mfge425_maxspeed.pdf

8/11/2019 MFGE425_Maxspeed.pdf

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AUTOMOTIVEAUTOMOTIVE

ENGINEERINGENGINEERING

(MFGE 425)(MFGE 425)

Asst. Prof. Dr. Serhat ERPOLAT

ATILIM UNIVERSTY

2007-Fall


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Basic PerformanceBasic Performance

CalculationsCalculations -- 33


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Maximum speed & accelerationMaximum speed & acceleration

To specify the performance of a vehicle, quote:

The time required for some specified change of speed V1

to V2 as a measure of the acceleration performance

The maximum gradient that the vehicle can climb

The fuel consumption for given driving conditions

The maximum speed


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=2

1

V

V n

eqF

dVmt The time taken to reach velocity V2from velocity V1

Vr

Siin

w

dte =

Engine speed in terms of vehicle velocity, S being slip factor

e

e

w

dttT

n

P

r

iiF

=

Tractive effort in terms of engine power & speed

32

eeee nCnBnAP ++=Engine power in terms of engine speed using

correct toque peak approximation



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Correct torque peak approximation

= n1/n2


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Tractive effort in terms of

vehicle speed

Resistance to motion:

Rolling resistance, Gradient resistance,

Air resistance

Fn = FT - (Rr + Rg + Ra) Net tractive effort



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32

2

1 aVaVaFn ++=

fD

w

dtt ACKC

r

iiSa

=

3

2

21 kph

N

WbBr

iiSa

w

dtt

*

2

2kph

N

=

[ ] ( ) sinN *3 +

= aWA

r

iia

w

dtt

The net tractive effort as a function of vehicle velocity:The net tractive effort as a function of vehicle velocity:


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5th

4th3th2

th

1th Gradients:

% 0-5-15-30-69

Tractive effort (kN)

Resistive force (kN)

Tractive effort curves:Tractive effort curves:


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Max. speed for each gear except the top gear

(mechanically limited)

Max. speed for passanger cars

(power limited)

An emprical equation for the max. speed

for a medium size passanger car

Maximum speed:Maximum speed:


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= n1/n2


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[ ] ( ) sinN *3 +

= aWA

r

iia

w

dtt

( )( )widthMaxheightMax.Af

..80

=

W

W

KKp

p

KKaa

R

Rref 2121

*


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WbBr

iiSa

w

dtt

*

2

2kph

N

=

fD

w

dtt ACKC

r

iiSa

=

3

2

21 kph

N


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Acceleration Performance:Acceleration Performance:


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mfge425_maxspeed.pdf

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