Bertrandt implements uncompromising vehicle concept
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Initially it was only a vision, then an idea and just six months later, a real car – the smart crossblade. A limited number of series vehicles will be made on the basis of the smart design study that was presented at the Geneva Motor Show in 2001, and received with considerable praise and enthusiasm. Bertrandt’s first offer contained a feasibility study to be able to de- fine the further process. It convinced the decision- makers at smart. Bertrandt was taken on board as the general contractor for this project.
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Feasibility study
To achieve maximum planning guarantees for the subsequent processes – and therefore come one step closer to implementation, Bertrandt first of all prepared a feasibility study. It was possible to clarify a large number of questions at an early stage. Was this project feasible in the short term? Should the car be rigid, safe, closed? Finally, should the vehicle manage without a roof, doors and windscreen? Which parts, which manufacturing process should be used to build it? And which suppliers should be involved in a?
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| Bertrandt answered these questions at the beginning of this demanding project: 2D and 3D concepts were prepared to specify the parts needed, the manufacturing process and also the suppliers’ panel. The schedule, the departments involved and the partners at the companies taking part were also determined at this early stage in the project. This process enabled us to achieve a sporting timeframe – a whole six months lay between the project decision and the SOP – and also to guarantee economic feasibility. Now there was nothing more to prevent a successful completion of the project. |
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Clay model and outside skin
The smart designers constructed a clay model in parallel with the feasibility study. During this work, rough surfaces were constructed at Bertrandt from these first data. These were then used as the basis for the first technical models of the outside skin. This time, i.e. immediately after the feasibility study and at the beginning of the development work, the smart designers moved into Bertrandt’s research centre in Enhningen to complete the clay model.
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Having the engineers and designers on the same site simplified communications, which were good in any case. Suggested improvements, which the engineers made on the basis of the sections through the C class surfaces, were immediately incorporated into the clay model. This resulted in an outside skin which took into account all production aspects, such as the lines of the joins and the position of component splits. The procedure demanded few compromises in terms of manufacturability in later development phases. Because of the many years of experience of Straker, the surfaces obtained from the final data of the completed clay model were first class. The component data, with all fastening points, wall thicknesses and flanges, were developed in a further stage.
Digital mock-up, rigidity and calculation
Virtual test runs, like collision tests and the simulation of production tolerances, for example, were performed on a digital mock-up (DMU) of the crossblade in parallel with the development work in order to be able to incorporate improvements at an early stage. The digital car has served as the central interface for all the departments involved in the development, on the basis of which current development stages, component weights and parts lists were input. The bending and torsion rigidity of the crossblade was to be the same level as the basic vehicle, the smart cabrio. The existing structure of the smart cabrio has been adopted, but because of the extraordinary vehicle concept, which was to give a feeling of unbounded freedom, important components of the structure, like doors and windscreen frame, for example, were not included.
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Bertrandt then calculated and compared the torsion and bending strength of several alternatives in order to be able to choose the best solution. The crash behaviour was also established mathematically for the crossblade in close co-operation with the customer. As a result, reinforcements along the door openings and also highly rigid struts guarantee the strength and rigidity of the body structure and therefore also the safety of the occupants.
Approval
With regard to the regulations that had to be satisfied for approval, some components were new territory for the companies involved. For example, what were TÜV‘s requirements with regard to a door that is not there? Together with smart, colleagues at the Federal Motor Vehicle Office and the TÜV, the people at Bertrandt clarified which regulations had to be met and were also practical. The windshield and the door members required some detective work to identify the relevant regulations, orders and approval conditions. Lively discussions also revolved around approval of the outside mirror, a component requiring type approval, which was solved in joint detail work. Today, Bertrandt manufactures the mirror system.
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Interior
The freedom of motorcycling is reflected in the open structure of the smart crossblade. However, this means at the same time that the vehicle has to be absolutely waterproof despite the lack of a roof. This presented all project members with a major challenge.
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Waterproof upholstery material was specially made for the crossblade and the seats have their own drain holes and intelligent measures had to ensure that all the electrics and electronics could function reliably in all kinds of wind and weather. The engineering solution speaks for itself. In the test phase, the crossblade shook off the monsoon like deluges to which it was exposed during several test runs.
Tests and trials
A type test programme with the crossblade was carried out and documented in detail during the development work by Bertrandt. Testing all the newly developed components and systems was particularly important. At the end of the day, everything had to work reliably throughout the life of the vehicle. Based on the customer’s specifications, and also the legally prescribed requirements, the crossblade underwent all the functional and endurance tests that occur during the development of a complete vehicle. These include component and function tests, endurance tests, operating strength and environmental simulation and climate change tests, head impact and airbag tests and also stationary and skid tests. A special test rig was developed and built for the door bar endurance test. The new parts developed for the crossblade had to prove their reliability in the various environmental simulation tests.
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Door bars had to open and close at all times without any problem, plastic parts must not deform, seat coverings must not fade even in strong sunlight. In order to determine the driving resistance parameters, the important exhaust and consumption values for licensing, Bertrandt carried out rolling tests. Smart and Bertrandt carried out crash tests together with the TÜV in order to check the results simulated previously and meet the approval requirements. Finally, the crossblade had to prove in a summer trial in Laredo, USA that it still worked perfectly after thousands of kilometres and had not damaged its looks. Two Bertrandt employees also attended the trial to help smart with the final modifications to the vehicle.
Prototype build and vehicle build
A total of twelve vehicles, known as trial vehicles, were made at Bertrandt before the actual start of the series. Through specific front loading, the Bertrandt team pulled out all the stops to avoid additional correction loops during subsequent toolmaking. The increased use of laser sintered parts (SLS), like 1:1 viewing models for smaller components and 1:4 models for larger components, established the form, function and therefore also the costs at an early stage. This process meant that iteration loops were possible within a few days. Consequently, the approval-related test for checking the outside mirror developed and made by Bertrandt was carried out on the basis of an SLS outside mirror base attached to the crossblade. Toolmaking for the injection moulding process only started at that point. Larger parts, like the floor pan, were sintered in SLS as a 1:4 model, milled 1:1 after the test and a pouring resin tool was made on the basis of this milled model.
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Bertrandt chose the methods suitable for the manufacture of the components from among various rapid prototyping and rapid tooling methods. For example, the front mud flap was made as an RRIM plastic part in an aluminium tool. This method was the best for the very high surface quality demanded. Vehicle Build, which assembled the trial vehicles, was responsible for putting together a car from all the parts. In view of the approaching start of the show in Geneva, and also the looming SOP date, the schedule for this work was extremely tight.
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In Vehicle Build, colleagues in the three areas, Body in White / Assembly, Raw Materials and Products and also Automation stepped on the gas once more. They made auxiliary fixtures for assembly and also for an assembly test on a first vehicle. Since these were prototype components, the last adjustments were made at this point. Joining techniques such as bonding, riveting and bolting allowed easy removal and improvement of the parts during the modi- fication work. At the same time, colleagues built the show vehicle, which incorporated the changes from the assembly test of the first trial vehicle. Because of the motivation and performance of all the employees involved, the first milestone was achieved with an excellent result – the perfect vehicle for the Geneva Motor Show.
Production planning, logistics and production
Before final manufacture of the crossblade started, employees of Bertrandt and Binz prepared an assembly plan. They established which arrangement of the individual stations was practical for an efficient production cycle. In the logistics area, Bertrandt was responsible for ensuring that the several hundred components made by different suppliers matched and were delivered on time. This process also included tool controlling, monitoring the toolmaking process, acquiring the part components required and also the co-ordination of the assembly of complete units – including guaranteeing small series production at Binz. A limited number of 2000 smart crossblades is being assembled here.
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Conclusion
The smart crossblade was an exciting and extraordinary project that inspired all those involved. Many aspects outside the normal course of development gave Bertrandt insights into new areas, such as obtaining approval from the Federal Vehicle Office. Bertrandt acted as a general contractor for the first time and took responsibility for the development and production of a vehicle. Bertrandt would like to thank the employees of smart and all the partners involved for their excellent co-operation, and is looking forward to further joint projects.
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