You hear the loud rumble in an eighteen wheeler as it approaches a steep decline. The noise of engine braking may be disconcerting, but you know its importance. That big rig is preparing to slow down for the decline to prevent jack-knifing. While most popular and recognizable in commercial vehicles, a similar approach is also seen in passenger cars when you shift gears before slowing your vehicle.
How engine braking works
Engine braking helps the engine slow down. The goal is to prevent the vehicle from picking up speed or going down a decline too fast. This method is most often seen in heavy-duty vehicles and commercial autos such as buses and semi-rigs. It is often referred to as the Jake brakes because of the main manufacturer, the Jacobs Vehicle Systems. The driver presses a button to shut off a certain number of cylinders through the compression-release engine brake. While the cylinders can still receive air, they don’t send the energy on through the rest of the system. Because fewer cylinders are running, the vehicle slows down.
Using an engine brake is important for heavy vehicles because the added weight pushes them forward. The regular brakes aren’t powerful enough to slow these vehicles down quickly enough.
Issues and benefits with engine braking
The main problem with engine braking is the noise it creates. The level of noise is at least 10 decibels over the highest level in normal conversation. A vehicle without the proper muffling can emit even higher ranges of sound. Because of this, some states don’t allow engine braking.
At the same time, engine braking can be beneficial. It not only helps the engine be more effective at reducing its speed, it can help extend the life of the traditional brakes. Fewer instances of brake failure are seen when the engine brake is used, which can improve safety for the vehicle and other automobiles around it. Wear on tires and brakes is reduced, which saves the owner money.
This article originally appeared on YourMechanic.com as What Is Engine Braking? and was authored by Joyce Morse.