Generator bearing

(1) Classification

There are two kinds of generator in automobile ignition system: parallel excited DC generator and semiconductor rectifier generator.

Among them, the alternator is developing rapidly because of its strong power generation capacity, large speed range, compact structure, reliable operation and long service life.For generator bearings, to adapt to this development means that the bearing capacity, limit speed, rotation accuracy, lubrication and sealing performance and noise performance must be improved

(2) Design analysis

The use of generator bearing in semiconductor rectifier alternator is shown in the figure

Generator bearings are generally deep groove ball bearings and deep groove ball bearings with dustproof or sealed structure, and double row ball bearings, cylindrical roller bearings or other structural types of bearings are sometimes used for the pulley side with greater stress.The selection of generator bearings should first consider the calculation life to meet the requirements, and then should consider the limit speed, sealing, lubrication, noise and clearance problems.

1, limit speed

The limit speed listed in the bearing sample is the limit speed under standard conditions, which should be modified according to the actual use conditions when the bearing is selected.When the repair value is lower than the service speed, another bearing should be selected or high-speed design.

2, sealing

High speed and airtightness are two contradictory characteristics of generator bearing seal design.The light contact high speed rotary sealing ring has good performance of torque, temperature rise, dust and grease sealing, but poor performance of mud and water.And the contact sealing ring which is based on sealing will produce too high temperature rise.Therefore, the two contradictory characteristics of high speed and sealing must be taken into account in the seal design of generator bearings.In order to give consideration to the tightness and high speed, a good sealing design is to add an oil swing ring outside the light contact sealing ring. The light contact sealing ring and the oil swing ring form a labyrinth seal, thus effectively preventing muddy water from entering the double sealing structure. The basic structure of this design is shown in the figure:

The outer sealing ring is composed of two parts: the oil throwing ring and the light contact sealing lip, and forms a labyrinth seal with the outer ring and the inner sealing ring. At high speed and low speed, the labyrinth seal and the light contact sealing lip are respectively used to prevent muddy water from entering, thus realizing the excellent sealing performance in the whole speed range from low speed to high speed.

3, lubrication

Generally, the choice of engine bearing grease is considered from the aspects of high speed, high temperature resistance, good low temperature starting performance and low noise.

The high speed adaptability of the grease can be determined by calculating the Ka Dm N value of the bearing from the table.

Due to the need of low noise, the generator bearing grease can not be too thick, in order to improve the damping effect of the grease on the vibration of the rolling body, and to prevent the increase of noise and starting torque caused by dry friction at low temperature.

Based on the above reasons and the consideration of high temperature resistance and waterproof performance, the lubrication of generator bearings generally adopts compound calcium base grease.

The filling amount of bearing grease can be determined according to the ratio of the limit speed of grease lubrication and the actual working speed.

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