MBD Simulation on IC Engine Valve Train

Motion analysis of IC engine valve train using solidworks

Aim

To create 3D models of CAM and other IC engine valve train parts and run a motion analysis on particular conditions.

Introduction

IC engine valve train

A valve train is a mechanical system that controls the intake and exhaust valves in IC engines.The intake valve is responsible for the flow of air fuel mixture inside the combustion chamber and the exhaust valve is responsible for flushing out the exhaust gases after combustion.

Cam

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

Push rod

These are rods operated by cam and it is responsible for transferring the motion from cam to the rocker arm

Rocker arm

A rocker arm is an oscillating lever that conveys radial movement from the cam lobe into linear movement at the valve to open or close it.

Valve

Engine valves are mechanical components that allow or restrict the flow of fluids inside the combustion chamber.

Valve mount

Valve mount is used to provide rigid support and hold the valve at correct position. A helical spring is placed in between the valve and valves mount which helps the valve to get back to its position.

3D model of components

Assembly

Cam design calculations

Case 1

cam lift=3.5mm

Taking D₁=20mm and D₂=10mm,

Cam lift= (L-R₁)+R₂

L= 3.5+10-5

L=8.5mm

Case 2

Cam lift =6mm

Taking D₁=20mm and D₂=10mm,

Cam lift= (L-R₁)+R₂

L=6+10-5

L=11mm

Material used

Material used for all the components during motion analysis is cast carbon steel.

Valve spring conditions

Free length- 55mm

Spring stiffness- 10 N/m

Motion analysis results

Case 1 (1500 rpm)

Linear displacement of valve

Contact force between cam and push rod

Contact force between push rod and rocker arm

Contact force between rocker arm and valve

Contact force between valve and rocker arm (x direction)

Case 2 (1500 rpm)

Linear displacement of valve

Contact force between cam and push rod

Contact force between push rod and rocker arm

Contact force between rocker arm and valve

Contact force between valve and rocker arm (x direction)

Observations and result

1. A rise in the linear displacement of the valve from 50.8 to 52.5 is observed as the cam lift is changed from 3.5mm to 6mm.
2. The contact force between cam and pushrod increases with increase in the cam lift
3. In both the cases, there always exist a minimum force between the rocker arm and the push rod as the spring is being compressed at the initial state.
4. The contact forces are non-uniform due to friction and vibrations.
5. The power output and efficiency of overhead valve engines (OHC) is much lower than overhead camshaft engines (OHV) due to lesser vibrations between the components.

Reason for variation in contact force between rocker arm and valve when measured in magnitude and X-direction.

While measuring along the x-direction, only the frictional force between the rocker arm and valve is obtained as the rocker arm slides over the valve whereas while measuring the magnitude, we get the actual force exerted by the rocker arm on the valve.

Animation