- What is four-wheel drive
- Types and types of all-wheel drive
- Four-wheel drive: design and operation
- Which four-wheel drive is better
- All-wheel drive benefits
- Cons of 4x4 drive
When a motorist chooses a new car, one of the indicators that is often paid attention to is what kind of drive the supposed "favorite" has. There is an established opinion among motorists that an efficient car must have a 4x4 chip.
Given the popularity of four-wheel drive vehicles, automakers produce off-road vehicles and crossovers from assembly lines, in which the transmission ensures the rotation of all wheels. Consider what modifications of this mechanism are, and most importantly: is it really practical to have a car with all-wheel drive?
What is four-wheel drive
All-wheel drive means a car in which all wheels are driving. The torque is evenly distributed by the transmission, which gives the machine increased flotation.
Four-wheel drive involves the use of additional units that transmit forces to each wheel. In this case, both axles of the vehicle work. Such a unit is more often used in models that often overcome off-road conditions. However, it is not uncommon for an ordinary passenger car on the trunk lid to have the coveted Quattro or 4x4 plate.
Types and types of all-wheel drive
Although there are many different modifications of all-wheel drive transmissions, there are only two main ones. They differ from each other in the type of connection of the additional axis. Consider these two types of drives, as well as the most common subspecies.
Pluggable (part time)
By default, in this case, the car will have front-wheel drive, and less often - rear-wheel drive. Turns on 4wd using a lever on the box selector or a button on the console.
This is the simplest variation of the basic drive type. Its peculiarity is its simplicity of design. A cam clutch is installed in the gearbox. It connects the secondary axis. When the system is active, all wheels receive power from the gearbox. The driver independently turns on the four-wheel drive.
Although the mechanism is simple in structure, it has a significant drawback. Four-wheel drive can only be engaged on unstable road surfaces. For example, when the driver sees sand or mud in front of the car, he needs to move the switch to the appropriate position.
The system cannot be used at high speed, as it does not use a center differential. For this reason, the handout (what is it and what kind of malfunctions occur, read in a separate article) will experience severe overloads when the driver forgets to turn off the drive on a flat road. This will damage the transmission.
Automatic (Automatic 4WD)
This is an automatic analogue of the previous transmission. It is activated electronically. The design of the unit uses a viscous coupling associated with the electronics of the car.
When the car hits an unstable road surface, one or both drive wheels begin to slip. The automation reacts to uneven rotation of the driving axle and activates the secondary axle.
This transmission has shown sufficient efficiency in mud, snow or sand. However, this modification has a significant drawback: without the drive wheel slipping, the control unit will not connect the system.
Another disadvantage is the frequent overheating of the viscous coupling. For this reason, the drive cannot be used off-road for a long time. Some car models have a lock with a button.
Full-time four-wheel drive (Full-time 4WD)
This type of transmission differs from the previous ones in that both axles have constant engagement. To reduce the load on the transfer case and improve the stability of the machine on smooth asphalt, the design uses an center differential. This element compensates for the difference in rotation of different wheels.
To provide increased cross-country ability of transport, it has differential lock buttons. Off-road, the driver can lock the cross-axle differential (this mechanism is described here), as well as an expansion joint between the axles. This option is activated either in automatic mode or in manual mode.
Most modern cars are equipped with this type of all-wheel drive. They have a good cross-country ability, and they are also less prone to drifts. If the car is equipped with manual blocking, then be sure to activate it before overcoming mud and similar road sections. For more information on what a differential lock is, told separately.
Multi-mode four-wheel drive (Selectable 4WD)
This modification has incorporated the advantages of all previous varieties. It eliminates the shortcomings of both the automatic and manual differential lock mechanisms, and also allows the driver to prepare the car for a trip on a specific surface. To do this, select the appropriate mode on the box selector, and the electronics will do everything on its own.
The only thing that can stop a motorist before buying a car with this type of all-wheel drive is its high cost. Moreover, in this case, you need to play ahead: in addition to the cost of the system itself, you need to take into account that it also needs to be serviced.
Four-wheel drive: design and operation
Most often in the car market you can find models in which a viscous clutch is installed. The device of such a system includes the following elements:
- A differential is installed between the wheels of the main axle;
- Checkpoint - it can be either an automatic option or a manual one;
- Differential to compensate for rotation between axles;
- Cardan shaft;
- Transfer case with main gear of the secondary axle;
- Viscous clutch.
If the car is front-wheel drive by default, then the engine and the box in it will be located across the body. In the case of the main rear-wheel drive, these units are located along the body. The shape and design of the connected elements of the secondary axis will depend on this.
When four-wheel drive is engaged, the transfer case distributes the torque evenly to each connected wheel, preventing them from slipping. When the deceleration speed is engaged, the torque is increased, which helps the vehicle to overcome difficult sections of the track.
The system works as follows. The motor transmits rotary movements to the clutch (if manual transmission) or to the torque converter (if automatic transmission). Depending on the speed of movement (it is better to overcome off-road in first gear), the torque enters the transfer case, in which it is converted and supplied to the drive wheels. The work is carried out through the cardan (how this transmission works was discussed a bit earlier).
Which four-wheel drive is better
Manual modification of PP is extremely rarely used in mass-produced vehicles. It is more intended for special equipment. The most common option is with automatic connection of the secondary axis. It can use a viscous coupling or electronics, which records the wheel rotation readings.
If you plan to use the car for offroad trips, then it is better not to stint and purchase the most advanced model - Selectable 4WD. It will allow you to use the car on the track as an ordinary passenger car, and when driving outside the high-quality coverage - as an all-terrain vehicle.
You should not buy a car with such a system on the principle “for every fireman” - this is an irrational use of funds. In this case, it would be more practical to buy a car with a viscous coupling.
All-wheel drive benefits
So why are XNUMXWD vehicles so popular (even passenger cars)? Here are some of the benefits of this transmission that many motorists are interested in:
- The car accelerates better on unstable roads, for example, wet in rain, ice or packed snow;
- When driving uphill, the driver will not worry that the road is slippery;
- Neither front-wheel drive, let alone rear-wheel drive, can boast of such effective cross-country ability;
- Due to the improved directional stability, the car remains stable on bends;
- Even a small car with a small engine displacement will have an enviable acceleration compared to a similar car with a single axle drive.
Cons of 4x4 drive
Before opting for a 4wd model, you should consider some disadvantages:
- An all-wheel drive car will be much more expensive, and this is not a marketing move, but a natural reason, since there are additional mechanisms of a complex design in the transport;
- Maintenance of such vehicles is much more expensive. In addition to the usual service, it will also require diagnostics of additional gearboxes, a transfer case in order to extend the life of the unit. In the event of a system breakdown, the owner will have to fork out for expensive repairs;
- Compared to the analogue, only on the front wheel drive, such cars are more "gluttonous". More often this applies to full-fledged SUVs, however, passenger cars with similar characteristics have a slightly increased fuel consumption.
As a conclusion, we offer a video on whether it is worth purchasing an all-wheel drive crossover or is it better to be content with front-wheel drive: