First, the cause of engine noise and its prevention measures Engine noise mainly includes combustion noise and mechanical noise: 1. Burning noise. The reason for the noise is due to the effect of the pressure of the gas in the cylinder cycle. It mainly depends on the way of burning and the speed of burning. In gasoline engines, if there is abnormal combustion such as knocking and surface ignition, a large combustion noise will be generated. The combustion noise of a diesel engine is the noise caused by the sudden increase in air pressure in the combustion chamber and the vibration of various parts of the engine. In general, diesel noise is much higher than gasoline engine noise. Preventive measures: The combustion noise of a gasoline engine can be reduced by removing the carbon from the combustion chamber and reducing or avoiding the occurrence of knocking. The main methods to reduce combustion noise in diesel engines are: control of engine cylinder pressure level (combustion chamber with low combustion noise, comprehensive debugging of various parameters in the fuel supply system, engine boost, etc.), and increase in the attenuation of combustion noise when the engine structure is increased (Using damping control, stiffness control, and larger stroke and bore ratio, etc.) 2. Mechanical noise. Mechanical noise is caused by the mechanical movement between the moving parts and between the moving parts and the fixed parts. It is related to the size of the exciting force and the structure of the moving parts. Mainly piston noise and valve mechanical noise. The main measures to prevent engine piston knocking noise are: reduce the gap between the piston and the cylinder wall, increase the length of the piston skirt, coat the piston surface with a layer of vinyl or use a low-noise piston; etc.; the main measures to reduce engine valve noise are: : Reduce valve clearance, use valve hydraulic drive and hydraulic tappet, improve cam machining accuracy and surface quality. In addition, exhaust noise and fan noise are also the main sources of noise in automotive engines. II. Causes of transmission mechanism and other noise and its prevention measures Transmission mechanism noise refers to the noise caused by the transmission mechanism and the vibration from the road when the car is moving, in which the mechanical noise of the gear transmission is the main part. The direct cause of gear noise is the impact sound generated when the gear meshes, the friction between the teeth as a result of the sliding between the teeth and the frictional force, and the impact sound caused by the change of the gear error and rigidity. The noise of gears is only a small part of the wave to the space, and most of them become the excitation source of the forced vibration of the rear axle of the transmission. The vibration of each part is caused by the shaft, the bearing, and the housing, and it becomes noise propagation. The gear noise will change with the change of the driving state, speed, and load of the car. It will increase monotonically with the increase of the car's speed and will become the maximum at a certain speed. The main measures to reduce gear noise include: improving the assembly accuracy of gears, using high internal resistance materials as much as possible, using gear lubricating oils with high viscosity as much as possible, using low-noise gear structures, and so on. Third, other noise 1. Tire noise. When the car is running, the air in the tread groove of the tire is squeezed when it is grounded, and there is noise emitted regularly. The main factors affecting the tire noise are tire tread, vehicle speed, load, and road surface conditions. In order to control and reduce noise, pitch pattern tires, rubber bushings and other elastic vibration isolation materials can be used to adjust the natural vibration frequency of each component and other measures. 2. Brake noise. The brake drum and the brake shoe friction brake generate frictional vibration when braking, and at the same time, the components of the brake that excite the natural frequency are relatively resonant and generate noise. The way to reduce the braking noise is to eliminate the high frequency vibration of the vibration mechanism and improve the stability of the system to vibration. In addition, electric vehicles can be used to reduce noise, and other types of vehicles such as magnetic levitation, air-cushion and other high-efficiency, low-noise vehicles or some new heat engines can be developed. Author: Department of Mechanical and Electrical Engineering, Heilongjiang College of Agricultural Economics
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