INTERNATIONAL TRUCK AND ENGINE CORPORATION BASE ENGINE DESIGN

Balance Shaft and Gear Train Modeling to Capture Gear Rattle Phenomenon

GT Suite Conference

13 November 2007 Justin Ferguson [email protected] INTERNATIONAL TRUCK AND ENGINE CORPORATION BASE ENGINE DESIGN

Balance Shaft Project Overview – Project background • Balance shaft function • Problem statement • Objective – Engine torsional vibration measurements • Crankshaft • Second order balance shaft – Multi-body dynamic simulation results • Crankshaft torsional vibration data used as input • Simplified gear train system modeled in GT Suite v6.2 • Investigate effect of constant system torque – Model validation: engine dyno test • Hydraulic pump connected to balance shaft • Pump output pressure adjusted to vary torque on balancer

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Background – Engine: 4.8L 90o V6 with 120o firing interval – Crankshaft: 30o crankpin offset – Engine balance • Shaking forces: naturally balanced • Rocking couples: requires counterbalancing – First order: rotates in same direction as crankshaft » Due to reciprocating and rotating masses » Requires crankshaft weights and primary balance shaft – Second order: rotates in opposite direction as crankshaft » Due to reciprocating masses » Requires counter-rotating secondary balance shafts • Balance shafts driven by gear train

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Primary Rear Gear Balancer Train (See Inset)

Secondary Balancer Drive

Vacuum Pump Driven at Front (Not Shown) Secondary Balancer

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Y-Axis (Yaw Couple)

X-Axis (Pitch Couple) Front of Engine

Rear of Engine Z-Axis (Roll Couple)

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o Unbalanced Couples in 90 V6 Engine

Engine Rotation (rear view)

w

a Secondary Couple Y Imbalance Primary Couple Imbalance (From Both Rotating & Reciprocating Components

Pitch

Primary Secondary Rotating

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Problem Statement • Excessive gear rattle concern is three-fold – Sound produced by rattle is a NVH issue – Gear teeth impact loads are greater than design – Bearing life is reduced • The design does not address gear rattle under lightly-loaded conditions – Idle/low speed – Low vacuum pump demand

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Objectives • Develop a simple, dynamic model capable of predicting stabilizing torque of the balancer gear train • Validate the dynamic model in engine dyno test • Use the predicted torque value as a design specification for implementing “zero backlash” gear system

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Experimental Torsional Vibration Data • 3rd order is the “firing order” for 4-cycle, 6-cylinder engine • Drop of 3rd order vibration magnitude at balancer indicates non-linear behavior in gear train (loss of tooth contact) • Design-intent engine includes a vacuum pump driven directly by the second-order balance shaft • Data collected from engine test serves two purposes: – Characterize the dynamic behavior of the gear train – Provide input data for dynamic model

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Torsional Vibration Data Collection

Balancer Gear (24 teeth) Hole for Flywheel Magnetic Ring Gear Pickup (Not Shown)

Magnetic Pickup

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Crankshaft Torsional Vibrations Balance Shaft Torsional Vibrations Zero Engine Load Zero Engine Load

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Crankshaft Torsional Vibrations Balance Shaft Torsional Vibrations 100% Engine Load 100% Engine Load

3rd Order Drop- Off 2389rpm (crank speed)

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Balancer Dynamic Simulation • Multi-body dynamics software GT Suite v6.2 used to model second-order balancer shaft, gear train, and external loading (vacuum pump, friction, hydraulic pump) • Objective of study: – Create simplified, user-friendly model of gear train – Correlate model results and measured torsional vibration data – Determine system-stabilizing torque value • Results – ~3 N*m of constant torque applied to balance shaft eliminates impact loading on gear teeth – Results are consistent with findings in lab tests and literature

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GT Suite Dynamic Model • Simplifying Assumptions – Spur gear compound object – Constant mesh stiffness • “Simple” tooth modeling option • Constant value in mesh stiffness vs. mesh cycle array (‘XYTable’ object) – Constant mesh damping – Rigid balance shaft – Nominal tangential backlash – Constant bearing friction values (assumed) • Inputs – Inertias calculated in CAD – Experimentally measured crankshaft torsional velocity versus time – Engine speeds • Output – Stabilizing torque versus engine speed (run as a 1 parameter DOE)

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3D CAD Geometry

GT Suite Geometry

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Balancer Gear Maximum Simulated Tangential Tooth Force No Vacuum Pump, Engine Load: 200 lbf*ft Torque 0.8 700rpm 750rpm 0.7 800rpm 850rpm 900rpm 0.6 950rpm 1000rpm 1050rpm 1500rpm 0.5 1700rpm x a m

F 0.4 / F No Vacuum Pump: 0.3 Stabilizing Torque = 3 Nm

0.2

0.1

0 0 1 2 3 4 5 6 7 8 9 N*m 13 November 2007 Ferguson, Justin 19 INTERNATIONAL TRUCK AND ENGINE CORPORATION BASE ENGINE DESIGN Calculated Tooth Loads

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Constant Balancer Torque Engine Test • Hydraulic pump used to apply constant torque to balancer system – Vacuum pump removed from front of engine – Hydraulic pump installed in place of vacuum pump – Pressure regulator installed in hydraulic circuit – Pump torque calculated via pump power curve • Results – Test data support dynamic model predictions – Constant torque system provides excellent dynamic stabilizing properties for gear train

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Adapter Plate

Hydraulic Pump Driven by Balance Shaft

Gear Train at Rear

Balance Shaft Housed in View from Crankcase Front of Engine

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Hydraulic Pump Curve

5bar (73psi) pump pressure: ~1.13kW @ 3000rpm = 3.6 Nm

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Balancer Torsional Test Data: Zero Engine Load Hydraulic Pump Attached

Baseline 60 psi 75 psi

3rd order level is 3rd order level is significantly reduced significantly reduced Significant 3rd order until 1200 rpm

90 psi 105 psi Third order impact phenomenon is

3rd order level is significantly reduced 3rd order level is significantly reduced significantly reduced even at the lowest pump pressure of 60 psi, which is less than 3.6 N*m of torque (per the pump power curve). 13 November 2007 Ferguson, Justin 24 INTERNATIONAL TRUCK AND ENGINE CORPORATION BASE ENGINE DESIGN

Balancer Torsional Test Data: Full-Load Sweep Hydraulic Pump Attached

Baseline 60 psi 75 psi

3rd order level is 3rd order level is significantly reduced significantly reduced Significant 3rd order until 2400 rpm

90 psi 105 psi Third order impact phenomenon is significantly reduced 3rd order level is even at the lowest pump 3rd order level is significantly reduced significantly reduced pressure of 60 psi, which is less than 3.6 N*m of torque (per the pump power curve). 13 November 2007 Ferguson, Justin 25 INTERNATIONAL TRUCK AND ENGINE CORPORATION BASE ENGINE DESIGN

Conclusions • The GT gear train model proved to be a quick, simple tool to accurately predict the stabilizing torque required to eliminate gear rattle in the second-order balancer gear train • The GT model is flexible enough such that future enhancements can be added to obtain more accurate results – Integration with other engine rotating systems for full-scale torsional vibration analysis – More accurate mesh stiffness values based on in-depth gear analyses • The predicted torque correlates well with the experimentally determined values

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Thank You

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References – Croker et al., “Heavy Duty Diesel Engine Gear Train Modelling to Reduce Radiated Noise,” SAE Technical Paper 951315, 1995. – Heisler, Heinz, “Advanced Engine Technology,” Butterworth-Heineman, Ltd., Oxford, 1992. – Rodriguez et al., “A Geartrain Model With Dynamic or Quasi-Static Formulation for Variable Mesh Stiffness,” SAE Technical Paper 2005-01-1649, 2005. – Smith, J. Derek, Gear Noise and Vibration, Marcel Dekker, Inc., New York, 1999.

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