Operation of Crescent Pump

Operation of Crescent Pump

The operation of this pump is based on the meshing of the gear teeth, the positioning of the ports in the housing and

alignment at each end of the crescent where the teeth move in and out of mesh. Oil is carried from the inlet port to the outlet port in the spaces

between the teeth and the crescent. This pump is used for engine lubrication and for automatic transmissions.

Vane-Type Pump ฀฀ The vane-type pump uses an eccentric rotor with vane plates set at right angles to the axis of the rotor and sitting in slots in the rotor. As the rotor rotates, the vanes sweep around inside the pump housing. The pump chambers increase in volume as the vanes move away from the housing walls, and reduce in volume as the vanes approach the walls. Oil is carried between the vanes and the pump housing from the inlet port to the outlet port.

Camshaft-Drive Arrangements Oil pumps are driven from the camshaft by gears on the camshaft and oil-pump spindle. Also, the drive gear is used often to drive the distributor for the ignition system. Another camshaft-drive arrangement is a direct drive from the end of the shaft. Some engines have used an auxiliary shaft to drive the pump and distributor, which has been driven from the crankshaft by a toothed belt or chain.

Direct-Drive Oil Pump ฀฀ Some modern engines are now using the crankshaft to give a direct drive to the oil pump. These pumps are of the gerotor or crescent design, and are fitted around the front of the crankshaft. This arrangement is used on many overhead-camshaft engines because it provides a low position for the pump. Geared drives from the crankshaft are also used by some manufacturers.

Pressure-Relief Valve (or Release Valve) The oil flow and pressure at low engine speeds must

be sufficient for all engine loads and, therefore, the performance of the pump is geared to low speeds. As the engine speed increases, so an excess of oil flow and pressure would occur.

Plunger and spring This would be detrimental to some engine

components and, therefore, the pressure must

be relieved. Pressure-Relief Valve Functions ฀฀ The pressure-relief valve

is a spring-loaded conical, or ball, valve that opens when the pressure in the oil exceeds the spring force acting on the valve seat. When the valve opens, a return drilling is uncovered and the excess oil flows through this to return to the sump.

Oil Filter Modern filters are canister types and consist of a micro-porous paper element in

a thin steel cartridge. The paper element filters small particles of carbon and dirt that are picked up in the oil. Chemical reactions by some of the oil additives help to separate water and acids that drain into the sump. These by-

products of combustion are also restricted from passing through the filter and collect on the feed side. Replacing the filter on a regular basis removes all these unwanted contaminants.

Oil Flow through the Filter ฀฀ Oil flow through the filter is from the outside of the element to the inside and then into the main gallery. Filters screw onto a threaded sleeve in the filter housing. Sealing is made with a rubber ‘O’ ring.