<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (August 2010) (Learn how and when to remove this template message) </Td> </Tr> <P> A compression release engine brake, frequently called a Jake nett brake or Jake brake, is an engine braking mechanism installed on some diesel engines . When activated, it opens exhaust valves in the cylinders after the compression cycle, releasing the compressed air trapped in the cylinders, and slowing the vehicle . </P> <P> The term Jake nett brake, which properly refers to the Jacobs brand of engine brakes, has become a genericized trademark, and is often used to refer to engine brakes or compression release engine brakes in general, especially on large vehicles or heavy equipment . </P> <P> The name is derived from the manufacturer, Jacobs (of drill chuck fame), and was patented 1962--1965 by Clessie Cummins . When the driver releases the accelerator on a moving vehicle powered by an internal combustion engine, the vehicle's forward momentum continues to turn the engine's crankshaft . With Mercedes diesel engines being a notable exception, diesels by design have no throttle butterfly in the intake so regardless of throttle setting a full charge of air is always drawn into the cylinder . As such, even with fuel supply cut off and thus new detonation prevented, each time air is compressed in a cylinder virtually 100% of that passively generated energy is returned to the crankshaft, providing very little in the way of engine braking to the vehicle . </P>

Where did the term jake brake come from
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