Traction Circuits: 4Wd Machines - Toro Groundsmaster 360 Service Manual

Traction Circuits: 4WD Machines (Fig. 10)
The traction system on 4WD machines allows hydraulic
drive to all four wheels. Traction components include a
transmission with two independent closed loop circuits,
two rear wheel motors, two front wheel motors and the
TM
CrossTrax AWD control manifold. The transmission
and rear wheel motors used on 4WD machines are the
same as the hydraulic components used on 2WD ma-
chines. The traction circuit on 4WD machines, there-
fore, operates basically the same as the traction circuit
on 2WD machines with the added benefit of the addition-
al front wheel motors. Refer to Traction Circuit: 2WD
Machines in this section for information on traction sys-
tem operation.
NOTE: On Groundsmaster 360 4WD machines, the
Automatic Speed Control (ASC) system is only active
when the machine is in the 4 wheel steering position.
Forward
For each of the transmission piston pumps, flow for the
forward direction is routed to a rear wheel motor and
then to the opposite front wheel motor (e.g. right rear
and then to left front) to maximize traction. Forward trac-
tion circuit relief valve setting of 4000 PSI (276 bar) is the
same as 2WD machines.
When operating the machine in a forward, straight direc-
tion (not turning), transmission oil flow to the two traction
circuits routes from a rear wheel motor to the opposite
front wheel motor. Both traction circuits require similar
flow to drive the wheel motors so minimal circuit flow
change is provided through the CrossTrax
trol manifold and balancing oil lines.
When turning the machine in a forward direction, the
four wheel motors require different flows due to different
wheel distances traveled going around the corner. The
balancing lines and the CrossTrax
ifold allow the two traction circuits to be connected so dif-
ferences in wheel motor flows can be achieved. In the
forward direction, pilot directional valves PD1 and PD2
TM
in the CrossTrax AWD control manifold are shifted.
These shifted valves along with the manifold check
valves (CV1 and CV2) help to provide oil where needed
in the traction circuits for optimal traction operation
when turning.
The control manifold includes a bi--directional relief
valve (CRV) and orifice fittings to prevent pressure dif-
ferences in the two circuits reducing tire scuffing when
turning.
Groundsmaster 360
TM
AWD con-
TM
AWD control man-
Page 4 - - 13
To provide 4--wheel dynamic braking when the traction
pedal is released, pilot directional valves PD1 and PD2
TM
in the CrossTrax AWD control manifold shift to their
normally closed position. This disables the manifold
check valves (CV1 and CV2) ensuring 4--wheel hydro-
static braking.
Reverse
The 4WD traction circuit operates essentially the same
in reverse as it does in forward. In the reverse direction,
transmission pump flow to the two traction circuits is
routed first to a front wheel motor and then to the oppo-
site rear wheel motor (e.g. right front and then to left
rear). The reverse traction circuit relief valve setting is
4000 PSI (276 bar).
In the reverse direction, pilot directional valves PD1 and
TM
PD2 in the CrossTrax AWD control manifold are not
shifted. This disables the manifold check valves (CV1
and CV2) ensuring optimal 4WD traction while in re-
verse.
Because vehicle speed in the reverse direction is typi-
cally reduced, there is less hydraulic flow through the
traction circuit. This lower flow results in less circuit flow
change necessary through the CrossTrax
trol manifold and balancing oil lines.
4WD Machine
Port D
Port C
Port B
Port A
Figure 11
TM
AWD con-
Balancing Hose
Balancing Hose
Hydraulic System