JP4545215B2 - Heater control device for exhaust gas sensor - Google Patents

Description

  The present invention relates to a heater control device for heating an oxygen concentration sensor that detects an oxygen concentration contained in exhaust gas of an internal combustion engine.

  By detecting the oxygen concentration contained in the exhaust gas of the internal combustion engine and performing feedback control of the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine in accordance with the detected oxygen concentration, purification of exhaust gas and improvement of fuel consumption are achieved. The technique to perform is well known and widely used in vehicular internal combustion engines. Exhaust gas sensors that detect oxygen concentration need to stabilize the oxygen concentration detection characteristics by maintaining the temperature in the activation region.To this end, the heater built in the sensor is energized to control the energization current. A heater control device that maintains the temperature of the sensor at a predetermined value is used, and various techniques are disclosed for this control method.

  For example, in Patent Document 1, the heater resistance value is detected from the heater voltage and current value, the heater temperature is calculated from the resistance value, and the activation state of the exhaust gas sensor is known. A technique is disclosed in which the energization current is duty-controlled and activation is accelerated by continuous energization at low temperatures such as when the internal combustion engine is started. Japanese Patent Laid-Open No. 9-292364 discloses that the resistance value of the exhaust gas sensor itself is accurately detected to detect the temperature, and in order to shorten the detection time, it is applied to the exhaust gas sensor at the time of detecting the oxygen concentration. A technique is disclosed in which the voltage is switched to a resistance detection voltage with a predetermined time constant, and the internal resistance value of the exhaust gas sensor is detected from the change state of the voltage and current at that time (see Patent Document 1).

  Further, in Patent Document 2, when the temperature of the exhaust gas sensor is controlled by turning on / off the heater, a delay time is provided for the on / off control, and the delay time is manipulated using the operating state of the internal combustion engine such as the rotational speed as a parameter. A technique for extending the life of the heater, stabilizing the element temperature of the exhaust gas sensor, and improving the accuracy of air-fuel ratio control by reducing the number of heater on / off operations is disclosed. In JP-A-1-172746, a target value of the heater resistance is set according to the heater power consumption and the exhaust gas flow rate, and the applied voltage is controlled so that the heater resistance value becomes equal to the target value. Thus, a technique for maintaining the accuracy of the heater temperature and improving the durability and the oxygen concentration detection accuracy is disclosed.

JP-A-8-31476 Japanese Patent Publication No.7-119736

  As shown in each of the above conventional examples, many techniques have been disclosed for improving the durability and the accuracy of detecting the oxygen concentration by controlling the temperature by performing energization management to the heater and at the same time accelerating the activation at the time of starting. However, the power source for heating the heater of the exhaust gas sensor used in the vehicle is a battery mounted on the vehicle, and the voltage fluctuation of the battery is large during operation of the vehicle. Therefore, if the heating capacity is improved in order to cope with this, the heater and the drive element are burned out at a high voltage, and troubles cannot be avoided in the temperature management by the conventional energization control. In particular, when the connection state between the battery and the charging generator for charging it deteriorates, the voltage of the charging generator rises transiently, and a relatively high voltage from this charging generator may be applied to the heater. In such a case, burnout accidents of the heater and the drive element have been unavoidable.

  The present invention has been made in order to solve such a problem, and is a small size with sufficient preventive safety measures that does not cause troubles such as burnout at the time of overvoltage even when a heater having a high heating capacity is used. An object of the present invention is to obtain an inexpensive heater control device for an exhaust gas sensor.

An exhaust gas sensor heater control device according to the present invention is provided in an exhaust passage of an internal combustion engine, detects an oxygen concentration in exhaust gas, a heater that heats the exhaust gas sensor to a predetermined temperature, and heating power to the heater A power supply comprising a battery for supplying the battery and a charging generator for charging the battery, a first switching element inserted in a circuit for supplying power from the power supply to the heater, and the temperature of the exhaust gas sensor are maintained at a predetermined value. said first control means the switching element consists of a microprocessor which controls energization to the circuit abnormality detecting means for outputting an abnormality detection signal by detecting a circuit abnormality of the current supply circuit to said heater, the voltage of the pre-Symbol charging generator An overvoltage detection element that outputs an abnormality detection signal when it rises and exceeds a predetermined value, and is inserted into a circuit that supplies power to the heater from the power source Are, together responsive to the abnormality detection signal of the circuit fault detecting means, the second switching element for interrupting the current flowing the in response to the abnormality detection signal of the overvoltage detection element to the heater, the abnormality detection signal from the overvoltage detecting element Is added directly without going through the control means, and includes a gate element that stops driving the first opening / closing element or the second opening / closing element, and the microprocessor includes an abnormality detection signal of the circuit abnormality detection means and In response to the abnormality detection signal of the overvoltage detection element, the energization command to the first switching element and the second switching element is canceled, and the abnormality detection signal from the overvoltage detection element is controlled by the gate element. By applying directly without going through the means, driving of the first switching element or the second switching element is stopped and the heater is energized. It is obtained by configured to block.

As described above, according to the exhaust gas sensor heater control apparatus of the present invention, the exhaust gas sensor provided in the exhaust passage of the internal combustion engine for detecting the oxygen concentration in the exhaust gas, and heating the exhaust gas sensor to a predetermined temperature. A power source comprising a heater, a battery for supplying heating power to the heater and a charging generator for charging the battery, a first switching element inserted in a circuit for supplying power from the power source to the heater, and an exhaust gas sensor control means consisting of a microprocessor to energization control the first switching element so as to maintain the temperature at a predetermined value, the circuit abnormality detecting means detects the abnormal circuit outputs an abnormality detection signal of the energizing circuit for the heater, before When the voltage of the charging generator rises and exceeds a predetermined value, an overvoltage detection element that outputs an abnormality detection signal, from the power supply to the heater Is inserted into the power supply circuit, as well as responsive to the abnormality detection signal of the circuit fault detecting means, the second switching element for interrupting a current flowing through the heater in response to the abnormality detection signal of the overvoltage detection element, the overvoltage An abnormality detection signal from a detection element is directly applied without going through the control means, and includes a gate element that stops driving the first switching element or the second switching element, and the microprocessor detects the circuit abnormality In response to the abnormality detection signal of the means and the abnormality detection signal of the overvoltage detection element, the energization command to the first switching element and the second switching element is canceled, and the gate element is supplied from the overvoltage detection element. When the abnormality detection signal is directly applied without going through the control means, the driving of the first switching element or the second switching element is stopped. And then, is cut off the power supply to serial heater, the heater is reliably protected, the normal may be used a heater at full capacity, without causing troubles such as burning, using the high heat capacity heater Thus, a heater control device capable of accelerating the activation of the exhaust gas sensor can be obtained.

1 is a circuit diagram of a heater control device for an exhaust gas sensor according to Embodiment 1 of the present invention. FIG. It is a flowchart explaining operation | movement of the heater control apparatus for exhaust gas sensors by Embodiment 1 of this invention. It is a flowchart explaining operation | movement of the heater control apparatus for exhaust gas sensors by Embodiment 1 of this invention. It is a circuit diagram of the heater control apparatus for exhaust gas sensors by Embodiment 2 of this invention. It is a flowchart explaining operation | movement of the heater control apparatus for exhaust gas sensors by Embodiment 2 of this invention.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram of a heater control apparatus for an exhaust gas sensor according to Embodiment 1 of the present invention, and FIGS. 2 and 3 are flowcharts for explaining the operation thereof. In FIG. 1, 1 is a heater control device, 2 is a battery that supplies power to the heater control device 1 and the like via a key switch 3, 4 is an in-vehicle charging generator that charges the battery 2, and 5 is a heater control device 1. The heater 6 is controlled to be energized, 6 is configured to be integrated with or adjacent to the heater 5 and heated, and an exhaust gas sensor having an internal resistance 7, 8 is driven from the heater control device 1 via the resistor 9. It is a light emitting diode as a display means.

  10 is a power supply line in the circuit of the heater control device 1, 11 is a constant voltage power supply for supplying a constant voltage (for example, DC 5V) to a microprocessor (hereinafter referred to as CPU) 12 as a control means, and 13 is a power supply line 10 to the heater 5. The second open / close element 13 is driven from the output terminal DR3 of the CPU 12 via the resistor 14 and the transistor 15 so that the transistor 15 is turned on. Thus, the second opening / closing element 13 is also turned on. Reference numeral 16 denotes a resistor that connects the collector of the transistor 15 and the base of the second switch element 13, reference numeral 17 denotes a stable resistor that connects the base and emitter of the second switch element 13, and reference numeral 18 denotes a base and emitter of the transistor 15. It is a stable resistor that connects between the two.

  A transistor 19 is connected between the other terminal 5b of the heater 5 and the current detection resistor 20, and serves as a first opening / closing element that controls on / off of the energization of the heater 5, from the output terminal DR4 of the CPU 12 to the gate element. 21 and a resistor 22 to be driven. Reference numeral 23 denotes a stable resistor connected to the base of the first switching element 19. The voltage 24 from the power supply line 10 is divided by resistors 25 and 26 and input to the (−) terminal. The (+) terminal has a pull-down resistor 27 connected to the other terminal 5 b of the heater 5. This is a circuit abnormality detection element that inputs the voltage and the voltage of the current detection resistor 20, and its output is input to the input terminal EM 1 of the CPU 12.

28, the voltage from the power supply line 10 is divided by the resistors 29 and 30 and inputted to the (−) terminal, and the voltage of the constant voltage diode 32 connected from the power supply line 10 through the resistor 31 is changed to the (+) terminal. The output terminal is connected to one input terminal of the gate element 21 and is connected to the input terminal EM2 of the CPU 12 via the high resistance 33. A capacitor 34 is connected to the EM2 terminal. The capacitor 34 is charged via the high resistance 33 when the overvoltage detection element 28 is at the H level, and is parallel to the high resistance 33 when the overvoltage detection element 28 is turned to the L level. The diode 35 and the low resistance 36 connected in series are discharged through a discharge path composed of a series connection.

  An amplifier 37 amplifies the output voltage of the exhaust gas sensor 6 and inputs the amplified output voltage to the A / D conversion input terminal AD2 of the CPU 12. The transistor 38 is driven via a resistor 39 by a signal voltage from the output terminal DR 1 of the CPU 12, and connects the load resistor 40 to the exhaust gas sensor 6. Reference numeral 41 denotes a stable resistor connected between the base and emitter of the transistor 38. Reference numerals 42 and 43 denote voltage dividing resistors, which divide the power supply voltage supplied from the battery 2 and input it to the A / D conversion input terminal AD1 of the CPU 12. The light emitting diode 8 is driven through a resistor 9 by a signal from the output terminal DR2 of the CPU 12.

  In the thus configured exhaust gas sensor heater control apparatus according to Embodiment 1 of the present invention, the CPU 12 operates as shown in the flowcharts of FIGS. In FIG. 2, when the operation starts in step 200, in step 201, the CPU 12 turns off the transistor 38 for a predetermined time based on the signal of the output terminal DR 1, and outputs the no-load output voltage of the exhaust gas sensor 6 via the amplifier 37. Capture to input terminal AD2. The input voltage of AD2 is a voltage corresponding to the oxygen concentration contained in the exhaust gas.

  Subsequently, at step 202, the transistor 38 is turned on for a predetermined time by the signal at the output terminal DR1, and the output voltage at load divided by the internal resistance 7 of the exhaust gas sensor 6 and the load resistance 40 is input via the amplifier 37 to the input terminal AD2. And the resistance value of the internal resistor 7 is calculated. Here, the unloaded output voltage of the exhaust gas sensor 6 at step 201 is E0, the loaded output voltage of the exhaust gas sensor 6 at step 202 is E1, the resistance value of the load resistor 40 is R1, and the internal resistance 7 of the exhaust gas sensor 6 is. If the resistance value of R1 is R0, the relationship E1 = E0 × R1 / (R1 + R0) is obtained, and R0 is calculated. Note that the value of R0 changes as an exponential function of the reciprocal of the absolute temperature of the exhaust gas sensor 6, and varies due to variations in products of the exhaust gas sensor 6 and aging.

  Next, in step 203, it is determined whether or not this routine is the first operation. If it is determined in this step that the operation is the first time, the routine proceeds to step 204 where the internal combustion engine has been stopped for a long time and whether or not the temperature of the exhaust gas sensor 6 has decreased to the outside temperature is not shown. Judgment by comparison with If it is determined in step 204 that the temperature of the exhaust gas sensor 6 has decreased to the outside air temperature, the routine proceeds to step 205, where the resistance value R0 of the internal resistance 7 obtained in step 202 is stored, and the outside air temperature is read by the outside air temperature sensor. Remember me. When the processing in step 205 is completed, the process proceeds to step 206, where an internal resistance value vs. temperature table is created from the stored resistance value R0 of the internal resistance 7 and the outside air temperature, and the routine returns to step 201 to repeat this routine. .

  Since it is determined in step 203 that the operation is not the first time after the second time, the process proceeds from step 203 to step 207. Further, if it is determined in step 204 that the stop time is not long enough to reduce the temperature of the exhaust gas sensor 6, the process proceeds to step 207, where the latest information on the resistance value R0 of the internal resistance 7 obtained in step 202 and the step The current temperature of the exhaust gas sensor 6 is calculated from the internal resistance value versus temperature table created in 206. When this temperature is calculated, the routine proceeds to step 208 and the routine is terminated. From this point, the routine returns to step 201 again, and the routine from step 201 to step 208 is repeated every predetermined time. The temperature is calculated, and this value is given to step 303 in FIG.

In the operation of FIG. 3, when the operation is first started in step 300, in step 301, the CPU 12 turns on the transistor 15 by the signal of the output terminal DR3, thereby causing the transistor 13 as the second opening / closing element to become conductive. In step 302, the CPU 12
The power supply voltage is measured from the signal input to the input terminal AD1. Next, the routine proceeds to step 303, where an on / off time ratio of energization to the heater 5, a so-called duty ratio, is calculated from the current temperature of the exhaust gas sensor 6 obtained at step 207 and the power supply voltage obtained at step 302. decide. Here, the duty is set higher as the current temperature of the exhaust gas sensor 6 is lower, and the duty is set higher as the power supply voltage is lower, thereby shortening the heating time. Further, in step 304, a signal is output from the DR4 of the CPU 12 according to the calculated ON time width of the energization, and the transistor 19 as the first opening / closing element is made conductive through the gate element 21.

  When the first switching element 19 and the second switching element 13 are conducted through the above steps, the heater 5 is energized and a voltage is generated across the current detection resistor 20. Step 305 is a step in which the signal from the circuit abnormality detection element 24 is inputted to the input terminal EM1 of the CPU 12 for determination. The voltage of the current detection resistor 20 becomes excessive due to a short circuit accident of the heater 5 or external wiring. For example, the (+) terminal voltage of the circuit abnormality detecting element 24 becomes large and the output of the circuit abnormality detecting element 24, that is, the input to the EM1 terminal becomes H level. If the value is normal, the (+) terminal voltage of the circuit abnormality detection element 24 is small, the input to the EM1 terminal is L level, and YES is determined in step 305.

  If the determination in step 305 is NO, that is, if an overcurrent is detected, the process proceeds to step 306 where the output of DR3 and DR4 of the CPU 12 is stopped and the first switching element 19 and the second switching element 13 are stopped. Is turned off and the energization of the heater 5 is stopped, and a signal is output from the DR2 terminal, the light emitting diode 8 is operated, and an abnormality alarm is given. Here, even if one of the first switching element 19 and the second switching element 13 is in a short-circuit damaged state due to an overcurrent, the current can be stopped by the other operation, and double safety measures are taken. Furthermore, in this step, the code number for the abnormal state is stored in the storage means of the CPU 12, and the cause of the abnormality can be read out as necessary.

  If the determination in step 305 is YES, the process proceeds to step 307, where it is determined whether or not the energization on-time width set in step 303 has elapsed. If this time width has not elapsed, the process returns to step 304, and step The routine up to 307 is repeated. If the predetermined on-time has elapsed in step 307, the process proceeds to step 308, where the DR4 signal of the CPU 12 is stopped and the first opening / closing element 19 is turned off. When the first switching element 19 is turned off, the voltage of the pull-down resistor 27 receiving the power supply voltage is added to the (+) terminal voltage of the circuit abnormality detection element 24. If the voltage is normal, the output voltage becomes H level. If there is an abnormality such as disconnection or poor contact in the heater 5 or the external circuit, the output voltage of the circuit abnormality detection element 24 becomes L level.

  In step 309, this is determined. If there is an abnormality, a signal is output from the DR2 terminal of the CPU 12 in step 310, the light emitting diode 8 operates, an abnormality alarm is given, and a code number for a disconnection trouble is stored. It is possible to read out the cause of the abnormality as necessary. As described above, the circuit abnormality detection element 24 has an abnormality monitoring function both when the first switching element 19 is on and when it is off. In step 311, it is determined whether the on / off total time of the duty control of the first switching element 19 calculated in step 303 has elapsed. If not, the routine from step 308 is repeated, and the time has elapsed. If so, the process returns from step 312 to step 300 to enter the next routine.

  Step 313 is a periodic interrupt routine for determining the logic level of the input terminal EM2 of the CPU 12. The voltage at the (+) input terminal of the overvoltage detection element 28 is set to a voltage higher than the voltage obtained by dividing the voltage of the constant voltage diode 32 by the voltage dividing resistors 29 and 30. H level. When the terminal of the battery 2 is loosened, the charging generator 4 becomes a light load, so that the generated voltage abnormally rises during the transient time required for voltage control. When such an overvoltage is applied to the heater control device 1 or the heater 5, the divided voltage by the voltage dividing resistors 29 and 30 becomes higher than the voltage of the constant voltage diode 32, the input of the EM2 terminal is changed to the L level, and step 314 In response to the signals DR3 and DR4, the first switching element 19 and the second switching element 13 are immediately turned off, and the heater 5, the first switching element 19 and the second switching element 13 have excessive current. To prevent the flow. In addition to this routine, the output of the overvoltage detection element 28 is applied to the gate element 21, and the first switching element 19 is immediately shut off without a time delay to protect the circuit.

  In the capacitor 34 connected to the EM2 terminal, the charging circuit is composed of the high resistance 33 and the discharging circuit is composed of the low resistance 36, so that the logic level of the overvoltage detection element 28 changes from H to L. When the voltage drops immediately and changes from L to H, it takes a predetermined time for the voltage to rise, the energization is stopped in response to a short time abnormality, and the recovery time is at a predetermined time. The safety is maintained by giving a constant. Note that this logic determination is canceled for a predetermined time after the power is turned on to prevent a malfunction when the power is turned on. When an overvoltage abnormality is detected in step 313, a signal is output from the DR2 terminal in step 314, the light emitting diode 8 operates, and a code number for the abnormal state is stored.

Embodiment 2. FIG.
4 is a circuit diagram of a heater control apparatus for an exhaust gas sensor according to Embodiment 2 of the present invention, and FIG. 5 is a flowchart for explaining the operation. The same reference numerals are given to the same components as those in Embodiment 1 above. Yes. In FIG. 4, 50 is a heater control device, 2 is a battery that supplies power to the heater control device 50 and the like via the key switch 3, 4 is an in-vehicle charging generator that charges the battery 2, and 5 is a heater control device 50. The heater is energized and is integrated with an exhaust gas sensor not shown in FIG. Reference numeral 8 denotes a light emitting diode as display means driven from the heater control device 50 via a resistor 9.

  10 is a power line in the circuit of the heater control device 50, 11 is a constant voltage power source for supplying a constant voltage (for example, DC 5V) to the CPU 51, and 13 is a second connected in series from the power line 10 to one terminal 5a of the heater 5. In this embodiment, the second switching element 13 is driven from the output terminal DR3 of the CPU 12 via the gate element 21, the resistor 14, and the transistor 15, and the transistor 15 is turned on so that the resistance is turned on. The second opening / closing element 13 is also turned on via 16. Reference numerals 17 and 18 are stable resistors.

  Reference numeral 19 denotes a transistor which is connected between the other terminal 5b of the heater 5 and the current detection resistor 20 and constitutes a first opening / closing element that controls on / off of the energization of the heater 5. In this embodiment, the CPU 51 It is configured to be driven from the output terminal DR4 via the resistor 22. Reference numeral 23 denotes a stable resistance. 28, the voltage from the power supply line 10 is divided by the resistors 29 and 30 and input to the (−) terminal, and the voltage of the constant voltage diode 32 connected from the power supply line 10 through the resistor 31 is the (+) terminal. Is connected to one input terminal of the gate element 21 and connected to the input terminal EM2 of the CPU 51 through the high resistance 33, and a capacitor 34 is connected to the EM2 terminal. The capacitor 34 is charged via the high resistance 33 when the overvoltage detecting element 28 is at the H level, and when the voltage is turned to the L level, the diode 35 and the low resistance 36 connected in parallel with the high resistance 33 are connected. It is comprised so that it may discharge through the discharge path which consists of serial connection.

  52 is input via a resistor 55 from an intermediate connection point between voltage dividing resistors 53 and 54 connected between the collector and emitter of the transistor 19 constituting the first switching element, and the output is for A / D conversion of the CPU 51. This is an amplifier applied to the input terminal AD3. The voltage dividing resistors 53 and 54 have a resistance 53 sufficiently larger than the resistance value of the heater 5, and the ratio of the value of the resistor 53 to the value of the resistor 54 is the resistance value of the heater 5. And the resistance value of the current detection resistor 20 are selected to be substantially equal. Further, as will be described later, these also constitute circuit abnormality detection means of the energization circuit for the heater 5.

  In the exhaust gas sensor heater control apparatus according to Embodiment 2 of the present invention configured as described above, the CPU 51 operates as shown in the flowchart of FIG. First, when the operation starts in step 500, in step 501, the CPU 51 turns on the transistor 15 via the gate element 21 by the signal of the output terminal DR3, thereby turning on the transistor 13 as the second switching element. In step 502, the power supply voltage is measured from the signal input to the input terminal AD3 of the CPU 51. In the measurement of the power supply voltage, when the second switch element 13 is turned on and the first switch element 19 is turned off, a voltage proportional to the power supply voltage is applied to the intermediate connection point between the voltage dividing resistors 53 and 54. This voltage is obtained by inputting the voltage to the AD3 terminal via the amplifier 52.

  Subsequently, in step 503, the on / off time ratio of energization to the heater 5 is calculated from the power supply voltage obtained in the above step 502 and the temperature of the heater 5 obtained in step 509 described later. 1, the duty ratio of energization to the heater 5 is determined from the temperature of the exhaust gas sensor and the power supply voltage value. Further, in step 504, a signal is output from DR4 of the CPU 51 based on the calculated ON time width of the energization, and the transistor 19 as the first switching element is made conductive through the resistor 22. When the first switching element 19 and the second switching element 13 are conducted through the above steps, the heater 5 is energized and a voltage is generated across the current detection resistor 20. In step 505, the voltage across the current detection resistor 20 is obtained from an intermediate connection point between the voltage dividing resistors 53 and 54, and is taken into the input terminal AD3 of the CPU 51 via the amplifier 52, thereby measuring the value of the current flowing through the heater 5. .

  Next, the process proceeds to step 506, where it is determined whether or not the current of the heater 5 obtained in step 505 is appropriate. Here, the current of the heater 5 increases due to a short circuit accident of the heater 5 or an external circuit, and if the voltage of the current detection resistor 20 is larger than a predetermined value, it is determined that the current is not appropriate, and the process proceeds to step 507, where the current is appropriate. If it is determined, step 508 follows. In step 507, the signals at the output terminals DR3 and DR4 of the CPU 51 are stopped, the first opening / closing element 19 and the second opening / closing element 13 are turned off to cut off the current of the heater 5, and the signal is output from the DR2 terminal. Then, the light emitting diode 8 is operated to give an abnormality alarm. Here, even if one of the first switching element 19 and the second switching element 13 is in a short-circuit damaged state, the current can be stopped by the operation of the other, and double safety measures are taken. In this step, the code number for the abnormal state is stored in the storage means of the CPU 51, and the cause of the abnormality can be read out if necessary.

  If the current value is normal, the process proceeds to step 508, where it is determined whether or not the energization ON time width set in step 503 has elapsed. Until this time width elapses, the process returns to step 504, and until step 508 Repeat the routine. When it is determined that the predetermined time width has elapsed, the process proceeds to step 509, where the resistance value of the heater 5 is calculated from the power supply voltage obtained in step 502 and the current value obtained in step 505, and the heater 5 stored in advance is stored. The current temperature of the heater 5 is calculated from the resistance value versus temperature characteristic table, and the temperature of the exhaust gas sensor is calculated from the temperature of the heater 5 based on a predetermined function. Since the predetermined on-time width has elapsed, in step 510, the output of the DR4 terminal of the CPU 51 is stopped and the first opening / closing element 19 is turned off.

In step 511, it is determined whether or not there is a signal from the amplifier 52 at the AD3 input terminal of the CPU 51. If a disconnection accident occurs in the heater 5 or the external wiring, no voltage is generated at the intermediate connection point between the voltage dividing resistors 53 and 54 even when the first switching element 19 is in the OFF state.
If no signal is input to the D3 input terminal and this signal is not input, the process proceeds to step 512, where a signal is output from the DR2 terminal, the light emitting diode 8 is operated to output a disconnection alarm, and a code number for the disconnection abnormality is set. Memorize and enable reading of the cause of abnormality as required. Thus, the signal input from the amplifier 52 to the AD3 terminal of the CPU 51 has an abnormality monitoring function both when the first switching element 19 is on and when it is off, and also functions as a circuit abnormality detecting means. .

  If there is a signal from the amplifier 52 in step 511, the process proceeds to step 513, where it is determined whether or not the total on / off time of duty control for the first switching element 19 calculated in step 503 has elapsed. If not, the routine returns from step 513 to step 510 to repeat the routine. If the time has elapsed, the routine returns from step 514 to step 500 to enter the next routine.

  Step 515 is a periodic interrupt routine for determining the logic level of the input terminal EM2 of the CPU 51. The voltage of the constant voltage diode 32 input to the (+) input terminal of the overvoltage detection element 28 is set to a voltage higher than the voltage generated by the voltage dividing resistors 29 and 30 input to the (−) input terminal. Sometimes the output of the overvoltage detection element 28 is at H level. As in the case of the first embodiment, when the terminal of the battery 2 is loosened, the generated voltage of the charging generator 4 rises abnormally during the transient time, and the abnormal voltage is applied to the heater control device 1 and the heater 5. However, in such a case, since the voltage by the voltage dividing resistors 29 and 30 becomes higher than the voltage of the constant voltage diode 32, the input of the EM2 terminal changes to L level, and when this L level is detected, step 516 In FIG. 1, the first switching element 19 and the second switching element 13 are immediately turned off by stopping the signals of DR3 and DR4, and an excessive current flows through the heater 5, the first switching element 19 and the second switching element 13. To prevent that. Further, as in the case of the first embodiment, the output of the overvoltage detection element 28 is added to the gate element 21 separately from this routine, and the second switching element 13 is immediately shut off without a time delay to protect the circuit. It is configured.

  Further, the operation for the capacitor 34 connected to the EM2 terminal of the CPU 51 is the same as that of the first embodiment, and the charging path is constituted by the high resistance 33 and the discharging path is constituted by the low resistance 36. When the logic level changes from H to L, the voltage immediately decreases. When the logic level changes from L to H, the voltage increase requires a predetermined time. In addition, safety is maintained by giving a predetermined time constant to the recovery time. This logic determination is canceled for a predetermined time after the power is turned on to prevent a malfunction at the time of power-on. When an overvoltage abnormality is detected at step 515, a signal is output from the DR2 terminal at step 516 and the light emitting diode 8 operates. The code number for the abnormal state is stored.

  In the exhaust gas sensor heater control apparatus of the first and second embodiments described above, the temperature of the exhaust gas sensor 6 or the vicinity thereof is detected, and feedback control is performed so that the temperature of the exhaust gas sensor 6 becomes a predetermined value. For example, after the start of the internal combustion engine until the output of the exhaust gas sensor reaches a predetermined value, the heater is heated by 100% energization when the cooling water temperature is low, and the cooling water temperature is equal to or higher than the predetermined value. The CPU can also be programmed to control the heating according to the operating state of the internal combustion engine so that it is heated at a duty ratio of 30% during light load operation and is stopped when the internal combustion engine is high load. The bipolar switch is used for the first and second switching elements, but MOS transistors with drain / source / gate are used. It is those that can be Rukoto.

1, 50 heater control device, 2 battery, 3 key switch,
4 charging generator, 5 heater, 6 exhaust gas sensor,
8 Light emitting diode (display means),
12, 51 microprocessor (control means),
13 Second switching element, 19 First switching element, 20 Current detection resistor,
21 gate element, 24 circuit abnormality detection element (circuit abnormality detection means),
28 Overvoltage detection element, 32 constant voltage diode, 52 amplifier.

Claims (5)

An exhaust gas sensor provided in the exhaust passage of the internal combustion engine for detecting the oxygen concentration in the exhaust gas;
A heater for heating the exhaust gas sensor to a predetermined temperature;
A power source comprising a battery for supplying heating power to the heater and a charging generator for charging the battery;
A first switching element inserted in a circuit for supplying power from the power source to the heater;
Control means comprising a microprocessor for controlling energization of the first switching element so as to maintain the temperature of the exhaust gas sensor at a predetermined value;
Circuit abnormality detection means for detecting a circuit abnormality of the energization circuit for the heater and outputting an abnormality detection signal;
When the voltage of the previous SL charging generator exceeds a predetermined value rises, the overvoltage detecting element for outputting an abnormality detection signal,
A second power supply is inserted into a circuit for supplying power to the heater from the power source, and responds to an abnormality detection signal of the circuit abnormality detection means and interrupts a current flowing through the heater in response to an abnormality detection signal of the overvoltage detection element. Opening and closing element,
A gate element that directly applies an abnormality detection signal from the overvoltage detection element without going through the control means, and stops driving the first switching element or the second switching element;
With
The microprocessor cancels the energization command to the first switching element and the second switching element in response to the abnormality detection signal of the circuit abnormality detection means and the abnormality detection signal of the overvoltage detection element;
The gate element applies the abnormality detection signal from the overvoltage detection element directly without passing through the control means, thereby stopping the driving of the first opening / closing element or the second opening / closing element to the heater. Cut off the power,
A heater control device for an exhaust gas sensor.   The exhaust gas sensor heater control device according to claim 1, wherein the control means controls the energization of the first opening / closing element at an opening / closing ratio corresponding to a value of a power supply voltage.   The control means measures the internal resistance value when the exhaust gas sensor is unloaded and the internal resistance value when the load is applied, calculates the temperature of the exhaust gas sensor from the ratio of both resistance values, and according to the temperature The heater control apparatus for an exhaust gas sensor according to claim 1, wherein the first opening / closing element is energized and controlled with an opening / closing ratio. The control means time-divisionally reads a voltage value between both ends of the first switching element when the first switching element is opened and a current value flowing through the first switching element when the first switching element is closed. The resistance value of the heater is calculated from the current value, the temperature of the exhaust gas sensor is calculated as a function of the resistance value of the heater, and the energization control of the first switching element is performed with the switching ratio according to the temperature of the sensor The heater control apparatus for an exhaust gas sensor according to claim 1. When the overvoltage detection element or the circuit abnormality detection means outputs an abnormality detection signal, a storage means for encoding and storing the signal content of the abnormality detection signal, and a display means for displaying that the abnormality detection signal has been output. The heater control device for an exhaust gas sensor according to any one of claims 1 to 4, wherein

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