JP2001250660A - Control method of heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method of a ceramic heater generating heat by the power supplied from a power source, which can prevent the breaking and cracking of heaters and control the quantity of heat at low cost. SOLUTION: At a heater control device, the example of implementation of which is shown in Figure (b), when an FET 17 comes to on-state, voltage of a power source 11 is applied to both ends of the serial circuit consisted of the first heater 13, the second heater 15 and the resistor 27 for voltage drop, and the conducting period to the heaters is controlled by a DUTY control. Thus, the effective value the applied voltage can be restrained below the allowable voltage, and the flow of big electric current to the heaters is prevented. Accordingly, the cracking at the heaters caused by sudden change of temperature and breakage of heaters caused by migration are prevented, and heaters are controlled by using the FET of low-cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater control method for a ceramic heater that generates heat by supplying power from a power supply device.

[0002]

2. Description of the Related Art Conventionally, in an apparatus provided with a ceramic heater (hereinafter, also simply referred to as a heater) which generates heat by power supply from a power supply apparatus which outputs a constant voltage (power supply voltage), a power supply voltage output from the power supply apparatus is conventionally used. By using a heater capable of withstanding the above, the power supply voltage is directly applied to the heater to operate the heater. That is, for example, as the voltage value of the power supply voltage output from the power supply device is higher,
A heater having a large resistance value (a high allowable withstand voltage value) has been used.

As a ceramic heater, a heater having a structure in which a heating resistor made of a tungsten alloy or the like is embedded in an insulating ceramic body made of, for example, alumina is known.

[0004]

However, there is a limit (upper limit) to increasing the resistance value of the ceramic heater. In other words, in order to increase the resistance value of the ceramic heater, the heating resistor must be thinned or its wiring pattern must be formed finely. However, there is a limit to forming the heating resistor or its wiring pattern finely. There is.

[0005] With respect to ceramic heaters provided in current internal combustion engines for automobiles, the output voltage (for example, 12 [V]) of an on-vehicle battery constituting an on-vehicle power supply device is used.
Alternatively, the output voltage of the generator (alternator) (for example,
14 [v]). As a specific example, for example, a solid electrolyte (such as zirconia) which is provided in an oxygen sensor installed in an exhaust pipe for controlling an air-fuel ratio of an internal combustion engine for an automobile and forms a detection element of the oxygen sensor is activated. For example, a ceramic heater may be used.

On the other hand, in recent years, in order to improve the control accuracy of each actuator mounted on an automobile and to reduce the weight of electric wires, the output voltage of an in-vehicle power supply of the automobile is increased to a voltage higher than the current voltage value (for example, , 42 [v]). For this reason, with respect to the higher power supply voltage,
The heater currently used (for example, when the allowable withstand voltage value is 14
When the [v] heater is used, a large current flows when the heater is energized, and the heating resistor is disconnected,
The heater may be damaged. That is, it is conceivable that the heater rapidly rises in temperature due to the flow of a large current (including an inrush current), and a crack (crack) occurs in the ceramic body due to thermal stress (thermal shock) generated by the rapid temperature change. . Then, when oxygen invades from the crack, the heating resistor is rapidly oxidized, and the heating resistor is separated or collapsed, resulting in disconnection.

In the ceramic heater, the higher the applied voltage value, the more the migration is likely to occur, and the more easily the heating resistor is disconnected. Note that migration refers to, for example, when an insulating ceramic base constituting a ceramic heater is formed mainly of alumina, cations of impurities (alkali metal or alkaline earth metal) contained in the alumina move. It is a phenomenon. When this migration occurs, the cations concentrate on the cathode terminal side of the heater, and the heating resistor may deteriorate with time and increase in resistance value, whereby the heating resistor may be disconnected.

In the case of a heater in which the heating resistor is made of tungsten or platinum, they are ionized and move from the anode terminal side to the cathode terminal side, and the anode terminal side of the heater becomes thinner. In some cases, the heater may be disconnected. On the other hand, conventionally, as a method for controlling the heat generation amount and power consumption amount of the heater, or for making the effective value of the voltage applied to the heater equal to or less than an allowable withstand voltage, the heater voltage is determined based on the voltage between both ends of the heater when energized. There is known a method of controlling a ratio between an energizing period and a non-energizing period. And
The control of the energization period of the heater can be realized, for example, by switching between energization and non-energization of the heater using switching means connected in series with the heater.

Here, the switching means includes:
For example, F which is a switching element made of a semiconductor element
Although ET is used, FETs with higher capacities that can withstand large currents become more expensive. When the power supply voltage is increased, the current value flowing through the heater and the FET is increased. Therefore, as the power supply voltage is increased, an expensive FET is used, and the heater energization period is controlled. The cost for this rises.

The present invention has been made in view of the above problems, and is directed to a method of controlling a ceramic heater that generates heat by supplying power from a power supply device, such as disconnection of a heating resistor or occurrence of cracks in a ceramic body. It is an object of the present invention to provide a heater control method capable of preventing breakage of the heater and controlling the amount of heat generated by the heater at low cost.

[0011]

According to a first aspect of the present invention, there is provided a heater control of a ceramic heater which comprises a heating resistor and a ceramic body, and which generates heat by supplying power from a power supply device. And a heater control method when the power supply voltage output from the power supply device is larger than the allowable withstand voltage value of the ceramic heater,
At least one or more voltage drop means for reducing the voltage applied to the ceramic heater to an allowable withstand voltage or less is connected in series to the ceramic heater, and a power supply voltage is applied to both ends of the ceramic heater.

That is, instead of directly applying the power supply voltage output from the power supply device to both ends of one heater, a voltage reduced by a voltage lowering means to the allowable withstand voltage value of the heater is applied to both ends of the heater. That is, the heater is controlled to generate heat. As a result, a voltage higher than the allowable withstand voltage is not applied to the heater, and even when the resistance of the heating resistor changes (depends on the temperature coefficient) due to the heat generation of the heater, the allowable withstand voltage can be reduced. Since the following voltages are applied, it is possible to suppress a rapid rise in the heater temperature and the occurrence of migration, and it is possible to suppress the occurrence of cracks in the ceramic body and disconnection of the heating resistor.

Therefore, according to the heater control method of the present invention (claim 1), even when a heater having a lower withstand voltage than the power supply voltage is used for a power supply device that outputs a high voltage as the power supply voltage. By connecting the voltage lowering means to the heater in series, disconnection of the heating resistor and occurrence of cracks in the ceramic body can be prevented, and the heater can operate normally.

In realizing such a heater control method, for example, as described in claim 2,
It is preferable to use a resistance element as one of the voltage drop means, connect the resistance element and the ceramic heater in series, and apply a power supply voltage output from the power supply device to both ends.

That is, when a voltage is applied to both ends of the resistance element and the heater in a state where the resistance element and the heater are connected in series, the voltage applied to the heater becomes a divided voltage value determined by the respective resistance values of the resistance element and the heater. At least the voltage value is lower than the power supply voltage. The voltage value applied to the heater can be arbitrarily set by changing the resistance value of the resistance element, and can be set to an optimum value according to the type of the heater (allowable withstand voltage value). For this reason, with respect to the resistive element, if the resistive element having the optimum resistance value is selected based on the power supply voltage value and the heater resistance value so that the voltage value applied to the heater is equal to or less than the allowable withstand voltage value of the heater. Good.

In order to realize the above-described heater control method by another method, for example, as one of the voltage drop means, a voltage drop different from the ceramic heater for heating is used as one of the voltage drop means. It is preferable to connect a heater for voltage drop and the ceramic heater for heat generation in series, and apply a power supply voltage output from a power supply device to both ends thereof.

That is, when a voltage is applied to both ends of a heater for voltage drop and a heater for heat generation in series, the voltage applied to the heater for heat generation is determined by the voltage drop heater and the heater for heat generation. , And becomes a voltage value lower than at least the power supply voltage.

Since the voltage value applied to the heater for heat generation changes according to the number of heaters for voltage drop,
The number of voltage drop heaters may be set to an optimum value according to the allowable withstand voltage value of the heater for heat generation. For example, when a heater having an allowable withstand voltage value of 14 [v] is controlled (heated) using a power supply device that outputs 42 [v] as a power supply voltage, two voltage drop heaters are prepared. , A total of three heaters including the heater for heating are connected in series,
A power supply voltage (42 [v]) may be applied to both ends.

The voltage drop heater used in the method of the present invention (claim 3) is used not only as a voltage drop means but also as a heater for heat generation, so that the power supplied from the power supply device can be used without waste. It is possible to improve the efficiency of power consumption. In particular, in a system including a plurality of heaters, by applying the method of the present invention, the efficiency of power consumption can be improved while preventing breakage of the heater, so that the effect of the method of the present invention is further enhanced.

As described above, as a method for controlling the amount of heat generated by the heater and for preventing breakage of the heater, a method of controlling the power supply period to the heater is known. As the switching time increases, the switching means (for example, FET) used for controlling the energization time becomes more expensive, and the heater control cost increases.

However, in the above-described heater control method, in addition to the voltage drop means, a switching means for switching between energization and non-energization of the ceramic heater is connected in series to the ceramic heater. In performing the DUTY control on the switching means based on the voltage between both ends of the ceramic heater when the switching means is turned on, D is set so that the effective voltage value applied to the ceramic heater is equal to or less than the allowable withstand voltage value of the ceramic heater.
By performing the heater control method for setting the UTY ratio, it is possible to suppress an increase in cost.

That is, in the apparatus to which the heater control method according to any one of claims 1 to 3 is applied,
Since the voltage applied to the heater is reduced to a value equal to or lower than the allowable withstand voltage by using a voltage drop means such as a resistance element or a voltage drop heater, an excessive current does not flow through the heater. Therefore, in the above heater control method, a switching means (for example, FE
T) does not cause excessive current to flow through the switching means.

For this reason, it is not necessary to use a switching means having a large capacity capable of withstanding a large current.
In controlling the power supply period to the heater, it is possible to use existing switching means at low cost. The effect of the heater control method according to any one of claims 1 to 4 can be further exerted by applying the heater control method to a ceramic heater provided in an internal combustion engine for an automobile.

As described above, the ceramic heater has a limit in forming the wiring pattern of the heating resistor finely, and although there is a limit in increasing the resistance of the ceramic heater, in recent years, there has been a limitation in the on-vehicle power supply device. There has been a movement to increase the output voltage of the device from the current level. For this reason, when the output voltage of the vehicle-mounted power supply that supplies power to the ceramic heater, which has a limit in increasing the resistance, is increased, the voltage applied to the ceramic heater becomes excessive, and exceeds the allowable withstand voltage of the ceramic heater. Would.

Therefore, the above-described heater control method is preferably applied to a method for controlling a ceramic heater provided in an internal combustion engine for an automobile. As a result, even when the output voltage of the vehicle-mounted power supply device is increased, it is possible to use a conventionally used ceramic heater without newly developing a ceramic heater having a high allowable withstand voltage value. it can. For this reason, the effects of the above-described heater control method (claims 1 to 4) can be further exhibited.

In particular, in an automobile internal combustion engine, a gas sensor is used to control the air-fuel ratio. This gas sensor has a detection element made of a solid electrolyte (for example, zirconia). It is usual to provide a ceramic heater to achieve early activation of the detecting element made of and to surely maintain the activation temperature.

For example, an automobile is provided with a typical oxygen sensor as a gas sensor in each exhaust pipe of a left / right bank in a V-type engine, and an upstream side and a downstream side of a catalyst provided in an exhaust pipe. Multiple oxygen sensors (gas sensors), such as those with an oxygen sensor on each side
Some have. By connecting the ceramic heaters provided in each of the plurality of gas sensors in series, even if the output voltage of the vehicle-mounted power supply device is increased, the voltage applied per ceramic heater can be tolerated. It can be effectively suppressed below the voltage value.

In applying the heater control method to an internal combustion engine for an automobile, when a resistance element is used as the voltage drop means, an existing resistance element mounted on a vehicle may be used. Accordingly, in realizing the heater control method of the present invention, it is not necessary to newly install a resistance element, and the mounting efficiency of each device in an automobile can be improved.

When a resistance element is used as a voltage drop means in the ceramic heater, for example, the resistance element may be built in the ceramic heater. Alternatively, for a gas sensor configured to include a gas detection element and a ceramic heater inside one structure, a resistance element may be provided inside the structure of the gas sensor. Thereby, the wiring for connecting the separate resistor element and the ceramic heater can be omitted, and the wiring work can be simplified. In this case, it is desirable to set the position where the resistance element is built in a position where the temperature is not affected by the exhaust gas or the heater.

[0030]

Embodiments of the present invention will be described below. As an embodiment, a heater control device for a ceramic heater provided in an oxygen sensor installed in an internal combustion engine for a vehicle will be described. The oxygen sensor includes a detection element made of a solid electrolyte (zirconia), and detects the oxygen concentration in the exhaust gas in order to control the air-fuel ratio of the internal combustion engine for a vehicle.

The ceramic heater is provided for activating the detection element, and activates the detection element at an early stage and heats it so as to surely maintain the activation temperature. . This ceramic heater is
For example, a heating resistor made of a tungsten alloy or the like is embedded in an insulating ceramic body mainly composed of alumina.

Next, several embodiments of a heater control device for a ceramic heater in an internal combustion engine for an automobile will be described. First, as a first embodiment, a heater control device for an automotive internal combustion engine including two ceramic heaters will be described. FIG. 1A is a schematic circuit diagram of the heater control device 1 according to the first embodiment.

The heater control device of the first embodiment is
The V-type engine is provided with one oxygen sensor (two in total) in each exhaust pipe of the left / right banks of the engine. Each oxygen sensor is provided with one ceramic heater.

As shown in FIG. 1A, the heater control device of the first embodiment comprises a first ceramic heater (hereinafter, referred to as a first heater) 13 and a second ceramic heater (hereinafter, referred to as a second heater).
A heater 15 is connected in series, and a power supply 11 is connected to this series circuit. That is, the power supply 11 and the series circuit including the first heater 13 and the second heater 15 form a closed loop.
1 is applied to both ends of a series circuit composed of the first heater 13 and the second heater 15.

The first heater 13 and the second heater 15 are composed of the same type of ceramic heater, and have the same resistance. For this reason, half of the power supply voltage output from the power supply 11 is applied to each of the first heater 13 and the second heater 15.

In the heater control device, the first heater 13 and the second heater 15 are provided with ceramic heaters whose allowable withstand voltage value is one half of the power supply voltage.
Each of the first heater 13 and the second heater 15 includes:
It is configured such that a voltage with an allowable withstand voltage value is applied.

For this reason, the voltage applied to each heater is equal to the allowable withstand voltage value. Therefore, after the internal combustion engine is started, the power supply to the first heater 13 and the second heater 15 is started. A voltage larger than the allowable withstand voltage is not applied and a large current does not flow continuously.

Therefore, according to the heater control device of the first embodiment, by connecting two heaters in series, the voltage applied to one heater can be made equal to or less than the allowable withstand voltage of the heater. Therefore, it is possible to prevent disconnection of the heating resistor or cracks (cracks) in the ceramic body due to a rapid change in temperature, and to prevent disconnection due to migration. ) Can be activated.

Next, as a second embodiment, a description will be given of a heater control apparatus for an internal combustion engine for an automobile, which is provided with two ceramic heaters and controls a period of current supply to the heaters. FIG.
(B) shows a schematic circuit diagram of the heater control device 1 of the second embodiment. The heater control device according to the second embodiment is provided in the V-type engine similarly to the first embodiment, and one oxygen sensor is provided for each exhaust pipe of the left / right banks of the engine ( 2 in total). And
Each oxygen sensor is provided with one ceramic heater.

As shown in FIG. 1B, the heater control device of the second embodiment includes a first ceramic heater (hereinafter, referred to as a first heater) 13 and a second ceramic heater (hereinafter, referred to as a second heater).
A heater 15) is connected in series, and a power supply 11 and an n-channel FET 17 which is a switching element made of a semiconductor element are connected in series to this series circuit. That is, the first heater 13, the second heater 15, the power supply 11 and the FET 17 form a closed loop, and when the FET 17 is turned on, the power supply voltage output from the power supply 11 changes the first heater 13 and the second heater 13. 15 is applied to both ends of the series circuit.

The ON state of the FET 17 means F
The OFF state indicates a state in which no current flows between the drain and the source of the FET 17, and the OFF state indicates a state in which no current flows between the drain and the source of the FET 17. The ON / OFF state of the FET 17 is determined by an FET command signal input to the gate 17a of the FET 17. In this embodiment, since the FET 17 is an n-channel type,
When the command signal goes to a high level (generally, a power supply voltage potential), the FET 17 is turned on, and when the FET command signal goes to a low level (generally, a ground potential), the FET 17 becomes O.
The state becomes the FF state.

The FET command signal is output from an electronic control unit (ECU). The ECU is composed of, for example, a microcomputer having a CPU, a RAM, and a ROM as main components. In order to keep the effective value of the voltage applied to each heater equal to or lower than the allowable withstand voltage, the power supply period of the heater and the power supply The ratio with the period is controlled. FIG.
In (b), the illustration of the ECU is omitted.

In the present heater control device, the first heater 13 and the second heater 15 have an allowable withstand voltage value of 1
The power supply 11 includes a 4 [v] ceramic heater, and outputs a power supply voltage of 42 [v]. Therefore, when the FET 17 is turned on, the first heater 13
And the second heater 15 have the same resistance value, so that a voltage (21
[V]) is applied.

On the other hand, the FET 17 is output from the ECU.
State (ON state or ON state)
OFF state), and the ECU determines that the first heater
13 and the effective value of the voltage applied to the second heater 15 is
The ON state of FET 17 so that it is lower than the allowable constant voltage value
The ratio between the period and the OFF state period is controlled. here,
When the voltage 21 [v] is applied at the duty ratio D [%],
Power (resistance = R [Ω]) is represented by [((21)
^Two × D / 100) / R]. In addition, this heater
Power consumption W when the DC conversion voltage becomes 14 [V]
2 is [(14) ^Two / R]. And
The reason why W1 and W2 are equal is that the duty ratio D = 44.4.
[%]. That is, in this heater control device,
The power supply period to the first heater 13 and the second heater 15
Control the ratio to the charging period (44:56 = 11:14)
The effective value of the voltage applied to each heater is
The duty of FET 17 is controlled so as to be less than the value.
Because

For this reason, the voltage value (effective voltage value) actually applied to each heater is 14 [v], which is not larger than the allowable withstand voltage value. Absent. Therefore, according to the heater control device of the second embodiment, the two heaters are connected in series, and the energization period is controlled so that the voltage applied to one heater is equal to or less than the allowable withstand voltage of the heater. can do.
Also, since two heaters are connected in series, the heater 1
Since the current value flowing through each heater and the FET 17 is smaller than in the case of a single device, an FET having a relatively small capacity can be used, and a heater control device can be realized at low cost.

Next, as a third embodiment, a heater control device for an automotive internal combustion engine having one ceramic heater will be described. FIG. 2A is a schematic circuit diagram of the heater control device 1 according to the third embodiment. As shown in FIG.
The heater control device according to the third embodiment includes a first ceramic heater (hereinafter, referred to as a first heater) 13 and a voltage drop resistor 27.
Are connected in series, and a power supply 11 is connected to this series circuit. That is, a series circuit including the first heater 13 and the voltage drop resistor 27 and the power supply 11
Form a closed loop, and a power supply voltage output from the power supply 11 is applied to both ends of a series circuit including the first heater 13 and the voltage drop resistor 27.

In the present heater control device, the resistance value of the first heater 13 is 13 [Ω] at room temperature, 26 [Ω] at high temperature use (around 700 ° C.), and the allowable withstand voltage value is 14
[V] ceramic heater, and a voltage drop resistor 27
And a resistance element of 52 [Ω].
A power supply 11 for outputting 2 [v] is provided.

For this reason, when energization to the first heater 13 is started, the first heater 13 is set to a voltage divided by the respective resistance values of the first heater 13 and the voltage drop resistor 27 to start applying a voltage. Sometimes, 8.4 [v] is applied, and the heater resistance rises as the heater temperature rises. When the heater resistance value at the time of high temperature use becomes 26 [Ω], it is equal to the allowable withstand voltage value of the first heater 13. Voltage (14
[V]) is applied.

Therefore, since the voltage applied to the first heater 13 can be made equal to the allowable withstand voltage value when the heater is used at a high temperature, after the internal combustion engine is started, the first heater 13 and the second heater 15 are energized. At the same time as the start, a large current does not continuously flow through the heater.

Here, in the method of connecting a plurality of heaters in series as in the above-described first and second embodiments, if the power supply voltage value is an integral multiple of the allowable withstand voltage value of the heater, the heater is connected to the heater. Can be set equal to the allowable withstand voltage value. On the other hand, in the method using the voltage drop resistor as in the third embodiment, since the resistance value of the voltage drop resistor can be set arbitrarily, the power supply voltage value is an integer of the allowable withstand voltage value of the heater. Even if it is not twice, it can be set optimally so that the voltage applied to the heater has an allowable withstand voltage value.

Next, as a fourth embodiment, a description will be given of a heater control device for an internal combustion engine for a vehicle, which is provided with one ceramic heater and controls the power supply period to the heater. FIG.
(B) shows a schematic circuit diagram of the heater control device 1 of the fourth embodiment. As shown in FIG. 2B, in the heater control device of the fourth embodiment, a first ceramic heater (hereinafter, referred to as a first heater) 13 and a voltage drop resistor 27 are connected in series. A power supply 11 and an n-channel FET 17 which is a switching element made of a semiconductor element are connected in series to the circuit. That is, the first heater 1
3, the voltage drop resistor 27, the power supply 11 and the FET 17 form a closed loop, and when the FET 17 is turned on, the power supply voltage output from the power supply 11
3 and a voltage drop resistor 27 are applied to both ends of a series circuit.

Here, the ON / OFF state of the FET 17 is determined by the FET command signal input to the gate 17a. In this embodiment, since the FET 17 is of the n-channel type, when the FET command signal becomes high level. ,
The FET 17 is turned on. The FET command signal is output from an electronic control unit (ECU). The ECU is composed of, for example, a microcomputer having a CPU, a RAM, and a ROM as main components. In order to keep the effective value of the voltage applied to each heater equal to or lower than the allowable withstand voltage, the power supply period of the heater and the power supply The ratio with the period is controlled. In FIG. 2B, the illustration of the ECU is omitted.

When the FET 17 is turned on,
A voltage is applied to the first heater 13 as a divided voltage determined by the respective resistance values of the first heater 13 and the voltage drop resistor 27. Here, in the heater control device, the first heater 13 has a resistance value of 13 at room temperature.
A resistance element having a resistance value of 26 [Ω] as a voltage drop resistance 27 is provided with a ceramic heater having a resistance value of 26 [Ω] and a permissible withstand voltage value of 14 [v] when a high temperature is used (around 700 ° C.). A power supply 11 that outputs 42 [v] as a power supply voltage
It has. For this reason, a voltage (21 [v]) larger than the allowable withstand voltage value is applied to the first heater 13 when the FET 17 is in the ON state and the high temperature is used.

On the other hand, similarly to the above-described second embodiment, the ECU controls the voltage drop resistor 27 during energization so that the effective value of the voltage applied to the first heater 13 is equal to or less than the allowable constant voltage value.
Is controlled to (11:14) on the basis of the voltage between both ends (21 [v]) of the first heater 13 to make the effective value of the voltage applied to the heater equal to the allowable value. The DUTY control of the FET 17 is performed so as to be equal to or less than the withstand voltage value.

For this reason, the voltage value (effective voltage value) actually applied to the heater is 14 [v] or less and does not become larger than the allowable withstand voltage value, so that a large current may continuously flow through the heater. Absent. Therefore, according to the heater control device of the fourth embodiment, the voltage applied to the heater is reduced to the allowable withstand voltage value of the heater or less by connecting the heater and the resistor for voltage drop in series and controlling the energization period. be able to. Further, since the heater and the resistance element are connected in series, the value of the current flowing through the FET 17 becomes smaller as compared with the case where the resistance element is not provided.
T can be used, and a heater control device can be realized at low cost.

Next, as a fifth embodiment, a description will be given of a heater control apparatus for an internal combustion engine for an automobile, which is provided with two ceramic heaters and controls the power supply period to the heaters. FIG.
(C) shows a schematic circuit diagram of the heater control device 1 of the fifth embodiment. The heater control device of the fifth embodiment is provided in a V-type engine, and one oxygen sensor is provided for each of the exhaust pipes of the left / right banks of the engine (two in total).
) Are provided. Each oxygen sensor is provided with one ceramic heater.

As shown in FIG. 2C, the heater control device of the fifth embodiment includes a first ceramic heater (hereinafter, referred to as a first heater) 13 and a second ceramic heater (hereinafter, referred to as a second heater).
A heater 15) and a voltage drop resistor 27 are connected in series, and a power supply 11 and an n-channel F which is a switching element made of a semiconductor element are connected to this series circuit.
ET17 is connected in series. That is,
First heater 13, second heater 15, voltage drop resistor 2
7, the power supply 11 and the FET 17 form a closed loop, and when the FET 17 is turned on, the power supply voltage output from the power supply 11 is a series circuit including the first heater 13, the second heater 15, and the voltage drop resistor 27. Is applied to both ends.

Here, in the present heater control device, the first heater 13 and the second heater 15 have resistance values of 13 at room temperature.
A resistance element having a resistance value of 26 [Ω] as a voltage drop resistance 27 is provided with a ceramic heater having a resistance value of 26 [Ω] and a permissible withstand voltage value of 14 [v] when a high temperature is used (around 700 ° C.). A power supply 11 that outputs 42 [v] as a power supply voltage
It has. For this reason, when the FET 17 is turned on, 10.5 [v] is applied to the first heater 13 and the second heater 15 at the start of voltage application, respectively, and at the time of high temperature use, a voltage (equal to the allowable withstand voltage value) is applied. 14
[V]) is applied.

Further, the heater control device of the fifth embodiment is
An FET 17 that operates based on the ET command signal is provided, and the ECU that outputs the FET command signal is configured to be able to control the power supply period to the heater, as in the fourth embodiment. In FIG. 2C, the illustration of the ECU is omitted.

When the FET 17 is turned on, a voltage equal to or less than the allowable withstand voltage (14 [v]) is applied to each heater.
The DUTY control of the FET 17 is performed so that the ratio between the current supply period to the heater and the non-current supply period is (1: 0). That is,
In the fifth embodiment, the FET 17 is set to D
UTY control.

Therefore, according to the heater control device of the fifth embodiment, the voltage applied to the heater can be made equal to or less than the allowable withstand voltage value of the heater, as in the fourth embodiment. It is possible to prevent disconnection and cracks (cracks) of the heater and disconnection due to migration.

Further, the heater control device of the fifth embodiment is provided with two heaters, and each heater can be used not only as a voltage drop means but also as a heater for heat generation. The supplied electric power can be used without waste. In the present embodiment, since the voltage applied to each heater at the time of energization is equal to or lower than the allowable withstand voltage, the FET 17 is duty-controlled so that the duty ratio becomes 100% by always energizing. If the voltage applied to the heater exceeds the allowable withstand voltage, the DUTY control is performed so that the effective value of the applied voltage becomes equal to or less than the allowable withstand voltage, thereby preventing the heater from being damaged.

Next, as a sixth embodiment, a heater control apparatus for an internal combustion engine for an automobile which includes one ceramic heater, detects the voltage actually applied to the heater, and controls the power supply period to the heater. Will be described. FIG. 3A is a schematic circuit diagram of the heater control device 1 according to the sixth embodiment.

As shown in FIG. 3A, in the heater control device of the sixth embodiment, a first ceramic heater (hereinafter, referred to as a first heater) 13 and a voltage drop resistor 27 are connected in series. A power supply 11 and an FET 17 which is a switching element made of a semiconductor element are connected in series to this series circuit. That is, the first heater 13, the voltage drop resistor 27, the power supply 11 and the FET 17 form a closed loop, and when the FET 17 is turned on, the power supply voltage output from the power supply 11 becomes the first heater 13 and the voltage drop The voltage is applied to both ends of the series circuit including the resistor 27.

The heater control device according to the sixth embodiment includes:
A voltmeter 23 for measuring the voltage across the voltage drop resistor 27 and an electronic control unit (ECU) 21 including a microcomputer are provided. The voltage value detected by the voltmeter 23 is input to the ECU 21. You.

The ECU 21 detects a power supply voltage value that may fluctuate at the time of starting the internal combustion engine or the influence of the generator, and detects the voltage drop resistor 27 detected by the voltmeter 23 from the detected power supply voltage value. The voltage value (instantaneous value) applied to the first heater 13 by subtracting the voltage value at both ends of
Is calculated. Then, based on the calculated voltage value (instantaneous value), the ECU 21 calculates the effective value of the voltage applied to the first heater 13 from the ratio of the current supply period to the heater and the non-current supply period. The effective value of the applied voltage is the first
By controlling the ON / OFF state of the FET 17 so as not to exceed the allowable withstand voltage value of the heater 13,
The power supply period to the heater is controlled.

Here, the above-described second and fourth embodiments,
In the heater control device of the fifth embodiment, the control of the power supply period to the heater is also performed. However, in these controls, the effective value of the voltage applied to the heater is controlled based on the theoretical value of the voltage across the heater. D which is predetermined to be equal to or less than the voltage value
This is performed by operating the FET at the UTY ratio. Therefore, when the voltage value fluctuates due to the influence of noise or the like, the heat value of the heater deviates from the target value, and
Control accuracy may be reduced. The theoretical value of the voltage between both ends of the heater can be calculated based on the theoretical value of the resistance value of the heater, the resistance value of the voltage drop resistor, and the theoretical value of the power supply voltage.

On the other hand, in the sixth embodiment, the applied voltage (effective value) actually applied to the first heater 13 is calculated, and the calculation result is fed back to control the power supply period to the heater. Therefore, even when a voltage fluctuation of the power supply voltage occurs, an error due to the voltage fluctuation can be suppressed, and more accurate heater energization control can be performed.

For this reason, since the voltage value (effective voltage value) actually applied to the heater does not become larger than the allowable withstand voltage value, a large current does not continuously flow through the heater.
Therefore, according to the heater control device of the sixth embodiment, the heater and the voltage-dropping resistor are connected in series, and the heater energization period is controlled based on the detected voltage applied to the heater. The voltage applied to the heater can be made equal to or less than the allowable withstand voltage value of the heater.

In the sixth embodiment, the current value flowing through the voltage drop resistor 27 can be calculated from the voltage value detected by the voltmeter 23 and the resistance value of the voltage drop resistor 27.
Thus, the value of the current flowing through the first heater 13 can be known. Therefore, since the applied voltage and current value of the first heater 13 can be calculated, the power consumption (heat generation amount) of the first heater 13 can be calculated from these values and the ratio between the heater energizing time and the non-energizing time. It can be calculated.

Therefore, according to the heater control apparatus of the sixth embodiment, the calorific value of the heater is feedback-controlled, and is processed in accordance with, for example, information on the temperature and flow rate of the exhaust gas to be measured by the oxygen sensor. In addition, it is possible to more accurately control the activation temperature of the detection element made of the solid electrolyte.

Next, as a seventh embodiment, a heater control device for an internal combustion engine for an automobile, which comprises two ceramic heaters, detects the voltage actually applied to the heaters, and controls the duration of energization to the heaters Will be described. FIG. 3B is a schematic circuit diagram of the heater control device 1 according to the seventh embodiment.

The heater control device of the seventh embodiment is
The engine is provided in a V-type engine, and one oxygen sensor is provided in each of the exhaust pipes of the left / right banks of the engine (two in total). Each oxygen sensor is provided with one ceramic heater.

As shown in FIG. 3B, the heater control device of the seventh embodiment comprises a first ceramic heater (hereinafter, referred to as a first heater) 13 and a second ceramic heater (hereinafter, referred to as a second heater).
A heater 15) and a voltage drop resistor 27 are connected in series, and a power supply 11 and an n-channel F which is a switching element made of a semiconductor element are connected to this series circuit.
ET17 is connected in series. That is, the first heater 13, the second heater 15, the voltage drop resistor 27, and the power supply 11
And FET17 form a closed loop, and FET1
When the switch 7 is turned on, the power supply voltage output from the power supply 11 is applied to both ends of the series circuit including the first heater 13, the second heater 15, and the voltage drop resistor 27.

The heater control device according to the seventh embodiment includes:
A voltmeter 23 for measuring the voltage across the second heater 15 or the voltage drop resistor 27, a changeover switch 25 for switching the voltage detection target of the voltmeter 23, and an electronic control unit (ECU) 21 including a microcomputer The voltage value detected by the voltmeter 23 is calculated by the ECU 2
1 is input.

Here, the changeover switch 25 is connected to the terminal p1 connected to the connection point between the first heater 13 and the second heater 15.
A terminal p2 connected to a connection point between the second heater 15 and the voltage dropping resistor 27; a voltage dropping resistor 27;
7 and a terminal p3 connected to the connection point.
When detecting the voltage across the second heater 15 based on the switching command signal from the ECU 21, the switch 25 short-circuits the terminals p 1 and p 2 and detects the voltage across the voltage drop resistor 27. When the terminal p2 and the terminal p3
And short circuit.

The voltmeter 23 is provided between a connection point between the second heater 15 and the voltage drop resistor 27 and a terminal p2 of the changeover switch 25. Then, the ECU 21 controls the changeover command signal to operate the changeover switch 25,
The voltage across each of the second heater 15 and the voltage drop resistor 27 is detected at regular intervals. Then, ECU
In 21, the power supply voltage value that fluctuates as described above is detected, and the detected second heater 1 is detected based on the detected power supply voltage value.
The voltage value (instantaneous value) applied to the first heater 13 is calculated by subtracting the sum of 5 and the voltage value across the voltage drop resistor 27.

Further, the ECU 21 determines the effective voltage applied to the first heater 13 and the second heater 15 based on the calculated or detected voltage value (instantaneous value) based on the ratio of the energizing time to the heater and the non-energizing time. Calculate the value. The ON / O of the FET 17 is controlled so that the calculated effective value of the applied voltage does not become larger than the allowable withstand voltage value of each heater.
By controlling the FF state, the power supply period to the heater is controlled.

For this reason, the present heater control device calculates the applied voltage (effective value) actually applied to the heater and feeds back the calculated result to supply the power to the heater in the same manner as in the sixth embodiment. , It is possible to suppress an error due to the fluctuation in the power supply voltage even when the power supply voltage fluctuates, and more accurate heater energization control becomes possible. Therefore, a large current does not continuously flow through the heater.

In the seventh embodiment, similarly to the sixth embodiment, the applied voltage and current value of each of the first heater 13 and the second heater 15 can be calculated.
The power consumption (calorific value) of each of the third and second heaters 15 can be calculated. Therefore, according to the heater control device of the seventh embodiment, the calorific value of the heater is feedback-controlled, for example, by processing it together with information on the temperature, flow rate, etc. of the exhaust gas to be measured by the oxygen sensor. It is possible to control the activation temperature of the detection element composed of a more accurate control.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments.
Various embodiments can be adopted. For example, in the above embodiment, the ceramic heater provided in the oxygen sensor has been described, but the application is not limited to the oxygen sensor.
For example, the present invention can be applied to other gas sensors, and further, the method of the present invention may be applied to heater control of a glow plug or a glow system including a ceramic heater.

In applying the above-described heater control method to an internal combustion engine for an automobile, when a resistance element is used as the voltage drop means, an existing resistance element mounted on a vehicle may be used. Accordingly, in realizing the heater control method of the present invention, it is not necessary to newly install a resistance element, and the mounting efficiency of each device in an automobile can be improved.

[Brief description of the drawings]

FIG. 1A is a schematic circuit diagram of a heater control device of a first embodiment, and FIG. 1B is a schematic circuit diagram of a heater control device of a second embodiment.

2A is a schematic circuit diagram of a heater control device according to a third embodiment, FIG. 2B is a schematic circuit diagram of a heater control device according to a fourth embodiment, and FIG. FIG. 2 is a schematic circuit diagram of the heater control device of FIG.

FIG. 3A is a schematic circuit diagram of a heater control device according to a sixth embodiment, and FIG. 3B is a schematic circuit diagram of a heater control device according to a seventh embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heater control device, 11 ... Power supply, 13 ... First heater
15: second heater, 17: FET, 21: electronic control unit (ECU), 23: voltmeter, 25: changeover switch, 27
... Resistor for voltage drop.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Isao Matsuoka 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi F-term in Japan Special Ceramics Co., Ltd. 3K058 AA22 AA45 BA00 CA02 CA03 CA46 CB09 CB14 CB19 CB22 CD02 CE04 CE13 CE19 CE26 CE28 3K092 PP15 QA05 QB02 RF03 RF11 RF17 RF27 UA20 UC07 VV08 VV18 VV28 VV31 VV34

Claims (6)

[Claims] 1. A heating resistor and a ceramic body,
A heater control method for a ceramic heater that generates heat by power supply from a power supply device, wherein the power supply voltage output from the power supply device is higher than an allowable withstand voltage value of the ceramic heater, Heater control, wherein at least one voltage drop means for reducing the voltage applied to the heater to the allowable withstand voltage value or less is connected in series to the ceramic heater, and the power supply voltage is applied to both ends of the ceramic heater. Method. 2. A resistance element is used as one of the voltage drop means, and the resistance element and the ceramic heater are connected in series.
2. The heater control method according to claim 1, wherein the power supply voltage is applied to both ends of the heater. 3. A voltage drop heater different from the heat-generating ceramic heater is used as one of the voltage drop means, and the voltage drop heater and the heat-generating ceramic heater are connected in series. The heater control method according to claim 1, wherein the power supply voltage is applied to both ends. 4. In addition to said voltage drop means, a switching means for switching between energization and non-energization of said ceramic heater is connected in series to said ceramic heater, and said ceramic heater when said switching means is turned on. When the duty ratio of the switching means is controlled based on the voltage at both ends, a duty ratio is set so that an effective voltage value applied to the ceramic heater is equal to or less than an allowable withstand voltage value of the ceramic heater. The heater control method according to any one of claims 1 to 3. 5. The heater control method according to claim 1, wherein the power supply voltage is an output voltage of a vehicle-mounted power supply device provided in a vehicle internal combustion engine. 6. The heater control method according to claim 5, wherein the ceramic heater is provided in a gas sensor installed in an automobile internal combustion engine.