JPH05319124A - Running control device for four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To provide sufficient running stability at turning a vehicle by giving respective wheels brake torque based on slip ratio differences among respective wheels so as to distribute torque to respective wheels, and providing a torque distribution control means to control a torque distribution changing means based on the above torque distribution. CONSTITUTION:Distribution of driving torque is performed according to slip ratio differences of respective wheels 6, 7, 8, 9. Namely, turning condition is judged, slip ratio differences of respective wheels are obtained by considering difference of loci and side slip angles due to wheel positions in this turning condition, and torque is distributed so as to eliminate slip ratio difference at each wheel. Slip ratio difference (s-w) generated at each wheel 6, 7, 8, 9 is obtained from the formula I. In the formula I, WV is wheel speed of each wheel, V is target mobility of each wheel, and -w is the position of each wheel, namely in response to right and left front wheel and right and left rear wheel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive control device for a four-wheel drive vehicle, and more particularly to a drive control device for a four-wheel drive vehicle that performs slip control by controlling the drive torque distribution to the four wheels.

[0002]

2. Description of the Related Art In a four-wheel drive vehicle in which front, rear, left, and right wheels are driven by engine output, the torque distribution of each wheel is not always made equal, but variably controlled according to the operating condition. 4 to perform the torque distribution control
A travel control device for a wheel drive vehicle is generally known.

For example, Japanese Patent Application Laid-Open No. 63-151523 discloses a technique for distributing torque of a vehicle in accordance with the sideslip angle of the vehicle. That is, the one disclosed in this publication obtains the vehicle running state related to the sideslip angle of the vehicle from the acceleration generated in the vehicle and the yaw rate, and the front and rear wheels of the vehicle are set so that the vehicle running state is within a predetermined range. By distributing the driving force to the vehicle, the running stability when the vehicle turns is improved.

[0004]

However, at the time of actual turning of the vehicle, the running locus of each wheel depends on the wheel position,
The sideslip angle of each wheel is different, and the relationship between the apparent slip ratio difference and the actual load on the wheel is different. Therefore, if the torque distribution of the vehicle is simply performed in accordance with only the sideslip angle of the vehicle as in the above-mentioned conventional technique, it is not sufficient to obtain the traveling stability during turning of the vehicle, and the above points are taken into consideration. There is a need.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and calculates the slip ratio difference of each wheel from the running locus of each wheel of the vehicle and the sideslip angle of each wheel. By providing torque distribution to each wheel so that the slip ratio difference between the wheels is zero, it is possible to provide a travel control device for a four-wheel drive vehicle that can obtain sufficient travel stability when the vehicle turns. Has a purpose.

[0006]

In order to achieve the above object, the present invention relates to a traveling control device for a four-wheel drive vehicle in which four wheels in front, back, left and right of the vehicle are driven by engine output. Torque distribution changing means for controlling the amount of transmission of engine output to change the distribution of drive torque to the four wheels, a steering angle sensor for detecting a steering angle, a wheel speed sensor for detecting a wheel speed of each wheel, and a vehicle body. A vehicle speed detecting means for detecting the speed, a yaw rate sensor for detecting the yaw rate of the vehicle, a turning radius of the vehicle is calculated from the steering angle and the vehicle speed, and sideslip angles of the front wheels and the rear wheels are calculated from the yaw rate, respectively. Target moving speed calculation means for calculating a target moving speed of each wheel from a turning radius of the vehicle and sideslip angles of front wheels and rear wheels;
Slip ratio difference calculating means for calculating the slip ratio difference of each wheel from the target moving speed of each wheel and each wheel speed detected by the wheel speed sensor, and each wheel based on the slip ratio difference of each wheel. A torque distribution control unit that distributes torque to each wheel by applying a braking torque and controls the torque distribution changing unit based on the torque distribution.

In the present invention, the target speed calculating means may calculate the target moving speed without considering the sideslip angles of the wheels when the vehicle is traveling at an extremely low speed. Further, in the present invention, the target moving speed calculating means may have a correcting means for smoothing the target moving speed in the connected travel area during extremely low speed traveling and during traveling other than extremely low speed.

In the present invention constructed as described above, first, the target moving speed calculation means calculates the turning radius of the vehicle from the steering angle and the vehicle speed, and the sideslip angles of the front and rear wheels from the yaw rate. Then, the target moving speed of each wheel is calculated from the turning radius of these vehicles and the sideslip angles of the front wheels and the rear wheels, and the target moving speed of each wheel and each wheel detected by the wheel speed sensor are calculated by the slip ratio difference calculating means. The slip rate difference of each wheel is calculated from the speed. Next, the torque distribution control means distributes the torque to each wheel by applying a braking torque to each wheel based on the slip ratio difference between the wheels, and the torque distribution changing means is controlled based on this torque distribution.

As described above, according to the present invention, the slip ratio difference of each wheel is calculated from the running locus of each wheel of the vehicle and the sideslip angle of each wheel, and the slip ratio difference of each wheel is set to zero. Since torque is distributed to each wheel, even if the apparent slip ratio difference and tire (wheel) load relationship may differ, calculate the slip ratio difference according to the actual running condition and Since the torque is distributed to each wheel so that the rate difference becomes zero, the controllability is improved, whereby sufficient traveling stability can be obtained when the vehicle turns.

Further, in the present invention, since the turning state differs depending on the vehicle speed, when the vehicle is traveling at an extremely low speed, the target moving speed of each wheel is calculated from the turning radius of the vehicle without considering the sideslip angle of the wheel, and the extremely low speed is calculated. When traveling other than the above, the target moving speed of each wheel is calculated in consideration of the turning radius of the vehicle and the sideslip angle of the wheels. As a result, the target moving speed can be calculated based on the actual behavior of the vehicle, and the controllability can be improved.

Further, in the present invention, correction is performed to smooth the target moving speed of each wheel in the connected traveling area during traveling at extremely low speeds and traveling at other than extremely low speeds, thus improving controllability. Can be planned.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram showing an embodiment of a traveling control device for a four-wheel drive vehicle of the present invention. 1 is a four-wheel drive vehicle, and this four-wheel drive vehicle 1 includes an engine 2. The output of this engine 2 is the transmission 31
A transfer 3 having a center differential for transmitting the engine output equally to the front wheel side and the rear wheel side via the
Entered in. The front differential 4 is connected to the front wheel side output shaft 32 of the transfer 3, and the driving force is transmitted to the left and right front wheels 6 and 7 via the front wheel drive shafts 33 on both sides. Similarly, the rear differential 5 is connected to the rear wheel side output shaft 33 of the transfer 3, and the driving force is transmitted to the left and right rear wheels 8 and 9 via the rear wheel drive shafts 35 on both sides.

On the other hand, each of the wheels 6, 7, 8 and 9 is provided with a brake device 11, 12, 13 and 14, respectively. The respective brake devices 11, 12, 13, 14 are controlled by the braking pressures supplied to these brake devices 11, 12, 13, 14, respectively.
The braking pressures for 8 and 9 are provided so that they can be controlled independently and individually. Reference numeral 10 is a brake controller (torque distribution changing means), and the brake controller 10 includes the above-mentioned brake devices 11, 12, 13,
A braking pressure control valve, which will be described later, that individually controls the braking pressure supplied to each wheel 14 for each wheel and its actuator are provided to distribute the torque to each wheel.

Further, the throttle valve 36 of the engine 2 is
The opening degree is adjusted by the throttle motor 37.
Reference numeral 15 denotes an engine controller. The engine controller 15 receives an accelerator signal from an accelerator sensor 38 for detecting an accelerator operation amount of a driver, outputs an operation control signal to the throttle motor 37, and outputs an accelerator operation amount of the driver. The opening degree of the throttle valve 36 is adjusted so as to correspond to, and the engine output is changed so that the engine output torque required to change the torque distribution is obtained by receiving the control signal from the torque distribution controller 16.

The torque distribution controller 16 receives the signals from the accelerator sensor 38 as well as the wheels 6, 7, 8 and
Various signals for detecting the amount of movement or the amount of operation for performing torque distribution control to 9 are input, and control signals are output to the brake controller 10 and the engine controller 15. The output sources of the respective signals are a steering angle sensor 40 for detecting the steering angle of the wheels, a wheel speed sensor 44 for detecting the wheel speeds of the wheels 6, 7, 8, 9 and a rotation speed sensor 45 for detecting the engine speed. , A vehicle speed sensor 46 for detecting the vehicle speed,
A gear position sensor 47 for detecting a gear position (gear stage) of the transmission 25, a throttle valve 36
And a yaw rate sensor 49 for detecting the yaw rate of the vehicle.

Next, the brake controller 10 will be described in detail with reference to FIG. Reference numeral 59 is a first hydraulic line for the brake device 11 of the left front wheel 6, and 60 is a second hydraulic line for the brake device 12 of the right front wheel 7, which are the first and second hydraulic lines for controlling the supply of braking pressure, respectively. Braking pressure control valve 6
1, 62 are interposed. Both braking pressure control valves 61,
In 62, the cylinders 61a and 62a are pistons 61a and 6a.
2b allows the variable volume chambers 61c and 62c and the control chamber 61d,
It is divided into 62d. Variable volume chamber 61c, 62c
Supplies the braking pressure generated in the master cylinder 58 to the braking devices 11 and 12.

The pistons 61a and 62b are provided with a spring 6
The variable volume chambers 61c and 62c are urged by 1e and 62e in a direction in which the volumes of the variable volume chambers 61c and 62c increase, and the control chamber 61
The spring 61 is controlled by the control pressure introduced to d and 62d.
The variable volume chambers 61c and 62c are moved in the direction of contracting against the urging of the variable volume chambers e and 62e, and the check valves 61f and 62f that close the braking pressure inlets of the variable volume chambers 61c and 62c by the contraction direction. Is equipped with. Therefore, when the braking pressure is introduced into the control chambers 61d and 62d and the pistons 61a and 62b move against the springs 61e and 62e, the master cylinder 58 and the variable volume chamber 61c,
62c is cut off, and these chambers 61 are
The braking pressure generated in c, 62c is the braking device 1
1, 12 will be supplied.

On the other hand, in order to operate the braking pressure control valves 61, 62, first and second actuators 63, 63 are respectively formed of pressure increasing solenoid valves 63a, 64a and pressure reducing solenoid valves 63b, 64b. 64 is provided. The solenoid valves 63a, 64a for increasing pressure are provided in the control chamber 6 of the braking pressure control valves 61, 62 from the oil pump 65 via the relief valve 66.
The pressure reducing solenoid valves 63b, 64b are arranged on the control pressure supply lines 69, 70 leading to 1d, 62d.
It is arranged on drain lines 67 and 68 led from 1d and 62d. Then, these solenoid valves 63a, 63
b, 64a and 64b are the torque distribution controller 16
Is controlled by a signal from the solenoid valve 63a for increasing pressure,
When 64a is opened and the pressure reducing solenoid valves 63b and 64b are shut off, the control chambers 61d and 6 of the braking pressure control 61 and 62 are controlled.
Control pressure is introduced into 2d, and solenoid valves 63a and 64a for increasing pressure are used.
The control pressure is discharged from the control chambers 61d, 62d when the pressure reducing solenoid valves 63b, 64b are opened.

Further, the braking device 1 for the left and right rear wheels 8 and 9
Although not shown in the drawings, the same structure as that of the brake devices 11 and 12 for the front wheels 6 and 7 is adopted for 3 and 14, and the brake devices 11 to 14 have such a structure.
Independent braking pressure can be applied to the. Next, the torque distribution controller 16 will be described. The torque distribution controller 16 calculates the turning radius of the vehicle and the sideslip angles of the front wheels and the rear wheels,
Target moving speed calculation means for calculating a target moving speed of each wheel from these turning radii and sideslip angles of the front wheels and the rear wheels,
It has a slip ratio difference calculating means for calculating the slip ratio difference between the wheels, and a torque distribution control means for distributing the torque among the wheels.

Next, these brake controllers 10,
The content of the traveling control of the four-wheel drive vehicle executed by the engine controller 15 and the torque distribution controller 16 will be described with reference to the flowchart shown in FIG. In FIG. 3, S indicates a step. After the start, S1
It is determined whether or not it is the measurement timing at every predetermined time. At this timing, in S2, the accelerator operation amount,
The momentum such as the steering angle, the throttle opening, the wheel speed of each wheel, the engine speed, the vehicle speed, the gear position, and the yaw rate is measured based on the signal from each sensor.

In S3, the driving torque (traction torque) required by the driver is calculated from the engine speed, the gear position, and the accelerator opening. In this step, first, a map is selected for the gear position and the engine speed, and the engine output torque, that is, the required drive torque, is obtained from the relationship between the accelerator opening and the engine output torque shown in the selected map. ing.

In S4, the drive torque to be distributed to each of the four wheels is set. In the present invention, the drive torque is distributed according to the slip ratio difference between the wheels. That is, the turning state is determined, the slip rate difference between the wheels is obtained by considering the difference in the trajectory depending on the wheel position and the sideslip angle in the turning state, and the slip rate difference is set to zero for each wheel. Torque distribution is performed.

The calculation of the slip ratio difference between the wheels executed in S4 will be described in detail below. Slip rate difference S occurring in each wheel 6, 7, 8, 9 w is
It is calculated from the following formula. Where WV is the wheel speed of each wheel, V is the target moving speed of each wheel, and w represents the position of each wheel and corresponds to the left and right front wheels and the left and right rear wheels. For example, in the case of the right rear wheel, the slip ratio difference S rr, wheel speed WV rr and target moving speed V Expressed as rr. Here, the wheel speed WV of each wheel
w is a value detected by the wheel speed sensor 44, and is the target moving speed V of each wheel. w is a value calculated by the formula described later.

Target moving speed V of each wheel The w is obtained as follows in consideration of the difference in the trajectory and the slip angle depending on the wheel positions in the turning state. Target moving speed V of each wheel w is a connection travel area (for example, when the vehicle travels at an extremely low speed (for example, less than 20 km / h), when the vehicle travels at a speed other than the extremely low speed (for example, 30 km / h or more), and when the vehicle operates at an extremely low speed and a speed other than the extremely low speed 20km / h-30km
/ H)), the running state of the vehicle is different. Therefore, the calculation is performed as follows.

First, the target moving speed V of each wheel in a case other than an extremely low speed (for example, 30 km / h or more) during normal traveling Calculation of w will be described with reference to FIG.
The turning radius Rt of the vehicle is calculated by the following equation. This turning radius Rt is the yawing center (center of rotation motion) b of the vehicle.
Is the distance between the turning center a and the yaw center at the center of gravity of the vehicle during normal traveling.

[0026] Here, L is a wheel base, δ is a steering angle, A is a constant (stability factor) determined for each vehicle, and V is a vehicle speed. Here, the vehicle body speed V is given an average value of four wheel speeds or a value detected by the vehicle speed sensor 46.

Next, the sideslip angle βf of the front wheels and the sideslip angle βr of the rear wheels generated by the yaw rate of the vehicle body when the sideslip angle of the vehicle body is set to zero are determined by the following equations. Here, γ is the yaw rate, Lf is the distance from the center of gravity of the vehicle to the front wheel drive shaft, and Lr is the distance from the center of gravity of the vehicle to the rear wheel drive shaft.

Next, from the turning radius Rt of the vehicle obtained by the equation (2), the turning radius R of each wheel is calculated. w is calculated by the following equation. R w = √ ((Rt ± Lt w / 2) ² + L w ² ) (5) w represents the wheel position and corresponds to the left and right front wheels and the left and right rear wheels, and Lt w represents a front wheel tret (Ltf) or a rear wheel tret (Ltr), and ± in the expression varies depending on the wheel position, and is + for the right wheel and − for the left wheel. Also, L w is the distance from the center of gravity to the front wheel drive shaft (Lf) or the distance to the rear wheel drive shaft (Lr)
Is represented.

Next, considering the sideslip angle βf of the front wheels and the sideslip angle βr of the rear wheels obtained by the equations (3) and (4),
The turning radius Rt of the vehicle obtained by the equation (2) and the turning radius Rt of each wheel obtained by the equation (5) From w, the target moving speed V of each wheel w is calculated by the following formula. However, w represents the wheel position and corresponds to the left and right front wheels and the left and right rear wheels, and βx means the sideslip angle (βf) of the front wheels or the sideslip angle (βr) of the rear wheels.

The turning radius Rt of the vehicle is calculated by the following equation.
The turning radius Rt is the distance between the yawing center (center of rotation movement) b of the vehicle and the turning center a, and the center of gravity of the vehicle is the yawing center during normal traveling. Next, in the case of an extremely low speed (for example, less than 20 km / h), the target moving speed V of each wheel The calculation of w will be described.

At extremely low speeds, the turning radius Rt of the vehicle and the turning radius Rt of each wheel Since the behavior of the vehicle is different from that of the case other than the extremely low speed, w is represented by the following equation, unlike the above equations (2) and (5). That is, the turning radius Rt during normal running is represented by the distance between the center of gravity of the vehicle and the center of turning, but the turning radius Rt during extremely low speed running is the center of the rear wheel axle, which is the center point of the tret of the rear wheels of the vehicle. Since the point c becomes the yawing center, it is represented by the distance between the rear wheel shaft center point c and the turning center a.

[0032] However, L represents a wheel base, δ represents a steering angle, and Ltr represents a rear wheel tret. R w = √ ((Rt ± Lt w / 2) ² + L w ² ) (8) w represents the wheel position and corresponds to the left and right front wheels and the left and right rear wheels, and Lt w represents a front wheel tret (Ltf) or a rear wheel tret (Ltr), and ± in the expression varies depending on the wheel position, and is + for the right wheel and − for the left wheel. Also, L w is wheel base L for the front wheels and zero for the rear wheels.

At extremely low speeds, the target moving speed V of each wheel is calculated by using the above equations (7) and (8) without considering the sideslip angle βf of the front wheels and the sideslip angle βr of the rear wheels. w is calculated by the following formula. On the other hand, the target moving speed V of each wheel When w is calculated, in order to smoothly connect during extremely low speed traveling and during other traveling, this connected traveling area (for example, 20 km / h to 30 km) is used.
/ H)), correction is performed using the following equation.

[0034] V w = V w2 · k + V w1 · (1-k) (12) where k is a correction coefficient, VT1 (for example, 20 km / h) and
And VT0 (for example, 30 km / h) set the vehicle speed for joint correction.
It is a constant area. Furthermore, V in equation (12) w1 is
For calculating the target moving speed of each wheel at extremely low speed
Target moving speed of each wheel calculated by equation (9)
Degree and V w2 is the eye of each wheel except for extremely low speed
Calculated by equation (6) used when calculating the target moving speed
In this way it is the target moving speed of each wheel that is issued,
Target moving speed V of each wheel according to each running state of the vehicle
w is the expression (6) (when it is not extremely low speed), the expression (9) (extremely low)
Speed) and (12) (connection travel area)
Calculated individually.

Finally, the target moving speed V of each wheel calculated in this way From w and the wheel speed WV of each wheel detected by the wheel speed sensor 44, the slip ratio difference S generated in each wheel 6, 7, 8, 9 is calculated by the above equation (1).
Calculate w respectively. Next, the calculated slip ratio difference S of each wheel Based on w, this slip ratio difference S
The amount of change in the drive torque is calculated for each wheel so that w is zero, and the amount of drive torque distributed to each wheel is set.

Next, in S5, the drive torque at each wheel is calculated. In this step, first, the drive torque of each wheel is calculated from the distribution amount of the drive torque of each wheel set in S4. Next, in order to determine whether or not the obtained driving torque of each wheel can be realized, the maximum driving torque among the driving torques of the respective wheels is compared with the engine torque when the throttle is fully opened. When the maximum drive torque is large, the drive torque at each wheel is corrected to the engine torque when the throttle is fully opened.

Next, in S6, engine output control is performed on the basis of the drive torque of each wheel calculated in S5. At this time, the driving torque from the engine is equally divided into four equal parts for each wheel by the center differential (transfer 3), the front differential 4 and the rear differential 5, and the same driving torque is obtained for each wheel. Be transmitted to.

Next, in S7, a difference between the actual engine output value output-controlled in S6 and the drive torque of each wheel, which is the target drive torque set in S4, is obtained, and this difference is converted into a brake torque. Then, this brake torque is further converted into brake pressure, and brake pressure control is performed for each wheel. In this way, the torque distribution is realized by applying the brake torque by the difference between the actual engine output value and the target drive torque.

[0039]

As described above, according to the present invention, the slip ratio difference of each wheel is calculated from the running locus of each wheel of the vehicle and the sideslip angle of each wheel, and the slip ratio difference of each wheel is zero. Since the torque is distributed to each wheel as described above, even if the relationship between the apparent slip ratio difference and the tire (wheel) load may differ, calculate the slip ratio difference according to the actual running condition. Since the torque is distributed to each wheel so that the slip ratio difference becomes zero, the controllability is improved, and thereby sufficient traveling stability can be obtained when the vehicle turns.

Further, in the present invention, since the turning state differs depending on the vehicle speed, when the vehicle travels at an extremely low speed, the target moving speed of each wheel is calculated from the turning radius of the vehicle without considering the sideslip angle of the wheel, and the extremely low speed is calculated. When traveling other than the above, the target moving speed of each wheel is calculated in consideration of the turning radius of the vehicle and the sideslip angle of the wheels. As a result, the target moving speed can be calculated based on the actual behavior of the vehicle, and the controllability can be improved.

Further, in the present invention, the correction is performed to smooth the target moving speed of each wheel in the connected traveling area during the extremely low speed traveling and the traveling other than the extremely low speed, so that the controllability is improved. Can be planned.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of a travel control device for a four-wheel drive vehicle of the present invention.

FIG. 2 is a circuit diagram showing torque distribution changing means of the present invention.

FIG. 3 is a flowchart showing the content of traveling control of a four-wheel drive vehicle executed according to the present invention.

FIG. 4 is a plan view showing a traveling state of the vehicle in a case other than an extremely low speed which is during normal traveling.

FIG. 5 is a plan view showing a traveling state of the vehicle at an extremely low speed.

[Explanation of symbols]

 1 4 Wheel Drive Vehicle 2 Engine 3 Center Differential 4 Front Differential 5 Rear Differential 6 to 9 Wheel 10 Brake Controller 11 to 14 Brake Device 15 Engine Controller 16 Torque Distribution Controller 40 Steering Angle Sensor 44 Wheel Speed Sensor 45 Rotation Sensor 46 Vehicle Speed Sensor 47 Gear Position Sensor 48 Throttle Opening Sensor 49 Yaw Rate Sensor

Claims (3)

[Claims] 1. A travel control device for a four-wheel drive vehicle in which four wheels in the front, rear, left, and right of the vehicle are driven by engine outputs, and the amount of transmission of the engine output to the four wheels is controlled to control the drive torque of the four wheels. A torque distribution changing means for changing the distribution, a steering angle sensor for detecting a steering angle, a wheel speed sensor for detecting a wheel speed of each wheel, a vehicle speed detecting means for detecting a vehicle speed, and a yaw rate of the vehicle. The yaw rate sensor, the turning radius of the vehicle is calculated from the steering angle and the vehicle speed, and the sideslip angles of the front and rear wheels are calculated from the yaw rate,
Target moving speed calculation means for calculating the target moving speed of each wheel from the turning radius of the vehicle and the sideslip angles of the front wheels and the rear wheels, and the target moving speed of each wheel and each wheel detected by the wheel speed sensor. The slip ratio difference calculating means for calculating the slip ratio difference between the wheels from the speed, and the torque distribution to each wheel by applying a braking torque to each wheel based on the slip ratio difference between these wheels, based on this torque distribution And a torque distribution control means for controlling the torque distribution changing means, and a travel control device for a four-wheel drive vehicle. 2. The four-wheel drive vehicle according to claim 1, wherein the target speed calculation means calculates the target moving speed without considering the sideslip angles of the wheels when the vehicle is traveling at an extremely low speed. Travel control device. 3. The target moving speed calculating means has a correcting means for smoothing the target moving speed in a connected traveling area during extremely low speed traveling and during traveling other than extremely low speed. 2. A traveling control device for a four-wheel drive vehicle according to item 2.