I'd be interested in hearing your take on this. My unscientific conclusions include the following:
1. Henry Ford is the dominant presence among American innovators, and has been for the last century. He died in 1947, which may explain the spike in interest in the 1950s as the press and historians tried to evaluate his contributions. Even with the ascension of GM after 1930, however, and the rise of Japanese automakers in the 1970s, Henry's star continues to shine. Only Bill Gates made a serious run at Ford around 2000, but since then has been in decline as his interests have shifted from Microsoft to philanthropy. Were the graph to extend to 2013, I presume Steve Jobs might be in the top 5, but as you can see, Edison, Carnegie and Rockefeller are true, long-term heavyweights. Needless to say, America is very much a culture defined by the automobile and computer.