ENGINE BRAKE SYSTEMS
18.1
OVERVIEW
MBE4000 engines can be equipped with an exhaust brake on the turbocharger in conjunction with
constant-throttle valves in the cylinder head to increase braking performance. The two systems
operate independently of each other. Both are standard on the MBE4000.
The engine brake options are
□
Constant-throttle Valves With Exhaust Brake (refer to section 18.2)
□
A Constant-throttle Valves With Turbobrake (refer to section 18.3)
18.2
CONSTANT-THROTTLE VALVES WITH EXHAUST
BRAKE
The constant-throttle valves use the air that escapes through them on the compression stroke to
provide braking force.
The constant-throttles valves are small,
fi
fth valves which are built into the cylinder head and
positioned opposite the exhaust valve. When open, a link is created between the combustion
chamber and the exhaust valve. When open, a link is created between the combustion chamber
and the exhaust port. When the engine brake is switched on, the constant throttles are activated by
engine oil pressure.
The exhaust brake is a pneumatically actuated butter
fl
y valve, located in the exhaust system,
downstream of the turbo. It restricts the
fl
ow of exhaust gases out of the engine. As a result,
pressure builds up in the exhaust system. When the piston tries to expel gases from the cylinder
during the exhaust stroke, it now has to push against that pressure, which absorbs horsepower.
When the braking effects of compression and exhaust brakes are combined in the same engine,
power is absorbed during the compression stroke and during the exhaust stroke.
18.3
CONSTANT-THROTTLE VALVES WITH TURBOBRAKE
(OPTIONAL)
An exhaust brake is built into the turbocharger and when operated it restricts the
fl
ow of exhaust
as well as redirects the
fl
ow of exhaust gasses to speed up the turbocharger compressor wheel.
The blade ring automatically slides into the exhaust scroll opening, redirecting air
fl
ow against the
turbine blade and increasing the turbo speed and air mass
fl
ow. Increased air
fl
ows through the
engine increases the decompression braking effect. See Figure 18-1 and Figure 18-2.
18-2
All information subject to change without notice.
(Rev. 03/06)
7SA250 0603
Copyright © 2006 DETROIT DIESEL CORPORATION