VEHICLE PASSENGER WEIGHT SENSORS

Abstract: A vehicle safety system has crash detection circuitry and an airbag (22) adjacent a vehicle seat further includes a system for determining the weight of a passenger on the vehicle seat. If the detected weight of the passenger does not exceed a predetermined weight threshold, the airbag is disabled. A forward sensor (44) and a rear sensor (46) are mounted in a vehicle seat adjacent a ferromagnetic structure element in the seat. The sensors measure strain on the ferromagnetic element (40), which is proportional to weight on the vehicle seat. A comparison of the measurements of the two sensors also provides an indication of the position of the passenger on the vehicle seat, such that the airbag may be disabled if the passenger is sitting too close to the airbag. Each of the sensors preferably employs an electromagnet (48) generating an oscillating magnetic field of a known frequency and a coil (50). Strain on the ferromagnetic element alters the magnetic field and such strain detected by the coil. The detected change in the magnetic field is proportional to the weight of the passenger.

Description: VEHICLE PASSENGER WEIGHT SENSORS The present invention relates to an improved system and method for detecting the weight of a person or thing seated within a motor vehicle, as may be useful in controlling actuation of a vehicle safety device such as a vehicle airbag. Current vehicles include an airbag for the driver as well as the front seat passenger. Manufacturers have sought to develop systems which would disable the passenger side airbag if the weight on the passenger seat is below a given threshold, thereby indicating either the present of an individual for whom the airbag would be dangerous or the absence of any passenger . Brief Description of the Drawings Figure 1 is a schematic for the vehicle safety system of the present invention; Figure 2 is a sectional view taken along line 2-2 of Figure 1 of the vehicle seat in Figure 1 ; Figure 3 is a sectional view similar to Figure 2 of an alternate seat frame structure; Figure 4 is a schematic view of an active sensor which can be used as the sensor of Figure 1; Figure 5 is a perspective view partially broken away of a passive sensor which can be used as the sensor in Figure 1; and Figure 6 is a sectional view of the sensor of Figure 5. DETAILED DESCRIPTION OF THE INVENTION A vehicle safety system 20 according to the present invention is shown in Figure 1 generally comprising a vehicle safety device 22, such as an airbag 22, installed forward of a vehicle seat 24 n a vehicle 26. The airbag 22 is shown installed forward of the vehicle seat 24 for illustrative purposes only, as side airbags are also well known, as are other vehicle safety devices 22 which would be installed adjacent an associated vehicle seat 24. The vehicle safety system 20 further generally comprises a weight system 28 measuring the weight on the vehicle seat 24. A microcontroller 30 controls operation of the vehicle safety system 20 based upon information from the weight system 28. The airbag 22 includes an actuator 32 and crash detection circuitry 34, such as is well known in the airbag art. The vehicle seat 24 includes a seating surface 36 over a foam cushion 39. The foam cushion 38 is supported by a support structure including at least one ferromagnetic element 40, such as a wire. The weigh system 28 preferably includes a forward sensor 44 measuring weight on a forward portion of the seat surface 36 and a rearward sensor 46 measuring weight on a rearward portion of the seating surface 36. As used herein, he terms "forward" and "rearward" refer to the position of the sensors 44, 46 relative to the airbag 22, such that the forward sensor 44 is closed to the airbag 22 than the rearward sensor 46. In the example of a forwardly positioned airbag 22, this would correspond to forward and rearward in the vehicle 26. Each sensor 44, 46 comprises a magnet 48 adjacent the ferromagnetic element 40 in the seat 24, such that the ferromagnetic element 40 lies within the magnetic field of the magnet 48. The magnet 48 can be a permanent magnet but is preferably an electromagnet. Each sensor 44, 46 further includes a coil 50 also positioned adjacent the ferromagnetic element 40. Signal processors 52, preferably including an amplifier 54, a band pass filter 56 and a comparator 58, receives a signal from each coil 50. Preferably, a function generator 60 excites the magnet 48 with a known function of a known frequency. In operation, the magnet 48 in each sensor 44, 46 preferably generates a sine wave magnetic field preferably between 100-50kHz which is received by the ferromagnetic element 40, thereby causing magnetic induction m the ferromagnetic element. An electromotive force voltage induced in the coil 50 by the magnetic induction and received by the signal processor 52. The signal is amplified by the amplifier 54 and filtered by the band pass filter 56. Preferably, the band pass filter 56 passes the third harmonic of the frequency of the magnetic field generated by the magnet 48. For example, for a magnet 48 generating a sinusoidal magnetic field at 20 kHz, the band pass filter 56 preferably sends the signal representing the 30 kHz component to the comparator 58, where the magnitude of that signal is compared to a given threshold. When a weight, such as a passenger, is placed upon the seating surface 36 of the vehicle seat 24, the weight is transmitted through the seating surface 36, foam cushion 38 to the ferromagnetic element 40, thereby inducing strain n the ferromagnetic element 40. The strain in the ferromagnetic element 40 alters the magnetic field and the electromotive force voltage generated by the coil 50. By measuring the amplitude of the third harmonic of the signal generated by the coil 50. By measuring the amplitude of the third harmonic of the signal generated by the coil 50, the weight upon the seating surface 36 can be determined and indicated to the microcontroller 30. The actuation of the airbag 22 is altered n several ways based upon information from the sensors 44, 46. First, if the total weight measured by the sensors 44, 46 does not exceed the predetermined threshold, the microcontroller 30 disables the vehicle safety device 22. Therefore, even if the crash detection circuitry 34 indicates a crash of sufficient magnitude, the actuator 32 will not activate the airbag 22. Alternatively, the microcontroller 30, based upon the total weight measured by the sensor 44, 46 could alter the activation of the airbag 22 by the actuator, such as reducing the speed of deployment of the airbag 22 when a passenger of lower weight is detected. Further, based upon the difference in the measured weight between the forward sensor 44 and the rearward sensor 46, the microcontroller 30 can determine the appropriate position of the passenger on the seating surface 36 relative tot he airbag 22. If the microcontroller 30 determines that the passenger is seated on the forward portion of the seating surface 36 (i.e. too close to the airbag 22), the microcontroller disables actuation of the airbag 22 or alters the deployment of the airbag 22, such as reducing the speed of deployment. Alternatively, if the magnets 48 are permanent magnets, the signal processor 52 and microcontroller 30 detect only changes in the strain on the ferromagnetic elements 40. The weight of the passenger is determined by determining when no passenger is present on the seating surface 36 and measuring the change in strain on the ferromagnetic element 40 as the passenger sits on seating surface 36. It should be recognized that the signal processor 52 and its components could be replaced by software implemented by the microcontroller 30. Digital filters and comparators are well within the skill of the art. Further, it is anticipated that additional filters, smoothing functions, or algorithms in general would be implemented to account for transient changes in weight, such as the passenger shifting his weight. The positioning of the sensors 44, 46 in the vehicle seat 24 is more particularly shown in Figure 2. A known vehicle seat 24 generally comprises a seat frame 66 having a plurality of springs 68 attached at a forward end 70 of the seat frame 66 and connected to a rod 72. Complementary rearward springs 47 attached to a rearward end 76 of the seat frame 66 are also attached to a rod 78. The ferromagnetic elements 40, such as wires, are strung between the two rods 72, 78. Preferably, the sensors 44, 46 are ;positioned adjacent the same ferromagnetic element 40. The forward sensor 44 is positioned generally between he rearward sensor 46 and airbag 22. In this manner, the proximity of the passenger relative tot he airbag 22 can be estimated. Figure 3 shows the position of the sensors 44,46 when the orientation of the seat frame 66 relative to the airbag 22 is rotated 90° degrees from that shown in figure 2. In this case, the forward sensor 44 is preferably mounted adjacent a forward ferromagnetic element 84 and the rearward sensor 46 preferably mounted adjacent a rearward ferromagnetic element 86. In any configuration, the forward sensor 44 is preferably located forward of the rearward sensor 46, wherein the term "forward" indicates a direction generally toward the airbag 22. Figure 4 illustrates a sensor 90 which can be sued as the forward sensors 44, 46 in Figure 1. The sensor 90 generally comprises a ferrite core 92 having a excitation coil 94 which when driven by the function generator 60 forms the magnet 48. The sensor 90 further includes a coil 50 which is also preferably coiled about the ferrite core 92. Figures 5 and 6 show an alternate passive sensor 104 which can be used as the sensors 44, 46 in Figure 1 with a permanent magnet 106. The permanent magnet 106 is generally cylindrical having a diametrically extending channel 108 forming a first let 110 and a second leg 112. Wire 114 is coiled about the first leg 110 and subsequently about the second let 112. The sensor 104 further includes a stainless steel casing 120 and about an epoxy 122.

Claims: CLAIMS : 1. A system for measuring a weight upon a seating surface within a motor vehicle, said system comprising: a ferromagnetic element (40) mechanically coupled to the seating surface (36) such that strain is induced in said ferromagnetic element responsive to the weight thereon; and a first sensor (46) generating a magnetic field, said magnetic field altered by said strain in said ferromagnetic element, said first sensor generates a signal based upon the alteration in said magnetic field. 2. The system for measuring a weight upon a seating surface within a motor vehicle of claim 1, wherein said first sensor (46) comprises a magnet (48) generating a magnetic field, said magnet mounted on the vehicle adjacent said ferromagnetic element (40) . 3. The system for measuring a weight upon a seating surface within a motor vehicle of claim 2, wherein said first sensor (46) further comprises an inductor (50) mounted on the vehicle adjacent said ferromagnetic element (40), said inductor generating a signal based upon said magnetic field and said strain in said ferromagnetic element. 4. The system for measuring a weight upon a seating surface within a motor vehicle of claim 2, wherein said magnet (48) is a permanent magnet. 5. The system for measuring a weight upon a seating surface within a motor vehicle of claim 3, wherein said magnet (48) is an electromagnet, said inductor (50) including a coil. 6. The system for measuring a weight upon a seating surface within a motor vehicle of claim 1, further includes an actuator (32) for a vehicle safety device (22), said actuator actuating said vehicle safety device based upon said signal from said first sensor (46) . 7. The system for measuring a weight upon a seating surface within a motor vehicle of claim 6, further including a second sensor (44) mounted adjacent said ferromagnetic element (40) closer to said vehicle safety device (22) than said first sensor (46) and said second sensor, said actuator (32) actuating said vehicle safety device based upon said signals from said first and second sensors and a comparison of said signals from said first and second sensors. 8. The system for measuring a weight upon a seating surface within a motor vehicle of claim 1, wherein said first sensor (46) measures variation in stain in said ferromagnetic element (40). 9. The system for measuring a weight upon a seating surface within a motor vehicle of claim 1, further including a signal processor (52) analyzing a third harmonic of said signal from said first sensor (46) . 10. The system for measuring a weight upon a seating surface within a motor vehicle of claim 9, wherein said signal processor (52) includes a filter.

Inventors: GIOUTSOS TONY, GIOUTSOS, TONY
Applicants: BREED AUTOMOTIVE TECH, BREED AUTOMOTIVE TECHNOLOGY, INC.
Application year: 1998
Main classification: G08B21
IPC codes: B60K28, B60N2, B60R21, G01G3, G01G19, G01L1