Review Reports

Round 1

Reviewer 1 Report

The study reports an interesting analysis on power usage for lightweight EV construction. Few items are to be addressed before publication. The manuscript can be improved by considering the following: 

• In abstract, please include critical decisions for designing ultra-lightweight design. Also, the key findings from this study.
• A detailed literature review is needed to bring out the need for the present work. Authors need to explain the limitations of existing simulation approaches and the identified research gap to be addressed in this study.
• Need further clarification on the environmental impact. What are the criteria e.g. in terms of greenhouse gases or anything else?
• Please clarify how the parameter values listed in Table 1 are obtained.
• Please concise the conclusions point-wise identifying the key points.

Author Response

 

• In abstract, please include critical decisions for designing ultra-lightweight design. Also, the key findings from this study.

Abstract has been modified by highlighting the key findings of the study and a brief explanation of how the findings of this study could support the designer in the design of such kind of vehicles.

• A detailed literature review is needed to bring out the need for the present work. Authors need to explain the limitations of existing simulation approaches and the identified research gap to be addressed in this study.

Introduction has been expanded with a more detailed analysis of the existing approaches on modelling and simulation of ultra-efficient lightweight vehicles (see lines 91-130).

Moreover, the following paragraph highlighting the main contribution of the paper has been added at line 130:

“Despite the large number of papers on the design and modelling of ultra-efficient lightweight vehicles, no references dealing with the study of the effect of the vehicle design parameters on the power demand have been found. This paper aims to provide a quantitative analysis of the effect of the main vehicle design parameters on the energy consumption. Actually, this is a fundamental information for the design engineers, allowing for a clear and well-defined identification of key vehicle parameters to keep under control in the design phase and of the most promising areas of action.”

 

• Need further clarification on the environmental impact. What are the criteria e.g. in terms of greenhouse gases or anything else?

The discussion is mainly focused on the GHG emission assessment. Clarifications have been added at lines 47-58.

• Please clarify how the parameter values listed in Table 1 are obtained.

Additional clarifications have been added after Table 1. In particular the mass was measured on a weight scale, while the Cx and f0 coefficients were experimentally identified by means of coastdown tests. The efficiency of the transmission has been estimated by means of eq. 4, added at line 307.

• Please concise the conclusions point-wise identifying the key points.

Conclusions have been rephrased by highlighting the main findings of this work.

 

 

Reviewer 2 Report

• It would be worth expanding the literature review with showing differences between this concept and others EV constructions.
• It would be worth expanding table 1 with comparisons with other existing models,
• Subtitles put on fig 3 is too small,
• It would be worth expanding information about signal of GPS frequency,
• It would be worth expanding information about safety. Authors proposed model of car but not consider safety aspects.

Author Response

 

• It would be worth expanding the literature review with showing differences between this concept and others EV constructions.

Additional statements have been added in Section 2 (lines 192-200) showing some common features and differences between our ultra-efficient lightweight vehicle and other EVs.

• It would be worth expanding table 1 with comparisons with other existing models

Tab. 2 is added in line 171 in order to present the main vehicle data of other vehicles competing to SEM. In this way it is possible to compare the parameters of the analysed vehicle with other vehicles built for the same purpose.

• Subtitles put on fig 3 is too small

Font size of Fig. 3 increased.

• It would be worth expanding information about signal of GPS frequency

Signals of GPS and joulemeter are sampled at 1Hz. A clarifying line was added at line 352.

• It would be worth expanding information about safety. Authors proposed model of car but not consider safety aspects

Safety is a primary issue in the design of a Shell Eco Marathon vehicle. Some information regarding safety is added in section 2.

 

Reviewer 3 Report

This paper presents a detailed analysis of the power demand of an ultra-efficient lightweight battery-electric vehicle. The method has also well described. The paper is generally well written with good quality. It can be accepted after address the following issues: 1. The focus is not well linked to the lightweight. Please explain more during the analysis for this special purpose. 2. As an important part of EV, the battery modelling is not sufficiently discussed. There have been many models on this, like the circuit model (e.g., IEEE Transactions on Industrial Electronics, DOI: 10.1109/TIE.2019.2962429) and the electro-thermal-aging multi-physics model (e.g., IEEE Transactions on Industrial Informatics, DOI: 10.1109/TII.2020.3014599). These works can be mentioned to provide more details about the battery modelling. 3. The conclusion can be further improved, by presenting only the primary findings with necessary quantitative evaluations. 4. The figures have low qualities, please modify.

Author Response

 

• The focus is not well linked to the lightweight. Please explain more during the analysis for this special purpose

Lightweight design allows to reduce the electric vehicle impact during the service life which helps in balancing the initial gap with respect to conventional vehicles. This means that lightweight is necessary for reducing the impact during service life. But if lightweight EVs waste energy during service life they could be worse than conventional vehicles. The solution of ultra-efficient lightweight EVs combines the lightweight advantages and minimizes the energy waste during service life.

This concept has been highlighted in the introduction at lines 42-64.   

• As an important part of EV, the battery modelling is not sufficiently discussed. There have been many models on this, like the circuit model (e.g., IEEE Transactions on Industrial Electronics, DOI: 10.1109/TIE.2019.2962429) and the electro-thermal-aging multi-physics model (e.g., IEEE Transactions on Industrial Informatics, DOI: 10.1109/TII.2020.3014599). These works can be mentioned to provide more details about the battery modelling

The equivalent RC circuit model with thermal dependencies is used for the battery.

The employed model does not account for the aging process the battery undergoes during repeated charge and discharge cycles. Actually, being the vehicle realised for competition purposes, the lifespan of the battery is limited and such kind of effect has a minor importance.

 

These additional details have been included in section 3.1, along with additional references including the suggested ones.

   

• The conclusion can be further improved, by presenting only the primary findings with necessary quantitative evaluations

Conclusions have been rephrased by highlighting the main findings of this work. Quantitative evaluations have been added.

• The figures have low qualities, please modify.

Fig. 3-4-6-9-10-11-12-13-14 have been modified, improving the quality and increasing the font size.