Transfer Case ( popular name – transfer box) – unit for the distribution of torque from the engine to several drive mechanisms, which in most cases also increase the number of gears in the transmission.
The Functions Of The Transfer Case
- Distributes torque between the driving axles in such a way as to ensure the best throughput of the vehicle without the occurrence of a negative phenomenon – “power circulation” in the transmission;
- Increases the torque on the driving wheels within the limits necessary to overcome the rolling resistance of the wheels when driving on bad roads and off-road, and also on steep slopes (see the multiplier );
- Provides a steady movement of the car at low speed when the engine is running at maximum torque.
Full transfer cases today are used on a lot of all-terrain vehicles, as well as military equipment. Both front and all-wheel drive crossovers and cars (sedans, coupes, etc.) are often equipped with a unit that combines the properties of a gearbox and transfer case. This node is called in English Transaxle, and outwardly quite easily distinguishable – the semi-axles and the propeller shaft (if any) come out directly from the gearbox housing. The descending gear range is missing in this case.
Types Of Transfer Cases
- Fully automatic: Switching drives occur with the help of servo drives or a hydraulic switch; switching decisions are made by electronic machine control systems. In common parlance, this is called electronic all-wheel drive. A huge plus is the correct distribution of traction in various road and off-road situations. The disadvantage is dependence on electronics, electrics, and hydraulics, as well as a weighting of the machine. The most interesting examples are “ 4-matic ”, “ Quattro ” and “ X-drive ” handouts. Electronic handouts are relevant not so much outside as on the road, especially if they are combined with electronic brake force distribution systems. For example, when braking from high speed, the electronic transfer box is capable of disabling the rear-wheel drive, passing braking force to it, while the front-wheel-drive continues to pull the car, thus maintaining straightness even on ice. At the same time, such transfer case may refuse, for example, as a result of soaking, therefore it is not particularly suitable for overcoming fords and similar off-road conditions.
- Semi-automatic: Semi-automatic transfer box differs in that the driver can intervene in the management of drives with the buttons on the dashboard. On the one hand, this makes it possible to forcibly turn on or off a necessary or unnecessary drive, on the other hand, it can distract the driver at an unnecessary moment, which may entail an accident. The most interesting examples of similar types of handouts are Kia Sorento and Mohave, some modern Jeep cars (Grand Cherokee III, IV, for example), Mitsubishi Pajero Wagon (III, IV), Nissan Murano and Pathfinder, also corresponding Infiniti models and a number of other similar cars.
- Manual: The governing body of such transfer box is an additional lever, usually located between the driver and passenger seat. A huge advantage of this transfer box is almost complete reliability and independence from electronics, in the off-road world there are many cases where you could safely manage bridges with a flooded cabin, but the disadvantage is the almost complete inability to switch on the go, and also not always convenient switching leverage. Carriers such transfer case is almost the entire family of UAZ, such trucks as the Urals and the marsh version of KAMAZ, MAZ and other competitors, both domestic and foreign production. Also, the transfer box manual can be found on the « Nissan Patrol, Jeep cars (from the moment of foundation and still on some models), “ Pajero ” of the first and second generations. Interestingly, the third-generation Pajero Wagon also has a massive gearshift lever in the above-mentioned location, but in reality, it is only a stylized joystick for electronic selection of the necessary gears.
- Simple (Non-Switchable): Also referred to as “permanent four-wheel drive”, that is a transfer box, in which there is no switching to the front or rear axle. A huge advantage of such a transfer box is its complete reliability, the absence of extra holes in the body for controls, that is, the lower probability of interior flooding when overcoming a ford, a clear disadvantage of such a transfer case is the inability to shut off extra drives in normal road conditions, which creates an extra load on the engine fuel consumption and complicates driving a little on the road. The most famous examples of such systems are “ Toyota Land Cruiser ” including “ Prado ”, “ Niva ”, “ Outlander ”, and also on such sports sedans as, for example, “ Subaru Impreza” And Mitsubishi Lancer Evolution. The sports “fast” versions of the third and fourth generation SRT-8 cars of the Jeep Grand Cherokee are also equipped with such transfer cases. In this case, the manufacturer logically assumed that these machines are not intended to leave the paved roads, and they do not need weighting and complication due to the addition of a downward row, so they left only four-wheel drive (On Demand system – rear with front axle connection).
6 Common transfer box problems
- Oil leaks. It can be both through the glands, and along the hull joints. In the case of the glands, you should not only replace them but also check the integrity of the seats under the glands – they can have cavities or cracks, through which oil can also go, even if the gland is in good condition. You should also inspect the surface, which fits lip gland – if it is on the development or grooves, the new seal will also become unusable. Backlash bearings, shafts or flanges also leads to the fact that the lip of the gland is deformed and becomes unable to maintain tightness. If the leak passes through the body joints, the transfer case must be disassembled right down to the leak location, cleaned, degreased, and then apply high-quality sealant using the instructions for its use.
- A noise in bearings. Determined during operation and when listening to individual components in the process of vehicle diagnostics at service stations. Manifested in motion by a constant howling, there may be sounds of frequent light strikes. Worn bearings should be replaced.
- Stretching the torque transmission chain. Typical transfer boxes have a straight shaft from the gearbox to the rear universal joint, and approximately in the middle of the shaft, the torque is transmitted through a Morse chain to a parallel shaft leading to the front universal joint. The stretched chain causes itself to slip relative to the gear teeth on which it sits. Best of all, this can be understood by turning the wheels all the way in all directions and abruptly moving off. A ringing crack from the transfer case will indicate that the chain is stretched. In the most neglected cases, the chain sags so much that it grinds off the gear teeth, and also begins to wipe the casing of the transfer case.
- Worn center differential. Their surfaces are constantly subjected to friction, and poor-quality lubricant or its absence, solid foreign particles like sand or metal crumbs damage the differential for several dozen kilometers. To trap the steel abrasive in the transfer cases use a magnetic liner, which is usually located at the bottom of the transfer case, near the oil intake tube.
- Worn electromagnetic clutch connecting the all-wheel drive. Some transfer boxes for the convenience of the user are equipped with an electromagnet, which, when turned on, engages an open torque transmission circuit, and the all-wheel-drive appears. The copper braid of electromagnets is sensitive to abrupt loads, which often leads to failure of the all-wheel-drive connection mechanism.
- Worn viscous coupling. The loss of control in corners, unstable passage of irregularities, low-frequency creaks in the transmission, presents itself as in uneasy cases uneven tire wear becomes the most obvious. When removing one of the drive shafts (if possible), the symptoms disappear completely. Worn viscous coupling should be repaired or replaced.
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