Internal combustion engine

Abstract

In the present invention, a dynamic damper (13) is set so that: there is a predetermined natural frequency (f3) at which engine vibration caused by torsional resonance of a crankshaft reaches a peak only in a high-RPM range where the engine rotational speed is high; and engine vibration in a lower-RPM range than this natural frequency (f3) changes in proportion to the rotational speed. An internal combustion engine (10) equipped with this dynamic damper (13) is controlled so as not to use engine rotational speeds close to the natural frequency (f3). Controlling the engine rotational speed so as to avoid the high-RPM-side (high-frequency-side) natural frequency enables the internal combustion engine (10) to benefit from the vibration characteristic of suppressed low-RPM-side vibration.

Description

Internal combustion engine

[0001] This invention relates to an internal combustion engine fitted with a dynamic damper.

[0002] For example, Patent Document 1 discloses a technique for shifting the engine speed at which the peak of the torsional resonance frequency characteristic with respect to engine speed of an internal combustion engine occurs to an engine speed that is lower than the normal operating speed range and an engine speed that is higher than the normal operating speed range.

[0003] However, in non-hybrid vehicles equipped with an internal combustion engine as the power source for driving the drive wheels, the operating speed range of the internal combustion engine is wide. Therefore, even if one attempts to shift the peak of the torsional resonance frequency characteristic with respect to engine speed towards the operating speed range, there is a risk that peaks will occur on both the high and low sides of the operating speed range.

[0004] In other words, there is still room for further improvement in suppressing vibrations caused by the natural frequencies of internal combustion engines.

[0005] Japanese Patent Publication No. 2006-315662

[0006] The internal combustion engine of the present invention has a natural frequency at which engine vibrations caused by torsional resonance of the crankshaft peak only in the high-speed range where the engine rotation speed is high. A dynamic damper is installed that is set so that the engine vibrations in the low-speed range below the natural frequency change in proportion to the rotation speed, and the engine is controlled so as not to use engine rotation speeds near the natural frequency.

[0007] The internal combustion engine of the present invention can enjoy the benefits of vibration characteristics in which vibrations at low rotational speeds are suppressed by controlling the engine speed to avoid natural frequencies at high rotational speeds (high frequency sides).

[0008] A schematic diagram illustrating the outline of the drive system of a vehicle equipped with an internal combustion engine according to the present invention. A diagram illustrating the relationship between the dynamic damper and the engine block of the internal combustion engine in a mechanical model. A diagram illustrating the relationship between the vibration frequency and the magnitude of vibration of an internal combustion engine. A diagram illustrating the relationship between the vibration frequency and the magnitude of vibration of an internal combustion engine according to the present invention. A diagram illustrating the relationship between the sixth-order crank torsion angle, which is representative of the crank torsional vibration of the crankshaft of the internal combustion engine according to this embodiment, and the engine speed. A diagram illustrating the relationship between the sixth-order crank torsion angle, which is representative of the crank torsional vibration of the crankshaft of an internal combustion engine according to a comparative example, and the engine speed.

[0009] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Figure 1 is a schematic diagram illustrating the drive system of a vehicle 1 equipped with an internal combustion engine 10 according to the present invention. The vehicle 1 includes a drive unit 3 that drives the drive wheels 2 and a power generation unit 4 that generates electricity to drive the drive wheels 2.

[0010] The drive unit 3 includes a drive motor 5, which serves as a second electric motor for rotating the drive wheels 2, and a first gear train 6 and a differential gear 7 that transmit the driving force of the drive motor 5 to the drive wheels 2. Power is supplied to the drive motor 5 from a battery 8 that is charged with electricity generated by the power generation unit 4.

[0011] The power generation unit 4 includes a generator 9 as a first electric motor that generates electricity to be supplied to the drive motor 5, an internal combustion engine 10 capable of driving the generator 9, and a second gear train 11 that transmits the rotation of the internal combustion engine 10 to the generator 9. The internal combustion engine 10 is, for example, a three-cylinder spark-ignition internal combustion engine mounted on the vehicle specifically for power generation. The internal combustion engine 10 is controlled by the control unit 12 to operate at a predetermined operating point (for example, an operating point for power generation).

[0012] Furthermore, the internal combustion engine 10 is fitted with a dynamic damper 13 that tunes the torsional resonance frequency characteristics with respect to engine rotation speed.

[0013] Figure 2 is an explanatory diagram illustrating the relationship between the dynamic damper 13 and the engine block 15 (e.g., cylinder block) of the internal combustion engine 10 in a mechanical model.

[0014] As shown in FIG. 2, for example, the dynamic damper 13 is attached to the crankshaft 16 of the internal combustion engine 10. The dynamic damper 13 is a so-called spring mass mechanism of a single-degree-of-freedom system composed of an elastic member 17 attached to the crankshaft 16 of the internal combustion engine 10 and a mass body (mass) 18 attached to the elastic member and having a predetermined mass.

[0015] The elastic member 17 is a member having a predetermined spring constant, and may be, for example, a rubber member made of a rubber material or a metal spring. The mass body 18 is connected to the crankshaft 16 via the elastic member 17.

[0016] In FIG. 2, the spring element 19 between the crankshaft 16 and the engine block 15 corresponds to the torsional rigidity of the crankshaft 16.

[0017] Vibration occurs in the internal combustion engine 10 as the crankshaft 16 rotates. The vibration associated with the rotation of the crankshaft 16 is, for example, as shown by the broken line in FIG. 3, a vibration (the resonance frequency is the natural frequency f ０ such that the magnitude of the vibration becomes maximum at a certain time) with a resonance frequency equal to the natural frequency f ０ of the vibration. FIG. 3 is an explanatory diagram showing the relationship between the vibration frequency and the magnitude of vibration of the internal combustion engine 10. The broken line in FIG. 3 shows the vibration associated with the rotation of the crankshaft 16 without the dynamic damper 13 attached.

[0018] Here, if the dynamic damper is adjusted to reduce the vibration at the natural frequency f ０ of the resonance point, as shown by the solid line in FIG. 3, although the vibration at the natural frequency f ０ is reduced, peaks of vibration will occur at the natural frequencies f ０ in a lower frequency range than the natural frequency f １ and the natural frequencies f ０ in a higher frequency range than the natural frequency f ２ That is, if the dynamic damper is adjusted to reduce the vibration at the natural frequency f ０ at the resonance point, the natural frequency f ０Vibration peaks will occur on both sides as rebounds.

[0019] Therefore, these natural frequencies f are obtained from the operating range (normal operating speed range) of the engine speed of the internal combustion engine 10. １ , f ２ It is difficult to make both of them disconnect, and the natural frequency f １ , f ２ At least one of these may adversely affect the vibration characteristics of the internal combustion engine 10.

[0020] Therefore, the dynamic damper 13 has a natural frequency f ０ Rather, the natural frequency f ０ By adjusting the dynamic damper 13 to reduce vibrations in the lower frequency range, the natural frequency f is reduced, as shown by the solid line in Figure 4. ０ This suppresses the peak gain in the lower frequency range, restoring the natural frequency of the internal combustion engine 10 to its original natural frequency f ０ A predetermined natural frequency f located on the higher frequency side than this. ３ This transitions to the next step. Figure 4 is an explanatory diagram showing the relationship between the frequency and magnitude of vibration of the internal combustion engine 10 according to the present invention. The dashed line in Figure 4 shows the vibration associated with the rotation of the crankshaft 16 when the dynamic damper 13 is not installed.

[0021] In other words, the dynamic damper 13 operates at a predetermined natural frequency f such that engine vibration (vibration of the internal combustion engine 10 caused by torsional resonance of the crankshaft) peaks only in the high-speed range where the engine rotation speed is high. ３ There exists this natural frequency f ３ The engine vibration at lower RPMs is set to change in proportion to the rotational speed (frequency), as shown by the upward slope in Figure 4.

[0022] In other words, the dynamic damper 13 restricts the natural frequency of the internal combustion engine 10 to only the high-frequency side, while maintaining the natural frequency f on this high-frequency side. ３ This suppresses the peak gain at lower frequencies, and reduces the natural frequency f ３The vibration characteristics at lower frequencies are set to be proportional to the frequency. The dynamic damper 13 is configured by changing the spring constant of the elastic member 17 and the weight of the mass body 18, so that the desired characteristics described above can be obtained.

[0023] The internal combustion engine 10 has a natural frequency f ３ The engine speed is controlled to avoid using engine speeds in the vicinity. Specifically, the internal combustion engine 10 uses a natural frequency f ３ To avoid being affected by vibrations, the engine speed is controlled to be below a predetermined speed (e.g., 5500 rpm). This predetermined speed is, for example, the natural frequency f ３ This results in an engine speed lower than the corresponding engine speed.

[0024] As a result, the internal combustion engine 10 has no vibration peaks on the low-speed side (low-frequency side) and the operating range of the engine speed is set to avoid vibration peaks on the high-speed side (high-frequency side), so the vibration characteristics in the operating range can be greatly improved to a degree that was not possible with conventional methods.

[0025] Furthermore, the internal combustion engine 10 can benefit from vibration characteristics that suppress vibrations at low rotational speeds by controlling the engine speed to avoid natural frequencies on the high rotational speed side (high frequency side).

[0026] Furthermore, since the internal combustion engine 10 is mounted on the vehicle solely for power generation, it is basically required to be operated in a relatively low rotation range, such as near the point of best fuel consumption, and its natural frequency f ３ This makes it possible to set a range of engine speeds that are not affected by other factors. In other words, the internal combustion engine 10 of the present invention is particularly well-suited for series hybrid vehicles.

[0027] By setting the dynamic damper 13 of the internal combustion engine 10 to have vibration characteristics as shown by the solid line in Figure 4, the vibration characteristics can be improved across the entire operating range of engine speeds, as shown in Figure 5. Figure 5 is an explanatory diagram showing the relationship between the sixth-order torsion angle of the crankshaft 16, which is representative of the crank torsional vibration of the internal combustion engine 10 in this embodiment, and the engine speed.

[0028] Incidentally, when the dynamic damper 13 is set such that the internal combustion engine has vibration characteristics as shown by the solid line in FIG. 3, as shown in FIG. 6, the peak of the crank torsional vibration remains not only on the high rotation side, and there is a possibility that the vibration characteristics cannot be sufficiently improved. FIG. 6 is an explanatory diagram showing the relationship between the crank sixth-order torsional angle, which represents the crank torsional vibration of the crankshaft of the internal combustion engine in the comparative example, and the engine speed.

[0029] Incidentally, the reference value S1 of the crank sixth-order torsional angle in FIGS. 5 and 6 is a predetermined index representing the magnitude of vibration. For example, if the crank sixth-order torsional angle is smaller than the reference value S1, it can be considered that the vibration level is small.

[0030] Further, even if an abnormality in control for increasing the engine speed occurs in the internal combustion engine 10, the various dimensions of the intake system are set so that the engine speed corresponding to the natural frequency f ３ cannot occur, and it is structurally formed so that the engine speed corresponding to the natural frequency f ３ does not occur.

[0031] Therefore, even if an abnormality in control occurs in the internal combustion engine 10 and, assuming that all control-induced intake air amount restrictions are removed, it is possible to prevent the engine speed from rising to the engine speed corresponding to the natural frequency f ３

[0032] As described above, the specific embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit thereof.

[0033] For example, if the dynamic damper 13 has a predetermined natural frequency f ３ at which the engine vibration peaks only in the high rotation range where the engine speed is high, and the engine vibration in the lower rotation range than the natural frequency f ３ changes in proportion to the engine speed (frequency), it may be a spring mass mechanism other than the single-degree-of-freedom system.

Claims

1. An internal combustion engine equipped with a dynamic damper, wherein there exists a natural frequency at which engine vibrations caused by torsional resonance of the crankshaft peak only in the high-speed range where the engine rotation speed is high, and the dynamic damper is set so that the engine vibrations in the low-speed range below the natural frequency change in proportion to the rotation speed, and the engine is controlled so as not to use engine rotation speeds near the natural frequency.

2. The internal combustion engine according to claim 1, which is mounted on a vehicle for power generation.

3. The dimensions of the intake system of the internal combustion engine are set such that even if a control abnormality occurs that causes the engine speed to increase, the engine speed corresponding to the above-mentioned natural frequency cannot be generated.

4. The internal combustion engine according to claim 1, wherein the dynamic damper is a one-degree-of-freedom spring-mass mechanism composed of an elastic member attached to the crankshaft of the internal combustion engine and a mass attached to the elastic member.

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