Lubrication 15 - Crescent Pump
|Mostly on the crank- or gearbox-entry shaft|
The crescent pump is relatively compact in its construction, with few rotary components integrated onto the drive shaft, it suctions hydraulic- or engine oil automatically. It generates, by continuous delivery, more a medium-size pressure. The internal gear wheel with the outside gear-teeth is nearly always the driven one. Of course other types of gearing than that shown above are also possible.
|Externally geared inside gear drives internally geared outside gear|
Through this gearing, the larger outside gear-wheel with internal gearing is driven. If it is, compared with the inside gear-wheel, eccentrically offset by only the tooth height, no appreciable space occurs between them. Only when there is a higher offset, as in the above figure, the remaining space can be compensated almost completely by a crescent shaped part.
|Clockwise rotation: left, the suction- right the pressure connection|
Assuming a clockwise rotation of the internal shaft above, the cogs move away to the left of each other and provide a suction chamber. On the right they mesh more and more to form the pressure side. It's interesting to note that the suction chamber is purposely not completely filled with the crescent shaped part. The lines which come from the side and lead into these areas are absolutely necessary. Shown in the above figure, is the oil pump for a fully automatic gearbox. Here the supply and removal of ATF oil would probably take place through the removed cap. In the internal combustion engine this type of pump is found directly on the crankshaft. If it is mounted lower down, to shorten the length of the inlet pipe, a different solution would be more advantageous. 10/08