April 20, 2024
Automatic Transmission Gears

Understanding the Automatic Transmission Gears that Drive Your Automobile

Types of Transmission Gears
There are different types of gears that make up an automatic transmission system in modern vehicles. The main gears include:

Planetary Gears – Planetary gears are the most common type used in automatic transmissions. They utilize a sun gear at the center surrounded by planet gears that revolve around the sun gear and mesh with an outer ring gear. By changing the rotation of one or more of these gears, different gear ratios can be achieved.

Spur Gears – Spur gears are simple circular gears that mesh together along parallel shafts. They are often used as intermediate gears between the planetary gears and output shafts in a transmission.

Bevel Gears – Bevel gears have cone-shaped teeth that allow the gear shafts to meet at an angle other than parallel. This enables the transmission of torque between shafts that are intersecting or perpendicular. Bevel gears are commonly found connecting the transmission input shaft to the planetary gear assembly.

Helical Gears – Helical gears have teeth cut at an angle across the face of the gear. This geometry allows for quieter operation and a higher load capacity compared to spur gears. They are frequently used as intermediate gears within the transmission.

Rack and Pinion Gears – The rack and pinion gear set converts rotational motion to linear motion, or vice versa. In transmissions, a pinion gear engages with a toothed rack bar to move components like shift forks or clutches for gear changes.

How Automatic Transmissions Work

A typical Automatic Transmission Gears utilizes planetary gear sets and hydraulically operated multi-plate clutches to achieve different gear ratios automatically based on the vehicle’s speed and throttle input.

When the vehicle starts from a stop, the outer clutch is engaged to connect the engine and a low gear ratio planetary set. As speed increases, the low gear ratio multiplies the engine’s torque for increased acceleration.

Once a predetermined road speed is reached, fluid pressure shifts to engage the second clutch which connects the transmission housing through a higher planetary gear ratio. The engine now turns relatively faster to maintain the same vehicle speed in a more fuel efficient manner.

As speeds continue to rise, additional clutches and gear sets are sequentially engaged to further increase the transmission ratios. Spur, bevel and helical intermediate gears rotate the planetary gear sets to smoothly shift between ratios.

At cruising speeds and light throttle, the highest overdrive gear ratio is selected. This allows maximum fuel efficiency by turning the engine at a lower RPM for a given road speed.

When more acceleration is needed, transmission controls shift down by disengaging one clutch and engaging another for a lower ratio through the same planetary gear sets. This process is repeated by monitor engine output and driver input to select the optimal gear for any situation.

Failure Modes of Common Transmission Gears

While gear sets are designed to last the lifetime of a vehicle, wear and mechanical failures can occur over time in high mileage transmissions:

Planetary Gear Damage – Excessive clutch slippage from worn friction material can cause planet gears to grind against each other leading to broken or stripped teeth. Oil contamination also accelerates wear.

Spur and Pinion Gear Wear – Long term engagement of these types of gears leads to abrasive tooth wear that degrades meshing and roundness. Tooth breakage is possible if this wear progresses.

Gear Fatigue – Repeated shifting actions cause slight flexing and stress concentrating impacts over millions of cycles. Microscopic cracks can grow and lead to premature tooth fractures.

Bevel Gear Issues – Misalignment from component relaxation or damage can introduce tooth contact pattern errors. Slapping noise and excessive wear result if not corrected.

Insufficient Lubrication – Lack of fresh, clean transmission oil allows components to run hotter and with less protection. This accelerates damaging wear patterns.

Any of these failures disrupt the precise gearing that allows smooth transmission of power through different ratios. Recognizing noise, harsh shifting, leaks or low fluid level issues can help repair problems before escalating.

Proper Transmission Gear Maintenance

To maximize gear longevity, service technicians recommend:

– Change transmission fluid and filter at the interval specified in your owner’s manual (usually every 30k-60k miles).

– Inspect fluid for contamination and have it analyzed for wear metals if performance issues arise.

– Examine transmission breather for carbon deposits that indicate possible fluid aeration from worn seals.

– Check gear teeth for signs of spalling, cracking or abnormal wear patterns during routine maintenance.

– Replace external shaft seals, gaskets or backup rings if leaking is detected early.

– Consider a transmission fluid flush for high mileage vehicles to fully remove sludge deposits.

– Correct drivability issues like delayed shifts or slipping that put extra burden on transmission components over time.

Following these practices extends the healthy lifespan of transmission gears so they continue delivering reliable power transfer. Understanding their functions provides insight to catch potential problems before expensive repairs are needed.

1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it