Power-assisted steering with hydraulic power assistance

• US 6,474,437 B1
• Filed: 03/05/2001
• Issued: 11/05/2002
• Est. Priority Date: 07/02/1998
• Status: Expired due to Fees

• Current Assignee: Robert Bosch Automotive Steering GmbH (Robert Bosch GmbH)
• Original Assignee: ZF Lenksysteme GmbH (Robert Bosch GmbH)
• Inventors: Zeitz, Wolfgang, Braun, Andreas, Elser, Dieter
• Primary Examiner(s): Hurley, Kevin
• Application Number:
  US09/720,763
• Time in Patent Office: 610 Days
• Field of Search: 180/417, 180/421, 180/422, 180/423, 180/405, 180/406
• US Class Current: 180/422
• CPC Class Codes: B62D 5/06 fluid, i.e. using a pressurised fluid for most or all the force required for steering a vehicle

Abstract

In a power steering system having hydraulic power support for motor vehicles, a steering gear shaft having a steering wheel is connected to an input element of a steering gear. An output element of the steering gear is connected to wheels of the vehicle to be steered. Two working chambers of a servo motor of a power boosting system can be supplied with a hydraulic medium from a servo pump through a steering valve in accordance with a torque applied in the area of the steering gear shaft input element. Two sensors for detecting an angle of rotation and a torque are provided on the steering gear shaft and on the output element of the steering gear accordingly. After the steering wheel has been released after a steering operation, the wheels to be steered and the steering gear can be returned with hydraulic support. Both the intensity and direction of the hydraulic power support as well as the returning of the wheels to be steered are controlled by a common, electronically controlled electromagnetic valve. In addition, only one steering force sensor and/or torque sensor is provided for detecting the steering force. With this sensor, the control distances can be reduced greatly, thus yielding a high steering accuracy.

Claims

1. A power steering system for a motor vehicle, the power steering system having hydraulic power support, the motor vehicle including a in steering wheel and wheels to be steered, the power steering system comprising:

a steering gear having an input element and an output element, the output element being connected to the wheels to be steered;

a steering gear shaft connected to the steering wheel and to the input element of the steering gear;

a steering valve;

a servo pump;

a power boosting system including a servo motor having two working chambers, the servo pump supplying a hydraulic fluid to the two working chambers through the steering valve in response to a torque applied to at least one of the steering gear shaft and the input element;

at least one first sensor arranged on the steering gear shaft, the at least one first sensor being configured to detect at least one of an angle of rotation and a torque;

a second sensor mounted on one of the output element and the input element, the second sensor being configured to detect a steering angle;

a returning device configured to provide hydraulic power support to return the steering gear and the wheels to be steered after the steering wheel is released after a steering operation; and

a common, electronically controlled electromagnetic valve configured to control an intensity and a direction of the hydraulic power support and the returning of the wheels to be steered;

wherein the at least one first sensor includes a single steering force sensor configured to detect a steering force, the steering force sensor including at least one of a force sensor and a torque sensor.

2. The power steering system according to claim 1, further comprising a short-circuit valve disposed between the steering gear shaft and the input element of the steering gear.

3. The power steering system according to claim 2, wherein the short-circuit valve connects the two working chambers of the servo motor when the short-circuit valve is in an open position.

4. The power steering system according to claim 1, further comprising an electronic unit configured to control the electromagnetic valve as a function of at least one parameter.

5. The power steering system according to claim 4, wherein the at least one parameter includes at least one of a vehicle speed, a steering rate, a yaw rate and a vehicle load.

6. The power steering system according to claim 1, further comprising a hydraulic fluid reservoir, and wherein the electromagnetic valve includes a closed center.

7. The power steering system according to claim 2, wherein the short-circuit valve is integrated with the electromagnetic valve, the short-circuit valve being electronically controllable.

8. The power steering system according to claim 7, further comprising a third sensor arranged on the input element of the steering gear, the third sensor being configured to detect an angle of rotation.

9. The power steering system according to claim 1, wherein the electronic unit and each sensor are provided redundantly.

10. The power steering system according to claim 1, wherein the electromagnetic valve includes a proportional valve.

11. The power steering system according to claim 1, wherein the single steering force sensor includes a piezoelectric element.