Toro Groundsmaster 5900 Series Service Manual page 117

Forward Direction
Groundsmaster ® 5900 & 5910
16227SL Rev B
Note: See Traction Circuit Operation (page 5–14)
function of the traction circuit.
With the low range traction speed (mow) 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 low range traction speed (mow) selected and the traction pedal pushed
in the forward direction, oil from the piston pump is routed out port A to traction
manifold port P1. Pump flow is then routed in parallel to half the displacement of
the front wheel motors through ports A1 and to the rear wheel motors through
unshifted traction manifold valve PD1. The flow that goes through the rear motors
is then routed to the opposite front motor through ports A2 of the front motors (left
rear to right front through unshifted PD2 and PD5, right rear to left front through
unshifted PD3 and PD4). Oil flow through the rear and front motors keeps all
wheel motors at their maximum displacement to allow a lower traction speed
along with CrossTrax TM
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 low
speed range, the traction manifold flow regulator (FR) allows approximately
1.9 LPM (0.5 GPM) of hydraulic fluid to bleed off for cooling of the closed loop
traction circuit when the shuttle valve (SH) is shifted. By limiting the amount of oil
that is removed from the traction circuit, the chance of a front tire losing traction
can be reduced. 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.
If a rear motor loses traction, pressure increases in the serial line because too
much flow is being sent to the opposite front motor. This lowers the torque
available to the tire trying to spin so that overall machine traction is maintained.
If a front tire loses traction, pressure increases in the low side of the traction
loop reducing the pressure differential across the front motor and increasing
pressure drop across the rear motors. This allows the rear motors to provide
more traction effort.
The traction manifold includes several components designed to enhance low
speed traction performance. Steering orifices in the manifold serial line (OR1
and OR2) prevent tire scuffing when turning. The serial line relief valve (RV1)
prevents tire scuffing and also increases rear motor life. Check valves CV1 and
CV2 prevent circuit cavitation if either of the front wheel motors lose traction.
4WD operation for enhanced traction while mowing.
Page 5–17 Hydraulic System: Hydraulic Flow Diagrams
for a description of general