MBD Simulation on IC Engine Valve Train
AIM : To create 3D models for IC Engine Valve Train,assemble it, and run the simulations in Solidworks.
OBJECTIVES :
- To run the motin study simulations for different cam heights.
| S.No. | CAM lift (mm) | Speed (RPM) | Material |
| 1. | 3.5 | 1500 | Cast Carbon Steel |
| 2. | 5 | 1500 | Cast Carbon Steel |
- To plot the following quantiies -
- (i) Valve Lift.
- (ii) The contact force between
- Cam and Push Rod
- Pushrod and Rocker Arm
- Rocker Arm and Valve
- Explain why the contact force between the Rocker arm and valve varies while measuring with respect to the X direction and measuring with respect to magnitude.
THEORY : A valve train mechanism of an internal combustion engine including a cylinder head formed with an intake port and an exhaust port, and a camshaft including a valve for opening or closing the intake port and the exhaust port formed in the cylinder head of the engine, a cam mounted to the camshaft so as to be rotated together, and a rocker arm supported on a rocker shaft to be swingable, in which the valve is opened or closed by swinging the rocker arm by rotation of the cam. The rocker shaft is formed with an oil passage, inside the rocker shaft, extending in an axial direction and with an oil outlet communicating with the oil passage and extending in a radial direction of the rocker shaft.
- Cam Shaft and Follower - A cam is a mechanical device used to transmit motion to a follower by direct contact. The driver is called the cam and the driven member is called the follower. In a cam follower pair, the cam normally rotates while the follower may translate or oscillate. A familiar example is the camshaft of an automobile engine, where the cams drive the push rods (the followers) to open and close the valves in synchronization with the motion of the pistons.
- Push Rod - A metal rod transmitting the reciprocating motion that operates the valves of an internal-combustion engine having the camshaft in the crankcase.
- Rocker Arm - A rocker arm (in the context of an internal combustion engine of automotive, marine, motorcycle and reciprocating aviation types) is an oscillating lever that conveys radial movement from the cam lobe into linear movement at the poppet valve to open it. One end is raised and lowered by a rotating lobe of the camshaft (either directly or via a tappet (lifter) and pushrod) while the other end acts on the valve stem. When the camshaft lobe raises the outside of the arm, the inside presses down on the valve stem, opening the valve. When the outside of the arm is permitted to return due to the camshafts rotation, the inside rises, allowing the valve spring to close the valve.
- Valve Guide and Stem - In most types of reciprocating engines, a valve guide is provided for each poppet valve in the cylinder head. Along with the valve spring, it serves to positively locate the valve so that it may make proper contact with the valve seat. A valve guide is a cylindrical piece of metal, pressed or integrally cast into the cylinder head, with the valve reciprocating inside it. Guides also serve to conduct heat from the combustion process out from the exhaust valve and into the cylinder head where it may be taken up by the cooling system.
PROCEDURE :
- 1. Sketching and 3D modelling of components -
- At first, various components are sketched and modelled according to the video itself in the front plane. For sketching the cams for different lifts the following formula was used -
- The diameters of both circles are kept according to the image shown above, the distance between two centres were found using putting required cam lift as,
- For Case 1, i.e., cam lift `3.5` mm, `implies 3.5 = (L_1-17.5)+10` , `implies L_1 = 11 mm`,
- Similarly for Case 2, i.e, cam lift `6` mm, `implies 6 = (L_2-17.5)+10` , `implies L_2 = 13.5 mm`
- Design of Cam for Case 1 -
- Design of Cam for Case 2-
- Design of Rocker Arm -
- Design of Valve -
- Design of Valve Stem -
- Design of Pushrod -
- 2. Assembly of components -
- All components sketched were imported into assembly and the first component inserted (cam) was made to float from being fixed. Temproary axes were switched on for better viewings. All components were bought to front plane and made coincident to this plane. The cam was positioned by also making it's axis coincident to top plane and right plane. Distance mate were provided to other component so that they do not obstruct each other during the motion and the axes of valve and valve stem were made coincident. Top plane of rocker arm and assembly top plane were provided an additional angle mate of 0 degree so that it remains parallel to this plane.
- After successfull assembly, it was made to move using the physical dynamics so that necessary clearance and contact are provided between components.
- Assembly for Case 1 -
- Assembly for Case 2 -
- 3. Motion Study and Analysis -
- 3.1 Case 1 (for cam lift 3.5 mm) : After successful assembly, Solidworks motion is selected from Solidworks add-ins and motion study is made active. For case 1, a motor/torque of 1500 rpm is provided to the cam axis. Solid contact between cam and pushrod, pushrod and rocker arm, rocker arm and valve were given and material provided was Steel(dry). A linear spring was provided between upper edge of valve stem and lower stem of valve with spring constant `k` as 15 N/mm. The spring was pretensioned by changing it's natural length to 45 mm. For solving the study more accurately 9000 fps were provided with precise contact. By selecting the complete assembly the material specified was Cast Carbon Steel.
- Plot for linear displacement of valve -
- Plot for contact force between Cam and Push Rod -
- Plot for contact force between Pushrod and Rocker Arm -
- Plot for contact force between Rocker Arm and Valve -
- The valve lift during motion was obtained from excel spreadsheet and from this maximum position of valve was `52.218 mm` while minimum one was `50.377 mm`. Hence valve lift can be calculated as the difference between these two positions and was `1.841 mm`.
- From the plot of contact force between cam and pushrod, initially the force was too high and was due to sudden contact and jerk of the system. After this the force varies with gradual ups and downs with a maximum value around 1300 to 1400 N.
- Similarly from the plots of contact force between rocker arm and pushrod, and contact force between rocker arm and valve, initially the force was too high and was due to sudden contact and jerk of the system. After this the force varies with gradual ups and downs with a maximum value around 1300 to 1400 N and 340-350 N respectively.
- 3.2 Case 2 (for cam lift 6 mm) : After successful assembly, Solidworks motion is selected from Solidworks add-ins and motion study is made active. For case 2, a motor/torque of 1500 rpm is provided to the cam axis. Solid contact between cam and pushrod, pushrod and rocker arm, rocker arm and valve were given and material provided was Steel(dry). A linear spring was provided between upper edge of valve stem and lower stem of valve with spring constant `k` as 15 N/mm. The spring was pretensioned by changing it's natural length to 50 mm. For solving the study more accurately 9000 fps were provided with precise contact. By selecting the complete assembly the material specified was Cast Carbon Steel.
- Plot for linear displacement of valve -
- Plot for contact force between Cam and Push Rod -
- Plot for contact force between Pushrod and Rocker Arm -
- Plot for contact force between Rocker Arm and Valve -
- The valve lift during motion was obtained from excel spreadsheet and from this maximum position of valve was `53.815 mm` while minimum one was `50.253 mm`. Hence valve lift can be calculated as the difference between these two positions and was `3.562 mm`.
- From the plot of contact force between cam and pushrod, initially the force was too high and was due to sudden contact and jerk of the system. After this the force varies with gradual ups and downs with a maximum value around 3500 N.
- Similarly from the plots of contact force between rocker arm and pushrod, and contact force between rocker arm and valve, initially the force was too high and was due to sudden contact and jerk of the system. After this the force varies with gradual ups and downs with a maximum value around 3600 N and 770-790 N respectively.
- Q. Explain why the contact force between the Rocker arm and valve varies while measuring with respect to the X direction and measuring with respect to magnitude.
- Ans . The contact force between the Rocker arm and valve varies while measuring with respect to the X direction and measuring with respect to magnitude because contact force line of action is changing continuously and along X direction the surfaces of valve and rocker arm rubs over each other and produces friction between them and is both positive and negative as obtained from the plots. This frictional force will tend to losses in energy and will dissipate as heat. Whereas the contact force magnitude calculates vector sum of forces in all three directions and will be greater than forces in either directions.
- For case 2, comparison of contact forces
- For case 1, comparison of contact forces
- The 3D model, assembly, simulation of case 1 and case 2 can be found from the following Google drive link : drive
- The link for the simulation of case 2 : link
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