Methodology for Predictive Engine Friction Modeling

Rob Zdrodowski, Arup GangopadhyayFord Motor Company

GT North American Conference

November 14, 2016

1

Acknowledgement

Zak Liu (Ford Motor Company)

Rifat Keribar (Gamma Technologies)

Marcin Okarmus (Gamma Technologies)

2

Introduction

Methodology

Example Applications of Friction Models:

• Roller finger follower valvetrain

• Crankshaft

• Piston ring & skirt

Summary

Agenda

3

Introduction

Methodology

Example Applications of Friction Models:

• Roller finger follower valvetrain

• Crankshaft

• Piston ring & skirt

Summary

Agenda

4

Objective:

Develop engine sub-system predictive friction models to enable:

• Better understanding of individual friction components

• Concept and design studies

• Tradeoff studies

• Development of lower friction engines

Motivation:

Current CAFE targets will require significant vehicle efficiency improvements

Friction reduction can contribute to improved fuel economy

Introduction

5

54.5 mpg

Lab bench tests

Fired engine tests

Motored tests

6

Engine Friction Test Sequence

Single camshaft Single cylinder Multi cylinder engine

• Full engine• Stripdown

CAE Engine Friction Tool

Single cylinder Multi cylinder

Introduction

Methodology

Example Applications of Friction Models:

• Roller finger follower valvetrain

• Crankshaft

• Piston ring & skirt

Summary

Agenda

7

Typical CAE Friction Model Input Parameters

Geometrical & Material Properties: Geometries (width, thickness, diameter) Journal bearing clearance Journal bearing grooves/ oil holes Skirt & ring profiles Camlobe profile Valve spring rate Piston ring tension Material properties (elastic modulus, Poisson’s ratio, mass)Operating Conditions: Engine speed Temperature (at the mechanical interface) Cylinder pressure vs. crank angleSurface & Lubricant Properties: Surface roughness profiles Oil viscosity Friction coefficient

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Methodology

Surface roughness• Broken-in parts• Multiple measurements

Oil viscosity • Shear rate• Temperature • Pressure

Boundary friction coefficient• Temperature• Oil formulation• Coating

9

15 mm

stroke

Stribek curve simulations run with fundamental cylinder-on-flat contact geometry at different roughness levels

Example of Physics– Contact Tribology Model

Predicted hydrodynamic friction coefficient agrees with measured values (0.02-0.03)

Transition from boundary to hydrodynamic regime

is smooth

Friction coefficient approaches measured boundary value at low speed

Smoother surface

Rougher surface

Effe

ctiv

e Fr

icti

on

Co

ef.

Sliding Velocity (m/s)

10

Introduction

Methodology

Example Applications of Friction Models:

• Roller finger follower valvetrain

• Crankshaft

• Piston ring & skirt

Summary

Agenda

11

A single exhaust camshaft was driven by an electric motor

An in-line torque meter was used to measured friction torque

Measured RFF Valvetrain Friction

12

RFF Valvetrain Friction Model

Simulations run with GT-SUITE v2016

Seven friction contacts included in the single camshaft model13

Camshaft bearings Shaft seal

Roller-Camlobe Finger-Valve tip Valve-Guide

Roller-Needle Finger-HLA

RFF Friction Model Validation

30 degC

110 degC90 degC

60 degC

14

Simulated RFF Friction by Component

30 degC

110 degC90 degC

60 degC

15

Introduction

Methodology

Example Applications of Friction Models:

• Roller finger follower valvetrain

• Crankshaft

• Piston ring & skirt

Summary

Agenda

16

Crankshaft Model Validation & Application

Friction torque was measured from the motored crankshaft-only portion of a stripdown test

GEM 3D was used to quickly build a crankshaft model from a CAD file

Friction reduction potential of reduced main bearing diameter is shown

17

21% reduction

Introduction

Methodology

Example Applications of Friction Models:

• Roller finger follower valvetrain

• Crankshaft

• Piston ring & skirt

Summary

Agenda

18

Ring & Skirt Friction Model

Objective: Predict the effect of bore/stroke ratio

on friction Friction prediction will be combined

with thermal efficiency model

Modeled Friction Contacts:1. Piston rings2. Piston skirts3. Piston pins4. LE bearings5. Main bearings6. Crank oil seals

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Ring & Skirt Friction Model Validation

Motored cranktrain model was tuned to match motored friction measurements

Modeled cylinder pressure and temperatures were changed appropriately for the fired cranktrain model

Fired

Motored

20

Effect of Bore/Stroke Ratio on Friction

Simulated cranktrain friction increases with decreased bore/stroke ratio

A majority of the increased friction is attributed to the pistons

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Introduction

Methodology

Example Applications of Friction Models:

• Roller finger follower valvetrain

• Crankshaft

• Piston ring & skirt

Summary

Agenda

22

Summary

Detailed measurements of lubricant properties and surface roughness were combined with established lubrication theory

A good agreement was generally observed between simulated and measured friction torque

• RFF valvetrain, 30-110 degC

• Crankshaft

• Piston rings & skirts

Contributions of individual friction components to overall friction loss were predicted

The CAE predictive friction tool has been useful in guiding new engine design and enhancing the performance of current engines

23