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

Stuttgart, Mar 02, 2006

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.

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 stage.

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

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

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 situations

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

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

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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