JP2002206436A - Variable-valve timing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable-valve timing device, capable of surely suppressing discharging of unburned HC by properly controlling the opening and closing timings of intake and exhaust valves at the time of cold starting SOLUTION: At the beginning of cold start, when an exhaust passage has yet to be sufficiently heated and afterburning effect cannot be expected, overlapping amount is increased (2, 3). As a result of this, the exhaust gas once passed through to the exhaust side is returned into a cylinder and burned to suppress the discharge of unburned HC, and the exhaust gas is allowed to make reverse flow in the intake side, to realize promotion of the vaporization of fuel and the temperature rise of the intake port. Then, when the exhaust passage is heated (4), the exhaust valve is spark-advanced to discharge the exhaust gas during combustion, and catalyst is activated earlier by the afterburning effect in the exhaust passage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable valve timing device for adjusting the opening and closing timing of an intake valve and an exhaust valve of an engine.

[0002]

2. Related Background Art As is well known, most of unburned HC discharged from an engine is generated during a cold start, and as a countermeasure, an improvement in catalyst performance, an increase in capacity, and the like have been attempted. However, in order to purify a large amount of unburned HC at the time of a cold start only by taking measures against the catalyst, there is a problem that the amount of noble metal used in the catalyst is greatly increased and cost efficiency is low.

Therefore, for example, Japanese Patent Application Laid-Open No. 11-336574
As disclosed in the variable valve timing device described in Japanese Patent Application Laid-Open Publication No. H10-175, a technique has been proposed in which the opening and closing timing of the intake and exhaust valves is appropriately controlled at the time of a cold start to activate the catalyst early to reduce unburned HC. . In this variable valve timing device, at the time of a cold start, the exhaust valve is advanced from normal time to discharge the exhaust gas during combustion, and the unburned HC contained in the exhaust gas is burned in the exhaust passage, and the afterburning effect is used. The catalyst is activated early. Further, in order to promote the after-burning effect at this time, the intake valve is greatly advanced to increase the amount of overlap with the exhaust valve, and the exhaust gas flowing backward to the intake side (internal EG)
R) is increased to slow down the combustion and increase the emission of unburned HC.

[0004]

However, in the variable valve timing device disclosed in the above-mentioned publication, as will be apparent from the description of the flow chart and the like, advance control of the intake and exhaust valves is performed simultaneously at the time of cold start. Failure occurs. The advance control of the intake and exhaust valves is performed after a few strokes from the initial explosion.At this point, since the temperature of the exhaust passage and the like has not been sufficiently raised, the exhaust gas during combustion is advanced by the advance of the exhaust valve. Even if the exhaust gas is exhausted, a situation occurs in which afterburning stops in the exhaust passage and the exhaust gas is exhausted as it is.

[0005] In the early stage of a cold start, fuel injected into the intake port accumulates in the port while the intake valve is closed, and flows into the cylinder with the opening of the intake valve. Some of them pass through the exhaust side as unburned HC during the overlap period without burning. At this time, since the exhaust valve is closed before the top dead center TDC, most of the unburned HC that has passed to the exhaust side is exhausted without being re-inhaled into the cylinder.

On the other hand, when the intake valve is advanced and opened early, a part of the exhaust gas flows backward to the intake side to promote the vaporization of the fuel in the intake port and to raise the temperature of the intake port itself. However, since the temperature of exhaust gas remaining in the cylinder is lowered by early opening of the exhaust valve, these favorable effects are greatly reduced. Due to the above factors, it is difficult to say that simultaneously advancing the intake and exhaust valves at the beginning of a cold start is optimal control, and more appropriate control that matches the temperature rise of the engine during cold start is desired. I was

An object of the present invention is to provide a variable valve timing device which can appropriately control the opening / closing timing of the intake / exhaust valve at the time of starting, thereby reliably suppressing the discharge of unburned HC.

[0008]

According to the first aspect of the present invention, there is provided a variable valve for varying the valve timing of an intake valve and an exhaust valve to vary the amount of overlap between the intake valve and the exhaust valve. In the timing device, at least one of an intake valve timing variable unit that varies a valve timing of an intake valve, an exhaust valve timing variable unit that varies a valve timing of an exhaust valve, and at least one of an intake valve timing variable unit and an exhaust valve timing variable unit when the engine is started. Valve timing control means for operating one of them to increase the amount of overlap and thereafter advancing the exhaust valve by means of exhaust valve timing variable means.

Therefore, when the engine is started, first, at least one of the intake valve timing varying means and the exhaust valve timing varying means increases the amount of overlap between the intake and exhaust, whereby the exhaust gas once passing through to the exhaust side is drawn back into the cylinder. And combusted, the emission of unburned HC is suppressed, and the exhaust gas flows back to the intake side to promote fuel vaporization and increase the temperature of the intake port. Is advanced, the exhaust gas during combustion is discharged, and the catalyst is activated early by the afterburning effect in the exhaust passage. That is, the opening / closing timing of the intake / exhaust valve is always optimally controlled according to the temperature rise state of the engine at the time of starting.

According to a second aspect of the present invention, in the variable valve timing apparatus for varying the valve timing of the intake valve and the exhaust valve to vary the amount of overlap between the intake valve and the exhaust valve, the valve timing of the intake valve is varied. A variable intake valve timing means, a variable exhaust valve timing means for varying the valve timing of an exhaust valve, and a variable exhaust valve timing means after a predetermined period of time from the start of the advance of the intake valve by the operation of the variable intake valve timing at engine start. And a valve timing control means for operating the exhaust valve to advance the exhaust valve.

Therefore, when the engine is started, first, the advance of the intake valve is started by the intake valve timing variable means, whereby the exhaust gas that has once passed to the exhaust side is drawn back into the cylinder and burns, and the unburned HC is removed. In addition to preventing exhaust, the exhaust gas flows back to the intake side to promote the vaporization of fuel and increase the temperature of the intake port. Thereafter, the exhaust valve is advanced by the exhaust valve timing variable means, and the exhaust gas during combustion is reduced. The catalyst is discharged and the catalyst is activated early by the afterburning effect in the exhaust passage. That is, the opening / closing timing of the intake / exhaust valve is always optimally controlled according to the temperature rise state of the engine at the time of starting.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] Hereinafter, a first embodiment will be described.
A variable valve timing device according to a first embodiment of the present invention will be described. 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 four-valve type is adopted as a valve operating mechanism thereof. Timing pulleys 4a, 4b are provided at the front ends of the intake cam shaft 3a and the exhaust cam shaft 3b on the cylinder head 2.
The timing pulleys 4 a and 4 b are connected to a crankshaft 6 via a timing belt 5. As the crankshaft 6 rotates, the timing pulley 4
The camshafts 3a and 3b are rotationally driven together with the camshafts 3a and 4b, and the camshafts 3 and 3b open and close the intake valve 7a and the exhaust valve 7b.

Each camshaft 3a, 3b and timing pulley 4
A vane-type timing variable mechanisms 8a and 8b are provided between the valves a and 4b as intake valve timing variable means and exhaust valve timing variable means. The configuration of the variable timing mechanisms 8a and 8b is described in, for example,
Although the details are not described because they are known in Japanese Patent No. 27609/27, a vane rotor is rotatably provided in a housing provided on the timing pulleys 4a and 4b, and the intake camshaft 3a or the exhaust camshaft 3b is connected to the vane rotor. It is configured. Oil control valves (hereinafter, referred to as OCVs) 9a, 9b are connected to the variable timing mechanisms 8a, 8b, and the vane rotors are switched according to the switching of the OCVs 9a, 9b using hydraulic oil supplied from an oil pump 10 of the engine 1. As a result, the phase of the camshafts 3a, 3b with respect to the timing pulleys 4a, 4b, that is, the opening / closing timing of the intake / exhaust valves 7a, 7b, is adjusted.

On the other hand, the intake port 11 of the cylinder head 2
The intake passage 12 is connected to the intake passage 12. The intake air introduced into the intake passage 12 from the air cleaner 13 as the piston 16 descends is adjusted from the fuel injection valve 15 after the flow rate is adjusted according to the opening of the throttle valve 14. And flows into the cylinder via the intake port 11 when the intake valve 7a is opened.

An exhaust passage 18 is connected to the exhaust port 17 of the cylinder head 2, and the exhaust gas ignited by the ignition plug 19 and burned is discharged as the piston 16 rises when the exhaust valve 7 b is opened. 17 to exhaust passage 18
And is discharged outside through the catalyst 20 and a muffler (not shown). In the passenger compartment, an input / output device (not shown), a storage device (ROM, RAM, BURAM, etc.) for storing control programs and control maps, and a central processing unit (C
An engine control unit (ECU) 31 is provided as valve timing control means including a PU (Pull-Down), a timer counter, and the like, and performs overall control of the engine 1. E
The input side of the CU 31 is provided with a rotation speed sensor 32 for detecting the engine rotation speed Ne and an opening degree T of the throttle valve 14.
Various sensors such as a throttle sensor 33 for detecting PS and a water temperature sensor 34 for detecting the cooling water temperature Tw are connected. The output side of the ECU 31 is provided with the OCVs 9a, 9
b, the fuel injection valve 15, the ignition plug 19 and the like are connected.

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

The phase angle control executed by the ECU 31 during the cold start will now be described with reference to FIGS. FIG. 2 is a time chart showing the phase angle control of the camshaft at the time of cold start, and FIG. 3 is an explanatory diagram showing the phase change of the camshaft at the time of cold start in order. First, when the engine is stopped, as shown in FIGS.
The phase a is held at the retard position, the phase of the exhaust camshaft 3b is held at the advanced position, and almost no overlap between intake and exhaust is formed. When the driver starts the ignition switch, cranking of the engine 1 is started at this phase position, and the ECU 31 executes ignition timing control and fuel injection control. At this time, the intake port 11 is equivalent to the outside air temperature, so that fuel vaporization is not promoted, and most of the large amount of injected fuel due to the increased amount of fuel accumulates in the intake port 11 as the liquid fuel while the intake valve 7a is closed. It flows into the cylinder with the opening of the valve 7a. Here, since the intake and exhaust do not substantially overlap as described above, the fuel that has flowed into the cylinder is burned without passing through to the exhaust side, and the first explosion occurs without discharging a large amount of unburned HC.

The phase angle control so far is common to the warm start and the cold start. When the ECU 31 determines that the engine is warm starting based on the cooling water temperature Tw or the like,
As long as the idle operation is continued even after the start is completed, the opening / closing timing of the intake valve 7a is held at the retard position, the opening / closing timing of the exhaust valve 7b is kept at the advanced position, and the engine speed is changed by starting the vehicle. When Ne and the throttle opening TPS increase, the advance is controlled accordingly.

On the other hand, during a cold start, after waiting for a predetermined time t (for example, 2 to 3 seconds) from the initial explosion, the phase of the exhaust camshaft 3b is controlled to the retard side as shown in FIGS. . As a result, the exhaust valve 7b is closed after the top dead center TDC, and the exhaust gas that has once passed to the exhaust side is drawn back into the cylinder by the lowering of the piston 16, and is burned in the next combustion stroke. Then, since the exhaust gas at this time is an exhaust gas at the end of the exhaust stroke that contains a particularly large amount of unburned HC, it is possible to prevent a situation in which a large amount of unburned HC is burned in the next combustion stroke and discharged as it is. Further, since the opening of the exhaust valve 7b is also delayed, the combustion period is prolonged to promote oxidation of unburned HC, and the temperature of exhaust gas in the cylinder is raised.

Further, since the amount of overlap increases with the retard of the exhaust camshaft 3b, the high-temperature exhaust gas flows back to the intake side as internal EGR to accelerate the vaporization of the fuel in the intake port 11. In addition to the effect of increasing the temperature of the intake port 11 itself, at this time, since the negative pressure on the intake side is increased due to the rapid increase in the engine rotation speed Ne due to the initial explosion, the backflow of exhaust gas becomes sharp, and the intake port 11
It also has the effect of blowing off the liquid fuel that has accumulated inside and atomizing it.

At the same time as the retard control of the exhaust camshaft 3b or at a timing slightly delayed, the phase of the intake camshaft 3a is controlled to the advanced side as shown in FIGS. The amount of overlap is further increased. At this time, the fuel is more likely to evaporate as the exhaust gas temperature rises as compared to the time of the first explosion, and the opening of the intake valve 7a is early, so that the in-cylinder temperature is increased together with the compression temperature. Since the atomization of the liquid fuel by the internal EGR is still performed, stable combustion is continued even if the internal EGR is increased by increasing the amount of overlap.

After the lapse of a predetermined time, the phase of the exhaust camshaft 3b is controlled to the advanced side as shown in FIGS. At this time, since the temperature of the exhaust passage 18 and the like has risen as compared with the above-mentioned time, when the exhaust gas during combustion is discharged by the advance of the exhaust valve 7b, the exhaust gas is exhausted by the afterburning effect. The combustion continues even within 18 and the catalyst 2
0 is activated early. Although the overlap amount decreases due to the advance angle of the exhaust valve 7b, at this time, since the negative pressure on the intake side is further increased, the above-mentioned effect of returning the exhaust gas into the cylinder is sufficiently exhibited. The emission of fuel HC is suppressed.

On the other hand, when a predetermined time elapses thereafter, the phase of the intake camshaft 3a is controlled to the retard side, and the amount of overlap between intake and exhaust is reduced, thereby stabilizing combustion. At the same time, the air-fuel ratio is controlled to the lean side to suppress the generation of unburned HC due to unburned fuel, and the ignition timing is adjusted to compensate for the decrease in the amount of heat generated by the lean operation and to raise the exhaust gas temperature. The retard is performed, and the temperature of the catalyst 20 is continuously raised.

As described above, in the variable valve timing apparatus according to the present embodiment, in the early stage of the cold start in which the exhaust passage 18 and the like are not sufficiently heated yet and the afterburning effect cannot be expected.
The overlap amount is increased by the retard angle of the exhaust valve 7b and the advance angle of the intake valve 7a (in FIG. 3), whereby the exhaust gas that has once passed to the exhaust side is drawn back into the cylinder and burned, and the unburned HC is reduced. In addition to preventing the exhaust gas, the exhaust gas is caused to flow back to the intake side to promote the vaporization of the fuel and to raise the temperature of the intake port 11. On the other hand, when the temperature of the exhaust passage 18 and the like is increased (FIG. 3), the exhaust gas is exhausted. The valve 7b is advanced to discharge the exhaust gas during combustion, and the after-burning effect in the exhaust passage 18 activates the catalyst 20 early.

That is, the intake / exhaust valve 7 is controlled according to the temperature rise condition of the engine 1 at the time of cold start (temperature rise condition of the exhaust passage 18 and the like).
Since the opening and closing timings of the valves a and 7b are always optimally controlled, the emission of unburned HC can be reliably suppressed.
Also, when the engine rotation speed Ne is low, such as at the time of starting, the hydraulic oil supplied from the oil pump 10 of the engine 1 is not sufficient, but at the time of the cold start, the intake and exhaust camshafts 3a, 3a, as described above. Since the phase of 3b is changed before and after, limited hydraulic oil is always intensively supplied to one of the variable timing mechanisms 8a and 8b, so that reliable phase angle control can be realized.

[Second Embodiment] Next, a variable valve timing apparatus according to a second embodiment of the present invention will be described. The variable valve timing device of the present embodiment includes:
The order of controlling the phase angle of the intake and exhaust camshafts 3a and 3b is changed, and the other configuration is the same as that of the first embodiment. Therefore, description of common components will be omitted, and differences will be mainly described.

FIG. 4 is a time chart showing the phase control of the camshaft at the time of cold start, and FIG. 5 is an explanatory diagram showing the phase change of the camshaft at the time of cold start. First, when the engine is stopped, the phases of the intake and exhaust camshafts 3a and 3b are both held at the retarded position as shown in FIGS. 4 and 5, and an overlap including the intake stroke and the exhaust stroke is formed. When starting is performed at this phase position, the exhaust gas that has once passed to the exhaust side is drawn back into the cylinder by the lowering of the piston 16 and burned in the next combustion stroke, leading to the first explosion without discharging unburned HC. At this time, an overlap only in the intake stroke may be formed. In this case, it is possible to more reliably prevent the exhaust gas from passing to the exhaust side.

At the time of cold start, after waiting for a predetermined time t (for example, 2 to 3 seconds) from the initial explosion, the phase of the intake camshaft 3a is controlled to the advanced side as shown in FIGS. . The operation at this time is the same as in the case of FIGS. 2 and 3 of the first embodiment. Exhaust gas that has passed to the exhaust side is drawn back into the cylinder to prevent unburned HC from being discharged, and to reduce the amount of overlap. Due to the increase, the internal EGR flowing backward to the intake side is increased, thereby promoting the vaporization of the fuel in the intake port 11 and increasing the temperature of the intake port 11 itself.

After a lapse of a predetermined time, the phase of the exhaust camshaft 3b is controlled to the advanced side as shown in FIGS. The operation at this time is the same as in the case of FIGS. 2 and 3 of the first embodiment. Exhaust gas during combustion is discharged by the advance angle of the exhaust valve 7b, and combustion continues in the exhaust passage 18 by the afterburning effect. Thus, the catalyst 20 is activated early. After the elapse of a predetermined time, the phase of the exhaust camshaft 3b is controlled to the retard side, and subsequently, the phase of the intake camshaft 3a is controlled to the retard side, and at the same time, as in the first embodiment. The air-fuel ratio is made lean and the ignition timing is retarded.

As described above, in the variable valve timing apparatus according to the present embodiment, at the beginning of the cold start where the afterburning effect cannot be expected, the overlap amount is increased by the advance angle of the intake valve 7a (FIG. 5). Thus, the exhaust gas is drawn back into the cylinder to prevent the emission of unburned HC, and the exhaust gas is caused to flow back to the intake side to promote fuel vaporization and increase the temperature of the intake port 11. When the temperature is increased (FIG. 5), the exhaust valve 7b is advanced to activate the catalyst 20 early by the afterburning effect. Therefore, the opening / closing timing of the intake / exhaust valves 7a and 7b can always be optimally controlled according to the temperature rise state of the engine 1 during a cold start, and the emission of unburned HC can be reliably suppressed.

In addition, since the phases of the intake and exhaust camshafts 3a and 3b are changed before and after, the limited hydraulic oil of the oil pump 10 is always supplied to one of the timing variable mechanisms 8a and 8b.
b is intensively supplied, so that reliable phase angle control can be realized. The description of the embodiment is finished above, but aspects of the present invention are not limited to the first and second embodiments. For example, in each of the above-described embodiments, the vane-type variable timing mechanisms 8a and 8b are provided. However, the configuration of the variable-timing mechanism is not limited to this. For example, the variable-timing mechanism may be replaced with a helical-type variable mechanism. An eccentric type variable timing mechanism that changes the amount of eccentricity of a cam, a switching type variable type mechanism that selectively operates cams having different characteristics, and an electromagnetic type variable timing mechanism that opens and closes a valve directly using an electromagnetic actuator. Etc. may be substituted.

In each of the above embodiments, the present invention is applied to the intake pipe injection type engine 1. However, for example, the invention may be applied to a direct injection type engine in which fuel is injected directly into a cylinder. Further, in each of the above embodiments, after the phase angle control of one camshaft 3a, 3b is completed, the phase angle control of the other camshaft 3a, 3b is started. For example, as shown by a broken line in FIG. 2, before the phase angle control of the exhaust camshaft 3b to the retard side is completed, the phase angle of the intake camshaft 3a to the advance side may be performed. Control may be started.

On the other hand, in each of the above-described embodiments, the cold start has been described as an example. However, the present invention is not necessarily limited to the cold start, and the same control may be executed at the warm start. .

[0034]

As described above, according to the variable valve timing apparatus of the present invention, the opening / closing timing of the intake / exhaust valve can be appropriately controlled at the time of starting, so that the emission of unburned HC can be reliably suppressed. .

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing a variable valve timing device according to first and second embodiments.

FIG. 2 is a time chart illustrating a phase angle control of a camshaft during a cold start by the variable valve timing device of the first embodiment.

FIG. 3 is an explanatory diagram sequentially showing a phase change of a camshaft during a cold start by the variable valve timing device of the first embodiment.

FIG. 4 is a time chart showing phase control of a camshaft at the time of a cold start by the variable valve timing device of the second embodiment.

FIG. 5 is an explanatory diagram sequentially showing a phase change of a camshaft during a cold start by a variable valve timing device according to a second embodiment.

[Explanation of symbols]

7a Intake valve 7b Exhaust valve 8a Variable timing mechanism (variable intake valve timing means) 8b Variable timing mechanism (variable exhaust valve timing means) 31 ECU (valve timing control means)

Claims (2)

[Claims] 1. A variable valve timing apparatus for varying the valve timing of an intake valve and an exhaust valve to vary the amount of overlap between the intake valve and the exhaust valve, wherein the variable valve timing of the intake valve is varied. Means, an exhaust valve timing variable means for varying the valve timing of the exhaust valve, and at least one of the intake valve timing variable means or the exhaust valve timing variable means at the time of starting the engine to increase the overlap amount, A variable valve timing device, comprising: valve timing control means for advancing the exhaust valve by exhaust valve timing variable means. 2. A variable valve timing apparatus for varying the valve timing of an intake valve and an exhaust valve to vary the amount of overlap between the intake valve and the exhaust valve, wherein the variable valve timing of the intake valve is varied. Means, an exhaust valve timing variable means for varying the valve timing of the exhaust valve, and a predetermined period after the start of advancement of the intake valve by the operation of the intake valve timing variable means at the time of engine start, the exhaust valve timing variable means. And a valve timing control means for operating the exhaust valve to advance the exhaust valve.