JP2008151098A - Valve opening characteristic variable type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technique capable of restraining complication of a structure and increase of a manufacturing cost in a valve opening characteristic variable type internal combustion engine performing internal EGR in a prescribed operation region. <P>SOLUTION: It is determined whether an exhaust valve closing angle Ae exceeds a second intake valve opening angle Ai2 by a middle lift cam 22b or not, and a low lift cam 22a is selected in a step S4 when the determination is No. When the determination in a step S3 is Yes, an ECU 9 determines whether the exhaust valve closing angle Ae exceeds a third intake valve opening angle Ai3 by a high lift cam 22c or not in a step S6, and the middle lift cam 22b is selected in a step S7 when the determination is No. When the determination in the step S6 is also Yes, the ECU 9 selects the high lift cam 22c in a step S8. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a variable valve opening characteristic internal combustion engine in which internal EGR is performed in a predetermined operating region, and more particularly to a technique for suppressing the complexity of the configuration and the increase in manufacturing cost.

  In recent years, in order to improve thermal efficiency, reduce harmful exhaust gas components, etc., development of an engine that operates in a premixed compression ignition mode (hereinafter referred to as HCCI) has been promoted (Patent Literature). 1). The HCCI mode is a combustion mode in which a premixed gas in which fuel and air are uniformly mixed is introduced into the combustion chamber and then compressed by a piston so that the premixed gas is self-ignited at multiple points simultaneously at a high temperature and high pressure. However, since it is difficult to control the ignition timing, in this type of engine, an HCCI mode and a spark ignition (hereinafter referred to as SI) mode are appropriately switched depending on the driving situation. In the operation in the HCCI mode, the temperature of the air-fuel mixture rises only by being compressed by the piston until ignition occurs. Therefore, the in-cylinder gas temperature at the start of compression is an important factor for controlling the ignition timing.

Therefore, when the engine is operated in the HCCI mode, the exhaust valve is closed before exhaust top dead center to increase the in-cylinder gas temperature at the start of compression, and the internal EGR (Exhaust gas recirculation) ) Is generally performed. Therefore, in the engine of Patent Document 1, variable valve mechanisms are provided on the intake side and the exhaust side, respectively, and in the HCCI mode, both the intake valve and the exhaust valve are closed in the crank angle range including the exhaust top dead center ( Hereinafter, a method of providing a negative overlap) is employed. In Patent Document 1, in order to increase the internal EGR gas and improve the ignitability, the negative overlap period is lengthened toward the lower load side. In order to reduce the pumping loss during the negative overlap period, the crank angle from the exhaust valve closing time to the exhaust top dead center (hereinafter referred to as the exhaust valve closing angle) and the exhaust top dead center to the intake valve The crank angle until the valve opening time (hereinafter referred to as the intake valve opening angle) is set equal.
Japanese Patent Laid-Open No. 2003-3873

  When operating in the HCCI mode, it is desirable to employ a continuously variable valve operating mechanism on the exhaust side and to control the amount of internal EGR gas with high accuracy and continuously according to the engine load and the like. However, when a continuously variable valve mechanism is employed on the exhaust side, a continuously variable valve mechanism must also be employed on the intake side in order to equalize the exhaust valve closing angle and the intake valve opening angle. Inevitably, the engine structure becomes complicated and the number of components increases.

  Therefore, the present inventors changed the intake valve opening angle with respect to the exhaust valve closing angle in order to confirm whether or not the pumping loss is minimized when the exhaust valve closing angle and the intake valve opening angle are equal. The engine was operated while testing how the pumping loss fluctuated. As a result, when the intake valve opening angle is somewhat smaller than the exhaust valve closing angle, the pumping loss is minimized, and the intake valve opening angle is slightly increased or decreased in the vicinity of the intake valve opening angle at which the pumping loss is minimized. However, it was found that the pumping loss hardly changed.

  The present invention has been made on the basis of the above knowledge, and provides a technique for suppressing a complicated configuration and an increase in manufacturing cost in a variable valve opening characteristic internal combustion engine that performs internal EGR in a predetermined operation region. With the goal.

  According to the first aspect of the present invention, there is provided an intake side valve mechanism for opening and closing an intake valve, an exhaust side valve mechanism for opening and closing an exhaust valve, and an exhaust side valve opening characteristic control for variably controlling the opening timing of the exhaust valve. A variable valve opening characteristic internal combustion engine that closes both the intake valve and the exhaust valve in a predetermined crank angle range including an exhaust top dead center in a predetermined operation region. The crank angle from the exhaust top dead center to the valve opening time of the intake valve is set in the range of −10 ° to 20 ° with respect to the crank angle from the exhaust valve closing time to the exhaust top dead center. And

  The invention according to claim 2 further includes an intake side valve opening characteristic control means for variably controlling the valve opening timing of the intake valve in a stepwise manner in the variable valve opening characteristic internal combustion engine according to claim 1. It is characterized by that.

  According to the first aspect of the present invention, it is not necessary to always make the intake valve opening angle and the exhaust valve closing angle equal without increasing the pumping loss, so that the degree of freedom in design of the intake side variable valve mechanism is improved. be able to. According to the invention of claim 2, the structure of the intake side variable valve mechanism is simplified, and the complication of the engine configuration and the increase in manufacturing cost are suppressed.

Hereinafter, an embodiment of an engine system to which the present invention is applied will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an engine system according to the embodiment, and FIG. 2 is a schematic configuration diagram of a variable valve mechanism according to the embodiment.

<Configuration of Embodiment>
The engine system shown in FIG. 1 has an in-line four-cylinder engine (variable valve opening type internal combustion engine: hereinafter referred to as an engine) 1 as a core, an intake system including an air cleaner 2, a surge tank 3, an intake manifold 4, and the like, and an exhaust system. An exhaust system including a manifold 5, an exhaust pipe 6, an exhaust purification catalyst 7, a muffler 8, and the like, and an ECU 9 that controls operation of the engine 1 are provided. For example, the ECU 9 performs operation control in the HCCI mode in the middle and low load operation region and performs operation control of the engine 1 in the SI mode in the high load operation region based on the load state of the engine 1 and the like.

  The cylinder head 10 of the engine 1 is provided with a pair of intake valves 11, a pair of exhaust valves 12, an in-cylinder fuel injection valve 14, and a spark plug 15 for each cylinder. The intake manifold 4 is provided with an intake pipe injection fuel injection valve 16 for each cylinder.

  As shown in FIG. 2, above the cylinder head 10, an intake side variable valve mechanism 21 that switches the lifts of both intake valves 11 stepwise, and an exhaust side variable that continuously changes the lifts of both exhaust valves 12. A variable valve mechanism 31 is installed. Although not shown, the cylinder head 10 is also provided with two VTC (Variable valve Timing Control) mechanisms that variably control the angle phases of intake and exhaust camshafts 22 and 32, which will be described later.

  The intake side variable valve mechanism 21 includes an intake camshaft 22 having three cams (a low lift cam 22a, a middle lift cam 22b, and a high lift cam 22c), three rocker arms 23a to 23c driven by the cams 22a to 22c, The rocker arms 23 a to 23 c are configured by a pin type switching mechanism 24 that switches connection / disconnection of the rocker arms 23 a to 23 c and hydraulic pressure supply paths 25 a and 25 b that supply hydraulic pressure to the switching mechanism 24. In the present embodiment, when a hydraulic control solenoid valve (not shown) is actuated by a command from the ECU 9, hydraulic pressure is supplied to or released from the switching mechanism 24 via the hydraulic supply paths 25a and 25b, and the rocker arms 23a to 23c are connected. The state changes and the lifts of both intake valves 11 are switched to three stages.

  When the operation of the engine 1 is controlled in the HCCI mode, the intake valve opening angle when the low lift cam 22a is selected (the crank angle from the exhaust top dead center to the opening timing of both intake valves: the first intake valve opening angle Ai1 ) Is smaller by a predetermined amount (for example, 18 °) than the intake valve opening angle (second intake valve opening angle Ai2) when the middle lift cam 22b is selected. The intake valve opening angle (third intake valve opening angle Ai3) when the high lift cam 22c is selected is compared with the intake valve opening angle (second intake valve opening angle Ai2) when the middle lift cam 22b is selected. Increases by a predetermined amount (for example, 18 °).

  On the other hand, the exhaust side variable valve mechanism 31 includes an intake camshaft 32 having a single cam 32 a, a rocker arm 33 that pushes down both exhaust valves 12, and a roller 34 a at the front end interposed between the cam 32 a and the rocker arm 33. The main components are the roller link 34, the gear link 35 to which the base end of the roller link 34 is connected, the drive gear 36 engaged with the gear link 35, and the electric motor 37 that drives the drive gear 36. In the case of this embodiment, when the electric motor 37 is actuated by a command from the ECU 9, the gear link 35 is rotationally driven via the drive gear 36, the swing fulcrum of the roller link 34 moves, and the lifts of both exhaust valves 12 continue. Changes.

<Operation of Embodiment>
When the engine system is activated, the ECU 9 performs operation control based on the operation information input from various sensors, for example, in the HCCI mode in the medium / low load operation region and in the SI mode in the high load operation region. When the engine 1 is operated in the HCCI mode, the ECU 9 controls a predetermined processing interval (for example, 10 ms) while controlling the angular phase of the intake and exhaust camshafts 22 and 32 by the VTC mechanism so that a negative overlap is realized. The valve lift control whose procedure is shown in the flowchart of FIG.

  When the valve lift control is started, the ECU 9 first sets the target internal EGR amount QEtgt based on the operating state of the engine 1 in step S1 of FIG. 3, and in step S2, the exhaust valve closing angle corresponding to the target internal EGR amount QEgtt. (Crank angle from exhaust valve closing time to exhaust top dead center) Ae is searched from a map (not shown).

  Next, the ECU 9 determines in step S3 whether or not the exhaust valve closing angle Ae exceeds the second intake valve opening angle Ai2 by the middle lift cam 22b. If this determination is No, the low lift cam is determined in step S4. 22a is selected, and drive commands are output to the intake side variable valve mechanism 21 and the exhaust side variable valve mechanism 31 in step S5.

  If the determination in step S3 is Yes, the ECU 9 determines in step S6 whether or not the exhaust valve closing angle Ae exceeds the third intake valve opening angle Ai3 by the high lift cam 22c. If No, the middle lift cam 22b is selected in step S7, and a drive command is output to the intake side variable valve mechanism 21 and the exhaust side variable valve mechanism 31 in step S5.

  Further, if the determination in step S6 is also Yes, the ECU 9 selects the high lift cam 22c in step S8, and outputs a drive command to the intake side variable valve mechanism 21 and the exhaust side variable valve mechanism 31 in step S5. .

  As a result, as shown in FIG. 4, during the operation in the HCCI mode, the intake valve opening angle Ai becomes negative over the exhaust valve closing angle Ae in a state where it becomes smaller in the angle range of 0 ° to 18 °. Wrapping is realized. FIG. 5 shows, as an example, a change in pumping loss when the intake valve opening angle Ai is increased or decreased when the exhaust valve closing angle Ae is 65 °. As can be seen from the figure, the pumping loss is minimized when the intake valve opening angle Ai is about 10 ° smaller than the exhaust valve closing angle Ae (when 55 °), and the intake valve opening angle Ai is the exhaust valve closing angle. It can be seen that there is almost no change in the angle range of −10 ° to 20 ° with respect to the angle Ae (45 ° to 75 °: indicated by hatching in the figure).

  As described above, in the present embodiment, by adopting the intake side variable valve mechanism 21 that switches the lifts of both intake valves 11 in stages, while suppressing the complexity of the configuration and the increase in manufacturing cost. The pumping loss during operation in the HCCI mode could be extremely reduced.

  Although the description of the specific embodiment is finished as described above, the present invention is not limited to the above embodiment and can be widely modified. For example, although the above embodiment is an application of the present invention to an internal combustion engine that is operated in the HCCI mode and the SI mode, it can also be applied to a diesel engine or the like. Further, in the above-described embodiment, the intake side variable valve mechanism that has been switched to three stages is adopted, but a mechanism that can be switched to two stages or a mechanism that can be switched to four or more stages may be employed. Further, the exhaust side variable valve mechanism is not limited to the above embodiment, and those having various structures can be adopted. Further, in the above embodiment, the intake valve opening angle is set to be smaller in the angle range of 0 ° to 18 ° with respect to the exhaust valve closing angle, but is arbitrarily set as long as it is within the angle range of −10 ° to 20 °. Is possible.

It is a principal part perspective view which shows the upper part of the engine which concerns on embodiment. It is a schematic block diagram of the variable valve mechanism which concerns on embodiment. It is a flowchart which shows the procedure of valve lift control. It is a graph which shows the relationship between the intake valve opening angle and exhaust valve closing angle in HCCI mode. It is a graph which shows the change of the pumping loss at the time of increasing / decreasing an intake valve opening angle.

Explanation of symbols

1 Engine (variable valve opening characteristics internal combustion engine)
11 Intake valve 12 Exhaust valve 21 Intake side variable valve mechanism (intake side valve mechanism, intake side valve opening characteristic control means)
22 Intake camshaft 31 Exhaust side variable valve mechanism (exhaust side valve mechanism, exhaust side valve opening characteristic control means)
32 Intake camshaft

Claims (2)

An intake side valve mechanism that opens and closes the intake valve, an exhaust side valve mechanism that opens and closes the exhaust valve, and an exhaust side valve opening characteristic control means that variably controls the opening timing of the exhaust valve. In the operating region, in the variable valve opening characteristic internal combustion engine that closes both the intake valve and the exhaust valve in a predetermined crank angle range including exhaust top dead center,
In the operating range, the crank angle from the exhaust top dead center to the intake valve open time is -10 ° to 20 ° relative to the crank angle from the exhaust valve close time to the exhaust top dead center. A variable valve opening characteristic internal combustion engine characterized by being set to   2. The variable valve opening characteristic internal combustion engine according to claim 1, further comprising intake side valve opening characteristic control means for variably controlling the valve opening timing of the intake valve in a stepwise manner.

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