Cummins Exhaust Brake Theory

Exhaust brakes use exhaust gases for braking power.

In the trades, Cummins exhaust brakes are colloquially referred to as jake brakes. This is because the Cummins E Brake was jointly designed by Cummins, Inc. and brake specialists Jacobs Vehicle Systems, Inc.

Normal Braking

Normal braking systems, including air brakes and disc brakes, slow vehicles by increasing resistance on the wheels as the driver reduces fuel to the cylinders by releasing pressure on the accelerator. Using this method, the crankshaft continues to turn until its inertia is spent.

Exhaust Braking

In exhaust braking, the exhaust flow is restricted. This causes a backup of exhaust gases. These gases remain in the cylinder, shortening the piston stroke. This impedes the rotation of the crankshaft on each stroke and, consequently, reduces vehicle momentum.

Effectiveness

In exhaust braking, the effectiveness of the method is in direct proportion to the speed of the engine. In a Cummins B5.9 diesel engine, for example, a Cummins E Brake applies 34 horsepower of resistance when engaged at 1400 RPM, 96 horsepower of resistance when engaged at 2200 RPM and 159 horsepower of resistance when engaged at 2800 RPM.

VG Turbo Exception

In variable geometry, or VG, turbochargers, exhaust breaking is incorporated into the turbocharger system. For this reason Cummins E Brakes are not installed on engines equipped with VG turbochargers.

References

• Cummins: Jacobs Exhaust Brake® for Cummins Medium Duty Engines (Non-Dodge Applications)