Variable flow pump

Details Variable flow pump Variable flow pump

1997-11-07

2001-03-13

Nguyen, Hoang (Department: 3748)

Rotary expansible chamber devices

With changeable working chamber magnitude

Cylinder or cylinder portion moved linearly and radially

C418S268000

Reexamination Certificate

active

06200114

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a pump for pumping fluids and particularly to a pump whose fluid delivery rate may be varied according to the discharge pressure.
In a known pump assembly a number of pumping elements such as rollers or pistons are spaced around a central rotating shaft and mounted in a carrier. A cam ring around the carrier and the pumping elements has an internal surface having one or more symmetric internal lobes, which cause the pumping elements to move radially with respect to the carrier as the carrier rotates. The cam ring and carrier arrangement is located between a pair of side plates. Suitably disposed inlet and outlet ports in the side plates can cause fluid to be drawn into and out of the circumferentially located spaces between the pumping elements; and the internal and external surfaces of the cam ring and the carrier respectively, in an axial direction. The fluid is drawn in at circumferential positions of the cam ring between the lobes and discharged at some angle further around the cam ring (near the lobe tops) at high pressure.
The difficulty with this arrangement is that the discharge flow rate is nominally fixed to be proportional to the rotational speed of the shaft. Any excess fluid flow has to be returned (via a valve) to the pump inlet, with a corresponding loss of volumetric efficiency. The valve is an additional device which should be avoided if possible.
SUMMARY OF THE INVENTION
According to the present invention there is provided a pump comprising an inlet port, an outlet port and a pumping mechanism for pumping fluid from the inlet port to the outlet port at a discharge flow rate. The pumping mechanism comprises a carrier including a plurality of pumping elements formed thereon or mounted therein and a cam ring which surrounds the carrier and has an internal cam surface which is followed by the pumping elements. The cam ring is flexible such that the discharge flow rate may be varied by varying the shape of the cam ring.
With the present invention, the cam ring is preferably sufficiently thin so that it can be elastically distorted. Deflection may be altered by fluid pressure, most conveniently supplied from the pump, and may act with or against the cam ring's inherent resilience and an additional force from a biasing device such as a spring. The control preferably operates in such a way that as the outlet fluid pressure increases, the cam ring deforms from an initially non-circular shape towards a more circular shape concentric with the shaft, resulting in a lower discharge flow rate. Thus, the pressure and flow rate can self adjust to suit the demands of the delivery circuit, with much less loss of volumetric efficiency.
In a preferred embodiment of the present invention, there is provided a pump comprising pumping elements which are sealed and may be rotated together with a shaft. A cam ring is mounted around the pumping elements, and the cam ring has a reduced thickness whereby it can be elastically deflected by the amount required to supply the required maximum flow rate. The cam ring may be held clear from side plates with a spacer ring radially outside of it, so that it is free to move radially. Initially the cam ring may be formed or deformed into a shape approximating to the required starting shape, within elastic stress limits of the cam material, and may be pressed into the pump to form a lobed symmetric shape, constrained by the outer, spacer ring to outer limits at lobe troughs and by pivoting blocks, projections, stop blocks and riding rollers or other support means at node points where no deflection is required. Near the lobe peaks (minimum radius points) biasing devices may be fitted.
The cavity between the cam ring and the outer or spacer ring is preferably circumferentially divided into a plurality of different regions, at least partially sealed from one another. One or more of the regions are high pressure regions and one or more of the regions are low pressure regions.


REFERENCES:
patent: 2842064 (1958-07-01), Wahlmark
patent: 3898021 (1975-08-01), Arnoulet
patent: 4091717 (1978-05-01), Bojas et al.
patent: 4354809 (1982-10-01), Sundberg
patent: 5630318 (1997-05-01), Folsom et al.
patent: 5733113 (1998-03-01), Grupping
patent: 2109112 (1972-09-01), None
patent: 1000591 (1965-08-01), None

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