GB2105815A - Planetary reduction gearing provided with a torque limiter - Google Patents

Abstract

A machine such as an agricultural cultivator is provided with planetary reduction gearing (8) in the transmission between the engine crank shaft (10) and cultivator rotors (6). In order to prevent damage to the transmission due to sudden or shock overloads applied to the rotors, the gearing (8) incorporates a torque limiter. During normal drive of the rotors (6), the ring gear (11) of the gearing (8) is locked against rotation by a lock-release mechanism (23) including spring- pressed balls (13) engaged in recesses (12) in the ring gear (11). When the rotors, and therefore the ring gear (11), are subjected to excessive rotational forces, the increased turning moment exerted by the ring gear forces the balls (13) out of the recesses (12), and the ring gear rotates until the overload is removed. <IMAGE>

Description

SPECIFICATION Planetary reduction gearing provided with a torque limiter The present invention relates to planetary reduction gearing provided with a torque limiter.

In a small-size agricultural machine of the walking type, a planetary reduction gearing is connected directly to an engine crank shaft, thereby to greatly reduce the speed of the device driven by the crank shaft, relative to the speed of the latter. The use of a planetary reduction gearing enables the travelling or working device to be driven via a relatively compact mechanism.

In such structure, if a sudden shock or overload is transmitted from the wheels or the working device to the engine crank shaft, there is the danger of the engine stalling or of the transmission gears or shafts being damaged.

It is an object of the present invention to provide a torque limiter incorporated in or associated with a planetary reduction gear system which is capable of preventing such damage.

In accordance with the present invention, the torque limiter is incorporated in or associated with planetary reduction gearing of the type which comprises an input shaft, a sun gear disposed thereon, a fixed ring gear, planet gears meshed with the sun gear and the fixed ring gear, a carrier for rotatably holding the planet gears, and an output shaft interlockingly connected to the carrier, and is characterized by provision of a locking-state releasing mechanism for releasing the locking state of the ring gear when a rotating force greater than a predetermined value is exerted to the ring gear.

According to the present invention, the fixed ring gear in the planetary reduction gearing is utilized.

Namely, the fixed ring gear is constructed so that, when a shock or overload is exerted on or applied to the ring gear, the ring gear is adapted to become rotatable, and thereby to interrupt the transmission of power, thus serving as a torque limiter.

A great operational effect can be obtained by efficiently utilizing the existing structure with simple improvements made thereto.

In order that the present invention may be more readily understood, reference will now be made to the accompanying drawings, in which: Figure lisa general side view of a walking-type agricultural machine incorporating a torque limiter and planetary reduction gearing embodying the present invention, Figure 2 is an enlarged vertical sectional view of main portions of the torque limiter and planetary reduction gearing shown in Figure 1; Figure 3 is a sectional view taken along the line Ill-Ill in Figure 2; and Figure 4 is a fragmentary perspective view of a locking-state releasing mechanism.

Figure 1 illustrates a walking-type cultivator, of which the machine body has an engine 1, a transmission case 2 disposed under the engine 1 containing a planetary gear type transmission gearing (hereinafter referred to an planetary reduction gearing and shown at 8 in Figures 2 and 3), a bumper 3 and a fender 4. The cultivator further has a steering handle 5 extended rearwardly from the lower portion of the machine body, cultivating rotors 6 drivingly mounted on opposite lateral sides of the lower portion of the transmission case 2, and a resistance rod 7 removably attached to the base of the handle 5.

In operation of the walking-type cultivator, the engine rotates the cultivating rotors 6, the rotors serving both to work the ground and draw or "walk" the cultivator along.

The description hereinafter will discuss the structure of the transmission gear mechanism by which the engine drives the rotors 6.

As shown in Figures 2 and 3, three planet gears 9 in the planetary reduction gearing 8 are meshed with a sun gear 10' integrally formed at the end of an input shaft to the planetary reduction gearing 8, wheel input shaft, in this embodiment, comprises the output shaft or crank shaft 10 of the engine 1. An internally toothed ring gear 11 is disposed around and meshed with these planet gears 9.

The ring gear 11 is provided in the outer periphery thereof with four recesses 12 having inclined side walls as viewed in Figure 3. A ball 13 is lockingly pressed into each recess 12 by a spring 14, each ball and associated spring being located in a passage in, and being supported by the transmission case 2.

Thus, the ring gear 11 is normally securely held or locked against rotation with respect to the nonrotatable transmission case 2 by the spring-pressed balls 13.

The springs 14 have a predetermined spring-load.

When an excessive rotational force is exerted on the ring gear 11, the side walls of the recesses 12 cooperate with the balls 13, causing the balls to ride out of the recesses, this being permitted by compression of the springs 14 by the balls. This allows the ring gear 11 to rotate relative to the transmission case 2. There is thus formed a torque-limiting, locking-state releasing mechanism 23.

A carrier 15 rotatably holds the three planet gears 9, and is driven in rotation when the planet gears 9 revolve around the sun gear 10. The carrier 15 has, at its center, a cylindrical portion 1 spa formed with ball holes 1 sub into which bals 1 Scare fitted.

A shaft 16, which is the output shaft of the gearing 8, and an intermediate shaft of the transmission, is disposed in a concentric and end-abutting relation to the input shaft 10. Formed adjacent the upper end of the output shaft 16 are splines or the like defining recesses 1 6a in which the balls 1 sic can be engaged.

A clutch actuating member 17 is slidably mounted on the cylindrical portion 15a, and a pressure or compression spring 18 is disposed between the clutch actuating member 17 and a portion of the carrier 15. The clutch actuating member 17 has, in the inner periphery thereof, recesses 17a into which the balls are capable of engaging, and balls restricting portions 17b. The ball restricting portions 17b normally hold the balls 15e so that they engage simultaneously in the ball holes 1 5b and the recesses 16a, as shown in Figure 2.

Accordingly, when the clutch actuating member 17 is slid upwardly against the action of the spring 18, the recesses 17a are moved to overly the position ofthe balls 15cto permit the balls 1into enter the recesses 17a. The balls are then no longer held in engagement in the recesses 1 6a, thereby interrupting the connection of the intermediate transmission shaft 16 with the carrier 15.

The intermediate transmission shaft 16 has, at its other or lower end, a threaded hole into which one end of a transmission shaft 19 isthreadedly inserted.

The transmission shaft 19 has at the other end thereof a bevel gear 20 secured to its other end.

An axle 21 isjournalled in the lower end of the transmission case 2, and has a bevel gear 22 meshed with the bevel gear 20. As also shown in Figure 1, the rotors 6 are mounted on, and drivingly connected to, opposite ends of the axle 21.

The transmission case 2 includes an upper portion 2a for housing the ring gear 11, and a lower portion 2b for housing the output shaft 16. The upper case portion 2a has a larger diameter than the lower case portion 2b, so that the transmission case 2 is generally funnel shaped in section. The clutch means comprising the balls 1 5c is therefore effectively housed in the larger space of the upper portion of the funnel-shaped transmission case 2.

When an overload is applied to the rotors 6 during operation of the cultivator, such overload is transmitted directly to the carrier 15, which impulsively transmits such overload to the ring gear 11 meshed with the planet gears 9 held by the carrier 15.

However, when a rotational force greater than a predetermined value is exerted upon the ring gear 11, the balls 13 are retracted from the recesses 12 against the action of the springs 14, thereby to release the locking state or condition of the ring gear 11 and allowing the latter to rotate. Thus, the mechanical connection between the output shaft 10 and the intermediate transmission shaft 16 is released, so that a torque limiting function is performed.

When the overload applied to the rotors 16 is released, there is provided a state where the balls 13 are able to re-engage in the recesses 12 under the action of their springs 14 after the ring gear 11 has been rotated by a predetermined number of revolutions.

It is to be noted that the combined planetary gearing and torque limiters embodying the present invention may be used to drive rotors and/or conventional wheels, or may be applied to any other type of transmission system.

As the lock-releasing mechanism 23, there may be used any mechanism having the same function, for example, a so-called disk-brake-type mechanism in which the ring gear 11 is sandwiched, with the brake mechanism cooperating with opposite sides of the ring gear.

Claims (8)

1. Planetary reduction gearing in combination with a torque limiter, the planetary reduction gearing comprising an input shaft, a sun gear connected thereto, a ring gear normally locked in a fixed position, planet gears meshed with said sun gear and said ring gear, a carrier rotatabily carrying said planet gears, and an output shaft interlockably connected to said carrier, wherein said torque limiter comprises a lock-releasing mechanism adapted to release the locked state of said ring gear, thereby to interrupt the transmission of power from said input shaft to the output shaft, when a rotational force greater than a predetermined value is exerted on said ring gear.

2. The combination claimed in claim 1, wherein the lock-releasing mechanism includes at least one recess formed in the periphery of the ring gear, at least one ball normally engaging in said at least one recess and carried by a non-rotatable member, and at least one spring for applying a spring-load to said ball so as normally to urge said ball into engagement with said recess to lock the ring gear against rotation, the arrangement being such that, when a rotational force greater than a predetermined value is exerted on the carrier, the ball is urged out of the recess against the force exerted by its associated spring, releasing said ring gear for rotation.

3. The combination claimed in claim 1 or2, wherein said input shaft is the output shaft of an engine, and the first-mentioned output shaft which is interlockably connected to the carrier is interlockably connected, through a geartransmission mechanism, to an axle on which are mounted wheels or rotors driven by the axle.

4. The combination claimed in any preceding claim, wherein, between the carrier and the firstmentioned output shaft, there is provided clutch means including a cylindrical portion of said carrier in which said output shaft is rotatably engaged, said cylindrical portion having recesses in which balls are fitted, the balls being releasably cooperable with said output shaft to lock the carrier and output shaft against relative rotation, the clutch means further including ball-restricting portions, normally biased by a spring so as to retain the balls in their locking condition, the ball-restricting portions being displaceable to release the balls and declutch the carrier cylindrical portion and output shaft.

5. The combination claimed in claim 2, or claim 2 in combination with claim 3 or 4, further comprising a transmission casing housing the ring gear, the lock-releasing mechanism and the first-mentioned output shaft, said transmission casing comprising an upper casing portion, which constitutes said nonrotatable member, housing said ring gear and a lower casing portion housing said first-mentioned output shaft, the upper casing portion having a larger diameter than the lower casing portion, and said transmission casing having a funnel-shape section.

6. A planetary reduction gearing and torque limiter combination, substantially as hereinbefore described with reference to the accompanying drawing.

7. An agricultural machine incorporating a combination as claimed in any preceding claim.

8. A machine as claimed in claim 7, which comprises a walking-type, powered cultivator.