System and Method of Occupant Detection with a Resonant Frequency

Abstract

An occupant detection system that includes an electrode, an electrical network, and a controller. The electrode is arranged to be proximate to an expected location of an occupant for sensing an occupant presence proximate the location. The electrode is configured to provide an electrode impedance indicative of the occupant presence. The electrical network is coupled to the electrode to form a resonant circuit and is configured to provide a network impedance. The resonant circuit is configured to exhibit a resonant frequency dependent on the network impedance and the electrode impedance. The controller is coupled to the resonant circuit and is configured to determine the resonant frequency and detect an occupant based on the resonant frequency.

1 . An occupant detection system comprising:
 an electrode arranged proximate to an expected location of an occupant for sensing an occupant presence proximate thereto, said electrode configured to provide an electrode impedance indicative of the sensed occupant presence;   an electrical network coupled to the electrode to form a resonant circuit, said electrical network configured to provide a network impedance, said resonant circuit configured to exhibit a resonant frequency dependent on the network impedance and the electrode impedance; and   a controller coupled to the resonant circuit, said controller configured to determine the resonant frequency and thereby detect an occupant based on the resonant frequency.   
     
     
         2 . The occupant detection system in accordance with  claim 1 , wherein the electrode is adjacent a seating surface of a vehicle seat to sense the occupant seated in the vehicle seat. 
     
     
         3 . The occupant detection system in accordance with  claim 1 , wherein said electrode impedance has an electrode capacitive part indicative of the occupant and an electrode resistive part indicative of an environmental condition, and wherein the controller detects an occupant based at least in part on the electrode capacitance part and the electrode resistive part. 
     
     
         4 . The occupant detection system in accordance with  claim 3 , wherein the environmental condition is humidity. 
     
     
         5 . The occupant detection system in accordance with  claim 3 , wherein said network impedance has a network inductive part that cooperates with the electrode capacitive part to influence the resonant frequency. 
     
     
         6 . The occupant detection system in accordance with  claim 5 , said controller comprising a signal generator coupled to the resonant circuit, said controller configured to output an excitation signal having an excitation frequency. 
     
     
         7 . The occupant detection system in accordance with  claim 6 , said controller comprising a voltage detector arranged to measure a network signal magnitude in response to the excitation signal. 
     
     
         8 . The occupant detection system in accordance with  claim 7 , said controller configured to vary the excitation frequency and measure the network signal magnitude to determine the resonant frequency and the environmental condition. 
     
     
         9 . The occupant detection system in accordance with  claim 8 , said controller configured to determine a wet seat fault condition based on the network signal magnitude being less than a threshold. 
     
     
         10 . The occupant detection system in accordance with  claim 1 , said system comprising an air bag module receiving an activation signal from the controller. 
     
     
         11 . The occupant detection system in accordance with  claim 1 , said electrical network impedance having a network capacitance part, and said controller configured to change the network capacitance part to reduce signal interference. 
     
     
         12 . A method for detecting a vehicle occupant comprising the steps of:
 arranging an electrode to provide an electrode impedance indicative of an occupant presence sensed proximate thereto;   coupling the electrode to an electrical network to form a resonant circuit that exhibits a resonant frequency indicative of the electrode impedance;   applying an excitation signal from a controller to the resonant circuit, said excitation signal having an excitation frequency;   generating a network signal in response to the excitation signal, said network signal having a network signal magnitude dependent on the electrode impedance;   measuring the network signal magnitude;   varying the excitation frequency;   determining the resonant frequency based on the network signal magnitude; and   detecting the presence of a sensed vehicle occupant based on the resonant frequency.   
     
     
         13 . The method in accordance with  claim 12 , wherein the step of determining the resonant frequency is based on determining an excitation frequency that causes a peak network signal magnitude. 
     
     
         14 . The method in accordance with  claim 12 , further comprising the step of determining an environmental condition based on the network signal magnitude. 
     
     
         15 . The method in accordance with  claim 14 , wherein the environmental condition is humidity. 
     
     
         16 . The method in accordance with  claim 15 , wherein the step of determining an environmental condition includes indicating a wet seat fault condition if the network signal magnitude is below a threshold. 
     
     
         17 . The method in accordance with  claim 12 , wherein the step of varying the excitation frequency includes selecting the excitation frequency from a list. 
     
     
         18 . The method in accordance with  claim 12 , further comprising the step of determining the activation status of an air bag module based on detecting the vehicle occupant. 
     
     
         19 . The method in accordance with  claim 12 , said electrical network impedance having a network capacitance part, said controller configured to change the network capacitance part, and said method further comprising changing the network capacitance part to reduce signal interference. 
     
     
         20 . A method for operating a vehicle occupant detection system comprising an electrode for sensing an occupant presence, an electrical network coupled to the electrode to form a resonant circuit, and a controller configured to output an excitation signal and measure a network signal magnitude, said method comprising:
 selecting an excitation frequency range and an excitation frequency step parameter for detecting an occupant presence;   outputting a plurality of excitation signals based on the excitation frequency range and the excitation frequency step parameter;   measuring a plurality of network signal magnitudes arising from the plurality of excitation signals;   determining a resonant frequency based on a maximum network signal magnitude;   detecting an occupant presence based on the resonant frequency; and   adjusting the excitation frequency range and the excitation frequency step parameter for performing another occupant detection at the adjusted values.