Thermal management controls for a vehicle with a rechargeable energy storage system

Abstract

Method for operating a RESS heating system (12) in a vehicle (10) comprising a coolant circuit (16) for passing a coolant through a rechargeable energy storage system (RESS) (44) and a refrigerant circuit (14) designed to selectively cool the coolant flowing through a radiator (38) in the coolant circuit (16), the method comprising the following steps: (a) Determining a current target temperature range for the RESS (44) based on at least one current vehicle operating mode and a current ambient temperature, wherein the target temperature range is variable based on the current vehicle operating mode and the current ambient temperature; (b) Determining a temperature of the RESS (44); (c) Determine whether the temperature of the RESS (44) needs to increase or decrease to remain within the current target temperature range; (d) if it is determined that the temperature of the RESS (44) needs to increase, determine whether to use active heating or passive heating of the coolant, with active heating using a greater amount of energy over a shorter period than passive heating; (e) Activating the active heating or passive heating of the coolant determined by step (d); (f) if it is determined that the temperature of the RESS (44) needs to decrease, determine whether to use active or passive cooling of the coolant, with active cooling using a greater amount of energy over a shorter period than passive cooling; and (g) Activating the active cooling or passive cooling of the coolant determined by step (f), characterized by the fact that then, when passive cooling is activated in step (g), the rate of change of the coolant temperature over time is monitored and compared with a desired passive cooling capacity, and the switch from passive cooling to active cooling occurs when the rate of change of the coolant temperature is below a predetermined threshold and the desired passive cooling capacity is not achieved, and then, when passive heating is activated in step (e), the rate of change of the coolant temperature over time is monitored and compared with a desired passive heating output, and the switch from passive heating to active heating occurs when the rate of change of the coolant temperature is below the predetermined threshold and the desired passive heating output is not reached.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to providing thermal management for vehicles that operate using non-conventional means, such as a rechargeable energy storage system (RESS), such as a battery pack that can be plugged into an electrical outlet for charging.

[0002] For vehicles with a RESS, which could be a battery pack, for example, the range the vehicle can travel using the RESS's stored energy is important. For battery packs in these vehicles, the temperature of the battery pack is a significant factor in maximizing the vehicle's range. Therefore, it is desirable to control the RESS thermal system to maximize the vehicle's range while also charging the RESS in an energy-efficient manner.

[0003] From US 2010 / 0 212 338 A1 a method according to the preamble of claim 1 is known.

[0004] DE 10 2010 031 414 A1 describes a cooling system for regulating the temperature of a high-performance battery. The cooling system's cooling capacity can be adjusted based on the current charging or discharging current as well as the ambient temperature, allowing for demand-oriented battery temperature control.

[0005] DE 101 28 164 A1 describes a method for operating a heating system in a vehicle, in which switching from passive to active cooling takes place depending on the ambient temperature and the heat load.

[0006] An object of the invention is to provide a method for operating a heating system for a rechargeable energy storage system in a vehicle, which allows maximizing the range of the vehicle. SUMMARY OF THE INVENTION

[0007] This object is achieved by a method having the features of claim 1.

[0008] One embodiment relates to a method for operating a RESS thermal system in a vehicle having a coolant circuit for conducting coolant through a RESS and a refrigerant circuit configured to selectively cool the coolant flowing through a radiator in the coolant circuit, the method comprising the following steps: determining a current target temperature range for the RESS based on at least one current vehicle operating mode and a current ambient temperature, wherein the target temperature range is variable based on the current vehicle operating mode and the current ambient temperature; determining a temperature of the RESS; determining whether the temperature of the RESS needs to increase or decrease to be within the current target temperature range;If it is determined that the temperature of the RESS needs to increase, determining whether to use active heating or passive heating of the coolant, where active heating uses a greater amount of energy for a shorter period of time than passive heating; and activating the determined active heating or passive heating of the coolant.

[0009] Further, upon determining that the temperature of the RESS needs to decrease, the method also includes determining whether active cooling or passive cooling of the coolant is utilized, wherein active cooling utilizes a greater amount of energy for a shorter period of time than passive cooling; and activating the determined active or passive cooling of the coolant.

[0010] A method for operating a RESS thermal system in a vehicle having a coolant circuit for conducting coolant through a RESS and a refrigerant circuit configured to selectively cool coolant flowing through a radiator in the coolant circuit, the method comprising the steps of: shutting down the vehicle; determining the RESS temperature at shutting down; determining an ambient temperature at shutting down; determining a waiting period after shutting down until waking up the RESS thermal system and, if necessary, providing heating and cooling of the RESS battery based at least on the determined RESS temperature and the ambient temperature at shutting down; waking up the RESS thermal system after the predetermined period of time; and, after waking up the RESS thermal system, providing RESS heating or cooling as needed.

[0011] One advantage of these methods is that the thermal management of the RESS allows for maximizing the vehicle's range while charging the RESS in an energy-efficient manner under varying vehicle operating and charging conditions. This can also extend the service life of the RESS. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic view of a RESS thermal system and a portion of a heating, ventilation, and air conditioning (HVAC) system for a plug-in electric vehicle. Fig. 2 is a schematic view similar Fig. 1, but with a slightly different arrangement of components. Fig. Figure 3 is a flowchart illustrating some of the thermal controls for a vehicle. Fig. Figure 4 is a flowchart illustrating part of a method for determining target temperatures for a RESS. Fig. Figure 5 is a graph illustrating target temperatures of a RESS during charging of the RESS. Fig. Figure 6 is a graph illustrating target temperatures of the RESS under different vehicle driving conditions. Fig. Figure 7 is a graph showing target temperatures of the RESS in a vehicle shutdown mode when the vehicle is not plugged into a charging device. DETAILED DESCRIPTION

[0012] With reference to Fig. 1, a vehicle is shown, indicated generally at 10. This vehicle 10 may be, for example, a plug-in hybrid electric vehicle or an extended-range electric vehicle. The vehicle 10 includes a RESS thermal system 12, which includes a refrigerant circuit 14 and a coolant circuit 16.

[0013] The refrigerant circuit 14 includes a refrigerant compressor 18 and a condenser 20, which may be part of a condenser / radiator / fan module (CRFM) 21. The CRFM 21 may include other heat exchangers 23 and fans 25 used to cool fluids from other vehicle systems. The refrigerant compressor 18 may be electrically driven, with the ability to adjust the compressor speed during operation.

[0014] The condenser 20 directs refrigerant into a refrigerant line 22, which is divided into an HVAC section 24 and a cooler section 26 of the refrigerant circuit 14. The HVAC section 24 directs the refrigerant through an expansion device 28 and into an evaporator 30 located in an HVAC module 32. Refrigerant exiting the evaporator can be conveyed back to the compressor 18.

[0015] The cooler section 26 directs the refrigerant through an expansion device 34 and then through a cooler (refrigerant-to-coolant heat exchanger) 36. The refrigerant exiting the cooler 38 is directed back to the compressor 18.

[0016] The cooler 38 is also in fluid communication with the coolant circuit 16. The dashed lines in Fig. 1 and Fig. 2 represent lines through which refrigerant flows, while the dashed lines represent lines through which a cooling liquid flows. The cooling liquid can be a conventional liquid mixture, such as a mixture of ethylene glycol and water, or it can be another type of liquid with suitable heat transfer properties.

[0017] The coolant circuit 16 includes a coolant pump 42 that pumps the coolant through the circuit and is controllable to vary the flow rate of the coolant flowing through the coolant circuit 16. The coolant circuit 16 also includes a chargeable energy storage system (RESS), such as a battery pack, 44 and an electric coolant heater 46. The coolant flowing through the RESS 44 is used to cool or heat the RESS as needed. The electric coolant heater 46 can be activated to heat the coolant flowing therethrough to provide heating of the RESS 44.

[0018] A variable four-way coolant bypass valve 48 is located within the coolant circuit 16 and can be selectively actuated to direct the coolant through three different branches of the coolant circuit 16. A first branch 50 includes a RESS radiator 52 positioned to receive air flow therethrough. The RESS radiator 52 may be mounted near an auxiliary power module 58 and a RESS charger 60 through which air is forced by a controllable fan 62. A second branch 54 forms a coolant bypass conduit, with the coolant not flowing through the RESS radiator 52 or the radiator 38. A third branch 56 directs the coolant through the radiator 38. All three branches combine to direct the coolant back through the RESS 44.

[0019] Various temperature and pressure sensors and a controller (not shown) may also be used to provide inputs to and control the various elements of the HVAC and RESS thermal system 12.

[0020] Fig. 2 illustrates another example of a vehicle 10 and the HVAC and RESS heating system 12. This may be, for example, a plug-in hybrid electric vehicle or an extended-range electric vehicle. Because this embodiment is similar to the first, similar element numbers are used for similar elements, and a detailed description thereof is omitted. In this embodiment, the RESS radiator 52 may be part of the CRFM 21. While the two embodiments may have slightly different configurations, the processes discussed below for cooling and heating the RESS 44, if necessary, may be substantially the same.

[0021] Fig. Figure 3 is a flow chart showing part of the thermal controls for use in a vehicle, such as those shown in, for example, Fig. 1 and Fig. 2. Various inputs are received, field 200. These inputs may include, for example, cell temperatures from the RESS, which enable the determination of the maximum and minimum cell temperatures from the RESS, the outside (ambient) air temperature, the RESS inlet and outlet coolant temperatures, time of day, estimate of the season or time of year, engine speed, vehicle speed, front-end blower speed, HVAC settings for the vehicle interior, and the operating mode the vehicle is in (e.g., whether the vehicle is plugged into a charger, in a shutdown mode, or whether the vehicle is running). Other inputs may also be used.

[0022] A target temperature range is determined for the RESS, field 202. The determination of the target temperature range is based on Fig. 4-7 explained. In Fig. 4, a determination is made as to whether the vehicle is plugged in (ie connected to a charging source for the RESS, such as a wall outlet), field 302. If so, a determination is made as to whether a delayed charge is in progress, field 304. If so, a RESS protection target temperature range for delayed charging is used, field 306. These temperature ranges are discussed below with respect to Fig. 5 - 7 explained.

[0023] If no delayed charging is occurring, field 304, then a determination is made whether the vehicle is charging but not charging near the end of charging or not charging near a vehicle departure time, field 308. If so, then an energy-efficient charging target temperature range is used, field 310. If the vehicle is charging near (or at) the end of charging or near a departure time, then an optimal RESS power charging temperature range is used, field 312.

[0024] If the vehicle is not plugged in at field 302, a determination is made as to whether the vehicle is running (i.e., being driven), field 314. If not, a determination is made as to whether a state of charge of the RESS is above a predetermined threshold, field 314. If so, a RESS protection target temperature range is utilized, field 324. If not, active heating and cooling are disabled, field 326. If the vehicle is running, field 314, a determination is made as to whether the vehicle is in a discharge driving mode, field 318. If so, a discharge driving target temperature range is utilized, field 320. If not, a charge sustaining driving target temperature range is utilized, field 322.

[0025] Fig. Figure 5 illustrates target temperature ranges of a RESS during an operating mode in which the RESS is plugged in and charging. The vertical axis is temperature, and the horizontal axis is time. The origin of the axes may be a plug-in event (i.e., when the charging device is plugged into the vehicle and the outlet). The horizontal phantom lines 402, 404 show the upper and lower temperatures for the optimal temperature range of the RESS. The vertical dashed lines represent the changes from one charging mode to another.

[0026] The first mode 406 shown is a delayed charging mode, in which the charging device is plugged in, but charging of the RESS is delayed until a more preferred time. This mode corresponds to field 306 in Fig. 4. If the RESS temperature is below the lowest recommended temperature 408, active heating of the RESS is activated, and if the RESS temperature is above the highest recommended temperature 410, active cooling of the RESS is activated. Below and above these temperature limits 408, 410, passive heating or cooling can still be attempted first if available. However, if it is not effective enough, active heating or cooling is used.

[0027] The second mode 412 shown is a vehicle charging process in which charging does not occur near the end of charging or a vehicle departure time. This mode corresponds to field 310 in Fig. 4. If the RESS temperature is below the lowest recommended temperature 414, then active heating of the RESS is activated, and if the RESS temperature is above the highest recommended temperature 416, then active cooling of the RESS is activated. Below and above these temperature limits 414, 416, passive heating or cooling can still be attempted first if available. However, if it is not effective enough, active heating or cooling is used.

[0028] The third mode 418 shown is a vehicle charging process where charging occurs near (or at) the completion of charging or a vehicle departure time. This mode corresponds to field 312 in Fig. 4. If the RESS temperature is below the lowest recommended temperature 420, then active heating of the RESS is activated, and if the RESS temperature is above the highest recommended temperature 422, then active cooling of the RESS is activated. As explained above, passive heating or cooling, if available, can be attempted first before using active heating or cooling. Charging is terminated when the RESS is fully charged. A vehicle departure time can be a time of day when the vehicle is typically unplugged from the charging device and driven. This time of day can be programmed by a user or, if necessary, can be estimated based on past usage times for that particular vehicle.

[0029] It will be noted that the temperature thresholds are different for the three different modes 406, 412, and 418. In the delayed charge mode 406, the RESS temperature is allowed to deviate further from the optimal RESS temperature range—it is undesirable to drain the RESS more than necessary in an attempt to maintain the RESS temperature, and the effectiveness of charging the RESS is irrelevant when no charging is taking place. Therefore, the lowest allowable temperature 408 is lower than the other two modes, and the highest allowable temperature 410 is higher than the other two modes.

[0030] In the third mode 318, when the RESS is nearly full, the maximum charge can be better stored in the RESS because it is closer to the optimal RESS temperature range. Furthermore, the RESS is already at a charge near the maximum range, so maintaining the temperature range more aggressively may be beneficial, even if more power is consumed by the vehicle to maintain this more aggressive temperature range. If the vehicle is just beginning to operate, it may be more beneficial for the RESS to be closer to the optimal RESS temperature range, which may justify the more aggressive RESS temperature targets.

[0031] Fig. Figure 6 illustrates target temperature ranges of a RESS during vehicle operation (e.g., driving the vehicle on a road). The vertical axis is temperature, and the horizontal axis is time. The origin of the axes may be the start of a vehicle driving session. The horizontal phantom lines 430, 432 show the upper and lower temperatures for the optimal temperature range of the RESS. The vertical dashed line represents the change from one driving mode to another.

[0032] The first mode 434 shown is a discharge driving mode in which the vehicle runs at least partially by drawing energy from the RESS. This mode corresponds to field 320 in Fig. 4. If the RESS temperature is below the lowest recommended temperature 436, then active heating of the RESS is activated, and if the RESS temperature is above the highest recommended temperature 438, then active cooling of the RESS is activated. As explained above, passive heating or cooling can be attempted first, if available, before using active heating or cooling.

[0033] The second mode 440 shown is a charge-sustaining driving mode in which the vehicle is running but generally at least retains the energy stored in the RESS. This mode corresponds to field 322 in Fig. 4. If the RESS temperature is below the lowest recommended temperature 442, active heating of the RESS is activated, and if the RESS temperature is above the highest recommended temperature 444, active cooling of the RESS is activated. The maintained temperature ranges vary depending on the vehicle's operating mode.

[0034] Fig. Figure 7 illustrates target temperature ranges of a RESS during vehicle operation (e.g., driving the vehicle on a road). The vertical axis is temperature, and the horizontal axis is time. The origin of the axes may be where the vehicle stops operating and is not plugged in for charging (e.g., when a vehicle is parked in a parking lot with no charging ports available)—a shutdown mode. The horizontal phantom lines 448, 450 show the upper and lower temperatures for the RESS's optimal temperature range. The vertical dashed line represents the change from one shutdown mode to another shutdown mode.

[0035] The first mode 452 shown is a shutdown mode in which the state of charge of the RESS is above a predetermined threshold. This mode corresponds to field 324 in Fig. 4. If the RESS temperature exceeds the highest recommended temperature (454), the RESS's active cooling is activated. Active heating is not used.

[0036] The second mode 456 shown is a shutdown mode in which the state of charge of the RESS is below the predetermined threshold. This mode corresponds to field 326 in Fig. 4. To avoid emptying the RESS, no active or passive heating or cooling is used.

[0037] For the target temperature ranges in Fig. 5 - 7 Adjustments can be made to the temperature ranges based on the ambient temperature, the time of day, and possibly also the season (time of year). For example, if the time of day is late evening, so the temperature naturally cools overnight, the high temperature threshold for active cooling can be raised by a predetermined amount. This amount can be changed based on the current season. The season can, for example, be determined by electronics set by user input, or can be forecast based on measured ambient air temperatures taken over a predetermined period of time. The current ambient temperature can also be used to adjust the temperature ranges, as this temperature can affect the effectiveness of the thermal system in its heating and cooling operations.For example, the RESS radiator is more effective at cooling the coolant when the ambient air temperature is five degrees Celsius than when the ambient air temperature is twenty-five degrees Celsius.

[0038] With reference again to Fig. 3 Once the desired inputs are known (field 200) and the target temperature range is determined (field 202), a determination is made as to whether the coolant temperature in the coolant loop needs to increase, decrease, or remain constant (field 204). The coolant temperature naturally affects the RESS temperature by absorbing heat from or rejecting heat to the RESS as the coolant flows through it. How much heat energy needs to be added to or removed from the RESS, as well as the current coolant temperature, can be used to determine how much heat needs to be added to the coolant to achieve the coolant temperature desired for thermal conditioning the RESS. The means by which the HVAC and RESS heating systems heat or cool the RESS is now determined.

[0039] A determination is made as to whether the RESS temperature is too high, box 206, and if so, a determination is made as to whether passive cooling is desired, box 208. If not, a determination is made as to whether active cooling is desired, box 210. If not, the coolant bypass valve is set to direct coolant through the bypass branch, box 212. In this situation, the coolant pump may also operate during RESS charging or vehicle operation to generate coolant flow through the RESS. In the various operating modes discussed herein, the coolant pump speed may be varied to maintain the instantaneous desired flow rate of coolant through the RESS. This may be varied based on the particular heating or cooling mode being used, as well as other vehicle and RESS conditions.In addition, the speed of the coolant pump can be changed to allow other vehicle systems to mask the noise, vibration, and harshness (NVH) characteristics of the pump or to skip resonance speeds of the pump.

[0040] On the other hand, if active cooling is desired, active cooling begins, block 214. This may involve activating the refrigerant compressor, moving the refrigerant bypass valve to direct the refrigerant through the chiller, and activating the refrigerant pump to pump the refrigerant through the RESS. The refrigerant flowing through the chiller absorbs heat from the coolant flowing through the chiller, with the cooled refrigerant flowing through the RESS to cool it. If less than maximum cooling is required, the bypass valve may be moved to a position where a portion of the refrigerant flows through the bypass branch, or the compressor operation may be altered to reduce the cooling effect of the refrigerant. The desired refrigerant temperature, the current refrigerant temperature, and the ambient temperature may be used as factors in determining control of compressor operation.If a high cooling load is required for the vehicle interior, then adjustments can be made to maintain adequate cooling in the vehicle interior, such as directing a portion of the coolant flow through the bypass branch.

[0041] If passive cooling is desired and available, field 208, then passive cooling is initiated, field 216. For passive cooling, the refrigerant bypass valve directs the refrigerant through the RESS radiator, the fans can be used to draw air through the CRFM, and the refrigerant pump is activated to pump refrigerant through the RESS. While passive cooling mode generally does not cool the refrigerant flowing into the RESS as quickly as active cooling mode, passive cooling mode has a much lower energy consumption rate than active cooling because the refrigerant compressor is not utilized to cool refrigerant for the chiller.

[0042] This method may also use feedback to ensure that thermal changes occur as desired. Therefore, after starting passive cooling, field 216, a check may be performed to determine if active cooling is available (based on energy consumption and vehicle operating conditions), field 218. If not, then passive cooling continues. In this case, the passive cooling performance is then monitored, field 220. The rate of RESS temperature change over time may be monitored and compared to the desired cooling performance. A check is performed to determine if the passive cooling performance is met, field 222. If so, passive cooling continues, field 216. If not, then active cooling may be initiated, field 214.

[0043] Furthermore, if desired, tests can also be used to ensure that active cooling is occurring as intended. This can be done if a fault has been detected in the cooling system. A test can be performed between the inlet and outlet temperatures of the coolant flowing through the radiator to ensure that heat is being dissipated to the refrigerant. If the temperature difference is less than a predetermined minimum value, then passive cooling, if available, or no cooling at all, can be used.

[0044] If the temperature is not too high, field 206, then a determination is made as to whether the RESS temperature is too low, field 230. If not, then no RESS heating or cooling is required, field 232. The coolant bypass valve can be set to direct coolant through the bypass branch, and the pump can be activated for the purpose of ensuring that the RESS temperature remains relatively uniform throughout the RESS.

[0045] If the RESS temperature is too low, then a determination is made as to whether passive heating is desired and available, field 234. If not, then a determination is made as to whether active heating is desired, field 236. If not, then the coolant bypass valve is set to direct coolant through the bypass branch, field 238. In this situation, the coolant pump may also operate during RESS charging or vehicle operation to generate coolant flow through the RESS.

[0046] On the other hand, if active heating is desired, active heating begins, block 240. This may involve activating the electric coolant heater and the coolant pump. The coolant bypass valve directs the coolant through the bypass branch. The coolant flowing through the coolant heater absorbs heat and then flows through the RESS, heating it. The electric heater may be controlled to ensure it operates within an allowable limit based on other electrical requirements of the vehicle at that time.

[0047] If passive heating is desired and available, field 234, then passive heating is initiated, field 242. For passive heating, the coolant bypass valve directs coolant through the RESS radiator, the fans can be used to control airflow through the CRFM, and the coolant pump is activated to pump coolant through the RESS. While passive heating mode generally does not heat the coolant flowing into the RESS as quickly as active heating mode, passive heating mode has a lower energy consumption rate than active heating because the coolant heater is not used to heat the refrigerant.

[0048] In both passive heating and passive cooling, the ability of the RESS radiator to heat or cool the coolant flowing through it can influence whether these passive heating or cooling resources are available at the specific time when heating or cooling of the RESS is required. If these resources are unavailable, active heating or cooling can be used on demand.

[0049] Feedback can be used to ensure that heat changes occur as desired. Therefore, after starting passive heating, field 242, a check can be performed to determine if active heating is available (based on energy consumption and vehicle operating conditions), field 244. If not, then passive heating continues. In this case, the passive heating output is then monitored, field 246. The rate of RESS temperature change over time can be monitored and compared to the desired heating output. A check is performed to determine if the passive heating output is met, field 248. If so, passive heating continues, field 242. If not, then active heating is initiated, field 240.

[0050] The thermal management controls for the vehicle may include a wake-up function to thermally condition the RESS when needed when the vehicle is off, whether plugged in and charging or unplugged (shutdown mode). The elapsed time before a wake-up occurs may be based on the then-current RESS temperature and ambient temperature at which the vehicle enters the sleep state (i.e., the vehicle shuts down because it is no longer in an operational mode). Time of day may also be a factor in determining the wait time before the wake-up occurs. The wake-up function may also be canceled or reset when a vehicle start, charging or wake-up initiates, and thermal conditioning initiates.The purpose of setting the time is to predict, based on environmental and other conditions, when the RESS may have exceeded its allowable temperature range and then wake up the vehicle systems sufficiently to thermally condition the RESS to bring the RESS temperature back into a desired range.

[0051] The Fig. 5 and Fig.The target temperature ranges explained in section 7 can be used during the wake-up process. During wake-up, a determination is made as to whether thermal conditioning of the RESS is required. If necessary, the coolant is thermally conditioned while pumped through the RESS to return the RESS temperature to the desired range. After the wake-up process, the thermal conditioning components are shut down again, and a new wake-up time can be set based on the updated RESS temperature and ambient temperature at the end of the wake-up process.

Claims

[1] A method for operating a RESS thermal system (12) in a vehicle (10) having a coolant circuit (16) for conducting a coolant through a rechargeable energy storage system (RESS) (44) and a refrigerant circuit (14) configured to selectively cool the coolant flowing through a radiator (38) in the coolant circuit (16), the method comprising the following steps: (a) determining a current target temperature range for the RESS (44) based on at least one current vehicle operating mode and a current ambient temperature, wherein the target temperature range is variable based on the current vehicle operating mode and the current ambient temperature; (b) determining a temperature of the RESS (44); (c) determining whether the temperature of the RESS (44) needs to increase or decrease to be within the current target temperature range; (d) if it is determined that the temperature of the RESS (44) needs to increase, determining whether to use active heating or passive heating of the coolant, wherein active heating uses a greater amount of energy over a shorter period of time than passive heating; (e) activating the active heating or passive heating of the coolant determined by step (d); (f) if it is determined that the temperature of the RESS (44) needs to decrease, determining whether to use active cooling or passive cooling of the coolant, wherein active cooling uses a greater amount of energy over a shorter period of time than passive cooling; and (g) activating the active cooling or passive cooling of the coolant determined by step (f), characterized by , that when passive cooling is activated in step (g), the rate of change of the coolant temperature over time is monitored and compared with a desired passive cooling performance, and switching from passive cooling to active cooling occurs when the rate of change of the coolant temperature is below a predetermined threshold and the desired passive cooling performance is not achieved, and when passive heating is activated in step (e), the rate of change of the coolant temperature over time is monitored and compared with a desired passive heating output, and switching from passive heating to active heating occurs when the rate of change of the coolant temperature is below the predetermined threshold and the desired passive heating output is not achieved. [2] The method of claim 1, wherein steps (f) and (g) are further defined by the active cooling comprising operating a refrigerant compressor (18) and passing the cooled refrigerant through the radiator (38) through which the coolant is passed, and the passive cooling comprising passing the coolant through a RESS radiator (52) and passing airflow through the RESS radiator (52) to absorb heat from the coolant. [3] The method of claim 1, wherein steps (d) and (e) are further defined by the active heating comprising operating an electric coolant heater (46) to heat the coolant shortly before flowing through the RESS (44), and wherein the passive heating comprises passing the coolant through a RESS radiator (52) and passing airflow through the RESS radiator (52) to add heat to the coolant. [4] The method of claim 1, wherein step (a) is further determined by adjusting the current temperature range based on the time of day at which the target temperature range is determined. [5] The method of claim 1, wherein step (a) is further determined by the current vehicle operating mode comprising a delayed charge mode, a vehicle charge mode, or a charge termination mode, and wherein the current target temperature range is different for each of the modes. [6] The method of claim 1, wherein step (a) is further determined by the current vehicle operating mode comprising a discharge driving mode or a charge maintenance driving mode, and wherein the current target temperature range is different for each of the modes. [7] The method of claim 1, further comprising: (f) switching off the vehicle (10); (g) Determine the RESS temperature at shutdown; (h) determining an ambient temperature at shutdown; (i) determining a waiting period after shutdown until the RESS thermal system (12) is awakened and, if necessary, providing heating and cooling of the RESS battery (44) based at least on the determined RESS temperature and the ambient temperature at shutdown; and (j) waking the RESS thermal system (12) after the predetermined period of time.

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