Driving force control device for four-wheel drive vehicle

Abstract

The invention provides a driving force control device capable of obtaining excellent operation performance while maintaining excellent traction performance. A driving force control device determines a front and rear wheel drive distribution, which is the ratio of the driving force of the front wheels to the driving force of the rear wheels in a four-wheel drive vehicle, and calculates an obtained positive or negative standard driving acceleration on the basis of the input quantity from a driving force instruction device of the vehicle and the vehicle speed. On the basis of the standard drive acceleration, dynamic load ratio distribution control in which the front and rear wheel drive distribution is determined in accordance with a dynamic load ratio distribution curve, which is a curve of a dynamic load ratio applied to the front and rear wheels with respect to the standard drive acceleration, and rear wheel distribution control in which the front and rear wheel drive distribution is determined in accordance with a dynamic load ratio distribution curve, which is a curve of a dynamic load ratio applied to the front and rear wheels with respect to the standard drive acceleration, are switched. In the rear wheel distribution control, the front and rear wheel drive distribution is determined in accordance with a rear wheel distribution curve that increases the rear wheel drive distribution than the dynamic load ratio distribution curve.

Description

Technical Field

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

[0002] Conventionally, there has been known a driving force control device that, in a four-wheel drive vehicle, monitors the longitudinal acceleration by means of an in-vehicle accelerometer, calculates the dynamic loads applied to the front and rear wheels taking into account the pitching moment due to the longitudinal acceleration, and performs front-rear driving force distribution (front-rear dynamic load distribution control) such that the ratio of the driving force of each of the front and rear wheels to the dynamic load does not exceed the traction limit of the tire (Patent Document 1).

[0003] There has also been known a driving force control device that further monitors the lateral acceleration during turning, calculates the dynamic loads applied to the respective left and right wheels taking into account the rolling moment generated by the lateral acceleration, and performs front-rear driving force distribution (inner wheel dynamic load ratio distribution control) such that the ratio of the driving force to the dynamic load of the one with the larger ratio (the inner side during turning) does not exceed the traction limit of the tire (Patent Document 2).

[0004] In addition, there has also been known a technique of calculating the yaw rate based on the value of a G sensor and performing feedback control on the front-rear driving force distribution ratio, but there is also a drawback that the control responsiveness of the feedback control based on the yaw rate is slow.

[0005] [Prior Art Documents]

[0006] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-187984

[0008] [Patent Document 2] Japanese Patent No. 7310703 Summary of the Invention

[0009] [Problems to be Solved by the Invention]

[0010] The front-rear wheel driving force distribution with the best traction, that is, the front-rear wheel driving force distribution with good passability on a low-μ road such as snow, is approximately half for the front and rear wheels. As the driving force distribution is shifted front and rear, the traction performance on a low-μ road deteriorates.

[0011] On the other hand, from the perspective of maneuverability, a front engine front drive (FF) vehicle (front wheel drive distribution 100%) tends to understeer (US), while a front engine rear drive (FR) vehicle (rear wheel drive distribution 100%) tends to oversteer (OS). When the front and rear wheel drive force distribution for optimal traction is approximately halfway between the front and rear wheels, the steering characteristic is between US and OS, but the linearity of the turning radius with respect to acceleration (steering characteristic) is not constant, so it is necessary to perform micro-correction operations of the accelerator and steering when turning. The steering characteristic is constant in the area where the rear wheel drive distribution is slightly higher (optimal operation area), and if the vehicle is driven in this area, it is not necessary to perform micro-correction operations of the accelerator and steering when turning.

[0012] As described above, since the front and rear wheel drive distribution for optimal traction is different from the front and rear wheel drive distribution for optimal maneuverability, the conventional driving force control device has a problem that it is not always possible to achieve both excellent traction performance and excellent maneuverability.

[0013] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a driving force control device that can achieve excellent drivability while maintaining excellent traction performance.

[0014] [Technical means to solve the problem]

[0015] In order to solve the above-mentioned problem, a driving force control device 1 of the present invention determines the ratio of driving force between the front wheels 21 and the rear wheels 22 in a four-wheel drive vehicle, i.e., the front-rear wheel drive distribution. The driving force control device 1 is characterized in that, based on the input amount from the driving force indicating device 42 of the vehicle and the vehicle speed, a positive or negative standard driving acceleration XG is calculated, and based on the standard driving acceleration XG, a dynamic load ratio distribution control and a rear wheel distribution control are switched and implemented. In the dynamic load ratio distribution control, the front-rear wheel drive distribution is determined according to a curve of the dynamic load ratio applied to the front wheels and the rear wheels relative to the standard driving acceleration XG, i.e., a dynamic load ratio distribution curve L1. In the rear wheel distribution control, the front-rear wheel drive distribution is determined according to a rear wheel distribution curve L2 that improves the rear wheel drive distribution more than the dynamic load ratio distribution curve.

[0016] According to the above structure, based on the dynamic load ratio distribution control with good traction performance, at the same time, when the vehicle accelerates and decelerates slowly, the driving stability starts to improve. Therefore, it can be switched to the rear-wheel-biased distribution control with good operability, which can stabilize characteristics such as oversteering and understeering. In addition, the specified driving acceleration XG (acceleration target value) is calculated according to the indication amount of the driving force indicating device (accelerator, brake, etc.), and control is carried out based on this. Therefore, compared with the feedback only based on the actual acceleration, etc., the responsiveness is improved.

[0017] Preferably, in addition to the transition curves L3 and L4 between each other, the dynamic load ratio distribution curve L1 and the rear-wheel-biased distribution curve L2 are respectively curves in which the higher the specified driving acceleration XG is, the higher the rear-wheel drive distribution is.

[0018] According to the above structure, in the dynamic load ratio distribution curve, considering the application of the pitching moment caused by the longitudinal acceleration to the front and rear wheels and the decrease in the ratio of the driving force of the front and rear wheels to the dynamic load, the margin with respect to the traction limit of the tire becomes larger. In addition, in the distribution curve closer to the rear wheels, even under the condition of high rear-wheel drive distribution, the margin with respect to the traction limit of the tire is relatively large.

[0019] The driving force control device 1 preferably implements the rear-wheel-biased distribution control when the specified driving acceleration XG is equal to or less than the first input amount XG1. The first input amount XG1 is preferably the specified driving acceleration XG that gives the following acceleration, which is the limit at which the driving wheels do not cause slipping on the road surface (dry, wet, snow) in a specified state.

[0020] In addition, the driving force control device 1 preferably implements the rear-wheel-biased distribution control when the specified driving acceleration XG is equal to or greater than the second input amount XG2. The second input amount XG2 is preferably the specified driving acceleration XG that gives the following deceleration, which is the limit at which the driving wheels do not cause slipping on the road surface (dry, wet, snow) in a specified state.

[0021] According to the above structure, when not accelerating or decelerating rapidly and within the traction limit on the road surface in a specified state, the operability can be improved by implementing the rear-wheel-biased distribution control.

[0022] The driving force control device 1 is preferably configured to be able to change the value of the first input amount XG1 through the mode switching operation of the driver. In addition, it is preferably able to change the value of the second input amount XG2 through the mode switching operation of the driver.

[0023] According to the above structure, a Sport mode and a Normal mode are prepared. When it is known that the road surface is not slippery, a wide area with high operating performance is ensured in the Sport mode. On the other hand, when it is known that the road surface is slippery, stability can be ensured in the Normal mode. In the Sport mode, the acceleration and deceleration range for rear-wheel distribution control is expanded by assuming only dry and wet road surfaces. In the Normal mode, the acceleration and deceleration range for rear-wheel distribution control is reduced by assuming dry, wet, and snow road surfaces in addition to the above.

[0024] The driving force control device 1 preferably does not perform the rear-wheel distribution control when the standard lateral acceleration YG calculated based on the steering amount of the vehicle's steering device and the vehicle speed is equal to or higher than a third input amount YG3. The third input amount YG3 is preferably the standard lateral acceleration YG at the limit where the driving wheels do not slip on the road surface in a specified state.

[0025] According to the above structure, in a state with lateral acceleration caused by sudden operation, driving stability can be ensured by not performing rear-wheel distribution control. In addition, control is performed based on the standard lateral acceleration YG (acceleration target value) calculated based on the steering angle of the steering device, which is an indication amount of the driver. Therefore, the responsiveness is improved compared to feedback based only on the actual acceleration, etc.

[0026] The driving force control device 1 preferably does not perform the rear-wheel distribution control when the vehicle speed V of the vehicle is lower than a first specified speed V1, and also preferably does not perform the rear-wheel distribution control when the vehicle speed V is higher than a second specified speed V2.

[0027] According to the above structure, during low speeds just after starting a vehicle that needs to be towed or just before stopping, or during high-speed driving that requires driving stability, regardless of the acceleration and deceleration in the front, rear, left, and right directions, the rear-wheel distribution control is not performed. Therefore, towing or driving stability in these situations can be ensured.

[0028] The drive source of the front wheels of the vehicle to which the driving force control device 1 is applied preferably includes a drive source with an electric motor. The drive source of the rear wheels of the vehicle preferably includes a drive source with an electric motor. The drive sources of the front and rear wheels of the vehicle preferably include a drive source with an electric motor.

[0029] The driving force control device 1 preferably has a map and determines the front and rear wheel drive distribution Rr based on the map. The map records the standard lateral acceleration YG calculated based on the vehicle speed V and the steering amount of the steering device, the standard drive acceleration XG calculated based on the vehicle speed V and the input amount from the driving force indicating device, and the front and rear wheel drive distribution Rr.

[0030] According to the above structure, the rear-wheel drive distribution can be determined earlier than by calculation, and the control speed of the driving forces of the front and rear wheels can be increased.

[0031] The driving force indicating devices 42 and 44 are at least one of an accelerator pedal (accelerator operating member) and a brake pedal (brake operating member), and the input amount from the driving force indicating device is preferably at least one of the depression amount (operating amount) of the accelerator pedal and the depression amount (operating amount) of the brake pedal.

[0032] According to these structures, a standard drive acceleration XG (acceleration target value) is calculated based on a driver's indicated amount such as an accelerator operation amount or a brake operation amount, and control is performed based thereon. Therefore, compared with feedback based only on an actual acceleration or the like, the responsiveness is improved.

[0033] [Effects of the Invention]

[0034] Based on the standard drive acceleration (acceleration target value), the driving force control device according to the present invention switches between a traction optimal control for determining the rear-wheel drive distribution according to an optimal traction curve and a rear-wheel-biased distribution control for determining the rear-wheel drive distribution according to a rear-wheel-biased distribution curve. Therefore, when traction is required such as during high acceleration and deceleration, the traction performance during traveling is maintained, and excellent operation performance can also be obtained when there is a surplus of traction such as during low acceleration and deceleration. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a block diagram showing the structure of a driving force control device according to an embodiment of the present invention.

[0036] Figure 2 is a graph showing a control curve of the front and rear wheel driving force distribution in a normal mode.

[0037] Figure 3 is a graph showing the loads and driving forces of the front and rear wheels.

[0038] Figure 4A , Figure 4B is a conceptual diagram showing the load change applied to a wheel due to a torque caused by an acceleration, Figure 4A shows the load change caused by the longitudinal acceleration, Figure 4B shows the load change caused by the lateral acceleration.

[0039] Figure 5 is a conceptual diagram showing the traction limit in each road surface state.

[0040] Figure 6 is a graph showing a control curve of the front and rear wheel driving force distribution in a sports mode.

[0041] Figure 7 It is a map of the front and rear wheel driving force distribution with respect to the standard lateral acceleration and the standard driving acceleration.

[0042] Figure 8 It is a map of the front and rear wheel driving force distribution with respect to the vehicle speed and the standard driving acceleration.

[0043] [Explanation of symbols]

[0044] 1: Driving force control device

[0045] 2: Driving acceleration calculation unit

[0046] 3: Lateral acceleration calculation unit

[0047] 4a, 4b: Maps

[0048] 5: Driving force distribution determination unit

[0049] 6: Output unit

[0050] 10: Main body

[0051] 100: Vehicle

[0052] 21: Front wheels

[0053] 21a: Left front wheel (front wheel)

[0054] 21b: Right front wheel (front wheel)

[0055] 22: Rear wheels

[0056] 22a: Left rear wheel (rear wheel)

[0057] 22b: Right rear wheel (rear wheel)

[0058] 31: Front-wheel drive motor

[0059] 32: Rear-wheel drive motor

[0060] 33: Front-wheel differential mechanism

[0061] 34: Rear-wheel differential mechanism

[0062] 40: Steering wheel (steering device)

[0063] 41: Steering angle sensor

[0064] 42: Accelerator pedal

[0065] 43: Accelerator depression amount sensor

[0066] 44: Brake pedal

[0067] 45: Brake Pedal Travel Sensor

[0068] 46: Vehicle Speed Sensor

[0069] 50: Electronic Control Unit (ECU)

[0070] 60: Battery

[0071] 61: Front Wheel Drive Circuit

[0072] 62: Rear Wheel Drive Circuit

[0073] ax: Longitudinal Acceleration

[0074] ay: Lateral Acceleration

[0075] L1, L1a: Dynamic Load Ratio Distribution Curve

[0076] L2, L2a: Rear Wheel Biased Distribution Curve

[0077] L3: Transition Curve

[0078] L4: Transition Curve

[0079] Ls, Lw, Ld: Traction Limit Line

[0080] Rr: Rear Wheel Distribution Ratio (Front - Rear Wheel Drive Distribution)

[0081] V: Vehicle Speed

[0082] V1: First Specified Speed

[0083] V2: Second Specified Speed

[0084] Wf, Wr: Load

[0085] ΔWx, ΔWy: Load Change

[0086] XG: Specified Driving Acceleration

[0087] XG1: First Input Quantity

[0088] XG2: Second Input Quantity

[0089] YG: Specified Lateral Acceleration

[0090] YG3: Third Input Quantity Detailed Embodiment

[0091] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0092] Figure 1 FIG. is a block diagram showing an example of the structure of a vehicle 100 including a driving force control device 1 according to an embodiment of the present invention.Figure 1 The vehicle 100 shown 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 configured to be 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 configured to be driven by the rear-wheel drive motor 32 via the rear-wheel differential mechanism 34.

[0093] The vehicle 100 further includes a steering wheel (steering device) 40 as an operation device, a steering angle sensor 41 that detects its steering amount, an accelerator pedal (accelerator operating member) 42, an accelerator depression amount sensor 43 that detects its depression amount (operation amount), a brake pedal (brake operating member) 44, a brake depression amount sensor 45 that detects its depression amount (operation amount), and a vehicle speed sensor 46.

[0094] The vehicle 100 also has a battery 60, a front-wheel drive circuit 61, and a rear-wheel drive circuit 62 as a drive system, and an electronic control unit (ECU) 50 as a control system. The electronic control unit 50 is a unit including a central processing unit (CPU) (not shown) for operation control, a memory (not shown) that stores an operation program, a memory (not shown) that stores data, etc., and is configured as a microcomputer, for example. 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 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.

[0095] 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, in the electronic control unit 50, a program that causes the CPU (not shown) to operate is included. The driving force control device 1 includes: a driving acceleration calculation unit 2, a lateral acceleration calculation unit 3, a map 4a, a map 4b, a drive distribution determination unit 5, and an output unit 6.

[0096] The driving acceleration calculation unit 2 calculates a positive or negative standardized driving acceleration XG (target value of acceleration) obtained based on 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. The reason is that it is considered that the driving acceleration of an actual vehicle is determined by the difference between the driving force determined by the depression amount of the accelerator pedal 42 and the air resistance or regenerative resistance determined by the current vehicle speed V.

[0097] The driving acceleration calculation unit 2 also calculates the obtained negative standardized driving acceleration XG (the target value of acceleration) based on 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. The reason is that it is considered that the driving acceleration of the actual vehicle is determined by the sum of the driving force determined by the depression amount of the brake pedal 44 and the air resistance or regenerative resistance determined by the current vehicle speed V.

[0098] The lateral acceleration calculation unit 3 calculates the obtained positive or negative standardized lateral acceleration YG (the target value of acceleration) based on 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 the control is based on the driver's instruction amounts such as the accelerator depression amount or the brake operation amount, the responsiveness is improved compared to the feedback control based only on the actual acceleration, etc.

[0099] The maps 4a and 4b are data that pre-record 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), and are stored in a memory (not shown) of the storage electronic control unit (ECU) 50, and are available for reference by the drive distribution determination unit 5. The detailed situation will be described later.

[0100] 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.

[0101] 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 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.

[0102] Next, the control of the front and rear wheel drive distribution of the driving force control device 1 configured as described above will be described in different situations.

[0103] (1) Dynamic load ratio distribution control (traction optimal control) when going straight in the normal mode

[0104] Figure 2 is a graph showing the control curve of the front and rear wheel driving force distribution (expressed by the rear-wheel distribution ratio Rr) in the normal mode with respect to the standardized driving acceleration XG. The drive distribution determination unit 5 basically performs according to Figure 2The dynamic load ratio distribution curve L1 shown determines the dynamic load ratio distribution control for front and rear wheel drive distribution.

[0105] The dynamic load ratio distribution curve L1 is a curve of the dynamic load ratio (horizontal axis) applied to the front wheels 21 and the rear wheels 22 with respect to the standard drive acceleration XG (vertical axis). The dynamic load ratio is the ratio of the load Wf and the load Wr applied to the Figure 3 front wheels 21 and the rear wheels 22 shown during vehicle travel, and is obtained by adding the load change ΔWx applied to the front wheels 21 and the rear wheels 22 due to the pitching moment caused by the longitudinal acceleration ax to the load Wf and the load Wr when the vehicle is stationary. Therefore, regarding Figure 4A the dynamic load ratio distribution curve L1 shown, it coincides with the static load ratio when the standard drive acceleration XG is zero, and the greater the standard drive acceleration XG (in the upward direction), the greater the load change ΔWx (refer to Figure 2 ), and thus the greater the rear wheel distribution ratio Rr (shifted to the right direction). Figure 4A

[0106] In the dynamic load ratio distribution control for front and rear wheel drive distribution determined according to the dynamic load ratio distribution curve L1, the ratio of the driving force to the dynamic load in the front wheels 21 and the rear wheels 22 ( Figure 3 Ff / Wf and Fr / Wr) is the same, and neither will protrude and become larger. Therefore, the margin until the ratio of the driving force to the dynamic load (Ff / Wf and Fr / Wr) reaches the traction limit of the friction coefficient μ between the road surface and the tire becomes larger. Therefore, in the dynamic load ratio distribution control, good traction performance can be ensured even under various road surface conditions or acceleration and deceleration conditions.

[0107] Figure 5 is a conceptual diagram showing the traction limit under each road surface state. The vertical axis represents the drive acceleration, and the horizontal axis represents the front and rear wheel drive distribution (rear wheel distribution ratio Rr). It is well-known that the friction coefficient μ between the tire and the road surface is approximately 1.0 on a dry road surface (Dry (DRY)), approximately 0.6 on a wet road surface (Wet (WET)), and approximately 0.3 on a snow-covered road surface (Snow (SNOW)). When the front and rear wheel drive distribution ratio (Rr) (horizontal axis) is the same as the static load ratio or the dynamic load ratio, the ratio of the driving force of each of the front wheels 21 and the rear wheels 22 to the load ( Figure 3 Ff / Wf and Fr / Wr) is equal to the ratio of the driving force to the total weight of the vehicle (the same as the ratio of the drive acceleration on the vertical axis to the gravitational acceleration). Therefore, the ratio of the drive acceleration to the gravitational acceleration (vertical axis) can be increased to the friction coefficient μ of each road surface state. On the other hand, when the front and rear wheel drive (horizontal axis) deviates from the static load ratio, the ratio of the driving force of the front wheels 21 and the rear wheels 22 to the load ( Figure 3The Ff / Wf and Fr / Wr) are different, and one of them is 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 coefficient of friction μ. Thus, in Figure 5 For each road surface condition, the traction limit line Ld, the traction limit line Lw, and the traction limit line Ls reach a peak (coefficient of friction μ) at approximately the center (static load ratio), and decrease towards the left and right. (In addition, Figure 5 The load change ΔWx shown in Figure 4A is not considered. If this is taken into account, each traction limit line Ld, Lw, Ls deforms in a manner that shifts further to the right as it goes upwards) 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. Therefore, good traction performance can be obtained within a wide acceleration range.

[0108] In addition, Figure 5 only the range of positive acceleration is shown, and the range of negative acceleration (deceleration) is not shown. However, even for the range of negative acceleration (deceleration), it can be considered that the traction limit lines (omitted from the illustration) are based on the curve of the positive acceleration range as the upper and lower reference. Therefore, even for the range of negative acceleration (deceleration), the dynamic load ratio distribution curve L1 of the dynamic load ratio distribution control passes through the peaks of each traction limit line (omitted from the illustration). Therefore, good traction performance can be obtained within a wide acceleration range.

[0109] Among them, since slipping is generally likely to occur during deceleration, a safety factor is multiplied in the design to reduce the absolute value of the acceleration of each traction limit line (omitted from the illustration).

[0110] (2) Rear-wheel-biased distribution control (operation optimal control) during straight driving in the normal mode

[0111] In the normal mode, when the specified driving acceleration XG is small, specifically, within the range of the specified driving acceleration XG inside the traction limit line Ls of "SNOW" where slipping does not occur even on a snow-covered road (refer to Figure 5 ), rear-wheel-biased distribution control (operation optimal control) is implemented to determine the front and rear wheel drive distribution according to the rear-wheel-biased distribution curve L2 shown in Figure 2 , instead of the dynamic load ratio distribution control. In addition, the specified driving acceleration XG (positive value) at the upper limit of the range where the rear-wheel-biased distribution control is implemented is called the first input quantity XG1, and the specified driving acceleration XG (negative value) at the lower limit is called the second input quantity XG2.

[0112] As shown in Figure 2As shown, the rear-wheel-biased distribution curve L2 is a curve that moves the dynamic load ratio distribution curve L1 in the direction (right side) where the rear-wheel distribution ratio Rr is higher. In the rear-wheel-biased distribution curve L2, the front-to-rear wheel drive distribution when the standard drive acceleration XG is zero is set to a distribution that further increases the rear-wheel distribution ratio Rr compared to the static load ratio, and is a distribution that does not require fine correction of the accelerator and steering when not turning. The rear-wheel-biased distribution curve L2 also takes into account Figure 4A the load change ΔWx caused by the acceleration, and the larger the standard drive acceleration XG (in the upward direction), the larger the rear-wheel distribution ratio Rr becomes (in the right direction). According to the above structure, even under the condition of a high rear-wheel drive distribution, the margin with respect to the traction limit of the tire is relatively large. Thus, when not accelerating or decelerating suddenly and being within the traction limit under any road surface conditions, by implementing the rear-wheel-biased distribution control, the operation performance can be improved.

[0113] The switching between the dynamic load ratio distribution control and the rear-wheel-biased distribution control is carried out along the transition curve L3 or the transition curve L4. The transition curve L3 is along the lower side of the upper traction limit line Ls of "SNOW" (refer to Figure 5 ), and the transition curve L4 is along the upper side of the lower traction limit line (not shown) of "SNOW". According to the above structure, the front-to-rear wheel drive distribution does not cross the traction limit of "SNOW", and the switching between the dynamic load ratio distribution control and the rear-wheel-biased distribution control can be carried out smoothly.

[0114] (3) Front-to-rear wheel drive distribution control during turning in the normal mode

[0115] The drive distribution determination unit 5 also performs the dynamic load ratio distribution control and the rear-wheel-biased distribution control during turning in the same way as during straight running. Among them, during turning, the rolling-direction moment generated by the lateral acceleration ay during vehicle turning as shown in Figure 4B is considered, and instead of the dynamic load ratio distribution curve L1 and the rear-wheel-biased distribution curve L2 during straight running as shown in Figure 2 , the dynamic load ratio distribution and the rear-wheel-biased distribution control are carried out according to the dynamic load ratio distribution curve L1a and the rear-wheel-biased distribution curve L2a that are slightly moved in the direction of increasing the rear-wheel distribution ratio Rr (right direction).

[0116] The reason is that, for example, when the vehicle turns to the right, as shown in Figure 4B , a negative load change ΔWy is applied to the inner wheels (right front wheel 21b and right rear wheel 22b) through the rolling-direction moment generated by the lateral acceleration ay during vehicle turning, so the load applied to the inner wheels (right front wheel 21b and right rear wheel 22b) is reduced. In particular, when the vehicle is accelerating, as shown in Figure 4A , a pitching-direction moment also applies a load to the front wheels 21 ( Figure 1A negative load change ΔWx is applied to the left front wheel 21a and the right front wheel 21b shown, so the load on the right front wheel 21b decreases the most and it is prone to skidding.

[0117] In addition, 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 it is prone to skidding.

[0118] Therefore, from the perspective of preventing skidding, in order to further reduce the drive force distribution to the right front wheel 21b or the left front wheel 21a, in the dynamic load ratio distribution curve L1a for turning or the rear-wheel-biased distribution curve L2a, the rear-wheel drive distribution is increased more than that in the dynamic load ratio distribution curve L1 or the rear-wheel-biased distribution curve L2a during straight running.

[0119] (4) Front and rear wheel drive distribution control in the sports mode

[0120] In the sports mode, when the reference drive acceleration XG is inside the traction limit line Lw of "WET" where skidding will not occur even on a wet road surface (refer to Figure 5 ), rear-wheel-biased distribution control (optimal operation control) is implemented, and when it is outside, dynamic load ratio distribution control (optimal traction control) is implemented. Figure 6 It is a diagram showing the control curve of the front and rear wheel drive forces distribution in the sports mode with respect to the reference drive acceleration XG. In the sports mode, as in the normal mode, during straight running, 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.

[0121] Among them, the first input value XG1 of the reference drive acceleration XG (positive value) which is the upper limit of the range for implementing the rear-wheel-biased distribution control, and the second input value XG2 of the reference drive acceleration XG (negative value) which is the lower limit are different from those in the normal mode and are set near the traction limit line Lw of "WET" shown in Figure 5 . Thus, the rear-wheel-biased distribution control (optimal operation control) is implemented in a wider acceleration range than in the normal mode.

[0122] The switching between the normal mode and the sports mode can be performed by the driver's mode switching operation. As described above, in the normal mode and the sports mode, the first input value XG1 which is the upper limit of the range of the reference drive acceleration XG for implementing the rear-wheel-biased distribution control, and the second input value XG2 which is the lower limit are different respectively, and these values can be changed by the driver's mode switching operation.

[0123] According to the above structure, a sport mode and a normal mode are prepared. When it is understood that the road surface is not slippery, a wide area with high operating performance is ensured in the sport mode. On the other hand, when it is understood that the road surface is slippery, stability can be ensured in the normal mode. In the sport mode, the acceleration and deceleration range for rear-wheel distribution control is expanded assuming only dry road surfaces and wet road surfaces. In the normal mode, the acceleration and deceleration range for rear-wheel distribution control is reduced assuming dry road surfaces, wet road surfaces, and snow road surfaces other than these.

[0124] (5) Front and rear wheel drive distribution control during sudden operations

[0125] The drive distribution determination unit 5 is configured such that when the standardized drive acceleration XG is small, but the standardized lateral acceleration YG calculated based on 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, rear-wheel distribution control is not performed. Here, the so-called third input amount YG3 is the standardized lateral acceleration YG at the limit where the drive wheels do not slip on the road surface in a specified state. The so-called "standardized lateral acceleration YG at the limit where the drive wheels do not slip on the road surface in a specified state" is, for example, the standardized lateral acceleration YG that does not exceed Figure 5 the traction limit in the specified road surface state shown.

[0126] Figure 7 A map 4a showing the front and rear wheel driving force distribution with respect to the standardized lateral acceleration YG and the standardized drive acceleration XG. The map 4a is data arranged in a matrix form, where the horizontal position corresponds to the standardized lateral acceleration YG and the vertical position corresponds to the standardized drive acceleration XG. In each cell, the front and rear wheel drive distribution corresponding to the horizontal position (YG) and the vertical position (XG) is stored as a discrete value.

[0127] As Figure 7 shown, in the region where the standardized lateral acceleration YG is not high and is to the left of the third input amount YG3, as described above, in the range where the standardized drive acceleration XG is small (between the first input amount XG1 and the second input amount XG2), rear-wheel distribution control (optimal operation control) is performed.

[0128] On the other hand, in the region where the standardized lateral acceleration YG is high and is to the right of the third input amount YG3, regardless of the standardized drive acceleration XG, rear-wheel distribution control is not performed.

[0129] According to the above structure, in a state where there is lateral acceleration caused by sudden operation, rear-wheel distribution control is not performed, thereby ensuring driving stability. In addition, since the control is performed based on the driver's instruction amount such as the steering angle of the steering wheel 40, the responsiveness is improved compared to feedback based only on actual acceleration, etc.

[0130] (6) Front and rear wheel drive distribution control at low speed and high speed

[0131] The drive distribution determination unit 5 is configured such that even when the reference drive acceleration XG is small, but when the vehicle speed V detected by the vehicle speed sensor 46 shown in Figure 1 is lower than the first specified speed V1, which is the vehicle speed immediately after starting and immediately before stopping, the rear wheel distribution control is not performed. Further, it is configured such that when the vehicle speed V is higher than the second specified speed V2, which is the speed during high-speed driving, the rear wheel distribution control is not performed.

[0132] Figure 8 A map 4b showing the front and rear wheel driving force distribution with respect to the vehicle speed V and the reference drive acceleration XG. The map 4b is also data arranged in a matrix form, and its horizontal position corresponds to the vehicle speed V, and its vertical position corresponds to the reference drive acceleration XG. In each cell, the front and rear wheel drive distribution corresponding to the horizontal position (vehicle speed V) and the vertical position (reference drive acceleration XG) is stored as a discrete value.

[0133] As Figure 8 shown, in the region from low speed to medium speed where the vehicle speed V is between the first specified speed V1 and the second specified 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), the rear wheel distribution control (operation optimal control) is performed. On the other hand, in the low-speed region further to the left than the first specified speed V1 and in the high-speed region to the right of the second specified speed V2, the rear wheel distribution control is not performed.

[0134] According to the above structure, at low speeds immediately after starting and immediately before stopping of a vehicle that needs to be towed, or during high-speed driving that requires driving stability, regardless of the accelerations and decelerations in the front, rear, left, and right directions, the rear wheel distribution control (operation optimal control) is not performed, and the dynamic load ratio control (towing optimal control) is performed. Therefore, towing or driving stability in these cases can be ensured.

[0135] Further, by preparing such a map 4a and a map 4b, if the drive distribution determination unit 5 designates the vehicle speed V and the reference drive acceleration XG, the corresponding front and rear wheel drive distribution can be immediately obtained. Therefore, the rear wheel drive distribution can be determined earlier than by calculating the rear wheel drive distribution through arithmetic operations, and the control speed of the driving forces of the front and rear wheels can be increased.

[0136] As described above, the embodiments of the present invention have been illustrated. However, the present invention is not limited to the described embodiments and can be variously modified within the scope of the technical idea described in the claims, the specification, and the drawings. For example, in the above-described embodiment, an application example of the driving force control device 1 to the vehicle 100 having a front and rear dual motor structure including the front wheel drive motor 31 and the rear wheel drive motor 32 has been illustrated. However, the present invention is not limited thereto, and it can also be applied to a vehicle having a four-motor structure with a drive motor for each of the four wheels, a single-motor structure in which the driving force of one drive motor is distributed to the four wheels, and a vehicle having a structure in which each of these motors is replaced with a gasoline engine.

Claims

1. A driving force control device for determining the ratio of driving force between the front wheels and the rear wheels in a four-wheel drive vehicle, i.e., front-rear wheel drive distribution, The driving force control device calculates the obtained positive or negative standard driving acceleration according to the input amount from the driving force indicating device of the vehicle and the vehicle speed, and switches the dynamic load ratio distribution control and the rear wheel distribution control based on the standard driving acceleration. In the dynamic load ratio distribution control, the front and rear wheel drive distribution is determined according to a dynamic load ratio distribution curve which is a curve of the dynamic load ratio applied to the front and rear wheels relative to the standard drive acceleration. In the rear wheel distribution control, the front and rear wheel drive distribution is determined according to a rear wheel distribution curve that increases the rear wheel drive distribution more than the dynamic load ratio distribution curve.

2. The driving force control device according to claim 1, wherein: The dynamic load ratio distribution curve and the rear wheel distribution curve are curves in which the higher the standard driving acceleration is, the higher the rear wheel drive distribution is, except for the transition curves between each other.

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

4. The driving force control device according to claim 3, wherein: The first input amount is a standard driving acceleration that provides an acceleration within a limit at which the driving wheels do not slip on a road surface in a predetermined state.

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

6. The driving force control device according to claim 5, wherein: The second input amount is a standard driving acceleration for providing a deceleration within a limit at which the driving wheels do not slip on a road surface of 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 a standard lateral acceleration calculated based on the steering amount of the steering device of the vehicle and the vehicle speed is equal to or greater than a third input amount, the rear wheel distribution control is not performed.

10. The driving force control device according to claim 9, wherein: The third input amount is a standard lateral acceleration within a limit at which the drive wheels do not slip on 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 distribution control is not performed.

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 distribution control is not performed.

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

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

15. The driving force control device according to any one of claims 1 to 10, wherein: The driving sources of the front wheels and the rear wheels of the vehicle include electric motors.

16. The driving force control device according to any one of claims 1 to 10 has a mapping map, and the front and rear wheel drive distribution is determined based on the mapping map, the mapping map records the standard lateral acceleration calculated based on the vehicle speed and the steering amount of the steering device, the standard driving acceleration calculated based on the vehicle speed and the input amount from the driving force indicating device, and the front and rear wheel drive distribution.

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 operating member and a brake operating member, and an input amount from the driving force indicating device is at least one of an operation amount of the accelerator operating member and an operation amount of the brake operating member.

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