Toro Groundmaster Series Service Manual page 100

Forward Direction
Hydraulic System: Hydraulic Flow Diagrams
The hydraulic traction circuit is a closed loop system consisting of a variable
displacement hydraulic piston (traction) pump and a series of hydraulic wheel
motors. The hydraulic fluid passes through the hydraulic manifold on its way to
and from the wheel motors. The traction pump is driven by the engine via a
multi-row V-belt. V-belt tension is controlled automatically by a spring loaded
idler.
Pushing the top of the traction pedal angles the piston (traction) pump (P1)
swash plate to create a flow of oil. This oil flow is directed to the wheel motors
via a hydraulic tube to drive the front wheels in the forward direction. Forward
traction pressure is limited to 25,000 kPa (3625 psi) by the forward traction relief
valve (R1) located in the traction pump.
The angle of the swash plate determines the stroke of the pump pistons and
therefore the volume of hydraulic fluid flow and ultimately traction speed. When
the traction pedal is pressed a small amount, the swash plate angle is slight
resulting in low pump output and lower traction speed. When the traction pedal is
pressed fully, the pump swash plate angle is dramatic providing maximum pump
output and maximum traction speed.
For 2WD machines, the hydraulic fluid flows from the front wheel motors and
passes through the hydraulic manifold. A control orifice in the hydraulic manifold
(OR at manifold port OR) equalizes traction system pressure to reduce tire
scuffing when turning. Hydraulic fluid exits the manifold and returns to the
variable displacement pump. Hydraulic fluid is continuously pumped through the
closed loop traction circuit as long as the traction pedal is pressed forward.
For 4WD machines, the hydraulic fluid flows from the front wheel motors and
passes through the hydraulic manifold. A control orifice (OR at manifold port
OR) and a bidirectional relief valve (CRV) in the hydraulic manifold equalize
traction system pressure to reduce tire scuffing when turning. Check valves in
the hydraulic manifold allow the rear wheel motors to over-run during tight turns.
Hydraulic fluid exits the manifold and returns to the variable displacement pump.
Hydraulic fluid is continuously pumped through the closed loop traction circuit as
long as the traction pedal is pressed forward.
The piston (traction) pump is equipped with a case drain to allow normal internal
leakage to be removed from the pump. The piston pump also includes a flushing
valve that bleeds off a small amount of hydraulic fluid from the low pressure
side of the circuit for cooling of the closed loop traction circuit. The case drain
and flushing valve are connected to the hydraulic reservoir. The charge system
replenishes oil that is bled from the traction circuit by the case drain and the
flushing valve.
Gear pump (P2) supplies oil flow for the steering circuit and lift circuit, and also
provides a constant supply of charge oil to the closed loop traction circuit. Gear
pump flow beyond the needs of the steering, lift, and charge circuits exits the
manifold. A check valve (CV2) in the manifold may open to provide an additional
path for charge circuit fluid to exit the manifold. This feature protects the oil
cooler from high pressure when the oil is cold. The hydraulic fluid returning from
the manifold provides most of the fluid for the gear pump (P2). The remainder
of the fluid necessary is supplied through the suction filter and suction hose
from the hydraulic reservoir.
The charge oil provides lubrication for traction circuit components and also
replenishes traction circuit oil that is lost due to internal leakage and cooling
(flushing) in the traction circuit. Charge pump flow is directed to the low pressure
side of the closed loop traction circuit. Charge pressure is limited by the charge
relief valve (R3) located in the piston (traction) pump to 896 kPa (130 psi).
Page 5–14 Groundsmaster ® 3200, 3300 and 3310
19240SL Rev A