Controller of electric vehicle

Abstract

To provide a controller of an electric vehicle which performs limitation to suppress deterioration of a battery while suppressing excessive limit.SOLUTION: A controller of an electric vehicle with a battery comprises: a control part which performs limit control to limit current of the battery according to an evaluation value representing a degree of high rate deterioration of the battery; a first determination part which compares prediction value of internal resistance of the battery with actual value to determine deterioration of the battery and determines whether the actual value is smaller than the prediction value corresponding to the assumed long-term deterioration; and a second determination part which determines, when the actual value of the internal resistance is determined to be smaller than the prediction value, whether the evaluation value exceeds a prescribed value. The control part shifts, when the second determination part determines that the evaluation value does not exceed the prescribed value, a control state from a limited state of limiting current of the battery to a relaxation state where restriction of use of current is alleviated relative to the limited state.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a control device for an electric vehicle.

Background Art

[0002] Patent Document 1 discloses that when a section with a continuous downhill slope is included in the traveling route of an electric vehicle, control is executed to reduce the remaining battery amount from before the downhill slope so that the regenerative energy recovered on the downhill slope becomes maximum when the electric vehicle reaches the end point of the downhill slope section.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the configuration described in Patent Document 1, the SOC (State Of Charge) of the battery is lowered every time there is a downhill slope section, so the frequency of traveling in a low SOC state increases. However, an increase in the usage frequency in the low SOC region promotes high-rate deterioration of the battery, and there is a risk that the battery usage will be restricted and the fuel efficiency will deteriorate.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a control device for an electric vehicle that can implement restrictions for suppressing battery deterioration without imposing excessive restrictions.

Means for Solving the Problems

[0006] The present invention relates to a control device for an electric vehicle equipped with a battery, comprising: a control unit that executes limit control for limiting the current of the battery according to an evaluation value indicating the degree of high-rate deterioration of the battery; a first determination unit that compares a predicted value and a measured value of the internal resistance of the battery to determine whether the measured value is smaller than the predicted value corresponding to assumed aging deterioration; and a second determination unit that determines whether the evaluation value exceeds a predetermined value when it is determined that the measured value of the internal resistance is smaller than the predicted value. The control unit is characterized in that when the second determination unit determines that the evaluation value does not exceed the predetermined value, the control state is shifted from a limit state in which the current of the battery is limited to a relaxation state in which the current use restriction is relaxed compared to the limit state.

Effects of the Invention

[0007] In the present invention, it is possible to implement restrictions for suppressing battery deterioration without imposing excessive restrictions.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

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Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0009] Hereinafter, the control device for an electric vehicle in the embodiments of the present invention will be specifically described. Note that the present invention is not limited to the embodiments described below.

[0010] FIG. 1 is a schematic diagram showing an electric vehicle in an embodiment. The electric vehicle 1 includes an engine 2, a motor (MG) 3, a power transmission device (T / M) 4, wheels 5, an inverter 6, a battery 7, and a control device (ECU) 10.

[0011] The electric vehicle 1 is a hybrid vehicle equipped with an engine 2 and a motor 3. The power output from the engine 2 is transmitted to the wheels 5 via the power transmission device 4. The power transmission device 4 includes a power split mechanism. The power split mechanism is constituted by a planetary gear mechanism having three rotating elements. The engine 2, the motor 3, and the wheel 5 side are respectively connected to each rotating element of the power split mechanism. This power split mechanism distributes the power from the engine 2 to the motor 3 side and the wheel 5 side.

[0012] The motor 3 is a motor generator that functions as an electric motor and a generator. The motor 3 is a three-phase AC motor and functions as a power source for traveling. In the electric vehicle 1, the wheels 5 are driven by the power output from the motor 3. The motor 3 and the wheels 5 are connected so as to be power-transmittable via the power transmission device 4. The power output from the motor 3 is transmitted to the wheels 5 via the power transmission device 4. During braking or downhill driving of the electric vehicle 1, the motor 3 performs regenerative braking and regenerative power generation. The electric vehicle 1 recovers regenerative energy by the motor 3 by implementing regenerative braking. The electric power generated by the motor 3 is stored in the battery 7. The motor 3 is electrically connected to the battery 7 via the inverter 6.

[0013] The inverter 6 converts the DC power from the battery 7 into AC power and supplies it to the motor 3. The inverter 6 drives the motor 3. The inverter 6 is composed of an electric circuit including a plurality of switching elements so as to be able to supply three-phase currents to the three-phase coils of the motor 3.

[0014] The battery 7 is a DC power source capable of charging and discharging. For example, the battery 7 is composed of a secondary battery such as a nickel-metal hydride battery or a lithium-ion battery. The battery 7 discharges power to the inverter 6 side, or charges the power supplied from the inverter 6 side. Note that a boost converter may be provided between the battery 7 and the inverter 6.

[0015] The control device 10 is an electronic control device that controls the electric vehicle 1. The control device 10 includes a processor and a memory. The processor is composed of a CPU or the like. The memory is composed of a RAM, a ROM, or the like. Signals from various sensors are input to the control device 10. Signals from a vehicle speed sensor that detects the vehicle speed, a signal from an accelerator opening sensor that detects the accelerator opening, a signal from a voltage sensor that detects the voltage of the battery 7, a signal from a current sensor that detects the current input to and output from the battery 7, etc. are input to the control device 10. The current value input from the current sensor to the control device 10 makes the current output from the battery 7 a positive value and the current input to the battery 7 a negative value. Then, the control device 10 executes various controls based on the signals input from various sensors. The control device 10 controls the engine 2, the inverter 6, and the battery 7. The control device 10 functions as an engine control unit, a motor control unit, and a battery control unit.

[0016] For example, the control device 10 executes limit control to limit the current of the battery 7 in order to suppress the deterioration of the battery 7. Also, when the electric vehicle 1 travels on a downhill road, the control device 10 executes downhill control to perform regenerative braking and recover regenerative energy.

[0017] As shown in FIG. 2, the control device 10 includes a calculation unit 11, a determination unit 12, and a control unit 13.

[0018] The calculation unit 11 calculates the SOC of the battery 7 based on the voltage and current of the battery 7. As shown in FIG. 3, when the control device 10 executes the downhill control, the calculation unit 11 calculates the target SOC. The control device 10 executes the downhill control so that the SOC follows the target SOC from the point P1 in front of the downhill slope that is the target of the downhill control. Various known methods can be used as the method for calculating the SOC. For example, the control device 10 controls the battery 7 so that the SOC of the battery 7 is within the range of 21% to 86%.

[0019] The calculation unit 11 calculates the internal resistance of the battery 7 based on the voltage and current of the battery 7. The calculation unit 11 calculates the measured value of the internal resistance of the battery 7 based on the signals input from the voltage sensor and the current sensor. The measured value of the internal resistance of the battery 7 is a value indicating the current internal resistance in the battery 7.

[0020] The calculation unit 11 calculates the damage amount D of the battery 7 based on the current input to the battery 7, the current output from the battery 7, and their energization time. The damage amount D represents the damage caused by the deviation of the salt concentration in the battery 7. The damage amount D is calculated at a predetermined cycle. Various known methods can be used as the method for calculating the damage amount D.

[0021] The calculation unit 11 calculates an evaluation value ΣD indicating the degree of high-rate deterioration of the battery 7 caused by the continuous deviation of the salt concentration of the battery 7 accompanying the charge and discharge of the battery 7. The progress state of the high-rate deterioration is evaluated using the integrated value of the damage amount D. Various known methods can be used as the method for calculating the evaluation value ΣD. For example, the evaluation value ΣD is calculated based on the following formula (1). ΣD n+1 =γΣD n +ηD n+1 ···(1)

[0022] In the above formula (1), ΣD n+1 represents the current calculated value of the evaluation value. ΣD n represents the previous calculated value of the evaluation value calculated in the previous cycle. γ is the attenuation coefficient. η is the correction coefficient. The attenuation coefficient γ is set to a value smaller than 1. The correction coefficient η is calculated based on the following formula (2). η = η 1 RI 2 +η 2 f(SOC)×I ···(2)

[0023] In the above formula (2), η 1 is a proportionality constant and a coefficient that depends on the current and temperature of the battery 7. η 2 is a proportionality constant and a coefficient that depends on the SOC and current of the battery 7. RI 2 is the expansion term of the electrolyte of the battery 7. f(SOC)×I is the expansion and contraction term of the negative electrode of the battery 7.

[0024] When the evaluation value ΣD increases in the negative direction (negative value) as the battery 7 is used in an overcharged manner, the bias in salt concentration corresponding to the overcharge increases. When the battery 7 is used in an overdischarged manner, the evaluation value ΣD increases in the positive direction (positive value) as the bias in salt concentration corresponding to the overdischarge increases.

[0025] High-rate degradation has the characteristic of being promoted when a charging-direction current flows in the low-SOC region. As shown in FIGS. 3 and 4, when comparing the transition of SOC with downslope control and the transition of SOC without downslope control, it can be seen that the SOC with downslope control transitions through the low-SOC region. When the electric vehicle 1 travels downhill, the control device 10 executes downslope control. In the downslope control, as shown in FIG. 3, the SOC is decreased from before the downhill so that the SOC of the battery 7 becomes maximum when the electric vehicle 1 descends the downhill. The SOC can be decreased to the target SOC while the electric vehicle 1 is traveling before the downhill. As shown in FIG. 4, the SOC is lower with downslope control. In a region where the SOC is low, the expansion and contraction of the negative electrode of the battery 7 become large, and the electrolyte in the battery cell is easily pushed out, so a salt concentration difference within the battery cell surface is likely to occur. When the battery 7 is used in the low-SOC region, high-rate degradation is promoted.

[0026] The determination unit 12 determines whether to limit the use of the battery 7 according to the evaluation value ΣD. The determination unit 12 determines whether the evaluation value ΣD has reached a predetermined value that is a negative value.

[0027] As shown in Fig. 5(a), the evaluation value ΣD corresponding to the damage accumulated in the battery 7 without downhill control transitions in a region not exceeding the threshold value A0 and stays at a predetermined value A1. As shown in Fig. 5(b), the evaluation value ΣD corresponding to the damage accumulated in the battery 7 with downhill control transitions in a region not exceeding the threshold value A0, but becomes a predetermined value A2 with a larger damage amount than the predetermined value A1. The absolute value of the predetermined value A1 and the absolute value of the predetermined value A2 are smaller than the absolute value of the threshold value A0. The absolute value of the predetermined value A1 is smaller than the absolute value of the predetermined value A2.

[0028] The control unit 13 executes limit control for limiting the current of the battery 7 according to the evaluation value ΣD. The control unit 13 restricts the use of the battery 7 so that the evaluation value ΣD does not exceed the threshold value A0. The use restriction of the battery 7 is a control state in which power can be taken out from the battery 7, but the available current is restricted.

[0029] The evaluation value ΣD increases in absolute value due to the occurrence of a bias in the salt concentration as the usage frequency in the low SOC region increases. The usage state of the battery 7 is restricted so that the evaluation value ΣD does not exceed the threshold value A0. The threshold value A0 is set assuming the evaluation value ΣD accumulated when the electric vehicle 1 travels at a high load. The amount of the evaluation value ΣD accumulated in the battery 7 changes depending on how the driver operates the electric vehicle 1. Comparing the case where the electric vehicle 1 travels at a normal load and the case where the electric vehicle 1 travels at a high load, more of the evaluation value ΣD is accumulated in the case of high load.

[0030] As shown in FIG. 6, according to the user presence frequency distribution, there are more users U2 performing normal load driving than users U1 performing high load driving. There are more general users U2 than high load driving users U1 with respect to the median value U0 of the user presence frequency distribution. The threshold value A0 is set to protect the high load driving user U1. In other words, it is conceivable that a threshold value set to protect the general user U2 exists separately from the threshold value A0. Therefore, as shown in FIGS. 7(a) and 7(b), the control device 10 calculates a threshold value A3 corresponding to the general user U2 and compares this threshold value A3 with the evaluation value ΣD. The threshold value A3 is a threshold value set when the driving load of the electric vehicle 1 is a normal load. The absolute value of the threshold value A3 is larger than the absolute value of the predetermined value A1 and smaller than the absolute value of the predetermined value A2.

[0031] As shown in FIG. 7(a), when the high load driving user U1 drives the electric vehicle 1, although the evaluation value ΣD is within a region that does not exceed the threshold value A0, it transitions through a region that exceeds the threshold value A3. As shown in FIG. 7(b), when the general user U2 drives the electric vehicle 1, the evaluation value ΣD is within a region that does not exceed the threshold value A0 and transitions through a region that does not exceed the threshold value A3. The evaluation value ΣD shown in FIGS. 7(a) and 7(b) shows the case with downhill control. It can be seen that the accumulated amount of the evaluation value ΣD differs depending on whether the user is the high load driving user U1 or the general user U2. The threshold value A0 is a threshold value set assuming the high load driving user U1. When the control device 10 implements the usage restriction of the battery 7 so that the evaluation value ΣD does not exceed the threshold value A0, by imposing a restriction to protect the high load driving user U1, it may result in an excessive restriction on the general user U2. Therefore, the control device 10 is configured to relax the usage restriction of the battery 7 when the driver of the electric vehicle 1 is the general user U2.

[0032] FIG. 8 is a flowchart showing a restriction relaxation process flow. The control shown in FIG. 8 is executed by the control device 10.

[0033] The control device 10 calculates a predicted value of the internal resistance of the battery 7 and a threshold value of the evaluation value ΣD (step S1). In step S1, using a map stored in advance in the storage unit, a predicted value of the internal resistance corresponding to the aging deterioration of the battery 7 and a threshold value of the evaluation value ΣD are calculated. The storage unit stores a map indicating the internal resistance increased due to aging deterioration. The calculation unit 11 can calculate the internal resistance corresponding to about five years of use of the battery 7 and the internal resistance corresponding to about ten years of use of the battery 7 based on this map. The calculation unit 11 calculates the threshold value of the evaluation value ΣD assuming the aging deterioration of the battery 7 used by a general user U2. For example, when the usage years of the battery 7 is five years, the calculation unit 11 calculates a predicted value of the internal resistance corresponding to five years from the map, and calculates a threshold value A3 of the evaluation value ΣD assuming the case where a general user U2 has used the battery 7 for five years.

[0034] The control device 10 acquires the running information of the electric vehicle 1 (step S2). In step S2, running information indicating the running history of the electric vehicle 1 stored in the storage unit of the electric vehicle 1 is acquired. The control device 10 acquires the actual data of the running history.

[0035] The control device 10 acquires the measured value of the internal resistance of the battery 7 (step S3). In step S3, the measured value of the internal resistance of the battery 7 is calculated. The calculation unit 11 calculates the measured value indicating the internal resistance of the current battery 7.

[0036] The control device 10 determines whether the measured value of the internal resistance of the battery 7 is smaller than the predicted value (step S4). In step S4, the predicted value of the internal resistance calculated in step S1 and the measured value of the internal resistance acquired in step S3 are compared, and it is determined whether the measured value is smaller than the predicted value. Since the internal resistance of the battery 7 increases due to aging deterioration, the determination unit 12 determines whether the aging deterioration of the battery 7 has not progressed more than expected by determining whether the measured value of the internal resistance is lower than the predicted value.

[0037] When it is determined that the measured value of the internal resistance of the battery 7 is not smaller than the predicted value (step S4: No), this control routine ends. When negatively determined in step S4, it is determined that the aging deterioration of the battery 7 has progressed more than expected, so this control routine ends.

[0038] When it is determined that the measured value of the internal resistance of the battery 7 is smaller than the predicted value (step S4: Yes), the control device 10 calculates an evaluation value ΣD (step S5). The calculation unit 11 calculates the current evaluation value ΣD using the above equations (1) and (2).

[0039] The control device 10 determines whether the evaluation value ΣD exceeds a threshold value (step S6). In step S6, the threshold value calculated in step S1 and the evaluation value ΣD calculated in step S5 are compared, and it is determined whether this evaluation value ΣD exceeds the threshold value. In step S1, a threshold value assuming a general user U2, that is, the threshold value A3 shown in FIG. 7, is calculated. Therefore, in step S6, the determination unit 12 determines whether the evaluation value ΣD exceeds the threshold value A3 set for the general user U2. When it is determined in step S6 that the evaluation value ΣD exceeds the threshold value A3, as shown in FIG. 7(a), it is determined that the driver of the electric vehicle 1 is the user U1 performing high-load driving. In step S6, it is discriminated whether the driver of the electric vehicle 1 is the user U1 performing high-load driving or the general user U2.

[0040] When it is determined that the evaluation value ΣD exceeds the threshold value (step S6: Yes), this control routine ends. When it is determined in step S6 that the evaluation value ΣD exceeds the threshold value A3, it is determined that the driver is the user U1 performing high-load driving.

[0041] When it is determined that the evaluation value ΣD does not exceed the threshold value (step S6: No), the control device 10 relaxes the usage restriction of the battery 7 (step S7). When it is determined in step S6 that the evaluation value ΣD does not exceed the threshold value A3, as shown in FIG. 7(b), it is determined that the driver of the electric vehicle 1 is an ordinary user U2. In step S7, the control unit 13 shifts the control state from the restricted state in which the current of the battery 7 is restricted to a relaxed state in which the usage restriction of the battery 7 is relaxed more than the restricted state. The relaxed state is a state in which a higher current than the restricted state can be used. Since the control device 10 can execute the downhill control, it executes the control to prevent the evaluation value ΣD from exceeding the threshold value A0 when the user U1 driving under high load runs. Therefore, in the state before the process of step S7 is performed, the usage of the battery 7 is restricted so that the evaluation value ΣD for the driving of the ordinary user U2 does not exceed the threshold value A0. That is, the control is applied quickly, and the performance of the battery 7 is not exhausted. Since the control is applied quickly in this way, the restriction is released or relaxed by the process of step S7. As a result, the performance of the battery 7 can be exhausted. When the process of step S7 is performed, this control routine ends.

[0042] As described above, according to the embodiment, since the ratio of users who drive in a state where high-rate deterioration is likely to occur is small, the control state is shifted from the restricted state assuming the high-load driving user U1 to the relaxed state assuming the ordinary user U2, whereby the current restriction of the battery 7 is relaxed. In the relaxed state, a larger current than the restricted state can be used, so the output of the engine 2 with respect to the required power of the electric vehicle 1 can be reduced, and the fuel efficiency is improved.

Description of Reference Numerals

[0043] 1 Electric vehicle 2 Engine 3 Motor (MG) 4 Power transmission device (T / M) 5 Wheel 6 Inverter 7 Battery 10 Control device (ECU) 11 Calculation unit 12 Judgment unit 13 Control unit

Claims

1. A control device for an electric vehicle equipped with a battery, comprising: a control unit that executes limit control to limit the current of the battery according to an evaluation value indicating the degree of high-rate deterioration of the battery; a first determination unit that compares a predicted value and a measured value of the internal resistance of the battery to determine whether the measured value is smaller than the predicted value corresponding to assumed aging deterioration; a second determination unit that determines whether the evaluation value exceeds a predetermined value when it is determined that the measured value of the internal resistance is smaller than the predicted value; and when it is determined by the second determination unit that the evaluation value does not exceed the predetermined value, the control unit shifts the control state from a restricted state in which the current of the battery is restricted to a relaxed state in which the restriction on the use of the current is relaxed compared to the restricted state. A control device for an electric vehicle, characterized by comprising the above.

2. The relaxed state is a state in which a current higher than that in the restricted state can be used. The control device for an electric vehicle according to Claim 1, characterized by the above.

3. The predetermined value is a threshold value set when the running load of the electric vehicle is a normal load. The control device for an electric vehicle according to Claim 2, characterized by the above.

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