EB2014-BA-007

ENHANCEMENT OF ENERGY EFFICIENCY, VEHICLE SAFETY AND

RIDE COMFORT FOR ALL-WHEEL DRIVE FULL ELECTRIC

VEHICLES 1Savitski, Dzmitry*,

1Augsburg, Klaus,

1Ivanov, Valentin

1Ilmenau University of Technology, Germany

KEYWORDS – brake force distribution, brake blending, optimization, regenerative braking,

electric vehicle

ABSTRACT

The optimal brake control in the case of a full electric vehicle must not only guarantee high

brake performance but also aim at maximum possible level of energy regenerated during the

manoeuvre. Targeting integrated electric vehicle control, the driving comfort should be also

considered as a component requiring optimization. These factors have motivated the

presented study and allowed to formulate the main objective: Development of optimal brake

control strategy based on three criteria – brake performance, energy efficiency, and ride

comfort.

The research is subjected to a full electric passenger vehicle equipped with four in-wheel

motors and an electro-hydraulic brake system. On the first stage of the research, the

optimization procedure is proposed for the brake torque distribution. Three domains are

chosen for the shaping of the corresponding optimization cost function: the brake

performance is being estimated by deceleration tracking during the manoeuvre; the energy

consumption is quantified through regenerative energy and tyre dissipation energy; the

indicator for the ride comfort (in the case of straight-line braking) is the pitch angle. The

verification of the developed brake control functions is carried out using the vehicle simulator

in IPG CarMaker and hardware-in-the-loop platform with installed electro-hydraulic brake

system.

The straight-line braking manoeuvre has been investigated as the case study. The proposed

technique allowed to reach an optimal brake force distribution with high level of brake energy

recuperation and simultaneous keeping of required safety level. The pitch oscillations caused

by the vehicle behaviour at emergency braking have been also reduced as compared with the

brake manoeuvre without brake distribution / blending control. The experiments were done on

the basis of model- and hardware-in-the-loop simulations. The characteristics of electric

motors are deduced from experimental data. The real hardware components of the brake

system are used including the hydraulic control unit. The controller is emulated in real-time

mode using dSPACE tools.

The results of the presented study have showed that an optimal brake control in the case of the

electric vehicle allows to achieve a multilateral effect in reduction of the brake distance,

increase of brake energy regeneration and improvement of the ride comfort at braking.

TECHNICAL PAPER

INTRODUCTION

New variants of powertrain and chassis architecture are continuously addressed in recent

studies in electric vehicle engineering. In particular, many trends in powertrain development

aim to reduce the complexity of transmission elements and size of electric motors with

simultaneous improvement of their performance. In this context, one of the promising

solutions is an on-board architecture with individually controlled motors on each wheel. Such

kind of architecture reduces the power losses due to absence of the central or axle differential,

improves compactness and proposes more flexible wheel torque control. Nevertheless the

half-shafts and reduction gears in this type of powertrain still exist. They can be eliminated

using the compact in-wheel motors transferring the power directly to the wheel without any

transmission elements. In general such powertrain composition provides much better response

time, extends the operational frequency and reduces power losses.

Modern electric vehicles are also using new brake architecture and, first of all, brake-by-wire

concepts represented by electro-mechanical (EMB) and electro-hydraulic (EHB) brake

systems. Nowadays EHB systems with hydraulically decoupled brake pedal and callipers are

gaining more and more acceptance due to benefits in fast response time and individual control

on each wheel in comparison to the conventional brake systems. In the case of electric fail the

EHB system maintains the functionality of the hydraulic brake system, but without boost

control.

Thus, a combined use of electric powertrain with the individually controlled motors and the

decoupled brake system can benefit energy efficiency, brake performance, fun-to-drive,

vehicle stability and handling, emissions reduction and other operational characteristics of the

vehicle. In the same time, several other characteristics, which can be also improved by using

of combined actuators of an electric vehicle, are still rarely investigated. In particular, it

concerns the ride comfort, which can be also potentially improved using the brake control.

Several preliminary solutions in this area are known from research literature. Fujimoto and

Sato propose in (1) and (2) the control of the pitch angle both through advancement of

conventional wheel slip control functions and electric motors. However, the proposed method

is applicable only at the low vehicle velocities. Morita and Matsukawa introduce the method

for pitch reduction by increasing of the rear brake force (3). This approach represents only a

particular case of brake force distribution and requires specific suspension adjustments.

In the proposed research the particular task of pitch angle reduction and improvement of ride

comfort is related to the optimal brake force distribution. The potential of such optimization is

mostly investigated in scope of energy efficiency and vehicle safety (4-5). Authors propose to

consider the correlation between all three vehicle characteristics and find optimal solution for

the different driving modes. This solution can be additionally used with brake blending

algorithms to gain their efficiency in any driving mode.

Since the most of optimization procedures are carried out without considering external

disturbances, the strategy of their compensation is proposed basing on approach proposed in

(6). This control strategy demonstrates its efficiency, when the long-term processes such as

wear of tires or brake pads influence on the braking efficiency.

Special attention in this paper is addressed to the testing procedure of control algorithms for

electric vehicles. Except of the spread used hardware-in-the-loop (10) technique the test rig

in-the-loop (TRIL) approach proposed by Augsburg et. al (7) realized particularly for the

EHB system and disc brakes. This testing method directly uses the information from other test

benches shorting the step between test bench experiments and the road tests.

Scanty exploration of integrated brake performance and ride control for electric vehicles has

motivated the presented study and allowed to formulate next objectives:

Development of optimization procedures allowing tuning of the base brake control

functions by criteria of vehicle safety, energy efficiency and ride comfort;

Realization of the developed optimization tools for specific electric vehicle

configuration with individually controlled in-wheel motors and decoupled electro-

hydraulic brake system;

Improvement of vehicle safety the developed brake controller through embedding of

correction mechanisms compensating external disturbances.

Experimental validation of the brake controller using hardware-in-the-loop (HIL)

platform and advanced with use dynamometric test bench.

The results of works performed in accordance with the proposed objectives are being

presented in next chapters of the paper.

MODEL OF ELECTRIC VEHICLE AND SUBSYSTEMS

The vehicle under investigation is the sport-utility vehicle (SUV) with overall mass of 2045

kg. The vehicle is equipped with an electro-hydraulic brake system and powertrain with

individual in-wheel electric motors, Figure 1.

Figure 1: Electric vehicle configuration

For the steady-state operation of electric motors the torque maps represented Figure 2 are

used. The transient operation of motors is described through the first-order transfer function

(13):

, 0.002

,

1

0.0022 1

em i s

ss

em i

Te

T s

. (1)

The suspension system is represented by (i) springs with constant stiffness of 26700 and

23000 N/m for front and rear axle respectively, (ii) stabilizers with stiffness of 8251.4 and

6833.5 N/m for front and rear axle correspondingly, and (iii) shock absorbers with

characteristics shown in Figure 3.

Figure 2: Torque-speed and efficiency characteristics of the in-wheel electric motor

Figure 3: Shock absorber characteristics

For the simulation and optimization procedures the behaviour of the brake system is

represented by the validated first-order transfer function:

0.0251

0.02 1

actsi

ref

i

pe

p s

. (2)

The vehicle is equipped with tyres 235/60 R18. Tyre parameters in the brake controller are

deduced with the use of Pacejka model.

CRITERIA FOR INTEGRATED ASSESSMENT OF VEHICLE DYNAMICS

A set of the assessment criteria require formulation to evaluate ride comfort, vehicle safety

and energy efficiency. These criteria can be further used for the purposes of optimization

related to the longitudinal brake events at any appropriate part of the vehicle controller.

The vehicle safety is characterized in the proposed optimization procedures through the error

between actual and reference vehicle deceleration. This criterion is covering in particular

some special cases as driving in platoon: underestimated braking distance can provoke an

accident. It is proposed to use integral of time-multiplied absolute value of deceleration

tracking error:

0

T

ITAE act ref

x x xa a a dt . (3)

The reference value of the vehicle deceleration is calculated from “brake pedal travel-

deceleration” characteristic implemented in the base-brake control algorithm and described

further.

Energy characteristics are estimated with two criteria. The most important and valuable of

them is the recuperated energy, which can be harvested using operation of electric motors in

the generator mode. This energy can be expressed through the electric motor power:

4

,

1 0

T

brake

em em i

i

E P dt

. (4)

Another parameter related to energy efficiency in the case of the longitudinal motion of the

vehicle is the tyre energy dissipation, which can be derived from the longitudinal tyre forces

and wheel slip speeds:

4

, ,

1 0

T

slip

tyre xw i xw i

i

E F V dt

. (5)

For the cases of vehicle braking on the flat road, ride comfort can be characterized by the

dynamics of the pitch angle both in steady-state and transient conditions. For this purpose the

integral value of the pitch angle error is proposed:

0

T

ITAE act ref dt , (6)

As soon as any vertical oscillations are negatively influence ride comfort, the reference value

of the pitch angle θref

(an ideal case) can be set to zero.

OVERALL CONTROL STRUCTURE

General Description

The brake controller of electric motors and electro-hydraulic brake subsystem consist of next

main functional parts,

Figure 4: (i) state and parameter estimation; (ii) base-brake controller; (iii) disturbances

compensator; (iv) brake force distribution; (v) brake blending.

Figure 4: Controller structure

The input from the driver is the brake pedal displacement acquired by corresponding sensor.

This signal is addressed to the base-brake controller calculating the total torque demand for

required level of deceleration. The demanded torque is corrected in accordance to the external

disturbances and addressed to the brake torque distribution block, where the demand is

separated to the front and rear axles according to the predefined algorithm. The brake

blending block allocates these torques individually to each wheel. The final torques are

realized by the corresponding vehicle subsystem: friction brake system or electric motors. The

state observer supplies the functional block with data which can be obtained only by indirect

methods. This state observer has a multiple-model structure with combined several

observation methods working in parallel. On the output there are tire forces, vehicle actual

mass, road grade, rolling resistance and air drag forces. The detailed description of the state

observer is skipped in the framework of the proposed research.

Base-brake Controller

The base-brake controller generates total torque demand for requested vehicle deceleration

and works in an open-loop mode. The reference deceleration value is calculated from the

relation between the brake pedal displacement and the vehicle deceleration,

Figure 5.

Figure 5: Reference deceleration level in accordance to brake pedal displacement

The total torque demand produced by base-brake controller can be formulated as follows:

ref

demand a x wT m a r , (7)

where m is the vehicle mass, rw is the wheel radius.

The torque demand from Eq. (7) does not consider external disturbances occurring during the

vehicle motion. A particular case with disturbances and their compensation will be discussed

in next chapters.

Brake Blending

The brake blending algorithm has individual wheel torque demands as the inputs and

separates them between the electric motors and the hydraulic brake system. The algorithm

takes into consideration the motor torque constraints determined by the battery limitation and

the motor operation mode. The presented brake blending strategy aims to the maximum

energy recuperation and maximum use of electric motors functionality on the high-frequent

operation modes. In general the brake blending algorithm logic is based on the set of rules and

limitations:

The torque of electric motor is used at maximum possible level in relation to the

hydraulic brake system to ensure the energy-efficient braking;

On low vehicle velocities only friction brake system is used due to the low efficiency

of electric motors in energy recuperation;

Torque demands of higher frequencies are realized through electric motors.

The calculated torque is sent to the low-level actuator controllers, which are responsible for

the realization of appropriate torque requests.

Brake Torque Distribution

The brake torque distribution block is responsible for the separation of the total torque

between the front and rear axle in accordance to the predefined rules. In contrast to the widely

used distribution strategies focused only on the vehicle safety, the influence of the brake force

distribution on some particular characteristics should be evaluated in the case of the electric

vehicle. Within this context, the presented work has studied the influence of the brake

distribution strategy on the assessment criteria from Eqs. (3)-(6) to estimate the feasibility of

the brake force distribution optimization in relation to integrated criteria of safety, energy

efficiency and ride comfort.

To show the potential benefits from optimization of brake force distribution, a set of typical

distributions has been analysed: (i) constant and (ii) bilinear distribution. The represented

distributions are investigated in several variations.

The brake force distributions operate with the ratio between the rear brake force and total

brake force:

br br

rear totalF F . (8)

This ratio can be both constant and variable in accordance to the current deceleration level Zi.

Constant Brake Force Distribution

The brake force distribution from Figure 6 is represented by the constant -ratio, i.e. the

front and rear brake forces have a linear relation. The -ratio is varied in range from 0.03,

which is close to the ECE limitations line, and up to 0.5. Some of corresponding distributions

are shown in Figure 6 as dashed lines.

Figure 6: Variations of constant brake force distribution

The distribution ratio influence on the pitch transient characteristics can be seen on Figure 7:

Pitch angle responseFigure 7, where the difference in the oscillations amplitude can reach up to 0.6

degree depending on the -value. It can be concluded that the increase of the brake force on

the rear axle can lead to the reduction of pitch angle. This effect is also discussed in studies of

other authors (3). Figure 8 shows a tendency of deceleration error decrease up to =0.18 and

then the ITAE-value raises again. Hence, with this brake distribution variant, the

improvement of vehicle safety criteria does not lead to a noticeably better ride comfort.

Figure 7: Pitch angle response

Figure 8: Deceleration ITAE

It is important to mention the correlation between the recuperated energy and tyre energy

dissipation in relation to the brake force distribution ratio, Figures 9 and 10. Minimum levels

of the tyre energy dissipation and the recuperated energy are observed for the same range of

the -ratio. On the other hand, the highest potential for the brake energy regeneration takes

place within the range the -ratio, where the tyre energy dissipation is increased. Hence, the

constant brake force distribution is characterized by a conflict between both criteria of energy

efficiency.

Figure 9: Recuperated energy

Figure 10: Tyre energy dissipation

Ideal (Bilinear) Brake Force Distribution

An ideal distribution in particular case is represented by a set of bilinear distributions. It

consists of two lines connected in the switch point. Figure 11 shows how they are being

changed in respect to the shifting of switch deceleration from 0.05 to 0.95 g with the step of

0.05 g. It can be seen, that the pitch angle represented in Figure 12 has actually no strong

dependence on switch point position. It means that the ideal brake force distribution has less

potential to an essential improvement of the ride comfort as compared with the case of the

constant distribution.

Figure 11: Variations of bilinear brake force distribution

Figure 12: Pitch angle response

Figure 13: Deceleration ITAE

The conflict between criteria of the tyre energy dissipation and energy regeneration, described

in previous section of the paper, takes place also at the ideal brake force distribution, Figures

14 and 15. However, it can be noted that more important criterion - recuperated energy - has

a good correlation with the deceleration error, Figures 13. It can guarantee maintenance of

high safety level for the energy efficient algorithms.

Figure 14: Recuperated energy

Figure 15: Tyre energy dissipation

As it can be seen from the aforementioned analysis, simultaneous improvement of ride

comfort, vehicle safety and energy efficiency is potentially feasible and can be realized

through the procedures of brake forces optimization, which are described in next chapter.

BRAKE FORCE DISTRIBUTION OPTIMIZATION

Previous chapter has indicated certain conflict between ride comfort, vehicle safety and

energy efficiency in the case of conventional variants of brake force distributions. To resolve

this task, optimization of the brake force distribution should be carried out. Since the

optimization procedure operate with different vehicle characteristics, a corresponding cost-

function has to be composed. For this purpose the criteria from Eqs. (3)-(6) can be used as

follows:

1 2 3 4

max( ) max maxmax

ITAE ITAE

x em tire

ITAE ITAEx em tire

f a f f E f EJ w w w w

a E E

. (9)

Weight coefficients wi are represented by three cases to cover three different driving modes

aimed to (i) pitch angle reduction, (ii) normal mode with approximately equivalent weights

for each parameter, and (iii) maximum energy recuperation respectively. The parameters to be

optimized are ratios Φi for the predefined decelerations Zi. In the proposed solution eight

points from 0.1 to 0.8 g with step of 0.1 g are used. Constraints imposed on the Φ-ratio are

represented by the two typical curves: ECE regulation curve and ideal distribution curve

(prevention of earlier lock of the rear axle).

The thermal constrains of brake discs and electric motors are neglected due to the complexity

of its estimation in the investigated wheel hub architecture.

The approach selected to solve the optimization procedure is based on the interior-point method. The output

vector consists of the eight Φi distribution ratios depicted as the red dots in

Figure 16.

Figure 16: Example of optimization procedure with found optimal points

The efficiency evaluation of the optimized distributions is done by means of the hardware-in-

the-loop technique and using the real electro-hydraulic brake system TRW SCB (8) and will

be further introduced.

It should be mentioned that the presented study has used a more complex vehicle model for

the offline optimization procedure in comparison to known approaches. In particular, the

computation of brake torques in accordance with optimized -ratio is advanced with the

correction mechanisms compensating the influence of external disturbances on the brake

dynamics. This aspect is rarely presented in the brake controller variants known from the

research literature. The basic information of the proposed compensators is presented in next

chapter.

DISTURBANCES COMPENSATOR

In the previous chapters the tracking of the longitudinal deceleration as the assessment

criterion of vehicle safety was investigated in scope of the absence of external disturbances. In

the reality the deceleration tracking can be worsen by resistance forces and degradation of

tyre and brake friction characteristics. Such decrease in tracking precision can be occurred in

the case of brake lining friction coefficient fluctuations that have been investigated within the

framework of the presented research. To improve tracking of the deceleration minimizing the

error in Eq. (3) and to enhance vehicle safety, an original disturbance compensation algorithm

is proposed. This compensation algorithm is based on the evaluation of correction factor used

to produce the compensation torque demand.

The longitudinal vehicle motion and rotational wheel dynamics neglecting the losses and

resistance of propulsion system can be written as follows (5):

4

1i

act act

a x x aero roll grade

i

m a F F F F

, (10)

w w w x wI T F r , (11)

Assuming that the component i iw wI is insignificant in comparison with the wheel torque

iwT

the Eq. (11) can be formulated as:

4

1

i

i

act

wact act

a x aero roll grade x aero roll grade

i w

Tm a F F F F F F F

r

. (12)

The actual torque i

act

wT can be distorted in comparison to the demand i

dem

wT due to the several

reasons such as tyre pressure inflection/deflection, tyre wear, brakes overheating, etc. To

compensate this difference, the correction factor fcor is proposed:

ref act

a x cor x aero roll gradem a f F F F F . (13)

The demanded deceleration can be expressed through the demanded brake force:

ref dem

a x x aero roll gradem a F F F F . (14)

Assuming precise estimation of the aerodynamic drag force, rolling resistance and road grade,

the following equation can be proposed:

ref ref act dem

a x cor a x x x compm a f m a F F F . (15)

Therefore the compensation torque compT required to minimize error between actual and

reference deceleration in relation to the correction factor can be expressed as follows:

1cor demand compf T T . (16)

To estimate the correction factor, the recursive least squares method is used with the

following formulation:

1ˆ ; ; act act

a x x aero roll grade

cor

y m a F F F Ff

. (17)

The correction factor can be applied for the case of lining friction coefficient deviation

between the value stored in the controller and the real value. Lining friction coefficient is used

in the calculation procedure for the conversion of the brake torque demand to the pressure

demand, which should be sent to the EHB system:

2

friction

actuali out

wc eff L

TP P

A r , (18)

where L is lining friction coefficient; friction

totalT is the friction brake system torque demand.

Due to the open-loop pressure control, the difference in the friction coefficient value stored in

the controller and the real value can cause the brake torque distortion. To avoid such a

situation, the mentioned compensation procedure is required. Its implementation will be also

presented in next chapter for the case of fading effect.

EXPERIMENTAL PLATFORM AND RESULTS

Experimental platform description

To approbate the developed controller set of the experiments is carried out on the

experimental test bench firstly represented in (10) and further used in particular for

development of base-brake control functions (8). The testing procedure is advanced with use

of dynamometric test bench for evaluation of compensation algorithm efficiency. Depicted in

Figure 17 as the principle scheme, the hardware-in-the-loop test platform is represented by

next main components: i) dSPACE real-time computer and interface modules; ii) Slip

Control Boost (SCB) EHB system, Figure 18; iv) External testing procedure information

about brake lining friction coefficient extracted from the brake dynamometer.

Figure 17: Hardware-in-the-loop test platform with use of external testing procedure at brake dynamometer

The HIL platform is based on the dSPACE instruments for real-time simulation, data

acquisition and the connection with the vehicle hardware: i) a processor board (ds1006) for

real-time simulations; ii) analogue input boards (ds2002) to acquire data from pressure

sensors, force and displacement from brake robot; iii) CAN communication board (ds4302) to

send a pressure demands to the brake system and acquire data from EHCU; iv) digital I/O

board (ds4004) controlling the brake robot.

Figure 18: Brake system installation on the hardware-in-the-loop test platform

For the investigations in the compensator functionality under long-term disturbances

influence, the brake dynamometer is used to collect a realistic data of brake lining coefficient

behaviour, Figure 19. The test bench has adjustable inertia mass and can be set to the

equivalent inertia value of the investigated vehicle. Time profile of the brake lining friction

coefficient extracted from the manoeuvre running on the dynamometer is further transmitted

to the HiL platform. This concept is a particular realization of test-rig-in-the loop (TRIL)

approach introduced in (11).

Figure 19: Brake dynamometer

Optimized brake force distribution

Three different strategies have been investigated with the HIL tests:

Minimization of the pitch angle (“Comfort” strategy)

Enhancement of all the criteria with equal weight coefficients (“Normal” strategy)

Improvement of the energy efficiency (“Eco” strategy).

To see the effect of optimization procedure two typical brake force distributions are analysed

in addition: the constant distribution with =0.25 and the ideal distribution.

All of the proposed cases should provide appropriate vehicle safety characteristics. As it can

be seen in Figure 20, all the distributions except "Comfort" mode provide precise tracking of

the reference deceleration. The "Comfort" mode produces underbraking and has the highest

stopping distance, Figure 21. Hence, the application of this mode cannot be recommended for

the use in the case of a high deceleration level. On the other hand, the “Comfort” mode

successfully decreased the pitch angle under the braking mode on 0.55 deg (15%) in

comparison to the other modes, Figure 22.

Figure 20: Deceleration ITAE

Figure 21: Stopping distance

Figure 22: Pitch angle

Analysis of the energy efficiency criteria shows that the target of the "Eco" mode in

increasing recuperated energy is successfully achieved, Figure 23. The worst results in this

respect are observed for the "Comfort" mode. It should be especially noted that the conflict

between minimization of the tyre energy dissipation, Figure 24, and improvement of the brake

energy recuperation has been observed for all the modes. Thus, enhancement in energy

harvesting with simultaneous reduction of tyre friction losses could not be achieved by means

of the optimization of brake force distribution.

Figure 23: Recuperated energy

Figure 24: Tyre energy dissipation

The represented strategies according to the represented results can be described and used as

follows:

The “Eco” drive mode should be used as the strategy with maximal energy

recuperation, but does not supply minimization of the tyre energy dissipation due to

the criteria conflict;

The “Comfort” strategy has more limited application and can be applied during the

service braking;

The use of “Comfort” strategy on the high deceleration level is impossible and

optimization weights should be redistributed to achieve more vehicle safety;

The “Normal” strategy is represented as balanced compromise between all three

characteristics (ride comfort, energy efficiency and vehicle safety) and can be used

with any further controller composition as the basis configuration.

Disturbances Compensation

In addition to the represented brake force distribution strategies the compensation algorithm

dedicated to improve the tracking of deceleration and improve vehicle safety is approbated

using the HIL and brake dynamometer testing facilities. At the first stage the behaviour of the

brake lining friction coefficient was investigated considering the full load of hydraulic brake

system, Figure 25. In such conditions the coefficient of friction shows the maximal influence

on the brake performance. The testing procedure is carried out in accordance with standard

ISO26867 (12). It consists of 15 braking applications with deceleration of 0.4 g from the

initial velocity of 100 km/h in each case.

Figure 25: Fading effect

For the efficiency assessment of the proposed control strategy case of controller without

compensation mechanism is represented. In the both compensated and non-compensated

cases the friction coefficient is changing as in abovementioned testing procedure. The

manoeuvre is the same as in (12) and both vehicles have enough precise tracking of the

vehicle velocity to produce deceleration of 0.4 g. As it can be seen in the Figure 26 in non-

compensated case deviation of the actual deceleration from reference signal characterized by

ITAE is increasing with the friction coefficient degradation. The proposed compensation

mechanism successfully evaluates the correction factor represented in Figure 27 filtering it

from the other disturbances as rolling resistance and air drag force. At the end of the

manoeuvre according to the set of proposed rules for stepwise change of the correction factor

it reaches a four times better results than in the non-compensated case.

Figure 26: Deceleration ITAE

Figure 27: Correction factor

Hence, the proposed disturbance compensation algorithm successfully evaluates the

correction factor to avoid the loss of brake efficiency during long-term processes in particular

in case of fading. This control strategy working in parallel with the proposed distribution

strategies and has been tested with the real EHB system and brake prototype to gain further

improvements in vehicle safety

CONCLUSIONS

The presented study has introduced procedures of multi-criteria optimization of the brake

control of the electric vehicle in terms of safety, energy efficiency and ride comfort. It was

shown that the selective optimization of the brake force distribution can result either in

achieving of high level of brake energy regeneration of in reduction of the pitch angle during

the straight-line braking with simultaneous keeping of required vehicle deceleration. The

proposed optimization procedure was implemented in the base brake controller of electro-

hydraulic brake system advanced with external disturbances compensator. The functionality

of the developed controller was investigated using HIL technique in combination with brake

dynamometer. The obtained results can be used by for development of the integrated chassis

control systems of electric vehicles.

ACKNOWLEDGEMENTS

The research relates to the research group PORT at Ilmenau University of Technology funded

by the European Social Fund ESF (project No. 2011 FGR 0120). The electro-hydraulic brake

system and kind support in its tuning is provided by the TRW Automotive, Koblenz.

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