JP2008175133A - Combustion chamber structure of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure a stable combustibility by producing a reverse tumble flow having a rotation directivity even in the case where the lift amount is extremely small, in an internal combustion engine for controlling the intake air amount by the lift amount of an air intake valve. <P>SOLUTION: A pair of inclined planes 8a, 8b is provided on both sides of a ridgeline r as a line linking two air intake valves and two exhaust gas valves in the top surface of a piston 8. A pair of dent parts 8A, 8B is formed elongating from the inclined planes 8a, 8b so as to have the maximum depth at the piston outer circumferential side away from the ridgeliner. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a combustion chamber structure of an internal combustion engine, and more particularly to a technique for maintaining good combustion stability by preserving intake air flow in a combustion chamber (suppressing attenuation).

  Patent Document 1 discloses a top surface structure of a piston of an internal combustion engine that forms a pair of swirling flows around a horizontal axis, and includes a valve recess for releasing each intake valve and each exhaust valve. A pair of recesses extending continuously and independently from each other from each valve recess to each valve recess for the intake valve facing each other so that the pair of swirling flows respectively advance in these recesses. A top surface structure is disclosed.

Patent Document 2 shows a structure in which a concave portion having inclined surfaces on both sides with a center line passing between the intake side and the exhaust side as a ridgeline is provided on the piston crown surface.
JP-A-9-317555 JP 2002-364368 A

  In the above-mentioned Patent Document 1, the concave portion for generating the tumble flow has a curved bottom surface, and in the vicinity of the intermediate lift of the intake valve, such as at low rotation and high load, the directivity in the tumble flow rotation direction is poor and unstable. It was difficult to ensure sufficient combustion stability.

  Also, Patent Document 2 does not have a function of enhancing the directivity of tumble flow rotation in the vicinity of the intermediate lift of the intake valve such as at low rotation and high load, and it has been difficult to ensure sufficient combustion stability.

For this reason, the present invention
In the combustion chamber structure of an internal combustion engine provided with two intake valves for each cylinder,
A pair of inclined surfaces are provided on both sides of the ridge line on the piston crown surface through the center of the piston and connecting the two intake valves and the exhaust side, and the ridge line is separated from the ridge line. A pair of recesses are formed so that the depth is maximum on the outer peripheral side of the piston.

  When the intake valve is operated in the vicinity of the intermediate lift of the intake valve, such as at low rotation and high load, a pair of symmetrical twin intake flows that flow into the combustion chamber from the intake port via the intake valve In the stroke, it turns substantially horizontally along the cylinder bore wall, but when entering the compression stroke, the flow toward the intake valve side is upward and the flow toward the exhaust valve side is due to the inclined surface of the concave portion of the piston crown surface. It is converted into a swirl in an oblique direction downward, and in a later stage of the compression stroke, it is converted into a swirl flow in a vertical direction (reverse tumble flow).

  Then, in the vicinity of the ignition timing, the reverse tumble flow with sufficiently enhanced rotation directivity as described above is disrupted and converted into turbulence, whereby combustion stability is improved, and fuel efficiency can be improved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 and FIG. 2 are a longitudinal sectional view and a transverse sectional view of a main part of a direct injection spark ignition internal combustion engine (hereinafter referred to as an engine) showing an embodiment of the present invention.

  In the combustion chamber 1 formed between the cylinder wall 11 and the piston 8 of the engine, an ignition plug 2 is disposed at a substantially central portion on the upper surface (cylinder head) side. Then, two intake ports 3A and 3B and two exhaust ports 4A and 4B are opened so as to surround the spark plug 2, and the intake valves 5A and 5B and the exhaust valves 6A and 6B are mounted respectively.

  The fuel injection valve 7 is installed between the intake ports 3A and 3B, is disposed obliquely downward on the side of the combustion chamber 1 on the intake valve 5A and 5B side, and has a predetermined direction from each of the plurality of formed injection holes. The fuel is injected toward the center of the combustion chamber 1 in the direction.

  The intake valves 5A and 5B (or the intake valves 5A and 5B and the exhaust valves 6A and 6B) continuously change the valve operating angle (open period) and the lift amount of the intake valves 5A and 5B as variable valve actuating devices. A valve operating angle and lift amount variable device (VEL) 21 that can be controlled is provided, and is configured to be electronically controlled by an ECU (electronic control unit) 20.

  A line connecting the two intake valves 5A and 5B and the two exhaust valves 6A and 6B is defined as a ridge line r on the crown surface of the piston 8, and a pair of inclined surfaces 8a and 8b are formed on both sides of the ridge line r. A pair of recesses 8A and 8B are formed so as to have a maximum depth on the outer peripheral side of the piston that is connected to the inclined surfaces 8a and 8b and is separated from the ridge line. The ridge line is defined as a line that connects between the two intake valves and the exhaust side through the center of the piston, and can be applied to other than the number of exhaust valves per cylinder.

  Here, as shown in FIGS. 3 and 4, the pair of inclined surfaces 8A and 8B are inclined linearly with a substantially constant degree of inclination, but as shown in FIG. The cross sections of 8A and 8B in the direction parallel to the ridgeline r are formed so as to be deepest at the intermediate portion (portion perpendicular to the ridgeline through the center of the piston) and become shallower as they move away from both sides. Yes.

  Next, variable valve gears for the intake valves 5A and 5B will be described with reference to FIGS.

  Above the valve lifter 40 at the ends of the intake valves 5A and 5B, a cam shaft 41 that is driven to rotate around the shaft in conjunction with a crankshaft (not shown) extends in the cylinder row direction. A swing cam 42 is fitted on the outer periphery of the cam shaft 41 so as to be swingable corresponding to the intake valves 5A and 5B. The swing cam 42 abuts on and presses the valve lifter 40. As a result, the intake valves 5A and 5B are driven to open and close against the spring force of a valve spring (not shown).

  Here, between the camshaft 41 and the swing cam 42, the posture of the link that mechanically links both 41 and 42 is changed, and the valve operating angles (open periods) and lift amounts of the intake valves 5A and 5B are changed. There is provided a valve operating angle and lift amount variable device (VEL device) capable of continuously variably controlling.

  The VEL device includes a drive cam 43 that is eccentrically provided on the cam shaft 41 and rotates integrally with the cam shaft 41, a ring-shaped link 44 that is fitted on the outer periphery of the drive cam 43 so as to be relatively rotatable, and a cam shaft 41. A control shaft 45 extending substantially parallel to the cylinder row direction, a control cam 46 provided eccentrically with respect to the control shaft 45 and rotating integrally with the control shaft 45, and rotatable relative to the outer periphery of the control cam 46 And a rocker arm 47 whose one end is rotatably connected to the tip of the ring-shaped link 44, and is rotatably connected to the other end of the rocker arm 47 and the tip of the swing cam 42. 42 has a rod-like link 48 that mechanically cooperates.

  The cam shaft 41 and the control shaft 45 are rotatably supported on the cylinder head side of the engine via a bearing bracket. One end of the control shaft 45 is connected to the output end of an actuator (VEL solenoid) 49 for changing the valve operating angle, and the control shaft 45 is driven to rotate around the shaft within a predetermined control angle range by the VEL solenoid 49. And at a predetermined rotational phase.

  With such a configuration, when the cam shaft 41 rotates in conjunction with the crankshaft, the ring-shaped link 44 substantially translates via the drive cam 43, and the rocker arm 47 swings around the control cam 46, The swing cam 42 swings through the rod-shaped link 48, and the intake valves 5A and 5B are driven to open and close.

  Further, when the control shaft 45 is rotated by the VEL solenoid 49, the center position of the control cam 46, which is the rocking center of the rocker arm 47, is changed, and the postures of the links 44, 48, etc. are changed. The swing angle range of 42 changes. As a result, the valve operating angle and the lift amount continuously change while the central phase of the valve operating angle remains substantially constant. More specifically, the valve operating angle and the lift amount are increased by rotating the control shaft 45 in one direction, and the valve operating angle and the lift amount are decreased by rotating in the other direction. Yes.

  Therefore, duty control of the energization amount of the VEL solenoid 49 with a signal from the ECU 20 can change the rotation phase of the control shaft 45 and change the valve operating angle and the lift amount of the intake valves 5A and 5B. Thus, a valve operating angle and lift amount variable device (VEL device) is configured.

  According to the variable valve system as described above, the combustion chamber is controlled by controlling the lift amount of the intake valves 5A and 5B while the throttle valve is basically fully opened (throttle control is performed only when the intake negative pressure is required). The amount of intake air can be controlled immediately before, and the loss can be reduced as compared with the case of controlling with the upstream throttle valve.

  In this system, the intake valves 5A and 5B are controlled in the vicinity of the intermediate lift, for example, at the time of low rotation and high load.

  The flow of intake air when the intake valve is controlled near the intermediate lift will be described.

  As shown in FIG. 7, the intake air flows into the combustion chamber 1 through an annular gap between the valve head upper surfaces of the intake valves 5A, 5B and the intake ports 3A, 3B, and the initial intake stroke is as shown in FIG. As shown in the figure, a twin-like intake air flow is formed which flows along the cylinder bore wall surface from the intake side to the exhaust side, and then swivels horizontally from the exhaust side through the center of the cylinder to the intake side.

  When entering the compression stroke, as shown in FIG. 9, due to the shape having the inclined surfaces 8a and 8b of the recessed portions 8A and 8B, the flow from the exhaust side to the intake side is high near the ridge line r of the inclined surfaces 8a and 8b. The flow on the outer peripheral side, which is pushed up along the portion and moves from the intake side to the exhaust side, acts to drop downward along the deep portion on the end side of the inclined surfaces 8a and 8b, and is converted into a vortex that swirls in an oblique direction. The

  Then, in the latter stage of the compression stroke, the above conversion action is promoted, and as shown in FIG. 10, it is converted into a substantially vertical swirl flow (reverse tumble flow).

  As described above, when the intake valves 5A and 5B are controlled near the intermediate lift at the time of low rotation and high load by being converted into the vertical swirling flow by the inclined surfaces 8a and 8b of the recessed portions 8A and 8B. However, a reverse tumble flow with sufficient directivity is formed, and finally the reverse tumble flow is collapsed and converted into turbulence near the ignition timing, thereby improving combustion stability and eventually improving fuel efficiency. it can.

  Further, in the present embodiment, as shown in FIG. 1, in the cross section in the direction parallel to the ridge line r, the intermediate part (the part passing through the piston central part and perpendicular to the ridge line) is the deepest and is separated from both sides. Therefore, since it is formed to be curved so as to become shallow, a tumble flow that smoothly flows in an arc shape along the curve can be generated.

  However, simply, as in the second embodiment shown in FIG. 11, the recessed portions 8A and 8B are formed so as to be linear with a constant depth in the cross section parallel to the ridge line r. May be.

  FIG. 12 shows a third embodiment in which the inclined surfaces 8a and 8b connected to both sides of the ridge line r are curved so that the inclination is large on the side close to the ridge line and gradually decreases as the distance from the ridge line increases. It is formed by inclining in a shape.

  In this way, in particular, a vortex swirling in an oblique direction in the first half of the compression stroke is efficiently generated, and a reverse tumble flow generation in the second half of the compression stroke is facilitated.

  FIG. 13 shows a fourth embodiment, in which two inclined surfaces 8a and 8b connected to both sides of the ridge line r are symmetric with respect to the deepest portion in a cross section in a direction parallel to the ridge line r. The planes 8ai and 8ae (8ai and 8ae) are connected to each other.

  In this way, the reverse tumble can be generated while minimizing the area of the piston crown surface and suppressing heat loss.

  FIG. 14 shows a fifth embodiment, in which the inclined surfaces 8a and 8b connected to both sides of the ridge line r have a step in the cross section in a direction parallel to the ridge line r and the deepest part with respect to the surfaces on both sides. It has a concave shape.

  In this way, since only the deepest part needs to be recessed, reverse tumble can be generated while suppressing an increase in the combustion chamber volume. Moreover, it can process easily, for example by extending the recessed part using the recessed part for valve recesses.

FIG. 2 is a longitudinal sectional view showing a main part of the direct-injection spark ignition internal combustion engine according to the first embodiment (A-A sectional view of FIG. 2). Cross-sectional view showing the main part of the internal combustion engine BB sectional view of FIG. CC sectional view of FIG. Configuration diagram of variable valve gear Cross-sectional view of the main part of FIG. Main part longitudinal cross-sectional view which shows the state when the intake_air | air_inflow in the combustion chamber in the vicinity of an intermediate | middle lift in embodiment same as the above flows. Similarly, a cross-sectional view showing the state of intake air flow during the intake stroke Similarly, a cross-sectional view showing the state of intake air flow in the first half of the compression stroke (cross-sectional view taken along the line AA in FIG. 8). Similarly, a longitudinal sectional view showing the state of intake air flow in the latter half of the compression stroke The figure equivalent to the AA cross section of FIG. 2 in 2nd Embodiment. The figure equivalent to the BB cross section and CC cross section of FIG. 2 in 3rd Embodiment The figure equivalent to the AA cross section of FIG. 2 in 4th Embodiment. The figure equivalent to the AA cross section of FIG. 2 in 5th Embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Combustion chamber 2 Spark plug 5A, 5B Intake valve 6A, 6B Exhaust valve 8 Piston 8a, 8b Inclined surface 8ai, 8be Inclined surface 8A, 8B Recessed part 20 ECU
21 Valve operating angle and lift variable device r Ridge line

Claims (7)

In the combustion chamber structure of an internal combustion engine provided with two intake valves for each cylinder,
A pair of inclined surfaces are provided on both sides of the ridge line on the piston crown surface through the center of the piston and connecting the two intake valves and the exhaust side, and the ridge line is separated from the ridge line. A combustion chamber structure for an internal combustion engine, wherein a pair of recesses are formed so that the depth is maximum on the outer peripheral side of the piston.   2. The combustion chamber structure of an internal combustion engine according to claim 1, wherein the pair of inclined surfaces are linearly inclined with a substantially constant inclination.   2. The internal combustion engine according to claim 1, wherein the pair of inclined surfaces are inclined in a curved line so that the inclination is large on a side close to the ridge line, and the inclination gradually decreases as the distance from the ridge line is increased. Engine combustion chamber structure.   The pair of recesses are formed so as to be deepest at the intermediate portion and become shallower as they move away from both sides in a direction parallel to the ridge line. A combustion chamber structure of an internal combustion engine according to any one of the above.   The combustion chamber structure for an internal combustion engine according to claim 4, wherein the inclined surfaces connected to both sides of the ridge line are formed by connecting two planes so as to be symmetrical with respect to the deepest portion.   5. The combustion chamber structure of an internal combustion engine according to claim 4, wherein the deepest portion of each inclined surface has a shape that is recessed with steps on both sides.   The combustion of the internal combustion engine according to any one of claims 1 to 3, wherein the pair of recesses are formed at a substantially constant depth in a direction parallel to the ridgeline. Chamber structure.

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