Car four-wheel drive works according to a completely understandable principle - the torque is distributed through the transmission unit between the four drive wheels. This design is very convenient and has many advantages. The main one is unpretentiousness to the type and quality of the road surface. The car shows equally good qualities on an icy track, dry asph alt and primer. In addition, such a unit is not afraid of sharp off-road exits, and on city streets it shows excellent dynamics and no slippage.
But even all-wheel drive does not give a 100% guarantee of the absence of various unpleasant incidents on the roads. Sometimes you can notice an impressive SUV with a huge ground clearance bogged down in a relatively small puddle. Often this is due to the inexperience of the driver or his driving style. However, it happens that the all-wheel drive transmission of the car is simply not designed for extreme tests. For many owners, this raises certain questions. Consider the features of such units and their varieties.
This type of all-wheel drive refers to the novice modifications among analogues. It works on the principlehard connection of the rear axle. In this case, all wheels rotate at the same speed indicator, the differential between the axles is not provided. There is a uniform distribution of torque between all elements. This design does not allow you to coordinate the supply of force at different speeds, except to make your own changes in the transmission unit.
In the traffic flow, it is better not to use the front axle connection. This is especially appropriate if you need to turn around. The problem arises because of the different path lengths of the bridges. Since the revs are distributed equally between the axles, the excess power is only manifested through wheel slip on one of the axles.
Pros and cons
Manual all-wheel drive is appropriate to use for frequent driving on rough terrain or off-road. Even if the wheels slip, there will be practically nothing to interfere with them due to poor grip on the surface. When driving on a dry hard surface, the power will have nowhere to go. Because of this, the transmission unit is subjected to increased loads, excessive wear of the rubber occurs, and controllability and directional stability at high speed are also lost.
For rough terrain, a car with manually connected all-wheel drive is quite appropriate. The bridge is activated immediately and hard, without the need to block anything. The design of such a unit is as simple as possible, does not contain complex and electronic elements, as well as additional pneumatics andhydraulics.
For the city, the considered version of the system is categorically not suitable, since it is inconvenient to make frequent switching between bridges. And moving with hard four-wheel drive will wear out a number of parts with subsequent damage.
4x4 all-wheel drive is devoid of the shortcomings of its predecessor. All wheels are driven, an independent differential is provided between the axles, which releases excess power by scrolling one of the gear satellites. This solution facilitates the movement of the machine on a permanently connected all-wheel drive. The main feature of this design is the presence of slip. That is, if the vehicle starts to slip on one axle, the second analog is automatically turned off.
In practice, the stop is not as fast as it seems. After turning off one wheel on the axle with the intermediate differential, the center analog turns off the second axle on the machine. As a result, the resulting dynamic process and inertia allow you to overcome several meters with the wheel turned off, which soon turns back on.
A 4x4 all-wheel drive car can stall sooner or later. To save all the operating parameters of an SUV, such machines are equipped with one or two forced center differential locks. The front element is rarely equipped with a factory lock, but it is quite possible to install it yourself.
However, permanent four-wheel drive is also not the standard for the manifestation of ideal driving performance on asph alt. In unforeseen situations, the SUV often pulls into the outer part of the turn, and the handling leaves much to be desired. Correct driving of such vehicles requires the driver to have the appropriate skills and excellent feeling of the car.
To improve handling, center differentials with forced locking are provided. In this matter, different manufacturers have proposed their solutions. The most popular options were the Torsen type system and the viscous coupling. However, these devices have the same task - to improve the controllability of the machine through equipping the differential with a partial lock.
When one of the axles slips, the locking mechanism is activated, preventing the differential from affecting the second axle, regardless of the torque applied to it. Some car modifications were additionally equipped with a similar system on the rear axle, which further improved the quality of control.
Features all-wheel drive with automatic connection
With the development of technology, engineers have developed an all-wheel drive system, introducing into it electronically controlled elements with the redistribution and transfer of torque. As a result, designs of stabilization and course stability, as well as anti-towing units, have been developed. They distribute torque optimally and are activated and controlled electronically. Complex andthe most modern schemes are used on expensive and elite SUVs.
For example, a four-wheel drive automatic transmission can be equipped with steering angle tracking, body roll and speed control, including the ability to take into account the frequency of wheel oscillations over a certain period of time. The on-board computer of the car performs the most complete collection of information about the behavior of the vehicle on the road. The ECU processes the information and corrects the torque transformation between the axles using an electronically controlled clutch. This element has replaced the center differential. This invention has been widely used in modern sports cars. Today, such systems are almost ideal in their behavior, especially if there are sensors and parameters that allow the node to work ahead of the curve.
Pros and cons of all-wheel drive with automatic connection will be considered further. This transmission design is suitable for use on asph alt, as well as dirt tracks with little off-road. This is due to the fact that electronic clutches, with significant slippage, begin to overheat and break. Moreover, for this it is not necessary to cross swamps and sands, 10-15 minutes on ice will be enough. With systematic overload, part failure is inevitable, and this is fraught with costly repairs.
The more "bells and whistles" in the system, the more it is prone to breakdowns. Therefore, before choosing a car, it is necessary to take into account the preferred routes, according towhich it will move. It is worth noting that if the wiring breaks on one of the ABS indicators, the entire system will be reset and will not receive important information from the outside. Also, troubles can happen with malfunctions in the electronics or when filling low-quality gasoline (which does not allow you to shift down).
On automatic and manual four-wheel drive with multiple modes is the most versatile system. It can be activated manually or automatically, forced to disable one of the bridges. The use of such a design does not increase fuel consumption, which is important, especially given the current fuel prices.
Separately, it is worth noting vehicles with selective transmission, which is a permanent four-wheel drive with the ability to disable the front axle. On some SUVs, you can select one of several modes (with automatic, hard lock or low gear activation).
The following is a list of some brands of vehicles with different types of transmission that most productively combine all the features of the nodes:
- Manual models: Suzuki Vitara, Toyota Land Cruiser, Nissan Navara, Ford Ranger, Nissan Patrol.
- Permanent four-wheel drive: UAZ, Lada 4x4, Toyota Prado, Land Rover Defender, Land Rover Discovery.
- Drive with automatic connection: Kia Sportage, Nissan Murano, MitsubishiOutlander”, “Toyota RAV-4”.
- Multi-mode version: Mitsubishi Pajero, Jeep Grand Cherokee.
The permanent all-wheel drive system (Full Time) provides a stable transmission of torque to all wheels of the vehicle. The unit includes a number of characteristic elements and parts: gearbox, clutch, transfer unit, cardan and final drives, inter-wheel and center differentials. The system under consideration can be used on machines with a longitudinal or transverse arrangement of the power unit. Similar nodes differ mainly in the design of the transfer case and cardan gears. More modern analogues with electronics are equipped with a special clutch instead of a differential, but they require careful handling and cost an order of magnitude more expensive.