1) The basic concepts of "brushless" and "brushed": At present, electric bicycles widely use DC permanent magnet motors. DC permanent magnet motors can be divided into brushed motors according to whether they use brush commutation. There are two types of brushless motors. Brushed motors are the mainstream products of DC motors. At present, most electric bicycle motors are brushed motors. The brushless motor is a special DC motor that uses a built-in sensor and an electronic commutator for electronic commutation. The brushless motor is mainly used to eliminate the wear of the brushes and the noise generated by the brush contact.
2) The shortcomings of brushed motors have not become factors that hinder its wide application in electric bicycles: Brush wear and motor noise are the two most important problems between "brushed" and "brushless" But despite these two shortcomings, why do most domestic brand manufacturers still use brush motor solutions? Don't they realize this problem? The reason is:
A) The wear of the brushes does not constitute a major problem. Electric bicycles are a means of transportation that work intermittently. The longest discharge time (riding time) of a set of batteries is generally 2- 3 hours. The average time users use the trade every day is about 1-2 hours. Nowadays, the disc rotor motors widely used in electric bicycles use flat commutators and high-quality extended brushes, and their working life is generally More than 1500 hours. Therefore, based on the average riding time of 1.5 hours per user per day, a set of brushes has been used for 1000 days. It can be seen that a set of qualified brushes has been in service for nearly three years, and the cost of replacing a set of brushes is only about 5 yuan, which is less than 2 yuan per year on average! What's more, after using an electric bicycle for three years, it is indeed necessary to conduct some comprehensive inspection and maintenance of the vehicle and replace some worn parts. The exaggerated view of promoting a commercial motor to be maintenance-free for ten years is suspected of misleading consumers.
B) It is normal for the motor to make a little noise. When the author visited the market, a promoter of a brushless motor electric vehicle demonstrated the silent characteristics of the brushless motor under no-load conditions to prove that there is no Brushed motors are much superior to brushed motors. In fact, buying an electric car is by no means buying air conditioning equipment. Consumers do not need to make a purchase decision based on whether it is noiseless. In fact, users who have used brushless motor electric vehicles will know that the sound emitted by the brushless motor is indeed very small when it is no-load or under low load (such as flat and windless conditions). However, when running to a heavy load state, For example, when going uphill or against the wind, it will often emit a much "bigger" sound than a brushed motor, and may even experience uncomfortable electromagnetic jitter. This kind of sound will not occur during a quiet store promotion. In fact, it is normal for the vehicle motor to make some noise when it is running. After all, it is a means of transportation used outdoors. The national noise qualification standard is less than 62 decibels. Most domestic brush motors can control the decibel value within Below 55 decibels, it is a qualified product. Brushless motor promoters lead consumers to pursue "silence" and promote electric vehicles like air conditioners, which is also suspected of misleading consumers. Too much noise from air conditioners will affect sleep, but a little sound from electric vehicles will not affect use. of!
3) A series of problems existing in the existing brushless motor solutions: An article in an evening newspaper "Brushless is Better than Brush" arbitrarily accused brushed motors of "short life, high noise, and low efficiency." , and even pointed out that "generally, the carbon brushes in the motor need to be replaced after 6 months to a year of use." The crusade has no worries! For this reason, this article will follow suit and briefly outline the disadvantages of brushless motors for electric bicycles.
A) The sensor working environment is poor, causing system failure! Formal brushless motor design generally requires the installation of photoelectric or magnetic (Hall element) sensors in non-heat source areas to detect the rotational position of the motor and send out signals to control commutation. However, most of the so-called electric bicycles currently on the market are dedicated to electric bicycles. Due to limitations of design size and installation method, the brushless motor hub cannot isolate the sensor from the heat source. Almost all sensors are installed by positioning slots on the iron core stator and fixing three Hall elements with glue. As we all know, , the heat source of the motor is an objective existence. It comes from the copper loss and iron loss of the motor. Especially when the motor works in a lower efficiency area, the heat accumulates very quickly, so the iron core will heat up and is placed directly in the heat source area. The performance of the sensing element will drift, resulting in commutation error. Once the commutation is wrong, it will cause a large drop in motor efficiency and further increase in temperature, leading to a vicious cycle and directly causing the electronic commutator to burn out. Generally, the performance as "short circuit". Once "short circuited", the brushless motor will feel "stuck" and it will be very difficult to rotate, and the user cannot even pedal. The only way is to ask a tricycle or taxi to transport it back. Experienced users will bring a pair of scissors. Once the short circuit is stuck, cut the motor input line to make it "open circuit". In this way, the burned "brushless" can be Went back to the maintenance department.
B) Induced electromotive force, causing the controller to burn out: When the author was visiting the market as a customer, a brushless salesman proudly introduced the "silent" feature to me and became interested again. She enthusiastically demonstrated the magical self-charging function of the brushless motor: turning off the main power supply, shaking the bottom bracket to rotate the rear wheels, and then beeping to indicate that power had been generated. The electricity generated by stepping on the foot was recycled into the battery. She told me, " "The battery can generate electricity by itself if there is no electricity", which is extremely miraculous, and it is extremely ridiculous not to evaluate how the "perpetual motion machine" property displayed by this demonstration violates the basic law of energy conservation. It is acceptable to deceive individual consumers. Experts absolutely cannot do it. On the contrary, this situation is exactly the sad point of "brushless". Since the brushless motor does not have an overrunning clutch, when the wheel rotates rapidly, an induced electromotive force will be formed at the input end of the motor. The faster the wheel rotates, the greater the induction force. The higher the electromotive force is, when it exceeds the withstand voltage value of the device, it will cause "voltage breakdown" of the electronic commutation system. The motor will short-circuit again, the wheel will suddenly get stuck, and it will be necessary to resort to "cutting to open the circuit". This kind of The situation often occurs when the user is riding a brushless electric bike uphill with great difficulty. When going downhill, he thought he could relax and let it glide freely. As the speed gets faster and faster, the induced electromotive force increases. The higher the value, the component will eventually be broken down and stop without braking. This is why many users report that the "brushless electric vehicle" does not break down when going uphill, but does not turn when going downhill.
C) It only says that the motor will never wear out, has a lifespan of ten years, and has a two-year warranty, but not the controller! Brushless is different from brushed. The brushed commutator is placed inside the motor, while the brushless is placed outside the motor. Therefore, the brushless motor system actually consists of two parts: a "motor" and an "electronic commutator". Made up of parts. The brushless motor part does have some kind of "never wear" property, but the brushless electronic commutator is a component with a high failure rate. Various faults as mentioned above occur on the controller. . At present, many brushless salesmen promise customers that the motor will be "guaranteed for 2, 5 or even 10 years", but the controller (electronic commutator) can only be guaranteed for one year, and replacing a controller costs as much as 200 yuan. In fact, if you include the maintenance cost of the brushless system controller, the maintenance cost will be much higher than the cost of replacing a few brushes of a brushed motor. Once an individual manufacturer withdraws its warranty commitment for the controller (commutator), the cost of use for consumers will increase rapidly.
D) The contradiction between system reliability and performance: Needless to say, the reliability of brushless motors has a great relationship with the maximum operating current. Reducing the maximum operating current will improve reliability, but if it is significantly reduced If the maximum operating current is too high, the brushless electric vehicle will have negative effects such as weak operation and poor performance. Consumers will not welcome it, and there will be no market for brushless electric vehicles. This is indeed a very serious issue facing the brushless system.
E) Brushless needs to be more "waterproof": I have not only seen some promoters of brushless motors immerse the entire brushless wheel hub in a "fish tank" to show off its "amphibiousness" Regarding the "excellent" characteristics of operation, brushed motors do have the disadvantage of difficulty in reversing underwater. However, electric bicycles are not submarines, so why do they need to travel in the water? This seemingly knowledgeable demonstration is really hard to understand! In fact, this can be regarded as a kind of "magic", because the brushless uses electronic commutation, and the demonstrator did not put the electronic commutation device in the water. If the entire controller (commutation device) is also placed in the fish tank, it will not work. The situation with a brushed motor will be worse than with a brush. In fact, both brushless and brushed products use NdFeB as permanent magnet material. This material has many excellent characteristics, but one of its biggest shortcomings is poor oxidation resistance. Placing it in water will undoubtedly destroy NdFeB. Exposed to the harshest conditions, the life of the motor will be lost due to oxidation. In addition, there are a large number of silicon steel sheets in the brushless motor, which will also rust, and it needs to be waterproof. Although such a demonstration can mislead some viewers, it will be meaningless if it is revealed.