JP2000356144A - Combustion control device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance control accuracy of knock avoidance by positively control ling a compression temperature which directly relates to a combustion condition. SOLUTION: This device comprises a mechanism 31 which is capable of variably controlling an intake valve close timing, and a mechanism 32 capable of controlling a throttle valve opening independently of an accelerator pedal. In this case, a target value of a compression temperature which is an air-fuel mixture temperature in the case where compression to a top dead center is carried out in a normal state with the intake valve close timing of a base as a reference without igniting is set by a setting means 33. A calculating means calculates the intake valve close timing based on the compression temperature target value and a compression start temperature, and a control means 35 control the intake valve close timing control mechanism 31 so as to be the calculated intake valve close timing. A calculating means 36 calculates a target throttle valve opening based on the intake valve close timing, engine speed, and a target torque, and a control means 37 controls the throttle valve opening control mechanism 32 so as to get this target throttle opening.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a combustion control device for an engine.

[0002]

2. Description of the Related Art In a gasoline engine, it is desirable to set the compression ratio of the engine as high as possible in order to improve fuel efficiency and output performance. However, since high compression ratio is limited mainly by generation of knock, The following proposal has been made to achieve both high compression ratio and avoidance of knock.

[0003] 1) A sensor for detecting the occurrence of knock is provided, and the knock is avoided by correcting the ignition timing to the retard side when the knock occurs based on the sensor detection value.

2) An intake valve closing timing control mechanism (a mechanism capable of variably controlling the intake valve closing timing) is provided to control the intake valve closing timing when the load detecting means detects a high load region where knock is likely to occur. Thus, the occurrence of knock is avoided by lowering the effective compression ratio (see JP-A-61-76723).

[0005] 3) A turbocharger and an intake valve closing timing control mechanism are provided, and when the intake air temperature detected by a sensor exceeds a predetermined value, the occurrence of knocking is avoided by advancing the intake valve closing timing (Japanese Unexamined Patent Publication (Kokai) No. 2002-157572). See JP-A-56-69411).

[0006]

In the above method 1), since the occurrence of knock is directly detected and fed back to the ignition timing, the feedback speed at the time of occurrence of knock is high, which is effective as a knock avoiding means. On the other hand, the ignition timing is set to MBT (Minimum Spark Advance for BestTorq
ue) is corrected to the retard side, so that deterioration of combustion and an increase in exhaust gas temperature cannot be avoided.

In the methods 2) and 3), the intake air temperature and the engine load may vary depending on the conditions in the combustion chamber where knocking occurs.
Even if the value is representative of (such as the temperature in the combustion chamber), it does not directly correspond to the combustion state itself. In other words, the methods 2) and 3) described above only control the combustion state indirectly, and there is a limit to the improvement in the control accuracy for avoiding knock. Further, there is a response delay in the intake valve closing timing control mechanism, and it is not possible to move the intake valve closing timing with a good response in response to the occurrence of knocking, so that knocking cannot be avoided during the response delay. Therefore, in the above methods 2) and 3), the actual compression ratio is set with a margin in consideration of the use conditions of the engine, the use environment, and the like, and the compression ratio cannot be made too high. .

Accordingly, the present invention defines the temperature of the air-fuel mixture when it is compressed to the top dead center without ignition in the standard state with reference to the closing timing of the base intake valve as the compression temperature, and sets the target value of the compression temperature as the compression temperature. By controlling the intake valve closing timing so as to obtain the compression temperature target value in advance (that is, actively controlling the compression temperature that is directly related to the combustion state), control accuracy of knock avoidance is improved. The purpose is to: Note that the base intake valve closing timing is the intake valve closing timing before the present invention is applied, as described later.

[0009]

According to a first aspect of the present invention, as shown in FIG. 19, an intake valve closing timing control mechanism 31 capable of variably controlling an intake valve closing timing, and a throttle valve opening degree independent of an accelerator pedal. Valve opening control mechanism 32 that can be controlled
And a target value τc of the compression temperature, which is the temperature of the air-fuel mixture when it is compressed to the top dead center without ignition in a standard state (for example, atmospheric pressure, 25 ° C.) based on the base intake valve closing timing (for example, Means 33 for setting a constant value, means 34 for calculating the intake valve closing timing IVC based on the compression temperature target value τc and the compression start temperature τs, and the intake valve closing timing IVC so as to achieve the intake valve closing timing IVC. Means 35 for controlling the timing control mechanism 31, means 36 for calculating the target throttle valve opening TVO based on the intake valve closing timing IVC, engine speed NE and target torque TT, and the target throttle opening TVO. Means 37 for controlling the throttle valve opening control mechanism 32 as described above.

In the second invention, a lower temperature is set as the compression temperature target value τc in the first invention so that knock does not occur at least in the knock region.

According to a third aspect of the present invention, in the first aspect, there is provided means for controlling the stoichiometric air-fuel ratio to be obtained in at least a part of the operating range, and combustion is established in the stoichiometric air-fuel ratio operating range and the non-knock range. Is set as the compression temperature target value τc.

According to a fourth aspect of the present invention, there is provided the first aspect of the present invention, further comprising means for controlling such that a lean air-fuel ratio is obtained in at least a part of the operating range. A high temperature is set as the compression temperature target value τc.

According to a fifth aspect, in the first aspect, the compression temperature target value τc is calculated according to the engine speed NE and the target torque TT.

According to a sixth aspect of the present invention, there is provided a supercharger (for example, a supercharger) according to the first aspect of the present invention, wherein the compression temperature target is set to a value including a temperature rise associated with an increase in supercharging pressure due to operation of the supercharger. Set the value τc.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects, there is provided a knock detecting means, and a means for feedback-correcting the ignition timing based on the knock detection signal so that knock does not occur. Then, the feedback correction amount KN of the ignition timing is replaced with a compression temperature correction amount Δτc so as to reduce the correction amount KN, and the compression temperature target value τc is corrected to a lower temperature with the compression temperature correction amount Δτc.

In the eighth invention, when the ignition timing correction amount KN is limited to the maximum value KNMAX in the seventh invention, when the ignition timing correction amount KN reaches the maximum value KNMAX at the time of knocking, , Compression temperature correction amount Δτc
Is increased by a fixed amount ΔτcINC.

In a ninth aspect, in any one of the first to eighth aspects, the compression start temperature τs is a value obtained by adding a temperature rise ΔTPL of the intake air due to a pumping loss to the intake temperature τB.

In a tenth aspect, in any one of the first to eighth aspects, the compression start temperature τs is a value obtained by adding a temperature rise ΔTFL of the intake air due to the flow energy of the air to the intake temperature τB. is there.

[0019]

As described above, in the conventional gasoline engine, the compression temperature is positively controlled only by controlling the air-fuel ratio and the ignition timing (and the degree of stratification of air and fuel) among the parameters relating to the combustion state. However, according to the first invention, the combustion state can be kept constant irrespective of the external environmental requirements such as the operating conditions and the outside air temperature by controlling the compression temperature directly related to the combustion state. it can. For example, if a lower temperature is set as the compression temperature target value so as to prevent knocking in the knocking region as in the second invention, knocking can be prevented even when the outside air temperature is high in the knocking region. It can be suppressed reliably. Further, knocking can be avoided without retarding the ignition timing or enriching the air-fuel ratio, so that a rise in exhaust gas temperature and emission of unburned HC can also be suppressed.

In this case, the control of the compression temperature is also performed in a steady state, and if it is in a steady state, the delay caused in the intake valve closing timing control device does not matter.

According to the third aspect of the invention, the cooling loss at the time of combustion at the stoichiometric air-fuel ratio can be reduced, and the fuel consumption is improved accordingly.

According to the fourth aspect, the combustion at the time of the combustion at the lean air-fuel ratio can be improved. If the target air-fuel ratio (lean air-fuel ratio) is the same, the air-fuel ratio can be further set to the lean side by the amount of improvement in combustion.

According to the fifth aspect, the compression temperature target value corresponding to the operating condition can be obtained.

According to the sixth aspect of the present invention, the temperature rise accompanying the boost pressure is set in advance in the compression temperature target value. However, knocking can be avoided without delaying the ignition timing or enriching the air-fuel ratio.

If the feedback correction amount of the ignition timing is large (at this time, the ignition timing is greatly retarded), the fuel consumption is deteriorated and the exhaust temperature is increased. According to the seventh aspect of the invention, the feedback correction amount of the ignition timing is reduced by an amount corresponding to the replacement of the feedback correction amount by the compression temperature correction amount, whereby deterioration of fuel efficiency and increase in exhaust temperature can be suppressed. Further, since there is room for correction by the ignition timing, occurrence of knock can be avoided even under more severe conditions for knock.

In this case, by replacing the feedback correction amount of the ignition timing with the compression temperature correction amount, the target value of the compression temperature is reduced, thereby producing an effect equivalent to lowering the compression ratio of the engine. Therefore, it is not necessary to set the compression ratio with a margin so as to be established in various environments as in the case of the existing engine, so that a higher compression ratio can be achieved, thereby greatly improving the fuel efficiency. .

If knocking still occurs after the ignition timing correction amount reaches the maximum value when knocking occurs, knocking cannot be stopped. In this case, according to the eighth aspect, the compression temperature correction amount Increases, and the target compression temperature decreases, so that knocking can be prevented even after the ignition timing correction amount reaches the maximum value when knocking occurs.

Since the intake air temperature represents the internal energy of the intake air, if only the intake air temperature is used, the heat and the energy associated with the flow given to the intake air cannot be completely expressed, and a deviation from the actual compression start temperature occurs. Occurs. For example, the lower the load, the greater the pumping loss when supercharging, and also at the time of high supercharging.The heat generated by this loss raises the temperature of the intake air. According to the ninth invention, the actual compression start temperature is accurately estimated even at a low load or a high supercharge where the pumping loss is large at the time of high supercharging. Can give well.

Also, the larger the amount of intake air, the greater the flow energy of the air. When air with a large flow energy enters the cylinder, the flow energy is converted into heat and the temperature of the air rises. However, if the intake air temperature alone is used, when the intake air amount is large, it is estimated to be lower than the actual compression start temperature. However, according to the tenth aspect, even when the intake air amount is large and the load is high, the actual The compression start temperature can be given with high accuracy.

[0030]

FIG. 1 is a block diagram of the entire system. In the figure, 1 is an engine body, 2 is an intake passage,
Reference numeral 3 denotes an exhaust passage, 4 denotes a fuel injection valve provided facing the intake port, 5 denotes an ignition plug, 7 denotes a throttle valve, and 8 denotes a throttle valve control device for electronically controlling the opening of the throttle valve 7.

A supercharger 11 is provided in the intake passage. The supercharging pressure by the supercharger 11 is basically determined by the engine speed. In order to obtain a target supercharging pressure according to the operating conditions, a bypass valve is provided in a passage 12 that bypasses the supercharger 11. In the operating range where supercharging is not required, the bypass valve 13 is fully opened by the bypass valve control device 14 to allow all of the intake air to flow into the bypass passage 12. 13 is closed and the intake air flows to the supercharger 11 to perform supercharging.

The engine 1 has a mechanism capable of arbitrarily adjusting the intake valve closing timing. Since this mechanism is well known, a detailed description thereof will be omitted, but only a drive device 15 responsive to a control signal is shown in the figure.

The control unit 21 receives a signal from a sensor 22 that outputs a signal corresponding to knock, an accelerator pedal opening signal from an accelerator opening sensor 23, a signal from a crank angle sensor 24, a signal from a cylinder discrimination sensor 25, An ECM (Electronic Control Module) 21 mainly composed of a microcomputer is input together with an intake air amount signal from the air flow meter 26, and the fuel injection from the fuel injection valve 4 is performed so as to obtain a target air-fuel ratio AF according to operating conditions. In addition to controlling the amount and opening of the throttle valve 7 simultaneously, the ignition timing and the supercharging pressure are controlled.

First, the air-fuel ratio control will be described. The target air-fuel ratio AF has a large operating range (1) a low-load low-rotation range, (2) a higher-load range, and (3) a full-load range. In a low-load, low-speed range where the demand for output is small, the target air-fuel ratio is set to a lean air-fuel ratio of about 22 to improve fuel efficiency and increase the load. In the region, the target air-fuel ratio is set to the stoichiometric air-fuel ratio (approximately 14.7), and the three components of the exhaust gas are simultaneously purified by a three-way catalyst (not shown) provided in the exhaust passage. In the vicinity of a full load region where a large output is required, the target air-fuel ratio is set to an air-fuel ratio richer than the stoichiometric air-fuel ratio. In FIG. 5, the “lean air-fuel ratio range” is the above-mentioned region (1), and the “stoichiometric air-fuel ratio region” is the above (2).
The region (3) is referred to as the “output air-fuel ratio region”.

In the ignition timing control, the ignition timing basic value ADV0
Is set in the MBT, and an ignition signal is output to an ignition device (not shown) so as to obtain the MBT.
Further, in order to prevent knocking #, the signal from knock sensor 22 is used as a feedback signal, and when it is determined that knock has occurred, the ignition timing is set to a fixed amount KNIN.
C, the ignition timing is set to a fixed amount KNDEC (KNDEC <KN) from the timing when knocking stops.
INC).

Each control of the air-fuel ratio and the ignition timing is the same as the conventional one.

In the ECM 21, the intake valve closing timing control device 15 is controlled so that a predetermined target compression temperature τc is obtained.
The combustion state is controlled by controlling the closing timing of the intake valve via the ECU, and the ignition timing correction amount KN in the knock control is gradually replaced with the compression temperature correction amount Δτc. Compression temperature τc
Is corrected to the lower side.

The contents of the control executed by the ECM 21 which is different from the conventional control will be described with reference to a flowchart.

FIG. 2 is for calculating the intake valve closing timing IVC, the target throttle valve opening TVO and the bypass valve opening TVO2, and for each cycle (for example, the Ref signal (4
This is executed at every 90 ° crank angle in a cylinder engine and every 120 ° in a 6-cylinder engine).

First, in step 1, the accelerator pedal opening AP
O, engine speed NE, intake air temperature τB, target air-fuel ratio A
The sensor output values of F, intake pressure PB, and intake air amount QA (mass flow rate) are read.

In this embodiment, the sensors 27 and 28 for detecting the intake air temperature τB and the intake air pressure PB are provided in the collector in this embodiment, but may be provided in the intake port.

In step 2, a target torque TT is calculated by searching a map having the contents shown in FIG. 3 from the accelerator opening APO and the engine speed NE.

The calculation of the target torque is not limited to this. For example, a target driving force PW is calculated by searching a map having the contents shown in FIG. 4 from the accelerator opening APO and the vehicle speed VSP, and is obtained by multiplying a value obtained by dividing the target driving force PW by the actual transmission ratio GR of the transmission by a coefficient. It does not matter.

The target compression temperature τc is calculated by retrieving a map having the contents shown in FIG. 5 in step 3 from the target torque TT and the engine speed NE thus obtained.

Here, the compression temperature is a standard condition (for example, atmospheric pressure, 25 ° C.) based on the base intake valve closing timing.
, The air-fuel mixture temperature when it is compressed to the top dead center without ignition, and this target value is the target compression temperature.

The base intake valve closing timing refers to the intake valve closing timing before the present invention is applied, and is set to a constant value here for simplicity. That is, when the present invention is applied to an engine in which the intake cam is driven by the fixed cam, the base intake valve closing timing becomes a constant value. Of course, the present invention can also be applied to an engine whose intake valve is driven by a variable cam (in this case, the base intake valve closing timing is a variable value).

The map value of the target compression temperature τc shown in FIG. 5 is set as follows according to the difference between the knock region (the region indicated by hatching with a broken line), the non-knock region, and the difference in the target air-fuel ratio AF. I have.

<1> Knock region: A lower temperature is set so that knock does not occur. For example, a constant temperature is set irrespective of operating conditions in the knock region. As a result, knocking can be suppressed even under conditions of equal air volume, regardless of external factors such as the outside air temperature.

<2> Non-knock range and stoichiometric air-fuel ratio range: A low temperature is set within a range where combustion is established. Thereby, the cooling loss at the time of combustion at the stoichiometric air-fuel ratio can be reduced.

<3> Lean region: The temperature is set as high as possible within a range where combustion is established. This can improve the combustion during lean combustion. If the target air-fuel ratio (lean air-fuel ratio) is the same, the air-fuel ratio can be further set to the lean side by the amount of improvement in combustion.

The relationship between the regions having different target air-fuel ratios and the knock regions is not limited to that shown in FIG. 5 (depending on the engine model).

In this embodiment, since the supercharging is performed, the characteristic shown in FIG. 5 includes an increase in the compression temperature due to an increase in the supercharging pressure. In detail, since the compression temperature rise due to the boost pressure rise is as shown in FIG. 6, the characteristic obtained by adding this characteristic to the characteristic of the target compression temperature for the NA engine (naturally aspirated engine) is the characteristic shown in FIG. Become.

The actual numerical value of the target compression temperature map may be set by actual measurement or may be obtained by calculation.

In step 4, the map value of the target compression temperature obtained in this way is corrected by the correction amount Δτc of the compression temperature (a value obtained by subtracting Δτc from τc is set to τc again). The calculation of the compression temperature correction amount Δτc is shown in FIG.
7 will be described later.

In step 5, the compression start temperature τs is calculated. This calculation will be described with reference to the subroutine of FIG.

In FIG. 11, in steps 11 and 12, a map containing the contents shown in FIG. 8 is retrieved from the intake pressure PB, the intake air amount QA, and the target air-fuel ratio AF to obtain the temperature rise ΔTPL of the intake air due to the pumping loss. A map containing the contents shown in FIG. 9 is retrieved from the intake air amount QA and the target air-fuel ratio AF to calculate the temperature increase ΔTFL of the intake air due to the flow energy of the air.
, A value added to the intake air temperature τB (detected value) is calculated as the compression start temperature τs.

This is because the rise in intake air (Δ
The compression start temperature τs is obtained by adding TPL and ΔTFL). The intake air temperature represents the internal energy of the intake air. If only this intake air temperature τB,
This is because energy due to heat or flow applied to the intake air cannot be fully represented, and a deviation from the actual compression start temperature occurs.

For example, the lower the load, the greater the pumping loss, especially at the time of supercharging (that is, at the time of high load) when supercharging is performed, and the heat generated by the pumping loss reduces the temperature of the intake air. In order to raise the temperature, if only τB is used, the temperature is estimated to be lower than the actual compression start temperature at the time of low load or high supercharging.

On the other hand, as the intake air amount QA increases, the flow energy of the air increases, and when the air having the high flow energy enters the cylinder, the flow energy is converted into heat to increase the temperature of the air. Also in this case, if only τB is used, when the intake air amount QA is large, it is estimated lower than the actual compression start temperature.

Therefore, by introducing the correction values (ΔTPL and ΔTFL) in consideration of the temperature rise of the intake air, at the time of a low load with a large pumping loss, a high supercharging, or a high load with a large intake air amount. Also, it is possible to accurately give the actual compression start temperature.

From the same viewpoint, when fuel is injected from the injection valve 4 toward the intake port, a portion of the latent heat of vaporization is taken from the air flowing into the cylinder as the injected fuel is vaporized. It doesn't matter.

In FIGS. 8 and 9, the horizontal axis represents the mass flow rate [kg / s] of the air-fuel mixture. It goes without saying that the intake valve must be closed at the start of compression.

When the calculation of the compression start temperature τs obtained in this way is completed, the flow returns to FIG. 2, and in step 6, the intake valve closing timing IVC is calculated. The intake valve closing timing can be determined by thermodynamic calculation using the basic specifications of the engine (bore diameter B, stroke S, compression ratio ρ, connecting rod length L), compression start temperature τs, compression temperature τc, and target air-fuel ratio AF. .
For example, in the case of adiabatic compression, if the specific heat ratio is constant, the compression temperature is uniquely determined from the compression start temperature and the volume change, so the intake valve closing timing is calculated so that the volume change up to the top dead center becomes a desired value. it can. Regarding the specific heat ratio, it is considered that the change in temperature is small because combustion is not involved here, and τs and τ
Use the average value of c. At this time, the specific heat is obtained from the target air-fuel ratio AF in consideration of the ratio of the mixed gas of fuel vapor and air. The method for determining the specific heat ratio is not limited to this.

The calculation of the intake valve closing timing IVC will be specifically described with reference to the subroutine of FIG. The following arithmetic expressions (known) are expressed in SI units.

In FIG. 10, in step 21, the average specific heat ratio κ of the air-fuel mixture is calculated using the target air-fuel ratio AF as follows. Now, assuming that the average temperature of the compression stroke is τm,

[0066]

Τm = (τs + τc) / 2 If the fuel weight ratio in the air-fuel mixture is mf and the air weight ratio in the air-fuel mixture is ma, (mf + ma = 1),
These are expressed as follows using the target air-fuel ratio AF.

[0067]

[Mathematical formula-see original document] mf = 1 / (AF + 1) ma = AF / (AF + 1) The gas constant R of the mixture and the constant pressure specific heat CP of the mixture are calculated as follows:

[0068]

R = mf × Rf + ma × Ra CP = mf × Cpf (τm) + ma × Cpa (τm) where Rf: gas constant of fuel vapor, Ra: gas constant of air, Cpf (τm): fuel vapor Constant pressure specific heat, Cpa (τm): constant pressure specific heat of air, defined by the formula:

[0069]

４ = CP / (CP-R)

In step 22, using this specific heat ratio κ

[0071]

(Equation 5)

The combustion chamber volume VS at the start of compression is calculated by the following equation. Equation 5 is

[0073]

(Equation 6)

Is obtained by solving the relational expression for VS. The clearance volume VT at the top dead center is known from the basic specifications of the engine as follows.

[0075]

VT = 0.25 × π × B ² × S / (ρ-1) where B: bore diameter, S: stroke, ρ: compression ratio,

[0076]

VS = VT + 0.25 × B ² × (S / 2) × ｛(1
−cos θ) + (1 / λ) × (1− (1−λ ² sin)
² theta) ^0.5) intake valve closing timing theta (theta satisfying the equation of} obtains the crank angle) which aimed behind the top dead center. Here, λ in Expression 8 is λ = (S / 2) / L (L is a connecting rod length).

The intake valve closing timing θ thus obtained is compared with the maximum value IVCMAX of the intake valve closing timing and the minimum value IVCMIN of the intake valve closing timing in steps 24 and 25.
If θ ≦ IVCMIN, the minimum value IVCMIN is the intake valve closing timing IVC, and if θ ≧ IVCMAX, the maximum value IVCMAX
Is set to the intake valve closing timing IVC, otherwise θ is set to the intake valve closing timing IVC.

After the intake valve closing timing IVC is calculated in this manner, the process returns to FIG. 2. In step 7, the target throttle valve opening TVO is calculated from the intake valve closing timing IVC in addition to the target torque TT and the engine speed NE. .

According to the characteristics of the TVO, under the condition that the rotational speed NE is constant, as shown in FIG. 11, as the IVC increases (the intake valve closing timing is delayed) and the target torque T
The value increases as T increases. Further, under the condition where the torque is constant, as shown in FIG. 12, the IVC mainly increases as the IVC increases (the intake valve closing timing is delayed).

In step 8, the target supercharging pressure TPB is calculated by searching a map having the contents shown in FIG. 13 from the target throttle valve opening TVO and the rotational speed NE obtained in this way. The bypass valve opening TVO2 is calculated by searching a map having the contents shown in FIG.

Here, the region of TPB = 1 is the bypass valve 1
3 is a region in which supercharging is not performed by fully opening (TVO2 = 4/4), and when TPB> 1, the bypass valve 13
Is gradually closed to increase the flow rate of air flowing to the supercharger 11 to perform supercharging (FIGS. 13 and 15).
reference). 14 shows the target boost pressure TPB with respect to the target throttle valve opening TVO when the rotation speed NE is constant, and FIG. 16 shows the bypass valve opening TVO2 with respect to the target boost pressure TPB when the rotation speed NE is constant. It is a characteristic.

The bypass valve opening TVO2 calculated in this way and the target throttle valve opening TVO are RA
The control device 8 controls the throttle valve 7 so that the opening of the throttle valve 7 becomes the TVO by a throttle valve driving routine (not shown) using the target throttle valve opening TVO.
Is controlled by Further, the controller 14 is controlled by the bypass valve driving routine (not shown) using the bypass valve opening TVO2 so that the opening of the bypass valve 13 becomes this TVO2.
Is controlled by

Next, the flowchart of FIG. 17 is for calculating the ignition timing correction amount KN and the compression temperature correction amount Δτc as feedback correction amounts based on the knock signal, and is executed at regular intervals (for example, every 10 msec). .

Before the description of the flow, how the compression temperature correction amount Δτc changes when knock occurs will be described with reference to FIG.

In this operation, the ignition timing is basically preceded by the feedback correction of the ignition timing with respect to the occurrence of the knock, and the ignition timing correction amount KN which is the feedback correction amount of the ignition timing in a state where the knock is no longer generated. Until the ignition timing correction amount becomes zero, the compression temperature correction amount Δτc is gradually converted. For example, in FIG.
When the knock occurs, the ignition timing correction amount (retard amount) KN
The knocking is eliminated by increasing the number of knocks. After increasing the compression temperature correction value (temperature decrease amount) Δτc by a fixed amount ΔτcADD at the timing of t2 when the knocking stops,
The ignition timing correction amount KN is gradually reduced. If knocking occurs at the timing of t3 because the compression temperature correction amount Δτc is insufficient (that is, the target compression temperature τc decreases), knocking is stopped by increasing the ignition timing correction amount KN again. At this time, the compression temperature correction amount Δτc is larger than that at the time of the previous knock occurrence, and the target compression temperature τc is correspondingly lower. Therefore, the ignition timing correction amount KN at the time when the knock generation stops is smaller than the previous time.

Thereafter, by repeating the same control for the occurrence of knock, the ignition timing correction amount KN becomes smaller in response to the compression temperature correction amount Δτc becoming larger. From the ignition timing correction amount KN, the compression temperature correction amount Δτc
As a result, no knock occurs even if the ignition timing correction amount KN becomes zero. In other words, in the present embodiment, knock can be avoided by reducing the compression temperature with respect to the occurrence of knock (there is two avoidance means against knock occurrence). Knock avoidance becomes possible.

Referring to FIG. 17, a knock signal is read in step 41, and the knock signal is compared with the slice level in step 42. If the knock signal exceeds the slice level (knock occurs), step 4
Proceeding to 3, the ignition timing correction amount KN is compared with the maximum ignition timing correction amount KNMAX. If KN <KNMAX,
Proceeding to step 44, the ignition timing correction amount KN is set to a fixed amount K
Increase by NINC (however, the value after the increase is KNM
When it becomes AX or more, it is limited to KNMAX). This is to gradually increase the ignition timing correction amount KN with the maximum value KNMAX as a limit during knock occurrence (t in FIG. 18).
1 to just before t2, t3 to just before t4, t5
To just before t6).

On the other hand, when knocking stops due to an increase in the ignition timing correction amount KN, the knock signal falls below the slice level, and
In this case, the process proceeds from step 42 to step 45, and it is determined whether or not knocking has been performed for the first time (first time). If it is the first time, the routine proceeds to step 46, where the compression temperature correction amount Δτc is increased by a fixed amount ΔτcADD (however, when the increased value is equal to or larger than the maximum value ΔτcMAX, it is limited to the maximum value ΔτcMAX). this is,
The ignition timing correction amount is replaced with the compression temperature correction amount at the timing when knocking no longer occurs (t in FIG. 18).
2, timings of t4 and t6).

It is not the first time without knock occurrence (2
At the time (after the first time), the routine proceeds from step 45 to step 47, where the ignition timing correction amount KN is compared with a minimum value of 0. K
If N> 0, the routine proceeds to step 48, where the ignition timing correction amount KN is reduced by a fixed amount KNDEC (however, if the value after the reduction becomes a negative value, it is limited to the minimum value of 0). . This means that the ignition timing correction amount KN is gradually reduced with 0 as a limit while knock does not occur (immediately after t2 to immediately before t3 and immediately after t4 to immediately before t5 in FIG. 18).

The compression temperature correction amount Δτc and the ignition timing correction amount KN calculated in this manner are stored in the RAM. Among them, in step 4 in FIG. 2, the correction amount Δτc is calculated from the target compression temperature (map value). The compression temperature is corrected to decrease by subtracting only the compression temperature.

The ignition timing correction amount KN is added to the basic ignition timing value ADV0 by an ignition timing calculation routine (not shown) to calculate an output ignition timing ADV (= ADV0 + KN). The ignition timing is controlled so as to reach the timing ADV (ignition advance value).

The ignition timing correction amount KN is the maximum value KNM.
Since the ignition timing is limited between AX and the minimum value of 0, the ignition timing cannot be further delayed after the ignition timing correction amount KN reaches the maximum value KNMAX at the time of knocking.
When knocking subsequently occurs, knocking cannot be stopped. Therefore, in this case, the process proceeds from step 43 to step 49, and the compression temperature correction amount Δτc and its maximum value Δτc
By comparing τcMAX, if Δτc <ΔτcMAX,
Proceeding to step 50, the compression temperature correction value Δτc is increased by a fixed amount ΔτcINC (ΔτcINC <ΔτcADD) (however, when the increased value is equal to or greater than the maximum value ΔτcMAX, the compression temperature correction value Δτc is limited to the maximum value ΔτcMAX). If the occurrence of knocking seems to continue due to the increase in the compression temperature correction amount Δτc, the compression temperature correction amount Δτc is further increased by a constant amount ΔτcINC. Thus, the target temperature τ
Since c decreases, knocking eventually stops. When feedback control of ignition timing is no longer effective,
By operating another knock avoiding means (compression temperature feedback control means), knock is avoided.

Similarly, after the ignition timing correction amount KN reaches the minimum value of 0 when no knock occurs, the process proceeds from step 47 to step 51, where the compression temperature correction amount Δτc is compared with the minimum value of 0, and Δτc If> 0, the routine proceeds to step 52, where the compression temperature correction value Δτc is set to a fixed amount ΔτcDEC (Δτc
cDEC ≦ ΔτcINC) (however, when the reduced value becomes a negative value, it is limited to 0).

Here, the operation of the present embodiment will be described.
In conventional gasoline engines, only controlling the air-fuel ratio and ignition timing (and the degree of stratification of air and fuel) among the parameters related to the combustion state did not actively control the compression temperature. However, according to the present embodiment, by controlling the compression temperature directly related to the combustion state, the combustion state can be kept constant irrespective of operating conditions and external environmental requirements such as the outside air temperature.

For example, if a lower temperature is set as the target compression temperature so that knock does not occur in the knock region, even if the outside air temperature becomes high in the knock region, the compression temperature becomes lower than the outside air temperature. It becomes the same as at the time, and the occurrence of knock can be suppressed reliably. Further, knocking can be avoided without retarding the ignition timing or enriching the air-fuel ratio, so that a rise in exhaust gas temperature and emission of unburned HC can also be suppressed.

In this case, the control of the compression temperature is also performed during a steady state. If the control is performed during the steady state, the delay caused in the intake valve closing timing control device does not matter.

Further, in the stoichiometric air-fuel ratio region and the non-knock region, a low temperature within a range in which combustion is established is set as the target compression temperature τc, so that the cooling loss at the time of combustion at the stoichiometric air-fuel ratio can be reduced, and the fuel consumption can be reduced. improves.

In the lean air-fuel ratio range, a high temperature within a range where combustion is established is set as the target compression temperature τc, so that the combustion during the lean air-fuel ratio combustion can be improved. If the target air-fuel ratio (lean air-fuel ratio) is the same, the air-fuel ratio can be further set to the lean side by the amount of improvement in combustion.

Further, since the target compression temperature τc is calculated according to the engine speed NE and the target torque TT, the target compression temperature according to the operating conditions can be obtained.

Further, since the temperature rise due to the boost pressure increase is included in the compression temperature target value in advance, even when supercharging is performed to obtain high output in a high load region, Knock can be avoided without retarding the ignition timing or enriching the air-fuel ratio.

Further, even if it is to prevent knocking, if the feedback correction amount of the ignition timing is large (the ignition timing is greatly retarded at this time), the fuel consumption deteriorates and the exhaust temperature rises. According to the present embodiment, however, the feedback correction amount of the ignition timing is reduced by the amount corresponding to the replacement of the feedback correction amount by the compression temperature correction amount, whereby deterioration in fuel efficiency and increase in exhaust temperature can be suppressed. Further, even in a case where a more severe condition is applied to the knock, the occurrence of the knock can be avoided because there is still room for correction by the ignition timing.

In this case, by replacing the feedback correction amount of the ignition timing with the compression temperature correction amount, the target compression temperature is lowered, thereby producing an effect equivalent to lowering the compression ratio. This allows a higher compression ratio to be set, thereby greatly improving fuel efficiency.

In the embodiment, the above <1>, <2>,
In the three operating ranges of <3>, the case where the target compression temperature τc is calculated according to the engine speed NE and the target torque TT has been described, but simply, a constant value is set for each of the three operating ranges. You can set it.

Although the embodiment has been described with respect to an engine that performs supercharging, the present invention is also applicable to an engine that does not perform supercharging. The supercharging method is not limited to the supercharger.

[Brief description of the drawings]

FIG. 1 is an overall control system diagram of an embodiment.

FIG. 2 is a flowchart for explaining calculation of a target intake valve closing timing, a target throttle valve opening, and a target bypass valve opening;

FIG. 3 is a characteristic diagram of a target torque.

FIG. 4 is a characteristic diagram of a target driving force.

FIG. 5 is a characteristic diagram of a target compression temperature.

FIG. 6 is a characteristic diagram of an increase in compression temperature due to an increase in supercharging pressure.

FIG. 7 is a flowchart for explaining the calculation of the compression start temperature.

FIG. 8 is a characteristic diagram of a temperature rise of intake air due to a pumping loss.

FIG. 9 is a characteristic diagram of the temperature rise of intake air due to the flow energy of air.

FIG. 10 is a flowchart for explaining calculation of a target intake valve closing timing.

FIG. 11 is a characteristic diagram of a target intake valve closing timing under a constant rotation speed condition.

FIG. 12 is a characteristic diagram of a target intake valve closing timing under a constant torque condition.

FIG. 13 is a characteristic diagram of a target supercharging pressure.

FIG. 14 is a characteristic diagram of a target supercharging pressure under a condition of a constant rotation speed.

FIG. 15 is a characteristic diagram of a target bypass valve opening degree.

FIG. 16 is a characteristic diagram of a target bypass valve opening degree under the condition that the rotation speed is constant.

FIG. 17 is a flowchart for explaining calculation of an ignition timing correction amount and a compression temperature correction amount.

FIG. 18 is a waveform diagram for explaining movements of an ignition timing correction amount and a compression temperature correction amount when knock occurs.

FIG. 19 is a diagram corresponding to claims of the first invention.

[Explanation of symbols]

 7 Throttle valve 8 Throttle valve control device 15 Intake valve closing timing control device 21 ECM

 ────────────────────────────────────────────────── ─── Continued on the front page F-term (reference) 3G084 AA04 BA05 BA07 BA09 BA15 BA17 BA22 BA23 DA00 DA02 DA10 EB11 FA02 FA07 FA10 FA11 FA12 FA19 FA25 FA32 FA33 FA38 FA39 3G092 AA01 AA09 AA11 AA18 BA04 BA09 BB01 DA01 DC03 DC03 DC03 EA01 EA02 EA03 EA04 EA05 EA06 EA07 EC01 FA16 FA18 FA24 HA01Z HA03X HA04Z HA05Z HA06X HA10X HA13X HA13Z HA16X HB01X HC05Z HC09X HE01Z HE03Z HE05Z HE06Z HF08Z

Claims (10)

[Claims] 1. An intake valve closing timing control mechanism capable of variably controlling an intake valve closing timing, a throttle valve opening control mechanism capable of controlling a throttle valve opening independently of an accelerator pedal, and a base intake valve closing timing. Means for setting a target value of the compression temperature, which is the mixture temperature when the fuel is compressed to the top dead center without ignition in the standard state based on the reference value, and closing the intake valve based on the target value of the compression temperature and the compression start temperature. Means for calculating the timing; means for controlling the intake valve closing timing control mechanism so as to achieve the intake valve closing timing; and setting a target throttle valve opening based on the intake valve closing timing, engine speed and target torque. An engine combustion control device comprising: means for calculating; and means for controlling the throttle valve opening control mechanism so as to achieve the target throttle opening. 2. The combustion control device for an engine according to claim 1, wherein a lower temperature is set as the compression temperature target value so that knock does not occur at least in a knock region. 3. A control means for controlling a stoichiometric air-fuel ratio to be obtained in at least a part of an operating range, wherein the low temperature in the operating range of the stoichiometric air-fuel ratio and in a range where combustion is established in a non-knock range is reduced. The engine combustion control device according to claim 1, wherein the temperature is set as a target temperature value. 4. A means for controlling a lean air-fuel ratio to be obtained in at least a part of the operating range, wherein a high temperature within a range where combustion is established in the operating range of the lean air-fuel ratio is set as the compression temperature target value. The engine combustion control device according to claim 1, wherein the setting is performed. 5. The combustion control system for an engine according to claim 1, wherein said compression temperature target value is calculated according to an engine speed and a target torque. 6. The compressor according to claim 1, further comprising a supercharger, wherein the compression temperature target value is set to a value including a temperature rise accompanying a rise in supercharging pressure due to the operation of the supercharger. Engine combustion control device. 7. A knock detecting means, and means for feedback-correcting the ignition timing based on the knock detection signal so as not to cause knocking, so that the feedback correction amount of the ignition timing is reduced. 7. The engine combustion control apparatus according to claim 1, wherein the compression temperature correction value is corrected to a lower temperature side with the compression temperature correction value. 8. When the ignition timing correction amount is limited to its maximum value, after the ignition timing correction amount reaches its maximum value at the time of knocking, the compression temperature correction amount is increased by a constant amount. The engine combustion control device according to claim 7, characterized in that: 9. The engine according to claim 1, wherein the compression start temperature is a value obtained by adding a temperature rise of intake air due to a pumping loss to an intake air temperature. Combustion control device. 10. The method according to claim 1, wherein the compression start temperature is a value obtained by adding a temperature rise of the intake air due to the flow energy of the air to the intake air temperature. Engine combustion control device.