How Automatic Transmissions Operate
If you’ve driven a car with an automatic transmission, you’re aware of two key differences from a manual transmission:
1. A Car Lift For Sale automatic transmission lacks a clutch pedal.
2. There’s no need for manual gear shifting; once in drive, the transmission handles all gear changes automatically.
While both automatic transmissions (with their torque converters) and manual transmissions (with their clutches) achieve the same result, their methods are fundamentally different. The way an automatic transmission accomplishes this is truly remarkable!
Trivia Questions (General Knowledge) No. 3
In this article, we’ll explore the inner workings of an automatic transmission, starting with the crucial planetary gearsets. We’ll then examine the Car Lift For Sale transmission’s structure, control mechanisms, and some of the complexities involved in its operation.
Contents
– Purpose of an Automatic Transmission
– The Planetary Gearset
– Planetary Gearset Ratios
– Compound Planetary Gearset
– First Gear
– Second Gear
– Third Gear
– Overdrive
– Reverse Gear
– When You Put the Car in Park
– Automatic Transmissions: Hydraulics, Pumps, and the Governor
– Automatic Transmissions: Valves and Modulators
– Electronically Controlled Transmissions
Purpose of an Automatic Transmission
The role of an automatic transmission is similar to that of a manual transmission: it allows the engine to run within a narrow speed range while providing a wide range of output speeds.
Without a transmission, a vehicle would be restricted to a single gear ratio, which would need to be chosen to achieve the desired top speed. For instance, a gear ratio that allows a top speed of 80 mph would be similar to third gear in many manual transmissions.
Attempting to drive a Car Lift For Sale manual car using only third gear would result in poor acceleration at low speeds and a screaming engine at high speeds, leading to rapid wear and a nearly undriveable vehicle.
The transmission uses gears to optimize engine torque and maintain the engine at an appropriate speed. When towing or carrying heavy loads, transmissions can become hot enough to damage the transmission fluid. To prevent serious damage, drivers who tow should use vehicles with transmission coolers.
The main distinction between manual and automatic transmissions is that manual transmissions manually lock and unlock different gear sets to achieve various gear ratios, while automatic transmissions use a single set of gears to produce all the required ratios. This function is made possible by the planetary gearset.
The Planetary Gearset
Inside an automatic transmission, you’ll find a compact yet intricate assembly of parts, including:
– A sophisticated planetary gearset
– Bands to lock parts of the gearset
– Wet-plate clutches to secure other parts
– A complex hydraulic system controlling the clutches and bands
– A large gear pump to circulate transmission fluid
The Car Lift For Sale planetary gearset, roughly the size of a cantaloupe, is the centerpiece of this system, creating all the different gear ratios. Everything else in the transmission supports the planetary gearset. This remarkable gearset is also featured in other mechanical devices, such as electric screwdrivers. An automatic transmission contains two complete planetary gearsets integrated into one component. For more details on planetary gearsets, see “How Gear Ratios Work.”
A planetary gearset consists of three main parts:
– The sun gear
– The planet gears and their carrier
– The ring gear
The function of each component—whether as input, output, or stationary—determines the gear ratio. Let’s examine a single planetary gearset.
Planetary Gearset Ratios
Consider a planetary gearset with a ring gear featuring 72 teeth and a sun gear with 30 teeth. This setup can generate various gear ratios.
Locking any two of the three components together will result in a 1:1 gear reduction. The gearset can produce multiple ratios, including reductions and overdrives, affecting the output speed relative to the input speed. This versatility allows the planetary gearset to handle all the gear ratio requirements of an automatic transmission.
Compound Planetary Gearset
The Car Lift For Sale automatic transmission employs a compound planetary gearset, which functions like two interconnected planetary gearsets within a single unit. It features one ring gear that always serves as the output, but includes two sun gears and two sets of planet gears.
The compound planetary gearset resembles a single planetary gearset but operates as two combined gearsets. By observing its parts, you can see how the planets interact and how the configuration affects gear ratios.
First Gear
However, it is held still by the one-way clutch, and the ring gear turns the output. The gear ratio calculation is:
Ratio = -R/S = -72/30 = -2.4:1
The negative ratio implies the output direction is opposite to the input, but due to the two sets of planet gears, the output direction actually matches the input direction.
Second Gear
To achieve the ratio for second gear, the transmission operates as two interconnected planetary gearsets. The first stage uses the larger sun gear as the ring gear, with the small sun gear as the input and the planet carrier as the output. The formula for this stage is:
1 + R/S = 1 + 36/30 = 2.2:1
In the second stage, the Car Lift For Sale planet carrier from the first stage becomes the input, and the larger sun gear is held stationary, with the ring gear as the output. The ratio is:
1 / (1 + S/R) = 1 / (1 + 36/72) = 0.67:1
Multiplying the ratios from both stages results in a combined reduction of 1.47:1 for second gear.
Third Gear
In most automatic transmissions, third gear operates with a 1:1 ratio. As explained earlier, achieving a 1:1 output typically involves locking any two of the three components of the Car Lift For Sale planetary gearset together. In this setup, the process is even simpler: we just need to engage the clutches that connect each sun gear to the turbine.
When both sun gears rotate in the same direction, the planet gears lock up because they can only move in opposite directions. This locks the ring gear to the planet gears, causing all parts to rotate together as a single unit, resulting in a 1:1 gear ratio.