A few days ago in a car group chat, the author put forward a topic: on the electric vehicle gearbox, how do you see?
I did not expect the answers of the group's friends to be varied. It really surprised me. For example, does the electric vehicle have a gearbox? There is a frequency converter, electric vehicle gearbox Why? Wheel hub motor directly drive the axle on it...
In fact, these questions are not difficult to answer. The group friends have the root cause of this idea. On the one hand, the vast majority of people are still aware of the concept of electric cars in low-speed car batteries. On the other hand, “academic thinking†is too strong. What inverters, wheel motors, and wheel motors are all considered in the industrial environment? These are not realistic.
Based on these questions, the author proposes a proposition: Does an electric car need a gearbox?
First of all, from a theoretical point of view, here is a picture from the CC CHAN review of academic masters. Structure of pure electric vehicles:
Among them C: Clutch, D: Differential, FG: Fixed gear, GB: Gearbox, M: Motor.
The above six maps generally describe the powertrain architecture of a pure electric vehicle. This shows that the electric vehicle gearbox is optional.
What determines the electric car needs a gearbox? The answer is the industrial environment. Although figure a is the most complicated, it is the most appropriate solution to balance the supporting infrastructure and costs of the current Chinese parts and components market. This is the framework of an electric logistics vehicle that I once opened; Figure f. Powertrain The architecture is the simplest, but the technical conditions are the highest. As a group of friends said, what is the frequency of the hub motor, but the author originally chatted with a Bosch engineer. He admitted that even in Germany, this technology is not very mature. Can do it, but there is still some distance from mass production.
From the above, it can be seen that, although the electric vehicle gearbox is theoretically dispensable, but considering the current industrial infrastructure supporting capabilities, and the market demand for electric vehicle performance, electric vehicles still need gearbox.
From traditional low-speed electric vehicles, electric bicycles, factory motors, and even motor drives in a broad sense (such as electric fans, razors, etc.), electric vehicles may indeed not require gearboxes. But why do electric vehicles need gearboxes?
Let us give a simple mathematical example. The maximum speed of a family car is limited to 240 kilometers per hour. The tire size is R16. Based on these two parameters, it can be roughly calculated that if the car reaches a speed of 240, then the tire's speed reaches about 3,000 rpm, that is, the maximum limit of the tire is at this speed, if it is accelerated again, then There will be sliding rather than rolling, but many passenger cars rated AC motor speed is 3,000, the maximum speed is eight or nine thousand, or even tens of thousands, remove the differential and the slightest half shaft deceleration, if you do not increase the speed Box, is equivalent to "direct drive", then what is the use of the speed behind the motor? As the vehicle's direct contact with the ground, the tire is a gathering point for various forces such as traction and resistance. If the tire is always under high rotational speed, the wear of the tire is also very serious, which is the so-called "burnt tire". This is unrealistic. of.
Secondly, the motor is a kind of engine and has its own unique characteristics. From the aspects of work efficiency and noise suppression, the electric passenger car also needs to add a gearbox.
As for the low-speed electric vehicles mentioned above, on the one hand, they mainly use a DC motor, the motor speed is very limited in size and range, or the AC motor is driven by a cheap and simple inverter, due to the special use of the electric passenger vehicle Most of them use high-speed AC motors. Therefore, the characteristics of the motor also determine that the electric passenger car needs a gearbox.
The above is the author of the analysis of why electric vehicles need gearboxes, and online with this topic is almost the article, their thinking is mainly to emphasize the benefits of gearbox, which told me that the reasons for the need for gearboxes are essentially different. Of course, there are still some benefits for gearboxes. Since this piece has already been described by many theories, here we borrowed the theory of the Great God “Zhang Kangkang†(thank you very much). He said very well.
Plus the benefits of the gearbox:
First, to expand the operating range of motor speed, if you add a multi-speed gearbox, clutch and other effects are better;
Secondly, it is able to control the motor to work in the effective range, and more "power saving", which is also one of the core of hybrid fuel economy;
Third, to avoid excessive high-speed motor, the mechanical damage, but also produce a lot of noise, affecting ride comfort;
Fourth, there is a certain increase in performance. For example, when the motor continues to turn high, that is, the end of the car's acceleration, it is difficult to increase the speed at that time. However, if a gearbox is added, there is more than a “last stop†in the common saying. After adding a multi-speed gearbox, the breakout point of the electric vehicle is more and more persistent. If there is no or a single-stage gearbox, then it will be a strong sense of pushback during the start-up period, and a relatively weak acceleration in the middle and later stages.
Fifth, in order to achieve the same performance, there is a transmission that can effectively reduce motor and battery indicators. For example, the first model of the Tesla Roadster was originally designed as a 180kW motor 2-speed gearbox. Later, due to the problem of transmission quality, The second option was forced to eliminate the transmission but increased the motor capacity to 240 kW to achieve the same performance. To accommodate larger motors, the battery also needs to be increased to 80kWh to provide more output power.
Finally, to sum up, in theory, the electric vehicle gearbox is optional. However, considering that the new energy automobile industry continues to move forward, various segments of the market have higher requirements for electric vehicles. For example, electric vehicle logistics vehicles are more likely to be installed due to their greater emphasis on the climbing ability of electric vehicles. A multi-tooth ratio gearbox; then the market's largest electric passenger car, in order to meet the more discerning eyes of consumers, the performance of electric vehicles need to be more powerful, but also put forward greater requirements on the gearbox.
At present, most of the electric cars in the market are single-stage gearboxes, such as luxury cars such as Tesla, and utilities such as beans. Although single-stage gearboxes are somewhat compromised in terms of performance, considering the market environment and costs, this is the most cost-effective option. In the future, multi-gear transmissions will certainly be the trend of electric vehicles, and it is also one of the core technologies that major component manufacturers and OEMs must pay attention to.
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