Speaking of the history of four-wheel drive, it can be traced back to 1907, when an important customer of Daimler Automobile Company ordered a car with excellent off-road performance. After repeated discussions and research, the engineers of Daimler Automobile Company designed and manufactured the world's first all-wheel drive car, named "Dernburg Wagan". After more than a hundred years, the four-wheel drive system has evolved and is no longer the patent of off-road vehicles. Many cars and SUVs can also see the application of four-wheel drive system.
Full-time four-wheel drive (car)
As the name implies, full-time four-wheel drive can be powered by all wheels of the vehicle in any state without human intervention. It has strong traction performance in all road conditions and is suitable for urban road conditions and low-intensity off-road. According to different adjustments, it can be widely used in various types of automobile products and also has a place in military vehicles and racing cars. Many people think that the full-time four-wheel drive system can only be equipped with a vertical engine platform, but it is not. Horizontal engine platform can realize full-time four-wheel drive through multi-disc clutch central differential and electronic power distribution.
Part-time four-wheel drive
Part-time four-wheel drive means that the driver can switch between two-wheel drive and four-wheel drive by connecting or disconnecting the front and rear axles according to the road conditions, so as to realize the free conversion between two-wheel drive and four-wheel drive. Part-time four-wheel drive usually only uses front wheel drive on urban asphalt roads, and can be switched to four-wheel drive on snow or gravel roads. Of course, this is also the most common driving mode of hard-core off-road vehicles. Its advantages are simple structure, high stability and durability, which can not only ensure the power and passability of vehicles, but also give consideration to fuel economy. It is a very good four-wheel drive scheme.
Timely four-wheel drive
Timely four-wheel drive literally means that vehicles only use four-wheel drive when appropriate, and in other cases, it is a two-wheel drive four-wheel drive system. Compared with full-time four-wheel drive, timely four-wheel drive has better fuel economy. But its physical structure is limited, and it is generally only suitable for urban road conditions. Timely four-wheel drive can be roughly divided into three types: the first one is timely four-wheel drive with hydraulic coupler, the second one is timely four-wheel drive with electric control multi-disc clutch, and the third one is timely four-wheel drive with intelligent electronics.
Hydraulic coupler type timely four-wheel drive
The core component of four-wheel drive is hydraulic coupler, which is filled with silicone oil. One end of the input shaft and the output shaft is connected with an impeller immersed in silicone oil, and the other end is connected with a front differential and a rear differential. During normal driving, the front and rear wheels keep driving at the same speed, and there is no speed difference between the two shafts of the hydraulic coupler. When the front wheel slips, the speed will exceed that of the rear wheel, resulting in the speed difference between the two impellers in the coupler. This speed difference will lead to a rapid increase in the temperature and viscosity of silicone oil, thus transmitting power to the rear wheels.
Multi-clutch timely four-wheel drive
The core component of this timely four-wheel drive is the multi-plate clutch limited slip differential. Multi-disc clutch differential mainly produces differential torque through wet clutch plates, and the compression and separation of clutch are controlled by electronic system. When the vehicle is running normally, the driving form is front wheel or rear wheel. For example, if the system detects wheel slip, the electronic system controls the clutch to compress, and then part of the power is transmitted to the rear wheel or the front wheel. Theoretically, the computer will automatically distribute the torque of the front and rear axles according to the vehicle speed and road conditions to achieve the best grip performance. However, this four-wheel drive system usually has a slow response speed, because after the main drive wheel loses its grip, other drive wheels will passively intervene.
Electronic timely four-wheel drive
This timely four-wheel drive can accurately control the intelligent transfer case to transmit controllable torque to the four wheels according to the actual adhesion between the four wheels and the ground, thus improving the acceleration, stability and fuel economy of the whole vehicle. When accelerating, all four wheels can reach the maximum traction, and the acceleration is better. If you slip on a slippery road, the slipping wheels can be braked by an electric submersible pump. Power is distributed to the wheels that maintain adhesion to eliminate the tendency of the vehicle to get out of control, and then the power is redistributed after the wheels regain adhesion. Interpretation of full-time four-wheel drive without trailer
For different four-wheel drive structures, there are different points for attention, especially for trailers. We can often see the sign "full-time four-wheel drive, please don't drag" on the back of SUV, so why can't full-time four-wheel drive drag?
In any state, all wheels of full-time four-wheel drive will get power. The abbreviation of "all-wheel drive" is AWD, which is different from 2WD. Full-time four-wheel drive distributes power to four wheels through a flexibly connected central differential and front and rear axle independent differentials. Different from pure mechanical differential lock, the differential of full-time four-wheel drive is mostly hydraulic coupler or multi-disc clutch. The two methods have one thing in common, that is, the speed difference between the front and rear axles and the left and right wheels can be allowed. Whether it is a full-time four-wheel drive depends entirely on the structure of the transfer case.
Full-time four-wheel drive vehicles always maintain the form of four-wheel drive during the whole driving process, and the torque output by the engine is distributed to the front and rear axles in a fixed proportion. This driving mode can always maintain good off-road ability and handling performance. It has greater traction in all kinds of road conditions. However, the torque distribution cannot be adjusted according to the road conditions, and the fuel consumption is relatively high.
Understand the connotation of full-time four-wheel drive, and then see how the trailer was towed away. Trailers can also be divided into many ways, such as pulling trailers (using ropes), lifting trailers (lifting front wheels or rear wheels), and flatbed cars (putting all cars on flatbed cars). There is naturally nothing to pay attention to with a flat trailer, because it is no different from a car parked on the ground. We are talking about lifting the trailer, because the front or rear wheels of the car will still move on the ground, so be careful.
Full-time four-wheel drive can't trailer, which means hanging the trailer. This is a common trailer method used by traffic police teams. The two front wheels are lifted and the rear wheel falls on the trailer. Because all four wheels of the full-time four-wheel drive are driving wheels, when being towed, the four wheels are still connected through the transmission shaft. No matter which set of wheels is installed on the trailer, the other set of wheels will rotate due to friction and rolling with the ground. The most direct consequence is that the central differential is broken. The faster the speed and the longer the distance, the greater the damage to the full-time four-wheel drive.
The gears in the full-time four-wheel drive central differential are connected with the front and rear axles of the car. Generally, when towing, the front wheel is suspended and the rear wheel touches the ground, which will result in the speed difference between the front and rear axles and the torque will be concentrated on the central differential. If it is a multi-disc clutch central differential, it will generate a lot of heat. Because the car doesn't run, the heat can't be dissipated, which will cause the central differential to burn out. If it is a gear-type central differential, such as a Torsten differential, it will cause damage to the turbine worm.
The correct traction method of full-time four-wheel drive is that four wheels must leave the ground. One is to lift the car with a flatbed, which is also the most commonly used method, and ordinary trailers can do it. If the model is too long and the trailer is too small to carry the car, then the rear wheel can also be used.
Million car purchase subsidy