caution - Toro
caution - Toro
caution - Toro
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Traction Circuit: 4WD (Mow)<br />
The traction circuit piston pump is a variable displacement<br />
pump that is directly coupled to the engine flywheel.<br />
Pushing the traction pedal engages a hydraulic<br />
servo valve which controls the variable displacement<br />
piston pump swash plate to create a flow of oil. This oil<br />
is directed to the front wheel and rear axle motors. Operating<br />
pressure on the high pressure side of the closed<br />
traction circuit loop is determined by the amount of load<br />
developed at the fixed displacement wheel and axle motors.<br />
As the load increases, circuit pressure can increase<br />
to relief valve settings: 4000 PSI (274 bar) in<br />
forward and 5000 PSI (343 bar) in reverse. If pressure<br />
exceeds the relief setting, oil flows through the relief<br />
valve to the low pressure side of the closed loop traction<br />
circuit. The traction circuit provides operation in either<br />
4WD (mow) or transport (2WD).<br />
Traction circuit pressure (forward and reverse) can be<br />
measured at test ports on the sides of the machine.<br />
The traction circuit pump and motors use a small<br />
amount of hydraulic fluid for internal lubrication. Fluid is<br />
designed to leak across traction pump and motor components<br />
into the case drain. This leakage results in the<br />
loss of hydraulic fluid from the closed loop traction circuit<br />
that must be replaced. The charge circuit is designed to<br />
replace this traction circuit leakage.<br />
The gear pump section that supplies oil to the steering<br />
and lift/lower circuits also provides oil for the charge circuit.<br />
This gear pump is driven directly off the traction<br />
pump. It provides a constant supply of charge oil to<br />
make up for oil that is lost due to internal leakage in the<br />
traction pump and motors.<br />
Pump flow for the charge circuit is directed through the<br />
oil filter and to the low pressure side of the closed loop<br />
traction circuit. A filter bypass valve allows charge oil<br />
flow to the closed loop if the filter becomes plugged.<br />
Charge pressure is limited to 250 PSI (17 bar) by a relief<br />
valve located in the oil filter manifold. Charge pressure<br />
can be measured at the charge circuit pressure test port<br />
on the oil filter manifold.<br />
Forward Direction<br />
When the transport/4WD switch is in the 4WD (mow)<br />
position and the traction pedal is pushed in the forward<br />
direction, oil from the piston pump is directed to the front<br />
wheel motors and 4WD manifold. Oil flow to the front<br />
wheel motors drives the motors in the forward direction<br />
and then returns to the hydrostat. Oil flow to the 4WD<br />
manifold enters the P1 port and then is directed to the<br />
PD1 cartridge and out of the manifold M1 port to drive<br />
the rear axle motor in the forward direction. Oil returning<br />
from the rear motor re--enters the 4WD manifold at the<br />
M2 port. Flow passes through the PD2 cartridge,<br />
through the CV check valve, out manifold port P2 and<br />
back to the hydrostat.<br />
When going down a hill, the tractor becomes an over--<br />
running load that drives the wheel and axle motors. In<br />
this condition, the rear axle motor could lock up as the<br />
oil pumped from the motor increases pressure as it returns<br />
to the hydrostat. To prevent rear wheel lock up, an<br />
adjustable relief valve (RV) in the 4WD manifold reduces<br />
rear axle motor pressure created in down hill, dynamic<br />
braking conditions.<br />
Reverse Direction<br />
The traction circuit operates essentially the same in reverse<br />
4WD (mow) as it does in the forward direction.<br />
However, the flow through the circuit is reversed. Oil flow<br />
from the hydrostat is directed to the front wheel motors<br />
and also to the 4WD manifold. The oil to the front wheel<br />
motors drives them in the reverse direction and then returns<br />
to the hydrostat. The oil to the 4WD manifold enters<br />
the manifold at port P2 and flows through pressure<br />
reducing valve (PR) which limits the down stream pressure<br />
to the rear axle motor to 650 PSI (45 bar) so the rear<br />
wheels will not scuff the turf during reverse operation.<br />
This reduced pressure flows through the PD2 cartridge<br />
and out port M2 to the rear axle motor. Return oil from<br />
the rear motor re--enters the 4WD manifold at port M1,<br />
flows through the PD1 cartridge, exits the manifold at<br />
port P1 and returns to the hydrostat.<br />
Hydraulic<br />
System<br />
Groundsmaster 4100--D<br />
Page 4 - 11<br />
Hydraulic System