Hydraulic power steering with a closed center

• US 6,250,416 B1
• Filed: 08/09/2000
• Issued: 06/26/2001
• Est. Priority Date: 07/31/1997
• Status: Expired due to Term

• Current Assignee: Thyssenkrupp Presta Steertec GmbH (Thyssenkrupp AG)
• Original Assignee: Mercedes-Benz Ludwigsfelde GmbH (Mercedes-Benz Group AG)
• Inventors: Pluschke, Albrecht, Stehli, Thomas
• Primary Examiner(s): Johnson, Brian L.
• Assistant Examiner(s): LUBY, MATTHEW D
• Application Number:
  US09/463,744
• Time in Patent Office: 321 Days
• Field of Search: 180/403, 180/404, 180/405, 180/417, 180/421-423
• US Class Current: 180/404
• CPC Class Codes: B60R 25/02 operating on the steering mechanism
• CPC Class Codes: B62D 5/06 fluid, i.e. using a pressurised fluid for most or all the force required for steering a vehicle
• CPC Class Codes: B62D 5/09 characterised by means for actuating valves

Abstract

A closed-center hydraulic power steering system includes a rechargeable hydraulic pressure accumulator being capable of being connected to a servomotor via controllable pressure-reducing valves which control the motor pressure according to a desired value predetermined by a control device, a connection also being made, if required, between the motor and a relatively pressureless reservoir.

Claims

1. Hydraulic power steering system with

a steering wheel (1), also

steerable vehicle wheels positively coupled to the latter for steering adjustment, and

a double-acting hydrostatic servomotor (4) positively coupled to the steerable vehicle wheels and/or the steering handle,

a hydraulic pressure-generating device (11, 13),

a relatively pressureless hydraulic reservoir (12),

a control-valve arrangement (7, 8) which has two parallel three-way pressure-reducing valves (7, 8) assigned in each case to one side or connecting line (5, 6) of the servomotor (4) and which makes it possible to connect both sides of the servomotor (4) to the pressure-generating device (11, 13),

a sensor (16) for detecting forces or moments transmitted between the steering wheel(1) and the steerable vehicle wheels, and also

an electronic control device (15) which is connected, on the input side, to the sensor (16) and which controls the control-valve arrangement (7, 8) as a function of the forces or moments transmitted between the steering wheel (1) and the steerable vehicle wheels, in such a way that the servomotor (4) generates a boosting force in order to reduce a manual force perceptible on the steering wheel (1), characterized in that

the pressure-generating device (11, 13) has a hydraulic pressure accumulator (11),

the three-way pressure-reducing valves (7, 8) are provided with a controllable motor-pressure desired value, and

the control-valve arrangement (7, 8) is controlled by controlling the motor-pressure desired values of the pressure-reducing valves (7, 8).

2. Hydraulic power steering system according to claim 1, characterized in that the pressure-reducing valves (7, 8) are designed as proportionally working valves.

3. Power steering system according to claim 1, characterized in that a non-return valve (9, 10), which prevents a return flow to the pressure accumulator (11), is arranged between each pressure-reducing valve (7, 8) and the pressure accumulator (11).

4. Power steering system according to claim 1, characterized in that the control device (15) permits to switch on an operating state which can be used as an immobilizer and in which the servomotor (4) is blocked hydraulically.

5. Power steering system according to claim 1, characterized in that the control device (15) predetermines desired values for the motor pressure which are varied as a function of parameters.

6. Power steering system according to claim 1, characterized in that each pressure-reducing valve (7, 8) is urged by a spring force (20) variable by means of the control device (15), counter to the pressure at a respective motor connection (5, 6), into a position connecting the pressure accumulator (11) to the motor connection (5, 6).

7. Power steering system according to claim 1, characterized in that the hydraulic pressure accumulator (11) is assigned an electrical charging pump (13) actuated by the control device (15).