JP2016217183A - Control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change an internal EGR rate in a wide range while securing high control responsiveness to the change of an engine load, and to suitably control ignition timing in HCCI combustion.SOLUTION: A control device for an engine (1) includes a VVL (71) for opening an exhaust valve (22) after valve opening timing of an intake valve (21), VVTs (72 and 75) for changing the valve timing of the intake and the exhaust valves, and a PCM (10) for changing the valve timing of the intake valve and the exhaust valve by controlling the VVT. The PCM executes control with the VVT so that the valve close timing of the intake valve is almost coincident with the valve close timing of the exhaust valve in an intake stroke when a requested internal EGR rate is equal to or more than a prescribed value, and a negative overlap period is shortened as the requested internal EGR rate becomes smaller than the prescribed value, and the valve open timing and the valve close timing of the exhaust valve in the intake stroke are delayed.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an engine control device, and in particular, provides a negative overlap period in which both an intake valve and an exhaust valve are closed during an exhaust stroke to an intake stroke of a cylinder so that burned gas remains in the cylinder. The present invention relates to an engine control device.

  2. Description of the Related Art Conventionally, an engine that performs compression ignition combustion by premixed compression self-ignition (HComogeneous-Charge Compression Ignition: HCCI) is known. In an engine that performs this HCCI combustion, a negative overlap period is provided in which both the intake valve and the exhaust valve are closed during the intake stroke from the exhaust stroke of the cylinder so that the burned gas remains in the cylinder and the exhaust gas is exhausted during the intake stroke. A so-called internal EGR system is used in which the temperature of the mixed gas in the combustion chamber is raised by opening and closing the valve and causing the burned gas to flow back into the cylinder (see, for example, Patent Document 1).

JP 2009-174432 A

By the way, in an engine that performs HCCI combustion, it is necessary to appropriately control the ignition timing in accordance with the load of the engine in order to achieve high thermal efficiency while suppressing combustion noise and ensuring combustion stability.
Therefore, the ratio of the burned gas remaining in the cylinder (internal EGR rate) in the total amount of gas introduced into the cylinder is changed according to the engine operating state (engine speed, load, etc.). Therefore, it is considered to control the ignition timing. In this case, in order to appropriately control the ignition timing, it is required to change the internal EGR rate in a wide range (for example, 20% to 80%).

  However, the conventional engine control device as described above provides a negative overlap period by controlling the closing timing of the exhaust valve and the opening timing of the intake valve by the variable valve timing mechanism, and the variable valve lift mechanism. It is used to open the exhaust valve during the opening period of the intake valve, and the control response of the internal EGR rate depends on the response of the variable valve timing mechanism and variable valve lift mechanism, so the control response is satisfied However, it is difficult to change the internal EGR rate in a wide range.

  The present invention has been made to solve the above-described problems of the prior art, and it is possible to change the internal EGR rate in a wide range while ensuring high control response to changes in engine load. An object of the present invention is to provide an engine control device that can appropriately control the ignition timing in HCCI combustion.

In order to achieve the above object, the engine control device of the present invention provides a negative overlap period in which both the intake valve and the exhaust valve are closed in the intake stroke from the exhaust stroke of the cylinder, and burnt gas is introduced into the cylinder. The engine control device is made to remain in the exhaust gas, and in the intake stroke, the exhaust side variable valve mechanism that opens the exhaust valve after the opening timing of the intake valve and the valve timing of the intake valve and the exhaust valve are changed. A variable valve timing mechanism, and a variable valve mechanism control means for controlling the variable valve timing mechanism based on the burnt gas demand according to the operating state of the engine to change the valve timing of the intake valve and the exhaust valve, The variable valve mechanism control means controls the intake valve closing timing and intake stroke by the variable valve timing mechanism when the burnt gas requirement amount is a predetermined value or more. The variable valve timing mechanism shortens the negative overlap period and the exhaust valve opening timing during the intake stroke as the required amount of burned gas becomes less than the predetermined value by making the exhaust valve closing timing substantially the same. And delaying the valve closing timing.
In the present invention configured as described above, when the required amount of burned gas is reduced below a predetermined value, the variable valve mechanism control means can reduce the amount of burned gas remaining in the cylinder by shortening the negative overlap period. In addition to the reduction, the exhaust valve is opened in the intake stroke while the cylinder is filled with air by opening the intake valve, and the exhaust valve is opened in the cylinder in the intake stroke. The amount of burnt gas that is taken in can be suppressed, whereby the amount of change in the internal EGR rate according to the amount of operation of the variable valve timing mechanism can be increased. Therefore, without providing a new mechanism in addition to the variable valve timing mechanism, the internal EGR rate can be changed over a wide range while ensuring high control responsiveness to changes in the engine load, and ignition in HCCI combustion Time can be controlled appropriately.

In the present invention, preferably, the variable valve mechanism control means is configured such that when the burnt gas requirement amount is equal to or greater than a predetermined value, the variable valve timing mechanism causes the intake valve to close and the exhaust valve to close in the intake stroke. The timing is substantially matched in the vicinity of the bottom dead center of the intake stroke.
In the present invention configured as described above, the period during which the exhaust valve is opened in the intake stroke can be kept within the intake stroke period, and accordingly, when the required amount of burned gas is equal to or greater than a predetermined value, the intake stroke The amount of burnt gas taken into the cylinder can be maximized by opening the exhaust valve at. Therefore, the internal EGR rate can be changed over a wide range with respect to changes in engine load.

In the present invention, preferably, the variable valve mechanism control means retards the valve closing timing of the exhaust valve in the exhaust stroke by the variable valve timing mechanism as the required amount of burned gas decreases.
In the present invention configured as described above, the negative overlap period is shortened as the required amount of burned gas decreases, and the amount of burnt gas remaining in the cylinder is reduced by providing the negative overlap period. Thereby, the internal EGR rate can be changed in a wide range with respect to the change of the engine load.

In the present invention, preferably, the variable valve mechanism control means advances the valve opening timing of the intake valve by the variable valve timing mechanism as the required amount of burned gas decreases.
In the present invention configured as described above, the negative overlap period is shortened as the required amount of burned gas decreases, and the amount of burnt gas remaining in the cylinder is reduced by providing the negative overlap period. Thereby, the internal EGR rate can be changed in a wide range with respect to the change of the engine load.

In the present invention, it is preferable that the variable valve mechanism control means is configured so that the variable valve timing mechanism determines the period from the exhaust valve closing timing to the top dead center of the exhaust stroke in the exhaust stroke, and the top dead center of the exhaust stroke. The period until the intake valve opening time is made equal.
In the present invention configured as described above, the compression work from the closing timing of the exhaust valve to the top dead center of the exhaust stroke is offset by the expansion work from the top dead center of the exhaust stroke to the opening timing of the intake valve. The pumping loss due to providing a negative overlap period can be reduced.

  According to the engine control apparatus of the present invention, the internal EGR rate can be changed over a wide range while ensuring high control responsiveness with respect to changes in engine load, and the ignition timing in HCCI combustion is appropriately controlled. be able to.

1 is a schematic configuration diagram of an engine to which an engine control device according to an embodiment of the present invention is applied. It is a block diagram which shows the electrical structure regarding the control apparatus of the engine by embodiment of this invention. It is explanatory drawing of the driving | operation area | region of the engine by embodiment of this invention. It is a diagram which shows the engine request | requirement internal EGR rate by embodiment of this invention. FIG. 4 is a diagram illustrating lift curves of an intake valve and an exhaust valve according to an embodiment of the present invention, in which (a) is a maximum of a negative overlap period, (b) is an intake valve at a minimum of a negative overlap period, and The lift curve of the exhaust valve is shown. It is a diagram which shows the control curve of the throttle opening of the engine by embodiment of this invention.

  Hereinafter, an engine control apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[Device configuration]
FIG. 1 shows a schematic configuration of an engine (engine body) 1 to which an engine control device according to an embodiment of the present invention is applied, and FIG. 2 is a block diagram showing the engine control device according to the embodiment of the present invention. .

  The engine 1 is a gasoline engine that is mounted on a vehicle and supplied with a fuel containing at least gasoline. The engine 1 includes a cylinder block 11 provided with a plurality of cylinders 18 (in FIG. 1, only one cylinder is illustrated, but four cylinders are provided in series, for example), and the cylinder block 11 is disposed on the cylinder block 11. The cylinder head 12 is provided, and an oil pan 13 is provided below the cylinder block 11 and stores lubricating oil. A piston 14 connected to the crankshaft 15 via a connecting rod 142 is fitted in each cylinder 18 so as to be able to reciprocate. A cavity 141 like a reentrant type in a diesel engine is formed on the top surface of the piston 14. The cavity 141 is opposed to an injector 67 described later when the piston 14 is positioned near the compression top dead center. The cylinder head 12, the cylinder 18, and the piston 14 having the cavity 141 define a combustion chamber 19. The shape of the combustion chamber 19 is not limited to the shape illustrated. For example, the shape of the cavity 141, the top surface shape of the piston 14, the shape of the ceiling portion of the combustion chamber 19, and the like can be changed as appropriate.

  The engine 1 is set to a relatively high geometric compression ratio of 15 or more for the purpose of improving the theoretical thermal efficiency and stabilizing the compression ignition combustion described later. In addition, what is necessary is just to set a geometric compression ratio suitably in the range of about 15-20.

  The cylinder head 12 is provided with an intake port 16 and an exhaust port 17 for each cylinder 18. The intake port 16 and the exhaust port 17 have an intake valve 21 and an exhaust for opening and closing the opening on the combustion chamber 19 side. Each valve 22 is disposed.

  Of the valve systems that drive the intake valve 21 and the exhaust valve 22, respectively, on the exhaust side, the operation mode of the exhaust valve 22 is switched between a normal mode and a special mode, for example, a hydraulically operated variable valve lift mechanism (FIG. 2). (Hereinafter referred to as VVL (Variable Valve Lift)) 71 and a phase variable mechanism (hereinafter referred to as VVT (Variable Valve Timing)) 75 capable of changing the rotational phase of the exhaust camshaft with respect to the crankshaft 15. , Is provided. Although the detailed illustration of the configuration of the VVL 71 is omitted, two types of cams having different cam profiles, a first cam having one cam crest and a second cam having two cam crests, and its first And a cam shifting mechanism that selectively transmits the operating state of one of the second cams to the exhaust valve 22. When the operating state of the first cam is transmitted to the exhaust valve 22, the exhaust valve 22 operates in the normal mode in which the valve is opened only once during the exhaust stroke, whereas the operating state of the second cam is the exhaust valve. When transmitting to the engine 22, the exhaust valve 22 operates in a special mode in which the exhaust valve is opened during the exhaust stroke and is also opened during the intake stroke so that the exhaust is opened twice. The normal mode and the special mode of the VVL 71 are switched according to the operating state of the engine. Specifically, the special mode is used in the control related to the internal EGR. An electromagnetically driven valve system that drives the exhaust valve 22 by an electromagnetic actuator may be employed.

  The VVT 75 may employ a hydraulic, electromagnetic, or mechanical structure as appropriate, and illustration of the detailed structure is omitted. The exhaust valve 22 can continuously change its valve opening timing and valve closing timing within a predetermined range by the VVT 75.

  As shown in FIG. 2, a VVL 74 and a VVT 72 are provided on the intake side in the same manner as the valve system on the exhaust side provided with the VVL 71 and the VVT 75. The intake side VVL 74 is different from the exhaust side VVL 71. The VVL 74 on the intake side includes two types of cams having different cam profiles: a large lift cam that relatively increases the lift amount of the intake valve 21 and a small lift cam that relatively decreases the lift amount of the intake valve 21; The cam shifting mechanism is configured to selectively transmit the operating state of one of the large lift cam and the small lift cam to the intake valve 21. When the VVL 74 is transmitting the operating state of the large lift cam to the intake valve 21, the intake valve 21 is opened with a relatively large lift amount, and the valve opening period is also extended. On the other hand, when the VVL 74 is transmitting the operating state of the small lift cam to the intake valve 21, the intake valve 21 is opened with a relatively small lift amount and the valve opening period is also shortened. The large lift cam and the small lift cam are set to be switched at the same valve closing timing or valve opening timing.

  As with the VVT 75 on the exhaust side, the intake-side VVT 72 may adopt a known hydraulic, electromagnetic, or mechanical structure as appropriate, and the detailed structure is not shown. The valve opening timing and the valve closing timing of the intake valve 21 can also be continuously changed within a predetermined range by the VVT 72. Note that, instead of applying the VVL 74 to the intake side, only the VVT 72 may be applied and only the valve opening timing and the valve closing timing of the intake valve 21 may be changed.

  In addition, for each cylinder 18, an injector 67 that directly injects fuel into the cylinder 18 (direct injection) is attached to the cylinder head 12. The injector 67 is disposed so that its nozzle hole faces the inside of the combustion chamber 19 from the central portion of the ceiling surface of the combustion chamber 19. The injector 67 directly injects an amount of fuel into the combustion chamber 19 at an injection timing set according to the operating state of the engine 1 and according to the operating state of the engine 1. In this example, the injector 67 is a multi-hole injector having a plurality of nozzle holes, although detailed illustration is omitted. Thereby, the injector 67 injects the fuel so that the fuel spray spreads radially from the center position of the combustion chamber 19. At the timing when the piston 14 is positioned near the compression top dead center, the fuel spray injected radially from the central portion of the combustion chamber 19 flows along the wall surface of the cavity 141 formed on the top surface of the piston. It can be paraphrased that the cavity 141 is formed so that the fuel spray injected at the timing when the piston 14 is located near the compression top dead center is contained therein. This combination of the multi-hole injector 67 and the cavity 141 is an advantageous configuration for shortening the mixture formation period and the combustion period after fuel injection. In addition, the injector 67 is not limited to a multi-hole injector, and may be an open valve type injector.

  A fuel tank (not shown) and the injector 67 are connected to each other by a fuel supply path. A fuel supply system 62 including a fuel pump 63 and a common rail 64 and capable of supplying fuel to the injector 67 at a relatively high fuel pressure is interposed on the fuel supply path. The fuel pump 63 pumps fuel from the fuel tank to the common rail 64, and the common rail 64 can store the pumped fuel at a relatively high fuel pressure. When the injector 67 is opened, the fuel stored in the common rail 64 is injected from the injection port of the injector 67. Here, although not shown, the fuel pump 63 is a plunger type pump and is driven by the engine 1. The fuel supply system 62 configured to include this engine-driven pump enables the fuel with a high fuel pressure of 30 MPa or more to be supplied to the injector 67. The fuel pressure may be set to about 120 MPa at the maximum. The pressure of the fuel supplied to the injector 67 is changed according to the operating state of the engine 1 as will be described later. The fuel supply system 62 is not limited to this configuration.

  A spark plug 25 that forcibly ignites the air-fuel mixture in the combustion chamber 19 is also attached to the cylinder head 12. In this example, the spark plug 25 is disposed through the cylinder head 12 so as to extend obliquely downward from the exhaust side of the engine 1. The tip of the spark plug 25 is disposed facing the cavity 141 of the piston 14 located at the compression top dead center.

  As shown in FIG. 1, an intake passage 30 is connected to one side of the engine 1 so as to communicate with the intake port 16 of each cylinder 18. On the other hand, an exhaust passage 40 for discharging burned gas (exhaust gas) from the combustion chamber 19 of each cylinder 18 is connected to the other side of the engine 1.

  An air cleaner 31 that filters intake air is disposed at the upstream end of the intake passage 30, and a throttle valve 36 that adjusts the amount of intake air to each cylinder 18 is disposed downstream thereof. A surge tank 33 is disposed near the downstream end of the intake passage 30. The intake passage 30 on the downstream side of the surge tank 33 is an independent passage branched for each cylinder 18, and the downstream end of each independent passage is connected to the intake port 16 of each cylinder 18.

Between the throttle valve 36 and the surge tank 33 in the intake passage 30, an ozone generator (O ₃ generator) 76 that adds ozone to fresh air introduced into the cylinder 18 is interposed. The ozone generator 76 generates ozone by silent discharge using oxygen contained in the intake air as a source gas. That is, when a high frequency alternating current high voltage is applied to the electrode from a power source (not shown), silent discharge is generated in the discharge gap, and the air (that is, intake air) passing therethrough is ozonized. The intake air thus added with ozone is introduced into each cylinder 18 from the surge tank 33 via the intake port 16. The ozone concentration in the intake air after passing through the ozone generator 76 is adjusted by changing the voltage application mode to the electrodes of the ozone generator 76 and / or changing the number of electrodes to which the voltage is applied. It is possible. The PCM 10 adjusts the ozone concentration in the intake air introduced into the cylinder 18 through the control of the ozone generator 76.

  The upstream portion of the exhaust passage 40 is constituted by an exhaust manifold having an independent passage branched for each cylinder 18 and connected to the outer end of the exhaust port 17 and a collecting portion where the independent passages gather. A direct catalyst 41 and an underfoot catalyst 42 are connected downstream of the exhaust manifold in the exhaust passage 40 as exhaust purification devices for purifying harmful components in the exhaust gas. Each of the direct catalyst 41 and the underfoot catalyst 42 includes a cylindrical case and, for example, a three-way catalyst disposed in a flow path in the case.

  A portion between the surge tank 33 and the throttle valve 36 in the intake passage 30 and a portion upstream of the direct catalyst 41 in the exhaust passage 40 are used for returning a part of the exhaust gas to the intake passage 30. They are connected via a passage 50. The EGR passage 50 includes a main passage 51 in which an EGR cooler 52 for cooling the exhaust gas with engine coolant is disposed. The main passage 51 is provided with an EGR valve 511 for adjusting the recirculation amount of the exhaust gas to the intake passage 30.

  The engine 1 is controlled by a powertrain control module (hereinafter referred to as PCM) 10. The PCM 10 includes a microprocessor having a CPU, a memory, a counter timer group, an interface, and a path connecting these units. This PCM 10 constitutes a controller.

As shown in FIGS. 1 and 2, detection signals from various sensors SW 1, SW 2, SW 4 to SW 18 are input to the PCM 10. Specifically, on the downstream side of the air cleaner 31, the PCM 10 includes a detection signal of an air flow sensor SW 1 that detects a flow rate of fresh air, a detection signal of an intake air temperature sensor SW 2 that detects the temperature of fresh air, and an EGR passage 50. The detection signal of the EGR gas temperature sensor SW4 that is disposed in the vicinity of the connection portion with the intake passage 30 and detects the temperature of the external EGR gas, and the intake air that is attached to the intake port 16 and immediately before flowing into the cylinder 18 The detection signal of the intake port temperature sensor SW5 for detecting the temperature, the detection signal of the in-cylinder pressure sensor SW6 attached to the cylinder head 12 and detecting the pressure in the cylinder 18, and the vicinity of the connection portion of the EGR passage 50 in the exhaust passage 40 And the detection signals of the exhaust temperature sensor SW7 and the exhaust pressure sensor SW8 that detect the exhaust temperature and the exhaust pressure, respectively. And it is disposed on the upstream side of the direct catalyst 41, disposed between the detection signal of the linear O ₂ sensor SW9 for detecting the oxygen concentration in the exhaust gas, the direct catalyst 41 and underfoot catalyst 42 and the exhaust A detection signal of a lambda O ₂ sensor SW10 that detects the oxygen concentration of the engine, a detection signal of a water temperature sensor SW11 that detects the temperature of engine cooling water, a detection signal of a crank angle sensor SW12 that detects the rotation angle of the crankshaft 15, A detection signal of an accelerator opening sensor SW13 that detects an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown) of the vehicle, detection signals of intake side and exhaust side cam angle sensors SW14 and SW15, and a fuel supply system A fuel pressure sensor S that is attached to the common rail 64 of 62 and detects the fuel pressure supplied to the injector 67. 16 a detection signal of a detection signal of the hydraulic sensor SW17 for detecting the oil pressure of the engine 1, and the detection signal of the oil temperature sensor SW18 for detecting the oil temperature of the engine 1, are input.

  The PCM 10 determines the state of the engine 1 and the vehicle by performing various calculations based on these detection signals, and accordingly, the injector 67, the spark plug 25, the VVT 72 and VVL 74 on the intake valve side, and the exhaust valve side Control signals are output to the VVT 75 and VVL 71, the fuel supply system 62, actuators of various valves (throttle valve 36, EGR valve 511), and the ozone generator 76. Thus, the PCM 10 operates the engine 1. Although details will be described later, the PCM 10 corresponds to an engine control device in the present invention, and functions as a variable valve mechanism control means and a throttle control means.

[Operation area]
Next, with reference to FIG. 3, the operating region of the engine according to the embodiment of the present invention will be described. FIG. 3 shows an example of the operation control map of the engine 1. In order to improve fuel efficiency and exhaust emission performance, the engine 1 is not subjected to ignition by the spark plug 25 in a low load region where the engine load is relatively low, and is premixed compression self-ignition (Homogeneous-Charge Compression) Compression ignition combustion by Ignition (HCCI) is performed. However, as the load on the engine 1 increases, in the compression ignition combustion, the combustion becomes too steep and causes problems such as combustion noise. Therefore, in the engine 1, in a high load region where the engine load is relatively high, compression ignition combustion is stopped and switched to forced ignition combustion (here, spark ignition combustion (SI)) using the spark plug 25. . As described above, the engine 1 is configured to switch between the HCCI mode in which the premixed compression self-ignition combustion is performed and the SI mode in which the spark ignition combustion is performed in accordance with the operation state of the engine 1, in particular, the load of the engine 1. ing. However, the boundary line for mode switching is not limited to the illustrated example.

[Required internal EGR rate]
Next, an internal EGR rate (required internal EGR rate) required for appropriately controlling the ignition timing in the engine according to the embodiment of the present invention will be described with reference to FIG. FIG. 4 is a state quantity map showing the required internal EGR rate of the engine 1 according to the embodiment of the present invention. Specifically, the required internal EGR rate corresponding to the engine load when the engine speed is 2500 to 4000 rpm. Shows changes. In FIG. 4, the horizontal axis represents the engine load, and the vertical axis represents the required internal EGR rate.
In the operation region corresponding to the map illustrated in FIG. 4, the engine 1 performs compression ignition combustion by HCCI in the low load region where the engine load is less than 600 kPa (IMEP), and by SI in the high load region of 600 kPa (IMEP) or more. Perform spark ignition combustion.

As shown in FIG. 4, in an HCCI region (region where the engine load is less than 600 kPa (IMEP)) in which compression ignition combustion is performed by HCCI, in a range less than a predetermined low load L ₁ (200 kPa (IMEP) in FIG. 4), The required internal EGR rate is constant at 80%. Further, in the range from the load L ₁ to the upper limit load L ₃ (600 kPa (IMEP) in FIG. 4) in the HCCI region, the required internal EGR rate decreases as the engine load increases and the required air amount increases. The minimum value is 20% at the load L ₃ . That is, in order to appropriately control the ignition timing in the HCCI region, it is necessary to change the internal EGR rate in the range of 20% to 80%.

[Operation of intake valve and exhaust valve]
Next, operations of the intake valve 21 and the exhaust valve 22 according to the embodiment of the present invention will be described with reference to FIG. FIG. 5 is a diagram showing lift curves of the intake valve 21 and the exhaust valve 22 when the engine 1 according to the embodiment of the present invention operates in the HCCI mode, and (a) shows the maximum time of the negative overlap period. (B) shows the lift curves of the intake valve 21 and the exhaust valve 22 at the minimum of the negative overlap period.

In the HCCI region, the PCM 10 has a negative overlap (NVO: Negative Valve Overlap) that closes both the intake valve 21 and the exhaust valve 22 from the exhaust stroke to the intake stroke in order to increase the temperature in the cylinder 18 with a large amount of burned gas. ) The period is set according to the required internal EGR rate, and the amount of burnt gas remaining in the cylinder 18 is controlled.
Specifically, the PCM 10 refers to a map set experimentally in advance, determines an NVO period for achieving the required internal EGR rate, and controls the VVT 72 and VVT 75 based on the NVO period. In the control map of VVT72 and VVT75, as shown in FIG. 5A, a period α from the closing timing (EVC1) of the exhaust valve 22 in the exhaust stroke to the top dead center (exhaust TDC) of the exhaust stroke, The operating amounts of the VVT 72 and the VVT 75 are set so that the period β from the exhaust TDC to the valve opening timing (IVO) of the intake valve 21 is equal, that is, the center of the NVO period is the exhaust TDC. Thus, by setting the center of the NVO period to the exhaust TDC, the compression work from the closing timing (EVC1) of the exhaust valve 22 to the exhaust TDC is performed, and the opening timing (IVO) of the intake valve 21 from the exhaust TDC. Can be offset by the expansion work up to, and the pumping loss due to the provision of the NVO period can be reduced.

Further, in the HCCI region, the PCM 10 opens the exhaust twice to open the exhaust valve 22 during the intake stroke.
Specifically, the PCM 10 transmits the operating state of the second cam having two cam peaks to the exhaust valve 22 by operating the VVL 71 in the special mode in the HCCI region. In this case, as indicated by broken lines in FIGS. 5A and 5B, the second cam of the VVL 71 opens the exhaust valve 22 during the exhaust stroke and opens the intake valve 21 during the intake stroke. (EVO2) is set to open after (IVO).

In particular, when the engine load is equal to or lower than a predetermined load L ₂ (about 350 kPa (IMEP) in FIG. 4), that is, the required internal EGR rate is equal to or higher than a predetermined value R ₂ (about 58% in FIG. 4) corresponding to the load L ₂ . In some cases, the PCM 10 uses the VVT 72 and the VVT 75 to maximize the NVO period, and the intake valve 21 closing timing (IVC) and the exhaust valve 22 closing timing (EVC2) in the intake stroke are dead in the intake stroke. Nearly match in the vicinity of the point (intake BDC).
Thus, by providing the NVO period, the amount of burned gas remaining in the cylinder 18 is maximized, and the period in which the exhaust valve 22 is opened twice is included in the intake stroke period, so that it is opened twice. The amount of burned gas taken in from the exhaust port 17 is maximized.

Then, PCM 10 is larger engine load than a predetermined load L _2, that is, as the required internal EGR rate becomes less than the predetermined value R ₂ corresponding to the load L _2, as shown in FIG. 5 (b), the exhaust valve by VVT75 By delaying the valve timing 22, the valve closing timing (EVC 1) of the exhaust valve 22 in the exhaust stroke is retarded, and the valve opening timing (EVO 2) and valve closing timing (EVC 2) of the exhaust stroke 22 in the intake stroke. ).
Further, the PCM 10 advances the valve timing of the intake valve 21 by the VVT 72 as the engine load becomes larger than the predetermined load L ₂ , thereby opening the valve opening timing (IVO) and the valve closing timing (IVC) in the intake stroke. ).
When the maximum load L ₃ in the HCCI region is 600 kPa (IMEP) in FIG. 4, that is, when the required internal EGR rate is the load R ₃ (20% in FIG. 4) corresponding to the load L ₃ , FIG. ), The closing timing (EVC1) of the exhaust valve 22 in the exhaust stroke and the opening timing (IVO) of the intake valve 21 in the intake stroke are close to the top dead center (exhaust TDC) of the exhaust stroke.

That is, as the required internal EGR rate becomes smaller than the predetermined value R ₂ , the valve closing timing (EVC1) of the exhaust valve 22 in the exhaust stroke is retarded and the valve opening timing (IVO) of the intake valve 21 is advanced. By shortening the period and providing the NVO period, the amount of burnt gas remaining in the cylinder 18 is reduced.
Further, the valve closing timing (IVC) of the intake valve 21 is advanced and the valve closing timing (EVC2) of the exhaust valve 22 opened in the intake stroke is delayed to close the exhaust valve 22 opened in the intake stroke. By delaying the valve timing (EVC2) with respect to the closing timing (IVC) of the intake valve 21, the period in which the exhaust valve 22 is opened twice is delayed from the period in which the intake valve 21 is opened. As a result, the exhaust valve 22 is opened twice while the cylinder 18 is filled with air to some extent by opening the intake valve 21, and the amount of burned gas taken in from the exhaust port 17 by opening twice is reduced. Suppress.
Further, by delaying (EVO2) and closing timing (EVC2) of the exhaust valve 22 in the exhaust stroke, the period during which the exhaust valve 22 is opened twice is retarded near the intake BDC where the movement amount of the piston 14 is small. By doing so, the amount of burned gas taken in from the exhaust port 17 is suppressed by opening the exhaust valve 22 twice.

[Throttle valve operation]
Next, the operation of the throttle valve according to the embodiment of the present invention will be described with reference to FIG. FIG. 6 is a diagram showing a control curve of the throttle opening of the engine 1 according to the embodiment of the present invention.

In the HCCI region, when the engine load is larger than a predetermined load L ₂ (about 350 kPa (IMEP) in FIGS. 4 and 6), that is, the required internal EGR rate is a predetermined value R ₂ (about 58 in FIG. 4) corresponding to the load L ₂ . 6), the PCM 10 sets the opening degree of the throttle valve 36 to 95% as shown in FIG. That is, in the region where the required internal EGR rate is less than the predetermined value R ₂ , the PCM 10 controls the internal EGR rate by changing the valve timings of the intake valve 21 and the exhaust valve 22 by the VVT 72 and VVT 75 as described above.

On the other hand, in the HCCI region, when the engine load is equal to or lower than the predetermined load L ₂ , that is, when the required internal EGR rate is equal to or higher than the predetermined value R ₂ corresponding to the load L ₂ , the PCM 10 detects the intake valve 21 and the exhaust valve 22. The NVO period and the twice opening period of the exhaust valve 22 are kept constant without changing the valve timing. In this case, the PCM 10 controls the internal EGR rate by controlling the opening of the throttle valve 36 and changing the amount of intake air into the cylinder 18.

Specifically, as shown in FIG. 6, when the engine load is greater than L ₁ (200 kPa (IMEP) in FIGS. 4 and 6) and less than or equal to L ₂ , that is, the required internal EGR rate is R ₂ (in FIG. 4). When it is about 58%) or more and less than R ₁ (80% in FIG. 4), the PCM 10 decreases the opening of the throttle valve 36 to 95% or less as the engine load decreases, that is, the required internal EGR rate increases. To do. In FIG. 6, when the engine load decreases to L ₁ , the PCM 10 decreases the opening of the throttle valve 36 to 20%.
In this way, by reducing the opening of the throttle valve 36 and reducing the amount of intake air into the cylinder 18, the internal EGR rate can be increased without changing the valve timing of the intake valve 21 and the exhaust valve 22. .
Further, as described above, in the HCCI region, the exhaust valve 22 is opened twice, and the intake valve 21 and the exhaust valve 22 are simultaneously opened during the intake stroke, so that the internal EGR rate is increased. In addition, even when the opening degree of the throttle valve 36 is reduced, an increase in suction negative pressure can be suppressed, and an increase in pumping loss during the intake stroke can be prevented.

Further, when the engine load is L ₁ or less, the required internal EGR rate is constant at R ₁ (80% in FIG. 4). Therefore, as shown in FIG. 6, the PCM 10 sets the opening degree of the throttle valve 36 to 20%. Hold on.

The control of the valve timing of the intake valve 21 and the exhaust valve 22 and the control of the opening degree of the throttle valve 36 by the PCM 10 are not necessarily performed separately, and may be performed simultaneously. For example, when the engine load increases rapidly from L ₁ to L ₃ , that is, when the required internal EGR rate decreases rapidly from R ₁ to R ₃ , the PCM 10 retards the valve timing of the exhaust valve 22 by VVT 75. The valve timing of the intake valve 21 is advanced by the VVT 72, and at the same time, the opening degree of the throttle valve 36 is increased. Thereby, even when the engine load changes rapidly, the internal EGR rate can be changed greatly with high responsiveness.

Next, further modifications of the embodiment of the present invention will be described.
First, in the above-described embodiment, the VVL 71 is hydraulically operated, and includes two types of cams having different cam profiles, a first cam having one cam peak and a second cam having two cam peaks, and Although it has been described that the cam shifting mechanism that selectively transmits the operating state of one of the first and second cams to the exhaust valve 22 is included, a VVL having a different configuration is used. Alternatively, electromagnetically driven or pneumatically driven VVL may be used.

  In the above-described embodiment, the switching instruction limit angle range in which the switching instruction of the VVL 71 is limited has been described by taking an in-line four-cylinder engine as an example. However, the technique disclosed herein is also applied to a multi-cylinder engine other than the in-line four-cylinder engine. Can be applied.

  Next, functions and effects of the above-described embodiment of the present invention and the engine control device 1 according to the modification of the embodiment of the present invention will be described.

First, when the required internal EGR rate is equal to or greater than the predetermined value R ₂ , the PCM 10 uses the VVT 72 and VVT 75 to calculate the closing timing (IVC) of the intake valve 21 and the closing timing (EVC 2) of the exhaust valve 22 in the intake stroke. The NVO period is shortened and the opening timing (EVO2) and closing timing (EVC2) of the exhaust valve 22 in the intake stroke are retarded as the required internal EGR rate becomes smaller than the predetermined value R ₂ . When the required internal EGR rate decreases below the predetermined value R ₂ , in addition to reducing the amount of burnt gas remaining in the cylinder 18 by shortening the NVO period, the intake valve 21 is opened to enter the cylinder 18. The exhaust valve 22 is opened twice with air filled to some extent, and the amount of burnt gas taken in from the exhaust port 17 can be suppressed by opening twice. Accordingly, it is possible to increase the change amount of the internal EGR rate corresponding to the operation amount of VVT72 and VVT75. Therefore, without providing a new mechanism in addition to VVT72 and VVT75, the internal EGR rate can be changed over a wide range while ensuring high control response to changes in engine load, and the ignition timing in HCCI combustion Can be controlled appropriately.

Further, when the required internal EGR rate is equal to or greater than the predetermined value R ₂ , the PCM 10 uses the VVT 72 and VVT 75 to calculate the closing timing (IVC) of the intake valve 21 and the closing timing (EVC 2) of the exhaust valve 22 in the intake stroke. Since the exhaust stroke 22 is almost coincident in the vicinity of the bottom dead center (intake BDC) of the intake stroke, the period during which the exhaust valve 22 is opened twice can be included in the intake stroke period. _When it is _two or more, the amount of burnt gas taken into the cylinder 18 from the exhaust port 17 can be maximized by opening twice. Therefore, the internal EGR rate can be changed over a wide range with respect to changes in engine load.

  Further, since the PCM 10 delays the closing timing (EVC1) of the exhaust valve 22 in the exhaust stroke by the VVT 75 as the required internal EGR rate decreases, the NVO period is shortened as the required internal EGR rate decreases. By providing the NVO period, the amount of burned gas remaining in the cylinder 18 can be reduced, and thereby the internal EGR rate can be changed over a wide range with respect to changes in engine load.

  Further, the PCM 10 advances the valve opening timing (IVO) of the intake valve 21 by the VVT 72 as the required internal EGR rate decreases, so the NVO period is shortened and the NVO period is shortened as the required internal EGR rate decreases. By providing, the amount of burnt gas remaining in the cylinder 18 can be reduced, and thereby, the internal EGR rate can be changed in a wide range with respect to the change of the engine load.

  Further, the PCM 10 uses the VVT 72 and the VVT 75 to perform a period α from the closing timing (EVC1) of the exhaust valve 22 in the exhaust stroke to the top dead center (exhaust TDC) of the exhaust stroke, and the opening timing of the intake valve 21 from the exhaust TDC. Since the period β until (IVO) is made equal, the compression work from the closing timing (EVC1) of the exhaust valve 22 to the exhaust TDC is caused by the expansion work from the exhaust TDC to the opening timing (IVO) of the intake valve 21. It is possible to cancel, and the pumping loss due to the provision of the NVO period can be reduced.

Further, when the required internal EGR rate is equal to or greater than a predetermined value R ₂ (about 58% in this embodiment), the PCM 10 controls the throttle valve 36 based on the required internal EGR rate to change the intake air amount to the cylinder 18. Therefore, the internal EGR rate can be changed without changing the valve timings of the intake valve 21 and the exhaust valve 22 by the VVT 72 and the VVT 75. That is, the operating amount of the VVT 72 and the VVT 75 can be suppressed while ensuring the range of change of the internal EGR rate, so that the internal EGR rate can be changed over a wide range while ensuring high control responsiveness against changes in the engine load. The ignition timing in HCCI combustion can be appropriately controlled.
Further, since the intake valve 21 and the exhaust valve 22 are simultaneously opened during the intake stroke, even when the opening degree of the throttle valve 36 is reduced to increase the internal EGR rate, an increase in the intake negative pressure can be suppressed. An increase in pumping loss in the intake stroke can be prevented.

Further, when the required internal EGR rate is equal to or greater than the predetermined value R ₂ , the PCM 10 reduces the opening of the throttle valve 36 to a predetermined opening (95% in the present embodiment) or less, so that, for example, the required internal EGR rate is Even when the valve timing of the intake valve 21 and the exhaust valve 22 is changed by the VVT 72 and the VVT 75, even when the internal EGR rate is not less than the maximum value that can be achieved, The internal EGR rate can be increased.

Further, when the required internal EGR rate is equal to or greater than the predetermined value R ₂ , the PCM 10 decreases the opening degree of the throttle valve 36 as the required internal EGR rate increases. Even if the valve timing is not changed, the intake air amount to the cylinder 18 can be decreased and the internal EGR rate can be increased as the required internal EGR rate is increased.

1 Engine (Engine body)
10 PCM
17 exhaust port 18 cylinder 21 intake valve 22 exhaust valve 36 throttle valve 71 VVL (exhaust side)
72 VVT (intake side)
74 VVL (intake side)
75 VVT (exhaust side)

Claims (5)

A control apparatus for an engine in which a negative overlap period for closing both an intake valve and an exhaust valve in an intake stroke from an exhaust stroke of a cylinder is provided so that burned gas remains in the cylinder,
An exhaust-side variable valve mechanism for opening the exhaust valve after the intake valve is opened in the intake stroke;
A variable valve timing mechanism for changing valve timings of the intake valve and the exhaust valve;
Variable valve mechanism control means for controlling the variable valve timing mechanism based on the burnt gas demand according to the operating state of the engine and changing the valve timing of the intake valve and the exhaust valve;
The variable valve mechanism control means uses the variable valve timing mechanism to set the closing timing of the intake valve and the closing timing of the exhaust valve in the intake stroke when the required amount of burned gas is equal to or greater than a predetermined value. The variable valve timing mechanism shortens the negative overlap period and the exhaust valve opening timing and closing time in the intake stroke as the burnt gas requirement amount becomes smaller than the predetermined value. An engine control device that retards a valve timing.   When the burnt gas demand is equal to or greater than the predetermined value, the variable valve mechanism control means uses the variable valve timing mechanism to close the intake valve closing timing and the exhaust valve closing timing in the intake stroke. The engine control device according to claim 1, wherein the engine speed is substantially matched near a bottom dead center of the intake stroke.   3. The engine according to claim 1, wherein the variable valve mechanism control means retards the closing timing of the exhaust valve in the exhaust stroke by the variable valve timing mechanism as the burnt gas requirement amount decreases. Control device.   4. The variable valve mechanism control means according to any one of claims 1 to 3, wherein the variable valve timing mechanism advances the valve opening timing of the intake valve as the burnt gas demand decreases. Engine control device.   The variable valve mechanism control means uses the variable valve timing mechanism to perform a period from the closing timing of the exhaust valve to the top dead center of the exhaust stroke in the exhaust stroke, and the intake valve from the top dead center of the exhaust stroke. The engine control device according to any one of claims 1 to 4, wherein the period until the valve opening time is made equal.

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