Seat heating
A seat heater is a radiant heating system, which is used for heating of the seat surfaces and to create a uniform thermal sensation. These are mainly used in the seats of motor vehicles in order to increase comfort. These are also increasingly being built into motorcycles , chairlifts and toilet seats .
Seat heating is often included in the scope of delivery for vehicles with leather upholstery. In the lower vehicle classes, seat heating for the front seats is usually subject to a surcharge, but is standard equipment in many models in the higher classes. In addition to seat heating in the front seats, seat heating for the rear seats is often available in these vehicle classes at an additional cost.
Working principle
A seat heater consists either of heating mats with heating wires, which are located between the cover and foam core of a car seat, or of heating wires incorporated into the seat or backrest cover. It is operated electrically and generates heat at the point of contact between a person and their seat. The heating elements consist of flexible resistance conductors that meander through the seat surface, the seat cheeks and the backrest. Alternative technologies use two electrodes with parallel network structures made of carbon fibers or a network structure . All technologies are based on the Electricity Heat Act .
Depending on the manufacturer, the heating output can be set steplessly or step-wise, usually using a push-button switch or a knurled wheel. For this purpose, the control element acts on a circuit in a control unit that uses pulse width modulation to set the effective voltage on the heating elements. Combinations of control element and control device are also possible. Overheating protection is provided by temperature sensors in the heating elements that are connected to the control unit.
variants
In manufacturing technology, a distinction is made between stranded, parallel and pressure technology. The manufacturers have a large number of brand names that stand for different material qualities and thus different durability of the heating conductor depending on the desired quality.
Litz technology
With the litz technique, an electrical conductor is laid in meanders across the surface and fixed with a cover layer or, more advantageously, an embroidery thread (embroidery technique). In the case of higher-quality structures, the conductor is embedded in a carrier foam and fixed with cover layers made of non-woven material to prevent the cover from becoming visible. The embroidery technique only uses one layer of material as a carrier for the heating wire fixed with an embroidery thread. The strand technology is characterized by extreme flexibility in the contour of the heated surface.
Parallel technique
The parallel technique uses parallel heating conductors, which are attached to a carrier material with a stitchbonding machine. The conductors are usually made of carbon fibers , but also steel or copper. In addition, two contact strips are introduced that supply the parallel conductors with power. By changing the laying pattern or pulling in or removing ladders, the heating output can be adapted to the respective areas. The strength of these elements manufactured in this way is a very even heating of square surfaces. The parallel structure enables it to be brought in very close to the cover and thus accelerates heating. Despite many improvements, the contact strips remain the weak point of these elements.
Printing technology
In this technology, silver electrodes are printed with a special conductive ink, the resistance of which increases sharply with increasing temperature ( PTC properties ). This is currently only used in series production on film carriers. The use of textile carrier materials is being researched, but not yet in series production. The self-regulating PTC property is advantageous in combination with a carrier film which melts in the event of local overheating and thus functions like a fuse. As a result, high power densities can be achieved and the system is intrinsically safe against misuse such as conductor damage, damming or double laying during production. The disadvantage is the practically non-existent breathability, as well as the long-term stability and the material costs. The technique is rarely used.
Series production
When the vehicle manufacturer installs seat heating as standard, a distinction is made between these variants:
- Integration in the PU foam of the seat, mostly the case with French car manufacturers ( Renault , Peugeot , Citroën )
- "Peel-and-stick" technique with sticking heating mats using double-sided adhesive tape on the upholstery foam
- Sewing the heater into the seat cover, especially in luxury vehicles (e.g. BMW, Daimler AG, Audi)
- Fastening with Velcro tape (Renault, Chrysler) or by means of anchoring when tensioning the cover
Aftermarket
Attachable heating pads or heating mats are also available in the accessories trade, which are also often marketed under the name seat heating. These non-vehicle-specific heating mats are suitable for the driver and front passenger seats with possible restrictions for special equipment such as sports seats, leather covers or seat ventilation. They are attached to the seat frame with hooks and elastic straps. They are available with a textile fabric or leather cover. The electrical connection is made via the on-board power socket . The heating elements consist of flexible wires that pull through the seat cushion. The disadvantage of these heating mats is that some versions do not heat the entire seat surface, and the cable feed must be laid through the vehicle interior. A distributor plug is usually required to heat both front seats.
In addition, integrable, non-vehicle-specific seat heaters are often available that can be adapted to the seats and installed under the seat cover. These solutions use elements that are similar or identical to those installed by the vehicle manufacturers as standard. In most cases, however, manufacturer-identical integration into the vehicle is not possible for cost reasons.
regulation
The following techniques are mainly used to regulate the seat heating:
- The most common is the NTC control using a thermistor . This is integrated into the mat or cover and records the temperature of the thermistor (not the surface). The electronics regulate the heating wire to a constant static temperature of approx. 60 to 80 ° C specified by the control element, depending on the reference thickness and the required surface temperature.
- Regulation with one or two thermostats is also common. The thermostats have the disadvantage of a noticeable hysteresis , which is inherent in the system because of the limited switching cycles and the energy required for switching that is obtained from the switching hysteresis.
- With some manufacturers, a time control, which can also be adjusted to the outside temperature, is used for regulation. The heating power is reduced after a defined time in order to keep the temperature on the surface constant after the heating phase. The heating often switches back or off automatically.
criticism
infertility
Again and again circulating the rumor, seat heating cabinets by the higher temperature of the testes which produce sperm and lead permanently to infertility . However, this is usually not a problem, as the duration of the use of the seat heating is far too short. The temperature of the testicles also naturally fluctuates during the day and is e.g. B. when lying down during sleep is already significantly higher than usual. Permanent damage would only occur after weeks or months of permanent increase in testicular temperature.
Vehicle fire
There have been repeated cases of seat heating becoming a safety risk and either causing burn holes in the seat surface or the fire of an entire vehicle. Here the difficulties in the construction of a seat heater are reflected: In order to ensure a good heating performance with a comparatively low current , the heating cables must be sufficiently thin and thus have enough electrical resistance . In addition, the lines must be close to the surface of the seat so that as much of the heat generated as possible reaches the person sitting on them. However, the combination of a thin cable cross-section and higher mechanical stress can lead to a cable break after a while , which in the best case results in a decrease in the heating output and even complete failure. However, if individually insulated heating conductors or contact strips are not used, the break in individual wires will overload the remaining strands. This local overheating (hot spot) can lead to burn holes and, in combination with flammable materials (e.g. covers made of non-flame-retardant material) also to an open fire . As soon as a "hot spot" or a reduction in performance (e.g. seat or backrest do not warm up) is noticed, the seat heating should not be switched on for safety reasons until it is repaired. If switching off does not work anymore, the fuse must be pulled.
Fuel consumption
The heating mat consumes approx. 100 W per seat in the heating phase and approx. 20 to 30 W in the continuous operation phase. 100 watts of electrical load in vehicles with internal combustion engines mean around 0.1 liters more fuel per 100 kilometers. Some OEMs have investigated a power reduction to save fuel. However, this reduction in output is directly at the expense of the heating rate, because the electric heater with integrated electronics converts 100% of the energy into heat. The leading OEMs have therefore discontinued these investigations and prefer to heat more surfaces (steering wheel, floor mats, armrests) electrically in order to save heating power when heating the air. In electric vehicles, it is much more economical to heat the seat directly than the entire interior.
See also
- Seat heating (chairlift) .
- antique heated seats in the Downing Street Guard Chairs .
swell
- ↑ Article at Autobild.de ( Memento from December 12, 2007 in the Internet Archive )
- ↑ ÖAMTC: Unconscious fuel consumers. (No longer available online.) Archived from the original on December 19, 2011 ; Retrieved November 13, 2012 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
