Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
1. Combustion engines main principles and definitions
2. Reciprocating combustion engines architecture
3. Reciprocating engines dynamic properties
4. Engine components and systems
5. The engine management system for gasoline and Diesel engines
6. The emission Requirements & Technology
7. Engine vehicle integration
7.1 Engine layout and mounting
7.2 Engine-vehicle cooling system
7.3 Intake system
7.4 Exhaust system
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 2
Crankcase
Cylinder head
Crankshaft
Camshaft
Connecting rod (con-rod)
Engine piston
Engine systems
Engine-vehicle systems
Main engine components and systems
The FIVE “C”
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 3
1. The block-crankcase
2. The cylinder head
3. The crankshaft
4. The connecting rod
5. The engine piston
6. The valve train
Engine components and systems
John Heywood, Internal Combustion Engine Fundamentals / McGraw-Hill
Charles F. Taylor, The internal Combustion Engine in Theory and Practice /The M.I.T. Press
Automotive Handbook – R. Bosch/SAE
Advanced engine technology (Heinz Heisler) – Butterworth/Heinemann
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 4
To support the force-transfer mechanism between
the cylinder head and the crankshaft assembly
To bear the crankshaft assembly’s support
bearings
To incorporate the cylinder sleeves
To include separate water jackets and sealed oil
chamber and galleries
To serve as a mounting and support surface for
most of the engine’s auxiliary devices
Blow-by channels
Oil draining
Crankshaft axial thrust bearing
The block-crankcase - Function and components
Bottom view
Side view
Top view
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 5
For an increased stiffness, the crankcase is
generally extended to below the crankshaft’s
axis center trough an extension of the block
itself (deep skirt) or through a separate
structure (bedplate) integrating the main
bearing caps
The block-crankcase - Function and components
Bedplate
Deep skirt
Single caps
Bottom view Top view
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 6
Piston cylinders may be:
Machined from the block casting
with special surface treatment for higher
wear resistance
Separate wet or dry liners, generally
cast iron (aluminum only for niche sport
applications); dry liners are generally
cast-in the cast iron blocks or forced
after a pre-machined cylinder
The cylinder blocks are manufactured by:
grey cast iron, very popular for past
and truck-Diesel engines
aluminum high-pressure die-casting
that is becoming a widely used technique
for passenger car blocks , also of Diesel
engines, because of its weight saving
potential
Machined liner
Separate liner
The block-crankcase - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 7
Cylinder top view
Cylinder bottom view
Cast iron liner top
Cast iron liner bottom
Cast-in iron liners into a light alloy block
The block-crankcase - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 8
Cylinder block construction takes two forms. Closed-deck construction (Figure slide
10) represents long-established practice and resembles a deep box-like enclosure for the
cylinder barrels that also serves as a coolant jacket . Transfer ducts are provided in the
top face or closed deck of the cylinder block, so as to permit the circulation of coolant to
the cylinder head.
With the open-deck construction (Figure slide 9) the cylinder barrels are free-standing
in that they are attached only to the lower deck of the cylinder block, which in past
applications utilized detachable cylinder liners that tended to result in a less rigid
construction. By dispensing with a continuous top face, the open-deck construction
nevertheless reduces the complexity of the cylinder block casting. Where gravity sand
casting is used it facilitates the coring for the mould into which the metal is poured.
However, the increasing preference for using aluminum alloy, rather than grey cast iron,
for the cylinder block and crankcase of modern lighter weight engines, has led to their
manufacture by high-pressure die casting in the interests of economical mass
production. Since this method of casting necessarily involves the use of steel
instead of sand moulds, the need for an open-deck construction to allow
withdrawal of the steel cores becomes mandatory. Also, the liners may be cast
directly into the cylinder block to restore structural rigidity. An open-deck construction
further allows inspection of the coolant jacket for accumulated deposits. To perform this
operation in a closed-deck cylinder block requires the addition of detachable cover
plates.
Cylinder block construction
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 9
Aluminum high pressure die-casting open deck block
Open deck
The block-crankcase - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 10
Cast-aluminum closed deck for high
performance application (Pmax>160 bar)
Aluminum bedplate
Cast iron liners casted-in to the
block
The cylinder head bolts oppose the
gas forces to facilitate a force transfer of
maximum linearity and minimal flexural
tendency through transverse support
walls and to the main bearings.
Closed deck
The block-crankcase - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 11
1
2
2
3
4
Block general load path
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 12
Cylinder liner temperature profile
The block-crankcase - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 13
The block-crankcase - Function and components
Liner deformation due to the
cylinder-head bolt tightening
Horizontal
section
Vertical
section
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 14
Pmax+3sP =160+3x160x(2.6/100)=173 bar
4th order less than 5mm with
thin wall liner
It includes compression ratio, VGT actuator,injector and
injection timing dispersion and combustion irregularity
The block-crankcase - Function and components
Liner deformation due to the
cylinder-head bolt tightening
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 15
Lower block side-bedpalte loads (V6 Diesel engine)
The block-crankcase - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 16
To seal the upper end of the blocks and of
the cylinders
To define the combustion chamber shape
together with the piston top surface
To house the gas exchange valves as well all
the intake and exhaust ducts
To house the spark plugs, injectors and
heating plugs
In most of the designs, to include also the
valve gear, as camshafts, drive gears, etc
The cylinder head - Function and components
Gasoline engine cylinder head
Diesel engine cylinder head
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 17
In truck and large industrial engines, individual
cylinder heads are often used on each cylinder for
better sealing force distribution and easier
maintenance and repair.
Separate cylinder head design is required for
improved cooling efficiency of air-cooled engines.
One cylinder head for all cylinders is generally
employed for passenger car engines
The cylinder head of industrial and truck large
water-cooled Diesel engines are made of gray cast
iron or of vermicular castings for more severe
applications (higher combustion pressure)
Aluminum material (AlSi9Mg) is widely used for
the cylinder heads of gasoline and Diesel engines
because of superior heat dissipation and lower
weight (tensile strength 250-300N/mm2, hardness
90-120 HB, elongation 3-5%). The greater heat
conductivity of aluminum alloy is beneficial in
maintaining a more uniform temperature throughout
the cylinder head.
The cylinder head - Function and components
Gasoline engine vertical cross section
Diesel engine vertical
cross section
Diesel engine horizontal
cross section
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 18
4 Cyl 16v Diesel engine cyl head
Inlet manifold bottom
part Swirl duct
Inlet manifold bottom
part Straight duct
Intake side view
Exhaust side view
The cylinder head - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 19
Swirl duct
inlet valve
Straight duct
inlet valve
Exhaust valve
Pre-heating
plug
4 Cyl 16v Diesel engine cylinder head
Bottom view
The cylinder head - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 20
Blind cam
bearings
machining4 Cyl 16v Diesel engine cyl head – Cam carrier
Bottom view
Top view
The cylinder head - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 21
Lubrication partial grooves feeded
from the hole on camshaft (the hole
position is in between the couple of
grooves)
No dowels to
center the cap
4 Cyl 16v Diesel engine cyl head – Camshaft bearing cap
The cylinder head - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 22
Pre-chamber undirect injection engine
INIETTORE
CANDELETTA DI
PRERISCALDO
PRECAMERA
CAMERA DI
COMBUSTIONE
Direct injection engine
ELETTROINIETTORE
CANDELETTA DI
PRERISCALDO
CAMERA DI COMBUSTIONE
Diesel engine cyl head cross section view
The cylinder head - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 23
Mercedes V6/90° 2.8l Diesel
The cylinder head - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 24
In the internal combustion a head gasket is necessary
between the engine block and cylinder head. The purpose is to
seal the cylinders to ensure maximum compression and to avoid
leakage of coolant or engine oil into the cylinders
The cylinder head gasket is the most sealing critical
application in any engine and shares the same strength severe
requirements of the other combustion chamber components.
Particularly it must guarantee adequate resistance to high
temperatures and pressures , to gas/water/oil corrosion and to
provide the elasticity necessary for compensating the thermal
expansion generated by the cyclic combustion in to the cylinders
Since mid 90’ years, because of increased cylinder pressure
(over 140bar in the CR Diesel engines) and of environment
reasons, most modern head engines are produced with Multi
Layer Steel gaskets: these typically consist of a number of
steel layers up to four, depending on the working maximum
cylinder pressure. The contact faces are usually coated with a
rubber-like coating such as Viton that adheres to the cylinder
block and cylinder head respectively whilst the thicker center
layer is bare.
The cylinder head - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 25
Thermal analysis
Temperature distribution
Strengths analysis
Interference force distribution
The cylinder head - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 26
The cylinder head - Function and components
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 27
The crankshaft - Function and components
To convert the reciprocating motion of the
piston, conveyed to it by the connecting rod and the
crank throws or pins, into rotary motion delivering
effective torque at the end of the crankshaft itself
To support the force system characterized by a
highly variable periodicity that generates a complex
stress pattern
To interface the bearing system: main and rod
journals.
To drive the auxiliary devices
To seal the block-crankcase at its ends
To supply engine speed and crank angle position
by proper sensors installed on the crankshaft
To connect the flywheel and the clutch
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 28
The crankshaft - Function and components
Engine balance - It is necessary to provide counterweights for the reciprocating
mass of each piston and connecting rod, which are typically cast or forged as part of the
crankshaft but, occasionally, are bolt-on pieces. While counter weights add a considerable
amount of weight to the crankshaft it provides a smoother running engine and allows
higher RPMs to be reached.
The number of crankshaft bearings is primarily determined by the overall load and
by the engine speed. High loads generally require to incorporate a main journal bearing
between each crankshaft throw and at each end
The fatigue strength of crankshafts - It is usually increased by using a radius at the
ends of each main and crankpin bearing. The radius itself reduces the stress in these
critical areas and frequently the radii are rolled to leave some compressive residual
stress in the surface which prevents cracks from forming.
Crankshaft vibration – Flexural vibration is not a critical factor for engine of 3
cylinders or more, while the rotational oscillation of the vibrating system formed by
crankshaft, connecting rods and pistons become increasingly critical with higher number
of cylinders. Vibration dampers are required to reduce the crankshaft torsional vibrations
to acceptable levels and it serves as a pulley for drive belts. The damper is composed of
two elements: a mass and an energy dissipating element: the mass resists the
acceleration of the vibration and the energy dissipating (rubber/clutch/fluid) element
absorbs the vibrations.
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 29
Overlap between main journal and crankpin
2cdD
cR=
The crankshaft - Function and components
The proportions of gasoline engine crankshafts are usually such
that the crankpin has a diameter of at least 0.60 of the cylinder
bore dimension and a length of not less than 0.30 of the pin
diameter. Web thickness of the crank-throw is generally in the
region of 0.20 of the cylinder bore dimension. The main bearing
journal is made larger than that of the crankpin with a diameter of
up to 0.75 of the cylinder bore dimension and a length of about
0.50 of the journal diameter.
Adequate crankshaft rigidity to resist both bending and twisting is
a major requirement for smooth operation. With current short-
stroke engines, the proportions of the crankshaft are generally
such that in themselves they contribute to greater rigidity. This
results from the combination of a smaller crank-throw radius and
larger bearing diameters, which permit a beneficial overlap
between the main journals and the crankpins
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 30
The crankshaft - Function and components
Since the crankshaft is subjected both to bending and to torsional load
reversals, it must also be designed to resist failure by fatigue. This
condition may be initiated at any point where there is a concentration of
stress or, in other words, a heavy loading confined to a very small area.
In practice, it may occur at any abrupt change of cross-section, or from
the sharp edge of an oil hole or a corner of a keyway. To avoid such
stress raisers and therefore extend the fatigue life of the crankshaft, the
areas in question are provided with carefully controlled small radii. For
example, the corners of each main bearing journal and crankpin may
be subject to what is termed ‘cold rolling’ to a specified fillet radius.
This confers a beneficial compressive stress on the crankshaft
material. The process of cold rolling basically involves rotating the
crankshaft against small hardened steel rollers, which are forced
against the corners of the crankshaft journals with a pressure
sufficient to cause local plastic deformation and therefore
compression of their surface layers. This widely used process
actually dates back to 1938, when J.O. Almen of General Motors in
America suggested its use to restore the durability of a Chevrolet truck
crankshaft following an increase in engine piston stroke
Crankshaft Radii “Cold Rolling”
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 31
The disturbing forces applied to the crankshaft are derived from the pulsating gas and inertia torques acting via each
piston, connecting rod and crankthrow combination. If the crankshaft were perfectly rigid, then the only effect of
these pulsating torques would be to cause some irregularity in its speed of rotation, which could be smoothed out by
the action of the flywheel. However the crankshaft cannot in reality be made perfectly rigid, with the result that
the torque pulses are capable of twisting it and therefore of exciting it into a state of torsional vibration.
This vibration is superimposed upon the continuous rotation of the shaft. If the frequency of the disturbing
vibrations should coincide with one of the natural frequencies of crankshaft vibration, then a condition
known as resonance will occur. A danger of resonant vibration is that the energy of the disturbing vibrations may
be greater than that lost by the twisting and untwisting of the crankshaft, so that the amplitude of torsional vibration
builds up to such a degree that the crankshaft can be over-stressed and eventually suffer a fatigue fracture. In
practice, of course, the design of the crankshaft system is contrived such that its natural frequency of vibration is
raised as high as possible: the natural frequency may be raised by making the shaft as short as possible,
increasing its diameter and using a lighter flywheel. A resonant or critical order vibration would therefore only be
expected to occur beyond the normal speed range of the engine, or in other words if the engine is over-revved.
However, it may still be necessary in the interests of both engine smoothness and satisfactory operation of the
timing drive to suppress the less critical orders of torsional vibration, which do occur within the normal speed range.
For this purpose the crankshaft can be fitted with some form of torsional vibration damper.
The most diffused is the rubber dumper in which two masses of different inertia, represented by the crankshaft and
in this case a single small flywheel, were separated by both frictional and elastic means through the medium of
rubber. In long-established practice the rubber damper essentially comprises three concentric parts, these being a
carrier cum hub assembly that is rigidly attached to the nose of the crankshaft, a ring-shaped flywheel or inertia ring
that may be grooved to accept a V-belt, and a layer of rubber which is either bonded to each of these components or
sandwiched between them under precompression, as in later designs.It will be appreciated that there is no other
connection between the carrier and the ring apart from that established by the intervening layer of rubber. The
advantages of the later non-bonded version are that it is less costly to manufacture and allows a wider choice of
rubber specification.
Crankshaft Torsional Damper
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 32
Internal Crankshaft Damper
Crankshaft Dampers
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 33
Flywheel with torsional vibration damper
Originally developed in the mid-1980s by Toyota for application to
a motor car turbocharged diesel engine, the flywheel with
torsional vibration damper or dual-mass flywheel (DMF) as it
is now often termed, has in more recent years become
increasingly adopted for Diesel engines where manufacturers
seek additional refinement for the transmission system. The
purpose of the dual-mass flywheel is to reduce the extent to
which periodic fluctuations in engine torque are passed on to the
transmission system, which otherwise create vibration, noise and
can lead to wear of components. Typically noticeable with a dual-
mass flywheel installation is therefore a reduction in
transmission gear noise at low engine speeds. In this context
there is a greater opportunity with a modern five-speed and
reverse, all-synchro-mesh, gearbox for light load rattles to occur
between the teeth of the more comprehensive train of constant-
mesh gears. As its name suggests, a dual-mass flywheel
basically comprises a two-piece flywheel with an engine-side
mass and a transmission-side mass. The latter is supported from
the former by an interposed ball-bearing race and its relative
oscillatory movements are cushioned by a series of
circumferentially spaced compression springs, which are retained
in windows shared by the two masses. Frictional resistance to
dampen the oscillatory movements between the two masses is
supplied in a similar manner to that for the centre-plate of a
friction clutch.
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 34
At TDC of combustion stroke
Pgas – Fm TDC in the crankshaft direction if Pgas > FmTDC
At TDC of gas exchange stroke
+ Fm TDC in the cylinder head direction
At BDC
- Fm BDC in the crankshaft direction
Crankshaft acting forces combination
Combustion gas forces (Pgas) and mass inertia forces (Fm)
For high combustion load it is convenient to design the crankshaft for the maximum
power operation, where the load oscillates between Pgas – FmTDC (combustion) and
FmTDC (gas exchange).
For high revs engines the engine over-speed operation (1000 revs higher than power
engine speed) might be the most severe condition, being the crankshaft load
oscillating between +FmTDC and -Fm BDC.
Engine components and systems
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Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 36
Monolithic crankshafts are most common, but some smaller and larger engines use
assembled crankshafts.
Crankshafts can be forged from a steel bar usually through roll forging or cast in ductile
steel. The actual manufacturer trend is favoring the use of forged crankshafts due to their lighter
weight, more compact dimensions and better inherent dampening. With forged crankshafts,
vanadium micro-alloyed steels are mostly used as these steels can be air cooled after reaching
high strengths without additional heat treatment, with exception to the surface hardening of the
bearing surfaces. The low alloy content also makes the material cheaper than high alloy steels.
Carbon steels are also used, but these require additional heat treatment to reach the desired
properties. Iron crankshafts are today mostly found in cheaper production engines where the
loads are lower. Some engines also use cast iron crankshafts for low output versions while
the more expensive high output version use forged steel.
Hardening - Most production crankshafts use induction hardened bearing surfaces since
that method gives good results with low costs. It also allows the crankshaft to be reground
without having to redo the hardening. But high performance crankshafts, billet crankshafts in
particular, tend to use nitridization instead. Nitridization is slower and thereby more costly, and
in addition it puts certain demands on the alloying metals in the steel, in order to be able to create
stable nitrides. The advantage with nitridization is that it can be done at low temperatures, it
produces a very hard surface and the process will leave some compressive residual stress in the
surface which is good for the fatigue properties of the crankshaft. The low temperature during
treatment is advantageous in that it doesn’t have any negative effects on the steel, such as
annealing and nitriding also leaves some compressive residual stresses in the surface.
The crankshaft - Construction
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 37
Breakage
starting
High- strength cast iron crankshaft
Flexional fatigue breakage of the first
crankpin (4 cyl Diesel engine) due to no
cold rolled radius
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 38
Superficie
di rottura
Perno
di biella
Maschetta
Perno
di biella
Macro ( X 10) picture of no cold rolled
radius: milling operation visible
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 39
Perno
di biella
Impronta
dovuta alla
rullatura
Maschetta
Macro ( X 10) picture of a cold rolled radius
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 40
Micro (X30) picture of a non cold rolled
crankshaft radius: no profile variation
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 41
Micro (X30) picture of a cold rolled
crankshaft radius: profile variation is visible
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
Basic functions
Transmission of the piston force and piston motion
to the crankshaft
A possible location for holes to supply the piston
with lubricating oil
Basic requirements
Sufficient mechanical strength
Sufficient bearing capacity
Mass as low as possible, because of the crankcase
stress generated by mass forces
Optimum length: short for a reduced engine height,
but not too short because of frictional work caused by
lateral forces and because the 2nd order unbalanced
forces of the 4 cylinder engines
The connecting rod
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
Design configuration
The small end (eye) of the connecting rod, into which the piston pin is inserted, is
connected to the big end via the connecting rod shank
The connecting rod big end is typically split to be assembled on a single-piece
cranckshaft
Connecting rod stress
The gas forces generate compressive stress on the connecting rod: the maximum
value occurs at ignition TDC
The mass forces generate a tensile stress which are maximum at gas exchange
TDC
This results in alternating stress between ignition TDC and gas exchange TDC:
the gas forces are important at low speed, the mass forces at high speed
The bending stress, caused by mass forces, is usually low and therefore is
neglected
The connecting rod eye and big end are stressed by tension forces and bending
moments
The bearing cap and relative bolts and threads are subjected at high stress,
because located in the power flow, and can be highly deformed weakening the
formation of a stable lubricating film
The connecting rod
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
Material and Construction
Connecting rod of today fast-running combustion engines are generally forged
in one piece. Once the bolt holes and threads are drilled, the connecting rod cap is
separated from the connecting rod big end
High-carbon steels (C35, C45) are used in standard applications; higher stress
applications require high-alloyed steel (Cr, Mo, Ni, V). For passenger car gasoline
engines malleable cast iron are sometime used while forged sintered connecting
rods are increasingly attractive because of lower weight vs forged
For both cast and forged steel as well sintered connecting rods, the bearing cap
can be separated from the big end through a cracking method, reducing the
manufacturing cost and improving the connection precision
The shaft is most often designed with I-cross section for higher stiffness in the
oscillating direction. To avoid the stress peaks, the transition from the shank to the
con-rod eye and con-rod big end must have large radii
A connecting rod divided at an angle can be necessary to enable disassembly
through the top of the cylinder.
The connecting rod
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
14.8
1.8
Steel con-rod for Diesel engines
Small
(eye)end
Big end
Shank
The connecting rod
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
Connecting rod drawing
The connecting rod
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
The connecting rod
In some designs the big-end bearing parting line is arranged diagonally (45° in the
Figure), because otherwise the width of the housing would be such that the
connecting rod could not be passed through the cylinder for assembly purposes.
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
The connecting rod
To resist the greater tendency for the cap to be displaced sideways relative to the rod, either a serrated or a stepped
joint is generally preferred for their mating faces. Hence, the securing setscrews in their clearance holes are relieved
of all shear loads. Where the parting line between the rod and cap is arranged at right angles to the axis of the shank,
the cap may be secured by either bolts and nuts, studs and nuts, or setscrews. They are produced from high-tensile
alloy steel with special care being taken in their detail design to avoid stress-raising corners, which would lower their
fatigue resistance. Their clamping load must always be such as to exceed the inertia forces acting on the rod.
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
Connecting rod guided by the piston (a) and by the crankshaft (b)
a b
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
The connecting rod
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 51
Main piston functions
Transmission of gas force generated by the combustion to the connecting
rod
Kinematic guidance, supporting the normal force applied to the cylinder walls
Together with the piston rings, sealing of the crankcase against combustion
gas and of the combustion chamber against oil
Support of sealing rings (piston rings)
Limit and design of the combustion chamber
Main piston stress due to
Gas and mass forces
Heat flow of the combustion chamber
Frictional forces at the shaft and in the ring grooves
Movements perpendicular to the running direction (“tilt”)
Main design target
Sufficient strength with as little mass as possible
Permissible temperatures through design (heat flow), material and cooling
Correct running clearance for all load levels
Quiet operation with limited tilt
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 52
Gasoline engine
piston
Diesel engine
piston
Piston rings Piston pins
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 53
Gasoline and Diesel pistons
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 54
Piston Rings functions
Sealing the combustion chamber to
the crankcase (compression rings)
Sealing the crankcase to the
combustion chamber (oil control rings)
Regulating the lubricating oil at the
cylinder wall
Heat conduction from the piston to
the cylinder wall
Piston rings must have a split at one
point (ring gap)
The gap clearance of the installed
ring must be small to reduce the
leakage but may never be zero to avoid
seizing
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 55
Gasoline Pistons
Weights:
Piston 170 g
Piston Pin 60 g
Ring Set 18 g
Circlips 2 g
Assy Weight: 250 g
typical small gasoline engine
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 56
Material and Construction
The ideal piston material should combine the following characteristics: high thermal
stability (hardness and elasticity), high thermal conductivity, low thermal expansion,
low modulus of elasticity, good running properties /wear and friction) and low density
(low weight)
Most of these requirements are well met by aluminum alloys containing silicon
between 11 and 26%; the only disadvantage is a high coefficient of linear expansion.
The raw mold of the light alloy piston are cast or pressed (forged).
For economical reason the raw piston for combustion engines are mainly produced
via die-casting, while forged piston, more solid and stronger than cast pistons, are
used for high performance applications where mechanical and thermal stress are
much higher
Heat treatment is necessary after casting process to optimize the required physical
properties
Aluminum piston are coated mainly by Fe when combined with aluminum cylinders
Grey cast iron pistons are used for very low speed engines or when thermal stress
are at very high level
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 57
High Power achieved by high pmi leads
to increased gas force and thermal load
Problem
• fatigue (piston crown, ring groove, pin
boss, skirt)
Solution
• cooling gallery
piston
Advantage
• Temperature reduction in critical areas (-
20°C)
• Permissible loading increased (8%)
• reduced knock sensibility (SPA + 3°)
--> increased power output
• additional reinforcement features
avoidable
Gasoline Pistons for High Power Output Engines
High Power achieved by high engine
speed leads to increased inertia force
Problem
• fatigue (pin boss, skirt fatigue)
Solution
• forged piston
(optimised
material
properties)
Disadvantage
• additional groove reinforcement
required
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 58
180bar,
58kW/l
160bar, 50kW/l
180bar, 60kW/l
160bar, 50kW/l
200bar, 60kW/l
180bar, 58kW/l
Various Gallery KS Pistons with Basic Engine Data
Combustion peak pressure, specific power output
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 59
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 60
Piston temperature profile
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 61
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 62
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 63
Mean stress in MPa
High speed DI-piston for Engine 2,0l
85mm dia., version with cooling gallery
Temperature distribution in °C
High speed DI-piston for Engine 2,0l
85mm dia., version with cooling gallery
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 64
Safety factors, HCF; 9*10*7 cycles
High speed DI-piston for Engine 2,0l
85mm dia., version with cooling gallery
Stress amplitude in MPa
High speed DI-piston for Engine 2,0l
85mm dia., version with cooling gallery
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 65
Diesel piston failure after 1000hr
durabilty bench testing
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 66
The Piston
Diesel piston failure after 1000hr
durabilty bench testing
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 67
Diesel engine pistons - 1000 hr test bench durability
The Piston
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 68
The function of the valve train in a 4-stroke engine is to allow and to control the
exchange of the gases in the internal combustion engine
The valve train includes the intake and exhaust valves, the springs which close them,
the camshaft drive assembly and the various force-transfer devices
The specific tasks of the valve train are to open and close the intake/exhaust valves in
time and to enable a sufficiently large flow cross section
The high acceleration and deceleration required of the valve train parts causes stress
due to mass forces rising with increasing speed
The exhaust valves are subjected to a high thermal stress, due to heat flow from the
combustion chamber and the exhaust gases
vavavahdA =
4
dA va
va
=
Partial lift
Full lift
Flow cross section
The valve train
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 69
Valve size
The valve diameter is defined as a compromise among various factors as optimization
of the combustion chamber, flow cross section and thickness of the “bridge” between the
valves or the valves and the spark plug/injector exposed at high thermal stress
according to the experience, for 2 valve gasoline engines:
and for 4 valve gasoline engines:
and for 4 valve DI Diesel engine, where the cylinder head is flat because combustion
chamber is designed inside the piston
The diameter of exhaust valve is generally smaller of about 10% to guarantee a
reasonable valve bridge and for a better cooling
D48.045.0dva
=
D34.032.0dva
=
D33.030.0dva
=
The valve train
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 70
4-stroke work cycle
Valve opening and closing timing in respect to TDC / BDC
The valve train
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 71
-20
-15
-10
-5
0
5
10
15
20
-80 -60 -40 -20 0 20 40 60 80
Cam Angle[deg]
Lif
t [m
m];
Ve
loc
ity
[m
m / r
ad
]
-100
-80
-60
-40
-20
0
20
40
60
80
100
Ac
ce
lera
tio
n [
mm
/ra
d²]
, J
erk
[m
m/r
ad
³]
Lift Velocity Acceleration
lift
acceleration
velocity
TDC
BDCExhaust valve opening
Intake valve
opening
Overlap
BDCBDC TDC
Exhaust valve Intake valve
overlap
Exhaust valve closing
Intake valve closing
Valve timing diagram showing
valve lift, valve velocity and
valve acceleration
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 72
Crankshaft driven camshaft (crank
case location) with push rod operation
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 73
Double (twin) overhead
camshaft with direct
tappet actuation
Overhead camshaft with
rocker arm actuation
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 74
4 cyl engine V6 engine
2 camshafts
for cylinder head
1 camshaft
for cylinder head
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 75
Direct acting camshaft with mechanical valve adjustment
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 76
Direct acting camshaft with hydraulic valve adjustment
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 77
Cross section of a direct acting camshaft
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 78
Rocker arm with insert valve lash adjustment element
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 79
Hydraulic Rocker Arm Components
Rocker arm
Hydraulic lash
adjuster
Support plate
Side washers (2x)
Set of needles
Outer ring
ShaftAssembly
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 80
Finger follower with roller and pivot element
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 81
Finger follower with roller and pivot element
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 82
Roller Finger Follower Valve Trains
Roller finger follower parts
Sheet Metal Body
16MnCr5
Outer Ring
100Cr6
Needles
100Cr6
Axle
100Cr6
Sheet Metal Thickness:
2,5 mm ... 3,5 mm
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 83
Roller Finger Follower Valve Trains
HLA composition
high pressure
chamber
reservoir chamber
socket plunger
housing
lower plunger
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 84
Variable valve trainsIn the last decades a certain number of unconventional valve trains have been developed to
vary valve timing and lift during operation with the target of controlling the gas exchange
cycle by optimizing the valve activation
Phasing – By camshaft phasing the variation of the intake timing influences on the
cylinder charge and allow a reasonable control of residual gas content, depending on
engine load and speed. The prerequisites for the system are that the engine must have one
intake and one exhaust camshaft and one cannot be driven by the other one. The first
application has been done by Alfa Romeo on the 4 cyl engine for USA spider of 1980 MY.
Transition between cam profiles – The variation of the valve lift is realized by a
transition between two different cams. Today different solution are on the market but the
first one has been the Honda VTEC system, where the second cam is designed to enhance
performance at high engine speed. In more recent application the second cam is designed
to actuate a low lift in order to reduce pumping loss at low load operation
Cylinder deactivation – With multi-cylinder engines fuel consumption can be reduced
under part-load operation through cylinder deactivation. The improvement is achieved
because the pumping losses of the deactivated cylinder s are eliminated and the activated
cylinders are de-throttled. Again technical solutions vary among the Car Makers and some
are substantially the previous one tuned for this target; the first application has been a 4cyl
Mitsubishi engine in middle ‘90 years, but Alfa Romeo in the early ’80s built up a taxi fleet
deactivating partially the cylinders by ignition interruption.
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 85
The first cam phase variator
helical/cilindrical toothing
(Alfa Romeo)
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 86
Variable cam phaser (Cam phase variator)
Content
• VCT-Concepts
• System function
• Components
• Development tools
• Applications
• Development trend
• Future systems
• Market position
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 87
Potential of VCT Concepts
typical benefits for FE & Emissions (related
to FTP 75 cycle)
DIPS
IPS EPS
DEPS
torque /
power
emissions internal EGR
catalyst heating
Fuel
economy
comfort idle
stability
FE ~ - 3%
NOx ~ - 50%
HC ~ - 10%
torque/power + 5%
FE ~ - 5 %
NOx ~ - 70 %
HC ~ - 15 %
torque/power + 10%
FE ~ - 3 %
NOx ~ - 70 %
HC ~ - 15 %
torque/power -
FE ~ - 4-6 %
NOx ~ - 50 %
HC -
torque/power -
( LIVC )
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 88
Hydraulic / electronic scheme
cam phasercam positon sensor
triggerwheel
Oil control valve
crank sensor
triggerwheel
connected to oil pump
connected to sump
Engine management system
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 89
Cam phase variator-Function (base position)
pump
tanksump
locking pin engaged
example for intake VCT
fully retarded cam position
oil control valve swiched
off
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 90
Cam phase variator-Function (shifting)
pump
sump
oil control valve fully
energized
VCT position change
commences
locking pin unlocks
example for intake
VCT
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 91
Cam phase variator-Function (controlled position)
pump
sump
oil control valve energized
to mid position (PWM
control)
VCT control position is
frozen
example for intake
VCT
locking pin remains
disengaged
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 92
Switchable Tappet Valve Train
Valve/Cylinder De-Activation / Cam Profile Switching
for SOHC and DOHC engines
Outer-Housing
Inner-Housing
Anti Rotation Device
Locking Spring
HLA
Inner Piston
Locking Piston
Lost-Motion-Spring
Electro-hydraulic
solenoid 2/3-Way
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 93
Switchable Tappet Valve Train
Valve/Cylinder De-Activation / Cam Profile Switching
for SOHC and DOHC engines
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 94
Combined CPV and switchable tappet
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 95
Variable valve trains - Flexible valve actuationA flexible valve control allows the possibility to adjust the free flow cross-section to the
engine speed and, overall, provides throttle-free control of load in gasoline engines.
Mechanical valve operation – The first application has been introduced by BMW (see
fig.) with a fully variable control which allows continuous variation of the intake valve lift. An
intermediate element, which is controlled by the eccentric shaft, is inserted between the
camshaft and the finger follower. Moving the intermediate element causes a variation of
valve lift and therefore also the effective opening time. The valve lift and the opening time
determine the quantity of the charge and therefore the engine load level: the timing of the
valve opening is controlled by cam phase variators on intake and exhaust camshafts. This
fully variable mechanical valve control makes load control possible without the throttle use
Hydraulic valve operation – This systems require a dedicated oil circuit and pump to
generate the pressure necessary to actuate the valves with some device: variation of the oil
pressure allows the control of valve lift, being the pressure controlled by electromagnetic
valves. The high complexity, the cost and the losses encored during the pressure
generation limit the use of hydraulic valve control to special applications.
Electromechanical valve operation – Opening the valves against the valve springs
force by using electromagnets requires an excessive amount of current, because the
magnetic field becomes weaker very rapidly with increasing distance. Notwithstanding a lot
of research and experimental activity, this system has not been qualified for vehicle
applications.
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 96
BMW Valvetronic – Mechanical variable valve lift
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 97
Valvetronic system cylinder head
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 98
Variable valve trains - Flexible valve actuation
Fiat Multiair system – It is the last system
introduced on Fire 1.4l engine in 2009. It can be
considered as mechanic-hydraulic valve operation,
using electro-hydraulic elements to manage a
continuously variable intake valve lift. The control piston
and the inlet valve are connected each other through an
oil pressure chamber, the pressure in which is
controlled by a solenoid valve. When the valve is in a
closed position, the inlet valve follows the cam profile.
An early close of the inlet valve can be achieved by
opening the solenoid valve after a particular degree
cam angle. The oil flows out of the high pressure
chamber into the reservoir. The valve is now decoupled
from the cam’s motion and hence is closed by the
return forces of the valve spring. The valve seating
velocities are held within safe limits by a hydraulic
damper. By means of a spring in the reservoir, the oil
flows back into the high pressure chamber after the
completion of the cam stroke. The Multiair system
allows a throttle-free load control and also the
optimization of cylinder filling at full load.
PistonIntake
Valve
Accumulator
Solenoid ValveHigh Pressure
Oil Chamber
Cam
Piston
Hydraulic
Brake &
Lash Adjiuster
Intake
Valve
Engine components and systems
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Crank Angle
0
1
2
3
4
5
6
7
8
9
10
320 360 400 440 480 520 560 600 640 680 720
LIVO
EIVC
Engine Valve Lift
TDC BDC
INTAKE VALVE ACTUATION MODES
F1 F2
SOLENOID VALVESACTIVATION
F1 F2 F1 F2 F1 F2F1F2
INTAKE VALVE LIFT
“FULL LIFT” “EIVC”Early Valve Closing
“LIVO”Late Valve Opening
“MULTI-LIFT”“FULL LIFT” “EIVC”
Early Valve Closing
“LIVO”
Late Valve Opening
“MULTI-LIFT”
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 100
High PressureChamber
High ResponseSolenoid Valve
(ON-OFF)
Individual Valve Actuation Assembly
(Piston + Brake + Lash Adjuster)
Pump Piston
Oil Reservoir
Camshaft(Intake + Exhaust)
Low Friction Tappet (RFF)
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
Fiat 1.4 Multiair - Electric / hydraulic variable valve lift system
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
Fiat 1.4 Multiair - Electric / hydraulic variable valve lift system
Engine components and systems
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
Fiat 1.4 Multiair - Electric / hydraulic variable valve lift system