Failure analysis of hydraulic and pneumatic devices for vehicles

2 Abstract The working principle and failure reason of the hydraulic valve lifter for the vehicle are analyzed, and the fault of the car air brake system during operation is described. 1 Foreword The development of the car technology. 3 The front liquid out pneumatic technology is more and more widely used in automobiles, especially imported cars and domestic new cars. However, when there is a work failure in the hydraulic or pneumatic system, the repair technician 4 and the operator feel that it is much more difficult to find the original vacancy than the mechanical ugly. Even in the afternoon, I still know what it is. In this 1 we analyzed the failure reason of the hydraulic valve lifter for the automobile and the frequent failure of the car air brake system, which is helpful to the relevant personnel.

2 hydraulic valve tappet The current valve lifter is hydraulically twisted and more and more, its structure 1. The working principle of hydraulic valve tappet is that when the gas is closed, the column is open, the position is elastic and the column is cold and putter庵 Pressing on the push rod, the push rod moves the rocker arm to make the valve gap disappear. When the tappet is moved by the cam press, the oil pressure of the working chamber 4 is quickly closed by the one-way valve. Since the oil in the working chamber is not compressible, the entire tappet is always like a rigid body, and the valve is opened by the push rod and the rocker arm. When the oil pressure is high, a little oil in the working chamber below the plunger will leak through the small gap between the inner wall of the tappet and the plunger, so that it will not affect the normal operation of the tappet to ensure zero clearance, and the giant can also The inner wall of the tappet and the plunger are lubricated. When the operating temperature causes the valve lifter to expand and expand longer. The oil pressure in the working chamber below the plunger also rises, and a small amount of oil will leak out from the small gap between the inner wall of the tappet and the plunger, thereby ensuring that the valve lifter does not have a valve closing/strict phenomenon when heated and expanded. Therefore, it is not necessary to reserve the valve clearance, and the mechanical valve lifter must reserve the valve clearance before working. The size of the valve clearance is very strict. Too large or too small will affect the normal operation of the car. This is the advantage of the hydraulic valve lifter.

Shi. Mainly engaged in teaching and research work in industrial engineering.

Switching to the question, improving synchronization accuracy and displacement accuracy. The structure can be extended from a two-stage sleeve to a multi-stage sleeve. The application can be extended to the body transport of the military shovel, and the transportation of precision instruments of the observatory is 1 1 Shi Bianfang. Elevator technology elbow. Beijing Electronic Industry Press. 1989.

Du Chongjie. A new type of hydraulic elevator Song Xueyi. Pocket Hydraulic and Pneumatic Handbook, 1995. Beijing Machinery Industry Publishing Mu Village Wu Xiong. elevator. Translated by Xiao Xiaosen. Beijing China Building Industry Press, 1979.

2.1 The cause of failure In addition to the hydraulic valve lifter, failure is its usual form of failure.

The main cause of the failure of the liquid music tappet is that the lubricating oil used is not clean. It causes the early wear of the tappet, sometimes causing oil deposit between the plunger and the tappet body, which seriously affects the normal operation of the tappet. The first is the exchange of precision parts during maintenance, the column cold and tappet body in the hydraulic valve lifter assembly is a close-coupled piece. 5 changes are not allowed.

Otherwise it will easily invalidate it early.

Sealing inspection method There are two methods for checking the sealing performance of the plunger and the tappet body member in the hydraulic valve lifter assembly. The first is to soak the tappet in kerosene or gasoline, and push and pull the plunger 35 to discharge it. If the air in the cavity is still not cleaned, it can be disassembled and cleaned. Of course, be careful when cleaning, so as not to hurt the couple. The first is to put the lifter body of the clean air on the platform and insert the plunger. At the beginning of the rod body, the vertical displacement of the plunger is applied and the slippage time is recorded. If there is a condition, special test bench equipment can be used. When the pressure of 2001 is applied directly to the column, the standard value of the downhill time is at 2016581. If the measured value is lower than the standard value, the hydraulic valve lifter assembly should be replaced. If there is no special test bench equipment, the comparison of the old and new hydraulic valve lifter slip time can be used to judge.

3 air brake system 3.1 air brake power failure phenomenon is a steam driving. Stepping on the brake pedal to the end + can make the brake immediately stop the brake distance exceeds the specified standard. This phenomenon is mostly 1 brake pedal free travel is too large; 2 the air pressure in the air reservoir is low; 3 the control valve exhaust valve is closed Not strict; 4 brake gap adjustment is too large; 5 gas 矜 joint has loose gas phenomenon 6 brake shoes are oily or rivet exposed.

3.2 Pneumatic brake runaway fault phenomenon There are 3 kinds of situations 1 regularly directional deviation in a certain direction; 2 irregularly flicker left and right; 3 suddenly deviation.

The original defense is more than 1 grease filling method is not, 2 the gap between the brake drum and the shoe automatically changes, mostly due to the unreliable positioning of the adjustment arm worm; 3 left wheel friction plate is not a card 4 thus causing 2 Wheel braking torque is uneven; 4 drum drum diameter difference is too large; 5 tire wear uneven, causing the diameter difference is too large, so that the wheel brake torque imbalance 6 front leaf spring left and right elastic + ± cut this will 4 load offset; 7 after the leaf spring fastener loose, it can make the rear axle displacement, causing the brake to suddenly run off; 8 left and right air chamber cup is not the same quality product, it can cause air chamber thrust Not equal, resulting in brake deviation.

3.3 Pneumatic brakes The phenomenon of drag and drop is that the brake valve does not vent or the exhaust is very slow after the brake is released, so that the brake cannot be immediately released. The reasons are mostly 1 brake pedal free travel is too small; 2 brake camshaft rotation is not flexible; 3 control valve exhaust valve is stuck; 4 brake shoe friction plate and brake drum clearance is too small; 5 brake drum + Roundness is usually not caused by the brake shoe support pin or camshaft of the big factory, so that the shoe can not be returned after the brake; 7 the friction plate is excessively worn or broken; 8 the brake shoe return spring is too soft or Broken, causing the brake shoe to not open after the brake.

4 Conclusion The fault of the liquid helium pneumatic assembly is divided into theoretical analysis, more people can be handy in the maintenance process.

Il Mechanical Industry Technician Evaluation Training Textbook Review Committee. Car repair technician training materials called. Beijing Machinery Industry Press, 2000I2 Yang Lan. The imported car maintenance and repair technical manual is called. Harbin Heilongjiang Science and Technology Press, 1996 3 Liu Ge. How to eliminate the fault in the car operation. Harbin Heilongjiang Science and Technology Press, 1997.

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