12 th GT-Suite User s Conference Performance Analysis of a Decompression Brake System for a Diesel Engine Ivan Miguel Trindade Vinicius J. M. Peixoto MWM International Motores November, 10th 2008
Presentation overview Introduction and objective of the engine brake Engine Brake Systems MWM Brake System GT-Power: Engine Brake Model Engine Brake Simulations Conclusion Performance Analysis of a Decompression Brake System for a Diesel Engine 2
Introduction Motivation of analysis High loads on hydraulic brake system during downhill routes Continuous brake applications can lead to excessive wear between brake rotors 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 Performance Analysis of a Decompression Brake System for a Diesel Engine 3
Concept Exhaust Brake Systems Engine is converted from a power-source to a power- absorbing bi machine Mechanism based on exhaust gases pressure rising Pressurized gases force the engine piston down during compression stroke summing with the power generated by engine friction Engine brake systems can achieve braking power so high as the engine output Performance Analysis of a Decompression Brake System for a Diesel Engine 4
Current MWM Engine Brake System Exhaust brake Flap valve with a drilled hole at the beginning of exhaust system blocks the gases from escaping Maximum brake power limited by exhaust valve bounce occurrence at intake stroke and also structural t issues If not avoided, bouncing can result in valve and valve seat damages Performance Analysis of a Decompression Brake System for a Diesel Engine 5
MWM Brake System Engine braking power using Engine Friction Motored brake flap system can achieve Exhaust Brake Flap values 3 times the engine Hyper Brake System friction 50% Braking power achieved using the decompression system 158% can be 5 times the engine friction, mainly at high speeds Curves of a 6 cylinder Diesel engine. Performance Analysis of a Decompression Brake System for a Diesel Engine 6
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 device Costs are expensive due to controlled actuation INTAKE COMPRESSION POWER EXHAUST Performance Analysis of a Decompression Brake System for a Diesel Engine 7
Operation Developed by MAN AG MWM Brake System Just one of the valves is actuated Valves actuated by exhaust pressure waves Hydraulic system keeps the valve opened Costs are lower than Jacobs brake Valve Lift locked through hydraulic actuation Normal valve lift / Gradual return to cam shape Valve opening due to high 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 Check valve locks the actuator t position and oil pressure avoid it to return During normal valve lift an oil passage is opened allowing the actuator returns to its original position Nut Pivot Pivot Seat Bracket + bolt Check valve Check valve spring Lock Pin Actuator Spring Actuator Performance Analysis of a Decompression Brake System for a Diesel Engine 9
MWM Brake System Bouncing movement Actuator Valve top/ Valve spring Unbalance between Valve spring Cylinder pressure Actuator inner spring Back pressure and Actuator oil pressure generates bounce in the exhaust valve Performance Analysis of a Decompression Brake System for a Diesel Engine 10
MWM Brake System Operation Exhaust flap with torsional spring can provide high backpressure even under low engine speeds Gases are dissipated through exhaust system during the compression stroke, decreasing the pressure area in power stroke Decompression brake: Higher effective brake area Exhaust brake: Spring effect of pressurized gases Performance Analysis of a Decompression Brake System for a Diesel Engine 11
GT-Power model Engine Brake Model Predict the engine brake operation Evaluate its effects on engine performance Investigation of bouncing mechanism was necessary to evaluate performance of the system parameters Model includes engine brake components, intake and exhaust systems Fuel injection is shut off Performance Analysis of a Decompression Brake System for a Diesel Engine 12
Engine Brake Model Valve 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 Model Hydraulic system: Feed reservoir for oil availability in the cylinder head Check valve = ball valve flow characteristics ti Flow split performs like actuator chamber 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
Engine Brake Simulation Backpressure waves on exhaust valves 6 cylinder engine Non interconnected exhaust manifold 3 main backpressure waves Necessity of avoid bouncing during intake stroke 4 cylinder engine Interconnected 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 pressure Drop on lift curve Leakdown 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 leakage Same back pressure valve of bench tests Same loads on exhaust valve similar performance from the engine test Performance Analysis of a Decompression Brake System for a Diesel Engine 19
Optimization studies Variables: Spring pre-load and exhaust pressure Target lowest value for the spring pre-load However 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
Actuator Lift Optimization studies 1500 rpm 2600 rpm Optimum lift change for every engine speed Small lifts exhaust gases remain trapped in the cylinder High lifts pressure is decreased and gases make less restriction on piston Performance Analysis of a Decompression Brake System for a Diesel Engine 21
Prediction of Braking Power Braking Power Exhaust pressure At low speeds valve may not open Reduction of spring pre-load Can generate bounce under high speeds Performance Analysis of a Decompression Brake System for a Diesel Engine 22
Bounce investigation Spring pre-load change backpressure level High pre-load increases backpressure Flap valve must release more gases to avoid bouncing or Spring pre-load must be increased Performance Analysis of a Decompression Brake System for a Diesel Engine 23
Conclusions The developed numerical model is robust enough to predict the brake system performance and its components behavior The DOE study was able to identify the optimized spring preload that improves the brake power capacity Back 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 backpressure Leakdown tests t are suitable to correct evaluate valve lift Holden valve lift has an optimum value for each engine speed Valve 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 Ball valve seat optimization i and high h oil pressure avoid drop in the valve lift To improve the model is necessary further calibration of the exhaust valve lift Performance Analysis of a Decompression Brake System for a Diesel Engine 24
Thanks Special thanks to Robert Wang and Shawn Harnish from Gamma Technologies MWM International Motores Product Development Department Performance Analysis of a Decompression Brake System for a Diesel Engine 25
Thank You! Ivan Miguel Trindade ivan.trindade@navistar.com.br Vinicius Peixoto vinicius.peixoto@navistar.com.br Performance Analysis of a Decompression Brake System for a Diesel Engine 26