ROTARY MOWING CUTTER AND PORTABLE POWER MOWER

Abstract: A rotary mowing cutter (10) includes a holder (11) attached to a drive shaft, at least one cutting element (12) fixed to the holder (11) and first and second covers (13, 14) between which the cutting element (12) is arranged. The cutting element (12) includes a deformable member (12a) attached to the holder (11) and a cutter member (12b) attached to the deformable member (12a). Part of the cutter member (12b) is caused to protrude from the first and the second covers (13, 14) when the deformable member (12a) extends radially of the drive shaft.

Description: DESCRIPTION ROTARY MOWING CUTTER AND PORTABLE POWER MOWER TECHNICAL FIELD The present invention relates to a rotary mowing cutter, and also to a portable power mower using such a mowing cutter. BACKGROUND ART As is well known, a typical portable power mower includes an elongated tubular body connected at its rear end to a small engine and supporting at its front end a rotary cutter. The cutter is connected to the engine via a transmission shaft extending through the tubular body. The cutter may be a serrated rotating disc, or a circular metal plate provided with a suitable number of cutting chips regularly arranged along the edge of the plate. Alternatively, the cutter may consist of flexible nylon cords or metal wires radially extending from a drive shaft. Serrated rotating discs, which are generally inexpensive, have been widely used in conventional power mowers . Disadvantageously, however, a serrated disc may be rather easily broken upon hitting against hard objects such as stones or metal blocks lying on the ground. Even if the serrated disc is not broken, hard objects flicked by the rotating cutter may injure the operator of the mower or people nearby. Clearly, a circular metal plate provided with cutting chips is apt to suffer from the same problems . As opposed to a serrated disc or metal plate with cutting chips, a cord-type rotary cutter may be free from the problem of flicking a hard object since the nylon cords or metal wires are too flexible to thrust the hard object away. However, when the flexible nylon cords (or metal wires) hit against stones for example, they may be broken or permanently deformed. Further, since these cords are rather small in weight, they may fail to cut down weeds properly. DISCLOSURE OF THE INVENTION The present invention has bee proposed under the above circumstances, and its object is to provide a rotary mowing cutter capable of overcoming the above problems . Specifically, an object of the present invention is to provide a rotary mowing cutter which is not easily broken even upon hitting against a hard object and does not flick the hard object toward the operator and people nearby. Another object of the present invention is to provide a portable power mower using a rotary mowing cutter of the above type. According to a first aspect of the present invention, there is provided a rotary mowing cutter comprising: a holder attached to a drive shaft; at least one cutting element fixed to the holder; and first and second covers between which the cutting element is arranged; wherein the cutting element includes a deformable member attached to the holder and a cutter member attached to the deformable member, part of the cutter member being arranged to protrude from the first and the second covers when the deformable member extends radially of the drive shaft. Preferably, part of the cutter member may be caused to protrude from the first and the second covers when the cutting element is rotated. In a preferred embodiment, the first and the second covers may be circular. The first and the second covers may be integrally rotated with the holder. In this case, the two covers and the holder may be formed integral with each other. In another preferred embodiment, the first cover may be stationary while the holder and the second cover may be integrally rotated. Preferably, the rotary mowing cutter of the present invention may further comprise deformation restricting means for preventing the cutting element from deforming beyond a predetermined extent. Preferably, the cutter member may have a round end. Further, the cutter member as a whole may be circular. For facilitating mowing, the cutter member may be provided with a cutting edge of a relatively small thickness. For protecting an operator from possible injury caused by the cutter member, the cutter member at rest may be retreated into a space between the first and the second covers. Only in operation, the cutter member may be caused to protrude from the first and the second covers. In a preferred embodiment, the cutter member may include an inner portion having a constant thickness and an outer portion having a relatively small thickness suitable for mowing . Preferably, the inner portion of the cutter member may be snugly held between the first and the second covers . Preferably, the holder may be formed with a fixing hole into which the deformable member is fitted. In this case, the fixing hole may include a flaring mouth portion for allowing movement of the deformable member. Similarly, the cutter member may be formed with a fixing hole into which the deformable member is fitted. Again, the fixing hole may include a flaring mouth portion for allowing movement of the deformable member. In a preferred embodiment, the holder may include a body and a circular piece connected to the deformable member, wherein the circular piece is pivotably received by the body. Likewise, the cutter member may include a body and a circular piece connected to the deformable member, wherein the circular piece is pivotably received by the body. Preferably, the body of the holder may be formed with a through-hole for receiving the circular piece. The body of the holder may also be formed with a cutout communicating with the through-hole for avoiding interference with the deformable member . Preferably, the deformable member may be made of metal wire. According to a second aspect of the present invention, there is provided a portable power mower comprising: a tubular body: a transmission shaft extending through the tubular body to be connected to an engine; a drive shaft connected to the transmission shaft; and a rotary mowing cutter connected to the engine, the mowing cutter comprising: a holder attached to the drive shaft; at least one cutting element fixed to the holder; and first and second covers between which the cutting element is arranged; wherein the cutting element includes a deformable member attached to the holder and a cutter member attached to the deformable member, part of the cutter member being arranged to protrude from the first and the second covers when the deformable member extends radially of the drive shaft. For achieving smooth operation of the mower over the ground, the second cover may be provided with a downwardly convex portion. Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a side view showing, partly in section, principal parts of a portable power mower incorporating a rotary mowing cutter according to a first embodiment of the present invention; Fig. 2 is a view taken along lines X2-X2 in Fig. 1; Fig. 3 is a side view showing, partly in section, principal parts of another portable power mower incorporating a rotary mowing cutter according to a second embodiment of the present invention; Fig. 4 is a perspective view showing principal parts of a rotary mowing cutter according to a third embodiment of the present invention; Fig. 5 is a plan view showing a rotary mowing cutter according to a fourth embodiment of the present invention; Fig 6 is a plan view showing a rotary mowing cutter according to a fifth embodiment of the present invention; Fig. 7 is a plan view showing a rotary mowing cutter according to a sixth embodiment of the present invention; Fig. 8 is a plan view showing a rotary mowing cutter according to a seventh embodiment of the present invention; Fig. 9 is an enlarged view showing a cutter member used in the rotary cutter of Fig. 8; Fig. 10 is a sectional view taken along lines X10-X10 in Fig. 9; Fig. 11 is a sectional view taken along lines Xll-Xll in Fig. 9; Fig. 12 is a plan view showing a rotary mowing cutter according to an eighth embodiment of the present invention; Fig. 13 is an enlarged view showing a cutter member used in the rotary cutter of Fig. 12; Fig. 14 is a sectional view taken along lines X14-X14 in Fig. 13; Fig. 15 is a sectional view taken along lines X15-X15 in Fig. 13; Fig. 16 is a perspective view showing principal parts of the rotary cutter of the eight embodiment; Fig. 17 is a side view showing, partly in section, a portable power mower incorporating a rotary mowing cutter according to a ninth embodiment of the present invention; Fig. 18 is a plan view taken along lines X18-X18 in Fig. 17 ; Fig. 19 is an enlarged view showing a cutter member used in the rotary cutter of the ninth embodiment; Fig. 20 is a sectional view taken along lines X20-X20 in Fig. 19; Fig. 21 is a sectional view taken along lines X21-X21 in Fig. 19; Fig. 22 is an enlarged view showing a principal part of a holder used in the rotary cutter of the ninth embodiment; Fig. 23 is a plan view illustrating the function of the rotary cutter of the ninth embodiment, with a cutter member hitting against a hard object; Fig. 24 is an enlarged view illustrating how a cord-like deformable member is bent relative to the cutter member; Fig. 25 is a plan view illustrating the function of the rotary cutter of the ninth embodiment, with a cutter member hitting against a relatively soft object; Fig. 26 is an enlarged view illustrating how a cord-like deformable member is bent relative to the holder; Fig. 27 is a plan view showing a rotary mowing cutter according to a tenth embodiment of the present invention; and Fig. 28 illustrates the function of the rotary cutter of the tenth embodiment, with a cutter member hitting against a hard object. BEST MODE FOR CARRYING OUT THE INVENTION Throughout the accompanying drawings, identical or similar parts are referred to by the same reference numerals and characters . Reference is first made to Figs. 1 and 2 illustrating principal parts of a portable power mower (generally represented by reference character 1) utilizing a rotary mowing cutter 10 according to a first embodiment of the present invention. The power mower 1 includes a tubular body 20 connected at its rear end to a small engine (not shown) . As shown in broken lines, a transmission shaft 21 extends through the tubular body 20 and is connected at its rear end to the non-illustrated engine. At its front end, the transmission shaft 21 is connected to a drive shaft 23 via a bevel gear mechanism (not shown) housed in a gear casing 22. The drive shaft 23 is rotatably supported by the gear casing 22 and formed at its lower end with a bore 23a for receiving a bolt 15. The rotary mowing cutter 10 is attached to the drive shaft 23. For preventing weeds from twining around the rotating drive shaft 23, a guard cover 24 is attached to the gear casing 22. According to the present invention, the non-illustrated engine may not necessarily be fixed to the rear end of the tubular body 20. For instance, the engine may be mounted on a casing carried on the back of an operator. In this case, the engine may be connected to the transmission shaft 21 via a flexible shaft. As shown in Figs. 1 and 2, the rotary cutter 10 basically includes a holder 11 fixed to the drive shaft 23, cutting elements 12 extending radially from the holder 11, a first cover 13 arranged above the cutting elements 12 , and a second cover 14 arranged under the cutting elements 12. In the illustrated embodiment, four cutting elements 12 are provided (see Fig. 2). However, the number of the cutting elements 12 is optional, and only one or more than four cutting elements may be used. As best shown in Fig. 2, the holder 11 is in the form of a disc of a predetermined thickness and formed with a center hole 11a into which the drive shaft 23 is fitted. Further, the holder 11 is formed with four horizontal fixing holes lib. These holes are equally spaced around the center hole 11a and extend radially of the holder 11 for fixing the inner ends of the cutting elements 12. Each cutting element 12 includes a cord-like deformable member 12a whose inner end is fitted into a respective one of the fixing holes lib of the holder 11, and a hard cutter member 12b fixed to the outer end of the deformable member 12a. The cutter member 12b is formed with a bore 12c into which the deformable member 12a is inserted. The deformable member 12a may be a metal wire (or wire strands) made of stainless steel for example. The cutter, member 12b may be made of a hard material obtained by quenching structural carbon steel . The deformable member 12a may be fixed to the holder 11 by soldering or calking. Likewise, the cutter member 12b may be fixed to the deformable member 12a by soldering or calking. The holder 11 has a thickness of about 6mm, while the deformable member 12a has a thickness of about 3mm. The cutter member 12b, which may be about 20-30mm long, has a generally circular cross section. The cutter member 12b is divided into two portions, namely, a diametrically larger inner portion connected to the deformable member 12a and a diametrically smaller outer portion. The outer diameter of the inner portion of the cutter member 12b may be equal to or slightly less than 6mm, while the diameter of the outer portion of the cutter member 12b is rendered small enough to enable effective mowing of weeds. In the normal state, as shown in Fig. 1, the inner portion of the cutter member 12b is disposed between the first cover 13 and the second cover 14, while the outer portion of the cutter member 12b protrudes radially outward of the first and the second covers 13, 14. In the illustrated embodiment, the length P of the protruding portion is about 6-12mm. The first cover 13 is a circular plate made of e.g. aluminum and formed with a center hole 13a into which the drive shaft 23 is fitted. Likewise, the second cover 14, which has also a circular configuration, is made of e.g. aluminum and formed with a center hole 14a. As shown in Fig. 1, the second cover 14 is provided with a bulging portion 14b which is downwardly convex. The bulging portion 14b is formed with a recess 14c communicating with the center hole 14a. To firmly attach the first cover 13, holder 11 and second cover 14 to the drive shaft 23, the bolt 15 is screwed into the bore 23a. As a result, the first cover 13, the holder 11 and the second cover 14 are caused to rotate together upon actuation of the drive shaft 23. It should be noted that the head of the bolt 15 is accommodated in the recess 14c. Thus, the bolt 15 does not protrude downward beyond the bulging portion 14b of the second cover 14. As previously stated, the thickness of the holder 11 is generally the same as the maximum diameter of each cutter member 12b, while the thickness (or diameter) of each deformable member 12a is smaller than those of the holder 11 and the cutter members 12b. Thus, as shown in Fig. 1, the first and the second covers 13 and 14 are vertically adjacent to the cutter members 12b, thereby preventing each cutter member 12b from deviating upward or downward in operation. The cutter members 12b are snugly held between the first and the second covers 13 , 14 so as to be movable therebetween . Thus, when an unduly large external force is exerted on any one of the cutter members 12b, the relevant deformable member 12b will be bent, as shown in phantom in Fig. 2, whereby the entirety of the particular cutter member 12b is retreated into the space between the first and the second covers 13, 14. The operations of the portable power mower 1 and the mowing cutter 10 will now be described. Though not illustrated, the tubular body 20 of the mower 1 is provided with a throttle lever to control the output of the engine. Thus, by manipulating the throttle lever, an operator can increase or decrease the rotational speed of the rotary cutter 10. The rotational speed may reach 7, 000-8, OOOrpm and the circumferential speed of the cutter 10 may be over 300km/h. To mow weeds, the operator moves the rotating cutter 10 over the ground, holding it close to the ground. In this manner, the cutter members 12b rotating at high speed will cut down the weeds . An advantage to be enjoyed by the illustrated embodiment is as follows. When the cutter members 12b hit against hard but rather small objects such as pebbles or bolts on the ground, those small objects will not be flicked toward the operator or people nearby, even though the cutter members 12b are rotated at high speed. This is because the kinetic energy of the cutter members 12b is very small due to a small mass (10-90 grams) of the cutter members 12b. Further, upon hitting against small stones or unmovable concrete blocks, the deformable members 12a are bent as shown in Fig. 2 (double-dot chain lines), so that the impact of the hitting is advantageously absorbed, thereby leaving the cutter members 12b intact. Further, since the cutter members 12b are not caught by the hard objects thanks to the deflection of the deflectable members 12a, the rotational speed of the rotary cutter 10 is advantageously maintained. Once being deformed, the deformable member 12a is instantly restored to the original, straight shape by the centrifugal force. According to the illustrated embodiment, the downwardly convex portion 14b is formed on the second cover 14. Thus, the operator of the power mower 1 is able to move the rotary cutter 10 smoothly over the ground, with the convex portion 14b held in sliding contact with the ground. Further, due to the convex portion 14b, the cutter members 12b are prevented from coming too close to the ground during the mowing operation. This is advantageous in preventing the cutter members 12b from coming into direct contact with the ground or small hard objects lying on the ground. Since the power mower 1 has the above-described advantages, the operator can conduct mowing without worrying about pebbles or bolts hidden in the weeds which would otherwise cause damage to the cutter members 12b or injure people. Thus, the operator can efficiently conduct the mowing by using the power mower 1. Further, due to the impact- absorbing function, the power mower 1 can cut down weeds growing beside a hard wall without damaging the cutter members 12b through contact with the wall . Fig. 3 shows a portable power mower 1A using a rotary mowing cutter 10A according to a second embodiment of the present invention. The power mower 1A and the rotary cutter 10A are substantially the same as those of the first embodiment except that a first cover 13 of the second embodiment is formed integral with a guard cover 24. Since the guard cover 24 is fixed to a stationary gear casing 22, the first cover 13 of this embodiment is not rotated together with cutting elements 12 and a second cover 14. The deformable members 12a are functionally similar to those of the first embodiment. Fig. 4 shows principal parts of a rotary mowing cutter 10B according to a third embodiment of the present invention. In this embodiment, as in the previous embodiments, each cutting element 12 is provided with a deformable member 12a and a cutter member 12b attached to the deformable member 12a. The cutter member 12b of the third embodiment differs from that of the first or second embodiment in the following respects. Specifically, as shown in Fig. 4, the cutter member 12b is provided with an inner portion 12ba and an outer portion 12bb protruding radially outward of first and second covers 13, 14. The inner portion 12ba has a rectangular cross section whose thickness is substantially the same as (or slightly smaller than) the space between the first cover 13 and the second cover 14. The protruding outer portion 12bb is provided with a sharp cutting edge 12bc . Thus, weeds are easily cut down by the cutting edge 12bc of the cutter member 12b rotating in the direction indicated by an arrow R. According to the illustrated arrangement, the rectangular inner portion 12ba of the cutter member 12b is snugly (but slidably) disposed between the first and the second covers 13, 14. Thus, the cutter member 12b is prevented from rotating about the radially extending axis Ax shown in Fig. 4. This is advantageous because the cutting edge 12bc is held in a predetermined posture suitable for conducting effective mowing . Fig. 5 shows a rotary mowing cutter IOC according to a fourth embodiment of the present invention. Basically, the mowing cutter IOC is similar to the mowing cutter 10 of the first embodiment. Specifically, the mowing cutter IOC includes a first cover 13, a plurality of cutting elements 12 and a second cover 14 which are all fixed to a common drive shaft 23 for simultaneous rotation. Differing from the first embodiment, however, the mowing cutter 10C of the fourth embodiment is provided with a plurality of deformation restricting members 16 (only one shown) disposed between the first and the second covers 13, 14. Each restricting member 16 corresponds to a respective one of the cutting elements 12 and is fixed to the inner surface of the second cover 14, as shown in Fig. 5. Alternatively, the restricting members 16 may be fixed to the first cover 13. As illustrated, each restricting member 16 comes into contact with the cutter member 12b of the relevant cutting element 12 when this particular cutting element 12 is bent, as shown in phantom. With such an arrangement, it is possible to prevent the deformable member 12a of each cutting element 12 from being subjected to bending beyond an acceptable degree. This is advantageous because, otherwise, the deformable member 12a when unduly bent would be unable to restore to the original straight form. Fig. 6 shows a rotary mowing cutter 10D according to a fifth embodiment of the present invention. The illustrated mowing cutter 10D also includes first and second covers 13, 14 and a plurality of cutting elements 12 (only one shown) disposed between the two covers 13, 14. Differing from the previous mowing cutters 10-10C, the cutting elements 12 of the mowing cutter 10D are entirely retreated into the space between the first and the second covers 13 and 14 when the cutter 10D is not rotated. For achieving this, each cutting element 12 at rest is arranged to extend along a line L which does not pass through the rotational center 0. When the cutter 10D is rotated, the centrifugal force causes the retreated cutting element 12 to move to the working position shown in double-dot chain lines. As a result, the outer portion of the cutter member 12b protrudes radially outward of the first and second covers 13 and 14, whereby intended weed mowing is performed. According to the fifth embodiment, the cutter members 12b in nonuse are safely kept between the first and the second covers 13 , 14. Such an arrangement is advantageous in protecting an operator from injury by the cutter members 12b. Fig. 7 shows a rotary mowing cutter 10E according to a sixth embodiment of the present invention. In this embodiment, a first cover 13, a second cover 14 and a holder 11 are formed e.g. by die-casting of aluminum, so that these components are integrally connected to each other. As illustrated, the mowing cutter 10E includes four radially elongated partitions 17 between the first and the second covers 13, 14. Each of the partitions 17, which may be formed integral with the two covers 13 and 14, is arranged between two adjacent cutting elements 12. Thus, four generally sectorial spaces SP are defined by the partitions 17 and the two covers 13 , 14. Each of the cutting elements 12 is movable within a respective one of the sectorial spaces SP. As in the fourth embodiment (Fig. 5), the partitions 17 may serve as deformation restricting means for the cutting elements 12. Fig. 8 shows a rotary mowing cutter 10F according to a seventh embodiment of the present invention. The illustrated cutter 10F is basically similar to the cutter 10 of the first embodiment (Fig. 2), except that each cutter member 12b has a round outer end. The specific configuration of the respective cutter members 12b will be described below with reference to Figs. 9-11. Fig. 9 is an enlarged plan view showing, partly in section, one of the identical cutter members 12b, while Fig. 5 10 is a sectional view taken along lines X10-X10 in Fig. 9, and Fig. 11 is a sectional view taken along lines Xll-Xll in Fig. 9. As seen from these figures, each cutter member 12b includes a rectangular inner portion 12ba and an outer portion 10 12bb processed suitably for mowing weeds . The outer portion 12bb extends radially outward from the inner portion 12ba. The inner portion 12ba has a thickness which is substantially equal to or slightly smaller than the distance between first and second covers 13-14, so that the inner portion 12ba is 15 snugly but slidably held between the two covers 13 and 14. The protruding amount P (Fig. 8) of the outer portion 12bb may be about 10-2Omm. As best shown in Fig. 10, the outer portion 12bb is gradually reduced in thickness, as viewed from the center of 20 the outer portion 12bb toward the respective edges 12bbe extending in parallel to the axis of the deformable member 12a. Such an arrangement serves to facilitate the mowing of weeds . According to the seventh embodiment, the free end 12bc of 25 the cutter member 12b has a round configuration which is convex radially outward, as shown in Fig. 9. Upon hitting against a hard object on the ground, the thus configured cutter member 12b is caused to slide over the surface of the hard object (see Fig. 8) with the deformable member 12a suitably bent. Thus, advantageously, the cutter member 12b is prevented from sticking in the hard object. As a result, the smooth rotation of the rotary cutter 10F is maintained even when the cutter 10F encounters hard objects. Further, since the cutter member 12b does not stick in the hard object, the deformable member 12a will not be sharply bent at the portion where the deformable member 12a is inserted into the cutter member 12b. In view of the above advantages , according to the illustrated embodiment, use may be made of a small, portable engine whose displacement volume is about 22-23cc for driving the rotary cutter 10F. the cutter 10F in operation may attain a rotation of about 6,000rpm, which renders the circumferential speed of the cutter 10F to be about 150km/h or more. Fig. 12 shows a rotary mowing cutter 10G according to an eighth embodiment of the present invention. As illustrated, the rotary cutter 10G includes a circular holder 11 from which three cutting elements 12 extend radially outward of the holder 11. The three cutting elements 12 are regularly spaced around a drive shaft 23. The holder 11 and the cutting elements 12 are arranged between first and second covers 13, 14. Each of the cutting elements 12 is provided with a deformable member 12a and a cutter member 32b. The deformable member 12a of this embodiment is identical or similar to that of the previous embodiments, while the cutter member 32b has a different configuration. Specifically, as best shown in Fig. 13, each cutter member 32b is in the form of a circle whose diameter may be about 25mm. The cutter member 32b is divided into two parts, namely, a flat inner portion 32ba and a crescent-shaped outer portion 32bb. As shown in Fig. 14, the inner portion 32ba has a predetermined uniform thickness, while the outer portion 32bb tapers toward its edge 32bc. As shown in Fig. 15, the inner portion 32bb is gradually reduced in thickness farther away from the center in the direction transverse to the axis of the deformable member 12a. Fig. 16 is a perspective view showing the cutter member 32 which is slidably moved between the first and the second covers 13 and 14. According to the eighth embodiment, each cutter member 32b as a whole is made circular. Thus, it is possible to reliably prevent the cutter member 32b from sticking in a hard object on the ground. Instead of being caught by e.g. a tree stump, the illustrated cutter member 32b is cause to slide over the surface of the tree stump upon contacting therewith. In the above embodiment, the three deformable members 12a have the same length, thereby equalizing the protruding amounts of the respective cutter members 32b. The present invention, however, is not limited to this, and the protruding amounts may be rendered different. For instance, the protruding amounts may be 17mm, 15mm and 14mm, respectively. Reference is now made to Fig. 17 showing a portable power mower incorporating a rotary mowing cutter 10H according to a ninth embodiment of the present invention. The illustrated power mower is basically similar to the power mower shown in Fig. 1 except that the rotary cutter 10H differs in arrangement from the rotary cutter 10 of the first embodiment. Referring to Fig. 18, the rotary cutter 10H includes a holder 11 from which three cutting elements 12 extend radially outward. The holder 11 is formed with a center hole 11a into which a drive shaft 23 (Fig. 17) is fitted. The cutting elements 12 are regularly spaced around the center hole 11a (120° apart) . The holder 11 and the cutting elements 12 are arranged between first and second covers 13, 14. Each cutting element 12 includes a deformable member 12a and a cutter member 12b fixed to the outer end 12aa of the deformable member 12a. Opposite to the outer end 12aa, the deformable member 12a has an inner end 12ab. The holder 11 is provided with three protrusions extending radially outward of the holder. As shown in Fig. 18, the three protrusions are regularly spaced around the center hole 11a (120° apart) . Each of the protrusions is formed with a bore lib into which the inner end 12ab of a corresponding deformable member 12a is inserted. The holder 11 may have a thickness of about 6mm and a maximum diameter (including the protrusions) of about 70mm. The width of each protrusion may be about 12mm. Each deformable member 12a may have a length of about 98mm and a diameter of about 3mm. Each cutter member 12b may have a thickness of about 6mm, a length of about 33mm and a width of about 15mm. The weight of each cutter member 12b may be about 10 grams. The circular first and the second covers 13-14 made of e.g. aluminum may have a thickness of about 1.5mm and an outer diameter of about 230mm. As seen from Figs. 19-21, each cutter member 12b includes an inner portion 12ba connected to a deformable member 12a. The inner portion 12ba has a constant thickness corresponding to the spacing between the first cover 13 and the second cover 14. The cutter member 12b also includes an outer portion 12bb protruding from the inner portion 12ba radially outward of the first and the second covers 13 , 14. The inner portion 12ba is formed with a bore 12c into which the outer end 12aa of the deformable member 12a is inserted. The overall depth Dl of the bore 12c may be about 21mm. As shown in Fig. 19, the bore 12c has a flaring mouth portion whose maximum width Wl may be about 6mm and whose depth D2 may be about 7mm. The remaining portion of the bore 12c has a depth D3 , which may be equal to 14mm, and has a constant diameter. This remaining portion of the bore 12c snugly receives the outer end 12aa of the deformable member 12a to render the outer end 12aa unmovable. On the other hand, the deformable member 12a is able to shift within the flaring mouth portion (Depth D2), as indicated in double-dot chain lines (see also Fig. 21) . As best shown in Fig. 20, the outer portion 12bb of the cutter member 12b is gradually reduced in thickness away from the center of the outer portion toward the respective edges 12bbe for facilitating the mowing of weeds. It should be noted that the free end 12bc of the outer portion 12bb is rendered round. With such an arrangement, it is possible to reduce the impact exerted on the outer portion 12bb upon hitting against a hard object. Referring now to Fig. 22, each bore lib formed in the relevant protrusion of the holder 11 has the same configuration as that of the bore 12c shown in Fig. 19. Specifically, the total depth dl of the bore lib may be about 21mm. The flaring mouth portion of the bore lib may have a maximum width wl of about 6mm and a depth d2 of about 7mm. The remaining portion of the bore lib may have a depth d3 of about 14mm and a constant diameter for snugly receiving the inner end 12ab of the deformable member 12a. Thus, within this remaining portion, the deformable member 12a is unmovable. On the other hand, the deformable member 12a is able to shift within the flaring mouth portion of the bore lib, as indicated by double-dot chain lines. According to the ninth embodiment, the rotary cutter 10H may be rotated at a speed of about 5,000rpm, which renders the circumferential speed of the rotary cutter 10H to be about 240km/h. For attaining required rotational speeds, an engine having a displacement volume of about 20cc may be used when the two covers 13, 14 have a diameter of 9 inches (about 230mm). When the two covers 13, 14 have a diameter of 10 inches (about 254mm) , use may be made of an engine whose displacement volume is about 30cc. In addition to the above-described advantages obtainable by the previous embodiments, the rotary cutter 10H of the ninth embodiment also enjoys the following advantages. Referring to Figs. 23 and 24, when a cutter member 12b hits upon a rather large stone SI, the deformable member 12a may seem to be sharply bent at a portion indicated by an arrow Jl. However, as viewed locally, the bent portion Jl of the deformable member 12a is not bent sharp, but only gradually bent due to the flaring mouth portion 12ca of the cutter member 12b, as shown in Fig. 24. Thus, the bending force acting on the deformable member 12a will be distributed so that the bending force does not concentrate in a limited part of the deformable member 12a. In this manner, the deformable member 12a is prevented from breaking at the bending portion Jl. When the cutter member 12b hits on a rather soft object such as a tree stump S2 , as shown in Fig. 25, it may stick in the soft object while the holder 11 is continued to rotate. In such an instance, as shown in phantom, the deformable member 12a is stretched, so that it seems to be sharply bent at the location shown by an arrow J2. As viewed locally, however, the deformable member 12a is only gradually bent at the location J2 due to the flaring mouth portion llba of the holder 11, as shown in Fig. 26. Thus, in this case again, the deformable member 12a will not be broken at the bending portion J2. Reference is now made to Figs. 27 and 28 illustrating a rotary mowing cutter 101 according to a tenth embodiment of the present invention. In this embodiment, the rotary cutter 101 includes a holder 30 to which three cutting elements are attached. The holder 30 is provided with a body 31 and three pivotable disks 32. The body 31 is formed with a center hole 30a into which a drive shaft (not shown) is fitted. The pivotable disks 32 are regularly spaced from each other around the center hole 30a. The holder 30 is provided with three protrusions corresponding to the pivotable disks 32. Each protrusion is formed with a through-hole 31a for rotatably receiving a respective one of the pivotable disks 32. As shown in Fig. 27, each protrusion of the holder 30 is formed with a cutout for exposing part of the pivotable disk 32 in the radially outward direction of the center hole 30a. The deformable members 12a of the respective cutting elements are fitted into fixing holes 32a of the pivotable disks 32. In this manner, as shown in Fig. 28, each deformable member 12a is pivotable about the center of the relevant pivotable disk 32 within a predetermined range, which is defined by the size of the radially outward cutout of the holder 30. The holder 30 is snugly disposed between first and second covers 13 and 14. Thus, the pivotable disks 32 are prevented from being accidentally removed from the through-holes 31a. As shown in Fig. 27, each cutting member includes a cutter member 40 provided with a body 41 and a pivotable disk 42. The body 41 is formed with a through-hole 41a for snugly receiving the pivotable disk 42. The body 41 is formed with a cutout for exposing the pivotable disk 42 in the radially inward direction of the center hole 30a. The pivotable disk 42 is formed with a fixing hole into which a deformable member 12a is fitted. With such an arrangement, as shown in Fig. 28, the deformable member 12a is pivotable with respect to the body 41 of the cutter member 40 within a predetermined range defined by the size of the radially inward cutout of the body 41. According to the tenth embodiment, as seen from Fig. 28, each deformable member 12a may remain straight even when the relevant cutter member 40 hits against a hard object SI. Thus, the deformable member 12a is prevented from breakage due to otherwise possible stress concentration. Further, even when the deformable member 12a is bent at a portion indicated by an arrow Jl or J2 in Fig. 28, the bending may not be severe due to the cutout. Thus, the deformable member 12a does not suffer from stress concentration. INDUSTRIAL APPLICABILITY As described above, the rotary mowing cutters and portable power mowers according to the present invention are suitable for mowing weeds, grasses, cereal crops, etc. without damaging the cutters nor injuring the operator or people nearby.

Claims: CLAIMS 1. A rotary mowing cutter comprising: a holder attached to a drive shaft; at least one cutting element fixed to the holder; and first and second covers between which the cutting element is arranged; wherein the cutting element includes a deformable member attached to the holder and a cutter member attached to the deformable member, part of the cutter member being arranged to protrude from the first and the second covers when the deformable member extends radially of the drive shaft. 2. The rotary mowing cutter according to claim 1, wherein said part of the cutter member is caused to protrude from the first and the second covers when the cutting element is rotated. 3. The rotary mowing cutter according to claim 1, wherein the first and the second covers are circular. 4. The rotary mowing cutter according to claim 1, wherein the first and the second covers are integrally rotated with the holder. 5. The rotary mowing cutter according to claim 1, wherein the first cover is stationary while the holder and the second cover are integrally rotated. 6. The rotary mowing cutter according to claim 1, further comprising deformation restricting means for preventing the cutting element from deforming beyond a predetermined extent . 7. The rotary mowing cutter according to claim 1, wherein the cutter member has a round end. 8. The rotary mowing cutter according to claim 1, wherein the cutter member as a whole is circular. 9. The rotary mowing cutter according to claim 1, wherein the cutter member is provided with a cutting edge of a relatively small thickness . 10. The rotary mowing cutter according to claim 1, wherein the cutter member at rest is retreated into a space between the first and the second covers, the cutter member in operation being caused to protrude from the first and the second covers. 11. The rotary mowing cutter according to claim 1, wherein the cutter member includes an inner portion having a constant thickness and an outer portion having a relatively small thickness suitable for mowing. 12. The rotary mowing cutter according to claim 11, wherein the inner portion of the cutter member is snugly held between the first and the second covers. 13. The rotary mowing cutter according to claim 1, wherein the holder is formed with a fixing hole into which the deformable member is fitted, the fixing hole including a flaring mouth portion for allowing movement of the deformable member. 14. The rotary mowing cutter according to claim 1, wherein the cutter member is formed with a fixing hole into which the deformable member is fitted, the fixing hole including a flaring mouth portion for allowing movement of the deformable member. 15. The rotary mowing cutter according to claim 1, wherein the holder includes a body and a circular piece connected to the deformable member, the circular piece being pivotably received by the body. 16. The rotary mowing cutter according to claim 1, wherein the cutter member includes a body and a circular piece connected to the deformable member, the circular piece being pivotably received by the body. 17. The rotary mowing cutter according to claim 15, wherein the body of the holder is formed with a through-hole for receiving the circular piece, the body of the holder being also formed with a cutout communicating with the through-hole for avoiding interference with the deformable member. 18. The rotary mowing cutter according to claim 1, wherein the deformable member is made of metal wire. 19. A portable power mower comprising: a tubular body: a transmission shaft extending through the tubular body to be connected to an engine; a drive shaft connected to the transmission shaft; and a rotary mowing cutter connected to the engine, the mowing cutter comprising: a holder attached to the drive shaft; at least one cutting element fixed to the holder; and first and second covers between which the cutting element is arranged; wherein the cutting element includes a deformable member attached to the holder and a cutter member attached to the deformable member, part of the cutter member being arranged to protrude from the first and the second covers when the deformable member extends radially of the drive shaft. 20. The portable power mower according to claim 19, wherein the second cover is provided with a downwardly convex portion.

Inventors: TERASHIMA HIDEO, YAMADA SAKUJI, TERASHIMA, HIDEO, YAMADA, SAKUJI
Applicants: TERASHIMA HIDEO, YAMADA MACHINERY IND CO LTD, YAMADA SAKUJI, TERASHIMA, HIDEO, YAMADA MACHINERY INDUSTRIAL CO., LTD., YAMADA, SAKUJI
Application year: 2000
Main classification: A01D34
IPC codes: A01D34