Traction Circuits - Toro Reelmaster 3100-D Service Manual

Traction Circuits

Forward
Reverse
Charge Circuit
Reelmaster ® 3100-D/3105-D
20252SL Rev A
The traction circuit of the hydraulic system consists of a hydrostat connected in a
closed loop circuit to three orbital vane wheel motors.
The mow/transport slide control on the machines has positions for mow and
transport. The mow position allows traction pedal inputs that are appropriate for
mow speeds by limiting the movement of the traction pedal and the piston pump
swash plate. The transport position allows full movement of the traction pedal so
complete pump swash rotation is possible.
The engine drives traction pump (P3) indirectly through pulleys and a V−belt.
The traction pump is a variable displacement piston pump. The traction pedal
connects through a cable to the trunnion shaft and swash plate of the pump. With
the engine running and the traction pedal in the neutral position, P3 supplies no
flow to the wheel motors. When the traction pedal is pressed to the forward
position, the cable from the pedal positions the swash plate in the traction pump
so fluid flows out of the lower port. Fluid flow out of the lower port goes to the
wheel motors and turns them in the forward direction. Fluid flowing out of the
wheel motors returns to upper port of the hydrostat and is continuously pumped
out of the lower port.
Operating pressure in the closed traction circuit is determined by the amount of
load developed by the wheel motors. As the load increases, circuit pressure can
increase to the relief valve setting of 241.3 bar (3500 PSI). In forward operation,
fluid flows through the internal hydrostat relief valve to the low pressure side of
the traction circuit when circuit pressure exceeds the relief setting.
The traction circuit operates essentially the same in reverse as it does in forward.
However, there are a few differences in operation.
When the reverse traction pedal is depressed, the cable from the pedal positions
the swash plate in the traction pump so fluid flows out of the upper port. Fluid
flow out of the upper port goes to the wheel motors and turns them in the reverse
direction. Fluid flowing out of the wheel motors returns to the lower port of the
hydrostat and is continuously pumped out of the upper port. Fluid by−passes the
rear motor in reverse because of the check valve inside the rear motor.
The traction pump uses a small amount of hydraulic fluid for internal lubrication.
Fluid is designed to leak across pump parts into the case drain. This leakage
results in the loss of hydraulic fluid from the closed loop circuit that must be
replenished.
The gear pump (P2) is directly coupled to the hydrostat through gear pump
(P1) and driven by the engine. Gear pump (P2) supplies hydraulic pressure for
operating the power steering system, raising and lowering the cutting units,
and operating the sidewinder unit. Gear pump (P2) may also be referred to as
the charge pump as flow from the gear pump also replenishes the closed loop
traction circuit. Hydraulic fluid exits the lift/sidewinder valve, passes through the
mow manifold and continues on to the hydrostat. A relief valve located in the
hydrostat provides sufficient resistance so that flow is guided to the low pressure
side of the traction circuit through one of two check valves (charge circuit). Pump
flow in excess of 6.9 to 10.3 bar (100 to 150 PSI) is relieved through the relief
valve back to the gear pump inlet and hydraulic tank.
Page 5–15 Hydraulic System: Hydraulic Flow Diagrams