MBD Simulation on IC Engine Valve Train

AIM:-MBD Simulation on IC Engine Valve Train

OBJECTIVE:-

• Model the parts and assemble them in SolidWorks. 
• Run the simulation using the below parameters

Obtain the

• Valve Lift. 
• 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.

INTRODUCTION:-

To plot the following quantiies 

 Valve Lift. 

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 cam is a common mechanism element that drives a mating component known as a follower. 

The cam accepts an input motion similar to a crank and imparts a resultant motion to a follower.

The valve train of an automotive engine. In this application, an oblong-shaped cam is machined on a shaft.

This camshaft is driven by the engine.

As the cam rotates, a rocker arm drags on its oblong surface.

The rocker arm, in turn, imparts a linear, reciprocating motion to a valve stem.

The motion of the valve must be such that the exhaust pathway is closed during a distinct portion of the combustion cycle and open during another distinct portion.

Thus, the application is perfect for a cam because timing and motion must be precisely sequenced.

The rocker arm follower needs to maintain contact with the cam surface to achieve the desired motion.

Thus, in most cam applications, the follower is forced against the cam surface through some mechanical means. Springs are very common for this purpose.

In cases where the follower is in the vertical plane, the weight of the follower may be sufficient to maintain contact.

Some cam designs capture the follower in a groove to maintain contact.

The important point is that contact between the cam and the follower must be sustained.

3D MODEL:-

CAM: A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion.

It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path.

PUSHROD:-

This is the part to which the lift is provided, which is transmitted to the rocker arm.

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.

FINAL ASSEMBLY:-

Assembly is made using the assembly mate option by properly aligning them as shown.

Physical dynamics is used here for making contact between valve, rocker arm, push rod and cam which locks them in position and motion analysis is performed.

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 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,

Cam Lift Formula: 

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.

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.

Contact Force plots:

Cam and Push Rod Magnitude:-

Pushrod and Rocker Arm Magnitude:-

Rocker Arm and Valve Magnitude:-

Rocker Arm and Valve X-Direction:-