[0001] This invention relates to oil pumps. Figures 1 and 2 of DAS 1231563 show a known
non-adjustable internally meshing gear pump in which a toothed rotor rotates in and
with an internally toothed annulus having one more tooth.
[0002] BP 1426223 shows a similar pump with the toothed annulus mounted in an eccentric
ring arranged to be oriven by a rack and pinion, with the intention of displacing
the axis of the annulus about that of the rotor. when saia axes and the axis of the
outer surface of the annulus lie in a common plane, the pump output is at a maximum.
Hence turning the annulus from that position reduces the output.
[0003] The output volume of the pump depends, among other factors, on the axial length of
the rotating parts. Smoothness of operation, in particular the (usually undesirable)
pulsating effect or lack of it, depend upon the number of teeth or lobes on the rotor
and in the annulus.
[0004] EP 0076033A proposes dividing the annulus into two axially spaced portions each with
its own gear set driven from a common pinion so that the annuli can be turneo in opposite
directions simultaneously. This has the advantage of giving adjustment of output in
the same way as in the mentioned BP but allows a smoother more ripple- free output
because the respective lobes can be out of phase. However it is found in practice
that the device of said BP is impractical.
[0005] The object of the present invention is to provide a variable output pump of this
kind which is practical.
[0006] According to the invention an internally meshing gear pump comprises a pair of axially
spaced internally toothed annulus portions each located in a corresponding eccentric
ring and both encompassing a common rotor, said rings being provided with gear teeth
meshed with a common pinion whereby the rings can be turned in opposite direction
to vary the eccentricity of the annuli likewise and hence vary the output of the pump,
and characterised in that each ring is journalled by a set of roller bearings.
[0007] Preferably needle roller bearings are used.
[0008] The invention is based on the discovery that the impracticability of the oesign of
said BP 0076033A is due to it jamming, and recognition that the jamming is due to
the ec centric rings being subject to forces which wedge them against the housing
bore.
[0009] Pumps of this kind are sometimes operated completely immersed in oil and it is to
be expected that all of the surfaces of the parts of the pump are well lubricated
and jamming was therefore not only impossible to predict or anticipate, but also difficult
to recognize.
[0010] One presently preferred embodiment of the invention is now more particularly described
with reference to the accompanying drawing in which the sole figure is a part sectionak
perspective view of a pump embodying the invention.
[0011] In the drawing, the cover plate (not shown) normally hela in place by screws engaging
with the tapped apertures 10, has been removed to reveal the internal parts. The inner
rotor 12 has n lobes, for example six lobes and meshes with the internally toothed
or lohea annulus 16 which has n + 1, in this instance seven, lobes. A single rotor
12 is proviaed ariven by shaft 14, but two annuli 16,18 (both alike) are proviaed
axially spaced on the rotor 12. The annuli lie within corresponainy rings 20,. 22
which are provided with peripheral gear teeth meshed with a common pinion 24. The
latter can be driven by a rack 30 to turn the rings 20,22 in opposite direction and
vary the eccentricity ot the axes of the annuli 16, 18 with respect to the axis of
the rotor 12.
[0012] A ring of needle roller bearings 40 is provided between the ring 20 and the body
and a comparable set between the body and the ring 22. One set is held in place axially
by the body, and the other similarly by the cover plate. In cases where the installation
space permits the rollers may be retainea axially within the axial length of the eccentric
rings by providing lips or flanges at the ends adjacent to the body and cover faces.
1. An internally meshing year pump comprising a pair of axially spacea internally
toothea annulus portions each located in a corresponding eccentric ring and both encompassing
a common rotor, saia rings being provided with gear teeth meshea with a common pinion
whereby the rings can be turned in opposite airection to vary the eccentricity of
the annuli likewise and hence vary the output of the pump, and characterised in that
each ring is, journalled by a set of roller bearings.
2. A pump as claimea in Claim 1 wherein the roller bearings are needle roller bearings.
3. An internally meshing gear pump substantially as described with reference to the
accompanying drawing.
