Case CX250D Crawler Excavator Repair Manual

Manuals: Service Manual
Introduction
Engine
Hydraulics System
Frames and Ballasting
Tracks and Track Suspension
Cab Climate Control
Electrical System
Booms, dippers and buckets
Dozer Blade and Arm
Platform, cab, bodywork and decals
Special Tools Index
Hydraulic Schematics
Electrical Schematics
Manual Extract: SWING PARKING CIRCUIT (BRAKE RELEASE)

When the engine is started and the swing lever is in neutral, the swing brake solenoid valve comes ON ( 24 V input), the pressure to the swing motor PR port is cut, and the swing parking brake works.

When the lever operation raises the reading to higher than the specified pressure value at the pressure sensor in the swing pilot line, the output from the main computer to the swing brake solenoid valve goes OFF, the swing motor PR port pressure rises, the swing parking brake is released, and swing becomes possible. As an example, this section explains the right swing operation.

By carrying out the right swing operation on the remote control valve, the pilot pressure oil is fed to the control valve pa3 port via the cushion valve and switches the swing spool to the right swing side.

At the same time, the main computer detects the swing pilot pressure sensor signal, judges that there is a swing operation, the electrical signal output from the main computer goes OFF, and switches the swing brake solenoid valve. The pilot pressure oil is fed to the swing motor PR port from the swing brake solenoid valve C2 port to release the swing parking brake.

The discharge oil from hydraulic pump A1 enters the control valve P1 port and is fed from the parallel oil path to the swing spool.

Switching the spool lets the oil flow into the swing motor A port and the right swing operation is carried out. The pressure oil from the swing motor B port goes through the swing spool and returns to the hydraulic tank. When this is followed by an attachment operation, the pilot pressure is detected by respective pressure sensors and the swing parking brake continues to be released.

After the swing operation ends, if about 5 s. pass with no upper operation, the swing brake solenoid valve output from the main computer comes ON and the swing parking brake works again.
After the swing ends, if this is followed by an upper operation, when about 1 s. passes after the end of the upper operation, the swing parking brake works again.
For upper independent operation, the swing parking brake is also released. When about 1 s. passes after the end of the upper operation, the swing parking brake works again.