Troubleshooting methods for the "equal gear" fault of the TY220 bulldozer

There was a TY220 bulldozer that had been in operation for about 2,000 hours. After starting, it experienced a "gear waiting" phenomenon. That is, the machine did not move after shifting gears and needed to run for 6 to 10 minutes before it could move, or it had to be manually vented from the pressure measurement port of the fine filter in the transmission oil circuit before it could move. After moving, everything worked normally.

The essence of "equal gear" is that the oil pressure is not established in time. The main reason why the oil pressure cannot be established in time is that the variable-speed pump sucks air. That is, there is air in the oil suction circuit of the variable-speed pump. During the operation of the variable-speed pump, oil and air are discharged simultaneously. Only when all the air in the oil suction circuit is discharged and the variable-speed pump no longer sucks air can the oil pressure be established. The possible reasons for the suction of the variable-speed pump could be: poor sealing of the pipe joints in the suction oil circuit; The oil suction hose is damaged. The oil seal of the variable speed pump skeleton is damaged, etc.

According to the principle of "from simple to complex", we conducted a thorough inspection of each machine one by one. First, the coarse filter and the O-ring at the suction port of the variable-speed pump were inspected and replaced, but the fault was not eliminated. The suction rubber hose of the variable speed pump was inspected again and a pressure test was conducted on the suction rubber hose. The result confirmed that there was no damage to the hose. Then we disassembled and inspected the variable-speed pump and found that the skeleton oil seal was not damaged. To be on the safe side, we still replaced it with a new variable-speed pump, but the fault was still not eliminated. Finally, it was found that there were oil leakage marks at the suction port of the steering pump. After inspection, it was found that it was caused by the loosening of the fastening bolts of the oil pipe. So, the O-ring at the suction port of the steering pump was replaced, the suction hose of the steering pump was inspected and tightened. As a result, the fault of "equal gear" was eliminated.

After analysis, it is known that the variable speed oil circuit and the steering oil circuit of this machine share one coarse filter, and the suction port of the steering pump is at the bottom, while that of the variable speed pump is at the top. When the oil suction pipeline of the steering pump leaks air, after the machine has been shut down for a period of time, there will be no oil left in the coarse filter. As a result, when the variable speed pump starts up, it will be sucked empty. This is the real reason why the machine is "waiting in gear".