Control device for internal combustion engine

Abstract

To provide a control device of an internal combustion engine capable of restraining a variation in combustion pressure between cylinders.SOLUTION: A control device for a multi-cylinder engine capable of individually controlling an ignition timing and a fuel injection amount, the control device comprising: a generator configured to generate a reaction torque corresponding to a torque transmitted from the engine; and a resolver configured to detect a rotation angle of the generator, A combustion pressure of each of the cylinders is estimated according to a change in a rotation angle of the power generator detected by a resolver (step S3), a combustion pressure difference between the estimated combustion pressure and an ideal combustion pressure is calculated for each of the cylinders (step S4), and when all the combustion pressure differences are not within a predetermined range, ignition timings or fuel injection amounts of all the cylinders are uniformly corrected, and when any one of the combustion pressure differences is not within the predetermined range, ignition timings or fuel injection amounts of the cylinders having the combustion pressure difference that is not within the predetermined range are individually corrected (steps S8 and S10).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a control device for an internal combustion engine having a plurality of cylinders. [Background technology]

[0002] Patent Document 1 describes a control device that retards ignition timing from normal ignition timing during cold start of an internal combustion engine to quickly heat up a catalyst for purifying exhaust gases, thereby suppressing variations in combustion pressure among cylinders and resulting in rotation fluctuations. Specifically, the control device first retards ignition timing to quickly heat up the catalyst during cold start, and determines the quality of combustion in each cylinder based on the ion current generation angle. This ion current generation angle is the crank angle at which the ion current output from an ion current measurement circuit via the spark plug exceeds a reference level. Next, if the ion current generation angle is greater than a predetermined value and a cylinder is determined to have a poor combustion state, the control device advances the ignition timing of that cylinder. The control device then advances the ignition timing of the other cylinders so that the difference between the ignition timing correction amount of the advanced cylinder and the ignition timing correction amount of the other cylinders that are not advanced is a predetermined guard amount. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-057554 Summary of the Invention [Problem to be solved by the invention]

[0004] The internal combustion engine control device described in Patent Document 1 determines whether the combustion state of each cylinder is good, corrects the ignition timing of the cylinder with a poor combustion state, and accordingly corrects the ignition timing of the other cylinders to prevent variations in the ignition timing of all cylinders. However, because the determination of whether the combustion state is good is based on the crank angle at which the ion current is equal to or greater than a reference level, it is not possible to detect or estimate the combustion pressure of each cylinder. Therefore, even if the combustion state of all cylinders can be made good, variations in the combustion pressure of each cylinder may occur, which may cause fluctuations (pulsations) in the torque output from the internal combustion engine.

[0005] The present invention has been made in light of the above technical problems, and aims to provide a control device for an internal combustion engine that can suppress variations in combustion pressure between cylinders. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the present invention provides a control device for an internal combustion engine having a plurality of cylinders that combust a mixture of air and fuel, and capable of individually controlling at least one of the ignition timing in the cylinders and the amount of fuel injected into the cylinders, the control device further comprising: a generator that generates a reaction torque corresponding to the torque transmitted from the internal combustion engine; a sensor that detects the rotation angle of the generator; and a controller that controls at least one of the ignition timing and the amount of fuel injected into the cylinders, wherein the controller estimates the combustion pressure for each of the cylinders in accordance with changes in the rotation angle of the generator detected by the sensor, calculates a combustion pressure difference between the estimated combustion pressure and a predetermined ideal combustion pressure for each of the cylinders, and if all of the calculated combustion pressure differences are not within a predetermined range, uniformly corrects the ignition timing or the fuel injection amount for all of the cylinders, and if any of the combustion pressure differences is not within the predetermined range, individually corrects the ignition timing or the fuel injection amount for the cylinder whose combustion pressure difference is not within the predetermined range. [Effects of the Invention]

[0007] According to the present invention, the combustion pressure for each cylinder is estimated in response to changes in the rotation angle of the generator, and the combustion pressure difference between the estimated combustion pressure and the ideal combustion pressure is calculated for each cylinder. In this way, a sensor that detects the rotation angle of the generator is more accurate than a sensor that detects the rotation angle of the internal combustion engine, and is less susceptible to the effects of resonance, etc. Therefore, the combustion pressure for each cylinder can be estimated individually with higher accuracy than if the combustion pressure for each cylinder were estimated based on the detection value of the sensor that detects the rotation angle of the internal combustion engine.

[0008] Furthermore, if all combustion pressure differences between the ideal combustion pressure and the estimated combustion pressure are not within a predetermined range, the ignition timing and fuel injection amount for all cylinders are uniformly corrected, thereby preventing the complicated control required to correct the combustion pressure to an appropriate level. Furthermore, if any combustion pressure difference is not within a predetermined range, the ignition timing and fuel injection amount are individually corrected for the cylinder with the combustion pressure difference outside the predetermined range, thereby preventing variations in combustion pressure between cylinders. As a result, relatively large pulsations in the torque output from the internal combustion engine can be prevented, thereby suppressing fluctuations in driving force. In other words, deterioration of drivability can be prevented. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a skeleton diagram illustrating an example of a hybrid vehicle equipped with an internal combustion engine according to an embodiment of the present invention. [Figure 2] 4 is a flowchart illustrating an example of control executed by a control device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described based on the embodiments shown in the drawings. Note that the embodiments described below are merely examples of specific implementations of the present invention and are not intended to limit the present invention.

[0011] Fig. 1 shows a skeleton diagram for explaining an example of a hybrid vehicle equipped with an internal combustion engine according to an embodiment of the present invention. The hybrid vehicle (hereinafter simply referred to as a vehicle) Ve shown in Fig. 1 includes an internal combustion engine (hereinafter referred to as an engine) 1, a first motor 2, and a second motor (not shown) as driving power sources.

[0012] The engine (ENG) 1 can be configured similarly to engines used as a driving force source in conventional engine vehicles or hybrid vehicles. Specifically, the engine (ENG) 1 includes an intake pipe that takes in outside air, multiple cylinders to which air is supplied from the intake pipe, injectors 3 that inject fuel, spark plugs 4 that ignite a fuel-air mixture, and exhaust pipes that discharge exhaust gas from the cylinders. The engine may be a port-injection type engine in which the injectors 3 are provided in the intake pipe, or a direct-injection type engine in which the injectors 3 are provided within the cylinders. The injectors 3 and spark plugs 4 are provided for each cylinder, allowing for individual control of the fuel injection amount and ignition timing. For convenience, only one injector 3 and one spark plug 4 are shown in FIG. 1.

[0013] The first motor (MG) 2 and the second motor can be configured in the same manner as motors used as driving power sources in conventional hybrid vehicles and electric vehicles. That is, in addition to functioning as motors that output driving torque when supplied with electric power, they also function as generators that convert the power of the output shaft into electric power when the output shaft is rotated. Specifically, they can be configured using a permanent magnet synchronous motor or induction motor. The first motor 2 corresponds to the "generator" in the embodiments of the present invention.

[0014] A vehicle Ve shown in Fig. 1 is equipped with a power split mechanism 5 that splits the output torque of an engine 1 between a first motor 2 and drive wheels (not shown). This power split mechanism 5 is configured with a single-pinion planetary gear. Specifically, it is configured with a sun gear S, a ring gear R arranged concentrically with the sun gear S, and a carrier C that holds a pinion gear P that meshes with the sun gear S and the ring gear R so that the pinion gear P can rotate and revolve. The sun gear S is connected to the first motor 2, the carrier C is connected to the engine 1, and the ring gear R is connected to an output gear 6 that transmits torque to the drive wheels.

[0015] A gear train unit (not shown) is provided to transmit torque from the ring gear R to the drive wheels, and the second motor is connected to the gear train unit so that torque can be transmitted. That is, the system is configured so that torque output from the second motor can be added to torque transmitted from the engine 1 to the gear train unit via the power split mechanism 5. The second motor is configured to be supplied with power stored in a power storage device (not shown) and power generated by the first motor 2.

[0016] 1 is provided with an electronic control device (hereinafter referred to as a controller) 7 that controls the engine 1, the first motor 2, and the second motor. Specifically, the controller 7 is configured to control the amount of fuel injected by the injector 3 provided in the engine 1, the ignition timing by the spark plug 4, the output torque of the first motor 2, and the output torque of the second motor.

[0017] Like controllers installed in conventional vehicles, this controller 7 is mainly composed of a microcomputer, and is configured to receive signals from various sensors installed in the vehicle Ve and output command signals for controlling the engine 1 and each motor based on the input signals and pre-stored arithmetic expressions, maps, etc.

[0018] 1 receives signals from an intake air temperature sensor 8 that detects the temperature of air flowing through the intake pipe, a water temperature sensor 9 that detects the temperature of the coolant for cooling the engine 1, a crank angle sensor 11 that detects the rotation speed of the engine 1, specifically the rotation angle of a crankshaft 10 that is the output shaft of the engine 1, an air flow meter 12 that detects the amount of intake air of the engine 1, a first resolver 13 that detects the rotation speed (rotation angle) of the first motor 2, and a second resolver (not shown) that detects the rotation speed (rotation angle) of the second motor. This first resolver 13 corresponds to the "sensor" in the embodiment of the present invention.

[0019] The power split mechanism 5 splits the torque input from the engine 1 between the first motor 2 (sun gear S) and the drive wheels (ring gear R) according to their gear ratios. Specifically, a reaction torque opposing the torque transmitted from the engine 1 to the first motor 2 is output from the first motor 2, and torque corresponding to the reaction torque is transmitted to the drive wheels. In other words, when the reaction torque from the first motor 2 is smaller than the torque transmitted from the engine 1 to the first motor 2, the rotation speeds of the engine 1 and the first motor 2 increase according to the magnitude of the torque deficiency. Conversely, when the reaction torque from the first motor 2 is greater than the torque transmitted to the first motor 2, the rotation speeds of the engine 1 and the first motor 2 decrease according to the magnitude of the surplus torque. In other words, the rotation speeds of the engine 1 and the first motor 2 are controlled by controlling the torque of the first motor 2.

[0020] Therefore, the above-mentioned controller 7 calculates the target rotation speed and target torque of the engine 1 based on the vehicle speed and the operation amount of the accelerator device (not shown). The controller 7 then calculates the target rotation speed of the first motor 2 based on the target rotation speed of the engine 1, the vehicle speed (i.e., the rotation speed of the ring gear R), and the gear ratio of the power split device 5, and calculates the target reaction torque of the first motor 2 by multiplying the target torque of the engine 1 by the gear ratio of the power split device 5. During the transitional period in which the engine rotation speed is shifting to the target rotation speed, the target reaction torque of the first motor 2 may be calculated by adding or subtracting a torque based on the rate of change of the rotation speed to or from the torque transmitted to the first motor 2 via the power split device 5. The torque of the second motor is controlled based on the difference between the torque transmitted from the engine 1 via the power split device 5 and the drive torque required for the vehicle Ve.

[0021] As described above, engine 1 has multiple cylinders. In such a multi-cylinder engine, each cylinder combusts the air-fuel mixture at a different timing, causing the output torque of engine 1 to pulsate. On the other hand, as described above, the rotation speed of first motor 2 (amount of change or rate of change in rotation angle) is maintained by outputting a reaction torque from first motor 2 that opposes the torque transmitted from engine 1. Therefore, when the torque of engine 1 pulsates, the rotation speed of first motor 2 fluctuates. In other words, the pulsating torque of engine 1, in other words, the combustion pressure generated by combusting the air-fuel mixture for each cylinder, can be estimated based on the output torque of first motor 2 and the rotation angle of first motor 2 detected by first resolver 13.

[0022] Therefore, the control device in this embodiment of the present invention is configured to estimate the combustion pressure generated in each cylinder and correct the ignition timing and fuel injection amount of each cylinder based on the estimated combustion pressure. Fig. 2 shows a flowchart for explaining an example of this control. In the control example shown in Fig. 2, first, various parameters are calculated based on detection values ​​of sensors that detect the operating state of engine 1 (step S1). The parameters in step S1 include, for example, engine intake temperature, engine water temperature, engine speed, and engine intake air amount.

[0023] Next, the ideal combustion pressure Pcyl(n) is calculated for each cylinder based on the parameters calculated in step S1 (step S2). The ideal combustion pressure Pcyl(n) in step S2 can be calculated by referring to a multidimensional map that is constructed in advance by conducting experiments or simulations to determine the ideal combustion pressure Pcyl(n) using the parameters calculated in step S1.

[0024] Next, the estimated combustion pressure P'cyl(n) is calculated (step S3). Specifically, the estimated combustion pressure P'cyl(1) of the first cylinder is calculated based on the torque (command torque) output from the first motor 2 and the rate of change of the rotation angle based on the detection signal of the first resolver 13 at the timing when the air-fuel mixture is combusted in the first cylinder. Similarly, the estimated combustion pressures P'cyl(2) and P'cyl(3) are calculated for each cylinder.

[0025] Then, the difference (combustion pressure difference) ΔP(n) between the ideal combustion pressure Pcyl(n) and the estimated combustion pressure P'cyl(n) for each cylinder is calculated (step S4). Specifically, the combustion pressure difference ΔP(n) for each cylinder is calculated by subtracting the estimated combustion pressure P'cyl(n) calculated in step S3 from the ideal combustion pressure Pcyl(n) calculated in step S2. That is, in the case of a three-cylinder engine, the combustion pressure differences ΔP(1), ΔP(2), and ΔP(3) are calculated for the first, second, and third cylinders, respectively.

[0026] Following step S4, it is determined whether the combustion pressures of all cylinders have increased or decreased to the same level (step S5). Specifically, it is determined whether all combustion pressure differences ΔP(all) calculated in step S4 are greater than a predetermined upper limit value THH1 or whether all combustion pressure differences ΔP(all) are smaller than a predetermined lower limit value THL1. The predetermined upper limit value THH1 and the predetermined lower limit value THL1 used in step S5 are allowable values ​​for possible combustion pressure differences and are stored in advance in the controller 7. Note that the predetermined upper limit value THH1 and the predetermined lower limit value THL1 may be changed depending on the output torque of the engine 1, etc.

[0027] If the answer to step S5 is affirmative because all combustion pressure differences ΔP(all) are greater than the predetermined upper limit value THH1 or all combustion pressure differences ΔP(all) are smaller than the predetermined lower limit value THL1, it means that the intended torque is not being output from the engine 1. Therefore, if the answer to step S5 is affirmative, the ignition timing and fuel injection amount for all cylinders are corrected (step S6) so that the actual combustion pressure becomes the ideal combustion pressure Pcyl(n), and this routine is temporarily terminated.

[0028] Specifically, if the answer to step S5 is affirmative because all combustion pressure differences ΔP(all) are greater than the predetermined upper limit THH1, the ignition timing is retarded or the fuel injection amount is reduced. Conversely, if the answer to step S5 is affirmative because all combustion pressure differences ΔP(all) are smaller than the predetermined lower limit THL1, the ignition timing is advanced or the fuel injection amount is increased.

[0029] In step S6, the advance or retard amount of the ignition timing or the fuel injection amount may be determined based on the maximum or average value of the combustion pressure difference ΔP(n) calculated in step S4, or may be set to a predetermined amount.

[0030] On the other hand, if the answer to step S5 is NO because all or any of the combustion pressure differences ΔP(all) are equal to or less than the predetermined upper limit THH1, or all or any of the combustion pressure differences ΔP(all) are equal to or greater than the predetermined lower limit THL1, the ignition timing and fuel injection amount are corrected for each cylinder. That is, from step S7 onwards, determinations and controls are performed for each cylinder.

[0031] Specifically, first, it is determined for each cylinder whether the combustion pressure difference ΔP(n) is greater than a predetermined upper limit value THH2 (step S7). Note that the predetermined upper limit value THH2 in step S7 may be the same as or smaller than the predetermined upper limit value THH1 in step S5.

[0032] If there is a target cylinder for which the combustion pressure difference ΔP(n) is greater than the predetermined upper limit value THH2 and therefore the answer to step S7 is affirmative, the ignition timing for that target cylinder is retarded or the fuel injection amount is reduced (step S8), and this routine is temporarily terminated.

[0033] Conversely, if the determination in step S7 is negative because all combustion pressure differences ΔP(all) are equal to or less than the predetermined upper limit THH2, or if there is a cylinder for which the determination in step S7 is negative because the combustion pressure difference ΔP(n) is equal to or less than the predetermined upper limit THH2, then it is determined for each cylinder whether the combustion pressure difference ΔP(n) is smaller than the predetermined lower limit THL2 (step S9). Note that the predetermined lower limit THL2 in step S9 may be the same value as the predetermined lower limit THL1 in step S5, or may be a value greater than that.

[0034] If there is a target cylinder for which the combustion pressure difference ΔP(n) is smaller than the predetermined lower limit value THL2 and therefore the answer to step S9 is affirmative, the ignition timing for that target cylinder is advanced or the fuel injection amount is increased (step S10), and this routine is temporarily terminated.

[0035] Conversely, if the determination in step S9 is negative because all combustion pressure differences ΔP(all) are equal to or greater than the predetermined lower limit THL2, the combustion pressures in all cylinders are approximately equal to the ideal combustion pressure Pcyl(n) or within an acceptable range. Alternatively, for cylinders for which the determination in step S9 is negative because the combustion pressure difference ΔP(n) is equal to or greater than the predetermined lower limit THL2, the combustion pressure is approximately equal to the ideal combustion pressure Pcyl(n) or within an acceptable range. Therefore, if the determination in step S9 is negative, this routine is immediately terminated.

[0036] As described above, the combustion pressure generated in each cylinder is estimated based on the reaction torque of the first motor 2 and the detection value of the first resolver 13. The detection value by the first resolver 13 is more accurate than the detection value of the crank angle sensor 11 and is less susceptible to the influence of resonance, etc. Therefore, the combustion pressure of each cylinder can be estimated individually with higher accuracy than estimating the combustion pressure of each cylinder based on the detection value of the crank angle sensor 11, in other words, on changes in the engine speed.

[0037] Furthermore, if all of the combustion pressure differences ΔP(n), which are the differences between the ideal combustion pressure Pcyl(n) and the estimated combustion pressure P'cyl(n), are higher than the predetermined upper limit value THH1 or lower than the predetermined lower limit value THL1, in other words, if the differences are not within a predetermined range, the ignition timing and fuel injection amount are corrected uniformly for all cylinders, thereby preventing the control required to correct the combustion pressure to an appropriate level from becoming complicated.

[0038] Furthermore, if any combustion pressure difference ΔP(n) is not within a predetermined range, the ignition timing and fuel injection amount are individually corrected for the cylinders with a combustion pressure difference ΔP(n) outside the predetermined range, thereby suppressing variations in combustion pressure among the cylinders. As a result, it is possible to suppress an increase in vibration and abnormal noise caused by the engine 1 being driven. It is also possible to suppress relatively large pulsations in the torque output from the engine 1, thereby suppressing fluctuations in driving force. In other words, it is possible to suppress a deterioration in drivability.

[0039] The vehicle Ve shown in FIG. 1 is a so-called series-parallel hybrid vehicle that converts part of the power of the engine 1 into electricity using the first motor 2 and transmits the surplus power to the drive wheels to run, but it may also be a so-called series hybrid vehicle that converts the power of the engine 1 into electricity using the first motor 2 and transmits power only from the second motor to the drive wheels to run. [Explanation of symbols]

[0040] 1 engine 2 motors 3 injectors 4 spark plugs 7 Controller 11 Crank angle sensor 13 Resolver Vehicle

Claims

[Claim 1] A control device for an internal combustion engine, which has a plurality of cylinders that combust a mixture of air and fuel, and which is capable of individually controlling at least one of an ignition timing in each of the cylinders and an amount of fuel injected into each of the cylinders, a generator that generates a reaction torque corresponding to the torque transmitted from the internal combustion engine; a sensor for detecting a rotation angle of the generator; a controller that controls at least one of the ignition timing and the fuel injection amount, The controller estimating the combustion pressure for each cylinder in accordance with a change in the rotation angle of the generator detected by the sensor; calculating a combustion pressure difference between the estimated combustion pressure and a predetermined ideal combustion pressure for each cylinder; If all of the calculated combustion pressure differences are not within a predetermined range, the ignition timing or the fuel injection amount is uniformly corrected for all of the cylinders, and if any of the combustion pressure differences is not within the predetermined range, the ignition timing or the fuel injection amount is individually corrected for the cylinder whose combustion pressure difference is not within the predetermined range. A control device for an internal combustion engine.

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