THEORY OF OPERATION - CONTINUED
ELECTRO-HYDRAULIC SYSTEM - CONTINUED
Ride control system is made up of lift cylinders, ride control accumulator, ride control solenoid valve, shuttle
valve, head end solenoid valve, head end check valve, and rod end solenoid valve.
Ride control system is controlled by ride control switch (TM 5-3805-291-10).
When engine start switch in set to ON and ride control is OFF, ride control solenoid valve is actuated.
Valve spool in solenoid valve shifts left. Head end solenoid valve and rod end solenoid valve are not actu-
ated. In this position, oil flow from accumulator to valve spool of shuttle valve is blocked. This prevents
oil from head end of lift cylinders from flowing to accumulator, which may eventually cause damage to
ride control system components.
Oil pressure in head end of lift cylinders will move spool in shuttle valve right. Pump supply oil flows to
check valve. Check valve opens and pump supply oil fills accumulator.
When engine start switch is set to OFF, solenoid valve is de-energized and spool in solenoid valve is
moved right. Oil pressure in accumulator acts against right end of valve spool in shuttle valve.
If oil pressure in head end of lift cylinders has decreased, valve spool in shuttle valve moves left, opening
path for oil from accumulator to hydraulic tank. Oil in accumulator will flow to hydraulic tank. Spool in
shuttle valve will stay left until pressures on each end are equalized. Spool will be centered when pressure
between accumulator and head end of lift cylinders is equal.
Automatic Ride Control.
To initiate automatic ride control, push top of ride control switch (TM 5-3805-291-10). In AUTO position,
ride control system functions automatically when machine's ground speed increases above approximately
6.0 mph (9.5 km/h). There is a one-second delay for pressure equalization before ride control is initiated.
When ride control switch is in AUTO and machine's ground speed increases above approximately 6.0 mph
(9.5 km/h), system will initiate ride control after one-second pressure equalization delay. Solenoid valve
will de-energize. Valve spool in solenoid valve moves right. A path of oil from ride control accumulator
will flow through solenoid valve, acting as pilot pressure on right side of shuttle valve. If accumulator
pressure is greater than cylinders' head end pressure, spool of shuttle valve will move left. With spool in
this position, accumulator will drain back to hydraulic tank.
Oil pressure in head end of lift cylinders acts as pilot pressure on left side of shuttle valve. If head end
pressure is greater than accumulator pressure, spool will move right. When spool is in this position, supply
oil from hydraulic pump flows through check valve to fill accumulator.
Spool in shuttle valve will move right to left and left to right to equalize pressure between head end of lift
cylinders and accumulator. When pressure in accumulator is equal to pressure in head end of lift cylinders,
valve spool for shuttle valve will be centered.
N OT E
The one-second pressure equalization period is the default, and can be changed using ET.
After a one-second pressure equalization period, rod and head end solenoid valves will energize. Valve
spool in head end solenoid valve will move left. In this position, pilot oil in spring chamber of 2-port car-
tridge check valve can flow back to tank to allow poppet of check valve to rise.
When valve poppet in 2-port cartridge check valve is raised, path of oil between head end of lift cylinders
and ride control accumulator is open. Oil flow from head end of lift cylinders acts against accumulator,
which works as a shock absorber. Oil entering accumulator is resisted by nitrogen precharge and forces of
work tool are dampened. This allows accumulator to act as a dampener to lift cylinders.
Simultaneously, rod end solenoid valve is energized. Oil from rod end of lift cylinders may flow back to
hydraulic tank. Hydraulic oil can flow from tank line to rod end of lift cylinders as makeup oil.