Lift Circuit: Lower Cutting Decks - Toro GroundsmasterR 4300-D Service Manual

Lift Circuit: Lower Cutting Decks

A four section gear pump is coupled to the piston (trac-
tion) pump. Gear pump section (P4) supplies hydraulic
flow to the lift control manifold and lift cylinders. The gear
pump takes its suction from the hydraulic reservoir.
The lift control manifold includes three (3) electrically
operated valves. Solenoid valve (S1) is used to direct oil
flow to extend the lift cylinders when energized or retract
them when de--energized. Solenoid valve (S2) allows
hydraulic flow from the rod end of the lift cylinders when
energized and prevents oil passage from the lift cylin-
ders when de--energized. Proportional relief valve
(PRV) is used to control the operation of the manifold
logic cartridge (LC) and also acts as a circuit relief valve.
While operating the machine during conditions of not
raising or lowering the cutting decks (joystick in the neu-
tral (center) position) (Fig. 19), all of the lift manifold
valves (S1, S2 and PRV) are de--energized. The de--en-
ergized relief valve (PRV) allows hydraulic flow to return
to tank through the manifold. This flow causes a pres-
sure differential that shifts the logic cartridge (LC) which
allows pump flow to bypass the lift cylinders. Flow re-
turns to the oil filter and then to the hydraulic reservoir.
NOTE: When the mow speed limiter is in the transport
position, the cutting decks will not lower.
Lower Cutting Decks (Fig. 18)
When the joystick is moved to the lower position, the
controller energizes all of the lift manifold valves (S1, S2
and PRV). The energized relief valve (PRV) prevents
flow through the valve which returns logic cartridge LC
to the unshifted position. With lift manifold cartridges in
this position, pump flow is directed to the barrel end of
all lift cylinders to extend the cylinders and lower the cut-
ting decks. Fixed orifices in the lift control manifold (C2,
C4, C6 and C8) control the lowering speed of the cutting
decks by providing a restriction for the return flow from
the lift cylinders.
While the cutting decks are being lowered, the propor-
tional relief valve (PRV) has a secondary function as a
circuit relief to limit lift circuit pressure to 2000 PSI (138
bar). Lift circuit pressure can be monitored at lift control
manifold port G4.
When the joystick is returned to the neutral (center)
position, all of the lift manifold valves (S1, S2 and PRV)
are de--energized. The de--energized relief valve (PRV)
allows hydraulic flow to return to tank through the man-
ifold. This flow causes a pressure differential that shifts
the logic cartridge (LC) which allows pump flow to by-
pass the lift cylinders. All lift cylinders and cutting decks
are held in position by de--energized valve S2.
Groundsmaster 4300--D
Counterbalance
Once the cutting decks are fully lowered, the lift control
manifold proportional relief valve (PRV) maintains back
pressure (counterbalance) on the deck lift cylinders.
This counterbalance pressure transfers cutting deck
weight to the machine to improve traction. A set of wires
located behind the control arm access cover allow coun-
terbalance pressure to be adjusted to one of three set-
tings.
A pressure transducer located in the forward traction hy-
draulic tube is used by the controller as an input to deter-
mine traction circuit pressure. Based on transducer
input and machine counterbalance setting, an electrical
output from the controller is provided to the lift control
manifold proportional relief valve (PRV) to vary counter-
balance pressure. As traction pressure increases (e.g.
climbing a hill) the counterbalance pressure also in-
creases to increase the weight on the tires and improve
traction.
LIFT CIRCUIT: NOT RAISING OR LOWERING
FROM
PUMP P4
TO OIL
FILTER
Page 4 - - 19
S1, S2 AND PRV
DE- -ENERGIZED
LC SHIFTED
LIFT
CONTROL
MANIFOLD
Figure 19
Hydraulic System