All-wheel drive bmw x3. BMW xDrive all-wheel drive: X-factor

The xDrive system is permanent all-wheel drive on BMW vehicles. It is based on the distribution of torque between the front and rear axles of the machine.

The rear axle drive is permanent. Traction is transmitted to the front axle through an electronically controlled clutch located in the transfer case. The xDrive system does not use a center differential. In the normal state, the couplings on the axles are partially engaged. The distribution of torque between the front and rear axles is 40/60. The system can continuously change the torque ratio from 50/50 to 0/100 on either axle in just 100 milliseconds, depending on which axle has the best grip. Climbing uphill on a slippery road, or going down a steep slope, the system itself, without driver intervention, selects the bridge and distributes the load so that the car has better grip and reduces wheel spin.

Thanks to the fact that the xDrive System works together with the DSC Dynamic Stability Control, the car behaves just as well in the city, where agility usually comes to the fore. So when skidding, the clutch is completely closed, and the thrust is distributed equally between the axles. The thrust applied to the front axle levels the car and distributes the load back after the maneuver is completed, imperceptibly for both the driver and passengers, that is, the system is preventive. With understeer, on the contrary, lowering the torque, the thrust is transferred to the rear axle, preventing the front wheels from leaving the lane.

If the distribution between the axles does not give the desired result, the DSC system brakes individually for each wheel, leveling the car. In addition, the DSC system reacts to the difference between the grip of the left and right wheels, which can lead to slip, and brakes the desired wheel separately, additionally providing the function of the cross-wheel lock. When starting off, the multi-plate friction clutch has a 50/50 distribution up to a speed of approximately 20-30 km/h. This helps to use the maximum traction in this mode. At high speed, the clutch is fully disengaged and the car behaves like a rear-wheel drive.

The interplay of xDrive, DSC and chassis is provided by ICM (Integrated Chassis Management). In a fraction of a second, it coordinates all functions with each other and gives a command to perform a specific operation. ICM also ensures that individual systems do not interfere with each other's work. Thanks to speed data collected from wheel sensors, engine parameters, lateral acceleration, xDrive recognizes the traffic situation and optimally distributes the moment between the rear and front axles.

For every BMW, the DSC system can be deactivated by the driver. This will be done for lovers of sports driving style. But the xDrive system's all-wheel drive system cannot be disabled. The perfection of the xDrive system does not allow losing a kilowatt of machine power due to poor grip.

The structure of the BMW xDrive system

The German concern BMW developed its own xdrive all-wheel drive system in the last century, but the system is constantly being improved and is still being installed on many models of the concern. Optimize driving as efficiently as possible and at the same time keep all indicators under control, entrusted to this particular system. Today, the xDrive all-wheel drive system is installed on the new generation of BMW SUVs:

• Sports Activity Vehicle x 6.

In addition, systems of this development are also installed on BMW passenger models, on the 3rd, 5th and 7th series. The system has proven itself well over the twenty-five years of its existence, and therefore the concern does not plan to abandon its use.

Main characteristics of the system

The xdrive intelligent all-wheel drive system controls the action of all forces in the car, both acting on it from the outside and its own. Traction and dynamism are distributed in a completely new way thanks to the action of this development. To make it clear what is at stake, some characteristics of the system should be given:

• It provides variable torque distribution of stepless nature. Thanks to this, the torque is distributed evenly between the rear and front wheels, increasing their speed many times;
• The system intelligently recognizes a change in the situation and, if necessary, redistributes the torque incredibly quickly;
• xDrive provides incredibly responsive steering so the driver doesn't have to make any effort while driving;
• The system very accurately doses and regulates braking, thanks to which the operation of the concern's vehicles has become even safer;
• The system includes elastic shock absorbers and elements that, due to their sensitivity, optimize and control vertical and longitudinal dynamic force moments;
• The system provides incredible stability and dynamic movement on any road surface.

From these characteristics, it becomes clear that BMW has done everything to make driving a four-wheel drive car completely safe and enjoyable for the driver. The machine, provided with the xDrive system, has tremendous power, but at the same time shows incredibly intelligent obedience to control. Years of work and continuous improvement of technology, the concern has ensured that the car equipped with the xDrive system has gained incredible variability and precision in response to the control message. The system adapts the drive forces in any situation, optimally adapting them to the situation and effectively improves driving dynamics.

In simple terms, the xDrive system intelligently adapts the all-wheel drive vehicle to the needs of the driver.

Four-wheel drive

Many manufacturers have all-wheel drive, but only BMW has xDrive. Traditionally, all-wheel drive is mainly aimed at minimizing the inconvenience caused by road surface, bumps, ground or ice. But if the efforts are distributed unevenly or inefficiently along the axes, then all-wheel drive will not bring driving pleasure. Characteristic of such an inefficient distribution will be the following management weaknesses:

• Limited sensitivity to steering wheel turns;
• Driving performance becomes insufficient;
• Rectilinear motion becomes unstable;
• Lost comfort when maneuvering.

But in the BMW concern, the issue of creating a new generation of all-wheel drive was approached in a completely different way. As a basis, the manufacturers took the proven and well-proven rear-wheel drive of the concern's cars. Having optimized and improved its characteristics, they were distributed to all four wheels.

And for a quarter of a century, BMW all-wheel drive has shown incredible dynamics and complete safety on the roads around the world.

What makes the system efficient

As mentioned above, the basic principle of the xDrive system is to evenly distribute torque to both vehicle axles. Such an efficient and precise distribution is made possible with the help of a transfer case, which has the form of a gear drive of the front axle. The box is controlled during the operation of the friction clutch. If the xDrive system is installed on a BMW sports utility vehicle, then the transmission is replaced by a gear-type transmission with a chain.

In addition, the efficiency of the system and additional options that are being introduced into the transmission along with it are significantly increased:

• Dynamic exchange rate control system;
• Electronic blocking of the differential moment;
• Traction control system;
• Downhill assistance system;
• Integral management system of running department;
• Active steering system;
• Basic principles of the system.

The BMW intelligent system has its own characteristic modes, which are determined by the friction clutch:

• Smooth starting off;
• Overcoming turns with excess type turnability;
• Overcoming turns with understeer type;
• Movement on slippery surfaces;
• Optimized parking.

When the vehicle starts in normal location and road conditions, the friction clutch is closed and the torque in this case has a distribution along the axes of 40:60, this leads to the most efficient traction during acceleration. After the car picks up a speed of 20 km / h, there is a redistribution of torque depending on the surface of the roadbed and control points.

Passing turning points

During oversteer maneuvers, the rear axle of the BMW may skid to the outside of the corner. To avoid this, the friction clutch carries out the closure with greater force, while the front axle takes on the torque. If the car goes through a very sharp turn, an angle that is not standard enough, then the dynamic control system comes to the rescue and stabilizes the movement with the help of some braking of the wheels.

If the vehicle is understeered in a corner, where the front axle is likely to skid to the outside of the corner, the friction clutch will disengage. In this situation, one hundred percent of the torque is distributed to the rear axle. If a non-standard situation arises, then the motion stabilization system enters the process.

When the car passes a corner with a non-standard steering pattern, the front axle of the car is skidded to the outside of the corner. In this case, the friction type clutch releases and 100% of the torque is distributed to the rear axle. If the car is not leveled, then the stability control system takes over.

When the vehicle is moving on a slippery road surface covered with water, people or snow, individual wheels may spin and the vehicle will skid. To prevent this from happening, the friction clutch is blocked, and if the situation does not come to stability, then an auxiliary system setting of dynamic directional stability comes into play.

The parking of a car equipped with the xDrive system concept occurs with a complete opening of the friction type clutch. In this case, the vehicle completely switches to the rear-wheel drive state, and thereby effectively reduces the transmission loads during steering. Reasonable and intelligent intervention of assistance systems when driving creates optimally comfortable driving conditions and increases driving safety many times over.

Not really

The xDrive all-wheel drive system is the best on the market - a firm opinion of BMW fans.

Let's look at why this xDrive is good, what generations exist, and most importantly, how it affects the car's habits.

Before starting to consider the history of this system, I would like to note that it was not created for off-road, but for confident movement on slippery and snowy roads.

Ideologically, it is based on the legendary BMW handling, which is achieved through rear-wheel drive. The developers tried to keep the habits of the car rear-wheel drive.

So, at the moment there are four generations of xDrive:

1. The foundation was laid in 1985 and was the control of the interaxle, as well as the interwheel rear differential using a viscous coupling. The torque ratio is 37% front, 63% rear. When blocking the viscous coupling, the moment was divided equally;
2. Then the second generation entered the market, in 1991. And it was distinguished by electronically controlled differential using multi-plate clutches. The default ratio was 36:64, but it became possible to transfer up to 100% to one of the axes;
3. Since 1999, the third generation has declared itself, BMW already receive free differentials. Blocking control is assigned to the brakes, using the readings of electronic sensors. It becomes possible to interact with the exchange rate stability system. The standard ratio is 38:62 and the ability to transfer all the torque to the front or rear axle is retained;
4. In 2003, the next generation enters the market, a feature of which is the complete integration of electronic components and assistants into a single vehicle system. Differentials have acquired electronic locking mechanisms. The thrust is redistributed in a ratio of 40:60, and if necessary, in a fraction of a second, the moment is transferred to one of the leading axles.

XDrive is installed both on BMW 3, 5 and 7 series cars, as well as on X1, X3, X5, X6 crossovers.

By the way, in the automotive world they say that a new fifth generation of this all-wheel drive will soon be presented.

How BMW xDrive All-Wheel Drive Works

Engineers from Bavaria have created an assistant for rear-wheel drive cars.

This drive provides control on slippery roads and improves stability at higher speeds.

This is what distinguishes xDrive from other systems and, in particular, from the main competitor - at AUDI.

In its most recent reincarnation, this type of all-wheel drive is fully controlled by an electronic unit. And cooperates very closely with other electronic assistants through integral control.

xDrive comes to the aid of stability and stabilization systems, as well as a traction control system.

And thanks to the tuned mechanisms to quickly and smoothly change the torque on the wheels, the car is always ready for changing road surfaces and different driving modes.

There are several basic algorithms for the operation of the all-wheel drive system:

• start of movement;
• demolition of the front axle;
• skidding of the rear axle;
• driving on a slippery road;
• parking mode.

Remarkably, at the beginning of the car, when the speed has not reached 20 km / h, the clutch is closed. That is, all the wheels are in contact with the road, the traction at the start of the car is maximum.

After 20 km/h, the clutch returns to standard torque mode (40% front, 60% rear)

XDrive solved the problem of the speed of operation of the controlled clutch. Now it works in milliseconds and transfers the torque to the desired axis (up to 100%).

And in the same milliseconds, it returns the engine thrust to its original position - (40% to the front and 60% to the rear axle).

The xDrive system recognizes the quality of the road in hundredths of a second and instantly distributes the torque. And it is on the wheel that has the best grip on the road.

xDrive operation while driving

When the front axle skids, the transmission transmits more torque to the rear wheels, thereby stabilizing the car.

In addition, xDrive can smoothly change the traction between the wheels of the rear axle, increasing the controllability of the machine even more in a critical situation.

When the rear axle is skidding, the four-wheel drive acts in a similar way, only now more effort goes to the front wheels and the front pulls the car, as it were, returning it to the correct trajectory.

At the same time, the all-wheel drive is configured in such a way that it allows experienced drivers to fool around a little, allowing a slight skid of the rear axle, of course, within reason.

When driving on ice, snow or mud, the full potential of xDrive is used.

It uses both DSC stability control and a friction clutch that instantly redistributes torque between the front and rear axles.

Thanks to the sensitive response of this advanced drive, the driver is much easier to cope with difficult conditions under the wheels.

He does not even feel the intensive work of the system, which ensures safe movement in difficult road conditions.

In addition, if this four-wheel drive does not cope and there is not enough traction, other nodes responsible for safety are connected to work.

For example, a machine may be forced to reduce its power to prevent dangerous situations.

But it is worth reiterating that xDrive is not designed to conquer formidable off-road. Its destiny is safety, which includes stability and handling at high speeds, as well as forgiving some driver mistakes.

SUV he is SUV.

When driving at low speeds (car parking) with xDrive, the front axle is completely disabled in order to reduce the effort on the steering wheel and reduce stress in the transmission.

At the end of the article, we can safely say that all-wheel drive on cars is needed. Of course, it increases the cost of the car, since the system is very complex, but on premium brands like BMW, this is fully justified.

With the xDrive system on the car, there is a different level of car experience. You can feel bolder on difficult sections of the road.

Driving such a car is a real pleasure. And the feeling when most cars barely move in winter, and you drive like on dry asphalt, is generally priceless.

I hope you were interested, but it will also be interesting to read how Mercedes engineers solved such a problem and embodied it in

The xDrive all-wheel drive system is a development of the BMW concern and belongs to permanent all-wheel drive systems. The system provides stepless, continuous and variable torque distribution between the front and rear axles depending on driving conditions. The xDrive system is currently installed on sport utility vehicles ( SAV, Sports Activity Vehicle) X1, X3, X5, X6 and cars of the 3rd, 5th and 7th series.

The history of the development of all-wheel drive from BMW includes four generations:

The xDrive all-wheel drive system basically uses the traditional BMW rear-wheel drive transmission scheme. The distribution of torque between the axles is carried out using a transfer case, which is a gear drive of the front axle drive, controlled by a friction clutch. In the transmission of sport utility vehicles, a chain drive is used instead of a gear train.

The xDrive system is integrated with DSC (Dynamic Stability Control). In addition to the electronic differential lock, the DSC system integrates the DTC (Dynamic Traction Control) traction control system, the HDC (Hill Descent Control) descent control system, etc.

The interaction of the xDrive and DSC systems is carried out using the ICM (Integrated Chassis Management) system. The ICM system also provides links to the AFS (Active Front Steering) active steering system.

How the system works

In the operation of the xDrive all-wheel drive system, several characteristic modes can be distinguished, determined by the friction clutch operation algorithm:

• starting off;
• cornering with oversteer;
• cornering with understeer;
• movement on slippery surfaces;
• parking.

When starting from a standstill, under normal conditions, the friction clutch is closed, the torque is distributed along the axes in a ratio of 40:60, which achieves maximum traction during acceleration. Upon reaching a speed of 20 km / h, the distribution of torque between the axles is carried out depending on road conditions.

When cornering with oversteer (the rear axle skids to the outside of the turn), the friction clutch closes with more force, and more torque is directed to the front axle. If necessary, the DSC system is activated, which stabilizes the movement of the car by braking the wheels.

When cornering with understeer (the front axle drifts to the outside of the turn), the friction clutch opens, and up to 100% of the torque is directed to the rear axle. If necessary, the DSC system is activated.

When driving on slippery surfaces (ice, snow, water), slipping of individual wheels is prevented by blocking the friction clutch and, if necessary, the electronic wheel lock of the DSC system.

During parking, the friction clutch is fully opened, the car becomes rear-wheel drive, which reduces the load in the transmission and steering.