| 摘要 |
A power assisted steering gear assembly having a first fluid system 5 comprising a first pressure operated device such as a double acting piston and cylinder, a first valve for controlling fluid flow to the first pressure operated means in response to a steering input in shaft 2 and a first fluid pump 7. The first pressure operated means can be a conventional power assisted steering gear 1 imparting rotation to a drop arm 8. A second fluid system 20 comprises second valve means controlling fluid flow from a second pump 26 to a second piston and cylinder device incorporated in a ram unit 12. The second valve in the ram unit 12 is responsive to displacement of the drop arm 8 and reacts to determine power assistance provided by the system 20 to a steering maneuver, such power assistance being additional to that provided by the system 5. Displacement of the ram unit 12 controls movement of a steering linkage through drag link 38. In a modification the system 20 can include an auxilliary valve which is responsive to fluid pressure in the system 5 so that when that pressure attains a predetermined value the auxilliary valve reacts to render ineffective power assistance from the ram unit 12. In the event of fluid pressure failure in the system 5 the auxilliary valve reacts to restore pressure fluid to the ram unit 12 and provide power assistance in the system 20. |
