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The transmission system is an important criterion to consider when buying a car. Two or four-wheel drive, traction or propulsion... each type of transmission has its advantages and disadvantages. Depending on the use of your vehicle, either will be more or less suitable. X AutoCare explains the operation of the transmission and the difference between the different existing systems:

OPERATION OF THE TRANSMISSION

Generally speaking, transmission refers to the whole system for transmitting torque and power from the engine to the wheels. This system is located between the engine and the driving wheels of the vehicle. In addition to its role of transmitting engine torque to wheels, it has also other crucial functions.
Distribute power between the two or four-wheel drive depending on their speed, even when the speed differs from one wheel to another.
Adjust engine power based on vehicle speed, accelerations, and decelerations.
The transmission consists of the flywheel, clutch, gearbox, differential or self-locking bridge, and drive shafts.

FLYWHEEL AND CLUTCH

These two pieces are closely related. They connect the engine to the gearbox and allow the torque and engine power to be conveyed to the gearbox. Depending on the position of the clutch pedal, the flywheel and clutch can be joined or disjoined. When joined, energy passes from the engine to the gearbox. On the contrary, when they are disconnected, there is no more engine torque transmission. This allows the driver to switch gear or stop the vehicle to go-to neutral.

THE GEARBOX

Its role is to coordinate the speed of the engine, transmitted through the flywheel and clutch, and the speed of rotation of the wheels. The gearbox is the element that allows the engine torque to be adjusted according to driving conditions. For example, when starting or climbing on a steep slope, your vehicle will need a lot of torque. The gearbox allows this torque to be delivered in the direction of the drive wheels.

DIFFERENTIAL (SELF-LOCKING BRIDGE)

The function of the differential is to transfer the torque delivered by the gearbox to the drive wheels, via the drive shafts. Thus, it can transmit a different speed of rotation to each wheel when necessary. For example, in turns, the wheel outside the curve always has more distance to travel than the other. To avoid a loss of grip, this wheel must rotate faster. This is possible thanks to the differential.

DRIVESHAFTS

The driveshafts are directly attached to the drive wheels, which they drive when rotated by the self-locking bridge. By this rotational movement transmitted to them, the drive wheels then drive the vehicle.

THE DIFFERENT TYPES OF TRANSMISSION

There are 3 types of transmission: traction, propulsion, and all-wheel drive.

TRACTION: FRONT TRANSMISSION

Traction is the most commonly used type of transmission on current automobiles. Both front wheels are driven and each is driven by a half-drive shaft.
There are two possible configurations of the front transmission: with a longitudinal (perpendicular to the engine axis) or transverse (parallel to the engine axis). The latter is newer and much more compact. Also, it has the advantage of offering better handling.

    The traction system offers several advantages:
  • The vehicle has a very good traction force in all conditions, including on snow or slippery floors. It offers better safety in winter.
  • All components involved in the transmission are in the same location, allowing the system to take up little space. This space-saving benefits the vehicle's interior.
  • This is the system with the best transmission efficiency. It consumes less fuel.
  • The main disadvantage of traction is the risk of spinning both front wheels when starting or accelerating at a low gear ratio. This risk increases in winter, on snow or ice.

PROPULSION: REAR DRIVE

In this configuration, both rear wheels are drive. It is always the front wheels that give the direction of the vehicle, but the rear wheels are to propel it. This type of transmission is found very much on heavier vans or premium vehicles. Three configurations are possible in a rear transmission, and each has advantages and disadvantages.

REAR ENGINE

On some propulsion vehicles, the engine and transmission are located at the far rear of the vehicle, behind the centreline of the wheels. This “overhang” configuration is quite common at Porsche.

    It has several advantages:
  • The motor skills are reinforced at the rear, which allows for better performance at the start and during accelerations.
  • The entire powertrain is focused at the rear, saving space and giving the vehicle more livability.
  • This configuration makes it easy to take turns and makes driving enjoyable on winding roads.
    But the overhang motor also has drawbacks:
  • Because the rear gear is heavier, it will be more likely to drive the vehicle. On a slippery road or in snow, the risk of head-to-tail is higher.
  • Because the front of the vehicle is lighter, it is more sensitive to side-wind or weak steering wheel strokes. Driving in a straight line at high speed is therefore more difficult to hold.

CENTRAL ENGINE

In this second configuration option, the engine is located in front of the axle of the rear wheels, close to the center of the vehicle. The transmission is placed behind the engine at the wheel axle.
The main advantage of a central engine is a better distribution of masses along the length of the vehicle and around the center of gravity. This induces better maneuverability. This configuration is ideal for competition.
However, it has also some drawbacks:

  • The volume of the passenger compartment is reduced, especially in the rear seats where space is occupied by the engine.
  • The engine is less accessible, so its maintenance is more complex.

FRONT ENGINE

Finally, the engine can be located in the front even if the rear wheels are driving. In this case, an intermediate transmission tube is added in the length of the vehicle, allowing energy from the powertrain (front) to the wheels (rear).
The advantages of this configuration are as follows:

  • With all the powertrain being concentrated in the front, the vehicle gains more livability.
  • The front gear is heavier due to the presence of the engine, so driving offers more safety.
The main disadvantage of a front-engine in propulsion is a loss of motor skills, especially in winter when the car will be much more likely to slide. Thus, to avoid skidding in winter, you will have to drive very carefully and especially do not forget to equip yourself with winter tires.

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