Abrasive tool making process – material – or composition – With carbohydrate or reaction product thereof
Patent
1993-05-19
1994-04-05
Rose, Robert A.
Abrasive tool making process, material, or composition
With carbohydrate or reaction product thereof
51105VG, 51289R, B24B 1902, B24B 536
Patent
active
052993884
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method and apparatus for manufacturing fluid control contours in components of rotary valves such as 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 the 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 the centred or neutral condition, 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, thereby determining the valve pressure characteristic.
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.
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. 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. Similarly it is important that the flow of oil divides equally amongst the aforementioned network of orifices, so further effectively increasing the above aspect ratio. This requires highly accurate angular spacing of the input-shaft metering edge contours as well as the precision of manufacture of each metering edge contour to ensure uniformity of depth along their length. Precision is most important in that portion of the metering edge contour controlling high pressure operation of the rotary valve associated with parking manoeuvres, where the pressure generated is typically 8 MPa and the metering edge contour depth only about 0.012 mm. This portion lies immediately adjacent to the outside diameter of the input-shaft, and is associated with the maximum normal operating angle of the valve. However, precision is also required in order to avoid hiss further down the metering edge contour where the pressure generated is typically 2 MPa and the contour depth about 0.024 mm. The remainder of the metering edge contour towards the centred position of the rotary valve is important in determining the valve pressure characteristic, but not valve noise.
It is also well known that cavitation is less likely to occur if the metering edge contour is of a wedge configuration having a slope of no more than about 1 in 12 with respect to the outside diameter of the input-shaft. The low slope of the metering edge contour in the parking region makes it difficult to achieve the above-mentioned highly accurate angular spacing of the metering edge contours, which latter spac
REFERENCES:
patent: 730445 (1903-06-01), Echols
patent: 1252509 (1918-01-01), Thomas
A. E. Bishop & Associates Pty. Limited
Rose Robert A.
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