Low temperature constant resistance moment and improvement of permanent magnet micromotor

The application of micro-motors in daily life has become increasingly widespread and has penetrated into all aspects of life, among which the largest amount of miniature permanent-magnet DC motor (PMDC) is used. PMDC has a simple structure, small size, less copper, high efficiency, and is very popular in the automotive industry.

Automotive motor application environment is generally harsh, and its actual use is not at room temperature, but at high / low temperature; such as the motor is often blocked due to high temperature rise, the motor is wrapped in poor thermal conductivity caused by plastic parts, Use cars or other vehicles in a warm or cold climate. Therefore, automotive motors must be able to withstand the high and low temperature test, generally -40 °C in practical applications, customers are more concerned about the performance of the motor's high and low temperature, such as low temperature start, low temperature noise, high and low temperature performance, thermal shock resistance, high resistance Low temperature storage, temperature rise control protection, etc.

This article focuses on the phenomenon of increasing motor starting torque at low temperatures. Starting voltage (V) Starting current (A) Starting voltage (V) Starting current (A) Forward rotation Reverse rotation Forward rotation Reverse rotation Forward rotation Reverse 3 Causes of increased resistance at low temperature start resistance Analysis of the structure of the electric motor shows that the no-load static torque T consists of two parts: mechanical static friction torque Tm and cogging torque, ie TfTVtT...

From the above, there is a change in the static torque at no load. The size of this change is tested on a certain type of motor, and the data is shown in the following table 2. The test method for the frictional torque is to demagnetize the permanent magnet and measure it.

Table 2 Comparison of low temperature and room temperature friction torque/total resistance moment From the data in Table 2, we can see: 1) The total static resistance moment at low temperature is much larger than normal temperature; 2) The total cogging torque, the cogging torque than the friction torque Larger, that is, the total static torque is mainly caused by the cogging torque: 3) The increase in temperature is mainly the cogging torque.

The cogging torque is an inherent phenomenon of the cogging permanent magnet motor and an important parameter of PMDC performance. In this kind of motor, the cogging torque is because the rotor has a tooth and a stator along a certain direction. The tendency of the magnets to align, and this tendency produces an oscillating torque. The cogging torque is generated from the tangential force between the rotor teeth and the stator permanent magnets and is the result of the interaction between the rotor teeth and the permanent magnet stator.

3.1 Influence of temperature on magnetic force The influence of temperature on magnetic force is mainly related to the thermal stability of permanent magnet I". Thermal stability refers to the degree of change in magnetic properties of a permanent magnet due to changes in the ambient temperature. Also known as temperature stability. When the ambient temperature of the permanent magnet rises from t to tl, the magnetic density decreases from B0 to B1: when the temperature returns from to, the magnetic density returns to B', instead of B0. When the temperature is known and changed The influence of the magneto-intensity on the pole-arc coefficient of the variation of 3.2 degrees between the 'and' 氐 and the pole-pole also affects the Tj. Many studies have shown that 121, the pole-arc coefficient has an optimal value for Tc. At this optimal value, Tq is the smallest, and greater than or less than this value T will increase. According to the data, PMDC's T becomes larger with pole arc in the 130-180 pole arc. The arc arc actually used in this factory is in this range.

In many of the factory's magnetizing fields, for certain specific reasons, it is sometimes intentionally magnetized and unsaturated in certain areas of the permanent magnets (most of which are boundary areas in the circumferential direction of the permanent magnets) during magnetization. For example, S1 magnetization method, its typical magnetic density distribution waveform, as can be seen from the figure: the permanent magnets have the highest saturation in the middle and the saturation in the boundary direction is getting smaller and smaller. In other words, there is an unsaturated area. At low temperatures, the Br in the unsaturated zone will increase, which in turn will increase the calculated magnetic flux density distribution waveform of the eight poles of S1 magnetization. 3.3 The effect of low temperature on the cogging torque The cogging torque and residual magnetic induction of the permanent magnet Strength or thickness Lm related. IEEE Du Hongjun et al. Analysis of Cogging Torque of Permanent Magnet Motors . Micro-motor,