GB2590958A

GB2590958A - Hybrid vehicle speed and torque control

Info

Publication number: GB2590958A
Application number: GB2000306.7A
Authority: GB
Inventors: Oliveira Jaccoud Rodolfo; Hancock Matthew; Jean Brice Roques Olivier
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2020-01-09
Filing date: 2020-01-09
Publication date: 2021-07-14
Anticipated expiration: 2040-01-09
Also published as: DE102021100233A1; GB202000306D0; GB2590958B

Abstract

A control system and a method controlling an engine and an electric traction motor of a hybrid electric vehicle are provided. The control system comprises one or more controllers. The control system is configured to: receive a signal indicative of a requirement to increase engine speed 600; control the electric traction motor and/or the engine to provide positive torque 612, 614 to increase engine speed, in dependence on receiving the signal; control the engine to provide a change in torque towards an engine torque target, different from a torque required to maintain engine speed at an engine speed target associated with the requirement to increase engine speed; and control the electric traction motor to provide an inhibiting torque (t2 to t3, Figure 6B) to inhibit the change in torque of the engine from causing a deviation of engine speed from the engine speed target 600.

Description

HYBRID VEHICLE SPEED AND TORQUE CONTROL

TECHNICAL FIELD

The present disclosure relates to a hybrid vehicle control system and method. In particular, but not exclusively it relates to a hybrid vehicle control system and method for controlling activation of an engine.

BACKGROUND

In a typical hybrid electric vehicle, one or more electric traction motors are used to contribute at least some tractive output torque ('torque' herein), to reduce or eliminate use of an internal combustion engine ('engine' herein) and therefore to reduce fuel consumption and emissions.

If torque demand is high, or a traction battery state of charge is low, a contribution from the engine may be needed.

An engine is less responsive than an electric traction motor. Responsiveness is defined as a latency between a requested change in torque and a change in output torque. Electric traction motor responsiveness is greater for various reasons. For example, engines have greater inertia than electric traction motors. A modified air charge takes considerable time to be inducted into the engine. Engines can rarely be operated at their greatest achievable thermal efficiency.

The responsiveness of an engine can be controlled to some extent, by adjusting its rate of change of output torque within a controllable range. The rate can be adjusted by changing parameters such as engine torque reserve (spark retard), air-fuel ratio, valve timing, and/or valve lift, for example.

SUMMARY OF THE INVENTION

It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

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

According to an aspect of the invention there is provided a control system for controlling an engine and an electric traction motor of a vehicle, the control system comprising one or more controllers, wherein the control system is configured to: receive a signal indicative of a requirement to increase engine speed; control the electric traction motor and/or the engine to provide positive torque to increase engine speed, in dependence on receiving the signal; control the engine to provide a change in torque towards an engine torque target, different from a torque required to maintain engine speed at an engine speed target associated with the requirement to increase engine speed; and control the electric traction motor to provide an inhibiting torque to inhibit the change in torque of the engine from causing a deviation of engine speed from the engine speed target.

An advantage is improved control of the engine, because engine speed and engine torque can be controlled concurrently to different setpoints for different purposes. For example, the engine speed target (setpoint) may be for clutch engagement synchronization. The engine torque target (setpoint) may be dependent on a received indication of torque demand. Once the clutch is engaged, the engine is already outputting the required torque to satisfy torque demand of the vehicle, and there is no delay in which a driver has to wait for the engine torque to change.

In some examples, the inhibiting torque is configured to charge a traction battery. An advantage is improved efficiency.

In some examples, a sum of the engine torque target and the inhibiting torque is substantially equal to a torque required to maintain engine speed at the engine speed target and/or to change engine speed towards the engine speed target.

In some examples, the engine torque target is greater than the torque required to maintain engine speed at the engine speed target, wherein the change in torque of the engine has a positive sign, and wherein the inhibiting torque has a negative sign.

In some examples, the engine speed target is dependent on a requirement to synchronize engine speed with a vehicle transmission input speed. An advantage of this method is reduced jerk and/or delay during synchronization, for example for connecting a clutch.

In some examples, the received signal indicative of a requirement to increase engine speed is associated with a requirement to transition the engine from a first mode to a second mode, wherein in the first mode the engine is in a deactivated state and a torque path between a first set of vehicle wheels and both the engine and the electric traction motor is disconnected, and wherein in the second mode the engine is in an activated state and the torque path is connected. The control system may be configured to provide an indication when engine speed has reached the required engine speed and torque of the engine has reached the engine torque target, to cause connection of the torque path. An advantage is that the engine can be activated and start providing torque quickly, before the torque path is connected. Potential use cases include: the first mode is an electric vehicle mode and the second mode is a hybrid electric vehicle mode; or the first mode is a gliding mode and the second mode is a non-gliding mode; or the first mode is a terrain-dependent mode and the second mode is another terrain-dependent mode.

The control system may be configured to release the inhibiting torque after connection of the torque path. An advantage is increased responsiveness as the inhibiting torque can be released quickly whereas engine torque changes slowly.

In the electric vehicle mode, a second electric traction motor may be operable to provide tractive torque to a second set of vehicle wheels. An advantage is that the vehicle can drive in electric vehicle mode if the (first) electric traction motor can only provide torque to vehicle wheels when the engine torque path is connected, for instance if the first electric traction motor is a belt integrated starter generator, and/or an engine accessory drive motor generator, or a crankshaft integrated motor generator.

In the hybrid electric vehicle mode, the second electric traction motor may be operable to provide torque to the second set of vehicle wheels (RL, RR). In an example, the first set of vehicle wheels are front wheels and the second set of vehicle wheels (RL, RR) are rear wheels, or the first set of vehicle wheels are rear wheels and the second set of vehicle wheels are front wheels. An advantage is that the vehicle can implement multi-axle drive, e.g. four-wheel drive, when in electric vehicle mode.

According to another aspect of the invention there is provided a vehicle comprising the control system, the engine and the electric traction motor.

According to another aspect of the invention there is provided a method of controlling an engine and an electric traction motor of a vehicle, the method comprising: receiving a signal indicative of a requirement to increase engine speed; controlling the electric traction motor and/or the engine to provide positive torque to increase engine speed, in dependence on receiving the signal; controlling the engine to provide a change in torque towards an engine torque target, different from a torque required to maintain engine speed at an engine speed target associated with the requirement to increase engine speed; and controlling the electric traction motor to provide an inhibiting torque to inhibit the change in torque of the engine from causing a deviation of engine speed from the engine speed target.

According to another aspect of the invention there is provided computer software that, when executed, is arranged to perform any one or more of the methods described herein.

According to a further aspect of the invention there is provided a non-transitory computer readable medium comprising computer readable instructions that, when executed by a processor, cause performance of any one or more of the methods described herein.

According to another aspect of the invention there is provided a control system configured to perform any one or more of the methods described herein.

The one or more controllers as described herein may collectively comprise: at least one electronic processor having an electrical input for receiving the signal; and at least one electronic memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to cause the control system to control the engine and the electric traction motor in dependence on the receiving a signal.

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

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig 1 illustrates an example of a vehicle; Fig 2 illustrates an example of a system; Fig 3A illustrates an example of a control system and Fig 3B illustrates an example of a non-transitory computer-readable storage medium; Fig 4 illustrates an example of a state diagram for switching between two modes; Fig 5 illustrates an example of a method; Fig 6A illustrates an example of a graph with speed and time axes. Fig 6B illustrates an example of a graph with torque and time axes, and Fig 6C illustrates another example of a graph with torque and time axes; and Fig 7 illustrates an example of a method.

DETAILED DESCRIPTION

Fig 1 illustrates an example of a vehicle 10 in which embodiments of the invention can be implemented. In some, but not necessarily all examples, the vehicle 10 is a passenger vehicle, also referred to as a passenger car or as an automobile. In other examples, embodiments of the invention can be implemented for other applications, such as industrial vehicles.

The vehicle 10 may be a hybrid electric vehicle (HEV). If the vehicle 10 is an HEV, the vehicle 10 may be a full HEV or a mild HEV. Mild HEVs do not have an electric-only mode of propulsion, but the electric traction motor may be configured to provide assistance such as boosting output torque of the engine. Full HEVs have an electric-only mode of propulsion.

If the vehicle 10 is an HEV, the vehicle 10 may be configured to operate as a parallel HEV.

Parallel HEVs comprise a torque path between the engine and at least one vehicle wheel, as well as a torque path between an electric traction motor and at least one vehicle wheel. The torque path(s) may be disconnectable by a torque path connector such as a clutch. Parallel HEVs differ from series HEVs, because in series HEVs the purpose of the engine is to generate electrical energy and there is no torque path between the engine and vehicle wheels.

Fig 2 illustrates a system 20 for a parallel HEV 10. The system 20 defines, at least in part, a powertrain of the HEV.

The system 20 comprises a control system 208. The control system 208 comprises one or more controllers. The control system 208 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 20 comprises an engine 202. The engine 202 is a combustion engine. The illustrated engine 202 is an internal combustion engine. The illustrated engine 202 comprises three combustion chambers, however a different number of combustion chambers may be provided in other examples.

The engine 202 is operably coupled to the control system 208 to enable the control system 208 to control output torque of the engine 202. The output torque of the engine 202 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 202.

The system 20 comprises an optional pinion starter 206 for starting the engine 202.

The system 20 comprises a vehicle transmission arrangement 204 for receiving output torque from the engine 202. The vehicle transmission arrangement 204 may comprise an automatic vehicle transmission, a manual vehicle transmission, or a semi-automatic vehicle transmission. The vehicle transmission arrangement 204 may comprise one or more friction clutches and/or a torque converter between the engine 202 and a gear train.

The system 20 may comprise a differential (not shown) for receiving output torque from the gear train. The differential may be integrated into the vehicle transmission arrangement 204 as a transaxle, or provided separately.

The engine 202 is mechanically connected or connectable to a first set of vehicle wheels (FL, FR) via a torque path 220. The torque path 220 extends from an output of the engine 202 to the vehicle transmission arrangement 204, 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 202. 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 20 is configured for front wheel drive by the engine 202. In another example, the first set of vehicle wheels (FL, FR) comprises rear wheels. 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 20, no longitudinal (centre) driveshaft is provided, to make room for hybrid vehicle components. Therefore, the engine 202 is not connectable to a second set of rear wheels (rear wheels RL, RR in the illustration). The engine 202 may be transverse mounted to save space. In an alternative example, the engine 202 may be configured to drive the front and rear wheels.

A torque path connector 218 such as a clutch is provided inside and/or outside a bell housing of the vehicle transmission arrangement 204. The clutch 218 is configured to connect and configured to disconnect the torque path 220 between the engine 202 and the first set of vehicle wheels (FL, FR). The system 20 may be configured to automatically actuate the clutch 218 without user intervention.

The system 20 comprises a first electric traction motor 216. The first electric traction motor 216 may be an alternating current induction motor or a permanent magnet motor, or another type of motor. The first electric traction motor 216 is located to the engine side of the clutch 218.

The first electric traction motor 216 may be mechanically coupled to the engine 202 via a belt or chain. For example, the first electric traction motor 216 may be a belt integrated starter generator. In the illustration, the first electric traction motor 216 is located at an accessory drive end of the engine 202, opposite a vehicle transmission end of the engine 202. In an alternative example, the first electric traction motor 216 is a crankshaft integrated motor generator, located at a vehicle transmission end of the engine 202.

The first electric traction motor 216 is configured to apply positive torque and configured to apply negative torque to a crankshaft of the engine 202, for example to provide functions such as: boosting output torque of the engine 202; deactivating (shutting off) the engine 202 while at a stop or coasting; activating (starting) the engine 202; and regenerative braking in a regeneration mode. In a hybrid electric vehicle mode, the engine 202 and first electric traction motor 216 are both operable to supply positive torque simultaneously to boost output torque. The first electric traction motor 216 may be incapable of sustained electric-only driving.

However, when the torque path 220 between the engine 202 and the first set of vehicle wheels (FL, FR) is disconnected, a torque path 220 between the first electric traction motor 216 and the first set of vehicle wheels (FL, FR) is also disconnected.

Fig 2 illustrates a second electric traction motor 212 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 212 is greater than a nominal maximum torque of the first electric traction motor 216.

Even if the torque path 220 between the engine 202 and the first set of vehicle wheels (FL, FR) is disconnected by the clutch 218, the vehicle 10 can be driven in electric vehicle mode because the second electric traction motor 212 is connected to at least one vehicle wheel.

The illustrated second electric traction motor 212 is configured to provide torque to the illustrated second set of vehicle wheels (RL, RR). 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 212 is operable to provide torque to the rear wheels RL, RR via rear transverse axles.

Therefore, the vehicle 10 is rear wheel driven in electric vehicle mode. In an alternative example, the second set of vehicle wheels comprises at least one vehicle wheel of the first set of vehicle wheels.

The control system 208 may be configured to disconnect the torque path 220 between the engine 202 and the first set of vehicle wheels (FL, FR) in electric vehicle mode, to reduce parasitic pumping energy losses. For example, the clutch 218 may be opened. In the example of Fig 2, this means that the first electric traction motor 216 will also be disconnected from the first set of vehicle wheels (FL, FR).

Another benefit of the second electric traction motor 212 is that the second electric traction motor 212 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.

In order to store electrical power for the electric traction motors, the system 20 comprises a traction battery 200. The traction battery 200 provides a nominal voltage required by electrical power users such as the electric traction motors. If the electric traction motors run at different voltages, DC-DC converters (not shown) or the like may be provided to convert voltages.

The traction battery 200 may be a high voltage 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 200 may have a voltage and capacity to support electric only driving for sustained distances. The traction battery 200 may have a capacity of several kilowatt-hours, to maximise range. The capacity may be in the tens of kilowatt-hours, or even over a hundred kilowatt-hours.

Although the traction battery 200 is illustrated as one entity, the function of the traction battery 200 could be implemented using a plurality of small traction batteries in different locations on the vehicle 10.

In some examples, the first electric traction motor 216 and second electric traction motor 212 may be configured to receive electrical energy from the same traction battery 200. By pairing the first (mild) electric traction motor 216 to a high-capacity battery (tens to hundreds of kilowatt-hours), the first electric traction motor 216 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 212, 216 may be paired to different traction batteries.

Finally, the illustrated system 20 comprises inverters. Two inverters 210, 214 are shown, one for each electric traction motor. In other examples, one inverter or more than two inverters could be provided.

In an alternative implementation, the vehicle 10 may be other than shown in Fig 2.

Fig 3A illustrates how the control system 208 may be implemented. The control system 208 of Fig 3A illustrates a controller 300. In other examples, the control system 208 may comprise a plurality of controllers on-board and/or off-board the vehicle 10.

The controller 300 of Fig 3A includes at least one electronic processor 302; and at least one electronic memory device 304 electrically coupled to the electronic processor 302 and having instructions 306 (e.g. a computer program) stored therein, the at least one electronic memory device 304 and the instructions 306 configured to, with the at least one electronic processor 302, cause any one or more of the methods described herein to be performed.

Fig 3B illustrates a non-transitory computer-readable storage medium 308 comprising the instructions 306 (computer software).

The control system 208 may be configured to provide controller outputs to manipulate a variable (torque) towards a setpoint. An example setpoint is at least one torque target. The at least one torque target may be normally based on torque demand such as driver torque demand (e.g. accelerator pedal depression, APD), an autonomous driving torque demand, or a cruise control torque demand. The at least one torque target may normally be proportional to torque demand. The torque target may comprise an engine torque target for controlling output torque of the engine. The torque target may comprise an electric traction motor torque target for controlling output torque of an electric traction motor.

Another example setpoint is an engine speed target. Engine torque may be controlled to match engine speed to the engine speed target, used during idling and other scenarios. Torque from the first electric traction motor may be controlled to match engine speed to the engine speed target, because the first electric traction motor is mechanically coupled to the crankshaft of the engine.

A system 20 such as the powertrain of Fig 2 can be operated in a plurality of modes. In one mode, the engine 202 is deactivated and the torque path 220 between the engine 202 and the first set of vehicle wheels (FL, FR) is disconnected. In another mode, the engine 202 is reactivated and the torque path 220 is re-connected.

Fig 4 illustrates a state diagram of modes of operation. The state diagram shows a first mode 400 and a second mode 402.

In the first mode 400, the engine 202 is in a deactivated state and the torque path 220 between the first set of vehicle wheels (FL, FR) and the engine 202 and first electric traction motor 216 is disconnected. In an example, the effect of the combined deactivation and disconnection is that engine speed falls towards zero. Deactivation relates to the engine 202 producing no positive output torque or insufficient positive output torque for a non-zero engine speed. Fuel injection may cease, to reduce fuel consumption.

In the second mode 402, the engine 202 is in an activated state and the torque path 220 is connected. In the activated state, fuel is combusted in the engine's combustion chambers, causing the engine 202 to provide positive output torque to the torque path 220.

In some examples, the first mode 400 is the above-described electric vehicle mode and the second mode 402 is the hybrid electric vehicle mode.

The state diagram illustrates a first transition condition 404 for transitioning from the first mode 400 to the second mode 402. The state diagram illustrates a second transition condition 406 for transitioning from the second mode 402 to the first mode 400.

The first transition condition 404 may require at least one of: a manual user selection; a traction battery state of charge falling below a threshold; torque demand rising above a threshold (e.g. kickdown function); a temperature being below a threshold (e.g. freezing weather); a change of driving dynamics mode; a change of terrain response mode; and/or the like.

The second transition condition 406 may require at least one of: a manual user selection; a traction battery state of charge rising above a threshold; torque demand falling below a threshold; a temperature being above a threshold; a change of driving dynamics mode; a change of terrain response mode; and/or the like.

A driving dynamics mode refers to a mode that configures one or more of: a suspension setting; a throttle response setting; a gear shift point setting; or a steering weighting setting. A terrain response mode refers to a mode that configures one or more of: a differential locking setting; a traction control setting. There may be overlap between driving dynamics modes and terrain response modes. The settings may be predetermined or configurable.

A manual user selection may comprise use of a human-machine interface input device. The input device may comprise an engine start button. The input device may comprise a driving dynamics mode selector. The input device may comprise a terrain response mode selector.

In some examples, a terrain response mode and/or driving dynamics mode may be changeable automatically.

In some examples, the first mode 400 is a gliding mode and the second mode 402 is a non-gliding mode. Gliding refers to deactivation and disconnection of the engine 202 while the vehicle 10 is moving without stopping, to reduce fuel consumption and pumping losses. The first transition condition 404 may require an above-threshold torque demand. The second transition condition 406 may require a below-threshold torque demand for an above-threshold time while the vehicle 10 is moving, for example. Gliding mode transitions are capable of being performed while the vehicle 10 is not braking. Gliding mode transitions are capable of being performed while the vehicle 10 is cruising at significant speeds, such as above 30 kilometres per hour.

In some, but not necessarily all examples, the vehicle 10 comprises terrain-dependent modes such as the above-described terrain response modes. The first mode 400 is a terrain-dependent mode and the second mode 402 is another terrain-dependent mode. Some terrain response modes require the engine 202 to be connected and activated, for example off-road related terrain response modes.

According to an aspect of the present invention, the control system 208 is configured to control the first electric traction motor 216 to reduce engine overshoot, by performing a method 500 comprising: receiving a signal indicative of a requirement to increase engine speed (block 502); controlling at least the engine 202 to provide positive torque to increase engine speed, in dependence on receiving the signal (block 506); and controlling the first electric traction motor 216 to provide negative torque to inhibit overshoot of engine speed above an engine speed target (block 508).

Fig 5 illustrates a flowchart for the method 500 according to an example use case, for transitioning from the first mode 400 (e.g. electric vehicle mode) to the second mode 402 (e.g. hybrid electric vehicle mode). The vehicle wheels may be moving, so a fast transition may be required to meet driver responsiveness expectations.

The control system 208 may be configured to synchronize the engine speed with the vehicle wheel speed before connecting the clutch 218, to avoid a torque shock which jerks vehicle occupants. The synchronization is complete when each side (e.g. plate) of the clutch 218 has the same speed as the other side (e.g. plate) of the clutch 218. Therefore, any torque provided by the engine 202 and/or first electric traction motor 216 is not tractive torque until the clutch 218 has been connected. It would be appreciated that the blocks 502, 506 and 508 of the method 500 could be applied to other use cases.

At block 502, the method 500 comprises receiving a signal indicative of a requirement to increase engine speed. In some, but not necessarily all examples, the received signal is based on a requirement to transition from the first mode 400 in which the engine 202 is disconnected and deactivated, to the second mode 402 in which the engine 202 is connected and activated.

The control system 208 may be configured to obtain an engine speed target based on the signal. The engine speed target in this example is for synchronizing the engine speed with the vehicle wheel speed, and is therefore a different target from other speed targets such as an engine idle speed target. For a vehicle moving at above-creep speeds (e.g. above 15 kilometres per hour), the engine speed target is likely to be greater than an engine idle speed target. Depending on vehicle wheel speed, the engine speed target may be greater than 1500rpm and could be as high as engine redline / above 3000-5000rpm.

At block 504, the method 500 comprises controlling the first electric traction motor 216 to at least start the engine 202 by providing positive torque to increase engine speed towards the engine speed target. The engine speed starts to rise under the assistance of the first electric traction motor 216, for example from a speed of zero. During block 504, the engine 202 may provide no positive torque, for example if the engine speed is below engine idle speed. The engine becomes capable of providing positive torque as engine idle speed is approached or reached. Engine idle speed is generally within the range 300-1500rpm, within which an engine idle speed target may reside for an idling engine. The engine may be capable of providing positive torque from around 200-400rpm, depending on implementation. In an alternative implementation, the engine 202 may be started by a pinion starter 206 rather than by the first electric traction motor 216.

The concept of using the first electric traction motor 216 to bring engine speed up towards engine idle speed is considered to be distinctly patentable, as part of the method 500 or in other use cases. Therefore, according to an aspect of the invention there is provided a method comprising: receiving a signal indicative of a requirement to increase engine speed from an engine speed at which the engine is not capable of providing positive torque to an engine speed at which the engine is capable of providing positive torque (e.g. block 502); and controlling the first electric traction motor 216 to provide positive torque to increase engine speed at least to the engine speed at which the engine 202 is capable of providing positive torque, in dependence on receiving the signal (e.g. block 504). This obviates the need to use a pinion starter 206 and then switch over to the first electric traction motor 216.

The first electric traction motor 216 may be controlled based on the above-mentioned engine speed target even before engine idle speed is reached. This is smoother and faster than a discontinuous method of implementing an engine idle speed setpoint for the first electric traction motor 216 and then raising the setpoint to the above engine speed target only once engine speed has reached/stabilised at the engine idle speed setpoint.

At block 506, the method 500 of Fig 5 comprises controlling at least the engine 202 to provide positive torque to increase engine speed. The control system 208 may control the engine 202 to start contributing positive torque in response to determining that the engine 202 is capable of providing positive torque.

In some, but not necessarily all examples, the first electric traction motor 216 may concurrently provide positive torque during block 506.

Blocks 504 and 506 are distinct because the engine 202 does not initially provide positive torque and needs to be started in block 504. It would however be understood that if the engine 202 is capable of providing positive torque (e.g. speed above 200-400rpm) from when the signal of block 502 is received, block 504 may be omitted because the engine 202 is in continuous operation.

In order to resist an overshoot of engine speed above the engine speed target, the method 500 proceeds to block 508, comprising controlling the first electric traction motor 216 to provide negative torque to inhibit overshoot of engine speed above the engine speed target. The negative torque may be provided by operating the first electric traction motor 216 in a regeneration mode, which charges the traction battery 200.

If the first electric traction motor 216 commences providing negative torque before the engine speed has reached the engine speed target, as illustrated, then the sum of positive torque from the engine 202 and the negative torque from the first electric traction motor 216 is controlled to be a positive value.

If the first electric traction motor 216 commences providing negative torque in response to the engine speed overshooting the engine speed target, the sum of torque from the engine 202 and the negative torque from the first electric traction motor 216 is controlled to be a negative value.

In an example implementation of blocks 506 and 508, the torque of the first electric traction motor 216 may be controlled in closed loop to reduce (e.g. minimise) a monitored error between current engine speed and the engine speed target, and the torque of the engine 202 may be controlled in open loop.

An example method for controlling the engine 202 in open loop comprises calculating engine torque required to bring engine speed up to the engine speed target, and controlling engine torque based on the calculated required torque without taking into account the monitored error.

The calculated required torque may follow a torque profile. The torque profile may be a virtual profile calculated based on a calculated engine speed profile between a current engine speed and the engine speed target, and based on calibration data associated with engine characteristics such as inertia. The engine speed profile may follow a linear or nonlinear (e.g. curved) trajectory. The gradient of the engine speed profile may decrease with increasing proximity to the engine speed target. Therefore, the torque profile may decrease with increasing proximity to the engine speed target. The gradient of the engine speed profile may initially increase in a curve from a current engine speed, to avoid an initial discontinuity. Therefore, the torque profile may increase and then decrease.

Since the engine is controlled in open loop while the electric traction motor is controlled in closed loop in this example, the monitored error between current engine speed and the engine speed target is fed back to control of torque of the first electric traction motor 216 rather than to control of torque of the engine 202. The torque of the first electric traction motor 216 is controlled to reduce (e.g. minimise) the monitored error according to a proportional-integralderivative or alternative control scheme, while the torque profile for the engine is fixed for a given required engine speed change.

This scheme enables the first electric traction motor 216 to reduce (e.g. minimise) overshoot by supplying negative torque before the engine speed target is reached. For example, the derivative gain of a proportional-integral-derivative control scheme may be configured to cause the first electric traction motor 216 to provide negative torque before engine speed has reached the engine speed target. This has the effect of further inhibiting (reducing magnitude and/or duration of) overshoot of engine speed above the engine speed target. The reduced overshoot enables a faster open loop control strategy for the engine 202, and enables higher proportional gains and/or integrator gains for the closed loop strategy.

The torque profile for the engine 202 may terminate at the engine speed target. Therefore, when the engine speed has reached the engine speed target, the torque profile may be removed. However, the first electric traction motor 216 may continue to operate in closed loop to remove any overshoot. The engine speed target may be maintained in closed loop for as long as required until the method 500 is complete or the engine speed target changes, for example due to changing vehicle wheel speed.

This scheme improves responsiveness and reduces overshoot because the low-latency/low- inertia first electric traction motor 216 is reducing (e.g. minimising) errors, rather than the high-latency/high-inertia engine 202. This scheme also improves efficiency because the engine 202 does not need to reduce the error term, therefore the engine 202 can be controlled with less or no inefficient engine torque reserve.

In some examples, the rate of change of engine speed may be controlled. The control system 208 may be configured to determine a rate of increase of engine speed in dependence at least on a difference between a current engine speed and the engine speed target. The determined rate of increase may become a rate target. A rate target may apply to a first derivative and/or to a higher order derivative of engine speed. The rate target may comprise an acceleration target. The rate target may be lower for smaller differences between the current engine speed and the engine speed target. The rate may be greater than a rate achievable by the engine 202 alone, so that the first electric traction motor 216 contributes torque. The control system 208 may control at least the first electric traction motor 216 to control a rate of increase of the engine speed towards the determined rate of increase target, which provides a smooth and rapid engine speed increase.

At block 510, the method 500 optionally comprises providing an indication when engine speed has reached the engine speed target, to cause connection of the torque path 220. The indication is provided to a controller of an actuator of the torque path connector 218 (e.g. clutch), which may be part of the control system 208. When the torque path 220 has been connected, control of engine torque may be based on other demands such as accelerator pedal demands or cruise control demands.

In order to control responsiveness of the method 500, a timing at which the torque of the first electric traction motor 216 is allowed to become negative may be controllable. The control may be implemented using a variable proportional, integral and/or derivative gain, and/or by controlling a threshold (e.g. based on the monitored engine speed error) at which the torque of the first electric traction motor 216 is allowed to become negative. The switch to negative torque may be delayed if a faster response is required. A faster required response could be differentiated from a slower required response using different demarcating thresholds associated with the mode transition, e.g. based on the magnitude of torque demand.

In some, but not necessarily all examples, use of the first electric traction motor 216 and/or use of the first electric traction motor 216 in closed loop may be conditional. The method 500 may require satisfaction of a condition to use the first electric traction motor 216 to provide torque and/or to provide positive torque.

Satisfaction of the condition may require, for example: an indication of required engine speed acceleration being above a threshold, to check whether assistance is needed; and/or an indication of a capability of the first electric traction motor 216 to provide torque, to check whether the first electric traction motor 216 is available.

An indication of required engine speed acceleration may be represented, for example, by a magnitude of the calculated engine torque and/or by a magnitude of a difference of the engine speed target from a current engine speed.

An indication of capability may be checked, for example, by obtaining an indication of whether the first electric traction motor 216 and/or traction battery 200 is de-rated, and/or whether state of charge is below a threshold.

In some, but not necessarily all examples, satisfaction of the condition may determine which one of the engine 202 or the first electric traction motor 216 operates in closed loop. lithe condition is not satisfied, the error term may be reduced by the engine 202 (closed loop), whereas if the condition is satisfied, the engine may operate in open loop while the first electric traction motor 216 reduces the error term in closed loop as described earlier. If the engine 202 is controlled in closed loop, the first electric traction motor 216 may be unused for the method 500, and may be used only for other purposes.

Figs 6A to 60 illustrate graphs of speed and torque of the engine 202 and of the first electric traction motor 216, controlled according to the method 500 of Fig 5.

Fig 6A illustrates the magnitude of a manipulated variable (engine speed) in the y-axis, against time in the x-axis, as a solid line curve 604. Fig 6A also illustrates the magnitude of a setpoint (engine speed target 600), which is shown as constant but could be time-variable if the vehicle 10 is decelerating or accelerating. The dashed line curve 602 is for comparative purposes, and illustrates the engine speed controlled without using the method 500. The dashed line overshoots the setpoint whereas the solid line does not overshoot the setpoint (or overshoots to a lesser extent).

Fig 6B illustrates the magnitudes of the controller outputs (first electric traction motor torque 612 and engine torque 614) in the y-axis, against time in the x-axis which is aligned with the time axis of Fig 6A. Fig 6C illustrates a variant of Fig 6B and will be described later.

Referring to Figs 6A-6B, the time period to to t1 corresponds to block 504 of the method 500, in which the first electric traction motor 216 outputs positive torque but the engine 202 does not output positive torque because the engine speed is too low. The engine speed increases at a relatively low rate. It would be appreciated that if the engine speed is high enough, then the engine 202 may supply positive torque in this time period. At time t1, the engine 202 becomes capable of providing positive torque, having a reached a speed of around 200-40Orpm.

Referring to Figs 6A-6B, the time period t1 to t2 corresponds to block 506 of the method 500, in which the engine 202 has started to contribute positive torque, while the first electric traction motor 216 concurrently outputs positive torque. The engine speed increases at a relatively high rate. Notably, the engine torque increases at a slower rate than the torque of the first electric traction motor 216, because the engine 202 is less responsive than the first electric traction motor 216.

Referring to Figs 6A-6B, the time period t2 to t3 corresponds to block 508 of the method 500, in which the engine speed is close to the setpoint but has not yet reached the setpoint, so the first electric traction motor 216 is controlled to provide negative torque to inhibit overshoot.

The timing of commencement of the negative torque is dependent on controller tuning.

During the same period 12 to t3, the positive torque of the engine 202 does not immediately decrease. The positive torque of the engine 202 may continue to increase as shown, or could stay the same. This ensures that the sum of torques of the engine 202 and the first electric traction motor 216 does not become negative before reaching the setpoint.

In an alternative implementation, the negative torque of the first electric traction motor 216 may commence after overshoot has been detected.

At time t3, the control system 208 determines that the engine speed has reached or settled at the setpoint. The speed synchronization is complete so the method 500 proceeds to block 510 comprising connecting the torque path 220 between the engine 202 and the first set of vehicle wheels (FL, FR). Once the torque path 220 is connected, the target (setpoint) controlling torque can resume being based on torque demands capable of accelerating and engine-braking the vehicle 10, such as a driver torque demand, an autonomous driving torque demand, or a cruise control torque demand.

According to a further aspect of the invention, Fig 6C illustrates an advantageous improvement of Fig 6B, to reduce response lag and/or jerk that may occur when the synchronization is complete and the engine 202 is reconnected. Jerk may occur due to a discontinuity in requested torque when the engine speed target is removed and replaced by an engine torque target based on torque demands, for example when torque demand is high. The improvement comprises, before the synchronization at time t3: adapting block 506 of the method 500 to control at least the engine 202 to provide a change in torque (line 624 in Fig 6C) towards an engine torque target 620, wherein the engine torque target 620 is different from (e.g. higher than) a torque required to maintain engine speed at the engine speed target 600; and adapting block 508 of the method 500 to control the first electric traction motor 216 to provide an inhibiting torque (line 622 of Fig 6C) to inhibit the change in torque of the engine 202 from causing a deviation of engine speed from the engine speed target 600.

The inhibiting torque has an opposite sign from the engine torque. The inhibiting torque ensures that the engine speed is correct for the speed synchronization, despite the engine torque being at a post-synchronization setpoint 620 required by the torque demands. This improves responsiveness and smoothness, particularly when a transition from the first mode 400 to the second mode 402 is triggered by high torque demand. This is because the first electric traction motor 216 can remove the inhibiting torque quickly when the torque path 220 has been reconnected, and then the engine 202 is already at or close to the engine torque target.

If the engine 202 did instead have to change its output torque immediately after reconnection of the torque path 220, a jerk may be felt by vehicle occupants. The jerk may be further increased by a lash crossing if the engine 202 had to transition from negative torque (e.g. overshoot control for synchronization) to positive torque. The above method reduces any jerk.

Consider an example in which 40Nm is required at time t3 for the mode transition to synchronize engine speed to the vehicle transmission input speed, and then 80Nm is required immediately on completion of the mode transition, to satisfy a higher torque demand. For the synchronization, the engine 202 may output 80Nm and the first electric traction motor 216 may provide a -40Nm inhibiting torque, resulting in the required 40Nm net torque at time t3. Once the synchronization is complete and the torque path 220 has been reconnected, the -40Nm inhibiting torque can be removed quickly, and the engine 202 is already at the required operating point outputting 80Nm of torque.

Fig 6C may be regarded as providing an improved torque reserve technique. Previous methods of implementing a torque reserve rely on controlling the engine 202 to operate in a less efficient way. Previous methods include, for example, throttling an air path through the engine 202, and/or operating the engine 202 with a spark timing retarded from a most efficient ignition timing allowed by a control map. When a fast response is required using previous methods, the spark timing can be advanced towards the most efficient timing and/or throttling losses in the air path can be removed, at the expense of reduced engine efficiency. The present method enables the most efficient ignition timing for a given engine 202 to be used. Ignition timing may be MBT (maximum brake torque) or less than 5 degrees of retard from the most efficient available timing available in a map, depending on engine calibration.

The inhibiting torque may be provided by operating the first electric traction motor 216 in the regeneration mode, configured to charge the traction battery 200. This is more efficient than engine torque reserve methods (spark retard).

Fig 6C shows the timing of when the engine torque starts to rise towards the engine torque target 620. In Fig 6C, it is assumed that the engine torque target 620 is greater than the torque required to maintain engine speed at the engine speed target. The illustrated engine torque target 620 is constant, however in practice the engine torque target 620 may vary in dependence on changes in load (torque demand).

The engine torque rises towards the engine torque target 620 before the engine speed has reached the engine speed target 600 and therefore before the torque path 220 is reconnected, which reduces the time taken to complete the method 500, compared to waiting for the reconnection before implementing the engine torque target 620.

If the first electric traction motor 216 commences providing inhibiting torque before the engine speed has reached the engine speed target 600, as illustrated, then the sum of positive torque from the engine 202 and the negative torque from the first electric traction motor 216 is controlled to be a positive value (if the engine speed target 600 is higher than the engine speed) or a negative value (if the engine speed target 600 is lower than the engine speed), until the engine speed target 600 is reached.

If the first electric traction motor 216 commences providing negative torque in response to the engine speed overshooting the engine speed target 600, the sum of torque from the engine 202 and the negative torque from the first electric traction motor 216 is controlled to be a negative value (if the engine speed target 600 is lower than the engine speed) or a positive value Of the engine speed target 600 is higher than the engine speed), until the engine speed target 600 is reached.

Open loop and/or closed loop control methods may be employed, to reduce errors from the targets. For example, the first electric traction motor 508 may be controlled in closed loop to reduce (e.g. minimise) error between current engine speed and the engine speed target, to provide the overshoot control as well as the inhibiting torque. The engine 202 may be controlled in open loop or closed loop based on the engine torque target 620.

Although Fig 6C shows an engine torque target 620 greater than the torque required for maintaining the engine speed target 600, in low-load use cases the engine torque target may be less than the torque required for maintaining the engine speed target 600 and the inhibiting torque could be positive.

Although Fig 6C shows engine speed rising towards an engine speed target 600 for transitioning from the first mode 400 to the second mode 402, in other examples the engine speed may be lowered for a lower engine speed target.

However, a use case in which this improved method is particularly advantageous is when a fast transition from the first mode 400 to the second mode 402 is required, due torque demand rising above a threshold. When torque demand such as driver torque demand is high, for example due to a kickdown, the improved method has the effect of significantly improving responsiveness by pre-loading the engine 202 before the mode transition is complete.

In some, but not necessarily all examples, the improved method of Fig 6C may be conditional. A decision to perform the improved method resulting in Fig 60 may require obtaining an indication of torque demand, and determining that an engine torque target based on the torque demand is above a threshold. The threshold may be equal to (or greater than) the engine torque required to maintain engine speed at the engine speed target. If the torque demand is lower than this threshold, the improved method may not be needed as there is less risk of jerk/torque shock, and the method 500 resulting in Fig 6B or another more conventional method may be performed instead.

Further, it would be appreciated that this improved method could be applied to use cases other than mode transitions as presently described, and to methods other than the method 500 of Fig 5.

In some examples as described above, the first electric traction motor 216 is used instead of the pinion starter 206 to start the engine 202 by bringing engine speed up towards engine idle speed. Therefore, the first electric traction motor 216 may obviate the requirement for a pinion starter 206. In some examples, the vehicle 10 may additionally comprise a pinion starter 206. The control system 208 may be configured to start the engine 202 using the first electric traction motor 216 in some scenarios, and using the pinion starter 206 instead in other scenarios. Fig 7 illustrates a method 700 comprising: determining whether a condition is satisfied (block 702); and when the condition is satisfied, control the first electric traction motor 216 to provide positive torque to increase engine speed at least to the engine speed at which the engine is capable of providing positive torque (e.g. 200-400rpm), in dependence on receiving the signal (block 704); and when the condition is not satisfied, control a pinion starter 206 to provide positive torque to increase engine speed at least to the engine speed at which the engine is capable of providing positive torque, in dependence on receiving the signal (block 706). After block 704 or 706, the method 700 may proceed to block 506 of the method 500 of Fig 5.

Using the first electric traction motor 216 to start the engine 202 is useful in situations when the engine torque needs to continue increasing past the torque required for engine speed to remain within an engine idle range (e.g. 300-1500rpm) or remain at an engine idle speed target within the engine idle range. Otherwise, the pinion starter 206 would be used to bring engine speed at least up to the speed at which the engine 202 is capable of providing positive torque, and then the engine 202 and/or first electric traction motor 216 takes over for the rest of the torque/speed increase. The takeover/handover would cause jerk, for example due to a gap in torque or due to the different torque rates of the first electric traction motor 216/engine 202 and the pinion starter 206.

Satisfaction of the condition of block 702 may therefore be associated with a requirement for engine torque to continue increasing past the torque required for engine speed to reach the engine speed at which the engine is capable of providing positive torque (e.g. 200-400rpm).

In some examples, satisfaction of the condition is dependent on the engine speed target 600. In an implementation, satisfaction of the condition at least requires the engine speed target 600 to be greater than a threshold associated with engine idling. The threshold may be equal to than an engine idle speed target and/or an engine speed from the range 300rpm to 1500rpm and/or may be exceeded by an engine speed target greater than approximately 2500rpm, because this indicates that torque must continue to rise after engine idle speed has been reached.

In some examples, satisfaction of the condition is dependent on torque demand. In an implementation, satisfaction of the condition at least requires torque demand to be greater than a threshold, or a torque target based on torque demand to be greater than a threshold..

For the above reasons, it would be appreciated that use of the first electric traction motor 216 to bring engine speed up to a speed at which the engine is capable of providing positive torque is advantageous for the method 500 of Fig 5, for example in the scenarios shown in Figs 6A-6C.

Satisfaction of the condition could be influenced by other factors. For example, the pinion starter 206 may be not used if vehicle speed is above a threshold such as Okph (vehicle 10 is moving). The pinion starter 206 may be not used if the torque path 220 between the engine 202 and the first set of vehicle wheels (FL, FR) is connected and the vehicle speed is above the threshold. The first electric traction may be not used if a power level and/or state of charge of the traction battery 200 is inhibited (e.g. deactivated or de-rated), e.g. a below-threshold state of charge and/or a below-threshold ambient temperature. This is because the pinion starter 206 may receive electrical power from a separate SLI (starting, lighting, ignition) battery (not shown).

For purposes of this disclosure, it is to be understood that the controller(s) 300 described herein can each comprise a control unit or computational device having one or more electronic processors 302. A vehicle 10 and/or a system thereof may comprise a single control unit or electronic controller or alternatively different functions of the controller(s) may be embodied in, or hosted in, different control units or controllers. A set of instructions could be provided which, when executed, cause said controller(s) or control unit(s) to implement the control techniques described herein (including the described method(s)). The set of instructions may be embedded in one or more electronic processors, or alternatively, the set of instructions could be provided as software to be executed by one or more electronic processor(s). For example, a first controller may be implemented in software run on one or more electronic processors, and one or more other controllers may also be implemented in software run on one or more electronic processors, optionally the same one or more processors as the first controller. It will be appreciated, however, that other arrangements are also useful, and therefore, the present disclosure is not intended to be limited to any particular arrangement. In any event, the set of instructions described above may be embedded in a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational device, including, without limitation: a magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Each passage described as an 'aspect of the invention' is a self-contained statement suitable for a current or future independent claim, with no additional features required.

The blocks illustrated in Figs 5 and 7 may represent steps in a method and/or sections of code in the computer program 306. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some steps to be omitted.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. A control system for controlling an engine and an electric traction motor of a vehicle, the control system comprising one or more controllers, wherein the control system is configured to: receive a signal indicative of a requirement to increase engine speed; control the electric traction motor and/or the engine to provide positive torque to increase engine speed, in dependence on receiving the signal; control the engine to provide a change in torque towards an engine torque target, different from a torque required to maintain engine speed at an engine speed target associated with the requirement to increase engine speed; and control the electric traction motor to provide an inhibiting torque to inhibit the change in torque of the engine from causing a deviation of engine speed from the engine speed target.
2. The control system of claim 1, wherein the one or more controllers collectively comprise: at least one electronic processor having an electrical input for receiving the signal; and at least one electronic memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to cause the control system to control the engine and the electric traction motor in dependence on the receiving a signal.
3. The control system of claim 1 or 2, wherein the inhibiting torque is configured to charge a traction battery.
4. The control system of claim 1, 2 or 3, wherein a sum of the engine torque target and the inhibiting torque is substantially equal to a torque required to maintain engine speed at the engine speed target and/or to change engine speed towards the engine speed target.
5. The control system of any preceding claim, wherein the engine torque target is greater than the torque required to maintain engine speed at the engine speed target, wherein the change in torque of the engine has a positive sign, and wherein the inhibiting torque has a negative sign.
6. The control system of any preceding claim, configured to receive an indication of torque demand, wherein the engine torque target is dependent on the received indication of torque demand.
7. The control system of claim 6, wherein the indication of torque demand is based on a driver torque demand or an autonomous driving torque demand or a cruise control torque demand.
8. The control system of any preceding claim, wherein the engine speed target is dependent on a requirement to synchronize engine speed with a vehicle transmission input speed.
9. The control system of any preceding claim, wherein the received signal indicative of a requirement to increase engine speed is associated with a requirement to transition the engine from a first mode to a second mode, wherein in the first mode the engine is in a deactivated state and a torque path between a first set of vehicle wheels and both the engine and the electric traction motor is disconnected, and wherein in the second mode the engine is in an activated state and the torque path is connected.
10. The control system of claim 9, configured to provide an indication when engine speed has reached the required engine speed and torque of the engine has reached the engine torque target, to cause connection of the torque path.
11. The control system of claim 10, configured to release the inhibiting torque after connection of the torque path.
12. The control system of claim 9, 10 or 11, wherein the first mode is an electric vehicle mode and the second mode is a hybrid electric vehicle mode.
13. The control system of claim 12, wherein in the electric vehicle mode a second electric traction motor is operable to output tractive torque to a second set of vehicle wheels.
14. The control system of claim 13, wherein in the hybrid electric vehicle mode the second electric traction motor is operable to output tractive torque to the second set of vehicle wheels.
15. The control system of claim 13 or 14, wherein the first set of vehicle wheels are front wheels and the second set of vehicle wheels are rear wheels, or wherein the first set of vehicle wheels are rear wheels and the second set of vehicle wheels are front wheels.
16. The control system of claim 9, 10 or 11, wherein: the first mode is a gliding mode and the second mode is a non-gliding mode; or the first mode is a terrain-dependent mode and the second mode is another terrain-dependent mode.
17. The control system of any preceding claim, wherein the electric traction motor is a belt integrated starter generator, and/or an engine accessory drive motor generator, or a crankshaft integrated motor generator.
18. A vehicle comprising the control system, the engine and the electric traction motor of any preceding claim. 20 19. A method of controlling an engine and an electric traction motor of a vehicle, the method comprising: receiving a signal indicative of a requirement to increase engine speed; controlling the electric traction motor and/or the engine to provide positive torque to increase engine speed, in dependence on receiving the signal; controlling the engine to provide a change in torque towards an engine torque target, different from a torque required to maintain engine speed at an engine speed target associated with the requirement to increase engine speed; and controlling the electric traction motor to provide an inhibiting torque to inhibit the change in torque of the engine from causing a deviation of engine speed from the engine speed target.
19. Computer software that, when executed, is arranged to perform a method according to claim 19.