Control method for electric vehicles and control device for electric vehicles

Abstract

The system appropriately determines whether or not it is necessary to suppress the rise in battery temperature, and only performs the necessary actions to suppress the temperature rise if it is deemed necessary. [Solution] A control method for an electric vehicle that runs by driving an electric motor with power supplied from a battery, wherein the controller estimates the actual total weight of the electric vehicle, detects the battery temperature, and if the actual total weight of the electric vehicle exceeds a predetermined weight and the battery temperature exceeds a predetermined temperature, estimates the amount of heat generated by the battery during travel to the destination, estimates the amount of battery cooling by the battery cooling device, limits the battery output if the amount of heat generated by the battery is greater than the amount of heat generated by the battery, and does not limit the battery output if the amount of heat generated by the battery is greater than the amount of heat generated by the battery.

Description

[[Technical Field]]

[0001] The present invention relates to a control method for an electric vehicle and a control apparatus for an electric vehicle. [[Background Art]]

[0002] As a control method for an electric vehicle, Patent Document 1 discloses a method that increases the cooling capacity of a cooling device for cooling a battery when the electric vehicle is towing another vehicle (during towing), compared to when the electric vehicle is not towing another vehicle (during non-towing). During towing, the driving load increases compared to during non-towing, so the load on the battery increases and the battery temperature tends to rise. However, as in the control described in the above document, increasing the cooling capacity of the cooling device during towing compared to during non-towing can suppress the temperature rise of the battery. In order to increase the cooling capacity, the operation start temperature of the cooling fan is lowered, and the air volume of the cooling fan under the same conditions is increased. [[Prior Art Literature]] [[Patent Literature]]

[0003] [[Patent Document 1]] Japanese Unexamined Patent Application Publication No. 2021-083217 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0004] In the control described in the above document, the cooling capacity is increased during towing compared to during non-towing, but there are cases where there is no need to increase the cooling capacity even during towing. For example, when the proportion of downhill slopes in the travel route is high, the driving load does not increase to an extent that requires an increase in cooling capacity. That is, in the control described in the above document, the cooling capacity is increased even when there is no need to increase the cooling capacity. For this reason, for example, the operating noise of the cooling fan increases in order to increase the cooling capacity, which may cause discomfort to the occupants.

[0005] Therefore, the present invention aims to provide a control system that appropriately determines whether or not it is necessary to suppress the temperature rise of the battery, and only performs processing to suppress the temperature rise if it is necessary. [Means for solving the problem]

[0006] According to one aspect of the present invention, a control method is provided for an electric vehicle that runs by driving an electric motor with power supplied from a battery. In this control method, the controller estimates the actual total weight of the electric vehicle, which is the total weight of the electric vehicle, detects the battery temperature, and if the actual total weight of the vehicle exceeds a predetermined weight and the battery temperature exceeds a predetermined temperature, estimates the amount of heat generated by the battery during travel to the destination, estimates the amount of battery cooling by the battery cooling device, limits the battery output if the amount of heat generated by the battery is greater than the amount of cooling by the battery, and does not limit the battery output if the amount of cooling by the battery is greater than the amount of heat generated by the battery. [Effects of the Invention]

[0007] According to the above embodiment, it is possible to provide control that appropriately determines whether or not it is necessary to suppress the temperature rise of the battery, and only performs processing to suppress the temperature rise if it is necessary. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a block diagram showing the schematic configuration of the cooling system for an electric vehicle. [Figure 2] Figure 2 is a graph showing an example of refrigerant flow rate distribution. [Figure 3] Figure 3 shows an example of a time chart when an electric vehicle is towed uphill and control is implemented to suppress the rise in battery temperature by limiting the vehicle speed. [Figure 4] Figure 4 is a block diagram showing the schematic configuration of the controller. [Figure 5] Figure 5 is a flowchart showing the control routine that the controller performs to suppress the rise in battery temperature. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the drawings.

[0010] Figure 1 is a block diagram showing the schematic configuration of the cooling system 10 of an electric vehicle to which this embodiment is applied.

[0011] The electric vehicle runs by driving the electric motor 16 (see Figure 4) with power supplied from the battery. In this embodiment, a so-called BEV (Battery Electric Vehicle) equipped only with an electric motor 16 as the drive source is used as an example, but it is not limited to this, and can also be applied to so-called HEV (Hybrid Electric Vehicle) and PHEV (Prug-in Hybrid Electric Vehicle) equipped with an internal combustion engine in addition to the electric motor 16 as a drive source. Furthermore, the battery can be any type commonly used in electric vehicles, for example, a lithium-ion battery.

[0012] The cooling system 10 has a configuration in which a battery cooling device 2 for cooling the battery and a cabin cooling device 3 for cooling the cabin where the occupants sit are connected in parallel to a compressor 1 that circulates the refrigerant. Although not shown in Figure 1, a condenser, receiver tank, and expansion valve, similar to those in a typical automotive air conditioning system, are provided between the compressor 1 and the flow control valve 4, and the refrigerant pumped from the compressor 1 is cooled by passing through these. The cabin cooling device 3 also includes an evaporator and a blower fan (neither of which are shown), similar to those in a typical automotive air conditioning system.

[0013] When the refrigerant flow path from compressor 1 to battery cooling system 2 is designated as the first flow path A, and the refrigerant flow path from compressor 1 to cabin cooling system 3 is designated as the second flow path B, a flow rate adjustment valve 4 is provided at the branching point between the first flow path A and the second flow path B. The controller 5 determines the distribution of the refrigerant flow rate supplied to the battery cooling system 2 and the refrigerant flow rate supplied to the cabin cooling system 3 based on the outside temperature and the cabin set temperature set by the occupant, and controls the flow rate adjustment valve 4 based on this distribution. In addition to, or instead of, the flow rate adjustment valve 4 may be provided at the junction of the first flow path A and the second flow path B.

[0014] Figure 2 is a graph showing an example of the refrigerant flow rate distribution described above. The vertical axis represents the refrigerant flow rate ratio, and the areas for "cabin cooling" and "battery cooling" each represent the amount of cooling. Here, the cases of ambient temperature T1 and ambient temperature T2 are shown. Ambient temperature T1 is set to a temperature at which the cooling capacity of the cooling system 10 must be maximized in order to achieve the cabin set temperature. The cabin set temperature here refers to the temperature set by the occupant via the air conditioning system interface. Ambient temperature T2 is set to a temperature lower than ambient temperature T1, at which the cabin set temperature can be achieved by utilizing only a portion of the cooling capacity of the cooling system 10.

[0015] When the ambient temperature is T1, the difference between the ambient temperature and the cabin set temperature is large, so it is necessary to increase the refrigerant flow rate to the cabin cooling system 3 in order to achieve the cabin set temperature. As a result, the refrigerant flow rate to the battery cooling system 2 becomes relatively small. In other words, the higher the ambient temperature, the less refrigerant flow is allocated to the battery cooling system 2, and there is a risk that the battery will not be cooled sufficiently.

[0016] On the other hand, when the ambient temperature is T2, there is a margin in the cooling capacity of the cooling system 10 relative to the cabin set temperature, so the distribution of refrigerant flow rate to the battery cooling device 2 can be increased compared to when the ambient temperature is T1.

[0017] Next, we will discuss battery temperature management.

[0018] A battery generates heat when discharging, and the greater the power supplied from the battery to an electrical load (hereinafter also referred to as battery output), the greater the amount of heat generated. Therefore, when an electric vehicle is traveling, temperature control is required to avoid the occurrence of thermal runaway of the battery. Providing a device such as the cooling system 10 can suppress an increase in battery temperature. However, when the traveling load is large, for example, when traveling up an uphill slope while towing, there is a risk that the battery temperature will reach the upper limit temperature. To address such cases, for example, a method is known in which the battery temperature at which thermal runaway of the battery may occur is previously examined through experiments or the like, this temperature is set as the upper limit temperature, and when the battery temperature approaches the upper limit temperature, an increase in the battery temperature is suppressed by limiting the vehicle speed and acceleration.

[0019] FIG. 3 is an example of a time chart when control for suppressing an increase in battery temperature by vehicle speed limitation is executed in a traveling scene where an electric vehicle including the cooling system 10 travels up an uphill slope while towing. In the drawing, as a comparative example, a chart when control for suppressing an increase in battery temperature is not executed is indicated by a broken line. In the vehicle speed chart, Vlim is the speed limit, in the battery temperature chart, Tlim is the upper limit temperature, and Tth is a temperature threshold serving as a predetermined temperature. The temperature threshold Tth is a temperature that can be arbitrarily set within a range lower than the upper limit temperature. However, the higher the temperature threshold Tth, the less margin there is before reaching the upper limit temperature, which necessitates stricter limitation of vehicle speed and the like, while the lower the temperature threshold Tth, the easier it is for vehicle speed and the like to be limited, which may lead to unnecessary degradation of drivability. Therefore, it is preferable to set the temperature threshold Tth in consideration of the heat capacity of the battery, the output of the electric motor, the cooling capacity of the cooling system 10, and the balance between suppression of increase in battery temperature and reduction in drivability.

[0020] For example, it is set in consideration of the heat capacity of the battery, the cooling capacity of the cooling system 10, and degradation of drivability caused by the above limitation.

[0021] When the battery temperature rises to the temperature threshold Tth at timing t1 during traveling, the vehicle speed starts to decrease as vehicle speed limitation is started. Then, after timing t2 when the vehicle speed V has decreased to the limited vehicle speed Vlim, the vehicle travels at the limited vehicle speed Vlim. Accordingly, an increase in the battery temperature after timing t1 is suppressed compared to a case where the vehicle continues traveling without vehicle speed limitation.

[0022] As described above, imposing vehicle speed limitation after the battery temperature reaches the temperature threshold Tth is effective for suppressing an increase in the battery temperature. However, if vehicle speed limitation is performed on the condition only that the battery temperature has reached the temperature threshold Tth, vehicle speed limitation will be activated even in traveling scenes where vehicle speed limitation is unnecessary, which may cause the occupants to feel dissatisfied with the driving performance. For example, if the traveling route after timing t1 in FIG. 3 is a flat road or a downhill road, there is a possibility that the battery temperature will not rise to the upper limit temperature Tlim even if vehicle speed limitation is not performed. Further, for example, even when the outside air temperature is low and the cooling capacity of the battery cooling device 2 has a margin, there is a possibility that vehicle speed limitation becomes unnecessary. On the other hand, it is necessary to avoid the occurrence of thermal runaway caused by not performing vehicle speed limitation in traveling scenes where vehicle speed limitation is required to suppress an increase in battery temperature.

[0023] Therefore, in the present embodiment, it is determined whether processing for suppressing an increase in battery temperature is necessary, and processing for suppressing an increase in battery temperature is performed only when it is determined to be necessary. This processing will be specifically described below.

[0024] FIG. 4 is a block diagram showing a schematic configuration of a controller 5 that controls an electric vehicle.

[0025] The controller 5 includes a battery temperature detection unit 5A, a heat generation amount estimation unit 5B, a cooling amount estimation unit 5C, a weight estimation unit 5D, and an output limitation unit 5E. Note that all of these mean functional configurations, and do not mean physical configurations.

[0026] The battery temperature detection unit 5A detects the battery temperature based on the detection signal input from the battery temperature sensor 11. Alternatively, instead of using the detection signal from the battery temperature sensor 11, the battery temperature may be estimated by calculation from the integrated value of the battery current.

[0027] The heat generation estimation unit 5B estimates the amount of heat generated by the battery ahead based on information obtained from the in-vehicle navigation system 12. For example, it first estimates the driving load along the route to the target location based on information such as the vehicle's current position, the target location, the driving route to the target location, the road gradient of the driving route, and the speed limit. Then, it estimates the amount of heat generated by the battery based on this driving load and the actual total vehicle weight, which will be described later.

[0028] The cooling amount estimation unit 5C estimates the cooling amount (heat exchange amount) of the battery cooling device 2 based on information obtained from the outside temperature sensor 13 and the air conditioning controller 14. For example, it calculates the distribution of refrigerant flow rate to the battery cooling device 2 and the refrigerant flow rate to the cabin cooling device 3 from the outside temperature and the cabin set temperature, and estimates the cooling amount of the battery cooling device 2 based on this distribution.

[0029] The weight estimation unit 5D estimates the actual total vehicle weight Wtotal based on information obtained from the acceleration sensor 15 and information stored in the controller 5. For example, it estimates the actual total vehicle weight m from the relationship between output and acceleration (F = Wtotal × a) using the acceleration a during the most recent acceleration and the driving force F during that acceleration. The actual total vehicle weight refers to the actual total weight of the vehicle, which is the weight of the vehicle itself plus the weight of the occupants and cargo, and also includes the weight of the towed object if the vehicle is being towed.

[0030] The output limiting unit 5E acquires the battery temperature and each estimated value mentioned above, and determines whether or not it is necessary to perform processing to suppress the battery temperature based on these. If it determines that it is necessary, it limits the battery output to control the electric motor 16. The specific method of determination will be described later. As for methods of limiting the battery output, there is a method of limiting the battery current value, but it is not limited to this. For example, a limit may be set on the target output of the electric motor, or on the target vehicle speed and target acceleration. This is because, as a result, the battery current value is limited and the battery output is limited.

[0031] Next, we will describe specific control examples for suppressing the rise in battery temperature.

[0032] Figure 5 is a flowchart showing the control routine executed by the controller 5.

[0033] In step S100, the battery temperature Tbat is detected. Specifically, the battery temperature detection unit 5A detects it.

[0034] In step S110, the output limiting unit 5E determines whether the battery temperature Tbat is higher than the temperature threshold Tth. If it is higher, it executes the process in step S120. If it is not higher, it decides in step S180 not to limit the battery output and terminates this routine.

[0035] In step S120, the actual vehicle gross weight Wtotal is estimated. Specifically, the weight estimation unit 5D performs the estimation.

[0036] In step S130, the output limiting unit 5E determines whether the actual total vehicle weight Wtotal is heavier than the weight threshold Wth. If it is heavier, it executes the process in step H S140; otherwise, it executes the process in step S180 described above and terminates the routine. The weight threshold Wth is a value that can be arbitrarily set within a range equal to or greater than the total vehicle weight (which is the weight of the vehicle plus the weight of the maximum number of passengers; if a maximum load capacity is set for the vehicle, the maximum load capacity is also added). However, as the weight threshold Wth increases, it becomes more difficult to limit the battery output, which may make it harder to suppress the rise in battery temperature. Conversely, as it decreases, it becomes easier to limit the battery output, which may lead to a decrease in drivability. Therefore, it is preferable to set the weight threshold Wth considering the balance between suppressing the rise in battery temperature and the decrease in drivability, in addition to the heat capacity of the battery, the output of the electric motor, and the cooling capacity of the cooling system 10.

[0037] In step S140, the amount of battery heat generated during the journey to the destination is estimated. Specifically, this is done by the heat generation estimation unit 5B.

[0038] In step S150, the battery cooling amount is estimated. Specifically, the cooling amount estimation unit 5C performs the estimation.

[0039] In step S160, the output limiting unit 5E determines whether the battery cooling amount is insufficient. If it is insufficient, it decides to limit the battery output in step S170 and terminates the routine. If it is not insufficient, it executes the process in step S180 and terminates the routine. Whether the battery cooling amount is insufficient is determined, for example, by calculating the amount of battery cooling necessary to suppress the rise in battery temperature (required battery cooling amount) based on the battery heat generation amount estimated in step S140, and comparing the battery cooling amount estimated in step S150 with the required battery cooling amount.

[0040] In step S170, the battery output is limited by keeping the battery current below a certain limit. This limit may be a pre-set fixed value, or it may vary depending on the difference between the battery's heat generation and its cooling capacity. Alternatively, the battery output may be limited by imposing restrictions on vehicle speed and acceleration.

[0041] Furthermore, before starting the battery output restriction in step S170, the processes in steps S100 to S160 may be repeated for a predetermined time, and if the result of the determination in step S110, S130, or S160 changes during this time, the battery output restriction may be avoided. In this way, by introducing a delay time between the fulfillment of the conditions for restricting battery output and the start of the restriction, unnecessary restriction of battery output can be avoided.

[0042] According to the control routine described above, the battery output will not be limited simply because the battery temperature Tbat reaches the temperature threshold Tth and the driving load is high, such as during toe-in, when the vehicle is fully loaded with passengers heavier than the assumed weight used to calculate the gross vehicle weight, or when the cargo area is fully loaded. In addition to the above, the battery output will not be limited unless the battery cooling amount is insufficient to meet the conditions for the amount of heat generated by the battery during future driving.

[0043] This eliminates the limitation of battery output in driving situations where it is not necessary. In other words, it prevents unnecessary restrictions on vehicle speed and acceleration, which can worsen drivability.

[0044] Furthermore, the closer the temperature at which battery output limitation begins is to the upper limit temperature, the more severely the battery output limitation needs to be imposed to suppress the rise in battery temperature. However, by appropriately setting the temperature threshold Tth, the rise in battery temperature can be suppressed without significantly limiting battery output. In other words, since vehicle speed and acceleration are not significantly restricted, the decrease in drivability associated with suppressing the rise in battery temperature can be suppressed.

[0045] Furthermore, according to the control routine described above, even if the battery output limiting is initiated, the battery output limiting is released when the result of the determination in step S110, S130, or S160 changes. This prevents unnecessary restrictions on vehicle speed and acceleration.

[0046] In this embodiment, a control method for an electric vehicle that runs by driving an electric motor 16 with power supplied from a battery is provided. In this control method, the controller 5 estimates the actual total weight of the electric vehicle, the battery temperature, and if the actual total weight of the electric vehicle exceeds a weight threshold (predetermined weight) and the battery temperature exceeds a temperature threshold (predetermined temperature), it estimates the amount of heat generated by the battery during travel to the destination, estimates the amount of battery cooling by the battery cooling device, and limits the battery output if the amount of heat generated by the battery is greater than the amount of battery cooling. If the amount of battery cooling is greater than the amount of heat generated by the battery, the battery output is not limited. As a result, control to suppress the rise in battery temperature is performed only when it is truly necessary, thereby suppressing the deterioration of drivability due to speed restrictions, etc., and the resulting dissatisfaction of the occupants.

[0047] In this embodiment, the controller 5 sets a delay time before starting to limit the battery output when it determines that the amount of heat generated by the battery is greater than the amount of heat generated by the battery. If the conditions for limiting the battery output are maintained until the delay time has elapsed, the limiting of the battery output is started. If the conditions for limiting the battery output are no longer met before the delay time has elapsed, the battery output is not limited. As a result, for example, if the battery temperature falls below the temperature threshold Tth immediately after it is determined that the amount of heat generated by the battery is greater than the amount of heat generated by the battery, the battery output will not be limited. This prevents unnecessary limiting of the battery output.

[0048] In this embodiment, the controller 5 releases the battery output restriction once the conditions for limiting the battery output are no longer met, after initiating the restriction. This prevents unnecessary restriction of the battery output.

[0049] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments. [Explanation of Symbols]

[0050] 1. Compressor, 2. Battery cooling system, 3. Cabin cooling system, 4. Flow control valve, 5. Controller, 10. Cooling system

Claims

1. In a control method for an electric vehicle that runs by driving an electric motor with power supplied from a battery, The controller is We estimate the actual total weight of the electric vehicle, which is the total weight of the vehicle. It detects the battery temperature, If the actual vehicle's total weight exceeds a predetermined weight and the battery temperature exceeds a predetermined temperature, To estimate the amount of battery heat generated during the journey to the destination, The amount of battery cooling by the battery cooling device is estimated, If the amount of heat generated by the battery is greater than the amount of cooling the battery, the battery output is limited. A control method for an electric vehicle, characterized in that the battery output is not limited when the battery cooling amount is greater than the battery heat generation amount.

2. In the electric vehicle control method described in claim 1, The controller, when it determines that the amount of heat generated by the battery is greater than the amount of heat generated by the battery, sets a delay time before starting to limit the battery output. If the conditions for limiting the battery output are maintained until the aforementioned delay time has elapsed, the limiting of the battery output will be initiated. A control method for an electric vehicle, wherein if the conditions for limiting the battery output are no longer met before the aforementioned delay time has elapsed, the battery output is not limited.

3. In the electric vehicle control method described in claim 1, A control method for an electric vehicle, wherein the controller releases the battery output restriction after initiating the restriction, once the conditions for restricting the battery output are no longer met.

4. In a control device for an electric vehicle that drives an electric motor using power supplied from a battery, A weight estimation unit that estimates the actual total weight of the electric vehicle, and A battery temperature detection unit that detects the battery temperature, A heat generation estimation unit that estimates the amount of heat generated by the battery while driving to the destination, A cooling amount estimation unit that estimates the amount of battery cooling by the battery cooling device, If the actual vehicle's total weight exceeds a predetermined weight and the battery temperature exceeds a predetermined temperature, If the amount of heat generated by the battery is greater than the amount of cooling the battery, the battery output is limited. An output limiting unit that does not limit the battery output if the battery cooling amount is greater than the battery heat generation amount, A control device for electric vehicles, characterized by comprising the following:

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