JP3627335B2 - Heater control device for catalyst downstream air-fuel ratio sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heater control device for an air-fuel ratio sensor provided downstream of a catalyst in an exhaust passage of an internal combustion engine.
[0002]
[Prior art]
When an air-fuel ratio sensor (generally an O ₂ sensor) is provided in the exhaust passage of an internal combustion engine to detect the exhaust air-fuel ratio (rich / lean), a heater is provided to activate the air-fuel ratio sensor and perform a predetermined operation. The heater is energized under conditions to heat the air-fuel ratio sensor (sensor element).
[0003]
However, when an air-fuel ratio sensor is provided downstream of the catalyst in the exhaust passage of the internal combustion engine for diagnosis of catalyst deterioration, etc., at a low temperature immediately after engine startup, moisture in the exhaust is condensed and accumulated in the container when passing through the catalyst, If this condensed water or water vapor generated by evaporation of the condensed water is applied to an air-fuel ratio sensor (sensor element) heated by a heater, element cracking may occur.
[0004]
Therefore, for example, as disclosed in Japanese Patent Publication No. 6-90167, temperature detection means for detecting the exhaust pipe wall temperature in the vicinity of the air-fuel ratio sensor is provided, and the temperature in the vicinity of the air-fuel ratio sensor indicates whether water in the exhaust pipe exists. In consideration of the above, it is conceivable that heating of the air-fuel ratio sensor by the heater is prohibited when it is equal to or less than a predetermined value set.
[0005]
[Problems to be solved by the invention]
However, by detecting the temperature in the vicinity of the air-fuel ratio sensor and prohibiting energization of the heater when this temperature is equal to or lower than a predetermined value, the method of uniquely determining the presence or absence of water on the upstream side of the air-fuel ratio sensor by the temperature, With the allowance in mind, the heater energization start temperature must be set to a fairly high temperature, and heating by the heater will continue to be prohibited for a while after the water has run out. There was a problem that the start of the catalyst deterioration diagnosis used was delayed.
[0006]
In view of such a conventional problem, the present invention provides a heater for heating a main catalyst downstream air-fuel ratio sensor particularly when an upstream pre-catalyst and a downstream main catalyst are provided as exhaust purification catalysts . An object of the present invention is to provide a heater control device for a catalyst downstream side air-fuel ratio sensor that can further prevent the element cracking of the sensor by making the energization prohibition control more appropriate, and can advance the energization start timing as much as possible. .
[0007]
[Means for Solving the Problems]
Therefore, according to the first aspect of the present invention, the exhaust passage of the internal combustion engine is provided with the upstream pre-catalyst and the downstream main catalyst as the exhaust purification catalyst, while the air-fuel ratio sensor provided downstream of the main catalyst. a heater for heating, the heater control device of the catalyst downstream air-fuel ratio sensor which is adapted to heat the air-fuel ratio sensor by energizing the heater at a predetermined operating condition, as shown in FIG. 1, the operating state of the engine Based on pre-applied heat amount calculating means for calculating the amount of heat given to the pre-catalyst every predetermined time, pre-accumulating means for accumulating the amount of heat given to the pre-catalyst from the start of the engine, and accumulation given to the pre-catalyst Pre-comparison means for comparing the amount of heat with a predetermined value, and heat transfer amount calculation means for calculating the amount of heat transferred after the pre-catalyst every predetermined time according to the comparison result, the pre-catalyst Based on the amount of heat transferring heat to the descending, provided applying heat calculating means for calculating an amount of heat given to the main catalyst. And further, from the time of engine start, the main accumulation means for accumulating the amount of heat given to the main catalyst, a main comparator means for comparing the cumulative amount of heat given to the main catalyst to a predetermined value, the comparison result fed to a main catalyst Heater energization prohibiting means for prohibiting energization of the heater while the accumulated amount of heat is not more than a predetermined value is provided .
[0008]
In the case where the pre-catalyst and the main catalyst are provided, moisture in the exhaust gas is also condensed in the pre-catalyst, and heat transfer from the pre-catalyst is started after evaporation of condensed water in the pre-catalyst is completed.
Therefore, it is determined whether or not the evaporation of condensed water in the pre-catalyst has been completed by calculating the cumulative amount of heat given to the pre-catalyst according to the operation history from the start of the engine and comparing this with a predetermined value. Then, according to the determination result, the amount of heat transferred to the pre-catalyst and thereafter is calculated, and the amount of heat given to the main catalyst is calculated based on the amount of heat transferred.
[0009]
Then, by accumulating the amount of heat given to the main catalyst, the accumulated amount of heat given to the main catalyst is obtained, and compared with a predetermined value, moisture in the exhaust gas condensed in the main catalyst container immediately after the engine is started. It is accurately determined whether or not the evaporation of the water has been completed, and while the accumulated heat amount is equal to or less than the predetermined value, it is determined that the evaporation of moisture has not been completed, and energization of the heater is prohibited.
[0010]
In the invention according to claim 2, the predetermined value for comparison in the main comparison means is an amount of heat necessary for vaporizing moisture in the exhaust gas condensed in the main catalyst container immediately after the engine is started. It is characterized by being variable depending on the cooling water temperature.
By setting the amount of heat required for vaporization in the main catalyst according to the cooling water temperature at the time of starting the engine, it is possible to easily and accurately determine the completion of the evaporation of moisture.
[0011]
In the invention according to claim 3 , the predetermined value for comparison in the pre-comparing means is an amount of heat necessary for vaporizing the moisture in the exhaust gas condensed in the pre-catalyst container immediately after the engine is started. It is characterized by being variable depending on the cooling water temperature.
By setting the amount of heat required for vaporization in the pre-catalyst according to the cooling water temperature at the time of starting the engine, it is possible to easily and accurately determine the completion of evaporation of water in the pre-catalyst.
[0012]
In the invention according to claim 4 , the applied heat amount calculating means includes a reaction heat amount calculating means for calculating a reaction heat amount generated in the pre-catalyst, and at least the reaction heat amount with respect to a heat amount transferred after the pre-catalyst. Is added to calculate the amount of heat given to the main catalyst (see FIG. 1 ).
Considering the amount of heat generated by the pre-catalyst, the amount of heat given to the main catalyst can be determined more accurately.
[0013]
In the invention according to claim 5 , the applied heat amount calculating means includes heat release amount calculating means for calculating a heat release amount in the exhaust passage from the pre-catalyst to the main catalyst, and with respect to the heat amount transferred after the pre-catalyst. At least, the amount of heat given to the main catalyst is calculated by subtracting the amount of heat release (see FIG. 1 ).
Considering the amount of heat released in the exhaust passage from the pre-catalyst to the main catalyst, the amount of heat given to the main catalyst can be obtained more accurately.
[0014]
【The invention's effect】
According to the first aspect of the present invention, the accumulated heat amount given to the pre-catalyst is obtained in accordance with the operation history from the time of starting the engine, and this is compared with a predetermined value, thereby evaporating condensed water in the pre-catalyst. When the pre-catalyst and the main catalyst are provided, the heat transfer from the pre-catalyst to the beginning of the heat transfer after the pre-catalyst is completed can be confirmed. Considering this, the amount of heat transferred to the pre-catalyst and the subsequent parts is calculated, and based on this amount of heat transferred, the amount of heat given to the main catalyst can be calculated accurately, and the estimation accuracy can be improved. . Then, the cumulative amount of heat given to the main catalyst is obtained and compared with a predetermined value to accurately determine whether or not the condensed water has evaporated in the catalyst immediately after the engine is started. By prohibiting energization of the heater, there is an effect that the energization start timing can be advanced as much as possible while reliably preventing element cracking of the air-fuel ratio sensor.
[0015]
According to the second aspect of the present invention, it is possible to easily and accurately determine the completion of moisture evaporation by setting the required amount of vaporization heat in the main catalyst according to the cooling water temperature at the time of starting the engine.
According to the invention of claim 3 , by setting the required amount of heat of vaporization in the pre-catalyst according to the cooling water temperature at the time of starting the engine, it is possible to easily and accurately determine the completion of evaporation of water in the pre-catalyst. can get.
[0016]
According to the fourth aspect of the present invention, the amount of heat given to the main catalyst can be obtained more accurately by taking into account the amount of heat of reaction generated in the pre-catalyst.
According to the invention which concerns on Claim 5 , the effect that the amount of heat given to a main catalyst can be calculated | required more correctly is acquired by considering the thermal radiation amount in the exhaust passage from a pre catalyst to a main catalyst.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
FIG. 3 is a system diagram showing an embodiment of the present invention.
A throttle valve 3 is interposed in the intake passage 2 of the internal combustion engine 1, and a fuel injection valve 4 for injecting fuel toward the intake port for each cylinder is provided on the downstream side thereof. The exhaust passage 5 is provided with an upstream pre-catalyst (manifold catalyst) 6 and a downstream main catalyst (underfloor catalyst) 7 as exhaust purification catalysts.
[0018]
The fuel injection valve 4 is an electromagnetic fuel injection valve that is energized and opened by a drive pulse signal from the control unit 8 and is closed after energization is stopped, and the fuel injection amount depends on the pulse width of the drive pulse signal. The air-fuel ratio is controlled by controlling the fuel injection amount.
In order to control this fuel injection amount, signals are input to the control unit 8 from various sensors.
[0019]
As the various sensors, for example, a hot-wire air flow meter 9 for detecting an intake air flow rate (mass flow rate) GA is provided upstream of the throttle valve 3 in the intake passage 2.
Further, a crank angle sensor 10 that outputs a reference crank angle signal and a unit crank angle signal is provided, and the engine speed NE can be calculated from the cycle of the reference crank angle signal.
[0020]
Further, a water temperature sensor 11 for detecting the cooling water temperature TW of the engine 1 is provided.
Further, an upstream air-fuel ratio sensor 12 is provided upstream of the pre-catalyst 6 in the exhaust passage 5, and a downstream air-fuel ratio sensor 13 is provided downstream of the main catalyst 7.
These air-fuel ratio sensors 12 and 13 are specifically O ₂ sensors, which generate an electromotive force according to the residual oxygen concentration in the exhaust gas. In particular, the electromotive force suddenly changes at the boundary of the theoretical air-fuel ratio, It becomes a high level (about 1V) on the rich side from the theoretical air-fuel ratio, and a low level (about 100mV) on the lean side. Therefore, rich lean can be detected.
[0021]
In addition, these air-fuel ratio sensors 12 and 13 incorporate heaters 12a and 13a, respectively, for activating the sensor elements, and the energization of these heaters 12a and 13a is controlled by signals from the control unit 8, respectively. It has become so.
In addition, a throttle sensor, a vehicle speed sensor, an outside air temperature sensor, and the like are provided, but the illustration is omitted.
[0022]
Here, the control unit 8 performs air-fuel ratio control by controlling the fuel injection amount by the fuel injection valve 4 based on signals from the various sensors by means of a built-in microcomputer.
That is, the intake air flow rate GA detected based on the signal from the air flow meter 9 and the engine speed NE calculated based on the signal from the crank angle sensor 10 correspond to the amount of air sucked into the engine. The basic fuel injection amount TP = K × GA / NE (K is a constant) corresponding to the theoretical air-fuel ratio is calculated. Then, the air-fuel ratio feedback correction coefficient α is calculated based on the output signal of the upstream air-fuel ratio sensor 12, and the final fuel injection amount TI = TP × α × COEF (COEF is various correction coefficients) is calculated. When calculating the air-fuel ratio feedback correction coefficient α, correction based on the output signal of the downstream air-fuel ratio sensor 13 may be performed.
[0023]
When the fuel injection amount TI is calculated, a drive pulse signal having a pulse width of TI is output to the fuel injection valve 4 at a predetermined timing synchronized with the engine rotation, and fuel injection is performed.
Further, the control unit 8 performs a deterioration diagnosis of the catalyst (the pre-catalyst 6 and the main catalyst 7) based on signals from the upstream air-fuel ratio sensor 12 and the downstream air-fuel ratio sensor 13, and when the catalyst deterioration is diagnosed. Turns on the warning light 14.
[0024]
That is, the rich / lean inversion cycle T1 of the output signal of the upstream air-fuel ratio sensor 12 is measured, and the rich / lean inversion cycle T2 of the output signal of the downstream air-fuel ratio sensor 13 is measured. If the catalysts 6 and 7 are normal, the reversal cycle T2 of the downstream air-fuel ratio sensor 13 is sufficiently longer than the reversal cycle T1 of the upstream air-fuel ratio sensor 12, but if the catalysts 6 and 7 deteriorate, the downstream air-fuel ratio sensor 13 deteriorates. The inversion period T2 of the fuel ratio sensor 13 is gradually shortened. Therefore, the ratio (T2 / T1) of the reversal period T2 of the downstream air-fuel ratio sensor 13 to the reversal period T1 of the upstream air-fuel ratio sensor 12 is monitored, and when this becomes below a predetermined value (near 1), the catalyst deteriorates. The warning lamp 14 is turned on.
[0025]
The control unit 8 controls the heaters of the upstream air-fuel ratio sensor 12 and the downstream air-fuel ratio sensor 13. In particular, the heater control of the downstream air-fuel ratio sensor 13 will be described in detail below.
Heater control of the downstream air-fuel ratio sensor 13 is performed according to the heater control routine of FIG. 4, the startup routine of FIG. 5, and the moisture evaporation determination routine of FIG.
[0026]
First, the heater control routine of FIG. 4 will be described.
In step 1 (denoted as S1 in the figure, the same applies hereinafter), it is determined whether or not the prohibition flag F according to the present invention is set (F = 1). If F = 1, step 6 is determined. Then, the heater 13a is turned off. If F = 0, go to Step 2. The prohibition flag F will be described later with reference to FIGS.
[0027]
In step 2, it is determined whether or not the engine is rotating. If the engine is not rotating, the process proceeds to step 6 where the heater 13a is turned off. If the engine is rotating, go to step 3.
In step 3, it is determined whether or not the engine rotational speed NE ≦ predetermined value. If the engine rotational speed NE> predetermined value (during high rotation), the routine proceeds to step 6 where the heater 13a is turned off. If the engine speed NE ≦ predetermined value (at low speed), the process proceeds to step 4.
[0028]
In step 4, it is determined whether engine load (basic fuel injection amount) TP ≦ predetermined value. If engine load TP> predetermined value (during high load), the routine proceeds to step 6 where the heater 13a is turned off. If the engine load TP ≦ predetermined value (low load), the process proceeds to step 5.
In step 5, it is determined whether or not battery voltage VB ≦ predetermined value (for example, 16V). If battery voltage VB> predetermined value (abnormally high voltage) , the process proceeds to step 6 and the heater 13a is turned off. If battery voltage VB ≦ predetermined value , the routine proceeds to step 7 where the heater 13a is turned on.
[0029]
That is, on the assumption that the prohibition flag F is released (F = 0), during engine rotation, the engine speed NE is less than or equal to a predetermined value (during low rotation), and the engine load TP is less than or equal to a predetermined value (during low load). When the battery voltage VB is equal to or lower than a predetermined value (for example, 16V), the heater 13a is energized.
The reason why the heater 13a is not energized at the time of high rotation or high load is that the exhaust gas temperature is high, so that excessive air temperature rise of the air-fuel ratio sensor 13 may cause burning, The reason why the heater 13a is prohibited from energizing when the battery voltage VB exceeds 16V is that, for example, the heater 13a may be overheated due to an abnormally high voltage.
[0030]
Next, the startup routine of FIG. 5 will be described.
In step 11, it is determined whether or not the engine is being started (when the key is ON).
Only at the time of start, the routine proceeds to step 12, the prohibition flag F is set (F = 1), and at step 13, the water temperature TW is detected based on the signal from the water temperature sensor 11, and this is detected as the water temperature at the start. Store and hold as TWst = TW.
[0031]
Next, the moisture evaporation determination routine of FIG. 6 will be described. This routine is executed at a predetermined time (for example, every 100 ms).
In step 21, the amount of heat Q0 given to the pre-catalyst 6 by the exhaust of the engine 1 is calculated by the following equation. This portion corresponds to pre-applied heat amount calculation means.
Q0 = GE × Cpg × (T0-343)
GE is the exhaust gas mass, and can be determined from the intake air flow rate GA by the following formula: GE = GA × (1 + 1 / 14.6), assuming the theoretical air-fuel ratio (A / F = 14.6). Cpg is exhaust gas specific heat, and is determined in advance from the mass ratio of N ₂ , CO ₂ , and H ₂ O (for example, Cpg = 0.274). T0 is the pre-catalyst inlet temperature (° K), and is obtained from the engine speed NE and the load TP with reference to the engine performance map. However, 343 ° K = 70 ° C was used as a reference.
[0032]
In step 22, the pre-cumulative heat quantity ΣQ0 is calculated by accumulating the amount of heat Q0 given to the pre-catalyst 6 from the start of the engine according to the following equation. This part corresponds to the pre-accumulating means.
ΣQ0 = ΣQ0 + Q0
In step 23, referring to the table of FIG. 7 in which the amount of heat Cp necessary for vaporizing the moisture in the exhaust gas condensed in the container of the pre-catalyst 6 immediately after the engine start is assigned according to the starting water temperature TWst. The pre-required vaporization heat quantity Cp is searched from the actual starting water temperature TWst.
[0033]
In step 24, the pre-cumulative heat quantity ΣQ0 is compared with the pre-necessary vaporization heat quantity Cp. This portion corresponds to pre-comparison means.
If ΣQ0 <Cp as a result of the comparison, the process proceeds to step 25.
That is, it is considered that the heat transfer to the pre-catalyst 6 and after starts after the evaporation of the condensed water in the pre-catalyst is completed, and the amount of heat Q1 transferred to the pre-catalyst 6 and after is set to 0 during the vaporization ( Q1 = 0).
[0034]
On the other hand, when ΣQ0 ≧ Cp, the routine proceeds to step 26.
That is, since the evaporation of the condensed water in the pre-catalyst 6 has been completed, the amount of heat Q1 transferred to the pre-catalyst 6 and thereafter is set to Q0 (Q1 = Q0). Considering heat transfer delay, it is even better. Here, steps 25 and 26 correspond to heat transfer amount calculation means.
In step 27, the reaction heat quantity QP generated in the pre-catalyst 6 is calculated by the following equation. Here, it is assumed that the temperature difference generated heat corresponding to a temperature increase of 50 ° K. This portion corresponds to the reaction heat amount calculation means.
ΔQP = GE × Cpg × 50
(However, when T0 <673 ° K, ΔQP = 0)
[0035]
In step 28, as shown in the following equation, the reaction heat quantity ΔQP is added to the heat quantity Q1 transmitted to the pre-catalyst 6 and the subsequent parts to calculate the pre-catalyst outlet side heat quantity Q2.
Q2 = Q1 + ΔQP
In step 29, the heat release amount ΔQF in the exhaust passage (front tube) from the pre-catalyst 6 to the main catalyst 7 is calculated by the following equation. This portion corresponds to a heat dissipation amount calculation means.
ΔQF = GE × Kft × Aft × ΔT
Kft is the conductivity of the front tube, Aft is the surface area of the front tube, and ΔT is the temperature difference between the pre-catalyst outlet side temperature and the outside air temperature.
[0036]
In step 30, the amount of heat Q3 given to the main catalyst 7 is calculated by subtracting the front tube heat release amount ΔQF from the pre-catalyst outlet side heat amount Q2 as in the following equation.
Q3 = Q2-ΔQF
In step 31, the main accumulated heat amount ΣQ3 is calculated by accumulating the amount of heat Q3 given to the main catalyst 7 from the start of the engine according to the following equation. This part corresponds to the main accumulating means.
ΣQ3 = ΣQ3 + Q3
[0037]
In step 32, referring to the table of FIG. 7 in which the amount of heat Cm necessary to vaporize the moisture in the exhaust gas condensed in the container of the main catalyst 7 immediately after the engine is started according to the starting water temperature TWst, The main required vaporization heat quantity Cm is searched from the actual starting water temperature TWst.
In step 33, the main accumulated heat quantity ΣQ3 is compared with the main required vaporization heat quantity Cm. This part corresponds to the main comparison means.
[0038]
As a result of the comparison, when ΣQ3 <Cm, this routine is finished as it is (while keeping the prohibition flag F = 1).
That is, assuming that the evaporation of the condensed water in the main catalyst 7 has not been completed, the energization of the heater 13a is continuously prohibited by maintaining the prohibition flag F = 1. Therefore, this portion corresponds to heater energization prohibiting means.
[0039]
On the other hand, when ΣQ3 ≧ Cm, the routine proceeds to step 34.
That is, it is considered that the condensed water has been evaporated in the main catalyst 7, and the prohibition flag F is canceled (F = 0). Thereby, as can be seen from FIG. 4, the heater 13a can be energized.
As described above, by comparing the cumulative amount of heat given to the catalyst with a predetermined value and determining whether or not the condensed water has evaporated, the evaporation is completed more accurately than in the case of temperature detection, as can be seen from FIG. The timing can be detected, and the heater control can be started early.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing the configuration of the present invention . FIG . 2 is a diagram showing characteristics after starting. FIG. 3 is a system diagram showing an embodiment of the present invention. Flow chart of start-up routine [FIG. 6] Flow chart of moisture evaporation determination routine [FIG. 7] A diagram showing a necessary vaporization heat amount table [Explanation of symbols]
1 Engine 5 Exhaust passage 6 Pre-catalyst 7 Main catalyst 8 Control unit 9 Air flow meter
10 Crank angle sensor
11 Water temperature sensor
12 Upstream air-fuel ratio sensor
12a heater
13 Downstream air-fuel ratio sensor
13a heater

Claims (5)

The exhaust passage of the internal combustion engine includes an upstream pre-catalyst and a downstream main catalyst as an exhaust purification catalyst, and a heater for heating an air-fuel ratio sensor provided downstream of the main catalyst, and has predetermined operating conditions. In the heater control device for the catalyst downstream air-fuel ratio sensor, the heater is energized to heat the air-fuel ratio sensor.
Pre-applied heat amount calculating means for calculating the amount of heat given to the pre-catalyst every predetermined time based on the operating state of the engine, pre-accumulating means for accumulating the amount of heat given to the pre-catalyst from the start of the engine, and the pre-catalyst Pre-comparison means for comparing the cumulative amount of heat given to a predetermined value, and heat transfer amount calculation means for calculating the amount of heat transferred after the pre-catalyst every predetermined time according to the comparison result, Based on the amount of heat transferred after the pre-catalyst, applied heat amount calculating means for calculating the amount of heat given to the main catalyst ,
Main accumulation means for accumulating the amount of heat given to the main catalyst from the time of engine start,
A main comparator means for comparing the cumulative amount of heat given to the main catalyst and a predetermined value,
As a result of the comparison, heater energization prohibiting means for prohibiting energization of the heater while the cumulative amount of heat given to the main catalyst is a predetermined value or less,
A heater control device for a catalyst downstream air-fuel ratio sensor. The predetermined value for comparison in the main comparison means is the amount of heat necessary for vaporizing the water in the exhaust gas condensed in the main catalyst container immediately after the engine is started, and is variable depending on the cooling water temperature at the time of engine start. The heater control device for a catalyst downstream air-fuel ratio sensor according to claim 1. The predetermined value for comparison in the pre-comparing means is the amount of heat necessary for vaporizing the water in the exhaust gas condensed in the pre-catalyst container immediately after starting the engine, and is variable depending on the cooling water temperature at the time of starting the engine. The heater control device for a catalyst downstream air-fuel ratio sensor according to claim 1 or 2 . The applied heat amount calculating means includes a reaction heat amount calculating means for calculating a reaction heat amount generated in the pre-catalyst, and at least the reaction heat amount is added to the heat amount transferred after the pre-catalyst to add to the main catalyst. The heater control device for a catalyst downstream air-fuel ratio sensor according to any one of claims 1 to 3, wherein the amount of heat applied is calculated. The applied heat amount calculation means has a heat release amount calculation means for calculating a heat release amount in an exhaust passage from the pre-catalyst to the main catalyst, and subtracts at least the heat release amount from the heat amount transferred after the pre-catalyst. The heater control device for the catalyst downstream air-fuel ratio sensor according to any one of claims 1 to 4 , wherein the amount of heat given to the main catalyst is calculated.

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