Combustion fluctuation determination device for internal combustion engine

Abstract

To provide a combustion fluctuation determination device for an internal combustion engine capable of accurately determining combustion fluctuation of the internal combustion engine.SOLUTION: A combustion fluctuation determination device for an internal combustion engine includes: an acquisition section that acquires a parameter related to a combustion state of the internal combustion engine including ignition timing, valve overlapping amount and an air-fuel ratio in the internal combustion engine; and a determination section that determines whether combustion fluctuation of the internal combustion engine increases on the basis of the parameter. When the ignition timing is on a timing delay side of MBT, the valve overlapping amount is a specified value or greater and the air-fuel ratio is on a lean side of a stoichiometric air-fuel ratio, the determination section determines that the combustion fluctuation of the internal combustion engine increases.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a combustion fluctuation determination device for an internal combustion engine. [Background technology]

[0002] BACKGROUND ART There is known a technique for warming up a catalyst by retarding the ignition timing in an internal combustion engine and increasing the amount of valve overlap (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-286869 Summary of the Invention [Problem to be solved by the invention]

[0004] Depending on the ignition timing and the amount of valve overlap, there is a risk that combustion fluctuations in an internal combustion engine may increase. For example, if combustion fluctuations in an internal combustion engine mounted on a vehicle increase, the internal combustion engine may resonate with the transmission to which the power of the internal combustion engine is transmitted, which may increase vehicle vibration. Therefore, it is conceivable to implement countermeasure control to suppress such vehicle vibration, but as a prerequisite for this, it is necessary to be able to accurately determine the increase in combustion fluctuations in the internal combustion engine.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a combustion fluctuation determination device for an internal combustion engine that can accurately determine combustion fluctuations in the internal combustion engine. [Means for solving the problem]

[0006] The above object can be achieved by a combustion fluctuation determination device for an internal combustion engine, which includes an acquisition unit that acquires parameters related to the combustion state of the internal combustion engine, including ignition timing, valve overlap amount, and air-fuel ratio in the internal combustion engine, and a determination unit that determines whether combustion fluctuation in the internal combustion engine will increase based on the parameters, wherein the determination unit determines that combustion fluctuation in the internal combustion engine will increase if the ignition timing is retarded from MBT, the valve overlap amount is equal to or greater than a predetermined value, and the air-fuel ratio is leaner than stoichiometric.

[0007] The parameters may include at least one of a temperature of the cooling water and a temperature of the hydraulic oil of the internal combustion engine, and the determination unit may further determine that combustion fluctuations of the internal combustion engine will increase when at least one of the temperature of the cooling water and the temperature of the hydraulic oil of the internal combustion engine is below a predetermined temperature that is lower by a predetermined value than a temperature that indicates that warm-up of the internal combustion engine has been completed.

[0008] The parameters include a gear stage established in a transmission to which the power of the internal combustion engine is transmitted, and the determination unit may further determine that combustion fluctuations in the internal combustion engine will increase when the gear stage is a specified gear stage in which the internal combustion engine and the transmission are likely to resonate. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a combustion fluctuation determination device for an internal combustion engine that can accurately determine combustion fluctuations in an internal combustion engine. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a vehicle. [Figure 2] FIG. 2 is a schematic diagram of the engine. [Figure 3] FIG. 3 is a timing chart showing an example of the combustion fluctuation determination control. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Vehicle outline] 1 is a schematic diagram of a vehicle 1. The vehicle 1 includes an engine 10, a torque converter 20, a lock-up clutch (hereinafter referred to as an LU clutch) 29, a transmission 40, a differential device 50, drive wheels 60, a hydraulic control circuit 70, and an ECU (Electronic Control Unit) 80.

[0012] The engine 10 is a driving force source for traveling, and is typically a multi-cylinder gasoline engine, but is not limited to this and may be, for example, a diesel engine. A crankshaft 111, which is the output shaft of the engine 10, is connected to a torque converter 20.

[0013] The torque converter 20 includes a pump impeller 21 on the input shaft side, a turbine runner 22 on the output shaft side, a stator 23 that exhibits a torque amplification function, and a one-way clutch 24, and transmits power between the pump impeller 21 and the turbine runner 22 via a fluid. The torque converter 20 is provided with an LU clutch 29. The LU clutch 29 is a single-plate or multi-plate hydraulic friction clutch that connects the input side and output side of the torque converter 20 directly or in a slip state.

[0014] The transmission 40 is a stepped automatic transmission and includes a plurality of hydraulic friction engagement elements and a planetary gear device. In the transmission 40, a plurality of gear stages can be selectively established by selectively engaging the plurality of friction engagement elements. As shown in FIG. 1 , an input shaft 41 of the transmission 40 is connected to the turbine shaft 26 of the torque converter 20. The turbine shaft 26 corresponds to the output shaft of the torque converter 20. An output shaft 42 of the transmission 40 is connected to drive wheels 60 via a differential device 50 and the like.

[0015] The engagement and disengagement of multiple friction engagement elements are controlled depending on whether the shift range of the transmission 40 is a parking range, a reverse drive range, a neutral range, or a forward drive range. In the forward drive range, the engagement and disengagement of multiple friction engagement elements are controlled so that one of eight forward gears is selectively established depending on the accelerator pedal position, vehicle speed, etc. Of the eight forward gears, the lowest gear with the largest gear ratio is the first gear, and the highest gear with the smallest gear ratio is the eighth gear. The multiple friction engagement elements are specifically multiple clutches and multiple brakes. The transmission 40 is not limited to an automatic transmission and may be, for example, a manual transmission. While the gears that can be established by the transmission 40 are eight forward gears, this is not limiting, and any gear with different gear ratios may be established.

[0016] The hydraulic control circuit 70 is a known hydraulic control circuit that uses a mechanical oil pump driven by the engine 10 as a hydraulic pressure supply source, and supplies hydraulic pressure to the torque converter 20, the LU clutch 29, and the transmission 40 to control their respective operations. Furthermore, hydraulic pressure command values output from the ECU 80 are input to the hydraulic control circuit 70, and the hydraulic pressures supplied to the torque converter 20, the LU clutch 29, and the transmission 40 are controlled based on the hydraulic pressure command values. Furthermore, the LU clutch 29 is switched between a released state, a slip state, and an engaged state depending on the hydraulic pressure supplied.

[0017] The ECU 80 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and a backup RAM. The ROM stores various control programs and maps referenced when executing the various control programs. The CPU performs calculations based on the various control programs and maps stored in the ROM. The RAM temporarily stores the results of calculations performed by the CPU and data input from various sensors, and the backup RAM is a non-volatile memory that stores data to be saved when the ignition is turned off, for example. The CPU, ROM, RAM, and backup RAM functionally implement an acquisition unit and a determination unit, which will be described in detail later.

[0018] Various sensors and switches, such as an ignition switch 90, an engine rotation speed sensor 91, an intake cam angle sensor 92, an exhaust cam angle sensor 93, an air-fuel ratio sensor 94, a gear position sensor 96, a water temperature sensor 98, and an oil temperature sensor 99, are connected to the ECU 80, and signals from these sensors and switches are input to the ECU 80. The ECU 80 controls the operating state of the engine 10 and the gear position of the transmission 40 based on the detection results of the various sensors, etc.

[0019] An ignition switch 90 detects whether the ignition is on or off. An engine rotation speed sensor 91 detects the rotation speed of the crankshaft 111 (referred to as engine rotation speed). An intake side cam angle sensor 92 and an exhaust side cam angle sensor 93 detect the phases of the intake side drive cam and the exhaust side drive cam of the engine 10 relative to the intake side camshaft and the exhaust side camshaft, respectively. An air-fuel ratio sensor 94 detects the air-fuel ratio of the exhaust of the engine 10. A gear position sensor 96 detects the gear position established in the transmission 40. A water temperature sensor 98 detects the temperature of the cooling water for the engine 10. An oil temperature sensor 99 detects the temperature of the hydraulic oil supplied to the torque converter 20, the LU clutch 29, and the transmission 40.

[0020] 2 is a schematic diagram of engine 10. Engine 10 is an example of an internal combustion engine, such as a gasoline engine, but may also be a diesel engine. Each cylinder 112 of engine 10 is provided with a piston 113. Piston 113 is connected to crankshaft 111, which is the output shaft of engine 110, via connecting rod 114.

[0021] A combustion chamber 116 is formed above the piston 113 in each cylinder 112, and a spark plug 118 that ignites the mixture of fuel and air is attached to this combustion chamber 116. The timing at which this spark plug 118 ignites the mixture is adjusted by an igniter 119 provided above the spark plug 118.

[0022] The cylinder 112 is provided with an intake valve 124 and an exhaust valve 125 that open and close the cylinder 112. When the intake valve 124 opens, the combustion chamber 116 and the intake passage 120 communicate with each other, and when the intake valve 124 closes, the communication between the combustion chamber 116 and the intake passage 120 is blocked. When the exhaust valve 125 opens, the combustion chamber 116 and the exhaust passage 121 communicate with each other, and when the exhaust valve 125 closes, the communication between the combustion chamber 116 and the exhaust passage 121 is blocked.

[0023] The intake valve 124 and the exhaust valve 125 are provided with an intake-side variable valve mechanism (hereinafter referred to as intake VVT) 126 and an exhaust-side variable valve mechanism (hereinafter referred to as exhaust VVT) 127, which change the opening and closing timings of the intake valve 124 and the exhaust valve 125, respectively. The intake VVT 126 changes the phase of an intake-side drive cam that opens and closes the intake valve 124, relative to the intake-side camshaft. This advances or retards the opening and closing timing of the intake valve 124. The exhaust VVT 127 changes the phase of an exhaust-side drive cam that opens and closes the exhaust valve 125, which is provided on the exhaust-side camshaft, relative to the exhaust-side camshaft. This advances or retards the opening and closing timing of the exhaust valve 125. The intake VVT 126 and the exhaust VVT 127 can adjust the amount of valve overlap, which is the crank angle period when both the intake valve 124 and the exhaust valve 125 are open.

[0024] The intake passage 120 is provided with a throttle valve 123 that adjusts the amount of air introduced into the combustion chamber 116. The exhaust passage 121 is provided with a catalyst 150.

[0025] Each intake port 120a constituting a part of the intake passage 120 is provided with a port injection valve 122 for injecting fuel into the intake port 120a for each cylinder 112. The engine 10 is provided with an in-cylinder injection valve 117 for directly injecting fuel into each combustion chamber 116. Note that the engine 10 is not limited to providing both the port injection valve 122 and the in-cylinder injection valve 117, and only one of them may be provided.

[0026] When the LU clutch 29 is in an engaged state, the crankshaft 111 of the engine 10 and the input shaft 41 of the transmission 40 are fastened together. If the frequency of torque fluctuations caused by combustion fluctuations in the engine 10 matches the primary torsional natural frequency of the transmission 40 in this state, the engine 10 and the transmission 40 may resonate, increasing vibrations in the vehicle 1. Therefore, the ECU 80 executes control to determine whether or not the combustion fluctuations in the engine 10 will increase, as described below. If the ECU 80 determines that the combustion fluctuations in the engine 10 will increase, for example, by the following control, the ECU 80 may execute control to suppress the above-described resonance.

[0027] [Combustion fluctuation judgment control] FIG. 3 is a flowchart showing an example of combustion fluctuation determination control. This control is repeatedly executed at a predetermined cycle while the ignition is on. First, the ECU 80 acquires parameters related to the combustion state of the engine 10 (step S1). The parameters related to the combustion state include the target ignition timing, the valve overlap amount, the target air-fuel ratio, the coolant temperature, the hydraulic oil temperature, and the gear position. The target ignition timing and the target air-fuel ratio are determined mainly based on the engine speed and the intake air amount. The valve overlap amount can be calculated based on the detection values of the engine speed sensor 91, the intake cam angle sensor 92, and the exhaust cam angle sensor 93. The coolant temperature and the hydraulic oil temperature can be detected by the water temperature sensor 98 and the oil temperature sensor 99, respectively.

[0028] Next, the ECU 80 determines whether or not the combustion fluctuation of the engine 10 will increase based on the acquired parameters (step S2). That is, if each parameter falls within a predetermined combustion fluctuation prediction range, it is determined that the combustion fluctuation will increase, and if each parameter does not fall within the combustion fluctuation prediction range, it is not determined that the combustion fluctuation will increase.

[0029] The combustion fluctuation prediction range is, for example, a range that is more retarded than MBT (Minimum Spark Advance for Best Torque) for the target ignition timing. The valve overlap amount is, for example, equal to or greater than a predetermined value greater than 0. This is because a large valve overlap amount increases the amount of internal EGR, which tends to increase combustion fluctuation. The target air-fuel ratio is, for example, leaner than stoichiometric. This is because a lean target air-fuel ratio reduces the degree of stratification of the combustible mixture around the spark plug 118, which tends to increase combustion fluctuation. The coolant temperature and hydraulic oil temperature are, for example, equal to or lower than a predetermined temperature that is lower by a predetermined value than the temperature that indicates completion of warming up of the engine 10. This is because low temperatures increase cooling loss and tend to increase combustion fluctuation. The gear position is, for example, a gear position at which the engine 10 and transmission 40 are likely to resonate. A gear position at which the engine 10 and transmission 40 are likely to resonate is, for example, any gear position excluding the lowest gear position and the highest gear position. The predicted combustion fluctuation range of each parameter is determined based on the results of experiments and simulations carried out in advance and is stored in the ROM of the ECU 80.

[0030] If each of the above parameters is within the combustion fluctuation prediction range, the determination in step S2 is Yes, and the ECU 80 determines that the combustion fluctuation will increase (step S3). If any of the above parameters is not within the combustion fluctuation prediction range, the determination in step S2 is No, and the ECU 80 assumes that the combustion fluctuation will not increase and determines that the combustion state is normal (step S4).

[0031] In this way, it is possible to accurately determine whether or not the combustion fluctuation of the engine 10 will increase based on a plurality of parameters. Also, it is possible to determine whether or not the combustion fluctuation will increase based on each parameter before an increase in the combustion fluctuation is actually detected based on the rotational fluctuation of the engine 10. Therefore, it is possible to execute countermeasure control against such an increase in the combustion fluctuation at an early stage.

[0032] In the above embodiment, the target ignition timing, the valve overlap amount, the target air-fuel ratio, the coolant temperature, the hydraulic oil temperature, and the gear position are exemplified as parameters related to the combustion state, but the parameters do not need to include all of these. For example, the parameters that have a large effect on the combustion state are the target ignition timing, the valve overlap amount, and the target air-fuel ratio. In this way, by determining whether combustion fluctuations are increasing using only the parameters that have a large effect on the combustion state, the processing load on the ECU 80 due to the determination can be reduced.

[0033] In the above embodiment, the cooling water temperature and the hydraulic oil temperature are used as parameters, but only one of them may be used. This is because if at least one of the temperatures can be obtained, the degree of cooling loss, which is one of the factors that cause combustion fluctuations in the engine 10, can be estimated.

[0034] In the above embodiment, a target air-fuel ratio is used as one of the parameters, but the air-fuel ratio detected by the air-fuel ratio sensor 94 may be used instead of the target air-fuel ratio. Also, in the above embodiment, a valve overlap amount calculated based on a detected value of the engine speed sensor 91 or the like is used as one of the parameters, but a target valve overlap amount calculated in accordance with the operating state of the engine 10 may be used instead.

[0035] In the above embodiment, the engine 10 mounted on the vehicle 1 is described as an example, but the present invention is not limited to this. For example, the contents of the above embodiment can also be applied to an engine mounted on a hybrid vehicle equipped with a motor as a driving power source.

[0036] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0037] 1 vehicle 10 Engine (internal combustion engine) 40 Transmission 80 ECU (combustion fluctuation determination device for internal combustion engine, acquisition unit, determination unit)

Claims

[Claim 1] an acquisition unit that acquires parameters related to a combustion state of the internal combustion engine, including an ignition timing, a valve overlap amount, and an air-fuel ratio in the internal combustion engine; a determination unit that determines whether or not combustion fluctuations in the internal combustion engine are increasing based on the parameters, the determination unit determines that combustion fluctuation in the internal combustion engine will increase when the ignition timing is retarded relative to MBT, the valve overlap amount is equal to or greater than a predetermined value, and the air-fuel ratio is leaner than stoichiometric, the parameter includes at least one of a temperature of a cooling water of the internal combustion engine and a temperature of a hydraulic oil, the determination unit further determines that combustion fluctuations in the internal combustion engine will increase when at least one of a temperature of a cooling water of the internal combustion engine and a temperature of a hydraulic oil is equal to or lower than a predetermined temperature that is lower by a predetermined value than a temperature that indicates that warm-up of the internal combustion engine has been completed, the parameters include a gear stage established in a transmission to which power from the internal combustion engine is transmitted, The determination unit further determines that combustion fluctuations in the internal combustion engine will increase when the gear is a predetermined gear in which resonance between the internal combustion engine and the transmission is likely to occur, A combustion fluctuation determination device for an internal combustion engine, wherein the predetermined gear is any gear excluding the lowest gear and the highest gear of the transmission.

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