JP7647665B2 - Hybrid vehicle engine misfire detection device - Google Patents

Description

This invention relates to a device for detecting misfires in an engine that, together with a motor, constitutes a driving force source in a hybrid vehicle, and in particular to a misfire detection device that identifies the cylinder in which a misfire occurs.

In an engine with multiple cylinders, if a misfire occurs in any of the cylinders, unburned fuel is sent to the exhaust gas purification catalyst and combusted, which may result in deterioration or damage to the exhaust gas purification catalyst. In addition, the torque output by the engine may fluctuate greatly, which may worsen the noise and vibration characteristics (NV characteristics) of the vehicle. A device for eliminating such inconveniences associated with misfires is described in Patent Document 1.

The device described in Patent Document 1 uses a misfire detection means to detect the presence or absence of a misfire, and uses a misfire cylinder discrimination means to identify the cylinder in which the misfire is occurring, and cuts fuel to the cylinder that corresponds to the misfire. In other words, if a misfire occurs in any one cylinder, the combustion interval becomes irregular, so the cylinder for which fuel is cut is selected so that the combustion interval becomes equal. As a result, combustion is no longer occurring in multiple cylinders, and engine torque decreases. To compensate for this, the device in Patent Document 1 uses a motor to supplement the driving torque.

JP 2007-069860 A

The device described in Patent Document 1 is said to be able to identify misfiring cylinders based on the fluctuation in rotation speed during the expansion stroke of each cylinder. For example, if a misfire occurs in cylinder #1, cylinder #4 is selected as the corresponding cylinder and fuel is cut in cylinder #4. If a misfire occurs in cylinder #2, cylinder #3 is selected as the corresponding cylinder and fuel is cut in cylinder #3. This type of determination of the misfiring cylinder and selection of the corresponding cylinder is possible when a misfire occurs in any one cylinder, but if a misfire occurs in, for example, any two cylinders, it is not possible to identify the misfiring cylinder.

That is, as described in Patent Document 1, the combinations of cylinders that will cause fuel cut due to misfire include the combination of cylinders #1 and #4, and the combination of cylinders #2 and #3, and in any of these combinations, combustion occurs at equal intervals, and when rotational fluctuations, for example, are detected as the engine's operating state, the detection results will be approximately the same. In other words, when a misfire occurs in each of the cylinders in the above combinations, the detectable engine operating state is approximately the same, so it is not possible to determine which two cylinders are misfiring based on the detection results.

Conventionally, as described above, when a misfire occurs in two or more cylinders, it is not possible to determine or identify the cylinder in which the misfire occurred, making it difficult to take appropriate measures against such an abnormality. Furthermore, when a misfire occurs in two cylinders, there is a possibility that the system will not be able to comply with OBD (on-board diagnosis) regulations that require a diagnostic function to identify the cylinder in which the misfire occurred.

This invention was made with a focus on the above technical problem, and aims to provide a device that can identify or identify the cylinders in which misfires occur when misfires occur in at least two cylinders in a multi-cylinder engine.

To achieve the above object, the present invention provides a misfire determination device for a hybrid vehicle that is equipped with a motor that compensates for a decrease in engine output torque and that determines misfires in cylinders in the engine and the cylinder in which the misfire has occurred, and is equipped with a multiple misfire detection means that detects misfires in multiple cylinders in the engine, and a misfiring cylinder determination means that determines the cylinder in which the misfire has occurred when a misfire in the multiple cylinders is detected by the multiple misfire detection means. The misfiring cylinder determination means is configured to sequentially switch the cylinders to which fuel supply is stopped, perform torque assist by the motor in response to the stop of the fuel supply, compare the engine speed fluctuation pattern obtained by operating the engine with the stop of the fuel supply and the torque assist by the motor with the engine speed fluctuation pattern when a misfire has occurred in the multiple cylinders, and determine the cylinder in which the misfire has occurred based on the result of the comparison and the cylinder to which the fuel supply has been stopped when the comparison result is obtained.

According to this invention, misfires are detected in multiple cylinders. The determination can be made, for example, based on the engine speed fluctuation pattern. That is, when misfires occur in multiple cylinders, the engine speed fluctuation pattern is different from when no misfire occurs and is a unique pattern according to the number of misfiring cylinders, so misfires in multiple cylinders can be determined based on the engine speed fluctuation pattern. A misfire in a cylinder is a state in which no combustion of the mixture occurs in that cylinder, and is therefore similar to a state in which no fuel is supplied to that cylinder. Therefore, if the cylinder to which fuel supply is stopped is the cylinder in which the misfire occurs, the rotation speed fluctuation pattern when the engine is operated with fuel supply stopped and torque assisted by the motor will be the same as the pattern in a state in which a misfire occurs and fuel supply is not stopped.

The device of this invention detects or identifies misfiring cylinders by running the engine while stopping the fuel supply to each cylinder in turn to find cylinders with the same rotation speed fluctuation pattern. Therefore, if misfires occur in multiple cylinders, it is possible to identify the cylinder in which the misfire occurred. In addition, by storing the identified results as data, misfire diagnosis by OBD becomes possible.

1 is a schematic diagram showing an example of a hybrid drive device in a hybrid vehicle to which the present invention is applied; 2 is a collinear diagram of the power split mechanism. 4 is a flowchart for explaining an example of control performed by the engine misfire determination device of the present invention. FIG. 1 shows engine torque and rotation speed fluctuation patterns, as well as motor assist torque, to explain the method (procedure) of this invention for determining which cylinders are misfiring. (A) shows a case where no misfire is occurring in any cylinder, (B) shows a case where misfires are occurring in cylinders #2 and #4, (C) shows a case where fuel is cut off in cylinder #1 when misfires are occurring in cylinders #2 and #4, and (D) shows a case where fuel is cut off in cylinder #2 when misfires are occurring in cylinders #2 and #4.

Next, an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described below is merely one example of how the present invention can be implemented, and is not intended to limit the present invention.

The vehicle in this embodiment of the invention is a hybrid vehicle in which a motor can assist in reducing the output torque of the engine, and an example of such a hybrid drive system is shown diagrammatically in FIG. 1. The engine 1 is a gasoline or diesel engine with multiple cylinders, such as four or six, and a power split mechanism 4 is connected to its output side via a damper 2 and a clutch 3. In the example shown here, the power split mechanism 4 is configured with a single-pinion type planetary gear mechanism, and therefore the power split mechanism 4 has a sun gear S as a reaction element, a ring gear R as an output element, and a carrier C as an input element that holds a pinion gear meshed with the sun gear S and the ring gear R.

Torque from the engine 1 is input to the carrier C. A brake 11 is provided to selectively stop the rotation of the carrier C. A first motor (MG1) 5 is connected to the sun gear S. The ring gear R is connected to a differential gear 7, which is a final reduction gear, via an output shaft 6, and is configured to transmit driving torque from the differential gear 7 to left and right driving wheels 8. A second motor (MG2) 9 is connected to the ring gear R or the output shaft 6. The first motor 5 and second motor 9 described above are configured as motor generators that function as a motor that outputs driving torque and as a generator that generates electric power. These motors 5 and 9 are electrically connected to each other via an inverter or a power storage device (not shown), and are configured to send electric power generated by the first motor 5 to the second motor 9, for example, to cause the second motor 9 to output driving torque.

The operating state of the hybrid drive system shown in FIG. 1 will be explained in terms of the operating state of the power split mechanism 4. FIG. 2 is a nomogram of the planetary gear mechanism constituting the power split mechanism 4, with the straight line HV indicating the operating state in hybrid mode and the straight line EV indicating the operating state in electric driving mode. The nomogram shows each rotating element in the planetary gear mechanism as parallel straight lines spaced apart according to the gear ratio (the ratio between the number of teeth of the sun gear S and the number of teeth of the ring gear R), and is configured so that the dimension from a base line perpendicular to these straight lines indicates the rotation speed or torque. In the nomogram shown in FIG. 2, the leftmost line indicates the sun gear S and the first motor (MG1) connected thereto, the center line indicates the carrier C and the engine 1 connected thereto, and the rightmost line indicates the ring gear R and the second motor (MG2) 9 connected thereto.

In the hybrid mode, the engine 1 outputs torque in the upward direction in FIG. 2, and the rotation direction is the so-called forward direction. Since the ring gear R is subjected to a running resistance in the downward direction in FIG. 2, it is necessary to output torque to overcome this resistance, and therefore the first motor 5 outputs torque in the downward direction in FIG. 2 while rotating in the forward direction. In other words, the first motor 5 functions as a generator. Also, the second motor 9 connected to the ring gear R outputs torque in the upward direction in FIG. 2 while rotating in the forward direction. In other words, the second motor 9 functions as a motor, and uses the power generated by the first motor 5 as its power. In this way, in the hybrid mode, a part of the power output by the engine 1 is directly output from the power split mechanism 4 to the output shaft 6, and the other part is converted into electricity and then output from the second motor 9 to the output shaft 6. In the process, the first motor 5 controls the rotation speed of the engine 1 to a rotation speed at which fuel consumption or energy efficiency is good.

In contrast, in the electric drive mode, the engine 1 is stopped and the vehicle runs on the torque of each of the motors 5 and 9. That is, the first motor 5 rotates downward in FIG. 2 and outputs torque, and the reaction force acts on the ring gear R as a torque in the positive direction. That is, the first motor 5 functions as a motor. In this case, as can be seen from FIG. 2, the carrier C or the engine 1 connected thereto serves as a fulcrum to support the reaction force, so it is preferable to fix the carrier C, for example, by the above-mentioned brake 11. In addition, the second motor 9 rotates upward in FIG. 2 and outputs an upward torque. That is, the second motor 9 functions as a motor. In this way, in the electric drive mode, each of the motors 5 and 9 functions as a motor, so these motors 5 and 9 are supplied with power from a storage device (not shown).

In the above hybrid drive system, the torque of each motor 5, 9 can be added to or subtracted from the torque output by the engine 1. Therefore, if the engine torque pulsates, a torque of the opposite phase to the engine torque is added to the output torque, suppressing the pulsation of the drive torque and enabling smooth driving. Also, if the engine torque is insufficient or decreases for some reason, the torque decrease can be compensated for by the torque of one of the motors 5, 9, thereby performing what is known as torque assist.

The engine 1 is configured to electrically control the supply and stop of fuel, the supply amount, ignition timing, etc. In addition, the operating state of each motor 5, 9, such as the torque and rotation direction, can be electrically controlled. An electronic control device (controller) 10 capable of performing these controls is provided. The controller 10 is mainly configured as a so-called microcomputer, and is configured to perform calculations using input data and pre-stored data, and to output the results of the calculations as control command signals. In particular, the controller 10 in this embodiment of the invention is configured to detect misfire in any cylinder of the engine 1, compensate for the output torque associated with the misfire by the motors 5, 9, and identify or specify the cylinder in which the misfire has occurred. Therefore, the controller 10 is functionally configured to include a multiple cylinder misfire detection means 10a that detects the occurrence of misfire in multiple cylinders, and a misfiring cylinder determination means 10b.

Next, an example of a control for identifying (specifying) the cylinder in which a misfire has occurred when a misfire occurs in multiple cylinders in the engine 1 will be described. Figure 3 shows a flowchart for explaining an example of such a control. The control shown here is executed by the controller 10 described above, and also functions as an OBD by outputting an appropriate code depending on the detected item.

In the example shown in FIG. 3, first, it is determined whether a misfire has been detected (step S1). This determination can be made, for example, based on the rotational fluctuation pattern of the engine 1. FIG. 4A shows the engine generated torque, the pattern indicating the rotational fluctuation, and the assist torque by the first motor 5 when normal combustion occurs in all cylinders of a six-cylinder engine. In a so-called normal operating state where no misfire occurs, the fluctuation pattern of the engine speed (hereinafter, sometimes referred to as the speed fluctuation pattern) has a waveform with a nearly constant period and amplitude, but if a misfire occurs in any cylinder, the speed fluctuation pattern differs from that in the case of a normal operating state. Therefore, whether a misfire has occurred can be determined based on the detected speed fluctuation pattern.

If the answer to step S1 is negative, i.e., if no misfire has occurred, the process returns without performing any particular control. On the other hand, if the answer to step S1 is positive, a determination is made as to whether or not misfire has occurred in multiple cylinders (step S2). The functional means for executing step S2 corresponds to the multiple misfire detection means in this invention. As described above, if a misfire occurs in any cylinder, the rotation speed fluctuation pattern differs from that in normal operation, and the rotation speed fluctuation pattern depends on the cylinders in which misfires have occurred and the number of cylinders, etc., so the determination in step S2 can be made based on the rotation speed fluctuation pattern.

Figure 4(B) shows the torque generated by the engine, the pattern of rotational fluctuations, and the assist torque by the first motor 5 when misfires occur in the second cylinder (hereafter referred to as cylinder #2) and the fourth cylinder (hereafter referred to as cylinder #4) in the appropriately assigned combustion order. As can be seen from Figure 4(B), the rotational fluctuations from the cylinder in which the misfire occurs until combustion occurs in the cylinder next to the misfired cylinder are larger than in the case of normal operation shown in Figure 4(A), so misfires in multiple cylinders can be determined from the difference in the rotational fluctuation patterns.

If the result of step S2 is negative, i.e., if a misfire is occurring in a single cylinder, the misfire code (single cylinder misfire code) is output (step S3), and an instruction to stop the supply of fuel (fuel cut: F/C) to the cylinder in which the misfire is occurring is issued (step S4), and the process returns. In the case of a misfire in a single cylinder, the cylinder in which the misfire is occurring can be identified based on the rotational fluctuation or output torque fluctuation and the crank angle. In step S4, an instruction to cut fuel for the cylinder in which the misfire is identified is issued.

On the other hand, if the result of step S2 is affirmative because multiple cylinders are misfiring, the misfire code (multiple cylinder misfire code) is output (step S5). Next, it is determined whether the cylinder in which the misfire is occurring has been identified (step S6). If multiple cylinders are misfiring and the cylinder in which the misfire is occurring has not been identified, torque limitation is executed as a fail-safe control, so the determination of step S6 can be made depending on whether the fail-safe torque limitation is being executed. If the result of step S6 is negative, that is, if the misfiring cylinder has been identified, the process proceeds to the above-mentioned step S4, and a fuel cut command is issued to the cylinder in which the misfire is occurring.

If misfires are detected in multiple cylinders for the first time after engine 1 starts operating, the misfiring cylinder identification is not complete, and so a positive determination is made in step S6. In that case, active misfire cylinder identification control is executed (step S7-1) to determine whether or not there is a misfire in the first cylinder (hereinafter referred to as cylinder #1) in the sequence appropriately assigned to the multiple cylinders. As will be described later, this active misfire cylinder identification control is executed in sequence for each cylinder until the cylinder in which the misfire is occurring is identified, and the details of this control are as follows:

First, it is determined whether active detection for cylinder #1 is incomplete (step S71). This determination can be made based on whether a flag or control switch is ON. If the result of step S71 is affirmative, control of fuel cut for cylinder #1 and torque replacement (torque assist) by the first motor (MG1) 5 is executed, and it is determined whether the control is completed (step S72).

The fuel cut control and torque replacement control will be explained with reference to FIG. 4(C). FIG. 4(C) shows the case where fuel is cut in cylinder #1 when misfires occur in cylinders #2 and #4. By cutting fuel in cylinder #1, torque is reduced at the timing of combustion in cylinder #1, so the negative torque from the first motor 5 is reduced by a predetermined amount (increased in the positive direction) in order to reduce the negative torque to the engine 1. In this state, no torque is output during the expansion stroke in cylinder #1, so the tendency for the rotation speed fluctuation to increase continues, and the rotation speed fluctuation pattern remains increased as shown in FIG. 4(C), and continues until combustion occurs in the third cylinder (hereinafter referred to as cylinder #3).

In this way, by continuing to operate engine 1 with misfire and fuel cut at a specified rotation speed (e.g., 200 rpm) for a specified period of time (e.g., 3 periods), it is possible to obtain the rotation speed fluctuation pattern when fuel is cut. Furthermore, since the rotation speed fluctuation pattern in this case differs from the rotation speed fluctuation pattern when misfires occur in cylinders #2 and #4 as shown in FIG. 4(B), it is possible to determine that no misfire occurred in cylinder #1.

In step S72, the fuel cut in cylinder #1 and the associated torque control of the first motor 5 are executed, and it is determined whether the associated misfire determination for cylinder #1 has been completed. Since such a misfire determination requires that the engine 1 be operated for the above-mentioned predetermined period, if that period has not elapsed, a positive determination is made in step S72. In that case, a flag or control switch that continues the torque limit request is turned ON (step S8), and the process returns to the main routine.

On the other hand, if the above-mentioned predetermined period has elapsed and the misfire judgment for cylinder #1 has been completed, step S72 is judged as positive. In that case, the judgment result of whether or not cylinder #1 has misfired, that is, whether or not cylinder #1 is a misfiring cylinder is judged (step S73). As described above, if the rotation speed fluctuation pattern when engine 1 is operated after fuel cut for cylinder #1 is different from the rotation speed fluctuation pattern when misfires occur in cylinders #2 and #4, cylinder #1 is judged not to be a misfiring cylinder, and step S73 is judged as negative. In that case, a flag or control switch indicating the completion of positive judgment control for cylinder #1 is turned ON (step S74). Then, it is judged whether or not the value of the cylinder identification counter, which indicates the number of cylinders for which the identification (judgment) of the presence or absence of misfire has been completed, is less than "2 cylinders", in other words, whether or not it has reached "2 cylinders" (step S76).

As described above, when misfire cylinder identification active control has been performed only on cylinder #1, the result of step S76 is negative. In this case, the process proceeds to step S8 described above and then returns to perform misfire cylinder identification active control on the other cylinders.

On the other hand, as will be explained later regarding misfire in cylinder #2, if the rotation speed fluctuation pattern when engine 1 is operated with fuel cut is the same as when fuel is not cut, then combustion has not occurred in the cylinder where fuel has been cut to begin with. In other words, a misfire has occurred in the cylinder where fuel has been cut. If a misfire does occur in cylinder #1, then the rotation speed fluctuation pattern when fuel is cut in cylinder #1 will be the same as when fuel is not cut in cylinder #1, in which case a positive determination is made in step S73. Then, proceed to step S75.

In step S75, a cylinder misfire code is output, which indicates that cylinder #1 is a misfiring cylinder. Next, the count value of the identified cylinder counter, which counts the number of times a misfiring cylinder has been identified, is increased by "1" (step S76). In other words, the counter is incremented (counted up). Next, the process proceeds to step S74 described above, where a flag or control switch indicating completion of active determination for cylinder #1 is turned ON. After that, the process proceeds to step S76 described above.

The control that performs the above-mentioned steps S71, S72, S73, S74, S75, and S76 in order is the misfire cylinder identification active control for cylinder #1, and each time this control is completed, the cylinder identification counter is incremented. At the stage where the presence or absence of misfire for cylinder #1 is determined, the value of the cylinder identification counter has not reached "2 cylinders", so the routine in FIG. 3 returns. In this case, it has already been determined in step S2 that misfires have occurred in multiple cylinders, but after the return, the above-mentioned steps S1, S2, S5, and S6 are executed in order in the same manner as described above, and then the determination in step S71 is made. In this case, the identification (determination) of cylinder #1 has been completed, so the determination in step S71 after the return is negative.

If the answer to the question in step S71 after the return is negative, i.e., if active detection for cylinder #1 is complete, active misfire cylinder identification control for cylinder #2 is executed (step S7-2). The content of this control is the same as the active misfire cylinder identification control for cylinder #1 described above. Therefore, it is determined whether active detection for cylinder #2 is complete, and if it is not complete, control is executed to cut fuel for cylinder #2 and to substitute torque (torque assist) by the first motor (MG1) 5, and if the control is not complete, the flow proceeds to step S8, and a flag or control switch that continues the torque limit request is turned ON.

The fuel cut control and torque replacement control for the #2 cylinder will be explained with reference to FIG. 4(D). FIG. 4(D) shows the case where fuel is cut in the #2 cylinder when misfires occur in the #2 and #4 cylinders. By cutting fuel in the #2 cylinder, torque is reduced due to the fuel cut at the timing of combustion in the #2 cylinder, so the negative torque by the first motor 5 is reduced by a predetermined amount (increased in the positive direction) in order to reduce the negative torque to the engine 1. In this case, since a misfire has already occurred in the #2 cylinder, the rotation speed fluctuation pattern is almost the same as the pattern shown in FIG. 4(B) when no fuel cut is performed. Therefore, it is identified (determined) that a misfire has occurred in the #2 cylinder based on the detected rotation speed fluctuation pattern. Note that (D) in Figure 4 shows an example of a case where a misfire also occurs in cylinder #2. However, in a case where there is no misfire in cylinder #2, the rotation speed fluctuation pattern when engine 1 is operated with fuel cut will be as shown in (B) in Figure 4 described above, and therefore cylinder #2 will be identified (determined) as not being a misfiring cylinder.

When the presence or absence of misfire is identified (determined) for cylinder #2 in this manner, the cylinder identification counter is incremented or not incremented, and the active determination completion flag or control switch for cylinder #2 is turned ON, just as in the case of cylinder #1 described above, and then the determination in step S9 described above is made. When the presence or absence of misfire for cylinder #2 is determined, the value of the cylinder identification counter has not reached "2 cylinders," so the determination in step S9 is affirmative, and, just as described above, the process proceeds to step S8 and then returns.

When the misfire cylinder identification active control for cylinder #2 (step S7-2) is completed and the misfire cylinder identification active control for cylinder #1 (step S7-1) returns a negative result in the determination of whether active detection is not yet complete (step S71), and the misfire cylinder identification active control for cylinder #2 (step S7-2) returns a negative result. In this case, the misfire cylinder identification active control for cylinder #3 is executed (step S7-3). The content of the control is the same as the misfire cylinder identification active control for cylinders #1 and #2 described above. Thereafter, the misfire cylinder identification active control is executed for each cylinder from cylinder #4 onwards (steps S7-4 to S7-6) until the determination of step S9 is negative, that is, until the number of cylinders for which the determination of the occurrence of misfires is established reaches "2 cylinders".

In the example shown in FIG. 4, misfires occur in cylinders #2 and #4, so a negative determination is made in step S9 when misfiring cylinder identification active control for cylinder #4 is completed. If a negative determination is made in step S9, that is, if misfires occur in two cylinders and the identification of the cylinders in which the misfires occur has been completed, the process proceeds to step S4 described above, where a fuel cut command is issued for the misfiring cylinder, and the process returns. Therefore, the functional means for executing the above-mentioned steps S7-1 to S7-6 corresponds to the misfiring cylinder determination means in this invention.

As described above, in this embodiment of the invention, when misfires are detected in multiple cylinders, fuel is cut off for each cylinder in turn, and the cylinder whose rotation speed fluctuation pattern when fuel is cut is the same as when fuel is not cut is detected, so that the misfiring cylinder can be identified (determined) reliably. Then, the result of this determination is output as a code, making it possible to diagnose misfires using OBD.

The present invention is not limited to the above-described embodiment, and the engine that is the subject of the present invention may be any engine having multiple cylinders, and may be an engine other than a six-cylinder engine. Furthermore, the hybrid vehicle that is the subject of the present invention is not limited to a vehicle equipped with a hybrid drive unit having the configuration shown in FIG. 1, and may be any hybrid vehicle equipped with a hybrid drive unit configured to assist the drive torque by a motor.

REFERENCE SIGNS LIST 1 Engine 2 Damper 3 Clutch 4 Power split mechanism 5 First motor (MG1)
6 Output shaft 7 Differential gear 8 Drive wheels 9 Second motor (MG2)
REFERENCE SIGNS LIST 10 Controller 10a Multiple cylinder misfire detection means 10b Misfiring cylinder determination means 11 Brake C Carrier R Ring gear S Sun gear

Claims (1)

A misfire determination device for a hybrid vehicle, comprising: a motor that compensates for a decrease in an output torque of an engine; and the device determines whether a misfire has occurred in a cylinder of the engine and which cylinder has the misfire,
a multiple misfire detection means for detecting misfires in multiple cylinders of the engine;
a misfire cylinder determination means for determining a cylinder in which a misfire is occurring when the misfire is detected in the plurality of cylinders by the plurality of misfire detection means,
The misfire cylinder determination means
Switching the cylinders to which fuel supply is to be stopped in sequence;
performing torque assist by the motor in response to the stop of the supply of the fuel;
comparing a rotation speed fluctuation pattern of the engine obtained by operating the engine by stopping the supply of fuel and performing torque assist by the motor with a rotation speed fluctuation pattern of the engine when a misfire occurs in the plurality of cylinders;
The engine misfire detection device for a hybrid vehicle is configured to determine which cylinder is misfiring based on the result of the comparison and the cylinder to which the fuel supply is stopped when the result of the comparison is obtained.

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