JP2007022432A - Load abnormality detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a load abnormality detection device capable of detecting the abnormality of a load in response to change of a resistance value of the load. <P>SOLUTION: The load abnormality detection device is provided with a constant voltage source 20 for applying a constant voltage to the load 30; and a constant current source 10 for feeding a diagnosis current to the load 30. A micro-computer 50 detects a potential V0 of one end (point a) of the load 30 when the constant voltage is applied to the load 30 at A/D port 60 and whereas the micro-computer 50 detects the potential Vi at the point a when the diagnosis current is fed to the load 30 at the A/D port 60 in addition to applying of the constant voltage. Abnormality detection of the load 30 is performed by comparing the potential V0 with the potential Vi. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a load abnormality detection device, and more particularly to a load abnormality detection device that detects a load abnormality by flowing a current through a load.

2. Description of the Related Art Conventionally, a detection circuit that performs open / short detection of a squib based on a potential difference between both ends of the squib when a diagnostic current is supplied to the squib (equivalently a resistor) is known (see, for example, Patent Document 1). This detection circuit performs open / short detection of a squib by a microcomputer (hereinafter referred to as “microcomputer”) reading a potential difference generated at both ends of the squib by a diagnostic current from a constant current source.
Japanese Patent No. 3517864

  By the way, when the microcomputer reads the input potential at the A / D port, a reading error (offset error) occurs. Therefore, the diagnostic currents I1 and I2 having two different magnitudes are supplied to the load by the constant current source, and the respective diagnostic currents are supplied. By taking the difference between the input potentials generated by flowing the current, the influence of the offset error can be canceled. By determining whether or not the difference exceeds a predetermined abnormality determination threshold value for determining the load as abnormal, it is possible to detect the load abnormality while eliminating the offset error.

  At this time, since the diagnostic current itself flowing from the constant current source includes not a little error or the diagnostic current itself slightly varies, in order to suppress the influence of the error and fluctuation of the diagnostic current on the above difference, One of the two diagnostic currents I1 and I2 needs to be somewhat larger than the other (for example, I1 << I2).

  However, if the load resistance increases due to changes over time, or if a load with a resistance larger than the designed resistance is installed, the resistance of the load when a diagnostic current is passed The voltage drop due to the minute becomes large, and the microcomputer may not be able to read the input potential through the A / D port. Here, this point has not been disclosed or suggested in the above-mentioned Patent Document 1, and has not been solved.

  Therefore, an object of the present invention is to provide a load abnormality detection device that can detect a load abnormality in response to a change in the resistance value of the load.

In order to solve the above problems, according to one aspect of the present invention,
A constant voltage source for applying a constant voltage to the load;
A constant current source for supplying a diagnostic current to the load;
First potential detecting means for detecting a potential at one end of the load when the constant voltage is applied to the load;
Second potential detecting means for detecting the potential of the one end when the diagnostic current is supplied to the load in addition to the application of the constant voltage;
A load abnormality detection device is provided that detects the load abnormality by comparing the potential detected by the first potential detection means with the potential detected by the second voltage detection means. .

  According to this, by using a constant voltage source, it is not necessary to flow diagnostic currents of two different magnitudes, and if the diagnostic current is set to a small value, the voltage drop even if the resistance value of the load increases. Therefore, there is no possibility that the microcomputer cannot read the input potential through the A / D port.

  In addition, in order to be able to detect the voltage across the load so as not to be affected by a change in the GND (ground) potential, the first potential detecting means further includes the one end when the constant voltage is applied to the load. The second voltage detecting means further detects the potential of the other end when the diagnostic current is supplied to the load in addition to the application of the constant voltage. Also good.

  According to the present invention, it is possible to detect a load abnormality in response to a load resistance value change.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a first embodiment of a load abnormality detection apparatus according to the present invention.

  The load 30 is a target on which the load abnormality detection device of the present invention performs abnormality detection (for example, open detection or short detection). The load 30 is a conductor having a resistance component. More specifically, the load 30 is a solenoid including an inductance component and a resistance component, or a squib for igniting a gas generating agent such as an air bag.

  The upstream of the load 30 is connected to a constant voltage source 20 described later, and the downstream is connected to a GND (ground) 60. The downstream of the load 30 and the GND 60 may be directly connected, or a circuit element (indicated by an abbreviation symbol 40) such as a resistor or a transistor may be inserted between the load 30 and the GND 60. The GND 60 may be connected to the GND 70 of the microcomputer 50 to be described later, or the GND 70 of the microcomputer 50 is affected by the current flowing through the load 30 (particularly, the drive current (operating current) for driving the load 30). It may be connected to GND 70 by a separate wiring so as not to give it.

  A constant current source 10 is connected to a point between the load 30 and the constant voltage source 20. The constant current source 10 supplies a diagnostic current Ii (constant current Ii) for detecting a load abnormality to the load 30. The supply of the diagnostic current Ii to the load 30 can be stopped. For example, the microcomputer 50 or the like transmits a stop signal to disconnect the constant current source 10 from the point a, or stop the supply of the diagnostic current Ii from the constant current source 10 itself.

  Further, the point a and the A / D port 60 of the microcomputer 50 are connected so that the potential at the point a can be detected. The A / D port 60 is connected to an A / D conversion unit (not shown) in the microcomputer 50. Then, a CPU (not shown) in the microcomputer 50 calculates the output data of the A / D converter (that is, the potential data at point a). Note that the microcomputer 50 (including its constituent CPU and RAM) operates based on the GND 70.

  Here, the state when the microcomputer 50 reads the input potential through the A / D port 60 will be briefly described with reference to FIGS. 3 and 4. 3 and FIG. 4, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  When the microcomputer 50 reads the input potential V1 through the A / D port 60 as shown in FIG. 3, a reading error (offset error err) occurs. Due to the offset error err, the arithmetic processing by the CPU based on the input potential V1 varies. Extremely speaking, when the offset error err increases, depending on the value (V1 + err) read by the A / D port 60 of the input potential V1 generated by flowing the diagnostic current I1 to the load 30, the load of the load 30 by the microcomputer 50 is increased. There is a case where the abnormality determination is erroneously determined.

  On the other hand, as shown in FIG. 4, two different magnitudes of diagnostic currents I2 and I3 are supplied to the load 30 by the constant current power source 10, and the input potential V2 generated by passing the diagnostic current I2 to the load 30 is represented by A. By taking the difference between the value (V2 + err) read by the / D port 60 and the value (V3 + err) read by the A / D port 60 from the input potential V3 generated by flowing the diagnostic current I3 to the load 30, the offset error is reduced. The influence can be canceled. That is, the CPU in the microcomputer 50 can perform arithmetic processing based on a value from which the influence of the offset error is eliminated, such as “(V3 + err) − (V2 + err) = V3−V2”. Thereby, the microcomputer 50 determines whether the difference (V3−V2) is within the normal determination region “Vmin <V3−V2 <Vmax”, thereby eliminating the influence of the offset error and Abnormality detection can be performed (Vmin is the lower limit value of the normal determination region, and Vmax is the upper limit value of the normal determination region). If the difference (V3−V2) is not within the normality determination region, the microcomputer 50 determines that the load 30 is abnormal (open failure or short failure).

  If the resistance value of the load 30 is R, the GND 70-based microcomputer 50 reads V3-V2 as "V3-V2 = (I3-I2) .R" (diagnostic currents I2, I3 The difference is calculated assuming that there is no difference in the amount of voltage drop at the omitted portion 40. If there is a difference, the difference term also appears in the above equation).

  However, the diagnostic currents I2 and I3 flowing from the constant current source 10 contain not a few errors, and the diagnostic currents I2 and I3 slightly vary. Therefore, in order to suppress the influence of errors and fluctuations of the diagnostic currents I2 and I3 on the difference (V3−V2), it is necessary to set “I2 << I3”.

  For example, when R = 3 [Ω], I2 = 0.1 [A], and I3 = 0.2 [A] are defined, the difference is “V3−V2 = (0.2−0.1) × 3 = 0.3 [V] ”, and R = 3 [Ω], I2 = 0.1 [A], and I3 = 1.0 [A], the difference is“ V3−V2 = (1.0− 0.1) × 3 = 2.7 [V] ”. Therefore, for example, even if there is an error or fluctuation of 0.15 [A] in the diagnostic current I2 or I3, the difference is defined when I2 = 0.1 [A] and I3 = 1.0 [A]. Has little effect on

  However, when the resistance value of the load 30 increases due to changes over time, or when a load having a resistance larger than the resistance value assumed in the design is attached, V2 is very large compared to V3. Become.

  For example, when the resistance value is R = 300 [Ω] when I2 = 0.1 [A] and I3 = 1.0 [A], “V2 = I2 · R = 30 [V]” , “V3 = I3 · R = 300 [V]”. That is, the voltage drop due to the load 30 is large and exceeds the power supply voltage value of the microcomputer of about several volts.

  Therefore, the microcomputer 50 cannot read the input potentials V2 and V3 through the A / D port 60. As a result, the difference (V3-V2) is not correctly processed, and the abnormality determination of the load 30 by the microcomputer 50 may be an erroneous determination. Note that a countermeasure for misjudgment may be implemented by adjusting the diagnostic current so as to match the target resistance, but the circuit and IC such as the constant current source 10 must be greatly changed.

  Therefore, the load abnormality detection device of the present invention includes a constant voltage source 20 as shown in FIG. A constant voltage source 20 is connected upstream of the load 30. The constant voltage source 20 applies a constant voltage to the load 30 with a voltage that does not affect the operation of the load 30. For example, the constant voltage source 20 may serve as an operating power source for the load 30 and may be lowered to a voltage that does not operate the load 30 when detecting an abnormality in the load 30. Alternatively, the constant voltage source 20 may not be an operating power source for the load 30 but may be a voltage source that applies a voltage that does not affect the operation of the load 30, and another voltage source (not shown) may be used as the operating power source for the load 30. . Note that a diode 21 may be inserted between the constant voltage source 20 and the load 30 in order to prevent current from flowing in, or a resistance 22 may be provided.

  Now, the operation of the load abnormality detection device of the present invention will be described with reference to FIG. FIG. 2 is an example of a processing operation flow of the microcomputer 50 of the load abnormality detection device of the present invention.

  In step 10, the microcomputer 50 applies a constant voltage to the load 30 in a state where the constant current source 10 is not connected or a diagnostic current Ii is not supplied from the constant current source 10. Then, the potential V0 at the point a is measured based on GND 70 (if the measured potential is E0 [V], “V0 = E0”). In addition, it is desirable to confirm that there is no abnormality other than the load 30 that is the abnormality detection target of the load abnormality detection device before the execution of Step 10.

  In step 12, the microcomputer 50 starts supplying the diagnostic current Ii from the constant current source 10. In step 14, the microcomputer 50 measures the potential Vi at the point a when the diagnostic current Ii is supplied to the load 30 in addition to the application of the constant voltage by the constant voltage source 10 based on the GND 70. By virtue of the superposition, “Vi = E0 + R · Ii” (calculated on the assumption that there is no voltage drop at the omitted portion 40 due to the diagnostic current Ii or a potential difference between the GND 70 and the GND 60. If there is a difference, there is also a term indicating it. Appears in the above formula). If the load 30 includes an inductance component, it is desirable to measure when the current or potential is stabilized.

  In step 16, the microcomputer 50 detects the abnormality of the load 30 by determining whether or not the difference (Vi−V0) is within the normal determination region “Vmin <Vi−V0 <Vmax”. If the difference (Vi−V0) is within the normal determination region “Vmin <Vi−V0 <Vmax”, the load 30 can be regarded as normal. On the other hand, if the load is not within the normal determination region in step 18, the load 30 can be regarded as an open failure or a short failure.

  It is possible to perform arithmetic processing as “Vi−V0 = (E0 + R · Ii) − (E0) = R · Ii”. Further, Vmin is a lower limit value of the normal determination area, and Vmax is an upper limit value of the normal determination area, and the value may be determined according to the required specification for abnormality detection.

  Therefore, according to the load abnormality detection device of the present invention, it is not necessary to use two constant currents (I2, I3) having different magnitudes as described above. If the diagnostic current Ii supplied from the constant current source 10 is set to a very small value, R · Ii does not increase even if the resistance value R of the load 30 increases. The potential difference (Vi−V0) can be correctly calculated within a range that can be read by the port 60. Further, the influence of the offset error described above can be eliminated by subtracting the potential. Furthermore, it is not necessary to greatly change the circuit and IC such as the constant current source 10.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  FIG. 5 is a diagram showing a second embodiment of the load abnormality detection device of the present invention. In the configuration of FIG. 5, the same components as those of FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

Downstream of the load 30, through resistor 23 and circuit such as a transistor element of the resistance value _{R 23} (indicated by ellipsis 40), leading to GND60.

  The point b and the A / D port 61 of the microcomputer 50 are connected so that the potential at the point b between the load 30 and the resistor 23 can be detected. The A / D port 61 is connected to an A / D conversion unit (not shown) in the microcomputer 50. A CPU (not shown) in the microcomputer 50 computes output data of the A / D converter (that is, potential data at point b).

  The load abnormality detection apparatus of the second embodiment shown in FIG. 5 also operates in the same manner as the processing operation flow shown in FIG.

In step 10, the microcomputer 50 applies a constant voltage to the load 30 in a state where the constant current source 10 is not connected or a diagnostic current Ii is not supplied from the constant current source 10. Then, the potential V0 at the point b is measured based on GND70. Assuming that the current flowing when the constant voltage source 20 applies a constant voltage to the load 30 is I ₀ , “V 0 = I ₀ · R ₂₃ ” is obtained.

In step 12, the microcomputer 50 starts supplying diagnostic current Ii from the constant current source 10. In step 14, the microcomputer 50 measures the potential Vi at the point b when the diagnostic current Ii is supplied to the load 30 in addition to the application of the constant voltage by the constant voltage source 10 based on the GND 70. By virtue of the superposition, “Vi = (I ₀ + Ii) · R ₂₃ ” (calculated on the assumption that there is no potential difference between GND 70 and GND 60. If there is a difference, a term indicating it also appears in the above equation).

  In step 16, the microcomputer 50 detects the abnormality of the load 30 by determining whether or not the difference (Vi−V0) is within the normal determination region “Vmin <Vi−V0 <Vmax”.

Here, the difference (Vi−V0) can be calculated as “Vi−V0 = ((I ₀ + Ii) · R ₂₃ ) − (I ₀ · R ₂₃ ) = R ₂₃ · Ii”. If the resistance value of the load 30 fluctuates, Ii also fluctuates. Therefore, the abnormality of the load 30 can be detected by comparing the calculated R ₂₃ · Ii with the normality determination region. If the difference (Vi−V0) is within the normal determination region “Vmin <Vi−V0 <Vmax”, the load 30 can be regarded as normal. On the other hand, if the load is not within the normal determination region in step 18, the load 30 can be regarded as an open failure or a short failure.

  Therefore, the load abnormality detection device of the second embodiment also brings about the same effect as that of the first embodiment.

  Furthermore, FIG. 6 is a figure which shows the 3rd Example of the load abnormality detection apparatus of this invention. In the configuration of FIG. 6, the same components as those of FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The point a and the A / D port 60 of the microcomputer 50 are connected, and the point b and the A / D port 61 of the microcomputer 50 are connected so that the potentials at both ends (points a and b) of the load 30 can be detected. . The A / D ports 60 and 61 are connected to an A / D conversion unit (not shown) in the microcomputer 50. A CPU (not shown) in the microcomputer 50 computes output data of the A / D converter (that is, potential data at points a and b).

  The load abnormality detection apparatus of the third embodiment shown in FIG. 6 also operates in the same manner as the processing operation flow shown in FIG.

  In step 10, the microcomputer 50 applies a constant voltage to the load 30 in a state where the constant current source 10 is not connected or a diagnostic current Ii is not supplied from the constant current source 10. Then, the potentials V00 and V01 at the points a and b are measured based on the GND70. Assuming that the measured potentials are E00 [V] and E01 [V], when the voltage across the load 30 (that is, the potential difference between the points a and b) is defined as V0, “V0 = E00−E01”.

  In step 12, the microcomputer 50 starts supplying the diagnostic current Ii from the constant current source 10. In step 14, the microcomputer 50 measures the voltage across the load 30 based on the GND 70 when the diagnostic current Ii is supplied to the load 30 in addition to the application of the constant voltage by the constant voltage source 10. By virtue of superposition, “Vi = (E00−E01) + R · Ii”.

  In step 16, the microcomputer 50 detects the abnormality of the load 30 by determining whether or not the difference (Vi−V0) is within the normal determination region “Vmin <Vi−V0 <Vmax”.

  Here, it is possible to perform arithmetic processing as “Vi−V0 = ((E00−E01) + R · Ii) − (E0−E01) = R · Ii” ”. Therefore, based on the same idea as described above, the load abnormality detection device of the third embodiment also brings about the same effect as that of the first embodiment.

It is a figure which shows the 1st Example of the load abnormality detection apparatus of this invention. It is an example of the processing operation | movement flow of the microcomputer 50 of the load abnormality detection apparatus of this invention. FIG. 4 is a diagram illustrating that the microcomputer 50 reads an input potential V1 generated by flowing a diagnostic current I1 through a load 30 through an A / D port 60. FIG. 4 is a diagram illustrating that the microcomputer 50 reads the input potentials V2 and V3 generated by flowing diagnostic currents I2 and I3 having two different magnitudes through the load 30 through an A / D port 60; It is a figure which shows the 2nd Example of the load abnormality detection apparatus of this invention. It is a figure which shows the 3rd Example of the load abnormality detection apparatus of this invention.

Explanation of symbols

10 constant current source 20 constant voltage source 21 diode 22, 23 resistance 30 load 50 microcomputer 60, 61 A / D port

Claims (2)

A constant voltage source for applying a constant voltage to the load;
A constant current source for supplying a diagnostic current to the load;
First potential detecting means for detecting a potential at one end of the load when the constant voltage is applied to the load;
Second potential detecting means for detecting the potential of the one end when the diagnostic current is supplied to the load in addition to the application of the constant voltage;
A load abnormality detection device that detects an abnormality of the load by comparing the potential detected by the first potential detection means with the potential detected by the second voltage detection means. The first potential detecting means further detects a potential of the other end with respect to the one end when the constant voltage is applied to the load,
The load abnormality detection device according to claim 1, wherein the second voltage detection unit further detects a potential of the other end when the diagnostic current is supplied to the load in addition to the application of the constant voltage.

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