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Accessible pre-design calculation tool to support the definition of EV components

  • M. Roche
  • D. Sabrià
  • M. Mammetti
Article

Abstract

The new freedoms in design that electric powertrains offer lead to a wide variety of configurations to consider when developing an electric vehicle (EV) from scratch. Furthermore, the strong relation of the battery size with vehicle weight, range and performances leads to a set of interrelated dependencies that can result in many design loops to fulfil the vehicle targets, market constraints and regulations simultaneously. The paper presents a pre-design tool to assist the electric vehicle development process by representing the different constraints and the possible feasible solutions in a single plot with the need of a small amount of inputs accesible to assess at pre-design phase. As a result, the tool depicts a set of feasible vehicle configurations that could fulfil the targets easing the interaction and loops among different expertise areas. To better assist selection, it also provides a sensitivity analysis of the performances to selected inputs and the user can introduce a cost function depending on vehicle weight and battery size. The tool is based on the vehicle longitudinal dynamics equations and equations that model the market and regulations constraints. It is aimed at providing an overview of the main specifications for component selection avoiding detailed vehicle modelling in the early pre-design phase at which the vehicle characteristics and even powertrain architecture are unknown. Finally, the tool results quality is evaluated by further developing one of its solutions for passenger car in four different vehicle configurations with the simulation software vemSim and AVL Cruise. The results of the simulations are compared to the solution of the pre-design tool to evaluate the level of fidelity and the deviations in the final result that can appear depending on the final architecture, components characteristics and control strategy.

Key words

Electric vehicle Energy consumption Target setting Simulation Performances 

Nomenclature

α

gradeability target, º

αref

reference grade for speed target, º

χ1(t)

true when positive or null acceleration in a cycle

χ2(t)

true when negative acceleration in a cycle

εbat

battery volumetric energy density, kWh/l

ηpeak

peak powertrain efficiency, %

πbat

battery volumetric power density, kW/l

ρair

air density, kg/m3

ρbat

battery density, kg/l

Af

aerodynamic frontal area, m2

B

consumption in a specific cycle, kWh

C

cost function as a function of battery capacity and vehicle mass

Cx

aerodynamic drag coefficient

D

distance overtook during a cycle, m

E

coefficient to compute the inertia contribution to the acceleration power requirements, W/kg

F

coefficient to compute the drag contribution to the acceleration power requirements, kW

F0

coast down coefficient to compute the constant resistance forces, N

F2

coast down coefficient to compute the squarespeed dependent resistance forces, N(m2/s2)

G

coefficient to compute the constant resistance forces contribution to acceleration power, m/s

f

tyre rolling resistance, kg/t

g

gravity constant, m/s2

Irot

relation of rotating parts equivalent inertia to vehicle mass, %

i

segment selected

k

vehicle inertia coefficient

m

vehicle mass, kg

mdriver

driver mass, kg

meq

equivalent total mass considering inertia, kg

mextra

extra mass applied (driver + load), kg

mload

payload mass, kg

mmax,i

upper vehicle mass limit per segment, kg

mmin,i

lower vehicle mass limit per segment, kg

mmax,a

quadricycles: acceleration target mass limit, kg

mmax,α

quadricycles: gradeability target mass limit, kg

mmax,v

quadricycles: speed target mass limit, kg

mT

total mass (vehicle + driver + load), kg

mW/O,min,i

lower limit to vehicle mass without battery, kg

mW/O,min,i

quadricycles: upper limit to vehicle mass without battery, kg

n

used for sensitivity analysis

PAux

auxiliaries power consumption, kW

Pa

acceleration power requirement, kW

Pα

gradeability power requirement, kW

Pmax,i

quadricycles: upper power limit

Pv

speed power requirement, kW

R1-3

vehicle range targets for three cycles, m

R

relation of recovered to recoverable energy in deceleration, %

SOClim

battery State Of Charge lower limit, %

Sn

sensitivity of consumption to the variation of parameter n, %

t

time, s

ta

acceleration time target, s

V

battery volume, l

Vmax,i

upper limit to battery volume, l

Vmin,i

lower limit to battery volume, l

v(t)

speed profile in a cycle, m/s

va

speed to achieve in acceleration target, m/s

vb

transition speed from constant torque to constant power in an electric motor, m/s

vb

corrected base speed for acceleration, m/s

vmax

target vehicle speed, m/s

vref

reference speed for gradeability target, m/s

x

motor torque curve characteristic

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References

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Copyright information

© The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  1. 1.Applus+ IDIADASanta Oliva (Tarragona)Spain

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