Double spaced final drive is used on trucks heavy duty when the transmission ratio io ≥ 11 and on multi-purpose vehicles to obtain the required ground clearance.
Advantages transfers:
Gear ratio transmission can reach 20...30;
Smaller dimensions and weight of the cross-axle differential and the diameter of the axle shafts;
compact central part the drive axle, which is important for obtaining a low floor level and the center of gravity of the car, as well as to ensure the required ground clearance;
Ability to adjust gear ratio main gear without changing the central part of the drive axle;
Onboard and wheel reduction gears carry only part of the load on the drive axle.
Flaws transfers:
High labor intensity of maintenance;
The complexity and cost of the design compared to the double central final drive due to a large number details;
Increase unsprung masses(especially when not dependent suspension wheels).
Most often, the spaced main gear consists of a central gearbox (bevel or hypoid gear) and a wheel (or onboard) gearbox. Such a 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 located on the body (or on the frame) of the car and is connected to the wheel gearboxes by cardan gears (with independent suspension wheels).
Wheel gears used in vehicle designs can be with fixed shaft axles or planetary. Their main schemes are shown in fig. 6.12. Most widespread received gearboxes made according to the schemes of Fig. 6.12, a, c, d. Gearboxes, schematically shown in fig. 6.12, a, b, c, g, have fixed shaft axes, and the rest are planetary gears. In gearboxes (Fig. 6.12, aib), the drive gear can be located below the axis of the driven gear, which makes it possible to lower the level of the floor in the car body.
Lubrication of parts of wheel gears is carried out by spraying oil poured into their crankcases.
Determining the parameters of gear wheels of wheel reduction gears, selecting bearings and calculating shafts is carried out according to 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 gears, the modular design principle is used. So, changing gear pairs in the planetary wheel reducer, you can change the total gear ratio of the main gear with a constant gear ratio in the central gearbox, i.e. receive a family of driving axles of various standard 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 with the same or different angular velocities, kinematically interconnected.
In addition to the general technical requirements for all transmission mechanisms, there is one requirement for differentials - they must distribute the torque between the wheels or axles in a proportion that provides the best operational properties vehicle (maximum traction, stability and controllability).
To increase the traction force of the car, it is necessary to distribute the torque along the wheels in proportion to the load on the wheel and the coefficient of adhesion. With different values of the friction coefficient under the wheels of the right and left sides, the traction forces along 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 vehicle, which worsens its stability and controllability. To ensure good stability of movement, the equality of traction forces on the wheels of the right and left sides is necessary. With different values of the friction coefficient under the wheels, this will lead to a limitation of the traction forces on all wheels by the traction force on the wheel with minimal grip, and, as a result, to a 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 gear ratio of the car's transmission. It ensures that the drive wheels roll without slipping when cornering and when driving over bumps in the road.
> 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 conical, 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 of small and medium 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. In addition, the 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 heavy-duty vehicles 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 drive mechanisms rear axle, which are placed 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 cup mounted on the crankcase 9 of the main drive. 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 .
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 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 are big sizes 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!
In this article we will tell you about the main gear device and why you need a car differential, their main malfunctions.
What is it needed for?
Torque from the engine crankshaft through the clutch, gearbox and driveline is transmitted to a pair of helical gears that are in constant mesh. Both wheels will rotate at the same angular velocity. But after all, in this case, turning the car is impossible, because. the wheels must travel an unequal distance during this manoeuvre!Let's take a look at the tracks left by the wet wheels of a car. Looking at these tracks with interest, you can see that the outer wheel from the center of the turn travels a much longer distance than the inner one.
If the same number of revolutions were transmitted to each wheel, then turning the car without black marks would be impossible. Consequently, any car has a certain mechanism that allows it to make turns without “drawing” rubber wheels on asphalt. And this mechanism is called a differential.
The car's differential is designed to distribute torque between the axle shafts of the driving wheels when turning the car and when driving over uneven roads. The differential allows the wheels to rotate at different angular speeds and travel a different path without slipping relative to the road surface.
In other words, 100% of the torque that goes 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 in place, while the other is slipping at this time. But this design allows the car to turn without skidding, and the driver does not change worn tires every day.
Structurally, the differential is made in one node together with the main gear and comprises:
- two gears of semiaxes
- two pinion gears
1 - half shafts; 2 - driven gear; 3 - drive gear; 4 - gears of semiaxes; 5 - satellite gears.
At front wheel drive cars mobile main gear 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 the torque by 90 O, as in rear wheel drive cars mobiles. But, the function of increasing the torque and distributing it along the axes of the wheels remains unchanged in this case as well.
Main malfunctions
Noise ("howl" of the main gear) when driving on high speed occurs due to wear of the gears, their incorrect adjustment, or in the absence of oil in the final drive housing. To eliminate the malfunction, it is necessary to adjust the gear engagement, replace worn parts, and restore the oil level.
Oil leakage can be through seals and loose connections. To eliminate the malfunction, replace the seals, tighten the fasteners.
How is the service?
Like any gear the main gear and differential gears require "lubrication and caress". Although all the details of the main gear and differential look like massive pieces of iron, they also have a margin of safety. Therefore, recommendations regarding abrupt starts and braking, rough clutch engagement and other overload of the machine remain in force.Friction parts and gear teeth, including, must be constantly lubricated. Therefore, oil is poured into the crankcase of the rear axle (for rear-wheel drive cars) or into the crankcase of the block - gearbox, main gear, differential (for front-wheel drive cars), the level of which must be periodically monitored. The oil in which the gears operate tends to "leak" through leaks in the joints 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, by engaging the gear, make this wheel rotate. Look at everything that is spinning, listen to everything that makes suspicious sounds. Then jack up the wheel on the other side. At increased noise, vibrations and oil leaks - start looking for a car service.
Modern car models have in their arsenal, as a rule, several engines - both gasoline and diesel. Engines differ in power, torque, speed crankshaft. WITH different engines apply and different boxes gears: mechanics, robot, CVT and of course automatic.
Adaptation of the gearbox to a specific engine and vehicle is carried out using the main gear, which has a certain gear ratio. This is the main purpose of the final drive of the car.
Structurally, the main gear is a gear reducer, which provides an increase in engine torque and a decrease in the rotational speed of the driving wheels of the vehicle.
On pre-wheel drive vehicles, the main gear is located together with the differential in the gearbox. In a car with rear wheel drive drive wheels, the main gear is placed in the crankcase of the drive axle, where, in addition to it, there is also a differential. The position of the main gear 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. Single main gear consists of driving and driven gears. Double final drive consists of two pairs of gears and is mainly used on trucks where an increase in gear ratio is required. Structurally, the double final drive can be central or divided. The central main gear is arranged in common crankcase leading bridge. In a split gear, the gear stages are spaced apart: one is located in the traveling axle, the other is in the hub of the drive wheels.
View gear connection defines 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 final drive 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 mechanical box several gears are used secondary shafts(two or even three), each of which has its own final 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 pre-wheel drive vehicles, the main gear can be replaced, which is integral part transmission tuning. This leads to an improvement in the acceleration dynamics of the car and a reduction in the load on the clutch and gearbox.
Bevel, hypoid and worm main gears are used on rear wheel drive vehicles, where the engine and gearbox are parallel to the movement, and the torque must be transmitted to the drive axle at a right angle.
Of all the types of final drive rear-wheel drive vehicles, the most popular is hypoid final drive, which is distinguished by a lower 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 cars 3.5-4.5, for trucks 5-7.
The bevel final drive is used where dimensions and the noise level is not limited. The worm final drive, due to the laboriousness of manufacturing and the high cost of materials, is practically not used in the design of the transmission of a car.
