Vehicle driving control system

Abstract

This travel control device 50 comprises: a target average slip rate calculation part 54 that calculates a target average slip rate Sta, which is the average value of target slip rates St of all four wheels, on the basis of a required braking / driving force Fd of a vehicle; a target front-rear relative slip ratio calculation part 55 that calculates a target front-rear relative slip rate ΔSt serving as a front-rear relative slip rate ΔS, which is the absolute value of a slip rate S of the front and rear wheels, on the basis of a yaw rate deviation ΔY, which is the deviation between a required yaw rate Yd for the vehicle and an actual yaw rate Y of the vehicle; a target slip rate calculation part 56 that calculates a target slip rate St of wheels 3 on the basis of the target average slip rate Sta and the target front-rear relative slip rate ΔSt; and a torque control part that controls torque imparted to the wheels 3 on the basis of the target slip rate St.

Description

Technical Field

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

Background Art

[0002] Conventionally, a technique for performing traction control of each wheel based on the slip ratio and yaw rate of the wheels is known. For example, Patent Document 1 describes an electric vehicle that controls the driving force of an electric motor so that the slip ratio of each wheel does not exceed a predetermined upper limit value within a range where the turning acceleration of the vehicle body becomes the turning acceleration corresponding to the steering angle.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, there has been a demand for traction control that can follow the movement of a vehicle without delay in response to a driver's driving operation and can realize easy-to-handle vehicle characteristics. However, the electric vehicle described in Patent Document 1 simply turns the vehicle in response to a turning request from the driver while suppressing slip of each wheel, and there is a possibility that the operation followability of the traction control and the ease of handling of the vehicle cannot be sufficiently improved.

[0005] The present invention has been made in view of such problems, and an object thereof is to provide a vehicle driving control device capable of realizing traction control with improved operation followability and ease of handling of the vehicle by the driver.

Means for Solving the Problems

[0006] To achieve the above objective, the vehicle driving control device of the present invention is a vehicle driving control device equipped with a driving electric motor, comprising: a target average slip ratio calculation unit that calculates a target average slip ratio, which is the average value of the target slip ratios of each front, rear, left, and right wheel, based on the required driving force of the vehicle; a target front and rear relative slip ratio calculation unit that calculates a target front and rear relative slip ratio as a target value of the front and rear relative slip ratio, which is the relative value of the slip ratios of the front and rear wheels, based on the yaw rate deviation, which is the deviation between the required yaw rate for the vehicle and the actual yaw rate of the vehicle; a target slip ratio calculation unit that calculates the target slip ratio of each wheel based on the target average slip ratio and the target front and rear relative slip ratio; and a torque control unit that controls the torque applied to each wheel based on the target slip ratio.

[0007] This configuration allows for the control of torque applied to each wheel by reflecting the target front-to-rear relative slip ratio, calculated based on the yaw rate deviation (the difference between the required yaw rate and the actual yaw rate), in the target slip ratio of each wheel, in addition to the required braking and driving force of the vehicle. As a result, yaw moment control can be performed with high responsiveness to driver input while obtaining braking and driving force that meets the driver's demands. Furthermore, the characteristics of the yaw moment control can be gradually changed in response to the driver's input, making the vehicle easier for the driver to handle. Therefore, the vehicle driving control device of the present invention makes it possible to achieve traction control that improves responsiveness to operation and ease of handling for the driver.

[0008] Furthermore, it is preferable that the target front-to-rear relative slip ratio calculation unit calculates the target front-to-rear relative slip ratio in accordance with the yaw rate deviation and the target average slip ratio, based on the relationship between the predetermined yaw rate deviation, the target average slip ratio, and the target front-to-rear relative slip ratio. With this configuration, the target front-to-rear relative slip ratio can be appropriately calculated according to the yaw rate deviation of the vehicle.

[0009] Furthermore, it is preferable that the target average slip ratio calculation unit calculates the target average slip ratio by multiplying a base value calculated based on the deviation between the required braking force and the actual braking force of the vehicle by a correction coefficient set according to the accelerator opening. With this configuration, in addition to the deviation between the required braking force and the actual braking force, the magnitude of the accelerator opening can be reflected in the target average slip ratio and, consequently, the target slip ratio of each wheel. As a result, it is possible to obtain a target slip ratio for each wheel that is suitable for the required braking force of the entire vehicle in response to the driver's accelerator operation. Moreover, even if the μ-S characteristics of the wheel change, the target average slip ratio and, consequently, the target slip ratio of each wheel can be set so as to approach the slip ratio that results in the maximum braking force with the driver's accelerator operation, thereby improving the ease of handling the vehicle by the driver.

[0010] Furthermore, it is preferable that the correction coefficient includes multiple patterns that can be changed according to the driver's requirements. This configuration allows the degree to which the target average slip ratio is corrected by the accelerator opening to be changed according to the driver's driving skills, making it possible to obtain vehicle characteristics that are easy for the driver to handle.

[0011] Furthermore, the system includes a wheel translational speed calculation unit that calculates the wheel translational speed of each wheel in the direction of vehicle travel based on the steering angle, vehicle speed, center of gravity slip angle, and vehicle specifications, and 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. Preferably, the torque control unit controls the torque by feedback control so that the wheel speed approaches the target wheel speed. With this configuration, the target wheel speed of each wheel can be calculated with high accuracy using the wheel translational speed that takes into account the difference between the inner and outer wheels of each wheel, and the torque applied to each wheel can be controlled with high accuracy. Therefore, the accuracy of traction control can be improved and the responsiveness to operation can be enhanced.

[0012] Furthermore, it is preferable that the wheel translational speed calculation unit and the target wheel speed calculation unit are included in the 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 speed. [Effects of the Invention]

[0013] The vehicle driving control device of the present invention makes it possible to achieve traction control that improves responsiveness to operation and ease of handling by the driver. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of a plug-in hybrid vehicle equipped with a driving control device according to an embodiment. [Figure 2] This is a block diagram showing the schematic configuration of the driving control device of the embodiment. [Figure 3] This is a block diagram illustrating the schematic configuration of the target average slip ratio calculation unit. [Figure 4] This is an explanatory diagram showing an example of how the accelerator opening, braking force, and slip ratio change over time due to torque control in the driving control device of the embodiment. [Figure 5] This is an explanatory diagram illustrating an example of the relationship between wheel braking / driving force and slip ratio. [Figure 6] This is a block diagram illustrating the schematic configuration of the unit that calculates the relative slip ratio before and after the target. [Figure 7] This is an explanatory diagram illustrating an example of the relationship between a vehicle's yaw rate and its relative front-to-rear slip ratio. [Figure 8] This is a schematic diagram illustrating a vehicle in a turning state. [Figure 9] This is an explanatory diagram showing the schematic configuration of the motor control unit and the brake control unit. [Modes for carrying out the invention]

[0015] Hereinafter, an embodiment of the present invention will be described based on the drawings.

[0016] (Vehicle) FIG. 1 is a schematic configuration diagram of a plug-in hybrid vehicle (hereinafter referred to as vehicle 1) equipped with a driving control device according to an embodiment. Vehicle 1 can travel by driving front wheels 3a and 3b by the output of engine 2, and is a four-wheel drive vehicle equipped with an electric front motor (travel electric motor) 4 for driving front wheels 3a and 3b and an electric rear motor (travel electric motor) 6 for driving rear wheels 3c and 3d. In the following description, when there is no particular need for distinction, front wheels 3a and 3b and rear wheels 3c and 3d are referred to as "wheels 3".

[0017] (Engine) Engine 2 can drive the drive shafts 8 of front wheels 3a and 3b via front transaxle 7, and can drive motor generator 9 via front transaxle 7 to generate electricity. Further, engine 2 and front wheels 3a and 3b are connected via a clutch 16 disposed within front transaxle 7. Note that vehicle 1 is equipped with a fuel tank (not shown) for storing fuel to supply fuel to engine 2.

[0018] (Motor) Front motor 4 is driven by being supplied with high-voltage power from drive battery 11 and motor generator 9 mounted on vehicle 1 via front motor control unit (sub-control unit) 10, and drives the drive shafts 8 of front wheels 3a and 3b via front transaxle 7. Rear motor 6 is driven by being supplied with high-voltage power from drive battery 11 via rear motor control unit (sub-control unit) 12, and drives the drive shafts 14 of rear wheels 3c and 3d via rear transaxle 13. The power generated by motor generator 9 can charge drive battery 11 via front motor control unit 10, and can supply power to front motor 4 and rear motor 6.

[0019] (Power battery) The drive battery 11 is composed of a secondary battery such as a lithium-ion battery and has a battery module (not shown) which is made up of multiple battery cells. The drive battery 11 is also equipped with a charge level detection unit 11a that detects the state of charge (SOC) of the drive battery 11. The vehicle 1 is also equipped with a charger 18 that can charge the drive battery 11 using an external power source.

[0020] (Motor control unit) The front motor control unit 10 controls the braking force of the front motor 4, i.e., the drive torque or regenerative braking torque of the front motor 4, based on a control signal from the main control unit 20 mounted on the vehicle 1, and also controls the amount of power generated and the output of the motor generator 9. The rear motor control unit 12 controls the braking force of the rear motor 6, i.e., the drive torque or regenerative braking torque of the rear motor 6, based on a control signal from the main control unit 20.

[0021] (Engine control unit) The engine control unit 22 is a control device for the engine 2 and includes input / output devices, memory devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), and a timer. Based on control signals (request outputs) from the main control unit 20, the engine control unit 22 controls the fuel injection amount and timing, intake air amount, etc., in the engine 2 to control the engine 2's operation.

[0022] (Main control unit) The main control unit 20 is a control device for the overall control of the vehicle 1, and is composed of input / output devices, memory devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), and timers. The front motor control unit 10, the rear motor control unit 12, and the 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, the rear motor control unit 12, the engine control unit 22, and the clutch 16 of the front transaxle 7 are connected to the output side of the main control unit 20.

[0023] The main control unit 20 calculates the vehicle request output required for driving the vehicle 1 based on various detected quantities such as the degree of accelerator operation of the vehicle 1 and various operational information, and transmits 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 the switching of driving modes (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.

[0024] In EV mode, engine 2 is stopped, and the vehicle is driven by power supplied from the drive battery 11 to power the front motor 4 and rear motor 6. In series mode, the clutch 16 of the front transaxle 7 is disengaged, and engine 2 operates the motor generator 9. The vehicle is then driven by power generated by the motor generator 9 and power supplied from the drive battery 11 to power the front motor 4 and rear motor 6. In series mode, the rotational speed of engine 2 is set to an efficient value, and the surplus power is supplied to the drive battery 11 to charge it. In parallel mode, the clutch 16 of the front transaxle 7 is engaged, and power is mechanically transmitted from engine 2 through the front transaxle 7 to drive the front wheels 3a and 3b. The vehicle is then driven by power generated by engine 2 operating the motor generator 9 and power supplied from the drive battery 11 to power the front motor 4 and rear motor 6.

[0025] The main control unit 20 sets the driving mode to parallel mode in areas where the engine 2 is efficient, such as high speeds. In areas other than parallel mode, i.e., low to medium speeds, it switches between EV mode and series mode based on the state of charge (SOC) of the drive battery 11.

[0026] (Brake system) Furthermore, each wheel 3 of the vehicle 1 is equipped with brake devices 30a, 30b, 30c, and 30d that apply braking torque. The front brake devices 30a and 30b are controlled by a front brake control unit (sub-control unit) 31, and the rear brake devices 30c and 30d are controlled by a rear brake control unit (sub-control unit) 32, so that the braking torque can be controlled independently for each wheel 3.

[0027] (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 also 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 also 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 operate and control the respective brake devices 30a, 30b, 30c, and 30d based on brake pedal operation signals from a brake pedal sensor (not shown), etc.

[0028] The front motor control unit 10, rear motor control unit 12, front brake control unit 31, and rear brake control unit 32 all consist of input / output devices, memory devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), and timers. These control units use components with a faster processing speed than the main control unit 20.

[0029] (Driving control device) Figure 2 is a block diagram showing the schematic configuration of the driving control device 50 of the embodiment. The driving control device 50 consists of 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). In Figure 2, one motor control unit and one brake control unit are shown, but in the vehicle 1 of this embodiment, two sets are provided, one for the front wheels 3a and 3b and one for the rear wheels 3c and 3d.

[0030] First, the configuration of the main control unit 20 will be described in detail. As shown in Figure 2, the main control unit 20 includes an actual braking force calculation unit 51, a requested braking force calculation unit 52, a requested yaw rate calculation unit 53, a target average slip ratio calculation unit 54, a target front-to-rear relative slip ratio calculation unit 55, a target slip ratio calculation unit 56, a wheel translation speed calculation unit 57, and a target wheel speed calculation unit 58.

[0031] (Braking and driving force calculation unit) The Actual Driving Force Calculation Unit 51 receives the current motor torque Tm of the front motor 4 and 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 rear motor 6. The motor torque Tm and brake torque Tb are command values ​​calculated by the motor control unit and brake control unit, respectively. The actual wheel speed Vw and actual motor rotation speed Vm are detected by sensors (not shown) and input to the main control unit 20. Based on the input values, the Actual Driving Force Calculation Unit 51 calculates the estimated total driving force F of the entire vehicle 1 at the moment. The Requested Driving Force Calculation Unit 52 receives the accelerator opening α and brake stroke Bs of the vehicle 1 and calculates the requested driving force Fd, which is the total driving force required for the entire vehicle 1 by the driver.

[0032] (Required yaw rate calculation section) The requested yaw rate calculation unit 53 receives the detected value of the steering angle (handle angle) δ and calculates the requested yaw rate Yd, which is the speed in the turning direction requested by the driver for the vehicle 1. The steering angle δ is detected by a sensor (not shown) and input to the main control unit 20.

[0033] (Target average slip ratio calculation unit) Figure 3 is a block diagram illustrating the schematic configuration of the target average slip ratio calculation unit 54. The target average slip ratio calculation unit 54 receives the braking force deviation ΔF, which is the difference between the actual braking force F calculated by the actual braking force calculation unit 51 and the required braking force Fd calculated by the required braking force calculation unit 52. The target average slip ratio calculation unit 54 also receives the accelerator opening α as input. Based on the input braking force deviation ΔF and accelerator opening α, the target average slip ratio Sta for each wheel 3 is calculated. The target average slip ratio Sta is the target value of the average slip ratio Sa (see Figure 4) for all wheels 3. In other words, the target average slip ratio Sta is the average value of the target slip ratio St (see “Stfl”, “Stfr”, “Strl”, “Strr” in Figure 2), which is the target value of the slip ratio S (see Figure 4) for each wheel 3.

[0034] Specifically, the target average slip ratio calculation unit 54 uses a map M1 in which the relationship between the braking force deviation ΔF and the first base value (base value) b1 of the target average slip ratio Sta is predetermined, and sets the first base value b1 according to the input braking force deviation ΔF. Map M1 is configured such that the first base value b1 changes in proportion to the braking force deviation ΔF. The target average slip ratio calculation unit 54 also uses a map M2 in which the relationship between the accelerator opening α and the first correction coefficient (correction coefficient) k1 is predetermined, and sets the first correction coefficient k1 according to the input accelerator opening α. Map M2 is configured such that the first correction coefficient k1 increases as the accelerator opening α increases, for example, as shown by the solid line in the figure. The target average slip ratio calculation unit 54 then calculates the 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.

[0035] The target average slip ratio Sta, set as described above, is used in the process described later to ensure that the average slip ratio Sa of each wheel 3 approaches the target average slip ratio Sta. Figure 4 is an explanatory diagram showing an example of how the accelerator opening, braking force, and slip ratio change over time due to torque control in the driving control device 50 of the embodiment. As described above, the target average slip ratio Sta is calculated to be proportional to the braking 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 corresponding to the braking force deviation ΔF and to a value suitable for the accelerator opening α, i.e., the required braking force Fd. In other words, by reflecting the accelerator opening α in the target average slip ratio Sta, it becomes possible to compensate the target average slip ratio Sta for the required braking force Fd. The first correction coefficient k1 can be determined based on the relationship between the braking force (braking force friction coefficient) and the slip ratio on the wheel (tire) (i.e., the μ-S characteristic; see Figure 5, for example). In addition, 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 slope. As a result, as the driver presses 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 friction margin (see dashed line) can be controlled to converge to the target average slip ratio Sta, which compensates for the required braking force Fd, as shown by the white arrows in Figure 4.

[0036] Figure 5 is an explanatory diagram illustrating an example of the relationship between the braking force and slip ratio of a wheel. As shown by the solid or dashed lines in the figure, the relationship between the braking force (braking force friction coefficient) and slip ratio (i.e., the μ-S characteristic) applied to the wheel (tire) changes depending on the 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 to approach the slip ratio that results in the maximum braking and driving force in response to the driver's accelerator operation, as shown by the white arrows in the figure.

[0037] Here, the first correction coefficient k1 may include multiple patterns that can be changed according to the driver's request. For example, as shown by the dashed line in map M2 of Figure 3, a pattern is prepared in which the increase in the first correction coefficient k1 with respect to the increase in accelerator opening α is larger compared to the one 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 wheel 3 according to the amount of accelerator depression, 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 opening α can be changed according to the driver's driving skills, making it possible to obtain vehicle characteristics that are easy for the driver to handle.

[0038] (Target front-to-back relative slip ratio calculation unit) Figure 6 is a block diagram showing the schematic configuration of the target front-to-rear relative slip ratio calculation unit 55. The target front-to-rear relative slip ratio calculation unit 55 calculates the target front-to-rear relative slip ratio ΔSt, which is the target value of the front-to-rear relative slip ratio ΔS (see Figure 7).

[0039] The front-to-rear relative slip ratio ΔS in this embodiment will now be explained. Let's assume that the slip ratio of the left front wheel 3a is "Sfl", the slip ratio of the right front wheel 3b is "Sfr", the slip ratio of the left rear wheel 3c is "Srl", and the slip ratio of the right rear wheel 3d is "Srr". In this case, the front-to-rear relative slip ratio ΔS is expressed by the following equation (1). Thus, the front-to-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-to-rear relative slip ratio is obtained 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. Note that here, the deviation is calculated by subtracting the slip ratios of the front wheels 3a and 3b from the slip ratios of the rear wheels 3c and 3d. Alternatively, the deviation could be calculated by subtracting the slip ratios of the rear wheels 3c and 3d from the slip ratios of the front wheels 3a and 3b.

[0040] ΔS=((Srl+Srr)-(Sfl+Sfr)) / 4 …(1)

[0041] Here, Figure 7 is an explanatory diagram illustrating an example of the relationship between the vehicle's yaw angular acceleration (derivative of yaw rate) and the longitudinal relative slip ratio ΔS. In Figure 7, the horizontal axis is plotted as the base value "ΔS / Sa", which is obtained by non-dimensionalizing the longitudinal relative slip ratio ΔS by the average slip ratio Sa. The relationship shown in Figure 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 the range of 1 or less in absolute value, the base value and the yaw angular acceleration are proportional. The relationship shown in Figure 7 also holds true in the region where the μ-S characteristic of the wheel is negative. Thus, the yaw angular acceleration with respect to the above base value can be obtained by vehicle behavior analysis, and the yaw angular acceleration can be controlled (yaw moment control) by changing the above base value.

[0042] Therefore, the target front-to-rear relative slip ratio calculation unit 55 calculates the target front-to-rear relative slip ratio ΔSt based on the relationship between the yaw angular acceleration exemplified in Figure 7 and the base value. Specifically, as shown in Figure 6, the target front-to-rear 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 front-to-rear relative slip ratio calculation unit 55 also receives the yaw rate deviation ΔY, which is the difference between the required yaw rate Yd calculated by the required yaw rate calculation unit 53 and the actual yaw rate Y. 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).

[0043] The target front-to-rear 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 the value obtained by non-dimensionalizing the target front-to-rear relative slip ratio ΔSt with respect to the target average slip ratio Sta. Map M3 has predetermined relationships between the yaw rate deviation ΔY, the target front-to-rear relative slip ratio ΔSt, and the target average slip ratio Sta (i.e., the second base value b2) based on the relationship illustrated in Figure 7. The yaw angular acceleration of the vehicle 1 with respect to the second base value b2 can be obtained by vehicle behavior analysis as illustrated in Figure 7, and the map M3 is configured such that the second base value b2 can be determined so that a desired yaw angular acceleration can be obtained for each yaw rate deviation ΔY. More specifically, map M3 is configured such that the second base value b2 increases as the yaw rate deviation ΔY increases, and decreases as the yaw rate deviation ΔY decreases. Furthermore, in map M3, the upper and lower limits of the second base value b2 are set to a value of 1 in absolute value. The target front-to-rear relative slip ratio calculation unit 55 calculates the target front-to-rear relative slip ratio ΔSt by multiplying the second base value b2 set from map M3 by the target average slip ratio Sta. The target front-to-rear relative slip ratio calculation unit 55 outputs the calculated value to the target slip ratio calculation unit 56.

[0044] As described above, by calculating the target front-to-rear relative slip ratio ΔSt according to the yaw rate deviation ΔY based on the relationship between yaw angular acceleration and the front-to-rear relative slip ratio ΔS illustrated in Figure 7, the influence of the yaw rate deviation ΔY can be appropriately reflected in the target front-to-rear relative slip ratio ΔSt. Consequently, 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, yaw moment control can be performed with high responsiveness to the driver's input. Furthermore, the characteristics of yaw moment control can be gradually changed according to the driver's input, making the vehicle 1 easier for the driver to handle. Note that the target front-to-rear relative slip ratio ΔSt is not limited to the method using a map; it may also be calculated using a formula that pre-defines the relationship between the yaw rate deviation ΔY, the target front-to-rear relative slip ratio ΔSt, and the target average slip ratio Sta (i.e., the second base value b2).

[0045] (Target slip ratio calculation unit) Returning to the explanation of Figure 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-to-rear relative slip ratio ΔSt calculated by the target front-to-rear relative slip ratio calculation unit 55. Then, using the input target average slip ratio Sta and target front-to-rear relative slip ratio ΔSt, the target slip ratio St for each wheel 3 is calculated according to the following equations (2) and (3). Here, in equation (2), "Stfl" is the target slip ratio of the left front wheel 3a, and "Stfr" is the target slip ratio of the right front wheel 3b. Also, in equation (3), "Strl" is the target slip ratio of the left rear wheel 3c, and "Strr" is the target slip ratio of the right rear wheel 3d. Thus, in this embodiment, the target slip ratios St of the left and right front wheels 3a and 3b are set to the same value, and the target slip ratios St of the left and right rear wheels 3c and 3d are also set to the same value. As a result, from the relationship in equation (1) above, the target slip ratio St (Stfl, Stfr, Strl, Strr) of each wheel 3 can be calculated by adding or subtracting the target front-to-rear relative slip ratio ΔSt to the target average slip ratio Sta. The target slip ratio calculation unit 56 outputs the calculated target slip ratio St of each wheel 3 to the target wheel speed calculation unit 58.

[0046] Stfl = Stfr = Sta - ΔSt …(2) Strl = Strr = Sta + ΔSt …(3)

[0047] (Wheel translation speed calculation unit) The wheel translational speed 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 speed V based on the input vehicle speed Vs, steering angle δ, and center of gravity slip angle β, and the vehicle specifications shown in equations (4) to (8) described later. The wheel translational speed V is the speed of each wheel 3 in the direction of vehicle travel, that is, in the direction in which each wheel 3 is translated, and is calculated taking into account the difference between the inner and outer wheels 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 Figure 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, and the vehicle specifications.

[0048] Here, Figure 8 is a schematic diagram illustrating the state in which vehicle 1 is turning. As shown in the figure, we assume that vehicle 1 is turning around the turning center O2. Note that Figure 8 illustrates the state in which vehicle 1 is skidding. When vehicle 1 is turning as shown in the figure, the turning radius R at the center of gravity O1 of vehicle 1 can be calculated according to the following equation (4). "A" is the acceleration at the center of gravity O1 of vehicle 1, and a value detected by a sensor not shown can be used. "L" is the distance (wheelbase) between the drive shafts 8 of the front wheels 3a and 3b and the drive shafts 14 of the rear wheels 3c and 3d in the longitudinal direction of the vehicle.

[0049] R = (1 + AV2)·L / δ …(4)

[0050] Furthermore, the turning radii Rfl of the front wheel 3a, Rfr of the front wheel 3b, Rfl of the rear wheel 3c, and Rrr of the rear wheel 3d can be calculated according to the following equations (5) to (8). "Lf" is the distance between the drive axle 8 of the front wheels 3a and 3b and the center of gravity O1 in the longitudinal direction of the vehicle, "Lr" is the distance between the drive axle 14 of the rear wheels 3c and 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 in Figure 8, only the turning radius Rfl of the front wheel 3a and the turning radius Rrl of the rear wheel 3c are shown as examples.

[0051]

number

[0052]

number

[0053]

number

[0054]

number

[0055] The wheel translational speed V of each wheel 3 can then be calculated according to the following equation (9). By replacing "x" and "y" with "f" or "r", the wheel translational speed Vfl of the left front wheel 3a, the wheel translational speed Vfr of the right front wheel 3b, the wheel translational speed Vrl of the left rear wheel 3c, and the wheel translational speed Vrr of the right rear wheel 3d are obtained. Note that in Figure 8, only the wheel translational speed Vfl of the front wheel 3a is shown as an example. The wheel translational speed calculation unit 57 calculates the wheel translational speed V (Vfl, Vfr, Vrl, Vrr; see Figure 2) of each wheel 3 as described above and outputs it to the target wheel speed calculation unit 58.

[0056] Vxy = Rxy / R·Vs …(9)

[0057] (Target wheel speed calculation section) The target wheel speed calculation unit 58 receives the target slip ratio St for each wheel 3 calculated by the target slip ratio calculation unit 56 and the wheel translation speed V for each wheel 3 calculated by the wheel translation speed calculation unit 57, and calculates the target wheel speed Vt for each wheel 3. Specifically, the target wheel speed calculation unit 58 calculates the target wheel speed Vt for each wheel 3 according to the following equation (10) based on the relationship between the slip ratio and the wheel speed. By replacing "x" and "y" in equation (10) with "f" or "r", the target wheel speed Vtfl for the left front wheel 3a, the target wheel speed Vtfr for the right front wheel 3b, the target wheel speed Vtrl for the left rear wheel 3c, and the target wheel speed Vtrr for the right rear wheel 3d. The target wheel speed calculation unit 58 outputs the calculated target wheel speeds Vt (Vtfl, Vtfr, Vtrl, Vtrr; see Figure 2) for each wheel 3 to the motor control unit and the brake control unit.

[0058] Vtxy = (1 + Stxy) · Vxy …(10)

[0059] The motor control unit and brake control unit, having received the target wheel speed Vt calculated as described above, perform feedback control to calculate the 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. This enables traction control of each wheel 3.

[0060] As described above, the driving control device 50 of this embodiment calculates the wheel translation speed V of each wheel 3 in the main control unit 20, and further calculates the target wheel speed Vt. This allows for accurate calculation of the target wheel speed Vt using the wheel translation speed V, which takes into account the difference in rotational speed between the inner and outer wheels of the wheel 3. Furthermore, the motor control unit and brake control unit perform feedback control of the wheel speed. In addition, the main control unit 20 calculates both the wheel translation speed V and the target wheel speed Vt, and the motor control unit and brake control unit, which receive the target wheel speed Vt as input, perform feedback control based on the wheel speed. As a result, the motor control unit and brake control unit do not need to have information on the wheel translation speed V.

[0061] Next, the motor control units 10 and 12 and the brake control units 31 and 32 will be described. Figure 9 is an explanatory diagram showing the schematic configuration of the motor control units 10 and 12 and the brake control units 31 and 32. For example, in situations where the road surface friction coefficient is low, there is a possibility of slippage where the wheels 3 spin freely or locking where the wheels 3 do not rotate. To suppress such slippage and locking, the motor control units 10 and 12 and the brake control units 31 and 32 are equipped with a torque control unit 60 which includes a PID control unit 61 and an initial torque reduction control unit 62.

[0062] (PID control unit) The PID control unit 61 performs feedback control so that each wheel 3 rotates at the target wheel speed Vt (Vtfl, Vtfr, Vtrl, Vtrr) and the actual wheel speed Vw. Specifically, the PID control unit 61 receives the deviation between the target wheel speed Vt and the actual wheel speed Vw, calculates a proportional term for the deviation using the proportional term calculation unit 61p, calculates a differential term for the deviation using the differential term calculation unit 61d, and calculates an integral term for the deviation using the integral term calculation unit 61i. In addition, the integral term calculation unit 61i calculates an integral term for a value that takes into account the second correction torque ΔT2, which will be described later, in addition to the above deviation. The PID control unit 61 adds 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 to correct the torque Td requested by the driver to the vehicle 1 so that the rotational speed of each wheel 3 approaches the target wheel speed Vt.

[0063] (Initial torque reduction control unit) The initial torque reduction control unit 62 calculates a second correction torque (torque reduction amount) ΔT2 to suppress slip and lock of the wheels 3. Specifically, the initial torque reduction control unit 62 receives the requested acceleration for the vehicle 1 from the driver, divides the input requested acceleration by the equivalent inertial mass of the vehicle 1 and the wheel diameter of each wheel 3, and calculates the requested acceleration Gwd for each wheel 3. The initial torque reduction control unit 62 also receives the actual wheel speed Vw of each wheel 3, and differentiates the input actual wheel speed Vw to calculate the actual acceleration Gw of each wheel 3.

[0064] The initial torque reduction control unit 62 calculates a deviation ΔGw by subtracting the required acceleration Gwd calculated from the actual acceleration Gw. Furthermore, the initial torque reduction control unit 62 calculates a third base value b3 by multiplying the deviation ΔGw by a predetermined torque conversion coefficient Kmv, and calculates the second corrected torque ΔT2 by multiplying this value by a second correction coefficient k2, which will be described later. Therefore, if the second correction coefficient k2, which will be described later, is not taken into consideration, the absolute value of the second corrected torque ΔT2 will be set to a large value as the actual acceleration is larger than the required acceleration and the deviation ΔGw is larger.

[0065] 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., the output value of the PID control, and then calculates the final correction torque ΔT after applying a predetermined phase lead compensation to the PID control in the phase lead control unit 63. The torque control unit 60 adds the calculated final correction torque ΔT to the requested torque Td from the driver to calculate the control torque for the wheel 3. This makes it possible to reduce the value of the final correction torque ΔT. As a result, in situations where driving torque is applied to the wheel 3 and the actual acceleration is large compared to the requested acceleration, making it highly likely that the wheel 3 is slipping, the driving torque is reduced in a way that tends to suppress slip, and the slip of the wheel 3 can be quickly suppressed. Also, in situations where braking torque is applied to the wheel 3 and the actual acceleration is small compared to the requested acceleration, making it highly likely that the wheel 3 is locked, the braking torque is reduced in a way that tends to suppress the locking of the wheel 3, and the locking of the wheel 3 can be quickly suppressed.

[0066] Furthermore, 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 value obtained by adding the second correction torque ΔT2, which is the deviation between the target wheel speed Vt and the actual wheel speed Vw multiplied by a conversion coefficient (not shown), is input to the integral term calculation unit 61i, and the integral term is calculated for this value. As a result, the I control in the PID control unit 61 is promoted by the amount of the value based on the second correction torque ΔT2 added. In other words, the larger the second correction torque ΔT2, the larger the amount of I control. As a result, the steady-state error of the PID control can be suppressed and the control accuracy can be improved.

[0067] 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, which 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. Map M4 is predetermined so that the larger the I control amount, the smaller the second correction coefficient k2 becomes, and when the I control amount exceeds a predetermined value, the second correction coefficient k2 becomes 0. As a result, the second correction torque ΔT2, calculated by multiplying the third base value b3 by the second correction coefficient k2, becomes smaller as the I control amount increases, and becomes 0 when the I control is sufficiently promoted. As a result, the contribution of the second correction torque ΔT2 to the correction is reduced as the output value of the PID control is settled, and after the slip and lock of the wheel 3 are 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.

[0068] (Effects of the embodiment) As described above, the driving control device 50 of the embodiment is a driving control device 50 for a vehicle 1 equipped with a front motor (driving electric motor) 4 and a rear motor (driving electric motor) 6, and comprises: a target average slip ratio calculation unit 54 that calculates a target average slip ratio Sta, which is the average value of the target slip ratios St of each of the front and rear left and right wheels 3, based on the required braking force Fd of the vehicle 1; a target front and rear relative slip ratio calculation unit 55 that calculates a target front and rear relative slip ratio ΔSt as a target value of the front and rear relative slip ratio ΔS, which is the relative value of the slip ratios of the front and rear wheels 3, based on the yaw rate deviation ΔY, which is the deviation between the required yaw rate Yd for the vehicle 1 and the actual yaw rate Y of the vehicle 1; a target slip ratio calculation unit 56 that calculates the target slip ratio St of each wheel 3 based on the target average slip ratio Sta and the target front and rear relative slip ratio ΔSt; and a torque control unit 60 that controls the torque applied to each wheel 3 based on the target slip ratio St.

[0069] This configuration allows for the acquisition of braking and driving forces that respond to the driver's demands, while simultaneously performing yaw moment control with high responsiveness to the driver's input and gradually changing the characteristics of the yaw moment control in response to the driver's input. Therefore, it becomes possible to achieve traction control that improves responsiveness to the driver's input and makes the vehicle easier to handle for the driver.

[0070] Furthermore, the target front-to-rear relative slip ratio calculation unit 55 calculates the target front-to-rear relative slip ratio ΔSt in accordance with the yaw rate deviation ΔY and the target average slip ratio Sta, based on the relationship between the predetermined yaw rate deviation ΔY, the target average slip ratio Sta, and the target front-to-rear relative slip ratio ΔSt. This configuration allows for the appropriate calculation of the target front-to-rear relative slip ratio ΔSt in accordance with the yaw rate deviation ΔY from the driver.

[0071] Furthermore, the target average slip ratio calculation unit 54 calculates the target average slip ratio Sta by multiplying a first base value (base value) b1, which is calculated based on the braking force deviation ΔF, which is the difference between the required braking force Fd and the actual braking force F, by a first correction coefficient (correction coefficient) k1, which is set according to the accelerator opening α. With this configuration, in addition to the braking force deviation ΔF, which is the difference between the required braking force Fd and the actual braking force F, it is possible to obtain a target slip ratio St for each wheel 3 that is suitable for the required braking force Fd of the entire vehicle 1 in response to the driver's accelerator operation. Moreover, 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 S that results in the maximum braking force with the driver's accelerator operation.

[0072] Furthermore, the first correction coefficient k1 may include multiple patterns that can be changed according to the driver's requirements. This configuration allows the degree to which the target average slip ratio Sta is corrected by the accelerator opening α can be changed according to the driver's driving skills, making it possible to obtain vehicle characteristics that are easy for the driver to handle.

[0073] Furthermore, the system includes a wheel translation speed calculation unit 57 that calculates the wheel translation speed V (Vfl, Vfr, Vrl, Vrr) of each wheel 3 in the direction of vehicle travel based on the steering angle δ, vehicle speed Vs, center of gravity slip angle β, and vehicle specifications of the vehicle 1, and a target wheel speed calculation unit 58 that calculates the target wheel speed Vt (Vtfl, Vtfr, Vtrl, Vtrr) of each wheel 3 based on the wheel translation speed and the target slip ratio St. The torque control unit 60 controls the torque by feedback control so that the wheel speed approaches the target wheel speed Vt. With this configuration, the target wheel speed Vt of each wheel 3 can be calculated with high accuracy using the wheel translation speed V that takes into account the difference between the inner and outer wheels of each wheel 3, and the torque applied to each wheel 3 can be controlled with high accuracy. Therefore, the accuracy of traction control can be improved and the responsiveness to operation can be enhanced.

[0074] Furthermore, the wheel translation speed calculation unit 57 and the target wheel speed calculation unit 58 are included in the main control unit 20, while the torque control unit 60 is included in a separate motor control unit (front motor control unit 10 and rear motor control unit 12, and sub-control unit) from the main control unit 20. With this configuration, the control torque for each wheel 3 can be calculated even if the motor control unit does not have information on the wheel translation speed V.

[0075] (modified version) This concludes the description of the embodiments, but the embodiments of the present invention are not limited to these embodiments. 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 be controlled by feedback control so that the slip ratio S of each wheel approaches the target slip ratio St.

[0076] Furthermore, the driving control device 50 of this embodiment includes 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. However, each of these may be provided for each motor or brake device, or one may be provided for each vehicle.

[0077] Furthermore, although the vehicle 1 in the above embodiment is a plug-in hybrid 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 vehicles (HEVs) and electric vehicles (EVs). The present invention can be applied to vehicles in which the four wheels can be independently driven or braked electrically. [Explanation of Symbols]

[0078] 1 vehicle 2 engines 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 54 Target Average Slip Ratio Calculation Unit 55 Target Front-Rear Relative Slip Ratio Calculation Unit 56 Target slip ratio calculation unit 57 Wheel translation speed calculation section 58 Target wheel speed calculation section 60 Torque Control Unit b1 First base value (base value) F Actual driving force Fd Required driving force k1 First correction factor (correction factor) M1, M2, M3, M4 Maps S slip rate Sa Average slip rate St Target slip rate Sta Target average slip rate V, Vfl, Vfr, Vrl, Vrr Wheel translation speed Vs vehicle speed Vt, Vtfl, Vtfr, Vtrl, Vtrr Target wheel speed Y Actual Yaw Rate Yd Required yaw rate α Accelerator opening β Center of gravity slip angle δ Steering angle (steering wheel angle) ΔF Braking / driving force deviation ΔS: Front-to-rear relative slip ratio ΔSt Target front-to-back relative slip ratio ΔY yaw rate deviation

Claims

1. A vehicle control device for a vehicle equipped with an electric motor for propulsion, A target average slip ratio calculation unit calculates the target average slip ratio, which is the average value of the target slip ratios of each wheel (front, rear, left, and right) based on the required braking force of the vehicle. A target front-to-rear relative slip ratio calculation unit calculates a target front-to-rear relative slip ratio, which is the relative value of the slip ratios of the front and rear wheels, based on the yaw rate deviation, which is the difference between the required yaw rate for the vehicle and the actual yaw rate of the vehicle. A target slip ratio calculation unit calculates the target slip ratio of each wheel based on the target average slip ratio and the target front-to-rear relative slip ratio, A torque control unit that controls the torque applied to each wheel based on the target slip ratio. A vehicle driving control device equipped with the following:

2. The vehicle driving control device according to claim 1, wherein the target front-to-rear relative slip ratio calculation unit calculates the target front-to-rear relative slip ratio in accordance with the yaw rate deviation and the target average slip ratio from the relationship between the predetermined yaw rate deviation, the target average slip ratio and the target front-to-rear relative slip ratio.

3. The vehicle driving control device according to claim 1, wherein the target average slip ratio calculation unit calculates the target average slip ratio by multiplying a base value calculated based on the deviation between the required braking force and the actual braking force of the vehicle by a correction coefficient set according to the accelerator opening.

4. The vehicle driving control device according to claim 3, wherein the correction coefficient includes a plurality of patterns that can be changed according to the driver's request.

5. A wheel translational speed calculation unit calculates the wheel translational speed of each wheel in the direction of vehicle travel based on the steering angle, vehicle speed, center of gravity slip angle, and vehicle specifications, A target wheel speed calculation unit calculates the target wheel speed for each wheel based on the wheel translation speed and the target slip ratio. Equipped with, The torque control unit controls the torque by feedback control so that the wheel speed approaches the target wheel speed. A vehicle driving control device according to any one of claims 1 to 4.

6. The vehicle driving control device according to claim 5, wherein the wheel translation speed calculation unit and the target wheel speed calculation unit are included in the main control unit, and the torque control unit is included in a sub-control unit separate from the main control unit.

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