JP2006329209A - Variable valve timing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable valve timing device capable of appropriately controlling an opening overlap of intake/exhaust valves and thereby positively suppressing discharge of unburned HC at a cold start. <P>SOLUTION: At the cold start of an engine, an overlap of the intake/exhaust valves is formed to be larger than at a warm start and to include a wide range of an intake stroke (see (2) in the figure), the overlap of an exhaust stroke range is increased, and without discharging liquid fuel accumulated inside the intake port as it is to the exhaust side, the liquid fuel is made to flow into a cylinder accompanying falling of a piston in the intake stroke to positively combust the fuel. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a variable valve timing device that adjusts the opening and closing timing of an intake valve and an exhaust valve of an internal combustion engine (hereinafter referred to as an engine).

There is a technique for reducing the discharge of unburned HC by increasing the valve opening overlap period of the exhaust valve and the intake valve during cold start. For example, in Japanese Patent Laid-Open No. 11-336574 (Patent Document 1), the normal exhaust valve is closed at the intake top dead center TDC, advanced at the time of cold start to improve the afterburning effect, and the intake valve Discloses a technique for increasing the internal EGR by increasing the maximum advance angle to increase the overlap period.
JP 11-336574 A

However, in the technique described in the above publication, since the overlap period is formed before the top dead center TDC, that is, in the exhaust stroke, when liquid fuel is present, a part of the fuel is discharged without going through the combustion stroke. There is a problem that it ends up.
Taking an intake pipe injection type engine as an example, the fuel injected into the intake port adheres to the back side of the intake valve and the intake port immediately after the cold start, and liquids near the lower valve seat due to its own weight during the valve opening period. It becomes and accumulates. If the intake valve opens during the exhaust stroke (the overlap is in the exhaust stroke), it flows directly into the cylinder during the initial explosion stroke of each cylinder. In addition, the exhaust in the cylinder flows backward to the intake pipe after the first explosion, but part of the exhaust flows into the cylinder by its own weight because the fuel is in a liquid state.

  And it will vaporize in the cylinder as it is by pushing out the piston, and a part will be discharged to the exhaust side in an unburned state. After this, the exhaust valve closes before the top dead center, so the unburned fuel that has passed through does not return to the cylinder, or the unburned fuel is low in temperature, so it is difficult for the afterburning to proceed and is discharged to the atmosphere as it is. . When the engine temperature rises after repeated combustion, the effect of fuel vaporization due to increased overlap during the exhaust stroke appears, and the inflow of liquid fuel into the cylinder is suppressed and the passage through the exhaust passage is reduced.

Therefore, in order to reduce the unburned HC emission at the cold start, it is necessary to prevent the liquid fuel that cannot be evaporated immediately after the start from being discharged before increasing the internal EGR and promoting the vaporization of the fuel. is there.
An object of the present invention is to provide a variable valve timing device that can appropriately control the opening overlap of intake and exhaust valves and thereby reliably suppress the discharge of unburned HC during cold start. .

  In order to achieve the above object, a first aspect of the present invention provides a variable valve timing device for increasing an overlap of an opening period of an intake valve and an exhaust valve of an intake pipe injection type internal combustion engine at the time of cold start. Occasionally, the exhaust stroke range is increased after an overlap is formed that includes a larger overlap than the exhaust stroke range that is on the front side of the top dead center and the intake stroke range that is on the rear side of the top dead center. It is characterized by comprising valve timing control means for increasing the overlap.

The invention of claim 2 is characterized in that, in the invention of claim 1, the valve timing control means continues a state in which an overlap with an increased overlap and a large intake stroke range is formed for a predetermined time. To do.
According to a third aspect of the present invention, in the first aspect of the invention, the valve timing control means sets the overlap to almost zero from the start of cranking to immediately after the first explosion at the time of cold start, and increases the increase immediately after the first explosion. The present invention is characterized in that an overlap including a large range of intake strokes is formed.

  According to a fourth aspect of the present invention, in the first aspect of the invention, the valve timing control means reduces the overlap of the intake stroke range when increasing the overlap of the exhaust stroke range.

  According to the variable valve timing apparatus of the first aspect of the present invention, at the time of the cold start, the overlap of the intake and exhaust valves is an overlap that is increased more than that at the time of the warm start and is an exhaust stroke that is in front of the top dead center. First, control is performed so as to form an overlap including a large intake stroke range on the rear side of the top dead center. During a cold start when fuel vaporization is not promoted, the fuel injected into the intake port remains in liquid form near the valve seat during the valve closing period. During the overlap of the intake stroke range, as the piston descends, it flows into the cylinder and burns reliably. If the overlap of the exhaust stroke range is increased thereafter, for example, the exhaust gas once exhausted to the exhaust side flows back into the intake port, thereby preventing liquid fuel from being discharged. The emission of unburned HC at the time can be suppressed.

  According to the variable valve timing apparatus of the second aspect of the present invention, at the time of cold start, the state of forming an overlap that is larger than that at the time of warm start and that includes a large intake stroke range is continued for a predetermined time. Therefore, by appropriately securing this predetermined time, the fuel accumulated in the vicinity of the valve seat can surely flow into the cylinder and burn during the overlap of the intake stroke range immediately after starting.

According to the variable valve timing device of claim 3 of the present invention, the overlap is almost zero at the time of cranking, so that the injected fuel is burned without passing through to the exhaust side, and the engine is easily subjected to the initial explosion. Can be reached.
According to the variable valve timing device of claim 4 of the present invention, when the overlap of the exhaust stroke range is increased, the overlap of the intake stroke range is decreased, so that most of the overlap is located in the exhaust stroke range. Thus, exhaust gas near the peak of the in-cylinder temperature is discharged by the early opening of the exhaust valve. Thereby, for example, when a catalyst is provided in the exhaust passage, early activation of the catalyst can be realized by the afterburning effect.

[First Embodiment]
A first embodiment in which the present invention is embodied in a variable valve timing device that varies the opening / closing timing of an intake valve will be described below.
FIG. 1 is an overall configuration diagram showing the variable valve timing device of the first embodiment. As shown in this figure, the engine 1 is configured as an intake pipe injection type engine, and a DOHC 4-valve type is adopted as the valve operating mechanism. Timing pulleys 4 a and 4 b are connected to the front ends of the intake cam shaft 3 a and the exhaust cam shaft 3 b on the cylinder head 2, and these timing pulleys 4 a and 4 b are connected to the crankshaft 6 via a timing belt 5. As the crankshaft 6 rotates, the camshafts 3a and 3b are rotationally driven together with the timing pulleys 4a and 4b, and the intake and exhaust valves 7a and 7b are driven to open and close by the camshafts 3 and 3b.

  A vane type variable timing mechanism 8 is provided between the intake camshaft 3a and the intake side timing pulley 4a. The configuration of the timing variable mechanism 8 is well known in, for example, Japanese Patent Application Laid-Open No. 2000-27609, and will not be described in detail. 3a is connected. An oil control valve (hereinafter referred to as OCV) 9 is connected to the timing variable mechanism 8, and hydraulic pressure is applied to the vane rotor in accordance with switching of the OCV 9 using hydraulic oil supplied from the oil pump 10 of the engine 1. As a result, the phase of the cam shaft 3a with respect to the timing pulley 4a, that is, the opening / closing timing of the intake valve 7a is adjusted.

On the other hand, an intake passage 12 is connected to the intake port 11 of the cylinder head 2, and intake air introduced into the intake passage 12 from the air cleaner 13 as the piston 16 descends flows in accordance with the opening of the throttle valve 14. After the adjustment, the fuel is mixed with the fuel injected from the fuel injection valve 15 and flows into the cylinder through the intake port 11 when the intake valve 7a is opened.
Further, an exhaust passage 18 is connected to the exhaust port 17 of the cylinder head 2, and the exhaust gas after being ignited by the spark plug 19 and exhausted is exhausted from the exhaust port 17 as the piston 16 rises when the exhaust valve 7 b is opened. It is guided to the passage 18 and discharged to the outside through the catalyst 20 and a silencer (not shown).

  In the vehicle compartment, an input / output device (not shown), a storage device (ROM, RAM, BURAM, etc.) used for storing control programs and control maps, an ECU (engine) equipped with a central processing unit (CPU), a timer counter, etc. A control unit 31 is installed and performs overall control of the engine 1. Various sensors such as a rotational speed sensor 32 for detecting the engine rotational speed Ne, a throttle sensor 33 for detecting the opening degree TPS of the throttle valve 14, and a water temperature sensor 34 for detecting the cooling water temperature Tw are connected to the input side of the ECU 31. Yes. Further, the OCV 9, the fuel injection valve 15, the spark plug 19 and the like are connected to the output side of the ECU 31.

  The ECU 31 determines an ignition timing, a fuel injection amount, and the like based on detection information from each sensor, and drives and controls the ignition plug 19 and the fuel injection valve 15. Further, the target phase angle of the timing variable mechanism 8 is calculated from the engine speed Ne and the throttle opening TPS according to a preset map, and the OCV 9 is driven to control the actual phase angle to the target phase angle. Further, when the engine 1 is cold-started, in order to suppress the discharge of unburned HC, dedicated phase angle control different from that at the time of warm-start is executed.

Therefore, the phase angle control executed by the ECU 31 at the cold start will be described based on the time chart of FIG.
The opening / closing timing of the intake valve 7a is adjusted by the timing variable mechanism 8 within the range of (1) to (3) in the figure, while the opening / closing timing of the exhaust valve 7b is fixed at the position shown in the figure. First, when the engine is stopped, the opening / closing timing of the intake valve 7a is held at the most retarded position shown in (1) in the figure, and the intake valve 7a starts to open after the intake top dead center TDC. It is like that. Since the timing of opening the valve is almost the same as the timing of closing the exhaust valve 7b, the valve opening overlap between the intake valve 7a and the exhaust valve 7b is almost zero.

  When the ignition switch is started by the driver, cranking of the engine 1 is started at this phase position, and ignition timing control and fuel injection control are executed by the ECU 31. Thus, since the valve opening overlap of intake and exhaust is set to 0 at the time of cranking, the injected fuel is burned without passing through to the exhaust side, and the engine 1 is easily cranked to reach the first explosion.

  The phase angle control up to this point is common to the warm start and the cold start. When the ECU 31 determines that the temperature is started based on the coolant temperature Tw or the like, the opening / closing timing of the intake valve 7a is kept at the most retarded position as long as the idling operation is continued even after the completion of the start. When the engine speed Ne and the throttle opening TPS increase due to the starting of the engine, etc., it is controlled to the advance side accordingly.

  On the other hand, at the time of cold start, after waiting for about 2 seconds from the first explosion, the opening / closing timing of the intake valve 7a is controlled to the advance side, and is shifted to the position (2) in the figure. By the control to the advance side, the intake valve 7a starts to open slightly ahead of the top dead center TDC. Therefore, a valve opening overlap is formed with the exhaust valve 7b, and most of this overlap period is located behind the top dead center TDC (hereinafter referred to as an intake stroke range).

  At the time of this cold start, vaporization of the fuel injected into the intake port 11 is not promoted, so that the fuel adheres to the back side of the intake valve 7a and the inner wall of the intake port 11 and is lowered by its own weight during the valve closing period. The liquid is collected near the valve seat. This trend is even more pronounced with increased fuel to ensure ignition. As described above, when the intake valve 7a is opened in the intake stroke range, the fuel flows into the cylinder as the piston 16 descends in the liquid state, burns in the combustion stroke through the compression stroke, and then exhausts in the exhaust stroke. Will be discharged to the side. That is, it is possible to prevent a situation in which the liquid fuel flowing into the cylinder is discharged to the exhaust side as it is, as in the prior art described in Japanese Patent Laid-Open No. 11-336574 that forms the overlap period in the exhaust stroke.

  In addition, since the opening of the intake valve 7a slightly precedes the top dead center TDC as described above, there is a very short overlap period on the front side of the top dead center TDC (hereinafter referred to as the exhaust stroke range). However, even if the liquid fuel passes through the exhaust side during this period, it is drawn back into the cylinder in the subsequent intake stroke range, and is reliably vaporized and burned. Furthermore, at this point, the engine temperature is still low and combustion is not stable, but the overlap is relatively small and internal EGR is difficult to occur. Therefore, the amount of exhaust gas that flows back into the cylinder after being discharged to the exhaust side is small. This makes it easy to maintain and raise the rotation after starting.

The above-described phase is continued for a predetermined time from the first explosion, and thereafter, the opening / closing timing of the intake valve 7a is further controlled to the advance side, and is held at the most advanced position (3) in the figure. Therefore, the valve opening overlap of the intake / exhaust valves 7a and 7b is greatly increased to the advance side, and completely includes the exhaust stroke range.
At this time, the timing at which the exhaust valve 7b closes is after the top dead center TDC, and at this point after several strokes from the initial explosion, a sufficient negative pressure is applied to the intake port 11 side as the engine rotational speed Ne increases. Since the pressure is generated, the internal EGR increases, and the exhaust gas once exhausted to the exhaust side (exhaust gas containing a large amount of unburned HC discharged at the end of the exhaust stroke) flows back into the intake port 11. The exhaust gas that has flowed back is burned in the next combustion stroke, and the intake port 11 is heated by receiving heat from the exhaust gas to promote the vaporization of the next injected fuel, so that the liquid fuel is surely discharged to the exhaust side. To be prevented.

Thereafter, when a predetermined time elapses, the opening / closing timing of the intake valve 7a is retarded and returned to the start-up start state shown in (1) in the figure. As a result, the valve opening overlap of the intake / exhaust valves 7a and 7b is reduced, the internal EGR is reduced, the combustion is stabilized, and a smooth idle operation is realized.
As described above, in the variable valve timing apparatus according to the present embodiment, immediately after the start of the cold start, the valve opening overlap of the intake and exhaust valves 7a and 7b is formed in the intake stroke range ((2) in FIG. 2). The liquid fuel in the intake port 7a is caused to flow into the cylinder as the piston 16 descends to be surely burned, thereby preventing the liquid fuel from being discharged as it is. Therefore, unlike the prior art in which the overlap period is formed in the exhaust stroke, it is possible to prevent the liquid fuel that has flowed into the cylinder from being discharged as it is, thereby reliably discharging unburned HC at the cold start. Can be suppressed.

In this embodiment, the opening / closing timing of the intake valve 7a is changed in the order of (1), (2), (3) in FIG. You may make it change in order of 2), (2), (3). Even in this case, similarly to the above, the liquid fuel in the intake port 7a can be reliably burned, and the discharge of unburned HC can be suppressed.
[Second Embodiment]
Next, a second embodiment in which the present invention is embodied in another variable valve timing device will be described. The variable valve timing device of the present embodiment can change the opening / closing timing of the exhaust valve 7b in addition to the intake valve 7a, and other configurations are the same as those of the first embodiment. Therefore, description of common components will be omitted, and differences will be described mainly.

  As shown in FIG. 1, a timing variable mechanism 41 similar to that on the intake side is provided between the exhaust camshaft 3b and the exhaust timing pulley 4b. The timing variable mechanism 41 is connected to the ECU 31 via the OCV 42. Has been. At the time of cold start, the timing variable mechanism 41 is controlled by the ECU 31 together with the intake-side timing variable mechanism 8, and the control state will be described below based on the time chart of FIG.

First, when the engine is stopped, the opening / closing timing of the intake valve 7a is held at the most retarded position shown in (4) in the figure, while the opening / closing timing of the exhaust valve 7b is the most advanced as shown in (7) in the figure. It is held in the angular position, and the valve opening overlap between them is completely zero.
The cranking of the engine 1 is started at this phase position, and after about 2 seconds, the opening / closing timing of the intake valve 7a is controlled to the advance side as indicated by (5) in the figure, and the opening / closing timing of the exhaust valve 7b. Is controlled to the retard side as indicated by (8) in the figure. As a result, an overlap is formed between the two, and most of the overlap period is located in the intake stroke range as in the case of the first embodiment ((2) in FIG. 2). Therefore, the liquid fuel accumulated in the intake port 11 flows into the cylinder as the piston 16 descends, and is reliably combusted and is prevented from being discharged in the liquid state.

  Thereafter, when a predetermined time has elapsed from the initial explosion, the opening / closing timing of the intake valve 7a is further controlled to the advance side as indicated by (6) in the figure, and the opening / closing timing of the exhaust valve 7b is controlled to the advance side. This returns to the position (7) in the figure. Therefore, most of the valve opening overlaps of the intake / exhaust valves 7a and 7b are located in the exhaust stroke range, and exhaust gas near the peak of the in-cylinder temperature is discharged by the early opening of the exhaust valve 7b, and the afterburning effect causes Early activation of the catalyst 20 is realized.

As described above, the variable valve timing device of the present embodiment forms the valve opening overlap of the intake / exhaust valves 7a and 7b in the intake stroke range immediately after the start of the cold start, as in the first embodiment (see FIG. 3). (5) and (8)), the liquid fuel in the intake port 11 can be reliably burned, and the discharge of unburned HC can be reliably suppressed.
Further, since the opening / closing timing of the exhaust valve 7b can be changed in addition to the intake valve 7a, the length and position of the overlap period can be freely set. As a result, for example, in the first embodiment, the overlap inevitably increases with the advance angle of the intake valve 7a (from (2) to (3) in FIG. 2), but in this embodiment, the overlap is increased. It is possible to move from the intake stroke range to the exhaust stroke range without performing ((5), (8) to (6), (7) in FIG. 3), and as a result, the optimum overlap amount for the current operating state That is, there is also an effect that the internal EGR amount can be achieved and stable combustion can be realized.

  In this embodiment, the opening / closing timing of the intake valve 7a is changed in the order of (4), (5), (6) in FIG. 3 in accordance with the starting process, and the opening / closing timing of the exhaust valve 7b is changed to (7). , (8), (7), but other control orders are also conceivable. For example, the intake valve 7a may be changed in the order of (5), (5), (6) as in the other example of the first embodiment, and the exhaust valve 7b may be changed to (8), (8 ), (7), or (7), (8), (8).

  Although the description of the embodiment is finished as described above, the aspect of the present invention is not limited to the first and second embodiments. For example, in each of the above embodiments, the vane type timing variable mechanism 8 is provided. However, the configuration of the timing variable mechanism is not limited to this, and for example, a helical type timing variable mechanism may be used. An eccentric timing variable mechanism that changes the amount of eccentricity, a switching timing variable mechanism that selectively operates cams of different characteristics, an electromagnetic timing variable mechanism that directly opens and closes a valve by an electromagnetic actuator, etc. It may be replaced.

  In each of the above embodiments, the present invention is applied to the intake pipe injection type engine 1. However, the present invention can also be applied to, for example, a cylinder injection type engine in which fuel is directly injected into a cylinder. Even in this case, by forming an overlap in the intake stroke range, the fuel injected in the vicinity of the top dead center TDC can be surely burned without being discharged as a result, and as a result, unburned as in the above embodiments. HC emission can be suppressed.

It is a whole lineblock diagram showing the variable valve timing device of a 1st embodiment. It is a time chart which shows the execution situation of phase angle control by the variable valve timing device of a 1st embodiment. It is a time chart which shows the execution situation of phase angle control by the variable valve timing device of a 2nd embodiment.

Explanation of symbols

7a Intake valve 7b Exhaust valve 31 ECU (valve timing control means)

Claims (4)

In the variable valve timing device for increasing the overlap of the valve opening period of the intake valve and the exhaust valve of the intake pipe injection type internal combustion engine at the time of cold start,
At the time of the cold start, an overlap that is larger than that at the time of the warm start and includes an intake stroke range that is behind the top dead center than the exhaust stroke range that is before the top dead center is formed. A variable valve timing device comprising valve timing control means for increasing the overlap of the exhaust stroke range.   2. The variable valve timing device according to claim 1, wherein the valve timing control means continues a state in which the increased overlap and an overlap including a large intake stroke range are continued for a predetermined time.   At the time of the cold start, the valve timing control means sets the overlap to almost 0 from the start of cranking to immediately after the first explosion, and includes the increased overlap immediately after the first explosion and including a large intake stroke range. The variable valve timing device according to claim 1, wherein the variable valve timing device is formed.   2. The variable valve timing device according to claim 1, wherein the valve timing control means reduces the overlap of the intake stroke range when increasing the overlap of the exhaust stroke range.

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