Hydraulic Flow Diagrams; Traction Circuit - Toro Greensmaster 3120 Service Manual

Hydraulic Flow Diagrams

Traction Circuit

Forward Direction
Reverse Direction
Greensmaster 3120
17230SL Rev C
The piston (traction) pump is driven directly by the engine. The traction circuit of
the hydraulic system acts essentially as a closed loop. With the engine running
and the traction pedal in the neutral position, the swash plate of the piston
pump is held in the vertical position, providing no flow in either direction and the
machine remains stationary. A pair of 0.031 inch orifices in the traction (piston)
pump (one on each side of the swash plate) help keep the system in neutral.
When the traction pedal is pressed to the forward position, the linkage from the
pedal positions the swash plate in the piston pump so fluid flows out the upper
port (A) of the pump; refer to
the wheel motors and turns them in the forward direction. The fluid flow out of
the wheel motors returns to the piston pump lower port (B) and is continuously
pumped while the traction lever is in the forward position.
As the traction load increases, the forward traction circuit pressure can increase
to the relief-valve setting of 19,994 kPa (2,900 psi). If the circuit pressure is more
than the relief-valve setting, fluid flows through the forward relief valve in the
transmission to the low-pressure side of the closed-loop traction circuit.
The piston pump uses a small amount of hydraulic fluid for internal lubrication.
The fluid is designed to leak across the pump parts into the pump case drain.
This leakage results in the loss of hydraulic fluid from the closed-loop traction
circuit that must be replaced by the traction charge circuit. Hydraulic fluid is
supplied to the traction pump charge circuit from the gear pump section (P3) after
servicing the demands of the steering and lift circuits. Charge circuit pressure
is maintained by a 276 kPa (40 psi) check valve (CV) located in the mower
manifold. A pair of check valves in the traction (piston) pump control the release
of charge circuit flow when fluid replacement is required by the closed-loop
system. Charge circuit flow in excess of closed-loop system requirements
returns to the hydraulic tank via the traction (piston) pump case drain.
The traction circuit operates essentially the same in reverse as it does in the
forward direction.
When the traction pedal is pressed to the reverse position, the linkage from the
pedal positions the swash plate in the piston pump so fluid flows out the lower
port (B) of the pump. Fluid flow out of the lower port goes to the wheel motors
and turns them in the reverse direction. The fluid flow out of the wheel motors
returns to the piston pump upper port (A) and is continuously pumped while the
traction lever is in the forward position
As the traction load increases, the reverse traction circuit pressure can increase
to the relief-valve setting of 19,994 kPa (2,900 psi). If the circuit pressure is more
than the relief-valve setting, fluid flows through the reverse relief valve in the
transmission to the low-pressure side of the closed-loop traction circuit.
The charge circuit functions the same in reverse as it does in the forward
direction.
Figure 19. Fluid flow out of the upper port goes to
Page 4–15 Hydraulic System: Hydraulic Flow Diagrams