Cylinder block

A cylinder block comprises bearing sections for supporting a rotatable shaft disposed within a crankcase inner chamber, the bearing sections being spaced from each other and from main bearing sections for supporting a crankshaft; and generally cylindrical hollow beam members each of which is interposed between the two opposite bearing sections in a manner to cover the rotatable shaft supported by the bearing sections, the hollow beam members being aligned in the direction of the row of cylinder barrels, thereby effectively increasing the total rigidity of the cylinder block while achieving engine weight-lightening.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a cylinder block of an internal combustion 
engine, arranged to lower the noise level of the engine. 
2. Description of the Prior Art 
As a cause of engine noise, there is vibration noise emitted from a 
so-called cylinder block skirt or lower section and an oil pan which noise 
is caused by the vibration of a cylinder block. In order to reduce such 
vibration noise it seems enough to suppress vibration, due to explosion 
torque, applied to a crankshaft by increasing the rigidity of the cylinder 
block. However, this unavoidably leads to an increase in cylinder block 
wall thickness and accordingly to a great increase in engine weight, 
thereby giving rise to new problems such as a deteriorated fuel economy. 
In view of this, a variety of propositions have been made to improve the 
rigidity of the cylinder block while suppressing the increase in cylinder 
block weight. 
BRIEF SUMMARY OF THE INVENTION 
In accordance with the present invention, the cylinder block is provided 
with cylinder barrels and a crankcase inner chamber. The crankcase inner 
chamber comprises a plurality of bearing sections for supporting a 
rotatable shaft disposed within the crankcase inner chamber. The bearing 
sections are spaced from each other and from main bearing sections for 
supporting a crankshaft. Additionally, a plurality of generally 
cylindrical hollow beam members are so provided that each is interposed 
between the two opposite bearing sections so as to connect them in a 
manner to cover the rotatable shaft supported by the bearing sections. The 
hollow beam members are aligned in the direction of the row of the 
cylinder barrels. With the thus arranged cylinder block, the cylinder 
block is increased in flexural and torsional rigidity while achieving 
engine weight lightening, thereby effectively lowering engine noise level.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 1A and 1B, a conventional cylinder block 1 will be 
described along with its major shortcomings. The cylinder block 1 is 
formed with a plurality of cylinder barrels 2 which are connected through 
upper and lower block decks 3, 4 with a cylinder block outer wall 5. 
Defined between cylinder barrels 2 and the cylinder block outer wall 5 is 
a water jacket 6 through which engine coolant circulates. A cylinder head 
(not shown) will be secured on the top surface of the upper block deck 3 
by means of head bolts (not shown). A so-called cylinder block skirt 
section 7 is securely connected to the lower block deck 4 and extends 
downwardly. The skirt section 7 is bulged laterally and outwardly in the 
downward direction in order to be located outside of the envelope of the 
outer-most loci of a rotating system including a crankshaft 8 and 
connecting rods (not shown). An oil pan (not shown) will be securely 
connected to the bottom edge of the skirt section 7, so that a crankcase 
inner chamber 9 is defined between the skirt section 7 and the oil pan. 
A plurality of main bearing bulkheads 10 are integrally connected to the 
inner wall of the skirt section 7 in such a manner as to divide the 
crankcase inner chamber 9 into a plurality of parts in the direction of 
the row of the cylinder barrels 2. Each bearing bulkhead 10 is formed with 
a main bearing section 11 for rotatably supporting the journal of the 
crankshaft 8. Each bearing bulkhead 10 is further formed with another 
bearing section 12A(12B) for rotatably supporting one of various shaft 
members, for example, a shaft for driving engine accessories such as an 
oil pump, or a camshaft for operating intake and exhaust valves. The 
bearing section 12A(12B) is located in the vicinity of the lower block 
deck 4 and formed in the shape of a boss having a central opening as shown 
in FIG. 1B. The above-mentioned shaft member is rotatably supported by the 
bearing sections 12A, 12B and disposed within the crankcase inner chamber 
9 in such a manner as to extend in the direction of the row of the 
cylinder barrels 2. In this connection, to obtain a space for the shaft 
member within the crankcase inner chamber 9, the cylinder block skirt 
section 7 is formed to be further bulged outwardly as shown in FIG. 1A. 
The reference numeral 13 denotes an oil passage from which lubricating oil 
is supplied through an oil supply passage 14 to the main bearing section 
11. 
However, the above-mentioned conventional cylinder block 1 has encountered 
the following shortcomings: The cylinder block is so constructed that the 
cylinder block skirt section 7 is largely bulged outwardly from the lower 
block deck 4. Accordingly, the skirt section 7 tends to readily vibrate, 
which induces vibration of the oil pan, thus emitting considerable 
vibration noise from the engine. Such a tendency of noise emission is 
remarkable particularly in cases where the wall thickness of the cylinder 
block is less and/or the cylinder block is formed of light alloy from the 
point of view of weight-lightening. Because, in such cases, the vicinity 
of the lower block deck 4 is further lowered in rigidity, and therefore 
the cylinder block 1 readily deforms by flexure in the axial direction of 
the cylinder block and by torsion around the axis of the crankshaft 8, 
which flexure and torsion are caused, for example, due to explosion 
pressure within cylinder barrels. Since such deformation of the cylinder 
block repeatedly takes place, the cylinder block skirt section 7 is 
vibrated, thereby causing the oil pan to largely vibrate. As discussed 
above, engine weight-lightening seems to be inconsistent with engine noise 
reduction, and therefore it is difficult to obtain an engine which is 
light in weight and of low noise level. 
In view of the above description of the conventional cylinder block, 
reference is now made to FIGS. 2A and 2B, wherein a preferred embodiment 
of a cylinder block of the present invention is illustrated by the 
reference numeral 20. The cylinder block 20 is, for example, of an 
automotive internal combustion engine. The cylinder block 20 is composed 
of a plurality of cylinder barrels 22 which are connected through upper 
and lower block decks 24, 26 with a cylinder block outer wall 28. A water 
jacket 30 is defined between the cylinder barrels 22 and the outer wall 
28. An engine coolant circulates through the water jacket 30. A cylinder 
head (not shown) will be secured on the top surface of the upper block 
deck 24 by means of head bolts (not shown). A so-called cylinder block 
skirt section 32 is integrally connected to the lower block deck 26 and 
extends downwardly so as to be located outside of the envelope of the 
outer-most loci (not shown) of a rotating system including a crankshaft 34 
and connecting rods (not shown). An oil pan (not shown) will be secured to 
the bottom edge of the skirt section 32, so that a crankcase inner chamber 
36 is defined between the skirt section 32 and the oil pan. 
A plurality of main bearing bulkheads 38 are integrally connected to the 
inner wall of the skirt section 32 in a manner to divide the crankcase 
inner chamber 36 into a plurality of sections along the axis of the 
cylinder block or the crankshaft 34. Each bearing bulkhead 38 is formed at 
its lower central part with a main bearing section 40 for rotatably 
supporting the journal of the crankshaft 34. 
As shown, each bearing bulkhead 38 is further formed with another bearing 
section 42A(42B) for supporting a rotatable shaft (not shown) except for 
the crankshaft 34. The rotatable shaft is, for example, a drive shaft for 
driving an engine accessory such as an oil pump, or a camshaft for 
operating intake and exhaust valves. The bearing section 42A(42B) is 
generally annular and defines thereinside a simple opening through which 
the rotatable shaft is rotatably disposed. 
Additionally, the annular bearing sections 42A, 42B of the oppositely 
located bearing bulkheads 38 are connected by a generally cylindrical 
hollow beam member 44A(44B, 44C) so that the openings of the annular 
bearing sections 42A, 42B merge into the inside opening of the hollow beam 
member 44B. The hollow beam member 44B is formed integrally with the 
bearing bulkheads 32 and so disposed as to cover the rotatable shaft which 
is rotatably supported by the bearing sections 42A, 42B. It will be 
understood that the other cylindrical beam members 44A, 44C are disposed 
in the same manner as in the hollow beam member 44B. 
As best shown in FIG. 2B, the hollow beam members 44A, 44B, 44C are so 
aligned that their axes lie on a straight line which extends along the 
axis of the cylinder block 20 and the crankshaft 34, i.e. in the direction 
of the row of the cylinder barrels 22, so that the aligned hollow beam 
members serve as a straight hollow beam structure which is located in the 
vicinity of the lower block deck 26 and extends along the cylinder block 
axis or the row of the cylinder barrels. It will be appreciated that the 
hollow beam members 44A, 44B, 44C are produced integrally with the block 
skirt section 32 and the bearing bulkheads 38 during casting of the 
cylinder block 20. 
In this instance, the cylindrical beam member 44A (44B, 44C) is generally 
in the shape of a cylinder having an inner diameter of not less than 30 mm 
and a basic thickness of not less than 4 mm. Besides, the cylindrical beam 
member 44A (44B, 44C) is formed with a rectangular opening 46A (46B, 46C) 
at the wall facing to the crankcase inner chamber 36, which rectangular 
opening serves to prevent interference of the outermost rotation loci of 
the rotating system including the crankshaft 34 and the connecting rods 
with the beam member 44A (44B, 44C), and to allow lubricating oil to drop 
therethrough. The beam members 44A, 44B, 44C are not limited in the shape 
having a generally annular section, and accordingly may be of the shape of 
a plygonal cylinder. The reference numeral 48 denotes an oil passage from 
which lubricating oil is supplied through an oil supply passage 50 to the 
main bearing sections 40. 
Thus, since the cylinder block 20 is so constructed and arranged that the 
straight hollow beam structure extends along the cylinder block axis in 
such a manner as to pierce the crankcase inner chamber 36, the cylinder 
block 20 is improved in its flexural rigidity in the direction of the 
cylinder block axis and in its torsional rigidity around the crankshaft 
axis. Furthermore, in this instance, the straight hollow beam structure is 
disposed in the vicinity of the lower block deck 26, and therefore the 
structure and lower block deck constitute a so-called double-wall 
construction, thereby further improving the rigidity of the lower block 
deck 26. 
As a result, deformation of the cylinder block 20 due to flexure in the 
cylinder block axis and to torsion around the crankshaft axis is 
suppressed, thereby greatly decreasing the vibration of the block skirt 
section 32 and the oil pan which vibration is generated by repeated input 
of the above-mentioned flexure and torsion. This noticeably suppresses 
vibration noise emitted from the cylinder block 20. 
Moreover, the beam members 44A, 44B, 44C are hollow and therefore the 
rigidity of the cylinder block can be increased without a considerable 
weight increase. In other words, it becomes possible to decrease the 
thickness of the cylinder block wall by an amount corresponding to the 
above-mentioned rigidity increase, thereby resulting in the 
weight-lightening of the engine. 
As will be appreciated from the above, according to the present invention, 
the cylinder block is provided with a hollow beam structure which is 
constructed upon employing the bearing sections for supporting the 
rotatable shaft except for the crankshaft. The hollow beam structure is 
formed in such a manner as to pierce the crankcase inner chamber in the 
direction of the cylinder block axis. Therefore, the rigidity of the 
cylinder block is improved in flexural and torsional rigidity in the 
cylinder block axis direction, without a noticeable weight increase of the 
cyliner block. This lowers the vibration level of the whole cylinder 
block, thus effectively lowering engine noise.