Mercedes Benz has announced its use of a computer simulation model to determine optimal climate conditions in vehicles' interiors. Using data from years of accumulated research on large numbers of drivers, the automaker has developed “TIM”, or 'Thermo-physiological Interior Model'. TIM is subjected to various virtual climates to see how a real human being would react with the goal to determine if “he” is comfortable.

[Source: Mercedes-Benz]

[Press release after the jump] OFFICIAL PRESS RELEASE

Mercedes-Benz SLK-Class: The latest computer models for climate  
control: Virtual driver tests climatic comfort in wind and weather

Stuttgart, Mar 02, 2006

Mercedes engineers are using an innovative process to optimise the  
climatic comfort of car occupants. With the aid of computer  
simulations, they send new models on virtual test drives and  
calculate the air and temperature distribution in the interior under  
different weather conditions. This computer model is based on  
research carried out with a large number of male and female drivers,  
who provided information about their personal comfort and the  
temperatures at which they felt most comfortable. The SLK Class was  
the first Mercedes passenger car to embark on such a computer-based  
climate test.

Controlling the climate in the interior is one of the most complex  
tasks in automobile development. Since the vehicle speed,  
temperature, level of sunlight and humidity change constantly when on  
the move, a car air conditioning system must respond very rapidly and  
flexibly if the occupants are to experience a uniform standard of  
comfort – neither feeling cold if the outside temperature suddenly  
falls nor perspiring if it increases. People only feel really  
comfortable if their climatic surroundings remain pleasantly constant.

In order to ensure this under all driving and weather conditions,  
climate control engineers must commence their tests as soon as  
possible during the development of a new car model. They are not able  
to wait for the first prototypes or pre-series vehicles, as the  
technology and design have been almost completely finalised by this  

This led to the development of "TIM" – the Thermo-physiological  
Interior Model, which allows the climatic comfort of future Mercedes  
models to be calculated and optimised in advance. At an early  
development stage it enables the engineers to establish the ideal  
output for the heating and air conditioning systems, how many  
ventilation vents are required and how large these should be in order  
to ensure the constant climatic comfort which is typical for a Mercedes.

"TIM": a virtual driver with almost every body function

"TIM" is the result of many years of work by DaimlerChrysler  
researchers on human thermal comfort levels. For example, 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  
climatic comfort to be defined for each part of the body. Specialists  
for example found that 80 percent of the individuals tested felt most  
comfortable in summer when the equivalence temperature at the torso  
and arms was between 19 and 28 degrees Celsius, while the comfort  
range for the lower legs and feet is between 23 and 27 degrees Celsius.

The "TIM" computer model is based on these and other findings about  
the sub-jective perception of comfort. It simulates most of the human  
body in a total of 14 areas, also taking into account the blood  
circulation and relative heat generation. The result is a virtual but  
certainly 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 he feel comfortable?

Airflow: comfort test at four million points of the interior

The SLK-Class is the first Mercedes model whose heating and automatic  
climate control systems were developed both by computer and by  
practical testing. "TIM" absolved test drives of many hours duration  
under the most varied driving and weather conditions in this sporty  
two-seater. In addition, "TIM" was linked to other computer  
programmes which for example divided the interior into up to four  
million spatial units and measured the airflow, 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 key strokes at  
the computer were enough to adjust the climate control system until  
the two virtual vehicle occupants began to transmit satisfactory data.

Climate control: thousands of key data for all driving and weather  

In this way the engineers fed thousands of key data into the control  
unit of the THERMOTRONIC automatic climate control system,  
subsequently verifying and refining these in practical trials. Once  
the computer recognises a certain situation on the basis of sensor  
data, it accesses the programmed values and adjusts the air  
conditioning accordingly. This activates up to five electric motors  
inside the air conditioning unit, which automatically open or close  
the air vents to adjust the air distribution. At the same time the  
fan speed is increased and the output of the compressor is adapted to  
the new conditions.

The results obtained from this computer simulation not only provide  
the basis for the key data in the climate control system, but also  
help developers to design the dashboard. The computer model gives  
them a precise indication of where the air vents should be located,  
and how large they should be, to ensure an effective i.e. draught-
free air distribution. The larger the cross-section of the vent, the  
lower the air speed and therefore the less draught to disturb the  
occupants. The striking air vents in the dashboard of the SLK sports  
car follow this principle, thereby combining form with function in an  
exemplary way.

Although they are not obvious, the six footwell vents on the  
underside of the dashboard are no less important for climatic  
comfort. Their location is likewise mainly based on the "TIM"  
simulation and other computer models. When the heating is on, 80  
percent of the air volume flows through these vents to warm the  
thermo-physiologically most sensitive body areas of the occupants,  
namely the feet.

Open-air experience: good heating performance even with the vario-
roof open

The intelligent climate control system of the SLK-Class also works  
when the vario-roof is open. As soon as the occupants decide to enjoy  
open-air driving, the automatic climate control system switches to  
special characteristic values and adjusts both the air distribution  
and temperature control. The basic settings for this are also  
supplied by computer models such as "TIM": the computer, for example,  
simulates an open-air drive on a fine day at an ambient temperature  
of ten degrees Celsius, calculating the airflow over and inside the  
Roadster at 80 km/h.

At an early development stage, this enables Mercedes engineers to  
achieve the right comfort (equivalence) temperatures at head level:  
for example by reducing the air speed with the help of the standard  
draught-stop and large air vents which direct warm air precisely at  
the car occupants. In conjunction with the unique AIRSCARF neck-level  
heating system, this achieves a level of thermal comfort unrivalled  
by any other convertible in this vehicle class.

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