[0001] This invention relates to pumps of the kind comprising a gerotor set of rotor with
n lobes meshed internally of an annulus with n+1 lobes. This creates a set of chambers
each defined between successive crests of the rotor lobes. When one rotor lobe is
fully meshed with the interlobe space of the annulus, the chambers immediately next
to that rotor lobe will be of minimum volume, whereas those more or less diametrically
opposed will be of maximum volume. In use, both rotor and annulus turn, albeit at
different speeds, and about parallel axes, and each chamber moves about the axes increasing
in volume and then decreasing in volume Inlet and outlet ports are located at one
or both axial ends of the chambers, and as the chambers move over the inlet port they
increase in volume and suck, and as they move over the outlet port they decrease in
volume and expel. This is responsible for the pumping action.
[0002] With a simple form of pump as herein described, the output volume is directly related
to drive speed.
[0003] A known type of this kind of pump has the annulus duplicated so that it forms two
end-to-end and relatively angularly movable portions. Each annulus lies in an eccentric
ring, arranged to be turned to vary the eccentricity of the corresponding annulus
relative to the rotor. When both are synchronised in the normal position where a plane
containing the axes of rotation of both annulus and rotor lies generally between the
inlet and outlet ports, maximum output is delivered, but by turning the two rings
in opposite directions output is reduced. This may be considered to be because the
chambers formed between the rotor and annuli will not be at minimum volume when they
first register with the inlet port and in one case will be reducing in volume for
a first part of their orbit, and will not have reached maximum volume when they move
out of register with the inlet port: in the other case the chambers will be increasing
in volume when they first register with the inlet but will reach and pass maximum
volume and hence either not fill completely or will expel some fluid into the inlet
port before leaving the inlet port. So the total output is reduced. Such a pump may
be used in situations where relatively large volume is needed at low speeds but relatively
lower volumes at higher speeds, for example.
[0004] EPA 0 076 033 shows a pump of the kind described in the preceding paragraph, but
one which has been found difficult to operate. EPA 0 174 734 shows an improved version
of the same pump using needle roller bearings in an attempt to overcome the difficulties
and EPA 0 284 226 shows a more refined version of the pump in a form which has been
commercially successful, but which is expensive to manufacture.
[0005] The object of the present invention is to provide similar results but to simplify
design and manufacture and hence enable less expensive pumps to be made.
[0006] According to the invention, a gerotor pump has a single annulus, and two axially
adjacent rotors which are arranged to be relatively angularly adjusted.
[0007] Preferably one of the rotors is angularly fixed in relation to a drive shaft, and
the other is movable between two extreme positions in which it is respectively synchronised
or wholly in phase with the first rotor, and 180 degree shifted to be wholly out of
phase with the first. This would give outputs from the complete pump varying between
zero and maximum, but in alternative designs variation would be between minimum and
maximum, i.e. not down to zero.
[0008] The invention is now more particularly described with reference to the accompanying
drawings wherein:
Figures 1-5 are diagrammatic representations showing a five lobe rotor engaged in
a six lobe annulus and illustrating five different relative angular positions between
the two rotor parts
Figure 6 is a sectional elevation of a presently preferred embodiment of the invention;
and
Figure 7 is a section taken on the line 7-7 of Figure 6.
[0009] Turning first to Figures 1 to 5, the rotor consists of two axially arranged, i.e.
end-to-end five lobed rotors 10 12. They are located within an annulus 16 having six
lobes. These figures also show the inlet port 18 formed in body 20 and the outlet
port 22 also formed in the body. The two ports are generally symmetrical of the plane
PP which contains the axis 14 of the rotor 10 and the axis 24 of the annulus.
[0010] Figure 1 shows the zero position in which the two rotor parts are phase synchronised:
both rotate about axis 14. The rotor lobe which is symmetrically arranged relative
to the plane PP is fully engaged with an annulus interlobe space and the maximum diameter
chamber is diametrically opposite, i.e. as indicated by the reference numeral 28.
Assuming rotation in the direction of the arrow A in Figure 1, the smallest chamber
30 overlaps one end of the inlet port 16 and the next largest chamber 32 overlaps
the other end of the inlet port. Similarly chambers 34 36 which are generally opposite
to chambers 32 30 overlap the outlet port.
[0011] Figure 2 shows the situation when the two rotor parts have been shifted so as to
be 45 degrees out of phase. Rotor 10 is still on axis 14 but rotor 12 is on axis 40
which is now spaced from axis 14 and also from axis 24 which is that of the annulus.
Each chamber may now be considered to be divided into two axially arranged i.e. end-to-end
portions (which necessarily communicate with one another) but the portion composed
of the space radially located between rotor 10 and annulus 16 is as in Figure 1, but
that between rotor 12 and the annulus is phase shifted so that effectively over the
area of the inlet port it is smaller, but over the area of the outlet port is larger.
[0012] Figure 3 shows the phase shift carried on so that the axis of the rotor part 12 is
now shown by the reference 40 and is 90 degree removed from the plane PP about the
point 24. In this position, the minimum volume chamber for rotor 12 has shifted to
be wholly located within the inlet port whereas two equal large volume chambers are
both substantially aligned with the outlet port. Figure 4 shows 135 degree phase shift
and Figure 5 shows 180 degree phase shift. In the latter case, the maximum volume
chamber for the rotor 10 is angularly aligned with the minimum volume chambers for
the rotor 12 and the total effect is a zero pumping action.
[0013] In short, Figure 1 shows the pump set for maximum pumping activity, Figure 5 shows
the pump set for minimum or zero pumping activity, and Figures 2-4 show intermediate
stages between these two extremes.
[0014] Turning now to Figure 6 which shows the rotors phase aligned, the same reference
numbers are used as with Figures 1-5. Rotor 10 is fast with shaft 50 which is also
fixed to drive gear 52, and the shaft is bushed at 54 in the pump body. Rotor 12 is
bushed at 56 on eccentric 58 carried on shaft 60. In both cases the bushes are merely
preferable. Shaft 60 is on axis 62, which is concentric with the annulus. Shaft 60
is also fast with pinion 64.
[0015] The pinion is meshed with a rack 66 which conveniently is mounted on piston rod 68
carried by piston 70 and slidable in a cylinder diagrammatically illustrated by the
reference numeral 72. The cylinder may be supplied with fluid at either end via shuttle
valve 74.
[0016] The shuttle valve may be connected to pump output or for example the main lubricant
gallery of an I.C. engine being supplied by the pump, so that pressure is communicated
via the pipe 76 and can act upon the spool 78 resisted by the spring 80. In the illustrated
position fluid flows through the spool, through radial ports in the spool and via
the passage 82. It can act upon the piston 70 to displace the rack and turn the pinion.
[0017] When the pressure is sufficient to displace the spool against the spring, line 82
is placed in communication with waist 84 on the spool and what was the return line
86 is placed in communication with the line 76 so as to reverse the direction of movement
of the piston 70. By selection of the spring relative to the oil pressure involved
the pump can be automatically turned between minimum and maximum positions and adjusted
to required positions therebetween
[0018] It will be appreciated that rotor 12 is driven indirectly by rotor 10 via the annulus.
That is to say the shaft 50 turns the rotor 10 which turns the annulus, and the annulus
turns the rotor 12.
[0019] In another embodiment not illustrated, rotor 12 is journalled on an eccentric bush
carried on an extension of the shaft 50.
[0020] In a further embodiment also not shown, the annulus is driven, and the two rotors
are journalled on respective eccentric bushes each provided with straight tooth spur
pinion gears carried on a common axis which is co-axial to the annulus. These pinions
are located outside the rotors, i.e. at opposite axial ends of the pump, and arranged
to be driven through equal and opposite amounts by a gear drive system for example
operated by pump hydraulic pressure acting in a piston and cylinder to drive a rack
turning the gears. Hence the axis of each rotor can be shifted through for example
90 degrees, and always in opposite directions, which amounts to 180 degree phase shift
possibility with like results as in the first mentioned embodiment. This gives a particularly
neat and simple construction.
[0021] The simplicity of the present invention, particularly in the version illustrated
in Figures 6 and 7, will be appreciated by those skilled in the art especially by
comparison with the mentioned prior art.
1. A gerotor pump having a single annulus and two axially adjacent rotors which are
relatively angularly adjustable.
2. A pump as claimed in Claim 1 wherein one of the rotors is angularly fixed in relation
to a drive shaft and the other of the rotors is movable between extreme positions
relative to said one rotor.
3. A pump as claimed in Claim 1 or Claim 2 wherein the second rotor is journalled
on an extension of the shaft which carries the first rotor.
4. A pump as claimed in any preceding claim wherein the other of the rotors is journalled
on an eccentric carried by a shaft which is journalled on the annulus axis and arranged
to be turned so as to shift the phase of the said other rotor relative to the said
one rotor.
5. A pump as claimed in Claim 4 wherein the said drive shaft and the shaft co-axial
with the annulus are located end-to-end.
6. A pump as claimed in Claim 4 or Claim 5 wherein said other shaft carries a pinion
engaged with a rack.
7. A pump as claimed in any preceding claim wherein the pump body is provided with
inlet ports at opposite axial ends and also with outlet ports at opposite axial ends.