What is the final drive and differential of the car

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What is final drive

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 the gear ratio of the main pair, the final traction and speed characteristics are determined. What is a differential, satellites, and other gearbox parts for - we will consider further.

Principle of operation

The principle of operation of the differential: while the car is moving, the engine transforms the torque that accumulates on the flywheel, and through the clutch or torque converter is transmitted to the gearbox, then through the propeller shaft or helical gear (front-wheel drive), ultimately the torque is transmitted to the main pair and wheels. The main characteristic of the GP (main pair) is the gear ratio. This term refers to the ratio of the number of teeth of the main gear to the shank or helical gear. More: if the number of teeth of the drive gear is 9 teeth, driven by 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 performance, but negatively affects the maximum speed. For more powerful motors, the acceptable main pair value may vary from 2.1 to 3.9.

Differential operation procedure:

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

Final drive device

What is the final drive and differential of the car

The main parts of the GPU and the device of the differential:

  • drive gear - takes torque directly from the gearbox or through the cardan;
  • driven gear - connects GP and satellites;
  • carrier - body for satellites;
  • sun gears;
  • satellites.

Classification of final drives

In the process of development of the automotive industry, differentials are constantly being modernized, the quality of materials is improving, as well as the reliability of the unit.

By the number of pairs of engagement

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

By the type of gear connection

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

By layout

  • in a gearbox (front-wheel drive with a transverse motor), the main pair and the differential are located in the gearbox housing, the gearing is helical or chevron;
  • 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 through the propeller shaft.

Major malfunctions

What is the final drive and differential of the car
  • failure of the differential bearing - in gearboxes, bearings are used to enable the differential to rotate. This is the most vulnerable part that operates under critical loads (speed, temperature drops). 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 the satellites and axle shafts;
  • triggering of GP teeth and satellites. The rubbing surfaces of the parts are subject to wear, with every hundred thousand kilometers of run, the teeth of the pair are erased, the gap between them increases, leading to increased vibration and hum. For this, an adjustment of the contact patch is provided, due to the addition of spacer washers;
  • cutting the teeth of the GP and satellites - occurs if you often start off with slipping;
  • licking of the spline 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 leak - possibly a consequence of an increase in pressure in the differential crankcase due to a clogged breather or due to a leakage of the gearbox cover.

How the service works

What is the final drive and differential of the car

The gearbox is rarely serviced, usually everything is limited to changing the oil. On mileage over 150 km, it may be necessary to adjust the bearing, as well as the contact patch between the driven and driving gear. When changing the oil, it is extremely important to clean the cavity of wear debris (small chips) and dirt. It is not necessary to use the flushing of the axle reducer, it is enough to use 000 liters of diesel fuel, let the unit run at low speeds.

Tips on how to prolong the performance of the GPU and differential:

  • change the oil in a timely manner, and if your driving style is more sporty, the car tolerates high loads (driving at high speed, transporting goods);
  • when changing the oil manufacturer or changing the viscosity, flush the gearbox;
  • when the mileage is 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 when the main pair is heavily worn, it makes no sense to use an additive;
  • avoid slipping.

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