Traction Circuit - Toro Groundsmaster 4100-D Service Manual

Traction Circuit

The traction circuit piston pump is a variable displace-
ment pump that is directly coupled to the engine fly-
wheel. Pushing the top of the traction pedal engages a
hydraulic servo valve which controls the variable dis-
placement piston pump swash plate to create a flow of
oil. This oil is directed to the 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 fixed displacement
wheel and axle motors. As the load increases, circuit
pressure can increase to relief valve settings: 4000 PSI
in forward and 5000 PSI in reverse. If pressure exceeds
the relief setting, oil flows through the relief valve to the
low pressure side of the closed loop circuit. The traction
circuit provides operation in either four wheel drive
(mow) or two wheel drive (transport).
Traction circuit pressure (forward and reverse) can be
measured at test ports on the sides of the machine.
The traction pump and wheel motors use a small
amount of hydraulic oil for internal lubrication. Oil is de-
signed to leak across pump and motor parts into the
case drain. This leakage results in the loss of hydraulic
oil from the closed loop traction circuit that must be re-
placed.
The gear pump that supplies oil to the steering and lift/
lower circuits also provides charge oil for the traction cir-
cuit. This gear pump is driven directly off the traction
pump. It provides a constant supply of charge oil to the
traction circuit to make up for oil that is lost due to inter-
nal leakage in the traction pump and motors.
Groundsmaster 4100--D
Charge pump flow is directed through the oil filter and to
the low pressure side of the closed loop traction circuit.
A filter bypass valve allows charge oil flow to the closed
loop if the filter becomes plugged. Charge pressure is
limited by a relief valve located in the oil filter manifold.
Charge pressure can be measured at the charge circuit
pressure test port on the oil filter manifold.
The 4WD/2WD control manifold provides hydraulic flow
management in a variety of situations. Pressure testing
of this control manifold can be performed at a test port
on the manifold.
1. Four wheel drive (mow) and two wheel drive (trans-
port) operation is controlled by a solenoid valve (SV) lo-
cated in the 4WD/2WD control manifold. When in
transport (2WD), the solenoid valve (SV) is energized
and directs charge pressure to shift the control valves
(PD1 and PD2). These shifted valves block hydraulic
flow to the rear axle motor in both forward and reverse
directions when in transport (2WD).
2. A pressure reducing valve (PR) in the 4WD/2WD
control manifold lowers pressure to the rear axle motor
when the machine is operated in reverse. The lower
pressure prevents rear tire scuffing and provides added
pressure to the front wheels during reverse operation.
3. An adjustable relief valve (RV5) in the 4WD/2WD
control manifold reduces rear axle motor pressure
created in down--hill, dynamic braking conditions.
To enhance traction control, the lift/lower circuit is
equipped with a counterbalance system. An adjustable
counterbalance valve located in the counterbalance
control manifold (in CB port) transfers cutting deck
weight to the machine to improve traction.
Rev. E
Page 4 - - 9 Hydraulic System