MWM Decompression Brake

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


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


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


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%


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


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)


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


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


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


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


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


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


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


• 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


Engine Brake Simulation

Bouncing at intake stroke – small cylinder pressureDrop on lift curveLeakdown test – predict actuator movement


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


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


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


Optimization studies

Actuator Lift

1500 rpm 2600 rpm

Optimum lift change for every engine speedSmall lifts – exhaust gases remain trapped in the cylinder


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


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


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


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


Thank You !Ivan Miguel Trindade – [email protected] Peixoto – [email protected]


Documents

MWM Decompression Brake