In general, the tooth side clearance of automobile gear is switched with the matching wheel. It only happens when the car gears mesh. In order to measure and calculate the clearance, the deformation of tooth thickness in the tooth groove must be found and measured. Unless otherwise specified, the position of the gap refers to the position at the pitch circle.
There are many reasons for the gap, but the failure to provide the specified processing conditions will not be considered. Usually, the purpose of clearance is to prevent the two teeth of automobile gear and mating wheel from meshing at the same time. Any machining error may interfere with normal automobile gear meshing, so we must increase enough clearance to ensure that this can not happen. Therefore, the smaller the clearance, the more accurate automobile gears must be processed. The gear ring diameter jump, tooth profile deviation, tooth thickness, helix angle and center distance of paired automobile gears all affect the clearance. On the other hand, there should be no excessive clearance, especially when the mating wheel often reverses or exceeds the design load. The size of the gap shall not exceed the demand of the work, but it shall be kept necessary and shall not exceed the machining cost.
In order to obtain the necessary clearance, it is necessary to reduce the tooth thickness of the part. Due to the manufacturing and assembly errors, this is always greater than the amount required by the design. The reduction in tooth thickness depends on the accuracy of the equipment, and the design amount of clearance must be verified according to the actual production conditions.
The tooth side clearance requires that each tooth of a pair of automobile gears contributes half of the tooth thickness. But sometimes there are exceptions. For example, on automobile gear parts with particularly small modulus, if the tooth thickness is reduced to increase the clearance, the strength of automobile gear will be affected.
In the process of spur and helical gear transmission, the allowable clearance is usually to increase the full tooth depth by increasing the hob relative to the theoretical standard depth. In the design of precision hob and semi precision hob, the clearance of hob is usually designed at the tooth part of hob, and the full tooth depth required by the design should be ensured. These hobs need an accurate amount of hob allowance to control.
To assist in determining the full tooth depth of hob, the target depth should be set and constantly changed according to the parts. For example, 14.5 ° pressure angle, the coefficient is 1.93; For a pressure angle of 20 °, it is 1.37. For other hobs, different pressure angles are multiplied by corresponding coefficients. The full tooth depth of hob is the sum of the coefficient and the full tooth depth of the part. Whether rough hob or fine hob, the full tooth depth is based on the standard full tooth depth of automobile gear parts.
Designers must determine the amount of backlash when designing automobile gears and mating wheels. This can avoid the confusion between automobile gear pairs. In this case, each car gear provides half the amount of clearance. Although this is a simple method to provide clearance, almost all automobile gear clearances can be determined by this method.
Another fairly common method is to specify the clearance of driving gear. However, the driving gear may vary greatly in tooth thickness. If the clearance is measured after the driving gear, the actual tooth thickness on the pitch circle can be determined.
Because the most common way to measure the clearance is to fix one car gear and swing another car gear repeatedly, while the clearance of helical gear usually refers to the plane in which the gear rotates. Therefore, if the required clearance is on the end face or shaft surface, it should be clearly indicated on the automobile gear drawing.
In addition, the clearance in the processing process needs to be taken as a reference according to other conditions in the process scheme.
In general, the clearance is the position of the rotation plane of the automobile gear in the actual operation. The minimum value is the gap at the tightest place. The maximum value may be anywhere, but it will not exceed the maximum value. The allowable value of tooth thickness position of indexing circle should include various factors, especially the possible clearance in the process of manufacturing and assembly of automobile gear parts.