1961: The Jacobs Engine Brake

February 10, 2011  | by: John Baxter

Clessie Cummins

Clessie Cummins invented the engine brake.

On the last page of Clessie Cummins’ 1967 book “My Days With the Diesel,” he writes of a project under development: “a relatively simple accessory which converts a diesel engine into a highly efficient air compressor whenever vehicle retardation is needed. This ‘engine brake’ will hold a 35-ton truck under complete control, limiting its speed to 19 mph, going downhill on a 10 percent grade — without the use of the service brakes.”

Both Cummins’ book and Jacobs Vehicle Systems’ website explain the development grew out of Cummins’ nerve-wracking ride in a runaway truck 30 years earlier. Later, as noted on the website, “An idea for a practical method came to Clessie in 1957 while in Phoenix, Ariz. [It] revolved around taking advantage of the perfectly timed motion already built into Cummins and Detroit Diesel engines; these engines have a third cam on the main camshaft that activates the fuel injector of each cylinder. A simple retrofit mechanism should be able to transfer this motion to open the exhaust valve.”

This ultimately led to the development of the engine brake of today. Jacobs was the first to exploit Cummins’ invention, but the expiration of the patent opened the door to competing products.

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One Response to “1961: The Jacobs Engine Brake”

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