Hydraulic steering device

• US 20050161278A1
• Filed: 03/13/2003
• Published: 07/28/2005
• Est. Priority Date: 04/25/2002
• Status: Active Grant

• Current Assignee: Bosch Rexroth AG (Robert Bosch GmbH)
• Original Assignee: Bosch Rexroth AG (Robert Bosch GmbH)
• Inventors: Bergmann, Erhard, Scandella, Walter, Bollero, Vincenzo Domenico, Harnischfeger, Edwin
• Granted Patent: US 7,306,071 B2
• Time in Patent Office: Days
• US Class Current: 180/441
• CPC Class Codes: B62D 5/093 Telemotor driven by steering wheel movement hydraulic steering gear B62D3/14

Abstract

What is disclosed is a hydraulic steering apparatus with steering amount amplification, wherein a metering device for supplying pressure medium to steering cylinders is actuated in accordance with an amount of rotation of the steering wheel. With the aid of a control block it is possible to deliver an additional pressure medium volume to the steering cylinders, wherein control of the control block in accordance with the invention is effected through the intermediary of a control circuit containing an effective control pressure that is substantially lower than the load pressure for transmitting the steering moment at the steering cylinder. There is moreover disclosed a spring assembly for the control block, wherein two springs are arranged in parallel, one of which only takes effect following a predetermined stroke of the control element. Hereby it is possible to adjust a characteristic line according to which the control element is biased into the zero position with a minimum bias, an optionally existing overlap may be passed through with a low control pressure difference, and the control pressure range for opening the control block is sufficiently large.

Claims

1. Hydraulic steering apparatus, including a metering device adapted to be actuated in accordance with a steering velocity, for supplying at least one steering cylinder with pressure medium, and including a control block whereby pressure medium may additionally be supplied from a pump to at least one steering cylinder in accordance with an amount of rotation of a steering wheel, characterized by control means whereby a control pressure supplied to a control chamber of said control block may be set to a pressure that is lower than the pressure medium pressure acting downstream from said metering device.

2. The steering apparatus in accordance with claim 1, wherein said control means have a regulating valve whereby said control chamber may be supplied with pressure medium by a control pump, wherein said regulating valve is controlled in accordance with the pressure downstream from said metering device.

3. The steering apparatus in accordance with claim 2, wherein a nozzle is arranged inside a work line between steering cylinder and metering device, and control of said regulating valve is effected in accordance with a pressure drop across said nozzle.

4. The steering apparatus in accordance with claim 2, wherein said regulating valve has a pressure port, a work port, and a tank port, and in a spring-biased basic position said pressure port is connected with said work port.

5. The steering apparatus in accordance with claim 2, wherein said control block has two control chambers for controlling direction and velocity of the pressure medium flow, and to each control chamber one regulating valve is associated.

6. The steering apparatus in accordance with claim 1, wherein said control means include second control apportioning means that are in operative connection with said metering device and may be supplied with pressure medium by a feed pump via a control circuit, and the outlet port of which is connected with said control chamber via a control line.

7. Control means in accordance with claim 6, wherein said control line is returned to the associated outlet port via a control nozzle and a check valve.

8. The steering apparatus in accordance with claim 7, wherein said control block has control chambers for adjusting direction and velocity of pressure medium flow, which control chambers are each connected to a respective outlet port of said control apportioning means, wherein return lines leading away from each control chamber are connected in the range between said nozzle and said check valve by means of a connecting line into which a pressure line of said feed pump merges.

9. The steering apparatus in accordance with claim 6, wherein said metering device operates in accordance with the gerotor principle, and said control apportioning means is formed by a conveying organ arranged on a shaft of said metering device.

10. The steering apparatus in accordance with claim 6, wherein the control pressure fed into said control circuit is variable.

11. The steering apparatus in accordance with claim 1, wherein said control block includes a proportional valve with associated pressure compensator, and the bias acting in the direction of opening said pressure compensator is variable.

12. The steering apparatus in accordance with claim 11, wherein the bias may be varied hydraulically with the aid of bias valve means, whereby different bias pressures may be applied in accordance with the condition of travel.

13. The steering apparatus in accordance with claim 12, wherein said valve assembly includes one nozzle for each operating condition, wherein the bias is adjustable as a function of the pressure drop across the said respective nozzle.

14. The steering apparatus in accordance with claim 1, wherein said control block includes a continuously variable directional control valve, the control element of which is biased by a spring assembly into its basic position, with two springs being provided, and a second spring only taking effect following a predetermined stroke of said valve element.

15. The steering apparatus in accordance with claim 14, wherein a first spring of said spring assembly is received with a bias.

16. The steering apparatus in accordance with claim 14, wherein said second spring has a lower spring rate than said first spring.

17. The steering apparatus in accordance with claim 14, wherein said second spring is guided so as to be coaxial with said first spring and following said stroke may be driven by a drive shoulder of a spring cup supported on said control element.

18. The steering apparatus in accordance with claim 1, including a valve assembly for changing the steering amount amplification, whereby the control pressure difference present at said control block may be modified.

19. The steering apparatus in accordance with claim 18, wherein a control pressure present at said control block may be limited to a maximum value through the intermediary of said valve assembly.

20. The steering apparatus in accordance with claim 19, wherein said valve assembly has a proportionally adjustable pressure limiting valve and two check valves each associated to one control side of said control block.

21. The steering apparatus in accordance with claim 1, including means for improving the response characteristics of said control block at a low steering velocity.

22. The steering apparatus in accordance with claim 21, wherein said means include two pressure difference valves associated with respective control sides of said control block.