When you press the accelerator pedal, the torque from the engine goes a long way before making the wheels spin. The central link of this chain is main-transmissionlocated inside the back axle crankcase or gearbox. It is this node that is responsible for the final rotational conversion, allowing the car to use the engine power efficiently.
Without the correct operation of this mechanism, the movement of the vehicle would be impossible or extremely inefficient. In this article, we will discuss in detail the design features, physical principles and subtleties of customization, which should know everyone who wants to deeply understand. motor-mechanics.
Appointment and basic principles of work
The main task of the main transmission is to increase the torque coming from the driveshaft or output shaft of the gearbox, while reducing the frequency of rotation. This process is necessary, as modern internal combustion engines give maximum power and torque at high revs, which is not advisable to directly transfer to the wheels.
The second critical function is to change the direction of rotation by 90 degrees. Since the engine crankshaft and gearbox shafts are usually oriented along the longitudinal axis of the car, and the wheels rotate in the transverse plane, a power flow rotation mechanism is needed. It is here, at the point of engagement of the gears, that the thrust vector turns to a right angle.
The efficiency of the unit directly affects fuel efficiency and dynamic characteristics. Engineers select the gear ratio so as to find a balance between the acceleration dynamics and the maximum speed. Too "short" transmission will give a jerk at the start, but will limit the "maximum speed", and too "long" will allow you to develop high speed, but will make acceleration sluggish.
Understanding these principles is important not only for engineers but also for owners who choose oil or diagnose extraneous noise. Incorrectly selected lubricant viscosity or wear of bearings can completely change the nature of the entire transmission.
Design and key elements of the node
Structurally, the main transmission is a gearbox consisting of two main gears: the lead and the driven. The lead gear, which has a smaller diameter and number of teeth, is connected to the tailing, which takes torque. The steered gear, much larger in size, is rigidly fixed on the differential.
To ensure smooth running and quiet operation in modern cars, hypoid gears are widely used. Unlike classical conical, the axes of the shafts in hypoid gear are displaced, which allows you to lower the driveshaft below and increase ground clearance. However, this design requires the use of special oils with anti-sharp additives.
- 🔧 The lead gear: transmits rotation, experiences high loads on bending and torsion.
- ⚙️ The guided gear: takes force, provides the main gear ratio.
- 🛢️ Bearing supports: provide accurate positioning of the shafts and minimize friction.
- 🔒 Adjustment washers: allow you to accurately adjust the contact spot of the teeth.
The quality of the teeth plays a crucial role. They undergo complex heat treatment and grinding to withstand colossal loads without breaking. Any roughness or microcrack can lead to rapid wear and the appearance of a characteristic howl.
When changing the oil in the gearbox, always check the state of the magnetic plug - metal shavings will indicate the incipient wear of gears or bearings.
Types of main transmissions: classification
In the automotive industry, various types of transmissions are used, the choice of which depends on the layout of the car and its purpose. The most common option for rear-wheel drive cars is conical or hypoid transmission. It is compact and has a high loading capacity.
For front-wheel drive cars where the engine is transversely located, it is often used cylinder transmission. It is easier to manufacture and cheaper, but has lower efficiency and requires more space in the cross-section of the transmission. Sometimes heavy trucks can be found in the truck. wormy transmission, which provides a huge gear ratio in one cascade, but has low efficiency and strong heating.
⚠️ Attention: It is strictly forbidden to mix oils of different types for hypoid and worm gears. The additives required for the hypoid pair to work can cause corrosion of non-ferrous metals in the worm gearbox.
The choice of transmission type is also dictated by noise requirements. Hypoid gears work quieter than cylindrical gears due to the larger contact area of the teeth and slipping rather than rolling. This makes them the standard for passenger cars, where comfort comes first.
Why does hypoid transmission require special oils?
In hypoidal transmission, not only rolling occurs, but also a significant slide of the teeth along the contact line. This creates extreme pressure and temperature at the point of contact, which requires high-sulphur and phosphorus (EP) oils to prevent bullying of the metal.
Transfer ratio and its effect on dynamics
One of the most important parameters is the gear ratio, which is the ratio of the number of teeth of the driven gear to the number of teeth of the leading gear. This value determines how many revolutions the driveshaft must make for the wheel to make one full revolution. For example, at 4.11, the cardan will make just over four turns.
Changing this parameter drastically changes the character of the car. Increased gear ratio (for example, replacing 3.7 by 4.3) makes the car more "rickety" at low speeds, improves acceleration and traction when towing. However, this leads to an increase in fuel consumption and a decrease in maximum speed, since the engine reaches the maximum speed faster.
Reduction of gear ratio, on the contrary, has a positive effect on efficiency and maximum speed, but the car becomes "sluggish" when starting from a traffic light. Owners often change the main pair when installing larger diameter wheels to compensate for the change in the effective rolling radius.
Calculating the required gear ratio is always a search for compromise. For the race track, you need "short" gears, for track cruisers - "long". Engineers lay the optimal value based on the purpose of the model.
Correctly selected gear ratio allows the engine to operate in the zone of maximum efficiency, which directly affects the engine life and fuel consumption.
Differential: Ensuring the independence of wheels
The main gear is inextricably linked to the differential, which allows the wheels of one axle to rotate at different angular speeds. This is critical when cornering when the outer wheel is more extensive than the inner wheel. Without the differential, the wheels would have towed and the tires would have worn out in a matter of miles.
The differential is a planetary transmission. Satellites attached to the body transmit torque to the semi-axial gears. Under normal conditions, the load is distributed equally (50/50), but when one of the wheels slips, the entire moment goes to it, leaving the other without traction.
To combat this effect, high-friction differentials (LSDs) or electronic imitations of locks are used. They redistribute torque in favor of a wheel that has better traction, which is especially true for SUVs and sports cars.
- 🚗 Open differential: standard solution for civil cars, provides comfort, but loses traction when diagonal hanging.
- 🚜 Blockable differential: rigidly connects the semi-axis, providing permeability, but impairs handling on asphalt.
- ⚡ Electronic locking: slows the towing wheel, simulating the operation of mechanical locking.
Malfunctions of the differential often manifest themselves in the form of knocks during a sharp start or braking. This indicates wear of slit joints or destruction of satellites, which requires immediate intervention.
Maintenance and diagnostics of malfunctions
Despite the reliability, the main transmission requires regular attention. The main enemy of the node is the loss of sealing of the ossels and the subsequent leakage of oil. Work "dry" leads to overheating and rapid destruction of expensive gears.
Diagnosis begins with a visual examination for oil leaks. Then check the oil level through the control hole. In the presence of a hum, which changes when the gas is discharged (unloading hum), one can judge the wear of bearings or the violation of the engagement of gears.
Adjustment of the contact spot is a delicate operation, available only to experienced masters. Shifting gears even by a few hundredths of a millimeter changes the nature of the entire node. For this purpose, special sets of probes and coloring compounds are used.
☑️ Diagnostics of main transmission
Timely oil replacement is the easiest way to extend the life of a gearbox. The wear products and loss of additive properties over time turn the lubricant into an abrasive porridge that destroys rubbing surfaces.
⚠️ Attention: When there is a metal ringing or a strong howl, intensifying with a set of speed, the operation of the car must be stopped. Further movement can lead to a jamming of the rear bridge and an accident.
Comparative Characteristics Table
To better understand the differences between the types of gears, let’s consider their main parameters in the comparative table. This will help to systematize knowledge about design features.
| Type of transmission | Efficiency | Noise level | Application |
|---|---|---|---|
| Conical | High-pitched | Medium. | Old models of cars, special equipment |
| hypoid | Medium. | Low. | Modern passenger and truck vehicles |
| Cylindrical | High-pitched | High-pitched | Front-wheel drive cars, motorcycles |
| Worm | Low. | Low. | Heavy trucks, gearboxes. |
As you can see from the table, hypoid gear is the gold standard for most modern cars, despite having slightly lower efficiency compared to cylindrical. This is due to the requirements for comfort and layout features.
Understanding these differences allows you to better approach the choice of spare parts and oils. You should not save on lubricants for the gearbox, since the cost of repairing the main pair always exceeds the price of the most expensive oil.
Frequently Asked Questions (FAQ)
How often should you change the oil in the main transmission?
The recommended replacement interval is from 60,000 to 90,000 km, however, when active off-road operation or heavy load towing, the interval should be reduced to 30,000 to 40,000 km. The exact details are always listed in your vehicle’s service book.
Can I drive if the main transmission is buzzing?
Short term, yes, unless the hum turns into a howl or a knock. However, ignoring the problem will lead to progressive destruction of bearings and gear teeth. As a result, the gearbox will jam, which can lead to an accident, especially at high speed.
Why should you replace the main pair?
The new gears have micro-nerves on the surface of the teeth. The process of laundry (run-in) with a duration of about 1000 km allows you to smooth out these irregularities and form an ideal contact spot, which guarantees a long service life and silent operation.
Does the size of the wheels affect the main transmission?
Yes, installing larger diameter wheels actually lengthens the main gear. The car loses in the dynamics of acceleration, the engine operates in a more intense mode at start, which may require replacing the main pair with a shorter one to restore factory performance.