Power steering gear valve

Fluid handling – Systems – Multi-way valve unit

Patent

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Details

91375A, 13762524, F15B 910

Patent

active

058787801

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to rotary valves such as are used in hydraulic power steering gears for vehicles. More particularly the present invention provides low noise rotary valves offering flexibility in the design of the boost characteristic.


BACKGROUND ART

Such rotary valves typically include an input-shaft which incorporates in its outer periphery a plurality of blind-ended, axially extending grooves separated by lands. Journalled on the input-shaft is a sleeve having in its bore an array of axially extending blind-ended slots circumferentially aligned with the lands on the input-shaft. The interfaces between the coacting input-shaft grooves and sleeve slots define axially extending orifices which open and close when relative rotation occurs between the input-shaft and the sleeve. The sides of the input-shaft grooves are contoured so as to provide a specific orifice configuration and are referred to as metering edge contours. These orifices are ported as a network such that they form sets of hydraulic Wheatstone bridges which act in parallel. Such hydraulic Wheatstone bridges are analogous in operation to conventional electrical Wheatstone bridges.
Drilled passages in the input-shaft and sleeve, together with circumferential grooves in the periphery of the sleeve, serve to communicate oil between the grooves in the input-shaft and the slots in the sleeve, a hydraulic pump, and right-hand and left-hand hydraulic assist cylinder chambers incorporated in the steering gear.
A torsion bar incorporated in the input-shaft serves to urge the input-shaft and sleeve towards a neutral, centred position when no power assistance is required. When input torque is applied by the driver to the steering wheel, the torsion bar deflects, causing relative rotation of the sleeve and input-shaft from the neutral position. This so called "valve operating angle" imbalances the sets of hydraulic Wheatstone bridges and hence causes a differential pressure to be developed between the right-hand and left-hand cylinder chambers. The "boost characteristic" of the rotary valve, that is the functional relationship between the above mentioned input torque and differential pressure, is largely determined for a given steering gear application by the geometry of the metering edge contours.
Traditionally the network of orifices in a rotary valve employ 2, 3 or 4 Wheatstone bridges, necessitating respectively 4, 6 or 8 input-shaft grooves and sleeve slots. Each Wheatstone bridge comprises a right-hand and a left-hand oil flow path, henceforth termed "limbs", and each right-hand and left-hand limb in turn comprises upper and lower portions. The upper and lower portions of each right-hand and left-hand limb meet respectively at a point of connection to the right-hand and left-hand cylinder chamber, henceforth termed the right-hand and left-hand "cylinder ports" of the valve.
In the neutral position of the rotary valve, oil from the hydraulic pump divides and enters each Wheatstone bridge at the valve "inlet port". At this point flow further divides and enters the upper right-hand and left-hand limbs, each containing an "inlet orifice". After being metered through such inlet orifices, oil is communicated to the respective cylinder ports and to the respective interconnection to the lower limbs. Depending on the intercylinder flow rate drawn by the motion of the piston in the cylinder chamber, oil continues to flow through the lower right-hand and left-hand limbs, metering through a "return orifice" in each limb, and recombining immediately upstream of the "return port" of the rotary valve.
The network of two inlet orifices and two return orifices, constituting each Wheatstone bridge, is ported in the rotary valve such that, for a given relative angular displacement of the input-shaft and sleeve from their neutral position, mutually opposite orifices on each Wheatstone bridge simultaneously close or open. For example, the left-hand inlet and right-hand return orifices both close (ie. increase in restriction to oil flow) while t

REFERENCES:
patent: 4470432 (1984-09-01), Kervagoret

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