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High Power Engine Crankshaft Design and Analysis

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in 1860 the very first internal

combustion engine was produced at Baron

coal gas and had a four percent

efficiency displacing 18 litres to

produce two horsepower by 1876 Nikolaus

Otto and Eugene Langley began work on a

much more efficient combustion engine

1885 saw the first car but it wasn't

exactly fast the operating principles

however remain exactly the same as a

modern engine a piston constrained in a

bore moves up and down it is connected

to a rod with the rod connected to a

crankshaft generally placed overhead is

a pair of camshafts the camshafts

control the opening and closing of the

intake and exhaust valves on the engine

the system is timed using a synchronous

drive and a spark plug is placed in the

combustion chamber to ignite the fuel

air mixture this mixture is drawn into

the intake valve compressed by the

piston and ignited by the spark ball the

expanding gas mixture forces the piston

down the last stroke the exhaust stroke

is used to force the remaining gases out

of the combustion chamber it might

surprise you that a treasonable

production engine speeds the piston can

go up and down all hundred senses

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that's right the class you barely passed

was actually pretty important but we're

not going to do a detailed thermodynamic

analysis I just want to remind you that

as the compression ratio increases the

efficiency of the combustion process

increases too and the more air and fuel

you can pack into the combustion chamber

the more power you can get out of the

engine on the same note more cylinders

you stack next to each other the more

force you can push down through that

crankshaft you might hear some

old-timers say there's no replacement

for displacement well this is what

they're talking about because v8 usually

make more power than 4-cylinder here's

an example

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however with today's environmental

protection requirements engineers are

trying to squeeze as much power as they

can of small four-cylinder engines

because consumers want a fast car that's

going gas all the while environmental

regulation requires minimal hydrocarbon

emissions the key to making this work is

the turbocharger the turbocharger pre

compresses the intake air causing a huge

bump in cylinder pressure and an

increase in performance while retaining

a relatively small engine a small engine

pushing a lot of power means a lot of

stress

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all and all this stress gets

concentrated directly at the crankshaft

failure of the crankshaft would mean

catastrophic engine damage and put the

driver and other users of the road at

risk

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let's take a look at what an engineer

needs to do to make sure this doesn't

happen this study focuses on the

crankshaft of the engine the component

used in this example was designed using

SolidWorks 2016

like most engine components the

crankshaft is already very well

developed so what better starting place

than an already proven design this

crankshaft was laying in my garage so I

thought we might as well use it it

belongs to the 1.8 liter 20 valve turbo

Volkswagen engine the same one I was

taking apart just few seconds ago with

the initial design complete it's time to

find out how much force is going to be

pushing down on those crank arms to find

the maximum force we need to find the

maximum cylinder pressure using a

pressure transducer equipped to a

Renault engine the maximum in cylinder

pressure was found to be five thousand

three hundred and twenty kilo Pascal's

or about fifty three bar this was on a

fairly moderate two-liter engine

producing 145 horsepower estimates for

our 1.8 liter producing 180 horsepower

brings from 75 to 100 bar so great we

now know the maximum normal operating

pressures but there is one more thing we

need to talk about and that is pre

ignition it's the mother of all engine

killers when the fuel air mixture

detonates the four top assist

a massive pressure wave is released as

the engine experiences pressures

exceeding 200 bar pistons melt rods Bend

and crank shafts break so when designing

the crankshaft we applied a large factor

safety to do with things like

pre-ignition

this brings us to the static failure

portion of the project the maximum force

was found by multiplying the pressure

times the area of the piston we account

for cylinder pressures of up to 250 bar

this resulted in a force of 128

kilonewtons at 25 degrees to the

vertical this force is applied directly

and uniformly to the rod journal on the

crankshaft

lastly the crankshaft is supported by

bearing fixtures and fixed where the

flywheel mount this should give us a

good indication of the maximum stress

when the engine is operating at steady

state like going up a hill at full

throttle with a bit of pre-ignition this

basic design proves very strong with the

maximum stress concentrated at the main

bearings this maximum stress came out to

be 280 1.7 mega Pascal's this yields

effective design factors ranging from

one point six seven to two point five

two depending on material and surface

treatment choice I'm sorry what anyways

with such high factors of safety

downsizing comes with ease provided that

the material is strong enough the

crankshaft use in this example could be

shaved down substantially when talking

engines any rotating mass that you can

remove is a really big deal it means

less material used and less mass to

accelerate but comes at the cost of

decreased rigidity and increased

deflections

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it should be noted that too much

deflection can cause premature bearing

away

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the fatigue failure test will give us an

idea of how long our part will last

paycheck failure occurs when a micro

craft propagates through the metal even

though the yield strength hasn't often

read it ends with a small area

supporting the full structural load that

small area eventually experiences

brittle fracture in the part usually

fails rapidly

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fatigue failure can be avoided by

keeping the stress amplitude below the

endurance limit of the steel some

materials don't have an endurance limit

but we won't be focusing about earlier

we found that our maximum peak cylinder

pressure under normal operating

conditions was about 100 bar the goal is

to get the crankshaft to last the right

amount of time and not break prematurely

the following calculations require that

the crankshaft last 3.9 four times ten

to the ninth cycles this is a view of

the car for one hour every single day

for 30 years the peak cylinder pressure

was found previously to be 100 bar that

equates to 51.3 kilonewtons now we can

run this to our finite element analysis

and use the integrated SolidWorks

fatigue study to find the total lifetime

of the part the SN curves are included

with the SolidWorks Simulation package

and then as forged surface finish was

chosen this will put us on the

conservative side of an already accurate

simulation but how thin can you make

those crankshaft walls

finally we're going to check out

materials and post-processing perhaps

one of the most important design factors

is material choice and subsequent

processing the most commonly used

materials are forged steel and cast iron

the cast parts are usually cheaper to

make but not as strong as their forged

counterparts casting requires a void to

be filled by a molten metal whereas the

forging process involves forcing a

billet into shape one of the strongest

materials available would be a billet

alloy steel like 4340 billet Klink

shafts are usually very expensive and

reserved for specialty parts

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once machining is complete there's a

number of strengthening mechanisms

available these serve to increase the

durability of the crankshaft and push

its 2t device even further shot peening

WPC and cryogenic hardening are a few

common treatments cryogenic hardening

serves to increase the martensite and

can have a profound effect on overall

wear characteristics and strength here

CW SP describes the shot peening

processed the application of controlled

shot peening improves performance

reduces maintenance and provides a cost

effective solution to premature failure

in critical components shot peening is a

method of inducing residual compressive

stress into the component by bombarding

the surface with high-quality spherical

media in a controlled operation the

media can be steel ceramic or glass and

each piece acts like a tiny painting

hammer producing a small indentation in

the surface

the application locally yields the

material inducing beneficial residual

compressive stress the characteristics

of which are dependent on the base

material and component design at the

same time unwanted tensile stresses are

removed the proven results from

controlled shot peening show a dramatic

beneficial effect on both the life and

strength of components welds and

materials making the material resistant

to fatigue fretting and stress corrosion

cracking taking all design factors into

consideration a crankshaft of infinite

life should be very possible to produce

the vr6 engine I turbocharged and

swapped into my Volkswagen has living

proof of a seriously strong crankshaft

it was originally intended to output 177

brake horsepower with the turbo and

stand-alone EFI system I built the

numbers are over 300 and while that

might not seem like a high specific

output honda just released the new type

r which is pushing similar power through

a four cylinder

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ah

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