Toro Groundsmaster 4500-D Series Service Manual page 120

Forward Direction
Hydraulic System: Hydraulic Flow Diagrams
The traction circuit piston pump is a variable displacement pump that is directly
coupled to the engine flywheel. This pump utilizes an integral electro-hydraulic
servo piston assembly that controls the rate and direction of hydraulic flow.
Pressing the traction pedal rotates a potentiometer that provides an input to the
machine TEC controller. The controller in turn sends a corresponding PWM
(Pulse Width Modulation) output to the electronic pump control to rotate the
pump swash plate accordingly to control pump output and direction. The swash
plate angle sensor is attached to the pump to provide the position of the swash
plate. Traction circuit oil is directed to the dual displacement front wheel and rear
axle motors. Operating pressure on the high pressure side of the closed traction
circuit loop is determined by the amount of load developed at the wheel and axle
motors. As the traction load increases, circuit pressure can increase to relief
valve settings: 350 bar (5075 PSI) in forward and 360 bar (5225 PSI) in reverse.
If traction circuit pressure exceeds the relief setting, oil flows through the piston
pump relief valve to the low pressure side of the closed loop traction circuit.
Front wheel and rear axle motors are positive displacement, two speed variable
motors. The dual displacement wheel and axle motors allow operation in either
LOW or HI range. The motors are spring biased to maximum displacement for
LOW speed and are hydraulically shifted to minimum displacement for HI range.
The rear axle motor includes a flushing valve that bleeds off a small amount of
hydraulic oil for cooling of the closed loop traction circuit. The charge circuit
replenishes oil that is bled from the traction circuit by the flushing valve.
An optional traction circuit flow divider is available that equally splits traction
pump flow between the front wheel motors and rear axle motor to prevent
excessive circuit flow going to a spinning wheel. If equipped, the front traction
manifold which includes the flow divider is mounted to the right, rear side of the
front frame.
The piston pump, front wheel motors and rear axle motor use small amounts of
hydraulic fluid for internal lubrication. Fluid is designed to leak across traction
pump and motor components into the case drain. This leakage results in the loss
of hydraulic fluid from the closed loop traction circuit that must be replaced. The
charge circuit is designed to replace this traction circuit leakage. The gear pump
section that supplies oil to the steering and lift/lower circuits also provides oil
for the charge circuit.
Gear pump flow for the charge circuit is directed through the oil filter and to the
low pressure side of the closed loop traction circuit. Charge pressure is limited to
18 bar (260 PSI) by a relief valve located in the piston pump.
With the armrest console Auto and Low mode control switch in the Auto mode
position, the TEC controller controls two speed shift manifold solenoid. The
solenoid valve in the two speed shift manifold is energized by the TEC controller
for HI range. This energized solenoid valve directs charge pressure to shift the
front wheel motors and rear axle motor to their minimum displacement. With
the motors at their minimum displacements, a faster traction speed is available
for transport.
When Auto mode is in HI range position with the traction pedal pushed in the
forward direction, oil from the piston pump oil is directed to the front wheel
motors and rear axle motor through a parallel system. Oil flow to the front wheel
motors drives the motors in the forward direction and then returns to the piston
pump. Oil flow to the rear axle motor drives the motor in the forward direction.
Oil returning from the axle motor enters the rear traction manifold at the M8
port. Flow bypasses the PR cartridge through the CV check valve, out manifold
port P2 and returns to the piston pump.
Page 5–18 Groundsmaster ® 4500-D/4700-D
19245SL Rev A