Power-assisted steering system

• US 4,858,713 A
• Filed: 03/03/1988
• Issued: 08/22/1989
• Est. Priority Date: 02/26/1986
• Status: Expired due to Fees

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Kishida, Fumio, Kawakami, Hiroshi, Sugihara, Koichi, Watanabe, Atsushi, Shiratori, Harunori
• Primary Examiner(s): Marmor, Charles A.
• Application Number:
  US07/163,947
• Time in Patent Office: 537 Days
• Field of Search: 180/143, 180/141, 180/142, 180/132, 180/133, 180/146, 180/147, 180/149, 91/375 R, 91/375 A, 91/434, 91/370, 91/371, 60/375
• US Class Current: 180/423
• CPC Class Codes: B62D 6/02 responsive only to vehicle speed
• CPC Class Codes: F42B 33/04 Fitting or extracting primers in or from fuzes or charges F42B33/004 takes precedence

Abstract

A power-assisted steering system includes a changeover valve unit comprising an input shaft to be rotated by the driver'"'"'s steering effort applied thereto, an output shaft operatively connected to a hydraulic power cylinder associated with the steering system, a valve assembly for controlling the supply of fluid under pressure from a hydraulic pump to the power cylinder in response to relative rotation between the input and output shafts; and a hydraulic reaction mechanism for applying a reaction force to the input shaft in accordance with a hydraulic reaction pressure applied thereto. The reaction mechanism includes a reaction fluid chamber to be constantly applied with a predetermined small quantity of fluid under pressure and to be applied with a hydraulic pressure caused by relative rotation between the input and output shafts through a throttle. The system is arranged to increase the hydraulic pressure in the reaction fluid chamber in accordance with an increase of travel speed of the vehicle.

Claims

1. A power-assisted steering system in an automotive vehicle, comprising:

a primary hydraulic pump driven by a prime mover of the vehicle for supply of fluid under pressure;

an auxiliary hydraulic pump driven by the prime mover for supply of a predetermined small quantity of fluid under pressure;

a hydraulic power cylinder operatively connected to the dirigible road wheels of the vehicle;

a changeover valve unit including an input member arranged to be moved by the driver'"'"'s steering effort applied thereto, an output member operatively connected to said power cylinder, and valve means for controlling the supply of fluid under pressure from said primary hydraulic pump to said power cylinder in response to relative movement between said input and output members;

a hydraulic reaction mechanism associated with said changeover valve unit to apply a reaction force to said input member in accordance with a hydraulic reaction pressure applied thereto, said reaction mechanism including a reaction fluid chamber connected to said auxiliary hydraulic pump to be supplied with the predetermined small quantity of fluid under pressure;

a first throttle disposed within a bypass circuit connecting a first fluid circuit between said primary hydraulic pump and said valve means of said changeover valve unit to a second fluid circuit between said auxiliary hydraulic pump and said reaction fluid chamber;

a second throttle disposed within a third fluid circuit connecting said second fluid circuit to a fluid reservoir; and

flow control valve means disposed within said third fluid circuit downstream of said second throttle to decrease the quantity of fluid discharged therethrough into said fluid reservoir in accordance with an increase of travel speed of the vehicle thereby increase the hydraulic pressure in said reaction fluid chamber.

2. A power-assisted steering system as recited in claim 1, wherein said auxiliary hydraulic pump is coaxially arranged with said primary hydraulic pump to be driven by the prime mover on a common drive shaft.

3. A power-assisted steering system as recited in claim 1, wherein said flow control valve means is a solenoid relief valve disposed within said third fluid circuit to be energized by an electric control signal indicative of travel speed of the vehicle.

4. A power-assisted steering system in an automotive vehicle, comprising:

a primary hydraulic pump driven by a prime mover of the vehicle for supply of fluid under pressure;

an auxiliary hydraulic pump driven by the prime mover for supply of a predetermined small quantity of fluid under pressure;

a hydraulic power cylinder operatively connected to dirigible road wheels of the vehicle;

a changeover valve unit including an input member arranged to be moved by the driver'"'"'s steering effort applied thereto, an output member operatively connected to said power cylinder, and valve means for controlling the supply of fluid under pressure from said primary hydraulic pump to said power cylinder in response to relative movement between said input and output members;

a hydraulic reaction mechanism associated with said changeover valve unit to apply a reaction force to said input member in accordance with a hydraulic reaction pressure applied thereto, said reaction mechanism including a reaction fluid chamber connected to said auxiliary hydraulic pump to be supplied with the predetermined small quantity of fluid under pressure;

flow control valve means disposed within a first fluid circuit, said first fluid circuit connecting a fluid reservoir to a second fluid circuit, said second fluid circuit between said auxiliary hydraulic pump and said reaction fluid chamber, said flow control valve means being arranged to decrease the quantity of fluid discharged therethrough into said fluid reservoir in accordance with an increase of travel speed of the vehicle; and

a throttle disposed within a bypass circuit connecting said second fluid circuit to a third fluid circuit between said primary hydraulic pump and said valve means of said changeover valve unit.

5. A power-assisted steering system as recited in claim 4, further comprising a throttle disposed within said first fluid circuit between said reaction fluid chamber and said flow control valve means.