Patent Application
20130146041
1. Field of the Invention
The invention relates to an internal combustion engine and a method of producing this internal combustion engine. More particularly, the invention relates to an internal combustion engine in which an anodic oxidation coating film is formed on all or a portion of the wall facing a combustion chamber of the internal combustion engine and relates to a method of producing an internal combustion engine having a feature in forming this anodic oxidation coating film.
2. Description of the Related Art
An internal combustion, engine, e.g., a gasoline engine or diesel engine, is composed primarily of an engine block and a cylinder head, and its combustion chamber is defined by the bore surface of the cylinder block, the top surface of the piston installed in this bore, the bottom surface of the cylinder head, and the head surfaces of the intake and exhaust valves that are disposed in the cylinder head. Accompanying the higher outputs being required of internal combustion engines at the present time, it has become crucial to lower their cooling losses. One strategy for lowering this cooling loss is to form a heat-insulating ceramic coating film on the inner wall of the combustion chamber.
However, these ceramics generally have a low thermal conductivity and have a high heat capacity, causing the appearance of a reduced intake efficiency and knocking (abnormal combustion caused by heat being retained within the combustion chamber), and as a consequence at the present time their use as a coating film material on the interior walls of the combustion chamber is not spreading.
In view of the preceding, the heat-insulating coating film formed on the wall of the combustion chamber must certainly be heat resistant and heat insulating and is desirably formed from a material that has a low thermal conductivity and a low heat capacity. Moreover, in addition to this low thermal conductivity and low heat capacity, the coating film is desirably formed from a material that can Withstand the expansion pressure and injection pressure during combustion in the combustion chamber and the repetitive stresses from thermal expansion and thermal shrinkage and is also desirably formed from a material that has a high adherence to the base material of, e.g., the cylinder block and so forth.
When one considers the conventional disclosed technology here, the cylinder head disclosed in Japanese Patent Application Publication No. 2003-113737(JP-A-2003-113737) has a microporous silicon dioxide-type or aluminum oxide-type coating film formed by anodic oxidation on both the bottom surface of the cylinder head and the inner surface of a water jacket that is defined within this cylinder head. Through the disposition in this cylinder head of the microporous coating film on both the bottom surface of the head and the inner surface of the jacket, the surface area of the bottom surface of the head and the jacket inner surface is enlarged by this coating film, and as a result the heat produced in the combustion chamber can be efficiently absorbed into the interior across the coating film and the inwardly absorbed heat can be efficiently discharged across the coating film at the jacket inner surface into the coolant. As a consequence, heating readily occurs through heat absorption while cooling readily occurs through heat release, resulting in a cylinder head for which a temperature increase is suppressed.
The internal combustion engine disclosed in Japanese Patent Application Publication No. 2009-243352 (JP-A-2009-243352) and WO 2009/020206 has a heat-insulating thin film in which bubbles are formed in the interior of a material that has a thermal conductivity lower than that of the base material forming the combustion chamber of the internal combustion engine and that has a heat capacity that is the same as or lower than that of the base material.
The art disclosed in the previously described JP-A-2003-113737, JP-A-2009-243352, and WO 2009/020206 is an art in which a coating film having a low thermal conductivity and a low heat capacity is formed on the inner wall of the combustion chamber of the internal combustion engine, and can provide heat-insulating coating films that exhibit excellent properties as described above.
However, it is not clear whether these coating film structures provide coating films that can withstand the expansion pressure and injection pressure during combustion in the combustion chamber and the repetitive stresses from thermal expansion and thermal shrinkage, or can provide coating films that can relax these pressures and stresses. The inventors found that it would be difficult to say that these coating film structures have an excellent pressure relaxing or stress relaxing behavior. One reason for this is that a coating film produced by anodic oxidation has a microstructure in which the constituent cells have voids in the interior while adjacent cells are almost gaplessly chemically bonded to each other, and as a result it is difficult to set up a satisfactory stress relaxation between these cells.
The invention was pursued in view of the problems identified above and provides an internal combustion engine that is equipped, on all or a portion of a wall that faces a combustion chamber, with an anodic oxidation coating film that has a low thermal conductivity and a low heat capacity and that exhibits an excellent ability to relax the expansion pressure and injection pressure during combustion in the combustion chamber and the repetitive, stresses from thermal expansion—shrinkage and that is therefore highly durable. The invention also provides a method of producing this internal combustion engine.
Therefore, according to a first aspect of the invention, an internal combustion engine is provided in which an anodic oxidation coating film is formed on all or a portion of a wall that faces a combustion chamber, wherein this anodic oxidation coating film has a structure that is provided with a bonding region in which each of hollow cells forming the coating film is bonded to the adjacent hollow cells, and a nonbonding region in which three or more adjacent hollow cells are not bonded to each other, and wherein a porosity of this anodic oxidation coating film is determined by a first void present in the hollow cell and a second void that forms the nonbonding region.
The internal combustion engine of the invention has an anodic oxidation coating film (or a heat-insulating film) on all or a portion of its combustion chamber. However, the internal combustion engine of the invention has a coating film that, unlike conventional anodic oxidation coating films, presents a microstructure that in addition to the hollow cells having avoid (the first void) in their interior has a void (the second void) that forms a nonbonding region at, for example, a triple point among adjacent hollow cells (Note: Polycrystalline metals are composed of a plurality of unit crystals (a plurality of cells here), which results in an adjacent relationship thereamong; when this occurs, the point at which three unit crystals coincide is called a triple point), while the bonding region, where the hollow cells are in contact with each other, has a chemically bonded structure.
Because the anodic oxidation coating film has voids, it has both a low thermal conductivity and a low heat capacity, but because it is also provided with a separate void (the second void) between/among cells while the hollow cells are also chemically bonded to each other; this coating film additionally has the ability to relax pressure, i.e., the expansion pressure and injection pressure during combustion in the combustion chamber, and the ability to relax the repetitive stresses from thermal expansion—shrinkage. In addition to the formation of a second void at all the triple points and so forth of three or more adjacent hollow cells constituting the coating film, this may be a film in which the second void is formed only at a portion of all the triple points and so forth.
The internal combustion engine of the invention may be directed to a gasoline engine or a diesel engine, and, with regard to its structure, as previously noted it is composed mainly of an engine block and a cylinder head. Its combustion chamber is defined by the bore surface of the cylinder block, the top surface of the piston installed in this bore, the bottom surface of the cylinder head, and the head surfaces of the intake and exhaust valves that arc disposed in the cylinder head.
The anodic oxidation coating film having the previously described microstructure may be formed over all of the wall facing the combustion chamber or may be formed only on a portion of this wall, and the latter case can be exemplified by embodiments such as only on the top surface of the piston or only on the valve head surface.
The base material forming the combustion chamber of the internal combustion engine can be exemplified by aluminum and its alloys and titanium and its alloys. An alumite coating film is formed when the anodic oxidation coating film is formed on a wall for which the base material is aluminum or an alloy thereof.
The mechanism for the fuel consumption improvement due to the formation of a low thermal conductivity low heat capacity anodic oxidation coating film (heat-insulating film) on the combustion chamber wall will be described with reference to
According to the inventors, when the heat-insulating anodic oxidation coating film has a thickness below 100 μm, the temperature rise of the coating film surface during the combustion cycle is inadequate and the heat-insulating behavior becomes inadequate and an improvement in fuel consumption, described below, cannot be achieved. The minimum thickness is therefore set to 100 μm in order to secure this improvement in fuel consumption.
On the other hand, the inventors have also ascertained that when the thickness of the anodic oxidation coating film exceeds 500 μm, it takes on a large heat capacity at this point and the swing behavior (the property wherein the temperature of the anodic oxidation coating film tracks the gas temperature in the combustion chamber, while also providing a heat-insulating behavior) is impaired because the anodic oxidation coating film itself is then prone to store heat. 500 μm is also the upper limit on the thickness of the anodic oxidation coating film from the standpoints of the production efficiency and ease of production since the production of an alumite film thicker than 500 μm is itself quite difficult. The previously mentioned porosity is also preferably 15 to 40%.
The inventors estimate that the formation of an anodic oxidation coating film having a porosity of 15 to 40% and a thickness of 100 to 500 μm over the entire combustion chamber surface of an internal combustion engine provides a maximum fuel consumption improvement of 5%, for example, for a small supercharged direct injection diesel engine for passenger vehicles at the optimal fuel consumption point corresponding to an engine rotation rate of 2100 rpm and an indicated mean effective pressure of 1.6 MPa. This 5% fuel consumption improvement is a value that demonstrates a clear significant difference for the fuel consumption improvement that rises above experimental measurement error. In addition, it is estimated that, at the same time that the fuel consumption is improved, the exhaust gas temperature is raised by about 15° C. by the heat insulation. In an actual engine, this rise in exhaust gas temperature is effective for shortening the warm-up time of the NOx reduction catalyst immediately after starting and is a value at which the NOx purification rate is improved and a reduction in NOx can be identified.
On the other hand, in a cooling test (quenching test) performed during the evaluation of the thermal properties of anodic oxidation coating films, a test piece is used having the anodic oxidation coating film executed on only one side, and, while continuing to heat the back side (the side on which an anodic oxidation coating film has not been executed) with a prescribed high-temperature jet, cold air at a prescribed temperature is sprayed from the front side of the test piece (the side on which the anodic oxidation coating filth has been executed). This serves to drop the front side temperature of the test piece, and this temperature is measured and a cooling curve is constructed from the temperature of the coating film surface and time in order to evaluate the temperature drop rate. This temperature drop rate is evaluated, for example, through the 40° C. drop time, which is read from the graph and is the time required for the temperature of the coating film surface to drop 40° C.
The quench test is run using test pieces with different porosities (the porosity of the anodic oxidation coating film is determined using the sum of the first void and second void); the 40° C. drop time is measured for each of these test pieces; and, for example, a fitted curve is constructed for the multiple plots defined by the porosity and 40° C. drop time.
By reading the porosity at the intersection of this fitted curve with the value of the 40° C. drop time (for example, 45 msec) that corresponds to the 5% fuel consumption improvement noted above, the inventors determined that this porosity is 15%. The thermal conductivity and heat capacity of the coating film are lower and the fuel consumption improving effect is higher at shorter 40° C. drop times.
On the other hand; anodic oxidation coating film test pieces are fabricated at different porosities and the microVickers hardness of each is measured and a fitted curve is constructed for the multiple plots defined by the porosity and the microVickers hardness. When the base material of the combustion chamber is composed of aluminum, the resulting alumite film desirably is harder than the aluminum base material, and, when this is taken in account by using the microVickers hardness of aluminum as the threshold value, the inventors determined a value of 40% for the porosity when the porosity established by the fitted curve and this threshold value is read off.
Thus the range for the porosity of the anodic oxidation coating film is set to a range of 15 to 40% based on the cooling test, microVickers hardness test, and 5% fuel consumption improvement
In addition, when the optimal range for the ratio φ/d—where φ is an average pore diameter of the first void (average value of pore diameters) and d is an average cell diameter of the hollow cells making up the anodic oxidation coating film is sought when the porosity is varied, the range corresponding to the previously described 15 to 40% porosity range has been identified by the inventors as 0.3 to 0.6.
The surface of the anodic oxidation coating film is preferably subjected to a sealing treatment with boiling water or steam, or a coating treatment with a thin film that lacks pores, or both treatments. Boiling water to which, for example, sodium silicate has been added as a sealing promoter may be used.
In order to prevent the penetration of fuel and combustion gas into the porous anodic oxidation coating film, for example, a thin film of an inorganic sealant such as sodium silicate coated in a layer thinner than the anodic oxidation coating film is applied as a surface treatment to the anodic oxidation coating film. Viewed from the perspectives both of having the anodic oxidation coating film display the various properties described above and avoiding an excessively large film thickness, this is desirably a thin film, for example, with a thickness of about 10 μm or less, in contrast to the previously described anodic oxidation coating Elm with its film thickness of 100 to 500 μm.
As described above, the anodic oxidation coating film is also preferably an alumite coating film. In addition, the microVickers hardness of this anodic oxidation coating film is preferably in the range from 110 to 400 HV0.025.
In another aspect the invention provides a method of producing an internal combustion engine, as described in the following. Thus, this production method is a method of producing an internal combustion engine by forming an anodic oxidation coating film on all or a portion of a wall facing a combustion chamber in the internal combustion engine, wherein an anode is formed by immersing all or a portion of the wall in an acidic electrolytic bath, a cathode is formed within the acidic electrolytic bath, and then a voltage adjusted to the range of 130 to 200 V for the maximum voltage is applied between the two electrodes, and electrolysis is performed at a heat removal rate adjusted to the range from 1.6 to 2.4 cal/s/cm2, to thereby form an internal combustion engine having, on the surface of all or a portion of the wall, an anodic oxidation coating film that has a structure provided with a bonding region in which each of hollow cells is bonded to the adjacent hollow cells, and a nonbonding region in which three or more adjacent hollow cells are not bonded to each other.
With regard to the conditions for the anodic oxidation treatment for forming the anodic oxidation coating film having the previously described microstructure on all or a portion of the combustion chamber wall of the internal combustion engine, the inventors discovered that electrolysis is favorably carried out by applying a voltage, adjusted to having a maximum voltage in the range from 130 to 200 V, between the anode and cathode in an acidic electrolytic bath in which all or a portion of the wall is immersed, while adjusting the heat removal rate to the range from 1.6 to 2.4 cal/s/cm2. Thus, the execution of electrolysis under these conditions can cause the acid to penetrate into the bottom region (deep region) of the anodic oxidation coating film that is formed and makes possible the production of the first and second voids in the desired size over the entire range reaching to the bottom region- of the anodic oxidation coating film.
This “heat removal rate” is the amount of heat captured by the electrolytic bath per unit time per unit surface are; and adjusting the temperature of the electrolytic bath to the range from −5 to 5° C. provides a beat removal rate in the range from 1.6 to 2.4 cal/s/cm2.
Another embodiment of the method of producing an internal combustion engine according to the invention preferably includes a first step of forming an anode by immersing all or a portion of the wall in an acidic electrolytic bath, forming cathode within the acidic electrolytic bath, and then applying between the two electrodes a voltage adjusted to the range of 130 to 200 V for the maximum, and performing electrolysis at a heat removal rate adjusted to the range from 1.6 to 2.4 cal/s/cm2, to thereby form, on the surface of all or a portion of the wall, an intermediate of the anodic oxidation coating film having a structure that is provided with a bonding region in which each of hollow cells is bonded to the adjacent hollow cells, and a nonbonding region in which three or more adjacent hollow cells are not bonded to each other; a second step of adjusting a porosity determined by a first void present in the hollow cell and a second void that forms the nonbonding region, by widening voids of the intermediate of the anodic oxidation coating film by carrying out a pore widening treatment using acid on all or a portion of the wall that is provided on the surface of the intermediate of the anodic oxidation coating film.
This production method by further widening the first and second voids through a pore widening treatment of the anodic oxidation coating film provided by electrolysis under the same conditions as in the previously described production method (this anodic oxidation coating film corresponds to the intermediate) can secure a more reliable generation of porosity in the desired range.
Specifically, by subsequently executing a separate acid-based pore widening treatment (an acid etch treatment in order to enlarge the voids) on an intermediate of the anodic oxidation coating film produced by the first step, the porosity as a whole can be adjusted by widening the first voids by dissolving the interior of the hollow cells and, at the same time., by also widening the second voids by dissolving the circumference of the second voids between the hollow cells. This makes possible the production of an internal combustion engine that is provided, on all or a portion of the combustion chamber wall, with a high thermal conductivity, high beat capacity anodic oxidation coating film that exhibits an excellent pressure relaxing behavior and an excellent thermal stress relaxing behavior.
Also in the production method of the invention, the thickness of the anodic oxidation coating film is preferably adjusted to the range from 100 to 500 μm; the porosity is preferably adjusted to the range from 15 to 40%; and thus the ratio φ/d, where φ is an average pore diameter of the first void present in the hollow cells and d is an average cell diameter of the hollow cell, is preferably adjusted to the range from 0.3 to 0.6.
In a preferred embodiment of the method according to the invention of producing an internal combustion engine, the production method is additionally provided with, after the formation of the previously described anodic oxidation coating film, a step of performing a sealing treatment with boiling water or steam, or a coating treatment with a thin film that lacks pores, or both treatments.
As with the previously described internal combustion engine of the invention, in order to prevent the penetration of fuel and combustion gases into the anodic oxidation coating film, a step may additionally be present of executing a sealing treatment, or coating the surface with a thin film, or carrying out both. For example, in the case of coating the surface with a thin film, the coating of the surface of the produced anodic oxidation coating film with a thin layer of an inorganic sealant such as sodium silicate can prevent the permeation of fuel and mixed gases into the interior of the anodic oxidation coating film and can, thereby secure the various properties possessed by the anodic oxidation coating film.
This anodic oxidation coating film is also preferably an alumite coating film. In addition, the microVickers hardness of this anodic oxidation coating film is preferably in the range from 110 to 400 HV0.025.
As can be understood from the preceding description, the internal combustion engine and method for its production of the invention through the formation, on all or a portion of a wall of a combustion chamber of the internal combustion engine, of an anodic oxidation coating film having a structure that has a void (the first void) in the interior of the hollow cells and that also has a void (the second void) at, for example, the triple points among adjacent hollow cells, while chemical bonding occurs in the bonding regions where the hollow cells are in contact with each other can provide an internal combustion engine provided with a coating film that has a low thermal conductivity and a low heat capacity and. thus an excellent heat-insulation behavior, and that also has an excellent ability to relax the expansion pressure and so forth during combustion in the combustion chamber and the repetitive stresses from thermal expansionshrinkage and that is therefore highly durable.
The features, advantages, and technical and industrial significance of this invention will be described in the following detailed description of example embodiments of the invention with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:
Embodiments of the internal combustion engine and the method of its production of the invention are described below with reference to the drawings. While the illustrated examples show embodiments in which the anodic oxidation coating film is formed over the entire wall facing the combustion chamber of the internal combustion engine, embodiments may also occur in which the anodic oxidation coating film is formed on only a portion of the wall facing the combustion chamber, e.g., only on the top Surface of the piston or only on the head surface of the valve.
The illustrated internal combustion engine 10 is directed to a diesel engine and is approximately composed of a cylinder block 1 having a coolant jacket 11 formed therein, a cylinder head 2 disposed above the cylinder block 1, an intake port 21 and an exhaust port 22 defined in the cylinder head 2 and an intake valve 3 and an exhaust valve 4 that are mounted in a freely vertically displaceable manner in the openings where the intake port 21 and exhaust port 22 face the combustion chamber NS, and a piston 5 formed in a manner freely vertically displaceable from the lower opening of the cylinder block 1. The internal combustion engine of the invention may of course be directed to a gasoline engine.
The various constituent members composing this internal combustion engine 10 are made of aluminum or an alloy thereof. In another embodiment, a constituent member may be formed of a material other than aluminum or an alloy thereof and the surface of the constituent member may be aluminized with aluminum or an alloy thereof.
In addition, an anodic oxidation coating film 61, 62, 63, 64 having a prescribed thickness and exhibiting the microstructure shown in
This microstructure and the method of producing this microstructure will be described using the anodic oxidation coating film 61 formed on the surface of the cylinder bore 12 as an exemplar.
The anodic oxidation coating film 61 formed on the surface of the aluminum or aluminum alloy cylinder bore 12 is alumite, and this anodic oxidation coating film 61 is fanned from a plurality of hollow cells C provided with a first void K1 in the interior and more specifically is a coating film that has a microstructure in which each of the hollow cells C is chemically bonded to adjacent hollow cells C, C and which is provided with a separate second Void K2 in a nonbonding region in which three or more adjacent hollow cells C are not bonded to each other, e.g., a triple point.
A conventional anodic oxidation coating film does not have a structure, like that of the illustrated anodic oxidation coating film 61, in which the second void K2 is provided among three or more adjacent hollow cells C rather, in a conventional anodic oxidation coating film the interior void-containing hollow cells are chemically bonded to another without a gap therebetween.
In contrast, the illustrated anodic oxidation coating film 61 has a first void K1 in the interior of the hollow cell C and has a separate second void K2 residing in the nonbonding region where the hollow cells C, are not bonded to one another, and the porosity of the anodic oxidation coating film 61 is determined from this first void K1 and second void K2. The size of the first void K1 and the production and size of the second void K2 can be adjusted, by adjusting as desired the maximum voltage and the acidic electrolyte bath temperature (or the heat removal rate) during the electrolysis that produces the anodic oxidation coating film and by a post-treatment in the form of a pore widening treatment such as an acid etching treatment.
Based on experiments by the inventors, vide infra, this porosity is desirably adjusted to the range from 15 to 40%. The porosity range can be identified by sectioning the anodic oxidation coating film in the middle of its thickness direction; performing ion beam polishing; and carrying out measurement by SEM image analysis. In addition, with regard to the ratio φ/d where φ is the average pore diameter of the first void K1 and d is the average cell diameter of the hollow cell C, a φ/d in the range from 0.3 to 0.6 corresponds to the aforementioned porosity range of 15 to 40%.
Moreover, the inventors have also ascertained that the thickness t1 of the anodic oxidation coating film 61 is desirably adjusted to the range from 100 to 500 μm.
That is, according to the inventors, when the heat-insulating anodic oxidation coating film has a thickness below 100 μm, the temperature rise of the coating film surface during the combustion cycle is inadequate and the heat-insulating behavior becomes inadequate and an improvement in fuel consumption cannot be achieved. Due to this, the minimum thickness, is set to 100 μm in order to secure this improvement in fuel consumption. On the other hand, the inventors also determined that when the thickness of the anodic oxidation coating film exceeds 500 μm, it takes on a large heat capacity at this point and the swing behavior is impaired because the anodic oxidation coating film itself is then prone to store heat. 500 μm is also the upper limit on the thickness of the anodic oxidation coating film from the standpoints of the production efficiency and ease of production since the production of an alumite film thicker than 500 μm is itself quite difficult The coating film thickness can be measured using, for example, an eddy-current film thickness analyzer and can be determined by taking the average of 10 points.
The anodic oxidation coating film 61, because it has a microstructure that is provided with the separate second voids K2 at, for example, triple points among the hollow cells C that have the first voids K1, has both a low thermal conductivity and a low heat capacity and, in combination with this, also has the ability to relax pressure, e.g., the expansion pressure and injection pressure during combustion in the combustion chamber NS, as well as the ability to relax the repetitive stress from thermal expansionshrinkage.
In addition, the adjustment of its thickness into the 100 to 500 μm range as described above secures its ease of production and provides a film having a heat-insulating behavior as well as a swing behavior, i.e., the temperature of the anodic oxidation coating film tracks the gas temperature in the combustion chamber NS.
Moreover, the inventors estimate that, through the adjustment of the range of the porosity determined by the first void K1 and the second void K2 into the 15 to 40% range, a maximum fuel consumption improvement of 5% is obtained, for example, for a small. supercharged direct injection diesel engine for passenger vehicles at the optimal fuel consumption point corresponding to an engine rotation of 2100 rpm and an indicated mean effective pressure of 1.6 MPa. In addition, at the same time that the fuel consumption is improved, the exhaust gas temperature is raised by about 15° C. by the heat insulation, which ties into shortening the warm-up time of the NOx reduction catalyst immediately after starting and improves the NOx purification rate and can realize a reduction in NOx.
In order to prevent the penetration of fuel and combustion gas into the anodic oxidation coating film 61 prodded with the first and second voids K1, K2, a thin film 7 may be formed at the surface of the anodic oxidation coating film 61 by the application of an inorganic sealant such as sodium silicate in a layer thinner than that of the anodic oxidation coating film 61.
Viewed from the perspectives both of having the anodic oxidation coating film display the various properties described above and avoiding an excessively large film thickness, the thickness t2 of this thin film 7 is desirably adjusted to, for example, a thickness of about 10 μm or less, in contrast to the film thickness t1 of 100 to 500 μm for the anodic oxidation coating film 61.
The method of producing the illustrated internal combustion engine 10 is summarized in the following with reference to the flow chart
An anodic oxidation coating film is first formed (step S1) by forming an anode by immersing the wall of the particular member that faces the combustion chamber NS in an acidic electrolytic bath (not shown) of, e.g., sulfuric acid, forming a cathode within the acidic electrolytic bath, and then applying between the two electrodes a voltage adjusted to the range of 130 to 200 V for the maximum voltage, and performing electrolysis at a heat removal rate adjusted to the range from 1.6 to 2.4 call/s/cm2. These numerical value ranges are discussed below. This “heat removal rate” is the amount of heat captured by the electrolytic bath Per unit time per unit surface area.
The execution of film formation under the aforementioned conditions in this anodic oxidation treatment step serves to promote hollow cell growth, to widen the first and second voids and thereby adjust the porosity into the 15 to 40% range, and to enable the production of a coating film with a film thickness in the 100 to 500 μm range.
Once the anodic oxidation coating film with the desired porosity has been produced, the surface of the anodic oxidation coating film is subjected to a sealing treatment with boiling water or steam, or a coating treatment with a thin film that lacks pores, or both treatments, in order to thereby produce an internal combustion engine that has, formed on a combustion chamber, wall, an anodic oxidation coating film that does not take fuel or mixed gas into the pores of the anodic oxidation coating film (step S2).
Once an anodic oxidation coating film having the desired thickness has been produced by carrying out this adjustment to generate the desired porosity, the internal combustion engine is produced by subjecting the surface of the anodic oxidation coating film, as in the production method in
By adjusting the maximum voltage into the 130 to 200 V range and adjusting the heat removal rate into the 1.6 to 2.4 cal/s/cm2 range, an anodic oxidation coating film can be formed in the desired thickness in this anodic oxidation treatment step and first and second voids having the desired size can be formed in this stage (voids of a certain size can be preliminarily produced in this stage as a pretreatment for the formation of voids with the desired porosity by the pore widening treatment step implemented as a post-treatment).
According to the inventors, the temperature of the electrolytic bath is desirably adjusted to the range from −5 to 5° C. for a heat removal rate in the range from 1.6 to 2.4 call/s/cm2. The heat removal rate can be adjusted using both the temperature of the electrolytic bath and the stirring rate for the electrolytic bath.
In the region which is the same heat removal rate region as the invention region but the maximum voltage is less than the invention region, i.e., the maximum voltage is less than 100 V, the hollow cell size ends up being small and a hard alumite region occurs in which the second void is not formed between cells.
On the other hand, in the region which is the same heat removal rate region as the invention region but the maximum voltage is higher than the invention region, i.e., the maximum voltage exceeds 200 V, a plasma anodic oxidation region occurs in which hollow cells are not formed.
In addition, in the heat removal rate region below the invention region, the anodic oxidation coating film cannot form the desired film thickness of at least 100 μm, and it has been determined that a coating film is formed in which there is no connection by chemical bonding between the cells.
Treatment conditions are shown below in Tables 1 and 2 for an anodic oxidation coating film formed in the invention region shown in
In the case of the coating film of the example, it can be confirmed from
In contrast, hi the case of the coating film of the comparative example in which film formation was carried, out in the hard alumite region, only very small voids are produced in the anodic oxidation treatment stage; the pore widening treatment results in just a minor widening of the voids in the cells, resulting in an unsatisfactory size; and voids are not produced at, for example, the triple points among cells.
In addition, in the case of the coating film of the comparative example in which film formation was carried out in the plasma anodic oxidation region, hollow cell production itself could not be confirmed, as shown in
Experiments that identify the porosity range and the results of these experiments are described in the following. The inventors carried out cooling tests, microVickers hardness testing, and experiments to identify the optimal, porosity range for the anodic oxidation coating film from the percentage improvement infuel consumption. First, with regard to the execution of, the cooling test, the casting shown in
The cooling test is summarized in the following. As shown in
The time required fox a 40° C. drop is read from the thusly constructed cooling curve to give the 40° C. drop time, and the thermal properties of the coating film are evaluated through this 40° C. drop time.
In the experiment under consideration, front side cooling is begun after stabilization at about 250° C. for 100 ms, as shown in
The inventors used a 5% fuel consumption improvement as a target value to be achieved during the experiments; by the performance of the anodic oxidation coating film constituting the combustion chamber of the internal combustion engine of the invention. A 5% fuel consumption improvement is a value that can clearly validate a. fuel consumption improvement without being obscured by measurement error and that, through the increase in the exhaust gas temperature, can shorten the warm-up time for the NOx reduction catalyst and can realize a reduction in NOx. The inventors sought to identify the porosity range for achieving this target value. The graph shown in
A fitted curve (quadratic curve) is constructed as shown in
In order to construct a correlation graph for the relationship between the cooling test and porosity and for the relationship between the microVickers hardness and porosity, test pieces were fabricated under the anodic oxidation treatment step conditions (and pore widening treatment step conditions for the examples) shown in Table 4 below using nine different porosities for the anodic oxidation coating filth, in accordance with Comparative Examples 1 to 5 and Examples 1 to 4. The results of measurement of the anodic oxidation coating film thickness, porosity, microVickers hardness, and 40° C. drop time are shown in Table 5 for each test piece.
In the microVickers hardness testing, the microVickers hardness was measured in the middle of the cross section of the anodic oxidation coating film, and the average value at five measurement points on each test piece at a measurement load of 0.025 kg was used as the microVickers hardness.
To determine the relationship between the cooling test and porosity, experiments were nm using the method shown in
Based on
The microVickers hardness and porosity of the test pieces are plotted in
Based on
Based on the preceding results; the optimal range for the porosity of the alumite (anodic oxidation coating film) formed on the combustion chamber wall of the internal combustion engine can be set to the range of 15 to 40%.
A graph correlating the φ/d in Table 5 with the porosity is shown in
SEM photographs of the cross sections in the examples and comparative examples are shown in
Based on the individual figures, the comparative examples do not have adequately large pores, and the following can also be confirmed from these figures: adequate gaps are not present between the cells (Comparative Examples 1, 2, and 3), and the voids are excessively large and/or the cells are not adequately chemically bonded to each other (Comparative Examples 4 and 5). In contrast, the following can be confirmed for the examples: the cells are provided in their interior with voids of a certain size; voids of a certain size are also present at the triple points among cells (nonbonding regions); and, because these voids are not excessively large, a bonding region is provided in which the cells are chemically bonded to each other at either points or sides.
Experiments for determining the relationship between the maximum voltage and the surface temperature drop rate will now be:described, as will the results of these experiments. The inventors measured the surface temperature drop rate (40° C. drop time) as a function of the maximum voltage on test pieces prepared using different maximum voltages in the anodic oxidation treatment, as shown in Table 6. These measurement results were plotted and a fitted curve was constructed for the plotted values, as shown in
Given that from Table 6 and
Experiments for identifying the relationship between the pore widening treatment time fox the anodic oxidation coating film and the porosity and surface temperature drop rate will be described, as will the results of these experiments. The inventors carried out experiments in order to identify the relationship between the pore widening treatment time and the porosity and surface temperature drop rate. Specifically, anodic oxidation treatments were carried out in the hard alumite region and the invention region as shown in
According to Table 7 and
The SEM photographs in
Engine performance evaluation experiments with a diesel engine are described below, as are the results of these experiments. The inventors carried out the formation of an alumite coating film, using the conditions described below, on only the top surface of the piston in the combustion chamber of the engine and measured the engine performance, e.g., the fuel consumption improvement and NOx change.
The engine used here has the following specifications: water-cooled horizontal single-cylinder DI diesel engine, φ 78×80 (382 cc), 5.1 kW @ 2600 rpm. The specifications for the alumite are as follows: film thickness=150 μm (after the sealing treatment: boiling water treatment), porosity corresponding to 15%. The alumite-treated article was the front (only the piston side of the combustion chamber) of the top of the diesel piston, and an aluznite treatment was not performed on the other members facing the combustion chamber, e.g., the cylinder bead, valves, and cylinder block.
Three parameters indicative of engine performance were measured with the following results: the fuel consumption was raised (improved) by 1.3%, the smoke change was a decrease of 29%, and the NOx change was a decrease of 4%.
The inventors estimate that an approximately 2.5-times larger fuel consumption improvement could be achieved for the formation of the same alumite coating Mira over the entire wall surface versus formation of the alumite coating film only on the piston top surface among the wall surfaces facing the combustion chamber of the diesel engine. In addition, the inventors estimate that an approximately 1.6-fold increase in the fuel consumption improvement would be recognized by the formation of the same coating film in a supercharger-equipped diesel engine over that for the non-supercharged (natural intake) DI diesel engine described above. Accordingly, a 5% improvement in fuel consumption can be achieved for the formation of the coating film that is the structural element of the invention over the entire combustion chamber of a supercharger-equipped direct-injection diesel engine.
Embodiments of the invention have been particularly described above using the drawings, but the specific structure is not limited to these embodiments, and design variations, workshop modifications, and so forth, that do not depart from the essential features of the invention are encompassed by the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-188450 | Aug 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB11/01924 | 8/23/2011 | WO | 00 | 2/20/2013 |
