Engine balance shafts supporting structure

[0002] 1. Field of the Invention

[0003] The present invention relates to an engine having balance shafts disposed below a cylinder block, and more particularly to a supporting structure for the balance shafts of the engine.

[0004] 2. Description of the Related Art

[0005] There have been existing heretofore engines having a balancer below the cylinder block (for instance, refer to the Japanese Patent Unexamined Publication (Kokai) No. Sho. 63-106443). In an engine of this type, the balancer comprises a pair of balance shafts supported on a casing disposed in an oil pan below the cylinder block. The balance shafts are intermeshed with each other, and the driving force of a crank shafts is transmitted therefrom to one of the balance shafts via a chain or the like, whereby the two balance shafts are rotated at twice the crankshaft revolution speed in opposite directions.

[0006] On the other hand, in the above construction, an oil pump is also disposed below the engine closer to the balancer with a view to making it smaller. To make this happen, it is desirable that the balancer casing and the oil pump body are made integral with each other.

[0007] In general, the aforementioned balancer shafts are supported at a plurality positions. With a large-diameter journal portion of the balance shaft that is rotatably supported by a bearing thereof, when rotating, the speed is increased at which the journal portion rotates while in sliding contact with the bearing, and since this causes the bearing and journal portion to get worn largely, it is preferable to make the diameter of the journal portion as small as possible to such an extent that the strength thereof can be secured.

[0008] As disclosed in the official gazette of Japanese Patent Unexamined Publication (Kokai) No. Hei. 9-210135, however, in a construction in which balance shafts are inserted from an axial direction, it is at least needed that a journal portion is made to have the largest diameter.

[0009] To cope with this, it is considered that a casing as described above and bearings for the balance shafts are divided in two halves in vertical directions, but when the entirety of the balancer is constructed to be so divided, an oil pump body cannot be molded integrally with the casing and therefore it has to be retrofitted, this leading to a drawback of increasing the number of components and assembling man hours.

[0010] On the other hand, it is possible that two casing halves including an oil pump body and an oil pump cap are subassembled and that thereafter mounting surfaces to the cylinder block of such a sub-assembly are processed, but this deteriorates the workability. Therefore, it is desirable that a mounting surface of each component to the cylinder block be processed, but this tends to cause processing errors and in a worse case, the balance shafts incline and this causes partial wear.

[0011] The present invention was made in view of the problem inherent in the prior art. It is a first object of the present invention to provide a balance shaft supporting structure for an engine that can improve the durability of a balancer, as well as the degree of freedom of designing the same without making the engine larger and increasing the number of components used. It is a second object of the present invention to provide a balance shaft supporting structure for an engine that can prevent partial wear of a balance shaft without deteriorating the workability in assembling.

[0012] According to the present invention, the first object can be attained by providing a balance shaft supporting structure for an engine having disposed therein a casing accommodating therein a pair of balance shafts below a cylinder block thereof, characterized in that the casing comprises an upper casing and a lower casing that can vertically be split, in that an oil pump body is molded integrally with one of the upper and lower casings, in that one end of each of the two casings is inserted into the oil pump body for support therein and in that the two balance shafts are each supported on a bearing provided between the two casings in such a manner as to be split into two halves at an intermediate portion or the other end thereof. With this structure, since the oil pump body can be molded together with the casing and one of the bearings can be split into two halves, when compared with other portions of the balance shafts, the journal portion can be thinned to such an extent that the strength thereof can be secured.

[0013] In addition, the second object can be attained by molding an oil pump body integrally with the lower casing, fastening the upper and lower casings to the cylinder block with a first fastening means, and fastening an oil pump cap attached to the oil pump body from a side opposed to the upper casing to the cylinder block with a second fastening means. This structure can allow the distance between the first and second means to be lengthened as long as possible, thereby making it easy to absorb errors.

[0014] FIG. 1 is a vertical sectional view showing a main part of an engine;

[0015] FIG. 2 is a sectional view taken along the line II—II of FIG. 1;

[0016] FIG. 3 is a sectional view taken along the line III—III of FIG. 2;

[0017] FIG. 4 is a drawing similar to FIG. 3 showing a modified example of a mode of implementation of the present invention;

[0018] FIG. 5 is a sectional view taken along the line V—V of FIG. 1;

[0019] FIG. 6 is a bottom view of a secondary balancer device to which the present invention is applied;

[0020] FIG. 7 is an enlarged view showing a main part of FIG. 5;

[0021] FIG. 8 is a sectional view taken along the line VIII—VIII of FIG. 5;

[0022] FIG. 9 is a sectional view taken along the line IX—IX of FIG. 5;

[0023] FIG. 10 is a sectional view taken along the line X—X of FIG. 2;

[0024] FIG. 11 is a sectional view taken along the line XI—XI of FIG. 2; and

[0025] FIG. 12 shows enlarged view shown in a main part of the engine as a modified embodiment shown in FIGS. 5 and 7.

[0026] Referring to the accompanying drawings, a preferred mode of implementation of the present invention will be described in detail below.

[0027] FIG. 1 is a vertical sectional view of a main part of an engine, and FIG. 2 is a sectional view taken along the line II—II of FIG. 1. An engine E is an in-line four-cylinder engine in which four cylinders are disposed substantially in a perpendicular direction and in which a crankshaft 1 is disposed in a horizontal direction. A main body of the engine comprises a cylinder head 2, a cylinder block 3 connected to a lower surface of the cylinder head, a lower block connected to a lower surface of the cylinder block 3 and an oil pan 5 connected to a lower surface of the lower block 4. A journal portion of the crankshaft 1 is rotatably supported on a bearing formed between the cylinder block 3 and the lower block in such a manner as to be split into two halves.

[0028] A secondary balancer device 6 for reducing secondary vibrations and an oil pump 7 comprising a trochoidal pump are integrally provided on the lower surface of the lower block 4.

[0029] The secondary balancer device 6 comprises a pair of balance shafts 8, 9, a upper casing 10aand a lower casing 10b, the upper and lower casings being adapted to support and receive those balance shafts 8, 9. The balance shafts 8, 9 are intermeshed to each other with gears 11a, 11b, and the driving force of the crankshaft 1 is transmitted to them via a sprocket 12 provided at one end of the balance shaft 8, an endless chain 13 and a sprocket 14 provided at one end of the crankshaft 1, whereby the respective balance shafts 8, 9 are adapted to be rotated in opposite directions at twice the revolution speed of the crankshaft 1.

[0030] First journal portions 8a, 9aand second journal portions 8b, 9b, each of which has a relatively small diameter, are provided in the vicinity of one end and the other end of the respective balance shafts 8, 9, respectively. In addition, balancer weights 8c, 8d, 9c, 9dare provided on the side of the other end and the respective balancer weights are divided into two axially longitudinal front and rear halves.

[0031] Here, bearings 16, 17 for the first journal portions 8a, 9aare formed substantially as a hole in an oil pump body 7aconstituting a part of the lower casing 10b, which will be described later. In addition, bearings 18, 19 for the second journal portions 8b, 9bprovided at intermediate portions of the respective balance shafts 8, 9 are metallic bearings which are each split into halves and are formed by aligning the upper casing 10aand the lower casing 10b. With this construction, when the respective balance shafts 8, 9 are received in between the upper and lower casings 10a, 10b, first, the respective balance shafts 8, 9 may be inserted into the bearings 16, 17, respectively, at one end thereof so as to be placed on the respective split halves of the bearings 18, 19 on the side of the lower casing 10b, and then the upper casing 10amay be assembled onto the lower casing so as to align therewith. Thus, this allows the respective journal portions 8a, 9a, 8b, 9bto be thinned to such an extent that their strength can be secured. This, in turn, allows the sliding friction between the respective journal portions 8a, 9a, 8b, 9band the respective bearings 16 to 10 to be reduced, thereby making it possible to make the casing smaller in size and lighter in weight. Furthermore, the second journal portions 8b, 9bmay be formed at the other end portion of the respective balance shafts 8, 9.

[0032] As shown in FIG. 3, the upper and lower casings 10a, 10bassembled together by casing fastening bolts 34, 35, 36 functioning as a third fastening means. The upper and lower casings 10a, 10bthus assembled are then fastened to the lower block 4 with through bolts 20, 21 functioning as a first fastening means. At this time, the casing fastening bolt 35 is disposed between the bearings 18, 19 for the balance shafts 8, 9 which are provided at an intermediate portion of the pair of balancer weights. As shown in FIG. 4, when this fastening is carried out, if the upper and lower casings 10a, 10bare directly fastened together to the lower block 4 with the through bolts 20, 21, the number of components and assembly man hours can be reduced.

[0033] As shown in FIG. 5, FIG. 7 showing an enlarged view of the main portion shown in FIG. 5, FIG. 8 showing a view taken along the line VIII—VIII of FIG. 7 and FIG. 9 showing a view taken along the line IX—IX of FIG. 7, portions of the upper casing 10awhich cover the gears 11a, 11bconstitute thrust bearings 22, 23 and abut against axial ends of the gear 11amade integral with the balance shaft 8. These portions of the upper casing 10awhich cover the gears 11a, 11bare swelled outwardly, in particular, upwardly, and oil passages 24, 25 are formed in front and rear surfaces of these swelled portions so as to communicate with an upper surface (outer surface) of the upper casing 10a. Ribs 10cextending in longitudinal directions are formed on the outer surface of the upper casing 10awith which the oil passages 24, 25 are caused to communicate in such a manner as to surround the periphery thereof, so that oil flying or dripping from the engine into between the ribs 10cor an oil reservoir is led to the oil passages 24, 25 for supply to the gears 11a, 11band the thrust bearings 22, 23 in a preferred fashion. In addition, it is needless to say that the ribs 10cimprove the rigidity of the upper casing 10a, and in particular, as shown in FIG. 5, the rib 10cprovided between the swelled portion covering the gears 11a, 11band the swelled portion covering the balancer weights 8c, 8d, 9c, 9dfunctions to markedly increase the rigidity thereat.

[0034] On the other hand, as shown well in FIG. 7, similar ribs 7fare also formed on an upper surface of the oil pump body 7a, which will be described later. Therefore, oil coming in between these ribs 7for an oil reservoir is also designed to be supplied to the thrust bearings 22, 23 via the upper surface of the upper casing 10aand the oil passage 24. Here, the upper surface of the oil pump body 7aor a bottom surface of the oil reservoir is raised higher by a height H than the upper surface of the upper casing 10aadjacent thereto or a bottom surface of the oil reservoir. As a result of this, even if there is a minor error in assembling, a sufficient amount of oil can be supplied to the thrust bearings 22, 23.

[0035] Furthermore, as shown in FIGS. 5, 6 and 10, the oil pump body 7aof the oil pump 7 is formed integrally with the lower casing 10b. The other balance shaft 9 is inserted into an oil pump chamber 7bof the oil pump body 7aat one end portion, and an inner rotor 7cof a trochoidal pump is attached thereto. The pump chamber 7band a part of the oil passage are defined by combining the innter rotor 7cand an outer rotor 7d, and aligning a pump cap 74 with the body for assembly thereto. Then, this pump cap 7eis fastened to the lower block 4 with bolts as a second fastening means. The bolts as the second fastening means are respectively inserted into bolt fastening holes 7gand 7hwhich are formed on the pump cap 7e. This, in cooperation with the through bolts as the first fastening means, completes the fixation of the secondary balancer device 6 and the oil pump 7 to the lower block 4. This allows the fastened portions to be spaced farther away from each other than in a case where the fastening to the lower block is effected only at the casing of the secondary balancer device 6, whereby even if any errors in accuracy at which the mounting surfaces to the lower block 4 (cylinder block) are processed, they can be absorbed to such an extent that the errors do not affect the balance shafts 8, 9.

[0036] In this state, the inner rotor 7cactually sucks up oil in the oil pan 5 from an oil strainer 27 provided at a lower portion of the lower casing 10bvia an oil introduction passage 28 in cooperation with the outer rotor 7dso as to supply oil so sucked to the respective portions of the engine.

[0037] Here, as shown in FIG. 6 and FIGS. 8 to 10, the oil introduction passage 28 extending from the oil strainer 27 to the oil pump chamber 7bis formed at a lower end of the lower casing 10bintegrally therewith, this reinforcing the lower casing 10b. In addition, the oil introduction passage 28 extends between the balance shafts 8, 9 in substantially paralell with the axes thereof, and is allowed to enter between the two balance shafts 8, 9. Accordingly, the oil introduction passage 28 does not have to be swelled downwardly by a large swelling amount, so that the downward selling amount can be reduced. This can make the entire construction smaller.

[0038] Now, by the expression made above, “between the balance shaft 8 and the balance shaft 9” or “between the balance shafts 8, 9,” it is meant that a part of the oil introduction passage 28 is disposed at the largest-diameter portions of the balance shafts or on the upper side of a tangent Lh common to rotating loci of the balancer weights 8c, 8d, 9c, 9d, or on the axial center side of the balance shafts 8, 9. This can be said about the expression, “between the gears 11a, 11b.”

[0039] In addition, as shown in FIG. 8, the oil introduction passage 28 is defined by swelling the bottom wall of the lower casing 10bin directions toward between the two balance shafts 8, 9 and the bottom side of the oil pan 5. This restrains the downward swelling of the passage and also prevents the swashing of oil in the oil pan 5 since a lower swelled portion of the passage is in contact with the oil level Lo of oil in the oil pan 5.

[0040] On the other hand, as shown well in FIG. 11 openings 30, 31 are formed between the upper and lower casings 10a, 10bat portions where the balancer weights 8c, 8d, 9c, 9dare located in such a manner as to be opened upwardly. This allows the respective balancer weights 8c, 8d, 9c, 9dto discharge oil reserved at the bottom of the lower casing 10bfrom the openings 30, 31 to the outside of the casing as the two balance shafts 8, 9 rotate. In addition, upper portions of these openings 30, 31 are covered, respectively, with elongated projections which also function as a reinforcing rib, with a gap being maintained therebetween, whereby unnecessary oil is prevented from entering the casing from the engine E main body.

[0041] In addition to this, FIG. 12 shows enlarged view shown in a modified main part of the engine as a modified embodiment shown in FIGS. 5 and 7.

[0042] As shown in FIG. 12, the upper casing 10ahas flange portions which are upwardly raised respectively, so as to only cover the side surfaces of the gears 11aand 11band to open the upper portion of the gears 11aand 11b. With this structure, it becomes easy to form a thrust bearing 23 and also to increase an amount of the lubricant supplied to the thrust bearing 23. Since the remain components containing the oil passages 24, 25 are the same as the embodiment shown in FIGS. 5 and 7, an explanation of the same is eliminated herein.

[0043] As is clear from the above description, since the balance shaft supporting structure according to the present invention is constructed such that a casing accommodating therein a pair of balance shafts below the cylinder block comprises an upper casing and a lower casing that can vertically be split, such that an oil pump body is molded integrally with one of the upper and lower casings, in that one end of each of the two casings is inserted into the oil pump body for support therein, and in that the two balance shafts are each supported on a bearing provided between the two casings in such a manner as to be split into two halves at an intermediate portion or the other end thereof, the oil pump body can be molded together with the casing, thereby making it possible to reduce the number of components used and assembly man hours. In addition, since one of the bearings can be split into two halves, when compared with other portions of the balance shafts, the journal portion can be thinned to such an extent that the strength thereof can be secured, thereby making it possible not only to reduce the sliding friction but also to make the casing smaller in size and lighter in weight. More over, the degree of freedom of designing balance shafts can also be improved. In addition, since an oil pump body is molded integrally with the lower casing and the upper and lower casings are fastened to the cylinder block with a first fastening means, with an oil pump cap attached to the oil pump body from a side opposed to the upper casing being fastened to the cylinder block with a second fastening means, the distance between the first and second means can be lengthened as long as possible, thereby making it easy to absorb errors in processing respective mounting surfaces of the upper casing and oil pump cap to the cylinder block.

[0044] The present invention is based on Japanese Patent Application No. Hei. 10-228150, which is incorporated herein by reference.

[0045] While there has been described in connection with the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, to cover in the appended claim all such changes and modifications as fall within the true spirit and scope of the invention.