JP2013002340A - Cylinder block - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylinder block capable of imparting an optimal lubricating characteristic, without causing overs and shorts in both a piston ring sliding contact surface different in bearing pressure applied to a sliding surface and a piston skirt sliding contact surface.SOLUTION: In this cylinder block, a cylinder bore slidingly contacted with a piston is formed of an aluminum alloy, and the ratio of Rk+Rvk of both sliding surfaces is set in the same ratio as the ratio of the bearing pressure applied to both sliding surfaces by making a plasma irradiating condition of plasma melting treatment different between a piston ring sliding surface and a piston skirt sliding surface.

Description

  The present invention relates to a cylinder block in which a cylinder bore slidably contacted with a piston is formed of an aluminum alloy.

  In recent years, replacement of cast block material with cast aluminum has been promoted for the purpose of reducing engine weight. In general, such a cylinder block made of an aluminum alloy is formed by integrating a cast iron cylinder liner into a block base made of aluminum alloy by casting or press-fitting. In such cylinder blocks, cast iron cylinder liners ensure the necessary wear resistance, scuff resistance, sliding characteristics, etc., on the cylinder bore surface.

  On the other hand, linerless aluminum cylinder blocks have been developed in which cast iron cylinder liners have been abolished in order to further reduce the weight and reduce manufacturing costs of such aluminum alloy cylinder blocks. These linerless aluminum cylinder blocks generally use an aluminum alloy with a high silicon content (high silincon aluminum) to ensure wear resistance, scuff resistance, sliding characteristics, etc. on the cylinder bore surface. It has become.

  Conventionally, in Patent Document 1, a piston ring sliding surface of a cylinder bore of an aluminum alloy cylinder block is irradiated with laser, and an oil sump provided in a scattered manner with a hard surface portion composed of a surface portion of a rapidly solidified structure. Forming a concave portion for use.

JP 2007-278090 A JP 2010-031840 A

  According to such a conventional cylinder block, it is possible to give good lubrication characteristics and improve the wear resistance of the sliding surface of the piston ring. However, because the piston ring sliding surface of the cylinder bore is also in sliding contact with the piston skirt, the sliding characteristics of the piston skirt sliding surface have the lubricating properties necessary to ensure wear resistance. Need to give. Therefore, if the piston skirt sliding surface is subjected to the same surface treatment as the piston ring sliding contact surface, sufficient lubrication characteristics can be imparted to the piston skirt sliding contact surface. However, if the piston skirt sliding contact surface has the same surface properties as the piston ring sliding contact surface, the surface pressure applied to the sliding surface during engine operation is smaller than the piston ring sliding contact surface. Will give excessive lubrication characteristics beyond what is needed. As a result, the opponent's aggressiveness against the piston skirt becomes too high due to the roughness of the surface, and the wear loss of the piston skirt increases.

  On the other hand, Patent Document 2 describes an aluminum alloy cylinder block in which the surface roughness of the upper 1/4 portion of the piston sliding surface is larger than the surface roughness of the lower 1/4 portion. ing. If it does in this way, while providing required abrasion resistance to a piston ring sliding contact surface and a piston skirt sliding contact surface, respectively, it becomes possible to suppress the other party aggression property with respect to a piston skirt. However, it is difficult to say that the lubrication characteristics of the piston ring sliding surface and the piston skirt sliding surface are optimized. May be more aggressive.

  The present invention has been made in view of such a situation, and the problem to be solved is excessive or insufficient in both the piston ring sliding contact surface and the piston skirt sliding contact surface having different surface pressures applied to the sliding surface. It is an object of the present invention to provide a cylinder block that can provide optimum lubrication characteristics without any problems.

  In order to solve the above-mentioned problem, the invention according to claim 1 as a cylinder block in which a cylinder bore slidably contacted with a piston is formed of an aluminum alloy has a difference in level of the core portion as Rk and a protruding valley portion depth as Rvk. When the ratio of Rk + Rvk of the piston ring sliding surface to Rk + Rvk of the piston skirt sliding surface is equal to the surface pressure applied to the piston ring sliding surface during use of the engine having the cylinder block, the piston skirt sliding The ratio is the same as the ratio to the surface pressure applied to the moving surface.

  If the surface pressure applied to the sliding surface decreases, the amount of oil retained on the sliding surface also decreases proportionally. The Rk + Rvk of the sliding surface necessary for forming an oil film having an appropriate thickness also decreases in proportion to the surface pressure applied to the sliding surface. In that respect, in the above configuration, the ratio of the piston ring sliding surface Rk + Rvk to the piston skirt sliding surface Rk + Rvk is the ratio of the surface pressure applied to the piston ring sliding surface to the surface pressure applied to the piston skirt sliding surface. The ratio is the same. Therefore, an oil film having an appropriate thickness is formed on both the piston ring sliding contact surface and the piston skirt sliding contact surface, and the lubricity of both sliding surfaces is suitably ensured regardless of the difference in surface pressure. be able to. Therefore, according to the above configuration, it is possible to give an optimum lubrication characteristic without excess or deficiency to any of the piston ring sliding contact surface and the piston skirt sliding contact surface having different surface pressures applied to the sliding surface. .

  The ratio of the surface roughness (Rk + Rvk) of the piston ring sliding surface and the piston skirt sliding surface can be set by adjusting the processing energy per unit area during plasma irradiation, as in claim 2. it can. In such a case, the required surface roughness can be given to each sliding surface only by adjusting the plasma irradiation energy, so that it is possible to easily change the surface roughness between both sliding surfaces. It is possible to suppress an increase in manufacturing time and manufacturing cost of the cylinder block by changing the surface properties every time.

  On the other hand, there is a generally direct relationship between the processing energy per unit area in plasma irradiation and the surface roughness formed by the irradiation. Therefore, as defined in claim 3, the ratio of the processing energy per unit area in the plasma irradiation of the piston ring sliding surface to the processing energy per unit area in the plasma irradiation of the piston skirt sliding surface is added to them. If the ratio is the same as the pressure ratio, the ratio of the surface roughness of both sliding surfaces can be the same as the ratio of the surface pressure applied to them.

  Further, according to claim 4, when the height of the protruding peak is Rpk, the ratio of the piston ring sliding surface Rk + Rpk to the piston skirt sliding surface Rk + Rpk is the same ratio as the ratio of the surface pressure applied to them. If so, the friction of both sliding surfaces can be made substantially equal regardless of the difference in surface pressure applied to the sliding surfaces.

  Further, according to claim 5, if the ratio of Rk of the piston ring sliding surface and Rk of the piston skirt sliding surface is the same as the ratio of the surface pressure applied thereto, the surface pressure applied to the sliding surface. Regardless of the difference, both sliding surfaces can be given almost the same scuff resistance.

Sectional drawing which shows the side part cross-sectional shape of the cylinder block which concerns on one embodiment of this invention. The figure which shows a special roughness curve and a load curve. The graph which shows the relationship between the oil retention amount of a piston ring sliding surface, and Rk + Rvk. The graph which shows the relationship between the oil retention amount of a piston skirt sliding surface, and Rk + Rvk. The graph which shows the relationship between the friction coefficient of a piston ring sliding surface, and Rk + Rpk. The graph which shows the relationship between the friction coefficient of a piston skirt sliding surface, and Rk + Rpk. The graph which shows the relationship between the scuff time of a piston ring sliding surface, and Rk. The graph which shows the relationship between the scuff time of a piston skirt sliding surface, and Rk. The graph which shows the relationship between the processing energy per unit area, and surface roughness.

Hereinafter, an embodiment of a cylinder block according to the present invention will be described in detail with reference to FIGS.
The cylinder block of the present embodiment uses an aluminum die-cast material (ADC12) for the cylinder bore portion. The cylinder block is manufactured by subjecting the surface of the cylinder bore to a plasma melting process for roughening and hardening, followed by a honing process.

  As shown in FIG. 1, in the present embodiment, the cylinder bore 1 of the cylinder block is slid only in two regions, that is, the piston ring sliding surface that is in sliding contact with the piston ring 3 of the piston 2 and the piston skirt 4 of the piston 2. The piston skirt sliding surface is in contact. In the figure, the position of the piston 2 at the top dead center is indicated by a solid line, and the position of the piston 2 at the bottom dead center is indicated by a one-dot chain line.

In the cylinder block of the present embodiment, the surface roughness parameters of the two sliding surfaces measured by the contact-type roughness measuring machine are set so as to satisfy the following conditions, respectively. The difference in the surface roughness parameter between the two sliding surfaces is set by changing the plasma irradiation conditions in the plasma melting process.
・ Piston ring sliding surface:
Rk> 0.65
Rk + Rpk <1.0
Rk + Rvk <2.0
・ Piston skirt sliding surface:
Rk> 0.30
Rk + Rpk <0.50
Rk + Rvk <1.0
The surface roughness parameters Rk, Rpk and Rvk are obtained as follows. The curve shown on the left side of FIG. 2 is obtained by filtering the surface roughness curve in a manner defined by ISO13565 and DIN4776 and removing the waviness. In addition, the load curve shown on the right side of FIG. 2 is obtained by using a special roughness curve as an extraction curve, and by using the evaluation length method and the μm method, and corresponds to the cumulative probability density function referred to in statistics. ing.

  Further, the line segment AB shown in the figure has a width of 40% in the direction of the load length ratio (tp value) in the load curve, and when a position where the difference in height between the both ends is minimized is searched for. A straight line (minimum inclination straight line) passing through the two points is shown. Note that point A in the figure is the intersection of this minimum inclination straight line and the limit line of tp = 0%, and point C is the intersection of the horizontal line from this point A and the load curve. Point B is the intersection of the minimum inclination straight line and the limit line of tp = 100%, and point D is the intersection of the horizontal line from this point B and the load curve.

  In these figures, the protruding peak height (initial wear height) Rpk is equal to the area of the portion surrounded by the 0% limit line, the side AC, and the load curve, and is a tp that forms a right triangle with the side AC as one side. = 0% above the limit line. Further, the protruding valley depth (oil sump depth) Rvk is equal to the area surrounded by the 100% limit line, the side BD, and the load curve, and has a 100% limit that forms a right triangle with the side BD as one side. It is the height above the line. The level difference (effective load roughness) Rk of the core portion is the difference in height between the points C and D.

  Next, the reason why the conditions of the surface roughness parameter as described above are set on both sliding surfaces will be described. Here, the above conditions are set from the three viewpoints of oil consumption, friction, and scuff resistance.

(Limit due to oil consumption)
The inventors have manufactured a plurality of test pieces with various surface properties changed by changing the conditions of plasma irradiation and honing processing, and conducting an evaluation test of their oil retention amounts. The oil retention amount of the test piece is calculated by leaving the test piece coated with oil standing for 4 hours and measuring the mass difference between the test piece before and after the test piece. Here, the value is used as an index value of oil consumption in an actual engine. According to the result, it has been confirmed that the oil retention amount has a strong correlation with Rk + Rvk, which is an index value for the surface-shaped concave portion.

  FIG. 3 shows the relationship between the oil retention amount obtained by the test and Rk + Rvk. As shown in the figure, in order to make the oil retention amount of the piston ring sliding surface equal to or less than the oil retention amount of the cast iron cylinder liner (1.0 milligram / square centimeter), the Rk + RvK is set to 2.0 micrometers. Must be less than

  On the other hand, the piston skirt sliding surface is not related to oil consumption, but it is necessary to secure an oil retention amount so as to satisfy the required lubrication characteristics. In the cylinder block of the present embodiment, the surface pressure applied to the oil film on the sliding surface of the piston skirt during actual use is about half that of the sliding surface of the piston ring, and the oil film forming ability is high. Necessary lubrication characteristics can be satisfied by securing an oil holding amount (0.50 milligram / square centimeter) that is approximately half of the sliding surface. As shown in FIG. 4, Rk + Rvk that can secure such an oil retention amount is less than 1.0 micrometer.

  In addition, although the test result when the surface pressure applied to the piston skirt sliding surface is ½ of the ring sliding region has been described here, Rk + Rvk that can satisfy the necessary lubrication characteristics is the sliding surface. It has been confirmed that it is almost proportional to the surface pressure applied to the surface. Therefore, if the ratio of the piston ring sliding surface Rk + Rvk to the piston skirt sliding surface Rk + Rvk is the same as the ratio of the surface pressure applied to each, sufficient lubrication characteristics can be provided to both sliding surfaces. Can be given.

(Limited by friction)
The inventors have evaluated the friction of the plurality of test pieces described above. Friction is evaluated by measuring the coefficient of friction of each test piece using a reciprocating sliding tester. According to the result, it has been confirmed that the friction has a strong correlation with Rk + Rpk which is an index value for the surface-shaped convex portion.

  FIG. 5 shows the relationship between the average friction coefficient obtained by the test and Rk + Rpk. As shown in the figure, in order to make the friction coefficient of the sliding surface of the piston ring equal to or less than the friction coefficient (0.03) of the cast iron cylinder liner, Rk + Rpk needs to be less than 1.0 micrometer. .

  On the other hand, the piston skirt sliding surface has a surface pressure applied to the oil film of about 1/2 that of the piston ring sliding surface, and has a high oil film forming force. Therefore, on the piston skirt sliding surface, as shown in FIG. 6, the friction coefficient can be made equal to or less than that of the cast iron cylinder liner by Rk + Rpk (= 0.50 micrometers) which is about half of the piston ring sliding surface. .

  In addition, although the test result when the surface pressure applied to the piston skirt sliding surface is ½ of the ring sliding region has been described here, Rk + Rpk that can make the friction coefficient below a certain value is sliding It has been confirmed that it is almost proportional to the surface pressure applied to the surface. Therefore, if the ratio of Rk + Rpk of the piston ring sliding surface and Rk + Rpk of the piston skirt sliding surface is the same as the ratio of the surface pressure applied to each, sufficient friction characteristics are provided to both sliding surfaces. Can be given.

(Restricted by scuff resistance)
The inventors have conducted an evaluation test on the scuff resistance of the plurality of test pieces described above. The scuff resistance of each test piece is evaluated by using a reciprocating sliding tester and measuring the time (scuff time) until the friction during sliding rises rapidly by scuffing. According to the result, it has been confirmed that the scuff resistance has a strong correlation with Rk.

  FIG. 7 shows the relationship between the scuff obtained by the test and Rk. As shown in the figure, in order to make the scuffing time of the piston ring sliding surface equal to or more than the scuffing time (5 minutes) of the cast iron cylinder liner, it is necessary to set Rk to 0.65 micrometers or more. .

  On the other hand, the piston skirt sliding surface has a surface pressure applied to the oil film of about 1/2 that of the piston ring sliding surface, and has a high oil film forming force. Therefore, on the sliding surface of the piston skirt, as shown in FIG. 8, the scuff time can be made equal to or less than that of the cast iron cylinder liner with Rk (= 0.3 micrometers) which is almost half of the sliding surface of the piston ring. .

  In addition, although the test result in the case where the surface pressure applied to the piston skirt sliding surface is ½ of the ring sliding region has been described here, Rk that can make the scuff time equal to or greater than a certain value is the sliding It has been confirmed that it is almost proportional to the surface pressure applied to the surface. Therefore, if the ratio of the Rk of the piston ring sliding surface and the Rk of the piston skirt sliding surface is the same as the ratio of the surface pressure applied to each, sufficient scuff resistance is provided to both sliding surfaces. Can be given.

  As described above, the difference in the surface roughness parameters of both sliding surfaces can be set by changing the plasma irradiation conditions in the plasma melting treatment. FIG. 9 shows the relationship between the surface roughness of the modified layer formed by the plasma melting process and the processing energy per unit area in the plasma melting process. As shown in the figure, there is a proportional relationship between the surface roughness and the processing energy per unit area. On the other hand, as described above, in order to satisfy the requirements of oil consumption, friction, and scuff resistance, the ratio of the surface roughness parameter of the piston ring sliding surface to the surface roughness parameter of the piston skirt sliding surface is set respectively. The ratio of the surface pressure applied to the sliding surface must be the same. Therefore, the ratio between the processing energy per unit area in plasma irradiation of the piston ring sliding surface and the processing energy per unit area in plasma irradiation of the piston skirt sliding surface is the ratio of the surface pressure applied to both sliding surfaces. The plasma melting process may be performed so that the ratio is the same.

According to the cylinder block of the present embodiment described above, the following effects can be achieved.
(1) In the present embodiment, the ratio of Rk + Rvk of the piston ring sliding surface and Rk + Rvk of the piston skirt sliding surface is the same as the ratio of the surface pressure applied to these sliding surfaces. Therefore, an oil film having an appropriate thickness is formed on both the piston ring sliding contact surface and the piston skirt sliding contact surface, and the lubricity of both sliding surfaces is suitably ensured regardless of the difference in surface pressure. be able to. Therefore, according to the above configuration, it is possible to give an optimum lubrication characteristic without excess or deficiency to any of the piston ring sliding contact surface and the piston skirt sliding contact surface having different surface pressures applied to the sliding surface. .

  (2) In the present embodiment, the ratio of Rk + Rpk of the piston ring sliding surface and Rk + Rpk of the piston skirt sliding surface is the same as the ratio of the surface pressure applied to them. Therefore, the friction of both sliding surfaces can be made substantially equal regardless of the difference in surface pressure applied to the sliding surfaces.

  (3) In the present embodiment, the ratio between the Rk of the piston ring sliding surface and the Rk of the piston skirt sliding surface is the same as the ratio of the surface pressure applied to them. Therefore, regardless of the difference in surface pressure applied to the sliding surfaces, both sliding surfaces can be given substantially the same scuff resistance.

  (4) In this embodiment, the ratio of the surface roughness parameters of the piston ring sliding surface and the piston skirt sliding surface is set by adjusting the processing energy per unit area during plasma irradiation. In such a case, the required surface roughness can be given to each sliding surface only by adjusting the plasma irradiation energy, so that it is possible to easily change the surface roughness between both sliding surfaces. It is possible to suppress an increase in manufacturing time and manufacturing cost of the cylinder block by changing the surface properties every time.

  (5) In the present embodiment, the ratio of the processing energy per unit area in plasma irradiation of the piston ring sliding surface and the processing energy per unit area in plasma irradiation of the piston skirt sliding surface is added to the surface The ratio is the same as the pressure ratio. Therefore, it is possible to easily and appropriately set the surface properties of both sliding surfaces so as to satisfy the requirements of oil consumption, friction, and scuff resistance.

In addition, the said embodiment can also be changed and implemented as follows.
In the above embodiment, the surface roughness of the piston ring sliding surface and the piston skirt sliding surface is made different by changing the processing energy per unit area of plasma irradiation in the plasma melting processing. However, if the surface roughness parameters of both sliding surfaces can be set similarly, the surface roughness of both sliding surfaces may be made different by a method other than changing the processing energy per unit area. .

  In the above embodiment, the ratio between the Rk of the piston ring sliding surface and the Rk of the piston skirt sliding surface is the same as the ratio of the surface pressure applied to these sliding surfaces. When it is not necessary to make the resistance equal, the ratio of Rk of both sliding surfaces may not be equal to the ratio of the above-mentioned surface pressure. Even in that case, if the ratio of Rk + Rvk of both sliding surfaces is equal to the ratio of the surface pressure applied to those sliding surfaces, both sliding contact surfaces having different surface pressures applied to the sliding surfaces can be used. Optimal lubrication characteristics without excess or deficiency can be provided.

  In the above embodiment, the ratio of Rk + Rpk of the piston ring sliding surface and the piston skirt sliding surface is the same as the ratio of the surface pressure applied to these sliding surfaces, but the friction characteristics of both sliding surfaces are the same. If it is not necessary, the ratio of Rk + Rpk of both sliding surfaces may not be equal to the ratio of the surface pressure. Even in that case, if the ratio of Rk + Rvk of both sliding surfaces is equal to the ratio of the surface pressure applied to those sliding surfaces, both sliding contact surfaces having different surface pressures applied to the sliding surfaces can be used. Optimal lubrication characteristics without excess or deficiency can be provided.

  DESCRIPTION OF SYMBOLS 1 ... Cylinder bore, 2 ... Piston, 3 ... Piston ring, 4 ... Piston skirt, Rk ... Level difference of core part (effective load roughness), Rpk ... Projection peak height (initial wear height), Rvk ... Projection Valley depth (oil sump depth).

Claims (5)

In the cylinder block in which the cylinder bore slidably contacted with the piston is made of aluminum alloy,
When the level difference of the core part is Rk and the depth of the protruding valley part is Rvk, the ratio of Rk + Rvk of the piston ring sliding surface to Rk + Rvk of the piston skirt sliding surface is the same as that described above during use of the engine equipped with the cylinder block. A cylinder block characterized by having a ratio equal to a ratio of a surface pressure applied to a piston ring sliding surface and a surface pressure applied to the piston skirt sliding surface. The piston ring sliding surface and the piston skirt sliding surface are subjected to plasma melting treatment, and the ratio of Rk + Rvk is set through adjustment of processing energy per unit area during plasma irradiation. The cylinder block according to claim 1. The ratio of the processing energy per unit area in the plasma irradiation of the piston ring sliding surface to the processing energy per unit area in the plasma irradiation of the piston skirt sliding surface is the same ratio as the ratio of the surface pressure. The cylinder block according to claim 2, wherein The ratio of Rk + Rpk of the piston ring sliding surface and Rk + Rpk of the piston skirt sliding surface is the same as the surface pressure ratio, where the height of the protruding peak is Rpk. The cylinder block according to any one of claims 1 to 3. The ratio between the Rk of the piston ring sliding surface and the Rk of the piston skirt sliding surface is the same as the ratio of the surface pressure. Cylinder block as described.

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