Issue link: https://read.dmtmag.com/i/306069
by Tom Kelley May '14 www.studentdriverplacement.com 5 the size of the foundation brake hardware. That same truck that had to slow down to 6 MPH without a retarder, can safely de- scend the same grade at approximately 41 MPH when equipped with a Jake Brake. The engine brake or exhaust brake hard- ware that makes this all possible is part of a larger category of products collectively re- ferred to as "retarding" systems. Although they are certainly among the most popular choices, engine and exhaust brake sys- tems are not the only way to augment the foundation brakes. Another way to use the drivetrain for retarding purposes involves adding an hy- draulic turbine either just ahead or just be- hind the truck's transmission. The hydraulic turbine uses the same basic technology as a typical window fan. If a stream of hydrau- lic fl uid is directed at the fan in the opposite direction that the fan is spinning, the fan will slow or stop. Alredy quite popular in heavy off-road equipment, Allison offers hydraulic retard- ers on some of its automatic transmissions for Class 8 trucks. The benefi ts to using a hydraulic retarder include minimal outside noise during operation, and easy manage- ment of the heat created in the retarding process. Additionally, a hydraulic retarding system can produce more braking horse- power than most other alternatives. While engine, exhaust and hydraulic re- tarders can augment the foundation brake system at every drive axle position, there are electric retarding systems that can even be used at non-drive axle positions, includ- ing those on the trailer. An electromagnetic retarder works on the same principle as an electric generator. Although electric retarding systems have long been popular in Europe, they are be- ginning to be integrated with hybrid drive- trains here in North America. In the hybrid system, the electricity created in the retard- ing process is stored in batteries, and then when the vehicle is accelerating, the re- tarder's "generator" windings are reversed, turning it into an electric motor which aug- ments the primary powerplant. Unfortunately, the volume required by the batteries for a system on a Class 8 truck is such that storing the energy would be impractical, so the electric retarders for this application just route the energy to a resistive coil where it's dissipated as waste heat. At present, engine and exhaust brakes have the lion's share of the North Ameri- can retarder market because the hardware involved is lightweight, and the absorbed energy is easily managed. However, that's not to say that these systems are without a few problems. One of the biggest problems with ex- haust brakes is that an unfortunate minority within the driver and owner-operator com- munity insist on unnecessarily misusing the technology as some sort of foolish fashion statement. These few "bad apples," who insist on unnecessarily using engine/exhaust brakes on moderate to level terrain in congested urban and suburban areas, many of whom further amplify their ignorance with an ille- gal exhaust system, have succeeded at in- viting additional regulation into our already over-regulated industry. As a result, many communities and regions have prohibited the use of engine/exhaust brakes entirely, even when that use is appropriately con- ducted. ◆ how it works 0514.indd 2 4/21/14 9:17 AM