Steering Circuit - Toro Groundsmaster 4700-D Service Manual

Steering Circuit

A four section gear pump is coupled to the piston (trac-
tion) pump. The gear pump section P3 supplies hydrau-
lic 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 located in the
fan control manifold. Steering circuit pressure is limited
to 1050 PSI (72 bar) by a relief valve located in the steer-
ing control valve.
With the steering wheel in the neutral position and the
engine running, pump section P3 flow enters the steer-
ing control valve at the P port and goes through the
steering control spool valve, bypassing 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 bypassed out the PB port back to the
oil filter and traction charge circuit. Second, the remain-
der of the flow is drawn through the rotary meter (V1)
and out the L port. Pressure contracts the lift cylinder for
a left turn. The rotary meter ensures that the oil flow to
STEERING CYLINDER
NO PISTON MOVEMENT
L
R
1050
PSI
T PB
P
STEERING
CONTROL
VALVE
NEUTRAL POSITION
Groundsmaster 4500--D/4700--D
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 control valve returns 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 bypassed 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 lift cylinder for a right 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 control valve returns to the neutral position
when turning is completed.
STEERING CYLINDER
PISTON MOVEMENT
L
R
1050
PSI
T PB
P
STEERING
CONTROL
VALVE
LEFT TURN
Figure 23
Page 4 - - 29
STEERING CYLINDER
PISTON MOVEMENT
L
R
1050
PSI
T PB
P
STEERING
CONTROL
VALVE
RIGHT TURN
Hydraulic System