JP4591645B2 - Variable valve timing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a variable valve timing device that adjusts opening and closing timings of an intake valve and an exhaust valve of an engine.
[0002]
[Related background]
As is well known, most of the unburned HC discharged from the engine is at the time of cold start, and as a countermeasure against this, improvement in the performance of the catalyst, increase in capacity, and the like are attempted. However, in order to purify a large amount of unburned HC at the time of cold start only by measures relating to this catalyst, there is a problem that the amount of noble metal used for the catalyst is greatly increased and the cost efficiency is poor.
[0003]
Therefore, for example, as in the variable valve timing device described in Japanese Patent Application Laid-Open No. 11-336574, the open / close timing of the intake and exhaust valves is appropriately controlled at the time of cold start, and the catalyst is activated at an early stage so that unburned HC is removed. Reduction techniques have been proposed. In this variable valve timing device, at the time of cold start, the exhaust valve is advanced from the normal time to discharge the exhaust gas during combustion, and the afterburning effect when the unburned HC contained in the exhaust gas burns in the exhaust passage, The catalyst is activated early. In order to promote the afterburning effect at this time, the intake valve is greatly advanced to increase the amount of overlap with the exhaust valve, and the exhaust gas (internal EGR) flowing back to the intake side is increased to slow down the combustion. To increase unburned HC emissions.
[0004]
[Problems to be solved by the invention]
However, as is apparent from the description of the flowchart and the like in the variable valve timing device of the above publication, the following problems arise because the advance / retreat control of the intake / exhaust valves is simultaneously performed at the cold start.
The advance control of the intake / exhaust valve is performed after several strokes have passed since the initial explosion.At this time, the temperature of the exhaust passage and the like has not yet been sufficiently raised, so the exhaust valve during combustion is controlled by the advance angle of the exhaust valve. Even if it is discharged, there will be a situation in which the afterburning in the exhaust passage stops and is discharged as it is.
[0005]
In addition, at the initial stage of cold start, fuel injected into the intake port accumulates in the port while the intake valve is closed, and flows into the cylinder as the intake valve opens, part of which is It passes 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 passing through the exhaust side is discharged as it is without being re-inhaled into the cylinder.
[0006]
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, promoting fuel vaporization in the intake port and raising the temperature of the intake port itself. Since the exhaust gas temperature remaining in the cylinder is lowered by the early opening of the valve, these preferable actions are greatly reduced.
Because of the above factors, it is difficult to say that the intake and exhaust valves are advanced simultaneously at the initial stage of cold start, which is not optimal control, and more appropriate control that matches the temperature rise of the engine at cold start is desired. It was.
[0007]
An object of the present invention is to provide a variable valve timing device that can appropriately control the opening / closing timing of an intake / exhaust valve at the time of start-up, thereby reliably suppressing the discharge of unburned HC.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, in a variable valve timing device that varies the valve timing of the intake valve and the exhaust valve to vary the overlap amount of the intake valve and the exhaust valve, the valve timing of the intake valve At least one of an intake valve timing varying means, an exhaust valve timing varying means for varying the valve timing of the exhaust valve, and an intake valve timing varying means or an exhaust valve timing varying means after a predetermined time from the initial explosion at the start of the engine. From the start of the increase of the overlap amount due to the operation of at least one of the intake valve timing variable means or the exhaust valve timing variable means by operating and increasing the overlap amount across the top dead center for the intake valve and the exhaust valve, respectively. Exhaust valve timing variable means after a predetermined period And a valve timing control means for advancing the exhaust valve Te.
[0009]
Therefore, after a predetermined time from the initial explosion at the start of the engine, first, at least one of the intake valve timing varying means and the exhaust valve timing varying means, the intake valve and the exhaust valve overlap each other over the top dead center. As a result, the exhaust gas that has once passed through the exhaust side is drawn back into the cylinder and burned, and the discharge of unburned HC is suppressed, while the exhaust gas flows backward to the intake side to promote fuel vaporization and the intake port. The exhaust valve is advanced by the exhaust valve timing varying means after a predetermined period from the start of the increase of the overlap amount due to the operation of at least one of the intake valve timing varying means or the exhaust valve timing varying means , and combustion is performed. The exhaust gas therein is discharged and the catalyst is activated early due to the afterburning effect in the exhaust passage. That is, the opening / closing timing of the intake / exhaust valve is always optimally controlled in accordance with the temperature rise state of the engine at the time of starting.
[0010]
According to a second aspect of the present invention, in the variable valve timing device that varies the valve timing of the intake valve and the exhaust valve to vary the overlap amount of the intake valve and the exhaust valve, the intake valve that varies the valve timing of the intake valve. Timing variable means, exhaust valve timing variable means for changing the valve timing of the exhaust valve, and intake valve timing variable means by operating the intake valve timing variable means to the advance side after a predetermined time from the initial explosion at the start of the engine A valve that increases the amount of overlap across each top dead center and operates the exhaust valve timing variable means to advance the exhaust valve after a predetermined period from the start of advancement of the intake valve by the operation of the intake valve timing variable means Timing control means.
[0011]
Therefore, after a predetermined time from the first explosion at the start of the engine, first, the intake valve timing advancement is started by the intake valve timing variable means, and the overlap amount increases across the top dead center for the intake valve and the exhaust valve, respectively. are, thereby temporarily exhaust gas through the exhaust side is burned pulled back into the cylinder, both the discharge of unburned HC can be prevented, the exhaust gas temperature of the vaporization promotion and the intake port of the fuel flows back to the intake side The exhaust valve is advanced by the exhaust valve timing variable means after a predetermined period from the start of the advancement of the intake valve, and the exhaust gas during combustion is discharged, and the catalyst is accelerated by the afterburning effect in the exhaust passage. Activated. That is, the opening / closing timing of the intake / exhaust valve is always optimally controlled in accordance with the temperature rise state of the engine at the time of starting.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
A variable valve timing apparatus according to a first embodiment embodying the invention of claim 1 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.
[0013]
Between the camshafts 3a and 3b and the timing pulleys 4a and 4b, vane type timing variable mechanisms 8a and 8b are provided as intake valve timing variable means and exhaust valve timing variable means. The structure of the timing variable mechanisms 8a and 8b is well known in, for example, Japanese Patent Application Laid-Open No. 2000-27609 and will not be described in detail. However, a vane rotor is rotatably provided in a housing provided in the timing pulleys 4a and 4b. And an intake camshaft 3a or an exhaust camshaft 3b. Oil control valves (hereinafter referred to as OCV) 9a and 9b are connected to the timing variable mechanisms 8a and 8b, and the vane rotor is switched according to the switching of the OCVs 9a and 9b using the hydraulic oil supplied from the oil pump 10 of the engine 1. As a result, the phase of the cam shafts 3a and 3b with respect to the timing pulleys 4a and 4b, that is, the opening and closing timings of the intake and exhaust valves 7a and 7b are adjusted.
[0014]
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.
[0015]
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 7b is opened. It is guided to the passage 18 and discharged to the outside through the catalyst 20 and a silencer (not shown).
Valve timing control provided with an input / output device (not shown), a storage device (ROM, RAM, BURAM, etc.), a central processing unit (CPU), a timer counter, etc. An ECU (engine control unit) 31 is installed as means, 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 OCVs 9a and 9b, the fuel injection valve 15, the spark plug 19 and the like are connected to the output side of the ECU 31.
[0016]
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 spark plug 19 and the fuel injection valve 15. Further, according to a preset map, the target phase angle of the timing variable mechanisms 8a and 8b is calculated from the engine speed Ne and the throttle opening TPS, and the actual phase angle is controlled to the target phase angle by driving the OCVs 9a and 9b. To do. 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.
[0017]
Therefore, the phase angle control executed by the ECU 31 at the cold start will be described with reference to FIGS.
FIG. 2 is a time chart showing camshaft phase angle control at the time of cold start, and FIG. 3 is an explanatory diagram sequentially showing phase changes of the camshaft at the time of cold start.
First, when the engine is stopped, the phase of the intake camshaft 3a is held at the retard position and the phase of the exhaust camshaft 3b is held at the advance position as shown in (1) of FIGS. Little overlap is formed. 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. Since the intake port 11 at this point corresponds to the outside air temperature, fuel vaporization is not promoted, and most of the large amount of injected fuel due to the increase in fuel remains in the intake port 11 while the intake valve 7a is closed as the liquid fuel. It flows into the cylinder as the valve 7a opens. Here, since the intake and exhaust air hardly 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.
[0018]
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, as long as the idling operation is continued even after the start is completed, the opening / closing timing of the intake valve 7a is held at the retard position, and the exhaust valve 7b The opening / closing timing of the engine is kept at the advance position, and when the engine speed Ne or the throttle opening TPS increases due to the start of the vehicle or the like, it is controlled to the advance side accordingly.
[0019]
On the other hand, at the time of cold start, after waiting for a predetermined time t (for example, 2 to 3 seconds) from the first explosion, the phase of the exhaust camshaft 3b is controlled to the retard side as shown in (2) of FIGS. . As a result, the exhaust valve 7b is closed after the top dead center TDC, and the exhaust gas that has once passed through the exhaust side is drawn back into the cylinder by the lowering of the piston 16 and burned in the next combustion stroke. Since the exhaust gas at this time is exhaust gas at the end of the exhaust stroke containing particularly a large amount of unburned HC, a situation where a lot of unburned HC is burned in the next combustion stroke and discharged as it is is prevented. Further, since the opening of the exhaust valve 7b is also delayed, the combustion period is lengthened to promote the oxidation of unburned HC and the exhaust gas temperature in the cylinder is raised.
[0020]
Further, since the overlap amount increases with the delay of the exhaust camshaft 3b, the high-temperature exhaust gas flows back to the intake side as the internal EGR, thereby promoting the vaporization of fuel in the intake port 11, and the intake port. 11 itself has a temperature raising action, and at this time, the negative pressure on the intake side is increased due to the rapid increase in the engine rotational speed Ne accompanying the first explosion, so that the backflow of the exhaust gas becomes abrupt, and the intake port 11 enters the intake port 11. There is also an effect of atomizing the remaining liquid fuel by blowing it off.
[0021]
The phase of the intake camshaft 3a is controlled to the advance side as shown in (3) of FIG. The amount of overlap is further increased. At this time, as the exhaust gas temperature rises, the fuel vaporization condition becomes easier as compared with the time of the first explosion, the intake valve 7a is opened earlier, and the in-cylinder temperature rises together with the compression temperature. Since the atomization effect of the liquid fuel by the internal EGR is still exhibited, stable combustion is continued even if the internal EGR is increased by increasing the overlap amount.
[0022]
Then, after the elapse of a predetermined time ( after a predetermined period) , the phase of the exhaust camshaft 3b is controlled to the advance side as shown in (4) of FIGS. At this time, since the temperature of the exhaust passage 18 and the like is increased compared to the time (3) described above, if the exhaust gas during combustion is exhausted by the advance angle of the exhaust valve 7b, the exhaust gas becomes an afterburning effect. Thus, the combustion is continued in the exhaust passage 18 and the catalyst 20 is activated early. Although the amount of overlap is reduced by the advance angle of the exhaust valve 7b, since the negative pressure on the intake side is further increased at this point, the above-described action of returning the exhaust gas into the cylinder has been sufficiently achieved. The emission of fuel HC is suppressed.
[0023]
On the other hand, when a predetermined time elapses thereafter, the phase of the intake camshaft 3a is controlled to the retard side, the overlap amount of intake and exhaust is reduced, and combustion is stabilized. 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 at the same time the ignition timing is set to compensate for the decrease in the heat generation amount due to the lean operation and to raise the exhaust gas temperature. Retarding is performed, and the temperature of the catalyst 20 is continuously increased.
[0024]
As described above, in the variable valve timing device according to the present embodiment, the exhaust valve 18b and the like are not sufficiently heated up and the afterburning effect cannot be expected. The amount of overlap is increased by the advance angle of the valve 7a ((2) and (3) in FIG. 3), whereby the exhaust gas that has once passed through the exhaust side is drawn back into the cylinder and burned to discharge unburned HC. In addition to preventing the exhaust gas from flowing backward to the intake side, fuel vaporization is promoted and the intake port 11 is heated. On the other hand, when the exhaust passage 18 and the like are subsequently heated ((4) in FIG. 3), The exhaust valve 7 b is advanced to discharge the exhaust gas during combustion, and the catalyst 20 is activated early by the afterburning effect in the exhaust passage 18.
[0025]
In other words, the open / close timing of the intake / exhaust valves 7a and 7b is always optimally controlled according to the temperature rise status of the engine 1 during the cold start (temperature rise status of the exhaust passage 18 and the like). Can be reliably suppressed.
In particular, when the engine rotational 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. However, as described above, the intake and exhaust camshafts 3a, 3a, Since the phase of 3b is changed before and after, limited hydraulic oil is always supplied intensively to one of the timing variable mechanisms 8a and 8b, and reliable phase angle control can be realized.
[0026]
[Second Embodiment]
Next, a variable valve timing apparatus according to a second embodiment embodying the invention of claim 2 will be described. The variable valve timing device of this embodiment is obtained by changing the order of phase angle control of the intake and exhaust camshafts 3a and 3b, and the 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.
[0027]
FIG. 4 is a time chart showing the phase angle control of the cam shaft at the cold start, and FIG. 5 is an explanatory diagram showing the phase change of the cam shaft at the cold start in order.
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 FIG. 4 and 5 (1), and an overlap including the intake stroke and the exhaust stroke is formed. ing. When starting is performed at this phase position, the exhaust gas that has once passed through 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 of only the intake stroke may be formed. In this case, passage of exhaust gas to the exhaust side can be more reliably prevented.
[0028]
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 advance side as shown in (2) of FIGS. . The operation at this time is the same as in the case of (3) in FIGS. 2 and 3 of the first embodiment, and the exhaust gas passing through the exhaust side is drawn back into the cylinder to prevent the unburned HC from being discharged and The increase in the lap amount increases the internal EGR that flows back to the intake side, thereby promoting the vaporization of fuel in the intake port 11 and raising the temperature of the intake port 11 itself.
[0029]
Further, after the elapse of a predetermined time ( after the predetermined period) , the phase of the exhaust camshaft 3b is controlled to the advance side as shown in (3) of FIGS. The operation at this time is the same as in the case of (3) in FIGS. 2 and 3 of the first embodiment, and the exhaust gas during combustion is discharged by the advance angle of the exhaust valve 7b, and also in the exhaust passage 18 by the afterburning effect. Combustion is continued and the catalyst 20 is activated early.
When a predetermined time elapses thereafter, the phase of the exhaust camshaft 3b is controlled to the retarded side, and subsequently the phase of the intake camshaft 3a is controlled to the retarded side. At the same time, as in the first embodiment. The air-fuel ratio is made lean and the ignition timing is retarded.
[0030]
As described above, in the variable valve timing apparatus of the present embodiment, the overlap amount is increased by the advance angle of the intake valve 7a in the initial stage of the cold start where the afterburning effect cannot be expected ((2) in FIG. 5). As a result, the exhaust gas is drawn back into the cylinder to prevent the discharge of unburned HC, and the exhaust gas is caused to flow backward to the intake side to promote fuel vaporization and to raise the temperature of the intake port 11, while thereafter the exhaust passage 18. When the temperature of the catalyst 20 is increased ((3) in FIG. 5), the exhaust valve 7b is advanced to activate the catalyst 20 early due to the afterburning effect. Therefore, the opening / closing timings of the intake / exhaust valves 7a, 7b can always be optimally controlled according to the temperature rise state of the engine 1 at the cold start, and the discharge of unburned HC can be reliably suppressed.
[0031]
Moreover, 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 in a concentrated manner. Reliable phase angle control can be realized.
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 mechanisms 8a and 8b are 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. Eccentric variable timing mechanism that changes the amount of cam eccentricity, or a switchable variable timing mechanism that selectively operates cams with different characteristics, or an electromagnetic timing variable mechanism that directly opens and closes a valve using an electromagnetic actuator. Or the like.
[0032]
In each of the above embodiments, the present invention is applied to the intake pipe injection type engine 1. However, for example, the present invention may be applied to an in-cylinder injection type engine in which fuel is directly injected into a cylinder.
Further, in each of the above embodiments, the phase angle control of the other cam shafts 3a and 3b is started after the phase angle control of the one cam shafts 3a and 3b is completed. For example, as shown by a broken line in FIG. 2, the phase angle of the intake camshaft 3a toward the advance side is completed before the phase angle control of the exhaust camshaft 3b toward the retard side is completed. Control may be started.
[0033]
On the other hand, in each of the above embodiments, the cold start time has been described as an example. However, the present invention is not necessarily limited to the cold start time, and the same control may be executed at the warm start time.
[0034]
【The invention's effect】
As described above, according to the variable valve timing device of the present invention, the opening / closing timing of the intake / exhaust valve can be appropriately controlled at the time of start-up, and the discharge 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 showing camshaft phase angle control during cold start by the variable valve timing device of the first embodiment;
FIGS. 3A and 3B are explanatory diagrams sequentially showing a phase change of a camshaft at the time of cold start by the variable valve timing device of the first embodiment. FIG. 4 at the time of cold start by the variable valve timing device of the second embodiment. 6 is a time chart showing phase angle control of the cam shaft.
FIGS. 5A and 5B are explanatory diagrams sequentially showing changes in the phase of the camshaft during cold start by the variable valve timing device of the second embodiment.
7a Intake valve 7b Exhaust valve 8a Timing variable mechanism (intake valve timing variable means)
8b Variable timing mechanism (exhaust valve timing variable means)
31 ECU (valve timing control means)

Claims (2)

In a variable valve timing device that varies 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,
Intake valve timing varying means for varying the valve timing of the intake valve;
Exhaust valve timing varying means for varying the valve timing of the exhaust valve;
Across top dead center, respectively Re Teso actuates at least one of the intake valve timing varying means or the exhaust valve timing varying means after a predetermined time from the initial explosion at the time of starting the engine to increase the overlap amount, the intake valve Valve timing control means for advancing the exhaust valve by the exhaust valve timing variable means when a predetermined period has elapsed from the start of an increase in overlap amount due to the operation of at least one of the timing variable means or the exhaust valve timing variable means. A variable valve timing device characterized by that. In a variable valve timing device that varies 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,
Intake valve timing varying means for varying the valve timing of the intake valve;
Exhaust valve timing varying means for varying the valve timing of the exhaust valve;
Predetermined time after the initial explosion at the time of starting the engine to actuate the intake valve timing varying means to the advance side by increasing the amount of overlap across the respective top dead center for the intake valves and the exhaust valves, the intake valve A variable valve comprising: valve timing control means for operating the exhaust valve timing enable means to advance the exhaust valve after a predetermined period from the start of advance of the intake valve by the operation of the timing variable means. Timing device.

Images