Cylinder block

A cylinder block includes a body part where a cylinder is formed, an outer wall part made of fiber reinforced resin and surrounding an outer circumference of the body part, and a metal member attached to the outer wall part. The outer wall part is comprised of an inner layer surrounding the outer circumference of the body part, and an outer layer surrounding an outer circumference of the inner layer. A density of reinforcing fiber contained in the outer layer is higher than a density of reinforcing fiber contained in the inner layer. The metal member is attached to the outer wall part so as to contact the outer layer. The reinforcing fiber contained in the outer layer has an electric insulating property.

TECHNICAL FIELD

The present disclosure relates to a cylinder block.

BACKGROUND OF THE DISCLOSURE

For reducing the weight of an engine for automobiles, etc. to improve fuel efficiency, various technologies of forming a cylinder block partially with resin are proposed.

For example, JP2019-015227A discloses a cylinder block which includes a metal body part having a cylinder and a resin outer wall part provided outside the body part. The outer wall part is comprised of two layers of inner and outer layers which are made of fiber reinforced resin. The outer layer is made of resin containing carbon fiber and the inner layer is made of resin containing glass fiber.

The body part in which the cylinder are formed is required to have sufficient heat resistance to the combustion gas, durability against combustion gas pressure, and durability against an axial force of cylinder head bolts, but it is difficult for the resin to satisfy such requirements. Thus, the body part is made of metal.

However, according to the cylinder block disclosed in JP2019-015227A, since the carbon fiber contained in the outer layer of the outer wall part is conductive, when the metal member contacts the outer layer (e.g., when the metal member (e.g., a boss) is attached to the outer wall part for bolt-fastening an engine component (e.g., an intake manifold) or an accessory (e.g., a starter motor), or when the cylinder block includes the metal part and the metal part partially contacts the outer layer), presence of moisture at the contact between the carbon fiber and the metal member may cause rusting (galvanic corrosion or electrolytic corrosion). Thus, a solution, such as formation of an insulating layer at the contact between the carbon fiber and the metallic member, is needed.

Further, according to the cylinder block of JP2019-015227A, the outer layer of the outer wall part is set to have a fiber density of 50 wt % or above (50-90 wt %), and the inner layer is set to have a fiber density of 60 wt % or above (60-70 wt %). That is, the fiber density is set high along the entire thickness direction of the outer wall part. Thus, the outer wall part has a high thermal effusivity along its entire thickness direction, and tends to release heat outside the cylinder block, which makes it difficult to secure heat retention.

SUMMARY OF THE DISCLOSURE

The present disclosure is made in view of the above situations, and one purpose thereof is to provide a cylinder block provided with a resin outer wall part, which can secure heat retention, improve rigidity, and prevent galvanic corrosion due to contact between the outer wall part and a metal member.

According to one aspect of the present disclosure, a cylinder block is provided, which includes a body part where a cylinder is formed, an outer wall part made of fiber reinforced resin and surrounding an outer circumference of the body part, and a metal member attached to the outer wall part. The outer wall part is comprised of an inner layer surrounding the outer circumference of the body part, and an outer layer surrounding an outer circumference of the inner layer. A density of reinforcing fiber contained in the outer layer is higher than a density of reinforcing fiber contained in the inner layer. The metal member is attached to the outer wall part so as to contact the outer layer. The reinforcing fiber contained in the outer layer has an electric insulating property.

According to this configuration, the outer wall part of the cylinder block is formed in the two-layer structure comprised of the inner layer and the outer layer, and the density of the reinforcing fiber contained in the outer layer is higher than the density of the reinforcing fiber contained in the inner layer. Therefore, it is possible to increase the rigidity of the outer layer in the outer wall part. In addition, by making the density of the reinforcing fiber in the inner layer relatively lower as compared with the outer layer, the thermal effusivity of the inner layer can be reduced to suppress the heat transfer from the body part to the inner layer. Therefore, it is possible to suppress a decrease in heat retention performance of the cylinder block.

Moreover, since the metal member is attached to the outer wall part so as to contact the outer layer and the reinforcing fiber included in the outer layer has the electric insulating property, it is possible to suppress galvanic corrosion which occurs between the reinforcing fiber having the conductivity like the carbon fiber, and the metal member.

An average thickness of the outer layer may be less than an average thickness of the inner layer.

The weight of the outer wall part may increase by setting the density of the reinforcing fiber in the outer layer higher than the inner layer. However, since the average thickness of the outer layer is less than the average thickness of the inner layer in this configuration, the outer layer is formed thinner than the inner layer, thereby suppressing the increase in the weight of the cylinder block.

The inner layer may contain hollow particles.

According to this configuration, by the inner layer containing the hollow particles, it is possible to further reduce the weight of the outer wall part.

The metal member may be a cylindrical member where a threaded hole with which a threaded member configured to give a clamping force to the outer wall part threadedly engages is formed. The outer layer may be formed so as to adhere to at least a part of an outer circumferential surface of the cylindrical member.

According to this configuration, since the outer layer with the high density of the reinforcing fiber adheres to the outer circumferential surface of the cylindrical member, it is possible to secure the strength of the outer wall part against the clamping force of the threaded member, such as a bolt.

The reinforcing fiber contained in the inner layer may have an electric insulating property. The metal member may be attached so as to contact both the outer layer and the inner layer.

According to this configuration, since not only the reinforcing fiber contained in the outer layer but also the reinforcing fiber contained in the inner layer is has the electric insulating property, it is possible to avoid galvanic corrosion, even when the metal member is attached so as to contact both the outer layer and the inner layer.

A volume ratio of the reinforcing fiber in the inner layer may be less than 70% and greater than 0%.

According to this configuration, it is possible to secure the heat retention performance of the inner layer.

The outer layer may be formed by sheets comprised of resin containing the reinforcing fiber having the electric insulating property being laminated in a thickness direction of the outer layer.

According to this configuration, it is possible to easily manage the thickness of the outer layer with sufficient accuracy, when forming the outer wall part.

The reinforcing fiber having the electric insulating property may be at least one selected from the group consisting of glass fiber, aramid fiber, and basalt fiber.

These fibers have the electric insulating property, which leads to avoiding galvanic corrosion with the metal member. In addition, they have sufficient strength to reinforce the outer wall part, and are easy to obtain on the market.

DETAILED DESCRIPTION OF THE DISCLOSURE

Hereinafter, one embodiment of the present disclosure is described in detail with reference to the accompanying drawings.

As illustrated inFIGS. 1 and 2, a cylinder block1includes a body part2in which cylinders2bextending in a vertical direction A about an axis C is formed, an outer wall part3made of a fiber reinforced resin which surrounds the perimeter of the body part2, and a boss part7as a metal member attached to the outer wall part3. An inner circumferential surface of each cylinder2bis covered with a cylinder liner13. As illustrated inFIG. 1, a crankcase4is attached to one end face of the body part2of the cylinder block1at a downward side A2. A cylinder head H is fixed to the other end face of the cylinder block1(both the body part2and the outer wall part3) at an upward side A1with cylinder-head bolts.

Although the engine according to this embodiment is a multi-cylinder engine, only one of the cylinders is described below in the interest of simplifying the description.

The body part2includes a circumferential wall2awhich forms the cylinder2bhaving a cylindrical shape extending in the vertical direction A, a bottom-wall forming part2cwhich protrudes outwardly from an external surface of the circumferential wall2a, and a plurality of boss parts2d. The body part2is made of a metal, such as an aluminum alloy, with a high heat resistance and high strength.

Here, the formation of the cylinder2bmeans integrating the cylinder2bmanufactured separately from the circumferential wall2awith the body part2by casting the body part2together with the cylinder2b, or machining the cast body part2to form the cylindrical body (the cylinder2b).

A cooling water passage8for circulating coolant W through the outer circumference of the body part2is formed by the circumferential wall2aof the body part2, the bottom-wall forming part2c, and the outer wall part3(particularly, an inner layer5) which covers the body part2from outside. A space between the bottom-wall forming part2cand the outer wall part3(particularly, the inner layer5) is sealed with a packing9.

The outer wall part3is comprised of the inner layer5which surrounds the outer circumference of the body part2, and an outer layer6which surrounds the outer circumference of the inner layer5.

At least the outer layer6among the inner layer5and the outer layer6is made of a fiber reinforced resin having an electric insulating property. In this embodiment, both the inner layer5and the outer layer6are made of the fiber reinforced resin having the electric insulating property.

The fiber reinforced resin having the electric insulating property contains at least one of fibers selected from a group consisted of glass fiber, aramid fiber, and basalt fiber.

A density of the reinforcing fiber contained in the outer layer6is higher than a density of the reinforcing fiber contained in the inner layer5.

For example, the weight percentage of the reinforcing fiber contained in the outer layer6is about 35 wt % when the aramid fiber is used, and about 54 wt % when the glass fiber is used.

On the other hand, the weight percentage of the reinforcing fiber contained in the inner layer5is set as 30 wt % when the glass fiber is used. Note that it is desirable for the inner layer5to contain hollow particles for improving heat retention performance.

Moreover, in order to suppress an increase in the weight of the outer wall part3, an average thickness t2of the outer layer6with the high-density reinforcing fiber (e.g., an average thickness in the circumferential direction of the cylinder block) is desirably less than the average thickness t1of the inner layer5. Here, the term “average thickness” as used herein refers to an average value of the thickness of a flat part where neither bosses nor ribs are formed.

As illustrated inFIG. 2, the outer layer6of this embodiment is constructed by sheets6a,6b, and6cmade of resin containing the reinforcing fiber having the electric insulating property being laminated in the thickness direction of the outer layer6. For example, the sheets6a,6b, and6care sheets where the reinforcing fiber is oriented in the surface direction, and may be made of nonwoven fabric where the reinforcing fiber is oriented randomly in the surface direction. Note that the reinforcing fiber may be oriented in an arbitrary direction in the sheet surface.

Each boss part7is a cylindrical member made of metal, such as steel, where a threaded hole7awith which a threaded member for giving a clamping force to the outer wall part3threadedly engages is formed. The boss part7is used for bolt-fastening engine components, such as an intake manifold and an exhaust manifold, and auxiliary machinery, such as a starter, to the outer wall part3.

The boss part7is attached to an outer circumferential surface of the outer wall part3at such a suitable position that it contacts the outer layer6. In this embodiment, since both the inner layer5and the outer layer6are made of the fiber reinforced resin having the electric insulating property, such as the glass fiber, the possibility of occurrence of the galvanic corrosion is low, even if the boss part7is attached so that it contacts both the outer layer6and the inner layer5as illustrated inFIG. 2.

Since the outer layer6is formed so as to adhere to at least a part of the outer circumferential surface of the boss part7, it is possible to secure the strength against the clamping force when fastening the threaded member to the boss part7. In the example illustrated inFIG. 2, a part of an opening edge around the boss part7in the sheets6a,6b, and6cof the outer layer6is adhered to the outer circumferential surface of the boss part7to secure the strength against the clamping force.

A volume ratio of the reinforcing fiber in the inner layer5is desirably less than 70% in order to secure the heat retention performance of the cylinder block1. The volume ratio may be calculated as a ratio of the volume of the reinforcing fibers within the layer to the total volume of the inner layer5. The reason for the volume ratio is as follows.

FIG. 3is a graph illustrating relationships between a glass-fiber (GF) blending ratio c (volume %) and a heat conductivity λ (W/m·K) when the glass fiber is used as the reinforcing fiber, which are calculated by four kinds of different expressions. [I] is a straight line calculated from a compound rule, [II] is a curve calculated from a series equation, [III] is a curve calculated from a Maxwell equation, and [IV] is a curve calculated from a Meredith equation.

Note that the series equation is a formula for calculating the heat conductivity of the entire model when glass-fiber resin is used as a series model in which glass fiber and the resin are connected in series.

Looking at the graph ofFIG. 3, it can be seen that, as for the straight line I, the heat conductivity λ increases at a fixed rate in proportion to a GF blending ratio c, but as for the other curves II-IV, the heat conductivity λ increases rapidly when the GF blending ratio c becomes 70% or more, thereby reducing the heat retention performance. Therefore, it is desirable that the GF blending ratio c is less than 70% in order to secure the heat retention performance of the cylinder block1.

For example, When manufacturing the outer wall part3having the two-layer structure of the inner layer5and the outer layer6which are made of the fiber reinforced resin described above, one sheet or a plurality of laminated sheets of nonwoven fabric sheet including a plurality of glass fibers which constitutes the outer layer6is placed on an inner circumferential surface of a die, and a molten resin material containing short glass fibers used as the material of the inner layer5is then poured into the die.

Features of this Embodiment

(1) The cylinder block1of this embodiment includes the body part2in which the cylinder is formed, the outer wall part3made of the fiber reinforced resin which surrounds the outer circumference of the body part2, and the boss part7as the metal member attached to the outer wall part3. The outer wall part3is comprised of the inner layer5which surrounds the outer circumference of the body part2, and the outer layer6which surrounds the outer circumference of the inner layer5. The density of the reinforcing fiber contained in the outer layer6is higher than the density of the reinforcing fiber contained in the inner layer5. The boss part7is attached to the outer wall part3so as to contact the outer layer6. The reinforcing fiber contained in the outer layer6is the reinforcing fiber having the electric insulating property.

With this configuration, the outer wall part3of the cylinder block1is formed in the two-layer structure comprised of the inner layer5and the outer layer6, and the density of the reinforcing fiber contained in the outer layer6is higher than the density of the reinforcing fiber contained in the inner layer5. Therefore, it is possible to increase the rigidity of the outer layer6in the outer wall part3. In addition, by making the density of the reinforcing fiber in the inner layer5relatively low as compared with the outer layer6, the thermal effusivity of the inner layer5can be reduced to suppress the heat transfer from the body part2to the inner layer5. Therefore, it is possible to suppress the decrease in heat retention performance of the cylinder block1.

Moreover, since the boss part7is attached to the outer wall part3so as to contact the outer layer6and the reinforcing fiber included in the outer layer6is the reinforcing fiber having the electric insulating property, it is possible to suppress the galvanic corrosion which occurs between the reinforcing fiber having the conductivity like the carbon fiber, and the boss part7.

(2) In the cylinder block1of this embodiment, the average thickness t2of the outer layer6is less than the average thickness t1of the inner layer5.

The weight of the outer wall part3may increase by setting the density of the reinforcing fiber in the outer layer6higher than the inner layer5. However, since the average thickness of the outer layer6is less than the average thickness of the inner layer5as described above, the outer layer6is formed thinner than the inner layer5, thereby suppressing the increase in the weight of the cylinder block1.

(3) In the cylinder block1of this embodiment, the inner layer5desirably contains the hollow particles. By the inner layer5containing the hollow particles, it is possible to further reduce the weight of the outer wall part3. In addition, by the inner layer5containing the hollow particles, it is also possible to improve the heat retaining effect of the inner layer5.

(4) In the cylinder block1of this embodiment, the boss part7as the metal member is the cylindrical member in which the threaded hole7awith which the threaded member for giving the clamping force to the outer wall part3threadedly engages is formed. The outer layer6is formed so as to adhere to at least a part of the outer circumferential surface of the cylindrical member.

With this configuration, since the outer layer6with the high density of the reinforcing fiber adheres to the outer circumferential surface of the cylindrical member, it is possible to secure the strength of the outer wall part3against the clamping force of the threaded member, such as the bolt.

(5) In the cylinder block1of this embodiment, the reinforcing fiber contained in the inner layer5is the reinforcing fiber having the electric insulating property. The boss part7is attached so as to contact both the outer layer6and the inner layer5.

With this configuration, since not only the reinforcing fiber contained in the outer layer6but also the reinforcing fiber contained in the inner layer5is the reinforcing fiber having the electric insulating property, it is possible to avoid the galvanic corrosion, even when the boss part7is attached so as to contact both the outer layer6and the inner layer5.

(6) In the cylinder block1of this embodiment, the volume ratio of the reinforcing fiber in the inner layer5is less than 70% and greater than 0%. With this configuration, it is possible to secure the heat retention performance of the inner layer5.

(7) In the cylinder block1of this embodiment, the outer layer6is constructed by the sheets6a,6b, and6cmade of the resin containing the reinforcing fiber having the electric insulating property being laminated in the thickness direction of the outer layer6. With this configuration, it is possible to easily manage the thickness t2of the outer layer6with sufficient accuracy, when forming the outer wall part3. Note that an adhesive layer may be provided between the sheets6a,6b, and6cfor the easiness of forming the laminated the sheets.

(8) In the cylinder block1of this embodiment, the reinforcing fiber having the electric insulating property is at least one of fibers selected from the group consisting of the glass fiber, the aramid fiber, and the basalt fiber. These fibers have the electric insulating property, which leads to avoiding the galvanic corrosion with the boss part7. In addition, they have sufficient strength as the reinforcing fibers which reinforce the outer wall part3, and are easy to obtain in the market. Note that considering the scope of the present disclosure, the phrase “having the electric insulating property” may be an insulating property which can at least avoid the galvanic corrosion, and it does not necessarily mean that it is fully insulated.

Modifications

(A) In the above embodiment, as illustrated inFIG. 2, the part of the opening edge around the boss part7in the sheets6a,6b, and6cof the outer layer6adheres to the outer circumferential surface of the boss part7to secure the strength against the clamping force. However, the present disclosure is not limited to this configuration, as long as the outer layer6adheres to at least a part of the outer circumferential surface of the boss part7which is the cylindrical member. Therefore, the outer layer6may adhere to the entire outer circumferential surface of the boss part7.

That is, like a modification of the present disclosure illustrated inFIG. 4, the sheets6aand6bof the outer layer6may be bent toward the inner layer5to form a cylindrical part10, and the cylindrical part10of the outer layer6may adhere to the entire outer circumferential surface of the boss part7. In this case, since the cylindrical part10of the outer layer6contacts the outer circumferential surface of the boss part7with a large contacting area to firmly support the boss part7, the strength of the outer wall part3against the clamping force of the threaded member can fully be secured.

Moreover, in the modification illustrated inFIG. 4, the sheet6awhich constitutes the outer layer6made of the fiber reinforced resin having the electric insulating property is provided between an end part of the boss part7and the inner layer5. Therefore, it is possible to avoid the galvanic corrosion, even if the inner layer5is a layer containing the carbon resin.

(B) In the above embodiment, as illustrated inFIG. 2, the metal boss part7for attaching the engine components such as the intake manifold and the auxiliary machinery such as the starter is described as one example of the metal member attached to the outer layer6of the outer wall part3. However, the metal member of the present disclosure is not limited to the boss part7, and it may include various members, as long as it is a metal member attached to the outer layer6of the outer wall part3.

For example, as another modification of the present disclosure, as illustrated inFIG. 5, a flange part HF of a cylinder head H may be fastened to an end face of the cylinder block1at the upward side A1with cylinder-head bolts. Metal cylindrical members11which each form a cylinder-head-bolt hole11ainto which the cylinder-head bolt is inserted in the vertical direction A may be attached to the outer layer6.

The cylindrical member11extends in the vertical direction A like the cylinder2bof the body part2. Although the outer wall part3ofFIG. 5is common to the above embodiment in that it has the two-layer structure of the inner layer5and the outer layer6, the configuration of the outer layer6is different. That is, the outer layer6ofFIG. 5is formed in a cylindrical shape by wrapping a sheet around the outer circumference of the cylindrical member11. The outer layer6adheres to the entire outer circumferential surface of the cylindrical member11. This sheet is, for example, a sheet made of nonwoven fabric containing the reinforcing fiber having the electric insulating property, such as the glass fiber.

The outer layer6ofFIG. 5has a cylindrical extended part6aextending to a lower part of the cylindrical member11, and a boss part2dof the body part2are inserted therein.

In a modification illustrated inFIG. 5, when fastening the cylinder head H to the end face of the cylinder block1at the upward side A1with the cylinder-head bolts, the cylinder-head bolt penetrates the cylinder-head-bolt hole11aextending in the vertical direction A, and a tip-end part of the cylinder-head bolt is then threadedly engaged with a threaded hole2eof the boss part2d. Therefore, the cylinder head H and the cylinder block1are fastened in the vertical direction with the cylinder-head bolts. Here, the fastening force of the bolts in the vertical direction A acts on the outer layer6through the cylindrical member11. However, since the outer layer6fixedly adheres to the entire outer circumferential surface of the cylindrical member11, the outer layer6contacts the outer circumferential surface of the cylindrical member11with a large contacting area to firmly support the cylindrical member11. Therefore, it is possible to fully secure the strength of the outer wall part3against the clamping force of the cylinder-head bolts.

(C) Although in the above embodiment both the inner layer5and the outer layer6are made of the fiber reinforced resin having the electric insulating property, only the outer layer6may be made of the fiber reinforced resin having the electric insulating property. For example, only the outer layer6may be made of the fiber reinforced resin having the electric insulating property, and the inner layer5may be made of the carbon resin. In this case, like the above modification (A) andFIG. 4, by providing the sheet6awhich constitutes the outer layer6made of the fiber reinforced resin having the electric insulating property between the end part of the boss part7and the inner layer5, it is possible to avoid the galvanic corrosion, even if the inner layer5is the layer containing the carbon resin.

(D) In the above embodiment, the weight percentage of the reinforcing fiber contained in the inner layer5when the glass fiber is used is set as 30 wt %, but the present disclosure is not limited to this configuration. For example, as a modification of the present disclosure, when the inner layer5contains the carbon fiber, the weight percentage of the carbon fiber may be 5 wt %. Alternatively, when using the carbon fiber as the inner layer5, the weight percentage of the carbon fiber may be 30 wt %, and 35 wt % of glass balloons may further be utilized as the hollow particles, to further improve the heat retaining effect while suppressing the increase in the weight of the cylinder block1.

DESCRIPTION OF REFERENCE CHARACTERS