Issue link: https://read.dmtmag.com/i/306069
4 www.studentdriverplacement.com May '14 It Works How by Tom Kelley Slowing Down A lthough a truck's basic "foundation" braking sys- tem should be suffi cient for stopping the truck without any aug- mentation from a retarding system, many factors can limit the basic system's performance. Heat is at the top of this list. When the truck is operated within the limitations of the foundation brak- ing system, factors including the mass of the braking hardware and airfl ow past that hardware combine to dissi- pate that heat suffi ciently to maintain the braking system performance. But once you add a maximum- weight load and a long downgrade to the picture, additional braking is nec- essary. If all of the additional braking is provided by the foundation brakes, they are also required to dissipate the additional heat. Keeping that addition- al heat from exceeding the limitations of the system requires one of two solutions, either using much larger brakes, or de- scending at a much slower average speed. According to the manufacturers of the "Jake Brake," when operating at maximum weight on a 6% downgrade, the maximum safe speed for a truck without any supple- mental retarding is about 6 MPH. To augment the foundation brakes, the truck's engine can be used to absorb some of the energy, but only if the transmission is kept in a lower gear, which again means operating at a lower average speed during the descent. Because a diesel engine is designed pri- marily to produce power rather than absorb it, by itself it's not the best way to augment the foundation brakes. With this in mind, some of the early diesel engine pioneers developed the means to temporarily turn the engine into a compressor, which is a far better consumer of energy than an engine. By making the engine better at absorbing power, the truck can safely maintain a high- er average speed without any increase in Retarders Help Brakes Control Speed how it works 0514.indd 1 4/21/14 9:17 AM