Physical quantity sensor having fault detection function

Details Physical quantity sensor having fault detection function Physical quantity sensor having fault detection function

2000-10-12

2002-02-05

Raevis, Robert (Department: 2856)

Measuring and testing

Instrument proving or calibrating

Fluid pressure

Reexamination Certificate

active

06343498

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to physical quantity sensors, and particular to a physical quantity sensor having a diagnosis function, and more particular to a physical quantity sensor for detecting physical quantity such as pressure and having a diagnosis function.
2. Related Art
A related art sensor apparatus, which is used for detecting pressure in a vehicle such as brake fluid pressure or fuel pressure, will be explained with reference to FIG.
10
. This kind of sensor apparatus is provided with a sensor portion
20
for outputting signals depending on pressure applied thereon and a control portion
10
such as an ECU for performing several controls based on the output signal from the sensor portion
20
.
A battery power supply Vcc (e.g., 12V) is converted to a constant voltage (e.g., 5V) by a regulator
11
provided in the control portion
10
. After being converted, the battery power supply is supplied to the sensor portion
20
via a power supply line L
P
. The sensor portion
20
performs several functions including a pressure detection, an output amplify, and an adjusting the output by using the supplied constant voltage as power. The sensor portion
20
also outputs output voltage Vo in proportion to applied pressure through an output line L
O
. The control portion
10
performs several controls based on the output voltage Vo.
It is necessary to electrically connect between the control portion
10
and the sensor portion
20
via the power supply line L
P
, the output line L
O
and a ground line L
G
. Generally, the control portion
10
and the sensor portion
20
are electrically connected by using a connector, soldering, welding or the like. Here, in
FIG. 10
, terminals of the control portion
10
which connecting each line L
P
, L
O
, L
G
are described as PE, OE, GE; and terminals of the sensor portion
20
which connecting each line L
P
, L
O
, L
G
are described as PS, OS, GS.
However, a poor connection (failure in connection) at a connection point between the control portion
10
and the sensor portion
20
may cause a fault due to an increase of a resistance of the line. Particularly, when such a fault occurs on the output line L
O
, an additional resistor Rx is added to the connection point. In this case, the output voltage Vo will fluctuate by &Dgr;Vo (=Io×Rx) depending on a current Io in the output line L
O
. Therefore, when the output voltage Vo from the sensor portion
20
changes, it is difficult to distinguish whether this change is caused due to pressure changes or due to poor connection.
Here, it assumes that a fault due to the poor connection is detected by measuring the output voltage Vo while no pressure is applied to the sensor portion. For example, when a load resistor R having 330 k&OHgr; is provided between the output line L
O
and the ground line L
G
, and the output voltage while no pressure is applied to the sensor portion is Vo=0.5 V, the current Io in the output line L
O
is Io=1.5 &mgr;A. Here, a standard output voltage Vo is set to, for example, 0.1 V. A diagnosis system is constructed to detect the fault of the pressure sensor when the output voltage excesses a range of Vo=0.5±0.1 V. In this case, when the resistance is increased by Rx due to the poor connection or the like, the diagnosis system cannot detect the increase of the resistance if the resistance increases by Rx=66 k&OHgr; (=0.1 V×1.5 &mgr;A) or less. Here, the tolerance standard ±0.1 V is determined by considering manufacturing deviation of the pressure sensor, and it is difficult to reduce this standard because it causes decrease of productivity of the sensors and it causes increase of manufacturing cost.
Incidentally, in general, the control portion
10
is provided with a load resistor RA between the output line L
O
and the ground line L
G
, so that the sensor output (normally within a range of 0.5 V−4.5 V) is positively changed into a fault signal (outside of the normal range, e.g., 4.8 V or more, or 0.2 V or less) when a short-circuit or a cut-off occurs on the lines L
P
, L
O
and L
G
. Therefore, the sensor output V
OE
to be received by the control portion
10
is determined by a resistance division between the load resistor RA and the increased resistance Rx. In detail, the V
O
, is calculated by V
OE
=V
OS
×RA/(RA +Rx).
For example, when the load resistor is PL=100 k&OHgr; and the sensor output from the sensor portion is V
OS
=0.5 V, as shown in
FIG. 11
, the sensor output V
OE
received by the control portion
10
changes in response to the resistance Rx added to the output line L
O
, and the sensor output deviates from the V
OS
which is outputted from the sensor portion
20
. Therefore, even when the sensor portion
20
outputs accurate sensor signal V
OS
in response to the applied pressure, the control portion
10
performs several controls based on the sensor signal V
OE
which is different from the sensor signal V
OS
outputted from the sensor portion
20
.
SUMMARY OF THE INVENTION
This invention has been conceived in view of the background thus far described and its object is to accurately detect a fault due to poor connection or the like at a connection portion between a sensor portion and a control portion.
According to a first aspect of the present invention, a diagnosis portion measures current flowing in one of external wirings to detect a resistance of a circuit system including the one of the external wirings in which the current flows. Then, the diagnosis portion detects a fault of the circuit system by processing measured current. Therefore, when the resistance is changed as a result of the fault such as a poor connection, such the fault can be easily detected.
According to a second aspect of the present invention, a diagnosis portion measures current flowing from the output line to the ground line. Then, the diagnosis portion detects an occurrence of fault by comparing a measured current value and a predetermined reference current value. Therefore, when the resistance is changed as a result of the fault such as a poor connection, such the fault can be easily detected.
According to a third aspect of the present invention, a diagnosis portion detects a difference between the sensor signal before changing the current and the sensor signal after changing the current.
The diagnosis portion detects an occurrence of fault based on the difference in the sensor signal. Therefore, when the resistance is changed as a result of the fault such as a poor connection, such the fault can be easily detected.


REFERENCES:
patent: 4853629 (1989-08-01), Rops
patent: 4878107 (1989-10-01), Hopper
patent: 5142235 (1992-08-01), Matsumoto et al.
patent: 5631602 (1997-05-01), Kearney et al.
patent: 5-52680 (1993-02-01), None
patent: 6-58989 (1994-04-01), None
patent: 6-347317 (1994-12-01), None
patent: 9-88708 (1997-03-01), None

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