JP2014085297A - Capacitance type occupant detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitance type occupant detection device capable of improving the occupant detection accuracy.SOLUTION: The capacitance type occupant detection device of the present invention includes: an electrostatic sensor 1 having a detection electrode 11 and a guard electrode 13; a detection voltage application section 21 that applies a detection voltage to the detection electrode 11 and creates an electric field between the detection electrode 11 and a reference electrode 3; a guard voltage application section 25 for applying a voltage of the same potential as the detection voltage to the guard electrode 13; current detection sections 22 and 42 for detecting a detection current as a current flowing through the detection electrode 11 and a guard current as a current flowing through the guard electrode 13; a capacitance detection section 23 for detecting a capacitance between the detection electrode 11 and the reference electrode 3 on the basis of the detection voltage, detection current, and guard current; and an occupant determination section 24 for determining an occupant of a seat 91 on the basis of the capacitance.

Description

  The present invention relates to an electrostatic capacity type occupant detection device that determines an occupant based on electrostatic capacity.

  The capacitance type occupant detection device is a device that determines the presence or absence and type of an occupant based on a change in capacitance between two electrodes. As an electrostatic capacitance type occupant detection apparatus, it describes in Unexamined-Japanese-Patent No. 2008-111809, for example. In the electrostatic capacity type occupant detection device, an electrostatic sensor (detection electrode, guard electrode, etc.) is arranged in a vehicle seat, and the presence or absence of the occupant and the type of occupant (adult or child seat) (Children who boarded (CRS)). A change occurs in the detected capacitance due to a difference in relative permittivity of the detection target interposed between the electrodes (for example, about air 1, about 2 CRS, about 50 adults), and the detection target is determined by the change. The

  In the capacitive occupant detection device, the guard electrode to which the same potential as the detection electrode is applied prevents the detection electrode from forming an electric field on the side opposite to the seat (occupant). Thereby, the occupant detection accuracy is improved.

JP 2008-111809 A

  In the electrostatic capacity type occupant detection device, strictly speaking, the electrostatic capacity is different between the detection electrode and the reference electrode and between the guard electrode and the reference electrode due to the difference in structure between the upper side and the lower side of the seat. Therefore, although a voltage having the same potential is applied to the detection electrode and the guard electrode, a potential difference is generated between the detection electrode and the guard electrode, and an electric field is formed between the electrodes. When an electric field is formed between the detection electrode and the guard electrode, the detection of the capacitance between the detection electrode and the reference electrode is affected. Thus, there is room for improvement in occupant detection accuracy.

  Conventionally, it has been difficult to specify in detail the failure of the electrode in the electrostatic sensor by arranging the guard electrode. For example, there are cases where it is difficult to determine whether the increase in capacitance is due to the seating of an occupant or the disconnection (breaking) of electrodes. Prevention of occupant misjudgment due to electrode failure is required.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a capacitive occupant detection device capable of improving the occupant detection accuracy. Another object of the present invention is to provide a capacitive occupant detection device that can detect an electrode failure in detail and suppress an erroneous determination of the occupant.

  The invention according to claim 1 is a capacitive occupant detection device, comprising a detection electrode (11) and a guard electrode (13) arranged to face the detection electrode (11), Between the electrostatic sensor (1) disposed on the sheet (91) and the reference electrode (3) to which a detection voltage is applied to the detection electrode (11) and a reference voltage is applied. A detection voltage application unit (21) for forming an electric field at the same time, a guard voltage application unit (25) for applying a voltage having the same potential as the detection voltage to the guard electrode (13), and a current flowing through the detection electrode (11). And a current detection unit (22, 42) for detecting a guard current that is a current flowing through the guard electrode (13), and the detection electrode based on the detection voltage, the detection current, and the guard current. (11) and the reference electrode ( Provided capacity detection unit for detecting an electrostatic capacitance between the) and (23), an occupant determination unit for determining an occupant of the seat (91) on the basis of the electrostatic capacitance (24), the.

  According to this configuration, since the guard current is detected in addition to the detection voltage and the detection current, it is possible to detect a more accurate capacitance in consideration of the potential difference between the main electrode and the guard electrode. And the passenger | crew detection precision can be improved by using the said electrostatic capacitance for passenger | crew discrimination | determination.

  The invention according to claim 9 is an electrostatic capacitance type occupant detection device having a detection electrode (11) and a guard electrode (13) arranged to face the detection electrode (11), Between the electrostatic sensor (1) disposed on the sheet (91) and the reference electrode (3) to which a detection voltage is applied to the detection electrode (11) and a reference voltage is applied. A detection voltage application unit (21) for forming an electric field at the same time, a guard voltage application unit (25) for applying a voltage having the same potential as the detection voltage to the guard electrode (13), and a current flowing through the detection electrode (11). A current detection unit (22, 42) for detecting a detection current and a guard current which is a current flowing through the guard electrode (13), and at least the detection electrode (11) based on the detection voltage and the detection current With the reference electrode (3) A capacitance detection unit (23) for detecting a capacitance of the vehicle, an occupant determination unit (24) for determining an occupant of the seat (91) based on the capacitance, the detection voltage, the detection current, and the A failure determination unit (23, 24) for determining a failure of the electrostatic sensor (1) based on a guard current.

  According to this configuration, since the guard current is detected in addition to the detection voltage and the detection current, the failure of the electrostatic sensor can be detected in more detail. According to this configuration, since the guard current is detected, it is possible to determine whether or not the guard electrode has failed. Since the failure can be detected in detail, an erroneous determination of occupant detection can be suppressed, and the occupant detection accuracy can be improved.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is a conceptual diagram which shows the structure of the electrostatic capacitance type occupant detection apparatus of 1st embodiment. It is a conceptual diagram which shows the circuit structure of the electrostatic capacitance type passenger | crew detection apparatus of 1st embodiment. It is sectional drawing which shows the electrostatic sensor of 1st embodiment. It is a circuit diagram which shows the equivalent circuit of the electrostatic capacitance type passenger | crew detection apparatus of 1st embodiment. It is a flowchart which shows control of the passenger | crew detection ECU of 1st embodiment. It is a graph which compares the electrostatic capacitance detected by 1st embodiment and the past. It is a conceptual diagram which shows the circuit structure of the electrostatic capacitance type occupant detection apparatus of 2nd embodiment. It is a conceptual diagram which shows the circuit structure of the electrostatic capacitance type passenger | crew detection apparatus of 3rd embodiment. It is a flowchart which shows control of the passenger | crew detection ECU of 3rd embodiment. It is explanatory drawing for demonstrating discrimination | determination of the passenger | crew discrimination | determination part of 4th embodiment. It is explanatory drawing for demonstrating discrimination | determination of the passenger | crew discrimination | determination part of 4th embodiment. It is explanatory drawing for demonstrating the discrimination | determination of the conventional passenger | crew. It is sectional drawing which shows the electrostatic sensor in a deformation | transformation aspect.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings. Each figure used for explanation is a conceptual diagram, and the shape of each part may not necessarily be exact.

<First embodiment>
As shown in FIGS. 1 and 2, the capacitive occupant detection device of the first embodiment includes an electrostatic sensor 1 and an occupant detection ECU 2. The electrostatic sensor 1 is a film-like sensor mat, and electrodes are arranged in a wave shape. The electrostatic sensor 1 is disposed in a vehicle seat 91. The electrostatic sensor 1 is disposed substantially parallel to the seating surface 911 of the seat 91.

  Specifically, as shown in FIG. 3, the electrostatic sensor 1 includes a main electrode (corresponding to “detection electrode”) 11, a guard electrode 13, and film members 14 to 16. The main electrode 11 is a flat conductive member and is disposed on the film member 15.

  The guard electrode 13 is a flat conductive member and is disposed so as to face the main electrode 11 with the film member 15 interposed therebetween. A film member 16 is disposed below the guard electrode 13. That is, the guard electrode 13 is disposed between the film member 15 and the film member 16. The main electrode 11 is disposed closer to the seating surface 911 of the seat 91 than the guard electrode 13. The film members 14 to 16 are made of an insulating material (for example, PET), and an adhesive is interposed between the film members 14 to 16, for example.

  The occupant detection ECU 2 is an electronic control unit, and includes a voltage application unit 21 (corresponding to a “detection voltage application unit”), a current detection unit 22, a capacity detection unit 23, an occupant determination unit 24, and an operational amplifier (“ Corresponding to a guard voltage applying unit ”25.

  The voltage application unit 21 is connected to the vehicle ground GND, the main electrode 11, and the operational amplifier 25. The voltage application unit 21 is an AC power supply, and applies an AC voltage (detection voltage) to the main electrode 11. Thereby, the main electrode 11 forms an electric field between the vehicle body 3 which is a reference electrode. The vehicle body 3 is a body part of the vehicle and constitutes an electrode, and is connected to a vehicle ground GND that is a reference potential.

  The current detection unit 22 includes a current that flows through the main electrode 11 by applying a voltage from the voltage application unit 21 (hereinafter also referred to as a detection current) and a current that flows through the guard electrode 13 by applying a voltage from the operational amplifier 25 (hereinafter also referred to as a guard current). Is detected.

  Specifically, the current detection unit 22 includes a current sensor (corresponding to a “current detection device”) 221, a switch unit 222, and a switch control unit 223. The current sensor 221 is a sensor that detects a current flowing through a connected detection target. Note that the connection of the current sensor to the detection target means a circuit state in which the current of the detection target can be detected.

  The switch unit 222 is a switch that can switch the connection destination of the current sensor 221 between the main electrode 11 and the guard electrode 13 in accordance with a signal from the switch control unit 223. The switch unit 222 includes a first switch 222a and a second switch 222b.

  The first switch 222a has one terminal connected to the main electrode 11, the other a contact connected to the current sensor 221 and the c contact of the second switch 222b, and the other b contact connected to the d contact and the operational amplifier of the second switch 222b. This is an electromagnetic switch connected to 25 output terminals. The second switch 222b has one terminal connected to the guard electrode 13, the other c contact connected to the current sensor 221 and the a contact of the first switch 222a, and the other d contact connected to the output terminal of the operational amplifier 25 and the first switch. This is an electromagnetic switch connected to the b contact of 222a.

  The switch control unit 223 is a control circuit that controls the connection destination of the switch unit 222. When the switch control unit 223 connects the first switch 222a to the contact a and the second switch 222b to the contact d, the current sensor 221 detects the current flowing through the main electrode 11. At this time, the main electrode 11 is connected to the voltage application unit 21 to apply a detection voltage, and the guard electrode 13 is connected to the operational amplifier 25 to apply a voltage having the same potential as the detection voltage (guard voltage). This connection state is referred to as a main detection state.

  Further, the switch control unit 223 connects the first switch 222 a to the b contact and the second switch 222 b to the c contact, so that the current sensor 221 detects the current flowing through the guard electrode 13. At this time, the guard electrode 13 is connected to the voltage application unit 21 to apply a detection voltage, and the main electrode 11 is connected to the operational amplifier 25 to apply a voltage having the same potential as the detection voltage. This connection state is referred to as a guard detection state. Thus, in the two connection states described above, the same potential voltage is applied to the main electrode 11 and the guard electrode 13. The switch control unit 223 of the present embodiment switches between the main detection state and the guard detection state every predetermined time.

  The capacity detection unit 23 is connected to the current detection unit 22 and the occupant determination unit 24. Specifically, the capacity detection unit 23 is connected to the occupant determination unit 24 and is also connected to the current sensor 221 via the switch control unit 223. The capacity detection unit 23 and the switch control unit 223 operate in conjunction with each other.

  The capacitance detection unit 23 calculates the electrostatic capacitance in the electric field formed by the main electrode 11 or the guard electrode 13 based on the voltage applied by the voltage application unit 21 and the current detected by the current detection unit 22. The capacitance can be calculated based on the imaginary component of the impedance (imaginary part of the admittance) in the current path when the voltage is applied, and the imaginary component can be calculated from the phase shift between the current and the voltage.

  The capacitance detection unit 23 is connected to the switch control unit 223, grasps the connection state of the switch unit 222 by the switch control unit 223, and determines whether the capacitance is the main electrode 11 or the guard electrode 13. ing. The calculation of the capacitance will be described later.

  The occupant determination unit 24 is connected to the capacity detection unit 23, and based on the detection result (capacitance) of the capacity detection unit 23 and a preset threshold value, the presence / absence of the occupant and whether the occupant is an adult or CRS. Determine if it exists.

  The operational amplifier 25 is an operational amplifier in which the voltage application unit 21 is connected to the input side and the switch unit 222 is connected to the output side. The operational amplifier 25 applies the same voltage to the guard electrode 13 as the voltage applied to the main electrode 11 in the main detection state. The guard electrode 13 has the same potential as the main electrode 11 below the main electrode 11, thereby suppressing the main electrode 11 from forming an electric field with the vehicle body 3 below the seating surface 911 of the seat 91. doing. That is, the guard electrode 13 is for the main electrode 11 to reliably form an electric field on the sheet 91.

  Here, the calculation of the capacitance by the capacitance detection unit 23 will be described. In the main detection state, the main electrode 11 and the guard electrode 13 do not actually have the same potential because the electrostatic capacities in the electric field formed are different. Accordingly, an equivalent circuit as shown in FIG. 4 is actually formed.

4, E is a voltage applied by the voltage application unit 21 and the operational amplifier 25, _Im is a current (detection current) flowing through the main electrode 11, and _Ig is a current flowing through the guard electrode 13 (guard current). is there. R _m is a resistance component of the main electrode 11, and R _g is a resistance component of the guard electrode 13. Z _m-body-GND is an impedance between the main electrode 11 and the vehicle body 3 (hereinafter referred to as a detection impedance), Z _m-g is an impedance between the main electrode 11 and the guard electrode 13, Z _g-GND is an impedance between the guard electrode 13 and the vehicle body 3 (hereinafter referred to as a guard impedance). Note that i _err is an unintended current that flows between the main electrode 11 and the guard electrode 13 due to a potential difference.
Here, the element necessary for occupant discrimination is the detection impedance Zm _-body-GND . R _m , R _g , and Z _m−g are design values and are values stored in the capacity detection unit 23 in advance. The detected impedance Z _m-body-GND can be calculated from the equivalent circuit by the following equation (1).

The capacitance detection unit 23 calculates the detection impedance Z _m-body-GND based on the equation (1), and calculates the capacitance based on the calculation result. As described above, the capacitance is an imaginary component of impedance (imaginary part of admittance), and can be calculated by obtaining the impedance. That is, the impedance and the capacitance correspond to each other, and calculating the impedance is equivalent to calculating the capacitance. In other words, the determination based on the capacitance is the same as the determination based on the impedance. The guard impedance _Zg-GND can be calculated by the following formula (2).

Control performed by the occupant detection ECU 2 of the present embodiment will be described. As shown in FIG. 5, first, the switch control unit 223 sets the switch unit 222 to the main detection state (the first switch 222a is a contact and the second switch 222b is a contact d) (S101). A current sensor 221 detects the detection current _{I m} (S102).

Subsequently, the switch control unit 223 sets the switch unit 222 to a guard detection state (the first switch 222a is a contact b and the second switch 222b is a contact c) (S103). A current sensor 221 detects the guard current _{I g} (S104). The capacitance detection unit 23 detects from the current information I _m and I _g from the current sensor 221, the applied voltage E of the voltage application unit 21, and the design values R _m , R _g , and Z _m-g using Equation (1) Impedance Zm _-body-GND is calculated (S105). The occupant determination unit 24 determines the presence and type of the occupant based on the calculation result of the capacity detection unit 23 (S106).

  As shown in FIG. 6, in the capacity conversion value (pF) from the detection current calculated by the capacity detection unit 23, a conventional occupant who does not consider the potential difference between the main guard and the adult in a thick-wearing adult and a one-year-old child (with a child seat) The capacitance difference (about 4.7 pF) in this embodiment is larger than the capacitance difference (about 4.1 pF) in the detection device. In other words, in the present embodiment, the discrimination between the two becomes clearer, and the occupant detection accuracy (occupant discrimination accuracy) is improved.

  As described above, according to the first embodiment, a guard current is detected, and a more accurate electrostatic capacity can be detected by using the guard current, so that occupant detection accuracy can be improved. In the first embodiment, only one current detection device such as a current sensor may be provided, and an existing switch can be used, which is excellent in terms of manufacturing cost. In the following embodiments, the detected impedance is calculated in the same manner as this embodiment, and FIG. 4 and Equation (1) can be referred to.

<Second embodiment>
A capacitive occupant detection device according to a second embodiment will be described with reference to FIG. The same reference numerals as those in the first embodiment indicate the same configurations as those in the first embodiment, and the preceding description is referred to. The capacitance type occupant detection device of the second embodiment differs from the first embodiment in the configuration of the current detection unit.

As illustrated in FIG. 7, the current detection unit 42 of the second embodiment includes a first current sensor 421 and a second current sensor 422. The first current sensor 421 is a current sensor in which one is connected to the voltage application unit 21 and the main electrode 11 and the other is connected to the capacitance detection unit 23. First current sensor 421, the current flowing through the main electrode 11 by applying a voltage of the voltage application section 21 (detection current) is detected I _m.

The second current sensor 422 is a current sensor in which one is connected to the operational amplifier 25 and the guard electrode 13 and the other is connected to the capacitance detection unit 23. Second current sensor 422 detects the current (guard current) _{I g} flowing to the guard electrode 13 by applying a voltage of the operational amplifier 25.

  According to the second embodiment, the same effect as the first embodiment is exhibited. Further, according to the second embodiment, the detection current and the guard current can be detected simultaneously without performing switch control. By detecting both currents at all times, a more accurate capacitance can be detected regardless of the seating timing of the occupant and the violent movement of the occupant on the seat 91.

<Third embodiment>
A capacitive occupant detection device according to a third embodiment will be described with reference to FIGS. The same reference numerals as those in the first embodiment indicate the same configurations as those in the first embodiment, and the preceding description is referred to. The capacitive occupant detection device of the third embodiment differs from the first embodiment mainly in that a third switch 5 is added and the capacitance detection unit 23 calculates a design value.

  As shown in FIG. 8, the third switch 5 is disposed between the second switch 222 b and the guard electrode 13. The third switch 5 is an electromagnetic switch having one terminal connected to the guard electrode 13, the other e-contact connected to one terminal of the second switch 222b, and the other f-contact connected to the vehicle ground GND. The third switch 5 is switched between the e-contact and the f-contact according to an instruction from the switch control unit 223.

  The capacity detector 23 instructs the switches 222a, 222b, and 5 via the switch controller 223 when calculating the design value. Specifically, the switch connection state when calculating the design value (hereinafter referred to as the design value detection state) is a state in which the first switch 222a is connected to the a contact and the third switch 5 is connected to the f contact. is there. In the design value detection state, the contact connection of the second switch 222b may be any and arbitrarily set.

In the design value detection state, the guard electrode 13 is connected to the vehicle ground GND, and the main electrode 11 is connected to the voltage application unit 21 and the current sensor 221. Thus, an electric field is formed between the main electrode 11 and the guard electrode 13 can be calculated design value R _m, R g, and _{Z m-g} from the voltage and current value at that time. The capacity detection unit 23 forms a design value detection state and calculates design values R _m , R _g , and Z _m−g before executing occupant detection. The capacitance detection unit 23 also serves as a design value calculation unit that calculates a design value by applying a reference potential (GND) to the guard electrode 13. It can also be said that the design value calculation unit is constituted by a part of the third switch 5 and the capacity detection unit 23 (a part for calculating the design value). In the main detection state and the guard detection state, the third switch 5 is connected to the e contact.

In the control of the occupant detection ECU 2 of the third embodiment, as shown in FIG. 9, first, the switch control unit 223 sets the switches 222a, 222b, and 5 to the design value detection state (S201). The capacity detection unit 23 is designed value _{R m,} R _g, and calculates the _{Z m-g} (S202). Subsequently, the switch control unit 223 sets the switches 222a, 222b, and 5 to the main detection state (the first switch 222a is a contact, the second switch 222b is a contact d, and the third switch 5 is an contact e) (S203). . Current sensor 221 detects a main current _{I m} (S204).

Subsequently, the switch control unit 223 sets the switches 222a, 222b, and 5 to the guard detection state (the first switch 222a is a contact b, the second switch 222b is a contact c, and the third switch 5 is an contact e) (S205). . Current sensor 221 detects a guard current _{I g} (S206). The capacitance detection unit 23 calculates the detection impedance Z _m-body-GND based on the detected design value, the current information from the current sensor 221 and the voltage value of the voltage application unit 21 based on the equation (1) (S207). And the passenger | crew discrimination | determination part 24 discriminate | determines a passenger | crew based on the detection result of the capacity | capacitance detection part 23 (S208).

  According to the third embodiment, in addition to the effects of the first embodiment, a design value can be measured by actual measurement, and a capacitance closer to an actual state can be detected. However, the design value may be stored as a fixed value calculated at the time of circuit design as in the first embodiment, and the first embodiment is superior in terms of manufacturing cost.

<Fourth embodiment>
A capacitive occupant detection device according to a fourth embodiment will be described with reference to FIGS. 2 and 10 to 12. The same reference numerals as those in the first embodiment indicate the same configurations as those in the first embodiment, and the preceding description is referred to. The capacitive occupant detection device of the fourth embodiment differs from the first embodiment mainly in that the occupant determination unit 24 performs failure determination. Therefore, the circuit configuration of the fourth embodiment is the same as that of the first embodiment (see FIG. 2).

  The occupant determination unit 24 determines whether or not the electrostatic sensor 1 has failed based on the detection result of the capacity detection unit 23. That is, the occupant determination unit 24 determines the occupant and also determines the failure of the electrostatic sensor 1 based on the detection result of the capacity detection unit 23. The occupant determination unit 24 and the capacity detection unit 23 correspond to the “failure determination unit” in the present invention.

  As shown in FIGS. 10 and 11, the occupant determination unit 24 determines a failure and an occupant based on the magnitude relationship between the impedance detected by the capacity detection unit 23 and a preset threshold value.

Specifically, the detection impedance (indicated as _{Z m} in this case) if the adult threshold (Th_adult_m) greater than the main side first fault threshold (Th_err_m) smaller, and the guard impedance (here indicated as _{Z g} ) Is larger than the guard-side second failure threshold (Th_empty_g) and smaller than the guard-side first failure threshold (Th_err_g), the occupant determination unit 24 determines that the occupant is “adult” with “no failure”.

In the case detection impedance Z _m is smaller than the larger adult threshold than children threshold (Th_child_m), and when the guard impedance Z _g is smaller than the large guard side first failure threshold than the guard-side second failure threshold value, determining an occupant 24 The passenger is determined as “child (child seat)” with “no failure”.

Also, if the detected impedance Z _m is the case larger than the main side a second failure threshold (Th_empty_m) smaller than the child threshold and guard impedance Z _g is smaller than the large guard side first failure threshold than the guard-side second failure threshold value, the passenger The determination unit 24 determines that the occupant is “vacant (vacant)” based on “no failure”.

Thus, for detecting the impedance Z _m, and adult threshold for determining whether an adult or a child, and a child threshold for determining whether a child or vacant, for determining whether the first fault or adult A main-side first failure threshold and a main-side second failure threshold for determining whether the second failure or vacant seat is set. Further, with respect to the guard impedance Z _g, and the guard-side first failure threshold determines whether the first fault, a second fault whether the guard-side second failure threshold determines, is set Yes.

Occupant determination section 24, if the detected impedance Z _m with guard impedance Z _g is other than the above three patterns, it determines the electrostatic sensor 1 has failed (the fault there), thereby notifying device (shown such as a display lamp To notify the user. Furthermore, in this embodiment, the type of failure (whether the electrode is disconnected or short-circuited) and the disconnection location (which electrode is disconnected) are determined in the case of disconnection.

For example, if half of the main electrode 11 is disconnected from the relationship of the electrode area and arrangement position occupying the electrostatic sensor 1, the detection impedance Z _m is decreased, the guard impedance Z _g is abnormally increased. The occupant determination unit 24 performs failure determination using such detection results. This will be specifically described below.

(Main electrode disconnection failure)
If the detected impedance Z _m is smaller than the adult threshold and guard impedance Z _g is greater than the guard-side first fault threshold, the occupant judgment unit 24 determines as "main electrode 11 breaks down." Here, as shown in FIG. 12, when "main electrode 11 disconnection fault" actual occupant is "adult", the detection impedance Z _m can be larger than the smaller children threshold than adults threshold. In this case, in the conventional configuration without the failure determination of the present embodiment, the passenger is erroneously determined as “child”. Further, when the actual occupant is “child” and “main electrode 11 disconnection failure”, the detected impedance Z _m can be smaller than the child threshold. In this case, in the conventional configuration, the passenger is erroneously determined as “vacant seat”.

The detection impedance Z _m is smaller than the main side a second failure threshold value, and, when the guard impedance Z _g is greater than the second threshold of failure smaller guard side of the guard-side first fault threshold, the occupant judgment unit 24, "the main electrodes "11 disconnection failure". Only be detected impedance Z _m is smaller than the main side a second threshold of failure, whether any of the electrodes of the main electrode 11 and the guard electrode 13 is disconnected can not be specified.

(Guard electrode disconnection failure)
On the other hand, if the detected impedance Z _m is large and guard impedance Z _g from the main side a second failure threshold is less than the guard-side second failure threshold, the occupant judgment unit 24 determines a "guard electrode 13 breaks down." Here, as shown in FIG. 12, when a "guard electrode 13 disconnection fault" actual occupant is "child", the detection impedance Z _m can be smaller than the larger main side first threshold than adults threshold. In this case, in the conventional configuration, the passenger is erroneously determined as “adult”. Also, if the actual occupant is "unoccupied" in the "guard electrode 13 disconnection failure", the detection impedance Z _m can be smaller than the larger adult threshold than children threshold. In this case, in the conventional configuration, the passenger is erroneously determined as “child”.

The detection impedance Z _m is greater than the main side first failure threshold value, and, when the guard impedance Z _g is greater than the second threshold of failure smaller guard side of the guard-side first fault threshold, the occupant judgment unit 24, "the guard electrode It is determined as “13 disconnection failure”.

(Other failures)
Also, if the detected impedance Z _m is small and the guard impedance Z _g from the main side a second failure threshold is less than the guard-side second failure threshold, the occupant judgment unit 24 includes a "main electrode 11 and the guard electrode 13 disconnection fault" judgment To do. Further, when large and guard impedance Z _g from detected impedance Z _m is the main side first failure threshold is greater than the guard-side first fault threshold, the occupant judgment unit 24, the "main electrode 11 and the guard electrode 13 short-circuited It is determined as “failure”.

Thus, according to the fourth embodiment, detecting a detection impedance Z _m and guard impedance Z _g in (and thus the detected voltage, detected current, and detecting the guard current), failure details (Type-position ) Can be specified, and occupant detection accuracy can be improved by suppressing erroneous determination. According to the fourth embodiment, since the failure of the guard electrode 13 can be detected, erroneous determination can be suppressed with higher accuracy. The occupant determination unit 24 can perform occupant determination based on the failure determination result.

  In the fourth embodiment, in addition to the detection voltage and the detection current, a guard current is detected, and these values are used to determine details of the failure and suppress erroneous determination. That is, the occupant determination unit 24 including the failure determination unit determines a failure based on the detected voltage, the detected current, and the guard current.

<Other variations>
The present invention is not limited to the above embodiment. For example, the electrostatic sensor 1 may have a sub electrode 12 as shown in FIG. In this case, the sub-electrode 12 is a flat conductive member, and is disposed on at least one side (here, both sides) of the main electrode 11 so as to be adjacent to the main electrode 11 on the film member 15. In other words, the sub electrode 12 is spaced apart from and parallel to the edge of the main electrode 11 (along the edge). A film member 14 is disposed on the main electrode 11 and the sub electrode 12. That is, the main electrode 11 and the sub electrode 12 are disposed between the film member 14 and the film member 15.

  In this case, the operational amplifier 25 has the voltage application unit 21 connected to the input side and the sub electrode 12 and the guard electrode 13 connected to the output side. The operational amplifier 25 applies the same voltage as the voltage applied to the main electrode 11 to the sub electrode 12 and the guard electrode 13.

  The sub electrode 12 suppresses the electric lines of force coming out from the end (edge) of the main electrode 11 from extending from the end of the main electrode 11 toward the vehicle body 3 without the seat 91 and the passenger. The sub-electrode 12 can also be used as an electrode for detecting the wetness of the sheet 91. In this case (during wet detection mode), a reference potential (vehicle ground GND) is applied to the sub-electrode 12, and an electric field is formed between the main electrode 11 to which the detection voltage is applied and the sub-electrode 12 of the reference potential. Then, the moisture is detected based on the capacitance between the electrodes.

When the above embodiment includes the sub electrode 12, R _g is a resistance component of the guard electrode 13 and the sub electrode 12, and Z _m−g is an impedance between the main electrode 11 and the guard electrode 13 (including the sub electrode 12). Thus, _Ig is a current value flowing through the guard electrode 13 and the sub electrode 12, and Z _{g -GND} is an impedance between the guard electrode 13 and the sub electrode 12 and the vehicle body 3. Also by this, the same effect as the said embodiment is exhibited.

  In the third embodiment, the third switch 5 may be disposed between the main electrode 11 and the first switch 222a. That is, the third switch 5 is an electromagnetic switch in which one terminal is connected to the main electrode 11, the other e-contact is connected to one terminal of the first switch 222a, and the other f-contact is connected to the vehicle ground GND. Thus, the one terminal of the second switch 222b and the guard electrode 13 are directly connected.

  The third switch 5 may be disposed between the main electrode 11 and the first switch 222a and between the guard electrode 13 and the second switch 222b. Also with these configurations, by switching the third switch 5, the reference potential (vehicle ground GND) can be applied to either the main electrode 11 or the guard electrode 13, and the same effect as the third embodiment is exhibited. The

  In the fourth embodiment, for occupant detection, the detection impedance may be detected from the detection voltage and the detection current as usual without using the guard current. That is, in the fourth embodiment, apart from occupant detection, only failure detection may be performed based on the detection voltage, detection current, and guard current. This also enables detailed failure determination.

Moreover, although the mathematical expression is a vector notation, it may be any mathematical expression that can be derived from the equivalent circuit, and may be expressed in a form other than the vector notation. Further, in the fourth embodiment, even when it is determined that there is a failure, the determination condition at the time of failure may be set with reference to the actually measured values in FIG. 11, and the occupant may be determined based on the impedances Z _m and Z _g. . The occupant detection ECU 2 may include a failure determination unit that determines a failure of the electrostatic sensor 1 based on the detection voltage, the detection current, and the guard current, separately from the capacity detection unit 23 and the occupant determination unit 24. Good.

  Further, the switching control method of the switch unit 222 by the switch control unit 223 is basically set to the main detection state, for example, so that the main detection state and the guard detection state are switched only when the detection current increases. May be set.

In addition, when the main electrode 11 and the sub electrode 12 to which the same voltage is applied form an electric field between the reference electrode (vehicle body 3), the sum of the currents flowing through the electrodes 11 and 12 is defined as the detection current _Im. It may be detected. In this case, the main electrode 11 and the sub electrode 12 serve as detection electrodes. Moreover, you may combine embodiment suitably, such as 2nd embodiment, 3rd embodiment, or 4th embodiment, 3rd embodiment, and 4th embodiment.

1: electrostatic sensor, 11: main electrode (detection electrode), 13: guard electrode,
2: occupant detection ECU, 21: voltage application unit (detection voltage application unit),
22, 42: current detection unit, 221: current sensor, 222: switch unit,
222a: first switch, 222b: second switch,
223: switch control unit, 421: first current sensor, 422: second current sensor,
23: Capacity detection unit, 24: Passenger discrimination unit, 5: Third switch

Claims (9)

An electrostatic sensor (1) having a detection electrode (11) and a guard electrode (13) disposed opposite to the detection electrode (11) and disposed on a vehicle seat (91);
A detection voltage applying unit (21) for applying a detection voltage to the detection electrode (11) and forming an electric field between the detection electrode (11) and a reference electrode (3) to which a reference potential is applied;
A guard voltage application unit (25) for applying a voltage having the same potential as the detection voltage to the guard electrode (13);
A current detection unit (22, 42) for detecting a detection current that is a current flowing through the detection electrode (11) and a guard current that is a current flowing through the guard electrode (13);
A capacitance detector (23) for detecting a capacitance between the detection electrode (11) and the reference electrode (3) based on the detection voltage, the detection current, and the guard current;
An occupant determination unit (24) for determining an occupant of the seat (91) based on the capacitance;
An electrostatic capacity type occupant detection device. The current detection unit (22)
A current detection device (221) for detecting current;
A switch unit (222) capable of switching the connection with the current detection device (221) between the detection electrode (11) and the guard electrode (13);
A switch control unit (223) for switching the connection of the switch unit (222);
The capacitive occupant detection device according to claim 1. The current detector (42)
A first current detection device (421) connected to the detection electrode (11) and detecting the detection current;
A second current detection device (422) connected to the guard electrode (13) for detecting the guard current;
The capacitive occupant detection device according to claim 1. The capacitance detecting section (23), the detection voltage is E, the detected current and I _m, the guard current and I _g, the resistance component of the detection electrode (11) and R _m, wherein the guard electrode ( the resistive component of 13) and _{R g,} wherein said detection electrode (11) wherein the detection impedance is the impedance between the reference electrode (3) and _{Z m-body-GND,} the detection electrode (11) guard The impedance between the electrode (13) is Z _m-g and the guard impedance, which is the impedance between the guard electrode (13) and the reference electrode (3), is Z _g-GND. The capacitance type occupant detection device according to any one of claims 1 to 3, wherein the capacitance is calculated based on the capacitance.

The reference potential is applied to the detection electrode (11) or the guard electrode (13), an electric field is formed between the detection electrode (11) and the guard electrode (13), and the resistance of the detection electrode (11) is increased. a component _{R m,} wherein the resistance component _{R g} of the guard electrode (13), said detection electrode (11) and the design value calculating unit that calculates an impedance _{Z m-g} between the guard electrode (13) (23 5) The capacitive occupant detection device according to claim 4, further comprising 5).   6. The apparatus according to claim 1, further comprising a failure determination unit (23, 24) that determines a failure of the electrostatic sensor (1) based on the detection voltage, the detection current, and the guard current. Capacitance type occupant detection device.   The failure determination unit (23, 24) is configured to detect a detection impedance which is an impedance between the detection electrode (11) and the reference electrode (3) based on the detection voltage, the detection current, and the guard current. Calculating a guard impedance which is an impedance between the guard electrode (13) and the reference electrode (3), and determining a failure of the electrostatic sensor (1) based on the detected impedance and the guard impedance The capacitive occupant detection device according to claim 6.   The electrostatic capacity type occupant detection device according to claim 6 or 7, wherein the failure determination unit (23, 24) determines whether or not the electrode is disconnected. An electrostatic sensor (1) having a detection electrode (11) and a guard electrode (13) disposed opposite to the detection electrode (11) and disposed on a vehicle seat (91);
A detection voltage applying unit (21) for applying a detection voltage to the detection electrode (11) and forming an electric field between the detection electrode (11) and a reference electrode (3) to which a reference potential is applied;
A guard voltage application unit (25) for applying a voltage having the same potential as the detection voltage to the guard electrode (13);
A current detection unit (22, 42) for detecting a detection current that is a current flowing through the detection electrode (11) and a guard current that is a current flowing through the guard electrode (13);
A capacitance detector (23) for detecting a capacitance between the detection electrode (11) and the reference electrode (3) based on at least the detection voltage and the detection current;
An occupant determination unit (24) for determining an occupant of the seat (91) based on the capacitance;
A failure determination unit (23, 24) for determining whether the electrostatic sensor (1) is disconnected based on the detection voltage, the detection current, and the guard current;
An electrostatic capacity type occupant detection device.

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