Cylinder block for engine

A cylinder block for an engine has a cylinder assembly having a plurality of cylinders, each corresponding to one of a plurality of pistons. A block body has an outer wall accommodating the cylinder assembly, a crankcase accommodating the crankshaft, and a plurality of partitions. The partitions divide the space in the crankcase into a plurality of crank chambers. The number of the crank chambers corresponds to the number of the cylinders. The outer wall, the crankcase, and the partitions are formed integrally. A partition through portion is formed in a predetermined one of the partitions to connect an adjacent pair of the crank chambers. The partition through portion opens toward the cylinders.

BACKGROUND OF THE INVENTION

The present invention relates to a cylinder block for an engine having at least one crank chamber, which cylinder block has a structure for suppressing pressure fluctuation in the crank chamber, thereby reducing pumping loss.

During the operation of an engine, reciprocation of pistons fluctuates the pressure in the crank chamber and the interior of the cylinders, which communicate with the crank chamber. Accordingly, pumping loss occurs.

Conventionally, to reduce pumping loss, a technique has been proposed in which adjacent crank chambers are connected with each other in a crankcase.

(1) Patent Document 1: Japanese Laid-Open Patent Publication No. 2000-136752 proposes a cylinder block in which through holes are formed in partitions, and the centers of the through holes in the partitions are not aligned.

(2) Patent Document 2: Japanese Laid-Open Patent Publication No. 2002-180900 discloses a technique for connecting adjacent cylinders by forming through holes in partitions, while biasing the through holes relative to the cylinder axes.

(3) Patent Document 3: Japanese Laid-Open Patent Publication No. 2003-74408 discloses a technique for forming a through hole in a cylinder block, which through hole has an axis parallel to the axis of a crankshaft, wherein part of the through hole opens to the inner surface of the cylinder bores.

(4) Patent Document 4: Japanese Laid-Open Patent Publication No. 2001-241356 discloses a technique for forming a through hole extending along an arrangement direction of cylinders, wherein the through hole is inside a wall that is located in a rear section of a cylinder block with respect to the fore-and-aft direction of the vehicle, and the through hole is connected with the crank chamber.

If adjacent crank chambers in a cylinder block are connected with each other, air that is pushed toward one of the crank chambers as the corresponding piston moves flows to the adjacent crank chamber, which suppresses pressure fluctuation in the crank chambers. Accordingly, the pumping loss is reduced.

If adjacent crank chambers in a cylinder block are connected to each other as in the above shown Patent Documents 1 to 3, the structural constraint only allows the through hole to be machined from the outside of the crankcase. Thus, when forming the through hole in a partition, an unnecessary hole that does not contribute to reduce pumping loss is formed in an outer wall of the crankcase.

Since combustion pressure acting on a crankshaft causes stress to be concentrated on areas about through holes, forming of unnecessary through holes as described above is best to be avoided. However, conventional cylinder blocks have no measures for such unnecessary holes.

On the other hand, with recent demands for engines of higher power and better fuel economy, a structure of through holes that effectively reduces pressure fluctuation (pumping loss) has been desired.

However, since the cylinder block disclosed in Patent Document 4 has a structure in which a through hole formed in an outer portion of the wall surrounding the cylinders is connected to the crank chamber through a connector passage, it is possible that, when each piston is reciprocated and pushes air in a section of the cylinder adjacent to the corresponding crank chamber, the air is not smoothly discharged to another crank chamber. In such a case, pressure fluctuation is not sufficiently reduced.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide a cylinder block having a structure that eliminates the necessity of forming unnecessary through holes in a crankcase, and a structure that efficiently reduces pressure fluctuations in crank chambers.

To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a cylinder block for an engine having a plurality of pistons and a crankshaft is provided. The cylinder block includes a cylinder assembly, a block body, and a partition through portion. The cylinder assembly has a plurality of cylinders, each corresponding to one of the pistons. The block body has an outer wall accommodating the cylinder assembly, a crankcase accommodating the crankshaft, and a plurality of partitions. The partitions divide the space in the crankcase into a plurality of crank chambers. The number of the crank chambers corresponds to the number of the cylinders. The outer wall, the crankcase, and the partitions are formed integrally. The partition through portion is formed in a predetermined one of the partitions to connect an adjacent pair of the crank chambers, and opens toward the cylinders.

The present invention provides another cylinder block for an engine having a plurality of pistons and a crankshaft. The cylinder block includes a cylinder assembly, a block body, and a cylinder through portion. The cylinder assembly has a plurality of cylinders, each corresponding to one of the pistons. The block body has an outer wall accommodating the cylinder assembly, a crankcase accommodating the crankshaft, and a plurality of partitions. The partitions divide the space in the crankcase into a plurality of crank chambers. The number of the crank chambers corresponds to the number of the cylinders. The outer wall, the crankcase, and the partitions are formed integrally. The cylinder through portion is formed in the cylinder assembly. The cylinder through portion opens toward the block body and connects the interiors of an adjacent pair of the cylinders with each other.

Further, the present invention provides another cylinder block for an engine having a plurality of pistons and a crankshaft. The cylinder block includes a cylinder assembly, a block body, a partition through portion, and a cylinder through portion. The cylinder assembly has a plurality of cylinders, each corresponding to one of the pistons. The block body has an outer wall accommodating the cylinder assembly, a crankcase accommodating the crankshaft, and a plurality of partitions. The partitions divide the space in the crankcase into a plurality of crank chambers. The number of the crank chambers corresponds to the number of the cylinders. The outer wall, the crankcase, and the partitions are formed integrally. The partition through portion is formed in a predetermined one of the partitions to connect an adjacent pair of the crank chambers. The partition through portion opens toward the cylinders. The cylinder through portion is formed in the cylinder assembly. The cylinder through portion opens toward the block body and connects the interiors of an adjacent pair of the cylinders with each other.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

A first embodiment of the present invention will now be described with reference toFIGS. 1 to 12.FIGS. 4,6,9,10,11, and12are cross-sectional views each taken along a plane perpendicular to the axis of a crankshaft14.

In this embodiment, a cylinder block11according to the present invention is applied to an in-line four-cylinder engine1.

FIG. 1illustrates the engine1that incorporates the cylinder block11. The engine1includes the cylinder block11, a cylinder head12, an oil pan13, and the crankshaft14. The cylinder head12is attached to the top of the cylinder block11.

The oil pan13is attached to the bottom of the cylinder block11. The crankshaft14is located in a space in the cylinder block11that is defined by a crankcase C and the oil pan13.

FIG. 2illustrates the cylinder block11. The cylinder block11includes a cylinder assembly3and a block body5. The cylinder assembly3is formed to have in it cylinders31. The block body5is formed to have in it a crankcase C and an outer wall51.

The cylinder assembly3is assembled with the block body5by placing the cylinder assembly3on a body flange52formed in the outer wall51of the block body5.

FIGS. 3 and 4show the cylinder assembly3. The cylinder assembly3has the cylinders31(a first cylinder31A, a second cylinder31B, a third cylinder31C, and a fourth cylinder31D) and a cylinder flange32. Each of the cylinders31A,31b,31C, and31D accommodates a piston of the engine. The cylinder flange32is formed to surround the upper end of the outer circumferential surface (a cylinder outer surface31F) of the cylinders31A,31b,31C, and31D. The cylinder assembly3is formed integrally by casting.

In the engine1of the present embodiment, air-fuel mixture is ignited in the order of the first cylinder31A, the third cylinder31C, the fourth cylinder31D, and then the second cylinder31B.

According to the order of ignition, the crankshaft14sets the stroke positions of pistons in the cylinders (the position of each piston in the corresponding cylinder) in the following manner. That is, the stroke positions of the pistons in the first cylinder31A and the fourth cylinder31D are set equal to each other. Also, the stroke positions of the pistons in the second cylinder31B and the third cylinder31C are set equal to each other.

The cylinder head12of the engine1is placed on an end face of the cylinder flange32of the cylinder assembly3, or on a cylinder deck surface31T. An end face opposite to the cylinder deck surface31T will be referred to as a cylinder bottom surface31U.

Bolt holes33for receiving bolts are formed in the cylinder flange32. The bolt holes33extend along the axes of the cylinders31.

<Structure of Block Body>

FIGS. 5 and 6show the structure of the block body5. The block body5includes the outer wall51for receiving the cylinder assembly3, and the crank case C for receiving the crankshaft14. The block body5is formed integrally by casting.

The inner surface of the outer wall51(outer wall inner surface51R) is shaped to correspond to the cylinder outer surface31F of the cylinder assembly3. When the block body5and the cylinder assembly3are assembled, the outer wall inner surface51R faces the cylinder outer surface31F with a predetermined space in between. In the cylinder block11, the space defined between the outer wall inner surface51R and the cylinder outer surface31F is used as a water jacket.

The outer wall51has a body flange52, on which the cylinder flange32of the cylinder assembly3is placed. The top surface of the block body5(a block body deck surface51T) contacts the cylinder flange32of the cylinder assembly3.

Bolt holes53are formed in the outer wall51at positions that correspond to the bolt holes33of the cylinder assembly3. The cylinder head12also has bolt holes (not shown) corresponding to the bolt holes33,53. Bolts are inserted in the sets of the bolt holes to assemble the cylinder block11and the cylinder head12to each other.

A coolant port54is formed in the outer wall51of the block body5to permit coolant to flow into or out of the water jacket. Inside the block body5, a cylinder support55is formed at the boundary between the outer wall51and the crankcase C to support the cylinder assembly3. The cylinder support55is formed along the entire perimeter of the inner surface of the block body5.

<Internal Structure of Block Body>

FIG. 7is a plan view illustrating the block body5as viewed at the top surface (in a direction of arrow VA inFIG. 6).FIG. 8is a plan view illustrating the block body5as viewed at the bottom surface (in a direction of arrow VB inFIG. 6).

In the crankcase C, a plurality of partitions (a first partition57A, a second partition57B, a third partition57C) are provided between a side wall56A and a side wall56B. A bearing portion58for the crankshaft14is formed in each of the side walls56A,56B and the partitions57A,57B,57C. The crankshaft14is installed in the block body5by supporting its journal at a crank cap from a direction facing the inner surfaces of the bearing portions58.

A space R in the crankcase C is divided into a first crank chamber R1, a second crank chamber R2, a third crank chamber R3, and a fourth crank chamber R4by the partitions57A,57B, and57C.

The first crank chamber R1is defined by the side wall56A of the crankcase C and the first partition57A. The first crank chamber R1corresponds to the first cylinder31A.

The second crank chamber R2is defined by the first partition57A and the second partition57B. The second crank chamber R2corresponds to the second cylinder31B.

The third crank chamber R3is defined by the second partition57B and the third partition.57C. The third crank chamber R3corresponds to the third cylinder31C.

The fourth crank chamber R4is defined by the side wall56B of the crankcase C and the third partition57C. The fourth crank chamber R4corresponds to the fourth cylinder31D.

The first crank chamber R1and the second crank chamber R2are connected to each other by a first partition through portion Hw1. The first partition through portion Hw1permits air to move from the first crank chamber R1to the second crank chamber R2and from the second crank chamber R2to the first crank chamber R1.

The second crank chamber R3and the fourth crank chamber R4are connected to each other by a second partition through portion Hw2. The fourth partition through portion Hw2permits air to move from the third crank chamber R3to the fourth crank chamber R4and from the fourth crank chamber R4to the third crank chamber R3.

FIG. 9is a cross-sectional view of the block body5.FIG. 10is a cross-sectional view of the cylinder block11.

The first partition through portion Hw1is formed to have a concave shape at a top portion of the first partition57A. That is, the first partition through portion Hw1is formed in the first partition57A as a recess open toward the body deck surface51T.

When the cylinder assembly3is installed in the block body5as shown inFIG. 10, the first partition through portion Hw1opens toward the cylinders31. The cylinder bottom surface31U and the top surface of the first partition57A (partition top surface57T) face each other with a predetermined space in between.

In a plane that is perpendicular to the axis of the crankshaft14, the first partition through portion Hw1is axially symmetric about the axis Lc of the corresponding cylinder31.

The width Lw1of the first partition through portion Hw1(the length along a direction perpendicular to the axis Lc of the corresponding cylinder31) is greater than the height Lw2of the first partition through portion Hw1(the depth of the recess along the axis of the corresponding cylinder31). That is, the first partition through portion Hw1is elongated along the direction perpendicular to the axis Lc of the corresponding cylinder31. The shape of the first partition through portion Hw1is optimized for avoiding interference with oil passages and bolt holes in the block body5, while satisfying an inequality Lw1>Lw2.

The cross-section of the block body5taken along line9A—9A ofFIG. 8is the same as the cross-section taken along line9C—9C ofFIG. 8, or as the cross-section shown inFIG. 9. That is, the second partition through portion Hw2is formed in the third partition57C in the same manner as the first partition through portion Hw1.

<Partition Having no Through Portion>

The top surface of the second partition57B (partition top surface57T) is substantially smooth. That is, unlike the first partition57A and the third partition57C, the second partition57B has no recess (through portion) for connecting the adjacent crank chambers with each other. Therefore, when cylinder assembly3is installed in the block body5as shown inFIG. 12, the cylinder bottom surface31U contacts the top surface of the first partition57A (the partition top surface57T).

The cross-section taken along line11A—11A and the cross-section taken along line11B—11B of the block body5ofFIG. 8is the same as the cross-section taken along line11C—11C ofFIG. 8, or as the cross-section shown inFIG. 11. That is, like the second partition57B, the side walls56A,56B has no recess (through portion) for connecting the adjacent crank chambers with each other.

The cylinder block11according to the first embodiment provides the following advantages.

(1) In the first embodiment, the cylinder block11is formed of the separately prepared cylinder assembly3and the block body5, and the partition through portions Hw1and Hw2are open to the cylinder.

Therefore, the shaping dies for the block body5can be formed to have portions corresponding to the partition through portions Hw1, Hw2. Unlike conventional cylinder blocks, no unnecessary through holes are formed.

Also, the partition through portions Hw1, Hw2open toward the cylinder, that is, the partition through portions Hw1, Hw2are formed in sections in the partitions that are closest to the cylinder. Therefore, when air in a crank chamber (including the interior of the corresponding cylinder connected to the crank chamber) is pushed by the piston, the pushed air is quickly discharged to an adjacent crank chamber.

Therefore, pumping loss caused by pressure fluctuation in the crank chamber is reduced.

By adopting the above configuration, the cylinder block11is provided that has a structure that eliminates the necessity of forming unnecessary through holes in the crankcase C, efficiently reduces pressure fluctuations in crank chamber R.

(2) Connecting adjacent crank chambers of a crank chamber with each other effectively reduces pumping loss. However, if the pistons of the cylinders corresponding to the connected crank chambers are set to have the same stroke positions, forming a through portion in the partition between the crank chambers does not reduce pressure fluctuation.

Accordingly, in the first embodiment, the second crank chamber R2and the third crank chamber R3, which have the same piston stroke positions, are not connected to each other. Therefore, the rigidity of the cylinder block11is not reduced by forming unnecessary through portions.

(3) In the first embodiment, the through portions Hw1, Hw2are formed in the topmost portions of the partitions57A,57C (portions closest to the cylinders31). Therefore, when air in a crank chamber is pushed as the corresponding piston moves, air is conducted to an adjacent crank chamber before the inertia becomes greater. Pumping loss is therefore more efficiently reduced.

(4) In a cylinder block in which through holes are formed in partitions, stress is concentrated on an area about each through hole due to combustion pressure that acts on the crankshaft. If the concentrated stress is excessively increased, the partition may be damaged.

In this respect, the through portions Hw1, Hw2are formed in the topmost portions of the partitions57A,57C in the first embodiment instead of forming through holes. Since this configuration extends the distance between each through portion Hw1, Hw2and the crank journal, concentration of stress on the through portions Hw1, Hw2is minimized.

(5) In the first embodiment, the width Lw1of each through portion Hw1, Hw2is greater than the height Lw2of each through portion.

Therefore, when the through portions Hw1, Hw2are formed to open toward the cylinders31, air is more quickly moved from one crank chamber to an adjacent crank chamber compared to a case where the width Lw1is less than the height Lw2. Therefore, pumping loss is more effectively reduced.

Adopting the configuration according to the first embodiment allows the limited space above the partitions to be effectively used, so that a structure of through portions suitable for reducing pumping loss is obtained.

(6) In the first embodiment, the first partition through portion Hw1is axially symmetric about the axis Lc of the corresponding cylinder31in a plane that perpendicular to the axis of the crankshaft14.

Therefore, when a piston causes air in the corresponding crank chamber to flow to an adjacent crank chamber, the flow of air is made uniform. Therefore, pumping loss is more efficiently reduced.

(7) In a conventional cylinder block, since through holes are formed by machining, residual stress may damage the cylinder block.

In this respect, the cylinder block11is formed by assembling the cylinder assembly3and the block body5, and the block body5is formed to have the partition through portions Hw1, Hw2. Accordingly, no structure for through portions needs to be machined, which eliminates the occurrence of residual stress.

Second Embodiment

A second embodiment of the present invention will now be described with reference toFIGS. 13 and 14.FIGS. 13 and 14are cross-sectional views each taken along a plane perpendicular to the axis of a crankshaft.

A cylinder block of the second embodiment has the same structure as the cylinder block11of the first embodiment with the following modifications. Specifically, in the cylinder assembly3, a through portion connecting an adjacent pair of the cylinders31is open to the cylinder bottom surface31U.

<Shape of Through Portions>

FIG. 13is a cross-sectional view showing a cylinder assembly3according to the second embodiment, which corresponds to a cross-section taken along line13C—13C ofFIG. 3.FIG. 14is a cross-sectional view showing the cylinder block11according to the second embodiment, which corresponds to a cross-section taken along line14C—14C ofFIG. 1.

In the cylinder assembly3, a cylinder through portion Hs is formed at a section where the circumferential wall of the first cylinder31A is connected to the circumferential wall of the second cylinder31B. The cylinder through portion Hs connects the interior of the first cylinder31A and the interior of the second cylinder31B with each other.

The cylinder through portion Hs is formed to have a concave shape at the bottom of the first cylinder31A and the second cylinder31B. That is, the cylinder through portion Hs is open to the cylinder bottom31U.

When the cylinder assembly3is installed in the block body5as shown inFIG. 14, the cylinder through portion Hs1opens toward the block body5. The cylinder bottom surface31U and the partition top surface57T face each other with a predetermined space in between.

In a plane that is perpendicular to the axis of the crankshaft14, the cylinder through portion Hs is axially symmetric about the axis Lc of the corresponding cylinder31.

The width Ls1of the cylinder through portion Hs1(the length along a direction perpendicular to the axes Lc of the cylinders31) is greater than the height Ls2of the cylinder through portion Hs1(the depth of the recess along the axes of the cylinders31). That is, the cylinder through portion Hs is elongated along the direction perpendicular to the axes Lc of the cylinders31.

The height Ls2of the cylinder through portion Hs1is set such that the cylinder through portion Hs1does not interfere with a piston ring in a state where the volume of the corresponding combustion chamber is maximized.

The cross-section of the cylinder assembly3of this embodiment, which corresponds to the cross-section taken along line13A—13A ofFIG. 3, is the same as the cross-section shown inFIG. 13. That is, a cylinder through portion Hs2is formed at a section where the circumferential wall of the third cylinder31C is connected to the circumferential wall of the fourth cylinder31D in the same manner as the first cylinder31A and the second cylinder31B.

In addition to the advantages listed in items (1) to (7) in the first embodiment, the cylinder block11of the second embodiment provides the following advantage.

(8) In addition to the partition through portions Hw1, Hw2, the cylinder through portions Hs1, Hs2are formed in the cylinders31in this embodiment. This increases the amount of air that is discharged from one crank chamber to an adjacent crank chamber by the corresponding piston. Therefore, pumping loss is more effectively reduced.

In the second embodiment, the partition through portions Hw1, Hw2and the cylinder through portions Hs1, Hs2are both formed. However, without forming the partition through portions Hw1, Hw2, only the cylinder through portions Hs1, Hs2may be formed to reduce pumping loss.

In the second embodiment, the cylinder through portions Hs1, Hs2are each substantially rectangular in a cross-section perpendicular to the axis of the crankshaft14. However, the cylinder through portions Hs1, Hs2may be formed to have other shapes. In short, as long as the width Ls1of the cylinder through portion Hs is greater than the height Ls2of the cylinder through portions Hs1, Hs2, the shape of the cylinder through portion Hs may be changed as necessary.

The above embodiments may be modified as follows.

In the illustrated embodiments, the partition through portions Hw1, Hw2are each substantially rectangular in a cross-section perpendicular to the axis of the crankshaft14. However, the partition through portions Hw1, Hw2may be formed to have other shapes. In short, as long as the width Lw1of the partition through portions Hw1, Hw2is greater than the height Lw2-of the partition through portions Hw1, Hw2, the shape of the partition through portions Hw1, Hw2may be changed as necessary.

In the illustrated embodiments, the present invention is applied to the cylinder block of an in-line four cylinder engine. However, the application of the present invention is not limited to the cylinder block of an in-line four cylinder engine. In short, the present invention may be applied to the cylinder block of any type of engine as long as it has a plurality of cylinders.