What is x drive. xDrive all-wheel drive: four generations of operation algorithm

Almost all automakers have all-wheel drive versions in their model lines. For the most part, only crossovers and SUVs have all-wheel drive. But there are also manufacturers who offer an all-wheel drive system on conventional passenger cars- sedans, station wagons. It is noteworthy that only branded companies, including BMW, are engaged in the release of such models.

At the same time, each of these manufacturers has its own patented all-wheel drive technology. For Bavarians, this is the xDrive system. It is worth noting here that this is not something special and unparalleled. The general concept of all-wheel drive is identical for all cars, and the patenting of certain systems only secures the right for some specific design solutions.

General concept

The first BMW models equipped with all-wheel drive appeared in 1985. At that time, such a class as a “crossover” did not yet exist, and this manufacturer was not engaged in SUVs. But appreciating the success of all-wheel drive Audi versions, the Bavarians decided to install all-wheel drive on cars of their two series - 3 and 5. Such a system was optional. That is, of the entire rather extensive line, only some versions were equipped with all-wheel drive, and even then - for a surcharge. In order to somehow designate cars with such systems, an “X” index was added to their name. Subsequently, this index grew into xDrive.

It is noteworthy that the xDrive all-wheel drive is not aimed at increasing the cross-country ability of the car, because an SUV will still not work out of a station wagon and a sedan. Its main task is to provide better handling and vehicle stability.

xDrive all-wheel drive device

The overall concept of all-wheel drive in BMW is classic, that is, it consists of:

• transfer box;
• drive shafts;
• Main gears of two bridges.

The list did not include differentials, because they are not so simple. BMW designers have constantly improved this type of drive, refining it and abandoning some constructive solutions for the benefit of others.

Drive designation

In general, with the advent of all-wheel drive versions and to the present, 4 generations of systems can already be counted. But the official name xdrive" she received only in 2003, with the release of the 4th generation, and before that everything all-wheel drive models marked with an "X". In 2006, the xDrive system became the main one, all others were abandoned. But the “xDrive” designation has completely taken root, which is why many motorists even call earlier generations xDrive all-wheel drive.

It is noteworthy that with the release of each subsequent generation, not only the design changed, but the type of all-wheel drive itself gradually changed.

The xDrive system is positioned by the automaker as permanent all-wheel drive (" full time"), but it is not such, it is only marketing ploy. It already belongs to the “On Demand” type, that is, with automatic connection second axis if necessary. And that's all previous versions were referred to as "Full Time", but they were used on a limited number of models, while xDrive is available for almost the entire line of models, from sedans to full-size crossovers.

1st generation

As noted, the first all-wheel drive BMW appeared in 1985. The 4WD used then provided a constant supply of torque to the wheels of two axles, while the system was asymmetric, the distribution along the axes was 37/63.

Separation along the axes was carried out by a planetary differential, to block which a viscous coupling was used. This design allowed, if necessary, to apply up to 90% tractive effort on any of the bridges.

The rear axle differential was also equipped with a blocking viscous coupling. But ahead, no locking mechanisms were used, the differential was free.

1985 4WD iX325 Model

Despite the supply of traction to both axles, models with such a drive system were considered rear-wheel drive by default, since the torque on rear axle served directly. The rotation of the front axle was carried out due to the power take-off by a chain-type transfer case.

The “weak point” in the first all-wheel drive system used by BMW was the viscous couplings, which were far inferior in reliability to the Torsen locks used by Audi.

The first generation systems were installed on the 3 Series E30 325iX sedan, station wagon and coupe. Their production continued until 1991.

2nd generation

In 1991, the 2nd generation of the drive appeared - asymmetrical, with a 36/64 distribution. The Bavarians began to install it on sedans and station wagons of the 5th series (E34 525iX). At the same time, in 1993, the system was modernized.

Model E34 525iX

Prior to the modernization of the system, a differential lock installed between the axles was used electromagnetic clutch controlled by the ESD system unit. The front end was also not equipped with any kind of blocking mechanism. The differential of the rear axle was blocked by an electro-hydraulic clutch. Due to the use of two clutches, it was possible to almost instantly distribute thrust between the axles with a ratio of up to 0/100.

After the upgrade, the design of the system has changed. The electromagnetic multi-plate clutch, which was controlled by the ABS unit, continued to be used as a central differential lock.

The use of locks on the main gears was completely abandoned, the differentials both front and rear were made free. But there was an imitation of a rear axle lock, the role of which was performed by the ABD (Automatic Differential Brake) system. The essence of its functioning is very simple - by means of wheel speed sensors, the system detected slippage and activated brake mechanism to slow down the slipping wheel, thereby transferring the moment to the other wheel.

3rd generation

In 1998, the 2nd generation was replaced by the 3rd. This type of all-wheel drive was also asymmetric, distributing power in a ratio of 38/62. They were equipped with models of the 3rd series (E46) in sedan and station wagon bodies.

This generation of all-wheel drive was different in that all differentials (center, wheel) were free. At the same time, there was an imitation of blocking the main gears by the system.

In 1999, the first crossover X5 appeared in the BMW model line. Its design also used the 3rd generation system. At the crossover, all differentials were free, but the cross-axle ones were blocked by the ADB-X system, in addition, the downhill motion control system, HDC, was also activated.

The 3rd generation of all-wheel drive on the 3rd series models was used until 2006, but it was replaced on the crossover in 2004. With this, the era of differential 4WD "Full Time" for BMW ended, and they were replaced by xDrive.

4th generation

The main feature of this type of drive is that the use of a center differential was completely abandoned. Instead, a multi-plate friction clutch was installed, controlled by a servo.

Handout xdrive box with drive gears used on passenger cars

In normal driving mode, the distribution of traction is carried out in a ratio of 40/60. But in a fraction of a second, it can change up to 0/100. The system is fully operational automatic mode, and there is no option to turn it off.

How xDrive works

Rotation is constantly applied to rear axle, that is, a car with such a drive is actually rear-wheel drive. In this case, the servo drive, due to the system of levers, presses friction discs center clutch, which allows you to take power and apply it to the front axle drive shaft.

If necessary, the servo drive changes the degree of pressure of the discs, changing the torque split. It either fully compresses them, providing a 50/50 transmission, or releases them, interrupting the supply of torque to the front.

Transfer case xDrive with chain drive for crossovers

The operation of the servo drive is controlled by a whole complex of systems, which ensures the redistribution of thrust between the axles in very short periods of time - 0.01 seconds.

For my work xDrive uses systems:

• Office undercarriage ICM. Its task is precisely to synchronize the drive with other systems;
• dynamic DSC stabilization (exchange rate stability). It not only manages the division of traction between axles. The system also "manages" and imitation of the differential locks installed on the main gears, slowing down the slipping wheels.
• Steering AFS. It provides stabilization of the car during braking, in which the wheels move on surfaces with different coefficients of friction.
• Traction control DTC;
• Help when driving downhill HDC;
• Redistribution of traction between the wheels of the rear axle DPC. It carries out "steering" when driving corners.

The main advantage of xDrive is its comparative design simplicity. The absence of mechanical differential locks greatly simplifies the drive unit and makes it very reliable.

Also, to change the parameters of functioning, it is not necessary to redo something in the design, it is enough to make changes to software drive control systems.

Key Benefits xDrive systems operationally are:

• Variable stepless torque sharing between the axles;
• Constant control over the behavior of the car and instant reaction to a change in the situation;
• Security high performance car handling;
• High accuracy of functioning of the brake system;
• Vehicle stability at different conditions movement.

Thanks to the used friction clutch with an electronic control system, the xDrive system has a number of operating modes that adjust the drive to the driving conditions:

• Smooth start of movement;
• Entering corners with oversteer;
• Driving in corners with understeer;
• Moving around slippery road;
• Parking in confined spaces.

Each mode has its own specific features. Yes, at startup friction clutch provides a redistribution of moments between the axles in a 50/50 ratio. This provides a dynamic set of speeds. But after reaching 20 km / h, the system starts to change the ratio depending on road conditions. The average ratio is 40/60, but this can quickly change if the electronics detect a change in conditions.

When entering a turn back the car begins to skid (oversteer), the servo instantly compresses the clutch discs, providing 50% of the thrust and more to the front, so that it begins to “pull out” the rear axle of the car from skidding. If these measures are not enough xDrive starts to use other systems to stabilize the car.

In the event of a drift of the front during a turn (lack of understeer), the drive, on the contrary, reduces the moment on the front axle up to its complete shutdown and, if necessary, still activates the stabilization systems.

When driving on slippery surfaces, xDrive makes the car all-wheel drive, providing up to 50% of traction to the front and including auxiliary systems.

In parking mode, as well as when driving at a very high speeds(over 180 km / h), the servo cuts off the supply of rotation to the front, making the car completely rear-wheel drive. This has its drawbacks, especially during parking. Due to the disengagement of the front, the car cannot always overcome even small obstacles (curbs) if the coating is slippery and the rear slips.

The disadvantage of xDrive is that it takes time to connect the axis, albeit a little. That is, the system includes front axle only after the skid has already begun. This can be somewhat disorienting for the driver, and he will take the wrong action.

The "weak" point in the very design of the xDrive all-wheel drive is considered to be a servo. But the constructors took care of this by placing this node with outside transfer box allowing quick replacement or repair.

Finally

The xDrive system is so well established that it is offered for everything model range– versions from the 1st to the 7th series, a number of cars equipped with 8-cylinder power plants(550i, 750i), and is also installed on all X-series crossovers.

Note that for sedans, station wagons and coupes, the system is structurally different from the crossover drive. The difference between them lies in the transfer case. In passenger cars, it is of a gear type, and in crossovers, it is of a chain type.

So far, the Bavarians are in no hurry to change the xDrive drive, because it is really good and works great. Therefore, all developments regarding the drive are just improvements. performance indicators, the design is not affected, because why redo something that functions perfectly.

Autoleek

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 thanks to 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 different electronic control differential with 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, with the help of indications 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 as on cars BMW Series 3, 5 and 7, and on crossovers X1, X3, X5, X6.

By the way, in automotive world Rumor has it that a new fifth generation of this all-wheel drive will soon be introduced.

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 electronic unit. And works very closely with others electronic assistants thanks to integrated 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 change. pavement And different regimes ride.

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% forward, 60% rear wheels )

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, all-wheel drive is configured so that it allows experienced drivers to fool around a little, allowing a slight skidding 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, it is much easier for the driver to cope with difficult environment 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 as a BMW it is fully justified.

With the xDrive system on the car, there is a different level of car experience. Can you feel more confident difficult areas roads.

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

xDrive - the inscription on BMW cars is put for a reason or some small addition, this is the first indicator of a difficult drive in a car. Consider the principle of operation and the history of occurrence.

The content of the article:

Good control over the forces that interact on the car while driving is the first thing you need to be safe while driving. Such aspects are taken into account by BMW engineers in the first place when developing a new model.

xDrive lettering on front fender BMW car put not casually, this is not a minor tuning or some specific addition. Such an inscription indicates that all-wheel drive is installed in the BMW.

The beginning of the existence of the xDrive system

BMW car specialists distinguish 4 generations. Rumor has it that in 2017, engineers want to introduce a new generation of all-wheel drive.

First generation
The xDrive all-wheel drive system dates back to 1985. The torque was distributed according to the principle: 63% was allocated to the rear axle and 37% to the front axle. The composition of such an all-wheel drive included a locking of the center and rear wheel differentials with the help of a viscous clutch.

It often happened that inexperienced drivers they forgot how to use the system, and it quickly broke down. But still, those who used BWM cars without xDrive and with this system stated that the difference in driving was significant.

Second generation
The beginning of the second generation xDrive falls on 1991. This time the distribution has changed a little, now 36% fell on the front axle and 64% on the rear wheels. center differential blocked by a multi-plate clutch on electromagnetic control. The rear cross-axle differential is locked using a multi-plate clutch based on electro-hydraulics. Thanks to this innovation, it was possible to redistribute the torque between the axles in any ratio from 0% to 100%.

Many motorists say that it was from this generation that many BMW cars began to be equipped with the xDrive system. Yes, and driving a car with such a system has become pleasant and safe. At one time, these machines began to be in great demand and quickly gained a positive reputation.

third generation
1999 was the beginning of the third generation xDrive. Torque distribution on the axle at normal driving became 62% on the rear and 38% on the front axle, and the inter-wheel and inter-axle differentials became free. Blocking of cross-axle differentials is carried out electronically, and a system of dynamic control of the vehicle's course stability appears to help with all-wheel drive.

fourth generation
In 2003, allocate last generation xdrive systems. Torque is distributed in a ratio of 60% to the rear axle and 40% to the front axle of the BMW. The center differential is carried out using a multi-plate friction clutch, and controlled electronically. Torque distribution is still possible from 0 to 100%. The cross-axle differential lock is electronic, due to which it interacts with the vehicle's Dynamic Stability Control (DSC) system.

fans brand bmw they say that thanks to such an xDrive system, cars have appeared with good cross-country ability, directional stability, and as a result, safety has improved.

The xDrive system is used for BMW vehicles with a rear-wheel drive transmission. Torque is distributed between the axles thanks to the transfer case. From itself, it represents a gear train on the front axle, which is controlled by a special, functional clutch.

But there is a nuance, in SUVs sports type instead of gear train torque chain is used.

We can say that xDrive is a set of several mechanisms and interaction electronic systems management. For example, in addition to the already named dynamic stability control system, the DTC traction control system is additionally used, as well as the HDC descent assistance system.

Such systems help xDrive correctly determine and distribute the load on the axles of the car, while maintaining full control without driver assistance. As you know, in such cases, at the slightest human factor, an error can pop up, and this can lead to unpredictable consequences.

All these systems are interconnected using ICM (Integral Vehicle Chassis Management) and AFS (Active Steering). Thanks to this interaction, the driver will fully feel the dynamics of the car and be confident in every movement of the steering wheel.

How xDrive works

The main task of xDrive can be called good cross off-road, driving slippery surface, passing sharp turns, parking and pulling away. It's not yet full list, where xDrive can help, as the automation itself calculates the axle load and torque distribution.

As an example, consider a few induced situations. Starting off, with normal conditions the clutch will be closed and the xDrive torque will be distributed in a ratio of 40% to the front axle and 60% to the rear axle. Thanks to this distribution, the thrust is evenly distributed around the entire perimeter of the machine. There will also be no wheel slip, which means that tires last longer. When the car reaches a speed of 20 km / h, xDrive torque will distribute according to road conditions.

When going through tight corners at speed, the xDrive situation is proportionately different than pulling away. The load will be on the front axle to a greater extent. The friction clutch will close with more force, and the torque will be distributed more to the front axle to get the car out of the turn.

To help xDrive, the DSC Dynamic Stability Program will be included, which, due to the braking of the wheels, will change the load on the vehicle's trajectory.

In a situation when driving on a slippery road, xDrive will remove wheel slip by blocking the friction clutch and, if necessary, center lock using electronics. As a result, the car will smoothly pass obstacles and easily get out of snowdrifts or wetlands.

As for the parking situation, the whole point of the xDrive system is aimed at facilitating. Thus, the lock is removed and the car becomes rear-wheel drive, which reduces the load on the steering wheel and front axle. As a result, the driver will be able to park effortlessly, and xDrive will facilitate this process.

Difficulties in using systems xDrive new there is no generation at all, since all electronics will decide for you.

Video about the principle of operation of the xDrive system:

xdrive- original system intelligent all-wheel drive developed by BMW. Although this system refers to permanent all-wheel drive, at its core it retains the classic rear-wheel drive transmission scheme for BMW, i.e. under normal driving conditions and road surface conditions, the car behaves predominantly as a rear-wheel drive. But if necessary, part of the torque is instantly transferred to the front wheels. In this way, the system constantly monitors the state of the car's movement, continuously distributing power between the axles in an optimal ratio. As a result, the xDrive system provides exceptional handling and dynamics when cornering and driving on slippery roads.

History of creation and development of the system

Proprietary system of complete BMW drive xDrive was officially introduced in 2003. Up to this point, its predecessor was a scheme with a constant distribution of torque between the axles in a fixed ratio. Initially, all-wheel drive was offered as an option for the rear-wheel drive models of the BMW 3 and 5 series of the 80s. The history of the development and improvement of BMW all-wheel drive systems has four generations.

All-wheel drive BMW model iX325 1985

1st generation

1985 - All-wheel drive system that distributes torque constantly in a ratio of 37:63 for the front and rear axles, respectively. The rear and center differentials were rigidly blocked when slipping by viscous couplings, the front differential was of a free type. Used on the 325iX model.

II generation

1991 - permanent drive with a power ratio between the axles of 36:64, with the possibility of redistribution to any axle up to 100% of the torque. was carried out using an electromagnetic multi-plate clutch, rear differential blocked by a clutch with an electro-hydraulic drive, the front one is free. In its work, the system took into account the readings of the wheel speed sensors, the current engine speed and the position of the brake pedal. Used on the 525iX model.

III generation

1999 - four-wheel drive with a constant power distribution in the ratio of 38:62, all differentials are free with electronic locking. The system functioned in conjunction with the dynamic stability control system. This all-wheel drive scheme was applied on the first generation X5 crossover and showed excellent results both when driving on asphalt, and in lung conditions off-road.

IV generation

2003 – intelligent system xDrive all-wheel drive was introduced as part of standard equipment the new model X3 and the updated model of the 3rd series E46. To date, xDrive is installed on all models of the X series, optionally - for all other BMW models, except for the 2nd series.

System elements

• in a housing with a multi-plate clutch that performs the function of an interaxle differential.

• Cardan gears (front and rear).

• Cross-axle differentials (front and rear).

Scheme of the all-wheel drive system BMW xDrive

Multi-plate friction clutch

Servo Driven Multi-Disc Friction Clutch

The function of power distribution between the axles is performed by a transfer box located in the body and driven by a servomotor. Depending on the model of the BMW car, a chain or gear type of drive may be used. driveline front axle. The clutch is activated by the command of the control unit and in a fraction of a second changes the ratio of torque transmission along the axes.

How the system works

At its core, the xDrive system uses a rear-wheel drive transmission scheme. Driving in normal mode provides for a torque distribution in the ratio of 40:60 (for front and rear axles). If necessary, on the axis with better grip with the road surface, the full power potential can be transmitted. xDrive works in harmony with all integrated systems active safety, including Active Steering and Vehicle Stability Control.

System operating modes

• Start of movement : differential locked, power between the axles is distributed in an optimal ratio of 40:60, at speeds above 20 km / h, the torque ratio is determined by the system based on current driving conditions and the road surface.
• Oversteer: when the xDrive system detects that the rear axle is moving outward from the pivot point more power redirected to the front axle; connected if necessary dynamic system directional stability, braking right wheels and leveling the car.
• Understeer: When the steering system registers the front axle away from the center of rotation, up to 100% of the torque is applied to the rear axle, and the stability control system helps to stabilize the vehicle if necessary.
• Driving on a slippery road: The torque is distributed electronically to the axle with the best grip, preventing slippage.
• car parking: all power is redirected to the rear axle, making it easier for the driver to control and reducing the load on the transmission elements.

Scheme of the xDrive system

Based on the readings of numerous sensors, the control electronics are able to accurately recognize the tendency of the car to drift when cornering or the imminent loss of traction of the wheels with the road surface. The system also takes into account the current parameters of the engine, the speed of the car, the speed of the wheels, the angle of their rotation and the lateral acceleration of the car. This allows you to proactively calculate and change the balance of power distributed between the axles in a fraction of a second. The stabilization of the car occurs on the verge of losing control, while maintaining traction and dynamics. The stability control system is activated at the last moment in the event that the intelligent all-wheel drive has not coped with the task.