1.Field of the Invention
The present invention relates to a device for controlling expansion of an air bag apparatus.
2. Description of the Related Art
Japanese Laid-open Patent Publication (unexamined) No. 10-31590discloses a device for controlling expansion of an air bag apparatus having a plurality of inflaters. This device includes an acceleration sensor for detecting an acceleration of a passenger compartment and a crash sensor located at a front portion of a vehicle body and having a switching mechanism that closes an electric circuit in the event of a collision above a predetermined level. The device determines based on a signal from the acceleration sensor whether or not the inflaters should be operated, and also determines the operation modes of the inflaters according to the degree of the collision within a predetermined time after the electric circuit has been closed, making it possible to optimize the operation of the inflaters.
As in the device of the above-described construction, the general practice is such that whether the inflaters should be operated is determined based on the signal from the acceleration sensor. From the viewpoint of operating the air bag apparatus at an early stage, it is preferred that a criterion for determining the necessity of operating the air bag apparatus be set to the lowest possible value (acceleration).
However, such setting cannot deal with a recent tendency of wheels toward increase in size. More specifically, as shown in FIG. 4, if a wheel 101 (phantom line depicts a conventional wheel) runs up onto a curb 102 or the like, there is a possibility that the acceleration sensor detects an acceleration signal for expanding the inflaters notwithstanding that no collision has occurred, resulting in erroneous operation of the air bag apparatus.
The present invention has been developed to overcome the above-described disadvantages.
It is accordingly an objective of the present invention to provide a device for controlling expansion of an air bag apparatus, which is capable of positively preventing erroneous operation of the air bag apparatus that may occur when an automotive vehicle runs up onto a curb or the like.
In accomplishing the above and other objectives, the device according to the present invention includes a first acceleration sensor mounted in a passenger compartment for detecting an acceleration thereof, a second acceleration sensor mounted in a front portion of a vehicle body, and a control unit electrically connected to the first and second acceleration sensors so that signals from the first and second acceleration sensors are inputted to the control unit. When a first value derived from a signal detected by the first acceleration sensor has exceeded a first criterion and when a second value derived from a signal detected by the second acceleration sensor has exceeded a predetermined value greater than the first criterion, the control unit outputs an operation signal for operating the air bag apparatus.
By this construction, in the event of a collision, because a very large impact force is applied to the front portion of the vehicle body, not only the first value exceeds the first criterion, but the second value also exceeds the predetermined value. As a result, the control unit actuates the air bag apparatus appropriately. On the other hand, If a shock is applied to the vehicle body due to a run-up of a wheel onto a curb or the like, and even if the first acceleration sensor outputs a signal that allows actuation of the air bag apparatus, the second acceleration sensor does not output the operation signal. The reason for this is that the operation signal from the second acceleration sensor is set so as not be outputted until a further greater shock is applied to the vehicle body, thus preventing erroneous operation of the air bag apparatus.
Advantageously, the control unit outputs the operation signal regardless of the presence or absence of the signal detected by the second acceleration sensor, when the first value has exceeded a second criterion greater than the first criterion.
This construction ensures appropriate actuation of the air bag apparatus under the condition in which the air bag apparatus should normally be actuated unless the second acceleration sensor is out of order (in the event of failure) or in which the air bag apparatus cannot be actuated by reason that the second acceleration sensor cannot detect the predetermined acceleration, although it is in good order (in the event of, for example, a rear end collision or a collision in which the vehicle rushes under a large vehicle).
The second criterion is so set as to be greater than the predetermined value. By so setting, the device according to the present invention can distinguish a shock caused by the run-up onto a curb or the like from a shock caused by a vehicle collision, making it possible to prevent erroneous operation of the air bag apparatus and guarantee appropriate actuation of the air bag apparatus.