Toro Groundsmaster 7210, Руководство по обслуживанию

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Traction Circuits
The traction system of the Groundsmaster consists of a transmission that is
directly connected to, and driven by, the engine flywheel. The transmission
provides 2 identical and independent closed loop traction circuits: one for
the right wheel motor and the other for the left wheel motor. Each of these
transmission circuits includes a variable displacement, slipper foot design piston
pump which provides hydraulic flow for a wheel motor. The swash plate in each
of these piston pumps is controlled by 1 of the operator traction levers.
The angle of the swash plate determines the pump flow and ultimately traction
speed. When a traction lever is moved a small amount, a small swash plate
rotation results in low pump output and lower traction speed. When the traction
lever is moved fully, the pump swash plate rotates fully to provide maximum
pump output flow and traction speed.
Because hydraulic fluid flow to each rear wheel is determined by the traction
lever movement and subsequent swash plate position, steering is accomplished
by moving the 2 traction levers a different amount or direction.
With the engine running and the traction levers in the N
EUTRAL
position, the
swash plates of the piston pump are held in the vertical position, providing no
flow to either wheel motor and the machine remains stationary. The transmission
reverse check valves include an orifice which makes it easier to locate the
transmission N
EUTRAL
position.
Forward Direction
When a traction lever is pushed forward, the rod connected to the traction lever
positions the swash plate in the piston pump to provide hydraulic fluid flow from
the transmission (port A for the right side or C for the left side). This fluid flows to
the wheel motor and turns the motor in the forward direction. The fluid flow from
the wheel motor returns to the transmission (port B or D) and is continuously
pumped while the traction lever is pushed forward.
As the traction load increases, the forward traction circuit pressure can increase
to the relief-valve setting of 27,600 kPa (4,000 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 pumps use a small amount of hydraulic fluid for internal lubrication.
The fluid is designed to leak across the pump parts into the transmission case
drain. This leakage results in the loss of hydraulic fluid from the closed loop
traction circuits that must be replaced.
A charge pump in the transmission supplies hydraulic flow for maintaining 480 to
690 kPa (70 to 100 psi) to the low-pressure side of the 2 traction circuits. The
charge pump also provides pressure for the transmission PTO drive system. The
charge pump replenishes the closed loop traction circuits with fluid from the
hydraulic tank. The charge-relief valve in the transmission maintains sufficient
pressure so that the charge-pump flow is guided past check valves to the
low-pressure side of each traction circuit. The charge-pump flow in excess of
system requirements is released through the charge-relief valve back to the
hydraulic tank.
The 2 transmission traction circuits include a flushing valve that bleeds off a
small amount of hydraulic fluid for cooling of the closed loop traction circuits.
The flushing valves are opened only during forward direction operation. When
the flushing valves are unseated, some fluid from the low-pressure side of the
traction loop is returned to the hydraulic tank. The fluid loss from the closed loop
due to the flushing valve is replaced by the charge pump.
Groundsmaster 7210 Page 4–15 Hydraulic System: Hydraulic Schematics
16222SL Rev C