Manufacture of rotary valves

Details Manufacture of rotary valves Manufacture of rotary valves

1995-04-20

1996-08-27

Kisliuk, Bruce M.

Abrading

Abrading process

451 49, 451 65, 451 72, B24B 100

Patent

active

055495044

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to the manufacture of rotary valves such as are used in hydraulic power steering gears for vehicles and in particular valves as disclosed in International Patent Application PCT/AU93/00015. That application describes a low noise rotary valve having a unique linear boost characteristic.
2. Description of the Related Art
In general, 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 and are referred to as the 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. The input-shaft and sleeve are biased towards the centred position by a torsion bar spring as is well known in the art. The relationship between the level of power assistance generated in the valve, as a function of input torque, is known as the boost characteristic, and is largely determined by the metering edge contours.
It is convenient to refer to the 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.
At the same time, increasing emphasis is placed on achieving a very low noise level, particularly when the valve is operating at high pressures such as in parking. Typically this is achieved by having each high pressure contour associated with the parking zone comprise a shallow chamfer which, in section, is inclined at a slope between about 4.degree. and 8.degree. at the junction between the chamfer and the periphery of the input-shaft. By this means, the overall flow at high pressures is divided equally into a series of thin sheets or jets between the several orifices which are closing simultaneously. Such thin sheet jets have been shown to be less likely to produce cavitation and associated valve hiss. At larger chamfer angles than about 8.degree., flow separation between the oil flow and adjacent periphery of the input-shaft may occur, also leading to cavitation. The shallow chamfer typically subtends an angle of about one degree at the input-shaft axis and thereafter extends towards the input-shaft groove edge as an intermediate contour in the form of a steeper chamfer or, preferably, in the form of a curved chamfer or scroll of decreasing radius. Such a latter scroll concept is earlier taught in EPO Patent 0196172 and provides a means of achieving a linear boost relationship in the cornering zone for a low noise valve.
The particular feature of International Application PCT/AU93/00015 is the addition of a longitudinal trough lying within some or all of the cornering zone chamfers, this trough serving to extend the linear boost region which otherwise ceases to be linear about half

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patent: 5267588 (1993-12-01), Bishop et al.
patent: 5299388 (1994-04-01), Bishop
patent: 5439412 (1995-08-01), Bishop

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