Power steering and limited slip differential system

• US 5,301,766 A
• Filed: 05/01/1991
• Issued: 04/12/1994
• Est. Priority Date: 05/07/1990
• Status: Expired due to Term

• Current Assignee: HINO Jidosha Kogyo Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: HINO Jidosha Kogyo Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Ohmori, Kenichi, Oku, Shinichi, Harada, Kohji, Momiyama, Fujio, Tokuda, Noriaki
• Primary Examiner(s): Focarino, Margaret A.
• Assistant Examiner(s): BOEHLER, ANNE MARIE M
• Application Number:
  US07/694,359
• Time in Patent Office: 1,077 Days
• Field of Search: 180/132, 180/141, 180/142, 180/143, 180/245, 180/246, 180/234, 180/152, 180/197, 475/231, 475/238, 475/86, 475/249, 475/257
• US Class Current: 180/197
• CPC Class Codes: B60K 23/04 for differential gearing
• CPC Class Codes: B62D 6/04 responsive only to forces disturbing the intended course of the vehicle, e.g. forces acting transversely to the direction of vehicle travel
• CPC Class Codes: B62D 7/159 characterised by computing methods or stabilisation processes or systems, e.g. responding to yaw rate, lateral wind, load, road condition

Abstract

A power steering and limited slip differential system is provided with a main booster generating a steering effort for front wheels, a directional control valve having a pair of reaction chambers and a friction clutch disposed between a differential gear mechanism and a driving wheel axle for rear wheels and is further added with an auxiliary booster generating a compensation steering effort for the front wheels and a clutch control air cylinder for coupling and decoupling the friction clutch. In the system, an injection pressure control valve injects compensating pressure oil into the auxiliary booster and the reaction chambers of the directional control valve in response to a vehicle speed and steering effort at the beginning of steering and steering back and concurrently controls the pressure of the injected compensating pressure oil, and a pressure air control valve charges and discharges operating compressed air to and from the clutch control air cylinder in response to the vehicle speed and the steering angle of the front wheels, and further in response to the slipping at one side and the both sides of the rear wheels and thereby controls the air pressure of the clutch control air cylinder.

Claims

1. A power steering and limited slip differential system comprising:

a main booster which generates a steering effort for front wheels;

an auxiliary booster which generates a compensation steering effort for the front wheels;

a directional control valve which has a pair of reaction chambers and which controls the direction of operating pressure oil which is supplied from a hydraulic pump to the main booster and concurrently discharged from the main booster to an oil reservoir;

a pressure oil setting valve which sets the pressure of the operating pressure oil supplied to the main booster, and the pressure of compensating pressure oil supplied to the auxiliary booster and the reaction chambers of the directional control valve;

injection pressure control valves which inject the compensating pressure oil into the reaction chambers of the directional control valve and the auxiliary booster in response to a vehicle speed and a manual steering force applied at the beginning of steering into a turn and the beginning of steering out of a turn, and concurrently controls the pressure of the injected compensation pressure oil;

a friction clutch disposed between a differential case of a differential gear mechanism and a driving wheel axle for rear wheels;

a clutch control air cylinder for coupling and decoupling the friction clutch; and

an air pressure control valve which charges and discharges operating compressed air to and from the clutch control air cylinder in response to the vehicle speed and the steering angle of the front wheels, and further in response to the slipping of at least one of the rear wheels, and controls the air pressure of the clutch control air cylinder.

2. A power steering and limited slip differential system according to claim 1, wherein said auxiliary booster is link-coupled to at least one of a knuckle and a tie rod of the front wheels through a link mechanism.

3. A power steering and limited slip differential system according to claim 1, wherein said auxiliary booster is constituted in a form of a double action cylinder having a pair of cylinder chambers and is link-coupled to a knuckle side of the front wheels via a link mechanism.

4. A power steering and limited slip differential system according to claim 1, wherein said directional control valve includes a bypass line which communicates the pair of reaction chambers to each other and a reaction adjustment valve disposed in the bypass line.

5. A power steering and limited slip differential system according to claim 4, wherein said reaction adjustment valve is orifice-adjusted in such a manner that the steering effort is relatively lighter during a stationary steering and a low speed running and somewhat heavier during a high speed running.

6. A power steering and limited slip differential system according to claim 1, wherein said pressure oil setting valve is disposed at an upstream side of the directional control valve in a supply side pressure oil piping which connects the main booster to the hydraulic pump via the directional control valve in order that the pressure of the compensating pressure oil led to a pair of cylinder chambers of the auxiliary booster and the pair of reaction chambers of the directional control valve is always set higher than that in the circuit of the main booster.

7. A power steering and limited slip differential system according to claim 1, wherein said pressure oil setting valve always sets the pressure of the compensating pressure oil higher by 5 Kg/cm² than that in a circuit of the main booster.

8. A power steering and limited slip differential system according to claim 1, wherein said injection pressure control valves are disposed between the hydraulic pump located upstream of the pressure oil setting valve and the oil reservoir located downstream of the main booster in compensating pressure oil pipings which correspondingly connect a pair of cylinder chambers of the auxiliary booster and the pair of reaction chambers of the directional control valve.

9. A power steering and limited slip differential system according to claim 1, wherein said injection pressure control valves are a pair of linear solenoid valves, and the pair of linear solenoid valves are correspondingly connected at the hydraulic pump located upstream of the pressure oil setting valve with auxiliary pressure oil pipings which connect a pair of cylinder chambers of the auxiliary booster with the pair of reaction chambers of the directional control valve and at the oil reservoir located downstream of the main booster with the auxiliary pressure oil pipings which connect the pair of cylinder chambers of the auxiliary booster with the pair of reaction chambers of the directional control valve.

10. A power steering and limited slip differential system according to claim 1, wherein said injection pressure control valves are operated by supplying the compensating pressure oil in a form of a pulse of pressure oil at the beginning of steering and of steering back.

11. A power steering and limited slip differential system according to claim 1, wherein said injection pressure control valves are operated by supplying the compensating pressure oil in a form of a pulse of pressure oil having a pulse width ranging from 0.1 through 0.25 wavelength with respect to a manual steering force wavelength at the beginning of steering into a turn and of steering out of a turn.

12. A power steering and limited slip differential system according to claim 1, wherein said injection pressure control valves are supplied with the compensating pressure oil in a form of a pulse of pressure oil at the beginning of steering into a turn and of steering out of a turn and a pulse width and a pulse amplitude of the pulse of pressure oil are determined in response to both variations of the manual steering force applied to a steering wheel and the rate of change thereof.

13. A power steering and limited slip differential system according to claim 1, wherein said clutch control air cylinder includes a ring cylinder which opens to a ring chamber and is formed in the differential case, and a ring piston which is fitted in the ring cylinder so as to permit slidable reciprocating movement while facing to the pressure ring of the friction clutch in order to form a cylinder chamber in the ring cylinder.

14. A power steering and limited slip differential system according to claim 13, wherein said clutch control air cylinder further includes a pressure air coupling which connects the cylinder chamber to a pressure air source via a pressure air piping.

15. A power steering and limited slip differential system according to claim 14, wherein said pressure air coupling includes a sealed slip ring fitted to a boss of the differential case so as to permit relative rotational movement thereto which is stopped by a ring gear boss in a differential carrier supporting the differential case, and an air lead pipe connecting the sealed slip ring to the pressure air line.

16. A power steering and limited slip differential system according to claim 1, wherein said air pressure control valve includes a normally closed two way solenoid valve disposed in a pressure air piping which connects the clutch control air cylinder to a pressure air source, and a normally opened two way solenoid valve disposed in the pressure air piping downstream the normally closed two way solenoid valve, and the normally closed two way solenoid valve supplies operating compressed air from the pressure air source to the clutch control air cylinder when the normally opened two way solenoid valve is closed and the normally opened two way solenoid valve discharges the operating compressed air to the air from the clutch control air cylinder when the normally closed two way solenoid valve is closed.

17. A power steering and limited slip differential system according to claim 1, wherein said air pressure control valve includes a normally closed two way solenoid valve and a normally opened two way solenoid valve integrally assembled with the normally closed two way solenoid valve downstream thereof, and the normally closed two way solenoid valve supplies operating compressed air to the clutch control air cylinder and the normally opened two way solenoid valve discharges the operating compressed air from the clutch control air cylinder.

18. A power steering and limited slip differential system according to claim 1, further comprising;

a steering wheel which includes a rim core integrated with a hub via spokes and a rim sheath covering the rim core via a roller so as to permit a slight free slidable rotation in a steering direction; and

a manual steering pressure sensor which includes a bending beam of which a root portion is secured at the side of the rim core and a top portion is fitted into a groove at the side of the rim sheath so as to represent by bending the sliding amount between the rim core and the rim sheath and an electromagnetic inductor sensor detecting the bending of the bending beam.