larry kelly

Machine Design

Fall 2015 HW 9 Due Tues Dec 1

1. Your company has a sole-source agreement for springs with Lee Spring Company. Make a robust choice for a spring from their catalogue for this cam-follower system. The preload on the spring must be 150 lbf at La=1.9”, and the lift on the camshaft is 0.55”. The rocker arm has a 1:1 ratio. The spring will operate at 4500 rev/min. The spring must fit inside of a pocket (counter bore) having 1.7” diameter. The spring operates in a hot oil environment and needs to have an infinite life.

a. What material from Lee Springs standard offerings are you going to use in this case? Why? Be sure to cite any sources you use. (you may need to use an additional source if you find the amount of information Lee Spring supplies about their materials to be insufficient to make an informed decision – do not just hand-wave a decision here – you should justify your choice with comparable material properties, cost, corrosion resistance, etc.)What type of end finish are you going to prescribe? Why?

b. What choice of d, D, N, and Lf do you recommend? Why?

c. What is your resulting static safety factor?

d. What is your fatigue safety factor?

e. Is your design at risk of suffering spring surge?

f. Is your design at risk for buckling?

2. Now assume that the rocker arm is held in place by a stud, as shown in the image below. You may assume that the stud has identical threads at the top and bottom. Engineer the rocker arm stud and provide the diameter and thread information to withstand the loading (fatigue, static, etc.) described above.