MBD Simulation on IC Engine Valve Train using Solidworks

Objective- To create a 3D model for IC Engine Valve Train and assemble and performed a motion analysis and also to study contact force between parts in the given cases.

Theory- A valvetrain or valve train is a mechanical system that controls the 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 valvetrain consists of valves, rocker arms, pushrods, lifters, and cam. Valvetrain opening/closing and duration, as well as the geometry of the valvetrain, controls the amount of air and fuel entering the combustion chamber at any given point in time. Valvetrains 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.

Components used in IC Engine valve train:

The parts are as follows :

1. Cam
2. Push-rod
3. Rocker Arm
4. Valve
5. Valve Mount

Cam: A camshaft is a device to convert rotational motion into reciprocating motion. which actuate the intake and exhaust valves of the cylinders.

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.

Rocker arm: A rocker arm is a pivoting lever that pushes on the valve stem. Rocker arms will sometimes be called rocker levers, or just rockers. Depending on the type of valve train, the rotating camshaft lobes will either push directly on the rocker arm, or on the push rods, which will conduct that motion up to the rocker arm. In an overhead cam engine, the cam follower is built into the rocker arm in the form of a roller. Rocker arm is an oscillating lever that conveys radial movement from the cam lobe into linear movement at the poppet valve to open it.

Valves: A valve is composed of two major sections, the valve head and valve stem. The head of the valve is what allows air into and out of the cylinder. The stem is what gets gets pressed on by the rest of the valve train. At the end of the stem are grooves that keepers will fit into to hold the valve in place. Some engines have only two valves per cylinder, and some have four. The more common number in the heavy duty diesel market is four. These are split evenly between intake and exhaust valves. 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: Valve Mount use to support the valve to move in correct direction and spring is attached to the valve mount.

Calculation:

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

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

Fig. CAM Lift Formula

Case 1: Motion Analysis for cam lift of 3.5mm:

To calculate the distance between the two centres(L)

R1 = 12.5mm

R2 = 5mm

Cam lift = 3.5mm

Cam lift = (L−R1)+R2(L-R1)+R2

L = (12.5+3.5) - 5 =11mm

With the above information, Cam is modelled for the case 1 analysis.

Case 2: Motion Analysis for cam lift of 6mm:

To calculate the distance between the two centres(L)

R1 = 12.5mm

R2 = 5mm

Cam lift = 3.5mm

Cam lift = (L−R1)+R2(L-R1)+R2

L = (12.5+6) - 5 = 13.5mm

With the above information, Cam is modelled for the case 2 analysis.

Creating model of all the parts of IC Engine valve train:

1) Cam- for creating model of cam using 2D diagram in different cases

Case 1: Motion Analysis for cam lift of 3.5mm:

Case 2: Motion Analysis for cam lift of 6mm:

2) Push-rod- for creating model of Push-rod using 2D diagram

3) Rocker Arm- for creating model of Rocker Arm using 2D diagram

4) Valve-for creating model of Valve using 2D diagram

5) Valve Mount- Following steps as shown in part tree are used for creating model of Valve Mount using 2D diagram

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, pushrod and cam which locks them in position and motion analysis is performed. Following mates were being used.

Motion Analysis

1. 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.
2. Next, give the rotation to the cam with 1500 RPM.
3. 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.
4. Change the frames to 9000 frames per sec and use precise contact.
5. Select the entire assembly and assign the material as follows, go to Material-Edit material and select Cast Carbon Steel and click apply.
6. Gravity in the Y direction.
7. Now click the calculation button.
8. Run the analysis for the required time.

Result & Plots: Calculating the motion analysis of Contact force between Cam and Push Rod, Pushrod and Rocker Arm, Rocker Arm and Valve for both x direction and magnitude.

Case1: Cam lift at 3.5mm

1) Valve lift ( Liner Displacement of Valve) at CAM lift of 3.5mm

2) Contact force b/w Cam and Push rod at 3.5mm

3) Contact force b/w Push rod and Rocker Arm at 3.5mm

4) Contact force b/w Rocker Arm and Valve at 3.5mm (X direction)

5) Contact force b/w Rocker Arm and Valve at 3.5mm (Magnitude)

Case2: Cam lift at 6mm

1) Valve lift ( Liner Displacement of Valve) at 6mm

2) Contact force b/w Cam and Push rod at 6mm

3) Contact force b/w Push rod and Rocker Arm at 6mm

4) Contact force b/w Rocker Arm and Valve at 6mm (X direction)

5) Contact force b/w Rocker Arm and Valve at 6mm (Magnitude)

Conclusion points:

1. Vibrations can be observed during retracing Valve back to to its original Position due to Spring with lower spring constant selected.
2. From both (case 1&2) the plots of Valve lift with increasing the CAM lift, Linear displacement of valve also increased. Valve lift mainly depend on the design of CAM. For the 1st case as we give cam lift 3.5 mm, the valve displacement is around 2.5 mm but when we increases the cam lift to 6 mm, we got valve displacement of around 5 mm.
3. The Magnitude represents net contact force between the parts, while the contact force along X direction is the frictional force between the bodies that arise due to the rocker arm sliding over the surface of the valve head. The change in direction of the force is because the rocker arm first slides towards origin giving a positive friction force (opposing the motion) and then slides away from the origin giving rise to friction in the negative x-direction. Therefore the plots are opposite to each other.
4. From both the case 1&2 contact force between Push rod and Cam, and Push rod and Rocker Arm are approximately same.
5. When comparing the contact forces between case 1&2 the contact forces is much more in case 2 then case 1. It's because the cam lift is more in case 2 so the force required compress the spring is more.