Toro Groundsmaster 5900 Series Service Manual page 120

Forward Direction
Hydraulic System: Hydraulic Flow Diagrams
Note: See Traction Circuit Operation (page 5–14)
function of the traction circuit.
When the high range traction speed (transport) is selected, solenoid valve (SV)
in the traction manifold is energized by the slave Toro electronic controller. The
shifted solenoid valve (SV) spool directs charge pressure in the traction manifold
to shift all six (6) pressure differential valves (PD1, PD2, PD3, PD4, PD5 and
PD6) in the manifold.
When the machine is in the high speed range, traction manifold steering orifices
(OR1 and OR2), relief valve (RV1) and check valves CV1 and CV2 have no
function.
With the high range traction speed (transport) selected and the traction pedal in
the neutral position, the swash plate in the piston pump is not rotated so there is
no oil flow from the pump and no machine traction movement.
With the high range traction speed selected and the traction pedal pushed in
the forward direction, oil from the piston pump is routed out pump port A and
then to traction manifold port P1. The shifted PD1 valve in the traction manifold
prevents piston pump hydraulic flow from reaching the rear wheel motors. With
flow blocked to the rear wheel motors, all piston pump flow is directed to the front
wheel motors when in the high speed range.
Total piston pump flow is routed in parallel to half the displacement of the front
wheel motors through ports A1 of the motors to drive the front motors at transport
speed. Higher machine transport speed is possible due to all of the pump flow
being routed to one section of each of the front wheel motors.
The shifted PD1, PD2 and PD3 valves in the traction manifold allow the rear
wheel motors to remain filled with hydraulic oil while they free−wheel in high
speed range. When in high speed, case pressure in the rear wheel motors keeps
the motor pistons retracted to reduce rolling resistance of the rear wheels.
Oil from the front motors exits the motors through port R and re−enters the
traction manifold through ports M9 and M10. This return oil is routed to the
shuttle valve (SH) that is shifted by front wheel traction pressure. When in high
speed range, approximately 18.6 LPM (4.8 GPM) of hydraulic fluid is released
from the closed loop traction circuit through the shifted shuttle valve (SH) and
shifted PD6. This release of oil from the traction circuit loop is also necessary to
keep the rear wheel motor pistons retracted when in the high (transport) speed
range. Return oil that is not bled from the traction circuit is returned to the piston
pump through traction manifold port P2 and piston pump port B.
The shifted PD4 and PD5 valves in the traction manifold recirculate return oil
from the driven front wheel motors to the second section of the front motors
through ports A2 of the motors. This recirculated flow provides cooling and
lubrication of the front wheel motors when in transport speed range.
Page 5–20
for a description of general
Groundsmaster ® 5900 & 5910
16227SL Rev B