JPS5885321A - Control method of supercharge pressure in turbosupercharged engine - Google Patents

Abstract

PURPOSE:To correct a value of the atmospheric condition and correct supercharge pressure, by calculating feedback air fuel ratio (air fuel ratio in an engine combustion chamber) on the basis of a feedback signal from an air fuel ratio sensor and correcting the ratio on the basis of a deviation of the feedback air fuel ratio from the basic air fuel ratio. CONSTITUTION:Conditions of idling (range A), low load (range B) and high load (range C) of an engine are detected, on the basis of a feedback signal from an air fuel ratio sensor 32, feedback air fuel ratio is calculated and a deviation of the feedback air fuel ratio from the basic air fuel ratio is calculated. If the deviation is at least a prescribed value in the three ranges A, B, C, the cause is decided due to change of a condition of the atmosphere, as the deviation becomes rich the opening of an exhaust relief valve 26 is decreased to increase rotary speed of a turbine 23 and supercharge pressure. As the deviation becomes lean, the opening of the valve 26 is increased to decrease the rotary speed of the turbine 23 and the supercharge pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for controlling the boost pressure of a turbocharged engine having a turbocharger in its intake system in relation to atmospheric conditions.

In particular, atmospheric conditions such as air density change depending on temperature, altitude, humidity, etc., but if boost pressure is controlled to be constant regardless of atmospheric conditions, engine operating performance will change as atmospheric conditions change. also changes.

In addition, since boost pressure has a significant impact on engine durability and supercharger heat resistance, it is necessary to determine durability and heat resistance by considering atmospheric conditions. Various sensors are required for detection. Therefore, in conventional turbocharged engines, the boost pressure is set to ensure the specified engine operability, engine durability, etc. even under the worst atmospheric conditions, so fuel consumption efficiency deteriorates under normal atmospheric conditions. , a problem such as a drop in output has occurred.

In addition, in electronically controlled fuel injection engines that calculate the fuel injection amount based on the intake air flow rate and supply fuel by operating the fuel injection valve based on this calculation result, the air density is determined by factors such as the atmospheric temperature and the vehicle's driving altitude. The air-fuel ratio of the air-fuel mixture in the combustion chamber must be kept at a predetermined value because the output characteristics of the air flow meter that detects the intake air flow rate change with the accumulation of dirt on the intake wall of the air flow meter. In order to maintain this, it is necessary to calculate a correction value related to changes in atmospheric conditions or the output characteristics of the air flow meter, and to correct the fuel supply amount based on this correction value.

Furthermore, in order to prevent fuel evaporative gas from being released into the atmosphere from the fuel tank, the fuel evaporative gas is adsorbed by activated carbon as an adsorbent, and the adsorbed fuel evaporative gas is released into the intake system during engine operation. In an engine that is purged, the air-fuel ratio of the air-fuel mixture, that is, the output of the air-fuel ratio sensor, changes not only in relation to the fuel supplied from the fuel injection valve but also in relation to the amount of fuel evaporative gas released. The normal method of calculating the correction value described above is to calculate the return air-fuel ratio (the feedback air-fuel ratio represents the actual air-fuel ratio in the engine combustion chamber) based on the feedback signal from the air-fuel ratio sensor, and then calculate the basic air-fuel ratio. The above-mentioned correction value is corrected based on the deviation of the return air-fuel ratio from the fuel ratio, but when engine operation is briefly stopped and then restarted, the air-fuel ratio sensor is appropriately heated to generate an effective output. Since it takes a predetermined period of time to complete the process, the fuel injection amount is calculated by open-loop control by cutting off the feedback signal from the air-fuel ratio sensor during this predetermined period of time and when the engine is at low temperature. In this case, the purge of fuel evaporative gas to the intake system is stopped, and the fuel injection amount and ignition timing are corrected based on the final correction values from the previous engine operation.

Corrections of the correction value due to the release of fuel vapor into the intake system must be avoided.

Therefore, the present applicant has proposed a method for correcting correction values related to atmospheric conditions using learning control without being affected by changes in the air flow meter's output characteristics caused by dirt, etc., and by fuel evaporation gas, etc. No. 56-106255.

An object of the present invention is to provide a supercharging pressure control method for a turbocharged engine that can satisfactorily control supercharging pressure in connection with the learning control of correction values related to atmospheric conditions as disclosed in Japanese Patent Application No. 56-106255. The goal is to provide the following.

In order to achieve this object, the present invention provides a boost pressure control method for a turbocharged engine equipped with a turbocharger in the intake system, in which the engine is controlled in an idling state, a low load state, and a high load state. is detected, first, second, and third data are provided corresponding to the operating status of each engine, and the feedback air-fuel ratio is calculated based on the feedback signal from the air-fuel ratio sensor, and the return air-fuel ratio is calculated based on the feedback signal from the air-fuel ratio sensor. Based on the deviation of the feedback air-fuel ratio, the data corresponding to the detected engine operating state is corrected, and if at least two pieces of data have a difference of more than a predetermined value from the reference value, the air-fuel ratio becomes the basic air-fuel ratio. Increase or decrease the boost pressure so that it approaches the air-fuel ratio.

Further, according to the present invention, in a boost pressure control method for a turbocharged engine equipped with a turbocharger in the intake system, an idle link state, a low load state, and a high load state of the engine are detected, and these states are detected. The first, second,
The feedback air-fuel ratio is calculated based on the feedback signal from the air-fuel ratio sensor, and based on the deviation of the feedback air-fuel ratio from the basic air-fuel ratio, data corresponding to the detected engine operating state is calculated. If at least two pieces of data have a difference of a predetermined value or more from the reference value, the atmospheric condition positive value is corrected, and the supercharging pressure is calculated based on this atmospheric condition correction value.

The present invention will be explained with reference to the drawings. - Figure 1 shows an overall schematic diagram of an electronically controlled engine equipped with a turbocharger. Air taken in from the air cleaner 1 passes through an air flow meter 2, the flow rate of which is controlled by a throttle valve 3 that is linked to an accelerator pedal (not shown) in the driver's cab, and is sent to the engine body via a surge tank 4 and an intake pipe 5. It reaches the combustion chamber 7. The combustion chamber 7 is divided by a cylinder head 8, a cylinder block 9, and a piston 1o,
After the fuel sucked through the intake valve 13 is combusted, it becomes exhaust gas and is sent from the exhaust valve 14 to the exhaust branch pipe 15. Catalytic converter 16 is commonly found in the exhaust system and contains a well-known three-way catalyst that promotes the oxidation of carbon monoxide and hydrocarbons and the reduction of nitrogen oxides in the exhaust gas. The turbo supercharger 19 has an air flow meter 2 in the intake passage 20.
The compressor (two superchargers) 21 is disposed between the throttle valve 3 and the compressor 2 disposed within the exhaust passage 22.
1 as a drive unit, and the turbine 23
The compressor 21 is provided with a shaft 24 that transmits the rotation of the compressor 21 to the compressor 21. The bypass passage 25 is provided in parallel to the exhaust passage portion of the turbine 23, and its flow cross-sectional area is controlled by an exhaust relief valve 26. EGR (exhaust gas recirculation) passage 27
connects the exhaust branch pipe 15 and the surge tank 4, and connects the EGR
A control well 30 controls the flow cross section. fuel injection valve 3
1 is attached to the intake pipe 5 and injects fuel toward the combustion chamber 7. The air-fuel ratio sensor 32 is provided in the exhaust system downstream of the turbine 23, and detects the air-fuel ratio based on the oxygen concentration in the exhaust gas. The pressure sensor 33 is provided in the intake system downstream of the compressor 21 and detects the discharge pressure of the compressor 21, that is, the boost pressure. The throttle position sensor 34 detects the opening degree of the throttle valve 30, the water temperature sensor 35 detects the cooling water temperature of the engine, the knock sensor 36 detects knocking from the vibration of the cylinder block 9, and the crank angle sensor 37 detects the opening of the power distributor 38. The crank angle is detected from the rotation of the shaft 390, and the vehicle speed sensor '42 detects the vehicle speed from the rotation of the output shaft of the automatic transmission 43. An electronic control unit 44 receives input from these sensors and sends output to a controller 45 for the actuators of the fuel injection valve 31 and exhaust relief valve 26.

FIG. 2 is a block diagram of the inside of the electronic control unit 44 shown in FIG. '1. Since the outputs of the air flow meter 2, pressure sensor 33, water temperature sensor 35, and knock sensor 36 are analog signals, they are sent to an A/D (analog/digital) converter 49 with a multiplexer. Output pulses from the air-fuel ratio sensor 32, throttle position device sensor 34, crank angle sensor 37, vehicle speed sensor 42, etc. are sent to the buffered personnel output interface 5o, and the output of the personnel output interface 50 is sent to the fuel injection valve 31 and It is sent to the controller 45. A/
D computer 49, attendance counter interface 50. C
PU (Central Processing Unit)51. ROM (read-only storage device) 52, RAMG, arbitrary access storage device) 53
, 54 are connected to each other by a bus 55, and the RAM 54
C-RAM (Complementary RAM) It is connected to an auxiliary power source and can retain memory even when the engine is stopped.

Figure 3 shows the relationship between the intake air flow rate and the air-fuel ratio deviation caused by the output error of air flow meter 2 (solid line), the release of fuel evaporative gas into the intake system (dashed line), and changes in atmospheric conditions (dotted-dash line). It shows. Note that FIGS. 3, 5, and 5 have already been disclosed by the present applicant in the earlier patent application No. Sho! Y6-106255, and please refer to that patent application for details. The stoichiometric air-fuel ratio corresponds to the deviation -〇.Ql < Q2 < Q3 < Q4 < Q
There is a relationship of 5 < Q6, where Q2 corresponds to the intake air flow rate when the throttle switch of the throttle position sensor 34 is reversed from on to off. is on when the rotation angle of the throttle valve shaft is 1.5 degrees or less, and is off when the throttle valve 3 is opened more than the idling opening. First region A (Ql<Q<92),
Ql or Ql so that region B of durability 2 (Q3<Q<Q4) and third region C (Q5<Q<96) correspond to the idle link state, low load state, and high load state of the engine, respectively. Q6 is selected, and the first to third value ranges A, B, and C do not overlap with respect to the intake air flow rate Q and are separated from each other. The air-fuel ratio deviation caused by the accumulation of dirt on the inner wall of the air flow meter 2 increases as the intake air flow rate decreases. The deviation in the air-fuel ratio due to the release of fuel evaporative gas is zero in the first region A, maximum in the second region B, and decreases in the third region C. Deviations in air-fuel ratio due to changes in atmospheric conditions such as altitude and intake temperature are constant regardless of intake air flow rate. The above is summarized in the table below.

In Figure 3, deviations in the air-fuel ratio due to changes in atmospheric conditions appear on the rich side compared to the stoichiometric air-fuel ratio, but this is because the air density decreases, for example when a car moves from a plain to a highland. On the other hand, when a car moves from a highland to a plain, the air density increases, so in this case the air-fuel ratio deviation appears on the lean side with respect to the stoichiometric air-fuel ratio. Assuming that the deviation in the stoichiometric air-fuel ratio is zero, and that the deviations on the lean side and rich side are positive and negative, respectively, the total deviation of the air-fuel ratio as a result of combining these causes is calculated by superimposing the characteristic lines in Figure 3. Almost equivalent to quarrel. Therefore, from the above characteristic analysis, if the total deviation is equal to or greater than the rating value in the three regions A, B, and C, it can be determined that a deviation in the air-fuel ratio has occurred due to changes in atmospheric conditions; The difference between the total deviation in A and the total deviation in the third area C is the second
If the difference between the total deviation in region B and the total deviation in third region C is greater than the difference, it can be determined that a deviation in the air-fuel ratio is caused by the air flow meter.

FIG. 4 is a flowchart of a program for calculating and storing deviation data.

In step 74, the average value of the intake air flow rate per two cycles of air-fuel ratio feedback control is calculated from the detection signal of the air flow meter 2. Step 3 75 calculates the deviation of the average return air-fuel ratio from the stoichiometric air-fuel ratio in the same two cycles as the two cycles in step 74. The unit of D is %, and a deviation on the lean side from the stoichiometric air-fuel ratio is positive, and a deviation on the rich side from the stoichiometric air-fuel ratio is negative. FIG. 5 illustrates the return air-fuel ratio. 81 is the output of the air-fuel ratio sensor 32;
S2 is an integral value of the output of the air-fuel ratio sensor 32 as the feedback air-fuel ratio. Note that this integral value is calculated by the CPU 51. The output of the air-fuel ratio sensor 32 is 1 when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio, that is, when the mixture is too rich.
It becomes 0 when the air-fuel ratio is larger than the stoichiometric air-fuel ratio, that is, when the air-fuel mixture is lean. CPt15t decreases the integral value S2 by a predetermined amount a at predetermined time intervals during the period when the output S1 of the air-fuel ratio sensor +1-32 is maintained at 1, and the output S1 of the air-fuel ratio sensor 32 is maintained at 0. In the period, the integral value S2 is increased by a predetermined amount a at predetermined time intervals. Further, when the output S1 of the air-fuel ratio sensor 32 is reversed, the integral value s2 is increased or decreased by another predetermined amount b (baa). a and b are changed in relation to vehicle speed, and b is set to improve responsiveness. The integral value s2 corresponds to the actual air-fuel ratio of the air-fuel mixture in the combustion chamber 7, that is, the return air-fuel ratio.

In step 76, it is determined whether or not the throttle switch of the throttle position sensor 34 is on. If the determination result is positive, the process proceeds to step 77; otherwise, the process proceeds to step 82. In step 77, it is determined whether or not Ql<Q<Q2, that is, whether or not the operating state of the engine is in the first region A. If the determination result is positive, the process proceeds to step 78; if not, this step is determined. Exit the program. In step 78, the first
Let 1/2 of the sum of the values MA and D of the first storage section M1 provided for area A of < MA be the new MA.
+'-MA). The value MA is cleared when the engine is stopped or when steps 109 and 124 (FIGS. 6 and 8) described below are executed. Instead of using D as a new MA, -2”- becomes a new MA.
The reason for this is to prevent MA from taking a completely unrelated value due to unforeseen causes and to improve the reliability of MA.

In step 79, the value C1 of the first counter provided for the first area A is incremented by one. The value C1 of the first counter is cleared when the engine operation is stopped or in steps 109 and 124 described later.

In step 8Q, it is determined whether the value C1 of the first counter is 3 or more, and if the determination result is positive, step 81
Proceed to , and if not, terminate the program. For example, even if the first D contains an error of 1096, step 79
By repeating 3 times, the MA error is 2.5% (=10
%÷2÷2), and the reliability of MA increases. In step 81, the first flag pit FA is changed from 0 to 1. Flag bit FA=l indicates that MA is sufficiently reliable.
It means that it is in a state. In step 82, Q2
It is determined whether or not < Q < Q4, that is, whether the operating state of the engine is in the second region B. If the determination result is positive, the process proceeds to step 83, and if not, the process proceeds to step 87. .

Steps 83, 84, 85, and 86 correspond to steps 78, 79, 80, and 81 described above. That is, in step 83, 1/2 of the sum of the values MB and D in the second storage section M2 provided for the second area B is set as a new MB (, uB-+-, I7- →MB). In step 84, for the second area B, the value C2 of the 20th counter provided is incremented by 1. Step 85
Then, it is determined whether the value C2 of the second counter is 3 or more, and if the determination result is positive, the process proceeds to step 86, and if not, the program is terminated. , in step 86 the second
flag) Set FB to 0 or 1.

In step 87, it is determined whether Q5 < (2 < Q6, that is, whether the operating state of the engine is in the third region C. If the determination result is positive, the process proceeds to step 88.
If not, terminate this program.

Steps 88, 89, 90, and 91 correspond to the aforementioned steps 78, 79, 80, and 81, respectively. That is, in step 88, 1/2 of the sum of the values MC and D in the third storage section M3 provided for the third area C is set as a new MC ( , -1→MC). Step 89
Then, the value C3 of the third counter provided for the third area C is incremented by 1. In step 9.degree., it is determined whether or not the value c3 of the third counter is 3 or more. If the determination result is positive, the program proceeds to step 91, and if not, the program is terminated.

In step 91, the third flag pick) changes the FC from 0 to 1.
Make it.

FIG. 6 shows the first to third storage units Ml, M2,
The value of M3, that is, the deviation data MA, MB', M
3 is a flowchart of a program for correcting supercharging pressure P based on C. At step 100, the flag picks) FA
.

Determine whether or not FB are both 1. If the determination result is positive, proceed to step 101; if not, proceed to step 102
Proceed to. In step 101, deviation data MA, M
It is determined whether or not B is both 2% or more, that is, there is a deviation of 2% or more toward the lean side with respect to the stoichiometric air-fuel ratio. If the determination result is positive, proceed to step 106; otherwise, step 104.
Proceed to. In step 102, the flag is FB,
It is determined whether or not both FCs are 1. If the determination result is positive, the process proceeds to step 103, and if not, the process proceeds to step 108. In step 103, it is determined whether the deviation data MB and MC are both 2% or more, that is, whether there is a deviation of 2% or more toward the lean side with respect to the basic air-fuel ratio. If the determination result [is positive, the process advances to step 106; If so, proceed to step 104.

When a vehicle moves from a highland to a plain, the return air-fuel ratio shifts to the lean side in the first, second, and third regions A, B, and C, as is clear from the above analysis in Figure 3. deviates by more than a predetermined value. However, in some cases, the engine is not operated in the third area C, but only in the first and second areas A, B, i.e. when the vehicle descends from a highland to a plain area without running under high load. Alternatively, it is expected that the engine will not be operated in the first area A but only in the second and third areas B and C, that is, the vehicle will descend from a highland to a plain area without stopping on the way. Therefore step 10
1, 103, both deviation data MA and MB are 296 or more, or deviation data MA, M
Both B are 2% or more, or deviation data MB
, MC are both 296 or more, it is assumed that the air density has increased due to a decrease, and step 106 described below is performed.
will be implemented.

In step 104, it is determined whether the flag, bits FA, FB, and FC are all 1 or not, and if the determination result is positive, the process proceeds to step 105; otherwise, the process proceeds to step 108. In step 105, the deviation data MA, MB
, determine whether the MC is 13% or less, that is, whether the return air-fuel ratio deviates more than 3% toward the rich side with respect to the 1' theoretical air-fuel ratio, and if the determination result is positive. BA STETSU°
If not, the process proceeds to step 108. If the determination result in step 105 is positive, it means that the air density has decreased due to the increase in altitude of the car, etc.
In this case step 107 is performed. Step 1
A negative determination result of 05 indicates that there is no change in air density, and in this case, step 108 is executed.

In step 106, when there is a change in atmospheric conditions such as an increase in air density, the supercharging pressure P at that time minus a predetermined value Ap is set as a new supercharging pressure P, and the supercharging pressure is decreased. In step 107, if there is a change in atmospheric conditions such as a decrease in air density, the predetermined value Ap of the supercharging indenter at that time is determined.
The supercharging pressure P is increased by setting the supercharging pressure P to ml. An increase in the boost pressure P increases the number of molecules of intake air sent to the combustion chamber 7, and a decrease in the boost pressure P decreases the number of molecules of intake air sent to the combustion chamber 7.

By increasing and decreasing the boost pressure in steps 106 and 107, the air-fuel ratio approaches the stoichiometric air-fuel ratio as the basic air-fuel ratio. In step 108, the boost pressure P is not corrected. The supercharging pressure P set in steps 106, 107, and 108
is stored in the c'-RAM 54, stored even when the engine is stopped, and used when the next engine operation starts. Supercharging H'p
To decrease the opening of the exhaust relief valve 260, the rotation of the turbine blade is decreased by increasing the opening of the exhaust relief valve 260, and to increase the boost pressure P, the opening of the exhaust relief valve 26 is decreased to reduce the rotation of the turbine blade.
Increase 0 rotation. FIG. 7 shows the relationship between the difference in the feedback air-fuel ratio with respect to the stoichiometric air-fuel ratio and the supercharging pressure P. As the difference increases, that is, as the air-fuel ratio shifts to the lean side due to a large flow rate of intake air, the supercharging pressure P is decreased. In step 109, data MA, MB, M
C, counters C1, C2, C3, and flags FA, F
B. Clear FC.

FIGS. 8 and 9 are flowcharts of programs according to other embodiments of the present invention. The program shown in FIG. 8 calculates the atmospheric condition correction value FHAC, and the program shown in FIG. 9 calculates the supercharging pressure P based on FHACK calculated by the program shown in FIG. Steps 115 to 118 are the same as steps 100 to 103 in FIG. 6, and their explanation will be omitted. If the determination result in step 116 is positive, the process proceeds to step 119; if not, the process proceeds to step 121. If the determination result is negative in step 117, the program is terminated. If the discrimination result is positive in step 118, proceed to step 120; if the discrimination result is distorted, proceed to step 1.
Proceed to 21. In step 119, the atmospheric condition correction value FHA is
The value obtained by adding ° deviation data MA to C, (FHAC + MA
) is the new FHAC.

In step 120, a value obtained by adding the deviation data MC to the atmospheric condition correction value FHAC (FHAC+MC) is set as a new atmospheric condition correction value. The reason why the deviation data MB is not used in steps 119 and 120 and the deviation data MA or MC is used is because the deviation data MA or MC is significantly affected by the release of fuel evaporative gas compared to the deviation data MB. This is because there are few. Step 121
Then, it is determined whether the flags FA, FB, and FC are all 1, and if the determination result is positive, step 12
Proceed to step 2, and if not, terminate this program. In step 122, it is determined whether the deviation data MA, MB, and MC are all less than -396, that is, whether they deviate from the stoichiometric air-fuel ratio by 3% or more toward the enriched side. If the determination result is positive, then Go to step 123; if not, end this program. In step 123, the one closest to zero among the deviation data MA, MB, and MC is added to the atmospheric condition correction value (in other words, the deviation data MA).

The smallest value among the absolute values of MB and MC is subtracted from the atmospheric condition correction value FHAC, and the value resulting from the calculation is used as the new atmospheric condition correction value. The smallest deviation data was selected because it is least likely to be affected by other influences other than changes in atmospheric conditions, such as fuel vapor emissions.

In step 126 of FIG. 9, supercharging pressure P=Po+C(1
,0-FHAC). However, Po is the basic value of boost pressure, and C is a constant. Further, in this formula, FHAC is expressed as a decimal. As explained above with reference to FIG. 7, the more the air-fuel ratio shifts to the lean side, the more the boost pressure P decreases.

As described above, according to the present invention, changes in atmospheric conditions are detected from the difference between the return air-fuel ratio and the basic air-fuel ratio (for example, the stoichiometric air-fuel ratio),
Boost pressure is set based on changes in atmospheric conditions. As a result, boost pressure is controlled to an appropriate value related to atmospheric conditions, and even under the worst atmospheric conditions, fuel consumption efficiency and output are maintained without affecting engine durability or supercharger heat resistance. It can be improved.

[Brief explanation of the drawing]

FIG. 1 is an overall schematic diagram of a supercharged engine to which the present invention is applied;
Figure 2 is a block diagram of the electronic control unit in Figure 1, Figure 3 is a graph showing air-fuel ratio deviations due to changes in atmospheric conditions, etc., and Figure 4 is a flowchart of a program that calculates and stores deviation data. , FIG. 5 is a diagram illustrating the relationship between the output of the air-fuel ratio' sensor and the return air-fuel ratio, FIG. 6 is a flowchart of a program for calculating boost pressure in the first embodiment of the present invention, and FIG. A graph showing the relationship between the difference in the return air-fuel ratio with respect to the stoichiometric air-fuel ratio and the supercharging pressure P, FIG. 8 is the second embodiment of the present invention.
FIG. 9 is a flowchart of a program for calculating the atmospheric condition correction value in the embodiment. FIG. 9 is a flowchart of a program for calculating the boost pressure based on the atmospheric condition correction value. 2... Air flow meter, 19... Turbo supercharger,
20... Intake passage, 21... Compressor, 26...
...Exhaust relief valve, 32...Air-fuel ratio sensor, 44...
Electronic control unit.

Claims (1)

[Claims] 1. A boost pressure control method for a turbocharged engine equipped with a turbocharger in the intake system, which detects an idle link state, a low load state, and a high load state of the engine, and detects these states. The first, second, and third data are provided corresponding to the operating state of each engine, and the return air-fuel ratio is calculated based on the feedback signal from the air-fuel ratio sensor, and the return air-fuel ratio is calculated based on the feedback signal from the air-fuel ratio sensor. Based on the deviation, the data corresponding to the detected engine operating state is corrected, and if at least two pieces of data have a difference of more than a predetermined value from the reference value, the air-fuel ratio approaches the basic air-fuel ratio. A method for controlling the boost pressure of a turbocharger, which is characterized by increasing and decreasing the boost pressure as follows. 2. In a boost pressure control method for a turbocharged engine equipped with a turbocharger in the intake system, the idling state, low load state, and high load state of the engine are detected, and the operating state of each of these engines is adjusted. Correspondingly, first, second, and third data are provided, a return air-fuel ratio is calculated based on the feedback signal from the air-fuel ratio sensor, and the detected air-fuel ratio is calculated based on the deviation of the return air-fuel ratio from the basic air-fuel ratio. The data corresponding to the engine operating state is corrected, and if at least two data have a difference of more than a predetermined value from the reference value, the atmospheric condition correction value is corrected, and the atmospheric condition correction value is corrected based on this atmospheric condition correction value. 1. A method for controlling boost pressure of a turbocharger, characterized in that boost pressure is calculated using the following steps.