Inspection methods for crawler-type hydraulic steering bulldozers without steering faults

During the operation of bulldozers, various fault phenomena such as difficulty in turning, inability to turn, cold vehicles being able to turn but hot vehicles being unable to turn (after the oil temperature of the transmission part rises to the working temperature) occur. After these fault phenomena occur, a classified analysis should be conducted based on the usage time of the bulldozer and the process of the fault occurrence, and a targeted inspection should be carried out. This can avoid unnecessary disassembly and reduce the pollution inside the machinery. The following introduces common fault phenomena of bulldozers and relevant knowledge about inspection and elimination.

If a bulldozer suddenly fails to turn on both sides during operation, the relief valve at the oil inlet of the directional control valve assembly can be disassembled and inspected. The reason is that the oil is too dirty, and impurities in the oil wear or scratch the inner surface of the overflow valve core and the valve body, causing the valve core to get stuck at the position of opening and connecting the return oil, losing its function of regulating the oil pressure and making the system pressure fail to reach the standard value. After disassembling the relief valve and inspecting the parts, if the damage is not particularly severe, 180 or 240 grit sandpaper can be used to grind the damaged parts. If the parts are severely damaged, they need to be replaced. While repairing, the oil and fine filter elements must be replaced and the coarse filter element cleaned.

During the operation of the bulldozer, the aforementioned fault phenomena gradually form. Whether it is on one side or both sides, pressure measurement and inspection should be carried out. The standard value of the oil pressure for the disengagement of the directional clutch is 1.1 to 1.3mpa. First, measure the port of the relief valve. If the pressure reaches the standard value, it indicates that there is no fault with the oil pump and the relief valve. Otherwise, the oil pump and the relief valve need to be inspected. After eliminating the oil pump and the relief valve, measure the outlet of the directional control valve (pull the control lever during measurement to keep the directional clutch in operation). If the pressure does not reach the standard value, it indicates that there is internal leakage. The locations where leakage can occur are as follows: First, the S-shaped oil pipe between the directional control valve and the bearing housing. The rear cover of the central transmission box can be opened to keep the oil pipe in operation. By directly observing it, the leakage of oil can be detected. Both ends of this oil pipe are sealed with O-rings. The main reason for oil leakage is the damage of the O-ring. Replace it with an O-ring of the same model and be careful not to damage the O-ring during installation. The second reason is that the connecting bolts between the connecting plate and the inner drum in the direction are loose, causing leakage. Here, if there is a leakage, open the direction cover pull rod adjustment cover to put the direction clutch in working condition, and then directly observe it to find the leakage point.

If the bolts are loose, they must be removed and left from the connection surface between the connecting plate and the inner drum before tightening to clear the deposits and check for any damaged parts. Then, repair or replace them and reinstall them according to the standards. The third issue is leakage at the dynamic sealing points between the connecting plate and the bearing housing, as well as between the piston and the inner drum. For the inspection of these two points, the direction cover should be removed. When the direction clutch is in operation, a direct visual inspection can be conducted to identify the leakage points.

When troubleshooting, it is necessary to prevent the disassembled parts from being bumped and the entry of sand and mud. The connecting plate and the shaft are spline connected. During installation at the manufacturing plant, they are pressed into place under a pressure of 30 tons, so disassembly is rather difficult and special tools need to be made. According to the dimensions and requirements on the drawing, manufacture the special pulling tools and two M20× 80,8.8 grade bolts. The hole with a spacing of 109mm in the drawing is for pulling the connection plate, and the hole with a spacing of 142mm is for pulling the drive plate. Before disassembling the connecting plate and the drive plate, mark the corresponding positions of the plate and the shaft. During installation, do not change the position during press-fitting. After tightening with the shaft end nut, the original installation accuracy can be guaranteed.

After the connecting plate is removed, it is necessary to carefully inspect the contact area between the ring groove, the inner wall of the bearing housing and the sealing ring. It must be smooth and flat without any damage. Otherwise, the sealing ring will still suffer abnormal wear after installation, which may cause the failure of the directional clutch to disengage again. When the directional separation oil circuit does not take in oil, there is no pressure in the annular oil passage between the connecting plate and the bearing housing. The side of the sealing ring moves relatively to the ring groove. If the ring groove is damaged or defective, it will cause the sealing ring to be worn or scratched and produce wear debris. This not only accelerates the wear on the side of the sealing ring but also causes abnormal wear or damage to related parts. When oil enters the separated oil circuit, the annular oil passage between the connecting plate and the bearing housing builds up pressure. The sealing ring connecting plate rotates together, and when the outer circle of the sealing ring and the inner hole of the bearing housing move relatively, these grinding chips will inevitably invade the relatively moving surface and cause damage. At the same time, grinding chips will also be produced. Some of the grinding chips produced at these two places will enter the working chamber with the oil. It caused damage to the piston sealing ring. Other grinding swarf flowing with the oil can also cause damage to the hydraulic components of the system. Therefore, during the repair process, the ring groove and the bearing housing must be carefully inspected to ensure that the precision meets the standard. Before installation, deburr and clean thoroughly. After the sealing ring is inserted into the ring groove, it should be flexible without any obstruction. When pushing the connecting plate into the bearing housing, do it slowly to prevent the sealing ring from being cut during the push.

When disassembling the sealing ring of the directional clutch piston, choose a stable and firm plane, and there should be a fulcrum above the center of the corresponding directional clutch. Place a circular steel part smaller than the diameter of the piston on a flat surface. Put the direction clutch piston downward on this steel part. The steel part must support the piston stably. Then, place a circular steel part smaller than the diameter of the inner hole of the pressure plate into the inner hole of the pressure plate and press it against the inner drum. Next, use a 5-ton jack to move the inner drum downward by 8mm. Remove the 8 fixing bolts of the pressure plate and then slowly release the jack. Move the inner drum upwards. When the piston sealing ring is exposed, position the jack and remove the piston sealing ring for inspection. Piston rings are generally not prone to damage under normal circumstances because they have a slight movement with the ring groove when expanding under pressure. The outer diameter of the ring's circumferential surface only has a reciprocating motion of 8 to 12mm as the piston works in the inner drum. The main reason for its damage is the grinding debris and sand in the oil. These impurities deposit in the ring groove, preventing the piston sealing ring from expanding under pressure and reducing its sealing performance. At the same time, they also cause damage to the piston sealing ring. When repairing, the piston rings and ring grooves should be cleaned and washed. Use the back of a hacksaw blade or a scraper to scrape off the dirt adhering to the side of the piston sealing ring. Flip it over and reinstall it for continued use. Whether it is a new part or a repaired one, measurement must be carried out. The standard diameter of the contact surface between the inner drum and the piston sealing ring is 245mm. In this diameter dimension, the opening clearance of the piston ring is 3.8 to 5.6mm. If it is less than 3.8mm, the opening clearance of the piston ring should be corrected to this size range. If it is greater than 5.6mm, the piston ring cannot be used and a new part needs to be replaced. After the piston rings are installed in the ring grooves, the side clearance of the rings must be between 0.20 and 0.40mm, with a maximum of no more than 0.6mm. Before installation after disassembling the parts for repair and measurement, they must be cleaned and washed, especially the inner cavities of the oil channels and oil pipes, which must be thoroughly cleaned. Otherwise, during the operation of the bulldozer, some impurities remaining in the oil will be washed into the annular oil channels and the working chamber of the directional clutch, leading to the recurrence of faults.

The special puller introduced earlier has a raised small circular surface that comes into contact with the shaft end as a fulcrum. During manufacturing, it can be processed separately and then welded to the large circular surface, but a certain degree of coaxiality must be ensured. After passing the two bolts through the 22mm through hole of the dedicated puller and screwing them into the disassembly screw holes of the connection plate or drive plate, the two bolts should be evenly tightened to keep the puller parallel to the shaft end and prevent the puller from tilting and damaging the shaft end threads.