automatic transmission final1

Planetary Gear Sets

  • Definition of Planetary Gear Sets
    A planetary gear set is a gear system consisting of a central sun gear, planet gears that rotate around the sun gear, and a ring gear that encircles the planet gears.

Gear Ratios in Planetary Gear Sets

  • Potential Gear Ratios

  • A single planetary gear set can provide a potential of seven gear ratios.

    • Not all ratios will be utilized for reverse applications.

    • Types of Ratios Available:

    • 2 reverse ratios.

    • 1 direct ratio.

    • 2 reduction ratios (for decreasing speed).

    • Multiple forward gears (for increasing speed).

Planet Carrier Role

  • Functionality: When the planet carrier is held (meaning it is fixed and unable to rotate), the output will be in reverse.

  • Essential Components of the System: There will always be:

    • A held member (fixed component).

    • A driven member (component moved by the system).

    • A drive member (the component that provides input).

Advantages of Planetary Gears

  • Constant Mesh: They are always in mesh, reducing the chances of breakage from tooth failure.

  • Compact Design: They tend to take up less space compared to other gear systems.

  • Increased Number of Planets: Incorporating four planet gears instead of three allows for greater tooth contact and increased torque capacity.

    • The added planetary gears act mainly as idlers, maintaining contact between the sun and ring gear, enhancing performance without significant changes in function.

Understanding Power Flow and Operation of Transmission

  • Simplified Explanation of Power Flow:

  • The explanation will remain general to avoid overwhelming complexity, but it lays the foundation for a deeper understanding of automatic transmissions.

Other Types of Automatic Transmission

  • Types: In addition to planetary automatic transmissions, other types include:

    • Power Shift Transmissions: These utilize multiple countershafts.

    • Example: Applied in front-end wheel loaders with multiple axles and an input positioned high.

Power Transfer Mechanism in Power Shift Transmissions

  • Cousin to automatic transmissions; they manage power transfer through clutch packs and pistons within counter shafts.

Clutch Packs and Their Functions

  • An automatic transmission generally has five clutch packs and three planetary gear sets:

    • Engagement of Clutch Packs: These clutch packs determine power transmission paths.

    • C1 and C2 are rotating clutch packs, which may not always rotate.

      • Engagement sends power through the main shaft to the specific sun gears of the planetary set.

    • Upon engaging, the corresponding planet carrier rotates with the applied input.

Direct Drive and Gear Ratios

  • Creating Direct Drive: A one-to-one gear ratio is created when two members within a planetary gear set are powered simultaneously.

  • The method used to engage clutch packs is by oil pressure rather than spring pressure; it involves hydraulic pistons that trap power and maintain engagement of gears.

Gear Engagement Example

  • First Gear Mechanism:

    • Engaging clutch pack C1 (attached to the sun gear) and C5 (holding the ring gear) results in power transfer through the planetary assembly to the output.

  • Calculating Gear Ratios: The ratio of output to input can be calculated based on compounded ratios present in the system, taking into account simultaneous rotations.

Detailed Examples of Gear Engagement

  • Second Gear:

    • C1 remains engaged while C4 is applied; this engages the planet carrier of the second gear set, thus affecting power output.

  • Third Gear:

    • C1 remains engaged, C3 is applied, which again modifies compounding gear ratios appropriately.

  • Fourth Gear:

    • Activating both C1 and C2 enables direct drive through one-to-one gear ratios with speeds compounded from each planetary component, facilitating rapid speed through the output shaft.

Visualization of Gear Ratios

  • A visual representation can greatly aid in understanding the engagement and holding of specific gears as various speeds are input.

  • Coloring mechanics (holding members, powered members etc.) contextualizes their positions for clarity.

Conclusion and Key Takeaways

  • Understanding gear ratios and their function within an automatic transmission illustrates the complexity but essential functionality and advantages of automatic systems in automotive engineering.

  • Overall, automatic transmissions are widely accepted in modern vehicles due to their ease of use and reliability.

Reminder:

  • The operation is largely hydraulic with interactions controlled by solenoids, which dictate the engagement of clutch packs based on the desired automotive functionality.