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Gearbox Make The Gears More Evenly Loaded And More Stable
- Oct 20, 2017 -

If a minor malfunction occurs, it can also be repaired by, for example, adjusting the tightness of the Gearbox line, fine-tuning the knob and tightening the limit screw, so as to achieve the purpose of continuing to ride. If the Gearbox has been seriously damaged, can not be used, then the chain must be interrupted to remove the Gearbox, and then the chain cut short back, to a single speed car ride, after the end of the ride, and then sent to the professional car shop for maintenance.

First, Gearbox noise source analysis:

Gearbox assembly noise sources are mainly: gear, gear shaft, box, bearing, side cover, clutch shell and so on;

1. Gear noise is the main source of noise in Gearbox assembly: in the gear noise according to the different forms of formation, can be divided into several categories: A, due to tooth meshing, separation of the meshing impact of the sound; b, friction caused by friction vibration; c, the impact sound generated by uneven operation of gear errors or changes in tooth stiffness ;

2, other sources of noise: Our theory and practice has proved that the box, bearings, shafts and other components are not only the source of noise, but also solid sound medium. They directly affect the Gearbox noise. Because the Gearbox noise is a complex system problem, it is not said that we designed and manufactured a suitable gear can be satisfied with the noise effect. So we must consider and analyze the Gearbox assembly as a whole.

Second, the Gearbox noise control measures:

1, from the gear design point of view:

A, the number of teeth and modulus: in the center of the determination, to meet the requirements of the strength of the gear, we should use as much as possible the number of teeth, less modulus design method. Smaller modulus can get greater overlap coefficients, in order to make the gear load more evenly, the Gearbox more stable; In addition the module is small, the week is small, because we in the actual manufacture, cannot manufacture two identical week's gears, therefore the smaller week section may reduce the meshing error, reduces the impact noise.

b, tooth width and helix angle: From the calculation of overlap coefficient, increase tooth width and helical angle can increase the overlap coefficient of gear pair, therefore, the larger the helix angle, the wider the tooth width, the lower the noise, but because of the increase in tooth width, will affect the overall axial length of the Gearbox and the machining error of the tooth, so can not blindly increase tooth width. The test results show that the fatigue strength of gears can be greatly reduced when the helix angle is close to or over 30 degrees.

c, pressure angle and tooth top high coefficient: gear in meshing if can have better "flexibility" can compensate to some extent due to gear error caused by the load mutation, the smaller the pressure angle, the higher the gear "flexibility", the higher the adaptability. The higher the height coefficient of the tooth, the greater the overlap coefficient, the longer the single tooth will be, and the "flexibility" of the tooth is added. So now many Gearbox gears are designed with slender teeth.

D, gear error and repair form: Due to gear processing in the tooth shape, the existence of the tooth direction and other errors, as well as the Gearbox in the load, the shaft and the elastic deformation of the box will cause uneven meshing, resulting in noise, so we now most of the gear to repair the shape to ensure that the gear pair in the loading can get a better contact area.

E, gear backlash: The nearest distance between the two base cylinders and the two non working teeth is called the normal lateral gap jn when the cylindrical gear pair contacts each other in the working tooth surface. The backlash between the meshing surfaces of gear drives is the condition of guaranteeing the free rotation of gears. The side gap is too small, will cause the gear two teeth too tight, the noise increases sharply, on the contrary, the backlash is too large, and will make the teeth collide with each other, the same effect on the noise.

2. Design of miscellaneous items

A, the gear box is a typical elastic structure system, it produces vibration and radiated noise under the action load of the bearing, it should improve the stiffness of the whole box, determine its weak position by finite element, and add reinforcing ribs appropriately, reduce the resonance, and can also apply the sound absorbing coating on the inner wall of the box, which has achieved the noise reduction effect.

B, the Gearbox is loaded when the axis is bound to occur elastic deformation, this time the number of axes deformation is related to the gear pair on the axis of the meshing situation, and the shaft itself will be due to elastic deformation and vibration, so we should be as far as possible to improve the rigidity of the shaft. When the shaft is designed, its diameter and length-diameter ratio should be guaranteed under full load, and its total deflection and angle shall not exceed 0 respectively. 15-0.13mm and 0.000123 radians so that the shaft has enough stiffness to not damage the normal installation and meshing of gears.

C, the selection of low noise bearings, in high-grade areas and the normal mesh area should be selected better bearings to meet the needs of high-speed operation.

D, lubricating oil has damping effect and can prevent the tooth surface direct contact, so the noise is generally decreased with the increase of oil and viscosity, the design of the full consideration of the lubrication effect and the use of better lubricants can also reduce noise.

3. Process Considerations

A, gear processing; To ensure the precision of gear processing, control the change of heat treatment, through the heat before the shape to meet the requirements of the precision of the gear, the higher the tooth surface roughness, the greater the gear friction, the larger the meshing noise; Burr will cause the gear to run unstable, most of the Gearbox noise caused by burrs.

B, assembly process, in the Assembly in accordance with the correct assembly process, bearing as far as possible the use of pressing process to avoid early bearing damage.