Electrical transmission or interconnection systems – Vehicle mounted systems – Automobile
Utility Patent
1998-12-04
2001-01-02
Fleming, Fritz (Department: 2836)
Electrical transmission or interconnection systems
Vehicle mounted systems
Automobile
C307S121000, C280S735000, C701S045000
Utility Patent
active
06169336
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a crew protection apparatus which inflates an air bag at the time of collision of a vehicle or the like to protect a passenger from the collision.
2. Description of the Related Art
Such an example of conventional passenger protection apparatus will be explained with reference to FIG.
3
.
In this figure, a reference numeral
1
depicts a vehicle-mounted battery,
2
an ignition switch and
3
a DC/DC converter for boosting the output voltage of the vehicle-mounted battery
1
and outputting the boosted voltage. A reference numeral
4
depicts a current limit circuit formed by a first field effect transistor
7
, a current detection resistor
9
, a comparison circuit
10
, a constant current source
11
, a resistor
12
, a charge pump circuit
13
, a switch circuit
14
or the like. Further, a reference numeral
5
depicts a reverse-current prevention diode,
6
a backup capacitor, and
8
a second field effect transistor.
The backup capacitor
6
is charged by the DC/DC converter
3
through the reverse-current prevention diode
5
. The second field effect transistor
8
has a drain side connected to the non-grounded side terminal of the backup capacitor
6
and a source side connected to a percussion cap or squib
15
described later. A current of about
2
amperes corresponding to 99%, for example, of the ignition current flowing into the squib
15
flows through the transistor
8
as an ignition current.
The current limit circuit, or a squib drive control circuit
4
will be explained below.
The first field effect transistor
7
is an N channel type with a small capacity for shunting the current flowing from the backup capacitor
6
and the reverse-current prevention diode
5
in order to control the current flowing through the second field effect transistor
8
. The first field effect transistor
7
is connected at its drain side to the drain side of the second field effect transistor
8
and connected at its source side to the source side of the second field effect transistor
8
through the current detection resistor
9
with a small allowable power. A small current of several milli-amperes (corresponding to the remaining 1%, for example, of the ignition current flowing into the squib
15
) flows through the first field effect transistor
7
.
The comparison circuit
10
has a non-inverted (+) input terminal supplied with a reference voltage generated by the constant current source
11
and the resistor
12
connected in series and has an inverted (−) input terminal supplied with the voltage generated by the current detection resistor
9
. The output terminal of the comparison circuit is connected to the output terminal of the switch circuit
14
and to the gates of the first and second field effect transistors
7
,
8
. The comparison circuit
10
changes its output into a high level when the reference voltage is larger than the input voltage and into a low level when the reference voltage is not larger than the input voltage.
A reference numeral
18
depicts an acceleration sensor for detecting an acceleration signal which is generated at the time of the collision of a vehicle. A reference numeral
19
depicts a microcomputer which determines the scale of the collision on the basis of the acceleration signal from the acceleration sensor
18
and supplies an ON signal to the switch circuit
14
when it is determined that the collision is a serious accident. The microcomputer
19
supplies a trigger signal to the charge pump circuit
13
when a power source is turned on.
The charge pump circuit
13
will be explained in detail with reference to FIG.
4
.
The charge pump circuit
13
includes a voltage doubler rectifier circuit formed by an oscillation circuit
13
g
, an inverter
13
a
, diodes
13
d
,
13
e
, capacitors
13
c
,
13
f
and a resistor
13
b
. When the oscillation circuit
13
g
is supplied with the trigger signal, for example, the signal which becomes high level at the time of the turning-on of the power source from the microcomputer
19
described later, the voltage doubler rectifier circuit generates a voltage twice the amplitude of the voltage (+V) of the power source (double-amplitude voltage) only during the period where the trigger signal is supplied thereto. The voltage doubler rectifier circuit supplies the double-amplitude voltage thus generated to the first field effect transistor
7
in order to drive the first and second field effect transistors
7
,
8
thereby to set the gate voltages of the transistors
7
,
8
higher than the drain side voltages thereof.
The squib
15
is connected at its one end to the output side of the squib drive control circuit
4
and at it's the other side to the ground through a reverse current prevention diode
16
and an acceleration switch
17
connected in series. The microcomputer
19
determines the state of the collision on the basis of the acceleration signal from the acceleration sensor
18
for detecting the collision of the vehicle. When the microcomputer determines that it is necessary to operate the air bag or the like, the microcomputer supplies the ON signal to the switch circuit
14
to turn it on and simultaneously supplies the trigger signal to the charge pump circuit
13
.
The operation of the aforesaid arrangement of the conventional crew protection apparatus will be explained.
(a) When the power source is turned on, the microcomputer
19
supplies the trigger signal of a high level to the charge pump circuit
13
thereby to continuously operate the oscillation circuit
13
g
and hence always charge the second capacitor
13
f
, whereby the charge pump circuit
13
outputs the double-amplitude voltage.
(b) In this state, if the microcomputer
19
does not output t he ON signal to the switch circuit
14
, the s witch circuit
14
is kept in an off state, so that the first and second transistors
7
,
8
are maintained in an off state.
(c) In contrast, when the microcomputer
19
determines due to the occurrence of a serious accident that the collision occurred is a serious accident on the basis of the output from the acceleration sensor
18
, the microcomputer
19
outputs the ON signal to the switch circuit
14
thereby to turn on the switch circuit
14
. As a consequence, the first and second field effect transistors
7
,
8
are supplied at the gates thereof with the voltage signals of a high level larger than the voltages of the source sides of the first and second field effect transistors
7
,
8
, respectively, so that the first and second field effect transistors
7
,
8
start to operate in an active area.
Thus, the ignition current flows into the squib
15
through the first and second field effect transistors
7
,
8
. The magnitude of the shunt current of the ignition current at this time is detected by the current detection resistor
9
, and the detection voltage of the current detection resistor
9
is supplied to the inverted (−) input terminal of the comparison circuit
10
. As a result, when the voltage of the inverted (−) input terminal of the comparison circuit
10
becomes larger than the reference voltage, the comparison circuit changes its output level into a low level to lower the gate voltages of the first and second field effect transistors
7
,
8
thereby to shift the operation states thereof toward the non-conductive states.
However, when the first and second field effect transistors
7
,
8
approach toward the non-conductive states, the voltage of the positive voltage side of the current detection resistor
9
decreases. When the voltage of the positive voltage side of the current detection resistor
9
becomes smaller than the reference voltage applied to the comparison circuit
10
, the output of the comparison circuit
10
becomes high level, so that the output voltage of the charge pump circuit
13
is outputted again through the switch circuit
14
. Accordingly, the gate voltages of the first and second field effect transistors
7
,
8
increase a
Hayashi Haruyoshi
Kaneko Kunihiro
Kishi Takayuki
Saito Yasuo
Calsonic Kansei Corporation
Fleming Fritz
Sughrue Mion Zinn Macpeak & Seas, PLLC
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