Passenger detection system

Details Passenger detection system Passenger detection system

1998-11-13

2001-12-04

Culbreth, Eric (Department: 3611)

Land vehicles

Wheeled

Attachment

C701S045000

Reexamination Certificate

active

06325413

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a system and a method for detecting a passenger seated on a seat of a vehicle, and in particular, to a passenger detection system and a passenger detection method which can also protect the passenger from injury due to deployment of an air bag when the upper body of the passenger is close to the dashboard.
1. Description of the Prior Art
Air bag units for absorbing shocks and providing relief from impact damage of car passengers in cases of collisions have become indispensable gear for car safety, and are being provided not only to driver's seats but also to passenger seats in recent years.
FIG. 1
is a circuit diagram showing a conventional circuit employed in air bag systems. The circuit of
FIG. 1
comprises a driver's seat squib circuit composed of a series connection of a safety sensor SS
1
such as a mechanical accelerometer, a squib SQ
1
, and a semiconductor switching device SW
1
such as an FET (Field-Effect Transistor), and a passenger seat squib circuit composed of a series connection of a safety sensor SS
2
, a squib SQ
2
, and a semiconductor switching device SW
2
such as an FET, and an electronic accelerometer (collision sensor) AM for detecting negative acceleration due to collisions, and a control circuit CC provided with functions for judging the presence or absence of a collision according to an output signal of the electronic accelerometer AM and supplying signals to the gates of the semiconductor switching devices SW
1
and SW
2
.
When a car provided with the air bag system collided with something, switches of the safety sensors SS
1
and SS
2
are closed with relatively small negative acceleration enabling the driver's seat squib circuit and the passenger seat squib circuit. If the control circuit CC judged that the car actually collided with something according to the output signal from the electronic accelerometer AM, the control circuit CC supplies signal to the gates of the semiconductor switching devices SW
1
and SW
2
and the semiconductor switching devices SW
1
and SW
2
are turned ON, thereby currents are passed through the two squib circuits. Due to the currents, the squibs SQ
1
and SQ
2
are heated and thereby the air bags for the driver's seat and the passenger seat are deployed to protect the passengers from impact damage by the collision.
Incidentally, such an air bag system is effective for saving the passenger in the case where an adult person P is seated on the seat
1
as shown in FIG.
2
A. However, in the case where an infant SP is seated on an infant seat
1
A fixed on the passenger seat facing rear (hereafter referred to as ‘RFIS (Rear Facing Infant Seat)’ as shown in
FIG. 2B
, deployment of the air bag might hurt the infant, and thus it is preferable that the air bag does not deploy on the collision. Further, in the case where a child SP′ is seated on a child seat
1
A′ fixed on the passenger seat facing forward (hereafter referred to as ‘FFCS (Forward Facing Child Seat)’ as shown in
FIG. 2C
, deployed air bag might cover the face of the child SP′ and suffocate the child SP′, and thus it is preferable that the air bag does not deploy on the collision similarly to the case of RFIS.
As a countermeasure against the above problems, a circuit for air bag systems shown in
FIG. 3
has been proposed, for example. The circuit of
FIG. 3
further comprises a passenger detection sensor device SD for detecting the status of the passenger on the passenger seat. The control circuit CC judges whether or not a passenger is seated on the passenger seat and the status of the passenger on the passenger seat, according to a detection signal from the passenger detection sensor device SD, and sets itself at a deployment mode in which the control circuit CC deploys the air bag on collision, or at a no deployment mode in which the control circuit CC does not deploy the air bag on collision. As the passenger detection sensor device SD, a device employing a weight sensor and a device employing image processing have been proposed. In the method employing image processing, the passenger is shot by a camera and it is judged whether the passenger is an adult person P or a child SP′ or an infant SP by means of image processing.
By the first method employing a weight sensor, whether the passenger is an adult P or a child SP′ or an infant SP can roughly be judged and the above unexpected accidents can basically be avoided by the setting of the control circuit CC into the deployment mode or the no deployment mode based on the judgment. However, such a method employing a weight sensor lacks precision since weight varies widely among individuals and there exist cases where a child SP′ weighs more than a very thin adult person P. Further, it is impossible to judge whether the status of a little child on the passenger seat is RFIS or FFCS.
By the second method employing image processing, it is possible to judge rather precisely whether or not a passenger is seated on the passenger seat, whether the passenger is an adult P or a child SP′ or an infant SP, and whether the status of a little child on the passenger seat is RFIS or FFCS. However, image processing and pattern matching against various kinds of patterns have to be executed to image data obtained by a camera, and thus complex and expensive image processing device is needed.
2. Description of the Related Art
In order to resolve the above problems, the present inventors have lately proposed a passenger detection system shown in FIG.
4
A through
FIG. 8
(Japanese Patent Application No.HEI9-42650). The system utilizes disturbance in a weak alternating electric field which is generated between two electrodes placed on a seat. Referring to
FIG. 4A
, an oscillator for generating high frequency low voltage is connected to an electrode E
1
, and another electrode E
2
is grounded. An alternating electric field is generated between the electrodes E
1
and E
2
according to the potential difference between the electrodes E
1
and E
2
, thereby a displacement current Id occurs between the electrode E
2
and the ground. In this situation, if an object OB is placed in the electric field as shown in
FIG. 4B
, the electric field is disturbed by the object OB and thereby the displacement current Id varies into Id
1
. Almost every object OB can be represented by a conductance and a capacitance, and the object OB is regarded to be connected to the ground via the capacitance.
As shown above, the displacement current varies depending on whether or not an object OB exists on a seat of a car, and the status of a passenger on the seat can be detected by utilizing the phenomenon. Especially, a lot of information about an object on the seat including a passenger can be obtained by increasing the number of electrodes which are placed on the seat, thereby precise detection of the situation on the seat can be executed.
In the following, a concrete example of a passenger detection system utilizing the phenomenon will be described referring to FIG.
5
through FIG.
8
.
FIG. 5
is a perspective view of a passenger seat which is provided with the passenger detection system which has been proposed by the present inventors. A plurality of electrodes are placed on the upper side of the passenger seat
1
. Concretely, electrodes E
1
and E
2
of quadrangular shapes for example are placed apart on the cushion section
1
a
, and electrodes E
3
and E
4
of almost the same shapes are placed apart on the back section
1
b
. The electrodes E
1
~E
4
are formed of electrically conductive fabrics in consideration of comfort of the passenger. However the electrodes E
1
~E
4
can also be formed by weaving stringy metal in fabric which covers the seat, by applying electrically conductive paint on fabric which covers the seat, etc., or it is also possible to form the electrodes E
1
~E
4
by metal plates. The electrodes E
1
~E
4
are connected to a circuit which is shown in FIG.
6
and FIG.
7
.
Referring to
FIG. 6
, the

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