How Does an Engine Brake Work?
Q: How do engine brakes work.?
Answer: Engine brakes work by compressing air. This makes driving downhill safer and extends the life of the service brakes on the truck and trailer.
Service brakes can absorb this energy at a fantastic rate when they are cold. This can be thousands of horsepower, as in a panic stop. But after the brakes get hot, they can only absorb as much power as they can dissipate, which can be as little as only a few hundred horsepower. If the driver descends too fast, the service brakes get even hotter and distort, losing effectiveness. As braking power ‘fades’, truck speed picks up, and the brakes get hotter faster. It becomes a vicious cycle, and you have a runaway.
Engine brakes have become the most popular auxiliary retarder to counter this problem. They work by altering the motion of the engine’s exhaust valves, so that valves open at the top of the compression stroke. This releases the air to the atmosphere, so that it cannot push down on the piston on the following downstroke, which has the net effect of absorbing energy.
Development of Engine Brake Mechanisms
Early engine brakes would use a hydraulic master and slave piston system to move the exhaust valve. They sensed the motion of something convenient, often the fuel injector, to open the exhaust valve a small amount at the proper time.
In 1970, Mack Trucks, Inc., invented the Dynatard engine brake, which was the first factory integrated engine brake. It used innovative hydraulic lash adjusters that “turned on and off”. As solid lash adjusters, the engine ran normally. On downhill segments, a solenoid opened a check valve which would fill the hydraulic lash adjusters with oil. This would cause them to
take up the lash on a special camshaft with two base circles, causing the exhaust valve to open slightly at the proper time to create the retardation effect.
In 1993, Volvo introduced the D12 engine with the VEB (Volvo Engine Brake). The stroke of genius here is a second bump on the cam that causes the exhaust valves to open briefly a second time in engine brake mode, during the intake stroke. With back pressure in the exhaust manifold, air briefly flows backwards into the cylinder, ‘supercharging’ it with more mass, making it more powerful.
The first VEB would absorb 350 HP at 2300 rpm and a strong 235 HP at 1500 rpm. The Volvo VEB has always been very strong at mid-range speeds, where today’s trucks cruise. Over the years this would improve. The 2010 D13 I-VEB will absorb all of 500 hp at 2200 rpm and 350 hp at 1500 rpm.
Where does this all lead? Today’s D13 can come down Fancy Gap VA, a seven mile, 4% downgrade (that has three emergency ramps for runaways), at only 1400 rpm at 65 mph, without even touching the service brakes, leaving them fully available for an emergency stop if necessary.
For parts for your Volvo D13 Truck Engine Parts check out www.Class8TruckParts.com
Answer: Engine brakes work by compressing air. This makes driving downhill safer and extends the life of the service brakes on the truck and trailer.
Service brakes can absorb this energy at a fantastic rate when they are cold. This can be thousands of horsepower, as in a panic stop. But after the brakes get hot, they can only absorb as much power as they can dissipate, which can be as little as only a few hundred horsepower. If the driver descends too fast, the service brakes get even hotter and distort, losing effectiveness. As braking power ‘fades’, truck speed picks up, and the brakes get hotter faster. It becomes a vicious cycle, and you have a runaway.
Engine brakes have become the most popular auxiliary retarder to counter this problem. They work by altering the motion of the engine’s exhaust valves, so that valves open at the top of the compression stroke. This releases the air to the atmosphere, so that it cannot push down on the piston on the following downstroke, which has the net effect of absorbing energy.
Development of Engine Brake Mechanisms
Early engine brakes would use a hydraulic master and slave piston system to move the exhaust valve. They sensed the motion of something convenient, often the fuel injector, to open the exhaust valve a small amount at the proper time.
In 1970, Mack Trucks, Inc., invented the Dynatard engine brake, which was the first factory integrated engine brake. It used innovative hydraulic lash adjusters that “turned on and off”. As solid lash adjusters, the engine ran normally. On downhill segments, a solenoid opened a check valve which would fill the hydraulic lash adjusters with oil. This would cause them to
take up the lash on a special camshaft with two base circles, causing the exhaust valve to open slightly at the proper time to create the retardation effect.
In 1993, Volvo introduced the D12 engine with the VEB (Volvo Engine Brake). The stroke of genius here is a second bump on the cam that causes the exhaust valves to open briefly a second time in engine brake mode, during the intake stroke. With back pressure in the exhaust manifold, air briefly flows backwards into the cylinder, ‘supercharging’ it with more mass, making it more powerful.
The first VEB would absorb 350 HP at 2300 rpm and a strong 235 HP at 1500 rpm. The Volvo VEB has always been very strong at mid-range speeds, where today’s trucks cruise. Over the years this would improve. The 2010 D13 I-VEB will absorb all of 500 hp at 2200 rpm and 350 hp at 1500 rpm.
Where does this all lead? Today’s D13 can come down Fancy Gap VA, a seven mile, 4% downgrade (that has three emergency ramps for runaways), at only 1400 rpm at 65 mph, without even touching the service brakes, leaving them fully available for an emergency stop if necessary.
For parts for your Volvo D13 Truck Engine Parts check out www.Class8TruckParts.com
Posted by Class8TruckParts Blog at 9/24/2010 12:03 PM 
Categories: Volvo Truck Parts, Heavy Duty Truck Parts, Maintenance Recommendations
Tags: Maintenance Tips OEM Truck Parts Volvo Trucks
Categories: Volvo Truck Parts, Heavy Duty Truck Parts, Maintenance Recommendations
Tags: Maintenance Tips OEM Truck Parts Volvo Trucks
I never knew how the engine works, but thanks to your article..Keep up the good work...
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I hope these breaks does not damage the engine cam shafts
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This breaks helps a lot in controlling the huge vehicle like truck and its ideal for the emergency breaking.
the engine break can give control over the vehicle within the lesser time than the normal wheel breaks and the rolling down of the vehicle is avoided!
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Nice article, thanks for the information.
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Using compressed air for braking is a pretty neat trick. It must save a ton of wear-and-tear on the parts of a vehicle since those parts aren't scraping together constantly.
In the picture, I wonder what happens when the truck stops halfway up that hill and starts heading back down...lol.
-Rob
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Great work dude, u gave nice post to us. Thanks for spending the time to discuss this, I feel strongly about it and love learning more on this topic.
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Thanks for the review and the discussion.Did not know much abut the brakes.There are so many new age engines and mechanisms.
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This would cause them to
take up the lash on a special camshaft with two base circles, causing the exhaust valve to open slightly at the proper time to create the retardation effect.
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Engine brake is really important. This is good posting.
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You have greatly explained Development of Engine Brake Mechanisms. It is really useful post.
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