Post on 13-Apr-2018
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