Motion analysis on the Planetary gear using Solidworks motion study
Planetary gear:
Planetary gear( also called as epicyclic gear )consists of a ring gear, planet gears and a sun gear. The sun gear is mounted at the centre around which the Planet gears are mounted which can revolve around them.The planet gears are meshing internally with the ring gear which is an internal gear.The planet gears are supported by a planetary carrier. The planetary gears are used in Automotive transmission, Steering system, etc.
The planet and sun gears mesh so that their pitch circles roll without slip. A point on the pitch circle of the planet gear traces an epicycloid curve. In this simplified case, the sun gear is fixed and the planetary gear(s) roll around the sun gear.
An epicyclic gear train can be assembled so the planet gear rolls on the inside of the pitch circle of a fixed, outer gear ring, or ring gear, sometimes called an annular gear. In this case, the curve traced by a point on the pitch circle of the planet is a hypocycloid. The combination of epicycle gear trains with a planet engaging both a sun gear and a ring gear is called a planetary gear train.
Planetary gear trains provide high power density in comparison to standard parallel axis gear trains. They provide a reduction in volume, multiple kinematic combinations, purely torsional reactions, and coaxial shafting. The efficiency loss in a planetary gear train is typically about 3% per stage.
The following inputs are used for designing the Planetary Gear
- Ring Gear
- Module = 2.5 (You must use the metric system in design modeler)
- Number of teeth = 46
- Sun Gear
- Number of teeth = 14
- Input Speed of the Gear = 200 rpm.
- Number of planet gears = 4
Aim:
- To calculate the number of teeth and the diameter of the planetary gears.
- To create the 3D model of the ring, the sun and the planetary gears.
- To do the simulations for the three cases, 1. fixed ring gear, 2. fixed sun gear, 3. fixed planetary gear.
Dimensions:
Module for all gears: 2.5
Ring gear:
- number of teeth:46
- Diameter: 46x2.5 = 115 mm
Sun gear:
- number of teeth: 14
- Diameter: 14x2.5 = 35 mm
Planetary gear:
Diameter of planetary gear = Radius of ring gear - Radius of Sun gear
= 115/2 - 35/2
= 40mm
Number of teeth of planetary gear = d/m = 40/2.5 = 16
Steps:
- For creating gear, go to the Tool Box -->Design library--> Tool Box--> ANSI metric -->power transmission
- For sun and planet gear choose Spur gear and for ring gear choose Internal Gear.
Analysis of motion:
There are three cases. In each, the input gear rotates at 200 rpm and motion study is done for 5 seconds.
The contacts that are made,
- between the carrier and planetary gear
- between the sun and planetary gear.
- between the planetary and Ring gear.
Analysis:
Select the Motion solid works add on and select motio analysis.
Fix the required component and give the required torque to the gears in steps.
Make sure that the contact solids includes all the components including the carrier and all the gears.
Run the simulation and save the video.
Case 1: Input-Sun,Output-Carrier,Fixed-Ring Gear
Case 2 : Input - Sun, Output - ring, Fixed - Carrier
Case 3 : Input - Ring, Output- Carrier, Fixed - Sun
Conclusion:
- The fluctuation of the angular speed with time denotes the rough contact between gears. This denotes that the gears are needed to be lubricated to reduce wear and tear during operation.
- In case 3, The angular velocity of the Carrier is higher than case 1 due to the high gear ratio between Ring gear and planetary gears. Depending upon the gear ratio and number of teeth of ring gear and planetary gears, the torque and speed of ring gear is multiplied.
- In order to obtain different speeds, inputs and outputs are changed accordingly which depends upon the operation to be performed.
- For the same speed of input, a relatively bigger output gear's speed is low as compared to a relatively smaller output gear's speed.
- Hence, the linear speed is indirectly proportional to the pitch diameter of gear.