Abnormality determination device of internal combustion engine

An abnormality determination device of an internal combustion engine in which a breather line connects an intake-air path positioned upstream from a forced-induction system and a crankcase includes an intake-air flow rate sensor that detects an intake air flow rate in the intake-air path, a pressure sensor that detects a pressure of the breather line, and an abnormality determination unit that determines abnormality of the breather line. The abnormality determination unit estimates an intake air resistance of the intake-air path from the pressure when the engine is under low load conditions under which the intake air flow rate is less than a predetermined value and the pressure when the engine is under high load conditions under which the intake air flow rate is the predetermined value or greater and determines abnormality of the breather line when the intake air resistance is less than a threshold.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2019-021325, filed Feb. 8, 2019, entitled “Abnormality Determination Device of Internal Combustion Engine.” The contents of this application are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to an abnormality determination device of an internal combustion engine in which an intake-air path positioned upstream from a forced-induction system and a crankcase are connected to each other by a breather line.

BACKGROUND

A method that is employed by such an abnormality determination device of an internal combustion engine is known from U.S. Patent Application Publication No. 2016/0097355A1. In the method, in a state where an internal combustion engine is under high load conditions under which the flow rate of intake air in an intake-air path is equal to or greater than a predetermined flow rate, the integrated value of an estimated pressure in a breather line over a predetermined period of time when the breather line is in a normal state and the integrated value of the actual pressure in the breather line over a predetermined period of time that is detected by a pressure sensor are calculated, and when the ratio of the integrated value of the actual pressure to the integrated value of the estimated pressure is equal to or less than a threshold, it is determined that a connecting portion of the breather line is disconnected.

With the above-mentioned method of the related art, it takes time to perform abnormality determination because it is necessary to integrate, over a relatively long period of time, each of the actual pressure and the estimated pressure of the breather line, and in addition, there is a possibility that the accuracy of the abnormality determination will deteriorate when the correspondence relationship between the actual pressure and the estimated pressure varies due to offset of the output of the pressure sensor.

SUMMARY

The present application describes, for example, an abnormality determination device of an internal combustion engine that determines abnormality of a breather line of the internal combustion engine in a short time with high accuracy.

An embodiment of an abnormality determination device of an internal combustion engine according to the present disclosure in which an intake-air path positioned upstream from a forced-induction system and a crankcase are connected to each other by a breather line includes an intake-air flow rate sensor that detects the flow rate of intake air in the intake-air path, a pressure sensor that detects a pressure of the breather line, and an abnormality determination unit that determines abnormality of the breather line. The abnormality determination unit estimates an intake air resistance of the intake-air path from the pressure when the internal combustion engine is under low load conditions under which the flow rate of the intake air is less than a predetermined value and the pressure when the internal combustion engine is under high load conditions under which the flow rate of the intake air is equal to or greater than the predetermined value and determines abnormality of the breather line when the intake air resistance is less than a threshold. Therefore, abnormality of the breather line can be determined in a short time, and in addition, abnormality determination is less likely to be influenced by offset of the output of the pressure sensor, so that the determination accuracy is improved.

Note that an airflow meter16according to an embodiment of the present disclosure corresponds to the intake-air flow rate sensor according to the present disclosure.

DETAILED DESCRIPTION

An embodiment of the present disclosure will be described below with reference toFIG. 1toFIG. 5.

As illustrated inFIG. 1, on an intake-air path12of an in-line four-cylinder four-cycle internal combustion engine11that is mounted on an automobile, an air cleaner15that removes dust contained in intake air, an airflow meter16that measures the flow rate of the intake air, a forced-induction system17that is formed of a turbocharger or a supercharger that pressurizes the intake air, and a throttle valve18that adjusts the flow rate of the intake air by reducing the diameter of the intake-air path12are arranged in this order in a direction from an intake port13toward an intake manifold14, the intake port13being positioned at the upstream end in a flow direction of the intake air, and the intake manifold14being positioned at the downstream end in the flow direction of the intake air. A portion of the intake-air path12that is located between the airflow meter16and the forced-induction system17and a crankcase19of the internal combustion engine11are connected to each other by a breather line20. In addition, the intake manifold14and the crankcase19of the internal combustion engine11are connected to each other by a positive crankcase ventilation (PCV) line21, and a PCV valve22opens and closes an intermediate portion of the PCV line21.

Blowby gas that is a portion of a fuel component contained in intake air, the portion having flowed in the crankcase19from a combustion chamber of the internal combustion engine11by passing through a gap between a piston and a cylinder, is caused to return to the intake-air path12through the breather line20or caused to return to the intake-air path12through the PCV line21, so that the fuel component contained in the blowby gas is prevented from being released to an atmosphere.

In other words, when the PCV valve22is opened in a state where the internal combustion engine11is in an unboosted state in which the forced-induction system17does not operate, atmospheric pressure acts on a portion of the intake-air path12that is positioned upstream from the throttle valve18, and in contrast, the intake negative pressure of the internal combustion engine11acts on a portion of the intake-air path12that is positioned downstream from the throttle valve18. Thus, the intake air in the intake-air path12positioned upstream from the throttle valve18flows into the crankcase19through the breather line20, and then, the intake air is returned to the intake manifold14through the PCV line21together with the blowby gas and is finally supplied to the combustion chamber of the internal combustion engine11together with the intake air.

When the internal combustion engine11is in a boosted state in which the forced-induction system17operates, although boost pressure acts on the portion of the intake-air path12positioned downstream from the forced-induction system17, closing the PCV valve22prevents the boost pressure from escaping to the crankcase19through the PCV line21. The blowby gas in the crankcase19is drawn into the intake-air path12by a negative pressure that is generated on the upstream side of the forced-induction system17, which is operating. Then, the blowby gas passes through the intake-air path12together with the intake air and is supplied to the combustion chamber of the internal combustion engine11.

When the internal combustion engine11is in the boosted state, for example, if a first connection portion23of the breather line20that is to be connected to the intake-air path12is disconnected from the intake-air path12, or if a second connection portion24of the breather line20that is to be connected to the crankcase19is disconnected from the crankcase19, there is a possibility that blowby gas flowing through the breather line20from the crankcase19toward the intake-air path12will be released to the atmosphere, and thus, it is necessary to detect abnormality of the breather line20and to issue a warning. Accordingly, the breather line20is provided with a pressure sensor29that detects the pressure in the breather line20.

As illustrated inFIG. 2, an abnormality determination unit30that is formed of an electronic control unit that determines abnormality of the breather line20is connected to the airflow meter16, the pressure sensor29, and a warning unit32. The warning unit32is formed of, for example, a liquid crystal panel that is included in an instrument panel.

The advantageous effects of the embodiment of the present disclosure that includes the above-described configuration will now be described.

As illustrated inFIG. 3, when the internal combustion engine11is under low load conditions under which the flow rate of intake air in the intake-air path12that is detected by the airflow meter16is small, the pressure in the breather line20is measured by the pressure sensor29for a predetermined period of time (e.g., about two seconds). In addition, when the internal combustion engine11is under high load conditions under which the flow rate of the intake air in the intake-air path12that is detected by the airflow meter16is large, the pressure in the breather line20is measured by the pressure sensor29for a predetermined period of time (e.g., about two seconds).

The pressure in the breather line20decreases as the intake negative pressure in the intake-air path12increases as a result of an increase in the load on the internal combustion engine11. However, in the case where the first connection portion23of the breather line20is disconnected from the intake-air path12, or the second connection portion24of the breather line20is disconnected from the crankcase19, and in the case where an intermediate portion of the breather line20breaks, the internal space of the breather line20is caused to communicate with the atmosphere, and thus, even if the intake negative pressure in the intake-air path12increases, the pressure in the breather line20is less likely to decrease. Therefore, abnormality of the breather line20can be determined on the basis of this phenomenon.

In the graph illustrated inFIG. 4, the horizontal axis (x-axis) denotes the flow rate of the intake air in the intake-air path12detected by the airflow meter16, and the vertical axis (y-axis) denotes the pressure in the breather line20detected by the pressure sensor29. A pressure y in the breather line20decreases as an intake air flow rate x in the intake-air path12increases, and its change characteristics are approximated by a quadratic curve y=−Ax2−B that is indicated by a solid line inFIG. 4.

The quadratic curve y=−Ax2−B can be calculated as a quadratic curve that passes through a low-load region of the internal combustion engine11in which the flow rate of the intake air in the intake-air path12detected by the airflow meter16is small, that is, an L point that corresponds to the pressure and the intake air flow rate detected when the internal combustion engine11is in idling operation or in a deceleration fuel cut-off mode, and a high-load region of the internal combustion engine11in which the flow rate of the intake air in the intake-air path12detected by the airflow meter16is large, that is, an H point that corresponds to the pressure and the intake air flow rate detected when the internal combustion engine11operates under a higher load than in the low-load region.

In a normal state in which the first connection portion23and the second connection portion24of the breather line20are not disconnected, and in which the intermediate portion of the breather line20is not broken, the pressure greatly decreases as the intake negative pressure increases, and thus, the quadratic curve y=−Ax2−B becomes like that indicated by a dashed line inFIG. 4. In this case, an intake-air-resistance coefficient A that represents the intake air resistance of the intake-air path12is equal to or greater than a threshold A0. In contrast, in an abnormal state in which the first connection portion23or the second connection portion24of the breather line20is disconnected, or in which the intermediate portion of the breather line20is broken, the pressure does not greatly decrease even when the intake negative pressure increases, and thus, the quadratic curve y=−Ax2−B becomes like that indicated by a one-dot chain line inFIG. 4. In this case, the intake-air-resistance coefficient A that represents the intake air resistance of the intake-air path12is less than the threshold A0. Consequently, by comparing the intake-air-resistance coefficient A that is calculated from the flow rate of the intake air in the intake-air path12and the pressure in the breather line20with the threshold A0, abnormality of the breather line20can be determined.

Next, steps for determining abnormality of the breather line20that are performed by the abnormality determination unit30will be described with reference to the flowchart illustrated inFIG. 5.

First, when a low-load side buffer completion flag is 0 in step S1, and accumulation of data regarding the intake air flow rate and the pressure in a state where the internal combustion engine11is under low load conditions is not completed, if the intake air flow rate detected by the airflow meter16is less than a predetermined value, and the internal combustion engine11is under low load conditions in step S2, the intake air flow rate detected by the airflow meter16and the pressure detected by the pressure sensor29are stored in a low-load side buffer in step S3. Each time step S2and step S3are repeated, a buffer counter is incremented. When the count value of the buffer counter is equal to or greater than a predetermined value in step S4, it is determined in step S5that the accumulation of data regarding the intake air flow rate and the pressure in a state where the internal combustion engine11is under low load conditions is completed, and the low-load side buffer completion flag is set to 1.

After the process of step S5has been performed, or when the low-load side buffer completion flag is 1 in step S1, or when the internal combustion engine11is not under low load conditions in step S2, the process continues to step S6. When a high-load side buffer completion flag is 0 in step S6, and accumulation of data regarding the intake air flow rate and the pressure in a state where the internal combustion engine11is under high load conditions is not completed, if the intake air flow rate detected by the airflow meter16is equal to or greater than the predetermined value, and the internal combustion engine11is under high load conditions in step S7, the intake air flow rate detected by the airflow meter16and the pressure detected by the pressure sensor29are stored in a high-load side buffer in step S8. Each time step S7and step S8are repeated, a buffer counter is incremented. When the count value of the buffer counter is equal to or greater than a predetermined value in step S9, it is determined in step S10that the accumulation of data regarding the intake air flow rate and the pressure in a state where the internal combustion engine11is under high load conditions is completed, and the high-load side buffer completion flag is set to 1.

After the process of step S10has been performed, or when the high-load side buffer completion flag is 1 in step S6, or when the internal combustion engine11is not under high load conditions in step S7, the process continues to step S11. If the low-load side buffer completion flag is 1, and the high-load side buffer completion flag is 1 in step S11, it is determined that the accumulation of data regarding the intake air flow rate and the pressure in a state where the internal combustion engine11is under low load conditions and the accumulation of data regarding the intake air flow rate and the pressure in a state where the internal combustion engine11is under high load conditions are both completed, and the representative value of the intake air flow rate and the pressure (point L inFIG. 4) is calculated as the average value of the plurality of data items accumulated in the low-load side buffer in step S12. In addition, the representative value of the intake air flow rate and the pressure (point H inFIG. 4) is calculated as the average value of the plurality of data items accumulated in the high-load side buffer in step S13.

Subsequently, in step S14, the quadratic curve y=−Ax2−B that passes through the representative value on the low-load side (point L inFIG. 4) and the representative value on the high-load side (point H inFIG. 4) is determined. As a result, if the quadratic curve y=−Ax2−B is in the state indicated by the dashed line, and the intake-air-resistance coefficient A representing the intake air resistance of the intake-air path12is equal to or greater than the threshold A0in step S15, it is determined in step S16that the breather line20is in the normal state. In contrast, if the quadratic curve y=−Ax2−B is in the state indicated by the one-dot chain line, and the intake-air-resistance coefficient A representing the intake air resistance of the intake-air path12is less than the threshold A0in step S15, it is determined in step S17that the breather line20is in an abnormal state, and the warning unit32is activated so as to issue a warning to an occupant in step S18.

As described above, according to the present embodiment, both when the internal combustion engine11is under low load conditions and when the internal combustion engine11is under high load conditions, the flow rate of the intake air in the intake-air path12and the pressure in the breather line20are each measured for a predetermined period of time, and the intake air resistance of the intake-air path12is estimated from the pressure when the internal combustion engine11is under low load conditions, under which the flow rate of the intake air is less than the predetermined value, and the pressure when the internal combustion engine11is under high load conditions, under which the flow rate of the intake air is equal to or greater than the predetermined value. When the intake air resistance is small, it is determined that leakage has occurred in the breather line20, and thus, determination of abnormality of the breather line20can be completed in a short time of about 2 seconds.

In addition, since the intake air resistance of the intake-air path12is estimated from the pressure in the breather line20when the internal combustion engine11is under low load conditions and the pressure in the breather line20when the internal combustion engine11is under high load conditions, both the pressure values being detected by the single pressure sensor29, abnormality determination is less likely to be influenced by offset of the output of the pressure sensor29. In other words, even if the output of the pressure sensor29is offset, only the value of B of the quadratic curve y=−Ax2−B in the graph illustrated inFIG. 4changes, and the value of the intake-air-resistance coefficient A does not change. Therefore, the accuracy of abnormality determination can be improved by accurately estimating the intake air resistance of the intake-air path12.

Although the embodiment of the present disclosure has been described above, various design changes can be made within the gist of the present disclosure.

For example, the number of cylinders of the internal combustion engine11is not limited to four, which is mentioned in the embodiment.

In addition, in the embodiment, although the breather line20is connected to the crankcase19, the advantageous effects of the present disclosure can also be obtained by causing the internal space of the crankcase19and the internal space of a head cover to communicate with each other and by connecting the breather line20to the head cover. Therefore, such a configuration in which the breather line20is connected to another space that is in communication with the crankcase19is also included in the technical scope of the present disclosure. Although a specific form of embodiment has been described above and illustrated in the accompanying drawings in order to be more clearly understood, the above description is made by way of example and not as limiting the scope of the invention defined by the accompanying claims. The scope of the invention is to be determined by the accompanying claims. Various modifications apparent to one of ordinary skill in the art could be made without departing from the scope of the invention. The accompanying claims cover such modifications.