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Abstract
As people strive to live more sustainable due to the change in climate, product developers need to adapt and create new and more sustainable solutions. In the car industry, companies work to minimize weight and adjust material selection in the cars to reduce emissions. The goal of this project was to find a new solution, in aspects of cost, weight and size, for fixating the hood on Lynk & Co's Model 01 on behalf of CEVT to create a more sustainable vehicle.
By using proven and recognized product development tools throughout the product development process, a new concept for fixing the hood could be evolved. This concept was then analyzed with regard to the developed requirements specification to ensure a good result. In this part, the finite element method and hand calculations were mainly used to analyze stresses in the material.
The result of the work was thus a proposal on how hoods for electric cars could be fixed in the future.
The concept consists of a hood that is held in place with the help of four hooks and which, when
serviced, is held parallel to the engine compartment with the help of two struts. The concept also
includes suggestions on locking mechanisms to limit the access for unauthorized users. This to ensure
that the engine is only handled by qualified personnel and therefore reduces wear. Throughout the
whole project, focus has been on sustainable development. The results has been analyzed and
compared to the existing model with this in mind.
Certification
This thesis has been submitted by Josefine Tempsch and Martin Granberg to the University of Skövde as a requirement for the degree of Bachelor of Science in Mechanical Engineering. The undersigned certifies that all the material in this thesis that is not our own has been properly acknowledged using accepted referencing practices and, further, that the thesis includes no material for which we have previously received academic credit.
Josefine Tempsch Martin Granberg
Skövde 2020-06-03 Skövde 2020-06-03
School of Engineering Science School of Engineering Science
Acknowledgements
We would like to acknowledge the people who have been involved in this project. First of all, we would
like to thank our supervisor Lennart Ljungberg, from the University of Skövde who has guided us
throughout the work. We would like to give special thanks to our supervisor Jerker Apell and his
colleagues Peter Stenbaek and Mikael Johansson from China Euro Vehicle Technology, for among other
things, their help with the development of the requirement specification. We would also like to thank
Andreas Andersson Lassila and Ola Nyqvist from the University of Skövde. Andreas assisted with
guidance in the finite element method and Ola helped define load cases. This could not have been
done without you.
Table of Contents
1 Introduction ...1
1.1 Company presentation ...1
1.1.1 Lynk & Co Model 01...1
1.2 Background ...2
1.3 Problem statement ...2
1.4 Purpose and milestones of project ...2
1.5 Method ...3
1.6 Demarcation ...3
2 Theory ...4
2.1 Literature study ...4
2.2 Field study ...4
2.3 Benchmarking ...5
2.4 Summary ...5
3 Requirements to concepts ...6
3.1 Specification ...6
3.2 Generating concepts ...7
3.2.1 Electromagnets ...8
3.2.2 Electric actuator ...8
3.2.3 Separate tool ...8
3.2.4 Fixed with hooks ...8
3.3 Concept selection ...8
4 Further development of chosen concept ... 10
4.1 Methods for analyzing concept ... 10
4.1.1 CAD – Computer Aided Design ... 10
4.1.2 Hand calculations ... 10
4.1.3 FEM - Finite Element Method ... 10
4.2 Visualization of concept using CAD ... 10
4.3 Load cases and hand calculations ... 12
4.4 Finite Element Analysis ... 13
4.4.1 Load case one ... 15
4.4.2 Load case two ... 16
4.4.3 Summary of load cases ... 18
4.5 Locking mechanism ... 18
5 Result... 19
5.1 Summary of the work in its entirety ... 19
5.2 Concept results with regard to requirement specification... 19
5.3 Project result with regard to goals and purpose ... 20
6 Discussion ... 21
7 Conclusion ... 23
References ... 24
Appendices ...i
Appendix 1: Work Breakdown and time plan...i
Appendix 2: Pictures from market survey ... ii
Appendix 3: Requirement specification ... iii
Appendix 4: Mind map ... iv
Appendix 5: Sketches of concepts ... v
Appendix 6: Basis to Pugh’s Matrix ... viii
Appendix 7: Hand calculation of load case 1 ... x
Appendix 8: Hand calculation of load case 2 ... xi
Appendix 9: Hand calculation of load case 3 ... xii
Appendix 10: Hand calculation of load case 4 ... xiii
Appendix 11: Boundary conditions ... xiv
Appendix 12: Mesh and Convergence analysis ... xv
Appendix 13: Locking mechanism ... xvii
Appendix 14: Weight comparison between existing solution and new concept ... xviii
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1 Introduction
As more people strive to live as sustainable as possible due to the change in climate, product developers need to adapt and create new and more sustainable solutions. In the car industry, companies work to minimize weight and adjust material selection in the cars to reduce emissions.
Battery electric vehicles (BEV’s) replaces combustion engines and carsharing is implemented in big cities worldwide (Kortum, Schönduwe, Stolte & Bock 2016). This project was carried out with the goal of finding new solutions for fixating the hood on Lynk & Co's Model 01 on behalf of CEVT.
1.1 Company presentation
CEVT, or China Euro Vehicle Technology is located at Lindholmen, Gothenburg and develops mobility solutions. CEVT is completely owned by the Geely Group and works mainly with modular development, advanced virtual engineering and software development for all the Geely Group Brands. The core of CEVT’s business is innovation and their ambition is to focus on sustainability in design and development considering the whole life cycle of the company’s products (CEVT 2020). The project was done in collaboration with the closures module team at the company. They provided the authors of this thesis with previous studies on the subject, computers with necessary software and simulation tools, access to the reference model and existing detail design.
1.1.1 Lynk & Co Model 01
The Lynk & Co 01, which can be seen in Figure 1, is the first model of the brand. It is a 5-door crossover SUV car which has been developed in association with Volvo Cars and CEVT. The model is based on the Compact modular architecture platform, seen in Figure 2, which is one of many components shared with the Volvo XC40 (Apell 2020). The car went on sale on August 4, 2017 and has until spring 2020 then been sold in more than 150 000 copies.
Figure 1: Lynk & Co model 01 (www.a2mac1.com , 2020) Figure 2: CMAD (www.global.geely.com , 2020)
2 Reference hood assembly system for Lynk & Co 01 is shown in Figure 3, which today opens and closes mechanically by using the inner latch handle inside the car. The inner latch handle is connected by a cable to two hood latches that holds down the hood and preventing unwanted openings.
Figure 3: Hood assembly (www.a2mac1.com , 2020)
1.2 Background
The car industry today is currently investing in development of electrically run vehicles to find more sustainable solutions using eco-design (International Organization for Standardization, ISO 14062:2002). The goal of this standard is to reduce adverse environmental impacts of product development throughout their entire life cycle. This method can be applied as a proactive approach when redesigning components and products that could lead to evaluation of environmental impacts in terms of a life cycle analysis (Shervin & Bhamra 1999). This is of great importance to industries that wish to decrease their ecological footprint over time. Mobility has for a long time been important to the human society, but with the increasing attention to climate change the demand for more sustainable transportations has increased. The automotive industry wants to maintain their role as a leading part by using effective development and solutions in form of shared cars, electric cars and ways to streamline already existing cars. From an ecological perspective the sharing of personal vehicles is the forward thinking needed in bigger cities and therefore the automotive industry must strive to aid customers in that direction (Kortum et al., 2016).
1.3 Problem statement
Hood fixation in the automotive industry has not changed much the past 50 years (Apell 2020), heavy hinges and heavy locks are currently used which require expensive manufacturing and results in heavier vehicles. Current research states that there is a relevant correlation between vehicle weight, energy consumption and emission (Li, Y. Ha & Li, T. 2019).
With this stated, CEVT is looking for new solutions for fixating hoods that could lead to a decrease in total weight, manufacturing costs and also limit the consumers access. This thesis project specifies to explore and propose future ways to fixate hoods with simple and efficient design solutions in cost, weight and size aspects. The goal of this project is to further develop one concept, simulate load cases and evaluate this against a requirement specification developed in association with CEVT.
1.4 Purpose and milestones of project
The main purpose of this project was to explore alternative ways to fixate a hood in aspects of costs,
size and weight that fulfills the dependability and demands of personal security. Operational and
owning standards were to be maintained or simplified and when choosing different concepts,
consideration should also be given to whether adapting them could work with existing applications.
3 The project will result in an analyzed concept that will be handed over to CEVT for further development. Further milestones of the project are presented. For the project to be considered fulfilled, all of these objects needed to be achieved.
Milestones that are to be reached:
1. Field Study research and benchmarking against competitive companies 2. Agile development solutions
3. Generate concept that fulfills requirement specification 4. Case Study and analysis of chosen concept
5. Presentation of result
1.5 Method
To streamline the project, it was divided into three phases. Each phase had its own timetable and goals to simplify the structure of the project and create sub-goals.
Introduction-phase
In the initial phase, a project specification was made in collaboration with the supervisors to make sure that all requirements and standards relating to the project from CEVT and the University of Skövde will be fulfilled during the thesis. A project plan, see Appendix 1, was also developed in this phase where milestones are set according to the timetable (Wikberg Nilsson, Ericson & Törlind 2015).
Concept-generation-phase
The main goal for the second phase was to develop one or several concepts. In order to do this, many studies need to be conducted. To evaluate existing solutions and products, a literature study followed by a field study was to be performed. The material from this would be used in a benchmark study which would generate in a requirement specification. At this point, the concept generation takes place using various methods such as mind mapping (Wikberg Nilsson et al. 2015) and brainstorming method (Wikberg Nilsson et al. 2015). The final concept was chosen using idea selection matrices (Cervone 2009).
Detail-design-phase
The final phase of the project contains detailed construction of the various parts that emerge in phase two. The concepts would be modulated using computer aided design (CAD). In order to ensure safety, these parts would be analyzed in terms of strength, for example through finite element (FE) analysis.
At the end of this phase, all material should be compiled and evaluated against the project specification to ensure that all requirements and goals are achieved.
1.6 Demarcation
This thesis shall first and foremost process proposals and possibilities of future hood fixation of electric
cars. The Lynk & Co model 01 was used as a reference. Developed concepts and generated ideas was
seen as general solutions of CEVT and would be left to CEVT for future work. Some concepts might
require major reconstruction of the hood assembly but this would not be taken into consideration
during this project with exceptions for hinges, latches and hooks. Other standards such as electronics
or hydraulics would not be investigated but left to CEVT for further investigation. No physical model
would be created, only digital prototypes would be produced using CAD.
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2 Theory
In this chapter, the basic theory for the project is presented. Innovation initiative of hood fixation for electric cars does not stand out from the crowd when compared to combustion engine vehicles. In order to think unconventionally, several hatch, hinge, latch and lock mechanisms, not only from the automobile industry, was studied.
2.1 Literature study
A literature study was performed where the authors searched the internet and the library at the University of Skövde to find relevant literature for the project. The information found using this method would be used throughout the project. Besides from old thesis projects, the authors studied patent solutions for locking mechanism in vehicles. Books and articles were also studied and will be presented throughout this report.
A market survey was also conducted to evaluate alternative opening mechanisms such as windows and security doors. This was done to broaden the knowledge base for the planned concept generation.
The result from this survey showed that in other industries, opening mechanisms such as electromagnets, door closers, actuators and simpler hinges are used. Some examples of this can be seen in Appendix 2. These alternatives are reviewed in the concept generation phase (see Chapter 3.2).
2.2 Field study
A field study was performed using the gemba walk method (Womack 2011) where the authors visited several car dealers in Skövde to interview the salesmen and study the locking mechanism of the hood for different brands and models. In addition to this, the authors visited CEVT’s test facility at Säve, Gothenburg to study the Lynk & Co Model 01.
The field study showed that all competing brands, as well as Lynk & Co, had great similarities in their solution for attaching and opening the hood. The solution consists of a latch located to the left of the clutch pedal in the coupe compartment, which is shown in Figure 4. By pulling this latch, one or two safety hooks which can be seen in Figure 5 is released and the hood partly opens. All models analyzed in the field study, except the Lynk & Co Model 01, uses a mechanical lever in the front to release the safety lock which is shown in Figure 6. The Lynk & Co Model 01 on the other hand, opens the hood completely by pulling the latch in the coupe twice. To prevent the hood to open by mistake, the driver door needs to be open.
Figure 4: Inner latch handle Figure 5: Safety hook Figure 6: Mechanical lever
At all car dealers, it was discussed which parts in the engine room that customers actually need to
access. For electric cars, this is mainly the filling of washing fluid but also the 12V battery. Other than
that, the customers has nothing to do in the engine space. If a customer would try to change or adjust
anything themselves, none of the brands warranties will apply.
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2.3 Benchmarking
In the field study process, a benchmarking study was made using A2mac1 (2020). Benchmarking is a systematic method used in organizations to evaluate the market and their own process in order to pinpoint positives and negatives in its own product (Talluri 2000). Benchmarking is understanding the position and the performance of the company, to learn from the rivals and see if they are ahead and why. These can be measured in forms of productivity, costs and quality to name a few. Results from the benchmarking study led to conclusions that were taken into consideration in the concept generating phase (see Chapter 3.2).
2.4 Summary
Automotive theory of hood fixation summarized points out that the market today is narrow and highly
based on mechanical hinges and lock mechanisms. A few high end vehicle brands stand out from the
crowd with unconventional electrical solutions built around these hinge and lock mechanisms. This
fact may lead to a conclusion that perhaps, even considered its weight, hinges are not so bad after all.
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3 Requirements to concepts
This chapter describes how the concepts were generated and evaluated based on requirements specification and collected data from, among other things, market research and literature study. The chapter also contains information on the methods used to select concepts for further investigation.
3.1 Specification
As this project aims to explore future solutions to fixate the hood of electric vehicles and the goal is to develop a concept for CEVT that they can continue working with, a brief requirements specification was developed. The specification would define the conditions that exist in the remaining parts of the project and is divided into five groups where the different groups cover one area each. These areas are functionality, strength, cost, manufacturing and environment. Further, the various groups are discussed and parts from the requirement specification is presented. The discussed requirements are the most important for the project. The specification as a whole can be seen in Appendix 3.
Functionality
In consultation with the closures team at CEVT, functional requirements was developed. The functional demands is not taken from standards but instead from observations and the project specification.
Some of the requirements of functionality are presented in table 1.
Table 1
1.1 No access to engine space for the consumer
1.2 Easy access to engine compartment during service and production
Strength
In this section of the specification, the load cases for the project are presented. These would be analyzed using calculations and simulations in phase three. A safety factor (𝑠 = 1.5) was used according to Vidosic (1957) during the calculation of load cases to ensure that the concept could withstand the imposed loads. The load cases were determined in collaboration with CEVT personnel and was set to reflect normal usage. Some of the requirements of strength are presented in table 2.
Table 2
2.1 Hold for a person of 100 kg sitting on front of hood 2.2 Hold for collision at 90 km/h
2.3 Hold for accelerating from rest to 100 km/h 2.4 Hold for retardation from 100 km/h to rest
Cost
One of the most important factors in the specification was the cost for the final solution. This includes,
among other things, manufacturing cost and material cost. Some of the requirements of cost are
presented in table 3.
7 Table 3
3.1 Manufacturing cost per unit lower than existing solution 3.3 Lower total cost than for existing solution
Manufacturing
As it is of importance that the concept generated would be compatible with the existing model, the manufacturing factor was of high value. When this part of the specification was created, the five designing guidelines for machining lay as a basis (Boothroyd 1988). These guidelines are standardization, raw material, component design, assembly and accuracy and surface finish. Some of the requirements of manufacturing are presented in table 4.
Table 4
4.2 Adapted for existing machinery 4.3 Compatible with existing model
Environment
In the environmental section of the specification, factors like operational temperature and recyclability were considered to create a sustainable solution. Some of the requirements of environment are presented in table 5.
Table 5
5.1 Highest / lowest temperature (operational) from -40℃ to +85℃
5.3 Highest / lowest humidity (operational) from 10% to 95%
3.2 Generating concepts
Combining knowledge and observation from field study, literature study and specification, made it possible for the work of generating concepts to start. Through meetings with CEVT closures personnel it was decided that concepts focus would be on the fixation and would not consider concepts regarding battery positioning, washer fluid or frunks. A first draft of concepts were created by mind mapping existing products and then brainstorming (Wikberg Nilsson et al. 2015). See mindmaps in Appendix 4.
In order to think unconventionally and with a futuristic perspective, the authors then used SCAMPER method (Wikberg Nilsson et al. 2015) to sketch presentable concepts. The first draft included 10 concepts which can be seen in Appendix 5.
After consultation with CEVT closures module team, to ensure that the concepts were of interest to them, the authors could narrow down the number of concepts to four. These four concepts which were electromagnets, electric actuators, separate tool and fixed with hooks were studied more closely in order to implement a definitive weighting matrix to evaluate which concept to further investigate.
The four concepts are presented in Chapters 3.2.1-3.2.4 and sketches are displayed in Appendix 5.
8 3.2.1 Electromagnets
This concept was inspired by the existing solution and magnets as a locking unit. Magnets possess a high capability to withstand shear and sufficient strength to hold down a hood. Electromagnetic locking is a concept that is preferred to be used together with another concept, such as a mechanical locking mechanism. This due to the two states of electromagnetic locks (Fail Secure and Fail safe). These two states are discussed in Door & Hardwares magazine article about maglocks (Greene 2019).
3.2.2 Electric actuator
The idea of using electric actuators came from an electric window opener manufacturer called LinkAYL, see Appendix 2, who creates linear actuators for opening and closing windows of different sizes. The concept developed consists of one linear actuator placed in the middle of the hood as seen in Appendix 5, Concept 10. Otherwise, the concept is similar to the existing model with hinges.
3.2.3 Separate tool
The idea of using a separate tool to open the hood was developed during the field study where all models used a mechanical handle at the front of the hood to access the engine compartment. The tool in this concept is used to open the hood and only available to authorized service personnel and therefore limits the consumer. Otherwise, the concept is similar to the existing model except that gas springs are removed and replaced with a simple stay, in addition only one hook is used instead of two.
3.2.4 Fixed with hooks
This concept was inspired by the existing solution in the Lynk & Co Model 01 with hooks as an attachment mechanism. When the hood is opened, the hooks are loosened completely and a strut holds up the device parallel to the engine compartment. The strut is inspired by door closers made by the manufacturer dormakaba, seen in Appendix 2, which was studied during the market survey.
3.3 Concept selection
To select the best-suited concept, Pugh’s Matrix Analysis (PMA) method were applied due to it being a well proved method in complex decision making (Cervone 2009). Criteria were set using the requirement specification and graded after consultation with company supervisor. The grading can be seen in the column “Factor Weight” in Figure 7 where “Weight” is seen as the most important factor and is therefore given ten points. The factor “Maneuvering” is not considered as important and is therefore only given two points. During the evaluation, the original model (Lynk & Co Model 01) is used as a reference when rating the concepts and therefore has a value of 0. Each concept was compared with the original model using data collected during the market survey regarding the criterias and was graded from -1 to 1 where -1 was inferior to the original model and 1 was better than the original model. The result of the weighting is obtained by summing the points for each individual concept and then comparing them. The concept with the highest score is chosen for further development. By using this method, the choice of concepts becomes highly objective and systematic. The only subjective assessment in the method was how the various criteria were graded. Since this was done together with CEVT staff, the result is considered satisfactory. Chosen criteria are listed below.
Weight - An important factor since the industry is always looking to reduce weight, in environmental aspects such as emissions and manufacturing.
Cost - From the specification it is desired to reduce manufacturing cost and roughly estimate the cost of the proposed solution.
Simplicity - Solution should be easy to use and manufacture.
Safety - Needs to be calculated and analyzed for every concept and is therefore set to zero in
the matrix. The goal is to maintain or increase the safety compared to existing solution.
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Environmental - The students desire to minimize the ecological footprint by decrease the amount of material and apply a cradle to cradle perspective (McDonough & William 2009).
Availability for production (AFP) - If the product is to be manufactured in large batches the availability for machining must be taken into consideration.
Availability for service personnel (AFSP) - Service personnel should be able to access the engine room.
Robustness - Stability in all available positions of hood assembly.
Maneuvering - Easily understood and manageable assembly.
Figure 7: Pugh’s matrix
As seen in Figure 7, concept “Fixed with hooks” had more points than the other concepts after
evaluation and was therefore chosen as the one to work further with. Documentation and basis of the
matrix can be seen in Appendix 6.
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4 Further development of chosen concept
This chapter includes calculation work, construction and simulations of the chosen concept. The different components in the developed concept is also presented, visualized and simulated with the given load cases. Proposals of locking devices is also presented.
4.1 Methods for analyzing concept
In order to evaluate if the developed concept would function safely during normal usage and to meet the requirement specification, calculations and FE-analysis were made. Further the different methods used to analyze the concept is presented.
4.1.1 CAD – Computer Aided Design
To construct and visualize the created concept in a digital environment CAD was used. The method was used due to the fact that no real prototype would be produced. CAD aims at streamlining the engineering process by creating a realistic 3D model in a digital environment, thus reducing paperwork and increasing creativity (Krouse 1982). The CAD-programs used in this project was CATIA V5 and Creo Parametric 4.0.
4.1.2 Hand calculations
Hand calculations were performed to get an idea of whether simpler components in the concept can withstand applied stresses and loads. One of the reasons why certain calculations were done by hand was to use knowledge in strength theory and mechanics. The basis for these calculations is course literature such as Mekanik - statistik & dynamik (Grahn & Jansson 2002), and Mechanical design of machine elements and machines (Collins, Busby & Staab 2010).
4.1.3 FEM - Finite Element Method
Finite element method is an analyzing tool utilized by engineers worldwide to interpret how a body is behaving during different kinds of loads. “The basic idea in the finite element method is to find the solution of a complicated problem by replacing it with a simpler one.” (Rao 2018, p. 3). By simplifying the problem, Rao (2018) also states that an approximate solution will be found rather than the exact solution.
In this project the finite element method was used as a complementary method to hand calculations with the purpose to simulate loads to the concept and analyze stresses. The result of this analysis will lay basis to the result of the entire study and decide whether to proceed with the concept development.
The analysis was done only with regard to the striker and the hook as these are the most exposed components of the fixation. All other components are not taken into account but are set as boundary conditions in the analysis. This is presented in Chapter 4.4.
ABAQUS CAE (Complete Abaqus Environment) was the software provided by the University of Skövde to perform finite element analysis and was therefore the software used in this project.
4.2 Visualization of concept using CAD
The developed concept does not differ much from the original model and therefore existing files from
the company was used with small modification. In Figure 8 the original hood assembly is shown from
above next to the new developed concept. Here, the difference between the different models is
highlighted in green. This was the only modification made to the existing files in order to visualize the
concept developed.
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Figure 8: New (to the left) and old (to the right) inner panel with reinforcement for fixations
In Figure 9 one of the four fixations of the hood is presented. The components shown are the ones that are essential for the concept created. In calculation work and FE-analysis the hook and striker are the only components analyzed, other components like the inner panel and latch are set as boundary conditions. This is presented and discussed further in Chapter 4.4.
Figure 9: One of four fixations in concept
As the striker and hook are taken from the original model, no modification were made regarding the material or dimensions which is presented in Chapter 4.4. The possibility exist to change materials and dimensions if stresses in FE-analysis are too high. Striker and hook can be seen in Figure 10.
Figure 10: Striker and hook
12 The concept also contains two struts as in the original model. The only difference is the length and placing. The struts hold the hood completely during service and are placed according to Figure 11.
Figure 11: Assembly of new concept
4.3 Load cases and hand calculations
The four load cases are taken from the requirement specification, see strength in Appendix 3. Here the forces for each load case is decided using hand calculation. This is presented below.
1. Hold for a person of 100 kilogram sitting on front of hood – What needed to be calculated was the forces on each front hook, these forces would be used in the FE – analysis of the hooks.
The load was assumed to be widespread on area A in Figure 12 which is the contact surface between the person and the vehicle. As the only components examined in the load case were the front hooks, the total force is assumed to be absorbed equally by them. This load case was calculated as a simplified static problem to simulate that the person of 100 kilograms is sitting still on the hood. As a help in calculations, chapter 4.2 of the book Mekanik by Grahn & Jansson (2002) was used. Assumptions made for this load case cause the force to be evenly distributed over the front hooks and can be calculated as 851 Newton for each hook in negative Z-direction (Figure 12). See entire calculation in Appendix 7.
Figure 12: Load case one – Sitting on front of hood (www.a2mac1.com , 2020) and coordinate system for all load cases
2. Hold for a collision at 90 km/h – The most important and hardest test of all hood fixations,
“forces or displacements to a structure or a machine part often produces stress levels and
deformations very much larger than would be generated by the same forces and
displacements applied gradually. Such rapidly applied loads or displacements are usually called
shock or impact loads”. (Collins, Busby & Staab 2010, p. 26). Therefore, this load case is
simulated as the reaction forces acting on hood fixations from impact of a collision. The
scenario is that a Lynk and Co 01 going 90 km/h hits a barrier and comes to a quick complete
stop in 0.2 seconds (Apell 2020), it is crucial that the hood stays attached on the car to ensure
13 pedestrian safety. This load case is simplified and simulated as an optimal collision whereas no deformation is caused on any other components than to the hook and striker. In a realistic scenario, deformations would occur on the hood and the force would be distributed over several components attached to it. However, in this project the objective was to look directly at the hood fixations, therefore this simplified solution on these components were made. The result of this load case will, because of these assumptions only reflect a very small part of the car’s various parts but is still considered relevant to the study. With a safety factor (𝑠 = 1.5 ) the estimated reaction force on each fixation was calculated to be 750 Newton in x-direction (Figure 12). See entire calculation in Appendix 8.
3. Hold for acceleration from rest to 100 km/h - This load case consists of a shear load on the hood fixations that will be analyzed using FEM. Hand calculations needed to be done to find the load on each fixation. The equation used for this load case is Newton’s second law, the law of acceleration 𝐹 = 𝑚 × 𝑎, where 𝐹 is the sum of all forces that affects the hood, 𝑚 is the total mass of the hood and 𝑎 is the mean acceleration during the distance (Grahn & Jansson 2002). To calculate the forces, the time needed to accelerate the car from 0 km/h to 100 km/h had to be decided. According to Hedberg (2018) this is 7.3 seconds. This results in the total force absorbed by a single fixation being about 22 Newton in X-direction (Figure 12). See entire calculation in Appendix 9.
4. Hold for retardation from 100 km/h to rest - This load case consists of a shear load on the hood fixations that will be analyzed using FEM. Hand calculations needed to be done to find the load on each fixation. The equation used for this load case is Newton’s second law, the law of acceleration 𝐹 = 𝑚 × 𝑎, where 𝐹 is the sum of all forces that affects the hood, 𝑚 is the total mass of the hood and 𝑎 is the mean acceleration during the distance (Grahn & Jansson 2002).
To calculate the forces, the retardation distance had to be decided. According to Volvo Cars (2020) this is 36 meters. This results in the total force absorbed by a single fixation being about 62 Newton in negative X-direction (Figure 12). See entire calculation in Appendix 10.
As a conclusion, the most critical load cases are load case one and two as these have the greatest reaction forces in given directions. The maximum acceleration in load case three and four can be up to twice the mean acceleration (Nyqvist 2020), which would double the force. However, the reaction forces of the load cases do not exceed the critical load cases even at double power. Load case one and two are therefore the only load cases that will be analyzed using FEM. Load case three and four are assumed to hold for imposed loads if the critical does. Consequences of assumptions for the load cases are further discussed in Chapter 6.
4.4 Finite Element Analysis
Finite element method was applied to simulate and analyze the results of critical load cases. In order to get acceptable approximated results, boundary conditions, load sets and convergence analysis of mesh were made.
Boundary conditions for the concept is set differently between the load cases due to reaction forces.
Viewed generally the hood striker is set as fixed to the inner panel and the hook is set fixed to the latch
as seen in Figure 9 and Appendix 11. The material used for the striker and hook in the analysis is
structural steel, this is the same material as in the original model. The properties of the material is
presented in table 6.
14 Table 6 - Properties of structural steel
Young’s Modulus 200 GPa Poisson’s ratio 0.266
Density 7860 kg/m³
Yield Strength 250 MPa
The dimensions of the striker and hook is of great importance in the FE-analysis. Figure 13 displays an overview of the size of these components which are taken from the original model. In addition to these dimensions, the thickness of the steel in the striker is 2mm and the diamter of the hook is 7mm apart from the wider section at the top measuring 8mm in diameter.
Figure 13: Dimensions of hook and striker
Parts are simulated separately as solids and the element type is set to tetrahedral quadratic to get the
most accurate result according to Wang, Nelson & Rauch (2004). To motivate reasonable final results
a convergence analysis were conducted to decide which mesh size to use, mesh and convergence
analysis can be seen in Appendix 12. The analysis resulted in a global mesh size of 1.8 mm for both
striker and hook. The mesh is visualized in Figure 14.
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Figure 14: Meshed hook
4.4.1 Load case one
In load case one, the striker and hook are assumed to be subject to reaction forces from a person sitting on the front of the hood. This load case is not assumed to be critical for the striker as other components stabilize this in the given power direction. Therefore, only the hook is analyzed. The boundary condition (B) was set as fixed at the surface connected to the latch and the load distribution (A) as a pressure on the upper surface connected to the striker. This is presented in Figure 15.
Figure 15: Boundary conditions and load distribution for hook in load case one
The aim of the FE-analysis is to investigate the stresses that arise in the material. These are shown in
Figure 16. As seen in Figure 16 the maximum stress in the hook for load case one was 169.8 MPa at
position indicated by arrow.
16
Figure 16: Stress concentration in hook for load case one (MPa)
4.4.2 Load case two
In load case two, the striker and hook are assumed to be subject to critical reaction forces from a collision, therefore both parts are analyzed. Boundary conditions (B) and load distribution (A & C) for the striker are shown in Figure 17 and Figure 18.
Figure 17: Striker from side view Figure 18: Striker from top view
Top surface (B) of the striker is set as encastre in all directions. Force (A) (see Appendix 8) is set as a
surface traction on the entire surface that is exposed to the force. In Figure 18 the reaction force (C)
is visible and set as a pressure over the surface where the striker and hook make contact. For more
information about the reaction forces in load case two, see Appendix 11.
17 For the hook, the boundary condition (D) was set as fixed at the surface connected to the latch and the load distribution (C) as a pressure on the surface connected to the striker for this load case. This is presented in Figure 19.
Figure 19: Boundary conditions and load distribution for hook in load case two
Maximum stress in striker and hook for load case two are visualized in Figure 20 and Figure 21. For the striker, the stress reach up to 132 MPa at position indicated by arrow (at upper edge) in Figure 20.
Figure 20: Stress concentration in striker for load case two (MPa)
18 As seen in Figure 21 the maximum stress in the hook for load case two was 309 MPa at position indicated by arrows. Since the stress must not exceed 250 MPa, this was an excessive value. To get a higher accuracy a greater number of elements or higher order elements could be used (Turcic & Midha 1984). This was not done due to the analysis being simplified because of technical limitations.
However, when the stress arises in direct connection with a fixed boundary condition, this can be seen as a singularity as the face between the excessive values in reality would not be infinitely fixed and would be able to move more (Liu & Quek 2003). Engineering judgement was used to assume that the hook would hold for load case two by analyzing elements close to the singularities which remain below the limit value of 250 MPa. This is discussed further in Chapter 6.
Figure 21: Stress concentration in hook for load case two (MPa)
4.4.3 Summary of load cases
After evaluation, FE-analysis show that load case one and two would hold for the predicted loads in the critical load cases. Further, load cases three and four are assumed to endure the applied stresses as discussed in Chapter 4.3.
4.5 Locking mechanism
To fulfill the requirement of limited access for consumers, several concepts were generated for a new
locking mechanism. These concepts were handed over to the company for further development. No
calculations or simulations were made on the concepts of locking mechanisms since it is not relevant
to the fixation of the hood. Sketches of locking mechanisms can be seen in Appendix 13.
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5 Result
In this chapter, the result of the project is presented. Among other things, the new concept is analyzed against the requirements specification that has been developed. In addition, it is investigated whether the project has fulfilled set goals and purpose.
5.1 Summary of the work in its entirety
What was accomplished during the course of the project is presented here in point form.
Project specification including problem statement.
Groundwork in the form of a literature study, market survey, field study and benchmarking.
Concept generation with regard to data collected during the groundwork and developed requirement specification.
Comparison of several developed concepts and further investigation of one of these.
Stress analysis of chosen concept using hand calculation and the finite element method.
Analyzed concept with regard to requirement specification.
The goal of the project was to come up with a proposal for an alternative hood fixation to electrically run vehicles in aspects of cost, weight and size. The final result was a concept called “fixed with hooks”
which consists of four hooks with reinforcements that fixates the hood to the vehicle. During service the hooks are completely loosened and the hood is held up by struts. The concept is presented in Figure 22 and Chapter 4.2.
Figure 22: Visualization of concept “fixed with hooks”
5.2 Concept results with regard to requirement specification
Here, the developed concept “fixed with hooks” is reviewed and compared to the requirement specification with regards to fulfillment and further evaluation. All requirements discussed in this chapter can be seen in Appendix 3.
Functionality
In terms of functionality, the demand of no maintenance during lifetime require further testing but
was assumed to have favorable odds as the hood would not open as often as the existing model as
consumers would not be able to access the engine compartment .The requirement of easy access for
service personnel also need further testing. Regarding access to engine space, concepts has been
created and handed over to CEVT for further development. Requirement 1.3 was also fulfilled as “fixed
with hooks” were created to work even when the vehicle lacks electricity as the solution was fully
mechanical.
20 Strength
Presented in Chapter 4, calculations were performed on all load cases presented in the requirement specification. The two most critical load cases was later analyzed using FEM. The result from the analysis show that the demands were met and since these passed, it can be assumed that requirement 2.3 and 2.4 would hold for predicted forces as mentioned in Chapter 4.3.
Cost
In terms of cost, no demands could be fully compared or evaluated due to lack of information from the companies providing the components used in the new concept. However, the total cost can be assumed to be lower than for existing solution as hooks are cheaper than hinges (Apell 2020).
Manufacturing
All requirements that have been set are met with exception of requirement 4.5, which state maximum weight for hood latch system to be less than 850 grams. However, “fixed with hooks” has a reduced total weight compared to the existing product seen in Appendix 14. “Fixed with hooks” was assumed to have a high manufacturing availability since all parts, excluding the struts, exist in the current product.
Environment
No testing were done on requirements 5.1 - 5.4 since the parts used in “fixed with hooks” was the same as in existing product. As no new components were added and less total material, including cosmetic covers in the engine compartment was used, “fixed with hooks” was assumed to fulfill requirements 5.1 - 5.4.
5.3 Project result with regard to goals and purpose
The objectives of this thesis project was to explore and propose future ways to fixate hoods in electric cars. In order to evaluate the project, a list of milestones were created (see Chapter 1.4) to be able to effectively determine if the goals of the work has been met. Further the evaluation is presented.
The first goal to fulfill in the project was to carry out a thorough groundwork, including field study and benchmarking. The main purpose of this was to be able to implement a concept generation with collected material. This goal was considered achieved as several new concepts were generated based on the data collected during the groundwork (see Chapter 3.2). The result of the groundwork can be seen in Chapter 2. The second goal was to generate agile development solutions this was also seen as achieved as a result of the generated concepts.
The third milestone to be reached was to generate a concept that fulfills the requirement specification.
Although some of the functionality and cost requirements need further investigation the goal was seen as set as the other demands were fulfilled (see Chapter 5.1).
To make a case study and analyze the chosen concept was milestone number four in the project. This was done using hand calculation and FEM as presented in Chapter 4. As the analysis achieved a result, this was seen as completed.
The fifth and final milestone that were to be reached was to present the result. This was made through oral presentation at the University of Skövde and through this report.
To briefly summarize the above, all set milestones and goals for the work were achieved.
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6 Discussion
This project has explored several, and displayed one, alternative way to fixate a hood that can be applied to battery electric vehicles in aspect of cost, weight and size. Because the work is primarily aimed at developing a concept for further development, the strength analysis is simplified in both calculations and load cases. Consequences of assumptions and simplifications will be discussed further in this chapter. If the result is the most optimized solution cannot be decided due to the delimited factors, such as the choice of material and dimensions, that this study does not take into consideration.
However, the goal of the work is considered to have been achieved since several concepts have been analyzed against the requirement specification developed and one concept has been further analyzed to create a good basis for future work.
For the chosen concept, the cost aspect was the most difficult to analyze, this was due to the circumstances of coronavirus spring 2020 and the fact that companies of interest that held information of importance were closed temporary during the course of this study. The consequences of that led to an approximated result of total cost based on the information given by CEVT, rather than price calculations from component providing companies.
Weight aspect of chosen concept could be calculated and is presented in Appendix 14. The weight of the concept itself turns out to be lower than that of the existing solution which was a result of the exchange of the heavy hinges to lighter hooks. In order to evaluate the total weight reduction of the vehicle, other factors such as locking mechanism and cosmetic covers in the engine compartment must be taken into consideration. This is however left for CEVT to evaluate.
In aspect of size, less raw material is used in the new concept and components are smaller.
The three phases of the project presented in Chapter 1.5 were carried out according to the schedule illustrated in Appendix 1. To split the work in different phases helped to define and streamline as more specific GANTT charts could be created that were easy to follow.
In the initial phase, an objective specification of the work was created in its entirety with respect to requirements from the University and CEVT. By doing this, the risk of deviation in the project is minimized as delimitations and objectives are clarified at an early stage.
In the concept generation phase, several methods like market research, literature study and GEMBA, among others, were used in order to collect data regarding the problem as a whole and to be able to further develop concepts. A mix of analytical, quantitative and objective methods were completed to generate concepts, by using multiple methods in each phase of the project the result receives higher credibility. However, the result can at the same time be deceptive unless the methods are properly implemented. To select a concept of interest for CEVT, Pugh’s Matrix Analysis method was used together with CEVT staff to objectively and systematic choose a concept for further development.
Since the main goal of the work was to develop a new thinking concept, strength analyzes in the final phase were conducted primarily to get an idea of whether the concept was at all worth working with.
Therefore, many assumptions and delimitations were made to adapt the work to the project specification and timeframe. One of the assumptions was how the load in each load case was evenly distributed among the fixations. It is very unlikely that the load is distributed like this in a real scenario.
However, the safety factor in the calculations is expected eliminate the risk of critical outcomes.
Further, the assumptions of mean acceleration were implemented using the law of acceleration to
simplify the calculations. The consequence of this assumption is that the calculations becomes
moderate and thus insufficient if a real scenario, where the acceleration can be up to twice the mean
acceleration, is to be simulated. Another assumption here is that the hook and striker are firmly
22 clamped and therefore set as locked at all stages of the FE-analysis. This means that the components are infinitely fixed on the surfaces that are considered locked in the program. One of the consequences of this is that singularities arise in direct connection with the attachments as seen in the hook in load case two. By analyzing elements close to the singularity credible data can still be read. Load case calculations are only done with existing dimensions and materials to create an idea of how the components behave under stress. In order to optimize the components in terms of strength, weight, cost and size, more analyzes need to be performed where other materials and dimensions are investigated.
FE-analysis show that load case one and two holds for the predicted loads. However, it is important to state that FE-analysis is an approximated solution for a simplified problem and therefore further testing is required where consideration is taken to other load cases and adjacent components.
Although calculations and analyzes are simplified and conservative, they are considered necessary for the study to get an idea of the strength of the concept.
Since the concept developed consist of existing components, the production potential is considered
good. Moreover, the change in the manufacturing process from the existing model becomes simple
for the same reason. In terms of sustainable development, the climate impact in the manufacturing is
widely unchanged because of this. For the project as a whole, on the other hand, the impact is good in
terms of this as it is carried out with great regard to social and environmental aspects.
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7 Conclusion
The goal of this project was to find a new solution, in aspects of cost, weight and size, for fixating the hood on Lynk & Co’s Model 01 on behalf of CEVT to create a more sustainable vehicle. This was done using proven and recognized product development tools throughout the project.
The project resulted, in a new concept called “fixed with hooks” which was evaluated against other developed concepts and the original model before being evaluated in terms of strength using hand calculations and the finite element method. After the strength calculations was performed, the concept was analyzed against the requirements specification developed in association with the company.
The result was seen as successful as all milestones, goals and the majority of specified requirements were met. Some requirements, such as functional, environmental and cost demands, need further investigation to be considered fulfilled.
The demarcations in the project enable several opportunities for continued work with related parts to the hood such as, the placing of washer fluid filling, removing embellished plastic covers in the engine compartment and overlook the materials and dimensions on existing components. It is not realistic to implement the new concept without analyzing it in its entirety to a greater extent and in more critical load cases.
Hopefully larger companies like CEVT will continue to invest in developing more sustainable solutions
with regard to climate, society and the economy as in this project.
24
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Appendices
Appendix 1: Work Breakdown and time plan
GANTT chart of all phases
GANTT chart of phase two
GANTT chart of phase three
ii
Appendix 2: Pictures from market survey
1. Door closer https://www.dormakaba.com/en/products/door-hardware/dorma-ts-93-door- closer-system-1568
2. Linear window actuator https://www.linkayl.com/project/linear-window-actuators-lk-l-s/
3. Roller rail https://www.beslagsbutiken.se/catalog/product/view/id/10148/s/rullskena-fr- 785-scc-sc-rostfritt-stal-60-kg/category/94/
4. Telescopic boom lift https://www.genielift.com/en/aerial-lift/telescopic-boom-lifts 5. Scissor lift https://www.genielift.com/en/aerial-lift/slab-scissor-lifts
6. Door hinge https://www.bygghemma.se/hus-och-bygg/dorrar-och- portar/ytterdorrar/tillval/gangjarn/dolda-gangjarn/p-202517-202518
7. Shear lock (electromagnet) https://www.maglocks.com/locking-devices-1/shear-locks.html
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Appendix 3: Requirement specification
Functionality
1.1 No access to engine space for the consumer
1.2 Easy access to engine compartment during service and production 1.3 Shall work under powerless condition
1.4 No maintenance during lifetime
Strength
2.1 Hold for a person of 100 kg sitting on front of hood 2.2 Hold for collision at 90 km/h
2.3 Hold for accelerating from rest to 100 km/h 2.4 Hold for retardation from 100 km/h to rest
Cost
3.1 Manufacturing cost per unit lower than existing solution 3.2 Raw material
3.3 Lower total cost than for existing solution
Manufacturing
4.1 Designed according to the five guidelines (Boothroyd, G. 1988) 4.2 Adapted for existing machinery
4.3 Compatible with existing model
4.4 Collision-free design minimum distance of 6 mm for moving parts and 3 mm for non moving parts 4.5 Maximum weight for hood latch system < 850 g
Environment
5.1 Highest / lowest temperature (operational) from -40℃ to +85℃
5.2 Recyclable
5.3 Highest / lowest humidity (operational) from 10% to 95%
5.4 Corrosion free
iv
Appendix 4: Mind map
v
Appendix 5: Sketches of concepts
Concept 1 - Lynk & Co logo on hood pops up when blipped and then works as a latch to open the hood.
Concept 2 - Different solutions to cover the latch in the coupe.
Concept 3 - Separate tool is used to mechanically open the hood in the front of the car.
Concept 4 - Examining the possibilities of bolting/screws solutions that only can be reached from a position beneath the vehicle.
Concept 5 - Fixed with hooks that replaces currently used hinges
vi
“Fixed with hooks”, which can be seen in concept 5, was inspired by the existing solution with hooks as an attachment mechanism. When the hood is opened, the hooks are loosened completely as seen in position 2 and a strut lifts the device. In
position 3, or the service position, the hood is held up parallel to the engine compartment.
