Variable Speed Transmission

The present invention relates to a transmission used for vehicles operated from a riding posture, such as three-wheeled or four-wheeled buggies, and more particularly, it relates to a variable speed transmission for controlling a variable speed by utilizing oil pressure.

In a vehicle of a related art such as, for example, a four-wheeled buggy as shown in FIG. 1, an engine 10 is arranged in such a way that a crank shaft (output shaft) of the engine extends vertically. Power generated by the engine 10 is transmitted to a transaxle 16 and a working apparatus such as a lawn mower 18 by the medium of V-shaped belts 12 and 14, respectively. A driving axle arrangement (not shown) for controlling a variable speed by utilizing oil pressure is incorporated into the trans-axle 16, and rear wheels 19 are rotatably mounted on both ends of the trans-axle 16.

However, in a variable speed transmission comprising the trans-axle 16 and the V-shaped belt 12 used in the four-wheeled buggy as shown in FIG. 1, since the V-shaped belt 12 is twisted laterally on its way, there is a problem regarding poor durability of the V-shaped belt 12. Further, in the above variable speed transmission, since the engine 10 and the trans-axle 16 are indirectly connected to each other by means of the V-shaped belt 12, the trans-axle 16 cannot be supported floatingly on a chassis of the buggy, due to the fact that if the trans-axle 16 is supported floatingly on the vehicle chassis the V-shaped belt 12 leads to misalignment. Accordingly, in the above variable speed transmission, a so-called "rigid axle" in which the trans-axle 16 is rigidly fixed to the vehicle chassis is inevitably used. Further, in the above variable speed transmission, since a hydro-static transmission is incorporated into the trans-axle 16 independently from the engine, there is a disadvantage that the temperature of the working oil in the hydro-static transmission is increased remarkably.

Further, in relation to such variable speed transmission, a multiple axis trans-axle has been proposed as described in the Japanese Utility Model Laid-Open No. 87324/1984. However, in the multiple axis trans-axle, since the trans-axle has a plurality of axes, the trans-axle itself is of a large size, thereby requiring a large space for accommodating the trans-axle on the vehicle.

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional variable speed transmission by providing an improved variable speed transmission in which a trans-axle of the transmission can be supported floatingly on a vehicle chassis by constituting the engine and the trans-axle as a unit.

According to the present invention, there is provided a variable speed transmission for transmitting power from an output shaft of an engine mounted on a vehicle to driven shafts arranged transversely of the vehicle, wherein it comprises a housing means fixedly connected to the engine body and encasing the output shaft and the driven shafts; a variable hydraulic pump which can be adjustably controlled to adjust an amount of oil discharged therefrom by an operator from outside and which is connected to the output shaft and encased in the housing means; and a driving axle arrangement constituted by a hydraulic motor for converting oil pressure from the variable hydraulic pump into a driving power, a reduction gear for reducing an output of said hydraulic motor, and a differential gear for transmitting the reduced output from the reduction gear to separated shafts constituting said driven shafts extending transversely of the vehicle, which is connected to said separated shafts and is encased by the housing means.

With the above-mentioned construction, since the variable hydraulic motor and the driving axle arrangement are accommodated into the housing means as a unit, there is no need for using a V-shaped belt for transmitting the engine power, and even when the driving axle is floatingly supported on the vehicle, there occurs no problem.

FIG. 1 is a perspective view of a four-wheeled buggy incorporating a variable speed transmission of a conventional design;

FIG. 2 is a perspective view of a four-wheeled buggy incorporating the variable speed transmission according to the present invention;

FIG. 3 is a partial broken view of an engine and a trans-axle mounted on the buggy, looked at from a direction of an arrow III of FIG. 2;

FIG. 4 is a fragmental sectional view showing the relationship between a variable hydraulic pump and a crescent hydraulic motor of the transmission; and

FIG. 5 is a sectional view taken along the line V--V of FIG. 3.

The present invention will now be explained with reference to the drawings. In a preferred embodiment shown in FIGS. 2-4, the variable speed transmission according to the present invention is adopted to a four-wheeled buggy. However, it should be noted that the present invention is not limited to the four-wheeled buggy, but can be adopted to any vehicles. In FIG. 2, an engine 20 is mounted on the four-wheeled buggy in such a way that a crank shaft or output shaft (not shown in FIG. 2) of the engine extends vertically. A trans-axle 22 is integrally connected to the engine 20. Power generated by the engine is transmitted to rear wheels 24 through the trans-axle 22. Further, the power from the engine is also transmitted to a working apparatus such as a lawn mower 17 by the medium of a V-shaped belt 13.

More particularly, as shown in FIG. 3 which is a partial broken view of the engine 20 and the trans-axle 22 looked at from a direction of an arrow III of FIG. 2, a piston 29 is connected to the crank shaft 26 of the engine 20 by means of a connecting rod 27. A variable hydraulic pump 30 is arranged around an output shaft portion 28 of the crank shaft 26, the pump 30 being surrounded by a pump cover 34 which forms a part of a housing 32, as will be fully described hereinbelow. Further, the output shaft portion 28 of the crank shaft 26 is provided at its lower end with a pulley 35 around which the V-shaped belt 13 is entrained; thus, the power generated by the engine 20 can be transmitted to the lawn mower 17 (FIG. 2) through the medium of the output shaft portion 28, pulley 35 and the V-shaped belt 13.

The housing 32 comprises the above-mentioned pump cover 34, a lower casing 36 and an axle housing 38 which are integrally connected to each other. More particularly, the lower casing 36 is connected or fixed to a bottom surface of a crankcase 20a of the engine 20 by means of bolts (not shown), the pump cover 34 is connected or fixed to the lower casing 36 by means of a plurality of bolts 34a, and the axle housing 38 is connected or fixed to side surfaces of the crankcase 20a and the lower casing 36 by means of a plurality of bolts 38a.

A crescent hydraulic motor 40 is housed to the axle housing 38. This hydraulic motor 40 forms a part of a driving axle arrangement which will be fully described hereinbelow, and imparts rotational movement to each of separated axles or shafts 41. On outer ends of the separated shaft 41, the corresponding rear wheel tires 24 having a large diameter, low pressure and good cushioning ability are mounted. Further, the crescent hydraulic motor 40 communicates with the variable hydraulic pump 30 through the medium of working oil passages 42 and 44 which are formed in walls of the lower casing 36 and the axle housing 38. Inner pipes 43 are arranged in the passages 42 and 44 at a junction between the lower casing 36 and the axle housing 38.

A hydro-static transmission (referred to as HST hereinafter) as described above is constituted by the variable hydraulic pump 30, the crescent hydraulic motor 40 and the like. FIG. 4 shows the construction of such HST.

In FIG. 4, the variable hydraulic pump 30 is constituted by a cylinder block 46, a plurality of ball pistons 47, and a cam ring 48 surrounding the ball pistons. The ball pistons 47 are slidably arranged in corresponding oil chambers 46a which are formed along the periphery of the cylinder block at equidistant intervals and which extend radially and outwardly of the cylinder block opening to the outside. The cam ring 48 which surrounds the ball pistons 47 is rockably supported on a pin 47a fixed to the pump cover 34 and lower casing 36 (FIG. 3). The ball pistons 47 are slidably engaged by a cam surface 48a of the cam ring 48. When the cylinder block 46 is rotated by the output shaft portion 28 of the crank shaft 26, which is fixed to a central opening of the cylinder block 46 by an appropriate means such as a press fit, the ball pistons 47 are reciprocated in the corresponding oil chambers 46a in such a way that oil introduced into each oil chamber 46a from an inlet conduit 30a is discharged from the chamber through an outlet conduit 30b. To this end, the inlet conduit 30a is communicated with the oil chambers 46a by means of an arcuate passage 46b and ports 46c, and the outlet conduit 30b is communicated with the oil chambers 46a by means of an arcuate passage 46d and ports 46e.

An adjustment rod 49 for adjusting the amount of oil discharged from the oil chambers 46a is fixedly mounted in a recess 48b formed in a right-hand end (FIG. 4) of the cam ring 48. By shifting the adjustment rod 49 in a direction as shown by an arrow A, the cam ring 48 is rocked or rotated around the pin 47a, thereby adjusting the degree of reciprocal movement of each ball piston 47, and accordingly, the amount of oil discharged from the variable hydraulic pump 30.

The outlet conduit 30b is connected to the working oil passage 44 (FIG. 3), and the inlet conduit 30a is connected to the working oil passage 42. Therefore, the pressurized oil discharged from the variable hydraulic pump 30 is supplied to the crescent hydraulic motor 40 through the outlet conduit 30b and the working oil passage 44 and is returned to the variable hydraulic pump 30 through the working oil passage 42 and the inlet conduit 30a. Accordingly, the oil circulation system includes the pump 30, the outlet conduit 30b, the working oil passage 44, the motor 40, the working oil passage 42 and the inlet conduit 30a. A suction conduit 51 for sucking oil from an oil tank 50 of the engine 20 is connected to the working oil passages 44 and 42 through the medium of check valves 44a and 42a, respectively.

The crescent hydraulic motor 40 includes an inner ring gear 52 fixed to one of the separated shafts 41 (FIG. 3), an outer ring gear 53 having an inner gearing 53a meshed with an outer gearing 52a of the inner gear 52, and an arcuate partition member 54 for dividing an oil chamber between the inner gearing 53a and the outer gearing 52a into two separate compartments. The inner ring gear 52 and the outer ring gear 53 are rotated in a direction shown by an arrow B by means of the pressurized oil supplied from the working oil passage 44 in a conventional manner. The crescent hydraulic motor 40 itself can be reversed by changing the direction of flow of the oil in the working oil passages 44 and 42, thereby permitting a rearward drive.

Next, the driving axle arrangement provided around the separated shafts 41 will be explained with reference to FIG. 5 which is a sectional view taken along the line V--V of FIG. 3. In FIG. 5, around the left-hand side separated shaft 41, the crescent hydraulic motor 40, a planetary reduction gear 55, a differential gear 56, a brake 57 and the like are arranged, these elements being encased by the axle housing 38.

The partition member 54 of the crescent hydraulic motor 40 is fixed to a side cover 58 forming a part of the axle housing 38 by means of bolts 54a. Further, the partition member 54 is integral with a motor housing 59 connected to the axle housing 38. The inner ring gear 52 of the crescent hydraulic motor 40 is connected, by a spline connection, to a tubular output shaft 60 arranged around and spaced apart from the separated shaft 41. On the right-hand end (FIG. 5) of the tubular output shaft 60, there is provided a sun gear 61 by which a planetary gear 62 of the planetary reduction gear 55 is engaged. The planetary gear 62 is also engaged, at its outer portion, by a ring gear 63 fixed to the axle housing 38 and is supported by a carrier 64 connected to a tubular shaft 65 by a spline connection.

A sun gear 66 is formed on the right-hand end of the tubular shaft 65, which sun gear 66 is engaged by a planetary gear 67. The planetary gear 67 is also engaged, at its outer portion, by a ring gear 68 fixed to the axle housing 38 and is supported by a carrier 69. The carrier 69 is in slidable contact with the carrier 64, between which a lubricant oil passage 69a is formed.

The carrier 69 is integral with a differential case 70 into which a center pin 71, differential pinions 72 mounted on the center pin, and differential side-gears 73 meshed with the differential pinions are accommodated. The left-hand and right-hand side-gears 73 are connected to the corresponding separated shafts 41 by spline connections, respectively.

With the above-mentioned construction, a driving power generated by the crescent hydraulic motor 40 can be decreased or decelerated by the planetary reduction gear 55 and then be transmitted to the separated shafts 41 (on which the rear wheels 24 are mounted) by means of the differential gear 56.

A brake disc 74 is arranged around the left-hand end portion of the tubular output shaft 60 and is connected thereto by means of a spline connection. A brake pad 75 is positioned to face the right side surface of the brake disc 74. On the left side of the brake disc 74, there is provided a push rod 77 having a brake pad 76 in such a way that the brake pad 76 faces the left side surface of the brake disc. When the push rod 77 is urged in a direction shown by an arrow C, a braking force is generated to stop the rotational movement of the separated shafts 41.

The separated shafts 41 are rotatably mounted at their outer ends on the axle housing 38 through the medium of bearings 78. Annular elastic (rubber) insulators 80 (only one of them is shown in FIG. 5) are positioned in corresponding annular grooves 79 formed in the axle housing 38. Further, the insulators 80 are supported by side frames 81 which form a part of the vehicle chassis. Therefore, the axle housing can be floatingly supported on the side frames 81 by elasticity of the elastic insulators 80.

Next, the function of the variable speed transmission according to the present invention will now be explained. With the above-mentioned construction, as shown in FIG. 3, since the axle housing 38 rotatably supporting the separated shafts 41 is fixedly connected to the lower casing 36 and to the crankcase 20a, and since the pump cover 34 encasing the variable hydraulic pump 30 is also fixedly connected to the lower casing 36, even when the axle housing 38 is floatingly supported by the elastic insulators 80 (FIG. 5) on the vehicle chassis, the engine 20 and the variable hydraulic pump 30 can be moved together with the axle housing 38 in a body.

Therefore, according to the present invention, there is no need for providing the V-shaped belt 12 for transmitting the power from the engine 10 to the trans-axle 16 as in the case of the transmission shown in FIG. 1; on the contrary, in the present invention, the power generated by the engine 20 is converted into the hydraulic pressure by means of the variable hydraulic pump 30, and said hydraulic pressure is transmitted, through the working oil passages 42, 44, to the crescent hydraulic motor 40 (FIG. 4) and is converted into the driving power by said crescent hydraulic motor 40. The driving power from the crescent hydraulic motor 40 is decreased or decelerated by the planetary reduction gear 55 and then transmitted to the separated shafts 41 through the medium of the differential gear 56.

The driving axle arrangement constituted by the crescent hydraulic motor 40, the planetary reduction gear 55, the differential gear 56, the brake 57 and the like is accommodated in the axle housing as a unit, thus making the axle housing 38 compact.

Further, as shown in FIG. 4, since the working oil circulating between the variable hydraulic pump 30 and the crescent hydraulic motor 40 is a part of a lubricating oil accumulated or reserved in the oil tank 50, friction heat generated by the crescent hydraulic motor 40 is cooled in the oil tank 50 having an excellent radiating ability, thus preventing the overheating of the working oil for the variable hydraulic pump 30 and the crescent hydraulic motor 40.

The viscosity of the working oil used with the variable hydraulic pump 30 and the crescent hydraulic motor 40 is required to be higher than that of the lubricating oil for the engine 20. Preferably, in the variable speed transmission according to the present invention, the so-called "multi-grade oil" having a wide range viscosity is used as the lubricating oil for the engine 20, and this lubricating oil is also used as the working oil for the variable hydraulic pump 30 and the crescent hydraulic motor 40.

It should be noted that the present invention is not limited to the embodiment illustrated above. For example, in place of the embodiment of FIG. 3 wherein the axle housing 38 is fixedly connected to the lower casing 36 and the crankcase 20a by mean of the bolts 38a, the axle housing 38 can be separated from the lower casing 36 by connecting them by means of any flexible hydraulic hose (not shown) thus providing the working oil passages (44, 42). In this case, the mass of the axle housing 38 is supported by the elastic insulators 80 (FIG. 5), and accordingly, the total mass supported by a spring force is decreased, and the vibration of the engine is not transmitted to the axle housing.

In conclusion, according to the variable speed transmission of the present invention, there are provided a housing 32 integrally connected to the engine body and encasing the output shaft portion 28 (driving shaft) of the crank shaft and the separated shafts 41 (driven shafts); a variable hydraulic pump 30, which can be adjustably controlled to adjust an amount of oil discharged therefrom by an operation from outside, connected to the output shaft portion 28 and encased by the pump cover 34 which is a part of the housing 32; the driving axle arrangement, which is constituted by the crescent hydraulic motor 40 for converting the oil pressure from the variable hydraulic pump 30 into the driving power, the planetary reduction gear 55 for decreasing or reducing the output of the hydraulic motor 40, and the differential gear 56 for transmitting the reduced driving power from the reduction gear 55 to the separated shafts 41 extending transversely of the vehicle, connected to said separated shafts and encased by the axle housing 38 which is also a part of the housing 32; and the working oil passages 42, 44 for communicating the variable hydraulic pump 30 with the crescent hydraulic motor 40, which are formed in the wall of the lower casing 36 which is also a part of the the housing 32.

With the construction as mentioned above, since the axle housing 38 is fixedly connected to the lower casing 36 and to the crankcase 20a and since the pump cover 34 encasing the variable hydraulic pump 30 is also fixedly connected to the lower casing 36, even when the axle housing 38 is floatingly supported by the elastic insulators (FIG. 5), the engine 20 and the variable hydraulic pump 30 can be moved together with the axle housing 38 in a body.

Accordingly, in the present invention, there is no need for providing the V-shaped belt 12 for transmitting the power from the engine 10 to the trans-axle 16 as in the case of the transmission shown in FIG. 1; on the contrary, according to the present invention, the power from the engine 20 can be converted into the hydraulic pressure by the variable hydraulic pump 30, said hydraulic pressure can be transmitted, through the working oil passages 42 and 44, to the crescent hydraulic motor 40 (FIG. 5) wherein the hydraulic pressure can be converted into the driving power or driving force. The driving power from the crescent hydraulic motor 40 can be decreased or reduced by the planetary reduction gear 55 and then be transmitted to the separated shafts 41 through the differential gear 56.

Further, since the driving axle arrangement constituted by the hydraulic motor 40, the planetary reduction gear 55, the differential gear 56, the brake 57 and the like is accommodated into the axle housing 38 as a unit, the axle housing 38 itself can be compact, and the driving axle arrangement can easily be mounted on a small-sized vehicle such as the four-wheeled buggy shown in FIG. 2.