1. Viscosity Modifiers for Next Generation Driveline Fluids
Dr. Hitoshi Hamaguchi
Dr. Michael Müller
Dr. Christoph Wincierz
Dr. Thorsten Bartels
Evonik RohMax Additives

2. Content
Background
Effect of dPAMA on EHL film formation, friction and wear
Effect of dPAMA on gear efficiency
Effect of dPAMA on anti-fatigue performance
Conclusions

3. Transmission – Hardware and Lubricant Technology is Changing Rapidly
Socio-economic and environmental perspective
Automobile consumer perspective
Global warming
Decreasing resources of fossil fuels
Dependency on crude oil deposits
Driving comfort
Adaptable transmission
Long drain intervals – Fill for life
Reduced operating and service cost
CO2 emission reduction
Significantly improved fuel economy
Hardware
Lubricant
Quantum leap in new transmission technologies
7- and 8-speed AT
New generation of CVTs
DCT
New transmissions need a new generation of lubricants
Low vis ATF/MTF/
CVTF/DCTF
Increased wear and
fatigue
Lubricants with boost in wear + pitting protection
High VI
Low KV40/KV20
Improved fuel economy in city cycle driving
High
friction
durability
over the
lifetime

4. Effect of different Viscosity Index Improvers on V-T behavior
loglog Viscosity
logT
base oil
Lower viscosity = reduced internal friction
= better energy efficiency
PAMAs allow to formulate to very high VI
Same KV 100 but much lower viscosities at lower temperatures
Yes, PAMAs show some shear thinning at high shear rates But: High shear rates = high entrainment speeds = thick hydrodynamic lubricant films

5. Wax Crystallization: Effect on Viscosity at Low Temperature
Effect of wax interaction of
PAMA VI Improver with PP function
or PAMA Pour Point Depressant
Log log
Viscosity
Expected V/T line for paraffin free fluid
The straight line shown on this graph shows the expected increase in viscosity as temperature falls for a pure fluid.
The presence of wax manifests itself as an increase in the viscosity of the oil beyond that that would be expected for the unwaxed oil.
There is also an increase in the pour-point and yield stress of the oil compared to the unwaxed oil.
Wax only makes up a small portion of the hydrocarbons in the oil and the wax structure contains a large amount of fluid trapped in quite a fragile structure.
This structure can be easily broken by mechanical action such as stirring or shaking, so wax isn’t an important factor when the oil is subjected to shearing as during engine cranking.
However, if the bulk of the oil is in a stagnate environment such as an oil sump or MRV TP-1 test, the wax structure will impair oil flow, limiting the utility of the lubricant at low temperature.
Insufficient oil flow can result in costly failures and so you need to ensure that adequate performance standards for the lubricant at low temperature have been defined.
Using a correctly selected PPD can greatly reduce the undesirable effects of wax structure and allow oils to meet the low temperature requirements and avoid equipment failures.
CloudPoint
-70 ºC
-50 ºC
-40 ºC
-30 ºC
-20 ºC
-10 ºC
0 ºC
40 ºC
100 ºC
Log Temperature

6. Specifically designed PAMAs can form thick boundary films in the lubricated contact
White Light
--Glass Disc
--Thin Cr Layer
SiO2 Spacer Layer
Lubricant
Lubricant Film
Thick boundary film = lower friction at low speed
= better energy efficiency
= better wear performance
Ultrathin film interferometry
to measure boundary film formation in situ and in contact
Besides their viscometric properties the tribological performance of PAMAs is of high interest and in the focus of our research since years.
We investigate film forming properties of lubricants were using UTFI. This is a well known technique which had been developed by Prof. Spikes of Imperial College.
Very brief introduction: What we are basically doing is: we are loading and rolling a reflective steel ball against a transparent disc coated with a 5nm semi-reflective Cr Layer and a silica spacer layer. White light is shone through disc and lubricant film and reflected a the ball. Optical retardation between light reflected from the ball and the Cr layer on the disc leads to interference which can be evaluated to determine the lubricant film thickness (in situ and in contact) very precisely and down to nanometers
We studied film thickness of polymer solutions in a mineral base oil. All fluids were blended to give similar viscosity at 120. A mineral oil mix blended tot the same KV 120 as the polymer solutions serves as a reference oil
We found that specifically designed PAMAs can form thick boundary films in the lubricated contact. This may have important performance advantages in practical use: Because thick boundary film = lower friction at low speed = better energy efficiency = better wear performance
We will see examples o the next slides
Measures the lubricant film thickness formed between a rolling steel ball and a silica-coated glass disc, as a function of rolling speed, down to < 2 nm

7. Dispersant PAMAs: Effect of polymer architecture on film thickness
1000
dPAMA O, stat
At high speed
dPAMA O, non-stat.
dPAMA N1, stat
100
dPAMA N1, non-stat.
Film Thickness [nm] 10
At slow speed 1
0.001
0.01
0.1 1 10
Speed [m/s]
This is a busy slide. It summarizes the major findings from our studies about the relation of PAMA structure to their tribological properties:
In order to form thick boundary films PAMA-VIIs need to contain specific functional groups which have the ability to strongly adsorb onto metal surfaces.
These functional groups have to be clustered, e.g. in block copolymers as shown here in direct comparison to random copolymers. Whereas random copolymers behave like the reference oil blockcopolymers give an order of magnitude thicker films at low speed.
What do we believe is the mechanism of boundary film formation through functionalized PAMA’s?  In high speed, thick film conditions bulk polymer solution is simply entrained into the lubricated contact and forms an EHD film  However at lower speeds there is an enhanced concentration of the flexible and thus low traction polymer – due to strong adsorption to the surface. A stable thick viscous boundary film is formed
Polymers with functional groups clustered in a block gave clear thick and considerably viscous boundary films
Polymer is adsorbed at the metal surface – boundary film contains higher polymer concentration than bulk fluid
Boundary film is stable and survives high pressure rolling- sliding contacts

8. Dispersant PAMAs: Effect of polymer architecture on friction
0.120
dPAMA O, stat.
dPAMA O, non-stat.
dPAMA N1, stat.
dPAMA N1, non-stat.
0.080
Friction coefficient
0.040
0.000
As you can see here the friction results for these polymers are in perfect correlation with the film thickness observations
Block copolymers have the effect of significantly reducing friction in mixed lubrication conditions. Or in other words: They are kind of shifting the Stribeck curve towards lower entrainment speed.
0.001
0.01
0.1 1 10
Mean rolling speed [m/s]
In correlation with film thickness results, non-statistically distributed block copolymers gave a very large reduction in friction at low speed

9. Dispersant PAMAs: Effect in a fully formulated 75W90 gear oil
75W90 + PAO 100
75W90 + dPAMA N1
Formulation based on group 3 oil.
Package contains:
Dispersant
S-based EP additive
Antioxidant, friction modifier
VII: PAO 100 or dispersant PAMA
As already mentioned: All experiments so far were carried out with solutions of polymer in oil. It is the target of our ongoing research to investigate interaction of polymer with package components and in fully formulated oils. Here is an example of a fully formulated 75W90 gear oil. It’s based on a group 3 base oil and contains a standard GO package. We are comparing a formulation containing a dispersant PAMA as VII in comparison to a formulation with a high molecular weight PAO as a thickener.
Even in the presence of a full gear oil package the dispersant PAMA shows boundary film formation and leads to significantly lower friction at low speed

10. MTM/ICP Wear Test Results for different PAMAs in oil
Block f-PAMAs completely prevent wear under the MTM/ICP conditions
Stat f-PAMAs are also quite effective
Non-functionalized PAMA reduces wear significantly. After an increase over the first hour wear comes to a halt
PIB has no marked influence on wear. In its presence wear increases linearly with time

11. FZG Efficiency Test Method to measure Lubricant Efficiency
Measures the lubricant torque transmitting efficiency through two sets of loaded gears
DIN 51354/5, VW PV 1456
Volkswagen Polo gear set
0, 135, and 302 Nm
1600 rpm
T = 20, 44, and 90 °C
Simulation of the MVEG cycle (5 speed MT)
Formulation details:
VII in mineral oil and PAO, commercial DI package
Viscosity according to SAE 75W-90

12. FZG Efficiency Test Method to measure Lubricant Efficiency
Gear set 2
Torsion Flange
Gear set 1
Torque Sensor
Drive-motor
Shaft 2
Shaft 1
Torque Adjustment
Flange

13. Temperature and Viscosity Effects on FZG Torque Loss
Conditions: 238 Nm applied torque, 2000 rpm 4 5 6 7 8 30 60 90
120
150
Oil Temperature (°C)
Torque Loss (Nm)
SAE 90
SAE 75W-90
Torque loss decreases with increasing temperature
Model for increased fuel economy with lower in-service viscosity
Multi-grade formulation shows expected benefit at lower temperatures
Why is there also a benefit ≥ 100ºC?

14. Influence of VII type on gear efficiency2 4 6
100
200
300
Transferred torque (Nm)
Absolute increase of
efficiency vs SAE 90
T = 20 °C
SAE 75W-90 (PAMA)
SAE 80W-90 (PIB)
Efficiency gains versus monograde decreases with increasing torque
PAMA improves significantly more than PIB

15. Influence of VII on load-dependant Losses
Mineral Oil (Group I) Formulations
PAO Formulations
Straight PAO 
PAO + PAMA 
PAO + PIB ▲
Torque Loss in Nm
Torque Loss in Nm
Straight Mineral Oil  SN PAMA  SN PIB▲ SN 90 + PAMA 
SN PIB + SN PAMA 
Kinematic Viscosity in mm2/s
Viscosity in Kinematic mm2/s
Conditions: 90ºC, 302 Nm applied torque
PAO formulations have lower torque loss than mineral oil PAO formulated with PAMA shows equal losses to straight PAO
Addition of PAMA to mineral oil causes a decrease in load dependent loss. Higher PAMA concentration increases the effect
Addition of PIB increases load dependent torque loss

16. Efficiency of multigrade MTF: Truck on Roller Dynamometer
ZF multigrade fluid
SAE 30
KV 100 / cSt
9.0
11.5
KV 30 / cSt 84
170
FIGE cycle (European stationary cycle for HDD), fuel savings
Urban traffic: 2.6 – 3.3 %
Suburban traffic: 1,1 – 1,2 %
Motorway: 0 % (direct drive)
Total Savings 0.7 – 1 %
Source: ZF
The ETC test cycle (also known as FIGE transient cycle) has been introduced for emission certification of heavy-duty diesel engines in Europe starting in the year The ETC cycle has been developed by the FIGE Institute, Aachen, Germany, based on real road cycle measurements of heavy duty vehicles. Different driving conditions are represented by three parts of the ETC cycle, including urban, rural and motorway driving. The duration of the entire cycle is 1800s. The duration of each part is 600s.
Part one represents city driving with a maximum speed of 50 km/h, frequent starts, stops, and idling.
Part two is rural driving starting with a steep acceleration segment. The average speed is about 72 km/h
Part three is motorway driving with average speed of about 88 km/h.
FIGE Institute developed the cycle in two variants: as a chassis and an engine dynamometer test.
Heavy truck field test revealed 0.5 to 5 % difference in fuel consumption between SAE 90 and SAE 75W-90 depending on topography and temperature.
Source: RohMax

17. Pitting – an increasing problem with low viscosity fuel efficient lubricants
Pitting = a fatigue failure occurring at metal surfaces as a consequence of load alternation
Target = no pitting over the lifetime of the equipment = long fatigue life
= good anti-fatigue performance
Strict CO2 emission requirements
Extreme reductions of fuel consumption
Lower viscosity of automotive lubricants required
Lower viscosity leads to increased wear and fatigue
Optimized lubricant formulations have to compensate for that
RohMax Solution: Tailor-made film forming VII or booster which improves anti-fatigue performance
Potential areas of application:
ATF, CVT, DCT, MTF, rear axle, transfer case
Engine oils
Boundary film reduces surface stress peaks at asperities which are responsible for micro crack formation leading to pitting

18. Film Forming PAMAs increase fatigue life: 4 ball screening test
150,000
conventional PAMA
40.000
80.000
148,000
rotations to damage
105,000
new film former 1
new film former 2
RohMax Test Conditions
Load N
Speed rpm
Temperature °C
p Hertz-max GPa
Example: 75W MTF oil

19. Film Forming PAMAs increase fatigue life: FE8 bearing pitting test
Test bearings
2,000 h
hours to damage
480 h
150 h
conventional PAMA
new film former 1
new film former 2
Test Conditions
According to VW specification
Load kN
Speed rpm / 750 rpm
Temperature °C
p Hertz-max GPa
Example: 75W MTF oil

20. Conclusions
Fuel economy in automotive transportation is important today and will be more important in the future.
New transmission hardware requires new generation of fluid technologies
Maximum fuel economy requires improvements in both engine and transmission lubricants, and will drive a shift to lower viscosity lubricants.
Lower viscosity lubricants can adversely affect wear and fatigue life if adequate lubricant film thickness is not maintained.
Tailor-made PAMA viscosity Index improvers simultaneously enable:
Reduction of base oil viscosity
Reduction of lubricant viscosity at lower temperatures through higher VI
Improved fuel economy
Increase in lubricant film thickness
Improved wear and fatigue life