JPH06135351A - Ground condition detection device - Google Patents

Abstract

PURPOSE:To detect ground condition at the time of straight travelling concerning a detection device to detect ground condition of the ground on which a vehicle having a four-wheel steering device capable of independently controlling steering ratios of front wheels and rear wheels travels. CONSTITUTION:At the time when a front wheel steering angle thetaf is lower than specified threshold value thetat, a computer judges it as straight traveling (step 102) and rear wheels are steered at specified angles in opposite phases to the left and the right (step 103). Continuously, by retrieving a map from selfaligning torque (SAT) of the rear wheels and a steering angle of the rear wheels, the computer computes a ground mu (step 106).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a road surface condition detecting device, and more particularly to a road surface condition detecting device for detecting a road surface condition of a vehicle having a four-wheel steering device capable of independently controlling the steering ratios of front wheels and rear wheels. .

[0002]

2. Description of the Related Art When a vehicle is turning at a low speed, the rear wheels are steered in anti-phase with respect to the front wheels to improve the small turning performance. In a vehicle having a four-wheel steering system capable of achieving stable running conditions, the running angle is further improved by correcting the steering angle of the rear wheels according to the friction coefficient (μ) of the road surface. It is known that you can. Therefore, conventionally, there is known a road surface condition detecting device which estimates a road surface μ by detecting a tire restoring torque (self-aligning torque: SAT) during steering of a steering wheel (Japanese Patent Laid-Open No. 63-64879). ).

[0003]

However, in the above-mentioned conventional road surface condition detecting device, since the SAT does not occur unless the tire slip angle occurs, the road surface μ can be estimated only when the steering wheel is steered. Since it is not possible to inform the driver of the road surface μ in advance when driving straight ahead, the vehicle may become unstable during steering of the steering wheel.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a road surface condition detecting device that solves the above problems by enabling the rear wheels of a vehicle to be steered when the steering wheel is not steered. And

[0005]

FIG. 1 is a block diagram showing the principle of the present invention for achieving the above object. As shown in the figure, the present invention detects a rear wheel steering means 11 for steering the rear wheels 14a, 14b of a vehicle in a left-right reverse phase at a predetermined angle during a predetermined operation, and a restoring torque generated in the rear wheel by the rear wheel steering. First detecting means 12, which detects the restoring torque and the rear wheel 14a,
It has the second detection means 13 for detecting the road surface condition from the steering angle of 14b.

[0006]

Operation: The front wheels 15a, 15 of the vehicle are driven according to a predetermined driving condition.
When b is in a predetermined steering angle range, the rear wheel steering means 11 steers the left rear wheel 14a and the right rear wheel 14b in opposite phases by a predetermined angle. At this time, the restoring force generated in each of the rear wheels 14a and 14b, that is, the self-aligning torque (SA
T) is detected by the first detecting means 12, and the second detecting means 13 detects the steering angle of each of the rear wheels 14a, 14b and the road surface condition. Therefore, in the present invention, the front wheels 15a, 1
It is possible to detect the road surface condition even when the vehicle is not moving to steer 5b and goes straight.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 2 is a block diagram of an embodiment of the present invention. In the figure, the left front wheel 21a (corresponding to 15a) and the right front wheel 21
b (corresponding to 15b) means the knuckle arm 22.
It is connected to the relay rod 24 via a and 22b and tie rods 23a and 23b. In addition, the handle 25 is connected to the relay rod 2 via a shaft 26 by a predetermined mechanism.
4 and the handle 25 is operated to displace the displacement relay rod 24 in the left or right direction in the figure according to the amount of operation of the handle, whereby the left front wheel 21a and the right front wheel 21 are moved.
Steer b and. A front wheel steering angle sensor 27 is provided in the middle of the shaft 26, and is configured to detect the operation amount of the handle 25, that is, the front wheel steering angle.

The arithmetic unit 28 is an electronic control unit composed of a microcomputer, and has the first and second detecting means 12 described above.
And 13 are realized by software processing, and the rear wheel steering means 11 is configured with the rear wheel drive mechanism such as the motor 29. The motor 29 is a rear-wheel drive motor that rotates in a direction and a rotation angle instructed by a drive signal from the arithmetic unit 28, and its motor shaft 30 is substantially connected to the pinion 33 via the steering angle sensor 31 and the strain sensor 32. It is connected.

For example, as shown in FIG. 3 which is an enlarged view of an essential part of FIG. 2, the steering angle sensor 31 has a central portion penetratingly fixed to the motor shaft 30, and a slit having a constant length in the circumferential direction at equal angular intervals. A rotary encoder including a disk 41 having a large number of holes 41a formed therein and a photo interrupter 42 for optically detecting the presence or absence of the slit 41a of the disk 41. The number of slit detection pulses from the photo interrupter 42 is calculated by an arithmetic unit. The steering angle of the rear wheels is detected by measuring at 28. The strain sensor 32 can also be configured by a strain gauge attached to the motor shaft 30.

Returning to FIG. 2 again, the left rear wheel 34 will be described.
a (corresponding to 14a above) and the right rear wheel 34b (corresponding to 14b above) are relay rods 37a and 37 via knuckle arms 35a and 35b and tie rods 36a and 36b, respectively.
They are respectively linked to b. Relay rods 37a, 37b
Racks 38a, 38b are formed in the. Rack 3
8a and 38b mesh with the pinion 33 at positions facing each other through the center of the pinion 33.

As a result, when the motor 29 rotates in the forward direction by a predetermined angle, the pinion 33 rotates, for example, in the clockwise direction by a predetermined angle in the figure, and as a result, the relay rod 37a on which the rack 38a is formed moves leftward in the figure. To the relay rod 37b which is displaced by a predetermined amount to and on which the rack 38b is formed.
Is displaced to the right in the figure by the same predetermined amount as above.

Accordingly, the front part of the left rear wheel 34a is pivotally displaced leftward by a predetermined steering angle by the leftward displacement of the relay rod 37a, and the right rear wheel 34b is also displaced by the rightward displacement of the relay rod 37b. The front portion of the is pivotally displaced to the right by a predetermined steering angle. That is, the left rear wheel 34a and the right rear wheel 34b
Are steered in opposite phases with the same steering angle in absolute value.

Further, due to the reverse-phase steering of the left and right rear wheels 34a and 34b, a restoring torque (SAT) is generated in the left and right rear wheels 34a and 34b and acts on the motor shaft 30 as a twisting force. It is detected by the strain sensor 32. The motor 29 rotates in the opposite direction to rotate the pinion 3
When 3 is rotated counterclockwise by a predetermined angle, the left and right rear wheels 34a, 34b are steered in opposite phases to the opposite direction.

Although not shown in FIG. 2, another drive system is separately provided for driving the left and right rear wheels 34a and 34b in the same phase based on the output control signal of the arithmetic unit 28 to determine whether or not the road surface state is determined. At times, the same four-wheel steering device as the conventional one may be realized by using it instead of the reverse phase drive mechanism.

Next, a road surface state detection routine executed by the arithmetic unit 28 will be described. The arithmetic unit 28 receives the output detection signals of the steering angle sensors 27, 31 and the strain sensor 32, and executes the road surface state detection routine of FIG. 4 every predetermined period. When the road surface state detection routine shown in FIG. 4 is driven, first, the front wheel steering angle θ _f is read based on the output detection signal of the front wheel steering angle sensor 27 (step 101), and then the front wheel steering angle θ _f It is determined whether the absolute value is less than a predetermined threshold value θ _t (step 102).

When | θ _f | is determined to be _{equal to} or greater than the threshold value θ _t, it is determined that the driving state is not the straight traveling state, the rear wheel steering is released (step 107), and this routine is ended. . On the other hand, when it is determined in step 102 that | θ _f | is less than the threshold value θ _t , the motor 29 is fixed in a predetermined direction in order to detect the road surface μ by determining that the operating state is straight traveling. By rotating the wheel by an angle, the left rear wheel 34a and the right rear wheel 34b are steered by a fixed angle in opposite phases as described above (step 103).

Subsequently, the arithmetic unit 28 outputs the strain sensor 32.
SAT is read based on the force detection signal (step 10
4), and the rear wheels based on the output detection signal of the steering angle sensor 31.
Rudder angle θ _RAfter reading (step 105), calculate in advance
As shown in FIG. 5, stored in memory within device 28.
Map the above SAT and rear wheel steering angle θ_RSearch with and the road
Calculate μ (step 106).

Here, the map shown in FIG. 5 shows that the road surface μ has a convex characteristic when the rear wheel steering angle is plotted on the horizontal axis and the self-aligning torque (SAT) is plotted on the vertical axis. There is. That is, the road surface μ is maximum at a predetermined rear wheel steering angle, and the road surface μ becomes smaller as it becomes larger and smaller than the predetermined rear wheel steering angle, and the road surface μ becomes larger as the SAT increases at the same rear wheel steering angle. μ becomes large.

The rotation angle of the motor 29 is controlled so that the absolute values of the left and right steering angles of the rear wheels 34a and 34b are in the vicinity of, for example, θ _R in FIG. In FIG.
_This is because the characteristic curve near _R is a steep portion, which is a sensitive portion where the road surface μ changes with a slight change in SAT.

When the calculation of the road surface μ by the map search is completed in step 106 of FIG. 4, the routine proceeds to step 107, where the motor 29 is rotated in the opposite direction to the above step 103 and at the same angle, so that the rear wheels 34a and 34b are rotated. Is returned to the state before the left-right reverse-phase steering, and this routine ends. As a result, when steering the steering wheel thereafter, only the front wheels 21a and 21b are steered in response to the steering wheel, and the rear wheels 34a, 3b
4b is not steered.

As described above, according to this embodiment, the motor 2
9, pinion 33, rear wheel steering mechanism such as racks 38a and 38b, steering angle sensor 27, and steps 102 and 1 in FIG.
The rear wheel steering means 11 is realized by 03, and the strain sensor 3
2 and step 104 realizes the first detecting means 12, and further the steering angle sensor 31 and steps 105 and 106.
By realizing the second detecting means 13 by
The road surface μ can be calculated when going straight, and therefore, the driver can be notified of the road surface μ in advance before steering the steering wheel.

The drive mechanism for driving the left rear wheel 34a and the right rear wheel 34b in phase based on the output control signal of the arithmetic unit 28 can be used by switching to the rear wheel left / right reverse phase drive mechanism shown in FIG. If yes, then step 107
When the rear-wheel steering is released, the rear-wheel left-right in-phase drive mechanism is switched and, for example, the steering ratio of the front and rear wheels (= front-wheel steering angle /
As shown in FIG. 6, the rear wheel steering angle k is as shown in FIG.
The rear wheels 34a and 34b are steered in reverse phase with respect to a and 21b, and the rear wheels 34a and 34b are steered with respect to the front wheels 21a and 21b at medium and high vehicle speeds.
You may make it steer a and 34b in-phase.

[0023]

As described above, according to the present invention, since the rear wheels are steered in the opposite phase to the left and right to read the SAT, the road surface condition can be detected even when going straight. is there.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a configuration diagram of an embodiment of the present invention.

FIG. 3 is an enlarged view of a main part in FIG.

FIG. 4 is a flow chart showing an embodiment of a road surface state detection routine of a main part of the present invention.

5 is a road surface μ used in the road surface state detection routine of FIG.
It is a map for calculation of.

FIG. 6 is a diagram showing conventional steering characteristics corresponding to vehicle speed.

[Explanation of symbols]

 11 Rear Wheel Steering Means 12 First Detecting Means 13 Second Detecting Means 14a, 34a Left Rear Wheels 14b, 34b Right Rear Wheels 15a, 21a Left Front Wheels 15b, 21b Right Front Wheels 25 Handle 27 Front Wheel Steering Angle Sensor 28 Computing Device 29 Motor 31 Steering angle sensor 32 Strain sensor 33 Pinion 38a, 38b Rack

Claims (1)

[Claims] 1. A rear wheel steering means for steering a rear wheel of a vehicle in a left-right opposite phase at a predetermined angle in a predetermined driving state, and a restoring torque generated in the rear wheel by steering the rear wheel by the rear wheel steering means. Road surface state detection, comprising: a first detection unit; and a second detection unit that detects the road surface state from the restoration torque detected by the first detection unit and the steering angle of the rear wheel. apparatus.