MBD simulation of an IC Engine Valve Train in Solidworks

Aim:

To perform MBD simulation on an IC Engine Valve Train in Solidworks.

Objective:

• To model and assemble the valve train.
• To perform motion analysis for different cam lifts.
• To analyse the resulting plots.

Theory:

Valve Train: A 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.

Valve Train Layout: A typical valve-train consists of valves, rocker arms, pushrods, lifters, and camshaft(s). 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. Timing for open/close/duration is controlled by the camshaft that is synchronized to the crankshaft by a chain, belt, or gear.

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.

Cam lift: is defined as the distance the cam lobe rises away from the base circle of the camshaft. It is the distance the lifter will move. It is also called "lobe lift” as depicted below

We will be conducting the study under the following conditions:

Setup Explanation:

1. First, the components are modelled as per known dimensions as shown and assigned material as cast carbon steel.

2. Then the model is assembled using appropriate mates as shown.

3. Using the move tool, the components are moved with physical dynamics enabled to position them such that they are just touching each other.

4. With the Solidworks motion add-in enabled, click on motion study 1 and then click on motion analysis.

5. Add a motor to the axis of the cam as shown. Set constant speed to 1500 rpm.

6. Set contacts between each pair of solid bodies as per logic and set material to steel (dry).

7. Insert a linear spring between the valve and the valve mount by using the spring option. Set stiffness to 10 N/mm and free length as 45 mm. The spring will turn red in colour to show pre-tension.

8. Go to settings and set frame rate to 9000 frames per second to get output reading for each degree rotation. Also enable precise contacts for accurate analysis.

9. Set key point time to 0.2 seconds for faster calculation time.

10. Hit calculate and wait for the analysis to complete.

11. Insert plots for the following things:

• Linear displacement of valve for valve lift.
• Contact force between am and pushrod.
• Contact force between pushrod and rocker arm.
• Contact force between rocker arm and valve (magnitude).
• Contact force between rocker arm and valve (x-direction)

12. Do the above processes for 2 cases: With cam lift as 3.5 mm and 6 mm.

Results:

1. Case 1:

• The cam lift is set to 3.5 mm by changing the upper circle diameter to 7 mm in the cam part file as shown.
• Animation: https://youtu.be/WWPbX_T9w60

2. Case 2:

• The cam lift is set to 6 mm by changing the upper circle diameter to 12 mm in the cam part file as shown.
• Animation: https://youtu.be/_7kFCt29pFI

Observations:

All the graphs are superimposed and the following observations are made.

1. The valve lift for case 1 is around 110 mm and that for case 2 is 115 mm.
2. The valve displacement value is more than the cam lift value.
3. The contact force remains constant for majority of the cycle.
4. The contact for case 2 is more than that of case 1 and varies with time. The high peaks can be ignored. They are probably errors.
5. The contact for in x direction achieves both positive and negative values.

Conclusions:

1. The valve lift increases with increase in cam lift.
2. The valve lift value is more than the cam lift value because the motion is amplified due to the the moment arm of the rocker arm (lever mechanism)
3. The constant value of contact force is due to the spring being in a pre-compressed state.
4. Contact force increases with increase in cam lift and attains it’s peak value when the cam is in the top most position and it’s variation depends on the cam profile. The contact force between rocker arm and valve changes in magnitude because the moment arm of the rocker arm (perpendicular distance between pivot and point of contact) changes with its angle.
5. The contact force between rocker arm and valve is essentially the friction force between the two surfaces. This force changes its direction as the rocker arm comes down (slides left) and goes up (slides right) and hence the value changes from positive to negative.

File Link: https://drive.google.com/open?id=1lGOIxHSEnId8X7SAQOLIZP8EJRJOwRNw