JP2023053444A - Control method of internal combustion engine and control device of internal combustion engine - Google Patents

Abstract

To reduce NOx in exhaust emission at a start of an internal combustion engine.SOLUTION: In an internal combustion engine 10, when an operation point exceeds a surge limit, combustion becomes instable, and when the operation points exceeds a knock limit, knocking becomes liable to occur. Then, a control unit 13 controls the operation point so as not to exceed the surge limit and the knock limit. That is, the control unit 13 leans an air-fuel ratio up to the surge limit at a start transition, raises an engine rotation number up to a rotation number at which stable combustion becomes possible at an air-fuel ratio which is leaned up to the surge limit, and raises the torque (engine load) of the internal combustion engine 10 up until reaching the knock limit at the engine rotation number at which the stable combustion becomes possible at the air-fuel ratio which is leaned up to the surge limit, and also, at an air-fuel ratio which is leaned up to the knock limit.SELECTED DRAWING: Figure 1

Description

The present invention relates to an internal combustion engine control method and an internal combustion engine control apparatus.

For example, in Patent Document 1, in a cylinder direct injection type internal combustion engine in which fuel is directly injected into the combustion chamber, the timing of fuel injection at the time of starting the internal combustion engine is set to the intake stroke, and the timing of fuel injection is set after that. Techniques for switching to the compression stroke are disclosed.

This Patent Document 1 makes it possible to improve the ignition and combustion performance during cranking, and to improve the startability by smoothing the rise of the engine speed after cranking and the transition to the idling state.

JP-A-10-103117

However, in an internal combustion engine that operates at an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio (lean air-fuel ratio), it is important to reduce NOx in exhaust gas generated by combustion.

However, in Patent Document 1, no consideration is given to NOx in the exhaust gas during the period from the start of the internal combustion engine to the operation at the lean air-fuel ratio, and there is room for further improvement in this respect.

The internal combustion engine of the present invention performs power generation operation at a predetermined steady engine speed, a predetermined steady engine load, and a predetermined steady air-fuel ratio of an air-fuel mixture in a cylinder, The internal combustion engine is started under operating conditions such that the rotation speed is lower than the steady speed, the load is lower than the steady load, and the air-fuel ratio is richer than the steady state air-fuel ratio. In the startup transition period until the rotation speed, the steady load, and the steady air-fuel ratio are reached, the air-fuel ratio lean processing is performed to make the air-fuel ratio lean while keeping the engine load and engine speed constant, and the engine A load increase process for increasing the load is repeatedly performed.

The internal combustion engine of the present invention can greatly reduce the amount of NOx emissions during the startup transition period by making the air-fuel ratio lean while keeping the engine load constant during the startup transition period.

1 is an explanatory diagram schematically showing an outline of a vehicle drive system to which the present invention is applied; FIG. FIG. 4 is an explanatory diagram schematically showing the correlation between the air-fuel ratio and the torque in the startup transition period; FIG. 4 is a timing chart showing an example of the behavior of the air-fuel ratio, etc. during the start transition period; FIG. 4 is a flow chart showing the flow of control during the startup transition period of the internal combustion engine in the first embodiment of the present invention; A subroutine showing the contents of step S1 in FIG. A subroutine showing the contents of step S2 in FIG. A subroutine showing the contents of step S3 in FIG. 4 is a flow chart showing the flow of control during the startup transition period of the internal combustion engine in the first embodiment of the present invention;

An embodiment of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is an explanatory diagram schematically showing an outline of a drive system of a vehicle 1 to which the present invention is applied. The vehicle 1 has a drive unit 3 that drives the drive wheels 2 and a power generation unit 4 that generates electric power for driving the drive wheels 2 .

The drive unit 3 includes a drive motor 5 as a second electric motor that rotationally drives the drive wheels 2, and a first gear train 6 and a differential gear 7 that transmit the driving force of the drive motor 5 to the drive wheels 2. ing. Electric power is supplied to the drive motor 5 from a battery 8 charged with electric power generated by the power generation unit 4 or the like.

The power generation unit 4 includes a generator 9 as a first electric motor that generates electric power to be supplied to the drive motor 5 , an internal combustion engine 10 capable of driving the generator 9 , and the rotation of the internal combustion engine 10 that is transmitted to the generator 9 . and a second gear train 11 .

The vehicle 1 is a so-called series hybrid vehicle that does not use the internal combustion engine 10 as power. The vehicle 1 drives the internal combustion engine 10 to charge the battery 8 and generates electricity with the generator 9, for example, when the remaining battery power of the battery 8 becomes low.

The drive motor 5 is a direct drive source for the vehicle 1 and is driven by AC power from the battery 8, for example. Further, the drive motor 5 functions as a generator when the vehicle 1 is decelerated.

The generator 9 converts rotational energy generated in the internal combustion engine 10 into electrical energy to charge the battery 8, for example. The generator 9 also has a function as an electric motor for driving the internal combustion engine 10, and motoring of the internal combustion engine 10 is possible. The generator 9 may function as a starter motor for the internal combustion engine 10 . The electric power generated by the generator 9 may be directly supplied to the driving motor 5 according to, for example, the operating state, instead of charging the battery 8 .

The internal combustion engine 10 is, for example, an in-cylinder direct injection type internal combustion engine capable of directly injecting fuel into a cylinder, and the rotation of the crankshaft can be transmitted to the rotor of the generator 9 . The internal combustion engine 10 can change the air-fuel ratio, and can be used by switching between stoichiometric combustion, which is combustion in the first combustion mode, and lean combustion, which is combustion in the second combustion mode. It is. Stoichiometric combustion is combustion in which the target air-fuel ratio is the stoichiometric air-fuel ratio (stoichiometric). Lean combustion is lean combustion in which the target air-fuel ratio is leaner than the stoichiometric air-fuel ratio.

The internal combustion engine 10 is controlled by a control unit 13 as a control section. The control unit 13 is a well-known digital computer equipped with a CPU, ROM, RAM and an input/output interface.

The control unit 13 includes an air flow meter 14 for detecting the amount of intake air, a crank angle sensor 15 for detecting the crank angle of the crankshaft (not shown) of the internal combustion engine 10, and an accelerator pedal (not shown) of the vehicle 1. Detected signals from various sensors such as an accelerator opening sensor 16 for detecting an air-fuel ratio, an A/F sensor 17 for detecting an air-fuel ratio, and an oxygen sensor 18 are inputted.

The crank angle sensor 15 can detect the engine speed of the internal combustion engine 10 .

The accelerator opening sensor 16 can detect the accelerator opening, which is the operation amount of the accelerator pedal, as well as the accelerator change speed, which is the operating speed of the accelerator pedal. That is, the accelerator opening sensor 16 corresponds to an accelerator operation amount detector.

The A/F sensor 17 is a so-called wide-range air-fuel ratio sensor having a substantially linear output characteristic corresponding to the exhaust air-fuel ratio. It is arranged on the inlet side (upstream side) of a catalyst (for example, a three-way catalyst). In other words, the A/F sensor 17 is arranged in the exhaust passage on the upstream side of the exhaust purification catalyst.

The oxygen sensor 18 is a sensor that changes its output voltage in an ON/OFF (rich, lean) manner in a narrow range around the theoretical air-fuel ratio, and detects only the rich or lean air-fuel ratio. side (downstream side). In other words, the oxygen sensor 18 is arranged in the exhaust passage on the downstream side of the exhaust purification catalyst.

Based on detection signals from various sensors, the control unit 13 optimally controls the injection amount and injection timing of the fuel injected from the fuel injection valve, the ignition timing of the internal combustion engine 10, the amount of intake air, and the like. The air-fuel ratio of the internal combustion engine 10 is controlled.

The control unit 13 uses the detected value of the accelerator opening sensor 16 to calculate the required load of the internal combustion engine 10 (the load of the internal combustion engine 10).

The control unit 13 controls the internal combustion engine 10 to operate at a predetermined power generation operating point. Specifically, when the generator 9 generates power, the control unit 13 sets the engine speed to a predetermined steady speed, the engine load to a predetermined steady load, and the air-fuel ratio of the air-fuel mixture in the cylinder to a predetermined steady air. The internal combustion engine 10 is operated in power generation operation with a fuel ratio. In other words, when the generator 9 generates power, the control unit 13 determines that the engine speed is the steady speed, the torque of the internal combustion engine 10 is the predetermined steady torque, and the air-fuel ratio of the air-fuel mixture in the cylinder is the steady air-fuel ratio. The internal combustion engine 10 is operated at different power generation operating points.

The steady-state air-fuel ratio is a charge-only air-fuel ratio used when charging the battery 8, and is an air-fuel ratio significantly leaner than the stoichiometric air-fuel ratio. When the engine load is a steady load, the torque of the internal combustion engine 10 becomes steady torque.

The internal combustion engine 10 is for driving the generator 9, and is started as necessary while the vehicle 1 is running. Since the internal combustion engine 10 is started by cranking from a stopped state while the vehicle 1 is running, the rotation speed is lower than the steady speed, the load is lower than the steady load, the air-fuel ratio is richer than the steady state air-fuel ratio, and the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. The internal combustion engine 10 is started under operating conditions. After starting, the internal combustion engine 10 changes the air-fuel ratio toward the steady air-fuel ratio while ensuring combustion stability.

Here, HC in the exhaust gas of the internal combustion engine depends on the engine speed and engine load of the internal combustion engine, but is less dependent on the lean air-fuel ratio within the range where the combustion of the internal combustion engine is stable. .

In other words, HC in the exhaust gas decreases as the engine speed of the internal combustion engine increases, and decreases as the engine load of the internal combustion engine increases. It doesn't change much. However, HC in the exhaust gas of the internal combustion engine rapidly increases when the combustion stability of the internal combustion engine deteriorates.

NOx in the exhaust gas of the internal combustion engine depends on the engine speed and the engine load of the internal combustion engine, but the dependence on leaning of the air-fuel ratio of the internal combustion engine is even greater. In other words, NOx in the exhaust gas decreases as the engine speed of the internal combustion engine increases, and decreases as the engine load of the internal combustion engine increases. decreases significantly (on a logarithmic scale) compared to

Therefore, after the internal combustion engine 10 is started, the control unit 13 causes the engine speed, engine load (torque of the internal combustion engine 10), and air-fuel ratio to reach the steady speed, steady load (steady torque), and steady air-fuel ratio, respectively. In the startup transition period up to , the air-fuel ratio is preferentially made lean toward the steady-state air-fuel ratio.

In other words, after the internal combustion engine 10 is started, the control unit 13 controls the engine speed, the engine load (torque of the internal combustion engine 10), and the air-fuel ratio for power generation where the steady speed, the steady load (steady torque), and the steady air-fuel ratio are achieved. In the startup transition period until the operating point is reached, air-fuel ratio lean processing is performed to make the air-fuel ratio lean while keeping the engine load (torque of the internal combustion engine 10) and engine speed constant, and the engine speed while keeping the air-fuel ratio constant. and a load increase process (torque increase process) for increasing the engine load by increasing the torque of the internal combustion engine 10 while keeping the air-fuel ratio constant.

More specifically, in the startup transition period, in order to ensure combustion stability, each of these processes is repeated in the order of air-fuel ratio lean processing, rotation speed increase processing, and load increase processing. point to power generation operating point.

The air-fuel ratio lean processing is performed so that the air-fuel ratio does not exceed the surge limit at which combustion becomes unstable. The engine speed increase process increases the engine speed to a speed at which stable combustion is possible with an air-fuel ratio made lean to the surge limit. The load increase process increases the torque (engine load) until it reaches the knock limit at the engine speed at which stable combustion is possible with the air-fuel ratio leaned to the surge limit and the air-fuel ratio leaned to the surge limit.

FIG. 2 is an explanatory diagram schematically showing the correlation between the air-fuel ratio and the torque during the start transition period. Torque, which is the vertical axis in FIG. 2, includes the effects of engine speed and engine load. A solid line P1 in FIG. 2 is a characteristic line indicating the knocking limit when the engine speed is a predetermined low speed. A solid line P2 in FIG. 2 is a characteristic line indicating the knocking limit when the engine speed is a predetermined middle speed. A solid line P3 in FIG. 2 is a characteristic line indicating the knocking limit when the engine speed is a predetermined high speed. A two-dot chain line Q1 in FIG. 2 is a characteristic line indicating the surge limit when the engine speed is at a predetermined low speed. A two-dot chain line Q2 in FIG. 2 is a characteristic line indicating the surge limit when the engine speed is a predetermined middle speed. A two-dot chain line Q3 in FIG. 2 is a characteristic line indicating the surge limit when the engine speed is a predetermined high speed. A dashed line R in FIG. 2 is a characteristic line indicating the surge limit in homogeneous lean combustion.

In the example shown in FIG. 2, the air-fuel ratio lean process implements homogeneous lean combustion and stratified lean combustion. Homogeneous lean combustion has a uniform air-fuel ratio in the cylinder. In stratified lean combustion, for example, fuel is injected into the cylinder in two stages, the first half of the intake stroke and the second half of the compression stroke, to create a rich air-fuel mixture around the spark plug, and then create a lean air-fuel mixture around it for combustion. .

The combustion of the internal combustion engine 10 becomes unstable when the operating point exceeds the surge limit, and knocking is likely to occur when the operating point exceeds the knock limit. If the air-fuel ratio is the same, the knock limit operating point has a higher load (higher torque) than the surge limit operating point. Therefore, the control unit 13 performs control so that the operating point does not exceed the surge limit and the knock limit.

That is, the control unit 13 makes the air-fuel ratio lean to the surge limit, increases the engine speed to a speed at which stable combustion is possible with the air-fuel ratio made lean to the surge limit, and increases the engine speed to the speed at which stable combustion is possible. The torque (engine load) of the internal combustion engine 10 is increased until the knock limit is reached at the engine speed at which stable combustion is possible with the air-fuel ratio made lean and the air-fuel ratio made lean to the surge limit.

When the air-fuel ratio made lean to the surge limit is richer than the steady-state air-fuel ratio, the control unit 13 further makes the air-fuel ratio lean after increasing the torque to the knock limit.

This is because, as shown in FIG. 2, the surge limit of the air-fuel ratio expands in the lean direction as the engine speed and the torque of the internal combustion engine 10 increase (increases in the engine load), and the knock limit of the torque of the internal combustion engine 10 becomes empty. This is because it expands in the increasing direction as the fuel ratio becomes leaner and the engine speed increases.

In the example shown in FIG. 2, the internal combustion engine 10 is started at the operating point A, then the air-fuel ratio is made lean until the operating point B by homogeneous lean combustion, and the combustion mode is switched from homogeneous lean combustion to stratified lean combustion at the operating point B. An air-fuel ratio lean process is performed to make the air-fuel ratio leaner until the operating point C is reached later.

That is, the first air-fuel ratio lean processing is to move (change) the operating point from A to C by making the air-fuel ratio lean.

The first rotational speed increasing process is to move (change) the operating point from C to D while keeping the air-fuel ratio constant.

The first engine load increasing process is to move (change) the operating point from D to E while keeping the air-fuel ratio and engine speed constant.

The second air-fuel ratio lean processing is to move (change) the operating point from E to F while keeping the engine speed and torque constant. In the example shown in FIG. 2, the air-fuel ratio reaches the steady-state air-fuel ratio, which is the target air-fuel ratio for power generation operation, in the second air-fuel ratio lean process.

The second rotational speed increase process is to move (change) the operating point from F to G while keeping the air-fuel ratio constant. In the example shown in FIG. 2, the engine speed reaches the steady-state speed, which is the target speed for power generation operation, in the second speed increase process.

The second engine load increase process moves (changes) the operating point from F to G while keeping the air-fuel ratio and the engine speed constant. In the example shown in FIG. 2, the torque of the internal combustion engine 10 reaches the steady torque in the second engine load increasing process, and the torque of the internal combustion engine 10 reaches the steady torque, which is the target torque of the operating point for power generation.

The combustion mode of the internal combustion engine 10 at operating points C to H is stratified lean combustion.

The operating point A is a starting operating point used when starting the internal combustion engine 10 at a lower rotation speed, lower torque (lower engine load), and a richer air-fuel ratio than the power generation operating point.

The air-fuel ratio at the operating point B is set to be as lean as possible within a range that does not exceed the surge limit in homogeneous lean combustion.

The air-fuel ratio at the operating point C is set to be as lean as possible within a range that does not exceed the surge limit in stratified lean combustion.

The engine speed and the torque of the internal combustion engine 10 at the operating points B and C are the same as the engine speed and the torque of the internal combustion engine 10 at the operating point A.

The engine speed at the operating point D is a speed within a range in which stable combustion is possible at the air-fuel ratio at the operating point C.

The torque at operating point E is set so as not to exceed the knock limit at the air-fuel ratio and engine speed at operating point D.

The air-fuel ratio at operating point F is set so as not to exceed the surge limit in stratified lean combustion. In the example of FIG. 2, the steady air-fuel ratio is within a range in which the torque at the operating point E does not exceed the surge limit in stratified lean combustion, so the air-fuel ratio at the operating point F is the steady air-fuel ratio for power generation operation.

The engine speed at the operating point G is a speed within a range in which stable combustion is possible at the air-fuel ratio at the operating point F, and is a steady speed. In the example of FIG. 2, since the steady engine speed is within the range where stable combustion is possible at the air-fuel ratio at the operating point F, the engine speed at the operating point G is the steady engine speed for power generation operation.

The operating point H is an operating point for power generation. In the example of FIG. 2, since the steady torque is within a range that does not exceed the knock limit at the air-fuel ratio and the engine speed at the operating point G, the torque at the operating point H is the steady torque for power generation operation.

FIG. 3 is a timing chart showing an example of the behavior of the air-fuel ratio, etc. during the startup transition period.

Time t1 is the timing at which fuel injection is started and the internal combustion engine 10 is started.

In the example of FIG. 3, the internal combustion engine 10 is motored by the generator 9 prior to firing (independent operation) of the internal combustion engine 10, and the intake air amount (intake air amount) is ensured before time t1. .

Time t2 is the timing to start the air-fuel ratio lean process. The air-fuel ratio lean process started at time t2 ends at time t4. In the example of FIG. 3, the period from time t2 to time t3 is the period in which homogeneous lean combustion is performed, and the period from time t3 to time t4 is the period in which stratified lean combustion is performed.

Time t4 is the timing to start the rotation speed increasing process. The rotational speed increasing process started at time t4 ends at time t5.

Time t5 is the timing to start the load increase process.

FIG. 4 is a flow chart showing the flow of control during the startup transition period (starting time) of the internal combustion engine 10 in the first embodiment of the present invention. The internal combustion engine 10 of the first embodiment performs only stratified lean combustion as the air-fuel ratio lean process.

When the internal combustion engine 10 is started, the air-fuel ratio of the internal combustion engine 10 is set in step S1. Step S1 is a step of performing air-fuel ratio lean processing. In step S2, the engine speed of the internal combustion engine 10 is set. Step S2 is a step of performing a rotation speed increasing process. In step S3, the load (torque) of the internal combustion engine 10 is set. Step S3 is a step of executing a load increase process. In step S4, it is determined whether or not the operating point is the operating point for power generation. In step S4, if the operating point is the operation for power generation, the operation at the operating point for power generation is started. In step S4, if the operating point is not the power generation operation, the process returns to step S1. That is, in the start transition period, steps S1 to S3 are repeated until the operating point reaches the power generation operating point.

FIG. 5 is a subroutine showing the contents of step S1 in FIG. 4, and is a flow chart showing the control flow of the air-fuel ratio lean process.

In step S11, various setting parameters are read from the control unit 13. FIG. In step S11, Δrpm_step, which is the difference between the current engine speed and the target speed for the speed increase process immediately after the current air-fuel ratio lean processing, A/F_final, which is the steady-state air-fuel ratio, and when changing the air-fuel ratio, Read ΔA/F, which is the amount of change in the air-fuel ratio allowed per time. In step S11, rpm_act, which is the current engine speed (at the start of the current air-fuel ratio lean process), is also read.

In step S12, rpm_mid, which is the intermediate target engine speed, is calculated. The intermediate target rotation speed is the sum of rpm_act and Δrpm_step. rpm_mid=rpm_act+Δrpm_step.

In step S13, various instantaneous parameters (current values) are read. In step S13, A/F_act, which is the current air-fuel ratio (at the start of the current air-fuel ratio lean process), Qair_act, which is the current intake air amount, and rpm_act, which is the current engine speed, are read.

In step S14, using rpm_act, Qair_act, and A/F_act, load_act, which is the current engine load (at the start of the current air-fuel ratio lean process), is calculated from a table (load calculation table) pre-stored in the ROM in the control unit 13. Calculate load_act=f(rpm_act, Qair_act, A/F_act).

In step S15, on the premise that the engine load is fixed, rpm_mid and load_act are used to ensure combustion stability from a table (surge limit air-fuel ratio calculation table) pre-stored in the ROM in the control unit 13. A/F_surge, which is the lean processing target air-fuel ratio, is calculated. A/F_surge=f(rpm_mid, load_act).

In step S16, A/F_int, which is the target air-fuel ratio when making the air-fuel ratio lean toward the lean processing target air-fuel ratio, is calculated. A/F_int is set multiple times while changing the value during the air-fuel ratio lean processing so that the air-fuel ratio during the air-fuel ratio lean processing approaches the lean processing target air-fuel ratio step by step. A/F_int=A/F_act+ΔA/F.

In step S17, it is determined whether or not the target air-fuel ratio is leaner than the lean processing target air-fuel ratio. If the target air-fuel ratio is leaner than the lean processing target air-fuel ratio in step S17, the process proceeds to step S18. If the target air-fuel ratio is not leaner than the lean processing target air-fuel ratio in step S17, the process proceeds to step S19.

In step S19, fuel injection is performed so as to achieve the target air-fuel ratio.

In step S20, it is determined whether or not the target air-fuel ratio is the lean processing target air-fuel ratio. If the target air-fuel ratio is the lean processing target air-fuel ratio in step S19, this subroutine ends. If the target air-fuel ratio is not the lean processing target air-fuel ratio in step S19, the process returns to step S13 to continue making the air-fuel ratio lean so that the air-fuel ratio becomes the lean processing target air-fuel ratio.

FIG. 6 is a subroutine showing the content of step S2 in FIG. 4, and is a flow chart showing the control flow of the rotation speed increasing process.

In step S31, various setting parameters are read from the control unit 13. FIG. In step S31, a preset Δrpm_inst, which is a change amount (increase amount) per one time allowed when changing the engine speed, the current engine speed, and the engine speed increase immediately after the current air-fuel ratio lean process. Read Δrpm_step, which is the difference from the target rotation speed of the process. In step S31, rpm_act, which is the current engine speed (at the start of the current speed increase process), is also read.

In step S32, rpm_mid, which is the intermediate target engine speed, is calculated. The intermediate target rotation speed is the sum of rpm_act and Δrpm_step. rpm_mid=rpm_act+Δrpm_step.

At step S33, various instantaneous parameters (current values) are read. In step S33, A/F_act, which is the current air-fuel ratio (at the start of the current rotation speed increase process), Qair_act, which is the current intake air amount, and rpm_act, which is the current engine speed, are read.

In step S34, using rpm_act, Qair_act, and A/F_act, load_act, which is the current engine load (at the start of the current air-fuel ratio lean process), is calculated from a table (load calculation table) pre-stored in the ROM in the control unit 13. Calculate load_act=f(rpm_act, Qair_act, A/F_act).

In step S35, on the premise that the engine load is fixed, rpm_mid and load_act are used to ensure combustion stability from a table (surge limit air-fuel ratio calculation table) stored in the ROM in the control unit 13 in advance. A/F_surge, which is the target air-fuel ratio for rotational speed increase processing, is calculated. A/F_surge=f(rpm_mid, load_act). The engine speed increase processing target air-fuel ratio becomes the same value as the lean processing target air-fuel ratio if the conditions are the same.

In step S36, rpm_int, which is the target engine speed when increasing the engine speed toward the intermediate target engine speed, is calculated. rpm_int is set multiple times while changing the value during the engine speed increase process so that the engine speed during the engine speed increase process gradually approaches the intermediate target engine speed. rpm_int=rpm_act+Δrpm_inst.

In step S37, A/F_int, which is the target air-fuel ratio during the rotation speed increasing process, is set to A/F_act, which is the current air-fuel ratio.

In step S38, it is determined whether or not the target air-fuel ratio is equal to or less than the rotational speed increase processing target air-fuel ratio. If the target air-fuel ratio is larger (lean) than the rotational speed increase processing target air-fuel ratio in step S38, the process proceeds to step S39. In step S38, if the target air-fuel ratio is less than or equal to the rotational speed increase processing target air-fuel ratio (rich), the process proceeds to step S40.

In step S39, the target engine speed is readjusted so that the air-fuel ratio does not exceed the surge limit. That is, rpm_int=rpm_act.

In step S40, the engine speed is increased to rpm_int, which is the target speed. Steps S36 to S40 repeat addition of a preset predetermined engine speed until the engine speed reaches the target engine speed for the increase process, and when the engine speed exceeds the target engine speed for the increase process, combustion stability is ensured. This corresponds to the step of adjusting the engine speed so that the

In step S41, fuel injection is performed so that the air-fuel ratio becomes A/F_int, which is the target air-fuel ratio.

In step S42, it is determined whether or not the target rotation speed is the intermediate target rotation speed. If the target engine speed is the intermediate target engine speed in step S42, this subroutine ends. If the target revolution speed is not the intermediate target revolution speed in step S42, the process returns to step S33 to continue the process of increasing the engine revolution speed so that the engine revolution speed becomes the intermediate target revolution speed.

FIG. 7 is a subroutine showing the content of step S3 in FIG. 4, and is a flow chart showing the control flow of the load increase process.

In step S51, various setting parameters are read from the control unit 13. FIG. In step S51, a preset Δload_inst, which is the amount of change (increase) per one time allowed when changing the engine load, and load_final, which is the steady load, are read.

At step S52, various instantaneous parameters (current values) are read. In step S52, A/F_act, which is the current air-fuel ratio (at the start of the current rotation speed increase process), Qair_act, which is the current intake air amount, and rpm_act, which is the current engine speed, are read.

In step S53, using rpm_act, Qair_act, and A/F_act, load_act, which is the current engine load (at the start of the current air-fuel ratio lean process), is calculated from a table (load calculation table) pre-stored in the ROM in the control unit 13. Calculate load_act=f(rpm_act, Qair_act, A/F_act).

In step S54, using rpm_act and load_act, A is the knock lower limit air-fuel ratio that avoids knocking and ensures combustion stability from a table (knock lower limit air-fuel ratio calculation table) pre-stored in the ROM in the control unit 13. Calculate /F_knock. A/F_knock=f(rpm_act, load_act).

In step S55, load_int, which is the target load for increasing the engine load, is calculated. load_int is set multiple times while changing the value during the load increase process so that the engine load during the load increase process gradually approaches the target load. load_int=load_act+Δload_inst.

In step S56, it is determined whether or not A/F_int, which is the target air-fuel ratio during the load increasing process, is equal to or greater than A/F_knock, which is the knock lower limit air-fuel ratio. If the target air-fuel ratio during the load increasing process is less than the knock lower limit air-fuel ratio in step S56, the process proceeds to step S57. If the target air-fuel ratio during the load increasing process is equal to or higher than the knock lower limit air-fuel ratio in step S56, the process proceeds to step S58.

In step S57, the target load is readjusted so that the air-fuel ratio does not fall below the knock lower limit air-fuel ratio. That is, load_int=load_act.

At step S58, the engine load is increased to load_int.

Steps S55 to S58 repeat addition of a predetermined load that is set in advance until the engine load reaches the target load for increase processing. It corresponds to the step of adjusting the load.

In step S59, fuel injection is performed so that the air-fuel ratio becomes A/F_int, which is the target air-fuel ratio.

In step S60, it is determined whether load_int, which is the target load for increasing the engine load, is load_final, which is the steady load. In step S60, if the target load is the steady load, the current routine ends. If the target load is not the steady load in step S60, the process proceeds to step S61.

In step S61, it is determined whether or not A/F_int, which is the target air-fuel ratio during the load increasing process, is greater than A/F_knock, which is the knock lower limit air-fuel ratio. If A/F_int, which is the target air-fuel ratio during the load increasing process, is equal to or less than A/F_knock, which is the knock lower limit air-fuel ratio, in step S61, this subroutine ends. If A/F_int, which is the target air-fuel ratio during the load increase process, is greater than A/F_knock, which is the knock lower limit air-fuel ratio in step S61, the process proceeds to step S52 to continue the process of increasing the engine load.

As described above, in the internal combustion engine 10 of the first embodiment, the air-fuel ratio is made lean while the engine load is kept constant during the startup transition period, thereby significantly reducing the amount of NOx emissions during the startup transition period. can.

Since the internal combustion engine 10 makes the air-fuel ratio lean to the lean processing target air-fuel ratio at which combustion stability can be secured at the engine load and engine speed at the start of the air-fuel ratio lean processing in the start transition period, the engine speed and the engine load It is possible to suppress an increase in NOx due to an increase in .

When the lean target air-fuel ratio is larger (lean) than the steady air-fuel ratio, the internal combustion engine 10 sets the steady air-fuel ratio to the lean target air-fuel ratio, thereby suppressing the deterioration of the combustion stability during the startup transition period. can do.

During the engine speed increase process, the internal combustion engine 10 increases the engine speed at a preset rate of increase up to the increase process target engine speed at which combustion stability can be ensured at the air-fuel ratio at the start of the engine speed increase process. An increase in load is suppressed, and an increase in NOx due to an increase in engine load can be suppressed.

The internal combustion engine 10 repeats addition of a preset predetermined number of revolutions until the engine revolution number reaches the target revolution number for the increase process, and when the engine revolution number exceeds the target revolution number for the increase process, combustion stability can be ensured. Adjust the engine speed so that Therefore, the internal combustion engine 10 can suppress the deterioration of the combustion stability during the rotation speed increasing process during the start transitional period.

When the increase processing target load set in the load increase processing is smaller than the steady load, the internal combustion engine 10 performs the air-fuel ratio lean processing after the end of the load increase processing, and increases the load after the end of the air-fuel ratio lean processing. Since the process is carried out, it is possible to reach the operating conditions for power generation operation while avoiding operating conditions that increase the amount of NOx emissions, thereby significantly suppressing the integrated amount of NOx during transient operation.

FIG. 8 is a flow chart showing the flow of control during the startup transition period (starting time) of the internal combustion engine 10 in the second embodiment of the present invention. The internal combustion engine 10 of the second embodiment performs the same control as the internal combustion engine 10 of the first embodiment described above, except that homogeneous lean combustion is performed prior to stratified lean combustion in the initial air-fuel ratio lean processing at start-up. It is carried out.

When the internal combustion engine 10 of the second embodiment is started, in step S71, the air-fuel ratio for homogeneous lean combustion of the internal combustion engine 10 is set. In step S72, the air-fuel ratio for stratified lean combustion of the internal combustion engine 10 is set. Steps S71 and S72 are steps for performing air-fuel ratio lean processing, and the details thereof are the same as those in FIG. 5 described above.

In step S73, the engine speed of the internal combustion engine 10 is set. Step S73 is a step of executing the rotation speed increasing process, the details of which are the same as those in FIG. 6 described above.

In step S74, the load (torque) of the internal combustion engine 10 is set. Step S74 is a step of executing a load increase process, the details of which are the same as in FIG. 7 described above.

In step S75, it is determined whether or not the operating point is the operating point for power generation. In step S75, if the operating point is the operation for power generation, the operation at the operating point for power generation is started. In step S75, if the operating point is not the power generation operation, the process returns to step S72. In other words, in the startup transition period, the processes of steps S72 to S74 are repeated until the operating point reaches the operating point for power generation.

In the internal combustion engine 10 of the second embodiment as described above, substantially the same effects as those of the internal combustion engine 10 of the first embodiment can be obtained.

Although specific 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 scope of the invention. The present invention relates to an internal combustion engine control method and an internal combustion engine control apparatus.

Reference Signs List 1 vehicle 2 drive wheel 3 drive unit 4 power generation unit 5 drive motor 6 first gear train 7 differential gear 8 battery 9 generator 10 internal combustion engine 11 second gear train 13 control unit 14 Airflow meter 15 Crank angle sensor 16 Accelerator opening sensor 17 A/F sensor 18 Oxygen sensor

Claims (13)

In a control method for an internal combustion engine in which the engine speed is a predetermined steady speed, the engine load is a predetermined steady load, and the air-fuel ratio of the air-fuel mixture in the cylinder is a predetermined steady-state air-fuel ratio, the power generation operation is performed,
starting the internal combustion engine under operating conditions such that the rotation speed is lower than the steady speed, the load is lower than the steady load, and the air-fuel ratio is richer than the steady state;
After starting the internal combustion engine, during the startup transition period until the engine speed, the engine load, and the air-fuel ratio reach the above steady speed, the above steady load, and the above steady air fuel ratio, the engine load and the engine speed are kept constant. A control method for an internal combustion engine that repeatedly performs an air-fuel ratio lean process for making the fuel ratio lean and a load increase process for increasing the engine load while keeping the air-fuel ratio constant. 2. The method of controlling an internal combustion engine according to claim 1, wherein during the startup transition period, the air-fuel ratio lean process and the load increase process are repeated in order so as to ensure combustion stability. 2. The control method for an internal combustion engine according to claim 1, wherein, during the startup transition period, in addition to air-fuel ratio lean processing and load increase processing, engine speed increase processing is performed to increase the engine speed while keeping the air-fuel ratio constant. 4. The control method for an internal combustion engine according to claim 3, wherein during the start transition period, each of these processes is repeated in order of air-fuel ratio lean process, rotational speed increase process, and load increase process so as to ensure combustion stability. 5. The internal combustion engine according to claim 3, wherein in the air-fuel ratio lean processing, the air-fuel ratio is made lean to a lean processing target air-fuel ratio that can ensure combustion stability at the engine load and engine speed at the start of the air-fuel ratio lean processing. control method. When the air-fuel ratio lean process is performed a plurality of times during the startup transition period, the lean process target air-fuel ratio set for each lean air-fuel ratio process is changed,
6. The method of controlling an internal combustion engine according to claim 5, wherein, when the lean processing target air-fuel ratio is higher than the steady-state air-fuel ratio, the steady-state air-fuel ratio is set as the lean processing target air-fuel ratio. The control of the internal combustion engine according to any one of claims 3 to 6, wherein the engine speed increase processing increases the engine speed to an increase processing target speed at which combustion stability can be secured at the air-fuel ratio at the start of the speed increase processing. Method. The engine speed increase process repeats addition of a predetermined engine speed until the engine speed reaches the target engine speed for the increase process, and when the engine speed exceeds the target engine speed for the increase process, combustion stability is ensured. 8. The method of controlling an internal combustion engine according to claim 7, wherein the engine speed is adjusted so that the engine speed can be adjusted. The control method for an internal combustion engine according to any one of claims 3 to 8, wherein the load increase process increases the engine load to an increase process target load limited by knocking. The load increase process repeats addition of a preset predetermined load until the engine load reaches the increase process target load. When the engine load exceeds the increase process target load, the engine load is reduced so as to ensure combustion stability. 10. The method of controlling an internal combustion engine according to claim 9, wherein the adjustment is performed. 11. The method of controlling an internal combustion engine according to claim 9, wherein, in the load increase process, when the increase process target load becomes larger than the steady load, the increase process target load is set to the steady load. When the increase processing target load set in the load increase processing is smaller than the steady load, the air-fuel ratio lean processing is performed after the load increase processing is completed, and the load increase processing is performed after the air-fuel ratio lean processing is completed. A control method for an internal combustion engine according to any one of claims 9 to 11. In a control device for an internal combustion engine that performs power generation operation with an engine speed of a predetermined steady speed, an engine load of a predetermined steady load, and an air-fuel ratio of an air-fuel mixture in a cylinder of a predetermined steady state air-fuel ratio,
The internal combustion engine is started at a rotation speed lower than the steady speed, a load lower than the steady load, and a richer side than the steady air-fuel ratio. In the startup transition period until the steady load and the steady air-fuel ratio are reached, air-fuel ratio lean processing is performed to make the air-fuel ratio lean while keeping the engine load and engine speed constant, and the engine load is increased while keeping the air-fuel ratio constant. A control device for an internal combustion engine having a control unit that repeatedly performs a load increase process to increase the load.

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