Patent Application
20110163765
The present invention generally relates to occupant sensing systems, and more particularly relates to a system and method for detecting an occupant on a vehicle seat that includes an electrode configured to generate a capacitance that is dependent on presence of an occupant.
Automotive vehicles are commonly equipped with air bags and other devices that are selectively enabled or disabled based upon a determination of the presence of an occupant in a vehicle seat. It has been proposed to place electrically conductive material in a vehicle seat to serve as an 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 an occupant detector for a vehicle seat assembly that includes an occupant sensing circuit that measures the impedance of an electric field generated by applying an electric signal to the electrode in the seat. The presence of an occupant affects the electric field impedance, particularly the load capacitance about the electrode that is measured by the occupant sensing circuit.
When the vehicle seat gets wet from liquid exposure such as from rain or spilled liquids, the electrical resistance of the seat typically changes significantly which, in turn, amplifies the difference between the transmitted and received signal amplitude. The occupant detection system generally may detect moisture in the seat and generate a wet set fault which may be used to illuminate a warning lamp to warn the passenger that the system is unable to operate properly due to the presence of liquid in the seat.
It would be desirable to provide for accurate sensing of occupancy of a seat using an electrode configured to sense capacitance of a load in a manner that effectively handles the wet seat scenario.
According to one aspect of the present invention, an occupant detection system is provided. The system includes a capacitive sensor comprising an electrode arranged in a seat proximate to an expected location of an occupant for sensing an occupant presence proximate thereto. The capacitive sensor is configured to provide an output indicative of the sensed occupant presence. The system further includes occupant detection circuitry for processing the capacitive sensor output and determining a wet seat condition and generating a wet seat fault based on a determined wet seat condition. The occupant detection circuitry further detects a state of occupancy of the seat based on the capacitive sensor output and the wet seat fault.
According to another aspect of the present invention, a method of detecting an occupant in a seat is provided. The method includes the steps of applying an alternating current signal to an electrode arranged in a seat proximate to an expected location of an occupant for generating an electric field at the expected location, detecting a voltage response to the electric field, and generating an output based on the voltage response indicative of a characteristic of an occupant. The method also includes the steps of detecting a wet seat condition, and generating a wet seat fault based on the detected wet seat condition. The method further includes detecting a state of occupancy of the seat based on the output and the wet seat fault.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring now to
The occupant detection system 20 is illustrated in
The ECU 60 is also shown having a signal generator 66 and a voltage detector 68. The signal generator 66 is configured to output a plurality of alternating current (AC) signals at different frequencies. This may include generating a first sine wave signal at a first frequency during a first time period and a second sine wave signal at a second frequency during a second time period. A total of n AC signals at n frequencies may be generated. The plurality of n signals may be output simultaneously or sequentially by the signal generator 66 and applied to the electrode 22 to generate an electric field proximate to the top side seat surface 14.
The signal generator 66 is configured to generate an electric field projected to a location at which an object (occupant) is to be detected, such as the top side seating surface 14 of the seat assembly 10. The impedance of a load affects the voltage response received by the voltage detector 68. The voltage detector 68 measures a voltage for each of the n frequencies at the n time periods. The measured voltages may depend upon the impedance of the load which may include impedance caused by an occupant and environmental conditions such as humidity, moisture from liquid and temperature.
It should be appreciated that the microprocessor 62 may include a plurality of noise filters (not shown) and may convert the measured voltages into digital voltage amplitudes. The voltage amplitudes may be compared to determine if a change in voltage has occurred amongst the plurality of frequencies. A change or difference in voltages is typically indicative of the presence of an environmental condition that will affect the impedance of a load.
The occupant detection system 20 advantageously processes the capacitive based sensor output and determines occupancy of the vehicle seat. The output of the occupant detection system 20 may be used to enable, disable or change the response of a vehicle air bag system or other vehicle systems. In some applications, deployment of an air bag may be enabled when a person or object of a specific size or shape is seated in the vehicle seat. The size of a person may be proportional to the person's impedance and will affect the voltage sensed by the electrode 22. Additionally, environmental conditions including a wet seat condition may affect the loading on the system, particularly the electrode 22. The electrode 22 may be compensated to actively control the deployment system(s) by compensating for the detected environmental condition(s).
The load includes the seat, any occupant and environmental conditions. The load generally acts as a high pass filter with a pole location of 1/(2πR(Cs+Cld)), where Cs is the sensed capacitance. The received signal RX may be represented by the following equation:
The capacitance related value QX may be defined by the following equation:
The capacitance related value QX may further be defined by the following equation:
Referring to
Returning back to step 106, if routine 100 determines that the frequency state is not in the transmit mode, routine 100 proceeds to step 118 to process the digital received RX filter. According to one embodiment, the RX filter uses a 1040 tap filter for the low frequency, and a 80 tap filter for the high frequencies. Next, routine 100 proceeds to decision step 120 to determine if the received RX sample_index is less than the received sample maximum minus two so as to determine whether or not RX signals have been received at all four frequencies. If the RX signals have not been received at all four frequencies, routine 100 proceeds to step 122 to increment the RX sample_index by one, and then determines in decision step 124 if the RX sample_index is within the gain sampling range and, if so, calculates a gain total at step 126. Otherwise, routine 100 ends at step 122. If the received signal has been received for all four frequencies, routine 100 proceeds to step 128 to calculate the peak-to-peak amplitude of the received RX signal for the current frequency. Next, at step 130, routine 100 performs a gain adjust to adjust the gain of the amplifier in the waveform generator to keep the average signal amplitude substantially constant. This may be achieved with a feedback loop to compensate for environmental effects, such as humidity. At step 132, routine 100 adjusts the ECU to calculate the QX raw value, which normalizes for variations in the ECU synthesizer chip, such that the output remains substantially stable. At decision step 134, routine 100 determines if the table index is equal to zero and, if not, ends at step 152. If the table index is set equal to zero, routine 100 proceeds to step 136 to calculate a noise flag and then proceeds to decision step 138 to determine if the table_index is less than the number of frequencies in the table minus one, which essentially checks for noise on each individual frequency signal. If the decision in step 138 is determined to be yes, routine 100 proceeds to step 140 to increment the table_index by one. Otherwise, the update algorithm classification flag is set at step 142. At decision step 144, routine 100 determines if the table_index is equal to the high frequency and, if so, sets the low select to low at step 146 before transitioning to the send TX signal at step 150 and ending at 152. Otherwise, the low select signal is set to high at step 148 before transitioning to the send TX signal at step 150.
Referring to
wherein QX is approximately on count per picofarad. At step 180, routine 160 may perform a buffer algorithm to buffer the data, before ending at step 182. Accordingly, it should be appreciated that the routines 100 and 160 advantageously provide for an output signal indicative of an occupant and the classification of the occupant based on the capacitive sensing.
The occupant detection system 20 may advantageously compensate for wet seat conditions of the seat and the sensor by adjusting the wet seat fault threshold, according to one embodiment. The detection system 20 employs the wet seat fault setting compensation routine 200 to periodically update wet seat faults. Additionally, occupant detection system 20 includes a wet seat fault clearing compensation routine 300 to periodically clear and update the wet seat fault settings so as to compensate for wet seat conditions.
The wet seat fault setting compensation routine 200 is illustrated in
The wet seat fault setting routine 200 thereby sets the wet seat fault when certain conditions are met. In the disclosed embodiment, routine 200 sets the wet seat fault when two conditions, namely, the difference between the low and high frequency QX values exceeds a fault limit and the resistance value exceeds a fault setting limit resistance value, simultaneously for a fault setting time period determined by the fault timer, such as sixty (60) seconds according to one example. If either of the two conditions does not exist, the wet seat fault timer is cleared and the wet seat fault is not set.
The wet seat fault clearing compensation routine 300 is illustrated in
Once set, the wet seat fault remains set for repeated uses until cleared by the wet seat fault clearing routine 300 which clears the wet seat fault when certain conditions are met. In the disclosed embodiment, routine 300 clears the wet seat fault when the conditions, namely, the difference between the low and high frequency QX values is less than the fault clearing limit and the calculated resistance value exceeds the fault clearing limit resistance value, simultaneously for a time period determined by the fault clearing timer, such as thirty (30) seconds according to one example. If either of the two conditions does not exist, then wet seat fault timer is cleared and the wet seat fault is not cleared.
The fault setting limit and the fault clearing limit values may be different values. According to one embodiment, the fault setting limit is greater than the fault clearing limit such that hysteresis is provided in the range between the two limit values. The fault setting limit resistance and the fault clearing limit resistance values may be different values. According to one embodiment, the fault clearing limit resistance is greater than the fault setting limit resistance, such that hysteresis is provided in the range between the two resistance values.
For each wet seat fault setting and clearing cycle, various parameters are recorded in non-volatile memory of the ECU. The recorded parameters may include the following: the wet seat fault occurrence counter representing the number of times the wet seat fault has been set (including the current occurrence); the vehicle engine ignition cycle counter value in the ignition cycle when the wet seat fault is set; the differential QX (low frequency−high frequency) value when the wet seat fault is set; the calculated seat resistance value when the wet set fault is set; and the ignition cycle counter value in the ignition cycle when the wet seat fault is cleared. According to one embodiment, the occupant detection system 20 records the above parameters for a set number X of wet seat fault setting clearing cycles, such as six cycles in one example. In one embodiment, the X event records include the first X−1 wet seat fault occurrences and the most recent wet seat fault occurrence.
The occupant detection system 20 may adjust the threshold value QX used to determine occupancy based on a wet seat fault occurrences. Multiple wet and dry cycles in a vehicle seat caused by repeated spills of liquid and/or exposure to rain may create a load capacitance offset in the seat. To compensate for changes caused by repeated wet seat faults in a seat, a wet seat fault occurrence counter may be used as an input to a lookup table to adjust the threshold, according to one embodiment. One example of a lookup table for providing wet seat fault compensation values based on the wet seat fault occurrence counter is provided in Table I below:
In the above Table I, the wet seat fault (WSF) occurrence counter has counts that correspond to the wet seat fault compensation of the QX value. Each counter value has a compensation value that corresponds thereto. The compensation value is used to increase the threshold value QX by the amount of compensation that corresponds to the WSF occurrence counter. Thus, for example, a count value of six provides a compensation of +25 to the QX value, according to the example shown. Thus, the occupant detection system 20 compensates for wet conditions of the seat based on the wet seat fault occurrences.
Accordingly, the occupant detection system 20 advantageously compensates for wet seat conditions detected in the seat and the sensor. Thus, changes due to the presence of liquid may be taken into consideration and compensated to provide for accurate occupant detection.
It will be understood by those who practice the invention and those skilled in the art, that various modifications and improvements may be made to the invention without departing from the spirit of the disclosed concept. The scope of protection afforded is to be determined by the claims and by the breadth of interpretation allowed by law.
