MBD Simulation on IC Engine Valve Train
AIM: - MBD Simulation on IC Engine Valve Train Using Solidworks.
OBJECTIVES: -
To create a model of the CAM and its associated parts for the IC Engine valve train then run motion analysis to find the contact force encountered between the parts(between cam and push rod, push-rod and rocker arm, and rocker arm and valve) and explain the results.
INTRODUCTION: -
A typical valve-train consists of valves, rocker arms, push-rod, lifters, and cam. Valve-train opening/closing and duration, as well as the geometry of the valve-train, controls the amount of air and fuel entering the combustion chamber at any given point in time. Valve-trains are built in several configurations, each of which varies slightly in layout but still performs the task of opening and closing the valves at the time necessary for proper operation of the engine.
THEORY: -
IC Engine Valve Train
- A valve train or valve train is a mechanical system that controls operation of the valves in an internal combustion engine, whereby a sequence of components transmits motion throughout the assembly.
- Conventional reciprocating internal combustion engine uses valves to control the flow of the air/fuel admix into and out of the combustion chamber.
- A typical valve train consists of valves, rocker arms, pushrods, lifters, and camshaft(s). Valve train opening/closing and duration, as well as the geometry of the valve train, controls the amount of air and fuel entering the combustion chamber at any given point in time.
- Timing for open/close/duration is controlled by the camshaft that is synchronized to the crankshaft by a chain, belt, or gear.
- The camshaft is located within the engine block, and operates directly on the valves, or indirectly via pushrods and rocker arms. Because they often require pushrods they are often called pushrod engines.
We have to design all the different parts of the valve train arrangement separately.
The parts are as follows:
- Cam
- Push-rod
- Rocker Arm
- Valve
- Valve Mount
Then, assemble the all parts.
- Camshaft
The timing and lift profile of the valve opening events are controlled by the camshaft, through use of a carefully shaped lobe on a rotating shaft.
- Pushrods
Pushrods are long, slender metal rods that are used in overhead valve engines to transfer motion from the camshaft to the valves.
- Rocker Arm
The valves are actuated by a rocker arm. This is part which is connected to push rod in one end and valve on the other end.
- Valve
This allows the air-fuel mixture to enter the cylinder or exhaust the gases out from the cylinder by opening and closing of the inlet/exhaust port.
- Valve Mount:
This acts as the stoppage for the valve and limits the movement of the valve.
Assembly
Motion Analysis
- To run the motion analysis first goes to motion study and establish contact between Cam and push rod, push rod and rocker arm, rocker arm and valve.
- Next, give the rotation to the cam with 1500 RPM.
- Set up a linear spring between a valve and the valve mount with the spring stiffness of 10 N/mm and free length 45 mm.
- Change the frames to 7200 frames per sec and use precise contact.
- Select the entire assembly and assign the material as follows, go to Material-Edit material and select Cast Carbon Steel and click apply.
- There will be an indication of the material assigned with a change in color of the entire assembly.
- Now click the calculation button.
- Run the analysis for the required time.
There are two cases to follow to get the desired motion analysis and the plots. They are as follows,
|
Sl.No |
CAM Lift (mm) |
Speed (RPM) |
Material |
|
1 |
3.5 |
1500 |
Cast Carbon Steel |
|
2 |
6 |
1500 |
Cast Carbon Steel |
The dimensions of the parts
Case I = Motion Analysis for cam lift of 3.5 mm:
To calculate the distance between the two centers (L)
Given: R1 = 12.5; R2 = 5; Cam lift = 3.5mm
Cam lift = (L-R1)+R2 L = (12.5+3.5) - 5
L = 11mm
Cam is modeled for the case 1 analysis with this information.
Contact Force plots:
Cam and Push rod
Push-rod and Rocker Arm
Rocker Arm and Valve
Rocker Arm and Valve (X-Direction)
Case 2: Motion Analysis for cam lift of 6mm:
To calculate the distance between the two centers (L)
Given: R1 = 12.5; R2 = 5; Cam lift = 3.5mm
Cam lift = (L-R1) +R2L = (12.5+6) – 5
L = 13.5mm
Cam is modeled for the case 1 analysis with this information.
Contact Force plots:
Cam and Push rod
Push-rod and Rocker Arm
Rocker Arm and Valve
Rocker Arm and Valve (X-Direction)
OBSERVATION AND RESULTS :-
- Q) 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.
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 the contact force of Rocker arm and valve along x-axis is frictional force that cause by the sliding of Rocker arm on the valve but the contact force of Rocker arm and valve along magnitude consider magnitude of both the friction force occurring in x direction and the force along the y direction to move the valve.
- The change in direction of the force is because the rocker arm first slides towards origin giving a positive friction force (opposing the motion) and then slides away from the origin giving rise to friction in the negative x-direction. Therefore the plots are opposite to each other.
- The explanation is same for the cam lift of 6 mm, only it differs in magnitude of contact forces. The movement in this case is quite smoother compared to the cam lift of 3.5 mm as observed. As the cam lift increases more air-fuel mixture can enter into the cylinder of IC engine.
ANIMATION :-