby to reduce vehicle noise, vibration and harshness (NVH).

The control means may be configured to limit a value of generator torque load imposed on the engine by the generator means such that it does not exceed a prescribed limit value, the limit value being responsive to values of driveline speed parameter and driveline ratio parameter, thereby to avoid operation at the prescribed one or more undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter.

The control means may be operable to determine the limit value of generator torque load by reference to a database.

The control means may be operable to control a vehicle to deliver torque to a driveline of a vehicle by means of the engine.

Thus a hybrid vehicle may be operable in a parallel mode.

The control means may be operable to command a hybrid vehicle to drive propulsion motor means thereof.

In one aspect of the invention for which protection is sought there is provided a hybrid electric vehicle comprising an engine, generator means, propulsion motor means, a transmission and control means as claimed in any preceding claim.

Optionally at least one of the generator means and motor means is operable to be coupled in a flowpath of power between the transmission and the engine.

The generator means and motor means may be provided by the same electric machine.

Optionally the motor means and generator means are provided by a crank integrated motor generator (dM3).

At least one of the generator means and motor means may be provided between the transmission and one or more wheels of the vehicle.

Optionally at least one of the motor means and generator means is provided by an electric axle drive unit comprising an electric machine arranged to drive an axle of the vehicle.

The axle drive unit may be operable in a generator mode in which an axle of the vehicle may drive the electric machine as a generator, for example in order to provide regenerative braking functionality. In addition or instead the axle drive unit may be operable in a propulsion motor mode in which the axle is arranged to be driven by the propulsion motor.

The axle may be any suitable axle of a vehicle such as a front axle, mid-vehicle axle, rear axle or an axle provided at any suitable position.

Optionally the motor means is provided by an electric rear axle drive unit.

In a further aspect of the invention for which protection is sought there is provided a method of controlling by control means a hybrid electric vehicle having an engine for powering a generator for generating electrical power for driving the vehicle, the method comprising: controlling a powertrain of the vehicle to avoid operation of the vehicle at prescribed undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter, whereby the driveline speed parameter corresponds to a speed of an output portion of a transmission and the driveline ratio parameter corresponds to a gear ratio between the engine and one or more driven wheels of the vehicle.

The method may comprise the step of monitoring the driveline speed parameter and driveline ratio parameter.

In an aspect of the invention for which protection is sought there is provided a method of controlling by control means a hybrid electric vehicle having an engine for powering a generator for generating electrical power for driving the vehicle, the method comprising: monitoring a driveline speed parameter corresponding to a speed of an output portion of a transmission and a driveline ratio parameter corresponding to a gear ratio between the engine and one or more driven wheels of the vehicle; controlling a powertrain of the vehicle to avoid operation of the vehicle at prescribed undesirable combinations of values of generator torque load as a function of driveline speed parameter and driveline ratio parameter.

In one aspect of the invention there is provided control means for a hybrid electric vehicle operable to control an amount of generator torque load imposed on an engine of the vehicle by generator means, the control means being configured to control a powertrain of the vehicle to avoid operation of the vehicle at a prescribed one or more undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter, where the driveline speed parameter corresponds to a speed of an output portion of a transmission of the vehicle and the driveline ratio parameter corresponds to a gear ratio between an output portion of the engine and one or more driven wheels of the vehicle thereby to reduce vehicle noise, vibration and harshness (NVH).

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. For example, features described with reference to one embodiment are applicable to all embodiments, unless such features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-FIGURE 1 is a schematic illustration of a hybrid electric vehicle according to an embodiment of the present invention; FIGURE 2 shows an example of a look-up table that may be used in an embodiment of the invention; FIGURE 3 is a function block diagram illustrating how a controller according to an embodiment of the invention determines a required gear to be selected by a transmission; and FIGURE 4 shows an example of a look-up table that may be used in a further embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a hybrid electric vehicle (HEV) 100 according to an embodiment of the present invention. The vehicle 100 has an internal combustion engine 121 releasably coupled to a crankshaft integrated motor/generator (CIMG) 123 by means of a clutch 122. The CIMG 123 is in turn coupled to an automatic transmission 124 which forms part of a driveline 130 of the vehicle 100. The vehicle 100 is operable to provide drive torque to the transmission 124 by means of the engine 121 alone, the CIMG 123 alone or the engine 121 and CIMG 123 in parallel.

It is to be understood that in some embodiments the transmission 124 may be a manual transmission instead of an automatic transmission. The transmission may comprise a manual gearbox, a continually variable transmission or any other suitable transmission.

It is to be understood that embodiments of the present invention are suitable for use with vehicles in which the transmission 124 is arranged to drive only a pair of front wheels 111, 112 or only a pair of rear wheels 114, 115, i.e. front wheel drive or rear wheel drive vehicles in addition to all wheel drive or selectable two wheel drive/four wheel drive vehicles.

Embodiments of the invention are also suitable for vehicles having less than four wheels or more than four wheels.

The vehicle 100 has a battery 150 connected to an inverter 151 that generates a three-phase electrical supply that is supplied to the 01MG 123 when the 01MG 123 is operated as a motor. The battery 150 is arranged to receive charge from the 01MG 123 when the 01MG 123 is operated as a generator.

The vehicle 100 is configured to operate in one of (1) a hybrid electric vehicle (HEV) mode, (2) a HEV inhibit mode in which hybrid functionality is suspended and the engine 121 alone drives the vehicle 100 and (3) a driver selectable electric vehicle only (EV-only) mode according to the state of a driver operable HEV mode selector switch 169.

In the HEV mode of operation the vehicle 100 is arranged to operate in one of a parallel boost mode, a parallel recharge mode, a parallel idle mode and a vehicle-selected EV mode.

In the parallel boost mode the engine 121 and 01MG 123 are both arranged to apply positive torque to the transmission 124 (i.e. clutch 122 is closed) to drive the vehicle 100. In the parallel recharge mode the engine 121 applies a positive torque whilst the 01MG 123 applies a negative torque whereby charge is generated by the 01MG 123 to charge the battery 150.

In the parallel idle mode the engine 121 applies a positive torque whilst the 01MG 123 applies substantially no torque. In the vehicle-selected EV mode (and in the driver selected EV-only mode) the clutch 122 is opened and the engine 121 is switched off. The 01MG 123 alone provided torque to drive the vehicle.

The vehicle has a controller 140 configured to control the vehicle 100 to operate in the parallel boost mode, parallel recharge mode or EV mode according to an energy management strategy implemented by the controller 140. The energy management strategy may also be referred to as a HEV control methodology.

It is to be understood that when in HEV mode the controller 140 is configured to determine a target torque that is to be developed by each of the engine 121 and 01MG 123 and to control the engine 121 and 01MG 123 to apply the respective target torques to an input shaft of the transmission 124. For example, if the controller 140 determines that operation in vehicle-selected EV mode is required, the controller 140 may set the target torque from the engine 121 to zero and provide a control signal to switch off the engine 121. If the controller determines that both the engine 121 and CIMG 123 are required to apply positive torque to the driveline 130 the controller 140 may control the engine 121 and CIMO 123 to provide the required respective torque values. If the controller 140 determines that the battery 150 is required to be charged, the 01MG 123 is controlled to apply a prescribed negative torque to the driveline 130 whereby the 01MG 123 acts as a generator to generate charge to charge the battery 150.

It is to be understood that other arrangements are also useful.

lithe driver selects operation of the vehicle 100 in EV-only mode and the engine 121 is running, the vehicle 100 is configured to open the clutch 122 and to switch off the engine 121. Again, the CIMO 123 is then operated either as a motor or as a generator. I! is to be understood that the CIMG 123 may be arranged to act as a generator in the EV-only mode in order to effect regenerative braking of the vehicle 100.

The controller 140 is arranged to monitor a speed of rotation Wtx of an output shaft 1 24S of the transmission 124, and an amount of charging torque TQ(charge) demanded by the CIMO 123 from the engine 121. That is, the torque loading placed on the engine 121 by the CIMG 123.

The controller 140 is provided with a database storing data corresponding to a maximum amount of charging torque TQ(maxcharge) permitted for prescribed values of Wtx for each gear TG in which the transmission 124 may operate. The values of TO(maxcharge) are selected so as to avoid operation of the vehicle 100 under conditions in which excessive NVH is suffered.

The controller 140 is operable repeatedly to determine the value of TQ(maxcharge) as the vehicle 100 is operated. In addition, as described above, the controller 140 determines a target value of torque to be delivered by the CIMG 123 at a given moment in time according to the HEV control methodology implemented by the controller 140.

If the controller 140 determines that it is desirable to operate the CIMO 123 as a generator and that the target value of 01MG torque does not exceed TQ(maxcharge), the controller 140 commands the CIMG 123 to deliver the desired target torque. However if the controller determines that the target value of 01MG torque exceeds TQ(maxcharge), the controller commands the 01MG 123 to deliver a value of torque corresponding to TQ(maxcharge); thus the value of TQ(maxcharge) represents an upper limit of allowable CIMG charging torque under the prevailing vehicle operating conditions.

FIG. 2 shows a table representing a portion of data stored in a database accessible to the controller 140. The data represents values of TQ(maxcharge) as a function of transmission output speed Wtx and current value of selected gear TG. The values are stored by the controller for TG=1,2 and Wtx=1 00, 200, 300. It can be seen from the table for example that when the transmission is in second gear (TG=2) and the transmission output shaft speed Wtx is 200rpm, the value of TQ(maxcharge) is -20Nm.

In some embodiments, if the controller 140 determines that a limit has been placed on the allowable value of 01MG charging torque at a given moment in time, the controller 140 may be configured to re-optimise vehicle operation (including determining whether to operate in a parallel charge mode, parallel recharge mode, parallel idle mode or EV mode) in light of the limit imposed. In some embodiments the controller 140 may be arranged to determine the maximum allowable value of 01MG charging torque and subsequently to determine values of torque to be provided by one or both of the engine 121 and 01MG 123 in order to optimise vehicle operation.

In some embodiments, instead of setting a limit to the allowable value of 01MG torque, TQ(maxcharge), the controller 140 is configured to force the transmission 124 to change gear whenever the value of 01MG torque exceeds or is at risk of exceeding TQ(maxcharge).

In some arrangements the controller 140 controls the transmission 124 to shift up a gear or shift down a gear depending on the value of one or more parameters such as the value of Wtx, the vehicle speed V, the value of driver demanded torque TQ(driver), vehicle road load LOAD(road), selected transmission mode of operation TM, vehicle angle of inclination, whether or not the vehicle is towing a load, and/or any other suitable parameter if required.

It is to be understood that this feature may enable a reduction in NVH in some situations where the vehicle is moving and able to change gear. In the case that the vehicle is stationary, a different means may be employed for reducing NVH due to charging load, for example by limiting the amount of charging torque that may be demanded whilst the vehicle is stationary substantially as described above.

In embodiments configured to force a gear change in order to reduce NVH, the controller may be provided with a database storing data in respect of whether an upshift of downshift should be triggered for given values (or ranges of values) of Wtx and currently selected gear TG.

In some embodiments the controller 140 is arranged to store data corresponding to values of Wtx and 01MG charging torque TQ(charge) at which a downshift is required, the controller 140 being operable only to trigger a downshift in order to reduce NVH.

FIG. 3 is a schematic illustration of a manner in which the controller 140 determines the gear that the transmission 124 is to operate in, i.e. the current value of TG the transmission is to be commanded to assume.

Look-up table (LUT) function block 140A is configured to output a value of parameter TG(LUT) corresponding to a gear that is to be assumed by the transmission 123 as a function of TO(driver), LOAD(road), V and TM. It is to be understood that TM may correspond to a selected vehicle program that configures one or more vehicle parameters according to a prescribed protocol. The program may for example be arranged to modify a throttle map (being a value of torque to be demanded of the vehicle 100 as a function of position of an accelerator pedal), an engine speed at which a transmission is arranged to shift up or down a gear from a given gear, a suspension characteristic such as hardness, and/or one or more other parameters.

The value of TG(LUT) is output to a decision function block 140B that also receives values of parameters REQ(charge) being a charging gear shift request and REQ(other) being a gear shift request due to other than 01MG charging load. Decision function block 140B outputs a value of a parameter TG(cmd) being the value of gear that the transmissionl23 is to be commanded to assume.

If REQ(charge) and REQ(other) are both set to logic LOW, decision function block 140B outputs a value of parameter TG(cmd) that is equal to that of parameter TG(LUT). That is, the value of TG(LUT) is passed directly to the output of function block 140B. The transmission 123 therefore assumes a gear corresponding to that of TG(LUT).

However if one or both of REQ(charge) and REO(other) are set to logic HIGH the controller determines that it is required that the transmission downshift by one gear. Thus the value of TG(cmd) is set to be equal to TG(LUT)-1, i.e. the transmission 123 is commanded to assume a gear corresponding to TG(LUT) downshifted by one gear.

In some embodiments the controller 140 may be configured to reduce NVH by controlling an amount of slip of clutch 122 between the engine 121 and CIMG 123. The amount of slip may be determined for example by reference to a database accessible to the controller, the database storing values of slip to be implemented as a function of charging torque and Wtx.

Slippage of the clutch has the advantage that the amount of charge torque that the CIMG 123 is commanded to apply to the driveline is not changed by the controller 140; rather, the controller controls clutch slippage in order to prevent an increase in NVH, or at least reduce an amount by which NVH is increased.

FIG. 4 shows example data that may be stored by a controller 140 configured according to this embodiment. It can be seen that when Wtx is 100rpm, the amount of slip is substantially zero. However, when Wtx is 200rpm and charging torque is -2ONm, slip of 30rpm is demanded of the clutch 122 by the controller 140. Other arrangements are also useful.

Embodiments of the present invention have the advantage that an amount of NVH suffered by a hybrid vehicle 100 due to charging torque may be reduced.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

CLAIMS: 1. A controller for controlling a powertrain of a hybrid electric vehicle to avoid operation of the vehicle at one or more undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter, wherein the driveline speed parameter corresponds to a speed of an output portion of a transmission of the vehicle and the driveline ratio parameter corresponds to a gear ratio between an output portion of the engine and one or more driven wheels of the vehicle.
2. A controller as claimed in claim 1 operable to command a change to the driveline ratio parameter responsive to values of generator torque load, driveline speed parameter and driveline ratio parameter thereby to avoid operation at the prescribed undesirable combinations of values of generator torque, driveline speed parameter and driveline ratio parameter.
3. A controller as claimed in claim 2 operable to command an increase in a driveline ratio parameter responsive to values of generator torque load, driveline speed parameter and driveline ratio parameter.
4. A controller as claimed claim 2 or claim 3 operable to command a decrease in a driveline ratio parameter responsive to values of generator torque load, driveline speed parameter and driveline ratio parameter.
5. A controller as claimed in any one of claims 2 to 4 operable prior to commanding a change in driveline ratio parameter to determine a future value of each of the driveline speed parameter, driveline ratio parameter and generator torque load that would be assumed by the vehicle following the commanded change, the controller being configured to determine whether to command a given change in driveline ratio responsive to a determination whether the future values correspond to one of said one or more undesirable combinations of values.
6. A controller as claimed in any preceding claim operable to command a change to an amount of generator torque load imposed on the engine by the generator means thereby to avoid operation at one of the one or more undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter.
7. A controller claimed in claim 6 operable to command a decrease in generator torque loading responsive to values of generator torque load, driveline speed parameter and driveline ratio parameter thereby to avoid operation at one of the one or more undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter.
8. A controller claimed in claim 6 or claim 7 operable to command an increase in generator torque loading responsive to values of generator torque load, driveline speed parameter and driveline ratio parameter thereby to avoid operation at one of the one or more undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter.
9. A controller as claimed in any one of claims 6 to 8 operable to determine in advance a future value of driveline speed parameter, driveline ratio parameter and generator torque that would be assumed by the vehicle following a given change in generator torque load, the controller being configured to determine whether to command a given change in generator torque load responsive to a determination whether the future values correspond to one of said prescribed undesirable combinations of values of generator torque, driveline speed parameter and driveline ratio parameter.
10. A controller as claimed in any preceding claim operable to determine the prescribed undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter by reference to a database.
11. A controller as claimed in any preceding claim configured to limit a value of generator torque load imposed on the engine by the generator means such that it does not exceed a prescribed limit value, the limit value being responsive to values of driveline speed parameter and driveline ratio parameter, thereby to avoid operation at the prescribed one or more undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter.
12. A controller as claimed in claim 11 operable to determine the limit value of generator torque load by reference to a database.
13. A controller as claimed in any preceding claim operable to control a vehicle to deliver torque to a driveline of a vehicle by means of the engine.
14. A controller as claimed in any preceding claim operable to command a hybrid vehicle to drive propulsion motor means thereof.
15. A hybrid electric vehicle comprising an engine, generator means, propulsion motor means, a transmission and a controller as claimed in any preceding claim.
16. A vehicle as claimed in claim 15 wherein at least one of the generator means and motor means is operable to be coupled in a flowpath of power between the transmission and the engine.
17. A vehicle as claimed in claim 16 wherein the generator means and motor means are provided by the same electric machine.
18. A vehicle as claimed in claim 17 wherein the motor means and generator means are provided by a crank integrated motor generator (dM3).
19. A vehicle as claimed in claim 16 or 17 wherein at least one of the generator means and motor means is provided between the transmission and one or more wheels of the vehicle.
20. A vehicle as claimed in claim 19 wherein at least one of the motor moans and generator means is provided by an electric axle drive unit comprising an electric machine arranged to drive an axle of the vehicle.
21. A vehicle as claimed in claim 20 wherein the motor means is provided by an electric rear axle drive unit.
22. A method of controlling by control means a hybrid electric vehicle having an engine for powering a generator for generating electrical power for driving the vehicle, the method comprising: controlling a powerirain of the vehicle to avoid operation of the vehicle at prescribed undesirable combinations of values of generator torque load, driveline speed parameter and driveline ratio parameter, whereby the driveline speed parameter corresponds to a speed of an output portion of a transmission and the driveline ratio parameter corresponds to a gear ratio between the engine and one or more driven wheels of the vehicle.
23. A method as claimed in claim 22 comprising the step of monitoring the driveline speed parameter and driveline ratio parameter.
24. A controller, a vehicle or a method substantially as hereinbefore described with reference to the accompanying drawings.