Real Drive Truth Test of the Toyota Yaris Hybrid 2020 and Energy Analysis Comparison with the 2017 Model

: This paper presents the performance analysis of a latest-generation hybrid vehicle (Toyota Yaris 2020) with a testing campaign in real road conditions and a comparison with the previous model (Toyota Yaris 2017). The study was conducted by applying the Real Drive Truth Test protocol, developed by the research group, validated and spread to other full hybrid vehicles: Toyota Prius IV (2016) and Toyota Yaris 2017 (2017). In the case of the 2020 tests, the co-presence on board— deemed unsafe in the usual ways given the ongoing pandemic—was achieved through precise and sophisticated remote control. An on-board diagnostic computer, video transmission and recording equipment guarantee the virtual co-presence of a technical control room and a driver. Thus, several engineers can follow and monitor each vehicle via a 4G modem (installed in each vehicle), analysing data, route and driver behaviour in real-time, and therefore even in the presence of a single occupant in the car under test. The utmost attention has also been paid to adopting anti-COVID behaviours and safety standards: limited personal interactions, reduced co-presence in shared rooms (especially in the control room), vehicle sanitising between different drivers, computers and technicians and video technicians working once at a time. The comparison between the two subsequent vehicle models shows a signiﬁcant improvement in the performance of the new generation Yaris, both in terms of operation in ZEV (zero-emission vehicle) mode (+15.3%) and in terms of consumption ( − 35.1%) and overall efﬁciency of the hybrid powertrain (+8.2%).


Introduction
Transport emissions account for around 25% of the European Commission (EU) total greenhouse gas emissions and have increased recently.One of the EU goals is to be the first climate-neutral continent by 2050, which requires ambitious changes in the transport sector.According to the EU, a clear path is, therefore, needed to achieve a 90% reduction in transport-related greenhouse gas emissions by 2050.The EU has adopted a series of proposals to transform climate, energy, transport and taxation policies [1], with the ambition to reduce net greenhouse gas emissions by at least 55% by 2030 compared to 1990 levels.
The EU proposes more ambitious targets for reducing the CO 2 emissions of new cars and vans: 55% reduction of emissions from cars by 2030, 50% reduction of emissions from vans by 2030 and zero emissions from new cars by 2035 [2].
This work aims to analyse the energy behaviour of the Toyota Yaris Hybrid Model Year 2020 vehicle by evaluating the ZEV indicator.Such an indicator is the percentage distribution of the total energy at the transmission between the electric motor (EM) and the internal combustion engine (ICE) with a particular interest in distance travelled with the ICE turned off (zero exhaust emissions).
The COVID-19 pandemic characterised the testing campaign, requiring a new mode to conduct the tests, innovative at the international level.
The driving tests, according to the protocol RDTT-Real Drive Truth Test [32,37], developed by the research group and validated-must be carried out with the co-presence on board of a driver and a researcher (responsible for supervising the test from the point of view of adherence to the planned route and correct driving style).
In the case of the 2020 tests, the co-presence on board-deemed unsafe in the usual ways given the ongoing pandemic-was achieved through precise and sophisticated remote control.
An on-board diagnostic computer, video transmission and recording equipment guarantee the virtual co-presence of a technical control room and a driver.Thus, several engineers can follow and monitor each vehicle via a 4G modem (installed in each vehicle), analysing data, route and driver behaviour in real-time, so even in the presence of a single occupant in the car under test.
The utmost attention has also been paid to adopting anti-COVID behaviours and safety standards: limited personal interactions, reduced co-presence in shared rooms (especially in the control room), vehicle sanitising between different drivers, computers technicians and video technicians worked once a time.
This paper is structured as follows: Section 2 describes the RDTT protocol; Section 3 describes the parameters, the data acquisition, the energy analysis and the operation in ZEV mode of the vehicles studied; Section 4 concerns the results of the analysis and comparisons, and Section 5 reports the conclusions and future developments of the work.

Real Drive Truth Test-RDTT Protocol
The Real Drive Truth Test protocol allows the standardisation of test methods and the acquisition of significant parameters in analysing and studying the energy behaviour in real conditions of hybrid vehicles used on the road [37].
These activities analyse, in particular, the operation in ZEV mode (zero-emission vehicle, i.e., with the internal combustion engine turned off) and the energy flows of the hybrid drive system.
The analysis of the operation in ZEV mode identifies the following parameters:  • EVt: time percentage of the electric-only powered motion phases; • EVS: space percentage of the electric-only powered motion phases.
The analysis of the energy flows of the hybrid traction system identifies: The RDTT protocol [37] defines the following phases for the analysis and study of hybrid vehicles energy behaviour: I.
Test definition; II.
Data collection; III.
Processing of acquired data; IV.
Results report.
In phase I, the protocol defines the test methods: number and characteristics of the drivers, the total number of tests and path characteristics (length, location, etc.).This definition aims to have scientifically correct and comparable, and, as far as possible, generalisable, results.
Phase II foresees a preliminary analysis of the available data from on-board diagnostics and the definition of the data needed for the study.
The third phase concerns the data validation, then a division of acquisitions by tests, drivers, road section, etc.Each division allows evaluating the parameters relating to zero-emission (ZEV), energy analysis, kinematics and driving style indicators; therefore, the evaluation of previous parameters can highlight potential correlations between a few parameters.
The report phase (IV) describes the results obtained, highlighting the most relevant aspects of the analysis regarding the vehicle ZEV, the electrical running and the energy behavior.

Test and Driver Number and Clusters
According to the RDTT protocol, they were carried out by clustered drivers: males/ females, more or less 35 years, each driver follows the same route three times, in the same time slots (traffic bands).
The three test bands are: • 60 tests in total (three for each driver).
To make the tests carried out comparable, specific characterisations of the vehicles used and the driving methods of the same have been imposed: eco mode, air conditioning off, respect for speed limits, windows closed (except for July tests, in which it was left to the driver the possibility of a partial opening only in the strictly urban part of the test).

Length, Characteristics and Journey Time
The planned route is the same as in previous tests [37]; it is in line with the average daily distances travelled per capita in Italy indicated by the latest ISFORT reports on mobility in Italy [38].
The route consists of a high-flow suburban and urban stretch and an urban stretch, as displayed in the overall view in Figure 1, also contextualised to the environmental protection strips of Rome.
Energies 2021, 14, x FOR PEER REVIEW 4 of 23 • 60 tests in total (three for each driver).
To make the tests carried out comparable, specific characterisations of the vehicles used and the driving methods of the same have been imposed: eco mode, air conditioning off, respect for speed limits, windows closed (except for July tests, in which it was left to the driver the possibility of a partial opening only in the strictly urban part of the test).

Length, Characteristics and Journey Time
The planned route is the same as in previous tests [37]; it is in line with the average daily distances travelled per capita in Italy indicated by the latest ISFORT reports on mobility in Italy [38].
The route consists of a high-flow suburban and urban stretch and an urban stretch, as displayed in the overall view in Figure 1, also contextualised to the environmental protection strips of Rome.

•
1st Section-Outward: high-speed suburban and urban route (Toyota Motor Italia Headquarters-Via Generale Amedeo Mecozzi, Via Colonnello Tommaso Masala, Complanare GRA, GRA, Via Aurelia, Via Baldo degli Ubaldi, Via Angelo Emo, Via Candia, Viale Giulio Cesare): o Length: 14.7 km  13.1 (89%) km outside the railway ring (Figure 2);   • 2nd Section-Urban: urban route that develops over three laps of itinerary desig ad hoc (Entrance to the urban circuit-corner V.le Giulio Cesare-Via Silla, V Germanico, Piazza dei Quiriti, Via Attilio Regolo, Via Virgilio, Via Cassiodoro, Tacito, Via Plinio, Via Catullus, Via Terenzio, Via dei Gracchi, Via Catone, V Germanico): o Length: 6 km  Everything inside the railway ring (Figure 3);      As described in Figure 5, the altimetric profile of the path highlight measuring between the First Section-Outward and the Third Section-Retu Urban Section has no gradients.The maximum elevation difference is 31 m section to the Second and from the Second to the Third.

Criteria for the Scenarios Evaluations
The parameters necessary for the energy analysis are: the energy flo the hybrid powertrain, distance travelled, speed and acceleration.A few pa to be calculated, e.g., the acceleration is the derivative of vehicle speed, the As described in Figure 5, the altimetric profile of the path highlights a symmetric measuring between the First Section-Outward and the Third Section-Return; the Second Urban Section has no gradients.The maximum elevation difference is 31 m, from the First section to the Second and from the Second to the Third.As described in Figure 5, the altimetric profile of the path highlights a symmetric measuring between the First Section-Outward and the Third Section-Return; the Second Urban Section has no gradients.The maximum elevation difference is 31 m, from the First section to the Second and from the Second to the Third.

Criteria for the Scenarios Evaluations
The parameters necessary for the energy analysis are: the energy flow from and to the hybrid powertrain, distance travelled, speed and acceleration.A few parameters have to be calculated, e.g., the acceleration is the derivative of vehicle speed, the kinetic energy, the mechanical power of the motors.
An on-board diagnostic system stores the data; it consists of an embedded PC that reads information through the car's on-board diagnostic (OBD) socket using the Tech-Stream software.
Like the majority of the electric and hybrid vehicles, this vehicle has two dedicated CAN networks and two relative Electronic Control Units (ECU).The first ECU, called

Criteria for the Scenarios Evaluations
The parameters necessary for the energy analysis are: the energy flow from and to the hybrid powertrain, distance travelled, speed and acceleration.A few parameters have to be calculated, e.g., the acceleration is the derivative of vehicle speed, the kinetic energy, the mechanical power of the motors.
Energies 2021, 14, 8032 7 of 22 An on-board diagnostic system stores the data; it consists of an embedded PC that reads information through the car's on-board diagnostic (OBD) socket using the Tech-Stream software.
Like the majority of the electric and hybrid vehicles, this vehicle has two dedicated CAN networks and two relative Electronic Control Units (ECU).The first ECU, called "Hybrid Control System", provides data from the safety sensors, vehicle kinematics, electric powertrain; the second ECU, called "Engine", uses the second CAN line.Both have two data lists with many parameters that can be monitored in real-time and stored on the PC.
The Hybrid Control System provides 22 selected parameters and the Engine 7 has more: The traction system of the Toyota Yaris object of this study (Figure 6) is a full hybrid consisting of a petrol-powered ICE, Atkinson cycle, two reversible electric machines MG (Motor/Generator) of the brushless type in alternating current and batteries of traction type nickel-metal hydride (Yaris 2017) or lithium-ion (Yaris 2020).The power divider is of the double planetary type.
The two motor/generators MG1 and MG2 can work as motor or generator; their working conditions depend on the kinematic constraint of the Power Split Device (PSD).
The Toyota hybrid powertrain has two separate functions: -MG1 is coupled through the PSD (not shown for simplicity in Figure 6) to the ICE and not to the transmission; -MG1 works as a motor exclusively for starting the ICE by absorbing electricity from the batteries; -In a typical operation, the ICE turns the MG1, which works as a generator.It can recharge the batteries (or directly power MG2 in engine operation); -MG2 is connected to the PSD and not to the ICE, so, in normal driving conditions, it works as a motor and provide mechanical power to the wheels; or, it works as a generator to charge the traction batteries (energy recovery) in case of batteries in a low state of charge.

Parameters Related to the Analysis of Zero-Emission Vehicle (ZEV) Mode
The percentage indices (in time and space) both of zero-emission operation and in electric vehicle mode [9,32,37], have been defined as follows: From the definition of these indices given by Equations ( 1)-( 7): EV value is equal to 0 for conventional ICE vehicles (also with stop and start system) and 1 for a battery electric vehicle (BEV), between 0 and 1 for full-hybrid vehicles. SZEV

Parameters Related to the Analysis of Zero-Emission Vehicle (ZEV) Mode
The percentage indices (in time and space) both of zero-emission operation and in electric vehicle mode [9,32,37], have been defined as follows: From the definition of these indices given by Equations ( 1)-( 7): Energies 2021, 14, 8032 EV value is equal to 0 for conventional ICE vehicles (also with stop and start system) and 1 for a battery electric vehicle (BEV), between 0 and 1 for full-hybrid vehicles.

Parameters Related to the Energy and Consumption Analysis
From the data acquired on fuel consumption (C fuel ), the mechanical energy delivered by ICE (E_ICE_OUT) and the mechanical energy to the transmission (E_T_IN), and from the value of the LHV fuel , it is possible to calculate the average efficiency of the ICE (η ICE ) and the hybrid system (η HS ) as follows: The equivalent fuel consumption considers the change in SOC (∆SOC positive or negative) in each section analysed.
In this way, fuel consumption counts the amount of electricity delivered (or stored) by the batteries.In the calculation of the equivalent consumption, the regeneration coefficient (REG) is considered, defined as follows: When ∆SOC is positive, the battery is charged between starting and stopping; otherwise, it discharges.The equivalent consumption is expressed as: where C B is the traction battery capacity, REG is the regeneration coefficient, η ICE and η G are the average efficiency of ICE and generator respectively, and the value of LHV fuel .The average efficiency of the generator (η G ) is calculated from the data acquired (mechanical energy absorbed by MG1 in generator operation EM_MG1_IN and electricity supplied by MG1 in generator operation EE_MG1_OUT) as follows: Mileage M and equivalent mileage Meq [g/km] are calculated as follows:

Results Analysis and Comparison between Yaris Hybrid 2020 and Yaris Hybrid 2017
Table 1 shows the main characteristics of the two Toyota Hybrid Yaris vehicles, 2017 and 2020.
The 2020 version has a three-cylinder in-line engine, a compression ratio of 14 and 64 kW (at 5500 rpm) of the maximum power.It has an increase of 18.5% in engine power (compared to the 2017 version).
Moreover, the 2020 version adopts a lithium-ion traction battery instead of the nickelmetal hydride battery; such a choice allows increasing the power of the electric motors up to 59 kW (an increase of 31.1% compared to the 45 kW of the 2017 version).
The vehicle's maximum power for the 2020 version is 85 kW compared to 74 kW of the 2017 version (an increase of 14.8%).Figure 7 illustrates a driving cycle (diagram v-t) of the test path used, described in Section 2.1.2;the distinction between the central urban section and the mixed outward and return sections is evident from the speed trend.

ZEV Mode Operation Analysis and Comparison between Yaris Hybrid 2020 and Yaris Hybrid 2017
Below are the results of the analysis of the operating parameters in ZEV mode.The main results of the tests carried out are shown in Table 2.For all parameters (ZEVt, ZEVS, EVt and EVS), for the two sections (urban and suburban) and the entire test, the values found for the Yaris 2020 are significantly higher than those for the Yaris 2017.The highest values of the parameters analysed occur in the suburban section; it is due to the greater power of the electric motor, which allows electric operation even for higher speeds and power requirements: +19.2% ZEVt, +83.3% ZEVS, +71.6% EVt and +195.9%ZEVS.

Energy capacity [Wh]
936 736 Powertrain Maximum power [kW] 74 85 Figure 7 illustrates a driving cycle (diagram v-t) of the test path used, described in Section 2.1.2;the distinction between the central urban section and the mixed outward and return sections is evident from the speed trend.

ZEV Mode Operation Analysis and Comparison between Yaris Hybrid 2020 and Yaris Hybrid 2017
Below are the results of the analysis of the operating parameters in ZEV mode.The statistical distribution of the values of the analysed parameters (Table 3) is very consistent with variations in the standard deviation normalised around 10%.In both cases, the parameters showing the smallest dispersions are the percentages over time (ZEVt, lower value, and EVt), while the percentages in the distance (ZEVS and EVS higher value) show higher dispersions.The ZEVt values were less dispersed in 2017 tests than in 2020 (Table 3); 86% of the tests had a ZEVt between 60% and 70%, and 14% of tests between 70% and 80%.
Similar considerations apply to the frequency distribution of the EVt and EVS values (Figures 10 and 11).In both test campaigns (2017 and 2020), the EVS values show a greater dispersion and the 2020 values are significantly higher than those of 2017.Table 4 shows the average values of the parameters calculated for the vehicle energy analysis.The difference between mileage and equivalent mileage is negligible (about 1%).Therefore, only the equivalent mileage will be considered.In 2020, it showed a reduction of 35.2%, compared to 2017, with an increase in the overall hybrid system efficiency of    Table 4 shows the average values of the parameters calculated for the vehicle energy analysis.The difference between mileage and equivalent mileage is negligible (about 1%).Therefore, only the equivalent mileage will be considered.In 2020, it showed a reduction of 35.2%, compared to 2017, with an increase in the overall hybrid system efficiency of

Energy Analysis and Comparison between Yaris Hybrid 2020 and Yaris Hybrid 2017 4.2.1. Mileage and Efficiency Analysis and Comparison
Table 4 shows the average values of the parameters calculated for the vehicle energy analysis.The difference between mileage and equivalent mileage is negligible (about 1%).Therefore, only the equivalent mileage will be considered.In 2020, it showed a reduction of 35.2%, compared to 2017, with an increase in the overall hybrid system efficiency of 8.2% (the ICE average efficiency remains steady).The equivalent mileage decrease is due to better overall average efficiency of the hybrid system and partly to the different traffic conditions that bring to a greater energy demand from the transmission in 2017 (see Section 4.2.2).The July 2020 tests were affected by the government-imposed travel restrictions in the COVID-19 pandemic.
Table 5 shows the maximum and minimum values and normalised standard deviation of the parameters for the energy analysis of the vehicle.Driving style and traffic conditions affect the equivalent mileage, which has a higher dispersion concerning the average value [19,[39][40][41][42]; indeed, they have a lower impact on the hybrid system efficiency.The driving style essentially affects the energy requirements of the wheels (and therefore, with the same efficiency, on consumption) and much less on the efficiency of the hybrid drive system.The traffic conditions and driving style affect also the amount of energy recoverable under braking.
The values of the average efficiency of the ICE have the lowest dispersion and are constant between the two test campaigns; it is due to the presence of the electric motor in the hybrid drive system, which allows the ICE to always work in the best conditions of efficiency.
Figure 12 shows the frequency distribution of the equivalent mileage values.These values present a quite relevant dispersion to the average value (Table 5); in fact, the normalised standard deviation is equal to 0.1469 (2020) and 0.0917 (2017) as they are greatly influenced by both driving style and traffic conditions.There is a similar trend, but the 2020 version has lower mileage than 2017.The maximum frequency distribution of the equivalent mileage for the 2020 version is 55% and refers to the range 20-25 g/km compared to 48% referring to 30-35 g/km for the 2017 version.Figure 14 shows how the frequency distribution of the hybrid system efficiency values present similar trends between the two versions but with higher efficiency values for the 2020 version (see Table 5).Figure 14 shows how the frequency distribution of the hybrid system efficiency values present similar trends between the two versions but with higher efficiency values for the 2020 version (see Table 5).Figure 14 shows how the frequency distribution of the hybrid system efficiency values present similar trends between the two versions but with higher efficiency values for the 2020 version (see Table 5).For Yaris 2020, the electric motor (MG2) provides about 60%, (about 271 kJ/km).For Yaris 2017, the MG2 provides only 32% (just over half) of the transmission energy with about 225 kJ/km of electric consumption.
The braking system recovers about 138 kJ/km of electricity (about 45% of the total produced) for Yaris 2020 and about 156 kJ/km (about 60% of the total produced) for Yaris 2017.Thanks to energy recovery, the ICE produces about 94% for the energy transmission (2017 Yaris), while in the 2020 Yaris, the percentage drops to 85% thanks to the system's improved efficiency.For Yaris 2020, the electric motor (MG2) provides about 60%, (about 271 kJ/km).For Yaris 2017, the MG2 provides only 32% (just over half) of the transmission energy with about 225 kJ/km of electric consumption.

Energy Flows Analysis and Comparison
The braking system recovers about 138 kJ/km of electricity (about 45% of the total produced) for Yaris 2020 and about 156 kJ/km (about 60% of the total produced) for Yaris 2017.Thanks to energy recovery, the ICE produces about 94% for the energy transmission (2017 Yaris), while in the 2020 Yaris, the percentage drops to 85% thanks to the system's improved efficiency.For Yaris 2020, the electric motor (MG2) provides about 60%, (about 271 kJ/km).For Yaris 2017, the MG2 provides only 32% (just over half) of the transmission energy with about 225 kJ/km of electric consumption.
The braking system recovers about 138 kJ/km of electricity (about 45% of the total produced) for Yaris 2020 and about 156 kJ/km (about 60% of the total produced) for Yaris 2017.Thanks to energy recovery, the ICE produces about 94% for the energy transmission (2017 Yaris), while in the 2020 Yaris, the percentage drops to 85% thanks to the system's improved efficiency.
Figure 16 illustrates that 27% of the energy used by Yaris 2020 derives from regenerative braking, a further 32% from electricity produced by ICE and 41% directly from ICE.For Yaris 2017, 18% of the energy derives from regenerative braking, 14% from electricity produced by ICE and 68% from ICE.
From the foregoing, it is evident that the operating modes of the traction system are strongly linked to the possibility of recovering energy during braking.
Energies 2021, 14, x FOR PEER REVIEW 17 of 23 Figure 16 illustrates that 27% of the energy used by Yaris 2020 derives from regenerative braking, a further 32% from electricity produced by ICE and 41% directly from ICE.For Yaris 2017, 18% of the energy derives from regenerative braking, 14% from electricity produced by ICE and 68% from ICE.
From the foregoing, it is evident that the operating modes of the traction system are strongly linked to the possibility of recovering energy during braking.

Comparison of Test Conditions
As already mentioned, the traffic conditions during the tests of the Yaris 2020 were conditioned by the travel restrictions imposed occurring during the COVID-19 pandemic.
Table 6 shows some data relating to the 2017 and 2020 tests.The difference between the test conditions is evident: in 2017, the average duration of the tests was about 30% higher, the stopping time was about 22%; in contrast, the average speed and the average speed with the vehicle in motion were approximately 23% and 20% lower.As mentioned, the energy requirement at the wheels in 2020 was 30% lower compared with 2017.
The influence of different traffic conditions can be considered with statistical analysis; a methodology is developed and applied to estimate the variation of a few energy parameters obtained.This statistical analysis is detailed in the paper under publication by the same authors that compare results of different on-road vehicle performance testing in this Toyota Yaris hybrid case study [43].It compares some energy indicators of 2020 (influenced by the travel restrictions of the pandemic) with the same indicators calculated in acquisition campaigns of 2017 (where there are typical traffic conditions).The main results show that the different traffic conditions involve an increase of about 1% of the ZEVt and ZEVS and about 0.05% of mileage and hybrid system efficiency in the Yaris 2020 campaign.Therefore, the performance improvements of Yaris 2020 compared to Yaris 2017 (Tables 2 and 4) are substantially confirmed even in the face of different traffic conditions.

Figure 1 .
Figure 1.Trial route (dark line) referring to the environmental protection strips of Rome.

Figure 1 .
Figure 1.Trial route (dark line) referring to the environmental protection strips of Rome.

Figure 3 .
Figure 3. Urban: route that develops over three laps.

Figure 3 .
Figure 3. Urban: route that develops over three laps.

Figure 5 .
Figure 5. Altimetric profile of the test-path.

Figure 5 .
Figure 5. Altimetric profile of the test-path.

Figure 5 .
Figure 5. Altimetric profile of the test-path.

Energies 2021 , 23 Figure 6 .
Figure 6.Simplified mechanical diagram of the Toyota Yaris hybrid drive system.

Figure 6 .
Figure 6.Simplified mechanical diagram of the Toyota Yaris hybrid drive system.

Figure 7 .
Figure 7. Driving cycle of the test route used in the Toyota Yaris 2020 test drives.

Figure 7 .
Figure 7. Driving cycle of the test route used in the Toyota Yaris 2020 test drives.

Figure 8
Figure 8 shows the frequency distribution of the ZEVt values in the tests of the Toyota Yaris 2017 and 2020.The ZEVt values were less dispersed in 2017 tests than in 2020 (Table3); 86% of the tests had a ZEVt between 60% and 70%, and 14% of tests between 70% and 80%.In 2020, the ZEVt values were higher with a greater dispersion; 62% of the tests had the ZEVt between 70% and 80%, 35% between 80% and 90%, and only 3% of tests between 60% and 70%.

Figure 9 .
Figure 9. Frequency distribution of the ZEVS values.Similar considerations apply to the frequency distribution of the EVt and EVS values (Figures 10 and 11).In both test campaigns (2017 and 2020), the EVS values show a greater

Figure 8 .
Figure 8. Frequency distribution of the ZEVt values.

Figure 9 .
Figure 9. Frequency distribution of the ZEVS values.Similar considerations apply to the frequency distribution of the EVt and EVS values (Figures10 and 11).In both test campaigns (2017 and 2020), the EVS values show a greater dispersion and the 2020 values are significantly higher than those of 2017.

Figure 9 .
Figure 9. Frequency distribution of the ZEVS values.

Figure 10 .
Figure 10.Frequency distribution of the EVt values.

Figure 11 .
Figure 11.Frequency distribution of the EVS values.

Figure 11 .
Figure 11.Frequency distribution of the EVS values.

Figure 12 .
Figure 12.Frequency distribution of the equivalent mileage values.

Figure 13
Figure 13 shows how the frequency distribution of the ICE efficiency values does not present significant deviation values between the 2020 version and the 2017 version, either in the statistical distribution or in the average values (see Table5).
Figure 13 shows how the frequency distribution of the ICE efficiency values does not present significant deviation values between the 2020 version and the 2017 version, either in the statistical distribution or in the average values (see Table5).

Figure 13 .
Figure 13.Frequency distribution of the ICE efficiency values.

Figure 12 .
Figure 12.Frequency distribution of the equivalent mileage values.

Figure 13
Figure 13 shows how the frequency distribution of the ICE efficiency values does not present significant deviation values between the 2020 version and the 2017 version, either in the statistical distribution or in the average values (see Table5).
Figure 13 shows how the frequency distribution of the ICE efficiency values does not present significant deviation values between the 2020 version and the 2017 version, either in the statistical distribution or in the average values (see Table5).

Figure 13
Figure 13 shows how the frequency distribution of the ICE efficiency values does not present significant deviation values between the 2020 version and the 2017 version, either in the statistical distribution or in the average values (see Table5).
Figure 13 shows how the frequency distribution of the ICE efficiency values does not present significant deviation values between the 2020 version and the 2017 version, either in the statistical distribution or in the average values (see Table5).

Figure 13 .
Figure 13.Frequency distribution of the ICE efficiency values.

Figure 13 .
Figure 13.Frequency distribution of the ICE efficiency values.

Energies 2021 , 23 Figure 14 .
Figure 14.Frequency distribution of the hybrid system efficiency values.4.2.2.Energy Flows Analysis and ComparisonFigure15shows the diagram of energy flows of the Yaris 2020 and 2017 estimated on the average value.

Figure 14 .
Figure 14.Frequency distribution of the hybrid system efficiency values.

Figure 15
Figure 15 shows the diagram of energy flows of the Yaris 2020 and 2017 estimated on the average value.

Energies 2021 , 23 Figure 14 .
Figure 14.Frequency distribution of the hybrid system efficiency values.4.2.2.Energy Flows Analysis and ComparisonFigure15shows the diagram of energy flows of the Yaris 2020 and 2017 estimated on the average value.

Figure 16 .
Figure 16.Distribution of energy flows to transmission.

Figure 17
Figure17shows the energy flow diagrams; it is evident that the improvements in 2020 Yaris come from the contribution of the hybrid system.The 2020 Yaris engine produces 349.60 kJ/km; 51.5% (180.27kJ/km) goes to the electrical part (through MG1), and 48.5% (169.33 kJ/km) goes directly to the transmission.The 2017 Yaris ICE produces 537.81 kJ/km; only 27.3% (146.82kJ/km) goes to the electric part, and 72.7% (390.99 kJ/km) goes directly to the transmission.The hybrid system of the 2017 Yaris produces 767.35 kJ/km of total power, 29.9% (229.54 kJ/km) are provided by energy recovery, and the same percentage can be measured in Yaris 2020 (total power of 506.22 kJ/km, with 30.9% from regenerative braking equal to 156.22 kJ/km).Such a difference in energy needs is probably due to the different traffic conditions influenced by the restrictions due to the COVID 2019 pandemic in the tests of the Yaris 2020: 571.61 kJ/km for the 2017 Yaris and 408.38 kJ/km (−28.6%) for the 2020 Yaris.

Figure 16 .
Figure 16.Distribution of energy flows to transmission.

Figure 17
Figure17shows the energy flow diagrams; it is evident that the improvements in 2020 Yaris come from the contribution of the hybrid system.The 2020 Yaris engine produces 349.60 kJ/km; 51.5% (180.27kJ/km) goes to the electrical part (through MG1), and 48.5% (169.33 kJ/km) goes directly to the transmission.The 2017 Yaris ICE produces 537.81 kJ/km; only 27.3% (146.82kJ/km) goes to the electric part, and 72.7% (390.99 kJ/km) goes directly to the transmission.The hybrid system of the 2017 Yaris produces 767.35 kJ/km of total power, 29.9% (229.54 kJ/km) are provided by energy recovery, and the same percentage can be measured in Yaris 2020 (total power of 506.22 kJ/km, with 30.9% from regenerative braking equal to 156.22 kJ/km).Such a difference in energy needs is probably due to the different traffic conditions influenced by the restrictions due to the COVID 2019 pandemic in the tests of the Yaris 2020: 571.61 kJ/km for the 2017 Yaris and 408.38 kJ/km (−28.6%) for the 2020 Yaris.

23 Figure 17 .
Figure 17.The energy flow of hybrid system Yaris 2020 and 2017.

Figure 17 .
Figure 17.The energy flow of hybrid system Yaris 2020 and 2017.

•
ZEVS: percentage of the distance travelled in ZEV: o ZEVS PT=0 : percentage of distance travelled in ZEV with zero or negative mechanical power from the electric motor to the wheels; o ZEVS EV : percentage of the distance travelled in ZEV with mechanical power required for motion provided only by the electric motor.

Table 1 .
Main features of the two Toyota hybrid Yaris vehicles.

Table 2 .
Summary of average percentage values ZEV mode parameters of Yaris Hybrid 2017 and 2020.

Table 3 .
Maximum values, minimum values and normalised standard deviation of the parameter values for the analysis of vehicle operation in zero-emission vehicle (ZEV) mode.

Table 4 .
Summary energy analysis parameters value of Yaris Hybrid 2017 and 2020.

Table 5 .
Maximum values, minimum values and normalized standard deviation of the parameter values for the energy analysis of the vehicle.

Table 6 .
Comparison between parameters of the 2017-2020 tests.