SUVs have gradually become a car purchase trend, and SUVs equipped with four-wheel-drive systems are often a bonus. In addition to SUVs, we can see four-wheel drive systems in some cars or wagons, such as the Cadillac CT6 that has just been launched. Audi A6   Allroad et al., we call these four-wheel-drive vehicles collectively as four-wheel drive vehicles. However, the four-wheel drive technologies of different models and different brands are also quite different. The average consumer simply understands the four-wheel drive as the driving force for all four wheels. Four-wheel drive has strong and weak points, there are differences between nobles and have their own areas of expertise. Consumers who choose four-wheel drive vehicles must be more concerned about their ability to go bad. Do you understand the characteristics of each four-wheel-drive system when choosing a car and what features do you really want? Today, we will take a look at the basic principles and composition of the mainstream brand four-wheel drive technology in the market.

Four-wheel-drive technology varies, how much do you know?

Take a look: the number of differential locks

If you want to quickly identify the skill of the four-wheel drive to take the bad road, grab one point: differential lock. The ability of a four-wheel drive vehicle to pass or fall depends on the number and type of differential locking devices they are equipped with. That is, if a wheel slips, the vehicle can completely deadlock the slippery wheels. The loss of power, and the ability to selectively allocate power to wheels that do not skid, determines its ability to pass.

Therefore, we can basically determine the off-road ability of the car from the number of differential locks. Such as the Jeep Wrangler, Mercedes-Benz G-Series, Land Rover Defenders, Nissan Petrol, etc., have used the front, middle, rear three differential locks, even in extreme cases, as long as there is a wheel with adhesion, they have to go out on their own The possibility of difficulties. The CR-V, RAV4, Outlander, Maverick, Pajero, X5, Q7, Prado, etc., all use only one differential lock, and the terrain that can be dealt with is relatively limited.

Of course, the more differential locks, the higher the cost and the more difficult the design is, especially for some hard-core SUVs. Driving them, walking on the road, you can't be very comfortable. You lock them in four-wheel drive. You may even find that they will hardly turn because they don't allow the slightest slip between the wheels. Even when turning, there are a few inside and outside wheels. With poor speed, they also think that there are wheels that are slipping and they are prohibited. Therefore, in paved roads, not their world, only in places with poor adhesion, they walk more stable. There, when turning, the wheels on the far side of the road were dragged away, but because of the low adhesion, you did not feel the resistance of the drag, nor did it cause any major wear on the tires.

Second look: differential lock type

In addition to the number of differential locks, the type of differential lock also determines the car's off-road capability. Differential locks are hydraulically coupled, torque sensitive, electro-hydraulic, and toothed, with different types of locking capabilities.

Hydraulic coupling type differential lock

Representative models: Honda CR-V, Toyota RAV4, Mitsubishi Outlander, Ford Maverick

At present, many four-wheel drive vehicles use hydraulic coupling differential lock because of its simple structure and convenient layout. Such as CR-V, RAV4, Outlander, Wing Tiger, B9 and so on. Hydrodynamic coupling differential lock has a characteristic: not very sensitive, there is hysteresis in the lock, that is, after a period of time when the wheel slips, it realizes that the lock is needed, and the locking ability is limited, and the impact is large when it is involved. Therefore, vehicles using this equipment do not pay special attention to off-road, but rather improve the passage and stability of vehicles on ice, snow, and gravel.

●Toson differential

Representative models: Audi Q7, Land Rover Range Rover

For torque-sensitive differential locks, we are familiar with the Tosen differential, the most famous Audi Quattro, and Land Rover Range Rover also use it. Its advantage is that the reaction is very sensitive. It takes advantage of the physical characteristics of mechanical gears to generate locks. The locking is very linear. It can lock in the moment of skid, and at the same time redistribute the driving force, so the passability is relatively high. It feels very smooth. Its only drawback is that it cannot lock 100% of the skid wheels. The distribution of driving force can only vary between 25% and 75%. For extreme off-road, it needs to use other types of locking differentials. Of course, the Q7 and Range Rover now have integrated EDL electronic differential locks, which can apply braking force to each wheel electronically to help achieve the purpose of locking. Although the role is limited, it still improves the overall passability.

●Electrohydraulic friction type differential lock

Representative models: Volvo XC90, BMW X5, Toyota Prado, Acura MDX, Jeep Cherokee, Porsche Cayenne, Volkswagen Touareg

This differential lock integrates computer functions, uses sensors to detect wheel slip, and drives an electric motor to control the hydraulic linings to lock and release the differential. Its response is also very fast. The locking range of the wheel is 0-100%. Theoretically, it has good off-road capability. In particular, the Grand Cherokee, Cayenne, and Touareg are equipped with three such differential locks that can cope with many difficulties. However, this is only theoretically, any SUV with too many electronic control devices is not a good thing for off-road, especially after wading through water, rocks, and shrubbery. The reliability of these electronic control devices is really hard to guarantee. .

●Indented differential lock

Representative models: Land Rover Defender, Jeep Wrangler, Mercedes-Benz G, Lexus LX570, Toyota Land Cruiser, Mitsubishi Pajero

The indented differential lock rigidly locks the differential through gears. The jaws feature only two states, either locked or released. Once locked, it is extremely fierce, especially the Wrangler, Mercedes-Benz G, Land Rover Defenders, etc., using three jaw differential locks, can rely on any one wheel forward. Compared with the other three differential locks, the toothed differential lock has a disadvantage that it does not allow the wheel to have a slight difference in rotational speed. On the road, the differential lock must be released, otherwise it is difficult to turn.

Three Looks: Rear Bridge Limited Slip Differential

In fact, many four-wheel drive models on the market are not equipped with rear axle limited slip differential. When the current wheel slipped, the central differential allocated power to the rear wheels. If one of the rear wheels is also slipping, what should be done? If you don't have very high requirements for the off-road performance of your vehicle, then a car with a differential lock will suffice. If you want your car to be able to handle more complex off-road conditions, then choosing a model with a rear limited-slip differential becomes necessary. When one of the rear wheels slips, the rotation of the pinion in the rear axle limited slip differential will apply pressure to the multi-plate clutch on the low speed side of the friction. At this point there is more torque on the side with friction.

Contrast 1: What is full-time, time-sharing, and timely selection?

● Full-time four-wheel drive

The so-called full-time four-wheel drive can be understood literally, that is, it is a four-wheel drive vehicle at any time. There are three differentials in the full-time four-wheel drive system: one for each of the front and rear axles and a central differential between the front and rear drive shafts. When the car is turning, the difference between the speeds of the front and rear wheels can be controlled by the central differential. Therefore, the full-time four-wheel drive vehicle can run on all roads including paved roads. Although this kind of driving mode has better off-road and maneuverability, it can't adjust the torque distribution according to the road conditions, and the fuel consumption is large and the economy is poor.

● Time-sharing four-wheel drive

The so-called time-sharing four-wheel drive is that the driver can select the driving mode, that is, two-wheel drive or four-wheel drive mode can be selected according to different road conditions. The time-sharing four-wheel drive system generally has a transfer case in the middle of the front and rear axles, which can harden the front and rear axles. connection. Because there is generally no central differential in the transfer case, it cannot be driven on paved roads after being attached to a four-wheel drive because it cannot turn smoothly when cornering. Of course, some manufacturers of the transfer device is equipped with a central differential (such as Mitsubishi and other manufacturers), but also can drive in the four-wheel drive mode. The advantage of time-sharing four-wheel drive is that it can ensure the power and passability of the vehicle, and can also take into account the fuel economy. The disadvantage is that the driver needs to determine the road conditions and select the manual operation drive mode.

● timely four-wheel drive

Timely four-wheel drive, also known as real-time four-wheel drive, is to automatically select the drive mode based on the road conditions. Compared with the full-time four-wheel drive, the timely four-wheel drive structure is simple and fuel-efficient; compared with time-sharing four-wheel drive, timely four-wheel drive is simple operation. However, the shortcomings of the timely four-wheel drive are equally obvious. At present, most timely four-wheel drive systems transmit power unevenly on the front and rear axles and cannot transmit more than 50% of the power to the rear axle. They can't easily control the harsh road conditions.

Contrast 2: Main Brand Four-wheel Drive Technology Competition

Nowadays, all kinds of four-wheel-drive vehicles are numerous. Nearly every depot has its own four-wheel-drive vehicle. Many depots have established their own four-wheel-drive brands. Different brands of four-wheel drive technologies have their own characteristics.

● Mercedes-Benz: 4MATIC

Mercedes-Benz's 4MATIC is actually just a collective name. Different models are not the same, simply look at the difference between the three differential locks, S and GLK do not, just rely on ABS and a multi-chip central differential to complete the torque distribution Mercedes-Benz called it 4ETS, the comfort of this four-wheel drive system is still very commendable, especially with the S-class air suspension; to GL this semi-road vehicle will have two differential locks, in special circumstances Can be locked, provides a very good off-road performance, to a G-class this textbook off-road vehicle on the front and rear in the three differential locks are all, and after all locked really is very powerful, plus the whole The car tends to off-road design, and has a superior rotting ability.

● BMW: xDrive

The main feature of xdrive is that it is specifically designed for dynamic driving performance. It is also an electronically controlled multi-disc clutch. In its publicity, it will often see such a word “fast”. Indeed, the response of electronic systems is very fast. It will be judged. The xdrive began to redistribute power before the vehicle reached its limit state, and with the help of the xdrive and DTCDSC, these two sets of electronic systems, the driver's driving experience was truly extraordinary. The xdrive is driven to the rear drive in everyday driving and has good road performance for driving pleasure. When there are special road conditions, the computer will automatically distribute the power of the front and rear axles, which is convenient and easy. The disadvantage is that the system is not designed for off-road design. The main consideration is to adjust the performance of highways, and the limited ability to slide between wheels is limited.

● Audi: Quattro

Audi's Quattro core is very different from BMW's. Its core is a fully mechanically adjusted differential, asymmetric dynamic torque distribution, and self-locking. And the difference is that unlike the BMW Benz, the Quattro was not originally used in civilian cars. It was taken off the track. It was characterized by stability and safety in normal driving, and it also had some off-road capabilities. And it is very stable and durable. After all, this is the inherent advantage of mechanical systems over electronic systems. The superiority of the Quattro four-wheel drive in terms of performance is largely due to the superiority of the Tosen differential. The pure mechanical work of the Tosen differential is fast and accurate, and it is a true high-speed off-road ride. Drive the commanding heights of technology. However, this mechanism requires very high processing accuracy, manufacturing process, and high-strength materials to ensure its performance, so the cost is very high. This is Quuttro's small defect. Although it is not easy to be bad, if it is to be changed, It's not a small money.

● Acura: SH-AWD

SH-AWD is a set of advanced electronic torque distribution four-wheel drive system, in addition to the free distribution of the front and rear wheel drive force 30% to 70%, but also to achieve the independent drive force distribution between the left and right rear wheels, left and right wheel drive The force distribution can be steplessly controlled from 100:0 to 0:100, allowing the cornering to be more flexible and stable, and due to the high precision of the electromagnetic clutch, the wheel slip control can be finely adjusted and the fuel consumption is also more economical.

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