LOW NOISE LEVEL INTERNAL COMBUSTION ENGINE

Abstract: An internal combustion engine (10) comprises a cylinder block having a skirt section (14), main bearing bulkheads (16), each bearing bulkhead being formed with a bearing section (16a) for receiving a crankshaft and including an upper part (16b) located above the level of the crankshaft axis, and a lower part (16c) located below the crankshaft axis level; and a main bearing cap (20) securely connected to each bearing bulkhead for being associated with the bulkhead bearing section (16a) so as to rotatably support the crankshaft. The engine is characterized by a damping member (26) made of a material which is of high damping capacity and oil- and heat-resistance, the damping member being disposed between the bearing bulkhead lower part (16c) and the bearing cap (20). The invention is useful for effectively damping the vibration of the bearing cap (20) in order to achieve noise reduction of the cylinder block skirt section.

Description: Low noise level internal combustion engine This invention relates to a low noise level internal combustion engine, and more particularly to an improvement in an automotive internal combustion engine for the purpose of decreasing noise emitted from the engine. In connection with prior art automotive internal combustion engines using a cylinder block of the so-called deep skirt type wherein a skirt section, forming there inside a part of the crankshaft bearing structure, extends downwardly below the level of the axis of the crankshaft, the skirt section tends to readily vibrate laterally or in the inward and outward direction during engine operation, thereby emitting considerable noise. Additionally, the thus vibrated skirt section excites an oil pan which is securely connected to the bottom edge of the skirt section, to allow the oil pan to emit vibration noise. It was confirmed that such skirt section vibration was mainly originated from the vibration of bearing caps which are secured to bearing sections of main bearing bulkheads integral with the skirt section at a part located below the level of the crankshaft axis, said bulkheads including an upper part and a lower part located above and below said axis, respectively. The object of the present invention is to obviate to such inconveniences in an internal combustion engine of the type comprising : a cylinder block which has a skirt section extending downwardly ; a plurality of main bearing bulkheads integral with the skirt section, each bearing bulkhead being formed with a bearing section for rotatably receiving the journal of a crankshaft and including an upper part located above the level of the axis of the crankshaft, and a lower part located below the level of the crankshaft axis and integrally connected to the skirt section at a part located below the level of crankshaft axis ; and a main bearing cap securely connected to each bearing bulkhead for being associated with the bearing section of the bearing bulkhead so as to rotatably support the crankshaft journal. The problem set is solved in accordance with the present invention by the provision of a damping member made of a material which is of high damping capacity and oil- and heat-resistance and disposed between the bearing bulkhead lower part and the bearing cap. With the thus arranged engine, by virtue of the connection between the bearing cap and the bearing bulkhead lower part through the damping member, the vibration of the bearing cap is largely damped, thereby effectively suppressing the vibration of the cylinder block skirt section. The features and advantages of the internal combustion engine according to the present invention will be more clearly appreciated from the following description taken in conjunction with the accompanying drawings given by way of merely illustrative examples only, in which like reference numerals designate the corresponding parts and elements, and in which Figure 1 is a vertical sectional view of a lower part of a conventional automotive internal combustion engine. Figure 2 is a perspective view of a model showing the vibrational state of each bearing bulkhead and its vicinity during their resonance vibration, in connection with the conventional engine. Figure 5 is a vertical sectional view of a lower part of a presently preferred embodiment of an internal combustion engine according to the present invention. Figure 4A is an enlarged sectional view taken in the direction of arrows substantially along the line 4-4 of Figure 3, showing the relationship between a damping member and its vicinity. Figure 4B is an enlarged sectional view similar to Figure 4A, but showing another example of the relationship between the damping member and its vicinity. Figure 5A is a wave form chart of the vibration of the bearing cap of the conventional engine of Figure 1. Figure 5B is a wave form chart of the vibration of the bearing cap of the engine according to the present invention of Figure 3. Figure 6 is a vertical sectional view of an essential part of another embodiment of the engine according to the present invention. And Figure 7 is a vertical sectional view similar to Figure 6, but showing a further embodiment of the engine according to the present invention. To facilitate understanding the present invention, a brief reference will be made to a conventional automotive internal combustion engine, depicted in Figure 1. Referring to Figure 1, the conventional engine includes a cylinder block 1 of the so-called deep skirt type wherein a skirt section 2 extends downwardly below the level of the axis of a crankshaft (not shown). The cylinder block 1 is provided with a plurality of main bearing bulkheads 3 which are integral with the inside walls of the skirt section 2. Each bearing bulkhead 3 is formed with a bearing section which associates with a bearing cap 4 so as to rotatably support the crankshaft journal therebetween. The bearing bulkhead 3 includes an upper part Sa located above the level of the crankshaft axis, and a lower part 3b located below the crankshaft axis level and integrally connected to the skirt section bottom part located below the crankshaft axis level. The bulkhead lower part 3b is usually called a "skirt truss part" and functions to diagonally connect the skirt section bottom part with a bulkhead bearing cap installation portion 5 to which the bearing cap 4 is secured. The skirt section bottom part is provided with a flange 6 to which an oil pan 7 is fixedly connected. With the thus arranged conventional engine, the top section of the bearing cap 4 is rigidly secured to the bearing cap installation portion 5 which is in turn rigidly integrally connected at its top with a lower block deck and at its sides with the skirt section 3. Therefore, the bearing bulkhead 3 and the bearing cap top portion are prevented from their severe vibrating. However, the bottom section of the bearing cap 4 is free from any restraint and subsequently tends to cause resonance vibration which originates from the central part of the bearing cap bottom section. Considering a model shown in Figure 2, the bottom section of the model vibrates with a much higher amplitude L2 than that L1 of the top section thereof. Accordingly, each bearing cap readily vibrates in the forward and rearward direction, which causes the skirt section to be deformed so as to vibrate laterally or in the open-and-close direction. Thus, the skirt section 2 itself generates high level noise and additionally excites the oil pan 7, thereby causing the oil pan 7 to emit noise. In view of the above description of the conventional automotive internal combustion engine arrangement, reference is now made to Figures 7 to 7, and more specifically to Figures 3 and 4A, wherein a presently preferred embodiment of an internal combustion engine according to the present invention is denoted by the reference numeral 10. The engine 10 is used, for example, for an automotive vehicle and comprises a cylinder block 12 which includes a skirt section 14. The skirt section 14 is as usual bulged laterally or outwardly and extends downward to define therein side a space forming an upper part of a crankcase. A plurality of main bearing bulkheads 16 are located inside of the skirt section 14 and integrally connected at their side sections with the inner wall of the skirt section 14 and at their top section with a lower block deck 18. Each bearing bulkhead 16 is formed with a bearing section or bearing cap installation section 16a to which a main bearing cap 20 is secured by means of bolts (without reference numeral to define therebetween a bore 22 for rotatably receiving the journal of a crankshaft (not shown). The bearing bulkhead 16 includes an upper part 16b, and a lower part 16c. The upper part 16b is located above the level of the axis of the crankshaft or the axis of the bore 22, whereas the lower part 16c is located below the level of the crankshaft axis. As shown, the bearing bulkhead lower part 16c includes two counterparts C1, C2 which are located symmetrically to each other with respect to the main bearing cap 20 and the bore 22 so that the main bearing cap 20 is interposed between the two opposite counterparts C1, C2 of the bearing bulkhead lower part 16c. Each counterpart C1, C2 is integrally connected to the inner wall of the skirt section at the lower part which is considerably below the level of the axis of the crankshaft. In this regard, this cylinder block 12 is of the so-called deep skirt type. Each counterpart C1, C2 is in the shape which is formed by inwardly and downwardly projecting a conventional "skirt truss part" in a manner to approach the main bearing cap 20. The counterpart C1, C2 of the bearing bulkhead lower part 16c is formed with a side surface 16d which is generally vertical and close to the vertical side surface 20a of the bearing cap 20 to form therebetween a slit 24. Disposed within the slit 24 is a damping member 26 made of a material which is of high damping capacity, such as oil- and heat-resisting rubber or the like. The damping member 26 is fixedly secured in position by any suitable means. In order to ensure the securing of the damping member 26 in position, the bearing cap 20 and the bearing bulkhead lower part 16c may be formed at respective side surfaces 20a, 16d with oppositely disposed vertical grooves 28, 30 which are entered by a part of the damping member 26 as clearly shown in Figure 4B. It anll be understood that the damping member 26 may be previously stuck on either one of the bearing cap side surface 20a and the bearing bulkhead lower part vertical surface 16d by, for example, baking the damping member thereon. The damping member 26 may be made of foam metal. As shown in Figure 3, the skirt section 14 is provided at its bottom with oppositely disposed flanges 14a to which an oil pan (not shown) is fixedly attached. The advantageous effect of the present invention will be now discussed with reference to Figures 5A and 53. In case of the conventional engine arrangement shown in Figure 1, an impact force (indicated by an arrow F) due to combustion in engine cylinders is applied to the bearing cap 4 ; the resonance vibration of the bearing cap 4 occurs, thereby vibrating the skirt section 2. As shown, this resonance vibration of the bearing cap 4 is gradually damped under the damping action of the structure of the cylinder block and under the internal damping action of the material of the bearing bulkhead 3. On the contrary, in case of the engine arrangement in accordance with the present invention, since the damping member 26 is interposed between the bearing bulkhead lower part 16c and the bearing cap 20, the vibration energy of the bearing cap 20 is converted into thermal energy in the damping member 26 by the relative displacement between the bearing cap 20 and the bearing bulkhead lower part 16c, so that the resonance vibration of the bearing bulkhead 16 is abruptly damped as shown in Figure 5B. At this stage, since a great damping is effected on the bearing cap 20 located at the bottom end of the bearing bulkhead 16 which bottom end is of higher vibration amplitude, the vibration of the bulkhead 16 as a whole is effectively damped. Accordingly, the vibration input level to the skirt section 14 is decreased to become lower, thereby lowering the vibration level of the skirt section 14. This decreases noise generation not only at the skirt section 14 itself but also at the oil pan due to the fact that the vibration input level to the oil pan is also lowered. Figure 6 illustrates another embodiment of the engine according to the present invention, in which the slit 24 is formed to widen itself downwardly or in the vertical direction away from the level of the crankshaft axis in order to facilitate the insertion of the damping member 26 thereinto. The slit 24 of this shape is formed, for example, by inclining the opposite surfaces 16d, 20a of the bearing bulkhead lower part 16c and the bearing cap 20 relative to a vertical plane (not shown) containing the axes of the engine cylinders (not shown). In this case, the damping member 26 is supported by a support member 32 which serves also as a washer for the bolt for securing the bearing cap onto the bearing bulkhead 16, for the purpose of ensuring the support of the damping member in position. Figure 7 shows a further embodiment of the engine according to the present invention which is similar to the embodiment of Figure 6 With the exception that the bearing cap 20 is provided at both respective opposite side surfaces thereof with two projections 34. Each projection 34 projects laterally and outwardly toward the bearing bulkhead lower part 16c. In this case, it will be understood that it is necessary to previously stick the damping member 26 to the bearing cap 20 or to the projection 34. As appreciated from the above, according to the present invention, the damping member made of oil- and heat-resisting rubber or the like is inserted between the so-called skirt truss part and the bearing cap side, and therefore the forward-and-rearward vibration of the crankshaft bearing section is abruptly damped, thereby effectively lowering the open-andclose vibration of the cylinder block skirt section. This greatly contributes to noise reduction of the cylinder block skirt section and other covers connected to the cylinder block.

Claims: Claims 1. Internal combustion engine (10) comprising a cylinder block (12) having a skirt section (14) extending downwardly, a plurality of main bearing bulkheads (16) integral with said skirt section, each bearing bulkhead (16) being formed with a bearing section (16a) for rotatably receiving the journal of a crankshaft, said bearing bulkhead including an upper part (16b) located above the level of the axis of the crankshaft, and a lower part (16c) located below the level of the axis of the crankshaft and integrally connected to said skirt section (14) at a part located below the level of the crankshaft axis ; and a main bearing cap (20) securely connected to each bearing bulkhead for being associated with the bearing section (1spa) of each bearing bulkhead so as to rotatably support the crankshaft journal ; and being characterized by a damping member (26) made of a material which is of high damping capacity and oil- and heat-resistance, said damping member (26) being disposed between said bearing bulkhead lower part (16c) and said bearing cap (20). 2. Internal combustion engine according to claim 1, characterized in that said bearing bulkhead lower part (16c) is formed with a side surface (16d) which is opposite to a side surface (20a) of said bearing cap to define therebetween a slit (24) within which said damping member (26) is securely located. 3. Internal combustion engine according to claim 2, characterized in that said side surface (16d) of said bearing bulkhead lower part is generally parallel to the side surface (20a) of said bearing cap. 4. Internal combustion engine according to claim 2, characterized in that said side surface (16d) of said bearing bulkhead is inclined relative to said side surface of said bearing cap to define therebetween said slit (24) which widens itself in the downward and vertical direction. 5. Internal combustion engine according to claim 2, characterized in that said bearing bulkhead lower part (16c) and said bearing cap (20) are formed at said side surface (16d, 20a) thereof with opposite grooves (30, 28), respectively, into which the damping member (26) is insertable. 6. Internal combustion engine according to claim 4, characterized by further comprising a support member (32) which serves as a washer of a bolt for securing said bearing cap (20) onto said bearing bulkhead, said support member (32) being disposed between the bottom surface of said bearing cap and the head of said bolt, said support member (32) extending toward said bearing bulkhead lower part (16c) to support said damping member (26) within said slit (24). 7. Internal combustion engine according to claim 4, characterized in that said bearing cap (20) is formed at its side surface (20a) with a projection (34) extending toward said bearing bulkhead lower part (16c) to support said damping member (26) within said slit (24).

Inventors: ISHIBASHI, HIDEO, KIKUCHI, KAZUHIRO
Applicants: NISSAN MOTOR CO., LTD.
Application year: 1982
Main classification: F02F7
IPC codes: F16C9, F16M1, F02F7