The electric vehicle itself is determined by its structure
One difference between electric vehicles and traditional fuel vehicles is that there is no transmission, that is, the electric motor directly drives the wheels forward through a fixed-ratio reducer, which means The output power of the electric motor is directly and positively related to the driving speed of the vehicle itself. The faster the vehicle speed, the greater the output power of the electric motor, and the power consumed at this time will increase significantly.
At high speeds, the output efficiency of the motor is significantly lower than its output efficiency at economical speeds. As the speed of electric vehicles increases, the speed of the electric motor also increases (without a transmission). When running at a sustained high speed (for example, 120 kilometers per hour), the output power of the electric motor will increase significantly, and more will be consumed at this time. of electrical energy.
When operating at high power, the discharge current of the battery will also increase, thus affecting the discharge efficiency of the battery.
Wind resistance increases exponentially
Friends who understand the wind resistance calculation formula should know that the size of wind resistance is proportional to the square of the speed. That is to say, when the speed accelerates from 30 kilometers per hour to At 90 kilometers per hour, the speed increases three times, but the wind resistance actually increases by as much as nine times. Therefore, under high-speed conditions, the increase in wind resistance is very large. According to the law of conservation of energy, the cruising range will definitely decrease significantly.
The structural characteristics of electric vehicles and the impact of wind resistance directly determine that electric vehicles are not suitable for high-speed driving. In other words, their biggest use scenario is urban transportation. Of course, when the cruising range of pure electric vehicles is greatly increased, the high-speed charging network is more complete, and high-power fast charging technology is commercialized and popularized at both the vehicle end and the pile end, there will be no problem in running it appropriately.
First of all, let me ask you a question - do you care about the drag coefficient of a car when buying a car?
For Zhixingjun, the first impression left by the term drag coefficient was in the car magazines he read when he was a child. I clearly remember that at that time, there was a supercar that shocked the entire industry and made the headlines of several magazines in a row - Bugatti Veyron.
However, in this article on the interpretation of the speed artifact, apart from the core W16 engine, a large part of the rest is given to its aerodynamic design. In other words, in addition to the engine, there is also the powerful enemy of wind resistance that affects the speed of this speed artifact. Therefore, when I was young, I first had the concept of drag coefficient on these super sports cars.
In fact, this is not unreasonable. There is data from a long time ago that when a car is traveling at a constant speed of 80 kilometers per hour, up to 60% of its power is used to overcome air resistance. What's more, it's a supercar that pursues extreme speed.
So don’t we pursue the drag coefficient on ordinary models? The answer is of course no. Wind resistance design will also affect a car's fuel consumption, battery life and even driving quality. But compared to the top speed of supercars, the drag coefficient of ordinary household fuel vehicles is not always the same.a core condition.
However, with the changes in the market structure - the growing new energy field, the drag coefficient, which originally only attracted attention on supercars, has become increasingly popular on new energy vehicles in recent years. Pay attention to.
Itchy spots turn into painful spots
First of all, we need to understand what the drag coefficient is.
Drag coefficient is actually the abbreviation of air resistance coefficient. It is a mathematical parameter determined through wind tunnel experiments and sliding experiments. This data can be used to calculate the air resistance of a car while driving. In layman's terms, the drag coefficient is the "wind impact degree" of the vehicle. The larger the value, the more severe the wind impact of the vehicle.
As the largest and most important external force that a car encounters when driving, the size of the wind resistance coefficient will greatly affect the driving quality and power system efficiency of the car. In terms of driving quality, it obviously refers to wind noise and high-speed stability, while power efficiency refers to nothing more than three aspects-top speed, fuel consumption and battery life.
The aerodynamic design of the above-mentioned super sports cars is undoubtedly designed for extreme speed; while the drag coefficient design of ordinary fuel vehicles is more for fuel consumption and battery life.
Apart from pursuing the ultimate sports car, the drag coefficient is definitely not a core point for ordinary fuel vehicles. The fuel consumption performance of a car will not directly have a serious impact on your car experience, and you will not make a decision directly because of whether the car is fuel-efficient. Consumers often have more considerations about other aspects of product strength, and fuel efficiency is just the icing on the cake. It can be said that now that the refueling conditions and endurance performance are very mature, the improvement in fuel economy brought about by the drag coefficient is just an improvement on an itch.
However, at the level of electric vehicles, the importance of drag coefficient is completely different.
This is an equation that is not difficult to calculate. Calculated based on the standard that a car must use 60% of its power to overcome air resistance at a constant speed of 80km/h. For the same model, every 10% reduction in the drag coefficient can increase fuel economy by 3%. When converted to an electric vehicle, it can increase by 3%. % of the cruising range. Rather than increasing battery capacity at high cost and weight, it is definitely more practical to reduce the drag coefficient to increase mileage.
The importance of battery life to electric vehicles is obviously not the same as the importance of fuel economy to traditional fuel vehicles.
Therefore, before the charging conditions and charging time and cost have been significantly improved, the increase in battery life brought about by the drag coefficient is definitely an improvement in the pain points for electric vehicles.
So with the vigorous growth of the electric vehicle field in recent years, the importance of the drag coefficient has become increasingly important. Moreover, electric vehicles and the drag coefficient themselves have a "mutually beneficial" relationship.
First, electric vehicles lacking an engine have no need for air intake, and can directly cancel the front air intake to reduce wind resistance;
Second, electric vehicles have a more streamlined power layout. Simple, no complicated exhaust system, no drive train such as drive shaftsystem. Easier to achieve a flat chassis structure.
Third, it is the difference in design concepts. More advanced design concepts often allow electric vehicles to have detailed designs that are more in line with reducing the drag coefficient. For example, hidden handles, camera-like rearview mirrors, and lower-resistance wheel shapes.
Wait. . . . . .
GAC New Energy Aion?S is a clear example. On the premise of meeting the requirements of good looks and large space, Aion?S achieves an excellent drag coefficient of 0.245Cd and a sturdy 510km range through supercar-style air diversion vents, reduction of the front windward area and maximization of chassis flatness. battery life.
The Rise of a Formation
Drag coefficient and electric vehicle user experience are two seemingly unrelated things, but they are closely related. Just like gyroscopes and Apple's HomePod Bluetooth speakers, they seem to have no connection, but they can greatly improve the biggest shortcoming of Bluetooth speakers - the sound field.
Therefore, many car companies are currently rushing to reduce the drag coefficient of a model. In addition to being a publicity stunt, it also serves the biggest pain point of electric vehicles - battery life. This is a trick, but it also comes first in terms of experience.
What’s more, the current drag coefficient of electric vehicles in the global market has reached a level that was unimaginable a few years ago.
For example, in the car formation. The nearly 4.8-meter GAC New Energy Aion?S and the mid-to-large sedan Tesla model?S both achieve a drag coefficient of about 0.24Cd. But you should know that the drag coefficient of most cars exceeds 0.25Cd, such as the 0.26Cd Mercedes-Benz A-Class, the 0.29Cd Lexus CT that focuses on fuel consumption, and so on. Not to mention the 0.22Cd of the Porsche electric car Taycan.
Another example is the SUV formation. In 2019, NIO ES6 measured a Cd score of 0.28Cd after 150 hours of testing. Compared with the 0.3Cd of the Audi Q5L of the same level, the 0.31Cd of the Mercedes-Benz GLC coupe, or the 0.29Cd of the smaller Mercedes-Benz GLA, the ES6 has obvious advantages. On the Weilai EC6 that was just tested not long ago, it achieved an excellent result of 0.26Cd. Such performance is not inferior at all even when compared with fuel-powered cars.
Even in the field of trucks, the advantage of electric vehicles in terms of drag coefficient is still huge. When Tesla unveiled its super electric truck in 2017, it announced its drag coefficient of 0.36Cd. A huge truck, but it has a drag coefficient comparable to that of a hard-core SUV, not to mention domestic trucks with a drag coefficient of 0.7-1Cd. Therefore, such an excellent drag coefficient combined with Tesla's electric system foundation allows this super electric truck to have a cruising range of 800km, which is also comparable to the cruising range of diesel trucks.
However, after checking various data, Zhixingjun discovered that autonomous electric vehicles have better performance in terms of wind resistance coefficient and battery life.In terms of performance, they all show the strength of being at the forefront of the world.
In addition to the continuous advancement of brands such as GAC New Energy and NIO, you must know that in just nine months from March to December 2019, the drag coefficient discipline of Chinese brand cars was refreshed three times .
The first time was the Geometry A released in March, with a drag coefficient of 0.2375Cd; the second time was the Xpeng P7 released in October, with a drag coefficient of only 0.236Cd; the third time, It is the BYD Han wind tunnel results announced by BYD in December - as low as 0.233Cd.
Under such a strong wind resistance coefficient, the difficulty of achieving excellent battery life has actually been greatly reduced. The GAC New Energy Aion LX and BYD Han, which have reached 600km, and the Xpeng P7, which has exceeded 700km, are all outstanding examples that are not inferior to or even ahead of foreign models.
There is no absolute in everything
However, there is no absolute in everything. We should not look at the drag coefficient from a single perspective.
I still remember that at the launch of Tesla’s super electric truck in 2017, there was a joke – Tesla compared the drag coefficient of the Bugatti Veyron with this electric truck. The result is clear: Tesla electric trucks win. But is it really won?
Air is the enemy of a car breaking through the top speed, but it is also a good helper.
In the 1999 Le Mans race, the Mercedes-Benz car flipped over without any external force due to its low drag coefficient, insufficient downforce and too fast speed. It became the most famous accident in the history of racing due to insufficient downforce.
In other words, the drag coefficient is a parameter that car companies will only consider after meeting other higher-priority needs. For example, for a sports car, the priority is downforce, not just the drag coefficient; for example, for a family car, the priority is more space, comfort, etc. After meeting these design goals, if the drag coefficient can still be reduced, then methods can be used to reduce it. It is impossible to sacrifice other priority designs in order to reduce the drag coefficient.
A brief description from other media is - "The drag coefficient is a priority, not a design goal."
Knowledge and practice have something to say
At this time, Take a look at the question at the beginning of the article - do you consider the drag coefficient of a car when buying a car? I believe that most of the answers are "no". After all, this is a question that engineers should think about.
It is undeniable that in the era of electric vehicles, the importance of drag coefficient is constantly increasing. But taken together, improving the drag coefficient is actually a huge and comprehensive system project, which cannot be measured or weighed in one aspect. Just like whether a car is excellent can not be judged by a single aspect such as the wind resistance coefficient.
A good user experience is actually more important. For example, before understanding the drag coefficient, we will pay more attention to appearance, comfort, space, etc., and pursuing the drag coefficient is actually just for a more powerful car.aviation, more economical power consumption. This is true for electric vehicles, and it is also true for fuel vehicles.
However, the excellent experience of independent electric vehicles in terms of drag coefficient and battery life gave Zhixingjun a surprise. Testing the drag coefficient of a car requires extremely high costs and perfect standards, while improving the drag coefficient is a complete and systematic project. Therefore, when independent models continue to make breakthroughs in drag coefficient and battery life, it means that independent brands are gradually improving their R&D standards and manufacturing processes.
This article comes from the author of Autohome Chejiahao and does not represent the views and positions of Autohome.