MBD Simulation on IC Engine Valve Train

AIM:

In this project, the main objective is to model an IC engine valve train which consists of essential parts such as a cam, push rod, rocker arm, valve mount, and valve, then assemble them in SolidWorks.

Objective:

To Run the simulation using the below parameters

SL.No.	CAM Lift (mm)	Speed (RPM)	Material
1.	3.5	1500	Cast carbon steel
2.	6	1500	Cast carbon steel

To obtain the contact force between

Cam and Push Rod

Pushrod and Rocker Arm

Rocker Arm and Valve

Introduction:

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. A 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, 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.

Principle:

Internal combustion heat engines work on the principle of the ideal gas law. Raising the temperature of a gas increases the pressure that makes the gas want to expand. An internal combustion engine has a chamber, which has fuel added to it which ignites in order to raise the temperature of the gas. When heat is added to the system, it forces gas inside to expand. With a piston engine, this causes the piston to rise and with a gas turbine, the hot air is forced into the turbine chamber, turning the turbine. By attaching the piston or turbine to a camshaft, the engine is able to convert a portion of the energy input to the system into useful work.To compress the piston in an intermittent combustion engine, the engine exhausts the gas. A heat sink is then used to keep the system running at a consistent temperature. A gas turbine, which uses continuous combustion, simply exhausts its gas continuously rather than in a cycle.

3D Models:

Cam: A part which provides the lift for the push rod which actuates the valve at regular time intervals.

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 vlave on the other end.

Valve: This allows the air fuel mixture to enter the cylinder or exhuast the gases out from the cylinder by opening and closing of the inlet/exhuast port.

Valve stem: 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.

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 valve and the valve stem with the spring stiffness of 10 N/mm and free lenght 45mm. 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 indication of the material assigned with change in color of the entire assembly. Now click the calculation button. Run the analysis for required time.

These are TWO cases to follow to get the desired motion analysis and the plots. They are as follows,

Case	Cam Lift (mm)	Speed (RPM)	Material
1.	3.5	1500	Cast carbon steel
2.	6	1500	Cast carbon steel

CAM LIFT Formula:

Case 1: Motion analysis for Cam lift of 3.5mm.

R1= 12.5mm

R2= 10mm

therefore, L=3.5+R1-R2

L=3.5+12.5-10 =6mm

Case 2: Cam lift of 6mm

R1= 12.5mm

R2= 10mm

therefore, L=6+R1-R2

L=6+12.5-10 =8.5mm

Contact Force Graphs for Case 1:

Cam and Push rod;

This shows the contact force between the Cam and the Push rod the maximum force is around 1460 N, this is when the push rod comes down after the cam lift. The contact force during the cam lift is around 200 N(between 0 & 366 N).The other forces are due to friction while the push rod slides over the cam.

Push rod and Rocker arm;

This is almost same as that of the graph between cam and push rod but only the magnitude of the contact force varies.

Rocker arm and Valve[magnitude];

Rocker arm and Valve[X direction];

Explaination:

The Magnitude represents net contact force between the parts, while the contact force along X direction is the frictional force between the bodies that arises due to the rocker arm sliding over the surface of valve head. The change in direction of the force is because the rocker arm first slides towards origin giving a postive friction force (opposing the motion) and then slides away from the origin giving rise to friction in negative x direction. Therefore the plots are opposite to each other.

Contact Force Graphs for Case 2:

Cam and Push rod;

Push rod and Rocker arm;

Rocker arm and Valve[magnitude];

Rocker arm and Valve[X direction];

The explanation is same for the cam lift of 6mm, only it differs in magnitude of contact forces. The movement in this case is quite smoother compared to the cam lift of 3.5mm as observed. As the cam lift increases more air-fuel mixture can enter into the cylinder of IC engine.

Animation Link for the final assembly working:

https://youtu.be/LUczHH5L_Qg