Electric vehicle system

Abstract

This technology provides an electric vehicle system equipped with a battery that can effectively prevent overcharging of the battery through regenerative charging. [Solution] The electric vehicle system 1 mounted on the electric vehicle 2 includes an in-wheel motor 3 that functions as a power converter, a battery 5, an inverter 6 that converts DC power output from the battery 5 into driving power and supplies it to the in-wheel motor 3, and also converts regenerative power output from the in-wheel motor 3 into DC power and supplies it to the battery 5, and a control unit 7. The control unit 7 controls the inverter 6 so that the vehicle speed of the electric vehicle 2 is below a predetermined upper limit speed. The control unit 7 also changes the upper limit speed of the electric vehicle 2 when the charge level of the battery 5 exceeds a predetermined upper limit and the electric vehicle 2 is traveling downhill, and when these speed change conditions are met.

Description

Technical Field

[0001] The present invention relates to an electric vehicle system.

Background Art

[0002] Conventionally, in order to extend the cruising range of an electric vehicle, a power conversion device for driving wheels is also used as a generator, and a system that regeneratively charges a battery using regenerative power generated by regenerative braking has been used. However, when the battery is fully charged, for example, when driving downhill, if the electric vehicle continuously uses regenerative braking, there is a risk that the battery will be overcharged by regenerative charging. On the other hand, in order to avoid the battery reaching a fully charged state during regenerative charging, if the upper limit of the battery charge rate (SOC) other than during regenerative charging is set low, the amount of electric power of the battery available for driving the electric vehicle decreases, and there is a demerit that the cruising range of the electric vehicle becomes short. Thus, in an electric vehicle, it is required to avoid overcharging of the battery while securing the cruising range.

[0003] Regarding the control of a vehicle that runs using electric power stored in a rechargeable battery, for example, Patent Document 1 is known. Patent Document 1 discloses a travel data acquisition device that acquires predetermined parameters such as vehicle speed as travel data, a probability distribution generation unit that generates a probability distribution of the predetermined parameters based on the travel data acquired by the travel data acquisition device, and using the probability distribution of the predetermined parameters, calculates an expected value of an evaluation value regarding the power consumption and fuel consumption when the vehicle travels a travel route from the current position to the destination, and a vehicle control unit that controls the vehicle based on the calculated expected value of the evaluation value.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] The vehicle control device described in Patent Document 1 controls the vehicle's driving mode in each section of the driving route so as to minimize the expected value of total fuel consumption, while satisfying the constraint that the expected value of total power consumption along the vehicle's driving route is less than or equal to the remaining battery power. However, this control device does not consider a control method for when the battery charge rate increases due to regenerative charging while the vehicle is running. Therefore, the risk of battery overcharging still exists.

[0006] In light of the above background, the object of the present invention is to provide a technology that can effectively prevent overcharging of a battery by regenerative charging in an electric vehicle system equipped with a battery. [Means for solving the problem]

[0007] The electric vehicle system according to the present invention is a system mounted on an electric vehicle and comprises: a power converter that drives the wheels of the electric vehicle using drive power and regenerates kinetic energy transmitted from the wheels to output regenerative power; a rechargeable battery that inputs and outputs DC power; an inverter that converts the DC power output from the battery into drive power and supplies it to the power converter, and converts the regenerative power output from the power converter into DC power and supplies it to the battery; and a control unit that controls the operation of the power converter by controlling the inverter. The control unit controls the inverter so that the running speed of the electric vehicle is less than or equal to a predetermined upper limit speed, and the control unit changes the upper limit speed when the battery charge rate exceeds a predetermined upper limit and the electric vehicle is traveling downhill, provided that the speed change conditions are met. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a technology that can effectively prevent overcharging of a battery in an electric vehicle system equipped with a battery through regenerative charging.

[0009] Other issues, configurations, and effects not mentioned above will be clarified by the following description of embodiments for carrying out the invention. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing the overall configuration of an electric vehicle system according to the first embodiment of the present invention. [Figure 2] This is a flowchart showing the control sequence for the flag setting process executed by the control unit in the electric vehicle system according to the first embodiment of the present invention. [Figure 3] This is a flowchart showing the control sequence of the regenerative braking control process executed by the control unit in the electric vehicle system according to the first embodiment of the present invention. [Figure 4] This is a flowchart showing the control sequence of the regenerative braking control process executed by the control unit in the electric vehicle system according to the first embodiment of the present invention. [Figure 5] This is a flowchart showing the control sequence of the regenerative braking control process executed by the control unit in the electric vehicle system according to the first embodiment of the present invention. [Figure 6] This is a schematic diagram showing the overall configuration of an electric vehicle system according to a second embodiment of the present invention. [Figure 7] This is a schematic diagram showing the overall configuration of an electric vehicle system according to a third embodiment of the present invention. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described below. In each embodiment and each figure, similar components are denoted by the same reference numerals to avoid repetition of similar descriptions. If there are differences among components denoted by the same reference numerals, those differences will be explained.

[0012] [First Embodiment] Hereinafter, an electric vehicle system according to the first embodiment of the present invention will be described with reference to Figures 1 to 5.

[0013] Figure 1 is a schematic diagram showing the overall configuration of an electric vehicle system according to the first embodiment of the present invention. As shown in Figure 1, the electric vehicle system 1 of this embodiment is mounted on an electric vehicle 2 and comprises an in-wheel motor 3, a rechargeable battery 5, an inverter 6 that performs power conversion between the in-wheel motor 3 and the battery 5, and a control unit 7 that controls the inverter 6.

[0014] The electric vehicle 2 has multiple wheels 20. In the following description, the electric vehicle 2 will be described as having four wheels 20, but the number of wheels 20 on the electric vehicle 2 is not limited to this. In Figure 1, in order to distinguish each wheel 20, the wheel 20 installed on the left front of the electric vehicle 2 is shown as the left front wheel 20FL, the wheel 20 installed on the right front of the electric vehicle 2 is shown as the right front wheel 20FR, the wheel 20 installed on the left rear of the electric vehicle 2 is shown as the left rear wheel 20RL, and the wheel 20 installed on the right rear of the electric vehicle 2 is shown as the right rear wheel 20RR.

[0015] The in-wheel motor 3 is installed within a wheel (not shown) of the wheel 20 and performs powered or regenerative operation according to the control of the inverter 6. During powered operation, the in-wheel motor 3 generates rotational driving force using drive power supplied from the battery 5 via the inverter 6 to drive the wheel 20. During regenerative operation, the in-wheel motor 3 regenerates kinetic energy (rotational energy) transmitted from the wheel 20 and outputs the resulting regenerated power to the inverter 6. In other words, in the electric vehicle system 1 of this embodiment, the in-wheel motor 3 functions as a power conversion device that performs power conversion to drive the wheel 20.

[0016] In Fig. 1, in-wheel motors 3 are installed for each of the wheels 20 (left front wheel 20FL, right front wheel 20FR, left rear wheel 20RL, right rear wheel 20RR), and an example is shown where each in-wheel motor 3 individually controls the driving state of each wheel 20 according to the control of the inverter 6. However, the in-wheel motors 3 do not necessarily have to be installed on all the wheels 20. For example, in-wheel motors 3 may be installed only on the left front wheel 20FL and the right front wheel 20FR, and the electric vehicle system 1 may be configured without installing in-wheel motors 3 on the left rear wheel 20RL and the right rear wheel 20RR.

[0017] The battery 5 is a secondary battery that can be charged and discharged by inputting and outputting DC power. For example, a battery pack composed of a combination of a plurality of lithium-ion batteries can be used as the battery 5.

[0018] The inverter 6 operates according to the control of the control unit 7 and adjusts the power input and output between the in-wheel motor 3 and the battery 5. During the power running operation of the in-wheel motor 3, the inverter 6 converts the DC power supplied from the battery 5 into AC power, and supplies the converted AC power to the in-wheel motor 3 as driving power for the in-wheel motor 3 to drive the wheel 20. Also, during the regenerative operation of the in-wheel motor 3, the inverter 6 converts the AC regenerative power output from the in-wheel motor 3 into DC power, and supplies the converted DC power to the battery 5 as power for charging the battery 5.

[0019] In Fig. 1, an example is shown where inverters 6 are provided for the in-wheel motors 3 installed for each of the wheels 20 (left front wheel 20FL, right front wheel 20FR, left rear wheel 20RL, right rear wheel 20RR), and each inverter 6 is controlled by a common control unit 7. However, the inverters 6 do not necessarily have to be provided individually for each in-wheel motor 3. Also, a control unit 7 may be provided for each inverter 6, and each control unit 7 may control the inverter 6 on a one-to-one basis. In addition to this, combinations of the wheel 20, the in-wheel motor 3, the inverter 6, and the control unit 7 can be arbitrarily selected.

[0020] The control unit 7 is a unit that controls the operation of each in-wheel motor 3 by controlling each inverter 6. The control unit 7 is, for example, a unit (ECU: Electronic Control Unit) capable of performing electronic arithmetic processing and control processing. As part of its functions, the control unit 7 controls each inverter 6 so that the traveling speed of the electric vehicle 2 is below a predetermined upper limit speed.

[0021] The electric vehicle 2 is equipped with a SOC sensor 8 that measures the state of charge (SOC) of the battery 5 and an inclination sensor 9 that measures the inclination angle of the electric vehicle 2. Information on the state of charge of the battery 5 measured by the SOC sensor 8 and information on the inclination angle of the electric vehicle 2 measured by the inclination sensor 9 are input to the control unit 7 respectively. The control unit 7 uses this information to judge the situation in which the electric vehicle 2 is placed, and controls each inverter 6 according to the judgment result. Thereby, the operation of each in-wheel motor 3 connected to each inverter 6 is controlled, and the electric vehicle 2 can be made to travel. The details of the method for controlling the inverter 6 by the control unit 7 will be described later.

[0022] Next, with reference to FIGS. 2 to 5, the processing content of the control unit 7 in the electric vehicle system according to the first embodiment of the present invention will be described.

[0023] FIG. 2 is a flowchart showing the control sequence of the flag setting process executed by the control unit 7 in the electric vehicle system according to the first embodiment of the present invention. The control unit 7 executes the flag setting process shown in the flowchart of FIG. 2, for example, at every predetermined calculation cycle during the traveling of the electric vehicle 2.

[0024] In step S10, the control unit 7 acquires the current state of charge of the battery 5. Here, the information transmitted from the SOC sensor 8 is received, and the current state of charge of the battery 5 is acquired based on this information.

[0025] In step S20, the control unit 7 determines whether the charge level of the battery 5 obtained in step S10 exceeds a predetermined upper limit. Here, the current charge level of the battery 5 obtained in step S10 is compared with a predetermined upper limit of the charge level (e.g., 100%) which is the maximum charge level that the battery 5 can charge. If the charge level of the battery 5 is equal to or greater than the upper limit, the process proceeds to step S30; otherwise, it proceeds to step S40.

[0026] In step S30, the control unit 7 internally sets an SOC limit flag, which is a flag indicating that the charge level of the battery 5 exceeds the upper limit. This SOC limit flag is monitored by the control unit 7 in step S110 of Figure 3, which will be described later.

[0027] In step S40, the control unit 7 clears the SOC upper limit flag that was set in a previous process. If the SOC upper limit flag is not set, no processing is required in step S40.

[0028] After performing the processing in step S30 or S40, in step S50, the control unit 7 obtains the current tilt angle of the electric vehicle 2. Here, it receives a signal transmitted from the tilt sensor 9 and obtains the current tilt angle of the electric vehicle 2 from this signal. In the following description, the tilt angle of the electric vehicle 2 is defined as a positive value when the direction of the electric vehicle 2 is upward relative to the horizontal, i.e., when the electric vehicle 2 is traveling uphill, and a negative value when the direction of the electric vehicle 2 is downward relative to the horizontal, i.e., when the electric vehicle 2 is traveling downhill.

[0029] In step S60, the control unit 7 determines whether the electric vehicle 2 is traveling downhill based on the inclination angle acquired in step S50. Here, the current inclination angle of the electric vehicle 2 acquired in step S50 is compared with a predetermined inclination angle less than 0 (for example, -5°) which is the inclination angle of the electric vehicle 2 that is required to be suppressed by the regenerative operation of the in-wheel motor 3 due to gravity. If the inclination angle is less than the predetermined inclination angle, that is, if the inclination angle is a negative value and its absolute value is greater than the absolute value of the inclination angle, the control unit 7 determines that the electric vehicle 2 is traveling downhill and proceeds to step S70. On the other hand, if the inclination angle is greater than or equal to the predetermined inclination angle, that is, if the inclination angle is 0 or a positive value, or if the inclination angle is a negative value and its absolute value is less than or equal to the absolute value of the inclination angle, the control unit 7 determines that the electric vehicle 2 is not traveling downhill and proceeds to step S80.

[0030] In step S70, the control unit 7 internally sets a downhill flag, which indicates that the electric vehicle 2 is traveling downhill. This downhill flag, like the SOC upper limit flag mentioned above, is monitored by the control unit 7 in step S110 of Figure 3, which will be described later.

[0031] In step S80, the control unit 7 clears the downhill flag that was set in a previous process. If the downhill flag is not set, no processing is required in step S80.

[0032] After completing the process in step S70 or S80, the control unit 7 terminates the flag setting process shown in the flowchart of Figure 2.

[0033] The control unit 7 performs the flag setting process shown in Figure 2, described above, at predetermined calculation cycles to determine the situation in which the electric vehicle 2 is located, and can appropriately set flags (SOC upper limit flag, downhill flag) according to the determination result.

[0034] Figures 3, 4, and 5 are flowcharts showing the control sequence of the regenerative braking control process executed by the control unit 7 in the electric vehicle system according to the first embodiment of the present invention. The control unit 7 executes the regenerative braking control process shown in the flowcharts of Figures 3 to 5, for example, at predetermined calculation cycles while the electric vehicle 2 is running. In the control unit 7, the regenerative braking control process in Figures 3 to 5 is executed in parallel with the flag setting process in Figure 2.

[0035] In step S110 of Figure 3, the control unit 7 monitors the settings of the aforementioned SOC upper limit flag and the downward slope flag, respectively.

[0036] In step S120, the control unit 7 determines whether the settings of the SOC upper limit flag and the downward slope flag, which were monitored in step S110, are both in the ON state. If both of these flags are in the ON state, the process proceeds to step S130; if at least one of the flags is in the OFF state, the process proceeds to step S220 in Figure 5.

[0037] In step S130, the control unit 7 sets the upper limit speed of the electric vehicle 2 to Vf, which is a predetermined value that is the upper limit speed when fully charged. Normally, the upper limit speed of the electric vehicle 2 is set to a predetermined value Vmax according to the driving performance of the electric vehicle 2. When step S130 is executed, the upper limit speed Vf when fully charged, which is a lower speed value than the normal upper limit speed Vmax, is set as the upper limit speed of the electric vehicle 2. As a result, when either the SOC upper limit flag or the downhill flag is ON, that is, when the charge rate of the battery 5 exceeds a predetermined upper limit and the electric vehicle 2 is traveling downhill, the upper limit speed of the electric vehicle 2 can be changed from Vmax to Vf when these speed conditions are met.

[0038] In step S140, the control unit 7 determines whether the current vehicle speed (the running speed of the electric vehicle 2) is equal to or greater than the modified upper limit speed Vf. If the vehicle speed is less than the upper limit speed Vf, the process proceeds to step S150; if it is equal to or greater than the upper limit speed Vf, the process proceeds to step S160.

[0039] In step S150, the control unit 7 determines whether or not the driver of the electric vehicle 2 has performed a brake operation. If a brake operation has been performed, the process proceeds to step S160; otherwise, it returns to step S110.

[0040] In step S160, the control unit 7 outputs a regenerative braking command to each inverter 6. In response to this regenerative braking command, each inverter 6 controls the operation of the corresponding in-wheel motor 3 to perform regenerative operation. Specifically, for example, each inverter 6 sets a negative torque value corresponding to the regenerative braking command as the torque command value, and controls the AC power flowing between the inverter 6 and the in-wheel motor 3 based on this torque command value. As a result, the control unit 7 can cause the electric vehicle 2 to perform regenerative braking when the vehicle speed is above the upper limit speed Vf or when the driver applies the brakes.

[0041] In step S170, the control unit 7 switches the control mode of each inverter 6 to self-consumption control mode. Self-consumption control mode is a mode in which each inverter 6 is controlled so that the regenerative power generated in the in-wheel motor 3 during regenerative operation is not returned to the battery 5, but is consumed in at least one of the in-wheel motor 3 and the electric vehicle 2. Details of the control method of the inverter 6 in self-consumption control mode will be described later.

[0042] In step S180 of Figure 4, the control unit 7 determines whether the driver of the electric vehicle 2 has finished braking. If the driver is still braking, the unit returns to step S160 and continues to output regenerative braking commands. If the braking operation is finished, the unit proceeds to step S190.

[0043] In step S190, the control unit 7 determines whether the current vehicle speed (the driving speed of the electric vehicle 2) is maintained at or above the upper limit speed Vf. If the vehicle speed remains at or above the upper limit speed Vf, the unit returns to step S160 and continues to output the regenerative braking command. If the vehicle speed falls below the upper limit speed Vf, the unit proceeds to step S200.

[0044] In step S200, the control unit 7 cancels the output of the regenerative braking command and turns off the self-consumption control mode. As a result, the regenerative braking in the electric vehicle 2 ends.

[0045] In step S210, the control unit 7 returns the upper limit speed of the electric vehicle 2, which was set to upper limit speed Vf in step S130, back to the upper limit speed Vmax before the change. After the process in step S210 is completed, the regenerative braking control process shown in Figures 3, 4, and 5 is terminated.

[0046] If, in step S120 of Figure 3, it is determined that at least one of the SOC upper limit flag and the downhill flag is in the OFF state, then in step S220 of Figure 5, the control unit 7 determines whether or not the driver of the electric vehicle 2 has performed a brake operation. If a brake operation has been performed, the process proceeds to step S230; otherwise, it returns to step S110 of Figure 3.

[0047] In step S230, the control unit 7 outputs a regenerative braking command to each inverter 6. In response to this regenerative braking command, each inverter 6 controls the operation of the corresponding in-wheel motor 3 to perform regenerative operation, similar to step S160 in Figure 3. However, unlike in step S170, the control unit 7 does not switch the control mode of each inverter 6 to the self-consumption control mode. This allows the regenerative power generated by the in-wheel motor 3 during regenerative operation to be returned to the battery 5, enabling normal regenerative braking operation.

[0048] In step S240, the control unit 7 determines whether the driver of the electric vehicle 2 has finished braking. If the driver is still braking, the unit returns to step S230 and continues to output regenerative braking commands. If the braking operation is finished, the unit proceeds to step S250.

[0049] In step S250, the control unit 7 cancels the output of the regenerative braking command. This ends the regenerative braking in the electric vehicle 2. After the process in step S250 is completed, the brake control process shown in Figures 3, 4, and 5 is terminated.

[0050] Next, the details of the control method for the inverter 6 in the self-consumption control mode, which is performed in step S170 of Figure 3, will be described below.

[0051] As described above, in self-consumption control mode, each inverter 6 is controlled so that the regenerative power generated in the in-wheel motor 3 during regenerative operation is consumed in at least one of the in-wheel motor 3 and the electric vehicle 2. Specifically, for example, the control unit 7 controls each inverter 6 to increase the d-axis current that each inverter 6 outputs to the in-wheel motor 3. This makes it possible for the in-wheel motor 3 to consume the regenerative power as copper loss. In this case, it is preferable for the control unit 7 to control each inverter 6 so that the temperature of each in-wheel motor 3, which is provided for each wheel 20 of the electric vehicle 2, becomes uniform.

[0052] Furthermore, for example, the control unit 7 may control each inverter 6 so that the in-wheel motor 3 connected to one of the multiple wheels 20 (left front wheel 20FL, right front wheel 20FR, left rear wheel 20RL, right rear wheel 20RR) of the electric vehicle 2 generates regenerative power through regenerative operation, and the in-wheel motor 3 connected to any other wheel 20 drives that wheel 20 through power operation. In this case, there may be one or more in-wheel motors 3 performing regenerative operation and in-wheel motors 3 performing power operation. This allows the electric vehicle 2 to be decelerated by a braking force equal to the difference between regenerative braking and power torque, while the regenerative power generated by the in-wheel motor 3 during regenerative operation is consumed by the losses of the in-wheel motor 3 and the power consumption and losses of the in-wheel motor 3 during power operation.

[0053] Furthermore, when regenerative and traction driving of the in-wheel motors 3 are used in combination as described above, the control unit 7 may control each inverter 6 so that the in-wheel motors 3 connected to the front wheels (left front wheel 20FL, right front wheel 20FR) generate regenerative power, and the in-wheel motors 3 connected to the rear wheels (left rear wheel 20RL, right rear wheel 20RR) generate traction torque to drive the rear wheels, thereby generating an upward force on the electric vehicle 2, and lifting the electric vehicle 2 upward relative to the road surface, thereby increasing its potential energy. In this way, not only is the regenerative power consumed by the in-wheel motors 3, but the potential energy of the electric vehicle 2 is also increased, making it possible to convert a portion of the regenerative power into potential energy for the electric vehicle 2 and consume it, thus efficiently self-consuming the regenerative power generated by regenerative driving.

[0054] Alternatively, the control unit 7 may control each inverter 6 so that, on at least one of the multiple wheels 20 of the electric vehicle 2, the electric vehicle 2 is decelerated by using both the regenerative braking provided by the in-wheel motor 3 during regenerative operation and the mechanical brake provided on that wheel 20 in a coordinated manner. This makes it possible to maintain the desired deceleration force by using the mechanical brake in conjunction with the in-wheel motor 3, even if the regenerative power generated by the regenerative braking cannot be self-consumed by the in-wheel motor 3 alone and therefore a sufficient deceleration force cannot be obtained from the regenerative braking.

[0055] Furthermore, in addition to the above, regenerative power can also be consumed using, for example, fluid friction generated inside the in-wheel motor 3, energy consumption in various auxiliary equipment mounted on the electric vehicle 2, and friction in various mechanical parts (suspension, etc.) mounted on the electric vehicle 2. This makes it possible to self-consume the regenerative power generated by regenerative braking without returning it to the battery 5.

[0056] [Effects of the first embodiment] In the electric vehicle system 1 of this embodiment, when the charge level of the battery 5 exceeds a predetermined upper limit and the speed change condition that the electric vehicle 2 is traveling downhill is met, the control unit 7 turns on the self-consumption control mode during regenerative braking, so that, as described above, the regenerative power generated by regenerative braking is not returned to the battery 5 but is self-consumed by the in-wheel motor 3. This is equivalent to converting the regenerative power generated in the in-wheel motor 3 into heat. In other words, when the self-consumption control mode is turned on, the in-wheel motor 3 generates heat equal to the amount of regenerated power. At this time, the heat generated in the in-wheel motor 3 is equal to the amount of regenerated power.

[0057] The amount of regenerative energy recovered by each in-wheel motor 3 is proportional to the product of the average braking torque of the multiple in-wheel motors 3 mounted on the electric vehicle 2 and the vehicle speed. Here, if the electric vehicle 2 meets the speed change conditions, and the self-consumption control mode is turned ON without changing the upper speed limit of the electric vehicle 2 to Vmax, the amount of heat generated in the in-wheel motors 3 according to the amount of regenerative energy may not be properly controlled. As a result, more heat than the cooling capacity of the in-wheel motors 3 may be generated, which may cause the in-wheel motors 3 to fail.

[0058] In the electric vehicle system 1 of this embodiment, when the speed change conditions are met, the upper limit speed of the electric vehicle 2 is changed from Vmax to a predetermined lower speed Vf, and the self-consumption control mode is turned ON. This suppresses the regenerative power of the in-wheel motor 3 and allows for appropriate control of the amount of heat generated by the in-wheel motor 3.

[0059] The modified upper limit speed Vf can be set, for example, according to equation (1) below. In equation (1), L is the circumference of the tire of wheel 20, Pcl is the cooling performance of the in-wheel motor 3, and τW is the braking torque of the in-wheel motor 3 (sum of the average braking torques of each in-wheel motor 3). The unit of Vf is meters per second, the unit of L is meters, the unit of Pcl is watts, and the unit of τW is Newton-meter. Vf <L×Pcl / (2π×τW) ···(1)

[0060] The above equation (1) is an inequality, and any value can be set as the upper limit speed Vf as long as it is lower than the normal upper limit speed Vmax and does not exceed the value on the right side of equation (1). Here, it is preferable to set each parameter of equation (1) (tire circumference L, cooling performance Pcl, brake torque τW) so that the upper limit speed Vf that satisfies the conditions of equation (1) becomes an appropriate value as the driving speed of the electric vehicle 2.

[0061] In equation (1), the cooling performance Pcl represents the amount of heat that can be cooled by all the in-wheel motors 3 mounted on the electric vehicle 2. The brake torque τW can be calculated based on the inclination angle of the slope on which the electric vehicle 2 is traveling and the weight of the electric vehicle 2. The inclination angle of the slope can be measured, for example, using a tilt sensor 9. The weight can be measured, for example, using a weight sensor (not shown). Alternatively, the weight of the electric vehicle 2 can be estimated based on the relationship between the torque command value of the in-wheel motors 3 and the change in vehicle speed.

[0062] As described above, in the electric vehicle system 1 of this embodiment, when the self-consumption control mode is turned ON during regenerative braking, the upper limit speed of the electric vehicle 2 is changed to Vf, thereby controlling the amount of heat converted from regenerative power by the in-wheel motor 3. The heat generated at this time is less than or equal to the cooling performance Pcl of the cooling system (not shown) of the in-wheel motor 3, so there is no risk of the in-wheel motor 3 overheating and failing due to heat originating from the regenerative power. In other words, in the electric vehicle system 1 of this embodiment, when both the downhill flag and the SOC upper limit flag are ON, the control unit 7 changes the upper limit speed of the electric vehicle 2 to a lower value than normal, thereby keeping the heat generated from the conversion of regenerative power within a range that can be cooled, and enabling self-consumption of regenerative power. Therefore, when the battery 5 is fully charged and the electric vehicle 2 is traveling downhill, the risk of overcharging the battery 5 by returning regenerative power to the battery 5 is reduced.

[0063] Furthermore, in the electric vehicle system 1 of this embodiment, regenerative braking can be utilized more effectively than in conventional systems, thereby reducing wear on the mechanical brakes (e.g., disc brakes or drum brakes) of the electric vehicle 2. As a result, the lifespan of the mechanical brakes can be extended, and the scattering of dust into the environment due to brake wear can be reduced.

[0064] Furthermore, in the electric vehicle system 1 of this embodiment, the control unit 7 controls each inverter 6 using only the control and measurement values ​​at the time of control of the electric vehicle 2 and the vehicle's initial design information, without using predicted or uncertain information from previous times. Therefore, when the battery 5 is fully charged and the electric vehicle 2 is traveling downhill, the risk of battery overcharging can be effectively reduced by returning regenerative power to the battery 5.

[0065] In particular, by setting the upper limit speed Vf of the modified electric vehicle 2 according to the aforementioned equation (1), the in-wheel motor 3 can continuously self-consume regenerative power even when the electric vehicle 2 travels downhill for a long period of time.

[0066] In the control sequences shown in Figures 3 to 5, if the period of the SOC upper limit flag monitoring event performed in step S110 is Ts, it is preferable that this period Ts be longer than the update period Tb of the regenerative brake command output in step S160. This allows the ON / OFF event period of the SOC upper limit flag to be matched with the control period of the in-wheel motor 3, and the ON / OFF command of the self-consumption control mode to follow the ON / OFF event of the SOC upper limit flag.

[0067] Furthermore, if we let Td be the period of the downhill flag monitoring event performed in step S110, it is preferable that this period Td be longer than the period Ta for acquiring a signal from the tilt sensor 9 in step S50 in Figure 2. By doing so, the ON / OFF event period of the downhill flag and the control period of the tilt sensor 9 can be matched, and the instantaneous measured values ​​of the tilt sensor 9 can be averaged, thereby suppressing fluctuations in the value of the upper limit speed Vf of the electric vehicle 2 set in step S130.

[0068] According to the first embodiment of the present invention described above, the electric vehicle system 1, which is a system mounted on the electric vehicle 2, includes an in-wheel motor 3 that drives the wheels 20 of the electric vehicle 2 using drive power and functions as a power conversion device that regenerates kinetic energy transmitted from the wheels 20 and outputs regenerative power, a rechargeable battery 5 that inputs and outputs DC power, an inverter 6 that converts the DC power output from the battery 5 into drive power and supplies it to the in-wheel motor 3, and converts the regenerative power output from the in-wheel motor 3 into DC power and supplies it to the battery 5, and a control unit 7 that controls the operation of the in-wheel motor 3 by controlling the inverter 6. The control unit 7 controls the inverter 6 so that the vehicle speed of the electric vehicle 2 is less than or equal to a predetermined upper limit speed. Furthermore, the control unit 7 sets the charge level of the battery 5 as exceeding a predetermined upper limit value and the electric vehicle 2 is traveling downhill as speed change conditions, and when these speed change conditions are met (step S120: Yes), it changes the upper limit speed of the electric vehicle 2 to Vf (step S130). In this way, in the electric vehicle system 1 equipped with battery 5, the amount of heat generated when the regenerative power from regenerative braking is self-consumed by the in-wheel motor 3 can be suppressed to a level below the cooling capacity of the in-wheel motor 3. Therefore, it becomes possible to self-consume the regenerative power from regenerative braking by the in-wheel motor 3 without returning it to battery 5, and as a result, overcharging of battery 5 due to regenerative charging can be effectively avoided.

[0069] [Second Embodiment] Hereinafter, an electric vehicle system according to a second embodiment of the present invention will be described with reference to Figure 6.

[0070] Figure 6 is a schematic diagram showing the overall configuration of an electric vehicle system according to a second embodiment of the present invention. As shown in Figure 6, the electric vehicle system 1A of this embodiment is mounted on an electric vehicle 2, similar to the electric vehicle system 1 described in the first embodiment. In this embodiment, a motor 4 is provided instead of the in-wheel motor 3 of the electric vehicle system 1. The motor 4 is connected to the left front wheel 20FL and the right front wheel 20FR via a drive shaft 21. That is, the motor 4 functions as a power converter that performs power conversion to drive the left front wheel 20FL and the right front wheel 20FR.

[0071] In the electric vehicle system 1A of this embodiment, the inverter 6 controls the operation of the motor 4 according to the control of the control unit 7. The control unit 7 controls the inverter 6 so that the motor 4 controls the driving state of multiple wheels 20 (left front wheel 20FL and right front wheel 20FR) together. Alternatively, the electric vehicle system 1A may be configured using an e-axle that combines the motor 4 and the inverter 6.

[0072] In this embodiment, the control unit 7 performs the same flag setting process and regenerative braking control process as described in the first embodiment. Specifically, in the flag setting process, the SOC upper limit flag and the downhill flag are set according to the control sequence shown in Figure 2. In the regenerative braking control process, regenerative braking is controlled according to the control sequences shown in Figures 3 to 5.

[0073] [Effects of the second embodiment] In the electric vehicle system 1A of this embodiment, since the motor 4 connected to the left front wheel 20FL and the right front wheel 20FR is used as a power converter, the same effects as in the first embodiment can be obtained while maintaining the configuration of a normal electric vehicle. Specifically, when both the downhill flag and the SOC upper limit flag are ON, the upper limit speed of the electric vehicle 2 is changed to Vf. As a result, in the electric vehicle system 1A equipped with a battery 5, the amount of heat generated when the motor 4 self-consumes the regenerative power generated by regenerative braking can be suppressed to be below the cooling performance of the motor 4. Therefore, it becomes possible to self-consume the regenerative power generated by regenerative braking in the motor 4 without returning it to the battery 5, and as a result, it is possible to effectively avoid overcharging of the battery 5 due to regenerative charging.

[0074] In this embodiment, the cooling performance Pcl in the aforementioned equation (1) refers to the cooling performance of the motor 4. Furthermore, the average brake torque τW refers to the average value of the brake torque generated by the regenerative braking of the motor 4 at the left front wheel 20FL and the right front wheel 20FR, respectively.

[0075] [Third Embodiment] Hereinafter, an electric vehicle system according to a third embodiment of the present invention will be described with reference to Figure 7.

[0076] Figure 7 is a schematic diagram showing the overall configuration of an electric vehicle system according to a third embodiment of the present invention. As shown in Figure 7, the electric vehicle system 1B of this embodiment is mounted on an electric vehicle 2, similar to the electric vehicle system 1 described in the first embodiment. In this embodiment, in addition to the components of the electric vehicle system 1, a notification unit 10 is further provided.

[0077] In the electric vehicle system 1B of this embodiment, the notification unit 10 notifies the driver of the electric vehicle 2 when the upper limit speed of the electric vehicle 2 is changed to Vf, in accordance with the control of the control unit 7. Specifically, the driver can be notified of the change in the upper limit speed of the electric vehicle 2 using various methods that the driver can perceive, such as outputting a warning sound from a speaker, vibrating parts of the electric vehicle 2 that come into contact with the driver's body (steering wheel, seat, etc.), lighting a warning lamp, or displaying a warning screen.

[0078] In this embodiment as well, the control unit 7 performs the same flag setting process and regenerative braking control process as described in the first embodiment. Specifically, in the flag setting process, the SOC upper limit flag and the downhill flag are set according to the control sequence shown in Figure 2. In the regenerative braking control process, regenerative braking is controlled according to the control sequence shown in Figures 3 to 5. When the control unit 7 executes the process in step S130, the notification unit 10 notifies the driver of the change in the upper limit speed of the electric vehicle 2 by any method.

[0079] [Effects of the third embodiment] In the electric vehicle system 1B of this embodiment, in addition to the same effects as in the first embodiment, the driver can be notified when the upper limit speed of the electric vehicle 2 is changed from Vmax to Vf. Therefore, when the driving speed of the electric vehicle 2 automatically decreases due to the change in the upper limit speed, it is possible to prevent the driver from mistakenly thinking that the electric vehicle 2 has malfunctioned.

[0080] [others] The present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. [Explanation of Symbols]

[0081] 1, 1A, 1B…Electric vehicle system, 2…Electric vehicle, 3…In-wheel motor, 4…Motor, 5…Battery, 6…Inverter, 7…Control unit, 8…SOC sensor, 9…Tilt sensor, 10…Notification unit, 20…Wheel, 20FL…Left front wheel, 20FR…Right front wheel, 20RL…Left rear wheel, 20RR…Right rear wheel, 21…Drive shaft

Claims

1. A system installed in an electric vehicle, A power converter that drives the wheels of the electric vehicle using driving power and regenerates kinetic energy transmitted from the wheels to output regenerative power, A rechargeable battery that inputs and outputs DC power, An inverter that converts the DC power output from the battery into drive power and supplies it to the power converter, and converts the regenerative power output from the power converter into DC power and supplies it to the battery, The system includes a control unit that controls the operation of the power converter by controlling the inverter, The control unit controls the inverter so that the driving speed of the electric vehicle is below a predetermined upper limit speed. The control unit is configured to change the upper speed limit when the battery charge level exceeds a predetermined upper limit and the electric vehicle is traveling downhill, and the speed change conditions are met.

2. In the electric vehicle system according to claim 1, An electric vehicle system in which the control unit changes the upper speed limit so that the changed upper speed limit is less than or equal to the upper speed limit before the change.

3. In the electric vehicle system according to claim 1, An electric vehicle system in which the control unit switches the control mode of the inverter to a self-consumption control mode for self-consumption of the regenerative power by the power converter when the speed change condition is met and the electric vehicle is performing regenerative braking.

4. In the electric vehicle system according to claim 3, An electric vehicle system in which the control unit controls the inverter in the self-consumption control mode to increase the d-axis current that the inverter outputs to the power converter.

5. In the electric vehicle system according to claim 4, The control unit controls the inverter so that the temperature of each power converter provided for each wheel becomes uniform in this electric vehicle system.

6. In the electric vehicle system according to claim 3, The control unit controls the inverter in the self-consumption control mode so that the regenerative braking by the power converter and the mechanical brakes provided on the wheels work in coordination.

7. In the electric vehicle system according to claim 3, The control unit controls the inverter in the self-consumption control mode such that the power converter connected to one of the multiple wheels of the electric vehicle generates regenerative power, and the power converter connected to any other wheel drives that wheel.

8. In the electric vehicle system according to claim 7, An electric vehicle system in which the control unit controls the inverter such that the power converter connected to the front wheels of the electric vehicle generates regenerative power and the power converter connected to the rear wheels of the electric vehicle drives the rear wheels, thereby increasing the potential energy of the electric vehicle.

9. In the electric vehicle system according to claim 1, The aforementioned power converter is installed for each wheel, The control unit controls the inverter so that the power converter controls the driving state of each wheel individually in this electric vehicle system.

10. In the electric vehicle system according to claim 1, The power conversion device is installed in common for multiple wheels, The control unit controls the inverter so that the power converter controls the driving state of multiple wheels collectively in an electric vehicle system.

11. In the electric vehicle system according to claim 1, The control unit sets a predetermined SOC upper limit flag if the battery charge level exceeds the upper limit. An electric vehicle system in which the monitoring period of the SOC upper limit flag in the control sequence of the inverter by the control unit is longer than the update period of the regenerative brake command for instructing the power converter to output the regenerative power.

12. In the electric vehicle system according to claim 1, The control unit sets a predetermined downhill flag when the electric vehicle is traveling downhill. An electric vehicle system in which the monitoring period of the downhill flag in the control sequence of the inverter by the control unit is longer than the signal acquisition period of the tilt sensor of the electric vehicle.

13. In the electric vehicle system according to claim 1, The control unit, Based on the inclination angle of the slope on which the electric vehicle travels and the weight of the electric vehicle, the brake torque of the electric vehicle is calculated. An electric vehicle system that sets the modified upper speed limit based on the cooling performance of the power converter and the brake torque.

14. In the electric vehicle system according to claim 13, The control unit is an electric vehicle system that estimates the vehicle weight of the electric vehicle based on the relationship between the torque command value of the power converter and the amount of change in vehicle speed.

15. In the electric vehicle system according to claim 13, The control unit sets the speed Vf, represented by the following equation (1), to the upper limit speed after modification, with L being the tire circumference of the wheel, Pcl being the cooling performance of the power converter, and τW being the brake torque. Vf<L×Pcl / (2π×τW) (1)

16. In the electric vehicle system according to claim 1, An electric vehicle system comprising a notification unit that notifies the driver of the electric vehicle when the upper speed limit is changed.

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