Materials and technologies for automotive engines

Material and technology
for Automotive engine:
brief overview

o The camshaft

o The crankshaft

Materials and technology for automotive engine

Catania, 06/07/2012, A.Manicone

The camshaft



The camshaft - 1

The valve operating mechanism
transforms rotation of the
crankshaft into reciprocating
motion in the valves.

The valves protrude into
the combustion chamber and
are pushed back by the reactive
force of the valve spring.

Ωcamshaft= Ωcrankshaft/2

- Ωcamshaft high: contact pressure is reduced by the inertia of the valve lifter (oil is
providing hydrodynamic lubrication);
- Ωcamshaft low: contact pressure is highest and lubrication most challenging.



The camshaft - 2
Machining, dimension
accuracy, clearance, rou
Wear of sliding portion
ghness Friction condition 1. Rugged surface due to wear
1. Lubrication
2. Contact 2. Adhesive wear
Lubricating oil 3. Foreign object 3. Fatigue wear
condition 4. Corrosive wear

Flaking (scagliatura)

Pitting (corrosione per vaiolatura)

• It is very important to choose an appropriate combination of materials.

• The torque from the crankshaft drives the camshaft: it must have high torsional rigidity.


The camshaft - 3

Chill hardening cannot be used where the gap between the cam lobes is narrow because
of the difficulty in using the chiller, so forged camshafts are used.

Tough martensite is more resistant to pitting than the chill microstructure.



The camshaft - 4
• Finishing – boring and grinding

• ASSEMBLING
• E.g.: Hydroforming



The crankshaft



The crankshaft - 1
The crankshaft converts reciprocative motion to rotational motion.

Two types:
• the monolithic type
• the assembled type



The crankshaft - 2

Note:
Included lead or MnS
Carbon steel particles significantly
function as a chip
breaker and a solid
Alloyed steel lubricant and increase
machinability.
Micro Alloyed steel

Typical materials • less expensive
• nodular cast iron: for high-
volume, low-load production. • lower rigidity: abnormal vibrations (resonance)

• increases in rigidity of more than 10%
• reduces noise levels and harshness
• forged steel: for fuel-efficient • makes possible a careful design
engines requiring a high power-to-
displacement ratio. • more expensive



The crankshaft - 3
• Static: combustion pressure, inertial
forces of the piston and con-
rod, bearing load and drive torque.
STRESS on
Crankshaft • Dynamic: The vibration causes
dynamic stress. If it occurs at the
resonating frequency, the deformation Fatigue fracture of a carbon steel
will be very high and will instantly S50C crankshaft

rupture the crankshaft.

HIGH STATIC AND DYNAMIC RIGIDITY:

- increasing the crankpin diameter (increasing weight)

- using forged steel

- Surface-hardening methods



Fatigue behaviour: principles and survey

Principi (macro)
σa Wöhler [1860]
Ampiezza
tensione
applicata
Vita finita * Legge di Basquin:
σa = σf’ (2Nf)b
*
Tipici
Curva tipica
acciai
per acciai
σL
Leghe di
alluminio
Vita infinita

104 105 106 107

Cicli alla rottura, Nf
Dipende da:
•Tipo di materiale • Concentrazione di • Contenuto di inclusioni e
tensioni impurezze
• Trattamento termico • Tensione media e
superficiale tipo di sollecitazione


The crankshaft - 4
HOT FORGING PROCESS (for a four-stroke crankshaft)

• The coarse structure is broke down and is
replaced, as recrystallisation proceeds, by one
which is of relatively fine grain

• Impuritires are redistribuited in a fibrous form

• Introduction of compressive residual stresses



The crankshaft - 5
SURFACE HARDENING
(carburizing, nitring, carbonitring and nitrocarburizing):
• CARBURIZING
O: origins

S: a few beachmarks

B: arrest lines

R: ratchet marks

Pitting observed at a crankpin surface



The crankshaft - 6
SURFACE HARDENING
• CARBURIZING

Compressive residual stress
generated by carburizing


The crankshaft - 7
Modern carburizing technology: Acetylene Vacuum Carburizing- AvaC

Steel

Fe
Acetilene Siti di adsorbimento
Cr
C H2
Mn

A. Manicone Catania, 06/07/2012, A.Manicone

The crankshaft - 7
Avac - Adsorbimento (T>Taustenitizzazione)

Steel

Fe
Cr
C H2
Mn


The crankshaft - 7
Avac - Decomposizione in radicali

Steel

Fe
Cr
C H2
Mn


The crankshaft - 7
Avac - Inizio cementazione (T>Taustenitizzazione)

Steel

Fe
Cr
C H2
Mn


The crankshaft - 7
Diffusione nell‘acciaio (T>Taustenitizzazione)

Steel

Fe
Cr
C H2
Mn


The crankshaft - 7
Saturazione

Steel

Fe
Cr
C H2
Mn


The crankshaft - 7
SURFACE HARDENING
• NITRING: NH3

decomposes at the steel surface to catalytically generate elemental nitrogen, which
diffuses into the material. The nitrogen expands the iron lattice and also forms hard
compounds (the nitrides Fe4N and Fe3N) with iron atoms.
Nitridable steel reaches the necessary hardness by forming stable nitrides (Al, Cr, V…)

• NITROCARBURIZING, CARBONITRURING

• higher hardness surface,
• but lower toughness

• INDUCTION HARDENING



The crankshaft - 8
RECENT TRENDS: Micro alloyed steel, via plasma ion nitring

Precipitation hardening is the main method for increasing strength at the
cooling stage after hot forging.

Micro-alloyed steel contains a small amount of V, which dissolves in the
matrix during hot forging above 1,200 °C. During air cooling, the dissolved V
combines with carbon and nitrogen to precipitate as vanadium carbide and
nitride at around 900 °C.

the vanadium
carbide and nitride will
be more finely
dispersed.



The crankshaft - 9
Manufacturing process

• Trade-off:
machinability-fatigue
resistance

• Surface roughness

For low and medium loaded bearings: Ra = 15
microinch max. Rz = 60 microinch max.

For highly loaded bearings: Ra = 10 microinch
max. Rz = 30 microinch max.



The crankshaft - 10
Conclusions: Methods to strengthen crankshafts



Material and technology
for Automotive engine:
brief overview

Thanks for
attention



Materials and technologies for automotive engines

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