The current cam and follower mechanism in four stroke internal combustion engine employs a flat follower. In this work an attempt is made to change the flat face of follower to a curved face follower, so that the required point contact can be achieved. As line contact between existing cam and follower mechanism results in high frictional losses which results in low mechanical efficiency. It is observed that the frequency of vibration in the existing and modified cam and follower mechanism remains almost same. The finite element approach is used to perform the analysis.
Cam and follower mechanism is preferred over a wide variety of internal combustion engines because due to the cam and follower it is possible to obtain an unlimited variety of motions. Again the cam and follower has a very important function in the operation of many classes of machines, especially those of the automatic type, such as printing presses, shoe machinery, textile machinery, gear-cutting machines, screw machines etc. The cam may be defined as a machine element having a curved outline or a curved groove, which, by its oscillation or rotation motion, gives a predetermined specified motion to another element called the follower. In other word, cam mechanism transforms a rotational or oscillating motion to a translating or linear motion. In fact, cam can be used to obtain unusual or irregular motion that would be difficult to obtain from other linkage. The variety of different types of cam and follower systems that one can choose from is quite broad which depends on the shape of contacting surface of the cam and the profile of the follower. The existing cams used in internal combustion engines are made in a variety of forms which have a line contact with follower. As line contact between current cam and follower mechanism results in high frictional losses which results in low mechanical efficiency. Hence in this work an attempt is made to change the flat face of follower to a curved face follower, so that the required point contact can be achieved to minimize frictional losses.
Valves in distribution systems of internal combustion engines must ensure a suitable filling of cylinders in gasoline-air mixture for SI engines and in air for Compression ignition engines. On the other hand, for high engine speeds, valves may not have time to return to initial positions. It follows a power loss and in certain cases interference between the valve head and piston causing a broken engine [1,2]. The dynamic behavior of the system camshaft, follower, push-rod and valve is in a great importance in the good working of the system [
According to Khin [
Hence in order to consider the effect of profile of the follower, in this work an attempt is made to convert the existing line contact [as shown in
Most of the internal combustion engines used in various applications such as automotive to power generation have roller cam and follower mechanisms, having a line contact between the cam and follower as shown in
Modal analysis of roller follower is performed by Ansys software to determine the vibrations characteristics such as natural frequencies and mode shapes.
To perform finite element analysis of roller follower, the solid model of the same is essential.
Roller follower first modeled in PRO/E WILDFIRE which is excellent CAD software, which makes modeling so easy and user friendly. The model is then transferred in IGES format and exported into the Analysis software ANSYS 11.0. The Follower is analyzed in ANSYS in
three steps. First is preprocessing which involves modeling, geometric clean up, element property definition and meshing. Next step includes solution of problem, which involves imposing boundary conditions on the model and then solution runs. Next in sequence is post processing, which involves analyzing the results plotting different parameters like stress, strain, natural frequency. The
The objective in building a solid model is to mesh that model with nodes and elements. Once the creation of solid model is completed, set element attributes and establishing meshing controls, which turn the ANSYS program to generate the finite element mesh. For defining the elements attributes, the user has to select the correct element type. This is most important task in finite element analysis because it decides the accuracy and computational time of analysis.
In this work Solid 90 element was used as element type. Solid 90 is a higher order version of the 3-D eight node thermal element (Solid 70). The element has 20 nodes with a single degree of freedom, temperature, at each node. The 20 node elements have compatible temperature shapes and are well suited to model curved boundaries. The 20 node thermal element is applicable to a 3-D, steady-state or transient thermal analysis. In this work Solid 90 is used for meshing of body of follower. The type of meshing used for follower is FREE mesh which is controlled by two parameters assigned to each mesh surface or volume that affect the size the elements generated. The meshed model and contact region is shown in
A free modal analysis was performed to determine the natural frequencies of the existing follower and modified follower by Ansys software. Block Lancoz solver was used and expansion pass settings were set as 12 modes to extract and 12 modes to expand. Zero to infinity range was set to calculate the natural frequencies for existing and modified follower as shown in Figures 5 and 9.
In this section detail of finite element analysis and element behavior is given.
The