[WapCar] The four-wheel drive metioned above is also divided into different forms, which mainly refers to four-round intervention time. Form this classification, at present the four-wheel in the market can be divided into three forms, that is full-time four-wheel drive, part-time four-wheel drive, timely four-wheel drive.
一、Full-time four-wheel drive
Representative technology: vertical engine Volkswagen 4MOTION, Audi quattro, Mercedes-Benz 4MATIC, etc.
Technical characteristics: fast reaction speed, strong ability to escape
Full-time four-wheel drive is called full-time all-wheel drive, abbreviated as AWD, 4WD, etc. As the name implies, all wheels of the vehicle will get power in any state. Compared with two-wheel drive and part-time four-wheel drive, timely four-wheel drive that we will introduce below, the full-time four-wheel drive vehicle has stronger ability to pass obstacles and faster reation speed. Therefore, full-time four-wheel drive is widely used in military and racing fields.
二、Part-time four-wheel drive
Installed model: Jeep Wrangler, Toyota FJ Cruiser, Landwind X8, Haval H5, etc.
Technical characteristics: strong reliability，switching between different modes needs manual operation, relatively low reaction speed, can not be used on paved roads
Part-time full-wheel drive is the four-wheel drive system that the driver can choose between two-wheel drive and four-wheel drive, the driver switches two-wheel drive or four-wheel drive mode through turning on or off transfer case according to the road condition, and this is also the commonly used four-wheel form of many "hardcore" off-road vehicles.
The method of realizing four-wheel drive is that the output power of the engine transmitted to the front and rear axle through transfer case, the switch between two-wheel drive, high-speed four-wheel drive and low-speed four-wheel drive is realized by transfer case. The part-time four-wheel drive vehicles have 2H (high-speed two-wheel drive), 4H (high-speed four-wheel drive), 4L (low-speed four-wheel drive).
In addition to supper-selected four-wheel of Mitsubishi brand, the general part-timen four-wheel drive transfer case does not have the center differential, after the four-wheel drive is connected, the front and rear axle are rigidly connected, and the power is distributed at a fixed radio. Since the turning radius of front wheel is bigger than the rear wheel on the same side when the vehicle is turning on the paved road, the speed of front wheel is faster than the rear wheel, and the front and rear axle have different speed, the phenomenon "turning braking" will appear. This situation will cause damage to transfer case, differential, transmission shaft and wheels, so the four-wheel drive mode is only suitable for using on snowfield, slippery roads or off-road, when driving on paved roads should be changed to two-wheel drive mode.
Althought it has the advantages of simple structure and high stability, and its shortcomings are also obvious, that is, the vehicle owner must stop and operate maually when the mode is switched, and the operation steps are complex. When encountering bad road conditions it can not respond rapidly, then will often miss the best time to get out of trouble. At the same time, because there is no center differential, the four-wheel drive system can not be used on paved roads and can not turn smoothly in corners.
三、Timely four-wheel drive
Installed model: Honda CR-V, Toyota RAV4, Nissan X-Trail, Mazda CX-5, etc.
Technical characteristics: compared with part-time four-wheel drive, mode switching is smarter
Timely four-wheel drive is the four-wheel drive system that the vehicle will use four-wheel drive only in suitable time, it is still two-wheel drive system in other situation. Compared with full-time four-wheel drive, the timely four-wheel drive has simpler structure is more suitable for the models equipped with front-transverse engine front drive platform, which makes it possible for the SUV or cars built on this platform to be equipped with four-wheel drive system.
Timely four-wheel drive will automatically switch two-wheel drive or rour-wheel drive according to the driving condition of the vehicles, without manual operation. Compared with part-time four-wheel drive system, this four-wheel drive system eliminates complicated manual operation, but its shortcoming is that when the front and rear axle transmit power, they are restricted by the defect of the structure itself and can not transmit more than 50% power to the rear axle. There are also many timely four-wheel drive system adopt open differential between the front axle and rear axle, when driving on some complex roads, when two wheels on one side slipped, the vehicle can not get out of trouble, so it can't do anything when encountering complex off-roads.
Besides it's worth noting that with the development of science and technology, the current four-wheel drive classification has become gradually "fuzzy". For example, in structure the four-wheel drive is full-time four-wheel drive, but it can be switched through stop lever to realize the function of part-time four-wheel drive, Mitsubishi Pajero is an excellent example.The super-selected four-wheel structure installed on it allows the vehicle owner freely switch 4H and 2H gears when the vehicle speed is below 100km/h. In other words, you can understand it as the addition of the high-speed four-wheel that can drive on paved roads on the basic of traditional hardcore part-time four-wheel drive system, so the rigorous judgement of four-wheel drive system is no longer 100% be applicable.