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.

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 proble .

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.

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.

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.

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.

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 .

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.

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 IS.

Passage 24 communicates pressure from outlet 18 to act upon the control valve 28 which may be spring urged at 30 to the closed positicrn 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. 3oth passages are effective to deliver oil to the engine and both pumps absorb energy.

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.