During the Spring Festival, a friend who had just purified the tram ran two high-speed trips back and forth to his hometown, and he had a big doubt. He described it this way: When driving a fuel car in the past, occasionally going out to pull the high speed, the fuel consumption will definitely be lower than the usual urban area; and now it is replaced by an electric car, and the mileage after getting on the high speed has dropped a little faster, and I am more worried about the lack of electricity, so I want to know what is the cause?
I believe that this friend of the author is not an isolated case, and many user friends who have just changed from oil trucks to trams may have similar troubles. In order to answer everyone's doubts, we first need to figure out the difference between the energy consumption characteristics of electric vehicles and fuel vehicles.
In terms of energy consumption, in fact, electric vehicles always have lower energy consumption than fuel vehicles. Today' world's top internal combustion engine, thermal efficiency can only be more than 40% of the head, this bottleneck has not been able to subvert for many years can not be disrupted. On the contrary, electric vehicles can easily go to 90% to 95% due to the power output characteristics of the motor, and there will be more kinetic energy recovery devices.
So, since the efficiency of the internal combustion engine is far less than that of electric vehicles, why is the high-speed endurance of the latter more urgent?
This issue should be viewed from a relative point of view.
Fuel vehicles are very familiar to everyone, knowing that the fuel consumption in the urban state is high, and the more smooth the elevated, loop, especially high-speed kilometers, the more fuel-efficient. This is because when driving at low speed in urban areas, it is often faced with stop-and-go congestion, and frequent braking will waste a lot of energy, so that the internal combustion engine is always in the inefficient working area, and it is impossible to achieve the "40%" thermal efficiency declared by the manufacturer, which is just an ideal value. The fuel vehicle in the high-speed road conditions, the efficiency is relatively high, note is relative, the efficiency of the gas turbine is not very low, the reason is that the waste of the brake is relatively small, the resistance is relatively small, so the engine can get a more economical fuel consumption level when running at high speed.
The dynamic characteristics of the electric motor and the internal combustion engine are completely different, because of the concept of the "reference speed" of the electric motor, that is, the benchmark speed of the electric vehicle is usually maintained at 1500-2000 revolutions, which is equivalent to the optimal efficiency range of the fuel vehicle. This means that the electric vehicle is more efficient and has relatively low energy consumption at low and medium, and when the speed of the vehicle is faster and the speed of the motor is pulled to a higher position, the corresponding energy consumption is also higher, and the endurance is naturally less.
In this regard, Tesla has done a set of special data statistics, the test results show that 60km/h is Tesla can achieve the longest endurance of the speed value, if the average speed is higher, the actual endurance of the vehicle will be stepped down.
From another point of view, fuel vehicles running high speed is only less expensive, while electric vehicles running high speed is relatively more expensive. The reason is the difference in the optimal economic working range of the internal combustion engine and the electric motor, the former concentrated in the medium and high speeds, the latter concentrated in the middle and low speeds.
After understanding the difference in the dynamic characteristics of electric vehicles and fuel vehicles, and judging the energy consumption of running high speeds, we must also see how much energy the two carry together. After all, the final endurance performance is inseparable from the total energy divided by the energy consumption.
If you take Weilai and Tesla, which rank first in the market for battery energy, for example, the Weilai ES8 is currently equipped with a battery with a maximum power of 100 degrees, and the 100D model of Tesla Model X is also 100 degrees of electricity as the name suggests.
In contrast, we assume that a fuel SUV of the same medium and large size has a fuel tank of about 75 liters, and the calorific value and density are calculated at 4.6E7J/kg and 0.73kg/l, respectively, and the result is 2.52GJ, which is simply converted to an energy equivalent to 700 degrees of electricity. Surprised? The energy difference between the equivalent level of oil trucks and trams is so large that the oil storage energy of a gas truck is equivalent to 7 top batteries of Weilai or Tesla.
So in the usual sense, we think that there is no mileage anxiety for fuel vehicles to run long-distance highways, and pure trams are just the opposite. In this way, in fact, another concept has been extended, that is, the wind resistance coefficient is also a very important parameter for endurance, whether it is a fuel vehicle or an electric vehicle, the power consumption to overcome the air resistance is three-dimensional relationship with the speed, and the resistance will be much greater under high-speed conditions. Usually, few people will care about the relationship between the drag coefficient of the fuel vehicle and the full fuel mileage, but for pure electric vehicles, the absolute mileage is the key parameter, and the impact of the wind resistance coefficient on the mileage is obviously more concerning.
We can see that the major electric vehicle manufacturers seem to be more willing to claim the results of their products in terms of wind resistance coefficient. At the same time, everything is used to reduce the drag coefficient, such as the now commonly used low wind resistance streamline body, closed front face, wheel cover, including electronic exterior mirrors that are trying to pass laws and regulations. It is precisely because in theory, for every 0.01 wind resistance coefficient reduced, the cruising range can be relatively increased by 20-30 kilometers, or even more. This value has almost no impact on the endurance of fuel vehicles, but for pure trams, it is an important factor of "everything that must be contested".
Mercedes-Benz Vision EQXX wind resistance coefficient 0.18CD
Another point that needs to be added is that the gearbox equipped with the fuel vehicle is also the key to running high-speed fuel saving, and the main function of the transmission is to keep the engine in the high efficiency operating range as much as possible. The vast majority of pure electric vehicles do not exist in the function of gear speed change, usually only the "single-stage reduction gear" setting, the use of speed to adjust the speed in the driving project, which is another large pure electric vehicle in the high-speed cruise energy consumption performance of the reason. If you've ever felt a shift bike that saves less effort than a regular bike when riding faster, you'll find that an electric car is just like that average bike.
Of course, in order to seek more efficient endurance performance, at this stage, some manufacturers have begun to develop and add "two-speed transmissions" for pure trams, high-end such as Porsche Taycan, independent brands such as GAC AION LX PLUS, but more mainstream models, for a long time or rely on single-stage gear speed.
It is clear to look at the problem by combining the above factors. Running high speed, whether it is burning oil or consuming electricity, energy consumption is relatively high. In fact, the situation is not that the electric vehicle you think consumes more energy at high speed than the fuel vehicle, but that the electric vehicle consumes more energy than the low speed. Electric vehicles are indeed the faster the more power consumption of the kind, the working conditions are relatively stable, low-speed energy conversion efficiency and high-speed energy conversion efficiency is not a lot worse; and fuel vehicles due to high-speed hanging on the high-speed gear, reducing the loss in the power transmission process, so the low-speed energy conversion efficiency is higher than the high-speed, the effect is that the high-speed on the surface is more fuel-efficient.
Of course, with the wide application of multi-gear transmission in the future, as well as the improvement of battery energy density, the problem of high-speed battery life of pure trams, we can expect to be gradually solved.
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