Controlling the temperature of an electric drive system of a vehicle

Abstract

Detailed are a control system (400, fig. 4), a system 300, a vehicle (1, fig. 1), a method (figures 6A-8B), and computer readable instructions (408) for controlling the thermal exchange between an ele

Description

TECHNICAL FIELD The present disclosure relates to controlling the temperature of an electric drive system of a vehicle. Aspects of the invention relate to a control system, to a system, to a vehicle, to a method, and to computer readable instructions. BACKGROUND It is known to provide a means for inhibiting heat exchange between an electric drive system (e.g„ electric drive unit) and a thermal management system (e.g., coolant system) of an electric vehicle, in dependence on the absolute temperature of the electric drive system. This allows rapid warmup of the electric drive system during a cold start scenario. It is an aim of the present invention to address one or more disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a control system, a system, a vehicle, a method, and computer readable instructions as claimed in the appended claims. According to an aspect of the present invention, there is provided a control system for controlling thermal energy exchange between an electric drive system of a vehicle and a thermal management system of the vehicle, the control system comprising one or more processors collectively configured to: receive signals from a plurality of sources; determine whether reactive thermal protection of the electric drive system is required, in dependence on the signal from a first source of the plurality of sources; output a first control signal to control thermal energy exchange between the electric drive system and the thermal management system, in dependence on the determination that reactive thermal protection is required, to cause thermal protection of the electric drive system; determine whether predictive thermal protection of the electric drive system is required, in dependence on the signal from a second source of the plurality of sources; and output a second control signal to control thermal energy exchange between the electric drive system and the thermal management system, in dependence on the determination that predictive thermal protection is required, to cause thermal protection of the electric drive system. An advantage is improved thermal control of the electric drive system. The electric drive system temperature can be reactively managed as sensed temperature rises, or as the temperature falls in the case of freezing conditions. The temperature can also be predictively managed to prolong the period for which the electric drive system can be run at a high operating point (speed, load) without being thermally de-rated. 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 cause: the receiving of the signals; the determinations; the outputting of the control signals; and any one or more of the other optional controller functions or method steps described herein. Optionally, the thermal management system may comprise a vehicle-level coolant system for supplying coolant to several modules including a module for the electric drive system. Optionally, the first and second control signals may each comprise a valve control signal and / or a pump control signal to control fluid flowthrough a heat exchanger for exchanging thermal energy between the electric drive system and the thermal management system. Optionally, the first and second control signals may each be configured to selectively direct (start or substantially increase) or inhibit (stop or substantially decrease) fluid flow through the heat exchanger. An advantage is that fluid flow through the heat exchanger can be stopped and started, or increased and decreased. Optionally, causing thermal protection of the electric drive system may comprise connecting or bypassing the heat exchanger. Additionally, or alternatively, the thermal protection may comprise controlling the operating point of a lubricant pump for pumping lubricant through the electric drive system, and / or a coolant pump for circulating coolant through the heat exchanger. Additionally, or alternatively, the thermal protection may comprise activating a temperature control means of the thermal management system (e.g., coolant system) such as activating an electric heater or refrigeration system or coolant radiator branch to increase or decrease the temperature of the coolant passing through a heat exchanger with the electric drive system. Optionally, the first and second control signals may each comprise a valve control signal. Optionally, the valve control signal may be configured to control a bypass valve. The bypass valve may be an active bypass valve. Optionally, the valve control signal may be configured to cause the bypass valve to control a fluid flow rate through the heat exchanger relative to a fluid flow rate through a bypass passage bypassing the heat exchanger. An advantage of controlling how much fluid flow bypasses the heat exchanger, rather than controlling the lubricant pump, is that the pump can continue operating to circulate lubricant within the electric drive system. Optionally, the valve control signal may be configurable to direct fluid flow through the heat exchanger by controlling a state of the bypass valve to select a fluid passage comprising the heat exchanger. Optionally, the valve control signal may be configurable to inhibit fluid flow through the heat exchanger by controlling the state of the bypass valve to select the bypass fluid passage to bypass the heat exchanger. If a pump is controlled, the pump control signal may optionally be configurable to direct fluid flow through the heat exchanger by controlling the pump to generate fluid flowthrough a fluid circuit comprising the heat exchanger. The pump control signal may optionally be configurable to inhibit fluid flow through the heat exchanger by controlling the pump to inhibit fluid flow in the fluid circuit comprising the heat exchanger. Optionally, the signal from the first source may be indicative of a detected temperature of the electric drive system. Optionally, the signal indicative of a detected temperature of the electric drive system may be indicative of a lubricant temperature of the electric drive system. Optionally, the lubricant temperature may be an oil temperature. Optionally, the electric drive system is fully- or substantially-oil cooled. Optionally, the signal from the first source may be dependent on a temperature measurement by a lubricant temperature sensor of the electric drive system. Optionally, the lubricant temperature sensor may be configured to measure a temperature in a lubricant circuit of the electric drive system. Optionally, determining whether the reactive thermal protection is required may comprise determining whether reactive overheating protection of the electric drive system is required, and may further comprise determining whether reactive cold protection of the electric drive system is required An advantage is the signal from the first source also indicates whether the electric drive system is too hot, affecting efficiency and the durability of components such as windings, bearings, insulation, wiring, and seals. Advantageously, the signal from the first source also indicates whether the electric drive system is cold, affecting efficiency due to factors such as lubricant viscosity and winding temperatures. Optionally, when the reactive overheating protection is required, the first control signal may be configured to cause thermal protection of the electric drive system by causing transfer of heat from the electric drive system to the thermal management system or by inhibiting transfer of heat from the thermal management system to the electric drive system, and whether the first control signal causes or inhibits transfer of heat may optionally be based on comparison of temperatures of the electric drive system and the thermal management system. Optionally, when the reactive cold protection is required, the first control signal may be configured to cause thermal protection of the electric drive system by causing transfer of heat from the thermal management system to the electric drive system or by inhibiting transfer of heat from the electric drive system to the thermal management system, and whether the first control signal causes or inhibits transfer of heat may optionally be based on comparison of temperatures of the electric drive system and the thermal management system. Optionally, when the predictive thermal protection is required, the second control signal may be configured to cause thermal protection of the electric drive system by causing transfer of heat from the electric drive system to the thermal management system or by inhibiting transfer of heat from the thermal management system to the electric drive system, and whether the second control signal causes or inhibits transfer of heat may optionally be based on comparison of temperatures of the electric drive system and the thermal management system. For example, the control system may optionally be configured to: receive a first signal indicative of a temperature of the electric drive system of the vehicle; receive a second signal indicative of a temperature of a thermal management system of the vehicle; compare the first and second signals; and configure the first / second control signal in dependence on the comparison. An advantage of the comparison is improved thermal management. A wide variety of thermal management scenarios can be accounted for during a drive cycle (journey) because the temperatures will diverge from each other. For example, the control system can determine whether to direct (start or substantially increase) or inhibit (stop or substantially decrease) fluid flowthrough a heat exchanger between the electric drive system and the thermal management system). If one of the systems requires additional thermal energy, and the other system is hotter, then flow can be directed through the heat exchanger to operate the hotter system as a heat source. However, if the other system is colder, then flowthrough the heat exchanger can be inhibited. Likewise, if one of the systems requires the removal of thermal energy, and the other system is colder, then flow can be directed through the heat exchanger to use the colder system as a heat sink. However, if the other system is hotter, then flow through the heat exchanger can be inhibited. Optionally, the first signal may be from the first source, e.g., the detected temperature of the electric drive system, such as the oil temperature. Optionally, the second signal may be indicative of a coolant temperature of the thermal management system. Optionally, the second signal may be dependent on a temperature measurement of a coolant temperature sensor of the thermal management system. Optionally, the coolant temperature sensor may be configured to measure a temperature in a coolant circuit of the thermal management system. Optionally, the comparison may comprise a reactive comparison based on the first and second signals. The temperatures may be real-time temperatures. In dependence on the reactive overheating protection being required, and the comparison indicating that the temperature of the electric drive system is hotter than the temperature of the thermal management system, the first control signal may optionally be configured to direct fluid flow through the heat exchanger. In dependence on the reactive overheating protection being required, and the comparison indicating that that the temperature of the thermal management system is hotter than the temperature of the electric drive system, the first control signal may optionally be configured to inhibit fluid flow through the heat exchanger. An advantage is that the heat exchanger will only be used if it is capable of cooling down the electric drive unit. In dependence on the reactive cold protection condition being required, and the comparison indicating that that the temperature of the thermal management system is hotter than the temperature of the electric drive system, the first control signal may optionally be configured to direct fluid flow through the heat exchanger. In dependence on the reactive cold protection condition being required, and the comparison indicating that that the temperature of the thermal management system is colder than the temperature of the electric drive system, the first control signal may optionally be configured to inhibit fluid flowthrough the heat exchanger. An advantage is that the heat exchanger will only be used if it is capable of warming up the electric drive unit. Optionally, determining that the reactive overheating protection is required may be based on an absolute temperature of the electric drive system. The signal from the first source may be indicative of an absolute detected temperature of the electric drive system. Optionally, determining that the reactive overheating protection is required may comprise determining that the signal from the first source is greater than an overheat temperature threshold. Optionally, the threshold may be an absolute temperature threshold based on said absolute temperature. Optionally, determining that the reactive cold protection is required may be based on an absolute temperature of the electric drive system. The signal from the first source may be indicative of an absolute detected temperature of the electric drive system. Optionally, determining that the reactive cold protection is required may comprise determining that the signal from the first source falling below a cold temperature threshold. The cold temperature threshold may optionally be an absolute temperature threshold based on said absolute temperature. The cold temperature threshold may optionally be a value lower than zero Celsius. Optionally, determining that predictive overheating protection is required may be dependent on a signal indicative of an operating point of the electric drive system. The signal from the second source may be indicative of the operating point of the electric drive system. The operating point may optionally be indicative of a requested load, e.g., power request, of the electric drive system. Optionally, determining that predictive overheating protection is required may comprise determining that the signal from the second source is greater than an operating point threshold. An advantage is that the current / requested operating point of the electric drive system is a predictor of the future temperature of the electric drive system. Therefore, by initiating the thermal protection based on the operating point before the overheat temperature threshold is exceeded, the electric drive system can be run for prolonged periods at a high operating point without reaching the overheat temperature threshold or a higher derate threshold. Optionally, determining whether reactive thermal protection of the electric drive system is required may be based on thresholds arranged to define a hysteresis control strategy. Optionally, determining whether predictive thermal protection of the electric drive system is required may be based on thresholds arranged to define a hysteresis control strategy. For example, one or more of the earlier-described thresholds may optionally depend on whether fluid flow is currently being directed through the heat exchanger or inhibited through the heat exchanger. For example, one or more of the earlier-described thresholds may optionally depend on the state of the bypass valve. An advantage is that the hysteresis control strategy prevents excessive valve switching, also referred to as chattering. Optionally, the control system may be configured to: determine whether thermal conditioning has been requested, in dependence on the signal from a third source of the plurality of sources; and output a third control signal to control thermal energy exchange between the electric drive system and the thermal management system, in dependence on the determination that thermal conditioning has been requested, to cause the thermal conditioning, wherein the control system is configured to allow a lower priority to causing the thermal conditioning than to causing the thermal protection of the electric drive system. An advantage is that the control system is able to accept lower-priority thermal conditioning requests, provided that no thermal protection is required. Thermal conditioning refers to heating or cooling the thermal management system, or a module thermally coupled to the thermal management system such as the electric drive system, a traction battery cooler, and / or a climate control module, for a thermal conditioning purpose. A thermal conditioning purpose can be energy optimisation or comfort, and is unrelated to thermal protection. Optionally, allowing a lower priority may comprise determining whether thermal conditioning has been requested in dependence on the determinations of whether reactive and predictive thermal protection of the electric drive system is required being negative. Optionally, allowing a lower priority may comprise determining whether thermal conditioning has been requested in dependence on the signal from the first source being less than the overheat temperature threshold and / or greater than the cold temperature threshold, and further in dependence on the signal from the second source being less than the operating point threshold. Therefore, advantageously, thermal conditioning actions are limited to situations when temperatures and requested power levels are normal. Optionally, the signal from the third source may be dependent on a request for heating or cooling a module of the vehicle which is thermally coupled to the thermal management system. Optionally, the signal from the third source may be dependent on a sensed temperature and / or a setpoint temperature of the module. Optionally, the thermal conditioning request may be based on an energy-efficiency algorithm, optionally a vehicle-level energy-efficiency algorithm. Optionally, the signal from the third source may be a request from a vehicle systems controller, the vehicle systems controller being the third source. Optionally, when the request is for heating and the module is a climate control module, the third control signal maybe configured to cause the thermal conditioning by causing transfer of heat from the electric drive system to the thermal management system or by inhibiting transfer of heat from the thermal management system to the electric drive system, and whether the third control signal causes or inhibits transfer of heat may optionally be based on comparison of temperatures of the electric drive system and the thermal management system. Optionally, when the request is for cooling and the module is the climate control module, the third control signal may be configured to cause the thermal conditioning by causing transfer of heat from the thermal management system to the electric drive system or by inhibiting transfer of heat from the electric drive system to the thermal management system, and whether the third control signal causes or inhibits transfer of heat may optionally be based on comparison of temperatures of the electric drive system and the thermal management system. Optionally, when the request is for heating and the module is the electric drive unit, the third control signal may be configured to cause the thermal conditioning by causing transfer of heat from the thermal management system to the electric drive system or by inhibiting transfer of heat from the electric drive system to the thermal management system, and whether the third control signal causes or inhibits transfer of heat may optionally be based on comparison of temperatures of the electric drive system and the thermal management system. According to another aspect of the invention, there is provided a system comprising the control system and the electric drive system, wherein the electric drive system comprises a lubricant circuit, a coolant-to-lubricant heat exchanger thermally coupling a coolant circuit to the lubricant circuit, a bypass passage bypassing the coolant-to-lubricant heat exchanger, and an active bypass valve controllable by the first and second control signals to control a fluid flow rate through the coolant-to-lubricant heat exchanger relative to a fluid flow rate through the bypass passage. Optionally, the system may further comprise the lubricant temperature sensor. The advantages are as described above. According to a further aspect of the invention, there is provided a vehicle comprising the control system or the system. According to a further aspect of the invention there is provided a method of controlling the temperature of an electric drive system of a vehicle, the method comprising: receiving signals from a plurality of sources; determining whether reactive thermal protection of the electric drive system is required, in dependence on the signal from a first source of the plurality of sources; outputting a first control signal to control thermal energy exchange between the electric drive system and the thermal management system, in dependence on the determination that reactive thermal protection is required, to cause thermal protection of the electric drive system; determining whether predictive thermal protection of the electric drive system is required, in dependence on the signal from a second source of the plurality of sources; and outputting a second control signal to control thermal energy exchange between the electric drive system and the thermal management system, in dependence on the determination that predictive thermal protection is required, to cause thermal protection of the electric drive system. According to a further aspect of the invention there is provided computer readable instructions which, when executed by a computer, are arranged to perform any one or more of the methods described herein. According to a further aspect of the invention there is provided a non-transitory computer readable medium comprising computer readable instructions that, when executed by one or more electronic processors, causes the one or more electronic processors to carry out any one or more of the methods described herein. According to a further aspect of the present invention, there is provided a control system for controlling thermal energy exchange between an electric drive system of a vehicle and a thermal management system of the vehicle, the control system comprising one or more processors collectively configured to: output a first control signal to control thermal energy exchange between the electric drive system and the thermal management system based on reactive temperature measurement; and output a second control signal to control thermal energy exchange between the electric drive system and the thermal management system based on temperature prediction. According to a further aspect of the present invention, there is provided a control system for controlling thermal energy exchange between an electric drive system of a vehicle and a thermal management system of the vehicle, the control system comprising one or more processors collectively configured to: receive signals from a plurality of sources; determine whether thermal protection of the electric drive system is required, in dependence on the signal from a source ofthe plurality of sources; output a control signal to control thermal energy exchange between the electric drive system and the thermal management system, in dependence on the determination that thermal protection is required, to cause thermal protection ofthe electric drive system; determine whether thermal conditioning has been requested, in dependence on the signal from a further source ofthe plurality of sources; and output a further control signal to control thermal energy exchange between the electric drive system and the thermal management system, in dependence on the determination that thermal conditioning has been requested, to cause the thermal conditioning, wherein the control system is configured to allow a lower priority to causing the thermal conditioning than to causing the thermal protection ofthe electric drive system. 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 falls within the scope of the appended claims. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination that falls within the scope of the appended claims, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 illustrates a perspective view illustrating an example of a vehicle; FIG. 2 is a schematic view illustrating an example of an electric vehicle; FIG. 3 is a schematic view illustrating an example of a system; FIG. 4 is a schematic view illustrating an example of a control system; FIG. 5 is a schematic view illustrating an example of a non-transitory computer-readable storage medium; FIG. 6A is a flowchart illustrating an example of a reactive overheating protection method; FIG. 6B is a graph illustrating an example use case for the method of FIG. 6A; FIG. 7A is a flowchart illustrating an example of a reactive cold protection method; FIG. 7B is a graph illustrating an example use case for the method of FIG. 7A; FIG. 8A is a flowchart illustrating an example of a predictive overheating protection method; FIG. 8B is a graph illustrating an example use case for the method of FIG. 8A; and FIG. 9 is a flowchart illustrating an example of a thermal conditioning request method. DETAILED DESCRIPTION A vehicle 1 in accordance with an embodiment of the present invention is described herein with reference to the accompanying FIG. 1. In some, but not necessarily all examples, the vehicle 1 is a passenger vehicle, also referred to as a passenger car or as an automobile. In other examples, embodiments of the invention can be implemented for other applications, such as commercial vehicles. FIG. 2 is a schematic view of the vehicle 1 where the vehicle is a battery electric vehicle (BEV) or hybrid electric vehicle (HEV). FIG. 2 illustrates the vehicle 1 comprising a traction battery 202 or an equivalent electrical energy storage means. The traction battery 202 is electrically connected to a DC-DC power converter 204. The DC-DC power converter 204 is electrically connected to an inverter 206 (DC-AC power converter). The inverter 206 is part of an electric drive system, referred to herein as an electric drive unit (EDU) 208 for illustrative purposes. The EDU 208 comprises an electric machine 210 operable as a traction electric machine. The traction electric machine 210 is operable as an electric motor and as an electric generator. The EDU 208 further comprises a transmission 212 associated with the traction electric machine 210. In use, the traction electric machine 210 provides torque to one or more wheels of the vehicle 1 via the transmission 212. The traction electric machine 210 is associated with the inverter 206, for providing an electrical supply from the traction battery 202 to the traction electric machine 210. The transmission 212 provides at least one gear ratio between an output of the traction electric machine 210 and the one or more wheels of the vehicle 1. In some embodiments, the traction electric machine 210 and the transmission 212 maybe integrated into a single unit or housing to provide the EDU 208 for the vehicle 1. In some embodiments, the traction electric machine 210 and the transmission 212 are associated with an axle of the vehicle 1 arranged to provide torque to first and second wheels associated with the axle, which may be each disposed at respective ends of the axle. However it will be appreciated that the EDU 208 may be associated with only one wheel of the vehicle 1. FIG. 3 illustrates an oil circuit 310 and a coolant circuit 350, thermally coupled together by a coolant-to-oil (coolant-to-lubricant) heat exchanger (‘heat exchanger’ herein) 324. In an example, the oil circuit 310 is a lubricant circuit forming part of the EDU 208. Oil within the oil circuit 310 both lubricates and cools the EDU 208. The coolant circuit 350 is part of a thermal management system of the vehicle 1 which may be a vehicle-level coolant system, referred to concisely as a coolant system 340. In other examples, the fluids are other than oil and coolant. The coolant system 340 is for exchanging thermal energy between the coolant and various modules thermally coupled or couplable to the coolant system 340. FIG. 3 depicts three such modules. These modules comprise: a traction battery cooler 360; a climate control module 362 (e.g„ coolant-to-coolant heat exchanger) for a heating ventilation and cooling system (HVAC); and a heat transfer module 345 for the EDU 208. The order of the modules, and the number of modules, are outside the scope of this disclosure. Components of the heat transfer module 345 for the EDU 208 are illustrated in FIG. 3. The heat transfer module 345 comprises an inlet 352 and an outlet 358 for receiving and outputting coolant fluid, respectively, flowing around the coolant circuit 350 of the coolant system 340. The heat transfer module 345 comprises a coolant temperature sensor 354 between the inlet 352 and outlet 358. The coolant temperature sensor 354 can therefore sense real-time coolant temperature locally within the heat transfer module 345. Coolant temperature sensors could alternatively, or additionally, be provided elsewhere in the coolant system 340. The heat transfer module 345 further comprises an inverter portion 356 for thermally coupling to the inverter 206. The inverter 206 may therefore be coolant-cooled. The coolant circuit 350 within the heat transfer module 345 flows through the heat exchanger 324. The oil circuit 310 also flows through the heat exchanger 324. The heat exchanger 324 provides a thermal bridge between the coolant circuit 350 of the coolant system 340 and the oil circuit 310 of the EDU 208. As will be described, the heat exchanger 324 can be selectively bypassed. In this implementation, the EDU 208 is fully oil-cooled. As a consequence, the heat transfer module 345 does not further comprise a coolant-filled jacket circulating coolant around a portion of the EDU 208, such as the stator. The stator jacket may instead be oil-filled. This means that the temperature of the EDU 208 can be managed independently of the coolant temperature, by controlling whether the heat exchanger 324 is bypassed. This hardware configuration means that the thermal condition of the EDU is strongly correlated with the oil temperature therein, with coolant temperature not being an interfering variable if the heat exchanger 324 is bypassed. In other examples, the EDU 208 maybe partially directly coolant-cooled. It will be noted that the order of the inverter portion 356, the heat exchanger 324, and the coolant temperature sensor 354 between the inlet 352 and outlet 358 may be different from that illustrated in FIG. 3 and is not restricted in this way. The illustrated oil circuit 310 of the EDU 208 is now described. It circulates oil through both the traction electric machine 210 and the transmission 212. An oil sump 312 is illustrated, from which oil flows via a pickup through an oil pump 314. The oil pump 314 is controllable by a pump control signal to vary an oil pressure and / or flow rate within the oil circuit 310. The oil then flows through an oil filter 316 to an active bypass valve 318. The active bypass valve 318 is an electronic valve that is controllable by a valve control signal to control whether the oil flows through a passage 322 comprising the heat exchanger 324 or through a bypass passage 320 that bypasses the heat exchanger 324. When the oil is hotter than the coolant and the active bypass valve 318 is closed, that is, the bypass passage 320 is closed and the heat exchanger passage 322 is open. The oil will then flow through the heat exchanger 324 and lose its heat to the coolant. The coolant in turn will heat up. If the active bypass valve 318 is open, that is, the bypass passage 320 is open and the heat exchanger passage 322 is closed, the oil will flowthrough the bypass passage and will not lose its heat to the coolant. It would be appreciated that the terms ‘closed’ and ‘open’ are non-limiting and merely refer to first and second states of the active bypass valve 318. By extension, if the oil is colder than the coolant and the active bypass valve 318 is closed, the coolant will warm up the oil via the heat exchanger 324. But if the active bypass valve 318 is open, the coolant will not warm up the oil. The temperature of the oil can be detected in real-time via an oil temperature sensor 326 (lubricant temperature sensor) in the oil circuit 310, which may optionally be an OTP (oil temperature-and-pressure sensor). By measuring and comparing the sensed real-time temperatures of the coolant and the oil via the sensors 354, 326, the active bypass valve 318 can be controlled with a full sensory awareness of the effect that a particular position of the active bypass valve 318 will have on oil temperature and coolant temperature. In the present example, the active bypass valve 318 is a binary valve such that all the oil flows through one or the other of those passages 320, 322. In other examples, the active bypass valve 318 could be controllable to provide a variable ratio of oil flow through each of the passages 320, 322. Although in the present example the active bypass valve 318 and bypass passage 320 belong to the oil circuit 310, in other examples they may belong to the coolant circuit 350 to provide the same function by directing coolant either through or around the heat exchanger 324. FIG. 3 further illustrates an oil stator jacket 328 in the oil circuit 310, to circulate oil around the stator of the electric traction machine. A transmission oil sprayer 330 is also illustrated, to spray oil at a mechanism of the transmission 212. The oil then passes back to the oil sump 312. It will be noted that the order of the oil pump 314, oil filter 316, active bypass valve 318, heat exchanger 324, oil temperature sensor 326, oil stator jacket 328, and transmission oil sprayer 330, may be different from that illustrated in FIG. 3 and is not restricted in this way. With reference to FIG. 4, there is illustrated a control system 400 for a vehicle 1. The control system 400 comprises one or more controllers 401. The control system 400 is configured to receive temperature data from a plurality of sources including the coolant temperature sensor 354 and the oil temperature sensor 326, and to compare them. The control system 400 may then output a control signal to control the active bypass valve 318 and / or the oil pump 314. The control system 400 as illustrated in FIG. 4 comprises one controller 401, although it will be appreciated that this is merely illustrative. The controller 401 comprises processing means 404 and memory means 406. The processing means 404 may be one or more electronic processing device 404 which operably execute computer-readable instructions. The memory means 406 may be one or more memory device 406. The memory means 406 is electrically coupled to the processing means 404. The memory means 406 is configured to store instructions, and the processing means 404 is configured to access the memory means 406 and execute the instructions stored thereon. The controller 401 comprises an input means 410 and an output means 412. The input means 410 may comprise an electrical input 410 of the controller 401. The output means 412 may comprise an electrical output 412 of the controller 401. The controller 401 may have an interface 402 comprising an electrical input / output I / O 410, 412, or an electrical input 410, or an electrical output 412, for receiving information and interacting with external components. The input 410 is arranged to receive temperature signals from the oil and coolant temperature sensors 326, 354, and one or more other internal or external controllers 327. The temperature signals are electrical signals which are indicative of absolute temperatures of the oil and coolant, respectively. The output 412 is arranged to output a valve control signal to the active bypass valve 318, and / or a pump control signal to the oil pump 314, indicative of a request for controlling a state of the active bypass valve 318 and / or a flow rate of the oil pump 314. FIGS. 3 and 4 together illustrate a system 300 comprising the control system 400 and the EDU 208, the active bypass valve 318 for the oil circuit 310 of the EDU 208 being controllable by a valve control signal from the control system 400 to control a fluid flow rate through the heat exchanger 324 relative to a fluid flow rate through the bypass passage 320. FIG. 5 illustrates a non-transitory computer-readable storage medium 500 comprising the instructions (computer software). FIGS. 6A and 7A illustrate methods 600, 700 defining reactive thermal protection methods, specifically wherein the method 600 defines a reactive thermal overheating protection method, and the method 700 defines a reactive cold protection method. FIG. 8A illustrates a method 800 defining a predictive thermal protection method, specifically wherein the method 800 defines a predictive overheating protection method. FIG. 9 illustrates a method 900 defining a thermal conditioning method. Firstly, FIG. 6A illustrates a method 600 according to an embodiment of the invention. The method 600 is a method of controlling thermal energy exchange between the EDU 208 and the coolant system 340 of the vehicle 1. In particular, the method 600 is a method of providing reactive overheating protection of the EDU 208. The method 600 may be performed by the control system 400 or system 300 illustrated in FIG. 6A. In particular, the memory 406 may comprise computer-readable instructions 408 which, when executed by the processor 404, perform the method 600. In summary, the method 600 comprises determining whether reactive overheating protection of the EDU 208 is required, indicating that the absolute oil temperature measured by the oil temperature sensor 326 is greater than a threshold. If so, then the oil and coolant temperatures are compared. If the oil temperature is greater than the coolant temperature, then directing oil through the heat exchanger 324 will assist with bringing down the oil temperature. If the oil temperature is less than the coolant temperature, then bypassing the heat exchanger 324 would prevent the oil from being further heated. Therefore, the control signal sent to the active bypass valve 318 not only depends on the requirement for reactive overheating protection, but also depends on the comparison of temperatures. An advantage is improved thermal protection because a need to thermally protect the EDU 208 is identified, then the control system 400 compares the temperatures to either side of the heat exchanger 324 to determine whether directing or inhibiting oil flowthrough the heat exchanger 324 would be more effective at thermally protecting the EDU 208. Block 602 represents the start of the method 600. At block 604, the method 600 comprises determining a current state of the active bypass valve 318. If the active bypass valve 318 is currently in a state where the oil flow is directed through the bypass passage 320, the flowchart proceeds along a first path (blocks 604, 606, 610, 613,614, 616) containing block 606. If the active bypass valve 318 is in the other state where oil flow is directed through the passage 322 comprising the heat exchanger 324, the flowchart proceeds along a second path (blocks 604, 608, 610, 613, 614, 616) containing block 608. These two paths enable a hysteresis control strategy to be used, which is described after the first path has been described in detail. Determining the current state of the active bypass valve 318 at block 604 is possible by interrogating a stored flag or interrogating a valve state sensor, for example. At block 606, the method 600 comprises determining whether reactive overheating protection of the EDU 208 is required, in dependence on a signal indicative of the temperature of the EDU 208 that is received at input block 605, for example the absolute oil temperature of the EDU 208 sourced from the oil temperature sensor 326. Later in the flowchart, this leads to a state change of the active bypass valve 318 to de-select the bypass passage 320 and instead direct fluid flow through the heat exchanger 324 to cool the EDU 208, if the coolant is colder than the oil. Block 606 comprises determining whether a reactive overheating protection condition is satisfied, which is a type of a thermal protection condition configured to identify present overheating of the EDU 208. In an implementation, the reactive overheating protection condition comprises a first overheat temperature threshold. This could be described as a threshold for changing the state of the active bypass valve 318 to direct oil flowthrough the heat exchanger 324, if the oil temperature is greater than the threshold, and also greater than the coolant temperature as determined in the subsequent decision block 613. The first overheat temperature threshold may be a value over a hundred Celsius, for example from the range 130 to 160 Celsius. This is lower than a separate de-rate threshold of the control system 400 which, if exceeded, may cause the control system 400 to de-rate the EDU 208 by limiting power output of the EDU 208. The difference between the first overheat temperature threshold and the de-rate threshold may be greater than 10 Celsius. In the above example, the condition (block 606) is based on the absolute oil temperature, meaning that the condition is mostly or entirely dependent on the oil temperature of the EDU 208. Since the EDU 208 is fully or substantially oil-cooled, the oil temperature is closely associated with the EDU temperature. Therefore, the coolant temperature, or the difference between coolant and oil temperatures, may not be a factor in this decision that overheating protection is required for the EDU 208, although the difference in oil and coolant temperatures is considered in the next block 613. In dependence on the oil temperature being less than the first overheat temperature threshold, the flowchart progresses to block 610 (no requested position) which allows the current state of the active bypass valve 318 to be maintained (and modified by the other different control methods 700, 800, 900). Block 610 may terminate the method 600 of FIG. 6A. The control system 400 may then progress to the method 700, 800, or 900 of FIG. 7A, 8A, or 9. However, in dependence on the oil temperature being greater than the first overheat temperature threshold, indicating a requirement for overheating protection, then a particular position of the bypass valve 318 is requested which depends on the result of the subsequent decision block 613. At block 613, the method 600 comprises comparing first and second signals received at input blocks 611 and 612, respectively. The first signal is indicative of the temperature of the EDU 208 of the vehicle 1, and refers to the same type of signal as input block 605, for example the oil temperature of the EDU 208 sourced from the oil temperature sensor 326. The second signal is indicativeof a temperature of the coolant system 340 of the vehicle 1, for example the coolant temperature of the coolant system 340 sourced from the coolant temperature sensor 354. Therefore, block 613 compares the temperature of the EDU 208 with the temperature of the coolant system 340. If the first signal is indicative of the oil temperature, and the second signal is indicative of the coolant temperature, then the comparison is between oil temperature and coolant temperature. Since the sensors are local to the heat exchanger 324, the comparison indicates the temperature to each side of the heat exchanger 324 and therefore in which direction thermal energy will transfer through the heat exchanger 324. An advantage is that the control system 400 can determine whether to direct or inhibit oil flowthrough the heat exchanger 324. The comparison may comprise a reactive comparison based on the first and second signals. The signals may indicate real-time sensed temperatures. A first control signal for overheating protection is output by block 614 or 616. In dependence on the first signal being greater than the second signal (oil temperature greater than coolant temperature), the flowchart progresses to block 616 which comprises configuring the first control signal to control thermal energy exchange between the EDU 208 and the coolant system 340, by requesting a state of the active bypass valve 318 that directs oil flow through the passage 322 comprising the heat exchanger 324 rather than the bypass passage 320. This causes reactive thermal protection of the EDU 208 because the heat of the oil is transferred to the colder coolant, cooling down the EDU 208. This advantageously reduces the likelihood of the EDU 208 reaching a de-rate temperature. However, in dependence on the first signal being less than the second signal (oil temperature less than coolant temperature), the flowchart progresses to block 614 which configures the first control signal to control thermal energy exchange between the EDU 208 and the coolant system 340, by requesting a state of the active bypass valve 318 that bypasses the heat exchanger 324 by directing oil flowthrough the bypass passage 320 rather than the passage 322 comprising the heat exchanger 324. Since the active bypass valve 318 is already in this state, the first control signal effectively requests this state to be maintained. In summary, the flowchart will change the state of the active bypass valve 318 from the state where the heat exchanger 324 is bypassed to the state where oil flows through the heat exchanger 324, to cool down the EDU 208, unless the coolant is hotter than the oil in which case the heat exchanger 324 will remain bypassed. The requested state of the active bypass valve 318, requested by block 614 or 616, is maintained (locked) until a subsequent iteration of the method 600 detects that the EDU temperature has returned to normal. In other words, the requested state is maintained until a subsequent iteration leads to block 610 (no requested position). The method 600 of FIG. 6A may be repeated continuously during a drive cycle of the vehicle 1. When implemented, the method 600 can optionally include additional measures such as activating a coolant refrigeration system or coolant radiator branch to further decrease the temperature of the coolant and therefore reduce the temperature of the oil. An advantage of basing the first control signal on the comparison rather than solely on the absolute temperature of the EDU 208, is that a wide variety of thermal management scenarios can be accounted for, especially during a drive cycle when the coolant and oil temperatures may begin to significantly diverge from each other, for instance the oil may heat up faster than the coolant. The above example refers to a valve control signal which has the advantage that the active bypass valve 318 is controlled, allowing the oil pump 314 to be controlled independently to maintain a desired oil pressure and flow rate. It should however be appreciated that blocks 614 and 616 could output a pump control signal instead of, or in addition to, a valve control signal. The pump control signal can control the oil pump 314 to increase or decrease oil flow through the heat exchanger 324, in dependence on the comparison of block 613. For example, when the coolant is colder than the oil, the oil flow rate may be increased at block 616. When the coolant is hotter than the oil, the oil flow rate maybe decreased at block 614. Therefore, a pump control signal provides the same technical effect as a valve control signal, but requires changing the operating point of the oil pump 314. Returning now to the initial decision block 604 which determines the current state of the active bypass valve 318, the second path (604, 608, 610, 613, 614, 616) of the flowchart is now described, the difference being that decision block 608 is executed instead of block 606. The different paths define a hysteresis control strategy as is now described. Whereas the first path is followed if block 604 determined that the active bypass valve 318 is currently in the state where the oil flow is directed through the bypass passage 320, the second path is followed if block 604 determined that the active bypass valve 318 is currently in the state where the oil flow is directed through the passage 322 comprising the heat exchanger 324. At block 608, the method 600 comprises determining whether reactive overheating protection of the EDU 208 is required, in dependence on a signal indicative of the temperature of the EDU 208 that is received at input block 607. Input block 607 refers to the same type of signal as input block 605, for example the absolute oil temperature of the EDU 208 sourced from the oil temperature sensor 326. The reactive overheating protection condition defined by block 608 comprises a second overheat temperature threshold, less than the first overheat temperature threshold. This could be described as a threshold for changing the state of the active bypass valve 318 to direct oil flowthrough the bypass passage 320 if the oil temperature is greater than this second threshold, and the coolant temperature is hotter than the oil temperature as determined in the subsequent decision block 613. The second overheat temperature threshold may be a value over a hundred Celsius, and less than the value of the first overheat temperature threshold to define a hysteresis gap. By having a lower second overheat temperature threshold for bypassing the heat exchanger 324 than the first overheat temperature threshold for connecting the heat exchanger 324, the heat exchanger 324 can remain connected until the temperature of the EDU 208 is brought significantly down. An advantage is that a hysteresis control strategy is defined, the difference between the thresholds defining a hysteresis gap. This is useful in examples where the active bypass valve 318 is binary, i.e., the method 600 is a bang-bang control method, because it prevents excessive valve state switching also referred to as chattering. If the second overheat temperature threshold is exceeded at block 608, then the flowchart progresses to block 613 which functions in the manner as described earlier. I n other words, if the oil temperature is greater than the coolant temperature, block 616 is selected which requests the state of the active bypass valve 318 that directs oil flow through the passage 322 comprising the heat exchanger 324 rather than the bypass passage 320. Since the active bypass valve 318 is already in this state, the valve control signal effectively requests this state to be maintained. However, if the oil temperature is less than the coolant temperature, block 614 is selected which requests the state of the active bypass valve 318 that directs oil through the bypass passage 320. This changes the state of the active bypass valve 318, de-selecting the current state where the heat exchanger 324 is used. FIG. 6B is a pair of graphs depicting an example use case where the reactive overheating protection method 600 of FIG. 6A is used. The upper graph depicts oil temperature ‘OT’ of the EDU 208, and coolant temperature ‘CT’ of the coolant system 340. The y-axis is temperature T and the x-axis is time t. The first overheat temperature threshold is at level 606, and the second overheat temperature threshold is at level 608, against which the oil temperature OT is compared. They are separated by a hysteresis gap. The thresholds are denoted by chain-dashed lines, which become thick solid lines while the threshold is active, i.e., the one that the control system 400 is currently comparing the oil temperature with. The lower graph depicts the requested valve state ‘VS’ of the active bypass valve 318. The y-axis is the percentage of flow through the heat exchanger 324, which is either 0% or 100% in the present example because the active bypass valve 318 is binary. 0% refers to a ‘bypass-open, heat exchanger (HEX)-inactive’ state where oil flow is directed through the bypass passage 320, and 100% refers to a ‘bypass-closed HEX-active’ state where oil flow is directed through the passage 322 comprising the heat exchanger 324 (HEX). The requested valve state VS is a broken line when no valve state is requested (block 610), and becomes a thick solid line when a particular valve state is requested (blocks 614, 616). At time tO, the active bypass valve 318 is determined to be in the bypass-open HEX-inactive state (block 604). Therefore, the relevant threshold is the first overheat temperature threshold 606. Since the oil temperature OT is less than said threshold, there is no requested valve position (block 610) and the current state of the valve (bypass-open) remains. At time t1, the oil temperature OT exceeds the first overheat temperature threshold 606. In response, the oil temperature OT is compared with the coolant temperature CT (block 613). Since the coolant temperature CT is colder than the oil temperature OT, the control system 400 requests the bypass-closed HEX-active state (block 616). After time t1, the oil temperature OT reaches a peak and starts to fall. Between times t1 and t3, the active bypass valve 318 is determined to be in the bypass-closed HEX-active state (block 604). Therefore, from time t1, the relevant threshold is now the second overheat temperature threshold 608. Since the oil temperature OT is greater than the second overheat temperature threshold 608, and is hotter than the coolant temperature CT (block 613), the control system 400 maintains the request for the bypass-closed HEX-active state (block 616). It does not matter that at time t2 the oil temperature falls below the first overheat temperature threshold 606, because that is not the currently-selected threshold. At time t3, the oil temperature OT passes below the coolant temperature CT. Even though the oil temperature OT is still hot (hotter than the second overheat temperature threshold 608), the control system 400 requests the bypass-open HEX-inactive state to prevent a situation where the coolant heats up the oil. After time t3, at the next cycle of the method 600, the active bypass valve 318 is determined to be in the bypass-open HEX-inactive state (block 604). Therefore, the relevant threshold has now returned to the first overheat temperature threshold 606. Since the oil temperature OT is less than the first overheat temperature threshold 606, there is no requested valve position (block 610), despite the oil temperature, at least for a time after t3, remaining above the (now inactive) second threshold temperature 608. FIG. 7A illustrates a method 700 according to an embodiment of the invention. The method 700 is a method of controlling thermal energy exchange between the EDU 208 and the coolant system 340 of the vehicle 1. In particular, the method 700 is a method of providing reactive cold protection of the EDU 208. When the EDU 208 is cold, its efficiency is detrimentally affected due to factors such as lubricant viscosity and winding temperatures. The method 700 may be performed by the control system 400 or system 300 illustrated in FIG. 4. In particular, the memory 406 may comprise computer-readable instructions 408 which, when executed by the processor 404, perform the method 700. Optionally, the method 700 of FIG. 7A may be performed as well as the method 600 of FIG. 6A, with the advantage that EDU 208 temperatures can be controlled in both hot and cold (e.g., freezing) conditions. The flowchart of FIG. 7A is similarly structured to the flowchart of FIG. 6A. For conciseness, only the differences will be described in detail, rather than the similarities. Block 702 is a start block. If the method 700 of FIG. 7A is performed after the method 600 of FIG. 6A, block 610 (no requested position) may trigger the start block 702 of the method 700. Or, they may be performed in the opposite order with block 710 (described further below) triggering the start block 602 of method 600. Block 704 is the same as block 604, to determine the current state of the active bypass valve 318. Regarding blocks 705, 706, and 710, the description of blocks 605, 606, and 610 apply except that block 706 defines a reactive cold protection condition for determining whether reactive cold protection of the EDU 208 is required, rather than a reactive overheating protection condition. The condition of block 706 therefore defines a first cold temperature threshold. The first cold temperature threshold may be a value lower than zero Celsius or lower than -20 Celsius, such as approximately -25 Celsius. If the absolute oil temperature of the EDU 208 is colder than the first cold temperature threshold, block 706 is satisfied and the flowchart proceeds to block 713. If it is warmer than the first cold temperature threshold, block 706 is not satisfied and the flowchart proceeds to block 710 (no requested position, equivalent to block 610). Regarding blocks 711, 712, and 713, the description of blocks 611, 612, and 613 apply. That is, the oil and coolant temperatures are compared. A first control signal for cold protection is output at block 714 or 716. If the oil temperature is less than the coolant temperature, the first control signal is configured at block 716 to request the state of the active bypass valve 318 that directs oil flowthrough the passage 322 comprising the heat exchanger 324 rather than the bypass passage 320, to allow the warmer coolant to warm up the oil. However, if the oil temperature is greater than the coolant temperature, the first control signal is configured at block 714 to request the state of the active bypass valve 318 that directs oil flow through the bypass passage 320 rather than the passage 322 comprising the heat exchanger 324, to prevent the colder coolant from further cooling down the oil. An advantage is that the heat exchanger 324 will only be used if it is capable of warming up the EDU 208. The method 700 of FIG. 7A further comprises a second path through block 708 instead of 706. The different paths define a hysteresis control strategy where the threshold that the oil temperature is compared with depends on the current state of the active bypass valve 318. Regarding block 708, the description of block 608 applies, except that block 708 defines a second cold temperature threshold. The second cold temperature threshold may be a value lower than zero Celsius such as approximately -20 Celsius, which is warmer than the first cold temperature threshold, creating a hysteresis gap therebetween. Therefore, if the absolute oil temperature of the EDU 208 is colder than the second cold temperature threshold, block 708 is satisfied and the flowchart proceeds to block 713. If it is warmer than the second cold temperature threshold, block 708 is not satisfied and the flowchart proceeds to block 710 (no requested position, equivalent to block 610) because reactive cold protection is not required. Advantageously, this allows the oil temperature to be warmed up to substantially warmer than the first cold temperature threshold before the heat exchanger 324 will again be bypassed. FIG. 7B is a pair of graphs depicting an example use case where the cold protection method 700 of FIG. 7A is used. The graphs are of the same format as FIG. 6B, except the thresholds are the first cold temperature threshold 706’, and second cold temperature threshold 708’. At time t4, the active bypass valve 318 is determined to be in the bypass-open HEX-inactive state (block 704). Therefore, the relevant threshold is the first cold temperature threshold 706. Since the oil temperature OT is warmer than said threshold, there is no requested valve position (block 710). At time t5, the oil temperature OT becomes colder than the first cold temperature threshold 706. In response, the oil temperature OT is compared with the coolant temperature CT (block 713). Since the depicted coolant temperature CT is warmer than the oil temperature OT, the control system 400 requests the bypass-closed HEX-active state (block 716). After time t5, the oil temperature OT starts to rise. Between times t5 and t6, the active bypass valve 318 is determined to be in the bypass-closed HEX-active state (block 704). Therefore, the relevant threshold is now the second cold temperature threshold 708. Since the oil temperature OT is colder than the second cold temperature threshold 708, and is colder than the coolant temperature CT (block 713), the control system 400 maintains the request for the bypass-closed HEX-active state (block 716). At time t6, the oil temperature OT rises above the second cold temperature threshold 708. Therefore, there is no requested valve position (block 710) because reactive cold protection is no longer required. FIG, 8A illustrates a method 800 according to an embodiment of the invention. The method 800 is a method of controlling thermal energy exchange between the EDU 208 and the coolant system 340 of the vehicle 1. In particular, the method 800 is a method of providing predictive overheating protection of the EDU 208. The method 800 may be performed by the control system 400 or system 300 illustrated in FIG. 4. In particular, the memory 406 may comprise computer-readable instructions 408 which, when executed by the processor 404, perform the method 800. Optionally, the method 800 of FIG. 8A may be performed as well as one or both of the methods 600,700 of FIG. 6A and 7A, with the advantage that EDU temperatures can be controlled pre-emptively to further reduce the chance of a de-rate of the EDU 208. Block 802 is a start block. If the method 800 of FIG. 8A is performed after the method 600, 700 of FIG. 6A or 7A, block 610 or 710 (no requested position) may trigger the start block 802 of the method 800. Or, they may be performed in the opposite order with block 810 (described further below) being a trigger for either of methods 600, 700. At block 806, the method 800 determines that a predictive overheating protection condition is satisfied, to determine that predictive thermal protection of the EDU 208 is required. The determination is dependent on a signal indicative of a requested operating point of the EDU 208 that is received at input block 805. The signal may be indicative of a requested load, e.g„ power request (kW or equivalent units), of the EDU 208. The signal may be sourced from an internal or external controller 327 for controlling the operating point of the EDU 208. The signal may be a feedforward signal or a feedback signal. Since the temperature of the EDU 208 increases in dependence on its operating point increasing, with a lag therebetween, a rapid and substantial increase in the requested operating point is a suitable predictor that the EDU temperature will shortly reach a de-rate threshold, and / or trigger the reactive overheating protection of FIG. 6A. The predictive overheating protection condition may comprise an operating point threshold, said condition being satisfied based on said operating point exceeding said threshold. The operating point threshold may a value greater than 30 kilowatts, or greater than 60 kilowatts, or greater than 90 kilowatts. In normalised terms, the threshold may be greater than 30% or greater than 60% or greater than 80% of a maximum requestable operating point of the EDU 208. In dependence on the operating point being less than the operating point threshold, the flowchart progresses to block 810 (no requested position) which allows the current state of the active bypass valve 318 to be maintained. Block 810 may terminate the method 800 of FIG. 8A. The control system 400 may then progress to another method depending on the order / priority of the methods, such as the method 900 of FIG. 9, or methods 600, 700 described above. Regarding blocks 811, 812, and 813, the description of blocks 611, 612, and 613 apply. That is, the oil and coolant temperatures are compared. A second control signal is output at block 814 or 816. If the oil temperature is greater than the coolant temperature, the second control signal is configured at block 816 to request the state of the active bypass valve 318 that directs oil flowthrough the passage 322 comprising the heat exchanger 324 rather than the bypass passage 320, to allow the colder coolant to cool down the oil. However, if the oil temperature is less than the coolant temperature, the second control signal is configured at block 814 to request the state of the active bypass valve 318 that directs oil flow through the bypass passage 320 rather than the passage 322 comprising the heat exchanger 324, to prevent the hotter coolant from heating up the oil. Blocks 814 and 816 are executed before the absolute oil temperature exceeds relevant threshold 606, 608, or a de-rate threshold. An advantage is that the heat exchanger 324 will only be used if it is capable of pre-emptively cooling down the EDU 208 in anticipation of the expected temperature rise of the EDU given the operating point requested. FIG. 8B illustrates three graphs depicting an example use case where the predictive overheating protection method 800 of FIG. 8A is used. The middle and bottom graphs are of the same format as FIGS. 6B and 7B. The top graph depicts the operating point ‘OP’ of the EDU 208 (solid line), relative to the operating point threshold 806 (chain-dashed line). At time t7, the operating point OP of the EDU 208 is less than the operating point threshold 806. Therefore, there is no requested valve position (block 810). At time t8, the operating point OP of the EDU 208 exceeds the operating point threshold 806. In response, the oil temperature OT is compared with the coolant temperature CT (block 813). Since the depicted oil temperature OT is hotter than the coolant temperature CT, the control system 400 requests the bypass-closed HEX-active state (block 816), to cause the coolant to cool the oil. After time t8, the oil temperature OT reaches a peak and starts to fall. At time t9, the oil temperature OT falls below the coolant temperature CT, for example due to the coolant temperature rising. However, the operating point OP still exceeds the operating point threshold 806. Nonetheless, the control system 400 requests the bypass-open HEX-inactive state (block 814), to prevent the now-hotter coolant from heating up the oil. At time t10, the operating point OP falls below the operating point threshold 806, or another lower hysteresis threshold. Therefore, there is no requested valve position (block 810) because pre-emptive thermal protection is not required. FIG. 9 illustrates a method 900 according to an embodiment of the invention. The method 900 is a method of controlling thermal energy exchange between the EDU 208 and the coolant system 340 of the vehicle 1. In particular, the method 900 is a method of allowing the active bypass valve 318 to be controlled based on thermal conditioning requests. The method 900 may be performed by the control system 400 or system 300 illustrated in FIG. 4. In particular, the memory 406 may comprise computer-readable instructions 408 which, when executed by the processor 404, perform the method 900. Thermal conditioning refers to heating or cooling the coolant system 340, or one of the modules 208,360,362 thermally coupled to the coolant system 340, for a thermal conditioning purpose. A thermal conditioning purpose can be energy optimisation or comfort, and is unrelated to thermal protection such as overheating or excessively cold temperatures. The thermal conditioning request may be determined by an energy-efficiency algorithm. The energy-efficiency algorithm may be a vehicle-level energy-efficiency algorithm, taking into account whole-vehicle energy consumption as a variable. For example, thermal conditioning during a drive cycle can comprise using the EDU 208 as a heat source to heat up the coolant to supply additional heat to the climate control module 362. This can help with cabin temperature warmup. Thermal conditioning may also be required outside of a drive cycle. A specific example of thermal conditioning is pre-conditioning or post-conditioning the oil of the EDU 208 before or after a drive cycle. For example, if the vehicle 1 is connected to a charger and a state of charge of the traction battery 202 has reached a suitable target, an electric heater or refrigeration system or coolant radiator branch may warm up or cool down the coolant in order to supply or remove heat to / from the EDU 208, or other modules. Pre-conditioning the EDU 208 can function as a pre-heater (or pre-cooler) of the EDU 208 to improve its efficiency. Optionally, the method 900 of FIG. 9 may be performed as well as one or more of the methods 600,700,800 of FIG. 6A to 8A, with a lower priority than the aforementioned methods. This has the advantage that if thermal protection is not required, then the active bypass valve 318 will become available to an optimisation controller for thermal conditioning purposes. Block 902 is a start block. If the method 900 of FIG. 9 is performed after the method 600, 700, 800 of FIG. 6A, 7A, or 8A, block 610 or 710 or 810 (no requested position) may trigger the start block 902 of the method 900. This means that the method 900 of FIG. 9 is a lower / lowest priority method than the preceding method(s), and can only be executed if the preceding higher-priority thermal protection method(s) allow the current state of the active bypass valve 318 to be modified by other lower-priority control methods such as the method 900 of FIG. 9, i.e., no requested state. At block 904, the method 900 comprises determining whether thermal conditioning has been requested, in dependence on a signal indicative of a thermal conditioning request that is received at input block 905. In a non-limiting example, the signal may require a particular state of the active bypass valve 318, sourced from an external controller of the vehicle 1, e.g., a Vehicle Systems Controller (VSC). The VSC may host the energy-efficiency algorithm configured to determine a requirement for thermal conditioning of the module, causing the VSC to output to the control system 400 the signal requesting a particular state of the active bypass valve 318. It should be appreciated that the decision could be made inside the control system 400, when the energy-efficiency algorithm is hosted by the control system 400 or where the control system 400 comprises the VSC. In dependence on the bypass-closed HEX-active state of the active bypass valve 318 not having been requested by a thermal conditioning request (block 904), the method 900 proceeds to block 914 which comprises requesting the other state of the active bypass valve 318 (bypass-open HEX-inactive) which directs oil flowthrough the bypass passage 320. For example, this valve position may be requested if no thermal conditioning request has been received, or if a thermal conditioning request has been received that requests said valve state. In dependence on the bypass-closed HEX-active state of the active bypass valve 318 having been requested by a thermal conditioning request (block 904), the method 900 proceeds to block 906 which outputs a pump control signal to the oil pump 314 to request a target or minimum oil flow rate, and then proceeds to block 916 in which a third control signal (valve control signal) is output to request the bypass-closed HEX-active state of the active bypass valve 318 to direct oil flowthrough the heat exchanger 324. The pump control signal advantageously allows heat to be circulated within the EDU 208 even outside a drive cycle of the vehicle 1 when there would normally be no oil flow. In other examples, the oil pump 314 may already be running and its flow rate may not be varied as part of this method 900. The target or minimum oil flow rate may be a default value, or may be dependent on information comprised in the thermal conditioning request. Although not shown, the particular requested state of the active bypass valve 318 could depend on a comparison of oil and coolant temperatures, to determine whether the EDU 208 wouId act as a heat source or heat sink for the coolant if the heat exchanger 324 is connected. In an example implementation: - If the thermal conditioning request of block 904 is for heating the climate control module 362, the third control signal may cause the thermal conditioning by changing the state of the active bypass valve 318 to select the heat exchanger 324 to enable transfer of heat from the EDU 208 to the coolant system 340. Or, if the oil is colder than the coolant, the bypass passage 320 may be selected to inhibit transfer of heat from the coolant system 340 to the EDU 208. - If the thermal conditioning request of block 904 is for cooling the climate control module 362, the third control signal may cause the thermal conditioning by changing the state of the active bypass valve 318 to select the heat exchanger 324 to enable transfer of heat from the coolant system 340 to the EDU 208. Or, if the oil is hotter than the coolant, the bypass passage 320 may be selected to inhibit transfer of heat from the EDU 208 to the coolant system 340. - If the thermal conditioning request is for heating the EDU 208 (e.g., pre-conditioning or post-conditioning the oil), the third control signal may cause the thermal conditioning by changing the state of the active bypass valve 318 to select the heat exchanger 324 to cause transfer of heat from the coolant system 340 to the EDU 208. Or, if the oil is hotter than the coolant, the bypass passage 320 may be selected to inhibit transfer of heat from the EDU 208 to the coolant system 340. In an example, the method 900 is executed in a loop for minimising energy consumption at the vehicle-level. The energy-efficiency algorithm controls, via the thermal conditioning request: a) direction of heat transfer; and b) quantity of the heat transfer (e.g., duration of actuation of the active bypass valve 318). The request may be capable of requesting a 0 (zero) transfer for optimal EDU efficiency in cold regions. To summarise the preceding description, an aspect that FIGS. 6A, 7A, and 8A have in common is a method 600, 700, 800 comprising: receiving signals 605,607,705, 707, 805 from a plurality of sources 354, 326, 327; determining 606, 608, 706, 708 whether reactive thermal protection of the electric drive system 208 is required, in dependence on the signal 605, 607, 705, 707 from a first source 326 of the plurality of sources; outputting a first control signal 614, 616, 714, 716 to control thermal energy exchange between the electric drive system 208 and the thermal management system 340, in dependence on the determination that reactive thermal protection is required, to cause thermal protection of the electric drive system 208; determining 806 whether predictive thermal protection of the electric drive system 208 is required, in dependence on the signal 805 from a second source 327 of the plurality of sources; and outputting a second control signal 814, 816 to control thermal energy exchange between the electric drive system 208 and the thermal management system 340, in dependence on the determination that predictive thermal protection is required, to cause thermal protection of the electric drive system 208. It is to be understood that the or each controller 401 can comprise a control unit or computational device having one or more electronic processors (e.g., a microprocessor, a microcontroller, an application specific integrated circuit (ASIC), etc.), and may comprise a single control unit or computational device, or alternatively different functions of the or each controller 401 may be embodied in, or hosted in, different control units or computational devices. As used herein, the term “controller,” “control unit,” or “computational device” will be understood to include a single controller, control unit, or computational device, and a plurality of controllers, control units, or computational devices collectively operating to provide the required control functionality. A set of instructions could be provided which, when executed, cause the controller 401 to implement the control techniques described herein (including some or all of the functionality required for the method(s) 600, 700, 800, 900 described herein). The set of instructions 408 could be embedded in said one or more electronic processors 404 of the controller 401; or alternatively, the set of instructions 408 could be provided as software to be executed in the controller 401. A first controller or control unit may be implemented in software run on one or more processors. One or more other controllers or control units may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller or control unit. Other arrangements are also useful. The, or each, electronic processor 404 may comprise any suitable electronic processor (e.g., a microprocessor, a microcontroller, an ASIC, etc.) that is configured to execute electronic instructions 408. The, or each, electronic memory device 406 may comprise any suitable memory device and may store a variety of data, information, threshold value(s), lookup tables or other data structures, and / or instructions therein or thereon. In an embodiment, the memory device 406 has information and instructions for software, firmware, programs, algorithms, scripts, applications, etc. stored therein or thereon that may govern all or part of the methodology described herein. The processor, or each, electronic processor 404 may access the memory device 406 and execute and / or use that or those instructions and information to carry out or perform some or all of the functionality and methodology described herein. The at least one memory device 406 may comprise a computer-readable storage medium (e.g. a non-transitory or non-transient storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors / computational devices. Examples of the form include, without limitation: a magnetic storage medium (e.g. floppy diskette); optical storage medium (e.g. CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g. EPROM ad EEPROM); flash memory; or electrical or other types of medium for storing such information / instructions. It will be appreciated that embodiments of the present invention can be realised In any suitable form of hardware, software or a combination of hardware and software. For example, it is contemplated that the present invention is not limited to being implemented by way of programmable processing devices, and that at least some of, and in some embodiments all of, the functionality and or method steps of the present invention may equally be implemented by way of non-programmable hardware, such as by way of nonprogrammable ASIC, Boolean logic circuitry, etc. 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. The blocks illustrated in the FIGS 6A, 7A, 8A, 9 may represent steps in a method and / or sections of code in the computer program 408. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some steps to be omitted. Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Claims

1. A control system for controlling thermal energy exchange between an electric drive system of a vehicle and a thermal management system of the vehicle, the control system comprising one or more processors collectively configured to:receive signals from a plurality of sources;determine whether reactive thermal protection of the electric drive system is required, in dependence on the signal from a first source of the plurality of sources;output a first control signal to control thermal energy exchange between the electric drive system and the thermal management system, in dependence on the determination that reactive thermal protection is required, to cause thermal protection of the electric drive system;determine whether predictive thermal protection of the electric drive system is required, in dependence on the signal from a second source of the plurality of sources; andoutput a second control signal to control thermal energy exchange between the electric drive system and the thermal management system, in dependence on the determination that predictive thermal protection is required, to cause thermal protection of the electric drive system.

2. The control system of claim 1, wherein the first and second control signals each comprise a valve control signal and / or a pump control signal to control fluid flow through a heat exchanger for exchanging thermal energy between the electric drive system and the thermal management system.

3. The control system of claim 1 or 2, wherein the signal from the first source is indicative of a detected temperature of the electric drive system.

4. The control system of claim 3, wherein the signal indicative of a detected temperature of the electric drive system is indicative of a lubricant temperature of the electric drive system.

5. The control system of any one of the preceding claims, wherein determining whether the reactive thermal protection is required comprises determining whether reactive overheating protection of the electric drive system is required, and further comprises determining whether reactive cold protection of the electric drive system is required.

6. The control system of claim 5, wherein when the reactive overheating protection is required, the first control signal is configured to cause thermal protection of the electric drive system by causing transfer of heat from the electric drive system to the thermal management system or by inhibiting transfer of heat from the thermal management system to the electric drive system, andwherein when the reactive cold protection is required, the first control signal is configured to cause thermal protection of the electric drive system by causing transfer of heat from the thermal management system to the electric drive system or by inhibiting transfer of heat from the electric drive system to the thermal management system.

7. The control system of any one of the preceding claims, wherein the signal from the second source is indicative of a requested operating point of the electric drive system.

8. The control system of any one of the preceding claims, wherein when the predictive thermal protection is required, the second control signal is configured to cause thermal protection of the electric drive system by causing transfer of heat from the electric drive system to the thermal management system or by inhibiting transfer of heat from the thermal management system to the electric drive system.

9. The control system of any one of the preceding claims, configured to:determine whether thermal conditioning has been requested, in dependence on the signal from a third source of the plurality of sources; andoutput a third control signal to control thermal energy exchange between the electric drive system and the thermal management system, in dependence on the determination that thermal conditioning has been requested, to cause the thermal conditioning,wherein the control system is configured to allow a lower priority to causing the thermal conditioning than to causing the thermal protection of the electric drive system.

10. The control system of claim 9, wherein the signal from the third source is dependent on a request for heating or cooling a module of the vehicle which is thermally coupled to the thermal management system.

11. The control system of claim 10, wherein when the request is for heating and the module is a climate control module, the third control signal is configured to cause the thermal conditioning by causing transfer of heat from the electric drive system to the thermal management system or by inhibiting transfer of heat from the thermal management system to the electric drive system,wherein when the request is for cooling and the module is the climate control module, the third control signal is configured to cause the thermal conditioning by causing transfer of heat from the thermal management system to the electric drive system or by inhibiting transfer of heat from the electric drive system to the thermal management system, andwherein when the request is for heating and the module is the electric drive unit, the third control signal is configured to cause the thermal conditioning by causing transfer of heat from the thermal management system to the electric drive system or by inhibiting transfer of heat from the electric drive system to the thermal management system.

12. A system comprising the control system of any one of the preceding claims, and the electric drive system, wherein the electric drive system comprises a lubricant circuit, a coolant-to-lubricant heat exchanger thermally coupling a coolant circuit to the lubricant circuit, a bypass passage bypassing the coolant-to-lubricant heat exchanger, and an active bypass valve controllable by the first and second control signals to control a fluid flow rate through the coolant-to-lubricant heat exchanger relative to a fluid flow rate through the bypass passage.

13. A vehicle comprising the control system of any one of the preceding claims or the system of claim 12.

14. A method of controlling thermal energy exchange between an electric drive system of a vehicle and a thermal management system of thevehicle, the method comprising:receiving signals from a plurality of sources;determining whether reactive thermal protection of the electric drive system is required, in dependence on the signal from a first source of the plurality of sources;outputting a first control signal to control thermal energy exchange between the electric drive system and the thermal management system, in dependence on the determination that reactive thermal protection is required, to cause thermal protection of the electric drive system;determining whether predictive thermal protection of the electric drive system is required, in dependence on the signal from a second source of the plurality of sources; andoutputting a second control signal to control thermal energy exchange between the electric drive system and the thermal management system, in dependence on the determination that predictive thermal protection is required, to cause thermal protection of the electric drive system.

15. Computer readable instructions which, when executed by a computer, are arranged to perform a method according to claim 14.21

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