JP5088255B2 - Vehicle motion control system - Google Patents

Description

  The present invention relates to a vehicle motion control system, and more specifically, a vehicle motion control system capable of maintaining the durability of a driving force distribution control device with respect to a dynamic load in a configuration in which a driving force distribution control device and a braking force control device cooperate. About.

  Recent vehicle motion control systems include a driving force distribution control device that can control the driving force distribution to the left and right drive wheels. This drive force distribution control device has a control differential, and controls the drive force distribution to the left and right drive wheels by actively providing a left-right difference in the differential output shaft speed (drive force distribution control). As a conventional vehicle motion control system that employs such a configuration, a technique described in Patent Document 1 is known.

Japanese Patent No. 2848126

  Also, recent vehicle motion control systems have a braking force control device that controls the braking force for each wheel. This braking force control device independently and actively controls the braking force on each wheel according to the moment of the entire vehicle and the slip speed of each wheel (braking force control). Thereby, an ABS (Antilock Brake System) function, a brake assist function, a TRC (Traction Control System) function, a VSC (Vehicle Stability Control) function, and the like are realized.

  However, if the driving force distribution control and the braking force control are performed in parallel, the wheel speed difference between the left and right drive wheels may be outside the design range of the driving force distribution control device (control differential). Then, the torque movement to the left and right drive wheels is not performed as designed, and the target vehicle motion (yaw rate, lateral acceleration, etc.) may not be achieved. Further, when the rotation speed ratio between the left and right drive wheels is outside the design range, the durability of the driving force distribution control device may be deteriorated (lifetime may be shortened).

  In such a problem, in the conventional vehicle motion control system, the durability of the driving force distribution control device is maintained against a static load, but cannot be maintained against a dynamic load. For example, when there is a possibility that the vehicle will fall into a sudden spin, a strong braking force is applied to the wheels on the outer side in the turning direction. Then, due to this braking force (transient external force), the wheel speed difference between the left and right drive wheels is outside the design range of the drive force distribution control device, and the durability of the drive force distribution control device may be deteriorated.

  Therefore, the present invention has been made in view of the above, and a vehicle capable of maintaining the durability of the driving force distribution control device against a dynamic load in a configuration in which the driving force distribution control device and the braking force control device cooperate. An object is to provide a motion control system.

  In order to achieve the above object, a vehicle motion control system according to the present invention provides a driving force distribution control device capable of applying driving force to left and right wheels and controlling driving force distribution to left and right driving wheels, and a control for each driving wheel. And a braking force control device capable of independently controlling power, and a vehicle motion control system in which the driving force distribution control device and the braking force control device cooperate to perform vehicle motion control. When in the steer state, the driving force distribution control device stops the driving force distribution control and the braking force control device performs the braking force control.

  In this vehicle motion control system, it is predicted in advance that the wheel speed difference between the left and right drive wheels is outside the design range of the drive force distribution control device, and the drive force distribution control is stopped. Therefore, the use of the control differential can be prevented quickly when greatly different driving force command values are issued between the left and right driving wheels. This has the advantage that the influence on the durability of the control differential is reduced. Further, since the braking force control is performed, there is an advantage that the behavior stability of the vehicle is ensured.

  In the vehicle motion control system according to the present invention, the counter steer state of the vehicle is determined by comparing a ratio between the steering angle of the vehicle and the converted value of the lateral acceleration with a predetermined threshold value.

  In the vehicle motion control system according to the present invention, there is an advantage that it is appropriately predicted that the difference between the left and right wheel speeds is outside the design range.

  In the vehicle motion control system according to the present invention, it is predicted in advance that the wheel speed difference between the left and right driving wheels is outside the design range of the driving force distribution control device, and the driving force distribution control is stopped. Therefore, the use of the control differential can be prevented quickly when greatly different driving force command values are issued between the left and right driving wheels. This has the advantage that the influence on the durability of the control differential is reduced. Further, since the braking force control is performed, there is an advantage that the behavior stability of the vehicle is ensured.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Further, the constituent elements of this embodiment include those that can be replaced while maintaining the identity of the invention and that are obvious for replacement. In addition, a plurality of modifications described in this embodiment can be arbitrarily combined within a range obvious to those skilled in the art.

  FIG. 1 is a block diagram showing a vehicle motion control system according to an embodiment of the present invention. FIG. 2 is a flowchart showing the operation of the vehicle motion control system shown in FIG.

[Vehicle motion control system]
The vehicle motion control system 1 controls the motion or behavior of the vehicle 10 (hereinafter referred to as vehicle motion control) to prevent the vehicle 10 from spinning, drifting out, wheel slipping, and the like. The vehicle motion control system 1 includes a driving force distribution control device 2, a braking force control device 3, and a control system 4 (see FIG. 1). In this embodiment, the vehicle 10 adopts the FR (Front engine Rear drive) type, and the left rear wheel 11RL and the right rear wheel 11RR of the vehicle 10 are drive wheels of the vehicle 10, and the left front wheel 11FL and the right side The front wheels 11FR are the steering wheels of the vehicle 10.

  The driving force distribution control device 2 is a device that distributes the driving force to the left and right driving wheels 11 RR and 11 RL, and includes, for example, a control differential 21. In the driving force distribution control device 2, when the engine 12 generates driving force, the driving force is transmitted to the control differential 21 through the transmission (reduction gear) 13, the propeller shaft 14 and the viscous coupling 15. Then, this driving force is distributed to the left and right drive shafts 22RR, 22RL by the control differential 21, and transmitted to the drive wheels 11RR, 11RL. At this time, the distribution ratio (torque difference) of the driving force with respect to each driving wheel 11RR, 11RL is controlled (driving force distribution control). In this embodiment, the driving force distribution control device 2 is disposed only on the rear wheels 11RR and 11RL of the vehicle 10. However, the present invention is not limited to this, and in a configuration in which the left and right of the rolling wheels 11FR and 11FL are coupled by shafts, the driving force distribution control device 2 may be installed on the rolling wheels 11FR and 11FL.

  The braking force control device 3 is a device that controls the braking force applied to the wheels 11FR to 11RL, and includes a hydraulic circuit 31, wheel cylinders 32FR to 32RL, a brake pedal 33, and a master cylinder 34. The hydraulic circuit 31 includes a reservoir, an oil pump, various valves, and the like (not shown). The braking force control device 3 applies a braking force to the wheels 11FR to 11RL as follows. That is, (1) during normal operation, when the brake pedal 33 is depressed by the driver, the depression amount is transmitted to the hydraulic circuit 31 via the master cylinder 34. The hydraulic circuit 31 adjusts the hydraulic pressures of the wheel cylinders 32FR to 32RL, so that the wheel cylinders 32FR to 32RL are driven to apply a braking force (braking pressure) to the wheels 11FR to 11RL. On the other hand, at the time of (2) vehicle motion control, the target braking force for each wheel 11FR to 11RL is calculated based on the motion state of the vehicle, and the hydraulic circuit 31 is driven based on this target braking force, and each wheel cylinder 32FR to 32RL. Is controlled (braking force control). By this vehicle motion control, an ABS (Antilock Brake System) function, a brake assist function, a TRC (Traction Control System) function, a VSC (Vehicle Stability Control) function, and the like of the vehicle 10 are realized.

  The control system 4 includes an ECU (Electronic Control Unit) 41, wheel speed sensors 42FR to 42RL that detect wheel speeds of the wheels 11FR to 11RL, a steering angle sensor 43 that detects a steering angle, and a yaw rate sensor that detects a yaw rate. 44, a longitudinal acceleration sensor 45 that detects longitudinal acceleration, a lateral acceleration sensor 46 that detects lateral acceleration, a vehicle speed sensor 47 that detects vehicle speed, an accelerator opening sensor 48, and a brake pedal force sensor 49. In the control system 4, the ECU 41 drives the engine 12, the driving force distribution control device 2, and the braking force control device 3 based on the detection results of the sensors 42 to 49. Thereby, total driving force control by the engine 12, driving force distribution control by the driving force distribution control device 2, and braking force control by the braking force control device 3 are performed, and vehicle motion control is performed.

[Vehicle motion control]
In general, in a configuration in which driving force distribution control and braking force control are used in combination, durability (life) of the control differential 21 may be deteriorated when an instantaneous dynamic load is applied to the control differential 21. For example, when a sudden vehicle behavior such as spin or drift out occurs, braking force control is performed to suppress the vehicle behavior. Then, a transient torque input is applied to the control differential 21, and the durability of the control differential 21 is deteriorated.

Therefore, in the vehicle motion control system 1, vehicle motion control is performed as follows (see FIG. 2). First, target braking / driving forces of the wheels 11FR to 11RL are calculated (ST1). The target braking / driving forces of the wheels 11FR to 11RL are calculated based on the steering angle of the vehicle 10, the accelerator opening, the brake pedaling force, and the like. Next, the difference | VwRR−VwRL | between the wheel speeds VwRR and VwRL of the left and right drive wheels 11RR and 11RL is calculated (ST2). Next, it is determined whether or not the wheel speed difference | VwRR−VwRL | is outside the design range of the driving force distribution control device 2 (ST3). For example, if the design range (limit) of the wheel speed difference | VwRR−VwRL | is within t [%], the success or failure of the following formula (1) is determined.

| VwRR−VwRL | ≦ Min (VwRR, VwRL) × t × 0.01 (1)

If Formula (1) is satisfied, it is determined that the wheel speed difference | VwRR−VwRL | is within the design range. If Formula (1) is not satisfied, the wheel speed difference | VwRR−VwRL | Determined to be out of range.

Next, when the wheel speed difference | VwRR−VwRL | is within the design range, it is determined whether or not the vehicle 10 is in an oversteer state (ST4). In this determination step, the target yaw rate γ * of the vehicle is compared with the actual yaw rate γ. The actual yaw rate γ is an output value of the yaw rate sensor 44. Specifically, assuming that the left turn of the vehicle is positive (+) and the hysteresis is k, the success or failure of the following equation (2) is determined when turning left, and the success or failure of the following equation (3) is determined when turning right. Determined.

When turning left: γ * + k <γ (2)
When turning right: γ <γ * -k (3)

When Formula (2) or Formula (3) is established, it is determined that the vehicle 10 is in an oversteer state (a strong oversteer suppression command is issued).

The target yaw rate γ * is calculated by, for example, the following formula (4). Here, n is a steering gear ratio, L is a wheel base, Kh is a stability factor, V is a vehicle body speed, and δ is a steering angle.

Formula (4)

Next, in the above determination step ST4, if it is determined that the vehicle 10 is not in the oversteer state, whether or not the wheel speed difference | VwRR−VwRL | on the left and right is predicted to be outside the design range. Is determined (ST5). In this determination step ST5, first, the output value (lateral acceleration Gy) of the lateral acceleration sensor 46 is converted into a steering angle δ_gy (Str_gy). At this time, the following conversion formula (5) is used. Where n is the steering gear ratio, L is the wheel base, Kh is the stability factor, and V is the vehicle speed.

δ_gy = {n · L (1 + Kh · V) ^ 2 / V ^ 2} · Gy (5)

Next, the steering angle δ_gy and the steering angle δ are compared using the following equation (6). The constant k is set to k = 0.5, for example.

δ / δ_gy <k (6)

When Formula (6) is established, it is determined that the countersteer is applied by the driver. That is, when the steering angle δ_gy and the steering angle δ are defined with the left turning direction of the vehicle 10 as positive, the ratio between the steering angle δ and the converted value (steer angle δ_gy) of the lateral acceleration Gy when the vehicle 10 turns left. When δ / δ_gy is smaller than the predetermined threshold k, it is determined that the countersteer is applied by the driver. In this case, the left and right wheel speed difference | VwRR−VwRL | is predicted to be outside the design range.

  Next, in the determination step ST5, when it is determined that the left and right wheel speed difference | VwRR−VwRL | is predicted to be outside the design range, the target braking / driving forces of the wheels 11FR to 11RL are determined. Based on the above, total driving force control by the engine 12, driving force distribution control by the driving force distribution control device 2, and braking force control by the braking force control device 3 are performed (ST6). These controls are performed as follows, for example.

(1) The total driving force target of the engine 12 is not less than the minimum driving force d, and the target left / right difference between the left and right driving wheels 11RR and 11RL (the driving force FxRR of the right rear wheel 11RR and the driving force FxRL of the left rear wheel 11RL) When the difference is within the allowable design value c of the driving force distribution control device 2 (| FxRR−FxRL | ≦ c), the target braking / driving force is distributed as follows.
Total driving force control: FxRR + FxRL
Driving force distribution control: right rear wheel FxRR and left rear wheel FxRL
Braking force control: Right rear wheel 0 and left rear wheel 0

(2) When the total driving force target of the engine 12 is equal to or greater than the minimum driving force d and the target left / right difference between the left and right driving wheels 11RR and 11RL is larger than the allowable design value c (| FxRR−FxRL |> c) The target braking / driving force is distributed as follows.
Total driving force control: FxRR + FxRL + | FxRR−FxRL | −c
Driving force distribution control: c
Braking force control: When FxRR> FxRL,
Right rear wheel 0 and left rear wheel-(FxRR-FxRL-c)
If FxRR <FxRL,
Right rear wheel-(FxRL-FxRR-c) and left rear wheel 0

(3) When the total driving force target of the engine 12 is less than the minimum driving force d, the target braking / driving force is distributed as follows.
Total driving force control: 0
Driving force distribution control: 0
Braking force control: Right rear wheel Min (0, FxRR) and left rear wheel Min (0, FxRL)

  On the other hand, when it is determined in the determination step ST3 that the wheel speed difference | VwRR−VwRL | between the left and right drive wheels 11RR and 11RL is outside the design range of the drive force distribution control device 2, a transient torque input is performed. It is necessary to protect the control differential 21 from the above. Therefore, the driving force distribution control by the driving force distribution control device 2 is stopped, and only the total driving force control by the engine 12 and the braking force control by the braking force control device 3 are performed (ST7).

  In general, when the vehicle 10 is in an oversteer state, braking force control by a braking force control device is performed to stabilize the movement of the vehicle 10. For example, when there is a possibility that the vehicle will fall into a sudden spin, a large braking force (correction moment) is applied to the wheels on the outer side in the turning direction. Then, this braking force (transient external force) tends to increase the wheel speed difference | VwRR−VwRL | between the left and right drive wheels 11RR and 11RL. Therefore, when the vehicle 10 is in the oversteer state, it can be predicted that the wheel speed difference | VwRR−VwRL | between the left and right drive wheels 11RR and 11RL is outside the design range of the drive force distribution control device 2.

  Therefore, even when it is determined in the determination step ST4 that the vehicle 10 is in the oversteer state, the driving force distribution control by the driving force distribution control device 2 is stopped and the engine 12 is protected in order to protect the control differential 21. Only the total driving force control and the braking force control by the braking force control device 3 are performed (ST7).

  In general, the driver applies counter-steer by detecting an oversteer state of the vehicle. However, a driver who has mastered operation often applies counter-steer by predicting in advance that the vehicle will fall into an oversteer state based on steering operation, accelerator operation, or vehicle yaw rate tracking. Further, when traveling on a circuit or the like, an oversteer state of the vehicle may be intentionally caused by an accelerator operation or a steering operation in order to change the direction of the vehicle. At this time, the driver applies counter-steer to adjust the direction of the vehicle. However, in these cases, strong spin behavior is often induced. That is, when the counter steer is inappropriate, such as when the driver's counter steer timing is late or the counter steer amount is small, a sudden spin behavior occurs in the vehicle. Then, braking force control such as VSC is performed, and a strong braking force is applied to one wheel. Therefore, it can be predicted that the wheel speed difference between the left and right wheels will be outside the design range of the control differential under the situation where the countersteer is applied by the driver.

  Therefore, in the determination step 5, even when the wheel speed difference | VwRR−VwRL | is predicted to be out of the design range by the driver's counter steering, the driving force distribution control by the driving force distribution control device 2 is stopped. Then, only the total driving force control by the engine 12 and the braking force control by the braking force control device 3 are performed (ST7).

In this embodiment, the total driving force control and the braking force control (ST7) are performed as follows. First, (1) when the total driving force target of the engine 12 is equal to or greater than the minimum driving force d, the target braking / driving force is distributed as follows.
Total driving force control: FxRR + FxRL + | FxRR-FxRL |
Braking force control: When FxRR> FxRL,
Right rear wheel 0 and left rear wheel-(FxRR-FxRL)
If FxRR <FxRL,
Right rear wheel-(FxRL-FxRR) and left rear wheel 0

(2) When the total driving force target of the engine 12 is less than the minimum driving force d, the target braking / driving force is distributed as follows.
Total driving force control: 0
Braking force control: Right rear wheel Min (0, FxRR) and left rear wheel Min (0, FxRL)

[effect]
As described above, in the vehicle motion control system 1, when the vehicle 10 is in the counter steer state (the counter steer is applied by the driver), the driving force distribution control device 2 stops the driving force distribution control. At the same time, the braking force control device 3 performs braking force control (ST5 and ST7) (see FIG. 2). In such a configuration, it is predicted in advance that the wheel speed difference | VwRR−VwRL | between the left and right drive wheels 11RR and 11RL is outside the design range of the drive force distribution control device 2, and the drive force distribution control is stopped. Therefore, the use of the control differential 21 can be prevented quickly when greatly different driving force command values are issued between the left and right driving wheels 11RR, 11RL. Thereby, there exists an advantage by which the influence on the durability of the control differential 21 is reduced. Moreover, since braking force control is performed, there exists an advantage by which the behavior stability of the vehicle 10 is ensured. In particular, the above-described configuration allows the advance time to stop the driving force distribution control for a driver who is familiar with the operation (a driver who can predict that the vehicle will fall into an oversteer state and apply a countersteer). It is very useful in terms of making money. For example, in the configuration in which the driving force distribution control is stopped after detecting the oversteer state of the vehicle, it is not possible to sufficiently obtain the advance time for stopping the driving force distribution control.

  In the vehicle motion control system 1 according to the present invention, the ratio δ / δ_gy between the steering angle δ and the converted value of the lateral acceleration Gy (steer angle δ_gy) is compared with a predetermined threshold k when the vehicle 10 turns left. Thus, the counter steer state of the vehicle 10 is determined (ST5). Accordingly, there is an advantage that the difference between the left and right wheel speeds | VwRR−VwRL | can be appropriately predicted to be out of the design range.

  As described above, the vehicle motion control system according to the present invention is useful in that the durability of the driving force distribution control device with respect to dynamic load can be maintained in the configuration in which the driving force distribution control device and the braking force control device cooperate. It is.

It is a block diagram which shows the vehicle motion control system concerning the Example of this invention. It is a flowchart which shows the effect | action of the vehicle motion control system described in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vehicle motion control system 2 Driving force distribution control device 21 Control differential 22RR, 22RL Drive shaft 3 Braking force control device 31 Hydraulic circuit 32FR-32RR Wheel cylinder 33 Brake pedal 34 Master cylinder 4 Control system 10 Vehicle 11FR-11RL Wheel 12 Engine 14 Propeller shaft 15 Viscous couplings 42FR to 42RL Wheel speed sensor 43 Steering angle sensor 44 Yaw rate sensor 45 Longitudinal acceleration sensor 46 Lateral acceleration sensor 47 Vehicle speed sensor 48 Accelerator opening sensor 49 Brake pedal force sensor

Claims (2)

A driving force distribution control device capable of applying driving force to the left and right wheels and controlling the driving force distribution to the left and right driving wheels; and a braking force control device capable of independently controlling the braking force of each driving wheel; A vehicle motion control system in which a driving force distribution control device and the braking force control device cooperate to perform vehicle motion control,
A vehicle motion control system in which the driving force distribution control device stops driving force distribution control and the braking force control device performs braking force control when the vehicle is in a counter-steer state.   The vehicle motion control system according to claim 1, wherein a counter steer state of the vehicle is determined by comparing a ratio between a steering angle of the vehicle and a converted value of lateral acceleration with a predetermined threshold.

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