JP2016098737A - Internal combustion engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly accurately calculate a combustion index using a reliable value out of signals output from a cylinder internal pressure sensor.SOLUTION: An internal combustion engine control device comprises: a cylinder internal pressure sensor which is inserted into a hole communicating with a combustion chamber of an internal combustion engine by forming a cavity between the cylinder internal pressure sensor and the hole, which is provided with a pressure reception member displacing in response to an internal pressure of the combustion chamber, and which outputs a signal in response to a displacement of the pressure reception member; a crank angle sensor; and an arithmetic processing unit which receives signals from the cylinder internal pressure sensor and the crank angle sensor and which performs an arithmetic operation for controlling a combustion state within the combustion chamber. The arithmetic processing unit is configured to execute first processing for estimating a deposit accumulation amount of the cylinder internal pressure sensor, second processing for setting a threshold higher as the deposit accumulation amount is larger and third processing for calculating a combustion index representing the combustion state within the combustion chamber using a signal higher than the threshold in an absolute value |ΔP| of a variation of a pressure P per unit crank angle in response to the signal from the cylinder internal pressure sensor.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine provided with an in-cylinder pressure sensor.

  An in-cylinder pressure sensor (also referred to as a combustion pressure sensor) attached to a combustion chamber of an internal combustion engine is known. The in-cylinder pressure sensor outputs a signal corresponding to the pressure level in the combustion chamber. The change of the in-cylinder pressure (combustion pressure) with respect to the crank angle depends on the combustion state in the combustion chamber. Therefore, it is possible to obtain a combustion index (parameter) representing the combustion state in the combustion chamber by receiving and processing the signal output from the in-cylinder pressure sensor. The combustion index includes, for example, a combustion ratio at a predetermined crank angle and a crank angle at which the combustion ratio becomes a predetermined ratio. In the latter, the crank angle at which the combustion ratio is 50% is particularly called the combustion center of gravity or CA50. These combustion indicators are used for controlling the combustion state. For example, CA50 is used for optimal ignition timing control.

  Various proposals have been made regarding the form of the in-cylinder pressure sensor. For example, Patent Literature 1 discloses an in-cylinder pressure sensor integrated with a glow plug. In the in-cylinder pressure sensor integrated with a glow plug, a heater rod, which is a heating element, also functions as a pressure receiving member. That is, the heater rod is displaced according to the pressure in the combustion chamber, and a signal corresponding to the displacement is output from the in-cylinder pressure sensor. However, deposits tend to adhere around the heater rod. The deposited deposit becomes resistance when the heater rod is displaced, and changes the displacement characteristic of the heater rod with respect to pressure. If the displacement characteristic of the heater rod with respect to the pressure changes, the output value of the in-cylinder pressure sensor deviates from the case where no deposit is attached.

  The applicant has recognized the following documents including the above-mentioned documents as related to the present invention.

JP 2009-2222031 A JP 2009-203938 A JP 2012-159048 A

  Combustion control using a combustion index such as CA50 can also be applied to an in-cylinder pressure sensor integrated with a glow plug. However, the in-cylinder pressure sensor integrated with the glow plug has its pressure receiving member inserted into a hole communicating with the combustion chamber, and is displaced between the hole and the pressure receiving member in the axial direction of the pressure receiving member according to the pressure in the combustion chamber. It is comprised so that the space | gap for it may be made. In the in-cylinder pressure sensor having such a configuration, deposits may adhere to the periphery of the pressure receiving member, which may change the displacement characteristics of the pressure receiving member with respect to pressure. If an error occurs in the value detected by the in-cylinder pressure sensor due to deposit accumulation, the calculation of the combustion index is affected. In order to calculate the combustion index with high accuracy and control the combustion state, it is necessary to use a reliable detection value.

  The present invention has been made in view of the above-described problems, and provides an internal combustion engine control apparatus capable of calculating a combustion index with high accuracy using a reliable value among signals output from an in-cylinder pressure sensor. The purpose is to do.

  In order to achieve the above object, a control device for an internal combustion engine according to the present invention is configured as follows. The control device according to the present invention includes an in-cylinder pressure sensor, a crank angle sensor, and an arithmetic processing device.

  The in-cylinder pressure sensor is inserted into a hole that leads to the combustion chamber of the internal combustion engine. The in-cylinder pressure sensor includes a pressure receiving member that is displaced according to the pressure in the combustion chamber, and is configured to output a signal according to the displacement of the pressure receiving member. A gap is provided between the pressure receiving member and the hole communicating with the combustion chamber so that the pressure receiving member can be displaced in the axial direction.

  The crank angle sensor is configured to output a signal synchronized with the rotation of the crankshaft of the internal combustion engine.

  The arithmetic processing unit is a unit that performs a calculation for controlling the combustion state in the combustion chamber, and receives a signal from the in-cylinder pressure sensor and a signal from the crank angle sensor for the calculation. The detailed configuration of the arithmetic processing unit is as follows.

  The arithmetic processing unit is configured to execute the following first process, second process, and third process. In the first process, the arithmetic processing unit estimates the deposit amount of the in-cylinder pressure sensor based on the signal from the in-cylinder pressure sensor and the signal from the crank angle sensor. In the second process, the arithmetic processing unit sets the threshold value higher as the deposit amount increases. In the third process, the arithmetic processing unit uses a signal in which the absolute value | ΔP | of the change amount per unit crank angle of the pressure P according to the signal of the in-cylinder pressure sensor is larger than the threshold value, Is calculated.

  When deposits accumulate in the in-cylinder pressure sensor as described above, the in-cylinder pressure measured from the signal of the in-cylinder pressure sensor is higher than the actual in-cylinder pressure after the compression top dead center (TDC), particularly in the late combustion period where the pressure change is small. Shows high pressure. Further, as the deposit accumulation amount increases, the portion with the lower sensor detection value becomes less reliable, and the reliable value becomes the higher portion. According to the present invention, focusing on | ΔP |, it is possible to improve the control accuracy by calculating the combustion index using the detected value of the in-cylinder pressure sensor that is greater than the threshold value and that is reliable. it can. Further, by setting the threshold of | ΔP | higher as the deposit accumulation amount increases, the combustion index can be calculated with higher accuracy according to the deposit accumulation amount.

It is a figure which shows the change of the relationship between the heat release rate computed based on the signal of the cylinder pressure sensor, and a crank angle. It is a figure which shows the relationship between the heat generation amount computed from the heat release rate data shown in FIG. 1, and a crank angle. It is a figure which shows the relationship between the combustion ratio calculated from the heat generation amount data shown in FIG. 2, and a crank angle. It is a figure which shows the relationship between | (DELTA) P | and a crank angle. 4 is a flowchart showing a specific flow of arithmetic processing programmed in the ECU in the first embodiment. It is a figure for demonstrating the asymmetry of the pressure waveform at the time of the motoring by deposit accumulation. 4 is a flowchart showing a specific flow of arithmetic processing programmed in the ECU in the first embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. However, in the embodiment shown below, when referring to the number of each element, quantity, quantity, range, etc., unless otherwise specified or clearly specified in principle, the reference However, the present invention is not limited to this number. Further, the structures, steps, and the like described in the embodiments below are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

Embodiment 1 FIG.
[System Configuration of Embodiment 1]
The system according to Embodiment 1 of the present invention includes an internal combustion engine configured as a diesel engine. The internal combustion engine includes at least one cylinder. A piston that reciprocates inside the cylinder of the internal combustion engine is provided. The piston is connected to the crankshaft via a connecting rod. The internal combustion engine includes a crank angle sensor that outputs a signal synchronized with the rotation of the crankshaft.

  The internal combustion engine includes a cylinder head. A combustion chamber is formed between the piston and the cylinder head. One end of the intake passage and the exhaust passage communicate with the combustion chamber. An intake valve and an exhaust valve are arranged in the intake passage and the exhaust passage, respectively. The cylinder head is provided with a fuel injection valve for injecting fuel into the cylinder. Further, an in-cylinder pressure sensor (combustion pressure sensor) is attached to the cylinder head so as to protrude from the top of the combustion chamber into the combustion chamber. The in-cylinder pressure sensor is a glow plug-integrated in-cylinder pressure sensor that also has a function as a glow plug by including a heater rod.

  The system according to the first embodiment includes an ECU (Electronic Control Unit). The ECU 50 includes a memory and a processor as a physical configuration. The memory stores a program for engine control, and the processor reads the program from the memory and executes it. Various other sensors are provided in the system, but the description thereof is omitted here. Further, the ECU outputs a drive signal to the fuel injection valve and supplies current to the glow plug of the in-cylinder pressure sensor.

  The ECU functions as an arithmetic processing device according to the present invention, and constitutes a control device according to the present invention together with the in-cylinder pressure sensor and the crank angle sensor. The ECU as the arithmetic processing unit calculates a combustion index based on each signal of the in-cylinder pressure sensor and the crank angle sensor, the fuel injection amount of the fuel injection valve, and the like, and controls the combustion state in the combustion chamber based on the combustion index. . Note that the combustion index calculated in this embodiment is CA50. In this embodiment, the combustion state is controlled by feeding back CA50 at the timing when fuel is injected from the fuel injection valve.

  Characteristic control of the invention according to Embodiment 1 is arithmetic processing for calculating a combustion index programmed in the ECU. The arithmetic processing programmed in the ECU relates to a problem related to the structure of the in-cylinder pressure sensor. The structure and problem of the in-cylinder pressure sensor will be described.

(Glow plug integrated cylinder pressure sensor structure and its problems)
The in-cylinder pressure sensor is a glow plug-integrated in-cylinder pressure sensor, and has a shape in which a heater rod protrudes in the axial direction from the tip of a cylindrical housing. A heating element is built in the heater rod. The in-cylinder pressure sensor functions as a glow plug by generating heat upon receiving a current supplied from the ECU. A strain gauge that comes into contact with the end of the heater rod is disposed inside the housing. The heater rod functions as a pressure receiving member that receives the pressure in the combustion chamber, and the pressure difference between the combustion chamber side and the strain gauge side becomes a driving force that displaces the heater rod toward the strain gauge side. The strain gauge outputs a signal corresponding to the displacement in the axial direction of the heater rod, that is, a signal corresponding to the pressure in the combustion chamber.

  The in-cylinder pressure sensor is inserted into a hole provided in the cylinder head. The hole communicates with the combustion chamber. In a state where the in-cylinder pressure sensor is inserted and fixed in the hole, the tip of the heater rod penetrates the hole and protrudes into the combustion chamber. A gap is formed between the hole and the heater rod so that the heater rod can be displaced in the axial direction.

  As can be seen from the above configuration, the periphery of the heater rod, which is a pressure receiving member, communicates with the combustion chamber, and there is room for the combustion gas to enter here. The combustion gas contains unburned components and oil components of the fuel. These components are liquefied, and after being reacted by ambient heat, they become oxides or carbonaceous materials to form deposits. In the case of the in-cylinder pressure sensor described above, deposits may adhere to the gap between the heater rod and the hole or the gap between the heater rod and the housing.

  The deposited deposit becomes a resistance when the heater rod changes in the axial direction. If it is the pre-combustion period when the pressure in the combustion chamber is rising, the influence of the resistance force that the heater rod receives from the deposit is small. This is because the force by which the rising combustion pressure pushes the heater rod toward the strain gauge is much larger than the resistance of the deposit, and the resistance of the deposit is negligible compared to that force. On the other hand, a restoring force such as a strain gauge acts on the heater rod in the late combustion stage when the pressure in the combustion chamber decreases. Since they are much smaller than the force due to the combustion pressure acting on the heater rod in the first stage of combustion, the influence of the resistance force that the heater rod receives from the deposit becomes relatively large.

  As a result, the in-cylinder pressure (combustion pressure) measured from the signal of the in-cylinder pressure sensor in the first half of combustion is the actual in-cylinder pressure, that is, the in-cylinder pressure measured when no deposit is attached, regardless of the adhesion of deposit. And correspond well. However, the in-cylinder pressure measured from the signal of the in-cylinder pressure sensor in the later stage of combustion becomes higher than the actual in-cylinder pressure due to the poor return of the heater rod due to the influence of the resistance force received from the deposit.

  FIG. 1 is a diagram showing a change in the relationship between the heat generation rate calculated based on the signal from the in-cylinder pressure sensor and the crank angle. The heat generation rate is the amount of heat per unit crank angle generated in the combustion chamber. In FIG. 1, curves showing changes in the heat generation rate with respect to the crank angle are drawn for three examples: an example in which there is no deposit, an example in which the deposit is small, and an example in which the amount of deposit is large.

  First, the change in the heat generation rate with respect to the crank angle when no deposit is attached will be described. A heat generation rate of zero (or nearly zero) means that combustion has not started in the combustion chamber. The crank angle at which the heat generation rate starts to rise is the combustion start angle. After the start of combustion, the heat generation rate continues to rise and eventually reaches a peak. After passing the peak, the heat generation rate decreases and eventually becomes zero. The crank angle at which the heat generation rate becomes zero (or is considered to have converged to zero) is the combustion end angle at which the combustion in the combustion chamber ends.

  The relationship between the heat generation rate and the crank angle in the first stage of combustion shows the same relationship regardless of whether deposits are attached or not. However, in the late combustion period, the effect of deposit resistance on the in-cylinder pressure sensor signal becomes very large, so the relationship between the heat generation rate and the crank angle is calculated based on the in-cylinder pressure as the deposit amount increases. The generated heat generation rate remains larger than the actual heat generation rate (heat generation rate when no deposit is attached). As a result, the crank angle at which the heat generation rate becomes zero shifts more to the retard side than the actual combustion end angle (combustion end angle when there is no deposit) as the deposit amount increases.

  FIG. 2 is a diagram showing the relationship between the heat generation amount calculated from the heat generation rate data shown in FIG. 1 and the crank angle. The amount of heat generated is the cumulative total from the start of combustion of the amount of heat generated in the combustion chamber in one combustion cycle. Therefore, the heat generation amount at an arbitrary crank angle is calculated by integrating the heat generation rates integrated for each unit crank angle, with the interval from the combustion start angle to the crank angle as an integration interval. The amount of heat generated in the combustion chamber in one combustion cycle is the final heat generation amount, that is, the final value of the heat generation amount.

  The heat generation amount (actual heat generation amount) when no deposit adheres converges to a constant value at a certain crank angle. The crank angle when the heat generation amount converges to a constant value is the combustion end angle. On the other hand, when there is deposit adhesion, the heat generation amount calculated based on the heat generation rate continues to increase after the actual heat generation amount converges to a constant value. The calculated final heat generation amount increases as the deposit amount increases.

  FIG. 3 is a diagram showing the relationship between the combustion ratio calculated from the heat generation amount data shown in FIG. 2 and the crank angle. The combustion ratio is also called a combustion mass ratio, and means the ratio of the mass burned out of the mass of fuel per combustion cycle supplied into the combustion chamber. In the first embodiment, the combustion ratio at an arbitrary crank angle is calculated as the ratio of the heat generation amount at the crank angle to the final heat generation amount. Therefore, as can be seen from the comparison of the three curves shown in FIG. 3, the combustion ratio at an arbitrary crank angle becomes smaller as the deposit amount increases. Further, the crank angle giving an arbitrary combustion ratio becomes the crank angle on the retard side as the deposit amount is larger. Accordingly, the crank angle at which the CA50, that is, the combustion ratio becomes 50%, is a value that is largely deviated from the actual CA50 (CA50 when there is no deposit) to the retard side as the deposit amount increases.

  As described above, the deposit attached to the in-cylinder pressure sensor changes the displacement characteristics of the heater rod, which is a pressure receiving member, and affects the accuracy of the combustion index calculated based on the signal from the in-cylinder pressure sensor. If the accuracy of the CA50 is low, the accuracy of the combustion control in which the CA50 is fed back also decreases, and it becomes difficult to realize a desired combustion state. Therefore, in the arithmetic processing programmed in the ECU 50, a device for eliminating the influence of deposit from the calculation of the CA50 is taken. Hereinafter, the contents of the arithmetic processing programmed in the ECU 50 will be described with reference to FIG.

[Characteristic Control in Embodiment 1]
As described above, the phenomenon in which the heat generation rate is larger than the actual heat generation rate due to poor return of the heater rod has a small effect when the pressure change is large, and does not affect when the pressure change is small. There is a feature that is large. In the invention according to the first embodiment using this feature, attention is paid to the absolute value | ΔP | of the amount of change per unit crank angle of the pressure P according to the signal of the in-cylinder pressure sensor. When | ΔP | is less than or equal to the threshold value, the heat generation rate is assumed to be unreliable and is not used for calculation of the combustion index. That is, in the invention according to Embodiment 1, the combustion index representing the combustion state in the combustion chamber is calculated using the signal of the in-cylinder pressure sensor in which | ΔP | is larger than the threshold value. Note that this feature is conspicuous when the heater rod, which is a pressure receiving member, returns (during pressure reduction). Therefore, even if the section is applied in a limited manner, for example, after TDC and | ΔP | is smaller than the threshold value. Good.

  FIG. 4 is a diagram showing the relationship between | ΔP | and the crank angle. As described above, | ΔP | that is larger than the threshold is used for calculation of the combustion index, and | ΔP | that is less than or equal to the threshold is not used. Here, the threshold value is set higher as the deposit amount is larger. The deposit amount is estimated based on the signal from the in-cylinder pressure sensor and the signal from the crank angle sensor. For example, it is possible to judge from the asymmetry of the pressure waveform during motoring, or to judge from the difference between the theoretical value and the measured value of the pressure change in the compression stroke.

  According to the present invention, when the in-cylinder pressure change is smaller than the threshold value, it is not used for the calculation of the combustion index. However, the in-cylinder pressure and the heat generation rate that are not used are sections in which no heat is generated and the deposit is not generated. Since it is a section where it appears that heat is generated due to adhesion, there is no concern about accuracy reduction due to not using the in-cylinder pressure and heat generation rate.

  According to the present invention, even when deposits are accumulated on the in-cylinder pressure sensor, highly accurate combustion feedback control is possible. Advantages of the present invention include improved fuel consumption and reduced NOx by controlling the combustion index (CA50) with high accuracy. In addition, since the frequency of glow plug heating that is performed to burn the deposit can be significantly reduced in order to eliminate the influence of deposit adhesion, it is possible to suppress deterioration in fuel consumption due to glow plug heating.

  In addition, for the problem that it is difficult to determine the combustion end angle as described above, the theoretical heat generation amount is calculated from the fuel injection amount, and the time when the detected heat generation amount exceeds the theoretical heat generation amount is determined as the combustion end angle. According to the conventional method, when determining the end of combustion, it is determined that the end of combustion after counting some extra heat generation. According to the present invention, detection of the in-cylinder pressure sensor with | ΔP | Since no value is used, extra heat generation is not counted, and further improvement in index accuracy and control accuracy can be expected.

(Flowchart: Deposit accumulation estimation)
FIG. 5 is a flowchart showing a specific flow of arithmetic processing programmed in the ECU in the first embodiment. FIG. 5 is a diagram for explaining an example in which the amount of deposit deposited on the in-cylinder pressure sensor is estimated from the asymmetry of the pressure waveform during motoring. This flow is executed every predetermined cycle.

  In order to acquire the pressure waveform during motoring, first, in step S100, the ECU determines whether or not a fuel cut is in progress. If the determination condition of step S100 is not satisfied, this routine is terminated, and this routine is restarted after a predetermined cycle.

  When the determination condition of step S100 is satisfied, in step S110, the ECU acquires the in-cylinder pressure measured from the signal of the in-cylinder pressure sensor for each crank angle during motoring.

  FIG. 6 is a diagram for explaining the asymmetry of the pressure waveform during motoring due to deposit accumulation. As described above, as the deposit accumulates in the in-cylinder pressure sensor, the in-cylinder pressure measured from the signal from the in-cylinder pressure sensor in the second half of combustion is higher than the actual in-cylinder pressure. For this reason, the crank angle at the specified pressure in the second half of combustion is retarded as the deposit amount increases. In step S120, the ECU calculates, from the in-cylinder pressure data acquired in step S110, the total value of the crank angle CA1 when the specified pressure is reached in the compression stroke and the crank angle CA2 when it is reduced to the specified pressure in the combustion stroke. calculate. The ECU stores in advance a relationship map that defines the relationship between the total value and the deposit amount, and acquires the deposit amount corresponding to the total value from the relationship map and stores it in the ECU.

  In step S130, the ECU turns on the deposit accumulation amount calculated flag and ends this routine.

(Flow chart: Heat generation calculation)
FIG. 7 is a flowchart showing a specific flow of arithmetic processing programmed in the ECU in the first embodiment. FIG. 7 is a diagram for explaining an example of calculating the heat generation amount in consideration of the deposit accumulation amount. This flow is executed every predetermined cycle.

  In step S200, the ECU determines whether or not the deposit accumulation amount calculated flag is ON. When the determination condition is not satisfied, the ECU ends this routine and executes the flow shown in FIG. 5 first.

  In step S210, the ECU acquires a deposit accumulation amount. The ECU acquires the deposit accumulation amount stored in step S120 of FIG.

  In step S220, the ECU calculates a threshold value of | ΔP |. The ECU calculates a threshold value from the deposit accumulation amount using a predetermined calculation formula. The ECU sets the threshold value higher as the deposit accumulation amount increases. The ECU may store in advance a relationship map that defines the relationship between the deposit accumulation amount and the threshold value of | ΔP |, and may acquire a threshold value corresponding to the deposit accumulation amount from the relationship map.

  In step S230, the ECU determines whether the number of repetitions i (initial value 0, natural number) is smaller than the repetition range n (natural number). The repetition range n is, for example, a number obtained by dividing the crank angle from the combustion start angle described above until the exhaust valve opens by a predetermined unit crank angle.

If i <n, in step S240, the ECU determines whether | ΔP _i | is greater than a threshold value. When | ΔP _i | ≦ threshold, the ECU ends this routine.

If | ΔP _i |> threshold, the ECU calculates the dQ / dθ integrated value _i in step S250. Specifically, the ECU calculates dQ / dθ integrated value _i by adding dQ / dθ _i to dQ / dθ integrated value _i−1 .

  Thereafter, in step S260, the ECU increments i and restarts the process from step S230. If i ≧ n is satisfied in step S230, the ECU ends this routine.

  As described above, according to the routines shown in FIGS. 5 and 7, the combustion index can be calculated using only the detected value of the in-cylinder pressure sensor, which is higher than the threshold and | ΔP |. For this reason, according to the system of this embodiment, the control accuracy can be improved. Further, by setting the threshold of | ΔP | higher as the deposit accumulation amount increases, the combustion index can be calculated with higher accuracy according to the deposit accumulation amount.

CA1 Crank angle when the specified pressure is reached during the compression stroke CA2 Crank angle when the pressure is reduced to the specified pressure during the combustion stroke

Claims (1)

A cylinder that is inserted into a hole communicating with the combustion chamber of the internal combustion engine with a gap between the hole and that is displaced according to the pressure in the combustion chamber, and that outputs a signal corresponding to the displacement of the pressure receiving member An internal pressure sensor;
A crank angle sensor that outputs a signal synchronized with the rotation of the crankshaft of the internal combustion engine;
An arithmetic processing unit that receives a signal of the in-cylinder pressure sensor and a signal of the crank angle sensor, and performs an operation for controlling a combustion state in the combustion chamber;
The arithmetic processing unit includes:
A first process for estimating a deposit accumulation amount of the in-cylinder pressure sensor based on a signal of the in-cylinder pressure sensor and a signal of the crank angle sensor;
A second process of setting the threshold value higher as the deposit accumulation amount increases;
A combustion index representing a combustion state in the combustion chamber is calculated using a signal in which the absolute value | ΔP | of the amount of change per unit crank angle of the pressure P according to the signal of the in-cylinder pressure sensor is larger than the threshold value. 3. A control device for an internal combustion engine, wherein the control device is configured to execute the processing of No. 3.

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