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Automotive Product Finder Magazine | Car body: Designing for perfection
Car body: Designing for perfection
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With safety and emission standards getting tighter, automakers are looking to develop car body which can fulfill these regulatory obligations. Changes in technology and homologation requirements pose a challenge to the auto body design when it comes to newer technologies such as electric vehicles. Rakesh Rao explores how automakers are employing different strategies to design a perfect car body.
Ever since the car was invented for private transport, body design has undergone various changes, in line with the needs of emerging trends, by embracing new technologies. “For the past 100 years, vehicle body design has evolved from a separate body and chassis design to integrated design (monocoque) to satisfy various market demands like need for mass production, light weight, consumer preferences, regulatory pressures and cost,” observes Ashok Khondge, Principal Engineer, ANSYS Customer Excellence, ANSYS Inc.
Body designing of a vehicle is not only an essential but also a critical stage of vehicle development. Design is responsible for the reduction of a vehicle’s body weight to improve capacity and comfort, aerodynamics (that determines the fuel consumption) and customer appeal. It is also very responsible for determining the safety of a vehicle. “At a time when the industry is under immense pressure to reduce the production cost and stay ahead of the competition, the designing stage has to become even more complex for automotive manufacturers. The engineering excellence of high intensity is required to manage the entire designing process so that the outcome proves beneficial for both the manufacturer as well as consumers and meet the safety standards, and reduce CO2 emission,” informs Shree Harsha, Director, Marketing, India, DASSAULT SYSTEMES.
Releasing a new product is a tedious process which needs acute attention to detail. The first step of the new product development process is idea generation and screening. Swapnil Sansare, CEO and Founder, Divide By Zero, elaborates, “During this process, one must flesh out the concept as well as its proposed features and benefits. This makes conceptualisation and designing the most critical step for new product development. A product might seem like a smart idea at its conception, but once the actual designing process starts and as we start building prototype models of it, we are bound to find minor or major vulnerabilities.”
Automotive design can be split into three main segments - exterior design, interior design and colour & graphic design. It is not only about designing of parts but it is the combination of form, fit and function, considering the overall vehicle package. “Usually, platform design is built around the USP of the product. For example, Tesla car is built around the battery (the chassis is designed around a large protected battery box) and SUV/ MUV platforms are built around strong shock absorption systems and higher ground clearance,” states Sansare.
The government of India is tightening the emissions and CAFE (Corporate Average Fuel Economy) norms with diligent implementation of BS VI regulations. To address occupant safety, the government has initiated Bharat New Vehicle Safety Assessment Programme (BNVSAP), proposing a star rating safety performance system and new car assessment programme (NCAP). These regulatory obligations are influencing the designing and development process of the car body.
When a passenger car is designed, the configuration, choice, and type of components depend on various factors. The use of the car is one factor. Some cars are required only for local driving; these cars may be capable of achieving good fuel economy on short trips, but they may be less comfortable to drive at high speeds. “A sports car, built for speed, will have enhanced steering and handling abilities, but requires a stronger engine, more fuel, and a more sophisticated suspension system. Yet, a car must also be flexible enough to perform in every situation and use. Other important factors include pollution-control components that have been used, safety features that go into the car, and materials used to construct the car body. The design of the body must incorporate standards of safety, size and weight,” says the Automotive Team of Tata Elxsi, which offers solutions in various areas of body design and development.
Aesthetics that complement aerodynamics is also an important factor to reduce drag and wind noise, minimising noise emission, and preventing undesired lift forces and other causes of aerodynamic instability at high speeds.
Fit and finish is becoming an increasingly important indicator – in the eyes of the end-user of overall vehicle quality. The important item in current automotive manufacturing is the body-in-white (BIW), which has two important characteristics that reflect its crucial importance. First, it is the most expensive part in the whole automotive plant, and second, its changeover in response to market trends occurs more often. As in the BIW, a side closures, and door is manufactured through process, such as blanking, rolling, stamping and assembly.
According to Automotive Team of Tata Elxsi, “Cost is an important factor in the design of a car. Many features useful for improving the various systems and characteristics of an automobile may make it too costly to produce and too expensive for many people to buy. The design of a car, therefore, is a balance of many factors. Each must be taken into consideration, and compromises among features satisfy as many factors as possible. Yet, for all the variety among automobiles, the basic systems remain essentially the same.”
Regulatory constraints on energy consumption have influenced vehicle design & development. With recent rises in oil prices due to increasing demand and unrest in the Middle East, and the increased prominence of global warming and other environmental concerns advances to improve vehicle efficiency are becoming increasingly important to competitiveness in the global automobile market.
“One key technical design strategy for improving vehicle efficiency is the reduction of vehicle mass, or light-weighting. Vehicle light-weighting not only enhances fuel efficiency, but also lowers vehicle emissions and improves driving performance,” informs the Automotive Team of Tata Elxsi.
Light-weight subsystems such as hoods, roof and decklids are already employed throughout the industry to achieve small weight savings. However, significant improvements in vehicle efficiency will require larger changes in mass. A primary target for this mass reduction is the body-in-white, whose standard steel version comprises 20-25 per cent of total vehicle curb weight. The two main strategic approaches for reducing weight in the BIW are vehicle architectural changes and material substitution.
“Among vehicle architecture alternatives, the unibody/monocoque body (chassis is integral part of BIW) is most mass efficient. The primary mechanism available for further reducing the weight of the body-in-white is the use of alternative materials. This study examines the potential cost-competitiveness of alternative body materials - such as magnesium, aluminium/Al composites, titanium, high strength steel, carbon fibre reinforcement polymer (CFRP) and glass fibre reinforcement polymer (GFRP) composites - against incumbent, mild steel,” observes Tata Elxsi officials.
Change in material leads to change in engineering and manufacturing process in terms of form fit and function, joining of similar or dissimilar material, manufacturing and assembly technique, difference in optimising weight to strength ratio, thermal behaviour of material, etc.
Today every OEM is looking for economy of scale, leveraging its own global R&D organisation or partner alliances. In order to define the global architecture of a vehicle, OEMs want to take benefit from the modularisation strategy in their vehicle development processes. “Modularisation is a way of breaking down a problem or a product into smaller and separate, interchangeable components, called ‘modules’. Modules also represent a separation of concerns and simplify product convergence and maintainability by defining clear functional boundaries and interfaces between components. Interfaces not only cover physical boundaries but also any functional and logical connection needed to ensure desired system behavior. Interface ensures interchangeability and enables minimum propagation of change impact between vehicle’s components,” comments Shree Harsha of
As customer and industry requirements become progressively more sophisticated, and demand cycles shorter, design and engineering efficiency and accuracy are critical success factors. Real-time collaboration on a virtual, integrated 3D platform can expedite convergence, and ensure ‘right the first time’ results.
Shree Harsha elaborates, “Global modular architecture solution delivers a unified collaborative environment as single source of truth for all the company and its extended partners in all domains: starting from product planning, early vehicle architecture and performance tradeoff, standardisation & sourcing, and up to test and validation.
For advanced management of multi-discipline design & validation, from BIW to systems engineering, to additive manufacturing/composites, global industry leaders have relied upon Dassault Systemes’ 3DEXPERIENCE cloud-based applications to capture and assess social media intelligence, analyse market demand, then develop and deliver customer-preferred innovations to market, faster and more efficiently than their global competitors.”
EV to trigger changes
The Government of India has introduced several incentives to encourage consumers to use electric vehicles in this year’s Budget. In addition, GST on EV has been reduced to 5 per cent from 12 per cent to promote EV usage. “To embrace the electro-mobility revolution and introduce this new generation of cars onto the road requires new vehicle innovators and OEM leaders alike to rethink the way we experience their products, and the way they engineer them,” observes Shree Harsha.
Electric cars have similar vehicle package layout as compared to internal combustion engine (ICE). Battery packs in EV are packaged under vehicle floor. It maximises the available cabin space to be used either by the vehicle occupants themselves or for storing their luggage.
Currently cooling fluid is used to keep the battery pack cool. On the other hand, the side members occupy some volume that is inaccessible to any function and can be considered loosen space. The side members are metal sheets which can be sealed and act like cooling ducts. The side members, which go directly to the floor structure, carry the accelerated air through the structure and then it is spread through cooling plates to the battery pack.
According to Automotive Team at Tata Elxsi, “Safety and reliability are the two key challenges for large-scale electrification. Current Li-ion battery packs are prone to failure due to reasons such as continuous transmission of mechanical vibrations, exposure to high impact forces and, thermal runaway. Robust mechanical design and battery packaging can provide greater degree of protection against all of these.”
Design elements like thermal barrier and gas exhaust mechanism that can be integrated into battery packaging to mitigate the high safety risks associated with failure of an EV battery pack. Several mechanical design solutions are developed with an aim to increase crashworthiness and vibration isolation in EV battery pack.
The sill structure of BIW is reinforced to accommodate the batteries safely. However, this creates large cross sections to withstand the stiffness of the entire monocoque in the floor area. A large sill creates some uncomfortable openings for the car’s doors, because it is high and wide, then the person has to largely extend his legs in order to get inside the cabin.
To address this situation two solutions were created. The doors are going to open like gull wings, with a hinge in the roof, allowing more space when open. The reinforced floor and larger sill cross sections creates a “U” shape in the cross section of the car.
The U shape has higher sills and lower floor. According to Tata Elxsi’s Automotive Team, “To ensure the easiness of access to the driver and the passenger, once the gull-wing doors are open the seat will turn 90 degrees facing outwards for the person to sit and get turned back to the driving position. The seat also elevates in order to minimise the gap of the sill and the floor, so the person has to incline less in order to get inside the car.”
The market share of full electric vehicle is very low at present – approximately 1 per cent of the total automotive sector. As fully electric systems take off in a big way, light weighting will also become more of a necessity in modern automobiles. To pack a car full of heavy batteries and get the best range in the market, the car has to be as light as possible. “Automakers are using multiple materials combination to build car body. For example, BIW are made from aluminium to decrease weight, the undercarriage is manufactured from titanium and high-strength steel is used in critical loading points to increase safety. This plays into the need to lightweight electric vehicles as well as the fact that one material isn’t the cure all to solving light weighting problems,” states the Automotive team at Tata Elxsi.
Some of the factors influencing the auto body designing processes are:.
Industry trends, competitive markets
New product development timelines
Government regulations & norms
Cost of development & manufacturing
International standards & pollution norms
Interchangeability between products
Patents and IPs of technology
Bharat New Vehicle Safety Assessment Programme Corporate Average Fuel Economy
New Car Assessment Programme
Global Modular Architecture Solution
Current Liion Battery Packs
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