Seat assembly having seat heating and occupant detection
A seat assembly including a seat cushion, a heating element, a heating circuit, a occupant sensing circuit, and an isolation circuit. The seat cushion has a seating surface, the heating element is adjacent the seating surface and is formed of electrically conductive material. The heating circuit is coupled to the heating element for supplying electrical current to the heating element for generating heat. The occupant sensing circuit is also coupled to the heating element for sensing the presence of an occupant near the heating element. The isolation circuit is interposed between the heating circuit and the heating element for isolating the heating circuit from the occupant sensing circuit.
1. A seat assembly, comprising:
a seat cushion having a seating surface;
a heating element adjacent the seating surface formed of electrically conductive material, wherein the heating element includes a first terminal and a second terminal;
a heating circuit coupled to the heating element for supplying an electrical current to the heating element effective for generating heat;
an occupant sensing circuit coupled to the heating element and effective for sensing the presence of an occupant near the heating element;
an isolation circuit interposed between the heating circuit and the heating element, said isolation circuit effective for isolating the heating circuit from the occupant sensing circuit, wherein the isolation circuit comprises a first electrical component coupling a first heater lead to the first terminal and a second electrical component coupling a second heater lead to the second terminal;
a first heating voltage source connected to the first electrical component for applying a first voltage to the first terminal as a reference voltage for establishing a first differential voltage across the first electrical component; and
a second heating voltage source connected to the second electrical component for applying a second voltage on the second terminal as a reference voltage for establishing a second differential voltage across the second electrical component, thereby isolating the heating circuit from the occupant sensing circuit.
2. The seat assembly in accordance with claim 1 , wherein the heating element is formed of metal wire, conductive fiber, metal foil, or metal ribbon.
3. The seat assembly in accordance with claim 1 , wherein
the heating circuit further comprises a heating switch having an open-switch impedance;
the heating switch having an closed state connecting one of the first and second heater leads to one of the first and second heating voltage sources for supplying electrical current to the heating element and an open state to disconnect the heater lead from the heating voltage source during occupant sensing, whereby the heating lead is coupled to the heating voltage source through the open-switch impedance.
4. The seat assembly in accordance with claim 1 , wherein the occupant sensing circuit measures a field impedance of the heating element, said field impedance being indicative of an occupant near the seating surface.
5. The seat assembly in accordance with claim 1 , wherein the first electrical component is a resistor, inductor, diode, or transistor.
6. The seat assembly in accordance with claim 1 , wherein the first electrical component has a blocking impedance for cooperating with the first heating voltage source to establish the differential voltage.
7. The seat assembly in accordance with claim 1 , wherein the first voltage source is an operational amplifier, said operational amplifier having an output and an inverting input contact the heater lead, said operational amplifier further having a non-inverting input contacting the heater element such that the differential voltage is zero.
8. The seat assembly in accordance with claim 1 , wherein the isolation circuit effectively isolates the heating circuit when at least one of the first and second differential voltages is zero.
9. The seat assembly in accordance with claim 1 , wherein the heating element includes a capacitor coupling the first terminal and the second terminal.
10. The seat assembly in accordance with claim 1 , wherein the occupant sensing circuit is coupled to a terminal of the heating element.
11. The seat assembly in accordance with claim 1 , wherein the heating circuit includes a first heating switch having a first open-switch impedance, and a second heating switch having a second open-switch impedance;
the first heating switch having a closed state connecting the first heater lead to the first heating voltage source, and the second heating switch having a closed state connecting the second heater lead to the second heating voltage source for supplying electrical current to the heating element; and
the first heating switch having an open state disconnecting the first heater lead from the first heating voltage source, and the second heating switch having an open state disconnecting the second heater lead from the second heating voltage source during occupant sensing, whereby the first heating lead is coupled to the first heating voltage source through the first open-switch impedance and the second heating lead is coupled to the second heating voltage source through the second open-switch impedance.
12. The seat assembly in accordance with claim 1 , wherein the first differential voltage magnitude is less than 1 millivolt and the second differential voltage magnitude is less than 1 millivolt.
13. The seat assembly in accordance with claim 1 , wherein the first differential voltage is zero and the second differential voltage is zero.
14. The seat assembly in accordance with claim 1 , wherein
the first electrical component is a P-channel MOSFET, comprising a drain connected to the first terminal, a source connected to the first heater lead, and a gate biased so as to turn the P-channel MOSFET on while the first heater lead is connected to the first voltage source and off while the first heater lead is disconnected from the first voltage source; and
the second electrical component is a N-channel MOSFET, comprising a drain connected to the second terminal, a source connected to the second heater lead, and a gate biased so as to turn the N-channel MOSFET on while the first heater lead is connected to the first voltage source and off while the first heater lead is disconnected from the first voltage source.
15. The seat assembly in accordance with claim 1 , wherein
the first heating voltage source is a first operational amplifier having an output and inverting input connected to the first heater lead, and further comprising a non-inverting input connected to the first terminal; and
the second heating voltage source is a second operational amplifier having an output and inverting input connected to the second heater lead, and a non-inverting input connected to the second terminal.