Travel control device for vehicle

Abstract

This travel control device for a vehicle uses feedback control to control torque imparted to front and rear left and right wheels so that the wheels rotate on the basis of a target slip rate St. The travel control device comprises a torque control unit 60 that calculates a second correction torque ΔT2, which tends to increase as the deviation ΔGw between a required acceleration Gwd for the wheels and an actual acceleration Gw for the wheels 3 increases, and subtracts the second correction torque ΔT2 (torque reduction amount) from a feedback control output value (first correction torque ΔT1) to correct the torque applied to the wheels.

Description

Vehicle driving control device

[0001] The present invention relates to a vehicle cruise control device.

[0002] Conventionally, there are known techniques for performing traction control for each wheel based on the slip ratio and yaw rate of the wheel. For example, Patent Document 1 describes an electric vehicle in which the braking / driving force of an electric motor is controlled within a range in which the slip ratio of each wheel does not exceed a predetermined upper limit so that the turning acceleration of the vehicle body corresponds to the turning acceleration according to the steering angle.

[0003] JP 2011-254590 A

[0004] In recent years, there has been a demand for traction control that can cause vehicle movement to follow driver operation without delay. The electric vehicle described in Patent Document 1 controls the slip ratio of each wheel so that it does not exceed a predetermined upper limit, but this control is only intended for vehicle cornering. As a result, in situations where the road surface friction coefficient is low, it may not be possible to sufficiently prevent slippage, in which the rotation speed of the wheels 3 is freewheeling, or locking, in which the wheels 3 do not rotate. In order to quickly prevent such wheel slippage or locking and allow vehicle movement to appropriately follow the driver's driving operation, a more accurate and responsive traction control is required.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a vehicle driving control device that can realize more accurate and more responsive traction control.

[0006] In order to achieve the above object, the vehicle driving control device of the present invention is a vehicle driving control device that includes an electric motor for driving and controls the torque applied to each of the front, rear, left, and right wheels by feedback control so that the wheels rotate based on a target slip ratio, and includes a torque control unit that calculates a torque reduction amount that tends to increase as the deviation between the required acceleration for the wheel and the actual acceleration of the wheel increases, and subtracts the torque reduction amount from the output value of the feedback control to correct the torque applied to each of the wheels.

[0007] With this configuration, the output value of the feedback control can be corrected by the torque reduction amount so that the torque applied to each wheel decreases as the deviation between the required acceleration and the actual acceleration for each wheel increases. This makes it possible to quickly suppress slippage or lockup, thereby bringing the wheel slip ratio closer to the target slip ratio, even when slippage occurs, causing the wheel rotation speed to increase or when the wheel locks up. Therefore, the vehicle driving control device of the present invention makes it possible to achieve more accurate and responsive traction control.

[0008] Preferably, the feedback control is PID control, and the torque control unit increases the I control amount of the PID control as the torque reduction amount increases. With this configuration, the I control of the PID control can be promoted as the torque reduction amount increases, thereby suppressing steady-state deviation and improving the accuracy of traction control.

[0009] Furthermore, it is preferable that the torque control unit reduces the contribution of the torque reduction amount to the correction of the output value of the PID control as the I control amount increases. With this configuration, as the I control is promoted and the output value of the PID control is settled, i.e., as the rotation speed of the wheels is settled, the contribution of the torque reduction amount can be reduced, and the value of the torque applied to each wheel can be stabilized.

[0010] The vehicle preferably further comprises a wheel translational speed calculation unit that calculates a wheel translational speed of each wheel in the vehicle traveling direction based on the steering angle, vehicle speed, center-of-gravity slip angle, and vehicle specifications, and a target wheel speed calculation unit that calculates a target wheel speed of each wheel based on the wheel translational speed and the target slip ratio, and the torque control unit controls the torque by the feedback control so that the wheel speed approaches the target wheel speed. This configuration makes it possible to accurately calculate the target wheel speed of each wheel using the wheel translational speed that takes into account the inner / outer wheel speed difference of each wheel, and to accurately control the torque applied to each wheel. Therefore, it is possible to achieve high-precision traction control.

[0011] Preferably, the wheel translational velocity calculation unit and the target wheel velocity calculation unit are included in a main control unit, and the torque control unit is included in a sub-control unit separate from the main control unit. With this configuration, the control torque for each wheel can be calculated even if the sub-control unit does not have information on the wheel translational velocity.

[0012] According to the vehicle driving control device of the present invention, it is possible to achieve more accurate and more responsive traction control.

[0013] 1 is a schematic configuration diagram of a plug-in hybrid vehicle equipped with a cruise control device of an embodiment. FIG. 2 is a block diagram showing the schematic configuration of the cruise control device of an embodiment. FIG. 3 is a block diagram showing the schematic configuration of a target average slip ratio calculation unit. FIG. 4 is an explanatory diagram showing an example of how the accelerator opening, braking / driving force, and slip ratio change over time due to torque control in the cruise control device of an embodiment. FIG. 5 is an explanatory diagram showing an example of the relationship between the braking / driving force of the wheels and the slip ratio. FIG. 6 is a block diagram showing the schematic configuration of a target longitudinal relative slip ratio calculation unit. FIG. 7 is an explanatory diagram showing an example of the relationship between the yaw rate of the vehicle and the longitudinal relative slip ratio. FIG. 8 is an explanatory diagram showing a schematic configuration of a motor control unit and a brake control unit.

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0015] (Vehicle) Figure 1 is a schematic diagram of a plug-in hybrid vehicle (hereinafter referred to as vehicle 1) equipped with a cruise control device according to an embodiment. Vehicle 1 is a four-wheel drive vehicle that can travel by driving front wheels 3a, 3b with the output of an engine 2, and that is equipped with an electric front motor (electric traction motor) 4 that drives the front wheels 3a, 3b, and an electric rear motor (electric traction motor) 6 that drives rear wheels 3c, 3d. In the following description, unless there is a particular need to distinguish between them, the front wheels 3a, 3b and the rear wheels 3c, 3d will be referred to as "wheels 3."

[0016] (Engine) The engine 2 is capable of driving a drive shaft 8 of the front wheels 3 a, 3 b via a front transaxle 7, and is also capable of driving a motor generator 9 via the front transaxle 7 to generate electricity. The engine 2 and the front wheels 3 a, 3 b are connected via a clutch 16 disposed within the front transaxle 7. The vehicle 1 is also provided with a fuel tank (not shown) that stores fuel to be supplied to the engine 2.

[0017] (Motor) The front motor 4 is powered by high-voltage power supplied from a drive battery 11 and a motor generator 9 mounted on the vehicle 1 via a front motor control unit (sub-control unit) 10, and drives the drive shaft 8 of the front wheels 3 a, 3 b via a front transaxle 7. The rear motor 6 is powered by high-voltage power supplied from the drive battery 11 via a rear motor control unit (sub-control unit) 12, and drives the drive shaft 14 of the rear wheels 3 c, 3 d via a rear transaxle 13. The power generated by the motor generator 9 can charge the drive battery 11 via the front motor control unit 10, and can also supply power to the front motor 4 and the rear motor 6.

[0018] (Driving Battery) The driving battery 11 is composed of a secondary battery such as a lithium-ion battery, and has a battery module (not shown) configured by a group of multiple battery cells. The driving battery 11 also has a charging rate detector 11a that detects the charging rate SOC of the driving battery 11. The vehicle 1 is also equipped with a charger 18 that can charge the driving battery 11 from an external power source.

[0019] (Motor Control Unit) Based on control signals from a main control unit 20 mounted on the vehicle 1, the front motor control unit 10 controls the braking / driving force produced by the front motor 4, i.e., the driving torque or regenerative braking torque of the front motor 4, and also controls the power generation amount and output of the motor generator 9. Based on control signals from the main control unit 20, the rear motor control unit 12 controls the braking / driving force produced by the rear motor 6, i.e., the driving torque or regenerative braking torque of the rear motor 6.

[0020] (Engine Control Unit) The engine control unit 22 is a control device for the engine 2, and is configured to include input / output devices, memory devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), a timer, etc. Based on a control signal (required output) from the main control unit 20, the engine control unit 22 controls the fuel injection amount, fuel injection timing, intake amount, etc. of the engine 2, thereby controlling the drive of the engine 2.

[0021] (Main Control Unit) The main control unit 20 is a control device for performing overall control of the vehicle 1, and is configured to include input / output devices, memory devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), a timer, etc. The front motor control unit 10, rear motor control unit 12, and engine control unit 22 are connected to the input side of the main control unit 20, and detection and operation information from these devices is input. On the other hand, the front motor control unit 10, rear motor control unit 12, engine control unit 22, and clutch 16 of the front transaxle 7 are connected to the output side of the main control unit 20.

[0022] The main control unit 20 calculates the vehicle output required to drive the vehicle 1 based on various detected quantities such as the accelerator operation information level of the vehicle 1 and various operation information, and sends control signals to the engine control unit 22, the front motor control unit 10, and the rear motor control unit 12. The main control unit 20 controls switching of the driving mode (EV mode, series mode, parallel mode), the output of the engine 2, the front motor 4, and the rear motor 6, the generated power and output of the motor generator 9, and the engagement and disengagement of the clutch 16 in the front transaxle 7.

[0023] In EV mode, the engine 2 is stopped, and the front motor 4 and rear motor 6 are driven by electric power supplied from the drive battery 11 to drive the vehicle. In series mode, the clutch 16 of the front transaxle 7 is disengaged, and the motor generator 9 is operated by the engine 2. The front motor 4 and rear motor 6 are driven by electric power generated by the motor generator 9 and electric power supplied from the drive battery 11 to drive the vehicle. In series mode, the rotational speed of the engine 2 is set to an efficient value, and electric power generated by surplus output is supplied to the drive battery 11 to charge the drive battery 11. In parallel mode, the clutch 16 of the front transaxle 7 is engaged, and power is mechanically transmitted from the engine 2 via the front transaxle 7 to drive the front wheels 3 a, 3 b. The front motor 4 and rear motor 6 are driven by electric power generated by the engine 2 operating the motor generator 9 and electric power supplied from the drive battery 11 to drive the vehicle.

[0024] The main control unit 20 sets the driving mode to parallel mode in a range where the engine 2 is efficient, such as a high-speed range. In a range other than parallel mode, i.e., a medium-to-low speed range, the main control unit 20 switches between EV mode and series mode based on the state of charge (SOC) of the drive battery 11.

[0025] (Brake Devices) Brake devices 30a, 30b, 30c, and 30d that apply braking torque are provided on each wheel 3 of the vehicle 1. The brake devices 30a and 30b on the front wheels are controlled by a front brake control unit (sub-control unit) 31, and the brake devices 30c and 30d on the rear wheels are controlled by a rear brake control unit (sub-control unit) 32, so that the braking torque for each wheel 3 can be controlled independently.

[0026] (Brake Control Unit) The front brake control unit 31 and the rear brake control unit 32 are connected to the main control unit 20 so as to be able to communicate with each other. The front brake control unit 31 may be connected to the main control unit 20 so as to be able to communicate with each other via the front motor control unit 10, and the rear brake control unit 32 may be connected to the main control unit 20 so as to be able to communicate with each other via the rear motor control unit 12. The front brake control unit 31 and the rear brake control unit 32 control the operation of each of the brake devices 30a, 30b, 30c, 30d based on a brake pedal operation signal from a brake pedal sensor (not shown) or the like.

[0027] The front motor control unit 10, rear motor control unit 12, front brake control unit 31, and rear brake control unit 32 are each configured to include input / output devices, memory devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), a timer, etc. These control units have faster processing speeds than the main control unit 20.

[0028] (Cruise Control Device) Figure 2 is a block diagram showing a schematic configuration of a cruise control device 50 according to an embodiment. The cruise control device 50 includes a main control unit 20, motor control units (front motor control unit 10, rear motor control unit 12), and brake control units (front brake control unit 31, rear brake control unit 32). Although Figure 2 shows one motor control unit and one brake control unit, the vehicle 1 according to this embodiment is provided with two sets, one for the front wheels 3a, 3b and one for the rear wheels 3c, 3d.

[0029] First, a specific description will be given of the configuration of the main control unit 20. As shown in Fig. 2, the main control unit 20 includes an actual braking / driving force calculation unit 51, a required braking / driving force calculation unit 52, a required yaw rate calculation unit 53, a target average slip ratio calculation unit 54, a target longitudinal relative slip ratio calculation unit 55, a target slip ratio calculation unit 56, a wheel translational speed calculation unit 57, and a target wheel speed calculation unit 58.

[0030] (Braking / driving force calculation unit) The actual braking / driving force calculation unit 51 receives the current motor torque Tm of the front motor 4 and the rear motor 6, the brake torque Tb of the brake devices 30a, 30b, 30c, and 30d, the actual wheel speed Vw of each wheel 3, and the actual motor rotation speed Vm of the front motor 4 and the rear motor 6. The motor torque Tm and the brake torque Tb are command values ​​calculated by the motor control unit and the brake control unit. The actual wheel speed Vw and the actual motor rotation speed Vm are detected by sensors (not shown) and input to the main control unit 20. The actual braking / driving force calculation unit 51 calculates an actual braking / driving force F, which is an estimate of the current total braking / driving force of the entire vehicle 1, based on the input values. The required braking / driving force calculation unit 52 receives the accelerator opening α and brake stroke Bs of the vehicle 1 and calculates a required braking / driving force Fd, which is the total braking / driving force required by the driver to apply to the entire vehicle 1.

[0031] (Required Yaw Rate Calculation Unit) The required yaw rate calculation unit 53 receives a detected value of the steering angle (handle angle) δ and calculates a required yaw rate Yd, which is the speed in the turning direction that the driver requires of the vehicle 1. The steering angle δ is detected by a sensor (not shown) and input to the main control unit 20.

[0032] (Target Average Slip Ratio Calculation Unit) Figure 3 is a block diagram showing the schematic configuration of target average slip ratio calculation unit 54. Target average slip ratio calculation unit 54 receives a braking / driving force deviation ΔF, which is the deviation between the actual braking / driving force F calculated by actual braking / driving force calculation unit 51 and the required braking / driving force Fd calculated by required braking / driving force calculation unit 52. Target average slip ratio calculation unit 54 also receives an accelerator opening α. Target average slip ratio calculation unit 54 calculates a target average slip ratio Sta for each wheel 3 based on the input braking / driving force deviation ΔF and accelerator opening α. Target average slip ratio Sta is a target value for the average slip ratio Sa (see Figure 4) of all wheels 3. In other words, the target average slip ratio Sta is the average value of the target slip ratios St (see "Stfl", "Stfr", "Strl", and "Strr" in FIG. 2), which are the target values ​​of the slip ratios S (see FIG. 4) for each wheel 3.

[0033] Specifically, target average slip ratio calculation unit 54 uses map M1, which defines a predetermined relationship between braking / driving force deviation ΔF and a first base value (base value) b1 of target average slip ratio Sta, to set the first base value b1 according to the input braking / driving force deviation ΔF. Map M1 is defined so that first base value b1 changes in proportion to braking / driving force deviation ΔF. Target average slip ratio calculation unit 54 also uses map M2, which defines a predetermined relationship between accelerator pedal position α and a first correction coefficient (correction coefficient) k1, to set the first correction coefficient k1 according to the input accelerator pedal position α. ​​Map M2 is defined so that the greater the accelerator pedal position α, the greater the first correction coefficient k1, as shown by the solid line in the figure. Target average slip ratio calculation unit 54 then calculates target average slip ratio Sta by multiplying the set first base value b1 by the first correction coefficient k1. The target average slip ratio calculation unit 54 outputs the calculated target slip ratio to the target slip ratio calculation unit 56 .

[0034] The target average slip ratio Sta set as described above is used in the process described below to bring the average slip ratio Sa of each wheel 3 closer to the target average slip ratio Sta. FIG. 4 is an explanatory diagram showing an example of how the accelerator opening, braking / driving force, and slip ratio change over time due to torque control by the cruise control device 50 of this embodiment. As described above, the target average slip ratio Sta is calculated to be proportional to the braking / driving force deviation ΔF and to increase as the accelerator opening α increases. As a result, the target average slip ratio Sta can be set to a value that corresponds to the braking / driving force deviation ΔF and is appropriate for the accelerator opening α, i.e., the required braking / driving force Fd. In other words, by reflecting the accelerator opening α in the target average slip ratio Sta, it is possible to compensate for the required braking / driving force Fd. The first correction coefficient k1 may be determined based on the relationship between the braking / driving force (brake / driving force friction coefficient) on the wheels (tires) and the slip ratio (i.e., the μ-S characteristic; see FIG. 5, for example). Furthermore, upper limits may be set for the first correction coefficient k1 and the first base value b1 in the range where the μ-S characteristic has a negative gradient. As a result, as the driver depresses the accelerator, the slip ratio S of the slipping wheel with no friction margin (see dashed line) and the slip ratio S of the gripping wheel with a friction margin (see two-dot chain line) can both be controlled to converge to the target average slip ratio Sta that compensates for the required braking / driving force Fd, as shown by the white arrows in Figure 4.

[0035] FIG. 5 is an explanatory diagram showing an example of the relationship between the driving / braking force of a wheel and the slip ratio. As shown by the solid or dashed lines in the diagram, the relationship between the driving / braking force (driving / braking force friction coefficient) on the wheel (tire) and the slip ratio (i.e., μ-S characteristics) varies depending on road surface conditions and wear. In this embodiment, as described above, the target average slip ratio Sta is calculated by reflecting the magnitude of the accelerator opening α. Therefore, even if the μ-S characteristics of the wheel 3 change, the target average slip ratio Sta can be set so as to approach the slip ratio that provides the maximum driving / braking force in response to the driver's accelerator operation, as shown by the white arrow in the diagram.

[0036] Here, the first correction coefficient k1 may include multiple patterns that can be changed in response to the driver's request. For example, as shown by the dashed line in map M2 of FIG. 3 , a pattern is prepared in which the increase in the first correction coefficient k1 relative to the increase in the accelerator pedal depression amount α is larger than that shown by the solid line. Furthermore, the driver can select which pattern of the first correction coefficient k1 to use via an interface such as a switch (not shown). This allows the driver to select the first correction coefficient k1 shown by the solid line if they want to increase the slip ratio S of the wheels 3 in response to the accelerator depression amount, and select the first correction coefficient k1 shown by the dashed line if they want to decrease it. In other words, the degree to which the target average slip ratio Sta is corrected by the accelerator pedal depression amount α can be changed in response to the driver's driving technique, thereby enabling vehicle characteristics that are easy for the driver to handle.

[0037] (Target relative front-rear slip ratio calculation unit) Fig. 6 is a block diagram showing a schematic configuration of the target relative front-rear slip ratio calculation unit 55. The target relative front-rear slip ratio calculation unit 55 calculates a target relative front-rear slip ratio ΔSt, which is a target value of the relative front-rear slip ratio ΔS (see Fig. 7).

[0038] The front-rear relative slip ratio ΔS in this embodiment will be explained. Let the slip ratio of the left front wheel 3a be "Sfl," the slip ratio of the right front wheel 3b be "Sfr," the slip ratio of the left rear wheel 3c be "Srl," and the slip ratio of the right rear wheel 3d be "Srr." In this case, the front-rear relative slip ratio ΔS is expressed by the following equation (1). As such, the front-rear relative slip ratio ΔS is the relative value between the slip ratios of the left and right front wheels 3a and 3b and the slip ratios of the left and right rear wheels 3c and 3d. In this embodiment, the front-rear relative slip ratio is calculated by dividing the difference between the sum of the slip ratios of the rear wheels 3c and 3d and the sum of the slip ratios of the front wheels 3a and 3b by a value of 4. Here, the deviation is calculated by subtracting the slip ratio of the front wheels 3a and 3b from the slip ratio of the rear wheels 3c and 3d. However, the deviation may also be calculated by subtracting the slip ratio of the rear wheels 3c and 3d from the slip ratio of the front wheels 3a and 3b.

[0039] ΔS=((Srl+Srr)-(Sfl+Sfr)) / 4...(1)

[0040] FIG. 7 is an explanatory diagram showing an example of the relationship between the yaw angular acceleration of a vehicle (the derivative of the yaw rate) and the front-rear relative slip ratio ΔS. In FIG. 7, the horizontal axis represents the base value "ΔS / Sa," which is the front-rear relative slip ratio ΔS non-dimensionalized by the average slip ratio Sa. The relationship shown in FIG. 7 is an example of the analysis results obtained by vehicle behavior analysis. As shown in the figure, even if the average slip ratio Sa changes, as long as the base value is within a range in absolute value of 1 or less, the base value and the yaw angular acceleration are proportional to each other. The relationship shown in FIG. 7 also holds true in a region where the μ-S characteristic of the wheel has a negative gradient. In this way, the yaw angular acceleration relative to the base value can be obtained by vehicle behavior analysis, and the yaw angular acceleration can be controlled (yaw moment control) by changing the base value.

[0041] Therefore, the target longitudinal relative slip ratio calculation unit 55 calculates the target longitudinal relative slip ratio ΔSt based on the relationship between the yaw angular acceleration and the above-mentioned base value, as shown in Fig. 7. Specifically, as shown in Fig. 6, the target longitudinal relative slip ratio calculation unit 55 receives the target average slip ratio Sta calculated by the target average slip ratio calculation unit 54. The target longitudinal relative slip ratio calculation unit 55 also receives a yaw rate deviation ΔY, which is the deviation between the actual yaw rate Y and the required yaw rate Yd calculated by the required yaw rate calculation unit 53. The actual yaw rate Y is the current turning speed of the vehicle 1, and is input to the main control unit 20 from a sensor (not shown).

[0042] The target longitudinal relative slip ratio calculation unit 55 then uses a map M3 in which the relationship between the input yaw rate deviation ΔY and the second base value b2 is predetermined, and sets the second base value b2 according to the input yaw rate deviation ΔY. The second base value b2 corresponds to a value obtained by non-dimensionalizing the target longitudinal relative slip ratio ΔSt using the target average slip ratio Sta. The map M3 predetermines the relationship between the yaw rate deviation ΔY, the target longitudinal relative slip ratio ΔSt, and the target average slip ratio Sta (i.e., the second base value b2) based on the relationship shown in FIG. 7. The yaw angular acceleration of the vehicle 1 relative to the second base value b2 can be obtained by vehicle behavior analysis, as shown in FIG. 7, and the map M3 determines the second base value b2 so as to obtain a desired yaw angular acceleration for each yaw rate deviation ΔY. More specifically, map M3 is determined so that the larger the yaw rate deviation ΔY, the larger the second base value b2 becomes, and vice versa. Furthermore, map M3 defines the upper and lower limits of second base value b2 as an absolute value of 1. Target front-rear relative slip ratio calculation unit 55 multiplies second base value b2, determined from map M3, by target average slip ratio Sta to calculate target front-rear relative slip ratio ΔSt. Target front-rear relative slip ratio calculation unit 55 outputs the calculated value to target slip ratio calculation unit 56.

[0043] As described above, by calculating the target longitudinal relative slip ratio ΔSt corresponding to the yaw rate deviation ΔY based on the relationship between the yaw angular acceleration and the longitudinal relative slip ratio ΔS illustrated in FIG. 7 , the influence of the yaw rate deviation ΔY can be appropriately reflected in the target longitudinal relative slip ratio ΔSt. Ultimately, the influence of the yaw rate deviation ΔY can be appropriately reflected in the target slip ratio St of each wheel 3, which will be described later. As a result, the yaw moment control can be performed with high responsiveness to the operation. Furthermore, the characteristics of the yaw moment control can be gradually changed in response to the driver's operation, making it easier for the driver to handle the vehicle 1. The target longitudinal relative slip ratio ΔSt is not limited to being calculated using a map, but may also be calculated using an equation that predefines the relationship between the yaw rate deviation ΔY, the target longitudinal relative slip ratio ΔSt, and the target average slip ratio Sta (i.e., the second base value b2).

[0044] (Target Slip Ratio Calculation Unit) Returning to the explanation of FIG. 2 , the target slip ratio calculation unit 56 receives the target average slip ratio Sta calculated by the target average slip ratio calculation unit 54 and the target front / rear relative slip ratio ΔSt calculated by the target front / rear relative slip ratio calculation unit 55. Using the input target average slip ratio Sta and target front / rear relative slip ratio ΔSt, the target slip ratio calculation unit 56 calculates the target slip ratio St for each wheel 3 according to the following equations (2) and (3). Here, "Stfl" in equation (2) is the target slip ratio for the left front wheel 3a, and "Stfr" is the target slip ratio for the right front wheel 3b. Furthermore, "Strl" in equation (3) is the target slip ratio for the left rear wheel 3c, and "Strr" is the target slip ratio for the right rear wheel 3d. In this embodiment, the target slip ratios St of the left and right front wheels 3 a, 3 b are set to the same value, and the target slip ratios St of the left and right rear wheels 3 c, 3 d are also set to the same value. This allows the target slip ratios St (Stfl, Stfr, Strl, Strr) of each wheel 3 to be calculated by adding or subtracting the target front-rear relative slip ratio ΔSt to or from the target average slip ratio Sta, based on the relationship in equation (1). The target slip ratio calculation unit 56 outputs the calculated target slip ratios St of each wheel 3 to the target wheel speed calculation unit 58.

[0045] Stfl=Stfr=Sta-ΔSt…(2) Strl=Strr=Sta+ΔSt…(3)

[0046] (Wheel Translational Velocity Calculation Unit) The wheel translational velocity calculation unit 57 receives the vehicle speed Vs, steering angle δ, and center-of-gravity slip angle β as input, and calculates the wheel translational velocity V based on the input vehicle speed Vs, steering angle δ, and center-of-gravity slip angle β, as well as vehicle specifications shown in equations (4) to (8) described below. The wheel translational velocity V is the velocity of each wheel 3 in the vehicle's traveling direction, i.e., the direction in which each wheel 3 translates, and is calculated taking into account the inner / outer wheel difference of each wheel 3. The vehicle speed Vs is input to the main control unit 20 from a sensor (not shown). The center-of-gravity slip angle β is the slip angle at the center of gravity O1 of the vehicle 1 (see FIG. 8 ), and can be estimated based on the vehicle speed Vs, the acceleration at the center of gravity O1 of the vehicle 1, the steering angle δ, the vehicle specifications, etc.

[0047] FIG. 8 is an explanatory diagram schematically illustrating a state in which the vehicle 1 is turning. As illustrated, it is assumed that the vehicle 1 is turning around a turning center O2. Note that FIG. 8 illustrates a state in which the vehicle 1 is skidding. When the vehicle 1 is turning as illustrated, the turning radius R at the center of gravity O1 of the vehicle 1 can be calculated according to the following equation (4). "A" is the acceleration at the center of gravity O1 of the vehicle 1, and a value detected by a sensor (not shown) can be used. Furthermore, "L" is the distance (wheelbase) between the drive shaft 8 of the front wheels 3a, 3b and the drive shaft 14 of the rear wheels 3c, 3d in the longitudinal direction of the vehicle.

[0048] R=(1+AV2)・L / δ...(4)

[0049] Furthermore, the turning radius Rfl of the front wheel 3a, the turning radius Rfr of the front wheel 3b, the turning radius Rfl of the rear wheel 3c, and the turning radius Rrr of the rear wheel 3d can be calculated according to the following equations (5) to (8). "Lf" is the distance between the drive shaft 8 of the front wheels 3a, 3b and the center of gravity O1 in the longitudinal direction of the vehicle, "Lr" is the distance between the drive shaft 14 of the rear wheels 3c, 3d and the center of gravity O1 in the longitudinal direction of the vehicle, and "d" is the distance between the wheels 3 in the lateral direction (tread). Note that Figure 8 only shows the turning radius Rfl of the front wheel 3a and the turning radius Rrl of the rear wheel 3c as an example.

[0050]

[0051]

[0052]

[0053]

[0054] The wheel translational velocity V of each wheel 3 can be calculated according to the following equation (9). By replacing "x" and "y" with "f" or "r", the wheel translational velocity V of the left front wheel 3a, the wheel translational velocity Vfr of the right front wheel 3b, the wheel translational velocity Vrl of the left rear wheel 3c, and the wheel translational velocity Vrr of the right rear wheel 3d are obtained. Note that FIG. 8 only illustrates the wheel translational velocity Vfl of the front wheel 3a. The wheel translational velocity calculation unit 57 calculates the wheel translational velocity V (Vfl, Vfr, Vrl, Vrr; see FIG. 2) of each wheel 3 as described above, and outputs the calculated values ​​to the target wheel speed calculation unit 58.

[0055] Vxy=Rxy / R・Vs…(9)

[0056] (Target Wheel Speed ​​Calculation Unit) The target wheel speed calculation unit 58 receives the target slip ratio St of each wheel 3 calculated by the target slip ratio calculation unit 56 and the wheel translational speed V of each wheel 3 calculated by the wheel translational speed calculation unit 57, and calculates the target wheel speed Vt of each wheel 3. Specifically, the target wheel speed calculation unit 58 calculates the target wheel speed Vt of each wheel 3 from the relationship between the slip ratio and the wheel speed according to the following equation (10). Replacing "x" and "y" in equation (10) with "f" or "r" results in the target wheel speed Vtfl of the left front wheel 3a, the target wheel speed Vtfr of the right front wheel 3b, the target wheel speed Vtrl of the left rear wheel 3c, and the target wheel speed Vtrr of the right rear wheel 3d. The target wheel speed calculation unit 58 outputs the calculated target wheel speeds Vt (Vtfl, Vtfr, Vtrl, Vtrr; see FIG. 2) of each wheel 3 to the motor control unit and the brake control unit.

[0057] Vtxy=(1+Stxy)・Vxy...(10)

[0058] The motor control unit and the brake control unit, to which the target wheel speed Vt calculated as described above is input, perform feedback control to calculate a control torque for each wheel 3 so that the actual wheel speed Vw of each wheel 3 approaches the target wheel speed Vt. As a result, the front motor 4, rear motor 6, brake devices 30a, 30b, 30c, 30d, etc. are controlled so that the set control torque is applied to each wheel 3. In this way, traction control for each wheel 3 can be performed.

[0059] As described above, the cruise control device 50 of this embodiment calculates the wheel translational speed V of each wheel 3 using the main control unit 20, and further calculates the target wheel speed Vt. This makes it possible to accurately calculate the target wheel speed Vt using the wheel translational speed V that takes into account the inner / outer wheel speed difference of the wheels 3. Furthermore, the motor control unit and the brake control unit perform feedback control of the wheel speed. Furthermore, the main control unit 20 calculates both the wheel translational speed V and the target wheel speed Vt, and the motor control unit and the brake control unit that receive the target wheel speed Vt perform feedback control based on the wheel speed. This eliminates the need for the motor control unit and the brake control unit to have information on the wheel translational speed V.

[0060] Next, the motor control units 10, 12 and the brake control units 31, 32 will be described. Figure 9 is an explanatory diagram showing the schematic configuration of the motor control units 10, 12 and the brake control units 31, 32. For example, in a situation where the road surface friction coefficient is low, there is a possibility that the wheels 3 may slip, causing them to spin freely, or may lock, preventing them from rotating. To prevent such slipping or locking, the motor control units 10, 12 and the brake control units 31, 32 are equipped with a torque control unit 60 that includes a PID control unit 61 and an initial torque reduction control unit 62.

[0061] (PID Control Unit) The PID control unit 61 executes feedback control based on the target wheel speeds Vt (Vtfl, Vtfr, Vtrl, Vtrr) and the actual wheel speed Vw so that each wheel 3 rotates at the target wheel speed Vt. Specifically, the PID control unit 61 receives a deviation between the target wheel speed Vt and the actual wheel speed Vw, calculates a proportional term for the deviation in a proportional term calculation unit 61p, calculates a differential term for the deviation in a differential term calculation unit 61d, and calculates an integral term for the deviation in an integral term calculation unit 61i. The integral term calculation unit 61i calculates an integral term for a value that takes into account not only the deviation but also a second correction torque ΔT2 (described later). The PID control unit 61 adds together the calculated proportional term, integral term, and differential term to calculate the first correction torque ΔT1. The first correction torque ΔT1 is calculated as a correction amount for correcting the torque Td required by the driver for the vehicle 1 so that the rotation speed of each wheel 3 approaches the target wheel speed Vt.

[0062] (Initial Torque Reduction Control Unit) The initial torque reduction control unit 62 calculates a second correction torque (torque reduction amount) ΔT2 for suppressing slippage or locking of the wheels 3. Specifically, the initial torque reduction control unit 62 receives a requested acceleration of the vehicle 1 from the driver, and divides the received requested acceleration by the equivalent inertial mass of the vehicle 1 and the wheel diameter of each wheel 3 to calculate a requested acceleration Gwd for each wheel 3. The initial torque reduction control unit 62 also receives an actual wheel speed Vw of each wheel 3, and differentiates the received actual wheel speed Vw to calculate the actual acceleration Gw of each wheel 3.

[0063] The initial torque reduction control unit 62 calculates a deviation ΔGw by subtracting the calculated required acceleration Gwd from the actual acceleration Gw. Furthermore, the initial torque reduction control unit 62 multiplies the deviation ΔGw by a predetermined torque conversion coefficient Kmv to calculate a third base value b3, and then multiplies this value by a second correction coefficient k2 (described later) to calculate a second correction torque ΔT2. Therefore, if the second correction coefficient k2 (described later) is not taken into consideration, the greater the actual acceleration is relative to the required acceleration and the greater the deviation ΔGw, the greater the absolute value of the second correction torque ΔT2 is set to.

[0064] The torque control unit 60 subtracts the second correction torque ΔT2 from the first correction torque ΔT1 calculated by the PID control unit 61, i.e., from the output value of the PID control, and then performs a predetermined phase lead compensation on the PID control by the phase lead control unit 63 to calculate the final correction torque ΔT. The torque control unit 60 calculates the control torque for the wheel 3 by adding the calculated final correction torque ΔT to the torque required by the driver. This reduces the value of the final correction torque ΔT. As a result, in a situation where a driving torque is applied to the wheel 3 and the actual acceleration is greater than the required acceleration, making it highly likely that the wheel 3 is slipping, the driving torque is reduced to tend to suppress slip, thereby enabling the wheel 3 to be promptly suppressed from slipping. Furthermore, in a situation where a braking torque is applied to the wheel 3 and the actual acceleration is smaller than the required acceleration, making it highly likely that the wheel 3 is locked, the braking torque is reduced to tend to suppress locking of the wheel 3, thereby enabling the wheel 3 to be promptly suppressed from locking.

[0065] In this embodiment, the second correction torque ΔT2 calculated by the initial torque reduction control unit 62 is also used in the integral term calculation unit 61i of the PID control unit 61, as shown in the figure. In the PID control unit 61, the difference between the target wheel speed Vt and the actual wheel speed Vw is multiplied by a conversion coefficient (not shown) and the resulting sum is input to the integral term calculation unit 61i, which then calculates the integral term for that value. As a result, the PID control unit 61 accelerates the I control by the amount that the value based on the second correction torque ΔT2 is added. In other words, the larger the second correction torque ΔT2, the larger the I control amount. As a result, the steady-state deviation of the PID control can be suppressed, thereby improving the control accuracy.

[0066] Furthermore, the integral term calculated by the integral term calculation unit 61i is output to the initial torque reduction control unit 62. The initial torque reduction control unit 62 sets a second correction coefficient k2 that is set according to the input integral term, i.e., the I control amount. Specifically, the initial torque reduction control unit 62 uses a map M4 in which the relationship between the I control amount and the second correction coefficient k2 of the second correction torque ΔT2 is predetermined, and sets the second correction coefficient k2 according to the input I control amount. The map M4 is preset so that the second correction coefficient k2 decreases as the I control amount increases and becomes zero when the I control amount becomes equal to or greater than a predetermined value. As a result, the second correction torque ΔT2 calculated by multiplying the third base value b3 by the second correction coefficient k2 decreases as the I control amount increases and becomes zero when I control is sufficiently promoted. This reduces the contribution of the correction by the second correction torque ΔT2 as the output value of the PID control is settled, and after slippage or locking of the wheel 3 has been sufficiently suppressed, the second correction torque ΔT2 is not reflected in the final correction torque ΔT, thereby stabilizing the value of the final correction torque ΔT.

[0067] Effect of the embodiment As described above, the cruise control device 50 of the embodiment is a cruise control device 50 for a vehicle 1 that includes a front motor (electric motor for driving) 4 and a rear motor (electric motor for driving) 6, and that controls the torque applied to each wheel 3 by feedback control so that the front, rear, left, and right wheels 3 rotate based on a target slip ratio, and includes a torque control unit 60 that calculates a second correction torque ΔT2 that tends to increase as the deviation ΔGw between the required acceleration Gwd for the wheel 3 and the actual acceleration Gw of the wheel 3 increases, and corrects the torque applied to each wheel 3 by subtracting the second correction torque (torque reduction amount) ΔT2 from the output value of the feedback control (first correction torque ΔT1).

[0068] With this configuration, the output value of the feedback control can be corrected by the second correction torque ΔT2 so that the torque applied to each wheel 3 decreases as the deviation ΔGw between the required acceleration Gwd and the actual acceleration Gw for each wheel 3 increases. As a result, even if slippage occurs in which the rotation speed of the wheel 3 increases or the wheel 3 locks up, the slippage or locking can be quickly suppressed to bring the slip ratio S of the wheel 3 closer to the target slip ratio St. This makes it possible to achieve traction control with higher accuracy and higher response.

[0069] The feedback control is a PID control, and the torque control unit 60 increases the I control amount of the PID control as the second correction torque ΔT2 increases. This configuration reduces steady-state deviation and improves the accuracy of traction control.

[0070] Furthermore, the torque control unit 60 reduces the contribution of the correction made by the second correction torque ΔT2 to the output value of the PID control (first correction torque ΔT1) as the I control amount increases. With this configuration, as the I control is promoted and the output value of the PID control is settled, that is, as the rotation speed of the wheels 3 is settled, the contribution of the second correction torque ΔT2 is reduced, and the value of the torque applied to each wheel 3 can be stabilized.

[0071] The vehicle control system also includes a wheel translational velocity calculation unit 57 that calculates wheel translational velocities V (Vfl, Vfr, Vrl, Vrr) of each wheel 3 in the vehicle traveling direction based on the steering angle δ, vehicle speed Vs, center-of-gravity slip angle β, and other vehicle specifications of the vehicle 1, and a target wheel speed calculation unit 58 that calculates target wheel speeds Vt (Vtfl, Vtfr, Vtrl, Vtrr) of each wheel 3 based on the wheel translational velocities and the target slip ratio St. A torque control unit 60 controls torque by feedback control so that the wheel speeds approach the target wheel speeds Vt. This configuration makes it possible to accurately calculate the target wheel speeds Vt of each wheel 3 using the wheel translational velocities V that take into account the inner and outer wheel speed difference of each wheel 3, thereby enabling accurate control of the torque applied to each wheel 3. This results in higher precision in traction control and improved steering response.

[0072] Furthermore, wheel translational speed calculation section 57 and target wheel speed calculation section 58 are included in main control unit 20, and torque control section 60 is included in a motor control unit (front motor control unit 10 and rear motor control unit 12, sub-control unit) separate from main control unit 20. With this configuration, even if the motor control unit does not have information on wheel translational speed V, it can calculate the control torque for each wheel 3.

[0073] (Modification) Although the description of the embodiment has been completed above, the aspects of the present invention are not limited to this embodiment. For example, in this embodiment, the torque applied to each wheel 3 is controlled by feedback control at the target wheel speed Vt calculated by the target wheel speed calculation unit 58. However, the torque applied to each wheel 3 may also be controlled by feedback control so that the slip ratio S of each wheel approaches the target slip ratio St.

[0074] In addition, the driving control device 50 of this embodiment has a front motor control unit 10 and a rear motor control unit 12 as motor control units, and a front brake control unit 31 and a rear brake control unit 32 as brake control units, but each may be provided for each motor or brake device, or one may be provided for each vehicle.

[0075] Furthermore, although the vehicle 1 in the above embodiment is a plug-in hybrid electric vehicle (PHEV) equipped with an engine 2 and capable of external charging and external power supply, the present invention can also be applied to hybrid electric vehicles (HEVs) and electric vehicles (EVs). The present invention can also be applied to vehicles in which the driving or braking of each of the four wheels can be electrically controlled independently.

[0076] REFERENCE SIGNS LIST 1 Vehicle 2 Engine 3 Wheels 4 Front motor (electric motor for driving) 6 Rear motor (electric motor for driving) 10 Front motor control unit (sub-control unit) 12 Rear motor control unit (sub-control unit) 20 Main control unit 31 Front brake control unit (sub-control unit) 32 Rear brake control unit (sub-control unit) 50 Driving control device 60 Torque control unit 61 PID control unit 62 Initial torque reduction control unit Gw Actual acceleration Gwd Required acceleration St Target slip ratio V, Vfl, Vfr, Vrl, Vrr Wheel translational speed Vs Vehicle speed Vt, Vtfl, Vtfr, Vtrl, Vtrr Target wheel speed β Center of gravity slip angle δ Steering angle (handle angle) ΔGw Deviation ΔT2 Second correction torque (torque reduction amount)

Claims

1. A vehicle running control device that includes an electric motor for running and controls the torque applied to each wheel by feedback control so that the front, rear, left, and right wheels rotate based on a target slip ratio, a torque control unit that calculates a torque reduction amount that tends to increase as the deviation between the required acceleration for the wheel and the actual acceleration of the wheel increases, and corrects the torque applied to each wheel by subtracting the torque reduction amount from the output value of the feedback control; a wheel translational speed calculation unit that calculates the wheel translational speed in the vehicle traveling direction of each wheel based on the steering angle, vehicle speed, center of gravity slip angle, and vehicle specifications; a target wheel speed calculation unit that calculates the target wheel speed of each wheel based on the wheel translational speed and the target slip ratio; and is provided with; The torque control unit is a vehicle running control device that controls the torque by the feedback control so that the wheel speed approaches the target wheel speed.

2. The feedback control is PID control, The torque control unit is the vehicle running control device according to claim 1, wherein the larger the torque reduction amount, the larger the I control amount of the PID control.

3. The torque control unit is the vehicle running control device according to claim 2, wherein the larger the I control amount, the lower the contribution degree of the correction to the output value by the torque reduction amount.

4. The wheel translational speed calculation unit and the target wheel speed calculation unit are included in a main control unit, and the torque control unit is included in a sub-control unit separate from the main control unit. The vehicle running control device according to claim 1.