Control device for internal combustion engines

Abstract

To stabilize a combustion state of an auxiliary chamber type internal combustion engine when an operating point fluctuates.SOLUTION: In an internal combustion engine which comprises a combustion chamber, an auxiliary chamber communicating with the combustion chamber through an injection hole at an upper center of the combustion chamber, a fuel injection valve injecting fuel into an intake passage, first ignition means facing the auxiliary chamber, and second ignition means facing the combustion chamber, an internal combustion engine control device is adapted to: (i) execute a first combustion mode to ignite the fuel in the auxiliary chamber (50) with the first ignition means (5) in a normal state, (ii) transfer to a second combustion mode to ignite the fuel in the combustion chamber (20) with the second ignition means (7) when it is determined that an operating point is changed in the normal state, and (iii) transfer to a third combustion mode to ignite the fuel with both the first ignition means (5) and the second ignition means (7) when it is determined that combustion in the second combustion mode is stable with transition of the operating point completed and transfer to the first combustion mode when it is determined that the combustion in the third combustion mode is stable.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for a prechamber type internal combustion engine having a spark plug in a prechamber communicating with a combustion chamber.

Background Art

[0002] A prechamber type internal combustion engine having a spark plug in a prechamber installed above a combustion chamber ignites the air-fuel mixture flowing into the prechamber through a communication hole during the compression stroke in the prechamber, and the flame ejected from the communication hole into the main combustion chamber rapidly burns the air-fuel mixture in the main combustion chamber, so that combustion energy is efficiently converted into pressure, and the thermal efficiency of the engine is improved. On the other hand, there is a problem that the combustion state becomes unstable in a specific situation.

[0003] For example, in Patent Document 1, in a prechamber type internal combustion engine, when fuel injection is performed immediately before ignition timing to suppress pre-ignition, the air-fuel mixture flows into the prechamber in an overly lean state without being sufficiently mixed, and combustion becomes unstable. To address this problem, when the engine load is less than a predetermined value, ignition is performed by a spark plug in the prechamber, and when the engine load is greater than or equal to the predetermined value, fuel is injected at a time later than a predetermined time, and ignition is performed by a spark plug in the main combustion chamber.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the combustion state of a pre-chamber internal combustion engine is not necessarily unstable in the high-load range; rather, it tends to be more difficult to get the air-fuel mixture into the pre-chamber in the low-load range where the intake airflow rate decreases. On the other hand, if the operating state changes abruptly due to load fluctuations or the introduction of EGR, the state of the air-fuel mixture flowing into the pre-chamber changes, which can lead to an unstable combustion state.

[0006] This invention has been made in view of the above-mentioned points of the prior art, and its purpose is to prevent the combustion state from becoming unstable when the operating point fluctuates in a pre-chamber type internal combustion engine. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides A control device for an internal combustion engine comprising: a combustion chamber defined between a piston and a cylinder head; a sub-chamber communicating with the upper center of the combustion chamber via an injection hole; a fuel injection valve for injecting fuel into an intake passage to the combustion chamber; a first ignition means facing the sub-chamber; and a second ignition means facing the combustion chamber, In a steady state, the first ignition means performs a first combustion mode in which ignition occurs in the sub-chamber. If a change in the operating point is detected in a steady state, the system transitions to a second combustion mode in which ignition occurs in the combustion chamber by the second ignition means. When the transition of the operating point is complete and it is determined that the combustion in the second combustion mode is stable, the system transitions to a third combustion mode in which ignition is performed by both the first and second ignition means. The control device for an internal combustion engine is configured to switch to the first combustion mode when it is determined that the combustion in the third combustion mode is stable. [Effects of the Invention]

[0008] The control device for an internal combustion engine according to the present invention has the advantage of preventing the combustion state from becoming unstable after a change or transition in operating point. This is achieved by executing a first combustion mode in a steady state in which ignition occurs in the sub-chamber, thereby rapidly burning the fuel-air mixture in the main combustion chamber with the flame ejected from the nozzle into the main combustion chamber, and improving the thermal efficiency of the engine. Furthermore, when the operating point is changed, it transitions to a second combustion mode in which ignition occurs in the combustion chamber, and after the transition in operating point is complete, it returns to the first combustion mode via a third combustion mode in which ignition occurs using both the first ignition means in the sub-chamber and the second ignition means in the combustion chamber. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view showing the basic configuration of an internal combustion engine. [Figure 2] This timing chart shows the basic ignition control when the operating point is changed. [Figure 3] This timing chart shows the control measures taken when instability is detected during the transition to the third combustion mode. [Figure 4] This timing chart shows the control system used when instability is detected during the transition from the third combustion mode to the first combustion mode. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described in detail below with reference to the drawings. (Basic configuration) Figure 1 shows the basic configuration of an internal combustion engine in which the present invention is implemented. In Figure 1, the internal combustion engine is a piston-reciprocating internal combustion engine comprising a piston 2 housed reciprocally and slidably within a cylinder 1, the piston 2 being connected to a crankshaft 24 via a connecting rod 23, and the reciprocating linear motion of the piston 2 being converted into rotational motion of the crankshaft 24.

[0011] A cylinder head is positioned at the top of the cylinder block that constitutes cylinder 1, defining a combustion chamber 20 between it and the crown surface 21 of piston 2. A cap 53 is positioned in the upper center of the combustion chamber 20, defining a sub-chamber 50, and a first spark plug 5 is provided on top of the cap 53.

[0012] The sub-chamber 50 has a volume that is significantly smaller than that of the combustion chamber 20 and communicates with the combustion chamber 20 through a plurality of injection holes 51 that penetrate the cap 53. As shown in Figure 2, the injection holes 51 (orifices) are oriented at an angle with respect to the central axis of the cap 53 and are provided at multiple locations, for example, six locations, in equiangled radial arrangements around the central axis.

[0013] Furthermore, the cylinder head includes an intake passage 3 that communicates with the combustion chamber 20 through an intake port 30 on one side of the ceiling surface, and an exhaust passage 60 that communicates with the combustion chamber 20 through an exhaust port 60 on the other side of the ceiling surface. It also includes an intake valve 31 for opening and closing the intake port 30, and an exhaust valve 61 for opening and closing the exhaust port 60. The opening and closing timings of the intake valve 31 and the exhaust valve 61 can be individually controlled by a variable valve timing mechanism (not shown).

[0014] Furthermore, the cylinder head is equipped with a fuel injector 4 for injecting fuel into the intake passage 3. The fuel injector 4 is positioned diagonally toward the back side of the intake valve 31. Although not shown in the diagram, an air cleaner is connected to the upstream side of the intake passage 3 via a surge tank, and an air flow sensor, throttle valve, intake air temperature sensor, intake air flow sensor, intake air pressure sensor, etc. are installed there.

[0015] On one side, downstream of the exhaust passage 6, an O2 sensor 16 (or an air-fuel ratio sensor) for detecting the oxygen concentration in the exhaust gas and an exhaust gas purification device 62 for removing harmful substances contained in the exhaust gas are arranged. Although not shown in the figure, an EGR passage for circulating a part of the exhaust gas from the exhaust passage 6 to the intake passage 3 is provided, and an EGR cooler and an EGR valve are arranged in this EGR passage, constituting an EGR system. By introducing the exhaust gas into the intake passage in the partial load region, the pumping loss can be reduced, and the cooling loss can be reduced by lowering the combustion temperature.

[0016] By the way, as already described, when the operating point and the operating state change suddenly due to load fluctuations or EGR introduction, etc., the state of the air-fuel mixture flowing into the auxiliary chamber changes, and the combustion state becomes unstable. In particular, in a port injection type auxiliary chamber internal combustion engine equipped with a fuel injection valve 4 in the intake passage 3, although the mixing of the air-fuel mixture is good, when the operating point and the operating state change, the state of the air-fuel mixture (the ratio of air, fuel, and residual gas), temperature, and pressure in the auxiliary chamber change suddenly. Even if the appropriate values of fuel and ignition are maintained beforehand, the state of the air-fuel mixture in the auxiliary chamber may not be stable, and the combustion may become unstable.

[0017] Therefore, the internal combustion engine according to the embodiment of the present invention includes a second ignition plug 7 (auxiliary ignition plug) facing the combustion chamber 20 separately from the first ignition plug 5 in the auxiliary chamber 50. As will be described later, in the steady state, ignition is performed in the auxiliary chamber 50 by the first ignition plug 5 (first combustion mode), and during the operating point change (operating point transition period), ignition is performed in the combustion chamber 20 by the second ignition plug 7 (second combustion mode) to avoid the combustion state from becoming unstable.

[0018] Preferably, as shown in FIG. 1, the second ignition plug 7 is arranged on the intake port 30 side (the peripheral part of the ceiling surface between the two intake ports) of the ceiling surface of the combustion chamber 20, but it may also be on the other side of the ceiling surface, for example, the peripheral part of the ceiling surface between the intake port 30 and the exhaust port 60.

[0019] The internal combustion engine includes a crank angle sensor 12 that detects the crank angle and engine speed from the timing rotor of the crankshaft 24, a cam angle sensor for cylinder discrimination, a throttle opening sensor, a water temperature sensor that detects the temperature of the cooling water, an outside air temperature sensor, an oil temperature sensor, a knock sensor, etc. More preferably, it includes an in-cylinder pressure sensor (combustion pressure sensor) that detects the combustion state of the engine. The detection values of each sensor are input to the ECU 10.

[0020] The ECU (engine control unit) 10 is an electronic control unit (computer) for optimizing the operating state of the engine based on the detection values of each sensor. It includes a CPU that performs arithmetic processing, a ROM that stores control programs and setting data, a RAM that reads out control programs and setting data and stores dynamic data and arithmetic processing results, and an input / output I / F, etc. It calculates based on the deviation between the target value based on the driver (accelerator opening) and / or the output requirement of the system (torque requirement, acceleration / deceleration requirement) and the actual value based on the engine state (engine speed, intake air volume, air-fuel ratio), and state values such as intake air temperature and intake air pressure, determines the control instruction values (throttle opening, fuel injection amount, ignition timing, EGR amount), and optimizes the operating state of the engine.

[0021] And the ECU 10 determines the change of the operating point of the engine according to the deviation between the target value and the actual value in parallel with the output requirement of the driver (output down requirement). (i) In the steady state where the deviation is within a predetermined range, it executes the first combustion mode in which ignition occurs in the auxiliary chamber 50 by the first spark plug 5. (ii) When it is determined that the operating point needs to be changed, it shifts to the second combustion mode in which ignition occurs in the combustion chamber 20 by the second spark plug 7. (iii) When the shift of the operating point is completed, it performs control to return to the first combustion mode through the third combustion mode in which ignition occurs by both the first spark plug 5 and the second spark plug 7.

[0022] As a criterion for determining a change in the engine's operating point, for example, the deviation of the actual engine speed from the target engine speed is monitored, and if the deviation of the actual engine speed from the target engine speed exceeds a predetermined value (e.g., 100 rpm), it is determined that a change in the operating point is required.

[0023] The following explains the control of the combustion mode in response to changes in the operating point, with reference to Figure 2.

[0024] (First combustion mode) The ECU 10 basically executes a first combustion mode in which the first spark plug 5 ignites in the sub-chamber 50 when the deviation between the driver's power request (power reduction request) and the actual value is less than a predetermined value.

[0025] In the first combustion mode, fuel injected into the intake passage 3 during the intake or exhaust stroke mixes with air flowing into the cylinder 1 during the intake stroke to form a fuel-air mixture. During the compression stroke, this mixture flows into the sub-chamber 50 through the nozzle 51 and is ignited in the sub-chamber 50 by the first spark plug 5. The flame then rapidly ejects radially into the combustion chamber 20 from the nozzle 51, rapidly burning the fuel-air mixture in the combustion chamber 20 and optimizing the engine's operating state for optimal thermal efficiency.

[0026] (Second combustion mode) During operation in the first combustion mode as described above, if, for example, at time t1 in Figure 1, an output request (output reduction request) is made that causes the deviation between the driver's output request (output reduction request) and the actual value to exceed a predetermined value, and it is determined that there is a request to change the operating point, the system will switch to the second combustion mode in which ignition occurs in the combustion chamber 20 by the second spark plug 7.

[0027] In the second combustion mode, instead of the first spark plug 5, the second spark plug 7 directly ignites the air-fuel mixture in the combustion chamber 20. Although this relatively reduces the engine's thermal efficiency, it prevents the combustion state from becoming unstable even when the state of the air-fuel mixture in the combustion chamber 20 changes due to fluctuations in intake airflow or EGR amount.

[0028] Furthermore, in the second combustion mode, which is ignited by the second spark plug 7, the combustion speed is slower compared to the first combustion mode, and the peak of the heat generation rate shifts to the retarded side. Therefore, it is preferable to advance the ignition timing of the second spark plug 7 in the second combustion mode compared to the ignition timing of the first spark plug 5 in the first combustion mode.

[0029] Subsequently, at time t2 in Figure 1, when the engine reaches the target operating point and the deviation between the driver's power request (power reduction request) and the actual value falls below a predetermined value, the engine combustion stability determination 1 is performed. The combustion stability determination is evaluated based on whether the rotational fluctuations during the determination period remain within a predetermined value, for example, within 100 rpm. Alternatively, it may be evaluated based on whether the combustion fluctuation rate (COV of IMEP) obtained from the in-cylinder pressure sensor is within a predetermined value, for example, within 4%. The engine for which the combustion stability determination is performed is not particularly limited, but it is typically for a few cycles to several tens of cycles.

[0030] (Third combustion mode) Then, at time t3 in Figure 1, once the combustion stability determination 1 is completed and it is determined that combustion in the second combustion mode is in a stable state, the system transitions to the third combustion mode, in which both the first spark plug 5 and the second spark plug 7 ignite. In other words, instead of immediately stopping the ignition by the second spark plug 7 in the second combustion mode, the ignition of the first spark plug 5 is started in parallel with the ignition of the second spark plug 7. This prevents the engine's combustion state from becoming unstable even if the ignition in the sub-chamber 50 by the first spark plug 5 does not immediately stabilize.

[0031] In the third combustion mode, the ignition timing of the second spark plug 7 is retarded compared to the ignition timing of the first spark plug 5, so that the second spark plug 7 ignites at the same time as the flame is ejected from the nozzle 51 by the ignition of the first spark plug 5. In other words, it is necessary to prevent the second spark plug 7 from igniting before the flame is ejected by the ignition of the first spark plug 5.

[0032] Furthermore, since the third combustion mode is a transient combustion mode, the engine combustion stability determination 2 is performed simultaneously with the transition to the third combustion mode. If it is determined that combustion in the third combustion mode is stable at time t4 in Figure 1, the engine switches to the first combustion mode, in which the second spark plug 7 is stopped and ignition occurs in the sub-chamber 50 by the first spark plug 5.

[0033] In this case, it is preferable to gradually reduce the discharge energy of the second spark plug 7 rather than immediately stopping the second spark plug 7. Simultaneously with the transition to the first combustion mode, the engine combustion stability determination 3 is performed, and if the determination period elapses while the engine remains in a stable state at time t5 in Figure 1, it returns to a steady state.

[0034] (If the combustion stability test determines that it is unstable) In the above embodiment, we described the case where the combustion state stabilizes within a predetermined period after transitioning to each combustion mode. However, if the combustion state does not stabilize after transitioning to each combustion mode, the following control is performed.

[0035] For example, as shown in Figure 3, if, after transitioning from the second combustion mode to the third combustion mode at time t3, it is determined that the combustion state is unstable at time t3', the system does not continue in the third combustion mode, but instead returns to the second combustion mode, in which the first spark plug 5 in the sub-chamber 50 is stopped and ignition is performed only by the second spark plug 7 in the combustion chamber 20.

[0036] Even after returning to the second combustion mode, the combustion stability check continues. If it is determined at time t4' that combustion in the second combustion mode is stable, the system transitions to the third combustion mode, in which both the first spark plug 5 and the second spark plug 7 ignite. Subsequently, if it is determined at time t5' that combustion in the third combustion mode is stable, the system transitions to the first combustion mode, in which the second spark plug 7 is deactivated and ignition occurs in the sub-chamber 50 by the first spark plug 5.

[0037] Furthermore, as shown in Figure 4, at time t4, the second spark plug 7 is stopped (gradually reducing the discharge energy), and after transitioning from the second combustion mode to the first combustion mode, if the combustion stability judgment 2 determines that it is unstable at time t4', it returns to the third combustion mode in which both the first spark plug 5 in the sub-chamber 50 and the second spark plug 7 in the combustion chamber 20 ignite. Subsequently, at time t5', if the combustion in the third combustion mode is determined to be stable, the second spark plug 7 is stopped (gradually reducing the discharge energy), and it transitions to the first combustion mode.

[0038] The combustion stability assessment period may be the same for combustion stability assessments 1 to 3 in each mode, but the assessment period for combustion stability assessment 2 in the third combustion mode may be longer than that for combustion stability assessment 1 in the second combustion mode, and the assessment period for combustion stability assessment 3 when transitioning to the first combustion mode may be longer than that for combustion stability assessment 2 in the third combustion mode. In other words, extending the stability assessment period when transitioning to a combustion mode that is prone to instability is advantageous in reducing the risk of combustion fluctuations and balancing combustion stability and responsiveness.

[0039] (Mechanism of Action and Effects) As described above, the control device for an internal combustion engine according to the present invention is (i) In a steady state, the first combustion mode is performed by igniting in the sub-chamber 50 by the first spark plug 5, and the flame ejected radially from the nozzle 51 into the combustion chamber 20 rapidly combusts the air-fuel mixture in the combustion chamber 20, so that the combustion energy is efficiently converted into pressure and the thermal efficiency of the engine can be improved. And in a steady state, (ii) If a change in the operating point is detected, the system switches to a second combustion mode in which ignition occurs in the combustion chamber 20 by the second spark plug 7, thereby preventing the combustion state from becoming unstable. (iii) When the transition to the operating point is complete, control is performed to return to the first combustion mode via a third combustion mode in which both the first spark plug 5 and the second spark plug 7 ignite, thereby preventing the combustion state from becoming unstable during the process of returning to a steady state after the transition to the operating point.

[0040] As described above, by controlling the system to transition to the second combustion mode (evacuation mode) and then to the third combustion mode (transition mode) before returning to the first combustion mode (sub-chamber combustion mode, steady state) when the operating point is changed, even if it causes a temporary decrease in thermal efficiency, it avoids the combustion state becoming unstable, thereby minimizing the decrease in thermal efficiency over the entire operating period and offering the advantages of improved thermal efficiency and reduced knocking in the first combustion mode (sub-chamber combustion mode).

[0041] In particular, when returning from the second combustion mode (evacuation mode) to the first combustion mode (sub-chamber combustion mode, steady state), passing through the third combustion mode (transition mode, buffer mode) has the advantage of enabling a smooth transition to the steady state.

[0042] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various further modifications and changes are possible based on the technical concept of the present invention. [Explanation of symbols]

[0043] 1 cylinder 2 pistons 3. Intake passage 4. Fuel Injector 5. First spark plug 6. Exhaust passage 7. Second spark plug 10. ECU (Engine Control Unit) 12 Crank angle sensor 16 O2 sensors 20 Combustion chamber 30 intake ports 31 Intake valve 50 Antechamber 51 nozzles 60 exhaust ports 61 Exhaust valve 62 Exhaust gas purification system

Claims

1. A control device for an internal combustion engine comprising: a combustion chamber defined between a piston and a cylinder head; a sub-chamber communicating with the upper center of the combustion chamber via an injection hole; a fuel injection valve for injecting fuel into an intake passage to the combustion chamber; a first ignition means facing the sub-chamber; and a second ignition means facing the combustion chamber, In a steady state, the first ignition means performs a first combustion mode in which ignition occurs in the sub-chamber. If a change in the operating point is detected in a steady state, the system transitions to a second combustion mode in which ignition occurs in the combustion chamber by the second ignition means. When the transition of the operating point is complete and it is determined that the combustion in the second combustion mode is stable, the system transitions to a third combustion mode in which ignition is performed by both the first ignition means and the second ignition means. A control device for an internal combustion engine, characterized in that it is configured to switch to the first combustion mode when it is determined that the combustion in the third combustion mode is stable.

2. The control device for an internal combustion engine according to claim 1, characterized in that the ignition timing of the second ignition means in the second combustion mode is advanced compared to the ignition timing of the first ignition means in the first combustion mode, and when transitioning from the second combustion mode to the third combustion mode, the ignition timing of the second ignition means is retarded compared to the ignition timing of the first ignition means.

3. The control device for an internal combustion engine according to claim 1 or 2, characterized in that if it is determined that the combustion in the third combustion mode is unstable, the first ignition means is stopped and the system returns to the second combustion mode.

4. The control device for an internal combustion engine according to claim 1 or 2, characterized in that if combustion is determined to be unstable after transitioning from the third combustion mode to the first combustion mode, it is configured to return to the third combustion mode.

5. The control device for an internal combustion engine according to claim 1 or 2, characterized in that, in the case where it is determined that the combustion in the third combustion mode is stable, the discharge energy of the second ignition means is gradually reduced to transition to the first combustion mode.

6. The period for determining the stability of combustion in the third combustion mode is longer than the period for determining the stability of combustion in the second combustion mode. The control device for an internal combustion engine according to claim 1 or 2, characterized in that the period for determining the stability of combustion in the first combustion mode is longer than the period for determining the stability of combustion in the third combustion mode.

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