predictive friction simulation of 3-cylinder and 4 ... · higher engine speeds 07-10-2019...

Predictive Friction simulation of 3-cylinder and

4-cylinder IC engines

Anoop Suryanarayana, Engine CAE, Volvo Cars, Security Class: Proprietary

AGENDAIntroduction1.

• Objective

• Motivation to predict friction

3-Cylinder Engines2.• Simulations performed by Gamma Technologies

• Validation with measurements

• Key observations and conclusions

4-Cylinder Engines3.• Simulation performed by Volvo Cars

• Validation with measurements

• Key observations and conclusions

Conclusions and further developments4.

07-10-2019 Predictive Friction simulation of 3-cylinder and 4-cylinder IC engines, Anoop Suryanarayana, Volvo Car Group 2

Introduction

Background and motivation:

Demand for fuel-efficient combustion technology has led to significant improvement in modern powertrains

About 40% of losses originate from power conversion system (PCS)*

Thus, reducing losses in PCS plays an important role in the drive to reduce CO2 emissions

Objective:

Development of 1D/2D predictive friction model for Volvo cars engines


Tribological overview of power conversion system*

*Source: Tribology and dynamics of engine and powertrain, Homer Rahnejat

3-Cylinder Engine

Acknowledgements

Pete Nguyen and Gamma Technologies team


3-Cylinder Engine

Acknowledgements

Pete Nguyen and Gamma Technologies team


Rigid Crankshaft model

Will be discussed here

Rigid Crankshaft model

GEM3D used to generate GT-SUITE crank model from CAD step file

• Conrod master weight added to crankpin

Model includes

• 2D Main Bearings

• Front and rear oil seals

• Thrust Bearings

Features

• Rigid crankshaft model

• Oil shear thinning model based on measured oil properties

• Bearing clearance, oil supply pressure, seal friction torque are matched to measured data

• Surface roughness values are assumed


GT-ISE v2017

3-Cylinder Engine

Comparison with measurements

• Friction is under predicted as speed increases

Crankshaft model Validation with measurements


FM

EP

[B

ar]

Measured trend is less linear!

3-Cylinder Engine

Various investigations were performed to explain the difference between

measured and simulated results

• Tuning of bearing heat loss fraction

• Tuning of bearing surface roughness

Both have a very small tuning effect and does not improve the results with respect to

measurement

Crankshaft model – Effects of tuning parameters


3-Cylinder Engine

Unique behavior of 3-Cylinder Crankshafts

Measured data from previous GT projects show similar non-linear trend

Also, from the scatter band it is clear that this trend is seen in other 3-cylinder crankshafts


3-Cylinder Engine

FM

EP

[B

ar]

Engine Speed [RPM]

Component friction results - CRANKSHAFT

Hypothesis: Possible effect of bending

The inline 3 has a unique topology

When no conrod/piston is assembled, the free crankshaft has a rigid whirl mode that causes edge loads in the bearings

Thus, asperity contact at the edges causes high friction which is seen at higher engine speeds


3-Cylinder Engine

Image for representation of our hypothesis*

*Source: Rotor Systems: Analysis and Identification, Rajiv Tiwari

Proposed study

Model Fidelity changes:

3D-Beam Dynamic Crankshaft

• Purely for tilt effect

• Local bending curvature is minimal

Bearings are Reynolds Eq. JournalBearingHD3D (asymmetric pressure)


3-Cylinder Engine

JournalBearingHD3D

In-Plane Loading Out-Of-Plane Loading Torsional Loading

Web Stiffness

Bending and Asperity

Low speeds – No Asperity, Hydrodynamic friction only

High speeds – Mixed (Asperity and Hydrodynamic friction) caused by the bending behavior. Asperity contact is the reason for the hook in FMEP.


Asperity Contact Pressure – 5000RPM

MB4 MB3 MB2 MB1

Speed – 5000RPM

MB4MB3

MB2MB1

3-Cylinder Engine

Speed – 1000RPM

Oil Film Pressure


Speed – 1000RPM

MB4 MB3MB2

MB1 MB4

MB3 MB2

MB1

Speed – 5000RPM

3-Cylinder Engine

Conclusion: Crankshaft only

Predicted FMEP for different models –Crankshaft only:

Measurement (Green line)

Rigid crankshaft with 2D mobility main bearings (Red solid line)

Bending crankshaft with 3D FE hydrodynamic main bearings (Blue solid line)

Thus, edge loading at high speed due to bending explains the non-linear increase in friction in the crankshaft.


FM

EP

[B

ar]

3-Cylinder Engine

4-Cylinder Engine

Developed at Volvo cars


Step - 1

• Friction analysis Crankshaft

• Includes Crankshaft with Main bearings, Master weights and Radial sealing rings

• FMEP is calculated using the friction torque

Step - 2

• Friction analysis Cranktrain

• Includes Crankshaft with Main bearings, Radial Sealing rings, Pistons, Rings, Pins, Connecting rods

• Open Cylinder, no gas forces on Piston


Step - 3

• Friction calculation of Piston group and connecting rod

• “FMEP of Step-2” minus “FMEP of Step-1”

• This gives us the friction in Piston group and connecting rod

Steps of friction strip Measurement


4-Cylinder Engine

Step-1: Rigid Crankshaft model

GEM-3D used to generate GT-SUITE crank model from CAD step file

• Conrod master weight added to crankpin

Model Includes• Main Bearings

• Front and rear oil seals

• Thrust Bearings

Features• Rigid crankshaft model

• Oil shear thinning model based on measured oil properties

• Oil supply pressure, seal friction torque are matched to measured data

• Bearing clearance, surface roughness values are assumed


GT-ISE v2019

4-Cylinder Engine

Validation with measurements

At 3000rpm, the step in the measurement is due to change in oil pressure.

Good match was seen against friction strip test results.


4-Cylinder Engine

FM

EP

[B

ar]

Step 2: Cranktrain with Piston group model

Model consists of• Piston

• Small end and big end bearings

• Conrod

• Mass balance system with roller bearings

Model features• Ring data

• Piston skirt data

• RollerBearing 2D template

Assumptions• Approximated clearances in cylinder bore and conrod

bearings

• Surface roughness

• Bore distortions are not considered


4-Cylinder Engine

Cranktrain Model Validation with measurements

At 3000rpm, the step in the measurement is due to change in oil pressure.

Good correlation with the friction strip test results.


4-Cylinder Engine

FM

EP

[B

ar]

FM

EP

[B

ar]

Step - 1

• Friction analysis Crankshaft

• Includes Crankshaft with Main bearings, Master weights and Radial sealing rings


Step - 2

• Friction analysis Cranktrain

• Includes Crankshaft with Main bearings, Radial Sealing rings, Pistons, Rings, Pins, Connecting rods

• Open Cylinder, no gas forces on Piston


Step - 3

• Friction calculation of Piston group and connecting rod

• “FMEP of Step-2” minus “FMEP of Step-1”

• This gives us the friction in Piston group and connecting rod

Steps of friction strip Measurement


4-Cylinder Engine

No need as GT-SUITE

provides us these results

Components frictions: Simulated vs Measurement results


4-Cylinder Engine

Temperature 90C

13-09-2019 VEP4 Gen3 HP Friction Simulation, Anoop Suryanarayana, Engine CAE Solids 23

4-Cylinder EngineCrankshaft friction: simulated vs measurement resultsTemperature 90C

Understanding the difference: Simulation vs Measurements


4-Cylinder Engine

Difference in simulation and measurement:

In the friction strip test, only rotating masses ofthe connecting rod is added as master weights.This reduces the bearing load.

Approx. 2.5 times increase in bearing load isobserved at 6000rpm with piston groupincluded due to piston reciprocating forces.

Thus, effects from the oscillating mass forcesare not seen in the measurement of crankshaftfriction.

0

0,2

0,4

0,6

0,8

1

1,2

0 2000 4000 6000 8000

NO

RM

AL

ISE

D F

OR

CE

[N

]ENGINE SPEED [RPM]

Maximum Bearing Load on MB 3

Maximum Bearing Load 3_Master weights

Maximum Bearing Load 3_Piston Group

Piston group friction: simulated vs measurement results


4-Cylinder Engine

Large difference between

simulation and measurement

There is a possibility that in reality

the friction in piston group is less

and our approach in measurement

is incorrect.

So simulation model is helpful to

find these details that we might

have missed in measurement.

GT-SUITE simulation model is a useful tool to understand friction behavior of individual

components, where measurements have limitations.

2D journal bearing model with mobility assumptions are sufficient to obtain faster results.

High fidelity model captures more details with higher accuracies but at the cost of

computational time.

The FMEP values obtained from these models are useful for 1D gas exchange simulation team

as they currently use approximated values.

Final Conclusion


Discussions with friction strip test supplier to improve the test methodology for piston group.

4-Cylinder engines

• Improve the model further to include camshafts and valve train.

• Methodology to predict friction in piston group assembly.

• Simulation of part load and full load cases to understand friction of the engine.

Future scope


Thank You

predictive friction simulation of 3-cylinder and 4 ... · higher engine speeds 07-10-2019...

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