Traction Circuits: 2Wd Machines - Toro Groundsmaster 360 Service Manual

Traction Circuits: 2WD Machines (Fig. 9)
The traction system for Groundsmaster 360 machines
with 2WD consists of a transmission that is directly
coupled to, and driven by, the engine flywheel. The
transmission provides two identical and independent
closed loop traction circuits: one for the right wheel mo-
tor and one for the left wheel motor. Each of these trans-
mission circuits include a variable displacement, slipper
foot design piston pump which provides hydraulic flow
for the wheel motor on one side of the machine. The
swash plate in each of the piston pumps is controlled by
the operator traction pedal through a linkage system.
The angle of the pump swash plates determines pump
flow and ultimately traction speed. When the traction
pedal is moved a small amount, a small swash plate
rotation results in low pump output and lower traction
speed. When the traction pedal is moved fully, the pump
swash plates rotate fully to provide maximum pump out-
put flow and traction speed.
With the engine running and the traction pedal in the
neutral position, the piston pump swash plates are held
in the vertical position, providing no flow to either of the
wheel motors so the machine remains stationary. The
transmission reverse check valves include an orifice to
make it easier to locate the neutral position.
Forward
When the traction pedal is pushed forward, the linkage
connected to the traction pedal positions the swash
plates in both piston pumps to provide oil flow from the
transmission (port A for the RH side and port C for the
LH side). This oil flows from the pumps to the wheel mo-
tors and turns the motors in the forward direction. Oil
flow from the wheel motors returns to the transmission
(port B for the RH side and port D for the LH side) and
is continuously pumped as long as the traction pedal is
pushed forward. A pair of hydraulic hoses connect the
pressure and return sides of the two traction circuits to
prevent unequal pressures in the circuits especially
when turning.
As the traction load increases, forward traction circuit
pressure can increase to the relief valve setting of 4000
PSI (276 bar). If pressure exceeds the relief setting, oil
flows through the transmission forward relief valve to the
low pressure side of the closed loop traction circuit.
The piston pumps use a small amount of hydraulic fluid
for internal lubrication. Fluid is designed to leak across
pump parts into the transmission case drain. This leak-
age results in the loss of hydraulic fluid from the closed
loop traction circuits that must be replenished.
A charge pump in the transmission supplies hydraulic
flow for maintaining 100 to 130 PSI (6.9 to 8.9 bar) to the
Groundsmaster 360
low pressure side of both of the traction circuits. The
charge pump also provides pressure for the transmis-
sion PTO drive system. The charge pump replenishes
the closed loop traction circuits with fluid from the hy-
draulic tank. The charge relief valve in the transmission
maintains sufficient pressure so that charge pump flow
is guided past check valves to the low pressure side of
each traction circuit. Charge pump flow in excess of sys-
tem requirements is relieved through the charge relief
valve back to the hydraulic tank.
Both of the transmission traction circuits include a flush-
ing valve that bleeds off a small amount of hydraulic fluid
for cooling of the closed loop traction circuits. The flush-
ing valves are opened only during forward direction op-
eration. When the flushing valves are unseated, a small
amount of oil from the low pressure side of the traction
loop is returned to the hydraulic tank. Oil loss from the
closed loop due to the flushing valve is replenished by
the charge pump.
The Groundsmaster 360 is equipped with Automatic
Speed Control (ASC) which modulates ground speed
when turning the machine. This modulation maintains
speed control and also minimizes possible turf and ma-
chine damage. The traction pedal linkage is designed to
limit traction pedal movement when the machine is turn-
ing.
Reverse
The traction circuit operates essentially the same in re-
verse as it does in forward.
When the traction pedal is pushed for reverse, the lin-
kage connected to the pedal positions the swash plates
in both transmission piston pumps to provide oil flow
from the transmission (port B for the RH side and port D
for the LH side). This oil flows to the wheel motors and
turns the motors in the reverse direction. Oil flow from
the wheel motors returns to the transmission (port A for
the RH side and port C for the LH side) and is continu-
ously pumped as long as the traction pedal is pushed for
reverse.
As the traction load increases, reverse traction circuit
pressure can increase to the relief valve setting of 4000
PSI (276 bar). If pressure exceeds the relief setting, oil
flows through the transmission reverse relief valve 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. The check valve placed in
the reverse side of the traction circuit includes an orifice
which allows the traction neutral position to be easier to
adjust. The transmission flushing valves remain seated
during reverse operation.
Page 4 - - 11 Hydraulic System