|
Digital prototype -- calculating the way ahead
- Complete digital depiction of new car models
- Early project verification thanks to simulation of all functions
- Comfort and handling can be experienced subjectively on test rigs
- C-Class marks premiere of new development process
Stuttgart, Jan 09, 2007
Prototypes are precious commodities in the automotive business – one-offs that are constructed by hand over a period of months but which only have a short yet action-filled life. Prototypes travel incognito, their true identity hidden by ugly matt black camouflage. It's all very hush-hush.
But prototypes are essential tools in the car developer's armoury. They are the only means of "teaching" future models to drive; and the only way of testing and further developing new technologies on board under realistic conditions at an early stage of development. Mercedes-Benz produced a total of 280 prototypes for the new C-Class. These were then sent around the world for rigorous testing, during which they clocked up millions of test kilometres.
But that is not all: in the case of the new C-Class, the word prototype has a double meaning for the first time. This is because, long before the first heavily camouflaged versions of the new saloon hit the road, a different kind of prototype had already successfully negotiated a series of tests. These virtual prototypes, many details of which depicted the later production model, allowed the car's characteristics to be experienced at an early stage of development. Mercedes experts talk about digital prototyping (DPT), by which they mean a new kind of development process. The new C-Class is the world's first production vehicle to be developed using this leading-edge method.
The digital prototypes incorporate the Sindelfingen experts' vast know-how in the field of computer simulation and calculation. Since the early eighties, when the first high-powered computers allowed more or less detailed crash simulations, rapid strides forward have been made on both the hardware and the software front. Whereas in 1989 crash calculations were still based on models which depicted the vehicle using around 26,000 elements, the new C-Class was split up into around 1.9 million elements, therefore allowing a far more precise and detailed deformation analysis. For such impact calculations, during which computers complete an almost unimaginable stream of up to 320,000 million operations, Mercedes-Benz uses one of the world's largest IT networks: over 1500 processors were involved in the development of the C-Class safety systems; and the Mercedes saloon completed around 5500 computer-aided crash tests.
This shows just what can be achieved using today's sophisticated simulation and calculation processes. They are not just used to optimise new-car safety, they now also assist the engineers with aerodynamic analyses, interior-climate simulations, durability analyses and engine development.
The digital prototype sees Mercedes-Benz bundling together all of its simulation methods for the very first time in order to produce an entirely virtual car.
Of course, the digital prototype does not replace the real prototypes and test cars which are still tested extensively in the field. However, the digital prototype can help to optimise the first ready-to-drive models. These models are therefore much closer to their subsequent production counterparts. Whereas in previous years the first prototypes were essentially based on the vast experience of the Mercedes engineers, with virtually no computer data to verify the validity of the concept as a whole, experts today work on a much more solid basis, even in the very early stages of development, thanks to the digital prototype.
Digital and real: passenger car development in two phases
The Mercedes-Benz Development System (MDS) is now therefore split into two main phases: concept development and calculation with the digital prototype in phase 1 and field testing with real prototypes in phase 2, during which simulation processes continue to be used for assistance and verification purposes.
All the data for the new model – from the dimensional concept to the shock-absorber characteristics – are incorporated into the digital prototype. These data are then conditioned. Once all the calculation models have been prepared, the status of the DPT is equivalent to that of an actual four-wheel prototype that is ready to drive. The virtual test drive can commence.
This involves tuning and defining right down to the last detail in order to verify the validity of the entire concept for the new model by way of calculation, solve trade-offs at an early stage and create the ideal conditions for the subsequent field-development and road-testing phase.
Furthermore, all model and engine variants can be tested digitally. Once the basic data for the new model have been compiled, changes or departures from the norm can be implemented by simply entering new data. This is a further advantage of the digital prototype: no workshops or production facilities are needed to build or convert test cars – it's all done by DPT experts with little more than a few clicks of a mouse.
Digital depiction: ten functions covering the key vehicle features
Of course, the digital prototype of the new C-Class was not tested as an entire vehicle using simulation techniques. This would scarcely be possible due to the vast data quantity of up to 2130 gigabytes and the colossal computing power required – nor would it be appropriate. Instead, the Mercedes engineers divided the car into the key functions which depict its fundamental characteristics.
These include crash safety, occupant protection, quiet running, vibrational comfort, body durability, ride comfort, handling characteristics, engine characteristics and several other aspects. The Sindelfingen experts use the digital prototype to depict a total of ten vehicle functions which cover the key features of the car.
In the case of the new C-Class, this enabled the calculation and realistic depiction of crash safety, body aerodynamics, engine cooling, brake cooling and energy management on board the future Mercedes model at a very early stage of development.
Sporty or comfortable: virtual road test with the digital prototype
Digital vehicle development is especially important when it comes to defining the handling characteristics. This involves a familiar trade-off between comfort and agility; however, solving this trade-off is important as this is what gives the new Mercedes model its unique character.
In this domain, the new DPT process served impressive notice of its potential. Before the first real C-Class test cars had been produced, the digital prototype had already covered around 1500 kilometres on virtual urban and country roads as well as motorways in order to define the ride comfort at an early stage. This virtual test volume is equivalent to around 2000 individual drives in reality. One of the focal points of this work involved assessing the vibration response between four and eight Hertz – a frequency range which can easily be perceived by humans. The acceleration data for these test drives were depicted realistically by computer; appropriate processing of these values made it possible to give an indication of their subjective effect.
In addition, the Mercedes experts completed more than 1500 typical driving manoeuvres in the virtual world – many of them in real-time simulations – in order to harmonise the handling characteristics. This series of tests included various standardised obstacle-avoidance tests, slaloms and braking on bends.
However, the work on the computer screen was only the first phase of comfort and handling harmonisation; the digital prototype also allowed the handling qualities of the C-Class to be experienced subjectively – on highly sophisticated test rigs controlled using detailed DPT data. The new process thus gave the Mercedes engineers a clear advantage in terms of both time and quality; the new C-Class was able to complete its first test aimed at harmonising comfort and handling several months before the field-testing phase began.
One of the test rigs that can use data to "drive" the digital prototype is the Driving Simulator at the DaimlerChrysler research facility in Berlin. Here the Mercedes engineers assessed the cornering capabilities, steering characteristics and braking performance of the C-Class and, at the end of the test series, defined the data for the shock absorber characteristics, the spring rates and the steering characteristics, for example, all of which laid solid foundations for the subsequent field-testing phase.
The comfort tests completed by the new C-Class before any ready-to-drive prototypes had even been produced are equally impressive and representative. In this case, the Mercedes experts used a new type of Ride Simulator which was programmed with the data for real test-track surfaces and the necessary C-Class chassis and function data. Thanks to the combination of sophisticated multibody simulations and state-of-the-art test rig technology, the system enabled the ride comfort to be experienced at an early stage. A driver and a front passenger sat in the test rig's two seats and proceeded to drive the new saloon. This was a purely digital but highly realistic exercise.
"TIM": a virtual driver with almost every body function
Digital prototyping also gave the engineers an insight into the virtual interior of the new C-Class, enabling them to check how the air conditioning system performed. For example, they were able to verify whether the occupants always had warm feet when driving in winter.
This climate-control simulation is one of the most complex calculation processes. Because the vehicle speed, temperature, level of sunlight and humidity change constantly when on the move, the computer program has to react just as quickly and flexibly as a car's air conditioning system if the occupants are to experience a consistently high level of comfort. After all, people only feel really comfortable if their climatic surroundings remain pleasantly constant.
TIM – the German acronym for "thermophysiological occupant model" – makes this possible. TIM is an instrument used to calculate and optimise climate comfort for future vehicles. It enabled the engineers to ascertain several features of the C Class at a very early stage of development, for instance the desired heating and air conditioning system output, the number of ventilation outlets required and the size of outlet needed to achieve typical Mercedes climate comfort.
TIM is the result of many years of work by DaimlerChrysler researchers in the field of human thermal comfort levels. A large number of male and female drivers provided the basic data for the so-called "equivalence temperature" which corresponds to the temperature "felt" by car occupants and enables the actual, perceived climate comfort to be defined for each part of the body. The "TIM" computer model simulates most of the human body in a total of 14 areas, also taking into account the blood circulation and heat generation. The result is a virtual but entirely representative car occupant who is sent to all the climatic zones of the world by computer and supplies Mercedes engineers with a mass of data. These are intended to answer only one question: does the occupant feel comfortable?
TIM also put in test drives of many hours duration under the most varied driving and weather conditions in the digital prototype of the new C-Class. In addition, TIM was linked to other computer programs which for example divided the interior into around 7.8 million spatial units and measured the air flow, temperature and other comfort parameters at each of these points.
On-screen readouts enabled the engineers to establish when the respective feel-good temperatures were reached and whether TIM indicated the right comfort level. If required, a few keystrokes at the computer were enough to adjust the climate-control system until the two virtual vehicle occupants began to transmit satisfactory data.
Something good in the wind: computer-simulated storm lasting 36 hours
For the aerodynamics engineers, work also began long before the first prototypes were ready to roll into action and took place in the model wind tunnel using the digital prototype. Based on the key exterior dimensions and the basic stylistic concept, the first 1:4 models of the new C-Class were produced and completed numerous tests in the wind tunnel, laying the groundwork for the new car's impressive aerodynamics. This experimental work was backed up by air flow simulations centred around Computational Fluid Dynamics - or CFD for short. This is the term experts use to describe the complex process involved in building up a simulation of air flow characteristics. State-of-the-art CFD software enables calculation and optimisation of the aerodynamic conditions under the bonnet, around the underbody and in specific areas of the car body. This allowed the Mercedes engineers to identify potential for further improvements at an early stage.
Working through these calculations is part of a process lasting several hours: in order to simulate the precise course of the air flow over and around individual areas of the car, such as the radiator grille or front apron, the powerful computer has to chart a path through highly complicated differential equations with more than 30 million fluid elements. It works for 36 hours at a time in order to calculate a single speed and pressure field, which is then displayed on the screen in the form of colour animations.
Audible results: acoustic calculations in all driving situations
NVH is an automotive engineering term that stands for noise, vibration and harshness.
In this important domain, too, the digital prototype performs invaluable tasks. With the help of computer simulations, the NVH experts were able to stipulate their requirements at an early stage of the vehicle project and actively help to shape the new C-Class. One example of this was the development of the bodyshell. In this case, specific stiffening or bending of the panels helps to substantially reduce the amount of noise that reaches the interior. Previously this type of modification could only be made at a later stage and therefore incurred much greater expense.
The NVH calculation model depicts the complete vehicle with its bodyshell, doors, powertrain and axles. The computer can simulate practically any everyday situation: engine idling, driving on uneven roads, tyre imbalance or sudden acceleration. The resultant vibrations are transferred to the car body and are ultimately perceived as disturbing noise by the car's occupants. Calculation of these vibrations requires a complex mathematical model which has to take into account the air inside the car as well as the various sources of vibration such as the engine, powertrain, axles and individual panel structures. After all, without air, the sound could not be heard.
During the virtual test drive, the computer depicts the sound pressure with a range of colours, thus enabling the experts to ascertain the percentage of the interior noise level attributable to specific sources of noise and at what points the sound radiation is at its greatest. The vibration and noise is assessed above all at those points where comfort is most important for the car occupants, for example at ear level, on the steering wheel and on the seats.
In summary, the development of the Mercedes-Benz C-Class has opened the door to a new, leading-edge development concept: the digital prototype improves processes, helps to save time, verifies the feasibility of projects at an early stage and ultimately gives new Mercedes models an even sharper competitive edge than before – in terms of both technology and quality.
Previous Page | Next Page
 The redeveloped version of the THERMOTRONIC automatic climate control system allows the desired temperature settings to be programmed separately for three different zones of the interior.
 An intelligently designed bodyshell provides an ideal basis for the excellent standard of ride comfort in the C-Class. Static torsional stiffness -- a key indicator for the body‘s vibration characteristics -- has been improved by some 13 percent compared to the outgoing model.
 An intelligently designed bodyshell provides an ideal basis for the excellent standard of ride comfort in the C-Class. Static torsional stiffness -- a key indicator for the body‘s vibration characteristics -- has been improved by some 13 percent compared to the outgoing model.
 Mercedes-Benz offers advanced versions of the multicontour seats as an option for the C-Class. Their design enables occupants to adapt the shape of the seat to their anatomy or to their individual comfort preferences.
 Mercedes-Benz offers advanced versions of the multicontour seats as an option for the C-Class. Their design enables occupants to adapt the shape of the seat to their anatomy or to their individual comfort preferences.
 An intelligently designed bodyshell provides an ideal basis for the excellent standard of ride comfort in the C-Class. Static torsional stiffness -- a key indicator for the body‘s vibration characteristics -- has been improved by some 13 percent compared to the outgoing model.
 An intelligently designed bodyshell provides an ideal basis for the excellent standard of ride comfort in the C-Class. Static torsional stiffness -- a key indicator for the body‘s vibration characteristics -- has been improved by some 13 percent compared to the outgoing model.
 An intelligently designed bodyshell provides an ideal basis for the excellent standard of ride comfort in the C-Class. Static torsional stiffness -- a key indicator for the body‘s vibration characteristics -- has been improved by some 13 percent compared to the outgoing model.
 An intelligently designed bodyshell provides an ideal basis for the excellent standard of ride comfort in the C-Class. Static torsional stiffness -- a key indicator for the body‘s vibration characteristics -- has been improved by some 13 percent compared to the outgoing model.
 An intelligently designed bodyshell provides an ideal basis for the excellent standard of ride comfort in the C-Class. Static torsional stiffness -- a key indicator for the body‘s vibration characteristics -- has been improved by some 13 percent compared to the outgoing model.
 An intelligently designed bodyshell provides an ideal basis for the excellent standard of ride comfort in the C-Class. Static torsional stiffness -- a key indicator for the body‘s vibration characteristics -- has been improved by some 13 percent compared to the outgoing model.
 The new C-Class is equipped with an amplitudedependent damping system as standard: under regular driving conditions with low levels of excitation, the damping forces are reduced automatically, which has tangible benefi ts for the saloon‘s road roar and tyre vibration characteristics -- without compromising driving safety in any way. When higher levels of excitation occur at the shock absorbers, for example when cornering at high speed or performing an evasive manoeuvre, the maximum damping force is activated so that the vehicle is stabilised effectively.
 An intelligently designed bodyshell provides an ideal basis for the excellent standard of ride comfort in the C-Class. Static torsional stiffness -- a key indicator for the body‘s vibration characteristics -- has been improved by some 13 percent compared to the outgoing model.
 The new C-Class is equipped with an amplitudedependent damping system as standard: under regular driving conditions with low levels of excitation, the damping forces are reduced automatically, which has tangible benefi ts for the saloon‘s road roar and tyre vibration characteristics -- without compromising driving safety in any way. When higher levels of excitation occur at the shock absorbers, for example when cornering at high speed or performing an evasive manoeuvre, the maximum damping force is activated so that the vehicle is stabilised effectively.
 The new C-Class is equipped with an amplitudedependent damping system as standard: under regular driving conditions with low levels of excitation, the damping forces are reduced automatically, which has tangible benefi ts for the saloon‘s road roar and tyre vibration characteristics -- without compromising driving safety in any way. When higher levels of excitation occur at the shock absorbers, for example when cornering at high speed or performing an evasive manoeuvre, the maximum damping force is activated so that the vehicle is stabilised effectively.
 Heating tests with the climate dummy.
 Heating tests with the climate dummy.
 Heating tests with the climate dummy.
 Measuring idling noises with the acoustic camera.
 Measuring idling noises with the acoustic camera.
 Measuring idling noises with the acoustic camera.
 Measuring and recording interior noises with the aid of dummy head stereophony.
 Measuring and recording interior noises with the aid of dummy head stereophony.
 Measuring idling noises with the acoustic camera.
 Large acoustics test rig for measuring driving noises.
 Pressure measurement for determining seating comfort.
 Pressure measurement for determining seating comfort.
 Pressure measurement for determining seating comfort.
 Test with a special dummy which simulates the vibrational response of the car‘s occupants.
 Test with a special dummy which simulates the vibrational response of the car‘s occupants.
 Aerodynamic development using data from the digital prototype.
 Aerodynamic development using data from the digital prototype.
 Aerodynamic development using data from the digital prototype.
 Climate control simulation using a thermophysiological occupant model (TIM).
 Climate control simulation using a thermophysiological occupant model (TIM).
 Conducting driving tests with the digital prototype to fi ne-tune comfort and handling characteristics.
 Investigating vibrations and acoustics with the aid of the digital prototype.
 Conducting driving tests with the digital prototype to fi ne-tune comfort and handling characterist ics .
 Investigating vibrations and acoustics with the aid of the digital prototype.
 Climate control simulation using a thermophysiological occupant model (TIM).
 Climate control simulation using a thermophysiological occupant model (TIM).
 Climate control simulation using a thermophysiological occupant model (TIM).
 Conducting driving tests with the digital prototype to fine-tune comfort and handling characteristics.
 Aerodynamic development using data from the digital prototype.
 Aerodynamic development using data from the digital prototype.
 Conducting driving tests with the digital prototype to fine-tune comfort and handling characteristics.
 Conducting driving tests with the digital prototype to fine-tune comfort and handling characteristics.
 Conducting driving tests with the digital prototype to fine-tune comfort and handling characteristics.
 Conducting driving tests with the digital prototype to fi ne-tune comfort and handling characteristics.
 Investigating vibrations and acoustics with the aid of the digital prototype.
 Investigating vibrations and acoustics with the aid of the digital prototype.
 Investigating vibrations and acoustics with the aid of the digital prototype.
 Aerodynamic development using data from the digital prototype.
 The Digital Prototype meant it was possible to experience the driving characteristics of the C-Class subjectively too – on state-of-art test rigs controlled with the highly detailed DPT data. For this purpose, the experts at Mercedes used an innovative ride simulator which they fed with data corresponding to the road surfaces of actual test tracks, along with the relevant chassis and functional data for the C-Class.
 Mapping and digitising real road surfaces using a special measurement vehicle.
 The Digital Prototype meant it was possible to experience the driving characteristics of the C-Class subjectively too – on state-of-art test rigs controlled with the highly detailed DPT data. For this purpose, the experts at Mercedes used an innovative ride simulator which they fed with data corresponding to the road surfaces of actual test tracks, along with the relevant chassis and functional data for the C-Class.
 Virtual comfort test drive with the revolutionary new ride simulator.
 The blend of sophisticated multi-body simulations and cuttingedge test rig technology made it possible to experience the vehicle‘s ride comfort at an early stage of development in the simulator. The driver and front passenger sat down on the test rig‘s two seats and took the new saloon on a purely digital, but nevertheless true-to-life drive.
 The blend of sophisticated multi-body simulations and cuttingedge test rig technology made it possible to experience the vehicle‘s ride comfort at an early stage of development in the simulator. The driver and front passenger sat down on the test rig‘s two seats and took the new saloon on a purely digital, but nevertheless true-to-life drive.
 The blend of sophisticated multi-body simulations and cuttingedge test rig technology made it possible to experience the vehicle‘s ride comfort at an early stage of development in the simulator. The driver and front passenger sat down on the test rig‘s two seats and took the new saloon on a purely digital, but nevertheless true-to-life drive.
Copyright © 2007, DaimlerChrysler AG
|
