CHARACTERISATION AND
FUNCTION OF CYLINDER LINER
SURFACES
Cecilia Anderberg • 2007 01 07
Handledare: BG Rosén
Examinator: BG Rosén
Ett examensarbete utfört enligt kraven för Högskolan i Halmstad för en
Magisterexamen i Teknisk Produkt- och Produktionsförbättring
Abstract
The demands on decreased environmental impact from vehicles force the automotive industry
to develop engines with reduced engine oil and fuel consumption. Engine oil consumption is
recognized to be a significant source of pollutant emissions. Unburned or partially burned oil
in the exhaust gases contribute directly to hydrocarbon and particulate emissions. Engine oil
and fuel consumption are to a great extend controlled by the topography of the cylinder liner
surface.
Recent engine tests have shown a promising reduction in oil consumption when using
cylinder liners with a smoother finish than the current plateau honing.
One approach to produce smoother liner surfaces is to replace SiC ceramic honing stones with
diamond tools. However, event though the diamond honing process results in higher
productivity, improved demands of quality control is needed to monitor the degree of cold
worked material - “blechmantel” (German), and the resulting risk of increased wear and
scuffing.
A number of petrol and diesel engine cylinder liners have been mapped to be able to verify
the quality and consequences, in terms of wear and function, of the honing process. A new
mapping method, combining SEM images and quantitative image analysis with traditional 2D
profilometry has been developed and tested in this study. The liners where tested in a
reciprocating rig of 8 mm stroke and with a frequency of 10 Hz, simulating the top-dead
center conditions in a running engine.
The tests where carried out in high- and low pressure conditions with smooth respectively
rough liner roughnesses against PVD coated piston rings. The developed surface mapping
method was employed before and after the test to study effect of running-in wear on the
surface, features characterized with the SEM- and the 2D profilometer.
The results show that combining SEM- and profilometric methods gives a good picture of the
effects of varying the cylinder liner pressure and roughness. The roughness of the core
decreases more for diesel liners than for petrol liners. In average (rough and smooth liners)
the diesel core roughness decreases 265% while the petrol liners average on a 60% decrease.
Blechmantel- and Irregularities ratio show a high sensitivity to varying conditions and
decrease 1180% to 100% for the diesel liners while the parameters increase between 106% to
18% for all the petrol liners. A probable cause is the more severe diesel high pressure run-in
conditions are able to effectively “truncate” the plateaux and remove residing plastically
deformed un-cut honing residues while the less severe petrol liner conditions not manage to
remove the blechmantel and irregularities in an important extent.
INDEX
Page
CHAPTER 1 INTRODUCTION
1.1
1.2
1.2.1
Background
Purpose and aim
Problem definition
4
5
5
CHAPTER 2 METHODS AND MATERIAL
2.1
2.2
2.3
2.4
2.5
2.6
2.7
Stylus measuring device
Scanning electron microscope-SEM
Software
Measuring procedures
Characterisation methods
Image analysis
2D profilometry
6
6
6
6
7
7
10
CHAPTER 3 TRIBOLOGY
3.1
3.1.1
Introduction to the tribology subject
The tribological system piston ring-cylinder liner surfaces.
13
16
CHAPTER 4 RESULTS
4.1
4.2
4.3
4.4
Quantification of the eight tested cylinder liners
Parameter correlation
Results from analysis of SEM pictures
Friction and wear results
24
24
27
28
CHAPTER 5 CONCLUSIONS
CHAPTER 6 FUTURE WORK
30
31
REFERENCES
32
3
1
Introduction
1.1
Background
The engine is a major contributor to weight in any vehicular design and a great deal of energy loss,
in the petrol and diesel engines comes from the cylinder liner wall surface – piston ring interactions.
Further, emission and service intervals are influenced by the engines oil consumption. External,
present and coming, demands on energy consumption and emissions, force the automotive industry
to seek and test new and improved techniques.
Both the oil consumption and friction loss are strongly influenced by the ring-liner roughness
and topography. Low friction coatings have shown a potential for further reduction of the friction, by
offering the possibility to use less viscous lubricant without causing an increase in wear. This means
that the tribological system, the ring-liner-lubricant, has to be optimised simultaneously in order to
design engines with low friction and oil consumption, paired with a cost effective manufacturing
processes.
Traditionally grey cast liner inserts or engine blocks are used both for car and truck engines.
The development of lightweight designs with aluminium or magnesium based engine blocks has
resulted in a range of technical solutions to master the tough tribological conditions in the cylinder
liner to piston ring interaction for the new materials.
Among the car manufacturers like Porsche and Jaguar have implemented aluminium – silicon
alloys replacing the current grey cast liner inserts used by e.g. Ford-Volvo Cars and Volvo Trucks.
Other ways to replace the traditional grey cast iron surfaces are thermal spraying of different
materials and laser cladding, aiming at strengthen the lightweight material in the engine block to
make the performance as good as, or better, than traditional solutions.
Old finishing processes, like plateau honing, can be used for finishing of some of the new liner
materials. Optimisation towards cost effective manufacturing has to be carried out in order to adopt
to the new materials properties, like increased hardness of the surface compared to the old grey cast
material and following requirements of tool materials and machining data.
In the last decade the trend in liner surface topography is to produce finer surfaces with Rk values
between 0.3 and 0.6. This because engine tests have shown promising result concerning oil
consumption reduction.
Introduction of diamond honing tools for plateau honing is improving the capability to manufacture
surfaces with finer topography but it also demands an improvement in process control. Monitoring
of surface topography parameters in the honing process is necessary to assure a functional liner
surface. In the surface specification the 2D parameters like Rpk, Rk and Rvk are used and controlled
in the manufacturing process. When changing material and honing tools, features, not possible to
detect with 2D parameters, can occur, e.g. the degree of cold worked material. Cold worked material
is when the surface material is not properly cut; the material is smeared over the surface and can
create hard particles that are worn off when the engine is in operation. Also the smearing can close
honing grooves, needed for good lubrication conditions. 2D parameters can not reveal this kind of
malfunction of the manufacturing process. Also introducing new liner concepts like thermal spray or
laser texturing creates a need for 3 D characterisation methods. In this study a number of cylinder
liner surfaces are analysed with a method combining 2D parameters and image analysis based 3D
parameters. SEM pictures of liner surfaces are used in the image analysis method to evaluate
parameters like honing angle, stray grooves, defects and degree of blechmantel.
4
1.2
Purpose and aims of the study
Propose and test a function related methodology for characterising cylinder liner surfaces.
1.2.1
Problem definition
In order to discriminate between different liner surface solutions, new characterization
methods are necessary and in practice there exist a need for detailed and automated
inspection, especially when new improved honing methods are being introduced.
Firstly, the scope of this study is to develop, implement and test a SEM image- and 2D stylus
profilometry characterisation method, taking in to account the advantages of the Goetze and
Beyerer approaches described in Chapter II.
Secondly, the aim is also to test the possibility to quantify different properties originated from
the manufacturing process and evaluate its impact on function.
5
2
METHODS AND MATERIAL
The study investigated in total 8 different types of grey cast iron cylinder liners. The liners
are centrifugally cast and inserted in injection mould alumina car engine blocks. The rough
liner types are cylindrically honed using silicon carbides abrasives. The smooth ones are
honed with diamond abrasives and represent the current commercial manufacturing concepts
on two separated roughness levels.
Rough liners are “plateau honed” liners having rougher surface structure amplitude while
smooth liners are manufactured under the same conditions using improved, finer, plateau
honing grit sizes than the rough type. The smooth honing liners represent the latest
developments in commercial liner manufacturing and current state-of-the-art.
The different liner types where tested in a reciprocating rig of 8 mm stroke and with a
frequency of 10 Hz [8], simulating conditions around the top-dead center in a running engine.
Piston ring – cylinder liner pressure where selected according to true running values for
petrol- (low pressure) and the diesel liners (high pressure) liners. Surface roughness were
measured before the test, after 3 hours of run in and finally after the test. Friction were
monitored during the tests. Wear volumes were calculated after the test.
2.1
Stylus Measuring device
The measuring device used in this study is a Surfascan 3CS mechanical stylus system. The
3CS has a maximal horizontal range of 100*100 mm and a minimum horizontal (x,y)
resolution of 2 µm. The vertical (z) resolution of the inductive laser linearised varying
difference transformer probe, is 6 nm and the maximal vertical range is 6 mm. The horizontal
resolution used for the 2D-measurements is 1 µm in x-direction using a 17.5 mm traversing
length. The stylus used has a 2 µm radius and a 90 degree tip angle. The traversing speed
used for the 2D measurements was 0.3 mm/s.
2.2
Scanning Electron Microscope -SEM
SEM images where produced by a the secondary electron detector of a JEOL JSM-6490LV
microscope with a maximum of 5nm lateral resolution.
2.3
Software
The software used for 2D profiles was the OmniSurf v1.67 and here the Surfascan type .smd
files were imported directly to the OmniSurf software. Image analysis of SEM pictures where
made using Matlab  (v.7.1) and the Matlab Image Toolbox 5.1 software.
2.4
Measuring procedures
All profile measurements were preconditioned in the respective software by leveling against a
least square line. Further, a form removal for 2D profiles by fitting and removing a 4’th
degree polynomial to measured data was carried out. 2D- measurements were band pass
filtered using cut-off wavelengths of 8 µm (ls) and 2.5 mm (lc) and the “robust Gaussian
filter” by Bodschwinna et al. [3].
The 2D and 3D measurements were located to start 20 mm below the top of the liner with the
positive x-axis direction (main measuring direction) of the measurements running co-linear
with the cylindrical liners’ centre line.
6
1800um
180mm
Fig. 1. Combining SEM images and profilometry
2.5
Characterisation method
To be able to analyse the result of the total honing process and to analyze changes in surface
roughness, including “blechmantel”, as a function of wear, eight petrol and diesel liners have
been tested. A new mapping method, combing SEM images and quantitative image analysis
with traditional 2D profilometry [zlates] has been developed and tested in this study. The
image analysis take advantage of the high magnification and the possibility to extract 3D
features not possible to easily extract from the 2D profiles measured by the stylus method.
Stylus profiles, however complete the SEM analysis with quantified measures of the “classic”
profile features like profile heights and lateral measures.
2.6
Image analysis
In order to extract and quantify lateral features associated with the honing process image analysis is
employed in order to utilize qualitative high magnificated SEM images. Ideally the honed structure
consist of a plane, intersected by a manufactured criss-cross pattern of grooves resulting from the
abrasive grits plowing trough the cylinder liner surface. The groove orientation is a result of the
combined machining horizontal- and vertical cutting speeds. Groove distribution, width and depth is
a result of honing tool grit density, size and pressure. The image analysis will therefore have the
purpose to isolate and put numbers to expected and groove features like orientation as well as
deviations from the perfect distributed groove pattern on the plane liner surface. The brightness and
greyscale histogram distribution can vary from image to image due to deviations in measuring
settings or differently tilted measuring objects. This calls for a preconditioning of the measurements
using average filtering to remove slopes and greyscale averaging to make different images
comparable on a more equal basis.
7
Numerical parameters;
blechmantel,
irregularities, holes
Background/foreground
separation by FFT
Preprocessing
(image equalization
and averaging)
SEM image
acquisition
Numerical parameters;
groove-balance, interrupts, -orientation,
stray grooves.
Edge detection and
Hough transform
Fig.2. Workplan for the image analysis method
After pre-processing, background and foreground are separated by a Fast Fourier filtering where the groove
components in a selected orientation are masked manually (fig. 3). When FFT filtering using the X-shaped
mask, the inverse FFT transform of the filtered image recompose the background without the grooves’
components (Fig. 3).
Filtering
-define groove
component
SEM
Image
FFT
filtered
FFT
Inverse FFT=
background
multiplication
Fig. 3 The different steps followed for extracting the parameters blechmantel, irregularities and holes .[11]
The inverse Fourier transform extracted background features consist of holes, blechmantel and
irregularities. Blechmantel and irregularities are brightness intensity non-groove elements which
size is larger respectively smaller than a set threshold. Holes are large low intensity areas in the
image. Two kind of thresholds are then computed to differentiate those three features in the
background : intensity threshold and size threshold.
8
Extracted
Background
parameters
(foreground/ groove
structure removed)
Blechmantel
Irregularities
Holes
Fig. 4. Background features extracted after FFT filtering and FFT inverse transformation for groove removal.
By employing edge detection to find distinct edges (valleys-, hole-, and blechmantel borders), linear
features ie. grooves and groove sections, can be separated using the Hough-transform (eq 1):
(1)
Here the main interest using this transform is to detect groove features in an image, where edges
(groove and groove segments) can be expressed as grey level intensity in the original image position
(x,y) as a function of distance from the centre point of the image in an orientation with the angle θ,
figure 5.
SEM
Image
Edge
detection
Hough
transform
(detection of two
orientations)
Groove analysing
using the Hough
transform
θ1
θ2
θ1
θ2
Fig.5. By a combination of SEM imagining, classic edge detection, and analysis of the strongest parts of the Hough
transform, dominant linear features as exemplified with the right most histogram at different θ-angles
9
Integration and thresholding in the different θ-angles enable quantification of orientations (stray and
expected orientations), grove interrupts and balance (strength) between grooves in different angles.
The groove orientation is naturally divided into left- and right hand grooves. By comparing the two
groups, a groove balance can be calculated. Stray grooves are oriented in other orientations than the
two main (left- right hand) directions whereas residual grooves are stray grooves with orientations
similar to previous machining step directions, eg. turning marks not removed by the finishing
plateau honing steps (fig 6).
Groove parameters
(extracted after edge
detection and Hough
transform)
Groove orientation
Groove balance
Stray-and residual
grooves
Fig. 6. After groove detection (left), groove balance (mid) and distribution of groove orientations can be calculated from
the histograms. The stray- and residual grooves (right) are oriented in direction other than the orientation of the two
dominating (left-, righthand) orientations θ1 and θ2 in fig 5 above .
2.6
2D Profilometry
SEM image analysis need to be completed with the stylus profiling technique to provide quantitative
depth information. Here, five (5) 2D parameters are used to quantify amplitude- and vertical
properties of the grove components. Two of them are the standardized parameters: Rmr (percentage
bearing ratio at depth of 1 µm and with the 5% highest peaks removed before calculation) and Wt
(macrowaviness).
Additionally, three non-ISO standardized groove parameters are calculated: the mean groove width
(a), the mean groove height (C) and the mean distance between grooves (d).
Grooves are defined as valleys deeper than the amplitude threshold c2. c2 need to be individually
selected for each surface type and was chosen to 1 um below the profile mean line in this study.
Groove width is defined as the mean line distance between the two profile points constructed as the
mean line crossing points when tracking the identified grooves’ deepest points forwards, and
backwards along the profile.
10
Fig. 7. Non-ISO standardized 2D profile parameters completing the SEM image analysis with groove characteristics.The three
groove parameters here are; mean groove width (a), mean groove height(c) and mean distance between grooves (d) [10].
2.7
Influence of SEM magnification on image analysis
The SEM has the advantage of a very broad range of possible magnifiction levels. For practical
purposes, the image analysis method suggested above need to be performed on a magnification level
chosen to result in parameters representative to the whole cylinder liner surface to be tested. To
select appropriate magnifications, the same area where captured by the SEM at different
magnifications to display the range and mean of the suggested image analysis parameters above.
For the honing groove orientation, groove balance, stray grooves, low magnifications, 50X-200X,
promotes the capture of enough number of grooves to reach a low variation [11].
For the parameter group analyzing the details of the surface: blechmantel, irregularities, holes,
groove interrupt, a compromise between a need of high magnifications to resolve details and the
risks of getting too big dispersions between results with a too high magnification is needed (Fig. 21.
holes (‰)
Groove interrupt (pixels)
35,00
4500
4000
30,00
28,90
3157
value (pixels)
25,00
value (‰)
3932
3709
3692
3500
26,44
20,00
15,00
13,27
3000
2714
2500
3403
3120
2968
2738
2679
2375
2000
1825
1500
10,00
1000
5,00
4,29
0,78
1,95
3,22
3,80
500
0
0,00
200
350
500
magnification
650
200
350
500
650
magnification
Fig.8. For 200X of magnification, holes and groove interrupt give a significantly smaller range of % holes than the larger
magnifications tested. The grove interrupt parameter seems to be less sensitive to magnification chosen.
A low range is desirable when selecting the best magnification. For the different magnifications
displayed in fig.xx above 200X magnification is selected due to the low ranges. In fig. 9 below,
11
500X magnification is selected for blechmantel and irregularities as a magnification where the mean
stabilise compared to the next larger magnification 650X. Remaining image analysis parameters
blechmantel and irregularities show a similar variation for the different magnifications tested.
Blechmantel (‰)
Irregularities (‰)
80,00
25,00
70,00
68,35
49,62
51,88
40,71
40,00
40,01
31,29
30,00
20,59
15,00
10,46
10,42
5,22
4,96
11,48
10,00
22,79
14,82
20,38
13,95
8,58
20,00
20,37
17,14
value (‰)
value (‰)
50,00
20,00
62,53
60,00
18,53
17,39
7,43
5,00
10,00
5,03
0,00
0,00
200
350
500
magnification
650
200
350
500
650
magnification
Fig. 9. Blechmantel- and irregularities parameters show a negliable sensitivity to magnification level in the SEM. Any
magnification from 200X to 650X are possible to use for the analysis.
12
3
TRIBOLOGY
3.1
Introduction to the tribology subject.
Tribology is defined as the science and technology of interacting surfaces in relative motion
and of related subjects and practices. It is dealing with every aspect of friction, lubrication and
wear.
Friction is the resistance to motion whenever one solid body moves over another with which it
is in contact.
Fig. 10. Already the Egypts were occupied with the problem of friction. From historical traditions we know that they wetted
the sand on which they transported their stones. Today we know that this reduced the friction coefficient indeed.
The laws of friction were first stated quantitatively by the french engineer Guillaume
Amonton in 1699, and have since become known by his name. The first of Amontons´ laws
states that the friction force between a pair of sliding surfaces is proportional to the applied
normal load. The second of Amontons laws states that the friction force between the two solid
bodies is independent of the apparent area of contact between them. The constant of
proportionality between friction force F and load W is known as the coefficent of friction µ.
The frictional force required to initiate motion is more than that needed to maintain the
surfaces in the subsequent relative sliding. In other words the coefficient of static friction µs is
greater than that of kinetic friction µk. This statement is sometimes called Amontons third law
of friction. In 1785 one of the most comprehensive studies of friction during this time period
was undertaken by Charles Coulomb. His work made it possible to distinguish between the
effect of adhesion and deformation. He also stated that kinetic friction is independent of
sliding velocity. (Coulombs Law)
13
These laws all attribute dry friction only. It has been known for a long time that lubrication
modifies the tribological properties significantly.
In 1883 Nikolai Petrov carried out a number of experiments In St Petersburg to examine how
frictional losses in a railway vehicle axle depended on the nature of the lubricant; he showed
that the frictional force was proportional to the product of bearing area, the sliding speed and
the lubricant viscosity, but inversely proportional to the bearing clearance. He was one of the
first investigators in the field to make viscosity rather than density the crucial lubricant
property. He did not continue to investigate the influence of these parameters on load-carrying
capacity of the bearing.
It was Beauchamp Tower (England 1883) who first discovered hydrodynamic lubrication . He
used a specially constructed test rig for journal bearings simulating the conditions found in
railway axle boxes. In order to achieve consistent results, the majority of Tower's
investigations were carried out with the shaft immersed into a bath of oil.
Tower investigated the influence of lubrication on friction at a high sliding velocity. Like
other researchers, he found that the friction coefficient strongly varied with the load and
velocity, contrary to what Coulomb had formulated. Dependent on the rotational velocity, a
very low friction coefficient of µ=0.001 to 0.01 was found.
In the final phase of his research, he decided to drill an oil feed hole in the bearing. During the
experiment, the oil was found to rise upwards in the feed hole and leaking over the top of the
bearing cap. A wooden plug used to block the hole was pushed out by the oil. He then
installed a pressure gauge and found it to be inadequate for measuring the high pressure
levels.
Fig.11. Towers test rig for hydrodynamic lubrication.
14
In addition of Towers discovery, two years later Osborne Reynolds (1886) published a
differential equation describing the pressure build up in the oil film.
The hydrodynamic theory is valid for oil film thicknesses h>> surface roughness R. That
means that the concurrent surfaces are completely separated by the intervening oil film. Since
the two surfaces are not in physical contact with each other the resistance to their tangential
motion is only due to viscous losses in the lubricant. If the lubricant exhibits Newtonian
rheological behaviour with constant viscosity then the value of this frictional forces ,and the
associated coefficient of friction, will increase with sliding velocity ν. The Stribeck curve
shows the coefficient of friction and oil film thickness h as a function of the velocity, the oil
viscosity and the specific contact pressure at the surfaces in relative motion.
Mixed
h=R
Elastohydro
dynamic
h>=R
Hydrodynamic
h>>R
Coefficient of friction µ
Oil film thickness h
Boundary
h->0
lubricant viscosity * sliding velocity
contact pressure
η*ν
P
Fig.12. The Stribeck graph (schematic) shows the coefficient of friction and oil film thickness as function of sliding velocity,
oil viscosity and specific contact pressure at the surfaces in relative motion.
A reduction in speed or an increase in contact pressure will lead to a decreasing coefficient of
friction. But there is a limit in this process; if the contact pressure gets to high or the velocity
to low, it becomes difficult to build up a sufficiently thick oil film that entirely separates the
mating surfaces. There will be some mechanical interaction between the opposing surface
asperities. In the boundary lubrication (Fig.3) regime the lubricant film are only a few
molecules thick. Within this operation range the lubricant bulk properties, density and
viscosity are of relatively little importance, while its chemical composition, as well as the
15
underlying metals or substrates, become increasingly significant. In the mixed lubrication
regime is an intermediate region between the elastohydrodynamic and boundary regime. In
the elastohydrodynamic lubrication regime the predicted oil film thickness is much less than
the roughness of the surfaces. It is most likely that interaction between the opposing solid
asperities which could result in unacceptable damage and wear during operation. But in a lot
of cases devices run quite satisfactorily under these sort of loads for a long time. The
complete explanation is not obvious but one important effect is the increase in oil film
thickness due to high pressures that arises locally when asperities in the surfaces come in
contact. Surfaces in this regime must deform, initially elastically, and even though these
deformations are small they play a vital role in forming the protective hydrodynamic oil film.
In the hydrodynamic lubrication regime the surfaces are completely separated by the oil film.
Generating a hydrodynamic lubrication relies on geometry and motion on the surfaces
together with the viscous nature of the lubricating fluid.
3.2 The tribological system piston ring-cylinder liner surfaces.
In this work the tribology in the cylinder system of internal combustion engines is studied. Internal
combustion engines generate a controllable torque within an engine speed range. The powertrain in a
reciprocating engine consists of piston, piston rings, cylinder barrel, connecting rods, crankshaft and
oil. The energy from the combustion is transferred to the crankshaft by the piston and the connecting
rods. The powertrain system is subject to friction in operation, the piston rings are metallic seals and
have the function of sealing the combustion chamber from the crankcase and assuring the flow of
heat from the piston to the cylinder. Other functions are to prevent oil not needed for lubrication
from passing from the crankcase to the combustion chamber and to provide a uniform oil film on the
cylinder bore surface
Fig.13. The powertrain in an internal combustion engine.
16
Liner
Ring
Fig14. Magnification of the ring liner contact..
The mechanical power loss in the engine accounts for about 40 % of the total energy losses in
the engine and half of this loss is caused by friction in the cylinder liner/piston ring interaction
(fig.15) with the oil ring accounting for 60 % of this figure.[1].
.
Balance Shafts
2 .50
4-Cylinder Gasoline Engine 2.2 L DOHC
Water Pump
Oil Pump
Lifters, Valves
2 .00
Ca mshaft, Drive
FMEP [bar]
Pistons, Rods
1 .50
Crankshaft, Bearings
1 .00
0 .50
0 .00
600
800
1200
1600
2000
2 400
2800
3200
3600
4000
4 400
4800
5200
5600
6000
6 400
Engine Speed [rpm]
Fig.15. Friction losses for engine components (FMEP=friction mean effective pressure)
Reducing this friction loss is a key factor in improving fuel consumption and environment
protection. The interest is great from customers, society and manufacturers to further get to know
and control the friction response and also to optimise the manufacturing processes. A number of
different engineering solutions exists. Different coatings of the piston ring and liner surface can
17
reduce friction in the boundary lubrication regime, fig. x. Selective chemical reactions between
coating and lubricant will form low friction tribofilms.
Mixed
h=R
Elastohydro
dynamic
h>=R
Hydrodynamic
h>>R
Coefficient of friction µ
Boundary
h→0
lubricant viscosity * sliding velocity
contact pressure
η*ν
P
Fig.16. Different coatings on piston rings and liner surface can reduce friction in the boundary lubrication regime.
Surface topography influence the friction at the mixed and hydrodynamic lubrication regimes.
Engineered surfaces like, for example, laser texturing of the cylinder liner surface can improve the
hydrodynamic lubrication regime by reducing the friction losses due to shear strength of the
lubrication fluid, fig.17.
Mixed
h=R
Elastohydro
dynamic
h>=R
Hydrodynamic
h>>R
Coefficient of friction µ
Boundary
h→0
lubricant viscosity * sliding velocity
contact pressure
η*ν
P
Fig. 17. Surface engineering can improve the hydrodynamic lubrication properties of a tribological system.
18
By selecting coatings (material and surface properties) of piston rings and surface topography of the
mating cylinder liner in a optimised way it is possible to move the mixed lubrication regime, fig. 18.
Mixed
h=R
Elastohydro
dynamic
h>=R
Hydrodynamic
h>>R
Coefficient of friction µ
Boundary
h→0
lubricant viscosity * sliding velocity
contact pressure
η*ν
P
Fig. 18. Moving the mixed lubrication regime decreases the asperity contact intensity
Piston rings experience a wide range of lubrication conditions as a result of the reciprocating nature
of the piston, high gas pressures present during parts of the stroke, and limited lubricant supply.
Boundary lubrication is present between ring and liner at top dead center were the piston turns. The
load is high due to the combustion pressure, and the velocity of the piston is low and, at the turning
position, equal to zero. There is insufficient lubrication available to wet the ring. Under this
lubrication regime, no hydrodynamic pressure is present and the ring load is carried by a rough
surface contact. Friction is proportional to ring load, analogous to dry surface contact. When the
piston starts to move downwards in the cylinder bore the velocity is increasing and the lubrication
regimes changes to mixed and eventually to hydrodynamic. Mixed lubrication occures when both
lubricant and rough surface contact is present between ring and liner. The ring load is carried by a
combination of hydrodynamic pressure and rough surface contact.
Besides friction, the oil consumption with unwanted of combustion products such as HC-, CO-, CO2,
NOx gas and particles emission can be controlled by the liner surface topography. [2].
Figure 19 show a number of different strategies for accomplishing a wear resistant and low friction
piston-liner system.
19
iron
Particles
GI-greycast iron
Infiltration-Locasil
CGI-Compacted
Graphite Iron
”Natural”
Sintering-nonmetallic particles &
lightmetal powder
Greycast structures
Porosity
Texturing
lightmetal
Hard particles in cast-Duralcan
Honed
Spraycompacted aluminum-silicon Alusil
Reactive particle in cast
Manufactured
Thermal spraying
Laser texturing
Chemical machining
Plasma coating
Waterjet
Burnishing
Fig. 19. Different surface engineering strategies for cylinder liner surfaces and piston rings.
Traditional honed grey cast iron engine blocks with steel piston rings has in many cases been
replaced by lighter alumina engine block concepts. In order to discriminate new liner surface
solutions new characterization methods are necessary.
Still, the grey cast iron liner material is commonly used as the functional surface against the sliding
piston ring contact. The finishing of the cylinder liner surface results in a criss-cross patterned
topography consisting of a series of honing valleys of different density, peak radii, depths and widths
related to selected machining parameters (speed, feed and surface pressure) along with selection of
honing tool composition of grain size, grain material (diamond or SiC), binding material and grain
density [5].
Fig. 20. Parameters for a honed surface
The basic prerequisite for a functioning cylinder bore tribological system is a hydrodynamic
lubrication film covering as large area of the stroke as possible. Piston and ring related conditions
20
(ring groove geometry, ring tension and geometry etc), the cylinder surface and the lubrication itself
are also contributing factors. The lubrication film properties are largely a result of the surface
topography provided by the honing process fig. 12.
The influence of the topography of the liner surfaces has been reported by Blunt et. Al. [3], Robota
and Schwein [4] and others. Several engine tests have shown a decrease in oil consumption when
using honed cylinder liner surfaces with a lower Rk value.
Rk=1.1um
Rk=0.7um
Rk=0.3um
Oil Consumption
200
150
100
50
0
1.1
0.7
0.45
0.3
0.25
Rk
Fig. 21. Engine tests have shown a reduction in oil consumption when introducing liners with a lower Rk value [2]
One approach to produce smoother liner surface with low Rk value is to replace SiC ceramic honing
stones with diamond tools.
The term –Gleithonung [4] has been introduced, for liners characterised by plateaux with an
amplitude range less than a third of the traditionally plateau honed liners, which in turn typically had
plateaux with half the amplitude range compared to the liners not subjected to the plateau honing.
The Gleithonung is based on traditional honing procedures and Diamond abrasive tools.
However, event though the diamond honing process results in higher productivity, improved
demands of quality control is needed for the honing process, parameters as for example the
degree of cold worked material - “blechmantel” (German) (fig. 14), and the resulting risk of
increased wear and scuffing. Table 1 describes other possible effects/defects and their major
causes from the honing process [10].
21
DEFAULT
Wide, deep cross
hatch grooves
EFFECT ON ENGINE
PERFORMANCE
Causes abnormal wear,
excessive oil consumption
COMMON MAJOR CAUSES
Stone grit too coarse, poor stone breakdown, coolant
viscosity too high, excessive stone pressure
Cross hatch grooves
irregularly spaced
Poor oil distribution
Stone grade too hard, stone grit too coarse, poor stone
breakdown
Cross hatch grooves
fragmented
Slows ring, causes scratching
and high wear, lowers life and
oil economy, raises ring
temperature, causes excessive
variation engine to engine
Insufficient dwell strokes at end of honing cut, stone
grit too coarse
One directional cut
cross hatch
Causes ring rotation, rapid wear
Excessive play in hone components, such as joints, or
stone holder to body clearance
Poor oil distribution, high impact
Low cross hatch angle forces on rings, excessive wear,
shortens life
Slows ring, causes scratching
and high wear, lowers life and
Particles embedded in
oil economy, raises ring
surface
temperature, causes excessive
variation engine to engine
Blechmantel
Particles in oil and fuel
Tool kinematics
Poor stone breakdown and cutting action, low coolant
volume
Diamond honing, poor stone breakdown
Table 1. Examples of defects and major causes in the honing process [10].
Fig.22. SEM pictures of two cylinder liner surfaces with different degree of folded material, so called “blechmantel”.
However, the amount of acceptable blechmantel is unknown. A comprehensive method to
judge the degree of blechmantel is described in the GOETZE Honing Guide [6], and is based
on roughness profile parameters, image analysis of SEM images of gold coated acetate
replicas of cylinder liners, -faxfilm, and metallographic sections of the liner surface. SEM
images are here visually compared with reference images. 2D profiles are evaluated manually
or with roughness parameters and a rating, 0-10 (10 is excellent) is estimated depending on
the weighting of five (5) non profiling properties (honing angle, orientation of grooves,
plateau formation, groove appearance, macro waviness) and five (5) profiling properties
(groove width (a), groove distance (d), grove height (C), bearing area at 2um (tp2), and micro
waviness (Wt)) of the surface to an overall mean rating.
22
Beyer, Krahe and Leon [7] introduced an automated inspection method based on image
analysis of SEM images. The honing structure where separated in background and honing
groove structure using the Fast Fourier Transform FFT. The FFT and Radon transforms
where then used to quantify background (holes, smearing, flakes) and groove features (groove
interrupts, stray grooves, groove balance, groove shape, turning- and chatter marks).
Additional profilometric quality criteria based on the ISO Ra, Rz, and Rmax as well as the
Abbot curve (ISO 13565-2) where also proposed as a complement to the SEM analysis.
Several engine manufacturers has developed different methods based on the manual SEM
analysis of the honing structures.
23
4
Results
4.1
Quantification of the eight tested cylinder liners
Table 2 below display image-, peak- and valley-, ampliude-, and “other”- roughness parameters for
worn and unworn diesel (high pressure) and petrol (low pressure) at two initial roughnesses (rough
and smooth). The roughness parameters have been divided into type of parameters (amplitude,
lateral) and class of parameters (peak, core and valley) to simplify the interpretation of the
measurements by grouping into logical families.
Table 2
parameter
angle
orientation
balance
stray ratio
holes ratio
"
blech ratio
"
irregularities
ratio
"
groove
interrupt
"
I
M
A
G
E
A
N
A
L
Y
S
I
S
P
E
A
K
a
n
d
V
A
L
L
E
Y
A
M
P
L
I
P
A
R
A
M
E
T
E
R
S
T
U
D
E
O
T
H
E
R
magn.
200X
200X
200X
200X
200X
500X
200X
500X
200X
unit
deg.
pixels
‰
‰
‰
no. of
pixels
Rpk
Rmr1
Rp
Rhsc(c=0.3um)
Rk
Rvk
Rmr2
Rv
Rvc(c=-1um)
Rt
Rz
µm
%
µm
no.
µm
µm
%
µm
no.
µm
µm
type of
parameter
amplitude
lateral
amplitude
lateral
amplitude
amplitude
lateral
amplitude
lateral
amplitude
amplitude
Ra
Rmr (5%, 1um)
a (width)
µm
%
µm
µm
µm
no.
µm
amplitude
lateral
lateral
lateral
amplitude
lateral
amplitude
d (distance)
C (depth)
ng (no. of)
Wt
DIESEL
Rough
Smooth
worn
worn
unworn
unworn
128,8
N/A
137,8
N/A
0,3
N/A
0,6
N/A
79,1
N/A
38
N/A
0,1
N/A
0,1
N/A
30
17
6
4
36
13
17
21
21
8
27
7
64
5
34
9
23
5
15
9
PETROL
Rough
Smooth
worn
unworn worn
unworn
133
133
133,3
135,3
0,3
0,6
0,5
0,6
71,9
46,5
36,7
37,6
0,8
0,2
0,3
0,1
8
N/A
11
13
12
N/A
18
19
3
16
14
7
17
35
28
37
8
23
10
17
500X
200X
20
3160
3
N/A
12
2944
6
N/A
17
3515
20
3162
10
3283
19
3312
500X
2633
N/A
2779
N/A
2988
2890
3022
3104
class of
parameter
peak
peak
peak
peak
core
valley
valley
valley
valley
extreme
extreme
0,44
7
2,19
128,4
1,47
1,71
80
6,61
35,8
8,80
7,05
0,21
14
0,56
19,2
0,33
1,60
84
5,31
16,0
5,88
4,82
0,33
10
1,38
73,8
0,90
1,66
82
5,96
25,9
7,34
5,93
0,14
10
0,63
21,0
0,32
1,33
81
4,30
18,0
4,94
4,45
0,33
7
1,80
160,0
1,30
1,55
80
5,43
44,0
7,23
6,28
0,25
8
1,22
116,0
0,66
1,66
75
5,65
32,4
6,86
5,58
0,26
7
0,94
131,6
0,51
1,39
68
3,79
37,6
4,73
4,03
0,14
8
0,76
63,4
0,41
1,16
74
4,24
30,4
5,00
4,03
mean
valley
valley
valley
valley
valley
extreme
0,64
60
44,92
167,18
2,36
28,4
0,04
0,28
92
51,41
283,10
2,15
14,8
0,03
0,46
76
48,16
225,14
2,25
21,6
0,04
0,27
93
42,13
271,29
2,14
16,2
0,03
0,57
67
34,84
136,35
2,11
35,6
0,03
0,47
83
31,88
171,50
2,28
27,8
0,03
0,45
83
31,30
147,41
1,83
33,0
0,02
0,33
90
27,98
173,67
1,70
27,6
0,02
Table 2. For 500X of magnification, blechmantel and irregularities have good accuracy with a reasonable dispersion.
4.2
Parameter correlation
High regression coefficients, R, between parameters (R= 0.87, R2=0.72 and higher) indicate that
parameters either are measure of the same property or that they are changing in similar ways as in
this study, roughness level, operating pressure and unworn- or worn status change. A linear
correlation of the two image analysis parameters blechmantel ratio and irregularities reveal a
relatively low correlation to the different roughness parameters (table. 1).
For the image parameters the maximum regression coefficient of 76% (R2=0.58) indicate a strong
separate description of features not measured by the other profile characterizing parameters. I.e.
image parameter are essential to describe lateral features not possible to measure with the stylus
technique.
24
Table 3
IMAGE
blech ratio
irregularities
ratio
Rpk
Rmr1
Rp
Rhsc
CORE
Rk
Rvk
VALLEY
Rmr2
Rv
Rvc
EXTREME-MEAN
Rt
Rz
Ra
Tpa
GOETZE
a
d
C
ng
Wt
PEAK
IMAGE
blech
ratio
100%
76%
62%
-56%
68%
49%
60%
27%
-26%
49%
47%
60%
50%
69%
-64%
-16%
-55%
20%
43%
33%
PEAK
irregularities
ratio
76%
100%
42%
-74%
66%
68%
60%
12%
-34%
38%
72%
51%
47%
68%
-58%
-55%
-78%
6%
70%
9%
CORE
VALLEY
Rpk
62%
Rmr1
-56%
Rp
68%
Rhsc
49%
Rk
60%
Rvk
Rmr2
Rv
Rvc
EXTREME-MEAN
Rt
Rz
Ra
GOETZE
Tpa
a
d
C
ng
Wt
27%
-26%
49%
47%
60%
50%
69%
-64%
-16%
-55%
20%
43%
33%
42%
100%
-37%
93%
67%
92%
77%
17%
77%
55%
89%
88%
92%
-95%
29%
-44%
60%
43%
68%
-74%
-37%
100%
-57%
-85%
-52%
13%
67%
7%
-90%
-18%
-21%
-68%
56%
73%
93%
21%
-91%
22%
66%
93%
-57%
100%
76%
99%
61%
12%
74%
69%
89%
91%
97%
-99%
6%
-60%
53%
58%
61%
68%
67%
-85%
76%
100%
73%
31%
-46%
25%
97%
47%
50%
88%
-76%
-47%
-93%
7%
94%
3%
60%
92%
-52%
99%
73%
100%
60%
19%
74%
67%
89%
91%
94%
-99%
11%
-55%
51%
55%
62%
12%
77%
13%
61%
31%
60%
100%
47%
87%
10%
83%
81%
58%
-59%
56%
1%
88%
-2%
80%
-34%
17%
67%
12%
-46%
19%
47%
100%
59%
-53%
44%
47%
-10%
-11%
85%
67%
66%
-64%
73%
38%
77%
7%
74%
25%
74%
87%
59%
100%
12%
96%
93%
63%
-69%
53%
-3%
85%
-2%
89%
72%
55%
-90%
69%
97%
67%
10%
-53%
12%
100%
35%
38%
81%
-70%
-60%
-97%
-13%
99%
-12%
51%
89%
-18%
89%
47%
89%
83%
44%
96%
35%
100%
99%
80%
-86%
38%
-26%
78%
22%
84%
47%
88%
-21%
91%
50%
91%
81%
47%
93%
38%
99%
100%
81%
-88%
37%
-26%
79%
24%
84%
68%
92%
-68%
97%
88%
94%
58%
-10%
63%
81%
80%
81%
100%
-96%
-9%
-73%
42%
72%
45%
-58%
-95%
56%
-99%
-76%
-99%
-59%
-11%
-69%
-70%
-86%
-88%
-96%
100%
-10%
59%
-47%
-59%
-58%
-55%
29%
73%
6%
-47%
11%
56%
85%
53%
-60%
38%
37%
-9%
-10%
100%
72%
64%
-70%
73%
-78%
-44%
93%
-60%
-93%
-55%
1%
67%
-3%
-97%
-26%
-26%
-73%
59%
72%
100%
24%
-99%
24%
6%
60%
21%
53%
7%
51%
88%
66%
85%
-13%
78%
79%
42%
-47%
64%
24%
100%
-26%
90%
70%
43%
-91%
58%
94%
55%
-2%
-64%
-2%
99%
22%
24%
72%
-59%
-70%
-99%
-26%
100%
-27%
9%
68%
22%
61%
3%
62%
80%
73%
89%
-12%
84%
84%
45%
-58%
73%
24%
90%
-27%
100%
Table 3. For 500X of magnification, blechmantel and irregularities have good accuracy with a reasonable dispersion
Within the Peak parameter family a relatively strong correlation between the Rpk- and the Rpparameters can be seen (R=0.93). The parameters both express amplitude of the peak portion of the
liner and can be mutually replaced.
Peak parameters Rp and Rpk are highly correlated to the core roughness Rk, (R=0.99 and R=0.93)
while the relation to the valley parameters are weaker as exemplified with an average regression
coefficient of R=0.50 for the eight peak and valley parameters.
The core parameter Rk have not only the strong relation to the peak parameters as mentioned
above but also a non existent or weak relation to valley parameters. The stronger correlation to peak
parts of the cylinder liner is complemented with an R=0.99 to the bearing parameter Rmr (1um, 5%)
as well as the strong correlation to average amplitude parameter Ra (R=0.94) and the extreme
amplitude parameters Rt and Rz (R=0.89 and R=0.91).
Valley parameters Rv and Rvk are very much stating the same fact about the surface profile and
have an R of 0.87 and a high correlation to Rt and Rz (R=0.96, R=0.93) for the Rv parameter but a
low correlation to the peak parameters, constituting a separation of the valley and peak performance
under the conditions tested in this study.
The average- and extreme ISO amplitude parameters show a high correlation to parameters from
all the peak-, core- and valley parameter groups. The broad correlation spectra between the average
and extreme amplitude parameters indicate the use of more specialized peak-, core-, and valley
descriptors like the parameters in this study to complete the picture of the cylinder liner surface
before- and after usage.
The non-standardised valley- (a, d, C, and ng), as well as Rmr and Wt-parameters show a high
coorelation (R=0.99) between the number of grooves, ng- and distance between grooves, d- and
R=0.90 for the Waviness, Wt, to groove depth, C-parameters. Naturally the non-standardised valley
parameters correlate best with the standard valley parameters.
The bearing parameter Rmr at 5% reference and at 1um depth show R=0.95 and R=0.99 for the
peak amplitude parameters Rpk and Rp, indicating this parameters possibility to be an alternative to
the two.
25
Topography transition from unworn to worn state
Peaks are the together with the core portion of the surface naturally the part of the cylinder liner who
immediately will be “hit” by the piston-ring and oil dynamic effect and modified by tribochemical
reactions.
The SEM-Image and stylus topography analysis verify the qualitative assumptions above but in
addition a quantitative measure and segmentation of the wear state can be made with relation to the
operating conditions like different combustion pressure (high pressure-diesel engine and lower
pressure-petrol engine), and initial roughness levels (rough and smooth).
Peaks are defined by Rpk (reduced peak height) and Rhsc (high spot count). Rhsc is generally
higher in this test for the petrol liners (132 and 63 for the rough- and smooth worn petrol engines)
than for the high pressure diesel liners (19 and 21). In other words, an average of diesel liner
decrease for rough and smooth liners’ Rhsc with 410% compared with 73% for the petrol liner.
Core roughness, Rk, in average, decrease more for diesel liners than for petrol liners. In average
(rough and smooth liners) the diesel core roughness decrease 265% while the petrol liners average
on a 60% decrease. Notable is that, rougher surfaces decrease Rk more than smoother surfaces but
the low pressure petrol liner stay at Rk=0.66um and Rk=0.41um for the rough- and smooth textures
while high pressure rough and smooth diesel liners smoothens down to a similar level of Rk=0.33um
and 0.31um. The higher petrol liner Rk in the end of the test either indicate a non-finished run-in
state or a combustion pressure and piston-ring material unable to decrease the plateau roughness
values at the diesel liner finishing Rk-levels.
Fig 23. Rk values before and after testing.
The valley roughness characterized by the C-parameter (valley depth) and Rvk, remain
approximately on the same level for all liners (10% and lower increase of the C-parameter and a 7%
to 25% decrease for the Rvk parameter. The most significant change is the number of grooves –ng
and corresponding valley count parameter –Rvc who both decrease significant (-92% and -124%
respectively).
For valley characterization, the non-standardised valley parameters follow the standardized ones
but in return deliver more detailed data about mean valley width (a), distance (d), number (ng) and
depth (C).
26
The Ra-parameter is sensitive only to the big changes of peak- and valley amplitudes for the high
pressure diesel liners (129% for the rough liner and 71% for the smooth liner). Decrease of Ra
values are much smaller for the petrol liners (21% for the rough liner and 36% for the smooth liner)
and further more, no distinction between core, valley and peak changes can be determined using the
Ra-parameter.
The extreme amplitude parameters Rt and Rz show the same behavior as the Ra-parameter and
again the parameters average out peak-, core- and valley amplitude changes and correlate highly
(table 444) to peak-(Rpk), core-(Rk) and valley-(Rvk) parameters.
4.3
Results from analysis of SEM pictures
Image parameters Blechmantel- and Irregularities ratio show a high sensitivity to varying
conditions and decrease 1180% to 100% for the diesel liners while the parameters increase between
106% to 18% for all the petrol liners. A probable cause is the more severe diesel high pressure runin conditions able to effectively “truncate” the plateaux and remove residing plastically deformed
un-cut honing residues while the less severe petrol liner conditions not manage to remove the
blechmantel and irregularities in an important extent.
blechmantel (‰)
70
60
50
40
smooth
rough
rough
30
20
smooth
10
unworn
0
diesel
worn
diesel
petrol
petrol
Fig.24. Changes in blechmantel ratio for the different test combinations.
27
4.4
Friction and wear results
The results from the SEM image analysis og blechmantel ratio is supported by the results of
the wear measurements of the tested liners. The tests with diesel engine conditions (higher
pressure) show larger wear volumes compared to the petrol engine conditions. The slope of
the wear curves reveals that rougher diesel surface shows a better run in process than the
smoother surface. The slope of the wear graph indicates if the wear has reached a steady state
or not. The same statement is valid for the petrol surfaces, figure 25.
Cylinder liner wear
0,12
volyme mm3
0,1
0,08
Rough diesel
Smooth diesel
Rough petrol
Smooth petrol
0,06
0,04
0,02
0
0
180
960
time [s]
Fig.25. Wear of the rough and smooth diesel liner is larger. The rough surfaces seems to perform a better run in process.
The smooth surfaces show a larger wear volume.
Fig. 26. Friction traces at different times through a complete cycle. The left picture shows friction for the petrol settings and
the right on shows diesel settings.
28
The lower coefficient of friction for the diesel liners implies a better run-in process compared
to the petrol liners, fig.26 and fig. 27. Worth noticing is that the coefficient of friction for the
rough liners are lower than for the smooth liners, opposite what engine tests have shown. This
is probably due to the fact that the rig testing is only simulating the turning positions (TDC
and BDC) of the piston where the lubrication regime is boundary. Surface topography has
little or no influence in boundary lubrication regime.
Friction coefficient
0,16
0,14
0,12
u
0,1
Rough diesel
Smooth diesel
Rough petrol
Smooth petrol
0,08
0,06
0,04
0,02
95
0
90
0
85
0
80
0
75
0
70
0
65
0
60
0
55
0
50
0
45
0
40
0
35
0
30
0
25
0
20
0
15
0
10
0
0
50
0
time [s]
Fig.27. Mean friction for the petrol and diesel settings during the rig test. Diesel show a lower coefficient of friction.
29
5
Conclusions
SEM quantitative image analysis can be used for groove and background separation of honed
structures.
The Hough transform is useful for groove analysis (orientation, balance, interrupts)
Two-dimensional profilometry give additional information of grove vertical- and horizontal
measures.
The profilometrical parameters give detailed information of the vertical peak-, core- and valley
regions, separately or as average.
Individual groove information regarding width, distance, number and depth are special groove
features possible to measure.
The parameters used, monitor the wear as a peak and core profile phenomena and valley regions are
left relatively intact.
Profiling Rpk,Rk, Rvk, and C parameters together with SEM image analysis parameters
(blechmantel) give information of the development of the vertical peak, core, valley and lateral
properties of a liner surface.
Traditional roughness parameters like Ra, Rt, and Rz indicate change of the liner surface due to wear
but are to related to each other and other parameters to distinguish wear regions and further, the wear
of the low pressure petrol liners
Low pressure petrol liners in this test either still are undergoing run-in wear or the final roughness
will be rougher than the high pressure diesel liners.
The rig testing performed in this study will not reveal whether a high ratio of blechmantel is
affecting function or not. A rig with longer stroke and higher velocities is needed to be able to reach
the mixed and hydrodynamic lubrication regimes.
30
6
Future work
The usage of the latest 3D topography parameters as suggested by Blunt et. al. is currently being
implemented and should be tested as a compliment to the combined SEM- and stylus techniques
suggested in this study.
The number of measurements to achieve significant measuring values need to be improved to ensure
the general application of liner characterisation.
Further test need to be carried out to clear out the last conclusion above, whether the low pressure
liners will stabilise on higher core roughness values (Rk) or not. The Rk believed to control both
friction and oil consumption, hence a parameter important to clarify in this case.
To be able to judge the impact of the honing process on function of the liner ring a more
controlled test procedure is necessary. Variables like valley depth, valley width, distance
between valleys, honing angle and others must be tested in a structured way to be able to
improve knowledge.
Acknowledgements
The author wish to thank the researchers at the Functional Surfaces Research Group at Halmstad
university, especially Professor BG Rosén, Frederic Cabanettes and Zlate Dimkovski, the KKfoundation, and Volvo Powertrain AB as well as Volvo Cars Inc. and Volvo Technology AB for
their kind contribution with money, man hours, liners and rings.
31
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