MBD Simulation on IC Engine Valve Train using SOLIDWORKS
MBD Simulation on IC Engine Valve Train
AIM:
- Create the 3d model of the parts and assemble all the parts to make mechanism.
- Analyze the motion study of valve train.
OBSERVATION:
- To create the 3d parts of the valve train and assemble all the components.
- To study the motion analysis.
- To plot the linear displacement of the valve.
- To plot the contact force graphs of cam and push rod, push rod and rocker arm, rocker arm and valve(Magnitude), rocker arm and valve(X Direction).
THEORY:
A valve train is a mechanical system that controls operation of the intake and exhaust valves in an internal combustion engine. The intake valves control the flow of air/fuel mixture (or air alone for direct-injected engines) into the combustion chamber, while the exhaust valves control the flow of spent exhaust gasses out of the combustion chamber once combustion is completed.
Components
The valve train consists of all the components responsible for transferring the rotational movement of the camshaft into the opening and closing of the intake and exhaust valves. Typical components are listed below in order from the crankshaft to the valves.
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. The camshaft is driven by the crankshaft and— in the case of a four-stroke engine— rotates at half the speed of the crankshaft.
Motion is transferred from the crankshaft to the camshaft most commonly by a rubber timing belt, a metallic timing chain or a set of gears.
Pushrod
Pushrods are long, slender metal rods that are used in overhead valve engines to transfer motion from the camshaft (located in the engine block) to the valves (located in the cylinder head). The bottom end of a pushrod is fitted with a lifter, upon which the camshaft makes contact. The camshaft lobe moves the lifter upwards, which moves the pushrod. The top end of the lifter pushes on the rocker arm, which opens the valve.
Rocker arm / bucket tappet
Depending on the design used, the valves are actuated by a rocker arm, finger or bucket tappet. Overhead camshaft engines use fingers or bucket tappets, upon which the cam lobes contact. Overhead valve engines use rocker arms, which are actuated by a pushrod and pivot on a shaft or individual ball studs in order to actuate the valves.
Valves
Most modern engines use poppet valves type, although sleeve valves, slide valves and rotary valves have also been used at times. Poppet valves are typically opened by the camshaft lobe or rocker arm, and closed by a coiled spring called a valve spring.
Valve float occurs when the valve spring is unable to control the inertia of the valve train at high engine speeds (RPM).
Creating 3D Model
1.CAM
2. Push rod
3.Rocker arm
4. Valve
5.Stem
Assembly of the train valve
Motion Analysis
- To run the motion analysis first go 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 stem 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.
- obtain all the plots of contact forces.
There are two cases to follow to get the desired motion analysis and the plots. They are as follows,
Case 1: Motion Analysis for cam lift of 3.5mm:
To calculate the distance between the two centres(L)
Given: R1 = 12.5; R2 = 5; Cam lift = 3.5mm
Cam lift = (L-R1)+R2
L = (12.5+3.5) - 5
L = 11mm
With the above information, Cam is modelled for the case 1 analysis.
Linear Displacement
Contact Force plots:
Cam and Push rod(Magnitude)
Push-rod and Rocker Arm(Magnitude)
Rocker Arm and Valve(Magnitude)
Rocker Arm and Valve (X-Direction)
Case 2: Motion Analysis for cam lift of 6mm:
To calculate the distance between the two centres(L)
Given: R1 = 12.5; R2 = 5; Cam lift = 3.5mm
Cam lift = (L-R1)+R2
L = (12.5+6) - 5
L = 13.5mm
With the above information, Cam is modelled for the case 2 analysis.
Linear Displacement
Contact Force plots:
Cam and Push Rod(Magnitude)
Pushrod and Rocker Arm (Magnitude)
Rocker Arm and Valve (Magnitude)
Rocker Arm and Valve (X-Direction)
ANIMATION VIDEO
Observation and Results
- The contact forces between each component and linear displacement of the valve for the cam lift of 6mm is larger than the cam lift of 3.5mm. It shows that Cam geometry affects the amount of opening of the valve through which the air-fuel mixture enters to the cylinder.
- The linear displacement of the valve is greater than the lift produced by the Cam as the moment arm towards the valve is greater than the pushrod.
- In the plot of contact forces against time for rocking arm and the valve, a minimum force is always present due to the initial compressed state of the spring.
- The contact forces are always present at the top(peak point) of the cam profile.
- Contact force between the Rocker arm and valve varies while measuring with respect to the X-direction and measuring with respect to magnitude because if we look at the plot of the X – component of the contact against time, it achieves negative force because the rocker arm slides both forwards and backward during one complete rotation of the Cam and hence the friction force acts in both direction. The magnitude of the contact force between the rocker arm and the valve pushes the valve downwards, but its X- component gives us only the friction force of the rocker arm sliding over the face of the valve head.
REFFERENCES