JP3339107B2 - Abnormality detection device in load control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for controlling loads such as a resistance type load such as a heater used for an oxygen sensor and a coil type load such as an electromagnetic valve used for a fuel injection valve. The present invention relates to an abnormality detection device in a load control device for detecting deterioration of a load and an abnormality occurring in a load control system.

[0002]

2. Description of the Related Art Conventionally, as an abnormality detecting device for detecting an abnormality of a load control system, for example, Japanese Patent Application Laid-Open No. 3-1652
No. 45 and Japanese Utility Model Application Laid-Open No. Sho 62-153566 are disclosed.

In the abnormality detecting device disclosed in Japanese Patent Application Laid-Open No. 3-165245, a heater (load) for heating an oxygen sensor is energized and controlled in accordance with the on / off operation of a transistor (switching element). The current value when the heater is turned on is detected, and the abnormality of the heater control system is determined based on the current value of the heater.

On the other hand, in the abnormality detecting device disclosed in Japanese Utility Model Laid-Open No. 62-153566, the heater (load) of the oxygen sensor is duty-controlled by a controller, and the ground voltage of the heater is controlled by a smoothing circuit. Had been smoothed. The controller has detected an abnormality in the heater control system based on a comparison between the heater voltage assumed by the control duty and the actual average heater voltage output from the smoothing circuit.

[0005]

However, in the above-described conventional abnormality detection device, the following problems have occurred. In other words, in Japanese Patent Application Laid-Open No. HEI 3-165245, a configuration is adopted in which a heater abnormality is detected when the heater is turned on.
The current flowing through the heater greatly changes under the influence of the loss of the switching element (ON resistance, saturation voltage). In particular, when the deterioration level of the heater is small, the current of the heater greatly depends on the loss of the switching element, so that the accuracy of detecting the current value is reduced, and accordingly, the accuracy of the abnormality determination may be reduced.

Further, in Japanese Utility Model Laid-Open Publication No. Sho 62-153566, there is a problem that if the driving duty of the heater is 100% for a long time, it becomes impossible to detect a heater abnormality, and the smoothing circuit has a sufficient smoothing. In order to have a function, it is necessary to set a large time constant, and there is also a problem in response.

In addition, in the configuration of the above-described conventional abnormality detection device, it is impossible to detect abnormality due to load degradation simply by detecting normality / abnormality of the load, and a device capable of detecting degradation abnormality is also desired. Was rare.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problem, and has as its object to make it possible to determine an abnormality accompanying deterioration of a load and to improve the accuracy of abnormality determination. An object of the present invention is to provide an abnormality detection device in a load control device.

[0009]

According to a first aspect of the present invention, a power supply, a load, and a switching element are connected in series, and the load is switched in accordance with the on / off operation of the switching element. It is used for a load control device that is configured to energize or cut off, and in series with the load,
A current detection resistor connected in parallel with the switching element, and a current value of the load detected by the current detection resistor when the current supply to the load is cut off is equal to or less than a predetermined threshold value. And an abnormality determining means for determining that an abnormality has occurred in the load.

According to a second aspect of the present invention, there is provided a load control device in which a power supply, a load, and a switching element are connected in series, and the load is energized or de-energized in accordance with the on / off operation of the switching element. And a current detection resistor connected in series with the load and in parallel with the switching element, and the load detected by the current detection resistor when the load is turned off. If the current value is equal to or less than a predetermined threshold value, it is determined that an abnormality has occurred in the load, and if the current value of the load is equal to or greater than a predetermined threshold value when the load is energized, the load And an abnormality determining means for determining that an abnormality has occurred in the control system.

Further, in the first or second aspect of the invention, a plurality of thresholds for determining the current value of the load may be provided. Further, when the voltage value of the power supply is equal to or less than a predetermined value, abnormality detection may be prohibited.

[0012]

According to the first aspect, the load is energized by the on operation of the switching element, and the energization of the load is cut off by the off operation of the switching element. Further, the current value of the load at the time when the load is cut off is detected by a current detecting resistor connected in series with the load and in parallel with the switching element. Then, the abnormality determining means determines that an abnormality has occurred in the load when the current value of the load is equal to or less than a predetermined threshold value when the energization of the load is cut off.

That is, for example, when the deterioration of the load progresses with time, the internal resistance of the load increases and the current value decreases. Therefore, an abnormality associated with the deterioration is determined by detecting a decrease in the current value of the load by the abnormality determining means. Further, since this abnormality determination is performed when the energization of the load is interrupted (when the switching element is turned off), the current value of the load is detected without being affected by the loss such as the on-resistance of the switching element, and the current value of the load is detected. As the detection accuracy is improved, the accuracy of the abnormality determination is improved.

[0014] According to the second aspect of the present invention, when the current supply to the load is interrupted, if the current value of the load detected by the current detecting resistor is equal to or less than a predetermined threshold value, the abnormality determining means may determine whether the load is in the off state. It is determined that an abnormality has occurred in the load control system if the current value of the load is equal to or greater than a predetermined threshold value when the load is energized.

That is, in the second aspect of the present invention, it is possible to determine an abnormality accompanying deterioration of the load when the energization of the load is cut off, and to control the load during the energization of the load in the same manner as in the first aspect. An abnormality occurring in the system can be determined.

Further, by providing a plurality of thresholds for determining the current value of the load, it is possible to determine the degree of deterioration of the load and abnormality of the control system. Further, when the voltage value of the power supply is equal to or lower than the predetermined value, the abnormality detection is prohibited, thereby preventing erroneous detection.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an abnormality detecting device in a load control device according to the present invention.

FIG. 2 is a diagram showing a schematic configuration of a multi-cylinder spark ignition gasoline engine mounted on a vehicle. In FIG. 2, a cylinder 4 is provided in an engine body 1 including a cylinder head 2 and a cylinder block 3, and a piston 5 is fitted into the cylinder 4. Further, an intake passage 8 and an exhaust passage 9 are connected to the engine body 1 via an intake valve 6 and an exhaust valve 7. In the cylinder 4, a cylinder head 2, a cylinder block 3, a piston 5, an intake valve 6
A combustion chamber 10 is formed so as to be surrounded by the exhaust valve 7 and the like, and an ignition plug 11 is provided in the combustion chamber 10. Water jacket 27 provided on cylinder block 3
Is provided with a water temperature sensor 26.
Outputs a water temperature signal TW corresponding to the temperature of the cooling water in the water jacket 27.

In the intake passage 8, sequentially from the upstream side,
An air filter 12 for purifying intake air, an air flow meter 13 for detecting the amount of intake air, a throttle valve 14 for opening and closing the intake passage 8 in conjunction with an accelerator pedal, and a fuel pumped from a fuel supply unit to the intake passage 8. A fuel injection valve 15 for injecting toward an intake port forming a downstream portion is provided.

In the exhaust passage 9, sequentially from the upstream side,
Oxygen sensor 17, three-way catalytic converter 18 for purifying exhaust gas, and silencer 19 for silencing exhaust noise
Is provided. The heater 16 as a load in the present embodiment is attached to the oxygen sensor 17. The oxygen sensor 17 is activated when the temperature of the sensor 17 exceeds approximately 650 ° C. When the air-fuel ratio of the air-fuel mixture, which operates normally in the active state and is supplied to the combustion chamber 10, becomes close to the stoichiometric air-fuel ratio as a boundary, the air-fuel ratio is on the rich side and the lean side. Output a binary oxygen concentration signal VO2 having different levels.

Further, a distributor 20 whose rotation shaft is driven to rotate by a crankshaft is attached to the engine body 1. The distributor 20 is provided with a crank angle sensor 21. The crank angle sensor 21 outputs a crank angle signal SC corresponding to the rotation speed of the engine. Further, an ignition coil unit 23 integrated with the ignition timing control unit 22 is connected to the distributor 20.

Electronic control unit (hereinafter referred to as ECU) 24
Is the fuel injection by the fuel injection valve 15 and the ignition plug 1
1 for controlling the ignition of each battery, and a battery voltage VB from a battery 25 as a power supply.
(12V). The ECU 24 receives the intake air amount signal SM from the air flow meter 13, the crank angle signal SC from the crank angle sensor 21, the oxygen concentration signal VO2 from the oxygen sensor 17, the water temperature signal TW from the water temperature sensor 26, and the like. You. The ECU 24 performs fuel injection control and ignition timing control based on output signals (SM, SC, VO2, TW) from various sensors. Further, in the present embodiment, the ECU 24 controls the energization of the heater 16 attached to the oxygen sensor 17 and determines an abnormality (the details will be described later).

Here, the fuel injection control by the ECU 24 will be described. When the operating state of the engine satisfies a predetermined condition, for example, when the operating state is neither an acceleration state nor a deceleration state, neither a high-load high-speed state nor a start state, the ECU 24 outputs the intake air amount signal. The basic fuel injection amount is calculated according to SM and the crank angle signal SC. Further, the ECU 24 corrects the basic fuel injection amount based on the oxygen concentration signal VO2 from the oxygen sensor 17, and generates an injection pulse signal CP having a pulse width corresponding to the fuel injection amount. For this correction, the ECU 24
Means that if it is detected from the oxygen concentration signal VO2 that the air-fuel ratio of the air-fuel mixture is lean relative to the stoichiometric air-fuel ratio, the basic fuel injection amount is increased by a predetermined amount, and it is detected that the air-fuel ratio is rich. In this case, the basic fuel injection amount is reduced by a predetermined amount. As a result, feedback control of the air-fuel ratio is performed, and the actual air-fuel ratio converges to the stoichiometric air-fuel ratio that is the target air-fuel ratio. Then, the fuel injection valve 15 is opened for a period corresponding to the pulse width of the injection pulse signal CP, and an amount of fuel corresponding to the operating state of the engine is injected into the intake port.

The ignition timing control by the ECU 24 will be described. The ECU 24 sets an ignition timing (normal ignition timing) according to the operating state of the engine based on the intake air amount signal SM, the crank angle signal SC, and the like. An ignition control signal Cq corresponding to the normal ignition timing is supplied to the ignition timing control unit 22. Thereby, the ignition coil unit 2
A secondary high voltage pulse having a timing corresponding to the ignition control signal Cq is obtained from 3, and is supplied to the ignition plug 11 via the distributor 20. And
The spark plug 11 emits a spark according to the ignition timing set by the ECU 24 and ignites the air-fuel mixture in the combustion chamber 10.

The ignited mixture becomes exhaust gas and is discharged from the combustion chamber 10 to the exhaust passage 9, purified by the three-way catalytic converter 18, and then discharged to the outside. Next, the ECU
The electrical configuration of 24 will be described with reference to FIG. FIG. 1 shows only the configuration related to the energization control and abnormality determination of the heater 16, and omits the configuration related to the fuel injection control and the ignition timing control shown in FIG.

As shown in FIG. 1, the ECU 24 includes a microcomputer (hereinafter abbreviated as a microcomputer) 28, a buffer 29, and a heater energizing circuit 30. The heater energizing circuit 30 includes the heater 16 described above. It is connected. The microcomputer 28 includes an A / D converter that inputs signals from various sensors, a ROM that stores various programs including a processing routine described below, a RAM that stores self-diagnosis results and is backed up by a power supply, and the like. ing.
Further, in the present embodiment, the microcomputer 28 constitutes an abnormality judging means, and the microcomputer 28 according to the current flowing through the heater 16, causes an abnormality due to the deterioration of the heater 16, an abnormality in the heater control system (such as a battery short-circuit, etc.). ) Is determined.

The heater energizing circuit 30 includes a heater energizing section 31 for controlling energization of the heater 16, a shunt resistor RT as a current detecting resistor, and a connection point P (a connection point between the heater 16 and the shunt resistor RT). And a voltage level determining unit 32 for determining the level of the detection voltage VHD.

More specifically, the heater energizing section 31 includes a MOS transistor (hereinafter abbreviated as a transistor) Tr1 as a switching element and a protection resistor RP. The heater 16 is turned on and off according to the on / off operation of the transistor Tr1. Control energization. The shunt resistor RT has a resistance value which is several to several tens times the resistance value of the transistor Tr1 (the resistance value of the transistor Tr1 and the resistance value of the protection resistor RP). The current value at the time of energization or at the time of energization cutoff is detected as a voltage value.

That is, according to the configuration of FIG.
5, a heater 16, a protection resistor RP and a transistor Tr1 are connected in series, and a shunt resistor RT is connected in series with the heater 16 and in parallel with the protection resistor RP and the transistor Tr1. Therefore, when the heater 16 is energized (when the transistor Tr1 is turned on), the detection voltage VHD is detected according to the resistance values of the transistor Tr1, the protection resistor RP, and the shunt resistor RT, and when the heater 16 is turned off (transistor Tr1). Is off), the shunt resistor R
The detection voltage VHD is detected according to the resistance value of T.

The voltage level determination section 32 includes comparators 33 and 34 and resistors R11 to R14 and R21 to R24. The comparators 33 and 34 are connected to the connection point P
, And the resistances R11 to R14 and R21 to R24.
Are compared with the threshold values VTH1 and VTH2 set by the above, and output signals C1 and C2 are output in accordance with the determination results. More specifically, if VHD ≧ VTH1, the output signal C1 of one comparator 33 goes low (low level), and if VHD <VTH1, the output signal C1 goes high (high level). If VHD ≧ VTH2, the output signal C2 of the other comparator 34 becomes L level,
If VHD <VTH2, the output signal C2 goes high. Here, the relationship between the threshold values VTH1 and VTH2 is VTH1
> VTH2 (see FIG. 7).

The heater 16 which is a resistance type load is deteriorated due to factors such as aging.
6 will be described. That is, as shown in FIG. 3, as the deterioration of the heater 16 progresses, its internal resistance increases and the value of the current flowing through the heater 16 decreases. The deterioration of the heater 16 causes a decrease in the heating temperature of the heater 16, which may cause a problem of a defective activation of the oxygen sensor 17. Therefore, in the present embodiment, the deterioration of the heater 16 is detected as a decrease in the detection voltage VHD.

Next, the operation of the present embodiment will be described with reference to FIGS. 4 to 6 show processing routines executed by the microcomputer 28. The heater control routine of FIG. 4 has a cycle of 16 ms, the heater control system abnormality determination routine of FIG. 5 has a cycle of 128 ms, and the heater deterioration detection of FIG. The routine is executed at a cycle of 64 ms. In each routine, a flag F is set to indicate various abnormal states.
1 to F6 are used. Among them, flags F1 to F3 indicate flags relating to the abnormality of the heater control system (F1: battery short-circuit flag, F2: heater control system abnormality flag, F3: normal flag), and flags F4 to F6 indicate abnormality due to deterioration of heater 16. (F4: heater deterioration large flag, F5: heater deterioration small flag, F6: normal flag).

When the heater control routine of FIG. 4 is started, the microcomputer 28 first sets a battery short-circuit flag F1, a heater control system abnormality flag F2, and a large heater deterioration flag F4 in step 101 (F1 = 1, F2 = 1,
F4 = 1) is determined. If all the flags have been cleared (F1 = 0, F2 = 0, F4 = 0), the microcomputer 28 proceeds to step 102. The processing related to each of the flags F1, F2, and F4 will be described later.

The microcomputer 28 increments the counter value K provided in the microcomputer 28 by "1" at step 102. The number of executions of this routine is measured based on the counter value K.

Thereafter, the microcomputer 28 proceeds to step 103
Then, it is determined whether or not the engine speed Ne calculated based on the crank angle signal SC at that time is equal to or less than 6000 rpm. This determination process is for confirming that the energization condition of the heater 16 is satisfied, and Ne ≦ 6.
If it is 000 rpm, the microcomputer 28 determines that the energization condition is satisfied and proceeds to step 104.

The microcomputer 28 determines in step 104 whether the counter value K measured in step 102 is equal to or greater than a predetermined value K0. If K <K0, the microcomputer 28 proceeds to step 105, where the heater 1
6 is turned on (energized). The energization of the heater 16 heats the oxygen sensor 17.

On the other hand, in step 101, F1, F2,
One of F4 is set (F1 = 1, F2 = 1, F
4 = 1) or Ne> 600 in step 103
0 rpm or in step 104, K ≧ K0
If so, the microcomputer 28 proceeds to step 106.
Then, the microcomputer 28 determines in step 106 that the heater 16
Is turned off (power cutoff).

As described above, the ON (energization) timing and the OFF (energization interruption) timing of the heater 16 are set according to the counter value K. In the operation of the microcomputer 28 described below, the abnormality determination processing of the heater control system is executed when the heater 16 is turned on, and the heater deterioration detection processing is executed when the heater 16 is turned off.

On the other hand, when the heater control system abnormality determination routine shown in FIG.
In step 1, it is determined whether or not the heater 16 is currently turned on (energized). If the heater is turned on, the process proceeds to step 202, and the subsequent control system abnormality determination process is performed.

That is, the microcomputer 28 determines in step 202
It is determined whether or not the heater deterioration large flag F4 is set (F4 = 1). Then, the microcomputer 28 executes F4
If F = 1, it is considered that the heater deterioration is large, and the routine is terminated. If F4 = 0, the heater deterioration is considered small, and the routine proceeds to step 203.

Thereafter, the microcomputer 28 proceeds to step 203
To determine whether the battery voltage VB is equal to or higher than a predetermined voltage (10 volts in this embodiment). This determination process is
This is for confirming that the detection condition of the detection voltage VHD is satisfied. If VB ≧ 10 volts, the microcomputer 28 determines that the detection condition is satisfied and proceeds to step 2
Move to 04. Further, the microcomputer 28 executes Step 2
In 04, it is determined whether or not Ne ≦ 6000 rpm.
If e ≦ 6000 rpm, the process proceeds to step 205.

In subsequent steps 205 and 206, the microcomputer 28 outputs the output signals C1 and C1 of the comparators 33 and 34.
2 is determined. For details, see the microcomputer 28
In step 205, C1 = "H" and C2 = ""
H ”, that is, the detection voltage V at the connection point P
It is determined whether or not HD is less than the threshold value VTH2. or,
The microcomputer 28 determines in step 206 whether C1 = "H" and C2 = "L", that is, whether the detection voltage VHD is within the range of the threshold values VTH2 to VTH1.

Then, C1 = "H", C2 = "H" (V
If HD <VTH2), the microcomputer 28 determines that the control system of the heater 16 is normal and proceeds to step 209.
After setting the normal flag F3 (F3 = 1), the routine ends.

On the other hand, C1 = "H", C2 = "L" (VTH
If 2 ≤ VHD ≤ VTH1, the microcomputer 28 proceeds to step 208, deems that an abnormality has occurred in the heater control system, and sets the heater control system abnormality flag F2 (F2 =
1) Yes. Also, C1 = "L", C2 = "L"(VHD> V
If TH1), the microcomputer 28 proceeds to step 207, and considers that a short circuit has occurred in the battery 25 and sets the battery short circuit flag F1 (F1 = 1).

After the processing in steps 207 and 208, the microcomputer 28 proceeds to step 210,
After fixing the switch 6 to the off (power cutoff) state, the routine ends. That is, when the flags F1 and F2 are set, it is considered that the heater 16 cannot be controlled due to the battery short circuit or the heater control system abnormality, and the heater control is forcibly stopped.

On the other hand, when the heater deterioration detection routine of FIG. 6 is started, the microcomputer 28 first determines in step 301 whether or not the heater 16 is currently turned off (power cutoff). If the heater is off, the microcomputer 28 shifts to step 302 to execute the subsequent heater deterioration detection processing.

That is, the microcomputer 28 determines in step 302
It is determined whether or not the battery short-circuit flag F1 or the heater control system abnormality flag F2 is set (F1 = 1 or F2 = 1). If the flags F1 and F2 are both cleared (F1 = 0, F2 = 0), the microcomputer 28 determines that there is no short circuit in the battery 25 and no abnormality in the heater control system, and proceeds to step 303.

Thereafter, the microcomputer 28 proceeds to step 303
To determine whether VB ≧ 10 volts,
In step 304, it is determined whether or not Ne ≦ 6000 rpm, and if both conditions are satisfied, the process proceeds to step 305.

Subsequently, the microcomputer 28 proceeds to step 305
It is determined whether or not the counter value K measured in step 102 of FIG. 4 is equal to or greater than a predetermined value K0, and it is determined in step 306 whether or not the counter value K is equal to or greater than a limit value (K0 + 10). . Then, K0≤K <(K0 + 1
If 0), the microcomputer 28 proceeds to step 307.

That is, when K ≧ K0, the heater 16 is turned off (power cutoff) in step 106 in FIG. 4. Immediately thereafter, when Ne> 6000 rpm, the processing in steps 101 → 102 → 103 → 106 in FIG. Are repeatedly executed, and the OFF state of the heater 16 is continued. When the heater is turned off, the heater temperature decreases. If the outputs of the comparators 33 and 34 are determined in this state, there is a risk of erroneous detection. Therefore, when the heater has been turned off for a predetermined time or more, the deterioration detection process is stopped by the process of step 306.

In subsequent steps 307 and 308, the microcomputer 28 outputs the output signal C of the comparators 33 and 34.
1, the output level of C2 is determined. More specifically, the microcomputer 28 determines in step 306 that C1 = "L" and C2
= L, that is, whether the detection voltage VHD exceeds the threshold value VTH1. Also, the microcomputer 28
In step 307, C1 = "H" and C2 = ""
L ”, that is, the detection voltage VHD is equal to the threshold VTH
It is determined whether it is within the range of 2 to VTH1.

Then, C1 = "L" and C2 = "L" (V
HD> VTH1), the microcomputer 28 proceeds to step 311
And the normal flag F6 is set (F6 = 1) assuming that the heater 16 is normal (no deterioration). Also, C1 = ”
If H ”, C2 =“ L ”(VTH2 ≦ VHD ≦ VTH1), the microcomputer 28 proceeds to step 310,
6 is considered to be small, and the heater deterioration small flag F5
Is set (F5 = 1).

After the processing in steps 310 and 311, the microcomputer 28 turns on (energizes) the heater 16 in step 313 and clears the counter value K to “0” in step 314. The heater deterioration small flag F
When 5 is set, that is, when a small degree of deterioration is confirmed, replacement of the heater 16 is prompted by a predetermined warning means (for example, a warning light, a buzzer, or the like).

On the other hand, C1 = "H", C2 = "H" (VHD
If <VTH2), the microcomputer 28 proceeds to step 309, deems that the deterioration of the heater 16 is large, sets the heater deterioration large flag F4 (F4 = 1), and turns off the heater 16 at step 312 (step 312). (Power cutoff) state. That is, when the degree of deterioration of the heater 16 is large, the heater control is forcibly stopped.

Next, the operation of the microcomputer 28 will be described with reference to FIGS.
This will be described with reference to the timing chart of FIG. FIG.
FIG. 7 is a timing chart corresponding to the heater deterioration detection routine of FIG. 6, which corresponds to t11 to t12 and t13 to t of FIG.
The timings of 14 and t15 to t16 respectively indicate the heater off period (the routine execution period in FIG. 6).

The detection voltage VHD changes depending on the ON / OFF state of the heater 16. That is, when the heater 16 is not deteriorated, the detection voltage VHD when the heater is off becomes larger than the threshold value VTH1, and the output signals C1 and C1 of the comparators 33 and 34, as shown at the timing of t11 to t12.
C2 is both at the L level. At this time, the heater deterioration large flag F4 and the heater deterioration small flag F5 are reset (F
4 = 0, F5 = 0) and the normal flag F6 is held in the set state (F6 = 1).

When the internal resistance of the heater 16 gradually increases as the heater 16 deteriorates, the output signal C1 of the comparator 33 goes high and the output signal C2 of the comparator 34 goes low, as shown at timings t13 to t14. . At this time, as shown in FIG. 7, the deterioration level of the heater 16 is between high and low, and the small heater deterioration flag F5 is set (F5 = 1).

Further, when the deterioration of the heater 16 progresses and its internal resistance becomes equal to or more than a predetermined allowable value (the deterioration level is large or equal to or more than that in FIG. 7), as shown in the timing of t15 to t16,
The output signals C1 and C2 of the comparators 33 and 34 are both H
Level. At this time, the heater deterioration large flag F4 is set (F4 = 1), and the heater 16 is fixed OFF after the timing t15 when F4 = 1.

FIGS. 8 and 9 are timing charts corresponding to the heater control system abnormality determination routine of FIG. 8 shows an abnormality determination operation when the degree of abnormality is small (for example, a contact failure of the soldered portion of the transistor Tr1 or the protection resistor RP), and FIG. 9 shows a case where the degree of abnormality is large (for example, battery 25 short-circuit, etc.).

In FIG. 8, before the timing of t21 (in a normal state), the detection voltage VHD when the heater is turned on is set.
Is smaller than the threshold value VTH2, and the output signals C1 and C2 of the comparators 33 and 34 are both at the H level. Therefore, the flags F1 and F2 indicating a control system abnormality
Are both cleared (F1 is not shown).

Then, when VTH2 ≦ VHD ≦ VTH1 due to a contact failure of the soldered portion of the transistor Tr1 or the protection resistor RP at timing t21, the output signal C1 of the comparator 33 becomes H level,
Output signal C2 attains an L level. At this time, the heater control system abnormality flag F2 is set (F2 = 1), and the heater 16 is fixed off.

On the other hand, in FIG. 9, before the timing of t31 (in a normal state), both the output signals C1 and C2 of the comparators 33 and 34 when the heater is turned on are at H level as in FIG.
Level. Accordingly, the flags F1 and F2 indicating the control system abnormality are both cleared (F2 is not shown).

Then, at the timing of t31, the battery 25
Is short-circuited and VHD> VTH1, the output signals C1 and C2 of the comparators 33 and 34 both become L level. At this time, the battery short-circuit flag F1 is set (F1 = 1), and the heater 16 is fixed off.

As described above in detail, in the abnormality detection device in the load control device of the present embodiment, when the heater 16 is turned off (power supply is cut off), the detection voltage VHD corresponding to the current value of the heater 16 becomes a predetermined threshold. If the value is equal to or less than the values VTH1 and VTH2, it is determined that an abnormality due to the deterioration of the heater 16 has occurred. If the detected voltage VHD corresponding to the current value of the heater 16 is equal to or higher than the predetermined threshold values VTH1 and VTH2 when the heater 16 is turned on (energized), an abnormality such as a short circuit has occurred in the control system of the heater 16. Was determined.

With this configuration, it is possible to determine an abnormality accompanying deterioration of the heater 16 (load). Since the deterioration is determined when the power supply to the heater 16 is cut off (when the transistor Tr1 is turned off), the current value of the heater 16 is detected without being affected by the loss such as the on-resistance of the transistor Tr1. The accuracy of value detection is improved, and the accuracy of abnormality determination is improved.

In this embodiment, the threshold value VTH1 for determining the detection voltage VHD corresponding to the current value of the heater 16 is set.
, VTH2 are set. Thus, the degree of deterioration of the heater 16 and the content of the control system abnormality of the heater 16 (an abnormality of the transistor Tr1, a short circuit of the battery 25, etc.) can also be determined. Further, the detection condition of the detection voltage VHD is set by the battery voltage VB. Thereby, erroneous detection of the detection voltage VHD is prevented, and the abnormality detection accuracy is improved.

Further, since the configuration of the smoothing circuit having a large time constant as in the conventional abnormality detecting device is eliminated, problems such as a delay in response are not caused. It should be noted that the present invention is not limited to the above embodiment, but may be embodied in the following modes.

For example, three or more threshold values may be set by providing three or more comparators of the voltage level determination unit 32. In this case, the degree of abnormality such as deterioration can be finely determined according to each threshold value,
The judgment sensitivity is improved.

In the above embodiment, the level of the detection voltage VHD corresponding to the current value of the heater 16 is determined by the comparator 33,
At 34, a comparison is made, and the comparison result is taken into the microcomputer 28 via the buffer 29.
The level of the level may be determined by taking in the microcomputer via the D converter and performing software processing.

Further, when the cause of the abnormality of the control system (such as short-circuit of the battery) is small, only the abnormality accompanying the deterioration of the heater 16 may be detected. In this case, the configuration can be simplified.

Further, in the above embodiment, the load is applied to the heater for the oxygen sensor having a resistance load. However, the invention can also be applied to abnormality detection for another resistance load.
Can be detected.

In addition, the load can be embodied as a coil type load (inductive type load). That is, the present invention can also be applied to abnormality detection for a coil-type load represented by an electromagnetic valve such as a fuel injection valve. However, in the case of a coil-type load, the configuration is such that the current after the surge is eliminated immediately after the energization is cut off.

[0073]

As described in detail above, according to the present invention,
It is possible to determine an abnormality due to the deterioration of the load, and it is possible to improve the determination accuracy of the abnormality.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of an ECU.

FIG. 2 is a configuration diagram schematically showing a multi-cylinder spark ignition gasoline engine.

FIG. 3 is a diagram for explaining deterioration of a heater.

FIG. 4 is a flowchart illustrating a heater control routine.

FIG. 5 is a flowchart illustrating a heater control system abnormality determination routine.

FIG. 6 is a flowchart illustrating a heater deterioration detection routine.

FIG. 7 is a timing chart relating to detection of deterioration of a heater.

FIG. 8 is a timing chart relating to abnormality determination of the heater control system.

FIG. 9 is a timing chart related to the abnormality determination of the heater control system, similarly to FIG.

[Explanation of symbols]

16: a heater as a load; 25, a battery as a power supply; 28, a microcomputer (microcomputer) as abnormality determination means; Tr1, a transistor as a switching element; RT, a shunt resistor as a current detecting resistor.

Continuation of the front page (56) References JP-A-3-165245 (JP, A) JP-A-3-150456 (JP, A) JP-A-4-1344063 (JP, U) JP-A-2-135855 (JP) , U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01M 13/00 G01N 27/409 G01N 27/12

Claims (4)

(57) [Claims] 1. A load control apparatus comprising: a power supply, a load, and a switching element connected in series, wherein the load is energized or de-energized according to an on / off operation of the switching element. A current detection resistor connected in series with the load and in parallel with the switching element; and a current value of the load detected by the current detection resistor when the current supply to the load is interrupted. An abnormality detection device for a load control device, comprising: abnormality determination means for determining that an abnormality has occurred in the load if the load is equal to or less than a threshold value. 2. A load control device, comprising: a power supply, a load, and a switching element connected in series, wherein the load is energized or de-energized in accordance with an on / off operation of the switching element. A current detection resistor connected in series with the load and in parallel with the switching element; and a current value of the load detected by the current detection resistor when the current supply to the load is interrupted. If the load value is equal to or less than the threshold value, it is determined that an abnormality has occurred in the load.If the current value of the load is equal to or greater than a predetermined threshold value when the load is energized, the load control system has an abnormality. An abnormality detection device in a load control device, comprising: an abnormality determination unit that determines that an error has occurred. 3. The abnormality detection device in the load control device according to claim 1, wherein threshold values for determining the current value of the load are provided in a plurality of stages. 4. The abnormality detection device according to claim 1, wherein the abnormality detection is prohibited when the voltage value of the power supply is equal to or less than a predetermined value.