All About Engine Braking

May 2, 2019 Published by Leave your thoughts

Engine braking is a kind of braking that occurs when you let the natural forces of the engine slow down a vehicle rather than using external braking. There are some circumstances in which it makes sense to use engine braking to increase fuel efficiency and general performance.

Here’s some information from a mobile mechanic in Flagstaff, AZ that you should know about engine braking, especially as a commercial vehicle driver.

Diesel vs. gasoline engines

When you’re driving a standard gasoline-powered vehicle, engine braking occurs when you release the accelerator pedal. Doing so causes the throttle valve to close, reducing the airflow that comes through the intake. This in turn results in a high manifold vacuum that slows down the cylinders, eventually slowing down the vehicle.

Compare this to diesel engines, which do not have engine braking in the sense described above. One of the ways diesel engines differ is that they vary the flow of fuel to control power, rather than throttling air intake and maintaining a regular fuel ratio. Because they do not have a throttle vacuum, they don’t experience the same engine braking effects.

A higher compression ratio in diesel engines means they can be harder to start up, but once running, the energy that gets expended in air compression returns during the expansion stroke, as that compressed air springs back, meaning the higher compression ratio causes a very small amount of engine braking.

Using engine braking

So, while semi-truck drivers aren’t really going to be doing any engine braking, other commercial drivers using gasoline engines (and people driving their own personal cars) very well could.

Engine braking helps to avoid wear on the brakes, and can also give a driver greater control over their vehicle. In a vehicle with manual transmission, using engine braking by shifting into a lower gear helps to control speed while going down long, steep slopes, which helps to avoid overheating of the brakes, which are still available to use to make emergency stops. You maintain your ideal speed by using engine braking in a way that counteracts the acceleration down the hill due to gravity.

Engine braking is a skill that a driver develops over time. Improper use of engine braking can result in the wheels skidding, especially if you’re on a slippery surface, because you’ve gone through too much deceleration. The vehicle will then not regain its traction until the wheels start spinning more quickly, meaning you may need to shift back up or disengage the clutch.

Keep in mind that engine braking isn’t always a practical option. In particularly dense urban environments, it might even be against local ordinances, as applying the brakes in heavy traffic illuminates your brake lights and helps keep drivers following behind you at a safe distance.

For more information about engine braking and what you need to know about using this method safely, we encourage you to contact a mobile mechanic in Flagstaff, AZ at Maclin Truck & Trailer with your questions. We look forward to assisting you soon!

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