Car final drive: types, purpose

2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:41

As you know, the main task of the engine is to generate torque, then the work is sent through the clutch to the box. These are the main components in any car. But few people thought about how the torque is further distributed to the wheels. The information will be useful to any motorist.

Characteristics and purpose of the main gear

So, what is this mechanism for? The purpose of the main gear of the car is to provide communication between the transmission and the drive wheels. It has its own gear ratio, and structurally it is a gear reducer. With a certain gear ratio, it increases the engine torque and reduces the speed of the drive wheels.

Where is it?

Most front wheel drive vehicles have a final drive built into the gearbox. There is also a differential here. The main elements are located in the front of the body. The main gear of the KamAZ vehicle and other rear-wheel drive vehicles is located in the bridge.

Elementclosed with a special housing - a stocking, which contains not only a gearbox with a differential, but also axle shafts.

Types and design

So, consider the types of main gears of the car. On front-wheel drive vehicles, where the motor with the box is placed transversely relative to the body, a cylindrical design is used. This transmission has gears with chevron and oblique teeth. If we talk about the gear ratio, it can range from 3.5 to 4.2. If this figure is increased, this will lead not only to an increase in the dimensions of the structure, but also to an increase in the noise level.

Modern gearboxes use two or three output shafts. Each of them has its own final drive gear. All of them have engagement with one, driven. Thus, the main gear of this type can have several gear ratios at once. According to this scheme, robotic DSG boxes from Volkswagen also work.

RWD vehicles may use different mechanisms. So, it can be conical, worm and hypoid. Similar types are also found on all-wheel drive vehicles, but this only applies to those vehicles where the engine is located along relative to the body. On modern crossovers, the rear axle can be driven like front-wheel drive cars through a viscous coupling. But that's another story.

Hypoid

This is the most sought after type of final drive on automobiles. GAZ "Volga" is also equipped with this gearbox. Among the differences of this type, it is worth noting the low noise level and less load on the teeth.

However, the hypoid gear has a serious drawback. So, due to the displacement of the gears, friction increases and productivity decreases. As a result, the car loses some of its power. If we talk about the gear ratio, it is different on cars and trucks. In the first case, the parameter is from 3.5 to 4.5. In the second case, it is 5 - 7.

Conical

It was actively used at the beginning of the last century. The transmission was created in 1913 by the Gleason company. It was this company that invented the engagement with a circular tooth. Among the design features of this mechanism, it is worth noting that the tops of the driven gears and the initial cones of the leading ones lie at one point. However, the moment acting between the gears of such a mechanism tends to disrupt the correct engagement of the elements. In view of this, it was necessary to ensure increased reliability of all bearing assemblies, shafts and crankcase. So, roller bearings with preload were installed on such cars, and the radius of curvature of the tooth of the drive gear was less than that of the driven gear. This was done to reduce the impact on engagement accuracy.

Among the main advantages of these structures, it is worth noting the high efficiency. Losses during operation are only 2%, since the sliding friction between the teeth is small. But due to significant disadvantages, this type of transmission is no longer used by automakers due to its large dimensions and insanely high noise levels.

Worm gear

This mechanism forCompared to the previous one, it has a fairly compact size; moreover, it is practically silent, although it has a low efficiency, which is 90%. The worm gear is difficult to manufacture, as it requires the use of tin bronze for the ring gear, so on cars such a gear is used only in the steering mechanism, and even then not always.

Tuning

Can the gear ratio be adjusted? This indicator can be changed only by replacing the gear reducer, which will require intervention in the box or rear axle (depending on the type of vehicle drive). Changing the gear ratio is a popular type of tuning that allows you to increase torque without interfering with the engine.

So, the car accelerates faster, but loses top speed. If you take the main gear of a VAZ-2101 car and install a gearbox from the "six", you can get an increase in torque. After all, from the factory, a gearbox with the number 4, 2 is put on the "penny", and on the "six" - 3, 9.

About differential

It is an integral part of the main transmission. What is a differential for? It interacts with a gear reducer. Structurally, the assembly (final gear with differential) consists of:

• Driven gear.
• Half axles.
• Drive gear.
• Satellites.
• Gear axles.

It is designed to distribute torque between the axle shafts of the wheels when turning the car. Differential allowswheel to rotate at different angular speeds. In this case, the wheels spin without slipping, which contributes to safer cornering (especially in winter), eliminating the risk of skidding.

In other words, 100% of the torque comes from the driveshaft differential. The incoming energy can be distributed both evenly, in a ratio of 50 to 50 (which happens with rectilinear motion), and in other proportions. Depending on the road situation, one wheel can have from 0 to 100% of the torque. As a rule, large run-ups appear when driving on rough terrain or in snow.

In the process of torque distribution, two gears of satellites and half shafts are involved. They are lubricated in a common "bath" of the crankcase with gear oil, which partially performs the function of cooling the parts, since the teeth constantly rub against each other.

Some people deliberately weld the differential on rear wheel drive cars to make it easier to skid. Thus, torque is always distributed in a 50/50 ratio. But there is also uneven tire wear, as they always slip when cornering.

Also note that on some passenger cars, an electronic differential lock is installed as an additional option. This is necessary so that the car can get out of the mud or snow captivity. A similar lock is present on all SUVs without exception.

Conclusion

So, we found out what the main gear is. As you can see, its function is no less important than the transmission function. This system contributes to more rotation of the wheels, but at the same time preserves the components of the box and engine. Today, two main types of main gears are used. If we talk about rear-wheel drive cars, it is hypoid, if we talk about front-wheel drive cars, it is cylindrical.