At present, a Shantui TY220 bulldozer is found to be unable to turn at any time according to the driver's wishes. The bulldozer turns only about 3 seconds after pulling the steering rod, and always turns sharply.

　　According to the analysis of the engineer, the power transmission of the steering clutch is normal, and it can also be separated, so it is unlikely to cause a failure. The steering can indicate that the steering hydraulic system pressure can reach the normal pressure value during steering. After pulling the steering rod for about 3 seconds The bulldozer only turned, indicating that the hydraulic pressure of the steering hydraulic system was delayed (that is, about 35 minutes after pulling the steering rod to reach the normal value). According to the analysis of the steering hydraulic system of the machine (Figure 1): the possibility of failure caused by the filter 1.3. steering pump 2. safety valve, flow distribution valve 4. etc. should be excluded,

　　Further analysis of the structure of the steering control valve (Figure 2), the steering control spool 7 has a small hole communicating with G (dark black in the figure), through which oil enters the left and right steering passages of E, F. If there is no such a small hole, the oil in the steering clutch cylinder will be lost along the oil passage under the action of centrifugal force to form a cavity under the action of the bulldozer. In this case, the steering pressure needs to be changed after the cavity is filled with oil. When the pressure rises to the specified value, the steering can be achieved. In this case, the steering lag fault occurs. Due to the reverse steering lag, the driver is used to pulling the steering lever fully, the steering clutch is disconnected, and the steering clutch braking is achieved almost simultaneously. Therefore, the bulldozer behaves as a sharp turn. It can be seen that the small hole on the spool 7 is the oil filling hole, and the left and right steering oil passages are continuously replenished with oil through the G hole to keep it filled with oil to ensure that the steering pressure can be established immediately when the steering lever is operated, so that Steering is sensitive to avoid the phenomenon of steering lag. Therefore, the fault is probably caused by the clogging of the charge hole on the right steering spool.

　　Through the engineer's disassembly and inspection, it was found that the spool oil filling hole was blocked by rubber particles. After clearing, the vehicle started and the fault was eliminated.