JPH11257059A - Catalytic heater power supply control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent excessive rise of temperature of a current carrying heater when increased fuel is supplied, by providing a power setting means that sets supply power value lower as the detected air-fuel ratio of engine gets richer, and by supplying power to the current carrying heater according to the supply power value immediately after the start of the engine. SOLUTION: When an engine 22 starts, an air-fuel ratio feedback is controlled so that an air-fuel ratio feedback correction coefficient is 1. In addition, immediately after the start of the engine 22, a fuel injection time is set larger as the temperature of the engine 22 is lower. When the fuel injection time is larger than the threshold at the engine start, a voltage applied to the heater is set low corresponding to the fuel injection time. Accordingly, even when unburned components increased in the exhaust gas in a driving condition where increased amount of fuel is supplied, if a current carrying heater 1 is heated with the combustion heat of the unburned components, the rise of the heater temperature up to the tolerable upper limit temperature of the current carrying heater 1 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalytic heater power supply control device for controlling power supply to an electric heater included in a catalytic converter provided in an exhaust system in order to reduce harmful components in exhaust gas of an internal combustion engine.

[0002]

2. Description of the Related Art A catalyst is provided in an exhaust pipe to reduce harmful components in exhaust gas of an internal combustion engine. Since the catalyst is not sufficiently activated unless its temperature rises to 350 ° C. or higher, an energized heater is provided upstream of the catalytic converter so that the catalyst always effectively purifies exhaust gas during operation of the engine. It is arranged. There is a catalyst heater power supply control device to control the power supply to the heater.

In the catalytic heater power supply control device, when the engine cooling water temperature and intake air temperature satisfy predetermined low-temperature conditions at the time of engine start, power supply to the energized heater is performed only for a predetermined period after the engine is started. You. Such a catalyst heater power supply control device is disclosed, for example, in Japanese Patent Application Laid-Open No. 4-279718.

[0004]

However, even when the engine cooling water temperature and the intake air temperature satisfy the low temperature condition at the time of starting the engine, the unburned components in the exhaust gas increase in an operating state in which the fuel is supplied in an increased amount. Therefore, the heater is heated by the combustion heat of the unburned component,
The temperature of the heater itself may rise excessively. If the temperature of the heater rises so as to reach the upper limit temperature (for example, 800 ° C.) of the heater, there is a problem that the heater is deteriorated or damaged.

It is an object of the present invention to provide a catalyst heater power supply control device capable of preventing an excessive rise in the temperature of a current-carrying heater when supplying an increased amount of fuel.

[0006]

A catalyst heater power supply control device according to the present invention is a catalyst heater power supply control device for controlling power supply to an electric heater included in a catalytic converter provided in an exhaust system of an internal combustion engine. Air-fuel ratio detection means for detecting the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine; power setting means for setting the power supply value to the energized heater lower as the air-fuel ratio detected by the air-fuel ratio detection means becomes rich; Power supply means for supplying power to the energized heater in accordance with the supplied power value.

That is, according to the present invention, the richer the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine, the lower the power supplied to the energized heater is set, and immediately after the engine is started, the power corresponding to the supplied power is reduced. It is supplied to the energized heater. With this configuration, in an operation state in which the air-fuel ratio is rich such that an increased amount of fuel is supplied, the unburned components in the exhaust gas increase, and the heater is heated by the combustion heat of the unburned components. Since the power supplied to the energized heater is suppressed low according to the degree of richness, the heat generated by the heater itself due to power supply is reduced, and an excessive rise in the heater temperature can be prevented.

In the catalytic heater power supply control device of the present invention, the power setting means continuously sets the power supply value to the energized heater to be lower as the air-fuel ratio detected by the air-fuel ratio detector becomes richer. By controlling the power supplied to the energized heater well, an excessive rise in the heater temperature can be accurately prevented. Further, the catalytic heater power supply control device according to the present invention is characterized in that the power setting means adjusts the power supply to the energized heater according to a new rich state of the detected air-fuel ratio by the air-fuel ratio detecting means during the power supply to the energized heater by the power supply means. A new value is set, and the power supply means supplies power to the energized heater according to the newly set supply power value. Here, depending on the rich state, the case where the air-fuel ratio simply changes, or the case where the rich state is, for example, 3
That is, when it lasts more than seconds. With this configuration, an excessive rise in the heater temperature can be accurately prevented.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a catalytic heater power supply control device according to the present invention. In this catalytic heater power supply control device, a DC voltage is applied to the energized heater 1 from the alternator 2 via the changeover switch 3.

The energized heater 1 is provided in a catalytic converter 21 as shown in FIG. The catalytic converter 21 is provided in an exhaust pipe 23 extending from an exhaust port of the engine 22, and is provided with an energized heater 1, a light-off catalyst 25, and a main catalyst 2 from upstream in a cylindrical case 24.
6 are provided in order. The energized heater 1 is formed of, for example, a honeycomb structure coated with a catalyst material, and itself is also configured to perform a catalytic action and be heated by the oxidizing heat of the unburned components of the exhaust gas. Heat exhaust gas. The structure of a catalytic converter having a current-carrying heater is disclosed in JP-A-8-218857 and JP-A-8-316660.

Returning to FIG. 1, the changeover switch 3 is also connected to the positive terminal of the battery 4, and the output of the alternator 2 is selectively connected to either the energized heater 1 or the battery 4 by the changeover switch 3. It is supposed to be. The steady state of the changeover switch 3 is a charging state in which the output of the alternator 2 is connected to the battery 4. The changeover operation of the changeover switch 3 is performed by an ECU (engine control unit).
6 is executed in response to a command from The alternator 2 is driven by the rotation of the engine 22 to generate an AC voltage, rectifies the AC voltage, and outputs it as a DC voltage. A regulator 5 is connected to the alternator 2 to set the DC voltage. The regulator 5 sets the output voltage of the alternator 2 according to a voltage setting command from the ECU 6.

The ECU 6 includes a CPU 1 as shown in FIG.
1, at least a ROM 12, a RAM 13, an A / D converter 14, a counter 15, an input interface circuit 16, an output interface circuit 17, and a timer 19, which are connected to each other by a common bus. A /
The D converter 14 has a cooling water temperature sensor 31 for detecting a cooling water temperature T _W of the internal combustion engine, an intake temperature sensor 32 for detecting an intake air temperature T _{A of the} engine, and a pressure in an intake pipe downstream of a throttle valve (not shown). Sensors such as an intake pipe internal pressure sensor 33 for detection and an oxygen concentration sensor 34 provided in the exhaust pipe 23 for detecting the oxygen concentration in the exhaust gas are connected. A /
The D converter 14 converts the output values of these sensors into digital values. The counter 15 measures a generation interval of a pulse output from the crank angle sensor 35 by counting the number of generations of a clock pulse output from a clock generator (not shown), and generates a signal indicating the engine speed Ne. The crank angle sensor 35 generates a TDC signal indicating the top dead center of the piston of each cylinder together with a reference position signal indicating the time when the rotation angle of the crankshaft is at a predetermined angular position, and these are supplied to the CPU 11. Input interface circuit 1
One end of an ignition switch 7 is connected to 6 so that ON / OFF of the ignition switch 7 is detected. The output interface circuit 17 is connected to the changeover switch 3 and the regulator 5 described above.
Injector 2 for injecting fuel at a predetermined timing according to fuel injection time Tout calculated in CU 6
7 is connected.

When the CPU 11 of the ECU 6 detects that the ignition switch 7 is turned on via the input interface circuit 16, the CPU 11 performs a power supply control operation of the electric heater 1.
This power supply control operation is performed by, for example, the ignition switch 7.
Is repeatedly executed until a predetermined time elapses from the turning on of. In the power supply control operation, as shown in FIG. 4, first, it is determined whether or not an operation state in which heater power supply should be performed (step S1). The determination as to whether or not the heater is in the operation state in which the heater is energized is made by comparing the intake air temperature T _A detected by the intake air temperature sensor 32 and the cooling water temperature T _W detected by the cooling water temperature sensor 31 via the A / D converter 14. Get,
As the intake air temperature T _A is the threshold value T1 (for example, 0 to 40 ° C.) when the low intake air temperature is less, and the cooling water temperature T _W is the threshold T2 (for example, 0 to 60 ° C.) is at low cooling water temperature is below This is done by detecting the state. T _A > T1 or T _W >
Since the warming-up as in T2 is in progress, if it is not the operation state in which the heater power should be supplied, a power supply stop command is generated (step S2), and the power supply flag FON is reset to be equal to 0 (step S3). ).

On the other hand, if the operation state is such that the heater is to be energized, it is determined whether or not power is being supplied to the energized heater 1 (step S4). This determination during power supply is made from the contents of the power supply flag FON set in step S3 or S10. If FON = 0, power is not being supplied, and it is determined whether the engine 22 has started (step S).
5). When the engine is started, for example, the engine speed Ne is reduced to a predetermined low speed (cranking speed) N1 (for example,
500 rpm) or more.

If the engine has not been started, the process proceeds to step S2. On the other hand, when the engine 22 is started, the latest fuel injection time Tout calculated in the fuel injection control operation is read (step S6), and the heater applied voltage _VEHC corresponding to the fuel injection time Tout is set (step S6).
7). The relationship between the fuel injection time Tout and the heater applied voltage V _EHC is, for example, as shown by the solid line in FIG.
Since a V _EHC data map is stored in advance in M12, the heater application voltage V _EHC corresponding to the fuel injection time Tout is retrieved and read from the V _EHC data map. The fuel injection time Tout will be described later.

[0016] CPU11 is setting the voltage applied to the heater V _EHC, generates a feed command in voltage applied to the heater V _EHC to the output interface circuit 17 (step S
8). Then, the timer 19 is started to measure time from the preset heater power supply time t _EHC (step S
9) Further, the power supply flag FON is set to be equal to 1 (step S10).

If it is determined in step S4 that power is being supplied to the energized heater 1, the timer 19 determines whether or not time measurement for the heater power supply time t _EHC has been completed (step S11). If the time measurement of the heater power supply time t _EHC has not been completed, the heater power supply control operation is temporarily terminated. On the other hand, when the measurement of the heater power supply time t _EHC has been completed, the power supply control operation has been completed.
The power supply stop command is generated, and the power supply flag FON is reset to be equal to 0 in step S3.

The output interface circuit 17 switches the changeover switch 3 from a steady state to an unsteady state in response to a power supply command. At the same time, the set voltage of the regulator 5 is switched from the supply voltage 14.5 V for charging the battery to the heater applied voltage V _EHC . Therefore, the output DC voltage of the alternator 2 is equal to the heater applied voltage V _EHC (for example, 30
V), and this DC voltage is applied to the energizing heater 1 via the changeover switch 3, so that the energizing heater 1 generates heat and heats the exhaust gas upstream of the light-off catalyst 25.

In response to the power supply stop command, the output interface circuit 17 switches the changeover switch 3 from the unsteady state to the steady state, and at the same time, changes the set voltage of the regulator 5 from the heater applied voltage V _EHC to the supply voltage for battery charging. Switch to 14.5V. Therefore, the output DC voltage of the alternator 2 becomes 14.5 V, and this DC voltage is applied to the battery 4 via the changeover switch 3, so that the battery 4 is charged, and
No voltage is applied to the heater 1 and further heating of the energized heater 1 is stopped.

The fuel injection time Tout is calculated by the CPU 11 according to the following calculation formula, for example.

[0021]

[Equation 1] Tout = Ti × K _O2 × K _WOT × K _TW × K _TA + T
_ACC + T _DEC where Ti is the engine speed Ne and the intake pipe pressure P _B
Is a basic fuel injection time which is an air-fuel ratio reference control value determined by a data map search from the ROM 12 in accordance with the above. K _O2 is an air-fuel ratio feedback correction coefficient set according to the output level of the oxygen concentration sensor 34, K _WOT is a fuel increase correction coefficient at a high load such as when the throttle valve is fully opened,
K _TW is a cooling water temperature correction coefficient set in accordance with the cooling water temperature T _W , K _TA is an intake air temperature correction coefficient set in accordance with the intake air temperature K _TA , and T _ACC is in accordance with the degree of acceleration of the engine speed Ne. The set acceleration increase value, T _DEC, is a deceleration decrease value set according to the degree of deceleration of the engine speed Ne. These correction coefficients K _O2 , K _WOT , K _TW , K _TA , and the acceleration increase value T
_ACC and deceleration reduction value T _DEC are determined by searching a data map from the ROM 12. The fuel injection time Tout determined in this way indicates the air-fuel ratio of the supplied air-fuel mixture, and the fuel injection is performed by the injector 27 at the timing determined by the TDC signal according to the injection command from the CPU 11 for the fuel injection time Tout. Done.

When the engine 22 is started, the air-fuel ratio feedback control coefficient K _O2 is 1 because the air-fuel ratio feedback control is not normally started. Further, since the cooling water temperature correction coefficient K _TW is set to be larger as the engine cooling water temperature T _W is lower, the fuel injection time Tout is set to be larger as the engine 22 is colder immediately after the engine is started.
That is, when the engine cooling water temperature T _W is low at the time of starting the engine, the air-fuel ratio of the supplied air-fuel mixture is enriched immediately after the start of the engine. As shown in FIG. 5, when the fuel injection time Tout is larger than the threshold value T _REF at the time of starting the engine, the heater applied voltage V _EHC is set to be low in accordance with the fuel injection time Tout. When the applied voltage V _EHC is applied, the heat generation of the current-carrying heater 1 due to the power supply itself is suppressed to a low level. On the other hand, in an operating state in which the fuel supply amount is increased, the unburned components in the exhaust gas increase, and the energized heater 1 is heated by the combustion heat of the unburned components, and the temperature of the heater itself increases. Rises. However,
By setting the heater applied voltage V _{EHC to} be low, as shown in FIG. 6, even if the fuel injection time Tout becomes long, the heater temperature T _EHC is maintained at the heater upper limit temperature (for example, 80 _{° C.).}
0 ° C.). This means that the fuel injection time Tout calculated at the time of starting the engine is larger than the threshold value T _{R EF} by not only the correction coefficient K _TW but also other correction coefficients K _WOT , K _TA , the acceleration increasing value T _ACC , and the deceleration decreasing value T _DEC . The same is sometimes true.

[0023] Incidentally, in the above embodiment, although the heater applied voltage V _EHC corresponding to the fuel injection time Tout is set, the correction coefficient K _WOT, K _TW, voltage applied to the heater V _EHC corresponding to K _TA May be set. Further, in the above-described embodiment, as shown in FIG. 5, the longer the fuel injection time Tout, that is, the richer the detected air-fuel ratio, the lower the power supply value to the energized heater is set to be continuously lower. Although the power supply to the energized heater can be accurately controlled to prevent the heater temperature from excessively rising, the power supply value to the energized heater can be set stepwise lower as the detected air-fuel ratio becomes richer. good. For example, as shown in FIG. 7, the heater applied voltage _VEHC is set stepwise in accordance with the fuel injection time Tout. Also,
As shown in FIG. 8, when the fuel injection time Tout is longer than a predetermined value, the heater applied voltage _VEHC may be simply set to V2 lower than V1. This predetermined value is the air-fuel ratio at which the energized heater is heated by the combustion heat of the unburned components in the exhaust gas,
For example, it corresponds to 13.

Further, in the above embodiment, the power supplied to the current-carrying heater 1 is changed by controlling the voltage V _EHC applied to the current-carrying heater 1, but the current supplied to the current-carrying heater may be controlled. . Further, in the above-described embodiment, once the heater application voltage V _EHC is set, the heater application voltage V _EHC is thereafter set until the energization of the heater ends.
_{Although the EHC} is maintained, even when the heater is energized, the heater application voltage V _EHC corresponding thereto may be reset using the newly calculated fuel injection time Tout. In this case, for example, as shown in FIG. 9, if it is determined in step S11 that the timer time measurement has not been completed, the latest fuel injection time Tout calculated in the fuel injection control operation is read (step S11). S
12) The heater application voltage V _EHC corresponding to the fuel injection time Tout is set (step S13), and the power supply command at the heater application voltage V _EHC is output to the output interface circuit 17.
(Step S14). With this configuration, steps S12 to S14 are repeated and the newly set heater applied voltage V _EHC is applied to the heater 1 unless the time measurement of the timer is completed immediately after the engine is started. The rise can be accurately prevented. Further, when the rich state continues, the inclination of FIG. 5 may be changed as shown by a broken line.

In the above embodiment, the CPU 1
1 executes the step S6 in the power supply control operation to constitute the air-fuel ratio detecting means, and executes the step S7 to constitute the electric power setting means.
11 performs steps S2, S8 and S9, and the alternator 2, switch 3, regulator 5 and output interface circuit 17 constitute a power supply means. Further, in the above-described embodiment, the heater applied voltage V _EHC is set lower as the fuel injection time Tout becomes longer. However, this configuration sets the power supply value to the energized heater lower as the detected air-fuel ratio becomes richer. Corresponding to This is because the fuel injection time Tout is a parameter indicating the air-fuel ratio of the supplied air-fuel mixture, as can be seen from the above formula for calculating the fuel injection time Tout.

[0026]

As described above, according to the present invention, as the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine becomes richer, the power supply value to the energized heater is set lower, and the power supply value is adjusted immediately after the engine is started. The supplied power is supplied to the energized heater. With this configuration, in an operation state in which the air-fuel ratio is rich such that an increased amount of fuel is supplied, the unburned components in the exhaust gas increase, and the heater is heated by the combustion heat of the unburned components. Since the electric power supplied to the energized heater is suppressed to be low in accordance with the degree of richness of the fuel ratio, the heat generated by the heater itself due to the power supply is reduced, and an excessive rise in the heater temperature can be prevented.

Further, in the catalytic heater power supply control device of the present invention, the power setting means sets the power supply value to the energized heater continuously lower as the air-fuel ratio detected by the air-fuel ratio detecting means becomes rich. With this configuration, it is possible to accurately control the electric power supplied to the energized heater and accurately prevent an excessive rise in the heater temperature. Further, in the catalytic heater power supply control device of the present invention, the power setting means supplies power to the energized heater in accordance with a new rich state of the detected air-fuel ratio by the air-fuel ratio detecting means during power supply to the energized heater by the power supply means. An electric power value is newly set, and the electric power supply means supplies electric power to the energized heater according to the newly set supply electric power value. With this configuration, an excessive rise in the heater temperature can be accurately prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an exhaust system of an engine provided with a catalytic converter.

FIG. 3 is a block diagram illustrating a configuration of an ECU.

FIG. 4 is a flowchart illustrating a power supply control operation.

FIG. 5 is a diagram showing a relationship between a fuel injection time and a heater applied voltage.

FIG. 6 is a diagram showing a relationship between a fuel injection time and a heater temperature.

FIG. 7 is a diagram showing a relationship between a fuel injection time and a heater applied voltage.

FIG. 8 is a diagram showing a relationship between a fuel injection time and a heater applied voltage.

FIG. 9 is a flowchart illustrating a power supply control operation.

[Description of Signs of Main Parts]

 REFERENCE SIGNS LIST 1 energized heater 2 alternator 3 selector switch 4 battery 5 regulator 6 ECU 7 ignition switch 21 catalytic converter 22 engine 23 exhaust pipe 24 cylinder case 25 light-off catalyst 26 main catalyst 27 injector 34 oxygen concentration sensor

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Kazuto Sawamura 1-4-1 Chuo, Wako-shi, Saitama

Claims (3)

[Claims] 1. A catalyst heater power supply control device for controlling power supply to an energizing heater included in a catalytic converter provided in an exhaust system of an internal combustion engine, wherein the air conditioner detects an air-fuel ratio of a mixture supplied to the internal combustion engine. Fuel-ratio detecting means, power setting means for setting the power supply value to the heater to be lower as the air-fuel ratio detected by the air-fuel ratio detector becomes richer, and supplying the power corresponding to the power supply value immediately after starting the engine. A catalyst heater power supply control device, comprising: a power supply unit that supplies power to a heater. 2. The catalyst according to claim 1, wherein the power setting means continuously sets a lower power supply value to the energized heater as the air-fuel ratio detected by the air-fuel ratio detecting means becomes richer. Heater power supply control device. 3. A power supply value to the energized heater according to a new rich state of the detected air-fuel ratio by the air-fuel ratio detection unit during power supply to the energized heater by the power supply unit. 2. The catalytic heater power supply control device according to claim 1, wherein the power supply unit supplies power to the energized heater according to the newly set power supply value. 3.