Method for controlling electric vehicle

Abstract

To provide a method for controlling an electric vehicle that can secure a sufficient electrical power receiving margin of a main battery.SOLUTION: A method for controlling an electric vehicle 10 for performing regeneration braking that obtains vehicle braking force by generating regenerative power and charging power-generating electrical power to a main battery 20 includes the steps of: cooling the main battery 20 in accordance with the temperature of the main battery 20; and, when the main battery 20 has a charging rate Cd that is more than a specified reference charging rate C*, changing an execution condition of the cooling 20 so as to increase electrical power consumption that is necessary for cooling the main battery 20 as compared to that when the charging rate is less than the reference charging rate C*.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] This specification discloses a method for controlling an electric vehicle that performs regenerative braking. [Background technology]

[0002] Regenerative braking is a technology that operates the motor generator as a generator to generate regenerative power when a braking request is made from the vehicle, and uses the regenerative resistance generated at this time as braking force for the vehicle. Electrically-powered vehicles (e.g., hybrid electric vehicles, electric vehicles, etc.) are usually equipped with such regenerative brakes.

[0003] Here, the regeneratively generated electric power is charged into the main battery, so when the SOC of the main battery is high and there is no room for accepting electric power, it is difficult to operate the regenerative brake.

[0004] Patent Document 1 discloses a technique for temporarily discharging battery power to a load means when it is difficult to operate the regenerative brake, thereby instantaneously increasing or decreasing the torque of the motor generator. According to this technique, the vehicle vibrates as the torque increases or decreases, thereby informing the user that it is difficult to operate the regenerative brake. In this case, the user operates the brake pedal or the like to obtain braking force. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2022-001000 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the technology described in Patent Document 1 only notifies the user of whether regenerative braking is enabled or disabled, and does not ensure sufficient room for the main battery to receive power required for regenerative braking. Therefore, this specification discloses a method for controlling an electric vehicle that can ensure sufficient room for the main battery to receive power. [Means for solving the problem]

[0007] The control method for an electric vehicle disclosed in this specification is a control method for an electric vehicle that performs regenerative braking to obtain braking force for the vehicle by generating power regeneratively and charging the generated power to a main battery, and is characterized in that the main battery is cooled in accordance with a temperature of the main battery, and when the charging rate of the main battery is equal to or higher than a specified reference charging rate, the execution conditions of the cooling are changed so that more power is required to cool the main battery than when the charging rate is less than the reference charging rate. Effect of the Invention

[0008] According to the technology disclosed in this specification, when the charging rate is high, power consumption is likely to increase, so it is possible to ensure sufficient room for the main battery to accept power. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a configuration of an electric vehicle. [Diagram 2] FIG. 11 is a diagram showing an example of a threshold profile for cooling a main battery. [Diagram 3] 4 is a flowchart showing a flow of cooling control of the main battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, a method for controlling an electric vehicle will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of an electric vehicle 10 equipped with a regenerative braking function. The electric vehicle 10 is a vehicle having a motor generator 14 as one of its power sources, and is, for example, a hybrid electric vehicle, a battery electric vehicle, a fuel cell vehicle, or the like. The motor generator 14 is mechanically connected to driving wheels 12. The motor generator 14 functions as an electric motor that outputs running power for driving the driving wheels 12 using electric power supplied from a main battery 20.

[0011] The motor generator 14 also functions as a generator that generates electric power using power supplied from the drive wheels 12. When the motor generator 14 functions as a generator, the regenerative resistance acts as a braking force on the drive wheels 12, causing the electric vehicle 10 to decelerate. The braking force thus generated by the power generation of the motor generator 14 is regenerative braking. The generated electric power resulting from the operation of the regenerative braking is charged to the main battery 20.

[0012] The PCU 16 is a power control device configured to be able to control input and output of power between the main battery 20 and a power load. The power load is an electric device that uses the power of the main battery 20, and includes the motor generator 14 described above and a water pump 28 described below. Although not shown, the PCU 16 includes a variety of devices. For example, the PCU 16 includes a system main relay (SMR) that can cut off an electrical connection between the main battery 20 and the power load. The PCU 16 also includes a converter that converts power from AC to DC or DC to AC between the main battery 20 and the motor generator 14, a transformer that converts voltage, and the like. The PCU 16 is electrically connected to the ECU 18, and the operation of the PCU 16 is controlled by the ECU 18.

[0013] The main battery 20 is a secondary battery that supplies power for powering the motor generator 14 and stores the power obtained by regeneration of the motor generator 14. The main battery 20 is formed, for example, by electrically connecting a plurality of unit battery cells. An example of the unit battery cell is a lithium ion battery cell.

[0014] The main battery 20 is equipped with sensors (neither shown) for detecting the charging rate Cd and temperature Tb of the main battery 20. The charging rate Cd indicates the ratio between the current charging amount of the main battery 20 and the fully charged amount, and is a parameter usually called SOC (State Of Charge). The ECU 18 controls the input and output of power to the main battery 20 and switches the operation of the power load so that the charging rate Cd does not become too high or too low. The ECU 18 also controls the operation of a battery cooling circuit 26 (described later) so that the temperature Tb of the main battery 20 (hereinafter referred to as "battery temperature Tb") does not become too high or too low.

[0015] The electric vehicle 10 is further provided with a battery cooling circuit 26 and an air conditioning circuit 32. The air conditioning circuit 32 is a circuit that circulates a refrigerant to condition the interior of the vehicle. The air conditioning circuit 32 has a flow path through which the refrigerant flows. The flow path is provided with a compressor 34 that pressurizes the refrigerant, a condenser 36 that exchanges heat between the refrigerant and outside air, an evaporator 38 that vaporizes the refrigerant, an expansion valve (not shown) that expands the refrigerant, a switching valve (not shown) that switches the refrigerant path, and the like. Since the air conditioning circuit 32 is a known technology, a detailed description is omitted. The flow path of the air conditioning circuit 32 is further provided with a chiller 30. The chiller 30 is a heat exchanger that exchanges heat between the refrigerant for air conditioning and the cooling water flowing through the battery cooling circuit 26, thereby cooling the cooling water.

[0016] The battery cooling circuit 26 is a circuit that circulates coolant for cooling the main battery 20. The flow path of the battery cooling circuit 26 passes through the main battery 20 and the chiller 30. In addition, a water pump 28 for pumping the coolant is provided in the flow path of the battery cooling circuit 26. The air conditioning circuit 32 and the battery cooling circuit 26 are driven in cooperation to cool the main battery 20. Specifically, when cooling the main battery 20, the water pump 28 is driven to circulate the coolant. In addition, each part of the air conditioning circuit 32 is driven so that the air conditioning refrigerant circulates through the chiller 30, the compressor 34, and the condenser 36. The amount of cooling of the main battery 20 is changed by adjusting the flow rate of the water pump 28, the amount of pressurization of the refrigerant by the compressor 34, and the like.

[0017] The ECU 18 is physically a computer equipped with a processor and a memory. The ECU 18 controls the operation of each part of the electric vehicle 10. For example, when there is a request to brake the vehicle, the ECU 18 controls the PCU 16 to operate the regenerative brake. The ECU 18 also controls the input / output of the main battery 20 according to the charging rate Cd of the main battery 20, and controls the cooling mechanism of the main battery 20 (in this example, the battery cooling circuit 26 and the air conditioning circuit 32) according to the battery temperature Tb.

[0018] Incidentally, when regenerative braking is to be performed on such an electric vehicle 10, it is of course necessary to generate regenerative power by the motor generator 14. The power generated by regenerative power generation is charged to the main battery 20. Therefore, when the charging rate Cd of the main battery 20 is high and the main battery 20 has no room to accept the generated power, regenerative power generation by the motor generator 14 cannot be performed and the regenerative brake cannot be operated. In this case, the user needs to use a foot brake or the like instead of the regenerative brake.

[0019] In this example, in order to more reliably ensure opportunities to utilize such regenerative braking, when the charging rate Cd of the main battery 20 is high, the execution condition temperature of cooling is changed so that the power consumption required for cooling the main battery 20 increases. This will be described with reference to FIG. 2. FIG. 2 is a diagram showing a normal threshold profile 50a and a special threshold profile 50b.

[0020] Since the main battery 20 deteriorates when it becomes excessively hot, the ECU 18 cools the main battery 20 according to the battery temperature Tb. This cooling is usually performed according to the normal threshold profile 50a indicated by the solid line in FIG. 2. The normal threshold profile 50a is a profile showing the correlation between the battery temperature Tb and the cooling capacity. In the case of FIG. 2, the horizontal axis represents the battery temperature Tb, and the vertical axis represents the cooling capacity. In the example of FIG. 2, the cooling capacity has three levels from level 1 to level 3, and the higher the level, the higher the cooling capacity and the power consumption. In the example of FIG. 2, cooling is started when the battery temperature Tb becomes T4 or higher. Also, when T4 ≤ Tb < T5, cooling is performed at level 1, when T5 ≤ Tb < T6, cooling is performed at level 2, and when T6 ≤ Tb, cooling is performed at level 3. Note that T4 < T5 < T6.

[0021] Normally, the ECU 18 compares the battery temperature Tb detected by the sensor with this normal threshold profile 50a, and determines whether cooling of the main battery 20 is necessary and the level when cooling is necessary. Then, the ECU 18 drives the cooling mechanism of the main battery 20 (in this example, the battery cooling circuit 26 and the air conditioning circuit 32) according to the determined conditions.

[0022] Here, as described above, when the charge rate Cd of the main battery 20 is high, the regenerative brake cannot be properly utilized. Therefore, when the charge rate Cd of the main battery 20 is equal to or higher than a pre-specified reference charge rate C*, the ECU 18 cools the main battery 20 based on a special threshold profile 50b instead of the normal threshold profile 50a. The line indicated by the dashed line in FIG. 2 is the special threshold profile 50b. As is clear from FIG. 2, the special threshold profile 50b is a profile in which the threshold temperature at which cooling starts and the threshold temperature at which the cooling level is increased are lower than those of the normal threshold profile 50a. That is, in the case of the special threshold profile 50b, cooling starts when T1 ≤ Tb, cooling is performed at level 1 when T1 ≤ Tb < T2, cooling is performed at level 2 when T2 ≤ Tb < T3, and cooling is performed at level 3 when T3 ≤ Tb (where T1 < T2 < T3 < T4).

[0023] By cooling the main battery 20 based on such a special threshold profile 50b, the opportunity to cool the main battery 20 increases and the power consumption required for the cooling increases compared to the case of using the normal threshold profile 50a. As a result, the charge rate Cd of the main battery 20 decreases, and the opportunity for regenerative charging, and thus the opportunity to utilize the regenerative brake, increases.

[0024] The value of the reference charging rate C* as a reference for threshold profile switching is not particularly limited. For example, the charging rate Cd at which regenerative braking is prohibited may be set as the reference charging rate C*. The reference charging rate C* may be a fixed value that is invariable or may be a variable value that changes according to the driving conditions. The reference charging rate C* may have a predetermined hysteresis. That is, an increasing reference charging rate C*up and a decreasing reference charging rate C*dn may be set as the reference charging rate C* (C*up>C*dn). When the charging rate Cd crosses the increasing reference charging rate C*up during the increasing process, the profile may be switched to the special threshold profile 50b. When the charging rate Cd crosses the decreasing reference charging rate C*dn during the decreasing process, the profile may be switched to the decreasing reference charging rate C*dn. In any case, by changing the cooling conditions of the main battery 20 according to the charging rate Cd, the opportunity to use the regenerative brake can be more reliably secured.

[0025] 3 is a flowchart showing the flow of cooling control of the main battery 20. When the vehicle system is started, the ECU 18 compares the charging rate Cd of the main battery 20 with the reference charging rate C* (S10). If the comparison result shows that the charging rate Cd is less than the reference charging rate C*, the main battery 20 selects the normal threshold profile 50a and controls the cooling of the main battery 20 based on the normal threshold profile 50a (S12, S16). On the other hand, if the charging rate Cd is equal to or greater than the reference charging rate C*, the main battery 20 selects the special threshold profile 50b and controls the cooling of the main battery 20 based on the special threshold profile 50b (S14, S16). Thereafter, the same process is repeated until the vehicle system is shut down.

[0026] As is clear from the above description, according to the technology disclosed in this specification, when the charging rate Cd of the main battery 20 is high, the power consumption required to cool the main battery 20 is likely to increase. As a result, there is room for the main battery 20 to accept electric power, so that opportunities to use regenerative braking can be more reliably secured.

[0027] The configuration described above is an example, and other configurations may be changed as long as the configuration described in claim 1 is included. For example, in the above description, a water-cooling mechanism is exemplified as the cooling mechanism of the main battery 20. However, the cooling mechanism of the main battery 20 may be an air-cooling mechanism. In this case, the ECU 18 may change the rotation speed of the cooling fan, and therefore the power consumption, according to the battery temperature Tb. In the above description, the cooling capacity is switched in stages according to the battery temperature Tb, but the cooling capacity may be switched continuously according to the battery temperature Tb. In another embodiment, the cooling capacity may be only one stage. In this example, two types of threshold profiles 50a and 50b are stored in advance, but the threshold profile when the charging rate Cd is high may be calculated by calculation or the like. For example, when the charging rate Cd is equal to or higher than the reference charging rate C*, a profile obtained by multiplying the battery temperature Tb at which the level is switched, which is specified in the normal threshold profile 50a, by a specified coefficient less than 1 may be used as the threshold profile 50. [Explanation of symbols]

[0028] 10 electric vehicle, 12 drive wheel, 14 motor generator, 18 ECU, 20 main battery, 26 battery cooling circuit, 28 water pump, 30 chiller, 32 air conditioning circuit, 34 compressor, 36 condenser, 38 evaporator, 50a threshold profile, 50b special threshold profile.

Claims

[Claim 1] A method for controlling an electric vehicle that performs regenerative braking to obtain a braking force for the vehicle by generating regenerative power and charging the generated power to a main battery, comprising: Cooling the main battery in accordance with a temperature of the main battery; changing an execution condition of the cooling so that, when the charging rate of the main battery is equal to or higher than a specified reference charging rate, the power consumption required for cooling the main battery is increased compared to when the charging rate is less than the reference charging rate; A method for controlling an electric vehicle.

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