1. Trouble phenomenon A batch of 2.5-ton forklifts generally have throttle failure after 500 hours of operation. The specific manifestations are as follows: one is that the accelerator pedal is stepped hard and does not return; the other is that the engine accelerates slowly when the accelerator pedal is stepped on. ; Third, the throttle does not return after the engine is running, causing the idle speed to be high. This model is a mature mass-produced model, and there has never been such a problem reported in China. 2. Working principle Forklift throttle mechanism is mainly composed of limit bolt 1, accelerator pedal 2, accelerator bracket 3, flexible shaft 4, joint 5, engine throttle arm 6, flexible shaft bracket 7, return spring 8, etc., as shown in Figure 1. Shown. One end of the flexible shaft 4 is fixed on the throttle bracket, and the other end is fixed on the flexible shaft bracket 7 on the engine. One end of the flexible shaft 4 is connected with the rocker arm of the throttle bracket 3, and the other end is connected with the engine throttle swing arm 6. When the engine is idling, the accelerator pedal 2 is stepped on, and the push rod under the accelerator pedal 2 drives the rocker arm on the accelerator bracket 3 to rotate. The rocker arm pulls the soft shaft 4 mandrel to drive the engine throttle arm 6 to swing, thereby causing The fuel supply of the engine is increased and the speed is increased. When the accelerator pedal 2 is released, under the action of the return spring 8, the mandrel of the flexible shaft 4, the engine throttle arm 6, the rocker arm of the throttle bracket 3, and the accelerator pedal 2 all return to their original positions, so that the engine fuel supply Decrease, the engine speed drops to idle speed. 3. The cause of the failure The on-site investigation found that the working environment of this batch of forklifts was heavily polluted by dust, the forklifts were very intensive and the working conditions were very bad. The analysis concluded that: the inner wall of the flexible shaft 4 casing has no lining material, the core shaft steel wire has no protective layer, and the flexible shaft 4 casing has no dustproof device at both ends. Under the above severe working conditions, the soft shaft 4 core shaft and the inner wall of the casing are in a state of dry friction, and the core shaft wire rope is easily broken due to wear. The burr produced after the wire of the mandrel wire rope is broken causes the resistance to increase when the flexible shaft is pulled, and finally leads to the failure of the throttle control. Figure 2 shows the structure of the flexible shaft before the improvement. 4. Improvement plan Through the analysis of the cause of the failure, it is known that the key to solving the failure of the throttle is to solve the problem of soft shaft wear. To this end, we have formulated the following solutions: one is to wrap the outside of the flexible shaft mandrel wire rope with a nylon protective layer, and increase the inner diameter of the flexible shaft sleeve joint with a nylon liner. The exterior of the nylon liner is flared, which can reduce the friction between the mandrel wire rope and the surface of the casing joint, as shown in Figure 3. The second is to add a dust cover to the sleeve joints at both ends of the flexible shaft, so as to effectively prevent dust from entering the inside of the flexible shaft casing and solve the problem of dust particles wearing the flexible shaft core wire rope. Third, before installing the flexible shaft 4, apply grease on the flexible shaft 4 core shaft to reduce the frictional resistance between the flexible shaft 4 core shaft and the sleeve. The improved flexible throttle shaft has been subjected to 1.5 million fatigue tests in the laboratory. The test result of the electric pallet truck
manufacturer shows that the flexible shaft has no obvious wear problem after the improvement. Installed on a forklift under severe working conditions, after 4000h of use, the above failure did not occur again, which proves the success of this improvement.
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