Time back 10 years, on the question of choosing a car, many friends will struggle: whether to choose a car or an SUV. Nowadays, with the rise of new energy vehicles, everyone has begun to pay attention to whether to choose "oil trucks" or "trams". In response to such a problem, I suddenly thought of a sentence by Li Bin, the founder of Weilai: where the oil car can go, the tram can also go. Is this really the case? I think the answer to this question is not something that can be made clear in just a few words.
Today, we will "narrow down" the problem and talk about the four-wheel drive system. Simply put, "oil trucks" are generally equipped with mechanical four-wheel drive, while "trams" are electric four-wheel drive. Mechanical four-wheel drive can make "oil trucks" go farther away, so what about electric four-wheel drive?
Let's take a brief look at the mechanical four-wheel drive system
In traditional fuel vehicles, the power comes from the engine, and after output, it needs to pass through the transfer box, drive shaft, and differential to transmit power to the four wheels to achieve four-wheel drive or other driving states. And this mechanical drive system is a mechanical four-wheel drive system.
Transfer case
According to the different forms and operating frequencies of the central differential, the mechanical four-wheel drive system can be roughly divided into full-time four-wheel drive, time-sharing four-wheel drive, and time-time four-wheel drive. Different four-wheel drive, its advantages are not the same, such as handling, get out of trouble, fuel saving. Regardless of the four-wheel drive form, the goal is the same when driving on the road with difficulty and low adhesion, which is to distribute power between the front and rear axles (including between the left and right wheels) when the wheels are slipping, to help the adhesion wheels drive the vehicle to drive stable driving. The power distribution ratio of the four-wheel drive system is not large enough, and the speed of distribution is not fast enough, which is an important factor affecting the ability of the vehicle to get out of trouble.
Central differential
Advantages and disadvantages of electric four-wheel drive
For new energy vehicles, compared with traditional fuel vehicles, there are more power sources, which can be two or even more motors in front and behind, or a combination of one engine and multiple motors. With the increase of power sources, the process of power transmission to the wheels is more direct, both the components of power distribution are reduced, and the proportion of distribution is more controllable. In addition, due to the fast response speed and high controllability of the motor, when needed, the power of the front or rear axle can be completely cut off, which is difficult to achieve in mechanical four-wheel drive.
E-Four system
For example, Toyota's E-Four system, installed on the RAV4 Rongfang Dual Engine E+, is equipped with a motor with a maximum power of 40kW and a maximum torque of 121N·m to drive the rear wheels, which can achieve 20% to 80% power distribution of the front and rear wheels. Another example is Audi's e-tron S, which is equipped with two motors on the rear axle, which not only can flexibly distribute the power of the left and right wheels when getting out of trouble, but also achieve a torque difference of 2098N·m between the wheels in just a few milliseconds when cornering at high speed, improving handling.
Therefore, with the advantages of electric four-wheel drive multi-power source and fast response speed, when new energy vehicles cope with some small ditches and small obstacles, or when wet and slippery roads, the upper limit of passivity will generally be higher than that of fuel vehicles without "locks". When it comes to complex road conditions and requires medium to heavy or even heavy off-road, the ability is still not as good as mechanical four-wheel drive. It is a simple truth, why Toyota's off-road vehicles can be famous in the world, not because of how advanced the electronic system is, but because the original mechanical structure is reliable and durable.
Take the Wrangler, its plug-in hybrid version, and did not use the form of electric four-wheel drive, although the power source has more motors, but its output power is still transmitted to the wheel by clutch, transfer box, transmission shaft. Simply put, the optimization is the power, the power performance is stronger, the low-speed torque is better, and the four-wheel drive system is still mechanical.
Ah Chuan commented on the car
Of course, it does not mean that the electric four-wheel drive can not achieve the strong performance of the mechanical four-wheel drive, but it is said that for most family cars, the advantage of the electric four-wheel drive is to improve the handling, rather than get out of trouble, which is a trade-off. As for going farther and going to more complex places, this is the embodiment of comprehensive capabilities, including endurance, as well as the design of the whole vehicle. Finally, I would like to say that even if it is a fuel vehicle, is choosing a four-wheel drive system a blind pursuit of off-road? Obviously not, the same is true for electric four-wheel drive. We also look forward to the day when pure off-road vehicles such as Wrangler and Big G can be fully electro-driven, and believe that their electric four-wheel drive can achieve better escape from difficulties.