JP2000073770A - Four-cycle internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize compressed self-ignition burning of premixed air and to save fuel consumption by setting a piston stroke area corresponding to a residual gas confinement time, of a cylinder bore wall forming a combustion chamber to an heat insulating structure. SOLUTION: A prescribed part of a cylinder bore wall 10, or one of the components of a combustion chamber 4, more practically, a piston stroke S part corresponding to the residual gas confinement time formed by minus overlap in loading an engine is set to an insulating structure. A level difference part is provided in an area S of a cylinder liner 11 constituting the cylinder bore wall 10 and a ceramic heat insulating liner 11a is fixedly provided in the level difference part so that a heat insulating structure is constituted. The heat emission from the cylinder bore wall 10 in low loading of the engine can be thus suppressed. By this constitution, the temperature reduction of the residual gas can be avoided, the activation of fresh air is accelerated, and the compressed self-ignition burning of the premixed air is stabilized to save the fuel consumption and improve heat efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-stroke internal combustion engine, such as a gasoline engine for an automobile.

[0002]

Means for improving the thermal efficiency of a four-stroke internal combustion engine include lean air-fuel mixture. However, in normal spark ignition and flame propagation combustion, the combustion becomes unstable, and the lean air-fuel mixture becomes lean. and it naturally occurs limit, since the time of the lean combustion becomes impossible exhibit the reducing ability of the purification performance as during combustion in the catalyst for exhaust gas purification is called stoichiometric ratio, in particular NO _x, in the lean combustion for the purpose of expansion and low NO _x emissions operable load range, attempts to compression self-ignition combustion of a premixed air-fuel mixture has been made at the time of low load of the engine.

In order to realize the compression self-ignition combustion of the premixed gas, it is necessary to activate the fresh air by using the high-temperature residual gas heat. As one of the methods, the closing timing of the exhaust valve is required. It is effective to confine the residual gas as soon as possible by delaying the opening timing of the intake valve.

In order to realize such confinement of the residual gas in the combustion chamber, for example, a variable valve timing control means of the intake and exhaust valves as disclosed in Japanese Patent Laid-Open No. 5-321702 can be effectively used. By using the high-temperature residual gas heat confined in the combustion chamber under the variable control of the valve timing, compression self-ignition combustion in the next cycle can be achieved.

However, at such a valve timing, the compression / expansion is performed in a state where the residual gas is confined in the combustion chamber, so that the mixture becomes lean due to pump loss due to blow-by gas and loss due to heat release from the combustion chamber wall. The cost of improving fuel economy due to this will decrease.

Accordingly, the present invention provides a four-stroke internal combustion engine which can stabilize the compressed self-ignition combustion of the premixed gas and improve fuel efficiency by suppressing the amount of heat released from the combustion chamber wall during the residual gas confinement period. To provide.

[0007]

According to the present invention, the valve timings of the intake valve and the exhaust valve are variably controlled when the engine is under a high load and when the engine is at a low load, and the exhaust valve is controlled in a low load region. By closing the high-temperature residual gas in the combustion chamber by advancing the valve closing timing and delaying the opening timing of the intake valve, the fresh air sucked in the middle of the intake stroke is activated to perform the compression self-ignition combustion. A cycle internal combustion engine, characterized in that at least a portion of a piston stroke region of a cylinder bore wall forming the combustion chamber corresponding to the residual gas trapping period has an adiabatic structure.

According to a second aspect of the present invention, the heat insulating structure of the cylinder bore wall according to the first aspect is constituted by a cylinder liner made of a heat insulating member.

According to the invention of claim 3, claims 1 and 2
The heat insulation structure of the cylinder bore wall described in (1) is characterized in that a cavity is provided on the back surface of the cylinder liner.

[0010] In the invention of claim 4, claims 1 to 3 are provided.
The heat insulating structure of the cylinder bore wall described in (1) is characterized in that the thickness of the predetermined area portion of the cylinder liner portion is made thicker than other portions.

In the invention of claim 5, claims 1 to 4 are provided.
The piston crown surface and the intake / exhaust valve forming at least the surface facing the combustion chamber are formed of a heat insulating member.

According to the sixth aspect of the invention, the first to fifth aspects are provided.
Inside the piston described in the above, while providing a cooling passage having an opening on the back side of the piston, an oil jet that injects cooling oil toward the opening below the piston is disposed, and detects the load on the engine. The operation of the oil jet is stopped when the load is low, and the oil jet is operated when the load is high.

According to the invention of claim 7, claims 1 to 6 are provided.
Wherein the cooling system of the cylinder head and the cylinder block of the four-stroke internal combustion engine described above is separately and independently constituted, and the supply of the engine coolant to the cylinder block is stopped when the engine is under a low load. .

In the invention of claim 8, claims 1 to 6
A partition is provided in a water jacket of a cylinder block of the four-stroke internal combustion engine described in the above, and the water jacket is provided in a first jacket provided in a piston stroke region corresponding to the residual gas trapping period and a second jacket provided below the first jacket. The engine is separated into two jackets, and the supply of the engine coolant to the first jacket is stopped when the load of the engine is low.

[0015]

According to the first aspect of the present invention, of the heat radiated from the combustion chamber to the outside, generally, the heat radiated from the piston ring to the cylinder bore wall is 60 to 70%.
However, since the cylinder bore wall has a heat insulating structure in the piston stroke region corresponding to the residual gas confinement period at a low engine load, it is necessary to suppress heat release from the cylinder bore wall during the period. Can be.

As a result, the temperature of the residual gas can be prevented from lowering, and the activation of fresh air can be promoted. As a result, the homogeneous charge compression self-ignition combustion can be stabilized and the fuel efficiency and the thermal efficiency can be improved.

According to the second to fourth aspects of the present invention, in addition to the effect of the first aspect of the present invention, the heat insulating structure can be easily formed by partially changing the structure of the cylinder bore wall, and the cost can be reduced. It can be obtained advantageously.

According to the invention described in claim 5, according to claim 1,
In addition to the effects of the inventions of (1) to (4), since the piston crown surface and the intake / exhaust valve have a heat-insulating structure, the effect of suppressing the temperature decrease of the residual gas can be further enhanced.

According to the invention described in claim 6, according to claim 1,
In addition to the effects of the fifth to fifth aspects, since the piston can be actively cooled by the cooling oil injected and supplied from the oil jet when the engine is under a high load, abnormal combustion can be avoided and a high output can be obtained.

According to the seventh and eighth aspects of the present invention, in addition to the effects of the first to sixth aspects, the cooling effect of the cylinder block is reduced when the engine is under a low load, so that the temperature of the residual gas decreases. The suppression effect can be further enhanced.

[0021]

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

In FIG. 1, 1 is a cylinder block, 2
Represents a piston, 3 represents a cylinder head, and 4 represents a combustion chamber formed by the cylinder block 1, the piston 2, and the cylinder head 3.

An intake valve 6 for opening and closing an intake port 5 and an exhaust valve 8 for opening and closing an exhaust port 7 are arranged in the cylinder head 3, and an ignition plug 9 is arranged at a substantially central position of the combustion chamber 4. It is set up.

The intake valve 6 and the exhaust valve 8 are variably controlled by switching the valve timing between a high load and a low load of the engine by a variable valve mechanism (not shown).

FIG. 5 shows an example of the variable control of the valve timing by the variable movement mechanism as a lift curve of the intake valve 6 (INT) and the exhaust valve 8 (EXH) with respect to the transition of the crank angle. When a load is applied, the closing timing of the exhaust valve 8 and the intake valve 6
Is set near the piston top dead center (TDC) and the required valve overlap is set.

When the engine is under a low load, the closing timing of the exhaust valve 8 is advanced to close during the exhaust stroke with respect to the high load, and the opening timing of the intake valve 6 is delayed during the intake stroke. , So that there is no valve overlap near the top dead center of the piston, and the state is to be called minus overlap.

By setting the valve timing to form a negative overlap when the engine is under a low load, the exhaust valve 8 is closed in the middle of the exhaust stroke, and the high-temperature burned gas corresponding to the volume of the combustion chamber at that time. Is retained in the combustion chamber 4 to be an internal EGR for the next cycle. In the next cycle, the intake valve 6 is opened during the intake stroke, fresh air is sucked, and the internal EGR is sucked.
The high-temperature and homogeneous mixture is formed by being stirred and mixed with the GR, and the compressed high-temperature homogeneous mixture is compressed, whereby the compressed self-ignition combustion of the lean mixture is realized near the top dead center of the piston. .

On the other hand, when the engine is heavily loaded, the valve timing is returned to the same as in a normal four-cycle gasoline engine, and fresh air is taken in and compressed, spark-ignited by the spark plug 9 and burned by flame propagation.

Here, it corresponds to a required portion of the cylinder bore wall 10 which is one of the components of the combustion chamber 4, specifically, a residual gas confinement period formed by minus overlap when the engine is under a low load. The portion of the piston stroke S has a heat insulating structure.

The piston stroke S is represented by the stroke of the piston top ring 12 which slides on the cylinder bore wall 10. Therefore, the heat insulating structure is used to close the exhaust valve 8 or open the intake valve 6 at a low engine load. Is applied to a range up to the vicinity of the position of the piston top ring 12 in the above.

In this embodiment, a step is provided in the region S of the cylinder liner 11 constituting the cylinder bore wall 10, and a heat insulating liner 11a made of ceramic is fixed to the step as a heat insulating member to constitute a heat insulating structure. However, the surface of the region S of the cylinder liner 11 may be coated with a heat insulating material such as ceramics.

In FIG. 1, reference numeral 13 denotes a water jacket of the cylinder block 1, and reference numeral 14 denotes a cylinder liner portion on an inner peripheral wall thereof.

As described above, according to this embodiment, of the heat radiated from the combustion chamber 4 to the outside, the heat radiated from the piston ring to the cylinder bore wall 10 is generally 60 to
It is said that the cylinder bore wall 10 occupies 70% of the piston stroke area S represented by the piston stroke corresponding to the residual gas trapping period at the time of low engine load, more specifically, the piston stroke of the piston top ring 12. Since the portion has a heat insulating structure, heat release from the cylinder bore wall 10 during the period can be suppressed.

As a result, a decrease in the temperature of the residual gas can be avoided, the activation of fresh air can be promoted, and the homogeneous charge compression self-ignition combustion can be stabilized, and the fuel efficiency and the thermal efficiency can be improved.

In particular, in this embodiment, the cylinder liner 11
Since the heat insulating structure is configured by disposing the heat insulating liner 11a in the region S, the structure can be simplified and the cost can be advantageously reduced without a significant structural change of the cylinder bore wall 10. Can be.

FIG. 2 shows a second embodiment of the present invention. In this embodiment, the heat insulating structure in the area S of the cylinder bore wall 10 is formed by providing a cavity 15 on the back surface of the cylinder liner 11. ing.

Therefore, according to the second embodiment, the cavity 1
In addition to the heat insulating effect of the fifth embodiment, the same effect as that of the first embodiment can be obtained. In addition, since a special heat insulating member is not used, it is possible to obtain more advantageous cost.

FIG. 3 shows a third embodiment of the present invention. In this embodiment, the heat insulating structure in the area S of the cylinder bore wall 10 is shown by the area of the cylinder liner portion 14 constituting the cylinder bore wall 10. The S portion is configured as a thick portion 14a which is thicker than other portions.

Therefore, according to the third embodiment, the same effect as that of the first embodiment can be obtained by the heat insulating effect of the thick portion 14a of the cylinder liner portion 14, and also in this embodiment, a dedicated heat insulating member is used. Since it is not used, it can be obtained more advantageously in terms of cost.

In the embodiment shown in FIG. 3, the thickness of the thick portion 14a of the cylinder liner 14 is gradually changed as it goes upward. However, as shown in FIG.
a.

In any of the above embodiments, the piston 2
If a heat insulating material such as ceramics is used to coat the crown surface of the piston 2 and at least the surfaces of the intake and exhaust valves 6 and 8 facing the combustion chamber 4 to form a heat insulating structure, heat radiation from the piston 2 and the intake and exhaust valves 6 and 8 can be achieved. Thus, the effect of suppressing the temperature decrease of the residual gas can be further enhanced.

Further, in conjunction with the adoption of these heat insulating structures,
For example, as shown in FIGS. 3 and 4, a cooling passage 16 having an opening 17 on the back side of the piston 2 is provided inside the piston 2, and cooling oil is injected toward the opening 17 below the piston 2. If the oil jet 18 is arranged, the load of the engine is detected, the operation of the oil jet 18 is stopped at a low load, and the oil jet 18 is operated at a high load. 18
The piston 2 can be actively cooled by the cooling oil injected from the opening 17 and supplied to the cooling passage 16 from the opening 17, and high output can be obtained by avoiding abnormal combustion at the time of high load.

As described above, by providing a heat insulating structure to a required portion around the combustion chamber 4, a temperature drop of the residual gas in the combustion chamber 4 at the time of a low engine load is suppressed, and the compression self-ignition of the premixed gas is performed. Although the combustion can be stabilized and the fuel efficiency and the thermal efficiency can be improved, the effect of suppressing the temperature decrease of the residual gas can be further enhanced by reducing the cooling action of the cylinder block 1 at a low engine load.

This will be described with reference to FIGS.
Denotes an engine cooling system, 21 is a radiator, 22 is a feed passage for the engine coolant, 23 is a return passage for the engine coolant, 24 is a water pump provided in the feed passage 22, and 25 is a return passage bypassing the radiator 21. Reference numeral 26 denotes a thermostat provided at a portion where the bypass passage 25 and the feed passage 22 communicate with each other.

The water jacket 13 of the cylinder block 1 (see FIGS. 1 to 4) communicates with a water jacket (not shown) of the cylinder head 3 to circulate the engine coolant from the cylinder block 1 to the cylinder head 3 side. This is similar to a normal four-stroke gasoline engine, except that the feed passages 22a, 22b
The engine coolant is supplied to the cylinder block 1 and the cylinder head 3 separately and independently.

A switching valve 27 which is operated via a drive device 29 based on a control signal of a control unit 28 is provided at a branch portion of the feed passages 22a and 22b. The engine coolant is supplied only to the cylinder head 3 side by shutting off the supply of the engine coolant to the cylinder block 3, and conversely, the supply of the engine coolant to the cylinder head 3 is shut off when the engine is under a high load. The engine coolant is supplied only to the side.

Therefore, according to this embodiment, when the engine is under a high load, the engine coolant is supplied to the cylinder block 1 as shown in FIG. The engine coolant is circulated to 3 to actively cool the engine body.

On the other hand, when the engine is under a low load, the supply of the engine coolant is performed only to the cylinder head 3 side as shown in FIG. 6, and the supply of the engine coolant to the cylinder block 1 is cut off. 4 can enhance the effect of suppressing the temperature decrease of the residual gas.

8 and 9 show different embodiments of the engine cooling system 20. In this embodiment, FIG.
As shown in (1), a partition wall 30 is provided on the water jacket 13 of the cylinder block 1, and the water jacket 13 is provided on a portion of the piston stroke region S corresponding to the above-described residual gas trapping period when the engine is under a low load.
The jacket 13A is separated from a second jacket 13B provided below the jacket 13A.

In this embodiment, the water jacket 13 of the cylinder block 1 and the water jacket (not shown) of the cylinder head 3 are not in communication with each other. Therefore, the first jacket 13A and the second jacket 13B and the water jacket of the cylinder head 3 are not provided. Is a branched passage 23a,
The return passages 23b and 23c are connected to the return passage 23 independently and separately.

On the other hand, the feed passages 22a and 22b
So that the engine coolant can be supplied to the first jacket 13A and the cylinder head 3 side separately and independently, and the engine is supplied to the second jacket 13B via a passage 22c branched from the passage 22b. Cooling liquid is supplied.

The control unit 2 is connected to the branch of the feed passages 22a and 22b in the same manner as in the above embodiment.
8, the operation of which is controlled by the drive unit 29 to shut off the passage 22a when the engine load is low, and to close the passages 22a and 22 when the engine load is high.
A switching valve 27 for opening both of 2b is provided.

That is, in this embodiment, when the engine is under a high load, the feed passages 22a, 22b, 22 are opened by opening both the feed passages 22a, 22b as shown in FIG.
The engine coolant is supplied to the first and second jackets 13A and 13B of the cylinder block 1 and the cylinder head 3 via the cylinder c, and the engine body is actively cooled.

On the other hand, when the engine is under a low load, the passage 22a is closed and the passage 22b is opened as shown in FIG. 8, so that the engine coolant is supplied to the second jacket 13B of the cylinder block 1 and the cylinder head 3. However, the supply of the engine coolant to the first jacket 13A of the cylinder block 1 is shut off.

As a result, when the engine is under a low load, only the portion of the combustion chamber 4 corresponding to the predetermined region S, which needs to suppress the residual gas temperature drop, is stopped from being cooled. Can be planned.

In FIGS. 6 to 9, the control flow of the engine coolant is indicated by arrows for easy understanding.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the present invention.

FIG. 3 is a sectional view showing a third embodiment of the present invention.

FIG. 4 is a sectional view showing a fourth embodiment of the present invention.

FIG. 5 is a diagram showing an example of valve timing of intake and exhaust valves in each embodiment of the present invention.

FIG. 6 is a diagram showing a flow of an engine coolant at a low engine load according to a fifth embodiment of the present invention.

FIG. 7 is a diagram showing a flow of an engine coolant at a high engine load in a fifth embodiment of the present invention.

FIG. 8 is a diagram showing a flow of an engine coolant at a low engine load according to a sixth embodiment of the present invention.

FIG. 9 is a diagram showing a flow of an engine coolant at the time of a high engine load according to a sixth embodiment of the present invention.

FIG. 10 is a sectional view showing a structure of a water jacket of a cylinder block according to a sixth embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 cylinder block 2 piston 3 cylinder head 4 combustion chamber 5 intake port 6 intake valve 7 exhaust port 8 exhaust valve 9 spark plug 10 cylinder bore wall 11 cylinder liner 11a heat insulating member 13 cylinder block water jacket 13A first jacket 13B second jacket 14 Cylinder liner part 14a Thick part 15 Cavity 16 Cooling passage 17 Opening 18 Oil jet 20 Engine cooling system S Piston stroke area corresponding to residual gas trapping engine

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Akihiro Iiyama F-term in Nissan Motor Co., Ltd. 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa 3G023 AA02 AA05 AA18 AB03 AB06 AD02 AD03 AD11 AE04 AE06 3G024 AA22 BA02 CA05 CA26 DA01 DA02 DA03 DA08 FA00 FA11 FA14 GA18 HA10 3G092 AA01 AA11 AB02 DA03 EA03 EA04 FA24 GA05 GA06 HA11Z

Claims (8)

[Claims] 1. The valve timing of an intake valve and an exhaust valve is variably controlled at a high load and a low load of an engine, and the closing timing of the exhaust valve and the opening timing of the intake valve are delayed in a low load range. A four-stroke internal combustion engine in which high-temperature residual gas is confined in a combustion chamber to activate fresh air sucked in the middle of an intake stroke to perform compression auto-ignition combustion, and at least the combustion chamber is formed. A four-stroke internal combustion engine, wherein a portion of a piston stroke region of a cylinder bore wall corresponding to the residual gas trapping period has a heat insulating structure. 2. The four-stroke internal combustion engine according to claim 1, wherein the heat insulating structure of the cylinder bore wall is constituted by a cylinder liner made of a heat insulating member. 3. The four-stroke internal combustion engine according to claim 1, wherein the heat insulating structure of the cylinder bore wall is formed by providing a cavity in a rear portion of the cylinder liner. 4. The heat insulating structure of a cylinder bore wall, wherein the thickness of the predetermined area portion of the cylinder liner portion is made thicker than other portions. A four-stroke internal combustion engine as described. 5. The four-stroke internal combustion engine according to claim 1, wherein a piston crown surface forming the combustion chamber and at least a surface of the intake / exhaust valve facing the combustion chamber are formed of a heat insulating member. organ. 6. A cooling passage having an opening on the back side of the piston is provided inside the piston, and an oil jet for injecting cooling oil toward the opening is provided below the piston to detect a load on the engine. The four-stroke internal combustion engine according to any one of claims 1 to 5, wherein the operation of the oil jet is stopped at a low load, and the oil jet is operated at a high load. 7. The cylinder head and the cooling system of the cylinder block are configured separately and independently, and the supply of the engine coolant to the cylinder block is stopped when the load of the engine is low. 4. The method according to any one of to 6,
Cycle internal combustion engine. 8. A partition provided in a water jacket of a cylinder block, wherein the water jacket is provided with a first jacket provided in a piston stroke region corresponding to the residual gas trapping period and a second jacket provided below the first jacket.
The four-stroke internal combustion engine according to any one of claims 1 to 6, wherein the engine is separated from the jacket and the supply of the engine coolant to the first jacket is stopped when the engine is under a low load.