Straight Travel

180

When the travel valve is returned to NEUTRAL, the counterbalance valve also returns to NEUTRAL.

When the counterbalance valve returns to NEUTRAL, the supply pressure to the motor drops as the motor continues to try to turn. Return oil to the travel control can be used as makeup oil to the low pressure side.

Due to the back pressure created by the slow return check valve, the check valve in the counterbalance valve can unseat and allow return oil to enter the low pressure side of the motor.

The crossover relief valve will also open to send oil in the high pressure side to the low pressure side of the travel motor to reduce motor cavitation.

181

Straight Travel

When both travel levers or pedals are shifted and at least one of the implements or the swing is selected, pilot oil pressure from the pilot manifold increases and shifts the straight travel valve down. The implement and travel pressure switches also close. The pressure switches send a signal to the Machine ECM indicating that machine travel and an implement have been activated.

When the straight travel valve shifts down all of the idler pump flow is directed equally to the travel control valves.

The drive pump flow is directed into the parallel feeder passages and to the activated implement circuit. In the illustration above forward travel and been selected and the bucket has been shifted to close.

At the travel motors, the counterbalance valves shift and direct idler pump supply oil to the motors. At the same time some of the supply oil is used to release the parking brake.

During straight travel mode, the machine can only run at low travel speed mode.

182

This illustration shows the straight travel valve position when only the travel function is activated. Pilot pressure from the pilot manifold is low. Spring force keeps the spool shifted to the right.

Oil flows from the drive pump through the right center bypass passage to the right travel control valve and through the right parallel feeder passage to the boom 1 control valve, the work tool control valve, the bucket control valve, and the stick 2 control valve.

Oil flows from the idler pump through the left center bypass passage to the left travel control valve and through the left parallel feeder passage to the swing control valve, the stick 1 control valve, and boom 2 control valve.

183

This illustration shows the straight travel valve position when both travel levers are activated and one of the implements are activated. Pilot pressure from the pilot manifold increases. Pilot oil pressure moves the spool to the left.

Oil flows from the drive pump:

-through the right parallel feeder passage to the boom 1 control valve, the work tool control valve, the bucket control valve, and the stick 2 control valve.

-through the left parallel feeder passage to the swing control valve, the stick 1 control valve, and the boom 2 control valve.

-into a passage in the center of the spool, through a check valve and orifice and combines with the idler pump oil flowing to the travel control valves.

Oil flows from the idler pump through the left center bypass passage to the left travel control valve and through the right center bypass passage to the right travel control valve.