Driving force control device for four-wheel drive vehicle

Abstract

To provide a driving force control device capable of achieving excellent handling performance while maintaining excellent traction performance.SOLUTION: A driving force control device (1) determines a front and rear wheel drive distribution which is a ratio of driving force between front wheels (21) and rear wheels (22) in a four-wheel drive vehicle. The driving force control device (1) calculates positive or negative standard driving acceleration (XG) obtained from an input amount from a driving force instruction device (42) of the vehicle and a vehicle speed, and on the basis of the standard driving acceleration (XG), switches between dynamic load ratio distribution control to determine the front and rear wheel drive distribution in accordance with a dynamic load ratio distribution curve (L1) which is a curve of a dynamic load ratio applied to the front wheels and the rear wheels with respect to the standard driving acceleration (XG), and rear wheel-biased distribution control to determine the front and rear wheel drive distribution in accordance with a rear wheel-biased distribution curve (L2) which increases a rear wheel drive distribution as compared to the dynamic load ratio distribution curve, and executes it.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a driving force control device for a four-wheel drive vehicle.

Background Art

[0002] Conventionally, in a four-wheel drive vehicle, the longitudinal acceleration is monitored by an in-vehicle accelerometer, and the dynamic loads applied to the front and rear wheels are calculated considering the pitching moment caused by the longitudinal acceleration, and the ratio of the driving force to the dynamic load of each of the front and rear wheels is such that the traction limit of the tire is not exceeded. A driving force control device for performing front-rear driving force distribution (front-rear dynamic load distribution control) is known (Patent Document 1). Furthermore, the lateral acceleration during turning is monitored, the dynamic loads applied to the left and right wheels are calculated considering the rolling moment caused by the lateral acceleration, and the ratio of the driving force to this dynamic load is larger (the inner wheel side during turning). A driving force control device for performing front-rear driving force distribution (inner wheel dynamic load ratio distribution control) so that the ratio does not exceed the traction limit of the tire is also known (Patent Document 2). In addition, a technique for calculating the yaw rate from the value of a G-sensor and performing feedback control on the front-rear driving force distribution ratio is known, but feedback control based on the yaw rate has a drawback that the responsiveness of the control is slow.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The front and rear wheel drive force distribution of a traction vest, that is, the front and rear wheel drive force distribution with good drivability on low-μ roads such as snow, is said to be approximately half for the front and rear wheels. As the drive force distribution is biased front and rear, the traction performance on low-μ roads decreases. On the other hand, from the perspective of handling performance, in FF vehicles (front-wheel drive distribution 100%), there is a tendency towards understeer (US), and in FR vehicles (rear-wheel drive distribution 100%), there is a tendency towards oversteer (OS). In the front and rear wheel drive force distribution of a traction vest, that is, approximately half for the front and rear wheels, the steering characteristics are in the middle between US and OS. However, since the linearity of the turning radius with respect to acceleration (steering characteristics) is not constant, during cornering, fine adjustments of the accelerator and steering are required. The steering characteristics become constant in a region where the rear-wheel drive distribution is slightly higher (handling vest region). When driving in this region, fine adjustments of the accelerator and steering during cornering are not required. Since the front and rear wheel drive distributions of the traction vest and the handling vest are different in this way, there has been a problem in conventional drive force control devices that it is not always possible to achieve both excellent traction performance and excellent handling performance.

[0005] The present invention has been made in view of the above points, and an object thereof is to provide a drive force control device that can obtain excellent handling performance while maintaining excellent traction performance.

Means for Solving the Problems

[0006] In order to solve the above problems, a driving force control device (1) according to the present invention is a driving force control device (1) that determines the front-to-rear wheel drive distribution, which is the ratio of the driving forces of the front wheels (21) and rear wheels (22) in a four-wheel drive vehicle. The driving force control device calculates a positive or negative standard driving acceleration (XG) from the input amount from the driving force indicating device (42) of the vehicle and the vehicle speed, and based on the standard driving acceleration (XG), according to a dynamic load ratio distribution curve (L1), which is a curve of the dynamic load ratio applied to the front and rear wheels with respect to the standard driving acceleration (XG), determines the front-to-rear wheel drive distribution by dynamic load ratio distribution control, and according to a rear-wheel-biased distribution curve (L2) in which the rear-wheel drive distribution is increased from the dynamic load ratio distribution curve, determines the front-to-rear wheel drive distribution by rear-wheel-biased distribution control, and is characterized by switching and implementing these controls.

[0007] According to this configuration, while basically using the dynamic load ratio distribution control with good traction performance, when the acceleration and deceleration of the vehicle are small, since the driving stability is good in the first place, it can be switched to the rear-wheel-biased distribution control with good handling performance, and characteristics such as oversteer and understeer can be stabilized. Also, since the standard driving acceleration (XG) (acceleration target value) is calculated from the indicated amount of the driving force indicating device (accelerator, brake, etc.) and control is performed based on this, the responsiveness is improved compared to feedback based only on the actual acceleration or the like.

[0008] It is preferable that the dynamic load ratio distribution curve (L1) and the rear-wheel-biased distribution curve (L2) are curves in which the higher the standard driving acceleration (XG), the higher the rear-wheel drive distribution, except for the transition curves (L3, L4) between them.

[0009] According to this configuration, in the dynamic load ratio distribution curve, the ratio of the driving force to the dynamic load applied to the front and rear wheels considering the pitching moment caused by the longitudinal acceleration becomes small, so the margin with respect to the traction limit of the tire increases. Also, in the rear-wheel-biased distribution curve, even under the condition of a high rear-wheel drive distribution, the margin with respect to the traction limit of the tire becomes relatively large.

[0010] The driving force control device (1) preferably performs the rear-wheel-biased distribution control when the reference driving acceleration (XG) is less than or equal to the first input amount (XG1). This first input amount (XG1) is preferably the reference driving acceleration (XG) that gives the limit acceleration at which the driving wheels do not slip on a road surface in a predetermined state (dry, wet, snow). Also, the driving force control device (1) preferably performs the rear-wheel-biased distribution control when the reference driving acceleration (XG) is greater than or equal to the second input amount (XG2). This second input amount (XG2) is preferably the reference driving acceleration (XG) that gives the limit deceleration at which the driving wheels do not slip on a road surface in a predetermined state (dry, wet, snow).

[0011] According to this configuration, when the vehicle is not accelerating or decelerating rapidly and is within the traction limit on a road surface in a predetermined state, the handling performance can be improved by performing the rear-wheel-biased distribution control.

[0012] The driving force control device (1) is preferably configured to be able to change the value of the first input amount (XG1) by a mode switching operation of the driver. Also, it is preferable that the value of the second input amount (XG2) can be changed by a mode switching operation of the driver.

[0013] According to this configuration, a Sport mode is prepared in which the acceleration / deceleration range for performing the rear-wheel-biased distribution control is expanded assuming only dry and wet road surfaces, and a Normal mode is prepared in which the acceleration / deceleration range for performing the rear-wheel-biased distribution control is narrowed assuming dry, wet, and snow road surfaces. When it is known that the road surface is not slippery, a wide area with high handling performance can be ensured in the Sport mode, while when it is known that the road surface is slippery, stability can be ensured in the Normal mode.

[0014] When the normalized lateral acceleration (YG) calculated from the steering amount of the steering device of the vehicle and the vehicle speed is equal to or greater than a third input amount (YG3), it is preferable that the drive force control device (1) does not perform the rear-wheel-biased distribution control. The third input amount (YG3) is preferably the limit normalized lateral acceleration (YG) at which the drive wheels do not slip on a road surface in a predetermined state.

[0015] According to this configuration, in a state where there is lateral acceleration due to sudden steering, the running stability can be ensured by not performing the rear-wheel-biased distribution control. In addition, since the control is based on the normalized lateral acceleration (YG) (the target value of acceleration) calculated from the driver's instruction amount, which is the steering angle of the steering device, the responsiveness is improved compared to feedback based only on the actual acceleration or the like.

[0016] When the vehicle speed (V) of the vehicle is lower than a first predetermined speed (V1), it is preferable that the drive force control device (1) does not perform the rear-wheel-biased distribution control. Also, when the vehicle speed (V) is higher than a second predetermined speed (V2), it is preferable that the drive force control device (1) does not perform the rear-wheel-biased distribution control.

[0017] According to this configuration, at low speeds immediately after vehicle start and immediately after stopping when traction is required, and during high-speed driving when running stability is required, regardless of the acceleration and deceleration in the front, rear, left, and right directions, the rear-wheel-biased distribution control is not performed, so traction and running stability in these cases can be ensured.

[0018] It is preferable that the drive source of the front wheels of the vehicle to which the drive force control device (1) is applied is a drive source including an electric motor, it is preferable that the drive source of the rear wheels of the vehicle is a drive source including an electric motor, and it is preferable that the drive sources of the front and rear wheels of the vehicle are drive sources including an electric motor.

[0019] The driving force control device (1) preferably has a map that records the vehicle speed (V), the standard lateral acceleration (YG) calculated from the steering amount of the steering device, the standard driving acceleration (XG) calculated from the input amount from the driving force instruction device, and the front-rear wheel drive distribution (Rr), and determines the front-rear wheel drive distribution (Rr) based on the map.

[0020] According to this configuration, it is possible to determine the rear-wheel drive distribution faster than calculating it by arithmetic operation, and the control speed of the driving force of the front and rear wheels can be increased.

[0021] The driving force instruction device (42, 44) is at least one of an accelerator pedal (accelerator operator) and a brake pedal (brake operator), and the input amount from the driving force instruction device is preferably at least one of the depression amount (operation amount) of the accelerator pedal and the depression amount (operation amount) of the brake pedal.

[0022] According to these configurations, the standard driving acceleration (acceleration target value) is calculated from the driver's instruction amounts such as the accelerator operation amount and the brake operation amount, and control is performed based on this. Therefore, the responsiveness is improved compared to feedback based only on the actual acceleration or the like.

Effect of the Invention

[0023] According to the driving force control device according to the present invention, based on the standard driving acceleration (acceleration target value), traction best control for determining the rear-wheel drive distribution according to the optimal traction curve and rear-wheel-biased distribution control for determining the rear-wheel drive distribution according to the rear-wheel-biased distribution curve are switched. Therefore, when traction is required such as during high acceleration and deceleration, the traction performance during running can be maintained, and when there is a margin in traction such as during low acceleration and deceleration, excellent handling performance can also be obtained.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing an example of the configuration of a vehicle 100 including a driving force control device 1 according to an embodiment of the present invention. The vehicle 100 shown in FIG. 1 is a four-wheel drive electric vehicle, and includes a main body 10, left and right front wheels 21a, 21b (hereinafter, also simply referred to as "front wheels 21"), left and right rear wheels 22a, 22b (hereinafter, also simply referred to as "rear wheels 22"), a front-wheel drive motor 31, a rear-wheel drive motor 32, a front-wheel differential mechanism 33, and a rear-wheel differential mechanism 34. The left and right front wheels 21a, 21b are driven by the front-wheel drive motor 31 via the front-wheel differential mechanism 33, and the left and right rear wheels 22a, 22b are driven by the rear-wheel drive motor 32 via the rear-wheel differential mechanism 34.

[0026] The vehicle 100 further includes, as operating devices, a steering wheel (steering device) 40, a steering angle sensor 41 that detects the amount of steering, an accelerator pedal (accelerator operating element) 42, an accelerator depression amount sensor 43 that detects the depression amount (operating amount) thereof, a brake pedal (brake operating element) 44, a brake depression amount sensor 45 that detects the depression amount (operating amount) thereof, and further a vehicle speed sensor 46.

[0027] The vehicle 100 further includes, as a drive system, a battery 60, a front-wheel drive circuit 61, and a rear-wheel drive circuit 62, and includes, as a control system, an electronic control unit (ECU) 50. This electronic control unit 50 is a unit including a CPU (not shown) for operation control, a memory (not shown) for storing an operation program, a memory (not shown) for storing data, etc., and is configured as, for example, a microcomputer. The electronic control unit 50 is configured to control the front-wheel drive circuit 61 and the rear-wheel drive circuit 62, and control the electric power supplied from the battery 60 to the front-wheel drive motor 31 and the rear-wheel drive motor 32 to control these driving forces.

[0028] The driving force control device 1 of the present embodiment is a device that determines the front and rear wheel drive distribution. In the present embodiment, it is configured by a program that operates a CPU (not shown) in this electronic control unit 50. The driving force control device 1 includes a driving acceleration calculation unit 2, a lateral acceleration calculation unit 3, maps 4a and 4b, a drive distribution determination unit 5, and an output unit 6.

[0029] The driving acceleration calculation unit 2 calculates a positive or negative standard driving acceleration XG (target value of acceleration) obtained from the depression amount of the accelerator pedal 42 detected by the accelerator depression amount sensor 43 and the current vehicle speed V detected by the vehicle speed sensor 46, and inputs it to the drive distribution determination unit 5. This is because the driving acceleration of an actual vehicle is considered to be determined by the difference between the driving force determined by the depression amount of the accelerator pedal 42 and the air resistance and regeneration resistance determined by the current vehicle speed V. The driving acceleration calculation unit 2 further calculates a negative standardized driving acceleration XG (the target value of acceleration) obtained from the depression amount of the brake pedal 44 detected by the brake depression amount sensor 45 and the current vehicle speed V detected by the vehicle speed sensor 46, and inputs it to the drive distribution determination unit 5. This is because the driving acceleration of the actual vehicle is considered to be determined by the sum of the braking force determined by the depression amount of the brake pedal 44 and the air resistance and regeneration resistance determined by the current vehicle speed V.

[0030] The lateral acceleration calculation unit 3 calculates a positive or negative standardized lateral acceleration YG (the target value of acceleration) obtained from the steering angle of the steering wheel (steering device) 40 detected by the steering angle sensor 41 and the current vehicle speed V detected by the vehicle speed sensor 46, and inputs it to the drive distribution determination unit 5. Since it is controlled based on the driver's instruction amounts such as the accelerator depression amount and the brake operation amount, the responsiveness is improved compared to the feedback control based only on the actual acceleration and the like.

[0031] The maps 4a and 4b are data in which the vehicle speed V, the standardized lateral acceleration YG, the standardized driving acceleration XG, and the optimal rear-wheel drive distribution (rear-wheel distribution ratio Rr) are recorded in advance, and are stored in a memory (not shown) that stores the data of the electronic control unit (ECU) 50 so that the drive distribution determination unit 5 can refer to them. Details will be described later.

[0032] The drive distribution determination unit 5 is a program that determines the front and rear wheel drive distribution based on the standardized driving acceleration XG input from the driving acceleration calculation unit 2, the standardized lateral acceleration YG input from the lateral acceleration calculation unit 3, and the vehicle speed V input from the vehicle speed sensor 46. The detailed operation will be described later.

[0033] The output unit 6 is a program that controls the front-wheel drive circuit 61 and the rear-wheel drive circuit 62 according to the front and rear wheel drive distribution determined by the drive distribution determination unit 5, and controls the electric power supplied from the battery 60 to the front-wheel drive motor 31 and the rear-wheel drive motor 32 to control these driving forces.

[0034] Next, the control of the front and rear wheel drive distribution by the driving force control device 1 configured as described above will be described according to the situation. (1) Dynamic load ratio distribution control during straight running in Normal mode (traction best control) FIG. 2 is a diagram showing a control curve of the front and rear wheel driving force distribution (represented by the rear wheel distribution ratio Rr) with respect to the standard driving acceleration XG in the Normal mode. The driving distribution determination unit 5 basically performs a dynamic load ratio distribution control for determining the front and rear wheel driving distribution according to the dynamic load ratio distribution curve L1 shown in FIG. 2.

[0035] The dynamic load ratio distribution curve L1 is a curve of the dynamic load ratio (horizontal axis) applied to the front wheel 21 and the rear wheel 22 with respect to the standard driving acceleration XG (vertical axis). This dynamic load ratio is the ratio of the loads Wf and Wr applied to the front wheel 21 and the rear wheel 22 shown in FIG. 3 during vehicle running, and is the load ratio obtained by adding the load change ΔWx applied to the front wheel 21 and the rear wheel 22 by the pitching moment in the longitudinal direction acceleration ax shown in FIG. 4(a) to the loads Wf and Wr when the vehicle is stationary. Therefore, the dynamic load ratio distribution curve L1 shown in FIG. 2 coincides with the static load ratio when the standard driving acceleration XG is zero, and as the standard driving acceleration XG increases (upward), the load change ΔWx (see FIG. 4(a)) increases, so the rear wheel distribution ratio Rr increases (shifts to the right).

[0036] In the dynamic load ratio distribution control for determining the front and rear wheel driving distribution according to this dynamic load ratio distribution curve L1, the ratios of the driving forces to the dynamic loads on the front wheel 21 and the rear wheel 22 (Ff / Wf and Fr / Wr in FIG. 3) are the same, and neither of them will protrude and become large. Therefore, the margin until the ratios of the driving forces to the dynamic loads (Ff / Wf and Fr / Wr) reach the traction limit of the friction coefficient μ between the road surface and the tire becomes large. For this reason, in the dynamic load ratio distribution control, good traction performance can be ensured even in various road surface conditions and acceleration / deceleration conditions.

[0037] FIG. 5 is a conceptual diagram showing the traction limits in each road surface condition. The vertical axis represents the driving acceleration, and the horizontal axis represents the front-rear wheel drive distribution (rear wheel distribution ratio Rr). The friction coefficient μ between the tire and the road surface is said to be approximately 1.0 on a dry road surface (DRY), approximately 0.6 on a wet road surface (WET), and approximately 0.3 on a snow-covered road surface (SNOW). When the front-rear wheel drive distribution ratio (Rr) (horizontal axis) is made the same as the static load ratio or the dynamic load ratio, the ratio of the driving force to the load on each of the front wheel 21 and the rear wheel 22 (Ff / Wf and Fr / Wr in FIG. 3) is equal to the ratio of the driving force to the weight of the entire vehicle (the same as the ratio of the driving acceleration to the gravitational acceleration on the vertical axis). Therefore, the ratio of the driving acceleration to the gravitational acceleration (vertical axis) can be increased to the friction coefficient μ of each road surface condition. On the other hand, when the front-rear wheel drive distribution (horizontal axis) is shifted from the static load ratio, the ratios of the driving force to the loads on the front wheel 21 and the rear wheel 22 (Ff / Wf and Fr / Wr in FIG. 3) are different, and one of them becomes larger than the ratio of the driving acceleration to the gravitational acceleration (vertical axis). Therefore, the ratio of the driving acceleration to the gravitational acceleration (vertical axis) cannot be increased to the friction coefficient μ. Thus, in FIG. 5, the traction limit lines Ld, Lw, Ls for each road surface condition peak (at the friction coefficient μ) at approximately the center (static load ratio) and decrease as going to the left and right. (Note that FIG. 5 does not consider the load change ΔWx shown in FIG. 4(a). Considering this, each traction limit line Ld, Lw, Ls is deformed so as to shift to the right as going upward.) Since the dynamic load ratio distribution curve L1 of the dynamic load ratio distribution control passes through the peaks of each traction limit line Ld, Lw, Ls, good traction performance can be obtained in a wide acceleration range.

[0038] Note that FIG. 5 shows only the range of positive acceleration and does not show the range of negative acceleration (deceleration). However, it is considered that in the range of negative acceleration (deceleration) as well, the traction limit line (not shown in the figure), which is the vertical mirror image of the curve in the range of positive acceleration, is obtained. Therefore, since the dynamic load ratio distribution curve L1 of the dynamic load ratio distribution control passes through the peaks of each traction limit line (not shown in the figure) even in the range of negative acceleration (deceleration), good traction performance can be obtained in a wide acceleration range. However, during deceleration, it is generally prone to slipping. Therefore, a safety factor is applied in the design to reduce the absolute value of the acceleration of each traction limit line (not shown).

[0039] (2) Rear-wheel-biased distribution control during straight running in Normal mode (handling best control) In Normal mode, when the reference driving acceleration XG is small, specifically, within the range of the reference driving acceleration XG inside the traction limit line Ls of "SNOW" (see Fig. 5) where no slipping occurs even on a snowy road, instead of the dynamic load ratio distribution control, a rear-wheel-biased distribution control (handling best control) is implemented to determine the front and rear wheel drive distribution according to the rear-wheel-biased distribution curve L2 shown in Fig. 2. The upper limit reference driving acceleration XG (positive value) of the range where the rear-wheel-biased distribution control is implemented is called the first input quantity XG1, and the lower limit reference driving acceleration XG (negative value) is called the second input quantity XG2.

[0040] As shown in Fig. 2, the rear-wheel-biased distribution curve L2 is a curve obtained by shifting the dynamic load ratio distribution curve L1 in the direction of higher rear-wheel distribution ratio Rr (right side). In this dynamic load ratio distribution curve L2, the front and rear wheel drive distribution when the reference driving acceleration XG is zero is set to a distribution with a higher rear-wheel distribution ratio Rr than the static load ratio, which is a distribution that does not require fine adjustment of the accelerator and steering during cornering. The rear-wheel-biased distribution curve L2 also takes into account the load change ΔWx due to acceleration in Fig. 4(a), and the larger the reference driving acceleration XG (upward), the larger the rear-wheel distribution ratio Rr (rightward). With this configuration, even under conditions with a high rear-wheel drive distribution, the margin with respect to the traction limit of the tire becomes relatively large. Thus, when not performing sudden acceleration or deceleration and within the traction limit in any road surface condition, the handling performance can be improved by implementing the rear-wheel-biased distribution control.

[0041] The switching between the dynamic load ratio distribution control and the rear-wheel-biased distribution control is performed along the transition curve L3 along the lower side of the upper traction limit line Ls of "SNOW" (see Fig. 5) or the transition curve L4 along the upper side of the lower traction limit line (not shown) of "SNOW". With this configuration, the front-rear wheel drive distribution can smoothly switch between the dynamic load ratio distribution control and the rear-wheel-biased distribution control without exceeding the traction limit of "SNOW".

[0042] (3) Front-rear wheel drive distribution control during turning in Normal mode Even during turning, the drive distribution determination unit 5 performs the dynamic load ratio distribution control and the rear-wheel-biased distribution control in the same manner as during straight travel. However, during turning, considering the rolling moment generated by the lateral acceleration ay during vehicle turning shown in Fig. 4(b), instead of the dynamic load ratio distribution curve L1 and the rear-wheel-biased distribution curve L2 during straight travel shown in Fig. 2, the dynamic load ratio distribution and the rear-wheel-biased distribution control are performed according to the dynamic load ratio distribution curve L1a and the rear-wheel-biased distribution curve L2a, which are slightly shifted in the direction of increasing the rear-wheel distribution ratio Rr (right direction).

[0043] The reason is that, for example, when the vehicle turns to the right, as shown in Fig. 4(b), due to the rolling moment generated by the lateral acceleration ay during vehicle turning, a negative load change ΔWy is applied to the inner wheels (right front wheel 21b and right rear wheel 22b), so the load applied to the inner wheels (right front wheel 21b and right rear wheel 22b) decreases. In particular, when the vehicle is accelerating, as shown in Fig. 4(a), a negative load change ΔWx is also applied to the front wheels 21 (left front wheel 21a and right front wheel 21b shown in Fig. 1) due to the pitching moment, so the load on the right front wheel 21b decreases the most and is likely to slip. Also, when the vehicle turns to the left, especially when the vehicle is accelerating, for the same reason, the load on the left front wheel 21a decreases the most and is likely to slip. Therefore, from the perspective of slip prevention, in order to further reduce the drive force distribution to the right front wheel 21b and the left front wheel 21a, the dynamic load ratio distribution curve L1a and the rear-wheel-biased distribution curve L2a for turning increase the rear-wheel drive distribution compared to the dynamic load ratio distribution curve L1 and the rear-wheel-biased distribution curve L2a during straight travel.

[0044] (4) Front and Rear Wheel Drive Distribution Control in Sport Mode In Sport mode, when the standard driving acceleration XG is inside the "WET" traction limit line Lw (see Fig. 5) where no slip occurs even on a wet road surface, rear-wheel-biased distribution control (handling best control) is implemented. When it is outside, dynamic load ratio distribution control (traction best control) is implemented. Fig. 6 is a diagram showing the control curve of the front and rear wheel driving force distribution with respect to the standard driving acceleration XG in Sport mode. Also in Sport mode, similar to Normal mode, during straight driving, the dynamic load ratio distribution is performed according to the dynamic load ratio distribution curve L1, and the rear-wheel-biased distribution control is performed according to the rear-wheel-biased distribution curve L2. During turning, the dynamic load ratio distribution is performed according to the dynamic load ratio distribution curve L1a, and the rear-wheel-biased distribution control is performed according to the rear-wheel-biased distribution curve L2a. However, different from Normal mode, the first input force XG1 which is the upper limit of the standard driving acceleration XG (positive value) of the range where the rear-wheel-biased distribution control is implemented, and the second input force XG2 which is the lower limit of the standard driving acceleration XG (negative value) are set near the "WET" traction limit line Lw shown in Fig. 5. Thereby, the rear-wheel-biased distribution control (handling best control) is implemented in an acceleration range wider than that in Normal mode.

[0045] The switching between this Normal mode and Sport mode can be performed by the driver's mode switching operation. As described above, in Normal mode and Sport mode, the first input force XG1 which is the upper limit of the standard driving acceleration XG range where the rear-wheel-biased distribution control is implemented, and the second input force XG2 which is the lower limit are different respectively, and these values can be changed by the driver's mode switching operation.

[0046] According to this configuration, there is a Sport mode in which the acceleration and deceleration range for performing rear-wheel-biased distribution control is expanded assuming only dry and wet road surfaces, and a Normal mode in which the acceleration and deceleration range for performing rear-wheel-biased distribution control is narrowed assuming dry and wet road surfaces as well as snow road surfaces. When it is known that the road surface is not slippery, a wide area with high handling performance is ensured in the Sport mode, while when it is known that the road surface is slippery, stability can be ensured in the Normal mode.

[0047] (5) Front and rear wheel drive distribution control during sudden steering Even when the reference drive acceleration XG is small, the drive distribution determination unit 5 is configured not to perform rear-wheel-biased distribution control when the reference lateral acceleration YG calculated from the steering amount of the steering wheel (steering device) 40 and the vehicle speed V and input from the lateral acceleration calculation unit 3 is equal to or greater than the third input amount YG3. Here, the third input amount YG3 is the reference lateral acceleration YG at the limit where the drive wheels do not slip with the road surface in a predetermined state. This "reference lateral acceleration YG at the limit where the drive wheels do not slip with the road surface in a predetermined state" is, for example, the reference lateral acceleration YG that does not exceed the traction limit in the predetermined road surface state shown in FIG. 5.

[0048] FIG. 7 shows a map 4a of the front and rear wheel drive force distribution with respect to the reference lateral acceleration YG and the reference drive acceleration XG. The map 4a is data arranged in a matrix, and the horizontal position corresponds to the reference lateral acceleration YG and the vertical position corresponds to the reference drive acceleration XG, respectively. In each cell, the front and rear wheel drive distribution corresponding to its horizontal position (YG) and vertical position (XG) is stored as a discrete value. As shown in FIG. 7, in the region where the reference lateral acceleration YG on the left side of the third input amount YG3 is not high, as described above, rear-wheel-biased distribution control (handling best control) is performed in the range where the reference drive acceleration XG is small (between the first input amount XG1 and the second input amount XG2). On the other hand, in the region where the reference lateral acceleration YG on the right side of the third input amount YG3 is high, rear-wheel-biased distribution control is not performed regardless of the reference drive acceleration XG.

[0049] According to this configuration, in a state where there is lateral acceleration due to a sudden steering operation, by not performing rear-wheel-biased distribution control, driving stability can be ensured. Further, since control is performed based on the steering angle of the steering wheel 40, which is the instruction amount of the driver, the responsiveness is improved compared to feedback based only on the actual acceleration or the like.

[0050] (6) Front and rear wheel drive distribution control at low speed and high speed Even if the reference drive acceleration XG is small, the drive distribution determination unit 5 is configured not to perform rear-wheel-biased distribution control when the vehicle speed V detected by the vehicle speed sensor 46 shown in FIG. 1 is lower than a first predetermined speed V1, which is the speed immediately after vehicle start and immediately before stop. Further, the drive distribution determination unit 5 is also configured not to perform rear-wheel-biased distribution control when the vehicle speed V is higher than a second predetermined speed V2, which is the speed during high-speed driving.

[0051] FIG. 8 shows a map 4b of the front and rear wheel drive force distribution with respect to the vehicle speed V and the reference drive acceleration XG. This map 4b is also data arranged in a matrix, and its horizontal position corresponds to the vehicle speed V and its vertical position corresponds to the reference drive acceleration XG, respectively. In each cell, the front and rear wheel drive distribution corresponding to its horizontal position (vehicle speed V) and vertical position (reference drive acceleration XG) is stored as a discrete value. As shown in FIG. 8, in the low to medium speed range where the vehicle speed V is between the first predetermined speed V1 and the second predetermined speed V2, as described above, in the range where the reference drive acceleration XG is small (between the first input amount XG1 and the second input amount XG2), rear-wheel-biased distribution control (handling best control) is performed. On the other hand, in the low speed range to the left of the first predetermined speed V1 and the high speed range to the right of the second predetermined speed V2, rear-wheel-biased distribution control is not performed.

[0052] According to this configuration, during low-speed operation immediately after vehicle start and immediately before stopping when traction is required, and during high-speed driving when driving stability is required, regardless of the acceleration and deceleration in the front, rear, left, and right directions, the rear-wheel-biased distribution control (handling best control) is not performed, and the dynamic load ratio control (traction best control) is performed. Therefore, traction and driving stability in these cases can be ensured.

[0053] Also, by preparing such maps 4a and 4b, when the drive distribution determination unit 5 designates the vehicle speed V and the reference drive acceleration XG, the corresponding front and rear wheel drive distributions can be obtained immediately. For this reason, the drive distribution to the rear wheels can be determined faster than by calculation, and the control speed of the driving force of the front and rear wheels can be increased.

[0054] As described above, embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the claims and the technical idea described in the specification and drawings. For example, in the above embodiment, an application example to a vehicle 100 having a front and rear twin motor configuration including a front wheel drive motor 31 and a rear wheel drive motor 32 of the driving force control device 1 has been described. However, the present invention is not limited thereto, and it is also applicable to a vehicle having a four-motor configuration having a drive motor for each of the four wheels, a single-motor configuration in which the driving force of one drive motor is distributed to the four wheels, and further to a vehicle having a configuration in which each of these motors is replaced with a gasoline engine.

Explanation of Reference Numerals

[0055] 1 Driving force control device 2 Drive acceleration calculation unit 3 Lateral acceleration calculation unit 4a, 4b Maps 5 Drive distribution determination unit 6 Output unit 10 Body 100 Vehicle 21 Front wheels 21a Left front wheel (front wheel) 21b Right front wheel (front wheel) 22 Rear wheels 22a Left rear wheel (rear wheel) 22b Right rear wheel (rear wheel) 31 Front wheel drive motor 32 Rear wheel drive motor 33 Front wheel differential mechanism 34 Rear wheel differential mechanism 40 Steering wheel (steering device) 41 Steering angle sensor 42 Accelerator pedal 43 Accelerator depression amount sensor 44 Brake pedal 45 Brake depression amount sensor 46 Vehicle speed sensor 50 Electronic control unit (ECU) 60 Battery 61 Front wheel drive circuit 62 Rear wheel drive circuit ax Longitudinal acceleration ay Lateral acceleration L1, L1a Dynamic load ratio distribution curve L2, L2a Rearward bias distribution curve L3 Transition curve L4 Transition curve Ls, Lw, Ld Traction limit line Rr Rear wheel distribution ratio (front - rear wheel drive distribution) V Vehicle speed V1 First predetermined speed V2 Second predetermined speed Wf, Wr Load ΔWx, ΔWy Load change XG Nominal driving acceleration XG1 First input force amount XG2 Second input force amount YG Nominal lateral acceleration YG3 Third input force amount

Claims

1. A driving force control device for determining the front-rear wheel drive distribution, which is the ratio of the driving forces of the front wheels and the rear wheels in a four-wheel drive vehicle, comprising: calculating a positive or negative standard driving acceleration obtained from the input amount from the driving force indicating device of the vehicle and the vehicle speed, and based on the standard driving acceleration, dynamic load ratio distribution control for determining the front-rear wheel drive distribution according to a dynamic load ratio distribution curve, which is a curve of the dynamic load ratio applied to the front and rear wheels with respect to the standard driving acceleration, and rear-wheel-biased distribution control for determining the front-rear wheel drive distribution according to a rear-wheel-biased distribution curve obtained by increasing the rear-wheel drive distribution from the dynamic load ratio distribution curve, and switching and implementing the above. A driving force control device.

2. The driving force control device according to claim 1, wherein the dynamic load ratio distribution curve and the rear-wheel-biased distribution curve are each a curve in which the rear-wheel drive distribution increases as the standard driving acceleration is higher, excluding the transition curve between them.

3. The driving force control device according to claim 1, wherein the rear-wheel-biased distribution control is implemented when the standard driving acceleration is less than or equal to a first input amount.

4. The driving force control device according to claim 3, wherein the first input amount is a standard driving acceleration that gives a limit acceleration such that the driving wheels do not slip with a road surface in a predetermined state.

5. The driving force control device according to claim 1, wherein the rear-wheel-biased distribution control is implemented when the standard driving acceleration is greater than or equal to a second input amount.

6. The driving force control device according to claim 5, wherein the second input amount is a standard driving acceleration that gives a limit deceleration such that the driving wheels do not slip with a road surface in a predetermined state.

7. The driving force control device according to claim 3, wherein the value of the first input amount can be changed by a mode switching operation of the driver.

8. The driving force control device according to claim 5, wherein the value of the second input amount can be changed by a mode switching operation of the driver.

9. The driving force control device according to claim 1, wherein when the standard lateral acceleration calculated from the steering amount of the steering device of the vehicle and the vehicle speed is greater than or equal to a third input amount, the rear-wheel-biased distribution control is not implemented.

10. The driving force control device according to claim 9, wherein the third input amount is a standard lateral acceleration that gives a limit such that the driving wheels do not slip with a road surface in a predetermined state.

11. The driving force control device according to any one of claims 1 to 10, wherein when the vehicle speed of the vehicle is lower than a first predetermined speed, the rear-wheel-biased distribution control is not implemented.

12. The driving force control device according to any one of claims 1 to 10, wherein when the vehicle speed of the vehicle is higher than a second predetermined speed, the rear-wheel-biased distribution control is not performed.

13. The driving force control device according to any one of claims 1 to 10, wherein a drive source of the front wheels of the vehicle is a drive source including an electric motor.

14. The driving force control device according to any one of claims 1 to 10, wherein a drive source of the rear wheels of the vehicle is a drive source including an electric motor.

15. The driving force control device according to any one of claims 1 to 10, wherein drive sources of the front wheels and the rear wheels of the vehicle are drive sources including an electric motor.

16. The driving force control device according to any one of claims 1 to 10, having a map recording a vehicle speed, a standard lateral acceleration calculated from a steering amount of a steering device, a standard driving acceleration calculated from an input amount from a driving force indicating device, and a front-rear wheel drive distribution, and determining the front-rear wheel drive distribution based on the map.

17. The driving force control device according to any one of claims 1 to 10, wherein the driving force indicating device is at least one of an accelerator operator and a brake operator, and the input amount from the driving force indicating device is at least one of an operation amount of the accelerator operator and an operation amount of the brake operator.

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