4matic system: design ,features
In this article we will tell you in detail about the system of full drive 4Matic from the German company Mercedes-Benz.
Modern vehicles have a large power threshold, so it is often not enough for a high-quality grip on the road cover of a single wheelset. Very often there is a slip. In order to increase the acceleration of the vehicle when touching, and to nullify the probability of slip, a system of correct torque distribution between all wheels is used. The presence of a four-wheel drive transmission allows to stabilize the movement and increase the controllability of the car. This has a favorable effect on the safety of driving in ice and when overcoming steep turns.
Features of early full drive systems
It is known that for maximum full drive productivity, several additional assemblies need to be included in the transmission design. But the machine from this becomes only heavier, the level of vibration increases and the level of noise increases. Since the four-wheel drive system has a complex structure, the price of the vehicle is therefore increased. As a result, the costs of maintenance and repair of cars are also increasing. Also, the additional mass of the four-wheel drive machine is the cause of increased fuel consumption.
As this was all difficult and costly until the late 1980s, the four-wheel drive transmission system was used only on off-road vehicles. The use of it on light-weight cars was considered inappropriate and unjustified. However, the situation has changed dramatically since the introduction of the 4matic system.
Constructional features of a system
The 4matic transmission is an automatic four-wheel drive system that was designed by the designers of Mercedes-Benz. It should be noted that the system is branded by the concern and installed exclusively with AKPP on most models.
The system operates according to the following principle: under normal traffic conditions, the leading car is the rear axle. As soon as wheel slip begins (for example, when driving in ice), the front drive is immediately switched on, and thus the car becomes four-wheel drive. Force distribution is performed among all wheels, however, its magnitude is different for each of them.
The control system for connection of the full drive reads readings from the following sensors:
- Determination of the turning angle;
- Brake system sensor.
The basis of the 4matic system design is an upgraded transfer box, which allows for the instantaneous redistribution of all the torque force between the axes of the vehicle. Also, the system device is supplemented with the following units:
- AUTOMATIC TRANSMISSION;
- Main force transmission system;
- Cardan drives of rear and front drive;
- Drive levers equipped with CV JOINTS;
- Front axle differential.
A little story in conclusion
The 4matic system has been developed and improved by Mercedes specialists for five generations. For the first time the first generation 4Matic system was installed on the W124 machine in the second half of the 1980s (1986) of the last century, was automatically included in the operation and had a mechanical unit of differential locking. Four-wheel drive was controlled by two hydraulic couplings. The drive was switched off after ABS was activated.
As the main advantage it is possible to distinguish – fuel economy in the mode of mono-drive. Disadvantages include design complexity and low efficiency in full drive mode.
The second generation of the 4Matic system as a dope company Mercedes began to install in 1997 on the model W210 E-class. By default, they were also tired on ML-ki in the W163 body and on R-class since 2005. The second generation 4matics was already a constant 4WD with three open differentials and simulating their locking using the 4 Wheel Electronic Traction System. Through planetary gear 35% of thrust is distributed to front axle, 65% to rear axle. In the score to the second generation of the system it is possible to put – simplicity of design and in contrast to the first generation good indicators of cross-country capacity. As a downside – increased fuel consumption, because in constant operation all 4 wheels.
In 2002, the third generation of 4Matic appeared on cars C, E and S- classes in the bodies of W203, W211 and W220, respectively. In fact – it was all also the second generation, but brought to mind by adding electronic assistants affecting the simulation of locks. These include ESP stabilization systems, ASR anti-slip, DSR descent control, 4ETS traction control, and ABS. Depending on the car model, the thrust distribution between the axles varied:
- Passenger cars, except for the S-class, and for light crossovers – 40% transfer axle/60% transfer axle;
- 50% by 50% for ML, GL and R classes;
- 45% by 50% for S- and V-classes;
- For Mercedes AMG – 33% by 67%.
What is the design feature of the third generation full 4Matic drive system? The main structural element of the system is the transfer box, which continuously distributes torque along the axes of the car. In addition, the transfer box is a place of interaction of the double planetary reduction gear, cylindrical gears and drive shafts. Drive shaft is connected with carrier of planetary reduction gear. Rear axle drive shaft rotates from larger-diameter sun gear. Drive shaft of front axle is hollow and connected with small-diameter sun gear.
The fourth generation appeared in 2006 on S550 and W204 cars. This generation is a further development of the last two. A cylindrical differential is used, “under-locked” by an unguided two-disc frictionless that distributes the input torque between the axles in a proportion of 45% front axle and 55% rear axle. When accelerated on a uniform slippery coating, the friccion blocks the interaxial differential, adding a stability car. In case the torque difference between the front and rear axles exceeds 50Nm, the friction slips. Operation of traction control is provided by 4ETS system with the help of service brakes. ESP, ASR, and 4ETS electronic assistants in the new system are calibrated to operate as late as possible, making it possible to maximize engine power.
The fifth generation of the 4Matic system appeared in 2013 on CLA 45 AMG and Mercedes-Benz GL 500 cars and is an on-demand 4WD (not permanent, but plug-in u/p) system on a front-wheel drive architecture with a transversely mounted front-end motor. The front and rear differentials are open, there is no interaxial differential. The set of electronic systems is the same, simulation of locks is also provided by 4ETS. The power take-off unit (PTU) built into the dual clutch 7G-DCT robotic transmission is used to take power to the rear axle. The PTU turned out to be very compact, and it has a common lubrication system with the box, saving up to 25% of the weight. In normal conditions torque is distributed between front and back axes in proportions from 100/0 to 50/50. So, at acceleration of the car with full load at a speed of 50 km/h the ratio changes on 60/40, at fast passings of turns becomes 50/50, at loss of coupling with the road of front wheels – 10/90, in case of sharp braking with ABS – 100/0. Moment redistribution is achieved due to variable compression ratio of interaxle coupling.