JP6418047B2 - Balance shaft support structure - Google Patents

Description

  The present invention relates to a support structure for a balance shaft provided with a support member that supports an outer peripheral surface of a balance shaft provided in an internal combustion engine so as to be slidably rotatable via lubricating oil.

  The internal combustion engine can be rotatably provided with a balance shaft that rotates in synchronization with the crankshaft. The balance shaft is provided with a counterweight so as to shift the center of gravity from the center of rotation thereof, and secondary vibration generated when the crankshaft rotates is suppressed by inertial force generated when the balance shaft rotates. The balance shaft is rotatably supported by the bearing member, and is slidably supported on the support surface of the bearing member in conjunction with a crankshaft that reciprocates the piston. At this time, in order to avoid the occurrence of seizure due to sliding friction between the balance shaft and the sliding surface, it is necessary to supply lubricating oil between the balance shaft and the sliding surface.

  As a technology for supplying lubricating oil to the sliding portion between the balance shaft and the sliding surface, Patent Document 1 discloses that an oil hole is formed in a bearing that supports the balance shaft, and the lubricating oil is supplied to the oil hole by an oil pump. A configuration is disclosed in which lubricating oil is supplied to a sliding portion between the bearing and the balance shaft by pumping. In the technique disclosed in Patent Document 1, the supply amount of lubricating oil supplied between the balance shaft and the bearing is set by the opening area of the oil hole formed in the bearing.

Japanese Patent Application Laid-Open No. 07-71217

  As described above, in the technique disclosed in Patent Document 1, the amount of lubricating oil supplied between the balance shaft and the bearing is controlled by the opening area of the oil hole formed in the bearing. There is a concern that the amount of oil is insufficient and seizure occurs.

  By providing the groove extending over the entire circumference of the bearing, the lubricating oil is retained in the angular region that does not contribute to lubrication, and therefore the lubrication to the angular region that requires lubrication is insufficient. There is a fear. On the other hand, in a crankshaft of an internal combustion engine in which a similar sliding bearing structure is adopted, the crankshaft is pressed to the lower side due to the in-cylinder pressure, so the groove only needs to be provided in the lower bearing member. The same structure cannot be adopted because it does not receive a pressing force on the lower side.

  The present invention has been made to solve the above problems, and can reduce friction generated between the balance shaft and the support member without being affected by the temperature of the lubricating oil, and the seizure between the balance shaft and the bearing member. It is an object of the present invention to provide a support structure for a balance shaft that can prevent the above-described problem.

In order to achieve the above object, the present invention provides a support structure for a balance shaft including a cylindrical support member having an inner peripheral surface that rotatably supports the outer peripheral surface of the balance shaft via lubricating oil. A groove extending in the circumferential direction of the outer peripheral surface of the balance shaft and formed in only a part of the entire circumference of the outer peripheral surface, and the groove has the balance when rotating the balance shaft. characterized in that for accommodating the lubricating oil in a region including a position gap between the outer peripheral surface and the inner peripheral surface of the front Symbol support shaft is minimized.

  According to the present invention, since the lubricating oil is held in the region including the position where the distance between the outer peripheral surface of the balance shaft and the peripheral surface without the support member is minimized, the balance shaft and the support are supported regardless of the temperature of the lubricating oil. Friction between the members can be reduced, and seizure between the balance shaft and the bearing can be prevented.

It is a front view which shows the balance shaft in embodiment of this invention. It is the II-II sectional view taken on the line of the balance shaft shown in FIG. It is a vertical side view which shows the balance shaft and supporting member which are shown in FIG. FIG. 4 is a bottom view of the upper housing shown in FIG. 3. FIG. 4 is a plan view of the lower housing shown in FIG. 3. It is the VI-VI sectional view taken on the line of FIG. It is a diagram which shows the movement locus | trajectory of the axial center of a balance shaft. It is a schematic diagram of the positional relationship between a balance shaft and a support member. It is a diagram which shows the relationship of the amount of lubricating oil leaks, oil film temperature variation | change_quantity, and the variation | change_quantity of friction torque with respect to engine speed, respectively.

  An embodiment of a support structure for a balance shaft according to the present invention will be described.

  The support structure of the balance shaft in the present embodiment is used for a balancer that suppresses secondary vibration generated in a reciprocating engine as an internal combustion engine. The balancer includes one or two balance shafts that are driven in synchronization with the rotation of the crankshaft. The balance shaft is rotatably supported by a balance shaft housing provided below a crankcase that rotatably supports the crankshaft.

  Here, the balance shaft and the support structure thereof in the present embodiment will be described in more detail with reference to the drawings. 1 is a front view of a balance shaft in the present embodiment, FIG. 2 is a sectional view taken along the line II-II of FIG. 1, and FIG. 3 is a longitudinal side view showing the balance shaft and the support member shown in FIG. Shows a state in which the support member is disassembled, and (b) shows a state in which the balance shaft is supported by the support member.

  As shown in FIGS. 1 and 2, concentric columnar journals 2a and 2b are formed on the balance shaft 1, and an unbalanced mass 3 is fixed between the journals 2a and 2b. The unbalance mass 3 has a substantially semi-cylindrical shape, and is provided so that the center of gravity is located at a position shifted from the central axis C1 of the journals 2a and 2b. The journals 2a and 2b of the balance shaft 1 are supported by a balance shaft housing 10 shown in FIGS.

  As shown in FIG. 3, a balance shaft housing (hereinafter simply referred to as a housing) 10 in the present embodiment is a support member that supports two balance shafts (first balance shaft 1A and second balance shaft 1B). It is configured as. As shown in FIG. 3A, the housing 10 includes an upper housing 20 and a lower housing 30. The upper housing 20 is formed with a semicylindrical recess 21 (see FIG. 4) at a position facing the upper half of the journals 2a and 2b of the balance shafts 1A and 1B. A semi-cylindrical bearing member 22 is fixed. The lower housing 30 is formed with a semi-cylindrical recess 31 at a position facing the lower half of the journals 2a and 2b of the balance shafts 1A and 1B, and a semi-cylindrical bearing member is formed in each of the recesses 31. 32 is fixed. As shown in FIG. 3B, the lower housing 30 and the upper housing 20 are fastened and fixed by bolts (not shown), whereby the bearing members 22 and 32 facing each other are combined. A cylindrical bearing 23 surrounding the entire circumference of each journal 2a, 2b of the second balance shaft 1A, 1B is constructed.

Of the upper housing 20, the journal 2a of the first balance shaft 1A, the positions corresponding to 2b, as shown in FIG. 6 Figures 4, first oil passage W1 passing through the recess 21 and the bearing member is formed ing. The outer end portion of the first oil passage W1 is connected to a lubricating oil feed passage (not shown) that feeds lubricating oil fed from a pump (not shown). Further, a second oil passage W2 is formed from a part of the recess 21 corresponding to the first balance shaft 1A to a part of the recess 21 corresponding to the second balance shaft 1B, and this second oil path. W2 communicates with the inner end of the first oil passage W1. 4 to 6, h1 is an insertion hole for a bolt for fixing the upper housing 20 and the lower housing, and h2 is a screw hole for screwing with the bolt.

  In the present embodiment, the two balance shafts are rotatably supported by bearings 23 arranged at two locations along the respective axial directions. Of the two balance shafts, the first balance shaft 1A is rotationally driven in conjunction with a crankshaft (not shown). Further, the second balance shaft 1B rotates in the reverse direction at the same rotation speed in conjunction with the first balance shaft 1A. For these two types of interlocking, a gear (not shown) is fitted to the enlarged diameter portion 2c of the balance shaft 1A. As a result, the inertial force generated in the first and second balance shafts 1A and 1B cancels out the inertial force generated along with the rotation of the crankshaft, thereby suppressing the occurrence of secondary vibration and driving with high silence. Can be realized.

  During the rotation of the first and second balance shafts, the lubricating oil sent from the pump via the lubricating oil supply passage is fed to the first oil passage W1 formed in the upper housing 20 by a pump (not shown). Is supplied. The lubricating oil supplied to the first oil passage W1 passes through the oil holes 22a (see FIG. 6) formed in the bearing member 22 corresponding to the first balance shaft 1A, and the journals 2a and 2b of the first balance shaft 1A. Between the outer peripheral surface and the inner peripheral surface of the bearing 23, and an oil film is formed between the two peripheral surfaces. Further, the lubricating oil supplied to the first oil passage W1 also flows into the second oil passage W2, and from here through the oil holes 22a formed in the bearing member 22, the journals 2a and 2b of the second balance shaft 1A. Between the outer peripheral surface and the inner peripheral surface of the bearing 23, and an oil film is formed between the two peripheral surfaces. The journals 2a and 2b can be rotated in a lubricated state by an oil film formed between the outer peripheral surfaces of the journals 2a and 2b and the inner peripheral surface of the bearing member 22. Moreover, the lubricating oil after being used for lubrication leaks from the axial ends of the journals 2a and 2b to the outside.

  By the way, the balance shafts 1A and 1B are provided with an unbalance mass 3, and the center of gravity of the balance shafts 1A and 1B is deviated from the center axis C1 of the journals 2a and 2b of the balance shafts 1A and 1B. As shown in FIG. 7, the center axis C1 of the journals 2a and 2b rotates along the inner peripheral surface of the bearing 23 while drawing an annular orbit Or about the center axis C0 of the inner peripheral surface of the bearing 23. . Therefore, the balance shafts 1A and 1B rotate in a state in which the fixed position P (see FIG. 8) in the outer peripheral surfaces of the journals 2a and 2b is always closest to the inner peripheral surface of the bearing 23. In the present embodiment, as shown in FIGS. 1 and 2, arc-shaped grooves G that contain lubricating oil are formed along the respective peripheral surfaces. In this embodiment, two grooves G are formed in each journal 2a, 2b. The arc-shaped groove G is formed in a part of the entire circumferential direction of the balance shafts 1A and 1B. When the balance shafts 1A and 1B are rotated, as described above, the journals 2a, 1B, It is a region of a predetermined circumferential angle range including the position P closest to the outer peripheral surface of 2b. In addition, the space | interval of the outer peripheral surface of journal 2a, 2b shown in FIG. 8 and the outer peripheral surface of balance shaft 1A, 1B is exaggerated on account of description.

  In the support structure of the balance shaft in the present embodiment configured as described above, the region R1 close to the upstream side of the position P in the rotation direction of the journals 2a and 2b (the direction indicated by the arrow in FIG. 8) The wedge effect is generated by the flow of the lubricating oil OL generated by the rotation of the journals 2a and 2b, and the oil film pressure is increased. On the other hand, the reverse wedge effect occurs in the region R2 close to the downstream side of the position P. This reverse wedge effect is a phenomenon in which a negative pressure is generated at a location where the gap between the sliding object and the sliding object is enlarged along the sliding direction. In this embodiment, the outer peripheral surfaces of the journals 2a and 2b and the bearing 23 are used. This occurs in a region R2 where the outer peripheral surface of the region expands. In the present embodiment, since the groove G is formed from the upstream side to the downstream side with respect to the position P where the peripheral surfaces of the journals 2a and 2b are closest to the inner peripheral surface of the bearing 23, it flows out of the bearing. The lubricating oil thus pulled is pulled back into the groove G by the negative pressure due to the reverse wedge effect, and the lubricating oil is maintained between the outer peripheral surfaces of the journals 2 a and 2 b and the inner peripheral surface of the bearing 23.

  That is, immediately after the start of the internal combustion engine in a low temperature environment, if the lubricating oil leaks to the outside from between the balance shaft and the bearing, the temperature rise of the lubricating oil will be delayed by that amount. Since the lubricating oil is held by the pressure reduction in the groove G formed in the region where the oil is likely to occur, the temperature of the lubricating oil is likely to rise, and the friction between the journals 2a and 2b and the bearing 23 can be reduced. It becomes possible.

  In addition, the groove G is not located in the entire area of the balance shaft 1A, 1B in the circumferential direction, but is installed in a place where the oil film thickness is thin and the friction is large due to the inertia force of the unbalance mass. Is obtained.

  Thus, in the present embodiment, when the temperature of the lubricating oil is low, the lubricating oil can be held in an appropriate state between the journals 2a and 2b and the bearing 23. FIG. 9A shows an example of the result of verifying the effect obtained by this embodiment. Here, the case where the oil temperature is low (5 degrees) and the case where the oil temperature is high (temperature exceeding 20 degrees) are taken as an example, and the amount of leakage of lubricating oil (L / min) with respect to the engine speed (rpm) The results of calculation prediction are shown. As shown in the figure, in this embodiment, the amount of lubricating oil flowing out of the bearing could be reduced even when the oil temperature was high (temperature exceeding 20 degrees).

  FIG. 9B is a diagram showing the result of calculating and predicting the relationship between the temperature change amount of the oil film formed between the journals 2a and 2b and the bearing 23 and the rotational speed (rpm) of the internal combustion engine. is there. As shown in the figure, according to the present embodiment, the amount of lubricating oil could be reduced, and the oil film temperature increased. As described above, the temperature of the low temperature oil film is rapidly increased, so that the resistance by the oil film is greatly reduced, and smooth rotation can be realized.

  FIG. 9C is a diagram showing the relationship between the amount of change in friction torque (Nm) during rotation of the journals 2a and 2b and the rotational speed of the internal combustion engine. As shown in the figure, the outflow amount of the lubricating oil is reduced and the oil film temperature is increased, so that the friction can be reduced.

  In the above embodiment, the example in which the two grooves G are formed in each of the journals 2a and 2b in the first and second balance shafts 1A and 1B is shown. However, the number of grooves formed in each journal is shown. It is possible to set other than two, and the present invention is not particularly limited to the above embodiment.

  The present invention is not limited to the case where the two balance shafts are supported by the housing, but can also be applied to the case where one balance shaft is supported.

1A, 1B Balance shaft 10 Housing 20 Upper housing 30 Lower housing G Groove R region

Claims (1)

A balance shaft support structure including a cylindrical support member having an inner peripheral surface that rotatably supports an outer peripheral surface of the balance shaft via lubricating oil,
A groove that extends in the circumferential direction of the outer peripheral surface of the balance shaft and is formed only in a partial region in the entire circumference of the outer peripheral surface;
The groove upon rotation of the balance shaft, characterized in that for accommodating the lubricating oil in a region including a position gap between the outer peripheral surface and the inner peripheral surface of the front Symbol supporting member of the balance shaft is minimized Balance shaft support structure.

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