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Synchro: synchronizer function: make the joint sleeve synchronize quickly with the engagement ring to reduce the shift time; play the role of locking, and ensure that the joint sleeve and the joint ring can not engage before the synchronization, thus avoiding the gear shift. The following is a case study of Beijing BJ2020S off-road vehicle, which illustrates the structure, principle and troubleshooting of the synchronizer. A Beijing BJ2020S off-road car, it is difficult to hang three gears in driving; once it is hard to hang on, it is difficult to take off, only after parking, both hands push or pull or hammer to strike the transmission rod to take off. Synchronizer structure and principle: in simple transmission gear shift is realized by gear gear meshing and dragging, but this simple transmission has a shortcoming easily caused by the gear gear, because the speed of each gear is different, there is also a shift noise problem. Synchronizer is installed in the transmission of modern cars to achieve synchronous gear shift. The installation position and decomposition of the synchronizer are shown in Figure 1. Different forms of synchronizer are used in modern cars, but their working principles are the same. The working principle of synchronizer shift is that the synchronizer is made up of input gear, conical surface, gear ring combination sleeve, gear hub, synchronizer spring and synchronizer lock pin. The shift fork moves to the left, and moves the gear ring combination sleeve and the hub to the left side. The hub and the sleeve are rotated together and continue to move to the left. The synchronous ring is rubbed together with the conical surface of the gear to be combined. This moves the two gear to the same speed. At this point, the hub is stationary but not meshed with the input shaft. The shift fork continues to move to the left, while the hub is kept in contact with the cone, and the ring continues to move to the left. As the two gears have the same speed, the gear and the input gear are very easy to engage. In most transmission, synchronizer moves more than gear, which is called constant meshing. Starting gears are engaged, but they are idling on the output shaft. When the shift synchronizer moves to the left, the output shaft will rotate at the same speed as a gear. When the two gear synchronizer moves to the right, the output shaft will rotate at the same speed as the two gear. When the three gear synchronizer moves to the left, the speed of the output shaft is the same as that of the input. Fault analysis of synchronizer: dismount the transmission on the gear (the gear is on the three gear), release the gear oil; first open the transmission cover, then clean the gear mechanism of the transmission, and hold the two or three gear shift gear to cover with the copper punch. According to the direction of the three gear to the two gear, slowly hammer with the hammer, let the gear sleeve fall to the neutral position. The transmission is decomposed, and the inertial synchronizer of two and three gears is removed, and the parts are checked. The synchronizer contacts the end face of the three gear, and there is a gap between the outer conical surface of the gear and the conical surface inside the lock ring. The spring of the synchronizer close to the three gear has almost no elasticity. The 3 sliders on one end of the three gear have been ground into sheets. Because the spring force of the synchronizer spring near the three gear is too small, the above fault occurs. When the three gear is hung, the shifting fork moves the engagement sleeve close to the three gear, and the groove in the joint sleeve pushes the slide block to move, and withstands the lock ring gap. The locking ring compacts the three gear cone surface close to the three gear, and the outer cone surface is gradually worn out due to sliding friction, resulting in a flake shape at the end of the slide block. After the three lock ring compacts the cone of the three gear, the gap between the end of the lock and the joint of the three gear is getting smaller and smaller until the two ends are in contact, and the synchronization is lost. After 3 sliders are grated near the direction of three gears, and then from two gear to three gear, when dialing fork moves two or three gear sets, the 3 slider ends of the plate can not hold the three gap of the three lock ring, so it is directly inserted between the cone and the outer cone of the three gear, causing the stagnation phenomenon and three The lock ring is quickly in line with the speed of the three gear. At this time, the chamfering angle in the joint covers the outer corner of the lock ring, although the joint sleeve, the lock ring and the three gear gear are synchronized, but due to the lock, the three gear and the slider, the normal ring torque on the lock ring does not move the lock ring, only exerting a very large force on the transmission rod to increase the joint intercropping. With the ring torque on the lock ring, the lock ring can be turned to a certain angle, so that the joint sleeve joins the lock to close to the joint of the three gear, which is the reason for the difficulty of the three gear. Synchronizer Troubleshooting: according to the synchronizer fault analysis, the fault requires the replacement of 1 three block rings, a synchronizer spring ring near the three gear and 3 sliders.