330D, 336D and 340D Excavators Hydraulic System – Travel Hydraulic System

Travel Control

The output flow from the drive pump flows through the swivel to the right travel motor. The output flow from the idler pump flows through the swivel to the left travel motor. The pump delivery flow causes rotation of the travel motors. The torque of the travel motors is transmitted to the final drives. The rotational speed of the travel motors is reduced by gear reduction in the final drive. The final drive (55) increases the torque and the rotational force drives track (53) via sprocket (54) .

The travel speed can be adjusted by the slight operation of the travel levers/pedals. The travel speed can also be controlled by travel speed control switch (56) . This changes the travel speed when the travel levers/pedals are moved to the maximum position. The travel speed control switch can be set at the LOW SPEED position or the HIGH SPEED position. When the travel speed control switch is set at the LOW SPEED position, the tortoise appears on the default message display of the monitor. When the travel speed control switch is set at the HIGH SPEED position, the rabbit appears on the default message display of the monitor. During travel on a flat surface or during gradual downhill travel, the travel speed is set at the HIGH SPEED position in order to realize increased mobility.

When travel speed control switch (56) is set at the HIGH SPEED position, the pressure sensors for pump delivery pressure detect the change in pump load. If the pressure sensors detect a high load, the travel speed is automatically adjusted to LOW SPEED. If the pressure sensors detect a small load, the travel speed is automatically adjusted to HIGH SPEED.

The direction of travel is relative to the position of the lower structure. For normal travel, idler (59) is positioned in front of cab (61) and travel motors (1) and (15) to the rear of the cab. With the machine in the normal position of travel, move the travel levers/pedals (58) and (60) forward. The machine will travel in forward direction (57) . This movement is called forward travel. When the travel levers/pedals (58) and (60) are moved toward the operator, the machine travels in reverse direction (62) . This direction is called reverse travel.

When cab (61) is rotated by 180 degrees, travel motors (1) and (15) are positioned in front of the cab. The direction of travel and the operation of the travel levers/pedals (58) and (60) are reversed from the normal travel direction.

When the machine is in the normal position of travel and when one of the travel levers/pedals (58) or (60) is moved forward, the respective track travels forward. The machine turns because the stationary track acts as the pivot point. This is called a pivot turn.

This machine will spot turn in order to change the travel direction of the machine in a narrow space. To complete a spot turn operation, move one travel lever/pedal to the rear and move the other travel lever/pedal forward at the same time. One track will travel to the rear and the other track will travel forward. The machine will spot turn around the center axis of the machine.

Forward Travel

When both of the travel levers/pedals are operated, pilot system oil pressure flows from travel pilot control valve (44) through pilot lines (42) and (43) to left travel control valve (38) and right travel control valve (41) . The pilot system oil pressure shifts the spools in both of the travel control valves in an upward direction. The travel control valves allow the oil delivery from the drive pump and the idler pump to flow to swivel (30) . The swivel transfers the oil delivery from the rotating upper structure to the lines in the lower structure. The oil delivery flows to left travel motor (1) and right travel motor (15) .

Note: The right and left travel controls function in the same manner. The explanation for the left travel control will be used to explain both the right and left travel controls.

When the left travel lever/pedal is moved to the FORWARD TRAVEL position, pilot system oil pressure from travel pilot control valve (44) flows through pilot line (42) to left travel control valve (38) . The spool in the left travel control valve shifts in an upward direction. The oil delivery from the idler pump in center bypass passage (40) flows through passage (39) , left travel control valve (38) , passage (35) , line (33) , swivel (30) and line (29) to left travel motor (1) .

The oil delivery from the idler pump enters left travel motor (1) and flows through counterbalance valve (8) and passage (5) to motor rotary group (3) . At the same time, a portion of the oil delivery from the idler pump flows through passage (7) and brake pilot valve (6) to parking brake (10) . The parking brake is released and the oil delivery from the idler pump causes the motor to rotate.

LOW SPEED

When travel speed control switch (56) is set at the LOW SPEED position, an electrical signal is sent to machine ECM (C) . The machine ECM does not energize travel speed solenoid valve (48) and pilot system oil pressure does not flow through pilot line (27) to displacement change valve (12) . The spool in the displacement change valve does not shift. Oil flows from the idler pump in passage (5) to the motor rotary group (3) . Since displacement change valve (12) is not shifted, oil is restricted from swashplate control piston (4) . The swashplate remains in the maximum displacement position. One rotation of motor rotary group (3) displaces a larger amount of oil flow. The rotational speed of the left travel motor decreases. The left track moves slowly and better traction is achieved.

The return oil from motor rotary group (3) flows through passage (11) , counterbalance valve (8) , line (28) and swivel (30) . The return oil then flows through line (34) , left travel control valve (38) , return passage (37) and return line (45) to the hydraulic tank.

Right travel motor (15) receives the oil delivery from the drive pump. The right travel motor functions in the same manner as the left travel motor in the LOW SPEED position.

HIGH SPEED

When travel speed control switch (56) is set at the HIGH SPEED position, an electrical signal is sent to machine ECM (D) . Pressure sensors (46) and (47) also send an electrical signal to the machine ECM. If the travel load is light and when the pump delivery pressure is below a certain pressure, the machine ECM energizes travel speed solenoid valve (48) . Pilot system oil pressure flows through travel speed solenoid valve (48) and line (27) to displacement change valve (12) . The spool in the displacement change valve (12) shifts. A portion of the oil delivery from the idler pump flows through the displacement change valve to swashplate control piston (4) . Swashplate control piston (4) moves swashplate (2) to the minimum displacement position. One rotation of motor rotary group (3) displaces a smaller amount of oil flow. The rotational speed of the left travel motor increases. The left track moves at a faster speed.

The return oil from motor rotary group (3) flows through passage (11) , counterbalance valve (8) , line (28) and swivel (30) . The return oil then flows through line (34) , left travel control valve (38) , return passage (37) and return line (45) to the hydraulic tank.

Right travel motor (15) receives the oil delivery from the drive pump. The right travel motor functions in the same manner as the left travel motor in HIGH SPEED position.

Automatic Travel Speed Change

Pressure sensor (46) monitors the delivery pressure of the drive pump. Pressure sensor (47) monitors the delivery pressure of the idler pump. The motor displacement is low when the travel speed control switch is set at the HIGH SPEED position and the travel load is light. As the pump load increases, the delivery pressure of the pumps increases. When the delivery pressure of the pumps reaches a certain pressure, the pressure sensor sends an electrical signal to the machine ECM. The machine ECM de-energizes travel speed solenoid valve (48) . Travel speed solenoid valve (48) blocks the flow of pilot system supply oil to displacement change valves (12) and (20) . The oil in swashplate control pistons (4) and (22) now flows into the case drain of the travel motors. Swashplates (2) and (16) move to the maximum displacement position. One rotation of the motor rotary groups in the travel motors displaces a larger amount of oil flow. The rotational speed of the travel motors decreases. The travel speed is automatically changed to LOW SPEED.

When the pump load decreases and the travel speed control switch is set at the HIGH SPEED position, pressure sensors (46) and (47) will now cause the machine ECM to energize travel speed solenoid valve (48) . Displacement change valves (12) and (20) will be shifted by pilot pressure so that the motor rotary groups will change to the minimum displacement position. One rotation of the motor rotary groups displaces a small amount of oil flow. The travel speed will automatically change to HIGH SPEED.

The ability of the machine to automatically change the travel speed allows good performance at high speed and better traction control.