Double spaced main gear used on trucks heavy lifting capacity, When gear ratio transmission io ≥ 11 and on multi-purpose vehicles to obtain the required ground clearance.
Advantages transmission:
The transmission ratio can reach 20...30;
Smaller dimensions and weight of the cross-axle differential and diameter of the axle shafts;
Compact central part of the drive axle, which is important for obtaining a low floor level and center of mass of the vehicle, as well as for ensuring the required ground clearance;
Possibility of adjusting the final drive gear ratio without changing the central part of the drive axle;
Final drives and wheel drives carry only part of the load on the drive axle.
Flaws transmission:
High labor intensity of maintenance;
The design becomes more complex and more expensive compared to a double central main gear due to the large number of parts;
Increase unsprung masses(especially when Not dependent suspension wheels).
Most often, a spaced main gear consists of a central gearbox (bevel or hypoid gear) and a wheel (or final drive) gearbox. This scheme is used both with a rigid axle housing (with dependent wheel suspension), and in the case of an articulated drive axle, when the central gearbox is placed on the body (or frame) of the car and is connected to wheel gearboxes by cardan transmissions (with independent wheel suspension).
Wheel gearboxes used in automobile designs can be with fixed shaft axles or planetary. Their main diagrams are shown in Fig. 6.12. Most widespread received gearboxes made according to the diagrams in Fig. 6.12, a, c, d. Gearboxes, shown schematically in Fig. 6.12, a, b, c, g, have fixed shaft axes, and the rest are planetary mechanisms. In gearboxes (Fig. 6.12, aib), the drive gear can be located below the axis of the driven gear, which allows the floor level in the car body to be lowered.
Lubrication of wheel gear parts is carried out by splashing oil poured into their crankcases.
Determination of the parameters of gear wheels of wheel reducers, selection of bearings and calculation of shafts is carried out using the same methods as for gearboxes. The materials used for the manufacture of gears and shafts are also similar.
When developing drive axles with wheel reduction gears, the modular design principle is used. Thus, by changing gear pairs in a planetary wheel reducer, it is possible to change the overall gear ratio of the main gear while maintaining a constant gear ratio in the central gearbox, i.e. receive a family of drive axles of various sizes.
Differentials
A differential is a transmission mechanism that performs the function of distributing the torque supplied to it between the wheels or axles and allowing the driven shafts to rotate at the same or different angular velocities, kinematically related to each other.
In addition to the general technical requirements for all transmission mechanisms, there is one requirement for differentials - they must distribute torque between the wheels or axles in a proportion that provides the best operational properties vehicle (maximum traction force, stability and controllability).
To increase the traction force of a car, it is necessary to distribute torque across the wheels in proportion to the load on the wheel and the coefficient of adhesion. With different values of the coefficient of adhesion under the wheels of the right and left sides, the traction forces on the sides will be different, as a result of which a moment of these forces will appear relative to the vertical axis passing through the center of mass of the car, worsening its stability and controllability. To ensure good motion stability, it is necessary to have equal traction forces on the wheels of the right and left sides. With different values of the coefficient of adhesion under the wheels, this will lead to limitation of the traction forces on all wheels by the traction force on the wheel that has minimal traction capabilities, and, as a result, to deterioration traction properties car. The noted contradiction is almost always resolved in favor of increasing the traction properties of the car.
It should be noted that the differential does not affect the overall transmission ratio of the vehicle. It ensures that the drive wheels roll without slipping when cornering and when driving over uneven roads.
In this article we will tell you about the final drive device and why a car differential is needed, and their main malfunctions.
What is it needed for?
Torque from the engine crankshaft is transmitted through the clutch, gearbox and cardan drive to a pair of helical gears that are in constant mesh. Both wheels will rotate at the same angular velocity. But in this case, turning the car is impossible, because The wheels must travel an unequal distance during this manoeuvre!Let's look at the marks left by the car's wet wheels when turning. Looking at these tracks with interest, you can see that the wheel outside the center of rotation travels a much longer path than the inside one.
If each wheel were given the same number of revolutions, then turning the car without black marks would be impossible. Consequently, any car has some mechanism that allows it to make turns without “drawing” the tires on the asphalt with rubber. And this mechanism is called a differential.
The car's differential is designed to distribute torque between the axle shafts of the drive wheels when turning the car and when driving over uneven roads. The differential allows the wheels to rotate at different angular speeds and travel different paths without slipping relative to the road surface.
In other words, 100% of the torque that comes to the differential can be distributed between the drive wheels as 50 x 50 or in another proportion (for example, 60 x 40). Unfortunately, the proportion can be 100 x 0. This means that one of the wheels is standing still, while the other is slipping at the same time. But this design allows the car to turn without skidding, and the driver does not have to change worn tires every day.
Structurally, the differential is made in one unit together with the main gear and comprises:
- two axle gears
- two satellite gears
1 - axle shafts; 2 - driven gear; 3 - drive gear; 4 - axle gears; 5 - satellite gears.
For front-wheel drive vehicles, the final drive and differential are located in the gearbox housing. The engine of such cars is located not along, but across the axis of motion, which means that initially the torque from the engine is transmitted in the plane of rotation of the wheels. Therefore, there is no need to change the direction of torque by 90 O, as in rear-wheel drive cars. But the function of increasing torque and distributing it along the wheel axles remains unchanged in this case.
Basic faults
Noise (“howl” of the main gear) when driving high speed occurs due to gear wear, improper adjustment, or lack of oil in the main gear housing. To eliminate the malfunction, it is necessary to adjust the gear engagement, replace worn parts, and restore the oil level.
Oil leakage can occur through seals and loose connections. To eliminate the malfunction, replace the seals and tighten the fastenings.
How does the service work?
Like any gears - The final drive and differential gears require lubrication and care. Although all the parts of the main gear and differential look like massive pieces of hardware, they also have a margin of safety. Therefore, recommendations regarding sudden starts and braking, rough clutch engagement and other overloading of the machine remain valid.Rubbing parts and gear teeth, among others, must be constantly lubricated. Therefore, into the crankcase rear axle(for rear-wheel drive cars) or into the crankcase - gearbox, main gear, differential (for front-wheel drive cars), oil is poured, the level of which must be periodically monitored. The oil in which the gears operate has a tendency to “leak” through leaks in the connections and through worn seals.
If you suspect any trouble with the transmission, jack up one of the driving wheels of the car. Start the engine and put the wheel in gear to rotate. Look at everything that is spinning, listen to everything that makes suspicious sounds. Then jack up the wheel on the other side. If there is increased noise, vibration and oil leaks, start looking for an auto service.
Modern car models usually have several engines in their arsenal - both gasoline and diesel. Engines vary in power, torque, speed crankshaft. WITH different engines apply and different boxes gears: manual, robot, variator and of course automatic.
Adaptation of the gearbox to specific engine and the car is carried out using a final drive having a certain gear ratio. This is the main purpose of the final drive of a car.
Structurally, the main gear is gear reducer, which provides an increase in engine torque and a decrease in the speed of rotation of the driving wheels of the car.
On front-wheel drive vehicles, the main gear is located together with the differential in the gearbox. In a car with rear wheel drive of the driving wheels, the main gear is placed in the drive axle housing, where, in addition to it, the differential is also located. Final drive position in vehicles with all-wheel drive depends on the type of drive, so it can be both in the gearbox and in the drive axle.
Depending on the number of gear stages, the main gear can be single or double. A single final drive consists of a drive and driven gear. The double final drive consists of two pairs of gears and is used mainly on trucks where an increase in gear ratio is required. Structurally, the double main gear can be central or divided. The central main gear is located in a common drive axle housing. In a split transmission, the gear stages are spaced apart: one is located in the driving axle, the other in the hub of the drive wheels.
The type of gear connection determines the following types of main gear: cylindrical, bevel, hypoid, worm.
Cylindrical final drive used on front-wheel drive vehicles where the engine and gearbox are located transversely. The transmission uses gears with oblique and chevron teeth. The gear ratio of the cylindrical main gear is in the range of 3.5-4.2. A further increase in the gear ratio leads to an increase in size and noise level.
IN modern designs manual box several gears are used secondary shafts(two or even three), each of which has its own main drive gear. All drive gears mesh with one driven gear. In such boxes, the main gear has several gear ratios. The main gear of the DSG robotic gearbox is arranged according to the same scheme.
On front-wheel drive vehicles, the main gear can be replaced, which is integral part transmission tuning. This leads to improved acceleration dynamics of the vehicle and reduced load on the clutch and gearbox.
Bevel, hypoid and worm final drives are used on rear-wheel drive vehicles, where the engine and gearbox are located parallel to the movement, and torque must be transmitted to the drive axle at a right angle.
Of all the types of final drive of rear-wheel drive cars, the most popular is hypoid final drive, which is characterized by less load on the tooth and low level noise. At the same time, the presence of displacement in the meshing of gears leads to an increase in sliding friction and, accordingly, a decrease in efficiency. The gear ratio of the hypoid final drive is: for passenger cars 3.5-4.5, for trucks 5-7.
Bevel final drive is used where dimensions and the noise level is not limited. Due to the complexity of manufacturing and the high cost of materials, worm main gears are practically not used in the design of car transmissions.
Completed by student of group No. 2307 Vasiliev S.V.
Laboratory work No. 5.
Main gear.
A gear mechanism that increases the gear ratio of a car transmission is called final drive.
main gear serves to constantly increase the engine torque supplied to the drive wheels and reduce their rotation speed to the required values.
main gear provides maximum vehicle speed in top gear and optimal consumption fuel in accordance with its gear ratio. The final drive ratio depends on the type and purpose of the vehicle, as well as the power and speed of the engine. The final drive ratio is usually 6.5...9.0 for trucks and 3.5...5.5 for cars. Used on cars Various types main gears ( picture 1).
Picture 1- Types of final drives
Single final drives
Single final drives consist of one pair of gears.
Cylindrical final drive It is used in front-wheel drive passenger cars with a transverse engine and is located in a common crankcase with a gearbox and clutch. Its gear ratio is 3.5...4.2, and the gears can be spur, helical and chevron. The cylindrical main gear has a high Efficiency- no less 0,98 , but it reduces the vehicle's ground clearance and is noisier.
Bevel final drive (Figure 2, a) is used on passenger cars and light and medium-duty trucks. The axes of the driving 1 and driven 2 gears in the bevel main gear lie in the same plane and intersect, and the gears are made with spiral teeth. The transmission has increased strength of gear teeth, is small in size and allows for a lower center of gravity of the vehicle. Efficiency bevel final drive with spiral tooth 0,97...0,98 . Gear ratios of bevel final drives 3.5...4.5 for cars and 5...7 for trucks and buses.
Figure 2- Main gears
a, b, c - single; g, d - double; e - gearbox; 1 - drive gear; 2 - driven gear; 3 - worm; 4 - worm gear; 5 - bevel gear; 6 - cylindrical gears; 7 - axle shaft; 8 - sun gear; 9 - satellite; 10 - axis; 11 - ring gear; l - hypoid displacement
Hypoid final drive (Figure 2, b) It has wide application on cars and trucks. The axes of the drive 1 and driven 2 gears of the hypoid main gear, unlike the bevel gear, do not lie in the same plane and do not intersect, but intersect. The transmission can be with upper or lower hypoid displacement l. A top-biased hypoid final drive is used on multi-axle vehicles, since the drive gear shaft must be through, and on front-wheel drive vehicles, based on the layout conditions. The final drive with lower hypoid displacement is widely used in passenger cars.
Gear ratios of hypoid final drives passenger cars 3.5...4.5, and trucks and buses 5...7. The hypoid main gear is more durable and quiet than others, has high smoothness of engagement, is small in size and can be used on trucks instead of a double main gear. She has Efficiency, equal 0,96...0,97 . With a lower hypoid offset, it is possible to position the cardan transmission and lower the vehicle's center of gravity, increasing its stability. However, the hypoid final drive requires high precision manufacturing, assembly and adjustment. Due to the increased sliding of gear teeth, it also requires the use of special hypoid oil with sulfur, lead, phosphorus and other additives that form a strong oil film on the gear teeth.
Worm final drive (Figure 2, c) can be with an upper or lower location of the worm 3 relative to the worm gear 4, has a gear ratio of 4...5 and is currently rarely used. It is used on some multi-axle, multi-wheel drive vehicles. Compared to other types, the worm final drive is smaller, quieter, provides smoother engagement and minimizes dynamic loads. However, the transmission has the smallest Efficiency (0,9...0,92 ) and in terms of the labor intensity of production and the materials used (tin bronze) is the most expensive.
Double final drives
These programs apply on medium- and heavy-duty trucks, 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 gearboxes. Such a gearbox ( Figure 2, f) 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, ground clearance increases and thereby improves 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.
Material from the Encyclopedia of the magazine "Behind the wheel"
Main gear is a mechanism, part of a car's transmission, that transmits torque from the gearbox to the drive wheels of the car. The main gear can be made in the form of a separate unit - the drive axle ( rear wheel drive cars classic layout), or combined with engine, clutch and gearbox into a single power block(rear engine and front wheel drive cars)
.
According to the method of transmitting torque, the main gears are divided into gear(gear) and chain. Chain final drives are currently used only on motorcycles and bicycles.
The chain main drive consists of two sprockets - a drive sprocket, mounted on the output shaft of the gearbox, and a driven one, combined with the hub of the drive (rear) wheel of the motorcycle. The final drive of a bicycle with a planetary gearbox is somewhat more complex in design. The driven sprocket, driven by a chain, rotates the gears of the planetary gearbox built into the wheel hub and, through it, the drive sprocket. rear wheel.
Sometimes, in classically designed motorcycles, a toothed reinforced belt is used in the final drive instead of a chain (for example, in the final drive of Harley-Davidson motorcycles). In this case, we usually talk about a belt drive as a separate type of main drive.
Belt main The transmission is widely used in light motorcycles and in scooters (motor scooters) with a continuously variable transmission. In this case, the variator serves as the final drive, since the driven pulley of the belt variator is integrated with the hub of the motorcycle's drive wheel.
Classification of gear final drives
Double final drive
Based on the number of gear pairs, the main gears are divided into single And double. Single final drives are found 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. Double gear capable of transmitting more torque than a single one.
On three-axle trucks and multi-axle 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.
The most widely used single main gears according to the type of gearing are divided into:
- 1. 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 large diameter, which depends on the gear ratio built into the design of the gearbox, 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.
- 2. 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.
- 3. Hypoid(or spiroid) main gears, in which torque is transmitted by a pair of gears with oblique or curved teeth. A pair of hypoid gears is 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 installed in cars and trucks classic (rear-wheel drive with front engine) and rear-engine layouts.
Double main gears according to the type of gearing are divided into:
- 1. 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.
- 2. 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 final drives are divided according to the type of meshing of gear pairs into:
- 1. Conical-cylindrical.
- 2. Cylindrical-conical.
- 3. 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. In heavy motorcycles with cardan transmission and the rear wheel drive does not use a differential. In motorcycles with a sidecar and all-wheel drive (on the rear wheel of the motorcycle and on the wheel of the sidecar), the differential is made in the form of a separate mechanism. Such motorcycles are equipped with two independent main gears connected to each other by a differential.
Operating principle of hypoid final drive
Torque is transmitted from the engine through the clutch, gearbox and driveshaft to the drive gear axis of the hypoid final drive. The axis of the drive gear is installed coaxially with the engine drive shaft and the gearbox driven shaft. As it rotates, the drive gear, which has a smaller diameter than the driven gear, transmits torque to the teeth of the driven gear, causing it to rotate. Since the surface contact of the teeth is increased due to their special shape - oblique or curved - the transmitted torque can reach very high values. However, the complex shape of the teeth leads to the fact that their surface is affected not only by shock loads, but also by frictional forces (due to the teeth slipping relative to each other). Therefore, in hypoid final drives they use special oil, with high lubricating properties and providing long term gear pair service.
Operating principle of worm final drive
By virtue of design features, large gear ratio (from 8 in steering mechanisms, up to 1000 in especially powerful winches) and low efficiency, the worm pair is not used in automobile final drives (with rare exceptions). It is most widespread in winches.
Torque is transmitted to the worm wheel through a power take-off connected to transfer case, installed (as a rule, there are other kinematic schemes) behind the vehicle’s gearbox. The axes of the worm and the driven gear (driven wheel) are located at right angles (but there is also a different arrangement of the axes of the worm pair). The worm wheel meshes with a driven helical (to ensure close contact and increase the meshing surface) gear wheel. Torque is transmitted from the helical groove of the worm to the teeth of the driven gear. The rotation speed of the worm is much higher than the rotation speed of the driven wheel. Due to this, the torque increases proportionally - the more gear ratio, the more force the winch can develop.
Worm gears have a number of advantages over other types of main gears. It is highly wear-resistant and does not require the use of high-quality lubricants. It is capable of transmitting ultra-high torque. It is characterized by low noise and smooth running (due to the absence of shock loads on the worm groove and the surface of the driven gear teeth). Finally, the worm gear has the property of self-braking - when the transmission of torque to the worm stops, the rotation of the driven wheel automatically stops.
To the disadvantages worm gear include a tendency to heat up due to frictional forces, to jamming of the mechanism with slight wear, and increased requirements for the accuracy of the assembly of the worm pair.
Worm main gear refers to irreversible gearboxes. If the force is transmitted from the driven gear wheel to the driving worm, that is, in the reverse order, the worm will not rotate. Consequently, the worm main gear prevents the vehicle from moving by inertia or coasting. Hence its use on low-speed transport equipment and special-purpose vehicles. On winches, to ensure free rotation of the drum, the worm pair is equipped with a free (reverse) clutch, which disconnects the drum and the driven gear when it rotates in reverse direction- unwinding the winch cable.
