What is the difference between double main gear and single. Double final drives

19.07.2019

LAB #15

Topic: "Purpose, device and principle of operation main gear and differential

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

On most modern cars the transmission includes one or more (according to the number of drive axles) main gears and the corresponding number of interwheel differentials. In addition, on vehicles with multiple drive axles (driving axles), center differentials can be installed.

The main gear on a car performs two functions:

1) speed matching crankshaft of the 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, turning the torque vector by 90 ° with a longitudinal engine).

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

The cross-axle differential serves for the kinematic mismatch of the wheels of one axle when the car is moving around corners or over bumps.

center differential serves for kinematic misalignment of wheels different axes when driving a car over bumps or when changing the speed of movement, as well as for constant distribution in a certain ratio of torque between the axles of all-wheel drive vehicles.

main gear

When the car is moving, the torque from the crankshaft of the engine 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 main gear is selected in such a way that the maximum torque and speed of the drive wheels are in the most optimal values for specific vehicle. In addition, the final drive is very often the subject of car tuning.

In essence, the main gear is nothing more than a gear reduction gear in which the pinion gear is connected to output shaft Gearbox, and driven - with the wheels of the car. Type gear connection main gears differ in the following varieties:

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

· conical- is used very rarely, as it has large dimensions And high level noise;

· hypoid- the most popular type of final drive, which is used on most cars with a classic rear wheel drive. The hypoid gear is small 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 cars have a different final drive arrangement. 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 vehicle also includes a 90-degree rotation due to bevel gears. Despite Various types and the location, purpose of the final drive remains unchanged.

The scheme of the main gear of the car
1 - flange; 2 - drive gear shaft; 3 - drive gear; 4 - driven gear; 5 - driving (rear) wheels; 6 - axle shafts; 7 - main gear housing

Differential

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

Differential device simple - a body, an axis of satellites and two satellites (gears). The housing is attached to the driven gear main couple and rotates with it. The satellites engage with the gears of the axle shafts, which directly rotate the wheels.

In this design, the satellites transmit more torque to the axle shaft, which has less resistance to rotation. That is, with more 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, the satellites do not rotate around their axis. In a turn, 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 the speed of its rotation.

But such a feature of the differential sometimes leads to very backfire. If, for example, one of the wheels hits a slippery surface, the differential will only rotate it, 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.

Whatever the car Dear friends, incredibly luxurious or spartan-budget, in its bowels there is always the only main process - the transfer of torque from the engine to the wheels. It takes part various knots and units, each of which bears a certain share of responsibility for our comfortable and moderately fast movement on the roads. And the main gear of the car is the node, thanks to which the wheels of the vehicle are spinning and we gain an unforgettable feeling of flight, even at a super low altitude.

So, the main gear of a car is a node, without which the efforts of the engine and gearbox would be a waste of energy. Why? The fact is that it is she who is responsible for transmitting torque from the directly driven wheels.

In addition, rotation, as a rule, still needs to change direction - from longitudinal (along the axis of the car) to transverse in order to get to the wheels. And all this is done, in fact, by one gear mechanism, also known as a gear reducer. In addition to everything, the ratios of the gears are chosen in such a way as to increase the torque of the motor.

Where is?

We seem to have found out the purpose of the main gear of the car, now it would be nice to find it. This can be a difficult task to do, because the location of this node is different and depends on the type of machine drive and the imagination of development engineers.

Fortunately, the flight of thought here is limited by the number of axles. So, for example, if we have front-wheel drive, then in this case it is worth looking for the main gear of the car in the checkpoint along with, in vehicles with rear driving wheels - right in the rear axle. If , then choose one of the above options.

Variety of main gears

As we already understood, the main gear of a car is a very serious knot. It is clear that for such a responsible task that is entrusted to him, you need a reliable and at the same time uncomplicated engineering solution, and here wide scope for action opened up for designers. Let's look at the types of main gears of cars. Depending on the number of gears, this node is as follows:

single;
double.

The first type is a combination of two gear parts - a driving and a driven gear. It is most common among passenger cars and small trucks. Double main gears have, as you might guess, several pairs of gears, and are usually used where an increase in gear ratio is necessary, for example, for buses and special equipment.

The picture would be incomplete without mentioning the types of gear connections used. There are many of them, and these are distinguished:

cylindrical;
hypoid;
conical;
worm.

Cylindrical final drive of the car is the most popular type for front-wheel drive, as well as a transversely mounted engine and gearbox. It uses, as the name implies, cylindrical helical, spur or chevron gears. The gear ratio of such nodes is in the range from 3.5 to 4.2 - it doesn’t work anymore, since the dimensions and noise from work increase exorbitantly.

No less popular, but, however, with the classic rear-wheel drive technology, the so-called hypoid gears. Their key feature are curved teeth, thanks to which it is possible to transmit a torque of large values.

In addition, the gears in this case can be shifted relative to each other, which allows, for example, to lower the level of the floor in the machine. The main gear of a car of this variety has a gear ratio in the range of 3.5-4.5.

As for the conical worm mechanisms, they are less common. You can see the main gear of a car of these types on various techniques with rear driving wheels, but because of their design features nowadays they are used less and less. The disadvantages of the former include large size and noise, while the latter require high precision in manufacturing, which entails extra costs.

Well, dear readers of our blog, you and I got acquainted with the purpose of the main gear of a car, found out what this node can be and where it is located. In the next publication, we will consider another, no less important unit of the machine. Which? Subscribe to us and be the first to know about it!

> Main gear

Transmission

Purpose and types of main gears.

The main gear serves to increase the torque and change its direction at right angles to the longitudinal axis of the vehicle. For this purpose, the main gear is made of bevel gears. Depending on the number of gears, the main gears are divided into single bevel, consisting of one pair of gears, and double, consisting of a pair of bevel and a pair of cylindrical gears. Single bevel gears, in turn, are divided into simple and hypoid gears.

1 - driving bevel gear, 2 - driven bevel gear,
3 - driving spur gear, 4 - driven spur gear.

Single conical simple transfers(Fig. a) are used mainly on cars And trucks small and medium load capacity. In these gears, the drive bevel gear 1 is connected to the cardan gear, and the driven gear 2 is connected to the differential box and through the differential mechanism to the axle shafts. For most vehicles, single bevel gears have hypoid gears (Figure 6). Hypoid gears have a number of advantages compared to simple ones: they have the axle of the drive wheel located below the axle of the driven one, which allows lowering cardan transmission, lower the floor of the car body. This lowers the center of gravity and increases vehicle stability. Besides, hypoid gear has a thickened shape of the base of the gear teeth, which significantly increases their load capacity and wear resistance. But this circumstance determines the use for gear lubrication special oil(hypoid), designed to work in conditions of transmission of large forces that occur in contact between the gear teeth.

Double main gears (Fig. C) are installed on cars heavy duty to increase the overall gear ratio of the transmission and increase the transmitted torque. In this case, the gear ratio of the main gear is calculated as the product of the gear ratios of the bevel (1, 2) and cylindrical (3, 4) pairs.

main transmission device.

The double main gear of the ZIL-130 car is part of the mechanisms of the rear drive axle, which are located in its beam 8. The drive shaft of the final drive is made in one piece with the drive bevel gear 1. It is mounted on tapered roller bearings in a glass mounted on the crankcase 9 of the main gear . Here, in the crankcase, an intermediate shaft with a driving cylindrical gear 12 is installed on roller conical bearings. The driven bevel gear 2 is rigidly fixed on the shaft flange, which is engaged with gear 1. The driven cylindrical gear 5 is connected to the left 3 and right 6 differential cups, forming it box. Differential parts are installed in the box: crosspiece 4 with satellites 11 and side gears 10.

Drive rear axle mechanisms

When the main gear is in operation, the torque is transmitted from the driveline to the flange of the drive shaft and its gear 1, then to the driven bevel gear 2, the intermediate shaft and its gear 12, the driven spur gear 5 and through the differential parts on the axle shaft 7 connected to the wheel hubs of the vehicle .

Double final drives find wide application on medium and heavy vehicles, when the required gear ratio cannot be obtained using single gear. One of the main purposes of using double final drives is also the need to unload the bevel pair and the drive shaft bearings from large circumferential, radial and axial forces. Double final drive gears can transmit large torque. The gear ratio of the bevel pair is usually from 1.5 to 2.5. Consequently, the main transformation of the torque occurs in the cylindrical pair.

IN domestic automotive industry most common central double main gear, in which both pairs of gears are placed in the crankcase located in the central part of the drive axle.

On fig. 14.9 shows the main gear of the KamAZ-4310. The first pair of gears is bevel, the second pair is cylindrical. Bevel gears have helical teeth, spur gears have helical teeth. The total gear ratio of the transmission is 7.22.

Rice. 14.9. The main gear of the KamAZ-4310 car: 1 - main gear case; 2 - filler plug; 3 - driven bevel gear; 4 - dowel; 5 - driving spur gear; 6 , 9, 16 - tapered bearings; 7 - glass; 8 - bearing cover; 10 , 19, 24 - support washers; 11 - screw; 12 - adjusting washer; 13 - adjusting gasket; 14 - pad; 15 - adjusting nut; 17 - differential cup; 18 - satellite; 20 - cross; 21 - semi-axial gear; 22 - differential mounting bolt; 23 - driven spur gear; 25 - satellite bushing;

26 - cylindrical bearing

The drive bevel gear of the rear axle reducer is mounted on the splines of the drive shaft. driven bevel gear 3 installed on the shaft of the driving spur gear on the key 4. Driving spur gear 5 made in one block with the shaft. driven spur gear 23 bolts 22 attached to cups //differential. The spur gear shaft is mounted in two tapered roller bearings 6 And 9, located in a glass 7, and one cylindrical 26, installed in the crankcase.

The preload of the bearings of the bevel gear pair is set by selecting the thickness of the shims 12, between the inner races of the bearings.

The engagement (contact patch) of the bevel gears is adjusted by selecting the thickness of the shim packs 13, which are installed under the flanges of the glasses 7 tapered bearings. Adjustment of the position of the driven spur gear relative to the leading one is carried out by adjusting nuts 15, located on both sides of the differential. To lubricate the bearings of the units, there are oil collectors in the gearbox crankcase, from which oil flows through the channels in the crankcase walls to the bearings.

The main gears of the middle and rear axles usually unified. The main gear housing is attached to the front axle with a flange located in a vertical plane. Therefore, the main gears front axle not interchangeable with the main gears of the middle and rear axles.

The dimensions of the main gear of the main gear directly affect the amount of ground clearance, and, consequently, the vehicle's patency on soft soils. In addition, the dimensions of the main gear of the front drive axle determine the height of the engine and the layout of the vehicle as a whole. Therefore, in order to increase the gear ratio of the main gear with the dimensions of the central gearbox unchanged, the second stage of the double gear is placed in the region of the drive wheels (Fig. 14.10).

A double final drive, in which the second pair of gears is driven to each of the drive wheels, is called split main gear. It consists of a central conical 1 or hypoid gear and two wheel planetary gears 2 (Fig. 14.10, A). Such gears make it possible to unload the bevel gear and cardan gear from high torques and, therefore, make these units reliable, compact and relatively small in weight. Torque increases mainly in wheel gears (Fig. 14.10, b) which include a sun gear 4, epicyclic gear 8, three satellites 5, rotating on axes 6, fixed in the carrier 7. The epicyclic gear is connected to the hub of the driving wheel of the car. The carrier is fixedly fixed on the flanges of the sleeves of the semi-axes. From the central bevel gear, the torque is transmitted through the axle shafts to the sun gears, which rotate the satellites, and those, in turn, to the epicyclic gears with hubs.

Rice. 14.10. Split main gear: A - circuit diagram; b - planetary wheel reducer; / - central bevel gear; 2 - wheel reducer; 3 - axle shaft; 4 - sun gear; 5 - satellite; 6 - axis of the satellite; 7 - carrier; 8 - epicyclic gear

On a number foreign cars In the planetary wheel reduction gear, the epicyclic gear wheel is stationary, and the carrier is connected to the wheel hub. This allows you to get a slightly larger gear ratio with the same overall dimensions. Wheel reducers can be a cylindrical pair of gears with internal gearing, as on a UAZ-469B car, or a bevel gear like an interwheel differential, as on MAN cars.

The disadvantages of spaced double main gear include the complexity of the design, the high complexity of maintenance.

At the same time, for most gearboxes, such a thing as the main gear of a car is relevant. Next, we will talk about what the main gear is and what it is for.

Read in this article

What is the main gear for and what is it

As you know, today the following types of gearboxes are installed on cars:

(transmission selection is carried out manually);
(provides automatic selection of the gear corresponding to the current traffic conditions);
(provides a smooth change in gear ratio.);
(mechanical box gears, clutch disengagement and gearshift functions are automated).

The main task of the gearbox is the transmission and change of torque from the engine to the drive wheels with the possibility of changing gear ratios. At the output of the box, the torque is small, and the rotation speed of the output shaft is high.

To increase the torque and reduce the speed of rotation, the main gear of the car, which has a certain gear ratio, is used. The gear ratio of the main gear depends on the type, purpose of the car and engine speed. Typically, the gear ratios of the main gears of passenger cars are in the range of 3.5-5.5, trucks 6.5-9.

Final drive in a car

The main gear of the car is a permanent gear gear reducer, consisting of driving and driven gears of different diameters. The location of the main gear of the car depends on the design features of the vehicle itself:

cars with front-wheel drive - the main gear is installed with a differential in a single gearbox housing;
cars with rear-wheel drive - the main gear is installed as a separate unit in the drive axle housing;
cars with all-wheel drive- the main gear can be installed both in the gearbox and separately in the drive axle. It all depends on the location ICE car(transverse or longitudinal).

There is also a classification of main gears according to the number of gear stages. Depending on the purpose and layout, both single and double main gears are used on cars.

A single main gear consists of one pair of gears leading and driven. Used on cars and trucks. The double final drive consists of two pairs of gears and is mainly used on medium and heavy trucks to increase torque or to increase ground clearance by off-road vehicles. The transmission efficiency is 0.93-0.96.

Double transmissions can be divided into two types:

double central final drive - both stages are located in one crankcase in the center of the drive axle;
double spaced main gear - the bevel pair is located in the center of the drive axle, and the cylindrical pair is in the wheel gears.

When the main gear is divided into two parts, the loads on and parts are reduced. The dimensions of the crankcase of the middle part of the drive axle are also reduced, as a result ground clearance and vehicle traffic. However, the spaced transmission is more expensive and difficult to manufacture, has a high metal content, and is more difficult to maintain.

Types of main gear by type of gear connection

If we divide the types of main gears, then we can distinguish:

cylindrical;
conical;
worm;
hypoid;

Cylindrical main gear is used on passenger front-wheel drive vehicles with a transverse engine and gearbox. Its gear ratio is in the range of 3.5-4.2.

The gears of the cylindrical final drive can be spur, helical and herringbone. Cylindrical gear has high efficiency(not less than 0.98) but it reduces ground clearance and is quite noisy.

The bevel final drive is used on rear wheel drive vehicles light and medium load capacity with longitudinal ICE location, Where dimensions does not matter.

The axes of the gears and the wheels of such a transmission intersect. These gears use straight, oblique or curved (spiral) teeth. Noise reduction is achieved by using an oblique or spiral tooth. The efficiency of the main gear with a spiral tooth reaches 0.97-0.98.

The worm main gear can be either with the lower or with the upper location of the worm. The gear ratio of such a final drive is in the range from 4 to 5.

Compared to other types of gears, the worm gear is more compact and less noisy, but has a low efficiency of 0.9 - 0.92. Currently, it is rarely used due to the complexity of manufacturing and the high cost of materials.

The hypoid main gear is one of the popular types of gear connection. This transmission is a kind of compromise between bevel and worm final drives.

The transmission is used on rear-wheel drive cars and trucks. The axes of the gears and the wheels of the hypoid gear do not intersect, but cross. The gear itself can be either with a lower or with an upper offset.

The bottom offset main gear allows the cardan gear to be positioned lower. Consequently, the center of gravity of the car is also shifted, increasing its stability when driving.

The hypoid gear, compared to the bevel gear, has greater smoothness, noiselessness, and smaller dimensions. It is used in cars with gear ratio from 3.5-4.5, and on trucks instead of a double final drive with a gear ratio of 5-7. In this case, the efficiency of the hypoid gear is 0.96-0.97.

With all its advantages, the hypoid gear has one drawback - the jamming threshold during the reverse motion of the car (exceeding the calculated speed). For this reason, the driver needs to be especially careful when choosing the reverse speed.

Summing up

So, having figured out what the main gear of the car is for and what types of main gears are used in the transmission, its purpose becomes clear. As you can see, the device and the principle of operation of this node are relatively simple.

At the same time, it is important to understand that given element transmission has a significant impact on fuel consumption, dynamics and whole line other characteristics and indicators of the car.