Uncomfortable seats while driving not only reduces concentration of the drivers and soon tire them but also lead to accidents. To avoid such serious situations, the Hohenstein Institutes have developed different test methods for objectively determining the physiological comfort of vehicle seats.
When it comes to ergonomics, the central issue is whether a vehicle seat offers enough mechanical support for the driver’s body without forcing them into an unnatural seating position and in case of material use whether the seat cover and the interior of the seat are capable of appropriately regulating the thermal balance and the moisture transport of the body in relation to the ambient conditions in the vehicle (temperature, humidity). If this is not the case, uncomfortable heat or humidity accumulations can occur, placing physical and mental strain on the driver. Sufficient seating comfort is only ensured if material and design of vehicle seats are ideally coordinated to produce a so-called ventilation effect between the body and the seat.
The researchers at the Hohenstein Institutes have established four key characteristics which determine the physiological comfort of vehicle seats:
1. Initial heat flux designates the driver’s heat perception directly upon first contact with the seat.
2. Breathability indicates how quickly moisture can be transported away from the seating material.
3. Thermal insulation is the measure of how well a seat warms the vehicle driver at low temperatures and how well it protects against heat accumulation at high temperatures.
4. Moisture buffering shows how much water vapour the seat can absorb without feeling subjectively damp.
Breathability and water vapour buffering of the seat are determined using the thermoregulatory model of the human skin, called the Skin Model. It consists of a porous, heatable metal plate which can release controlled water vapour to simulate sweating as a function of different physical activity levels.
The Hohenstein Institutes have two special measuring devices for quantifying the comfort of vehicle seats. To simulate the body’s heat emission, an aluminium stamp in the shape of the human buttocks, the so-called Upholstery Tester, is pre-heated to skin temperature and pressed into the seat. Heat flow sensors integrated into the device record the level of heat insulation of the seat upon first contact and after reaching the temperature balance between body and seat.
Breathability and water vapour buffering of the seat are determined using the thermoregulatory model of the human skin, called the Skin Model. It consists of a porous, heatable metal plate which can release controlled water vapour to simulate sweating as a function of different physical activity levels. Moisture sensors between measuring surface and test object provide reliable information about the buffer effect of the seat cover. The device also measures how much water vapour the seating material can transport away from the body within a certain period of time and under defined ambient conditions.
The newly developed laboratory tests are also suitable for determining the comfort of other seating systems, like buses, trains or aeroplanes.
