330D, 336D and 340D Excavators Hydraulic System – Control Valve (Straight Travel)

Straight travel (tracking) can be maintained even though there is a swing operation or implement operation during travel.

Straight travel control valve (2) maintains straight travel even though there is a swing operation or implement operation during travel. The straight travel control valve also improves pipelayer control or placement of timbers.

When the machine travels without swing operation or implement operation, the pressure switch for left travel and the pressure switch for right travel are ON. The implement/swing pressure switch is OFF. The oil delivery from the drive pump flows through right travel control valve (1) to the right travel motor. The oil delivery from the idler pump flows through straight travel control valve (2) and left travel control valve (3) to the left travel motor. Because both travel circuits are separated, the machine continues to travel straight, unless a difference in travel resistance occurs between the right and left tracks.

The straight travel system ensures the straight travel of the machine when other circuits are operated during travel. The idler pump and the drive pump supply oil to the travel motors. The idler pump and the drive pump also supply oil for a swing or implement operation. During travel, if an implement operation or a swing operation occurs the oil supply to each travel motor will differ. This would cause the right travel motor and the left travel motor to rotate at different speeds. The different speeds will cause the machine to turn.

The following actions occur when the straight travel control valve is activated.

• The pressure switch for left travel and the pressure switch for right travel are ON.

• The implement/swing pressure switch is ON.

• The drive pump supplies oil to the left travel circuit and to the right travel circuit in order to drive both motors in parallel.

• The swing circuit and implement circuits receive oil from the idler pump. When the machine is travelling, the swing circuit and implement circuits do not require a large amount of oil flow. The swing circuit and implement circuits are operated at speeds that are low enough for stable machine operation. The remainder of the oil is shared by the right travel circuit and the left travel circuit.

Pilot oil pressure is sent from the pilot oil manifold to straight travel solenoid (14). When only the travel levers/pedals are activated, straight travel solenoid (14) is not energized. Pilot oil flow to pilot passage (5) and straight travel control valve (13) is blocked at the straight travel solenoid. The oil pressure in piston chamber (6) is low and spool (12) is shifted to the right by the force of spring (7). The oil delivery from the idler pump and the drive pump flows in the following manner.

• The oil delivery from the drive pump flows through line (10) to passage (11) in the straight travel control valve. The oil delivery from the drive pump separates into two flow paths. One path flows through center bypass passage (3) and into the right travel control valve. The other path flows through parallel feeder passage (4) .

• The oil delivery from the idler pump flows through line (9) to passage (8) in the straight travel control valve. The oil delivery from the idler pump separates into two flow paths. One path flows through parallel feeder passage (1). The other path flows through center bypass passage (2) and into the left travel control valve.

When the travel levers/pedals are activated at the same time as either one of the joysticks, straight travel solenoid (14) is energized. The pilot oil flows through the straight travel solenoid to straight travel control valve (13). The pilot oil enters piston chamber (6). The pilot oil pressure in piston chamber (6) increases. Spool (12) shifts to the left against the force of spring (7). The oil delivery from the idler pump and the drive pump flows in the following manner.

• The oil delivery from the drive pump flows through line (10) and passage (11) in the straight travel control valve. The oil delivery from the drive pump separates into two flow paths. One path flows through center bypass passage (2) and into the left travel control valve. The other path flows through center bypass passage (3) and into the right travel control valve.

• The oil delivery from the idler pump flows through line (9) and passage (8) in the straight travel control valve. The oil delivery from the idler pump separates into two flow paths. One path flows through parallel feeder passage (1). The other path flows through passage (16) and into parallel feeder passage (4). Part of the oil delivery from the idler pump in passage (16) flows through orifice (18) in spool (12) and opens check valve (15). The oil now flows through passage (17) to center bypass passage (2). The oil delivery from the idler pump combines in center bypass passage (2) with the oil delivery from the idler pump. This increases the drive speed of the right travel motor and the left travel motor.