Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle diagnosis or maintenance indication
Reexamination Certificate
1998-04-02
2001-02-06
Louis-Jacques, Jacques H. (Department: 3614)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle diagnosis or maintenance indication
C701S031000, C701S045000, C102S215000, C102S217000, C180S271000, C180S286000, C324S537000
Reexamination Certificate
active
06185488
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims priority from Japanese Patent Application No. H. 9-102627 filed Apr. 4, 1997, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a trouble diagnosing apparatus for passenger protective systems which are deployed at the time of a vehicle collision to protect passengers.
2. Description of the Related Art
Conventionally, a circuit, as shown in
FIG. 7
, for activating a passenger protective system such as an airbag system or a seatbelt retractor is well known. In this circuit, transistors
31
,
34
are connected in series to the both ends of a squib
33
. When the two transistors
31
,
34
simultaneously turn on, a large current flows through the squib
33
so that the squib
33
is ignited.
To ensure the reliability of the passenger protective system, it is diagnosed, either periodically or at the time of an engine start, whether the transistors
31
,
34
normally turn on in response to respective turn-on signals. In this diagnosis, the transistor
31
is determined to be normal if the potential of the squib
33
(the potential of the intermediate point M, hereinafter referred to as an intermediate point potential) becomes equal to a power source potential when only the transistor
31
is turned on. If not, the transistor
31
is determined to be abnormal. Also, the transistor
34
is determined to be normal if the intermediate point potential becomes equal to a ground potential when only the transistor
34
is turned on. If not, the transistor
34
is determined to be abnormal.
During this diagnosis, if a line L
2
is being short-circuited to ground, or if a line L
1
is being short-circuited to a power supply line, a large current is supplied to the squib
33
, and thereby the squib
33
is erroneously ignited. To solve this problem, as shown in
FIG. 7
, resistors
32
and
35
are respectively connected in parallel to the transistors
31
,
34
. The intermediate point potential is detected while the transistors
31
,
34
are being turned off to determine in advance the occurrence of short-circuits of the lines L
1
and L
2
. If no short-circuits have occurred, the diagnosis is then carried out. That is, unless short-circuits occur in the lines, the intermediate point potential is an approximate V/2 (V: power source potential) since the power source potential V is divided by the resistors
32
,
35
.
To the contrary, if the line L
2
is short-circuited to ground, the intermediate point potential is an approximate ground potential. Also, if the line L
1
is short-circuited to the power supply line, the intermediate point potential is an approximate power source potential. Therefore, the short-circuits of the lines L
1
, L
2
can be detected based on the intermediate point potential.
The intermediate point potential is, however, detected on the basis of either instantaneously sampled voltages or an average voltage at the intermediate point M. Therefore, in a case where the line L
1
or the line L
2
instantaneously and repeatedly makes contact with the power supply line or ground, such a short-circuit of the line L
1
or the line L
2
cannot be detected. For this reason, while the diagnosis is carried out and the transistors
31
,
34
are alternately turned on, if the line L
1
makes contact with the power supply line, or if the line L
2
makes contact with ground, the large current instantaneously flows through the squib
33
, thereby causing the squib
33
to ignite erroneously.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a diagnosing apparatus for a passenger protective system which can prevent an igniting current from flowing through a squib even when either one of two ends of the squib is short-circuited to ground or a power supply.
In order to achieve the above-mentioned object, according to the present invention, the diagnosing apparatus for the passenger protective system includes a power transistor connected in series to at least one end of a squib. The power transistor is made up of a plurality of transistor cells connected in parallel. The diagnosing apparatus for the passenger protective system utilizes a part of the transistor cells as a check transistor which allows a small current incapable of igniting the squib to flow into the squib. The diagnosing apparatus turns only the check transistor on to detect a potential of the squib. The trouble of the check transistor can be diagnosed on the basis of the detected potential. Because the check transistor is formed by a part of the transistor cells, if any trouble occurs therein, it can be considered that the power transistor formed by the remainder of the transistor cells also has trouble. Such trouble may be caused by a defective cell or a faulty connection at a gate electrode, a source electrode or a drain electrode of the power transistor. Therefore, the power transistor can be diagnosed from the detected potential of the squib. Further, because the check transistor allows only a small current incapable of igniting the squib to flow into the squib, even if a line connected to one end of the squib is instantaneously and repeatedly short-circuited to ground or a power supply, erroneous ignition of the squib can be prevented due to the check transistor being turned on.
Preferably, the power transistors including the check transistor are provided on both sides of the squib. In this case, because the igniting current flows through squib by way of the turned on power transistors, a large current can be easily supplied to the squib. In addition, even when one of two power transistors fails so that the power transistor allows the igniting current to flow into the squib, the ignition of the squib can be prevented due to another normally operating power transistor.
Several check transistors can be defined in the plurality of transistor cells of the power transistor. In this case, it is preferable to cause the several check transistors to turn on one by one in order to determine whether each of the several check transistors is normal or abnormal. As a result, because a large area (a plurality of cells) of the power transistor can be actually diagnosed, reliability of the diagnosis for the power transistor can be further enhanced.
In addition, the check transistor may be turned on along with the power transistor when the squib is to be ignited. Due to this fact, it is possible to effectively utilize a current flow capacity of the power transistor.
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Denso Corporation
Louis-Jacques Jacques H.
Pillsbury Madison & Sutro LLP
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