Planetary Gear
Planetary Gear:
Aim: To create the Planetary gear setup in SolidWorks and create a motion study on it applying various cases given.
Theory:
The planetary gear setup is a power transmission mechanism usually consisting of three main parts known as the sun gear, planet gear, and the ring gear. The planet gear revolves around the sun gear and these are arranged in such a way that their pitch circles always roll upon each other without slip. This implies that the pitch circles of these gears are always tangent to each other. The number of planet gears might vary and also the part that is fixed in the transmission may also vary.
This system is also known as the epicyclic gearing system. There can also be a part that holds all these components in the mechanism known as the carrier. Carrier has mounts that facilitate the planet and sun gears to sit about their axes.
So the main components of a planetary gear system are
- Sun gear
- Planet gear
- Ring gear
- Carrier
The mechanism usually works by fixing a part of it and providing torque to one of the gears and transmit power from one component to another. An example can be given by fixing the carrier and giving the power input to the sun gear. we see that the power is transmitted from the sun gear to the planet gears and ring gear.
Applications of the planetary gear system can be found in many cases like wheel hub motors of electric vehicles where the system helps in reducing the load on the motor and also effectively transmitting torque. These are seen to be used in tractors and construction equipment where there is a high torque requirement. Due to the number of contact areas and surface area in contact between the gears being high the load is evenly distributed and power transmission is done in an efficient way.
Below is a picture of the planetary gear system and a representative animation.
Introduction:
Given data:
The following are inputs for designing the Planetary Gear.
- Module = 2.5 (using the metric system in design modeler)
- Ring Gear
- 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, we are going to run a simulation on the following cases,
| Sl.No | Input | Output | Fixed |
| 1 | Sun Gear | Carrier | Ring Gear |
| 2 | Ring Gear | Carrier | Sun Gear |
| 3 | Sun Gear | Ring Gear | Carrier |
Calculation:
Using the given data we calculate the pitch circle diameters of the ring gear and sun gear as follows.
Now we draw a sketch with the pitch circles of the sun gear and ring gear. Then, we draw a circle that is tangent to both the pitch circles of the sun gear and ring gear to measure its diameter. This is because we know that the pitch circles of all 3 gears roll on each other without slip which means they are tangent.
From this calculation, we got to know that the pitch circle diameter of the planet gear is 40mm. using this value we calculate the number of teeth of planet gear as follows.
Setup:
Now we have the pitch circle diameter, number of teeth and module of the ring gear, planet gear, and sun gear.
So, we use those dimensions and create the sun gear, planet gear, and ring gear parts as shown below.
Sun gear Planet gear
Ring gear
as we know the dimension of the bore of all the planet and sun gears as 15mm, we create a carrier accordingly keeping the shaft diameter or the diameter of the gear mounts as 15mm. this is shown below.
Now the parts are assembled and given constraints to function as a planetary gear system. the following picture shows the assembly.
Motion Study:
Once the assembly is done after constraining all the components to function properly, we start the motion study with the three cases given.
Case 1:
| Sl.No | Input | Output | Fixed |
| 1 | Sun Gear | Carrier | Ring Gear |
According to this condition, we first fix the ring gear component and give motor input to the sun gear with speed at 200rpm. we also set up the motion at 120fps. Contacts are also provided between the sun gear and planet gears and also the planet gears and ring gear.
Now we click on calculate button in the motion study and the output motion is obtained the following way.
Case 2:
| Sl.No | Input | Output | Fixed |
| 2 | Ring Gear | Carrier | Sun Gear |
According to this condition, we first fix the sun gear component and give motor input to the ring gear with speed at 200rpm. we also set up the motion at 120fps. Contacts are also provided between the sun gear and planet gears and also the planet gears and ring gear.
Now we click on calculate button in the motion study and the output motion is obtained the following way.
Case 3:
| Sl.No | Input | Output | Fixed |
| 3 | Sun Gear | Ring Gear | Carrier |
According to this condition, we first fix the carrier component and give motor input to the sun gear with speed at 200rpm. we also set up the motion at 120fps. Contacts are also provided between the sun gear and planet gears and also the planet gears and ring gear.
Now we click on calculate button in the motion study and the output motion is obtained the following way.
In all the three cases we plot the angular velocity for the output component and analyze it.
Plots:
Case 1:
Here we fixed the ring gear and gave input to the sun gear to observe the output on the carrier. as the ring gear is fixed and the sun gear drives the planet gears and in turn drives the carrier, the speed is seen to be lower which is an indication of high torque. So using this case would result in low speed and high torque.
Also from the plot, we can observe that the meshing of gears creates a disturbance in the angular velocity curve which goes high at point of contact between gears and decreases when there is no contact.
Case 2:
Here we fixed the sun gear and gave input to the ring gear to observe the output on the carrier. as the sun gear is fixed and the ring gear drives the planet gears and in turn drives the carrier, the speed is seen to be highest among all the cases which is an indication of very low torque. So using this case would result in high speed and low torque.
Also from the plot, we can observe that the meshing of gears creates a disturbance in the angular velocity curve. but the disturbance is very low compared to the first case.
Case 3:
Here we fixed the carrier and gave input to the sun gear to observe the output on the ring gear. as the carrier is fixed and the sun gear drives the planet gears and in turn drives the ring gear, the speed is seen to be much lower than case 2 but higher than case 1which is an indication of relatively low speed and high torque. So using this case would result in low speed and high torque.
Also from the plot, we can observe that the meshing of gears creates a disturbance in the angular velocity curve. But compared to case 1 and case 2, this curve is more stable in nature.
Conclusion:
Comparing the plots of the three cases we get to know that the first case has the highest torque and the second case gives the highest speed but very low torque. The third case gives high torque and low speed and the mechanism of case 3 is seen mostly in wheel hub motors where the torque requirement is higher than the speed requirement.
So this way the planetary gear system is created in Solidworks and a motion study is created on it in various cases and analyzed.