GB2630082A

GB2630082A - Controlling an engine start of a hybrid vehicle

Info

Publication number: GB2630082A
Application number: GB2307312.5A
Authority: GB
Inventors: Harrison Alex; Roques Olivier; Jones Gareth; Gregersen Anders; Vaquerizo Sanchez Daniel; Lacroisille Romain
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2023-05-17
Filing date: 2023-05-17
Publication date: 2024-11-20
Also published as: GB202307312D0; WO2024236117A1

Abstract

A control system (100) for controlling an engine start of a hybrid vehicle (300) operable to control an engine start using a plurality of engine start modes and configured to receive (410) a first signal (160) indicating that an engine start is required; analyse (420), in response to the first signal, an operating conditions signal (165) indicative of one or more operating conditions of the vehicle, wherein the one or more operating conditions comprise a power demand signal (165) indicative of a power request; select (430) an engine start mode from a predetermined prioritised list of a plurality of engine start modes based on the analysed one or more operating conditions; and output (440) a control signal (170) to the powertrain system to control the engine start in accordance with the selected engine start mode, wherein at least a first of the engine start modes comprises a slip start mode in which the electric traction motor is operated to start the engine and at least a second of the engine start modes comprises a starter motor mode in which a starter motor (219) is operated to start the engine.

Description

CONTROLLING AN ENGINE START OF A HYBRID VEHICLE

TECHNICAL FIELD

The present disclosure relates to controlling an engine start of a hybrid vehicle. Aspects of the invention relate to a control system, a system, a vehicle, a method and computer readable instructions.

BACKGROUND

It is known for vehicles to be powered by an internal combustion engine and one or more electric traction motors (also referred to as electric motors (EM)). When a vehicle is operating such that only the electrical traction motor is being used to provide motive power, it can sometimes become necessary to initiate an engine start such that both the electric traction motor and the engine are operating. Such hybrid powertrain system are operable to perform different engine start modes depending on the environmental conditions and needs of the driver of the vehicle, but the selection of some start modes in certain conditions can result in reduced vehicle performance.

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

SUMMARY OF THE INVENTION

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

This disclosure provides a technique for controlling an engine start of a hybrid vehicle. The technique selects an engine start mode from a prioritised list of start modes depending on the power being demanded when the engine start is required and one or more operating conditions of the vehicle.

According to an aspect of the present invention there is provided a control system for controlling an engine start of a hybrid vehicle having a powertrain system comprising an engine and an electric traction motor, the powertrain system being operable to control an engine start using a plurality of engine start modes, the control system comprising one or more processors. The one or more processors are collectively configured to receive a first signal indicating that an engine start is required, and analyse, in response to the first signal, an operating conditions signal indicative of one or more operating conditions of the vehicle, wherein the one or more operating conditions comprise a power demand signal indicative of a power request. The one or more processors are further configured to select an engine start mode from a predetermined prioritised list of a plurality of engine start modes based on the analysed one or more operating conditions, and output a control signal to the powertrain system to control the engine start in accordance with the selected engine start mode.

At least a first of the engine start modes comprises a slip start mode in which the electric traction motor is operated to start the engine and at least a second of the engine start modes comprises a starter motor mode in which a starter motor is operated to start the engine.

In this way, a start mode is selected that will maintain the performance of the electric traction motor and ensure there is no significant or noticeable loss in the torque being applied to the drivetrain as the engine is started. It does this because the pinion starter can be used to start the engine if the electric traction motor is not available.

The control system comprises one or more controllers collectively comprising at least one electronic processor having an electrical input for receiving an input signal; and at least one 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 receive a first signal indicating that an engine start is required; analyse, in response to the first signal, an operating conditions signal indicative of one or more operating conditions of the vehicle, wherein the one or more operating conditions comprise a power demand signal indicative of a power request; select an engine start mode from a predetermined prioritised list of a plurality of engine start modes based on the analysed one or more operating conditions; and output a control signal to the powertrain system to control the engine start in accordance with the selected engine start mode, wherein at least a first of the engine start modes comprises a slip start mode in which the electric traction motor is operated to start the engine and at least a second of the engine start modes comprises a starter motor mode in which a starter motor is operated to start the engine.

Optionally, the control system is configured to select the slip start mode in which the electric traction motor is operated to start the engine if the power demand signal is below a maximum power threshold. Optionally, the maximum power threshold may correspond to the upper limit of the power from a traction battery available for use by the electric traction motor. In this way, a slip start mode will only be selected if the electric traction motor has enough power available to perform an engine start without a noticeable loss in torque being applied to the drivetrain.

Optionally, the one or more operating conditions comprise at least one of: a speed of the electric traction motor, and a gear selection.

Optionally, the control system is configured to select a first slip start mode or a second slip start mode in dependence on the speed of the electric traction motor, the gear selection and a rate of change of the power demand signal. For example, the first slip start mode occurs when a first clutch between the electric traction motor and the engine is partially engaged to start the engine, and a second clutch between the electric traction motor and the drivetrain is partially engaged to start the engine, the first and second clutches being fully engaged once the engine speed matches the electric traction motor speed, to thereby provide a smooth transition. The second slip start mode occurs when the first clutch between the electric traction motor and the engine is partially engaged to start the engine and fully engaged once the engine speed matches the electric traction motor speed, whilst the second clutch between the electric traction motor and the drivetrain is fully engaged throughout, to thereby provide a rapid transition.

Optionally, the control system is configured to select the first slip start mode if the rate of change of the power demand signal is below a threshold level defined by the speed of the electric traction motor and gear selection.

In this respect, the threshold level is a dynamically adjustable parameter that varies according to the speed of the vehicle and the selected gear. If the rate of acceleration does not exceed the threshold level, a rapid engine start is more likely to produce noticeable oscillations, and thus the first slip start mode can be selected.

Optionally, the control system is configured to select the second slip start mode if the rate of change of the power demand signal is above the threshold defined by the speed of the electric traction motor and gear selection. In this way, if the rate of acceleration exceeds the threshold level, a rapid engine start is needed, and thus the second slip start mode can be selected as any resulting oscillations will be less noticeable.

Optionally, the control system is configured to select the starter motor start mode if the power demand signal is above or equal to the maximum power threshold. In this way, if the electric traction motor does not have enough power available to perform an engine start without a noticeable loss in torque being applied to the drivetrain, the starter motor will be used to start the engine.

Optionally, the one or more operating conditions further comprise one or more of: a power output signal from the electric traction motor, and a temperature of a component of the electric traction motor.

Optionally, the control system is further configured to select the starter motor start mode if the one of more operating conditions comprise one or more of a power output signal indicating that the electric traction motor is outputting a power close to its maximum power capability, a power demand signal indicating an increasing power request, a power output signal indicating a reduction in the power capability of the electric traction motor, and a temperature of a component of the electric traction motor is within a predefined temperature range. For example, the temperature range may be between -10°C and 50°C. In this way, if the operating conditions are such that the electric traction motor cannot be used to perform an engine start, the starter motor will be used to start the engine.

Optionally, in response to the first signal, the control system is configured to determine, in dependence on one or more operating conditions of the vehicle, a predicted gear selection associated with an engine start, determine, in dependence on the predicted gear selection and the one or more operating conditions, a first portion of a power capability of the electric traction motor for use in offsetting a gear ratio reduction, and output a control signal to the powertrain system to make the first portion of the power capability available for use in offsetting the gear ratio reduction. As such, a portion of the power capability of the electric traction motor is made available for use in offsetting a change in gear ratio as the engine is started, the remaining power capability of the electric traction motor thus defining the maximum power threshold used to determine whether to perform the engine start a slip start mode or the starter motor start mode.

Optionally, the one or more operating conditions comprise a current gear selection and a speed of the vehicle. For example, the predicted gear selection may be determined by comparing the current gear selection and vehicle speed to a look up table stored in a memory of the control system.

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

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

According to a further aspect of the invention, there is provided a method for controlling an engine start of a hybrid vehicle having a powertrain system comprising an engine and an electric traction motor, the powertrain system being operable to control an engine start using a plurality of engine start modes. The method comprises receiving a first signal indicating that an engine start is required, and analysing, in response to the first signal, an operating conditions signal indicative of one or more operating conditions of the vehicle, wherein the one or more operating conditions at least comprise a power demand signal indicative of a power request. The method further comprises selecting an engine start mode from a predetermined prioritised list of a plurality of engine start modes based on the analysed one or more operating conditions, and outputting a control signal to the powertrain system to control the engine start in accordance with the selected engine start mode. At least a first of the engine start modes comprises a slip start mode in which the electric traction motor is operated to start the engine and at least a second of the engine start modes comprises a starter motor mode in which a starter motor is operated to start the engine.

According to a still further aspect of the invention, there is provided a computer readable instructions which, when executed by a computer, are arranged to perform the method as mentioned above.

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: Figure 1 shows a block diagram illustrating a control system according to an embodiment of the present invention; Figure 2 shows a powertrain system according to an embodiment of the present invention; Figure 3A shows a schematic illustration of a vehicle according to an embodiment of the present invention; Figure 3B shows a schematic illustration of a rear-view of the vehicle of Figure 3A; Figure 4 shows a first flow chart showing operations performed by the control system of Figure 1 according to an embodiment of the present invention; and Figure 5 is a graph further illustrating an embodiment of the present invention.

DETAILED DESCRIPTION

With reference to Figure 1, there is illustrated a control system 100 for a vehicle. The control system 100 comprises one or more controller 110.

The control system 100 as illustrated in Figure 1 comprises one controller 110, although it will be appreciated that this is merely illustrative. The controller 110 comprises processing means 120 and memory means 130. The processing means 120 may be one or more electronic processing device 120 which operably executes computer-readable instructions. The memory means 130 may be one or more memory devices 130. The memory means 130 is electrically coupled to the processing means 120. The memory means 130 is configured to store instructions, and the processing means 120 is configured to access the memory means 130 and execute the instructions stored thereon.

The controller 110 comprises an input means 140 and an output means 150. The input means 140 may comprise an electrical input 140 of the controller 110. The output means 150 may comprise an electrical output 140 of the controller 110. The input 140 is arranged to receive an engine start signal 160 from one or more sensors indicative that an engine start is required. For example, the engine start signal 160 may comprise one or more of a power demand signal indicative of the power demand (e.g., by a driver) from a power demand sensor, and an electric traction motor (also referred to herein as an electric machine (EM)) battery charge signal indicative of a state of battery charge of the EM battery from an EM battery power sensor. The engine start signal 160 is an electrical signal which is indicative of an engine start being required such that both the EM and an engine are operated to deliver torque to the vehicle transmission, as will be described further below. The input 140 is also arranged to receive an operating conditions signal 165 from one or more sensors indicative of one or more operating conditions of the vehicle. For example, the operating conditions signal 165 may include one or more of a power demand signal indicative of the driver demand from a driver demand sensor, an EM speed signal indicative of the speed of the EM from an EM speed sensor, a vehicle speed signal indicative of the speed of the vehicle from a vehicle speed sensor, a gear selection signal indicative of a currently selected gear from a gear selection sensor, an EM power signal output indicative of a power currently output by the EM from an EM power output sensor, and an EM temperature signal indicative of a temperature of one or more components of the EM from an EM temperature sensor. The operating conditions signal 165 is an electrical signal which is indicative of one or more operating conditions of the vehicle. The output 150 is arranged to output a start mode control signal 170 is indicative of a start mode selection for controlling the powertrain, in particular, controlling the mode in which the engine start is performed. For example, the start mode control signal 170 may control a starter motor to start the engine, or the start mode control signal 170 may control the EM to start the engine in accordance with one or more possible start modes. Optionally, the output 150 is arranged to output a power control signal 172 to thereby cause the powertrain system to make a portion of the power capability of the electric traction motor available for use in offsetting a gear ratio reduction.

Figure 2 illustrates an example system 20 for a parallel hybrid electric vehicle (HEV). The system 20 defines, at least in part, a powertrain of the HEV. The system 20 comprises the control system 100, as explained with reference to Figure 1. The control system 100 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 may be a combustion engine. The illustrated engine 202 is an internal combustion engine. The illustrated engine 202 comprises four 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 100 to enable the control system 100 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 further comprises an electric traction motor 216. In some embodiments, the system 20 has one electric traction motor. In other embodiments, the system 20 has more than one electric traction motor. The first electric traction motor 216 may be an alternating current induction motor or a permanent magnet motor, or another type of motor. The electric traction motor is also referred to herein as an electric machine (EM). The electric traction motor 216 may be a crankshaft integrated motor generator (CIMG). The electric traction motor 216 is configured to apply positive or negative torque to the crankshaft or to an output shaft connected to the crankshaft, for example to provide functions such as: boosting output torque of the engine 202; deactivating (shutting oft) 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 electric traction motor 216 may both be operable to supply positive torque simultaneously to boost output torque. The electric traction motor 216 may be capable of electric only driving.

The system 20 comprises a vehicle transmission arrangement 204 for receiving output torque from the engine 202 and/or from the electric traction motor 216. The vehicle transmission arrangement 204 may comprise an automatic vehicle transmission, a semi-automatic vehicle transmission, or a manual vehicle transmission.

The engine 202 is mechanically connected or connectable to the electric traction motor 216 via a first torque path connector in the form of a first clutch 212. The electric traction motor 216 is mechanically connected or connectable to the transmission 204 via a second torque path connector in the form of a second clutch 218.

The second clutch 218 is illustrated in Figure 2 as a single clutch located along the drive shaft between the electric traction motor 216 and the transmission 204. In other embodiments, the second clutch 218 could be integrated with the electric traction motor 216 and/or with the transmission 204. In the latter example, the second clutch could be a core clutch used for gear shifts. The function of the second clutch could be provided by a single clutch, as illustrated, or a by plurality of clutches which are each configured to connect the electric traction motor 216 to the transmission 204 and thereby fulfil the function of the second clutch. For example, the second clutch could comprise a clutch which is operable to connect the electric traction motor 216 to the transmission 204 when the transmission is in one of a first set of gears (e.g., gears 1-4) and one or more further clutches which are operable to connect the electric traction motor 216 to the transmission 204 when the transmission is in one of a second set of gears (e.g., gears 5-8). The electric traction motor 216 is mechanically connected or connectable to a first set of vehicle wheels (RL, RR) via a torque path which extends from an output of the electric traction motor 216 to the second clutch 218 then to the transmission 204, then to the axle/driveshafts 220, and then to the first set of vehicle wheels (RL, RR). The engine 202 is mechanically connected or connectable to the first set of vehicle wheels (RL, RR) via a torque path which extends from an output of the engine 202, then to the first clutch 212, then to the electric traction motor 216, then to the second clutch 218, then to the transmission 204, then to the a>de/driveshafts 220, and then to the first set of vehicle wheels (RL, RR). One or both of the engine 202 and the electric traction motor 216 are able to provide torque to a first axle 220 of the vehicle. However, when the torque path between the electric traction motor 216 and the first set of vehicle wheels (RL, RR) is disconnected, the torque path 220 between engine 202 and the first set of vehicle wheels (RL, RR) is also disconnected. In a vehicle overrun and/or friction braking situation, torque may flow from the first set of vehicle wheels (RL, RR) to the electric traction motor 216 and optionally to the engine 202. Torque flow towards the first set of vehicle wheels (RL, RR) is positive torque, and torque flow from the first set of vehicle wheels (RL, RR) is negative torque. The illustrated first set of vehicle wheels (RL, RR) comprises rear wheels. Therefore, the illustrated system 20 is configured for rear wheel drive. In another example, the first set of vehicle wheels may be front wheels (FL, FR). The illustrated front wheels (FL, FR) is a pair of vehicle wheels, however a different number of vehicle wheels could be provided in other

examples.

The system 20 may comprise a differential 217 for receiving output torque from the transmission 204, i.e., from the gear train. The differential may be integrated into the vehicle transmission arrangement 204 as a transaxle, or provided separately.

The illustrated system 20 comprises one electric traction motor 216. In other embodiments, the system 20 may have more than one electric traction motor. The system (20) may further comprise a starter motor 219 which is mechanically connected or connectable to the engine 202. For example, the starter motor 219 may be a belt integrated starter generator (BiSG) or a pinion starter motor. In the illustration, the starter motor 219 is located at an accessory drive end of the engine 202, opposite a vehicle transmission end of the engine 202.

The control system 100 may be configured to disconnect the torque path between the engine 202 and the first set of vehicle wheels (RL, RR) in electric vehicle mode, for example to reduce parasitic pumping energy losses or to operate in an electric vehicle mode. For example, the first clutch 212 may be opened.

In some embodiments, the vehicle comprises another motive power source, or prime mover, arranged to provide torque to at least one wheel (FL, FR) of another axle of the vehicle. For example, the system (20) may further comprise a second electric traction motor (not shown) or a second internal combustion engine (not shown), either of which may provide positive torque alone or in combination with the electric traction motor 216 and/or the engine 202.

In order to store electrical power for the electric traction motor 216, 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 motor.

The traction battery 200 may be a high voltage (HV) battery. High voltage traction batteries provide nominal voltages in the hundreds of volts, as opposed to traction batteries for mild HEVs which provide nominal voltages in the tens of volts. The traction battery 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 in the hundreds of 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.

The system 20 may comprises one or more inverters 214. One inverter 214 is shown, for the electric traction motor 216. In other examples, two or more inverters could be provided.

It can be appreciated from the foregoing that the vehicle may be provided with motive torque from a combination of sources.

Figures 3A-B illustrate a vehicle 300 according to an embodiment of the present invention. The vehicle 300 comprises a control system 100 as illustrated in Figure 1. The controller 110 is shown as mounted within the vehicle 300 and is in communication with the powertrain 20. The powertrain 20 is a hybrid powertrain system of the vehicle 300. The powertrain 20 comprises an engine 202 and an EM 216. Figure 3B illustrates a rear-view of the vehicle 300 of Figure 3A.

Figure 4 illustrates a method 400 according to an embodiment of the invention. The method 400 is a method of controlling a hybrid powertrain system 20 of a vehicle 300, such as the vehicle 300 illustrated in Figures 3A and 3B, to perform an engine start. The hybrid powertrain system 20 is operable to perform an engine start using a plurality of engine start modes, the hybrid powertrain system 20 comprising an engine 202 (an internal combustion engine which may be powered by petrol, diesel, hydrogen, an e-fuel, for example, or any suitable combustible fuel) and an electric traction motor 216. The method 400 may be performed by the control system 100 illustrated in Figure 1. In particular, the memory 130 may comprise computer-readable instructions which, when executed by the processor 120, perform the method 400 according to an embodiment of the invention.

When the vehicle 300 is operating such that only the electrical traction motor 216 is supplying output torque to the transmission 204, it can sometimes become necessary to initiate an engine start such that both the electric traction motor 216 and the engine 202 are operating to supply output torque. An engine start may be required for a variety of reasons, including but not limited to, an increase in driver demand that requires a torque output that exceeds the power capability of the electric traction motor 216, or a traction battery 200 having a low charge. Other reasons for performing an engine start may also include powertrain system issues (e.g., related to the function of the traction battery 200 or electric traction motor 216) or selection of a gear mode that requires use of the engine 202. The hybrid powertrain system 20 is operable to start the engine 202 using a number of different engine start modes, and the suitability of each engine start mode will depend on the operating conditions of the vehicle at the point at which the engine start is required. An engine start mode should thus be chosen that will maintain the performance of the electric traction motor 216 and ensure there is no significant or noticeable loss in the torque being applied to the transmission 204 as the engine 202 is started. The method 400 determines which of the possible engine start modes should be chosen based on one or more operating conditions to maintain performance, and thus provide a smooth driving experience.

For example, the plurality of engine start modes may include a comfort slip start mode, a response slip start mode and a starter motor start mode.

A comfort slip start mode occurs when the first clutch 212 between the electric traction motor 216 and the engine 202 is partially engaged to start the engine while the second clutch 218 between the electric traction motor and the transmission 204 of the vehicle is also partially engaged, with the first and second clutches being fully engaged only once the engine speed is matched to the electric traction motor speed. This mode allows the vehicle to smoothly switch from using the electric traction motor only to using the engine either alone or in combination with the electric traction motor, by transferring torque from the electric traction motor to the engine via the first clutch to get the engine running prior to the switch. By slipping (i.e., partially engaging) the second clutch, oscillations or torque spikes which can occur due to the transfer of torque are damped, thus providing a smoother driver experience.

A response slip start mode occurs when the first clutch between the electric traction motor and the engine is partially engaged to start the engine and is fully engaged once the engine speed is matched to the electric traction motor speed, while the second clutch between the electric traction motor and the transmission remains fully engaged throughout. This differs from the comfort slip start mode above in that the second clutch is not slipped (i.e., the second clutch remains fully engaged). This mode can be used, for example, when driver demand is high, i.e., rapid acceleration is desired. This mode provides a faster vehicle response, but can mean that the ride is less smooth. In comfort slip start modes, oscillations can be less noticeable because the slipped clutch connecting the EM to the gearbox/wheels dampens the oscillations. This means the driver does not feel the oscillations as much. It can be important to have a fast controller in slip start modes because overshooting the engine/EM speed can have negative consequences on the NVH characteristics of the vehicle. Fast controllers have less overshoot than slow controllers.

A starter motor start mode occurs when the starter motor 219 is operated to start the engine 202. The starter motor 219 may be a belt integrated starter generator (BiSG) or a pinion starter motor. This differs from the comfort slip start and response slip start in that no torque is transferred from the electric traction motor 216 to the engine 202. This mode can be used, for example, when driver demand is high, i.e., rapid acceleration is desired, or if the traction battery 200 is running low on charge. This mode also provides a faster vehicle response, but can again mean that the ride is less smooth.

It will of course be appreciated that the hybrid powertrain system may be configured to perform other start modes, such as emergency start modes. For example, in cases where the electric traction motor 216 or the starter motor 219 cannot be used to start the engine 202, an "inertia" start mode may be used whereby the first clutch 212 is engaged when the vehicle 300 is moving to use the power generated by the wheels to start the engine 202. This can cause a noticeable deceleration as the power required to start the engine 202 is taken from the kinetic energy of the vehicle 300.

At step 410, the control system 100 is configured to receive an engine start signal 160 indicating that an engine start is required. Optionally, this engine start signal 160 is produced by the controller based on receiving data relating to a power demand signal indicative of the power demand or an EM battery charge signal indicative of the state of battery charge of the traction battery 200 for the electric traction motor 216, or some other data indicating that than engine start is required (e.g., a system issue). For example, if the power demand signal indicates that the driver is requesting to accelerate such that a torque output required exceeds the capabilities of the electric traction motor, the engine start signal 150 will be generated. As another example, if the EM battery charge signal indicates that the battery charge of the traction battery 200 is below a predetermined threshold, the engine start signal 150 will be generated.

At step 420, the control system 100 is configured to analyse one or more operating conditions of the vehicle.

300. The control system analyses the one or more operating conditions of the vehicle 300 based on the received operating conditions signal 165. As discussed above, the one or more operating conditions may include one or more of a power demand, a speed of the EM, a gear selection, a power output by the EM, and a temperature of one or more components of the EM.

At step 430, the control system 100 is configured to select an engine start mode from a predetermined prioritised list of engine start modes based on the analysis of the one or more operating conditions. In this respect, the control system 100 will consider the list of engine start modes in a prioritised order and determine, based on the one or more operating conditions, which each engine start mode should be selected. For example, the control system 100 may consider the engine start modes in the order of comfort slip start, response slip start, and starter motor start. The control system 100 will consider each engine start mode in turn, and then select the first engine start mode where the one or more operating conditions meet a set of criteria defined for the respective engine start mode.

Firstly, the control system 100 is configured to determine whether a slip start can be selected based on the power demanded, for example, by the driver. For example, if the power being demanded does not exceed a maximum power threshold, it is determined that a slip start of some type will be possible. In this respect, the maximum power threshold corresponds to the upper limit of the amount of power available for use by the electric traction motor 216 for delivering torque to the transmission 204. Optionally, the upper limit of the power from the traction battery 200 available for use by the electric traction 216 for delivering torque to the transmission 204 may correspond to the maximum power capability of the electric traction motor 216.

Optionally, as illustrated by the graph 500 shown in Figure 5, the upper limit of the power available for use by the electric traction 216 for delivering torque to the transmission 204 (as denoted by line "A") may correspond to a first portion of the maximum power capability of the electric traction motor 216 (as denoted by line "B"), wherein one or more further portions of the power capability may be reserved or used for other operational purposes. For example, a second portion of the maximum power capability B may be reserved for use in performing a slip start (i.e., the region between the maximum power threshold A and the maximum power capability B), whilst the first portion of the maximum power capability B (i.e., the region under the maximum power threshold A) is made available for use by the electric traction motor 216 for delivering torque to the transmission 204. In such case, the maximum power threshold A is the limit of the first portion of the maximum power capability B. Optionally, a third portion of the maximum power capability (i.e., the region between the maximum power threshold A and the line "C") may be made available for use by the electric traction motor 216 in offsetting the torque increase needed to compensate for a gear ratio reduction which may occur when the engine 202 is first turned on, to thereby maintain expected vehicle acceleration. The gear ratio reduction may be requested due to differences in operating efficiency of the electric traction motor 216 and the engine 202 at different speeds. While dependent on vehicle speed, the most efficient operating speed for the electric traction motor 216 on its own is generally higher than the most efficient operating speed for the combination of the engine 202 and the electric traction motor 216. Consequently, before the engine 202 is started, the electric traction motor 216 may run at a higher speed than if the engine 202 is connected via the first clutch 212, and so when the engine 202 is started, an upshift in gear may be required to bring the speed of the electric traction motor 216 down for synchronisation with the lower desired speed of the engine 202. Whether or not an upshift, i.e., a gear ratio reduction, is desirable will depend on the vehicle speed, with an upshift being more favourable at some vehicle speeds than others. As such, after receiving the engine start signal 160, the control system 100 may be optionally configured to calculate, or otherwise determine, the portion of power capability needed for offsetting the gear ratio reduction, i.e., the third portion. In response to the engine start signal 160, the control system 100 may be configured to determine, in dependence on one or more of the operating conditions of the vehicle, a predicted gear selection associated with an engine start. For example, based on the current gear selection of the vehicle and a speed of the vehicle, the control system 100 may be configured to determine a predicted gear selection that will be needed when the engine 202 is started (i.e., whether there is an upshift). The control system 100 may then be configured to determine, in dependence on the predicted gear selection and one or more of the current gear selection and vehicle speed, a portion of the power capability of the electric traction motor 216 needed for offsetting the expected reduction in gear ratio. Optionally, the predicted gear selection may be determined by comparing the current gear selection and vehicle speed to a look-up table stored in the memory 130. The control system 100 may then be configured to output a control signal to the powertrain system 20 to make that portion of power capability available for use in offsetting the expected reduction in gear ratio. Optionally, the portion of the power capability of the electric traction motor 216 needed for offsetting the expected reduction in gear ratio corresponds to the amount of torque required to maintain the wheel torque generated at the current vehicle speed with a different gear ratio. The remaining portion of maximum power capability B being made available for use in delivering torque to the transmission 204, and optionally, for use in performing a slip start. The third portion of the maximum power capability B, which can be considered as an "additional torque offset", is preferably taken from the first portion of the maximum power capability (i.e., the region under the line denoted "A") so that the second portion of the maximum power capability B, which is reserved for use in performing a slip start, is maintained. In such embodiments, the upper limit of the power available for use by the electric traction 216 for delivering torque to the transmission 204, i.e., the first portion of the power capability, may correspond to the maximum power capability B of the electric traction motor 216 minus the second and third portions which are reserved for use in performing a slip start operation and made available for use in compensating for a gear ratio reduction, respectively. It will also be appreciated that one or more portions of the power capability of the traction battery 200 may be reserved for other operational purposes, such as operating air conditioning, screen heaters and other power consuming devices of the vehicle 300.

If the power demand does not exceed the maximum power threshold A, it can be determined that the electric traction motor 216 has power available for performing a slip start. If the power being demanded is equal to or exceeds the maximum power threshold A, then neither a comfort slip start or a response slip start will be possible, and hence a starter motor engine start will be selected.

If it is determined that a slip start of some type is possible, the control system 100 will determine whether a comfort slip start is possible. To determine whether a comfort slip start should be selected, the control system 100 is configured to analyse one or more of: the speed of the electric traction motor 216, a gear selection and a rate of change of the power demand (i.e., how quickly the driver is accelerating). The control system 100 is configured to determine whether the rate of change of the power demand is above a threshold level defined by the speed of the electric traction motor 216 and the gear selection, to thereby determine whether a refined transition (i.e., a comfort slip start) or a rapid engine start (i.e., a response slip start or starter motor start) should be prioritised. If the rate of change of the power demand is below the threshold level, a comfort slip start is selected. If the rate of change of power demand is above the threshold level, a comfort slip start is ruled out and will not be selected. In this respect, the threshold level is a dynamically adjustable parameter that varies according to the speed of the electric traction motor 216 and the gear selection. As one example, if the vehicle 300 is moving slowly (i.e., the EM speed is low) and the vehicle 300 is in low gear (e.g., first gear), the threshold level for the rate of change of the power demand will be relatively high since a rapid engine start (i.e., a response slip start) is more likely to produce noticeable oscillations and thus a comfort slip start will be prioritised. As another example, if the vehicle 300 is moving very quickly (i.e., the EM speed is high) and the vehicle 300 is in a high gear (e.g., fifth gear), the threshold level for the rate of change of the power demand will be relatively low since a rapid engine start (i.e., a response slip start) will start the engine 202 more quickly and any resulting oscillations are less likely to be felt by the driver, in which case a comfort slip start will not be selected.

The control system 100 will also determine whether a slip start (comfort or response) can be selected based on the analysis of one or more operating conditions, and if not, will determine that a starter motor start should be selected. To determine whether a slip start (comfort or response) or a starter motor start should be selected, the control system 100 is configured to analyse one or more of the power demand being demanded by the driver, a power output by the electric traction motor 216, and a temperature of a component a temperature of one or more components of the electric traction motor 216. It will of course be appreciated that there may be other operating conditions that may be used to determine whether a slip start is possible. As noted above, if the power being demanded by the driver is equal to or above the maximum power threshold (i.e., the power available to the electric traction motor 216 for use in providing torque to the transmission), a slip start of any type will be ruled out and the starter motor start mode will be selected. However, if the power being demanded is below the maximum power threshold A, one or more further operating conditions will be analysed to determine whether a slip start can be selected. For example, if the power being output by the electric traction motor 216 is close to the maximum power capability of the electrictraction motor 216 (e.g., above the maximum threshold A), or if the power being output is decreasing but the power being demanded is still increasing (i.e., indicating that the power capability of electric traction motor 216 is decreasing), then a slip start of any type will be ruled out and the starter motor start will be selected. However, if there is no indication that the power being output is not close to the maximum power capability or decreasing, then a slip start will not be ruled out. As another example, if the power being demanded is increasing quickly (i.e., the driver is quickly accelerating at a rate such that the power being demanded is quickly approaching the maximum power capability of the electric traction motor 216), a slip start of any type will be ruled out and the starter motor start will be selected.

However, if the power being demanded is not increasing quickly and rapidly approaching the maximum power capability of the electric traction motor 216, then a slip start will not be ruled out. Similarly, if a temperature of at least one component of electric traction motor 216 is above or below a temperature range (i.e., indicating that the electric traction motor 216 is beginning to overheat or too cold to perform an engine start), a slip start will be ruled out and the starter motor start mode will be selected. For example, if the transmission oil of the electric traction motor 216 is below -10°C, a slip start may not be possible as the viscosity of the oil may be too high to provide accurate control of the clutches. Similarly, if a component of the electric traction motor 216 is above 50°C, it may not be possible to perform a slip start at this temperature and thus the starter motor start mode will be selected. However, if the temperature of the components of the electric traction motor 216 is within the temperature range, a slip start will not be ruled out. As such, if a slip start is not ruled out based on any of the analysed operating conditions, the control system 100 will determine that a slip start can be selected, with the determination between a comfort slip start or a response slip start being as described above. Conversely, if a slip start of any type is ruled out based on any of the analysed operating conditions, the control system 100 will determine that a starter motor start should be selected.

In summary, a comfort slip start will be selected if the power being demanded does not exceed a maximum power threshold of the electric traction motor 216, the rate of change of the power being demanded is below a threshold level defined by the speed of the electric traction motor 216 and the gear selection, and one or more further operational conditions including one or more of the power demand being demanded by the driver, a power output by the electric traction motor 216, and a temperature of a component a temperature of one or more components of the electric traction motor 216 meet a pre-defined set of criteria. A response slip start will be selected if the power being demanded does not exceed the maximum power threshold of the electric traction motor 216, the rate of change of the power being demanded is below the threshold level defined by the speed of the electric traction motor 216 and the gear selection, and one or more further operational conditions including one or more of the power demand being demanded by the driver, a power output by the electric traction motor 216, and a temperature of a component a temperature of one or more components of the electric traction motor 216 meet a pre-defined set of criteria. A starter motor start will be selected if the power being demanded is equal to or above the maximum power threshold of the electric traction motor 216, or the one or more further operational conditions do not meet the pre-defined criteria required for a slip start. By applying this set of rules for selecting a start mode based on the operational conditions of the vehicle, an engine start mode is selected that will maintain the performance of the electric traction motor 216 and ensure that there is no significant or noticeable loss in the torque being applied to the transmission 204 as the engine 202 is started.

Once the control system 100 has selected an engine start mode from the prioritised list of start modes, the control system 100 is configured to output, at step 440, a control signal 170 to cause the powertrain system to start the engine in accordance with the selected engine start mode. Optionally, if a comfort slip start is selected, the control system 100 is configured to output a control signal 170 to the powertrain system 20 to partially engage the first clutch 212 between the electric traction motor 216 and the engine 202, and partially engage the second clutch 218 between the electric traction motor 216 and the transmission 204 to thereby transfer torque from the electric traction motor 216 to the engine 202, the first and second clutches 212, 218 then being fully engaged once the speed of the engine 202 matches the speed of the electric traction motor 216. Optionally, if a response slip start is selected, the control system 100 is configured to output a control signal 170 to the powertrain system 20 to partially engage the first clutch 212 between the electric traction motor 216 and the engine 202, whilst keeping the second clutch 218 between the electric traction motor 216 and the transmission 204 fully engaged, to thereby transfer torque from the electric traction motor 216 to the engine 202, the first clutch 212 then being fully engaged once the speed of the engine 202 matches the speed of the electric traction motor 216. Optionally, if a starter motor start is selected, the control system 100 is configured to output a control signal 170 to the powertrain system 20 to operate the starter motor 219 to thereby start the engine 202, and then engage the first clutch 212 between the engine 202 and the electric traction motor 216 once the speed of the engine 202 matches the speed of the electric traction motor 216.

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.

Claims

CLAIMS1. A control system for controlling an engine start of a hybrid vehicle having a powertrain system comprising an engine and an electric traction motor, the powertrain system being operable to control an engine start using a plurality of engine start modes, the control system comprising one or more processors, the one or more processors collectively configured to: receive a first signal indicating that an engine start is required; analyse, in response to the first signal, an operating conditions signal indicative of one or more operating conditions of the vehicle, wherein the one or more operating conditions comprise a power demand signal indicative of a power request; select an engine start mode from a predetermined prioritised list of a plurality of engine start modes based on the analysed one or more operating conditions; and output a control signal to the powertrain system to control the engine start in accordance with the selected engine start mode, wherein at least a first of the engine start modes comprises a slip start mode in which the electric traction motor is operated to start the engine and at least a second of the engine start modes comprises a starter motor mode in which a starter motor is operated to start the engine.
2. The control system of claim 1, wherein the control system is configured to select the slip start mode in which the electric traction motor is operated to start the engine if the power demand signal is below a maximum power threshold.
3. The control system of claim 2, wherein the one or more operating conditions comprise at least one of: a speed of the electric traction motor, and a gear selection.
4. The control system of claim 3, wherein the control system is configured to select a first slip start mode or a second slip start mode in dependence on the speed of the electric traction motor, the gear selection and a rate of change of the power demand signal.
5. The control system of claim 4, wherein the control system is configured to select the first slip start mode if the rate of change of the power demand signal is below a threshold level defined by the speed of the electric traction motor and gear selection.
6. The control system of claim 5, wherein the control system is configured to select the second slip start mode if the rate of change of the power demand signal is above the threshold defined by the speed of the electric traction motor and gear selection.
7. The control system of any of claims 2 to 6, wherein the control system is configured to select the starter motor start mode if the power demand signal is above or equal to the maximum power threshold.
8. The control system of any preceding claim, wherein the one or more operating conditions further comprise one or more of: a power output signal from the electric traction motor, and a temperature of a component of the electric traction motor.
9. The control system of any preceding claim, wherein the control system is further configured to select the starter motor start mode if the one of more operating conditions comprise one or more of: a power output signal indicating that the electric traction motor is outputting a power close to its maximum power capability; a power demand signal indicating an increasing power request; a power output signal indicating a reduction in the power capability of the electric traction motor; and a temperature of a component of the electric traction motor 216 is within a predefined temperature range.
10. The control system of any preceding claim, wherein, in response to the first signal, the control system is configured to: determine, in dependence on one or more operating conditions of the vehicle, a predicted gear selection associated with an engine start; determine, in dependence on the predicted gear selection and the one or more operating conditions, a first portion of a power capability of the electric traction motor for use in offsetting a gear ratio reduction; and output a control signal to the powertrain system to make the first portion of the power capability available for use in offsetting the gear ratio reduction.
11. The control system of claim 10, wherein the one or more operating conditions comprise a current gear selection and a speed of the vehicle.
12. A system comprising the control system of any preceding claim and a powertrain system of a vehicle, the powertrain system comprising an engine and an electric traction motor.
13. A vehicle comprising the system of claim 12 or the control system of claims 1 to 11.
14. A method for controlling an engine start of a hybrid vehicle having a powertrain system comprising an engine and an electric traction motor, the powertrain system being operable to control an engine start using a plurality of engine start modes, the method comprising: receiving a first signal indicating that an engine start is required; analysing, in response to the first signal, an operating conditions signal indicative of one or more operating conditions of the vehicle, wherein the one or more operating conditions at least comprise a power demand signal indicative of a power request; selecting an engine start mode from a predetermined prioritised list of a plurality of engine start modes based on the analysed one or more operating conditions; and outputting a control signal to the powertrain system to control the engine start in accordance with the selected engine start mode, wherein at least a first of the engine start modes comprises a slip start mode in which the electric traction motor is operated to start the engine and at least a second of the engine start modes comprises a starter motor mode in which a starter motor is operated to start the engine.
15. Computer readable instructions which, when executed by a computer, are arranged to perform a method according to claim 14.