Traction Circuit - Toro Groundsmaster 3280-D Service Manual

Traction Circuit

Forward Direction (Fig. 8)
The hydrostatic transmission input shaft is rotated by a
drive shaft off the front of the engine crankshaft. Pushing
the top of the traction pedal rotates the variable dis-
placement pump swash plate in the transmission to
create a flow of oil. This oil is directed to the fixed dis-
placement motor in the transmission which turns the
front axle input shaft to drive the front wheels in the for-
ward direction.
Oil flowing from the motor returns to the variable dis-
placement pump and is continuously pumped through
the closed traction circuit as long as the traction pedal
is pushed.
A gerotor charge pump in the hydrostat provides a
constant supply of charge oil to the closed loop traction
circuit for lubrication and to make up for oil that is lost
due to internal leakage in the transmission pump and
motor. The charge pump takes its suction through a filter
from the reservoir (front axle). Charge pump flow is di-
rected to the low pressure side of the closed loop circuit.
Charge pressure is limited by backpressure created by
the lift control valve. Charge pressure can be monitored
at the transmission charge pump test port. Charge
pump flow in excess of traction circuit charge needs pro-
vides hydraulic flow for the steering and lift circuits.
Groundsmaster 3280--D/3320
Reverse Direction
The traction circuit operates essentially the same in re-
verse as it does in the forward direction. However, the
flow through the circuit is reversed. Pushing the bottom
of the traction pedal rotates the variable displacement
pump swash plate in the transmission to create a flow of
oil. This oil is directed to the fixed displacement motor in
the transmission which turns the differential input shaft
to drive the front wheels in a reverse direction.
Oil flowing from the motor returns to the variable dis-
placement pump and is continuously pumped through
the closed traction circuit as long as the traction pedal
is pushed.
The charge circuit functions the same in reverse as it
does in the forward direction.
Page 5 - - 9 Hydraulic System