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All about the system of full drive

Full drive – the design of automotive transmission, which transmits the torque produced by the motor on all wheels. At first, this system has only been used for all-terrain SUV. But, since 80-ies of the last century, became widely used by many manufacturers to improve road characteristics of the produced cars.

The main advantages of four-wheel drive transmission are:

The main drawback of such transmission is the complexity of the design, which entail a high cost base and the cost of repair. In addition, it leads to a slight increase in fuel consumption.

According to the principle of functioning of system of a full drive is distributed on:

 Diagram of a full drive

Permanent all-wheel drive

System operating on the principle of permanent all-wheel drive, consists of the following structural elements:

Such a design of transmission can be applied regardless of the location of the engine and the gearbox (link). The main differences between such systems among themselves are caused by application of different types of cardan transmission and transfer box.

From the engine torque is transmitted to the transfer case. In a box with interaxle differential is its distribution between the front and rear axle of a car. So, first moment passes on the drive shaft, which is transferred through the gear and межколесные differentials. Through axis differentials transmit torque to the wheels. In case of non-uniform motion of the wheels, caused by entering the turn or exit, on a slippery surface, it is locked down interaxle and cross-axle differential.

The most well-known designs transmissions with permanent all-wheel drive system are Quattro Audi, BMW xDrive, 4Matic from Mercedes.

Quattro was the first serial analogue transmission with permanent all-wheel drive for sedans. She appeared in 1980. This system is designed for installation in a longitudinal arrangement of the engine. After several upgrades are widely used in modern Audi models.

System xDrive was developed by BMW for use in its own sports off-road vehicles and passenger cars. She appeared in 1985. In the last upgrade in the xDrive have integrated a few modern systems that turned it into an active transmission.

4Matic – all-wheel drive transmission, developed by Mercedes. It was introduced in 1986. In our time, is installed on several models of cars of the German manufacturer. A distinctive feature is the possibility to use only совместительстве with automatic transmission.

 The scheme of permanent all-wheel drive

Full drive is connected automatically

Normally, such a system consists of the following elements:

Transmission with an all-wheel drive is the most popular among all-wheel-drive systems. Nearly every manufacturer has a model that uses a similar design. It is perfectly suited for use on passenger cars, as it can provide a full drive, when you need it, but it is much cheaper transmission with permanent all-wheel drive.

System with an all-wheel drive is activated when there is slipping of wheels of the front axle. In normal condition, the torque from the engine is transferred to the main axis via the clutch transmission and differential. In addition, through the transfer box moment passes on the main element management system – a friction clutch. In normal rectilinear movement of the clutch transmits only 10% of torque to the rear axle, and the pressure it remains minimal. In the case of wheel slippage of the front axle, the clutch is increased, and carries moment from the engine to the rear axle. Depending on the intensity of sliding front wheels, the degree of transmission of torque to the rear axle may vary.

The most famous transmission with an all-wheel drive is designed Volkswagen system 4Motion. It is used in the construction of cars of concern since 1998. In the latest version of 4Motion as a work item is used Haldex.

 Diagram plugin-wheel drive

Full drive plug-in manually

In the classic version of the system has virtually the same construction as transmission with permanent all-wheel drive.

Modern vehicles have this type of transmission is not applied. This system has very low efficiency. Its only advantage it provides the torque distribution between the axles at a ratio of 50 to 50, which is not available in any other form of transmission. Therefore, it is considered to be ideal for high-end SUVs.

Principle of operation of the transmission with manual connecting wheel drive is similar system with permanent all-wheel drive. The only thing manage the transfer box are available directly from the passenger compartment using a special lever.

One of the most serious weaknesses of – the impossibility of its use for a prolonged period of time. This means that it can connect temporarily at hit on a slippery or wet surface, but then you should immediately disable it. Long-term use of this drive leads to the increase of vibration, noise and fuel consumption.