Steering Circuit - Toro Groundsmaster 4500-D Service Manual

Steering Circuit

A three section gear pump is coupled to the piston (trac-
tion) pump. The gear pump section (P3) supplies hy-
draulic flow to the steering control valve and the lift/lower
control valve. Pump hydraulic flow is delivered to the two
circuits through a proportional flow divider. The gear
pump takes its suction from the hydraulic reservoir.
Steering circuit pressure is limited by a relief valve lo-
cated in the steering control.
Pressure to the steering control valve can be monitored
at a port on the end of the gear pump.
With the steering wheel in the neutral position (rear
wheels positioned straight ahead) and the engine run-
ning, flow enters the steering control valve at the P port
and goes through the steering control spool valve, by--
passing the rotary meter (V1) and steering cylinder.
Flow leaves the control valve through the PB port to the
oil filter and traction charge circuit.
Left Turn
When a left turn is made with the engine running, the
turning of the steering wheel positions the spool valve so
that flow goes through the top of the spool. Flow entering
the steering control valve at the P port goes through the
spool and is routed to two places. First, most of the flow
through the valve is by--passed out the PB port back to
the oil filter and traction charge circuit. Second, the re-
mainder of the flow is drawn through the rotary meter
(V1) and out the L port. Pressure contracts the piston for
STEERING CYLINDER
NO PISTON MOVEMENT
L
R
1180
PSI
T PB
P
STEERING
CONTROL
NEUTRAL POSITION
Groundsmaster 4500--D/4700--D
a left turn. The rotary meter ensures that the oil flow to
the cylinder is proportional to the amount of the turning
on the steering wheel. Fluid leaving the cylinder flows
back through the spool valve then through the T port and
to the hydraulic reservoir.
The steering wheel and steering control valve return to
the neutral position when turning is completed.
Right Turn
When a right turn is made with the engine running, the
turning of the steering wheel positions the spool valve so
that flow goes through the bottom of the spool. Flow en-
tering the steering control valve at the P port goes
through the spool and is routed to two places. As in a left
turn, most of the flow through the valve is by--passed out
the PB port back to the oil filter and traction charge cir-
cuit. Also like a left turn, the remainder of the flow is
drawn through rotary meter (V1) but goes out port R.
Pressure extends the piston for a right turn. The rotary
meter ensures that the oil flow to the cylinder is propor-
tional to the amount of the turning on the steering wheel.
Fluid leaving the cylinder flows back through the spool
valve then through the T port and to the hydraulic reser-
voir.
The steering wheel and steering control valve return to
the neutral position when turning is completed.
STEERING CYLINDER
PISTON MOVEMENT
L
R
1180
PSI
T PB
P
STEERING
CONTROL
LEFT TURN
Figure 18
Page 4 - - 19
STEERING CYLINDER
PISTON MOVEMENT
L
R
1180
PSI
T PB
P
STEERING
CONTROL
RIGHT TURN
Hydraulic System (Rev. A)