JP2014227909A - Engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine in which a degree of freedom and flexibility of a vehicle design can be improved.SOLUTION: The engine is provided with a counter weight 5 for providing an unbalance mass to a rotation shaft C of a crank shaft 1. Also, end weights 6a, 7a for providing an unbalance mass to the rotation shaft C of the crank shaft 1 are respectively provided on a crank pulley 6 and a drive plate 7 provided at both ends of the crank shaft 1. Furthermore, an over-balance rate δof the end weights 6a, 7a is set larger than an over-balance rate δof the counter weight 5.

Description

  The present invention relates to an engine that suppresses vibration by using an unbalanced mass with respect to a rotation shaft of a crankshaft.

  2. Description of the Related Art Conventionally, a technique for suppressing engine vibration by reducing an inertia force or an inertia moment generated during operation of an engine with a counterweight is known. In general, in such a technology, mechanical elements included in the power transmission system path from the crankshaft to the piston are classified into reciprocating motion elements (vibration elements) and rotary motion elements (rotation elements), and each motion element is engine vibration. It will be analyzed what kind of effect it will have. Here, the former mass is called reciprocating mass, and the latter mass is called rotating mass.

  In the case of a single cylinder engine, if the mass of the counterweight (unbalance mass) is set to a value equivalent to the rotational mass, the rotational motion element and the counterweight are balanced, and the lateral direction (perpendicular to the rotation axis of the crankshaft) Direction, and a direction perpendicular to the vibration direction of the reciprocating motion element) is zero. In this way, a state in which an unbalance mass having a magnitude that cancels out the inertial force in the lateral direction of the engine is attached is referred to as “overbalance ratio is 0% (balance ratio is 100%)”. In this state, the inertial force in the longitudinal direction of the engine (the vibration direction of the reciprocating motion element) remains. The inertia force in the vertical direction can be offset by setting the mass of the counterweight to a value corresponding to the sum of the reciprocating mass and the rotating mass.

  Further, in an in-line three-cylinder engine, the inertial force between the cylinders is balanced regardless of the mass of the counterweight. On the other hand, since the generation direction and timing of the inertia force are different among the cylinders, the couple remains in the pitch direction with respect to the crankshaft. Therefore, by setting the counterweight for each cylinder to be slightly heavy, a couple having a phase opposite to that of the above-described residual couple is generated to reduce the residual couple. In this way, a method of adjusting the vibration characteristics of the engine by setting the mass of the counterweight to be larger than the state where the balance ratio is 100% is called an over-balancing method (see, for example, Patent Document 1).

  In the over-balancing method, a counterweight having a larger unbalance mass than the “balance rate of 100%” state is attached to the crankshaft. As a result, the weight of the engine body increases and fuel consumption tends to deteriorate, making it difficult to reduce the size of the engine. In particular, when the unbalance mass of the counterweight is increased in order to reduce the residual couple of the engine as in an in-line three-cylinder engine, the weight and size of the engine increase as the balance ratio increases.

  In response to the above problem, a technique has been developed that generates an unbalanced mass equivalent to that of a counterweight by adding an unbalanced mass to the end of the crankshaft. For example, a technique has been proposed in which an unbalanced mass is set in a crank pulley, a flywheel, a drive plate, or the like that is fixed to an end of a crankshaft, and the dynamic balance of the engine is controlled (for example, Patent Document 2). 3). With such a device, the balance of the crankshaft can be corrected.

Japanese Patent Laid-Open No. 10-258794 Japanese Patent Publication No. 07-030777 Japanese Utility Model Publication No. 50-025844

  However, the conventional over-balancing method does not consider the relationship between the balance rate derived from the unbalanced mass of the counterweight and the balance rate derived from the unbalanced mass outside the crankcase. Therefore, when the existing engine is applied to different vehicle types, the balance ratio of the entire engine may not be set to a desired value only by adjusting the balance ratio outside the crankcase. For example, when the diameter of the crank pulley or drive plate is restricted due to layout restrictions, or when the axial distance of the crankshaft is restricted, an allowance for adjusting the unbalanced mass outside the crankcase is secured. Can not. As a result, the crankshaft must be redesigned for each vehicle type, and the existing engine cannot be diverted to a different vehicle type.

  One of the objects of the present case was created in view of the above-described problems, and is to provide an engine that can improve the degree of freedom and flexibility of vehicle design. The present invention is not limited to this purpose, and is a function and effect derived from each configuration shown in the embodiments for carrying out the invention described later, and other effects of the present invention are to obtain a function and effect that cannot be obtained by conventional techniques. Can be positioned.

  (1) An engine disclosed herein is provided on a crankshaft and is provided with a counterweight for providing an unbalanced mass with respect to the rotating shaft of the crankshaft, and an unbalanced mass with respect to the rotating shaft provided at both ends of the crankshaft. And an end weight for providing. The end weight overbalance ratio is set to a value larger than the counterweight overbalance ratio.

  Here, the overbalance rate is a parameter corresponding to a ratio (a ratio of exceeding the balance) in which the unbalanced mass of the engine is added beyond the balance with the rotational motion element of the engine. Here, the mechanical elements included in the crankshaft are classified into reciprocating motion elements (vibration elements) and rotational motion elements (rotating elements). The former mass is called reciprocating mass, and the latter mass is called rotating mass.

  The overbalance ratio is obtained by subtracting the rotating mass from the product of the ratio of the rotating radius to the crank arm length (distance from the crank journal to the crankpin) (that is, the rotating radius ratio) and the unbalanced mass for a certain unbalanced mass. It is calculated as a ratio with the value as the numerator and the reciprocating mass as the denominator (for example, see Equation 1 below).

  The reciprocating mass includes the mass of the piston, the mass of the piston pin, the mass of the piston ring, the mass of a part of the connecting rod, and the like. The rotational mass includes the mass of the crankpin, the mass of the web, the mass of a part of the connecting rod, and the like. Typically, about 1/3 of the total mass of the connecting rod is considered reciprocating mass, and about 2/3 of the total mass of the connecting rod is considered rotary mass. More precisely, the equivalent mass at the upper end of the connecting rod is obtained as the reciprocating mass, and the equivalent mass at the lower end is obtained as the rotating mass.

(2) The counterweight overbalance ratio is set to a value of 0 [%] or more, and the added value of the counterweight overbalance ratio and the end weight overbalance ratio is 100 [%] or less. Is preferably set to a value of.
That is, it is preferable that each of the counterweight and the end weight is overbalanced, and each of the pitching moment and the yawing moment is equal to or less than a predetermined value.

  In an in-line three-cylinder engine (in the case of equidistant ignition), when the overbalance ratio is 0%, the yawing moment generated in the engine becomes 0, and the pitching moment remains. Each of these pitching moment and yawing moment is a free moment of inertia generated in the engine. Further, when the overbalance ratio increases, the pitching moment decreases instead of increasing the yawing moment. When the overbalance ratio is 100%, the pitching moment becomes 0 and the yawing moment remains. The added value of the pitching moment and the yawing moment is constant regardless of the magnitude of the overbalance ratio.

  (3) Also, the counterweight unbalance mass on the front side of the engine in the pitching direction of the engine is set to be balanced with the counterweight unbalance mass on the rear side of the vibration center axis. It is preferred that The parameters set here are preferably the unbalanced mass and the distance from the vibration center axis.

For example, it is preferable that m ₁ l ₁ ≈m ₂ l ₂ with respect to the vibration center axis in the pitching direction.
m ₁ : Front counterweight unbalanced mass
m ₂ : Unbalanced mass of the rear counterweight
l ₁ : Distance from the vibration center axis to the unbalanced mass of the front counterweight
l ₂ : Distance from the vibration center axis to the unbalanced mass of the rear counterweight

  (4) Further, the unbalanced mass of the end weight disposed on the front side of the vibration center axis in the pitching direction of the engine and the unbalance mass of the end weight disposed on the rear side of the vibration center axis. It is preferably set so that the balance mass is balanced.

For example, it is preferable that m ₁ l ₁ + M ₁ L ₁ ≈m ₂ l ₂ + M ₂ L ₂ with reference to the vibration center axis in the pitching direction.
M ₁ : Unbalance mass of front end weight
M ₂ : Rear end weight unbalanced mass
L ₁ : Distance from vibration center axis to unbalanced mass of front end weight
L ₂ : Distance from the vibration center axis to the unbalance mass of the rear end weight

In addition to the above relational expression, m ₁ l ₁ ≦ M ₁ L ₁ is preferably satisfied, and L ₁ > L ₂ is preferably satisfied. In other words, it is preferable that the distance from the vibration center axis to the front end weight is set to be longer than the distance from the rear end weight. The engine is preferably an in-line three-cylinder engine.

  According to the disclosed engine, the overweight ratio of the end weight is set to be larger than the overbalance ratio of the counterweight, so that the adjustment range of the overbalance ratio of the entire engine can be increased. For example, by adjusting the unbalance mass of the end weight, the overbalance rate of the entire engine can be at least halved without changing the counterweight. Thereby, it becomes easy to change the overbalance ratio for each vehicle on which the engine is mounted, and the degree of freedom and flexibility of vehicle design can be improved.

It is a disassembled perspective view which shows the mechanical element incorporated in the engine which concerns on one Embodiment. It is a top view for demonstrating the structure of the crankshaft of FIG. It is a graph which shows the relationship between the overbalance rate and primary moment (a pitching moment, a yawing moment) in an in-line three cylinder engine.

  An engine as an embodiment will be described with reference to the drawings. Note that the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described in the following embodiment. Each configuration of the present embodiment can be implemented with various modifications without departing from the spirit of the present embodiment, and can be selected or combined as necessary.

[1. overall structure]
FIG. 1 is an exploded perspective view for explaining main mechanical elements from a crankshaft 1 to a piston 9 built in the engine 10 of the present embodiment, and FIG. 2 is a state in which the crankshaft 1 is looked down from the cylinder side. FIG. As shown in FIGS. 1 and 2, the engine 10 is an in-line three-cylinder engine having no balancer shaft, and the piston 9 is slidable in the vertical direction inside the cylinders arranged in parallel. It is provided as follows. Each piston 9 is connected to the upper end of a connecting rod 8 (connecting rod) via a piston pin 9a. The upper end of the connecting rod 8 supports the piston 9 rotatably.

  The lower end of each connecting rod 8 is connected to the crankshaft 1 via the crankpin 3. The crankpin 3 is provided in parallel to the rotation axis C of the crankshaft 1 and is arranged at a predetermined interval in a direction away from the rotation axis C. Further, one crankpin 3 is provided for each of the three cylinders, and each crankpin 3 is arranged so that the phase angle with respect to the rotation axis C differs by 120 °. Each crankpin 3 and crank journal 2 are connected by a planar web 4. The orientation of the surface of the web 4 is substantially perpendicular to the rotation axis C.

  A crank pulley 6 and a drive plate 7 are provided at both ends of the crankshaft 1. The crank pulley 6 is a belt wheel for driving accessories of the engine 10, and the drive plate 7 is for transmitting the rotational power of the crankshaft 1 to the transmission side. The crank pulley 6 is provided with a front end weight 6a (one end weight) as an unbalanced mass with respect to the rotation axis C. Similarly, the drive plate 7 is also provided with a rear end weight 7a (one end weight) as an unbalanced mass with respect to the rotation axis C. The gravity center positions of the front end weight 6a and the rear end weight 7a are provided such that the phase angle with respect to the rotation axis C differs by 180 °, for example.

  Hereinafter, with respect to the extending direction of the rotating shaft C, the side on which the crank pulley 6 is disposed when viewed from the crankshaft 1 is the front side (front) of the engine 10 and the opposite side is the rear side (rear) of the engine 10. . The numbers of the cylinders are the first cylinder, the second cylinder, and the third cylinder in order from the front side of the engine 10. Each crankpin 3 is supported by the crankshaft 1 with its front and rear sandwiched between webs 4 having substantially the same shape. In each web 4, a counterweight 5 is integrally formed on the opposite side of the crankpin 3 with the rotation axis C interposed therebetween.

  The counterweight 5 is an unbalanced mass for giving unbalance to the rotation of the crankshaft 1 inside the crankcase 11 and is provided so as to be biased with respect to the rotation axis C. The distance from the rotation axis C to the position of the center of gravity of the counterweight 5 is called the rotation radius of the counterweight 5. The front end weight 6a and the rear end weight 7a described above are unbalanced masses with respect to the rotation axis C for giving unbalance to the rotation of the crankshaft 1 outside the crankcase 11.

[2. Settings for vibration characteristics]
[2-1. Counterweight overbalance ratio]
In the engine 10, the vibration center axis P in the pitching direction is set immediately below the center of the cylinder of the second cylinder, as shown in FIG. The vibration center axis P is an axis that passes through the center of gravity of the engine 10 and is orthogonal to the rotation axis C of the crankshaft 1 in a top view. The intersection of the rotation axis C and the vibration center axis P in FIG. 2 is the vibration center in the yawing direction. Further, in the crankcase 11 of the engine 10, the counterweight 5 is uncoupled with respect to the rotation axis C for each of the front side (front side) and the rear side (rear side) of the engine 10 that is divided by the vibration center axis P. The balance mass m _w is set. That is, the unbalance mass m ₁ ahead of the vibration center axis P and the unbalance mass m ₂ behind the vibration center axis P are set individually.

These unbalance masses m ₁ and m ₂ are at least an overbalance ratio δ depending on the reciprocating mass m _rec and the rotating mass m _{rot of the} mechanical elements included on the power transmission path from the crankshaft 1 to the piston 9. ₁ is set to be 0 [%] or more (that is, the balance rate is 100 [%] or more) (0 ≦ δ ₁ ). The overbalance rate [delta] ₁ of the front side of the vibration center axis P, is set to the same value as the overbalance rate [delta] ₁ of the rear side. Specifically, the overbalance rate Δ ₁ is set to a value of about 25 to 75 [%], for example.

The definition of the overbalance rate δ ₁ [%] is shown in Equation 1 below. In each of the reciprocating mass m _rec and the rotating mass m _rot in Equation 1, values for elements included in the range divided by the vibration center axis P are substituted. Further, when the rotation radius ratio of the counterweight 5 is common to each cylinder, the unbalance masses m ₁ and m ₂ are expressed as the following Expression 2. However, just because the overbalance rate δ ₁ is the same, the unbalance masses m ₁ and m ₂ are not necessarily the same, and may take different values.

r : Turning radius of crankpin 3
r _w : turning radius of counterweight 5
m _w : Unbalance mass of counterweight 5 (total value)
m ₁ : Unbalanced mass ahead of vibration center axis P
m ₂ : Unbalanced mass behind the vibration center axis P
m _rec : Reciprocating mass
m _rot : Rotational mass

The reciprocating mass m _rec includes the mass of the piston 9, the mass of the piston pin 9a, the mass of the piston ring, the mass of a part of the connecting rod 8, and the like. Further, the rotational mass m _rot includes the mass of the crankpin 3, the mass of the web 4, the mass of a part of the connecting rod 8, and the like. Typically, about 1/3 of the total mass of the connecting rod 8 is considered as the reciprocating mass m _rec and about 2/3 of the total mass of the connecting rod 8 is considered as the rotating mass m _rot .

In order to obtain the reciprocating mass m _rec and the rotating mass m _rot more accurately, the equivalent masses of the upper end and the lower end of the connecting rod 8 may be obtained. That is, the equivalent mass at the upper end of the connecting rod 8 is the reciprocating mass m _rec, and the equivalent mass at the lower end of the connecting rod 8 is the rotating mass m _rot , and the three types of equilibrium equations (force, moment, mass inertia) can be solved simultaneously. . In addition, “r _w / r” in the expression 1 is a rotation radius ratio of the counterweight 5.
The unbalance mass m ₁ on the front side includes the unbalance mass on the front side of the engine among the counterweights 5 connected to the crankshaft 1. Further, the unbalance mass m ₂ on the rear side includes the unbalance mass on the rear side of the engine.

[2-2. Edge balance overbalance ratio]
An overbalance ratio δ ₂ with respect to the rotation axis C is also set for each of the front end weight 6a of the crank pulley 6 and the rear end weight 7a of the drive plate 7. This overbalance rate δ ₂ functions to give unbalance to the engine 10 outside the crankcase 11 of the engine 10.

The value of overbalance rate [delta] _2, by substituting the unbalanced mass M ₂ of the unbalance mass M ₁ and the rear end portion weights 7a of the front end weights 6a in place of the unbalanced mass m _w in Equation 1 above Calculated. In this case, the rotation radius ratio r _w / r of the counterweight 5 is replaced with the rotation radius ratio R _W / r of each of the end weights 6a and 7a as shown in the following Expression 3. Further, here, the overbalance rate δ ₂ is set to a value larger than the above-described over balance rate δ ₁ (that is, 0 ≦ δ ₁ <δ ₂ ).

r : Turning radius of crankpin 3
R _w : rotation radius of each of the end weights 6a and 7a
M _w : Unbalance mass of each of the end weights 6a and 7a
m _rec : Reciprocating mass
m _rot : Rotational mass

However, the value of the overbalance ratio δ ₂ is set so that the added value (δ ₁ + δ ₂ ) with the overbalance ratio δ ₁ inside the crankcase 11 is 100% or less. Specifically, the overbalance rate δ ₂ is set to a value equal to or greater than the over balance rate δ ₁ . Further, the added value (δ ₁ + δ ₂ ) with the overbalance rate δ ₁ is set, for example, within the range of 0 to 100 [%] (the balance rate is within the range of 100 to 200 [%]).

  In the in-line three-cylinder engine 10, the total overbalance ratio δ when the counterweight 5 and the end weights 6a and 7a are taken into account influence the ratio of the free moment of inertia during operation. That is, as shown in FIG. 3, when the total overbalance ratio δ is 0 [%], the yawing moment of the engine 10 becomes 0, and the pitching moment remains. As the total overbalance ratio δ increases, the pitching moment decreases instead of increasing the yawing moment. When the overbalance rate is 100 [%], the pitching moment becomes 0 and the yawing moment remains. The added value of the pitching moment and the yawing moment is constant regardless of the total overbalance ratio δ. In this regard, in the engine 10 described above, the total overbalance ratio δ is limited to a value of 100 [%] or less, so that the pitching moment is suppressed without an excessive yawing moment.

The front end overbalance rate [delta] ₂ of overbalance ratio [delta] ₂ and the rear end portion weights 7a of weights 6a, is set to the same value. However, just because the overbalance rate δ ₂ is the same as described above, the unbalance masses M ₁ and M ₂ are not necessarily the same and may take different values. For example, as the setting position of the unbalance mass is further away from the rotation axis C of the crankshaft 1 (the rotation radius is increased), the unbalance mass that gives the same overbalance ratio δ ₂ decreases.

[2-3. Moment due to unbalanced mass]
The distance to the unbalance mass m ₁ of the counterweight 5 on the front side of the vibration center axis P (distance to the center of gravity) is set as l ₁ , and the distance to the unbalance mass m ₂ of the counterweight 5 on the rear side is l Set to ₂ . In the engine 10, the moment m ₁ l ₁ generated by the unbalance mass m ₁ on the front side and the moment m ₂ l generated by the unbalance mass m ₂ on the rear side with respect to the vibration center axis P in the pitching direction. _The unbalance mass m ₁ and the unbalance mass m _{2 with} respect to the distances l ₁ and l ₂ are set so that ₂ is substantially the same (that is, m ₁ l ₁ ≈m ₂ l ₂ ). As a result, a pitching moment around the vibration center axis P that dynamically varies with the rotation of the crankshaft 1 is generated, and the pitching vibration of the engine 10 is suppressed.

When the two counterweights 5 connected to the piston 9 of each cylinder have the same shape, the distance l ₁ corresponds to the distance between the cylinder centers of the first cylinder and the second cylinder, and the distance l 1 ₂ corresponds to the distance between the cylinder centers of the second and third cylinders. When the distance between the cylinder centers is constant, the distances l ₁ and l ₂ have the same value. In this case, the unbalance mass m ₁ on the front side and the unbalance mass m ₂ on the rear side are the same.

Further, the vibration center axis P of the crankshaft direction distance to the front end weights 6a (center of gravity of the unbalance mass M ₁₎ L ₁ Distant, from the vibration center axis P rear end weights 7a (unbalanced mass M ₂ placing the crankshaft direction distance to the center of gravity position) and L _2. In the engine 10, the moment M ₁ L ₁ generated by the unbalanced mass M ₁ of the front end weight 6a and the moment M generated by the unbalanced mass M ₂ of the rear end weight 7a with respect to the vibration center axis P. _The unbalance masses M ₁ and M ₂ of the crank pulley 6 and the drive plate 7 are set so that ₂ L ₂ is substantially the same (that is, m ₁ l ₁ + M ₁ L ₁ ≈m ₂ l ₂ + M ₂ L ₂ ). Thus, not only the inside of the crankcase 11 of the engine 10 but also the entire engine 10 including the outside of the crankcase 11 has a pitching moment around the vibration center axis P that dynamically varies with the rotation of the crankshaft 1. As a result, the pitching vibration of the engine 10 is suppressed.

Furthermore, in the engine 10, so that the distance L ₁ from the oscillation center axis P to the front end weights 6a, is longer than the distance L ₂ to the rear end weights 7a, the crank pulley 6, the position of the drive plate 7 Is set (ie, L ₁ > L ₂ ). As a result, the unbalance mass M ₁ of the front end weight 6a becomes smaller than the unbalance mass M ₂ of the rear end weight 7a (that is, M ₁ <M ₂ ).

[3. Action, effect]
(1) In the engine 10 described above, the overbalance rate δ ₂ outside the crankcase 11 is set larger than the overbalance rate δ ₁ inside the crankcase 11. Thereby, the adjustment range of the overbalance rate δ of the entire engine 10 can be increased. For example, by adjusting the unbalance masses M ₁ and M ₂ of the end weights 6 a and 7 a provided at the front end portion and the rear end portion of the crankshaft ₁ , the entire engine 10 can be changed without changing the counter weight 5. The overbalance rate δ can be adjusted. This makes it easy to change the overbalance ratio for each vehicle type and vehicle on which the engine 10 is mounted (specifically, depending on the vehicle grade, specifications, destination type, etc.), and freedom in vehicle design. The degree can be increased.

Here, a specific setting example of the overbalance ratio is shown in Table 1 below.

In the setting A, the overbalance rate δ ₁ inside the crankcase 11 is set to 20 [%], the overbalance rate δ ₂ outside the crankcase 11 is set to 60 [%], and the total overbalance rate δ is set. Is 80 [%]. When the engine 10 is applied to other vehicle types and the total overbalance ratio δ is to be halved (setting B), only the overbalance ratio δ ₂ outside the crankcase 11 is changed to 20 [% ] That is, it is not necessary to change the overbalance ratio δ ₁ inside the crankcase 11, in other words, it is not necessary to change the counterweight 5.

Further, if the overbalance ratio δ ₂ outside the crankcase 11 is reduced to 0 [%], the total overbalance ratio δ is reduced to 1/4 of the setting A (setting C). The width of such adjustment margin varies depending on the values of the overbalance ratios δ ₁ and δ ₂ before the change. However, in the engine 10 described above, since the relationship of δ ₁ <δ ₂ is always established, at least the total over balance rate δ can be halved regardless of the value of the over balance rate δ ₁ . Therefore, the freedom degree of vehicle design improves and a more flexible design is attained.

Further, by using the counterweight 5 and the end weights 6a and 7a in combination, the weight of the counterweight 5 can be reduced while keeping the relationship between the pitching moment and the yawing moment constant, and the engine 10 is reduced in weight. can do. Further, since the end weights 6a and 7a are provided at both ends of the crankshaft 1, even if the unbalance masses M ₁ and M _{2 at} the end weights 6a and 7a are slightly increased, the center positions of pitching and yawing are set. Can be moved greatly. That is, by finely adjusting the unbalance masses M ₁ and M ₂ of the end weights 6a and 7a, the center position (center of gravity position) of pitching and yawing when the engine 10 is mounted on the vehicle without changing the weight of the counter weight 5 ) Can be moved. Therefore, it becomes easy to improve the vibration characteristics when the engine 10 is mounted on the vehicle.

(2) In the engine 10, the overbalance rate δ ₁ of the counterweight 5 is set to 0 [%] or more, and the total overbalance rate δ is set to 100 [%] or less. The value of the free inertia moment (pitching moment and yawing moment) of the in-line three-cylinder engine in such an overbalance ratio setting range is a trade-off in which if one is suppressed, the other increases as shown in FIG. It becomes the relationship.

  On the other hand, since the total overbalance ratio δ is not set outside the range of 0 <δ ≦ 100 [%], at least both the pitching moment and yawing moment values can be kept within the positive range. That is, the total overbalance ratio δ can be set within a range in which the total absolute value of the free moments of inertia does not become excessive. Therefore, it is possible to improve the vibration characteristics of the engine 10 while increasing the degree of freedom in vehicle design, that is, it is possible to realize a more productive vehicle design with improved vibration characteristics.

(3) In the engine 10, as shown in FIG. 2, the unbalance mass m ₁ on the front side and the unbalance on the rear side are based on the vibration center axis P in the pitching direction set immediately below the second cylinder. The mass m ₂ is set to be balanced (m ₁ l ₁ ≈m ₂ l ₂ ). With such setting, the pitching vibration of the engine 10 can be suppressed by the pitching moment generated around the vibration center axis P. Therefore, a more productive vehicle design with improved vibration characteristics can be realized.

(4) Further, such a pitching moment around the vibration center axis P is generated not only in the crankcase 11 but also in the entire engine 10 including the outside of the crankcase 11. In other words, balance is unbalanced mass M ₂ of the unbalance of the front end weights 6a mass M ₁ and the rear end portion weights _{7a (m 1 l 1 + M} 1 L 1 ≒ m 2 l 2 + M 2 L 2) is set so as The With such a setting, pitching vibration can be more effectively suppressed in the entire engine 10 including the outside of the crankcase 11.

(5) In the engine 10 described above, the overbalance rate δ ₂ outside the crankcase 11 is set larger than the overbalance rate δ ₁ inside the crankcase 11. This compensates for the shortage in the former with respect to the role sharing between the internal unbalanced mass (eg, m ₁ , m ₂ ) of the crankcase 11 and the external unbalanced mass (eg, M ₁ , M ₂ ). Rather, it means that the latter is basically covered by the latter to provide the desired imbalance. Therefore, the former unbalanced mass (m ₁ , m ₂ ) can be minimized.

  The vibration characteristics required for the engine 10 vary in various ways depending on the support method of the engine 10, the type of engine mount, and the like. For example, in the in-line three-cylinder engine 10, whether it is better to suppress the pitching vibration and eliminate the yawing vibration with the engine mount, or whether to suppress the yawing vibration and eliminate the pitching vibration with the mount? There is no one and only answer.

On the other hand, in the engine 10 described above, when it is desired to suppress yawing vibration, the total overbalance ratio δ of the engine 10 is reduced by reducing only the unbalance amount of the end weights 6a and 7a. Can be easily reduced. On the other hand, when it is desired to suppress the pitching vibration, the total overbalance ratio δ of the engine 10 can be easily increased by increasing only the unbalance amounts M ₁ and M ₂ of the end weights 6a and 7a. it can. At this time, since the unbalance masses M ₁ and M ₂ are set so that the unbalance characteristic of the engine 10 is m ₁ l ₁ + M ₁ L ₁ ≈m ₂ l ₂ + M ₂ L ₂ , The vibration characteristics are not significantly changed by the movement of. Therefore, there is a merit that the degree of freedom in selecting the support method of the engine 10 and designing the engine mount can be improved.

[4. Modified example]
In the above-described embodiment, the counterweight 5 formed integrally with the web 4 of the crankshaft 1 is illustrated, but the position where the counterweight 5 is provided is not limited to this. For example, some unbalanced mass may be set for the crank journal 2 and the crankpin 3 of the crankshaft 1.

  The same applies to the front end weight 6a and the rear end weight 7a. For example, an unbalance mass may be set on a flywheel fixed to the crankshaft 1, or directly in the vicinity of the end of the crankshaft 1. You may form the site | part which gives unbalance mass to.

  Further, in the engine 10 described above, the inline three-cylinder engine 10 is exemplified, but the number of cylinders and the cylinder arrangement of the engine are not limited thereto. For example, in an in-line five-cylinder engine, a free moment of inertia similar to that in an in-line three-cylinder engine can occur. By applying the above configuration in such a case, the same effects as those of the above-described embodiment can be obtained.

  In addition to an in-line engine in which a plurality of cylinders are arranged in series, application to a V-type engine, a VR-type engine, a W-type engine, a horizontally opposed engine, a star engine, a single-cylinder engine, or the like is also possible. Further, the combustion method such as diesel engine and gasoline engine is not required, and it can be applied not only to a four-stroke engine but also to a two-stroke engine.

1 Crankshaft 5 Counterweight 6 Crank Pulley 6a Front End Weight (End Weight)
7 Drive plate 7a Rear end weight (end weight)
C Rotation axis P Vibration center axis δ ₁ , δ ₂ Overbalance rate

Claims (4)

A counterweight provided on the crankshaft to give an unbalanced mass to the rotation axis of the crankshaft;
An end weight provided at each of both ends of the crankshaft to give an unbalanced mass with respect to the rotation shaft,
The engine according to claim 1, wherein an overbalance ratio of the end weight is set to a value larger than an overbalance ratio of the counterweight. The counter balance overbalance rate is set to a value of 0% or more,
2. The engine according to claim 1, wherein an addition value of the counterweight overbalance ratio and the end weight overbalance ratio is set to a value of 100% or less. The counterweight unbalance mass on the front side of the vibration center axis in the pitching direction of the engine is set so as to balance the counterweight unbalance mass on the rear side of the vibration center axis. The engine according to claim 1 or 2. The unbalanced mass of the end weight disposed on the front side of the vibration center axis in the pitching direction of the engine balances the unbalanced mass of the end weight disposed on the rear side of the vibration center axis. The engine according to any one of claims 1 to 3, wherein the engine is set as follows.

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