Fluid handling – Systems – Multi-way valve unit
Patent
1997-11-06
2000-01-25
Michalsky, Gerald A.
Fluid handling
Systems
Multi-way valve unit
91375A, 13762523, F15B 910
Patent
active
060168374
DESCRIPTION:
BRIEF SUMMARY
The invention pertains to a steering valve with a closed center for supplying a control element with hydraulic pressure, consisting of an input shaft, an output shaft, a torsionally elastic element that is connected at one end to the input shaft and at the other to the output shaft, a control pressure switching device and a torque/axial force converter unit.
Steering valves of this class are utilized in particular in servo-steering systems. The structure of such servo-steering systems is conventional. An input shaft connected to a steering rod is connected to an output shaft equipped with a pinion. In a familiar manner, it is possible to insert a torsionally elastic element, a torsion rod, for instance, between the two shafts. The pinion acts on the toothed rack of a steering unit. The use of steering valves for such steering systems is familiar. For this purpose, a control pressure switching unit is provided, which may, for instance, be a valve casing engaged with the output shaft and surrounding the input shaft. Hydraulic fluid is pumped through the system with a pump. In case of a twisting of the input shaft relative the valve casing, hydraulic pressure is fed to a hydraulic motor, which assists the rack motion in one of the two possible directions.
A valve without torque/axial force converter unit is known from DE 37 31 258 A1, with a hydraulic-carrying line formed in the input shaft.
Steering valves employed in servo-steering systems are divided roughly into two groups. One type of steering valve employed in servo-steering systems is the steering valve with a so-called open center. In the neutral position of the steering valve with open center hydraulic fluid at low pressure is pumped through the open valve into a reservoir by a pump. A twisting of the input shaft relative to the valve casing causes an elevation in pressure, which is then fed to the servomotor. The disadvantage of steering valves with open center is that a steady hydraulic flow must be maintained even in the neutral position. Thus, wasted power must be produced by the drive motor, derived primarily from the pressure accumulation and the volume flow.
Such a steering valve, which has all the features of this class, apart from the open center, is disclosed in DE 43 17 818 C1. A reaction piston with an electrohydraulic converter EHW is employed as a torque/axial force converter unit.
Another type of steering valve used in servo-steering systems is the steering valve with a so-called closed center. The hydraulic flow to the two cylinder sides is interrupted in the neutral position of the valve by the closed center position. Thus, there is no hydraulic flow in the neutral position. An operating pressure, which, upon opening of the valve, only has to be held in prescribed limits by the pump then going into action, is applied to the practically closed valve and a reservoir. Because of the wasted power appearing for steering valves with open center even when the steering is not being operated, the steering valves with closed center are superior in the neutral position from the standpoint of power. They have the disadvantage, however, that practically no direct correlation exists between input torque and working pressure in the cylinder. In the prior art, therefore, additional measures were taken in order to provide the operator with a relationship between the steering force to be input and the resulting hydraulic pressure. Conventional seat valve arrangements are not without problems, since the seat valves undergo a certain wear and require considerable manufacturing and assembly effort. Moreover, they confront the operator with a threshold torque.
A fundamental problem in all embodiments of steering valves of the types mentioned above results from the arrangement of the hydraulic lines and the conduction of the hydraulic fluid. The steering valve, constructed in modular fashion, has essentially radial connection boreholes for hydraulic lines, accessible from the outside, in its housing. Accordingly, channels, grooves and the like, which direc
REFERENCES:
patent: 5697400 (1997-12-01), Pfeifer
Pritchard Geoffrey
Spillner Robert
Vile David
Michalsky Gerald A.
TRW Fahrwerksysteme GmbH & Co. KG
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