GB2638688A - Control system for controlling a powertrain of a hybrid electric vehicle - Google Patents

Abstract

A control system for a hybrid electric vehicle (10) comprising an internal combustion engine, an electric machine, a drivetrain configured to receive torque from the electric machine, one or more clutches and one or more processors. The processors configured to receive a gear change signal 210 and an engine start signal 220. In dependence on the gear change and engine start signals output an electric machine torque signal 230 to cause the electric machine to output a torque which is at least partially applied to the engine. The torque is used to crank the engine and once the engine is running generate a further signal 240 indicating the engine is past the cranking phase. Once this signal is received generate a gear change signal 250.

Description

Control System for Controlling a Powertrain of a Hybrid Electric Vehicle

TECHNICAL FIELD

The present disclosure relates to a control system for controlling a powertrain of a hybrid electric vehicle.

Aspects of the invention relate to a control system for controlling a powertrain of a hybrid vehicle, a system comprising the control system and a powertrain, a vehicle and a method.

BACKGROUND

It is known to provide a hybrid vehicle where the vehicle may be propelled by an electric machine and an internal combustion engine. The internal combustion engine may be turned off when it is not required in order to save energy. The electric machine may also provide a cranking torque to the engine when the engine is to be started. There may also be one or more gear changes made when starting the engine in order to change the electric machine speed from a more efficient speed to a speed that is more appropriate to synchronise with an engine speed.

The present inventors have realised that known engine starting schemes may result in undesirable vehicle characteristics, such as a drop in wheel torque and corresponding reduced acceleration.

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 for controlling a powertrain of a hybrid vehicle, a system comprising the control system and a powertrain, a vehicle and a method as claimed in the appended claims According to an aspect of the present invention, there is provided a control system for controlling a powertrain of a hybrid electric vehicle, the powertrain comprising an internal combustion engine, an electric machine, a drivetrain arranged to receive torque from the internal combustion engine and the electric machine and one or more clutches, the drivetrain comprising a gearbox, the control system comprising one or more processors collectively configured to: receive an engine start signal indicative of an expected engine start; in dependence on the engine start signal, output a first electric machine torque signal to cause the electric machine to generate a first electric machine torque, wherein at least a part of the first electric machine torque is to be applied to the internal combustion engine; receive an engine started signal comprising information indicative that the engine has completed a cranking phase; and in dependence on the engine started signal, output a gear change signal to cause the gearbox to change a torque ratio of the gearbox.

The control system may receive a gear change signal indicative of an expected gear change and may output the first electric machine torque signal dependent on the gear change signal.

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 carry out the required method.

In hybrid electric vehicles where the electric machine may be used to generate a cranking torque, there may be a torque limit applied to the electric machine such that the electric machine has a reserve torque for cranking the engine at any time. This therefore reduces the torque available from the electric machine for propelling the vehicle.

In particular, a lack of available torque may be felt during a gear change to a higher gear. It is often desirable to increase the torque generated by a power source during a gear change in order to account for the increase in torque ratio, providing a consistent torque at the wheels of the vehicle. However, where an increase in torque from the power source, the torque at the wheels may reduce, resulting in a reduction in acceleration of the vehicle.

By completing a cranking phase of the engine before changing gear, more torque may be available from the electric machine for propulsion. The torque from the electric machine may therefore be increased during a gear change to provide a more consistent torque at the wheels. This may result in more consistent acceleration of the vehicle.

The electric machine may be coupled to the engine via a first clutch, and the one or more processors may be collectively configured to, in dependence on the engine start signal, output a first clutch engagement signal to cause the first clutch to at least partially engage to allow the at least a part of the first electric machine torque to be applied to the internal combustion engine.

By engaging the first clutch, the electric machine may provide torque to the engine to crank the engine. This may remove the need for a starter motor, reducing overall vehicle weight and cost.

The one or more processors may be collectively configured to: prior to the engine start signal, maintain a torque generated by the electric machine below a first electric machine torque threshold; and subsequent to the engine start signal, allow a torque generated by the electric machine to exceed the first electric machine torque threshold.

The electric machine torque may be limited to be below a first threshold prior to the engine starting, so that the torque can be increased to crank the engine whenever necessary. After the engine is started, there is no need to provide a torque reserve for cranking the engine and so the electric machine torque may be greater than the first threshold. This may allow the vehicle to accelerate more quickly.

The one or more processors may be collectively configured to, in dependence on the engine started signal, output a second electric machine torque signal to cause the electric machine to generate a second torque greater than the first electric machine torque threshold.

By producing a higher torque, the electric machine may accelerate the vehicle more quickly. In particular, where the electric machine is started immediately before a gear change, the torque produced by the electric machine may be increased during the gear change such that the torque at the wheels is more consistent during the gear change.

The gearbox may be coupled to the first electric machine via a second clutch, and the one or more processors may be collectively configured to, in dependence on the engine start signal, output a second clutch engagement signal to cause the second clutch to be at least partially disengaged.

By at least partially disengaging the second clutch, the torque transferred to the gearbox and thereby to the wheels may be more accurately controlled. As the torque required to crank the engine is difficult to predict, using the leftover torque from the electric machine, after the torque required to crank the engine is subtracted, may be different from the amount that is to be transferred to the wheels. However, by partially disengaging the clutch, the torque transferred to the gearbox may be maintained constant. In this case, the electric machine torque may be increased above the predicted required cranking torque of the engine and the required propulsive torque, in order to reduce the prospect of there being insufficient torque at the wheels.

The engine started signal may comprise information indicating that the engine has a speed above an engine started threshold speed.

The engine starting may be determined by the engine speed reaching above a threshold value. This may reliably indicate that no cranking torque is required and that the electric machine may therefore provide a propulsive torque above the first threshold.

The gear change signal may be indicative of an expected upshift of the gearbox.

An upshift is often accompanied by an increase in torque demanded from the electric machine. It may therefore be particularly beneficial to start the engine before an upshift takes place, so that the electric machine may increase the torque output by the electric machine during and after the upshift.

According to a further aspect of the invention, there is provided a system comprising the control system of the first-mentioned aspect and a powertrain, the powertrain comprising the internal combustion engine, the electric machine, the drivetrain arranged to receive torque from the engine and the electric machine, and one or more clutches, the drivetrain comprising the gearbox.

The engine may be coupled to the electric machine via a first clutch and the electric machine is coupled to the gearbox via a second clutch.

According to a still further aspect of the invention, there is provided a vehicle comprising the system of the further aspect or the control system of the first mentioned aspect.

According to a yet still further aspect of the invention, there is provided a method for controlling a powertrain of a hybrid electric vehicle, the powertrain comprising an internal combustion engine, an electric machine, a drivetrain arranged to receive torque from the internal combustion engine and the electric machine and one or more clutches, the drivetrain comprising a gearbox, the method comprising: receiving a gear change signal indicative of an expected gear change; receiving an engine start signal indicative of an expected engine start; in dependence on the gear change signal and the engine start signal, outputting a first electric machine torque signal to cause the electric machine to generate a first electric machine torque; receiving an engine started signal comprising information indicative that the engine has completed a cranking phase; and in dependence on the engine started signal, outputting a gear change signal to cause the gearbox to change a torque ratio of the gearbox.

According to another aspect of the invention, there is provided computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform the method according to the yet still further aspect.

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 vehicle according to the invention; Figure 2 shows a schematic representation of a vehicle according to the invention; Figure 3 shows a flowchart illustrating a method according to the invention; Figure 4 shows a flowchart illustrating a second method according to the invention; Figures 5a to 5c show graphs illustrating a known gear change and engine start method; Figures 6a and 6b show graphs illustrating a gear change and engine start method according to the invention; and Figures 7a and 7b show further graphs illustrating the gear change and engine start method according to the invention.

DETAILED DESCRIPTION

Hybrid vehicles have an internal combustion engine that is powered by fossil fuels such as petrol or diesel and an electric motor that is battery powered. In order to improve efficiency, the internal combustion engine may be turned off or stopped when it is not needed, such as when the vehicle is driving at low speed or has a low torque requirement. In order to turn on or start an internal combustion engine, an external torque input is required to the engine. In some cases, the input torque, which may be referred to as a cranking torque, may be provided by a starter motor that is a dedicated electric motor usually arranged to apply torque to the fly wheel of the internal combustion engine in order to crank the engine to allow it to start. However, in hybrid vehicles, it has been identified that the electric machine used to propel the vehicle may be used to supply the cranking torque to the engine, meaning that no starter motor is required. This may reduce the weight and cost of the hybrid vehicle. Where the propulsive electric machine is used to crank the internal combustion engine, a cranking torque headroom of the electric machine may be reserved when the internal combustion engine is turned off, so that there is no need to reduce the torque transferred to the wheels during a cranking phase of the engine.

In cases where the vehicle is being driven with the electric machine only, the vehicle may be driven with a low gear as electric machines are often more efficient when running at a high speed. However, where it is determined that a greater torque may be required and that therefore the internal combustion engine should be used in conjunction with the electric machine, which may be due to an increased torque demand, one or more upshifts may be required to allow the electric machine to run at a speed that is compatible with an internal combustion engine. In this case, an engine start signal and a gear change signal may be output simultaneously or at very close times.

Alternatively, a gear change, in particular an upshift, may mean that more torque is required from the power source of the vehicle immediately after the upshift, due to the reduced torque ratio in the drivetrain. In this case, an engine start signal and a gear change signal may be generated at the same time.

The present inventors have realised that, where there may be a requirement to increase the torque output by the power sources immediately after a gear change, it may be advantageous to start the internal combustion engine before the gear change so that there is no requirement to reserve the torque headroom for cranking the engine during the gear change and immediately after the gear change. This may provide more consistent torque at the wheels of the vehicle and a smoother acceleration for passengers of the vehicle.

Figure 1 shows a vehicle 10 comprising a control system 100 and a powertrain 111. The control system 100 is arranged to control the powertrain 111. The vehicle 10 is a hybrid vehicle having both an internal combustion engine and an electric machine arranged to propel the vehicle.

The vehicle 10 may be a mild hybrid electric vehicle (MHEV). An MHEV may be characterised by having no capacity to charge an electric battery using mains electricity and the electric battery may be charged by the internal combustion engine and regenerative braking only. Considered another way, the only primary energy source for an MHEV may be fossil fuels, for example petrol and diesel and the MHEV may have no electrical connection for charging the battery from an external source. The capacity of the battery of an MHEV may be less than 2 kwh. The battery voltage of an MHEV may be 48 volts or less.

Alternatively, the vehicle 10 may be a plug-in hybrid electric vehicle (PHEV). A PHEV may be characterised by being arranged to receive electrical energy from an external source, such as via a connection to mains electricity. A PHEV may therefore comprise an external electrical connection for charging the battery.

Figure 2 shows a schematic diagram of the vehicle 10. The diagram shows the control system 100 that is arranged to control the powertrain 111 and how signals from the control system 100 may be transferred to different components of the powertrain 111 and vice versa.

The control system 100 as illustrated in Figure 2 comprises one controller, although it will be appreciated that this is merely illustrative. The controller comprises processing means and memory means. The processing means may be one or more electronic processing devices which operably execute computer-readable instructions. The memory means may be one or more memory devices. The memory means is electrically coupled to the processing means. The memory means is configured to store instructions, and the processing means is configured to access the memory means and to execute the instructions stored thereon.

The controller comprises an input means and an output means. The input means may comprise an electrical input of the controller. The output means may comprise an electrical output of the controller. The input is arranged to receive signals. The output is arranged to output control signals indicative of commands for controlling the electric machine, the engine and the clutches.

The powertrain 111 comprises an internal combustion engine 110. The internal combustion engine 110 may receive a start signal or a torque signal 113 from the control system 100. Generally, the control system 100 may control the function of the engine by the supply of signals 113 to cause the internal combustion engine 110 to start cranking and/or to produce a specific amount of torque. It will be understood that reference to control of the internal combustion engine 110 includes control of ancillary components of the internal combustion engine including a fuel pump and throttle valve. The internal combustion engine 110 or an associated sensor may transmit signals 112 to the control system 100, such as an engine speed signal or engine torque signal that informs the control system 100 of the torque output by the engine and/or the rotational of speed of the engine. Generally, the engine may output an engine started signal 112 that is indicative of the engine having finished a cranking phase and being in a self-sustaining idle mode.

The internal combustion engine 110 may transfer torque 115 to downstream components via a clutch 120. The clutch 120, which may be referred to as an engine clutch, a first clutch, and/or a KO clutch, may be arranged to transfer torque between the engine 110 and an electric machine 130. The clutch 120 may be actuated by a clutch actuator 123. The control system 100 may output a first clutch signal 121 to cause the first clutch actuator 123 to output a force 124 to cause the first clutch 120 to be partially or fully disengaged. A partially disengaged clutch may transmit a consistent and controllable amount of torque across it, governed by the engagement force between the clutch plates and the friction between the clutch plates.

The internal combustion engine 110 may also receive a cranking torque 117 from the first clutch 120. The cranking torque may be a torque applied to the internal combustion engine during a start-up, cranking phase of the engine to allow the engine to transition from stationary to an idle mode. The first clutch 120 may be disengaged while the engine is turned off and may be engaged where the engine 110 is producing a positive torque to drive the vehicle or when it requires cranking to start running.

The system may further comprise a gearbox (not shown) between the engine and the electric machine. The gearbox may be a single stage gearbox that allows the electric machine and the engine to rotate at speeds that are efficient for both when being coupled in rotation. For example, when the KO clutch 120 is closed, the electric machine may rotate 1.6 times faster than the engine.

The vehicle 111 has the electric machine 130 arranged to produce torque for propelling the vehicle and for cranking the engine. The electric machine 130 may also receive torque from the internal combustion engine 110 and/or from the wheels during regenerative braking and may convert this energy into electricity for charging a battery and/or powering internal electrical devices (neither being shown). The electric machine 130 may transfer a cranking torque 127 to the first clutch 120 to crank the engine 110 as explained above and, where the internal combustion engine 110 is producing a positive torque to drive the vehicle, the torque may be transferred from the engine 110 to the clutch 120 and then to the electric machine 130 as torque 125.

The electric machine 130 may receive torque demand signals 131 from the control system 100, which may cause the electric machine 130 to generate a certain amount of torque and the electric machine 130 may transfer signals, such as speed signals 133 to the control system 100.

The electric machine 130 is arranged to transfer torque 135 to a second clutch 140. The second clutch 140 may also be referred to as a gearbox clutch, a transmission clutch and/or a B clutch. The second clutch 140 may be actuated by a second clutch actuator 143. The second clutch actuator 143 may act to move the clutch plates of the second clutch 140 closer together or further apart by exerting a force 144 on the clutch plates. The clutch actuator 143 may be actuated by a second clutch engagement signal 141, or a second clutch disengagement signal 141. The second clutch 140 may represent a plurality of clutches arranged to control an automatic gearbox 150 and generally applies to any clutch downstream of the electric machine 130.

Downstream of the second clutch 140 is the gearbox 150, which may be an automatic gearbox that is arranged to receive torque 145 from the second clutch 140 and to convert the torque to provide a different torque at the wheels (not shown). The gearbox 150 may have a plurality of gears and so may be able to change the torque conversion ratio through the gearbox by changing gear. Generally, a gear change in the gearbox 150 that means that a given input torque will result in a lower output torque (but greater speed at the wheels) may be described as an upshift and a gear change in the gearbox that will result in a given input torque resulting in a higher output torque (but lower speed at the wheels) may be described as a downshift.

Figure 3 shows a flowchart illustrating a method 200 of controlling the powertrain 111. Figure 3 illustrates a method 200 according to an embodiment of the invention. The method 200 is a method of controlling a powertrain of a vehicle 10, such as the vehicle 10 illustrated in Figure 1. In particular, the method 200 is a method of controlling a powertrain of a vehicle during a gear change and engine start. The method 200 may be performed by the control system 100 illustrated in Figure 2. In particular, a memory of the control system may comprise computer-readable instructions which, when executed by a processor of the control system, perform the method 200 according to an embodiment of the invention.

At step 210, the control system receives a gear change signal. The gear change signal may be an upshift signal and may be indicative of an expected gear change in the gearbox, which may be an expected upshift in the gearbox. The gear change signal may be received from a transmission control unit, which may determine, such as based on a torque demand from a driver or ADAS and/or an electric machine speed, that a gear change, is necessary. Alternatively, the gear change signal may instead be a determination of the control system that a gear change is required based on an electric machine speed and/or a torque demand from a user or ADAS. The gear change signal may be received due to being published on a CAN bus.

At step 220, the control system receives an engine start signal. The engine start signal may be received from a power source control unit or may be determined by the control system based on a torque demand from a driver or ADAS and/or an electric machine speed and/or battery charge level. The engine start signal and gear change signal may be received or determined simultaneously, such as by being determined in the same calculation. For example, the control system may determine an expected torque that will be required after the upshift and may determine the engine start signal based on the expected torque required after the upshift. Alternatively, the system may receive a torque demand and determine that an engine start is required for delivering the demanded torque. In order for the electric machine and the engine to work together, an upshift may be required in order to change the electric machine rotational speed.

At step 230, the control system outputs a first electric machine torque signal to cause the electric machine to generate a first electric machine torque. The first electric machine torque may be an increase in torque generated by the electric machine, such that the electric machine may provide a torque to the internal combustion engine to crank the internal combustion engine. The first electric machine torque may therefore be calculated as the torque required for propelling the vehicle plus the internal combustion engine cranking torque.

The engine may then be cranked by the electric machine via the first clutch. During this time, the engine may receive an ignition signal to control the engine to enter an idle mode, which may include a signal to ancillary parts of the engine and fuel may be input into the engine. After a certain time, the engine may have achieved a sufficient rotational speed and/or temperature to be self-sustaining. At this point the engine may increase in speed in order to reach a speed at which the k0 clutch may be closed and the engine and electric machine may rotate together. During the subsequent increase in speed, no further torque from the electric machine may be required. Alternatively, in some cases, the engine may run in an idle mode after cranking.

Once the engine has achieved a self-sustaining state, the engine, or an engine control system, may output an engine started signal to communicate to the control system that the engine has started. The engine started signal may also be referred to as an engine idle signal. Therefore, at step 240, the control system may receive an engine started signal. The engine started signal may be determined based on a rotational speed of the engine or on a reduction in required cranking torque.

At step 250, once the engine started signal has been received, the control system may output a gear change signal to cause the gearbox to change a torque ratio of the gearbox. The gear change signal may be output to a transmission control unit or may be internally published on a CAN bus, with the control system then putting out clutch control signals and gearbox solenoid control signals in order to effect the gear change.

Figure 4 shows a flow chart of a further method 300 of controlling the powertrain. The steps labelled 210, 220, 230, 240 and 250 are substantially similar to those already described and so will not be described again here.

At step 235, after the first torque signal is output, a first clutch signal is output to at least partially engage the first clutch. Generally, when the internal combustion engine is off, the first clutch is disengaged such that energy is not wasted in cranking the internal combustion engine. However, at step 235, the first clutch may be engaged fully in order to transfer maximum torque to the internal combustion engine, or may be partially engaged in order to control the torque transfer to the internal combustion engine more carefully.

Further, at step 235, a second clutch signal may be output to cause the second clutch to be partially disengaged. A partially disengaged clutch may transfer a controllable amount of torque that is determined by the force between the two plates of the clutch. The resistive torque provided by an engine during cranking may be difficult to predict and so, by partially disengaging the second clutch, the torque transmitted to the wheels, which may be the difference between the torque generated by the electric machine and the resistive torque of the internal combustion engine, may be controlled more carefully and made more consistent, improving the drivability of the vehicle.

The second clutch may remain partially disengaged throughout the engine cranking and the subsequent gear change so that the torque at the wheels may remain substantially constant.

At step 255, after the gear change has occurred, the control system may output a further second clutch signal to fully engage the second clutch. At this stage, the engine may also produce a positive torque to propel the vehicle. A further first clutch signal may also be output by the control system at step 255. The further first clutch signal may be to fully disengage the first clutch to allow the engine to idle separately from the electric machine.

Alternatively, the further first clutch signal may be arranged to fully engage the first clutch so that torque can be transferred from the engine to the electric machine to propel the vehicle and/or to charge the vehicle battery.

Figures 5A to 5C show how different vehicle parameters may vary across the engine start and gear change using a known method. Throughout the figures, the gear change time period is labelled GC and the engine start period is labelled ES. The control system may receive a gear change signal and optionally an engine start signal at the beginning of the time period GC.

Figure 5A shows the change in torque ratio across the gearbox during an upshift. Generally, during an upshift, the gear ratio r may reduce, such that a given input torque produces a lower output torque and higher speed.

The gear ratio r may vary linearly during the gear change as one gear may be gradually disengaged while a second gear is gradually engaged, giving a linear change in overall effective gear ratio. Alternatively, the gear change period GC may have subphases of a torque phase and an inertia phase. Due to clutch slip during the torque phase, the ratio may be kept constant and the electric machine speed may increase, with the torque ratio varying and the electric machine speed reducing during the inertia phase.

As illustrated in Figure 5B, which shows a variation in electric machine torque T against time T, in order to provide a consistent torque at the wheels of the vehicle, a power source torque may be increased during the gear change, such that the product of the gear ratio and the power source torque remains constant. However, this may not necessarily be achievable where a torque limit or threshold of the power source is reached.

As has been described previously, the electric machine may have a first torque limit TL1, which is an electric machine torque limit that reserves a portion of the electric machine torque to be used for cranking the engine. Therefore, the torque output by the electric machine may be limited to being at or below the first torque limit TL1 when the internal combustion engine is turned off and not cranking. Generally, the first torque limit TL1 may be applied when the engine is not idling.

Line 420 shows a desired torque variation for an electric machine during a gear change, where the electric machine torque may increase linearly throughout the gear change. However, as shown by line 425, which represents a real electric machine torque, the electric machine torque may be limited by the first torque threshold TL1 until the time at which the engine has started. Therefore, the electric machine torque may increase linearly from the start of the gear change until the first torque threshold TL1 is reached and may then remain at the first torque threshold TL1 until the engine is started at the end of time ES. After the engine is started, the electric machine torque may increase to the required torque, if the required torque is below the second torque threshold TL2, which may be a higher electric machine torque threshold which represents a torque that may be generated by the electric machine while the internal combustion engine is idling, since there is no need to reserve a cranking torque headroom.

Figure 5C shows the torque at the wheels of the vehicle during and after the gear change, and it can be seen that the desired, constant torque at the wheels 430 is not achieved and that, due to the limit on the electric machine torque, the real torque 435 that is felt at the wheels includes a torque-lag, which may be felt by a driver as a reduced acceleration of the vehicle.

The present invention looks to avoid the reduction in torque at the wheels. Figures 6A and 6B illustrate the variation in torque of the electric machine and at the vehicle wheels respectively during a gear change. As can be seen, in the present invention the engine start ES takes place before the gear change GC. The change in torque ratio during the gear change may be similar to that shown in Figure 5A, with a linear change in torque ratio during the gear change portion GC, but after an engine start time ES.

However, as shown in Figure 6A, the engine start ES may take place before the gear change GC. Therefore, the first torque limit TL1 may be applied only until the end of the engine start ES and the second torque limit TL2 may be applied during the gear change GC. The torque that may be generated by the electric machine during the gear change GC may therefore be increased, meaning that the torque, as illustrated by line 520, may increase linearly throughout the gear change GC and, as shown in Figure 6B, the torque at the wheels 530 may be constant through the engine start ES and the gear change GC.

In this way, the present invention may reduce or eliminate a torque-lag.

Figures 7A and 7B further illustrate how the torques and speeds of the electric machine and the engine may vary during the engine start and gear change.

While Figures 6A and 5B illustrate the net torque output by the power sources during the gear changes, Figure 7A shows the torque output by the electric machine 520 and the torque output by the internal combustion engine 530 during the engine start and the gear change. It can be seen that, during the engine start ES, the electric machine torque 520 is increased to provide a cranking torque to the engine and that, correspondingly, the torque output by the engine is negative as the engine provides a resistive torque while it is cranked. The extra cranking torque produced by the electric machine and the resistive cranking torque of the engine therefore cancel out, providing a substantially constant net power source torque during the engine start phase. Due to the increased torque threshold in the subsequent process, the electric machine torque 520 may then be increased linearly during the gear change, while the engine may output substantially no torque and may be idling.

Figure 7B shows a variation in engine and electric machine rotational speed during the engine start and gear change. It can be seen that the electric machine speed 550 may increase prior to an engine start and gear change. The gear change may be required based on the electric machine speed reaching a speed threshold or to reduce the electric machine speed to a speed compatible with the engine. During the engine start phase ES, the electric machine speed may be increased above the usual electric machine speed for the current vehicle speed to allow for slip of the first clutch during cranking and slip of the second clutch to provide a consistent torque at the wheels.

During the gear change, the electric machine speed may be reduced in orderto provide a substantially constant wheel rotational speed due to the corresponding change in speed ratio during the change in gear ratio. The electric machine speed may also increase during the first phase of the gear change GC, with the increase in speed being accounted for by clutch slip and may then reduce to maintain a consistent wheel speed.

The engine speed 560 may vary by increasing from a zero speed at the start of the engine start time, until the engine reaches a self-sustaining state, which may be an idle speed, at which the engine start time is ended.

The engine may then produce positive torque to propel the vehicle, which may be during the gear change phase or after. Alternatively, the engine may remain idle throughout the gear change. It will be understood that the engine may subsequently provide a positive torque in order to accelerate the vehicle.

The engine speed 560 and electric machine speed 550 may be synchronised after the gear change and the KO clutch may be closed. At this stage the engine and the electric machine may rotate at the same speed or with their speeds at a fixed ratio.

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 (12)

1. CLAIMS1. A control system for controlling a powertrain of a hybrid electric vehicle, the powertrain comprising an internal combustion engine, an electric machine, a drivetrain arranged to receive torque from the internal combustion engine and the electric machine and one or more clutches, the drivetrain comprising a gearbox, the control system comprising one or more processors collectively configured to: receive a gear change signal indicative of an expected gear change; receive an engine start signal indicative of an expected engine start; in dependence on the gear change signal and the engine start signal, output a first electric machine torque signal to cause the electric machine to generate a first electric machine torque, wherein at least a part of the first electric machine torque is to be applied to the internal combustion engine; receive an engine started signal comprising information indicative that the engine has completed a cranking phase; and in dependence on the engine started signal, output a gear change signal to cause the gearbox to change a torque ratio of the gearbox.
2. 2. The control system according to claim 1, wherein the electric machine is coupled to the engine via a first clutch, and wherein the one or more processors are collectively configured to, in dependence on the engine start signal, output a first clutch engagement signal to cause the first clutch to at least partially engage to allow the at least a part of the first electric machine torque to be applied to the internal combustion engine.
3. 3. The control system according to claim 1 or 2, wherein the one or more processors are collectively configured to: prior to the engine start signal, maintain a torque generated by the electric machine below a first electric machine torque threshold; and subsequent to the engine start signal, allow a torque generated by the electric machine to exceed the first electric machine torque threshold.
4. 4. The control system according to claim 3, wherein the one or more processors are collectively configured to, in dependence on the engine started signal, output a second electric machine torque signal to cause the electric machine to generate a second torque greaterthan the first electric machine torque threshold.
5. 5. The control system according to any preceding claim, wherein the gearbox is coupled to the first electric machine via a second clutch, and wherein the one or more processors are collectively configured to, in dependence on the engine start signal, output a second clutch engagement signal to cause the second clutch to be at least partially disengaged.
6. 6. The control system of any preceding claim, wherein the engine started signal comprises information indicating that the engine has a speed above an engine started threshold speed.
7. 7. The control system of any preceding claim, wherein the gear change signal is indicative of an expected upshift of the gearbox.
8. 8. A system comprising the control system of any preceding claim and a powertrain, the powertrain comprising the internal combustion engine, the electric machine, the drivetrain arranged to receive torque from the engine and the electric machine, and one or more clutches, the drivetrain comprising the gearbox.
9. 9. The system of claim 8, wherein the engine is coupled to the electric machine via a first clutch and the electric machine is coupled to the gearbox via a second clutch.
10. 10. A vehicle comprising the system of claim 8 or 9 or the control system of any one of claims 1 to 7.
11. 11. A method for controlling a powertrain of a hybrid electric vehicle, the powertrain comprising an internal combustion engine, an electric machine, a drivetrain arranged to receive torque from the internal combustion engine and the electric machine and one or more clutches, the drivetrain comprising a gearbox, the method comprising: receiving a gear change signal indicative of an expected gear change; receiving an engine start signal indicative of an expected engine start; in dependence on the gear change signal and the engine start signal, outputting a first electric machine torque signal to cause the electric machine to generate a first electric machine torque; receiving an engine started signal comprising information indicative that the engine has completed a cranking phase; and in dependence on the engine started signal, outputting a gear change signal to cause the gearbox to change a torque ratio of the gearbox.
12. 12. Computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform the method according to claim 11.