Jacobsen AR3, Техническое руководство по ремонту

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5-6 4181384 First Edition
HYDROSTATIC POWER TRAIN
5
Traction Circuit Reverse Schematic
and Theory of Operation
See Figure 5-4.
System Conditions:
• Engine running
• Park brake released
• Traction pedal depressed (reverse position)
Charge Pressure Circuit
Operating pressure oil from the cutting unit pump enters
the mow and brake valve at port “CP” and is directed to
the pilot line circuits of the relief valve, mow solenoid
valve, and the load control valve.
Operating pressure oil flows through the valve and exits
the mow and brake valve at port “MP” and flows to the
hydraulic oil filter. Oil flows through the oil filter, enters the
traction drive pump at port “E,” and is routed to the pilot
line of the charge pressure relief valve and to the traction
drive circuit/pump. The charge pressure relief valve
regulates the charge pressure applied to the traction
drive circuit/pump. If the incoming charge pressure oil
reaches 160 psi (11 bar), the charge pressure relief valve
will open, venting excess oil flow to the hydraulic tank.
Park Brake Circuit
The front wheel motors are equipped with multi-disk wet
brakes. The brakes are spring-applied and released with
charge-pressure oil controlled by the brake solenoid
valve in the mow and brake valve.
The park brake circuit is equipped with a lever-operated
park brake release valve to allow the release of the
brakes with a dead engine for towing purposes. The park
brake release valve is normally in the operating position,
directing the charge oil from the mow and brake valve to
the brake pistons in the front wheel motors to release the
parking brakes.
When the park brake release lever is moved to the
released position, the oil passage from the mow and
brake valve is closed, and the passage is opened to the
steering cylinder. This oil pathway provides a means to
release the parking brakes with the engine off by turning
the steering wheel, routing oil from the steering circuit to
the parking brake to release the brakes.
Traction Pump Circuit
The traction drive pump receives a supply of filtered,
charge pressure oil from the charge pressure circuit.
When the traction pedal is moved to the reverse position,
the engine-driven traction pump supplies high-pressure
oil to the rear wheel motor and the check valve in the
flushing valve through port “A” of the traction drive pump.
The check valve in the flushing valve opens, and allows
the high-pressure oil to bypass the rear wheel motor,
resulting in two-wheel drive when in reverse. The oil
flowing through the check valve is routed to the two front
wheel motors, rotating them in the reverse direction. Oil
then returns to the traction drive pump through port “B”
and back into the closed-loop system.
Flushing Valve
The flushing valve is used to remove hot oil from the
closed-loop traction drive circuit when moving forward
only. When driving in reverse, the oil pressure routed to
the pilot line of the flushing valve drops, shifting the valve
spool and closing the valve. Oil then flows through the
check valve as described in “Traction Pump Circuit.”