Occupant determination apparatus using load sensor

An occupant determination apparatus includes a load sensor and a determination section. The load sensor detects a load of an occupant seated in a seat of a vehicle to provide the detected load as a load signal. The determination section determines presence or absence of the occupant and a physical size of the occupant by classifying the load signal into a subject class among a plurality of classes that are ordered from small to large according to the physical sizes based on predetermined threshold loads. The subject class is stored as a determined class. The determination section permits the determined class to transition from a present class to an immediately adjacent larger class when the load signal equal to or larger than a threshold load between the present class and the immediately adjacent larger class continues being received for a threshold time.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on Japanese Patent Application No. 2013-71477 filed on Mar. 29, 2013, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an occupant determination apparatus in a vehicle for determining an occupant in the vehicle using a load sensor provided in an in-vehicle seat to suitably a control safety apparatus against collision such as an airbag.

BACKGROUND ART

In order to control inflation of an airbag, it is desirable to (i) recognize beforehand the physical size of an occupant, who is to be protected and (ii) control an inflation mode of the airbag. To that end, a load sensor has been built into a vehicle or a seat in the vehicle to provide an output voltage according to a load due to an occupant. The output voltage is then classified into one of classes (i.e., states) including a vacant seat class, a child class, an adult class, etc. based on predetermined threshold loads.

The output of a load sensor varies according to the change in occupant's posture or an acceleration G at travel motion. The resultant change in the output of the load sensor provide outputs of temporary incorrect determination when threshold values are fixed.

Patent Literature 1 discloses a technology to overcome such an issue, for example. The technology includes a load sensor to detect a load, which is applied to a seat in a vehicle; and a determination section to determine (i) presence or absence of an occupant and (ii) the physical size of the occupant by classifying the detected load into one of several classes using predetermined class threshold loads. When a detected load continuously remains in a subject class among a plurality of classes longer than a predetermined threshold time (duration), an inter-class transition into the subject class is determined to have arisen. Mutually different predetermined threshold times are prepared to at least some of the inter-class transitions.

Incidentally, in order to improve occupant protection, the number of classes of occupant physical sizes tends to increase to realize an airbag control that can respond to an individual occupant physical size. To that end, an occupant determination apparatus is also required to prepare multiple classes of occupant.

Patent Literature 1 discloses an example that classifies an occupant state into three classes of (i) a vacant seat class, (ii) a child class; and (iii) an adult class. One of the conditions of loads for such classification is as follows. For example, when the child class is in between the vacant seat class and the adult class, the child class is determined by whether a load W is detected in between a threshold load Wth2for the vacant seat class and a threshold load Wth1for the adult class.

SUMMARY

The present Inventor considered the following. Suppose a case of increasing the number of classes in Patent Literature 1 by dividing the adult class into a large adult class and a small adult class. Such a case causes the following issue. Some factor such an improper posture of an occupant being a large adult may involve an incorrect determination that mistakenly determines the large adult as being classified into the child class. The occupant then adjusts their posture more properly; this increases a detected load. Further, the detected load may vary as fluctuating up and down around a threshold load between the small adult class and the large adult class while farther crossing over a threshold load between the child class and the small adult class. Each time the detected load provides anew a value that does not satisfy the individual load condition, a counting timer may be reset. Regardless of the detected load providing minimally a value larger than that of the small adult class, the incorrect determination of classifying the large adult into the child class is maintained without being eventually classified into the small adult. This disables an appropriate airbag control. To prevent an incorrect determination, an inter-class transition may be determined according to an accumulated time period that is obtained by summing up a plurality of condition-satisfied times or durations; each condition-satisfied duration is a duration during which the detected load continues satisfying the loading condition of each class. However, such determination of the inter-class transition based on the accumulated time period tends to delay as compared with the case of using only each condition-satisfied duration.

It is an object of the present disclosure to provide an occupant determination apparatus to permit a proper airbag control to protect an occupant by certainly performing an inter-class transition, excluding determinations at the time when an occupant gets in a vehicle and at the time when an occupant gets off a vehicle. The inter-class transition can be minimally performed even when a detected load varies as fluctuating up and down around a different threshold value other than a threshold value between a present class and an adjacent class immediately adjacent to the present class.

To achieve the above object, according to an example of the present disclosure, an occupant determination apparatus is provided to include a load sensor and a determination section. The load sensor is to detect a load of an occupant who is seated in a seat of a vehicle to provide the detected load as a load signal. The determination section is to receive the load signal and determine (i) presence or absence of the occupant and (ii) a physical size of the occupant by classifying the load signal into a subject class among a plurality of classes, which are ordered from small to large according to the physical size, based on predetermined threshold loads, the subject class being stored as a determined class. The determination section performs an inter-class transition that permits the determined class to transition from a present class to an adjacent class that is immediately adjacent to the present class (i) when the load signal equal to or larger than a first threshold load, which is defined between the present class and the adjacent class that is larger than the present class, continues being received for a first threshold time, or (ii) when the load signal smaller than a second threshold load, which is defined between the present class and the adjacent class that is smaller than the present class, continues being received for a second threshold time.

That is, such a configuration permits the occupant determination apparatus operates as follows. When a load signal equal to or larger than a first threshold load between a present class and an adjacent large class that is large than and immediately adjacent to the present class is continuously received or provided for a first threshold time, the determined class is permitted to transition from the present class to the adjacent large class. Alternatively, when a load signal smaller than a second threshold load between a present class and an adjacent small class that is smaller than and immediately adjacent to the present class is continuously provided or received for a second threshold time, the determined class is permitted to transition from the present class to the adjacent small class. Therefore, even if a detected load varies and fluctuates up and down around a separate threshold value that is different from a threshold value defined between the present class and the adjacent class that is immediately adjacent to the present class, the inter-class transition from the present class into the adjacent class immediately adjacent to the present class can be made minimally. This can provide an advantageous effect to control an airbag to protect an occupant minimally.

DETAILED DESCRIPTION

An embodiment according to the present disclosure will be explained with reference to drawings.

With reference toFIGS. 1 and 2, an occupant determination apparatus according to an embodiment of the present disclosure includes a seat1of a vehicle; a plurality of load sensors3; and an occupant determination unit4. The plurality of load sensors3may be correctively referred to as a load sensor device3. The load sensors3are disposed in a leg portion between a bottom of a seating portion2of the seat1and a vehicle-body floor8; the load sensors3are to detect the weight of an occupant who is seated on the seating portion2. The occupant determination unit4includes a microcomputer that performs arithmetic processing of load signals from the load sensors3; the microcomputer comes with an A/D converter. The occupant determination unit4may be also referred to as a determination section.

Each load sensor3includes (i) a rubber layer and (ii) a pair of electrodes. The rubber layer is mixed with conductive particles to reduce an electric resistance value depending on compressive force. The pair of electrodes are provided to be stuck firmly to the respective opposite sides of the rubber layer such that the rubber layer is sandwiched in between two electrodes. When a human body (or physical solid) is seated on the seat1, the electrical resistance in between the electrodes falls with the increase of the weight of the human body. In between the electrodes, a predetermined direct current voltage or a constant electric current is applied via a load resistance; this exhibits a voltage drop. The occupant determination unit4converts the resultant voltage drop into a digital signal using the A/D converter and reads the signal to thereby detect the weight of the occupant seated on the seat1. It is noted that each load sensor3may be shaped of a sheet and embedded in an upper portion of the seating portion2.

The load sensor3may be differently provided to be a load cell such as a strain gauge type, a semiconductor type, a magnetostriction type, and an electrostatic capacity type. Those types may be used suitably depending on each characteristic or cost. Here, any one of those types provides an analog output; this requires an A/D converter. In addition, in the present embodiment, the load sensor device is provided as being configured by four separate load sensors3; however, the number of load sensors3constituting the load sensor device3may be changed to another number as needed.

The occupant determination unit4sums up the load signals of the plurality of the load sensors3to obtain a detected load W of the load sensor device3. The detected load W is a digital signal into which the analog signals of the load sensors3are converted by the A/D converter of the occupant determination unit4. It is noted that the detected load W may be a present value (i.e., instantaneous value) detected presently by the load sensors3or an average value, which is based on the detected values during the just previous short period of time while undergoing the removal of the high frequency noise components.

With reference toFIG. 3, threshold loads Wth1to Wth4are provided as becoming greater or ascending from small to large in value or load in the following order from Wth1, through Wth2and Wth3, to Wth4. Based on threshold loads Wth1to Wth4, the detected load W is classified into one (i.e., subject class) of five occupant classes, which are (i) a “vacant seat” class, (ii) a “CRS(Child Restraint System)+infant” class, (iii) a “child” class, (iv) a “small adult (adult having a small physical size)” class, and (v) a “large adult (adult having a large physical size)” class. The classifying-resultant subject class is stored as a determined class C in a storage portion of the occupant determination unit4. The determined class C is transmitted as one of state signals to the airbag drive unit6.

According to the received signal, the airbag drive unit6controls the airbag7to selectively perform one of four inflation states of (i) a none inflation state corresponding to both the “vacant seat” class and the “CRS(Child Restraint System)+infant” class, (ii) a weak inflation state corresponding to the “child” class, (iii) an intermediate (middle) inflation state corresponding to the “small adult” class, and (iv) a strong inflation state corresponding to the “large adult” class. Further, the “vacant seat” class and the “CRS+infant” class each may be referred to as a none-airbag-inflating class, which disables inflating the airbag7at a collision of the vehicle or is not a target class of inflating the airbag7. In contrast, the “child” class, the “small adult”, and the “large adult” class each are an airbag-inflating class, which enables inflating of the airbag7at a collision of the vehicle, or is a target class of inflating the airbag7.

Furthermore, the airbag drive unit6controls a lamp state or a lighting state of an indicator depending on the inflation state performed in the airbag7. It is noted that the number of the occupant classes may be changed as needed depending on vehicle types or vehicle grades. In addition, the airbag drive unit6may be provided as an integrated unit by further incorporating the function of the occupant determination unit4.

Processes of determination/inter-class transition executed by the occupant determination unit4(i.e., microcomputer of the occupant determination unit4) will be explained with reference to flowcharts inFIGS. 4 to 9. It is noted that an inter-class transition may be defined as a transition of the class C or determined class from a transition source class into a transition destination class. It is further noted that a flowchart in the present application includes sections (also referred to as steps), which are represented, for instance, as S1. Further, each section can be divided into several sections while several sections can be combined into a single section. Furthermore, each of thus configured sections can be referred to as a module, device, or means and achieved not only (i) as a software section in combination with a hardware unit (e.g., computer), but also (ii) as a hardware section (e.g., integrated circuit, hard-wired logic circuit), including or not including a function of a related apparatus. Further, the hardware section may be inside of a microcomputer.

First,FIG. 4is a flowchart diagram illustrating a class determination process when and after an occupant gets in a vehicle. At S1, timers Tm1to Tm8are reset while the determined class C is designated as the “vacant seat” class. At S2, the load signals of the load sensors3are read and converted to obtain a detected load W. At S3, it is determined whether the determined class C is the “vacant seat” class at present. When it is the “vacant seat” class, at S4it is determined whether the load W is equal to larger than the threshold load Wth1. When the load W is equal to or larger than the threshold load Wth1, at S5the timer Tm1starts to increment a count. At S6, it is determined whether the count of the timer Tm1reaches a threshold time Tth1. When it is determined at S4that the load W is smaller than the threshold load Wth1, at S10the timer Tm1is reset; then, the processing returns to “I” to repeat the flow from S2.

When it is determined at S6that the count of the timer Tm1reaches the threshold time Tth1, at S7it is determined whether the load W is equal to larger than the threshold load Wth2. In addition, when it is determined at S6that the count of the timer Tm1does not reach the threshold time Tth1, the processing returns to “I” to repeat the flow from S2.

When it is determined at S7that the load W is equal to or larger than the threshold load Wth2, at S8it is determined whether the load W is equal to larger than the threshold load Wth3. In addition, when it is determined at S7that the load W is smaller than the threshold load Wth2, at S11it is determined that the class C is anew the “CRS+infant” class and the timer Tm1is reset.

When it is determined at S8that the load W is equal to or larger than the threshold load Wth3, at S9it is determined whether the load W is equal to larger than the threshold load Wth4. In addition, when the load W is smaller than the threshold load Wth3, at S12it is determined that the class C is anew the “child” class and the timer Tm1is reset.

When it is determined at S9that the load W is smaller than the threshold load Wth4, at S13it is determined the class C is anew the “small adult” class and the timer Tm1is reset. In addition, when the load W is equal to or larger than the threshold load Wth4, at S14it is determined that the class C is anew the “large adult” class and the timer Tm1is reset.

Thus, when an occupant gets in the vehicle and is seated on the seating portion2, the detected load W is compared with the threshold loads Wth1, Wth2, Wth3, and Wth4. This achieves an initial determination of the class C to determine the class C to be one of four classes of (i) the “CRS+infant” class, (ii) the “child” class, (iii) the “small adult” class, and (iv) the “large adult” class.

When it is determined at S3that the present class C is not the “vacant seat” class, namely, when the present class C is one of the “CRS+infant” class, the “child” class, the “small adult” class, and the “large adult” class, the processing proceeds to “II” inFIG. 5.FIG. 5is a flowchart diagram illustrating a process which performs an inter-class transition from the “CRS (child restraint system)+infant” class into the “child” class. At S15, it is determined whether the present determined class C is the “CRS+infant” class. When it is determined at S15that the class C is the “CRS+infant” class, at S16it is determined whether the load W is equal to larger than the threshold load Wth2. When the load W is equal to or larger than the threshold load Wth2, at S17the timer Tm8is reset, and at S18the timer Tm2starts to increment a count. At S19, it is determined whether the count of the timer Tm2reaches a threshold time Tth2. When it is determined at S19that the count of the timer Tm2reaches the threshold time Tth2, at S20the determined class C transitions into the “child” class and the timer Tm2is reset. The processing then returns to “I” inFIG. 4. When it is determined at S19that the count of the timer Tm2does not reach the threshold time Tth2, the processing similarly returns to “I” inFIG. 4.

When it is determined at S16that the load W is smaller than the threshold load Wth2, at S21the timer Tm2is reset. At S22, it is determined whether the load W is smaller than the threshold load Wth1. When the load W is smaller than the threshold load Wth1, the processing proceeds to “VI” inFIG. 9. When the load W is equal to or larger than the threshold load Wth1, at S23the timer Tm8is reset. The processing then proceeds to “I” inFIG. 4.

When it is determined at S15that the present class C is not the “CRS+infant” class, namely, when the class C is one of the “child” class, the “small adult” class, and the “large adult” class, the processing proceeds to “III” inFIG. 6.FIG. 6is a flowchart diagram illustrating a process which performs an inter-class transition from the “child” class into the “small adult” class or the “CRS+infant” class. At S24it is determined whether the present determined class C is the “child” class. When it is determined at S24that the class C is the “child” class, at S25it is determined whether the load W is equal to larger than the threshold load Wth3. When the load W is equal to or larger than the threshold load Wth3, at S26the timer Tm4and the timer Tm8are reset. At S27, the timer Tm3starts to increment a count. At S28, it is determined whether the count of the timer Tm3reaches a threshold time Tth3. When it is determined at S28that the count of the timer Tm3reaches the threshold time Tth3, at S29the determined class C transitions into the “small adult” class and the timer Tm3is reset. The processing then returns to “I” inFIG. 4. When it is determined at S28that the count of the timer Tm3does not reach the threshold time Tth3, the processing similarly returns to “I” inFIG. 4.

When it is determined at S25that the load W is smaller than the threshold load Wth3, at S30the timer Tm3is reset. At S31, it is determined whether the load W is smaller than the threshold load Wth2. When the load W is smaller than the threshold load Wth2, at S32the timer Tm4starts to increment a count. At S33, it is determined whether the count of the timer Tm4reaches a threshold time Tth4. When it is determined at S33that the count of the timer Tm4reaches the threshold time Tth4, at S34the determined class C transitions into the “CRS+infant” class and the timers Tm3, Tm4, and Tm8are reset. The processing then proceeds to “I” inFIG. 4.

When it is determined at S31that the load W is equal to or larger than the threshold load Wth2, at S35the timer Tm4is reset. The processing then proceeds to “I” inFIG. 4. When it is determined at S33that the count of the timer Tm4does not reach the threshold time Tth4, at S36it is determined whether the load W is smaller than the threshold load Wth1. When the load W is smaller than the threshold load Wth1, the processing proceeds to “VI” inFIG. 9. When the load W is equal to or larger than the threshold load Wth1, at S37the timer Tm8is reset. The processing then proceeds to “I” inFIG. 4.

When it is determined at S24that the present class C is not the “child” class, but the “small adult” class or the “large adult” class, the processing proceeds to “IV” inFIG. 7.FIG. 7is a flowchart diagram illustrating a process which performs an inter-class transition from the “small adult” class into the “large adult” class or the “child” class. At S38, it is determined whether the present class C is the “small adult” class. When it is the “small adult” class, at S39it is determined whether the load W is equal to larger than the threshold load Wth4. When the load W is equal to or larger than the threshold load Wth4, at S40the timer Tm6and the timer Tm8are reset. At S41the timer Tm5starts to increment a count. At S42, it is determined whether the count of the timer Tm5reaches a threshold time Tth5. When the count of the timer Tm5reaches the threshold time Tth5, at S43the determined class C transitions into the “large adult” class and the timer Tm5is reset. The processing then returns to “I” inFIG. 4. When it is determined at S42that the count of the timer Tm5does not reach the threshold time Tth5, the processing similarly returns to “I” inFIG. 4.

When it is determined at S39that the load W is smaller than the threshold load Wth4, at544the timer Tm5is reset. At S45, it is determined whether the load W is smaller than the threshold load Wth3. When the load W is smaller than the threshold load Wth3, at S46the timer Tm6starts counting or increment. At S47, it is determined whether the count of the timer Tm6reaches a threshold time Tth6. When the count of the timer Tm6reaches the threshold time Tth6, at S48the determined class C transitions into the “child” class and the timers Tm5, Tm6, and Tm8are reset. The processing proceeds to “I” inFIG. 4.

When it is determined at S45that the load W is equal to or larger than the threshold load Wth3, at S49the timer Tm6is reset. The processing then proceeds to “I” inFIG. 4. When it is determined at S47that the count of the timer Tm6does not reach the threshold time Tth6, at S50it is determined whether the load W is smaller than the threshold load Wth1. When the load W is smaller than the threshold load Wth1, the processing proceeds to “VI” inFIG. 9. When the load W is equal to or larger than the threshold load Wth1, at S51the timer Tm8is reset. The processing then proceeds to “I” inFIG. 4.

When it is determined at S38that the class C is not the “small adult” class, but the “large adult” class, the processing proceeds to “V” inFIG. 8.FIG. 8is a flowchart diagram illustrating a process which performs an inter-class transition from the “large adult” class into the “small adult” class. At S52, it is determined whether the load W is smaller than the threshold load Wth4. When the load W is smaller than the threshold load Wth4, at S53the timer Tm7starts to increment a count. At S54, it is determined whether the count of the timer Tm7reaches a threshold time Tth7. When the count of the timer Tm7reaches the threshold time Tth7, at S55the determined class C transitions into the “small adult” class and the timers Tm7and Tm8are reset. The processing proceeds to “I” inFIG. 4. When it is determined at S52that the load W is equal to or larger than the threshold load Wth4, at S56the timer Tm7is reset. The processing then proceeds to “I” inFIG. 4. When it is determined at S54that the count of the timer Tm7does not reach the threshold time Tth7, at S57it is determined whether the load W is smaller than the threshold load Wth1. When the load W is smaller than the threshold load Wth1, the processing proceeds to “VI” inFIG. 9. When the load W is equal to or larger than the threshold load Wth1, at S58the timer Tm8is reset. The processing then proceeds to “I” inFIG. 4.

FIG. 9is a flowchart diagram illustrating a class determination process when and after the occupant gets off the vehicle. Reference to “VI” inFIG. 9that is called for from “VI” inFIGS. 5 to 8, at S59the timer Tm8starts to increment a count. At S60, it is determined whether the count of the timer Tm8reaches a threshold time Tth8. When the count of the timer Tm8reaches the threshold time Tth8, S61is processed as follows. That is, (i) the determined class C transitions into the “vacant seat” class; (ii) it is determined that the present state is a state where the occupant leaves or gets off the vehicle; and (iii) the timer Tm8is reset. The processing then proceeds to “I” inFIG. 4. When it is determined at S60that the count of the timer Tm8does not reach the threshold time Tth8, the processing similarly proceeds to “I” inFIG. 4.

In the above-mentioned explanation, the threshold time Tth1corresponds to the timer Tm1used for initial determining of the class C from the “vacant seat” class into one of four classes of the “CRS+infant” class, the “child” class, the “small adult,” and the “large adult” class. Thus, in order to perform seated occupant classification or determination quickly when an occupant gets in the vehicle, the threshold time Tth1is designated as a time such as three (3) seconds comparatively shorter than other threshold times for inter-class transitions.

The threshold time Tth2corresponds to the timer Tm2used for inter-class transition of the class C from the “CRS+infant” class into the “child” class. In order to require the reliability on inter-class transition or the stability of determination, the threshold time Tth2is designated as a time such as 20 to 30 seconds comparatively longer than the threshold time Tth1for the initial determination of the class C when an occupant gets in the vehicle.

The threshold time Tth3corresponds to the timer Tm3used for inter-class transition of the class C from the “child” class into the “small adult” class. In order to require the reliability on inter-class transition or the stability of determination, the threshold time Tth3is designated as a time such as 20 to 30 seconds comparatively longer than the threshold time Tth1for the initial determination of the class C when an occupant gets in the vehicle.

The threshold time Tth4corresponds to the timer Tm4used for inter-class transition of the class C from the “child” class into the “CRS+infant” class. In order to require the reliability on inter-class transition or the stability of determination, the threshold time Tth4is designated as a time such as 20 to 30 seconds comparatively longer than the threshold time Tth1for the initial determination of the class C when an occupant gets in the vehicle.

The threshold time Tth5corresponds to the timer Tm5used for inter-class transition of the class C from the “small adult” class into the “large adult” class. In order to require the reliability on inter-class transition or the stability of determination, the threshold time Tth5is designated as a time such as 20 to 30 seconds comparatively longer than the threshold time Tth1for the initial determination of the class C when an occupant gets in the vehicle.

The threshold time Tth6corresponds to the timer Tm6used for inter-class transition of the class C from the “small adult” class into the “child” class. In order to require the reliability on inter-class transition or the stability of determination, the threshold time Tth6is designated as a time such as 20 to 30 seconds comparatively longer than the threshold time Tth1for the initial determination of the class C when an occupant gets in the vehicle.

The threshold time Tth7corresponds to the timer Tm7used for inter-class transitioning of the class C from the “large adult” class into the “small adult” class. In order to require the reliability on inter-class transition or the stability of determination, the threshold time Tth7is designated as a time such as 20 to 30 seconds comparatively longer than the threshold time Tth1for the initial determination of the class C when an occupant gets in the vehicle.

The threshold time Tth8corresponds to the timer Tm8used for determining of the class C from one of the “CRS+infant” class, the “child” class, the “small adult,” and the “large adult” class into the “vacant seat” class. In order to once determine the “vacant seat” class quickly when an occupant gets off the vehicle and then perform initial determination of the class C from the “vacant seat” class, the threshold time Tth8is designated as a time such as two (2) seconds comparatively shorter than other threshold times for inter-class transition.

As explained above, the occupant determination apparatus using a load sensor according to the present embodiment is provided as follows. First, the seated occupant classes include, in ascending order (or load-increasing order) of detected load W, from the smallest class through intermediate classes to the largest class, namely, from the “vacant seat” class; through the “CRS+infant” class, the “child” class, and the “small adult” class; to the “large adult” class. Now, a “vacant seat”-excluded inter-class transition may be defined as inter-class transitions excluding each of (i) the vehicle-getting-in determination that permits the determined class C to transition from the “vacant seat” class into another class when an occupant gets in the vehicle and (ii) the vehicle-getting-off determination that permits the determined class C to transition into the “vacant seat” class from another class when the occupant gets off the vehicle. Under the “vacant seat”-excluded inter-class transition, the determined class C is permitted to transition from a present class to an adjacent large class that is larger than and immediately adjacent to the present class when the detected load W equal to or larger than a first threshold load defined between the present class and the adjacent large class continues being provided for a first threshold time. In contrast, the determined class C is permitted to transition from the present class to an adjacent small class that is smaller than and immediately adjacent to the present class when the detected load W smaller than a second threshold load between the present class and the adjacent small class continues being provided for a second threshold time.

Suppose that the detected load W may range over a different separate threshold load that is other than (i) a large-side adjacent threshold load defined between a present class and an adjacent large class that is larger than and immediately adjacent to the present class and (ii) a small-side adjacent threshold load defined between a present class and an adjacent small class that is smaller than and immediately adjacent to the present class. Even in such a case that the detected load W ranges over the different separate threshold load, the inter-class transition from the present class into the immediately adjacent class is permitted to be performed with certainty and high reliability. This can provide an advantageous effect to control an airbag to protect an occupant minimally.

With reference toFIG. 3, a comparative example will be explained. For example, a subject child with a physical size close to that of a small adult (i.e., an adult having a small physical size) is seated on a front portion of a seat; and the class C is first determined to be the “CRS+infant” class. Then the subject child shifts their hip to be seated deeply on the seat; this increases the detected load W to not only cross over the threshold load Wth2but also fluctuate up and down around the threshold load Wth3. In this case, when the condition of the detected load W for the inter-class transition from the “CRS+infant” class into the “child” class is specified to be “Wth2≦W<Wth3”, i.e., equal to or larger than the threshold load Wth2and smaller than the threshold load Wth3, the timer Tm2needs to be reset each time the detected load W becomes equal to or larger than the threshold load Wth3. This disables even the inter-class transition from the “CRS+infant” class into the “child” class regardless of the load larger than the “child” class being continuously provided or inputted at least. In contrast, according to the present embodiment of the present disclosure, the condition of the detected load W for the inter-class transition from the “CRS+infant” class into the “child” class is specified to be “Wth2≦W”, i.e., to be equal to or larger than the threshold load Wth2, alone, instead of being both (i) equal to or larger than the threshold load Wth2, and, simultaneously, (ii) smaller than the threshold load Wth3. Such a configuration or specification permits certainly the inter-class transition from the “CRS+infant” class into the “child” class while permitting an airbag control or an airbag inflating to be suitable for the child's physical size. Even when the above case may apply to a subject small adult having a physical size close to that of the “child” class, the determined class C certainly permits the inter-class transition from the “CRS+infant” class into the “child” class. This can provide a minimal airbag inflation at least. Further, for example, a subject large adult having a large physical size is seated on a front portion of a seat; and the class C is first determined to be the “CRS+infant” class. Then the subject large adult shifts their hip to be seated deeply on the seat; this increases and maintains the detected load W to be equal to or larger than the threshold load Wth4. In this case, the inter-class transition of the determined class C is permitted from the “CRS+infant” class, through the “child” class and the “small adult” class, into the “large adult” class. This can also provide a suitable airbag inflation.

As explained above, the present embodiment provides the load sensor device including four load sensors3that detect all the load applied to the seating portion2. For instance, when the number of load sensors3is reduced to three, a load may incline to a none-sensor portion where no load sensor is provided. In such a case, the load inclining to the none-sensor portion cannot be detected; this reduces the load total of the load sensors as compared with the case where there is no inclination. Therefore, when the number of load sensors3is reduced, the change in the detected load increases as compared with the case of detecting all the load applied to the seating portion. This increases the repetition times of inter-class transitions. Thus, when the number of load sensors is reduced, the present embodiment can provide a more advantageous effect as compared with a conventional technology.

First Modification Example

The threshold times Tth2to Tth7are defined or used for inter-class transitions due to the change in the occupant's posture. Suppose that a basis class is assigned to the class determined at the initial determination using the threshold time Tth1. Further, an inter-class transition from a present determined class C into a next determined class C may be referred to as an inter-class transition from a transition source class into a transition destination class. As such a transition destination class becomes more distant or is farther from the basis class, the corresponding threshold time is designated to be longer. For example, suppose that the “CRS+infant” class is a basis class. The threshold time Tth3for the inter-class transition from the “child” class into the “small adult” class is longer than the threshold time Tth2for the inter-class transition from the “CRS+infant” class into the “child” class. The threshold time Tth5for the inter-class transition from the “small adult” into the “large adult” class is longer than the threshold time Tth3for the inter-class transition from the “child class” into the “small adult” class.

In other words, a plurality of threshold times are assigned to inter-class transitions that permit the determined class to transition from a present class serving as a transition source class into an immediately adjacent large class or an immediately adjacent small class serving as a transition destination class. Further, a basis class may be defined as a class that is initially determined as the determined class C when the occupant gets in the vehicle (i.e., at the initial determination when an occupant gets in a vehicle). As the transition destination class is farther from the basis class, the corresponding threshold time is designated to be longer. That is, the vehicle is in stopped state when the occupant gets in the vehicle; thus, any acceleration G due to travel motion of the vehicle is not applied to the occupant. Thus, the initial determination may be reliable. A threshold time may be provided to be lengthened as the transition destination class separates farther from the basis class of the initial determination; this makes it more difficult to transition into a class farther from the reliable basis class. In addition, the threshold times may be provided to be designated to make the inter-class transition into the basis class from other class easier. Thus, it is more difficult to mistakenly determine the class C due to the occupant's posture change or the acceleration G due to the travel motion of the vehicle. Even if an incorrect determination is made, transition into the reliable basis class can be made promptly. This can control an airbag effectively.

Second Modification Example

Similar to the first modification example, the threshold times Tth2to Tth7are used for inter-class transitions due to the change in the occupant's posture. Suppose that a basis class is assigned to the class determined when the speed signal from the speed sensor5of the vehicle inputted into the occupant determination unit4reaches a predetermined value or speed. Similarly, as a transition destination class becomes more distant or is farther from the basis class determined when the speed signal reaches the predetermined speed, the corresponding threshold time is designated to be longer.

In other words, a plurality of threshold times are assigned to inter-class transitions that permit the determined class to transition from a present class serving as a transition source class into an immediately adjacent large class or an immediately adjacent small class serving as a transition destination class. Further, a basis class may be defined as the determined class C that is determined when the speed signal from the speed sensor5of the vehicle inputted into the occupant determination unit4reaches a predetermined value or vehicle speed. As the transition destination class is farther from the basis class, the corresponding threshold time is designated to be longer. As explained above, the initial determination made when the occupant gets in the vehicle provides a high reliability, but may be subjected to the state where the occupant is seated in a front part of the seating portion of the seat while a vehicle door is still open. In contrast, while the vehicle travels at a predetermined speed, the occupant may not be seated in a front part of the seating portion of the seat. Thus, the determination made when the vehicle travels at the predetermined speed can provide a higher reliability. Therefore, the determined class C made when the vehicle travels at the predetermined speed may be defined as a basis class, and the threshold times (i.e., durations) may be designated to cause the inter-class transition into a class farther from the basis class to be more difficult. In addition, the threshold times may be designated to make the inter-class transition into the basis class from another class easier. Thus, it is more difficult to mistakenly determine the class C due to the occupant's posture change or the acceleration G due to the travel motion of the vehicle. Even if an incorrect determination is made, transition into the reliable basis class can be made promptly. This can control an airbag effectively.

Third Modification Example

In the inter-class transition due to the change in the occupant's posture, the designation for threshold times may be differently made as follows. With reference toFIG. 3, the “CRS+infant” class may be referred to as a none-airbag-inflating class that is not a target class of inflating the airbag7. In contrast, the “child” class, the “small adult”, and the “large adult” class each are an airbag-inflating class that is a target class of inflating the airbag7. The threshold times Tth2and Tth4for inter-class transition to range over the threshold load Wth2in between (i) the “child” class belonging to the airbag-inflating class and (ii) the “CRS+infant” class belonging to the none-airbag-inflating class are designated to be shorter than the threshold times Tth3, Tth5, Tth6, and Tth7for inter-class transition between the “child” class, the “small adult” class, and the “large adult” class, each of which belongs to the airbag-inflating class.

In other words, the threshold times Tth2and Tth4correspond to inter-class transition to cross over the threshold load Wth2defined between (i) the airbag-inflating class that is designed to enable inflating of an airbag at a collision of the vehicle and (ii) the none-airbag-inflating class that is designed to disable inflating of an airbag at a collision of the vehicle. In contrast, the threshold times Tth3, Tth5, Tth6, and Tth7correspond to inter-class transition defined between the airbag-inflating classes that are designed to enable inflating of an airbag. Herein, the threshold times Tth2and Tth4are designated to be shorter than the threshold times Tth3, Tth5, Tth6, and Tth7. This permits a quick inter-class transition from the airbag-inflating class into the none-airbag-inflating class or from the none-airbag-inflating class into the airbag-inflating class, as compared with the inter-class transition between the airbag-inflating classes. This can control an airbag effectively at a collision of the vehicle.

Fourth Modification Example

In the inter-class transitioning due to the change in the occupant's posture, the designation for threshold times may be differently made as follows. Again, with reference toFIG. 3, the “CRS+infant” class may be referred to as a none-airbag-inflating class that is not a target class of inflating the airbag7. In contrast, the “child” class, the “small adult”, and the “large adult” class each are an airbag-inflating class that is a target class of inflating the airbag7. The threshold time Tth4for the inter-class transition from the “child” class belonging to the airbag-inflating class into the “CRS+infant” class belonging to the none-airbag-inflating class is designated to be longer than the threshold time Tth2for the inter-class transition from the “CRS+infant” class belonging to the none-airbag-inflating class into the “child” class belonging to the airbag-inflating class. In contrast, the threshold times Tth3, Tth5, Tth6, Tth7for the inter-class transitions between the “child” class, the “small adult” class, and “large adult” class, each of which belongs to the airbag-inflating class, are designated to be longer than the threshold time Tth4for the inter-class transition from the “child” class belonging to the airbag-inflating class into the “CRS+infant” class belonging to the none-airbag-inflating class.

In other words, the threshold time Tth4corresponds to inter-class transition from the airbag-inflating class that is designed to enable inflating of an airbag into the none-airbag-inflating class that is designed to disable inflating of an airbag. The threshold time Tth2corresponds to inter-class transition from the none-airbag-inflating class that is designed to disable inflating of an airbag into the airbag-inflating class that is designed to enable inflating of an airbag. The threshold times Tth3, Tth5, Tth6, and Tth7correspond to inter-class transition in between the airbag-inflating classes that are designed to enable inflating of an airbag. Herein, the threshold times Tth3, Tth5, Tth6, and Tth7are designated to be longer than the threshold time Tth4, whereas the threshold time Tth4is designated to be longer than the threshold time Tth2. The load detected by a load sensor is typically smaller than a proper load since the proper load decreases due to the acceleration due to the travel motion of the vehicle applied to the occupant or the occupant's posture change; it is a rare case that a detected load is larger than a proper load. To that end, it is designed to make the inter-class transition into the reliable class quickly and, simultaneously, to make the inter-class transition into the airbag-inflating class that needs an airbag inflation quickly. This can control an airbag effectively.