Patent Description:
It is increasingly known for vehicles to be powered by more than one motive or traction power source, such as an internal combustion engine and one or more electric machines or motors. However, management of multiple traction power sources may be problematic.

Document <CIT> describes a vehicle hybrid system which includes a transmission mechanically coupled with an engine, a drive shaft mechanically coupled with the transmission, a rotation-transmitting part coupled with the drive shaft, a power connecting-disconnecting part coupled with the drive shaft via the rotation-transmitting part, a motor generator mechanically coupled with the power connecting-disconnecting part, and a directional power transmission part for transmitting power in a direction from the motor generator to the engine to drive the engine and for not transmitting power in a direction from the engine to the motor generator to drive the motor generator.

Document <CIT> describes a hybrid drive arrangement for a motor vehicle including an internal combustion engine, which is connected or can be connected in a wheel-driving manner, via a first torque transmission path, to a driving wheel of the motor vehicle. An electric machine, which is operable at least as a motor, is fed from an electrical energy source of the motor vehicle and is connected or can be connected in a wheel-driving manner, via a second torque transmission path, to the driving wheel. Arranged in the first and/or the second torque transmission path are coupling elements which, in a first operating state, permit the driving of the motor vehicle by the wheel-driving torque of the electric machine, operated as a motor, without mechanical torque support from the internal combustion engine, and which, in a second operating state, permit the driving of the motor vehicle by the internal combustion engine, without mechanical torque support from the electric machine. Depending on the driving speed of the motor vehicle, an electronic driving control system activates the first operating state, at least in a first range of driving speeds including standstill of the vehicle, if the driving speed is less than a predetermined speed limit, and activates the second operating state, at least in a second range including the maximum speed of the vehicle, if the driving speed is greater.

Document <CIT> describes a vehicle which includes a powertrain having an electric machine configured to selectively apply regenerative torque to cause deceleration in response to braking demand; the powertrain further including a torque converter configured to decouple the electric machine from wheels of the vehicle. The vehicle is also provided with a controller programmed to, during a regenerative braking event, receive a signal defining a regenerative torque limit, and in response to a fault condition associated with the regenerative torque limit, generate a replacement regenerative torque limit based upon a torque converter open speed to decrease roughness during transitions into and out of regenerative braking.

Aspects and embodiments of the invention provide a control system, a powertrain, a vehicle, a method and computer software as claimed in the appended claims.

According to an aspect of the invention, there is provided an electric machine control system comprising one or more controllers, wherein the vehicle comprises an electric machine arranged to be selectively coupleable to provide torque to at least one wheel of an axle of the vehicle, the control system comprising input means to receive a speed signal indicative of a speed of the vehicle, processing means arranged to determine a desired coupling state of the electric machine to the at least one wheel of the axle in dependence on the speed signal, wherein the processing means is arranged to determine the desired coupling state as: a decoupled state in dependence on the speed signal being indicative of a vehicle speed equal to or greater than a first high-speed threshold (<NUM>); and a no-request state in dependence on the speed signal being indicative of vehicle speed equal to or below a second high-speed threshold (<NUM>), wherein the no-request state is indicative of not requesting a specific coupling state of the electric machine (<NUM>) to the at least one wheel of the axle and the second high-speed threshold (<NUM>) represents a vehicle speed lower than the first high-speed threshold (<NUM>); and output means arranged to output a coupling signal indicative of the coupling state to control coupling of the electric machine to the at least one wheel of the axle. The processing means is further arranged to: determine the desired coupling state as the decoupled state in dependence on the speed signal last intersecting the first high speed threshold (<NUM>) and being indicative of a vehicle speed below the first high-speed threshold (<NUM>); and, determine the desired coupling state as the no-request state in dependence on the speed signal last intersecting the second high speed threshold (<NUM>) and being indicative of a vehicle speed above the second high-speed threshold (<NUM>). Advantageously the processing means is arranged to determine the coupling of the electric machine to the at least one wheel of the axle in dependence on the speed of the vehicle.

Advantageously the decoupled state prevents excessive rotation speed of the electric machine.

Advantageously the processing means does not request a coupling state at lower rotation speeds of the electric machine. Advantageously two thresholds are used thereby improving control of the coupling. Advantageously the no-request is determined at a lower speed than the decoupled state.

The output means is optionally arranged to output the coupling signal indicative of a request to decouple the electric machine from the at least one wheel of the axle in dependence on the desired coupling state being decoupled. Advantageously the output means indicates the desired decoupling in dependence on the decoupled state being determined.

Advantageously excessive or frequent switching of coupling states is prevented.

The input means may be arranged to receive a temperature signal indicative of one or more of: an ambient temperature of the vehicle, one or more units of the vehicle, and fluids used for cooling said units of the vehicle, and the processing means may be arranged to determine the desired coupling state in dependence on the temperature signal. Advantageously temperature may be considered in determining the coupling state.

The processing means may be arranged to determine one or both of the first and second high-speed thresholds in dependence on the temperature signal. Advantageously one or both of the thresholds may be responsive to the temperature.

The processing means is optionally arranged to reduce one or both of the first and second high-speed thresholds in dependence on the temperature signal being indicative of at least a first predetermined temperature. Advantageously, the decoupling may be determined at lower speeds in a presence of higher temperatures. The first predetermined temperature may be at least <NUM>. Advantageously when the temperature is at least <NUM> one or both of the thresholds may be reduced.

Optionally the processing means is arranged to reduce one or both of the first and second high-speed thresholds in dependence on the temperature signal being indicative of less than or equal to a second predetermined temperature. Advantageously, the decoupling may be determined at lower speeds in a presence of lower temperatures.

Optionally the processing means is arranged to reduce one or both of the first and second high-speed thresholds proportional to temperature. Advantageously, the decoupling may be determined at lower speeds proportional to temperature. Optionally one or both of the first and second high-speed thresholds are reduced proportional to temperature in a range between -<NUM> and -<NUM>. Advantageously, in the range between -<NUM> and -<NUM> the decoupling may be determined proportional to temperature.

The second predetermined temperature may be less than or equal to -<NUM>. Advantageously, the decoupling may be determined at lower speeds in a presence a temperature below -<NUM>. Optionally the decoupling may be determined at lower speeds in a presence a temperature below -<NUM>.

The input means may be arranged to receive a charge signal indicative of a state of charge (SoC) of one or more batteries of the vehicle for providing electrical power to the electric machine. The one or more batteries may be traction batteries. The processing means is optionally arranged to determine the desired coupling state in dependence on the charge signal. Advantageously, the state of charge of the one or more batteries may be considered in determining the coupling.

The processing means may be arranged to determine the second high-speed threshold in dependence on the charge signal. Advantageously, the determination of the no-request state may be made in dependence on the state of charge.

The processing means may be arranged to determine the desired coupling state of the electric machine as decoupled in dependence on the charge signal being indicative of a state of charge of the one or more batteries being less than a predetermined threshold and the speed signal being indicative of vehicle speed below the second threshold.

The input means may be arranged to receive one or more further signals indicative of a state of one or more further vehicle subsystems or one or more further attributes of the vehicle. The processing means may be arranged to determine the desired coupling state of the electric machine at least in part on dependence on the one or more further signals. Advantageously, the state of the one or more further vehicle subsystems or one or more further attributes may be considered in the determination of the coupling state.

The processing means is optionally arranged to determine the desired coupling state of the electric machine in precedence on the speed signal over the one or more further signals. Advantageously, the speed signal is given a higher priority.

The first high-speed threshold may represent a vehicle speed which is less than a desired decoupling vehicle speed, such that when the vehicle is accelerating the electric machine is decoupled from the at least one wheel of the axle when the vehicle reaches the desired decoupling vehicle speed. Advantageously, a delay in implementing the decoupling may be accounted for to prevent excessive rotation speed of the electric machine.

According to a still further aspect of the invention, there is provided a powertrain comprising the system as described above.

According to yet another aspect of the invention, there is provided a vehicle comprising the control system or the powertrain as described above.

The electric machine may be arranged to be selectively coupleable to provide torque to at least one wheel of a first axle of the vehicle, and the vehicle optionally comprises a second motive power source arranged to provide torque to at least one wheel of a second axle of the vehicle. Advantageously, the coupling of the electric machine is determined with torque optionally provided to the second axle by the second electric machine. The second motive power source may comprise a second electric machine. Advantageously, the vehicle may be an electric vehicle.

According to another aspect of the invention, there is provided a method of controlling coupling of an electric machine to provide torque to at least one wheel of an axle of a vehicle, the method comprising receiving a speed signal indicative of a speed of the vehicle, determining a coupling state of the electric machine to the at least one wheel of the axle in dependence on the speed signal, determining the desired coupling state as: a decoupled state in dependence on the speed signal being indicative of a vehicle speed equal to or greater than a first high-speed threshold; and a no-request state in dependence on the speed signal being indicative of vehicle speed equal to or below a second high-speed threshold (<NUM>), wherein the no-request state is indicative of not requesting a specific coupling state of the electric machine to the at least one wheel of the axle and the second high-speed threshold represents a vehicle speed lower than the first high-speed threshold (<NUM>); determining the desired coupling state as the decoupled state in dependence on the speed signal last intersecting the first high speed threshold (<NUM>) and being indicative of a vehicle speed below the first high-speed threshold (<NUM>); determining the desired coupling state as the no-request state in dependence on the speed signal last intersecting the second high speed threshold (<NUM>) and being indicative of a vehicle speed above the second high-speed threshold (<NUM>); and, outputting a coupling signal indicative of the coupling state to control coupling of the electric machine to the at least one wheel of the axle.

The method may comprise outputting the coupling signal indicative of a request to decouple the electric machine from the at least one wheel of the axle in dependence on the desired coupling state being decoupled.

The method may comprising receiving a temperature signal. The coupling state is optionally determined in dependence on the temperature signal.

The method may comprise receiving a charge signal indicative of a state of charge of one or more batteries for providing electrical power to the electric machine and determining the coupling state in dependence on the charge signal.

The processing means m be arranged to determine the desired coupling state as coupled in dependence on a speed signal being indicative of a vehicle speed equal to or below a first low-speed threshold. Advantageously the processing means is arranged to determine the coupling of the electric machine as coupled to the at least one wheel of the axle at lower speeds.

According to another aspect of the invention, there is provided computer software which, when executed by a computer, is arranged to perform a method as described above. The computer software may be stored on a computer-readable medium. The computer software may be tangibly stored on the computer readable medium.

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

<FIG> illustrates a vehicle <NUM> according to an embodiment of the invention. The vehicle <NUM> provides space within a cabin of the vehicle <NUM> for one or more occupants. In some embodiments, the vehicle <NUM> may be manually driven by one of the occupants representing a driver of the vehicle <NUM>, although the vehicle <NUM> may have an at least partly autonomous driving capability in some embodiments. The vehicle <NUM> is an at least partly electric-powered vehicle <NUM>, as will be explained, with an internal combustion engine and one or more electric machines or traction electric motors for providing motive torque, thereby the vehicle being a hybrid electric vehicle (HEV). In some embodiments the vehicle <NUM> may be entirely electric powered i.e. a battery electric vehicle (BEV) without an internal combustion engine.

<FIG> illustrates a system <NUM> for a parallel HEV <NUM>. The system <NUM> defines, at least in part, a powertrain of the HEV. The system <NUM> comprises a control system <NUM>. The control system <NUM> comprises one or more controllers. The control system <NUM> may comprise one or more of: a hybrid powertrain control module; an engine control unit; a transmission control unit; a traction battery management system; and/or the like. The system <NUM> comprises an engine <NUM>. The engine <NUM> is a combustion engine. The illustrated engine <NUM> is an internal combustion engine. The illustrated engine <NUM> comprises three combustion chambers, however a different number of combustion chambers may be provided in other examples.

The engine <NUM> is operably coupled to the control system <NUM> to enable the control system <NUM> to control output torque of the engine <NUM>. The output torque of the engine <NUM> may be controlled by controlling one or more of: air-fuel ratio; spark timing; poppet valve lift; poppet valve timing; throttle opening position; fuel pressure; turbocharger boost pressure; and/or the like, depending on the type of engine <NUM>.

The system <NUM> comprises a vehicle transmission arrangement <NUM> for receiving output torque from the engine <NUM>. The vehicle transmission arrangement <NUM> may comprise an automatic vehicle transmission or a semi-automatic vehicle transmission. The vehicle transmission arrangement <NUM> comprises a fluid-coupling torque converter <NUM> between the engine <NUM> and a gear train.

The system <NUM> may comprise a differential (not shown) for receiving output torque from the gear train. The differential may be integrated into the vehicle transmission arrangement <NUM> as a transaxle, or provided separately.

The engine <NUM> is mechanically connected or connectable to a first set of vehicle wheels (FL, FR) via a first torque path <NUM>. The first torque path <NUM> extends from an output of the engine <NUM> to the vehicle transmission arrangement <NUM>, then to axles/driveshafts, and then to the first set of vehicle wheels (FL, FR). In a vehicle overrun and/or friction braking situation, torque may flow from the first set of vehicle wheels (FL, FR) to the engine <NUM>. Torque flow towards the first set of vehicle wheels (FL, FR) is positive torque, and torque flow from the first set of vehicle wheels (FL, FR) is negative torque.

The illustrated first set of vehicle wheels (FL, FR) comprises front wheels, and the axles are front transverse axles. Therefore, the system <NUM> is configured for front wheel drive by the engine <NUM>. In another example, the first set of vehicle wheels (FL, FR) comprises rear wheels (RL, RR). The illustrated first set of vehicle wheels (FL, FR) is a pair of vehicle wheels, however a different number of vehicle wheels could be provided in other examples.

In the illustrated system <NUM>, no longitudinal (centre) driveshaft is provided, to make room for hybrid vehicle components. Therefore, the engine <NUM> is not connectable to a second set of rear wheels (rear wheels RL, RR in the illustration). The engine <NUM> may be transverse mounted to save space.

A torque path connector <NUM> such as a clutch is provided inside and/or outside a bell housing of the vehicle transmission arrangement <NUM>. The clutch <NUM> is configured to connect and configured to disconnect the torque path <NUM> between the engine <NUM> and the first set of vehicle wheels (FL, FR). The system <NUM> may be configured to automatically actuate the clutch <NUM> without user intervention.

The system <NUM> comprises a first electric traction motor <NUM>. The first electric traction motor <NUM> may be an alternating current induction motor or a permanent magnet motor, or another type of motor. The first electric traction motor <NUM> is located to the engine side of the clutch <NUM>.

The first electric traction motor <NUM> may be mechanically coupled to the engine <NUM> via a belt or chain. For example, the first electric traction motor <NUM> may be a belt integrated starter generator (BiSG). In the illustration, the first electric traction motor <NUM> is located at an accessory drive end of the engine <NUM>, opposite a vehicle transmission end of the engine <NUM>. In an alternative example, the first electric traction motor <NUM> is a crankshaft integrated motor generator, located at a vehicle transmission end of the engine <NUM>.

The first electric traction motor <NUM> is configured to apply positive torque and configured to apply negative torque to a crankshaft of the engine <NUM>, for example to provide functions such as: boosting output torque of the engine <NUM>; deactivating (shutting off) the engine <NUM> while at a stop or coasting; activating (starting) the engine <NUM>; and regenerative braking in a regeneration mode. In a hybrid electric vehicle mode, the engine <NUM> and first electric traction motor <NUM> are both operable to supply positive torque simultaneously to boost output torque. The first electric traction motor <NUM> may be incapable of sustained electric-only driving, although in other embodiments the first electric traction motor <NUM> may be capable of electric only driving particularly an embodiment without the engine <NUM>. One or both of the engine <NUM> and the first electric traction motor <NUM> are able to provide torque to a first axle <NUM> of the vehicle.

However, when the torque path <NUM> between the engine <NUM> and the first set of vehicle wheels (FL, FR) is disconnected, a torque path <NUM> between the first electric traction motor <NUM> and the first set of vehicle wheels (FL, FR) is also disconnected.

<FIG> illustrates a second electric traction motor <NUM> configured to enable at least an electric vehicle mode comprising electric-only driving. In some, but not necessarily all examples, a nominal maximum torque of the second electric traction motor <NUM> is greater than a nominal maximum torque of the first electric traction motor <NUM>.

Even if the torque path <NUM> between the engine <NUM> and the first set of vehicle wheels (FL, FR) is disconnected by the clutch <NUM>, the vehicle <NUM> can be driven in electric vehicle mode because the second electric traction motor <NUM> is connected to at least one vehicle wheel. The at least one vehicle wheel may be one, or both, of the rear wheels (RL, RR) of the vehicle <NUM> associated with a second axle <NUM> of the vehicle <NUM>.

The illustrated second electric traction motor <NUM> is configured to provide torque to the illustrated second set of vehicle wheels (RL, RR) of the second axle <NUM> of the vehicle. The second set of vehicle wheels (RL, RR) comprises vehicle wheels not from the first set of vehicle wheels (FL, FR). The illustrated second set of vehicle wheels (RL, RR) comprises rear wheels, and the second electric traction motor <NUM> is operable to provide torque to the rear wheels (RL, RR) via rear transverse axles forming the second axle <NUM>. Therefore, the vehicle <NUM> may be rear wheel driven in electric vehicle mode.

The control system <NUM> may be configured to disconnect the torque path <NUM> between the engine <NUM> and the first set of vehicle wheels (FL, FR) in electric vehicle mode, to reduce parasitic pumping energy losses. For example, the clutch <NUM> may be opened. In the example of <FIG>, this means that the first electric traction motor <NUM> will also be disconnected from the first set of vehicle wheels (FL, FR).

Another benefit of the second electric traction motor <NUM> is that the second electric traction motor <NUM> may also be configured to operable in a hybrid electric vehicle mode, to enable four-wheel drive operation despite the absence of a centre driveshaft.

The second electric traction motor <NUM> may be selectively coupled to one or both wheels RL, RR of the second axle <NUM>. Coupling of a torque path between the second electric traction motor <NUM> and the one or both wheels RL, RR of the second axle <NUM> may be achieved via a second clutch <NUM>. The second clutch <NUM> may be controlled to open, such as via an actuator under control of a received signal, to disconnect the torque path between the second electric traction motor <NUM> and the one or both wheels (RL, RR) of the second axle <NUM>. In some embodiments the second clutch <NUM> may be a dog cutch.

Thus it will be appreciated that the second electric traction motor <NUM> is arranged to be selectively coupleable to provide torque to at least one wheel (RL, RR) of an axle of the vehicle <NUM>. In some embodiments, the vehicle <NUM> comprises another motive power source arranged to provide torque to at least one wheel (FL, FR) of another axle of the vehicle <NUM>. In the illustrated embodiment the another motive power source power source comprises another electric machine <NUM> in the form of the first electric traction motor <NUM>. The another motive power source may, in some embodiments, comprise an internal combustion engine <NUM> which may provide positive torque alone or in combination with the first electric traction motor <NUM>.

In order to store electrical power for the electric traction motors <NUM>, <NUM>, the system <NUM> comprises a traction battery <NUM>. The traction battery <NUM> provides a nominal voltage required by electrical power users such as the electric traction motors. If the electric traction motors <NUM>, <NUM> run at different voltages, DC-DC converters (not shown) or the like may be provided to convert voltages.

The traction battery <NUM> may be a high voltage (HV) battery. High voltage traction batteries provide nominal voltages in the hundreds of volts, as opposed to traction batteries for mild HEVs which provide nominal voltages in the tens of volts. The traction battery <NUM> may have a voltage and capacity to support electric only driving for sustained distances. The traction battery <NUM> may have a capacity of several kilowatt-hours, to maximise range. The capacity may be in the tens of kilowatt-hours, or in the hundreds of kilowatt-hours.

Although the traction battery <NUM> is illustrated as one entity, the function of the traction battery <NUM> could be implemented using a plurality of small traction batteries in different locations on the vehicle <NUM>.

In some examples, the first electric traction motor <NUM> and second electric traction motor <NUM> may be configured to receive electrical energy from the same traction battery <NUM>. By pairing the first (mild) electric traction motor <NUM> to a high-capacity battery (tens to hundreds of kilowatt-hours), the first electric traction motor <NUM> may be able to provide the functionality of the methods described herein for sustained periods of time, rather than for short bursts. In another example, the electric traction motors <NUM>, <NUM> may be paired to different traction batteries.

Finally, the illustrated system <NUM> comprises one or more inverters. Two inverters <NUM>, <NUM> are shown, one for each electric traction motor <NUM>, <NUM>. In other examples, one inverter or more than two inverters could be provided.

It can be appreciated from the foregoing that the vehicle <NUM> may be provided with motive torque from a combination of sources. Embodiments of the present invention relate to determining which of the sources of motive torque to utilise.

<FIG> illustrates a control system <NUM> according to an embodiment of the invention. The control system <NUM> may be formed by one or more controllers <NUM>. The control system <NUM> illustrated in <FIG> comprises one electronic controller <NUM> although it will be appreciated that this is merely illustrative. The, or each, controller <NUM>, comprises a processing means <NUM> and a memory means <NUM>. The processing means <NUM> may be one or more electronic processors <NUM> or processing devices <NUM>, such as CPUs, for executing computer readable instructions. The memory means <NUM> may be one or more memory devices <NUM>. The one or more memory devices <NUM> may store computer-readable instructions for execution by the at least one processing device <NUM>.

The controller <NUM> comprises an input means <NUM> and an output means <NUM>. The input means <NUM> is arranged to receive one or more signals <NUM>. The input means <NUM> may be an electrical input to the controller <NUM> for receiving one or more electrical signals <NUM>. The output means <NUM> is arranged to output at least one signal <NUM>, which is provided in <FIG> to one or both of the second clutch <NUM> and second electric traction motor <NUM> to control coupling to the second torque path to provide torque to one or both wheels of the second axle <NUM>. The output means <NUM> is an electrical output of the controller <NUM>. The output means <NUM> is operable by the processing device <NUM> to output the signal <NUM> under control thereof. The signal <NUM> may cause the second electric traction motor <NUM> to 'spin-up' or accelerate to a rotation speed suitable to couple with the second axle <NUM> i.e. bearing in mind that the vehicle <NUM> may be in motion through torque provided by the first electric traction motor <NUM> and/or engine <NUM>. The signal <NUM> may cause closing of the second clutch <NUM> to couple the second electric traction motor <NUM> to the second torque path.

The electrical input <NUM> and output <NUM> of the controller <NUM> may be provided to/from a communication bus or network of the vehicle, such as a CANBus or other communication network which may, for example, be implemented by an Internet Protocol (IP) based network such as Ethernet, or FlexRay or a Single Edge Nibble Transmission (SENT) protocol, although other protocols may be used.

<FIG> schematically illustrates a portion of the controller <NUM> comprising the input means <NUM> and output means <NUM> of the system <NUM>. <FIG> illustrates inputs <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> to the input means <NUM> of the controller <NUM> which form the signal <NUM> illustrated in <FIG> further illustrates modules <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or functional units, which may operatively execute on the processing device <NUM> of the controller <NUM>. Each of the inputs <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> provides information relating to one or more aspects or attributes of the vehicle <NUM> or the powertrain <NUM> thereof.

The inputs <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may comprise one more of one or more speed signals <NUM>, a temperature signal <NUM>, a fault-derived coupling state request (FDCSR) signal <NUM>, a driving mode (DM) signal <NUM>, a state of charge (SoC) signal <NUM> and an inhibit signal <NUM> which provide information or data on which a desired coupling state is determined by one or more of the modules <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> as will be explained. The desired coupling state is a desired coupling of the torque path between the second electric traction motor <NUM> and the one or both wheels RL, RR of the second axle <NUM> of the vehicle <NUM> which is determined by one or more of the modules <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

The one or more speed signals <NUM> is indicative of one or more of a speed of the vehicle <NUM> i.e. a speed of the vehicle <NUM> over ground, a wheel speed signal indicative of a speed of rotation of one or more wheels of the vehicle and a motor speed signal indicative of a speed of one or both of the speed of the first and second electric traction motors <NUM>, <NUM>.

The temperature signal <NUM> is indicative of one or more of an ambient temperature and a temperature of one or more units, or a temperature of fluids associated with one or more units, particularly fluids used for cooling said units i.e. coolant fluid, of the vehicle <NUM>. For example the coolant fluid may be a coolant fluid of one or both traction electric motors <NUM>, <NUM>. In some embodiments, the temperature signal <NUM> comprises a temperature associated with one more units of the powertrain. In some embodiments, the temperature associated with one more units of the powertrain comprises a temperature of one or more of one or both of the inverters <NUM>, <NUM>, one or both of the electric traction motors <NUM>, <NUM>, a coolant temperature, and an indication of a temperature of the traction battery <NUM>. The indication of the temperature of the traction battery <NUM> may be indicative of a power capability of the traction battery <NUM>, which is a function of temperature and a State of Charge (SoC) of the traction battery <NUM>. Thus in some embodiments the temperature signal <NUM> may comprise a signal indicative of the power capability of the traction battery <NUM>, this being indicative of temperature.

The fault-derived coupling state request signal (FDCSR) <NUM> is indicative of a request for a coupling state derived in determination of a fault associated with the vehicle <NUM>, such as a fault associated with the powertrain. For example, where a fault associated with the second clutch <NUM> is detected by a fault management module (not shown), the fault management module may request that a coupling state of coupled or decoupled in order to control a state of the clutch <NUM> i.e. open or closed, in order to manage or resolve the fault. Other faults may be appreciated to cause a desired coupling state to manage or ameliorate the fault. In some embodiments, a fault management module <NUM> may be executed upon the processing device <NUM> and thus the FDSCR signal <NUM> may be generated internal to the controller <NUM>.

The driving mode signal <NUM> may be indicative of a driving mode of the vehicle <NUM> which may be automatically determined, such as by an intelligent driving mode or terrain response (TR) determination unit, an autonomous driving controller, such as an ADAS system, or selected by an occupant of the vehicle <NUM>. The driving mode signal <NUM> may be indicative of selection of an efficiency-based driving mode i.e. to provide minimal fuel and/or energy usage, a four wheel-drive driving mode, such as where a number of driven wheels may be automatically selected, and a selected driving gear i.e. neutral, drive (D), reverse (R) etc..

The state of charge (SoC) signal <NUM> is indicative of the SoC of the traction battery <NUM>.

The inhibit signal <NUM> is indicative of one or more inhibited coupling states. For example, the inhibit signal <NUM> may indicate that a state of coupled is inhibited to prevent coupling of the second electric traction motor <NUM> to the one or both wheels (RL, RR) of the second axle <NUM>, or that a state of decoupled is inhibited to prevent decoupling of the second electric traction motor <NUM> from the one or both wheels (RL, RR) of the second axle <NUM>.

The inputs <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may, in some embodiments, comprise a coupling status signal <NUM> which is indicative of an actual coupling status of the second electric traction motor <NUM> to the one or both wheels of the second axle <NUM>. In some embodiments, the coupling status signal <NUM> has states of coupled and decoupled indicative the respective coupling. The coupling status signal <NUM> reports the physical status of the coupling of the second electric traction motor <NUM> to the second torque path via the second axle <NUM> and is thus indicative of successful coupling or decoupling of the second electric traction motor <NUM>.

In some embodiments, the modules <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> comprise a high-speed module <NUM>, a low-speed module <NUM>, a fault management module (FMM) <NUM>, an anti-fussiness module <NUM>, an inhibit module <NUM>, a driving mode module (DMM) <NUM> and an arbitrator <NUM>. It will be appreciated that not all modules are present in all embodiments, thus embodiments of the present invention may comprise one or more of the aforementioned modules. Each of the modules will be explained below. Each of the high-speed module <NUM>, the low-speed module <NUM>, the fault management module <NUM>, the anti-fussiness module <NUM>, the inhibit module <NUM>, the efficiency module <NUM>, as present in the relevant embodiment, may determine a respective desired coupling state. An indication of the desired coupling state is provided to the arbitrator <NUM> to determine the coupling state of the electric machine <NUM> to the axle <NUM> i.e. as an arbitrated coupling state.

An embodiment of the high-speed module (HSM) <NUM> will now be explained with reference to <FIG> & <FIG>. The HSM <NUM> is operatively executable by the processing device <NUM> to determine a coupling state of the electric machine <NUM> to the at least one wheel of the axle <NUM> in dependence on the speed signal <NUM> indicative of the speed of the vehicle <NUM>. In some embodiments, the HSM <NUM> and the arbitrator <NUM> are arranged to cause the controller <NUM> to output a coupling signal <NUM> to control coupling of the second electric traction motor <NUM> to the at least one wheel of the axle <NUM> dependent on the speed signal <NUM> as will be explained. The HSM <NUM> is arranged to cause decoupling of the second electric traction motor <NUM> from the at least one wheel of the axle <NUM> a high-speeds of the vehicle <NUM> which, advantageously, prevents rotation of the second electric traction motor <NUM> at excessive speeds which may damage the second electric traction motor <NUM>.

<FIG> illustrates a method <NUM> according to an embodiment of the invention which may be performed by the HSM <NUM> executed by the processing device <NUM> of the controller <NUM>. The method <NUM> will be explained with reference to <FIG> which illustrates a speed of the vehicle <NUM>, as indicated by the speed signal <NUM>, over a period of time. Also illustrated in a lower portion of <FIG> is a desired coupling signal <NUM> output by the HSM <NUM> which represents a request <NUM>, <NUM> for the desired coupling state from the HSM <NUM> determined in dependence on the speed signal <NUM>.

The method <NUM> comprises a step <NUM> of receiving one or more signals, such as data representing the one or more signals, at the HSM <NUM>. In the illustrated embodiment the HSM <NUM> is arranged to receive the speed signal <NUM>, which as discussed above may be indicative of the speed of the vehicle <NUM>. In some embodiments, the HSM <NUM> is arranged to receive the temperature signal <NUM> as discussed above. In some embodiments, the HSM <NUM> is arranged to receive the SoC signal <NUM> indicative of the state of charge of one or more traction batteries <NUM> for providing electrical power to the traction electric machines <NUM>, <NUM>. In some embodiments, the HSM <NUM> may receive a signal indicative of a power limit or capability of the traction battery <NUM> which, as discussed above, is indicative of the temperature of the traction battery <NUM>.

Step <NUM> comprises determining a desired coupling state of the second electric traction motor <NUM> to the at least one wheel (RL, RR) of the second axle <NUM> in dependence on the speed signal <NUM>. Step <NUM> comprises determining whether the speed of the vehicle <NUM> is equal to or greater than a first high-speed threshold <NUM> shown in <FIG>. Thus step <NUM> comprises comparing the speed of the vehicle <NUM> against one or more thresholds <NUM>, <NUM>, where the one or more thresholds <NUM>, <NUM> comprise the first high-speed threshold <NUM>. In some embodiments, the one or more thresholds <NUM>, <NUM> comprise a second high-speed threshold <NUM>. The second high-speed threshold <NUM> represents a vehicle speed lower than the first high-speed threshold <NUM>. The first <NUM> and second <NUM> high-speed thresholds are illustrated in <FIG>.

If the speed of the vehicle <NUM> is equal to or greater than a first high-speed threshold <NUM> then the method <NUM> moves to step <NUM>. If, however, the speed of the vehicle <NUM> is less than the first high-speed threshold <NUM> then the method <NUM> moves to step <NUM>.

In the example of <FIG>, the method <NUM> progresses to step <NUM> prior to time t<NUM>. Prior to time t<NUM> as will be appreciated the vehicle <NUM> is generally accelerating which may be caused by positive torque applied by the first electric traction motor <NUM> and/or engine <NUM>, and the second electric traction motor <NUM> which is coupled to the second torque path via the second axle <NUM>.

In step <NUM> the desired coupling state is determined as decoupled in dependence on the speed signal <NUM> being indicative of a vehicle speed equal to or greater than the first high-speed threshold <NUM>. In step <NUM> the HSM <NUM> may output an indication <NUM> of the desired coupling state of decoupled to the arbitrator <NUM> indicative of a request to decouple <NUM> the second electric traction motor <NUM> from the second axle <NUM>. The indication <NUM> of the desired coupling state of decoupled <NUM> may be referred to as the high-speed coupling state request <NUM>, <NUM>. The arbitrator <NUM> may in some embodiments arbitrate between multiple requests for desired coupling states as will be explained. In the absence of any other competing requests from other modules, the arbitrator <NUM> is arranged to output, via the output means <NUM>, the high-speed coupling state request <NUM> for the decoupled state <NUM> as output signal <NUM>. In some embodiments, the high-speed coupling state request <NUM> may be provided from the HSM <NUM> directly to the output means <NUM> of the controller <NUM>.

After time t<NUM>, i.e. once the speed of the vehicle <NUM> exceeds the first high-speed threshold <NUM>, it has been determined that it is desirable to decouple the second electric traction motor <NUM>. Continued coupling of the second electric traction motor <NUM> to the wheel(s) of the vehicle <NUM> causes the second electric traction motor <NUM> to exceed a predetermined rotation speed. The predetermined rotation speed may be a motor speed of <NUM>,<NUM> rpm, although it will be appreciated that other predetermined rotation speeds may be selected. The predetermined rotation speed may correspond to a vehicle speed of 140kmh-<NUM> although it will be appreciated that this depends on a gearing between the second electric traction motor <NUM> and the wheels of the vehicle <NUM> and a diameter of the wheels. Furthermore, in some embodiments, the vehicle speed corresponding to the first high speed threshold <NUM>, and thus the rotation speed of the second electric traction motor <NUM>, may be determined in dependence on temperature as will be explained with reference to <FIG>.

The output means <NUM> of the controller <NUM> is arranged to output the coupling signal <NUM>, <NUM>, <NUM> indicative of a request to decouple <NUM> the second electric traction motor <NUM> from the at least one wheel of the second axle <NUM> in dependence on the desired coupling state being decoupled.

If, in step <NUM>, the speed of the vehicle <NUM> is less than the first high speed threshold <NUM>, the method moves to step <NUM>. In step <NUM> it is determined whether the speed of the vehicle <NUM> is less than or equal to the second high speed threshold <NUM>. If the speed of the vehicle <NUM> is less than or equal to the second high speed threshold <NUM> the method moves to step <NUM>.

In step <NUM> the HSM <NUM> is arranged not to request a desired coupling state of the second electric machine <NUM>. The HSM <NUM> outputs a request for a coupling state to the arbitrator <NUM> or may, as illustrated in <FIG>, output a 'no-request' signal <NUM> to the arbitrator <NUM>, where the no-request signal <NUM> is indictive of the HSM <NUM> not requesting a specific coupling state of the second electric traction motor <NUM> to the one or more wheels of the second axle <NUM>. Thus, prior to time t<NUM> in <FIG>, the HSM <NUM> outputs the no-request signal <NUM> to the arbitrator <NUM>, or may output no signal to the arbitrator <NUM> in other embodiments. The arbitrator <NUM> may have a default coupling state. The default coupling state may be coupled i.e. for the second electric traction motor <NUM> to be coupled to the torque path of the second axle <NUM>. Thus when either a 'no-request' signal <NUM>, or no request signal is received by the arbitrator <NUM>, the arbitrator <NUM> may output a determined coupling request via the output means <NUM>.

In some embodiments, the HSM <NUM> is arranged to output the coupling signal <NUM>, indicative of a request to couple the second electric traction motor <NUM> machine to the at least one wheel of the second axle <NUM>. It will be appreciated that the HSM <NUM> may, in some embodiments, request the default state of coupled when the speed signal <NUM> is indicative of a low vehicle speed.

In some embodiments, the HSM <NUM> may apply hysteresis to the speed signal <NUM> to determine the coupling state. That is, the coupling state of decoupled may be determined for a vehicle speed greater than that at which the second electric traction motor <NUM> is recoupled to the torque path via the second axle <NUM> i.e. above the second high-speed threshold <NUM>. Advantageously this assists in preventing 'hunting' or 'flickering' between the decoupled and coupled states as the speed of the vehicle varies around (above and below) the first high speed threshold <NUM>. Use of the second high speed threshold <NUM> provides the hysteresis in some embodiments. As can be appreciated from <FIG>, between t<NUM> and prior to time t<NUM> the vehicle deaccelerates from a peak speed, such that the speed signal <NUM> drops below the first high speed threshold <NUM>. As can be appreciated from the lower portion of <FIG>, the 'no-request' signal <NUM> is not output immediately upon the speed of the vehicle <NUM> falling below the first high-speed threshold <NUM>.

Instead, in a region between the first and second high speed thresholds <NUM>, <NUM> the coupling state of decoupled <NUM> is maintained until the vehicle speed falls below the second high-speed threshold <NUM>. In step <NUM>, which is reached when the vehicle speed is between the first and second high speed thresholds <NUM>, <NUM> the desired coupling state is determined in dependence on the speed signal <NUM> in dependence on a last intersected of the first and second high-speed thresholds <NUM>, <NUM>. Thus, prior to time t<NUM> when the speed signal <NUM> is below the first high-speed threshold <NUM> the coupling state is determined in step <NUM> as decoupled based on last-intersecting the first high speed threshold <NUM>. Thus the method moves to step <NUM>. Similarly, prior to time t<NUM>, when the speed signal <NUM> is above the second high-speed threshold <NUM>, the method moves to step <NUM> wherein the 'no request' output signal <NUM> is maintained such that the arbitrator <NUM> in the example embodiment determines the coupling state as coupled.

Thus it can be appreciated that embodiments of the invention select coupling of the second electric traction motor <NUM> in dependence on the speed of the vehicle <NUM>.

<FIG> illustrates motor speed, i.e. speed (RPM) of the second electric traction motor <NUM>, against temperature according to an embodiment of the invention. Illustrated in <FIG> is the first high speed threshold <NUM> which, according to some embodiments of the invention varies dependent upon temperature. As described above, in some embodiments of the invention the controller <NUM> receives the temperature signal <NUM>. In some embodiments, the first high speed threshold <NUM> adopts a first value <NUM> between first and second temperatures <NUM>, <NUM>. The first temperature <NUM>, below which one or both of the first and second high-speed thresholds <NUM>, <NUM> reduces may correspond to a cold-temperature, such as a temperature below <NUM>, such as -<NUM>, although it will be realised that other temperatures may be selected. It will be appreciated that, although not illustrated, the second high speed threshold <NUM> may follow the first high speed threshold <NUM>.

Below the first temperature <NUM>, in some embodiments the first high speed threshold <NUM> reduces i.e. to value <NUM>, such that the coupling state of the second electric traction motor <NUM> is determined as decoupled at a lower speed, as illustrated. In some embodiments, one or both of the first and second high-speed thresholds <NUM>, <NUM> may reduce proportional to temperature during one or more temperature regions. Advantageously, the reduction in the first high speed threshold <NUM>, <NUM> allows for changes in, for example, coolant of the second electric traction motor <NUM> or a reduced viscosity of fluids associated with the second torque path via the second axle <NUM>, such that rotation of the motor <NUM> may consume more energy and therefore lower-speed decoupling is more efficient. In the embodiment shown in <FIG>, the first high speed threshold <NUM>, <NUM> is arranged to decrease in dependence on temperature over a first temperature range <NUM>, <NUM>. The temperature range may be between -<NUM> and -<NUM>, although other temperature ranges may be selected. In other embodiments, the first high speed threshold <NUM> may reduce instantaneously, however advantageously having a gradual change may be less noticeable to occupants of the vehicle <NUM>. Below a third temperature <NUM> the first thigh speed threshold <NUM> corresponds to a minimum threshold speed <NUM>.

Similarly, in some embodiments, above the second temperature <NUM> the first thigh speed threshold <NUM> is arranged to decrease in dependence on temperature over a second temperature range <NUM>, <NUM> to a fourth temperature <NUM>. Above the fourth temperature <NUM> the first thigh speed threshold <NUM> adopts a constant value <NUM> in some embodiments, which may be different to the minimum threshold speed <NUM> as shown in <FIG>, although in other embodiments the two speeds <NUM>, <NUM> may be equal. Advantageously the reduction in the first thigh speed threshold <NUM>, <NUM> at higher speeds may reduce cooling issues associated with the second electric traction motor <NUM>. The temperature <NUM> may be at least <NUM> or at least <NUM>, such as in some embodiments a temperature of between <NUM> and <NUM>.

As described above, in some embodiments, the controller <NUM> is arranged to receive the SoC signal <NUM>. In some embodiments, one or both the first high speed threshold <NUM> and second high speed threshold <NUM> is determined in dependence on the SoC of the traction battery <NUM>. As described above, in some embodiments, the arbitrator <NUM> may be arranged to achieve the default coupling state of coupled in absence of a request from the HSM <NUM> for the decoupled state. In this way, the HSM <NUM> and arbitrator <NUM> operate to decouple the second electric traction motor <NUM> when the vehicle <NUM> speed is above first high speed threshold <NUM> and coupled when the vehicle <NUM> speed is below the second high speed threshold <NUM>. To couple the second electric traction motor <NUM> to the second axle in some embodiments the second electric traction motor <NUM> is required to 'spin-up' or accelerate from a low, such as zero, rotation speed to generally a speed of rotation of the rear axle <NUM> before the second clutch <NUM> can be closed to couple the second electric traction motor <NUM> to the axle <NUM>. As can be appreciated, accelerating the second electric traction motor <NUM> consumes energy from the traction battery <NUM>. When the vehicle <NUM> is operative with a traction battery <NUM> having a low SoC, one or both the first high speed threshold <NUM> and second high speed threshold <NUM> may be reduced in dependence on the SoC. Advantageously, by reducing the speed corresponding to one or both the first high speed threshold <NUM> and second high speed threshold <NUM>, the second electric traction motor <NUM> is only required to 'spin-up' to a lower rotation speed to recouple to the second axle <NUM>, thereby requiring less energy consumption when the traction battery <NUM> has a lower SoC.

An embodiment of the low-speed module (LSM) <NUM> will now be explained with reference to <FIG> and <FIG>. The LSM <NUM> is operatively executable by the processing device <NUM> to determine a coupling state of the electric machine <NUM> to the at least one wheel of the second axle <NUM> in dependence on the speed signal <NUM> indicative of the speed of the vehicle <NUM>. In some embodiments, the LSM <NUM> and arbitrator <NUM> are arranged to cause the controller <NUM> to output a coupling signal <NUM> to control coupling of the electric machine <NUM> to the at least one wheel of the second axle <NUM> dependent on the speed signal <NUM>, as will be explained. As will be explained the LSM <NUM> is arranged to cause coupling of the electric machine <NUM> to the at least one wheel of the axle <NUM> a low-speeds which, advantageously, enables the electric machine <NUM> to provide motive torque for the vehicle at low speeds, especially from stationary. Furthermore, the LSM <NUM> is arranged to control the coupling of the electric machine to avoid, or reduce, undesirable characteristics which may be noticeable to an occupant of the vehicle <NUM> as will be explained.

<FIG> illustrates a method <NUM> according to an embodiment of the invention which may be performed by the LSM <NUM> executed by the processing device <NUM> of the controller <NUM>. The method <NUM> will be explained with reference to <FIG> which illustrates a speed of the vehicle <NUM>, as indicated by the speed signal <NUM>, over a period of time. Also illustrated in a lower portion of <FIG> is a desired coupling signal <NUM> output by the LSM <NUM> which represents a request <NUM>, <NUM> for the desired coupling state from the LSM <NUM> determined in dependence on the speed signal <NUM>.

The method <NUM> comprises a step <NUM> of receiving one or more signals, such as data representing the one or more signals, at the LSM <NUM>. In the illustrated embodiment the LSM <NUM> is arranged to receive the speed signal <NUM> indicative of the speed of the vehicle <NUM>.

Step <NUM> comprises determining a desired coupling state of the second electric traction motor <NUM> to the at least one wheel (RL, RR) of the second axle <NUM> in dependence on the speed signal <NUM>. Step <NUM> comprises determining whether the speed of the vehicle <NUM> is equal to or less than a first low-speed threshold (LST) <NUM>. Thus step <NUM> comprises comparing the speed of the vehicle <NUM> against one or more thresholds <NUM>, <NUM>, where the one or more thresholds <NUM>, <NUM> comprise the first LST <NUM>. In some embodiments, the one or more low-speed thresholds <NUM>, <NUM> comprise a second LST <NUM>, as shown in <FIG>. The second LST <NUM> represents a vehicle speed greater than the first LST <NUM>. The first <NUM> and second <NUM> LSTs are illustrated in <FIG>.

In step <NUM> the desired coupling state is determined as coupled in dependence on the speed signal <NUM> being indicative of a vehicle speed equal to or below than the first LST <NUM>. In step <NUM> the LSM <NUM> may output an indication <NUM> of the desired coupling state of coupled to the arbitrator <NUM> indicative of a request to couple <NUM> the second electric traction motor <NUM> to the second axle <NUM>. The indication <NUM> of the desired coupling state of coupled <NUM> may be referred to as the low-speed coupling state request <NUM>, <NUM>. The arbitrator <NUM> may in some embodiments arbitrate between multiple requests for desired coupling states. In the absence of any other competing requests from other modules, the arbitrator <NUM> is arranged to output, via the output means <NUM>, the low-speed coupling state request <NUM> for the coupled state <NUM> as output signal <NUM>. In some embodiments, the low-speed coupling state request <NUM>, <NUM> may be provided from the LSM <NUM> directly to the output means <NUM> of the controller <NUM>.

Referring to <FIG>, after time t<NUM>, i.e. once the speed of the vehicle <NUM> is equal to or below the first LST <NUM>, it has been determined that it is desirable to couple the second electric traction motor <NUM>. For example, it can be envisaged that the vehicle <NUM> is about to stop and that torque from the second electric traction motor <NUM> will be useful e.g. for a standing start.

A predetermined vehicle speed corresponding to the first LST <NUM> may be a vehicle speed of 10kmh-<NUM> although it will be appreciated that other vehicle speeds may be selected. In some embodiments, the vehicle speed corresponding to the first LST <NUM> may be selected or determined based on a deacceleration rate of the vehicle <NUM>, which may be determined based on a rate of change of the speed signal <NUM>. In the presence of a large deceleration i.e. above a deacceleration threshold the vehicle speed corresponding to the first LST <NUM> may be increased to advantageously allow for coupling of the second electric traction motor <NUM> prior to the vehicle <NUM> stopping.

The output means <NUM> of the controller <NUM> is arranged to output the coupling signal <NUM>, <NUM> indicative of a request to couple <NUM> the second electric traction motor <NUM> to the at least one wheel of the second axle <NUM> in dependence on the desired coupling state being coupled, as in step <NUM>.

In some instances, due to a default state being coupled as shown in Table <NUM> below, the request to couple <NUM> shown in <FIG> output as a result of the speed of the vehicle dropping through the LST <NUM> will have no practical effect (change in state) as the second electric traction motor <NUM> will already be coupled to the second axle <NUM> as a result of the default state being coupled. However, in some instances, the second electric traction motor <NUM> will be decoupled from the second axle <NUM> when the speed of the vehicle drops through the LST <NUM>. In such situations, the arbitrator <NUM> may determine an arbitrated coupling state with respect to the LTS <NUM> in dependence on a reason why the second electric traction motor <NUM> is disconnected. If the arbitrated coupling state is decoupled whilst the vehicle speed is above the LST <NUM> for a high priority reason, such as a fault, then the arbitrator <NUM> will not change the arbitrated coupling state to coupled responsive to the request to couple <NUM> from the LSM <NUM>. However, if the reason for the decoupled state is lower priority, such as a preferential reason, the arbitrator <NUM> may change the arbitrated coupling state to coupled responsive to the request to couple <NUM> from the LSM <NUM>.

If, in step <NUM>, if the speed of the vehicle <NUM> is greater than the first LST <NUM>, the method moves to step <NUM>. In step <NUM> it is determined whether the speed of the vehicle <NUM> is greater than or equal to the second LST <NUM>. If the speed of the vehicle is greater than or equal to the second LST <NUM> the method moves to step <NUM>.

In step <NUM> the LSM <NUM> is arranged not to request a desired coupling state of the second electric machine <NUM>. The LSM <NUM> outputs a request for a coupling state to the arbitrator <NUM> and may, as illustrated in <FIG>, output a 'no-request' signal <NUM> to the arbitrator <NUM>, where the no-request signal <NUM> is indictive of the LSM <NUM> not requesting a specific coupling state of the second electric traction motor <NUM> to the one or more wheels of the second axle <NUM>. Thus, prior to time t<NUM> in <FIG>, the LSM <NUM> outputs the no-request signal <NUM> to the arbitrator <NUM>, or may output no signal to the arbitrator <NUM> in other embodiments. The arbitrator <NUM> may have a default coupling state. The default coupling state may be coupled i.e. for the second electric traction motor <NUM> to be coupled to the torque path of the second axle <NUM>. Thus when either a 'no-request' signal <NUM>, or no request signal is received by the arbitrator <NUM>, the arbitrator <NUM> may output a determined coupling request via the output means <NUM>.

In some embodiments, the LSM <NUM> is arranged to output the coupling signal <NUM>, indicative of a request to couple the second electric traction motor <NUM> to the at least one wheel of the second axle <NUM>. It will be appreciated that the LSM <NUM> may, in some embodiments, request the default state of coupled when the speed signal <NUM> is indicative of a low vehicle speed i.e. below the first LST <NUM>.

In some embodiments, the LSM <NUM> may apply hysteresis to the speed signal <NUM> to determine the coupling state. That is, the coupling state of coupled may be determined for a vehicle speed greater than that at which the second electric traction motor <NUM> is determined to be coupled to the torque path via the second axle <NUM> i.e. above the first LST <NUM>. Advantageously this assists in preventing 'hunting' or 'flickering' between decoupled and coupled states as the speed of the vehicle varies around (above and below) the first LST <NUM>. Use of the second LST <NUM> provides the hysteresis in some embodiments. As can be appreciated from <FIG>, between t<NUM> and prior to time t<NUM> the vehicle accelerates from a minimum speed, such that the speed signal <NUM> exceed the first LST <NUM> for a period of time prior to time t<NUM>. As can be appreciated from the lower portion of <FIG>, the 'no-request' signal <NUM> is not output immediately upon the speed of the vehicle <NUM> exceeding the first LST <NUM> i.e. coupled <NUM> is maintained.

Instead, in a region between the first and second LSTs <NUM>, <NUM> the coupling state of coupled <NUM> is maintained until the vehicle speed falls exceeds the second LST <NUM> at time t<NUM>. In step <NUM>, which is reached when the vehicle speed is between the first and second LSTs <NUM>, <NUM> the desired coupling state is determined in dependence on the speed signal <NUM> in dependence on a last intersected of the first and second LSTs <NUM>, <NUM>. Thus, prior to time t<NUM> when the speed signal <NUM> is below the second LST <NUM> the coupling state is determined in step <NUM> as coupled based on last-intersecting the first LST <NUM>. Similarly, immediately prior to time t<NUM>, when the speed signal <NUM> is above the first LST <NUM>, the 'no request' output signal <NUM> is maintained as the last intersected threshold is the second LST <NUM>.

As can be appreciated from <FIG>, some embodiments of the LSM <NUM> comprise a third LST <NUM>. The coupling of the motor <NUM> is inhibited if not successfully coupled to the second torque path via the second axle <NUM> when the vehicle speed <NUM> is equal to or less than the third LST <NUM>. The third LST <NUM> may correspond to a speed of, for example, 5kmh-<NUM> although it will be appreciated that other speeds may be selected.

In some embodiments, the LSM <NUM> is arranged to receive a signal indicative of a coupling status <NUM> of the second electric traction motor <NUM> to the at least one wheel of the axle <NUM>. The signal <NUM> reports whether the second electric traction motor <NUM> is successfully coupled to the at least one wheel of the axle <NUM>. In some situations, the coupling state may be determined as coupled and a corresponding request output by the controller <NUM>. However for electrical and/or mechanical reasons it may not be possible, at least immediately, to couple the motor <NUM> to the second torque path. For example, the second clutch <NUM> may not have yet successfully engaged a drive output of the motor <NUM> to the axle <NUM>. In particular, it may be difficult to successfully couple the motor <NUM> when the vehicle is moving slowly or has become stationary. Furthermore, attempted coupling of the motor <NUM> to the axle may be increasingly noticeable, such as in the form of noise and/or vibration, to occupants of the vehicle <NUM> at slow speeds and may possibly cause damage if attempted whilst stationary. Use of the third LST <NUM> reduces such risks.

The LSM <NUM> in some embodiments determines a coupling inhibited state. The LSM <NUM> in some embodiments outputs a coupling inhibit signal <NUM> in the coupling inhibited state when the speed signal <NUM> is indicative of a vehicle speed equal to or below the third LST <NUM>. The LSM <NUM> may output the coupling inhibit signal <NUM> when the vehicle speed is below the third LST <NUM> and the coupling status signal <NUM> is indicative of the second electric traction motor <NUM> being decoupled from the second axle <NUM> i.e. successful coupling caused by the vehicle speed being below the first LST <NUM> has not yet occurred.

In some embodiments, the LSM <NUM> may apply hysteresis to the speed signal <NUM> to determine the coupling inhibited state. That is, the coupling inhibited state may be determined for a vehicle speed greater than the third LST <NUM>. Advantageously this assists in preventing 'hunting' or 'flickering' between the decoupled and coupled states as the speed of the vehicle varies around (above and below) the third LST <NUM>. Use of a fourth LST <NUM>, as shown in <FIG> provides the hysteresis in some embodiments. The fourth LST <NUM> defines a maximum speed of a coupling inhibition region <NUM> defining the coupling inhibited state. The third and fourth LSTs <NUM>, <NUM> act as described above with respect to the first and second LSTs <NUM>, <NUM> and the speed signal <NUM>.

Some embodiments of the invention comprise a fault management module (FMM) <NUM>. The FMM <NUM> is arranged to determine a desired coupling state of the second electric traction motor <NUM> to the at least one wheel (RL, RR) of the second axle <NUM> in dependence on detection or determination of one or more faults associated with the vehicle <NUM>. The coupling state determined by the FMM <NUM> is selected to manage or mitigate faults associated with the vehicle <NUM>. For example, the FMM <NUM> may receive the temperature signal <NUM>, wherein the temperature signal <NUM> is indicative of an invertor temperature associated with the second electric traction motor <NUM>. In the event of the temperature signal <NUM> indicating that the invertor has a high temperature (above a predetermined threshold), the FMM <NUM> is arranged to determine the coupling state as decoupled in order to allow the second electric traction motor <NUM> to be inactive thereby allowing the invertor to cool for a period of time. In another example, the FMM <NUM> is arranged to receive the coupling status signal <NUM> discussed above. The coupling status signal <NUM> may be indicative of a failure to decouple the second electric traction motor <NUM> to the axle. Therefore the FMM <NUM> may determine the coupling state as coupled in dependence thereon to reduce problems associated with the problematic decoupled state. The FMM <NUM> is arranged to output a fault-derived coupling state request (FDCSR) signal <NUM> in dependence on one more received signals indicative of fault state associated with the vehicle <NUM>. The FDCSR signal <NUM> is indicative of a coupling state request determined by the FMM <NUM> in response to one or more faults or undesirable conditions or parameters associated with the vehicle. The FDCSR signal <NUM> is received by the arbitrator <NUM> in some embodiments as shown in <FIG>.

In some embodiments, the FMM <NUM> is arranged to manage retries, i.e. further attempts, of changes in the coupling state of the second electric traction motor <NUM> in the presence of a failure to successfully change the coupling state. In particular, in some embodiments, the FMM <NUM> is arranged to control the output means <NUM> of the controller <NUM> to output a signal <NUM> indicative of a retry, i.e. to request a further attempt, of a change in the coupling state of the second electric traction motor <NUM> as will be explained.

<FIG> illustrates a method <NUM> according to an embodiment of the invention. The method <NUM> is a method of managing retries of a change in coupling state of the second electric traction motor <NUM>.

In step <NUM> the coupling state of the second electric traction motor <NUM> is determined. The coupling state may be determined by one of the modules <NUM>-<NUM> and a consequent coupling state request signal received at the arbitrator <NUM>, or by the arbitrator <NUM> such as in the case of the default coupling state in the absence of any requests from the modules <NUM>-<NUM>.

In step <NUM>, a coupling state request signal <NUM> is output from the controller <NUM> via the output means <NUM> to request the determined coupling state. For example, the coupling state request may be a request for one of a coupled or decoupled state of the second electric traction motor <NUM> to the second axle <NUM>.

In step <NUM> the FMM <NUM> is arranged to determine whether a failure to change the coupling state of the second electric traction motor <NUM> to the second axle <NUM> has occurred. As discussed above, the coupling status signal <NUM> is indicative of the actual coupling status of the second electric traction motor <NUM> to the one or both wheels of the second axle <NUM>. Therefore, the FMM <NUM> is able to determine, in dependence on the coupling status signal <NUM>, whether the failure has occurred i.e. whether the actual coupling state reflects the requested coupling state. Step <NUM> may be performed after a delay to allow a change in coupling state to be implemented, such as the second clutch <NUM> being opened or closed. If the change in coupling state is successful the method returns to step <NUM>. If, however, the change was not successful i.e. a failure to change the coupling state of the second electric traction motor <NUM> has occurred as indicated by the coupling status signal <NUM>, the method moves to step <NUM>.

In step <NUM> a speed of the vehicle <NUM> is determined. Step <NUM> comprises receiving the speed signal <NUM> indicative of the speed of the vehicle <NUM>. Controlling the output means <NUM> of the controller <NUM> to output the coupling signal <NUM> indicative of a retry of the change in the coupling state is performed in dependence on the speed signal <NUM> as will be explained.

In some embodiments, the FMM <NUM> is arranged to defer controlling the output means <NUM> to output the coupling signal <NUM> indicative of the retry of the change in the coupling state in dependence on the speed signal <NUM> being indicative of the speed of the vehicle <NUM> being at least a predetermined minimum speed. The predetermined minimum speed may be, for example, a speed greater than substantially 0kmh-<NUM>. Other predetermined minimum speeds may be, for example, 5kmh-<NUM> although it will be appreciated that other minimum speeds may be selected. Advantageously, preventing a retry of the change in coupling state, particularly from changes from decoupled to coupled, at to too low a vehicle speed may prevent the retry of the engagement of the second electric traction motor <NUM> with the axle being noticeable to occupants of the vehicle <NUM>. For example, such as (although not exclusively) where the second clutch <NUM> is a dog clutch, attempting the retry may cause noise and/or vibration at low vehicle speeds.

In some embodiments, the FMM <NUM> is arranged to defer controlling the output means <NUM> to output the coupling signal <NUM> indicative of the retry of the change in the coupling state in dependence on the speed signal being indicative of the speed of the vehicle <NUM> being less than a maximum speed. The maximum speed may be, for example up to 50kmh-<NUM> or up to 30kmh-<NUM> or up to <NUM> kmh-<NUM> although other maximum speeds may be chosen. As noted above, in order to couple the second electric traction motor <NUM> to the second axle <NUM> it may be necessary to 'spin-up' or accelerate the motor <NUM> to approximately the rotation speed of the axle <NUM>. Advantageously the maximum speed prevents or reduces energy used in coupling the motor <NUM> to the axle <NUM>. Furthermore, changing from the decoupled to the coupled state at vehicle speed below the maximum speed may avoid attempting to couple the second electric traction motor <NUM> to the axle during periods of large deacceleration i.e. during heavy braking or other slowing of the vehicle <NUM> when it may be difficult to match the rotation speed of the second electric traction motor <NUM> to the axle <NUM>. Thus the FMM <NUM> defers controlling the output means <NUM> to output the coupling signal <NUM> indicative of the retry of the change in the coupling state in dependence on the speed signal <NUM> being indicative of the speed of the vehicle being less than or equal to the predetermined maximum speed.

In step <NUM> the FMM <NUM>, when it is determined that the speed of the vehicle <NUM> is either above the minimum speed or above the minimum speed and below the maximum speed considered in step <NUM>, the FMM <NUM> is arranged to output a signal <NUM> indicative of a request to retry the change of coupling state. The signal <NUM> may be a further request for the change in coupling state such as a request for one or the coupled or decoupled state. The request may be received by the arbitrator <NUM> which outputs a corresponding request or signal <NUM> via the output means <NUM> to cause the retry of the change in coupling state. Once the retry of the change has been requested the method returns to step <NUM>, where it is considered whether the retry has been successful.

In some embodiments, for every iteration of step <NUM> a counter is maintained to track a number of retries of the change in coupling state. The FMM <NUM> in some embodiments is arranged to attempt the retry up to a predetermined maximum number of times. That is, to perform step <NUM> up to the maximum number of times. The maximum number of times may be <NUM>, <NUM> or <NUM> in some embodiments. Advantageously the maximum number of retries may prevent excessive numbers of retries to avoid damaging the system <NUM>, and/or reduces energy wasted 'spinning-up' the second electric traction motor <NUM> to attempt further retries.

Some embodiments of the invention comprise an anti-fussiness module (AFM) <NUM>. The AFM <NUM> is arranged to control changes in coupling state of the second electric traction motor <NUM>. In particular, the AFM <NUM> is arranged to control a timing of changes in the coupling state of the second electric traction motor <NUM>. The AFM <NUM> may ensure that changes in the coupling state of the second electric traction motor <NUM> do not occur too frequently i.e. that at least a predetermined period of time is provided between changes in coupling state of the second electric traction motor <NUM>. The AFM <NUM> is illustrated in <FIG> as forming part of the arbitrator <NUM>. It will, however, be realised that the AFM <NUM> may be located elsewhere i.e. that other structures may be envisaged.

<FIG> illustrates a method <NUM> according to an embodiment of the invention. The method <NUM> is a method of controlling changes in coupling state of the second electric traction motor <NUM> according to an embodiment of the invention. The method <NUM> may be performed by the AF module <NUM>.

In step <NUM> of the method a coupling state of the second electric traction motor <NUM> to the second torque path via the second axle <NUM> is determined. In other words, step <NUM> comprises determining whether the second electric traction motor <NUM> is coupled to one or more wheels (RR, RL) of the second axle <NUM> of the vehicle <NUM>. The determination is performed in dependence on at least one attribute signal, such as the speed signal <NUM> indicative of the speed of the vehicle <NUM>, or the driving mode signal <NUM>. As described above, the coupling state of the second electric traction motor <NUM> may be determined by one of modules <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and a corresponding signal or request provided to the arbitrator <NUM>. For example, the HSM <NUM> may provide a request to decouple the second electric traction motor <NUM> from the rear axle <NUM>, whilst the FMM <NUM> may provide a request to couple the second electric traction motor <NUM> to the rear axle <NUM>. Thus requests for various coupling states may originate from different modules. Advantageously the AF module <NUM> is arranged to prevent frequent changes in coupling state of the second electric traction motor <NUM> in order to avoid such changes being noticeable to occupants of the vehicle <NUM>. Step <NUM> may comprise one or more requests for a coupling state being received at the arbitrator <NUM> and, in particular, the AFM <NUM>.

Step <NUM> comprises determining whether a predetermined period of time has elapsed since a last, or most recent previous, change in coupling state of the second electric traction motor <NUM>. The predetermined period of time may be a period of time since a last request for a change in coupling state was output by the controller <NUM>, or since a successful change in coupling state reported by the coupling status signal <NUM>. The predetermined period of time may be, for example, at least <NUM> second, at least <NUM> seconds, at least <NUM> seconds or at least <NUM> seconds. It will be appreciated that other periods of time may be envisaged. If the predetermined period of time has elapsed the method <NUM> moves to step <NUM>.

If the predetermined period of time has not elapsed, the method moves to step <NUM> where the AFM <NUM> is arranged to wait i.e. to defer controlling the output means <NUM> of the controller <NUM> to output the coupling signal <NUM> indicative of the requested change in the coupling state until expiry of the predetermined period of time since the last change in the coupling state. The AFM <NUM> may buffer incoming or received coupling state requests from the modules <NUM>, <NUM>, <NUM>, <NUM>, <NUM> until expiry of the predetermined period of time, as it will be appreciated that the desired coupling state may be continuously re-evaluated during the predetermined period of time. Thus upon expiry of the predetermined period of time the coupling state may be determined based upon most recently-received coupling state requests rather than implementing a first-buffered request. Advantageously this ensures that the requested coupling state upon expiry of the predetermined period of time reflects most recent attributes of the vehicle <NUM>. Upon expiry of the predetermined period of time the method moves to step <NUM>.

In step <NUM> the AF module <NUM> is arranged to control the output means <NUM> of the controller <NUM> to output the coupling request signal <NUM> to control coupling of the second electric traction motor <NUM> to the rear axle <NUM>. In some embodiments, the inhibit module is provided with a signal <NUM> indicative of an arbitrated coupling request, as will be explained.

Some embodiments of the invention comprise an inhibit module <NUM>. The inhibit module <NUM> is arranged to control changes in coupling state of the second electric traction motor <NUM>. In particular, the inhibit module <NUM> is arranged to allow for inhibition of one or more coupling states of the second electric traction motor <NUM> to the rear axle <NUM>. The inhibition of a coupling state prevents the inhibited coupling state being requested by the controller <NUM>. The inhibit module <NUM> is illustrated in <FIG> as forming part of the arbitrator <NUM>. It will, however, be realised that the inhibit module <NUM> may be located elsewhere i.e. that other structures may be envisaged.

The inhibit module <NUM> is arranged to receive the inhibit signal <NUM>. The inhibit signal is indicative of one or more coupling states of the second electric traction motor <NUM> to the rear axle <NUM> which are prohibited or inhibited. The inhibit signal <NUM> may be indicative or one of the coupled and decoupled states of the second electric traction motor <NUM> to the rear axle <NUM>. Whilst the inhibit signal <NUM> is shown as one signal it will be appreciated that in other embodiments a respective signal may be provided for each of the coupled and decoupled coupling states to indicate whether each state is inhibited. The inhibit module is arranged to output a coupling state inhibit signal <NUM> to the arbitrator which is indicative of a request for a coupling state as described below. In particular, the coupling state inhibit signal <NUM> is indicative of a request for a coupling state when that coupling state is not inhibited, thereby further indicating which coupling states are not inhibited.

<FIG> illustrates a method <NUM> according to an embodiment of the invention. The method <NUM> is a method of controlling changes in coupling state of the second electric traction motor <NUM> according to an embodiment of the invention. The method <NUM> may be performed by the inhibit module <NUM>.

In step <NUM> of the method a coupling state of the second electric traction motor <NUM> to the second torque path via the second axle <NUM> is determined. In other words, step <NUM> comprises determining whether the second electric traction motor <NUM> is coupled to one or more wheels (RR, RL) of the second axle <NUM> of the vehicle <NUM>. The determination may be performed in dependence on a determination of an expected amount of power required to spin-up the second electric traction motor <NUM> to the speed of the rear axle as compared to an amount of power available from the traction battery <NUM>. As described above, the coupling state of the second electric traction motor <NUM> may be determined by one of modules <NUM>, <NUM>, <NUM>, <NUM> and a corresponding signal or request provided to the arbitrator <NUM>. For example, the HSM <NUM> may provide a request to decouple the second electric traction motor <NUM> from the rear axle <NUM>, whilst the FMM <NUM> may provide a request to couple the second electric traction motor <NUM> to the rear axle <NUM>. Thus requests for various coupling states may originate from different modules. Advantageously the inhibit module <NUM> is arranged to prevent a coupling state of the second electric traction motor <NUM> being selected, such as in order to avoid a state associated with a fault. For example, when it is determined that a fault exists which prevents the second electric traction motor <NUM> from coupling to the rear axle <NUM>, the inhibit module <NUM> may inhibit the coupled state to avoid the coupled state being selected. Similarly, in some embodiments, one or more coupling states may be inhibited dependent upon one or more of a power limit or capability of the traction battery <NUM>. For example, if it is determined that the capability of the traction battery <NUM> to provide sufficient power to spin up the second electric traction motor <NUM> for coupling to the rear axle <NUM>, the coupled state may be inhibited in step <NUM>.

Step <NUM> may comprise one or more requests for a coupling state being received at the arbitrator <NUM> and, in particular, the inhibit module <NUM>. As explained below, the arbitrator <NUM> may determine an arbitrated coupling state in dependence on the received requests.

In step <NUM> it is determined whether the determined coupling state is inhibited. The determined coupling state may be the arbitrated coupling state determined by the arbitrator <NUM>. Step <NUM> comprises comparing the determined coupling state against the one or more inhibited coupling states, such as where the coupled state is indicated as inhibited by the inhibit signal <NUM>. Where the determined coupling state and the coupling state indicated by the inhibit signal differ, or no coupling state is indicated as inhibited, the method moves to step <NUM>. If, however, the determined coupling state is indicated as inhibited by the inhibit signal <NUM> the method returns to step <NUM>. In other words, the method <NUM> prevents a request for an inhibited coupling state being output in step <NUM>.

In step <NUM> the inhibit module <NUM> is arranged to control the output means <NUM> of the controller <NUM> to output the coupling request signal <NUM> to control coupling of the second electric traction motor <NUM> to the rear axle <NUM>. That is, when the determined coupling state is not indicated as inhibited by the inhibit signal <NUM> a request for the determined coupling state is output by the controller <NUM>.

Some embodiments of the invention comprise a driving mode module (DMM) <NUM>. The DMM <NUM> is arranged to determine a coupling state of the second electric traction motor <NUM> in dependence on a driving mode of the vehicle <NUM>. The driving mode of the vehicle <NUM> is indicated by the driving mode signal <NUM>. The driving mode of the vehicle <NUM> may be selected by a driver or occupant of the vehicle <NUM>, or may at least in part be determined by a module or system of the vehicle <NUM>, such as a terrain-response (TR) module which adaptively selects a driving mode including one or more settings of the vehicle and, in particular, a powertrain thereof such as a traction control mode thereof, for example. The driving mode may include driving selected settings, such as of the powertrain, including a driving mode of the vehicle including one of forward, reverse or neutral in the case of an automatic gearbox or a gear selection of a manual gearbox. The driving mode may include a selection of one of sport, normal or economy driving modes where settings of one or more of the engine, first and/or second electric motors, suspension etc of the vehicle <NUM> may be adapted accordingly. Data indicative of the selected driving mode(s) is provided by the driving mode signal.

<FIG> illustrates a method <NUM> according to an embodiment of the invention. The method <NUM> is a method is a method of controlling changes in coupling state of the second electric traction motor <NUM> according to an embodiment of the invention. Some of the steps of the method <NUM> may be performed by the DMM <NUM>.

In step <NUM> an attribute-based coupling state of the second electric traction motor <NUM> to the second axle <NUM> is determined. The determination in step <NUM> is performed in dependence on at least one attribute signal, such as the speed signal <NUM> indicative of the speed of the vehicle. As described above, the coupling state of the second electric traction motor <NUM> may be determined by one of modules <NUM>, <NUM>, <NUM>, <NUM> and a corresponding signal or request provided to the arbitrator <NUM>. For example, the HSM <NUM> may provide a request to decouple the second electric traction motor <NUM> from the rear axle <NUM>, whilst the FMM <NUM> may provide a request to couple the second electric traction motor <NUM> to the rear axle <NUM>. Thus requests for various coupling states may originate from different modules. Step <NUM> may be performed by one of more the HSM <NUM>, the LSM <NUM>, and FMM <NUM>. Step <NUM> may be performed in dependence on signals <NUM>, <NUM>, <NUM> except for the driving mode signal <NUM>. One of more signals indicative of the determined coupling states is provided to the arbitrator <NUM>. The one or more coupling states determined in step <NUM> may be together referred to as first coupling states of the second electric traction motor <NUM>.

In step <NUM> a driving-mode-based coupling state of the second electric traction motor <NUM> to the second axle <NUM> is determined. Step <NUM> is determined in dependence on the driving mode signal <NUM>.

In one example, the driving mode signal <NUM> may indicate a selected driving mode of the vehicle including selection of an efficiency-based driving mode. The efficiency-based driving mode is selected in order to provide improved efficiency of the vehicle <NUM>, i.e. reduced energy consumption, such as the expense of performance of the vehicle <NUM>. The efficiency may be to improve consumption of fuel provided to the engine <NUM> or to conserve electrical power consumed the motors <NUM>, <NUM>. The driving mode signal <NUM> is indicative of the selection of the efficiency based driving mode which may be manually or automatically selected. Similarly, in another example, the driving mode signal may be indicative of a neutral gear of the vehicle <NUM> being selected.

In dependence on the driving mode signal <NUM> the DMM <NUM> is arranged to determine the coupling state of the second electric traction motor <NUM> to the rear axle <NUM>, such as one of coupled and decoupled. A signal <NUM> indicative of the driving-mode-based coupling state is provided to the arbitrator <NUM>. The driving-mode-based coupling state may be referred to as a second coupling state of the second electric traction motor <NUM>. Thus the coupling state determined in step <NUM> may be decoupled.

In another example, the driving mode signal <NUM> may indicate either a driver-selected or automatically-selected, such as by the terrain response module, driving mode such as requesting four-wheel drive of the vehicle <NUM> which requires coupling of the second electric traction motor <NUM> to provide power to the rear axle <NUM>. Thus the coupling state may be determined as coupled in step <NUM>.

In step <NUM> it is determined whether the first and second coupling states are the same i.e. equal. That is, whether the first coupling state as one of coupled or decoupled is equal to the second coupling state as one of coupled or decoupled. If the first and second coupling states are equal then, method moves to step <NUM>. If, however, the first and second coupling states differ then the method moves to step <NUM>.

In step <NUM>, the output means <NUM> is controlled to output the coupling signal <NUM> indicative of the first and second coupling states i.e. one of coupled or decoupled.

In step <NUM>, the output means <NUM> is controlled to output the coupling signal <NUM> indicative of the first coupling state i.e. the attribute-based coupling state when the determined first and second coupling states differ. That is, the arbitrator <NUM> is arranged to allocate a higher priority to the first coupling state than the second coupling state. This is reflected in Table <NUM> below, as will be explained, by the efficiency column being right-most such that coupling states determined e.g. by the HSM <NUM> etc take precedence. Only when no requests are received from the other modules does arbitrated coupling state independently follow the coupling state determined by the DMM <NUM>.

<FIG> illustrates a coupling state determined by the DMM <NUM> according to some embodiments of the invention. In some embodiments, the DMM <NUM> is arranged to determine the coupling state of the second electric traction motor <NUM> in dependence on the driving mode signal <NUM> being indicative of a mode, or gear selection, of the powertrain in particular a gearbox thereof, such as one of drive (D), neutral (N) and Reverse (R) i.e. a shifter position. As can be appreciated, the DMM <NUM> is arranged to not to request <NUM> a coupling state <NUM> when the powertrain is not in neutral i.e. one of D or R is selected, or a gear of the gearbox is selected. In such a state the DMM <NUM> may output the no-request NR signal. However, when N is selected <NUM>, as indicated by the driving mode signal <NUM>, the DMM <NUM> is arranged to output the coupling signal <NUM> to request the decoupled state <NUM>. Thus the second electric traction motor <NUM> is requested to be decoupled when N is selected.

As described above, some embodiments of the present invention comprise the arbitrator <NUM>. The arbitrator <NUM> is arranged to receive one or more requests for coupling states of the second electric traction motor <NUM> and to determine an overall or arbitrated coupling state of the second electric traction motor <NUM> to the second axle <NUM>. The arbitrator <NUM> is arranged to control the output means <NUM> of the controller <NUM> to output the coupling signal <NUM> indicative thereof. The arbitrator <NUM> is arranged to allocate a predetermined precedence or priority to at least some of the requests for coupling states from different modules. Table <NUM> below identifies requests for coupling state requests received from the various modules of the controller <NUM>, a default coupling state i.e. in the absence of any other requests, and a determined coupling state of the arbitrator <NUM>.

The arbitrator <NUM> is arranged to receive the FDCSR signal <NUM> from the FMM <NUM> at an input means thereof. It can be appreciated that the arbitrator <NUM> also receives a plurality of further coupling state request signals <NUM>, <NUM>, <NUM>, i.e. from each of modules <NUM>, <NUM>, <NUM>. Each coupling state request signal is indicative of a request for a coupling state of the second electric traction motor <NUM> to the at least one wheel of the second axle <NUM>.

Referring to <FIG>, which illustrates a method of determining the coupling state in the presence of an FDCSR <NUM> from the FMM <NUM>. The arbitrator <NUM> is arranged to determine an arbitrated coupling state of the second electric traction motor <NUM> to the at least one wheel of the second axle <NUM> in dependence on the FDCSR signal <NUM> and the at least one further coupling state request signal <NUM>, <NUM>, <NUM>. The arbitrator <NUM> is arranged to determine the arbitrated coupling state of the second electric traction motor <NUM> in precedence on the FDCSR signal <NUM> over the at least one further coupling state request signal <NUM>, <NUM>, <NUM>.

In <FIG>, in step <NUM> the arbitrator <NUM> is arranged to receive the FDCSR signal <NUM> from the FMM <NUM>. The FDCSR signal <NUM> is indicative of a coupling state request as explained above. For example, the FDCSR signal <NUM> is indicative of a request for one of a coupled or decoupled state as indicated in Table <NUM>.

In step <NUM> the arbitrator <NUM> is arranged to receive any other coupling state request signals i.e. from modules <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. It will be appreciated, as contemplated by Table <NUM>, that at some points in time no other coupling state request are received at the same time as the FDCSR <NUM>.

In step <NUM>, a coupling state of the second electric traction motor <NUM> is determined in dependence on the FDCSR <NUM> and any other received coupling state requests. As can be appreciated from Table <NUM> above, when the FDCSR signal <NUM> is indicative of the decoupled state (D), the arbitrator <NUM> is arranged to determine the arbitrated coupling state as decoupled irrespective of a state of the further coupling state request signals <NUM>, <NUM>, <NUM>. Thus the arbitrator <NUM> is arranged to determine the coupling state of the electric machine <NUM> in precedence on the FDCSR signal <NUM> over the any further coupling state request signals. In particular, the arbitrator <NUM> is arranged to determine the decoupled state of the second electric traction motor <NUM> in precedence on the FDCSR signal <NUM> being indicative of a request to decouple the second electric traction motor <NUM> over any further coupling state requests.

When the arbitrator <NUM> receives the high-speed coupling state request <NUM>, HSCSR, signal from the HSM <NUM> which is indicative of a request to disconnect (D) the second electric traction motor <NUM> from the second axle <NUM>, as can be appreciated from Table <NUM>, when no FDCSR <NUM> is received (NR) or when the FDCSR signal <NUM> is indicative of a coupled (C) request, the arbitrator <NUM> determines the arbitrated coupling state of the second electric traction motor <NUM> as decoupled in dependence on the request from the HSM <NUM> to, advantageously, protect the second electric traction motor <NUM> from excessive rotation speed. Thus, the decoupled request from the HSM <NUM> takes precedence over the FDCSR <NUM> when in contradiction.

In step <NUM>, the arbitrator <NUM> is arranged to output an arbitrated coupling request signal <NUM> indicative of the arbitrated coupling state to control coupling of the second electric traction motor <NUM> to the at least one wheel (RL, RR) of the second axle <NUM>. The arbitrated coupling request signal <NUM> is output via the output means <NUM> of the controller <NUM> to control the coupling of the second electric traction motor <NUM>.

<FIG> illustrates an overall operation of the system <NUM>. Trace <NUM> represents an arbitrated coupling state request output by the controller <NUM> as signal <NUM>. Trace <NUM> represents an actual coupling state of the second electric traction motor <NUM> to the at least one wheel (RL, RR) of the second axle <NUM>. Trace <NUM> is a connection inhibit signal and trace <NUM> is disconnection or decoupled state inhibit signal.

As can be appreciated, during period <NUM> the DMM <NUM> determines the coupling state is decoupled such as based on the driving mode signal <NUM> being indicative of the efficiency-based driving mode. The coupling state of coupled being inhibited, as indicated by <NUM>, does not have an effect since the arbitrated coupling state is decoupled. During period <NUM> the DMM <NUM> determines the coupling state as coupled based on the IDD driving mode indicated by the driving mode signal <NUM>. However, the connection inhibit signal <NUM> indicates that the coupled state is inhibited, thereby the actual state of the coupling is decoupled i.e. the coupling inhibited state takes precedence over the coupled state requested by the DMM <NUM>. However, during period <NUM> once the coupled state inhibit signal <NUM> indicates that the coupled state is not inhibited, the coupled state is achieved. During period <NUM> the coupled state is requested as a default coupling state of the arbitrator <NUM>, although partially during period <NUM> the decoupled state is inhibited as shown by trace <NUM> although this does not affect the coupling state during period <NUM> as coupled is still requested by the arbitrator <NUM>. However, during period <NUM> when the decoupled state requested by the HSM <NUM>, due to decoupled still being inhibited, the coupled state is maintained. Once the inhibition is cancelled during period <NUM> the coupling state of decoupled is requested by the arbitrator <NUM> corresponding to the requested state of the HSM <NUM>. During period <NUM> the LSM <NUM> requests the coupled state.

It will be appreciated that embodiments of the present invention can be realised in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs that, when executed, implement embodiments of the present invention. Accordingly, embodiments provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine readable storage storing such a program. Still further, embodiments of the present invention may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same.

Claim 1:
An electric machine control system for a vehicle (<NUM>), the electric machine control system comprising one or more controllers, wherein the vehicle (<NUM>) comprises an electric machine (<NUM>) arranged to be selectively coupleable to provide torque to at least one wheel of an axle of the vehicle (<NUM>), the control system comprising:
input means to receive a speed signal (<NUM>) indicative of a speed of the vehicle (<NUM>);
processing means arranged to determine a desired coupling state of the electric machine (<NUM>) to the at least one wheel of the axle in dependence on the speed signal, wherein the processing means is arranged to determine the desired coupling state as:
a decoupled state in dependence on the speed signal being indicative of a vehicle speed equal to or greater than a first high-speed threshold (<NUM>); and
a no-request state in dependence on the speed signal being indicative of vehicle speed equal to or below a second high-speed threshold (<NUM>), wherein the no-request state is indicative of not requesting a specific coupling state of the electric machine (<NUM>) to the at least one wheel of the axle and the second high-speed threshold (<NUM>) represents a vehicle speed lower than the first high-speed threshold (<NUM>); and
output means arranged to output a coupling signal indicative of the desired coupling state to control coupling of the electric machine to the at least one wheel of the axle;
characterized in that
the processing means is further arranged to: determine the desired coupling state as the decoupled state in dependence on the speed signal last intersecting the first high speed threshold (<NUM>) and being indicative of a vehicle speed below the first high-speed threshold (<NUM>); and, determine the desired coupling state as the no-request state in dependence on the speed signal last intersecting the second high speed threshold (<NUM>) and being indicative of a vehicle speed above the second high-speed threshold (<NUM>).