JP7596935B2 - Vehicle control device - Google Patents

Description

The present invention relates to a vehicle control device.

Patent document 1 discloses a technology in which, in a control device for a vehicle with independent drive system for left and right wheels, a final torque for each of the left and right wheels is calculated by adding or subtracting a speed difference correction torque calculated based on the rotation speeds of the left and right wheels to the torque command output from a torque command setting unit, and a final torque command that absorbs the imbalance in the speed difference between the left and right wheels is given to the left wheel drive motor and the right wheel drive motor.

Japanese Patent Application Publication No. 08-242506

The technology disclosed in Patent Document 1 requires that the vehicle's running behavior be stabilized based on the minute speed difference between the left and right wheels at low speeds, so there is a demand for even higher accuracy in detecting the speed difference.

The present invention was made in consideration of the above problems, and its purpose is to provide a vehicle control device that can stabilize the driving behavior of an electric vehicle at low vehicle speeds.

In order to solve the above problems and achieve the objective, the vehicle control device of the present invention is a vehicle control device mounted on an electric vehicle, capable of controlling a plurality of rotating electric machines capable of independently driving the left and right wheels, so as to reduce the wheel speed difference when a wheel speed difference occurs between the left and right wheels, and is characterized in that when a correlation parameter correlating with the vehicle speed of the electric vehicle is less than a predetermined value, the vehicle control device controls the plurality of rotating electric machines so as to reduce the wheel speed difference based on information regarding the rotation angle difference between the left and right wheels.

This allows the occurrence of a wheel speed difference between the left and right wheels at low vehicle speeds to be accurately detected using information relating to the difference in rotation angle between the left and right wheels, stabilizing the driving behavior of the electric vehicle.

In addition, in the above, the information regarding the difference in rotation angle between the left wheel and the right wheel may be the difference in rotation angle between the rotors of each of the multiple rotating electric machines.

This allows the occurrence of a wheel speed difference between the left and right wheels to be accurately detected using the difference in rotation angle between the rotors of the rotating electric machines that drive the left and right wheels, even at low vehicle speeds, making it possible to stabilize the running behavior of the electric vehicle.

The vehicle control device according to the present invention has the advantage of being able to accurately detect the occurrence of a wheel speed difference between the left and right wheels, even at low vehicle speeds, by using information relating to the difference in rotation angle between the left and right wheels, thereby stabilizing the driving behavior of the electric vehicle.

FIG. 1 is a diagram showing a schematic configuration of an electric vehicle according to an embodiment. FIG. 2 is a block diagram showing an example of a control circuit of the electric vehicle according to the embodiment. FIG. 3 is a diagram showing the setting of the velocity term gain (kv) and the angle term gain (kθ) by the controller. FIG. 4 is a diagram showing the relationship between the vehicle speed and the angle term gain (kθ). FIG. 5 is a diagram showing the relationship between the vehicle speed and the speed term gain (kv). FIG. 6 is a diagram for explaining the difference calculation process when setting the angle term gain (kθ). FIG. 7 is a diagram showing an example of the offset cancellation process. FIG. 8 is a flowchart showing an example of the control executed by the cancellation determination unit. FIG. 9 is a diagram showing signal waveforms of the rotation angles θ _L and θ _R. FIG. 10 is a diagram showing an example of a method for calculating the rotation angle difference in the first pattern. FIG. 11 is a diagram showing an example of a method for calculating the rotation angle difference in the second pattern. FIG. 12 is a diagram showing an example of a method for calculating the rotation angle difference in the third pattern. FIG. 13 is a diagram showing an example of a method for calculating the rotation angle difference in the fourth pattern.

The following describes an embodiment of a vehicle control device according to the present invention. Note that the present invention is not limited to this embodiment.

Figure 1 is a diagram showing a schematic configuration of an electric vehicle 100 according to an embodiment. As shown in Figure 1, the electric vehicle 100 includes a left front wheel FL and a right front wheel FR, a left rear wheel RL and a right rear wheel RR, motor generators MGL and MGR, a battery 8, inverters 20L and 20R, and an ECU (Electronic Control Unit) 30. The electric vehicle 100 employs a two-wheel independent drive system in which the left front wheel FL and the right front wheel FR are drive wheels, the left rear wheel RL and the right rear wheel RR are driven wheels, and the left front wheel FL and the right front wheel FR are independently driven by the motor generators MGL and MGR, respectively.

The electric vehicle 100 may be configured such that the left rear wheel RL and the right rear wheel RR are drive wheels, and the left front wheel FL and the right front wheel FR are driven wheels, with the left rear wheel FL and the right rear wheel FR being driven independently by the motor generators MGL and MGR, respectively. The electric vehicle 100 may also be configured such that one of the left front wheel FL and the right front wheel FR or the left rear wheel RL and the right rear wheel RR is driven independently by the motor generators MGL and MGR, and the other is driven by one common motor generator. The electric vehicle 100 may also be configured such that the four wheels, the left front wheel FL and the right front wheel FR, and the left rear wheel RL and the right rear wheel RR, are driven independently by four motor generators, respectively.

The motor generators MGL, MGR are connected to the drive shafts 2, 4 of the left front wheel FL and the right front wheel FR, respectively, and drive the left front wheel FL and the right front wheel FR independently via the drive shafts 2, 4. The motor generators MGR, MGL are, for example, three-phase AC motors, and are driven by the electric power stored in the battery 8.

When the electric vehicle 100 is in regenerative braking mode, the motor generators MGL and MGR are rotated by the left and right front wheels FL and FR, respectively, and operate as generators. At this time, the electric power generated by the motor generators MGL and MGR is charged to the battery 8 via the inverters 20L and 20R.

The battery 8 may be, for example, a secondary battery such as a nickel-metal hydride battery or a lithium-ion battery. Alternatively, a large-capacity capacitor such as an electric double-layer capacitor may be used as a power storage device instead of the battery 8.

Inverters 20L, 20R drive and control motor generators MGL, MGR, respectively. When DC voltage is supplied from battery 8, inverters 20L, 20R convert the DC voltage to AC voltage based on signals PWMIL, PWMIR from ECU 30 and supply it to motor generators MGL, MGR. As a result, motor generators MGL, MGR are driven to generate torque according to the required drive torque.

In addition, during regenerative braking of the electric vehicle 100, the inverters 20L, 20R convert the AC voltage generated by the motor generators MGL, MGR into a DC voltage based on the signals PWMIL, PWMIR from the ECU 30, and supply the converted DC voltage to the battery 8.

The electric vehicle 100 includes an accelerator position sensor 50 that detects an accelerator pedal position (accelerator opening) AP, a brake pedal position sensor 52 that detects a brake pedal position BP, a shift position sensor 54 that detects a shift position SP, a steering wheel 7, and a steering angle sensor 56 that detects a steering wheel angle (steering angle) _θs of the steering wheel 7. The electric vehicle 100 also includes wheel speed sensors 40, 42, 44, 46 that detect rotational speeds ωFL, ωFR of the left front wheel FL and the right front wheel FR and rotational speeds ωRL, ωRR of the left rear wheel RL and the right rear wheel RR, respectively. The electric vehicle 100 also includes rotational angle sensors 60L, 60R that detect rotational angles _θL , _θR of the rotors of the motor generators MGL, MGR. Detection signals from these sensors are input to the ECU 30.

The ECU 30 is a vehicle control device that is electrically connected to the inverters 20L, 20R and the battery 8, and controls the driving state of the motor generators MGR, MGL and the charging state of the battery 8 in an integrated manner.

In the electric vehicle 100 according to the embodiment, the left front wheel FL and the right front wheel FR are driven independently by the motor generators MGL and MGR, respectively. Therefore, if a speed difference occurs between the rotational speeds (wheel speeds) ωFL and ωFR of the left front wheel FL and the right front wheel FR, the traveling behavior of the electric vehicle 100 may become unstable.

For example, when the electric vehicle 100 is traveling on a highway at a high vehicle speed, if it encounters a crosswind when exiting a tunnel or overtaking a large vehicle, the electric vehicle 100 will experience a trajectory deviation (yaw movement and inner/outer wheel difference), resulting in a wheel speed difference between the left front wheel FL and the right front wheel FR.

For example, when the electric vehicle 100 is stopped at an intersection or the like, if the vehicle speed is low and the left front wheel FL and the right front wheel FR are in a rut formed on the road surface, a wandering phenomenon occurs in which the left front wheel FL and the right front wheel FR move sideways within the rut, resulting in a wheel speed difference between the left front wheel FL and the right front wheel FR.

Therefore, in the electric vehicle 100 according to the embodiment, when a wheel speed difference occurs between the left front wheel FL and the right front wheel FR, the ECU 30 controls the motor generators MGL and MGR to reduce the wheel speed difference.

The wheel speed difference between the left front wheel FL and the right front wheel FR that occurs when the electric vehicle 100 is in a high vehicle speed range is large enough to be easily detected. On the other hand, the wheel speed difference between the left front wheel FL and the right front wheel FR that occurs when the electric vehicle 100 is in a low vehicle speed range is small enough to be difficult to detect.

Therefore, in the electric vehicle 100 according to this embodiment, when a correlation parameter (vehicle speed or wheel speed) correlated with the vehicle speed is less than a predetermined value, in other words, when the vehicle speed is in the low vehicle speed range, the ECU 30 controls the motor generators MGL, MGR so as to reduce the wheel speed difference based on the difference between rotation angles _θL , _θR of the rotors provided in the motor generators MGL, MGR as information relating to the rotation angles of the left front wheel FL and the right front wheel FR. Also, when the correlation parameter correlated with the vehicle speed is equal to or greater than a predetermined value, in other words, for example, when the vehicle speed is in the high vehicle speed range, the ECU 30 controls the motor generators MGL, MGR so as to reduce the wheel speed difference based on the wheel speed difference between the left front wheel FL and the right front wheel FR.

Figure 2 is a block diagram showing an example of a control circuit of the electric vehicle 100 according to the embodiment. Figure 3 is a diagram showing the setting of the speed term gain (kv) and the angle term gain (kθ) by the controller 32. Figure 4 is a diagram showing the relationship between the vehicle speed and the angle term gain (kθ). Figure 5 is a diagram showing the relationship between the vehicle speed and the speed term gain (kv).

As shown in FIG. 2, the ECU 30 corrects pre-correction driving forces _{Fx_L} , _{Fx_R} , which are calculated based on the accelerator position AP detected by the accelerator position sensor 50 and the shift position SP detected by the shift position sensor 54, with correction driving forces calculated by a controller 32 contained in the ECU 30 using the rotation angles _θL , _θR , and outputs the corrected driving forces _{F'x_L} , _{F'x_R} to inverters 20L, 20R, which control the drive of motor generators MGL, MGR.

As shown in Fig. 3, the controller 32 uses the rotation angles _θL , _θR detected by the rotation angle sensors 60L, 60R to set a speed term gain (kv) and an angle term gain (kθ) as control gains of feedback control that corrects the pre-correction driving force with the corrected driving force so as to reduce the wheel speed difference between the left front wheel FL and the right front wheel FR. That is, as shown in Fig. 3, in the controller 32, a differential processing unit 322 performs differential processing on the rotation angles _θL , _θR , a difference calculation unit 324 performs difference calculation processing on the result of the differential processing, and a speed term gain setting unit 326 sets the speed term gain (kv). Also, as shown in Fig. 3, in the controller 32, a difference calculation unit 328 performs difference calculation processing on the rotation angles _θL , _θR , and an angle term gain setting unit 330 sets the angle term gain (kθ). In this case, as shown in Figures 4 and 5, the angle term gain (kθ) is increased in the low vehicle speed range (e.g., vehicle speed of 20 km/s or less), and the speed term gain (kv) is increased in the high vehicle speed range (e.g., vehicle speed of 80 km/s or more).

6 is a diagram for explaining the difference calculation process performed by the difference calculation unit 328 to set the angle term gain (kθ). The rotation angle sensors 60L, 60R output signals of rotation angles θ _L and θ _R of 0 to 360 [deg]. In the method of detecting the wheel speed difference using the rotation angle difference as in the present embodiment, the rotation angles θ _L and θ _R must be the same when the electric vehicle 100 is in a straight-line state. Therefore, in the difference calculation process performed by the difference calculation unit 328 to set the angle term gain (kθ), as shown in FIG. 7, when the ECU 30 determines that the electric vehicle 100 is in a straight-line state while traveling, it subtracts the rotation angle at the time of determining the straight-line state (time T in FIG. 7) as an offset amount and performs an offset cancellation process to reset the rotation angles θ _L and θ _R to 0 [deg] at the same time.

The determination as to whether or not to perform the offset cancellation process is made by the cancellation determination unit 340 of the controller 32 by determining whether or not the electric vehicle 100 is moving straight from the vehicle speed and the steering wheel angle _θs .

Figure 8 is a flowchart showing an example of the control performed by the cancellation determination unit 340.

First, in step S1, the cancellation determination unit 340 determines whether or not the vehicle speed is greater than a preset threshold value A. If the cancellation determination unit 340 determines that the vehicle speed is greater than threshold value A (Yes in step S1), then in step S2, the cancellation determination unit 340 determines whether or not the absolute value of the steering wheel angle _θs is smaller than a preset threshold value B. If the cancellation determination unit 340 determines that the absolute value of the steering wheel angle _θs is smaller than threshold value B (Yes in step S2), then in step S3, the cancellation determination unit 340 determines that the electric vehicle 100 is in a straight-ahead state, turns on the cancellation execution flag, and ends the series of controls.

If the cancellation determination unit 340 determines that the vehicle speed is not greater than the threshold A (No in step S1), it determines in step S4 that the electric vehicle 100 is not traveling straight, turns off the cancellation execution flag, and ends the series of controls.

Furthermore, if the cancellation determination unit 340 determines that the absolute value of the steering wheel angle _θs is not smaller than the threshold value B (No in step S2), then in step S4 it determines that the electric vehicle 100 is not moving straight, turns off the cancellation execution flag, and ends the series of control operations.

Then, when the cancellation determination unit 340 determines that the electric vehicle 100 is in a straight-line traveling state, the "cancellation execution flag" is turned ON, and the offset cancellation units 342L, 342R of the controller 32 perform offset cancellation processing for the signals of the rotation angles _θL , _θR .

The rotation angles θ _L and θ _R after the offset cancellation process are subjected to a rotation angle difference calculation process in a rotation angle difference calculation unit 344 to calculate a rotation angle difference (Δθ _F ).

FIG. 9 is a diagram showing the signal waveforms of the rotation angles θ _L and θ _R. As shown in FIG. 9, the signals of the rotation angles θ _L and θ _R from the rotation angle sensors 60L and 60R are sawtooth waves of 0 to 360 [deg]. On the other hand, when the difference between the rotation angles θ _L and θ _R is calculated, the rotation angle difference may jump. Therefore, the rotation angle difference calculation unit 344 corrects and calculates the rotation angle difference based on the four condition patterns of the first pattern to the fourth pattern. Note that the rotation angle difference between the rotation angles θ _L and θ _R is set as a default value to the value (θ _L - θ _R ) obtained by subtracting the rotation angle θ _R from the rotation angle θ _L , and this default value (θ _L - _{θ R} ) is appropriately corrected.

Figure 10 shows an example of a method for calculating the rotation angle difference in the first pattern. In Figure 10, ΔT is the control period, and n and n-1 are the number of periods. In Figure 10, an upward arrow indicates that the rotation angle difference is a positive value.

The first pattern is when the rotation angle difference dθ _F (n-1) between rotation angles θ _L and θ _R at time (n-1)ΔT is a positive value (dθ _F (n-1)>0) and the rotation angle difference dθ _F (n) between rotation angles θ _L and θ _R at time nΔT is a positive value (dθ _F (n)>0). In the first pattern, the rotation angle difference is calculated as Δθ _F = θ _L - θ _R.

Figure 11 shows an example of a method for calculating the rotation angle difference in the second pattern. In Figure 11, an upward arrow indicates that the rotation angle difference is a positive value, and a downward arrow indicates that it is a negative value.

The second pattern is when the rotation angle difference dθ _F (n-1) between rotation angles θ _L and θ _R at time (n-1)ΔT is a positive value (dθ _F (n-1)>0) and the rotation angle difference dθ _F (n) between rotation angles θ _L and θ _R at time nΔT is a negative value (dθ _F (n)<0). In the second pattern, the rotation angle difference is calculated as Δθ _F = θ _L - θ _R + 360.

Fig. 12 is a diagram showing an example of a method for calculating the rotation angle difference Δθ _F in the third pattern. In Fig. 12, a downward arrow indicates that the rotation angle difference is a negative value.

The third pattern is when the rotation angle difference dθ _F (n-1) between rotation angles θ _L and θ _R at time (n-1)ΔT is a negative value (dθ _F (n-1)<0) and the rotation angle difference dθ _F (n) between rotation angles θ _L and θ _R at time nΔT is a negative value (dθ _F (n)<0). In the third pattern, the rotation angle difference is calculated as Δθ _F = θ _L - θ _R.

Figure 13 shows an example of a method for calculating the rotation angle difference in the fourth pattern. In Figure 13, an upward arrow indicates that the rotation angle difference is a positive value, and a downward arrow indicates that it is a negative value.

The fourth pattern is a case where the rotation angle difference dθ _F (n-1) between rotation angles θ _L and θ _R at time (n-1)ΔT is a negative value (dθ _F (n-1)<0) and the rotation angle difference dθ _F (n) between rotation angles θ _L and θ _R at time nΔT is a positive value (dθ _F (n)>0). In the fourth pattern, the rotation angle difference is calculated as Δθ _F = θ _L - _{θ R} - 360.

Returning to FIG. 3 , the controller 32 inputs signals of the velocity term gain (kv) and the angle term gain (kθ) set by performing the various processes described above using the rotation angles θ _L and θ _R to a calculator 332 for addition processing, and finally outputs the signals as a corrected driving force.

Returning to Fig. 2, the corrected driving force signal output from controller 32 is input to calculator 34L for the left front wheel and calculator 34R for the right front wheel, where it is added to or subtracted from pre-correction driving forces _{Fx_L} , _{Fx_R,} respectively, and finally output to inverters _20L , _20R , respectively, as corrected driving forces F'x_L, F'x_R. Inverters 20L, 20R control motor generators MGL, MGR so that motor generators MGL, MGR are driven with corrected driving forces _{F'x_L} , _{F'x_R} . This makes it possible to reduce the wheel speed difference between the left front wheel FL and the right front wheel FR driven by motor generators MGL, MGR.

In the electric vehicle 100 according to the embodiment, in a low vehicle speed range where a correlation parameter correlated with the vehicle speed is less than a predetermined value, the ECU 30 feedback controls the motor generators MGL, MGR so as to reduce the wheel speed difference based on the difference in rotation angles _θL , _θR of the rotors provided in the motor generators MGL, MGR as information related to the rotation angles of the left front wheel FL and right front wheel FR, rather than the wheel speed difference between the left front wheel FL and right front wheel FR. As a result, in the electric vehicle 100 according to the embodiment, even in a low vehicle speed range, it is possible to accurately detect the occurrence of a wheel speed difference between the left front wheel FL and right front wheel FR using the difference in rotation angles _θL , _θR , and stabilize the traveling behavior of the electric vehicle 100.

8 Battery 20L, 20R Inverter 30 ECU
32 Controller 34L, 34R, 332 Calculator 40, 42, 44, 46 Wheel speed sensor 50 Accelerator position sensor 52 Brake pedal position sensor 54 Shift position sensor 56 Steering angle sensor 60L, 60R Rotation angle sensor 100 Electric vehicle 340 Cancellation determination unit 342L, 342R Offset cancellation unit 344 Rotation angle difference calculation unit FL Left front wheel FR Right front wheel RL Left rear wheel RR Right rear wheels MGL, MGR Motor generator

Claims (2)

A vehicle control device mounted on an electric vehicle, the vehicle control device being capable of controlling a plurality of rotating electric machines capable of independently driving a left wheel and a right wheel, when a wheel speed difference occurs between the left wheel and the right wheel, so as to reduce the wheel speed difference,
a control device for a vehicle, characterized in that, when a correlation parameter correlating with a vehicle speed of the electric vehicle is less than a predetermined value, the plurality of rotating electric machines are controlled so as to reduce the wheel speed difference based on information regarding a rotation angle difference between the left wheel and the right wheel. The vehicle control device according to claim 1, characterized in that the information relating to the difference in rotation angle between the left wheel and the right wheel is the difference in rotation angle between the rotors of each of the multiple rotating electric machines.

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