Vibration damping structure for engine

Abstract

To provide a vibration damping structure for an engine capable of effectively damping vibration in a multi-cylinder reciprocating engine.SOLUTION: An engine includes a plurality of cylinders disposed in series. The engine also includes: a plurality of pistons; a crank shaft; a cylinder block having a plurality of crank journal parts that journal the crank shaft; and a dynamic damper 80 mounted to a lower part of at least one of the crank journal parts in the cylinder block. The dynamic damper 80 integrally includes: a fixation part 800 mounted to a lower part of the crank journal part and extending downwardly in a Z direction; and a beam part 801 connected to a lower part of the fixation part 800 and extending in an X direction; and two mass parts 802, 803 connected at connection parts 801a, 801b on one side and the other side in the X direction of the beam part 801, respectively and each extending in a Y direction while separating from each other in the X direction.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a vibration damping structure of an engine, and particularly to a vibration damping structure of a multi-cylinder reciprocating engine.

Background Art

[0002] In a multi-cylinder reciprocating engine mounted on a vehicle, vibration occurs during driving. The vibration generated by the engine is propagated as radiated sound into the passenger compartment through a transmission or the like. From the viewpoint of ensuring the comfort of the passengers, it is required to suppress the propagation of the radiated sound into the passenger compartment.

[0003] As a measure to suppress the propagation of the radiated sound into the passenger compartment, it is conceivable to cover the entire engine with a sound insulation material. By covering the entire engine with a sound insulation material, it is possible to reduce the sound radiated to the outside of the engine at all frequencies. However, it is difficult to insulate the sound to the target level at some resonance frequencies only by covering the engine with a sound insulation material.

[0004] As a measure to reduce the level at some resonance frequencies as described above, for example, Patent Document 1 proposes the following structure.

[0005] Patent Document 1 discloses a structure in which a plurality of main bearing caps are integrally connected by an integral beam, and an inertia mass is attached to the integral beam via an elastic member. In Patent Document 1, by attaching the inertia mass to the integral beam as described above, it is said that the engine vibration can be effectively reduced without increasing the dimensions and weight of the integral beam itself.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the vibration damping structure disclosed in Patent Document 1, the vibration of the engine cannot be sufficiently damped, and there may be a case where the radiated sound is propagated into the passenger compartment. That is, in the structure disclosed in Patent Document 1, since only one inertial mass is attached via an elastic member below the integral beam, there is considered to be a vibration mode that is difficult to damp.

[0008] The present invention has been made to solve the above problems, and an object thereof is to provide a vibration damping structure for an engine that can effectively damp the vibration in a multi-cylinder reciprocating engine.

Means for Solving the Problems

[0009] A vibration damping structure for an engine according to an aspect of the present invention is a vibration damping structure for an engine including a plurality of cylinders arranged in series, including pistons reciprocally fitted to each of the plurality of cylinders, and when the top dead center side of the piston in the cylinder axis direction is up and the bottom dead center side is down, a crankshaft that is disposed below the piston and is connected to the piston via a connecting rod and rotates, a cylinder block disposed below the crankshaft and having a plurality of crank journal portions that support the crankshaft between adjacent cylinders in the crankshaft, and a dynamic damper attached to a lower portion of at least one crank journal portion in the cylinder block. The dynamic damper includes a fixing portion attached to the lower portion of the crank journal portion and extending downward from the lower portion, a beam portion connected to the lower portion of the fixing portion and extending in the cylinder row direction, which is the arrangement direction of the plurality of cylinders, and two mass portions connected to each other at connection portions on one side and the other side in the cylinder row direction of the beam portion and each extending in the intake and exhaust direction of the engine while being separated from each other in the cylinder row direction.

[0010] In the vibration damping structure of the engine according to the above aspect, a dynamic damper having a fixed part, a beam part, and two mass parts integrally is attached to the lower part of the crank journal in the cylinder block. And the two mass parts are connected at each connecting part of the beam part and are formed to extend in the intake / exhaust direction. For this reason, even when vibrations having amplitudes in the cylinder axis direction and the intake / exhaust direction occur in the crankshaft as the engine is driven, the vibration energy is input to the dynamic damper via the crank journal and consumed by the dynamic damper. Specifically, when the vibration energy is input to the dynamic damper, the beam part is deformed in the cylinder axis direction by the vibrations of the two mass parts, consuming the vibration energy in the vertical direction (cylinder axis direction), and is deformed in the intake / exhaust direction, also consuming the vibration energy in the intake / exhaust direction.

[0011] Therefore, in the vibration damping structure of the engine according to the above aspect, not only the vibration energy in the cylinder axis direction is consumed as in the structure disclosed in Patent Document 1, but also the vibration energy in both the vertical direction and the intake / exhaust direction can be consumed. From this, in the vibration damping structure of the engine according to the above aspect, vibrations in a multi-cylinder reciprocating engine can be attenuated more effectively than before, and the resonance peak of the vibrations can be suppressed low.

[0012] In the vibration damping structure of the engine according to the above aspect, the fixed part may have a column shape, and when assuming a virtual plane passing through the column center in the fixed part and orthogonal to the cylinder row direction, the dynamic damper may have a shape symmetric with respect to the virtual plane.

[0013] In the vibration damping structure of the engine according to the above aspect, since the dynamic damper is configured to be symmetric with respect to the virtual plane, the beam part and the mass part can be vibrated in antiphase with respect to torsional and bending deformations, which is effective for suppressing the resonance peak associated with the vibration of the crankshaft low.

[0014] In the engine vibration damping structure according to the above aspect, when the beam portion and the two mass portions are viewed from the side in one of the intake and exhaust directions, the beam portion may be formed such that the thickness dimension in the vertical direction of the beam portion is smaller than the thickness dimension in the vertical direction of each of the two mass portions.

[0015] In the engine vibration damping structure according to the above aspect, since the thickness dimension of the beam portion in the dynamic damper is made smaller than the thickness dimension of the mass portion, when vibration energy from the crankshaft is input into the dynamic damper via the crank journal, both mass portions are likely to deform with the connection portion as a fulcrum. Therefore, in the engine vibration damping structure according to the above aspect, the vibration of the crankshaft can be more effectively consumed by the dynamic damper, and it is more effective in suppressing the resonance peak to a low level.

[0016] In the engine vibration damping structure according to the above aspect, when the beam portion and the two mass portions are viewed from the side in one of the intake and exhaust directions and when viewed from the plane in one of the vertical directions, the beam portion and the two mass portions may both form an H shape.

[0017] In the engine vibration damping structure according to the above aspect, since the dynamic damper is configured such that the beam portion and the mass portion both form an H shape when viewed from the side and when viewed from the plane, when vibration energy is input from the crankshaft, the mass portion can be easily deformed with the connection portion as a fulcrum. For this reason, in the engine vibration damping structure according to the above aspect, the vibration of the crankshaft can be more effectively consumed by the dynamic damper, and it is more effective in suppressing the resonance peak to a low level.

[0018] In the engine vibration damping structure according to the above aspect, the dynamic damper may be formed using cast iron.

[0019] In the engine vibration damping structure according to the above aspect, since the dynamic damper is formed using cast iron, vibration energy can be effectively consumed even with a small occupied volume. This is because the specific gravity of cast iron is significantly higher, at about 7.0, compared to the specific gravity of about 2.7 of the aluminum alloy used as the forming material for the cylinder block and the like. Therefore, in the engine vibration damping structure according to the above aspect, while realizing high space efficiency, the vibration of the crankshaft can be more effectively consumed by the dynamic damper.

[0020] In the engine vibration damping structure according to the above aspect, it may further include a flywheel fixed to one end of the crankshaft, and the dynamic damper may be attached to the cylinder block at only one position offset to the other end side of the crankshaft from the central position of the cylinder block in the cylinder bank direction.

[0021] In the engine vibration damping structure according to the above aspect, since only one dynamic damper is attached at a position offset to the other end side (the side opposite to the side where the flywheel of the crankshaft is fixed) from the central position of the cylinder block in the cylinder bank direction, vibration can be effectively suppressed while suppressing an increase in engine weight and engine size. That is, since a flywheel is fixed to one end of the crankshaft, the crankshaft vibrates with a large amplitude at the portion on the other end side (the side opposite to the side where the flywheel is fixed) from the longitudinal center. Therefore, by attaching a dynamic damper below the portion where the crankshaft vibrates with a large amplitude, vibration energy can be effectively consumed.

Effect of the Invention

[0022] In the engine vibration damping structure according to each of the above aspects, vibration in a multi-cylinder reciprocating engine can be effectively attenuated.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0024] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the embodiments described below are illustrative of the present invention, and the present invention is not limited to the following embodiments except for its essential configuration.

[0025] In the figures used in the following description, the "X direction" is the cylinder row direction in which a plurality of cylinders in the engine are arranged, the "Y direction" is the intake / exhaust direction which is the direction between the intake side and the exhaust side in each cylinder of the engine, and the "Z direction" is the cylinder axis direction in which the piston reciprocates in each cylinder of the engine. Further, in the Z direction, the "+Z side" which is the top dead center side of the piston is referred to as "up", and the "-Z side" which is the bottom dead center side is referred to as "down".

[0026] 1. Structure of Engine 1 The configuration of the engine 1 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. Note that in FIG. 1, illustration of the upper cylinder block, cylinder head, head cover, oil pan, etc. in the engine 1 is omitted.

[0027] As shown in FIG. 1, the engine 1 is an in-line six-cylinder reciprocating engine, and six cylinders 1a to 1e are provided in the X direction. In the following description, from the +X side toward the -X side, they are referred to as cylinder #1 1a, cylinder #2 1b, cylinder #3 1c, cylinder #4 1d, cylinder #5 1e, and cylinder #6 1f.

[0028] The engine 1 includes pistons 11 to 16 that reciprocate in the Z direction in each cylinder 1a to 1f. Connecting rods 21 to 26 are connected to each of the pistons 11 to 16.

[0029] The connecting rods 21 to 26 are pivotally supported by crank pins 43 to 48 of the crankshaft 30 in a rotatable state at their lower portions. Crank webs 33 to 42 are disposed on the +X side and -X side of each of the crank pins 43 to 48.

[0030] The crankshaft 30 is rotatably supported by a combination of crank journal portions 61 to 67 disposed on the -Z side of the crankshaft 30 and bearing caps 71 to 77 attached to each of the crank journal portions 61 to 67.

[0031] The crank journal parts 61 to 67 and the bearing caps 71 to 77 are arranged on the +X side of the #1 cylinder 1a and the -X side of the #6 cylinder 1f, and between the respective cylinders 1a to 1e. Hereinafter, regarding the crank journal parts 61 to 67, from the +X side toward the -X side, they are called the #1 crank journal part 61, the #2 crank journal part 62, the #3 crank journal part 63, the #4 crank journal part 64, the #5 crank journal part 65, the #6 crank journal part 66, and the #7 crank journal part 67.

[0032] Here, in the engine 1 of the present embodiment, the seven crank journal parts 61 to 67 are integrally formed with the lower cylinder block 60.

[0033] With respect to the crankshaft 30, a pulley 51 is fixed to the end on the +X side, and a flywheel 52 is fixed to the end on the -X side. When the engine 1 is mounted vertically in the engine room of a vehicle, it is arranged such that the side to which the pulley 51 is fixed is the front side of the vehicle, and the side to which the flywheel 52 is fixed is the rear side of the vehicle.

[0034] As shown in FIGS. 1 and 2, a dynamic damper 80 is attached to the lower part (-Z side) of the #3 crank journal part 63 in the lower cylinder block 60. The attachment of the dynamic damper 80 to the lower cylinder block 60 is made, for example, by fastening using bolts 81.

[0035] Note that the central position of the lower cylinder block 60 in the X direction is the location where the #4 crank journal portion 64 is arranged. In this embodiment, the dynamic damper 80 is arranged offset to the +X side (the side where the pulley 51 is fixed to the crankshaft 30) with respect to the central position of the lower cylinder block 60 in the X direction. The reason for this is that when the engine 1 is driven, the amplitude of the shaft vibration on the side where the flywheel 52 is fixed to the crankshaft 30 is smaller than that on the side where the pulley 51 is fixed. That is, the crankshaft 30 has higher rigidity due to the fixing of the flywheel 52 on the side where the flywheel 52 is fixed, so the amplitude of the shaft vibration is suppressed to be smaller on the -X side than the central position.

[0036] 2. Structure of the dynamic damper 80 The structure of the dynamic damper 80 will be described with reference to FIGS. 3 to 5.

[0037] The dynamic damper 80 is formed using cast iron as an example. As shown in FIGS. 3 to 5, it has a fixing portion 800, a beam portion 801, and two mass portions 802, 803. The fixing portion 800 is attached to the lower part of the #3 crank journal portion 63 in the lower cylinder block 60 and is formed to extend in the Z direction. The fixing portion 800 has a columnar shape with an outer peripheral surface formed as a curved surface. And the fixing portion 800 has a through hole 800a through which the threaded portion of the bolt 81 (see FIGS. 1 and 2) can be inserted, and a pin hole 800b for receiving the insertion of a pin for preventing rotation with respect to the lower cylinder block 60.

[0038] The beam portion 801 is connected to the fixing portion 800 on the -Z side and is formed to extend in the X direction. The beam portion 801 has a flat plate shape or a prismatic shape and is formed to protrude beyond the fixing portion 800 on both the +X side and the -X side.

[0039] The two mass portions 802 and 803 each have a prismatic shape and are formed to extend in the Y direction. The mass portion 802 is connected to the beam portion 801 at the connection portion 801a. The mass portion 803 is connected to the beam portion 901 at the connection portion 801b. That is, the mass portion 802 and the mass portion 803 are arranged to be separated by the length of the beam portion 801 in the X direction. Note that each of the mass portions 802 and 803 is formed such that the +Y side and the -Y side from the connection portions 801a and 801b have substantially the same mass (allowing a difference of about 8 g).

[0040] Here, as shown in FIGS. 3 to 5, assume a virtual plane VP passing through the column center in the fixing portion 800 and orthogonal to the X direction. In this case, as shown in FIGS. 4 and 5, the dynamic damper 80 has a shape symmetric with respect to the virtual plane VP. And as shown in FIG. 4, when the beam portion 801 and the mass portions 802 and 803 are viewed from the -Y side in side view, the beam portion 801 and the mass portions 802 and 803 are formed to have an H shape.

[0041] Also, as shown in FIG. 5, when the beam portion 801 and the mass portions 802 and 803 are viewed from the -Z side in plan view, the beam portion 801 has a shape symmetric with respect to the virtual plane VP in the X direction, and the mass portion 802 and the mass portion 803 have shapes symmetric with respect to each other in the X direction with respect to the virtual plane VP. And as shown in FIG. 5, also in the plan view from the -Z side, the beam portion 801 and the mass portions 802 and 803 are formed to have an H shape.

[0042] 3. Sizes of the Beam Portion 801 and the Mass Portions 802 and 803 The sizes of the beam portion 801 and the mass portions 802 and 803 in the dynamic damper 80 will be described with reference to FIG. 6. Note that in FIG. 6, only the mass portion 803 of the two mass portions 802 and 803 is shown, but the size relationship of the mass portion 802 with respect to the beam portion 801 is the same.

[0043] As shown in FIG. 6, the beam portion 801 is connected to the mass portion 803 at the connection portion 801b. The connection portion 801b is arranged to include the centroid position of the mass portion 803 in the Y direction. The beam portion 801 is formed with a size (width) of W in the Y direction and a size (height) of H in the Z direction.

[0044] On the other hand, the mass portion 803 is formed with a size of W0 in the Y direction and a size of H0 in the Z direction. The mass of the mass portion 803 is set based on the magnitude of the amplitude at the resonance frequency. As an example, the mass of the mass portion 803 is set within the range of 250 g to 350 g. More specifically, the mass of the mass portion 803 is set within the range of 275 g to 300 g.

[0045] In the dynamic damper 80, the sizes H, W of the beam portion 801 with respect to the sizes H0, W0 of the mass portion 803 are set based on the frequency of the resonance peak to be reduced. As an example, the ratio of W / WO is set within the range of 1 / 10 to 1 / 3, and more specifically within the range of 1 / 5 to 1 / 4.

[0046] Also, the ratio of H / H0 is set within the range of 1 / 5 to 1 / 2, and more specifically within the range of 1 / 4 to 2 / 5.

[0047] 4. Bottom Surface Shape of Dynamic Damper 80 and Peripheral Members The relationship between the shape of the bottom surface 80a of the dynamic damper 80 and the peripheral members will be described with reference to FIG. 7. Note that FIG. 7 is a rear view of the dynamic damper 80 and the peripheral members from the -X side, and the illustration of the beam portion 801 and the mass portion 802 of the dynamic damper 80 is omitted.

[0048] First, the engine 1 according to the present embodiment is mounted vertically in an engine room provided at the front part of the vehicle. And the target vehicle is a four-wheel drive vehicle and includes a front drive shaft 91 extending in the vehicle width direction in the engine room. For this reason, the oil pan 90 has a shaft insertion portion 90a through which the front drive shaft 91 is inserted. The axis Ax91 of the front drive shaft 91 inserted through the shaft insertion portion 90a is arranged along the vehicle width direction.

[0049] Next, the engine 1 is arranged to be inclined such that the intake side (+Y side) is positioned above the exhaust side (-Y side). For this reason, also with respect to the oil pan 90 attached to the lower part of the lower cylinder block 60 (refer to FIG. 1 etc.), the upper surface is inclined (inclined line LN90).

[0050] As shown in FIG. 7, the dynamic damper 80 is arranged above the shaft insertion portion 90a formed in the oil pan 90. For this reason, the lower surface 80a of the dynamic damper 80, that is, the lower surface of the mass portions 802, 803 (in FIG. 7, the illustration of the mass portion 802 is omitted) in the dynamic damper 80 is arranged to be substantially parallel to the outer surface of the upper part of the shaft insertion portion 90a so as to avoid interference with the outer surface of the shaft insertion portion 90a. For this reason, when a virtual line LN80 along the lower surface 80 of the dynamic damper 80 is drawn, the virtual line LN80 is substantially parallel to the axis Ax91 of the front drive shaft 91 and is arranged in a direction intersecting the inclined line LN90 at an acute angle.

[0051] 5. Control according to the operating state of the engine 1 The control according to the operating state of the engine 1 will be described with reference to FIG. 8.

[0052] The engine 1 according to the present embodiment is drive-controlled by a PCM (Power Control Module). The PCM has a microprocessor that executes arithmetic processing and a memory in which maps for each operation region are stored in advance. FIG. 8 is a diagram showing an operation map for explaining the difference in combustion control according to the rotational speed and load of the engine 1.

[0053] As shown in FIG. 8, the operating region of the engine 1 is roughly divided into two operating regions A1 and A2 according to the difference in combustion modes. Assuming the first operating region A1 and the second operating region A2 respectively, the second operating region A2 is a high-speed region where the rotational speed of the engine 1 exceeds the first rotational speed N1, and the first operating region A1 is a low- and medium-speed region where the rotational speed of the engine 1 is equal to or less than the first rotational speed N1. The outline of combustion control in each operating region A1 and A2 is as follows.

[0054] (1) First operating region A1 In the first operating region A1 (low- and medium-speed region) where the rotational speed of the engine 1 is equal to or less than the first rotational speed N1, partially premixed charge compression ignition combustion (SPCCI) that combines spark ignition (SI) combustion and compression ignition (CI) combustion is performed.

[0055] SI combustion is a combustion mode in which a mixture is ignited by a spark generated from a spark plug, and the mixture is forcibly combusted by flame propagation that expands the combustion region from the ignition point to the surroundings.

[0056] CI combustion is a combustion mode in which a mixture is combusted by self-ignition in an environment sufficiently heated and pressurized by the compression of pistons 11 to 16.

[0057] SPCCI combustion that combines SI combustion and CI combustion is a combustion mode in which a part of the mixture in the combustion chamber is combusted by spark ignition performed in an environment just before the mixture self-ignites, and then the other mixture in the combustion chamber is combusted (CI combustion) by self-ignition (due to further heating and pressurization accompanying the SI combustion).

[0058] In SPCCI combustion, heat generation by SI combustion and heat generation by CI combustion occur successively in this order. At this time, due to the property that the combustion speed of CI combustion is faster, the rise of heat generation during CI combustion is steeper than that during SI combustion. Therefore, the waveform of the heat generation rate in SPCCI combustion has an inflection point that appears at the timing of switching from SI combustion to CI combustion.

[0059] The crank angle corresponding to the inflection point that appears at the timing of switching from the above SI combustion to CI combustion is defined as the start timing of CI combustion. When driving the engine 1 in the first operation region A1, the PCM that executes the drive control of the engine 1 controls the injection amount and injection timing of combustion by the injector, and the ignition timing by the spark plug so that the start timing of this CI combustion becomes an appropriate timing considering thermal efficiency and the like, and the output of the engine 1 becomes the required value.

[0060] (2) Second operation region A2 In the second operation region A2 (high-speed region) where the rotational speed of the engine 1 is higher than the first rotational speed N1, control is executed to burn the air-fuel mixture by SI combustion. For example, the PCM controls the injector so that the required amount of fuel is mainly injected during the intake stroke, and causes the spark plug to perform spark ignition near top dead center of compression. Then, SI combustion is started triggered by the spark ignition, and all of the air-fuel mixture in the combustion chamber burns by flame propagation.

[0061] 6. Contribution of each of cylinders 1a to 1f to in-vehicle noise Regarding the noise radiated from the engine 1 and propagated into the vehicle interior, the contribution of each of cylinders 1a to 1f will be described with reference to FIG. 9. FIG. 9 is a graph showing the partial pressures of each of cylinders 1a to 1f in the engine 1.

[0062] As shown in Fig. 9, the partial pressure in the #6 cylinder 1f showed the lowest measurement result among the six cylinders 1a to 1f. This is presumably because the flywheel 52 is fixed to the -X side end of the crankshaft 30 extending in the X direction, suppressing the vibration in the -X side portion of the crankshaft 30. Regarding the partial pressure of each of the #1 to #5 cylinders 1a to 1e, it will be described based on the partial pressure of the #6 cylinder 1f.

[0063] The partial pressure in the #1 cylinder 1a showed a measurement result about 40% higher than the partial pressure in the #6 cylinder 1f. Similarly, the partial pressure in the #2 cylinder 1b showed a measurement result about 67% higher, the partial pressure in the #3 cylinder 1c showed a measurement result about 140% higher, the partial pressure in the #4 cylinder 1d showed a measurement result about 67% higher, and the partial pressure in the #5 cylinder 1e showed a measurement result about 87% higher.

[0064] From the above, in the in-line multi-cylinder (in-line 6 cylinders as an example) engine 1, it can be seen that the contribution of the #3 cylinder 1c at a position offset +X side from the center positions of the cylinders 1a to 1f in the X direction (cylinder row direction) is high. Therefore, in the present embodiment, as described above, the dynamic damper 80 is attached to the lower part of the #3 crank journal portion 63 at a position offset +X side (the side where the pulley 51 is fixed to the crankshaft 30) with respect to the center position in the X direction in the lower cylinder block 60.

[0065] 7. Vibration mode of the dynamic damper 80 when the engine 1 is driven The vibration mode of the dynamic damper 80 when the engine 1 is driven will be described with reference to Fig. 10. Fig. 10(a) is a diagram showing the vibration mode in the cylinder axis direction (Z direction), and Fig. 10(b) is a diagram showing the vibration mode in the intake / exhaust direction (Y direction).

[0066] As shown in Fig. 10(a), when vibration energy is input from the crankshaft 30 to the dynamic damper 80 via the lower cylinder block 60 as the engine 1 is driven, the mass portions 802 and 803 vibrate vertically as indicated by the dashed arrow Vz. As a result, the beam portion 801 vibrates in a mode in the cylinder axis direction (Z direction).

[0067] Also, as shown in Fig. 10(b), when vibration energy from the crankshaft 30 is input, the ends of the mass portions 802 and 803 vibrate as indicated by the dashed arrow Vy in directions approaching and separating from each other. As a result, the beam portion 801 vibrates in a mode in the intake / exhaust direction (Y direction).

[0068] 8. Reduction of Engine Radiated Noise for Each Frequency #3 The effect of attaching the dynamic damper 80 having the above structure to the lower part of the crank journal portion 63, that is, the reduction of engine radiated noise, will be described for each frequency with reference to Fig. 11. In the graph of Fig. 11, the engine radiated noise of the engine 1 with the structure of the present embodiment is shown by a solid line, and the engine radiated noise of the engine with a structure in which the dynamic damper 80 is not attached to the engine 1 is shown by a dashed line.

[0069] As shown in Fig. 11, in the case of the comparative example shown by the dashed line, the largest resonance peak was measured near a frequency of 1600 Hz. Also, in the case of the comparative example, a resonance peak was measured near 4000 Hz.

[0070] On the other hand, in the case of the example, the component near 1600 Hz in the engine radiated noise became about 2 dB lower than that of the comparative example. Also, the component near 4000 Hz became about 3 dB lower than that of the comparative example, and no peak appeared.

[0071] 9. ERP in #3 and #4 Crank Journal Portions 63 and 64 An embodiment in which a dynamic damper 80 having the above structure is attached to the lower part of the #3 crank journal portion 63 and a comparative example in which it is not attached will be described with reference to FIG. 12 regarding the Equivalent Radiated Power (ERP) at 1600 Hz in the #3 and 4 crank journal portions 63 and 64. FIG. 12(a) shows the ERP of the embodiment, and FIG. 12(b) shows the ERP of the comparative example.

[0072] As shown in FIG. 12(b), in the comparative example where the dynamic damper 80 having the above structure was not attached to the lower part of the #3 crank journal portion 63, the ERP in the Y direction of the #3 crank journal portion 63 was 55 dBA, the ERP in the Z direction was 62 dBA, and the total of the #3 and #4 crank journal portions 63 and 64 was 63.5 dBA.

[0073] On the other hand, as shown in FIG. 12(a), in the embodiment where the dynamic damper 80 having the above structure was attached to the lower part of the #3 crank journal portion 63, the ERP in the Y direction of the #3 crank journal portion 63 was 35 dBA, the ERP in the Z direction was 42 dBA, and the total of the #3 and #4 crank journal portions 63 and 64 was 55.6 dBA. Comparing FIG. 12(a) and FIG. 12(b), in the embodiment where the dynamic damper 80 was attached to the lower part of the #3 crank journal portion 63, the ERP in the Y direction and the Z direction in the #3 crank journal portion 63 was significantly lower than that in the comparative example. Specifically, in the embodiment, a 20 dBA decrease was observed in both the Y direction and the Z direction compared to the comparative example.

[0074] 10. Effects In the engine 1 according to the present embodiment, as described with reference to FIG. 8, SPCCI combustion is executed in the first operation region A1 (low and medium speed region) where the rotational speed of the engine 1 is equal to or lower than the first rotational speed N1. As a result of intensive studies by the inventors of the present application, it was concluded that knock sound propagation from the engine 1 into the passenger compartment via the transmission becomes a problem with the execution of SPCCI combustion. Then, in order to suppress this knock sound propagation, the engine 1 according to the present embodiment adopted the vibration damping structure as described above.

[0075] In the vibration damping structure of the engine 1 according to the present embodiment, a dynamic damper 80 in which a fixing portion 800, a beam portion 801, and two mass portions 802 and 803 are integrally formed is attached to the lower portion of the crank journal in the lower cylinder block 60 (in the present embodiment, as an example, the lower portion of the #3 crank journal portion 63). The two mass portions 802 and 803 are connected by the respective connecting portions 801a and 801b of the beam portion 801 and are formed to extend in the intake / exhaust direction (Y direction). Therefore, even when vibrations having amplitudes in the cylinder axis direction (Z direction) and the intake / exhaust direction (Y direction) occur in the crankshaft 30 as the engine 1 is driven, the vibration energy is input to the dynamic damper 80 via the #3 crank journal 63 (lower cylinder block 60) and consumed by the dynamic damper 80. Specifically, when the vibration energy is input to the dynamic damper 80, the beam portion 801 is deformed in the Z direction and the Y direction by the vibrations of the two mass portions 802 and 803, and the vibration energy in both directions is consumed.

[0076] Therefore, in the vibration damping structure of the engine 1 according to the present embodiment, not only the vibration energy in the cylinder axis direction is consumed as in the structure disclosed in the above Patent Document 1, but also the vibration energy in both the Z direction and the Y direction can be consumed. Thus, in the vibration damping structure of the engine 1, vibrations in a multi-cylinder (in the present embodiment, as an example, a 6-cylinder) reciprocating engine can be more effectively attenuated than before, and the resonance peak of the vibrations can be suppressed low.

[0077] Further, in the vibration damping structure of the engine 1 according to the present embodiment, the dynamic damper 80 is configured to be symmetric (plane-symmetric) with respect to the virtual plane VP shown in FIGS. 3 to 5. Therefore, it can be made out-of-phase with respect to torsional and bending deformations, which is effective for reducing block bearing resonance and suppressing the resonance peak associated with the vibration of the crankshaft 30 low.

[0078] In addition, in the vibration damping structure of the engine 1 according to the present embodiment, the thickness dimension H of the beam portion 801 in the dynamic damper 80 is made smaller than the thickness dimension H0 of the mass portion (see FIG. 6). Therefore, when the vibration energy from the crankshaft 30 is input to the dynamic damper 80 via the #3 crank journal portion 63, the two mass portions 802 and 803 are likely to deform with the connection portions 801a and 801b as the fulcrums. Thus, in the vibration damping structure of the engine 1, the vibration of the crankshaft 30 can be more effectively consumed by the dynamic damper 80, which is more effective in suppressing the resonance peak to a lower level.

[0079] In addition, in the vibration damping structure of the engine 1 according to the present embodiment, when the beam portion 801 and the mass portions 802 and 803 are viewed in side view and plan view, the dynamic damper 80 is configured to have an H shape in both cases (see FIGS. 4 and 5). Therefore, when vibration energy is input from the crankshaft 30, the mass portions 802 and 803 can be easily deformed with the connection portions 801a and 801b as the fulcrums. For this reason, in the vibration damping structure of the engine 1, the vibration of the crankshaft 30 can be more effectively consumed by the dynamic damper 80, which is more effective in suppressing the resonance peak to a lower level.

[0080] In addition, in the vibration damping structure of the engine 1 according to the present embodiment, since the dynamic damper 80 is formed using cast iron, vibration energy can be effectively consumed even in a small occupied area. This is because the specific gravity of cast iron is significantly higher, at about 7.0, compared to the specific gravity of about 2.7 of the aluminum alloy used as the forming material for the cylinder block 60 and the like. Thus, in the vibration damping structure of the engine 1, while achieving high space efficiency, the vibration during the rotation of the crankshaft 30 can be more effectively consumed by the dynamic damper 80.

[0081] In addition, in the vibration damping structure of the engine 1 according to the present embodiment, only one dynamic damper 80 is attached to a position offset by +X side (the side opposite to the side where the flywheel 52 of the crankshaft 30 is fixed) from the center position of the lower cylinder block 60 in the cylinder row direction (X direction) (#3 crank journal portion 63). Therefore, while suppressing an increase in the weight and size of the engine 1, it is possible to effectively suppress the transmission of vibration into the passenger compartment. That is, since the flywheel 52 is fixed to one end (-X side end) of the crankshaft 30, the crankshaft 30 vibrates with a large amplitude at a portion on the side opposite to the side where the flywheel 52 is fixed (+X side) from the center in the Z direction. For this reason, by attaching the dynamic damper 80 below the portion where the crankshaft 30 vibrates with a large amplitude (in this embodiment, as an example, the #3 crank journal portion 63), it is possible to effectively consume the vibration energy.

[0082] As described above, in the vibration damping structure of the engine 1 according to the present embodiment, it is possible to effectively attenuate the vibration in a multi-cylinder reciprocating engine (in this embodiment, as an example, a 6-cylinder reciprocating engine).

[0083] [Modification Example] In the above embodiment, an in-line 6-cylinder reciprocating engine is adopted as the engine 1. However, the present invention is not limited to the above embodiment as long as it is an in-line multi-cylinder reciprocating engine.

[0084] In addition, the mounting direction of the engine 1 with respect to the engine room is not particularly limited. That is, the engine may be mounted longitudinally or transversely with respect to the engine room.

[0085] In the above-described embodiment, although the applicable ranges of H / H0 and W / W0 in the dynamic damper 80 were described as an example, they can be variously changed according to the resonance peak frequency of the vibration generated with the rotation of the engine crankshaft. Also, regarding the mass of the mass portion, it can be variously changed according to the frequency to be consumed by the dynamic damper.

[0086] In the above-described embodiment, the dynamic damper 80 having two mass portions 802 and 803 was adopted. However, in the present invention, three or more mass portions may be connected to the beam portion.

[0087] In the above-described embodiment, only one dynamic damper 80 was attached to the lower part of the #3 crank journal portion 63 in the lower cylinder block 60. However, in the present invention, a plurality of dynamic dampers each having the same configuration as the above-described dynamic damper 80 may be attached to the lower parts of a plurality of crank journal portions.

[0088] Also, the position where the dynamic damper 80 is attached does not necessarily have to include the #3 crank journal portion 63. That is, according to the characteristics of the engine, the location where the amplitude of the vibration is the largest is determined, and by attaching a dynamic damper having the same configuration as the above to that location, high vibration damping performance can be ensured.

[0089] In the above-described embodiment, the dynamic damper 80 integrally formed using cast iron was adopted. However, in the present invention, it is not necessarily required to adopt cast iron as the constituent material of the dynamic damper. By forming the dynamic damper using a material having a higher specific gravity than the constituent material of the lower cylinder block or the like, the same effects as above can be achieved. Also, the dynamic damper does not necessarily have to be of an integral structure, and it is also possible to adopt a dynamic damper formed by combining a plurality of members.

Explanation of Reference Numerals

[0090] 1 Engine 1a - 1f Cylinders 30 Crankshaft 51 Pulley 52 Flywheel 60 Lower Cylinder Block 61 - 67 Crank Journal Parts 80 Dynamic Damper 81 Bolt 800 Fixed Part 801 Beam Part 801a, 801b Connection Parts 802, 803 Mass Parts

Claims

1. A vibration damping structure for an engine having a plurality of cylinders arranged in series, a piston reciprocally fitted to each of the plurality of cylinders, a crankshaft disposed below the piston and connected to the piston via a connecting rod to rotate when the top dead center side of the piston in the cylinder axis direction is above and the bottom dead center side is below, a cylinder block disposed below the crankshaft and having a plurality of crank journal portions for pivotally supporting the crankshaft between adjacent cylinders of the crankshaft, a dynamic damper attached to a lower portion of at least one crank journal portion of the cylinder block, comprising: The dynamic damper has a fixing portion attached to the lower portion of the crank journal portion and extending downward from the lower portion, a beam portion connected to the lower portion of the fixing portion and extending in the cylinder row direction which is the arrangement direction of the plurality of cylinders, and two mass portions connected to respective connection portions on one side and the other side in the cylinder row direction of the beam portion and each extending in the intake and exhaust direction of the engine while being separated from each other in the cylinder row direction, integrally. A vibration damping structure for an engine.

2. The fixing portion has a column shape, When assuming a virtual plane passing through the column center of the fixing portion and orthogonal to the cylinder row direction, the dynamic damper has a shape symmetric with respect to the virtual plane. The vibration damping structure for an engine according to Claim 1.

3. When viewing the beam portion and the two mass portions from one side in the intake and exhaust direction in side view, the beam portion is formed such that the thickness dimension in the vertical direction of the beam portion is smaller than the thickness dimensions in the vertical direction of each of the two mass portions. The vibration damping structure of the engine according to claim 1.

4. When the beam portion and the two mass portions are viewed from one side in the intake / exhaust direction and in plan view from one direction in the vertical direction, the beam portion and the two mass portions both form an H shape. The vibration damping structure of the engine according to any one of claims 1 to 3.

5. The dynamic damper is formed using cast iron. The vibration damping structure of the engine according to any one of claims 1 to 3.

6. Further comprising a flywheel fixed to one end of the crankshaft. The dynamic damper is attached to the cylinder block at only one position offset to the other end side of the crankshaft from the center position of the cylinder block in the cylinder row direction. The vibration damping structure of the engine according to any one of claims 1 to 3.

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