Patent Description:
It is known to provide a hybrid electric vehicle having an internal combustion engine operable to provide drive torque to drive the vehicle and an electrical propulsion motor operable to provide drive torque when the vehicle is operated in an electric vehicle (EV) mode. A vehicle control system determines when to switch the internal combustion engine on or off, and when to open or close a clutch K0 between the engine and a transmission. In some vehicles the electric propulsion motor is integrated into the transmission.

It is also known to provide an electric machine as a starter for cranking the engine when an engine start is required. Known starters include belt-integrated starter/generators. Such devices are operable as electrical generators driven by the engine as well as a starter. The vehicle may include a belt integrated starter generator in addition to a starter for starting the engine, in some embodiments.

<CIT>) relates to a Hybrid vehicle and hybrid vehicle control method.

<CIT>) and <CIT>) relate to a Control device of hybrid vehicle.

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

Aspects of the present invention provide a controller, a hybrid electric vehicle powertrain, a hybrid electric vehicle, a method and a computer readable medium.

In one aspect of the invention for which protection is sought there is provided a controller for a hybrid electric vehicle according to claim <NUM>.

Embodiments of the present invention have the advantage that the operating mode of the powertrain at a given moment in time may be influenced by adjustment of the reference value of the state of charge depending on the selected hybrid driving mode. Thus, according to the invention the controller is configured to favour operation of the powertrain in the EV mode when a particular driving mode is selected. Thus if a user wishes to enjoy vehicle operation in EV mode more than a mode in which the engine is switched on, the user may select a corresponding hybrid driving mode.

It is to be understood that reference to an instant state of charge is to be understood to mean a prevailing or current state of charge of the energy storage means. The instant state of charge may be the most recently available measured value of state of charge of the energy storage means in some embodiments.

The engine may be an internal combustion engine. The engine may be petrol fired or diesel fired. Other arrangements are also useful.

The controller may be operable to determine the appropriate powertrain operating mode in dependence at least in part on a deviation of the signal indicative of the instant state of charge from the reference value of state of charge.

According to the invention the controller is arranged to promote charging of the energy storage means to a higher state of charge when the powertrain is in the engine charging mode, thus favouring operation of the powertrain in the EV mode for longer periods when the engine is switched off.

According to the invention the controller is operable to determine which of the powertrain operating modes is appropriate at a given moment in time according to a value of a cost function for each powertrain operating mode, the value of the cost function being determined at least in part by reference to the signal indicative of the instant state of charge and the reference value of state of charge of the respective powertrain operating modes.

Optionally, the value of the cost function of each powertrain operating mode is determined at least in part in further dependence on at least one selected from amongst a rate of fuel consumption of the vehicle, a rate of emission of a gas by the vehicle and an amount of noise generated by the vehicle.

The controller may be configured to determine the required powertrain operating mode according to a feedback Stackelberg equilibrium control optimisation methodology.

Such a methodology is known, and may be understood for example by reference to UK patent application <CIT>.

In some embodiments, the cost function is responsive at least in part to a deviation of a state of charge of the energy storage means from the reference value.

The controller may be arranged to receive a signal indicative of the required hybrid driving mode from a user.

That is, the user may input a signal indicative of the required hybrid driving mode.

According to the invention, the hybrid driving modes include a first driving mode favouring prolonged operation in EV mode, and a second driving mode favouring a reduction in fuel consumption, wherein the value of reference state of charge in the first driving mode is higher than that in the second driving mode.

The first mode may correspond to a selectable electric vehicle (SEV) mode. The second mode may correspond to a general or default hybrid electric vehicle (HEV) driving mode. In embodiments, other modes may be available and/or useful.

Advantageously, when the powertrain is in the EV powertrain mode the controller may be operable to cause the powertrain to assume the engine charging powertrain mode in dependence at least in part on driver torque demand. If the vehicle is in the first mode and the powertrain is in the EV powertrain mode, the controller may be arranged to cause the powertrain to switch from the EV mode to the engine charging powertrain mode only above a threshold value of driver torque demand that is higher than that when the vehicle is operating in the second mode.

Advantageously, when the powertrain is in the engine charging operating mode the controller may be configured to cause the generator means to apply a greater charging load to the engine when the vehicle is in the first driving mode compared with the second driving mode.

This feature has the advantage that, because the energy storage means is charged more aggressively in the first mode, the state of charge increases more quickly, enabling the vehicle to spend a greater amount of time in the EV powertrain operating mode.

Optionally when the powertrain is in the EV operating mode the controller is operable to cause the engine to switch on when vehicle speed exceeds a prescribed value, the prescribed value being higher when the vehicle is operating in the first mode relative to the second mode.

The prescribed vehicle speed for engine start may be gradient dependent. That is, the threshold may be greater when the vehicle is descending a hill compared with travel over flat terrain, or uphill. The speed may increase with increasing downhill gradient steepness.

The engine may be switched on to provide drive torque in the case of a parallel hybrid vehicle, or so that the powertrain can assume the engine charging mode in the case of a parallel hybrid electric vehicle or a series hybrid electric vehicle.

Optionally, when the controller causes the vehicle to operate in the first mode or the second mode the controller causes the engine to turn on in dependence at least in part on an amount by which an accelerator pedal is depressed.

If the accelerator pedal is not depressed, or depressed by less than a threshold amount, the controller may cause the powertrain to remain in the EV mode. Thus if a vehicle speed increases above a turn-on threshold due to coasting downhill, the vehicle may remain in the EV mode.

Optionally the state of charge of the energy storage means is permitted to take a value from a prescribed absolute minimum state of charge to a prescribed soft minimum value greater than the prescribed absolute minimum state of charge only when the vehicle is operating in the first hybrid operating mode or upon vehicle initialisation.

The magnitude of the interval from the prescribed absolute minimum state of charge to the prescribed soft minimum value may be approximately <NUM>% of the magnitude of the interval from the prescribed absolute minimum state of charge to a prescribed absolute maximum state of charge.

This has the benefit that the powertrain is more likely to operate in the EV mode when the driver selects the first mode because the interval of state of charge values below the soft minimum value (that is, in the so-called 'reserved' interval) will normally be available for use. The reserved interval may be used automatically upon vehicle initialisation thus providing a smooth vehicle departure from rest. Once the vehicle has operated in the reserved interval, the controller may subsequently inhibit vehicle operation in said reserved interval when the state of charge value increases above the prescribed soft minimum value. This helps to some extent to ensure that the driver does not experience prolonged periods when the engine is on and/or periods where a greater charging load to the engine is applied when the vehicle is no longer operating in the first mode.

The controller may be operable to cause the engine to be drivably coupled to one or more wheels of the vehicle in addition to the electric propulsion means.

Thus the controller may be suitable for controlling a parallel hybrid vehicle.

The controller may be operable to cause the engine to deliver drive torque when the powertrain is operated in the engine charging mode.

The controller may be operable to cause the powertrain to operate in a parallel boost mode in which the engine delivers drive torque in addition to the electric propulsion means.

In a further aspect of the invention for which protection is sought there is provided a hybrid electric vehicle powertrain according to claim <NUM>.

Optionally, the electric generator means and the electric propulsion means are each provided by an electric machine.

The controller may be operable to cause the electric machine to be operated as a propulsion motor or a generator.

The generator means may comprise an electric generator and the electric propulsion means may comprise a propulsion motor.

In a further aspect of the invention there is provided a hybrid electric vehicle according to claim <NUM>.

The vehicle may be operable in a parallel mode in which the engine delivers drive torque to the powertrain.

The vehicle may be operable in a series mode in which the engine drives the generator means to develop charge to recharge the battery or power the propulsion motor whilst the propulsion motor delivers drive torque to the powertrain.

In a further aspect of the invention for which protection is sought there is provided a method of controlling a hybrid electric vehicle according to claim <NUM>.

In one aspect of the invention for which protection is sought there is provided a computer readable medium according to claim <NUM>.

Embodiments of the invention will now be described with reference to the accompanying figures in which:.

In one embodiment of the invention a hybrid electric vehicle <NUM> is provided as shown in <FIG>. The vehicle <NUM> has an engine <NUM> coupled to a belt integrated starter generator (BISG) 123B. The BISG 123B may also be referred to as a belt integrated (or belt mounted) motor generator and is operable to crank the engine <NUM> when starting is required. In addition or instead, a dedicated starter motor may be provided. In some embodiments therefore, a BISG may be provided but a separate starter motor is employed for starting the engine <NUM>. The engine <NUM> is coupled in turn to a crankshaft-integrated starter/generator (CIMG) 123C by means of a clutch <NUM>. The clutch <NUM> may also be referred to as a K0 clutch <NUM>.

The CIMG 123C is integrated into a housing of a transmission <NUM> which is in turn coupled to a driveline <NUM> of the vehicle <NUM> thereby to drive a pair of front wheels <NUM>, <NUM> and a pair of rear wheels <NUM>, <NUM> of the vehicle <NUM>. The driveline <NUM> in combination with the transmission <NUM>, CIMG 123C, clutch <NUM>, engine <NUM> and BISG 123B may be considered to form part of a powertrain <NUM> of the vehicle <NUM>. Wheels <NUM>, <NUM>, <NUM>, <NUM> arranged to be driven by the driveline <NUM> may also be considered to form part of the powertrain <NUM>.

It is to be understood that other arrangements are also useful. For example the driveline <NUM> may be arranged to drive the pair of front wheels <NUM>, <NUM> only or the pair of rear wheels <NUM>, <NUM> only, or to be switchable between a two wheel drive mode in which the front or rear wheels only are driven and a four wheel drive mode in which the front and rear wheels are driven.

The BISG 123B and CIMG 123C are arranged to be electrically coupled to a charge storage module <NUM> having a battery and an inverter. The module <NUM> is operable to supply the BISG 123B and/or CIMG 123C with electrical power when one or both are operated as propulsion motors. Similarly, the module <NUM> may receive and store electrical power generated by the BISG 123B and/or CIMG 123C when one or both are operated as electrical generators. In some embodiments, the CIMG 123C and BISG 123B may be configured to generate different electrical potentials to one another. Accordingly, in some embodiments each is connected to a respective inverter adapted to operate at the corresponding potential of the CIMG 123C or BISG 123B. Each inverter may have a respective battery associated therewith. In some alternative embodiments the CIMG 123C and BISG 123B may be coupled to a single inverter which is adapted to receive charge from the CIMG 123C and BISG 123B at the respective potentials and to store the charge in a single battery. Other arrangements are also useful.

As noted above, the BISG 123B has an electric machine 123BM that is drivably coupled to a crankshaft 121C of the engine <NUM> by means of a belt 123BB. The BISG 123B is operable to provide torque to the crankshaft 121C when it is required to start the engine <NUM> or when it is required to provide torque-assist to the driveline <NUM> as discussed in further detail below.

The vehicle <NUM> has a vehicle controller <NUM> operable to command a powertrain controller <NUM> PT to control the engine <NUM> to switch on or off and to generate a required amount of torque. The vehicle controller <NUM> is also operable to command the powertrain controller 141PT to control the BISG 123B to apply a required value of positive or negative torque (operating as a propulsion motor or a generator) to the engine <NUM>. Similarly, the vehicle controller <NUM> may command the CIMG 123C to apply a required value of positive or negative torque (again operating as a propulsion motor or a generator) to the driveline <NUM> via the transmission <NUM>.

The vehicle has an accelerator pedal <NUM> and a brake pedal <NUM>. The accelerator pedal <NUM> provides an output signal to the vehicle controller <NUM> indicative of an amount by which the pedal <NUM> is depressed. The vehicle controller <NUM> is arranged to determine the amount of driver demanded torque based on the accelerator pedal position and one or more other vehicle parameters including engine speed W.

The vehicle <NUM> of <FIG> is operable by the vehicle controller <NUM> in an electric vehicle (EV) mode in which the clutch <NUM> is open and the crankshaft 121C is stationary. In EV mode the CIMG 123C is operable to apply positive or negative torque to the driveline <NUM> via the transmission <NUM>. Negative torque may be applied for example when regenerative braking is required under the control of a brake controller 142B.

The powertrain <NUM> is operable in one of a plurality of parallel modes in which the engine <NUM> is switched on and the clutch <NUM> is closed. The parallel modes include a 'parallel boost' mode in which the CIMG 123C is operated as a motor to provide drive torque to the driveline <NUM> in addition to the torque provided by the engine <NUM>. In the present embodiment the powertrain <NUM> is operated in the parallel boost configuration when the amount of driver demanded torque exceeds the maximum torque available from the engine <NUM>. The amount of additional torque available from the CIMG 123C may be determined in dependence on the vehicle configuration as described in more detail below. It is to be understood that the feature of torque boost increases the available drive torque beyond that which is available from the engine <NUM> alone.

The parallel modes also include a parallel torque filling mode and a parallel torque assist mode. The parallel torque filling mode is a mode in which the CIMG 123C delivers drive torque to the driveline <NUM> in addition to the engine <NUM> in order to meet driver demand for torque more quickly than if the engine <NUM> alone delivers drive torque. Torque filling provides the benefit that driver torque demand may be satisfied more quickly, improving a responsiveness of the vehicle to an increase in torque demand.

In the present embodiment torque filling is implemented when a rate of increase of driver torque demand relative to the amount of torque delivered by the engine <NUM> exceeds a prescribed value. Once driver torque demand has been satisfied, the amount of torque delivered by the CIMG 123C decreases as the amount of torque delivered by the engine <NUM> increases to meet driver demand substantially entirely, without a requirement for additional torque from the CIMG 123C.

In the torque-assist parallel mode the CIMG 123C provides steady-state drive torque in addition to the engine <NUM> in order to relieve loading on the engine <NUM>. This may assist in reducing fuel consumption. Torque-assist may be considered to be distinct from 'torque filling', the latter being employed in a transient manner when an increase in drive torque is required.

The powertrain <NUM> may alternatively be operated in a parallel recharge mode in which the CIMG 123C is driven as a generator by the engine <NUM> to recharge the charge storage module <NUM>.

In the present embodiment, the vehicle <NUM> is also operable in one of a plurality of hybrid operating modes. The hybrid operating modes include a default hybrid electric vehicle (HEV) operating mode and a user-selectable EV hybrid operating mode, referred to herein as a 'selectable EV operating mode' (SEV operating mode). The SEV operating mode is selected by a user by means of SEV selector button <NUM> accessible to a driver whilst driving. When depressed, the SEV button <NUM> illuminates to confirm the SEV operating mode has been selected.

In the present embodiment the vehicle <NUM> is also operable in a selectable hybrid inhibit (SHI) hybrid operating mode in which the controller <NUM> causes the engine <NUM> to latch in the on condition, and in a command shift or 'tip shift' (TIP) hybrid operating mode.

Whether the vehicle is operating in the HEV hybrid operating mode, the SEV hybrid operating mode, the SHI hybrid operating mode or the TIP operating mode the controller <NUM> is configured to determine in which available powertrain mode the powertrain <NUM> should be operated in dependence on an energy optimisation strategy that employs game theory. It is to be understood that in the SHI hybrid operating mode the EV mode is not available since the engine <NUM> is latched in the on condition. The controller <NUM> is configured to take this factor into account in determining the required powertrain mode, however in the present embodiment the controller <NUM> still employs the same energy optimisation strategy. Other arrangements are also useful.

The non-cooperative approach of game theory is applied by considering a multi-stage game played by the following two players: a) a first player, the driver, represented by a discrete set of load sites (for example wheel torque, wheel speed and gear selected), covering the powertrain capability, and b) a second player, the powertrain, represented by a discrete set of operating modes.

The first player is interested in minimizing a cost functional while the second player is interested in maximizing the cost functional. The cost functional is formed as a sum of incremental cost values over a finite horizon.

In respect of the embodiment of <FIG> the cost functional of the game is based on the following incremental cost function L related to the control action, u, the state vector, x, and the operating variable, w : <MAT> where u ∈ U is the control action (U is the set of powertrain modes in this case which include the parallel boost mode and parallel recharge mode), x∈ X is the state vector (X is the set of discretised high voltage battery SoC (state of charge) values in this case) and w∈ W is the vector of operating variables which is also referred to as the load site (discretised wheel speed, wheel torque and gear selected in this case). In the above equation, Fuel denotes engine fuel consumption, NOx denotes engine NOx emission mass flow rate, SoCSetPoint denotes the desired SoC set-point at the end of the cycle, ΔSoC(u, w) denotes the deviation of SoC resulting from a defined control action at a given load site.

Here G denotes a positive Gaussian function with the centre at the centre of mass of a defined drive cycle, introduced to focus the optimization on specific load sites.

In the present embodiment, the value of SoC set-point (which may be referred to also as a target value or a reference value) is changed in dependence on whether the vehicle <NUM> is operated in the SEV mode, the HEV mode or the TIP mode. The SoC set-point may also be changed in dependence on transmission operating mode. The value of SoC set-point is set to a higher value for operation in the SEV mode, TIP mode and transmission sport operating mode (when in the HEV mode) compared with operation in the HEV mode in the drive transmission operating mode in order to promote charging of the charge storage module <NUM>. In the present embodiment, if the vehicle <NUM> is operated in the SEV mode, TIP mode or if the transmission <NUM> is operated in the sport mode whilst in HEV mode, the value of SoC set-point (that is, Game Theory setpoint, also referred to as target value or reference value) is set to <NUM>% (other values are also useful) whilst if the vehicle <NUM> is operated in the HEV mode (with the transmission in the drive mode) the value of SoC set-point is set to <NUM>%. Other values are also useful. Similarly, other values of SoC set-point whilst operating in various hybrid and transmission operating modes are also useful. The fact that the value of SoC set-point is set to a higher value in the SEV mode causes the controller <NUM> to tend to charge the charge storage module <NUM> to higher values of state of charge (SoC). For operation in the SHI and TIP hybrid modes, the SoC set-point may be set to the same value as the HEV mode, or to any other suitable value.

<FIG> are graphical illustrations of the manner in which the controller <NUM> causes the vehicle <NUM> to operate when the HEV and SEV driving modes are selected, respectively. The figures show state of charge of the charge storage module <NUM> along a horizontal axis. The content of the figures will now be discussed.

In order to promote operation of the vehicle <NUM> in the EV mode when the vehicle is in the SEV mode, the controller <NUM> is configured to implement the following measures:.

In the present embodiment, if the SoC of the charge storage module <NUM> reaches a value below a prescribed engine start SoC value, the controller <NUM> forces the powertrain to assume the parallel recharge mode until the SoC of the charge storage module <NUM> exceeds a prescribed minimum engine stop SoC value. Once the SoC exceeds the minimum engine stop SoC value the powertrain <NUM> may resume operation in the EV mode if the controller <NUM> determines this is the optimum mode according to the energy optimisation strategy. If the powertrain <NUM> resumes operation in the EV mode once the SoC exceeds the prescribed minimum engine stop SoC value following an engine start due to the SoC falling below the engine start SoC value, the minimum engine stop SoC value is incremented by a prescribed increment amount. In the present embodiment, the prescribed increment amount is higher when operating in SEV mode compared with HEV mode although in some embodiments the increment amounts may be substantially equal. This feature has the effect that when the engine <NUM> is next started, it must charge the energy storage module <NUM> to a higher SoC before the engine <NUM> may be switched off, increasing the available charge for operation in EV mode.

In the present embodiment, when operating in HEV mode the prescribed increment amount is <NUM>% each time the engine is stopped as soon as the SoC reaches the minimum engine stop SoC value. When operating in SEV mode the prescribed increment amount is <NUM>%. Other values are also useful.

Advantageously, the minimum engine stop SoC is higher when operating in the SEV mode compared with the HEV mode. This allows longer uninterrupted periods of operation in EV mode in a number of situations. In the present embodiment the minimum engine stop SoC is around <NUM>% when operating in HEV mode and around <NUM>% when operating in SEV mode. Other values are also useful.

This feature has the advantage that a time period for which the powertrain <NUM> operates in EV mode may be increased.

When the powertrain <NUM> is operated in a parallel mode, the controller <NUM> is operable to assume the parallel torque boost mode when an amount of driver torque demand exceeds that which may be provided by the engine <NUM> alone at its maximum torque output. As noted above, driver torque demand is related to accelerator pedal position. In the SEV mode, the controller <NUM> limits provision of torque boost to situations in which the accelerator pedal is depressed more than a prescribed amount (which may be specified in terms of a proportion of full travel in some embodiments). In the present embodiment, when the vehicle is operated in the SEV mode the parallel torque boost mode is only permitted when the accelerator pedal <NUM> is depressed by more than <NUM>%, corresponding to movement of the pedal <NUM> beyond the 'kick down' detent in the present embodiment. Other arrangements are also useful. However, this feature advantageously reduces draining of charge from charge storage module <NUM> relative to operation in the HEV hybrid operating mode.

In some embodiments the controller <NUM> may suspend provision of torque boost in the SEV mode altogether.

Furthermore, the provision of torque filling is also restricted when in the SEV mode compared with the HEV mode. In some embodiments torque filling is not permitted in the SEV mode.

In some embodiments, energy overrun charging (i.e. use of the engine to drive the CIMG 123C in order to slow the vehicle when the engine <NUM> is switched on) is not permitted in the HEV mode, but is permitted in the SEV mode. Other arrangements are also useful.

Claim 1:
A controller (<NUM>) for a hybrid electric vehicle (<NUM>) having a powertrain, the powertrain including an engine (<NUM>), electric propulsion means powered by energy storage means (<NUM>) and electric generator means operable to be driven by the engine (<NUM>) to recharge the energy storage means (<NUM>), the controller (<NUM>) being operable to:
receive a signal indicative of a required hybrid operating mode of the vehicle (<NUM>) the hybrid operating modes including a first hybrid operating mode favouring prolonged operation in an electric vehicle (EV) powertrain mode by promoting charging of the energy storage means and a second hybrid operating mode favouring a reduction in fuel consumption, wherein in each hybrid operating mode, the powertrain is configured to operate in a plurality of different powertrain modes;
receive a signal indicative of a state of charge of the energy storage means (<NUM>);
determine which of the plurality of powertrain modes is appropriate for vehicle operation at a given moment, the powertrain modes including an engine charging powertrain mode in which the engine (<NUM>) drives the generator means to recharge the energy storage means (<NUM>) and the electric vehicle (EV) powertrain mode in which the engine (<NUM>) is switched off and the electric propulsion means is operable to develop drive torque to drive the vehicle (<NUM>); and
cause the powertrain to assume the appropriate powertrain mode, wherein the controller (<NUM>) is operable to determine which of the plurality of powertrain modes is appropriate for vehicle operation in dependence at least in part on the signal indicative of the instant state of charge of the energy storage means (<NUM>) and a reference value of state of charge, the reference value in the first hybrid operating mode being higher than that in the second hybrid operating mode, and the controller (<NUM>) being operable to set the reference value of state of charge to one of a plurality of different respective values in dependence on the signal indicative of the required hybrid operating mode;
wherein the controller is operable to determine which of the powertrain modes is appropriate at a given moment in time according to a value of a cost function for each powertrain mode, the value of the cost function being determined at least in part by reference to the signal indicative of the instant state of charge and the reference value of state of charge of the respective powertrain modes.