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Carter Excavator Repair

Carter CAT excavator walking system overview

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The excavator's walking hydraulic system mainly includes: front and rear pumps 2, 3, pilot pump 4, main safety valve 11, shuttle valve 5. Left and right travel control valves 12, 14 and straight travel control valves 13. Swivel joint 15, left and right travel motors 22,23. Equipped with motors are balance valves 16,17, mutual injection valves 18,19, brake pilot valves 20, and variable valves 21. There are also a variable speed solenoid valve 7, an automatic speed change valve 6, a hydraulically operated control valve 8, and a pilot control valve 9. Fuel tank 1, proportional valve 25, etc. The above hydraulic components constitute a complete walking hydraulic system. The following briefly describes its operation and control principle: the high-pressure oil pumped from the front pump 2 (rear pump 3) to the right (left) travel control valve 12 (14), and then to the right (left) travel motor 23 (22) through the central rotary joint ) Counterbalance valve 16 (17).
A pressure oil is discharged from the balance valve 16 to the brake pilot valve 20. Release the walking brake in advance to make the excavator walk smoothly. When the system has a shock load (system pressure reaches 368 bar), it is removed by the mutual injection valves 18,19. When the excavator runs downhill at an overspeed, the balancing valve 16 can automatically close the oil return path to slow down the equipment brake. The high pressure generated by closing the oil return path is discharged to the side of the vacuum through the mutual injection valves 18 and 19 to prevent The generation of cavitation. The two check valves 24 provide control pressure oil for the variable valve 21. When the system pressure reaches 306 bar, the shuttle valve 5 provides pressure oil to control the automatic shift valve 6 to cut off the pilot oil to the variable valve 21. In order to realize automatic speed change from high speed to low speed, the working pressure of the system is set by the main safety valve 343bar; the high-pressure oil pumped by the pilot pump 4 goes all the way to the variable speed solenoid valve 7.
Controlled by the solenoid valve 7 to the automatic shift valve 6 and then to the variable valve 21, the valve core is pushed so that the pressure oil from the two check valves 24 enters the piston cylinder that controls the swash plate, and the swash plate tilt angle is changed to achieve speed change; The control valve 8 reaches the pilot control valve 9. The pilot valve 9 is then controlled to operate the left and right travel control valves 12, 14. Control walking or reversing; all the way through the proportional valve to the servo valve to control the pump flow to achieve power shift. 2 All actuators are weak. (1) Operate the joystick. If you do not hear the sound of engine refueling, you can turn on the data output of the maintenance program of the automatic control system (you can also pull out the pressure relay connector and manipulate the control handle. Use a multimeter to check the pressure relay, which should be turned on normally), and check whether the pressure relay has failed If it fails, replace it, otherwise check the engine speed.
If the speed is not normal, check and maintain the engine; (2) Check whether the system has air, and if there is air, exhaust ;; (3) Check whether the suction filter is blocked, and replace the filter; (4) Check The pump's oil outlet pipe is unobstructed; (5) Check the pilot pressure: Connect a 60bar pressure gauge to the pilot pressure measurement point to see if the pressure meets the requirements (the standard is). If it does not match, adjust the pilot pressure control valve. If not, check the pilot pressure control valve: whether the valve core is worn (replaced or repaired), the adjustment spring (standard length) is fatigued or broken (replacement of the spring), whether it is stuck (remove foreign matter), and the pilot gear pump may be faulty when normal , Repair or replace the gear pump; (6) Check the safety valve pressure: Connect two 600bar pressure gauges to the pressure measuring ports of the two pumps.
Then clamp the track and operate the walking pilot handle. If the pressure of the pump is abnormal (standard 343bar), adjust the pressure of the main safety valve to the specified value. If the pressure cannot be increased, check and eliminate the failure of the main safety valve, mainly: A, The cone of the safety valve spool is stuck in the open position by a foreign object (remove the foreign object); B. Adjust the spring fatigue or break (replace the spring); C, the sealing cone of the safety valve is severely worn and closed poorly (repair or replace); D, the damping hole is blocked (remove the blockage), if the pressure of the pump is normal, proceed to the next step;, ( 7) Check the shift pressure: If the shift pressure is too high, the flow of the pump will be too small. Causes slow motion and weakness. You can connect a 60bar pressure gauge to the shift pressure pressure port and start the maintenance program to see if the data displayed on the display is normal and equal to the reading of the pressure gauge.
If it is abnormal, you can adjust it through the maintenance procedure. If it is not adjustable, check and clean the proportional valve to eliminate the malfunction of the proportional valve. If the proportional valve is normal and the shift pressure cannot be adjusted, troubleshoot the electrical system; (8) Check whether the two reverse flow control oil pipes are blocked (or whether the hydraulic control piston is stuck). If it is blocked, it will be cleared (unblocking); (9) Check the flow of the pump: the engine speed is 1800rpm and the output pressure is 9800kpa, the flow rate of the pump is 180l / min, and the use limit is 170l / min. If the flow is too small, adjust the flow adjustment bolt of the pump to adjust the flow. If the requirements cannot be met, it is possible that A, the mating surface of the oil distribution plate and the copper cylinder is worn (grinding the mating surface); B, the compression spring is fatigued or broken (replace the spring); C. The gap between the plunger and the hole is too large (repair or replace the plunger and the copper cylinder); D.
The pump servo piston is stuck in the small flow position (remove foreign matter); E. Servo valve issue card (remove foreign matter); F. The servo valve spring is fatigued or broken (replaced); 3 Only the walking mechanism is weak, (1) Operate the walking control handle, listen to the engine sound, and manipulate the walking control handle, otherwise check and maintain the engine; and (2) Low travel pilot oil pressure: check For travelling pilot pressure, unscrew the plug on the travelling pressure switch connector, connect a 60bar pressure gauge, and operate the travelling pilot handle (the push should be greater than 30bar at the end, and some should be about 18bar); if it is abnormal, check and repair or replace the pilot valve Mainly: insufficient travel (adjustment), too soft pressure regulating spring (replacement), stuck or worn valve stem (removal of blockage or repair, replacement); (3) Checking the pressure of the cross-fire relief valve: before and after The pressure gauge of the pump is connected to a pressure gauge of 600 bar.
Stuck the track and operate the walking joystick. The normal pressure should be 368 bar. If the pressure is not normal, try to adjust the overflow pressure of the mutual injection relief valve. If the height cannot be adjusted, check the cross-fire relief valve. Mainly check the pressure regulating spring for fatigue (replacement) and sealing cone surface (grinding), and remove foreign matter if it is caught by foreign matter. If the mutual injection relief valve is normal and the pressure is not high, proceed to the next step; (4) Check the leakage of the central rotary joint: Disassemble the two high-pressure pipe joints on the left (right) side and plug them with plugs . Operate the walking joystick. If there is a large amount of oil flowing out of the two ports of the rotary joint, it indicates that the leakage is serious, repair and replace the seal (or rotary joint), and then proceed to the next step; (5) Check motor leakage: Disassemble the motor drain pipe. Connect a tubing from the drain to a container.
If leakage is serious. Repair and replace the motor; motor leakage is under 200bar pressure. Each minute does not exceed 15l; (You can also check this way: open the high-pressure oil pipe of the motor and plug it with a plug. Read the pressure value, if the pressure is higher than the original, the motor leaks); (6) Check the multi-way valve : If the multi-way valve stem is stuck in the semi-closed position or the mating clearance is too large, the leakage will be severe, which will cause the action to be weak. The former can be eliminated by removing foreign matter. The latter requires repair of the valve stem and valve sleeve; (To check the leakage of the multi-way valve, you can also use the following method: remove the reverse flow control pipe joint of the pump, connect the three-way joint and a 60 bar pressure gauge, and push the walking handle According to my experience, it is still normal for the pressure gauge reading to be less than 2 ~ 4bar, this method is only for comparison); (7) The brake is not completely released: the reasons why it cannot be completely released are: A.
Brake pilot valve is stuck (cleared) by foreign matter; B. The brake cylinder oil seal is damaged and leaked (replace the seal); C, the oil passage from the balance valve to the brake pilot valve is blocked (cleared). If all are normal, the motor bearing or the reduction mechanism may be stuck. Check for and remove foreign objects. We have encountered this situation in maintenance practice. Weak walking and the engine tends to stall. Check according to (1) in (2) and (4) in (3). It was found that the pressure relay failed and all the rotary joint seals were broken. The suction filter is clogged with debris from the seal, and the seal is replaced. Clean the hydraulic system. Works normally; another example: a CAT320 excavator has this situation. When turning in the mud, it is impossible to make a turn. Everything else is normal. After inspection, we found that the pressure is normal. Later, we learned that the high pressure oil pipe was cracked.
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