Abstract:
A vehicle weight classification system determines the weight of a seat occupant for controlling airbag deployment. Strain gauge sensors preferably provide signals having a magnitude that is indicative of the weight of the seat occupant. A converting module converts the sensor signals into timing information. A microprocessor, which includes a timer module, receives the timing information and makes a weight determination from the timing information.

Description:
RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Application No. 60/152,426, which was filed on Sep. 3, 1999. This application is a Continuation-in-Part of U.S. application Ser. No. 09/548,485, filed on Apr. 13, 2000, which is a continuation of application Ser. No. 09/191,719, which was filed on Nov. 12, 1998, now U.S. Pat. No. 6,070,115, which claims the benefit of U.S. Provisional Application No. 60/065,115, which was filed on Nov. 12, 1997. 

   BACKGROUND OF THE INVENTION 
   In general terms, this invention relates to vehicle weight classification systems for classifying the weight of an occupant on a vehicle seat. More particularly, this invention relates to a signal processing system and method for handling weight information in a vehicle weight classification system. 
   Modern day vehicles typically include safety restraints to protect passengers and drivers during impact. Such restraints include seat belts and airbags, for example. It has recently become apparent that customized control of airbags is desirable. The owner of this application has developed a vehicle weight classification system that is useful for determining the size or weight of a seat occupant and controlling an airbag deployment responsive to that determination. 
   One of the challenges in designing a weight classification system is keeping the system simple and robust. For example, there are limited choices among sensor arrangements that will provide desired results over the life of a vehicle seat. Additionally, space constraints and economic considerations place limitations on the components to be included in such a system. 
   One particular challenge is presented in processing signals that are available from conventional-type sensors that provide signals indicative of the seat occupant&#39;s weight. In one example, strain gauge sensors are used in a vehicle seat. The strain gauge sensors provide electrical signals indicative of the weight on the seat. Typical strain gauge sensor output, however, is not readily usable by a microprocessor with out special modification. The sensor signals are typically too weak to be immediately recognized. Further, typical analog-to-digital converters provided on conventional microcontrollers do not have sufficient resolution capability to make an accurate enough weight determination. 
   This invention provides a solution that converts such sensor signal information into a useful form that is readily used within a single microcontroller that preferably is also responsible for other operations of the weight classification system. 
   SUMMARY OF THE INVENTION 
   In general terms, this invention is a vehicle weight classification system useful for determining the size or weight of a seat occupant in the vehicle. A system designed according to this invention includes at least one sensor that provides a signal indicative of the seat occupant&#39;s weight. A converting module converts the sensor signal into timing information. A controller has a timer module that communicates with the converting module such that the controller determines the weight of the seat occupant as sensed by the sensor from the timing information. Using the timing information allows the controller to more accurately and more readily make a weight determination. 
   A method according to this invention includes several basic steps. First, the signal indicating the weight is generated. Next, timing information from that signal is determined. The weight information is then determined from the timing information. In a preferred embodiment, the timing information is received by a timer module on a microprocessor. The microprocessor preferably determines the weight information based upon the timing information rather than directly from a signal directly from the sensor. 
   The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  diagrammatically illustrates a system designed according to this invention. 
       FIG. 2  is a schematic diagram illustrating a preferred embodiment of circuitry used with this invention. 
       FIG. 3A  is a graphical illustration of a reference signal used with this invention. 
       FIG. 3B  is a graphical illustration of a preferred final output signal used with this invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A vehicle weight classification system  20  is schematically illustrated in  FIG. 1. A  seat  22  includes a seat back  24  and a seat base portion  26 . A plurality of sensors  28  are associated with the seat  22  and preferably supported in the seat base  26 . The sensors  28  preferably are strain gauge sensors that provide an electrical signal indicative of a seat occupant&#39;s weight. 
   The signals from the sensors  28  are processed by a converting module  30 , which provides timing information corresponding to the magnitude of the signals from the sensors  28 . The magnitude of the sensor signals preferably is indicative of the seat occupant&#39;s weight. Although a single converting module  30  is illustrated for discussion purposes, it is within the scope of this invention to provide an individual converting module associated with each individual sensor  28 . 
   A system controller  32  preferably includes a timer module  34  that communicates with the converting module  30 . The timer module  34  receives an output from the converting module and the controller  32  preferably is programmed to use timing information from the output of the converting module  30  as the basis for determining the seat occupant&#39;s weight. 
     FIG. 2  schematically illustrates a preferred embodiment of the converting module  30 . An output  40  from each sensor  28  preferably is amplified using an amplifier  42 . The preferred embodiment of the amplifier  42  is a two-stage amplifier including a first stage  44  and a second stage  46 . The amplified sensor signal  48  is provided to a comparator  50 . The other input  52  to the comparator  50  is an output of a reference signal generator  54 . In the illustrated example, the reference signal generator is an integrator that is provided with a reference voltage from the voltage reference circuit  56 . A reset circuit  58  preferably is provided so that the reference signal  52  has a time-dependent pattern or cycle. A temperature sensor and zero control circuit portion  60  preferably senses temperature and provides signal zero function. The temperature information preferably is used by the controller to compensate for temperature behavior of this strain gauge signal  40 . The same output  80  can be used as a zero function command input by the controller. Zero function preferably is used to short out the strain gauge input signal to measure the weight signal zero off set. The zero off set measurement then preferably is compensated in the controller such that the signal is properly processed to ascertain the weight information. 
   In one example implementation of this invention, the reference signal generator  54  provides a saw-tooth shaped signal  52  as seen in FIG.  3 A. The amplified sensor signal  48  and the reference signal  52  preferably are provided to the comparator  50 , which provides an output  70  that includes timing information that is received by the timer module  34  on the controller  32 . The plot  72  in  FIG. 3A  graphically illustrates a relationship between the amplified sensor signal  48  and the reference signal  52 . 
     FIG. 3B  is a plot  74  of pulses  76 , which comprise the output  70  from the comparator  50 . In the illustrated example, whenever the reference signal  52  has a value that is greater than the magnitude of the amplified sensor signal  48 , the comparator  50  provides a logic high output until such time that the reference signal falls below the magnitude of the amplified sensor signal  48 . This relationship between the amplified sensor signal  48  and the reference signal  52  provides timing information that is indicative of the weight of the seat occupant. In the illustrated example, the width of each pulse  76  is interpreted by the controller  32  to determine the seat occupant&#39;s weight. The controller  32  preferably is programmed to utilize the timing information from the output  70  of the comparator to make an appropriate weight determination. Given this description, those skilled in the art will be able to appropriately program a commercially available microprocessor to accomplish the results needed for a particular situation. 
   A significant advantage to this invention is that output signals from sensors, such as strain gauge sensors, are converted in a manner that enables a conventional microprocessor to make a more accurate weight determination. If, for example, the sensor outputs were fed directly to an analog-to-digital converter on the microprocessor, there typically is not enough resolution to make an accurate weight determination. Further, the nature of such output signals of such strain gauge sensors does not lend itself to be readily and accurately handled by a microprocessor to make a weight determination. Utilizing a signal converting module  30  designed according to this invention provides greater accuracy in making a weight determination than would otherwise be available using typical microprocessors. 
   The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art that do not necessarily depart from the purview and spirit of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims.