Torsional element for steering valves and spring characteristic

Details Torsional element for steering valves and spring characteristic Torsional element for steering valves and spring characteristic

1997-04-25

1998-12-22

Oberleitner, Robert

Spring devices

Vehicle

Torsion

74388PS, 91375A, 180417, 180441, B62D 506, F16D 372

Patent

active

058510060

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention pertains to a method for improving the spring characteristic of a torsion element for steering valves in power steering systems for motor vehicles, wherein said torsion element comprises two fastening end areas and at least one torsional area. The invention also discloses a new torsion element.
Steering valves of the aforementioned type are, in particular, used in power steering systems. An input shaft that is connected to a steering rod hydraulically cooperates with a valve sleeve that surrounds the input shaft and is connected to an output shaft with a pinion. The pinion of the output shaft acts upon the toothed rack of the steering system. Hydraulic fluid is pumped through the system under low pressure by means of a pump. If the input shaft is turned relative to the valve sleeve, hydraulic pressure is supplied to a hydraulic motor that boosts the movement of the toothed rack in one of the two possible directions. The input shaft and the output shaft are connected to one another via an elastic torsion element, preferably a torsion rod, in order to generate a certain torsional stiffness. A reaction device that can be charged with pressure may be arranged in the system in order to generate an additional centering moment. A reaction piston that is prestressed by a compression spring and, for example, may be additionally charged with hydraulic pressure as a function of the speed is usually used for this purpose, with the additional hydraulic pressure varying the torsional moment that must be overcome in order to turn the input shaft relative to the valve sleeve as a function of the speed. Known reaction pistons of this type are fixed relative to the input shaft in rotationally rigid fashion by means of balls that are guided in longitudinal grooves arranged in the input shaft. In addition, the reaction piston is prestressed in the direction toward the valve sleeve by means of a compression spring. If a torsional moment is exerted upon the input shaft, said torsional moment is converted into an axial force via the reaction piston and a ball coupling, with the axial force acting against the force of the spring that acts upon the reaction piston. As soon as this axial force generated by the ball coupling exceeds the counteracting spring force, the reaction piston is moved away from the valve sleeve axially, and the input shaft can be turned relative to the valve sleeve. A variation in the torsional moment can be realized by adjusting a corresponding hydraulic pressure on the side of the reaction piston which is situated opposite to the spring.
If a reaction piston that is charged with pressure via a coil spring is used for centering purposes, the resulting prestress of the reaction piston depends on the quality of the valve preassembly. The spring prestress to be adjusted varies within an undesirably broad range. In addition, the spring force acting upon the reaction piston is not concentric due to the utilization of a coil spring. This leads to distortions of the valve, which manifest themselves in the form of several complications, e.g., input shaft friction and hysteresis problems.
In addition to the previously described disadvantages, e.g., the difficult mechanical adjustment, the high expenditure of components and, if the reaction piston is charged with pressure, a difficult hydraulic seal, the main disadvantage of previously known steering valves of this type can be seen in the fact that the structural size, in particular, the structural length, cannot be reduced due to the reaction elements that essentially act in the axial direction.
In another known method, a metal bellows that is torsionally stiff but axially elastic is used instead of coil springs. Such a metal bellows makes it possible to attain a defined moment by means of a preadjustment during its assembly.
All described systems have the disadvantage that various elements must be mounted and centered or hydraulically balanced relative to one another at different locations.
A centering device of this type

REFERENCES:
patent: 4774847 (1988-10-01), Breitweg
patent: 5571238 (1996-11-01), Bretiweg et al.
patent: 5687810 (1997-11-01), Chol et al.
patent: 5697400 (1997-12-01), Pfeifer
patent: 5707049 (1998-01-01), Dodak

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