Steering Circuits: 2Wd Machines - Toro Groundsmaster 360 Service Manual

Steering Circuits: 2WD Machines (Fig. 12)
The Groundsmaster 360 Quad Steer
ing system uses Ackermann four wheel steering. Acker-
mann steering enables the inside and outside wheels to
turn around a common pivot point. This results in re-
duced turf damage and greater operator response when
turning.
A single section gear pump is directly coupled to the
transmission which is driven by the engine. This gear
pump supplies hydraulic flow for both the steering and
lift/lower circuits. Hydraulic pump flow from the gear
pump is routed to the steering control valve first so the
steering circuit has priority. The pump takes its suction
from the hydraulic tank. Steering circuit pressure is limit-
ed to 1800 PSI (125 bar) by a relief valve located in the
gear pump. Two (2) steering cylinders are used to pro-
vide four wheel steering: one cylinder turns the front
wheels and the second cylinder turns the rear wheels.
The steering control valve includes a check valve that al-
lows steering operation when the engine is not running.
Steering wheel rotation with the engine off causes oil
flow from the steering control gerotor. The check valve
opens in this situation to allow oil flow from the steering
control to the steering cylinder in a closed loop.
To allow for synchronization of the front and rear steer-
ing cylinders, both steering cylinders include an internal
re--phasing check valve assembly in the cylinder piston
(Fig. 13). While rotating the steering wheel for a turn
when in 4 wheel steer (either right or left), the cylinder
check valve will open once the cylinder is fully extended
or retracted. Once both cylinders have moved fully, the
4 wheel steering system has been synchronized. If the
steering wheel continues to be turned, the check valves
will stay open and will allow flow through the circuit.
With the steering wheel in the neutral position and the
engine running, gear pump flow enters the steering con-
trol valve at the P port and goes through the steering
control spool valve, bypassing the rotary meter and
steering cylinders. Flow leaves the control valve through
the E port and is routed to the lift/lower circuit, oil cooler
and transmission case. The transmission case drain al-
lows oil to return to the hydraulic tank.
Left Turn (Fig. 12)
When a left turn is made with the engine running, the
turning of the steering wheel positions the steering con-
trol spool valve so that gear pump flow is directed
through the top of the spool. Flow entering the steering
control valve at the P port goes through the spool, is
routed through rotary meter and out the control valve L
port. This flow moves to the front steering cylinder to ex-
Groundsmaster 360
TM
all wheel steer- tend the cylinder and turn the front wheels in the direc-
tion for a left turn. The oil displaced from the extending
front cylinder is directed to the rear steering cylinder to
extend that cylinder and turn the rear wheels in the direc-
tion for a left turn. The rotary meter ensures that the oil
flow to the steering cylinders is proportional to the
amount of turning on the steering wheel. Fluid leaving
the rear steering cylinder flows back through the steer-
ing control spool valve and then out of the steering con-
trol valve through the T port and is routed to the oil cooler
and transmission case.
The steering control valve returns to the neutral position
when turning is completed.
Right Turn (Fig. 12)
When a right turn is made with the engine running, the
turning of the steering wheel positions the steering con-
trol spool valve so that gear pump flow is directed
through the bottom of the spool. Flow entering the steer-
ing control valve at the P port goes through the spool, is
routed through rotary meter and out the control valve R
port. This flow moves to the rear steering cylinder to re-
tract the cylinder and turn the rear wheels in the direction
for a right turn. The oil displaced from the retracting rear
cylinder is directed to the front steering cylinder to re-
tract that cylinder and turn the front wheels in the direc-
tion for a right turn. The rotary meter ensures that the oil
flow to the steering cylinders is proportional to the
amount of turning on the steering wheel. Fluid leaving
the front steering cylinder flows back through the steer-
ing control spool valve and then out of the steering con-
trol valve through the T port and is routed to the oil cooler
and transmission case.
The steering control valve returns to the neutral position
when turning is completed.
1. Cylinder piston
Page 4 - - 15
1
2
Figure 13
2. Check valve assembly
Hydraulic System