Steering Circuit - Toro Groundsmaster 4000-D Service Manual

Steering Circuit

A four section gear pump is coupled to the piston (trac-
tion) pump. The third gear pump section 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 located in the
fan drive manifold. The gear pump takes its suction from
the hydraulic reservoir. Steering circuit pressure is limit-
ed to 1350 PSI (93 bar) by a relief valve located in the
steering control.
With the steering wheel in the neutral position and the
engine running, 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 steering
cylinder piston for a left turn. The rotary meter ensures
STEERING CYLINDER
NO PISTON MOVEMENT
L
R
1350
PSI
T PB
P
STEERING
CONTROL
NEUTRAL POSITION
Groundsmaster 4000--D
that the oil flow to the cylinder is proportional to the
amount of the turning on the steering wheel. Fluid leav-
ing 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 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 steering cylinder piston for a right
turn. The rotary meter ensures that the oil flow to the cyl-
inder 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
1350
PSI
T PB
P
STEERING
CONTROL
LEFT TURN
Figure 13
Page 4 - - 23
STEERING CYLINDER
PISTON MOVEMENT
L
R
1350
PSI
T PB
P
STEERING
CONTROL
RIGHT TURN
Hydraulic System