What is the main gear and differential of the car
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What is the main gear and differential of the car

What is the main gear

The main gear is the transmission unit of the car, which converts, distributes and transmits torque to the drive wheels. Depending on the design and gear ratio of the main pair, the final traction and speed characteristics are determined. Why do we need a differential, satellites, and other parts of the gearbox - we will consider further.

Principle of operation 

The principle of operation of the differential: while the car is moving, the operation of the engine converts the torque that accumulates on the flywheel, and is transmitted through the clutch or torque converter to the gearbox, then through the cardan shaft or helical gear (front-wheel drive), ultimately the moment is transmitted to the main pair and wheels. The main characteristic of the GP (main pair) is the gear ratio. This concept implies the ratio of the number of teeth of the main gear to the shank or helical gear. More details: if the number of teeth of the drive gear is 9 teeth, the driven gear is 41, then by dividing 41:9 we get a gear ratio of 4.55, which for a passenger car gives an advantage in acceleration and traction, but negatively affects the maximum speed. For more powerful motors, the acceptable value of the main pair can vary from 2.1 to 3.9. 

Differential order:

  • torque is supplied to the drive gear, which, due to the engagement of the teeth, transfers it to the driven gear;
  • driven gear and cup due to rotation make the satellites work;
  • satellites ultimately transmit the moment on the axle shafts;
  • if the differential is free, then with a uniform load on the axle shaft, the moment will be distributed 50:50, while the satellites do not work, but rotate with the gear, describing its rotation;
  • when turning, where one wheel is loaded due to the bevel gear, one half-axis rotates faster, the other slower.

Final drive

rear axle device

The main details of the GP and the differential device:

  • drive gear - receives torque directly from the gearbox or through a cardan;
  • driven gear - connects the GPU and satellites;
  • carrier - housing for satellites;
  • sun gears;
  • satellites.

Main gear classification

In the process of developing the automotive industry, differentials are constantly being upgraded, the quality of materials, as well as the reliability of the assembly, are improved.

By the number of gear pairs

  • single (classic) - the assembly consists of a driving and driven gear;
  • double - two pairs of gears are used, where the second pair is located on the hubs of the drive wheels. A similar scheme is used only on trucks and buses to provide an increased gear ratio.

By type of gear connection

  • cylindrical - used on front-wheel drive vehicles with a transverse engine, helical gears and a chevron type of engagement are used;
  • conical - mainly for rear-wheel drive, as well as the front axle of an all-wheel drive car;
  • hypoid - often used on passenger cars with rear-wheel drive.

By layout

  • in the gearbox (front-wheel drive with a transverse engine), the main pair and differential are located in the gearbox housing, helical gearing or chevron gearing;
  • in a separate housing or axle stocking - used for rear-wheel drive and all-wheel drive vehicles, where the transmission of torque to the gearbox is transmitted via a cardan shaft.

Major faults

differential and satellites
  • failure of the differential bearing - in gearboxes, bearings are used to allow the differential to rotate. This is the most vulnerable part that operates under critical loads (speed, temperature changes). When the rollers or balls are worn, the bearing emits a hum, the volume of which increases in proportion to the speed of the car. Neglect of timely replacement of the bearing threatens to jam the gears of the main pair, subsequently - to the replacement of the entire assembly, including satellites and axle shafts;
  • triggering teeth GP and satellites. The rubbing surfaces of the parts are subject to wear and tear, the teeth of the pair are erased with every hundred thousand kilometers, the gap between them increases, leading to increased vibration and hum. For this, an adjustment of the contact spot is provided, due to the placement of distance washers;
  • shearing of the teeth of the GPU and satellites - occurs if you often start off with slippage;
  • licking of the splined part on the axle shafts and satellites - natural wear and tear according to the mileage of the car;
  • turning the axle shaft sleeve - leads to the fact that the car in any gear will stand still, and the gearbox will rotate;
  • oil leakage - possibly a consequence of an increase in pressure in the differential crankcase due to a clogged breather or due to a violation of the tightness of the gearbox cover.

How is the service

differential and satellites

Gearbox maintenance is rare, usually everything is limited to changing the oil. Over a range of over 150 km, it may be necessary to adjust the bearing, as well as contact spots between the driven and pinion gears. When changing the oil, it is extremely important to clean the cavity of wear products (fine chips), as well as dirt. It is not necessary to use the flushing of the gearbox of the bridge, it is enough to use 000 liters of diesel fuel, let the unit work at low speeds.

Tips on how to extend the performance of the GP and differential:

  • change the oil in a timely manner, and if your riding style is more sporty, the car suffers high loads (driving at high speed, transportation of goods);
  • when changing the oil manufacturer or changing the viscosity, flush the gearbox;
  • with a mileage of over 200 km, it is recommended to use additives. Why do you need an additive - molybdenum disulfide, as part of the additive, allows you to reduce the friction of parts, as a result of which the temperature decreases, the oil retains its properties longer. Remember that with a strong wear of the main pair, it does not make sense to use an additive;
  • Avoid starting with slipping.

Questions and answers:

What is the main gear for? The main gear is a part of the car's transmission (two gears: drive and driven), which converts torque and transfers it from the motor to the drive axle.

What is the difference between the final drive and the differential? The main gear is the part of the gearbox whose task is to transfer torque to the wheels, and the differential is needed so that the wheels can have their own rotational speed, for example, when cornering.

What is the purpose of the main gear in the transmission? The gearbox receives torque from the engine flywheel via the clutch basket. The very first pair of gears in a gearbox is a key element in converting traction to the drive axle.

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