JP2000335363A - Occupant posture detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the operation in developing an air bag by detecting the posture of an occupant. SOLUTION: A pair of electrodes 5a, 5b whose capacity is changed according to the distance from a human body are arranged on a rear surface of an air bag pad 3 at the center of a steering wheel 1. The posture of an occupant is detected by detecting the change in capacity between the electrodes 5a, 5b by a posture detecting circuit. The operation of an air bag is controlled according to the detected result. A guard electrode 5c is arranged on the receiving electrode 5b side between a pair of electrodes 5a, 5b to prevent the direct coupling between the electrodes 5a, 5b and improve the detection sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an occupant posture detecting apparatus which is installed in a seat of an automobile or an aircraft and detects an occupant's posture.

[0002]

2. Description of the Related Art Conventionally, an airbag device has been used as an occupant protection device mounted on a vehicle from the viewpoint of safety. When the vehicle suddenly decelerates, the airbag device detects this, ignites the inflator, burns the gas generating agent contained inside the inflator, and momentarily generates the gas generated in the bag body. By sending the bag, the bag is instantly inflated to function as a cushion for protecting the occupant's head and the like from impact. The bag body and the inflator of this airbag device are usually housed in a center pad of the steering wheel on the driver's seat side, and are housed in a dashboard or the like on the passenger seat side. Also recently,
In order to cope with a collision from the side, a type provided with a side airbag is also known. In this case, the side airbag is accommodated in a door lining or the like.

[0003]

In the conventional airbag device, the airbag is deployed regardless of the posture of the occupant. Therefore, the airbag operates in a state where the inflator and the occupant's head are extremely close to each other. There is. In this case, a large impact is applied to the occupant's head by the deployment of the airbag. In order not to cause such a problem, it is necessary to accurately detect the distance between the occupant and the inflator.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an occupant posture detecting device capable of detecting the occupant's posture and suppressing the operation when the airbag is deployed.

[0005]

An occupant posture detecting apparatus according to the present invention is arranged near an accommodating portion of an airbag which inflates at the time of a vehicle collision, and has at least one pair whose capacity changes according to a distance from a human body. And a transmission circuit for supplying a predetermined transmission signal to the transmission electrode, and a transmission circuit disposed between the transmission electrode and the reception electrode to prevent direct coupling from the transmission electrode to the reception electrode. A guard electrode,
A posture detection circuit for detecting a change in capacitance between the transmission electrode and the reception electrode to detect a posture of the occupant.

According to the present invention, at least a pair of transmitting electrodes and receiving electrodes are arranged near the accommodation portion of the airbag, and the distance between these electrodes and the human body is detected as a capacitance value. It can be determined accurately.
When the head or the like is close to the airbag, the operation of the inflator is suppressed, so that the impact on the head due to the deployment of the airbag can be prevented.

[0007] The electrode may be placed on, for example, the back of an airbag pad at the center of the steering of a vehicle,
Dashboards, door linings, etc. are possible.

According to the present invention, a guard electrode is arranged between the transmitting electrode and the receiving electrode to prevent direct coupling between these electrodes, so that an external human body against a current flowing directly between the electrodes is provided. The ratio of the current flowing through the gate electrode can be made higher than that without the guard electrode. Thereby, the detection sensitivity when a human body approaches between the electrodes can be increased. The guard electrode is desirably arranged near the receiving electrode so as not to block the electric field from the transmitting electrode to the outside human body.

In the case where an airbag operation control device for controlling the operation of an airbag using the attitude control device of the present invention is constructed, the above-described attitude control device is replaced with an airbag control device for controlling the deployment of the airbag. What is necessary is just to combine with a circuit. The airbag control circuit only needs to control the operation of the airbag so as to suppress the operation of the airbag when the posture detection circuit detects that the occupant's head is close to the airbag.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining an electrode arrangement of the occupant posture detection device according to the present invention. The steering 1 of the car is a wheel body 2
And an airbag pad 3 provided at the center of the steering wheel 1 to accommodate an airbag inflator (not shown) and a bag body, and a hub 4 connecting the two. In this embodiment, a rectangular transmission electrode 5a and a reception electrode 5b are arranged on the back surface of the airbag pad 3 at a predetermined interval, and a guard electrode 5c is arranged near the reception electrode 5b between the electrodes 5a and 5b. are doing.

FIG. 2 shows a structure for electrically connecting the electrodes 5a, 5b, 5c to the main body. Electrodes 5a, 5 attached to steering 1
The clock spring 12 electrically connects the b, 5c and the airbag module 11 to a controller and a posture detection circuit (not shown) of the vehicle body. As a result, the electrodes 5a, 5
The connection between b, 5c and the attitude detection circuit is not interrupted.

FIG. 3 is a circuit diagram showing an example of a posture detecting circuit to which the electrodes 5a and 5b are connected. The oscillation circuit 21
A transmission signal of a predetermined frequency is supplied to the transmission electrode 5a. The transmission signal from the transmitting electrode 5a is received by the receiving electrode 5b. A guard electrode 5c arranged between the electrodes 5a and 5b and grounded is provided to prevent direct coupling from the transmission electrode 5a to the reception electrode 5b. The received signal received by the receiving electrode 5b is divided into a reference capacitor 22 and an amplifier 23.
, And amplified by an amplifier 24 including resistors 35 and 36 and a capacitor 37 for preventing DC saturation of the amplifier 23. The amplification factor is determined by the ratio between the capacitance between the electrodes 5a and 5b and the reference capacitance 22. The output of the amplifier 24 includes an amplifier 25, resistors 26 and 27 respectively connected to an inverting input terminal and a non-inverting input terminal of the amplifier 25, a diode 28 connected in a feedback direction to a feedback path of the amplifier 25, and an amplifier 25. 25
Is rectified by a half-wave rectifier circuit 31 including a diode 29 connected in the reverse direction to the output of the amplifier 29 and a resistor 30 connected to a feedback path from the anode side of the diode 29 to the inverting input terminal of the amplifier 25. The output is smoothed by a smoothing circuit 34 including a resistor 32 and a capacitor 33, and is taken out as a DC signal indicating the capacity between the electrodes 5a and 5b.

According to this configuration, as shown in FIG. 4A, when no human body exists near the electrodes 5a and 5b, a predetermined capacitance value is observed. However, when the human body 41 exists near the electrodes 5a and 5b, a shunting current I2 is generated as shown in FIG.
The capacity of 5b is apparently lower than that of FIG. This capacitance change is detected by the detection circuit of FIG.

That is, as shown in FIG. 3, the electrodes 5a, 5b
Assuming that the inter-capacitance is C, the reference capacitance 22 is Cr, and the input voltage of the amplifier 24 is Vin, the output voltage Vout of the amplifier 24 is expressed by the following equation (1).

[0015]

Vout = (C / Cr) Vin

Therefore, when the human body approaches the center of the steering wheel 1 and the capacitance C between the electrodes 5a and 5b decreases, the output voltage Vout also decreases. This is shown in the graph of FIG. This graph shows the output voltage of the detection circuit with respect to the distance between the electrode and the occupant. As is clear from this figure, when the occupant is close to the electrodes, the output voltage of the detection circuit is greatly reduced, so that the occupant's posture can be detected.

By the way, as shown in FIG. 4B, when the guard electrode 5c does not exist between the electrodes 5a and 5b, the current I1 flowing by the direct coupling from the transmission electrode 5a to the reception electrode 5b is generated by the human body 41. Is much larger than the leakage current I2 through the electrodes, and when the distance between the electrodes 5a and 5b and the human body 41 is several tens of cm, the rate of change of the capacitance C between the electrodes is small. Therefore, when the distance between the human body 41 to be detected and the electrodes 5a and 5b is large, the detection sensitivity is low.

Therefore, as shown in FIG.
When the guard electrode 5c is disposed between the transmission electrode 5a and the
Since most of the electric field from a is shielded by the guard electrode 5c, the direct coupling between the electrodes 5a and 5b is reduced, and the current I1 'flowing directly between the electrodes 5a and 5b is also reduced. As a result, I2 '/ I1'> I2 / I1, and the detection sensitivity is improved.

FIG. 6 is a graph showing the amount of change in output voltage with respect to the distance between the electrodes 5a and 5b and the object to be detected as a ratio to the initial value. As is apparent from this figure, in the embodiment with the guard electrode, the amount of change in the output voltage is larger than in the comparative example without the guard electrode, and the detection sensitivity is improved. FIG. 7 is a graph showing the improvement rate of the change amount of the output voltage due to the addition of the guard electrode with respect to the distance between the electrode and the detection target. As is clear from this figure, by adding the guard electrode, the improvement rate of the change rate at each distance is 20% or more.

The present invention is not limited to the embodiment described above. In the above embodiment, the rectangular electrodes 5a to 5a
Although 5c is used, for example, as shown in FIG. 8, a transmitting electrode 6a, a receiving electrode 6b, and a guard electrode 6c which are arranged concentrically can be used. Since the electrodes 6a to 6c are arranged concentrically, the influence of the human body located on the side of the electrodes 6a to 6b is small, and the detection directivity in the direction orthogonal to the paper surface is improved. FIG. 8A shows an example in which the transmitting electrode 6a is arranged at the center. In this case, an annular guard electrode 6c is arranged immediately inside the annular receiving electrode 6b.
FIG. 8B shows an example in which the receiving electrode 6b is arranged at the center.
In this case, a ring-shaped guard electrode 6c is arranged immediately around the center of the circular reception electrode 6b.

[0021]

As described above, according to the present invention, at least a pair of electrodes are arranged near the accommodation portion of the airbag, and the distance between the electrodes and the human body is detected as a capacitance value. Since the guard electrode is provided, it is possible to reduce the current value due to direct coupling between the electrodes, thereby providing an effect of increasing the detection sensitivity.

[Brief description of the drawings]

FIG. 1 is a plan view of a steering wheel for explaining an electrode arrangement of a posture detecting device according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view showing a structure of a steering in which the electrode is housed.

FIG. 3 is a circuit diagram of a posture detection circuit in the device.

FIG. 4 is a diagram for explaining the principle of attitude detection in the device.

FIG. 5 is a graph showing a relationship between a distance between an electrode and an occupant in the apparatus and an output voltage of a detection circuit.

FIG. 6 is a graph showing a change amount of an output voltage with respect to a distance between a detection target and an electrode in the same device.

FIG. 7 is a graph showing an improvement rate of an output voltage change amount by a guard electrode with respect to a distance between a detection target and an electrode in the same device.

FIG. 8 is a view showing an electrode pattern according to another embodiment of the present invention.

[Explanation of symbols]

1 ... steering, 3 ... airbag pad, 5a, 6a
... Transmitting electrodes, 5b, 6b ... Receiving electrodes, 5c, 6c ... Guard electrodes.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukio Koganei, 1440, Mukurosaki, Sakura City, Chiba Prefecture Inside Fujikura Sakura Plant (72) Inventor, Kiyoji Ohba 1440, Musaki, Sakura City, Chiba Prefecture Inside Fujikura Sakura Plant 72) Inventor Kazuya Akashi 1440 Mutsuzaki, Sakura City, Chiba Prefecture Inside Fujikura Sakura Plant, Inc. (72) Inventor Ichiro Terunuma 1440 Mutsuzaki, Sakura City, Chiba Prefecture Inside Fujikura Sakura Plant, F-term (reference) DA01 DA05 HA01 3D054 AA02 AA03 AA13 AA14 EE11 EE27 FF16

Claims (2)

[Claims] At least one pair of a transmission electrode and a reception electrode, which are arranged near an accommodation portion of an airbag that inflates at the time of a vehicle collision, and whose capacity changes according to a distance from a human body, A transmission circuit for supplying a transmission signal; a guard electrode disposed between the transmission electrode and the reception electrode to prevent direct coupling from the transmission electrode to the reception electrode; and a capacitance change between the transmission electrode and the reception electrode. And a posture detection circuit for detecting the posture of the occupant by detecting the occupant posture. 2. The occupant posture detecting device according to claim 1, wherein the guard electrode is arranged near the receiving electrode.