Four-wheel steering device for vehicle

• US 4,828,064 A
• Filed: 06/24/1987
• Issued: 05/09/1989
• Est. Priority Date: 06/06/1984
• Status: Expired due to Fees

• Current Assignee: Mazda Motor Corporation
• Original Assignee: Mazda Motor Corporation
• Inventors: Masumoto, Hideharu, Takatani, Teruhiko, Kanazawa, Hirotaka, Furutani, Shigeki
• Primary Examiner(s): Marmor, Charles A.
• Assistant Examiner(s): Diederiks, Jr., Everett G.
• Application Number:
  US07/065,651
• Time in Patent Office: 685 Days
• Field of Search: 180/140, 180/141, 180/142, 180/143, 180/79.1, 180/252, 280/91, 364/424
• US Class Current: 180/412
• CPC Class Codes: B62D 6/00 Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits means for initiating a change in direction B62D1/00; steering valves B62D5/06; combined with means for inclining the vehicle body or wheels on bends B62D9/00
• CPC Class Codes: B62D 7/14 the pivotal axes being situated in more than one plane transverse to the longitudinal centre line of the vehicle, e.g. all-wheel steering

Abstract

In a four-wheel steering system for a vehicle, a rear wheel turning mechanism for turning the rear wheels is controlled so that the ratio of the rear wheel turning angle to the front wheel turning angle changes with change in the vehicle speed. The ratio of the rear wheel turning angle to the front wheel turning angle is set so that the vehicle lateral acceleration response characteristics and the vehicle heading response characteristics generated by operation of the steering wheel approximate each other as far as possible.

Claims

1. A method of controlling a four-wheel steering system for a vehicle including a vehicle speed sensor, a front wheel steering means, means for generating a signal representative of the turning angle of the front wheels, means for obtaining the rear wheel turning angle in response to the turning angle of the front wheels and the vehicle speed, and means for turning the rear wheels, the method comprising:

detecting actuation of the front wheel steering means;

detecting the vehicle speed sensed by the vehicle speed sensor;

obtaining by a computing means the ratio of the rear wheel turning angle to the front wheel turning angle in response to said detected vehicle speed where said ratio is such that, at a predetermined steering wheel operating speed, the vehicle response to (a) lateral acceleration and (b) heading are substantially equal for (i) a first range of detected vehicle speeds where the front and rear wheels are turned in the reverse phase with respect to each other and (ii) a second range of detected vehicle speeds faster than the first range of speeds where the front and rear wheels are turned in the same phase; and

turning the rear wheels through a turning angle determined by the obtained value of the ratio of the rear wheel angle to the front wheel turning angle and said turning angle of the front wheels.

3. A method as in claim 1 or 2 where said four-wheel steering vehicle system includes a memory and said method includes storing said ratio of the rear wheel turning angle to the front wheel turning angle for said first and second vehicle speed ranges and where said ratio obtaining step includes reading from said memory the ratio corresponding to a particular vehicle speed.

4. A method as in claims 1 or 2 where said four-wheel steering vehicle system includes a steering wheel turning angle sensor as the means for generating said signal representative of the turning angle of the front wheels and said method turns the rear wheels in accordance with the sensed turning angle of the steering wheel and the obtained ratio of the rear wheel turning angle to the front wheel turning angle.

5. A method as in claim 1 and 2 where said four-wheel steering vehicle system includes a load sensor for detecting load on the vehicle and said method includes changing said ratio of the rear wheel turning angle to the front wheel turning angle according to the detected load.

2. A method of controlling the steering of a four-wheel steering system for a vehicle including a steering wheel, a front wheel turning means for turning the front wheels in response to operation of the steering wheel, means for generating a signal representative of the turning angle of the front wheels, a rear wheel turning means for turning the rear wheels in response to turning the front wheels, a vehicle speed sensor which detects the vehicle speed and outputs a vehicle speed signal, a steered angle ratio setting means which receives the vehicle speed signal and sets, at a predetermined steering wheel operating speed, the ratio of the rear wheel turning angle to the front wheel turning angle with reference to the vehicle speed to obtain a wheel turning angle ratio characteristic and a control means which controls the rear wheel turning means on the basis of the steered angle ratio characteristic set by the steered angle ratio selecting means and a turning angle of the front wheels, said method comprising

obtaining by a computing means said ratio of the rear wheel turning angle to the front wheel turning angle in response to the sensed vehicle speed to lateral acceleration and response of the vehicle to heading substantially coincide with each other for (i) a first range of values of speeds sensed by said vehicle speed sensor where the front and rear wheels are turned in the reverse phase with respect to each other and (ii) a second range of sensed vehicle speeds where the front and rear wheels are turned in the same phase.

6. A method for determining desired ratios of the rear wheel turning angle to the front wheel turning angle in a four-wheel steering system for a vehicle over a predetermined range of vehicle speeds, said method comprising the steps of:

(a) selecting a current value of said ratio for a predetermined steering wheel operating speed;

(b) selecting a current speed of said vehicle;

(c) determining the lateral acceleration response and the heading response of the vehicle for the current value of the ratio and said current speed;

(d) determining whether said lateral acceleration response and the heading response are substantially equal;

(e) if the lateral acceleration response and the heading response are not equal, incrementing the current value of said vehicle speed by a predetermined amount;

(f) repeating steps (c) through (e) until the lateral acceleration response and the heading response are equal to thereby determine said desired ratio for the current value of the incremented speed where the desired ratio corresponds to said current value of the ratio;

(g) incrementing said current value of the ratio by a predetermined amount;

(h) repeating the steps (b) through (f) until the desired ratio for the current value of the vehicle speed is determined; and

(i) repeating steps (g) and (h) until said desired ratios are determined over said predetermined range of vehicle speeds.

7. A method for determining desired ratios of the rear wheel turning angle to the front wheel turning angle in a four-wheel steering system for a vehicle over a predetermined range of vehicle speed, said method comprising the steps of:

(a) selecting a current speed of said vehicle for a predetermined steering wheel operating speed;

(b) selecting a current value of said ratio;

(c) determining the lateral acceleration response and the heading response of the vehicle for the current value of the ratio and said current speed;

(d) determining whether said lateral acceleration response and the heading response are substantially equal;

(e) if the lateral acceleration response and the heading response are not equal, incrementing the current value of said ratio by a predetermined amount;

(f) repeating steps (c) through (e) until the lateral acceleration response and the heading response are equal to thereby determine said desired ratio for the current value of the speed where the desired ratio corresponds to said current value of the ratio;

(g) incrementing said current value of the speed by a predetermined amount;

(h) repeating steps (b) through (f) until the desired ratio for the current value of the vehicle speed is determined; and

(i) repeating steps (g) and (h) until said desired ratios are determined over said predetermined range of vehicle speeds.

8. A method of controlling a four-wheel steering system for a vehicle including a vehicle speed sensor, a front wheel steering means, means for generating a signal representative of the turning angle of the front wheels, means for obtaining the rear wheel turning angle in response to the turning angle of the front wheels and the vehicle speed, and means for turning the read wheels, the method comprising:

detecting actuation of the front wheel steering means;

detecting the vehicle speed sensed by the vehicle speed sensor;

determining the lateral acceleration of the vehicle;

determining the heading of the vehicle;

determining by computing means the ratio of the rear wheel turning angle to the front wheel turning angle where said ratio is such that for said detected vehicle speed, the vehicle response to (a) said lateral acceleration and (b) said heading are substantially equal for (i) a first range of detected vehicle speeds where the front and rear wheels are turned in the reverse phase with respect to each other and (ii) a second range of detected vehicle speeds faster than the first range of speeds where the front and rear wheels are turned in the same phase; and

turning the rear wheels through a turning angle determined by the obtained value of the ratio of the rear wheel angle to the front wheel turning angle and said turning angle of the front wheels.