National Historic Mechanical Engineering Landmark The

National Historic The American Society of Mechanical Engineering Mechanical Engineers Landmark Jacobs® Engine Brake Retarder Bloomfield, Connecticut October 17, 1985 would normally be the power stroke, no pressure remains in the cylinder to act on the piston. Thus, the energy transferred from the driving wheels into the compressed and highly heated air (through gravity or forward momen- tum of the vehicle) goes mostly out the exhaust pipe, with a portion en- tering the cooling water from heat transfer through the cylinder walls. This has two results: on long down- grades the engine cooling system remains at near normal operating temperatures, and in the case of tur- bocharged engines there is sufficient exhaust energy to allow the turbine of the turbocharger to power the companion compressor and main- tain a high enough degree of boost to increase the retarding effort. A diesel, being a free-breathing engine by virtue of having no valving or venturi restrictions (carburetor) offers inherently less braking effort than a gasoline (spark ignition) engine even though the diesel engine has about twice the compression Clessie L. Cummins at work in his Sau - A History of The Jacobs ® ratio of the spark ignition engine salito shop. Engine Brake (which obviously means that it re- By C. Lyle Cummins, Jr. quires more effort to force up the Long steep downhill grades not only piston on the compression stroke), provide anxious moments for truck that work is given almost entirely drivers, but they also add extra back (less friction and heat transfer hours behind the wheel. The advent losses) when the air is allowed to ex- of the Jake Brake® compression en- pand on the next outward stroke. gine retarder brought an oppor- Conversely, the spark ignition engine tunity to end this fear almost entirely becomes a vacuum pump when and at the same time to safely raise being motored with the throttle average speeds. closed. This is a basic reason why To a motorist or a bystander, the the spark ignition engine is so much Jacobs Engine Brake, commonly less efficient than the diesel or com- known as the “Jake Brake,” iS pression ignition engine when oper- sometimes associated with a char- ating at idle or light loading. Of acteristic “popping” exhaust noise course this assumes that the fuel is heard when a truck is decelerating essentially shut off and no combus- or descending a hill. To the truck tion can occur–which is true with driver, it is a device that turns his the diesel engine but not so with the engine into a retarder, giving him spark ignition engine. about the same braking effort at the Although the Jacobs Engine wheels as his engine puts out when Brake has been on the market since it is producing power. 1961, the need for it was terrifyingly How does this work? Quite sim- demonstrated to its inventor, Clessie ply, the Jake Brake retarder turns a L. Cummins, some thirty years ear- diesel engine into an air compressor. lier. In those times, Clessie was try- Rather than store the energy of the ing to prove the worth of the pressurized air in the cylinder, cre- automotive diesel engine as well as ated by the piston coming up on the to learn firsthand the kind of engine compression stroke, the Jake Brake the trucking industry most needed. retarder mechanism hydraulically In August of 1931, one of these com- opens the exhaust valve near the bination test and publicity stunts end of the upward piston stroke. The found him, Ford Moyer, and Dave stored energy in the cylinder iS re- Evans driving a Cummins Diesel- leased to the atmosphere so that powered Indiana truck from New when the piston descends on what York to Los Angeles in an attempt to set a new truck speed record across the continent. One of the first things proven was that the diesel engine does in- deed offer less braking than a gasoline engine of equivalent size, placing a greater burden on the vehicle’s braking system. With the higher speeds being driven on this test run, plus the load on board that included the Cummins Diesel 1931 Indi- anapolis race car and extra equip- ment, the intrepid trio soon found it necessary to place more reliance on prayer than on brake linings. All went reasonably well until the descent of Cajon Pass, on old U.S. 66 leading into San Bernardino, Cal- ifornia. A long, winding and steep gravel road, criss-crossed by a busy mainline railroad, almost led to the demise of the truck, its driver Clessie L. Cummins (who was to become the “father of the U.S. automotive diesel”), and a frantic crew who were tossed around their bunks in the cargo box behind the cab. In Clessie’s words: “About dusk on the fifth day, we caboose loomed out of the darkness. An American Automobile Association reached the top of Cajon Pass west of Its red lights cleared the highway just official (with flag at left) begins count- Barstow, California. Before retiring to down for a December, 1931 endurance as we reached the tracks We had run at Indianapolis Speedway. The Cum- the sleeping compartment, Dave had escaped certain death by Inches.” mins Diesel-powered Indiana truck had warned me against this thirty-five- The memory of the dark night been used in an August, 1931 cross- mile stretch of mountainous down- was never forgotten. The venerable country trip which demonstrated the grade. ‘Wake up Ford and me when diesel-powered lndiana did set a new need for an engine brake. Clessie L. Cummins, Ford Moyer, Dave Evans and you get to Kayhone Pass,’ I had un- coast-to-coast truck speed record of T. E. Myers (Speedway Vice President) derstood him to say, ‘I don’t want to 97 hours, 20 minutes running time are poised in readiness for the run. be in this box when you start down for the 3,214 miles, and one of its that twister with the kind of brakes drivers vowed someday to make his we’ve got.’ I had heard but not seen, engine work when going downhill just my Spanish being nonexistent, the as well as going uphill. word Cajon failed to register when the Twenty-four years later, in 1955, sign appeared. Soon, however, I real- Clessie Cummins’ inventive genius ized my error. The brakes wouldn’t again addressed the engine retarding hold. Now running in third gear, I tried question. In retirement in Sausalito, desperately to get into a lower speed. California, he began studying what Nothing doing. I saw I would just have might be done to turn his engine into to ride it out. an effective “brake.” Well down the long grade by now, It was also in 1955 that Clessie I suddenly saw something moving enticed his youngest son Lyle, a across the road ahead. There was a graduate mechanical engineer, to long dark shadow and then a red join forces and form the large con- glow flared in the sky. I realized with cern which he named Centco (short new alarm that a freight train was for Cummins Enterprises Company), cutting across our path. The truck a name chosen to keep the house- roared on. Dave and Ford screamed hold accounts separate from bloody murder in the compartment Clessie’s ventures in the basement. behind me. And I clung to that steer- The basement was actually an area ring wheel like a madman. Had Mack that included an office with a view, a Sennett been on hand with a movie soon to be equipped machine shop camera, he would have gotten with the usual lathes, milling ma- enough footage for one of his famous chine, etc. and a four-car garage. An- Keystone Kops features. other member of the Centco team, As we raced inexorably toward added in 1957, was Ray Hansen. the crossing and doom, the train’s Hansen was an able machinist, The Engine without a Jake Brake welder, and sheet metal bender scratch pad and was telephoned During the piston’s normal compression whose hobby was building and rac- back to son Lyle in Sausalito early the stroke (2), air compressed in the cylin- next morning. By the time the vaca- ders raises internal heat to almost ing sports cars. 1,000°F. At this point, fuel is injected Lyle’s initial effort was expended tioning Stella and Clessie Cummins and combustion occurs, raising temper- on thermodynamic analyses to prove returned home, layouts of possible ature even further. Pressure from this the Clessie’s idea of turning the en- design solutions were waiting, albeit expanded gas forces the piston down gine into a compressor really would in retrospect, they were more compli- (3). The engine has thus produced the positive power necessary to turn the provide sufficient retarding potential. cated than proved to be necessary. crankshaft. The answer was an unqualified An important subtlety of the in- “yes,” but how to do it? One scheme vention made it novel enough that a was to clutch-in a high pressure very broad patent was ultimately pump and a timed distributor to granted, affording strong patent pro- carry hydraulic force to a slave tection dating from the time of its piston, which in turn would act on the application. The application was in exhaust valve to open it at the proper the U.S. Patent Office for seven years point on the compression stroke. A due to new pertinent additions being second method considered was to twice added after the original filing in use a multi-plunger pump 1957.

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