JP4984093B2 - Power transmission mechanism - Google Patents

Description

  The present invention relates to a support structure for a gear shaft in a power transmission mechanism that transmits power between two gears via an idler gear.

  Conventionally, an engine provided with a balancer shaft in order to reduce vibration is known. This engine includes a balancer shaft that rotates in synchronization with a crankshaft, and cancels vibrations associated with piston reciprocation. In particular, in an engine having a large torque fluctuation such as a diesel engine, a gear may be used for power transmission between these shafts so that the crankshaft and the balancer shaft are accurately synchronized. In this case, an idler gear may be provided between the crank gear provided on the crankshaft and the balancer gear provided on the balancer shaft (Patent Document 1).

JP 2007-239521 A

  In an engine having an idler gear as in Patent Document 1, both ends of an idler gear shaft that supports the idler gear are fixed to the cylinder block and the gear case, and a bearing or the like is provided between the idler gear shaft and the idler gear. In general, the structure is made rotatable. In order to improve the assemblability, one end (outer end) of the idler gear shaft is fixed to the gear case with a bolt or the like, while the other end (inner end) is a bearing hole provided in the cylinder block. It has a structure to be inserted into. Further, a thrust plate is provided between the idler gear and the cylinder block in order to prevent seizure of the idler gear. This thrust plate is prevented from turning by a D-cut portion provided at the other end of the idler gear shaft.

However, in the structure as described above, since the other end portion of the idler gear shaft provided with the D cut portion is inserted into the bearing hole, the direction of the force acting on the idler gear shaft varies, so that the D cut portion There is a possibility that the corners of the cylinder and the inner wall of the bearing hole of the cylinder block repeatedly collide, the inner wall of the bearing hole is gradually worn, and finally rattle occurs.
The objective of this invention is providing the power transmission mechanism which suppresses abrasion with a D cut part and a bearing hole in the rotation prevention structure of the gear shaft provided with the D cut part.

  In order to achieve the above object, an invention according to claim 1 is directed to an input gear shaft that supports an input gear, an output gear shaft that supports an output gear that is spaced apart from the input gear, and an axial center of the input gear shaft. An idler gear, which is arranged offset from a line connecting the shaft center and the shaft center of the output gear shaft, meshes with the input gear and the output gear and transmits power from the input gear to the output gear, is rotatably supported, and one end portion And an idler gear shaft that is formed in a D-cut portion with a D-shaped cross-section and is inserted into a bearing hole provided in the support member and is supported in a non-rotatable manner. In the transmission mechanism, the D-cut portion is parallel to a first line connecting a first meshing point where the idler gear and the input gear mesh with each other and a second meshing point where the idler gear and the output gear mesh with each other. To the second line passing through the axis of the Hydra gear shaft, other party side of the rotational direction of the input gear in the first engagement point is characterized in that it is smaller than the opposite side of the rotation direction.

  According to a second aspect of the present invention, in the first aspect, on the plane perpendicular to the axial center of the idler gear shaft, the outer side of the idler gear shaft excluding the D-cut portion on the front side in the rotational direction with respect to the second line D cut so that the first distance projected onto the second line is greater than the second distance projected onto the second line on the opposite side of the rotation direction with respect to the second line. The circumferential position of the part is set.

According to a third aspect of the present invention, in the second aspect, the torque transmitted from the input gear to the idler gear fluctuates positive and negative with respect to the rotational direction, and the ratio between the first distance and the second distance is transmitted from the input gear to the idler gear. The circumferential direction position of the D-cut portion is set so as to coincide with the ratio of the maximum value on the rotational direction side of the torque to be rotated and the maximum value on the opposite side to the rotational direction.
The invention of claim 4 is characterized in that, in claim 1 or 2, the input gear shaft is an engine crankshaft and the output gear shaft is an engine balancer shaft.

  According to the power transmission mechanism of claim 1 of the present invention, when the input gear rotates and power is transmitted to the idler gear, the idler gear shaft has the same rotational direction as the input gear at the first meshing point. Since the force acts in the direction of, the D-cut part is formed in the part on the front side in the rotational direction smaller than the part on the opposite side, thereby suppressing the reduction of the area receiving the force and suppressing the surface pressure. it can. Therefore, it is possible to suppress wear of the inner walls of the idler gear shaft and the bearing hole of the support member.

According to the power transmission mechanism of claim 2 of the present invention, by setting the circumferential position of the D-cut portion so that the first distance is larger than the second distance, the power transmission from the input gear to the idler gear can be performed. The surface pressure can be reliably suppressed corresponding to the direction of the force applied to the idler gear shaft.
According to the power transmission mechanism of the third aspect of the present invention, even if the direction of the force acting on the idler gear shaft is reversed due to the fluctuation of the input gear torque and the reversal of the positive and negative, the surface at the maximum value of each positive and negative. The pressure can be set to coincide with each other, and the surface pressure can be minimized by making full use of the entire circumference of the idler gear shaft.

  According to the power transmission mechanism of claim 4 of the present invention, the surface pressure of the support member of the idler gear shaft in the power transmission part of the balancer shaft can be suppressed, wear of the support member can be suppressed, and durability can be improved.

It is a perspective view which shows the structure of the balancer shaft drive part of the engine which concerns on this embodiment. It is a front view which shows the structure of a balancer shaft drive part. It is sectional drawing which shows the structure of a balancer shaft drive part. It is explanatory drawing which shows the circumferential direction position of the D cut part in an idler gear shaft. It is a graph which shows the fluctuation | variation of the torque which concerns on a crank gear.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 3 are structural views of a power transmission mechanism portion of the balancer shaft 2 of the engine 1 according to the present embodiment. FIG. 1 is a perspective view, FIG. 2 is a front view, and FIG.
As shown in FIGS. 1-3, the balancer shaft 2 arrange | positioned in parallel with the crankshaft 4 is provided in the lower part of the crankcase 3 of the engine 1 of this embodiment.

The balancer shaft 2 is formed so that the center of gravity is unevenly distributed from the axial center, and the crankshaft 4 is offset so as to cancel vibrations generated when the piston of the engine 1 reciprocates due to the inclination of the connecting rod. Is driven to rotate in synchronization.
The crankshaft 4 and the balancer shaft 2 are rotatably supported by the crankcase 3, and one end portion projects outward from the side wall 3 a of the crankcase 3.

  Power transmission from the crankshaft 4 to the balancer shaft 2 is performed by gears. A crank gear 5 is fixed to one end of the crankshaft 4. On the other hand, a balancer gear 6 is fixed to one end of the balancer shaft 2. Further, an idler gear 7 is provided between the crank gear 5 and the balancer gear 6. The crank gear 5, the balancer gear 6 and the idler gear 7 are arranged on the same plane in the vicinity of the outside of the side wall 3a of the crankcase 3, so that the crank gear 5 and the idler gear 7 mesh with each other, and the balancer gear 6 and the idler gear 7 mesh with each other. Is arranged.

A gear cover 8 that covers the balancer gear 6 and the idler gear 7 is fastened to the lower portion of the crankcase 3 by bolts 9. The gear cover 8 is provided with a bearing hole 10 so as to rotatably support one end of the balancer shaft 2 when fixed to the crankcase 3.
The idler gear 7 is rotatably supported on the idler gear shaft 21. The idler gear shaft 21 is disposed in parallel with the crankshaft 4 and the balancer shaft 2, and one end thereof is fastened to the gear cover 8 with a bolt 22. The other end of the idler gear shaft 21 is inserted into and supported by a bearing hole 23 provided in the side wall 3a (support member) of the crankcase 3.

  Between the idler gear 7 and the side wall 3a of the crankcase 3a, a disc-shaped thrust plate 24 that receives the axial movement of the idler gear 7 is provided. A D-cut portion 25 is provided at the end of the idler gear shaft 21 on the side inserted into the bearing hole 23, and the D-cut portion is also provided in the bearing hole of the thrust plate 24 so as to face the D-cut portion 25. Is provided. Therefore, the idler gear shaft 21 and the thrust plate 24 are locked so as not to rotate, and the thrust plate 24 is prevented from rotating.

FIG. 4 is an explanatory view showing the circumferential position of the D-cut portion 25 of the idler gear shaft 21.
As shown in FIG. 4, the axis C1 of the idler gear shaft 21 is arranged offset to the right in the figure from the line L1 connecting the axis C2 of the crankshaft 4 and the axis C3 of the balancer shaft 2. In this example, the crank gear 5 rotates rightward (clockwise) in the figure. In such an arrangement, the force acting on the idler gear shaft 21 has a first meshing point P1 where the crank gear 5 and the idler gear 7 mesh with each other and a second meshing point P2 where the balancer gear 6 and the idler gear 7 mesh with each other. Acts in the direction in which the line L3 extending perpendicular to the connecting line L2 (first line) and passing through the axis C1 of the idler gear shaft 21 extends. In the engine 1 of the present embodiment in which the crank gear 5 rotates to the right, the force acting on the idler gear shaft 21 acts greatly in the left direction in the figure along the line L3 (A in the figure). That is, the outer peripheral wall of the idler gear shaft 21 on the left side in the drawing is larger than the right side in the drawing relative to the line L4 (second line) parallel to the line L2 and passing through the axis C1 of the idler gear shaft 21. A reaction force is received from the inner wall of the hole 23.

FIG. 5 is a graph showing fluctuations in the torque of the crank gear 5. In FIG. 5, the upper side in the figure is the positive rotation direction (right rotation direction) of the crank gear 5, and the lower side in the figure is the negative rotation direction (left rotation direction) of the crank gear 6. The minimum value (maximum value in the negative direction) is shown.
As shown in FIG. 5, the crank gear 6 of the engine 1 generates torque that is less in the negative rotation direction than in the positive rotation direction as well as in the positive rotation direction. Therefore, due to such torque reversal, the force acting on the idler gear shaft 21 acts not only in the left direction (A direction) but also in the right direction (B direction) in FIG. In the engine 1 of this embodiment, the maximum value of torque related to the crank gear 6 is a, and the minimum value (maximum value in the negative direction) is b.

As shown in FIG. 4, the circumferential position of the D-cut portion 25 formed on the idler gear shaft 21 is set based on the maximum value a and the minimum value b measured in advance.
Specifically, as shown in the following formula (1), a distance La projected on the line L4 on the left side of the outer periphery of the idler gear shaft 21 excluding the D cut part 25 (shaded part in the figure) with respect to the line L4. The ratio between the (first distance) and the distance Lb (second distance) obtained by projecting the right portion onto the line L4 matches the ratio between the maximum value a and the minimum value b of the torque related to the crank gear 6. In this way, the circumferential position of the D-cut portion 25 is set.

La: Lb = a: b (1)
As described above, by setting the circumferential position of the D-cut portion 25, the surface pressure of the idler gear shaft 21 is about the same in the case of the maximum value a and the minimum value b (maximum value in the opposite direction). It becomes. Therefore, the surface pressure can be suppressed by uniformly distributing the positive / negative reversing force relating to the idler gear shaft 21 to the peripheral wall. Thereby, the contact pressure with the corner | angular part of D cut part 25 and the inner wall of the bearing hole 23 is suppressed, and wear of an inner wall can be suppressed.

In order to suppress the surface pressure within an allowable range, it is not necessary to increase the diameter of the idler gear shaft 21, and the power transmission portion can be reduced in size.
In the present embodiment, the circumferential position of the D-cut portion 25 is set based on the maximum value a and the minimum value b of the torque related to the crank gear 5, but the present invention is not limited to this. For example, in the above embodiment, the D-cut portion 25 may be provided on the right side of the line L4 in FIG. In this way, when the torque related to the crank gear 5 is the maximum value a during normal rotation, the idler gear shaft 21 can receive a force on the entire left peripheral surface that is in contact with the bearing hole 23. The surface pressure during the positive rotation can be reduced to the maximum. Further, if the circumferential direction position of the D-cut portion 25 is set so that at least the distance La is larger than the distance Lb, the surface pressure during forward rotation can be reduced.

  Moreover, in the above embodiment, although it provided in the support part of the idler gear shaft 21 which supports the idler gear 7 between the balancer gear 6 and the crank gear 5 of the engine 1, this invention is not limited to this, It can be widely used in other power transmission mechanisms having a D-cut portion as a rotation stop of a gear shaft, such as an engine timing gear system.

1 Engine 2 Balancer shaft 3 Crankcase 3a Side wall (support member)
4 Crankshaft 5 Crank gear 6 Balancer gear 7 Idler gear 21 Idler gear shaft 23 Bearing hole 25 D cut part

Claims (4)

An input gear shaft that supports the input gear;
An output gear shaft that supports an output gear that is spaced apart from the input gear;
A shaft center is disposed offset from a line connecting the shaft center of the input gear shaft and the shaft center of the output gear shaft, and meshes with the input gear and the output gear to transmit power from the input gear to the output gear. The idler gear is pivotally supported, and a D-cut portion having a D-shaped cross section is formed at one end, and the D-cut portion is inserted into a bearing hole provided in the support member so as not to rotate. In a power transmission mechanism comprising a supported idler gear shaft,
The D-cut portion is parallel to a first line connecting a first meshing point where the idler gear and the input gear mesh with each other and a second meshing point where the idler gear and the output gear mesh with each other. A power transmission mechanism characterized in that, with respect to the second line passing through the shaft center of the shaft, the front side of the input gear in the rotational direction at the first meshing point is formed smaller than the opposite side of the rotational direction. .   Of the outer periphery of the idler gear shaft excluding the D-cut portion on a plane perpendicular to the axis of the idler gear shaft, the portion on the front side in the rotational direction with respect to the second line is the second portion. The D-cut portion of the D-cut portion is configured such that the first distance projected on the line is larger than the second distance projected on the second line at a portion opposite to the rotation direction with respect to the second line. The power transmission mechanism according to claim 1, wherein a circumferential position is set. The torque transmitted from the input gear to the idler gear fluctuates positive and negative with respect to the rotational direction,
The ratio between the first distance and the second distance matches the ratio between the maximum value on the rotational direction side of the torque transmitted from the input gear to the idler gear and the maximum value on the opposite side of the rotational direction. The power transmission mechanism according to claim 2, wherein a circumferential position of the D-cut portion is set. The input gear shaft is an engine crankshaft;
The power transmission mechanism according to claim 1, wherein the output gear shaft is a balancer shaft of the engine.

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