Planetary Gear

Aim: To design and create a motion study on planetary gear mechanism

Introduction:

A planetary gear mechanism is widely known as epicyclic gear train. The epicyclic gear train has a wide application in the automatic transmission in the automotive industry. The epicyclic gear train consists of:

1. Sun gear that is located at the center and rotates about its own axis. It is meshed against the planetary gears.
2. Planetary gears are the gears which is smaller than the sun gear and meshes with both sun gear and the ring gear. It rotates about its own axis.
3. Ring gear or annulus gear is the big gear having its teeth inwards. The ring gear rotates about the axis same as that of sun gear.

In transmission applications brake bands are used to stop motion of the gears such as sun gear, planet gears or the ring gear to attain desired output which can be used to vary the speeds. Perfect examples of the planetary gear set ups are being used in Model-T transmission, Chevrolet’s Turbo Glide etc.

Steps while CAD Model and Assembly:

1. Open SolidWorks and go to Assembly and adjust the unit system to MMGS.
2. All the gears were imported from design library.
3. Design library-Toolbox-American Inches-Power Transmission-Spur gears or Internal spur gears.
4. Based on the dimensions provided, the diameter or number of teeth were entered.
5. For placing the gears, individual circles with the diameters for sun gear, planet gears and ring gears were created on the right plane. All the circles were created having required tangent.
6. Assembly or meshing the gears were done as per the sketched drawing.

Note: While creating models the models were properly defined such as constraints such as vertical, horizontal, centricity was followed.

Steps taken in Motion study:

1. SolidWorks Add ins- assign motor as per requirement-Specifying contact type and material.
2. Move components-Physical dynamics.
3. Change settings from animation to motion analysis.
4. Select calculate to run simulation.
5. Select result and plots-Identify the parameter that is needed for plot-Magnitude -Graph obtained.
6. Save the graphs.

Considerations:

1. No planet carrier was used. Total 4 planet gears were used.
2. No gear mate was applied.
3. The Fixing of gears individually to understand its motion analysis could not be performed due to operating system issue.

Calculations:

1. Formula used: D = M X Nt

D = Pitch Diameter;

M = module;

Nt = Number of teeth of a gear;

Calculated Results:

GEARS	Module	Pitch Diameter	Number of teeth
Ring Gear	2.5	115	46
Sun Gear	2.5	35	14
Planet Gear	2.5	40	16

Final Assembly:

Observation:

1. The only simulation that was able to obtain a result and simulation was without fixing any gear.
2. The possible explanation for not getting simulation result for fixed cases was due to mating and longer time for running the simulation analysis.2.
3. Based on the graph obtained, it is clear that when sun gear is rotated in clockwise or anti-clockwise, the planet gears rotate in opposite direction and this inturn drives the ring gear in the same direction to that of planet gears.