JP2010133291A - Cooling device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve cooling performance and reduction in flow resistance at a high level, in a water-cooled type cooling device for an internal combustion engine. <P>SOLUTION: Surfactant of critical concentration or more is contained in cooling water, and the flow resistance is reduced by the formation of bar-like micelles 21. A surface of a water jacket wall 12 in contact with cooling water has concave-convex surface structure. Firstly, a flow of the cooling water flowing along a wall face is physically agitated, and the bar-like micelles 21 are broken by a shear force thereof. Secondly, air dissolved in the cooling water is grown as air bubbles by the concavity and convexity of the surface to be easily separated therefrom. Similarly, generation-separation of the air bubbles by nucleate boiling is promoted, and the cooling water is agitated by the dissolved air or air bubbles 23 by subcooled boiling, so that the bar-like micelles are broken and divided into spherical micelles 22. A heat transfer coefficient is recovered by breakage-division of the bar-like micelles 21. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a cooling device for an internal combustion engine that cools each part of a cylinder head and a cylinder block by forced circulation of cooling water.

  Patent Document 1 discloses that a rod-like micelle using a surfactant in cooling water as a cooling device for an internal combustion engine for a vehicle can reduce turbulent frictional resistance of cooling water. While the power of the water pump is reduced by this, in the heat radiating parts such as radiators and heater cores, since the Reynolds number of the flow is large, the action of reducing the turbulent frictional resistance by the rod-like micelles is suppressed, and a relatively high heat exchange action is achieved. can get.

Patent Document 2 discloses that rod-like micelles formed in a fluid for reducing pipe resistance are destroyed by heating to recover the heat transfer coefficient.
Japanese Patent Laid-Open No. 11-173146 JP 2006-336944 A

  When a rod-like micelle is formed in the cooling water to reduce the water flow resistance in the cooling water system as in Patent Document 1, the water jacket around the cylinder and the combustion chamber has a flow path as compared with a radiator or the like. Since the cross-sectional area is large, laminar flow is maintained and the heat transfer coefficient is relatively low. That is, with the reduction of the turbulent frictional resistance due to the rod-like micelles, the heat transfer rate from the water jacket wall surface to the cooling water decreases, and heat cannot be removed effectively.

  Moreover, the method of destroying rod-like micelles by heating and recovering the heat transfer coefficient as in Patent Document 2 cannot be adopted as a cooling device for the purpose of removing heat.

  The cooling device for an internal combustion engine according to the present invention uses cooling water containing a surfactant having a concentration capable of forming rod-like micelles, thereby reducing water flow resistance. And the inner surface of at least one part of the water jacket through which this cooling water circulates has the uneven surface structure which destroys a rod-like micelle. This uneven surface structure not only simply stirs the flow of the cooling water near the surface to destroy the rod-like micelles, but also the dissolved air grows as air bubbles or bubbles are generated by nucleate boiling (subcool boiling). The action which destroys a rod-like micelle by these bubbles is acquired. Thus, by destroying the rod-like micelles near the inner surface of the water jacket, the heat transfer coefficient is recovered, and heat is effectively removed from the inner surface of the water jacket to the cooling water.

  According to the present invention, it is possible to reduce the water flow resistance by the rod-like micelle as the whole cooling device, for example, it is possible to reduce the energy consumption in the water pump and to maintain the heat transfer from the water jacket inner surface to the cooling water well. In addition, it is possible to achieve both cooling performance and water resistance reduction at a high level.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an example of a basic configuration of a cooling device for an internal combustion engine to which the present invention is applied. Cooling water is introduced into the cylinder block 4 and the cylinder head 5 of the internal combustion engine E as is well known. A water jacket is formed for flow. In this embodiment, the cooling water flows in the water jacket along the cylinder row direction, and the cooling water taken out from the engine rear end of the cylinder head 5 is supplied to the radiator 1 including the fan 6. The cooling water guided and cooled to a low temperature by the radiator 1 is returned to the engine front end portion of the cylinder block 4 via the thermostat 2 and the water pump 3.

  Here, the cooling water is, for example, an aqueous solution of ethylene glycol, so-called antifreeze, and contains a relatively high concentration of a surfactant, whereby rod-like micelles in which spherical micelles are combined are formed. Such a rod-like micelle has a turbulent flow suppression effect and a tube frictional resistance reducing effect due to its elastic effect, and shows a turbulent flow characteristic when normal water exceeds the Reynolds number 2000 as a tube friction coefficient. On the other hand, in the cooling water containing rod-like micelles, the laminar frictional characteristics are maintained up to about Reynolds number 20000. When the Reynolds number exceeds, for example, 20000, the rod-like micelles are divided by the shearing force of the flow and become turbulent characteristics. Therefore, the Reynolds number in the water jacket is basically 20000 or less. As an example of the surfactant, cetyltrimethylammonium bromide is used at a concentration of about 60 to 70 ppm. However, the present invention is not limited to this, and an appropriate surfactant is so-called critical. It may be contained at a concentration higher than the concentration.

  FIG. 2 is an enlarged sectional view (a) of a water jacket 11 and a water jacket wall (cast as a part of the cylinder block 4 or the cylinder head 5) 12 constituting the water jacket 11 according to the present invention, and the water jacket. 11 shows a comparison with the ratio (b) of the rod-like micelles in the cooling water flowing in the water 11, and in the present invention, the water jacket wall 12 has a fine uneven surface structure that breaks the rod-like micelles. The uneven surface structure may be formed over the entire water jacket of the cylinder block 4 and the cylinder head 5, or may be partially only on a specific portion that requires improved heat transfer, for example, a portion with a high heat load. You may form in.

  The micelles contained in the cooling water flowing through the water jacket 11 are rod-like micelles at positions away from the wall surface (uneven surface structure) of the water jacket 11, and the flow maintains a laminar flow. On the other hand, at a position close to the concavo-convex surface structure, the flow is agitated to divide the rod-like micelles into spherical micelles, and the flow becomes turbulent. For this reason, heat transfer from the water jacket wall 12 to the cooling water is restored, and good cooling is performed.

  FIG. 3 is a diagram for explaining the mechanism of destruction and fragmentation of rod-like micelles. The uneven surface structure of the water jacket wall 12 firstly physically flows the cooling water that is about to flow along the wall surface. Stir and break the rod-like micelle 21 with the shearing force. Second, due to the surface irregularities, the dissolved air in the cooling water grows as air bubbles and becomes easy to leave. Similarly, the generation and separation of bubbles due to nucleate boiling (subcool boiling) is promoted, and the cooling water is stirred by these dissolved air and bubbles 23 due to subcool boiling. As a result, the rod-like micelles 21 are destroyed and turned into spherical micelles 22. Divided.

  In the present invention, the heat transfer rate is also improved by providing the water jacket wall 12 with an uneven surface structure to promote the generation and separation of bubbles. FIG. 4 shows the relationship between the cooling water temperature in the vicinity of the water jacket wall 12 and the heat flux. As shown in the figure, the characteristic that the heat flux rapidly increases at a specific temperature as a boundary is obtained. This is because the minute uneven surface increases the surface area surrounding the cooling water, so that the gas dissolved in the cooling water is likely to grow into bubbles, and further, the bubbles quickly leave before growing into the film. Because. That is, when the cooling water temperature near the surface exceeds a certain temperature, bubbles are generated and detached one after another, and the heat transfer rate is improved. The same phenomenon occurs even when the boiling water temperature near the surface locally exceeds the saturation temperature.

  FIG. 5 shows the relationship between the heat load generated by the internal combustion engine and the coolant temperature near the water jacket wall 12 for each engine speed (for example, 2000 rpm, 4000 rpm, 6000 rpm). The dotted line shows the saturation temperature of the cooling water at each engine speed, but the pressure in the water jacket 11 is determined by the engine speed, so the saturation temperature is constant for each engine speed. On the other hand, the cooling water temperature near the water jacket wall 12 rises with a heat load, but at a low speed (2000 rpm), the cooling water temperature near the water jacket wall 12 even when the internal combustion engine is fully loaded. Is below the saturation temperature and therefore no boiling occurs. On the other hand, at medium speed (4000 rpm) to high speed (6000 rpm), the cooling water temperature near the water jacket wall 12 becomes higher than the saturation temperature when the internal combustion engine is heavily loaded, and local boiling occurs. . As a result, effective cooling by latent heat is performed, and the destruction and division of the rod-like micelles as described above are promoted, and the heat transfer rate is improved.

  Accordingly, overcooling can be prevented on the low speed and low load side to improve fuel efficiency, and heat of the internal combustion engine can be reliably transferred to the outside on the high speed and high load side. Moreover, since the frequency that the cooling water reaches the local boiling is low in the practical area, the deterioration due to the boiling of the cooling water is small.

  The present invention is particularly advantageous in a configuration in which the main flow of cooling water flows along the cylinder row direction as shown in FIG. FIG. 6 shows changes in the cooling water temperature and the like at each part flowing in the cylinder row direction from the cooling water inlet to the cooling water outlet. The cooling water receives heat as it flows through the water jacket 11, and the temperature Since it rises, the cooling water temperature is higher in the downstream. Therefore, the heat transfer surface temperature difference ΔT between the water jacket wall 12 and the downstream is smaller. On the other hand, since the heat transfer coefficient α is constant as shown by the broken line in the conventional one, the heat flux indicated by the product (α × ΔT) of the both is conventionally smaller as shown in the broken line as it is shown downstream. As a result, the cooling performance deteriorates. That is, the cylinder at the rear end of the engine near the coolant outlet is thermally disadvantageous.

  On the other hand, in the present invention, the number (ratio) of rod-like micelles in the vicinity of the water jacket wall 12 decreases toward the downstream. In other words, the rod-like micelles are broken and divided on the downstream side of the flow with a time margin, so that the rod-like micelles are relatively advanced as compared with the upstream side. Along with this, the heat transfer coefficient α becomes higher toward the downstream as shown by the solid line. Accordingly, the heat flux is maintained high on the downstream side as indicated by the solid line, and the cylinder at the rear end of the engine close to the coolant outlet can be cooled in the same manner as the cylinder at the front end of the engine.

  As an example of the uneven surface structure in the water jacket wall 12, as shown in FIGS. 7A and 7B, an oxide film 31 having a large number of minute columnar recesses 32 is provided on the surface of the water jacket wall 12. ing. This is formed by anodic oxide film treatment of the base material itself of the cylinder block 4 or the cylinder head 5. As for the size of the columnar recess 32, the average diameter d is preferably in the range of 25 nm ≦ d ≦ 1 μm. If it is smaller than 25 nm, it is difficult for the cooling water to enter the recess 32 even when there is no bubble inside, and if it is larger than 1 μm, the effect as a heat bath for locally heating the cooling water is reduced. More specifically, the average diameter d is desirably in the range of 40 nm ≦ d ≦ 450 nm. If it is smaller than 40 nm, it is difficult for the cooling water to enter the recess 32 when there are bubbles inside. If it is larger than 450 nm, the effect as a heat bath is small even if bubbles are present inside.

  As a base material of the cylinder block 4 or the cylinder head 5 on which the oxide film 31 is formed, pure aluminum or an aluminum alloy is preferable because alumina can be easily formed by anodic oxidation as an oxide film. As an example of the process of forming the oxide film 31, it has a surface polishing process, an anodic oxidation process, and an etching process.

  In the polishing step, buffing and electrolytic polishing are performed on the surface of the water jacket wall 12 of the cylinder block 4 or the cylinder head 5 to adjust the surface shape. One of buffing and electropolishing can be omitted as appropriate.

  In the anodizing step, the inner wall surface whose surface shape is adjusted is immersed in the electrolytic solution, and a voltage is applied to form an anodized film. The electrolytic solution is, for example, an acid system. The applied voltage is, for example, 70 to 80V. The anodic oxide film is an oxide film made of alumina and has fine pores. This fine hole becomes the columnar recess 32 described above.

  In the etching step, the inner wall surface on which the oxide film is formed is immersed in an etching solution in order to expose the clean surface. The etchant is, for example, acid-based. The immersion time is, for example, 15 minutes.

  Thereby, as shown in FIGS. 7A and 7B, an oxide film 31 having a large number of fine columnar recesses 32 is obtained. Such anodization is preferable because the columnar recesses 32 can be easily and inexpensively formed over a wide range. In particular, it is effective in places where it is difficult to machine directly from the outside, such as the inner wall of the water jacket 11. In addition, the average diameter and average depth of the micropores used as the columnar recessed part 32 can be adjusted by controlling selection of the component composition of the aluminum base material, selection of the component composition of the electrolytic solution, anodizing conditions, and the like.

  Next, FIG. 8 shows an embodiment in which fine particles 41 having an average particle size (for example, about several tens of μm to several hundreds of μm) larger than the irregularities of the irregular surface structure are mixed in the cooling water in which the rod-like micelles 21 are formed. Show. As the fine particles 41, for example, a microcapsule containing a heat storage latent heat material is used, and due to its size, it flows in the water jacket 11 together with cooling water without entering the columnar recess 32 of the cylinder head wall 12. When the above-described stirring action on the surface of the cylinder head wall 12 is received, the destruction and division of the rod-like micelle 21 are further promoted by the fine particles 41. In addition, in the location where the cooling water flows as a laminar flow, the fine particles 41 also flow smoothly together with the rod-like micelles 21, so that the rod-like micelles 21 are not broken or divided. In addition, when the heat storage latent heat material is included in the microcapsule as the fine particles 41, the temperature increase of the cooling water mainstream can be suppressed by the heat capacity.

BRIEF DESCRIPTION OF THE DRAWINGS Basic structure explanatory drawing of the cooling device of the internal combustion engine to which this invention is applied. The figure which contrasted and showed the expanded sectional view (a) of a water jacket and a water jacket wall, and the ratio (b) of a rod-shaped micelle. Explanatory drawing explaining the mechanism of destruction and parting of a rod-like micelle. The characteristic view which showed the relationship between the cooling water temperature near a water jacket wall, and a heat flux. The characteristic view which showed the relationship between the thermal load which an internal combustion engine generate | occur | produces, and the cooling water temperature of the water jacket wall vicinity for every engine speed. The characteristic view which showed the change of the cooling water temperature etc. in each part which flows into a cylinder row direction from a cooling water inlet to a cooling water outlet. The top view (a) and sectional drawing (b) which the water jacket wall surface part expanded. Explanatory drawing similar to FIG. 3 which shows the Example which mixed the fine particle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Water jacket 12 ... Water jacket wall 21 ... Rod-like micelle 22 ... Spherical micelle 32 ... Columnar recessed part 41 ... Fine particle

Claims (7)

  The cooling water containing a surfactant having a concentration capable of forming rod-like micelles is used, and at least a part of the inner surface of the water jacket through which the cooling water circulates has an uneven surface structure that breaks the rod-like micelles. A cooling device for an internal combustion engine characterized by the above.   2. The cooling apparatus for an internal combustion engine according to claim 1, wherein the inner surface has a number of fine columnar recesses as the uneven surface structure.   3. The cooling apparatus for an internal combustion engine according to claim 2, wherein an average diameter d of the columnar recesses is in a range of 25 nm ≦ d ≦ 1 μm.   The cooling apparatus for an internal combustion engine according to claim 2, wherein an average diameter d of the columnar recesses is in a range of 40 nm ≤ d ≤ 450 nm.   The cooling apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the uneven surface structure is made of an anodized film having fine holes.   The cooling apparatus for an internal combustion engine according to any one of claims 1 to 5, wherein fine particles having an average particle size larger than the unevenness of the uneven surface structure are mixed in the cooling water.   The cooling apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein a main flow of the cooling water flowing in the water jacket flows in a cylinder row direction.

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