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TRANSCRIPT
12th GT-Suite User’s Conference
Performance Analysis of a Decompression Brake SystemDecompression Brake System
for a Diesel EngineIvan Miguel TrindadeVinicius J. M. Peixoto
November, 10th 2008
MWM International Motores
Presentation overview
Introduction and objective of the engine brake
Engine Brake SystemsEngine Brake Systems
MWM Brake System
GT-Power: Engine Brake Model
Engine Brake SimulationsEngine Brake Simulations
Conclusion
Performance Analysis of a Decompression Brake System for a Diesel Engine 2
IntroductionfMotivation of analysis
● High loads on hydraulic brake system during downhill routes
● Continuous brake applications can lead to excessive wear between brake
t d b k drotors and brake pads
● Increasing of repair and stand still costs
● Low engine brake capacity leads to more robust system, heavier and more expensive
Objective:● Analyze the brake system dynamics and predict engine
Performance Analysis of a Decompression Brake System for a Diesel Engine 3
y y y p gperformance
Exhaust Brake SystemsConcept● Engine is converted from a power-source to a power-
b bi hiabsorbing machine
● Mechanism based on exhaust gases pressure rising● Pressurized gases force the engine piston down during
compression stroke summing with the power generatedby engine frictionby engine friction
● Engine brake systems can achieve braking power so highas the engine outputas the engine output
Performance Analysis of a Decompression Brake System for a Diesel Engine 4
Current MWM Engine Brake SystemExhaust brake● Flap valve with a drilled hole at
the beginning of exhaust systemthe beginning of exhaust systemblocks the gases from escaping
● Maximum brake power limited byexhaust valve bounce occurrenceat intake stroke and alsot t l istructural issues
● If not avoided, bouncing can, gresult in valve and valve seatdamages
Performance Analysis of a Decompression Brake System for a Diesel Engine 5
MWM Brake System
Engine braking power usingbrake flap system can achieve Engine Friction Motoredp yvalues 3 times the enginefriction 50%
Exhaust Brake Flap
Hyper Brake System
Braking power achieved usingthe decompression system 158%the decompression systemcan be 5 times the enginefriction, mainly at high speeds
158%
Performance Analysis of a Decompression Brake System for a Diesel Engine 6
Curves of a 6 cylinder Diesel engine.
MWM Brake System
State-of-art ● Hydraulic actuation of the exhaust valves● “Valve brake” can be controlled to actuate at any engine speed● Requires excessive room package in the cylinder head for the
hydraulic devicehydraulic device● Costs are expensive due to controlled actuation
Performance Analysis of a Decompression Brake System for a Diesel Engine 7
INTAKE COMPRESSION POWER EXHAUST
MWM Brake System
Operation● Developed by MAN AG● Just one of the valves is actuated● Valves actuated by exhaust pressure waves● Hydraulic system keeps the valve opened y y● Costs are lower than Jacobs brake
Normal valve lift /
Valve opening due to high back pressure (bouncing)
Valve Lift locked through hydraulic actuation
Normal valve lift /Gradual return to cam shape
back pressure (bouncing)
Performance Analysis of a Decompression Brake System for a Diesel Engine 8
MWM Brake System
● Actuator follows the exhaust valve during bounce movement
Ch k l l k th t t iti d il● Check valve locks the actuator position and oil pressure avoid it to return
PivotNut
Check valve
Bracket + bolt
Pivot Seat● During normal valve lift an oil passage is opened
Lock Pin
Check valve
Check valvespring
allowing the actuator returns to its
Actuator
Actuator Springoriginal position
Performance Analysis of a Decompression Brake System for a Diesel Engine 9
MWM Brake SystemBouncing movement
▀ Unbalance between
• Valve springActuator
• Cylinder pressure
• Actuator inner springp g
• Back pressure andValve top/Valve spring
• Actuator oil pressure generates bounce in the
h l
Performance Analysis of a Decompression Brake System for a Diesel Engine 10
exhaust valve
MWM Brake System
● Exhaust flap with torsional spring can provide highb k d l i d
Operation
backpressure even under low engine speeds● Gases are dissipated through exhaust system during the
compression stroke, decreasing the pressure area incompression stroke, decreasing the pressure area inpower stroke
Exhaust brake:“Spring” effect of pressurized gases
Decompression brake:Higher effective brake area
Performance Analysis of a Decompression Brake System for a Diesel Engine 11
Engine Brake Model
GT-Power model● Predict the engine brake operation
E l t it ff t i f● Evaluate its effects on engine performance
Investigation of bouncing g gmechanism was necessaryto evaluate performance of the system parametersy p
Model includes engine brake components, intake andcomponents, intake and exhaust systems
Fuel injection is shut off
Performance Analysis of a Decompression Brake System for a Diesel Engine 12
Fuel injection is shut off
Engine Brake ModelValve train components:● Modeled using GT-Power templates● Rocker Arm – Ground (imposed movement)● Valve and actuator – Linked masses● Connections
• Calibration to reproduce the same contact behavior• Spring connections simulate valve and actuator spring
Performance Analysis of a Decompression Brake System for a Diesel Engine 13
Engine Brake ModelHydraulic system:● Feed reservoir for oil availability in the cylinder head
Ch k l b ll l fl h t i ti● Check valve = ball valve flow characteristics● Flow split performs like actuator chamber● Leakage orifice reproduces clearance in the top of rocker arm● Leakage orifice reproduces clearance in the top of rocker arm
Performance Analysis of a Decompression Brake System for a Diesel Engine 14
Engine Brake Model
Subassembly interaction● Inputs from the Main model: Valve train loads
• Cylinder pressure• Exhaust pressure
● Output from the engine brake model• Valve Lift
Exhaust system● Flap valve modeled as a throttle with variable diameter
Exhaust pressure is kept in a constant value
Performance Analysis of a Decompression Brake System for a Diesel Engine 15
• Exhaust pressure is kept in a constant value
B k h t l
Engine Brake SimulationBackpressure waves on exhaust valves● 6 cylinder engine
Non interconnected exhaust manifold• Non interconnected exhaust manifold• 3 main backpressure waves• Necessity of avoid bouncing during intake stroke
● 4 cylinder engine• Interconnected exhaust manifoldInterconnected exhaust manifold• 4 backpressure waves resultant from all cylinders
Performance Analysis of a Decompression Brake System for a Diesel Engine 16
Engine Brake Simulation
Bouncing at intake stroke – small cylinder pressureDrop on lift curveLeakdown test – predict actuator movement
Performance Analysis of a Decompression Brake System for a Diesel Engine 17
Engine Brake Simulation
Mass flow rate through exhaust valve● Cylinder decompression at power stroke
Effect of cylinder pressure on actuator● Pressures are amplified● High difference of surface area
Performance Analysis of a Decompression Brake System for a Diesel Engine 18
Engine Brake Simulation - Correlation
Calibration of flap valve leakageSame back pressure valve of bench testsSame loads on exhaust valve similar performance fromSame loads on exhaust valve – similar performance fromthe engine test
Performance Analysis of a Decompression Brake System for a Diesel Engine 19
Optimization studies Variables: Spring pre-load and exhaust pressureTarget lowest value for the spring pre-loadHowever higher spring pre-load● Higher backpressure = higher braking power
Backpressure limited by turbocharger restriction
Performance Analysis of a Decompression Brake System for a Diesel Engine 20
Optimization studies
Actuator Lift
1500 rpm 2600 rpm
Optimum lift change for every engine speedSmall lifts – exhaust gases remain trapped in the cylinder
Performance Analysis of a Decompression Brake System for a Diesel Engine 21
g yHigh lifts – pressure is decreased and gases make less restriction on piston
Prediction of Braking Power
Braking Power Exhaust pressure
At low speeds valve may not openReduction of spring pre-load
Performance Analysis of a Decompression Brake System for a Diesel Engine 22
Reduction of spring pre-load● Can generate bounce under high speeds
Bounce investigation
Spring pre-load change backpressure level● High pre-load increases backpressure
Flap valve must release more gases to avoid bouncingor
Performance Analysis of a Decompression Brake System for a Diesel Engine 23
orSpring pre-load must be increased
ConclusionsThe developed numerical model is robust enough to predict the brake system performance and its components behaviorThe DOE study was able to identify the optimized spring preload that improves the brake power capacityBack pressure waves have strong influence on the dynamic of engine brake components● 4 cylinder engine – Firing order dictates interconnected manifold● 6 cylinder engine – Non interconnected manifold to prevent earlier bouncing and
increase backpressureL kd t t it bl t t l t l liftLeakdown tests are suitable to correct evaluate valve liftHolden valve lift has an optimum value for each engine speedValve bouncing can still occurs at high speeds● Lower valve pre-load can bring high braking power at low speeds● Higher valve pre-load can prevent bouncing at high speeds● Softer flap valve pre-load can decrease the braking power at high speeds
B ll l t ti i ti d hi h il id d i th l lift
Performance Analysis of a Decompression Brake System for a Diesel Engine 24
Ball valve seat optimization and high oil pressure avoid drop in the valve liftTo improve the model is necessary further calibration of the exhaust valve lift
Thanks
Special thanks to● Robert Wang and Shawn Harnish from Gamma
TechnologiesMWM International MotoresProduct Development Department
Performance Analysis of a Decompression Brake System for a Diesel Engine 25
Thank You !Ivan Miguel Trindade – [email protected] Peixoto – [email protected]
Performance Analysis of a Decompression Brake System for a Diesel Engine 26