The Jake Brake's biggest advantage is preventing brake overheating, which will gradually inhibit the brakes from working properly, or stopping.
"Jake Brake", or "compression release brake", is a component installed on diesel engines that slows the vehicle without the driver having to apply the service (foot) brakes.
The Jake Brake releases compressed air from the cylinder, slowing the vehicle by absorbing the engine's power.
Jake Brakes are commonly used to control the truck speed while descending a steep grade, rather than using the foot brakes, saving wear on the brakes.
For most truck driver's purposes, diesel "engine brake" will be used as a generic term to mean "Jake Brake". There are actually several different types of engine braking, which use different methods.
The Jake Brake is technically classified as a "compression release engine brake".
Some municipalities and jurisdictions will have local codes or laws against the use of Jake Brakes within a certain area or certain times, as the sheer volume of the brake might startle or disturb the local population and peace.
It is a separate component installed on diesel engines, that when engaged, releases stored, compressed air from the cylinder at the top of the piston's stroke, preventing it from from returning it's energy to the crankshaft and powering the down-stroke, and slowing the vehicle as the air is compressed.
In other words, it puts resistance or drag on the crankshaft, and thus on the drive tires, to slow the vehicle.
When the accelerator is released and the clutch disengaged, diesel engines, without the Jake Brake engaged, continue their forward momentum and continue to generate power to the drive wheels, rather than slow the vehicle down, the opposite of what gasoline engines do.
The Jake Brake will slow the vehicle without using the service (foot) brakes, when the truck is in gear and both the throttle and clutch are released.
The Jake Brake is actually an engine retarder, using the kinetic energy of the vehicle's engine to slow the vehicle without using the service (foot) brakes.
It is generally recommended that drivers not use the Jake Brake on slippery or potentially slippery road conditions, as it only affects the drive tires and increases the chance of an uncontrolled skid or jackknife.
"The Jacobs Engine Brake (also known as the "Jake Brake®") is a diesel engine retarder that uses the engine to aid in slowing and controlling the vehicle. When activated, the engine brake alters the operation of the engine's exhaust valves so that the engine works as a power-absorbing air compressor. This provides a retarding, or slowing, action to the vehicle's drive wheels, enabling you to have improved vehicle control without using the service brakes*. This conservation results in reduced service brake maintenance, shorter trip times, and lower total cost of ownership."
This video shows the mechanical theory and operation of the Jake Brake Engine Brake.
Because of the loud and deep rumble that Jake Brakes make when engaged, many communities and municipalities in both the United States and Canada have enacted laws prohibiting their use within or near residential areas.
In this instance, street signs will normally be posted, and penalties will take the form of civic fines. The signs may not reference "Jake Brakes" directly, as there have been trademark and copyright issues, but may use the more generic "Engine Braking" or "Compression Braking". Watch for them.
While the noise has been compared to a large lawnmower in terms of decibel level, in the quieter times of day late at night of early in the morning, it can be quite startling and disruptive to the residents in the community.
In 1960, Jacobs Manufacturing Company formed the Clessie L. Cummins Division specifically to manufacture Cummins' engine brake. Later re-named Jacobs Vehicle Systems, the "Jake" in Jake Brake is short for "Jacobs".
The Jacobs Engine Brake has been on the market since 1961.
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