Automotive four wheel steering system

• US 4,941,542 A
• Filed: 06/07/1989
• Issued: 07/17/1990
• Est. Priority Date: 10/01/1986
• Status: Expired due to Fees

• Current Assignee: Mazda Motor Corporation
• Original Assignee: Mazda Motor Corporation
• Inventors: Itoh, Takaaki, Kijima, Takao, Tomoda, Atsuo
• Primary Examiner(s): Marmor, Charles A.
• Assistant Examiner(s): Kagen, Alan M.
• Application Number:
  US07/363,432
• Time in Patent Office: 405 Days
• Field of Search: 180/140, 180/133, 180/136, 180/153, 180/154, 180/158, 92/60
• US Class Current: 180/414
• CPC Class Codes: B62D 7/1563 provided with fluid control means B62D7/1572 takes precedence

Abstract

An automotive vehicle having a fluid-operated, four wheel steering system for steering not only the front wheel pair, but also the rear wheel pair as a function of the amount of turn of the front wheel pair with respect to the direction of straightforward run of the vehicle. The system makes use of a front cylinder operatively associated with a steering gear assembly and a rear cylinder operated by a fluid medium supplied from the front cylinder for steering the rear wheel pair. In order for the steering system to be responsive to the vehicle running speed thereby to control the amount of turn of the rear wheel pair appropriate for a particular range of vehicle running speed, a device is provided for accommodating a portion of the fluid medium to be supplied to the rear cylinder when the pressure of the fluid medium increases to a value higher than a predetermined pressure. Increase of the fluid pressure over the predetermined value takes place when the steering wheel is turned during the low speed run of the vehicle.

Claims

1. In an automotive vehicle having front and rear wheel pairs and a steering wheel drivingly coupled with the front wheel pair for steering the vehicle with respect to the direction of run of the vehicle, said steering wheel being rotatable in opposite directions from a neutral position at which the vehicle can run straightforward, a fluid-operated, four wheel steering system which comprises:

a front wheel steering mechanism including a front steering rod that is adapted to steer the front wheel pair in response to rotation of the steering wheel;

a fluid-operated front cylinder means actuated in response to the rotation of the steering wheel from the neutral position, said front cylinder means including a front piston member that is mechanically coupled to the front steering rod for movement in response to rotation of the steering wheel, said front cylinder means having first and second front cylinder chambers positioned on opposite sides of said front piston member, said first front cylinder chamber having a volume that is adapted to be reduced when the steering wheel is rotated to turn the front wheel pair leftwards with respect to the direction of movement of the vehicle, and the second front cylinder chamber having a volume that is adapted to be reduced when the steering wheel is rotated to turn the front wheel pair rightwards with respect to the direction of movement of the vehicle;

a fluid-operated rear cylinder means for steering the rear wheel pair for turning at least one rear wheel of the rear wheel pair with respect to the direction of straightforward run of the vehicle, said rear cylinder means including a first rear cylinder assembly and a second rear cylinder assembly, said first rear cylinder assembly being adapted to cause a right-hand rear wheel of the rear wheel pair to turn when supplied with a fluid medium and said second rear cylinder assembly being adapted to cause a left-hand rear wheel of the rear wheel pair to turn when supplied with a fluid medium;

said front and rear wheel pairs being adapted to turn in the same direction;

a fluid passage means for operatively coupling the front and rear cylinder means together to permit a fluid medium to be supplied from the front cylinder means to the rear cylinder means to thereby actuate the rear cylinder means, said fluid passage means including a first fluid passage that communicates the first front cylinder chamber with the first rear cylinder assembly for supplying fluid medium under pressure to the first rear cylinder assembly and a second fluid passage that communicates the second front cylinder chamber with the second rear cylinder assembly for supplying fluid medium under pressure to the second rear cylinder assembly; and

a fluid medium accommodating means disposed in the rear cylinder means for accommodating a portion of the fluid medium being supplied from the front cylinder means to the fluid-operated rear cylinder means only when the pressure of the fluid medium in the front cylinder means increases such that the pressure in the rear cylinder means increases to a value greater than a predetermined value as a result of rotation of the steering wheel when the automotive vehicle is traveling at relatively low speeds, said fluid medium accommodating means being operable to accommodate a portion of the fluid medium independent of the turn of the rear wheel pair.

2. The steering system as claimed in claim 1, wherein the fluid medium accommodating means comprises a piston member forming an end wall of each of the first and second rear cylinder assemblies and a biasing means for exerting a biasing force on a rear surface of each of the piston members, said piston members being movable against the biasing force when the pressure inside the respective rear cylinder assembly becomes higher than the predetermined value.

3. The steering system as claimed in claim 1, wherein said rear cylinder means is used to turn both rear wheels forming the rear wheel pair with respect to the direction of straightforward run of the vehicle.

4. The steering system as claimed in claim 1, wherein the rear cylinder means is operable to toe in one of the rear wheels, forming the rear wheel pair, which is situated outwardly with respect to the center of curvature of the path along which the vehicle is turned.

5. The steering system as claimed in claim 4, wherein said front steering rod has opposite ends that are operatively coupled with respective front wheels forming the front wheel pair and wherein said first rear cylinder assembly includes a first rear piston member disposed inside one end of a first rear steering rod operatively coupled with a right-hand rear wheel forming a part of the rear wheel pair, and a first rear cylinder supporting the first rear piston member for sliding movement within the first rear cylinder, said second rear cylinder assembly including a second rear piston member disposed inside one end of a second rear steering rod operatively coupled with a left-hand rear wheel forming the other part of the rear wheel pair, and a second rear cylinder supporting the second rear piston member for sliding movement within the second rear cylinder.

6. The steering system as claimed in claim 5, wherein each of said first and second rear steering rods is provided with a toe-out stopper for restricting the toe-out of the associated rear wheel.

7. The steering system as claimed in claim 3, further comprising a reservoir tank and wherein the front cylinder means is provided with first and second communicating passages leading from the reservoir tank to the first and second front cylinder chambers, both of said first and second front cylinder chambers being communicated with the reservoir tank when and so long as the front steering rod is in a neutral position corresponding to the neutral position of the steering wheel.

8. The steering system as claimed in claim 5, further comprising a reservoir tank and wherein the front cylinder means is provided with first and second communicating passages leading from the reservoir tank to the first and second front cylinder chambers, both of said first and second front cylinder chambers being communicated with the reservoir tank when and so long as the front steering rod is in a neutral position corresponding to the neutral position of the steering wheel.