This paper deals with a mathematical analysis of pump
efficiencies in an internal gear and balanced vane pumps. They are
commonly used in current automatic transmissions including a
continuously variable transmission. For these pumps, the influence
of oil temperature as well as pump-operating pressures and pump
speeds is clarified by using mathematical models taking oil
temperature into consideration, which are constructed on the basis
of actual measured flow and torque data under various
pump-operating conditions. For fuel economy in a vehicle, because
the pump should be operated under conditions to obtain higher pump
efficiencies, it is very important to understand the relationship
between the pump efficiencies and the pump-operating
conditions.
This paper reveals that the mathematical models representing the
leakage flow and friction torque characteristics accurately is
helpful to investigate the pump efficiencies as well as the flow
and torque performance under various pump-operating conditions. As
a result, the overall efficiency decreases at extremely low and
high oil temperatures. In the internal gear and the balanced vane
pumps tested in this work, the region with a higher overall
efficiency lies around an oil temperature of 80°C.
