Engine braking occurs when a slowing force in the engine is used to slow the vehicle down, as opposed to using additional external braking mechanisms such as friction brakes or magnetic brakes.
The term is often confusing with some other types of braking, especially the compression-release braking or "jake braking" which uses different mechanisms.
Traffic regulations in a large number of countries require trucks to always drive with affected gear, which in turn provides a certain amount of engine braking (viscous losses to engine oil and engine-pumped air and frictional losses to walls and cylinder pads) when the accelerator pedal is not applied.
Video Engine braking
Type
Gasoline engine
The term "engine braking" refers to the braking effect that occurs in the gasoline engine when the accelerator pedal is released. This produces a throttle valve that controls intake airflow intake and airflow through the intake becomes very limited (but not completely disconnected). This leads to a high manifold vacuum that must work against the cylinder - reducing energy and generating most of the engine braking force.
While some braking forces are generated due to friction on the drive train, this is negligible compared to the effects of the vacuum manifold caused by air flow restrictions.
Diesel engine
Diesel engines do not have engine braking in the above sense. Unlike gasoline engines, diesel engines convert the fuel flow into control forces, rather than strangling the air intake and maintaining a constant fuel ratio like that of a gasoline engine. Because they do not keep the throttle vacuum, they do not experience the same braking effect. These are some of the reasons why non-turbo diesel-engined vehicles can go on longer gears than equivalent gasoline engines.
Higher compression ratios in diesel engines mean they are more difficult to start, but once they run the energy released in compressed air are recovered during stroke expansion when compressed air is allowed to "spring" back, so a higher compression ratio causes the engine to be ignored. through the energy lost as friction and compressed air heat to the engine block.
Removal of compression release
Compression release brake (also known as Jacobs brake or "jake brake"), is the type of brake most often confused with real engine braking; is used primarily in large diesel trucks and works by opening the exhaust valve at the top of the compression step, so a large amount of energy stored in compressed air is not returned to the crankshaft, but released into the atmosphere.
Usually, during the compression step, energy is used as a trip piston to the top of the air compress in the cylinder; the compressed air then acts as a compressed spring and pushes the piston back down. However, with the jake brakes in operation, the compressed air suddenly slips off just before the piston begins its journey down. (This sudden release of compressed air creates audible soundwaves similar to the widespread gas coming out of the muzzle of a firearm.) After the loss of energy stored in compressed air, there is no "spring back" so that the engine has to spend more energy. pull the piston back down again.
This type of brake is prohibited or restricted in many locations where people live because it creates machine guns such as sounds loud enough to disturb the tranquility, including waking people at night. This is very effective, however, and creates a large number of braking styles that significantly extend the life of friction brakes - the 565 hp (421 kW) diesel engine can produce up to 600 hp (450 kW) braking power at 2,100 RPM.
Dispose brake
Brake exhaust works by causing restrictions on the exhaust, as does the throttle intake that causes the gasoline engine. Simply put, it works by increasing the exhaust back pressure. Almost all of these brakes are butterfly valves similar to throttle valves, which are mounted downstream of the turbocharger if present.
Smoke Constraints
Modern diesel engines are subject to many tight controls on emissions and often have many obstructions in the exhaust, which causes them to feel like they have some engine braking like a gasoline engine. The main ones are:
- Turbocharger generates backpressure when jammed
- The exhaust gas recirculator (EGR) valve diverts the exhaust gas back to the intake engine, often through narrow/narrow pipes.
- Diesel particulate filter (DPF) is designed to capture soot particles that otherwise released into the atmosphere; it greatly hinders the flow of exhaust gases and can weaken almost the same as the power of a small AC pump.
Two-stroke engine
Engine braking in two-pronged engines can be very dangerous for engines, because cylinder and piston lubricants are shipped to each cylinder mixed with fuel. As a result, during engine braking, the engine not only engulfs fuel but also lubricates, causing accelerated wear. Many old two-stroke cars (Saab, Wartburg, etc.) have freewheel devices on the transmission to make the braking optional. Most two-stroke motorcycles since the 1970s have lubrication by oil pumps, independent of gas and fuel systems, such as the Suzuki Posi-Force system.
Maps Engine braking
Apps
As soon as the accelerator is released enough to slow down the engine, engine braking starts to take hold as long as the wheel remains connected through transmission to the engine. The slipped or unconnected clutch, or torque converter, will release the wheel or absorb the braking energy. The braking force varies depending on the engine, and the transmission gear comes in. The lower the gear, the higher the braking effect due to higher rpm and torque being transferred through the transmission (higher torque delivered from the engine in the lower teeth).
Engine braking avoids damage to the brakes, and can help the driver maintain control of the vehicle. The active use of engine braking by shifting lower gears can help control the speed while driving down a very steep and long slope, thereby saving brakes from overheating or excessive wear. If applied before the brake is used, the brakes may be available for emergency stop. The desired speed is maintained by using engine braking to counteract the acceleration of gravity. Use of potential transmission caused by engine braking can be reduced by certain techniques. Throw the clutch to complete the decline of the tooth wear clutch plate because it slows down the vehicle, do the job of brake pads or shoes. A well-executed rev-match in the same setting minimizes the pressure on the transmission component, so the engine braking does the job of slowing down the vehicle.
Improper engine braking techniques can cause the wheels to slip (also called locks), especially on slippery surfaces, as a result of too much slowdown. As in slippage caused by overbraking, the vehicle will not regain traction until the wheels are allowed to spin faster. If the driver reduces the engine braking by shifting back, or releasing the clutch on a manual transmission, traction may return.
In hybrid electric vehicles, such as the Toyota Prius, the engine braking is simulated by computer software to match the feel of a traditional automatic transmission. For long runs, the "B" mode acts like a lower gear, using a higher RPM than an internal combustion engine to dispose of energy, preventing the battery from overloading. Almost all electric and hybrid vehicles are able to convert kinetic motion into electricity, ie regenerative brakes, but since internal combustion engines are not used to slow down a vehicle while using regenerative braking, it's not the same as engine braking.
Limitations
Engine braking is a generally accepted practice and can help save wear on friction brakes. Even used in some motor sport to reduce the risk of overheating brake friction. In addition, fuel injection engines generally do not use any fuel during engine braking. This is known as dashed fuel deceleration (DFCO).
Although it is no longer manufactured in most countries, there are still many operating carburizing engines, with which the counter-productive engine braking for fuel economy due to lack of DFCO mechanism. The cost of wasted fuel can also exceed the benefits of reduced brake wear.
Compression tension ("Jake") braking, a form of engine braking that is used almost exclusively on diesel engines, generates a large amount of noise pollution if there is no exhaust on the engine intake manifold. Anecdotally, it sounds similar to a jackhammer, but its loudness is between 10 and 20 times the jackhammer sound pressure level (10 to 13 dB larger). Many cities, towns, states, and provinces prohibit the use of unleaded compression brakes, which are usually only legal on distant streets of the population. In Australia, traffic cameras are currently being tested that automatically shoot heavy vehicles using compression braking.
See also
- Dynamic braking, similar effects to electric engines
- Retarder
- Several types of braking in steam locomotives are conceptually comparable (using compression on steam engine cylinders for braking)
- Brake countersteam
- Backpressure brake
References
Source of the article : Wikipedia
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