The present invention relates to a passenger protecting apparatus such as an airbag system etc. which is used to protect a passenger at the time of a vehicle collision.
An airbag, at the time of a vehicle collision, is expanded abruptly between a steering wheel or dashboard and a passenger to protect the passenger. It is known, however, that there are cases where this airbag expansion inflicts an injury on the passenger in case a driver drives in a position close to the steering wheel because of his low stature, and in case a distance is very short between the steering wheel or dashboard and the passenger, such as in case a child stands in front of an assistant driver's seat. Thus, in order to prevent such a phenomenon, America intends to legislate for the obligation to install a passenger detecting unit in the passenger protecting apparatus using an airbag.
As a passenger protecting apparatus having a passenger detecting unit therein for this purpose, for example, the one as described in the Unexamined Japanese Patent Application Publication No. Hei 10-100858 is known. The construction of this apparatus will be explained with reference to FIG. 5. In the figure, the reference numeral 1 depicts a windshield of a vehicle, 2 a dashboard, 3 an airbag for a frontal crash housed in the dashboard 2, 4 an assistant driver's seat, 5 a critical region where a person if any is in danger of getting injured in case the airbag is expanded, 6 an interior ceiling of the vehicle, 11 an infrared emission means provided on the dashboard 2 for emitting an infrared beam, and 16 an infrared detection means, provided likewise on the dashboard 2, having a PSD therein, and a position detecting means 20 is composed of the infrared emission means 11 and the infrared detection means 16.
Next, an explanation will be given of the operation. An infrared beam is emitted obliquely upward as shown in the figure from the infrared emission means 11. In case no person is present in the critical region, such as in case an adult sits normally in the assistant driver's seat, etc., this infrared beam reaches the interior ceiling 6 to form an infrared spot thereon. On the contrary, in case a person is present in the critical region, such as in case a child stands in front of the assistant driver's seat, the infrared beam is intercepted by the body of the person so that the infrared spot is formed on the body of the person. By detecting the position of this infrared spot through the infrared detecting means 16, the distance between the dashboard and the body of the person can be detected on the principle of trigonometrical survey. A not-shown ECU, upon determining that this detected distance is so short that it is dangerous to expand the airbag, suppresses the airbag expansion even in case a collision is detected by a not-shown acceleration sensor, so as to prevent the airbag expansion from inflicting an injury on the passenger.
Also, as an example of the passenger protecting apparatus characterized in that there is provided a position detecting means detecting the distance between a dashboard and the body of a person, some methods are known, such as the one using an ultrasonic sensor as described in the Unexamined Japanese Patent Application Publication No. Hei 11-286256, the one using an optical sensor as described in the Unexamined Japanese Patent Application Publication No. Hei 11-217056, etc. However, in any case, the position detecting means is provided on the dashboard ahead of a passenger or at the front end of the interior ceiling of a vehicle to measure the distance to the front surface of the passenger. Accordingly, there is a problem, for example, that, in case the passenger opens up a magazine or newspaper or stretches his arms to the fore, the system misidentifies that a person is present in the critical region so that airbag expansion is suppressed even in the case of the collision which requires the airbag expansion.
Further, since a passenger does not always sit in a normal position, i.e., sometimes sits sidewise out of position, as in the above-mentioned conventional example, in some cases, the method using one infrared beam causes no infrared beam to strike on the body of the passenger.
Meanwhile, as shown in U.S. Pat. No. 5,118,134, a method is known by which the movement of a passenger at the time of a collision is detected by a position detecting means, thereby detecting the collision so as to control the operation of a passenger protecting unit such as an airbag etc. However, in reality, the responsibility and disturbance resistance of a distance sensor are not sufficient, and thus the method has not yet been put to practical use. For example, in the distance sensor using an ultrasonic wave, there is a problem that, due to the limitation of the sound speed, for example, in order to detect a distance of 1 m, in principle, the responsibility cannot be made quicker than 6 mS which the sound takes to travel 1 m back and forth. Also, in the position detecting means using a PSD, there is a problem that, upon attempting to assure a normal operation even under the influence of a strong disturbance light, such as in case the direct sunlight strikes on a passenger, the responsibility cannot be quickened.
Furthermore, there is a problem that, upon attempting to detect not only a longitudinal collision but also a lateral collision by the position detecting means, another position detecting means detecting a lateral position is required separately.