Car’s Automatic Transmission Shifting Into Drive
Originally, vehicles operated on manual transmissions which required the driver to master a symphony of movement commonly known as shifting gears. However, today’s cars and trucks can be fitted with automatic transmissions giving drivers the option to let their vehicles do the shifting for them. While both types of systems have their respective advantages and drawbacks, automatic transmissions are better suited for stop-and-go driving and navigating areas with steep grades.
In this article, I’ll describe the torque converter, gearset, and other parts involved in your vehicle’s auto shifting. We’ll also take a closer look at the different positions controlled by the gearset.
The Main Parts
Today’s automatic transmission consists of three key components: the torque converter, planetary gearset, and valve body. The torque converter hydraulically connects your vehicle’s engine to the transmission, and allows your car to rest without stalling.
The second major component of an automatic is the planetary gearset. In a manual vehicle, the gears slide along shafts in accordance with the shift lever. In an automatic, the gears are stationary. A planetary gearset consists of a sun gear mounted in the center surrounded by multiple “planet” gears, all of which are enclosed by an outer ring with inward-facing teeth. When different gear ratios are engaged, the power flow is shifted as the gears spin or lockup in various combinations.
Lastly, the valve body is responsible for setting the gear ratios in accordance with the speed and RPM of your car. This unit receives pressurized fluid from a pump operated by the torque converter. The fluid manipulates a complex system of servos, valves, and other parts in order to trigger the proper gear ratio. Because the hydraulic fluid is constantly subjected to these intense pressures and temperatures, it must be replaced regularly to ensure that your vehicles operates smoothly.
Modes Of Operation
As opposed to a manual shifter where the gears are described as “1,” “2,” “3,” “4,” etc., an automatic transmission uses an array of modes. Each mode corresponds to a particular driving situation. You’re familiar (hopefully) with the common settings – “Park (P),” “Drive (D),” “Reverse (R),” and “Neutral (N).” Specialty modes can provide advantages for a wide range of driving circumstances. For example, “OverDrive (OD)” forces the car to shift into a higher gear while operating between 35 and 45 mph, thus increasing fuel economy at the expense of torque.
In bad weather, the “First (1)” and “Second (2)” modes are critical for maintaining control. “First (1)” limits your car to first gear only, while “Second (2)” locks the car into the first two gears. This provides the torque boost necessary to climb steep hills, tow heavy loads, and navigate snow and ice.
Ideally, you’ll never need to think about your vehicle’s automatic transmission. It should operate seamlessly for years and only require periodic replenishment of the fluid. If you experience any problems, you’ll need to visit a trained auto technician. While the cost of repairs will depend largely upon the make and model you’re driving, expect to pay at least $1,500 for a complete overhaul.
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