Abrading – Precision device or process - or with condition responsive... – Computer controlled
Patent
1993-07-28
1995-08-15
Rachuba, Maurina T.
Abrading
Precision device or process - or with condition responsive...
Computer controlled
451 8, 451252, B24B 4900
Patent
active
054414385
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an apparatus for use in conjunction with the manufacture of components of rotary valves such as are used in hydraulic power steering gears for vehicles. 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 henceforth referred to as the valve operating angle. The edges of the input-shaft grooves are contoured so as to provide a specific orifice configuration often referred to as metering. 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.
BACKGROUND OF THE INVENTION
The general method of operation of such rotary valves is well known in the art of power steering design and so will not be described in any greater detail in this specification. A description of this operation is contained in U.S. Pat. No. 3,022,772 (Zeigler), commonly held as being the "original" patent disclosing the rotary valve concept. According to that patent, 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 pressure characteristic. This valve pressure characteristic is therefore determined by the geometry of the changing orifice area as a function of valve operating angle.
Such 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 input-shaft metering edge contours and the adjacent edges of the sleeve slots particularly during times of high pressure operation of the valve such as during vehicle parking manoeuvres, where pressures typically as high as 8 MPa can be generated. It is well known in the art of power steering valves than 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 that the flow of oil is divided equally amongst the aforementioned network of orifices, so further effectively increasing the aspect ratio. 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 of no more than about 1 in 12 slope. Typically, during high pressure operation of the rotary valve, one edge of each sleeve slot is angularly displaced about one half of a degree from the point of intersection of this chamfer with the input-shaft outside diameter, and the radial depth of the orifice so formed is about 0.012 mm.
As the input-shaft
REFERENCES:
patent: 3433238 (1969-03-01), Nightingale
patent: 3620239 (1971-11-01), Bright
patent: 3628372 (1971-12-01), Honda
patent: 3914754 (1975-10-01), Kirk
patent: 5209103 (1993-05-01), Dririere et al.
patent: 5299388 (1994-04-01), Bishop
A.E. Bishop & Associates PTY LTD.
Rachuba Maurina T.
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