performance et comportement des vehicules · 2015-10-11 · 2.255 210@5300 210@3500 15.9 15.7 bmw...

Vehicle Performance

Pierre Duysinx Research Center in Sustainable Automotive

Technologies of University of Liege

Academic Year 2015-2016

1

Lesson 1: Power sources and Transmission

2

Outline

MOTORIZATION CHARACTERISTICS

Piston engines

Torque speed curves

Approximation of curves

Electric machines

POWER AND TRACTIVE FORCE AT WHEELS

Transmission efficiency

Gear ratio

Expression of power and forces at wheels

Power and forces diagram

3

References

T. Gillespie. « Fundamentals of vehicle Dynamics », 1992, Society of Automotive Engineers (SAE)

J.Y. Wong. « Theory of Ground Vehicles ». John Wiley & sons. 1993 (2nd edition) 2001 (3rd edition).

W.H. Hucho. « Aerodynamics of Road Vehicles ». 4th edition. SAE International. 1998.

M. Eshani, Y. Gao & A. Emadi. Modern Electric, Hybrid Electric and Fuel Cell Vehicles. Fundamentals, Theory and Design. 2nd Edition. CRC Press.

R. Bosch. « Automotive Handbook ». 5th edition. 2002. Society of Automotive Engineers (SAE)

4

Piston engines

5

4 stroke engines: gasoline

In 1862, Beau de Rochas developed a operation sequence that is still now the basis of any piston engine operations

The 4-stroke engine requires to 2 crankshaft revolutions to accomplish one thermodynamic cycles, which means 2 compression and expansion motions of the piston.

6

4 stroke engines: gasoline

Stroke 1: Fuel-air mixture introduced into cylinder through intake valve

Stroke 2: Fuel-air mixture compressed

Stroke 3: Combustion (roughly constant volume) occurs and product gases expand doing work

Stroke 4: Product gases pushed out of the cylinder through the exhaust valve

Compression

Stroke

Power

Stroke Exhaust

Stroke

A

I

R

Combustion

Products

Ignition

Intake

Stroke

FUEL

Fuel/Air

Mixture

7

4 stroke engines: diesel

The Four stroke Compression Ignition (CI) Engine is generally denoted as the Diesel engine

The cycle is similar to Otto cycle albeit that it requires a high compression ratio and a low dilution (air fuel) ratio.

Air is admitted in the chamber and then compressed. The temperature rises the ignition point and then the fuel is injected at high pressure. It can inflame spontaneously.

There is no need for a spark and so stoichiometric air fuel ration is not necessary.

8

4 stroke engines: diesel

Stroke 1: Air is introduced into cylinder through intake valve

Stroke 2: Air is compressed

Stroke 3: Combustion (roughly constant pressure) occurs and product gases expand doing work

Stroke 4: Product gases pushed out of the cylinder through the exhaust valve

Compression

Stroke

Power

Stroke

Exhaust

Stroke

A

I

R

Combustion

Products

Intake

Stroke

Air

Fuel Injector

9

2-stroke engines

Dugald Clerk has invented the 2-stroke engine in 1878 in order to increase the power to weight ratio for a equal volume.

The 2-stroke engines is also simpler with regards to valve system

The 2-stroke principle is applicable to both spark ignition engine and compression ignition engine. It is however more usual with spark ignition engines.

The 2-stroke engine involves two strokes and the cycle is carried out during one single crankshaft revolution.

10

2-stroke engines

Intake (“Scavenging”)

Compression Ignition

Exhaust Expansion

Fuel-air-oil

mixture

Fuel-air-oil

mixture

compressed

Crank

shaft

Check

valve

Exhaust

port

11

2-stroke engines

Stroke 1: Fuel-air mixture is introduced into the cylinder and is then compressed, combustion initiated at the end of the stroke

Stroke 2: Combustion products expand doing work and then exhausted

* Power delivered to the crankshaft on every revolution

12

Troque-speed curves of ICE engines

13

Torque speed curves of ICE

Suppose that the gas pressure is remaining constant along the power stroke, its work is given by:

The work of the n pistons over the cycle is:

For an k-stroke engine the duration of the cycle is given by

14

Torque speed curves of ICE

It comes the power curves with respect to rotation speed:

The torque speed curve is

w w 15

Indicated mean effective pressure

The indicated mean effective pressure imep is a fictitious constant pressure that would produce the same work per cycle if it acted on the piston during the power stroke

imep does not depend on engine speed, just like torque

imep is a better parameter than torque to compare engines for design and output because it is independent of engine speed, N, and engine size, Vd.

R

pp

R

di

d

Ri

d

i

n

UAimep

n

NVimepW

NV

nW

V

Wimep

2

Puisque alors imepcycleT W T

16

Brake mean effective pressure

The brake mean effective pressure (bmep) is defined similarly to the indicated mean effective pressure as a fictitious constant pressure that would produce the same brake work per cycle if it acted on the piston during the power stroke

2 C

2

b dR

d d R

W bmep VC nbmep

V V n

17

Brake and indicated mean effective pressure

Order of magnitude of the brake mean effective pressure of modern engines:

Four-stroke engines:

Atmospheric

SI engine: 850 – 1050 kPa

CI engine: 700 – 900 kPa

Turbocharged

SI engine: 1250 - 1700 kPa

CI engine: 1000 - 1200 kPa

Two-stroke engines

SI engine : idem 4 stroke

Large 2-stroke diesel engines (e.g. boat) ~1600 kPa

Remark

Bmep is maximum at maximum torque and wide open throttle

At nominal power, the bmep is lower by 10 to 15%

18

Brake and indicated mean effective pressure

Vehicle Engine

type

Displ.

(L)

Max Power

(HP@rpm)

Max Torque

(lb-ft@rpm)

BMEP at

Max BT

(bar)

BMEP at

Rated BP

(bar)

Mazda

Protégé LX

L4 1.839 122@6000 117@4000 10.8 9.9

Honda

Accord EX

L4 2.254 150@5700 152@4900 11.4 10.4

Mazda

Millenia S

L4

Turbo

2.255 210@5300 210@3500 15.9 15.7

BMW

328i

L6 2.793 190@5300 206@3950 12.6 11.5

Ferrari

F355 GTS

V8 3.496 375@8250 268@6000 13.1 11.6

Ferrari

456 GT

V12 5.474 436@6250 398@4500 12.4 11.4

Lamborghini

Diablo VT

V12 5.707 492@7000 427@5200 12.7 11.0

19

Piston engines characteristics

Good combustion properties (and so the maximum torque) are obtained for a medium (design) rotation speed.

For increasing rotation speed, the admission pressure drop and the engine frictions are increasing and the brake mean effective (and the torque) pressure is dropping.

Power = torque x speed is still increasing till the torque drops is so high than power is falling as well.

A low regimes, the dilution is high and the combustion is deteriorated, while heat transfer to piston and walls is becoming more important. It comes that the mean effective pressure and the torque is also reduced. 20

Piston engines characteristics

Gillespie, Fig. 2.1

21

Standard performances of ICE

Torque-curves provided by the manufacturer are giving the basic power of the engine

Basic power = performance with requirement equipment to insure the normal conditions: ventilator, water pump, oil pump, exhaust pie, air filter

Pay attention to the multiplication of accessories and auxiliary equipments (air conditioned, steering wheel assistance, braking systems, electric generator) reduce the power available at the wheels by a significant part.

22

Standard performances of ICE

SAE (Society of Automotive Engineers, USA): the power of the engine without its auxiliaries, with parameters adapted to each regimes (ignition advance, carburetor). Ideal maximum power.

DIN (Deutsche Industrie Normen) and CE. The engine has to provide the power necessary to operate all its needed auxiliaries while the parameters settings are the standard ones.

CUNA. Italian system that is in between DIN and CAE: no accessories but standard settings.

23

Power consumption of auxiliaries

The power consumption of the accessories is increasing and has a significant impact on the output power available for the propulsion especially for the small engines and the electric motors

24

Effect of atmospheric conditions

The atmospheric conditions (temperature, pressure, hygrometry) affects the engine performances.

Reference atmospheric conditions:

T°=15.5°C = 520°R = 60°F

p= 101.32 kPa = 14.7 psi = 76 cm Hg

Wong is referring to the correction formulae proposed by Taborek (1956):

Ba barometric pressure

T the temperature (in °R) at admission pipe

Bv vapour pressure to account for the effect of the humidity

25


For SI engines (gasoline)

For CI engines (diesel) the effect of atmospheric pressures is more complex:

The atmospheric conditions may impact significantly tje engine performances (Wong Fig. 3.24)

00

0

( )a vB B TP P

B T

00

0

( )a vB B TP P

B T

26


Norm EEC 80/1269 – ISO 1585 – JIS D 1001 – SAE J1349 for SI engines (gasoline)

Standards conditions (temperature T0= 298 K and dry air pressure p0= 99 kPa)

Corrected power

PP a0

298/)(

)(/99

6.02.1

KTB

kPapA

BA

p

PT

a

27


Norm EEC 80/1269 – ISO 1585 – JIS D 1001 – SAE J1349 for CI engines (diesel)

Standards conditions (temperature T0= 298 K and dry air pressure p0= 99 kPa)

Corrected power

298/)(

)(/99

5.17.0

KTB

kPapA

BA

p

PT

a

PP a0

28

Curve fitting of ICE characteristics

Two families of curves

Fitting to a power function

Fitting of a polynomial

Data

Nominal (maximum) power

Maximum torque

r¶egimes. Par c

le P1 = Pmaxe !1 = !nom;

al C2 = Cmaxt !2 = !Cmax .

29

Power approximation

On look for a power function of the type

Data

That is

!1 = !nom P1 = Pmax!2 = !Cm ax

P2 = Cmax!Cm axd C

d!

¯¯!2

= 0

¯ ¯ ¯ ¯

P = P 1 ¡ A j ! ¡ ! 1 j b b > 0

A =

P 1 ¡ P 2

j ! 1 ¡ ! 2 j b

j ¡ j

b =

! 1

! 2

¡ 1

P 1

P 2

¡ 1

¯

30

Power approximation

Maximum power in P1: OK

Maximum torque in w2:

Given (maximum) torque w2 :

be de couple y passe par un max

P(!2) = P2 = Cmax !Cmaxd C

d!

¯¯!2

=d (P=!)d!

¯¯!2

= 0¯¯

¯¯

µere des deux condition

a =P1 ¡P2j!1 ¡ !2jb P = P1 ¡ (P1 ¡P2)

¯¯ !1 ¡ !!1 ¡ !2

¯¯b

31

Power approximation

Maximum torque in w2:

Derivative of the power

Leads to the condition

¯¯

¯¯

ximal en ! = !2. On a :

d C

d!

¯¯!2

=!2

dPd!

¯!2¡P2

!22= 0 P2 = !2

dPd!

¯¯!2

¯¯

iv¶ee de l'expression de la puissance, il vient :

dPd!

¯¯!2

= ¡a b j!1 ¡ !2jb¡1 sign(!1 ¡ !2) (¡1) = a b (!1 ¡ !2)b¡1

pu etre omis puisque !1 > !2. On obtient ¯

P2 = !2 a b (!1 ¡ !2)b¡1 = b !2P1 ¡P2!1 ¡ !2

32

Power approximation

Fitted exponent b

Fitted approximation

j ¡ j

b =

! 1

! 2

¡ 1

P 1

P 2

¡ 1

¯

P

P ¡

P

P 1

= 1 ¡

µ

1 ¡

P 2

P 1

¶ ¯ ¯ ¯ ¯ ¯

1 ¡ !

! 1

1 ¡ ! 2

! 1

¯ ¯ ¯ ¯ ¯

b

C = P = !

33

Power approximation

Example: Peugeot engine XV3 943 cm³

One gets

uver pour l'approximation de type puiss

b =

!1!2¡ 1

P1P2 ¡ 1

=2¡ 1

1; 5996¡ 1 = 1; 698

34

Power approximation

Example: Peugeot engine XV3 943 cm³

Inserting this value into the expression of the curvature coefficient A

Finally the expression of the power approximation of the power writes

35

Polynomial approximation


Power

Torque

proximation peut s'¶ecrire de maniµe

P(!)=Pmax 'nX

i=0

ai (!=!nom)i

. Le couple moteur est donn¶e par

C(!)=C1 'nX

i=0

ai (!=!nom)i¡1

36


Polynomial approximation of order 3

Identification of the coefficients

lynome du troisiµeme ordre (n=3).

P(!)=P1 = a0 + a1 (!=!1) + a2 (!=!1)2 + a3 (!=!1)3

rmettant de

e P(0) = 0 endre en compte l

ue P(!1) = Pmax.

d que P(0) = 0 et qu

a0 = 0

a1 + a2 + a3 = 1

que ce maximum vaut Cmax :

P(!2) = P2 = Cmax !Cmaxd C

d!

¯¯!2

= 0

¯¯

posons n2 = !2=!1, il vient :

a1 n2 + a2 n22 + a3 n

32 = P2=P1

a2 + 2 a3 n2 = 0

¯¯

imer ces deux

s n2 = !2=!1,

37



Identification of the coefficient

Same as polynomial of order 3 + new condition on the maximum power in w1:

iµeme degr¶e.

P(!)=P1 = a0 + a1 (!=!1) + a2 (!=!1)2 + a3 (!=!1)

3

+ a4 (!=!1)4

le en !1, soit :

a1 +2 a2 +3 a3 +4 a4 = 0

38



Value of the coefficients

iµeme degr¶e.

P(!)=P1 = a0 + a1 (!=!1) + a2 (!=!1)2 + a3 (!=!1)

3

+ a4 (!=!1)4

:

a1 + a2 + a3 + a4 = 1

a1 + 2 a2 + 3 a3 + 4 a4 = 0

a1 n2 + a2 n22 + a3 n

32 + a4 n

42 = P2=P1

a2 + 2 a3 n2 + 3 a4 n22 = 0

¯¯

imer ces deux

s n2 = !2=!1,

39

Example: 2.0 HDI PSA engine

40


0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000

1

2

3

4

5

6

7

8

9

10

x 104 Caractéristique moteur

Vitesse moteur [min-1]

Puis

sance m

ote

ur

[W]

Cubique

Type Puissance

41


0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000

50

100

150

200

250

300

350

Couple moteur

Vitesse moteur [min-1]

Couple

mote

ur

[N.m

]

Cubique

Type Puissance

42

Engine Universal Performance Map

Golverk (SAE 941928) showed the a response surface with quadratic terms can represent with a sufficient accuracy the engine map

be [gr/kWh] the BFSC

T [Nm], the brake torque

N [rpm], the engine rotation speed

ai: Empirical coefficients to be identified

43

Engine Universal Performance Map

44

Electric machines

45

Performance curves of electric machines

46

Power electronic and control of DC machines

Working principle of a chopper 47

Power electronic and control of AC machines

Working principle of an inverter 48

DC motor: series and separated excitation

DC series motor DC motor with separated excitation

49

AC motors: induction vs synchronous

AC induction motor AC synchronous motor 50

Traction motor characteristics

At low speed: constant torque

Voltage supply increases with rotation speed through electronic converter while flux is kept constant

At high speed: constant power

Motor voltage is kept constant while flux is weakened, reduced hyperbolically with the rotation speed

Base speed: transition speed from constant torque to constant power regime

51


Independently from the motor technology, the global performance of the combined motor and its power electronic system offer three regimes

In low regimes, the current is limited and the torque is kept constant

Then, power becomes constant, which means that maximum torque as to reduced as P/N

At very high speed: the max power regime can not be maintained and power drops. Generaly this part is not considered in the EV design.

52


Speed ratio x = ratio between maximum rotation speed to base speed X ~ 2 Permanent Magnet motors

X ~ 4 Induction motors

X ~ 6 Switched Reluctance motors

For a given power, a long constant power region (large x) gives rise to an important constant torque, and so high vehicle acceleration and gradeability. Thus the transmission can be simplified.

53


Traction electric motor are able to sustain overcharging during a short period of time, typically 1 to 2 minutes.

Overcharging factor depends of the electric motor technology but can range from 2 to 4.

Thus one distinguishes the continuous power from the peak power (which is much higher)

One can admit as a basic approximation that both regimes can be deduced from each other by just a scaling factor

54


Electric machine efficiencies to transform the electric power to mechanical power is dependent on the working conditions

It can mapped on the torque/speed or power speed space

The efficiency mapping can be different when working as a motor (generally lower) than as a generator (often better)

55

Propulsion system architecture

56

Propulsion system

Gillespie, Fig 2.3 57

Layout of transmission

Transversal mounting Longitudinal mounting 58

Friction Clutch

Clutch in closed position Clutch in open position

59

Hydraulic coupling

Principle: use hydro kinetic energy of the fluid to transfer smoothly the power from the source to the load while amplifying the output torque

The input wheel plays the role of a pump whereas the output wheel acts as a turbine

One may add a fixed wheel (stator) to improve the efficiency

60

Friction and hydraulic clutches

Clutch efficiency

Friction clutch h=1

Hydraulic coupler: h~0.9

61

Manual gear boxes

Gear box principles

Input shaft

Output shaft

Intermediate shaft

Direct transmission

62

Manual gear boxes

63

Manual gear boxes

Neutral

1st 2nd

3rd

Reverse 64

Manual gear boxes

Gear selection 65

Manual gear boxes

Gear selection And selection mechanism

66

Power and tractive efforts at wheels

67

Power and tractive efforts at wheels

Manual gearbox efficiency:

Efficiency of a pair of gear (good quality) h= 99% à 98.5 %

Gear box: double gear pairs: h = 97.5%

Gear box: direct drive: h = 100%

Differential efficiency:

Longitudinal engine layout: axis offset and change of direction with hypoid gears: h = 97,5 %

Transverse engine layout (no change of direction): regular gears : h = 98,75%

68

Automatic gear boxes

The basic element of automatic gear boxes is the planetary gear train

Sun = planétaire Planet = satellite Annulus = Couronne 69

Planetary gear pair

Kinematics: Willys formula

Relation between the rotation speed of the different gear trains and the ratio of teeth of the sun and the annulus

Static: Equilibrium of torques

wCwCwPS

wSwP

C

P

Zi

Z

( )C C P P PS C PZ Z Z Zw w w

1(1 )PS P C

iT i T T

i

(1 )P C PSi iw w w

70

Automatic gear box

Principle of an automatic gear box based on double planetary gear trains

Mèmetaux Fig 5.9 71

CVT : Van Doorne System

Pulleys with variable radii

72

CVT : Van Doorne System

Working principle

By modifying the distance between the two conical half shells, one modifies the effective radii of the pulleys and so the reduction ratio

Originally the system was based on the centrifugal forces, but nowadays the system is actuated by depression engines and controlled by microprocessors

PERFORMANCES

Variable reduction ratios varying between 4 to 6 are achieved

Variable efficiency variable with the input torque and the rotation speed

73

Differential system

During turn, the inner and outer wheels have different rotation speeds because of different radii.

Differential systems allow a different speed in left / right wheels while one single input torque

Differential systems can be studied as planetary gears with equal number of teeth for sun and annulus.

Input shaft (engine)

Output shafts (wheels)

74

Differential system

Working principle of differential system 75

Differential system

Efficiency of differential

Longitudinal layout: 90 change of direction (bevel pair) + offset of the shaft (hypoïd gear): h = 97,5 %

Transversal layout: no bevel good quality gear pair: h = 98,75%

76

Transfer box

Special differential system for 4-wheel drive vehicle

The transfer box splits the torque between the front and rear axles.

77

performance et comportement des vehicules · 2015-10-11 · 2.255 210@5300 210@3500 15.9 15.7 bmw...

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