Fluid handling – Systems – Multi-way valve unit
Patent
1994-07-15
1995-10-17
Rivell, John
Fluid handling
Systems
Multi-way valve unit
13762522, 91375A, F15B 1304, B62D 5083
Patent
active
054581532
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 with a substantially linear boost characteristic.
BACKGROUND ART
Such rotary valves 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 matching the grooves in the input-shaft, but in underlap relationship thereto, the slots of one being wider than the lands of the other so defining a set of axially extending orifices which open and close when relative rotation occurs between the input-shaft and the sleeve from a centred position. The magnitude of such rotation is hereinafter referred to as the valve operating angle. The edges 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 to communicate oil between the grooves in the input-shaft and the slots in the sleeve, and hence between an engine driven oil pump, and right-hand and left-hand hydraulic assist cylinder chambers incorporated in the steering gear.
Typically, the input-shaft and sleeve are biased towards the centred position by a torsion bar spring. Thus when small input torques are applied to the steering wheel and hence the input-shaft, only a small magnitude of relative rotation occurs between the input-shaft and sleeve and, for such low valve operating angles, little power assistance is provided by the valve. For larger input torques proportionately greater valve operating angles are generated, leading to much greater levels of power assistance. The relationship between the level of power assistance generated in the valve, as a function of input torque, is known as the valve boost characteristic, and is largely determined by the metering edge contours.
It is convenient to refer to these metering edge contours as controlling three zones of the boost characteristic, the high pressure contour associated with the parking zone, an intermediate contour associated with the cornering zone, and a central zone associated with straight ahead driving where normally minimum boost is desired. For many vehicles it is becoming increasingly accepted that in the critical cornering zone, a truly linear relationship should exist between input torque applied by the driver and the level of power assistance, that is, a linear boost characteristic.
Rotary valves are nowadays regularly incorporated in firewall- mounted rack and pinion steering gears, and in this situation, any noises such as hiss emanating from the valve are very apparent to the driver. Hiss results from cavitation of the hydraulic oil as it flows in the orifices defined by the metering edge contours and the adjacent edges of the sleeve slots, particularly during times of high pressure operation of the valve such as during parking, where pressures typically as high as 8 MPa can be generated. It is well known in the art of power steering valves that an orifice is less prone to cavitation if the metering edge contour has a high aspect ratio of width to depth, thereby constraining the oil to flow as a thin sheet of constant depth all along any one metering edge contour and if, furthermore, the flow of oil is evenly divided amongst several metering edges ported to act in parallel, so further effectively reducing the flow of oil that may flow through any one orifice. It is also well known that cavitation is less likely to occur if the metering edge contour, where it intersects the outside diameter of the input-shaft, is nearly tangential thereto, hence constituting a shallow chamfer typically inclined at an angle of between 5.degree. to 8.degree.. This high pressure contour is operative at large valve operating angles and
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A. E. Bishop & Associates Pty. Limited
Rivell John
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