Editing Compression release engine brake

{{Short description|Mechanism of some diesel engines}}
[[File:Jake Brake.jpg|thumb|A compression release engine brake from Jacobs Vehicle Systems, popularly known as a "Jake brake"]]
[[File:Unit injector.jpg|thumb|A view of engine compression brake rocker arm (the thinnest arm at the left of each set)]]
[[File:Jacobs engine brake division badge 001.jpg|thumb|Jacobs Engine Brake Division logo]]

A '''compression release engine brake''', '''compression brake''', or '''decompression brake''' is an [[engine braking]] mechanism installed on some [[diesel engine]]s. When activated, it opens [[4-stroke cycle engine valves#Internal combustion engine|exhaust valves]] to the cylinders, right before the compression stroke ends, releasing the compressed gas trapped in the cylinders. The compression followed by the "wasteful" release consumes great amount of energy, effectively slowing the vehicle.

[[Clessie Cummins]] was granted a patent for the engine compression brake in 1965, and the first company to manufacture them was [[Jacobs Vehicle Systems]].<ref>{{cite patent |country=US |number=3220392 |status=patent |title=Vehicle engine braking and fuel control system |pubdate= |gdate=November 30, 1965 |fdate=June 4, 1962 |pridate= |inventor-last=Cummins |inventor-first=Clessie L. |inventor-link=Clessie Cummins}}</ref><ref>{{Cite web |url=http://files.asme.org/ASMEORG/Communities/History/Landmarks/5577.pdf |title=Jacobs® Engine Brake Retarder |date=October 17, 1985 |publisher=[[The American Society of Mechanical Engineers]] |url-status=dead |archive-url=https://web.archive.org/web/20110816064603/http://files.asme.org/ASMEORG/Communities/History/Landmarks/5577.pdf |archive-date=2011-08-16 |access-date=2010-04-30}}</ref>  Therefore, the brakes are commonly known as '''Jake brakes'''. 

==Function==
When the driver releases the accelerator on a moving vehicle powered by an [[internal combustion engine]], the vehicle's forward [[momentum]] continues to turn the engine's [[crankshaft]]. Most diesel engines do not have a throttle body, so regardless of the throttle setting, air is always drawn into the cylinders (excluding the valve fitted to certain diesels, such as fire appliances and generators on oil and gas platforms, to prevent [[diesel engine runaway]]). The fuel-free air mix that is compressed on the compression stroke now starts to act as an air spring. After the piston reaches maximum compression, the compressed air mixture returns its energy to the piston by pushing the piston back down. The result is that even if the fuel supply to the cylinder is stopped, some energy absorbed during the compression stroke is still returned to the crankshaft. Because of this returned energy, there is very little engine braking applied to the vehicle.

The typical compression brake consists of a hydraulic system using engine oil which transfers the motion of the fuel injector rocker arm to the engine's exhaust valve(s). When activated, the exhaust valve opens very briefly near the engine's [[Dead centre (engineering)|top dead center]], and releases the compressed air in the cylinder so that the air compression energy is not returned to the crankshaft. A compression release engine brake can assist a vehicle to maintain or even reduce speed with minimal use of friction brakes. The power of this type can be around the same as the engine power.<!--partial ref; compare with [[Caterpillar C13]] --><ref>[http://electracold.com/CAT.pdf Understanding Tractor-trailer Performance], page 20. ''[[Caterpillar Inc.]]''</ref>

In contrast, a [[gasoline engine]] under deceleration runs with a closed [[throttle]] that prevents free flow of air into the cylinders, resulting in little pressure to release at the top of the compression stroke. The closed throttle provides engine braking by forcing the engine to generate a vacuum between the throttle and the cylinders.

Typically, the controls for a compression brake consist of an on/off switch and often a selector that controls the number of cylinders on which the brake is active. Throttle and clutch switches are integral with the system. Activation occurs when both the clutch and the throttle are released with the transmission in gear. It is the driver's job to ascertain the correct transmission gear to use, depending on factors such as the steepness of the grade and the vehicle's load.

==Limitations==
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[[File:No Jake brakes within city limits.jpg|thumb|No Jake brakes sign]]
The use of engine compression brakes may cause a vehicle to make a loud "[[growling]]", "[[machine gun]]", or "[[jackhammer]]" like exhaust noise, especially vehicles having no mufflers, which has led many communities in the [[United States]], [[Canada]], and [[Australia]] to prohibit compression braking within municipal limits. Drivers are notified by roadside signs with text such as "Brake Retarders Prohibited," "No Engine Brake," "No Jake Brakes," "Compression Braking Prohibited," or "Unmuffled Engine Braking Prohibited," and enforcement is typically through traffic [[fine (penalty)|fines]]. Such prohibitions have led to the development of new types of [[muffler]]s and [[turbocharger]]s to better silence braking noise.

Jacobs claims that the use of the term "Jake Brake" on signs prohibiting engine retarding brakes violates their trademark and discriminates against Jacobs-brand products.<ref>{{cite web |url= http://jake-brakes.com/about-us/noise-concerns.php |archive-url= https://archive.today/20130127022926/http://jake-brakes.com/about-us/noise-concerns.php |url-status= dead |archive-date= January 27, 2013 |title=Jacobs Vehicle Systems - Noise Concerns |work=jake-brakes.com  |access-date=August 20, 2012}}</ref><ref>{{Cite news|author=Zolkos, Rodd | title=Road signs violate trademark; Municipals urged to stop using 'Jake Brakes' brand name |work=Business Insurance |publisher=Crain Communications Inc.|date=February 28, 2000}}</ref>

In the U.S. state of [[Ohio]], state law allows a [[Ohio county government|board of county commissioners]] or township trustees to prohibit the use of compression brakes within unincorporated areas. These local regulations apply to all state- and locally-maintained roads except [[Interstate Highway System|Interstate highway]]s. The state's standard "No Engine Brake" sign is designed to avoid discriminating against the Jacobs brand name.<ref>{{cite book|chapter=Signs|chapter-url=http://www.dot.state.oh.us/Divisions/Engineering/Roadway/DesignStandards/traffic/TEM/Documents/Part_02_Complete_071919Revision_bookmarked_061819.pdf|title=Traffic Engineering Manual|publisher=[[Ohio Department of Transportation]]|orig-year=2002|date=July 19, 2019|access-date=August 23, 2019|at=p. 2-15|url=http://www.dot.state.oh.us/Divisions/Engineering/Roadway/DesignStandards/traffic/TEM/|format=PDF}}</ref>

==See also==
*[[Engine braking]]
*[[Compression release]]
*[[Exhaust brake]]
*[[Retarder (mechanical engineering)]]
*[[Jacobs Vehicle Systems]]

== References ==
{{Reflist}}

[[Category:Vehicle braking technologies]]

[[de:Motorbremse#Dekompressionsbremse]]