GB2122303A - Safety mechanism for reduction gearing - Google Patents

Abstract

A safety mechanism for reduction gearing in which a holder 14 for supporting larger diameter 16 and smaller diameter 17 reduction gears of a reduction gearing is frictionally secured to a transmission case 2, and the frictional securing state of the holder to the transmission case is released when a load exceeding a preset value is applied to the holder. As shown the outer circumference of the holder has a plurality of concave portions into which spring loaded balls 19 are fitted. The safety mechanism may be incorporated into a walking-type cultivator. <IMAGE>

Description

SPECIFICATION Safety mechanism for reduction gearing The present invention relates to a safety mechanism for reduction gearing in which an input shaft interlocked with an engine is disposed coaxially with an output shaft interlocked with an axle, larger diameter gears to which power is transmitted from the input shaft in a speed reduction manner and smaller diameter gears which transmit power to the output shaft in a speed reduction manner, are connected to intermediate transmission shafts, and a holder for rotatably supporting the intermediate transmission shafts is attached to a transmission case.

In such reduction gearing of the type abovementioned, increase in an axle driving load may cause the transmission system to be damaged. In this connection, in the middle course of the transmission system from the output shaft to the axle, the transmission shafts are connected to each other through shear pins or safety clutch means adapted to be released when load exceeding a preset value is applied.

In either case, however, change in torque caused by axle load variations is small, thereby to make it difficult to set a limit load.

In view of the foregoing, it is an object of the present invention to provide a safety mechanism for reduction gearing having provision to facilitate setting of a limit load, thus enabling to avoid damage of the transmission system otherwise resulted from increase in an axle driving load.

In order to achieved this object, a safety mechanism for reduction gearing of the type abovementioned in accordance with the present invention is characterised in that the holder is frictionally secured to the transmission case, so as to be rotatable when a load exceeding a preset value is applied to the holder. That is, the present invention adopts such a novel construction as to rotate the holder itself of the transmission shafts for the intermediate gears in the reduction gearing. In particular, when the load exceeds a preset value due to increase in an axle driving load, the holder is adapted to be rotated with respect to the transmission case. Such an arrangement makes it possible to set a limit load at the larger diameter holder, i.e., a portion which undergoes a great change in load resulting from variations of an axle driving load.

Furthermore, such load setting may be facilitated.

It is therefore possible to set a limit load such that power transmission is interrupted at the critical point where the axle driving load is so increased as to cause the transmission system to be damaged.

Conventionally, it has been difficult to set a limit load and therefore one has been obliged, in view of safety, to set a limit load smaller than a necessary value, thus causing interruption of power transmission to stop the travelling operation, although there is no possibility of the transmission system being damaged. On the contrary, the present invention may avoid such unnecessary interruption of the travelling operation, and also efficiently avoid damage of the transmission system otherwise resulting from an increase of the axle driving load.

It is noted that the present invention may be widely applied to a working machine such as a cultivator.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a general side view of a walking-type cultivator provided with a safety mechanism for reduction gearing in accordance with the present invention; Figure2 is a longitudinal sectional view of main portions of Figure 1; Figure 3 is a sectional view, with portions broken away, along the line Ill-Ill in Figure 2; Figure 4 is an exploded view of main portions of a handle; Figure 5 is a side view, with portions broken away, of main portions of the handle; Figure 6 is a longitudinal sectional view in front elevation of another embodiment of safety mechanism for reduction gearing in accordance with the present invention and Figure 7 is a sectional view, with portions broken away, taking along the line VII-VII in Figure 6.

Figures 1 to 5 illustrate a walking-type cultivator adapted to perform a cultivating operation when travelling with cultivator claws 4a simultaneously forming propelling wheels. In this cultivator, a transmission case 2 is connected to the lower portion of an engine 1, a cultivator claw shaft 4 is attached to an axle 3 projected from the lower portion of the transmission case 2, a handle 5 is rearwardly extended from the transmission case 2, and a support rod 6 is provided.

An input shaft 7 interlocked with the engine 1 is vertically disposed coaxially with a vertical output shaft 8 on which a first cylindrical shaft 9 is rotatably disposed integrally with the output shaft 8. The input shaft 7 is interlockingly connected to a second cylindrical shaft 10 through a reduction bearing 11.

The second cylindrical shaft 10 is interlockingly connected to the first cylindrical shaft 9 through a ball clutch 12, and the output shaft 8 is interlockingly connected to the axle 3 through a bevel gear mechanism 13. With such an arrangement, power from the engine 1 may be transmitted to the axle 3.

The reduction gearing 11 comprises an annular holder 14 attached to the transmission case 2, intermediate transmission shafts 15 having an angular phase of 180 rotatably attached to the holder 14, larger diameter gears 16 respectively attached on the upper portions of the intermediate transmission shafts 15 so as to be rotatable therewith, and smaller diameter gears 17 respectively connected to the lower portions of the intermediate transmission shafts 15. The larger diameter gears 16 are meshed with a gear member 7a connected to the lower end portion of the input shaft 7, while the smaller diameter gears 17 are meshed with a gear member 10a connected to the second cylindrical shaft 10, so that the power is transmitted from the input shaft 7 to the output shaft 8 in a two-stage reduction manner.

The holder 14 is rotatably attached to the transmis sion case 2 and has in its outer circumference a plurality of concave portions 18 with an angular phase of 90 . The case wall 2a of the transmission case 2 incorporates a plurality of balls 19, which are spring-loaded by springs 20 so as to be fitted in the concave portions 18, respectively. When an axle driving load exceeds a preset value, the balls 19 are adapted to be disengaged from the concave portions 18 against spring-load of the springs 20, thereby to automatically interrupt power transmission from the input shaft 7 to the second cylindrical shaft 10. There is thus formed a safety mechanism or torque limiter 21.

Such a safety mechanism 21 may be modified in construction, as far as the holder 14 is frictionally secured to the transmission case 2 so as to be rotatable when a load exceeding a preset value is applied to the holder 14. For example, the holder 14 may be held at the periphery thereof by a pair of plate members, to one of which a spring or the like is attached to provide a predetermined holding force.

The handle 5 has a first member 5a at the side of the transmission case 2 and a second member Sb at the side of a grip 22. The second member Sb can be turned such that the handle weight may be changed according to the physical condition of the operator in a manner described below.

As shown in Figures 4 and 5, the second member Sb is attached at the lower portion thereof to a pair of brackets 23, between which a fulcrum shaft 24 is disposed. Each of the brackets 23 has a guide groove 26, which forms an arc of a circle around the fulcrum shaft 24 and has three engagement portions 25.

The first member 5a has its upper end a concave portion 27 with and from which the fulcrum shaft 24 may be engaged and disengaged. The first member 5a also has, under the concave portion 27, slots 28 formed in the longitudinal direction of the first member 5a. A fastening bolt 29 passes through the guide grooves 26 in the second member 5b, and the slots 28. A bracket 30 bolted to the first member 5a at the rear side of the upper end thereof, has a concave portion 27a with and from which the fulcrum shaft 24 may be engaged and disengaged.

With the fastening bolt 29 loosened, the second member Sb may be moved toward or away from the first member 5a through the slots 28, and the fulcrum shaft 24 is engaged with either one of the concave portions 27 and 27a. With such a situation, the second member Sb may be vertically swung and one of the fastening bolt engagement portions 25 is selected. Thereafter, the fastening bolt 29 is fastened to secure the second member Sb to the first member 5a. Thus, the height and position of the handle 5 can be adjusted in six stages, as a whole.

Figures 6 and 7 illustrate another embodiment of the present invention with the reduction earing 11 having the above-mentioned safety mechanism partially modified.

The reduction gearing 11' shown in Figures 6 and 7 comprises an annular holder 114 attached to the transmission case 2, support shafts 1 14a having an angular phase of 1200 attached to the holder 114, cylindrical intermediate transmission shafts 115 rotatably attached to the support shafts 114a, respectively, larger diameter gears 116 respectively attached to the upper portions of the intermediate transmission shafts 115 so as to be rotatable therewith, and smaller diameter gears 117 respectively attached to the lower portions of the intermediate transmission shafts 115.The larger diameter gears 116 are meshed with the gear member 7a, while the smaller diameter gears 117 are meshed with a gear member 110a connected to a second cylindrical shaft 110, so that power is transmitted in a two-stage speed reduction manner from the input shaft 7 to the output shaft 8.

With such an arrangement, the reduction ratio of power transmission from the input shaft to the output shaft may be changed by changing the gear members having external teeth, such as larger diameter or smaller diameter gears. In particular, there are used gears having readily machinable external teeth, as the gear members for changing the transmission reduction ratio. The manufacturing cost of such gear members is therefore reduced, so that a change in transmission reduction ratio can be economically realized.

The holder 114 is rotatably attached to the transmission case 2 and has in the outer circumference thereof concave portions 118 having an angular phase of 90". The case wall 2a of the transmission case 2 incorporates the balls 19 which are springloaded by the spring 20 so as to be fitted in the concave portions 118, respectively. When an axle driving load exceeds a preset value, the balls 19 are adapted to be disengaged from the concave portions 118 against spring-loading of the springs 20, thereby to automatically interrupt transmission of power from the input shaft 7 to the second cylindrical shaft 10. There is thus formed a safety mechanism or a torque limiter 21 '.

This torque iimiter 21' may be variously modified in construction, insofar as the holder 114 is frictionally secured to the transmission case 2 so as to be rotatable when a load exceeding a preset value is applied to the holder 114. For example, the holder 114 may be held, at the periphery thereof, by a pair of plate members, to one of which a spring or the like is attached to provide a predetermind holding force.

In order to change the reduction ratio of power transmission from the input shaft 7 to the output shaft 8, the intermediate transmission shafts 115 to which are attached gears having different diameters, such as the larger diameter gears 116 and the smaller diameter gears 117, may be attached to the holder 114 at positions diametrically different from those in the example discussed hereinbefore. Various kinds of such asemblies may be prepared and suitably replaced as necessary.

The holder 114 may have slots in an inclined direction with respect to the radial direction of the holder 114, such that the support shaft 1 14a fixing positions may be radially changed. Larger and smaller diameter gears 116 and 117 having different diametrical ratios may be attached to the intermediate transmission shafts 115, or the second cylindrical shaft 110 may be replaced with one having a gear member 110a having a different diameter.

Furthermore, the number of the intermediate transmission shafts 115 may be two, four or more.

The support shafts 1 14a may be rotatably attached to the holder 114, and larger and smaller diameter gears 116 and 117 may be attached to these support shafts 1 14a so as to be rotatable therewith, so that the support shafts 1 14a constitute the intermediate transmission shafts 115.

Claims (5)

1. A safety mechanism for reduction gearing comprising an input shaft for connection with an engine; an output shaft for connection with an axle and disposed coaxiallywith said input shaft; larger diameter gears to which power is transmitted from said input shaft in a speed reduction manner; at least two smaller diameter gears which transmit power to said output shaft in a speed reduction manner, said larger and smaller diameter gears being connected to each other so as to be integrally rotatable; and a holder for rotatably supporting said larger and smaller diameter gears, said holder being frictionally secured to a transmission case so as to be rotatable when a load exceeding a preset value is applied to said holder.

2. A safety mechanism as claimed in claim 1, wherein the larger diameter gears and the smaller diameter gears are secured to intermediate transmission shafts which are rotatably supported by the holder.

3. A safety mechanism as set forth in claim 1, wherein the larger diameter gears and the smaller diameter gears are integrally formed and rotatably supported by support shafts secured to the holder.

4. A safety mechanism as set forth in claim 2 or 3, wherein the holder has in the outer circumference thereof a plurality of concave portions into which are respectively fitted bal Is spring-loaded by springs in the transmission case, so that said holder is frictionally secured to the transmission case by predetermined spring-loading of said springs.

5. A cultivator incorporating a safety mechanism for reduction gearing as claimed in any one of the preceding claims.