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China's electric car crisis: multi-gear gearbox is coming

Publish Time: 2020-10-09 Origin: site

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China's electric car crisis: multi-gear gearbox is coming

At present, a company named "Drive System Design" (hereinafter referred to as DSD) is seeking investors around the world, and its purpose is to commercialize the company's latest multi-gear gearbox. .

   Seeing this right now, some people may disagree-isn't it just a gearbox! As for such fanfare?


In fact, well-known companies such as AVL, Delta Racing, GKN, Jaguar Land Rover, Indian Tata Steel, Williams, Zytek, etc. have established a joint venture capital consortium for this project. The university provides continuous technical support for the commercial development of the project.


  


   It must be popularized here first. The internal code of this multi-speed gearbox developed by DSD is MSYS and has five independent global patented technologies. The models targeted are electric vehicles and hybrid vehicles.


  Since the torque output of the electric motor has nothing to do with the speed of the electric motor, most new energy vehicles that rely on electric motors for end-drive are equipped with single-stage gearboxes or reducers-usually called fixed gear ratio gearboxes.


   Limitations of fixed gear ratio transmissions


   Compared with ordinary gearboxes, fixed gear ratio gearboxes have high transmission efficiency, simple and reliable structure, small size and easy installation, and there is no calibration difficulty, so they become the first choice for end-motor-driven models.


   However, recent technical calls for multi-gear ratio gearboxes have been clamoring. The reason is the problem of the drive structure.


  


   Tesla Model S accelerates very well from 100 kilometers, but it is restricted by the lack of a multi-gear ratio gearbox, impotence in the middle and rear acceleration performance, and poor battery endurance per unit


   Take the DC battery car running all over the street as an example. Under the condition of the speed limit, the torque output is still the same as at the start, but the speed cannot be further improved.


   Looking at the higher end, the asynchronous motor, also called induction motor, is better than the DC motor of the battery car. Its maximum speed is twice as high as that of a DC motor, and its power density is also significantly higher than that of a DC motor.


  Under the premise of the same rated power, electric vehicles using asynchronous motors have faster speeds, but after matching with fixed gear ratio transmissions, there will still be a problem of low high-speed economy.


For example, the Tesla Model S driven by an asynchronous motor has a very strong starting ability, but the acceleration performance in the middle and late stages is also poor, and the endurance per unit of electricity is even less than that of the domestic Tengshi-this is actually a fixed gear ratio variable speed Due to the limitations of the box.


In order to solve this problem, BMW matched the drive motor of the i8 with a 2-speed automatic transmission supplied by GKN. Although in the industry, this 2AT can only be called 1.5AT at best, but it is enough to make the BMW i8 in It takes significantly shorter time to accelerate to 250km/h in pure electric mode than Tesla Model S, which is one of the main reasons why BMW has the confidence to dismiss Tesla.


   A 2AT alone is enough to slow down the speed. So, why can't electric cars be equipped with ordinary gearboxes? The main reason is that the volume and weight of ordinary gearboxes are too large compared to electric vehicles, followed by poor transmission efficiency, and the difficulty of installation design and matching.


Taking the current dual-clutch gearbox with the highest transmission efficiency as an example, the actual transmission efficiency is about 87%, which means that the original 100km endurance is only 87km, and considering the weight of the gearbox, the actual endurance is still reduced-as we all know, endurance It is the biggest fate of electric cars!


  If a fixed gear ratio gearbox is used, the endurance may be reduced at a speed of 100km/h


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