Toro 30857 - Steering Circuit

Groundsmaster 4500--D/4700--D Hydraulic SystemPage 4 -- 29
Steering Circuit
A four section gear pump is coupled to the piston (trac-
tion)pump. Thegearpump sectionP3supplieshydrau-
lic flow to the steering control valve and the lift/lower
controlvalve.Pumphydraulicflowisdeliveredtothetwo
circuitsthroughaproportionalflowdividerlocatedinthe
fan control manifold. Steering circuit pressure is limited
to1050PSI(72bar)byareliefvalvelocatedinthesteer-
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
steeringcontrol spoolvalve,bypassing therotarymeter
(V1)andsteeringcylinder.Flowleavesthecontrolvalve
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
turningofthesteeringwheelpositionsthespoolvalveso
thatflowgoesthroughthetopofthespool.Flowentering
thesteering control valveat the P port goesthroughthe
spool and is routed to two places. First, most of the flow
throughthevalveisbypassedoutthePBportbacktothe
oil filter and traction charge circuit.Second, the remain-
der of the flow is drawn through the rotary meter (V1)
andouttheLport.Pressurecontracts theliftcylinderfor
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
backthroughthespoolvalvethenthroughtheTportand
to the hydraulic reservoir.
Thesteeringcontrolvalvereturnstotheneutralposition
when turning is completed.
Right Turn
When a right turn is made with the engine running, the
turningofthesteeringwheelpositionsthespoolvalveso
thatflowgoesthroughthebottomofthespool. Flow en-
tering the steering control valve at the P port goes
throughthespoolandisroutedtotwoplaces.Asinaleft
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
proportionaltothe amountoftheturningon thesteering
wheel.Fluid leaving the cylinder flows back through the
spool valve then through the T port and to the hydraulic
reservoir.
Thesteeringcontrolvalvereturnstotheneutralposition
when turning is completed.
Figure 23
1050
PSI
PB
STEERING
T
R
P
L
PISTON MOVEMENT
CONTROL
1050
PSI
PB
STEERING CYLINDER
T
R
P
L
PISTON MOVEMENT
1050
PSI
PB
STEERING CYLINDER
T
R
P
L
LEFT TURN
NEUTRAL POSITION
RIGHT TURN
NO PISTON MOVEMENT
STEERING CYLINDER
VALVE
STEERING
CONTROL
VALVE
STEERING
CONTROL
VALVE
Hydraulic
System