Major double gears. Purpose, design and principle of operation of the main gear Double main gear device

15.07.2019

Body

main gear

In rear-wheel drive cars, the main gear is structurally combined with the drive axle. Design final drive rear wheel drive car shown in Fig. 4.23.

Fig 4 23 Main gear:
1 - gear housing rear axle; 2 - flange for connection to the cardan shaft; 3 - drive shaft gear; 4 - driven gear; 5 - satellites; 6 - differential box; 7 - satellite axis;
8 - axle gears

The main gear is made in the form of a bevel pair: gears and wheels. At the same time, the gear is smaller and has fewer teeth. It is the drive wheel, and the gear wheel is the driven wheel. The bevel gear made it possible to transmit torque from the engine to rear wheels at right angles, and the combination
size and number of gear teeth - reduce the speed, increasing the torque.
On vehicles with front-wheel drive, the final drive housing is structurally integrated with the gearbox housing. In this case, torque is transmitted to the wheels through special shafts. Cars with any drive scheme are equipped with a final drive differential, the operating diagram of which is shown in Fig. 4.24.

The need to use a differential is due to the fact that when cornering, the wheel located on the outside of the turn travels a greater distance than the wheel moving from it. inside.
The differential allows the drive wheels to rotate at different angular speeds. The differential housing is rigidly connected to the driven bevel wheel (larger). The differential housing contains two gears, which are connected to the driving wheels of the vehicle using axle shafts (rear-wheel drive) or special shafts (front-wheel drive). Between these gears, two or four satellite gears are located in constant engagement with them, the axes of which are rigidly connected to the differential housing.
When the car moves in a straight line, the differential housing rotates as a single unit with the bevel wheel (larger driven wheel), the satellite gears do not rotate, the drive wheels rotate at the same angular speed. When the car moves in a turn, the satellite gears begin to rotate around their axes, which is why the left and right gears associated with the drive wheels can rotate with at different speeds. Besides positive effect, there is also a negative side to using a differential in the final drive. If the car's left wheels hit a section of the road with one coefficient of adhesion, and the right wheels - with another, very different, the differential can do a bad job. You've probably noticed how in winter a car with one drive wheel on the ice cannot move, although the other drive wheel located on clean asphalt. And all this is because of the differential. It automatically redistributes all torque to the wheel under which there is less resistance. Vehicles designed to operate in such harsh conditions, equip special systems, allowing you to block the differential. In this case, the same amount of torque is supplied to both drive wheels.

main gear- a mechanism, part of a car's transmission that transmits torque from the gearbox to the drive wheels of the car.

Main gear is a gear mechanism that increases the gear ratio of a vehicle's transmission. It serves to constantly increase the engine torque supplied to the drive wheels and reduce angular velocity their rotation to the required values.

The main gear can be made in the form of a separate unit - the drive axle (rear-wheel drive cars of a classic layout), or combined with the engine, clutch and gearbox into a single power block(rear-engine and front-wheel drive cars).

Based on the number of gear pairs, main gears are divided into single and double. Single final drives are installed on cars and trucks and contain one pair of constant mesh bevel gears. Double final drives are installed on trucks, buses and heavy transport vehicles special purpose. In a double final drive, two pairs of gears are constantly meshed - bevel and cylindrical. A double gear can transmit more torque than a single gear.
On triaxial trucks and multi-axis transport technology Through-type main gears are used, in which torque is transmitted not only to the middle drive axle, but also to the subsequent one, also the drive one. In the vast majority of passenger cars and two-axle trucks, buses, and other transport equipment with one drive axle, non-through final drives are used.

Single main gears are divided into:

Worm, in which torque is transmitted by a worm to a worm wheel. Worm gears, in turn, are divided into gears with a lower and upper worm. Worm final drives are sometimes used in multi-axle vehicles with a straight-through main gear (or with several straight-through main gears) and in automotive auxiliary winches.

In worm gears, the driven gear wheel has the same type of device (always of a large diameter, which depends on the gear ratio built into the design of the gearbox, and is always made with oblique teeth). And the worm can have a different design.

According to their shape, worms are divided into cylindrical and globoid. In the direction of the coil line - left and right. According to the number of thread grooves - single-start and multi-start. According to the shape of the threaded groove - worms with an Archimedean profile, with a convolute profile and an involute profile.

Cylindrical main gears in which torque is transmitted by a pair of cylindrical gears - helical, spur or herringbone. Cylindrical final drives are installed in front-wheel drive vehicles with a transversely mounted engine.

Hypoid (or spiroid) main gears, in which torque is transmitted by a pair of gears with oblique or curved teeth. Pair of gears hypoid transmission either coaxial (less common), or the gear axes are offset relative to each other - with a lower or upper offset. Due to the complex shape of the teeth, the meshing area is increased, and the gear pair is capable of transmitting more torque than other types of final drive gears. Hypoid gears are installed in cars and trucks of classic (rear-wheel drive with front engine) and rear-engine configurations.

Transmission type	Advantages	Flaws
Gears	Cylindrical	1. Compactness. 2.Possibility to transmit high power	1. the difficulty of transmitting motion over significant distances;
2. transmission rigidity;
3. noise during operation;	4. need for lubrication.	Conical Screw Worm	1.large

gear ratios

1. ; 2.smooth and silent operation;

2. 3.high kinematic accuracy; 4.self-braking. 1. low efficiency factor; 2. wear, seizing;

3. use of expensive materials;

1. 4. requirements for high precision assembly.

2. Double main gears are divided into:

3. Central one and two stage.

. In two-stage final drives, pairs of gears are switched to change the torque transmitted to the drive wheels. Such final drives are used on tracked and heavy transport equipment for special purposes.

Spaced main gears with wheel or final drives

. Such main gears are installed on Cars(jeeps) and trucks to increase ground clearance, on wheeled transporters for military purposes.

In addition, double main gears are divided according to the type of engagement of gear pairs into: Conical-cylindrical. Cylindrical-conical. Cone-planetary In cars, gear final drives are made as a single unit with a differential - a mechanism for dividing torque between the two wheels of the drive axle.

Operating principle of hypoid final drive.

Torque is transmitted from the engine through the clutch, gearbox and cardan shaft and light and medium-duty trucks. The gear in it is connected to the cardan transmission, and the wheel is connected to the differential box and through the differential to the axle shafts. The single final drive can be equipped with conventional bevel and hypoid gears.

Worm main gears are characterized by their small size with large gear ratios and the absence of noise during operation. However, due to lower efficiency compared to bevel or hypoid gears, the need to use expensive materials and high production costs worm gearboxes received limited distribution. But hypoid gears, which differ from bevel gears in the smoothness of their engagement, on the contrary, have become more in demand in the automotive industry. By the way, this also happened because the range of products on the market has expanded significantly. lubricants, providing increased strength of the oil film (this is required to neutralize significant slip in the contact of the teeth).

The advantage of a hypoid transmission is that the axis of its gear is located below the axis of the driven wheel (the axis of the rear axle). As a result, the vehicle's center of gravity is lower and its stability is better. Hypoid transmission is more reliable, smooth and quiet than transmission with conventional spiral gears.

Single gears with bevel gears with spiral teeth are used on cars of the ZAZ and UAZ families, and hypoid single gears are used on cars GAZ-3307, GAZ-3102 "Volga", VAZ family.

Rice. 15.3. Main gears:

A - conical; b-hypoid; V-double; 1 And 2 - the gear and wheel are bevel, respectively; 3 And 4 - the gear and wheel are cylindrical, respectively

When the car moves, torque is transmitted from and then, through the main gear and differential, to the drive wheels. allows you to increase or decrease the torque transmitted and at the same time reduce and accordingly increase the speed of rotation of the wheels. Gear ratio in the main gear is selected in such a way that the maximum torque and rotation speed of the drive wheels are in the most optimal values for specific car

. In addition, the final drive is very often the object of car tuning.

Final drive device In fact, the main gear is nothing more than a gear reduction gearbox, in which the drive gear is connected to the secondary shaft of the gearbox, and the driven gear is connected to the wheels of the car. Type Main gears are divided into the following types:

cylindrical - in most cases used on vehicles with a transverse gearbox and front-wheel drive;
conical - used very rarely, as it has large dimensions And high level noise;
hypoid is the most popular type of final drive, which is used on most cars with classic rear wheel drive. The hypoid gear is small in size and low level noise;
worm - practically not used on cars due to the complexity of manufacturing and high cost.

It is also worth noting that front-wheel drive and rear-wheel drive vehicles have different final drive locations. IN front wheel drive cars with a transverse arrangement of the gearbox and power unit, the cylindrical main gear is located directly in the gearbox housing.

In cars with classic rear-wheel drive, final drive installed in the drive axle housing and is connected to the gearbox via . The functionality of the hypoid transmission of a rear-wheel drive car also includes a 90-degree rotation due to bevel gears. Despite Various types and the location and purpose of the main gear remains unchanged.

Car differential

Car differential most often combined with the main gear and located, respectively, in the gearbox housing or in the rear axle housing. However, a differential can also be installed between the drive axles of an all-wheel drive vehicle. The differential represents and is divided into the following types:

conical - in most cases it is installed together with the main gear between the wheels of one drive axle;
cylindrical - most often used to decouple the drive axles of all-wheel drive vehicles;
worm - is universal and is installed both between the wheels and between the drive axles.

The main purpose of the differential is to distribute torque between the wheels of the car and change their rotational speed relative to each other. For example turning a car without a differential would be simply impossible, since when turning, the outer wheel must necessarily rotate at a higher frequency than the inner one.

There are symmetrical and asymmetrical differentials. A symmetrical differential transmits equal torque to both wheels and is most often installed together with the main gear. An asymmetrical differential allows you to transmit torque in different proportions and is installed between.

The differential consists of a housing, pinion gears and side gears. The housing is usually combined with the driven gear of the main drive. The satellite gears play a role planetary gearbox and connect the side gears to the differential housing. The semi-axial (sun) gears are connected to the drive wheels via axle shafts with splined joints.

With all the advantages of the simplest differential there is also a disadvantage. The fact is that the rotation speed can be distributed to the wheels not only in a ratio, for example 50/50, 40/60 or 35/65, but also 0/100. That is, absolutely all the torque can be transmitted to one wheel of the car, while the second wheel will be absolutely static. This happens when the car gets stuck in mud or ice.

However modern differentials more perfect and practically devoid of this drawback. Many differentials have hard automatic or manual locking. In addition, modern passenger all-wheel drive vehicles are equipped with a system directional stability, which is based on the optimal distribution of torque between the axles and individual wheels depending on the trajectory.

The double central main gear allows for a large gear ratio with sufficiently high ground clearance under the axle housing. Such a main gear is installed, for example, in the drive axles of some cars.

The main gear housing 18, together with the drive axle beam 7, is a rigid structure, which helps ensure proper gear engagement.

The main gear consists of a pair of bevel gears 13 and 14 with spiral teeth and a pair of spur gears 11 and 12 with helical teeth. This tooth shape helps reduce noise during operation of the main gear, and careful processing of the gear teeth increases the efficiency of the main gear. The drive bevel gear 14 is made as a single unit with the drive shaft of the main gear mounted on two roller tapered bearings 16, the housing of which is bolted to the flange of the main gear housing, and on one cylindrical roller bearing 17. On the specified shaft between the inner rings of the bearings 16 there are washers for adjusting the preload of the bearings.

Between the flange of the bearing housing 16 and the main gear housing 18, adjusting shims are installed to adjust the engagement of a pair of bevel gears. The driving bevel gear 14 meshes with the driven bevel gear 13, which is keyed and pressed onto an intermediate shaft manufactured integrally with the driving cylindrical gear 12. This shaft is installed in the internal partition of the crankcase on a cylindrical roller bearing, and its outer end is located on a double-row tapered roller bearing. , the housing of which, together with the cover, is bolted to the side flange of the main gear housing. Gaskets are installed under the housing flange to adjust the engagement of the bevel gears, and to adjust the tapered roller bearing, shims are placed between its inner rings.

Rice. Diagram of the drive mechanism of the steered drive axle

The drive cylindrical gear 12 meshes with the driven gear 11, bolted to the differential housing 10, placed in the sockets of the main gear housing on tapered roller bearings, which are adjusted using nuts with a locking device.

The main gear housing has holes for filling, checking and draining oil, closed with plugs. The oil level is checked during operation with a special dipstick. The crankcase has cavities (pockets) into which oil enters when the gears rotate, from where it flows through channels to the bearings of the drive and driven bevel gears, improving their lubrication. The main gear housing communicates with the atmosphere through the breather.

The main gears of all axles of a car have the same design, but the main gear housings of the middle and rear axles differ from the front axles in shape and location relative to the beams of their axles. In addition, the drive shaft of the middle axle is made through (through) to drive the main gear of the rear axle, therefore both ends of this shaft are sealed with self-clamping oil seals and flanges are secured with nuts on both ends on splines cardan joints 15 cardan drives drive axles.

LABORATORY WORK No. 15

Topic: “Purpose, design and principle of operation of the main gear and differential”

Goal of the work: study of the purpose, structure and principle of operation of the main gear and differential.

General provisions

On most modern cars The transmission includes one or more (according to the number of drive axles) main gears and a corresponding number of cross-axle differentials. In addition, on vehicles with several drive axles (drive axles), center differentials can be installed.

The final drive on a car performs two functions:

1) speed matching crankshaft engine and drive wheels and the resulting constant increase in torque transmitted to the drive wheels;

2) changing the direction of the torque vector in accordance with the layout of the car (for example, rotating the torque vector by 90° with a longitudinal engine).

Differential is a vehicle transmission mechanism that distributes the torque supplied to it between the shafts and allows them to rotate at unequal angular speeds.

The cross-wheel differential serves for kinematic misalignment of the wheels of one axle when the vehicle moves around corners or over uneven surfaces.

Center differential serves for kinematic misalignment of wheels different axes when the vehicle moves over uneven surfaces or when the speed changes, as well as for constant distribution of torque in a certain ratio between the axles of all-wheel drive vehicles.

main gear

When the car moves, torque from the engine crankshaft is transmitted to the gearbox and then, through the main gear and differential, to the drive wheels. The main gear allows you to increase or decrease the torque transmitted to the wheels of the car and at the same time reduce and accordingly increase the speed of rotation of the wheels.

The gear ratio in the final drive is selected in such a way that the maximum torque and speed of rotation of the drive wheels are in the most optimal values for a particular vehicle. In addition, the final drive is very often the object of car tuning.

In fact, the main gear is nothing more than a gear reduction gearbox, in which the drive gear is connected to the secondary shaft of the gearbox, and the driven gear is connected to the wheels of the car. According to the type of gear connection, the main gears differ into the following: varieties:

· cylindrical– in most cases it is used on cars with a transverse engine and gearbox and front-wheel drive;

· conical– used very rarely, as it has large dimensions and a high noise level;

· hypoid– the most popular type of final drive, which is used on most cars with classic rear-wheel drive. Hypoid transmission is characterized by its small size and low noise level;

· worm– practically not used on cars due to the complexity of production and high cost.

It is also worth noting that front-wheel drive and rear-wheel drive vehicles have different final drive locations. In front-wheel drive vehicles with a transverse gearbox and power unit, the cylindrical main gear is located directly in the gearbox housing. In cars with classic rear-wheel drive, the main gear is installed in the drive axle housing and is connected to the gearbox via cardan shaft. The functionality of the hypoid transmission of a rear-wheel drive car also includes a 90-degree rotation due to bevel gears. Despite the different types and locations, the purpose of the final drive remains the same.

Scheme of operation of the main transmission of a car
1 - flange; 2 - drive gear shaft; 3 - drive gear; 4 - driven gear; 5 - driving (rear) wheels; 6 - axle shafts; 7 - final drive housing

Differential

Differential- this is a mechanism that allows (if necessary) the driving wheels of a car to rotate at different speeds. What is it for? When driving in a straight line, the wheels travel the same distance, but when turning, the outer wheel travels a longer path than the inner wheel. Therefore, in order to “keep up” with the car, the outer wheel must rotate faster.

Differential device simple - a housing, a satellite axis and two satellites (gears). The housing is attached to the driven gear main couple and rotates with her. The satellites mesh with the axle gears, which directly rotate the wheels.

In this design, the satellites transmit more torque to the axle shaft that has less resistance to rotation. That is, with higher speed the wheel will rotate, which is easier for the differential to spin. When driving in a straight line, the wheels are loaded equally, the differential divides the torque equally, and the satellites do not rotate around their axis. When turning, the inner wheel is loaded more, the outer wheel is unloaded. Therefore, the satellites begin to rotate around the axis, twisting the less loaded wheel, thereby increasing its rotation speed.

But this feature of the differential sometimes leads to very unpleasant consequences. If, for example, one of the wheels hits a slippery surface, the differential will only rotate that one, completely ignoring the wheel that has normal contact with the road. That is, the car will “slip”.

To combat this phenomenon, differential locks are used. Many locking methods have been invented - from simple mechanical to sophisticated electronic ones.

The main gear of a car is a transmission element, in the most common version, consisting of two gears (driven and driven), designed to convert the torque coming from the gearbox and transmit it to the drive axle. Directly depends on the design of the main gear traction and speed characteristics car and fuel consumption. Let's consider the device, principle of operation, types and requirements for the transmission mechanism.

. In addition, the final drive is very often the object of car tuning.

In cars with classic rear-wheel drive, final drive installed in the drive axle housing and is connected to the gearbox via a cardan shaft. The functionality of the hypoid transmission of a rear-wheel drive car also includes a 90-degree rotation due to bevel gears. Despite the different types and locations, the purpose of the final drive remains the same.

Principle of operation

The main characteristic of this gearbox is the gear ratio. This parameter reflects the ratio of the number of teeth of the driven gear (connected to the wheels) to the drive gear (connected to the secondary shaft of the gearbox). The higher the gear ratio, the faster car accelerates (torque increases), but at the same time the maximum speed decreases. Reducing the gear ratio increases maximum speed, and the car begins to accelerate more slowly. For each car model, the gear ratio is selected taking into account the characteristics of the engine, gearbox, wheel size, brake system etc. The principle of operation of the main gear is quite simple: while the car is moving, torque from the engine is transmitted to the gearbox variable gears(gearbox), and then, through the main gear and differential, drive shafts car. Thus, the final drive directly changes the torque that is transmitted to the wheels of the machine. Accordingly, through it the speed of rotation of the wheels also changes.

Primary requirements. Modern tendencies

The main gears are subject to many requirements, the main ones being:

Reliability;
Minimal maintenance required;
High efficiency indicators;
Smooth and silent;
Minimum possible overall dimensions.

Naturally, there is no ideal option, so designers have to look for compromises when choosing the type of final drive.

It is not yet possible to abandon the use of final drives in transmission design, so all developments are aimed at improving performance indicators.

It is noteworthy that changing the operating parameters of the gearbox is one of the main types of transmission tuning. By installing gears with a changed gear ratio, you can significantly influence the dynamics of the car, maximum speed, fuel consumption, load on the gearbox and power unit.

Finally, it is worth mentioning the design features robotic gearboxes With double clutch, which also affects the main gear design. In such gearboxes, paired and unpaired gears are separated, so there are two outputs secondary shaft. And each of them transmits rotation to its own drive gear of the main gear. That is, in such gearboxes there are two driving gears, and only one driven gear.

DSG gearbox diagram

This design feature allows you to make the gear ratio on the gearbox variable. To do this, only drive gears with different numbers of teeth are used. For example, when using a number of unpaired gears to increase traction force a gear is used that provides a larger gear ratio, and the gear of a paired row has a lower value of this parameter.

Double final drives

These programs apply on medium and medium sized trucks heavy lifting capacity, on all-wheel drive three-axle vehicles and buses to increase the transmission ratio to ensure the transmission of high torque. The efficiency of double final drives is within 0,93…0,96 .

Double final drives have two gear pairs and usually consist of a pair of bevel gears with spiral teeth and a pair of spur gears with straight or oblique teeth. The presence of a cylindrical pair of gears allows not only to increase the gear ratio of the main gear, but also to increase the strength and durability of the bevel gear pair.

IN central final drive (Figure 2, d) bevel and spur gear pairs are located in one crankcase in the center drive axle. The torque from the bevel pair is supplied through the differential to the driving wheels of the car.

IN spaced main gear (Figure 2, d) bevel gear pair 5 is located in the housing in the center of the drive axle, and cylindrical gears 6 are in the wheel gearboxes. In this case, the cylindrical gears are connected by axle shafts 7 through a differential with a bevel pair of gears. The torque from the bevel pair through the differential and axle shafts 7 is supplied to the wheel gearboxes.

Widely used in spaced main gears got single row planetary wheel reducers . Such a gearbox consists of spur gears - solar 8, crown 11 and three satellites 9. The sun gear is driven into rotation through the axle shaft 7 and is in mesh with three satellites, freely mounted on axes 10, rigidly connected to the beam bridge. The satellites mesh with a ring gear 11 attached to the wheel hub. The torque from the central bevel gear pair 5 to the hubs of the drive wheels is transmitted through the axle differential 7, sun gears 8, satellites 9 and ring gears 11.

When separated final drive the load on the axle shafts and differential parts is reduced by two parts, and the dimensions of the crankcase and the middle part are also reduced drive axle. As a result, it increases ground clearance and thereby increases the vehicle's cross-country ability. However, the spaced main gear is more complex, has a higher metal consumption, is expensive and labor-intensive to maintain.

Classification of final drives

By the number of pairs of gears

Single and double final drive

Single - has only one pair of gears: driven and driven.
Double - has two pairs of gears. Divided into double central or double spaced. The double central one is located only in the drive axle, and the double spaced one is also located in the hub of the drive wheels. Applies to freight transport, since it requires a higher gear ratio.

By type of gear connection

By layout Cylindrical. Used on front-wheel drive vehicles in which the engine and gearbox are transversely located. This type of connection uses gears with herringbone and helical teeth.
Conical. Used on those rear wheel drive cars, in which the dimensions of the mechanisms are not important and there are no restrictions on the noise level.
Hypoid is the most popular type of gear connection for rear-wheel drive vehicles.
Worm gear is practically not used in the design of car transmissions.

Placed in the gearbox or in power unit. On front-wheel drive vehicles, the main gear is located directly in the gearbox housing.
Placed separately from the checkpoint. In rear-wheel drive vehicles, the main pair of gears is located in the drive axle housing along with the differential.

Note that in four-wheel drive vehicles The location of the main pair of gears depends on the type of drive.

Advantages and disadvantages

Cylindrical main gear. The maximum gear ratio is limited to 4.2. A further increase in the tooth ratio leads to a significant increase in the size of the mechanism, as well as an increase in the noise level. Each type of gear connection has its own pros and cons. Let's look at them:

Hypoid final drive. This type is characterized by low tooth load and reduced noise level. In this case, due to the displacement in the meshing of the gears, sliding friction increases and efficiency decreases, but at the same time it becomes possible to lower the driveshaft as low as possible. Gear ratio for passenger cars – 3.5-4.5; for freight – 5-7;.
Bevel main gear. Rarely used due to big size and noise.
Worm main gear. This type of gear connection is practically not used due to the complexity of manufacturing and the high cost of production.