crank axle
The crankshaft design with varying lateral bending stiffness ratios and increased torsional stiffness addresses the challenge of suppressing engine vibrations and noise, enhancing ride comfort and fuel efficiency by reducing critical vibration amplitudes without increasing weight.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- NIPPON STEEL CORPORATION
- Filing Date
- 2022-09-30
- Publication Date
- 2026-07-23
AI Technical Summary
Existing crankshafts in internal combustion engines generate significant vibrations and noise, which are transmitted to the engine's surface, causing air vibrations and noise, and current methods to suppress these, such as using sound-absorbing materials or dampers, lead to increased weight and size, negatively impacting fuel efficiency.
A crankshaft design with eccentrically positioned pins and varying lateral bending stiffness ratios between throws, specifically setting the lateral bending stiffness of the first throw to be less than that of the second throw, and increasing torsional stiffness, to reduce overall engine vibrations without significantly increasing weight.
The designed crankshaft effectively suppresses vibrations and noise by reducing the amplitude of critical vibration modes, improving ride comfort and reducing noise emissions while maintaining fuel efficiency.
Smart Images
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Abstract
Description
Technical Field
[0001] This disclosure relates to a crankshaft.
Background Art
[0002] Conventionally, automobiles have used internal combustion engines as power sources. Internal combustion engines generate power efficiently but cause vibrations and are prone to generating noise. Automobiles equipped with internal combustion engines are required to suppress vibrations and noise for improved ride comfort and environmental protection. In particular, the maximum level of noise is regulated by law. Therefore, suppressing noise in automobiles is not only a technical challenge but also important from the perspective of compliance with the law.
[0003] Internal combustion engines are used not only in automobiles but also in vehicles such as ships and construction heavy machinery, mobile machines such as hand-held snow blowers, hand-held machines such as chain saws and lawn mowers, or stationary machines such as generators. Suppressing noise is also important in these machines.
[0004] As a method of suppressing noise, it is conceivable to attach a member (such as a sound-absorbing material or a sound-insulating material) that absorbs sound to a cover or the like surrounding the internal combustion engine. However, in this method, the weight of the entire machine increases with the installation of the sound-absorbing material or the like, and moreover, the entire machine becomes larger due to the installation space for the sound-absorbing material or the like. In particular, for an automobile, which is a moving body, an increase in weight leads to a deterioration in fuel efficiency. Also, as a method of suppressing vibrations, it is conceivable to install a damper between the frame of the machine and the internal combustion engine body and block the vibrations with the damper. However, there is a limit to blocking vibrations with a damper, and it is technically difficult to design the damper appropriately. Therefore, installing a sound-absorbing material for suppressing noise and installing a damper or the like for suppressing vibrations involve technical difficulties.
[0005] Incidentally, in machines equipped with internal combustion engines, vibrations generated by the engine are transmitted to the surface of the machine, and these transmitted vibrations cause the air to vibrate. This air vibration generates noise. From this, it can be seen that if the vibrations generated from the internal combustion engine can be suppressed, the noise can also be suppressed.
[0006] Generally, the largest moving part in an internal combustion engine is the crankshaft. Suppressing the vibration of this crankshaft can be expected to reduce the overall vibration of the internal combustion engine. Therefore, suppressing crankshaft vibration is crucial for reducing vibration and noise generated by an internal combustion engine.
[0007] For example, Patent Document 1 discloses a crankshaft for an inline four-cylinder engine having eight crank shoulders (crank shoulders 1 to 8) in order from the auxiliary drive end. Each crank shoulder connects the main journal to the crank pin. Patent Document 1 states that by setting the stiffness ratio (ratio of bending stiffness to torsional stiffness) of the 7th crank shoulder to less than 1.8, crankshaft vibration and, consequently, engine noise can be reduced. [Prior art documents] [Patent Documents]
[0008] [Patent Document 1] Japanese Patent Publication No. 2021-148281 [Overview of the project] [Problems that the invention aims to solve]
[0009] The crankshaft rotates and vibrates simultaneously within the engine. This vibration can be broken down into vibration modes (hereinafter simply referred to as modes). In other words, the sum of the vibrations of each mode represents the overall vibration of the crankshaft.
[0010] Generally, the amplitude of crankshaft vibration differs for each mode. Amplitude represents the magnitude of the vibration energy for each mode. Crankshaft vibration is transmitted to parts outside the crankshaft (such as the engine block). This vibration is measured as the vibration of the entire engine, or as the vibration of parts of the engine where vibration is a problem (e.g., bearings and mounts). Here, the influence of each mode's vibration on the overall engine vibration is not uniform. In short, certain modes of vibration contribute significantly to the overall engine vibration. Therefore, by properly designing the crankshaft and reducing the amplitude of vibrations in modes that contribute greatly to the overall engine vibration, crankshaft vibration can be suppressed.
[0011] Furthermore, crankshaft vibration can be suppressed by significantly improving the rigidity of each part of the crankshaft and suppressing the amplitude of vibrations in all modes. However, in this case, the weight of the crankshaft increases significantly. An increase in crankshaft weight is undesirable because it leads to a decrease in fuel efficiency. Therefore, it is necessary to suppress crankshaft vibration, which has a large contribution to the overall engine vibration, without significantly increasing the weight of the crankshaft.
[0012] This disclosure aims to provide a crankshaft that can suppress vibrations throughout the entire engine. [Means for solving the problem]
[0013] The crankshaft for a four-cylinder engine of this disclosure comprises a plurality of journals, a plurality of pins, a plurality of arms, a front, and a flange. The plurality of pins are eccentrically positioned with respect to the plurality of journals. The plurality of arms each connect the corresponding journal and pin. The front is to which the engine's accessories are mounted. The flange is to which the flywheel is mounted. The plurality of journals include, in order from the front toward the flange, a first journal, a second journal, and a third journal. The plurality of pins include, in order from the front toward the flange, a first pin, a second pin, and a fourth pin. The plurality of arms include, in order from the front toward the flange, a first arm, a second arm, a third arm, and a fourth arm. The lateral bending stiffness of the first throw is less than that of the second throw. The first throw consists of a first journal, a first arm, a first pin, a second arm, and a second journal. The second throw consists of a second journal, a third arm, a second pin, a fourth arm, and a third journal. [Effects of the Invention]
[0014] The crankshaft described herein can suppress vibrations throughout the entire engine. [Brief explanation of the drawing]
[0015] [Figure 1] Figure 1 is a front view showing an example of a typical crankshaft. [Figure 2] Figure 2 is a side view of the counterweight arm on the crankshaft shown in Figure 1. [Figure 3] Figure 3 is a front view of the crankshaft according to this embodiment. [Figure 4] Figure 4 is a schematic diagram showing the analysis conditions for longitudinal bending stiffness. [Figure 5] Figure 5 is a schematic diagram showing the analysis conditions for transverse bending stiffness. [Figure 6] Figure 6 is a schematic diagram showing the analysis conditions for torsional stiffness. [Figure 7] Figure 7 is a side view of the crank arm. [Figure 8]FIG. 8 is a front view of the slow part of the crankshaft. [Figure 9] FIG. 9 is a diagram showing the results of this embodiment.
MODE FOR CARRYING OUT THE INVENTION
[0016] FIG. 1 is a front view showing an example of a general crankshaft 90. The crankshaft 90 is mounted on a four-cylinder engine. Referring to FIG. 1, the crankshaft 90 includes five journals J1 to J5, four pins P1 to P4, eight arms A1 to A8, eight counterweights W, a front Fr, and a flange Fl. FIG. 2 is a side view of the arm A with the counterweight W in the crankshaft 90 shown in FIG. 1. In FIG. 2, the first arm A1 is shown representing the arm A.
[0017] Referring to FIGS. 1 and 2, the crankshaft 90 rotates around the central axis X1. The first journal J1 to the fifth journal J5 each have a substantially cylindrical shape with the central axis X1 as the central axis. The first journal J1 to the fifth journal J5 are arranged in this order from the front Fr toward the flange Fl along the direction in which the central axis X1 extends, and constitute the main shaft portion of the crankshaft 90. The first journal J1 is connected to the front Fr. The fifth journal J5 is connected to the flange Fl. An auxiliary machine (not shown) is attached to the front Fr. The auxiliary machine is, for example, a pulley for driving a timing belt, a fan belt, etc. A flywheel (not shown) is attached to the flange Fl. Hereinafter, when there is no need to particularly distinguish the five journals J1 to J5, these are collectively referred to as the journal J.
[0018] The first pin P1 to the fourth pin P4 are each substantially cylindrical and are alternately arranged with the journal J along the central axis X1. The first pin P1 to the fourth pin P4 are arranged in this order from the front Fr toward the flange Fl. However, each of the first pin P1 to the fourth pin P4 is eccentric with respect to the journal J. The first pin P1 to the fourth pin P4 are arranged with a predetermined phase difference around the central axis X1. The first pin P1 and the fourth pin P4, and the second pin P2 and the third pin P3 are arranged around the central axis X1 with a phase difference of 180°. Hereinafter, when there is no need to particularly distinguish the four pins P1 to P4, these are collectively referred to as pin P.
[0019] Each of the first arm A1 to the eighth arm A8 is arranged between the journal J and the pin P in the direction in which the central axis X1 extends. The first arm A1 to the eighth arm A8 each connect the journal J and the pin P. The first arm A1 to the eighth arm A8 are arranged in this order from the front Fr toward the flange Fl. Hereinafter, when there is no need to particularly distinguish the eight arms A1 to A8, these are collectively referred to as arm A.
[0020] The first arm A1 is arranged between the first journal J1 and the first pin P1 and connects the first journal J1 and the first pin P1. The second arm A2 is arranged between the first pin P1 and the second journal J2 and connects the first pin P1 and the second journal J2. The third arm A3 is arranged between the second journal J2 and the second pin P2 and connects the second journal J2 and the second pin P2. The fourth arm A4 is arranged between the second pin P2 and the third journal J3 and connects the second pin P2 and the third journal J3. The fifth arm A5 is arranged between the third journal J3 and the third pin P3 and connects the third journal J3 and the third pin P3. The sixth arm A6 is arranged between the third pin P3 and the fourth journal J4 and connects the third pin P3 and the fourth journal J4. The seventh arm A7 is arranged between the fourth journal J4 and the fourth pin P4 and connects the fourth journal J4 and the fourth pin P4. The eighth arm A8 is arranged between the fourth pin P4 and the fifth journal J5 and connects the fourth pin P4 and the fifth journal J5.
[0021] Each of the first arm A1 to the eighth arm A8 is provided with a counterweight W. Each of the counterweights W is integrally formed with each of the arms A1 to A8.
[0022] In the following, for the sake of explanation, the direction in which the central axis X1 of the crankshaft 90 extends will also be referred to as the axial direction. The direction in which the pin P is eccentric will also be referred to as the vertical direction, and the direction perpendicular to both the axial direction and the vertical direction will also be referred to as the width direction. Furthermore, in this specification, within the vertical direction, the direction in which the first pin P1 is eccentric with respect to the central axis X1 of the crankshaft 90 will be referred to as "up," and the direction in which the second pin P2 is eccentric will be referred to as "down."
[0023] The inventors decomposed the vibration of the crankshaft 90 into vibration modes and analyzed the influence of each vibration mode on the overall engine vibration. Here, the vibrations decomposed into vibration modes are, for example, longitudinal bending vibration, transverse bending vibration, and torsional vibration. As a result of the analysis, it was found that the influence of transverse bending vibration and torsional vibration was relatively large among the vibration modes. Transverse bending vibration in the crankshaft 90 means vibration that displaces a part of the crankshaft 90 in the width direction, causing the crankshaft 90 to bend in the width direction. Torsional vibration in the crankshaft 90 means vibration that rotates a part of the crankshaft 90 around the axial direction, causing the crankshaft 90 to twist.
[0024] Conversely, the analysis revealed that the effect of longitudinal bending vibration was smaller compared to lateral bending vibration and torsional vibration. Longitudinal bending vibration in the crankshaft 90 refers to vibration that displaces a part of the crankshaft 90 in the vertical direction, causing the crankshaft 90 to bend in the vertical direction.
[0025] Therefore, if the amplitude of lateral bending vibration and torsional vibration in the crankshaft 90 is small, the vibration of the entire engine will be suppressed. Furthermore, the inventors analyzed various parts of the crankshaft with varying stiffnesses to investigate which part of the crankshaft's stiffness affects the vibration of the entire engine. As a result, the inventors revealed that defining the ratio of the lateral bending stiffness of the first throw to the lateral bending stiffness of the second throw (lateral bending stiffness ratio) is particularly important for suppressing vibration. Here, a throw consists of one pin, arms connected to both sides of the pin, and journals connected to each of the arms. The crankshaft 90 is equipped with first to fourth throws in order from the front Fr toward the flange Fl. The first throw consists of a first journal J1, a first arm A1, a first pin P1, a second arm A2, and a second journal J2. The second throw consists of a second journal J2, a third arm A3, a second pin P2, a fourth arm A4, and a third journal J3.
[0026] The reason why defining the lateral bending stiffness ratio of the first and second throws is important for suppressing vibration is that the lateral bending vibrations of the first and second throws contribute significantly to the overall engine vibration. The flywheel and transmission (or the shaft connecting to the transmission) are connected to the flange Fl side of the crankshaft 90. The mass and inertia of these components are very large relative to the crankshaft 90. Therefore, a strong restraining force acts on the flange Fl side of the crankshaft 90. Consequently, the amplitude of vibration is relatively small on the flange Fl side of the crankshaft 90. Conversely, the amplitude is larger on the front Fr side of the crankshaft 90, i.e., the first and second throws, compared to the flange Fl side. It is presumed that the large-amplitude vibrations acting on the first and second throws are transmitted to parts outside the crankshaft, such as the engine block, which increases the overall engine vibration.
[0027] The crankshaft according to the embodiment of this disclosure is completed based on the above findings.
[0028] A crankshaft for a four-cylinder engine according to this embodiment comprises a plurality of journals, a plurality of pins, a plurality of arms, a front, and a flange. The plurality of pins are eccentrically positioned relative to the plurality of journals. The plurality of arms each connect a corresponding journal and pin. The front is to which engine accessories are mounted. The flange is to which the flywheel is mounted. The plurality of journals include, in order from the front toward the flange, a first journal, a second journal, and a third journal. The plurality of pins include, in order from the front toward the flange, a first pin and a second pin. The plurality of arms include, in order from the front toward the flange, a first arm, a second arm, a third arm, and a fourth arm. The lateral bending stiffness of the first throw is less than that of the second throw. The first throw consists of a first journal, a first arm, a first pin, a second arm, and a second journal. The second throw consists of a second journal, a third arm, a second pin, a fourth arm, and a third journal (first configuration).
[0029] In the first crankshaft configuration, the lateral bending stiffness of the first throw is set to be smaller than that of the second throw. By defining the relative magnitudes of the lateral bending stiffness of the first and second throws in the crankshaft in this way, the amplitude of lateral bending vibration in the crankshaft can be reduced. As mentioned above, lateral bending vibration of the crankshaft has a significant impact on the vibration of the entire engine. Therefore, the crankshaft configuration of the first configuration can suppress the vibration of the entire engine.
[0030] In the first configuration of the crankshaft, preferably, the lateral bending stiffness of the first throw is 0.95 times or more and less than 1.00 times the lateral bending stiffness of the second throw (second configuration). In the second configuration of the crankshaft, the ratio of the lateral bending stiffness of the first throw to the lateral bending stiffness of the second throw (lateral bending stiffness ratio) is specifically defined as 0.95 or more and less than 1.00. This ensures that vibrations of the entire engine are reliably suppressed.
[0031] In the first or second configuration of the crankshaft, preferably, the torsional rigidity of the first throw is greater than that of the second throw (third configuration). As described above, not only lateral bending vibration of the crankshaft but also torsional vibration has a significant impact on the overall vibration of the engine. In the third configuration of the crankshaft, the relative magnitudes of the torsional rigidity of the first and second throws are defined. This makes it possible to reduce the amplitude of torsional vibration in the crankshaft and further suppress the overall vibration of the engine.
[0032] Hereinafter, the crankshaft according to the embodiment of this disclosure will be described with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and redundant explanations will be omitted as appropriate.
[0033] [crank axle] Figure 3 is a front view (viewed along the width direction) of the crankshaft 10 according to this embodiment. The crankshaft 10 has a configuration that is generally the same as the crankshaft 90 shown in Figure 1. Therefore, the following will describe the parts of the crankshaft 10 that differ from those of the crankshaft 90.
[0034] The lateral bending stiffness of the first throw T1 is smaller than that of the second throw T2. Preferably, the lateral bending stiffness of the first throw T1 is 0.95 times or more and less than 1.00 times that of the second throw T2. In other words, the ratio of the lateral bending stiffness of the first throw to that of the second throw T2 (lateral bending stiffness ratio) is preferably 0.95 or more and less than 1.00. The method for calculating the lateral bending stiffness of each throw will be described later.
[0035] In this embodiment, the torsional stiffness of the first throw T1 is greater than that of the second throw T2. In other words, the ratio of the torsional stiffness of the first throw to that of the second throw T2 (torsional stiffness ratio) is greater than 1.00. The method for calculating the torsional stiffness of each throw will be described later.
[0036] As mentioned above, a strong restraining force acts on the flange Fl side of the crankshaft 10. Therefore, the rigidity of the flange Fl side portion of the crankshaft 10, i.e., the third throw T3 and the fourth throw T4, does not have much effect on engine vibration. For this reason, the lateral bending rigidity and torsional rigidity of the third throw T3 and the fourth throw T4 are not particularly limited. Here, the third throw T3 consists of the third journal J3, the fifth arm A5, the third pin P3, the sixth arm A6, and the fourth journal J4. The fourth throw T4 consists of the fourth journal J4, the seventh arm A7, the fourth pin P4, the eighth arm A8, and the fifth journal J5.
[0037] Furthermore, among the vibration modes of the crankshaft 10, the influence of longitudinal bending vibration on the overall engine vibration is smaller compared to lateral bending vibration and torsional vibration. Therefore, the longitudinal bending stiffness of each throw is not particularly limited.
[0038] The crankshaft 10 comprises first to fourth throws T1 to T4. Each of the first to fourth throws T4 has two arms A. These two arms A are typically symmetrical in the axial direction. That is, in the axial direction, the first arm A1 is symmetrical with the second arm A2, the third arm A3 is symmetrical with the fourth arm A4, the fifth arm A5 is symmetrical with the sixth arm A6, and the seventh arm A7 is symmetrical with the eighth arm A8.
[0039] [Method for calculating stiffness] The following describes how to calculate the longitudinal bending stiffness, transverse bending stiffness, and torsional stiffness of the crankshaft 10. To calculate the longitudinal bending stiffness, transverse bending stiffness, and torsional stiffness, an analysis model should be created for each throw of the crankshaft 10, and a stiffness analysis should be performed. The following describes the calculation of the longitudinal bending stiffness, transverse bending stiffness, and torsional stiffness for the first throw T1, but the longitudinal bending stiffness, transverse bending stiffness, and torsional stiffness for the second throw T2 to the fourth throw T4 can be calculated using the same procedure.
[0040] Figure 4 is a schematic diagram showing the analysis conditions for longitudinal bending stiffness. Figure 4 is a front view (viewed along the width direction) of the analysis model of the first throw T1 of the crankshaft 10. In the analysis of longitudinal bending stiffness, a downward load F1 is applied in the vertical direction to the axial center of the first pin P1. The load F1 is applied to the upper end of the first pin P1. At this time, the axial center of the first journal J1 and the axial center of the second journal J2 of the crankshaft 10 are constrained, respectively. The constraint positions of the first journal J1 and the second journal J2 are on the opposite side in the vertical direction from the side to which the load F1 is applied to the first pin P1 (the lower ends of the first journal J1 and the second journal J2). As a result, translation and rotation around the central axis X1 are constrained at the constraint points of the first journal J1 and the second journal J2, respectively. Due to the load F1 applied to the first pin P1, the crankshaft 10 is deflected in the vertical direction.
[0041] Under these conditions, the vertical displacements of point B on the first journal J1, point C on the first pin P1, and point D on the second journal J2 after applying load F1 are analyzed. Here, before load F1 is applied to the first pin P1, point B is located at the centroid of the first journal J1, point C is located at the centroid of the first pin P1, and point D is located at the centroid of the second journal J2. Then, the difference (displacement difference Δ1) between the displacement of point C after applying load F1 and the average of the displacements of point B and point D is calculated. The longitudinal bending stiffness is calculated by dividing the load F1 by the displacement difference Δ1.
[0042] Figure 5 is a schematic diagram showing the analysis conditions for lateral bending stiffness. Figure 5 is a top view (viewed along the vertical direction) of the analysis model of the first throw T1 of the crankshaft 10. In the analysis of lateral bending stiffness, a widthwise load F2 is applied to the axial center of the first pin P1. At this time, the axial center of the first journal J1 and the axial center of the second journal J2 of the crankshaft 10 are constrained, respectively. The constraint positions of the first journal J1 and the second journal J2 are on the opposite side in the widthwise direction from the side on which the load F2 is applied to the first pin P1. As a result, translation and rotation around the central axis X1 are constrained at the constraint points of the first journal J1 and the second journal J2, respectively. Due to the load F2 applied to the first pin P1, the crankshaft 10 is deflected in the widthwise direction.
[0043] Under these conditions, the displacements in the width direction of point B in the first journal J1, point C in the first pin P1, and point D in the second journal J2 after applying load F2 are analyzed. Then, the difference (displacement difference Δ2) between the displacement of point C after applying load F2 and the average of the displacements of point B and point D is calculated. The transverse bending stiffness is calculated by dividing the load F2 by the displacement difference Δ2.
[0044] Figure 6 is a schematic diagram showing the analysis conditions for torsional stiffness. Figure 6 is a front view of the analysis model of the crankshaft 10 at the first throw T1. In the torsional stiffness analysis, a torque T is applied to the second journal J2 around the central axis X1. At this time, the axial end of the first journal J1 on the front Fr (Figure 3) side is constrained. As a result, the front Fr side end face of the first journal J1 is completely constrained. Due to the torque T applied to the second journal J2, the crankshaft 10 is twisted around the central axis X1.
[0045] Under these conditions, we analyze the angle θ formed by the straight line connecting points E and F on the first journal J1 after torque T is applied, and the straight line connecting points G and H on the second journal J2, when viewed along the axial direction. Here, points E and F are located at the center of the first journal J1 in the axial direction. Before torque T is applied to the second journal J2, point E is located at the upper end of the first journal J1, and point F is located at the lower end of the first journal J1. Points G and H are located at the center of the second journal J2 in the axial direction. Before torque T is applied to the second journal J2, point G is located at the upper end of the second journal J2, and point H is located at the lower end of the second journal J2. Torsional stiffness is calculated by dividing the torque T by the angle θ.
[0046] [Shape of the crank axle] In the crankshaft 10 according to this embodiment, the lateral bending stiffness of the first throw T1 is smaller than that of the second throw T2. On the other hand, the torsional stiffness of the first throw T1 is larger than that of the second throw T2. The specific shape of the crankshaft 10 that satisfies these conditions for lateral bending stiffness and torsional stiffness will be described below.
[0047] To increase the lateral bending rigidity and torsional rigidity of the crankshaft 10, the width L and thickness t of arm A should be increased. Here, the width L of arm A is the dimension in the width direction of the upper end of arm A. The thickness t of arm A is the dimension in the axial direction of the upper end of arm A. However, the lateral bending rigidity of the crankshaft 10 is more easily increased by increasing the thickness t of arm A than by increasing the width L of arm A. On the other hand, the torsional rigidity of the crankshaft 10 is more easily increased by increasing the width L of arm A than by increasing the thickness t of arm A.
[0048] Figure 7 is a side view of arm A of the crankshaft 10. In Figure 7, the first arm A1 is shown as representative of arm A. Referring to Figure 7, the first arm A1 may include a reinforced portion 11. The reinforced portion 11 is provided to increase the width L of arm A. In short, arm A including the reinforced portion 11 has a larger width L than arm A without the reinforced portion 11. The reinforced portion 11 is provided on both sides in the width direction of arm A near pin P.
[0049] Figure 8 is a front view of the throw of the crankshaft 10. In Figure 8, the first throw T1 is shown as representative of the throw. Referring to Figure 8, the first arm A1 and the second arm A2 of the first throw T1 may include a reinforced portion 12. The reinforced portion 12 is provided to increase the thickness t of the arm A. In short, the arm A including the reinforced portion 12 has a greater thickness t than the arm A without the reinforced portion 12. The reinforced portion 12 is provided on the surface of the arm A near the pin P. Specifically, in the axial direction, the reinforced portion 12 is provided on the side of the arm A that is connected to the journal J.
[0050] In the crankshaft 10, the first arm A1 and the second arm A2 of the first throw T1 include the reinforced portion 11, while the third arm A3 and the fourth arm A4 of the second throw T2 do not necessarily include the reinforced portion 11. In this case, the width L of the first arm A1 and the second arm A2 is greater than the width L of the third arm A3 and the fourth arm A4. Therefore, the torsional rigidity of the first throw T1 is greater than that of the second throw T2. Alternatively, in the crankshaft 10, the first arm A1 and the second arm A2 may not include the reinforced portion 12, while the third arm A3 and the fourth arm A4 may include the reinforced portion 12. In this case, the thickness t of the first arm A1 and the second arm A2 is smaller than the thickness t of the third arm A3 and the fourth arm A4. Therefore, the lateral bending rigidity of the first throw T1 is less than that of the second throw T2. In other words, if the first throw T1 and the second throw T2 are shaped in this way, the above-mentioned conditions for lateral bending rigidity and torsional rigidity are satisfied.
[0051] [effect] Lateral bending vibrations of the crankshaft 10 have a significant impact on the overall engine vibration. Therefore, in the crankshaft 10 according to this embodiment, the lateral bending stiffness of the first throw T1 is set to be smaller than that of the second throw T2. By defining the relative magnitudes of the lateral bending stiffnesses of the first throw T1 and the second throw T2 in the crankshaft 10 in this way, the amplitude of lateral bending vibrations in the crankshaft 10 can be reduced. Consequently, the crankshaft 10 according to this embodiment can suppress the overall engine vibration.
[0052] In the crankshaft 10 according to this embodiment, the ratio of the lateral bending stiffness of the first throw T1 to the lateral bending stiffness of the second throw T2 (lateral bending stiffness ratio) is specifically defined as 0.95 or more and less than 1.00. This ensures that vibrations of the entire engine are reliably suppressed.
[0053] Torsional vibrations of the crankshaft 10, like lateral bending vibrations, have a significant impact on the overall engine vibration. In this embodiment of the crankshaft 10, the relative magnitudes of the torsional stiffness of the first throw T1 and the second throw T2 are defined. This makes it possible to reduce the amplitude of torsional vibrations in the crankshaft 10, thereby further suppressing the overall engine vibration. [Examples]
[0054] To confirm the effect of the crankshaft according to the embodiment, the lateral bending stiffness and torsional stiffness were varied for the first and second throws of the crankshaft, and the magnitude of vibration (vibration level) of the entire engine was evaluated. In this embodiment, a model was created that included the crankshaft, engine block, engine mount used to fix the engine to the automobile, flywheel attached to the crankshaft flange, and transmission, and the vibration of the entire model was investigated by numerical analysis. Specifically, the vibration level at the engine mount was investigated. If the vibration level at the engine mount is small, the vibration transmitted to the automobile will be small, improving the ride comfort of the automobile and reducing the noise emitted from the automobile. However, since it is only necessary to check vibrations at frequencies perceptible to humans, vibrations with a frequency of 1000 Hz or less were used as the evaluation target.
[0055] Figure 9 shows the results of this embodiment. In Figure 9, the vertical axis represents the vibration level (G) of the crankshaft, and the horizontal axis represents the ratio of the lateral bending stiffness of the first throw to the lateral bending stiffness of the second throw (lateral bending stiffness ratio). Referring to Figure 9, when the lateral bending stiffness ratio was 1.00 or greater, the vibration level was greater than 8 (G) in all cases. On the other hand, when the lateral bending stiffness ratio was less than 1.00, the vibration level was 7 (G) or less in all cases. Among these, when the lateral bending stiffness ratio was less than 1.00 and the torsional stiffness ratio was greater than 1.00, the vibration level was particularly small. From the above, it can be seen that if the lateral bending stiffness ratio is less than 1.00, that is, if the lateral bending stiffness of the first throw is smaller than the lateral bending stiffness of the second throw, the vibration of the entire engine can be suppressed.
[0056] The embodiments of this disclosure have been described above. However, the embodiments described above are merely examples for implementing this disclosure. Therefore, this disclosure is not limited to the embodiments described above, and the embodiments described above can be modified as appropriate without departing from the spirit of this disclosure. [Explanation of symbols]
[0057] 10, 90: Crank axle J: Journal P: Pin A: Arm Fr: Front Fl: Flange T1: First throw T2: 2nd throw
Claims
1. A crankshaft for a four-cylinder engine, Multiple journals, Multiple pins arranged eccentrically with respect to the multiple journals, Multiple arms, each connecting the corresponding journal and pin, The front where the engine's auxiliary components are mounted, It is equipped with a flange to which a flywheel is attached, The plurality of journals include, in order from the front toward the flange, a first journal, a second journal, a third journal, a fourth journal, and a fifth journal. The plurality of pins include, in order from the front toward the flange, a first pin, a second pin, a third pin, and a fourth pin. The plurality of arms include, in order from the front toward the flange, a first arm, a second arm, a third arm, a fourth arm, a fifth arm, a sixth arm, a seventh arm, and an eighth arm. The lateral bending stiffness of the first throw, consisting of the first journal, the first arm, the first pin, the second arm, and the second journal, is smaller than the lateral bending stiffness of the second throw, consisting of the second journal, the third arm, the second pin, the fourth arm, and the third journal. A crankshaft in which the torsional rigidity of the first throw is greater than that of the second throw.
2. A crankshaft according to claim 1, A crankshaft in which the lateral bending stiffness of the first throw is 0.95 times or more and less than 1.00 times the lateral bending stiffness of the second throw.