All About Car Automatic Transmission
What is an automatic transmission?
An automatic transmission is a type of transmission that automatically selects the correct gear ratio for the current driving conditions. This is in contrast to a manual transmission, which requires the driver to manually select the gear ratio by moving a gear lever.
Automatic transmissions are typically found in passenger cars and light trucks. They are also becoming increasingly common in heavy-duty vehicles, such as buses and trucks.
How does an automatic transmission work?
Automatic transmissions use a variety of sensors and actuators to determine the current driving conditions and select the appropriate gear ratio.
- Throttle position sensor
- Brake pedal position sensor
- Vehicle speed sensor
- Engine speed sensor
The actuators used in automatic transmissions include the:
- Transmission control module (TCM)
- Solenoids
- Hydraulic valves
The TCM is the brains of the automatic transmission. It receives signals from the sensors and uses them to determine the appropriate gear ratio. The TCM then sends signals to the solenoids and hydraulic valves, which control the flow of hydraulic fluid to the transmission’s clutches and bands.
Types of automatic transmissions
There are two main types of automatic transmissions: planetary gear sets and continuously variable transmissions (CVTs).
Planetary gear sets
Planetary gear sets are the most common type of automatic transmission. They use a set of gears that are arranged in a planetary configuration. The gears are connected by a series of clutches and bands, which control the flow of power through the transmission.
Planetary gear sets are typically used in passenger cars and light trucks.
Continuously variable transmissions (CVTs)
CVTs are a type of automatic transmission that uses a continuously variable ratio instead of a set of fixed gear ratios. This allows the CVT to provide a smooth, seamless transition between gears.
CVTs are typically used in small cars and hybrids.
Advantages of automatic transmissions
There are a number of advantages to using an automatic transmission, including:
- Convenience: Automatic transmissions are much easier to drive than manual transmissions. The driver simply needs to select the desired gear (e.g., drive, park, reverse) and the transmission will automatically select the appropriate gear ratio.
- Fuel efficiency: Automatic transmissions can help to improve fuel efficiency by selecting the most efficient gear ratio for the current driving conditions.
- Reduced emissions: Automatic transmissions can also help to reduce emissions by selecting the most efficient gear ratio for the current driving conditions.
Disadvantages of automatic transmissions
There are also a few disadvantages to using an automatic transmission, including:
- Cost: Automatic transmissions are typically more expensive than manual transmissions.
- Complexity: Automatic transmissions are more complex than manual transmissions, which can make them more difficult to repair.
- Weight: Automatic transmissions are typically heavier than manual transmissions, which can reduce the vehicle’s fuel efficiency.
Conclusion
Automatic transmissions are a convenient and efficient way to drive a vehicle. They are particularly well-suited for vehicles that are used in stop-and-go traffic or for drivers who are not familiar with manual transmissions.
However, automatic transmissions are typically more expensive and complex than manual transmissions. They are also heavier, which can reduce the vehicle’s fuel efficiency.
