JP5552869B2 - Engine control device - Google Patents

Description

  The present invention includes a plurality of intake valves and a plurality of exhaust valves per cylinder, a timing variable mechanism that variably sets the operation timings of the intake valves and the exhaust valves, and the exhaust valve as well as the exhaust stroke. An opening / closing switching mechanism that can switch between opening the valve in the stroke or opening only in the exhaust stroke, and valve control that controls the opening / closing operation of the intake valve and the exhaust valve by driving the timing variable mechanism and the opening / closing switching mechanism. And an engine control apparatus configured to perform compression self-ignition combustion in an HCCI region set in an operation region including at least a partial load region of the engine.

  Conventionally, in the field of gasoline engines, for example, a combustion mode in which an air-fuel mixture is forcibly ignited by spark discharge from an ignition plug has been common, but in recent years, instead of such spark ignition combustion, so-called compression self Research is underway to apply ignition combustion to gasoline engines. In this compression self-ignition combustion, the air-fuel mixture generated in the cylinder (combustion chamber) is compressed by a piston, and the air-fuel mixture is self-ignited regardless of spark ignition in a high temperature / high pressure environment. . Compressed self-ignition combustion is combustion in which self-ignition occurs simultaneously at various locations in the cylinder, and is said to have a shorter combustion period and higher thermal efficiency than combustion by spark ignition.

  For example, in Patent Document 1 below, the exhaust valve is opened not only in the exhaust stroke but also in the intake stroke, and the high-temperature burned gas once exhausted is caused to flow backward from the exhaust port into the cylinder, thereby increasing the in-cylinder temperature. In order to promote the self-ignition of the air-fuel mixture.

JP 2007-132319 A

  If the exhaust valve is opened during the intake stroke and a high-temperature burned gas is introduced into the cylinder as in the above-mentioned Patent Document 1, the air-fuel mixture is generated in the low load region of the engine where the air-fuel mixture is difficult to self-ignite. It is possible to effectively promote self-ignition and reliably cause compression self-ignition combustion. However, when the operation of introducing the burned gas into the cylinder as described above is continued up to an operation region where the load is relatively high (that is, the amount of fuel injection is large), the air-fuel mixture is self-ignited. It may be promoted excessively to cause abnormal combustion such as premature ignition.

  The present invention has been made in view of the above circumstances, and by appropriately controlling the amount of burned gas introduced into the cylinder according to the load, proper compression self-ignition combustion is wider. An object of the present invention is to provide an engine control device that can be operated in a load range.

In order to solve the above problems, the present invention includes two intake valves and two exhaust valves per cylinder, and a timing variable mechanism that variably sets the operation timing of the intake valves and the exhaust valves. And an intake side opening / closing switching mechanism that can switch whether or not the intake valve opens during the intake stroke, and the exhaust valve is opened not only in the exhaust stroke but also in the intake stroke, or opened only in the exhaust stroke. An exhaust side opening / closing switching mechanism capable of switching whether to valve, and a valve control means for controlling the opening / closing operation of the intake valve and the exhaust valve by driving the timing variable mechanism , the intake side opening / closing switching mechanism , and the exhaust side opening / closing switching mechanism ; And an engine control device configured to perform compression self-ignition combustion in an HCCI region set in an operation region including at least a partial load region of the engine. Te, the HCCI region, the relatively low load and low-load region, the first medium load range of a load higher than the low-load region, and a second medium load range of a load higher than the first medium load range, The valve control means is divided into a plurality of load areas including a third medium load area having a higher load than the second medium load area and a high load area having a higher load than the third medium load area. In the low load region, one intake valve and two exhaust valves in each cylinder begin to open during the intake stroke, and the opening timing of the intake valve and the exhaust valve and the valve open during the exhaust stroke By setting the closing timing of the exhaust valve to a timing separated by a predetermined period across the exhaust top dead center, a negative overlap period in which both the intake valve and the exhaust valve are closed is formed , and the first in the HCCI region is set . in the middle load region, the number of intake and exhaust valves to be opened during the intake stroke In addition, the number of intake valves opened during the intake stroke in the second medium load region in the HCCI region is set to two and opened during the intake stroke. The number of exhaust valves to be valved is one, the negative overlap period is formed, and the number of intake valves that are opened during the intake stroke in the third middle load region in the HCCI region is two. The number of exhaust valves opened during the intake stroke is made zero, the negative overlap period is formed, and the number of intake valves opened during the intake stroke in the high load region within the HCCI region is two. In addition, the number of exhaust valves that are opened during the intake stroke is reduced to zero, and when the load increases, the closing timing of the exhaust valves that are opened during the exhaust stroke and the intake valves that are opened during the intake stroke are reduced . Change the opening time in a direction that approaches the exhaust top dead center. By that, is characterized in that the gradually reducing the negative overlap period (claim 1).

According to the present invention, in the low load region in the HCCI region, the two exhaust valves in each cylinder are opened not only in the exhaust stroke but also in the intake stroke, and the number of intake valves opened during the intake stroke is one. In addition, since a so-called negative overlap period is provided in which both the intake valve and the exhaust valve are closed before and after exhaust top dead center, a large amount of burned gas can be introduced into the cylinder, The proportion of fresh air in the can can be made relatively small. This greatly increases the in-cylinder temperature and creates an environment in which the air-fuel mixture easily ignites. Therefore, even in a situation where the load is low and the fuel injection amount is small, the compression self-ignition combustion is surely caused. it can.

In the regions where the load is higher than the low load region ( first, second, third medium load region and high load region), the number of intake valves that are opened during the intake stroke is increased according to the increase in load. While increasing the number from 1 to 2 and gradually reducing the number of exhaust valves that open during the intake stroke from 2 to 1 to 0, and further shortening the negative overlap period, burned gas in the cylinder and new The ratio of the qi can be adjusted appropriately according to the load, and proper compression self-ignition combustion can be continued even in a situation where the load has increased to some extent.

In the present invention, preferably, a period from a closing timing of an exhaust valve that opens during an exhaust stroke to an exhaust top dead center in the low load region and the first, second, and third medium load regions in the HCCI region. The period from the earlier opening timing of the intake valve and the exhaust valve that are opened during the intake stroke to the exhaust top dead center is set to be substantially the same ( Claim 2 ).

  According to this configuration, it is possible to effectively prevent an increase in pumping loss that may occur during the period while introducing the burned gas into the cylinder using the negative overlap period.

The geometric compression ratio of the engine according to the present invention is preferably 15 or more and 22 or less ( Claim 3 ).

  When the configuration of the present invention is applied to such an engine having a relatively high compression ratio, a method of opening the exhaust valve during the intake stroke in order to introduce burned gas into the cylinder (so-called exhaust double opening method) ) Can be appropriately performed over a wide load range while fully utilizing the advantages of the above.

  As described above, according to the engine control apparatus of the present invention, by appropriately controlling the amount of burned gas introduced into the cylinder in accordance with the load, appropriate compression self-ignition combustion can be performed with a wider load. Can be done in the area.

It is a figure showing the whole engine composition concerning one embodiment of the present invention. It is a schematic diagram which shows the kind of variable mechanism applied to the intake / exhaust valve of the said engine. It is a block diagram which shows the control system of the said engine. It is a figure which shows an example of the driving | operation area | region map of the said engine. It is a flowchart which shows the procedure of the control operation performed in the said engine. It is a figure for demonstrating the content of the opening / closing pattern A of the intake / exhaust valve performed in the low load area | region R1 of FIG. It is a figure for demonstrating the content of the opening / closing pattern B of the intake / exhaust valve performed in 1st middle load area | region R2a of FIG. It is a figure for demonstrating the content of the opening / closing pattern C of the intake / exhaust valve performed in 2nd middle load area | region R2b of FIG. It is a figure for demonstrating the content of the opening / closing pattern D of the intake / exhaust valve performed in 3rd middle load area | region R2c of FIG. It is a figure for demonstrating the content of the opening / closing pattern E of the intake / exhaust valve performed in the high load area | region R3 of FIG. It is a graph which shows the measurement result of the fresh air filling rate obtained when an intake / exhaust valve is controlled along each said opening / closing pattern. It is a graph which shows the measurement result of the combustion gravity center position obtained when the intake / exhaust valve is controlled along each opening / closing pattern.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing an overall configuration of an engine according to an embodiment of the present invention. The engine shown in the figure is a reciprocating piston type multi-cylinder gasoline engine mounted on a vehicle as a power source for driving driving. An engine body 1 of this engine includes a cylinder block 3 having a plurality of cylinders 2 (only one of which is shown in the drawing) arranged in a direction orthogonal to the paper surface, and a cylinder head 4 provided on the upper surface of the cylinder block 3. And a piston 5 inserted in each cylinder 2 so as to be slidable back and forth. In addition, the fuel supplied to the engine body 1 may be anything that contains gasoline as a main component, and the contents may be all gasoline, or gasoline containing ethanol (ethyl alcohol) or the like. But you can.

  The piston 5 is connected to the crankshaft 7 via a connecting rod 8, and the crankshaft 7 rotates around the central axis in accordance with the reciprocating motion of the piston 5.

  A combustion chamber 6 is formed above the piston 5, an intake port 9 and an exhaust port 10 are opened in the combustion chamber 6, and an intake valve 11 and an exhaust valve 12 that open and close the ports 9 and 10 are connected to the cylinder head 4. Are provided respectively. The illustrated engine is a so-called double overhead camshaft (DOHC) engine, and two intake valves 11 and two exhaust valves 12 are provided for each cylinder (see FIG. 2).

  The intake valve 11 and the exhaust valve 12 are driven to open and close in conjunction with the rotation of the crankshaft 7 by valve mechanisms 13 and 14 including a pair of camshafts (not shown) disposed in the cylinder head 4. The

  A VVT 15 is incorporated in the valve operating mechanism 13 for the intake valve 11. The VVT 15 is called a variable valve timing mechanism that can continuously change the operation timing of the intake valve 11 and corresponds to a timing variable mechanism according to the present invention. Further, the valve operating mechanism 14 for the exhaust valve 12 incorporates a VVT 17 that is a timing variable mechanism similar to the VVT 15.

  The VVT 15 is provided so that the operation timings of all the intake valves 11 of the engine can be changed at once, and the VVT 17 can be changed all of the operation timings of all the exhaust valves 12 of the engine. Is provided. When these VVT 15 and VVT 17 are driven, the operation timing of the pair of intake valves 11 and the operation timing of the pair of exhaust valves 12 in each cylinder 2 are simultaneously changed. As a result, the lift amount is increased in each valve. The opening timing (valve opening start timing) and closing timing are each changed by the same amount while maintaining the same.

  The VVTs 15 and 17 having such a function are, for example, a phase in which a cam pulley coupled to a crankshaft via a chain or the like and a camshaft driven to rotate by the cam pulley are coupled to each other so as to be relatively rotatable. This can be realized by incorporating a changing member. A VVL 16 having a similar structure is already known, and a specific example thereof is disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-85241 (referred to as VCT in the same document).

The valve mechanism 14 for the exhaust valve 12 incorporates a VVL 18 that is an ON / OFF type variable valve lift mechanism (Variable Valve Lift Mechanism) that enables or disables the function of pushing down the exhaust valve 12 during the intake stroke. ing. Specifically, the VVL 18 has a function of enabling the exhaust valve 12 to be opened not only in the exhaust stroke but also in the intake stroke, and switching whether the exhaust valve 12 is opened or stopped during the intake stroke. This corresponds to the exhaust side opening / closing switching mechanism according to the present invention.

  The ON / OFF type VVL 18 is provided corresponding to all the exhaust valves 12 of the engine, and individually opens the valve during the intake stroke with respect to the pair of exhaust valves 12 of each cylinder 2. Configured to run or stop.

  The VVL 18 having such a function includes, for example, a sub cam that pushes down the exhaust valve 12 during the intake stroke separately from a normal cam for driving the exhaust valve 12 (that is, a cam that pushes down the exhaust valve 12 during the exhaust stroke), and this sub cam. A so-called lost motion mechanism that cancels the transmission of the drive force to the exhaust valves 12 can be realized by providing each exhaust valve 12 individually. A VVL 18 having a similar structure is already known, and a specific example thereof is disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-85241 (referred to as a valve operation switching mechanism in the same document).

  The valve mechanism 13 for the intake valve 11 incorporates a VVL 16 (corresponding to the intake side opening / closing switching mechanism according to the present invention) which is an ON / OFF type variable valve lift mechanism similar to the VVL 18. However, the VVL 16 is not applied to one of the pair of intake valves 11 provided in each cylinder 2, and the VVL 16 is applied only to the other intake valve 11 (see FIG. 2). The VVL 16 is provided so as to execute or stop the opening of the other intake valve 11 during the intake stroke, and when the VVL 16 is driven, the other intake valve 11 is set to the intake stroke. It is possible to switch between a state in which the valve is opened and a state in which the valve is not opened over the entire period including the intake stroke.

  In this specification, when “XX valve opens in XX stroke” or “XX valve that opens during XX stroke”, etc., the opening period of the XX valve (after opening (Period until closing) is mainly set to overlap with the XX stroke, and does not necessarily mean that the entire valve opening period is in the XX stroke. On the other hand, for example, when “XX valve starts to open (or starts to open) in XX stroke”, literally, XX valve opening timing (valve opening start timing) at a predetermined time in XX stroke. Is set.

  For example, when “exhaust valve 12 opens during exhaust stroke” or “exhaust valve 12 that opens during exhaust stroke”, it means that the opening period of exhaust valve 12 mainly overlaps with the exhaust stroke. However, as shown in lift curves EX1 and EX2 in FIGS. 6 to 10 described later, this also applies to a mode in which opening begins before the exhaust stroke (second half of the expansion stroke) and closes later in the second half of the exhaust stroke. On the other hand, for example, when “the exhaust valve 12 starts to open (or starts to open) during the intake stroke”, the opening timing of the exhaust valve 12 (see lift curves EX1a and EX2a in FIGS. 6 and 7 described later) It means that the valve opening start time) is set within the period of the intake stroke.

  FIG. 2 collectively shows the types of variable mechanisms applied to the intake and exhaust valves 11 and 12. As described above, in the present embodiment, both the pair of exhaust valves 12 in each cylinder 2 include the VVT 17 for changing the operation timing, and the ON / OFF type VVL 18 for executing or stopping the valve opening during the intake stroke. Are applied respectively. Further, the VVT 15 is applied to both of the pair of intake valves 11 in each cylinder 2, and the ON / OFF type VVL 16 is applied to only one of the intake valves 11.

  Returning to FIG. 1, the cylinder head 4 of the engine body 1 is provided with one set of spark plugs 20 and injectors 21 for each cylinder 2.

  The injector 21 is provided so as to face the combustion chamber 6 from the side of the intake side, and injects fuel (fuel mainly composed of gasoline) supplied from a fuel supply pipe (not shown) from the tip. Then, fuel is injected from the injector 21 into the combustion chamber 6 during the intake stroke of the engine, and the injected fuel is mixed with air, so that an air-fuel mixture having a desired air-fuel ratio is generated in the combustion chamber 6. It is like that.

  The spark plug 20 is provided so as to face the combustion chamber 6 from above, and discharges a spark from the tip in response to power supply from an ignition circuit (not shown).

  The engine main body 1 configured as described above has a geometric compression ratio set to 15 or more. That is, while the geometric compression ratio of a general gasoline engine is about 9 to 11, the geometric compression ratio of the engine body 1 of the present embodiment is set to a fairly high value of 15 or more. Has been.

  An intake passage 23 and an exhaust passage 24 are connected to the intake port 9 and the exhaust port 10 of the engine body 1, respectively. That is, intake air (fresh air) from the outside is supplied to the combustion chamber 6 through the intake passage 23 and burned gas (exhaust gas) generated in the combustion chamber 6 is discharged to the outside through the exhaust passage 24. It has become so.

  A throttle valve 25 is provided in the intake passage 23. The throttle valve 25 is an electronically controlled throttle valve and is not linked to an accelerator pedal (not shown) that is depressed by the driver.

  The exhaust passage 24 is provided with a catalytic converter 26 for purifying exhaust gas. For example, a three-way catalyst is incorporated in the catalytic converter 26, and harmful components in the exhaust gas passing through the exhaust passage 24 are purified by the action of the three-way catalyst.

(2) Control System FIG. 3 is a block diagram showing an engine control system. The ECU 40 shown in the figure is a device for comprehensively controlling each part of the engine, and includes a well-known CPU, ROM, RAM, and the like.

  The ECU 40 receives detection signals from various sensors. That is, the ECU 40 determines the opening of the engine rotation speed sensor 30 that detects the rotation speed Ne of the crankshaft 7, the airflow sensor 31 that detects the flow rate Qa of the intake air passing through the intake passage 23, and the accelerator pedal opening (not shown). It is electrically connected to the accelerator opening sensor 32 to be detected, and the state quantity detected by each of these sensors is sequentially input to the ECU 40 as an electrical signal.

  The ECU 40 is also electrically connected to the VVTs 15, 17, VVLs 16, 18, spark plug 20, injector 21, and throttle valve 25, and outputs drive control signals to these devices. It is configured.

  A more specific function of the ECU 40 will be described. The ECU 40 includes a storage unit 41, a fuel control unit 42, an ignition control unit 43, and a valve control unit 44 as main functional elements.

  The storage means 41 stores various data and programs necessary for controlling the engine. As an example, the storage means 41 stores an operation region map shown in FIG. This operation region map defines in what manner the engine should be operated according to the engine speed Ne and load T (required torque).

  In the operation region map of FIG. 4, an HCCI region R is set in the partial load region of the engine, and in this HCCI region R, compression self-ignition combustion is performed in which the air-fuel mixture is combusted by self-ignition. The HCCI region R is roughly divided into a low load region R1, a medium load region R2 having a higher load, and a high load region R3 having a higher load. Among these, the medium load region R2 is further subdivided into three regions, which are, in order from the lowest load, a first medium load region R2a, a second medium load region R2b, and a third medium load region R2c. . In each of these load regions (R1, R2a, R2b, R2c, R3), the compression self-ignition combustion is performed while changing the opening / closing control pattern of the intake / exhaust valves 11, 12 respectively. (Details will be described later).

  The fuel control means 42 controls the injection amount and timing of fuel injected from the injector 21 into the combustion chamber 6. More specifically, the fuel control means 42 performs target fuel injection based on information such as the engine speed Ne input from the engine speed sensor 30 and the intake air amount Qa input from the airflow sensor 31. The amount and the injection timing are calculated, and the valve opening timing and valve opening period of the injector 21 are controlled based on the calculation result.

  The ignition control means 43 outputs a power supply signal to the ignition circuit of the spark plug 20 at a predetermined timing determined in accordance with the operating state of the engine, whereby the spark plug 20 performs a spark discharge (ignition timing). Etc. are controlled. However, in the present embodiment, at least in the HCCI region R shown in FIG. 4, compression self-ignition combustion that performs self-ignition of the air-fuel mixture is executed regardless of spark ignition. The spark ignition from the spark plug 20 is stopped.

  The valve control means 44 drives the VVLs 16 and 18 to execute or stop the opening of the intake and exhaust valves 11 and 12 during the intake stroke, and drives the VVTs 15 and 17 to drive the intake and exhaust valves 11 and 12. The operation timing is variably set. In particular, in the HCCI region R, the valve control means 44 adjusts the amount of fresh air introduced into the cylinder (inside the cylinder 2) based on the control of the intake and exhaust valves 11 and 12 as described above, It has a function of adjusting the in-cylinder temperature by increasing / decreasing the amount of burned gas introduced into the cylinder.

  For example, the presence or absence of valve opening during the intake stroke on one side of the pair of intake valves 11 is switched by the VVL 16, thereby increasing or decreasing the number of intake valves 11 opened during the intake stroke. The amount of fresh air introduced into is adjusted.

  Further, the presence or absence of the valve opening during the intake stroke of the pair of exhaust valves 12 is switched by the VVL 18 so that the amount of burnt gas flowing back into the cylinder is increased and decreased, and the increase range of the in-cylinder temperature is adjusted. . For example, when at least one of the pair of exhaust valves 12 is opened during the intake stroke, the high-temperature burned gas (exhaust gas) once discharged to the exhaust port 10 flows backward from the exhaust port 10 and enters the cylinder again. It is introduced and the in-cylinder temperature rises. Further, when such a backflow of burned gas occurs, the flow of fresh air from the intake port 9 is limited by that amount, so the amount of fresh air in the cylinder decreases. Conversely, if the exhaust valve 12 does not open during the intake stroke, the burnt gas backflow as described above does not occur, so that the in-cylinder temperature relatively decreases and the amount of fresh air increases.

  Further, by setting the operation timing of the intake / exhaust valves 11 and 12 by the VVT 15 and 17, a period (so-called negative overlap period) in which both the intake valve 11 and the exhaust valve 12 are closed from the middle of the exhaust stroke to the intake stroke is provided. As a result, the in-cylinder temperature and the amount of fresh air are adjusted based on the remaining burned gas. That is, when the negative overlap period is provided, since a part of the burned gas generated in the cylinder is confined in the cylinder as it is, the in-cylinder temperature rises due to the presence of the remaining burned gas, Inflow of fresh air is limited. Accordingly, the negative overlap period is increased or decreased by driving the VVTs 15 and 17, so that the amount of burned gas remaining in the cylinder is increased or decreased, and the increase range of the in-cylinder temperature and the amount of fresh air are accordingly increased. Adjusted.

  In addition, since the operation of causing the burned gas to remain (or backflow) in the cylinder as described above is called internal EGR (Internal Exhaust Gas Recirculation), hereinafter, the operation of the burnt gas remaining (or backflow) in the cylinder is referred to. This is sometimes called EGR gas.

  The valve control means 44 adjusts the amount of EGR gas and the amount of fresh air appropriately based on the control of the intake and exhaust valves 11 and 12 as described above, so that the engine can be operated in any of the HCCI regions R. Even when the air-fuel mixture is used, the air-fuel mixture is surely self-ignited at an appropriate time, and plays a role of continuously performing stable compression self-ignition combustion.

  Note that, as described above, in the HCCI region R, the fresh air amount is adjusted based on the control of the intake and exhaust valves 11 and 12 by the valve control means 44. Therefore, the throttle control of the intake passage 23 by the throttle valve 25 is basically performed. The opening of the throttle valve 25 is maintained fully open (100%) or in the vicinity thereof, except when the engine is stopped, for example.

  Here, the combustion control in the operation region other than the HCCI region R will be briefly described. If the operation region other than the HCCI region R, that is, the region combining the rotation region on the higher rotation side than the HCCI region R and the load region on the higher load side than the HCCI region R is defined as SR, Combustion by spark ignition or compression self-ignition combustion in a mode different from that of the HCCI region R is performed.

  For example, on the higher rotation side than the HCCI region R, since the heat receiving period of the fuel is short and it is difficult to self-ignite the air-fuel mixture, compression self-ignition combustion is not performed, and forced ignition by spark ignition using the spark plug 20 is performed. Combustion (SI combustion) is performed.

  Further, on the higher load side than the HCCI region R, switching to SI combustion may be performed in the same manner as the control on the higher rotation side described above. For example, when the engine is a supercharged engine, the intake valve 11 It is also possible to continue compression self-ignition combustion by supplementing the shortage of fresh air with supercharging while greatly reducing the effective compression ratio of the engine by shifting the closing timing significantly with respect to the intake bottom dead center. That is, simply increasing the fuel injection amount on the higher load side than the HCCI region R may cause abnormal combustion such as pre-ignition, but supercharging is performed while reducing the effective compression ratio of the engine. If this is done, the temperature of the combustion chamber 6 near the compression top dead center can be lowered while sufficiently securing fresh air. Therefore, pre-ignition can occur even at a higher load side than the HCCI region R. It is possible to continue the compression self-ignition combustion without causing etc.

  However, in the present invention, what kind of combustion control is performed outside the HCCI region R is not particularly a problem. Therefore, only the control operation in the HCCI region R will be described below.

(3) Control operation in HCCI region R Next, the contents of the control operation in the HCCI region R will be described with reference to FIGS. FIG. 5 is a flowchart showing a control procedure executed by the ECU 40, and FIGS. 6 to 10 show the suction selected in the load regions R1, R2 (R2a to R2c), R3 of the HCCI region R. It is a figure which shows the opening / closing pattern of the exhaust valves 11 and 12. FIG.

  When the process shown in the flowchart of FIG. 5 starts, first, control for reading various sensor values is executed (step S1). Specifically, the engine speed Ne, the intake air amount Qa, and the accelerator opening degree AC are read from the engine speed sensor 30, the airflow sensor 31, and the accelerator opening degree sensor 32, respectively, and are input to the ECU 40. The

  Next, control for determining whether or not the engine operating point determined based on the information read in step S1 is in the HCCI region R shown in FIG. 4 is executed (step S2). Specifically, the engine rotational speed Ne read in step S1 and the engine load (requested torque) T calculated based on the accelerator opening degree AC and the like are both included in the range of the HCCI region R in FIG. It is determined whether or not.

  When it is determined YES in step S2 and it is confirmed that the engine operating point is in the HCCI region R, it is further determined whether or not the engine is in the low load region R1 (step S3). .

  When it is determined YES in step S3 and it is confirmed that the vehicle is in the low load region R1 in the HCCI region R, the process proceeds to the next step S7, and intake / exhaust along the predetermined opening / closing pattern A Control for opening and closing the valves 11 and 12 is executed.

  FIG. 6 shows lift curves of the intake and exhaust valves 11 and 12 based on the opening / closing pattern A. In the drawing, EX1 is a lift curve when one of a pair of exhaust valves 12 provided in each cylinder 2 is opened during the exhaust stroke, and EX2 is an exhaust valve of the other exhaust valve 12 is exhausted. This is the lift curve when the valve is opened during the stroke. EX1a is a lift curve when the one exhaust valve 12 is opened during the intake stroke, and EX2a is a lift curve when the other exhaust valve 12 is opened during the intake stroke. is there. Furthermore, IN1 is a lift curve when one of the pair of intake valves 11 provided in each cylinder 2 is opened. The lift curve when the other intake valve 11 is opened is shown as IN2 as shown in FIGS.

  6 represents the crank angle, TDC represents the top dead center, and BDC represents the bottom dead center. On the horizontal axis, the start point and end point of the lift curve represent the valve opening timing (valve opening timing) and the closing timing, respectively. It is not the time to become zero, but refers to the opening timing and closing timing when the section excluding the ramp part of the lift curve (the part where the lift amount changes gently) is defined as the valve opening period. The same applies to the cases of FIGS. 7 to 10 described later.

  As shown in FIG. 6, in the open / close pattern A selected in the low load region R1, the pair of exhaust valves 12 in each cylinder 2 are both opened during the exhaust stroke (EX1, EX2) and during the intake stroke. (EX1a, EX2a). Further, only one of the pair of intake valves 11 in each cylinder 2 is opened during the intake stroke (IN1). The valve control means 44 controls the driving of the VVTs 15 and 17 and the VVLs 16 and 18 in accordance with such valve opening / closing pattern settings.

  More specifically, in the case of the opening / closing pattern A, the pair of intake valves 11 in each cylinder 2 starts to open from the middle of the intake stroke delayed from the exhaust top dead center (TDC), only one of them. It is closed on the retard side from the intake bottom dead center (BDC on the right side) (IN1). On the other hand, with respect to the other intake valve 11, the valve opening during the intake stroke is stopped, and the closed state is maintained over the entire period including the intake stroke.

  On the other hand, both of the pair of exhaust valves 12 in each cylinder 2 begin to open from the front before the expansion bottom dead center (left BDC), and in the middle of the exhaust stroke before the exhaust top dead center (TDC). (EX1, EX2). Further, in the middle of the exhaust stroke delayed from the exhaust top dead center, both of the pair of exhaust valves 12 begin to open again and are closed on the retard side from the intake bottom dead center (BDC on the right side) (EX1a, EX2a). .

  The pair of exhaust valves 12 that are opened during the intake stroke have their opening timing (valve opening start timing) set simultaneously with the opening timing of the one intake valve 11. The period from the opening timing of the intake valve 11 and the exhaust valve 12 that are opened during these intake strokes to the exhaust top dead center just before that is Y, and from the closing timing of the exhaust valve 12 that is opened during the exhaust stroke, Assuming that the period until the exhaust top dead center immediately after is X, the period X and the period Y are set to be substantially the same (both are about 45 ° CA in the example of FIG. 6). A symmetrical lift curve is formed. This also applies to the opening / closing patterns B to D shown in FIGS.

  The total period (X + Y) obtained by adding the period X from the closing timing of the exhaust valve 12 to the exhaust top dead center and the period Y from the opening timing of the intake valve 11 and the exhaust valve 12 to the exhaust top dead center is: This is a so-called negative overlap period in which both the intake valve 11 and the exhaust valve 12 are closed. If such a negative overlap period (X + Y) is provided before and after the exhaust top dead center, the cylinder is sealed before the piston 5 reaches the exhaust top dead center. A part of the gas remains in the cylinder.

  Further, from the middle of the intake stroke after the negative overlap period (X + Y), as described above, the exhaust valve 12 is opened again (EX1a, EX2a), and during that time, the exhaust port 10 was once exhausted. A phenomenon occurs in which part of the burned gas flows backward into the cylinder. As described above, in the open / close pattern A, a negative overlap period is provided to allow the burned gas to remain in the cylinder, and then the exhaust valve 12 is restarted during the intake stroke so that the burned gas is discharged into the cylinder. I try to make it flow backward. The introduction operation of these two types of burned gas is performed as the internal EGR, so that a considerably large amount of burned gas is secured in the cylinder and the temperature in the cylinder is increased.

  Further, in the opening / closing pattern A, as described above, only one of the pair of intake valves 11 opens during the intake stroke, and the other intake valve 11 does not open. Inflow of fresh air is restricted. As a result of the interaction between this and the introduction of the EGR gas, the amount of fresh air is greatly reduced and the proportion of EGR gas is increased. As a result, the in-cylinder temperature rises to a considerably high temperature. Yes.

  Returning to the flowchart of FIG. 5 again, the control operation when NO is determined in step S3 will be described. In this case, control for determining whether or not the current engine operating point is in the first medium load range R2a of FIG. 4 is executed (step S4). If the determination here is NO, it is next determined whether or not the operating point of the engine is in the second middle load range R2b (step S5). Furthermore, the determination here is also NO. In this case, it is determined whether or not the vehicle is in the third middle load range R2c (step S6).

  When it is determined YES in any of the above steps S4, S5, and S6 and it is confirmed that the current engine operating point is in the first to third middle load ranges R2a to R2c (that is, the middle load range R2). Shifts to one of steps S8, S9, and S10, and executes control for opening and closing the intake and exhaust valves 11 and 12 along any one of the predetermined opening and closing patterns B, C, and D. In these open / close patterns B, C, and D, the number of intake valves 11 that open during each intake stroke in each cylinder 2 is increased from one to two, while the exhaust that opens during each intake stroke in each cylinder 2 is increased. The number of valves 12 is gradually reduced from 2 → 1 → 0 as the load increases. Hereinafter, specific control contents in each of the open / close patterns B, C, and D will be described.

  First, the opening / closing pattern B (step S8) selected in the first medium load region R2a will be described with reference to FIG. As shown in this figure, in the open / close pattern B, unlike the open / close pattern A described above, both the pair of intake valves 11 in each cylinder 2 are opened during the intake stroke (IN1, IN2). That is, in the opening / closing pattern A (FIG. 6) selected in the low load region R1, only one of the pair of intake valves 11 is opened during the intake stroke, and the other intake valve 11 remains closed. However, when the load increases to the first middle load region R2a and the switching is made to the opening / closing pattern B, the VVL 16 is driven by the valve control means 44, and the opening of the other intake valve 11 is lifted. Both intake valves 11 are opened during the intake stroke.

  On the other hand, the pair of exhaust valves 12 in each cylinder 2 is opened in both the intake stroke and the exhaust stroke, as in the case of the opening / closing pattern A. For this reason, the length of the negative overlap period in which both the intake valve 11 and the exhaust valve 12 are closed is also the same X + Y as in the opening / closing pattern A.

  Thus, in the opening / closing pattern B, the number of opening of the intake valve 11 is increased from one to two per cylinder while executing the same control as the opening / closing pattern A for the exhaust valve 12. As a result, the amount of fresh air flowing into the cylinder from the intake port 9 increases, and the amount of burned gas (EGR gas) introduced into the cylinder correspondingly decreases.

  Next, the opening / closing pattern C (step S9) selected in the second medium load region R2b will be described with reference to FIG. As shown in this figure, in the open / close pattern C, only one of the pair of exhaust valves 12 in each cylinder 2 opens during the intake stroke, and the other exhaust valve 12 does not open during the intake stroke. That is, when the VVL 18 is driven by the valve control means 44 and the function of depressing the other exhaust valve 12 during the intake stroke is disabled, the other exhaust valve 12 is opened only during the exhaust stroke. (EX2) The valve will not open during the intake stroke.

  On the other hand, one of the exhaust valves 12 is opened during both the exhaust stroke and the intake stroke (EX1, EX1a). In this manner, the number of exhaust valves 12 that are opened during the intake stroke in each cylinder 2 is reduced from two to one, so that the amount of EGR gas decreases and the amount of fresh air increases. The operation of the other valves is the same as in the opening / closing pattern B. Also, the same amount (X + Y) is ensured during the negative overlap period when both the intake and exhaust valves 11 and 12 are closed.

  Next, the opening / closing pattern D (step S10) selected in the third middle load region R2c will be described with reference to FIG. As shown in this figure, in the opening / closing pattern D, the valve opening during the intake stroke is prohibited for both the pair of exhaust valves 12 in each cylinder 2. That is, the VVL 18 is driven by the valve control means 44, and both the functions of pushing down the pair of exhaust valves 12 during the intake stroke are disabled. As a result, the pair of exhaust valves 12 are both opened only during the exhaust stroke (EX1, EX2), and are not opened during the intake stroke. Thus, the number of exhaust valves 12 that are opened during the intake stroke is reduced to zero, whereby the amount of EGR gas is further reduced and the amount of fresh air is increased.

  In the open / close pattern D, the valve operations other than those described above are the same as in the open / close pattern C. Also, the same amount (X + Y) is ensured during the negative overlap period when both the intake and exhaust valves 11 and 12 are closed. As described above, in the open / close pattern D, the number of exhaust valves 12 that are opened during the intake stroke is zero, but the presence of the negative overlap period (X + Y) ensures a certain amount of EGR gas. Is done. That is, in the open / close pattern D, the exhaust valve 12 does not make one incision valve during the intake stroke, and the backflow of the burned gas from the exhaust port 10 hardly occurs, but the burned gas during the negative overlap period (X + Y). Since this still remains, the remaining burned gas is ensured as EGR gas.

  Returning to the flowchart of FIG. 5 again, the control operation when NO is determined in step S6 will be described. In this case, the current engine operating point is in the high load region R3 of FIG. Then, the process proceeds to the next step S11, and control for opening and closing the intake and exhaust valves 11 and 12 along a predetermined opening / closing pattern E is executed.

  FIG. 10 shows lift curves of the intake and exhaust valves 11 and 12 based on the opening / closing pattern E. As shown in this figure, in the opening / closing pattern E selected in the high load region R3, the pair of exhaust valves 12 of each cylinder 2 opens during the exhaust stroke, and the pair of intake valves 11 opens during the intake stroke. Although the valve is the same as the opening / closing pattern D, it is different from the opening / closing pattern D. As indicated by the arrows in the figure, the operation timings of the intake valve 11 and the exhaust valve 12 correspond to the increase in load. Are shifted toward each other.

  That is, by driving the VVTs 15 and 17 by the valve control means 44, the operation timing of the pair of exhaust valves 12 is shifted to the retard side (right side in the figure) as the load increases, The operation timing of the intake valve 11 is shifted to the advance side (left side in the figure). As a result, the closing timing of the exhaust valve 12 and the opening timing (opening start timing) of the intake valve 11 both approach the exhaust top dead center (TDC), and finally reach the vicinity of the upper limit value of the high load range R3. When the load increases, as shown in the figure, the closing timing of the exhaust valve 12 and the opening timing of the intake valve 11 substantially coincide at the exhaust top dead center. As a result, there is no negative overlap period in which both the intake and exhaust valves 11 and 12 close before and after the exhaust top dead center, so there is almost no EGR gas introduced into the cylinder, and a sufficient amount of fresh air is secured. It becomes like this.

(4) Operational Effects As described above, in the present embodiment, a pair of intake valves 11 and a pair of exhaust valves 12 are provided for each cylinder 2, and the HCCI region R operated by compression self-ignition combustion is a partial load. In the engine set in the region, the HCCI region R is divided into a low load region R1, a medium load region R2 (first to third medium load regions R2a to R2c), and a high load region R3 in order of increasing load, In each load region, the intake / exhaust valves 11 and 12 are controlled along the open / close patterns as shown in FIGS. According to such a configuration, proper compression self-ignition combustion can be performed in a wider load region by appropriately controlling the amount of EGR gas according to the load.

  For example, in the low load region R1 with the lowest load in the HCCI region R, as shown in the opening / closing pattern A in FIG. 6, the pair of exhaust valves 12 in each cylinder is opened not only in the exhaust stroke but also in the intake stroke. In addition, since only one of the pair of intake valves 11 in each cylinder 2 is opened in the intake stroke, the high-temperature burned gas once discharged to the exhaust port 10 can be made to flow back into the cylinder, The amount of fresh air can be reduced by restricting the flow of fresh air into the interior. Further, the exhaust valve 11 and the exhaust valve 12 begin to open during the intake stroke, and the opening timing (valve opening start timing) and the closing timing of the exhaust valve 12 that opens during the exhaust stroke are determined as exhaust top dead. Since the point (TDC) is set at a predetermined time interval, a negative overlap period (X + Y) in which both the intake valve 11 and the exhaust valve 12 are closed is provided before and after the exhaust top dead center. By sealing the inside, high-temperature burned gas can remain in the cylinder.

  The operation for sealing the inside of the cylinder before and after the exhaust top dead center as described above and the operation for resuming the exhaust valve 12 during the intake stroke are the operations for introducing the burned gas into the cylinder (internal EGR), and by reducing the number of intake valves 11 to one, a large amount of burned gas (EGR gas) can be secured in the cylinder, and the proportion of fresh air in the cylinder is relatively Can be made smaller. This greatly increases the in-cylinder temperature and creates an environment in which the air-fuel mixture easily ignites. Therefore, even in a situation where the load is low and the fuel injection amount is small, the compression self-ignition combustion is surely caused. it can. Further, by introducing a large amount of EGR gas, there is an advantage that the negative pressure in the cylinder can be reduced and the pumping loss can be effectively reduced.

  However, if the introduction of a large amount of EGR gas as described above is continued in a situation where the load has increased to some extent, not only the amount of new air is insufficient, but also the self-ignition of the air-fuel mixture is promoted too much. For example, there is a possibility that abnormal combustion called pre-ignition in which the air-fuel mixture self-ignites at an abnormally early timing may occur. Therefore, in order to avoid such a situation, in the above embodiment, in the medium load region R2 (first to third medium load regions R2a to R2c) and the high load region R3 having a higher load than the low load region R1, By increasing the number of intake valves 11 opened, reducing the number of exhaust valves 12 opened during the intake stroke, and further shortening the negative overlap period, the ratio of EGR gas and fresh air can be adjusted according to the load. Adjustments were made accordingly.

  Specifically, in the first intermediate load region R2a having the lowest load among the intermediate load regions R2, the number of intake valves 11 is increased from one to two (open / close pattern B in FIG. 7), and the cylinder By increasing the amount of fresh air and reducing the amount of EGR gas by promoting the inflow of fresh air, the in-cylinder temperature is lower than that in the low load range R1 while reducing the pumping loss. And the proper compression self-ignition combustion can be continued.

  Next, in the second intermediate load region R2b and the third third intermediate load region R2c that are higher in load than the first intermediate load region R2a in the intermediate load region R2, the exhaust valve 12 that opens during the intake stroke is used. Since the number is reduced from two to one and further reduced to zero (opening and closing patterns C and D in FIGS. 8 and 9), the amount of EGR gas obtained by the backflow from the exhaust port 10 is gradually increased according to the load. By reducing the temperature, the in-cylinder temperature can be further lowered than in the first middle load range R2a.

  Finally, when the engine load increases to the high load range R3, the closing timing of the exhaust valve 12 that opens during the exhaust stroke and the opening timing of the intake valve 11 that opens during the intake stroke are set. In addition, since both are shifted toward the exhaust top dead center according to the increase in load, the negative overlap period in which both the intake valve 11 and the exhaust valve 12 are closed before and after the exhaust top dead center is gradually shortened. The amount of EGR gas obtained by sealing in the cylinder during the period can be gradually reduced. Thus, there is an advantage that a sufficient amount of fresh air corresponding to a high load can be secured, and the in-cylinder temperature can be kept lower, and abnormal combustion such as pre-ignition can be effectively prevented.

  Further, in the above embodiment, the exhaust valve 12 that opens during the exhaust stroke in the low load region R1 and the medium load region R2 in the HCCI region R, as shown in the open / close patterns AD of FIGS. Period X from the closing timing of the engine to the exhaust top dead center and the period from the opening timing of the intake valve 11 and the exhaust valve 12 (only the intake valve 11 in the opening / closing pattern D) that opens during the intake stroke to the exhaust top dead center Since Y is set to be substantially the same, there is an advantage that an increase in pumping loss can be effectively prevented while securing the burned gas remaining as a result of sealing in the cylinder as EGR gas.

  For example, the operation of causing the burned gas to remain in the cylinder is possible only by setting the closing timing of the exhaust valve 12 that opens during the exhaust stroke to some extent before the exhaust top dead center and ensuring the period X. Yes, the intake valve 11 or the exhaust valve 12 may be started immediately after passing the exhaust top dead center (that is, the period Y is not necessarily required). However, if the intake valve 11 or the exhaust valve 12 starts to open immediately after passing the exhaust top dead center, the pressure in the cylinder increased by the compression action of the piston 5 during the period X is It will drop to atmospheric pressure at a dead point. For this reason, on the PV diagram, a predetermined area is formed between the pressure change line during the exhaust stroke and the pressure change line during the intake stroke, and energy is consumed for work corresponding to the area. Will be.

  On the other hand, when the period X and the period Y are set to be substantially the same as in the above embodiment, the pressure change line during the exhaust stroke and the pressure change during the intake stroke on the PV diagram. When the lines follow substantially the same path, almost no area is formed between the two lines, and the above-described extra work does not occur. For this reason, according to the embodiment in which the period X and the period Y are set to be substantially the same, an increase in pumping loss that can occur within the period can be effectively prevented while securing EGR gas.

  FIG. 11 is a graph showing the results of an experiment conducted by the inventor of the present application in order to confirm the effects as described above. The geometric compression ratio of the engine used in this experiment was 20, and the bore × stroke was φ87.5 × 83.1. Then, using such an engine, an operation by compression self-ignition combustion was performed, and the filling rate (filling efficiency) ηv of fresh air at that time was measured. The engine speed Ne during measurement was constant at 1000 rpm, and the intake air temperature was constant at 50 ° C.

  The plots of “◆”, “■”, “▲”, “▼”, and “●” marks in the graph are obtained when the intake and exhaust valves 11 and 12 are controlled according to the open / close patterns shown in FIGS. The value of the fresh air filling rate ηv is shown. That is, “◆” is a value when the open / close pattern A (FIG. 6), “■” is a value when the open / close pattern B (FIG. 7), “▲” is a value when the open / close pattern C (FIG. 8), “▼” indicates a value when the open / close pattern D (FIG. 9), and “●” indicates a value when the open / close pattern E (FIG. 10). Of these, for the plot of “●” for the open / close pattern E, as shown in FIG. 10, both the closing timing of the exhaust valve 12 and the opening timing of the intake valve 11 are set near the exhaust top dead center. The fresh air filling rate ηv in a state where the negative overlap period is substantially zero is shown.

  In the graph of FIG. 11, IMEP on the horizontal axis indicates the indicated mean effective pressure that is an index representing the magnitude of the load (work). The difference in the position in the horizontal axis direction between the plots represents the difference in the fuel injection amount according to the load, and the more the fuel injection amount is located on the right side.

  As shown in the graph of FIG. 11, it can be seen that the fresh air filling rate ηv increases stepwise in the order of the open / close patterns A → B → C → D → E. That is, the fresh air filling rate ηv is slightly less than 20% in the case of the open / close pattern A, but is slightly over 30% in the open / close pattern B, up to over 50% in the open / close pattern C, and over 60% in the open / close pattern D. The opening / closing pattern E is increased to about 100%. Note that the plot “●” for the open / close pattern E shows the fresh air filling rate ηv in a state where the negative overlap period is substantially zero. The value of the filling rate ηv is naturally smaller than “●” and approaches the value of “▼” of the pattern D.

  On the other hand, the gray area in the graph excluding the fresh air area indicates the amount of EGR gas introduced into the cylinder, and this EGR gas ratio (EGR rate) is opposite to that of fresh air. The opening / closing pattern A is gradually reduced in the order of A → B → C → D → E. The reason why the upper side portion of the gray region indicating the EGR rate is lowered to the left is that the density decreases as the amount of EGR gas increases.

  As is clear from the above experimental results, the opening / closing patterns of the intake / exhaust valves 11 and 12 are switched in the order of patterns A → B → C → D → E in accordance with the increase in load as indicated by broken arrows in the graph. In this case (that is, when the same control as that in the above embodiment is performed), the amount of fresh air can be increased stepwise according to the load, and the amount of EGR gas can be decreased. That is, in the open / close pattern A, the EGR gas is introduced to the maximum to raise the temperature in the cylinder, and from this state, the open / close pattern is shifted from B → C → D → E as the load increases. As a result, the amount of EGR gas can be decreased stepwise to suppress the in-cylinder temperature and increase the amount of fresh air.

  FIG. 12 shows the result of an experiment for confirming the combustion state when operating under the same conditions as in FIG. 11, and the vertical axis of the combustion center of gravity is the time when 50% mass of the fuel burns (50% MB) is shown. According to the graph of FIG. 12, the position of the combustion center of gravity in any of the open / close patterns A, B, C, D, and E is also within the appropriate range P on the retard side from the compression top dead center (0 ° CA). It can be seen that it is mostly included. As a result, it has been found that by switching the opening / closing pattern from A → B → C → D → E as the load increases as described above, proper compression self-ignition combustion can be continuously performed regardless of the load. .

  The experimental results described above were obtained using a high compression ratio engine with a geometric compression ratio of 20. However, if the compression ratio is somewhat high, the same result as above can be obtained. Is possible. However, it is desirable that the geometric compression ratio is 15 or more in order to make full use of the feature of the above-described embodiment in which at least a part of the EGR gas is secured by the restart valve of the exhaust valve 12 during the intake stroke.

  For example, in the open / close patterns A to C, in order to introduce burned gas into the cylinder, not only the exhaust valve 12 is restarted during the intake stroke, but also the intake and exhaust valves 11 and 12 before and after the exhaust top dead center. A negative overlap period (X + Y in FIGS. 6 to 8) for closing both sides is provided before and after exhaust top dead center, but this negative overlap period (X + Y) is longer than the examples in FIGS. By doing so, it is possible to secure a similar amount of EGR gas without restarting the exhaust valve 12 during the intake stroke. However, if the negative overlap period is extended and both the intake and exhaust valves 11 and 12 are closed for a considerable period of time, a large amount of burned gas remaining in the meantime is compressed and near the exhaust top dead center. Since the temperature is further increased, a large amount of heat is released to the outside (that is, the cooling loss is increased), and the effect of increasing the in-cylinder temperature near the compression top dead center may be diminished.

  Such a concern becomes greater as the engine has a higher compression ratio. Specifically, the operation of introducing burned gas into the cylinder using the negative overlap period is NVO EGR, and the burned gas is introduced into the cylinder by opening the exhaust valve 12 during the intake stroke. Assuming that the operation is EGR with the exhaust double opening method, according to the research of the present inventor, even when the same amount of EGR gas is secured, the NVO method is more effective than the EGR with the exhaust double opening method. It has been found that the increase range of the in-cylinder temperature is small and the decrease range increases as the compression ratio increases. For example, when the in-cylinder temperature at the compression top dead center is compared between the NVO method and the exhaust double opening method, the temperature difference between the two is about 20 ° C. for an engine with a geometric compression ratio of 15. As a result, the engine with a geometric compression ratio of 20 increased to about 50 ° C. On the other hand, in the engine having a geometric compression ratio of 10, no significant temperature difference was observed.

  In view of the above, especially in a high compression ratio engine, at least a part of the EGR gas is secured by EGR of the exhaust double opening type, and cooling loss is secured rather than securing EGR gas only by the NVO type EGR. It can be kept low, which is advantageous in terms of ignitability and efficiency. The advantage of such an exhaust double opening method is that the engine having a geometric compression ratio of 15 or more can be more advantageous as the compression ratio becomes higher than 15.

  However, even if the geometric compression ratio is increased, there is a practical limit, and even if the compression ratio is increased excessively, the resulting effect gradually diminishes. Considering these points, the geometric compression ratio of the engine should be 22 or less.

  That is, in an engine having a geometric compression ratio of 15 or more and 22 or less, the exhaust gas double opening type EGR is performed, and the intake / exhaust valves 11 and 12 are controlled as in the above-described opening / closing patterns A to E according to the load. Thus, highly efficient compression self-ignition combustion can be appropriately executed over a wide load range while fully utilizing the advantages of the exhaust double opening method.

(5) Modification In the embodiment described above, the open / close pattern A shown in FIG. 6 is selected in the low load region R1 having the lowest load among the HCCI regions R that perform compression self-ignition combustion, and the intake stroke is being performed. In addition, only one of the pair of intake valves 11 provided in each cylinder 2 is opened and the other intake valve 11 is kept closed. Instead, both the pair of intake valves 11 are opened. You may make it open a valve. In this way, the VVL 16 applied to the other intake valve 11 can be omitted. However, if both of the pair of intake valves 11 are opened, the amount of fresh air flowing into the cylinder increases and the ratio of EGR gas decreases, so if necessary (especially extremely low near no load) In the load region), in order to secure a sufficient amount of EGR gas, the negative overlap period (X + Y) for closing both the intake and exhaust valves 11 and 12 may be extended.

  In the above embodiment, the opening timing of the exhaust valve 12 that opens during the intake stroke and the opening timing of the intake valve 11 are set at the same time in the open / close patterns A to C. The opening time may be off. However, even in this case, it is desirable to fix the opening timing of the earlier opening of both the valves at a timing delayed by the period Y from the exhaust top dead center. As a result, the period in which the inside of the cylinder is sealed becomes substantially bilaterally symmetric with respect to the exhaust top dead center, and as described above, the pumping loss that occurs during the negative overlap period can be minimized.

  Further, in the above-described embodiment, the exhaust gas is exhausted from the period X from the closing timing of the exhaust valve 12 that opens during the exhaust stroke to the exhaust top dead center and the opening timing of the intake valve 11 and the exhaust valve 12 that opens during the intake stroke. The period Y to the top dead center (or the period Y from the opening timing of the intake valve 11 alone to the exhaust top dead center when the exhaust valve 12 does not open during the intake stroke) is set to be substantially the same. Therefore, it is preferable that the period X is slightly longer than the period Y. That is, there is a slight time lag from when the intake valve 11 or the exhaust valve 12 starts to open during the intake stroke until the fresh air or burned gas actually flows into the cylinder. If so, it is assumed that the in-cylinder pressure temporarily temporarily decreases due to the time lag and a pumping loss occurs. Therefore, if X> Y is set and the intake valve 11 or the exhaust valve 12 starts to open somewhat earlier, the occurrence of the pumping loss as described above can be avoided. However, if the period Y is made too short with respect to the period X, as described above, a pumping loss due to a sudden decrease in the in-cylinder pressure once increased due to compression occurs, so the difference between the period X and the period Y is 10 °. It is desirable to stay within CA.

  In the above embodiment, two intake valves 11 and two exhaust valves 12 are provided for each cylinder 2. However, the number of intake / exhaust valves 11, 12 is not limited to this, and at least one of the intake / exhaust valves 11, 12 is provided. You may increase to three. For example, when the number of exhaust valves 12 is three per cylinder, the number of exhaust valves 12 that are opened during the intake stroke in the medium load region R2 in the HCCI region R is increased according to the increase in load. What is necessary is just to reduce it like 3-> 2-> 1-> 0, and by doing in this way, the amount of fresh air and the amount of EGR gas can be adjusted more finely.

11 Intake valve 12 Exhaust valve 15, 17 VVT (variable timing mechanism)
16 VVL (Intake side open / close switching mechanism)
18 VVL ( exhaust side open / close switching mechanism)
44 Valve control means R HCCI region R1 Low and medium load region
R2a First medium load range
R2b Second medium load range
R2c Third medium load range R3 High load range

Claims (3)

A timing variable mechanism that includes two intake valves and two exhaust valves per cylinder, and that variably sets operation timings of the intake valves and the exhaust valves, and an operation in which the intake valves are opened during the intake stroke. an intake on-off switching mechanism that can switch whether the exhaust-side opening and closing the switching mechanism capable of switching whether to open or to open, or only in the exhaust stroke in the intake stroke as well exhaust stroke the exhaust valve, Valve control means for controlling the intake valve and exhaust valve opening / closing operation by driving the variable timing mechanism , the intake side opening / closing switching mechanism, and the exhaust side opening / closing switching mechanism, and at least in an operation region including a partial load region of the engine. An engine control device configured to cause compression self-ignition combustion in a set HCCI region,
The HCCI region includes a low load region having a relatively low load, a first medium load region having a higher load than the low load region, a second medium load region having a higher load than the first medium load region, and a second Divided into a plurality of load areas including a third medium load area having a higher load than the medium load area and a high load area having a higher load than the third medium load area ;
The valve control means is
In the low load region in the HCCI region, one intake valve and two exhaust valves in each cylinder begin to open during the intake stroke, and the intake valve and exhaust valve open timing and open during the exhaust stroke By setting the closing timing of the exhaust valve to be a time separated by a predetermined period across the exhaust top dead center, a negative overlap period in which both the intake valve and the exhaust valve are closed is formed ,
In the first medium load region in the HCCI region, the number of intake valves and exhaust valves that are opened during the intake stroke is both two, and the negative overlap period is formed,
In the second medium load region in the HCCI region, the number of intake valves that are opened during the intake stroke is two, the number of exhaust valves that are opened during the intake stroke is one, and the negative overlap Forming period,
In the third medium load region in the HCCI region, the number of intake valves opened during the intake stroke is set to two, the number of exhaust valves opened during the intake stroke is set to zero, and the negative overlap period Form the
In the high load region in the HCCI region, the number of intake valves that are opened during the intake stroke is set to two, the number of exhaust valves that are opened during the intake stroke is set to zero, and the load is increased, By gradually changing the closing timing of the exhaust valve that opens during the exhaust stroke and the opening timing of the intake valve that opens during the intake stroke in a direction approaching the exhaust top dead center, the negative overlap period is gradually increased. An engine control device characterized in that it is shortened . The engine control device according to claim 1 ,
In the low load region and the first, second, and third medium load regions in the HCCI region, the period from the closing timing of the exhaust valve that opens during the exhaust stroke to the exhaust top dead center, and the valve that opens during the intake stroke An engine control device characterized in that a period from an earlier opening timing to an exhaust top dead center of the intake valve and the exhaust valve to be set is set to be substantially the same. The engine control apparatus according to claim 1 or 2 ,
An engine control device, wherein a geometric compression ratio of the engine is set to 15 or more and 22 or less.