Traction Forward And Reverse - Toro Greensmaster 3150 Service Manual

Traction Forward and Reverse

Forward
The piston (traction) pump is driven directly by the en-
gine. The traction circuit of the hydraulic system acts es-
sentially as a closed loop. Taking its suction directly from
the return side of the wheel motors of the traction circuit,
the piston pump supplies oil flow to the wheel motors
through the supply side of the traction circuit.
With the engine running and traction pedal in the neutral
position, the piston pump supplies no flow to the wheel
motors. When the traction pedal is pressed to the for-
ward position, the linkage from the pedal positions the
swash plate in the piston pump so oil flows out the top
port of the pump. Oil flow out of the top port goes to the
wheel motors and turns them in the forward direction.
Oil flowing out of the wheel motors returns to the bottom
port of the piston pump and is continuously pumped out
the top port as long as the traction pedal is pressed for
the forward direction.
Hydraulic oil is supplied to the traction charge circuit
from the rear gear pump section though the steering
valve, control manifold and back through the charge cir-
cuit check valves in the piston (traction) pump. This oil
replaces oil losses from flow through the internal case
drain, shuttle valve and small amounts of traction circuit
leakage. Charge circuit pressure is maintained by the
charge relief valve that is attached to the piston pump
back plate.
Greensmaster 3150
Reverse
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.
With the engine running and traction pedal in the neutral
position, the piston pump supplies no flow to the wheel
motors. When the traction pedal is pressed to the re-
verse position, the linkage from the pedal positions the
swash plate in the piston pump so oil flows out the bot-
tom port of the pump. Oil flow out of the bottom port goes
to the wheel motors and turns them in the reverse direc-
tion.
Oil flowing out of the wheel motors returns to the top port
of the piston pump and is continuously pumped out the
bottom port as long as the traction pedal is pressed for
the reverse direction.
The charge circuit functions the same in reverse as it
does in the forward direction.
Traction Circuit Cooling
The piston pump includes a shuttle valve that bleeds off
a small amount of hydraulic fluid for cooling of the closed
loop traction circuit. This valve allows a small amount of
hydraulic oil to pass from the low pressure side of the
traction circuit while operating the traction unit in either
direction. A relief valve in the piston pump back plate
prevents shuttle valve bleed off until the relief valve
opens (70 to 100 PSI / 5 to 7 bar). The charge circuit re-
plenishes oil that is bled from the traction circuit by the
shuttle valve.
NOTE: The shuttle valve assembly is located in the pis-
ton pump back plate. Access to the shuttle valve re-
quires removal of the back plate from the piston pump.
Page 4 - - 11 Hydraulic System