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[YesAuto four-wheel drive detailed] In this episode of “Fun Four-wheel Drive”, let’s talk about BMW’s four-wheel drive technology. There are currently 5 BMW SUV models on sale in China, including BMW X1, BMW X3, and BMW X4. , BMW X5 and BMW X6. What are the differences in the performance and structure of these four-wheel drive systems? We will tell you through tests.

BMW X1 model introduction:

BMW X1 2014 xDrive28i X design package

Model Homepage| Parameters Configuration| Picture| Word of Mouth| Model Quotation
Manufacturer's guide price

43.60 million

The BMW X1 is currently the only domestically produced SUV in the BMW “X” series. At present, BMW X1 is divided into 18i, 20i and 28i, among which there are two types of sDirve and xDirve according to the different driving modes. Among them, sDirve is a front-rear drive version, used on the 18i series, xDirve is a four-wheel drive version, used on some models of 20i and 28i, our test is the xDrive 28i design package version, which is powered by a 2.0T turbo The supercharged engine has a maximum power of 245 horsepower and a maximum torque of 350 N·m.

The BMW X1 is equipped with a full-time four-wheel drive system that distributes power to the front axle by a transfer case and a multi-disc clutch. The front and rear axle wheels are all open differentials, which are biased towards the rear-wheel drive. The power of the rear wheels comes directly from the input of the drive shaft, while the front wheels use a multi-disc clutch-type limited slip differential and transfer case to achieve power transmission. In addition, the entire DSC electronic stability system can also achieve the limited slip function between wheels.

Power distribution test between front and rear axles and cross axle test

The test of the two sets of pulleys is relatively simple, and does not form a big test for the performance of the front and rear axle power distribution. Whether it is the loss of adhesion of the two front wheels or the two rear wheels, there is no problem for it, and it passes smoothly without difficulty.

The cross-axle project tests the performance of the four-wheel drive system. Two pulley blocks are placed on the front and rear axles to simulate the situation of one wheel slipping on the front and rear axles. At this time, the vehicle is required to have the ability of limited slip between the wheels to be able to successfully escape. . BMW X1 can achieve limited slip between wheels through electronic auxiliary braking, helping the vehicle to successfully get out of trouble.

Single wheel landing

Single-wheel landing, this test is to make the three wheels of the vehicle lose their adhesion, and only rely on one wheel to get out of trouble. It is the most difficult test item in the four-wheel drive test. First of all, we made the BMW X1 a rear wheel with adhesion. During the whole process, it can be seen that the electronic auxiliary system has been working. When the front wheel is braked, the driving force of the single rear wheel is sufficient to make the vehicle out of trouble.

However, after we installed pulley blocks on the two rear wheels and one front wheel, the situation has changed. Although the electronic assistance system can brake the rear wheels and the front wheels can also obtain a certain driving force, the front axle The wheels on the ground have been slipping and the grip is insufficient, and the vehicle has not successfully escaped.

According to our analysis of the above situation, BMW is a full-time four-wheel drive system that is more biased towards the rear drive. Under normal road conditions, the power distribution of the front and rear wheels is 40:60. In extreme cases, the power of the engine can be 100% transmitted. To the rear wheels, the power input of the front wheels is transmitted through the multi-disc clutch and transfer case. Theoretically, the front axle can only be allocated up to 50%. Therefore, we can see in the test that the BMW X1 has a different ability to escape under these two different states.

● Introduction to BMW X4 models

BMW X4 2014 xDrive35i M Sport

Model Homepage| Parameters Configuration| Picture| Word of Mouth| Model Quotation
Manufacturer's guide price

77.40 million

BMW X3 and BMW X4 are built on the same platform as BMW. Except for the appearance of BMW X4 with Coupe styling, the interior and powertrain are exactly the same as BMW X3. Therefore, we only selected the BMW X4 35i M sports model for testing. It is powered by a 3.0L inline 6-cylinder twin-scroll single-turbocharged engine with a maximum power of 306 horsepower and a maximum torque of 400 N·m. , Matching 8-speed automatic transmission.

The four-wheel drive system of the BMW X4 is also a set of full-time four-wheel drive based on rear-wheel drive. The structure is exactly the same as that of the BMW X1. The four-wheel drive system does not have any control buttons in the car and is completely controlled by the vehicle itself, but if you want to get For greater power to get out of trouble, you can consider setting the driving mode to “SPORT+” mode before the test. The power output of the engine in the early stage is significantly more aggressive.

Power distribution test between front and rear axles and cross axle test

When the two sets of pulleys test the power distribution between the front and rear axles, when the two front wheels or two rear wheels are on the ground, the four-wheel drive system of the BMW X4 can quickly respond and switch the power, whether it is two front wheels on the ground or The two rear wheels landed on the ground, and it was very easy to get out of trouble.

In the test of the cross-shaft project, the power distribution between the wheels mainly relied on the DSC dynamic stability control system to brake the slipping wheels. The performance of the BMW X4 was also quite good. The power was more smoothly transferred to the adherent axles, and the whole escape process was not difficult. .

Single wheel landing

Single-wheel landing is the most difficult test, and it is also the focus of our test. We first land a front wheel of the BMW X4. The BMW X3 is a four-wheel drive model based on the rear drive, so theoretically the rear axle can get 100% power, while the front axle is only 50% at most. In the actual test, when a single front wheel hits the ground, we found that the effect of electronic limited slip is still relatively obvious. The slippery tire has obvious braking effect, and the front wheel with grip can obtain power, but it is limited by the BMW X4 1.92 tons The self-weight of the car and the tire's own grip are insufficient. The front wheel with grip has slipped like the situation encountered by the BMW X1 just now, which eventually caused the vehicle to be unable to “get out of trouble”.

Next, we let the single rear wheel land on the ground, and the situation has changed significantly. The landed rear wheel can also obtain obvious power output, and there is basically no slipping. After some struggle, it successfully escaped. In the later stage, we analyzed the reasons why the single rear wheel can successfully get out of the trouble. In addition to the BMW rear wheel can get more power, the tire size is also one of the reasons. The BMW X4 35i M sports front wheel tire size is 245/ 45 R19, while the size of the rear wheel is 275/40 R19, the tread is wider and the grip is stronger.

Although compared with the BMW X1, the BMW X4 cannot get out of trouble based on the single front wheel landing, but the power system of the BMW X4 is much stronger, which makes up for the lack of performance of the four-wheel drive system. We can clearly feel that the wheels on the ground have The power output is only limited by the insufficient grip of the tires, which fails to push the vehicle out of trouble.

● Detailed explanation of BMW X6 models

BMW X6 2015 xDrive35i exclusive type

Model Homepage| Parameters Configuration| Picture| Word of Mouth| Model Quotation
Manufacturer's guide price

117.30 million

Like X3 and X4, we also only chose BMW X6 for testing on BMW X5 and X6. BMW X6 can be described as the top model in the X series. At first, our expectations for it were relatively high. After all, we were doing the same level of Mercedes-Benz M-Class. During the test, all the tests were passed. This time we chose the BMW X6 xDrive35i for the test. The power is equipped with a 3.0T turbocharged engine with a maximum power of 306 horsepower and a maximum torque of 400 Nm. It is matched with an 8-speed automatic transmission.

The four-wheel drive system of BMW X6 is slightly different from BMW X1, X3, X4, etc. The rear axle of X6 adds a set of DPC dynamic power distribution system (multi-disc clutch) on the basis of ordinary xDrive open differential to achieve The power distribution of the left and right rear wheels further enhances the performance of the vehicle's sportiness and handling. In fact, the hardware configuration of the BMW X6 is relatively lacking compared to the Mercedes-Benz M-Class of the same class. The Mercedes-Benz M-Class not only has a low-speed torque amplification gear, but also has a multi-road condition adaptation system for the top model.

Power distribution test between front and rear axles and cross axle test

◆ Three sets of open pulley block test

Although the BMW X6 adds a dynamic power distribution system (DPC) on the basis of xDrive, this design is entirely for road sports performance and handling performance services, not for off-road design, so the BMW X6 still can only rely on points to get out of trouble. The power output before and after the adjustment of the gearbox and the use of electronic systems to limit the slip between the wheels to help the vehicle get out of trouble. According to the actual results, when the single front wheel touches the ground, the power allocated to the front wheel is obviously insufficient, and it can't push the body at all. It is a sign of getting out of trouble, and when the single rear wheel hits the ground, it is the same situation. After struggling for a while, he barely passed the test. This kind of performance is basically at the bottom of its class. In fact, the BMW X5 and BMW X6 are indeed more suitable for driving on urban paved roads, and off-road is not its best job.

◆ Advantages and disadvantages of BMW X series four-wheel drive system:

Advantages: daily driving tends to be rear-drive, driving fun and good road performance. When there are special road conditions, the computer will automatically distribute the power of the front and rear axles, which is convenient and easy.

Disadvantages: The electronic system is not specifically designed for off-road. The main consideration is to adjust the road performance. The limited slip ability between wheels is limited, and the ability to escape difficulties is average.

Edit summary:

After completing the four-wheel drive test of the BMW X series, we can clearly see that the mechanical structure of the BMW X1/X3/X4/X5 is basically the same, while the X6 and X5 (optional DPC) have added DPC systems, but off-road The performance has not been significantly improved. We also consulted relevant BMW staff in the later period. They said that the electronic limited-slip mechanism was re-adjusted on the basis of the existing structure, and the problem of passing the test should not be big. This shows that for BMW, handling and sportiness are what they really pursue.