JP2008025404A - Calibrating device for cylinder pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the variation of the sensitivity of cylinder pressure sensors provided at a plurality of cylinders. <P>SOLUTION: This calibrating device for the cylinder pressure sensor includes a means S103 for measuring cylinder pressure at each cylinder at predetermined two points of timing by means of the cylinder pressure sensors, a means S104 for calculating the differential pressure of the measured cylinder pressure at each cylinder, and a means S108 for calculating sensor sensitivity correction coefficients of the cylinder pressure sensors of the cylinders other than a predetermined reference cylinder on the basis of the differential pressure of the predetermined reference cylinder and the differential pressure of the cylinders other than the reference cylinder. Based on the cylinder pressure sensor of the reference cylinder, the sensor sensitivity correction coefficients of the cylinder pressure sensors of the cylinders other than the reference cylinder are calculated and the variation of the sensor sensitivity between and among the cylinders can be eliminated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a calibration apparatus for an in-cylinder pressure sensor, and more particularly to an apparatus for calibrating an in-cylinder pressure sensor provided in at least two cylinders of a multi-cylinder internal combustion engine.

  2. Description of the Related Art In recent years, control devices for internal combustion engines have been developed that detect in-cylinder combustion states using in-cylinder pressure detected by an in-cylinder pressure sensor and control various control amounts such as ignition timing based on the results. Yes. In the case of a multi-cylinder internal combustion engine, an in-cylinder pressure sensor is provided in each cylinder, and control based on the detected in-cylinder pressure is performed for each cylinder. As a related art related to this in-cylinder pressure sensor, Patent Document 1 compares the intake air amount calculated from the combustion pressure with the intake air amount calculated from the intake pipe pressure, and the sensitivity of the combustion pressure sensor is based on the latter. There is disclosed a technique for calculating an abnormality of a combustion pressure sensor based on whether or not the calculated value of the sensitivity of the combustion pressure sensor falls within a predetermined range.

No. 7-55303

  Incidentally, the sensitivity of the in-cylinder pressure sensor has variations due to individual differences, mounting loads, and the like. Therefore, there is variation among cylinders in the in-cylinder pressure measured by the in-cylinder pressure sensor. On the other hand, the measured in-cylinder pressure value is processed by the same control logic for all cylinders. Therefore, if there is a variation in the in-cylinder pressure value, various control amounts as a result of the calculation will inevitably vary, which improves fuel consumption and emissions. It will cause trouble.

  In general, the measurement range of the in-cylinder pressure sensor covers a relatively wide range of 0 to several MPa. However, in recent years, in-cylinder air amount is measured as one of the application controls of the in-cylinder pressure sensor. In this case, a low pressure portion of several hundred kPa or less is used in the measurement range of the in-cylinder pressure sensor, and several kPa is used. Order measurement accuracy is required. Therefore, the use of such a low pressure part inevitably increases the influence of sensitivity variations of the in-cylinder pressure sensor, and an effective improvement measure is awaited.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a calibration apparatus for an in-cylinder pressure sensor that can effectively eliminate variations in sensitivity of the in-cylinder pressure sensor.

  In order to achieve the above object, an in-cylinder pressure sensor calibration apparatus according to an aspect of the present invention is an apparatus for calibrating an in-cylinder pressure sensor provided in at least two cylinders of a multi-cylinder internal combustion engine, the in-cylinder pressure sensor. Measuring means for measuring in-cylinder pressure at each predetermined timing for each cylinder, and differential pressure calculating means for calculating, for each cylinder, a differential pressure between the in-cylinder pressure at the two timings measured by the measuring means. A non-reference cylinder sensor sensitivity correction for calculating a sensor sensitivity correction coefficient of an in-cylinder pressure sensor of a cylinder other than the reference cylinder based on the differential pressure of a predetermined reference cylinder and the differential pressure of a cylinder other than the reference cylinder And a coefficient calculating means.

  According to this aspect of the present invention, it is possible to calculate the sensor sensitivity correction coefficient of the in-cylinder pressure sensors of cylinders other than the reference cylinder with reference to the in-cylinder pressure sensor of the reference cylinder. That is, when the engine operating state is steady, the in-cylinder pressure differential pressure between the same two timings is the same for the reference cylinder and the cylinders other than the reference cylinder. Therefore, using this, based on the differential pressure between the in-cylinder pressure measured by the in-cylinder pressure sensor of the reference cylinder and the in-cylinder pressure difference measured by the in-cylinder pressure sensor of the cylinder other than the reference cylinder, The sensor sensitivity correction coefficient of the cylinder pressure sensor of the cylinder can be calculated. By using the calculated sensor sensitivity correction coefficient of the in-cylinder pressure sensor of the cylinder other than the reference cylinder, the sensor sensitivity of the in-cylinder pressure sensor of the reference cylinder and the in-cylinder pressure sensor of the cylinder other than the reference cylinder can be equalized. Thus, variations in sensor sensitivity among cylinders, and in other words, variations in in-cylinder pressure measurement values based on this can be eliminated.

  Here, it is preferable that the timing of the two predetermined points is a timing of two points during the compression stroke. By doing so, the differential pressure between the timings of the two points can be increased, and the calculation accuracy can be improved.

  Alternatively, one of the two predetermined timings is a timing during the exhaust stroke and the exhaust valve is open and the intake valve is closed, and the other is during the intake stroke and the exhaust valve is closed, It is also preferable that the timing when the intake valve is opened. By doing so, it is possible to eliminate the influence of manufacturing variations caused by dimensional tolerances and the like, and the sensor sensitivity correction coefficient can be calculated with high accuracy.

  In this case, it is preferable to provide a fuel cut execution means for executing fuel cut when the in-cylinder pressure is measured by the measurement means. This is because the differential pressure can be increased by executing the fuel cut.

  Preferably, a sensor sensitivity correction coefficient of an in-cylinder pressure sensor of a cylinder other than the reference cylinder is a value obtained by dividing a differential pressure of the reference cylinder by a differential pressure of a cylinder other than the reference cylinder.

  Preferably, the measuring means repeatedly performs the measurement of the in-cylinder pressure a plurality of times during steady operation of the internal combustion engine, and the differential pressure calculating means performs each time based on each in-cylinder pressure measured by the measuring means. The final differential pressure is calculated by averaging the differential pressure at each time. By performing such an averaging process, the calculation accuracy can be improved.

  And an air-fuel ratio sensor for detecting an exhaust air-fuel ratio, and a reference cylinder sensor sensitivity correction coefficient calculating means for calculating a sensor sensitivity correction coefficient of an in-cylinder pressure sensor of the reference cylinder, wherein the measuring means is a predetermined unit during the compression stroke. The in-cylinder pressure is measured at the timing of the two points, and the reference cylinder sensor sensitivity correction coefficient calculating means detects the differential pressure of the in-cylinder pressure of the reference cylinder calculated by the differential pressure calculating means and the air-fuel ratio sensor. The sensor sensitivity correction coefficient of the in-cylinder pressure sensor of the reference cylinder is preferably calculated based on the exhaust air / fuel ratio.

  That is, the sensor sensitivity of the in-cylinder pressure sensor of the reference cylinder varies even between the solids of the internal combustion engine. This preferred embodiment is effective in calculating the sensor sensitivity correction coefficient of the in-cylinder pressure sensor of the reference cylinder so as to eliminate the variation. is there. If the variation is eliminated, the sensor sensitivity of the in-cylinder pressure sensor of the reference cylinder can be made equal in different internal combustion engines, and the same control logic and control data can be shared to control different engines with high accuracy. .

  In this case, fuel injection means for injecting a fuel injection amount set in advance so that the exhaust air-fuel ratio becomes a predetermined target air-fuel ratio is provided, and the reference cylinder sensor sensitivity correction coefficient calculation means performs fuel injection by the fuel injection means. Preferably, a value obtained by dividing the exhaust air-fuel ratio detected by the air-fuel ratio sensor by the target air-fuel ratio is calculated as a sensor sensitivity correction coefficient of the in-cylinder pressure sensor of the reference cylinder.

  Furthermore, it is preferable that correction means for correcting sensor sensitivity correction coefficients of cylinders other than the reference cylinder is provided based on the sensor sensitivity correction coefficient of the reference cylinder calculated by the reference cylinder sensor sensitivity correction coefficient calculation means. Thereby, the sensor sensitivities of all in-cylinder pressure sensors of different internal combustion engines can be made equal, and variations in sensor sensitivity between cylinders and between engine solids can be eliminated.

  According to the present invention, an excellent effect is exhibited that sensitivity variations of the in-cylinder pressure sensor can be effectively eliminated.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 schematically shows a control device for an internal combustion engine including a calibration device for an in-cylinder pressure sensor according to the present invention. Unlike a general conventional device, this control device controls various control amounts based on the in-cylinder pressure detected by the in-cylinder pressure sensor. That is, in the conventional apparatus, map control is performed in which the control amount that seems to be optimal for each operating state of the engine is obtained by an experiment in advance and mapped, and the engine is controlled by applying each map value during actual engine operation. Was common. In contrast, in the control device of the present embodiment, the in-cylinder combustion state during engine operation is directly detected by the in-cylinder pressure sensor, and the detected combustion state is matched with a predetermined optimum combustion state. Control various control amounts. According to this new method, it is possible to greatly simplify the process of creating various maps, that is, the adaptation, which has conventionally required a lot of time and labor, and to greatly shorten the development period. There is. In addition, there is an advantage that variations among cylinders due to individual differences of each part are eliminated, and an optimal combustion state can be obtained individually for each cylinder. Control amount to be controlled includes combustion start timing (ignition timing for spark ignition type engine, fuel injection timing for compression ignition type engine), fuel injection amount, fuel injection timing (for spark ignition type engine), etc. Is representative.

  As shown in the figure, the internal combustion engine 1 generates power by burning a mixture of fuel and air inside a combustion chamber 3 formed in a cylinder block 2 and reciprocating a piston 4 in the combustion chamber 3. To do. The internal combustion engine 1 is configured as a multi-cylinder engine (however, only one cylinder is shown), and in the present embodiment, is configured as a 4-cylinder engine. The internal combustion engine 1 of the present embodiment is a spark ignition internal combustion engine, more specifically a gasoline engine.

  In the cylinder head of the internal combustion engine 1, an intake valve Vi for opening and closing the intake port and an exhaust valve Ve for opening and closing the exhaust port are provided for each cylinder. Each intake valve Vi and each exhaust valve Ve are opened and closed by a camshaft (not shown). At least the camshaft on the intake side has a variable phase difference with the crankshaft by a variable valve timing mechanism (VVT) (not shown), so that at least the valve timing of the intake valve is variable.

  The intake port of each cylinder is connected to a surge tank 8 serving as an intake air collecting chamber via a branch pipe for each cylinder. An intake pipe L1 that forms an intake manifold passage is connected to the upstream side of the surge tank 8, and an air cleaner 9 is provided at the upstream end of the intake pipe L1. An air flow meter 5 for detecting the intake air amount and a throttle valve (electronically controlled in this embodiment) 10 are incorporated in the intake pipe L1 in order from the upstream side. On the other hand, the exhaust port of each cylinder is connected to an exhaust pipe 6 forming an exhaust collecting passage through a branch pipe for each cylinder. The exhaust pipe 6 includes a front-stage catalyst device 11a including a three-way catalyst and a NOx storage reduction catalyst. A post-catalyst device 11b including is attached. An air-fuel ratio sensor 13 for detecting the air-fuel ratio of the exhaust gas is installed in the exhaust pipe 6 on the upstream side of the upstream catalyst device 11a.

  A spark plug 7 for igniting the air-fuel mixture in the combustion chamber 3 is attached to the top of the cylinder head. Further, the internal combustion engine 1 has an injector (fuel injection valve) 12 for each cylinder, and the injector 12 is disposed in the cylinder head so as to face the corresponding combustion chamber 3. Each piston 4 of the internal combustion engine 1 is configured as a so-called deep dish top surface type, and a recess 4a is formed on the upper surface thereof. In the internal combustion engine 1, fuel is directly injected from each injector 12 toward the recess 4 a of the piston 4 in each combustion chamber 3 in a state where air is sucked into each combustion chamber 3. As a result, in the internal combustion engine 1, the fuel / air mixture layer is formed (stratified) in the vicinity of the spark plug 7 in a state of being separated from the surrounding air layer. Stable stratified combustion can be executed using the gas.

  The spark plug 7, the throttle valve 10, the injector 12, and the like described above are electrically connected to an electronic control unit (hereinafter referred to as ECU) 20 as control means. The ECU 20 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like, all not shown. As shown in the figure, the ECU 20 includes an air flow meter 5, an air-fuel ratio sensor 13, a crank angle sensor 14 that detects the crank angle of the internal combustion engine 1, an accelerator opening sensor 7 that detects the accelerator opening, and other components. Various sensors are electrically connected via an A / D converter (not shown) or the like. The ECU 20 controls the spark plug 7, the throttle valve 10, the injector 12, and the like so as to obtain a desired output based on detection values of various sensors.

  The internal combustion engine 1 has an in-cylinder pressure sensor 15 including a semiconductor element, a piezoelectric element, an optical fiber detection element, or the like in each cylinder. Each in-cylinder pressure sensor 15 is disposed on the cylinder head so that the pressure receiving surface faces the corresponding combustion chamber 3, and is electrically connected to the ECU 20 via an A / D converter (not shown). Each in-cylinder pressure sensor 15 provides the ECU 20 with a voltage signal proportional to the in-cylinder pressure (relative pressure) in the corresponding combustion chamber 3. Furthermore, the internal combustion engine 1 has an intake pressure sensor 16 that detects the intake pressure as an absolute pressure. The intake pressure sensor 16 is attached to the surge tank 8 and is electrically connected to the ECU 20 via an A / D converter (not shown) or the like, and gives a voltage signal proportional to the pressure in the surge tank 8 to the ECU 20. The detection values of the in-cylinder pressure sensor 15 and the intake pressure sensor 16 are sequentially given to the ECU 20 every minute time, and are stored and held by a predetermined amount in a predetermined storage area (buffer) of the ECU 20.

  Next, calibration of the in-cylinder pressure sensor will be described.

  According to the in-cylinder pressure sensor calibration apparatus of this embodiment, the in-cylinder pressure sensors of all cylinders are calibrated through the following steps 1 to 3.

  Step 1: Calculate / determine a sensor sensitivity correction coefficient for in-cylinder pressure sensors of cylinders other than the reference cylinder with reference to an in-cylinder pressure sensor of a predetermined reference cylinder. For convenience, an in-cylinder pressure sensor of the reference cylinder is appropriately referred to as a “reference cylinder sensor”, a cylinder other than the reference cylinder is referred to as a “non-reference cylinder”, and an in-cylinder pressure sensor of a cylinder other than the reference cylinder is appropriately referred to as a “non-reference cylinder sensor”. By this step 1, the sensor sensitivities of the reference cylinder sensor and the non-reference cylinder sensor are made equal, and the sensor sensitivity variation among the cylinders, and hence the variation of the in-cylinder pressure measurement value based on this is eliminated. Although the reference cylinder can be arbitrarily set, in the present embodiment, it is set to the first cylinder. The ignition order of the 4-cylinder engine of the present embodiment is as follows: No. 1 cylinder → No. 3 cylinder → No. 4 cylinder → No. 2 cylinder.

  Step 2: Calculate and determine the sensor sensitivity correction coefficient of the in-cylinder pressure sensor of the reference cylinder. Since there is a variation in the sensor sensitivity of the in-cylinder pressure sensor of the reference cylinder even between the engine solids, the sensor sensitivity correction coefficient of the reference cylinder sensor is calculated and determined so as to eliminate this variation. This step 2 is advantageous for suppressing variations in sensor sensitivity among engine solids, and hence in-cylinder pressure measurement values based on this. Further, when different engines are controlled by sharing the same control logic and control data, it is advantageous to obtain desired performance in each engine.

  Step 3: Based on the sensor sensitivity correction coefficient of the in-cylinder pressure sensor of the reference cylinder calculated and determined in Step 2, the sensor sensitivity correction coefficient of the in-cylinder pressure sensor of the cylinders other than the reference cylinder is corrected. This step 3 makes it possible to equalize the sensor sensitivities of the in-cylinder pressure sensors of the cylinders of different engines, and to eliminate variations in sensor sensitivity between cylinders and between engine solids, and hence variations in in-cylinder pressure measurement values based on the sensor sensitivities.

  Here, the sensor sensitivity of the in-cylinder pressure sensor and its correction coefficient will be described. FIG. 2 shows the output characteristics of the in-cylinder pressure sensor, where the horizontal axis represents the output voltage E (V) and the vertical axis represents the in-cylinder pressure P (MPa) as an input. As shown in the figure, the in-cylinder pressure P and the output voltage E are in a proportional relationship, and these relationships are represented by ΔP = k · G · ΔE. G is a conversion coefficient for converting the output voltage E into the in-cylinder pressure P, that is, a specific sensor sensitivity, and is a specific fixed value inherent in the in-cylinder pressure sensor. That is, the output characteristic of the in-cylinder pressure sensor is generally expressed as ΔP = G · ΔE ± α (%), and includes a manufacturing error of α (%) (usually a value of 2 to 3%). It is normal. However, when high-precision in-cylinder pressure measurement is performed as described above, especially when an attempt is made to measure the low-pressure portion of the in-cylinder pressure sensor with high accuracy, the manufacturing error greatly affects the measurement accuracy. become. Therefore, the correction coefficient k corrects the sensor sensitivity G so as to eliminate the manufacturing error. Here, the in-cylinder pressure sensor is mainly intended for measuring the amount of pressure change. Therefore, the output characteristic of the in-cylinder pressure sensor is also defined by the relationship between the pressure change amount and the output voltage change amount.

  In FIG. 2, the output characteristic of the in-cylinder pressure sensor as an intermediate product with a manufacturing error of 0% is indicated by I. In this case, the output voltage change amount ΔE with respect to the in-cylinder pressure change amount ΔP, and the sensor correction coefficient k = 1.0. However, in the case of the in-cylinder pressure sensor indicated by II, the output voltage change amount ΔE + e1 with respect to the in-cylinder pressure change amount ΔP, and an output voltage change amount larger than the intermediate product is obtained. If the two sensor sensitivities are to be made equal, a sensor correction coefficient k smaller than 1.0 must be set in order to associate the output voltage change amount ΔE + e1 with the in-cylinder pressure change amount ΔP. Specifically, k = ΔE / (ΔE + e1). On the contrary, in the case of the in-cylinder pressure sensor indicated by III, the output voltage change amount ΔE-e2 with respect to the in-cylinder pressure change amount ΔP, and an output voltage change amount smaller than the intermediate product is obtained. When the sensor sensitivity of this in-cylinder pressure sensor is to be aligned with that of the intermediate product, a sensor correction coefficient k greater than 1.0 must be set in order to associate the output voltage change amount ΔE-e2 with the in-cylinder pressure change amount ΔP. . Specifically, k = ΔE / (ΔE−e2).

[Step 1: Calculation of sensor sensitivity correction coefficient of non-reference cylinder sensor]
Next, calculation of the sensor sensitivity correction coefficient of the non-reference cylinder sensor related to Step 1 will be described.

  First, the first aspect of this calculation will be described. Generally speaking, this first mode measures the in-cylinder pressure at each of the two timings during the compression stroke for each cylinder, and assumes that the differential pressure between the in-cylinder pressures at these two timings is the same for all cylinders. The sensor sensitivity correction coefficient of the non-reference cylinder sensor is calculated based on the differential pressure of the reference cylinder and the differential pressure of the non-reference cylinder.

  FIG. 3 shows changes in in-cylinder pressure (solid line), intake pressure (one-dot chain line), and exhaust pressure (broken line) with respect to a crank angle θ of a specific cylinder. The crank angle θ = 0 ° is the compression top dead center. As can be seen, the in-cylinder pressure rises in the compression stroke (−180 ° to 0 °) and peaks near the compression top dead center. In this aspect, as indicated by P1 and P2 in the figure, the in-cylinder pressure is measured by the in-cylinder pressure sensor at two timings during the compression stroke. The timings at these two points are such that a differential pressure as large as possible is generated between the measured in-cylinder pressures, and the later timing is before the ignition timing. Therefore, it is preferable that the previous timing is near or before the timing when the in-cylinder pressure starts to rise, and the subsequent timing is immediately before the ignition timing.

Now, in a state where the engine is in steady operation, the in-cylinder pressures P1 (i) and P2 (i) at two timings are measured for each cylinder. Here, i is a cylinder number, i = 1, 2, 3, 4. For the reference cylinder, i = ix = 1, and for the non-reference cylinder, i = iy = 2, 3, and 4. P1 (i) and P2 (i) are expressed as follows in relation to the sensor output voltage (see FIG. 2).
P1 (i) = k (i) · G · E1 (i)
P2 (i) = k (i) · G · E2 (i)
... (2)
k (i) is a sensor sensitivity correction coefficient of the i-th cylinder. Here, the sensor sensitivity correction coefficient k (ix) of the reference cylinder is set to an initial value 1.0.

The in-cylinder pressure differential pressure Psub (i) between the timings of the two points is Psub (i) = P2 (i) −P1 (i)
= K (i) .G. (E2 (i) -E1 (i)) (3)
It is represented by Here, since the differential pressure Psub (ii) of the non-reference cylinder can be regarded as being equal to the differential pressure Psub (ix) of the reference cylinder, the following equation is established.
k (ii) · Psub (iy) = Psub (ix) (4)

Accordingly, the sensor sensitivity correction coefficient k (iy) of the non-reference cylinder is calculated based on the following equation (5).
k (ii) = Psub (ix) / Psub (iy) (5)

  The sensor sensitivity correction coefficient k (iy) of the non-reference cylinder calculated in this way is replaced with an existing value (for example, an initial value of 1.0).

  As understood from the above description, according to the first aspect, the sensor sensitivity (k (ix) · G) of the non-reference cylinder is made equal to the sensor sensitivity (k (ix) · G) of the reference cylinder. This can eliminate variations in sensitivity among cylinders of the in-cylinder pressure sensor. Then, in the control of the internal combustion engine, the sensor sensitivity correction coefficient k (iy) calculated in this way is used for the in-cylinder pressure sensor of the non-reference cylinder, thereby eliminating the inter-cylinder variation in the in-cylinder pressure measurement value and controlling with high accuracy. Can be realized.

  Next, a more specific calculation process of the first aspect described here will be described based on the flowchart of FIG. The illustrated process is executed by the ECU 20, and an averaging process is added here mainly from the viewpoint of improving accuracy and ensuring reliability. This averaging process has the advantage that the influence of sensor noise can be reduced.

  First, in step S101, a count value j of a counter that counts the number of processing cycles is set to an initial value 1. Next, in step S102, it is determined whether or not the operating state of the internal combustion engine is a steady operating state. The steady operation state is when the fluctuation range of the engine speed and the accelerator opening is within a predetermined value, for example, an idle operation state. The ECU 20 has an engine rotational speed NE calculated based on a detection value of the crank angle sensor 14 within a predetermined rotational speed α (for example, 700 ± 50 rpm) centered on a predetermined idle rotational speed NEi. When the detected accelerator opening is fully closed, it is determined that the vehicle is in a steady operation state.

  The steady operation state may be an operation state other than idle. For example, it is also preferable that the vehicle is in a steady operation state at a medium rotation and high load with a small intake pulsation and a large amount of cylinder air. This is because the smaller the intake pulsation, the less the variation in the in-cylinder pressure, and the less the in-cylinder pressure measurement value will be, and the more the in-cylinder air amount, the greater the differential pressure between the two points and the smaller the error. Because. Such a steady operation state can be realized when, for example, the vehicle is traveling uphill on a highway. Preferably, the condition includes that the intake / exhaust valves do not overlap or that the variable valve timing mechanism is controlled so as to do so. This is because if this is included, exhaust gas blow-back is eliminated, and the in-cylinder air amount of each cylinder, and thus the differential pressure, can be kept constant.

  If it is determined in step S102 that the vehicle is not in a steady operation state, the process returns to step S101. On the other hand, if it is determined in step S102 that the vehicle is in the steady operation state, in-cylinder pressures P1 (i, j) and P2 (i, j) at two timings are measured by the in-cylinder pressure sensor 15 in step S103. This measurement is performed in the order of the ignition cylinder, and when all the cylinders are measured, step S103 is completed. These in-cylinder pressures P1 (i, j) and P2 (i, j) are temporarily stored in a storage device (buffer).

Next, in step S104, based on these in-cylinder pressures P1 (i, j) and P2 (i, j), the differential pressure Psub (i, j) is calculated by the following equation.
Psub (i, j) = P2 (i, j) −P1 (i, j) (6)

  The differential pressure Psub (i, j) of the current cycle thus obtained is temporarily stored in a storage device (buffer). FIG. 5 shows how the differential pressure Psub (i, j) is sequentially stored in the storage device for each cycle.

  Thereafter, in step S105, the count value j of the counter is incremented by 1, and in step S106, the count value j is compared with a predetermined value N (for example, 128). If the count value j does not exceed the predetermined value N, the process returns to step S102 and steps S102 to S105 are repeatedly executed. When the engine is not in a steady operation state during this iterative process, the process is stopped (S102: NO), and the process starts again from S101. Further, when the differential pressure Psub (i, j) obtained during the iterative process deviates from the initial differential pressure Psub (i, 1) by a predetermined value or more, it is considered that the differential pressure fluctuation is too large and the process is stopped. May be.

When the count value j exceeds the predetermined value N, as shown in FIG. 5, differential pressure data for N cylinders is stored in the storage device of the ECU 20. Then, step S107 is executed, and the average differential pressure Psubav (i) of each cylinder is calculated by the following equation based on the differential pressure data of each N cylinders.
Psubav (i) = ΣPsub (i, j) / N (7)

Then, in step S108, the sensor sensitivity correction coefficient k (iy) of the non-reference cylinder is calculated by the following equation (8) based on the average differential pressure Psubav (i) of each cylinder.
k (ii) = Psubav (ix) / Psubav (ii) (8)

  The sensor sensitivity correction coefficient k (iy) of the non-reference cylinder thus calculated is replaced with an existing value (for example, an initial value of 1.0), and is used for subsequent in-cylinder pressure measurement.

  Next, a second mode of calculating the sensor sensitivity correction coefficient of the non-reference cylinder sensor will be described.

  In the first aspect, the processing is performed under the assumption that the differential pressure between the in-cylinder pressures at two timings is the same for all cylinders. In other words, as long as the engine operating state is steady, the same amount of air flows into all cylinders, and as long as the in-cylinder pressure is measured at the same timing, the differential pressure between the in-cylinder pressures of all cylinders is assumed to be equal. However, manufacturing variations due to dimensional tolerances and the like exist between cylinders. For example, the in-cylinder air amount may not be equal because the in-cylinder volume is different even at the same timing. In this case, the in-cylinder pressure differential pressure between the same two timings differs between the cylinders, and an error occurs in the finally calculated sensor sensitivity correction coefficient.

  Therefore, in order to solve this problem, the timing of the two points in the second mode is different from that in the first mode.

  FIG. 6 shows the timing of two points in the second mode. As can be seen from the figure, one of the timings at which the in-cylinder pressure P1 is measured first is during the exhaust stroke (−540 to −360 °), the exhaust valve Ve is opened, and the intake valve This is the timing when Vi is closed. Further, one point where the in-cylinder pressure P2 is measured later is the timing when the exhaust valve is closed and the intake valve is open during the intake stroke (−360 to −180 °). In this embodiment, both the first point and the subsequent one point are set as late as possible in order to eliminate the influence of the air flow in the cylinder, and the previous one point is a timing immediately before the exhaust valve Ve is closed, and the subsequent one point. The point is set at the timing of the intake bottom dead center (−180 °).

  For the previous point, when the exhaust valve Ve is open and the intake valve Vi is closed, the combustion chamber 3 is open to the exhaust system, and the in-cylinder pressure is balanced with the exhaust pressure. Further, when the exhaust valve Ve is closed and the intake valve Vi is opened at the later one point, the combustion chamber 3 is opened to the intake system, and the in-cylinder pressure is balanced with the intake pressure. As long as the engine operating state is steady, the exhaust pressure and the intake pressure can be regarded as the same for all cylinders. By adopting these two timings, the effects of manufacturing variations are eliminated, and the in-cylinder pressure of each cylinder is adjusted under the same conditions. It can be measured.

  The sensor sensitivity correction coefficient of the non-reference cylinder sensor is calculated by the same method as in the first aspect except for the following points. That is, in the second mode, the magnitude relationship between the in-cylinder pressures P1 and P2 at the previous and subsequent timings is opposite to that in the first mode. Therefore, when calculating the differential pressure Psub related to step S104, A value obtained by subtracting the in-cylinder pressure P2 at a later timing from the internal pressure P1 or an absolute value of (P2−P1) is defined as a differential pressure Psub.

  In relation to step S102, the steady operation state is preferably an idle operation state in which the throttle valve opening is minimum, the intake pressure is low, and a relatively large differential pressure is obtained.

  In order to prevent blow-in of the intake air into the exhaust system or return of the exhaust gas to the intake system, the calculation is executed in a state where the intake / exhaust valves are not overlapped or the variable valve timing mechanism is controlled so as to do so. . This is because there is a possibility that the equilibrium state between the exhaust pressure or the intake pressure and the in-cylinder pressure varies between the cylinders if there is a blow-through or blow-back.

  Next, a third mode of calculating the sensor sensitivity correction coefficient of the non-reference cylinder sensor will be described.

  As described in the second aspect, in order to calculate the sensor sensitivity correction coefficient with high accuracy, it is desirable that the differential pressure between the intake pressure and the exhaust pressure is as large as possible. In the second aspect, the in-cylinder pressure is measured during idling when the throttle valve opening is minimum and the intake pressure is low. In this third aspect, the in-cylinder pressure is increased during fuel cut in order to further increase the differential pressure. Make measurements. That is, the throttle valve opening is minimum even during fuel cut, and the engine rotation speed is higher than the idle rotation speed, so that the intake pressure becomes lower and the exhaust pressure becomes higher. Therefore, the differential pressure can be increased and the sensor sensitivity correction coefficient calculation accuracy can be improved.

  FIG. 7 shows a flowchart relating to the calculation process of the third aspect. The illustrated process is substantially the same as the process of the first mode shown in FIG. 4, and the difference will be mainly described below.

In this third aspect, steps S201 and S203 to S208 are the same as steps S101 and S103 to S108 of the first aspect. However, in step S204, since the magnitude relationship between the in-cylinder pressures P1 and P2 at the previous and subsequent timings is opposite to that in the first mode, the differential pressure Psub is calculated by the following equation (6) ′.
Psub (i, j) = P1 (i, j) −P2 (i, j) (6) ′

  In the third mode, the following step S202 is replaced with step S102 of the first mode. That is, in step S202, it is determined whether the operating state of the internal combustion engine is a fuel cut state. In the control device of the present embodiment, the ECU 20 has a higher actual engine speed than the predetermined rotation speed slightly higher than the idle rotation speed, and the accelerator opening is fully closed (that is, the throttle valve opening is fully closed). At this time, the energization to the injector 12 is stopped and fuel cut is performed. Therefore, the ECU 20 determines that it is in the fuel cut state when it is performing the fuel cut.

  Alternatively, the fuel cut state of the engine may be determined by the following method. That is, FIG. 8 shows the in-cylinder pressure waveform when combustion is being performed (during firing) and the in-cylinder pressure waveform when combustion is not being performed (during motoring, that is, during fuel cut). Is shown. As can be seen, the waveform near the compression top dead center TDC increases gradually before and after the compression top dead center TDC at the time of firing, whereas the waveform near the compression top dead center TDC at the time of motoring. It reaches a peak at TDC, and the pressure value increases and decreases before and after that.

Therefore, using this characteristic, as shown in FIG. 9, the ECU 20 calculates the in-cylinder pressure Pc (TDC) measured at the compression top dead center TDC and the compression top dead center TDC in a predetermined cylinder (for example, the reference cylinder). The following relationship between the in-cylinder pressure Pc (TDC−d1) measured at the timing before d1 (°) and the in-cylinder pressure Pc (TDC + d2) measured at the timing after d2 (°) from the compression top dead center When is established, it is determined that the engine is in a fuel cut state. In this embodiment, d1 = d2 = 5 (°), but other values can be set.
(TDC-d1) <Pc (TDC) and (TDC + d2) <Pc (TDC)
... (9)

  Returning to FIG. 7, in the third mode, step S204A is added between step S204 and step S205. In this step S204A, the difference between the differential pressure Psub (i, j) of each cylinder obtained by the j-th cycle process and the differential pressure Psub (i, 1) of each cylinder obtained by the first-cycle process. An absolute value of ΔPsub (i, j) = (Psub (i, j) −Psub (i, 1) is calculated, and the absolute value of the difference ΔPsub (i, j) is a relatively small value. It is compared with the threshold value ε.

  If the difference ΔPsub (i, j) is smaller than the threshold value ε, the process is continued assuming that the variation of the in-cylinder pressure difference Psub is within an allowable range, that is, the engine operating state is steady, and the process proceeds to step S205. On the other hand, if the difference ΔPsub (i, j) is greater than or equal to the threshold value ε, the process is stopped assuming that the fluctuation of the in-cylinder pressure difference Psub is outside the allowable range, that is, the engine operating state is not steady, and the process proceeds to step S201. As described above, in this embodiment, there is provided means for determining whether or not the internal combustion engine is in a steady operation state based on the difference in the in-cylinder pressure.

  As described above, according to Step 1, the sensor sensitivity of the non-reference cylinder sensor can be set to be equal to the sensor sensitivity of the reference cylinder sensor. In other words, the sensor sensitivity of the reference cylinder sensor is used as a reference. Variation in sensor sensitivity of the non-reference cylinder sensor can be eliminated. Therefore, it is possible to eliminate variations in sensor sensitivity among cylinders and in-cylinder pressure measurement values based on the variations.

[Step 2: Calculation of sensor sensitivity correction coefficient of reference cylinder sensor]
Next, calculation of the sensor sensitivity correction coefficient of the reference cylinder sensor related to Step 2 will be described. This calculation is mainly characterized in that the exhaust air-fuel ratio detected by the air-fuel ratio sensor 13 is used. The calculation process here is executed when the engine operation state is a steady operation state such as an idle operation state.

Referring to FIG. 3, if the compression in the compression stroke is regarded as adiabatic compression, the following equation is established between the in-cylinder pressures P1 and P2 at two timings during the compression stroke.
(P1 + ΔP) ^V1κ = (P2 + ΔP) ^V2κ (10)
Here, the in-cylinder pressures P1 and P2 are relative pressures as detected by the in-cylinder pressure sensor 15, and ΔP is an absolute pressure correction value. By using the intake pressure as the absolute pressure detected by the intake pressure sensor 16, the pressure value detected by the in-cylinder pressure sensor 15 can be corrected by the absolute pressure. V1 and V2 are in-cylinder volumes at the previous and later timings, and can be calculated based on the crank angle θ.

When the equation (10) is modified, the following equation (11) is obtained, and it can be seen that the differential pressure between the in-cylinder pressures P1 and P2 (relative pressure) during the compression stroke is proportional to the absolute pressure of the in-cylinder pressure P2.
P2−P1 = (P2 + ΔP) {1− (V2 / V1) ^κ } (11)

Here, regarding the reference cylinder, if the sensor sensitivity correction coefficient k (ix) of the reference cylinder sensor is 1.0 (initial value), the differential pressure between the cylinder pressures P1 and P2 (relative pressure) on the left side of the equation (11) is It is expressed by equation (12) (see FIG. 2).
P2-P1 = k (ix) .G.E2-k (ix) .G.E1
= K (ix) · G · (E2-E1) (12)

On the other hand, since the filling rate KL (%) of the in-cylinder air amount is proportional to the compression pressure, the filling rate KL is calculated by the ECU 20 using the differential pressure (P2-P1) of the in-cylinder pressure measurement value by the following equation (13). Is done.
KL = a · (P2−P1) + b (13)

  a and b are predetermined constants, which are obtained in advance by experiments or the like. The filling rate is the ratio between the amount of air actually contained in the cylinder and the maximum amount of air that can enter the cylinder. For example, when the maximum amount of air is actually contained in the cylinder, the filling rate is 100%. Become. Here, if there is an overlap in the valve timing of the intake / exhaust valves, it is necessary to subtract the increase in the cylinder pressure due to the residual gas. When there is no overlap, for example, during idling, there is no increase in the in-cylinder pressure due to such residual gas, so this subtraction can be omitted.

  By the way, in the present embodiment, the fuel injection amount is set in advance such that the actual exhaust air-fuel ratio becomes a predetermined target air-fuel ratio. That is, the ECU 20 sets the fuel injection amount Q that makes the actual exhaust air-fuel ratio AF coincide with a predetermined target air-fuel ratio AFt (for example, stoichiometric air-fuel ratio = 14.6) by the filling rate KL calculated by the equation (13). Is determined using a predetermined map or function, and the fuel injection amount Q is injected from the injector 12.

At this time, the ECU 20 measures the exhaust air-fuel ratio AF by the air-fuel ratio sensor 13. Then, the sensor sensitivity correction coefficient k (ix) of the in-cylinder pressure sensor of the reference cylinder is calculated by the following equation (14).
k (ix) = AF / AFt (14)

  Then, the ECU 20 changes the sensor sensitivity correction coefficient k (ix) of the reference cylinder sensor from the existing value (for example, the initial value 1.0) to a value calculated by the equation (14).

  For example, assuming that the target air-fuel ratio AFt is stoichiometric air-fuel ratio = 14.6, the measured actual exhaust air-fuel ratio AF is richer than the target air-fuel ratio AFt (AF <14 .6, for example AF = 13). Since the actual exhaust air-fuel ratio AF is 13 even though the fuel injection amount Q that makes the exhaust air-fuel ratio 14.6 is injected, the actual amount of in-cylinder air amount is less than the expected amount Means that. Therefore, from the equation (13), the in-cylinder pressure differential pressure (P2−P1) is less than the expected value. Therefore, k (ix) may be changed to a value smaller than the initial value 1.0 by the equation (12). On the other hand, the ECU 20 replaces the sensor sensitivity correction coefficient k (ix) = 13 / 14.6 = 0.89 obtained by the equation (14) with the initial value 1.0. By doing so, the sensor sensitivity correction coefficient k (ix) is changed to a smaller appropriate value. Thereafter, it is possible to obtain an accurate in-cylinder pressure measurement value and realize an accurate control. In this example, the actual exhaust air-fuel ratio AF can also be set to 14.6 when the fuel injection amount Q that makes the exhaust air-fuel ratio 14.6 is injected.

  Also, consider the reverse case, that is, the measured actual exhaust air-fuel ratio AF is leaner than the target air-fuel ratio AFt (AF> 14.6, for example AF = 16). Since the actual exhaust air-fuel ratio AF is 16, even though the fuel injection amount Q that makes the exhaust air-fuel ratio 14.6 is injected, the actual amount of in-cylinder air amount is larger than the expected amount. Means that. Therefore, the differential pressure (P2-P1) of the in-cylinder pressure shows a value larger than the planned value according to the equation (13). Therefore, k (ix) may be changed to a value larger than the initial value 1.0 by the equation (12). On the other hand, the ECU 20 replaces the sensor sensitivity correction coefficient k (ix) = 16 / 14.6 = 1.10 obtained by the equation (14) with the initial value 1.0. By doing so, the sensor sensitivity correction coefficient k (ix) is changed to a larger appropriate value, and thereafter, it is possible to obtain an accurate in-cylinder pressure measurement value and realize an accurate control. The actual exhaust air-fuel ratio AF can also be set to 14.6 when the fuel injection amount Q that makes the exhaust air-fuel ratio 14.6 is injected.

  As described above, according to the calculation process of the sensor sensitivity correction coefficient of the reference cylinder sensor according to step 2, the sensor sensitivity variation of the reference cylinder sensor among the engine solids can be eliminated. This is advantageous for suppressing variations in sensitivity, and in other words, variations in in-cylinder pressure measurement values based thereon. Further, when different engines are controlled by sharing the same control logic and control data, it is advantageous to obtain desired performance in each engine.

[Step 3: Correction of sensor sensitivity correction coefficient of non-reference cylinder sensor]
Next, correction of the sensor sensitivity correction coefficient of the non-reference cylinder sensor related to Step 3 will be described. Here, simply, the ECU 20 calculates the sensor sensitivity correction coefficient k (iy) of the non-reference cylinder sensor calculated and determined in step 1 based on the sensor sensitivity correction coefficient k (ix) of the reference cylinder sensor obtained by the equation (14). ) Is corrected or updated as shown in the following equation (15).
k (ii) = k (ix) · k (ii) (15)

  By this step 3, the sensor sensitivities of all the cylinder pressure sensors of different engines, in particular, the cylinder pressure sensors of the non-reference cylinders, can be made equal. Variations in internal pressure measurement values can be eliminated.

  The preferred embodiment of the present invention has been described in detail above, but various other embodiments of the present invention are conceivable. For example, the internal combustion engine 1 described above is a spark ignition type internal combustion engine (gasoline engine), but is not limited thereto, and the present invention can also be applied to a compression ignition type internal combustion engine (diesel engine). In the embodiment, the control amount is directly controlled based on the detected in-cylinder pressure. However, the application of the present invention is not limited to this, and a conventional map control method is conventionally used. The present invention can also be applied to a control device to be employed. In the embodiment, the in-cylinder pressure sensors are provided in all the cylinders of the multi-cylinder internal combustion engine. However, it is not always necessary to provide all the cylinders, and the present invention can be applied if the in-cylinder pressure sensors are provided in two or more cylinders. .

  The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

It is a block diagram which shows roughly the control apparatus of the internal combustion engine containing the calibration apparatus of the cylinder pressure sensor which concerns on this invention. It is a graph which shows the output characteristic of a cylinder pressure sensor. 4 is a graph showing changes in in-cylinder pressure, intake pressure, and exhaust pressure with respect to a crank angle of a specific cylinder, and timings of two points in the first mode of Step 1; It is a flowchart which shows the process of the 1st aspect of step 1. FIG. It is a figure which shows the differential pressure Psub (i, j) of the in-cylinder pressure of each cylinder memorize | stored for every cycle in the memory | storage device of ECU, and the average differential pressure Psubav (i) calculated | required from this. 4 is a graph showing changes in in-cylinder pressure, intake pressure, and exhaust pressure with respect to a crank angle of a specific cylinder, and timings of two points in the first mode of Step 1; It is a flowchart which shows the process of the 3rd aspect of step 1. It is a graph which shows the cylinder pressure waveform at the time of firing and at the time of motoring. FIG. 9 is an enlarged view in the vicinity of TDC of the in-cylinder pressure waveform at the time of motoring in FIG. 8, for explaining fuel cut determination.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 3 Combustion chamber 7 Spark plug 12 Injector 13 Air-fuel ratio sensor 15 In-cylinder pressure sensor Vi Intake valve Ve Exhaust valves P1 and P2 In-cylinder pressure k Sensor sensitivity correction coefficient Psub In-cylinder pressure differential pressure Psubav Average differential pressure i Cylinder number ix Cylinder number iy of reference cylinder Cylinder number AF of cylinder (non-reference cylinder) other than reference cylinder Exhaust air / fuel ratio AFt Target air / fuel ratio Q Fuel injection amount KL Filling rate

Claims (9)

An apparatus for calibrating an in-cylinder pressure sensor provided in at least two cylinders of a multi-cylinder internal combustion engine,
Measuring means for measuring the in-cylinder pressure for each cylinder at the timing of two predetermined points by the in-cylinder pressure sensor;
Differential pressure calculation means for calculating, for each cylinder, a differential pressure between in-cylinder pressures at the timing of the two points measured by the measurement means;
A non-reference cylinder sensor sensitivity correction coefficient for calculating a sensor sensitivity correction coefficient of an in-cylinder pressure sensor of a cylinder other than the reference cylinder based on the differential pressure of a predetermined reference cylinder and the differential pressure of a cylinder other than the reference cylinder An in-cylinder pressure sensor calibration apparatus comprising: a calculating means.   2. The in-cylinder pressure sensor calibration device according to claim 1, wherein the timing of the two predetermined points is a timing of two points during the compression stroke.   Of the two predetermined timings, one is during the exhaust stroke and the exhaust valve is open and the intake valve is closed, and the other is during the intake stroke and the exhaust valve is closed and the intake valve is closed. The in-cylinder pressure sensor calibration device according to claim 1, wherein the timing is an open timing.   4. The in-cylinder pressure sensor calibration apparatus according to claim 3, further comprising a fuel cut executing unit that executes fuel cut when the in-cylinder pressure is measured by the measuring unit.   The sensor sensitivity correction coefficient of an in-cylinder pressure sensor of a cylinder other than the reference cylinder is a value obtained by dividing a differential pressure of the reference cylinder by a differential pressure of a cylinder other than the reference cylinder. The in-cylinder pressure sensor calibration apparatus according to any one of 1 to 4.   The measuring means repeatedly executes the in-cylinder pressure measurement a plurality of times during steady operation of the internal combustion engine, and the differential pressure calculating means calculates the differential pressure of each time based on the in-cylinder pressure of each time measured by the measuring means. 6. The in-cylinder pressure sensor calibration apparatus according to claim 1, wherein the final differential pressure is calculated by calculating and averaging the differential pressure of each time. An air-fuel ratio sensor for detecting an exhaust air-fuel ratio, and a reference cylinder sensor sensitivity correction coefficient calculating means for calculating a sensor sensitivity correction coefficient of an in-cylinder pressure sensor of the reference cylinder,
The measuring means measures the in-cylinder pressure at two predetermined timings during the compression stroke,
The reference cylinder sensor sensitivity correction coefficient calculating means calculates the reference cylinder based on the differential pressure of the in-cylinder pressure of the reference cylinder calculated by the differential pressure calculating means and the exhaust air / fuel ratio detected by the air / fuel ratio sensor. The in-cylinder pressure sensor calibration apparatus according to claim 1, wherein a sensor sensitivity correction coefficient of the in-cylinder pressure sensor is calculated. Fuel injection means for injecting a fuel injection amount set in advance so that the exhaust air-fuel ratio becomes a predetermined target air-fuel ratio;
The reference cylinder sensor sensitivity correction coefficient calculation means obtains a value obtained by dividing the exhaust air-fuel ratio detected by the air-fuel ratio sensor when the fuel is injected by the fuel injection means by the target air-fuel ratio. The in-cylinder pressure sensor calibration device according to claim 7, wherein the calibration is performed as a sensor sensitivity correction coefficient of the in-cylinder pressure sensor of the cylinder.   8. A correction means for correcting sensor sensitivity correction coefficients of cylinders other than the reference cylinder based on the sensor sensitivity correction coefficient of the reference cylinder calculated by the reference cylinder sensor sensitivity correction coefficient calculation means. Or the in-cylinder pressure sensor calibration device according to 8.

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