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NEW MATERIALS IN AUTOMOTIVE TRIBOLOGY

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NEW  MATERIALS  IN AUTOMOTIVE  TRIBOLOGY Powered By Docstoc
					  NEW MATERIALS IN
AUTOMOTIVE TRIBOLOGY




                      Presented by,
               K.Arun (094ED101)
                           ME-ED
              BIT-Sathy, Tamilnadu
                              India
Contents
• Trends of Automotive Tribology
• Materials for automotive tribo-components
     – Cylinder, piston and piston ring
     – Plane bearings
     – Valve trains
• New material processing for tribo-components
• Conclusion
Trends of Automotive Tribology
The main demands for a passenger car are:
• Efficient use of resources (recyclability,
  substitute fuel and fuel economy)
• Environmental protection (fuel economy,
  reduction of emissions of exhaust and toxic or
  polluting substances)
• Customer satisfaction (reliability, fuel economy,
  safety, low maintenance, comfort and low cost)
There are essentially three ways to approach an optimum
 tribological solution lubrication, design and materials
                  (so called LUDEMA)
Materials for automotive tribo-components
Engine group
The engine system is divided into three components:
• A piston component (a cylinder, a piston and a
  piton ring)
• A crank component (a crank shaft, bearings and
  a connecting rod
• A valve-train component (a cam, a shim, a valve,
  a valve sheet and a valve guide)
Cylinder, piston and piston ring
• In order to improve fuel economy, reduction of the
  weight of any components and of the friction loss of
  tribo-components is important, they are closely related
  to the design of the engine system
• Engine cylinder block made of cast iron is the heaviest
  unit, and largest friction loss occurs in the engine
• An aluminum-alloy (Al–Si–Cu) engine block with an
  insert of cast iron cylinder liner
• Achieving a 30% weight reduction
• Wear-resistant overlays or surface modifications on the
  inner face of the aluminum alloy have also to be developed,
  where SiC dispersed Ni–P plating, plasma spray coating of
  hard ferrous or nonferrous alloys, etc
• Surface modifications and coatings are applied on the
  piston crown and piston ring groove made of aluminum
  alloy
• Thermal-resistant coating is required on the crown part of
  the piston
• Wear resistance is required for the piston ring groove,
  where typical surface treatments are anodic oxidizing and
  electroplating with Ni or Cr
• The friction coefficient of the newly developed coating
  on the engine skirt was 0.035 in an engine bench test,
  which was 20% smaller than that of conventional resin
  bonded coatings
• Recently, a Cr–N ion plated stainless steel ring, prepared
  by an arc-ion plating method, has been developed
  (thickness is 50 m)
• Application of the Cr–N ion-plating resulted in a 90%
  reduction of the top ring wear and about 15% reduction
  of the cylinder bore wear compared to a conventional Cr
  plated ring
 Plane bearings
• Recent trends towards higher power efficiency of
  engines with multiple valves, turbo-charger systems,
  direct injection of fuel, etc..
• Mean that bearings must have a higher load-carrying
  capacity and better anti-seizure performance
• In a conventional bearing, tribological problems occur
  in that frictional heat raises the temperature of the
  lubricating oil, reducing oil thickness
• As a result, the bearing surface sometimes melts
• The tribo-materials used for crankshaft bearings require
  high performance in terms of running-in, wear resistance
  and embeddability of foreign particles
• A conventional bearing is typically composed of a top layer
  of Pb–Sn–In or Pb–Sn–Cu plating of thickness 10–25 m
• A second layer of Cu–Pb Kelmet alloy or Al–Sn alloy 200–
  300 m thick and a cold-rolled steel sheet as the backing
  metal
• An Ni barrier plating of 1–3 m thick is made between top
  plating layer and a second Kermet layer to prevent thermal
  diffusion of Pb from the second to top layer
• Electro-deposition method could be applied to the bearing
  overlay
• Crystallographically-oriented Pb alloy electro-deposit
  having the plane on the bearing exhibited good wettability
  for lubricating oil
• The anti-seizure parameter of PV value of the oriented
  deposit on the bearing was improved by as much as 30%
  compared with that of a conventional deposit
• A bearing having a micro-groove depth of 4–4.5 m and
  pitch of 0.2–0.25 mm at the surface has been developed
  and its running-in performance were improved
Valve trains
• Valve-train friction accounts for approximately 30% of all
  engine friction
• Valve-train components are operated under cyclic loading
  and exposure to high temperature exhaust of about 900 C
• Heat-resistant materials are required for the valve-train
  components
• A conventional valve is made of heat-resistant steel on
  which Co or Ni based alloys are deposited on the valve
  face for wear resistance
• High wear resistance and low abrasion effect against the
  valve are required for the valve sheet material
• The exhaust valve is subjected to severe thermal effects,
  the valve sheet material should have a high thermal
  diffusivity
• An inserted ring, however, has a problem of lower
  thermal diffusivity
• To overcome this problem, laser-cladding of Cu–Ni–Si
  alloy directly fabricated on an aluminum alloy cylinder
  has been utilized in practice
• A ferrous alloy ring, electroplated with Cu, Zn or Sn of
  2 m thick, was bonded well on the aluminum alloy by
  means of an electric resistant-bonding method
New material processing for tribo-components

• Various types of surface modifications and coatings
  have been utilized for a variety of tribo-components
  in automobiles to improve the friction and wear
  properties
• The hardness of modifications and coatings against
  process temperature
• Laser hardening and cladding have been utilized,
  because localized modifications can be made on a
  desired part of the component
• Further development of laser technologies is desired
  to create high performance tribo-materials
• A promising technique is a combination of laser with
  low-pressure plasma spraying (LPPS)
• Laser plasma hybrid spraying (LPHS) has the
  potential to create metallic alloy coatings having a
  fine-grained structure and also coatings having
  mixed-metal phases
• The LPHS coatings of Mo–Cu showed better
  tribological performance than the LPPS coating
• Physical vapor deposition (PVD) was successfully
  developed to form metallic compound films, such as
  TiN and CrN for practical tribo-applications
• Diamond and diamond-like films produced by PVD
  or chemical vapor deposition (CVD) may also be
  applied to sliding parts such as a valve-train
  components
• Because they show a lower friction coefficient of
  0.05–0.1 without lubricants
Conclusion
• Mass-produced automobiles have to be optimized by
  considering the best balance between automotive
  technologies and the environments and resources
• Most of materials used can be recycled and working to
  replace the petroleum fuel engine with other types of
  engine based on new energy sources such as bio-mass
  based fuel, electric, hydrogen and others
• The respective technologies require new design of the
  system, in which tribo-components must operate well
  under more severe conditions

				
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posted:12/28/2010
language:English
pages:17