Controlling engine start of hybrid vehicle

Abstract

Aspects of the present disclosure relate to a control system (100) for controlling an engine start of a hybrid vehicle (300) having a powertrain system (20) including an engine (202) and an electric traction motor (216), the powertrain system (20) being operable to control the engine start using a plurality of engine start modes, the control system (100) includes one or more processors (120), the one or more processors (120) being collectively configured to: receive (410) a first signal (160) indicating that an engine start is required; analyzing (420), in response to the first signal (160), an operating condition signal (165) indicative of one or more operating conditions of the vehicle (300), where the one or more operating conditions include a power demand signal (165) indicative of a power request; selecting (430) an engine start mode from a predetermined priority list of a plurality of engine start modes based on the analyzed one or more operating conditions; and outputting (440) a control signal (170) to the powertrain system (20) to control an engine start according to the selected engine start mode, where at least a first of the engine start modes includes a slip start mode in which the electric traction motor (216) is operated to start the engine (202), and where at least a second of the engine start modes includes a slip start mode in which the electric traction motor (216) is operated to start the engine (202). And at least a second of the engine start modes includes a starter motor mode in which the starter motor (219) is operated to start the engine (202). Aspects of the invention also relate to a system including the control system (100) and a powertrain system (20) having an engine (202) and an electric traction motor (216), a vehicle (300) including the control system (100), and a method (400) of controlling an engine start of the vehicle (300).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to controlling engine starting of a hybrid vehicle. Aspects of the invention relate to control systems, systems, vehicles, methods and computer readable instructions. BACKGROUND

[0002] Vehicles are known to be powered by an internal combustion engine and one or more electric traction motors (also referred to as electric motors (EM)). When the vehicle is operating such that only the electric traction motor is used to provide power, it can sometimes be necessary to initiate engine starting such that both the electric traction motor and the engine are operating. Such hybrid powertrain systems are capable of operating to perform different engine starting modes depending on environmental conditions and the needs of the vehicle driver, but the selection of some starting modes under certain conditions can result in reduced vehicle performance.

[0003] It is an object of the invention to address one or more of the drawbacks associated with the prior art. SUMMARY

[0004] Aspects and embodiments of the invention provide control systems, systems, vehicles, methods and computer readable instructions as claimed in the appended claims.

[0005] The present disclosure provides a technique for controlling engine starting of a hybrid vehicle. The technique selects an engine starting mode from a prioritised list of starting modes depending on the power required at the time of the engine starting and one or more operating conditions of the vehicle.

[0006] According to an aspect of the invention, there is provided a control system for controlling engine starting of a hybrid vehicle, the hybrid vehicle having a powertrain system comprising an engine and an electric traction motor, the powertrain system being operable to control engine starting using a plurality of engine starting modes, the control system comprising one or more processors. The one or more processors are collectively configured to: receive a first signal indicative of a need for engine starting; and in response to the first signal, analyse operating condition signals indicative of one or more operating conditions of the vehicle, wherein the one or more operating conditions include a power demand signal indicative of a power request. The one or more processors are further configured to: select an engine starting mode from a predetermined prioritised list of the plurality of engine starting modes based on the analysed one or more operating conditions; and output a control signal to the powertrain system to control engine starting in accordance with the selected engine starting mode. At least a first one of the engine starting modes comprises a slip starting mode in which the electric traction motor is operated to start the engine, and at least a second one of the engine starting modes comprises a starter motor mode in which a starter motor is operated to start the engine.

[0007] In this way, a start mode is selected that will preserve the performance of the electric traction motor and ensure that there is no significant or noticeable loss of torque applied to the driveline when the engine is started. This is done because if the electric traction motor is not available, pinion start can be used to start the engine.

[0008] The control system comprises one or more controllers collectively comprising: at least one electronic processor having electrical inputs for receiving input signals; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored in the at least one memory device; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions on the at least one memory device to receive a first signal indicative of a need for engine start; in response to the first signal, analyse operating condition signals 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 a powertrain system to control 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.

[0009] 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 can correspond to an upper limit of power from the traction battery that can be used by the electric traction motor. In this way, the slip start mode will only be selected if the electric traction motor has sufficient power available to perform engine start without a noticeable loss of torque applied to the driveline.

[0010] Optionally, the one or more operating conditions comprise at least one of: a speed of the electric traction motor and a gear selection.

[0011] Optionally, the control system is configured to select the first or 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 the first clutch between the electric traction motor and the engine is partially engaged to start the engine and the second clutch between the electric traction motor and the driveline 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, thereby providing 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 is fully engaged once the engine speed matches the electric traction motor speed, whilst the second clutch between the electric traction motor and the driveline is always fully engaged, thereby providing a fast transition.

[0012] 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 the gear selection. In this regard, the threshold level is a dynamic adjustable parameter that varies in dependence on the speed of the vehicle and the selected gear. If the rate of acceleration does not exceed the threshold level, then a fast engine start is more likely to produce noticeable oscillations and so the first slip start mode can be selected.

[0013] 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 a threshold defined by the speed of the electric traction motor and the gear selection. In this way, if the rate of acceleration exceeds the threshold level, then a fast engine start is required and so the second slip start mode can be selected as any resulting oscillations will be less noticeable.

[0014] Optionally, the control system is configured to select the start motor start mode if the power demand signal is above or equal to a maximum power threshold. In this way, if the electric traction motor does not have sufficient power available to perform an engine start without a significant loss of torque applied to the driveline, then a start motor will be used to start the engine.

[0015] 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.

[0016] Optionally, the control system is further configured to select the starter motor start mode if the one or more operating conditions comprise one or more of: the power output signal indicates that the electric traction motor is outputting power close to its maximum power capability; the power demand signal indicates an increasing power request; the power output signal indicates a reduction in 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 can 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.

[0017] 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 power capability of the electric traction motor to be used to offset the reduction in drive ratio; and output a control signal to the powertrain system to enable the first portion of power capability to be used to offset the reduction in drive ratio. Thus, when the engine is started, a portion of the power capability of the electric traction motor is made available to offset the change in drive ratio, the remaining power capability of the electric traction motor thus defining a maximum power threshold used to determine whether to perform an engine start, a slip start mode or a starter motor start mode.

[0018] Optionally, the one or more operating conditions comprise a current gear selection and a speed of the vehicle. For example, the predicted gear selection can be determined by comparing the current gear selection and the speed of the vehicle with a look-up table stored in a memory of the control system.

[0019] According to a further aspect of the application, there is provided a system comprising a control system as mentioned above and a powertrain system of a vehicle, the powertrain system comprising an engine and an electric traction motor.

[0020] According to a further aspect of the application, there is provided a vehicle comprising a system as mentioned above or a control system as mentioned above.

[0021] According to a further aspect of the application, there is provided a method for controlling engine starting of a hybrid vehicle having a powertrain system comprising an engine and an electric traction motor, the powertrain system being operable to control engine starting using a plurality of engine starting modes. The method comprises receiving a first signal indicative of a requirement for engine starting; and in response to the first signal, analysing operating condition signals indicative of one or more operating conditions of the vehicle, wherein the one or more operating conditions comprise at least a power demand signal indicative of a power request. The method further comprises selecting an engine starting mode from a predetermined prioritised list of the plurality of engine starting modes based on the analysed one or more operating conditions, and outputting a control signal to the powertrain system to control engine starting in accordance with the selected engine starting mode. At least a first of the engine starting 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 starting modes comprises a starter motor mode in which a starter motor is operated to start the engine.

[0022] According to yet a further aspect of the application, there is provided computer readable instructions which, when executed by a computer, are arranged to perform the method as mentioned above.

[0023] Within the scope of the present application, it is expressly intended that each aspect, embodiment, example, and alternative described in the preceding paragraphs, in the claims, and / or in the following description and drawings can be employed independently or in any combination with any of the other aspects, embodiments, examples, and alternatives described therein, particularly in regard to each feature of each aspect, embodiment, example, and alternative. That is, all possible combinations of the various aspects, embodiments, examples, and alternatives described herein are specifically intended to be within the scope of the present application. Applicants reserve the right to change any originally laid-opened claim, or a corresponding claim in any application, including the application as filed, or involving any patent issuing thereon, in accordance with 37 C.F.R. § 1.321 as newly amended. BRIEF DESCRIPTION OF DRAWINGS

[0024] One or more embodiments of the present application will now be described, by way of example only, with reference to the accompanying drawings in which:

[0025] Figure 1 A block diagram illustrating a control system according to an embodiment of the application is shown;

[0026] Figure 2 A powertrain system according to an embodiment of the application is shown;

[0027] Figure 3A A schematic illustration of a vehicle according to an embodiment of the application is shown;

[0028] Figure 3B a rear view of a vehicle according to an embodiment of the application is shown; Figure 3A

[0029] Figure 4 a first flowchart showing operations performed by a control system of Figure 1

[0030] Figure 5 are diagrams that further illustrate embodiments of the application. DETAILED DESCRIPTION

[0031] Referring to Figure 1 , a control system 100 for a vehicle is shown. The control system 100 comprises one or more controllers 110.

[0032] The control system 100 as shown in Figure 1 comprises one controller 110, but it will be appreciated that this is illustrative only. The controller 110 comprises a processing device 120 and a memory device 130. The processing device 120 can be one or more electronic processing devices 120 operable to execute computer-readable instructions. The memory device 130 can be one or more memory devices 130. The memory device 130 is electrically coupled to the processing device 120. The memory device 130 is configured to store instructions, and the processing device 120 is configured to access the memory device 130 and execute the instructions stored on the memory device 130.

[0033] ​​The controller 110 includes an input 140 and an output 150. The input 140 can include an electrical input 140 of the controller 110. The output 150 can include an electrical output 140 of the controller 110. The input 140 is arranged to receive, from one or more sensors, an engine start signal 160 indicative of a need for an engine start. For example, the engine start signal 160 can include one or more of: a power demand signal from a power demand sensor indicative of a power demand (e.g., of a driver), and an electric motor (EM) battery power signal from an EM battery power sensor indicative of a state of charge of an EM battery. The engine start signal 160 is an electrical signal indicative of a need for an engine start, such that both the EM and the engine are operated to deliver torque to the vehicle transmission, as will be further described below. The input 140 is also arranged to receive, from one or more sensors, an operating condition signal 165 indicative of one or more operating conditions of the vehicle. For example, the operating condition signal 165 can include one or more of: a power demand signal from a driver demand sensor indicative of a driver demand, an EM speed signal from an EM speed sensor indicative of an EM speed, a vehicle speed signal from a vehicle speed sensor indicative of a vehicle speed, a gear selection signal from a gear selection sensor indicative of a currently selected gear, an EM power output signal from an EM power output sensor indicative of a power currently output by the EM, and an EM temperature signal from an EM temperature sensor indicative of a temperature of one or more components of the EM. The operating condition signal 165 is an electrical signal indicative of one or more operating conditions of the vehicle. The output 150 is arranged to output a start mode control signal 170 indicative of a start mode selection, the start mode control signal 170 for controlling a mode of the powertrain, in particular a mode in which the engine start is performed. For example, the start mode control signal 170 can control a starter motor to start the engine, or the start mode control signal 170 can control the EM to start the engine according to one or more possible start modes. Optionally, the output 150 is arranged to output a power control signal 172, thereby enabling a powertrain system to make available a portion of a power capability of the electric traction motor to offset a drop in gear ratio.

[0034] Figure 2 An example system 20 for a parallel hybrid electric vehicle (HEV) is shown. The system 20 at least partially defines a powertrain of the HEV. As Figure 1The illustrated system 20 includes a control system 100. The control system 100 can include one or more of a hybrid powertrain control module, an engine control unit, a transmission control unit, a traction battery management system, etc. The system 20 includes an engine 202. The engine 202 can be a combustion engine. The illustrated engine 202 is an internal combustion engine. The illustrated engine 202 includes four combustion chambers, although a different number of combustion chambers can be provided in other examples.

[0035] The engine 202 is operatively coupled to the control system 100 to enable the control system 100 to control the output torque of the engine 202. The output torque of the engine 202 can be controlled in accordance with the type of engine 202 by controlling one or more of the following: air-fuel ratio, ignition timing, lift valve lift, lift valve timing, throttle valve opening position, fuel pressure, turbocharger boost pressure, etc.

[0036] The system 20 also includes 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 can 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 can 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: boost the output torque of the engine 202; disable (shut down) the engine 202 when stopped or coasting; enable (start) the engine 202 and regenerative braking in a regenerative mode. In a hybrid electric vehicle mode, both the engine 202 and the electric traction motor 216 can be operable to simultaneously supply positive torque to boost the output torque. The electric traction motor 216 can be capable of pure electric drive.

[0037] The system 20 includes a vehicle driveline 204 for receiving output torque from the engine 202 and / or from the electric traction motor 216. The vehicle driveline 204 can include an automatic vehicle transmission or a semi-automatic vehicle transmission, or a manual vehicle transmission.

[0038] 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 in the form of a dog clutch in the illustrated example, although other types of clutches can be provided in other examples. Figure 2The second clutch 218 is shown 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 can be integrated with the electric traction motor 216 and / or with the transmission 204. In the latter example, the second clutch can be a core clutch used for shifting. The function of the second clutch can be provided by a single clutch as shown, or by multiple clutches each configured to connect the electric traction motor 216 to the transmission 204, thereby fulfilling the function of the second clutch. For example, the second clutch can include a clutch 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 additional clutches 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 that extends from an output of the electric traction motor 216 to the second clutch 218, then to the transmission 204, then to the axle / differential 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 that 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 axle / differential 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 capable of providing torque to the 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 broken, the torque path 220 between the engine 202 and the first set of vehicle wheels (RL, RR) is also broken. In the event of vehicle overrun and / or friction braking, torque can flow from the first set of vehicle wheels (RL, RR) to the electric traction motor 216, and optionally to the engine 202. Torque flowing toward the first set of vehicle wheels (RL, RR) is positive torque, and torque flowing from the first set of vehicle wheels (RL, RR) is negative torque. The first set of vehicle wheels (RL, RR) shown includes rear wheels. Thus, the system 20 shown is configured for rear-wheel drive. In another example, the first set of vehicle wheels can be front wheels (FL, FR). The front wheels (FL, FR) shown are a pair of vehicle wheels, however, a different number of vehicle wheels can be provided in other examples.

[0039] The system 20 can include a differential 217 for receiving output torque from the transmission 204, i.e., from the gear train. The differential can be integrated into the vehicle driveline 204 as a transaxle, or can be provided separately.

[0040] The illustrated system 20 includes one electric traction motor 216. In other embodiments, the system 20 can have more than one electric traction motor. The system (20) can also include a starter motor 219 that is mechanically connected or connectable to the engine 202. For example, the starter motor 219 can be a belt integrated starter generator (BiSG) or pinion starter motor. In the illustration, the starter motor 219 is located at the accessory drive end of the engine 202 opposite the vehicle drive end of the engine 202.

[0041] The control system 100 can be configured to disconnect the torque path between the engine 202 and the first set of vehicle wheels (RL, RR) in electric vehicle mode, e.g., to reduce parasitic pumping energy losses or to operate in electric vehicle mode. For example, the first clutch 212 can be open.

[0042] In some embodiments, the vehicle includes another 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) can also include a second electric traction motor (not shown) or a second internal combustion engine (not shown), either of which can provide positive torque alone or in combination with the electric traction motor 216 and / or the engine 202.

[0043] To store electrical power for the electric traction motor 216, the system 20 includes a traction battery 200. The traction battery 200 provides a nominal voltage required by power consumers such as the electric traction motor.

[0044] The traction battery 200 can be a high voltage (HV) battery. A high voltage traction battery provides a nominal voltage of hundreds of volts, as opposed to a traction battery for a light HEV that provides a nominal voltage of tens of volts. The traction battery 200 can have a voltage and capacity to support pure electric driving for a sustained distance. The traction battery 200 can have a capacity of thousands of watt-hours to maximize range. The capacity can be tens of watt-hours, or hundreds of watt-hours.

[0045] Although the traction battery 200 is shown as one entity, the functionality of the traction battery 200 can be implemented using multiple small traction batteries in different locations on the vehicle.

[0046] The system 20 can include one or more inverters 214. One inverter 214 is shown for the electric traction motor 216. In other examples, two or more inverters can be provided.

[0047] From the above it can be understood that the vehicle can be powered by a combination of sources.

[0048] Figures 3A-3B A vehicle 300 according to an embodiment of the application is shown. The vehicle 300 comprises a control system 100 as shown. Figure 1 The controller 110 is shown as being mounted within the vehicle 300 and 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 A rear view of the vehicle 300 is shown. Figure 3A

[0049] Figure 4 A method 400 according to an embodiment of the application is shown. The method 400 is a method of controlling a hybrid powertrain system 20 of a vehicle 300 (e.g. the vehicle 300 shown in Figure 3A and Figure 3B to perform engine starting. The hybrid powertrain system 20 is operable to perform engine starting using a plurality of engine starting modes, the hybrid powertrain system 20 comprising an engine 202 (an internal combustion engine which can be powered by, for example, petrol, diesel, hydrogen, e-fuel or any suitable combustible fuel) and an electric traction motor 216. The method 400 can be performed by a control system 100 as shown. In particular, the memory 130 can comprise computer readable instructions which, when executed by the processor 120, perform the method 400 according to an embodiment of the application. Figure 1

[0050] ​​When the vehicle 300 is operating such that only the electric traction motor 216 is supplying output torque to the transmission 204, it can sometimes be 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 can be required for a variety of reasons, including but not limited to: an increase in driver demand requiring a torque output that exceeds the power capability of the electric traction motor 216, or the traction battery 200 has a low charge. Other reasons for performing an engine start can also include powertrain system issues (e.g. related to the functionality of the traction battery 200 or electric traction motor 216) or a selection of gear mode requiring use of the engine 202. The hybrid powertrain system 20 is operable to start the engine 202 using a plurality of different engine start modes, and the suitability of each engine start mode will depend on the operating conditions of the vehicle at the time the engine start is required. Therefore, the engine start mode should be selected that will preserve the performance of the electric traction motor 216 and ensure that there is no significant or noticeable loss of torque applied to the transmission 204 when the engine 202 is started. The method 400 determines, based on one or more operating conditions, which of the possible engine start modes should be selected to preserve performance, and therefore provide a smooth driving experience.

[0051] For example, the plurality of engine start modes can include a comfort slip start mode, a responsive slip start mode and a launch motor start mode.

[0052] The 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, whilst the second clutch 218 between the electric traction motor and the transmission 204 of the vehicle is also partially engaged. The first and second clutches are only fully engaged when the engine speed and the electric traction motor speed are matched. This mode allows the vehicle to be smoothly switched from using only the electric traction motor to using the engine 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 run the engine before the switch. By having the second clutch slip (i.e. partially engaged), vibrations or torque spikes that can occur due to the torque transfer are dampened, thus providing a smoother driver experience.

[0053] The responsive slip start mode occurs when the first clutch between the electric traction motor and the engine is partially engaged to start the engine and once the engine speed matches the electric traction motor speed, the second clutch between the electric traction motor and the transmission is always fully engaged. This differs from the comfortable slip start mode described above in that the second clutch does not slip (i.e. the second clutch remains fully engaged). This mode can be used, for example, when the driver demand is high, i.e. a rapid acceleration is desired. This mode provides a faster vehicle response, but can mean that the ride is less smooth. In the comfortable slip start mode, the vibrations can be less noticeable as the slip clutch connecting the EM to the gearbox / wheels dampens the vibrations. This means that the driver does not feel as much vibration. It can be important to have a fast controller in the slip start mode as engine / EM speed overshoots can have negative consequences on the NVH characteristics of the vehicle. A fast controller has less overshoot than a slow controller.

[0054] The starter motor start mode occurs when the starter motor 219 is operated to start the engine 202. The starter motor 219 can be a belt integrated starter generator (BiSG) or a pinion starter motor. This differs from the comfortable slip start and responsive 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 the driver demand is high (i.e. a 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 also mean that the ride is less smooth.

[0055] Of course, it will be appreciated that the hybrid powertrain system can be configured to perform other start modes, for example an emergency start mode. For example, in the event that the electric traction motor 216 or the starter motor 219 is not available to start the engine 202, an “inertia” start mode can 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 results in a noticeable deceleration as the power required to start the engine 202 is taken from the kinetic energy of the vehicle 300.

[0056] At step 410, the control system 100 is configured to receive an engine start signal 160 indicating that an engine start is required. Optionally, the engine start signal 160 is generated by the controller based on receiving data related to a power demand signal indicating a power demand or an EM battery charge signal indicating a battery charge state of the traction battery 200 for the electric traction motor 216, or some other data indicating that an engine start is required (e.g., a system problem). For example, if the power demand signal indicates that the driver is requesting acceleration such that the required torque output exceeds the capability 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.

[0057] At step 420, the control system 100 is configured to analyze one or more operating conditions of the vehicle 300. The control system analyzes one or more operating conditions of the vehicle 300 based on the received operating condition signal 165. As discussed above, the one or more operating conditions can include one or more of the following: a power demand, an EM speed, a gear selection, a power output of the EM, and a temperature of one or more components of the EM.

[0058] At step 430, the control system 100 is configured to select an engine start mode from a predetermined prioritized list of engine start modes based on the analysis of the one or more operating conditions. In this regard, the control system 100 will consider the list of engine start modes in order of priority and determine which engine start mode should be selected based on the one or more operating conditions. For example, the control system 100 can consider the engine start modes in the order of comfort glide start, responsive glide start, and start motor start. The control system 100 will consider each engine start mode in turn and then select the first engine start mode for which the one or more operating conditions satisfy a set of criteria defined for the respective engine start mode.

[0059] First, the control system 100 is configured to determine whether a glide start can be selected based on, for example, the power required by the driver. For example, if the required power does not exceed a maximum power threshold, it is determined that some type of glide start will be possible. In this regard, the maximum power threshold corresponds to an upper limit on the amount of power that can be used by the electric traction motor 216 to transfer torque to the transmission 204. Optionally, the upper limit on the power from the traction battery 200 that can be used by the electric traction device 216 to transfer torque to the transmission 204 can correspond to the maximum power capability of the electric traction motor 216. Optionally, as discussed above, the control system 100 can be configured to determine whether a glide start is possible based on the temperature of one or more components of the electric traction motor 216. Figure 5As shown in the graph 500, the upper limit of power that can be used by the electric traction device 216 to transmit torque to the transmission 204 (as represented by line "A") can correspond to a first portion of the maximum power capability of the electric traction motor 216 (as represented by line "B"), where one or more additional portions of the power capability can be reserved or used for other operational purposes. For example, a second portion of the maximum power capability B can be reserved for performing a slip start (i.e., the region between the maximum power threshold A and the maximum power capability B), while a first portion of the maximum power capability B (i.e., the region below the maximum power threshold A) is available to the electric traction motor 216 for transmitting torque to the transmission 204. In this case, the maximum power threshold A is the limit of the first portion of the maximum power capability B.

[0060] Optionally, a third portion of the maximum power capability (i.e., the area between the maximum power threshold A and the line“C”) can be made available to the electric traction motor 216 to offset the torque increase needed to compensate for a gear ratio drop that can occur when the engine 202 is first turned on, thereby maintaining the expected vehicle acceleration. The gear ratio drop can be requested due to the difference in operating efficiency of the electric traction motor 216 and the engine 202 at different speeds. While dependent on the vehicle speed, the most efficient operating speed of the electric traction motor 216 by itself is typically higher than the most efficient operating speed of the combination of the engine 202 and the electric traction motor 216. Thus, before the engine 202 is started, the electric traction motor 216 can be operating at a higher speed than if the engine 202 were connected via the first clutch 212, and thus when the engine 202 is started, a gear up can be needed to reduce the speed of the electric traction motor 216 to synchronize with the lower desired speed of the engine 202. Whether a gear up (i.e., a gear ratio drop) is desired will depend on the vehicle speed, with a gear up being more advantageous at some vehicle speeds than at other vehicle speeds. Thus, after receiving the engine start signal 160, the control system 100 can optionally be configured to calculate or otherwise determine the portion of the power capability needed to offset the gear ratio drop, i.e., the third portion. In response to the engine start signal 160, the control system 100 can be configured to determine a predicted gear selection associated with the engine start as a function of one or more of the operating conditions of the vehicle. For example, based on the current gear selection of the vehicle and the speed of the vehicle, the control system 100 can be configured to determine the predicted gear selection that will be needed when the engine 202 is started (i.e., whether there is a gear up). The control system 100 can then be configured to determine the portion of the power capability of the electric traction motor 216 needed to offset the expected drop in the gear ratio as a function of the predicted gear selection and one or more of the current gear selection and the vehicle speed. Optionally, the predicted gear selection can be determined by comparing the current gear selection and the vehicle speed to a lookup table stored in the memory 130. The control system 100 can then be configured to output a control signal to the powertrain system 20 to make that portion of the power capability available to offset the expected drop in the gear ratio. Optionally, the portion of the power capability of the electric traction motor 216 needed to offset the expected drop in the gear ratio corresponds to the amount of torque needed to generate the wheel torque at the current vehicle speed with a different gear ratio. The remaining portion of the maximum power capability B can be used to transfer torque to the transmission 204 and optionally to perform a slip start. The third portion of the maximum power capability B that can be considered an“additional torque offset” is preferably taken from the first portion of the maximum power capability (i.e., the area below the line denoted as“A”) so that the second portion of the maximum power capability B that is reserved for performing a slip start is maintained.In such an embodiment, the first portion of the power capability, i.e. the upper limit of the power that can be used by the electric traction device 216 for transmitting torque to the transmission 204, can correspond to the maximum power capability B of the electric traction motor 216 minus the second and third portions, which are reserved for performing the slip start operation and for compensating for the drop in transmission ratio, respectively. It will also be appreciated that one or more portions of the power capability of the traction battery 200 can be reserved for other operational purposes, such as operating the air conditioning, screen heater and other power consuming devices of the vehicle 300.

[0061] 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 demand is equal to or exceeds the maximum power threshold A, then neither a comfort slip start nor a responsive slip start will be possible, and so the starter motor engine start will be selected.

[0062] If it is determined that a slip start of some kind is possible, the control system 100 will determine whether a comfort slip start is possible. In order to determine whether a comfort slip start should be selected, the control system 100 is configured to analyse one or more of the following: the speed of the electric traction motor 216, the gear selection and the rate of change of the power demand (i.e. the speed at which 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 determine whether a fine shift (i.e. a comfort slip start) or a fast engine start (i.e. a responsive slip start or a starter motor start) should be prioritised. If the rate of change of the power demand is below the threshold level, then a comfort slip start is selected. If the rate of change of the power demand is above the threshold level, then the comfort slip start is excluded and will not be selected. In this regard, the threshold level is a dynamic 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 a low gear (e.g. first gear), then the threshold level for the rate of change of the power demand will be relatively high, as a fast engine start (i.e. a responsive slip start) is more likely to produce noticeable vibrations, and so 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), then the threshold level for the rate of change of the power demand will be relatively low, as a fast engine start (i.e. a responsive slip start) will start the engine 202 more quickly, and the driver is less likely to feel any resulting vibrations, in which case a comfort slip start will not be selected.

[0063] The control system 100 will also determine whether a slip start (comfort or response) can be selected based on an analysis of one or more operating conditions, and if not, will determine that a start motor start should be selected. To determine whether a slip start (comfort or response) or a start motor start should be selected, the control system 100 is configured to analyze one or more of the following: the power demand required by the driver, the power output by the electric traction motor 216, and the temperature of components (the temperature of one or more components of the electric traction motor 216). Of course, it should be understood that there can be other operating conditions that can be used to determine whether a slip start is possible. As noted above, if the power required by the driver is equal to or greater than the maximum power threshold (i.e., the power that the electric traction motor 216 can use to provide torque to the transmission), then any type of slip start will be excluded and the start motor start mode will be selected. However, if the power required is below the maximum power threshold A, then one or more additional operating conditions will be analyzed to determine whether a slip start can be selected. For example, if the power output by the electric traction motor 216 is approaching the maximum power capability of the electric traction motor 216 (e.g., above the maximum threshold A), or if the power output is decreasing but the power required is still increasing (i.e., indicating that the power capability of the electric traction motor 216 is decreasing), then any type of slip start will be excluded and the start motor start will be selected. However, if there is no indication that the power output is not approaching the maximum power capability or is decreasing, then a slip start will not be excluded. As another example, if the power required is increasing rapidly (i.e., the driver is accelerating at a rate such that the power required is rapidly approaching the maximum power capability of the electric traction motor 216), then any type of slip start will be excluded and the start motor start will be selected. However, if the power required is not increasing rapidly and is not rapidly approaching the maximum power capability of the electric traction motor 216, then a slip start will not be excluded. Similarly, if the temperature of at least one component of the 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 overcool and cannot perform an engine start), then a slip start will be excluded and the start motor start mode will be selected. For example, if the transmission oil of the electric traction motor 216 is below -10°C, then a slip start can not be possible because the viscosity of the oil can be too high to provide precise control over the clutch. Similarly, if a component of the electric traction motor 216 is above 50°C, then it can not be possible to perform a slip start at that temperature and, therefore, the start motor start mode will be selected. However, if the temperature of a component of the electric traction motor 216 is within a temperature range, then a slip start will not be excluded. Thus, if a slip start is not excluded based on any of the analyzed operating conditions, then 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 any type of slip start is excluded based on any of the analyzed operating conditions, the control system 100 will determine that a motor start should be selected.

[0064] In summary, if the required power does not exceed the maximum power threshold of the electric traction motor 216, the rate of change of the required power is below the threshold level defined by the speed of the electric traction motor 216 and the gear selection, and one or more of one or more additional operating conditions including the power demand required by the driver, the power output by the electric traction motor 216, and the temperature of components (the temperature of one or more components of the electric traction motor 216) meet a predefined set of criteria, a comfort slip start will be selected. If the required power does not exceed the maximum power threshold of the electric traction motor 216, the rate of change of the required power is below the threshold level defined by the speed of the electric traction motor 216 and the gear selection, and one or more of one or more additional operating conditions including the power demand required by the driver, the power output by the electric traction motor 216, and the temperature of components (the temperature of one or more components of the electric traction motor 216) meet a predefined set of criteria, a responsive slip start will be selected. If the required power is equal to or above the maximum power threshold of the electric traction motor 216, or one or more additional operating conditions do not meet the predefined criteria required for a slip start, a motor start will be selected. By applying this set of rules for selecting a start mode based on the operating conditions of the vehicle, an engine start mode is selected that will preserve the performance of the electric traction motor 216 and ensure that there is no significant or noticeable loss of torque applied to the transmission 204 when the engine 202 is started.

[0065] Once the control system 100 has selected an engine start mode from the prioritized list of start modes, the control system 100 is configured to output a control signal 170 at step 440 to cause the powertrain system 20 to start the engine in accordance with the selected engine start mode. Optionally, if the Comfort Glide 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, thereby transferring torque from the electric traction motor 216 to the engine 202, the first clutch 212 and the second clutch 218 fully engaging once the speed of the engine 202 matches the speed of the electric traction motor 216. Optionally, if the Responsive Glide 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, while maintaining the second clutch 218 between the electric traction motor 216 and the transmission 204 fully engaged, thereby transferring torque from the electric traction motor 216 to the engine 202, the first clutch 212 fully engaging once the speed of the engine 202 matches the speed of the electric traction motor 216. Optionally, if the 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 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.

[0066] It will be understood that various changes and modifications can be made to the application without departing from the scope thereof.

Claims

1. A control system for controlling engine starting of a hybrid vehicle having a powertrain system including an engine and an electric traction motor, the powertrain system operable to control engine starting using a plurality of engine starting modes, the control system comprising one or more processors collectively configured to: receive a first signal indicative of a need for engine starting; in response to the first signal, analyzing an operating condition signal indicative of one or more operating conditions of the vehicle, wherein the one or more operating conditions including a power demand signal indicative of a power request; select an engine starting mode from a predetermined prioritized list of a plurality of engine starting modes based on the analyzed one or more operating conditions; and output a control signal to the powertrain system to control the engine starting in accordance with the selected engine starting mode, wherein at least a first of the engine starting modes includes a slip start mode in which the electric traction motor is operated to start the engine, and at least a second of the engine starting modes includes 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 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 including 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 configured to select a first slip start mode or a second slip start mode in dependence on a rate of change of the power demand signal, the speed of the electric traction motor and the gear selection.

5. The control system of claim 4, wherein, the control system 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 the gear selection.

6. The control system of claim 5, wherein, the control system 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 the gear selection.

7. The control system of any one of claims 2 to 6, wherein, the control system 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 including 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 further configured to select the starter motor start mode if the one or more operating conditions include one or more of: the power output signal indicates that the electric traction motor is outputting power close to its maximum power capability; the power demand signal indicates an increasing power request; the power output signal indicates a reduction in power capability of the electric traction motor; and the 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 configured to: determining, in dependence on one or more operating conditions of the vehicle, a predicted gear selection associated with engine start; determining, in dependence on the predicted gear selection and the one or more operating conditions, a first portion of power capability of the electric traction motor to be used to offset a reduction in drive ratio; and outputting a control signal to the powertrain system to enable the first portion of power capability to be used to offset the reduction in drive ratio.

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 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 engine start using a plurality of engine start modes, the method comprising: receiving a first signal indicative of a need for engine start; in response to the first signal, analysing operating condition signals indicative of one or more operating conditions of the vehicle, wherein the one or more operating conditions comprise at least 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 the method of claim 14.

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