. Mercedes-Benz SLK-Class: The latest computer
models for climate control
Virtual driver tests
climatic comfort in wind and weather
Stuttgart - 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 stage.
Photos: DC
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 situations
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.
