WO2006075960A1

WO2006075960A1 - A seat heating device

Info

Publication number: WO2006075960A1
Application number: PCT/SE2006/000058
Authority: WO
Inventors: Pär OHLSSON
Original assignee: Calesco Foil Aktiebolag
Priority date: 2005-01-17
Filing date: 2006-01-16
Publication date: 2006-07-20
Also published as: SE0500118L; SE528149C2

Abstract

A device for heating a seat (1, 2) such as the seat (1, 2) of an automotive vehicle. The seat (1, 2) has arranged therein an electrical resistor (3) which can be connected to an electrical current source (5). A control unit (4) is coupled to the resistor (3) for controlling the temperature of the seat (1, 2). According to the invention, the resistor (3) is comprised of a material that has temperature dependent resistivity. The control unit (4) is adapted to sense the resistance of the resistor when the resistor (3) is connected to the current source (5).

Description

A SEAT HEATING DEVICE

Field of invention

The present invention relates to a seat heating device, preferably to a device for heating a seat of an automotive vehicle, comprising a seat-mounted electrical resistor that can be connected to a power source and that is coupled to a seat temperature control unit. The invention also relates to a seat equipped with such a heating device.

Background of the invention

It is known generally to heat the seat of an automotive vehicle with the aid of metal heat resistors embedded in the seat. The metal heat resistors are connected to an electric power source, for instance to the battery of the vehicle. The metal heat resistors then form an electric resistance and are heated by the electric current and the heat then transferred to the seat.

It is necessary to control heating of the seat so as to avoid the temperature of the metal resistor and the vehicle seat becoming too high and therewith detracting from the comfort of the person seated in the seat and, in the worst case, constituting a fire risk. It is known to provide temperature monitoring control means which prevent the temperature from becoming too high. Examples of heated automobile seats that are provided with temperature control means are described in US 4633061 , US 4998006, US 5981918, US 6140622, US 6252208, US 6369468 and US 6552442.

These known control means include a special temperature sensing device. The sensor is connected with a control unit which functions to enable the electric current to be broken and therewith heating of the seat interrupted when a temperature of a certain magnitude is sensed. Because this control system requires a special temperature measuring apparatus, such a heating system is relatively complicated and expensive.

Against this background, the aim of the present invention is to avoid said drawbacks and to provide a heating device of the aforesaid kind that is both simpler and less expensive than prior art devices. Summary of the invention

This aim is achieved in accordance with the invention by virtue of a device of the kind defined in the preamble of claim 1 , wherein the electrical resistor of the inventive device is comprised of a material that has a material-temperature- dependant resistivity, and wherewith the control means is adapted to measure the resistance of the resistor.

By measuring the resistance of the resistor when it is connected to the power source there is obtained as a result of the temperature-dependence of the resistivity a measurement value which provides an indication of the temperature of the resistor and, indirectly, also of the temperature of the actual seat structure. The sensed resistance value can be related to a reference value of the resistance at a reference temperature and compared with a curve or graph which denotes the resistivity as a function of the temperature of the material in the resistor. The resistance across the resistor is measured simply in one and the same seat-heating electric circuit, therewith obviating the need for any direct additional components in order to obtain temperature-related information. Thus, the present invention enables the need of a special temperature sensor to be eliminated, therewith providing a device which is simpler and cheaper than a device according to known techniques.

The possibility of obtaining indirectly an indication of the temperature level of an electric current resistor comprised of a material that has temperature-dependent resistivity is known to the art and applied in various contexts. For example, US 6521868 described the application of this principal in connection with the heating of a glass sheet.

According to one preferred embodiment of the invention the inventive heating device is comprised of material of a kind where the resistivity increases as a function of increased temperature.

Since it is more usual with a positive correlation between the temperature and the resistivity of a material, this embodiment is beneficial because it provides a greater possibility of finding appropriate material when it is necessary to take other aspects into account with regard to the choice of material. According to another preferred embodiment of the invention, the material chosen is of a kind in which said increase is generally linear.

This allows the control unit to be given a simple design, since all it needs to include is a simple proportionality function for converting resistance to temperature.

According to another preferred embodiment, the material chosen is a metal or a metal alloy.

The advantage of metals is that they generally have good properties for high heat development and enable the use of generally conventional materials.

According to another preferred embodiment of the invention, the resistor is comprised of a wire.

A resistor in the form of a wire is optimal in the majority of cases with respect to effective heating of a relatively large body that has a relatively large surface area, such as the seat of an automobile. The wire form of the resistor also affords favourable working conditions when the resistor shall be mounted in the seat.

According to another preferred embodiment of the invention the control unit is adapted to influence the power supply from the power source when the resistor is connected to said power source and a pre-defined resistance is sensed.

This enables the heating intensity to be reduced automatically in the absence of any manual action, therewith ensuring a high degree of safety with respect to overheating.

According to a further preferred embodiment of the invention, this influence of the power supply causes the current to be switched-off.

This results in a total discontinuation of the heating process, therewith limiting the risk of overheating in the quickest fashion possible. Moreover, this affords a relatively simple design of the control unit, since this way of influencing the power supply simply requires an on/off function.

According to another preferred embodiment of the invention is designed to re-connect the current for sensing of the resistance of the resistor subsequent to the current having been switched off and pre-determined time interval has elapsed. This embodiment enables the seat to be kept warm with the aid of a simple control on/off function.

According to another preferred embodiment, the control unit is provided on a chip.

The control functions to be included are relatively uncomplicated and can readily be accommodated on a chip. The control unit is therewith a space-saving element which is inexpensive in manufacture.

According to another preferred embodiment, the resistor is disposed between two sheets of plastic foam in the seat.

These sheets protect against external influences and provide good and uniform distribution of the heat.

These preferred embodiments of the inventive heating device are set forth in the claims dependent on claim 1.

The invention will be described in more detail with reference to a detailed exemplifying embodiment thereof and also with reference to the accompanying drawings.

Brief description of the drawings

Figure 1 is a perspective view of a car seat provided with an inventive heating device.

Figure 2 is a graph which illustrates the temperature dependence of the resistance of a wire included in an inventive seat heating device.

Figure 3 is a block diagram illustrating the function of the invention.

Figure 4 is a circuit diagram of an inventive control unit. Description of exemplifying embodiments

Figure 1 illustrates schematically a car seat equipped with a heating device according to the present invention. A copper wire 3 is embedded in the material of the car seat 1 and the seat backrest 2 and extends backwards and forwards in loops in said material. The pattern in which the wire extends may vary and may be more complicated than the relatively simple pattern illustrated in the figure. The copper wire 3 is connected to a power source 5, e.g. to a 12V car battery, via a control unit 4. The copper wire has typically a diameter of 0.2mm and a length of about 4m. Its resistance is about 0.3ohm/m at room temperature, which gives a total resistance of 1.3 ohm. The wire heats-up when connected to the power source 5 with the heat spreading to the surrounding stuffing material of the seat, e.g. plastic foam. In order to avoid an excessively high seat temperature, the control device is adapted to interrupt heating of the seat when a given temperature has been reached. Hitherto, this describes a conventional technique of heating a car seat. In addition to what is shown in the figure conventional technology includes a special temperature sensor which is designed to send a signal to the control unit 4 causing the power supply to be switched off when the temperature has become sufficiently high. The need for such a temperature sensor is eliminated by means of the present invention, by virtue of the fact that the means of switching the current on and off is integrated in the actual control unit 4, in a manner described in more detail hereinafter.

According to the present invention this method of control is based on the well known fact that the resistivity of most metals is dependent on temperature. This temperature dependency is often positive and the resistivity is linear in many cases. This is the case with, e.g., copper. Figure 2 illustrates the resistance of a copper wire having a length of 10 m and a diameter of 0.2 mm as a function of the temperature of the wire. As will be seen, the resistance of this wire is about 3, 2 ohm at room temperature 32 degrees C and is 3, 6 ohm at 60 degrees C.

The control unit 4 includes a circuit which measures the resistance across the copper wire 3 in the car seat 1 , 2. When the wire 3 is connected to the power source and heating commences there is sensed a resistance which, with the dimensions given in the example, reaches about 1.3 ohm when heating commences at room temperature and to about 1.0 ohm when heating commences at -20 degrees C. The resistance of wire increases continuously during heating of the wire and is measured continuously or at short intervals. The control unit is designed to switch-off the supply of current when the measured resistance reaches a pre-determined value, e.g. a value of 1.45 ohm. This corresponds to a wire temperature of about 60 degrees C.

The seat will be warm at this temperature and the current supply is consequently switched off. The temperature of the wire will then decrease and the seat will gradually cool down. The control unit is designed to close the electric circuit at given time intervals in this stage of the seat heating process, for instance every fifth minute, so as to enable the value of the resistance at that time to be measured. If this value is below a pre-determined value, the supply of power is continued, and the seat heating process is continued until the resistance of 1.45 ohm is reached again, wherewith the power supply is discontinued.

The block diagram of figure 3 illustrates the logic construction of the control unit 4. Thus, the block diagram of figure 3 illustrates a measuring stage 41 , a power stage 42 and logic block 43. This latter block is for control settings and status.

The measuring stage 41 measures the resistance in the heating element 3. The prevailing resistance can be measured in the voltage input range with a sufficiently high degree of accuracy when there is used a coupling or measuring process which is insensitive to disturbances and eliminates variations in the supply voltage.

The power stage 42 consists of a power transistor which is controlled from the logic block 43.

The temperature of the heating element can be determined by measuring the resistance in said element 3.

If the temperature of the heating element 3 is the same as or higher than the set temperature, the power stage 42 is switched off, wherewith no current will pass through the heating element 3. After a short rest period, the power stage 42 is reactivated and a new measurement is made. If the temperature of the heating element 3 is lower than the desired temperature, the power stage 42 is kept active until the desired temperature is reached.

The logic block 43 presents the prevailing temperature to all observers. It is also possible to set-in the desired temperature and to calibrate the circuit for the type of wire material concerned and the length of the wire.

The construction can be implemented in many different ways, for instance with discrete electronics or digital electronics, with the aid of an A/D converter and processor. The control value of set-point value A is the temperature of the connected heating element. The setting may be a digital setting or an analogue setting. For instance, the temperature can be selected through the medium of a connected button or a connected "spinning" wheel.

The real value B denotes the temperature measured. The value may be either presented as a digital or analogue reading. The connection is included for future use?

Calibration data C is programmed at the time of mounting the device, in order to calibrate the control circuit with the heating element connected.

Figure 4 illustrates a circuit diagram for the control unit 4. The control unit is thus connected to the wire 3 which is symbolized in the figure as a resistor. The control unit includes a measuring bridge containing the resistors R7, R8, R11 , R12 and R13. If the wire has a resistance that is lower than that corresponding to the desired attained temperature, the MMOSFT-transistor D1 will remain active until the set pre-determined resistance has been reached. A clock circuit 8 having connections 6, 7 will deliver a short pulse of adjustable frequency. Measurement of the resistance in the heating element takes place with each pulse. The pulse frequency is controlled by the capacitor C1 which provides a frequency of 2 Hz with a capacitance of 1π F. The ratio R6/R5 determines the smallest till-time?, in this case 5 percent. The resistor R12 is adapted for setting the resistance range 22-1.8 ohm in respect of the wire 3. The supply voltage is normally 9-24 V DC. The output stage has a tolerance of about 3 A. The power tolerance of the resistors R7-R10 and the wrong-polarization protector D2 are limiting factors. It will be understood that the illustrated circuit may have a layout different to that described while retaining the basic principles regarding its function. For example, the analogue solution comprising a comparator can be replaced with a logic block and A/D-converter. This can afford greater regulating options and fewer components.

The control unit 4 may conveniently comprise a semi-resistor chip that measures 10x10 mm.

Claims

1. A device for heating a seat (1 , 2), such as the seat of an automotive vehicle, comprising an electrical resistor (3) which can be connected to a source of electric current (5), and a control unit (4) coupled to the resistor (3) for controlling the temperature of the seat (1 , 2), characterized in that the resistor (3) is comprised of a material that has temperature-dependent resistivity, and in that the control unit (4) is adapted to sense the resistance of the resistor (3) when the resistor (3) is connected to the source of electric current (5).

2. A heating device according to claim 1 , characterized in that the material is of a kind in which the resistivity increases as a function of increased temperature.

3. A heating device according to claim 2, characterized in that the material is of a kind in which said increase is generally linear.

4. A heating device according to any one of claims 2-3, characterized in that the material is a metal or a metal alloy.

5. A heating device according to any one of claims 2-4, characterized in that the resistor (3) has the form of a wire.

6. A heating device according to any one claims 2-5, characterized in that the control unit (4) is adapted to influence the supply of electric current from the current source (5) when the resistor (3) is connected to said source and a pre-determined sensed resistance is reached.

7. A heating device according to claim 6, characterized in that said influence is a discontinuation of the current supply.

8. A heating device according to claim 7, characterized in that the control unit (4) is adapted to restore the current supply for sensing the resistance of the resistor (3) subsequent to the current having been switched off and the elapse of a predetermined time interval.

9. A heating device according to any one claims 1-8, characterized in that the control unit is mounted on a chip.

10. A heating device according to any one of claims 1-10, characterized in that the resistor (3) is disposed between two sheets of plastic foam in the seat (1 , 2).

11. A seat (1 , 2), for instance the seat of an automotive vehicle, characterized in that the seat (1 , 2) is provided with a heating device according to any one of claims