JP4061870B2 - Control device for direct injection spark ignition engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for a direct-injection spark ignition engine, and in particular, for heating an exhaust aftertreatment catalyst of this type of internal combustion engine to an activation temperature by exhaust gas or maintaining the same at an activation temperature. It relates to combustion control.
[0002]
[Prior art]
Currently, a direct injection spark ignition engine that directly injects fuel into a combustion chamber and ignites and burns the fuel consumption and output are both compatible. In this type of internal combustion engine, the combustion mode is generally switched in accordance with the operating state. That is, the fuel is diffused into the combustion chamber by injecting it into the intake stroke, and the homogeneous combustion is formed by uniformly forming the air-fuel mixture, and the fuel is injected into the compression stroke to be locally distributed near the spark plug and mixed. This is stratified combustion performed by forming a gas in layers.
[0003]
Even in such a direct injection spark ignition engine, a catalyst device is provided in the exhaust passage in order to suppress the release of harmful exhaust components into the atmosphere. Then, the catalyst does not function effectively unless it is in an appropriate temperature range where the catalyst is in an active state, and harmful exhaust components flow down without being purified. Therefore, it is important to keep the catalyst in this temperature range. Therefore, at the time of cold start after a long-term stop or when the catalyst temperature falls outside the appropriate temperature range due to the continued operation state with a low exhaust temperature, the catalyst is heated and the temperature is quickly raised to the appropriate temperature range. It is necessary to let In particular, at the time of cold start, since a slightly larger amount of fuel is injected in order to make the air-fuel ratio of the air-fuel mixture around the spark plug substantially constant, the catalyst is activated early, and the harmful exhaust components flow down quickly. The need to deter from the stage is even higher.
[0004]
In response to such demands, various types have been proposed that utilize the features of the direct injection type.
For example, in Japanese Patent Laid-Open No. 10-169488, by performing compression stroke injection in which the air-fuel ratio of the entire combustion chamber is slightly lean from the stoichiometric air-fuel ratio under a catalyst temperature increase request, and by greatly delaying the injection timing, A method is disclosed in which stratified combustion is performed with the air-fuel mixture in the vicinity of the spark plug being in an overrich state (8 to 10 in the air-fuel ratio).
[0005]
Further, in Japanese Patent Laid-Open No. 2000-240485, stratified combustion is performed with a slightly lean air-fuel ratio of the entire combustion chamber under a catalyst temperature increase request, and at the time of cold start, before the transition to stratified combustion, an expansion stroke is performed. Discloses a method in which the temperature of the catalyst is raised to some extent in advance by performing post injection.
All of these known techniques cause incomplete combustion by making the fuel thicker than normal stratified combustion near the spark plug, and the resulting unburned hydrocarbons (HC) and carbon monoxide (CO) are produced. The catalyst is heated by using heat generated when post-reacting with the remaining oxygen.
[0006]
[Problems to be solved by the invention]
However, if an overrich air-fuel mixture is formed according to the former method, incomplete combustion products such as HC are not completely burned out, and some of them may be released as harmful exhaust components. Japanese Patent Application Laid-Open No. 10-169488 discloses that a part of fuel is pre-injected in an intake stroke as an incidental means for generating an ignition inducer that promotes a post reaction. By taking such measures, it will be possible to obtain the effect of suppressing the release of harmful exhaust components, but in this case, there is another problem that the fuel consumption deteriorates. If the air-fuel mixture is formed in layers by the preceding injection and there is a difference in fuel concentration between the vicinity of the spark plug and the vicinity of the combustion chamber wall surface, a larger amount of fuel is required to obtain a constant torque due to a decrease in combustion efficiency. Because. As a conclusion, the catalyst can be heated by the post reaction of the incomplete combustion product, but in this case, the multistage injection is not preferable in terms of efficiency, and even if the fuel is concentrated near the spark plug for the post reaction, It is thought that it is necessary to suppress to an appropriate air-fuel ratio.
[0007]
On the other hand, according to the latter method, since the injection timing is not retarded so much, an air-fuel mixture in which the air-fuel ratio becomes overrich is not formed, and it is considered that there is no problem in exhaust performance as described above. However, since the fuel property is not taken into consideration at the time of the compression stroke injection, the following problems still remain even when this method is adopted. Since the fuel properties vary somewhat from one fueling station to another, fuel of the same property is not always supplied. In addition, engine control systems are typically designed to fit heavy fuels. For this reason, if the fuel stored in the tank is lighter than the setting and the injection is performed according to the setting for the heavy fuel in a state where the volatility of the fuel is high, the fuel around the spark plug becomes excessively thick. As a result, combustion may not be established (fire may be lost). Such a tendency becomes a problem particularly at the time of cold start in which a difference in the vaporization characteristics of the fuel according to the property appears remarkably. According to the above Japanese Patent Laid-Open No. 2000-240485, since it is switched to the compression stroke injection in a state where the warm-up has progressed to some extent by post injection, the problem of misfire will be avoided, but the fuel that does not contribute to the engine output Since the fuel is injected, the fuel efficiency is deteriorated accordingly.
[0008]
An object of the present invention is to use exhaust gas to activate a catalyst or to maintain the active state of the catalyst, and in particular, at this time, it prevents emission of harmful exhaust components and realizes low fuel consumption. In the point.
[0009]
[Means for Solving the Problems]
  Therefore, in the first aspect of the invention, the control device for the direct injection spark ignition engine includes (A) fuel injection means for directly injecting fuel into the cylinder, and (B) the specific operation conditionsFuel injectionMeans for injecting fuel into the compression stroke to perform stratified combustion, (C) fuel property estimating means for estimating fuel property, and (D) determining whether or not the exhaust gas temperature should be raised The exhaust temperature rise requirement establishment determining means is configured to be included. When it is determined by the exhaust temperature increase requirement establishment determining means that the exhaust temperature is in a condition to be increased, BurningThe fuel injection amount that makes the air-fuel ratio of the entire firing chamber the stoichiometric air-fuel ratio or a slightly leaner side than this,The basic injection amount corresponding to the target air-fuel ratio at that time isCorrection is made according to the fuel property estimated by the fuel property estimating means, and the calculated fuel injection amount is injected in the compression stroke to perform stratified combustion.(Combustion control means).
[0010]
  BookThe invention performs stratified combustion in which the air-fuel ratio of the entire combustion chamber is set lower than usual in order to raise the exhaust temperature, and in such stratified combustion, the fuel properties are reflected in the calculation process of the fuel injection amount. Is the gist. According to the above configuration, the air-fuel ratio around the spark plug can be accurately controlled to be slightly lower than the theoretical air-fuel ratio. For this reason, incomplete combustion products such as unburned HC are generated by stratified combustion, but this can be post-reacted with oxygen remaining in the cylinder and burned out. Further, the exhaust temperature is raised by the heat generated at this time. In the present specification, stratified combustion performed by adjusting the air-fuel ratio as described above in order to raise the exhaust gas temperature is particularly referred to as “exhaust temperature stratified combustion”.
  Further, in the first aspect of the invention, when the engine is started, the homogeneous combustion is first performed, and the predetermined condition including that the exhaust temperature should be increased is satisfied. Directly switch to exhaust-temperature stratified combustion (without operation), and set a target air-fuel ratio transition period immediately after switching from homogeneous combustion to exhaust-temperature stratified combustion. In this transition period, after the target air-fuel ratio transition is completed The fuel injection amount was calculated by setting it lower than the above.
  Considering the case of the cold start, when the combustion chamber is further warmed by switching to the exhaust temperature stratified combustion, the fuel (wall surface attached fuel component) attached to the combustion chamber wall is easily vaporized. However, if this is not yet sufficiently warm, the fuel component adhering to the wall surface is difficult to vaporize, and there is a possibility that the air-fuel ratio around the spark plug will deviate from an appropriate range. Therefore, a period (transition period) in which the target air-fuel ratio is lowered immediately after switching is provided, and a large amount of fuel is injected during that period.
  Further, during the transition period, the target air-fuel ratio is increased with a predetermined rate of change according to the coolant temperature, and the coolant temperature is higher than the target air-fuel ratio during transition when a certain control cycle has elapsed after switching. I decided to give it a large value.
  In the invention according to claim 2, the predetermined rate of change is set based on the engine temperature.
  In the invention according to claim 3, the predetermined change rate is set to a larger value as the cooling water temperature as the engine temperature is higher, and the switching is completed quickly.
[0011]
  Claim4In the invention described in, when it is necessary to heat the exhaust aftertreatment catalyst interposed in the exhaust passage, it is determined that the exhaust temperature is in a condition to be raised.
[0015]
  Claim5In the invention described in the above, the exhaust-temperature stratified combustion is permitted only when the estimation by the fuel property estimating means is completed.
  Claim6In the invention described in the above, the exhaust temperature stratified combustion is permitted only when it is determined that the piston crown surface temperature (crown surface temperature) is equal to or higher than a predetermined temperature indicating a high temperature state.
  This is because in the stratified combustion, the piston crown surface is actively used for transporting the fuel spray, and as long as the crown surface temperature is low beyond the appropriate range, the air-fuel mixture is difficult to be formed well.
[0016]
  Claim7In the invention described in (1), the fuel injection amount is corrected to be reduced largely as the fuel is lighter according to the estimated fuel property.
  If the fuel is light, the volatility is high and it is easy to vaporize.Therefore, by injecting a small amount of fuel compared to the case of using heavy fuel, the air-fuel ratio around the spark plug is always kept within the appropriate range. is there.
[0017]
  Claim8In the invention described in claim 1, the correction amount corresponding to the fuel property is determined based on the engine speed, and the claim9In the invention described in (4), the fuel injection amount is increased as the engine speed is lower in accordance with the correction amount.
  This is because when the engine is rotating at a low speed, the gas flow in the cylinder is weak and the fuel is difficult to vaporize.
  Claim10In the invention described in, the correction amount corresponding to the fuel property is set.Cooling waterTo be determined based on temperature, and claims11In the invention described in, the fuel injection amount is increased as the cooling water temperature is lower in accordance with the correction amount.
[0018]
  Claim12In the invention described in (4), correction according to the fuel properties is performed.FeeThis was done during the open control of the injection amount.
  Claim13In the invention described in the above, the correction according to the fuel property is performed during the feedback control of the fuel injection amount.
[0019]
【The invention's effect】
According to the first aspect of the present invention, the fuel injection amount is corrected in accordance with the fuel properties when performing the exhaust-temperature stratified combustion, so that the air-fuel mixture around the spark plug (the air-fuel mixture around the plug) is the fuel property. Regardless of the difference, the air-fuel ratio can always be controlled appropriately. For this reason, misfire due to the air-fuel ratio around the spark plug deviating from the appropriate range (mainly excessive fuel concentration) and the release of harmful exhaust components due to over-riching of the air-fuel mixture are prevented. it can.
[0020]
  In addition, since the air-fuel mixture around the plug is strictly controlled in consideration of the fuel properties, the amount of incomplete combustion products (determined by the fuel injection amount) is suppressed to the minimum necessary for raising the exhaust temperature and ignition is performed. Even if there is no inducer or the like, the post reaction can be completed satisfactorily. For this reason, the fuel injection amountButReduction (especially when light fuel is used)And laterLow fuel consumption can be realized because multistage injection is not required for reaction.
  Furthermore, when the engine is started, homogeneous combustion is first performed, and when the predetermined condition is satisfied, the engine is directly switched from homogeneous combustion to exhaust-temperature stratified combustion, so that the entire engine, particularly the exhaust aftertreatment catalyst, can be warmed up with low fuel consumption. .
  Here, immediately after switching to exhaust gas temperature-stratified combustion, a period (transition period) in which the target air-fuel ratio is set lower is provided, so that the air-fuel ratio around the spark plug is prevented from rising outside the appropriate range. Further, during this transition period, the target air-fuel ratio can be set to follow the progress of warming up of the combustion chamber by increasing the target air-fuel ratio with a predetermined rate of change according to the coolant temperature.
  According to the second aspect of the invention, the predetermined rate of change is set based on the engine temperature, so that it can be easily adapted to the warm-up state of the combustion chamber.
  According to the third aspect of the present invention, the rate of change is increased as the coolant temperature as the engine temperature is higher, and the switching is completed quickly, so that the fuel injection amount becomes excessive when the temperature becomes high. The mixture around the plug can be prevented from becoming excessively thick.
[0021]
  Claim4According to the invention, the exhaust aftertreatment catalyst is activated immediately after starting, and can be maintained at the activation temperature after being activated.
[0024]
  Claim5According to the invention according to the present invention, the exhaust gas temperature stratified combustion is not performed before the fuel property estimation is completed, so that the air-fuel ratio of the air-fuel mixture around the plug varies from an appropriate value by correction based on an inaccurate fuel property. Therefore, it is possible to prevent the combustion from becoming unstable.
  Claim6According to the invention, the mixture around the plug can be satisfactorily formed by utilizing the piston crown surface by performing exhaust temperature stratified combustion after the crown surface temperature reaches a high temperature state.
[0025]
  Claim7In accordance with the invention, the lighter the fuel, the larger the fuel injection amount is corrected to decrease, so that the fuel injection amount is increased or decreased according to the difference in volatility, and the air-fuel ratio of the mixture around the plug is always in the appropriate range. Can hold.
  Claim8According to the invention, the fuel injection amount can be corrected corresponding to the gas flow speed by determining the correction amount based on the engine speed. In particular, the claims9By increasing the fuel injection amount when the engine speed is lower, that is, when the gas flow is underdeveloped, the wall-attached fuel component that does not evaporate is compensated for and the air-fuel ratio of the mixture around the plug is further increased. It can be controlled accurately.
[0026]
  Claim10According to the invention according toCooling waterBy determining based on the temperature, the fuel injection amount can be corrected in accordance with the warm-up state. In particular, the claims11According to the invention according to the invention, the air-fuel ratio of the mixture around the plug is further increased by increasing the fuel injection amount as the cooling water temperature is lower, i.e., when the warm-up is not progressing and the wall-attached fuel component is difficult to vaporize. It can be controlled accurately.
[0027]
  Claim12According to the invention, the correction according to the fuel property is performed during the open control of the combustion injection amount, whereby the variation in the air-fuel ratio with respect to the stored value due to the difference in the fuel property can be compensated.
  Claim13According to the invention according to the present invention, the target air-fuel ratio can be accurately achieved by performing the correction according to the fuel property during the feedback control of the fuel injection amount. Alternatively, the oxygen necessary for the after-reaction of the incomplete combustion product can be ensured accurately.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a configuration of a direct injection spark ignition engine (engine) according to an embodiment of the present invention. An intake pipe 2 is connected to a cylinder head of the engine body 1 (indicated by a two-dot chain line C in the figure), and an air cleaner (not shown) is attached to the introduction portion. The intake air passes through the air cleaner, then receives control by the electronically controlled throttle valve 3, flows into the surge tank 4, and is distributed to each cylinder in an intake manifold connected thereto. In the present embodiment, the swirl control valve 5 is provided in order to form a swirling flow in the cylinder of the intake air.
[0029]
In the combustion chamber, a spark plug 6 is installed facing substantially the upper center of the combustion chamber, and a high-pressure injector 7 serving as a fuel injection means is installed facing the lower side of the intake port. The injector 7 is driven to open based on a control signal from an electronic control unit described later, and directly injects fuel pumped by a fuel pump (not shown) into the cylinder. The fuel supplied to the injector 7 is configured to be adjusted to a predetermined pressure by a pressure regulator. The work generated by the combustion is transmitted from the piston 8 to the crankshaft 10 through the connecting rod 9 and taken out as a rotational motion.
[0030]
An exhaust pipe 11 is connected to the cylinder head, and an exhaust aftertreatment device (catalytic converter) 12 is interposed downstream of the exhaust manifold. The catalyst provided here includes a three-way catalyst that efficiently achieves oxidation of hydrocarbon (HC) and carbon monoxide (CO) and reduction of nitrogen oxide (NOx) in the vicinity of the theoretical air-fuel ratio, and HC and CO. An oxidation catalyst that oxidizes is employed. The exhaust gas is discharged into the atmosphere after passing through the exhaust aftertreatment device 12.
[0031]
The electronic control unit (ECU) 21 includes a microcomputer including a CPU, a ROM, a RAM, an A / D converter, and an input / output interface, and detects the engine speed Ne as an index indicating the current operating state. Detection signal from the crank angle sensor 31 (unit crank angle signal or reference crank angle signal), detection signal from the water temperature sensor 32 to detect the engine cooling water temperature (cooling water temperature) Tw, intake air amount A detection signal from the air flow meter 33 for detecting Qa, a detection signal from the throttle sensor 34 for detecting the opening (strol opening) TVO of the throttle valve 3, and a driver's accelerator operation amount (accelerator opening) ) A detection signal from the accelerator sensor 35 for detecting APO is input. The accelerator sensor 35 can also be used as an idle switch.
[0032]
In addition to these, air-fuel ratio sensors 36 and 37 are installed in the exhaust pipe 11 upstream and downstream of the catalytic converter 12, and these detection signals are also input to the ECU 21. The upstream air-fuel ratio sensor 36 is of a type that outputs a signal indicating lean or rich according to the concentration of a characteristic component (for example, oxygen) in the exhaust gas, or linearly the air-fuel ratio over a wide range. The detection type is adopted. The downstream air-fuel ratio sensor 37 is preferably of a type that outputs a signal indicating lean or rich according to the concentration of a specific component (for example, oxygen) in the exhaust gas.
[0033]
The ECU 21 corrects the air-fuel ratio feedback control based on the input signal from the upstream air-fuel ratio sensor 36 based on the input signal from the downstream air-fuel ratio sensor 37, thereby causing a control error due to deterioration of the upstream air-fuel ratio sensor 36 or the like. Preventing the occurrence of If such compensation is not performed, the downstream air-fuel ratio sensor 37 is unnecessary, and if the air-fuel ratio feedback control itself is not performed, these air-fuel ratio sensors 36 and 37 are both unnecessary. Become.
[0034]
The ECU 21 controls the injector 7 based on the input signals from the various sensors described above, and injects fuel at a predetermined time set for each operation region. Specifically, fuel is injected during the compression stroke in the low load and medium load ranges (FIG. 2A), and a flammable mixture is formed in the vicinity of the spark plug 6 to perform stratified combustion. On the other hand, in the high load region, fuel is injected during the intake stroke ((b) in the same figure), and the air-fuel mixture is formed almost uniformly in the entire cylinder to perform homogeneous combustion.
[0035]
Further, the ECU 21 controls the drive device (DC motor) 41 of the throttle valve 3 in addition to operating the spark plug 6 at a predetermined timing to perform an ignition operation. Specifically, the throttle valve 3 is controlled to a position where the required torque calculated based on the accelerator opening APO or the like can be achieved.
FIG. 3 is a flowchart of the combustion control performed for catalyst activation at the start of the control executed by the ECU 21.
[0036]
In S (step) 1, it is determined whether or not the ignition signal of the key switch 38 is turned on, in other words, whether or not the key is set to the ignition on position. If it is determined that the ignition is on, the process proceeds to S2, and nothing is done since the engine is stopped unless the ignition is on.
[0037]
In S2, it is determined whether or not the start signal of the key switch 38 is turned on, in other words, whether or not the key is set to the start position. If it is determined that the start position has been reached, it is determined that there is a cranking request, and the process proceeds to S3, where the starter motor is driven to perform cranking and the engine is started by intake stroke injection. Thereafter, when the start signal is turned off, it is determined that the engine has started, and the process proceeds to S4. Note that the processes of S1 to S3 are repeated during cranking.
[0038]
In S4, homogeneous combustion is performed by intake stroke injection in order to maintain the self-sustaining rotation and continue the warm-up operation thereafter. The air-fuel ratio at this time is controlled to be rich by the post-startup increase correction coefficient Kas.
In S5, it is determined whether or not the catalyst is activated. This determination can be replaced by determining whether or not the downstream air-fuel ratio sensor (oxygen sensor) 37 is activated, for example, as shown in FIG. Alternatively, the cooling water temperature Tw or the lubricating oil temperature is detected, the catalyst or its outlet temperature is estimated, and it is determined whether or not the catalyst has been activated based on the result, and further, the catalyst or its outlet temperature. May be detected and detected directly. If it is determined that the catalyst is not activated, the process proceeds to S6. If it is determined that the catalyst is activated, control for catalyst activation is unnecessary, and thus this routine is terminated (normal combustion). Control).
[0039]
In S6, it is determined whether or not switching to stratified combustion is possible based on the surface temperature (crown surface temperature) of the piston 8 (particularly, the bowl portion (reference numeral 8a in FIG. 2) formed on the crown surface). judge. This determination is performed by determining whether or not the crown surface temperature is equal to or higher than a predetermined temperature. For example, as shown in FIG. 9 described later, it is preferable to employ a pseudo water temperature Twf that is a parameter correlated with the crown surface temperature. It is. Alternatively, the crown surface temperature may be estimated from the coolant temperature Tw or the lubricating oil temperature, and the determination may be made based on the result, or the thermocouple may be embedded in the piston 8 and the crown surface temperature may be directly detected and determined. . The predetermined temperature is set to a temperature at which air-fuel mixture formation using the piston crown surface (fuel spray is guided by the bowl portion 8a) can be satisfactorily achieved. As a result of the determination, if the crown surface temperature is equal to or higher than the predetermined temperature, the process proceeds to S7, and if the predetermined temperature is not reached, vaporization on the piston crown surface is not promoted and the combustion stability is adversely affected. , Return to S4 and continue the operation by homogeneous combustion.
[0040]
In S7, it is determined whether or not the fuel property has already been estimated. This determination is performed as shown in FIG. The fuel properties are preferably estimated by the method disclosed in the prior publication of the present applicant (Japanese Patent Laid-Open No. 2000-297689).
This method is based on so-called learning control, and is roughly as follows. The learning action is carried out when the predetermined fuel property estimation / permission permitting conditions are satisfied at the start. Then, under this condition, the response waveform of the exhaust air / fuel ratio with respect to the change in the fuel injection amount is sampled, and the fuel properties are estimated by analyzing the input / output data. Specifically, the parameters of the plant model are adjusted based on the input / output data so that the prediction error from the reference model (generally heavy fuel) with respect to the reference model that is a plant model is minimized, Identify the plant model for the fuel used. And the cut-off frequency fc of the identified plant model_Real, Calculated fc_RealThe cut-off frequency fc of the reference model_RefCompare with As a result, fc_Real> Fc_RefIf so, it is estimated that the fuel used is lighter than the reference fuel.
[0041]
If it is determined in S7 that the fuel property estimation has been completed based on the flag or the like, the process proceeds to S8. If it is determined that the fuel property estimation has not been completed, the process returns to S4 and the operation by homogeneous combustion is continued. In addition to the above method, various methods such as direct detection by a sensor can be adopted for the fuel property estimation.
In S8, it is determined whether or not an execution permission condition for stratified combustion (exhaust temperature stratified combustion described in the next step) is satisfied. This determination is performed, for example, by determining whether or not the engine is in an operating state in which exhaust-temperature stratified combustion can be performed stably (the engine operability is not impaired) as shown in FIG. If it is determined that the condition is satisfied, the process proceeds to S9. If it is determined that the condition is not satisfied, this routine is terminated (normal combustion control is performed).
[0042]
In S9, the combustion mode is switched from homogeneous combustion to exhaust temperature stratified combustion in order to increase the exhaust temperature for catalyst activation. Specifically, a fuel that can be burned substantially with the amount of intake air per combustion cycle (a fuel required to form a stoichiometric air-fuel ratio or a slightly leaner air-fuel mixture) is compressed into a compression stroke. The air-fuel mixture is slightly richer than the stoichiometric air-fuel ratio in the vicinity of the spark plug 6 and stratified combustion is performed. The effect of the present invention can be obtained if such an air-fuel mixture having a relatively high fuel concentration is formed in the vicinity of the spark plug 6, so that the air-fuel ratio of the entire combustion chamber is appropriately selected within the range of about 14-17. You can do it. The injection timing is set within a range of 50 to 80 ° before compression top dead center.
[0043]
In S10, it is determined whether or not the catalyst is activated by the same method as described in S5. If it is determined that it has been activated, the routine is terminated and the routine shifts to normal combustion control. If it is determined that the routine has not yet been activated, the process returns to S9, and exhaust gas temperature-stratified combustion is performed until the catalyst is activated. Continue driving. In normal combustion control, the combustion mode is switched between homogeneous stoichiometric combustion, homogeneous lean combustion, and stratified lean combustion in accordance with the operating conditions to achieve the desired exhaust performance, fuel efficiency performance, and operational performance (output, stability). To do.
[0044]
In this control, when the crown surface temperature of the piston 8 is lower than the predetermined temperature in S6, the shift to the stratified combustion is prohibited and the adverse effect on the combustion stability is avoided, but the catalyst activation is prioritized. In such a case, the process may be skipped from S5 to S7.
Here, before explaining various determinations to be described later, it will be described whether the fuel injection amount is calculated according to the combustion mode.
[0045]
In the case of a combustion mode other than exhaust temperature stratified combustion, the fuel injection amount is calculated as follows.
The ECU 21 calculates a basic fuel injection pulse width (basic injection amount) Tpt corresponding to the target air-fuel ratio based on the intake air amount Qa and the engine speed Ne. C is a constant.
[0046]
Tpt = C × Qa / Ne
Then, the calculated Tpt is corrected by the water temperature correction coefficient Kw, the post-startup increase correction coefficient Kas, the air / fuel ratio feedback correction coefficient LAMD, the target air / fuel ratio correction coefficient Z, and the like to calculate the effective fuel injection pulse width CTI. Ts is an invalid injection time.
[0047]
CTI = Tpt × (1 + Kw + Kas +...) × LAMD × Z + Ts
In the equation, LAMD is increased or decreased by proportional-integral control or the like according to the air-fuel ratio detection result based on the input signal from the upstream air-fuel ratio sensor 36. By correcting Tpt thereby, The fuel ratio is feedback controlled to the target air fuel ratio. Note that LAMD is fixed to a predetermined value (for example, 1) when air-fuel ratio feedback correction is not performed, such as during exhaust temperature stratified combustion.
[0048]
In the case of exhaust temperature stratified combustion, the fuel injection amount is calculated as follows.
The effective fuel injection pulse width CTI in this case is calculated by changing a correction term related to Tpt (for example, the post-startup increase correction coefficient Kas) in the injection amount calculation formula. A procedure for calculating the correction coefficient Kas during exhaust temperature stratified combustion will be described with reference to the flowchart shown in FIG. This routine is executed in the ECU 21 every predetermined time (for example, 10 ms).
[0049]
In S21, it is determined whether or not the exhaust gas temperature raising control is permitted. If it is determined that it is permitted, the post-startup increase correction coefficient Kas is replaced with NAKAS, and the process proceeds to S22 in order to use this as the correction coefficient in the exhaust temperature stratified combustion. On the other hand, when it is determined that it is not permitted, a normal post-startup increase correction coefficient Kas corresponding to the coolant temperature Tw is obtained. At this time, Kas is set to a smaller value as Tw becomes higher, and the target equivalent ratio changes as indicated by t2 to 5 in FIG.
[0050]
In S22, the coolant temperature Tw and the engine speed Ne are detected based on the input signals from the water temperature sensor 32 and the crank angle sensor 31.
In S23, the water temperature correction amount NTKAS of the post-startup increase correction coefficient is read with reference to a map having a tendency as shown in FIG. 5 based on the cooling water temperature Tw. NTKAS is generally set to a larger value as Tw is lower. Since the combustion chamber wall surface is cold at low water temperature and it can be determined that the fuel component adhering to the wall surface is difficult to vaporize, the amount of fuel to be injected to form an air-fuel mixture with the same air-fuel ratio around the spark plug 6 is small. Because it will increase.
[0051]
Further, the water temperature correction amount NTKAS is set to a different value depending on the fuel property even for a constant water temperature, and is set to a smaller value as the fuel is lighter. Light fuel has higher volatility than heavy fuel, and even if the same amount is injected, the amount of fuel adhering to the wall surface is reduced. This is because the air-fuel ratio is made the same.
[0052]
In S24, based on the engine speed Ne, the rotational speed correction amount NTNKAS of the post-startup increase correction coefficient is read with reference to a map having a tendency as shown in FIG. NTNKAS is generally set to a larger value as Ne is lower. Since the gas flow in the cylinder is weak at low rotation and the fuel component adhering to the wall is difficult to vaporize, the amount of fuel to be injected is large in order to form the same air-fuel mixture around the spark plug 6 Because it becomes.
[0053]
Further, the rotational speed correction amount NTKAS is set to a different value according to the fuel property even at a constant rotational speed, and is made smaller as the fuel is lighter. This is because the injection amount itself is reduced in consideration of the high volatility of the light fuel, and the air-fuel ratio around the spark plug 6 is set to the same air-fuel ratio.
Note that the maps shown in FIGS. 5 and 6 may be used only during traveling (for example, a low load region other than the idle region), and NTKAS and NTNKAS set as fixed values may be used during idling.
[0054]
In S25, a product NAKAS of the water temperature correction amount NTKAS and the rotation speed correction amount NTNKAS is calculated.
In S26, the latest NAKAS is stored. The stored NAKAS is reflected in the calculation of the effective fuel injection pulse width CTI as the correction coefficient Kas during exhaust temperature stratified combustion (Kas = NAKAS = NTKAS × NTNKAS).
[0055]
In the following, various determinations to be described later will be sequentially described.
First, the catalyst activity determination (S5 in FIG. 3) will be described with reference to the flowchart shown in FIG. Here, FIG. 8 shows changes with time in the oxygen sensor output, the catalyst inlet / outlet temperature, and the catalyst conversion rate from the start.
[0056]
  In S41, it is determined whether the downstream air-fuel ratio sensor (oxygen sensor) 37 is not heated by the heater. If it is determined that it has not been performed, S42If it is determined that the process is being performed, this routine is terminated. This is because the influence of heating by the heater is large, and there is a possibility that an error may occur in the activation determination of the oxygen sensor 37 and the catalyst.
[0057]
In S42, it is determined whether or not the oxygen sensor 37 is activated. Here, for example, as shown in FIG. 8, it can be determined that the oxygen sensor 37 has been activated when it reaches a predetermined level (V0 + dVR) from the state where the output voltage of the oxygen sensor 37 is maintained at the initial voltage V0. On the contrary, it can be determined that the activation has been reached when the predetermined level (V0 + dVL) is reached. In addition to the method based on the displacement of the output voltage as described above, it may be determined that the output of the oxygen sensor 37 has been activated with a predetermined number of inversions to the lean or rich side. If it is determined that the catalyst has been activated, the process proceeds to S43. If it is determined that the catalyst has not yet been activated, the same determination is repeated until it is determined that the catalyst has been activated.
[0058]
In S43, it is determined that the catalyst is activated when the oxygen sensor 37 is activated. The activation of the oxygen sensor 37 installed downstream of the catalyst is due to an increase in the catalyst outlet temperature. The increase in the catalyst outlet temperature has led to a state where the oxidation of specific exhaust components such as HC is promoted. This is because the exhaust temperature has increased.
[0059]
In S44, the heater for the oxygen sensor 37 is energized, and control for maintaining the sensor in an appropriate temperature range is started.
Next, the stratified combustion switching permission determination (S6 in FIG. 3) will be described with reference to the flowchart shown in FIG. Here, as described above, the determination is made based on the pseudo water temperature Twf that correlates with the crown surface temperature of the piston 8, and the time-dependent changes in the cooling water temperature Tw and the pseudo water temperature Twf from the start are shown in FIG.
[0060]
In S51, the simulated water temperature Twf is calculated. Twf is estimated and calculated by the following equation as a function of the elapsed time t from when the ignition signal is turned on. That is, starting from an initial value Twf [0] corresponding to the starting water temperature Tw [0], the current cooling water temperature Tw [1] is first-order-delayed by a delay correction coefficient Ktwf determined per unit time according to the intake air amount Qa. converge toward t]. Here, Twf [0] is read from the map shown in FIG. 10A based on Tw [0], and Ktwf is read from the map shown in FIG. 10B based on Qa.
[0061]
Twf [t] = Tw [t] − (Tw [t] −Twf [t−1]) × (1−Ktwf)
In S52, it is determined whether or not the pseudo water temperature Twf [t] is equal to or higher than a predetermined temperature Twf1. When it determines with it being Twf1 or more, it progresses to S53 and it is determined that the crown surface temperature became more than predetermined temperature. On the other hand, before reaching Twf1, the process returns to S51, and the same determination is repeated for the newly calculated pseudo water temperature Twf [t].
[0062]
Next, the fuel property estimation end determination (S7 in FIG. 3) will be described with reference to the flowchart shown in FIG.
In S61, it is determined whether the starter motor is driven and the engine speed becomes equal to or higher than the predetermined speed, and then the start signal is turned off (the key is in the ignition on position). Since the cranking is in progress until the start signal is not turned off, fuel property estimation is not performed. Therefore, in this case, this routine is terminated.
[0063]
In S62, it is determined whether or not a complete explosion has occurred. Fuel properties are not estimated until the explosion is complete.
In S63, it is determined whether or not input signals from various sensors are normal. If there is an abnormality, the fuel property is not estimated.
In S64, it is determined whether or not a normal fuel injection calculation is being executed, not during a fuel cut. If it is determined that the fuel is being cut (deceleration, throttle valve 3 is fully closed, etc.), fuel property estimation is not performed.
[0064]
As a result of the above determination, only when the key is in the ignition on position (S61), the complete explosion has been completed (S62), there is no abnormality in any of the sensor signals (S63), and the fuel is not being cut (S64). Proceed to S65.
In S65, 1 is substituted into a flag FLG indicating that the fuel property estimation has been completed, and this routine ends.
[0065]
  Next, the exhaust gas temperature raising control / execution permission determination (S8 in FIG. 3) will be described with reference to the flowchart shown in FIG.
  In S71, the coolant temperature Tw, the engine speed Ne, the torque Tq, and the intake air amount Qa are detected based on input signals from various sensors.
  In S72, each detected value is compared with a stored value in a RAM built in the ECU 21, and any of them is determined.Is cheapIt is determined whether or not it is within a set range for the fixed exhaust temperature stratified combustion. If it is determined that it is within the set range, the exhaust temperature stratified combustion is allowed to be performed in S73, whereas if it is determined that it is not within the set range, this is prohibited in S84. In the present embodiment, the exhaust temperature stratified combustion is permitted to be performed when the operation state is in the idle region or in a low load region other than the idle region.
  In this embodiment, when the combustion mode is switched from homogeneous combustion to exhaust-temperature stratified combustion, the target air-fuel ratio is a value slightly leaner than the theoretical air-fuel ratio (14.7) (for example, 16). Immediately after this switching, the target air-fuel ratio is set slightly lower than the original value (that is, 16), and is gradually shifted to the original value with a predetermined change rate. The pulse width CTI is calculated.
[0066]
Next, the operation of the combustion control according to the present embodiment will be described with reference to the time chart shown in FIG. The chart shows changes over time in the ignition timing, the opening degree of the swirl control bubble 5, the target equivalence ratio, and the engine speed, in contrast to the transition of the combustion mode from start to warm-up.
According to the present embodiment, when the start signal is turned on at time t0, the engine is cranked, and the ignition timing is gradually advanced in accordance with the rotation at that time. When the complete explosion is completed at time t1 and the start signal is turned off, the ignition timing is fixed at a predetermined timing set in accordance with the coolant temperature Tw and the engine speed Ne.
[0067]
The target equivalence ratio is corrected and set to a richer side than the stoichiometric air-fuel ratio in accordance with the coolant temperature Tw for stability from the start. When the warm-up operation is started, the fuel increase is gradually reduced as Tw increases.
When it is determined that the fuel property estimation is completed at time t2 (1 is assigned to the flag FLG), and when it is determined that the crown surface temperature of the piston 8 has risen to a predetermined temperature or higher at time t3, the exhaust gas rise is increased. Switching to warm stratified combustion is allowed. In response to this, the swirl control valve 5 is driven to the fully closed position (the ignition timing is retarded correspondingly), and when it is determined that the swirl control valve 5 is fully closed at time t4, time t5 The combustion mode is switched from homogeneous combustion to exhaust temperature stratified combustion. At this time, the ignition timing is retarded in response to the fuel injection timing being changed to the compression stroke (50-80 ° before compression top dead center).
[0068]
In the exhaust-temperature stratified combustion from time t5, the target equivalent ratio is set to a theoretical air fuel ratio or slightly higher than that in the entire combustion chamber. However, as a result of setting the post-startup increase correction coefficient Kas (= NAKAS) as described above, the target equivalence ratio is set to a different value depending on the fuel property, and the lower the value is, the lower the fuel injection amount. Is reduced. Here, according to the present embodiment, the cooling water temperature Tw also contributes to the setting of the target equivalence ratio, but for the sake of brevity, the movement caused by the change in Tw is not shown here.
[0069]
With such an equivalence ratio setting, an air-fuel mixture whose air-fuel ratio is slightly lower than the stoichiometric air-fuel ratio is formed in the vicinity of the spark plug 6 at the ignition timing. Accordingly, the fuel does not completely burn out in the vicinity of the spark plug 6 and incomplete combustion products such as unburned HC and CO are generated, but the generated amount of these products is appropriate and remains in the cylinder. It reacts with oxygen and burns out. The combustion gas is heated by the heat generated at this time, and the exhaust temperature is raised.
[0070]
When it is determined that the catalyst is quickly heated and activated at time t6 while the exhaust gas temperature is maintained at a high temperature by exhaust temperature stratified combustion, normal combustion control (here, homogeneous) is performed at time t6. Shift to stoichiometric combustion. Correspondingly, the ignition timing is advanced. However, even before the catalyst is activated, when the accelerator is greatly depressed, the routine shifts to normal combustion control at that time in order to ensure the operation performance.
[0071]
When the swirl control valve 5 is driven toward the fully open position in response to the transition of the combustion mode, the ignition timing is advanced correspondingly.
15 and 16 are time charts showing the effects of the combustion control according to the present embodiment.
FIG. 15 shows changes over time in the exhaust temperature from the start, the HC exhaust amount, the intake air amount, and the engine speed. For comparison with the case according to the present embodiment (solid line A), a dotted line B indicates a case where warm-up is performed only by homogeneous combustion.
[0072]
As is clear from the figure, since the high-temperature exhaust gas can be obtained by switching to the exhaust temperature stratified combustion, the time required for activation can be shortened by heating the catalyst more quickly to the activation temperature.
Further, although the HC emission amount temporarily increases immediately after switching, it is uniformly reduced thereafter. For this reason, if it considers over the whole warm-up period, it can be said that a significant reduction is possible.
[0073]
On the other hand, the fuel consumption is improved as compared with the case of performing the multistage injection, although a slight deterioration is observed as compared with the case of only homogeneous combustion (appears as an increase in the intake air amount).
FIG. 16 shows the air-fuel ratio of the air-fuel mixture formed around the spark plug 6 when the same amount of fuel is injected according to the fuel properties. In the figure, the solid line A is for heavy fuel, and the dotted line B is for light fuel.
[0074]
The engine control system is generally designed to be adapted to the case where combustion is heavy. However, in such a design, when the fuel actually stored by refueling or the like becomes lighter than the setting, the air-fuel ratio around the spark plug 6 becomes low due to the high volatility of the fuel, and the rich limit There is a risk of misfire.
According to the present embodiment, the mixture formation around the spark plug 6 can be strictly controlled by correcting the fuel injection amount in accordance with the fuel properties. Therefore, even if the fuel having any property is used. The air-fuel ratio around the spark plug 6 can always be controlled to an appropriate range (in the position indicated by A), and combustion stability is not impaired.
[0075]
  This embodimentThenTo exhaust temperature stratified combustionImmediately after switching the combustion mode, the target air-fuel ratio isValueSet a little lowerShiGradually shift to this original value with a predetermined rate of change.AndTo do.
[0076]
  FIG. 17 shows an example. In this embodiment,Combustion formWhen the target equivalence ratio is made rich (greater than 1) by the post-startup increase correction coefficient Kas, first, control is performed to a predetermined equivalence ratio (here, equivalent to the theoretical air-fuel ratio (= 1)), From here, it is gradually changed to the original target equivalent ratio for exhaust temperature stratified combustion, and the change rate dF / A at that time is changed according to the cooling water temperature Tw at the time of switching. That is, when switching is performed in a state where Tw is low and the warm-up is not so advanced, it is considered that a considerable amount of time is required until the combustion chamber is sufficiently warmed. Therefore, compared with the case where Tw is high, dF / A Is set to a small value, and the target equivalent ratio is shifted over time. If the warm-up is not progressing, the fuel component adhering to the wall surface is difficult to evaporate, and if the target equivalence ratio is rapidly reduced in this state, the fuel concentration around the spark plug 6 may become excessively low. . Then, the basic injection amount corresponding to the target equivalence ratio that shifts at a speed based on Tw is corrected in accordance with the fuel properties (FIG. 5), and the amount is reduced as the fuel is lighter. It becomes.
[0077]
  Another example is shown in FIG. here,Combustion formAt the time of switching, the target equivalence ratio is decreased according to the cooling water temperature Tw at that time, and the lower the Tw, the lower the value from the higher value to the final value. If the amount of increase based on the final value is D, and the combustion chamber warms up after a certain number of cycles n has elapsed since switching regardless of the combustion chamber temperature at the time of switching, the rate of change D / n for each control cycle is Tw A lower value is set to a larger value. According to this method, it is possible to prevent the fuel concentration around the spark plug 6 from becoming excessively low due to the combustion chamber not being sufficiently warmed during and immediately after switching.
[0078]
  In the above, the control from start to warm-up has been explained.EmbodimentThe exhaust temperature stratified combustion according toIn addition to this,It is also possible to prevent the catalyst temperature from deviating from the active temperature range during operation.
  For that purpose, for example, if the sensor output is monitored and it is detected that the operation state in which the exhaust gas temperature is lowered continues for a predetermined time or more, and if this is detected, the exhaust temperature stratified combustion can be stably performed, Switch to exhaust temperature stratified combustion to heat the catalyst. Then, when it is determined that the catalyst has been sufficiently warmed based on the elapsed time after switching or the like, the normal combustion control may be restored.
[0079]
  In the above description, the air-fuel ratio feedback correction coefficient LAMD of the injection amount calculation formula is fixed to 1 at the time of exhaust temperature stratified combustion, and the fuel isFeeAlthough the injection amount is controlled to be open, the LAMD may be operated to perform feedback control to the target air-fuel ratio, and the fuel property may be reflected in the injection amount calculation formula at this time.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a direct injection spark ignition engine according to an embodiment of the present invention.
FIG. 2 is a conceptual diagram of fuel injection according to the combustion mode.
FIG. 3 is a flowchart of a combustion control routine according to an embodiment of the present invention.
FIG. 4 is a flowchart of a routine for calculating an exhaust gas temperature increase control / after-startup increase correction coefficient Kas (NAKAS).
[Fig. 5] Same as above, Setting map of correction coefficient water temperature correction NTKAS
[Fig. 6] Same as above, Correction coefficient rotation speed correction amount NTNKAS setting map
FIG. 7 is a flowchart of a catalyst activity determination routine.
FIG. 8 is a time chart showing changes in catalyst downstream air-fuel ratio sensor output, catalyst upstream / downstream temperature, and conversion rate during warm-up.
FIG. 9 is a flowchart of a piston crown surface temperature increase determination routine.
FIG. 10: Setting map for parameters for calculating simulated water temperature
FIG. 11 is a time chart showing changes in cooling water temperature and simulated water temperature during warm-up.
FIG. 12 is a flowchart of a fuel property estimation end determination routine.
FIG. 13 is a flowchart of an exhaust gas temperature raising control / execution permission determination routine.
FIG. 14 is a time chart showing the operation of combustion control according to an embodiment of the present invention.
FIG. 15 is an explanatory diagram of the effect of the above control (exhaust characteristics).
FIG. 16 is an explanatory diagram of the effect of the control (the air-fuel ratio around the spark plug)
FIG. 17 is a conceptual diagram showing an example of setting a target air-fuel ratio immediately after switching combustion modes.
FIG. 18 is a conceptual diagram showing another example of setting the target air-fuel ratio.
[Explanation of symbols]
1. Engine body
2 ... Intake pipe
3 ... Throttle valve
5 ... Swirl control valve
6 ... Spark plug
7 ... Injector
11 ... Exhaust pipe
12 ... Catalytic converter
21 ... ECU (electronic control unit)
31 ... Crank angle sensor
32 ... Water temperature sensor
33 ... Air flow meter
34 ... Throttle sensor
35 ... Accelerator sensor
36, 37 ... Air-fuel ratio sensor
38 ... Start switch

Claims (13)

Fuel injection means for directly injecting fuel into the cylinder;
Combustion control means for performing stratified combustion by injecting fuel into the compression stroke by the fuel injection means under specific operating conditions;
Fuel property estimation means for estimating the fuel property;
An exhaust temperature increase requirement establishment determining means for determining whether or not the exhaust temperature is in a condition to be increased,
The combustion control means includes
Wherein when it is determined that the condition to raise the exhaust temperature by the exhaust temperature rise requirements establishment determining means, the stoichiometric air-fuel ratio or this fuel injection amount to slightly lean side from the air-fuel ratio of the entire combustion chamber, The basic injection amount corresponding to the target air-fuel ratio at that time is corrected and calculated in accordance with the fuel property estimated by the fuel property estimating means, and the calculated fuel injection amount is injected in the compression stroke, and the exhaust gas temperature raising stratification is performed. While burning ,
When the engine is started, first, homogeneous combustion is performed, and when the predetermined condition including the determination result of the exhaust temperature increase requirement establishment determination means is satisfied, the homogeneous combustion is directly switched to the exhaust temperature stratified combustion,
A target air-fuel ratio transition period is provided immediately after switching from the homogeneous combustion to the exhaust-temperature stratified combustion, and in this transition period, the fuel injection amount is calculated by setting the target air-fuel ratio lower than that after completion of the transition. ,
In the transition period, the target air-fuel ratio is set to a predetermined value corresponding to the coolant temperature so that the target air-fuel ratio during transition at the time when a certain control cycle has elapsed after switching is increased as the coolant temperature increases. A control device for a direct-injection spark ignition engine characterized by being raised at a rate of change . It said combustion control means, the control apparatus for a direct injection type spark ignition engine according to claim 1 to set on the basis of the predetermined rate of change in the engine temperature. It said combustion control means, the predetermined rate of change, based on the cooling water temperature as the engine temperature, the control apparatus for a direct injection type spark ignition engine according to claim 2 which is to set to a larger value as is higher . The exhaust temperature rise requirements establishment determining means, one determines claims 1-3 and is in condition to raise the exhaust gas temperature when it is necessary to heat the interposed in an exhaust passage exhaust aftertreatment catalysts The control apparatus of the direct injection type spark ignition engine as described in one . The control apparatus for a direct injection spark ignition engine according to any one of claims 1 to 4 , wherein the exhaust temperature-stratified combustion is permitted only when the estimation by the fuel property estimating means is completed. The direct injection spark ignition engine according to any one of claims 1 to 5 , wherein the exhaust temperature-stratified combustion is permitted only when it is determined that a piston crown surface temperature is equal to or higher than a predetermined temperature indicating a high temperature state. Control device. The control device for a direct injection spark ignition engine according to any one of claims 1 to 6 , wherein the combustion control means corrects the fuel injection amount to be decreased more as the fuel is lighter according to the estimated fuel property. . The control device for a direct injection spark ignition engine according to any one of claims 1 to 7 , wherein a correction amount corresponding to the fuel property is determined based on an engine speed. The control device for a direct injection spark ignition engine according to claim 8 , wherein the fuel injection amount is increased as the engine speed is lower in accordance with the correction amount. The control device for a direct injection spark ignition engine according to any one of claims 1 to 9 , wherein a correction amount corresponding to the fuel property is determined based on a coolant temperature. The control device for a direct injection spark ignition engine according to claim 10 , wherein the fuel injection amount is increased as the coolant temperature is lower in accordance with the correction amount. It said combustion control means, the control apparatus for a direct injection type spark ignition engine according to any one of claims 1 to 11 for performing the correction in accordance with the fuel property during the open control of the fuel injection amount. The control device for a direct injection spark ignition engine according to any one of claims 1 to 11 , wherein the combustion control means performs correction in accordance with fuel properties during feedback control of a fuel injection amount.

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