MBD Simulation on IC Engine Valve Train (Multibody Dynamics using Solidworks)

Motion analysis is important because product design frequently requires an understanding of how multiple moving parts interact with each other and their environment. From automobiles and aircraft to washing machines and assembly lines - moving parts generate loads that are often difficult to predict. Complex mechanical assemblies present design challenges that require a dynamic system-level analysis to be met. Accurate modeling can require representations of various types of components, like electronic controls systems and compliant parts and connections, as well as complicated physical phenomena like vibration, friction, and noise. Motion analysis enables one to meet these challenges by quickly evaluating and improving designs for important characteristics like performance, safety, and comfort.

 

 

A valvetrain is a mechanical system that controls the 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.

 

The valvetrain layout is largely dependent on the location of the camshaft(s). The common valvetrain configurations for piston engines are:

Cam-in-block camshaft is located within the engine block, as either an overhead valve (OHV) or a flathead engine. Because they often use pushrods, OHV engines are often called "pushrod engines".

Overhead camshaft (s) are located near the top of the engine, above the combustion chamber.

Camless

This layout uses no camshafts at all. Technologies such as solenoids are used to individually actuate the valves.

Components

The valvetrain 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 the 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

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.

 

To Find,

• Valve Lift. 
• The contact force between 
  • Cam and Push Rod
  • Pushrod and Rocker Arm
  • Rocker Arm and Valve

and to 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. 

Data,

 

Sl.No	CAM Lift (mm)	Speed (RPM)	Material
1	3.5	1500	Cast Carbon Steel
2	6	1500	Cast Carbon Steel

 

Procedure,

1. All individual Parts are Modelled in SolidWorks.
2. 2 Separate CAMs are modeled one with a 3.5mm lift and the other with a 6mm lift.
3. Assembly is done using proper constraints.
4. Motion Analysis is performed on the assembly where motor rotation is given to the CAM axis with 1500 RPM.
5. Linear spring is added between the surface of the valve and valve mount with a spring constant of 10N/mm and a free length of 45mm.
6. Change the frame to 9000 per second with precise contact.
7. Apply Cast Carbon Steel material to the entire assembly.
8. Run the Simulation and plot the desired Results.

 Design Geometry of Parts

 Rocker Arm

Valve

Valve Mount

Push Road

CAMs

Consider R1=12.5mm, R2=5mm

CAM 1:- To lift 3.5mm    

CAM LIFT = (L-R1)+R2
3.5=(L-12.5)+5
-1.5=L-12.5
-1.5+12.5=L
L=11

 L1=11mm

 

 

CAM 2 :- To lift 6mm    

CAM LIFT = (L-R1)+R2
6=(L-12.5)+5
1=L-12.5
1+12.5=L
L=13.5

 L1=13.5mm

Valve Train Assembly

 

Case 1:- 3.5mm Lift Simulation Results

Valve Displacement 

 

Contact Force Plots

Contact Force b/w CAM & Push Rod

Contact Force b/w Push Rod & Rocker Arm

Contact Force(Magnitude) b/w Rocker Arm & Valve

Contact Force(X-direction) b/w Rocker Arm & Valve

Case 2:- 6mm Lift Simulation Results

Valve Displacement 

Contact Force Plots

Contact Force b/w CAM & Push Rod

Contact Force b/w Push Rod & Rocker Arm

Contact Force(Magnitude) b/w Rocker Arm & Valve

Contact Force(X-direction) b/w Rocker Arm & Valve

 

Observations:-

• With Increased CAM lift, Valve Displacement can be increased.
• Valve lift mainly depends on the Design of CAM and Rocker Arm.
• Selection of Suitable spring (free length & Spring constant) plays a vital role in the Valve lift Mechanism.
• Vibrations can be observed during retracing Valve back to its original Position due to Spring with lower spring constant selected.
• The contact force between the Rocker arm and valve varies while measuring with respect to the X-direction and measuring with respect to magnitude because of the fact that an overall net force acting on the systems point of contact is calculated in the Magnitude whereas only the Force/reaction force/ Frictional force/Drag Force between Rocker Arm surface and Valve Surface during sliding is calculated in X direction Evaluation.