Optimally designed vehicle seats are said to be at the basis of providing the driver with the necessary comfort during their journey, the Hohenstein Institute reports.

They may allow drivers to assume an ergonomic seating position and feature good climate properties. On the other hand, poor seating comfort is said to decrease the concentration and drivers tire more easily, which, according to the Institute, in the worst case scenario may lead to an accident.

Hohenstein Institute has developed different test methods to objectively determine the physiological comfort of vehicle seats, in order to assist modern automotive manufacturers, who have been using the laboratory tests for many years to check the materials and seating systems they use.

Driving comfort

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.

A comfortable climatic comfort is equally important, as it indicates 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, such as temperature and humidity.

In case the seating fails to provide that thermoregulation, uncomfortable heat or humidity accumulations can occur, placing physical and mental strain on the driver.

Testing criteria

The researchers at the Hohenstein Institute have established four key characteristics to determine the physiological comfort of vehicle seats:

• Initial heat flux designates the driver's heat perception directly upon first contact with the seat.
• Breathability indicates how quickly moisture can be transported away from the seating material.
• 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.
• Moisture buffering shows how much water vapour the seat can absorb without feeling subjectively damp.

Measurements

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 preheated 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 the body and the seat.

Breathability and water vapour buffering of the seat are determined using the thermoregulatory model of human skin – the Skin Model. It consists of a porous, heatable metal plate which can controlled release water vapour to simulate the sweating as a function of different physical activity levels.

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.

Wide application range

Apart from vehicle seats for passenger cars and HGVs, the Hohenstein Institutes’ laboratory tests may also be used for determining the comfort properties of other seating systems, for example, in public transport vehicles, such as buses, trains or aeroplanes.

www.hohenstein.com