JP2004011850A - Crankshaft bearing structure - Google Patents

Abstract

An object of the present invention is to improve reliability by reliably preventing backlash of a bearing that supports a crankshaft and removal of the bearing.
A roller bearing (30) and a ball bearing (40) are assembled to frames (16, 17) formed in a crankcase (3). The roller bearing 30 and the ball bearing 40 support both ends 20a and 20b of the crankshaft 20, respectively. At least the inner race 41 of the ball bearing 40 is fixed on the crankshaft 20, and the outer race 42 is fixed to the frame 17 by a restraining plate 43 while being clamped.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a crankshaft bearing structure.
[0002]
[Prior art]
In general, in an engine, when a crankshaft receives a radial load from a piston during an explosion stroke during combustion, bending vibration and torsional vibration due to torque fluctuation occur in the crankshaft. For this reason, when both ends of the crankshaft are supported by a pair of bearing members on a frame in the crankcase, the natural frequency of the crankshaft system and the frequency of torque fluctuation resonate, generating large engine noise. easy.
[0003]
For example, Japanese Patent Laying-Open No. 2000-177607 (hereinafter referred to as Prior Example 1) discloses a structure in which two ball bearings are used to support a crankshaft. Generally, a roller bearing has a large resistance to a load in the radial direction due to linear contact with the roller surface, whereas a ball bearing has a small resistance to a load in the radial direction due to point contact by the spherical surface of the ball. On the other hand, ball bearings have a greater resistance to load in the thrust direction than roller bearings. Further, the ball bearing occupies more space than the roller bearing because the ball bearing has a larger capacity (size) than a roller bearing having substantially the same proof stress against a load in the radial direction. For this reason, when two ball bearings are used to support the crankshaft as in the first example, it is disadvantageous in reducing the size of the crankcase. Further, in the first prior art, since the proof stress against the load in the radial direction is small, the crankshaft is likely to bend and vibrate due to torque fluctuation.
[0004]
Therefore, for example, Japanese Patent Application Laid-Open No. 2001-32886 (hereinafter, referred to as Prior Example 2) or Japanese Patent Application Laid-Open No. 8-216711 (hereinafter, referred to as Prior Example 3) discloses a bearing structure combining a roller bearing and a ball bearing. It has been disclosed. In Prior Example 2, one end of a crankshaft provided with a dynamic damper on the transmission side is supported by a highly rigid roller bearing, and the other end is supported by a ball bearing. Further, in the preceding example 3, a pair of bearing members that support the both end sides of the bevel pinion shaft provided in the transfer case are configured by a roller bearing and a ball bearing as in the above-described prior example 2. I have. The roller bearing is fixed to the frame of the transfer case, and the ball bearing is mounted together with other press-fit parts such as the output gear by a tightening nut.
[0005]
[Problems to be solved by the invention]
In the above-described prior example 2, in addition to absorbing the vibration energy by the dynamic damper, the roller bearing on the dynamic damper side has higher rigidity than the other ball bearing. Thereby, the natural frequencies of the bending vibration and the torsional vibration of the crankshaft system are increased, and the resonance of the torsional vibration due to the bending vibration and the torque fluctuation of the crankshaft is prevented, and the engine noise is significantly reduced. However, most of the thrust-direction load generated on the crankshaft is applied to the ball bearing because the roller bearing does not have sufficient strength against the thrust-direction load. When such a load in the thrust direction acts on the ball bearing for a long period of time, the ball bearing may come off from the crankshaft. The reason is that the ball bearings are assembled. That is, the ball bearing is usually assembled in a tight state by press-fitting the inner race to the crankshaft side and press-fitting the outer race to a frame integrally formed in the cylinder case. Then, in the engine operating state, as the engine temperature rises, the tightness becomes smaller due to the difference in thermal expansion coefficient between the cylinder case and the ball bearing. Further, when the load in the thrust direction of the crankshaft repeatedly acts on the ball bearing for a long period of time, the outer race of the ball bearing may come off from the frame, and may be damaged.
[0006]
Further, in the prior example 3, since the roller bearings are constituted by a bearing set of a tapered roller pair, the overall capacity (size) is large and occupies a relatively large space, which hinders downsizing of the engine. is there. Further, the inner race of the ball bearing is fixed to the transfer shaft by a tightening nut, but the outer race is merely press-fitted into the frame in the transfer case. For this reason, similarly to the above-mentioned prior art example 2, if the load in the thrust direction generated on the transfer shaft repeatedly acts on the ball bearing for a long period of time, the outer race may come off from the frame, and may be damaged.
[0007]
The present invention has been made in view of such circumstances, and an object of the present invention is to improve reliability of a crankshaft bearing structure by reliably preventing breakage of the bearing due to slipping out.
[0008]
[Means for Solving the Problems]
In order to solve such a problem, a first invention is mounted on a frame formed in a crankcase, and includes a roller bearing for supporting one end of a crankshaft, and a frame formed in the crankcase. A ball bearing that supports the other end of the crankshaft, a first fixing member that fixes at least the inner race of the ball bearing to the crankshaft, and a ball bearing that fixes the outer race of the ball bearing to the frame. The present invention provides a crankshaft bearing structure having two fixing members.
[0009]
A second invention is mounted on a first frame formed in a crankcase, and is mounted on a roller bearing for supporting one end of a crankshaft and on a second frame formed in the crankcase. A ball bearing that supports the other end of the crankshaft, an annular recess formed in the second frame and into which the ball bearing is pressed, and an inner race of the ball bearing that is pressed into the crankshaft. Together with the other press-fitting parts to fasten the nut to fix it to the crankshaft and the outer race of the ball bearing attached to the second frame and fitted in the annular recess by pressing down from the open end face side of the annular recess. A bearing structure for a crankshaft having a restraining plate.
[0010]
Here, in the second invention, the roller bearing is press-fitted into an annular recess formed in the first frame, and the inner race of the roller bearing is fixed together with other press-fitted parts, and the roller bearing is fixed. It is preferable that the outer race is fixed by being held down from the open end face side of the annular concave portion by a restraining plate attached to the first frame.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a cross-sectional view schematically showing an overall configuration of an engine according to the present embodiment, for example, a small general-purpose engine used for an off-road vehicle or a private generator. The engine body E mainly includes a cylinder case 1, a cylinder head 2, and a crankcase 3. The crankcase 3 is formed by a pair of split cases 3a and 3b that are split into two in the axial direction of a crankshaft 20 described later. A combustion chamber 4 into which fuel is sprayed from an injector (not shown) is provided in the cylinder head 2, and a piston 5 is provided to be displaceable in opposition to the combustion chamber 4. Above the piston 5, a pair of intake / exhaust valves (only intake valves are shown) 6 facing the inside of the combustion chamber 4 is provided, and these intake valves 6 are controlled to open and close by a cam drive mechanism 7, respectively. A sprocket 8 is provided on a camshaft 7a of the cam drive mechanism 7, and the sprocket 8 is linked via a chain belt 9 to a sprocket 10 provided on a crankshaft 20 described later. Thereby, the rotational force of the crankshaft 20 is transmitted to the camshaft 7a of the cam drive mechanism 7.
[0012]
The crankshaft 20 is formed by a pair of split shafts 21 and 22. These split shafts 21 and 22 have crank arms 21 b and 22 b integrally formed with crank weights 21 a and 22 a connected to each other by a crank pin 23. This crank pin 23 connects between the piston 5 and the crankshaft 20 via the connecting rod 11. Thereby, displacement due to reciprocation of the piston 5 in a series of combustion strokes is transmitted as a rotational force around a center line OO extending in the axial direction of the crankshaft 20. A sprocket 10 and a drive gear 12 are press-fitted into one end 20a of the crankshaft 20 and fixed by a fixing nut 13. The chain belt 9 described above is stretched around the sprocket 10. Drive gear 12 is engaged with a driven gear (not shown) provided on main shaft 14a in transmission case 14 shown in FIG. By the engagement between the drive gear 12 and the driven gear, the power of the crankshaft 20 is transmitted to the transmission system. Further, an oil pump unit 15 is integrally attached to the crankcase 3 on one end portion 20a side of the crankshaft 20. The power of the oil pump unit 15 is obtained by a transmission mechanism (not shown) between the oil pump unit 15 and the crankshaft 20. On the other hand, the other end 20b side of the crankshaft 20 faces a generator (generator) 16 integrated with the crankcase 3, and transmits torque to a generator 16a of the generator 16.
[0013]
Further, the crankcase 3 is provided with a pair of frames 17 and 18 separated from each other in the axial direction of the crankshaft 20. One of the frames 17 is formed integrally with and protrudes into the split case 3a. The frame 17 holds a roller bearing 30 that supports the one end 20a side of the crankshaft 20. The other frame 18 is formed so as to protrude integrally into the split case 3b. The frame 18 holds a ball bearing 40 that supports the other end 20b of the crankshaft 20.
[0014]
By the way, in the small general-purpose engine as in the present embodiment, generally, the cylinder parts such as the cylinder case 1, the cylinder head 2, and the crankcase 3 are made of a light alloy made of aluminum. Is lighter. On the other hand, the crankshaft 20 and the bearing members such as the roller bearing 30 and the ball bearing 40 are made of a different metal such as iron having a different coefficient of thermal expansion from that of the cylinder component. Therefore, cylinder components such as the cylinder case 1 and the crankcase 3 have a larger coefficient of thermal expansion than the roller bearing 30 and the ball bearing 40. Therefore, when the roller bearings 30 and the ball bearings 40 are assembled to the frames 17 and 18 in the crankcase 3 at room temperature during the assembly of the engine, the bearing mounting portions of the frames 17 and 18, particularly, The bearing fitting part becomes loose. As a result, the bearing is likely to be loose, or the above-described conventional outer race is liable to be damaged due to slippage, resulting in reduced reliability.
[0015]
2 to 5 show the state of the shaft support of the crankshaft in the present embodiment. FIG. 2 and FIG. 3 are cross-sectional views showing a state in which the crankshaft is supported by roller bearings. FIG. 4 and FIG. 5 are cross-sectional views showing a state where the crankshaft is supported by ball bearings. As shown in FIGS. 2 and 3, an annular recess 25 and a screw hole 26 provided on the outer periphery of the annular recess 25 are formed on the inner surface 17 a side of the frame 17 formed in one of the divided cases 3 a. ing. The inner race 31 of the roller bearing 30 is fitted into the outer peripheral surface of the crankshaft 20 in a press-fit state and assembled. The outer race 32 of the roller bearing 30 is fitted into the annular recess 25 of the frame 17 in a press-fit state and assembled.
[0016]
A plurality of restraining plates 33 are provided on the inner surface 17 a side of the frame 17, and the restraining plates 33 are fixed by countersunk screws 34 engaged with the screw holes 26. That is, a part of each restraining plate 33 holds the outer race 32 of the roller bearing 30 fitted in the annular recess 25 of the frame 17 from the inside, in other words, from the open end face side of the annular recess 25, and fixes the outer race 32 in a sandwiched state. . Further, the inner race 31 of the roller bearing 30 is fixed by a snap ring 35. The snap ring 35 is suppressed by a sleeve 10 a of a sprocket 10 for hanging a chain belt provided on the crankshaft 20 on the outer surface side of the roller bearing 30. As a result, the inner race 31 of the roller bearing 30 is fixed by being sandwiched between the sleeve 19 a of the output gear 19 provided on the crankshaft 20 on the inner surface side of the roller bearing 30 and the snap ring 35. As a result, the roller bearing 30 receives the radial load acting on the crankshaft 20 due to the displacement of the piston 5, and the displacement of the roller race 30 with respect to the load in the thrust direction, particularly, the displacement of the outer race 32 is reliably prevented.
[0017]
As shown in FIGS. 4 and 5, on the inner surface 18a side of the frame 18 formed in the other divided case 3b, an annular concave portion 27 and a screw hole 28 provided on the outer periphery of the annular concave portion 27 are formed. ing. Then, the inner race 41 of the ball bearing 40 is fitted into the outer peripheral surface of the crankshaft 20 in a press-fit state and assembled. The outer race 42 of the ball bearing 40 is fitted into the annular concave portion 27 of the frame 18 by press-fitting and assembled. A plurality of restraining plates 43 are provided on the inner surface 18 a side of the frame 18, and the restraining plates 43 are fixed by countersunk screws 44 engaged with the screw holes 28. That is, a part of each restraining plate 43 holds the outer race 42 of the ball bearing 40 fitted in the annular concave portion 27 of the frame 18 from the inside, in other words, from the open end surface side of the annular concave portion 27, and fixes the outer race 42 in a sandwiched state. .
[0018]
Further, a threaded portion 24 is threaded on the outer peripheral surface on the other end 20b side of the crankshaft 20 to which the ball bearing 40 is assembled. A tightening nut 45 is screwed into the screw portion 24. The tightening nut 45 is tightened together with the crank weight 22 a of the crank shaft 20 from the outer surface 18 b side of the frame 18, and is fixed by sandwiching the inner race 41 of the ball bearing 40. As a result, the ball bearing 40 is not displaced by the load in the thrust direction as before, so that the ball bearing 40 is reliably prevented from coming off from the crankshaft 20. In addition, when the ball bearing 40 is mounted on the frame 18, the inner and outer races 41 and 42 do not need to be subjected to special processing, so that the current ball bearing 40 can be used as it is, and the cost is reduced. Can be reduced.
[0019]
Next, a procedure for assembling the roller bearing 30 and the ball bearing 40 to the crankshaft 20 in the crankcase 3 will be described. In a process before assembling the crankcase 3 to the cylinder case 1, the oil pump unit 15 and the generator 16 have been removed from the crankcase 3. First, a roller bearing 30 is attached to one of the two divided cases 3 a of the crankcase 3. That is, as shown in FIGS. 2 and 3, the roller bearing 30 is fitted into the annular concave portion 25 of the frame 17 of the divided case 3a from the inner surface 17a side of the frame 17 in a press-fit state. Next, the suppression plate 33 is applied to the outer race 32 of the roller bearing 30 from the inner surface 17 a side of the frame 17. The suppression plate 33 is fixed by a countersunk screw 34 engaged with the screw hole 26. As a result, the outer race 32 of the roller bearing 30 is fixed to the frame 17 of the divided case 3a by the restraining plate 33 in a sandwiched state.
[0020]
After fixing the roller bearing 30 to the frame 17, one of the split shafts 21 of the crankshaft 20 is inserted into the inner race 31 of the roller bearing 30 from the inner surface 17 a side of the frame 17 in a press-fit state. In this case, the output gear 19 is fitted into the split shaft 21 in advance in a press-fitted state on the side of the crank weight 21a, and the end surface of the sleeve 19a of the output gear 19 abuts on the inner surface side of the inner race 31 of the roller bearing 30. Is done. After the division shaft 21 is inserted into the roller bearing 30, the snap ring 35, the sprocket 10, and the drive gear 12 are sequentially fitted into the division shaft 21 from the outer surface 17 b side of the frame 17 in a press-fit state, and fixed by the fixing nut 13. You. As a result, the snap ring 35 abuts on the outer surface of the inner race 31 of the roller bearing 30. At this time, the snap ring 35 is restrained from the outside by the end face of the sleeve 10a of the sprocket 10 together with the drive gear 12 fixed by the fixing nut 13. As a result, the inner race 31 of the roller bearing 30 is fixed to the divided shaft 21 by the end face of the sleeve 19a of the output gear 19 and the end face of the sleeve 10a of the sprocket 10.
[0021]
On the other hand, a ball bearing 40 is mounted on the frame 18 on the other split case 3b side. That is, as shown in FIGS. 4 and 5, first, the ball bearing 40 is fitted into the annular concave portion 27 of the frame 18 from the inner surface 18 a side of the frame 18 in a press-fit state. Next, the suppression plate 43 is applied to the outer race 42 of the ball bearing 40 from the inner surface 18 a side of the frame 18. The suppression plate 43 is fixed by a countersunk screw 44 engaged with the screw hole 28. Thus, the outer race 42 of the ball bearing 40 is fixed to the frame 18 of the divided case 3b by the restraining plate 43.
[0022]
After the ball bearing 40 is fixed, the other split shaft 22 of the crankshaft 20 is inserted into the inner race 41 of the ball bearing 40 in a press-fit state from the inner surface 18 a side of the frame 18. In this case, the end surface of the crank weight 22 a of the split shaft 22 abuts on the inner surface side of the ball bearing 40. A tightening nut 45 is inserted into the split shaft 22 inserted into the inner race 41 of the ball bearing 40 from the outer surface 18 b side of the frame 18. The tightening nut 45 is screwed into the screwing portion 24 formed on the outer peripheral surface of the split shaft 22 to tighten the inner race 41 of the ball bearing 40 from the outer surface side. As a result, the inner race 41 of the ball bearing 40 is clamped and fixed on the divided shaft 22 by the end face of the crank weight 22a and the tightening nut 45.
[0023]
After the bearings 30 and 40 and the split shafts 21 and 22 are respectively assembled to the two split cases 3a and 3b in this way, the two split cases 3a and 3b are integrated by bolts (not shown). When the split cases 3a and 3b are integrated, the crank arms 21b and 22b of both split shafts 21 and 22 are connected by a crank pin 23, and the connecting rod 11 is attached to the crank pin 23. As a result, the divided cases 3a and 3b are integrally assembled simultaneously with the connection of the divided shafts 21 and 22.
[0024]
In the embodiment described above, the inner races 31, 41 and the outer races 32, 42 of both the roller bearing 30 and the ball bearing 40 are fixed to the crankshaft 20 side and the crankcase 3 side, respectively. However, the present invention is not limited to this, and in particular, may be applied only to the ball bearing 40 that receives a thrust load. In addition, the restraining plates 33, 43 used to fix the roller bearing 30 and the ball bearing 40, respectively, may have a ring-like shape that suppresses the entire circumference of the outer races 32, 42.
[0025]
【The invention's effect】
Thus, according to the crankshaft bearing structure of the present invention, both ends of the crankshaft are supported by the roller bearing and the ball bearing. At least the inner race of the ball bearing is fixed to the crankshaft, and the outer race is fixed to the frame on the crankcase side. For this reason, the ball bearing does not shift in position with respect to the load in the thrust direction. As a result, the outer race of the ball bearing does not come off from the conventional frame, and the bearing can be reliably prevented from being damaged, so that the reliability can be further improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing an entire configuration of an engine according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a main part showing a state where a crankshaft is supported by roller bearings. FIG. FIG. 4 is a cross-sectional view of a main part showing a state where a crankshaft is supported by a ball bearing. FIG. 5 is a cross-sectional view of the crankshaft taken along line BB in FIG. 4.
E Engine body 1 Cylinder case 2 Cylinder head 3 Crank case 4 Combustion chamber 5 Piston 17 Frame 18 Frame 20 Crankshaft 20a One end 20b Other end 24 Threaded portion 25 Annular recess 26 Screw hole 27 Annular recess 28 Screw hole 30 Roller bearing 31 inner race 32 outer race 33 restraining plate 34 countersunk screw 35 snap ring 40 ball bearing 41 inner race 42 outer race 43 restraining plate 44 countersunk screw 45 tightening nut

Claims (3)

In the crankshaft bearing structure,
A roller bearing attached to a frame formed in the crankcase and supporting one end of the crankshaft;
A ball bearing attached to a frame formed in the crankcase and supporting the other end of the crankshaft;
A first fixing member for fixing the inner race of the ball bearing to the crankshaft;
A second fixing member for fixing the outer race of the ball bearing to the frame. In the crankshaft bearing structure,
A roller bearing mounted on a first frame formed in the crankcase and supporting one end of the crankshaft;
A ball bearing attached to a second frame formed in the crankcase and supporting the other end of the crankshaft;
An annular recess formed in the second frame and press-fitted with the ball bearing;
A tightening nut for tightening the inner race of the ball bearing attached to the crankshaft together with other press-fit parts and fixing the inner race to the crankshaft;
A bearing structure for a crankshaft, comprising: a suppression plate attached to the second frame and holding down and fixing an outer race of the ball bearing fitted into the annular recess from an open end surface side of the annular recess. . The roller bearing is press-fitted into an annular recess formed in the first frame,
The inner race of the roller bearing is fixed together with other press-fit parts,
The bearing structure for a crankshaft according to claim 2, wherein the outer race of the roller bearing is fixed by being held down from the open end face side of the annular concave portion by a restraining plate attached to the first frame. .

Images