JP2006283618A - Control device for spark ignition type engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to improve fuel economy in a heavy load side by expanding operation zone in which compression self ignition operation is executable to the heavy load side and to materialize compression self ignition in wider operation zone. <P>SOLUTION: Intake air temperature T is maintained high in predetermined light load side operation zones D<SB>0</SB>, D<SB>1</SB>. Compression self ignition operation is executed to a predetermined heavy load operation zone D<SB>2</SB>by reducing intake air temperature T as load increases when load exceeds predetermined light load. In light load side in which combustion stability is bad, misfire in light load side can be prevented since intake air temperature is maintained high. In another hand, when engine load exceeds predetermined light load, combustion becomes slow since intake air temperature T drops as load increases. That is favorable for knocking countermeasures. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device for a spark ignition type engine, and more particularly, to a spark having an operation mode in which premixed compression auto-ignition combustion (HCCI) is performed. The present invention relates to a control device for an ignition engine.

In a spark ignition type engine, an engine having intake air heating means for heating intake air in order to accelerate the compression self-ignition timing is known. For example, in the technique disclosed in Patent Document 1, when shifting from a high load operation in which forced ignition is performed by spark ignition to a low load operation in which compression self-ignition operation is performed, the temperature of the air-fuel ratio is increased by increasing the temperature of the mixture. On the other hand, when shifting from low load operation to high load operation, the pumping loss is reduced between the misfire region and the knocking region by lowering the temperature of the mixture and changing the air-fuel ratio to the rich side. Both reduction and knocking prevention are achieved.
JP 2003-269201 A

  By the way, in order to expand the operation region in which the compression self-ignition operation can be performed, the air-fuel ratio and the intake air temperature are set between the operation region in which the compression self-ignition operation is performed and the operation region in which the forced ignition operation is performed. It is not sufficient to change only, and it is necessary to adjust the air-fuel ratio and the intake air temperature in accordance with the operation state even in the operation region where the compression self-ignition operation is executed.

  However, in the invention of Patent Document 1, control for changing the air-fuel ratio and the intake air temperature is not performed in the operation region in which the compression self-ignition operation is executed. For this reason, if the intake air temperature on the low load side is set high to prevent misfire, the region where knocking occurs is widened, but if the intake air temperature is lowered to avoid knocking on the high load side, misfire on the low load side will occur. Therefore, it is not possible to set a wide operation range in which the compression self-ignition operation can be performed.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a spark ignition engine control device capable of realizing compression self-ignition in a wider operating range.

  In order to solve the above problems, the present invention provides an intake air heating means for heating the intake air to the cylinder, an operating state detecting means for detecting the operating state of the engine, and an intake air heating means based on the detection of the operating state detecting means. By controlling the spark ignition type gasoline engine control device having a control means for performing compression self-ignition operation in a predetermined operation region, the intake air temperature is maintained at a high temperature on a predetermined low load side, and the predetermined The control means controls the intake air heating means so as to execute the compression self-ignition operation to a predetermined high load operation region by reducing the intake air heating as the load increases when the low load is exceeded. This is a control device for a spark ignition engine. In this aspect, in the operation region where the compression self-ignition operation is executed, the intake air temperature is maintained high on the low load side where the combustion stability is poor, so that misfire on the low load side can be prevented. On the other hand, if the engine load exceeds a predetermined low load, the intake air temperature decreases as the load increases, so that combustion becomes slow, which is advantageous as a countermeasure against knocking. As a result, it is possible to extend the operation range in which the compression self-ignition operation can be performed to the high load side, and to improve the fuel consumption on the high load side.

In a preferred embodiment, in the operation region where the compression self-ignition operation is performed, in the operation region where the maximum heat generation rate is after the compression top dead center, the intake air temperature is maintained at a predetermined high temperature, and as the engine load increases. Control means controls the intake air heating means to reduce intake air heating. In this aspect, even when the engine load increases, the compression self-ignition operation on the high load side can be executed. That is, as a result of diligent research by the present inventors, when the intake air heating is reduced as the load increases and the intake air temperature is lowered, the start of combustion is delayed, and the maximum heat generation rate ((J / deg · m ³ ) MAX) is obtained. It turns out that it moves toward compression bottom dead center. Therefore, by maintaining the intake air temperature at the maximum within a range where the maximum heat generation rate is after the compression top dead center, the compression self-ignition operation on the low load side is maintained and the intake air is increased as the engine load increases. By reducing the heating, it is possible to expand the operation range in which the compression self-ignition operation can be performed to the high load side.

  In a preferred embodiment, in the operation region where the compression self-ignition operation is performed, the control means is configured to maintain the intake air temperature at the lowest temperature at which the compression self-ignition is possible in the operation region where the maximum heat generation rate is before the compression top dead center. Controls the intake air heating means. In this aspect, by maintaining the intake air temperature at the minimum necessary temperature (for example, 270 ° C.), the compression self-ignition operation can be performed in a state of no load or close to it while suppressing adverse effects of reverse torque due to premature combustion to a minimum. Can be realized.

  In a preferred aspect, ignition promoting means for accelerating the ignition timing in the predetermined high load operation region is provided. In this aspect, when maintaining the compression self-ignition operation in the high load operation region, the ignition timing of the air-fuel mixture is promoted by the ignition facilitating means when the predetermined low load is exceeded. It becomes possible to suppress the slowness and output a high torque.

  In a preferred aspect, the ignition promoting means includes a plurality of spark plugs per cylinder and the control means for igniting the spark plugs at multiple points before the start of compression self-ignition. In this aspect, it is possible to reliably realize the ignition timing with a relatively simple configuration.

  In a preferred aspect, there is provided a combustion speed promoting means for accelerating the combustion speed of the air-fuel mixture after ignition in the predetermined high load operation region. In this aspect, when maintaining the compression self-ignition operation in the high load operation region, the combustion speed of the air-fuel mixture after ignition is promoted by the combustion speed acceleration means when the predetermined low load is exceeded. It is possible to suppress the combustion from becoming too slow, increase the combustion energy of the air-fuel mixture, and output a high torque.

  In a preferred aspect, the combustion speed promoting means includes a plurality of spark plugs per cylinder and the control means for igniting the spark plugs at multiple points after the start of compression self-ignition. In this aspect, it is possible to reliably promote the combustion speed with a relatively simple configuration.

  In a preferred embodiment, an external EGR system for returning EGR gas to the intake passage is provided, and the control means controls the external EGR system so that EGR gas is introduced into the intake passage at least on the high load side of the predetermined high load operation region. . In this aspect, in a predetermined high load operation region where the compression self-ignition is slow, the EGR gas is introduced by the external EGR system, so that the ignition timing by the ignition promoting means and the combustion speed by the combustion speed promoting means are moderately accelerated. While maintaining, knocking can be avoided and good exhaust performance can be obtained.

  In a preferred aspect, in the engine, the cylinder bore center of the cylinder is offset to the right side from the rotation center of the crankshaft when viewed from the side in which the rotation direction of the crankshaft is clockwise. In this aspect, when the cylinder bore center of the cylinder is offset from the rotation center of the crankshaft, the lifting speed of the piston is asymmetric with respect to the top dead center, and the descending speed of the piston in the expansion stroke is relatively slow. For this reason, since the combustion speed becomes relatively faster than the descending speed of the piston, it is possible to maintain a good combustion environment, and it becomes possible to increase the energy acting on the piston and improve the fuel consumption. .

  In a preferred embodiment, spark ignition is performed by stopping the intake air heating means in a high load region exceeding the predetermined high load operation region.

  As described above, in the present invention, it is possible to expand the operation range in which the compression self-ignition operation can be performed to the high load side and to improve the fuel consumption on the high load side. This produces a remarkable effect that compression self-ignition can be realized.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram illustrating a schematic configuration of a control device 10 according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view illustrating a structure of one cylinder of the four-cycle gasoline engine 20 according to FIG. .

  With reference to FIGS. 1 and 2, the illustrated control apparatus 10 includes a four-cycle gasoline engine 20 and a control unit 100 for controlling the engine 20.

  The engine 20 integrally includes a cylinder block 22 that rotatably supports the crankshaft 21 and a cylinder head 23 disposed on the upper portion of the cylinder block 22, and the cylinder block 22 and the cylinder head 23 include A plurality of cylinders 24 are provided.

  Each cylinder 24 is provided with a piston 26 connected to the crankshaft 21 via a connecting rod 25 and a combustion chamber 27 formed in the cylinder 24 by the piston 26. In the present embodiment, the geometric compression ratio of each cylinder 24 is set to 14.

  Referring to FIG. 2, in the engine 20 according to the present embodiment, the cylinder bore center Z of the cylinder 24 is the center of the crankshaft 21 as viewed from the side in which the rotation direction of the crankshaft 21 is clockwise (that is, the state of FIG. 2). It is offset from the center of rotation O to the right. This offset amount S is set to, for example, 1 mm to 2 mm when the bore diameter of the cylinder 24 is 70 mm.

  FIG. 3 is a model diagram of the piston in the present embodiment.

With reference to the figure, the connecting rod 25 and the piston 26 and A ₁ the distance of the rotation center of the rotation center of the connecting pin 25b that connects the connecting rod 25 and the crankshaft 21 of the connecting pin 25a for connecting the _rotation of the connecting pin 25b The distance between the center and the rotation center O of the crankshaft 21 is A ₂ , the offset amount is S, the angle between the vertical line LN1 passing through the connecting pin 25b and the connecting rod 25 is α, and the angular velocity of the crankshaft 21 is ω.

According to FIG. 3, the coordinates (Xp, Yp) of the rotation center of the connecting pin 25a and the coordinates (Xc, Yc) of the rotation center of the connecting pin 25b are the horizontal line passing through the center O of the crankshaft 21 and the cylinder bore center Z. If the intersection coordinates are (0, 0), (Xp, Yp) = (0, A ₂ cosωt + A ₁ cosα) (Equation 1)
(Xc, Yc) = (A ₂ sin ωt−S, A ₂ cos ωt) (Expression 2)
It becomes. The constraint condition of the piston 26 is
A ₂ sin ωt−S = A ₁ sin α (Expression 3)
It becomes. Here, if both sides of (Equation 3) are differentiated,

・・・（式４）
が得られる。

... (Formula 4)
Is obtained.

  Next, the Yp component of (Equation 1) is differentiated by t, and (Equation 4) is substituted to obtain the velocity v of the piston 26.

・・・（式５）
が得られる。また、（式３）より

... (Formula 5)
Is obtained. From (Equation 3)

・・・（式６）
であるから、（式６）を（式５）に代入すると、

... (Formula 6)
Therefore, if (Equation 6) is substituted into (Equation 5),

・・・（式７）
が得られる。

... (Formula 7)
Is obtained.

  FIG. 4 is a graph showing the piston speed with respect to the crank angle. FIG. 5 is a model diagram showing the relationship between the crank angle and the piston movement amount.

  4 and 5, as is clear from (Equation 5), when offset amount S = 0, since tan α = 0, the speed v of the piston 26 becomes equal to a sine wave.

On the other hand, when the offset amount S> 0, the waveform of the piston 26 becomes asymmetric according to the value of the second term of (Equation 5) and (Equation 7), and the point P ₁ where the piston 26 moves at the highest speed, P ₂ (contact point formed by a straight line passing through the top dead center of the piston 26 on the locus 25L of the connecting pin 25b) is asymmetrical. As a result, if the movement amounts Y ₁ and Y ₂ of the same amount of crank angle ωt (= 30 °) around the point P ₀ when the piston 26 is at the top dead center are considered, it is clear from FIG. Thus, the movement amount Y ₁ from the vicinity of the top dead center to the top dead center becomes relatively large, and the piston 26 moves at a high speed, whereas the movement amount Y ₂ after exceeding the top dead center. Will be relatively small and the piston 26 will move at a relatively slow speed.

  FIG. 6 is a schematic plan view showing the cylinder 24 in an enlarged manner.

  Referring to FIG. 6, a ceiling portion of combustion chamber 27 is formed for each cylinder 24 on the lower surface of cylinder head 23, and this ceiling portion has two inclined surfaces extending from the central portion to the lower end of cylinder head 23. It is a pent roof type.

  Two independent intake ports 28 and exhaust ports 29 are opened substantially symmetrically in the ceiling portion of the combustion chamber 27, and an intake valve 30 and an exhaust valve 31 are provided at the open ends of the ports 28 and 29. ing.

  A fuel injection valve 32 that receives a fuel injection pulse from the control unit 100 and injects fuel corresponding to the pulse width into the combustion chamber 27 is provided at the side of the combustion chamber 27.

  Referring also to FIG. 2, each cylinder 24 is provided with three spark plugs 34 that are fixed to the cylinder head 23 and emit a spark in the combustion chamber 27. The spark plugs 34 are arranged along the cylinder diameter parallel to the ridge line portion of the piston 26, the center one is disposed on the cylinder bore center Z, and both sides are disposed on the side edge of the combustion chamber 27. Each ignition plug 34 is connected to an ignition circuit 35 capable of controlling the ignition timing by electronic control. By controlling the ignition circuit 35 by the control unit 100, the ignition plug 34 is selectively ignited. To be controlled.

  Next, referring to FIG. 2, each of the intake valve 30 and the exhaust valve 31 of each cylinder 24 is provided with a known tappet unit 36. The tappet unit 36 is periodically driven by cams 37 a and 38 a of camshafts 37 and 38 of a valve mechanism provided in the cylinder head 23. The valve operating mechanism for the intake valve 30 is provided with a variable valve timing mechanism 40 that can change the opening / closing timing of the intake valve 30. The variable valve timing mechanism 40 has a valve according to the operating state over a first timing in which the intake valve opening timing is near the intake top dead center and a second timing in which the intake valve opening timing is advanced. The timing is changed.

  Next, referring to FIGS. 1 and 2, a branch intake pipe 43 of the intake manifold 42 is connected to the intake port 28 of the engine 20. The branch intake pipe 43 is provided for each cylinder 24 and is connected to the intake manifold 42 in a state where an equal-length intake path is formed. In the illustrated embodiment, each cylinder 24 is formed with a pair of intake ports 28, and the downstream end of the branched intake pipe 43 is bifurcated corresponding to the intake port 28 of each cylinder 24. Has been. An open / close valve 44 is provided at the upstream side merge portion of the branch intake pipe 43. The on-off valve 44 is embodied by a three-way solenoid valve, and is configured such that the actuator 45 can individually open and close the aggregate portion of the branch intake pipe 43 by a desired amount. On the other hand, a known swirl on / off valve 43a is provided at one branch portion of the branch intake pipe 43 branched into two branches as shown in FIG. The swirl on / off valve 43a is driven by an actuator 43b to open and close. When one of the branch portions of the branch intake pipe 43 is closed by the swirl on / off valve 43a, the swirl on / off valve 43a passes through the other branch. The swirl is generated in the combustion chamber 27 by the intake air, and the swirl is weakened as the swirl generation opening / closing valve 43a is opened.

  An intake passage 46 for introducing fresh air into the intake manifold 42 is connected to the upstream side of the intake manifold 42. A throttle valve 47 is provided in the intake passage 46. A three-way solenoid valve 48 is provided on the upstream side of the throttle valve 47, and a heater 50 as intake air heating means is provided in a bypass passage 49 connected to the three-way solenoid valve 48. Therefore, by switching the three-way solenoid valve 48, fresh fresh air can be introduced as it is into the intake manifold 42, or air heated by the heater 50 can be introduced into the intake manifold 42. .

  Next, as shown in FIG. 1, the exhaust port 29 is connected to a bifurcated branch exhaust pipe 51 formed in pairs for each cylinder 24. The downstream end of each branch exhaust pipe 51 is connected to the exhaust manifold 52. An exhaust passage 53 for discharging burned gas is connected to the exhaust manifold 52.

  Next, referring to FIGS. 1 and 2, an external EGR system 60 is provided between the intake manifold 42 and the exhaust manifold 52 to recirculate the exhausted burned gas to the intake manifold 42.

  The external EGR system 60 is connected to a recirculation passage 61 formed between the intake manifold 42 and the exhaust manifold 52, and includes an EGR cooler 62, an EGR valve 63, and an actuator 64 that drives the EGR valve 63. Valve system.

  FIG. 7 is a block diagram showing a configuration of an intake air heating system 70 as intake air heating means according to the embodiment of FIG.

  Referring to FIG. 7, a three-way solenoid valve 48 is provided in the intake passage 46 upstream of the throttle valve 47, and a heater 50 is provided in a bypass passage 49 connected to the three-way solenoid valve 48. ing. The three-way solenoid valve 48 is configured to be able to change the valve opening ratio under the control of the control unit 100, similarly to the on-off valve 44. Therefore, by switching the three-way solenoid valve 48, outside air can be introduced into the intake manifold 42 at a desired rate, or air heated by the heater 50 can be introduced into the intake manifold 42. .

  Further, a heating passage 71 is branchedly connected to the intake passage 46. In the middle of the heating passage 71, a cooling water heat exchanger 72 and an exhaust heat exchanger 73 are connected.

  The heating passage 71 is for returning the heat absorbed through the heat exchangers 72 and 73 to the intake side. A branch pipe 71 a branched for each cylinder 24 is provided on the downstream side of the heating passage 71, and each branch pipe 71 a is connected to a port on the intake side of the corresponding on-off valve 44.

  The cooling water heat exchanger 72 is connected to the water cooling system 74 of the engine 20 to absorb the heat absorbed by the cooling water returning from the engine 20 to the radiator (not shown) into the intake air passing through the heating passage 71. Is.

  The exhaust heat exchanger 73 is connected to the exhaust passage 53 of the engine 20 to absorb the heat of burned gas into the intake air passing through the heating passage 71. The exhaust heat exchanger 73 is disposed on the downstream side of the cooling water heat exchanger 72 in the heating passage 71.

  In the present embodiment, the heater 50 and the heat exchangers 72 and 73 described above constitute a main part of the intake air heating system 70.

  Referring to FIG. 1, in order to detect the operating state of engine 20, air flow sensor SW1 is provided in intake passage 46, and intake temperature sensor SW2 for predicting the in-cylinder temperature downstream of on-off valve 44. (See FIG. 2). The cylinder block 22 is provided with a crank angle sensor SW3 for detecting the rotation speed of the crankshaft 21 and an engine water temperature sensor SW4 for detecting the temperature of the cooling water (see FIG. 2). Further, the exhaust passage 53 is provided with an oxygen concentration sensor SW5 for controlling the air-fuel ratio. Further, the heater 50 is provided with a temperature sensor SW7 so that the temperature of the intake air in the bypass passage 49 heated by the heater 50 can be detected.

  The engine 20 is provided with a control unit 100 as control means. The control unit 100 includes an air flow sensor SW1, an intake air temperature sensor SW2, a crank angle sensor SW3, an engine water temperature sensor SW4, an oxygen concentration sensor SW5, an accelerator opening sensor SW6 for detecting engine load, and a temperature sensor SW7. Connected as. Each of these sensors SW1 to SW7 is a specific example of the driving state detection sensor in the present embodiment. On the other hand, the control unit 100 includes an actuator 45 of the on-off valve 44, an actuator of the throttle valve 47, a variable valve timing mechanism 40, an actuator 43b of the swirl generating on-off valve 43a, a three-way electromagnetic valve 48 of the intake passage 46, a heater 50, an external An actuator 64 of the EGR system 60 is connected as a control element.

  Referring to FIG. 1, a control unit 100 has a CPU 101, a memory 102, an interface 103, and a bus 104 for connecting these units 101 to 103. The control unit 100 operates according to programs and data stored in the memory 102. The operation state determination means for determining is functionally configured.

  FIG. 8 is a characteristic diagram illustrating an example of operation region setting for performing control according to the operation state according to the embodiment of FIG. 1. FIG. 9 is a characteristic diagram of the air-fuel ratio, intake air temperature, and EGR gas introduction amount set in the partial load operation region D of FIG.

  Referring to FIG. 8, in the illustrated embodiment, the compression self-ignition operation is executed in the partial load operation region D where the engine speed N is equal to or less than the predetermined engine speed N1, and the forced ignition operation by spark ignition is performed in the remaining region. Is set to run.

In the partial load operation region D in which the compression self-ignition operation is executed, the air-fuel ratio is set so as to rise almost linearly to the rich side as it goes from the low load side to the high load side, as shown in FIG. Has been. On the other hand, with respect to the intake air temperature T, in the operation regions D ₁ and D ₀ below a predetermined low load, as shown in FIG. 9, the intake air temperature T is kept relatively high, and the high load operation region D exceeding this low load. _{On the second} side, the intake air temperature T is set to decrease as the load increases.

  10 to 12 are graphs showing the relationship between the crank angle and the heat generation rate dQ / dθ, which are the basis of the control conditions set in the control unit 100. These graphs are obtained based on the research results of the present inventors, and a control map based on these graphs is stored in the memory 102 of the control unit 100. In each figure, the curve indicated by the broken line indicates the characteristic when the minimum fuel injection amount capable of compression self-ignition is set when the throttle is fully opened, and the curve indicated by the solid line indicates the air-fuel ratio up to the knocking limit at the same intake air temperature T as the broken line. The characteristic when lowered is shown. Further, the curve sign indicated by the solid line is obtained by adding a subscript to the sign of the curve indicated by the broken line corresponding to the intake air temperature T.

Referring to FIG. 10, when engine 20 is operated in a no-load state by compression self-ignition, intake air temperature T needs to be set to T1 (= 270 ° C.). At this T1, the maximum heat generation rate (dQ / dθ) MAX is generated before the compression top dead center. Therefore, if the air-fuel ratio is lowered as it is, the reverse torque increases. Also, even at T2 (= 250 ° C), which is 20 ° C lower than T1, the maximum heat generation rate (dQ / dθ) MAX still occurs before the compression top dead center. Torque is generated. Therefore, in the present embodiment, as shown in FIG. 9, the operation region D in which the maximum heat generation rate (dQ / dθ) MAX occurs before the compression top dead center at the intake air temperature for performing the compression self-ignition operation. _{At 0} , the intake air temperature is set to the minimum temperature necessary for the compression self-ignition operation, and the air-fuel ratio is set to be extremely lean.

Next, referring to FIG. 11, when the load becomes high, the intake air temperature T is T3 (= 225 ° C.), T4 (= 205 ° C.), T5 (= 190 ° C.), T6 (= 175 ° C.), As shown by each curve of T7 (= 160 ° C.), the maximum heat release rate (dQ / dθ) MAX appears after compression top dead center. Therefore, in this embodiment, as shown in FIG. 9, in the operating region D _1, the intake air temperature T held at T3, and so as to increase the amount of fuel injection until knock marginal.

On the other hand, if it exceeds operating range D _2, by reducing the intake air temperature T gradually T4 later according to the load, while suppressing the occurrence of knocking, the compression-ignition operation capable operating region to the high load side It can be set widely.

  Next, referring to FIG. 12, when the intake air temperature characteristics T1 to T7 are overlapped, the heat generation rate dQ / dθ is approximately a predetermined value (about 80 J / deg · m 3), as indicated by a virtual line. A mountain-shaped knocking limit curve with a peak is drawn. Therefore, in this embodiment, the intake air temperature T is set to be reduced with the predetermined heat generation rate dQ / dθ (about 80 J / deg · m 3) as an upper limit. In FIG. 12, the straight line on the left side of the figure shows the combustion start timing at each intake air temperature T1 to T7, and the right straight line shows the combustion end (MFB = 95%) limit where the combustion fluctuation rate is less than 5%. Represents.

Referring to FIGS. 11 and 12, when the load state further increases and the intake air temperature T continues to be lowered along with this, the combustion of the air-fuel mixture delays the combustion start timing itself in proportion to the temperature decrease, and the maximum heat The incidence (dQ / dθ) MAX gradually approaches the compression bottom dead center. Therefore, as shown in FIG. 12, at a predetermined low temperature T8 (= 150 ° C.), the air-fuel ratio capable of compression self-ignition becomes A / F = 30 (λ = 2), and the maximum heat generation rate (dQ / dθ) MAX However, the crank angle exceeds 15 °. Therefore, in the present embodiment, in the case of a naturally aspirated engine having no external EGR, the upper limit of the operation region D _{2 in} FIG. 8 is determined with the air-fuel ratio being λ2, and the upper limit of the operation region D ₂ is exceeded. In the high load operation region, the forced ignition operation by spark ignition is set to be executed.

  As described above, as the intake air temperature T decreases, the combustion start timing is delayed, and the maximum heat generation rate (dQ / dθ) MAX also appears in the crank angle shifted from the compression top dead center toward the compression bottom dead center. It becomes like this. Therefore, in this embodiment, the operating region in which compression self-ignition can be performed is expanded to the high load side by increasing the ignition timing and the combustion speed by various methods.

  FIG. 13 is a diagram showing the ignition timing according to the embodiment of the present invention.

8 and 9, and FIG. 13, the engine, when a transition is made to the operating region D ₂ of the high-load side during compression-ignition operation by the intake air temperature T is lowered, the combustion start is delayed, The maximum heat generation rate (dQ / dθ) MAX is considerably delayed as indicated by a virtual line shown in FIG. In the present embodiment, in the operating region D ₂ executes the multipoint ignition SP _bf a maximum heat release rate (dQ / dθ) MAX than appear before the crank angle CA, to promote ignition timing Is set to Thereby, the ignition timing by compression self-ignition is accelerated like the characteristic shown with a continuous line from the characteristic shown with a virtual line.

Further, in the operating region D _2, perform the multipoint ignition SP _af crank angle CA after maximum heat generation rate (dQ / dθ) MAX appears, is set so as to promote the combustion rate. Thereby, the combustion speed by compression self-ignition is accelerated like the characteristic shown with a continuous line from the characteristic shown with a virtual line.

By the way, when the ignition promoting means and the combustion speed promoting means as shown in FIG. 13 are employed, it may be assumed that knocking is likely to occur due to multipoint ignition. Therefore, in the present embodiment, as shown in FIG. 9, in the operating region D _2, in the high-load side so as to introduce external EGR.

  In FIG. 13, SP indicates spark assist ignition before compression top dead center.

As described above, in the present embodiment, in the operation region D in which the compression self-ignition operation is performed, the intake air temperature T is maintained high in the operation regions D ₀ and D ₁ on the low load side with poor combustion stability. In addition, misfire on the low load side can be prevented. On the other hand, when the engine load exceeds a predetermined low-load operating region D _1, since the intake air heating with increasing load is reduced, lower the intake air temperature T, the combustion becomes slow, knocking measures is advantageous. As a result, it is possible to expand the operation region D in which the compression self-ignition operation can be performed to the high load side, and to improve the fuel consumption on the high load side.

In this embodiment in particular, in the operating region D to perform compression self-ignition operation, the operating region D ₁ the maximum heat generation rate is (dQ / dθ) MAX becomes a point after a compression TDC, a high intake air temperature T a predetermined temperature The control unit 100 controls the heater 50 so as to reduce intake air heating as the engine load increases. For this reason, in this embodiment, even if the engine load increases, it becomes possible to execute the compression self-ignition operation on the high load side. That is, as shown in FIGS. 10 to 12, when the intake air heating is reduced as the load increases, the combustion start is delayed, and the maximum heat generation rate ((J / deg · m ³ ) MAX) (dQ / dθ) It was found that MAX moved toward compression bottom dead center. Therefore, by maintaining the intake air temperature T at the maximum within the range where the maximum heat generation rate (dQ / dθ) MAX is after the compression top dead center, the compression self-ignition operation on the low load side is maintained and the engine By reducing the intake air heating as the load increases, the operation region D in which the compression self-ignition operation can be performed can be expanded to the high load side.

Further, in the present embodiment, in the operation region D in which the compression self-ignition operation is performed, the compression self-ignition is possible in the operation region D ₀ where the maximum heat generation rate (dQ / dθ) MAX is before the compression top dead center. The control unit 100 controls the heater 50 so as to maintain the intake air temperature T at a minimum temperature. For this reason, in the present embodiment, by maintaining the intake air temperature T at a necessary minimum temperature (for example, 270 ° C.), the adverse effect of reverse torque due to premature combustion is suppressed to a minimum, and in an unloaded state or a state close thereto. A compression self-ignition operation can be realized.

  Further, in the present embodiment, the control shown in FIG. 13 is performed as an ignition promoting means for accelerating the ignition timing in the predetermined high load operation region D. For this reason, in this embodiment, when maintaining the compression self-ignition operation in the high load operation region D, the ignition timing of the air-fuel mixture is promoted when the predetermined low load is exceeded. It becomes possible to suppress the slowness and output a high torque.

  In particular, in the present embodiment, the ignition promoting means includes a plurality of spark plugs 34 per cylinder and the control unit 100 that ignites the spark plugs 34 at multiple points before the start of compression self-ignition. For this reason, in this embodiment, it is possible to reliably realize the ignition timing with a relatively simple configuration.

  Further, in the present embodiment, the control shown in FIG. 13 is performed as a combustion speed promoting means for promoting the combustion speed of the air-fuel mixture after ignition in the predetermined high load operation region D. For this reason, in the present embodiment, when maintaining the compression self-ignition operation in the high load operation region D, the combustion speed of the air-fuel mixture after ignition is promoted at a point in time when the predetermined low load is exceeded. It is possible to suppress the engine from becoming excessively slow, increase the combustion energy of the air-fuel mixture, and output a high torque.

  In particular, in the present embodiment, the combustion speed promoting means includes a plurality of spark plugs 34 per cylinder and the control unit 100 that ignites the spark plugs 34 at multiple points after the start of compression self-ignition. For this reason, in the present embodiment, it is possible to surely promote the combustion speed with a relatively simple configuration.

Further in this embodiment, the outside EGR system 60 is provided, the predetermined high-load operating region D ₂ of at least a high load side in the control so as to introduce the EGR gas into the intake passage 46 units for recirculating EGR gas to the intake passage 46 100 controls the external EGR system 60. Therefore, in this embodiment, the compression of the predetermined ignition is slow high-load operation region D ₂ of the high-load side, since the EGR gas is introduced by an external EGR system 60, the ignition timing and combustion speed by ignition facilitating unit It is possible to avoid knocking while maintaining moderate acceleration of the combustion rate by the accelerating means and to obtain good exhaust performance.

  Particularly in the present embodiment, the engine 20 has the cylinder bore center Z of the cylinder offset from the rotation center O of the crankshaft 21 to the right as viewed from the side in which the rotation direction of the crankshaft 21 is clockwise. For this reason, in the present embodiment, the cylinder bore center Z of the cylinder 24 is offset from the rotation center O of the crankshaft 21, so that the lifting speed of the piston 26 becomes asymmetric with respect to the top dead center, and the piston 26 in the expansion stroke The descending speed is relatively slow. For this reason, since the combustion speed is relatively faster than the descending speed of the piston 26, it is possible to maintain a good combustion environment, and the energy acting on the piston 26 is increased, so that the fuel consumption can be improved. become.

  In the present embodiment, in a high load region exceeding the predetermined high load operation region D, the heater 50 is stopped and spark ignition is executed.

  As described above, according to the present embodiment, it is possible to expand the operation region in which the compression self-ignition operation can be performed to the high load side, and to improve the fuel efficiency on the high load side. This produces a remarkable effect that compression self-ignition can be realized.

It is a block diagram which shows schematic structure of the control apparatus which concerns on one Embodiment of this invention. 2 is a schematic cross-sectional view showing the structure of one cylinder of the four-cycle gasoline engine according to FIG. 1. It is a model figure of the piston in this embodiment. It is a graph showing the speed of the piston with respect to a crank angle. It is a model figure which shows the relationship between a crank angle and piston movement amount. It is a plane schematic diagram expanding and showing a cylinder. It is a block diagram which shows the structure of the intake-air heating system as an intake-air heating means which concerns on embodiment of FIG. It is a characteristic view which shows an example of the driving | operation area | region setting for performing control according to the driving | running state which concerns on embodiment of FIG. FIG. 9 is a characteristic diagram of air-fuel ratio, intake air temperature, and EGR gas introduction amount set in the partial load operation region of FIG. 8. It is a graph which shows the relationship between the crank angle used as the basis of the control conditions set to a control unit, and a heat release rate. It is a graph which shows the relationship between the crank angle used as the basis of the control conditions set to a control unit, and a heat release rate. It is a graph which shows the relationship between the crank angle used as the basis of the control conditions set to a control unit, and a heat release rate. It is a figure which shows the ignition timing which concerns on embodiment of this invention.

Explanation of symbols

20 4-cycle gasoline engine 21 Crankshaft 24 Cylinder 26 Piston 27 Combustion chamber 34 Spark plug 46 Intake passage 50 Heater (an example of intake air heating means)
60 External EGR system (an example of an external EGR device)
100 Control unit CA Crank angle D Partial load operation region D ₀ , D ₁ Low load operation region D ₂ High load operation region
dQ / dθ Heat generation rate (dQ / dθ) MAX Maximum heat generation rate N Engine speed O Center of rotation S Offset amount SW1 Air flow sensor (an example of operation state detection means)
SW2 intake air temperature sensor (an example of operation state detection means)
SW3 Crank angle sensor (an example of operation state detection means)
SW4 engine water temperature sensor (an example of operation state detection means)
SW5 Oxygen concentration sensor (an example of operation state detection means)
SW6 Accelerator opening sensor (an example of operation state detection means)
T Intake temperature Z Cylinder bore center ωt Crank angle

Claims (10)

Intake air heating means for heating the intake air to the cylinder;
An operating state detecting means for detecting the operating state of the engine;
In a control device for a spark ignition gasoline engine, comprising: a control means for executing a compression self-ignition operation in a predetermined operating region by controlling the intake air heating means based on the detection of the operating state detecting means;
On the predetermined low load side, the intake air temperature is maintained at a high temperature, and when the predetermined low load is exceeded, the compression self-ignition operation is executed up to a predetermined high load operation region by reducing the intake air heating as the load increases. A control device for a spark ignition engine, wherein the control means controls the intake air heating means. The control device for the spark ignition engine according to claim 1,
In the operation region where the compression self-ignition operation is executed, in the operation region where the maximum heat generation rate is after compression top dead center, the intake air temperature is maintained at a predetermined high temperature, and the intake air heating is reduced as the engine load increases. A control device for a spark ignition engine, wherein the control means controls the intake air heating means. The control device for the spark ignition engine according to claim 2,
In the operation region where the compression self-ignition operation is performed, in the operation region where the maximum heat generation rate is before the compression top dead center, the control means is the intake air heating means so as to maintain the intake air temperature at the lowest temperature capable of compression self-ignition. A control device for a spark ignition engine characterized by controlling the engine. The control device for a spark ignition engine according to any one of claims 1 to 3,
A control device for a spark ignition type engine, characterized by comprising an ignition acceleration means for accelerating an ignition timing in the predetermined high load operation region. The control device for the spark ignition engine according to claim 4,
The ignition accelerating means includes a plurality of spark plugs per cylinder and the control means for igniting the spark plugs at multiple points before the start of compression self-ignition. . The control device for a spark ignition engine according to any one of claims 1 to 7,
A control device for a spark ignition type engine, characterized by comprising combustion speed promoting means for accelerating the combustion speed of the air-fuel mixture after ignition in the predetermined high load operation region. The control device for the spark ignition engine according to claim 6,
The combustion speed accelerating means is composed of a plurality of spark plugs per cylinder and the control means for igniting the spark plugs at multiple points after the start of compression self-ignition. . The control device for a spark ignition engine according to any one of claims 4 to 7,
An external EGR system for returning EGR gas to the intake passage is provided,
A control device for a spark ignition engine, wherein the control means controls the external EGR system so that EGR gas is introduced into the intake passage at least on the high load side of the predetermined high load operation region. The control device for a spark ignition engine according to any one of claims 1 to 8,
The spark ignition engine control device according to claim 1, wherein the cylinder bore center of the cylinder is offset to the right side from the rotation center of the crankshaft when viewed from the side where the rotation direction of the crankshaft is clockwise. The control device for a spark ignition engine according to any one of claims 1 to 9,
The spark ignition type engine control device is characterized in that in a high load region exceeding the predetermined high load operation region, the intake air heating means is stopped to perform spark ignition.

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