Balance Shaft and Gear Train Modeling to Capture … · Modeling to Capture Gear Rattle Phenomenon...

INTERNATIONAL TRUCK AND ENGINE CORPORATIONBASE ENGINE DESIGN

Balance Shaft and Gear Train Modeling to Capture Gear Rattle

Phenomenon

GT Suite Conference

13 November 2007Justin Ferguson

[email protected]

13 November 2007 Ferguson, Justin 2


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



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



Primary Balancer

Secondary Balancer

Vacuum Pump Driven at Front

(Not Shown)

Secondary Balancer Drive

Rear Gear Train

(See Inset)



Y-Axis (Yaw Couple)

X-Axis (Pitch Couple)

Z-Axis (Roll Couple)Rear of Engine

Front of Engine



Unbalanced Couples in 90o V6 Engine

Pitch

Yaw

Primary Secondary Rotating

Engine Rotation

(rear view)

Secondary Couple Imbalance Primary Couple

Imbalance

(From Both Rotating & Reciprocating

Components



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



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



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



Torsional Vibration Data Collection

Flywheel Ring Gear

Magnetic Pickup

Balancer Gear (24 teeth) Hole for

Magnetic Pickup

(Not Shown)



Crankshaft Torsional VibrationsZero Engine Load

Balance Shaft Torsional VibrationsZero Engine Load



Crankshaft Torsional Vibrations100% Engine Load

Balance Shaft Torsional Vibrations100% Engine Load

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



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



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)



3D CAD Geometry

GT Suite Geometry



Balancer Gear Maximum Simulated Tangential Tooth ForceNo Vacuum Pump, Engine Load: 200 lbf*ft Torque

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 1 2 3 4 5 6 7 8 9

N*m

F/F m

ax

700rpm750rpm800rpm850rpm900rpm950rpm1000rpm1050rpm1500rpm1700rpm

No Vacuum Pump: Stabilizing Torque = 3 Nm



Calculated Tooth Loads



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



Hydraulic Pump Driven by

Balance Shaft

Adapter Plate

Balance Shaft Housed in Crankcase

Gear Train at Rear

View from Front of Engine



Hydraulic Pump Curve5bar (73psi) pump pressure:

~1.13kW @ 3000rpm = 3.6 Nm



Balancer Torsional Test Data: Zero Engine LoadHydraulic Pump Attached

105 psi

Baseline

Significant 3rd order until 1200 rpm

60 psi 75 psi

90 psi

Third order impact phenomenon is 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).

3rd order level is significantly reduced






Balancer Torsional Test Data: Full-Load SweepHydraulic Pump Attached

Baseline

Significant 3rd order until 2400 rpm

60 psi 75 psi

90 psi 105 psi





Third order impact phenomenon is 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).



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



Thank You



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.

Balance Shaft and Gear Train Modeling to Capture … · Modeling to Capture Gear Rattle Phenomenon...

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