Four-wheel drive means that torque is supplied to each wheel. Moreover, so that the wheel can move and turn relative to the body

Actually, the drive rotates the wheels. When on screen dashboard your SUV appears an animated picture of the distribution of traction along the axles and wheels, it exactly repeats the real system of shafts under its bottom. These shafts are thick metal rods or tubes with hinged ends. The hinge allows you to transfer rotation at an angle: the wheels, together with the suspension, go up and down, and the front ones also turn at a decent angle.

FIRST SHAINS

At first, the world of drive was dominated by leather belts, the same as those used in machine tools. At the then low speeds and ridiculous engine power, this was still fine, but as the speeds increased, roller chains with moving links, like on motorcycles, became popular. The transmission at the rear of the car ended with a conventional axle rigidly fixed to the frame. Instead of wheels, driving sprockets were attached to its ends, and driven ones were attached to the wheels suspended on springs. For a couple rear wheels there were two bridges - leading and suspension, and the free slack of the chains provided some mobility of the latter. There was no question of driving the front swivel wheels with their help.

This scheme was quickly abandoned due to its cumbersomeness and unreliability and began to come up with more advanced ones.

WHERE ARE THE JACKETS?
Unequal angular velocity refers to rotation in which the wheel is continuously accelerated and decelerated every quarter of its revolution. In addition to the unpleasant effects on steering and suspension (jerks), work with an uneven angular speed is fraught with rapid wear of the entire transmission. Irregularity of rotation cardan transmission the greater, the greater the angle between the axes of its shafts. In this case, the leading part of the hinge rotates uniformly.

CARDANO AND LEONARDO

Just think, the principle of cardan transmission was described in detail by Girolamo Cardano in the 16th century, and was first mentioned by Leonardo da Vinci! But it's one thing to come up with something, and quite another - to embody it in metal.

The first cardan shafts settled in cars in the first decade of the twentieth century. Of all the mobile gears used today, the cardan is the simplest. Four needle bearings and a spider. Its simplicity is compensated for by one important disadvantage: small working angles. Up to 12 degrees, it still spins more or less smoothly. Higher - with jerks. Few people know that even without an angular difference, it is harmful for the cardan to work: the fixed needles of the bearings make grooves in the support pins of the crosspieces, depriving the joint of mobility. Therefore, usually a small (1.5–2 °) working angle is assigned to universal joints.
The cardan is suitable for driving slow-moving rear wheels, but what about the front ones, where the turning angles are often close to 30 degrees?

IN front axle the familiar Jeep has lived for many years with dual universal joints. The ingeniously simple solution - to divide the working angle in half between the two hinges - has two noticeable drawbacks: the bulkiness of the structure and all the same jerks with the steering wheel turned as much as possible. It was necessary to come up with something radically new.

PARRALLELS DO NOT CONNECT
In conventional cardan shafts for driving axles, two crosses are used, the ears of which are located on one shaft in the same plane. The shafts themselves are positioned, if possible, so that the axles of the output shaft of the transfer case (or gearbox) and the axis of the drive shaft rear gear were parallel. Identical, but multidirectional angles of inclination of such crosses cardan shaft contribute to the compensation of angular pulsations. One of the reasons for the emergence of independent rear suspension in that their gearbox hardly moves relative to the rest of the transmission. In this case, the angles of the cardan joints are unchanged and minimal.

Union of needles. No hinge simpler crosspieces cardan.
But the elementary construct entails operational subtleties.
Four needle bearings need lubrication -
set at the factory or periodically replenished during the ride

Side by side. Double crosspiece allows you to divide the harmful angle
equally between the halves of the hinge.
Rough decision "head-on" turned out to be effective and
quite budgetary, but cumbersome

WORLD OF SLIDING BALLS

Transmit rotation with equal angular velocity for the first time and replace cardan bearings The German inventor Karl Weiss discovered movable balls in the early 1920s. His invention, the very first CV joint, consisted of two forks at the ends of two shafts, in the paired grooves of which four balls rolled. The fifth ball in the center served as a hinge against which the shafts tilted. Some time later, the Weiss patent was bought by the company of the American inventor and industrialist Vincent Hugo Bendix, and we can still see the Bendix-Weiss CV joints, for example, in the front axle of the UAZ.

This design is well suited for the transmission of solid torque in heavy off-road vehicles, but still has a low resource and noticeable losses at large angles due to the small total contact surface (only two balls work at the same time). The path of improvement corner joints became obvious: an increase in the number of contacting parts.

Familiar Bendix. Hinge design well known to owners
UAZs and a good half of other SUVs.
Simple, technologically advanced and inexpensive. One trouble - only two balls
simultaneously transmit rotation, which makes the working surface small

BIGGER IS BETTER

In 1936, inventor Alfred Rcepp managed to achieve unprecedented uniformity of the angular velocity of the shafts. The ingredients for success are six balls instead of four, a spherical hinge and long guide grooves. Most often, it is this hinge today that we call the CV joint - a hinge of equal angular velocities... Strictly speaking, there are hardly noticeable jerks in the Rceppa hinge, but they are so small that even with a huge operating angle of 40 degrees by the standards of drives, they can be neglected. However, these hinges conquered the world rather slowly: the manufacture of complex spatial parts - inner and outer cages, a cage with holes, precise spherical mates - required the most precise equipment and high-quality materials. But it is the CV joints "Rceppa" and their various descendants ("Bearfields" and GKN) that now rule the show in the systems all-wheel drive... The familiar to us "grenade" in the drive is it, the Rceppovska six-ball clutch.

THE CURSE OF THE CARDAN
The problem of unequal angular velocity is well known lada owners 4 × 4 and Chevrolet niva... Cardan joint between gearbox and transfer case the old version of the transmission, coupled with the influence of the two drive axle driveshafts, is the source of the most unpleasant vibration of an SUV. One of the good recipes against vibrations - rigid fastening of transmission units to each other - was ignored in the Niva, having received an ineradicable source of various transmission jerks. Less technological, but following the "golden rule" UAZ received a monoblock transmission without intermediate cardan shafts and a quiet, without pulsations, transmission.

Sphere in sphere. The basis of Rcepp's invention is
spherical surfaces sliding in each other.
Very precise equipment is required for their manufacture.

SIDE AND BACK

But not only CV joint "Rceppa" turns wheels on off-road vehicles. The high-precision openwork design benefits from compactness, but has torque limits. In simple terms, it is well suited for SUVs and crossovers, but too expensive and unreliable for use in heavy military and special vehicles. For them, simplicity and low cost are important, and jerks in the transmission are a secondary matter.

Manufacturers of front-wheel drive cars, unwilling to pay money to the companies that own the Bendix-Weiss and Rceppa patents, have developed simplified designs. For example, the Tract hinge is a combination of cams and bushings connected by sliding parts with large grinding surfaces. A similar device has a domestic cam-disk hinge, which is successfully used on all-wheel drive KAMAZ, KRAZ and URALs. Large dimensions and the huge friction surface of such hinges is not terrible on large equipment with a high motor torque, and the limited resource of parts is compensated for by their cheapness and ease of replacement.

Sly Thomson. By placing one crosspiece inside the other,
engineer Thomson won in size, but lost in strength.
Pay attention to the complex system of indexing levers.

Another ersatz-hinge has the cunning name "tripod". Everything is simple here: three axles sticking out in different directions at the end of the drive are carried along a roller with a spherical surface. The rollers fit into the three cutouts of the outer cage. The system is simple and reliable, but does not get along well with large angles. However, the tripod is often used as an internal hinge at the front. The reason is still the same - relative simplicity and cheapness.

Tripod. Uncomplicated design with rollers and grooves in the outer cage.
Not afraid of gaps, but dislikes large angles.
Often works as an internal front wheel drive joint

Cardan transmission

General information about cardan drives:

An intermediate gear on cars on tractors transmits torque, if an intermediate gear is placed between units rigidly connected to the frame or body of cars, then the angle between the axes of their shafts when the frame is skewed should be no more than 2-3 degrees. If while driving vehicle one or both connected units move together with the wheels (bridges), then the angle between the axes of the shafts of these units increases, reaching in the range from 15 to 20 degrees, and in off-road vehicles the limit reaches from 30 to 45 degrees. Intermediate connections or transfers include:

Cardan gears of equal and unequal angular speeds

The following requirements are imposed on them:

Transmission of torque without creating additional bending and twisting moments

Vibration and axial loads

Ensuring equality of angular velocities

Quiet operation

Intermediate gears according to their purpose, that is, according to the transmission of torque, are divided into:

Elastic connections

Cardan transmission

Constant Velocity Joints

Cardan drives of cars and tractors consist of the following main parts:

Elastic connections (Soft gimbals)

Elastic connections are installed between the transmission elements in order to reduce dynamic loads with a sharp increase in it, damp vibrations and torsional vibrations, that is, to damp load fluctuations. Most often, rubber cushions or bushings are used as an elastic element. The most common elastic joints are of two types:

With elastic disc

With rubber bush

With resilient disc, it works satisfactorily at an angle of 2 to 5 degrees

With rubber-metal bushings, the numbers of which are chosen from 4 to 8 degrees, depending on the value of the transmitted torque and depending on the type road surface operating conditions, etc. The permissible angle between the shafts in the rubber-metal sleeve of the universal joint increases to 12 degrees. The physical and mechanical properties of rubber used in rubber-metal bushings are as follows:

Tensile strength must ensure from 150 kPa

Elongation not less than 350%

Asynchronous gimbals.

Cardan drives consist of one or two cardan joints. The hinge is a fork-shaped part connected by crosses and serves to connect the input and output shafts, as well as to transmit torque.

The operating conditions of the cardan drive are determined by the angle between the axes of their shafts: the larger the angle, the more difficult the operating conditions. The efficiency decreases sharply depending on external factors. When the shafts are rotated at an angle, the cross piece swings on the spikes within the angle, which causes uneven rotation of the shaft, with uniform rotation of the input shaft. For any position of the shafts, the equality is equal:

Where are the corners turning the master and slave. The inner forks of the hinges are placed on the shaft in one plane, while marking with a mark. If the angles are the same, that is, a1 \u003d a2, then the synchronization of rotation of the entire system is ensured. Cardan transmission is a combination of cardan joints and cardan shafts, which is designed or used to connect transmission units, the axes of which do not coincide, as well as to transmit torque. Each hinge consists of forks, a crosspiece, needle bearings, the glasses of which are fixed with covers and bolts. An oiler is sometimes provided in the cross, and long-term grease is pumped into the bearing. Axial movement cardan shafts is carried out through the use of a movable joint, movable joints can be with rolling friction. Their working elements, i.e. balls or rollers, have a cylindrical or spherical surface shape and move in the grooves of the corresponding profile.

In the design of cardan drives, movable joints with sliding friction are most often used. In this case, the shafts are made with splined involute or rectangular profiles. To increase the wear resistance, the splines are covered with antifriction polymer materials, during rotation or when transmitting torque over a long distance, two cardan shafts are used with three hinges and with an intermediate support of one of the shafts (outboard bearing).

Hinges of equal angular velocities - hinges are used primarily when transferring torque to driving steered wheels. In this case, uniform rotation of the wheels is ensured at large varying angles between the shafts. When installing the CV joint, the angular speeds of the shafts they connect will be the same for any angular movement. CV joints (synchronous joints) are distinguished by the type of working elements, double universal joints with cross and needle bearings, ball with 4, 6 balls, disk. On off-road vehicles, ball CV joints with dividing grooves and a dividing lever are widely used

Federal Agency for Education

Siberian State Automobile and Highway Academy (SibADI)

Department "Cars and tractors"

DRIVE GEAR

Methodical instructions for the implementation of laboratory work on the discipline "Construction of cars and tractors" for students of the specialty 190100

Compiled by A.M. Zarshchikov

THEM. Knyazev

I.V. Khamov

Publishing house - SibADI

Reviewer doct. those. Sciences, prof. V.V. Evstifeev

The work was approved by the scientific and methodological council of the specialty "Automobiles and Automotive Industry" as guidelines to implementation laboratory work in the discipline "Construction of cars and tractors" for students of the specialty 190100.

Cardan transmission: Methodical instructions for laboratory work in the discipline "Construction of cars and tractors" for students of specialty 190100 / Comp .: A.M. Zarshchikov, I.M. Knyazev, I. V. Khamov - Omsk: Publishing house SibADI, 2013.- 18 p.

Variants of cardan transmissions of a car, their work are considered. and calculation elements.

Il. 15. Bibliography: 3 titles.

© Compiled by A.M. Zarshchikov, I.M. Knyazev, I. V. Khamov

2013 G.

1. BASIC PROVISIONS …………………………………… ...… ... 4

1.1. Classification of cardan drives ..… .. ………………………… ... 4

1.2. Kinematics of Hooke's asynchronous universal joint …………… .9

1.3. Critical frequency of rotation of the cardan transmission (KCHV) ......... 13

2. ORDER OF CONDUCTING THE WORK ……………………………… ... 15

3. CONTROL QUESTIONS ………………………………………… 15

REFERENCES ……………………………………… ..... 16

Purpose of work: to study the structure and operation of an automobile cardan transmission.

Equipment: stand with a mock-up of a cardan transmission based on Hooke's asynchronous hinge.

MAIN PROVISIONS

1.1. Driveline classification

The cardan drive is used to transfer the power flow between the transmission units, the mutual linear and angular position of which changes during operation.

Driveline requirements

Provide a synchronous connection of the angular speeds of rotation of the driving and driven links.

Allow angles of deviation between the axes of the shafts exceeding the maximum possible during operation.

The critical speeds must exceed the maximum possible during the entire period of operation.

Provide partial damping of dynamic transmission loads.

Avoid the occurrence of noise and vibrations throughout the entire operating speed range.

Classification:

1. On kinematics:

Equal Velocity Joints (CV joints).

Unequal angular velocity joints.

2. By design:

With simple cardan joints (Fig. 1. Hooke's joint). These are joints of unequal angular velocity (asynchronous).

A constant velocity joint (CV joint) with a "Rcepp" -type indexing lever (Fig. 2.).

Ball joints of equal angular velocity with indexing arms or indexing grooves (fig. 3).

Figure: 1. Hooke's asynchronous gimbal

Figure: 2. Hinge of constant angular velocities with indexing lever:

1 - driven shaft; 2 - dividing lever; 3 - spherical cup (part of the driven shaft); 4 - spherical fist (on the splines of the drive shaft); 5 - drive shaft; 6 - spherical ball separator; 7 - compression spring for backlash-free installation of the lever

The most widespread are CV joints with pitch grooves. On modern domestic cars, front-wheel drive is carried out using just such hinges. Outside (near the wheel) a Beerfield six-ball joint is usually installed. It allows you to turn the steered wheel up to 45 0.

In fig. 3a shows a drawing of the hinge, and Fig. 3b diagram of the hinge and the placement of the ball 2 in the body 1 and the knuckle 4. Number 3 shows a spherical separator, which simultaneously mates with the spherical surface of the body 1 along the radius R 2 and the spherical surface of the fist 4 along the radius R one . Shaft 5 through an internal hinge is connected to main gear, and the drive wheel of the car is attached to the shaft coming from the housing 1.

Figure: 3. Joint of equal angular velocities with pitch grooves

The internal hinge (Fig. 4), also of equal angular velocities, still allows you to change the length of the drive to compensate for the suspension travel, moving longitudinally. Therefore, it is called universal.

Figure: 4. Internal universal SHRUS

In it, the separator 4 has different centers of the outer and inner spheres. In addition, the sphere of the separator, which mates with the housing 1, passes in its narrow part into a generally tapered surface. The grooves in the body 1 and fist 3 are longitudinal, so the ball not only rolls, but also slips during the longitudinal movement of the shaft with fist 4. The maximum angle of inclination of such a hinge, in connection with the above, does not exceed 20 0.

Three-stud cardan joints of equal angular velocities (fig. 5):

Figure: 5. Three-stud CV joint

a) rigid (only changes the angle between the shafts, therefore it stands outside (Fig. 5);

b) a universal joint of the same type allows the drive to have longitudinal movements to compensate for movement from the suspension.

Rollers 3 are put on three spikes 2, which roll over fork 4. In addition, it is possible to move the roller along the spike 2.

CV joints of this type are not widely used due to the greater load on the parts.

Cam (Fig. 6.) and disc (Fig. 7.) CV joints.

Figure: 6. Cam CV joint

Figure: 7. Disk CV JOINT

3. By torsional rigidity:

With rigid hinges.

With resilient (elastic) hinges.

4. By the limiting angle of deviation:

With full cardan shafts (deflection angle over 40 0). These hinges are discussed above.

With semi-cardan joints (angles do not exceed 1.5 ... 2.0 0, Fig. 8).

Figure: 8. Semi-cardan joint

The middle shaft in Fig. 8.At the edges it has gears that mesh with gear couplings, and those, in turn, overlap with their teeth the gears of the driving (left) and driven (right) shafts. In each gearing, a slight misalignment is possible, which makes it possible to obtain a small angular deviation of the driven shaft relative to the driving one. But, since the gear mates are skewed, they wear out quickly and unevenly.

Elastic couplings also belong to semi-cardan joints.