WO2015098000A1

WO2015098000A1 - Control device of internal combustion engine

Info

Publication number: WO2015098000A1
Application number: PCT/JP2014/006070
Authority: WO
Inventors: Yuichi Miyazaki
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2013-12-26
Filing date: 2014-12-04
Publication date: 2015-07-02
Also published as: JP2015124658A; EP3090165A1; JP6252167B2

Abstract

A control device of an internal combustion engine includes: an internal combustion engine that has an exhaust valve; an exhaust passage that is connected to the internal combustion engine; a turbine of a supercharger that is provided in the exhaust passage; a bypass passage that bypasses the turbine; a bypass valve that opens and closes the bypass passage; a valve-operating device that is capable of switching between a first mode and a second mode, the first mode being a mode in which the exhaust valve is opened at least in a part of an exhaust stroke, the second mode being a mode in which the exhaust valve is opened at least in a part of the exhaust stroke, a lift amount of the exhaust valve is increased at least in a part of an intake stroke and the exhaust valve is closed after that; and a controller that switches a mode to the second mode and closes the aperture of the bypass valve, or controls the aperture of the exhaust valve to a smaller side than an aperture of the bypass valve of the first mode.

Description

CONTROL DEVICE OF INTERNAL COMBUSTION ENGINE

The present invention relates to a control device of an internal combustion engine.

Patent Document 1 discloses a technology in which an exhaust valve is opened not only in an exhaust stroke but also in an intake stroke and an inner EGR amount is increased. Patent Document 2 discloses a technology in which exhaust gas bypasses a turbine of a supercharger. Patent Document 3 discloses a technology in which an exhaust pressure is higher than an intake pressure in a supercharging range.

Japanese Patent Application Publication No. 2005-105954 Japanese Patent Application Publication No. 2001-107722 Japanese Patent No. 3551436

When exhaust gas bypasses a turbine, an amount of exhaust gas passing through the turbine is reduced and an exhaust pressure is reduced with respect to an intake pressure. When the exhaust pressure is reduced in this manner and an exhaust valve is opened in an intake stroke in order to increase an inner EGR amount, it is difficult to return the exhaust gas into a cylinder. Thereby, there are possibilities that the inner EGR amount is not secured.

It is an object to provide a control device of an internal combustion engine that is capable of securing an inner EGR amount.

The above-mentioned object is solved by a control device of an internal combustion engine including: an internal combustion engine that has an exhaust valve; an exhaust passage that is connected to the internal combustion engine; a turbine of a supercharger that is provided in the exhaust passage; a bypass passage that bypasses the turbine; a bypass valve that opens and closes the bypass passage; a valve-operating device that is capable of switching between a first mode and a second mode, the first mode being a mode in which the exhaust valve is opened at least in a part of an exhaust stroke, the second mode being a mode in which the exhaust valve is opened at least in a part of the exhaust stroke, a lift amount of the exhaust valve is increased at least in a part of an intake stroke and the exhaust valve is closed after that; and a controller that switches a mode to the second mode and closes the aperture of the bypass valve, or controls the aperture of the exhaust valve to a smaller side than an aperture of the bypass valve of the first mode.

The controller may switch the mode to the second mode and closes the bypass valve when combustion condition of the internal combustion engine is unstable and switches the mode to the first mode when the combustion condition of the internal combustion engine is stable.

The controller may open the bypass valve in the first mode when the combustion condition of the internal combustion engine is stable and warming-up of a catalyst provided in the exhaust passage on the downstream side of the bypass passage is requested.

The controller may determine stability of the combustion condition of the internal combustion engine based on a changing rate of the rotation speed of the internal combustion engine.

The controller may determine stability of the combustion condition of the internal combustion engine based on each cylinder pressure of a plurality of cylinders of the internal combustion engine.

It is possible to provide a control device of an internal combustion engine that is capable of securing an inner EGR amount.

FIG. 1 illustrates an engine system in accordance with an embodiment; FIG. 2A illustrates an engine of an embodiment;FIG. 2B illustrates a valve-operating device of an embodiment; FIG. 3 illustrates a lift condition of an intake valve and an exhaust valve in a first mode; FIG. 4 illustrates a lift condition of an intake valve and an exhaust valve in a second mode; FIG. 5 illustrates a flowchart of an example of a control performed by an ECU; FIG. 6 illustrates a flowchart of a determination method of a combustion condition performed by an ECU; FIG. 7 illustrates another example of a determination method of a combustion condition performed by an ECU; and FIG. 8 illustrates a graph of a lift condition of an intake valve and an exhaust valve of a modified embodiment of a second mode.

A description will be given of embodiments with reference to drawings.

FIG. 1 illustrates an engine system in accordance with an embodiment. An engine 1 is a diesel engine having a plurality of cylinders 2a to 2d. The engine 1 may be a gasoline engine. The engine 1 may have a single cylinder. An exhaust passage 3 and an intake passage 4 are connected to the engine 1. A turbine housing 50 of a supercharger 5 is provided in a middle of the exhaust passage 3. An upstream portion of the exhaust passage 3 with respect to the turbine housing 50 communicates with a downstream portion of the exhaust passage 3 with respect to the turbine housing 50 via a bypass passage 30. A bypass valve 31 is located in the bypass passage 30. The bypass valve 31 is also called a west gate valve. The exhaust passage 3 has a catalyst 20 on the downstream side compared to a connection portion of the bypass passage 30. The catalyst 20 is an oxidation catalyst but may be a three-way catalyst or a NOx catalyst.

Temperature sensors

13 and 14 for detecting a temperature of exhaust gas are provided before and after the catalyst 20. The engine 1 has a crank angle sensor 9.

A compressor housing 51 of the supercharger 5 is provided in a middle of the intake passage 4. An intercooler 6 is provided in the intake passage 4 on the downstream side compared to the compressor housing 51. A throttle valve 7 is provided in the intake passage 4 on the downstream side compared to the intercooler 6. An intake pressure sensor 11 is provided in the intake passage 4 on the downstream side compared to the throttle valve 7.

A turbine 500 is provided in the turbine housing 50. A compressor 501 is provided in the compressor housing 51. The turbine 500 and the compressor 501 are connected by a turbine shaft acting as an identical axis. When the turbine 500 is rotated by exhaust gas, the compressor 501 is also rotated. And the intake-air in the intake passage 4 is supercharged.

An ECU 8 has a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory) and so on. The ECU 8 controls an overall operation of the engine system based on an output from each sensor. The ECU 8 is an example of a controller. The ECU 8 determines whether combustion condition of the engine 1 is stable or not. Details will be described later. And, the engine 1 determines whether warming-up of the catalyst 20 is requested. The request of warming-up of the catalyst 20 is requested when the temperature of the catalyst 20 is less than an activation temperature. The ECU 8 estimates whether the temperature of the catalyst 20 is less than the activation temperature based on output values of the

temperature sensors

13 and 14, a temperature of coolant water of the engine 1 or the like. The ECU 8 performs a warming-up control of the catalyst 20 when the temperature of the catalyst 20 is less than the activation temperature.

FIG. 2A illustrates the engine 1 of the embodiment. A piston Pa moves back and forth in the cylinder 2a. A fuel injection valve Fa directly injects the fuel into the cylinder 2a. An intake valve V1 and an exhaust valve V2 move up and down in a predetermined stroke respectively in accordance with a rotation of an intake cam shaft S1 and a rotation of an exhaust cam shaft S2, and open and close an intake port PT1 and an exhaust port PT2. Two pairs of the intake port PT1 and the exhaust port PT2 and two pairs of the intake valve V1 and the exhaust valve V2 are provided in a single cylinder 2a. The cylinders 2b to 2d have the same structure as the cylinder 2a. A valve-operating device L2 is capable of changing a period where the exhaust valve V2 opens.

FIG. 2B illustrates the valve-operating device L2 of the embodiment. The valve-operating device L2 has a first cam CM1, a second cam CM2, a locker arm R1 and an oscillation arm R2. The first cam CM1 and the second cam CM2 are arrayed along an axis direction of the exhaust cam shaft S2 and have a different outer shape. The locker arm R1 is driven by the first cam CM1 and lifts the exhaust valve V2. The oscillation arm R2 is driven by the second cam CM2 and is capable of switching from non-connection with the locker arm R1 to connection with the locker arm R1. The locker arm R1 and the oscillation arm R2 support pins P1 and P2 respectively. Hydraulic pressure is applied to the pins P1 and P2 by an oil control valve OCV that is controlled by the ECU 8. When the hydraulic pressure is not applied to the pin P1 or the pin P2, the locker arm R1 and the oscillation arm R2 respectively support the pins P1 and P2, and the locker arm R1 is not connected to the oscillation arm R2. When the hydraulic pressure is applied to the pins P1 and P2, the pins P1 and P2 move against biasing forces of a spring SP, and the pin P1 is engaged with the locker arm R1 and the oscillation arm R2. Thereby, the locker arm R1 is connected to the oscillation arm R2. When the hydraulic pressure is released, the pins P1 and P2 are respectively supported by the locker arm R1 and the oscillation arm R2 with use of the biasing force of the spring SP. And, the locker arm R1 is not connected to the oscillation arm R2. The valve-operating device L2 may be a device disclosed in Japanese Patent Application Publication No. 6-212925 and Japanese Patent Application Publication No. 2009-264200 and so on.

The non-connection mode is referred to as a first mode. The connection mode is referred to as a second mode. In the first mode, opening of the exhaust valve V2 is kept at least in a part of the exhaust stroke. In the second mode, the opening of the exhaust valve V2 is kept at least in a part of the exhaust stroke, a lift amount of the exhaust valve V2 is increased at least in a part of the intake stroke, and after that, the exhaust valve V2 is closed. Therefore, an outer shape of the first cam CM1 is formed so that the opening of the exhaust valve V2 is kept at least in the part of the exhaust stroke. An outer shape of the second cam CM2 is formed so that the lift amount of the exhaust valve V2 is increased at least in the part of the exhaust stroke with the locker arm R1 being connected to the oscillation arm R2 and the exhaust valve V2 is closed after that.

A description will be given of the lift condition of the exhaust valve V2. FIG. 3 illustrates the lift condition of the intake valve V1 and the exhaust valve V2 in the first mode. Lift curves C1 and C2 respectively indicate the lift amount of the intake valve V1 and the exhaust valve V2. The engine 1 performs an expansion stroke, an exhaust stroke, an intake stroke and a compression stroke in order, and repeats the strokes.

As illustrated in FIG. 3, in the first mode, the exhaust valve V2 is opened in the period of the exhaust stroke and is closed in a former period of the expansion stroke, the period of the intake stroke, and the period of the compression stroke. And, the intake valve V1 is opened in the period of the intake stroke, and is closed in the period of the expansion stroke, the period of the exhaust stroke, and a latter period of the compression stroke.

FIG. 4 illustrates the lift condition of the intake valve V1 and the exhaust valve V2 in the second mode. As illustrated in FIG. 4, in the second mode, the exhaust valve V2 is opened in the period of the exhaust stroke and is opened in the latter period of the intake stroke and the former period of the compression stroke. Details will be described later. When the exhaust valve V2 is opened in the intake stroke in the case where the bypass valve 31 is closed, the exhaust gas is introduced into the cylinder and an inner EGR amount is secured. Therefore, the lift curve C2 illustrated in FIG. 3 and FIG. 4 is achieved by the first cam CM1. The lift curve C2' illustrated in FIG. 4 is achieved by the second cam CM2.

In the first mode, an operation angle and a maximum lift amount of the intake valve V1 and the exhaust valve V2 are not limited to the lift curves C1 and C2 illustrated in FIG. 3. The exhaust valve V2 has only to open at least in a part of the exhaust stroke. The exhaust valve V2 may start to open in the exhaust stroke and may be closed in the exhaust stroke. The intake valve V1 may start to open in the intake stroke, and may be closed in the intake stroke. There may be an overlap period where both the intake valve V1 and the exhaust valve V2 open around a crank angle of 360 degrees. There may be no overlap period. In the second mode, the lift curve C2' is not limited to FIG. 4. The exhaust valve V2 may increase the lift amount in the intake stroke and may be closed in the intake stroke. The maximum lift amount of the exhaust valve V2 in the intake stroke is not limited.

The expansion stroke corresponds to the period of the crank angle of 0 degree to 180 degrees. The exhaust stroke corresponds to the period of the crank angle of 180 degrees to 360 degrees. The intake stroke corresponds to the period of the crank angle of 360 degrees to 540 degrees. The compression stroke corresponds to the period of the crank of 540 degrees to 720 degrees. When the crank angle is 0 degree, 360 degrees or 720 degrees, the piston is positioned at a top dead point. When the crank angle is 180 degrees or 540 degrees, the piston is positioned at a bottom dead point.

Next, a description will be given of an example of the control performed by the ECU 8. FIG. 5 illustrates a flowchart of an example of the control performed by the ECU 8. The ECU 8 determines whether the combustion condition of the engine 1 is stable (Step S1). Details of the determination method of the combustion condition will be described later. When it is determined as No in the Step S1, that is, when the combustion condition is not stable, the ECU 8 switches the mode of the valve-operating device L2 to the second mode (Step S2), and completely closes the bypass valve 31 (Step S3). When the bypass valve 31 is completely closed, the amount of the exhaust gas passing through the turbine 500 increases. Therefore, reduction of the exhaust pressure can be suppressed. Thus, the reduction of the exhaust pressure can be suppressed with respect to the intake pressure. Therefore, when the exhaust valve V2 is opened in the intake stroke, the amount of the inner EGR can be secured. Thus, the temperature in the cylinder is increased, and the combustion condition can be stabilized. The ECU 8 continues the Step S2 and the Step S3 until the combustion condition is stabilized.

When it is determined as Yes in the Step S1, that is, when the combustion condition is stable, the ECU 8 switches the mode of the valve-operating device L2 to the first mode (Step S4). Next, the ECU 8 determines whether the warming-up of the catalyst 20 is requested (Step S5). When it is determined as Yes in the Step S5, the ECU 8 keeps the opening of the bypass valve 31 (Step S6). For example, the ECU 8 keeps full-throttle of the bypass valve 31. Thus, much amount of the exhaust gas passes through the turbine 500, releases heat, suppresses of temperature reduction, and introduces the high temperature exhaust gas to the catalyst 20. Thereby, the catalyst 20 can be warmed up speedily. The step S6 corresponds to the warming-up control of the catalyst 20. The ECU 8 determines whether the warming-up of the catalyst 20 is finished (Step S7). Until the warming-up of the catalyst 20 is finished, the Step S6 continues. The ECU 8 determines that the warming-up of the catalyst 20 is finished when the temperature of the catalyst 20 is equal to or more than the activity temperature.

When it is determined as No in the Step S5, that is, when the warming-up of the catalyst 20 is not requested, or when it is determined as Yes in the Step S7, that is, when the warming-up of the catalyst 20 is finished, the ECU 8 performs a normal control of the bypass valve 31 normally (Step S8). The normal control is a control in which the aperture angle of the bypass valve 31 is controlled to an angle regulated in a map that is made in accordance with the operation condition of the engine 1 in advance.

As mentioned above, when the bypass valve 31 is closed in the second mode, the reduction of the exhaust pressure is suppressed and the inner EGR amount can be secured. When the mode is switched to the second mode and the bypass valve 31 is closed in the case where the combustion condition is not stable, the inner EGR amount can be secured and the combustion condition can be stabilized. When the combustion condition is stable, the bypass valve 31 is opened and the catalyst 20 is warmed-up. In this case, the warming-up of the catalyst 20 is prevented when the combustion condition is not stable. Therefore, accidental fire or reduction of torque caused by the opening of the bypass valve 31 when the combustion condition is not stable can be suppressed.

For example, in the embodiment, when the combustion condition is not stable at the starting of the engine 1 and the temperature of the catalyst 20 is less than the activation temperature, the stabilization of the combustion condition is performed before the warming-up of the catalyst 20. Thus, the accidental fire of the engine 1 is prevented preferentially and the catalyst 20 is activated after that.

The aperture angle of the bypass valve 31 in the second mode is not limited to zero. The aperture angle has only to be smaller than the aperture angle of the bypass valve 31 in the first mode. For example, the aperture angle of the bypass valve 31 in the second mode may be smaller than the aperture angle of the bypass valve 31 that is normally controlled in the same operation condition as that of the second mode. For example, when the mode is switched from the first mode to the second mode in a specific operation condition, the aperture angle of the bypass valve 31 in the second mode is controlled to be smaller than the aperture angle of the bypass valve 31 in the first mode. This is because the reduction of the exhaust pressure is suppressed and the inner EGR amount can be secured.

The bypass valve 31 in the warming-up control of the catalyst 20 is not limited to full throttle and may be more than zero aperture. The aperture angle of the bypass valve 31 in the warming-up control of the catalyst 20 may be larger than the aperture angle of the bypass valve 31 that is normally controlled in the same operation condition as that of the warming-up control of the catalyst 20.

Next, a description will be given of a determination method of the combustion condition performed by the ECU 8. FIG. 6 illustrates a flowchart of the determination method of the combustion condition performed by the ECU 8. The ECU 8 calculates a changing rate of the rotation speed of the engine 1 in a predetermined period based on an output signal from the crank angle sensor 9 (Step S21). Next, the ECU 8 determines whether the changing rate is less than a predetermined value (Step S22). The predetermined value is a changing rate in which the combustion condition of the engine 1 is possibly not stable and the accidental fire or the reduction of torque possibly occurs. When it is determined as No in the Step S22, that is, when the changing rate of the rotation speed is large, the ECU 8 determines that the combustion condition is not stable because the rotation speed of the engine 1 changes rapidly (Step S23). When it is determined as Yes in the Step S22, that is, when the changing rate of the rotation speed is small, the ECU 8 determines that the combustion condition is stable (Step S24).

Next, a description will be given of another example of the determination method of the combustion condition performed by the ECU 8. FIG. 7 illustrates another example of the determination method of the combustion condition performed by the ECU 8. The ECU 8 detects a cylinder pressure of all of the cylinders 2a to 2d (Step S31). In concrete, the ECU 8 detects each cylinder pressure based on signals of pressure sensors that are respectively provided in the cylinders 2a to 2d. Next, the ECU 8 determines whether a variation value of the cylinders pressures of the cylinders 2a to 2d is less than a predetermined value (Step S32). The variation value of the cylinder pressure is the largest difference between maximum values of the cylinder pressures of the cylinders 2a to 2d. The predetermined value is a difference between a maximum value of a cylinder pressure of a cylinder in which it is thought that the combustion condition is stable and there are no possibilities of accidental fire and a maximum value of a cylinder pressure of a cylinder in which it is thought that the combustion condition is not stable and there is a possibility of accidental fire. The ECU 8 determines whether the variation value of the cylinder pressures is less than the predetermined value. When it is determined as No, that is, when the variation value of the cylinder pressure is large, the ECU 8 determines that the combustion condition is unstable (Step S33). For example, when a maximum value of a cylinder pressure of a cylinder is much smaller than each maximum value of cylinder pressures of other cylinders, it is determined that the combustion condition of the engine 1 is unstable because the combustion condition of the cylinder pressure is unstable.

When it is determined as Yes in the Step S32, that is, when the variation value of the cylinder pressure is small, the ECU 8 determines whether a variation value of a cylinder pressure among cycles is less than a predetermined value (Step S34). The variation value of the cylinder pressure among cycles is calculated as follows. For example, maximum values of the cylinder pressure of each cycle of the cylinder 2a is calculated. And, differences between the maximum values are calculated. Similarly, maximum values of the cylinder pressure of each cycle of the cylinders 2b to 2d are calculated. And, differences between the maximum values are calculated. A maximum value of the differences between the maximum values is set as a variation value of the cylinder pressure of each cycle. The predetermined value is a difference between the maximum values of the cylinder pressure of each cycle in a cylinder in which the combustion condition is not stable and there is a possibility of accidental fire. When it is determined as No in the Step S32, that is, when the variation value of the cylinder pressure among cycles is large, the ECU 8 determines that the combustion condition is unstable (Step S33). For example, a difference between a maximum value of a first cycle of a cylinder pressure of a cylinder and a maximum value of a second cycle is large, it is determined that the combustion condition of the engine 1 is unstable because the combustion condition of the cylinder is unstable.

When it is determined as Yes in the Step S34, that is, when the variation value of the cylinder pressure among cycles is small, it is determined that the combustion condition of the engine 1 is stable (Step S35). An order of the Step S32 and the Step S34 is no object. Both of the flowcharts illustrated in FIG. 6 and FIG. 7 may be executed and the combustion condition may be determined.

A description will be given of a modified embodiment of the second mode. FIG. 8 illustrates a graph of the lift condition of the intake valve V1 and the exhaust valve V2 in the modified embodiment of the second mode. As illustrated in FIG. 8, the lift amount of the exhaust valve V2 may be decreased in the latter half of the exhaust stroke, and the lift amount of the exhaust valve V2 may be increased again in the intake stroke with the exhaust port PT2 being opened at a predetermined lift amount. For example, in accordance with a shape of the second cam achieving the lift curve C2², it is possible to keep the exhaust valve V2 open at a small lift amount for a predetermined period. In other word, the number of opening and closing of a single cycle of the exhaust valve V2 is not limited to two or more. As illustrated in FIG. 8, the number of the opening and closing of a single cycle may be one, and the lift amount may be increased in the intake stroke. The inner EGR amount can be secured in this case.

In the embodiment, the mode of the valve-operating device L2 is switched to the second mode when the combustion condition is unstable. However the structure is not limited to the case. For example, the bypass valve 31 may be closed when the mode of the valve-operating device L2 may be switched to the second mode in order to increase the inner EGR amount by reducing the aperture angle of the throttle valve 7 in order to reduce the pumping loss. That is, the reason for switching the mode of the valve-operating device L2 to the second mode is no object. The mode of the valve-operating device L2 is switched to the second mode when the increase of the inner EGR amount is requested, and the bypass valve 31 may be closed. Thus, the inner EGR amount can be secured.

For example, the valve-operating device L2 may be a device that has the first cam and the second cam that are arrayed along an axis direction of an exhaust cam shaft, in which contact condition with a cam follower is switched in accordance with the movement of the exhaust cam shaft in the axis direction. In this case, only the first cam contacts the cam follower in the first mode. Only the second cam contacts the cam follower in the second mode. Alternately, only the first cam contacts the cam follower in the first mode. Both the first cam and the second cam contact the cam follower in the second mode. The valve-operating device L2 may be a device disclosed in Japanese Patent Application Publication No. 2013-060823.

The valve-operating device L2 may be an electromagnetic drive device that drives the exhaust valve V2 with use of electromagnetic force. The valve-operating device L2 may be a device disclosed in Patent Document 1.

The combustion condition may be determined as follows. For example, it may be determined that the combustion condition may be degraded when an actual cylinder pressure is lower than a cylinder pressure obtained from a map regulating a relationship among the rotation number of the engine, the load of the engine and the cylinder pressure in a case of preferable combustion condition by a predetermined value or more. In a case of a gasoline engine, it may be determined that the combustion condition is degraded when increasing rate of the pressure after outputting of an ignition signal from the ECU is less than a predetermined value.

The present invention is not limited to the specifically disclosed embodiments and variations but may include other embodiments and variations without departing from the scope of the present invention.

1 internal combustion engine
3 exhaust passage
5 supercharger
8 ECU (control unit)
17 and 18 temperature sensor
20 catalyst
30 bypass passage
31 bypass valve
500 turbine
V2 exhaust valve

Claims

A control device of an internal combustion engine comprising:
an internal combustion engine that has an exhaust valve;
an exhaust passage that is connected to the internal combustion engine;
a turbine of a supercharger that is provided in the exhaust passage;
a bypass passage that bypasses the turbine;
a bypass valve that opens and closes the bypass passage;
a valve-operating device that is capable of switching between a first mode and a second mode, the first mode being a mode in which the exhaust valve is opened at least in a part of an exhaust stroke, the second mode being a mode in which the exhaust valve is opened at least in a part of the exhaust stroke, a lift amount of the exhaust valve is increased at least in a part of an intake stroke and the exhaust valve is closed after that; and
a controller that switches a mode to the second mode and closes the aperture of the bypass valve, or controls the aperture of the exhaust valve to a smaller side than an aperture of the bypass valve of the first mode.
The control device as claimed in claim 1, wherein
the controller switches the mode to the second mode and closes the bypass valve when combustion condition of the internal combustion engine is unstable and switches the mode to the first mode when the combustion condition of the internal combustion engine is stable.
The control device as claimed in claim 2, wherein
the controller opens the bypass valve in the first mode when the combustion condition of the internal combustion engine is stable and warming-up of a catalyst provided in the exhaust passage on the downstream side of the bypass passage is requested.
The control device as claimed in claim 2 or 3 wherein the controller determines stability of the combustion condition of the internal combustion engine based on a changing rate of the rotation speed of the internal combustion engine.
The control device as claimed in claim 2 or 3 wherein the controller determines stability of the combustion condition of the internal combustion engine based on each cylinder pressure of a plurality of cylinders of the internal combustion engine.