Page 280 - Design for Six Sigma a Roadmap for Product Development
P. 280
250 Chapter Eight
Body
#8 Seal
Ring bore
Spring pressure
Control
Rotor port
Vane
#4 Seal
#6 Seal
#7 Seal
Figure 8.8 Pump top view.
expanding and collapsing. Expansion is needed at the pump inlet to
draw fluid into the pump, while collapsing will occur at the outlet
to force fluid into the system under pressure. The variable-vane pump
is a rotary-type pump with variable capacity. The output will vary
according to the requirements of the transmission to conserve power.
The advantages are many. Chief among them are the ability to deliver
a large capacity when the demand is high, especially at low speeds,
and the minimal effort needed to drive at high speeds.
The mechanism of operation is as follows. When the priming spring
moves the slide to the fully extended position, the slide and rotor are
eccentric. As the rotor and vanes rotate within the slide, the expand-
ing and contracting areas form suction (expanding) and pressure
(collapsing) chambers. The hydraulic medium trapped between the
vanes at the suction side is moved to the pressure side. A large quan-
tity of fluid is moved from the pressure side back to the suction side as
the slide moves toward the center (Fig. 8.6). A neutral condition (with
no volume change) is created when concentricity is attained between
the slide and rotor.
The function of the priming spring is to keep the slide in the fully
expanded position such that full output can be commanded when the