Impact of Different Driving Cycles and Operating Conditions on ... - MDPI

energies Article

Impact of Different Driving Cycles and Operating Conditions on CO2 Emissions and Energy Management Strategies of a Euro-6 Hybrid Electric Vehicle Claudio Cubito 1 ID , Federico Millo 1, *, Giulio Boccardo 1 , Giuseppe Di Pierro 1 ID , Biagio Ciuffo 2 , Georgios Fontaras 2 , Simone Serra 2 ID , Marcos Otura Garcia 2 and Germana Trentadue 2 1 2

*

Department of Energy, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy; [email protected] (C.C.); [email protected] (G.B.); [email protected] (G.D.P.) Joint Research Centre—European Commission, Via Enrico Fermi 2749, 21027 Ispra, Italy; [email protected] (B.C.); [email protected] (G.F.); [email protected] (S.S.); [email protected] (M.O.G.); [email protected] (G.T.) Correspondence: [email protected]; Tel.: +39-011-090-4517

Received: 29 August 2017; Accepted: 26 September 2017; Published: 13 October 2017

Abstract: Although Hybrid Electric Vehicles (HEVs) represent one of the key technologies to reduce CO2 emissions, their effective potential in real world driving conditions strongly depends on the performance of their Energy Management System (EMS) and on its capability to maximize the efficiency of the powertrain in real life as well as during Type Approval (TA) tests. Attempting to close the gap between TA and real world CO2 emissions, the European Commission has decided to introduce from September 2017 the Worldwide Harmonized Light duty Test Procedure (WLTP), replacing the previous procedure based on the New European Driving Cycle (NEDC). The aim of this work is the analysis of the impact of different driving cycles and operating conditions on CO2 emissions and on energy management strategies of a Euro-6 HEV through the limited number of information available from the chassis dyno tests. The vehicle was tested considering different initial battery State of Charge (SOC), ranging from 40% to 65%, and engine coolant temperatures, from −7 ◦ C to 70 ◦ C. The change of test conditions from NEDC to WLTP was shown to lead to a significant reduction of the electric drive and to about a 30% increase of CO2 emissions. However, since the specific energy demand of WLTP is about 50% higher than that of NEDC, these results demonstrate that the EMS strategies of the tested vehicle can achieve, in test conditions closer to real life, even higher efficiency levels than those that are currently evaluated on the NEDC, and prove the effectiveness of HEV technology to reduce CO2 emissions. Keywords: Hybrid Electric Vehicles; CO2 emissions; WLTP; NEDC

1. Introduction Increasing environmental awareness has been a key driver during the past two decades for the introduction of stricter regulations for the control of pollutant and CO2 emissions from passenger cars. In particular the European Union (EU) has committed to reducing greenhouse gas emissions from road transport by 60% by 2050 compared to 1990 levels [1]. To meet these challenging CO2 targets, vehicle manufacturers, while relentlessly continuing the research for more efficient powertrains based on Internal Combustion Engines (ICEs), have been developing new technologies such as Electric Vehicles (EVs) and Fuel Cells Vehicles (FCEVs), which can both provide the benefits of zero tail pipe emissions Energies 2017, 10, 1590; doi:10.3390/en10101590

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and can rely on the production of electricity and hydrogen from renewable energy sources [2–6]. However, the market penetration of these new technologies is still quite limited, struggling with often inadequate range capabilities, high costs and lack of infrastructures [7–11]. In this framework Hybrid Electric Vehicles (HEVs) represent an extremely promising solution for the automotive industry to bridge the gap between the desirable features of electric powertrains, the range capability and the more affordable costs of conventional vehicles, because they can ensure higher fuel efficiency and lower pollutant emissions compared to conventional powertrains due to the flexibility provided by the integration of the ICE with the electric powertrain, while still maintaining comparable range capabilities and costs [12,13]. However, the effective potential of HEVs in terms of CO2 emissions reduction in real world driving conditions strongly depends on the performance of their Energy Management System (EMS) [14–16] and on its capability to maximize the efficiency of the powertrain in real life as well as in the chassis dyno tests, which are prescribed for Type Approval (TA). Moreover, since the procedure used to date in Europe for TA [17,18], based on the New European Driving Cycle (NEDC), has been widely criticized and it has been proved to be not representative of real world driving conditions [19,20], the European Commission has decided to introduce from September 2017 the Worldwide Harmonized Light duty Test Procedure (WLTP) [21], replacing the previous procedure in an attempt to close the gap between TA and real world CO2 emissions. The introduction of the WLTP will bring several testing and procedural changes compared to the NEDC, but how this will affect the evaluation of the CO2 reduction potential of HEVs has not yet been fully explored. Very limited number of studies provide experimental evidence of the impact of the introduction of the WLTP on CO2 emissions from HEVs [22–24]. Within this context, the aim of this work is the analysis of the impact of different driving cycles and operating conditions on CO2 emissions and EMS strategies of a Euro-6 HEV. The vehicle measurements were carried out over both the NEDC and the Worldwide Harmonized Light duty Test Cycle (WLTC), which is the reference cycle of the WLTP procedure described in [21]. The characterization of the vehicle EMS was carried out through the limited amount of information available from the TA test, without any detailed characterization of the high voltage battery, the electric machines and the ICE [22,24–26]. After presenting the testing methods and procedures in Section 2 (Methodology), the effects of the new test procedure on CO2 emissions and on the performance of the EMS at different SOC levels, ranging from 40 to 65%, and engine thermal states, from −7 ◦ C to 70 ◦ C, are reported in Section 3 (Results). Finally, the main findings of the work are summarized in Section 4 (Conclusions), highlighting how the change of test conditions from NEDC to WLTP led to an important increase of the specific energy demand of about 50%, and to a corresponding increase of CO2 emissions of about 30%, thus demonstrating that the EMS strategies of the tested vehicle can achieve, in test conditions closer to real life, even higher efficiency levels than those which are currently evaluated on the NEDC. 2. Methodology 2.1. Tested Vehicle The B-Segment HEV features a complex hybrid powertrain, in which an Electric Continuous Variable Transmission (eCVT) is coupled with a Spark Ignition (SI) engine. The main vehicle characteristics are listed in Table 1. In the eCVT system the rotational shaft of the planetary gear carrier is directly linked to engine and it transmits the motive power to the outer ring gear and the inner sun gear via pinion gears. The ICE is a four-cylinder in-line 1.5 L naturally aspirated gasoline with a maximum power of 55 kW at 4800 rpm. The rotational shaft of the ring gear is directly linked to the 45 kW Motor Generator 2 (MG2) and it transmits the drive force to the wheels, while the rotational shaft of the sun gear is directly linked to the electric generator (MG1) [27]. The high voltage battery is a nickel metal hydride unit (NiMH) containing 120 cells connected in series.

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Table 1. Vehicle and powertrain main characteristics [27]. Energies 2017, 10, 1590

Table 1. Vehicle and powertrain main characteristics [27].

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Technical Data Technical Data Table Vehicle and powertrain1120 main [27]. Curb Mass1. kgcharacteristics Curb Mass 1120 kg 1565 kg GrossGross MassMass 1565 kg Technical Data Spark Ignition Naturally Aspirated Spark Ignition Naturally Aspirated Curb Mass 1120 kg Displacement: 1.5 LL Displacement: 1.5 Gross Mass 1565 kg ICE ICE Rated power: kW 4800rpm rpm Rated power: 5555 kW @@ 4800 Spark Ignition Naturally Aspiratedrpm Rated torque: Nm 3600–4800 Rated torque: 111111 Nm @@ 3600–4800 rpm Displacement: 1.5 L ICE Permanent Magnet Synchronousmotor motor Permanent Magnet Synchronous Rated power: 55 kW @ 4800 rpm Maximum output power:4545kW kW MG1-MG2 MG1-MG2 Maximum output Rated torque: 111 Nmpower: @torque: 3600–4800 rpm Maximum output 169 Nm Maximum output torque: 169 Nm Permanent Magnet Synchronous motor Type: NiMH NiMH MG1-MG2 MaximumType: output power: Capacity: 6.5 Ah 45 kW Capacity: 6.5 Ah Battery Maximum output torque: 169VNm Battery Nominal voltage: 144 Nominal voltage: 144 V Energy: 1 kWh Type: NiMH Energy: 1 kWh Capacity: 6.5 Ah Battery Nominal voltage: 144 V vehicle cancan operate in in two depending on the vehicle speed, power demand The vehicle operate twodifferent differentmodes, modes, depending Energy: 1 kWh on the vehicle speed, power demand

The and battery SOCSOC [27]:[27]: and battery 1.

The vehicle can(EV): operate in two the different modes, depending on the vehicle speed, power demand 1. Electric Vehicle whenever ICE would would operate ininanan inefficient range, suchsuch as atas very low low Electric Vehicle (EV): whenever the ICE operate inefficient range, at very and battery SOC [27]: load levels, the ICE is turned off and the traction power is demanded to the MG2, as illustrated

load levels, the ICE is turned off and the traction power is demanded to the MG2, as illustrated

in Figure 1; (EV): whenever the ICE would operate in an inefficient range, such as at very low 1. Electric in Figure 1;Vehicle load levels, the ICE is turned off and the traction power is demanded to the MG2, as illustrated High Voltage Battery in Figure 1; High Voltage InverterBattery Planetary Gear Inverter MG2 Planetary Gear ICE

MG1 MG2

ICE

MG1

Figure 1. EV mode.

Figure 1. EV mode. Parallel Hybrid (PH): at higher load levels the is enabled and it supports the vehicle driving, Figure 1. ICE EV mode. Parallel Hybrid at higher load levels ICE isways enabled and it on supports the vehicle driving, allowing the(PH): powertrain to operate in twothe different depending battery SOC and on the accelerator pedal position: allowing the powertrain operate twothe different ways depending on battery SOCdriving, and on the 2. Parallel Hybrid (PH): at to higher loadin levels ICE is enabled and it supports the vehicle

2.

2.

accelerator pedal position: the powertrain to operate in two different ways depending on battery SOC than and on the allowing Smart Charge (SC): the ICE operating points are shifted at higher load levels those

•

accelerator pedal position: required for the vehicle propulsion, closer to the optimal efficiency area, and the power Smart Charge (SC): the ICE operating points are shifted at higher load levels than those exceeding the vehicle propulsion needs points is used are to recharge batteryload through thethan generator  Smart Charge (SC): the ICE operating shifted the at higher levels those required for the vehicle propulsion, closer to the optimal efficiency area, and the power MG1, as depicted in Figure 2 by the path “A”; required for the vehicle propulsion, closer to the optimal efficiency area, and the power

exceeding the vehicle propulsion needs is used to recharge the battery through the generator exceeding the vehicle propulsion needs is used to recharge the battery through the generator MG1, as as depicted path“A”; “A”;High Voltage Battery MG1, depictedininFigure Figure22 by by the the path

A

High Voltage InverterBattery Planetary Gear Inverter

A

MG2 Planetary Gear

ICE

MG1 MG2

ICE

MG1

Figure 2. SC mode. Figure 2. SC mode.

Figure 2. SC mode.

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•

ElectricBoost Boost(E-Boost): (E-Boost): order to support engine during sudden demands, the Electric in in order to support thethe engine during sudden loadload demands, the high high voltage battery provides an extra power contribution to the MG2, represented by the voltage battery provides an extra power contribution to the MG2, represented by the path pathas“B”, as illustrated in Figure 3. “B”, illustrated in Figure 3. High Voltage Battery

Inverter Planetary Gear MG2

ICE

MG1

B

Figure 3. E-Boost mode. Figure 3. E-Boost mode.

2.2. Test Conditions 2.2. Test Conditions The experimental testing campaign was carried out at the Vehicle Emission LAboratory (VELA) of the Joint Research Centre The test is equipped with a four wheel-drive (4WD) (VELA) chassis The experimental testing(JRC). campaign was rig carried out at the Vehicle Emission LAboratory dynamometer, made Centre of two roller 48 inches m). The(4WD) chassischassis dyno, of the Joint Research (JRC).benches The testwith rig isa diameter equippedof with a four (1.219 wheel-drive located in a climatic chamber, allows a maximum traction torque of 3300 Nm and the vehicle mass dynamometer, made of two roller benches with a diameter of 48 inches (1.219 m). The chassis dyno, range permitted varies from 454 to 2720 kg. Duringtraction the teststorque CO2 and pollutants emissions, as well as located in a climatic chamber, allows a maximum of 3300 Nm and the vehicle mass measurements the engine and thekg. battery were Engine operating parameters, such range permittedon varies from 454 to on 2720 During the recorded. tests CO2 and pollutants emissions, as well as as the revolution and and the coolant temperature, were acquired an On Board Diagnostic measurements on speed the engine on the battery were recorded. Engineusing operating parameters, such as (OBD) scan tool. Instead, thecoolant batterytemperature, current and were voltage were acquired a Yokogawa WT1800 the revolution speed and the acquired using an using On Board Diagnostic (OBD) precision thanks to the access the battery terminals [27]. WT1800 precision scan tool. power Instead,analyzer, the battery current anddirect voltage weretoacquired using a Yokogawa The WLTC thanks and NEDC cyclestowere used for the chassis power analyzer, to thedriving direct access the battery terminals [27]. testing [17,21]. As far as the WLTC concerned, the Class-3 adopted, since characteristics correspond to the TheisWLTC and NEDC drivingwas cycles were used for the the vehicle chassis testing [17,21]. As far as the WLTC highest power to mass ratio. Road Loads (RLs) and test mass definitions prescribed in [17,21] were is concerned, the Class-3 was adopted, since the vehicle characteristics correspond to the highest power applied the NEDC tests. As for and the WLTC tests, requirements of RLs and test mass follow the WLTP to mass to ratio. Road Loads (RLs) test mass definitions prescribed in [17,21] were applied to the regulation adopted for the and two test driving are listed in regulation Table 2. [21]. NEDC tests.[21]. As Coast for thedown WLTCcoefficients tests, requirements of RLs masscycles follow the WLTP Coast down coefficients adopted for the two driving cycles are listed in Table 2. Table 2. Vehicle test conditions [27]. Table 2. Vehicle test conditions [27]. Unit NEDC Test Mass kg 1130 Unit NEDC F0 N 61 Coast Down Test Mass kg 1130 F1 N/(km/h) 0.19 F0 N 61 Coefficients Coast 2 F2 N/(km/h) 0.0269 F1 N/(km/h) 0.19 Down Coefficients

F2

N/(km/h)2

0.0269

WLTP 1325 WLTP 120.5 1325 0.33 120.5 0.330.0302 0.0302

An important difference between the WLTP and NEDC procedures is the substantial increase of the energy demand,difference as shownbetween in Figurethe 4, which both the traction specific energyincrease (i.e., the An important WLTPillustrates and NEDC procedures is the substantial integral of thedemand, positiveastraction requested the entire cycle referred to the travelled of the energy shown power in Figure 4, whichalong illustrates both the traction specific energy (i.e., distance) and the brake specific energy (i.e., the integral of the negative power requested during the the integral of the positive traction power requested along the entire cycle referred to the travelled entire cycle referred to the travelled distance). distance) and the brake specific energy (i.e., the integral of the negative power requested during the An increase of about 50% in the traction specific energy demand when moving from the NEDC entire cycle referred to the travelled distance). to the WLTP can be clearly noticed, while the brake energy only increases by than 15%, showing reduced opportunities for the exploitation of regenerative braking.

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(a) 100 93.1

ECE 85.6

80

EUDC

Cycle Energy [Wh/km]

72.8 60

NEDC

40

20

0 -20.8

-20

-27.2 -38.0

-40 TRACTION ENERGY

BRAKE ENERGY

-60

(b) Figure 4. Traction energy demand and brake energy demand along the WLTC (a) and NEDC (b): for

Figure 4. Traction energy demand and brake energy demand along the WLTC (a) and NEDC (b): for each driving cycle the values of the different phases (Low, Medium, High and Extra-High for WLTC each driving cycle the values of the different phases (Low, Medium, High and Extra-High for WLTC and ECE and EUDC for NEDC) and for the whole cycle are shown. and ECE and EUDC for NEDC) and for the whole cycle are shown.

2.3. Test Protocol

An increase of about 50% in the traction specific energy demand when moving from the NEDC to was tested under different initialenergy batteryonly Stateincreases of Chargeby (SOC) over both the WLTPThe canvehicle be clearly noticed, while the brake thanconditions 15%, showing reduced driving cycles. This aspect is of crucial importance for a HEV, because the battery works as an energy opportunities for the exploitation of regenerative braking.

buffer, since the electric energy, which is used during the discharge phase, has then to be supplied backwards 2.3. Test Protocolthrough the SC or through regenerative braking. Therefore, the same cycle was tested considering two opposite initial SOC conditions: battery fully charged (or “High SOC”) and fully The vehicle was SOC”). tested Itunder different battery State“High of Charge (SOC) conditions discharged (“Low is worth to pointinitial out that the terms SOC” and “Low SOC” are over the usualThis range of exploitation of NiMH batteries, which a maximum of 70% both referred drivingtocycles. aspect is of crucial importance for a ranges HEV, from because the battery works a minimum of 30% [28–30]. The battery conditioning performed at constant as antoenergy buffer, since the electric energy, which iswas used during by thedriving discharge phase,speed has then the chassis dynamometer until the charge or regenerative discharge of the battery was achieved.the Thesame to beonsupplied backwards through thecomplete SC or through braking. Therefore, evolution of the battery energy level was monitored through the battery indicator on the cockpit [27]. cycle was tested considering two opposite initial SOC conditions: battery fully charged (or “High Moreover, the vehicle was tested considering different thermal states of the ICE to appreciate SOC”) and fully discharged (“Low SOC”). It is worth to point out that the terms “High SOC” and the effect of coolant temperature on the EMS logic, combined with different SOC levels at the “Lowbeginning SOC” are referred to the usual range of exploitation of NiMH batteries, which ranges from of the cycle, as summarized in Table 3. Along the NEDC and WLTC cycles, the vehicle a maximum of 70% toout a minimum ofthe 30% [28–30]. The battery conditioning was performed by driving tests were carried considering initial coolant temperature at 25 °C, referred as “Cold”, and at at constant speed on chassis dynamometer untilthe thecharacterization complete charge or EMS discharge the battery 70 °C, referred as the “Hot”. Finally, to further extend of the logic, aofcoolant was achieved. The evolution of the battery energy temperature of −7 °C was considered for the WLTClevel only.was monitored through the battery indicator

on the cockpit [27]. Moreover, the vehicle was tested considering different thermal states of the ICE to appreciate the effect of coolant temperature on the EMS logic, combined with different SOC levels at the beginning of the cycle, as summarized in Table 3. Along the NEDC and WLTC cycles, the vehicle tests were carried out considering the initial coolant temperature at 25 ◦ C, referred as “Cold”, and at 70 ◦ C, referred as

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“Hot”. Finally, to further extend the characterization of the EMS logic, a coolant temperature of −7 ◦ C was considered for the WLTC only. Table 3. Test matrix. NEDC

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SOC ◦C

−7 COLD HOT SOC

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High Low High Low Table 3. Test matrix. x x x NEDC x x WLTC x x x x x High Low High Low

−7 °C COLD HOT

3. Results

WLTC

x x

x x

x x x

x x x

The first part of this section focuses on the impact of WLTP procedure on CO2 emissions for different battery SOC levels and engine thermal states, providing a preliminary analysis of the EMS first part of operating this sectionconditions. focuses on Thereafter, the impact of procedure on CO2 emissions behavior The under different theWLTP EMS logic was investigated with aforhigher different battery SOC levels and engine thermal states, providing a preliminary analysis of the EMS detail level, detecting the engine enabling logic and the actuation of the SC/E-boost, depending on the behavior under different operating conditions. Thereafter, the EMS logic was investigated with a battery SOC, vehicle speed and acceleration. Then, the effects of the Cold start event on the control higher detail level, detecting the engine enabling logic and the actuation of the SC/E-boost, depending logicon were throughspeed the comparison withThen, vehicle performed with engine coolant the investigated battery SOC, vehicle and acceleration. thetests effects of the Cold startthe event on the ◦ temperature around C. control logic were70 investigated through the comparison with vehicle tests performed with the engine 3. Results

coolant temperature around 70 °C.

3.1. CO2 Emissions

3.1. CO2 Emissions

The WLTP procedure, as already shown in previous Section 2.2, is more energy demanding WLTP procedure, already in previous Section is more to energy demanding comparedThe to the current NEDCasbased TAshown procedure. Therefore, it is2.2, expected lead to an increase of compared the current NEDC based TA procedure. Therefore, it is expected to lead to an increase the overall COto 2 emissions, as already reported in literature for vehicles equipped with conventional of the overall COThis 2 emissions, as already reported in literature for vehicles equipped with conventional powertrains [31,32] section provides an additional contribution, analyzing the impact of the new powertrains [31,32] This section provides an additional contribution, analyzing the impact of the new TA procedure on a test case vehicle representative of current state of the art of the hybrid technology. TA procedure on a test case vehicle representative of current state of the art of the hybrid technology. The CO2 emissions measured after a Cold start, as required by the TA procedures, are shown The CO2 emissions measured after a Cold start, as required by the TA procedures, are shown in in Figure 5 for the two different SOC levels: the WLTP procedure leads to an average increase of Figure 5 for the two different SOC levels: the WLTP procedure leads to an average increase of CO2 CO2 emissions emissionsofof g/km corresponding to aabout a 30% increase, almost independently from the 2626 g/km corresponding to about 30% increase, almost independently from the starting starting SOC level. Instead, the different initial battery level causes a variation of about 6 g/km SOC level. Instead, the different initial battery level causes a variation of about 6 g/km of COof 2 CO2 emissions for the same driving cycle emissions for the same driving cycle[27]. [27]. 140 NEDC

WLTP

120

114 108

CO2 [g/km]

100

94 80

88 81

76

60

40

20

0

LOW SOC

HIGH SOC

TA

Figure 5. Cold start—COemissions 2 emissions according the WLTP and NEDC procedures for the Low SOC, Figure 5. Cold start—CO according the WLTP and NEDC procedures for the Low SOC, 2 High SOC and TA cases. High SOC and TA cases.

However, it will shownininmore moredetails details in section, both under LowLow SOC SOC and and However, as itaswill be be shown in the thefollowing following section, both under High SOC conditions, the EMS promotes a quite aggressive battery recharging for both driving High SOC conditions, the EMS promotes a quite aggressive battery recharging for both driving cycles, cycles, leading to SOC values at the end of the driving cycles significantly higher than the values leading to SOC values at the end of the driving cycles significantly higher than the values recorded at recorded at cycle start. Therefore, the computation of the CO2 emissions should take into account that cycleastart. Therefore, theenergy computation of the takecontent into account that a fraction of 2 emissions fraction of the fuel consumed wasCO used to increaseshould the energy of the battery, and not for vehicle traction. A correction factor, named “K factor”, should be applied to the measured CO2 emissions, as prescribed by the regulations [18,21], in order to obtain the TA CO2 values shown in Figure 5. These two values correspond to the CO2 emissions that would be measured in case of a

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the fuel energy consumed was used to increase the energy content of the battery, and not for vehicle traction. A correction factor, named “K factor”, should be applied to the measured CO2 emissions, as prescribed by the regulations [18,21], in order to obtain the TA CO2 values shown in Figure 5. These two values correspond to the CO2 emissions that would be measured in case of a neutral battery Energies 2017, 10, energy balance (in1590 other words with SOC level at cycle end equal to SOC level at cycle start).7 of As18far as TA CO2 emissions are concerned, passing from NEDC to WLTP an increase of 18 g/km, corresponding neutral battery energy balance (in other words with SOC level at cycle end equal to SOC level at cycle to about 23%, was observed, which is noticeably lower than the increases measured for both the Low start). As far as TA CO2 emissions are concerned, passing from NEDC to WLTP an increase of 18 SOC g/km, and High SOC conditions. corresponding to about 23%, was observed, which is noticeably lower than the increases The effects thethe ICE thermal status theconditions. start of the driving cycle are reported in Figure 6, measured forof both Low SOC and Highat SOC considering High as reference case. Asthe already in literature The only effectsthe of the ICESOC thermal status at the start of drivingpointed cycle areout reported in Figure[33] 6, for considering only the High SOC as reference As2 already pointed out inpassing literature [33]NEDC for conventional powertrains, the effect of Cold startcase. on CO emissions is reduced from to conventional the effect The of Cold on CO emissions is reduced NEDC WLTP also for thepowertrains, hybrid powertrain. CO2start penalty is2 limited thanks to thepassing higherfrom power demand WLTPpermitting also for thea more hybridrapid powertrain. Theup COcompared 2 penalty is limited thanks to the higher power of thetoWLTP, ICE warm with the NEDC, and thanks to the longer demand of the WLTP, permitting a more rapid ICE warm up compared with the NEDC, and thanks duration of the WLTC driving cycle, since the relative weight of the higher fuel consumption during to the longer duration of the WLTC driving cycle, since the relative weight of the higher fuel the warm-up phase is significantly reduced. As a result, CO2 emissions increase by only 4 g/km, consumption during the warm-up phase is significantly reduced. As a result, CO2 emissions increase corresponding to a percentage growth slightly lower than 4%, lower whenthan passing from passing Cold tofrom Hot start by only 4 g/km, corresponding to a percentage growth slightly 4%, when conditions for the WLTP, while for the NEDC an increase of about 10 g/km, corresponding to about Cold to Hot start conditions for the WLTP, while for the NEDC an increase of about 10 g/km, 12%, corresponding from Cold to to Hot was registered. about 12%, from Cold to Hot was registered. 140 COLD

HOT

120

108

CO2 [g/km]

100

80

103.8

81 71.3

60

40

20

0

NEDC

WLTP

Figure 6. Effect of the Cold startononCO CO2emissions emissions along and WLTP cycles for the Figure 6. Effect of the Cold start alongthe theNEDC NEDC and WLTP cycles forHigh the High 2 SOC case. SOC case.

CO2 [g/km]

Finally, the effect of extremely low temperatures on CO2 emissions along the WLTC cycle was Finally, the effect of extremely low temperatures on CO2 emissions along the WLTC cycle was investigated for different SOC levels, as reported in Figure 7. investigated for different SOC levels, as reported in Figure 7. 140 COLD -7 The emissions increase passing from Cold case to −7 ◦ C case is of about 16.5% for the Low SOC 132.9 131 case, and of about 21% for120the High SOC case. It is worth pointing out that the initial battery SOC level has a very limited effect on CO2 emissions at −7 ◦ C, since the increase from the High to the Low SOC 114 108 100 case is lower than 2 g/km, which is significantly less than the 6 g/km increment measured for the Cold start case (see again results 80 shown in Figure 5). This result suggests a limited influence of the initial SOC level on the exploitation of the electric drive at −7 ◦ C, which could be explained by the need to keep the ICE switched on 60to obtain a fast warm-up, regardless of the need to charge the battery. 40

20

0

LOW SOC

HIGH SOC

Figure 7. Impact on CO2 emissions of −7°C test for the Low SOC and High SOC cases along the WLTC.

The emissions increase passing from Cold case to −7 °C case is of about 16.5% for the Low SOC case, and of about 21% for the High SOC case. It is worth pointing out that the initial battery SOC level has a very limited effect on CO2 emissions at −7 °C, since the increase from the High to the Low

0

NEDC

WLTP

Figure 6. Effect of the Cold start on CO2 emissions along the NEDC and WLTP cycles for the High SOC case. Energies 2017, 10, 1590

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Finally, the effect of extremely low temperatures on CO2 emissions along the WLTC cycle was investigated for different SOC levels, as reported in Figure 7. 140

COLD

132.9

-7

131

120

114 108

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CO2 [g/km]

100

8 of 18

80

SOC case is lower than 60 2 g/km, which is significantly less than the 6 g/km increment measured for the Cold start case (see again results shown in Figure 5). This result suggests a limited influence of the initial 40 SOC level on the exploitation of the electric drive at −7 °C, which could be explained by the need to keep the ICE switched on to obtain a fast warm-up, regardless of the need to charge the battery. 20

3.2. Analysis of the EMS Logic 0

SOC of the EMS logics for HIGH This section presents a detailedLOW analysis theSOC two different SOC levels, using the limited amount of information available from the chassis dyno tests. The investigation procedure Figure 7. Impact on CO 2 emissions of −7°C for the Low SOC and High SOC cases along the WLTC. Figure 7. Impact on CO emissions of −7◦ C test test SOC and High SOC cases WLTC. 2operating correlated the vehicle conditions suchfor asthe theLow vehicle speed, acceleration and along motivethe power to identify the engine enabling strategy and the use of peculiar operating modes of hybrid The emissions increase passing from Cold case to −7 °C case is of about 16.5% for the Low SOC powertrains, such Logic as the SC and the E-Boost [27]. Figures 8 and 9 illustrate the ICE On/Off logic, 3.2. Analysis of the EMS case, and of about 21% for the High SOC case. It is worth pointing out that the initial battery SOC represented as Boolean variable (0 = Off, 1 = On), on a time basis, along with the battery SOC for the level has a very limited aeffect on CO2 emissions at −7 °C, since from the High to the Lowusing This section presents detailed analysis of the EMS logicsthe forincrease the two different SOC levels, two different initial levels along the WLTC and NEDC cycles. the limited amount of information from chassis dynothat tests. procedure From Figure 8, which refersavailable to the High SOCthe case, it is evident the The EMS investigation permits all-electric driving only at low/medium vehicle speeds accelerations, which happens when the power correlated the vehicle operating conditions suchand as for thelow vehicle speed, acceleration and motive power quite limited. Therefore, the use usage the ICE isoperating more frequent overofthe WLTCpowertrains, than to identify thedemand engineisenabling strategy and the ofofpeculiar modes hybrid over the NEDC, due to the higher power demand. Moreover, in the High SOC case it can be observed such as the SC and the E-Boost [27]. Figures 8 and 9 illustrate the ICE On/Off logic, represented as that the battery charge increases by about 15% on WLTC and by about 10% on NEDC, highlighting Booleanthe variable (0 = Off, 1 = On), on a time basis, along with the battery SOC for the two different frequent exploitation of the SC to increase the load of the ICE and consequently its efficiency, well initial levels along the to WLTC and NEDC cycles. beyond the need keep the battery energy at a constant level.

(a)

(b) Figure 8. High SOC Cold start: ICE On/Off status, battery SOC and vehicle speed over the WLTC (a)

Figure 8. High SOC Cold start: ICE On/Off status, battery SOC and vehicle speed over the WLTC and the NEDC (b). (a) and the NEDC (b).

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In the Low SOC case, depicted in Figure 9, the ICE is more frequently enabled in the first portion of the driving cycles (particularly on the NEDC), enabling a fast battery recharge until the reaching of “normal” operating conditions (about 55% of SOC), after which the EMS tends to operate in a Energies 2017, 10, 1590 9 of 18 similar way to the High SOC case.

(a)

(b) Figure 9. 9. Low status, battery SOC and vehicle speed over thethe WLTC (a) Figure Low SOC SOC Cold Coldstart: start:ICE ICEOn/Off On/Off status, battery SOC and vehicle speed over WLTC andand thethe NEDC (b).(b). (a) NEDC

Moreover, even though the power demand quiteitlow duringthat the initial phases of both cycles, From Figure 8, which refers to the High SOCiscase, is evident the EMS permits all-electric Figures 8 and 9 show that the engine is On for approximatively 100 s, probably to warm-up the afterdriving only at low/medium vehicle speeds and for low accelerations, which happens when the power treatmentissystem. demand quite limited. Therefore, the usage of the ICE is more frequent over the WLTC than over However, forthe better understanding theMoreover, EMS logicinathe deeper investigation correlation the NEDC, due to higher power demand. High SOC case it canofbethe observed that between the driving conditions and the hybrid powertrain operating modes is necessary. Therefore, the battery charge increases by about 15% on WLTC and by about 10% on NEDC, highlighting the the battery and the engine measurements were kinematic and dynamic frequent exploitation of the SC to increase the loadcorrelated of the ICEwith and vehicle consequently its efficiency, well measurements, such as vehicle speed, vehicle acceleration and traction power [27]. beyond the need to keep the battery energy at a constant level. Figure 10 reports the ICE statusin(On/Off) theisoperating points recorded over WLTC as In the Low SOC case, depicted Figure 9,for theallICE more frequently enabled in thethe first portion a function of battery SOC and traction power. Theenabling cross and diamond represent of the driving cycles (particularly on the NEDC), a fast batterymarkers recharge until therespectively reaching of the ICE Off and On conditions, while the “Start” arrow identifies the battery initial SOC on x-axis. “normal” operating conditions (about 55% of SOC), after which the EMS tends to operate inthe a similar It cantobe seen case. that in both cases the EMS enables the electric driving (corresponding to the way theclearly High SOC “ICEMoreover, Off” conditions) up to kW. demand Moreover, for both cases the ICE cut-off even though the10power is quite low during the initial phasesduring of bothvehicle cycles, deceleration and the stop-start functionalities are both disabled at the beginning of the cyclethe to Figures 8 and 9 show that the engine is On for approximatively 100 s, probably to warm-up accelerate the engine and after-treatment system warm-up, as it can be inferred from the presence of after-treatment system. ICE On points in the negative power region. However, for better understanding the EMS logic a deeper investigation of the correlation between the driving conditions and the hybrid powertrain operating modes is necessary. Therefore, the battery and the engine measurements were correlated with vehicle kinematic and dynamic measurements, such as vehicle speed, vehicle acceleration and traction power [27]. Figure 10 reports the ICE status (On/Off) for all the operating points recorded over the WLTC as a function of battery SOC and traction power. The cross and diamond markers represent respectively

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the ICE Off and On conditions, while the “Start” arrow identifies the battery initial SOC on the x-axis. It can be clearly seen that in both cases the EMS enables the electric driving (corresponding to the “ICE Off” conditions) up to 10 kW. Moreover, for both cases the ICE cut-off during vehicle deceleration and the stop-start functionalities are both disabled at the beginning of the cycle to accelerate the engine and after-treatment system warm-up, as it can be inferred from the presence of ICE On points in the Energies 2017, 10, 1590 10 of 18 negative power region.

Start

(a)

Start

(b) Figure 10. 10. WLTC WLTCCold Coldstart: start: ICE ICE On/Off On/Off vs. Figure vs. battery battery SOC SOC for for High High SOC SOC (a) (a) and and Low Low SOC SOC (b) (b) cases. cases.

Finally,ititcan canbebenoticed noticed that Low SOC the EMS the electric at power Finally, that in in thethe Low SOC casecase the EMS limitslimits the electric drive drive at power levels levels below 2.5 kW, until SOC values of about 50% are reached. below 2.5 kW, until SOC values of about 50% are reached. The same same analysis analysis carried carried out The out on on the the NEDC, NEDC, which which is is not not reported reported here here for for sake sake of of brevity, brevity, highlighted a similar EMS behavior. highlighted a similar EMS behavior. Another important important parameter, parameter, which which plays plays aa key key role role in in the the EMS EMS logic, logic, is is the the product product of of vehicle vehicle Another speed and andacceleration. acceleration.The The analysis of data the recorded data recorded the shown WLTC,inshown 11, speed analysis of the on the on WLTC, Figure in 11, Figure highlights highlights that the electric drive both for the High SOC and Low SOC cases is confined in a wellthat the electric drive both for the High SOC and Low SOC cases is confined in a well-defined region defined region to 4.5 m2/s3. More specifically, EMS drive limitstothe drive to the from −3.5 to 4.5 from m2 /s3−3.5 . More specifically, the EMS limits thethe electric theelectric conditions when: conditions when:  

Vehicle speeds are in the medium range (below 60 km/h) and the accelerations are very low (below 0.5 m/s2); Accelerations are moderate (below 1 m/s2) and speeds are low (below 20 km/h) [27].

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Vehicle speeds are in the medium range (below 60 km/h) and the accelerations are very low (below 0.5 m/s2 ); Accelerations are moderate (below 1 m/s2 ) and speeds are low (below 20 km/h) [27].

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(a)

(b) Figure 11. 11. WLTC WLTC Cold Coldstart: start: ICE ICE On/Off On/Off status speed and and acceleration acceleration Figure status vs. vs. the the product product between between vehicle vehicle speed for High High SOC SOC (a) (a) and and Low LowSOC SOC(b) (b)cases. cases. for

Finally,further furtheranalyses analyseswere werecarried carriedout outto tocharacterize characterizein in more moredetail detail the the ICE ICE operation operation modes modes Finally, during the PH operation. In particular, the SC or the E-Boost can be identified by comparing the during the PH operation. the E-Boost can be identified by comparing the batterycurrent currentsignal signalwith withthe theICE ICEOn/Off On/Offcondition: condition:current currentflowing flowingfrom from the battery when ICE battery the battery when thethe ICE is is On corresponds to E-Boost, while current flowing into the battery when the ICE is On corresponds On corresponds to E-Boost, while current flowing into the battery when the ICE is On corresponds to to SC. A further operating condition when engine is On without providing traction power to SC. A further operating condition when the the engine is On without providing any any traction power to the the vehicle as during vehicle decelerations) can identified as a “Catalyst Heating” condition, vehicle (such(such as during vehicle decelerations) can identified as a “Catalyst Heating” condition, since since thescope main of scope of this operation is to warm-up the after-treatment system. The same the main this operation mode is mode to warm-up the after-treatment system. The same operating operating pointsover recorded over which the WLTC, wereshown previously shown Figures 10 and have points recorded the WLTC, were which previously in Figures 10in and 11, have been11, plotted been plotted in Figures and 13, as function SOC and ofbetween the product between speed and in Figures 12 and 13, as a12function of aSOC and ofofthe product vehicle speedvehicle and acceleration acceleration respectively. The square markers diamond markers for respectively. The square markers represent SC represent condition,SC thecondition, diamondthe markers stand for thestand E-Boost, the E-Boost, and the X markers indicate the Cat-Heating. and the X markers indicate the Cat-Heating. The engine most frequent operating condition is the SC throughout all operating domain, especially when the battery SOC is below 55%, as it is evident from Figure 12, but also the exploitation of the E-Boost for both SOC levels is not negligible for power demands ranging from 10 to 50 kW when the battery SOC is above 60% [27]. The same data, plotted in Figure 13 as a function of the product between vehicle speed and acceleration, confirm the predominance of SC along the WLTC.

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Start

(a)

Start

(b) Figure 12. 12. WLTC Cold start: start: ICE ICE operating operating conditions conditions for for High High SOC SOC (a) (a) and and Low Low SOC SOC (b) (b) as as aa function function Figure WLTC Cold of battery SOC. of battery SOC.

The engine most frequent operating condition is the SC throughout all operating domain, especially when the battery SOC is below 55%, as it is evident from Figure 12, but also the exploitation of the E-Boost for both SOC levels is not negligible for power demands ranging from 10 to 50 kW when the battery SOC is above 60% [27]. The same data, plotted in Figure 13 as a function of the product between vehicle speed and acceleration, confirm the predominance of SC along the WLTC. Finally, the time share of the different operating modes along the WLTC and the NEDC is reported in Figures 14 and 15, where the term “Other” refers to non-specific operating conditions such as engine cranking, or to the impossibility to associate a measurement to a particular mode due to problems of signal phasing. It is evident that passing from the NEDC to the WLTC the reduction of the electric drive is significant, from 35% to 20%, for the High SOC and from 30% to 17% for the Low SOC.

(a)

(b) Figure 12.1590 WLTC Cold start: ICE operating conditions for High SOC (a) and Low SOC (b) as a function Energies 2017, 10, 13 of 18 of battery SOC. Energies 2017, 10, 1590

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(a) (b) Figure 13. WLTC Cold start—ICE operating conditions for High SOC (a) and Low SOC (b) as a function the product between vehicle speed and acceleration.

Finally, the time share of the different operating modes along the WLTC and the NEDC is reported in Figures 14 and 15, where the term “Other” refers to non-specific operating conditions such as engine cranking, or to the impossibility to associate a measurement to a particular mode due to problems of signal phasing. It is evident that passing from the NEDC to the WLTC the reduction of the electric drive is significant, from 35% to 20%, for the High SOC and from 30% to 17% for the Low SOC. Moreover, both graphs confirm that the exploitation of the SC mode is wider than the E-Boost, which is almost negligible (below 1%) on the NEDC, since, due to the low power demand of this driving cycle, the EMS constantly tries to increase the load on the ICE to increase its efficiency through the SC. On the WLTC instead, due to the higher power demand of the driving cycle, the exploitation of the E-Boost is not negligible (about 7% of the total time), although still two-three times less frequent than the SC. (b) Finally, passing from the NEDC to the WLTC will lead to a significant reduction of both the Figure 13. WLTC WLTC Coldstart—ICE start—ICE operating conditions for High SOC (a) andSOC Low SOC (b) as a Figure 13. operating for High SOC (a) and as [27]. a function stop-start (from about Cold 19% to 10%) and of the conditions Cat-Heating (from about 5%Low to about(b) 3%) function the between product vehicle betweenspeed vehicle speed and acceleration. the product and acceleration.

Finally, the time share of the different operating modes along the WLTC and the NEDC is reported in Figures 14 and 15, where the High term “Other” conditions SOC refers to non-specific operating Low SOC such as engine cranking, or to the impossibility to associate a measurement to a particular mode due to problems of signal 17% 20% 21%to the WLTC the reduction of the electric drive is phasing. It 20% is evident that passing from the NEDC significant, from 35% to 20%, for the High SOC and from 30% to 17% for the Low SOC. Electric Vehicle Electric Vehicle Regenerative Brakingof the SC mode is wider Regenerative Moreover, both graphs confirm that the exploitation than theBraking E-Boost, 3% Start/Stop Start/Stop which is almost negligible (below 1%) on4% the NEDC, since, due to the low power demand of this Smart Charge Smart Charge 6%cycle, the EMS constantly tries to increase driving the load on the ICE to20% increase itsElectric efficiency Boost through Electric Boost 8% Cat Heating Cat Heating the SC. On the WLTC instead, due 22%to the higher power demand of the driving cycle, the exploitation Other Other of the E-Boost is not negligible (about 7% of the total time), although still two-three times less frequent than the SC. 19% 20% Finally, passing 10% from the NEDC to the WLTC will lead 10% to a significant reduction of both the stop-start (from about 19% to 10%) and of the Cat-Heating (from about 5% to about 3%) [27]. (a)

(b)

Figure 14. WLTC Cold start—Vehicle operating mode share for High SOC (a) and Low SOC (b) [27]. Figure 14. WLTC Cold start—Vehicle operating mode share for High SOC (a) Low and Low SOC (b) [27]. High SOC SOC 20%

3%

20%

21% Electric Vehicle Regenerative Braking Start/Stop 4% Smart Charge

17% Electric Vehicle Regenerative Braking Start/Stop Smart Charge

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1% 1%

5% 5%

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High SOC

4% 4%

5%

0%

5%

35% 35%

23% 23%

19%

13%

19%

13%

Low SOC

7%

High SOC 0%

Low SOC

7% 30%

Electric Vehicle Regenerative Braking Electric Vehicle Start/Stop Regenerative Smart Charge Braking 26% Start/Stop Electric Boost Smart Charge Cat Heating 26% Electric Boost Other Cat Heating Other

Electric Vehicle Regenerative Braking Electric Vehicle Start/Stop Regenerative Smart Charge Braking Start/Stop Electric Boost Smart Charge Cat Heating Electric Boost Other Cat Heating Other

30%

14% 14%

18% 18%

(a)

(b)

(a) (b) Figure Figure15. 15.NEDC NEDCCold Coldstart start--Vehicle Vehicle operating operating mode mode share share for for High High SOC SOC (a) (a) and and Low Low SOC SOC (b) (b) [27]. [27]. Figure 15. NEDC Cold start - Vehicle operating mode share for High SOC (a) and Low SOC (b) [27].

3.3. Analysis of the Impact of theconfirm Cold Start theexploitation EMS Logics of the SC mode is wider than the E-Boost, Moreover, both graphs thatonthe which is effect almost (below 1%) NEDC, since, duealong to the low power of this 3.3. Analysis of of thenegligible Impact of the Starton on the thewas EMS Logics The Cold start on Cold the EMS logic then analyzed the WLTC anddemand NEDC cycles, driving cycle, the the EMS constantly triessince to increase the load on thecould ICE to increase its efficiency through focusing High SOC case, similar done also for the Low SOC The only effecton of Cold start on the EMS logic was observations then analyzed alongbethe WLTC and NEDC cycles, the SC. On the WLTC instead, due to the higher power demand of the driving cycle, the exploitation test. For a meaningful comparison similar battery SOC values at the beginning of the cycle were focusing only on the High SOC case, since similar observations could be done also for the Low SOC of the E-Boost is not negligible (about 7% in of Figure the total16. time), although still two-three times less frequent considered (between 60–70%), as shown However, worth pointing to test. For a meaningful comparison similar battery SOC values itatisthe beginning ofout thethat, cycledue were than the SC. the impossibility to recharge externally battery,16. it would be almost impossible guarantee considered (between 60–70%), as shownthe in Figure However, it is worth pointingtoout that, duethe to Finally, passing from the NEDC to cycles. the WLTC will lead to a significant reduction of both the same initial battery SOC for the different the impossibility to recharge externally the battery, it would be almost impossible to guarantee the stop-start (from from aboutFigure 19% to16, 10%) and the Cat-Heating (from about 5% to about 3%) [27]. evident SOCoftrends sameAs initial battery SOC for the the different cycles.are quite similar for the two different test conditions (i.e., Cold and Hot) over both16,driving cycles, and main difference is represented by the engine As evident from Figure the Start SOC trends arethe quite 3.3. Analysis of the Impact of the Cold on the EMS Logicssimilar for the two different test conditions management at the beginning of the cycles, as highlighted Figure 17,iswhich compares (i.e., Cold and Hot) over both driving cycles, and the mainindifference represented by the the engine engine The effect of Cold start on the EMS logic was then analyzed along the WLTC and NEDC cycles, speed profiles for the two thermal conditions. The fuel cut-off and the engine stop-start are disabled management at the beginning of the cycles, as highlighted in Figure 17, which compares the engine focusing only on High SOCtocase, since could also for the SOC in the first portion of cycles fasten the similar warm-up of cut-off the engine and of done the after-treatment system. speed profiles forthe thethe two thermal conditions. The observations fuel and the be engine stop-start areLow disabled test. For a meaningful comparison similar battery SOC values at the beginning of the cycle were Once the warm-up has been achieved, both for the WLTC and for the NEDC cycles, the engine speed in the first portion of the cycles to fasten the warm-up of the engine and of the after-treatment system. considered (between 60to and as shown in Figure 16.perfectly However, is worth pointing out that, due profiles corresponding Hot70%), and Cold startsfor are almost for both driving cycles. Once the warm-up has been achieved, both the WLTC and foroverlapped theit NEDC cycles, the engine speed to the impossibility to recharge externally the are battery, it would be almost impossible todriving guarantee the profiles corresponding to Hot and Cold starts almost perfectly overlapped for both cycles. same initial battery SOC for the different cycles.

(a)

(b)

(a)for HOT (Red) and COLD (Blue) start, during WLTC (a) (b)and NEDC (b) for the Figure 16. Battery SOC High SOC Figure 16. case. Battery (a) and and NEDC NEDC (b) (b) for for the the Figure 16. Battery SOC SOC for for HOT HOT (Red) (Red) and and COLD COLD (Blue) (Blue) start, start, during during WLTC WLTC (a) High SOC case. High SOC case.

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As evident from Figure 16, the SOC trends are quite similar for the two different test conditions (i.e., Cold and Hot) over both driving cycles, and the main difference is represented by the engine management at the beginning of the cycles, as highlighted in Figure 17, which compares the engine speed profiles for the two thermal conditions. The fuel cut-off and the engine stop-start are disabled in the first portion of the cycles to fasten the warm-up of the engine and of the after-treatment system. Once the warm-up has been achieved, both for the WLTC and for the NEDC cycles, the engine speed Energies 2017, 10, 1590 15 of 18 profiles corresponding to Hot and Cold starts are almost perfectly overlapped for both driving cycles. Energies 2017, 10, 1590

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(a)

(b)

(b) (a) and NEDC (b) for Figure 17. Engine (a) speed for HOT (Red) and COLD (Blue) start, during WLTC Figure 17. Engine speed for HOT (Red) and COLD (Blue) start, during WLTC (a) and NEDC (b) for the the High SOC case. Figure Engine speed for HOT (Red) and COLD (Blue) start, during WLTC (a) and NEDC (b) for High SOC17. case. the High SOC case.

The pie charts of Figure 18 illustrate the share of the different operating modes along the WLTC

The pie charts of Figure 18 illustrate the share of the different operating modes along the WLTC andThe NEDC for theofHot start18 case. Comparing these with those reported in Figures 14 and 15 at pie charts Figure illustrate the share ofresults the different operating modes along the WLTC and NEDC for the Hot start case. Comparing these results limited with those reported in Figures 14 and 15 comparable level, it iscase. possible to observe anresults extremely increase of Figures the electric drive and NEDC forSOC the Hot start Comparing these with those reported in 14 and 15 over at at comparable SOC (from level, it istopossible to observe an to extremely limited increase of the theNEDC electric drive the WLTCSOC cycle 21%to passing from Cold Hot start conditions), while on comparable level, it20% is possible observe an extremely limited increase of the electric drive overthe over the WLTC cycle (from 20% to 21% passing from to Hot start while onpower the effect is more significant 35% to 37%). This different can beconditions), ascribed higher the WLTC cycle (from 20%(from to 21% passing from Cold toCold Hotbehavior start conditions), while to onthe the NEDC the NEDC demand of the WLTP, (from which requires ato more frequent use of the behavior ICE at medium/high loads, theeffect effect more significant (from 35% 37%). This different can be ascribed to the to higher isis more significant 35% to 37%). This different behavior can be ascribed to the higherleading power a reduction of the warm-up time, to a limited impact of the thermal status of the engine on the electric power demand of the WLTP, which requires a more frequent use of the ICE at medium/high demand of the WLTP, which requires a more frequent use of the ICE at medium/high loads, leading to loads, drive and vehicle CO 2 emissions, as it was already pointed out in Figure 6. leading toexploitation a reduction of on thethe warm-up time, to a limited impact of the thermal the engine a reduction of the warm-up time, to a limited impact of the thermal status of the enginestatus on the of electric driveelectric exploitation on the vehicle CO 2 emissions, as itCO was already pointed in already Figure 6. pointed out in on the driveand exploitation and on the vehicle as itout was 2 emissions, Figure 6.

(a)

(b)

(a)start: vehicle operating mode time-share for WLTC (b) Figure 18. Hot (a) and NEDC (b) cycles for the High18. SOC case. Figure Hot start: vehicle operating mode time-share for WLTC (a) and NEDC (b) cycles for the

Figure 18. Hot start: vehicle operating mode time-share for WLTC (a) and NEDC (b) cycles for the High SOC case. High SOC case. 4. Conclusions

4. Conclusions Experimental tests carried out on a chassis dyno on a Euro 6 HEV, representative of the state of theExperimental art hybrid powertrain technology, according to on both the current TA procedure, based onofthe tests carried out on a chassis dyno a Euro 6 HEV,EU representative of the state and powertrain the future WLTP procedure, highlighted switching the currentbased NEDC theNEDC, art hybrid technology, according to boththat, the current EU from TA procedure, onbased the procedure to the future WLTP procedure: NEDC, and the future WLTP procedure, highlighted that, switching from the current NEDC based procedure the future WLTP procedure:  The to specific energy demand increases of about 50%; The electric drive demand reduces of about 13%, leading to a 30% increase of CO2 emissions;   The specific energy increases of about 50%;  The electric drive reduces of about 13%, leading to a 30% increase of CO2 emissions;

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4. Conclusions Experimental tests carried out on a chassis dyno on a Euro 6 HEV, representative of the state of the art hybrid powertrain technology, according to both the current EU TA procedure, based on the NEDC, and the future WLTP procedure, highlighted that, switching from the current NEDC based procedure to the future WLTP procedure:

• • •

The specific energy demand increases of about 50%; The electric drive reduces of about 13%, leading to a 30% increase of CO2 emissions; The effect of the Cold start on CO2 emissions is reduced for WLTP to a percentage growth slightly lower than 4%, from about 12% for the NEDC.

These results demonstrate that the EMS strategies of the tested vehicle can achieve, in test conditions closer to real life such as those corresponding to the WLTP, even higher efficiency levels than those that are currently evaluated on the NEDC, and prove the effectiveness of HEV technology to reduce CO2 emissions. Acknowledgments: The valuable support provided to the research activity by the Joint Research Centre is gratefully acknowledged. The authors would like to thank all the staff of the Vehicle Emission LAboratory (VELA) of the JRC, and in particular Jelica Pavlovic and Ricardo Suarez Bertoa, for their precious and constant contribution to the work. Author Contributions: Claudio Cubito, Biagio Ciuffo and Simone Serra planned the experimental test campaign for the hybrid vehicle. Marcos Otura Garcia, Germana Trentadue, Claudio Cubito and Simone Serra with the supervision of Biagio Ciuffo carried out the experimental campaign on the hybrid vehicle at the chassis dyno rig. Claudio Cubito, Federico Millo, Giulio Boccardo, Giuseppe Di Pierro and Georgios Fontaras analyzed the experimental data and conducted the analysis on the EMS of the hybrid powertrain. Conflicts of Interest: The authors declare no conflict of interest.

Acronyms 4WD E-Boost eCVT EMS EU EV FCV HEV ICE JRC MG NEDC NiMH OBD PH RL SC SI SOC TA VELA WLTC WLTP

Four Wheel Drive Electric Boost Electric Continuous Variable Transmission Energy Management System European Union Electric Vehicle Fuel Cell Vehicle Hybrid Electric Vehicle Internal Combustion Engine Joint Research Centre Motor Generator New European Driving Cycle Nickel Metal Hydrate On Board Diagnostic Parallel Hybrid Road Load Smart Charge Spark Ignition State Of Charge Type Approval Vehicle Emissions Laboratory Worldwide Harmonized Light duty Test Cycle Worldwide Harmonized Light duty Test Procedure

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