Torque distribution control method and torque distribution control device

Abstract

This torque distribution control method is an electrically-driven vehicle torque distribution control method that carries out torque distribution control for multiple drive wheels. Said method includes: calculating the torque distribution value of any drive wheel of multiple drive wheels based on a first parameter; and calculating a correction value for the torque distribution value based on the deviation between the actual value and a target value of a second parameter and correcting the torque distribution value by the calculated correction value. The correction value is limited based on the torque distribution value.

Description

[Technical Field]

[0001] The present invention relates to torque distribution control. [Background technology]

[0002] JP2614836B discloses a torque distribution control device for a four-wheel drive vehicle that variably controls torque distribution to each wheel in accordance with a plurality of control parameters, each of which indicates a different driving state. This device prioritizes the plurality of control parameters, and when the engine output required to achieve a target distribution set in accordance with these parameters cannot be obtained, torque distribution control is performed by sequentially eliminating torque distribution based on control parameters with lower priorities. Summary of the Invention

[0003] In an electric vehicle, the torque distribution value of the drive wheels may be corrected according to the driving state, which is represented by, for example, longitudinal acceleration. The correction can be performed by calculating a correction value for the torque distribution value based on the deviation between the actual value and the target value of a parameter representing a correction factor, and correcting the torque distribution value with the calculated correction value. The correction factor is, for example, slip, and in this case, the parameter representing the correction factor is, for example, the differential rotation between the slipping drive wheel and the other drive wheels.

[0004] However, for example, if different diameter tires are mounted on the front and rear wheels, this can cause a rotational difference. In other words, the parameter representing the correction factor may remain unchanged due to factors other than the correction factor. In this case, the calculated correction value may become inappropriate, resulting in an inappropriate torque distribution value. If the torque distribution value becomes inappropriate, torque distribution according to the driving state will be disrupted, which may affect the vehicle's cornering characteristics, etc.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to prevent the torque distribution value from becoming inappropriate. [Means for solving the problem]

[0006] A torque distribution control method according to one aspect of the present invention includes calculating a correction value for a torque distribution value for drive wheels of an electric vehicle based on a deviation between an actual value and a target value, and correcting the torque distribution value with the calculated correction value. The method further includes limiting the correction value based on the torque distribution value.

[0007] According to another aspect of the present invention, there is provided a torque distribution control device corresponding to the torque distribution control method described above. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram illustrating the configuration of a vehicle. [Figure 2] FIG. 2 is a functional block diagram of the motor controller. [Figure 3] FIG. 3 is a flowchart showing the slip correction torque calculation process. [Figure 4] FIG. 4 is a diagram showing an example of setting the I-term limiter distribution value. [Figure 5] FIG. 5 is a flowchart showing the limiter setting process. [Figure 6] FIG. 6 is a diagram illustrating a first example of a timing chart. [Figure 7] FIG. 7 is a timing chart of a comparative example. [Figure 8] FIG. 8 is a diagram showing a second example of the timing chart. DETAILED DESCRIPTION OF THE INVENTION

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

[0010] FIG. 1 is a block diagram illustrating the configuration of a vehicle 100 according to this embodiment. The vehicle 100 is an electric vehicle. An electric vehicle is a vehicle equipped with an electric motor (hereinafter simply referred to as a motor) as a drive source and propels itself by generating drive force resulting from torque generated by the motor on one or more wheels. Therefore, electric vehicles include not only so-called electric automobiles but also hybrid vehicles that use both a motor and an engine as a drive source. For example, electric vehicles also include hybrid vehicles that use a motor as a drive source for one of the front or rear wheels and an engine as a drive source for the other wheels. Furthermore, a four-wheel drive vehicle is a vehicle that uses four wheels as drive wheels. Four-wheel drive vehicles include vehicles that always use four wheels as drive wheels, as well as vehicles that can switch between two-wheel drive (front-wheel drive or rear-wheel drive) and four-wheel drive. Furthermore, a four-wheel drive vehicle can control some of its four wheels as drive wheels in conjunction with one another, or control all four wheels as drive wheels that are driven independently. Therefore, in this embodiment, the electric four-wheel drive vehicle refers to a vehicle that runs by generating driving force due to torque generated by a motor on some or all of the four wheels.

[0011] 1, the vehicle 100 is an electric four-wheel drive vehicle. The vehicle 100 includes a front drive system fds, a rear drive system rds, a battery 1, and a motor controller 2 (controller).

[0012] The front drive system fds receives power from a battery 1 and drives the front wheels 9f under the control of a motor controller 2. The front drive system fds includes a front inverter 3f, a front drive motor 4f, a front reduction gear 5f, a front rotation sensor 6f, a front drive shaft 8f, and front wheels 9f. The subscript f indicates a front-side configuration. The front wheels 9f are a pair of wheels that are relatively forward of the vehicle 100, out of the four wheels equipped on the vehicle 100. The forward direction of the vehicle 100 is a predetermined direction that is formally determined depending on the orientation of the driver's seat, etc. The front drive system fds causes the front wheels 9f to function as drive wheels 9 that generate driving force for the vehicle 100.

[0013] The rear drive system RDS receives power from a battery 1 and drives the rear wheels 9r under the control of a motor controller 2. The rear drive system RDS is symmetrical to the front drive system FDS and includes a rear inverter 3r, a rear drive motor 4r, a rear reduction gear 5r, a rear rotation sensor 6r, a rear drive shaft 8r, and rear wheels 9r. The subscript r indicates a rear-side configuration. The rear wheels 9r are a pair of wheels that are relatively rearward of the vehicle 100 out of the four wheels equipped on the vehicle 100. The rearward direction of the vehicle 100 refers to the direction opposite to the forward direction of the vehicle 100. With the rear drive system RDS, the rear wheels 9r function as drive wheels 9 that generate driving force for the vehicle 100.

[0014] The battery 1 is connected to the motor 4 via an inverter 3 and supplies drive power to the motor 4 by discharging. The battery 1 can also be charged by receiving regenerative power from the motor 4. In the front drive system FDS, the battery 1 is connected to the front drive motor 4F via a front inverter 3F. Similarly, in the rear drive system RDS, the battery 1 is connected to the rear drive motor 4R via a rear inverter 3R.

[0015] The motor controller 2 is a control device for the vehicle 100 and is a computer comprising a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), an input / output interface (I / O interface), etc. The motor controller 2 generates control signals for controlling the front drive motor 4f and the rear drive motor 4r based on vehicle variables of the vehicle 100. The vehicle variables are information indicating the operating state or control state of the entire vehicle 100 or of each part constituting the vehicle 100, and can be obtained by detection, measurement, calculation, etc. The vehicle variables include, for example, the accelerator opening APO, longitudinal and lateral G, vehicle speed V, gradient value, steering angle, and wheel speed, as well as the rotational speeds Nmf and Nmr of the motors 4f and 4r, and three-phase AC current, as described below. The motor controller 2 uses these vehicle variables to control the front drive motor 4f and the rear drive motor 4r, respectively.

[0016] The front inverter 3f and the rear inverter 3r convert the direct current supplied from the battery 1 into alternating current and adjust the current supplied to the front drive motor 4f and the rear drive motor 4r, respectively, by turning on and off switching elements in response to drive signals generated by the motor controller 2. In addition, each of the inverters 3f, 3r inversely converts the alternating current generated by the front drive motor 4f and the rear drive motor 4r due to regenerative braking force back into direct current, and adjusts the current supplied to the battery 1.

[0017] The front drive motor 4f and the rear drive motor 4r are, for example, three-phase AC motors that generate drive force (torque T) using AC current supplied from the connected inverter 3. The drive force generated by the front drive motor 4f is transmitted to the front wheels 9f via the front reduction gear 5f and the front drive shaft 8f. Similarly, the drive force generated by the rear drive motor 4r is transmitted to the rear wheels 9r via the rear reduction gear 5r and the rear drive shaft 8r. When rotated along with the front wheels 9f and the rear wheels 9r, the front drive motor 4f and the rear drive motor 4r generate regenerative braking force and recover the kinetic energy of the vehicle 100 as electrical energy. The front drive motor 4f constitutes a drive source (front drive source) that drives the front wheels 9f. Similarly, the rear drive motor 4r constitutes a drive source (rear drive source) that drives the rear wheels 9r independently of the front wheels 9f.

[0018] The front reduction gear 5f and the rear reduction gear 5r are composed of, for example, multiple gears. Each of these reduction gears 5f, 5r reduces the rotational speed Nm of the motor 4 connected to it and transmits it to the drive shaft 8, thereby generating a driving torque or braking torque proportional to the reduction ratio. The front rotation sensor 6f and the rear rotation sensor 6r detect the rotor phase of the motor 4 connected to them and output the detected rotor phase to the motor controller 2. The motor controller 2 detects the rotational speed Nmf of the front drive motor 4f based on the output of the front rotation sensor 6f, and the rotational speed Nmr of the rear drive motor 4r based on the output of the rear rotation sensor 6r. The front current sensor 7f and the rear current sensor 7r detect the current flowing through the motor 4 connected to them and output the detected current to the motor controller 2. In this embodiment, these current sensors 7f, 7r detect the three-phase AC current of each of the motors 4f, 4r, respectively.

[0019] The vehicle 100 is equipped with various sensors 15 in addition to the front rotation sensor 6f, front current sensor 7f, rear rotation sensor 6r, and rear current sensor 7r described above. The various sensors 15 include, for example, an accelerator opening sensor 15a, an acceleration sensor 15b, a vehicle speed sensor 15c, a gradient sensor, a steering angle sensor, a wheel speed sensor, and the like. The accelerator opening sensor 15a detects the accelerator opening APO, which is the amount of accelerator operation. The acceleration sensor 15b detects the acceleration in the longitudinal and lateral directions of the vehicle 100, i.e., the longitudinal G and lateral G. The vehicle speed sensor 15c detects the vehicle speed V of the vehicle 100. The vehicle speed V is the moving speed of the entire body of the vehicle 100, i.e., the vehicle speed. The gradient sensor detects the gradient value, which is the gradient of the road on which the vehicle 100 is traveling. The steering angle sensor detects the steering angle of the steering wheel. The wheel speed sensors detect the wheel speeds of each drive wheel 9. The detected values ​​by the various sensors 15 are input to the motor controller 2.

[0020] In the vehicle 100, the target drive torque T_req, which is the torque requested by the driver, is distributed to the front wheels 9f and the rear wheels 9r. Therefore, once either the front torque distribution value RTf, which is the torque distribution value RT for the front wheels 9f, or the rear torque distribution value RTr, which is the torque distribution value RT for the rear wheels 9r, is determined, the other is also determined, and as a result, the torque distribution to the front and rear wheels 9f, 9r is also determined. For this reason, in the vehicle 100, a rear torque Tr, which is the torque T of the rear drive motor 4r, is calculated based on the driving state represented by a first parameter such as front and rear G, as will be described later. As a result, the rear torque distribution value RTr becomes calculable, and torque distribution control for the front and rear wheels 9f, 9r is performed by essentially calculating the rear torque distribution value RTr.

[0021] Slippage may occur in the vehicle 100. Slippage, which is a correction factor, can be determined based on the differential rotation speed Nd by using the differential rotation speed Nd between the front wheels 9f and rear wheels 9r as a parameter representing the correction factor. Slippage can also be suppressed by reducing the torque T of the slipping drive wheels through correction of the rear torque distribution value RTr. The rear torque distribution value RTr can be corrected by a correction value for the rear torque distribution value RTr (slip correction torque distribution value RTrslp, described later), and the correction value can be calculated based on the deviation DV between the actual differential rotation speed Nd_a, which is the actual value of the differential rotation speed Nd, and the target differential rotation speed Nd_t, which is the target value of the differential rotation speed Nd.

[0022] However, if different diameter tires are mounted on the front and rear wheels 9f, 9r, this will cause a rotational speed difference Nd. In other words, even if slippage does not occur, the rotational speed difference Nd will occur and remain unchanged due to a factor other than the correction factor of the different diameter tires being mounted. In this case, there is a concern that the calculated correction value will be inappropriate, resulting in an inappropriate torque distribution value RT. If the torque distribution value RT becomes inappropriate, torque distribution according to the driving state will be disrupted, which may affect, for example, the vehicle's cornering characteristics.

[0023] In view of these circumstances, in this embodiment, the motor controller 2 is configured as described below.

[0024] Figure 2 is a functional block diagram of the motor controller 2. Figure 2 shows a functional block diagram of torque distribution control. The motor controller 2 performs torque distribution control by calculating the rear torque Tr. The motor controller 2 is configured as a controller for a torque distribution control device by being programmed to configure each of the functional blocks shown in Figure 2.

[0025] The motor controller 2 includes a rear torque calculation unit 21, a correction torque calculation unit 22, a limiter setting unit 23, and an adder 24. The rear torque calculation unit 21 calculates the rear torque Tr. The rear torque Tr is calculated as a target torque for the rear drive motor 4r. The rear torque calculation unit 21 calculates the rear torque Tr based on first parameters, thereby calculating the rear torque Tr according to the driving state of the vehicle 100. The first parameters are parameters that indicate the driving state of the vehicle 100, and include longitudinal G, gradient value, lateral G, vehicle speed V as vehicle speed, and target driving torque T_req of the vehicle 100.

[0026] The target drive torque T_req is set in advance according to the vehicle speed V and the accelerator opening APO, and is distributed to a front torque Tf, which is the torque T of the front drive motor 4f, and a rear torque Tr. Therefore, once the rear torque Tr is calculated, the front torque Tf is determined from the target drive torque T_req and the rear torque Tr, and the torque distribution is therefore determined automatically. In other words, the calculation of the rear torque Tr serves as an index for the calculation of the torque distribution between the front and rear wheels 9f, 9r. Therefore, the calculation of the rear torque Tr serves as an index for the calculation of the rear torque distribution value RTr as well as for the calculation of the front torque distribution value RTf.

[0027] The rear torque calculation unit 21 includes a first rear torque calculation unit 211, a second rear torque calculation unit 212, and a rear torque selection unit 213. Here, the above-mentioned first parameter includes a first driving state parameter and a second driving state parameter. The first driving state parameter is a parameter that indicates the first driving state, and the first driving state is a driving state for driving performance-prioritized torque distribution that prioritizes driving performance. The first rear torque calculation unit 211 receives input of the longitudinal G, gradient value, and lateral G as the first driving state parameters. This is because these parameters affect driving performance. The second driving state parameter will be described later.

[0028] The first rear torque calculation unit 211 calculates the first rear torque Tr1 based on the first operating state parameter. This makes it possible to calculate a driving performance prioritized torque distribution according to the first operating state. That is, the first rear torque calculation unit 211 essentially calculates the driving performance prioritized torque distribution by calculating the first rear torque Tr1. Specifically, the first rear torque calculation unit 211 performs the calculation as follows.

[0029] The first rear torque calculation unit 211 includes a front / rear wheel load ratio calculation unit 211a, a gradient correction torque calculation unit 211b, a lateral G correction torque calculation unit 211c, an adder 211d, and an adder 211e. The front / rear wheel load ratio calculation unit 211a calculates a basic dynamic front / rear wheel load ratio based on the front / rear G. The front / rear wheel load ratio calculation unit 211a also calculates a basic torque of the first rear torque Tr1 according to the basic dynamic front / rear wheel load ratio. By calculating the basic dynamic front / rear wheel load ratio, it becomes possible to calculate the basic torque distribution to the front / rear wheels 9f, 9r according to the basic dynamic front / rear wheel load ratio, and therefore the basic torque can also be calculated. The basic torque is calculated so that the torque distribution to the front / rear wheels 9f, 9r is optimized according to the front / rear G from the standpoint of acceleration, etc.

[0030] The gradient correction torque calculation unit 211b calculates the gradient correction torque based on the gradient value. The gradient correction torque is a torque correction value for the basic torque according to the road gradient, and the calculated gradient correction torque is input to the adder 211d. The basic torque is also input to the adder 211d from the front / rear wheel load ratio calculation unit 211a, and the adder 211d adds the gradient correction torque to the basic torque, thereby correcting the basic torque according to the road gradient. As a result, the torque distribution to the front and rear wheels 9f, 9r is further corrected to be optimal according to the road gradient from the perspective of vehicle propulsion force, etc.

[0031] The lateral G correction torque calculation unit 211c calculates the lateral G correction torque based on the lateral G. The lateral G correction torque is a torque correction value of the basic torque according to the lateral G, and the calculated lateral G correction torque is input to the adder 211e. The basic torque corrected by the gradient correction torque from the adder 211d is also input to the adder 211e, and the adder 211e adds the lateral G correction torque to the basic torque, thereby further correcting the basic torque according to the lateral G. As a result, the torque distribution to the front and rear wheels 9f, 9r is further corrected to be optimal according to the lateral G from the standpoint of turning performance and stability during cornering. The first rear torque calculation unit 211 uses the basic torque corrected by the gradient correction torque and the lateral G correction torque in this way as the first rear torque Tr1.

[0032] The second rear torque calculation unit 212 calculates the second rear torque Tr2 based on the second driving state parameter. The second driving state parameter is a parameter that indicates the second driving state, which is a driving state for fuel-efficiency-prioritized torque distribution. Here, during low-torque driving, such as low-speed driving or slow acceleration, there is little concern that slip will disturb the behavior of the vehicle 100, and the low-torque region in which low-torque driving is performed is set in advance according to the vehicle speed V and the target drive torque T_req. For this reason, the vehicle speed V and the target drive torque T_req are input to the second rear torque calculation unit 212 as the second driving state parameter so that during low-torque driving, fuel-efficiency-prioritized torque distribution gives priority to fuel economy over driving performance-prioritized torque distribution.

[0033] In the second rear torque calculation unit 212, when the operating point corresponding to the vehicle speed V and the target drive torque T_req is in the low torque region, the rear torque Tr corresponding to the fuel efficiency prioritized torque distribution is calculated as the second rear torque Tr2. The fuel efficiency prioritized torque distribution is, for example, a torque distribution in which the front torque distribution value RTf is 100% and the rear torque distribution value RTr is 0%. By calculating the second rear torque Tr2 based on the second operating state parameter, the fuel efficiency prioritized torque distribution is essentially calculated. In addition to when the operating point is in the low torque region, the second rear torque calculation unit 212 also calculates the second rear torque Tr2 when, for example, a torque distribution favoring the front is desired in consideration of energy efficiency. In cases in which the fuel efficiency prioritized torque distribution is not calculated, such as when the operating point is not in the low torque region, the second rear torque Tr2 is calculated to be an invalid value. The invalid value is a value that is not selected by the rear torque selection unit 213. The calculated second rear torque Tr2 is input to the rear torque selection unit 213. The rear torque selection section 213 also receives the first rear torque Tr1 from the first rear torque calculation section 211.

[0034] The rear torque selection unit 213 selects the smaller of the input first rear torque Tr1 and second rear torque Tr2 as the rear torque Tr. The rear torque selection unit 213 selects the second rear torque Tr2 when fuel efficiency prioritized torque distribution is calculated, for example, when the operating point is in a low torque region, and selects the first rear torque Tr1 when fuel efficiency prioritized torque distribution is not calculated. In other words, the rear torque selection unit 213 is configured to make a selection depending on whether fuel efficiency prioritized torque distribution is calculated or not by selecting the minimum value. When the selection is switched from one of the first rear torque Tr1 and the second rear torque Tr2 to the other, the rear torque selection unit 213 can calculate the rear torque Tr so that it gradually changes from one to the other. The selected first rear torque Tr1 or second rear torque Tr2 is set as the rear torque Tr, and the rear torque calculation unit 21 calculates the rear torque Tr based on this.

[0035] The correction torque calculation unit 22 calculates the slip correction torque Trslp. The slip correction torque Trslp is a correction torque for the rear torque Tr and is used for slip correction of the rear torque Tr. The calculation of the slip correction torque Trslp is indexed by the calculation of the slip correction torque distribution value RTrslp, which is a slip correction value for the rear torque distribution value RTr. Specifically, the calculation is performed in the correction torque calculation unit 22 as follows.

[0036] The correction torque calculation unit 22 includes a differential rotation calculation unit 221, a target differential rotation calculation unit 222, and a slip correction torque calculation unit 223. The rotation speeds Nmf and Nmr are input to the differential rotation calculation unit 221, and the vehicle speed V is input to the target differential rotation calculation unit 222. The differential rotation calculation unit 221 calculates an actual differential rotation Nd_a of the front and rear wheels 9f, 9r based on the rotation speeds Nmf and Nmr, and the target differential rotation calculation unit 222 calculates a target differential rotation Nd_t based on the vehicle speed V. The actual differential rotation Nd_a is calculated by subtracting the rotation speed Nmr from the rotation speed Nmf. The differential rotation Nd corresponds to a second parameter, and differs from the first parameter that constitutes a parameter referenced in feedforward control in that it is a parameter that constitutes the actual value and target value in feedback control that converges the actual value to the target value based on a deviation. The actual rotational difference Nd_a and the target rotational difference Nd_t are input to a slip correction torque calculation unit 223 .

[0037] The slip correction torque calculation unit 223 calculates the slip correction torque Trslp based on the deviation DV between the actual differential speed Nd_a and the target differential speed Nd_t. The deviation DV is calculated by subtracting the target differential speed Nd_t from the actual differential speed Nd_a. The slip correction torque Trslp is calculated by PI control and is composed of the sum of P*DV, which is the P term (proportional term) of PI control, and ∫I*DV, which is the I term (integral term), where P is the proportional gain and I is the integral gain. The processing performed by the slip correction torque calculation unit 223 will be described in further detail below. The calculated slip correction torque Trslp is input to the limiter setting unit 23. The slip correction torque Trslp can be input to the limiter setting unit 23 in a state in which the P term component and the I term component can be distinguished.

[0038] The limiter setting unit 23 limits the slip correction torque Trslp by providing an I-term limiter using an I-term limiter torque Trslp_ILMT for the I-term component of the PI control. The I-term limiter torque Trslp_ILMT is a limiter for the I-term component. While a limiter is provided for the I-term component, no limiter is provided for the P-term component. The rear torque Tr is input to the limiter setting unit 23, and the I-term limiter torque Trslp_ILMT is set in accordance with the rear torque distribution value RTr. The setting of the I-term limiter torque Trslp_ILMT will be described in more detail later. The limiter setting unit 23 may be configured as a part of the slip correction torque calculation unit 225.

[0039] Slip correction torque Trslp, which is the slip correction torque Trslp after limiting * is input to the adder 24. The rear torque Tr is also input to the adder 24 from the rear torque calculation unit 21, and the adder 24 adds the slip correction torque Trslp to the rear torque Tr. * As a result, the rear torque Tr after slip correction is calculated as follows: * is finally calculated as the target torque for the rear drive motor 4r.

[0040] FIG. 3 is a flowchart showing an example of the slip correction torque calculation process performed by the motor controller 2. FIG. 3 shows an example of determining slip of the front wheel 9f. The process of this flowchart is performed by the slip correction torque calculation unit 223 and can be repeatedly executed, for example, at each calculation cycle. In step S1, the deviation DV is calculated. In step S2, it is determined whether slip correction is being performed. In the first routine, slip correction is not being performed. Therefore, in the first routine, a negative determination is made in step S2, and the process proceeds to step S6. In step S6, it is determined whether the deviation DV is equal to or greater than a threshold value DV1. The threshold value DV1 is a value used to determine whether slip is occurring in the front wheel 9f and is set in advance. When determining slip of the rear wheel 9r, in step S6, it is possible to determine whether the deviation DV is equal to or less than a negative threshold value DV1 (DV≦−DV1), with the threshold value DV1 being positive. If the determination in step S6 is affirmative, it is determined that slip is occurring, and the process proceeds to step S7. In step S7, the slip correction torque Trslp is calculated by PI control. If the determination in step S6 is negative, it is determined that slip is not occurring, and in step S8 the slip correction torque Trslp is set to zero. After steps S7 and S8, the process temporarily ends.

[0041] If the determination in step S6 is affirmative, rearThe torque Tr is corrected by the slip correction torque Trslp, and slip correction is now being performed. Therefore, in the next routine, a positive determination is made in step S2, and the process proceeds to step S3. In step S3, it is determined whether the slip correction torque Trslp is equal to or less than a threshold value Trslp1. When slip of the rear wheel 9r is to be suppressed, step S3 determines whether the slip correction torque Trslp is equal to or greater than a negative threshold value Trslp1 (Trslp≧−Trslp1), with the threshold value Trslp1 set to a positive value. The threshold value Trslp1 is a preset determination value for determining whether the slip has converged. If a negative determination is made in step S3, it is determined that the slip has not converged, and in step S5, the slip correction torque Trslp continues to be calculated by PI control. If a positive determination is made in step S3, it is determined that the slip has converged, and the slip correction torque Trslp is set to zero in step S4. As a result, slip correction is no longer performed. The process ends once steps S4 and S5 are completed.

[0042] 4 is a diagram showing a setting example of the integral term limiter distribution value RTrslp_ILMT. The integral term limiter distribution value RTrslp_ILMT is obtained by converting the integral term limiter torque Trslp_ILMT from a torque display to a torque distribution value display, and uses the integral term limiter torque Trslp_ILMT as an index. The first rear torque distribution value RTr1 indicates the rear torque distribution value RTr when the rear torque Tr is the first rear torque Tr1.

[0043] Here, the I-term limiter distribution value RTrslp_ILMT is calculated by subtracting the rear torque distribution value RTr from the first rear torque distribution value RTr1 (RTrslp_ILMT=RTr1-RTr). In other words, the I-term limiter distribution value RTrslp_ILMT is calculated so that the value obtained by adding the I-term limiter distribution value RTrslp_ILMT to the rear torque distribution value RTr becomes the first rear torque distribution value Tr1 (RTr+RTslp_ILMT=RTr1). By calculating in this manner, even if the rear torque Tr is corrected with the I-term component of the PI control, the rear torque Tr * The I-term component of the slip correction torque Trslp is limited so that the maximum value of the I-term component of the slip correction torque Trslp is the first rear torque Tr1.

[0044] As a result, the integral term limiter distribution value RTrslp_ILMT is set to decrease as the rear torque distribution value RTr increases. The integral term limiter distribution value RTrslp_ILMT is set to the first rear torque distribution value RTr1 when the rear torque distribution value RTr is zero, and is set to zero when the rear torque distribution value RTr is the first rear torque distribution value RTr1. The integral term limiter distribution value RTrslp_ILMT is further set to zero when the rear torque distribution value RTr is greater than the first rear torque distribution value RTr1.

[0045] In this way, the I-term limiter distribution value RTrslp_ILMT can be set in advance according to the rear torque distribution value RTr. rear If the torque Tr is input to the limiter setting unit 23, the input rear Since the rear torque distribution value RTr according to the torque Tr is known, the corresponding integral term limiter distribution value RTrslp_ILMT is also known, making it possible to calculate the integral term limiter torque Trslp_ILMT. The integral term limiter torque Trslp_ILMT and the integral term limiter distribution value RTrslp_ILMT are calculated in this way according to the rear torque distribution value RTr. The integral term limiter includes the integral term limiter torque Trslp_ILMT when the torque is displayed and the integral term limiter distribution value RTrslp_ILMT when the distribution value is displayed, and is calculated according to the rear torque distribution value RTr. The integral term limiter Trslp is calculated to a torque value according to the integral term limiter distribution value RTrslp_ILMT obtained by subtracting the rear torque distribution value RTr from the first rear torque distribution value RTr1.

[0046] FIG. 5 is a flowchart showing an example of the limiter setting process performed by the motor controller 2. The process of the flowchart shown in FIG. 5 is performed by the limiter setting unit 23, and can be executed repeatedly, similar to the slip correction torque calculation process. In step S11, the I-term limiter torque Trslp_ILMT is calculated as explained using FIG. 4. In step S12, it is determined whether the I-term (I-term component) of the slip correction torque Trslp is equal to or greater than the I-term limiter torque Trslp_ILMT. If the determination in step S12 is negative, the I-term is not limited by the I-term limiter torque Trslp_ILMT, and the process is temporarily terminated. If the determination in step S12 is positive, the I-term is equal to or greater than the I-term limiter torque Trslp_ILMT, and so in step S13 the I-term is set to the I-term limiter torque Trslp_ILMT. In other words, the I-term is limited by the I-term limiter torque Trslp_ILMT. As a result, in step S14, the slip correction torque Trslp after limitation is calculated. * is the sum of the P term and the I term limited by the I term limiter torque Trslp_I.

[0047] FIG. 6 is a diagram showing a first example of a timing chart corresponding to the torque distribution control of this embodiment. FIG. 7 is a diagram showing a timing chart for a comparative example. FIGS. 6 and 7 show a case where tires of different diameters are mounted. The comparative example shows a case where the slip correction torque Trslp is limited to a constant value. Slip correction distribution value RTrslp * is the slip correction torque Trslp * is converted from a torque display to a torque distribution value display.

[0048] Before time T1, the accelerator is not operated. Therefore, the accelerator opening APO, target drive torque T_req, and rear torque distribution value RTr are all zero. At time T1, the accelerator opening APO begins to increase in response to accelerator operation. As a result, the target drive torque T_req also begins to increase accordingly. In this example, torque distribution is biased toward the front at this time, taking energy efficiency into consideration. Therefore, the second rear torque distribution value RTr2 is selected as the rear torque distribution value RTr, and the rear torque distribution value RTr becomes zero.

[0049] From timing T1, the slip correction distribution value RTrslp is calculated according to the differential rotation Nd caused by the different diameter tires. * As a result, the rear torque distribution value RTr * is the slip compensation distribution value RTrslp * The rear torque Tr * The front torque Tf is calculated by subtracting the target drive torque T_req from the rear torque Tr * is set to the value obtained by subtracting

[0050] In the comparative example shown in FIG. 7, the slip correction distribution value RTrslp increases as the accelerator opening APO increases from timing T1. * is limited to a constant value. As a result, the rear torque distribution value RTr * , rear torque Tr * In this embodiment, the rear torque distribution value RTr is constant. * The maximum rear torque distribution value RTr is only the first rear torque distribution value RTr1. * becomes constant at the first rear torque distribution value RTr1 according to the target drive torque T_req at this time, and the rear torque Tr * The front torque Tf also becomes constant.

[0051] At timing T2, the accelerator operation amount increases further. This causes the accelerator opening APO and target drive torque T_req to increase further, and a switch is made from fuel economy prioritized torque distribution to driving performance prioritized torque distribution, resulting in the rear torque distribution value RTr being configured as the first rear torque distribution value RTr1. The rear torque distribution value RTr gradually increases from the second rear torque distribution value RTr2 in response to the increase in target drive torque T_req, to ​​become the first rear torque distribution value RTr1. The first rear torque distribution value RTr1 becomes larger than before timing T2 in response to the target drive torque T_req at this time. As a result, the rear torque distribution value RTr * also starts to increase from timing T2.

[0052] In the comparative example, the slip correction distribution value RTrslp is limited to a constant value. * is added to the rear torque distribution value RTr, resulting in the slip-corrected rear torque distribution value RTr * Therefore, from timing T2 onwards, the slip correction distribution value RTrslp * Rear torque distribution value RTr * As a result, the vehicle's turning characteristics become oversteered.

[0053] In this embodiment, the slip correction distribution value RTrslp * is limited by the limiter distribution value RTrslp_ILIMT, which is expressed by the relational expression RTrslp_ILIMT=Rtr1-RTr. * From timing T2, the rear torque distribution value RTr gradually decreases in accordance with the increase in the rear torque distribution value RTr, and becomes zero when the rear torque distribution value RTr becomes the first rear torque distribution value TRr1. * becomes the first rear torque distribution value RTr1 which has increased in response to the accelerator operation from timing T2, and the slip correction distribution value RTrslp * As a result, the vehicle turning characteristics are prevented from becoming inappropriate.

[0054] FIG. 8 shows a second example of a timing chart corresponding to the torque distribution control of this embodiment. The changes before timing T3 are the same as those in FIG. 6, and in this example, slip occurs between timing T3 and timing T4. As mentioned above, the limiter setting unit 23 does not provide a limiter for the P term component of the PI control. Therefore, when slip begins at timing T3, the increase in the P term component causes the slip correction distribution value RTrslp * As a result, the rear torque distribution value RTr * and rear torque RTr * Slip correction distribution value RTrslp also increases. * When the slip begins to decrease, the P component decreases, and when the slip converges at timing T4, it becomes zero. As a result, the rear torque distribution value RTr * and rear torque RTr * Therefore, in this embodiment, by not providing a limiter for the P term, the rear torque distribution value RTr * This prevents inappropriateness while also being able to deal with slips if they occur.

[0055] Next, the main effects of this embodiment will be described.

[0056] In this embodiment, a torque distribution control method for vehicle 100, which is an electric vehicle, controls torque distribution between front and rear wheels 9f, 9r. The method includes calculating a rear torque Tr, which is the torque T of rear wheel 9r, which is one of a plurality of drive wheels, based on a first parameter; calculating a slip correction torque Trslp for rear torque Tr based on a second parameter, which is a deviation DV between actual value Nd_a of differential rotation Nd and target value Dd_t; and correcting rear torque Tr with the calculated slip correction torque Trslp (which indicates correcting rear torque distribution value RTr with the calculated slip correction distribution value RTrslp and corresponds to correcting the torque distribution value with the calculated correction value). The method limits slip correction value Trslp based on rear torque Tr (which indicates limiting slip correction distribution value RTrslp based on rear torque distribution value RTr and corresponds to limiting the correction value based on the torque distribution value).

[0057] According to this method, the rear torque distribution value RTr * Therefore, it is possible to limit the slip correction distribution value RTrslp so that the rear torque Tr * Therefore, even if the rotational speed difference Nd, which is an example of a parameter representing a correction factor, remains changed due to a factor other than the correction factor, it is possible to prevent the slip correction distribution value RTrslp as a correction value from becoming an inappropriate value. Therefore, the rear torque distribution value RTr as the torque distribution value of the drive wheels after correction * This makes it possible to prevent the vehicle from becoming inappropriate, thereby making it possible to prevent the vehicle's turning performance and the like from being affected.

[0058] The slip correction torque Trslp is calculated by PI control (which indicates that the slip correction distribution value RTrslp is calculated by PI control, and corresponds to the correction value being calculated by PI control), and is limited by providing an I-term limiter torque Trslp_ILMT for the I-term component of the PI control (which indicates that the I-term limiter distribution value RTrslp_ILMT is provided, and corresponds to providing an I-term limiter), while no limiter is provided for the P-term component of the PI control. According to this method, the rear torque distribution value RTr * It can handle slips while preventing inappropriate behavior.

[0059] The I-term limiter based on the I-term limiter distribution value RTrslp_ILMT is calculated in accordance with the rear torque distribution value RTr. * Therefore, it is possible to appropriately limit the slip correction distribution value RTrslp so that the maximum slip correction distribution value RTrslp is the rear torque distribution value RTr.

[0060] The first parameters include a first operating state parameter and a second operating state parameter. The method according to this embodiment includes calculating, based on the first operating state parameter, a first rear torque Tr1 such that the torque distribution is a driving performance-prioritized torque distribution that prioritizes driving performance (this indicates calculating a first rear torque distribution value RTr1, and corresponds to calculating a driving performance-prioritized torque distribution value). The method also includes calculating, based on the second operating state parameter, a second rear torque Tr2 such that the torque distribution is a torque distribution that prioritizes fuel economy over driving performance-prioritized torque distribution (this indicates calculating a second torque distribution value RTr2, and corresponds to calculating a fuel economy-prioritized torque distribution value). The rear torque Tr is calculated to be the first rear torque Tr1 or the second rear torque Tr2 (this indicates calculating the rear torque distribution value RTr to be the first rear torque distribution value RTr1 or the second rear torque distribution value RTr2, and corresponds to calculating the torque distribution value to be the first torque distribution value or the second torque distribution value). The integral term limiter based on the integral term limiter distribution value RTrslp_ILMT is obtained by subtracting the rear torque distribution value RTr from the first rear torque distribution value RTr1.

[0061] According to this method, the rear torque Tr * By limiting the I-term component of the slip correction torque Trslp so that the maximum value of the slip correction distribution value RTrslp is the first rear torque Tr1, the slip correction distribution value RTrslp can be appropriately limited.

[0062] The vehicle 100 is an electric four-wheel drive vehicle. The torque distribution value RT of one of the multiple drive wheels is set to the torque distribution value RT of the rear wheel 9r, which is one of the front and rear drive wheels of the electric four-wheel drive vehicle, that is, the rear torque distribution value TRr. The second parameter is the differential rotation speed Nd of the front and rear wheels 9f, 9r, and the correction value of the rear torque distribution value RTr is set to the slip correction distribution value RTrslp, which is a slip correction value used for slip correction of the rear torque distribution value RTr. This method makes it possible to prevent the slip correction distribution value RTrslp from becoming an inappropriate value in a situation where the differential rotation speed Nd remains changed due to tires with different diameters. Therefore, the rear torque distribution value RTr * This makes it possible to prevent the vehicle turning characteristics from becoming inappropriate, thereby making it possible to prevent the vehicle turning characteristics from becoming oversteered.

[0063] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

[0064] For example, in the above-described embodiment, the calculation is performed using the rear torque Tr as the calculation target, but the calculation may be performed using the front torque Tf as the calculation target. Even in this case, since the calculation of the front torque Tf serves as an index for the calculation of the torque distribution between the front and rear wheels 9f, 9r, the same effects as when the rear torque Tr is calculated can be obtained.

[0065] Although the above embodiment has mainly described the case where the front wheel 9f slips, the present invention may also be applied to the case where the rear wheel 9r slips, in which case it is possible to prevent the corrected front torque Tf from becoming excessive or otherwise inappropriate.

[0066] The torque distribution value RT of any one of the multiple drive wheels 9 does not necessarily have to be the torque distribution value RT of the front wheels 9f or the rear wheels 9r, and the correction factor does not necessarily have to be slip. Even in this case, if a correction value for the torque distribution value RT is calculated based on the deviation between the actual value and the target value and the torque distribution value RT is corrected using the calculated correction value, the correction value can be limited based on the torque distribution value RT to prevent the corrected torque distribution value RT from becoming inappropriate. For example, if the correction is performed based on the output of a sensor, it is possible to prevent the correction from becoming inappropriate due to sensor failure.

Claims

1. A torque distribution control method for an electric vehicle that controls torque distribution to a plurality of drive wheels, comprising: calculating a torque distribution value for any one of the plurality of drive wheels based on a first parameter; calculating a correction value for the torque distribution value based on a deviation between an actual value and a target value of a second parameter, and correcting the torque distribution value with the calculated correction value; Including, limiting the correction value based on the torque distribution value; Torque distribution control method.

2. 2. The torque distribution control method according to claim 1, The correction value is calculated by PI control and is limited by providing an I-term limiter for an integral term component of the PI control, while no limiter is provided for a proportional term component of the PI control. Torque distribution control method.

3. 3. The torque distribution control method according to claim 2, The I-term limiter is calculated according to the torque distribution value. Torque distribution control method.

4. 4. The torque distribution control method according to claim 2 or 3, the first parameters include a first operating state parameter and a second operating state parameter; calculating a first torque distribution value that is a driving performance prioritized torque distribution value that prioritizes driving performance based on the first driving state parameter; and calculating a second torque distribution value that is a fuel efficiency prioritized torque distribution value that prioritizes fuel efficiency compared to the driving performance prioritized torque distribution value based on the second driving state parameter, The torque distribution value is calculated to be the first torque distribution value or the second torque distribution value, The limit is obtained by subtracting the second torque distribution value from the first torque distribution value. Torque distribution control method.

5. 5. The torque distribution control method according to claim 1, the electric vehicle is an electric four-wheel drive vehicle, the torque distribution value is a torque distribution value for one of the front and rear drive wheels of the electric four-wheel drive vehicle, the second parameter is a differential rotation between the front and rear wheels, The torque distribution control method, wherein the correction value is a slip correction value used in slip correction of the torque distribution value.

6. A torque distribution control device for an electric vehicle including a controller that controls torque distribution to a plurality of drive wheels, the controller is configured to calculate a torque distribution value for any one of the plurality of drive wheels based on a first parameter, calculate a correction value for the torque distribution value based on a deviation between an actual value and a target value of a second parameter, and correct the torque distribution value with the calculated correction value; The controller is further configured to limit the correction value based on the torque distribution value. Torque distribution control device.

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