Cam Profile Design Class - lesson 6

This is the conclusion and summary of the previous five lessons. We have created the opening ramp of the profile, the opening side of the profile, the closing side of the profile, and the closing ramp of the profile. We then put all four sections together and created the cam profile. In all reality a fairly easy process if you have a computer program that does the math for you. You have to admire the people that did this stuff before the assistance of a computer or even an electronic calculator.

Here is my unique example of what the tappet will experience during its travel up and down the lobe. You need to image that you are the tappet. You are going up one side of a hill and down the other side. You start off walking up the hill (opening ramp) at around a constant pace (velocity and acceleration). Like walking up the stairs. At some point your pace will start to increase. You are now running. You will reach maximum acceleration first and then maximum velocity. If you are a flat tappet the maximum velocity will be determined by your diameter. A roller tappet will limit your maximum acceleration. If you exceed either limit you will fall down, skin yourself up, and roll down the hill. Basically the tappet and the camshaft will be destroyed. If you are not destroyed, your pace will start to slow as you reach the top of the hill (maximum lift).

From this point you will travel down the other side of the hill. You will go through the same velocity and acceleration forces just in the opposite direction. You will reach maximum velocity first and then maximum acceleration. Eventually you will slow down and stop at the bottom of the hill (closing ramp). You can follow along by using the profile graph showing the velocity and acceleration curves.

Velocity, acceleration, and jerk can be confusing. An easy way to understand these forces is in your car. The velocity is the speed, the reading on the speedometer. Velocity is usually associated with acceleration. Acceleration is how quickly you get to that speed. Jerk is the forward and backward movement that you feel when speeding up and slowing down quickly. That "jerky" motion. It can be very annoying. It is also very annoying in lobe profile designs. A lot of jerk creates a lot of stress in the valve train just like in the car. All of these forces are easy to experience while driving your car (try it). You want all of these forces to be nice and smooth, not to harsh and not to soft, just right.

As I have said before, the software only does the math. It is up to the lobe designer to create a good profile design. As you better understand these forces and how they affect the lobe profile, the better your designs will be. Some other calculations you will need to do are the maximum velocity for the flat tappet diameter, radius of curvature of the lobe, valve closing velocity, base circle diameter of the lobe, pressure angle between the tappet and the lobe, duration at different tappet heights, valve lift, and valve lash.

All of this stuff is just math, physics, and numbers. No magic. As long as your lobe design doesn't tear-up something, consider it a good design. It may not make as much power as you would like but that's ok for now. It all just takes time. Hopefully you enjoyed these introductory lessons to the cam profile design process. Depending on the response to these lessons, I can go further into the design process using more examples with more detail. Let me know if you have any questions or suggestions or if you want to purchase the program. Good luck to everyone. Class dismissed.