MBD Simulation on IC Engine Valve Train

AIM :-

To run an MBD simulation of an IC engine valvetrain using Solidworks for different cam lifts.

SOLIDWORKS MODELS :-

1. Cam,

Two cams are designed with lifts of 3.5 mm and 6 mm. The lift is varied by changing the diameters of the smaller circle.

Cam model with 3.5 mm lift is given below.

The cam model with 6 mm lift is given below.

2. Pushrod Model,

3. Rocker Arm Model,

4. Valve Model,

5. Valve Mount Model,

Assembly of the Valve Train,

MOTION ANALYSIS :-

Motor input is provided to the cam and clockwise rotation is selected. An input speed of 1500 rpm is selected. All the parts are selected for mechanical contact. A spring is added between the valve and the valve mount. This is to ensure that the valve goes back to it's initial position. The spring is pretensioned and stifness of 10 N/mm is provided or else when the cam lifts the pushrod, all the parts will continue to move in the forward direction and will collapse.

Four plots are obtained for two types of cam lift and they are,

• Valve lift.
• Contact force between cam and pushrod.
• Contact force between pushrod and rocker arm.
• Contact force between rocker arm and valve.

1. Cam with 3.5 mm Lift,

The plot of the valve lift is shown below.

The valve lift can be calculated by subtracting the highest displacement with the lowest displacement which is 52.7-50.85 = 1.85 mm. This can be varied by adjusting the rocker arm ratio.

The plot of the contact force between the cam and the pushrod is given below.

The initial reaction force is high, but settles down after 0.05s. The highest point is when the pitch curve comes in contact with the pushrod.

The contact force between the pushrod and the rocker arm is given below.

The initial force is 0 and when the pushrod starts to push the rocker arm, the contact force starts to increase. The highest point being 525 N is maximum force occured as the pitch curve of the cam passes along the pushrod.

The contact force between rocker arm and valve is given below,

The initial force is 0. The maximum force being 189 N occurs when the valve reaches it's final position where the spring fully compresses. The contact force then starts to decrease as the valve moves to it's initial position.

2. Cam with 6 mm Lift,

The plot of the valve lift is shown below.

The valve lift can be calculated by subtracting the highest displacement with the lowest displacement which is 55-51 = 4 mm. This can be varied by adjusting the rocker arm ratio.

The plot of the contact force between the cam and the pushrod is given below.

The initial reaction force is 0. The highest point is when the pitch curve comes in contact with the pushrod which is 941 N. Variation in the contact force at different cycles is observed due to low frame rate. By increasing the frame rate a more smoother plot is obtained as the calculations are more precise with the downside of longer simulation time.

The contact force between the pushrod and the rocker arm is given below.

The initial force is 0 and when the pushrod starts to push the rocker arm, the contact force starts to increase. The highest point being 647 N is maximum force occured as the pitch curve of the cam passes along the pushrod.

The contact force between rocker arm and valve is given below.

The initial force is 0. The maximum force being 265 N occurs when the valve reaches it's final position where the spring fully compresses. The contact force then starts to decrease as the valve moves to it's initial position.

CONCLUSION :-

A valvetrain assembly is modelled and the motion study is conducted for two different cam lifts and the valve lift and contact forces between the parts are plotted.