The sliding contact of the commutator, and the composition and contact characteristics of the brushes can directly affect the quality of the commutation and the degree of wear of the motor. The contact characteristics of the brushes mainly refer to a pair of brushes. Contact pressure drop (because the contact pressure drops under the positive and negative brushes are not equal, so a pair of brushes is used to evaluate the contact pressure drop) and the coefficient of friction, these factors affect the relationship between the brush and the converter when the motor is running. Contact loss (including electrical loss and friction loss) and abrasion. The main factors affecting the contact characteristics of the brush are peripheral speed, current density, and unit pressure applied to the brush. For DC motors for electric bicycles, the peripheral speed is not large. Generally can meet the requirements. The brushes of this DC motor generally put forward the following requirements:
(1) Because the electric bicycle uses a low-voltage power source, the contact voltage drop of a pair of brushes cannot be large, and it should generally be below 1v, so that the power loss is small.
(2) If the user does not need to replace the brushes after 2 years of use, and the daily riding time is 2 hours, the brush life should be about 1500 hours. The brush life is determined by the height allowed for wear, and the permitted wear height is determined by the allowed spring The minimum pressure and the stability of the brush in the brush box after short grinding.
(3) The size of the cross-sectional area of the brush should be consistent with the allowable current density of the brush. If the current density is too large, it will cause excessive heating, the friction coefficient will increase, and it will easily cause sparks, and the motor will not even run normally.
(4) The wear of the commutator should be within the allowable range, and the running noise is small.