JP2001108645A - Abnormality detecting apparatus for load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize an abnormality detecting apparatus which detects the abnormality of a load itself or its electrification route. SOLUTION: A detecting resistance 16 is installed in parallel to a driving transistor Tr1. First, on the basis of respective voltage values VBLOff, VDoff of the electrification route of a heater 11a at a time when the driving transistor Tr1 is turned off and on the basis of the resistance value RD of the detecting resistance 16 stored in advance in a ROM 13b, the resistance value RH of the heater 11a is calculated. In addition, on the basis of respective voltage values VBon, VDon of the electrification route of the heater 11a at a time when the driving transistor Tr1 is turned on and on the basis of the resistance value RH of the heater 11a which is already calculated, the current value ILon of the electrification route of the heater 11a is calculated. It is judged whether the calculated resistance value RH and the calculated current value ILon are within a prescribed range stored. in the ROM 13b in advance. Thereby, the abnormality of the heater 11a or its electrification route is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for energizing a load such as a heater incorporated in an oxygen sensor, for example, to detect an abnormality in the load itself or an energizing path thereof.

[0002]

2. Description of the Related Art Conventionally, when a load such as a heater is energized, a switching element (FET, transistor, etc.) is provided in the energizing path of the load, and this is turned on / off by a duty-controlled control signal. Thus, the amount of current flowing to the load is controlled.

In this type of load driving device, an abnormality in the load energizing path (a disconnection of the load itself or its energizing path,
As a method for detecting anomalies that detect short-circuits, etc., a method is used in which a resistor for current detection is connected in series with a load, and the voltage across the resistor is measured to calculate the current and determine whether or not an error has occurred. Is generally known.

[0004] As such an abnormality detecting device, for example, a device disclosed in Japanese Utility Model Registration No. 2532682 is known. The present invention relates to a heater abnormality diagnosis device for an oxygen sensor for detecting an oxygen concentration in exhaust gas for controlling an air-fuel ratio of an internal combustion engine. In this heater abnormality diagnosis apparatus, for example, as shown in FIG. 6, a battery, a detection resistor 62 for current detection, and an FE
T (field effect transistor) 63 is connected in series to form an energizing path for the heater 61. Then, the potential difference between both ends of the detection resistor 62 is amplified by the differential amplifier circuit 64, A / D converted inside the control unit or the like to obtain a current, and this current is set in advance (according to the fluctuation of the power supply voltage). By comparing the upper limit value and the lower limit value set in this manner, an abnormality such as a short circuit or disconnection of the heater 61 or its energizing path is detected. That is, when the current is equal to or higher than the upper limit, it is determined that a short circuit has occurred, and when the current is equal to or lower than the lower limit, it is determined that a break has occurred.

A heater provided near the oxygen concentration detecting element (for example, a zirconia solid electrolyte) of the oxygen sensor is used to maintain the sensing element at an active temperature of about 700 ° C. in order to obtain a stable output from the oxygen sensor. Things. Another method for detecting an abnormality is disclosed in JP-A-7-43.
A failure detection device disclosed in Japanese Patent Publication No. 336 is also known. This also relates to a heater failure detection device for an oxygen sensor, as in the above publication. In this failure detection device, for example, as shown in FIG. 7, an FET 72 and a detection resistor 73 are connected in series in the middle of a heater energization path including a heater 71, and a drain side voltage of the FET 72 is compared with a reference voltage by a comparator 74. The result is output to the CPU 75. Therefore, for example, when the drain side voltage of the FET 72 is higher than a predetermined reference voltage, that is, when the voltage drop by the heater 71 is small, it is determined that a failure has occurred due to a short circuit.

[0006]

However, in each of the abnormality detection devices disclosed in the above publications, a detection resistor having a large rated power is inevitably inserted because a detection resistor is inserted in series in a load conduction path. Must be used. That is, if a resistance (for example, several tens of kΩ) that is much larger than the resistance value (about 1 to 10Ω) of the heater is used as the detection resistance, most of the power supply power is consumed by the detection resistance, and the heater fulfills its function. Disappears. Therefore, in order to sufficiently maintain the function of the heater, for example, a resistance smaller than the resistance value of the heater must be used as the detection resistance. However, as a result, the rated power of the detection resistor also becomes large. Higher power ratings increase the size of the resistor in addition to increasing costs. As electronic control devices such as ECUs are rapidly becoming smaller in size, the above-mentioned increase in the size of components has a serious adverse effect.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to reduce the size of an abnormality detection device for detecting an abnormality in a load itself or an energization path thereof.

[0008]

Means for Solving the Problems and Effects of the Invention In order to solve the above-mentioned problems, the abnormality detecting device according to the first aspect of the present invention comprises a power supply path in which a power supply, a load, and switching means are connected in series. The switching means is provided at a position downstream of the load with respect to the direction of current flowing through the current path, and turns on the switching means.
An abnormality detection device that detects abnormality of the load or the energization path with respect to a load driving device that controls energization to the load by performing off-control, wherein the abnormality detection device is configured to be in series with the load and in parallel with the switching unit. And a voltage value VLo of an energizing path between the load and the switching means when the switching means is off.
ff, and off-state voltage detection means for detecting the voltage value VBLoff of the power supply, and based on the voltage value VLoff detected by the off-time voltage detection means, the voltage value VBLoff of the power supply, and the resistance value of the detection resistor. Load resistance calculating means for calculating the resistance value of the load, and determining whether or not the resistance value of the load calculated by the load resistance calculating means is within a predetermined range set in advance. If the resistance value is not within the predetermined range, there is provided a resistance value abnormality determining means for determining an abnormality.

In order for the abnormality detecting device to detect an abnormality in the load or the conduction path, first, the switching means is turned off. At this time, although the switching means is off, the detection resistor is provided in parallel with the switching means, so that a current flows through the load and the detection resistor, and a voltage drop occurs. In the state where the switching means is turned off in this way, the voltage value VLoff of the current path between the load and the switching means, and the voltage value VBLoff of the power supply
Is detected by the off-state voltage detection means, and the resistance value of the load is calculated by the load resistance calculation means based on the detected voltage values and the resistance value of the detection resistor.

Then, the resistance value abnormality determining means determines whether or not the resistance value of the load calculated by the load resistance calculating means is within a predetermined range set in advance. It is determined that the load or the current path is normal. The predetermined range is set in consideration of, for example, variations in the resistance value of the load depending on the product and changes with time.

When the calculated resistance value of the load is not within a predetermined range, for example, when the resistance value is below the predetermined range,
Judge that the load or its energization path is short-circuited,
If the calculated resistance value of the load exceeds a predetermined range, it is determined that the load or the current-carrying path is broken, and in any case, it is determined that the load is abnormal. The type of the load is not particularly limited, for example, a heater, a lamp, a DC motor, a solenoid, and the like.

As described above, the load resistance is calculated based on the voltage value of each part of the energizing path and the detected resistance value when the switching means is turned off, and whether the calculated resistance value is within the range of the expected resistance value is determined. Is determined, it is possible to detect an abnormality in the load or its energization path.

Therefore, according to the above abnormality detecting device, since the detection resistor is provided in parallel with the switching means, the resistance value of the detection resistor can be set large, and the current flowing through the detection resistor can be suppressed small. A small resistor (for example, a chip resistor) having a small rated power can be used as the detection resistor, so that the size of the abnormality detection device and the size of the load driving device can be reduced. The larger the resistance of the detection resistor, the smaller the power consumption of the detection resistor when the switching unit is turned off, so that it is more preferable from the viewpoint of power saving.

Further, the abnormality detecting device according to claim 2 is
The abnormality detection device according to claim 1, wherein instead of or in addition to the resistance abnormality determination unit, when the switching unit is on, an energization path between the load and the switching unit is turned off. On-time voltage detecting means for detecting the voltage value VLon and the voltage value VBLon of the power supply, and the voltage value VLon and the voltage value VBLon of the power supply detected by the on-time voltage detecting means, and the load resistance calculating means. Current value calculating means for calculating a current value flowing through the current path based on the calculated resistance value of the load; and the current value calculated by the current value calculating means is within a predetermined range set in advance. Current value abnormality determination means for determining whether or not the current value is not within the predetermined range, and determining that the current value is abnormal.

In the above abnormality detection device, the switching means is first turned off, and the voltage value VLoff of the current path between the load and the switching means and the voltage value VBLoff of the power supply are turned off.
Is detected by the off-state voltage detection means. Then, based on the detected voltage values and the resistance value of the detection resistor,
The resistance value of the load is calculated by the load resistance calculating means.

Next, when the switching means is turned on, the voltage value VLon of the power supply path between the load and the switching means and the voltage value VBLon of the power supply are detected by the on-time voltage detection means, and the detection is performed. Based on the obtained voltage values and the resistance value of the load calculated by the load resistance calculating means, a current value flowing through the conduction path is calculated by the current value calculating means.

Then, it is determined whether the calculated current value is within a predetermined range set in advance. If the calculated current value is within the predetermined range, it is determined that the load or its energizing path is normal. . If the calculated current value is not within the predetermined range, for example, if the calculated current value is less than the predetermined range, it is determined that the load or its energizing path is disconnected, and the calculated current value is within the predetermined range. If the value exceeds
It is determined that the load or its energization path is short-circuited, and in any case, it is determined that there is an abnormality.

As described above, the value of the current flowing through the current path is calculated based on the voltage value of each part of the current path when the switching means is turned on and the resistance value of the load calculated when the switching means is turned off. Is always within the range of the expected current value, and the load or the current path is always accurately detected based on the current value of the current path without being affected by the load resistance over time. can do.

Therefore, according to the above abnormality detecting device, the detection resistor is provided in parallel with the switching means.
Since the resistance value of the detection resistor can be set to a large value and the current flowing through the detection resistor can be suppressed to a small value, a small resistor (for example, a chip resistor) having a small rated power can be used as the detection resistor. Equipment miniaturization,
Further, the size of the load driving device can be reduced.

Further, the abnormality detecting device according to a third aspect of the present invention is the abnormality detecting device according to the first aspect, wherein when the resistance value abnormality determining means does not determine an abnormality, the switching means is turned on. On-state voltage detecting means for detecting a voltage value VLon of an energizing path between the load and the switching means, and a voltage value VBLon of the power supply, and the voltage value VLon detected by the on-state voltage detecting means. And a voltage value VBLon of the power supply, and a current value calculating means for calculating a current value flowing through the conduction path based on the resistance value of the load calculated by the load resistance calculating means, and a current value calculating means. It is determined whether or not the current value is within a predetermined range set in advance, and when the current value is not within the predetermined range, a current value abnormality determination procedure for determining an abnormality is performed. And a step.

In the above abnormality detecting device, the load resistance is calculated by the load resistance calculating means, and the calculated resistance of the load is calculated by the resistance abnormality determining means. If the value is less than the predetermined range, it is determined that the load or the current path is short-circuited, and if the value is outside the predetermined range, the load or the current path is broken. Is determined.

On the other hand, when the calculated resistance value of the load is within a predetermined range, that is, when the resistance value abnormality determination means does not determine that the load value is abnormal, the resistance value when the switching means is turned on continues. The voltage value VLon of the current path between the load and the switching means, and the voltage value VBLon of the power supply
Is detected by the on-time voltage detecting means, and a current value flowing through the current path is calculated by the current value calculating means based on the detected voltage values and the resistance value of the load calculated by the load resistance calculating means. I do.

Then, it is determined whether or not the calculated current value is within a predetermined range set in advance. If the calculated current value is within the predetermined range, it is determined that the load or the current path is normal. . If the calculated current value is not in the predetermined range, for example, if the calculated current value is less than the predetermined range,
Judge that the load or its energization path is disconnected,
If the calculated current value is outside the predetermined range, it is determined that the load or the current path is short-circuited, and in any case, it is determined that there is an abnormality.

That is, in the above abnormality detecting device, first,
The resistance value of the load is calculated, and an abnormality is determined based on the resistance value. If no abnormality is determined at this time, the current value is calculated using the calculated resistance value, and the abnormality is determined again based on the current value. Therefore, according to this abnormality detection device, since the determination by the resistance value abnormality determination unit and the determination by the current value abnormality determination unit are performed, an abnormality determination device with higher reliability in addition to the function and effect of claim 1 or 2 is provided. Can be realized.

In any of the abnormality detecting devices according to claims 1 to 3, the switching means is provided as a so-called low-side switch on the downstream side of the current from the load. Even in the case where a so-called high-side switch is provided on the upstream side of the current, it is possible to detect an abnormality in the load or the conduction path thereof in the same manner as described above.

Therefore, the abnormality detecting device according to claim 4 is
A power supply, a load, and a switching unit are connected in series to form an energizing path, and the switching unit is provided at a position upstream of the load with respect to a direction of a current flowing through the energizing path, and turns on the switching unit. An abnormality detection device that detects an abnormality in the load or the energization path with respect to a load driving device that controls energization to the load by performing off-control, in series with the load, and A detection resistor provided in parallel,
When the switching means is off, the voltage value VHoff of the current path between the load and the switching means, the voltage value VBHoff of the power supply, and the current direction flowing through the current path on the downstream side of the load. An off-state voltage detecting means for detecting a voltage value VEoff of the energization path; and the voltage value VHoff detected by the off-state voltage detecting means.
Load resistance calculating means for calculating the resistance value of the load based on the voltage value VBHoff of the power supply, the voltage value VEoff, and the resistance value of the detection resistor; and the resistance of the load calculated by the load resistance calculating means. Resistance value abnormality determination means for determining whether the value is within a predetermined range set in advance, and determining that the load is abnormal when the resistance value of the load is not within the predetermined range. In the abnormality detection device described above, the voltage value detected by the off-state voltage detection means includes a voltage value VHoff of an energizing path between the load and the switching means, a voltage value VBHoff of a power supply, and a current flowing through the energizing path. The voltage value VEoff of the energization path on the downstream side of the load with respect to the direction (hereinafter, simply referred to as “downstream side of the load”), and the load resistance calculating means detects each voltage value VHoff detected by the off-state voltage detecting means. , V Although the resistance value of the load is calculated based on BHoff and VEoff and the resistance value of the detection resistor, the other components are exactly the same as those of the abnormality detection device according to claim 1 and will not be described. Is omitted.

As described above, even if the switching means is provided as a so-called high-side switch, it is possible to detect an abnormality in the load or its energizing path based on the resistance value of the load, as in the case of the low-side switch. Therefore, according to the abnormality detection device described above, since the detection resistor is provided in parallel with the switching means, the resistance value of the detection resistor can be set large, and the current flowing through the detection resistor can be suppressed small. For example, a small resistor (for example, a chip resistor) having a small rated power can be used. As a result, the size of the abnormality detection device and the size of the load driving device can be reduced.

The abnormality detecting device according to claim 5 is
The abnormality detection device according to claim 4, wherein instead of or in addition to the resistance abnormality determination unit, when the switching unit is on, an energization path between the load and the switching unit is connected. On-time voltage detecting means for detecting a voltage value VHon, and a voltage value VEon of the energizing path downstream of the load with respect to the direction of current flowing through the energizing path, and the voltage detected by the on-time voltage detecting means. Current value calculating means for calculating a current value flowing through the energizing path based on the value VHon, the voltage value VEon, and the resistance value of the load calculated by the load resistance calculating means, and a current value calculated by the current value calculating means. It is determined whether the current value is within a predetermined range set in advance,
Current value abnormality determining means for determining that the current value is abnormal when the current value is not within the predetermined range.

In the above abnormality detection device, the switching means is first turned off, and the voltage value VHoff of the current path between the load and the switching means, the voltage value VBHoff of the power supply, and the voltage value of the current path downstream of the load are set. VEoff is detected. Then, based on the detected voltage values and the resistance value of the detection resistor, the load resistance value is calculated by the load resistance calculation means.

Next, when the switching means is turned on, the voltage value VHon of the current path between the load and the switching means and the voltage value VEon of the current path on the downstream side of the load are detected by the on-time voltage detecting means. Based on the detected and detected voltage values and the resistance value of the load calculated by the load resistance calculating means, a current value flowing through the current path is calculated by the current value calculating means. Based on the calculated current value, it is determined whether the load or the current path is abnormal, as in the second aspect of the invention.

Therefore, according to the above abnormality detecting device, similarly to the abnormality detecting device according to the second aspect, it is possible to accurately detect the load or the abnormality of the current path through the current value of the current path. A small resistor (for example, a chip resistor) having a small rated power can be used as the detection resistor, and the abnormality detection device and the load driving device can be reduced in size.

The abnormality detecting device according to a sixth aspect of the present invention is the abnormality detecting device according to the fourth aspect, wherein when the resistance value abnormality determining means does not determine that there is an abnormality, the switching means is turned on. On-time voltage detection for detecting the voltage value VHon of the current path between the load and the switching means and the voltage value VEon of the current path on the downstream side of the load with respect to the direction of current flowing through the current path. Means for calculating a current value flowing through the current path based on the voltage value VHon and the voltage value VEon detected by the on-time voltage detection means, and the resistance value of the load calculated by the load resistance calculation means. Determining whether the current value calculated by the current value calculation means is within a predetermined range set in advance, and determining whether the current value is A current value abnormality judging means for judging an abnormality when the current value is not within the predetermined range.

In the above abnormality detecting device, the load resistance is calculated by the load resistance calculating means, and the calculated resistance of the load is calculated by the resistance abnormality determining means. If the value is less than the predetermined range, it is determined that the load or the current path is short-circuited, and if the value is outside the predetermined range, the load or the current path is broken. Is determined.

On the other hand, when the calculated resistance value of the load is within the predetermined range, that is, when the resistance value abnormality determination means does not determine that the load value is abnormal, the resistance value when the switching means is turned on continues. A voltage value VHon of an energizing path between the load and the switching means and a voltage value VEon of the energizing path on the downstream side of the load are detected by an on-state voltage detecting means, and the detected voltage values and load resistance calculating means are detected. The value of the current flowing through the conduction path is calculated by the current value calculation means based on the resistance value of the load calculated by the above.

Then, it is determined whether or not the calculated current value is within a predetermined range set in advance. If the calculated current value is within the predetermined range, it is determined that the load or its energizing path is normal. . If the calculated current value is not in the predetermined range, for example, if the calculated current value is less than the predetermined range,
Judge that the load or its energization path is disconnected,
If the calculated current value is outside the predetermined range, it is determined that the load or the current path is short-circuited, and in any case, it is determined that there is an abnormality.

Therefore, according to this abnormality detecting device, similarly to the abnormality detecting device according to the third aspect, the judgment by the resistance value abnormality judging means and the judgment by the current value abnormality judging means are performed. In addition to the operation and effect described above, an abnormality determination device with higher reliability can be realized.

According to a seventh aspect of the present invention, there is provided the abnormality detecting device according to any one of the first to sixth aspects, wherein the load driving device includes, as a load, an oxygen sensor provided in an exhaust passage of an internal combustion engine. The heater control device includes a heater for holding the oxygen concentration detecting element of the sensor at an active temperature, and adjusts the temperature of the oxygen concentration detecting element by duty controlling the amount of current flowing through the heater.

The oxygen concentration detecting element of the oxygen sensor generates, for example, a feedback signal for controlling the air-fuel ratio of the air-fuel mixture, and is one of the most important elements among various sensors used in controlling the internal combustion engine. That is, it is necessary to constantly monitor whether the heater required to maintain the oxygen concentration detecting element at the activation temperature is normal. Therefore, in such a heater driving device for an oxygen sensor, by providing the abnormality detecting device according to the first to sixth aspects, the heater and its energizing path can be constantly monitored, and thus the heater caused by the abnormality of the heater can be monitored. There is no possibility that appropriate air-fuel ratio control is performed, and appropriate air-fuel ratio control can always be performed. As a result, it is possible to improve fuel efficiency and prevent deterioration of exhaust emission.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 is a schematic configuration diagram showing a configuration of a heater control device for an oxygen sensor according to the present embodiment. As shown in FIG. 1, a heater control device 10 according to the present embodiment includes an oxygen sensor 11 provided in an exhaust path of an internal combustion engine, and an electronic control device (hereinafter referred to as “ECU”) that controls energization of a heater 11 a of the oxygen sensor 11. ) 12).

The oxygen sensor 11 includes an oxygen concentration detecting element 11
b and a heater 11a. As is well known, the basic fuel injection amount is corrected on the basis of the oxygen concentration in the exhaust gas to supply the combustion chamber of the internal combustion engine with a view to reducing the exhaust emission of the automobile and improving the fuel efficiency. The air-fuel mixture is controlled to a predetermined air-fuel ratio (for example, a stoichiometric air-fuel ratio). The oxygen concentration detecting element 11b has a structure in which a porous platinum electrode is coated on both inner and outer surfaces of a zirconia solid electrolyte formed in a test tube, so that the inner electrode is in contact with the atmosphere and the outer electrode is in contact with exhaust gas. At the exhaust path. The oxygen concentration detecting element 11b needs to be maintained within a predetermined activation temperature range (around 700 ° C.) in order to maintain stable output characteristics. Therefore, the oxygen concentration detecting element 11b is heated by the heater 11a. I have. Heater 1
The energization of 1a is duty-controlled by the ECU 12 described later.

The ECU 12 includes a microcomputer (hereinafter referred to as "microcomputer") 13, a power supply device 14, a heater energization control circuit 15, and a detection resistor 16.
The heater controls the air-fuel ratio of the air-fuel mixture based on the detection signal taken from the oxygen concentration detecting element 11b of the oxygen sensor 11, that is, controls the fuel injection amount of the injector and maintains the oxygen concentration detecting element 11b at the active temperature. 11a
Is controlled. The microcomputer 13 also has a well-known diagnosis function for performing self-diagnosis and storing and displaying abnormalities of the heater 11a, other sensors, actuators, and the like. When the error occurs, a diagnostic corresponding to the situation is output.

Since the impedance of the oxygen concentration detecting element 11b has the property of changing with temperature, the detection signal taken from the oxygen concentration detecting element 11b includes
In addition to the signal component depending on the oxygen concentration, the oxygen concentration detecting element 1
The temperature-dependent component 1b is also included. Therefore, by extracting this temperature-dependent component from the detection signal, the temperature of the oxygen concentration detecting element 11b can be constantly monitored, and the heater 11
The feedback control is performed to a desired temperature by controlling the energization to a.

Here, a positive voltage VB is applied to one end of the heater 11a of the oxygen sensor 11 from a positive terminal of a battery 17, which is a power supply of an automobile equipped with an internal combustion engine. The other end of the heater 11a is connected to a heater energization control circuit 15, and is connected to a negative electrode of the battery 17 via a field effect transistor (FET) (hereinafter referred to as a "drive transistor Tr1") for controlling a current flowing through the heater 11a. It is grounded to a ground line at the same potential as the terminal.

The drive transistor Tr1 has a drain connected to the heater 11a and a source grounded, and is provided as a so-called low-side switch in the power supply path of the heater 11a. In the heater power supply control circuit 15, the CPU
By inputting the control signal input from 13a to the gate of the driving transistor Tr1 via the resistor 15b, the driving transistor Tr1 is turned on / off according to the control signal. In addition, as such a switching means, other switching elements such as a bipolar transistor can be used in addition to the field effect transistor.

In the energization path of the heater 11a,
Battery 17, heater 11a, and drive transistor Tr1
The resistance value RD
Are connected. Specifically, as shown in FIG. 1, a battery 17, a heater 11a, and a drive transistor Tr1 are connected in series, and
The detection resistor 16 is connected in series with the a and in parallel with the driving transistor Tr1.

The detection resistor 16 has a resistance value (several tens of k) which is much larger than the resistance value RH (about 5Ω) of the heater 11a.
Ω), and in the abnormality detection processing described later,
When the drive transistor Tr1 is on or off,
The voltage value VD of the current path between the heater 11a and the detection resistor 16 (in other words, between the heater 11a and the drive transistor Tr1) is detected. When the driving transistor Tr1 is turned on, the voltage value VD (hereinafter referred to as “V”) is determined according to the resistance values of the heater 11a, the driving transistor Tr1, and the detection resistor 16.
When the drive transistor Tr1 is turned off, a voltage value VD (hereinafter referred to as "VDoff") is detected according to the resistance values of the heater 11a and the detection resistor 16.

The microcomputer 13 includes a CPU 13a, a ROM 1
3b, a RAM 13c, an A / D converter 13d, and the like, and fetches the voltage value of each part of the energization path of the heater 11a as described later, and based on the voltage value, the heater 11a or the energization path of the heater 11a is abnormal. Is determined. The power supply unit 14 converts the voltage VB of the battery 17 into a power supply (for example, DC 5 V) necessary for operating the microcomputer 13 and the like, and supplies the power to each unit in the ECU 12.

Next, the operation of the heater control device 10 according to the present embodiment will be described. Each time the ignition switch is turned on, the CPU 13a reads out an abnormality detection processing program from the ROM 13b as a recording unit in which a plurality of programs are recorded, and executes processing according to the program. FIG. 2 is a flowchart of the abnormality detection process.

When this process is started, first, in step (hereinafter abbreviated as "S") 210, the control signal output from CPU 13a to drive transistor Tr1 is turned off, and drive transistor Tr1 is turned off. At this time, although the drive transistor Tr1 is off, the detection resistor 16 having the resistance value RD is connected in parallel with the drive transistor Tr1, so that a small amount of current flows through the heater 11a and the detection resistor 16. However, since this current is very small, the heater 11a is in a state of not performing a predetermined function as a heater.

Next, at S220, the voltage value of the terminal of the heater 11a on the battery 17 side, that is, the power supply voltage value VBLoff,
The voltage value at the other end of the heater 11a, that is, the voltage value VDoff of the power supply path between the heater 11a and the driving transistor Tr1 is taken into the CPU 13a via the A / D converter 13d. Then, in S225, CP is determined based on the voltage values VBLoff and VDoff taken into the CPU 13a and the resistance value RD of the detection resistor 16 stored in the ROM 13b in advance.
In U13a, the resistance value R of the heater 11a is calculated by the following equation (1).
Calculate H.

[0051]

(Equation 1)

Then, in S230 and S240, S2
It is determined whether the resistance value RH calculated in step 25 is within a predetermined range. In the ROM 13b, in addition to the resistance value RD of the detection resistor 16, the expected resistance value of the heater 11a is stored in advance in a predetermined range (allowable range). Here, the lower limit value of the predetermined range is r0, and the upper limit value is r0. The value is r1. First, in S230, it is determined whether RH> r0, that is, whether RH is greater than a lower limit value r0 of a predetermined range, and RH> r0.
If it is r0, the process proceeds to S240. In S240, RH <r
1, that is, whether RH is smaller than an upper limit value r1 of a predetermined range. If RH <r1, it is determined that there is no abnormality in the heater 11a and its energizing path, and the process proceeds to next S240.

On the other hand, when it is determined in step S230 that RH ≦ r0, the resistance value RH of the heater 11a is less than the predetermined range, and it is determined that a short circuit has occurred in the heater 11a or its energizing path. Then, a diagnosis of the short-circuit of the conduction path is output to prevent the drive transistor Tr1 from being turned on. If it is determined in step S240 that RH ≧ r1, the resistance value RH of the heater 11a is outside the predetermined range, and it is determined that a break has occurred in the heater 11a or its energizing path, and the process proceeds to S300. A diagnosis of the energization path open is output so that the drive transistor Tr1 is not turned on.

In S250, it is determined whether or not the control signal output from the CPU 13a to the drive transistor Tr1 is on by executing a heater control program different from this abnormality detection processing. If the drive transistor Tr1 is turned on, S26
Go to 0. If the control signal for turning on the drive transistor Tr1 has not been output, the process returns to S220 and returns to S2.
Perform 20 or less processes.

In S260, the battery 1 of the heater 11a is
The voltage value of the terminal on the 7th side, that is, the power supply voltage value VBLon, and the voltage value of the other end of the heater 11a, that is, the voltage value VDon of the energization path between the heater 11a and the drive transistor Tr1, are represented by A
The data is taken into the CPU 13a via the / D converter 13d. Then, in S265, based on the voltage values VBLon and VDon taken into the CPU 13a and the resistance value RH of the heater 11a calculated in S225, the current value I flowing through the current path of the heater 11a in the CPU 13a by the following equation (2).
Calculate Lon.

[0056]

(Equation 2)

The current ILon is determined by the driving transistor T
This is the value of the current flowing through the conduction path when r1 is turned on. Then, in S270 and S280, it is determined whether or not the on-state current value ILon calculated in S265 is within a predetermined range stored in the ROM 13b in advance. Here, the lower limit of the predetermined range is I0 and the upper limit is I1. First, in S270, it is determined whether ILon <I1, that is, whether ILon is smaller than an upper limit value I1 of a predetermined range.
If n <I1, the process proceeds to S280. In S280, ILo
It is determined whether n> I0, that is, if ILon is greater than a lower limit value I0 of a predetermined range.
It is determined that 1a and its energization path are normal, and the abnormality detection processing ends.

On the other hand, when it is determined in S270 that ILon ≧ I1, it is determined that a short circuit has occurred in the heater 11a or its energizing path because the ON-time current value ILon exceeds a predetermined range. Proceeding to S290, a short-circuit diagnosis of the conduction path is output, and the driving transistor Tr1 is output.
Do not turn on. If it is determined in S280 that ILon ≦ I0, the current value ILon at the time of ON is less than the predetermined range, it is determined that the heater 11a or its energizing path is disconnected, and the process proceeds to S300 to open the energizing path. Is output to prevent the drive transistor Tr1 from being turned on.

The predetermined range (allowable range) of the resistance value RH of the heater 11a stored in advance in the ROM 13b is, for example, a range in which a certain degree of variation is assumed in the rated resistance value of the heater 11a, and the predetermined range of the current value ILon is set. The (permissible range) may be a range that can be obtained when the resistance value RH of the heater 11a is within a predetermined range, for example. Also, RO
As the M13b, a non-erasable data such as a mask ROM or a non-volatile memory (for example, an EPROM or an EEPROM) capable of data rewriting / rewriting can be used.
M), the predetermined range stored in the ROM 13b may be appropriately changed according to the heater 11a of the oxygen sensor 11 to be used.

According to the present embodiment, the detection resistor 16 is provided in parallel with the driving transistor Tr1 in order to determine the abnormality of the heater 11a or its energizing path.
The resistance value RD can be set to be much larger than the resistance value RH of the heater 11a, and the current flowing through the detection resistor can be suppressed to a small value. 16 W chip resistor) can be used. Therefore, the entire ECU 12 including the detection resistor 16 can be reduced in size, and as a result, the heater control device 10 can be reduced in size.

Also, the heater 11a
Alternatively, even if an abnormality such as an open or a short circuit occurs in the current supply path, the abnormality is detected, and in the event of an abnormality, the drive transistor Tr1 is not turned on. be able to.

Further, the resistance value RH of the heater 11a varies greatly between products and changes with time, and the power supply voltage value VBL slightly varies depending on whether the drive transistor Tr1 is turned on (VBLon) or turned off (VBLoff). It will be different,
By using the equations (1) and (2) of the present embodiment, the resistance value RH of the heater 11a and the current value ILon flowing through the energization path can be accurately calculated, and accurate abnormality detection is performed based on the calculated value. be able to.

Further, even if the current path is not determined to be abnormal in the determination based on the resistance value RH, the current value I
Since the judgment based on Lon is also performed, the resistance value RH or the current value I
Abnormality detection can be performed more reliably than when the determination is made based on only one of Lon. As a result, due to the occurrence of an abnormality, the oxygen concentration detecting element 11b of the oxygen sensor 11 does not function properly, and the actual air-fuel ratio to be obtained by the air-fuel ratio control deviates from the target air-fuel ratio to deteriorate the exhaust emission. Can be prevented.

[Second Embodiment] FIG. 3 is a schematic configuration diagram showing the configuration of a heater control device for an oxygen sensor according to this embodiment. As shown in FIG. 3, the heater control device 3 of the present embodiment
0 denotes an oxygen sensor 11 provided in the exhaust path of the internal combustion engine.
And an ECU 31 that controls the energization of the oxygen sensor 11 to the heater 11a. The oxygen sensor 1
1. The microcomputer 13, the power supply device 14, the drive transistor Tr1, the resistor 15b, and the detection resistor 16 in the heater energization control circuit 32 have the same configuration as in the first embodiment. With the same sign,
The description is omitted.

The ECU 31 includes the microcomputer 13, the power supply device 14, the heater energization control circuit 32, and the detection resistor 16, and similarly to the first embodiment, the ECU 31
The air-fuel ratio of the air-fuel mixture is controlled based on the detection signal taken from the oxygen concentration detecting element 11b, that is, the fuel injection amount of the injector is controlled, and power is supplied to the heater 11a for maintaining the oxygen concentration detecting element 11b at the activation temperature. Control.

Here, one end of the heater 11 a of the oxygen sensor 11 is connected to the drive transistor T of the heater energization control circuit 32.
r1 is connected to the source of the driving transistor Tr1.
, A positive battery voltage VB is applied to the heater 11a. The other end of the heater 11a is connected to the battery 17
And is connected to the A / D converter 13d in the ECU 31.

The drive transistor Tr1 has a drain connected to the positive electrode side of the battery 17, and a source connected to the heater 11a.
Heater 11a as a high-side switch connected to the
Are provided in the current supply path. A detection resistor 16 having a resistance value RD is connected in series with the heater 11a and in parallel with the drive transistor Tr1 in an energizing path of the heater 11a including the battery 17, the drive transistor Tr1, and the heater 11a.

In the abnormality detection processing described later, the heater 11a is turned on or off when the drive transistor Tr1 is turned on or off.
And the detection resistor 16 (in other words, between the heater 11a and the driving transistor Tr1), the voltage value VS of the current path is detected. When the drive transistor Tr1 is on,
Heater 11a, drive transistor Tr1, and detection resistor 1
The voltage VS (hereinafter referred to as "VSon") according to the resistance value of No. 6
Is detected, and when the drive transistor Tr1 is turned off, the voltage VS is determined according to the resistance values of the heater 11a and the detection resistor 16.
(Hereinafter referred to as "VSoff").

In the microcomputer 13, as will be described later, the drain side voltage value of the drive transistor Tr1, ie, the power supply voltage VBH, and the source side voltage value VS of the drive transistor Tr1
And the ground side voltage value VE of the heater 11a, and it is determined whether or not the heater 11a or its energization path is abnormal based on the value.

Next, the operation of the heater control device 30 of this embodiment will be described. Each time the ignition switch is turned on, the CPU 13a reads out an abnormality detection processing program from the ROM 13b as a recording unit in which a plurality of programs are recorded, and executes processing according to the program. FIG. 4 is a flowchart of the abnormality detection process.

When this process is started, first, in S410, the control signal output from the CPU 13a to the drive transistor Tr1 is turned off. Next, in S420, the voltage value on the drain side of the drive transistor Tr1, that is, the power supply voltage value V
BHoff, the source-side voltage value of the driving transistor Tr1, that is, the voltage value VSoff of the power supply path between the driving transistor Tr1 and the heater 11a, and the ground-side voltage value VEoff of the heater 11a, are transmitted via the A / D converter 13d. CP
Import to U13a. Then, in S425, the CPU 13a
The CPU 13a calculates the resistance value RH of the heater 11a in the CPU 13a according to the following equation (3) based on the voltage values VBHoff, VSoff, and VEoff taken into the CPU 13a and the resistance value RD of the detection resistor 16 stored in the ROM 13b in advance.

[0072]

(Equation 3)

Then, in S430 and S440, S4
The presence / absence of an abnormality is determined based on the resistance value RH calculated in step 25, and if it is not determined that there is an abnormality, that is, r0 <RH <r
If 1, go to S450. Abnormal at S430, that is, RH
When it is determined that ≦ r0, the process proceeds to S490, and when it is determined that RH ≧ r1 at S440, the process proceeds to S500 to output a diagnostic indicating that each is abnormal so that the drive transistor Tr1 is not turned on. . S4
90 and S500 are respectively S290 and S290 of the first embodiment.
This is the same processing as S300.

In S450, it is determined whether or not the control signal output from the CPU 13a to the drive transistor Tr1 is on by executing a heater control program different from this abnormality detection processing.
If not, the process returns to step S420 to perform the processes from step S420.

In S460, the drive transistor Tr1 and the heater 11 are turned on when the drive transistor Tr1 is turned on.
The voltage value VSon of the energization path and the ground side voltage value VEon of the heater 11a are taken into the CPU 13a via the A / D converter 13d. Then, in S465, the CP
The voltage values VSon and VEon taken into U13a, and S
Based on the resistance value RH of the heater 11a calculated in 425, the current value IHon flowing through the power supply path of the heater 11a is calculated in the CPU 13a by the following equation (4).

[0076]

(Equation 4)

The current value IHon is determined by the driving transistor T
This is the value of the current flowing through the conduction path when r1 is turned on. Then, in S470 and S480, the presence / absence of an abnormality is determined based on the current value IHon. If the abnormality is not determined, that is, if I0 <IHon <I1, the abnormality detection processing ends. If it is determined in S470 that an abnormality has occurred, that is, if IHon ≧ I1, it is determined in S490 that an abnormality has occurred in S480, that is, IHon
If it is determined that .ltoreq.I0, the process proceeds to S500, in which a diagnostic indicating that each is abnormal is output, and the driving transistor T
Do not turn on r1.

In order to determine the presence or absence of the above-described abnormality, the ground side voltage values VEoff and VEon of the heater 11a are determined by the CPU1.
What was taken into 3a is the driving state of the car and the heater 11
This is because the ground-side voltage values VEoff and VEon of the heater 11a may not always match the negative-side voltage (0 V) of the battery due to the influence of the grounding position a.

According to the present embodiment, the driving transistor T
Even when r1 is used as a high-side switch in the conduction path, the same operation and effect as those of the first embodiment can be obtained. In the above embodiment, the heater control device 1
0 or the heater control device 30 corresponds to the load driving device of the present invention, the battery 17 corresponds to the power source of the present invention, the heater 11a corresponds to the load of the present invention, and the driving transistor Tr1 corresponds to the switching of the present invention. Means, C
The PU 13a corresponds to the off-time voltage detection means, the on-time voltage detection means, the load resistance calculation means, the current value calculation means, the resistance value abnormality determination means, and the current value abnormality determination means of the present invention. Further, for each voltage and current value of the above embodiment, VDoff and VDon correspond to VLoff and VLon of the present invention, respectively, and VSoff and VSon respectively represent VHoff and Vof the present invention.
Equivalent to Hon.

In each of the abnormality detection processes of FIGS. 2 and 4 in the above embodiment, S220 and S420 are processes executed by the off-time voltage detection means of the present invention.
25 and S425 are processes executed by the load resistance calculating means of the present invention, S230 and S240 and S430 and S440 are processes executed by the resistance value abnormality determining means of the present invention, and S260 and S460 are performed when the present invention is on. This is a process executed by the voltage detecting means, and includes steps S265 and S465.
Is a process executed by the current value calculating means of the present invention.
Steps 70 and S280 and steps S470 and S480 are processes executed by the current value abnormality determination unit of the present invention.

The embodiments of the present invention are not limited to the above-described embodiments, and it goes without saying that various forms can be adopted as long as they fall within the technical scope of the present invention. For example, in the above embodiment, the driving transistor Tr
In order to calculate the current value of the energizing path at the time of turning on the first transistor 1, the resistance value RH of the heater 11a was calculated first when the drive transistor Tr1 was turned off, but instead of calculating the resistance value RH by such calculation, An appropriate value of RH (for example, the rated value of the resistance of the heater 11a) may be stored in the ROM 13b, and the current value of the energization path may be calculated based on the value. However, in order to further increase the calculation accuracy of the current value, it is preferable to calculate the current value by the method described in the above embodiment.

Although the abnormality detection processing shown in FIG. 2 or FIG. 4 is performed every time the ignition switch is turned on in this embodiment, the abnormality detection processing is performed periodically (for example, several seconds) after the ignition switch is turned on. Every or every few ms)
The abnormality detection process may be executed first. This is more preferable because the heater 11a can be constantly monitored during the operation of the vehicle.

In the first embodiment, the heater 11
Although the case where a is one is shown, even when there are a plurality of heaters 11a, for example, a circuit as shown in FIG.
Oxygen sensors (oxygen concentration detecting elements are not shown) 51, 5
In each of the heaters 51a, 52a, 53a and the heater energization control circuit 54 thereof, the same abnormality detection processing as in the above embodiment may be performed by the CPU 13a in the ECU 55. In this case, the same operation and effect as those of the above embodiment can be obtained. The same applies to the case where there are a plurality of heaters 11a in the second embodiment.

Further, in the above embodiment, the case where the heater of the oxygen sensor is used as the load has been described. However, the load is not limited to this, and any load such as a resistance load such as a sheet heating device, a lamp, a window heater, a DC motor or a solenoid, etc. Can be applied to load. As a result, it is possible to detect an abnormality in these loads or their energizing paths without inserting a detection resistor in series with the energizing paths, and it is possible to reduce the size of a device that controls energization.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a configuration of a heater control device of an oxygen sensor according to a first embodiment.

FIG. 2 is a flowchart showing an abnormality detection process of the heater control device of the oxygen sensor according to the first embodiment.

FIG. 3 is a schematic configuration diagram illustrating a configuration of a heater control device for an oxygen sensor according to a second embodiment.

FIG. 4 is a flowchart illustrating an abnormality detection process of the heater control device of the oxygen sensor according to the second embodiment.

FIG. 5 is a schematic configuration diagram showing another embodiment of the heater control device.

FIG. 6 is a schematic explanatory view showing a conventional abnormality detection method.

FIG. 7 is a schematic explanatory view showing a conventional abnormality detection method.

[Explanation of symbols]

 11, 51, 52, 53 ... oxygen sensor 11a, 51a, 52a, 53a ... heater 11b ... oxygen concentration detecting element 12, 31, 55 ... ECU 13 ... microcomputer, 13a ... CPU 13b ROM, 13c RAM 13d A / D converter 14 Power supply 15, 32, 54 Heater energization control circuit 16 Detection resistor 17 Battery 61: heater 62, 73: detection resistor 64: differential amplifier circuit, 71: heater 74: comparator Tr1: driving transistor

Claims (7)

[Claims] A power supply, a load, and switching means connected in series to form an energizing path; the switching means is provided at a position downstream of the load with respect to a direction of current flowing through the energizing path; An abnormality detection device that detects an abnormality in the load or the energization path with respect to a load driving device that controls energization to the load by performing on / off control of the switching unit. And detecting a detection resistor provided in parallel with the switching means, a voltage value VLoff of an energizing path between the load and the switching means and a voltage value VBLoff of the power supply when the switching means is off. Off-time voltage detection means, the voltage value VLoff and the power supply voltage value VBLoff detected by the off-time voltage detection means, and the detection resistor Load resistance calculating means for calculating the resistance value of the load based on the resistance value; and determining whether the resistance value of the load calculated by the load resistance calculating means is within a predetermined range set in advance. A load abnormality detecting device, further comprising: a resistance value abnormality determining unit that determines that the load is abnormal when the resistance value of the load is not within the predetermined range. 2. A power supply, a load, and a switching means are connected in series to form an energizing path, and the switching means is provided at a position downstream of the load with respect to a direction of a current flowing through the energizing path. An abnormality detection device that detects an abnormality in the load or the energization path with respect to a load driving device that controls energization to the load by performing on / off control of the switching unit. And detecting a detection resistor provided in parallel with the switching means, a voltage value VLoff of an energizing path between the load and the switching means and a voltage value VBLoff of the power supply when the switching means is off. Off-time voltage detection means, the voltage value VLoff and the power supply voltage value VBLoff detected by the off-time voltage detection means, and the detection resistor Load resistance calculating means for calculating the resistance value of the load based on the resistance value; and when the switching means is on, a voltage value VLon of an energizing path between the load and the switching means, and a voltage of the power supply. On-time voltage detecting means for detecting the value VBLon, the voltage value VLon and the power supply voltage value VBLon detected by the on-time voltage detecting means, and the resistance value of the load calculated by the load resistance calculating means. Current value calculating means for calculating a current value flowing through the energizing path based on the current value, and determining whether the current value calculated by the current value calculating means is within a predetermined range set in advance, and A load abnormality detection device, comprising: a current value abnormality determination unit that determines an abnormality when the value is not within the predetermined range. 3. The abnormality detection device according to claim 1, wherein when the resistance abnormality determination unit does not determine that there is an abnormality, when the switching unit is turned on, the connection between the load and the switching unit is turned on. Of the current path VLo
n, and an on-time voltage detecting means for detecting the voltage value VBLon of the power supply, and the voltage value VLon and the voltage value VBLon of the power supply detected by the on-time voltage detecting means are calculated by the load resistance calculating means. Current value calculating means for calculating a current value flowing through the current path based on the resistance value of the load, and whether the current value calculated by the current value calculating means is within a predetermined range set in advance. A load abnormality detecting device, comprising: a current value abnormality determining unit that determines whether the current value is not within the predetermined range and determines that the current value is abnormal. 4. A power supply path is formed by connecting a power supply, a load, and switching means in series, and the switching means is provided at a position upstream of the load with respect to a direction of current flowing through the current supply path. An abnormality detection device that detects an abnormality in the load or the energization path with respect to a load driving device that controls energization to the load by performing on / off control of the switching unit. A detection resistor provided in parallel with the switching means; a voltage value VHoff of an energizing path between the load and the switching means when the switching means is off; a voltage value VBHoff of the power supply; An off-state voltage detecting means for detecting a voltage value VEoff of the energization path on the downstream side of the load with respect to a direction of a current flowing through the path; Wherein said voltage value VHoff detected by the detecting means and the voltage value VBHoff of the power supply voltage value VEof
f, and a load resistance calculating unit that calculates the resistance value of the load based on the resistance value of the detection resistor, and the resistance value of the load calculated by the load resistance calculating unit is within a predetermined range. A load abnormality detection device, comprising: a resistance abnormality determination unit that determines whether the load is outside the predetermined range and determines that the load is abnormal when the resistance is not within the predetermined range. 5. A power supply path is formed by connecting a power supply, a load, and switching means in series, and the switching means is provided at a position upstream of the load with respect to a direction of current flowing through the current supply path. An abnormality detection device that detects an abnormality in the load or the energization path with respect to a load driving device that controls energization to the load by performing on / off control of the switching unit. A detection resistor provided in parallel with the switching means; a voltage value VHoff of an energizing path between the load and the switching means when the switching means is off; a voltage value VBHoff of the power supply; An off-state voltage detecting means for detecting a voltage value VEoff of the energization path on the downstream side of the load with respect to a direction of a current flowing through the path; Wherein said voltage value VHoff detected by the detecting means and the voltage value VBHoff of the power supply voltage value VEof
f, and load resistance calculating means for calculating the resistance value of the load based on the resistance value of the detection resistor, and when the switching means is on, a voltage value of an energizing path between the load and the switching means. VHon, and an on-state voltage detecting means for detecting a voltage value VEon of the energizing path downstream of the load with respect to a direction of current flowing through the energizing path, and the voltage value VHon detected by the on-state voltage detecting means. Current value calculating means for calculating a current value flowing through the energizing path based on the voltage value VEon and the resistance value of the load calculated by the load resistance calculating means; and the current value calculated by the current value calculating means. Current value abnormality determining means for determining whether the current value is within a predetermined range set in advance and determining that the current value is abnormal when the current value is not within the predetermined range; Abnormality detection apparatus for a load, characterized in that it comprises a. 6. The abnormality detection device according to claim 4, wherein when the resistance abnormality determination unit does not determine that there is an abnormality, when the switching unit is turned on, the state is between the load and the switching unit. Voltage value of the current path VHo
n, and on-state voltage detecting means for detecting a voltage value VEon of the energizing path on the downstream side of the load with respect to the direction of current flowing through the energizing path, and the voltage value VHon detected by the on-state voltage detecting means Current value calculating means for calculating a current value flowing through the energizing path based on the voltage value VEon and the resistance value of the load calculated by the load resistance calculating means; and the current value calculated by the current value calculating means. Current value abnormality determining means for determining whether the current value is within a predetermined range set in advance, and determining that the current value is abnormal when the current value is not within the predetermined range. Load abnormality detection device. 7. The load driving device includes, as a load, a heater for maintaining an oxygen concentration detecting element of an oxygen sensor provided in an exhaust path of an internal combustion engine at an active temperature, and duty-controls an amount of current flowing through the heater. The load abnormality detecting device according to any one of claims 1 to 6, wherein the device is a heater control device that adjusts the temperature of the oxygen concentration detecting element.