[0001] This invention relates to oil pumps for I.C. engines. Such pumps are engine driven,
and as such, the pump output is nominally proportional to engine speed.
[0002] Now as the engine demand curve for oil pressure is not normally proportional to engine
speed, a quantity of oil in excess of that needed to maintain the bearing pressure
is diverted to the sump via a control valve mechanism. If this were not so, the result
would be excessive pressures causing possible engine damage. This excessive oil represents
wasted energy. Many proposals have attempted to deal with this problem for example
by using a gerotor pump and varying the eccentricity of the axes so as to reduce output
at higher speeds. The object of the invention is to provide a new solution to this
old problem.
[0003] According to the invention, an engine oil pump comprises a drive shaft connected
to a pair of pumps having a common inlet supply and separate but connected outlets,
including a diverter valve in one of the outlets effective to return oil from the
corresponding pump direct to supply at higher delivery rates/pressures.
[0004] According to a preferred version of the invention, an engine oil pump comprises a
drive shaft connected to a pair of gerotor oil pumps having their inlets connected
to a common supply, and their outlets connected to a common delivery passage, and
with a control valve located between one of the outlets and the delivery passage arranged
to divert oil from one of the gerotor sets to the common supply when the valve is
open, and with the valve arranged to open automatically at higher pressures/delivery
rates.
[0005] The valve may be a simple spring controlled valve. When the pump output pressure
is low, the valve remains closed and all output goes to the delivery passage. As pressure
rises, primarily with speed of the engine, but possibly also due to reduction in viscosity
as in the case of low temperatures the valve opens and allows some and then all of
the output from the one gerotor set to bypass the delivery passage and return directly
to the supply source, for example the sump.
[0006] The power utilization of the gerotor set depends upon the outlet pressure: hence
by connecting the outlet direct to sump the pressure is effectively zero so that the
workload on the pump is relieved and the gerotor set in question uses minimal energy
at such time.
[0007] Gerotor pumps are well understood in the art and comprise a male lobed rotor with
n lobes located in a female lobed annulus having
n+1 lobes. This forms a series of chambers between the rotor and annulus, each bounded
by the pump body in planes normal to the axis of rotation and also bounded by the
lines of contact between the parts. As the rotor and annulus rotate albeit at different
speeds, the chambers revolve about the axes (the rotor and annulus are on parallel
not coincident axes) and vary in size. They increase in one half revolution from the
minimum where a lobe on one part is located midway between two lobes on the other
part to a maximum at a point diametrically opposite, and as they increase they move
over the inlet port. In the second and subsequent half revolution the chambers decrease
in size and move over the outlet port leading to the delivery passage.
[0008] The accompany diagrammatic drawings show a preferred arrangement in the full flow,
i.e. both pumps operative position in Figure 1 and in the low flow, one pump operative
position in Figure 2. In the drawings, the drive shaft 10 extends through and is angularly
fast with the rotor of each of two gerotor pumps indicated by the reference numerals
12 14. The common inlet passage 16 is connected to both pumps. Outlet passage 18 from
pump 12 is connected to the delivery passage 20 leading to for example the main oil
gallery of the engine.
[0009] The outlet passage 22 from the pump 14 extends to a sump, that is the same source
of supply as the inlet 16, with a pair of connection passages 24 26 extending from
the passage 22 to the passage 18.
[0010] Passage 24 communicates pressure from outlet 18 to act upon the control valve 28
which may be spring urged at 30 to the closed position illustrated in Figure 1. In
this position ball valve 32 in passages 26 is open to allow flow from passage 22 via
26 to the outlet 20. Both passages are effective to deliver oil to the engine and
both pumps absorb energy.
[0011] When the pressure rises in passage 18 it can overcome the spring 30, the valve 28
moves to open the path in passage 22 direct to the sump, and the ball valve also seats
so that there is no flow between passages 18 22 in either direction and the one pump
delivers to the engine and the other pump delivers back to the sump. At this time
pump 14 uses but little energy.
1. An engine oil pump comprising a pair of pumps driven from a common drive shaft, having
a common inlet supply and connected but separate outlet passages including a diverter
valve in one of the outlets effective to return oil from the corresponding pump direct
to supply avoiding the lubricant delivery passage unless the valve is in a closed
position.
2. An engine oil pump comprising a drive shaft connected to a pair of gerotor oil pumps
having their inlets connected to a common supply, and their separate outlets connected
to a common delivery passage, and with a control valve located in between one of the
outlets and the delivery passage arranged to divert oil from one of the gerotor sets
direct to the common supply when the valve is open.
3. A pump as claimed in Claim 2 wherein the valve is arranged in the outlet line from
one of the pumps to be operated by pressure in the outlet line from the other of the
pumps.
4. A pump as claimed in Claim 2 and Claim 3 wherein the outlet line from one pump is
connected to the delivery passage, the outlet line from the other pump is connected
to the inlet source or line, and a pair of passages connect the two lines, one containing
a diverter valve for operation by pressure in the other line, and the other containing
a ball check valve.
