JP2016109016A - Engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately estimate generation of pre-ignition by taking into consideration of fuel property to effectively avoid pre-ignition.SOLUTION: An engine control device estimates an octane number of fuel based on an alcohol concentration of the fuel detected by concentration detection means and a knock learning value learned by knock learning means, estimates presence/absence of generation of pre-ignition at start of fuel injection based on the estimated octane number and an engine operational state, and executes control for avoiding pre-ignition (such as fuel injection in an expansion stroke) when generation of pre-ignition is estimated.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an engine control apparatus that prevents pre-ignition.

  Some engines have made it possible to use fuel containing alcohol such as ethanol. When a fuel containing alcohol is used, since the octane number is high, it is possible to increase the efficiency by increasing the effective compression ratio. On the other hand, the higher the alcohol concentration, the worse the fuel vaporization performance and the worse the cold startability. For this reason, Patent Document 1 discloses a method for calculating the alcohol concentration.

JP 2014-145327 A

  Pre-ignition is likely to occur when the fuel is changed from a fuel with high alcohol concentration to a fuel with poor properties (for example, fuel with low alcohol concentration or fuel with poor properties only) with the same effective compression ratio. Become. In particular, when the engine is started by turning on the ignition switch from the engine stop state, the margin period for self-ignition becomes longer in a predetermined low rotational speed range (for example, 200 rpm) which is the time point at which fuel injection is started. , Pre-ignition is likely to occur. In particular, depending on the vehicle, it may be used in an area where only poor fuel can be secured due to its movement, and how to prevent pre-ignition becomes a problem.

  In order to prevent pre-ignition, it is important to accurately detect whether or not pre-ignition occurs. In particular, pre-ignition may or may not occur even when the engine is in the same operating condition due to changes in alcohol concentration, etc. It becomes important to.

  The present invention has been made in view of the above circumstances, and its purpose is to accurately predict the occurrence of a pre-ignition taking into account the properties of the fuel and to effectively avoid the pre-ignition. It is to provide a control device.

In order to achieve the above object, the following solution is adopted in the present invention. That is, as described in claim 1,
A control device for an engine, which is a direct injection type in which fuel is directly injected into a cylinder from a fuel injection valve and is capable of using a fuel containing alcohol,
Concentration detecting means for detecting the alcohol concentration of the fuel;
A knock learning means for detecting ease of knocking,
Octane number estimation means for estimating the octane number of the fuel based on the alcohol concentration detected by the concentration detection means and the knock learning value learned by the knock learning means;
Based on the octane number estimated by the octane number estimating means and the operating state of the engine, a pre-ignition predicting means for predicting the occurrence of the pre-ignition at the start of fuel injection;
Pre-ig avoiding control means for performing control to avoid the pre-ignition when the pre-ig predicting means predicts the occurrence of the pre-ig, and
It is supposed to be equipped with. According to the above solution method, the octane number of the fuel is estimated using the alcohol concentration and the knock learning value, and the occurrence of the pre-ignition when the fuel injection is started is predicted based on the estimated octane number and the engine operating state. Therefore, it is possible to accurately predict whether or not pre-ignition will occur due to the start of fuel injection. When the occurrence of the pre-ignition is predicted, the pre-ignition is prevented by performing the pre-ignition avoidance control. In addition, since it is possible to accurately predict whether or not pre-ignition will occur, it is also preferable in terms of avoiding a situation in which pre-ignition avoidance control is unnecessarily performed.

A preferred mode based on the above solution is as described in claim 2 and the following claims. That is,
The fuel injection start timing is set to be the fuel injection timing for the first explosion when starting the engine (corresponding to claim 2). In this case, the pre-ignition is likely to occur at the first explosion especially at the time of starting the engine, but the pre-ignition at the first explosion can be prevented.

  The pre-ignition predicting means calculates a pre-ignition generation effective compression ratio limit when performing the initial explosion based on a fuel property and an engine operating state, and calculates the pre-ignition generation effective compression ratio limit and the initial explosion When the effective compression ratio based on the operating state of the engine at the time of performing is close, it is predicted that pre-ignition will occur (corresponding to claim 3). In this case, a more specific method is provided for predicting the occurrence of pre-ignition. In particular, the pre-ignition generation effective compression ratio limit at the start of fuel injection is calculated based on the fuel properties and the engine operating state, and the actual effective compression ratio is calculated with respect to the calculated pre-ignition generation effective compression ratio limit. By comparing, it is predicted whether or not pre-ignition will occur, so that the prediction accuracy is extremely accurate.

  According to the present invention, the occurrence of a pre-ignition can be accurately predicted in consideration of the properties of the fuel, and the pre-ignition can be effectively prevented.

1 is a cross-sectional view showing an example of an engine to which the present invention is applied. The time chart which shows the example of control of pre-ignition avoidance. The figure which shows the example of a control system of this invention. The figure which shows the map which determines an octane number from alcohol concentration and a knock learning value. The flowchart which shows the example of control for avoiding a pre-ignition. The flowchart which shows the example of control for estimating generation | occurrence | production of a pre-ignition.

  The engine E shown in FIG. 1 is a multi-cylinder (in-line four-cylinder in the embodiment) engine for automobiles. In FIG. 1, 1 is a cylinder block, 2 is a cylinder head, and 3 is a cylinder head cover. A piston 4 is slidably fitted into the cylinder block 1, and a space above the piston 4 is a combustion chamber 5.

  An intake port 6 is opened in the combustion chamber 5 and an exhaust port 7 is opened. The intake port 6 is opened and closed by an intake valve 8, and the exhaust port 7 is opened and closed by an exhaust valve 9. An intake passage 10 is connected to the intake port 6. An exhaust passage 11 is connected to the exhaust port 7.

  A first exhaust gas purification catalyst 12 and a second exhaust gas purification catalyst 13 are connected to the exhaust passage 11 sequentially from the upstream side to the downstream side. A linear O 2 sensor 14 is connected to the exhaust passage 11 upstream of the first exhaust gas purification catalyst 12. A lambda O 2 sensor 15 is connected between the exhaust gas purification catalysts 112 and 13 in the exhaust passage 11.

  The intake valve 8 is opened / closed by a camshaft 22 via a rocker arm 21. The exhaust valve 9 is driven to open and close by a camshaft 24 via a rocker arm 23. A hydraulic valve timing variable mechanism 25 is provided at the end of the camshaft 22 for the intake valve 8. This valve timing variable mechanism 25 is designed to change the closing timing of the intake valve 8 in particular. When the hydraulic pressure is not supplied, the variable valve timing mechanism 25 is fixed at a position where the intake air amount becomes maximum, and the intake air pressure increases as the supplied hydraulic pressure increases. The intake air amount is reduced due to the late closing.

  An ignition plug 31 and a fuel injection valve 32 are disposed facing the combustion chamber 5. As described above, the engine E is a direct injection type in which fuel is directly injected into the cylinder (combustion chamber 5) from the fuel injection valve 32 and is a spark ignition type engine. The engine E is set on the premise that gasoline containing alcohol (particularly ethanol) is used as a fuel, and therefore, the geometric compression ratio is large (for example, 13 to 14).

  In FIG. 1, U is a controller (PCM = Powertrain Controle Module) configured using a microcomputer. As will be described later, the controller U performs pre-ignition generation prediction and fuel injection timing change control. Specifically, the fuel injection is basically controlled in the intake stroke, and when the occurrence of the pre-ignition is predicted, the fuel injection is performed in the expansion stroke. For the above control, in addition to the signal from the knock sensor 35 attached to the cylinder block 1, signals from various sensors described later are input to the controller U.

  Here, focusing on the fuel injection timing, the outline of the control according to the present invention will be described with reference to FIG. Pre-ignition is likely to occur immediately after the initial fuel injection in the engine starting process. Specifically, pre-ignition is likely to occur when the cranking rotation speed by the starter motor reaches the first predetermined rotation speed (200 rpm in the embodiment) at which the fuel pressure is sufficiently increased and becomes the fuel injection start time. is there. For this reason, whether or not pre-ignition occurs when fuel is injected when the first predetermined rotation speed is reached from the start of cranking to the first predetermined rotation speed is predicted. . When it is predicted that the pre-ignition will occur, the fuel injection is performed not by the intake stroke injection but by the expansion stroke that can completely prevent the pre-ignition.

  Based on the above assumptions, the ignition switch is turned on at time t1 in FIG. 2 and the occurrence of pre-ignition is predicted at time t2, so that a flag indicating that expansion stroke injection is to be performed is set to 1. As a result of cranking, the engine speed is increased from time t3, and when the engine speed reaches 200 rpm as the first predetermined speed, fuel injection is started in the expansion stroke. This prevents pre-ignition at the start of fuel injection that is most likely to occur. The fuel injection timing in the expansion stroke is, for example, in the range of 4 to 8 degrees after compression top dead center in the crank angle, and is 6 degrees in the embodiment. That is, even if fuel is injected during the expansion stroke, a position that is as close as possible to the compression top dead center is selected from the viewpoint of reducing the amount of fuel adhering to the top surface of the piston 4 and ensuring torque as much as possible.

  The engine E rotates by fuel injection, and at time t4, the engine speed increases to a second predetermined speed (500 rpm). When the engine speed has increased to the second predetermined speed, the pre-ignition will no longer occur, so that a flag indicating that fuel injection should be performed in the expansion stroke is reset to 0, and fuel injection Is set to 1 indicating that is to be executed in the compression stroke. Thereby, after time t4, fuel injection is performed in the compression stroke. The fuel injection timing in the compression stroke is in the range of 30 degrees to 50 degrees before the compression top dead center at the crank angle, and is 40 degrees in the embodiment. That is, the combustion chamber 5 is sufficiently cooled by the vaporization heat of the injected fuel, and the fuel is injected at a timing that is preferable for uniform fuel.

  The transition from the fuel injection in the expansion stroke to the fuel injection in the compression stroke is performed at once rather than gradually shifting the injection timing to the compression stroke side (for example, fuel at around 6 degrees after compression top dead center). Switch from injection to fuel injection at around 40 degrees before compression top dead center). Thereby, it can shift to the fuel injection in a compression stroke, preventing the fuel adhesion amount to the piston 4 top surface increasing.

  The engine speed further increases, and at time t5, the engine speed is increased to a third predetermined speed (for example, 750 rpm). After this time t5, a flag indicating that fuel injection should be executed in the compression stroke is reset to 0, and thereafter, fuel injection is performed in the normal intake stroke (from the fuel injection control at the start, The control is shifted to the fuel injection control during idling-the idling speed is, for example, 600 to 650 rpm.

  As described above, when the occurrence of the pre-ignition is predicted, the fuel injection is performed in the expansion stroke, and the occurrence of the pre-ignition is prevented. After the fuel injection in the expansion stroke is performed, the process proceeds to the fuel injection in the compression stroke as soon as possible. That is, by shortening the fuel injection period in the expansion stroke as much as possible, it is possible to shorten the period during which the torque is reduced or the amount of unburned fuel discharged is increased.

  By inserting the fuel injection in the compression stroke between the fuel injection in the expansion stroke and the fuel injection in the intake stroke, the combustion chamber 5 before ignition is cooled by the vaporization of the injected fuel, and then there is a risk of occurrence of pre-ignition. The torque is reduced and the torque is secured. In addition to this, in the case of a multi-cylinder engine (for example, a four-cylinder engine), the combustion order (ignition order) is determined between the cylinders, but by injecting fuel during the compression stroke, the expansion stroke is performed based on the combustion order. Combustion can also be performed in a cylinder that should be combusted next to the fuel-injected cylinder (to ensure a rapid increase in engine speed). By the way, when the fuel injection in the expansion stroke is switched to the fuel injection in the intake stroke at once, the cylinder in which combustion should be performed next in the combustion sequence has already lost the opportunity of fuel injection in the intake stroke. Therefore, in the combustion order, combustion is performed only from the next cylinder, which is not preferable in that the engine speed is quickly increased.

  Next, an example of determination control for determining whether the fuel injection is performed in the expansion stroke or the compression stroke will be described with reference to FIG. First, the determination part (calculation part) K1 calculates the effective compression ratio limit of pre-ignition generation. In this determination unit K1, the estimation of the alcohol concentration in the fuel is completed, and the estimated concentration value is input. In addition, 200 rpm is set as the engine speed for predicting the occurrence of pre-ignition. The octane number, in-cylinder temperature, and intake manifold pressure (intake pressure) signals of the fuel that has been used are input. In the embodiment, the intake manifold pressure is used as a substitute for the in-cylinder pressure. The determination unit K1 calculates the maximum effective compression ratio that is a limit at which pre-ignition does not occur based on the various signals described above. This calculation is performed using an effective compression ratio limit polynomial model with the intake manifold pressure as a variable. Since this calculation can use the technique described in Japanese Patent Application Laid-Open No. 2012-52472 as it is, further explanation regarding the calculation of the effective compression ratio limit is omitted.

  In the determination unit K2, the deviation between the effective compression ratio limit calculated by the determination unit K1 and the effective compression ratio at which the engine E is warm-locked by the pre-ignition is calculated as the pre-ignition margin. That is, it is calculated as the effective compression ratio limit-the effective compression ratio of the level at which the warm lock occurs = the pre-ignition margin. This pre-ignition margin indicates the degree of whether or not the effective compression ratio when the engine speed is 200 rpm is close to the effective compression ratio limit.

  The determination unit K3 compares the pre-ignition margin determined by the determination unit K2 with a predetermined threshold value, and a signal that is predicted to generate a pre-ignition when the pre-ignition margin is smaller than the predetermined threshold value. Is output to the determination unit K5. In other words, the processing of the determination units K1 to K3 is, after all, the effective compression ratio based on the operating state of the engine at the time of the initial explosion (this effective ratio) with respect to the pre-ignition generation effective compression ratio limit calculated as described above. This is equivalent to the determination process of whether or not the compression ratio is close to the property of the fuel.

  The determination unit K5 is an AND circuit. When the determination unit K3 predicts the occurrence of pre-ignition, the engine speed is 200 rpm or less, and the learning of the alcohol brain concentration is completed, AND A SET signal for “SET” the determination unit K6 including a circuit is output. This SET signal corresponds to a signal indicating that fuel should be injected in the expansion stroke.

  When the set signal from the determination unit K5 is input, the determination unit K6 outputs a SET signal to the determination unit K8 including an AND circuit. On the other hand, when the RST signal (reset signal) is input from the determination unit K4, the determination unit K6 outputs an RST signal to the determination unit K8. This determination unit K4 starts fuel injection when an edge signal with an engine speed of a predetermined value (200 rpm) or less is input, or when a signal with an engine speed greater than a predetermined value B (750 rpm) is input. When a signal indicating that the count signal of the number of times of fuel injection from is input to a predetermined value or more is satisfied, an RST signal is output to the determination unit K6.

  The determination unit K8 indicates that the fuel injection should be performed in the expansion stroke when both conditions are satisfied when the SET signal from the determination unit K6 is input and the SET signal from the determination unit K7 is input. Outputs a request signal.

  The determination unit K7 outputs an RST signal to the determination unit K8 when a signal having an engine speed greater than a predetermined value A (500 rpm) is input. On the other hand, the determination unit K7 outputs a SET signal to the determination unit K8 when a signal having an engine speed of a predetermined value A (500 rpm) or less is input.

  The determination unit K9 determines whether or not to output a request signal indicating that fuel injection should be performed in the compression stroke. This determination unit K9 is a signal requesting fuel injection in the compression stroke on condition that a signal indicating that the engine speed is greater than a predetermined value A (500 rpm) and a SET signal from the determination unit K6 are input. Is output.

  By the control described above, the fuel injection is performed in the expansion stroke when the engine speed is in the range of 200 rpm to 500 rpm, and the fuel injection is performed in the compression stroke in the range of 500 rpm to 750 rpm or less. When the engine speed exceeds 750 rpm or the number of fuel injections exceeds a predetermined number, the fuel injection in the compression stroke is switched to the fuel injection in the intake stroke (this switching is also performed at once, not gradually). .

  Here, the alcohol concentration may be detected or estimated directly using an alcohol concentration sensor. In addition to this, for example, as shown in Patent Document 1, it is estimated based on the output of the linear O2 sensor 14. For example, it can be appropriately detected (estimated) by a conventionally known method.

  Further, the octane number input to the determination unit K1 can be estimated using, for example, a map having the alcohol concentration and the knock learning value shown in FIG. 4 as parameters. The knock learning value is a value obtained by learning the deviation between the control amount for preventing knocking using the knock sensor 35 and the reference value.

  FIG. 5 shows a flowchart for performing control for avoiding the pre-ignition as shown in FIG. Hereinafter, FIG. 5 will be described. In the following description, Q represents a step. First, in Q1, it is determined whether or not there is a possibility of pre-ignition when the engine speed set as the fuel injection start time is 200 rpm. When the determination in Q1 is YES, it is determined in Q2 whether or not the number of fuel injections from the start of fuel injection is a predetermined value (for example, twice) or less. If the determination in Q2 is YES, it is determined in Q3 whether or not the engine speed is equal to or less than a predetermined engine speed A (500 rpm). If the determination in Q3 is YES, fuel injection in the expansion stroke is performed in Q4.

  If NO in Q3, it is determined in Q5 whether the engine speed is equal to or less than a predetermined value B (750 rpm). If the determination in Q5 is YES, fuel injection in the compression stroke is performed in Q6.

  When NO is determined in Q5, NO is determined in Q2, or NO is determined in Q1, return is made without passing through Q4 or Q6, respectively (the fuel injection execution in the normal intake stroke and Become).

  Next, a control example for predicting whether or not pre-ignition will occur will be described with reference to the flowchart of FIG. First, at Q11, the knock learning value k and the alcohol concentration p are read. Next, at Q12, the knock learning value k and the alcohol concentration p are collated with the map shown in FIG. 4 to estimate the octane number.

  After Q12, it is determined at Q13 whether or not the ignition switch is turned on. If the determination in Q13 is YES, in Q14, for example, the pre-ignition generation effective compression ratio limit at 200 rpm is calculated based on the operating state of the engine and the estimated octane number. Thereafter, in Q15, for example, it is determined whether or not the effective compression ratio at 200 rpm is close to the pre-ignition generation effective compression ratio limit. When the determination in Q15 is YES, in Q16, it is predicted that the possibility of the occurrence of pre-ignition is large (high) (results in the prediction that pre-ignition will occur). Further, when the determination in Q15 is NO, the possibility of the occurrence of pre-ignition is predicted to be small (low) (results in the prediction that no pre-ignition will occur). Of course, the prediction results at Q15 and Q16 are used for the determination at Q1 in FIG.

  Although the embodiments have been described above, the present invention is not limited to the embodiments, and appropriate modifications can be made within the scope of the claims. For example, the alcohol contained in the fuel may be methanol or the like in addition to ethanol. The engine speed at which fuel injection is initially started at start-up (200 rpm in the embodiment), the upper limit engine speed at which fuel injection is performed in the expansion stroke (500 rpm in the embodiment), and fuel injection in the expansion stroke The engine speed (750 rpm in the embodiment) at the time of switching from the fuel injection to the compression stroke can be appropriately changed according to the characteristics of the engine E and the like. Switching from fuel injection in the expansion stroke to fuel injection in the compression stroke may be performed only by the number of fuel injections from the start of fuel injection without using the engine speed as a parameter. Specifically, for example, when the fuel injection is performed once (or twice), the fuel injection is switched to the fuel injection in the compression stroke, and after the fuel injection in the compression stroke is performed once (or twice), the intake stroke is performed. It is also possible to switch to the other fuel injection. By the way, normally, the engine speed is increased to around 500 rpm by the first fuel injection (and subsequent combustion), and the engine speed is surely increased to 500 rpm or more by the second fuel injection (and subsequent combustion). be able to. The number of cylinders of the engine E is not limited to four cylinders, and may be an appropriate number of cylinders such as three cylinders, six cylinders, and eight cylinders.

  The control for avoiding the pre-ignition is not limited to the fuel injection in the expansion stroke, and for example, the following appropriate method can be adopted. When the valve timing variable mechanism 25 is an electric type, the effective compression ratio may be reduced by, for example, late intake closing. Also, appropriate control for avoiding pre-ignition such as reducing the intake air amount by throttle the throttle valve, or split fuel injection (for example, 50% fuel injection in the intake stroke, 50% fuel injection in the compression stroke, etc.) Method can be adopted. The present invention can also be grasped as an engine control method. Of course, the object of the present invention is not limited to what is explicitly stated, but also implicitly includes providing what is substantially preferred or expressed as an advantage.

  The present invention can avoid the pre-ignition by accurately predicting the occurrence of the pre-ignition in consideration of the properties of the fuel.

E: Engine U: Controller 4: Piston 5: Combustion chamber 8: Intake valve 22: Intake valve camshaft 25: Variable valve timing mechanism 31: Spark plug 32: Fuel injection valve

Claims (3)

A control device for an engine, which is a direct injection type in which fuel is directly injected into a cylinder from a fuel injection valve and is capable of using a fuel containing alcohol,
Concentration detecting means for detecting the alcohol concentration of the fuel;
A knock learning means for detecting ease of knocking,
Octane number estimation means for estimating the octane number of the fuel based on the alcohol concentration detected by the concentration detection means and the knock learning value learned by the knock learning means;
Based on the octane number estimated by the octane number estimating means and the operating state of the engine, a pre-ignition predicting means for predicting the occurrence of the pre-ignition at the start of fuel injection;
Pre-ig avoiding control means for performing control to avoid the pre-ignition when the pre-ig predicting means predicts the occurrence of the pre-ig, and
An engine control device comprising: In claim 1,
The engine control apparatus according to claim 1, wherein the fuel injection start timing is a fuel injection timing for an initial explosion when the engine is started. In claim 2,
The pre-ignition predicting means calculates a pre-ignition generation effective compression ratio limit when performing the initial explosion based on a fuel property and an engine operating state, and calculates the pre-ignition generation effective compression ratio limit and the initial explosion An engine control device characterized by predicting that pre-ignition occurs when the effective compression ratio based on the operating state of the engine at the time of performing is close.

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