Planetary Gear
Project Title:
To run the motion analysis on the planetary gear with a sun gear, a ring gear, a carrier and four planet gears.
Aim:
- To access the gears from the toolbox in SOLIDWORKS present in the ANSI metric system.
- Provide the required parameters for defining each and every gear.
- Designing the carrier, depending upon the shaft diameter of the planet gears.
- Assembling them in SolidWorks and giving correct constraints to all the parts so that the assembly is perfect for running the motion analysis study.
Theory:
A Planetary gear (also known as epicyclic gear train) consists of a larger Ring gear, planet gears and a sun gear. The sun gear is mounted at the center 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. A carrier is mounted to the planet gears as shown in the image. The combination of epicyclic gear trains with a planet engaging both a sun gear and a ring gear is called a planetary gear train.
The most basic form of planetary gearing involves three sets of gears with different degrees of freedom. Planet gears rotate around axes that revolve around a sun gear, which spins in place. A ring gear binds the planets on the outside and is completely fixed. The concentricity of the planet grouping with the sun and ring gears means that the torque carries through a straight line. Many power trains are "comfortable" lined up straight, and the absence of offset shafts not only decreases space, it eliminates the need to redirect the power or relocate other components.
In a simple planetary setup, input power turns the sun gear at high speed. The planets, spaced around the central axis of rotation, mesh with the sun as well as the fixed ring gear, so they are forced to orbit as they roll. All the planets are mounted to a single rotating member, called a cage, arm, or carrier. As the planet carrier turns, it delivers low-speed, high-torque output.
Problem Statement:
- 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
The dimensions of the carrier depend on the shaft diameter of the planet gear.
With the above input parameters, you are going to run a simulation on the following cases,
|
Serial no. |
Input |
Output |
Fixed |
|
1. |
Sun gear |
Carrier |
Ring gear |
|
2. |
Ring gear |
Carrier |
Sun gear |
|
3. |
Sun gear |
Ring gear |
Carrier |
Calculation of:
Diameter of the Planet gear:
Radius of Ring gear= Diameter of the Planet gear + radius of sun gear
Rr = Dp + Rs
Therefore,
Dp =Rr - Rs
Dp=115/2 - 35/2 = 40mm
Number of teeths of Planet gear:
Pitch diameter, D=m*T
where m=module
T= Number of teeth
therefore, T=D/m = 40/2.5 = 16
3D Models and Assembly:
The created models are as shown.
Pressure angle = 20 degree
Face Width = 20 mm
The Internal Gear/Ring Gear:
The Sun Gear:
The Planet Gears:
The Carrier:
Final Assembly:
The ring gear, planet gears, sun gear and the carrier are assembled as shown in the below image. The assembly is done using the mate option by properly aligning all the components in such a way that no components overlap on each other. Here we are not using mechanical gear mates as we have to analyse the motion for 3 cases.
Motion analysis:
In the motion study make contacts between the followings.
Carrier and the Planet gears
Sun gear and the Planet gears
Ring gear and the Planet gears
The material for each contact is Steel (Dry) .
There are 3 Cases;
The input speed to the motor in each case is 200 RPM. The motion analysis is done for 5 seconds.
Case 1:
Ring gear fixed. Motor - sun gear.
The plot of an angular velocity of the carrier against time.
Case 2:
Sun gear fixed. Motor - Ring gear.
The plot of an angular velocity of the carrier against time.
Case 3 :
Carrier fixed. Motor - Sun gear.
The plot of an angular velocity of the Ring against time.
CONCLUSION:
- In case I; when the input is given to the sun gear and output is obtained at the carrier keeping the ring gear fixed, the planet not only rotates about their axis but is also forced to roll on the inside of the ring gear since it is fixed. This results in low speed and high torque transmitting capacity.
- In case II; when the input is given to the ring gear and output is obtained from the carrier keeping the sun gear fixed, the angular velocity achieved is maximum since the internal gear is quite big and planet gears are small so, when a large gear meshes with a small gear the velocity achieved from the small gear is very much because the velocity ratio is high.This is even shown in the plot of angular velocity.
3.In case III; when the carrier is fixed and output is to be obtained from the ring gear the opposite happens. The planet gears rotate only about their axis and transmit motion from sun to the ring and since the ring gear is big in diameter the angular velocity achieved is less.
- The deviations that are visible in the graphs show that there are points where sliding is occurring between the gears while transmission.For making the graph a bit more smoother precise contact can be selected with higher values of frames per second.
Links of Simulation: