Vehicle drive force control device

Abstract

The present application provides a vehicle drive force control device that ensures stability of an all-wheel drive vehicle and suppresses a reduction in maneuverability during travel in a normal travel state on a low-friction road surface. In the low-friction road surface control mode, front-wheel drive force and rear-wheel drive force are generated during travel of the all-wheel drive vehicle. In addition to this, in the normal travel state, the front-wheel drive force and the rear-wheel drive force are controlled in such a manner that the rear-wheel distribution ratio is set to be less than or equal to half of the front-wheel distribution ratio. Here, it is found that in the all-wheel drive vehicle, during travel in the normal travel state on the low-friction road surface, even if the rear-wheel distribution ratio is less than or equal to half of the front-wheel distribution ratio, as long as the all-wheel drive state in which the front-wheel drive force and the rear-wheel drive force are generated is maintained, stability can be ensured. Therefore, stability of the all-wheel drive vehicle during travel in the normal travel state on the low-friction road surface can be ensured and a reduction in maneuverability can be suppressed.

Description

Technical Field

[0001] This invention relates to the control of the driving force distribution between the front and rear wheels. Background Technology

[0002] Vehicle drive force control devices that control the drive force of all-wheel drive vehicles are known. For example, the vehicle behavior control device described in Patent Document 1 is such a control device. Patent Document 1 discloses a technology that has multiple driving modes, including a low-friction road driving mode for driving on low-friction road surfaces, and when the low-friction road driving mode is set, controls the braking force and drive force of the wheels for driving on low-friction road surfaces.

[0003] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2014-237386 When a vehicle is starting, increasing the rear-wheel drive distribution can improve acceleration. However, when an all-wheel-drive vehicle is in its normal driving state (other than starting), if the rear-wheel drive distribution is not set appropriately—for example, if it is set too high—while straight-line performance may be improved, handling may be reduced. This phenomenon is particularly noticeable on low-friction surfaces. The rear-wheel drive distribution ratio is the proportion of rear-wheel drive force to the total drive force obtained by adding the front and rear-wheel drive forces. Summary of the Invention

[0004] The present invention was made against the background described above, and its object is to provide a vehicle drive force control device that can ensure the stability of an all-wheel drive vehicle and suppress the reduction of handling during normal driving conditions on low-friction road surfaces.

[0005] The subject of the first invention is, (a) a vehicle drive force control device for controlling the drive force of an all-wheel drive vehicle, the vehicle drive force control device including a drive control unit, the drive control unit being configured to: (b) have multiple predetermined control modes or one predetermined control mode as a control mode for controlling the all-wheel drive vehicle, wherein, in the case of having the multiple predetermined control modes, the predetermined control mode includes a low-friction road surface control mode suitable for driving on low-friction road surfaces, and in the case of having the one predetermined control mode, the predetermined control mode is set as the low-friction road surface control mode, (c) In the low-friction road surface control mode, during the driving of the all-wheel drive vehicle, a front-wheel drive force driving the front wheels and a rear-wheel drive force driving the rear wheels are always generated. The front-wheel drive force and the rear-wheel drive force are controlled in a manner that, in the normal driving state other than the starting state, the rear-wheel drive force is less than half of the front-wheel drive force. The rear-wheel drive force is the ratio of the rear-wheel drive force to the total drive force obtained by adding the front-wheel drive force and the rear-wheel drive force, and the front-wheel drive force is the ratio of the front-wheel drive force to the total drive force.

[0006] Furthermore, the second invention is that, in the vehicle drive force control device described in the first invention, the drive control unit controls the front wheel drive force and the rear wheel drive force in the normal driving state of the low-friction road surface control mode, such that the rear wheel distribution ratio during deceleration is larger than the rear wheel distribution ratio in a steady state of constant speed driving or acceleration driving.

[0007] Furthermore, the third invention is that, in the vehicle drive force control device described in the second invention, the drive control unit controls the front wheel drive force and the rear wheel drive force in a manner that makes the rear wheel distribution ratio during the turn greater than the rear wheel distribution ratio in the steady state other than during the turn, when the normal driving state is in the low friction road surface control mode and the vehicle is also turning.

[0008] Furthermore, the fourth invention is that, in the vehicle drive force control device described in the third invention, the drive control unit controls the front wheel drive force and the rear wheel drive force in the normal driving state of the low-friction road surface control mode, such that the rear wheel distribution ratio during turning is greater than the rear wheel distribution ratio during deceleration.

[0009] Furthermore, the fifth invention is that, in the vehicle drive force control device described in any one of the first to fourth inventions, the drive control unit controls the front wheel drive force and the rear wheel drive force in the starting state of the low-friction road surface control mode in such a way that the rear wheel distribution ratio is greater than half of the front wheel distribution ratio.

[0010] Invention Effects According to the first invention, in the control mode for low-friction surfaces, front-wheel drive force and rear-wheel drive force are always generated during the driving of an all-wheel drive vehicle. Furthermore, under normal driving conditions, the front-wheel drive force and rear-wheel drive force are controlled such that the rear-wheel distribution ratio is less than half of the front-wheel distribution ratio. In other words, under normal driving conditions, the front-wheel drive force and rear-wheel drive force are controlled such that the rear-wheel distribution ratio does not exceed half of the front-wheel distribution ratio. Here, it has been found that in an all-wheel drive vehicle, even if the rear-wheel distribution ratio is less than half of the front-wheel distribution ratio during normal driving on low-friction surfaces, stability can be ensured as long as front-wheel drive force and rear-wheel drive force are generated in the all-wheel drive state. Therefore, the stability of the all-wheel drive vehicle can be ensured and the reduction in handling can be suppressed during normal driving on low-friction surfaces.

[0011] Furthermore, according to the second invention, in the normal driving state under the control mode on low-friction surfaces, the front-wheel drive force and rear-wheel drive force are controlled in such a way that the rear-wheel distribution ratio during deceleration is larger than the rear-wheel distribution ratio in the steady state. Thus, a suitable balance between the stability and handling of the all-wheel drive vehicle can be achieved during normal driving on low-friction surfaces.

[0012] Furthermore, according to the third invention, in the normal driving state under the control mode on low-friction surfaces, when both in a steady state and turning, the front-wheel drive force and rear-wheel drive force are controlled in such a way that the rear-wheel drive force distribution ratio during turning is larger than the rear-wheel drive force distribution ratio in the steady state other than during turning. Thus, a suitable balance between the stability and handling of the all-wheel drive vehicle can be achieved during normal driving on low-friction surfaces.

[0013] Furthermore, according to the fourth invention, in the normal driving state under the control mode for low-friction surfaces, the front-wheel drive force and rear-wheel drive force are controlled in such a way that the rear-wheel drive force distribution ratio during cornering is larger than the rear-wheel drive force distribution ratio during deceleration. Thus, a suitable balance between the stability and handling of the all-wheel drive vehicle can be achieved during normal driving on low-friction surfaces.

[0014] Furthermore, according to the fifth invention, in the starting state of the control mode for low-friction surfaces, the front-wheel drive force and rear-wheel drive force are controlled such that the rear-wheel drive force distribution ratio is greater than half of the front-wheel drive force distribution ratio. This suppresses tire slippage during driving in the starting state on low-friction surfaces. Attached Figure Description

[0015] Figure 1 This diagram illustrates the general configuration of a vehicle to which the present invention is applied, and also illustrates the main components of the control functions used for various controls in the vehicle.

[0016] Figure 2 This is a flowchart illustrating the main parts of the control operation of the electronic control device, and a flowchart illustrating the control operation used to ensure vehicle stability and suppress the reduction of handling during normal driving conditions.

[0017] Figure 3 This diagram illustrates an example of rear-drive distribution settings in snow mode.

[0018] Figure 4 This is a diagram illustrating an example of the relationship between axle load distribution and front-rear acceleration during deceleration.

[0019] Figure 5 This is a flowchart illustrating the main parts of the control operation of the electronic control unit. It is used to explain the control operations that ensure vehicle stability and prevent a decrease in handling during normal driving conditions. This flowchart is... Figure 2 The flowchart illustrates the control operation in S80.

[0020] Explanation of reference numerals in the attached figures: 10: Vehicle (all-wheel drive vehicle); 12: Front wheel; 14: Rear wheel; 50: Electronic control unit (vehicle drive force control unit); 52: Drive control unit; 54: Mode setting unit. Detailed Implementation

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0022] [Example] Figure 1 This diagram illustrates the general configuration of a vehicle 10 to which the present invention is applied, and also illustrates the main components of the control functions used for various controls in the vehicle 10. Figure 1In this vehicle 10, there are left and right front wheels 12, left and right rear wheels 14, a front drive unit 20, and a rear drive unit 30. The front wheels 12 include a left front wheel 12L and a right front wheel 12R. The rear wheels 14 include a left rear wheel 14L and a right rear wheel 14R. The front drive unit 20 is a drive unit for the front wheels 12. The rear drive unit 30 is a drive unit for the rear wheels 14. The rear drive unit 30 and the front drive unit 20 are provided independently. Furthermore, the vehicle 10 includes a battery 40, which serves as a DC power source capable of charging and discharging. It should be noted that the term "left and right" refers to left and right relative to the direction of travel of the vehicle 10.

[0023] Vehicle 10 is an all-wheel drive vehicle of the present invention capable of adjusting the drive force distribution between the front wheels 12 and the rear wheels 14. Vehicle 10 has two front wheels 12 and two rear wheels 14, making it a four-wheel vehicle and therefore a four-wheel drive vehicle. In this embodiment, all-wheel drive (AWD) and four-wheel drive (4WD) are synonymous. In addition to driving under AWD control (AWD state is also synonymous) that drives both the front wheels 12 and the rear wheels 14, vehicle 10 can also drive under two-wheel drive (=2WD (Two-Wheel Drive)) control (2WD state is also synonymous) that drives only one of the front wheels 12 and the rear wheels 14. For example, it can perform driving under front-wheel drive (FWD) control (FWD state is also synonymous) that drives only the front wheels 12 and / or driving under rear-wheel drive (RWD) control (RWD state is also synonymous) that drives only the rear wheels 14.

[0024] The front drive unit 20 includes a front motor 22 (see “MGF” in the figure), a front PCU (Power Control Unit) 24, and a front power transmission device 26. The rear drive unit 30 includes a rear motor 32 (see “MGR” in the figure), a rear PCU 34, and a rear power transmission device 36.

[0025] The front motor 22 and the rear motor 32 are both known rotating electromechanical devices (so-called electric generators). The front motor 22 and the rear motor 32 function as power sources for the vehicle 10. The front motor 22 is connected to the battery 40 via the front PCU 24. The rear motor 32 is connected to the battery 40 via the rear PCU 34.

[0026] The front PCU24, for example, includes an inverter and is a power control device that controls the power supplied between the battery 40 and the front motor 22. The front PCU24 controls the front motor 22. The rear PCU34, for example, includes an inverter and is a power control device that controls the power supplied between the battery 40 and the rear motor 32. The rear PCU34 controls the rear motor 32.

[0027] The front power transmission device 26 is a gear mechanism (not shown) connected to the front motor 22, including a differential gear (not shown) connected to the gear mechanism and left and right front drive shafts 28 connecting the differential gear to the front wheel 12. The front drive shafts 28 include a left front drive shaft 28L and a right front drive shaft 28R. The front power transmission device 26 is a front wheel power transmission device that transmits power from the front motor 22 to the front wheel 12.

[0028] The rear power transmission device 36 includes a gear mechanism (not shown) connected to the rear motor 32, a differential gear (not shown) connected to the gear mechanism, and left and right rear drive shafts 38 connecting the differential gear to the rear wheel 14. The rear drive shafts 38 include a left rear drive shaft 38L and a right rear drive shaft 38R. The rear power transmission device 36 is a power transmission device that transmits power from the rear motor 32 to the rear wheel 14.

[0029] The vehicle 10 also includes an electronic control unit 50 as a controller. The electronic control unit 50 is configured, for example, as a so-called microcomputer including a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), input / output interfaces, etc. The CPU, for example, performs various controls of the vehicle 10 by utilizing the temporary storage function of RAM and processing signals according to a program pre-stored in the ROM. The electronic control unit 50 is a vehicle drive force control device of the present invention that controls the drive force Fd of the vehicle 10.

[0030] Various signals based on detection values ​​obtained from various sensors equipped on the vehicle 10 are supplied to the electronic control unit 50. These sensors include, for example, an MGF rotation sensor 70, an MGR rotation sensor 72, wheel speed sensors 74, an accelerator opening sensor 76, a brake sensor 78, a steering sensor 80, a G-sensor 82, a yaw rate sensor 84, and a mode selection switch 86. Various signals include, for example, MGF rotation speed Nmgf, MGR rotation speed Nmgr, left front wheel rotation speed Nwfl, right front wheel rotation speed Nwfr, left rear wheel rotation speed Nwrl, and right rear wheel rotation speed Nwrr. Furthermore, various signals include, for example, accelerator opening θacc, brake operation amount θbp, steering angle θsw, steering direction Dsw, front-rear acceleration Gx, left-right acceleration Gy, yaw rate Ryaw, and mode selection signal Smode. The electronic control unit 50 obtains the vehicle speed V based, for example, on the speed of the left front wheel Nwfl, the speed of the right front wheel Nwfr, the speed of the left rear wheel Nwrl, and the speed of the right rear wheel Nwrr.

[0031] MGF speed Nmgf is the speed of the front motor 22. MGR speed Nmgr is the speed of the rear motor 32. Accelerator opening θacc is a signal indicating the magnitude of the driver's acceleration operation, representing the amount of accelerator operation. Brake operation θbp is a signal indicating the state of the brake pedal operated by the driver, representing the magnitude of the brake pedal depressing operation. Steering angle θsw is the steering angle of the steering wheel. Steering direction Dsw is the steering direction of the steering wheel. Rear acceleration Gx is the acceleration of vehicle 10 in the rear-rear direction. Lateral acceleration Gy is the acceleration of vehicle 10 in the lateral direction. Yaw rate Ryaw is the rotational angular velocity about the vertical axis of vehicle 10.

[0032] The mode selection switch 86 is a manually operated switch for selecting the control mode MODEcn used to control the vehicle 10. The mode selection switch 86 is, for example, an automatic reset type, meaning a momentary operating element that returns to its original position without external force. The mode selection signal Smode is a signal indicating that the mode selection switch 86 has been manually operated. The mode selection signal Smode is output each time the mode selection switch 86 is operated. The control mode MODEcn is, for example, set to any one of several specified control modes MODEcnf suitable for various driving conditions.

[0033] The specified control modes MODEcnf include, for example, a pre-determined standard mode, power mode, energy-saving mode, and snow mode. The standard mode is, for example, a pre-determined control mode MODEcn for driving in a manner that maximizes power performance while maintaining good energy efficiency. The power mode is, for example, a pre-determined control mode MODEcn for driving in a manner that prioritizes power performance over energy efficiency compared to the standard mode. The energy-saving mode is, for example, a pre-determined control mode MODEcn for driving in a manner that prioritizes energy efficiency over power performance compared to the standard mode. The snow mode is, for example, a pre-determined control mode MODEcn for stable driving on low-μ roads (low-μ roads). Low-μ roads are, for example, low-friction roads with a very low coefficient of friction, such as snow tracks or icy roads. The snow mode is a low-friction road control mode of the present invention suitable for driving on low-friction roads.

[0034] The mode selection switch 86 is operated to select the control mode MODEcn in the following order: standard mode, power mode, energy-saving mode, snow mode, standard mode, ... The control mode MODEcn is set in the following order each time the mode selection signal Smode is output: standard mode, power mode, energy-saving mode, snow mode, standard mode, ... The mode selection switch 86 may include, for example, switches operated to select standard mode, power mode, energy-saving mode, and switches operated to select snow mode.

[0035] The electronic control unit 50 outputs various command signals to various devices equipped in the vehicle 10. These devices include, for example, the front PCU 24 and the rear PCU 34. The command signals include, for example, the MGF control command signal Smgf and the MGR control command signal Smgr. The MGF control command signal Smgf is a torque indication value used to control the MGF torque Tmgf, which is the torque of the front motor 22. The MGR control command signal Smgr is a torque indication value used to control the MGR torque Tmgr, which is the torque of the rear motor 32.

[0036] The electronic control unit 50 includes a drive control unit 52 and a mode setting unit 54 to realize various controls in the vehicle 10.

[0037] The drive control unit 52 controls the front drive unit 20 and the rear drive unit 30 respectively. For example, the drive control unit 52 calculates the driver's drive request quantity DEM for the vehicle 10 by applying the accelerator opening θacc and vehicle speed V to a drive request quantity mapping diagram. This drive request quantity mapping diagram is a pre-determined relationship used to calculate the drive request quantity DEM, obtained and stored in advance through experiments or design. The drive request quantity DEM is, for example, the requested drive force Fddem, which is the requested value of the force Fd in the wheels (front wheels 12, rear wheels 14), i.e., the drive force Fd. The drive request quantity DEM can also be, for example, the requested drive torque Tddem, which is the requested value of the torque Td in the wheels, i.e., the drive torque Td. The drive control unit 52 controls the front motor 22 and the rear motor 32, for example, to achieve drive control of the requested drive force Fddem. It should be noted that, unless otherwise specified, torque and force (drive force) are synonymous.

[0038] The driving force Fd is the total driving force of the present invention, obtained by adding the front driving force Fdf and the rear driving force Fdr. The front driving force Fdf is the driving force that drives the front wheel 12, and is the front wheel driving force of the present invention. The rear driving force Fdr is the driving force that drives the rear wheel 14, and is the rear wheel driving force of the present invention. The requested driving force Fddem is the value obtained by adding the requested front driving force Fdfdem (which is the requested value of the front driving force Fdf) and the requested rear driving force Fdrdem (which is the requested value of the rear driving force Fdr). The drive control unit 52 outputs the MGF control command signal Smgf, which is used to control the front motor 22 to realize the requested front driving force Fdfdem, to the front PCU 24. The drive control unit 52 outputs the MGR control command signal Smgr, which is used to control the rear motor 32 to realize the requested rear driving force Fdrdem, to the rear PCU 34.

[0039] The mode setting unit 54 sets any one of the specified control modes MODEcnf as the control mode MODEcn. For example, the mode setting unit 54 sets the control mode MODEcn by switching between standard mode, power mode, energy-saving mode, snow mode, standard mode, ... each time the mode selection switch 86 is manually operated.

[0040] When the drive control unit 52 is set to the standard mode as the control mode MODEcn, it calculates, for example, the drive request quantity DEM that balances energy efficiency and power performance for acceleration operations. When the drive control unit 52 is set to the power mode as the control mode MODEcn, it calculates, for example, the drive request quantity DEM whose output is advanced for acceleration operations. When the drive control unit 52 is set to the energy-saving mode as the control mode MODEcn, it calculates, for example, the drive request quantity DEM whose output is suppressed for acceleration operations.

[0041] When the drive control unit 52 is set to any one of the standard mode, power mode, and energy-saving mode as the control mode MODEcn, it performs AWD control driving in the starting state, for example. When the drive control unit 52 is set to any one of the standard mode, power mode, and energy-saving mode as the control mode MODEcn, it performs FWD control driving in the normal driving state other than the starting state. For example, if the front wheels 12 slip during FWD control driving, the drive control unit 52 switches to AWD control driving, controlling the front drive force Fdf and the rear drive force Fdr. In each of the standard mode, power mode, and energy-saving mode, during AWD control driving, the drive control unit 52 sets the front drive distribution [%] and rear drive distribution [%] based on a predetermined front and rear wheel drive force distribution ratio. The front drive distribution is the ratio of the front drive force Fdf to the drive force Fd, which is the front wheel distribution ratio of the present invention. The rear drive distribution is the ratio of the rear drive force Fdr to the drive force Fd, which is the rear wheel distribution ratio of the present invention. For example, when the driving force Fd is evenly distributed between the front wheel 12 and the rear wheel 14, the "front drive distribution: rear drive distribution" is set to "50:50".

[0042] The starting state is the driving state of vehicle 10 starting from a stationary state. The starting state is, for example, a driving state with the accelerator engaged, where the vehicle speed V is less than the low speed threshold Vlow. The low speed threshold Vlow is, for example, a predetermined threshold used to determine whether vehicle 10 is in a starting state. The low speed threshold Vlow is, for example, 10 [km / h]. The normal driving state is the driving state of vehicle 10 other than the starting state. The normal driving state includes, for example, a steady-state driving state and a decelerating driving state. The steady-state driving state is a driving state of constant speed or acceleration, for example, a driving state where the vehicle speed V is greater than or equal to the low speed threshold Vlow. The steady-state driving state includes, for example, driving straight, changing lanes, and turning. The decelerating driving state is, for example, a driving state in which vehicle 10 decelerates by disengaging the accelerator or engaging the brake. The driving force Fd in the steady-state driving state is set to a positive value. The driving force Fd in the decelerating driving state is set to a negative value. The driving force Fd in the decelerating driving state is synonymous with the braking force. A positive value of the driving force Fd is the value of the driving force Fd in the direction that accelerates the vehicle 10. A negative value of the driving force Fd is the value of the driving force Fd in the direction that decelerates the vehicle 10. The driving force Fd (braking force) in the deceleration state achieved by accelerator shutdown is generated, for example, by regenerative braking through the regenerative operation of the front motor 22 and the rear motor 32. It should be noted that when the power source is an engine, the braking force is generated by engine braking along with accelerator shutdown.

[0043] The following details the rear drive allocation when the snow mode is set as the control mode MODEcn.

[0044] A higher rear drive distribution of vehicle 10 results in higher straight-line stability. However, experimental results show that when the rear drive distribution increases beyond a certain level, it becomes difficult to improve straight-line stability, and handling tends to decrease. The load distribution (rear load distribution) in the rear drive axle 38 is generally set to around 30-45%. Therefore, when the rear drive distribution exceeds a certain level and approaches the rear load distribution, due to tire characteristics, the driving force Fd is biased towards the straight-line direction, and the holding force of the lateral swaying force decreases, making it difficult to improve straight-line stability. When straight-line stability increases, the tendency for understeer increases, and the initial steering response decreases, thus easily reducing handling. Moreover, when the rear drive distribution increases, the yaw motion of vehicle 10 increases after the start of a turn, leading to a tendency for oversteer, and cornering stability tends to decrease. It was found that even if the rear drive distribution does not increase beyond a certain level, as long as the rear drive force Fdr is output, tire slippage can be suppressed on low-μ roads, improving stability. In other words, a large rear-wheel drive distribution beyond a certain level is only needed in situations requiring off-road capability, such as starting or wheel-off states. It was discovered that under normal driving conditions, it is possible to balance stability and comfortable handling by setting the rear-wheel drive distribution below a certain level.

[0045] The "certain level" is, for example, half of the front drive distribution. It was found that in vehicle 10, under normal driving conditions, even if the rear drive distribution is less than half of the front drive distribution, stability can be ensured as long as it is in an AWD state that generates front drive force Fdf and rear drive force Fdr. It was also found that in vehicle 10, as long as the rear drive distribution is less than half of the front drive distribution, a decrease in handling can be suppressed. This insight is significant when driving on low-μ roads.

[0046] The electronic control unit 50 also includes a status determination unit 56 to control the rear drive distribution in snow mode.

[0047] The state determination unit 56 determines whether the snow mode has been set as the control mode MODEcn by the mode setting unit 54. The state determination unit 56 determines whether the vehicle 10 is in a stopped state based on whether the vehicle speed V is zero (determination value Vf). The state determination unit 56 determines whether the vehicle 10 is in a starting state based on whether it is in a driving state with the accelerator engaged and whether the vehicle speed V is less than the low vehicle speed determination value Vlow. The state determination unit 56 determines whether the vehicle 10 is in a normal driving state based on whether it is in a driving state other than a starting state.

[0048] When the state determination unit 56 determines that the snow mode is set as the control mode MODEcn, the drive control unit 52 continuously generates front drive force Fdf and rear drive force Fdr during the driving of the vehicle 10. Furthermore, in the normal driving state of the vehicle 10, the drive control unit 52 controls the front drive force Fdf and rear drive force Fdr such that the rear drive distribution is less than half of the front drive distribution. In other words, in the normal driving state of the vehicle 10, the drive control unit 52 controls the front drive force Fdf and rear drive force Fdr such that the rear drive distribution does not exceed half of the front drive distribution. For example, the rear drive distribution is set to 30% [%, and the "front drive distribution: rear drive distribution" is set to "70:30"]. The rear drive distribution is set to 15% [%, and the "front drive distribution: rear drive distribution" is set to "85:15".

[0049] When the state determination unit 56 determines that the snow mode is set as the control mode MODEcn, the drive control unit 52 controls the front drive force Fdf and the rear drive force Fdr in a manner that makes the rear drive distribution more than half the size of the front drive distribution when the vehicle 10 is in the starting state. For example, the rear drive distribution is set to 45% and the "front drive distribution: rear drive distribution" is set to "55:45".

[0050] The rear drive distribution control described above in snow mode controls the distribution of drive force between the front and rear wheels before the vehicle's behavior becomes unstable. The normal driving state of vehicle 10 is a state where the tires do not slip or lock up, and the vehicle's behavior does not become unstable. In other words, the normal driving state of vehicle 10 is the normal driving state before the vehicle's behavior becomes unstable.

[0051] Figure 2 This is a flowchart illustrating the main parts of the control operation of the electronic control device 50, and a flowchart illustrating the control operation used to ensure the stability of the vehicle 10 and suppress the reduction of handling during normal driving conditions, for example, being repeatedly executed.

[0052] exist Figure 2First, in step S10 (steps omitted below) corresponding to the function of the state determination unit 56, it is determined whether the snow mode is set as the control mode MODEcn. If the determination in S10 is negative, in step S20 (corresponding to the function of the drive control unit 52), the rear drive allocation is set to a setting under a control mode MODEcn other than the snow mode. If the determination in S10 is positive, in step S30 (corresponding to the function of the state determination unit 56), it is determined whether the vehicle 10 is in a stopped state. If the determination in S30 is positive, in step S40 (corresponding to the function of the drive control unit 52), the rear drive allocation setting is reset. If the determination in S30 is negative, in step S50 (corresponding to the function of the state determination unit 56), it is determined whether the vehicle 10 is in a starting state. If the determination in S50 is positive, in step S60 (corresponding to the function of the drive control unit 52), the front drive force Fdf and the rear drive force Fdr are generated. Furthermore, the rear drive allocation is set to a value greater than half the front drive allocation. For example, the rear drive distribution is set to 45% to 50%. If the determination in S50 is negative, in S70, which corresponds to the function of the state determination unit 56, it is determined whether the vehicle 10 is in a normal driving state. If the determination in S70 is negative, the routine ends. If the determination in S70 is positive, in S80, which corresponds to the function of the drive control unit 52, the front drive force Fdf and the rear drive force Fdr are generated. Otherwise, the rear drive distribution is set to a value less than half of the front drive distribution.

[0053] Figure 3 This diagram illustrates an example of rear-drive distribution settings in snow mode. Figure 3During the driving of vehicle 10, it is always set to AWD mode. This improves handling and stability. When vehicle 10 is starting, the rear drive distribution is set to a value greater than half the front drive distribution, for example, around 45-50%. This allows vehicle 10 to start powerfully and stably. During normal driving, the rear drive distribution is set to less than half the front drive distribution. In steady states other than cornering (such as straight driving and lane changes), the rear drive distribution is set to around 15%. This allows vehicle 10 to drive straight smoothly and steadily without swaying. Vehicle 10 has a good feel for the rear wheels 14 and can make stable lane changes. The transition from cornering to straight driving is smooth. During cornering in normal driving, the rear drive distribution is set to around 33%. This is particularly noticeable in the latter half of the corner when the accelerator is engaged. Handling is improved when the current drive force Fdf decreases during accelerator engagement. Therefore, in the latter half of a turn, compared to the steady state outside of the turn, the front drive distribution is reduced and the rear drive distribution is increased. This makes it easier to stay on the intended path while turning.

[0054] During deceleration accompanied by accelerator deactivation or brake activation, the load distribution in the front drive axle 28 (front load distribution) increases, making tire grip for steering more susceptible to damage on low-μ roads. It was found that increasing the rear drive distribution during deceleration compared to the steady-state distribution (during straight driving and lane changes) reduces the front drive distribution, thus facilitating tire grip in the steering direction. It was also found that increasing the rear drive distribution generates an anti-dive force that causes vehicle movement, thus effectively suppressing excessive pitching behavior and inhibiting the increase in front load distribution on low-μ roads. The anti-dive force is a force that reduces the nose dive phenomenon caused by the braking force acting on the rear wheels 14 and the load shifting to the front wheels 12, achieved through suspension characteristics. It is a force that lifts the vehicle body, particularly suppressing the lifting of the rear wheels 14. During deceleration, similarly to the steady-state, vehicle stability is ensured by maintaining the rear drive distribution at less than half of the front drive distribution. When the rear drive distribution increases excessively during deceleration, pitch behavior becomes difficult to produce, and the increased grip of the front wheels is barely perceptible. Therefore, the rear drive distribution is set to a maximum of half the front drive distribution. It was found that during deceleration, the rear drive distribution increases compared to steady-state conditions other than during cornering, and the rear drive distribution is set to less than half the front drive distribution, thereby ensuring stability, comfortable handling, and moderate pitch behavior during deceleration. Figure 3As shown, during deceleration in normal driving conditions (with the accelerator off), the rear drive distribution is set to, for example, around 20%. Therefore, vehicle 10 can decelerate with moderate pitch and a good sense of ground contact. Vehicle 10 can decelerate in a stable state with easy steering. When vehicle 10 changes from deceleration to cornering, the transition from accelerator off to accelerator on is smooth.

[0055] When the state determination unit 56 determines that the snow mode is set as the control mode MODEcn, the drive control unit 52 controls the front drive force Fdf and the rear drive force Fdr in a manner that increases the rear drive distribution during deceleration compared to the rear drive distribution in a steady state, under normal driving conditions. However, when the drive control unit 52 is in a turning position while in a steady state under normal driving conditions, it controls the front drive force Fdf and the rear drive force Fdr in a manner that increases the rear drive distribution during turning compared to the rear drive distribution in a steady state other than during a turning. In this case, the drive control unit 52 controls the front drive force Fdf and the rear drive force Fdr in a manner that increases the rear drive distribution during turning compared to the rear drive distribution during deceleration, under normal driving conditions.

[0056] Figure 4 This is a diagram illustrating an example of the relationship between axle load distribution and front-rear acceleration Gx during deceleration. Figure 4In this context, axle load distribution represents the front load distribution and rear load distribution. Deceleration acceleration represents the absolute value of the front and rear acceleration Gx during deceleration. The vehicle shown by the solid line [1] has a "front load distribution: rear load distribution" of "50:50" when stationary. The vehicle shown by the dashed line [2] has a "front load distribution: rear load distribution" of "55:45" when stationary. The vehicle shown by the double-dotted line [3] has a "front load distribution: rear load distribution" of "60:40" when stationary. On low-μ roads, changes occur in the portion enclosed by the single-dotted line, for example, when the accelerator is closed and the brake is open, due to deceleration. In vehicle [3], the front load distribution during deceleration reaches, for example, 70% [%,] and the grip of the front wheels 12 is easily saturated, leading to a tendency for understeer where steering becomes difficult to take effect. Therefore, during deceleration, when the front drive distribution is reduced and the rear drive distribution is increased compared to the steady state other than during cornering, it is easier to ensure stability, comfortable handling, and moderate pitch behavior during deceleration. In cold regions, such as on low-μ roads, there is a tendency for understeer, which needs to be considered. The same applies to vehicles [1] and [2] that are prone to excessive front load distribution during deceleration. On the other hand, in vehicle [3], the rear load distribution drops to around 30% for example. Therefore, during deceleration, when the rear drive distribution is excessively increased, the rear wheel 14 is prone to slippage, and there is a tendency for oversteer. Therefore, during deceleration, it is appropriate to maintain an upper limit of the rear drive distribution that ensures stability and increase the rear drive distribution.

[0057] When the state determination unit 56 determines that the vehicle 10 is in a normal driving state, it determines whether the vehicle is turning, not turning (driving straight, changing lanes, etc.), or decelerating. For example, the state determination unit 56 determines whether the vehicle 10 is in a steady state based on whether it is in a driving state with the accelerator engaged and whether the vehicle speed V is greater than or equal to the low vehicle speed determination value Vlow. When the state determination unit 56 determines that the vehicle 10 is in a steady state, it determines whether the vehicle 10 is turning or not turning based on the steering angle θsw, steering direction Dsw, lateral acceleration Gy, and yaw rate Ryaw. The state determination unit 56 determines whether the vehicle 10 is decelerating based on the accelerator opening θacc, brake operation amount θbp, and longitudinal acceleration Gx.

[0058] Figure 5 This is a flowchart illustrating the main parts of the control operation of the electronic control device 50. It is a flowchart illustrating the control operation used to ensure the stability of the vehicle 10 and suppress the reduction of handling during driving in normal driving conditions, and is repeatedly executed, for example. Figure 5 Yes Figure 2 The flowchart illustrates the control operation in S80.

[0059] exist Figure 5 First, in S81, corresponding to the function of the state determination unit 56, it is determined whether the vehicle 10 is in a steady state and not in a turning position. If the determination in S81 is affirmative, in S82, corresponding to the function of the drive control unit 52, the front drive force Fdf and the rear drive force Fdr are generated. Furthermore, the rear drive distribution is set to a value less than half of the front drive distribution, for example, A [%] (see reference). Figure 3 15% of the above. If the judgment in S81 is denied, in S83, which corresponds to the function of the state determination unit 56, it is determined whether the vehicle 10 is decelerating. If the judgment in S83 is affirmed, in S84, which corresponds to the function of the drive control unit 52, the front drive force Fdf and the rear drive force Fdr are generated. In addition, the rear drive distribution is set to a value larger than the rear drive distribution except during cornering, for example, B% (>A%), and is set to a value less than half of the front drive distribution (see reference). Figure 3 (20% of the above) If the judgment in S83 is denied, in S85 corresponding to the function of the state determination unit 56, it is determined whether the vehicle 10 is in a steady state and turning. If the judgment in S85 is denied, the routine ends. If the judgment in S85 is affirmative, in S86 corresponding to the function of the drive control unit 52, the front drive force Fdf and the rear drive force Fdr are generated. In addition, the rear drive distribution is set to a value larger than the rear drive distribution during turning and deceleration, for example, C% (>B%), and is set to a value less than half of the front drive distribution (see reference). Figure 3 33% of the total.

[0060] As described above, according to this embodiment, when the snow mode is set as the control mode MODEcn, a front drive force Fdf and a rear drive force Fdr are always generated during the driving of the vehicle 10. Furthermore, under normal driving conditions of the vehicle 10, the front drive force Fdf and the rear drive force Fdr are controlled such that the rear drive distribution is less than half of the front drive distribution. In other words, under normal driving conditions of the vehicle 10, the front drive force Fdf and the rear drive force Fdr are controlled such that the rear drive distribution does not exceed half of the front drive distribution. Therefore, the stability of the vehicle 10 can be ensured and the reduction in handling can be suppressed during normal driving conditions on low-μ roads.

[0061] Furthermore, according to this embodiment, under normal driving conditions with snow mode set, the front drive force Fdf and rear drive force Fdr are controlled such that the rear drive distribution during deceleration is greater than the rear drive distribution in steady state. Therefore, a suitable balance between vehicle stability and handling can be achieved during normal driving conditions on low-μ roads.

[0062] Furthermore, according to this embodiment, under normal driving conditions with snow mode set, when both in a steady state and turning, the front drive force Fdf and rear drive force Fdr are controlled such that the rear drive distribution during turning is greater than the rear drive distribution in a steady state other than during turning. Thus, a suitable balance between vehicle stability and handling can be achieved during normal driving conditions on low-μ roads.

[0063] Furthermore, according to this embodiment, under normal driving conditions with the snow mode set, the front drive force Fdf and rear drive force Fdr are controlled such that the rear drive distribution during cornering is greater than the rear drive distribution during deceleration. Therefore, a suitable balance between vehicle stability and handling can be achieved during normal driving conditions on low-μ roads.

[0064] Furthermore, according to this embodiment, during the start-up state with snow mode set, the front drive force Fdf and rear drive force Fdr are controlled such that the rear drive distribution is half the size of the front drive distribution. This suppresses tire slippage during start-up on low-μ roads.

[0065] Furthermore, according to this embodiment, the vehicle 10 is an AWD vehicle powered by electricity, thus suppressing the reduction in energy efficiency when it is always set to AWD mode.

[0066] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention can also be applied to other solutions.

[0067] For example, in the above embodiments, multiple predetermined control modes MODEcnf are used as control mode MODEcn. The predetermined control mode MODEcnf includes a snow mode. When snow mode is set, the vehicle 10 is always in AWD mode during driving, and in the normal driving state of the vehicle 10, the front drive force Fdf and rear drive force Fdr are controlled in a manner where the rear drive distribution is less than half of the front drive distribution. However, this is not a limitation. For example, a predetermined control mode MODEcn could also be used. When the predetermined control mode is set to a control mode that enables stable driving on low-μ roads, the vehicle 10 is always in AWD mode during driving, and in the normal driving state of the vehicle 10, the front drive force Fdf and rear drive force Fdr are controlled in a manner where the rear drive distribution is less than half of the front drive distribution. Thus, a balance between the stability and handling of the vehicle 10 can be achieved during normal driving on low-μ roads. Furthermore, in the above-described case, the rear drive distribution for each of the following conditions—turning, steady state (other than turning), and deceleration—is set in the same manner as in the above embodiment, under normal driving conditions. This allows for a proper balance between vehicle stability and handling during normal driving on low-μ roads. Moreover, in the above-described case, the vehicle 10 is always in AWD mode while driving, and during vehicle start-up, the front drive force Fdf and rear drive force Fdr are controlled such that the rear drive distribution is half the size of the front drive distribution. This suppresses tire slippage during start-up on low-μ roads.

[0068] Furthermore, in the above embodiments, the rear drive allocation is set differently in steady state between turning and other situations (such as going straight, lane changing, etc.), but this approach is not limited to this one. For example, the rear drive allocation in steady state may not be differentiated between turning and other situations. In the case of no differentiation, the rear drive allocation in steady state is set to the rear drive allocation for situations other than turning. In this case, Figure 5 In step S81 of the flowchart, a determination is made as to whether the state is in a steady state, including both during a turn and other steady states. Furthermore, it is not necessary to have... Figure 5 S85 and S86 in the flowchart.

[0069] Furthermore, in the above embodiments, the control mode MODEcn can be automatically set based on the driving status of the vehicle 10, the external environment of the vehicle 10, etc.

[0070] Furthermore, in the above embodiments, the power source driving the front wheels 12 can be, for example, an internal combustion engine instead of the front motor 22, or an internal combustion engine in addition to the front motor 22. Similarly, the power source driving the rear wheels 14 can be, for example, an internal combustion engine instead of the rear motor 32, or an internal combustion engine in addition to the rear motor 32. Alternatively, the vehicle 10 can be, for example, a vehicle with an in-wheel motor configuration, equipped with an electric motor that individually drives either the front wheels 12 or the rear wheels 14. Alternatively, the vehicle 10 can be, for example, an AWD vehicle that distributes power to the other wheel via an electronically controlled coupling, based on the drive of one of the front wheels 12 and the rear wheels 14. In short, the present invention can be applied to any AWD vehicle that allows adjustment of the drive distribution between the front wheels 12 and the rear wheels 14.

[0071] It should be noted that the above content is only one implementation method, and the present invention can be implemented with various changes and improvements based on the knowledge of those skilled in the art.

Claims

1. A vehicle drive force control device (50) for controlling the drive force Fd of an all-wheel drive vehicle (10), characterized in that, The vehicle drive force control device (50) includes a drive control unit (52), which is configured to: The system has multiple specified control modes MODEcn or one specified control mode MODEcn as the control mode MODEcn for controlling the all-wheel drive vehicle (10). In the case of having multiple specified control modes MODEcn, the specified control mode MODEcn includes a low-friction road surface control mode suitable for driving on low-friction road surfaces. In the case of having only one specified control mode MODEcn, the specified control mode MODEcn is set as the low-friction road surface control mode. In the low-friction road surface control mode, during the driving of the all-wheel drive vehicle (10), a front wheel driving force Fdf that drives the front wheel (12) and a rear wheel driving force Fdr that drives the rear wheel (14) are always generated. The front wheel driving force Fdf and the rear wheel driving force Fdr are controlled in a manner that the rear wheel distribution ratio Fdr / Fd is less than half of the front wheel distribution ratio Fdf / Fd, which is the normal driving state other than the starting state. The rear wheel distribution ratio Fdr / Fd is the ratio of the rear wheel driving force Fdr to the total driving force Fd obtained by adding the front wheel driving force Fdf and the rear wheel driving force Fdr, and the front wheel distribution ratio Fdf / Fd is the ratio of the front wheel driving force Fdf to the total driving force Fd.

2. The vehicle drive force control device (50) according to claim 1, characterized in that, In the normal driving state of the low-friction road surface control mode, the drive control unit (52) controls the front wheel drive force Fdf and the rear wheel drive force Fdr in such a way that the rear wheel distribution ratio Fdr / Fd during deceleration is greater than the rear wheel distribution ratio Fdr / Fd in the steady state of constant speed driving or acceleration driving.

3. The vehicle drive force control device (50) according to claim 2, characterized in that, In the normal driving state of the low-friction road surface control mode, when both in the steady state and turning, the drive control unit (52) controls the front wheel drive force Fdf and the rear wheel drive force Fdr in such a way that the rear wheel distribution ratio Fdr / Fd during the turn is greater than the rear wheel distribution ratio Fdr / Fd in the steady state other than during the turn.

4. The vehicle drive force control device (50) according to claim 3, characterized in that, In the normal driving state of the low-friction road surface control mode, the drive control unit (52) controls the front wheel drive force Fdf and the rear wheel drive force Fdr in such a way that the rear wheel distribution ratio Fdr / Fd during turning is greater than the rear wheel distribution ratio Fdr / Fd during deceleration.

5. The vehicle drive force control device (50) according to any one of claims 1 to 4, characterized in that, In the starting state of the low-friction road surface control mode, the drive control unit (52) controls the front wheel drive force Fdf and the rear wheel drive force Fdr in such a way that the rear wheel distribution ratio Fdr / Fd is greater than half of the front wheel distribution ratio Fdf / Fd.

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