JPH0641744B2 - Exhaust gas recirculation control device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas recirculation control device for an internal combustion engine.

(Prior Art) In order to suppress the generation of harmful components in combustion exhaust gas of internal combustion engines, especially NO _X , an exhaust gas recirculation system in which a part of the combustion exhaust gas is added to intake air has been widely adopted. There is. This type of system is disclosed, for example, in Japanese Patent Laid-Open No. 59-743.
As disclosed in Japanese Patent Laid-Open No. 64, in addition to calculating a basic target EGR rate (exhaust gas recirculation rate) obtained from a fuel injection amount and a rotation speed of the engine, some basic operating conditions of the engine such as atmospheric pressure are calculated. A correction coefficient corresponding to the value is calculated for each desired operating condition, and the correction coefficient thus obtained is used as the basic target EG.
The R rate is multiplied to obtain the target EGR rate, and the EGR rate adjusting means is closed-loop controlled so that the actual EGR rate becomes the above-mentioned target EGR rate. Such correction calculation means is also disclosed in, for example, Japanese Patent Application Laid-Open No. 59-63356, and these configurations have the advantage that each correction coefficient can be calculated by a map calculation using a three-dimensional map. Have

(Problems to be Solved by the Invention) However, according to the configuration of the above conventional technique,
For example, if the cooling water temperature is high and the load is light during flatland driving, the correction coefficient that should be multiplied by the basic EGR rate becomes too large, and the target value is set within the range in which the actual EGR rate cannot physically exist. Occurs. By the way, in the above control device, in order to check whether or not the closed loop control system is operating normally, whether or not a state occurs in which the difference between the target value and the actual value is equal to or more than a predetermined value for a predetermined time or more. In some cases, a configuration may be adopted in which the control is switched to a backup system prepared in advance, assuming that some kind of failure occurs in the closed-loop control system when the above-mentioned state occurs. When adopted, when the target value becomes a physically non-existent value, the system is switched to the backup system and a failure display is displayed.

In order to solve this kind of defect, it is sufficient to increase the dimension of the map for correcting the above defect or the map data for calculating the correction coefficient (for example, use of a four-dimensional map). With the configuration, the required memory capacity becomes extremely large, which inevitably leads to a direct increase in cost, and as the number of maps increases, the matching process also increases, so the cost of matching increases. This also causes a problem that the price of the device becomes extremely high.

Therefore, an object of the present invention is, therefore, to make it possible to set the target value of the EGR rate within a feasible range without increasing the scale of map calculation. To provide.

(Means for Solving the Problems) According to the present invention, a means for outputting data indicating the operating conditions of the internal combustion engine, and an exhaust gas which responds to a part of the data and which corresponds to the operating conditions of the internal combustion engine at that time Means for calculating and outputting basic target data related to the gas recirculation rate, means for calculating and outputting correction data in response to at least a part of the data and complying with the operating conditions at that time, the basic target data and the correction data Means for responding to the calculation and outputting the corrected target data, adjusting means for adjusting the exhaust gas recirculation rate, means for outputting actual data related to the actual exhaust gas recirculation rate adjusted by the adjusting means, Limiting means for limiting the correction target data so that the exhaust gas recirculation rate indicated by the correction target data becomes a value within a physically possible range, and an output obtained from the limiting means. Means for controlling the adjusting means so that the difference between the actual data and the output data becomes zero in response to the force data and the actual data,
And a means for detecting whether or not a failure has occurred in the control system based on the difference.

(Operation) In order to obtain the target value of the exhaust gas recirculation rate, the correction target data is first calculated by the basic target data and the correction data, and thereafter, the exhaust gas recirculation rate indicated by the correction target data is physically determined. The value of the correction target data is limited so that the value is within a possible range. This limitation of the correction target data limits the upper limit and / or the lower limit of the value of the correction target data obtained by performing the calculation between the basic target data calculated by the map calculation and one or more correction data, respectively. Therefore, the map calculation is not necessary. Therefore, the same memory capacity as before is sufficient, and the target data becomes a value that can actually exist without increasing the calculation scale, and the failure of the closed loop control system is determined based on the difference between the target data and the actual data. However, there is no inconvenience.

(Embodiment) FIG. 1 shows an embodiment of an exhaust gas recirculation control device for an internal combustion engine according to the present invention. The exhaust gas recirculation control device 1 is a device for adjusting the amount (EGR rate) of exhaust gas returned to the intake side of an internal combustion engine (not shown) to an optimum value according to the engine operating conditions at that time. And has a passage 2 for guiding a part of the combustion exhaust gas of the engine to the intake side of the engine. The passage 2 includes an inlet port 2a that communicates with the exhaust side of the engine and an outlet port 2a that communicates with the intake side of the engine.
b. Inlet port 2a to outlet port 2b
To adjust the amount of combustion exhaust gas that is introduced into the passage 2
Inside, a metering valve 4 driven by a negative pressure actuator 3 is provided. Negative pressure chamber 3a of negative pressure actuator 3
Is communicated with a negative pressure source 6 by a pipe 5, and an electromagnetic valve 7 for introducing atmospheric pressure into the pipe 5 is provided in the middle of the pipe 5. The electromagnetic valve 7 has an atmospheric pressure port 7b that is open to atmospheric pressure, and when the electromagnetic valve 7 is in an open state, atmospheric pressure is introduced into the pipe 5 from the atmospheric pressure port 7b. ing. Therefore, by adjusting the opening degree of the solenoid valve 7, the atmospheric pressure introduced into the pipe 5 from the atmospheric pressure port 7b is adjusted, thereby controlling the negative pressure in the negative pressure chamber 3a, and the metering valve 4 The opening degree of can be adjusted to a desired value.

In the illustrated embodiment, the exciting coil 7a of the solenoid valve 7 has a pulse width modulator 8 whose duty ratio is controlled as described later.
Is applied as a drive signal through the amplifier 9, and the solenoid valve 7 is on / off controlled according to its duty ratio, and its average opening degree is adjusted. Reference numeral 10 is a pressure sensor for detecting a negative pressure value in the pipe 5, and the pressure sensor 10 outputs an actual pressure signal indicating the pressure in the pipe 5.
Pa is output. Since the negative pressure actuator 3 operates in response to the pressure in the pipe 5 and the adjustment valve 4 is adjusted,
The actual pressure signal Pa is a signal related to the actual EGR rate.

The actual pressure signal Pa is input as a feedback signal in order to obtain a control signal for closed-loop control of the EGR rate according to the operating state of the internal combustion engine, and it operates in response to a signal indicating the operating state of the internal combustion engine at each time. A control circuit 20 is provided, and the control circuit 20 outputs a control signal CS for controlling the duty ratio of the pulse signal PS output from the pulse width modulator 8. In this embodiment, the first
As shown in the figure, from a sensor unit 21 for detecting the operating state of the internal combustion engine from time to time, a speed signal N indicating the engine speed, a load signal L indicating the load of the engine, and a cooling water temperature of the engine are indicated. The water temperature signal T and the atmospheric pressure signal A indicating the atmospheric pressure are input to the control circuit 20 as signals indicating the operating state.

In order to calculate the basic EGR rate according to the engine speed and the engine load, the control circuit 20 is provided with a basic calculation unit 22 to which the speed signal N and the load signal L are input,
In the basic operation unit 22, the load values L ₁ , L ₂ , ... L _n (L ₁ <L ₁ <according to the operation map shown in FIG.
Basic EG according to the engine speed at that time according to L ₂ <... <L _n )
The value E of the R rate is subjected to map calculation, and basic target data D ₀ indicating the result is output. In order to correct the basic target data D ₀ according to the values of the cooling water temperature and the atmospheric pressure at each time, first and second correction data calculation units 23 and 24 are provided, and the first correction data calculation unit 24 is provided. Is
In response to the velocity signal N and the water temperature signal T, the water temperature values T ₁ , T ₂ , ... T _n (T ₁ <T
₂ <... the first correction value k ₁ according engine speed at the map calculation in response to <T _n), and outputs the first correction data K ₁ showing the value k _1. On the other hand, the second correction data calculation unit 24 responds to the speed signal N and the atmospheric pressure signal A by
According to the calculation map shown in Figure (c), the atmospheric pressure values A ₁ , A ₂ ,
... the second correction value k ₂ maps computation according engine speed at that time in response to _{A n (A 1 <A 2} <... <A n), and outputs the correction data K ₂ indicating the value k _2.

First, the basic target data D ₀ is first calculated in the adder 25.
The correction data K ₁ is added, and the addition result is further added with the second correction data K ₂ in another adder 26,
The adder 26 outputs the correction target data D indicating the correction target EGR rate E _t at that time, that is, the value of E + k ₁ + k ₁ .

The value of the correction target data D obtained as described above may be a value that cannot physically exist under a special condition such as a high cooling water temperature and a low load in flatland traveling. In such a case, for the purpose of limiting the value of the correction target data D within the range in which the actual EGR rate can physically exist, the data D _max indicating the upper limit value E _max of the correction target data D is set.
And a minimum data calculation unit 28 for calculating and outputting the data D _min indicating the lower limit value D _min of the correction target data D. The maximum data calculation unit 27 has a speed signal N and an atmospheric pressure signal A.
In response to, the data D _max indicating the upper limit value E _max at that time is calculated and output according to the atmospheric pressure values A ₁ , ... A _n according to the calculation map shown in FIG. In the illustrated example, the upper limit value E
The value of _max is set only in relation to the value of atmospheric pressure. On the other hand, the minimum data calculation unit 28 also responds to the speed signal N and the atmospheric pressure signals A, in accordance with calculation map shown in FIG. 3 (b), the value A ₁ of the atmospheric pressure, A _2, ... A _n and the engine speed And data D _min indicating the lower limit value E _min at each time according to
Is calculated and output.

The data D _max is input to the first limiting unit 29 together with the correction target data D, and the data having the smaller value of these two data is taken out as the output data D ₁ . Therefore, if the content of the correction target data D is smaller than E _max , the correction target data D is taken out as the output data D ₁ , but if the content of the correction target data D is larger than E _max , the data D _max is output data D _1. As a result, the value of the correction target data D is limited so as not to exceed E _max .

The output data D ₁ is further input to the second limiting unit 30 to which the data D _min is input, and the data having the larger value of these two data is taken out as the output data D ₂ . Therefore, the content of the output data D ₁ is E _min
In the above case, the output data D ₁ is taken out as it is as the output data D ₂ , but if the content of the output data D ₁ is smaller than E _min , the data D _min is taken out as the output data D ₂ . As a result, the value of the data D is limited so as not to be smaller than E _min .

Therefore, the output data D ₂ extracted from the second limiting unit 30 is data indicating the physically possible EGR rate as a target.

The actual pressure signal Pa is input to the data processing unit 31,
Here, the actual EGR rate converted at each time corresponding to the pressure indicated by the actual pressure signal Pa, and the actual data Da indicating this actual EGR rate is the adder 32 to which the output data D ₂ is input.
, The data D ₂ and Da are added with the polarities shown in the figure, and error data De indicating the deviation between the actual EGR rate and the target EGR rate is output.

The error data De is input to the PID control unit 33, where data processing necessary for PID control is performed,
The result is output as the control signal CS, and the switch 34
Is input to the pulse width modulator 8 as a duty ratio control signal. As a result, the average opening degree of the solenoid valve 7 is controlled according to the control signal CS, and the metering valve 4 is driven so that the deviation between the actual EGR rate and the target EGR rate becomes zero.

The device 1 further includes a fault detection unit 35 for detecting whether or not a fault has occurred in the closed loop control system described above in response to the error data De. In addition to the error data De, the actual pressure signal Pa is input to the failure detection unit 35, the negative pressure indicated by the actual pressure signal Pa is within a predetermined range, and the actual EG indicated by the error data De is input.
When the deviation between the R rate and the target EGR rate does not exceed the predetermined value continuously for a predetermined time or longer, it is determined that the control system is operating normally. When the failure detection unit 35 determines that the control system is functioning normally, the operation signal OS switches the switch 34 as indicated by the solid line, and the control signal CS is input to the pulse width modulator 8. It On the other hand, when the failure detection unit 35 determines that some failure has occurred in the control system,
In other words, the negative pressure indicated by the actual pressure signal Pa is not within the predetermined range, and / or the deviation between the actual EGR rate and the target EGR rate continues to be a predetermined value or more and continues for a predetermined time or more. In this case, the switch 34 is switched by the operation signal OS as shown by the dotted line. As a result, instead of the control signal CS, the preliminary control signal CT output from the preliminary control signal output unit 36 is input to the pulse width modulator 8, and the average opening degree of the solenoid valve 7 is controlled according to the preliminary control signal CT. .

The preliminary control signal output unit 36 can be configured, for example, so that the data indicating the temporary target EGR determined according to the speed of the engine is output as the preliminary control signal CT, but the solenoid valve is opened. Data for setting the EGR rate to zero may be output as the preliminary control signal CT.

According to such a configuration, the data D indicating the target EGR rate is obtained by adding the calculation results based on the three-dimensional maps in each of the units 22, 23, 24, and the value of the target EGR rate obtained as a result is obtained. , The data D _max and D _min are limited by the first and second limiting units 29 and 30 within the physically possible range. As a result, the first
If the closed-loop control system shown in the figure is operating normally, the actual EG
Since the R rate always changes in accordance with the target EGR rate indicated by the output data D ₂ , the failure detection unit 35 does not switch the switch 34 to the side of the preliminary control signal output unit 36. Here, the calculation of the target EGR rate is
Since all can be performed by the three-dimensional map calculation, the circuit scale does not increase due to the calculation of the target EGR rate.

The control circuit 20 shown in FIG. 1 can also be realized by using a microcomputer and executing a predetermined control program by the microcomputer.

FIG. 4 is a flow chart showing an example of such a control program for obtaining a control function equivalent to that of the control circuit 20 shown in FIG. Explaining this flowchart, after initialization is performed in step 41, it is determined in step 42 whether or not the flag F _E that becomes "1" when the control system has a failure is "1". , F _E = “0”, each signal from the sensor unit 21 and the actual pressure signal Pa are input as data (step 43), and the basic target EGR rate E, the first correction value k ₁ , the second correction value ₂ , the upper limit value E _max and the lower limit value E _min are respectively calculated in steps 44 to 48, and the correction target at that time is calculated.
The EGR rate E _t is calculated (step 49). After that, E
_It is determined whether _max ≧ E _t (step 50). If the result of this determination is YES, the process proceeds to step 51, where E _t ≧
It is determined whether E _min or not. Steps 50 and 51
If both of the determination results are YES, that is, E _min ≤E _t ≤
In the case of E _max , the value of E _t is the final target EGR rate E
_{t '} (step 52). On the other hand, if the determination result of step 50 is NO, then E _{t ′} = E _max is set (step 53), and if the determination result of step 51 is NO, then E _{t ′} = E _{max.
t '} = E _min is set (step 54).

As described above, the value of the target EGR rate E _{t ′} is calculated in step 4
9 is limited to a value that can physically exist regardless of the value of the calculation result in 9, and in step 55, the deviation ΔE between this target EGR rate _{Et ′} and the actual EGR rate Ea is calculated, and this value ΔE is determined. It is determined whether or not the value is α or more (step 56). If ΔE is smaller than α, step 5
The determination result of 6 is NO, the value of the variable C is set to zero (step 57), and the PID calculation based on the value of ΔE is performed (step 58). The result of this calculation is the pulse width modulator 8
Is output as a control signal CS for duty ratio control with respect to (step 59), and the process returns to step 42.

If the determination result of step 56 is YES, step 6
The process proceeds to 0, the value of the variable C is increased by 1, and it is determined in step 61 whether or not the value of C is equal to or larger than a predetermined constant B. If C <B, step 58
Then, the EGR rate is controlled based on the calculation result of step 55. However, the condition of ΔE ≧ α continues, and C ≧
When it becomes B, the determination result of step 61 becomes YES, the control of the EGR rate is stopped at step 62, the flag F _E is set to "1" (step 63), and the failure display of the control loop is performed (step 64). ), Step 42
Return to.

In each of the above examples, the maximum and minimum values of the target EGR rate are calculated, and the target EGR rate is limited so that the target EGR rate falls within this range.However, the target EGR rate is the minimum value described above. In the following cases, it is considered that the map calculation system described above rarely occurs. Therefore, only the maximum value may be limited.

(Effect) According to the present invention, as described above, in order to obtain the target value of the exhaust gas recirculation rate, the basic target data and the correction data are calculated separately, and thereafter, the correction target data is calculated using these data. Further, the correction target data is limited so that the exhaust gas recirculation rate indicated by the correction target data becomes a value within a range in which it can physically exist, and the limited data is exhausted. Since the configuration is used as the target value for control, the calculation for obtaining the target exhaust gas recirculation rate that matches the operating conditions of the internal combustion engine can be performed without making it large-scale and complicated, and the target The exhaust gas recirculation rate can be set as a value that is actually feasible. As a result, an unrealizable target value is set, and the deviation between the target value and the actual value is not reduced below a predetermined value by the control, and it is indistinguishable from the case where a failure occurs in the control system. Since there is no possibility of causing a malfunction, it is possible to obtain an effect that the failure monitoring of the control loop based on this deviation can be performed with high reliability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
(a) to FIG. 2 (c), FIG. 3 (a) and FIG. 3 (b) are characteristic diagrams showing the characteristics of the map calculation in the control device shown in FIG.
FIG. 4 is a flow chart showing an example of a control program when a control function equivalent to the control circuit of the control device shown in FIG. 1 is realized by a microcomputer. 1 ... Exhaust gas recirculation control device, 4 ... Metering valve, 7 ...
Solenoid valve, 10 ... pressure sensor, 20 ... control circuit, 21
...... Sensor unit, 22 …… Basic operation unit, 23
...... First correction data calculation unit, 24 ...... Second correction data calculation unit, 25, 26, 32 ...... Adder, 27
...... Maximum data calculation unit, 29 ...... First limit unit, 35 …… Fault detection unit, D ₀ …… Basic target data, K ₁ , K ₂ …… Correction data, D …… Correction target data,
D _max ... data, D ₂ ... output data, De ... error data, CS ... control signal.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masato Ueno Masato Ueno 3-13-26, Yasumi-cho, Higashimatsuyama-shi, Saitama Diesel Equipment Co., Ltd. Higashimatsuyama Factory (56) Reference JP-A-55-123345 (JP, A) Japanese Patent Laid-Open No. 59-60060 (JP, A)

Claims (1)

[Claims] 1. A means for outputting data indicating an operating condition of an internal combustion engine, and basic target data related to an exhaust gas recirculation rate corresponding to a current operating condition of the internal combustion engine in response to a part of the data. Means for calculating and outputting, means for calculating and outputting correction data in response to at least a part of the data and complying with the operating conditions at that time, and means for calculating and outputting correction target data in response to the basic target data and the correction data Adjusting means for adjusting the exhaust gas recirculation rate, means for outputting actual data related to the actual exhaust gas recirculation rate adjusted by the adjusting means, and the exhaust gas recirculation rate indicated by the correction target data In response to the limiting means for limiting the correction target data so that the correction target data is a value within a physically possible range, and the output data and the actual data obtained from the limiting means. A means for controlling the adjusting means so that the difference between the data and the output data becomes zero; and a means for detecting whether or not a failure has occurred in the control system based on the difference. Exhaust gas recirculation control device for internal combustion engine.