Control method of electric vehicle, and control system of electric vehicle

Abstract

To provide a control method of an electric vehicle which can execute a slip control with high accuracy in a four-wheel driving electric vehicle.SOLUTION: A control method of an electric vehicle 100 with a motor driving front wheels 22 and a motor driving rear wheels 32, controls the respective motors through slip control when the electric vehicle 100 is accelerated so that wheel speeds of the front wheels 22 and the rear wheels 32 follow a target wheel speed that is obtained by adding a prescribed target slip amount to a basic vehicle body speed of the electric vehicle 100. The control method of the electric vehicle comprises the steps of: setting a wheel speed of driving wheel whose wheel speed is the lowest wheel speed among the front wheels 22 and the rear wheels 32 as a first estimation vehicle body speed; calculating a second estimation vehicle body speed based on acceleration of the electric vehicle 100; setting a lower value out of the first estimation vehicle body speed and the second estimation vehicle body speed as a basic vehicle body speed; and setting, when the wheel speeds of the front wheels 22 and the rear wheels 32 is deviated from the target wheel speed toward a high speed rotation side, the second estimation vehicle body speed as the basic vehicle body speed.SELECTED DRAWING: Figure 8

Description

[Technical field]

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

[0002] Patent Document 1 discloses a method for determining wheel slippage in a four-wheel drive vehicle when the wheel speed increases suddenly or when the wheel speed deviates from the vehicle body speed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-181564 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, one of the four drive wheels is selected based on predetermined conditions, and the speed of the vehicle body is calculated based on the wheel speed of that drive wheel. Therefore, when all four wheels are slipping, the basic vehicle body speed for slip judgment, which is set based on the wheel speed of the drive wheels, deviates from the actual vehicle speed, making it difficult to perform slip control (torque limiting) with high precision.

[0005] An object of the present invention is to provide an electric vehicle control method and an electric vehicle control system that are capable of executing slip control (torque limiting) with high accuracy in a four-wheel drive electric vehicle. [Means for solving the problem]

[0006] The control method for an electric vehicle according to the present invention is a control method for an electric vehicle, which includes a first drive motor for driving a pair of first drive wheels and a second drive motor for driving a pair of second drive wheels, and slip-controls the first drive motor so that the wheel speed of the first drive wheels follows a first target wheel speed obtained by adding a predetermined first slip amount to a basic vehicle speed of the electric vehicle, and slip-controls the second drive motor so that the wheel speed of the second drive wheels follows a second target wheel speed obtained by adding a predetermined second slip amount to the basic vehicle speed, during acceleration of the electric vehicle. In this control method, the wheel speed of the drive wheel having the lowest wheel speed among the first drive wheel and the second drive wheel is set as a first estimated vehicle speed. Also, a second estimated vehicle speed is calculated based on the acceleration of the electric vehicle. Then, the lower of the first estimated vehicle speed and the second estimated vehicle speed is set as the basic vehicle speed, and further, when the wheel speed of the first driving wheel deviates from the first target wheel speed and the wheel speed of the second driving wheel deviates from the second target wheel speed, the second estimated vehicle speed is set as the basic vehicle speed. Effect of the Invention

[0007] According to the present invention, the basic vehicle speed is calculated with high accuracy by appropriately selecting the first estimated vehicle speed and the second estimated vehicle speed depending on the conditions, and slip control (torque limiting) is executed based on the basic vehicle speed, thereby enabling highly accurate slip control when the electric vehicle is accelerating. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing the system configuration of an electric vehicle to which a control system for an electric vehicle according to this embodiment is applied. [Diagram 2] FIG. 2 is a flowchart showing the flow of processing performed by the motor controller. [Diagram 3] FIG. 3 is a block diagram for implementing torque limiting in a motor controller. [Figure 4] FIG. 4 is a control flow of the first estimated vehicle body speed calculation unit. [Diagram 5]FIG. 5 shows the control flow of the gradient resistance calculation unit. [Figure 6] FIG. 6 is a control flow of the second estimated vehicle body speed calculation unit. [Figure 7] FIG. 7 is a map showing the relationship between the total driving force of the electric vehicle and the lower limit value of the acceleration of the electric vehicle used for calculating the second estimated vehicle body speed. [Figure 8] FIG. 8 shows a control flow of the basic vehicle speed selection unit. [Figure 9] FIG. 9 shows a control flow of the target wheel speed calculation unit. [Figure 10] FIG. 10 shows a control flow of the torque limiting unit. [Figure 11] FIG. 11 is a time chart showing a case where the drive wheels are in a free-spin state during acceleration of the vehicle in slip control of the comparative example. [Figure 12] FIG. 12 is a time chart showing a case where the drive wheels are locked during deceleration of the vehicle in slip control of the comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0010] 1 is a diagram showing a system configuration of an electric vehicle 100 to which a control device for an electric vehicle 100 according to the present embodiment is applied. The electric vehicle 100 is equipped with a plurality of drive wheels and a plurality of electric motors that generate drive forces for the plurality of drive wheels. In the present embodiment, the electric vehicle 100 is a so-called four-wheel drive vehicle, and is equipped with front wheels 22 and rear wheels 32 that are drive wheels, and a front motor 21 and a rear motor 31 that generate braking and driving forces for the drive wheels, respectively.

[0011] As shown in FIG. 1, an electric vehicle 100 includes a front drive system 11, a rear drive system 12, a battery 13, and a motor controller 14 (control unit).

[0012] The front drive system 11 is a system that drives front wheels 22 by a front motor 21. In addition to the front motor 21 (first drive motor) and front wheels 22 (first drive wheels), the front drive system 11 includes a front inverter 23, a rotation sensor 24, a current sensor 25, a front reduction gear 26, a front drive shaft 27, etc.

[0013] The front motor 21 is, for example, a three-phase AC synchronous motor, and is driven by AC power input from the front inverter 23. The output torque of the front motor 21 generates torque (driving force) on the front wheels 22. Furthermore, when the drive shaft of the front motor 21 is rotated together with the front wheels 22, the front motor 21 generates so-called regenerative torque. This allows the front motor 21 to recover the kinetic energy of the electric vehicle 100 as electrical energy.

[0014] The front wheels 22 are a pair of drive wheels arranged at the front of the electric vehicle 100. The front wheels 22 are connected to the front motor 21 via a front reduction gear 26 and a front drive shaft 27. In this embodiment, the front wheels 22 consist of a right front wheel and a left front wheel. However, since the right front wheel and the left front wheel are connected by the front drive shaft 27 and driven integrally, in this embodiment, the right front wheel and the left front wheel may not be distinguished from each other and may be collectively referred to as the front wheels 22. In addition, the front wheels 22 are the first drive wheels in comparison with the rear wheels 32, which are another drive wheel.

[0015] The front inverter 23 includes two pairs of switching elements for each phase of the front motor 21. The front inverter 23 opens and closes these switching elements in response to a PWM (Pulse Width Modulation) signal input from the motor controller 14.

[0016] The rotation sensor 24 detects the rotor phase (α f ) is detected. f ) is a so-called electrical angle [rad]. The rotation sensor 24 is, for example, a resolver or an encoder. The detected rotor phase (αf ) is input to the motor controller 14.

[0017] The current sensor 25 detects the current (i uf ,i vf ,i wf ) (hereinafter referred to as three-phase current). uf ,i vf ,i wf ) is input to the motor controller 14.

[0018] The front reduction gear 26 transmits the braking and driving force of the front motor 21 to the front wheels 22 via the front drive shaft 27. At that time, the front reduction gear 26 adjusts the rotation speed of the front motor 21 to a predetermined gear ratio (N f ) rotates the front drive shaft 27 and the front wheels 22 at a reduced rotation speed.

[0019] The rear drive system 12 is a system that drives rear wheels 32 by a rear motor 31, and is configured symmetrically to the front drive system 11. Therefore, in addition to the rear motor 31 (second drive motor) and rear wheels 32 (second drive wheels), the rear drive system 12 also includes a rear inverter 33, a rotation sensor 34, a current sensor 35, a rear reduction gear 36, a rear drive shaft 37, etc. These components that configure the rear drive system 12 function in the same way as the components of the front drive system 11. In other words, the rear wheels 32 are a pair of drive wheels arranged at the rear of the electric vehicle 100. The rear wheels 32 consist of a right rear wheel and a left rear wheel, but in this embodiment, no distinction is made between these, and the right rear wheel and the left rear wheel may be collectively referred to as the rear wheels 32. The rear wheels 32 are the second drive wheels in comparison with the front wheels 22, which are the other drive wheels. The rotor phase of the rear drive system 12 detected by the rotation sensor 34 is "α r The current flowing through each phase of the rear motor 31 detected by the current sensor 35 is "i ur ,i vr ,i wr "

[0020] The battery 13 is provided in common to the front drive system 11 and the rear drive system 12, and supplies power to drive the front motor 21 and the rear motor 31. During regenerative control, the battery 13 is charged by regenerative power generated by the front motor 21 and the rear motor 31.

[0021] The motor controller 14 is a control device for the electric vehicle 100. The motor controller 14 is configured with one or more computers including, for example, a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). The motor controller 14 is also programmed to control the front motor 21, the rear motor 31, and the like at a predetermined control period. For example, the motor controller 14 acquires various vehicle variables (vehicle information) and generates PWM signals for driving the front motor 21 and the rear motor 31 based on these vehicle variables. The motor controller 14 then inputs the generated PWM signals to the front inverter 23 and the rear inverter 33, respectively, to drive the front motor 21 and the rear motor 31 in accordance with the vehicle variables.

[0022] The vehicle variables are parameters that represent the control state of the electric vehicle 100. The motor controller 14 may, for example, determine the rotor phase (α f ) and three-phase current (i uf ,i vf ,i wf ), the rotor phase of the rear motor 31 (α r ) and three-phase current (i ur ,i vr ,i wrIn addition, the motor controller 14 acquires, for example, an accelerator opening (APO) input from an accelerator opening sensor 41, acceleration (front-rear acceleration, left-right acceleration) input from an acceleration sensor 42, a steering angle (θ) of the steering wheel (front wheels 22) input from a steering angle sensor 43, the wheel speeds of the front wheels 22 (right front wheel, left front wheel) and the rear wheels 32 (right rear wheel, left rear wheel) input from a wheel speed sensor 44, a shift position of the vehicle input from a shift lever 45, and a DC voltage (V dc ) are acquired as vehicle variables. The accelerator opening is a parameter that indicates the amount of accelerator pedal operation by the driver. The wheel speed is the rotation speed of the drive wheel multiplied by the radius of the drive wheel. The DC voltage (V dc The vehicle variables such as the vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed, vehicle speed,

[0023] Fig. 2 is a flowchart showing the flow of processing performed by the motor controller 14. As shown in Fig. 2, the motor controller 14 executes input processing S101, driver request torque calculation processing S102, front / rear driving force distribution processing S103, torque limiting processing S104 (slip control), vibration suppression control calculation processing S105, current command value calculation processing S106, and current control calculation processing S107, etc. That is, the motor controller 14 is programmed to function as an input processing unit that executes the input processing S101, a motor torque command value calculation processing unit that executes the driver request torque calculation processing S102, a torque limiting processing unit that executes the torque limiting processing S104, a vibration suppression control calculation processing unit that executes the vibration suppression control calculation processing S105, a current command value calculation processing unit that executes the current command value calculation processing S106, and a current control calculation processing unit that executes the current control calculation processing S107.

[0024] The input process S101 is a process for acquiring or calculating vehicle variables and the like required for controlling the front motor 21 and the rear motor 31.

[0025] In addition, in the input process S101, the motor controller 14 determines the rotor phase (α f ), the rotor phase of the rear motor 31 (α r ), accelerator opening (APO), steering angle (θ), and DC voltage of battery 13 (V dc ) to get the

[0026] In the input process S101, the motor controller 14 also receives, for example, the rotational angular velocity (ω mf ) [rad / s], and the rotational angular velocity (ω mr ) [rad / s].

[0027] In this embodiment, the rotational angular velocity (ω mf ) and the rotational angular velocity (ω mr However, for example, the rotation speed (N mf ) [rpm], and the rotation speed of the rear motor 31 (N mr ) [rpm] may be used as a parameter representing the rotational speed of the motor.

[0028] The driver request torque calculation process S102 calculates a command value (hereinafter, driver request torque (T m1 * In this embodiment, the motor controller 14 calculates the rotational angular velocity (ω mf ), and referring to an accelerator opening-torque table (a table showing the correlation between accelerator opening, rotational angular velocity, and torque), a driver requested torque (T m1 * ) is calculated.

[0029] In the front and rear driving force distribution process S103, the driver's requested torque (T m1* ) is the front driver required torque (T mf1 * ) and rear driver required torque (T mr1 * ) is distributed to the front driver's required torque (T mf1 * ) is a command value that represents a target torque to be output by the front motor 21. mr1 * ) is a command value that represents the target torque to be output by the rear motor 31. mf1 * ) and rear driver required torque (T mr1 * ) to the driver's requested torque (T m1 * ) distribution ratio (K f ) is set, for example, based on the difference between the wheel load of the front wheels 22 and the wheel load of the rear wheels 32. The difference between the wheel load of the front wheels 22 and the wheel load of the rear wheels 32 is calculated, for example, based on the inclination of the road on which the electric vehicle 100 runs.

[0030] The torque limiting process S104 (slip control) is a process for limiting the front speed (T) when the front wheels 22 are in a spinning state (when they start to spin) during acceleration of the electric vehicle 100, or when the front wheels 22 are in a locked state (when they do not rotate) (when they start to lock) during deceleration of the electric vehicle 100, as described later. m1Lf * ) and calculate the front driver required torque (T mf1 * ) instead of the front speed limiting torque (T m1Lf * ) is set as an input value for vibration suppression control calculation process S105.

[0031] In addition, in the torque limiting process S104, when the spinning or locking state of the front wheels 22 is eliminated, the front speed limiting torque (T m1Lf * ) instead of the front driver required torque (T mf1 * ) is set as an input value for vibration suppression control calculation process S105.

[0032] Similarly, the torque limiting process S104 (slip control) is a process for limiting the rear speed (T m1Lr * ) and calculate the rear driver required torque (T mr1 * ) instead of rear speed limiting torque (T m1Lr * ) is set as an input value for vibration suppression control calculation process S105.

[0033] In addition, in the torque limiting process S104, when the freewheeling or locked state of the rear wheels 32 is eliminated, the rear speed limiting torque (T m1Lr * ) instead of the rear driver required torque (T mf1 * ) is set as an input value for vibration suppression control calculation process S105.

[0034] In the torque limiting process S104, the front speed limiting torque (T m1Lf * ) and rear speed limiting torque (T m1Lr * ) may be simultaneously set as input values ​​to the vibration suppression control calculation process S105. In this case, the front wheels 22 and the rear wheels 32 start to spin or lock at the same time. The torque limiting process S104 will be described in detail later.

[0035] The vibration suppression control calculation process S105 is a process for reducing vibrations occurring in the driving force transmission mechanism from the front motor 21 to the front wheels 22 and the driving force transmission mechanism from the rear motor 31 to the rear wheels 32. In the vibration suppression control calculation process S105, the motor controller 14 calculates the front driver request torque (T mf1 * ) (or Front Speed ​​Limit Torque (T m1Lf * )) to the front motor 21 (hereinafter, the front final torque command value (Tmff * The front final torque command value (T mff * ) executes feedforward control to cause the front motor 21 to output the required torque while reducing the torsional vibration of the front drive shaft 27. Similarly, in the vibration suppression control calculation process S105, the motor controller 14 executes feedforward control to cause the front motor 21 to output the required torque (T mr1 * ) (or rear speed limiting torque (T m1Lr * )) to the rear motor 31 (hereinafter, rear final torque command value (T mrf * The rear final torque command value (T mrf * ) executes feedforward control to output a required torque from the rear motor 31 while reducing torsional vibrations of the rear drive shaft 37. Note that the vibration suppression control calculation process S105 is a conventional technique, and therefore a detailed description thereof will be omitted.

[0036] The current command value calculation process S106 is a process for calculating a command value of a current (hereinafter, referred to as a current command value) to be input to the front motor 21 and the rear motor 31. The motor controller 14 calculates a current command value in a so-called dq-axis coordinate system. Specifically, the motor controller 14 calculates a front final torque command value (T mff * ), the rotational angular velocity (ω mf ), and the DC voltage of the battery 13 (V dc ), a table is referenced based on these as input values ​​to determine the dq-axis current command value (i df * ,i qf * Similarly, the motor controller 14 calculates the rear final torque command value (T mrf * ), the rotational angular velocity (ω mr ), and the DC voltage of the battery 13 (V dc), a table is referenced based on these as input values ​​to determine the dq-axis current command value (i dr * ,i qr * ) is calculated.

[0037] The current control calculation process S107 is a process for calculating the PWM signals for driving the front motor 21 and the rear motor 31. The motor controller 14 calculates the PWM signal for driving the front motor 21 as follows. First, the motor controller 14 calculates the three-phase current (i uf ,i vf ,i wf ) and rotor phase (α f ) based on the dq axis current (i df ,i qf Next, the motor controller 14 calculates the dq-axis current command value (i df * ,i qf * ) and dq axis current (i df ,i qf ) based on the deviation of the dq-axis voltage command value (v df ,v qf At this time, the motor controller 14 may add a so-called non-interference control. In addition, the motor controller 14 calculates the dq-axis voltage command value (v df ,v qf ) and rotor phase (α f ), the three-phase voltage command value (v uf ,v vf ,v wf ) and the motor controller 14 calculates the three-phase voltage command value (v uf ,v vf ,v wf ) and the DC voltage of battery 13 (V dc) A PWM signal is calculated based on the calculated PWM signal. The switching elements of the front inverter 23 are opened and closed by the PWM signal calculated in this manner, thereby driving the front motor 21 to output the required torque. Although the calculation of the PWM signal for driving the front motor 21 has been described above, the calculation of the PWM signal for driving the rear motor 31 is similar.

[0038] [Torque limit (slip control)] Fig. 3 is a block diagram for executing torque limitation in the motor controller 14. As shown in Fig. 3, the motor controller 14 includes a wheel speed calculation unit 1401, a first estimated vehicle body speed calculation unit 1402, a slip determination unit 1403, a lock determination unit 1404, a running resistance calculation unit 1405, a gradient resistance calculation unit 1406, a second estimated vehicle body speed calculation unit 1407, a basic vehicle body speed selection unit 1408, a target wheel speed calculation unit 1409, and a torque limiting unit 1410.

[0039] The wheel speed calculation unit 1401 receives the wheel speeds of the front wheels 22 (left front wheel, right front wheel) and the rear wheels 32 (left rear wheel, right rear wheel) from the wheel speed sensor 44, and also receives the steering angle (θ) from the steering angle sensor 43.

[0040] When the steering angle (θ) is zero, that is, when the electric vehicle 100 is moving straight, the wheel speed calculation unit 1401 outputs the wheel speed input from the wheel speed sensor 44 as is to the first estimated vehicle body speed calculation unit 1402 and the like.

[0041] Furthermore, when the steering angle (θ) is not zero, that is, when the electric vehicle 100 is turning, the wheel speeds of the front wheels 22 (right front wheel, left front wheel) and the rear wheels 32 (right rear wheel, left rear wheel) are different from each other. Therefore, the wheel speed calculation unit 1401 corrects all the wheel speeds to wheel speeds equivalent to the center of gravity of the electric vehicle 100 based on the steering angle (θ), and corrects them to the same value when the front wheels 22 and rear wheels 32 are not slipping.

[0042] The first estimated vehicle body speed calculation unit 1402 receives the corrected wheel speeds of the front wheels 22 (right front wheel, left front wheel), the corrected wheel speeds of the rear wheels 32 (right rear wheel, left rear wheel), and the motor torque (for example, a front final torque command value (T mff * ), or rear final torque command value (T mrf * )) is entered.

[0043] Fig. 4 is a control flow of the first estimated vehicle body speed calculation unit 1402. As shown in Fig. 4, in step S201, the first estimated vehicle body speed calculation unit 1402 determines whether or not the electric vehicle 100 is decelerating by, for example, referring to the sign of the motor torque, and if YES, proceeds to step S202, and if NO (driving at a constant speed or accelerating), proceeds to step S203.

[0044] In step S202, the first estimated vehicle body speed calculation unit 1402 selects the wheel speed of the driving wheel with the lowest wheel speed from the wheel speeds of the front wheels 22 (right front wheel, left front wheel) and the wheel speeds of the corrected rear wheels 32 (right rear wheel, left rear wheel) as the first estimated vehicle body speed (V1).

[0045] In step S203, the first estimated vehicle body speed calculation unit 1402 selects the wheel speed of the driving wheel having the highest wheel speed from the wheel speeds of the front wheels 22 (right front wheel, left front wheel) and the wheel speeds of the corrected rear wheels 32 (right rear wheel, left rear wheel) as the first estimated vehicle body speed (V1).

[0046] 3, the corrected wheel speeds of the front wheels 22 (right front wheel, left front wheel), the corrected wheel speeds of the rear wheels 32 (right rear wheel, left rear wheel), and the motor torque are input to the spin determination unit 1403. The spin determination unit 1403 also includes a map showing the relationship between the motor torque and the estimated acceleration of the electric vehicle 100 (the amount of change in the wheel speed of the drive wheels when the electric vehicle 100 accelerates while the drive wheels are slipping at a predetermined slip ratio), which is the response to the motor torque.

[0047] When the sign of the motor torque is positive (the electric vehicle 100 is accelerating or traveling at a constant speed), the spin determination unit 1403, upon receiving the corrected wheel speeds of the front wheels 22 (right front wheel, left front wheel) and the corrected wheel speeds of the rear wheels 32 (right rear wheel, left rear wheel), differentiates these with respect to time to calculate the amount of change in each wheel speed.

[0048] Then, when the difference between the amount of change in the wheel speed of the corrected front wheels 22 (right front wheel, left front wheel) and the estimated acceleration based on the motor torque and the map, and the difference between the amount of change in the wheel speed of the corrected rear wheels 32 (right rear wheel, left rear wheel) and the estimated acceleration all exceed a predetermined threshold value (fourth threshold value), the spin determination unit 1403 determines that the electric vehicle 100 (front wheels 22 and rear wheels 32) will be in a spinning state (start to be in a spinning state), and outputs a spin detection signal to the gradient resistance calculation unit 1406. Here, the spinning state is a state in which the wheel speed of the front wheels 22 (right front wheel, left front wheel) deviates toward a higher rotation speed from a first target wheel speed of the front wheels 22 described later, and the wheel speed of the rear wheels 32 (right front wheel, left front wheel) deviates toward a higher rotation speed from a second target wheel speed of the rear wheels 32 described later. On the other hand, if the difference between any of the changes in wheel speed and the estimated acceleration is equal to or less than a predetermined threshold (fourth threshold), the spin determination unit 1403 determines that the electric vehicle 100 (front wheels 22 or rear wheels 32) is not in a spinning state, and does not output a spin detection signal.

[0049] The slip determination unit 1403 does not operate when the motor torque is negative (when the electric vehicle 100 is decelerating). After outputting the slip detection signal, the slip determination unit 1403 executes the first torque limit and / or the second torque limit, and stops outputting the slip detection signal when the slip state of the front wheels 22 and / or the rear wheels 32 is resolved.

[0050] 3, the corrected wheel speeds of the front wheels 22 (right front wheel, left front wheel), the corrected wheel speeds of the rear wheels 32 (right rear wheel, left rear wheel), and the motor torque are input to the lockup determination unit 1404. The lockup determination unit 1404 also includes a map showing the relationship between the motor torque and the estimated acceleration of the electric vehicle 100 (the amount of change in the wheel speed of the drive wheels when the electric vehicle 100 decelerates while the drive wheels are slipping at a predetermined slip ratio), which is the response to the motor torque.

[0051] When the sign of the motor torque is negative (the electric vehicle 100 is decelerating), the lock determination unit 1404 receives the corrected wheel speeds of the front wheels 22 (right front wheel, left front wheel) and the corrected wheel speeds of the rear wheels 32 (right rear wheel, left rear wheel) and differentiates them with respect to time to calculate the amount of change in each wheel speed.

[0052] Then, when the difference between the amount of change in wheel speed of the rear wheels 32 (right rear wheel, left rear wheel) after correction and the estimated acceleration based on the motor torque and the map, and the difference between the amount of change in wheel speed of the rear wheels 32 (right rear wheel, left rear wheel) after correction and the estimated acceleration all exceed a predetermined threshold value (fifth threshold value), the lock determination unit 1404 determines that the electric vehicle 100 (front wheels 22 and rear wheels 32) is in a locked state (starts to be in a locked state), and outputs a lock detection signal to the gradient resistance calculation unit 1406. Here, the locked state is a state in which the wheel speed of the front wheels 22 (right front wheel, left front wheel) deviates toward the low rotation speed side from a third target wheel speed of the front wheels 22 described later, and the wheel speed of the rear wheels 32 (right front wheel, left front wheel) deviates toward the low rotation speed side from a fourth target wheel speed of the rear wheels 32 described later. On the other hand, if the difference between any of the changes in wheel speed and the estimated acceleration is equal to or less than a predetermined threshold (fifth threshold), the lock determination unit 1404 determines that the electric vehicle 100 (front wheels 22 or rear wheels 32) is not in a locked state, and does not output a lock detection signal.

[0053] The lockup determination unit 1404 does not operate when the motor torque is positive (when the electric vehicle 100 is accelerating or traveling at a constant speed). After outputting the lockup detection signal, the lockup determination unit 1404 executes the first torque limit and / or the second torque limit, and stops outputting the lockup detection signal when the locked state of the front wheels 22 and / or the rear wheels 32 is resolved.

[0054] The running resistance calculation unit 1405 receives the motor torque (for example, the front final torque command value (T mff * ), or rear final torque command value (T mrf *) and the motor rotation speed (the detection value of the rotation sensor 24, the detection value of the rotation sensor 34) are input.

[0055] The running resistance calculation unit 1405 calculates the front final torque command value (T mff * ) and the response thereof, which is the front rotation speed of the front motor 21 when there is no running resistance; and mrf * ) and the response thereto as the rear rotation speed of the rear motor 31 when there is no running resistance.

[0056] The running resistance calculation unit 1405 calculates the front running resistance applied to the front motor 21 from the difference between the detection value of the rotation sensor 24 and the front rotation speed, calculates the rear running resistance applied to the rear motor 31 from the difference between the detection value of the rotation sensor 34 and the rear rotation speed, and calculates the running resistance of the entire electric vehicle 100 by adding the front running resistance and the rear running resistance.

[0057] The gradient resistance calculation unit 1406 receives the corrected wheel speeds of the front wheels 22 (right front wheel, left front wheel), the corrected wheel speeds of the rear wheels 32 (right rear wheel, left rear wheel), the longitudinal acceleration (including longitudinal acceleration components and gradient components) from the acceleration sensor 42, the motor torque (for example, the front final torque command value (T mff * ), or rear final torque command value (T mrf * )) is input, and further, a slip detection signal or a lock detection signal can be input.

[0058] FIG. 5 shows a control flow of the gradient resistance calculation unit 1406.

[0059] In step S301, the gradient resistance calculation unit 1406 determines whether the electric vehicle 100 is stopped or not, and if YES, the process proceeds to step S309, and if NO, the process proceeds to step S302. Here, the gradient resistance calculation unit 1406 determines that the electric vehicle 100 is stopped, for example, when the first estimated vehicle speed or a second estimated vehicle speed described below is zero.

[0060] In step S302, the gradient resistance calculation unit 1406 determines whether the electric vehicle 100 is decelerating, and if YES, proceeds to step S305, and if NO, proceeds to step S303. The gradient resistance calculation unit 1406 determines that the electric vehicle 100 is decelerating when the motor torque is negative, and determines that the electric vehicle 100 is accelerating or traveling at a constant speed when the motor torque is positive.

[0061] In step S303, the gradient resistance calculation unit 1406 determines whether or not the drive wheel with the lowest wheel speed and the drive wheel with the second lowest wheel speed among the front wheels 22 (right front wheel, left front wheel) and rear wheels 32 (right rear wheel, left rear wheel) are in a spinning state (whether or not a spin detection signal has been input), and if the result is YES, the process proceeds to step S310, and if the result is NO, the process proceeds to step S304.

[0062] Here, the gradient resistance calculation unit 1406 determines that the front wheels 22 (right front wheel, left front wheel) are spinning when the difference between the first target wheel speed described below and the wheel speed of the front wheels 22 (right front wheel, left front wheel) is greater than a predetermined threshold (first threshold (during acceleration)), and determines that the front wheels 22 (right front wheel, left front wheel) are not spinning when the difference is equal to or less than the threshold (first threshold (during acceleration)).

[0063] Similarly, the gradient resistance calculation unit 1406 determines that the rear wheels 32 (right front wheel, left front wheel) are spinning when the difference between the second target wheel speed described below and the wheel speed of the rear wheels 32 (right front wheel, left front wheel) is greater than a predetermined threshold (second threshold (during acceleration)), and determines that the rear wheels 32 (right front wheel, left front wheel) are not spinning when the difference is equal to or less than the threshold (second threshold (during acceleration)).

[0064] In step S304, the gradient resistance calculation unit 1406 calculates the wheel speed of the driving wheel having the lowest wheel speed among the front wheels 22 (right front wheel, left front wheel) and the rear wheels 32 (right rear wheel, left rear wheel) and the average wheel speed of the driving wheel having the second lowest wheel speed.

[0065] In step S305, the gradient resistance calculation unit 1406 determines whether or not the drive wheel having the highest wheel speed and the drive wheel having the second highest wheel speed among the front wheels 22 (right front wheel, left front wheel) and the rear wheels 32 (right rear wheel, left rear wheel) are locked (whether or not a lock detection signal has been input), and if the result is YES, the process proceeds to step S311, and if the result is NO, the process proceeds to step S306.

[0066] Here, the gradient resistance calculation unit 1406 determines that the front wheels 22 (right front wheel, left front wheel) are locked when the difference between the first target wheel speed described below and the wheel speed of the front wheels 22 (right front wheel, left front wheel) is greater than a predetermined threshold (first threshold (during deceleration)), and determines that the front wheels 22 (right front wheel, left front wheel) are not locked when the difference is equal to or less than the threshold (first threshold (during deceleration)).

[0067] Similarly, the gradient resistance calculation unit 1406 determines that the rear wheels 32 (right front wheel, left front wheel) are locked when the difference between the second target wheel speed described below and the wheel speed of the rear wheels 32 (right front wheel, left front wheel) is greater than a predetermined threshold (second threshold (during deceleration)), and determines that the rear wheels 32 (right front wheel, left front wheel) are not locked when the difference is equal to or less than the threshold (second threshold (during deceleration)).

[0068] In addition, the first threshold (when accelerating) and the first threshold (when decelerating) may be the same value or different values, and the second threshold (when accelerating) and the second threshold (when decelerating) may be the same value or different values.

[0069] In step S306, the gradient resistance calculation unit 1406 calculates the average wheel speed of the driving wheel having the highest wheel speed among the front wheels 22 (right front wheel, left front wheel) and the rear wheels 32 (right rear wheel, left rear wheel) and the wheel speed of the driving wheel having the second highest wheel speed.

[0070] In step S307, the gradient resistance calculation unit 1406 calculates the acceleration (G) of the electric vehicle 100 by differentiating the average wheel speed.

[0071] In step S308, the gradient resistance calculation unit 1406 calculates gradient resistance by multiplying a value obtained by subtracting acceleration (G) from the longitudinal acceleration input from the acceleration sensor 42 by the weight of the electric vehicle 100 and the gravitational acceleration (g).

[0072] In step S309, the gradient resistance calculation unit 1406 multiplies the longitudinal acceleration input from the acceleration sensor 42 by the weight of the electric vehicle 100 and the gravitational acceleration (g) to calculate the gradient resistance.

[0073] In steps S310 and S311, the gradient resistance calculator 1406 outputs the previous value of gradient resistance.

[0074] As shown in Fig. 3, the second estimated vehicle body speed calculation unit 1407 receives as input the total driving force of the electric vehicle 100, the running resistance calculated by the running resistance calculation unit 1405, and the gradient resistance calculated by the gradient resistance calculation unit 1406. Here, the total driving force is the sum of a front driving force obtained by multiplying the front motor torque of the front motor 21 by the gear ratio between the front motor 21 and the front drive shaft 27 and dividing the result by the radius of the front wheels 22, and a rear driving force obtained by multiplying the rear motor torque of the rear motor 31 by the gear ratio between the rear motor 31 and the rear drive shaft 37 and dividing the result by the radius of the rear wheels 32. In addition, the front motor torque is calculated based on a front final torque command value (T mff * ), or a value obtained by converting the current value detected by the current sensor 25 into a torque is applied. Similarly, the rear motor torque is determined based on the rear final torque command value (T mrf * ), or a value obtained by converting the current value detected by the current sensor 35 into a torque is applied.

[0075] Fig. 6 shows a control flow of the second estimated vehicle body speed calculation unit 1407. Fig. 7 shows a map showing the relationship between the total driving force of the electric vehicle 100 and the lower limit value of the acceleration of the electric vehicle 100 used to calculate the second estimated vehicle body speed.

[0076] In step S401, the second estimated vehicle body speed calculation unit 1407 calculates a road surface transmitted driving force, which is the driving force actually transmitted by the front wheels 22 and the rear wheels 32 to the road surface, by subtracting the running resistance and the gradient resistance from the total driving force.

[0077] In step S402 , the second estimated vehicle body speed calculation unit 1407 calculates a first estimated acceleration of the electric vehicle 100 by dividing the road surface transmitted driving force by the weight of the electric vehicle 100 .

[0078] In step S403, the second estimated vehicle body speed calculation unit 1407 refers to the map shown in FIG. 7 (described later) to extract an acceleration lower limit value of the electric vehicle 100 corresponding to the total driving force, and sets the larger of the first estimated acceleration and the acceleration lower limit value as the second estimated acceleration. In step S404, the second estimated vehicle body speed calculation unit 1407 calculates the second estimated vehicle body speed by integrating the second estimated acceleration.

[0079] Since the second estimated vehicle body speed is calculated by integrating the second estimated acceleration, for example, even if all four wheels, the front wheels 22 and the rear wheels 32, are in a spinning or locked state, the second estimated vehicle body speed will be a value that is close to the actual vehicle speed of the electric vehicle 100 at the start of the spinning or locked state. Therefore, even if all four wheels start to spin or lock, the state can be quickly resolved by setting the second estimated vehicle body speed to the basic vehicle body speed of the electric vehicle 100 and simultaneously executing a first torque limit on the front wheels 22 (front motor 21) and a second torque limit on the rear wheels 32 (rear motor 31) so as to follow a target wheel speed obtained by adding a predetermined slip amount to the basic vehicle body speed.

[0080] Unlike the first estimated vehicle body speed, the second estimated vehicle body speed is calculated while estimating the acceleration in the front-rear direction of the electric vehicle 100, and therefore the second estimated vehicle body speed is more accurate than the first estimated vehicle body speed calculated based on the wheel speed, and also reflects the actual vehicle speed of the electric vehicle 100 even at the stage when the front wheels 22 and the rear wheels 32 start to spin and lock. However, as described above, the second estimated vehicle body speed is calculated by integrating the second estimated acceleration, and therefore there is a risk that the second estimated vehicle body speed may deviate from the actual vehicle speed of the electric vehicle 100 over time.

[0081] For example, if the error accumulates in the direction that makes the second estimated vehicle speed lower than the actual vehicle speed of the electric vehicle 100, then implementing the torque limit described above will result in excessive suppression of drive wheel slippage, resulting in lower acceleration after the torque limit during acceleration and lower deceleration after the torque limit during deceleration.

[0082] FIG. 7 shows the upper limit value of the acceleration (absolute value) at which acceleration is possible without spinning (deceleration is possible without locking) relative to the total driving force, and by setting this upper limit value as the lower limit value (map) of the acceleration for calculating the second estimated vehicle body speed, the discrepancy between the second estimated vehicle body speed and the actual vehicle speed of the electric vehicle 100 is reduced.

[0083] The map in Fig. 7 is appropriately set based on the type of road surface. For example, (μ3) is a map showing the relationship between the lower limit value of the estimated acceleration corresponding to the friction coefficient between the drive wheels and the road surface when the electric vehicle 100 runs on a normal paved road surface and the total driving force, (μ2) is a map showing the relationship between the lower limit value of the estimated acceleration corresponding to the friction coefficient between the drive wheels and the road surface when the electric vehicle 100 runs off-road and the total driving force, and (μ2) is a map showing the relationship between the lower limit value of the estimated acceleration corresponding to the friction coefficient between the drive wheels and the road surface when the electric vehicle 100 runs on a snowy or icy road and the total driving force. These maps are selected based on information from the shift lever 45 (drive mode), road surface detection using a camera, and friction coefficients estimated from the total driving force and the angular velocity of the drive wheels.

[0084] The second estimated vehicle body speed calculation unit 1407 compares the second estimated vehicle body speed with the first estimated vehicle body speed when the slip determination unit 1403 does not output a slip detection signal and the lock determination unit 1404 does not output a lock detection signal, and updates the second estimated vehicle body speed with the value of the first estimated vehicle body speed when the difference between the second estimated vehicle body speed and the first estimated vehicle body speed exceeds a predetermined third threshold. In this case, since the first estimated vehicle body speed is a value that reflects the actual vehicle speed of the electric vehicle 100, by updating the second estimated vehicle body speed with the value of the first estimated vehicle body speed, it is possible to reduce the deviation between the second estimated vehicle body speed and the actual vehicle speed of the electric vehicle 100.

[0085] The second estimated vehicle body speed calculation unit 1407 updates the second estimated vehicle body speed with the value of the first estimated vehicle body speed after the elimination of the idling state when the idling state is eliminated (output of the idling detection signal stops) by the first torque limit (limiting the torque of the front motor 21) and the second torque limit (limiting the torque of the rear motor 31) after the front wheels 22 (right front wheel, left front wheel) and the rear wheels 32 (right front wheel, left front wheel) are in an idling state (a idling detection signal is outputted). In addition, the second estimated vehicle body speed calculation unit 1407 updates the second estimated vehicle body speed with the value of the first estimated vehicle body speed after the elimination of the idling state when the front wheels 22 (right front wheel, left front wheel) and the rear wheels 32 (right front wheel, left front wheel) are in a locked state (a locking detection signal is outputted) and the locked state is released (output of the locking detection signal stops) by the first torque limit and the second torque limit. In this case too, since the first estimated vehicle body speed is a value that reflects the actual vehicle speed of the electric vehicle 100, the deviation between the second estimated vehicle body speed and the actual vehicle speed of the electric vehicle 100 can be reduced by updating the second estimated vehicle body speed with the value of the first estimated vehicle body speed.

[0086] As shown in FIG. 3, the first estimated vehicle body speed and the second estimated vehicle body speed are input to the basic vehicle body speed selection unit 1408, and further, a slip detection signal or a lock detection signal can be input.

[0087] FIG. 8 shows a control flow of the basic vehicle speed selection unit 1408.

[0088] In step S501, the basic body speed selection unit 1408 determines whether or not a spin detection signal or a lock detection signal has been input, i.e., whether or not all four wheels are in a spinning or locked state (whether or not they are starting to become in a spinning or locked state), and if the result is YES, the process proceeds to step S502, and if the result is NO, the process proceeds to step S503.

[0089] In step S502, the basic vehicle body speed selection unit 1408 selects the second estimated vehicle body speed (V2) as the basic vehicle body speed (V0).

[0090] In step S503, the basic vehicle body speed selection unit 1408 determines whether the electric vehicle 100 is decelerating, and if YES, proceeds to step S504, and if NO, proceeds to step S505. As described above, the basic vehicle body speed selection unit 1408 determines that the electric vehicle 100 is decelerating if the sign of the motor torque is negative, and determines that the electric vehicle 100 is accelerating or traveling at a constant speed if the sign of the motor torque is positive.

[0091] In step S504, the basic vehicle body speed selection unit 1408 selects the higher one of the first estimated vehicle body speed (V1) and the second estimated vehicle body speed (V2) as the basic vehicle body speed (V0).

[0092] In step S505, the basic vehicle body speed selection unit 1408 selects the lower one of the first estimated vehicle body speed (V1) and the second estimated vehicle body speed (V2) as the basic vehicle body speed (V0).

[0093] In the case of steps S504 and S505, i.e., when neither the front wheels 22 nor the rear wheels 32 transition to a spinning state or a locked state, the first estimated vehicle speed (V1) or the second estimated vehicle speed (V2), whichever is closer to the actual vehicle speed of the electric vehicle 100, can be selected as the basic vehicle speed, so that the first torque limit and the second torque limit described below can be executed with high accuracy.

[0094] As shown in FIG. 3, the target wheel speed calculation unit 1409 receives as input the basic vehicle speed selected by the basic vehicle speed selection unit 1408, the longitudinal acceleration detected by the acceleration sensor 42 (or the acceleration (G) calculated by the gradient resistance calculation unit 1406), and the lateral acceleration.

[0095] Fig. 9 shows a control flow of the target wheel speed calculation unit 1409. Fig. 9 shows a flow when the electric vehicle 100 accelerates.

[0096] In step S601, the target wheel speed calculation unit 1409 calculates a first target slip amount for the front wheels 22 and a second target slip amount for the rear wheels 32 based on the longitudinal acceleration and the lateral acceleration. Note that the first target slip amount and the second target slip amount are each an added value, and may be the same value or different values.

[0097] The friction force (longitudinal) related to the longitudinal force of the drive wheels (maximum friction force when the slip ratio is set) increases monotonically as the slip ratio increases from zero, reaches a maximum at the optimum slip ratio (S0) (e.g. 10%), and then decreases monotonically as the slip ratio is increased beyond that slip ratio. On the other hand, the friction force (lateral) related to the lateral force of the drive wheels is maximum when the slip ratio is zero, and decreases monotonically as the slip ratio is increased.

[0098] The target wheel speed calculation unit 1409 sets the first target slip amount and the second target slip amount (for example, basic wheel speed x slip ratio) so as to obtain an optimum slip ratio (S0) at which the frictional force (longitudinal) is maximized when the lateral acceleration is zero. Furthermore, the target wheel speed calculation unit 1409 sets the slip amount so that the slip ratio becomes lower than the optimum slip ratio (S0) as the ratio of the lateral acceleration to the longitudinal acceleration increases. Note that the slip ratio may be set so as not to be lower than a predetermined lower limit (Smin) (the slip ratio when the frictional force (longitudinal) and the frictional force (lateral) are equal) so as to ensure both the frictional force (longitudinal) and the frictional force (lateral) simultaneously.

[0099] In step S602, the target wheel speed calculation unit 1409 calculates a first target wheel speed by adding the first target slip amount to the basic vehicle body speed, and calculates a second target wheel speed by adding the second target slip amount to the basic vehicle body speed. Here, the first target wheel speed and the second target wheel speed may be the same value or may be different values.

[0100] When the electric vehicle 100 decelerates, the target wheel speed calculation unit 1409 calculates a third target slip amount of the front wheels 22 and a fourth target slip amount of the rear wheels 32 based on the longitudinal acceleration and the lateral acceleration. Here, the third target slip amount and the fourth target slip amount are subtraction values, respectively, and the calculation method thereof is the same as the calculation method of the first target slip amount and the second target slip amount described above. Note that the third target slip amount and the fourth target slip amount may be the same value as each other, or may be different values. Also, the absolute value of the third target slip amount and the absolute value of the first target slip amount may be the same value as each other, or may be different values. Similarly, the absolute value of the fourth target slip amount and the absolute value of the second target slip amount may be the same value as each other, or may be different values.

[0101] The target wheel speed calculation unit 1409 calculates the third target wheel speed by subtracting the third target slip amount from the basic vehicle body speed, and calculates the fourth target wheel speed by subtracting the fourth target slip amount from the basic vehicle body speed. Here, the third target wheel speed and the fourth target wheel speed may be the same value or may be different values.

[0102] As shown in FIG. 3, the torque limiting unit 1410 receives the first target wheel speed and the second target wheel speed calculated by the target vehicle body speed calculation unit, the corrected wheel speeds of the front wheels 22 (right front wheel, left front wheel) and the corrected wheel speeds of the rear wheels 32 (right rear wheel, left rear wheel) calculated by the wheel speed calculation unit 1401, and the front driver required torque (T mf1 * ), and rear driver required torque (T mr1 * ) is entered.

[0103] FIG. 10 is a control flow of the torque limiting unit 1410. mf1 * ) or front speed limiting torque (T mfL1 * ) and the rear driver request torque (T mr1 * ) or rear speed limiting torque (T mrL1 * ) and is independent for the front and rear sides.

[0104] In step S701, the torque limiting unit 1410 determines whether it is the front speed limiting torque (T mfL1 * If the front driver request torque (T mf1 * If it is determined that the option ) is selected, the process proceeds to step S702.

[0105] In step S702, the torque limiting unit 1410 judges whether the difference between the first target wheel speed and the wheel speed of the front wheels 22 is greater than a predetermined first threshold value. If NO, the process proceeds to step S703. If YES, the process proceeds to step S704. Here, when the electric vehicle 100 is accelerating, the torque limiting unit 1410 selects the front wheels 22 (right front wheel, left front wheel) which have a lower wheel speed, and when the electric vehicle 100 is decelerating, the torque limiting unit 1410 selects the front wheels 22 (right front wheel, left front wheel) which have a higher wheel speed. The torque limiting unit 1410 calculates the amount of change (time differential) in the wheel speed of the front wheels 22 (right front wheel, left front wheel), and when the amount of change is positive, the torque limiting unit 1410 judges that the electric vehicle 100 is accelerating, and when the amount of change is negative, the torque limiting unit 1410 judges that the electric vehicle 100 is decelerating.

[0106] In step S703, the torque limiting unit 1410 calculates the front driver request torque (T mf1 * ) output.

[0107] In step S704, the torque limiting unit 1410 calculates the front driver request torque (T mf1 * ) to front speed limiting torque (T mfL1 * ) to switch to the front speed limit torque (T mfL1 * ) and output. Here, the front speed limit torque (T mfL1 * ) is a torque command value for the front motor 21 that is feedback-controlled so that the wheel speeds of the front wheels 22 (right front wheel, left front wheel) follow the first target wheel speed.

[0108] In step S705, the torque limiting unit 1410 determines whether the difference between the first target wheel speed and the wheel speed of the front wheels 22 is equal to or smaller than a predetermined first threshold value and the front driver request torque (T mf1 * ) and front speed limiting torque (T mfL1 * If the difference between the first threshold value and the second threshold value is equal to or smaller than a predetermined threshold value (sixth threshold value), the process proceeds to step S706 if the difference is YES, and if the difference is NO, the process proceeds to step S707. Here, for example, the first threshold value in step S705 may be set lower than the first threshold value in step S702, and hysteresis may be set for the wheel speed determination.

[0109] In step S706, the torque limiting unit 1410 calculates the front speed limiting torque (T mfL1 * ) output.

[0110] In step S707, the torque limiting unit 1410 calculates the front speed limiting torque (T mfL1 * ) to the front driver required torque (T mf1 * ) to the front driver request torque (T mf1 * ) and output it.

[0111] Although not shown in the drawings, the second torque limit will also be described below.

[0112] In step S701, the torque limiting unit 1410 determines whether it is the rear speed limiting torque (T mrL1 * If the selection is YES, the process proceeds to step S705. If the selection is NO, the process proceeds to step S706. mr1 * If it is determined that the option ) is selected, the process proceeds to step S702.

[0113] In step S702, the torque limiting unit 1410 judges whether the difference between the second target wheel speed and the wheel speed of the rear wheels 32 is greater than a predetermined second threshold value. If NO, the process proceeds to step S703. If YES, the process proceeds to step S704. Here, when the electric vehicle 100 is accelerating, the torque limiting unit 1410 selects the rear wheels 32 (right rear wheel, left rear wheel) which have a lower wheel speed, and when the electric vehicle 100 is decelerating, the torque limiting unit 1410 selects the front wheels 22 (right front wheel, left front wheel) which have a higher wheel speed. The torque limiting unit 1410 calculates the amount of change (time differential) in the wheel speed of the rear wheels 32 (right rear wheel, left rear wheel), and when the amount of change is positive, the torque limiting unit 1410 judges that the electric vehicle 100 is accelerating, and when the amount of change is negative, the torque limiting unit 1410 judges that the electric vehicle 100 is decelerating.

[0114] In step S703, the torque limiting unit 1410 calculates the rear driver request torque (T mr1 * ) output.

[0115] In step S704, the torque limiting unit 1410 calculates the rear driver request torque (T r1 * ) to rear speed limiting torque (T mrL1 * ) to switch to the rear speed limit torque (T mrL1 * ) is selected and output. Here, the rear speed limit torque (T mrL1 *) is a torque command value for the rear motor 31 that is feedback-controlled so that the wheel speeds of the rear wheels 32 (right rear wheel, left rear wheel) follow the second target wheel speed.

[0116] In step S705, the torque limiting unit 1410 determines whether the difference between the second target wheel speed and the wheel speed of the rear wheels 32 is equal to or smaller than a predetermined second threshold value and whether the rear driver request torque (T mr1 * ) and rear speed limiting torque (T mrL1 * If the result is NO, the process proceeds to step S706, and if the result is YES, the process proceeds to step S707.

[0117] In step S706, the torque limiting unit 1410 calculates the rear speed limiting torque (T mrL1 * ) output.

[0118] In step S707, the torque limiting unit 1410 calculates the front speed limiting torque (T mfL1 * ) to the front driver required torque (T mf1 * ) to the front driver request torque (T mf1 * ) and output it.

[0119] In addition, in electric vehicle 100 of this embodiment, a right front wheel drive motor that drives the right front wheel and a left front wheel drive motor that drives the left front wheel may be configured separately with respect to front wheels 22, and a right rear wheel drive motor that drives the right rear wheel and a left rear wheel drive motor that drives the left rear wheel may be configured separately with respect to rear wheels 32, and a configuration in which the above-mentioned torque limiting is performed independently for the right front wheel drive motor, left front wheel drive motor, right rear wheel drive motor and left rear wheel drive motor may be applied.

[0120] In addition, in electric vehicle 100 of this embodiment, a right front wheel drive motor that drives the right front wheel and a left front wheel drive motor that drives the left front wheel may be configured separately with respect to front wheels 22, and a right rear wheel drive motor that drives the right rear wheel and a left rear wheel drive motor that drives the left rear wheel may be configured separately with respect to rear wheels 32, and a configuration in which the above-mentioned torque limiting is performed independently for the right front wheel drive motor, left front wheel drive motor, right rear wheel drive motor and left rear wheel drive motor may be applied.

[0121] [Time chart for comparison example] Fig. 11 is a time chart showing a slip control of the comparative example in which the drive wheels spin while the vehicle is accelerating. Fig. 12 is a time chart showing a slip control of the comparative example in which the drive wheels lock while the vehicle is decelerating. In the comparative example, it is assumed that all the drive wheels (right front wheel, left front wheel, right rear wheel, left rear wheel) are attached to different drive motors, as in the above. In the comparative example, the basic vehicle speed is calculated using only the first estimated vehicle speed.

[0122] As shown in Fig. 11, at time t0, the wheel speed of the driving wheels (front wheels 22, rear wheels 32) of the electric vehicle 100 starts to increase from zero, and immediately after time t0, the vehicle speed of the electric vehicle 100 increases from zero. From immediately after time t0 to time t1, the driving wheels rotate while gripping the road surface with a predetermined slip amount (slip ratio) (a state in which the driving force is applied from the driving wheels to the road surface and the electric vehicle 100 can accelerate due to a reaction force from the road surface caused by friction), and the wheel speed of the driving wheels and the vehicle speed increase monotonically. At this time, the basic vehicle body speed is set to the first estimated vehicle body speed, that is, the value of the wheel speed of the driving wheel having the lowest wheel speed among the right front wheel, the left front wheel, the right rear wheel, and the left rear wheel. However, since all the driving wheels rotate while gripping the road surface at a target wheel speed including a predetermined slip amount (for example, a slip ratio of +10%), the basic vehicle body speed can be estimated to be almost the same as the actual vehicle speed of the electric vehicle 100.

[0123] At time t1, for example, the electric vehicle 100 enters a section with low road surface resistance (friction coefficient), causing three of the four drive wheels to slip toward the high-speed rotation side (the wheel speed of the drive wheels deviates from the target wheel speed toward the high-speed rotation side, and the slip amount of the drive wheels rises sharply from the predetermined slip amount), and the wheel speed also rises sharply. However, the remaining one drive wheel grips the road surface while maintaining a predetermined slip amount, and the wheel speed of the one drive wheel follows the target wheel speed. Therefore, by limiting the torque of the drive motor that drives the three drive wheels so that the target wheel speed of the three drive wheels follows the wheel speed of the one drive wheel, for example, at time t2 after time t1, the slip amount of the three drive wheels converges to the target slip amount, and it is avoided that the four drive wheels simultaneously enter a spinning state. Also in this case, the basic vehicle speed can be estimated to be almost the same as the actual vehicle speed of the electric vehicle 100.

[0124] At time t3, the electric vehicle 100 enters an area with even lower road resistance, causing the multiple drive wheels to slip one after another to rotate at higher speed, and at time t4, when the last remaining drive wheel slips to rotate at higher speed, the first estimated vehicle body speed becomes higher than the actual speed of the electric vehicle 100, and the basic vehicle body speed and the target wheel speed based on the first estimated vehicle body speed also become higher. For this reason, even if the wheel speeds of the four drive wheels suddenly increase, the slip cannot be detected, and even if all four drive wheels are in a spinning state, this cannot be resolved.

[0125] In this embodiment, from time t0 to just before time t4, the basic vehicle body speed selection unit 1408 (Figure 3) sets the lower of the first estimated vehicle body speed (V1) and the second estimated vehicle body speed (V2) as the basic vehicle body speed (V0), and at time t4, sets the second estimated vehicle body speed (V2) as the basic vehicle body speed (V0).

[0126] From time t0 to just before time t4, the basic vehicle body speed (V0) set in this embodiment is set based on the lower of the first estimated vehicle body speed (V1) and the second estimated vehicle body speed (V2), and is therefore closer to the actual vehicle speed of the electric vehicle 100 than the basic vehicle body speed (V0) set based on the first estimated vehicle body speed (V1) as in the comparative example (the same is true for the case of Figure 12).

[0127] On the other hand, at time t4, the slip determination unit 1403 (FIG. 2) outputs a slip detection signal, causing the basic vehicle body speed selection unit 1408 to set the second estimated vehicle body speed (V2) to the basic vehicle body speed (V0) (FIG. 8, step S502).

[0128] At this time, an error may occur due to integration between the second estimated vehicle body speed (V2) and the actual vehicle speed of the electric vehicle 100. However, if the difference between the second estimated vehicle body speed (V2) and the first estimated vehicle body speed (V1) exceeds a predetermined third threshold value before time t4, the second estimated vehicle body speed (V2) is updated to the value of the first estimated vehicle body speed (V1), so that even at time t4, there is no large deviation between the basic vehicle body speed (V0) based on the second estimated vehicle body speed (V2) and the actual vehicle speed of the electric vehicle 100. Even if the four wheels, the front wheels 22 and the rear wheels 32, slip toward the high-speed rotation side and enter a spinning state (the same applies to a locked state), the value at the start of the spinning state is close to the actual vehicle speed of the electric vehicle 100.

[0129] Therefore, at time t4, the target wheel speeds (first target wheel speed, second target wheel speed) are set by the basic vehicle speed (V0) based on the second estimated vehicle speed (V2), and the torque of each drive wheel (each drive motor) is limited (slip control) so that the wheel speed of the drive wheel follows the target wheel speed, that is, feedback control is performed by the speed limit torque. This reduces the sudden increase in the slip amount in the high-speed rotation direction that occurs in the drive wheel midway, and allows the wheel speeds of all drive wheels to converge to the target slip amount after a predetermined time has passed.

[0130] As a modified example, the first estimated vehicle speed (V1) may be set as the basic vehicle speed (V0) from time t0 until just before time t4, and at time t4, a second estimated vehicle speed (V2) may be calculated based on the acceleration of the electric vehicle 100, and this may be set as the basic vehicle speed (V0).

[0131] At time t4, for example, a slip detection signal is input to the second estimated vehicle body speed calculation unit 1407, causing the second estimated vehicle body speed calculation unit 1407 to calculate the second estimated vehicle body speed (V2), and the basic vehicle body speed selection unit 1408 sets the second estimated vehicle body speed (V2) to the basic vehicle body speed (V0). In this case, a delay occurs from time t4 until the second estimated vehicle body speed (V2) is set to the basic vehicle body speed (V0).

[0132] Therefore, from time t4 until the time when the delay time has elapsed, it is not possible to detect slip of the last remaining drive wheel toward the higher rotation speed side, and as a result, all drive wheels continue to slip toward the higher rotation speed side. Furthermore, since the second estimated vehicle body speed (V2) calculated in the modified example is higher than the second estimated vehicle body speed (V2) calculated in this embodiment, the maximum slip amount (maximum wheel speed) is larger than in this embodiment. And, in the comparative example, it is possible to cause the slip amounts of all drive wheels to converge to the wheel speeds that are the target slip amounts, as in this embodiment, but the timing of this convergence is slower than in this embodiment.

[0133] As shown in Fig. 12, at time t0, the wheel speed of the driving wheels (front wheels 22, rear wheels 32) of the electric vehicle 100 starts to decrease from a predetermined speed, and the vehicle speed of the electric vehicle 100 decreases from the predetermined speed immediately after time t0. From immediately after time t0 to time t1, the driving wheels rotate while gripping the road surface with a predetermined slip amount (slip ratio) (a state in which the driving wheels apply a driving force (braking force) to the road surface and the electric vehicle 100 can decelerate due to a reaction force from the road surface caused by friction), and the wheel speed of the driving wheels and the vehicle speed decrease monotonically. At this time, the basic vehicle speed is set to the first estimated vehicle speed, that is, the value of the wheel speed of the driving wheel having the highest wheel speed among the right front wheel, the left front wheel, the right rear wheel, and the left rear wheel. However, since all the driving wheels rotate while gripping the road surface at a target wheel speed including a predetermined slip amount (for example, a slip ratio of -10%), the basic vehicle speed can be estimated to be almost the same as the actual vehicle speed of the electric vehicle 100.

[0134] At time t1, for example, the electric vehicle 100 enters a section with low road resistance, causing three of the four drive wheels to slip to the low rotation speed side (the wheel speed of the drive wheels deviates from the target wheel speed to the low rotation speed side, and the slip amount of the drive wheels drops sharply from the predetermined slip amount), and the wheel speed also drops sharply. However, the remaining one drive wheel grips the road surface while maintaining a predetermined slip amount, and the wheel speed of the one drive wheel follows the target wheel speed. Therefore, by limiting the torque of the drive motor that drives the three drive wheels so that the target wheel speed of the three drive wheels follows the wheel speed of the one drive wheel, for example, at time t2 after time t1, the slip amount of the three drive wheels converges to the original target slip amount, and it is avoided that the four drive wheels are locked at the same time. Also in this case, the basic vehicle speed can be estimated to be almost the same as the actual vehicle speed of the electric vehicle 100.

[0135] At time t3, when electric vehicle 100 enters an area with even lower road resistance and multiple drive wheels slip to the lower rotation speed side, and at time t4 the last remaining drive wheel slips to the lower rotation speed side, the first estimated vehicle body speed becomes lower than the actual speed of electric vehicle 100, and therefore the basic vehicle body speed and target wheel speed based on the first estimated vehicle body speed also become lower. For this reason, even if the wheel speeds of the four drive wheels suddenly drop, the slip cannot be detected, and even if all four drive wheels are locked, this cannot be resolved.

[0136] On the other hand, in this embodiment, at time t4, the lock determination unit 1404 (FIG. 2) outputs a lock detection signal, causing the basic vehicle body speed selection unit 1408 to set the second estimated vehicle body speed (V2) to the basic vehicle body speed (V0) (FIG. 8, step S502).

[0137] Therefore, at time t4, the target wheel speeds (first target wheel speed, second target wheel speed) are set by the basic vehicle speed (V0) based on the second estimated vehicle speed (V2), and the torque of each drive wheel (each drive motor) is limited (slip control) so that the wheel speed of the drive wheel follows the target wheel speed, that is, feedback control is performed by the speed limit torque. This reduces the sudden increase in the amount of slip in the low-speed rotation direction that occurs in the drive wheels midway, and allows the wheel speeds of all drive wheels to converge to the target amount of slip after a predetermined time has passed.

[0138] In the case of the above-mentioned modified example, at time t4, for example, a lock detection signal is input to the second estimated vehicle body speed calculation unit 1407, so that the second estimated vehicle body speed calculation unit 1407 calculates the second estimated vehicle body speed (V2), and the basic vehicle body speed selection unit 1408 sets the second estimated vehicle body speed (V2) to the basic vehicle body speed (V0). In this case as well, a delay occurs from time t4 until the second estimated vehicle body speed (V2) is set to the basic vehicle body speed (V0).

[0139] Therefore, from time t4 until the time when the delay time has elapsed, it is not possible to detect slip of the last remaining drive wheel toward the lower rotation speed side, and as a result, slip of all drive wheels toward the lower rotation speed side progresses. Furthermore, since the second estimated vehicle body speed (V2) calculated in the modified example is lower than the second estimated vehicle body speed (V2) calculated in this embodiment, the maximum value of the slip amount (minimum value of the wheel speed) is larger than in this embodiment. And, in the comparative example, it is possible to cause the slip amounts of all drive wheels to converge to the wheel speeds that are the target slip amounts, as in this embodiment, but the timing of this convergence is slower than in this embodiment.

[0140] [Effects of this embodiment] According to the control method for the electric vehicle 100 of this embodiment, when the electric vehicle 100 accelerates, the wheel speed of the first drive wheel (front wheel 22) or the second drive wheel (rear wheel 32) which has the lowest wheel speed is set as the first estimated vehicle body speed (V1), a second estimated vehicle body speed (V2) is calculated based on the acceleration of the electric vehicle 100, and the lower of the first estimated vehicle body speed (V1) and the second estimated vehicle body speed (V2) is set as the basic vehicle body speed (V0). Furthermore, if the wheel speed of the first drive wheel (front wheel 22) deviates from the first target wheel speed toward the higher rotation speed and the wheel speed of the second drive wheel (rear wheel 32) deviates from the second target wheel speed toward the higher rotation speed, the second estimated vehicle body speed (V2) is set as the basic vehicle body speed (V0).

[0141] According to the above method, the basic vehicle speed (V0) is calculated with high accuracy by appropriately selecting the first estimated vehicle speed (V1) and the second estimated vehicle speed (V2) depending on the conditions, and slip control (torque limitation) is executed based on the basic vehicle speed (V0), thereby enabling highly accurate slip control when accelerating the electric vehicle 100.

[0142] Furthermore, in the control method for the electric vehicle 100 of this embodiment, when the electric vehicle 100 accelerates, the wheel speed of the first drive wheel (front wheel 22) or the second drive wheel (rear wheel 32) which has the lowest wheel speed value is selected as a first estimated vehicle body speed (V1) and the first estimated vehicle body speed (V1) is set as a basic vehicle body speed (V0), and further, when the wheel speed of the first drive wheel (front wheel 22) deviates from the first target wheel speed toward a higher rotation speed and the wheel speed of the second drive wheel (rear wheel 32) deviates from the second target wheel speed toward a higher rotation speed, a second estimated vehicle body speed (V2) is calculated based on the acceleration of the electric vehicle 100 and the second estimated vehicle body speed (V2) is set as the basic vehicle body speed (V0).

[0143] By using the above method, even if all four wheels, the front wheels 22 and the rear wheels 32, begin to spin, this can be quickly resolved.

[0144] In this embodiment, when the electric vehicle 100 decelerates, the wheel speed of the first drive wheel (front wheel 22) or the second drive wheel (rear wheel 32) which has the highest wheel speed is set as the first estimated vehicle body speed (V1), and the higher of the first estimated vehicle body speed (V1) and the second estimated vehicle body speed (V2) is set as the basic vehicle body speed (V0). Furthermore, when the wheel speed of the first drive wheel (front wheel 22) deviates from the third target wheel speed toward the lower rotation speed and the wheel speed of the second drive wheel (rear wheel 32) deviates from the fourth target wheel speed toward the lower rotation speed, the second estimated vehicle body speed (V2) is set as the basic vehicle body speed (V9).

[0145] The above method enables highly accurate slip control when the electric vehicle 100 is decelerating, as well as when the electric vehicle 100 is accelerating.

[0146] In this embodiment, when the electric vehicle 100 decelerates, the wheel speed of the first driving wheel (front wheel 22) or the second driving wheel (rear wheel 32) which has the highest wheel speed is set as the first estimated vehicle body speed (V0), and the higher of the first estimated vehicle body speed (V1) and the second estimated vehicle body speed (V2) is set as the basic vehicle body speed (V0). Furthermore, when the wheel speed of the first driving wheel (front wheel 22) deviates from the third target wheel speed to the lower side and the wheel speed of the second driving wheel (rear wheel 32) deviates from the fourth target wheel speed to the lower side, a second estimated vehicle body speed (V2) is calculated based on the acceleration of the electric vehicle 100, and the second estimated vehicle body speed (V2) is set as the basic vehicle body speed (V0).

[0147] By using the above method, when the four wheels, the front wheels 22 and the rear wheels 32, begin to spin, the above-mentioned four wheels can be quickly resolved even when the four wheels begin to lock.

[0148] In this embodiment, the acceleration (G) of the electric vehicle 100 is calculated based on the torque command value (front driver required torque (T mf1 * ), rear driver required torque (T mr1 * )), the gradient resistance of the road surface on which the electric vehicle 100 is traveling, and the weight of the electric vehicle 100.

[0149] According to the above method, the acceleration (G) of the electric vehicle 100 can be calculated in a simple manner.

[0150] In this embodiment, when an acceleration sensor 42 that detects force is mounted on the electric vehicle 100, during acceleration of the electric vehicle 100, gradient resistance is calculated based on the amount detected by the acceleration sensor 42, the amount of change (time derivative) in the wheel speed of the first drive wheel (front wheel 22) or the second drive wheel (rear wheel 32) whichever has the lower wheel speed, and the weight of the electric vehicle 100, and during deceleration of the electric vehicle 100, gradient resistance is calculated based on the amount detected by the acceleration sensor 42, the amount of change in the wheel speed of the first drive wheel (front wheel 22) or the second drive wheel (rear wheel 32) whichever has the higher wheel speed, and the weight of the electric vehicle 100.

[0151] According to the above method, the gradient resistance can be calculated in a simple manner, and the acceleration (G) of the electric vehicle 100 can be calculated with high accuracy.

[0152] In this embodiment, a lower limit value for the absolute value of the acceleration (G) of the electric vehicle 100 corresponding to the total driving force is set, and the acceleration of the electric vehicle 100 corresponding to the total driving force is set to be equal to or greater than the lower limit value.

[0153] By using the above method, in a case where the second estimated vehicle body speed is lower than the actual vehicle speed of the electric vehicle 100 and the second estimated vehicle body speed, which is the integral value of the acceleration (G), deviates from the actual vehicle speed of the electric vehicle 100 over time, the deviation between the second estimated vehicle body speed and the actual vehicle speed of the electric vehicle 100 is reduced by setting a lower limit value for the acceleration (G), and acceleration and deceleration during torque limiting can be prevented from becoming smaller than necessary.

[0154] In this embodiment, the acceleration (G) of the electric vehicle 100 when the wheel speed of the first drive wheel (front wheel 22) deviates from the first target wheel speed to the higher rotation speed and the wheel speed of the second drive wheel (rear wheel 32) deviates from the second target wheel speed to the higher rotation speed, resulting in a spinning state, is calculated based on the gradient resistance immediately before the spinning state is entered, and the acceleration (G) of the electric vehicle 100 when the wheel speed of the first drive wheel (front wheel 22) deviates from the first target wheel speed to the lower rotation speed and the wheel speed of the second drive wheel (rear wheel 32) deviates from the second target wheel speed to the lower rotation speed, resulting in a locked state, is calculated based on the gradient resistance immediately before the locked state is entered. By using the above method, the acceleration (G) can be calculated with high accuracy even when the drive wheels are in a free-spinning or locked state.

[0155] In this embodiment, when the difference between the second estimated vehicle body speed (V2) and the first estimated vehicle body speed (V1) exceeds a predetermined threshold (third threshold), the second estimated vehicle body speed (V2) is updated with the value of the first estimated vehicle body speed (V1). By using the above method, the error in the second estimated vehicle body speed (V2), which increases with time, can be corrected using the first estimated vehicle body speed.

[0156] In this embodiment, when a spinning state in which the wheel speed of the first driving wheel (front wheel 22) deviates from the first target wheel speed toward a higher rotation speed and the wheel speed of the second driving wheel (rear wheel 32) deviates from the second target wheel speed toward a higher rotation speed is eliminated (by slip control for the front motor 21 and the rear motor 31), the second estimated vehicle body speed (V2) is updated by the value of the first estimated vehicle body speed (V1) after the spinning state is eliminated, and when a locked state in which the wheel speed of the first driving wheel (front wheel 22) deviates from the first target wheel speed toward a lower rotation speed and the wheel speed of the second driving wheel (rear wheel 32) deviates from the second target wheel speed toward a lower rotation speed is eliminated (by slip control for the front motor 21 and the rear motor 31), the second estimated vehicle body speed (V2) is updated by the value of the first estimated vehicle body speed (V1) after the locked state is eliminated.

[0157] By using the above method, the second estimated vehicle speed (V1), which has an error due to passing through a spinning state and a locked state, can be corrected by the first estimated vehicle speed (V1) after the spinning state and the locked state are released.

[0158] The control system for the electric vehicle 100 of this embodiment is a control system for the electric vehicle 100 in which, when the electric vehicle 100 accelerates, a control unit (motor controller 14) executes the first slip control, and the control unit (motor controller 14) sets the wheel speed of the driving wheel having the lowest wheel speed among the first driving wheel (front wheel 22) and the second driving wheel (rear wheel 32) as a first estimated vehicle body speed (V1), calculates a second estimated vehicle body speed (V2) based on the acceleration of the electric vehicle 100, sets the lower of the first estimated vehicle body speed (V1) and the second estimated vehicle body speed (V2) as a basic vehicle body speed (V0), and further sets the second estimated vehicle body speed (V2) to the basic vehicle body speed (V0) when the wheel speed of the first driving wheel (front wheel 22) deviates from the first target wheel speed toward the higher rotation speed and when the wheel speed of the second driving wheel (rear wheel 32) deviates from the second target wheel speed toward the higher rotation speed.

[0159] With the above configuration, the basic vehicle speed (V0) is calculated with high accuracy by appropriately selecting the first estimated vehicle speed (V1) and the second estimated vehicle speed (V2) depending on the conditions, and slip control (torque limitation) is executed based on the basic vehicle speed (V0), thereby enabling highly accurate slip control when accelerating the electric vehicle 100.

[0160] Furthermore, in the control system for the electric vehicle 100 of this embodiment, when the electric vehicle 100 accelerates, the control unit (motor controller 14) selects the wheel speed of the driving wheel having the lowest wheel speed among the first driving wheel (front wheels 22) and the second driving wheel (rear wheels 32) as a first estimated vehicle body speed (V1) and sets the first estimated vehicle body speed (V1) to a basic vehicle body speed (V0), and further, when the wheel speed of the first driving wheel (front wheels 22) deviates from the first target wheel speed toward a higher rotation speed and the wheel speed of the second driving wheel (rear wheels 32) deviates from the second target wheel speed toward a higher rotation speed, calculates a second estimated vehicle body speed (V2) based on the acceleration of the electric vehicle 100 and sets the second estimated vehicle body speed (v2) to the basic vehicle body speed (V0).

[0161] With the above-described configuration, even if all four wheels, the front wheels 22 and the rear wheels 32, begin to spin, this can be quickly resolved.

[0162] The above describes an embodiment of the present invention. However, the configurations described in the above embodiment and each modified example are merely examples of application of the present invention and are not intended to limit the technical scope of the present invention. [Explanation of symbols]

[0163] 14 motor controller, 21 front motor, 22 front wheel, 31 rear motor, 32 rear wheel, 100 electric vehicle

Claims

1. A control method for an electric vehicle, comprising: a first drive motor for driving a pair of first drive wheels and a second drive motor for driving a pair of second drive wheels, the control comprising: slip-controlling the first drive motor so that a wheel speed of the first drive wheels follows a first target wheel speed obtained by adding a predetermined first target slip amount to a basic vehicle speed of the electric vehicle; and slip-controlling the second drive motor so that the wheel speed of the second drive wheels follows a second target wheel speed obtained by adding a predetermined second target slip amount to the basic vehicle speed, setting a wheel speed of the drive wheel having the lowest wheel speed among the first drive wheel and the second drive wheel as a first estimated vehicle body speed; Calculating a second estimated vehicle body speed based on an acceleration of the electric vehicle; a first estimated vehicle speed and a second estimated vehicle speed, whichever is lower, set as the basic vehicle speed; and, if the wheel speed of the first driving wheel deviates from the first target wheel speed toward a higher rotation speed and the wheel speed of the second driving wheel deviates from the second target wheel speed toward a higher rotation speed, set the second estimated vehicle speed as the basic vehicle speed.

2. A control method for an electric vehicle, comprising: a first drive motor for driving a pair of first drive wheels and a second drive motor for driving a pair of second drive wheels, the control comprising: slip-controlling the first drive motor so that a wheel speed of the first drive wheels follows a first target wheel speed obtained by adding a predetermined first target slip amount to a basic vehicle speed of the electric vehicle; and slip-controlling the second drive motor so that the wheel speed of the second drive wheels follows a second target wheel speed obtained by adding a predetermined second target slip amount to the basic vehicle speed, a wheel speed of the first drive wheel and the second drive wheel which has the lowest wheel speed value is selected as a first estimated vehicle body speed, and the first estimated vehicle body speed is set as the basic vehicle body speed; and, when the wheel speed of the first drive wheel deviates from the first target wheel speed and the wheel speed of the second drive wheel deviates from the second target wheel speed, a second estimated vehicle body speed is calculated based on the acceleration of the electric vehicle, and the second estimated vehicle body speed is set as the basic vehicle body speed.

3. When the electric vehicle is decelerating, the first drive motor is slip-controlled so that the wheel speed of the first drive wheel follows a third target wheel speed obtained by subtracting a predetermined third target slip amount from the basic vehicle body speed, and the second drive motor is slip-controlled so that the wheel speed of the second drive wheel follows a fourth target wheel speed obtained by subtracting a predetermined fourth target slip amount from the basic vehicle body speed, setting a wheel speed of the first drive wheel or the second drive wheel having the highest wheel speed as the first estimated vehicle body speed; 2. The method for controlling an electric vehicle according to claim 1, further comprising the steps of: setting the first estimated vehicle body speed or the second estimated vehicle body speed, whichever is higher, as the basic vehicle body speed; and further setting the second estimated vehicle body speed as the basic vehicle body speed when the wheel speed of the first driving wheel deviates from the third target wheel speed to a lower rotation speed and when the wheel speed of the second driving wheel deviates from the fourth target wheel speed to a lower rotation speed.

4. When the electric vehicle is decelerating, the first drive motor is slip-controlled so that the wheel speed of the first drive wheel follows a third target wheel speed obtained by subtracting a predetermined third target slip amount from the basic vehicle body speed, and the second drive motor is slip-controlled so that the wheel speed of the second drive wheel follows a fourth target wheel speed obtained by subtracting a predetermined fourth target slip amount from the basic vehicle body speed, setting a wheel speed of the first drive wheel or the second drive wheel having the highest wheel speed as the first estimated vehicle body speed; 3. The method for controlling an electric vehicle according to claim 2, further comprising the steps of: setting the first estimated vehicle body speed or the second estimated vehicle body speed, whichever is higher, as the basic vehicle body speed; and further calculating the second estimated vehicle body speed based on an acceleration of the electric vehicle and setting the second estimated vehicle body speed to the basic vehicle body speed when the wheel speed of the first driving wheel deviates from the third target wheel speed to a lower speed side and the wheel speed of the second driving wheel deviates from the fourth target wheel speed to a lower speed side.

5. 5. The method for controlling an electric vehicle according to claim 1, further comprising the steps of: calculating an acceleration of the electric vehicle based on a total driving force of the first drive motor and the second drive motor, which are driven based on a torque command value; a gradient resistance of a road surface on which the electric vehicle travels; and a weight of the electric vehicle.

6. In the case where an acceleration sensor that detects a force is mounted on the electric vehicle, calculating the gradient resistance based on an amount detected by the acceleration sensor during acceleration of the electric vehicle, an amount of change in the wheel speed of one of the first drive wheel and the second drive wheel which has a lower wheel speed, and a weight of the electric vehicle; 6. The method for controlling an electric vehicle according to claim 5, further comprising the step of calculating the gradient resistance based on the detected amount, the amount of change in the wheel speed of one of the first drive wheel and the second drive wheel which has a higher wheel speed, and a weight of the electric vehicle during deceleration of the electric vehicle.

7. setting a lower limit value of an absolute value of the acceleration of the electric vehicle corresponding to the total driving force; The method for controlling an electric vehicle according to claim 5 , further comprising the step of: setting an acceleration of the electric vehicle corresponding to the total driving force to be equal to or greater than the lower limit value.

8. calculating an acceleration of the electric vehicle when a wheel speed of the first drive wheel deviates from the first target wheel speed toward a higher rotation speed and a wheel speed of the second drive wheel deviates from the second target wheel speed toward a higher rotation speed, based on the gradient resistance immediately before the wheel speed is reduced; 6. The method for controlling an electric vehicle according to claim 5, further comprising the step of calculating, based on the gradient resistance immediately before the electric vehicle enters a locked state in which the wheel speed of the first drive wheel deviates from the first target wheel speed to a lower rotation speed and the wheel speed of the second drive wheel deviates from the second target wheel speed to a lower rotation speed, the acceleration of the electric vehicle when the locked state is entered.

9. 3. The method for controlling an electric vehicle according to claim 1, further comprising updating the second estimated vehicle body speed with a value of the first estimated vehicle body speed when a difference between the second estimated vehicle body speed and the first estimated vehicle body speed exceeds a predetermined threshold value.

10. when a spin state in which the wheel speed of the first drive wheel deviates from the first target wheel speed toward a higher rotation speed and the wheel speed of the second drive wheel deviates from the second target wheel speed toward a higher rotation speed is eliminated, the second estimated vehicle body speed is updated by the value of the first estimated vehicle body speed after the elimination of the spin state; 5. The method for controlling an electric vehicle according to claim 1, further comprising the steps of: updating the second estimated vehicle body speed with a value of the first estimated vehicle body speed after a locked state in which the wheel speed of the first drive wheel deviates from the first target wheel speed toward a lower rotation speed and the wheel speed of the second drive wheel deviates from the second target wheel speed toward a lower rotation speed is eliminated.

11. A pair of first drive wheels; a first drive motor that drives the first drive wheel; A pair of second drive wheels; a second drive motor that drives the second drive wheel; a control unit that drives the first drive motor and the second drive motor, wherein the control unit slip-controls the first drive motor such that, during acceleration of the electric vehicle, the wheel speed of the first drive wheel follows a first target wheel speed obtained by adding a predetermined first target slip amount to a basic vehicle speed of the electric vehicle, and slip-controls the second drive motor such that the wheel speed of the second drive wheel follows a second target wheel speed obtained by adding a predetermined second target slip amount to the basic vehicle speed, The control unit is setting a wheel speed of the drive wheel having the lowest wheel speed among the first drive wheel and the second drive wheel as a first estimated vehicle body speed; Calculating a second estimated vehicle body speed based on an acceleration of the electric vehicle; a first estimated vehicle speed and a second estimated vehicle speed, whichever is lower, set as the basic vehicle speed; and, when the wheel speed of the first drive wheel deviates from the first target wheel speed toward a higher rotation speed and the wheel speed of the second drive wheel deviates from the second target wheel speed toward a higher rotation speed, set the second estimated vehicle speed as the basic vehicle speed.

12. A pair of first drive wheels; a first drive motor that drives the first drive wheel; A pair of second drive wheels; a second drive motor that drives the second drive wheel; a control unit that drives the first drive motor and the second drive motor, wherein the control unit slip-controls the first drive motor such that, during acceleration of the electric vehicle, the wheel speed of the first drive wheel follows a first target wheel speed obtained by adding a predetermined first target slip amount to a basic vehicle speed of the electric vehicle, and slip-controls the second drive motor such that the wheel speed of the second drive wheel follows a second target wheel speed obtained by adding a predetermined second target slip amount to the basic vehicle speed, The control unit is a wheel speed of the first drive wheel and the second drive wheel which has the lowest wheel speed value as a first estimated vehicle body speed, and sets the first estimated vehicle body speed to the basic vehicle body speed; and, when the wheel speed of the first drive wheel deviates from the first target wheel speed and the wheel speed of the second drive wheel deviates from the second target wheel speed to the high speed rotation side, calculates a second estimated vehicle body speed based on the acceleration of the electric vehicle, and sets the second estimated vehicle body speed to the basic vehicle body speed.

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