TRANSMISSION DEVICE

Abstract: A transmission device adopted for a working tool such as a weed cutter having an engine, a rotary blade, and a gear case for supporting the rotary blade. The transmission device comprises an operation pipe for connecting the engine with the gear case, a transmission shaft disposed inside the oper­ ation pipe to transmit the torque of the engine to the rotary blade, and a bearing pipe interposed between the operation pipe and the transmission shaft. The inner surface of the bearing pipe contacts with the outer surface of the transmis­ sion shaft to support the transmission shaft rotatably. A plurality of grooves are formed circumferentially on the surface of the bearing pipe with predetermined intervals to reduce the contacing area thereof with respect to the trans­ mission shaft. The transmission device further comprises a vibration isolator which is fixed to an end of the operation pipe and removably engaged with a clutch housing of the engine.

Description: The present invention relates generally to a transmission device for transmitting the torque of an engine to an output device, and particularly to a transmission device adopted for a working tool such as a weed cutter having an engine, a rotary blade, and a gear case for supporting the rotary blade rotatably, wherein the transmission device comprises an operation pipe for connecting the gear case with the engine and a transmission shaft disposed inside the operation pipe to transmit the engine torque to the rotary blade via the gear case. The transmission device of the present invention comprises a vibration isolator interposed between the operation pipe and a clutch housing of the engine. Figured 2 is a view showing a vibration isolating connection between the operation pipe 7 and a clutch housing of the engine 5 according to the prior art. In the figure, a vibration isolator 201 made of rubber, etc., for preventing vibrations generated by the engine 5 from propagating to the operation pipe 7 is fixed by burning or adhesion to the periphery of an inner cylinder 203. The inner cylinder 203 has grooves 205 and is engaged with an end of the operation pipe 7. After the engagement, the inner cylinder 203 is tightened by a clamp 207 at the grooves 205 such that the inner cylinder 203 is fixed to the operation pipe 7. The periphery of the vibration isolator 201 is provided with projections 209 formed in an axial direction to removably engage with grooves 211 formed in an axial direction on a cylindrical portion 213 of a clutch housing 215 of the engine 5. According to this arrangement of the prior art, there are many parts to be assembled for constituting the vibration isolating connection between the operation pipe 7 and the clutch housing 215 of the engine 5 so that the assembling work may be bothersome, and the total weight increased. From FR-A 2 559 342 a transmission device for a working tool is known, having an engine with a clutch housing, a rotary blade and a gear case for supporting said rotary blade, said transmission device comprising an operation pipe for connecting said engine with said gear case, a transmission shaft rotatably disposed inside operation pipe and extending along the total length of said operation pipe to transmit the torque of said engine to said rotary blade; and a vibration isolator having an outer surface and an inner surface interposed between said operation pipe and said clutch housing for preventing transmission vibration of the engine to the operation pipe. The vibration isolator of this prior art is built-up by two or one pair of annular vibration isolation parts made of rubber, which are disposed around the operation pipe between the operation pipe and the gear case. The transmission device of FR-A 2 559 342, however, has the disadvantage that according to the annular rubber rings, there is the danger that a relative movement between the operation pipe and the gear case occurs so that there is the possibility that there is movement of the gear case in respect to the operation pipe, rendering the transmission device inoperable. It is, therefore, an object of the present invention to provide a transmission device for a working tool such as a weed cutter, in which safe operation is achieved by providing an appropriate vibration isolation between the gear case and the operation pipe. This object is achieved by the characterizing part of claim 1. In particular, a safe function of the transmission device is achieved by providing notches in the operation pipe as well as in the clutch housing, so that rotation of said operation pipe with respect to the said clutch housing caused by vibration of the engine is prevented. These and other objects, features and advantages of the present invention will become apparent from the following descriptions of preferred embodiments taken in conjunction with the accompanying drawings in which: Fig. 1 is a perspective general view showing a weed cutter; Fig. 2 is a cross-sectional side view showing a vibration isolating connection according to a prior art; Fig. 3 is a cross-sectional side view showing an embodiment of a vibration isolating connection of the weed cutter according to the present invention; and Fig. 4 is a cross sectional front view showing a modification of the vibration isolating connection of the weed cutter according to the present invention. A first embodiment of the present invention will be described with reference to Fig. 1. In the figure, a rotary blade 1 is rotatably supported by a gear case 3 and partly covered by a blade cover 4 which protects the rotary blade 1 from being damaged when the weed cutter 2 is placed on the ground. The blade 1 is connected via the gear case 3 with an engine 5 by an operation pipe 7. A fuel tank 6 is arranged on top of the engine 5. In operation, the weed cutter 2 is suspended from a shoulder of an operator through a shoulder band (not shown) attached to a hanger 20, and held by hands with grips 24 of a handle 25. The torque of the engine 5 is transmitted to the rotary blade 1 through the transmission shaft 15 to rotate the rotary blade 1. In Fig. 1, a reference numeral 21 represents a cable for performing a throttle operation. One end of the cable 21 is connected to a throttle lever 27, and the other end thereof enters into a hole formed on the operation pipe 7, passes through a hollow portion defined by the operation pipe 7, a bearing pipe, and adjacent support plates, comes out of another hole formed on the operation pipe 7, and is connected to a throttle device (not shown) of the engine 5. Due to this arrangement of the cable 21 inside the operation pipe 7, the cable 21 will not be caught by outside obstacles such as trees and twigs. Figure 3 shows an embodiment of a vibration isolating connection according to the present invention. In Fig. 3, the same reference numerals as those shown in previous figures, particularly in Figs. 1 and 2 represent the corresponding parts. In the figure, one end of a crank shaft 217 of the engine 5 is provided with a clutch 219 which is connected by a centrifugal force to a clutch drum 221 disposed adjacent to the periphery of the clutch 219. A boss portion 223 of the clutch drum 221 is supported by a bearing 225, which is supported by a bearing portion 227 of a clutch housing 215. Further, the bearing 225 is fitted to the bearing portion 227 by a snap ring 229. One end of the transmission shaft 15 is fitted to the boss portion 223 with a spline 231. Fixed by burning to the periphery of one end of the operation pipe 7 is a vibration isolator 201 made of rubber. The periphery of the vibration isolator 201 is provided with projections 209 extending in an axial direction. The projections 209 engage with grooves 211 provided in an axial direction on the inner surface of a cylindrical portion 213 of the clutch housing 215. An end portion of the cylindrical portion 213 is engaged with a cap 233 and fixed by a bolt 235. According to the above arrangement, when the engine 5 is driven to carry out the cutting work of weeds and bushes by rotating the rotary blade 1, the vibration isolator 201 absorbs vibrations generated by the engine 5 to prevent them from being transmitted to the operation pipe 7. Figure 4 is a cross-sectional front view showing a modification of the vibration isolator. In this modification, a vibration isolator 201'' is divided into two portions along a dividing plane in an axial direction, and inward projections 241 formed on the inner surface of the vibration isolator 201'' are fitted to notches 243 provided on an operation pipe 7'. Outward projections 245 formed on the outer surface of the vibration isolator 201'' are fitted to grooves 247 formed in an axial direction on the inner surface of a cylindrical portion 213''. According to the above arrangement, in comparison with the vibration isolating connection of the prior art device shown in Fig. 2, the number of parts of the vibration isolating connection will be reduced to make the assembling work thereof easy, the total weight reduced, and the operation pipe held strongly to perform the cutting work smoothly.

Claims: A transmission device for a working tool such as a weed cutter having an engine (5) with clutch housing (215, 213), a rotary blade (1) and a gear case (3) for supporting said rotary blade (1), said transmission device comprising: an operation pipe (7, 7') for connecting said engine (5) with said gear case (3); a transmission shaft (15) rotatably disposed inside said operation pipe (7, 7') and extending along the total length of said operation pipe (7') to transmit the torque of said engine (5) to said rotary blade (1); and a vibration isolator (201, 201', 201'') having an outer surface and an inner surface interposed between said operation pipe (7, 7') and said clutch housing (215, 213) for preventing transmitting vibration of the engine to the operation pipe; characterized in that said operation pipe (7') having an end around which a plurality of notches (243) are axially formed; said clutch housing (215, 213) having an inner surface with a plurality of grooves (247) formed in the axial direction thereon; and said vibration isolator (201'') is fixed onto the end of said operation pipe (7'), and said vibration isolator (201'') further comprising a plurality of inward projections (241) axially formed on said inner surface thereof so as to engage with said notches (243) of said operation pipe (7') and a plurality of outward projections (245) axially formed on said outer surface of said vibration isolator (201'') so as to removably engage with said grooves (247) of said clutch housing (213''). A transmission device as claimed in claim 1, wherein said vibration isolator (201'') is heat-sealed to said operation pipe (7'). A transmission device as claimed in claim 1, wherein said vibration isolator (201'') is divided into at least two portions along a dividing plane in an axial direction. A transmission device as claimed in claim 1, wherein the number of the notches (243) formed on the operation pipe (7') is two and the number of the grooves formed on the inner surface of the clutch housing is four, and the numbers of the inward and outward projections of the vibration isolator are corresponding to the numbers of the notches and the grooves, respectively.

Inventors: AKASHI, TOSHIO, EBINUMA, TAKANORI, KATO, HIROSHI, SAWADA, TOSHIHARU
Applicants: KOMATSU ZENOAH CO.
Application year: 1987
Main classification: A01D34
IPC codes: A01D34