AXLE DRIVING APPARATUS

Abstract: A housing cannot be made compact by only securing a space corresponding to a reserver tank at the upper part of the housing, and the space at the upper part of the housing cannot be utilized if the reserver tank is integrally provided to the upper part of the housing. An axle driving apparatus comprising a tubular reserver tank (10) erected on the upper surface of the upper wall surface of the housing for accommodating an HST, wherein, since the reserver tank (10) is thinly elongated and is freely bendable, it can be disposed in a limited space, the housing is divided into a first room (R1) and a second room (R2) with which the reserver (10) communicates, further, a magnet (71) is disposed at a position where the first and second rooms (R1), (R2) are connected, and a magnet (63) is disposed in the proximity of an oil filter connected to a closed circuit of the HST so that impurities can be removed.

Description: Field of the invention The present invention relates to an axle driving system according to the preamble portion of claim 1, in which a hydrostatic transmission (hereafter referred to as HST), an axle, and a drive train for connecting the HST and the axle for driving are housed in a common housing. BACKGROUND TECHNIQUE Conventionally, a housing that houses an HST is filled with hydraulic oil that is also used as lubricating oil. A temperature of the hydraulic oil is increased by driving the HST. The increase in temperature of the hydraulic oil results in an increase in its volume. In order to receive the increase in the volume, a technique of providing a reservoir tank on an outside of the housing or forming space having a volume corresponding to the increase within the housing to form a reservoir room is known. For example, there is a technique disclosed in U.S. Patent No. 4,987,796 or U.S. Patent No. 5,440,951. However, an axle driving apparatus that utilizes a reservoir tank structure requires additional space, a mounting member for mounting the reservoir tank and piping for connecting the reservoir tank and the housing. In addition, the number of man-hours required for assembly increases, the reservoir tank is difficult to handle, and cost increases. By positioning the reservoir tank at an upper portion of the housing, a vertical length of the housing increases to inhibit miniaturization of the axle driving system and an air layer is created in the housing to cause air to be swallowed in oil when the oil within the housing is stirred. If this oil is charged into a closed circuit of the HST as the hydraulic oil, volumetric efficiency of the HST is reduced, which may generate noise or reduce durability. Further, it is difficult to integrally form the reservoir tank at the upper portion of the housing for a lawn tractor having a rear discharge method because a chute passes above the axle driving system. WO 98 40237 A discloses an axle driving system with the features of the preamble portion of claim 1. In this system an oil flow-through port is mounted on a top wall surface of an upper half housing so that a chamber within the housing and an external remote and separate oil reservoir tank fluidly communicate with each other through a piping made of a rubber hose or the like so as to enable operating oil in the oil sump of the housing to be maintained at a predetermined amount. JP 03159822 A discloses another axle driving system in which an external cup-like reservoir tank is directly mounted on top of the upper surface of the housing. SUMMARY OF THE INVENTION It is the object of the present invention to provide an axle driving system which is further improved with respect to the positioning of the reservoir tank. This object is solved by providing an axle driving system as defined in claim 1. Preferred embodiments are defined in the dependent claims and outlined further below. According to the present invention, a resilient tubular reservoir tank is mounted to stand on an upper face of an upper wall face of a housing that houses an HST including a hydraulic pump and a hydraulic motor. The reservoir tank communicates with an oil reservoir within the housing. Therefore, it is possible to easily mount the reservoir tank by a simple structure, to form the reservoir tank from low-priced members, and to reduce cost. The reservoir tank is formed of a resilient tubular member. Therefore, if there is a member such as a chute that is related to the vehicle main machine above the housing, it is possible to mount the reservoir tank by bending the reservoir tank. Therefore, it is possible to easily mount the reservoir tank by causing the reservoir tank to make way for the member that interferes with the reservoir tank, thereby increasing the number of applications in which the axle driving system may be used. The housing is partitioned into a first room housing the HST and a second room housing an axle and a gear train for transmitting power from the hydraulic motor to the axle. The first and second rooms communicate with each other such that the oil with which both the rooms are filled can circulate between both the rooms The reservoir tank is disposed on the second room. Therefore, it is possible to position a mounting portion of the reservoir tank in a high position, thereby easily purging air generated within the reservoir tank. Because the reservoir tank may be disposed in a position isolated from the pump shaft, it is possible to easily prevent the reservoir tank from interfering with a rotary member such as an input pulley or a cooling fan. A communicating position connecting the first room and the second room allows oil to pass therebetween. A filter member for removing impurities included in oil is disposed in the communicating position. Therefore, it is possible to remove impurities included in the oil when the oil circulates between the first room and the second room due to the variation in volume of the respective rooms which occurs with a change in oil temperature or stirring by actuation of the HST or rotation of a gear. The impurities can be removed by means of the filter member disposed in an oil hole for hydraulic oil of the HST, the oil within the first room can be cleaned, and durability of the HST can be further improved. Because the filter member is formed of a magnet, the filter member can be formed at low cost and can be miniaturized. Therefore, limitations to a place where the filter member is disposed can be reduced, durability of the filter member is high, and the filter member can be cleaned easily. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a general side view of a lawn tractor to which an axle driving system of the present invention is mounted, FIG. 2 is a sectional view taken in a direction of an arrow A-A in FIG. 1, FIG. 3 is a back perspective view of an axle driving system, FIG. 4 is a sectional view taken in a direction of an arrow B-B in FIG. 2, FIG. 5 is a sectional view taken in a direction of an arrow C-C in FIG. 4. FIG. 6 is a sectional view taken in a direction of an arrow D-D in FIG. 4, FIG. 7 is a sectional view taken in a direction of an arrow E-E in FIG. 4. FIG. 8 is a sectional view taken in a direction of an arrow F-F in FIG. 4, FIG. 9 is a sectional view showing another embodiment in which a magnet is disposed in the vicinity of an oil filter, and FIG. 10 is a perspective view of a mounting seat. PREFERRED EMBODIMENT OF THE INVENTION In FIGS. 1, 2, and 3, a lawn tractor of a rear discharge method has a vertical crankshaft-type engine 100 disposed on a front portion of a bodywork frame 101. Steerable left and right (front) follower wheels 102, 102 are suspended from the front portion of the bodywork frame 101, an axle driving system 6 having left and right (rear) driving wheels 103, 103 is suspended from a rear portion, a grass box 104 is mounted to a rear end by a working machine mounting device (not shown) such that the grass box 104 can be hoisted and lowered, and a mower 105 is mounted to a lower portion of the bodywork between the follower wheels 102, 102 and the driving wheels 103, 103 through a hoisting and lowering mechanism (not shown). A discharge opening of the mower 105 and ah entrance of the grass box 104 are connected through a chute 106. The chute 106 extends diagonally upward and rearward from an upper portion of the mower 105, passes above the axle driving system and between the left and right driving wheels 103, 103, and connects to the entrance of the grass box 104. Therefore, grass mowed by the mower 105 is blown rearward, passes through the chute 106 and between the left and right driving wheels 103, 103, and is housed in the grass box 104. As shown in FIG. 1, two pulleys 108 and 109 are fixed onto a vertical output shaft 107 of the engine 100. The pulley 108 has an electromagnetic clutch and transmits power through a belt 110 to an input pulley 112 fixed onto an input shaft 111 of the mower 105 to drive the mower 105, thereby rotating a cutting blade 115 of the mower 105. As shown in Fig. 3, five tension pulleys 114, pivoted on the bodywork frame 101, allow a belt 113 to navigate around the chute 106. The belt 113 is attached to the other pulley 109 and an input pulley 43, which is fixed onto a pump shaft 3. Pump shaft 3 is an input shaft projecting upward from the housing of the axle driving system 6. A reference numeral 44 designates a cooling fan for cooling the axle driving system and fixed to a lower face of the input pulley 43 on the pump shaft 3. As shown in FIG. 2, the axle driving system 6 is hung on left and right mount members 101a, 101a which are parts of the bodywork frame 101. Left and right axles 7L and 7R project from side faces of the housing of the axle driving system 6 and the driving wheels 103, 103 are mounted to end portions of the axles 7L and 7R. Next, in FIGS. 4 to 8, a general structure of the axle driving system 6 will be described. The housing of the axle driving system 6 is formed of two housing members, i.e., an upper housing 1 and a lower housing 2, which are joined to each other at their flat and peripheral joint faces in a horizontal plane. At the joint face of the housing, bearing portions of a motor shaft 4 and a counter shaft 26 are provided. The axles 7L and 7R are disposed in parallel with the joint face of the housing. The bearing portions of the axles 7L and 7R are displaced upward from the joint face and disposed within the upper housing 1 to rotatably support the axles 7L and 7R. The respective axles 7L and 7R are connected in a differential manner by a differential gear 23 and opposite ends of the axles 7L and 7R project outward from left and right outer walls of the housing. An inside of the housing is partitioned by an inner wall 8 into a first room R1 for housing the HST and a second room R2 for housing a drive train. The drive train is formed of a plurality of gears for transmitting power from the motor shaft 4 to the differential gear 23 and the differential gear 23 and the axles 7L and 7R. The inner wall 8 is formed of a portion extending along and in parallel with a longitudinal direction of the axles 7L and 7R and a portion extending in a direction perpendicular to the longitudinal direction. These portions are formed seamlessly and the first room R1 is adjacent to the second room R2. The inner wall 8 is formed of a wall portion hanging from an inside of the upper housing 1 toward the joint face and a wall portion standing from an inner wall of the lower housing 2 toward the joint face. End faces of the upper and lower wall portions are placed on each other at the joint face, thereby partitioning the inside of the housing into two independent rooms. The first room R1 is disposed at the rear of the axles 7L and 7R and on the left of a power transmission device for transmitting power from the motor shaft 4 to the differential gear 23 in the housing as shown in Fig. 4. In the first room R1, a center section 5 constituting the HST is detachably mounted to the inside of the upper housing 1. The center section 5 is disposed such that a longitudinal direction of the center section 5 is in a longitudinal direction of the bodywork and is substantially perpendicular to the axles 7L and 7R. A vertical face is formed at a rear portion of the center section 5, a motor attachment face 41 is formed on the vertical face, and a hydraulic motor 51 is disposed on the motor attachment face 41. A horizontal face is formed at a front portion of the center section 5, a pump attachment face 40 is formed on the horizontal face, and a hydraulic pump 50 is disposed on the pump attachment face 40. Therefore, the hydraulic pump 50 is disposed between the hydraulic motor 51 and the axles 7L and 7R when viewed in the longitudinal direction of the bodywork. The pump shaft 3 is vertically supported at a center of the pump attachment face 40. The pump shaft 3 extends between the hydraulic motor 51 and the axles 7L and 7R, passes through an upper wall of the upper housing 1, and projects wherein the input pulley 43 is mounted thereon. In a thick-walled portion of the center section 5, a straight first oil path 5a and a straight second oil path 5b are formed in parallel with each other in upper and lower positions for respectively connecting arcuate ports on the pump attachment face 40 and arcuate ports 41a and 41b on the motor attachment face 41 are formed in parallel with each other in upper and lower positions. One of the arcuate ports on the pump attachment face 40 communicates with the oil path 5d formed in a diagonal direction shown in FTG. 7 and the oil path 5d communicates with the second oil path 5b. These oil paths constitute a closed circuit for circulating the hydraulic oil between the hydraulic pump 50 and the hydraulic motor 51. An annular oil filter 56 is disposed between a lower face of the center section 5 and an inner bottom face of the lower housing 2 such that a periphery of an opening portion at a lower end of the oil hole 5c is covered with the oil filter 56. The oil filter 56 is formed by sandwiching a ring-shaped porous member that is a filter main body between upper and lower cover plates 57 and 58 and disposing a cylindrical support cylinder 59 such as net or punching metal at an inner peripheral face portion of the porous member as shown in FIGS. 5 and 7. Because an opening 57a is formed at a center portion of the upper cover plate 57, filtered oil that has flowed from an outer peripheral portion of the oil filter 56 into an inside of the oil filter 56 can flow into the oil hole 5c of the center section 5 through the opening 57a. The cover plates 57 and 58 are formed of a steel sheet such as an iron sheet and a nickel sheet which can be magnetized and a magnet 63 is placed on an upper face of an inner face of the lower cover plate 58 to magnetize the lower cover plate 58. In this manner, iron powder included in the reservoir of the first room R1 is collected by the lower cover plate 58 and even extremely fine iron powder that has passed through the oil filter 56 is collected by the magnet 63 or the lower cover plate 58 and is not introduced into the closed circuit, thereby preventing damaging of the sliding face and the like. A position where the magnet 63 is disposed is not limited to the upper face of the lower cover plate 58 and the magnet 63 may be also disposed on a lower face of the lower cover plate 58 or at the upper cover plate 57. If the magnet 63 is disposed at the upper cover plate 57, it is necessary to provide a bridge, a mount, or the like such that the magnet 63 can be hung within the oil filter 56. If the magnet 63 is provided to the lower face of the lower cover plate 58, as shown in FIG. 9, a depression or a recessed portion 2a is formed at the lower housing 2 at a lower portion where the oil filter 56 is positioned to form a space where dust and the like accumulate. Three or more projections 2b, 2b, are formed on an inner face of the lower housing 2 in peripheral positions of the space where the oil filter 56 is positioned and the lower face of the lower cover plate 58 is placed on the projections 2b, 2b, thereby supporting the oil filter 56. Thus, a passage is formed by the projections 2b, 2b, between the lower cover plate 58 and the bottom face of the lower housing 2 and between the projections 2b, 2b, , dust and the like pass through the passage and accumulate in the recessed portion 2a that is less subject to flow of oil when the oil is stirred, and the iron powder is collected by the magnet 63. By the projections 2a, 2a, , the lower cover plate 58 is disposed in a higher position, thereby forming a space where the magnet 63 is disposed. Furthermore, if there is extremely fine iron powder that has passed through the oil filter 56, the iron powder is collected by an upper face of the lower cover plate 58 because the lower cover plate 58 is magnetized by the magnet 63. The motor shaft 4 is locked onto a rotation axial center of the cylinder block 17 such that the motor shaft 4 cannot rotate with respect to the cylinder block 17. The hydraulic motor shaft 4 is oriented in a substantially horizontal direction. One end of the motor shaft 4 is supported in a bearing hole in the motor attachment face 41 of the center section 5, the other side of the motor shaft 4 is supported through a bearing 76 on the inner wall 8 formed at the joint face between the upper housing 1 and the lower housing 2, and a tip end projects into the second room R2. A bearing with a seal is used as the bearing 76 so as to separate the first room R1 and the second room R2. The drive train for transmitting power from the motor shaft 4 to the differential gear system 23 is formed of a gear 25 secured onto the motor shaft 4 projecting into the second room R2, a large-diameter gear 24 that constantly meshes with the gear 25 and is supported on the counter shaft 26, a small-diameter gear 21 supported on the counter shaft 26 rotating with the large-diameter gear 24, and a ring gear 22 of the differential gear 23 with which the small-diameter gear 21 constantly meshes as shown in FIGS. 4 and 6. The counter shaft 26 is disposed within the second room R2 to be in adjacent to and orthogonal to the pump shaft 3. The first room R1 and the second room R2 are filled with common lubricating oil to form the oil reservoir. As shown in FIGS. 4 to 8, a communicating room 9 is formed at an upper portion of the inner wall 8 that partitions the inside of the housing into the first room R1 and the second room R2. An oil inlet 9a communicating with the first room R1 and an oil inlet 9b communicating with the second room R2 open into a side face and a bottom of the communicating room 9. An opening portion 1c to which a filter member that will be described below is mounted is formed at the upper housing above the oil inlets, and the opening portion 1c is closed by a lid 65. A mounting seat 66 formed by press forming an iron sheet into a cup shape is placed on a bottom face of the communicating room 9 and a magnet 71 as a filter member for removing impurities is placed and fixed onto the mounting seat 66. The magnet 71 is formed into a disc shape, and as shown in FIG. 10, an elongated hole 66a is formed on an upper face of the mounting seat 66. By inserting the magnet 71 into the elongated hole 66a and bringing tongue chips 66b extending from opposite sides of the elongated hole 66a to face each other into resilient contact with opposite faces of the magnet 71, the magnet 71 and the mounting seat 66 are integrated with each other. The integrated magnet 71 and mounting seat 66 are inserted into the communicating room 9 that opens at an upper wall of the upper housing 1 and the opening is closed by the lid 65, thereby achieving completion. A reference numeral 66c in FIG. 10 designates notches each formed by partially notching a lower end face of the mounting seat 66. A width of the notch 66c is equal to a thickness of a portion of the inner wall 8 positioned at the bottom face of the communicating room 9. By inserting the portions of the inner wall 8 into the notches 66c when the mounting seat 66 is placed on the bottom face of the communicating room 9, rotation of the magnet 71 within the communicating room can be prevented. The magnet 71 is fixed such that the magnet 71 is oriented to be diagonal with respect to the oil inlets 9a and 9b so as to increase a contact area in flowing of the oil. However, the magnet 71 may have a rectangular shape and a shape of the magnet 71 is not limited. With the above structure, iron powder generated in the first room R1 and the second room R2 when the oil within the housing circulates between the first room R1 and the second room R2 is attracted by the magnet 71 and adheres to the magnet 71 and the mounting seat 66 to maintain the oil that has accumulated in the first room R1 in a clean state, thereby improving durability of the HST. As shown in FIGS. 2 and 6, an oil circulating hole 1a opens at the upper wallface of the upper housing 1 forming the second room R2 in a position where the hole does not interfere with the input pulley 43 and the cooling fan 44. A joint pipe portion 1b is formed on a periphery of the oil circulating hole 1a. A tubular reservoir tank 10 formed of a rubber hose or a resilient member is fitted with the joint pipe portion 1b such that the reservoir tank 10 communicates with the second room R2 in a fluidic manner. A lower portion of the reservoir tank 10 is fastened and fixed by the joint pipe portion 1b and bands 69a. An opening at an upper end of the reservoir tank 10 is closed by a breather cap 70 and fastened and fixed by bands 69b. If the first and second rooms R1 and R2 are filled with oil after .assembling the axle driving system, an oil level 0L is determined within both the rooms R1 and R2 as shown in FIGS. 5 to 8. The oil level OL is uniform because both the rooms R1 and R2 communicate with each other through the communicating room 9. If a volume of the oil within the first room R1 varies depending on whether the HST is driven, the oil level OL shifts upward or downward from the position shown in the drawings. An air layer with a variable volume is formed above the oil level OL within the reservoir tank 10 that opens into the atmosphere through the breather cap 70. The air layer allows variation in the volume of the oil that is allowed due to presence of the air layer. Thus, the hydraulic oil expands and the volume of the hydraulic oil increases when a temperature of the hydraulic oil within the oil reservoir increases due to driving of the HST. The volume can be adjusted by causing the increase in the volume to flow into the reservoir lank 10 and a vertical length of the tube portion of the reservoir tank 10 is set at such a value as to keep at least a volume corresponding to an oil amount by which the volume of the housing increases. The reservoir tank 10 can be easily mounted by only inserting the reservoir tank 10 into the joint pipe portion 1b on the outer wall of the housing and fastening the reservoir tank 10 by the band 69a. As shown in FIG. 2, if the chute 106 and the like exist above the housing, the reservoir tank 10 can be bent naturally to make way for the chute 106 and the like because of resiliency of the reservoir tank 10 itself. Therefore, it is possible to reduce limitations on disposition of the reservoir tank 10. Industrial Applicability As described above, the axle driving system according to the invention is a system suitable for driving an axle of a field-work vehicle, a vehicle of construction equipment, a mowing vehicle, a snow removal vehicle, or the like and especially suitable to a lawn tractor of a rear discharge method having a chute above the housing.

Claims: An axle driving system wherein a reservoir tank (10) is connected to an upper face of an upper wall face of a housing (1,2) that houses a hydrostatic transmission (HST) including a hydraulic pump (50) and a hydraulic motor (51) and said reservoir tank (10) communicates with an oil reservoir within said housing (1,2), characterized in that said reservoir tank (10) is tubular and is resilient and is mounted so as to stand on the upper face of the upper wall of the housing (1,2). An axle driving system according to claim 1, wherein said housing (1,2) is partitioned into a first room (R1) housing said HST and a second room (R2) housing an axle (7L,7R) and a gear train for transmitting power from said hydraulic motor (51) to said axle (7L,7R), both said rooms (R1,R2) communicate with each other such that oil with which both said rooms (R1,R2) are filled can circulate between said rooms (R1,R2), and said reservoir tank (10) is disposed on said second room (R2). An axle driving system according to claim 2, wherein a filter member (71) for removing impurities included in oil passing through a communicating position (9) connecting said first room (R1) and said second room (R2) is disposed in said communicating position (9). An axle driving system according to claim 3, wherein said filter member is formed of a magnet (71). An axle driving system according to any one of claims 1 to 4, wherein said tubular reservoir tank (10) is provided with a breather cap (70). An axle driving system according to any one of claims 1 to 5, wherein the vertical length of said tubular reservoir tank (10) is set at such a value as to keep at least a volume corresponding to an oil amount by which the volume of the oil within the housing (1,2) increases during operation.

Inventors: IIDA MASARU, SHIMIZU HIROAKI, IIDA, MASARU, SHIMIZU, HIROAKI, IIDA, Masaru Kanzaki Kokyukoki MFG. Co., Ltd., SHIMIZU, Hiroaki Kanzaki Kokyukoki MFG. Co., Ltd.
Applicants: KANZAKI KOKYUKOKI MFG CO LTD, KANZAKI KOKYUKOKI MFG. CO., LTD.
Application year: 1998
Main classification: F16H57
IPC codes: B60K17, F16H48