MBD Simulation on IC Engine Valve Train
AIM: Multi-Body Dynamics Simulation on IC Engine Valve train.
Objectives of the project:
- To perform the motion analysis for different cam lift.
- To plot linear displacement of valve lift at each cam lift.
- To plot the contact force between cam and push rod.
- To plot the contact force between push rod and rocker arm.
- To plot the contact force between rocker arm and valve.
Introduction:
A valvetrain or 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 combusion chamber once combustion is completed.
3D Models of Part and Assembly of IC Engine Valve Train:
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 (e.g. an eccentric wheel) or shaft (e.g. a cylinder with an irregular shape) that strikes a lever at one or more points on its circular path. The cam can be a simple tooth, as is used to deliver pulses of power to a steam hammer, for example, or an eccentric disc or other shape that produces a smooth reciprocating (back and forth) motion in the follower, which is a lever making contact with the cam.
Push Rod:
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:
A rocker arm (in the context of an internal combustion engine of automotive, marine, motorcycle and reciprocating aviation types) is an oscillating lever that conveys radial movement from the cam lobe into linear movement at the poppet valve to open it. One end is raised and lowered by a rotating lobe of the camshaft (either directly or via a tappet (lifter) and pushrod) while the other end acts on the valve stem. When the camshaft lobe raises the outside of the arm, the inside presses down on the valve stem, opening the valve. When the outside of the arm is permitted to return due to the camshafts rotation, the inside rises, allowing the valve spring to close the valve.
Valve:
A valve is a device or natural object that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Most modern engines use poppet valves type, although sleeve valves, side 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 Mount:
A valve mount is used to support the valve component to move in correct direction when the spring is attached between the contact faces of valve and valve mount.
Assembly of IC Engine valve train:
Procedure:
- Creating a required 3D model of all Parts of IC Engine valve train.
- Creating two separate part for of cam for cam lift of 3.5mm and 6mm.
- Assembling the parts with the help of contraints.
- The input motor is given to axis of cam with an input speed of 1500rpm and also the contact between the parts is build under motion analysis.
- Linear spring is added between the surface of valve and valve mount with spring constant 10 N/mm and free length of 45mm.
- In this study of motion analysis, we use 7200 frames per second with precise contact.The material used is Cast Carbon Steel.
Motion Analysis of Engine Piston Assembly:
Crank Speed=1500Rpm
No. of frames per second (fps) =7200 with precise contact
Material selected for each contact= Cast Carbon Steel
Given Conditions:
|
Sr. No |
CAM lift(mm) |
Speed(RPM) |
Material |
|
1 |
3.5 |
1500 |
Cast Carbon Steel |
|
2 |
6 |
1500 |
Cast Carbon Steel |
Calculation Formula for Cam lift:
Case 1: Cam lift at 3.5mm
Here, Radius of Lower Circle (R1) =12.5mm
Radius of Upper Circle (R2) =5mm
So, CAM LIFT= (L-R1) +R2
3.5= (L-12.5) +5
L=11mm
Results Obtained:
Output Plots:
Linear Displacement of valve lift (Magnitude):
Contact Force b/w Cam and Push Rod (Magnitude):
Contact Force b/w Push Rod and Rocker Arm (Magnitude):
Contact Force b/w Rocker Arm and Valve (Magnitude):
Contact Force b/w Rocker Arm and Valve (in X direction):
Animation Link:https://youtu.be/2Y99wLxv5aw
Case 2: Cam lift at 6mm
Here, Radius of Lower Circle (R1) =12.5mm
Radius of Upper Circle (R2) =5mm
So, CAM LIFT= (L-R1) +R2
6= (L-12.5) +5
L=13.5mm
Results Obtained:
Output Plots:
Linear Displacement of valve lift (Magnitude):
Contact Force b/w Cam and Push Rod (Magnitude):
Contact Force b/w Push Rod and Rocker Arm (Magnitude):
Contact Force b/w Rocker Arm and Valve (Magnitude):
Contact Force b/w Rocker Arm and Valve (in X direction):
Animation Link:https://youtu.be/rLmjVw28F1I
Conclusion:
- With the increase in the cam lift, linear displacement of valve also increases.
- The magnitude represents the net contact force between the parts in all direction, while contact force in x-direction gives only the force acting in x-direction both positive and negative and is mainly due to the frictional force acting between the bodies of rocker arm sliding over the surface of valve.
- Hence, the contact force between rocker arm and valve with magnitude is much higher than that in x-direction only.