Textron Jacobsen SLF530, Repair Manual

Page: 142 / 352

5-16 673831-Rev A
HYDROSTATIC POWER TRAIN
5
Traction Circuit—Reverse Schematic
and Theory of Operation
System Conditions:
• Engine running
• Parking brake switch in the OFF position
• Traction pedal in the REVERSE position
Charge Pressure Circuit
The traction pump and gear pump are both driven by the
engine. Section 2 of the gear pump provides operating
pressure oil for the rear reel valve, and charge pressure
oil for the traction pump.
Oil is drawn from the hydraulic tank through a 100-mesh
screen, and enters the gear pump, supplying oil to all
three pump sections. Operating pressure oil from section
2 of the gear pump is routed to port “P” of the rear reel
valve and out port “T” to the charge filter and the brake
valve port “CHG”.
The charge filter uses a 10-micron filter to remove debris
from the oil. In the event of the charge filter becoming
plugged, a 25 psi (1.7 bar) pressure indicator is installed
on the filter head, and a bypass valve will open to provide
oil to the traction pump. Charge pressure oil is then
routed to the traction pump.
The traction pump includes a charge relief valve that will
open to dump oil to the case drain when the charge
pressure reaches 200 psi (14 bar).
Brake Circuit
When the parking brake switch is moved to OFF position,
the MCU will energize the brake valve solenoid coil,
shifting the solenoid valve. This allows charge pressure
oil to flow through the needle valve against the 507 psi
(35 BAR) brake relief valve and hand pump check valve.
Charge pressure oil also flows out brake valve Port PB2
to the left and right front wheel motors Port X. The charge
pressure oil will cause the brake piston to compress the
brake spring in the wheel motors, releasing the pressure
on the friction discs, allowing the wheel motors to rotate.
3WD Option Traction Drive Circuit
When the traction pedal is moved to REVERSE position,
the swash plate is moved, stroking the pump. This
change of the swash plate angle produces an increase of
oil flow on one side of the pump. Oil at operating pressure
is then routed against the Port A side check valve and
4060 psi (2
8 0 bar) reverse relief valve, and exits the
traction pump at Port A. The oil is then routed through the
3WD check valve to the left front wheel motor port R and
the right front wheel motor Port L, driving the front wheel
motors in the reverse direction. Oil exiting the front wheel
motors is returned to the traction pump Port B to
replenish the intake side of the pump.
The reverse operating pressure oil flows through the
3WD check valve and is not forced through the rear
wheel motor. The hose connections on both sides of the
check valve provides no driving force to the rear wheel
motor, but allows the motor to rotate freely as the mower
travels in the reverse direction.
4WD Option Traction Drive Circuit
When the traction pedal is moved to Reverse position,
the swash plate is moved, stroking the pump. This
change of the swash plate angle produces an increase of
oil flow on one side of the pump. Oil at operating pressure
is then routed against the Port A side check valve and
4060 psi (2
8 0 bar) reverse relief valve, and exits the
traction pump at Port A. The oil is then routed to the left
front wheel motor port R, right front wheel motor Port L
and 4WD valve Port B, driving the front wheel motors in
the reverse direction. Oil exiting the front wheel motors is
returned to the traction pump to replenish the intake side
of the pump.
The operating pressure oil from 4WD Port (B) is blocked
by the reverse check valve. The 4WD solenoid valve
allows oil to flow between the motor ports when the
solenoid is not energized. This provides no driving force
to the rear wheel motors, but allows the motors to rotate
freely as the mower travels in the reverse direction.
Circuit Relief
The forward traction circuit is protected by a relief valve.
The relief valve will open if the pressure rises to 4060 psi
(2
8 0 bar), allowing oil to dump to the charge side of the
circuit.
Loop Flushing
The traction pump has a loop flushing valve to lower the
operating temperature. The higher pressure on the Port A
side of the traction loop will shift the loop flushing valve,
allowing oil from the Port B side of the loop to be returned
to the tank. Oil that is removed through the loop flushing
valve is replenished by flow from the charge pump
through the Port B side check valve.