Toro Sand Pro 3040 Service Manual page 84

Forward Direction
Reverse Direction
Hydraulic System: Hydraulic Flow Diagrams
The hydraulic traction circuit is a closed loop system consisting of a variable
displacement piston (traction) pump, three wheel motors, and a remote mounted
relief valve. The traction pump is driven by the engine directly through a rubber
drive coupling. The traction pump swash plate and trunnion shaft is moved by
the traction pedal through a neutral detent linkage assembly.
With the engine running and the traction pedal in the neutral position, the traction
pump (P1) supplies no flow to the wheel motors. When the traction pedal is
pressed to the forward position, the linkage from the pedal positions the swash
plate in the traction pump so hydraulic fluid flows out the B port (right side of the
pump). Fluid flow out of the B port goes through the front wheel motor first and
then through the right and left rear wheel motors. Fluid from the rear wheel
motors returns to the traction pump A port (left side of pump). Hydraulic fluid is
continuously pumped through the closed loop traction circuit as long as the
traction pedal is pressed forward. The traction pump includes a relief valve
(forward direction) that limits forward traction circuit pressure to 22,063 kPa
(3200 psi) bar).
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.
A remote mounted relief valve exists in the traction circuit to prevent the rear
wheel motors from engaging too aggressively if the traction pedal is moved in the
forward direction abruptly. The relief valve is set to open at 15,858 kPa (2300
psi). The relief valve only operates in the forward direction.
The piston (traction) pump uses a small amount of hydraulic fluid for internal
lubrication during operation. The pump is equipped with a case drain to allow
the normal internal leakage to be removed from the pump. The left rear wheel
motor includes a flushing valve that bleeds off a small amount of hydraulic fluid
for cooling the closed loop traction circuit. The flushing valve only operates in
the forward direction. The case drain and flushing valve are connected to the
hydraulic reservoir. The loss of hydraulic fluid from the closed loop system is
replenished by the traction pump's internal implement/charge pump (P2).
The implement/charge pump (P2) is a fixed displacement gerotor pump that is
part of the traction pump. The implement/charge pump replenishes the closed
loop traction circuit with hydraulic fluid from the tank. The charge relief valve
supplies sufficient head pressure so that charge pump flow is guided to the low
pressure side of the traction circuit. Charge pressure is limited by the charge
relief valve located in the piston (traction) pump to 689 kPa (100 psi). Charge
pump flow in excess of traction circuit replenishment requirements is used for
the steering circuit on Sand Pro 5040 machines, and the lift circuit for both Sand
Pro 3040 and 5040 machines.
The front wheel motor has a check valve across its ports that allows the motor to
over run during tight turns in the forward direction.
The traction circuit operates essentially the same in reverse as it does in the
forward direction. However, the flow through the circuit is reversed. When the
traction pedal is pressed to the reverse position, the linkage from the pedal
positions the traction pump swash plate so fluid flows out of the A port (left side
of pump). Fluid flow out of the A port goes to the rear wheel motors and turns
them in the reverse direction. The fluid flow is then directed to the front wheel
Page 5–14 Sand Pro ® 3040 and 5040
20251SL Rev A