Metal working – Method of mechanical manufacture – Shaping one-piece blank by removing material
Patent
1993-05-11
1995-02-21
Briggs, William
Metal working
Method of mechanical manufacture
Shaping one-piece blank by removing material
29890132, 409244, 409293, B23P 1300, B21D 5300
Patent
active
053904087
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method and apparatus for manufacturing a plurality of parallel, longitudinally extending slots in the bore of a component. One example of such a component is the sleeve element of an automotive rotary power steering valve in which the slots are usually blind-ended and form a series of hydraulic ports circumferentially spaced within the sleeve bore, and which operate, in conjunction with similar circumferentially spaced ports in a co-acting cylindrical input-shaft element housed within the sleeve, upon slight relative rotation between these components. The present invention will be in particular reference to such sleeves even though it will be understood that it has wider application in the manufacture of parallel, longitudinally extending internal slots in the bore of components generally.
The prior art which is most closely related to that of the present invention is disclosed in U.S. Pat. No. 4,154,145 (Bishop) and Australian Provisional Patent Application PK3520 (Bishop). These so called "slotting machines" machine the slots in the bore of power steering valve sleeves. The design of these machines calls for each of the slots to be scooped out of the bore of a turned blank by a finger-like cutting tool mounted in a cutting spindle which angularly reciprocates about an axis in a series of progressively deeper cutting and return strokes so forming a closed chamber, or hydraulic port, which is arcuate in longitudinal section. The sleeve is held in a work holding collet, in turn mounted in a work holding spindle, having a rotational axis perpendicular to and offset with respect to the cutting spindle axis. By accurately indexing the work holding spindle upon completion of each slot, the required number of slots are precisely machined in the sleeve, usually 4, 6 or 8 slots for most automotive applications.
Many rotary power steering valves today are incorporated in firewall-mounted rack and pinion steering gears and, in this situation, any noises emanating from the valve are very apparent to the driver due to the required relatively rigid mounting of the steering gear and its proximity to the driver. However, even in the case of the more remotely located cross-member-mounted rack and pinion steering gears, or indeed the classical recirculating ball-nut steering boxes, valve noise can be transmitted up the steering shaft and therefore still be audible to the driver. The type of valve noise of greatest concern to the rotary valve designer is the "hiss" resulting from cavitation of the hydraulic oil as it flows through the axially extending array of control orifices in the valve. These orifices are formed by the interaction of adjacent sets of input-shaft metering edges and sleeve slot edges, and therefore open and close when relative rotation occurs between the input-shaft and sleeve. The orifices are ported as a network such that they form sets or arrays of hydraulic Wheatstone bridges which act essentially in parallel. Hiss is particularly evident during times of high pressure operation of the valve such as during parking manoeuvres.
It has been found that hiss is significantly reduced in rotary valves if the various input-shaft metering edges are manufactured extremely precisely so that oil flow in the sets or arrays of hydraulic Wheatstone bridges is distributed equally between them, so avoiding instances where the flow density per unit length of metering edge greatly exceeds the mean overall value, with consequent triggering of violent turbulent flow and hence cavitation. Such "feather" form metering edges, for example those described in U.S. Pat. No. 4,460,016 (Haga), are frequently ground to a fine depth and angular index tolerance in order to achieve this end. However, as referred to earlier, the hydraulic orifices in a rotary valve are equally determined by the angular position of the sleeve slot edges.
Therefore refinements in the design and the manufacture of the sets of input-shaft metering edges are totally wasted if the sets of corresponding sleeve slot edges are inaccu
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"Back End Work", pp. 12-14, Automatic Machining, Jul. 1972.
PCT/US90/02402, Published Nov. 15, 1990.
Baxter John
Bishop Arthur E.
McLean Lyle J.
Roeske Klaus J.
A.E. Bishop & Associates Pty. Limited
Briggs William
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