Efficiency in design and production to achieve sustainable development challenges in the automobile industry: Modular electric vehicle platforms

Electric vehicles have been based on a new product architecture: modular electric vehicle platforms (MEVPs). Through a case study, this paper uses efficiency and sustainability criteria to analyse this modular architecture as implemented by three automobile manufacturers in their European production networks. The results show that MEVPs have been adopted to achieve the efficiency of mass-production electric vehicles in order to comply with regulatory environmental requirements. MEVPs are designed with structural compatible modules, an electric drive system architecture and modular batteries that can be adapted to each vehicle. These designs are focused on limiting energy consumption by reducing weight with the use of high-performance materials or extra-thin batteries. Some of these MEVPs use fewer components in their design to facilitate disassembly and recycling. This new modular architecture has been implemented through compatible, flexible production systems accompanied by different sustainable production initiatives. The production system has incorporated carbon-neutral production processes or circular economy production models, which include remanufacturing and reuse. Networks resulting from these new MEVPs are geographically concentrated and are not conditioned by location factors. The roles of the plants have been mainly driven by economies of scale to achieve high-performance specialised products and high volumes. These plants play a role as hubs for electric vehicle production in the manufacturers' European production networks.


| INTRODUCTION
Stakeholder pressure and the need to comply with legislation are forcing the automobile industry to design and manufacture fuel-efficient, low-impact, environmentally responsible and sustainable vehicles (Jasi nski et al., 2021;Szász et al., 2021). Road transport (goods and passengers) accounts for approximately one-fifth of EU emissions.
Cars are the main pollutant, accounting for 60.6% of total European road transport CO 2 emissions (EPRS, 2020). In the US, the transportation sector is one of the largest contributors to anthropogenic greenhouse gas (GHG) emissions. According to the national inventory that the US prepares annually under the United Nations Framework Convention on Climate Change, transportation accounted for the largest portion (27%) of total US GHG emissions in 2020, and cars account for 57% of total transportation (EPA, 2022).
As an example, the urgency for climate change mitigation led to a ratcheting-up of legal CO 2 emission limits for passenger cars by the European Commission (European Parliament and the Council of the European Union, 2019). Competitiveness in the automobile industry involves designing sustainability strategies to ensure compliance with these policies on environmental issues (Gu et al., 2021;Jiang et al., 2018). The incorporation of alternative powertrains, particularly for battery-powered electric vehicles, has been one of the main strategies for complying with these regulations (Gunther et al., 2015). This strategy has been accompanied by important changes related to the vehicles' product architecture.
The solution to respond to the efficiency challenges in product architecture has been modular platforms (MPs) (Lamp on et al., 2019;Lamp on & Rivo-L opez, 2021). Under the product architecture approach, the design of these MPs has combined the advantages of modularity with those of platforms (Mikkola & Gassmann, 2003). The scalable design of MPs allows the structural dimensions of this basic element of the automobile to be varied. Thus, several automobile models from different segments 1 (different sizes) can be incorporated on a single MP (Buiga, 2012;Schuh et al., 2013). In terms of production systems, the modularity offered by MPs makes it possible to include flexible production systems and to reorganise facilities so that their specificity can be changed (Lamp on, Cabanelas, & González-Benito, 2017). Moreover, MPs have allowed automobile manufacturers to obtain efficiency in production networks. With MPs, production mobility is possible among plants that produce automobile models from different segments and implies that the network's manufacturing resources can be shared by a large number of automobile models and by a larger volume of units (Lamp on & Cabanelas, 2014;Lamp on, Cabanelas, & González-Benito, 2017). In summary, modular product architecture has had an impact on performance in terms of product variety and design costs (Gauss et al., 2020;Stadtherr & Wouters, 2021), manufacturing flexibility (Pashaei & Olhager, 2019) and network outputs (Lamp on et al., 2019;Lamp on & Rivo-L opez, 2021).
Despite the interesting findings of these previous works on the impact of modular product architecture and in particular of MPs, their analyses have not included sustainability criteria. Modular product architecture has recently gained special attention in sustainable product design and in sustainable production processes (Ma & Kremer, 2016). In the automobile industry, some of the key aspects in this sustainable context have been the development and production of electric vehicles, reduction of environmental impact over the product's lifetime, and ensuring reactivity to respond to changes in regulatory requirements (Go et al., 2015;Schöggl et al., 2017). In terms of product architecture, the sustainability challenges in this industry have but also new elements (e.g., batteries, electric drive system) (Nicoletti et al., 2020). The adoption of these new MEVPs also implies significant changes in production systems and production networks.
This research contributes to the identification of the main features regarding product design, production systems, production networks and sustainable development derived from the adoption of MEVPs to meet the demanding challenges of sustainability that automobile manufacturers are facing.
In order to study how MEVPs are implemented based on efficiency and sustainability criteria, the paper is structured as follows.
The first section reviews the modular product architecture and its impact on product design, production systems and production networks. The second section presents a case study of the implementation of MEVPs in the European production networks of three automobile manufacturers. The last section presents the conclusions and proposes future lines for research.

| MEVPs and product design
The product architecture approach focuses on features related to product design in which product variety, modularity and the platform are the key elements (Mikkola & Gassmann, 2003;Shamsuzzohaa & Helob, 2017). The platform is defined as a common structure from which a stream of derivative products can be developed (Simpson et al., 2014). The automobile platform is the core framework of the vehicle in which the basic element is the under-body (Lundbäck & Karlsson, 2005;Muffatto & Roveda, 2000), although other components have been included such as axles or the suspensions train (Muffatto & Roveda, 2000).
From the product architecture perspective, MPs combine the platform with the advantages of modularity. The advantage of modularity in the automobile industry is that it offers greater levels of customisation in a high-volume context, efficiency in terms of product variety, module sharing, and improvements in operational aspects of design (Gauss et al., 2020;Piran et al., 2020). Among other factors, the dimensional parameters of the platform determine product variety because an excess of commonality in physical product dimensions may limit the possibilities for product differentiation (Sköld & Karlsson, 2007). MPs adopt different configurations from a scalable design that is made up of compatible modules and allows structural dimensions to be varied (Lamp on et al., 2019;Lamp on, Cabanelas, & Carballo-Cruz, 2017;Lamp on, Cabanelas, & González-Benito, 2017). This design allows several automobile models from different segments to be incorporated on a single MP (Buiga, 2012;Schuh et al., 2013).
In recent years, automobile manufacturers have been developing new MEVPs to produce electric vehicles (Krings & Monissen, 2020).
In terms of product architecture, the design of the MEVPs includes new elements, particularly the batteries and the electric drive system, and has different design requirements to the MPs (Nicoletti et al., 2020). The design efficiency of MEVPs is mainly related to the architecture and layout of these new elements that comprise it. In terms of product variety, MEVP design offers more than the variety offered by MPs (models from different segments) as it must also allow variety in the power and autonomy of the different models. (Nicoletti et al., 2021). Autonomy is closely related to the capacity and architecture of the batteries, which are tailored to the type of vehicle. In order to look in depth at MEVP design, the following research question is posed: RQ1. What are the main product design features of the MEVPs related to the product variety, modularity and platform?

| MEVPs and production systems
There is a link between modular product architecture and the performance of production systems. The literature demonstrates a straight relationship between greater modularity and the ease of assembling a large variety of products (Fixson, 2007;Pashaei & Olhager, 2017;Watanabe & Ane, 2004). Modularity allows the reconfiguration and performance of production systems, especially the flexibility and compatibility of processes and facilities (Francas et al., 2009;Huang et al., 2005). In automobile assembly plants, 2 body-in-white assembly processes are particularly important as they create the vehicle platform and bodywork. Modularity of MPs allows a modular design of the body-in-white assembly process so that different models can share the same flexible line configured through the different sequences of welding stations (Lamp on, Cabanelas, & González-Benito, 2017). In the final assembly process, flexibility has been achieved through the implementation of so-called mixed-model assembly lines. These lines allow the assembly of the different models and ensure fast and flexible changes in the sequence of models (Ponticel, 2006;Zeltzer et al., 2017).
Production systems for new MEVPs must have the efficiency required for the mass production of electric vehicles (Krings & Monissen, 2020). In 2030, 30% of all vehicles worldwide are predicted to be electric (Rietmann et al., 2020), although the final percentage will depend on how society takes up new trends in mobility (e.g., Mobility-as-a-Sevice or Peak Car) (Turienzo et al., 2022). Elements such as the flexibility of production processes are key to producing these high volumes of different products (Asadi et al., 2017).
Moreover, production systems adopting MEVPs will have to be able to launch new electric models quickly (Hertzke, 2019). This implies versatile facilities that can be updated or modified for model launches and avoid large investments (Omar, 2011). A study of the production systems in MEVP adoption is therefore required and the following research question is posed: RQ2. What are the main production systems features of MEVPs related to compatibility and flexibility?

| MEVPs and production networks
The production network approach is the framework for analysing the key elements of production networks: configuration, coordination mechanisms, the role played by each plant, and network outputs (Cheng & Farooq, 2018;Christodoulou et al., 2019;Miltenburg, 2009;Shi & Gregory, 1998). The production networks of automobile manufacturers are based on platforms where the plants assemble the automobile models that share the same platform (Frigant & Zumpe, 2017). In this production context, carmakers have been using operational flexibility to transfer production between plants to optimise the network's capacity Automobile manufacturers must select the plants in their production networks where electric vehicles will be assembled using MEVPs.
Assembly of the new elements (e.g., batteries, electric drive system) that MEVPs incorporate (Nicoletti et al., 2020) involves changes in those production plants. The automobile manufacturers must decide whether to integrate electric vehicle production by adapting existing facilities and processes at the plants (Herrmann et al., 2012) or completely transform the plants with specific facilities and processes to produce the electric vehicles (Luccarelli et al., 2013). This decision conditions which plants make up the electric vehicle production network and can be taken on the basis of location criteria (e.g., technological factors) (Pavlínek, 2020) or on plant focus (e.g., focus on economies of scope to assemble all the different models) (Lamp on & Rivo-L opez, 2021). Moreover, these decisions involve other aspects such as the geographic dispersion of the production network and the intensity of the coordination mechanisms among the plants in the network. In order to analyse the production networks derived from MEVP adoption, the following research question is posed: RQ3. What are the main production network features in terms of configuration, coordination mechanisms and plant roles resulting from the adoption of MEVPs?

| MEVPs and sustainable development
Electric vehicles as part of sustainable transportation are at the heart of the United Nation's Sustainable Development Goals (SDGs). They are directly linked to many SDGs including SDG3 (good health and well-being), SDG7 (clean energy), SDG13 (climate), and SDG12 (sustainable production and consumption) (Onat et al., 2021). Moreover, production of electric vehicles has been one of the main initiatives of automobile manufacturers for complying with a sustainable development strategy (Gunther et al., 2015). From this perspective, the implementation of MEVPs is decisive in order to achieve these sustainable development goals.
In terms of sustainability criteria, the reduction of environmental impact and ensuring reactivity to respond to changes in regulatory requirements are key in the automobile industry (Schöggl et al., 2017).
The industry has achieved compliance with environmental regulations thanks, in the main, to mass production of electric vehicles. (Jasi nski et al., 2021;Krings & Monissen, 2020). In this context, these vehicles need to be based on a modular platform design that allows different models to be manufactured on the same platform.
MEVP design, and that of the production systems that will adopt them, must allow the electric vehicles to be produced efficiently.
Sustainable product design includes different relevant aspects (Keitsch, 2012), and what is key in the case of the automobile industry is the reduction of environmental impact over the product's lifetime (Schöggl et al., 2017). Among other things, practices aimed at such sustainable design in the industry include product design for be recycling or reusing at the end of its lifecycle; use of materials with less environmental impact or use of fewer materials overall in the design (Staniszewska et al., 2020). All these aspects must be taken into account when designing MEVPs in this context.
As far as production processes are concerned, MEVPs can manufacture by using traditional sustainability initiatives such as using fewer resources during the production process or producing less F I G U R E 1 Framework of the research. Source: Own elaboration pollution and waste. However, in recent works on the automobile industry, researchers have focused on designing production processes that facilitate reuse and recycling, particularly in processes linked to battery production and assembly (Fujita et al., 2021;Pagliaro & Meneguzzo, 2019). Therefore, bearing sustainability criteria in mind, the final research question is posed: RQ4. How does the adoption of MEVPs contribute to the sustainable development strategy?
As a summary, the framework of this research is presented in

| METHODOLOGY AND DATA
To respond to the objective of this research, the empirical work was qualitative in its approach and used the case study as a research methodology. Qualitative research allows a rich description and full comprehension, exploration and understanding of a phenomenon (Yin, 2014). One of the methods that serve the purpose of qualitative research is the case study. Case studies allow the analysis of real-life events and an in-depth and detailed examination of either a specific case or a small number of cases (Creswell, 2014). This empirical work consisted of a case study of three automobile manufacturers.
A questionnaire was used to gather the primary data about the adoption of these MEVPs. This questionnaire was built based on the literature review. The information covered is detailed in the Appendix.
It comprises four parts: Block (1) the sustainability strategy; Block (2) the elements related to the product design; Block (3) the elements related to the production system; and Block (4) the aspects related to the production network. Block (1) contains the information regarding the general sustainability strategy that provides the framework for MEVP adoption. Sustainable development goals (e.g., environmental impact) and sustainable development initiatives (e.g., sustainable production processes) are included in the questionnaire (Jasi nski et al., 2021). Block (2) relates to product design: platform, modularity and product variety are the key elements in the questionnaire. For the platform, the design elements included are the electric drive system architecture and features of the batteries (Chan, 2002;Ehsani et al., 2007). The product variety in this research refers to different automobile models classified based on sizes (segments) (MacDuffie, 2013) and of type of motorisation (hybrid or electric) (Pistoia, 2010). Regarding modularity, two aspects were included. First, the number of modules and their compatibility (Sánchez, 2004). In this study, a compatible module is one that can be shared and exchanged among different automobile models; it is defined as a compatible structural module when it also determines the structure and support for the other components making up the vehicle (Lamp on et al., 2019). Second, the questionnaire includes the variation of the structural dimensions involved in the platform design (Simpson et al., 2014). In Block (3), the compatible and flexible production system is included in the questionnaire. This includes the standardisation of production processes and implementation of versatile facilities (Lamp on, Cabanelas, & González-Benito, 2017).
In Block (4), configuration, coordination mechanisms, plant roles and network outputs are the elements included in the questionnaire. The production network configuration is examined in terms of geographical dispersion (Miltenburg, 2009), defined as the number and location of production plants involved in MEVP adoption. The coordination mechanism incorporated in the questionnaire was knowledge transfer among production plants (Shi & Gregory, 1998). Regarding plant roles, the questionnaire includes the traditional location factors and plant focus to study how roles are assigned (Feldmann & Olhager, 2019).
Finally, network outputs include the scope and scale economies, measured by the number of models and production volume that can be shared on the production network (Wilhelm, 1997), and operational flexibility, measured by the number of plants that allow production to be transferred between them (Lamp on, 2020; Lamp on et al., 2015).
A process of validation of the questionnaire (Forza, 2002) was carried out. This validation was done by means of a pilot test with one of the manufacturers. A first version of the questionnaire was emailed together with instructions for filling it out to the head of design and implementation of the MEVP. Additionally, a conference call was arranged to provide support from the research team in filling out the questionnaire. The pilot checked the validity and understanding of the elements comprising the questionnaire tested, and verified the procedure for receiving, completing and returning it.
To collect the data, the validated questionnaire was sent to the three carmakers. The fieldwork was done from October 2019 to January 2020. The emailed questionnaire also included the instructions for filling it out. As the information could belong to more than one department of the manufacturer, it was decided to channel the information request via a single interlocutor whom each manufacturer identified as being responsible for the development and industrialisation of the modular electric vehicle platform. Respondents were given time to collect data, complete the form and email it back. Later, there was a chance to review the data jointly during a conference call with the research team before finalising data collection.

| Production network
With this product architecture, the plan is for five of the manufacturer's plants in Europe to comprise the electric vehicle production network.
These plants are located in three countries (France, Spain and Slovakia).
Production from these plants is destined for the European market. The coordination mechanisms among plants have been intensified. Knowledge transfer has been used to allow them to share different models and different modular platform production (internal combustion engine, hybrid and electric vehicles) among the plants. The roles are assigned by plant focus criteria, in particular a focus on flexibility, by which the carmaker has the intention for the production of all models to be shared among the plants of the network. This objective is strongly conditioned by the reorganisation of all their supply chains, and will therefore be difficult to implement. As a result, operational flexibility for transferring production is possible among the five plants. In terms of the economies of scope and scale, nine models, with a production volume of four hundred thousand units, will share the manufacturing resources of the production network in 2022.

| Sustainable development
The objective of the general sustainable development strategy is to achieve carbon neutrality in 2050. The MEVP strategy of the carmaker is not to develop higher capacity batteries, but will focus on achieving the best balance between cost and range through economies of scale. This strategy started in 2020 with the production of vehicles under MEVP2 across all the carmaker's brands.
The whole architecture is created to improve energy consumption and aerodynamics, using lightweight materials to lower the overall weight. Moreover, the modular design of the batteries is linked to their thickness as they are extra-thin, which allows them to be horizontally and vertically modular (the batteries can be used as stackable modules).
The launch of vehicle production using new modular electric vehicle architecture is accompanied by the first initiative for a circular economy plant. The implementation of this circular economy production model started in 2021 at this production plant, replacing its production of new vehicles. The circular economy production model implemented is based on a set of elements (maintenance, remanufacturing and recycling), aimed at reusing different vehicle components.
This pilot plant has a line installed for dismantling end-of-life vehicles.
This new facility recovers different parts and materials as well as the batteries. With this production model, the carmaker is aiming for the plant to achieve a negative carbon balance by 2030.

| Production system
The sharable production system is particularly relevant in the case of this carmaker. The carmaker's standard integrated production system was deployed in the plants of the production network. This standard production system was the result of a process of identification and sharing of the best practices at the carmaker plants and has been replicated for the electric vehicle production plants. A circular economy production model has been implemented in a pilot plant, the aim being to spread the circular economy to the other plants in the electric vehicle production network.

| Production network
With this MEVP2, the plan for 2022 is that three plants (of 12 plants in the carmaker's European network) form the electric vehicle production network. The locations of these plants are geographically concentred in France and the UK, and the production from them is destined for the European market. Regarding coordination mechanisms, a common corporate operations management is shared among plants of the carmaker.
The plant roles are assigned based on plant focus. The assignment of roles to production plants is driven by economies of scale and by flexibility to produce different product variants. These plants are relatively autonomous in terms of production in relation to other plants in the network. They play a role as hubs for electric vehicle production in the Manufacturer's European production network.
In terms of network outputs, operational flexibility for transferring production models is allowed among the three plants. Eight electric models with a production volume of five hundred thousand units will share the manufacturing resources of the production network (year 2022).

| Sustainable development
With the sustainable deployment strategy, the manufacturer foresees the production of 1.5 million electric vehicles in 2025 (in three different modular electric vehicle platforms). This objective implies highvolume series production of electric vehicles that requires an efficient adoption of these new platforms. This strategy started in 2019 with the production of vehicles under MEVP3 across the manufacturer's brands.
In terms of sustainability, MEVP3 is focused on a sustainable production process. The sustainable strategy includes the objective of carbon-neutral production at all MEVP3 locations in Europe. The initial goal is to reduce the environmental impact of production processes by 2025 in areas such as energy usage, CO 2 emissions, waste and the use of water by 45% per vehicle compared to 2010.
In terms of network coordination mechanisms, the adoption of MVEP3 has gone hand in hand with the deployment of a common strategy on the production process and facilities to produce with a neutral carbon balance. The plants of the production network share knowledge and best practices on sustainable procedures and sustainable technology in the facilities.

Sustainable development
Environmental impact and regulatory requirements MEVPs are adopted to achieve the efficiency of massproduction electric vehicles, complying with regulatory environmental requirements. 100% of the manufacturer's range (40 hybrid and electric models) will be electrified in 2025 MEVPs are adopted to achieve the efficiency of massproduction electric vehicles to achieve carbon neutrality in 2050 MEVPs are adopted to achieve the efficiency of massproduction electric vehicles, complying with regulatory environmental requirements (1.5 million electric vehicles in 2025)

Sustainable product design
The platform is focused on sustainable product design. The platform is designed to limit CO 2 emissions.
Weight reduction using high-performance materials.
This design also includes fewer components than the platform it replaces in order to facilitate disassembly and recycling The design is created to improve energy consumption, using lightweight. Moreover, the modular battery design seeks to reduce vehicle weight. The batteries are extra-thin, allowing vertical modularity (they can be used as stackable modules) Sustainable production process MEVP2 is implemented with a pilot circular economy production model (maintenance, remanufacturing and recycling). This pilot process includes a line for dismantling end-of-life vehicles. This new facility recovers different parts and materials as well as the batteries MEVP3 is focused on sustainable production process. The platform is implemented with the adoption of carbon-neutral production processes, energy and water usage, CO 2 emissions, and waste generated Coordination mechanisms among plants are intensified to deploy the common carbon-neutral production processes. Knowledge transfer specifically on sustainable procedures and sustainable production technologies

| Production system
The plants will be configured for the new MEVP3 and entirely converted from internal combustion engine vehicle production to exclusively electric vehicle production. The conversion of the plants also includes a plan to produce with a neutral carbon balance. Regarding production systems, multi-brand production has been stepped up. In some plants, multi-brand production has been implemented for the first time with MEVP adoption. This has been done particularly on the mixedmodel final assembly lines, which must be shared by different models.
Plant-1, in which production under MEVP3 was launched, produces six models of three brands, including a premium brand. This flexible production system ensures flexible changes of models without losing production capacity (in plant-1 production can reach 1500 vehicles/day).

| Production network
With this modular architecture, the plan for 2022 is that five plants In terms of networks outputs (expected for the year 2022), the operational flexibility for transferring production of the MEVP3 models will be possible among five plants. A total of 700,000 units of 12 electric models can share the manufacturing resources of the production network.  All the production of the plants is destined for the European market Five plants geographically concentred in two countries (out of 24 plants and nine countries of the manufacturer's European network) All the production of the plants is destined for the European market Coordination mechanisms Ties among all the plants: benchmarking, exchange and collaborative learning processes to share the different (internal combustion engine, hybrid and electric) vehicles production The plants are relatively autonomous in terms of production.  (Buiga, 2012;Schuh et al., 2013) and that integrate the new specific elements of electric vehicles in a skateboard design (batteries in the floor and electric motors in the axles).
Modularity of MEVPs derived from compatible structural modules allows a product variety that includes models from different segments (sizes) in their design. Moreover, the electric drive system architecture and modular batteries that MEVPs integrate allow this platform to assemble a product variety defined by a broad model range in terms of power and autonomy.
Regarding production systems (research question RQ2), MEVPs have been adopted by means of efficient production systems to achieve mass-production and to launch new electric vehicle models quickly. These efficient production systems have been deployed using flexible production processes to produce high volumes of different models, and versatile facilities to avoid large investments when launching new models. Finally, in order to adopt MEVPs, the production system has incorporated carbon-neutral production processes or circular economy production models, which include aspects of remanufacturing and reusing. To deploy these common carbon-neutral production processes, knowledge transfer specifically on sustainable procedures, and sustainable production technologies have been implemented among the production networks' plants. On the other hand, MEVPs form part of a comprehensive strategy of automobile manufacturers for sustainability that goes beyond the industry itself. The different initiatives on sustainable design such as the weight reduction to save energy or the use of fewer components to facilitate recycling, and on the sustainable production process such as the implementation of carbon-neutral production processes have a relevant impact on society in general. In fact, these initiatives have a direct influence on meeting some of the SDGs such as SDG7 (clean energy), SDG12 (sustainable production and consumption) or SDG13

| Practical implications
(climate). Therefore, institutions, particularly the governments of countries with a strong presence in automobile industry, should implement active industrial policies in MEVPs adoption. The introduction of investment incentives or the fostering of a favourable technological environment that is suitable for MEVPs development and production are possible recommendations for public policy that can be derived from the research.

| Future research
The analysis in this research into MEVPs has focused on the design and production stages within the product lifecycle. Although some aspects of use and end-of-life have been identified, they have not been looked at in depth. Future research could analyse the adoption of MEVPs during the use and end-of-life of the product lifecycle.
At the same time, MEVPs are not fully implemented in all three of the analysed cases. Future research could carry out longitudinal studies to analyse the evolution of implementation. In particular, comparison could be made of the proposed objectives and those that were finally achieved by implementation. Furthermore, a comparison could be made of the impact in terms of sustainability and efficiency resulting from the differences in the strategies used by each automobile manufacturer when adopting their MEVPs.

ACKNOWLEDGMENTS
The research has been funded by the Spanish Ministry of Science and Innovation under the reference project: PID2020-116040RB-I00,