Seat control structure for occupant classification systems

An occupant classification system is provided based upon the use of an array of electrical switches arranged between a seat trim and a reactive surface. The switches produce selective outputs signals as an engaging surface makes contact with one or more of the switches when an occupant occupies the seat. The output signals are interpreted into a control signal to distinguish between occupants for controlling an inflatable restraint system. The occupant classification system also includes a control structure which defines a distance between the array of switches and the engaging surface that is greater than zero when the seat is unoccupied so that the switches are insensitive to the initial forces applied to the seat through the seat trim. The distance between one or more of the switches and the engaging surface decreases to zero when the occupant occupies the seat to produce the selective output signals.

FIELD OF THE INVENTION

This invention relates to a system for classifying occupants of a motor vehicle, specifically for purposes related to its inflatable restraint system.

BACKGROUND OF THE INVENTION

Air cushion restraint systems or inflatable restraints have been in use for several decades in automobiles. These systems have demonstrated their effectiveness in reducing occupant injuries in the event of vehicle impacts. Inflatable restraints are typically used to provide frontal impact protection, and variants are used for protection in side impact conditions. These systems generally incorporate a gas generator, referred to as an inflator, coupled with a flexible fabric bag which is stored in a folded condition and is inflated by the gasses generated by the inflator upon receiving a deployment signal. These devices are stored behind interior compartment panels and are normally hidden from view. Various types of impact sensors are located at strategic locations around the vehicle to detect the deceleration forces associated with a vehicle impact. A restraint system controller receives crash sensor inputs, evaluates them, and sends an appropriate deployment signal to initiate the deployment sequence when the sensors detect a particular crash-type and severity level.

Designers of inflatable restraint systems have made significant advancements in the design and manufacture of such systems. One area of development has been in the design of multiple level inflator systems. These systems incorporate an inflator capable of modulating the volume of produced gas and the deployment timing sequence as needed for a particular category of occupant or type of impact. In order for such systems to properly adapt to the occupant, some type of sensing system is needed to classify the occupant within certain ranges of seating height, mass, etc.

Frontal impact inflatable restraint systems are designed for seated occupants within a given seated height and mass range. Presently available inflatable restraint systems are not intended to provide impact protection for belted child restraints, or for various small sized children occupants. For these particular types of occupants, it is preferred to disable the inflatable restraint system entirely for that designated seating position.

Disabling an inflatable restraint for a given designated seating position may be accomplished through a manual driver input as is currently done with certain presently available vehicles. This approach is primarily provided for two-passenger vehicles where it may be necessary for a driver to place a child restraint seat in the front passenger seat of the vehicle. In such cases, the driver has a keyed switch to disable the inflatable restraint system for that designated seating position. Although such a manual inflatable restraint override switch is effective when used properly, there are concerns both by automotive manufacturers and governmental regulatory authorities that such an approach is cumbersome and unreliable. Improperly used, such systems can result in inappropriate deployment in some instances, and deactivation in conditions where the system could provide impact protection for the seated occupant.

In order to overcome the disadvantages of a manually operated inflatable restraint override switch, manufacturers have investigated and developed a number of technical solutions which automatically evaluate an occupant sitting in a vehicle. Examples of such automated systems include ultrasonic ranging systems which evaluate a sonic return signal as a means of classifying an occupant. Another general category of such occupant classification systems include the use of seat carried sensors. The seats are instrumented with a number of sensors which are activated to produce signals which are interpreted by the inflatable restraint system controller. Such switches may sense pressure, force, displacement, or may be sensitive to an electrical signal parameter such as capacitive coupling. Although such systems have proved effective, there is a continuing need to improve their reliability, ease of assembly, and enable the outputs of the seat sensors to be processed rapidly.

SUMMARY OF THE INVENTION

In accordance with the present invention, an occupant classification system is provided based upon the use of an array of electrical switches arranged beneath the seat cushion. These switches are placed in strategic locations or zones. Through the use of the data analysis techniques in accordance with this invention, occupant classification can be conducted rapidly and reliably.

In some embodiments, the array of electrical switches is arranged between a seat trim and a reactive surface. The switches produce selective outputs signals as an engaging surface makes contact with one or more of the switches when an occupant occupies the seat. The output signals are interpreted into a control signal to distinguish between occupants for controlling an inflatable restraint system. The occupant classification system also includes a control structure which defines a distance between the array of switches and the engaging surface that is greater than zero when the seat is unoccupied so that the switches are insensitive to the initial forces applied to the seat through the seat trim. The distance between one or more of the switches and the engaging surface decreases to zero when the occupant occupies the seat to produce the selective output signals.

Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

A seat assembly incorporating the features of this invention is illustrated in an exploded manner inFIG. 1and is generally designated there by reference number10. Seat assembly10principally comprises seat cushion12and seat back14which provide the primary seating surfaces for the occupant. Underlying seat cushion12and providing structural support for the seat assembly10is seat suspension assembly16. A number of individual electrical switches20, such as on/off switches, are arranged in a desired pattern and carried by switch array mat18. As will be explained in further detail later in this description, the outputs of on/off switches20from mat18may be analyzed in a variety of manners to provide signals concerning the type of occupant occupying the seat assembly10.

The outputs from the individual on/off switches20of mat18are processed using microprocessor based controller22. Controller22receives inputs from crash sensors (not shown) on lines24and outputs an inflation signal on line25based on internal logic signal processing.

As further shown inFIG. 1, a belt restraint system36is provided for seat assembly10. The belt restraint system includes a belt tension sensor or other high belt load indicator38. Sensor38is provided to identify seat belt tension loads that are higher than the comfort level of a normally seated adult occupant. Controller22receives the outputs from sensor38on line27and disables the associated inflatable restraint system when high belt loads are detected which are associated with cinching a child seat in position within seat assembly10. Since belt loads on a child's seat can cause switches20to turn-on in a manner similar to a heavier occupant, the belt tension sensor38is required to measure a belt tension load which exceeds some threshold of, for example, twenty or thirty pounds or higher, to indicate to the system that a small occupant with a large belt load on the child's seat is present.

Various designs of on/off switches20may be used in connection with this invention.FIG. 2illustrates in a cross-sectional view the construction of one of the on/off switches20. As illustrated, the switches20are placed between seat foam layer26and a flexible plastic sheet28which directly contacts seat suspension16. An elastomeric dome structure30supports switch contact32. When compressed by a sufficient force, dome structure30collapses and switch contact32falls into physical contact with switch contacts34carried by switch base sheet29bridging those contacts to provide a closed electrical circuit. Switches such as these are referred to electrically as single-pole, single-throw, normally-open types.

A preferred material for forming elastomeric dome structure30is silicone rubber, which is believed to provide a desired level of performance, ruggedness, and reliability. Plastic sheet28over the suspension system16provides a stable surface for the activation forces on switches20. The force necessary to close the contacts for switches20would be based upon experimental investigation. In one implementation of the present invention, on/off switches20were selected having a turn-on force of 3.86 N (exerted in a direction compressing dome30downwardly). Other seat configurations would likely require different turn-on forces necessary to distinguish between occupants such as adult and child occupants.

Other configurations of switches20may be used with this invention such as normally closed types in which an electrical circuit is opened when a force exceeding a threshold level acts on the switch. Further, other switch variations could be used for detecting displacement, force, or pressure acting on the seat such as variable resistors which provide a range of outputs over a continuum.

Switches20are located to detect the critical pressure points by a process used for initially selecting the switch locations for a particular motor vehicle and seat application. Implementations can detect various types of occupants for use with multiple level inflators. In an initial calibration and design process, various occupants and FMVSS 208 anthropoids are placed in seat assembly10. During that initial design process, a switch array mat having a large number, for example 2,016 individual pressure cells or switches, are located and carried by the array mat. The critical pressure points are identified from the signals generated from the array of switches for different sized occupants, with and without child seats, with and without different seat belt tensile loads, at the various seat back14recline angles. Various types of occupants which would include fifth, fiftieth, and ninety-fifth percentile male and female, and various sized child anthropoids along with various child restraint systems, are installed in the seat. Electrical signal patterns are developed by the individual switches, are analyzed for each condition. Based on the particular patterns of activation, a smaller number of on/off switches20are strategically located on mat18. In the example illustrated, array mat18features seventy switches20.

For any of the examples above, if a seat belt tension load above a predetermined level is sensed by the belt tension sensor38, the associated inflatable restraint system is disabled, irrespective of the activation pattern of switches20.

The classification system also incorporates other features which control the forces acting on the switches20. For purposes of illustrations,FIG. 3Adepicts the forces acting on a standard seat structure60. In particular, a total force F(t) is generated by the assembly of a seat trim62, a foam layer26of the seat cushion, and a seat pan66. This force F(t) is equal to the sum of the attachment forces FA1and FA2applied at the edges of the fabric or trim62covering the seat60. The force F(t) can range from zero to an unknown value and may also change over the life of the vehicle.

The attachment forces FA1and FA2affect the pressure and displacement of the “A” and “B” surfaces of the foam layer26. These surfaces are typically the installation locations for an occupant classification sensor that measures pressure, displacement, and/or force produced when an occupant sits in the seat60. For example, there is shown inFIG. 3Ba sensor63positioned between the “B” surface of the cushion26and the seat pan66. In such an arrangement, variations in the assembly process, part tolerance, and material aging have a direct affect on the sensor's63ability to classify occupants accurately and reliably over time because of the variability of the forces (indicated by the downward arrows) imparted on the sensor63.

Because of the variability of the force F(t) that may occur over time, in accordance with the invention, a control layer or control structure68is positioned between the “B” surface and the seat pan66, as shown inFIG. 3C, thereby defining a control interface region69between “B” surface of the foam layer26and the sensor63. Functionally, the control layer68controls the forces applied to the sensor63by generating a reaction surface71around the sensor63, for example, and therefore removes the variations and errors that affect the sensor's performance. The distance between the sensor63and the foam layer26and the compressibility of the control layer68can be modified to compensate for the different pressures, displacements, and/or forces (indicated by the downward arrows) that occur over time. For example, the greater the thickness of the control layer68, the greater the distance between the sensor63and the actuation surface “B”, resulting in an increase in tolerance for variations in the attachment forces FA1and FA2. That is, the larger effective distance between the sensor63to the actuation surface “B” results in more force being necessary to generate the required displacement or pressure on the sensor63. Further, the gap, d, between the control layer68and the sensor63also affects the amount of force that has to be applied through the seat to cause the actuation surface “B” to contact the sensor63. For example, as the gap, d, is increased, the effective length of the actuation surface “B” between the left and right portions of the control layer68is increased. As such, less force is needed to cause the actuation surface “B” to contact the sensor63.

Moreover, the compressibility or rigidity of the control layer68also affects its performance. That is, as the stiffness or rigidity of the a control layer68increases, the control layer68compresses less for a given amount of force applied to the control layer68. Accordingly, more force is necessary to generate the desired pressure on and/or displacement on the sensor63.

In conjunction with the sensors63, the control layer68creates a foam to sensor layer control interface region. Thus, such a combination may be used to create an occupant classification system that is used in a vehicle seat system. As such, the occupant classification system may be used to enable or suppress an air bag control system to meet FMVSS 208 requirements.

The use of the control layer68differs from other types of strategies that sense the occupant with sensors that are always in contact with the bottom or “B” side of the cushion foam layer26. In particular, aspects of the invention employ a frame to control the interface between the foam layer26and the sensor63. The frame allows the system to be tuned independently of the sensor63to compensate for variations in seat designs, foam design, and trim tension variations. In addition, the control layer68may be located in the seat to calibrate the sensor63to certain occupant sizes and positions.

As discussed in detail below, the control layer68can be a frame that totally surrounds the sensor system (FIGS. 4A and 4B). Alternatively, the control layer68can be strips of specific geometry placed at discrete locations near the sensor63(FIGS. 7A and 7B).

FIGS. 4A and 4Bdepict an integrated unit70including the sensor63surrounded by the control layer68. The sensor63may include an array of switches such as the on/off switches20carried by the array mat18. The control layer68has a thickness of D1, and the difference between D1and the height of the switches20define the control interface region69(as identified inFIG. 3C) with a thickness D2. Thus, as a compressive load is applied to the control layer68when an occupant sits on the seat centered more or less in the X-Y plane over the occupant midsagital plane, D1and of course D2decreases in the Z direction. Although the “B” surface is not initially in contact with the switches20when the seat is unoccupied, D2ultimately decreases to zero so that contact is made between the “B” surface and one or more switches20when the occupant sits in the seat. In some configurations, once contact is made between one or more switches20and the “B” surface, the respective switch produces an “on” signal. Alternatively, the switch may produce a variable output related to the amount of load applied by the “B” surface to the switch.

Accordingly, the integrated unit70manages and maintains the interface between the “B” surface of the seat foam layer26and the sensor system63. This enables the sensor system63to cope with, and maintain, various trim tension levels applied to the trim62covering the seat foam layer26. Moreover, the integrated unit70defines the surface area for the interface between the “B” surface and the sensor system63. This enables the sensor system63to define and control a particular pressure area interface with this sensor system63for different load geometries. By defining and managing the distance between the bottom or “B” surface of the seat cushion26and the top of the sensor system63, the integrated unit70establishes a no load condition for the sensor system63during empty seat conditions, enables the sensor system63to manage and maintain sensitivity, and enables the sensor system63to have different sensitivities for different zones, as discussed in greater detail in connection withFIGS. 7A and 7B.

The integrated unit can be used in various types of seating configurations. For example,FIGS. 5A and 5Bdepict the integrated unit70employed in a bucket seat72with a seat cushion74and a seat back76. The seat cushion74and the seat back76provide the primary seating surfaces for the occupant. A recliner unit77couples the seat cushion74to the seat back76and allows the seat back76to recline or move forward relative to the seat cushion74, for example, to allow access to the back seat of the vehicle. The integrated unit70is positioned between the “B” surface of the seat cushion74and a cushion frame or pan78. The pan78slides along an upper rail80and a lower rail82combination. The lower rail82is mounted on top of a riser84which is supported by a set of feet86bolted to the floorboard of the vehicle. Thus, as an occupant sits on the “A” surface of the seat cushion74, the seat foam layer26compresses and imparts a force through the “B” surface to the integrated unit70.

Referring now toFIGS. 6A and 6B, there is shown a bench style seat90with a pair of integrated units70aand70bpositioned between the seat foam layer26and the frame or pan78, where features similar to those shown inFIGS. 5A and 5Bare designated by like reference numerals. Such an arrangement creates multiple, isolated sensing locations within a seat sensor system. This enables the sensor system to accommodate simultaneous loading of multiple occupants in a bench style seat system while maintaining isolation between the loading conditions. Moreover, the sensor system creates isolated calibration and sensing areas for the sensor system to accommodate multiple seated occupants and to control area specific sensitivity.

In another embodiment, rather than totally surrounding the sensor63, the control layer of the integrated unit70can be arranged as strips or segments of specific geometries68a-68g,as depicted inFIGS. 7A and 7B. As shown, the control layer includes a set of four elongated strips68a,68b,68c,68d,two smaller rectangular segments68e,68f,and a circular segment68g.The strips68a,68bdefine an interior region96, while the strips68c,68ddefine an interior region98, with each region96,98being occupied by a number of sensors20. A region100is located between the rectangular segments68e,68f,where a pair of sensors20reside outside the circular segment68g,and a fourth region102is located within the region100, as defined by the interior of the circular segment68g,in which a single sensor20resides.

The arrangement of the control layer strips and segments68a-68gdefine the shape and geometry of the cushion foam interface to the sensor63and creates individual zones within a sensing system to facilitate calibration of the system. This arrangement also enables the sensor system to establish and maintain different sensitivity levels for different areas of the seat, enables the sensor system to be less sensitive to certain loading conditions and profiles, and enables the sensor system to be less sensitive to child restraint system loading conditions.

Although the control layer68and sensor63are described above as a single integrated unit70, these components can be assembled in a number of configurations. For example, as shown inFIGS. 8A and 8B, the control layer68is formed as part of the seat foam layer26, while the sensor63is carried by the reactive layer71. When assembled, the reactive layer71and the seat foam layer26are brought together such that the sensor63resides within the interior of the control layer68.

Referring now toFIGS. 9A and 9B, the control layer68is formed as part of the reactive layer71, and the sensor63is carried by the reactive layer71and positioned in the interior region of the control layer68. The unit is assembled by matting the seat foam layer26to the control layer68.

Another configuration is illustrated inFIGS. 10A and 10B, where the control layer68is formed as part of the sensor63. The combined unit63,68is mounted to the reactive layer71, and the final assembly is formed by mating the control layer68to the seat foam layer26.

The “B” surface may be provided with a material or surface treatment that interfaces with the switches20. As an example, the surface treatment is provided in an integrated unit100(FIGS. 11A and 11B) as a load diffusion layer102(FIG. 11B) with a thickness t positioned a distance D3below the surface “B”. As shown, the diffusion layer102resides inside the control layer68, covering the entire array of switches20. Alternatively, the diffusion layer may reside on top of the control layer68or it can be part of the control layer assembly resting on top of the switches. In some configurations, the diffusion layer102is attached directly to the “B” surface. Depending on the application, the load diffusion layer can be a plastic sheet, a fabric type material, or any other suitable material. The diffusion layer can be used to control wear on the various seat components and/or noise generated by the seat structure. Thus the surface treatment material can be used to prolong the age of the seat foam, as well as affect the product performance of the seat over its lifetime.

While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims. For example, it is not necessary that the switches20are on/off switches. Other types of switches can be used, such as analog switches or any other types of suitable switches. The switches may for instance provide a range of outputs rather than a single “on” signal when contact is made. Moreover, the control structure or layer68and the associated sensor63may be located in other parts of the seat, such as the seat back.