It has long been considered desirable to have a heating system for the vehicular steering wheel.

During cold weather while a vehicle is not in operation, a vehicular steering wheel can become bitterly cold. When an operator of a vehicle initially grasps the steering wheel, he may experience discomfort, and this discomfort can persist until the steering wheel warms up. The discomfort can cause a lapse in the operator's concentration and could potentially adversely affect his driving performance.

For individuals suffering from arthritis and other diseases of the hand, the discomfort from the cold steering wheel can be acute. Even after the vehicle has reached a comfortable temperature, the steering wheel usually remains cold to the touch and might require the use of gloves by the driver. For the above-mentioned reasons, there has been a desire to develop a means to rapidly increase the temperature of a vehicle steering wheel.

There have been a number of proposals for this steering wheel problem such as the use of hot air, heated coolants, and electric resistance (resistance wire technology). The use of resistance wire technology became the most popular method of tackling this problem. This method achieved the goal of warming a steering wheel by using lengths of resistance wire as heating elements. The wire was embedded within the steering wheel and the passage of electrical current through the wire would generate

heat. Thus the popularity of this method stemmed from its simplicity and reliability. An advantage of using resistance wire is the flexible installation possibilities; however, the major drawback to this technology is that the steering wheel does not uniformly increase in temperature. Use of resistance wire would create areas or zones on the steering wheel that was cold to the touch and areas or zones that were warm to the touch. Also, the resistance wire is much easier to be damaged, once the wire is broken at any place along the steering wheel rim, the wheel will no longer be able to be heated.

US 4 640 340 teaches an apparatus for heating and cooling a steering wheel. In US 4 640 340 the thermoelectric transducers are responsible for generating or absorbing heat. The thermoelectric transducer either generates heat or absorbs heat depending on which direction the electric current flows. The thermoelectric transducers are situated below a conductive plate, which is situated underneath the skin layer.

US 5 847 360 teaches an electric steering wheel heating element mounting on top of a steering wheel rim. The heating element is made of three electrically conductive segments: one linear segment and two curved adjacent segments.

US 6 093 908 teaches a heated steering wheel having a heating element made from a carbon fiber woven material. The heating element has the unique property of a negative temperature coefficient.

The present invention provides a steering wheel that is capable of being uniformly heated. According

the present invention the heated steering wheel comprises an armature, a substrate, a heating element, a foam layer, and a leather wrapping. The heating element in the present invention is a thin fabric woven made from nylon coated with silver. The foam layer is positioned around the heating element and is made from a material that is substantially conductive so that heat generated from the heating element can reach the surface of the steering wheel rim. The foam layer is included in the heated steering wheel to conceal the presence of the bus bar.

Brief Description of the Drawings Fig 1. is a perspective view of a heated steering wheel.

Fig. 2. is a cross sectional view of the heated steering wheel rim in Fig 1. along section line 2-2.

Fig. 3. is a circuit diagram for the heated steering wheel.

Detailed Description of the Invention The heated steering wheel comprises a conventional vehicle steering wheel, which can be of any desired shape and dimension. Fig. 1 shows an exemplary steering wheel for an automobile. The steering wheel includes an outer rim 1, and a spoke cavity 2.

As shown in Figs. 1 and 2, the steering wheel includes a frame or an armature 4 that defines the shape of the steering wheel. Preferably, the armature is made from the metal such as aluminum or magnesium. A substrate 6 encloses the armature of the steering wheel providing cushion to the steering wheel. The substrate comprises foam and can be made from cellular urethane or neoprene.

According to the present invention, the vehicular steering wheel has a heating systems comprising a heating element 8, wire harness, temperature sensor 13, switch 15, power source 16, and temperature controller 12. Fig. 3 shows an exemplary electrical circuit containing the foregoing components.

The heating element 8 is a thin fabric woven made from nylon coated with silver. The resulting fabric is very flexible and contains a two-dimensional conductive array. This allows the fabric to be cut into a variety of shapes and still function effectively. The heating element includes an electrically conductive metalized fabric. The heating element used in the present invention is purchased from Warme-und Elektrotechnik B. Automotive Systems Ltd. (W. E. T.). The heating element is fastened

directly to the substrate of the steering wheel, and is wrapped around at least part of the steering wheel rim. Preferably, all of the steering wheel rim is wrapped with the heating element, but a lesser amount could be wrapped leaving a gap at the seam. A possible attachment method is by having one side of the fabric coated with an adhesive film. The heating element can also be attached to the substrate 6 by a thin double stick tape.

One skilled in the art will appreciate that the heating element 8 can have a negative temperature coefficient, positive temperature coefficient, and a constant temperature coefficient. For the steering wheel application, the voltage is kept constant. If a heating element has a negative temperature coefficient while the voltage is kept at a constant, there is an inverse relationship between the temperature and the resistance. Hence, as the temperature is decreased, the heat generated is diminished. If a steering wheel has a constant temperature coefficient, then temperature change does not have a bearing on the amount of heat produced. In the claimed invention, the heating element has a constant temperature coefficient and thus a decrease in temperature does not have an adverse affect on the heat generation.

A foam layer 9 surrounds the heating element of the steering wheel. The purpose of the foam layer is to hide the heating element as well as the bus bar, which is two thin metal strips at the two ends of the heating element. An important characteristic of the foam is that it is substantially thermally conductive because the foam is disposed between the leather

wrap 10 and the heating element 8. It is highly undesirable for the foam to insulate because this will elongate the time necessary to heat the steering wheel. Several different foam materials may be used for the present invention including Ensolite AMC, Poron 4701-40, and Rubatex 1400 N. Ensolite AMC foam is a butadiene acrylonitrile rubber and was purchased from RBX Corporation. Poron 4701-40 is a polyurethane foam and was purchased from Rogers Corporation.

Lastly, Rubatex 1400 N is a neoprene foam and was purchased from RBX Corporation. Those skilled in the art will appreciate that other foam materials can be employed in the heating steering wheel. The preferred thickness range for the foam layer is 1.5 mm to 2.5 mm.

The heated steering wheel may include a foam layer underneath the heating element (not shown in the figures). This foam layer needs to have very little thermal conductivity to allow the heat to more efficiently be channeled to the outside portion of the steering wheel rim.

The heated steering wheel in figure 2 includes an outer covering made from leather 10. It is understood that the heating element disclosed herein may also be used in a steering wheel having an outer shell made from wood veneer. Furthermore, the heated steering wheel can properly function in a steering wheel made from leather, wood veneer, fiberglass, and other exterior material.

A temperature sensor 13, often called a negative temperature coefficient sensor (hereinafter referred to as"NTC"), is used to monitor the actual

temperature of the steering wheel surface. The information from the temperature sensor is used to determine the intervals of operation of the heating element.

The temperature controller 12 reads the condition of the temperature sensor and makes the determination of when to turn the heating element on and off. The controller has been designed to turn the heating element on and off electronically rather than electromechanically to eliminate audible noise and greatly reduce electromagnetic signal emission.

Preferably, the temperature controller is installed in the spoke cavity of the steering wheel.

The wire harness provides the interconnection among the various system components and the power leads coming from a power source 16 clockspring or slipring. Preferably, the wire harness includes a fuse to protect the controller from a voltage surge.

The switch 15 may be either an on-off switch or a multiple position switch allowing a choice of temperature settings. The switch may be located on the steering wheel or elsewhere in the vehicle such as the arm rest or instrument panel. The switch can be designed to have six different positions or preferably can be three position switch (low-high-off).

According to the present invention, the heating element can be used in a full leather wrapping steering wheel. The method for assembling the full leather wrapping steering wheel comprises the following steps. First, the seams for two pieces of leather are machine sewn. Next, the grooves on the base steering wheel are cut for burying the wire

harness. A steering wheel base is understood to be a metal armature having at least a rim that is encased with a substrate. Then, adhesive is applied over a foam padding and leather pieces, followed by the foam padding being applied over the leather. Next the cover tape is peeled from the heating element, and the heating element is attached over the foam. It is important to place the busbar at the correct relative location over the foam and leather, so when they are assembled over steering wheel rim, the busbar will be at 3 and 9 o'clock position.

The sub-assembly of the heating element with the foam padding and leather are applied onto the steering wheel rim. The wire harness is then adjusted into the groove and the NTC is applied in between the sub- assembly of the heating element, foam, and leather with the steering wheel substrate. Next, adhesive is applied in between the heating element and the steering wheel rim. Subsequently, the leather is sewn. Finally the excessive leather is trimmed at the spoke area, excessive adhesive is removed, and the leather is heated to remove the wrinkles.

According the present invention, the heating element can be used in a wood shell and leather wrapping steering wheel. The method for assembling the wood shell and leather wrapping steering wheel is similar to the method for assembling the full leather wrapping steering wheel. The major difference is that the wood shell and leather wrapping steering wheel has an outer covering for the steering wheel rim comprising wood veneer and leather. For the leather wrapping steering wheel, only leather is used for the

outer covering. Notwithstanding the addition of wood veneer to the steering wheel, the methods for the wood shell and leather wrapping steering wheel and full leather wrapping steering wheel are the same.