JP4631854B2 - engine - Google Patents

Description

  The present invention relates to a technique for improving the roundness of a cylinder bore formed in a cylinder block during actual operation of the engine when the cylinder head of the engine is fixed to the cylinder block.

In recent years, automobile engines that require environmental performance have been required to improve fuel consumption and combustion efficiency. If fuel consumption is improved and combustion efficiency is improved, it is possible to reduce the amount of gas that is relatively discharged by enabling the automobile to travel a longer distance with less fuel. Moreover, the improvement of combustion efficiency can aim at the purification of exhaust gas by incomplete combustion by raising efficiency when burning fuel.
Various methods have been proposed as a method for improving the fuel consumption of the engine and improving the combustion efficiency. One of the methods is to increase the roundness of the cylinder bore of the engine. There is.

First, the structure of the engine will be briefly described.
In the most popular reciprocating engine, a cylinder block having a cylinder bore in which a piston moves up and down, a cylinder head in which a combustion chamber is formed and having a valve, a head cover, parts such as an oil pan, a camshaft and a crank Consists of shafts and other auxiliary equipment.
During actual operation of the reciprocating engine, fuel is combusted in the combustion chamber, the piston slides in the cylinder bore formed in the cylinder block, and power is generated by transmitting the energy as rotation to the crankshaft.

A piston ring is provided between the cylinder bore and the piston, and this piston ring slides directly with the cylinder bore. The piston ring is provided in a state of stretching inside the cylinder bore. And it plays the role which scrapes off so that the minimum required oil film may be ensured, maintaining the airtightness of the combustion chamber side and ensuring the splash of engine oil from the crankshaft side.
In order to ensure proper oil film thickness and confidentiality, the roundness of the cylinder bore must be maintained high, and when the roundness is low, proper oil film thickness and air tightness are ensured. Therefore, it is necessary to increase the force that pushes the cylinder bore, that is, the tension inside the bore.

However, when the tension of the piston ring is increased, the sliding resistance between the cylinder bore and the piston increases, resulting in a deterioration in fuel consumption.
It is said that the mechanical loss of each rotating part and sliding part causes the engine efficiency to drop during actual operation of the engine.
One third of the mechanical loss is said to be due to sliding resistance around the piston. Specifically, in addition to the sliding of the piston and cylinder bore, the resistance during rotation of the camshaft and crankshaft affects the engine efficiency as a mechanical loss, so improving these results in a reduction in fuel consumption. It can be expected to lead to improvement and improvement of combustion efficiency.
Therefore, securing the roundness of the cylinder bore is a very important issue in designing and manufacturing the engine.

There are roughly two types of techniques for ensuring the roundness of the cylinder bore of the cylinder block. One is to secure the roundness of a static cylinder bore, and the other is to secure the roundness of a dynamic cylinder bore.
Many methods have been proposed for securing the roundness of a static cylinder bore, such as a method of increasing the roundness at the time of engine production, and a method using a dummy head.
On the other hand, in order to secure the roundness of the dynamic cylinder bore, there has been a difficulty that it is necessary to predict a change in the shape of the cylinder bore during actual operation of the engine.

Examples of the technology related to distortion generated in a dynamic engine include those disclosed in Patent Documents 1 to 3.
Patent Document 1 discloses a technique relating to a deformation preventing means during actual operation of the cylinder head.
When a cylinder head made of aluminum alloy and a cylinder block made of cast iron are fastened with head bolts and operated as an engine, the metal expands due to the heat generated, but the aluminum alloy has a higher linear expansion coefficient than cast iron, so the cylinder The amount of expansion due to the influence of heat differs between the head and the cylinder block. As a result, the cylinder head made of aluminum alloy tends to expand more, but because it is constrained by the head bolt, the expanded portion loses the escape area, and as a result, deforms into a convex shape, and the journal of the camshaft There is a risk of local contact between the bearing and the bearing.
In order to improve such an influence on the bearing portion, in Patent Document 1, a reinforcing member having a thermal expansion coefficient smaller than that of the aluminum alloy is buried along the longitudinal direction of the cylinder head. As a result, when the reinforcing member having a smaller thermal expansion coefficient is affected by heat, the deformation of the cylinder head is suppressed, so that it is possible to reduce the local contact that occurs in the journal and the bearing portion of the camshaft.

Patent Document 2 discloses a cylinder head fixing structure for an internal combustion engine.
During actual operation of the engine, the generated temperature differs between the intake port and the exhaust port provided in the cylinder head. Accordingly, among the head bolts for fixing the cylinder head to the cylinder block, the intake side head bolt provided on the intake side is about 100 ° C., whereas the exhaust side head bolt provided on the exhaust side is about 200 ° C. , Each expansion amount is different.
Therefore, a gasket is sandwiched between the cylinder head and the cylinder block to prevent gas leakage and cooling water leakage. However, the difference in expansion between the intake side head bolt and the exhaust side head bolt causes a difference in the cylinder head and cylinder block. The surface pressure between them becomes uneven, causing gas leakage and cooling water leakage.
In order to improve such non-uniform surface pressure, Patent Document 2 changes the material of the intake side head bolt and the exhaust side head bolt and changes the linear expansion coefficient, thereby causing a temperature difference during engine operation. However, the cylinder head and the cylinder block are fixed with a constant force so as not to cause uneven surface pressure.

Patent Document 3 discloses a metal member coupling structure.
During engine operation, the cylinder head made of the first metal member, the cylinder block made of the second metal member, and the head bolt made of the third metal member have different linear expansion rates, so that heat is applied during engine operation. The head bolt is loosened by being repeatedly cooled at the time of stopping. In anticipation of this, if the tightening force of the head bolt is increased, there is a problem that the cylinder bore is deformed.
In order to control the tightening force of the head bolt, in Patent Document 3, the linear expansion coefficient A of the cylinder head, the linear expansion coefficient B of the cylinder block, the linear expansion coefficient C of the head bolt, and the cylinder head By satisfying (AC) X = (CB) Y, the relationship between the thickness X of the fastening portion and the distance Y from the female thread portion formed on the cylinder block to the contact surface with the cylinder head, The fastening state by the head bolt can be stably held corresponding to the change due to the temperature.
Japanese Utility Model Publication No. 3-43401 Japanese Utility Model Publication No. 3-127061 JP 2004-225872 A

However, it is considered that there are the following problems in applying the conventional techniques disclosed in Patent Documents 1 to 3 to securing the roundness of a dynamic cylinder bore.
(1) Deformation of Cylinder Head As a result of investigation by the applicant, it has been found that angle deformation occurs in the cylinder head and the cylinder block during actual operation of the engine. Unlike the convex deformation of Patent Document 1, this chevron deformation occurs even if both the cylinder block and the cylinder head are made of an aluminum alloy.
The cylinder block and the cylinder head have different temperatures set during actual operation, and the cylinder head expands more than the cylinder block. Since the cylinder block and the cylinder head are firmly fixed by the head bolt, when the amount of expansion on the cylinder head side increases, the expanded portion loses the escape place and is eventually deformed into a mountain shape.
With this mechanism, it was found that the cylinder head deformed in an angle when the engine was in operation, and when the cylinder head deformed in an angle, the cylinder block fixed by the head bolt was also pulled and deformed, and the roundness of the cylinder bore was increased. It turned out to be a factor to reduce.

(2) Application of Patent Document 1 to Patent Document 3 The method of Patent Document 1 is a technique for suppressing the convex deformation of the cylinder head by embedding a reinforcing member in the cylinder head, and basically the cylinder block and the cylinder head. Is assumed to be formed of a different material, but it is also possible to cope with the chevron deformation confirmed by the applicant.
In other words, by embedding a reinforcing member having a small linear expansion coefficient in the cylinder head, it is possible to suppress the mountain-shaped deformation of the cylinder head, and as a result, it is possible to suppress the deformation of the cylinder block and the decrease in the roundness of the cylinder bore. There is sex.
However, embedding a reinforcing member having a size capable of suppressing deformation of the cylinder head in the cylinder head may obstruct the flow path of the water jacket formed in the cylinder head. Moreover, it is not desirable to reduce the cooling efficiency for an engine that is becoming smaller and having higher output.
In addition, the work of casting the reinforcing member into the cylinder head is required, and there is a problem that a new process is required and the cost is increased.

The method of Patent Document 2 is a method in which the linear expansion coefficient of the intake head bolt on the intake port side and the exhaust head bolt on the exhaust port side is changed in accordance with the temperature difference between the intake port side and the exhaust port side. It is thought that it is impossible to suppress the Yamagata deformation.
The method of Patent Document 3 is a method for defining the relationship between the material of the head bolt, the thickness of the fastening portion of the cylinder head, the depth of the internal thread portion of the cylinder block, and the material of the cylinder head and the cylinder block. Therefore, it is considered that the mountain-shaped deformation of the cylinder head cannot be suppressed.

  As described above, the conventional techniques disclosed in Patent Documents 1 to 3 do not have the idea that a mountain-shaped deformation occurs due to a temperature difference between the cylinder head and the cylinder block. The technique for embedding the reinforcing member may affect the cooling efficiency of the engine and is expensive. Therefore, even if Patent Documents 1 to 3 are combined, it is difficult to suppress the chevron deformation of the cylinder head at low cost and to ensure the dynamic roundness of the cylinder bore.

  Therefore, in order to solve such problems, the present invention provides an engine capable of suppressing the mountain-shaped deformation of the cylinder head at low cost and ensuring the roundness of the dynamic cylinder bore formed in the cylinder block. With the goal.

In order to achieve the above object, an engine according to the present invention has the following characteristics.
(1) In an engine including a cylinder head in which a combustion chamber is formed, a cylinder block in which a cylinder is formed in series, and a head bolt that fixes the cylinder head to the cylinder block,
Among the head bolts, front and rear end head bolts fastened to both ends of the cylinder block are made of a material having a larger linear expansion coefficient than other head bolts fastened to other positions.

(2) In the engine according to (1), the temperature of the production time of the previous SL cylinder head and the cylinder block are different, expansion of the cylinder head becomes larger than the amount of expansion of the cylinder block, the When the cylinder head causes a chevron-shaped deformation due to the action of the cylinder head extending in the longitudinal direction, the front and rear end head bolts are made of a material having a larger linear expansion coefficient than the other head bolts. Due to the heat generated during actual operation, an axial force difference is generated between the front and rear end head bolts and the other head bolts, and due to the axial force difference, a force in the direction opposite to the angle deformation is generated in the cylinder head. Therefore, the chevron deformation of the cylinder head is suppressed.

  Here, the axial force refers to the force with which the cylinder head is pressed against the cylinder block by the head bolt. A head bolt made of a material having a linear expansion coefficient different from that of the cylinder head and the cylinder block has a smaller expansion coefficient than the cylinder head and the cylinder block when the head bolt expands due to heat generated during actual operation. As a result, the axial force generated against the cylinder head increases.

(3) In the engine according to (1) or (2),
When the cylinder head and the cylinder block are made of an aluminum alloy, the front and rear end head bolts are made of stainless steel, and the other head bolts are made of steel.

(4) In the engine according to (1),
The head bolt is made of a material having a higher linear expansion coefficient as it is provided at the end portion than the center portion in the longitudinal direction of the cylinder block.

With the engine according to the present invention having such characteristics, the following operations and effects can be obtained.
First, the invention described in (1) is a material in which, among the head bolts, the front and rear end head bolts fastened to both ends of the cylinder block have a larger linear expansion coefficient than other head bolts fastened to other positions. Therefore, an axial force difference is generated between the axial force of the front and rear end head bolts generated by the heat generated during engine operation and the axial force of other head bolts.
For example, as described in (3), the front and rear end head bolts are made of stainless steel, and the other head bolts are made of steel. A little axial force difference occurs. Due to this axial force difference, the front and rear ends of the cylinder head are likely to expand, and as a result, a deformation that tends to warp contrary to the chevron deformation as described in the problem occurs.
The reverse warp deformation generated in the cylinder head generates a force in the opposite direction to the chevron deformation, thereby suppressing the chevron deformation. As a result, the amount of angle deformation of the cylinder head is reduced and the influence on the cylinder block is reduced.

By reducing the influence of the chevron deformation applied to the cylinder block, it is possible to contribute to ensuring the roundness of the dynamic cylinder bore during engine operation.
Further, since the front and rear end head bolts are only made of a material having a high linear expansion coefficient, it is possible to contribute to securing the roundness of the cylinder bore at a low cost.
By improving the roundness of the cylinder bore of the engine during actual operation, the circularity of the cylinder bore can be maintained even during actual operation of the engine, and the tension of the piston ring included in the piston sliding on the cylinder bore can be set low. Contributes to reduction of friction loss and contributes to improvement of engine fuel efficiency.

Further, the present invention is included in this (2), in the engine according to (1), the temperature of the production time of the sheet cylinder head and the cylinder block are different, expansion of the cylinder head, from the amount of expansion of the cylinder block When the cylinder head is deformed in a chevron shape, the front and rear end head bolts are made of a material having a higher linear expansion coefficient than other head bolts. The axial force difference between the front and rear end head bolts and the other head bolts is generated by the heat generated during actual operation, and the cylinder head generates a force in the opposite direction to the angle deformation due to the axial force difference. Suppresses the mountain-shaped deformation.
In this way, the material of the front and rear end head bolts and other head bolts is used to increase the linear expansion coefficient of the front and rear end head bolts, thereby contributing to ensuring the roundness of the dynamic cylinder bore at low cost. can do.
And by improving the roundness of the cylinder bore of the engine during actual operation, the roundness of the cylinder bore can be maintained even during the actual operation of the engine, and the tension of the piston ring included in the piston sliding on the cylinder bore can be set low. Therefore, it contributes to the reduction of friction loss, which can contribute to improvement of engine fuel efficiency.

Further, in the invention described in (3), in the engine described in (1) or (2), when the material of the cylinder head and the cylinder block is an aluminum alloy, the material of the front and rear end head bolts is stainless steel. Since other head bolts are made of steel, stainless steel, which has a higher linear expansion coefficient than steel, can generate an axial force difference depending on the temperature generated during engine operation. As a result, the cylinder head and cylinder block Can be suppressed.
The front and rear end head bolts may be of the same size as the other head bolts, but the same tightening torque can be managed. Therefore, it is possible to suppress the chevron deformation by a simple method, and it does not cost much.
That is, the roundness of the dynamic cylinder bore can be improved at low cost.

  In the engine described in (4), in the engine described in (1), the head bolt is made of a material having a higher linear expansion coefficient as it is provided at the end than the center in the longitudinal direction of the cylinder block. Therefore, the axial force difference of the head bolt becomes low as it is provided at the end of the cylinder head during engine operation, and the reverse warping deformation that the cylinder head warps in the opposite direction to the chevron deformation is made to match the shape of the chevron deformation. Can be generated.

By setting not only the head bolts at the front and rear ends but also the linear expansion coefficient of the head bolt corresponding to the center line in the longitudinal direction of the cylinder head symmetrically so that the linear expansion coefficient gradually increases toward the end, It becomes possible to generate the reverse warp deformation in a form corresponding to the chevron deformation.
If the engine has a small number of cylinders, such as an in-line 4-cylinder engine or a V6 engine, the number of head bolts used is small. Therefore, by increasing the linear expansion coefficient of the front and rear end head bolts, it is possible to obtain an effect of suppressing mountain deformation. it can.
However, as the number of cylinders arranged in series increases, not only does the linear expansion coefficient of the front and rear end head bolts increase, but also the linear expansion coefficient of the head bolt corresponding to the center line in the longitudinal direction of the cylinder head is symmetrical. It can be expected that the effect of suppressing the mountain-shaped deformation is further enhanced by setting the linear expansion coefficient to gradually increase toward the portion.

Next, embodiments of the present invention will be described with reference to the drawings.
First, the outline of the configuration of the engine of this embodiment will be briefly described.
FIG. 1 shows a cross-sectional view of the engine 10.
The engine 10 includes a cylinder head 20, a cylinder block 30, a crankcase 40, an oil pan 50, a head cover 60, and the like. A crankshaft 35 is provided below the cylinder block 30, and a valve shaft 25 is provided above the cylinder head 20. As shown in FIG. 1, the engine 10 of this embodiment is an in-line four-cylinder engine.
The cylinder head 20 is made of an aluminum alloy, has four combustion chambers 21, and an intake port and an exhaust port (not shown) are connected to each other. The combustion chamber 21 is provided with four valves 22. The connection port between the intake port and the combustion chamber 21 is opened and closed by the intake valve 22, and the connection port between the exhaust port and the combustion chamber 21 is an exhaust valve. 22 is opened and closed.

A valve lifter 23 is provided at the tip of the valve 22, and the valve 22 closes the connection port to the intake port and the exhaust port when the cam provided on the valve shaft 25 presses the valve lifter 23. Since the valve 22 is provided with a valve spring 24, a connection port to the combustion chamber 21 and the intake port and the exhaust port can be opened and the passage can be communicated.
The valve shaft 25 is rotatably supported at the upper part of the cylinder head 20 by a bearing, and a valve sprocket 26 is provided at the tip.
The cylinder block 30 is made of an aluminum alloy, and four cylindrical cylinder bores 31 serving as cylinders are formed in series, and a piston 32 slides inside the cylinder block 30. The piston 32 has a cylindrical shape, and a piston ring 34 is provided on the outer periphery thereof. A connecting rod 33 is connected to the piston 32, and the connecting rod 33 is connected to a crankshaft 35.

The crankshaft 35 is rotatably supported by a bearing below the cylinder block 30, and a crank sprocket 36 is provided at the tip. The crank sprocket 36 transmits the rotation of the crankshaft 35 to the valve shaft 25 via the valve sprocket 26. In addition, it is connected to an output shaft (not shown) to extract power.
The crankcase 40 is a component provided at the lower part of the cylinder block 30. The crankshaft 35 is rotatably held so as to be sandwiched between the cylinder block 30 and the crankcase 40. In some cases, the cylinder block 30 and the crankcase 40 may be integrated depending on the production of the engine 10.
The oil pan 50 is provided below the crankcase 40 and has a function of accumulating engine oil.
The head cover 60 is a cover provided on the upper part of the cylinder head 20.

FIG. 2 shows a three-dimensional perspective view schematically showing the engine 10.
The cylinder head 20 is coupled to the cylinder block 30 by a head bolt 28 via a gasket (not shown).
Since the head bolt 28 in this embodiment is a four-cylinder engine 10, ten head bolts are provided. For convenience, the first head bolt 28a, the second head bolt 28b, the third head bolt 28c, and the fourth head bolt are provided. 28d and the fifth head bolt 28e will be referred to.
As for the material of the head bolt 28, the first head bolt 28a and the fifth head bolt 28e located at both ends of the engine 10 are stainless steel, and the other second head bolt 28b, third head bolt 28c, and fourth head bolt 28d. Is made of steel. The size of the head bolt 28 may be the same for all of the first head bolt 28a to the fifth head bolt 28e.

The head bolt 28 is tightened with a tightening force of several tons so that combustion gas and coolant liquid do not leak from between the cylinder head 20 and the cylinder block 30. This tightening force is set so as not to be loosened by heat generated during actual operation of the engine 10.
The cylinder bore 31 is also referred to as a first cylinder 31a, a second cylinder 31b, a third cylinder 31c, and a fourth cylinder 31d for convenience.
Therefore, as shown in FIG. 2, with respect to the cylinder block 30, the first head bolt 28a is located outside the first cylinder 31a, and the second head bolt 28b is located between the first cylinder 31a and the second cylinder 31b. The third head bolt 28c is between the second cylinder 31b and the third cylinder 31c, the fourth head bolt 28d is between the third cylinder 31c and the fourth cylinder 31d, and the fifth head bolt 28e is the fourth cylinder. A female screw hole for tightening the head bolt 28 is formed outside 31d.

Since the engine 10 of the present embodiment is configured as described above, the following operations and effects are achieved.
The operation of the engine 10 will be briefly described. By causing the fuel to explode and vaporize in the combustion chamber 21, the upper surface of the piston 32 receives a force. The piston 32 receiving this force slides on the cylinder bore 31 and moves downward in FIG. The connecting rod 33 connected to the piston 32 transmits a force to a crankshaft 35 that is rotatably connected to the other end. Since the crankshaft 35 is rotatably held by the cylinder block 30 via a bearing, power is taken out using the force received by the piston 32 as a rotational force.
The crank sprocket 36 provided on the crankshaft 35 transmits power to the valve sprocket 26 provided on the valve shaft 25 via a chain indicated by a two-dot chain line in FIG. The valve shaft 25 that is rotated by the power transmitted to the valve sprocket 26 is provided with a cam. By pressing the tip of the valve lifter 23, the valve 22 is moved, and connection ports to an intake port and an exhaust port (not shown) are provided. It opens and supplies air to the combustion chamber 21 or exhausts the gas after combustion.

During actual operation of the engine 10, each component functions as described above. At this time, the temperature managed by the cylinder head 20 and the cylinder block 30 is different, and a temperature difference close to 100 degrees occurs depending on the engine 10. .
The cylinder head 20 and the cylinder block 30 are provided with a water jacket, and the coolant is circulated. Although the cylinder head 20 and the cylinder block 30 are cooled to an appropriate temperature by this coolant liquid, the cylinder head 20 side is made to explode the fuel in the combustion chamber 21 to improve the thermal efficiency. The temperature setting is relatively high.
On the other hand, when the piston 32 slides on the cylinder bore 31, the cylinder block 30 has a relatively low temperature setting in order to prevent consumption of the lubricating oil used for the oil film controlled by the piston ring 34.

As described above, the cylinder head 20 and the cylinder block 30 have different temperatures when the engine 10 is actually operated. Therefore, even if the cylinder head 20 and the cylinder block 30 are both made of an aluminum alloy, an expansion amount is generated due to a temperature difference. There will be a difference.
The linear expansion coefficient of the aluminum alloy is about 24 × 10 ⁻⁶ , although it is slightly affected by the type of the alloy. If there is a temperature difference of about 100 °, it is about 2.4 × 10 ⁻³ mm per 1 mm. There will be a difference in elongation. Since the engine 10 is an in-line four-cylinder engine, the engine 10 has a laterally long shape. However, if the engine 10 has a length of several hundred mm, the cylinder head 20 may cause a difference of a little less than 1 mm in the longitudinal direction with respect to the cylinder block 30. become.
However, since the cylinder head 20 and the cylinder block 30 are fastened by the head bolt 28, the cylinder head 20 side having a high control temperature cannot be freely extended, resulting in a mountain-shaped deformation. At this time, the cylinder block 30 to which the cylinder head 20 is fixed is also pulled by the head bolt 28 and causes the same deformation.
This deformation is a mountain-shaped deformation of the engine 10 described in the problem.

FIG. 3 is a side view schematically showing the mountain-shaped deformation state of the engine 10.
When the engine 10 is stationary, as shown in the upper part of FIG. 3, the cylinder head 20 and the cylinder block 30 are substantially the same temperature as the outside air temperature and are not deformed. In this state, the crankcase 40, the oil pan 50, and the head cover 60 are not firmly fixed as much as the cylinder head 20 and the cylinder block 30, and the rigidity of the parts themselves is not so high. Omitted for convenience.
On the other hand, as shown in the lower part of FIG. 3, in actual operation, the cylinder head 20 generates a temperature difference of nearly 100 degrees as compared with the cylinder block 30 and is fixed to the head bolt 28, so Deformation will occur. The lower diagram of FIG. 3 is schematically expressed in an easily understandable manner.

When such a mountain-shaped deformation occurs in the engine 10, the roundness of the cylinder bore 31 and the valve shaft 25 and the crankshaft 35 are affected.
As long as the applicant has confirmed, in the inline 4-cylinder engine, the cylinder head 20 and the cylinder block 30 are deformed by several tens of μm.
On the other hand, the valve shaft 25 and the crankshaft 35 are held by bearings provided in the cylinder head 20 and the cylinder block 30. In general, sliding bearings are used for these bearings, and the clearance between the cylinder head 20 and the shaft portion of the cylinder block 30 is controlled to about several tens of μm.
The bearing portion of the crankshaft 35 differs depending on the engine 10, but in the case of an in-line 4-cylinder, the cylinder block 30 is provided with about five locations. Therefore, the bearing provided near the center of the cylinder block 30 due to the chevron deformation. As a result, the bearings provided at the ends of the cylinder block 30 are relatively lowered, resulting in a difference in height.
Compared with the clearance between the crankshaft 35 and the bearing, when the amount of deformation due to the angle deformation increases, the height of the bearing of the crankshaft 35 varies, so that the bearing is always one-sided and at a speed of several thousand revolutions per minute. Will rotate. As a result, a large friction loss occurs.

The same applies to the valve shaft 25 as with the crankshaft 35. The cylinder head 20 is provided with a plurality of bearing portions, and the valve shaft 25 is rotatably held. However, when the valve shaft 25 rotates, the cylinder head 20 is deformed in a chevron shape so that the bearings are in contact with each other every minute. It will rotate at a speed of several thousand revolutions.
Therefore, as with the crankshaft 35, a large friction loss occurs.
Since the engine 10 has four in-line cylinders and four valves per cylinder, the engine 10 is often provided with two valve shafts 25, but if there are two valve shafts 25, the friction loss is proportional to that. And get bigger.

Further, the cylinder block 30 is deformed in a mountain shape according to the deformation of the cylinder head 20, which causes a decrease in the cylindricity and the roundness of the cylinder bore 31.
Speaking of the cylindricity of the cylinder bore 31, the first cylinder 31a and the fourth cylinder 31d are particularly affected, and the first cylinder 31a and the fourth cylinder 31d are also bent outward in accordance with the mountain-shaped deformation of the cylinder block 30. Become. Since the piston 32 that slides in the cylinder bore 31 tends to go straight, the sliding resistance is correspondingly increased.
The roundness of the cylinder bore 31 is considered to deteriorate as the axial force of the head bolt 28 increases. The increase in the axial force of the head bolt 28 will be described later.
The piston 32 that slides on the cylinder bore 31 also needs to select a piston ring 34 that allows for the deterioration of the roundness due to the reduced roundness of the cylinder bore 31, resulting in an increase in sliding resistance. It becomes friction loss.

In this way, in this embodiment, the material of the first head bolt 28 a and the fifth head bolt 28 e of the head bolt 28 is made to be less than that of the other head bolts 28 in order to alleviate the chevron deformation that causes friction loss. Made of stainless steel with high linear expansion coefficient.
The stainless steel used for the material of the first head bolt 28a and the fifth head bolt 28e is nearly 1.5 times the steel used for the material of the second head bolt 28b, the third head bolt 28c, and the fourth head bolt 28d. It has a linear expansion coefficient. The linear expansion coefficient of steel for bolts is approximately 11.7 × 10 ⁻⁶ , whereas the linear expansion coefficient of stainless steel is approximately 17 × 10 ⁻⁶ .
Since the head bolt 28 also penetrates through the cylinder head 20, the temperature is almost the same as that of the cylinder head 20. Accordingly, although elongation occurs, the linear expansion coefficient is lower than that of the aluminum alloy constituting the cylinder head 20, and as a result, the axial force of the head bolt 28 is increased.
If the axial force increase due to the heat of the head bolt 28 is estimated, it is considered that the axial force increase is about 20% less than the initial tightening force.
Such an increase in axial force is a force that pulls up the cylinder block 30.

Four head bolts 28 are provided for each cylinder, and the cylinder head 20 and the cylinder block 30 are connected to each other. However, as the axial force of the head bolt 28 increases, a female screw portion provided in the cylinder block 30 is provided. The force pulled up to the cylinder head 20 side acts on the center.
It has been found that such pulling-up force affects the roundness of the cylinder bore 31. For details, refer to Japanese Patent Application No. 2006-048437 filed by the applicant for the mechanism.
As the axial force of the head bolt 28 increases, the cylinder bore 31 is deformed so as to swell inward in the vicinity where the female screw portion of the head bolt 28 is provided, and the roundness of the cylinder bore 31 is deteriorated.

FIG. 4 is a side view schematically showing deformation taking into account the increase in axial force during actual operation of the engine 10.
When the engine 10 is actually operated, the material of the head bolt 28 is selected as the first head bolt 28a and the fifth head bolt 28e, that is, the head bolt 28 at the front and rear ends of the engine 10 by selecting a material having a high linear expansion coefficient. As shown in the lower stage, the outside of the cylinder head 20 expands in the axial direction of the head bolt 28. The upper part of FIG. 4 is the same as the upper part of FIG.
Since the linear expansion coefficient of stainless steel is nearly 1.5 times higher than that of steel, the first head bolt 28a and the fifth head bolt 28e extend about 1.5 times at the same temperature. Therefore, the axial force generated is smaller than that of the second head bolt 28b, the third head bolt 28c, and the fourth head bolt 28d, and as a result, the cylinder head 20 is allowed to expand. Such expansion of the cylinder head 20 causes reverse warping deformation, which is deformation in the opposite direction to the above-described chevron deformation.

On the other hand, since the expansion due to the temperature difference between the cylinder head 20 and the cylinder block 30 as shown in the lower part of FIG. 3 also occurs at the same time, the engine 10 is combined with the influence of the axial force difference generated in the head bolt 28 in the lower part of FIG. Will cause the deformation shown in.
That is, both ends of the cylinder head 20 are deformed so as to spread in the axial direction of the head bolt 28.
Thus, the reverse warp deformation of the cylinder head 20 caused by the difference in the axial force of the head bolt 28 occurs in the opposite direction to the chevron deformation of the cylinder head 20, thereby reducing the effect of the chevron deformation on the cylinder block 30. be able to.
That is, since the amount of mountain-shaped deformation of the cylinder block 30 is reduced, the contact of the crankshaft 35 provided in the cylinder block 30 with the bearing is alleviated. Similarly, since the mountain-shaped deformation amount of the cylinder head 20 is reduced, the contact of the valve shaft 25 provided in the cylinder head 20 with the bearing on the bearing is reduced.
In addition, the reduction in the effect of the chevron deformation applied to the cylinder block 30 contributes to maintaining the roundness of the cylinder bore 31 provided in the cylinder block 30, and the resistance when the valve shaft 25 and the crankshaft 35 are rotated. Will not increase.

The axial force of the head bolt 28 during actual operation of the engine 10 is greater in the first head bolt 28a and the fifth head bolt 28e than in the second head bolt 28b, the third head bolt 28c, and the fourth head bolt 28d. However, the sealing force between the cylinder head 20 and the cylinder block 30 is not hindered because the axial force is not lower than the axial force when the engine 10 is stopped.
As described above, since the head bolt 28 is tightened to the cylinder block 30 in consideration of expansion due to heat, the sealing performance is ensured even when the engine 10 is actually operated, and there is a possibility that the combustion gas or the coolant liquid may leak. Absent.

The cylinder bore 31 of the cylinder block 30 can improve the static roundness to a certain extent by performing honing using a dummy head. It has never been done.
However, as in the present embodiment, the material of the head bolt 28 is changed between the first head bolt 28a, the fifth head bolt 28e, the second head bolt 28b, the third head bolt 28c, and the fourth head bolt 28d. By doing so, reverse warping deformation that cancels the chevron deformation is generated, which leads to suppression of the chevron deformation.
According to the applicant's estimation, stainless steel is used for the first head bolt 28a and the fifth head bolt 28e, and steel is used for the second head bolt 28b, the third head bolt 28c, and the fourth head bolt 28d. It is possible to reduce the axial force increase rate of less than%.
In this way, reducing the axial force increase rate of the first head bolt 28a and the fifth head bolt 28e causes reverse warpage deformation and suppresses the mountain deformation of the cylinder head 20 as described above. Thus, the influence on the cylinder block 30 can be minimized.
Therefore, the influence on the cylinder bore 31 formed in the cylinder block 30 is reduced, which contributes to improvement in roundness.

In particular, at the front and rear end portions of the engine 10, the influence of the increase in the axial force of the head bolt 28 on the roundness of the cylinder bore 31 tends to increase. In other words, the first head bolt 28a and the fifth head bolt 28e pull the outside of the first cylinder 31a and the outside of the fourth cylinder 31d, and thus, for example, like the second head bolt 28b, the first cylinder 31a and the second head bolt 28e. The effect on the roundness of the bore is greater than when pulling between the cylinders 31b.
This is because the first head bolt 28a and the fifth head bolt 28e are provided at the end of the cylinder block 30, and, for example, the rigidity is lower than that provided between the first cylinder 31a and the second cylinder 31b. Because it is.
For this reason, the reduction in the axial force increase rate of the first head bolt 28a and the fifth head bolt 28e can be expected to improve the roundness of the cylinder bore 31.
Further, since the bolt sizes of the head bolts 28 are the same, the female screw holes provided in the cylinder block 30 may be the same size, and the tightening torque to be managed may be the same. For this reason, the equipment load is also light, and the roundness of the cylinder bore 31 can be expected to be improved without much cost.

By the way, as for the linear expansion coefficient of the head bolt 28, the linear expansion coefficient of the head bolt 28 increases from the center to the end so as to be symmetric with respect to the longitudinal center of the cylinder head 20 if possible. It is desirable that it can be set as follows.
For example, a material having a large linear expansion coefficient is selected for the first head bolt 28a and the fifth head bolt 28e, and the second head bolt 28b and the fourth head bolt 28d are selected as compared with the first head bolt 28a and the fifth head bolt 28e. A material having a low linear expansion coefficient is selected, and a material having a lower linear expansion coefficient than the second head bolt 28b and the fourth head bolt 28d is selected for the third head bolt 28c. If selected, it is considered that the reverse warpage deformation becomes closer to canceling the chevron deformation.
Ideally, it is desirable to generate a reverse warp deformation that completely cancels the chevron deformation generated in the cylinder head 20, but the required linear expansion coefficient is arbitrarily set depending on whether an appropriate material exists.

However, assembling several materials for the head bolt 28 together results in a complicated assembly process. Therefore, from the viewpoint of cost, it is preferable that the number of bolt types is about two to three. Increasing the types of bolts may lead to erroneous assembly of the bolts in the wrong place, and it becomes necessary to manage a plurality of bolts, leading to an increase in cost. Moreover, although it is conceivable to divide the process in order to eliminate erroneous assembly, it leads to an increase in cost.
In view of the effect and cost, it is considered that the in-line four-cylinder engine 10 and the V6 engine of the present embodiment are good enough to change the material of the head bolts 28 at both ends of the engine 10.

As described above, the engine 10 shown in the present embodiment can have the following configurations, operations, and effects.
(1) In the engine 10 including the cylinder head 20 in which the combustion chamber 21 is formed, the cylinder block 30 in which the cylinder is formed in series, and the head bolt 28 that fixes the cylinder head 20 to the cylinder block 30, Among them, the first head bolt 28a and the fifth head bolt 28e fastened to both ends of the cylinder block 30 are compared with the second head bolt 28b, the third head bolt 28c and the fourth head bolt 28d which are fastened to other positions. Since it is made of a material having a large linear expansion coefficient, the axial force of the first head bolt 28a and the fifth head bolt 28e generated by the heat generated during the actual operation of the engine 10, the second head bolt 28b, and the third head bolt An axial force difference is generated between the axial force of 28c and the fourth head bolt 28d.
For example, as described in (3), the first head bolt 28a and the fifth head bolt 28e are made of stainless steel, and the second head bolt 28b, the third head bolt 28c, and the fourth head bolt 28d are made of steel. If the engine 10 is of a general size, an axial force difference of slightly less than 10% is generated when the engine 10 is actually operated. Due to this difference in axial force, the front and rear ends of the cylinder head 20 are likely to expand, and as a result, a deformation that warps contrary to the mountain-shaped deformation as described in the problem occurs.
The reverse warp deformation generated in the cylinder head 20 generates a force in the opposite direction to the chevron deformation, thereby suppressing the chevron deformation. As a result, the amount of angle deformation of the cylinder head 20 is reduced, and the influence on the cylinder block 30 is reduced.

By reducing the influence of the chevron deformation applied to the cylinder block 30, it is possible to contribute to ensuring the roundness of the dynamic cylinder bore 31 when the engine 10 is actually operated.
Further, since only the first head bolt 28a and the fifth head bolt 28e are made of a material having a high linear expansion coefficient, it is possible to contribute to securing the roundness of the cylinder bore 31 at a low cost.
By improving the roundness of the cylinder bore 31 of the engine 10 during actual operation, the roundness of the cylinder bore 31 is maintained even during the actual operation of the engine 10, and the piston ring 34 of the piston 32 that slides on the cylinder bore 31 is maintained. The tension can be set low, which contributes to the reduction of friction loss and contributes to the improvement of the fuel consumption of the engine 10.

Engine according to (2) (1), the temperature of the production time of the sheet cylinder head 20 and the cylinder block 30 are different, expansion of the cylinder head 20 becomes larger than the amount of expansion of the cylinder block 30, cylinder When the cylinder head 20 undergoes a chevron-like deformation due to the action of the head 20 extending in the longitudinal direction, the first head bolt 28a and the fifth head bolt 28e are the second head bolt 28b, the third head bolt 28c, and The first head bolt 28a, the fifth head bolt 28e, the second head bolt 28b, the third head bolt 28c, and the second head bolt 28a are made of a material having a linear expansion coefficient larger than that of the fourth head bolt 28d. An axial force difference is generated between the four head bolts 28d, and the cylinder head 20 is deformed into the above-mentioned mountain shape by the axial force difference. Since the reverse direction of the force is generated, since which comprises suppressing a chevron deformation of the cylinder head 20, to suppress the chevron deformation of the cylinder head 20.
Thus, the first head bolt 28a and the fifth head bolt 28e, the second head bolt 28b, the third head bolt 28c, and the fourth head bolt 28d are made of the same material as the first head bolt 28a and the fifth head bolt 28e. By increasing the expansion coefficient, it is possible to contribute to securing the roundness of the dynamic cylinder bore 31 at a low cost.
Further, by improving the roundness of the cylinder bore 31 of the engine 10 during actual operation, the roundness of the cylinder bore 31 is maintained even during the actual operation of the engine 10, and the piston ring provided in the piston 32 that slides on the cylinder bore 31 is provided. The tension of 34 can be set low and contributes to the reduction of friction loss, which can contribute to the improvement of fuel consumption of the engine 10.

(3) In the engine according to (1) or (2), when the material of the cylinder head 20 and the cylinder block 30 is an aluminum alloy, the material of the first head bolt 28a and the fifth head bolt 28e is stainless steel. Since the second head bolt 28b, the third head bolt 28c and the fourth head bolt 28d are made of steel, stainless steel having a linear expansion coefficient higher than that of steel is a temperature generated during actual operation of the engine 10. Thus, a difference in axial force can be generated, and as a result, it is possible to suppress the chevron deformation of the cylinder head 20 and the cylinder block 30.
The first head bolt 28a and the fifth head bolt 28e need only be used with the same size as the second head bolt 28b, the third head bolt 28c, and the fourth head bolt 28d. The tightening torque can be the same. Therefore, it is possible to suppress the chevron deformation by a simple method, and it does not cost much.
That is, the roundness of the dynamic cylinder bore 31 can be improved at low cost.

(4) In the engine 10 according to (1), the head bolt 28 is made of a material having a higher linear expansion coefficient as it is provided at the end than the center in the longitudinal direction of the cylinder block 30. Sometimes, the axial force difference of the head bolt 28 becomes so low that it is provided at the end of the cylinder head 20, and the reverse warping deformation that causes the cylinder head 20 to warp in the opposite direction to the chevron deformation occurs in accordance with the shape of the chevron deformation. It becomes possible to make it.

While the present invention has been described with reference to the embodiments, it is needless to say that the present invention is not limited to the above embodiments, and can be appropriately modified and applied without departing from the scope of the invention.
For example, in the present embodiment, the in-line four-cylinder engine 10 has been described as an example. However, if the engine has a layout in which the cylinder bores 31 are arranged in series, the in-line layout, the V-type layout, The present invention can also be applied to a horizontally opposed layout.
In the present embodiment, the in-line four-cylinder engine 10 is described on the assumption that ten head bolts 28 are tightened. However, even if the number of tightened head bolts 28 increases, the cylinder head 20 An equivalent effect can be obtained by setting the linear expansion coefficient of the head bolt 28 so that the reverse warpage deformation that suppresses the mountain-shaped deformation occurs.
As for materials used for the head bolt 28, stainless steel and steel are listed as examples of general metals. However, if the material can set an appropriate linear expansion coefficient and can generate a necessary tightening force, Does not interfere with use.

The cross-sectional view of the engine 10 of the present embodiment is shown. The solid perspective view which showed the engine 10 of the present Example typically is shown. The side view which represented typically the mountain-shaped deformation state of the engine 10 of a present Example is shown. The side view which represented typically the deformation | transformation which considered the axial force increase at the time of actual operation of the engine 10 of a present Example is shown.

Explanation of symbols

10 Engine 20 Cylinder head 21 Combustion chamber 22 Valve 23 Valve lifter 24 Valve spring 25 Valve shaft 26 Valve sprocket 28 Head bolt 30 Cylinder block 31 Cylinder bore 32 Piston 33 Connecting rod 34 Piston ring 35 Crankshaft 36 Crank sprocket 40 Crankcase 50 Oil pan 60 head cover

Claims (4)

In an engine comprising a cylinder head in which a combustion chamber is formed, a cylinder block in which cylinders are formed in series, and a head bolt that fixes the cylinder head to the cylinder block,
The engine characterized in that, among the head bolts, front and rear end head bolts fastened to both ends of the cylinder block are made of a material having a larger linear expansion coefficient than other head bolts fastened to other positions. The engine according to claim 1 ,
The temperature of the production time of the before and SL cylinder head the cylinder block are different, in function of the expansion of the cylinder head becomes larger than the amount of expansion of the cylinder block, the cylinder head is going Nobiyo longitudinally , When the cylinder head is deformed
The front and rear end head bolts are made of a material having a larger linear expansion coefficient than the other head bolts, so that an axial force difference between the front and rear end head bolts and the other head bolts is generated by heat generated during actual operation. Occurs,
Since the axial force difference generates a force in the direction opposite to the chevron deformation in the cylinder head, the chevron deformation of the cylinder head is suppressed. The engine according to claim 1 or 2,
When the material of the cylinder head and the cylinder block is an aluminum alloy,
The engine characterized in that the front and rear end head bolts are made of stainless steel, and the other head bolts are made of steel. The engine according to claim 1,
The engine is characterized in that the head bolt is made of a material having a higher linear expansion coefficient as it is provided at an end portion than a center portion in the longitudinal direction of the cylinder block.

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