JP2011111906A - Diagnostic device for cylinder pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable accurate detection of the change of the output characteristics of a cylinder pressure sensor. <P>SOLUTION: At the unburnt rotation of an internal combustion engine, measurement data is obtained which is measured by the cylinder pressure sensor when a cylinder in which the cylinder pressure sensor is installed is in a compression process. Also, measurement data is obtained which is measured by the cylinder pressure sensor when the cylinder is in an expansion process. Then, indication that shows the level of the change of the output characteristics of the cylinder pressure sensor is calculated by inputting each measurement data to a computer model that has the rotating speed of the internal combustion engine and the cooling water temperature as parameters. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

    The present invention relates to a diagnostic apparatus for an in-cylinder pressure sensor that measures an in-cylinder pressure of an internal combustion engine.

  An in-cylinder pressure sensor is used as a means for measuring the in-cylinder pressure of the internal combustion engine. Since the output of the in-cylinder pressure sensor is used for combustion control of the internal combustion engine, when any change occurs in the output characteristics of the in-cylinder pressure sensor, it is desirable to detect the change quickly.

  As one aspect of the change in the output characteristics of the in-cylinder pressure sensor, hysteresis occurring in the output value is known. The hysteresis here means that when the in-cylinder pressure is changed from a certain value and returned to the original value, the output value of the in-cylinder pressure sensor does not coincide between the starting point and the ending point. The cause of such an abnormality is that the deposit generated by combustion in the cylinder sticks to the periphery of the in-cylinder pressure sensor, resulting in a sliding resistance of the pressure receiving part, and the components of the in-cylinder pressure sensor have deteriorated. And so on. If such hysteresis occurs in the output value of the in-cylinder pressure sensor, the change in the in-cylinder pressure cannot be measured accurately, and various problems may occur when performing combustion control of the internal combustion engine.

  In order to accurately detect the occurrence of hysteresis, it is necessary to quantify the degree of the hysteresis so that it can be quantitatively determined. With regard to this point, in the technique disclosed in Japanese Patent Application Laid-Open No. 2009-203938 (hereinafter, “prior art”), the pressure difference between the in-cylinder pressure waveform when the internal combustion engine is motored and the reference in-cylinder pressure waveform is determined as a predetermined crank angle. An absolute value is obtained for each phase, and a value obtained by integrating them is calculated as a hysteresis amount. By comparing this amount of hysteresis with a threshold value, it is possible to quantitatively determine whether or not the hysteresis occurring in the output value of the in-cylinder pressure sensor is within an allowable range.

JP 2009-203938 A JP 2007-303293 A Japanese Patent Laid-Open No. 11-082148

  In the above prior art, there are several types of reference in-cylinder pressure waveforms depending on the operating state of the internal combustion engine, specifically, the intake air amount obtained by the air flow meter, the engine speed, the engine load, etc. It is prepared. Of the prepared reference in-cylinder pressure waveforms, the one corresponding to the operating state of the internal combustion engine at the time of measurement by the in-cylinder pressure sensor is selected and used for comparison with the in-cylinder pressure waveform measured by the in-cylinder pressure sensor. It has become so.

  However, it is not realistic to prepare a reference in-cylinder pressure waveform for all operating states that the internal combustion engine can take. For this reason, the reference in-cylinder pressure waveform corresponding to the operation state at the time of measurement by the in-cylinder pressure sensor may not be prepared. In that case, it is conceivable to approximate with the reference in-cylinder pressure waveform corresponding to the operation state closest to the operation state at the time of measurement, but the error due to the approximation reduces the accuracy of the hysteresis amount which is the final calculated value. become.

  In addition, many of the physical quantities representing the operating state of the internal combustion engine affect the in-cylinder pressure waveform, but there are limits to the types of physical quantities that can be actually acquired. For this reason, the reference in-cylinder pressure waveform selected based on a limited number of physical quantities does not necessarily match the true reference in-cylinder pressure waveform in the operation state at that time. Unless the accuracy of the selected reference in-cylinder pressure waveform is sufficiently high, the accuracy of the hysteresis amount as the final calculated value does not increase.

  As described above, the prior art has room for improvement in the detection accuracy of hysteresis generated in the output value of the in-cylinder pressure sensor, and more generally in the detection accuracy of the change in the output characteristic of the in-cylinder pressure sensor.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a diagnostic apparatus that can accurately detect a change in output characteristics of an in-cylinder pressure sensor.

For the above purpose, the diagnostic device of the first invention provides:
An in-cylinder pressure sensor diagnostic device for measuring an in-cylinder pressure of an internal combustion engine,
Measurement data by the in-cylinder pressure sensor when the cylinder to which the in-cylinder pressure sensor is attached is in the compression stroke and non-combustion rotation of the internal combustion engine, and measurement by the in-cylinder pressure sensor when the cylinder is in the expansion stroke Means for obtaining data respectively;
Means for calculating an index indicating the degree of change in output characteristics of the in-cylinder pressure sensor by inputting each measurement data into a calculation model prepared in advance;
The calculation model has the rotational speed and cooling water temperature of the internal combustion engine as parameters.

The diagnostic device of the second invention is the diagnostic device of the first invention,
The calculation model is
An element for calculating a polytropic index in the compression stroke (hereinafter referred to as a compression polytropic index) from measurement data obtained in the compression stroke;
An element for calculating the polytropic index in the expansion stroke (hereinafter referred to as the expansion polytropic index) from the measurement data obtained in the expansion stroke;
An element for calculating a ratio of the compressed polytropic index and the expanded polytropic index;
An element for calculating a difference between the ratio and a reference value as the index;
An element for determining the reference value according to the rotational speed of the internal combustion engine and the coolant temperature;
It is characterized by having.

The diagnostic device of the third invention is the diagnostic device of the first or second invention,
A means for determining abnormality of the in-cylinder pressure sensor by comparing the index with a threshold value is provided.

  The in-cylinder pressure waveform measured by the in-cylinder pressure sensor during non-combustion rotation of the internal combustion engine is symmetrical between the expansion stroke and the compression stroke with reference to TDC in an environment where ideal adiabatic compression and adiabatic expansion is performed. Become. However, if there is a change in the output characteristics of the in-cylinder pressure sensor due to sliding resistance due to deposit adhesion, deterioration of components, etc., the in-cylinder pressure waveform measured by the in-cylinder pressure sensor is asymmetric between the expansion stroke and the compression stroke. become. Therefore, if the in-cylinder pressure is measured by the in-cylinder pressure sensor in each of the compression stroke and the expansion stroke, a change in the output characteristic of the in-cylinder pressure sensor can be detected from these measurement data. That is, it is not necessary to prepare reference data to be compared with measurement data.

  However, the compression stroke and the expansion stroke in an actual internal combustion engine are not strictly heat insulation, and there is a heat loss from the inside of the cylinder to the outside. For this reason, even if there is no change in the output characteristics of the in-cylinder pressure sensor, the in-cylinder pressure waveform measured by the in-cylinder pressure sensor is not necessarily symmetrical between the expansion stroke and the compression stroke. Therefore, in order to accurately detect the change in the output characteristics of the in-cylinder pressure sensor from the measurement data, it is necessary to consider the heat loss of the in-cylinder gas.

  In this regard, in the diagnostic device according to the first aspect of the invention, the rotational speed of the internal combustion engine and the coolant temperature are used as parameters for calculating an index indicating the degree of change in the output characteristics of the in-cylinder pressure sensor. Since the rotational speed and cooling water temperature of the internal combustion engine are the main factors that determine the heat loss of the in-cylinder gas, the calculation considering the heat loss of the in-cylinder gas is possible by using them as parameters. Therefore, according to the diagnostic apparatus of the first invention, it is possible to accurately detect a change in the output characteristic of the in-cylinder pressure sensor based on the calculated index value.

  In the diagnostic device of the second invention, by taking the ratio of the polytropic index in each of the compression stroke and the expansion stroke, the waveform of the in-cylinder pressure measured in the compression stroke and the waveform of the in-cylinder pressure measured in the expansion stroke Symmetry is quantified. However, the value of this ratio includes the effect of changes in the output characteristics of the in-cylinder pressure sensor on the symmetry of the in-cylinder pressure waveform and the effect of heat loss on the symmetry of the in-cylinder pressure waveform. Yes. Therefore, in the diagnostic device of the second invention, the reference value is determined according to the rotational speed of the internal combustion engine and the cooling water temperature, and the difference between the ratio and the reference value is taken, so that the heat loss is symmetrical to the in-cylinder pressure waveform. Eliminate the effects on sex from the figures. Since the numerical value calculated in this way is used as the index, according to the diagnostic device of the second invention, it is possible to accurately detect the change in the output characteristic of the in-cylinder pressure sensor.

  According to the diagnostic device of the third aspect of the present invention, it is possible to accurately determine whether any abnormality has occurred in the in-cylinder pressure sensor, specifically, whether the output value of the in-cylinder pressure sensor has hysteresis.

1 is a diagram showing an internal combustion engine to which a diagnostic device for an in-cylinder pressure sensor as an embodiment of the present invention is applied. FIG. It is a PV diagram which shows the change of the cylinder pressure at the time of the non-combustion rotation of an internal combustion engine. It is a figure which expands and shows the broken-line frame of FIG. It is a figure which shows an example of the map for determining the correction coefficient _KCOOL which _concerns on a cooling loss from an engine speed and a cooling water temperature. It is a flowchart which shows the procedure of the hysteresis abnormality determination of the in-cylinder pressure sensor performed in embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 5.

  FIG. 1 is a diagram showing an internal combustion engine (hereinafter simply referred to as an engine) to which an in-cylinder pressure sensor diagnostic device according to an embodiment of the present invention is applied. The engine shown in FIG. 1 is a spark ignition type 4-stroke reciprocating engine provided with a spark plug 6. Moreover, it is also a cylinder direct injection engine provided with the fuel direct injection injector 7 which injects a fuel directly in a cylinder. Although only one cylinder is depicted in FIG. 1, a general vehicle engine is composed of a plurality of cylinders. An in-cylinder pressure sensor 5 for measuring the in-cylinder pressure Pc is attached to at least one of the cylinders. The engine is also provided with a crank angle sensor 8 that outputs a signal CA according to the rotation angle of the crankshaft, and a water temperature sensor 9 for measuring the cooling water temperature Tw. From the signal CA of the crank angle sensor 8, the in-cylinder volume determined by the engine speed (the number of revolutions per unit time) and the position of the piston can be calculated. An air cleaner 1 is provided at an inlet of an intake passage connected to the cylinder, and a throttle 2 is disposed downstream of the air cleaner 1. A surge tank 4 is provided downstream of the throttle 2, and an intake pressure sensor 3 for measuring the intake pressure Pim is attached to the surge tank 4. The engine also includes an arithmetic processing unit 10. The arithmetic processing unit 10 processes signals from the sensors 3, 5, 8, 9 and reflects the processing results on the operations of the actuators 2, 6, 7.

  In the present embodiment, the arithmetic processing device 10 functions as a diagnostic device for the in-cylinder pressure sensor 5. Hereinafter, a method for diagnosing the in-cylinder pressure sensor 5 performed by the arithmetic processing device 10 will be described.

  FIG. 2 is a PV diagram showing the relationship between the in-cylinder pressure and the in-cylinder volume when the engine is motored. The in-cylinder pressure P measured by the in-cylinder pressure sensor 5 is logarithmically plotted on the vertical axis, and the in-cylinder volume V calculated from the signal of the crank angle sensor 8 is logarithmically plotted on the horizontal axis. FIG. 3 is an enlarged view of the broken-line frame in FIG. At the time of non-combustion rotation such as motoring operation, there is no heat balance due to chemical change of the constituent gas or combustion. For this reason, adiabatic compression and adiabatic expansion are performed in the cylinder, and the locus of the compression stroke and the locus of the expansion stroke in the PV diagram should match. However, in practice, as indicated by the solid line in each figure, a deviation occurs between the locus of the compression stroke and the locus of the expansion stroke.

  There are two causes for the deviation between the locus of the compression stroke and the locus of the expansion stroke. The first cause is a hysteresis in the output value of the in-cylinder pressure sensor 5 (hereinafter, this is referred to as “hysteresis abnormality”). The hysteresis of the output value of the in-cylinder pressure sensor 5 is caused by a change in the output characteristics of the in-cylinder pressure sensor due to sliding resistance due to deposit fixation, deterioration of components, or the like. Another cause is that the actual compression stroke and expansion stroke are not adiabatic, and heat loss (cooling loss) from the cylinder to the outside occurs. Therefore, whether or not a hysteresis abnormality has occurred in the in-cylinder pressure sensor 5 is determined such that the deviation between the locus of the compression stroke and the locus of the expansion stroke obtained from the measurement data of the in-cylinder pressure sensor 5 is larger than the deviation caused by the cooling loss. It can be judged by whether or not. The trajectory indicated by the alternate long and short dash line in each figure is the trajectory of the expansion stroke when there is no abnormality in the in-cylinder pressure sensor 5, that is, the trajectory of the expansion stroke when only the cooling loss is considered.

The degree of deviation between the compression stroke and the expansion stroke actually occurring is quantified by calculating the polytropic index of the in-cylinder gas in the compression stroke and the expansion stroke, and calculating the ratio between them. can do. When the polytropic index of the in-cylinder gas in the compression stroke (hereinafter referred to as the compression polytropic index) is η _comp , and the polytropic index of the in-cylinder gas in the expansion stroke (hereinafter referred to as the expansion polytropic index) is η _exp , respectively, Can do.
η _comp = (lnP ₂ −lnP ₁ ) / (lnV ₂ −lnV ₁ )
η _exp = (lnP ₄ −lnP ₃ ) / (lnV ₄ −lnV ₃ )

In the above equation of η _comp , P ₁ and P ₂ are measured values of the in-cylinder pressure sensor 5 obtained at any two different points during the compression stroke, and V ₁ and V ₂ are the contents of the cylinder at each measurement time point. Is the product. Similarly, in the above equation of η _exp , P ₃ and P ₄ are measured values of the in-cylinder pressure sensor 5 obtained at any two different points during the expansion stroke, and V ₃ and V ₄ are measured at each measurement time point. The in-cylinder volume. Here, the measurement points of the in-cylinder pressure for calculating the polytropic index are two, but the polytropic index may be calculated by the least square method taking three or more measurement points.

Next, it will be considered to quantify the degree of deviation between the locus of the compression stroke and the locus of the expansion stroke caused by the cooling loss. In the compression stroke, although there is no energy balance due to combustion, the temperature of the in-cylinder gas rises due to adiabatic compression. In the expansion stroke after the piston exceeds TDC, cooling loss occurs due to heat radiation from the in-cylinder gas that has become high temperature to the cylinder wall surface. The expansion polytropic index η _exp is smaller than the compression polytropic index η _comp by this cooling loss, and the relationship is expressed by the following equation.
η _exp = K _COOL × η _comp

In the above formula, K _COOL is a correction coefficient related to the cooling loss (hereinafter referred to as a cooling loss correction coefficient). Here, the cooling loss during the motoring operation can be expressed by the following equation, for example.
Cooling loss = NE × Σ {S × h × (T−Tw)}

  In the above cooling loss equation, Σ means the integration from TDC to the exhaust valve opening timing (for example, ATDC 120 °). NE is the engine speed, S is the combustion chamber surface area, h is the heat transfer coefficient, T is the compression end temperature, and Tw is the cooling water temperature.

Furthermore, according to the gas equation of state, the compression end temperature T can be expressed by the following equation.
T = P _MAX × V _TDC / (n × R) = β × P _MAX × V _TDC / KL

In the above equation of T, β is a constant coefficient, P _MAX is the maximum value of the in-cylinder pressure, V _TDC is the in-cylinder volume when the piston is TDC, and KL is the charging efficiency. By applying the equation of T to the equation of cooling loss, it can be seen that the cooling loss is determined by NE, Tw, P _MAX , and KL.

The fact that the cooling loss is determined by NE, Tw, P _MAX and KL means that the cooling loss correction coefficient K _COOL is also determined by NE, Tw, P _MAX and KL. Accordingly, the cooling loss correction coefficient K _COOL can be expressed as a function f of NE, Tw, P _MAX , and KL as shown below.
K _COOL = f (NE, Tw, P _MAX , KL)

Here, among the variables that determine the cooling loss correction coefficient K _COOL , P _MAX and KL are set to a substantially constant value by adjusting the operating state of the engine, such as setting the throttle opening to a preset opening. be able to. Therefore, the cooling loss correction coefficient K _COOL can be mainly regarded as a function of the engine speed NE and the cooling water temperature Tw. FIG. 4 is a diagram showing an example of a map for determining the cooling loss correction coefficient K _COOL from the engine speed NE and the coolant temperature TW. As shown in FIG. 4, the maximum value of the cooling loss correction coefficient K _COOL is 1, and the value of the cooling loss correction coefficient K _COOL becomes smaller as the engine speed is lower and the cooling water temperature TW is lower.

The cooling loss correction coefficient K _COOL calculated as described above indicates the degree of deviation between the compression stroke locus and the expansion stroke locus caused by the cooling loss. On the other hand, as described above, the ratio η _exp / η _comp between the compression polytropic index η _comp and the expansion polytropic index η _exp indicates the degree of deviation between the actual compression stroke locus and the expansion stroke locus. ing. Therefore, by calculating the difference between the cooling loss correction coefficient K _COOL and the polytropic index ratio η _exp / η _comp , the degree of deviation between the compression stroke locus and the expansion stroke locus caused only by the hysteresis abnormality is quantified. Can do. Therefore, in the present embodiment, the difference between the cooling loss correction coefficient K _COOL and the polytropic index ratio η _exp / η _comp is defined as a hysteresis amount as shown in the following equation. The amount of hysteresis is an index for quantitatively determining whether or not the hysteresis generated in the output value of the in-cylinder pressure sensor 5 is in an allowable range, that is, whether or not a hysteresis abnormality has occurred.
Hysteresis amount = K _COOL − (η _exp / η _comp )

  Hereinafter, the procedure for determining hysteresis abnormality of the in-cylinder pressure sensor 5 performed by the arithmetic processing unit 10 will be described with reference to the flowchart of FIG.

  In the first step S2, the arithmetic processing unit 10 determines whether or not the vehicle is decelerating and the engine fuel cut is being performed. When the fuel cut is performed, the vehicle is driven by repulsion, and the engine is motored by reverse input from the drive system. When the condition of step S2 is satisfied, the arithmetic processing device 10 executes the processing after step S4.

First, in step S4, the arithmetic processing unit 10 acquires in-cylinder pressure measurement data in the compression stroke by the in-cylinder pressure sensor 5, and calculates a compression polytropic index η _comp from the measurement data. In the next step S6, the arithmetic processing unit 10 acquires the in-cylinder pressure measurement data in the expansion stroke by the in-cylinder pressure sensor 5, and calculates the expansion polytropic index η _exp from the measurement data. In the next step S8, the arithmetic processing unit 10 acquires the engine speed NE and the cooling water temperature Tw, and searches for a map of the cooling loss correction coefficient K _COOL using these as keys.

In the next step S10, the arithmetic processing unit 10 calculates the compressed polytropic index η _comp calculated in step S4, the expanded polytropic index η _exp calculated in step S6, and the cooling loss correction coefficient K obtained by searching in step S8. _The amount of hysteresis defined by the above equation is calculated using _COOL . Then, the arithmetic processing unit 10 determines whether or not the hysteresis amount is larger than a predetermined threshold value α. The threshold value α is a limit value of an allowable hysteresis amount. Therefore, when the hysteresis amount exceeds the threshold value α, it can be determined that the hysteresis occurring in the output value of the in-cylinder pressure sensor 5 exceeds the allowable range, that is, that a hysteresis abnormality has occurred. .

  As a result of the determination in step S10, the process in step S12 is executed only when the hysteresis amount exceeds the threshold value α. In step S12, the arithmetic processing unit 10 determines that a hysteresis abnormality has occurred in the in-cylinder pressure sensor 5, and turns on the MIL (malfunction indicator light) in the dashboard. The user of the vehicle recognizes that an abnormality has occurred in the engine by watching the lighting of the MIL.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the following modifications can be made.

  Instead of calculating the ratio between the polytropic index in the compression stroke and the polytropic index in the expansion stroke, the integrated value (compression work) of the in-cylinder pressure measured by the in-cylinder pressure sensor 5 in the compression stroke and the in-cylinder pressure sensor in the expansion stroke The ratio of the in-cylinder pressure measured by 5 with the integrated value (expansion work) may be calculated. Alternatively, the ratio between the measured value by the in-cylinder pressure sensor 5 when the in-cylinder volume becomes a predetermined volume in the compression stroke and the measured value by the in-cylinder pressure sensor 5 when the in-cylinder volume becomes the predetermined volume in the expansion stroke is calculated. You may calculate. In calculating the index indicating the degree of change in the output characteristic of the in-cylinder pressure sensor 5, if measurement data by the in-cylinder pressure sensor 5 in the compression stroke and measurement data by the in-cylinder pressure sensor 5 in the expansion stroke are used. There is no limitation on the processing method of the measurement data.

  In the above-described embodiment, the MIL is turned on based on the diagnosis result of the in-cylinder pressure sensor 5, that is, the value of the hysteresis amount, but the diagnosis result may be used for other purposes. For example, the diagnosis result can be used for correcting the output value of the in-cylinder pressure sensor 5. Further, if the in-cylinder pressure sensor 5 includes a heater for removing deposits, the energization of the heater can be controlled according to the diagnosis result.

  The engine to which the present invention is applied is not limited to the in-cylinder direct injection engine as in the above-described embodiment. The present invention can also be applied to a port injection type engine. Further, the present invention can be applied not only to a spark ignition type engine but also to a compression self-ignition type engine.

  In the above-described embodiment, the in-cylinder pressure sensor 5 is diagnosed using the motoring operation of the engine that occurs as a result of the fuel cut during deceleration. However, in the case of a so-called hybrid vehicle, the in-cylinder pressure sensor 5 may be diagnosed by actively motoring the engine with an electric motor.

DESCRIPTION OF SYMBOLS 1 Air cleaner 2 Throttle 3 Intake pressure sensor 4 Surge tank 5 In-cylinder pressure sensor 6 Spark plug 7 Fuel direct injection injector 8 Crank angle sensor 9 Water temperature sensor 10 Arithmetic processing unit

Claims (3)

An in-cylinder pressure sensor diagnostic device for measuring an in-cylinder pressure of an internal combustion engine,
Measurement data by the in-cylinder pressure sensor when the cylinder to which the in-cylinder pressure sensor is attached is in the compression stroke and non-combustion rotation of the internal combustion engine, and measurement by the in-cylinder pressure sensor when the cylinder is in the expansion stroke Means for obtaining data respectively;
Means for calculating an index indicating the degree of change in output characteristics of the in-cylinder pressure sensor by inputting each measurement data into a calculation model prepared in advance;
The in-cylinder pressure sensor diagnostic apparatus characterized in that the calculation model has the rotational speed and cooling water temperature of the internal combustion engine as parameters. The calculation model is
An element for calculating a polytropic index in the compression stroke (hereinafter referred to as a compression polytropic index) from measurement data obtained in the compression stroke;
An element for calculating the polytropic index in the expansion stroke (hereinafter referred to as the expansion polytropic index) from the measurement data obtained in the expansion stroke;
An element for calculating a ratio of the compressed polytropic index and the expanded polytropic index;
An element for calculating a difference between the ratio and a reference value as the index;
An element for determining the reference value according to the rotational speed of the internal combustion engine and the coolant temperature;
The in-cylinder pressure sensor diagnostic apparatus according to claim 1, further comprising:   The in-cylinder pressure sensor diagnostic apparatus according to claim 1 or 2, further comprising means for determining an abnormality of the in-cylinder pressure sensor by comparing the index with a threshold value.

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