Differential apparatus with oil lubrication passages

Abstract: A differential apparatus comprises a: differential casing rotated by an engine power; a plurality of pinion gears slidably housed in accommodation holes formed in the differential casing; a pair of side gears geared with each other via the pinion gears, two opposing end surfaces thereof being slid each other directly or via a thrust washer; and a block member interposed between two inner circumferential surfaces of the two side gears so as to center the side gears, respectively. In particular, at least one oil sump is formed between the block member and the side gears, to supply lubricant to sliding portions between the block member and the side gears and between two opposing end surfaces of the two side gears, by a centrifugal force generated by the rotating differential casing. Further, it is preferable to further form at least one central oil passage at the centering portion so as to extend from an inner circumferential side to an outer circumferential side of the boss portions of the two side gears. Further, it is also preferable to form at least two radial oil passages, between inner wall surfaces of the differential casing and the side gears, respectively in such a way that a radially inward end thereof communicates with the helical oil passage and a radially outward end thereof communicates with sliding portion between the side gear and the differential casing, respectively.

Description: The present invention relates to a differential apparatus according to the preamble of independent claim 1. Such a differential apparatus is applicable to front, center and rear differential gears for an automotive vehicle. A differential apparatus as indicated above is known from prior art document EP 0 622 569 A1. Some examples of prior art differential apparatus related to a first aspect of the present invention will be described hereinbelow with reference to the attached drawings. Fig. 1 shows a first prior art differential apparatus disclosed in Japanese Published Unexamined (Kokai) Utility Model Application No. 1-146062. This differential apparatus includes a plurality of worm wheel sets each composed of two worm wheels in mesh with each other at each spur gear portion thereof and a pair of worm gears (i.e., side gears) each in mesh with each worm wheel, separately. Further, the two worm gears are spline-coupled with two output (wheel drive) shafts of an automotive vehicle, respectively. Therefore, when a differential casing is rotated by an engine power, the drive power of the engine is distributed to both right and left output (wheel drive) shafts from the worm wheel sets to the two worm gears (i.e., two side gears), respectively. In this case, the differential motion can be limited by frictional resistances generated between the worm wheels and worm gears, respectively. Fig. 2 shows a second prior art differential apparatus whose structure is similar to that disclosed in Japanese Published Unexamined (Kokai) Patent Application No.6-207645. This differential apparatus includes a pair of helical pinion gears and slidably rotatably housed in accommodation holes formed in a differential casing, respectively and in mesh with each other, and a pair of helical side gears in mesh with the helical pinion gears, respectively. Further, the helical side gears are spline-coupled with two output (wheel drive) shafts of an automotive vehicle, respectively. Therefore, when a differential casing is rotated by an engine power, the drive power of the engine is distributed to both right and left wheels from the helical pinion gears to the helical side gears, respectively. In this case, the differential motion can be limited by frictional resistances generated between the respective helical gears due to thrust forces generated by gearing between the respective helical gears, and by other frictional resistance generated between the respective helical gears and the inner wall surfaces of accommodation holes or sliding portions of the differential casing due to reaction forces generated between the respective helical gears. Here, in the differential apparatus, the two helical side gears are directly slid with respect to each other at each inner end surface thereof. Fig. 3 shows a third prior art differential apparatus disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 7-71560. This differential apparatus includes two helical side gears and a thrust washer interposed between the two side gears. In this differential apparatus, the two helical side gears are indirectly slid with respect to each other via the thrust washer. In order to obtain a stable differential limiting force generated due to the sliding motion between the two helical side gears; that is, to prevent the vibration of the two helical side gears, the helical side gear is formed with a cylindrical projected portion and the helical side gear is formed with a cylindrical recessed portion so that the two helical side gears can be aligned with each other at a centering portion. In addition, a thrust block is interposed between two inner circumferential surface portions of the two helical side gears in such a way as to be brought into contact with the inner ends of the two output shafts fixed to the two side gears, respectively. In the above-mentioned first prior art differential apparatus shown in Fig. 1, a helical oil groove is formed in the differential casing for lubrication. Further, in the differential apparatus shown in Fig. 3, in general, some oil gaps (i.e., grooves) are formed by cutting off some teeth formed at the spline portion between the each helical side gear and the each output shaft, in order to introduce lubricant from the helical oil groove (e.g., as shown in Fig. 1) into an inner side between the two helical side gears. In other words, in the differential apparatus, although some oil passages are generally formed to introduce lubricant from the outside of the differential casing to the inside of the differential casing, when the thrust block is interposed in the inner circumferential surface portions of the two helical side gears as shown in Fig. 3, since lubricant flow is shut off by the presence of the thrust block, it is difficult to allow the introduced lubricant to flow to the respective sliding portions between the thrust block and the two inner end surfaces of the two helical side gears, so that there exists such a problem in that seizure occurs at the inner end surfaces of the two helical side gears. In addition, when the centering portion is formed as shown in Fig. 3, since the lubricant is further difficult to flow smoothly, there exists another problem in that seizure occurs at the sliding portion at this centering portion. In addition, once lubricant flow is shut off as described above, since lubricant cannot flow smoothly through the gaps formed between the helical side gears and the output shafts respectively, there arises another problem in that cracks are easily produced due to the fretting corrosion at the spline portions between the side gears and the output shafts, respectively. In addition, when the centering portion is formed as shown in Fig. 3, since the two helical side gears cannot be used in common, there exists such a disadvantage that the number of parts increases. An example of a further prior art differential apparatus will be described hereinbelow with reference to the attached drawings. Figs. 4(a) and 4(b) show a fourth prior art differential apparatus disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 6-207646. This differential apparatus is of parallel shaft type, in which a differential limiting force can be obtained by rotational frictional forces generated between some pinion gears and two side gears. In the differential apparatus shown in Fig. 4(a), a pair of side gears are rotatably disposed in a differential casing coaxially with the casing so as to confront with each other at the central portion of the casing. Further, the two side gears are aligned with each other at a centering portion by butting an inner projecting end surface of the side gear into an inner recessed end portion of the side gear. Further, a plurality of pairs of pinion gears are arranged within the differential casing in parallel with and around the rotational axis of the two side gears. One of the two pinion gears of each pair is in mesh with the left side gear and the other (not shown) of the two pinion gears of each pair is in mesh with the right side gear. Further, the two pinion gears for constructing one pair are in mesh with each other. The differential casing is formed with accommodation holes for housing these pinion gears respectively, so that each of these pinion gears is slidably and rotatably housed in each of these accommodation holes. Further, the differential casing is formed with a lubricant opening in the outer circumferential wall thereof to exhaust lubricant from the rotating pinion gears to the outside of the differential casing. Therefore, when the differential casing is rotated, an engine power is distributed from the pinion gears to the two side gears; that is, to the two output shafts, respectively. In more detail, the engine power can be distributed differentially to the right and left wheels, respectively on the basis of rotations of the respective pinion gears each rotating on its own axis according to a difference in drive resistance between the two wheels. In this case, since the pinion gears are slidably rotating in the accommodation holes formed in the differential casing, respectively, once a differential motion occurs, a differential limiting force can be obtained due to the frictional resistances generated between the respective pinion gears, the side gears and the other members (e.g., inner wall surfaces of the differential casing) in contact with these gears. In the differential apparatus shown in Fig. 4(a), it is effective to provide a centering portion between two inner end surfaces of the two side gears, in order to prevent misalignment between each pinion gear and the center of each accommodation hole; that is, to stabilize the differential limiting characteristics, without causing any seizure between each pinion gear and each accommodation hole. Further, in the differential apparatus of this type, it is well known that frictional force can be increased and thereby the differential limiting force can be strengthened by constructing the respective gears into helical type; that is, by sliding the outer end surface portions of the two side gears with inner wall surfaces of the differential casing according to the drive torque inputted to the differential casing, and by sliding the inner end surfaces of the two side gears with each other. Here, it is preferable to interpose a washer at each of these sliding portions to prevent the end surfaces of the side gears and the wall surface of the differential casing from being worn off easily, to eliminate the heat treatment process, and to smoothen the slidable motion for stabilization of the differential limiting characteristics, as disclosed in Japanese Published Unexamined Patent Application Nos. 6-1017414, and 6-185581. However, in the prior art differential apparatus as shown in Fig. 4(a), since the boss portions of the two side gears are formed into cylindrical shape, respectively, lubricant flows into the inner space formed between the two end surfaces of the two side gears through oil gaps formed by cutting off some teeth of each spline portion between the inner circumferential surface of the side gear and the outer circumferential surface of the output shaft, respectively, as shown by arrows shown in Fig. 4(b). In the prior art differential apparatus shown in Fig. 4(a), however, since the inner space formed between the two end surfaces of the two side gears is closed by the fitting surface at the centering portion between the two side gears, the lubricant entering the inner space between the two side gears cannot flow radially outward to the outer circumferential surfaces of the boss portion of the two side gears, with the result that there exists a problem in that lubricant cannot flow smoothly. In other words, at the centering portion, since both the side gears are aligned with each other by bringing the two circumferential fitting surfaces of both the side gears into sliding contact with each other, the sliding contact portions are shut off and thereby the lubricant passage is closed, so that it has been impossible to obtain a definite lubricant flow. Further, in the case where other boss portions are formed on the side of the axially outer end surfaces of the two side gears in order to form two centering portions of the two side gears by use of the inner wall surfaces of the differential casing, since the lubricant passage is blocked, a definite lubricant flow cannot be obtained. Some examples of a further prior art differential apparatus will be described hereinbelow with reference to the attached drawings. Fig. 5 shows a fifth prior art differential apparatus disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 59-97346. In this differential apparatus, a differential casing is composed of a casing body and two casing covers. An engine power for rotating the differential casing is transmitted from three pairs of first and second pinion gears to two output shafts via two right and left side gears. The first and second pinion gears and the right and left side gears are all of spur gear type. Further, each pair of the two pinion gears is slidably and rotatably housed in a pair of accommodation holes formed in the casing body of the differential casing. When an engine torque is transmitted to the output shafts during straight drive or turning drive, the two pinion gears are brought into pressure contact with the wall surfaces of the accommodation holes due to the gearing between the two pinion gears and the two side gears, respectively or due to the gearing between the two pinion gears themselves, so that pinion gears rotate under frictional contact with the differential casing. The frictional resistance generated as described above becomes a differential limiting force of the differential apparatus. Fig. 6 shows a sixth prior art differential apparatus disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 60-175843. In this differential apparatus, a drive power of an engine for rotating a differential casing is transmitted from pairs of two pinion gears to the two output shafts via two output side gears, respectively. These pinion gears are also slidably and rotatably housed in accommodation holes formed in the differential casing, respectively. The pinion gears and the side gears are all of helical gear type. Further, the differential casing is formed with an opening on the side wall portion thereof to introduce lubricant from the outside thereof into the differential casing. When a torque is being transmitted, since the helical pinion gears are brought into pressure contact with the wall surfaces of the accommodation holes of the differential casing, respectively by reaction force generated due to the gearing between the helical pinion gears and the helical side gears respectively, frictional forces can be generated thereat. Further, other frictional forces can be also generated between the helical side gears and between the respective helical gears and the inner wall surfaces of the differential casing due to thrust force generated by the gearing between the helical gears. The frictional resistance generated as described above becomes a differential limiting force of the differential apparatus. Figs. 7(a) and 7(b) show a seventh prior art differential apparatus disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 6-323373. In this differential apparatus, a drive power of an engine for rotating a differential casing composed of a differential body and a cover is transmitted from a plurality (three in this example) of pairs of pinion gears in mesh with each other (these pinion gears belong to central pinion gears of different pairs, respectively) to two output shafts via two right and left side gears, respectively. These pinion gears are also slidably and rotatably housed in accommodation holes formed in the differential casing, respectively. The pinion gears and the side gears are all of helical gear type. Further, the differential casing is formed with an opening on the outer circumferential wall portion of the casing body so as to communicate with the outside of the differential casing. When a torque is being transmitted, since the pinion gears are brought into pressure contact with the wall surfaces of the accommodation holes of the casing body, respectively by reaction force generated due to the gearing between the pinion gears and the side gears, respectively, frictional forces can be generated thereat. Further, other frictional forces can be also generated between side gears and between the respective gears and the differential casing due to thrust force generated by the gearing between the respective helical gears. The frictional resistance generated as described above becomes a differential limiting force of the differential apparatus. In the above-mentioned prior art differential apparatus as shown in Figs. 5, 6, and 7(a) and 7(b), the differential limiting force can be obtained on the basis of the respective gearing reaction forces generated between the pinion gears and the side gears according to the input torque and on the basis of the frictional resistance generated between the pinion and side gears and the differential casing due to the gearing thrust force. Accordingly, when sufficient lubricant is not supplied into the differential casing, that is, to the sliding portions between the pinion gears and the accommodation holes, respectively, there arises a serious problem in that seizure and scuffing (gall) occur, with the result that a stable differential limiting force cannot be obtained. In particular, as with the case of the differential apparatus as shown in Figs. 6, 7(a) and 7(b), when the side gears and the pinion gears are of helical gear type, since the frictional forces generated at the end surfaces of the pinion gears and the side gears due to the above-mentioned thrust force contributes much to the differential limiting force, sufficient lubrication is particularly essential at the respective end surfaces of these gear elements. In other words, it has been impossible to obtain sufficient lubrication by introducing lubricant only through the opening formed in the side wall or the outer circumferential wall of the differential casing. This is because when lubricant is introduced into the differential casing through the opening, since the introduced lubricant is scattered rearward and outward by centrifugal force of the various gears, the lubrication effect is particularly small at the sliding portions between the end surfaces of the side gears and the differential casing and at the sliding portions between the end surfaces of the pinion gears and the differential casing, so that there arises a serious problem in that seizure and scuffing occur frequently at these sliding portions, with the result that a stable differential limiting force cannot be so far obtained. It is an objective of the present invention to provide a differential apparatus as indicated above having improved lubricating properties. According to the present invention said objective is solved by a differential apparatus having the features of independent claim 1. Preferred embodiments are laid down in the dependent claims. Accordingly, a differential apparatus is provided which can obtain a sufficient lubrication at various sliding portions between the pinion gears, the side gears and the inner wall surfaces of the differential casing, for providing a stable differential limiting function. Preferably, the differential apparatus provide a sufficient lubrication at the opposing end surfaces of the two side gears, and the spline portions between the two side gears and the two output shafts, respectively. According to an advantageous embodiment, the radially outward ends of said radial oil passages are formed at such positions as to communicate with sliding portions between said side gears and said differential casing and further at such positions as to correspond to gearing portions between said pinion gears and said side gears, respectively. Preferably, the radially outward ends of said radial oil passages are formed at such positions as to communicate with sliding portions between said side gears and said differential casing and further at such positions as to correspond to gearing portions between said pinion gears, respectively. Advantageously, the radially outward ends of said radial oil passages are formed at such positions as to communicate with sliding portions between said side gears and said differential casing and further at such positions as to correspond to sliding portions between end surfaces of said pinion gears and an inner wall surface of said differential casing, respectively. According to a preferred embodiment, the radially outward ends of said radial oil passages are formed at such positions as to communicate with mutual engaging portions between said pinion gears. Preferably, said radial oil passages are formed for each mutually gearing pinion gear pair or for each pinion gear. Preferably, said helical oil passages are formed in inner circumferential surfaces of boss portions of said differential casing or outer circumferential surfaces of two output shafts, respectively; and said radial oil passages are formed in said differential casing or said side gears, respectively so as to extend radially outward. Preferably, said helical oil passages are of helical oil groove formed in inner circumferential surfaces of the boss portions of said differential casing, respectively in such a way as to be inclined by an inclination angle in a direction that lubricant can be introduced from an outside oil reservoir into said differential casing when said differential casing is rotated; said radial oil passages are formed in said differential casing in such a way that one end thereof communicates with the helical oil passages, respectively and the other ends thereof extend radially outward; and said differential casing is formed with openings communicating between inside and outside of said differential casing at such positions as being further radially outward away from the other ends of said radial oil passages, two oil circulation passages being formed by way of said two helical oil passages, said two radial oil passages, the accommodation holes of said differential casing and the openings, respectively to circulate lubricant by centrifugal force generated by rotation of said differential casing. The invention provides the following effects: The helical oil grooves are formed between the inner circumferential surfaces of the boss portions of the differential casing and the outer circumferential surfaces of the output shafts respectively, and further the radial oil passages are formed between the two side gears and the differential casing, respectively in such a way that the radially inward ends thereof communicate with the ends of the helical oil grooves and further with the sliding portions between the side gears and the inner walls of the differential casing, respectively. Consequently, lubricant introduced from the oil reservoir due to the rotation of the differential casing can be supplied to the sliding portions between the side gears and the differential casing, so that it is possible to prevent seizure at these sliding portions and thereby a stable differential limiting force can be obtained. Preferably, the radially outward ends of the radial oil passages are located at the gearing portions between the pinion gears and the side gears. Consequently, it is possible to prevent seizure and gall at the sliding portions between the side gears and the differential casing, the gearing portions between the pinion gears and the side gears, and the sliding portions between the pinion gears and the accommodation holes of the differential casing. Further, when the pinion gears and the side gears are being rotated, since lubricant can be supplied to the sliding portions between the side gears and the differential casing due to the pumping action of the pinion and side gears, it is possible to prevent seizure and gall at the sliding portions. The oil sump or the oil sumps are formed between the thrust block member (for centering the two side gears) and the two side gears, respectively, and further the lubricant stored in the oil sumps can be supplied to the centering sliding portions of the thrust block member (i.e., between the two helical side gears) and to the two opposing end surface portions of the two side gears by a centrifugal force generated by the two side gears. Consequently, the two helical side gears can be lubricated sufficiently, so that it is possible to obtain a stable differential limiting force. The lubricant stored in the oil sumps can be moved radially outward by a centrifugal force of the side gears. Consequently, lubricant is sucked from the outside of the differential apparatus inward smoothly along the spline portions between the two side gears and the two output shafts respectively, so that the fretting corrosion can be prevented at the spline portions. As a result, it is possible to move the two side gears smoothly in the axial direction thereof. The two helical side gears can be centered each other by the thrust block member. Consequently, it is unnecessary to form the two different shaped centering portions in the two helical side gears; that is, the two side gears of the same shape can be used in common, so that it is possible to reduce the number of parts of the differential apparatus. The lubricant passage is formed within the differential casing by way of the helical oil grooves formed in the inner circumferential surfaces of the two boss portions of the differential casing, the axial oil grooves formed at the spline portions between the two side gears and the two output shafts; and the oil sumps formed by the thrust block, the accommodation holes for housing the pinion gears, and the openings formed in the differential casing. Consequently, it is possible to improve the lubrication effect markedly. The thrust block member is used for forming the oil sumps and for locating the axial positions of the output shafts in common. Consequently, it is possible to reduce the number of parts of the differential apparatus. The outer diameter of the oil sumps is determined larger than the inner diameter of the boss portions of the two helical side gears, respectively. Consequently, a great amount of lubricant can be allowed to flow into the oil sumps effectively by a centrifugal force of the two side gears, so that it is possible to improve the lubrication effect more effectively. Hereinafter the present invention is illustrated and explained by means of preferred embodiments in conjunction with the accompanying drawings. In the drawings wherein: Fig. 1 is a cross-sectional view showing a first example of prior art differential apparatus related to the first aspect of the present invention; Fig. 2 is a cross-sectional view showing a second example of prior art differential apparatus related to the first aspect of the present invention; Fig. 3 is a cross-sectional view showing a third example of prior art differential apparatus related to the first aspect of the present invention; Figs. 4A and 4B are cross-sectional views showing a fourth example of prior art differential apparatus related to the second aspect of the present invention, in which Fig. 4B shows only a lubricant flow passage of the same differential apparatus; Fig. 5 is a cross-sectional view showing a fifth example of prior art differential apparatus related to the third aspect of the present invention; Fig. 6 is a cross-sectional view showing a sixth example of prior art differential apparatus related to the third aspect of the present invention; Fig. 7A is a cross-sectional views showing a seventh example of prior art differential apparatus related to the third aspect of the present invention; Fig. 7B is an external views showing the seventh example of prior art differential apparatus shown in Fig. 7A; Fig. 8A is a cross-sectional view showing a first embodiment of the differential apparatus of the third aspect of the present invention; Fig. 8B is a cross-sectional view showing the same first embodiment taken along the line 14A - 14A shown in Fig. 8A; Fig. 8C is a cross-sectional view showing the same first embodiment taken along the line 14B - 14B shown in Fig. 8A; Fig. 9A is a cross-sectional view showing a second embodiment of the differential apparatus of the third aspect of the present invention; Fig. 9B is a cross-sectional view showing the same second embodiment taken along the line 15A - 15A shown in Fig. 9A; Fig. 10A is a cross-sectional view showing a third embodiment of the differential apparatus of the third aspect of the present invention; and Fig. 10B is an inner cross-sectional view showing a cover for constituting the differential casing of the same third differential apparatus shown in Fig. 16A. Embodiments of the differential apparatus will be described hereinbelow with reference to the attached drawings. The teaching of the embodiments is directed to a plurality of radial oil passages extending from the helical oil grooves formed in boss portions of the differential casing to gearing portions between the side gears and the pinion gears, respectively. A first embodiment will be described hereinbelow with reference to Figs. 8A to 8C. In Fig. 8A, the differential apparatus 807 is composed of a casing body 831 and a cover 833 fixed to the casing body 831 with bolts. Within the differential casing 821', a pair of left and right helical side gears 835 and 837 are arranged. Further, two boss portions 849 and 851 of the differential casing 821 of the differential apparatus 807 are rotatably supported by a differential carrier (not shown) via bearings. When not rotated by an engine power, the differential apparatus 807 is dipped in lubricant 808 stored in an oil reservoir (not shown). Two hollow boss portions 839 and 841 of the two side gears 835 and 837 are rotatably supported by two support portions 843 and 845 of the differential casing 821, respectively. Inside the two side gears 835 and 837, a thrust block 847 is disposed in such a way as to extend axially along two inner circumferential surfaces of the two side gears 835 and 837 and as to support the respective inner free ends of the two side gears 835 and 837 for centering (alignment), respectively. Left and right output shafts (not shown) are passed through two boss portions 849 and 851 of the differential casing 821 and further spline-coupled with two spline portions of-the two side gears 835 and 837, respectively. Two thrust washers 853 and 855 are interposed between the inner wall surfaces of differential casing 821 and the two side gears 835 and 837, respectively. Further, a thrust washer 857 is interposed between the two side gears 835 and 837 and on the outer circumferential surface of the thrust block 847. The differential casing 821 is formed with a plurality (four in this embodiment) of paris of long accommodation hole 859 and short accommodation hole 861, which are arranged at regular angular intervals along the circumferential direction of the casing 821. A long helical pinion gear 863 is slidably and rotatably housed in each of the long accommodation holes 859, and a short helical pinion gear 865 is slidably and rotatably housed in each of the short accommodation holes 861, respectively. Each long helical pinion gear 863 is formed with a first gear portion 867, a second gear portion 869 and a small diameter axle portion 871 for connecting the first and second gear portions 867 and 869. The first gear portion 867 of the long helical pinion gear 863 is in mesh with the right side gear 837. On the other hand, the short helical pinion gear 865 is formed with first gear portion 873 and a second gear portion 875 formed integral with each other. The first gear portion 873 of the short helical pinion gear 865 is in mesh with the left side gear 835, and the second gear portion 875 of the short helical pinion gear 865 is in mesh with the second gear portion 869 of the long helical pinion gear 863. In operation, an engine power is transmitted to the differential casing 821. When the differential casing 821 is rotated, the engine power is distributed to the left and right output shafts via the two long and short helical pinion gears 863 and 865 and the two side gears 835 and 837, respectively. In more detail, when a difference in driving resistance is produced between the two output (wheel drive) shafts during travel on a muddy road for instance, since the long and short helical pinion gears 863 and 865 are rotated on their own axes, respectively, an engine drive power can be distributed differentially to the left and right output shafts, appropriately. When an engine torque is being transmitted, since the respective helical pinion gears 863 and 965 are brought into pressure contact with the inner wall surfaces of the respective accommodation holes 859 and 861 due to reaction force generated by gearing between the respective long and short helical pinion gears 863 and 865 and the two side gears 835 and 837, respectively, a frictional resistance is generated. Further, since the end surfaces of the respective long and short helical pinion gears 863 and 865 are brought into contact with the inner wall surfaces of the differential casing 821 due to thrust force generated by gearing between the long and short helical pinion gears 863 and 865, another frictional resistance is generated. In addition, another frictional resistance is generated between the two inner end surfaces of the two side gears 835 and 837 via the thrust washer 857 or between the respective side gears 837 and 837 and the inner wall surfaces of the differential casing 821 via the thrust washers 853 and 855, respectively. On the basis of these frictional resistances, it is possible to obtain a differential limiting function of torque sensitive type. As shown in Fig. 8A, a helical oil groove 877 with an inclination angle () is formed in the inner circumferential surface of the boss portion 849 of the differential casing 821 to introduce lubricant 808 in the oil reservoir to the inside of the differential casing 821 whenever the differential casing 821 is rotated in one direction. Further, another helical oil groove 879 with an inclination angle () in opposite direction is formed in the inner circumferential surface of the boss portion 851 of the differential casing 821 to introduce lubricant 808 in the oil reservoir to the inside of the differential casing 821 whenever the differential casing 821 is rotated in the other direction. Further, the cover 833 is formed with a radial oil passage 881 having one end 880 communicating with the helical oil groove 877 and the other end 887 extending to the gearing portion between the second gear portion 875 of the short pinion gear 865 and the second gear portion 869 of the long pinion gear 863 (which is located radially outward from the gearing portion between the short pinion gear 865 and the left side gear 835) (See Fig. 8B). Therefore, the other end 887 of the radial oil passage 881 is located radially outward from the one end 880 thereof with respect to the axis 826 of the differential casing 821. The radial oil passage 881 can be formed when the cover 833 is casted. In the same way, the casing body 831 is formed with a radial oil passage 885 having one end 884 communicating with the helical oil groove 879 and the other end 889 extending to the first gear portion 867 of the long pinion gear 863 (which is located radially outward from the gearing portion between the first gear portion 867 of the long pinion gear 863 and the right side gear 837) (See Fig. 8B). Therefore, the other end 889 of the radial oil passage 885 is located radially outward from the one end 884 thereof with respect to the axis 826 of the differential casing 821. The radial oil passage 885 can be formed when the casing body 831 is casted. The thrust block 847 is formed into an elongated oblong shape in such a way that two axial cutout portions 891 are formed at regular angular intervals along the outer circumference thereof. Therefore, two oil sumps can be formed between the two cutout portions 891 of the thrust block 847 and the inner circumferential surfaces of the two side gears 835 and 837, respectively. Further, some of the spline teeth formed between the boss portion 839 of the side gear 835 are cut off to form axial oil grooves communicating with the helical oil groove 877 formed in the cover 833. In the same way, some of the spline teeth formed between the boss portion 841 of the side gear 837 are cut off to form axial oil grooves communicating with the helical oil groove 879 formed in the casing body 831. Therefore, the two oil sumps formed between the two cutout portions 891 of the thrust block 847 can communicate with the two helical oil grooves 877 and 879 through the axial oil grooves formed at the spine portions between the two side gears 835 and 837 and the output shafts, respectively. In addition, the differential casing 821 is formed with openings 893, 895 and 897 in the outer wall surface of the differential casing 821, which are all located further radially outward from the other ends 887 and 889 of the radial oil passages 881 and 885. Accordingly, it is possible to provide a first oil circulating passage between the outside and inside of the differential passage by way of the helical oil grooves 877 and 879, the axial oil grooves formed at the cut-off spline portions, the oil sumps of the thrust block 847, and the openings 893, 895 and 897; and a second oil circulating passage between the outside and the inside of the differential casing 821, by way of the helical oil grooves 877 and 879, the radial oil grooves 881 and 885, and the openings 893, 895 and 897, respectively. Accordingly, when the differential casing 821 is rotated, since lubricant stored in a differential carrier (not shown) for accommodating the differential casing 821 is leaped, the leaped lubricant is introduced from the two helical oil grooves 877 and 879 formed in the boss portions 849 and 851 of the differential casing 821 into the inside of the differential casing 821; flows along the two radial oil passages 881 and 885, by a centrifugal force of the side gears 835 and 837, to the respective sliding portions between the two side gears 835 and 837 and the two thrust washers 853 and 855 and between the two side gears 835 and 837 and the inner wall surfaces of the differential casing 821; lubricates the gearing portions between the respective gears and the sliding portions between the respective gears and various inner wall surfaces (e.g., the accommodation holes 859 and 861) of the differential casing 821; and lastly exhausted to the outside of the differential casing 821 through the openings 893, 895 and 897 due to the same centrifugal force of the differential apparatus, so that the lubricant can be returned to the oil reservoir of the differential carrier. Since the lubricant circulating passage is formed as described above, lubricant can flow smoothly, so that it is possible to improve both the lubrication effect and the cooling effect. In particular, since the lubricant circulating passage is so formed as to extend radially outward from the two helical oil grooves 877 and 879 to the openings 893, 895 and 897 radially away from the central rotational axis of the differential casing 821, the lubricant can be moved easily radially outward due to a centrifugal force of the various gears, so that the flow of lubricant is enhanced effectively. Further, when a differential motion occurs between the two side gears 835 and 837, on the side of the left radial oil passage 881, since lubricant is introduced from the second gear portion 875 of the short pinion gear 865 to the gearing portion between the second gear portion 875 of the short pinion gear 865 and the second gear portion 869 of the long pinion gear 863 due to the gearing motion between the short and long pinion gears 865 and 863, the lubricant flow can be enhanced. Further, the lubricant introduced into the gearing portion between the first gear portion 873 of the short pinion gear 865 and the left side gear 835 is pushed into the sliding portion among the side gear 835, the thrust washer 853 and the inner wall of the differential casing 821 due to the pumping action of the gears. Further, on the side of the right radial oil passage 885, lubricant is sacked through the radial oil passage 885 due to the pumping action of the gearing between the first gear portion 867 of the long pinion gear 863 and the right side gear 837, and then introduced into the sliding portions between the side gear 837, the thrust washer 855 and the inner wall surface of the differential casing 821. As described above, a great amount of lubricant can be supplied to the respective sliding portions and the respective gearing portions between the two side gears 835 and 837, the two thrust washers 853 and 855, and the inner wall surfaces of the differential casing 821 and further to the other lubrication portions such as the accommodation holes 859 and 861 of the long and short pinion gears 863 and 865, so that the lubrication effect can be further improved. As a result, it is possible to prevent seizure and gall (or scuffing) at the sliding and gearing portions between the two side gears 835 and 837, the two thrust washers 853 and 855 and the inner wall surfaces of the differential casing 821, and further to prevent pitching and gall (or scuffing) at the respective gearing portions between the long and short pinion gears 863 and 865 and the two side gears 835 and 837 and the gearing portions between the long and short pinion gears 863 and 865, respectively. On the other hand, the lubricant introduced into the differential casing 821 through the two helical oil grooves 877 and 879 flows into the oil sumps of the thrust block 847 through the cut-off spline tooth portions to lubricate the sliding portions between the thrust block 847 and the two side gears 835 and 837; pushed radially outward to the thrust washer 857 due to a centrifugal force to lubricate the sliding portions between the thrust washer 857 and the two side gears 835. and 837 and further to the respective gearing portions between the pinion gears 863 and 865 and the inner wall surfaces of the accommodation holes 859 and 861; and then exhausted to the outside of the differential casing 821 through the openings 893, 895 and 897, being returned to the oil reservoir of the differential carrier. As described above, since a definite lubricant circulating passage can be formed, it is possible to smoothen the lubricant flow, so that the lubrication effect can be improved. Further, in this embodiment, since the respective gears are of helical gear type, thrust forces generated by various gears are applied to the respectively sliding portions between the two side gears 835 and 837, the two thrust washer 853 and 855, and the wall surfaces of the differential casing 821 according to the torque inputted to the differential casing 821, so that the sliding pressure increases. In this embodiment, however, since the oil passages are securely formed, it is possible to supply sufficient lubricant to the respective sliding portions. Further, since the outer diameter of the thrust block 847 is determined larger than the inner diameter of the boss portions 839 and 841 of the two side gears 835 and 837, lubricant can smoothly flow due to a centrifugal force applied to the differential casing 821, so that the lubrication effect can be further improved at the sliding portions between the thrust washer 857 and the two side gears 835 and 837 and other lubrication portions. In the present embodiment, since a great amount of lubricant can be supplied to the various sliding portions between the thrust washers 853 and 855 and the side gears 835 and 837, between the side gears 835 and 837 and the differential casing 821, between the thrust washer 857 and the side gears 835 and 837, between the pinion gears 863 and 865 and the accommodation holes 859 and 861 of the differential casing 821, and between the respective pinion gears 863 and 865 and thereby sufficient and secure lubrication can be realized, experiments indicated that seizure and gall or scuffing did not occur, even if a drive torque twice larger than the ordinary drive torque was applied to the differential casing 821 under the same test conditions excepting the drive torque. This indicates that the lubrication structure of the present embodiment can provide a stable differential limiting function. As a result, when the differential apparatus 807 as described above is mounted on an automotive vehicle, since the various sliding portions and gearing portions will not be seized or scuffed, an excellent driving or steering stability can be obtained. Further, since the sliding portions between the two side gears 835 and 837 and the differential casing 821 can be sufficiently lubricated as described above, it is possible to eliminate the thrust washers 853 and 855, respectively. Further, without being limited only the above-mentioned structure, the oil grooves can be formed in different ways. For instance, it is possible to form the helical oil grooves on the outer circumferential surfaces of the output shafts, respectively instead of the helical oil grooves 877 and 879, and to form the radial oil passages on the end surfaces of the two side gears, respectively instead of the radial oil passages 881 and 885. Further, the number of the radial oil passages 881 and 885 can be increased in such a way as to be formed for each pair of the long and short pinion gears 863 and 865 or for each of all long and short pinion gears 863 and 865. When the number of the radial oil passages is increased, the lubrication effect can be improved to that extent. Further, it is also possible to form the radial oil passages 881 and 885 in such a way as to directly communicate with the gearing portions between the long and short pinion gears 863 and 865. In this case, the lubrication effect at the gearing portions can be further increased. A second embodiment will be described hereinbelow with reference to Figs. 9A to 9B, in which only a cover 833B of the second embodiment of the differential apparatus is shown. The feature of this embodiment is to form the radial oil passages whose number is the same as that of pairs of the pinion gears. Fig. 9A is a plane view obtained when the cover 833B is seen from the inner side of the differential casing, and Fig. 9B is a cross-sectional view taken along the line 15A - 15A shown in Fig. 9A, in which the same reference numerals have been retained for similar parts having the same functions as with the case of the first embodiment shown in Fig. 8A. In the cover 833B shown in Figs. 9A and 9B, two helical oil grooves 877 are formed in the inner circumferential surface of the boss portion 849 of the cover 833B. Further, four radial oil passages 881 are formed in the boss portion 849 thereof at regular angular intervals along the circumferential direction thereof. Therefore, in this second embodiment, lubricant can be supplied securely and sufficiently to each pair of short and long pinion gears, so that the lubrication effect can be further improved. This is because in the case of only the single radial oil passage 881 as shown in Fig. 8B, since there exists a dam portion between a pair of the pinion gear accommodation holes and an adjacent pair of the pinion gear accommodation holes, the quantity of lubricant supplied to the adjacent accommodation holes is relatively small. In contrast with this, in this second embodiment, since lubricant is supplied to each pair of the pinion gear accommodation holes along each radial oil passage 881, it is possible to supply a sufficient amount of lubricant to each pinion gear pair, respectively. Further, in this embodiment, two radially inward ends 880 of the two adjacent radial oil passages 881 are connected to one of the two helical oil grooves 877, and two radially inward ends 880 of the other two adjacent radial oil passages 881 are connected to the other of the two helical oil grooves 877. Further, in this embodiment, the radial oil passage 881 is formed so as to communicate with the succeeding pinion gear (rotated after the precedent pinion gear) in the ordinary (frontward drive) rotational direction. In more detail, in Fig. 9A, when the differential casing 821 is rotated in the arrow direction R in the frontward vehicle drive, the radial oil passage 881 is formed so as to communicate with the succeeding accommodation hole 863 of a pair of the two rotating accommodation holes 861 and 863. This is because when the two precedent and succeeding pinion gears are rotating around an axis of the differential apparatus together with the differential casing 821, a frictional force generated between the succeeding pinion gear and its accommodation hole is larger than that generated between the precedent pinion gear and its accommodation hole. As described above, since lubricant is directly introduced into the succeeding rotating pinion gear side, it is possible to sufficiently supply lubricant more effectively to the sliding portions between the pinion gears and the inner wall surfaces of the accommodation holes of the differential casing. Further, when the radial oil passages 881 are introduced into the accommodation holes of the precedent pinion gears, when the differential casing is rotated, it is possible to expect the lubricant flow from each precedent pinion gear to each succeeding pinion gear smoothly. Further, although not shown, two helical oil grooves 879 are formed in the inner circumferential surface of the boss portion 851 of the casing body 831. Further, four radial oil passages 885 are also formed in the boss portion 851 of the casing body 831 at regular angular intervals along the circumferential direction thereof, in the same way as in the cover 833B. A third embodiment will be described hereinbelow with reference to Figs. 10A to 10B. Fig. 10A is a side cross-sectional view of the differential apparatus 900, taken along the line 16A - 16A shown in Fig. 10B. Fig. 10B is a plane view obtained when the cover is seen from the inner side of the differential casing in Fig. 10A. In this embodiment, the differential casing 921 of the differential apparatus 900 is composed of a casing body 931 having a side wall portion 932 and a cylindrical boss portion 934, and a cover 933 having a cylindrical boss portion 935. The cover 933 is fixed to the casing body 931 with bolts (not shown) in such a way as to close the opening surface of the differential casing 921 on the side opposite from the side wall portion 932. Within the differential casing 921, two left and right side gears 939 and 941 are disposed. The left side gear 939 is spline engaged with a left output shaft (not shown) via a boss portion 943 thereof, and the right side gear 941 is spline engaged with a right output shaft (not shown) via a boss portion 945 thereof. The respective output (drive wheel) shafts are spline-engaged with the two side gears 939 and 941 being passed through the boss portion 935 of the cover 933 and the boss portion 934 of the casing body 931, respectively. Two helical oil grooves 979L and 979R are formed in the inner circumferential surfaces of the boss portion 935 of the cover 933 and the inner circumferential surface of the boss portion 934 of the casing body 931, respectively, in the same way as with the case of the first embodiment shown in Fig. 8A. Further, two washers 951 and 953 are interposed between the boss portions 943 and 945 of the two side gears 939 and 941 and the inner wall surfaces of the differential casing 921, respectively. Further, a washer 955 is interposed between two inner end surfaces of the two side gears 939 and 941. In the differential casing 921, a plurality of pairs of accommodation holes 957 and 959 are formed at regular angular intervals in the circumferential direction thereof. Two pinion gears 961 and 963 are slidably and rotatably housed in the two accommodation holes 957 and 959, respectively. The two pinion gears 961 and 963 are of the same shape, but inserted into the two accommodation holes 957 and 959 in the opposite direction with respect to each other. Further, the two side gears 939 and 941 and the two pinion gears 961 and 963 are all of helical gear type. The pinion gears 961 and 963 are composed of first gear porions 965 and 966, second gear portions 967 and 968, and small diameter axle portions 969 and 970 for connecting the first and second gear portions, respectively. The first gear portion 965 of one pinion gear 961 is in mesh with the left side gear 939. Further, the first gear portion 966 of the other pinion gear 963 accommodated in opposite direction is in mesh with the right side gear 941. Further, the two second gear portions 967 and 968 of the two pinion gears 961 and 963 are in mesh with each other on both axially ends of the two pinion gears 961 and 963. Between these mutually gearing portions of both the pinion gears 961 and 963, the pinion gear 961 is in mesh with the left side gear 939, and the pinion gear 963 is in mesh with the right side gear 941. On both end surfaces of the two pinion gears 961 and 963, two center holes are formed as chucking holes when machined by a lathe, for instance. Further, a plurality (two) of radial oil passages 977 are formed in an inner wall surface (the sliding surface of the two pinion gears 961 and 963 and the two side gears 939 and 941) of the cover 933 so as to extend radially outward of the differential casing 921 at such a position as to correspond to the two accommodation holes 957 and 959 for housing the pinion gears 961 and 963, respectively. In the same way, a plurality (two) of radial oil passages 978 are formed in an inner wall surface of the side wall portion 932 of the casing body 931 so as to extend radially outward of the differential casing 921 at such a position as to correspond to the two accommodation holes 957 and 959 for housing the pinion gears 961 and 963, respectively. A radially inward end portion 977a of the radial oil passage 977 communicates with the helical groove 979L. A radially inward end portion 978a of the radial oil passage 978 communicates with the helical oil groove 979R. Each radially outward end portion 977b of the radial oil passage 977 communicates with the center hole 975 formed in the end surface of the pinion gear 961 or 963, and each radially outward end portion 978b of the radial oil passage 978 communicates with the center hole 975 formed in the end surface of the inion gear 961 or 963. Further, in order to securely communicate the helical oil grooves 979L and 979R with the radial oil passages 977 and 978, two radially inward opening ends 977a and 978a of the radial oil passages 977 and 978 are chamfered at the chamfered portions 936 and 937 at which the radial oil passages 977 and 978 open toward the through holes of the boss portions 935 and 934. Therefore, the helical oil grooves 979L and 979R communicate with the radial oil passages 977 and 978 through gaps formed between the chamfered portions 936 and 937 and the washers 951 and 953, respectively. Instead of the chamfered portions 936 and 937, it is also possible to communicate the radial oil passages 977 and 978 with the helical oil grooves 979L and 979R, respectively by forming annular cutouts or stepped portions, respectively. Further, the differential casing 921 is formed with a plurality of openings 980 communicating with the accommodation holes 957 of the pinion gears 961, and a plurality of openings 981 communicating with the accommodation holes 959 of the pinion gears 963. Therefore, when the differential apparatus 900 is rotated, lubricant in a differential carrier (not shown) leaped by a ring gear fixed to the differential casing 921 is exhausted from the differential casing 921 through these openings 979 and 981, respectively. In the differential apparatus 900 of this embodiment, since the radial oil passages 977 and 978 extend to the positions communicating with the centered holes 975 formed in the end surfaces of the pinion gears 961 and 963, respectively, it is possible to supply lubricant introduced into the helical oil grooves 979L and 979R sufficiently to the sliding portions between the end surfaces of the two side gears 939 and 941 and the inner wall surfaces of the differential casing 921, to the gearing portions between the side gears 939 and 941 and the pinon gears 961 and 963, and to the sliding portions between the end surfaces of the pinion gears 961 and 963 and the inner wall surfaces of the differential casing 921, respectively. Therefore, since the various sliding and gearing portions within the differential casing 921 can be lubricated sufficiently, it is possible to prevent seizure, gall (scuffing) or abnormal noise from being produced from the differential apparatus. In particular, since the sliding portions at the end surfaces of the pinion gears 961 and 963 and the side gears 939 and 941 against the inner wall surfaces of the differential casing 921 can be sufficiently lubricated, the differential limiting characteristics can be stabilized. In addition, since the other sliding portions and the mutual gearing portions of the pinion gears 961 and 963 can be sufficiently lubricated, the lubrication effect can be improved. Further, since the differential casing 921 is formed with openings 980 and 981, it is possible to further smoothen the lubricant flow in the same way as with the case of the first embodiment shown in Fig. 8A. Further, as shown in Fig. 10A, when the right radial oil passage 978 is formed with a stepped portion 978c midway from the radially inward end 978a and the radially outward end 978b of the right side radial oil passage 978 and further when the cross-sectional area of the radial oil passage 978 is reduced from the inward end 978a to the outward end 978b, since the moving speed of the lubricant flowing through the radial oil passage 978 due to a centrifugal force of the differential casing 921 can be increased, it is possible to more effectively move the lubricant radially outward to the end surfaces of the pinion gears 961 and 963. Further, without being limited to only the above-mentioned embodiment, it is possible to form the helical oil grooves 979L and 979R in the outer circumferential surfaces of the output shafts and the radial oil passages 977 and 978 in the end surfaces of the boss portions 943 and 945 of the side gears 939 and 941, respectively. The above-mentioned differential apparatus 807 and 900 can be used as a rear wheel side differential gear for distributing engine power to the rear right and left wheels, a front wheel side differential gear for distributing engine power to the front right and left wheels, or as a center differential gear for distributing engine power to the front and rear wheels), respectively. As described above, with the embodiments, the following effects can be obtained: (1) Since the helical oil grooves are formed between the inner circumferential surfaces of the boss portions of the differential casing and the outer circumferential surfaces of the output shafts respectively, and since the radial oil passages are formed between the two side gears and the differential casing, respectively in such a way that the radially inward ends thereof communicate with the ends of the helical oil grooves and further with the sliding portions between the side gears and the inner walls of the differential casing respectively, lubricant introduced from the oil reservoir due to the rotation of the differential casing can be supplied to the sliding portions between the side gears and the differential casing, so that it is possible to prevent seizure at these sliding portions and thereby a stable differential limiting force can be obtained. (2) Since the radially outward ends of the radial oil passages are located at the gearing portions between the pinion gears and the side gears, it is possible to prevent seizure and gall at the sliding portions between the side gears and the differential casing, the gearing portions between the pinion gears and the side gears, and the sliding portions between the pinion gears and the accommodation holes of the differential casing. Further, when the pinion gears and the side gears are being rotated, since lubricant can be supplied to the sliding portions between the side gears and the differential casing due to the pumping action of the pinion and side gears, it is possible to prevent seizure and gall at the sliding portions.

Claims: A differential apparatus (807; 900) comprising: a differential casing (821; 921) disposed in an oil reservoir (808) and rotated by an engine power; a pair of side gears (835, 837; 939, 941) slidable at each end surface thereof directly or via a thrust washer (853, 855, 857; 951, 953, 955), said side gears (835, 837; 939, 941) being formed with boss portions (839, 841; 943, 945) connected to output shafts, respectively; at least one pair of pinion gears (863, 865; 961, 963) disposed on a radially outward side of said side gears (835, 837; 939, 941) and in mesh with each other, each pinion gear (863, 865; 961, 963) being in mesh with said side gear (835, 837; 939, 941) respectively, and slidably and rotatably housed in accommodation holes (859, 861; 957, 959) formed in said differential casing (821; 921), respectively; two helical oil passages (877, 879; 979L, 979R) formed between two outer circumferential surfaces of two output shafts and two inner circumferential surfaces of the two boss portions (849, 851; 935, 934) of said differential casing (821; 921), respectively; characterized by two radial oil passages (881, 885; 977, 978) formed between inner wall surfaces of said differential casing (821; 921) and said side gears (835, 837; 939, 941), respectively; a radially inward end (880, 884; 977a, 978a) of said radial oil passages (881, 885; 977, 978) is communicating with one of said helical oil passages (877, 879; 979L, 979R) and a radially outward end (887, 889; 977b, 978b) of said radial oil passages (881, 885; 977, 978) is communicating with a sliding portion between said side gear (835, 837; 939, 941) and an inner wall surface of said differential casing (821; 921), respectively. A differential apparatus according to claim 1, characterized in that the radially outward ends (887, 889) of said radial oil passages (881, 885) are formed at such positions as to communicate with sliding portions between said side gears and said differential casing and further at such positions as to correspond to gearing portions between said pinion gears and said side gears, respectively. A differential apparatus according to claim 1 or 2, characterized in that the radially outward ends (887, 889; 977b, 978b) of said radial oil passages (881, 885; 977, 978) are formed at such positions as to communicate with sliding portions between said side gears and said differential casing and further at such positions as to correspond to gearing portions between said pinion gears, respectively. A differential apparatus according to at least one of the preceding claims 1 to 3, characterized in that the radially outward ends (889; 977b, 978b) of said radial oil passages (885; 977, 978) are formed at such positions as to communicate with sliding portions between said side gears and said differential casing and further at such positions as to correspond to sliding portions between end surfaces of said pinion gears and an inner wall surface of said differential casing, respectively. A differential apparatus according to at least one of the preceding claims 1 to 4, characterized in that the radially outward ends (887, 889; 977b, 978b) of said radial oil passages (881, 885; 977, 978) are formed at such positions as to communicate with mutual engaging portions between said pinion gears. A differential apparatus according to at least one of the preceding claims 1 to 5, characterized in that said radial oil passages (881, 885; 977, 978) are formed for each mutually gearing pinion gear pair or for each pinion gear. A differential apparatus according to at least one of the preceding claims 1 to 6, characterized in that said helical oil passages (877, 879; 979L, 979R) are formed in inner circumferential surfaces of boss portions (849, 851; 935, 934) of said differential casing or outer circumferential surfaces of two output shafts, respectively; and said radial oil passages are formed in said differential casing or said side gears, respectively so as to extend radially outward. A differential apparatus according to at least one of the preceding claims 1 to 7, characterized in that: said helical oil passages (877, 979; 979L, 979R) are of helical oil groove formed in inner circumferential surfaces of the boss portions (849, 951; 935, 934) of said differential casing (821; 921), respectively in such a way as to be inclined by an inclination angle in a direction that lubricant can be introduced from an outside oil reservoir into said differential casing when said differential casing is rotated; said radial oil passages (881, 885; 977, 978) are formed in said differential casing in such a way that one end thereof communicates with the helical oil passages, respectively and the other ends thereof extend radially outward; and said differential casing is formed with openings (893, 895, 897; 980, 981) communicating between inside and outside of said differential casing at such positions as being further radially outward away from the other ends of said radial oil passages, two oil circulation passages being formed by way of said two helical oil passages, said two radial oil passages, the accommodation holes of said differential casing and the openings, respectively to circulate lubricant by centrifugal force generated by rotation of said differential casing.

Inventors: AIBA SATOSHI, HIRAISHI KENJI, ONO SHUHEI, TERAOKA MASAO, UGAJIN KAZUMITSU, AIBA, SATOSHI, HIRAISHI, KENJI, ONO, SHUHEI, TERAOKA, MASAO, UGAJIN, KAZUMITSU, Aiba, Satoshi, c/oTochigi Fuji Sangyo K.K., Hiraishi, Kenji, c/oTochigi Fuji Sangyo K.K., Ono, Shuhei, c/oTochigi Fuji Sangyo K.K., Teraoka, Masao, c/oTochigi Fuji Sangyo K.K., Ugajin, Kazumitsu, Tochigi Fuji Sangyo K.K.
Applicants: TOCHIGI FUJI SANGYO KK, TOCHIGI FUJI SANGYO KABUSHIKI KAISHA
Application year: 1996
Main classification: F16H48
IPC codes: F16H57, F16H48