Patent Application
20110307148
The invention generally relates to vehicle passenger occupant detection, and more particularly relates to a system and method to electrically isolate a seat heater element so the heater element does not interfere with the determining of an occupant.
It is known to selectively enable or disable a vehicle air bag or other occupant protection device based on the presence of an occupant in a seat. It has been proposed to place electrically conductive material in a vehicle seat to serve as an occupant detection electrode for detecting the presence of an occupant in the seat. For example, U.S. Patent Application Publication No. 2009/0267622 A1, which is hereby incorporated herein by reference, describes a vehicle occupant detector that determines the presence of an occupant by applying an excitation signal to the occupant detection electrode and analyzing how the occupant influences the excitation signal. The occupant affects the electrical field radiated by the occupant detection electrode in response to the excitation signal, and thereby influences the excitation signal. Humidity and liquid moisture also influence the excitation signal and so may affect the accuracy of determining an occupant.
In accordance with one embodiment of this invention, a system for determining an occupant proximate to a vehicle seat is provided. The system includes an occupant detection electrode, a heater element, and an electrical isolation means. The occupant detection electrode is configured to influence an excitation signal in accordance with an occupant presence proximate to the vehicle seat for determining the occupant. The heater element is configured to generate heat in response to a heater voltage for warming the occupant. The electrical isolation means selectively electrically isolates the heater element such that the heater element does not interfere with a determination of the occupant.
In another embodiment of the present invention, a controller for determining an occupant proximate to a vehicle seat is provided. The controller includes an excitation signal output, a heater voltage output, and an electrical isolation means. The excitation signal output is configured to allow an excitation signal applied to an occupant detection electrode to be influenced in accordance with an occupant presence proximate to the vehicle seat for determining the occupant. The heater voltage output is configured to supply a heater voltage to a heater element to generate heat in response to the heater voltage for warming the occupant. The electrical isolation means is configured to selectively electrically isolate the heater element such that the heater element does not interfere with determining the occupant.
In yet another embodiment of the present invention, a method for electrically isolating a heater element from an occupant detection electrode is provided. The method includes the steps of coupling a first contact of a heater element to a first voltage output of a heater voltage source with a first electrically isolating switch and coupling a second contact of a heater element to a second voltage output of a heater voltage source with a second electrically isolating switch. The method also includes the step of operating the first electrically isolating switch to a first switch open state and the second electrically isolating switch to a second switch open state to electrically isolate the heater element such that the heater element does not interfere with a determination of an occupant.
Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.
The present invention will now be described, by way of example with reference to the accompanying drawings, in which:
In accordance with an embodiment of a system for determining an occupant proximate to a vehicle seat,
The system may also include a heater element 28 configured to generate heat in response to a heater voltage source VH for warming the occupant 16. The heater element 28 may be formed of electrically conductive material that exhibits an electrical resistance so that when the heater voltage source VH is applied to the heater element 28, a heater current IH is generated that flows through the heater element 20 to generate heat. The heater voltage source VH is illustrated in
A typical vehicle seat 12 may include a cushion 30 that typically is formed of foam and shaped to be comfortable to sit upon. The cushion 30 may be covered with a seat cover 32 that may be formed of fabric or leather to make the vehicle seat 12 attractive. As suggested above, it may be preferably for the occupant detection electrode 24 and the heater element 28 to both be located as close to the occupant 16 as possible. For example, the occupant detection electrode 24 and the heater element 28 may be positioned between the cushion 30 and the seat cover 32. In one embodiment the occupant detection electrode 24 is arranged within the vehicle seat 12 proximate to a seating surface, and the heater element 28 is arranged proximate to the occupant detection electrode 26 opposite the seating surface; that is below the electrode 26. For this embodiment, and other embodiments having the occupant detection electrode 24 and the heater element 28 in close proximity to each other, it has been observed that the presence or absence of the heater element 28 may affect or interfere with the accuracy of determining the occupant 16. It has also been observed that when liquid moisture is introduced into such a vehicle seat 12, for example by a spilled beverage, a wet bathing suit, or from rain entering an open vehicle window; the occupant detection system 14 may further interfere with the accuracy of determining the occupant 16. Furthermore, it has been observed that the degree of interference that the heater element 28 has on determining the occupant 16 may correspond to the amount of moisture, liquid or vapor, present in or on the cushion 30. Testing has indicated that an electrically resistive leakage path between the electrode 24 and the heater element 28 may occur when liquid water is pour onto the cushion 30. For a controller 22 having a voltage detector 54 that determines an amplitude of the excitation signal 26, the resistive portion of an impedance exhibited by the electrode 24 may cause the amplitude detected by the voltage detector 54 to decrease and then, for example, the controller 22 may indicate the presence of an occupant when none is actually present, or indicate that the occupant is larger than actual.
Testing has demonstrated that if the heater element 28 is electrically isolated from the system 14, the accuracy of determining the occupant 16 is improved. As used herein, the use of the term ‘electrically isolate’ means to electrically disconnect or electrically decouple an object such as the heater element 28 so there is no substantial electrical communication with the object. Electrical communication is generally characterized as being through a conductive path or through capacitive coupling. Use of the term ‘electrically isolate’ with regard to the heater element 28 means that the heater element 28 is electrically disconnected or electrically decoupled from any signal source such that the heater element 28 is electrically floating and not biased to any particular voltage potential. By electrically isolating the heater element 28 it is believed that influence on the electric field 25 radiated by the occupant detection electrode 24 is minimized. As such, when the excitation signal 26 present on the occupant detection electrode 24 is analyzed, the heater element 28 does not substantially influenced the excitation signal 26 and so does not interfere with determining the occupant 16. According to this definition, a heater element 28 connected to a signal source that provides a guarding signal to match the voltage of a heater element to the voltage of an occupant detection electrode, such as described in EP2085263 by Petereit et al., is not electrically isolated and so is specifically excluded by this definition. It follows that it may be advantageous for the system 14 to include an electrical isolation means 34 configured to selectively electrically isolate the heater element 28 such that the heater element 28 does not interfere with a determination of the occupant 16.
It has been observed that environmental conditions such as temperature, relative humidity, or the presence of liquid moisture may affect the process of determining the occupant 16. As such, it may be advantageous for the system 14 to include an environmental detection means configured to detect an environmental condition. Based on the environmental condition detected, the system 14 may be configured so the electrical isolation means electrically isolates the heater element when the environmental condition is indicated. The environmental detection means may be by way of a discrete sensor, such as a temperature sensor (not shown) or a separate humidity sensor (not shown).
It has been suggested that the excitation signal may be analyzed to determine relative humidity and/or liquid moisture in the vehicle seat 12, see U.S. patent application Ser. No. 12/700,243 filed Feb. 4, 2010, the entire contents of which is hereby incorporated herein by reference. It follows that the environmental condition indicated may be based on the excitation signal 26. It also follows that the environmental condition indicated may include an indication of a presence of moisture proximate to the occupant detection electrode 24. As used herein, the presence of moisture proximate to the electrode includes, but is not limited to conditions where moisture is present either within or on top of the seat cushion 30, either in the form of vapor or liquid, and so may or may not be indirect contact with the electrode 24. The system 14 may be configured to selectively electrically isolate the heater element 28 either only when an environmental condition such as a wet seat is detected, or only when the excitation signal 26 is present, or only when both the environmental condition is detected and the excitation signal 26 is present. The conditions selected for when the heater element is to be isolated may be determined based on empirical testing, or may be selected based on other design features of the electrical isolation means 34.
In one embodiment of the system 14, the heater element may be formed of a length of electrically conductive material as suggested above. The length of electrically conductive material may include a first contact at a first end of the length of electrically conductive material, and a second contact at a second end of the length of electrically conductive material opposite the first end. For example, the heater element 28 may be a length of wire with the first and second contacts located at opposite ends of the wire. Alternately, the heater element may be in the form of a sheet or ribbon of conductive material with the first and second contacts generally located at opposite sides of the sheet or ribbon so that current passing through the heater element 28 is effective to generate heat over a area of the sheet or ribbon. The system 14 may further comprise a heater voltage source VH source having a first voltage output VP and a second voltage output VN. The heater voltage source VH is shown separate from the controller 22; however it will be appreciated that the heater voltage source VH could be incorporated within the controller 22. When the heater voltage source VH is electrically connected to the heater element 28, the first voltage output VP and the second voltage output VN cooperate to supply a heater current to warm the heater element. For example, the first voltage output VP may have a first voltage value that is greater than a second voltage value of the second voltage output VN such that a heater current IH is supplied to the heater element 28 as illustrated in
The electrical isolation means 34 may include a first electrically isolating switch 36A coupling the first contact of the heater element 28 to the first voltage output VP. The first electrically isolating switch 36A may be operable to a first switch closed state that electrically connects the first contact to the first voltage output VP, and a first switch open state that electrically isolates the first contact from the first voltage output VP. The electrical isolation means 34 may also include a second electrically isolating switch 36B coupling the second contact of the heater element 28 to the second voltage output VN. The second electrically isolating switch 36B may be operable to a second switch closed state that electrically connects the second contact to the second voltage output VN, and a second switch open state that electrically isolates the second contact from the second voltage output VN. As such, the switches 36A and 36B may be operated to selectively electrically isolate the heater element, such as when necessary during certain selected conditions.
The first switch 36A and the second switch 36B may receive independent first and second control signals 38A, 38B from the controller 22. With this arrangement, the switches 36A and 36B may be operated independently or simultaneously by the controller 22. In one instance, operating the first electrically isolating switch 36A to the first switch closed state and the second electrically isolating switch 36B to the second switch closed state electrically connects the heater voltage source VH to the heater element 28 so the heater current IH flows from the heater voltage source VH to the heater element 28. In another instance, operating the first electrically isolating switch 36A to the first switch open state and the second electrically isolating switch 36B to the second switch open state electrically isolates the heater element 28.
A non-limiting example of the electrical isolation means 34 has a first electrically isolating switch 36A that includes a first relay and the second electrically isolating switch 36B includes a second relay. In one embodiment, the switches 36A and 36B may consist of only a first and second relay respectively, such as electromechanical relays having mechanical contacts. Typical electromechanical relays suitable for switching the voltages and currents present in the heater element 28 will exhibit virtually no conductivity, for example open state resistances greater than 10 Mega-Ohms (10E6 Ohms), and very low capacitive coupling, for example less than 5 pF. In another embodiment, each electrically isolating switch 36A and 36B may include both a relay for electrical isolation switch, and solid state devices such as MOSFETs for pulse width modulating power from the heater voltage source VH to the heater element 28 to regulate the average power dissipated by the heater element 28. In another embodiment, the electrically isolating switches 36A and 36B may be formed of only solid state devices such as shown in U.S. patent application Ser. No. 12/443,923 filed May 1, 2009, the entire contents of which is hereby incorporated herein by reference.
At step 230, it may be determined if the excitation signal 26 is present on the occupant detection electrode 28. If the excitation signal 26 is not present, then the routine may return to step 210 and so the heater element 28 remains electrically coupled to the heater voltage source VH. If an excitation signal 26 is present on the occupant detection electrode 24, then the method 200 may proceed to step 240. Alternately, it may be desirable to electrically isolate the heater element 28 anytime the excitation signal 26 is present, and so the method 200 may bypass step 240 and proceed directly to step 250 where the heater element 28 is eclectically isolated by the electrical isolation means 34.
At step 240, it may be determined if moisture, either vapor or liquid, is present proximate to the heater element 28. If no moisture is detected, it may be unnecessary to electrically isolate the heater element 28 for some configurations of the seat 12, and so the method 200 may return to step 210. However, for some configurations of the seat 12, the presence of moisture or liquid proximate to the occupant detection electrode 24, it may be advantageous to electrically isolate the heater element 28 such that the heater element 28 does not interfere with a determination of an occupant 16. An alternate embodiment of the method 200 may omit step 230 such that the only criteria used for deciding to electrically isolate the heater element 28 is the presence of moisture. The inclusion of steps 230 and 240 as illustrated provides a method 200 that electrically isolates the heater element when both the environmental condition is determined and an excitation signal 26 is present on occupant detection electrode 24.
Accordingly, a system 14 for determining an occupant proximate to a vehicle seat, a controller 22 for use in the system 14, and a method 200 for electrically isolating a heater element from an occupant detection electrode is provided. When a heater element 28 in a seat 12 is coupled to a heater voltage source VH to generate heat, the heater element 28 may influence an electric field 25 generated by an occupant detection electrode 24 in such a way as to interfere with determining an occupant 16 proximate to the seat. Depending on the arrangement of the electrode 24 and the heater element 28, such interference may be present at all times when the electrode 24 is connected to the heater voltage source VH, or may only be problematic when the seat 12 is wet with liquid moisture. By electrically isolating the heater element 28, the influence on the electric field 25 may be reduced so the process of determining if an occupant 16 is present in the seat 12 is not interfered with.
While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.
