Low-Friction Engineered Surfaces

Argonne: George Fenske, Ali Erdemir, Oyelayo Ajayi, Robert Erck, and Osman Eryilmaz Ricardo: James Kezerle and Lee Oberto UMich: Zoran Filipe

DEER 2007: Diesel Engine-Efficiency and Emissions Research (DEER) 2007 Conference

Detroit, Michigan

August 12-16, 2007

ACKNOWLEDGEMENT - Research sponsored by the U.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies, as part of the Hybrid and Vehicle Technologies, and, Materials Technologies Programs, under Contract No. DE-AC02-06CH11357 with UChicago, Argonne LLC.

Role of Friction & Wear in Vehicles � Traditionally, the role of friction and wear in transportation has addressed

issues associated with reliability and durability – engineering the tribological system (consisting of lubricants & additives, materials & coatings, and component geometry/finish) to improve component lifetime and mitigate catastrophic failure (e.g. scuffing) – Changing environments continue to challenge the ability of current

tribological systems (low-lubricity fuels, low SAPS lubricants, greater loads, EGR, etc.)

� Increasing fuel prices, tighter emission standards, and concerns over global warming gases are now driving researchers worldwide to develop more efficient tribological systems to reduce parasitic friction losses. – More energy is lost to friction than is delivered to the wheel.

Approximately 10 % of the fuel consumed in transportation is lost to friction in the engine. Another 6% is consumed by friction in the driveline

� Fuel savings in the range of 3-5 % can be achieved by reducing parasitic engine losses, while another 2-4 % can be saved by reducing parasitic driveline losses

More Energy is Lost to Friction Than Delivered to the Wheel

� Energy Map- Passenger Vehicle EPA Cycle – Roughly 10% of energy input consumed by

friction

– >1 million barrels/day lost to friction intransportation

Energy In

100%

Indicated HP

35%

Exhaust

35%

Engine Cooling

30%

Brake HP

23%

At Wheels

9.5%

Other Engine Friction

0.4%

Piston Assembly

2.8%

Valve Train

1.3%

Bearings

1.0%

Seals

0.5%

Air Pumping

6%

Others

1.6%

Transmission

2.0%

Braking

2.0%

Coast/Idle

4.0%

Axle

1.6%

Accessories

Oil Pump - 0.5%

Air Pump – 0.1%

Water Pump - 0.1%

Fuel Pump - 0.1%

Power Steering – 0.5%

Cooling Fan – 0.5%

Alternator – 0.5%

Viscous Loss – 1.35%

Friction Forces – 0.95%

Blowby – 0.5% Aero Drag

4.0%

Tires

5.5%

15% of IMEP (Indicated Mean EffectivePressure – HP normalized to engine displacement)

Strategy of Parasitic Friction & Wear Research � Develop and Apply Mechanistic Models of

Friction (Boundary and Viscous) Losses to Predict Parasitic Losses as a Function of Engine Conditions (Load & Speed), and Tribological Conditions (Boundary Friction and Oil Viscosity)

– Scale fuel consumption as a function of FMEP and IMEP for a prototypical HD diesel engine

– Predict the impact of low-friction (boundary-layer friction) and low-viscosity lubricants on fuel economy

� Evaluate/Screen the Potential of Candidate Surface Treatments and Additives to Reduce Boundary Friction Under Lab Conditions Prototypical of Engine Environments

– Benchtop friction tests using prototypical engine components

– Impact of materials, coatings, surface texture, and lubricant additives and viscosity

� Validate Codes/Models and High-Potential Solutions in Fired Engines Using In-Situ Friction Measurement Techniques

RINGPAK PISDYN ORBIT VALDYN

Integrated Mechanistic Models to Predict Impact of Low-Friction Surfaces and Low-Viscosity Lubricants on Parasitic Energy Losses(FMEP) and Fuel Economy

Spee

d (rp

m)

�

1900

1700

1500

1300

1100

900

700

500 0 500 1000 1500 2000

Load/IMEP (kPa)

1 (52%) 52%

2 (3%) 5.4%

3 (4%) 5.8%

4 (15%) 8.5%

5 (8%) 6.2%

6 (6%) 26%

7 (8%) 8.9%

8 (5%) 6.2%

Weighting factor – FMEP/IMEP

RINGPAK PISDYN ORBIT VALDYN

FMEP calculated at 8 different modes and weighted to predict effect on fuel consumption •Rocker bushing *for a HD driving cycle •Rocker tip to valve *

•Pushrod to rocker interface *

•Piston pin bearing * •Rings * •Piston Skirt *

•Cam - follower interface * •Cam bearings * •Follower - pushrod interface * •Timing drive

•Journal bearings •Crankshaft windage

•Crankshaft main bearings •Main seals *

•Oil Pump

FCSF = (Fuel Consumption Scaling Factor)

IMEP + ΔFMEP IMEP

•Fuel injection system

* interface considered in current study

Role of Boundary and Hydrodynamic Lubrication Regimes- Tribological System

� Different regimes of lubrication depending on the degree of contact between sliding surfaces

� Boundary lubrication characterized by solid-solid contact – asperities of mating surfaces in contact with one another

� Contrast boundary lubrication with full-film lubrication in which mating surfaces are separated by a film.

� In between, mixed lubrication occurs.

Boundary Lubrication

Mixed Lubrication

Full Film Lubrication

Viscosity * Speed/Load

Fric

tion

Coe

ffici

ent

Boundary and Hydrodynamic Friction: Model Impact onFMEP and Wear Severity � Total FMEP is the sum of the Asperity friction and the hydrodynamic friction

– Boundary FMEP decreases with increasing lubricant viscosity – shifting from BL to ML regime – Hydrodynamic FMEP increases with increasing viscosity

Piston FMEP versus Viscosity Grade Normalized Piston - Liner Contact Severity

0

5

10

15

20

25

10 20 30 40 50 SAE Viscosity Grade

FMEP

(kPa

)

No Treatment Total Est 30% Reduction Total Est 60% Reduction Total 90% Reduction Total Hydrodynamic Asperity / No Treatment Asperity / Est 30% Asperity / Est 60% Asperity / 90%

Rel

ativ

e W

ear L

oad

Viscous FMEP

4.5

Asperity 4.0 FMEP

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0 0 10 20 30 40 50

SAE Viscosity Grade

Low-Friction (Boundary-Friction) Surfaces Enable Use ofC

hang

e in

Fue

l Con

sum

ptio

n (%

)Low-Viscosity Lubricants to Provide Fuel Savings up To 5% � Low Boundary Friction Only – up to 1% savings � Low Boundary Friction AND Low Viscosity – 3-5 % savings � Estimates of Payback on Technology

Skirt: Impact of Reduced Asperity Friction on Fuel Savings (gals) @ 1000 hrs Operation 3

-1

-2

SAE Lubricant Grade

Baseline Friction - 0% Reduction

30% Asperity Friction Reduction

60% Asperity Friction Reduction

90% Asperity Friction Reduction

60% Asperity Friction INCREASE

Increase in friction - increase in fuel consumption

200Baseline Friction -0% Reduction 30% Asperity Friction Reduction 60% Asperity Friction Reduction 90% Asperity Friction Reduction 60% Asperity Friction INCREASE

0 10 20 30 40 50

SAE Lubricant Grade

2

Gal

lons

of F

uel S

aved

per

100

0 H

ours

Ope

ratio

n 150

1

100

0

50

0

-50-3

-4 -100

-5 -150 0 10 20 30 40 50 60

60

Identifying Low-Friction Technologies that Enable Low-Viscosity Lubricants and Maintain Durability/Reliability

� Measurement of friction using benchtop tribometers providing data on the potential of advanced engineered surfaces and lubricants to provide low-friction tribological systems

– Benchtop test configurations • Unidirectional Sliding

– Pin-on-Disc – Block-on-Ring

• Reciprocating Sliding – Ring-on-Liner

– Candidate low-friction technologies

• Coatings (Amorphous carbon, Superhard nanocomposites, Commercial Coatings – CrN, E-NiB …)

• Lubricants (Additives – formation of low-friction boundary films)

• Textured surfaces

Near Frictionless Carbon Films

Plasma-assisted CVD

� Non-crystalline 0.6 structure

– a-C:H 0.5 � Near RT process Test Conditions:

Load: 10 N Speed: 0.5 m/s Distance: 1305 km Environment: Dry N2 Temperature: 22oC Wear rate: 7.4X10-11mm 3/N.m Coated M50 Steel Ball (9.5 mm diameter) Coated H13 Steel Disk

17,500,000 passes

Test machine failed

SEM

Fric

tion

Coe

ffici

ent

– Ceramics, metals, polymers

� Ultra-low friction – < 0.001

� Reduced Wear – 105 lower

0.4

0.3

0.2

0.1

0 0 5 10 15 20 25 30 35

Time (days)

Pin-on-Disc Evaluation of Low-Friction Superhard Coatings – 50 % Reduction in Boundary Layer Friction

Fric

tion

Coe

ffici

ent

� Engineered coating0.12 microstructure and15W-40 Formulated Mineral Oil

composition to provide0.10 superhardness and tribochemistry for0.08 enhanced low-friction properties0.06

0.04

Weak columnar 0.02 to hardsteel/steel 10 rpm distance vs steel/steel 10 rpm µ

steel/SHNC 10 rpm distance vs steel/SHNC 10 rpm µ nanocrystalline 0.00

0 10000 20000 30000 40000 50000

Sliding Distance (cm)

Block-on-Ring Evaluation of Scuff Resistant Coatings

Steel/Steel 600 N scuffing load

0.00

0.05

0.10

0.15

0.20

0 480 960 1440 1920 2400 2880 3360 3840 4320

Time (s.)

Fric

tion

Coe

ffici

ent

0

200

400

600

800

1000

1200

1400

1600

1800

2000 Friction Coefficient

Load

Load

(N)

SHNC/SHNC >1700 N scuffing load

� Low-friction technologies must also maintain or improve the durability and reliability of critical engine components – a challenge for low-viscosity lubricants.

� Strategies are being developed to identify pathways to improve scuff-resistance while enabling use of low-friction, low-viscosity lubricants

Severe deformation

Technology Development & Validation – Low-Friction Additives

� Development of Low-Friction Additives

– Developed test rig to simulate ring-on-liner and piston-on-liner tribological environments

– Discovered low-friction nature of boric-acid (BA) based additives, Developed concept of boric-acid based additives (fuels & lubes)

– Developing technology to produce nm-sized BA additives

– Demonstrating low-friction properties of BA in lab tests prior to engine validation studies

Ring Segment

Liner Additized Segment Oil

Blue trace shows friction coefficient during cyclic heating tests – Note how cyclic heating activates the action of the BA additive to produce low friction

10W30 synthetic + 10 % E Additive � Comparison:

– No significant difference in contact resistance in time or between different lubricants

– It can be shown that the decreases in friction at low temperature as cycles occur are due to greater hydrodynamic lubrication as a result of fine polishing of the liner

10W30 10W30 + E Additive

PAO 10 + 10% E - Additive

� Specimen and cup were cleaned well to remove any chemical additives and filled with PAO 10 – Boundary friction at 100°C = 0.108 – Minor change of friction at low temperatures as tests progress – Significant Impact of E Additive on friction

PAO 10 PAO 10 + E - Additive

0

Low-Friction Additive Consumed During 9-Day Benchtop Test

� During extended break-in tests with low-friction additive, the friction was initially low, continued to decrease, then increased as the additive was depleted

0.15 0.15 0.15 060319 10 rpm 150N silk first 3600 s 060319 10 rpm 150N silk 3600 s at 240,000s 060319 10 rpm 150N silk mid 3600 s

0.1 0.1 0.1

0.05 0.05 0.05

µ 0 µ 0

-0.05 -0.05 -0.05

-0.1 -0.1 -0.1

µ

-0.15 -0.15-1.5 -1 -0.5 0 0.5 1 1.5 -1.5 -1 -0.5 0 0.5 1 1.5 -0.15Position (cm) Position (cm) -1.5 -1 -0.5 0 0.5 1 1.5

Position (cm)

Textured Surfaces � Textured surfaces with ‘oil reservoirs’ produced by laser dimpling or

control of coating morphology during deposition

Partial Laser Texturing of Hard (1800 HK), ElectrolessHard Cr Coated Cylindrical Ni3B Coating After ‘PlateauPiston Ring – Etsion (COST Polishing’ – UCT Defense, June 2007) LLC

Textured Surfaces as a Method to Reduce Hydrodynamic and Mixed Lubrication Friction

Mixed LubricationFull Film

Lubrication

Fric

tion

Coe

ffici

ent

With LST

BoundaryLubrication

Viscosity * Speed/Load

Microdimples created by LST act as oil reservoirs thereby minimizing boundary and mixed lubrication friction

� Argonne (in collaboration with Technion University – Prof. I. Etsion) is evaluating the potential of laser surface texturing to reduce friction on engineered surfaces

� Results suggest LST may provide significant energy savings regimes where conformal contact is presentFe

U

Textured ring

Liner

5.00 5.50 6.00

500 600 700 800 900 1000 1100 1200 Angular Velocity, RPM

Etsion - Technion

Fric

tion

Forc

e, N

4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00

Untextured Full texturing Partial texturing

Ricardo/U-Mich – In-Cylinder Validation of Models and Low-Friction Technology

� Single Cylinder, Fired Diesel Test

�

Engine – Ricardo Hydra Engine Modified to Monitor Friction Force Between the Piston (Skirt & Rings) and Liner Continuously

Friction Force

Strain Gauge

Sleeve

Liner

Support Wire

Coolant

Friction Force

Thermocouples

In-Situ Measurement of Ring/Piston – Liner Friction

� U-Michigan instrumented liner installed in single-cylinder Hydra engine

� Preliminary friction force trace as a function of crank angle under motored conditions

� 4-valve DI cylinder head to be installed for in-situ friction force measurements under fired conditions

Summary & Future Directions

� Significant Fuel Savings can be Achieved by Reducing Parasitic Friction Losses in Engines and Drivelines – 3-5% - Engine – 2-4% - Driveline

� Suite of Mechanistic Models Integrated to Examine the Role of Low-Friction Technologies and Low-Viscosity Lubricants on Fuel Savings

� Benchtop/Lab Techniques Identify Potential Pathways to Low-Friction Technologies

– Depending on operating conditions, boundary friction reductions up to 90 % can be achieved

� Engine Validation Studies in-progress

� Future Directions – Single-cylinder studies – Low-friction technology development & evaluations – Multi-cylinder validation – Accessories – modeling of parasitic friction losses

Acknowledgement

� Research sponsored by the U.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies, as part of the Hybrid and Vehicle Technologies, and, Materials Technologies Programs, under Contract No. DE-AC02-06CH11357 with UChicago, Argonne LLC.

r

ng

r scu

1

2

3

10 1010

30 3030

35 3535

Boundary Lubrication Mechanisms – Scientific Understanding of Friction, Wear, & Lubrication

� Developing and using advanced x-Using the APS to analyze boundary lubrication

ray techniques to investigate friction and wear mechanisms – Formation of protective

tribofilms

– Surface failure mechanisms (Scuffing)

Squeeze films in oil: Analyze with XRD

Surface tribofilms:

Analyze with XRF, XRR,

XRD

Near-surface deformation:

Analyze with XRD

Ball

Flat

Oil

0 5 10 15 20

3

1 2

Befo e scuffing

Duri scuffing

Afte ffing

0 5 10 15 20

3

12

1

2

3

Before scuffing

During scuffing

After scuffing

0.80.8404040

0.70.7

Coe

ffic

ient

of F

rictio

nC

oeff

icie

nt o

f Fric

tion0.60.6

252525 0.50.5

Load

(lbf

Load

(lbf

)

ANL model predicts that the critical shear strain to initiate scuffing is given by:

202020 0.40.4

151515 0.30.3

0.20.2

555 0.10.0.11

000 000

Time (min)Time (min)

Progression to Scuffing

3

1

2

Scuffing produced severely deformed surface layer (~ 20 µm) in fraction of second.

20 µm

10W30 synthetic + 10 % E BA

� Comparison: – No significant difference in contact resistance in time or between different

lubricants – It can be shown that the decreases in friction at low temperature as cycles

occur are due to greater hydrodynamic lubrication as a result of liner wear during running

10W30 10W30 + E BA

Transient Speed Tests - PAO 10 + 10% E - Additive

� Data were obtained at 100 C at end of test for various reciprocating speeds:

Benchtop Studies – What Is the Magnitude of Friction Savings That Can be Achieved, and What Level of Increased Protection

� Models assumed 30, 60, and 90% reductions in boundary friction – what are realistic friction coefficients, how do they compare to the baseline assumptions – are there technologies that can provide these levels of improvements

� Pin-on-Disc, Reciprocating, Block-on-Ring, and Ring-on-Liner Configurations

– Friction, Wear, Scuffing-Resistance of test coupons and prototypic rings and liner segments

� Coatings, Surface Texturing, and Additives

Technology Development to Technology Implementation& Commercialization� Argonne’s Tribology Section heavily focused on MultiCylinder

technology development, evaluation, and testing. Engine/Transmission � Develop close alliances with industry to validate Validation

prototype components and commercialize Fired Singletechnology Cylinder

EngineComponent Validation Rig Tests

Ring & Liner

BenchtopTests

TechnologyDevelopment

CoatingsLubricants

Nanofluids, etc.

Ramped Speed Tests - PAO 10 + 10% E - Additive

� Sliding is strongly hydrodynamic, even at slowest sliding speeds – Thus, actual boundary friction coefficient cannot be determined from

these graphs

Friction Analysis - PAO 10 + 10% E - Additve

� Graphs of friction at 100°C as a function of position near start of test and near end of test are strikingly different from each other

� Near end of test, sliding is largely hydrodynamic, even at 100°C