JP6160302B2 - Reciprocating engine crankshaft and design method of the crankshaft - Google Patents

Description

  The present invention relates to a crankshaft mounted on a reciprocating engine such as a general-purpose engine such as an automobile engine, a marine engine, or a generator, and a method for designing the crankshaft.

  The reciprocating engine needs a crankshaft to convert the reciprocating motion of the piston in the cylinder (cylinder) into a rotational motion to extract power. Crankshafts are broadly classified into those manufactured by die forging and those manufactured by casting. Particularly, for the multi-cylinder engine having two or more cylinders, the former die forging crank superior in strength and rigidity. Axes are frequently used.

  FIG. 1 is a side view schematically showing an example of a crankshaft for a general multi-cylinder engine. The crankshaft 1 illustrated in the figure is mounted on a four-cylinder engine, and includes five journal portions J1 to J5, four pin portions P1 to P4, a front portion Fr, a flange portion Fl, and journal portions J1 to J1. It consists of 8 crank arm parts (hereinafter also simply referred to as “arm parts”) A1 to A8 that connect J5 and the pin parts P1 to P4, respectively. This is a crankshaft of a 4-cylinder-8-counterweight having W1 to W8.

  Hereinafter, when the journal portions J1 to J5, the pin portions P1 to P4, the arm portions A1 to A8, and the weight portions W1 to W8 are collectively referred to, the reference numerals are “J” for the journal portion and “P” for the pin portion. Also, “A” for the arm portion and “W” for the weight portion. The pin portion P and a pair of arm portions A (including the weight portion W) connected to the pin portion P are collectively referred to as “slow”.

  The journal portion J, the front portion Fr, and the flange portion Fl are arranged coaxially with the rotation center of the crankshaft 1, and the pin portion P is arranged eccentric from the rotation center of the crankshaft 1 by a distance that is half the piston stroke. . The journal portion J is supported by the engine block by a sliding bearing and serves as a rotation center. A large end portion of a connecting rod (hereinafter also referred to as “connecting rod”) is connected to the pin portion P by a sliding bearing, and a piston is connected to a small end portion of the connecting rod by a piston pin. The front portion Fr is one shaft end of the crankshaft 1, and a damper pulley 2 for driving a timing belt and a fan belt is attached to the front portion Fr. The flange portion Fl is the other shaft end of the crankshaft 1, and the flywheel 3 is attached to the flange portion Fl.

  As the fuel explodes in each cylinder of the engine, the combustion pressure due to the explosion causes the reciprocating motion of the piston to act on the pin portion P of the crankshaft 1, and at the same time, the arm connected to the pin portion P It is transmitted to the journal part J via the part A and converted into a rotational motion. At that time, the crankshaft 1 rotates while repeating elastic deformation.

  Lubricating oil exists in the bearing that supports the journal part of the crankshaft, and the oil film pressure and oil film thickness in the bearing depend on the bearing load and the axial center locus of the journal part according to the inclination and elastic deformation of the crankshaft. It changes while interrelated. Furthermore, depending on the surface roughness of the journal part in the bearing and the surface roughness of the bearing metal, not only the oil film pressure but also local metal contact occurs. Ensuring the oil film thickness is important for preventing bearing seizure due to running out of oil and preventing local metal contact, and affects fuel efficiency.

  Further, the elastic deformation accompanying the rotation of the crankshaft and the axial locus that moves in the clearance in the bearing cause a shift of the rotation center, which affects the engine vibration (mount vibration). Furthermore, the vibration propagates through the vehicle body and affects noise and riding comfort in the passenger compartment.

  In order to improve such engine performance, the crankshaft is required to be lightweight, highly rigid, and difficult to deform.

  FIG. 2 is a diagram showing an in-cylinder pressure curve in a four-cycle engine. As shown in the figure, when the pin portion of the crankshaft is at the top dead center of the compression process (crank angle θ is 0 °), an explosion occurs immediately after the top dead center of the compression process. The pressure in the cylinder) becomes the maximum combustion pressure when the crank angle θ reaches about 8 to 20 °. The crankshaft is loaded with the in-cylinder pressure (combustion pressure) and the rotational centrifugal force shown in FIG. In order to obtain the deformation resistance against these loads, the objective of the crankshaft design is to improve the bending rigidity and further the torsional rigidity and at the same time reduce the weight.

  In general, in designing the crankshaft, first, main specifications such as the diameter of the journal portion, the diameter of the pin portion, and the piston stroke are determined. After the main specifications are determined, the design items that can be changed to ensure bending rigidity and torsional rigidity are limited to the shape of the arm portion. For this reason, the design of the arm shape is an important factor that affects the performance of the crankshaft. As described above, the arm portion here is strictly a portion limited to a region connecting the journal portion and the pin portion, and does not include the portion of the counterweight portion region.

  For example, Patent Document 1 discloses a technique in which a hollow portion is provided in the central portion of the pin side surface and the journal side surface of the arm portion in order to increase the torsional rigidity and the bending rigidity while reducing the weight of the crankshaft. ing. The technology disclosed in this document focuses on reducing the weight and increasing rigidity of the arm when the crank angle is 0 °, that is, when the crankshaft pin is at the top dead center of the compression process. The method is shown. In other words, when the crank angle is 0 °, the design method shows how to reduce the weight of the arm when a design stiffness target is given. This is a design method that shows how to increase the rigidity of the arm when a target value for weight reduction is given.

  Further, Patent Document 2 uses a three-moment method of material mechanics, approximates the crankshaft with a stepped round bar beam, and minimizes the load value applied to the journal part and the rigidity of the arm part and the arm. An optimization calculation method for obtaining an optimum distribution of the mass moment of the counterweight portion from the mass moment of the portion is shown. The technique disclosed in this document adopts an existing value for the rigidity of the arm part or determines it by another method, and then a plurality of (for example, four cylinders) so as to minimize the bearing load of the journal part. This is a method of adjusting the mass moment distribution of the counterweight portion of the eight counterweight crankshafts.

Japanese Patent No. 4998233 Japanese Patent Laid-Open No. 10-169637

  As shown in FIG. 2, the in-cylinder pressure becomes the maximum combustion pressure not when the crank angle θ is 0 ° but when the crank angle θ is about 8 to 20 °. For this reason, the maximum combustion pressure is applied to the pin portion of the crankshaft via the connecting rod when the crank angle θ is about 8 to 20 °. At this time, the direction in which the combustion pressure is applied to the pin portion is the direction from the axial center of the piston pin (the axial center of the small end portion of the connecting rod) toward the axial center of the pin portion. For this reason, the maximum load due to the maximum combustion pressure is not applied to the arm part in a direction along the straight line connecting the axis of the pin part and the axis of the journal part (hereinafter also referred to as “arm part center line”). It is loaded in a direction inclined with respect to the arm center line.

  In this regard, in the design of the arm portion shape in Patent Document 1, the maximum load due to the maximum combustion pressure is applied to the arm portion in a state where the crank angle is 0 °, that is, in the direction along the arm portion center line. It is assumed that this is done. Then, since the arm part shape obtained by the technique disclosed in Patent Document 1 is not obtained under conditions that reflect the actual situation, it is not necessarily appropriate for improving rigidity and reducing weight. Cannot be said. Further, the technique disclosed in Patent Document 2 is not intended to improve the arm rigidity.

  The present invention has been made in view of such circumstances, and the crankshaft of a reciprocating engine capable of improving bending rigidity and simultaneously reducing the weight reflecting the actual situation, and the design of the crankshaft. It aims to provide a method.

  In order to solve the above-mentioned problems, the present invention is summarized as a crankshaft of a reciprocating engine shown in (I) below and a crankshaft design method shown in (II).

(I) It has a journal part serving as a rotation center, a pin part eccentric with respect to the journal part, and a crank arm part connecting the journal part and the pin part, and is mounted on a reciprocating engine. A crankshaft on which a load due to combustion pressure is applied in a direction from the axial center of the piston pin to the axial center of the pin portion via a connecting rod;
Crank the crank arm so that the bending rigidity of the crank arm in the load direction of the maximum load satisfies the target rigidity and the weight of the crank arm satisfies the target weight when the load due to the combustion pressure becomes maximum. The reciprocating engine crankshaft is characterized in that the shape of the arm portion is asymmetrical with respect to an arm portion center line connecting the axis of the pin portion and the axis of the journal portion.

(II) It has a journal part serving as a rotation center, a pin part eccentric to the journal part, and a crank arm part connecting the journal part and the pin part, and is mounted on a reciprocating engine. A crankshaft design method in which a load due to combustion pressure is applied in a direction from the axial center of the piston pin to the axial center of the pin portion via a connecting rod,
Crank the crank arm so that the bending rigidity of the crank arm in the load direction of the maximum load satisfies the target rigidity and the weight of the crank arm satisfies the target weight when the load due to the combustion pressure becomes maximum. The crankshaft design method is characterized in that the shape of the arm portion is asymmetrical with respect to an arm portion center line connecting the axis of the pin portion and the axis of the journal portion.

  In this design method, the shape of the crank arm portion can be designed so that the bending rigidity of the crank arm portion in the load direction due to the combustion pressure becomes maximum when the load load due to the combustion pressure becomes maximum. preferable.

  Further, in the above design method, when the load of the load due to the combustion pressure becomes maximum, the weight of the crank arm portion is minimized under the condition that the bending rigidity of the crank arm portion in the load direction of the maximum load is constant. In this manner, the shape of the crank arm portion can be designed.

  According to the present invention, since the shape of the arm portion is asymmetric with the center line of the arm portion as a boundary under conditions that reflect the actual situation, the bending rigidity of the arm portion is improved with high reliability. The weight of the arm can be reduced.

It is a side view which shows typically an example of the crankshaft for a general multicylinder engine. It is a figure which shows the in-cylinder pressure curve in a 4-cycle engine. It is a schematic diagram for demonstrating the evaluation method of the bending rigidity of an arm part. It is a schematic diagram for demonstrating the evaluation method of the torsional rigidity of an arm part, The figure (a) shows the side view of 1 throw, and the figure (b) shows the front view in the axial direction view, respectively. It is a figure which shows typically the arm part shape of the conventional crankshaft, The figure (a) shows the front view in an axial view, The figure (b) shows a side view, respectively. It is a figure which shows typically an example of the arm part shape of the crankshaft of this invention, The figure (a) is a front view in an axial view, The figure (b) is AA in the right half of an arm part. 'Cross sectional view, (c) shows a BB' sectional view in the left half of the arm part. FIGS. 7A and 7B are diagrams in which the right half of the arm portion of FIG. 6 is extracted, in which FIG. 6A shows a front view in an axial view, and FIG. FIGS. 7A and 7B are diagrams in which the left half of the arm portion of FIG. 6 is extracted, in which FIG. 6A shows a front view in an axial view, and FIG. It is a conceptual diagram explaining the selection freedom degree of the design parameter of the arm part rigidity in the crankshaft of this invention. It is a figure which shows the geometrical relationship between the arm part of a crankshaft, and a connecting rod at the time of the load of combustion pressure becoming the maximum. It is a figure which shows the correlation with crank angle (theta) and the maximum load load angle (alpha) in the time of the load of combustion pressure becoming the maximum. It is a figure which shows another example of the geometric relationship between the arm part of a crankshaft, and a connecting rod at the time of the load of combustion pressure becoming the maximum. It is a flowchart which shows an example of the design point of the arm part in the crankshaft of this invention. It is a figure which shows an example of the beam shape in the beam theory of material mechanics, Comprising: The figure (a) shows a rectangular beam, The figure (b) shows a weight reduction beam, respectively. It is a figure which shows the left-right asymmetric arm part shape using the concept of the weight reduction beam shown in FIG.14 (b). It is a figure which shows designing an arm part shape so that the bending rigidity of an arm part may become the maximum when the load by combustion pressure becomes the maximum. FIG. 14 is a diagram showing that minimizing weight and maximizing bending rigidity are equivalent as objective functions in the design procedure of the arm portion shown in FIG. 13. It is a figure which shows an example of the arm part shape in the crankshaft of this invention. It is a figure which shows an example of the arm part shape in the conventional crankshaft. It is a figure which compares and shows each bending rigidity of the arm part of this invention shown in FIG. 18, and the conventional arm part shown in FIG. It is a figure which compares and shows the weight of 1 throw of each of the arm part of this invention shown in FIG. 18, and the conventional arm part shown in FIG. It is a figure which shows another example of the arm part shape in the crankshaft of this invention.

  Hereinafter, embodiments of the crankshaft of the reciprocating engine of the present invention and the design method of the crankshaft will be described in detail.

1. 1. Basic technologies to be considered in crankshaft design 1-1. Bending Rigidity of Arm Part FIG. 3 is a schematic diagram for explaining a method for evaluating the bending rigidity of the arm part. As shown in the figure, for each throw of the crankshaft, the combustion pressure load F caused by ignition and explosion in the cylinder is applied to the pin portion P via the connecting rod. At this time, since the journal portions J at both ends are supported by the bearings in each throw, the load F is transmitted from the pin portion P to the journal bearing through the arm portion A. As a result, the arm portion A enters a three-point bending load state, and a bending moment M acts on the arm portion A. Along with this, in the arm part A, compressive stress is generated on the outer side in the plate thickness direction (journal part J side), and tensile stress is generated on the opposite inner side (pin part P side). At this time, the bending rigidity Mc of the arm portion A affects. This bending rigidity Mc and the bending rigidity Mt of the entire one throw including the bending rigidity of the pin part and the journal part can be evaluated by the following equation (1).

Mt = F / u (1)
In the equation, F is a combustion pressure load applied to the pin portion, and u is a displacement in the combustion pressure loading direction at the axial center of the pin portion.

1-2. FIG. 4 is a schematic diagram for explaining an evaluation method of the torsional rigidity of the arm part. FIG. 4A is a side view of one throw, and FIG. 4B is an axial view thereof. The front view at is shown respectively. Since the crankshaft rotates around the journal portion J, a torsion torque T is generated as shown in FIG. Therefore, in order to ensure smooth rotation without causing resonance with respect to the torsional vibration of the crankshaft, it is necessary to increase the torsional rigidity Tc of the arm portion A. This is because the torsional rigidity of each throw greatly depends on the torsional rigidity of the arm part A when the diameter of the pin part P and the diameter of the journal part J are specified. The torsional rigidity Tc of the arm part A and the torsional rigidity Tt of one entire throw including the torsional rigidity of the pin part and the journal part are given by the following equation (2).

Tt = T / γ (2)
In the formula, T is a torsion torque, and γ is a torsion angle of the journal portion.

  For these reasons, it is necessary to improve both the bending rigidity and torsional rigidity of the arm part in designing the crankshaft. The weight portion W hardly contributes to bending rigidity and torsional rigidity. For this reason, the shape of the arm part A is mainly related to the improvement of the bending rigidity and the torsional rigidity, and the shape of the weight part W is not related. The weight part W mainly plays a role of adjusting the position of the center of gravity and the mass to balance the mass.

2. 2. Crankshaft of the present invention and design method thereof 2-1. Outline FIG. 5 is a view schematically showing the shape of an arm portion of a conventional crankshaft. FIG. 5 (a) shows a front view in an axial direction, and FIG. 5 (b) shows a side view. As shown in the figure, the arm portion A of the conventional crankshaft has a symmetrical shape with an arm portion center line Ac connecting the shaft center Pc of the pin portion P and the shaft center Jc of the journal portion J as a boundary. Has been. That is, in the arm portion A, the right half (hereinafter also referred to as “arm right half”) Ar and the left half (hereinafter also referred to as “arm left half”) Af are symmetrical with respect to the arm portion center line Ac. This is because the conventional shape design of the arm portion A is performed on the assumption that the maximum load on the arm portion A due to the maximum combustion pressure is applied in the direction along the arm portion center line Ac.

In contrast, the arm portion of the crankshaft of the present invention has the following characteristics.
6A and 6B are diagrams schematically showing an example of the shape of the arm portion of the crankshaft of the present invention, where FIG. 6A is a front view in an axial view, and FIG. 6B is a right half of the arm portion. A sectional view taken along the line AA ′ in FIG. 1, and FIG. 4C shows a sectional view taken along the line BB ′ in the left half of the arm portion. As shown in the figure, the arm portion A of the crankshaft of the present invention has an asymmetric shape with the arm portion center line Ac as a boundary. That is, the arm right half Ar and the arm left half Af are asymmetric with respect to the arm center line Ac.

  The shape design of the arm part A in the present invention is such that the maximum load Fmax to the arm part A due to the maximum combustion pressure reflects the actual state and the load is applied to the arm part A in a state where the crank angle θ is about 8 to 20 °. That is, it is performed on the assumption that the load is applied in a direction inclined at an angle α with respect to the arm center line Ac. Then, the respective shapes of the arm right half Ar and the arm left half Af are individually changed, and the bending rigidity of the arm part A in the load direction of the maximum load Fmax to the arm part A satisfies the target rigidity, and The shape of the arm part A is determined so that the weight of the arm part A satisfies the target weight.

  In the following description, the crossing angle of the load direction of the load on the arm part A due to the combustion pressure with respect to the arm part center line Ac (the direction from the axis of the piston pin to the axis of the pin part) is also referred to as the load load angle β. Called. Among the load load angles β, the crank angle θ is about 8 to 20 ° and the maximum load Fmax due to the maximum combustion pressure is applied is also referred to as the maximum load load angle α.

  FIGS. 7A and 7B are diagrams in which the right half of the arm portion in FIG. 6 is extracted. FIG. 7A is a front view in an axial direction, and FIG. 7B is a cross-sectional view along A-A ′. 8A and 8B are diagrams in which the left half of the arm portion in FIG. 6 is extracted. FIG. 8A shows a front view in an axial direction view, and FIG. 8B shows a B-B ′ sectional view. FIG. 9 is a conceptual diagram illustrating the degree of freedom in selecting design parameters for arm portion rigidity in the crankshaft of the present invention.

  As shown in FIG. 7, when extracting the right half Ar of the arm part A in the crankshaft of the present invention and extracting the left half Af of the arm part A as shown in FIG. As shown, the total bending rigidity Mc of the arm part A is the sum of the bending rigidity “Mr / 2” of the arm right half Ar and the bending rigidity “Mf / 2” of the arm left half Af. Similarly, the total torsional rigidity Tc of the arm portion A is the sum of the torsional rigidity “Tr / 2” of the arm right half Ar and the torsional rigidity “Tf / 2” of the arm left half Af.

  FIG. 9 also shows the bending rigidity Mp and torsional rigidity Tp of the arm portion A in the conventional crankshaft. In the case of the conventional crankshaft, since the shape of the arm portion is symmetrical, the design parameter is one. For this reason, the bending stiffness Mp and the torsional stiffness Tp have a one-to-one correspondence with the design parameter. When the design parameter is selected, there is no degree of freedom in selecting the combination of the bending stiffness Mp and the torsional stiffness Tp.

  On the other hand, in the crankshaft of the present invention, the shape of the arm part A is different between the right half Ar and the left half Af, so the design parameter increases to two. Therefore, the bending rigidity “Mr / 2” and the torsional rigidity “Tr / 2” of the arm right half Ar and the bending rigidity “Mf / 2” and the torsional rigidity “Tf / 2” of the arm left half Af are selected independently. be able to. The sum of these becomes the overall rigidity of the asymmetric arm portion A. That is, in order to reduce the weight of the crankshaft, the options for the stiffness design parameter increase.

  In short, the rigidity of the arm portion is expressed by the bending rigidity Mp and the torsional rigidity Tp in the conventional crankshaft, but can be expressed by the following expressions (3) and (4) in the crankshaft of the present invention. Therefore, the crankshaft of the present invention has an advantage that the degree of freedom of design is increased because the left and right shapes of the arm portions can be independently selected.

Flexural rigidity: Mc = (Mr + Mf) / 2 (3)
Torsional rigidity: Tc = (Tr + Tf) / 2 (4)

  And since the freedom degree of selection of a design parameter increases, as shown in the following (5) Formula and (6) Formula by selecting each of the shape of the right-and-left half of an arm part appropriately at the time of weight reduction. Therefore, there is a possibility that the rigidity of the asymmetrical arm portion can be made larger than the rigidity of the symmetrical arm portion. That is, the weight is increased and the degree of freedom to increase the rigidity is increased, resulting in a merit.

Mc = (Mr + Mf) / 2> Mp (5)
Tc = (Tr + Tf) / 2> Tp (6)

  FIG. 10 is a diagram showing a geometric relationship between the arm portion of the crankshaft and the connecting rod when the combustion pressure load becomes maximum. FIG. 11 is a diagram showing a correlation between the crank angle θ and the maximum load load angle α at the time when the load of the combustion pressure becomes maximum. Regarding the bending load, the combustion pressure in the cylinder shows the maximum value as shown in FIG. 2 when the crankshaft rotates slightly from the top dead center of the compression process and the crank angle θ is about 8 to 20 °. It is.

  As shown in FIG. 10, the arm portion A receives a maximum load Fmax due to the maximum combustion pressure in a direction inclined at a maximum load load angle α with respect to the arm portion center line Ac. The maximum load load angle α is the crank angle “θ” at the time when the maximum combustion pressure is applied, and half of the piston stroke Ls (distance between the axis Pc of the pin portion P and the axis Jc of the journal portion J). Ls / 2 ", and the outer angle of the triangle determined from two corners of the distance" Lc "between the axis 4Sc (axis of the piston pin) of the small end 4S of the connecting rod 4 and the axis Pc of the pin P. . That is, the arm portion A receives a bending load inclined with respect to the arm portion center line Ac at a maximum load load angle α (approximately 10 to 20 degrees) slightly larger than the crank angle θ (approximately 8 to 20 °). (See FIG. 11).

  FIG. 12 is a diagram showing another example of the geometric relationship between the arm portion of the crankshaft and the connecting rod at the time when the combustion pressure load becomes maximum. In the engine shown in the figure, the position of the axis Jc of the journal part J (crank rotation axis) is offset at a position slightly away from the cylinder center axis, or the position of the axis Jc of the journal part J is the center of the cylinder. Although arranged on the shaft, the position of the axial center of the piston pin is offset to a position slightly away from the cylinder center axis. In this case, the maximum load load angle α is obtained by geometrically considering the same triangle and offset amount Lo as those described in FIG.

2-2. Design Procedure Non-parametric shape optimization software can be used for the actual design to increase the bending rigidity of the arm. In the non-parametric shape optimization software, the arm part to which a bending load with a maximum load load angle α inclined to about 10 to 20 degrees is used as a model, the objective function is the bending stiffness, the constraint is the weight, Asymmetrical arms with high torsional rigidity can be designed.

  As another design method, create multiple models with asymmetrical left and right arms, and apply FEM analysis to each model with a bending load or torsional torque inclined at the maximum load load angle α, and make it the target A trial and error design method may be used in which the best one that can provide rigidity is selected. In that case, an approximately asymmetrically shaped arm portion that is approximately optimal is obtained.

  However, the use of non-parametric shape optimization software is more useful in that it is a more theoretically extremized lightweight and highly rigid crankshaft, and more desirable results can be obtained. However, whatever design method is used, basically, the left and right shapes of the arm portions may be designed asymmetrically so that the bending rigidity is maximized by the bending load inclined to the maximum load load angle α.

  FIG. 13 is a flowchart showing an example of the design procedure of the arm portion in the crankshaft of the present invention. Here, non-parametric shape optimization software is used. First, with the arm portion of the crankshaft as a design region, a bending load Fmax inclined at the maximum load load angle α is applied to a one-throw analysis model. Next, a shape restriction on the shape of the arm part is added. In other words, in the case of a die forging crankshaft, a range of allowable shapes is added due to design and manufacturing restrictions, such as adding a draft angle for a die forged crankshaft.

  Furthermore, in the optimization analysis, an analysis is performed such that the bending rigidity increases as much as possible based on the initial model of the analysis, with the improvement of the bending rigidity as an objective function. The constraint condition at this time is a reduction in the weight of the arm portion, and a change amount of reduction with respect to the weight of the initial model is set. When reducing the weight, it is specified in the form of a weight reduction of minus X% with respect to the initial model.

  In the iterative calculation, the shape of the arm portion is slightly changed so that the weight reduction that is a constraint condition is satisfied first. When the constraint condition (weight reduction) is satisfied, a minute correction of the arm portion shape is added so that the bending rigidity, which is the objective function, is increased while maintaining the constraint condition.

  Further, it is determined whether or not the bending rigidity has increased to the limit and has reached an extreme value (maximum value). That is, the state in which the change in the objective function (bending stiffness) is eliminated is regarded as an extreme value, and when this state is reached, it is determined that the calculation has converged. At this time, the arm part weight satisfies the target weight reduction weight, and at the same time, the rigidity against the maximum bending load inclined at the maximum load load angle α is theoretically maximized, and the bending rigidity of the arm part satisfies the target high rigidity. doing. At this time, the shape of the arm part is asymmetrical with respect to the arm part center line.

2-3. Specific Example 2-3-1. Maximizing bending rigidity as an objective function To design the arm part shape so that the bending rigidity of the arm part is maximized when the bending load at the maximum load angle α is applied, an asymmetrical arm part shape is required. It is a condition. In the following, a simple specific example based on material mechanics is shown, but it is not limited to this.

  (A) Basic knowledge based on material mechanics

  Regarding the bending stiffness, taking a rectangular beam as an example from the knowledge of general material mechanics, the relationship between the bending stiffness and the moment of inertia of the cross section is expressed by the following equations (7) to (8). From the relationship of the same formula, increasing the moment of inertia of the cross section increases the bending rigidity.

Bending rigidity: E × I (7)
Sectional moment of inertia: I = (1/12) × b × h ³ (8)
Deflection displacement: v = k (M / (E × I)) (9)
In the formulas (7) to (9), the cross section of the arm portion is regarded as a rectangle, and b: arm portion width, h: arm portion thickness, E: longitudinal elastic modulus, M: bending moment, k: shape factor.

  On the other hand, regarding torsional rigidity, from a general knowledge of material mechanics, if a round bar is given as a simple example, the relationship between the torsional rigidity and the moment of inertia of the cross-sectional pole is expressed by the following equations (10) to (12). Is done. From the relationship of the same formula, it is desirable to increase the torsional rigidity by forming the cross section in a circular shape and increasing the cross-sectional pole secondary moment. Here, if the substance (mass) is arranged far from the torsional central axis, the cross-sectional pole secondary moment increases. For this reason, in order to increase the torsional rigidity, it is desirable to form a large mass in a circular shape with a large radius around the torsion center or to form a shape close to a circular shape. Here, the direction of the design guidelines is pointed out.

Torsional rigidity: T / γ (10)
Sectional pole secondary moment: J = (π / 32) × d ⁴ (11)
Twist angle: γ = T × L / (G × J) (12)
In the formulas (10) to (12), L: axial length, G: transverse elastic modulus, d: radius of a round bar, and T: torsion torque.

  In general, it is necessary to increase the bending rigidity of the arm portion of the crankshaft. In practice, it is also necessary to increase the torsional rigidity. Therefore, it is desirable to increase the bending rigidity of the arm portion and further increase the torsional rigidity. However, since the improvement in torsional rigidity is additive, the following description does not actively describe the torsional rigidity.

(B) Explanation of the shape of the arm portion that is lightweight and highly rigid with respect to bending as described above is left-right asymmetric. As described above, the arm portion has a maximum in the direction inclined at the maximum load load angle α with respect to the arm center line. The bending load is applied. Focusing on this point, it will be shown below that it is effective to make the arm shape asymmetrical from the shape of a light and rigid beam.

  FIG. 14 is a diagram showing an example of a beam shape in the beam theory of material mechanics. FIG. 14A shows a rectangular beam, and FIG. 14B shows a lightened beam. When considered in terms of material mechanics and simplified by the beam theory, a beam subjected to a bending load has a high rigidity, a small deformation, and the lightest two-dimensional beam shape (having a constant thickness t) as shown in FIG. As shown in FIG. 14B, the beam is not a rectangular beam having a constant plate width B, but a light-weight beam in which the plate width B increases monotonously from the load point toward the fixed end.

  15A and 15B are diagrams showing the shape of an asymmetrical arm portion using the concept of the lightening beam shown in FIG. 14B, where FIG. 15A is a perspective view and FIG. 15B is an arm portion. Sectional views perpendicular to the center line are shown respectively. As shown in FIG. 10 and FIG. 12, the arm portion A to which the maximum bending load is applied in the direction inclined at the maximum load angle α with respect to the arm center line is as shown in FIG. Suppose that a plurality of beams having a thickness t are stacked and synthesized. Then, if the cross-sectional shape of the plurality of beams is a lightened beam whose plate width B monotonously increases toward the fixed end as shown in FIG. Can be assumed. If the arm portion A is cut along a plane perpendicular to the arm portion center line Ac as shown in FIG. 15A, the cross section of the arm portion A as shown in FIG. The shape is asymmetrical with respect to the center line Ac.

  As described above, the arm portion A is asymmetrical with respect to the maximum bending load applied to the arm portion A at the maximum load load angle α. Although many asymmetric shapes of the arm part A are conceivable, as shown in FIG. 16, the load load angle β is changed as a parameter, and when the load load angle β is the maximum load load angle α, that is, the load applied by the combustion pressure. If the arm portion A is designed to have a left-right asymmetric shape so that the bending rigidity is maximized at the time when becomes maximum, it is possible to achieve the most efficient weight reduction without luxury. Thereby, the arm part A becomes the lightest and most rigid, and the crankshaft performance can be maximized.

2-3-2. Minimize weight as objective function Design the arm shape so that the weight of the arm is minimized under the condition that the bending rigidity of the arm is constant when the bending load at the maximum load angle α is applied. As described above, this is equivalent to designing the arm portion shape so that the bending rigidity of the arm portion is maximized when the bending load at the maximum load load angle α is applied. That is, minimizing the weight as the objective function is a change in maximizing the bending rigidity in terms of expression, and both indicate the same arm shape after the optimum design, meaning that the requirements are the same.

  FIG. 17 is a diagram showing that minimizing weight and maximizing bending rigidity are equivalent as objective functions in the design procedure of the arm portion shown in FIG. 13. As shown in the figure, the optimal design of the arm part is when the constraint condition is set to increase rigidity and the objective function is set to weight reduction (right side in FIG. 17). There are cases where the reduction and the objective function are set to increase rigidity (on the left side in FIG. 17). The optimization of the two differs in the course of the process, but the design shape that finally converges is the same. For example, in both cases, the convergence shape is -B% lighter, the rigidity is increased by A%, and the arm part shape is the same.

2-3-3. Example of Shape of Arm Part FIG. 18 is a diagram showing an example of the shape of the arm part in the crankshaft of the present invention. FIG. 19 is a diagram showing an example of the shape of an arm portion in a conventional crankshaft. In any of the drawings, (a) shows a perspective view of one throw, and (b) shows a cross-sectional view at a CC ′ position perpendicular to the center line of the arm portion in (a). Furthermore, (c) shows a cross-sectional view at a DD ′ position different from the CC ′ position perpendicular to the arm portion center line in (a).

  As shown in FIG. 13, the arm portion A of the present invention shown in FIG. 18 is derived under a bending load inclined at the maximum load load angle α according to the design procedure using the non-parametric shape optimization software. In addition, it is lightweight and has high bending rigidity, and has an asymmetrical shape with the arm center line Ac as a boundary. On the other hand, the conventional arm portion A shown in FIG. 19 has a symmetrical shape with the arm portion center line Ac as a boundary.

  FIG. 20 is a diagram comparing the bending rigidity of the arm portion of the present invention shown in FIG. 18 and the conventional arm portion shown in FIG. FIG. 21 is a diagram comparing and comparing the weights of their respective one throws. In any of the figures, the ratio is displayed based on the conventional arm portion as a reference (100%).

  As shown in FIG. 20, the bending rigidity of the arm part of the present invention is larger than that of the conventional arm part. Moreover, as shown in FIG. 21, the weight of 1 throw including the arm part of this invention becomes lighter than the conventional arm part. That is, the asymmetrical arm portion as in the present invention is lightweight and has high bending rigidity.

  FIG. 22 is a diagram showing another example of the arm portion shape in the crankshaft of the present invention. In the same figure, (a) shows a perspective view of one throw, (b) shows a cross-sectional view at a CC ′ position perpendicular to the arm center line in (a), and (c) shows (a). Sectional drawing in DD 'position different from CC' position perpendicular | vertical to the arm part centerline in FIG. The shape of the arm shown in the figure was analyzed with this shape constraint in addition to allowing the formation of a recess in order to actively reduce weight as a shape constraint in the design procedure shown in FIG. Is.

  As described above, the crankshaft of the present invention has a highly reliable bending rigidity because the shape of the arm portion is asymmetrical with the center line of the arm portion as a boundary under conditions that reflect the actual situation. At the same time, the weight can be reduced. Such a crankshaft can be effectively obtained by the design method of the present invention.

  The crankshaft of the present invention is intended for a crankshaft mounted on any reciprocating engine. That is, the number of cylinders of the engine may be any of 2, 3, 4, 6, 8, and 10 cylinders, or more. The arrangement of the engine cylinders is not particularly limited, such as an in-line arrangement, a V-type arrangement, or an opposed arrangement. The fuel of the engine is not limited to gasoline, diesel or biofuel. The engine also includes a hybrid engine formed by combining an internal combustion engine and an electric motor.

  The present invention can be effectively used for a crankshaft mounted on any reciprocating engine.

1: crankshaft,
J, J1-J5: Journal part, Jc: Axis of journal part,
P, P1-P4: Pin part, Pc: Axis center of the pin part,
Fr: front part, Fl: flange part,
A, A1 to A8: Crank arm part, Ac: Arm part center line,
Ar: right half of arm part, Af: left half of arm part,
W, W1-W8: counterweight part,
2: damper pulley, 3: flywheel,
4: Connecting rod, 4S: Small end,
4Sc: Axis of small end (axis of piston pin)

Claims (2)

It has a journal part that is the center of rotation, a pin part that is eccentric with respect to this journal part, and a crank arm part that connects the journal part and the pin part, and is mounted on a reciprocating engine, and a connecting rod is attached to the pin part. A crankshaft design method in which a load due to combustion pressure is applied in a direction from the axial center of the piston pin to the axial center of the pin portion,
When the load of the load due to the combustion pressure becomes maximum, the bending rigidity of the crank arm in the load direction of the maximum load is maximized while satisfying the target rigidity, and the weight of the crank arm reaches the target weight. The crankshaft design method is characterized in that the shape of the crank arm portion is asymmetrical with respect to the center line of the arm portion connecting the axis of the pin portion and the axis of the journal portion so as to satisfy. It has a journal part that is the center of rotation, a pin part that is eccentric with respect to this journal part, and a crank arm part that connects the journal part and the pin part, and is mounted on a reciprocating engine, and a connecting rod is attached to the pin part. A crankshaft design method in which a load due to combustion pressure is applied in a direction from the axial center of the piston pin to the axial center of the pin portion,
At the time when the load of the load due to the combustion pressure becomes maximum, the bending rigidity of the crank arm portion in the load direction of the maximum load satisfies the target rigidity, and the bending rigidity of the crank arm portion is constant. The shape of the crank arm part should be asymmetric with respect to the arm center line connecting the axis of the pin part and the axis of the journal part so that the weight of the crank arm part is minimized.
Crankshaft design method characterized by

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