The Electric Heater In Cold Weather

In cold weather, when handling the steering wheel to give a driver comfortable feeling, the rim portion of steering wheel is warmed to a suitable degree by an electric heater mounted in it, but there is no uniform distribution of temperature throughout. The electric heater which is mounted on the rim portion tends to have high temperatures at the portion where terminal ends of electric heater are located. This causes a driver some source of discomfort. To overcome this problem, the steering wheel consist of the rim portion which has metal core inserted in it. The heat conductive sheet such as copper film, an aluminum film which covers the rim portion. This metal film can be deposited by meta vaporization technique. An electrically insulating sheet like plastic film- polyamide plastics covering the heat conductive sheet.

The heat generating member is covering the electrically insulating sheet. If the material used for insulating sheet are thermoplastics then there would be bonding between the insulating sheet and generating member by a hot-press bonding technique. Finally, a cover made of a woven fabric, leather is wrapped around the heat generating member as well as remaining insulating sheet. The electrically heat generating sheets consists of two lead wires which are connected to terminal ends.

One of the wire leads to metal core of one of spokes of steering wheel. These metal cores are grounded and connected to negative terminal of DC power source. Another wire leads to switch mounted on spoke which connects the slip ring. The slip ring is situated in hub portion of steering wheel and used to maintain electrical connection between lead wires and positive terminal of electric source. When, in operation the switch is closed, the heat produced at terminal ends of generating sheets are higher than of intermediate portion because of its electrical resistance. Due to this non-uniform temperature distribution takes place. This can be reduced by using high heat conductive sheet. The high heat at terminal ends of generating sheet is transmitted to conductive sheet from then to intermediate portion.

Now the intermediate portion of generating sheet has high temperature which is equal to terminal ends. Therefore, each generating sheet has uniform heat distribution which leads to give a drive comfortable feeling. In the graph it describes the temperature changes at given portion of heater-mounted steering wheel w.r.t time elapsed. The graph represents curves which in indicated with references a and b. The reference ‘a’ shows the temperature changes in the intermediate portion of generating sheet, while ‘b’ shows the temperature changes at terminal ends of generating sheet.