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. 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 gear ratio, and constructively is a gear reducer. Thanks to a certain gear ratio, it increases the engine torque and reduces the speed of the drive wheels.
Where is?
Most front-wheel drive vehicles have a final drive integrated in the gearbox. There is also a differential. The main elements are located in the front of the body. The main gear of the KamAZ car and other rear-wheel drive cars is located in the bridge.
The element is closed by a special case - a stocking, in which there are not only a gearbox with differential, but also half shafts.
Types and Design
So, consider the types of main gears of the car. On front-wheel drive cars, where the engine with the box is placed transversely relative to the body, a cylindrical design is used. Such a transmission has gears with chevron and oblique teeth. If we talk about the gear ratio, it can be 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 boxes use two or three secondary shafts. Each of them has its own driving gear of the main transmission. All of them are engaged with one, driven. Thus, the main transmission of this type can have several gear ratios at once. According to this scheme, including robotic DSG boxes from Volkswagen.
On rear-wheel drive cars, different mechanisms can be used. So, it can be conical, worm and hypoid. Similar types are found on all-wheel drive cars, but this only applies to those machines where the engine is located along relative to the body. On modern crossovers, the rear axle can be driven like a front-wheel drive car through a viscous clutch. But that is another story.
Hypoid
This is the most popular type of main gears in cars. GAZ Volga is also equipped with this gear. Among the differences of this type, it is worth noting the low noise level and less load on the teeth.
However, hypoid transmission has a serious drawback. So, due to the displacement of the gears, friction increases and productivity decreases. As a result, the car loses part of its power. If we talk about the gear ratio, it differs in cars and trucks. In the first case, the parameter is from 3.5 to 4.5. In the second - 5 - 7.
Conical
It was actively used at the beginning of the last century. The transmission was created in 1913 by Gleason. It was this firm that invented gearing 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 violate the correct engagement of the elements. In view of this, it was required to provide 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 driving gear was less than the driven one. 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 the large size and insanely high noise level.
Worm-gear
This mechanism is quite compact in comparison with the previous one; moreover, it is practically silent although it has a low efficiency, which is 90%. The worm gear is difficult to manufacture, since it requires the use of tin bronze for the ring gear, so on cars such a gear is used only in the steering gear, and even then not always.
Tuning
Is gear ratio adjustable? This indicator can only be changed 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 at maximum speed. If you take the main gear of the VAZ-2101 car and install the gearbox from the "six", you can get an increase in torque. Indeed, from the factory, a gear with the number 4.2 is put on the “penny”, and 3.9 on the “six”.
About differential
It is an integral part of the main transmission. What is the differential used for? It interacts with a gear reducer. Structurally, the unit (main gear with differential) consists of:
- Driven gears.
- Half shafts.
- Pinion gear.
- Satellites.
- Gear axle shafts.
It is designed to distribute torque between the axles of the wheels when turning the car. Differential allows the wheel to rotate at different angular speeds. In this case, the wheels spin without slipping, which contributes to a safer cornering (especially in winter), eliminating the risk of skidding.
In other words, the differential from the propeller shaft accounts for 100% of the torque. The incoming energy can be distributed both uniformly, in a proportion of 50 to 50 (which happens with rectilinear movement), and in other proportions. Depending on the traffic situation, one wheel may account for from 0 to 100% of the torque. As a rule, large runaways appear when moving on bumpy terrain or in the snow.
In the process of torque distribution, two gears of the satellites and the semi-axles are involved. They are lubricated in a common “crankcase” by gear oil, which partially fulfills the function of cooling parts, since the teeth constantly rub against each other.
Some intentionally brew a differential on rear-wheel drive cars to make it easier to skid. So, the torque is always distributed in the proportion of 50 to 50. But there is also uneven wear of the tires, since they always slip on the corners.
Also note that on some cars, an electronic differential lock is installed as an additional option. This is necessary so that the car could 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 a greater rotation of the wheels, but at the same time retains the nodes of the box and engine. Today, two main types of main gears are used. If we talk about rear-wheel drive cars - it’s hypoid, if we talk about front-wheel drive - cylindrical.