WO2014057325A1

WO2014057325A1 - Balancer device

Info

Publication number: WO2014057325A1
Application number: PCT/IB2013/002160
Authority: WO
Inventors: Nobuhiko SATAKE; Jun Hattori
Original assignee: Toyota Jidosha Kabushiki Kaisha; Otics Corporation
Priority date: 2012-10-09
Filing date: 2013-09-19
Publication date: 2014-04-17
Also published as: JP2014077455A

Abstract

A balancer device includes: a shaft (2) rotating around a rotational axis line; and a balancer mass (23) mounted on the shaft (2) and disposed eccentrically relative to the rotational axis line (CL1), the balancer mass (3) having a recessed portion (23a) on an outer periphery of the balancer mass to extend along a rotational direction of the balancer mass (23).

Description

BALANCER DEVICE

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a balancer device provided to an engine or other apparatuses.

2. Description of Related Art

[0002] Generally in a four-cylinder engine (internal combustion engine), rotational imbalance of the crankshaft takes place due to the secondary inertia force generated by the vertical reciprocating motion of a piston, resulting in a vertical vibration of the engine. A balancer device is provided to the engine to suppress this type of vibration.

[0003] The balancer device has, for instance, two balance shafts on each of which a balancer mass is provided eccentrically, and a housing disposed in the oil pan below the cylinder block and rotatably supporting these two balance shafts, to suppress the engine vibration by rotating the two balance shafts in the opposite directions to each other by means of the torque of the crankshaft. (Refer to Japanese Patent Application Publication No. 2006-275082 (JP 2006-275082 A), for instance.)

[0004] By the way, as the oil level in the oil pan becomes higher after shutting off the engine, oil flows into the housing of the balancer device to make the balancer mass immersed in oil (oil submergence). If the engine is started to rotate the balance shaft in this condition (that is, the condition of the balancer mass oil submergence), a rotational resistance is generated as the balancer mass rotates agitating the oil. Especially when the engine is started in the low temperature, the rotational resistance for the balance shaft becomes bigger due to the higher density of the oil, leading to the deteriorated startability of the engine.

[0005] Now, it should be noted that the rotational resistance with the balancer mass being immersed in oil is governed by the amount of oil contained in the housing. Namely, when larger amount of oil is contained in the housing, the balancer mass agitates larger amount of oil, resulting in higher rotational resistance. In consideration of such concerns, it would be practicable to reduce rotational resitance of the balancer by providing smaller clearance between the outer periphery of the balancer mass and the inner surface of the housing to reduce the amount of oil in the housing. However, with smaller clearance between the balancer mass and the housing, flow resistance of the gas between the balancer mass and the housing become larger in the normal operating range where the balancer mass is not immersed in oil, resulting in the increased rotational resistance of the balance shaft.

SUMMARY OF THE INVENTION

[0006] The present invention provides a balancer device with which the assurance of startability of the engine in the low temperature and the reduction of rotational resistance of the balance shaft in the normal operating range can be achieved at the same time.

[0007] The balancer device according to an embodiment of the present invention is a balancer device having a shaft (shaft body) rotatable around a rotational axis line and a balancer mass disposed eccentrically relative to the rotational axis line, in which a recessed portion is provided on an outer periphery of the balancer mass to extend along a rotational direction of the balancer mass.

[0008] The operation of the present invention will be described in the following sections. First, according to the embodiment of the present invention, the clearance between the outer periphery of the balancer mass (that is, maximum outer diameter portion except for the recessed portion) and the inner surface of the housing is made as small as practicable so that the amount of oil in the housing is reduced while the engine is shut off (that is, while the balancer mass is immersed in oil).

[0009] According to the embodiment of the present invention, the recessed portion is provided on the outer periphery of the balancer mass and additional amount of oil is contained in the housing while the engine is shut off in comparison with the case where the outer periphery of the balancer mass is a flat surface. Nevertheless, the startability of the engine in the low temperature can be assured. This aspect will be discussed in the following sections.

[0010] When the balance shaft rotates with the balancer mass being immersed in oil, the pressure within the recessed portion on the balancer mass becomes higher than the pressure in the areas other than the recessed portion. Namely, the flow speed (peripheral speed) of the oil dragged by the rotation of the balancer mass in the recessed portion (with smaller outer diameter and lower peripheral speed) is slower than the flow speed of the oil dragged on the outer peripheral surface (that is, at the maximum outer diameter portion). Thus, the pressure within the recessed portion becomes higher than the pressure in the areas other than the recessed portion (that is, the maximum outer diameter portion). The oil within the recessed portion is discharged toward the outside because of the pressure difference between the inside and the outside of the recessed portion. Accordingly, the provision of the recessed portion on the balancer mass enables to assure the startability of the engine in the low temperature despite of the increased amount of oil in the housing.

[0011] In addition, even if the clearance between the outer periphery of the balancer mass (that is, the maximum outer diameter portion other than the recessed portion) and the inner surface of the housing is small, the provision of the recessed portion on the balancer mass enables to substantially reduce the flow resistance of the gas. Accordingly, the rotational resistance of the balance shaft can be reduced in the normal operating range where the balancer mass is not immersed in oil.

[0012] As described above, according to the embodiment of the presnet invention, assurance of startability of the engine in the low temperature and the reduction of rotational resistance of the balance shaft in the normal operating range can be achieved at the same time.

[0013] According to the embodiment of the present invention, an inclined plane may be provided in the recessed portion of the balancer mass so that an outer diameter of the inclined plane gradually increases toward an end of the balancer mass in a direction of the rotational axis line of the balancer mass. When the inclined plane is provided in the recessed portion in this way and the balancer mass is immersed in oil, the oil within the recessed portion on the balancer mass is discharged effectively to the outside of the recessed portion 23a along the inclined planes due to the centrifugal force generated in association with the rotation of the balancer mass. Thus, the startability of the engine in the low temperature can be improved further.

[0014] According to the emboiment of the present invention, the recessed portion is provided on the outer periphery of the balancer mass, which enables to achieve simultaneously the assurance of the startability of the engine in the low temperature and the reduction of the rotational resistance of the balance shaft in the normal operating range where the balancer mass is not immersed in oil.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic configuration diagram showing an example of an engine to which a balancer device of the present invention is applied.

FIG. 2 is a side view of the balancer device.

FIG. 3 is a plain view of the balancer device. Note that an upper housing is removed in the state shown in FIG. 3.

FIG. 4 is a cross-sectional view taken along the line 4A -4A in FIG. 2.

FIG. 5 is a cross-sectional view taken along the line 5A-5A in FIG. 2.

FIG. 6 is a perspecrtive view selectively showing only the first balance shaft that constitutes the balancer device.

FIGs. 7A, 7B are a front elevational view (FIG. 7A) and a side view (FIG. 7B) selectively showing only the first balance shaft that constitutes the balancer device.

FIGs. 8A, 8B are a front elevational view (FIG. 8A) and a side view (FIG. 8B) selectively showing only the second balance shaft that constitutes the balancer device. FIG. 9 is a cross-sectional view taken along the line 9A-9A in FIG. 7A.

FIG. 10 is a cross-sectional view taken along the line 10A - 10A in FIG. 8 A.

FIG. 11 is a drawing to show the engagement of the drive gear provided on the crankshaft^ and the driven gear provided on the balancer device, as well as the engagement of the driven gears provided on each of the two balance shafts of the balancer device.

FIG. 12 is a drawing illustrating the effect of the recessed portion provided on the balancer mass, and

FIGs. 13 A, 13B and 13C are drawings to show the examples of variation of the ressed portion provided on the outer periphery of the balancer mass.

DETAILED DESCRIPTION OF EMBODIMENTS

[0016] An embodiment of the present invention will be described hereinafter with reference to the drawings.

- Engine - An engine (an internal combustion engine) to which a balancer device according to the present invention is applied will be described referring to FIG. 1. Note that FIG. 1 shows the structure of only one of the cylinders in the engine.

[0017] An engine 100 according to the present embodiment is a four-cylinder gasoline engine having a cylinder block 101, a cylinder head 102, a cylinder head cover 103, a crankcase 104, an oil pan 105 and so on. A piston 106 is disposed in each cylinder (cylinder bore) 101 a of the cylinder block 101.

[0018] The piston 106 is linked to a crankpin 181 on a crankshaft 108 via a connecting rod (conn-rod) 107. The crankshaft 108 has the crankpin 181, a counter- weight 182 and so on. Also, the crankshaft 108 is integrally rotatably provided with a drive gear 200 (see FIG. 11 and others) which is engaged with a first driven gear 21 of a balancer device 1 which will be described later.

[0019] The crankshaft 108 is disposed within the crankcase 104, and is rotatably supported by the crankcase 104. The crankcase 104 is mounted below the cylinder block 101 , and the oil pan 105 for storing the oil (engine oil) is mounted below the crankcase 104. While the engine 1 is in operation, the oil stored in the oil pan 105 is pumped up by the oil pump (not shown) via an oil strainer for removing foreign matters, and supplied to each part of the engine including the piston 106, the crankshaft 108 and the connecting rod 107, to be used for lubricating and cooling each part. After being supplied in this way and used for the lubrication and cooling of each part of the engine, the oil is returned to the oil pan 105 and stored there until it is pumped up again by the oil pump.

[0020] On the other hand, the cylinder head 102 is provided on top of the cylinder block 101. A combustion chamber 101b is provided between the cylinder head 102 and the piston 106. A spark plug 140 is disposed in the cylinder head 102, with the tip of the spark plug 140 being exposed to the inside of the combustion chamber 101b.

[0021] An intake passage 110 and an exhaust passage 120 are connected to the combustion chamber 101b of the engine 100. Part of the intake passage 110 is composed of an intake port 111 and an intake manifold 1 12. Similarly, part of the exhaust passage 120 is composed of an exhaust port 121 and an exhaust manifold 122.

[0022] An intake valve 113 is provided between the intake passage 110 (or the intake port 111) and the combustion chamber 101b. The intake passage 110 and the combustion chamber 101b are communicated or isolated by driving the intake valve 113 for opening and closing. Similarly, an exhaust valve 123 is provided between the exhaust passage 120 (or the exhaust port 121) and the combustion chamber 101b. The exhaust passage 120 and the combustion chamber 101b are communicated or isolated by driving the exhaust valve 123 for opening and closing. The driving operation for opening and closing the intake valve 113 as well as the exhaust valve 123 is performed by the respective rotations of an intake camshaft 114 and an exhaust camshaft 124 to which the rotation of the crankshaft 108 is transmitted via a timing chain or other mechanisms.

[0023] An injector (a fuel injection valve) 130 which is capable of injecting the fuel is disposed in the intake port 111 of the intake passage 110. The injector 130 is provided for each cylinder. These injectors 130 are connected to a common delivery pipe 131. The fuel stored in a fuel tank of a fuel supply system which is not shown is fed into the delivery pipe 131 , and then the fuel is injected into the intake port 111 through the injector 130. The injected fuel is mixed with the intake air to form an air-fuel mixture which is then introduced into the combustion chamber 101b of the engine 100. The air-fuel mixture (mixture of fuel and air) introduced into the combustion chamber 101b is ignited by the spark plug 140 to be combusted and exploded. The piston 106 is reciprocated by a combustion gas of high temperature and pressure generated through this process, whereby the crankshaft 108 is rotated and the driving force (output torque) of the engine 100 is obtained. The combustion gas is discharged into the exhaust passage 120 upon the opening of the exhaust valve 123.

[0024] In the present embodiment, a balancer device 1 is disposed inside the oil pan 105 below the crankcase 104, to suppress the vertical vibration of the engine 100. The balancer device 1 is supported by the wall of the cylinder block 101 mounted on top of the crankcase 104, via the plural number of bolts (not shown).

[0025] - Balancer device - Next, the balancer device 1 will be described referring to FIGs. 2 through 11.

[0026] The balancer device 1 in the present embodiment has a first balance shaft 2, a second balance shaft 3, a housing 10 and so on.

[0027] The housing 10 is composed of an upper housing 11 and a lower housing 12. The upper housing 11 and the lower housing 12 are tightened with each other by the plural number of bolts 13. Then, the housing 10 is supported by the wall of the cylinder block 101 mounted on top of the crankcase 104 via the plural number of bolts (not shown), whereby the entire balancer device 1 is supported by the cylinder block 101 .

[0028] The first balance shaft 2 and the second balance shaft 3 are rotatably supported by the housing 10 respectively. The first balance shaft 2 is rotatable around a rotational axis line CL1, while the second balance shaft 3 is rotatable around a rotational axis line CL2 which is in parallel with the aforementioned rotational axis line CL1. When the balancer device 1 is assembled to the engine 100, the rotational axis line CL1 of the first balance shaft 2 and the rotational axis line CL2 of the second balance shaft 3 run in parallel with a rotational axis line of the drive gear 200 (a helical gear) which rotates integrally with the crankshaft 108 (or in parallel with a rotational axis line of the crankshaft 108).

[0029] The first balance shaft 2 has a shaft body 20, a first driven gear 21 and a second driven gear 22 which are integrally rotatably provided on the shaft body 20, and a balancer mass 23 integrally rotatably provided on the shaft body 20.

[0030] Cylindrical journal portions 20a, 20b, which axes lie on the rotational axis line CL1, are provided each at both ends of the shaft body 20. The journal portion 20a positioned at one end is rotatably supported by the housing 10 via a bearing 4a. The journal portion 20b positioned at the other end is rotatably supported by the housing 10 via a bearing 4b. Thus, the first balance shaft 2 is made to be rotatable around the rotational axis line CL1.

[0031] The first driven gear 21 is a helical gear engaging with the drive gear 200 (a helical gear) integrally rotatably provided on the crankshaft 108, and integrally attached to the shaft body 20 by means of press-fit or other methods. The first driven gear 21 is disposed generally in the center of the shaft body 20 in the axial direction. In addition, the gear ratio between the first driven gear 21 and the drive gear 200 on the crankshaft 108 is set to be 1 :2, which means that the first balance shaft 2 rotates at double the rotational speed of the crankshaft 108.

[0032] The second driven gear 22 is a helical gear engaging with a driven gear 32 on the second balance shaft 3 which will be described later, and is integrally attached to the shaft body 20 by means of press-fit or other methods. The second driven gear 22 is disposed between the first driven gear 21 and the journal portion 20a provided at one end. Note that the first driven gear 21 and the second driven gear 22 may be spur gears or other types of gears.

[0033] The balancer mass 23 is integrally formed on the shaft body 20. The balancer mass 23 is a member formed into a generally solid semi-cylindrical shape, and provided in a state where its center of gravity is eccentric relative to the rotational axis line CL1 of the first balance shaft 2. That is, the balancer mass 23 is disposed eccentrically relative to the rotational axis line CL1. The balance mass 23 is disposed between the first driven gear 21 and the journal portion 20b provided at the other end. Outer peripheral surface of the balancer mass 23 (that is, a maximum outer diameter portion 23b other than a recessed portion 23a) forms an arc-like curved surface centered at the rotational axis line CL1 of the first balance shaft 2.

[0034] The second balance shaft 3 has a shaft body 30, and the driven gear 32 and a balancer mass 33 which are integrally rotatably provided on the shaft body 30.

[0035] Cylindrical journal portions 30a, 30b, which axes lies on the rotational axis line CL2, are provided each at both ends of the shaft body 30. The journal portion 30a positioned at one end is rotatably supported by the housing 10 via a bearing 5a, while the journal portion 30b positioned at the other end is rotatably supported by the housing 10 via a bearing 5b. Thus, the second balance shaft 3 is made to be rotatable around the rotational axis line CL2.

[0036] The driven gear 32 is a helical gear engaging with the second driven gear 22 (a helical gear) integrally rotatably provided on the first balance shaft 2, and integrally attached to the shaft body 30 by means of press-fit or other methods. Note that the driven gear 32 may be a spur gear or other types of gears.

[0037] The balancer mass 33 is integrally formed on the shaft body 30. The balancer mass 33 is a member formed into a generally solid semi-cylindrical shape, and disposed in a state where its center of gravity is eccentric relative to the rotational axis line CL2 of the second balance shaft 3. That is, the balancer mass 33 is disposed eccentrically relative to the rotational axis line CL2. Outer peripheral surface of the balancer mass 33 (that is, a maximum outer diameter portion 33b other than a recessed portion 33a) forms an arc-like curved surface centered at the rotational axis line CL2 of the second balance shaft 3. The position of the balancer mass 33 in the direction of its rotational axis coincides with the position of the balancer mass 23 on the first balance shaft 2 in the direction of its rotational axis.

[0038] In addition, the number of teeth on the driven gear 32 of the second balance shaft 3 is set to be equal to the number of teeth on the driven gear 22 of the first balance shaft 2 (gear ratio = 1 : 1), which makes the first balance shaft 2 and the second balance shaft 3 rotate in the opposite directions (in reverse) to each other at the same rotational speeds. The rotation of these two balance shafts 2, 3 makes the balancer mass 23 and the balancer mass 33 rotate in the opposite directions (in reverse) to each other at the same rotational speeds. The balancer mass 23 and the balancer mass 33 are positioned symmetrically in the course of the rotation. Namely, the balancer mass 23 and the balancer mass 33 are symmetrical with respect to the vertical plane which is perpendicular to the plane passing through the two rotational axis lines CL1 and CL2, and passing through the midpoint between the two rotational axis lines CL1 and CL2 while they are rotating.

[0039] By the way, the bearings 4a, 4b supporting the first balance shaft 2, and the bearings 5a, 5b supporting the second balance shaft 3 are composed of, for instance, two metal bearings formed into semi-cylindrical shape, with the two metal bearings being combined into a cylindrical shape for use. Oil is supplied to the bearings 4a, 4b, 5a, and 5b. The metal bearings of semi-cylindrical shape that compose each of the bearings 4a, 4b, 5a, and 5b are disposed in a semicircular notch provided at the mating surface (division surface) of the upper housing 11 and the lower housing 12.

[0040] The balancer device 1 according to this embodiment is assembled to the engine 100 in a state where the first driven gear 21 of the first balance shaft 2 is engaged with the drive gear 200 provided on the crankshaft 108 (See FIG. 1 and FIG. 11). As the first balance, shaft 2 and the second balance shaft 3 (or the balancer mass 23 and the balancer mass 33) rotate in the opposite directions to each other by means of the torque of the crankshaft 108, the vertical vibration of the engine 100 caused by the secondary inertial force is suppressed.

[0041] — The housing— The housing 10 is composed of the upper housing 11 and the lower housing 12, as described above.

[0042] In the upper housing 11, a peripheral wall 11a covering around the second driven gear 22 and the balancer mass 23 on the first balance shaft 2 outwardly in radial direction, and a peripheral wall 11a covering around the driven gear 32 and the balancer mass 33 on the second balance shaft 3 outwardly in radial direction are respectively formed into a semi-cylindrical shape. The inner peripheral surface of each peripheral wall 11a composes an arc-like curved surface centered at the rotational axis lines CL1 and CL2, respectively. Also, an opening l ib is provided on the upper housing 11 at the position corresponding to the area above the first driven gear 21 of the first balance shaft 2. Upper part of the first driven gear 21 is partially exposed to the outside through the opening l ib. Thus, the first driven gear 21 engages with the drive gear 200 of the crankshaft 108. For reference, openings for discharging oil may be provided on the upper housing 11 at the positions corresponding to the area above each balancer mass 23, 33.

[0043] In the lower housing 12, a peripheral wall 12a covering around the second driven gear 22 and the balancer mass 23 on the first balance shaft 2 outwardly in radial direction, and a peripheral wall 12a covering around the driven gear 32 and the balancer mass 33 on the second balance shaft 3 outwardly in radial direction are respectively formed into a semi-cylindrical shape. The inner peripheral surface of each peripheral wall 12a composes an arc-like curved surface centered at the rotational axis lines CL1 and CL2, respectively. Note that the lower housing 12 has an oil discharge hole 12b at the center of the bottom area, that is, the position below the first driven gear 21.

[0044] According to the present embodiment, a clearance Cmin (see FIG. 12) is set as small as practicable between the outer periphery of the balancer mass 23 on the first balance shaft 2 (that is, the maximum outer diameter portion 23b) and the inner peripheral surface of the peripheral wall 12a on the lower housing 12 (and also the inner peripheral surface of the peripheral wall 11a on the upper housing 11), in order to reduce the amount of oil remaining in the housing 10 after shutting off the engine. Further, a clearance is set as small as practicable between the outer periphery of the balancer mass 33 on the second balance shaft 3 (that is, the maximum outer diameter portion 33b) and the inner peripheral surface of the peripheral wall 12a on the lower housing 12 (and also the inner peripheral surface of the peripheral wall 1 la on the upper housing 11).

[0045] — Characterizing part— Next, characterizing part of the present embodiment will be described. The groove-like recessed portion 23a is provided on the outer periphery (or the outer peripheral area) of the balancer mass 23 on the first balance shaft 2 along the rotational direction of the balancer mass 23. The outer periphery on both sides of the recessed portion 23a constitutes the maximum outer diameter portion 23b on the balancer mass 23. The recessed portion 23a has a minimum outer diameter portion 23c in the center and inclined planes 23d. The inclined planes 23d have an outer diameter that is gradually increasing from the portion of minimum outer diameter 23 c toward both ends of the balancer mass 23 (that is, both ends along the rotational axis line CL1, or the maximum outer diameter portion 23b). The minimum outer diameter portion 23c of the recessed portion 23a is an arc-like curved surface centered at the rotational axis line CL1 of the first balance shaft 2, and the two inclined planes 23d are made into tapered surfaces.

[0046] The groove-like recessed portion 33a is provided on the outer periphery (or the outer peripheral area) of the balancer mass 33 on the second balance shaft 3 along the rotational direction of the balancer mass 33. The outer periphery on both sides of the recessed portion 33a constitutes the maximum outer diameter portion 33b on the balancer mass 33.

Similar to the recessed portion 23a on the first balance shaft 2, the recessed portion 33a on the second balance shaft 3 has a minimum outer diameter portion 33c in the center and inclined planes 33d. The inclined planes 33d have an outer diameter that is gradually increasing from the minimum outer diameter portion 33c toward both ends of the balancer mass 33 (that is, both ends along the rotational axis line CL2, or the maximum outer diameter portion 33b). The minimum outer diameter portion 33c of the recessed portion 33a is an arc-like curved surface centered at the rotational axis line CL2 of the second balance shaft 3, and the two inclined planes 33d are made into tapered surfaces.

[0047] Assurance for the startability of the engine 100 in the low temperature, and the reduction of rotational resistance regarding the balance shafts 2, 3 in the normal operating range of the engine 100 can be achieved simultaneously by providing the recessed portions 23a, 33a on each outer periphery of the balancer masses 23, 33 on each balance shaft 2, 3 in the manner described above. This aspect will be described in the following sections.

[0048] At first, problems will be discussed assuming that the outer periphery of the balancer mass is flat without a recessed portion provided on it.

If the balancer device is provided in the oil pan below the engine block, the balancer mass becomes immersed in oil (oil submergence), since oil level becomes higher in the oil pan (to reach as high as the rotation center of the balance shaft, for instance) after the engine is shut off. If the engine is started to rotate the balance shaft in the condition described above (that is, the condition of the balancer mass oil submergence), the rotational resistance is generated as the balancer mass rotates agitating the oil. Especially when the engine is started in the low temperature, the rotational resistance for the balance shaft becomes bigger due to the higher density of the oil, leading to the deteriorated startability of the engine.

[0049] In the state where the balancer mass is immersed in oil as described above, the agitating resistance becomes smaller if the amount of oil in the housing is smaller. Considering this point, it would be practicable to secure the startability in the low temperature by making the clearance between the balancer mass and the housing smaller (that is, by reducing the amount of oil in the housing). With smaller clearance, however, flow resistance of the gas between the balancer mass and the housing becomes larger in the normal operating range where the balancer mass is not immersed in oil, resulting in the increased rotational resistance of the balance shaft. In addition, if the oil is present between the balancer mass and the housing in the normal operating range, the drag resistance of the oil causes additional rotational resistance of the balance shaft.

[0050] According to the present embodiment, on the other hand, the recessed portions 23a, 33a are provided on the outer periphery of the balancer masses 23, 33, which makes it possible to restrain the aforementioned problems and to obtain the operational advantage described below.

[0051] First, provision of the recessed portions 23a, 33a on the outer . periphery of the balancer masses 23, 33 makes it possible to secure the startability of the engine in the low temperature, even though the amount of oil in the housing 10 increases slightly while the engine is shut off. This aspect will be described referring to FIG. 12.

[0052] When the first balance shaft 2 rotates with the balancer mass 23 being immersed in oil, the pressure within the recessed portion 23a on the balancer mass 23 becomes higher than the pressure in the areas other than the recessed portion 23 a. Namely, the flow speed (peripheral speed) of the oil dragged by the rotation of the balancer mass 23 at the minimum outer diameter portion 23c in the recessed portion 23a, is slower than the flow speed of the oil dragged at the maximum outer diameter portion 23b. In other words, the peripheral speed at the maximum outer diameter portion 23b is higher than the peripheral speed at the minimum outer diameter portion 23c. Thus, the pressure within the recessed portion 23a becomes higher than the pressure in the areas other than the recessed portion 23a (that is, the maximum outer diameter portion 23b), and the oil within the recessed portion 23a is discharged toward the outside because of

i the pressure difference between the inside and the outside of the recessed portion. (Refer to the dotted arrow mark in FIG. 12.) In addition, the inclined planes 23d, 23d are provided in the recessed portion 23 a according to the present embodiment, and thus, when the balancer mass 23 is immersed in oil, the oil within the recessed portion 23a on the balancer mass 23 is discharged effectively to the outside of the recessed portion 23a along the inclined planes due to the centrifugal force generated in association with the rotation of the balancer mass 23. Accordingly, the provision of the recessed portion 23a on the balancer mass 23 enables to secure the startability of the engine in the low temperature despite of the increased amount of oil inside the housing 10.

[0053] In addition, even when the clearance Cmin between the outer periphery of the balancer mass 23 (that is, the maximum outer diameter portion 23b) and the inner peripheral surface of the peripheral wall 12a on the housing 10 is small, the provision of the recessed portion 23a on the balancer mass 23 enables to substantially reduce the area of small clearance between the balancer mass 23 and the housing 10 (that is, the area of Cmin) because of the presence of the recessed portion 23a with large clearance (maximum clearance Cmax). In this way, the rotational resistance of the first balance shaft 2 (that is, the flow resistance of the gas) can be reduced in the normal operating range where the balancer mass 23 is not immersed in oil. Even when the oil is present between the balancer mass 23 and the peripheral wall 12a on the housing 10 in the normal operating range, the drag resistance of the oil can be reduced.

[0054] FIG. 12 shows only the recessed portion 23a provided on the balancer mass 23 of the first balance shaft 2, however, it should be noted that the equivalent recessed portion 33a is also provided on the balancer mass 33 of the second balance shaft 3, and the operational advantage equal to the first balance shaft 2 is obtained with regard to the second balance shaft 3.

[0055] As described above, according to the present embodiment, assurance of the startability of the engine 100 in the low temperature, and the reduction of rotational resistance regarding the balance shafts 2, 3 in the normal operating range where the balancer masses 23, 33 are not immersed in oil (the temperature range from 80 to 90 degree C, and the rotational speeds of 2000 rpm or lower, for instance) can be achieved simultaneously, since the recessed portions 23a, 33a extending along the rotational direction of the balancer mass 23, 33 are provided on the outer periphery of the balancer masses 23, 33.

[0056] - Examples of variation - According to the embodiment described above, the recessed portions 23a, 33a on the balancer mass 23, 33 are shaped to have the minimum. outer diameter portion 23c, 33c in the center, and the inclined planes 23d, 33d with gradually increasing diameters from the minimum outer diameter portions 23c, 33c toward the maximum outer diameter portion 23b, 33b. The shape of the recessed portion is not limited thereto.

[0057] As shown in FIG. 13 A, the recessed portion provided on the balancer masses 23, 33 on each balance shaft 2, 3 may be shaped as a groove-like recessed portion having an arc-shaped cross section 231 , 331a, for instance. Or, as shown in FIG. 13B, they may be shaped as a groove-like recessed portion having a V-shaped cross section 232a, 332a. Further, as shown in FIG. 13C, they may be shaped as a groove-like recessed portion having a cross section with fillet radii 233a, 333a. [0058] — Other embodiments— In the embodiment described above, a gear drive system is employed to transmit the rotation of the crankshaft 108 to each balance shaft 2, 3, however, other transmission system such as chain-driven system or belt-driven system may be employed.

[0059] In the embodiment described above, the present invention is applied to the biaxial balancer device having the first balance shaft 2 and the second balance shaft 3, however, the present invention may be applied to a single-axis balancer device having one balance shaft, or to a multi-axis balancer device having three or more balance shafts.

[0060] In the embodiment described above, the present invention is applied to the balancer device for a four-cylinder gasoline engine, but the present invention is not limited thereto, and may be applied to a balancer device for other types of gasoline engines having an arbitrary number of cylinders. Also, the present invention is applicable not only to the balancer device for a port injection type gasoline engine, but also to the balancer device for an in-cylinder direct injection gasoline engine.

[0061] In the embodiment described above, the present invention is applied to the balancer device for a gasoline engine, but the present invention is not limited thereto, and may be applied to the balancer device for other types of engines (internal combustion engines) such as a diesel engine.

[0062] In the embodiment described above, the present invention is applied to the balancer device for an engine, but the present invention is not limited thereto, and may be applied to the balancer device for suppressing the vibration of other types of equipment and apparatuses.

[0063] The present invention is applicable to a balancer device having a balancer mass. More specifically, the present invention is effectively applicable to a balancer device for suppressing the engine vibration.

Claims

1. A balancer device comprising:

a shaft rotating around a rotational axis line; and

a balancer mass mounted on the shaft and disposed eccentrically relative to the rotational axis line, the balancer mass having a recessed portion on an outer periphery of the balancer mass, and the recessed portion extending along a rotational direction of the balancer mass.

2. The balancer device according to claim 1 , wherein the balancer mass is mounted on the shaft in a state where the center of gravity of the balancer mass is eccentric relative to the rotational axis line.

3. The balancer device according to claim 1 or 2, wherein the recessed portion of the balancer mass is provided with an inclined plane, an outer diameter of the inclined plane gradually increases toward an end of the balancer mass in a direction of the rotational axis line of the balancer mass.

4. The balancer device according to claim 1 or 2, wherein the recessed portion has an arc shaped cross section.

5. The balancer device according to claim 1 or 2, wherein the recessed portion has a V-shaped cross section.