Fluid handling – Systems – Multi-way valve unit
Reexamination Certificate
1999-10-21
2001-05-15
Fox, John (Department: 3753)
Fluid handling
Systems
Multi-way valve unit
C251S086000
Reexamination Certificate
active
06230742
ABSTRACT:
TECHNICAL FIELD
The present invention relates to poppet valves, and more particularly, to a force-balanced poppet valve assembly wherein two valve heads disposed on a common pintle shaft open and close simultaneously with respect to their respective valve seats.
BACKGROUND OF THE INVENTION
Poppet valves are widely used for opening and closing flow paths for gases and liquids, for example, as shift diverter valves in vehicles; for channeling hydrogen into reformers in fuel cells; and as intake, exhaust, and exhaust gas recirculation valves in internal combustion engines. A poppet valve typically comprises a circular valve head mounted transversely on a pintle shaft for axial motion thereof to form or eliminate a flow gap between the valve head and a mating circular valve seat in a valve body. A pintle shaft is also known as a valve shaft or valve stem.
Poppet valves can be very demanding in their design and fabrication tolerances. For example, some poppet valves are provided with conical mating surfaces on the valve head and valve seat; however, leak-free sealing over the entire mating surfaces depends on near-perfect circularity, coaxiality, and smoothness of both surfaces. In addition, the surfaces must have substantially identical cone angles. The highest quality valves are ground on a precision lathe and then the valve head is lap-ground to its dedicated seat. This is labor-intensive, time-consuming, and expensive. U.S. Pat. No. 4,565,217 discloses a poppet valve having a conical head and a curved seat such that head and seat can seal along a circular line of contact, thereby obviating the need for matching cone angles.
Known poppet valves further require that the valve head be mounted perfectly orthogonal to the valve stem and that a plane containing the valve seat be perfectly parallel to a plane containing the valve head. Deviation in any of these relationships can cause the head to mate imperfectly with the seat, which can result in valve leakage.
Poppet valves used to divert a portion of an engine's exhaust gas stream into the intake stream (Exhaust Gas Recirculation, or EGR) can encounter significantly different pressures in these two streams, such that a single poppet control valve between them may require a powerful actuator to overcome the pressure difference. It is known to provide, therefore, a force-balanced poppet valve, having two valve elements operated by a single pintle shaft, one valve opening into the exhaust stream and the other opening into the intake stream, wherein the intake vacuum and exhaust pressure exerted across the two valves substantially cancel each other, permitting the valve to be controlled by an inexpensive, low-power actuator.
An important performance criterion for such a force-balanced valve is that the two valves open and close to a high degree of synchronicity. This requires that the spacing of the valve heads on the pintle shaft be identical with the spacing of the valve seats in the valve body. It requires further that the identical spacing be maintained over the full range of operating conditions, particularly temperatures.
The latter behavior can be provided by constructing the valve body, valve heads, and pintle shaft of the same material, for example, stainless steel, such that these components expand and contract at the same rate in response to thermal changes.
The requirement for identical spacing of the heads is more difficult to satisfy. Typically, during assembly, the first head is installed on the pintle shaft, either by being formed with the shaft or by being attached thereto, and seated on its seat; then the second head is slid onto the pintle shaft, seated against its own seat, and secured to the shaft as by welding, bolting, or the like. A problem with these techniques is that the second head and/or shaft may be deformed thereby, ruining the synchronicity of the assembled valve. If the head or shaft is distorted so that the head is not perfectly orthogonal to the shaft, the resulting valve cannot close properly. Such deformation can also create error in the axial location of the distal end of the pintle shaft, which may be cooperative with a position sensing apparatus during throttling operation of the valve. Valves thus deformed, if still usable, may require individual calibration after assembly, which is costly and time-consuming.
Alternatively, the shaft may be provided with an accurately-located inner shoulder against which the second valve head may be seated in the proper relationship to the first valve head and then be secured as described supra. Such a configuration is highly intolerant of error in placement of the shoulder or error during assembly, and is also vulnerable to the deformation potential noted above.
What is needed is a two-headed poppet valve wherein the spacing of the valve heads along the pintle shaft is directed by the spacing between the valve seats, wherein at least one of the valve heads is compliantly mounted on the pintle shaft, and wherein the compliantly-mounted head may be so mounted without engendering errors in spacing of the valve seats along the pintle shaft.
SUMMARY OF THE INVENTION
The present invention is directed to an improved two-headed poppet valve assembly wherein the spacing of the valve heads along the pintle shaft is directed by the spacing between the valve seats and wherein at least one of the valve heads is compliantly mounted on the pintle shaft.
The assembly has a valve body having a central chamber separating first and second valves. The valves comprise first and second valve seats and first and second valve heads coaxially disposed in spaced-apart relationship at opposite ends of the chamber for ingress and/or egress of gas or liquid, one of the valves opening into the chamber and the other valve opening out of the chamber. The valve seats are spaced apart by a selected axial distance. The valve assembly further comprises a pintle shaft for axially actuating the valve heads, the shaft being disposed coaxially through the valve seats. The first and second valve heads are spaced apart along the pintle shaft at the same axial distance as the distance between the valve seats, such that axial motion of the pintle shaft causes the first and second valves to be opened or closed simultaneously.
One of the valve heads is fixed to the pintle shaft and, when placed against its respective seat, provides a valve-closed reference position for the pintle shaft. The other valve head is axially slidable on the shaft. During assembly of the valve, the second valve head is seated against the second valve seat to establish the correct head spacing. The shaft is then provided with head-restraining means, for example, as by bolting and preferably by swaging of the shaft outboard of the second head to prevent the head from sliding outwardly along the shaft to an increased spacing from the first head. Such means does not connect the head to the shaft but serves only to limit outward travel of the head along the shaft away from the first head to a distance equal to the spacing between the valve seats. Inboard of the second head along the pintle shaft, a compression spring is compressedly retained thereon to bear upon the inner surface of the second head to continuously urge the second head against the head-retaining means, thereby preventing the second head from sliding inwardly along the shaft during valve actuation. Assembly tolerances between the second head and the pintle shaft swaging permit the head to pivot minutely on the shaft to conform to the angle of the valve seat such that intimate seating of the valve head on the valve seat is assured.
REFERENCES:
patent: 245662 (1881-08-01), Rinderknecht
patent: 4565217 (1986-01-01), McIntyre
patent: 1369952 (1964-07-01), None
patent: 11835 (1897-09-01), None
Delphi Technologies Inc.
Fox John
VanOphem John A.
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