Prime mover of work machine

A prime mover of a mower that is a work machine comprises: a motor having a motor rotation shaft extended along a substantially vertical direction, and a motor housing disposed coaxially with the motor rotation shaft; a centrifugal fan disposed above the motor; and a motor cover that accommodates the motor and the centrifugal fan so as to extend to the upper end of a side part of the centrifugal fan. A cooling air inlet is formed in the motor housing, the centrifugal fan having a base part provided above the cooling air inlet, and the outer diameter of the base part being greater than the outer diameter of the cooling air inlet.

TECHNICAL FIELD

The present invention relates to a prime mover of a work machine such as a lawn mower.

BACKGROUND ART

A lawn mower includes a motor for rotating a cutter blade for cutting the grass on lawns. The temperature of such a motor may become high depending on the conditions in which it is used. Japanese Patent No. 5271517 discloses a prime mover for a lawn mower in which a suction-type fan is provided under a motor in order to cause a flow of cooling air inside the motor.

SUMMARY OF INVENTION

Causing a flow of cooling air inside the motor under the action of a fan may cause foreign matter, such as mown grass, dirt, dust, rain water, etc., to flow into the motor together with the cooling air. When a mesh filter member is provided to prevent the entry of foreign matter into the motor, cleaning the filter member is necessary. Further, the motor cannot be cooled sufficiently if the filter member is clogged.

The present invention has been made considering such a problem, and an object of the present invention is to provide a prime mover of a work machine that can prevent the entry of foreign matter into the motor and can cool the motor effectively with a simple structure.

In order to achieve the object above, a prime mover of a work machine according to the present invention includes: a motor including a motor rotary shaft extending along substantially a vertical direction, and a motor housing disposed coaxially with the motor rotary shaft; a centrifugal fan disposed above the motor; and a motor cover accommodating the motor and the centrifugal fan in such a manner that the motor cover extends to an upper end of a side portion of the centrifugal fan, wherein a cooling air inlet is formed in the motor housing, the centrifugal fan includes a base located above the cooling air inlet, and the base has an outer diameter that is larger than an outer diameter of the cooling air inlet.

According to the configuration above, since the base of the centrifugal fan is disposed above the cooling air inlet, it is possible to reduce the inflow of foreign matter into the motor from above through the cooling air inlet. Furthermore, foreign matter is pushed out radially outward by the centrifugal fan together with the cooling air, to the wall of the motor cover, and therefore cooling air containing no foreign matter can efficiently flow into the cooling air inlet located under the centrifugal fan. It is thus possible to prevent the foreign matter from flowing into the motor and to effectively cool the motor with a simple structure.

In the work machine prime mover above, the centrifugal fan may be disposed coaxially with the motor rotary shaft.

According to the configuration above, it is possible to efficiently cause the cooling air to flow into the motor from the cooling air inlet. Further, the centrifugal fan can effectively reduce the inflow of foreign matter into the motor from the cooling air inlet.

In the work machine prime mover above, the motor may include a rotor attached to the motor rotary shaft, and a stator provided on an outer circumferential side of the rotor, and the outer diameter of the base may be larger than an outer diameter of the stator.

According to the configuration above, the centrifugal fan can further effectively reduce the inflow of foreign matter into the motor from the cooling air inlet.

In the work machine prime mover above, the motor cover may have a peripheral wall formed to cover an outer circumferential portion of the centrifugal fan and part of an area above the centrifugal fan, a cooling air introducing port may be formed in a portion of the motor cover, the portion being above the centrifugal fan, and the cooling air introducing port may have a diameter that is smaller than the outer diameter of the base.

According to the configuration above, it is possible to cause foreign matter entering the motor cover to flow radially outward together with the cooling air by the action of the centrifugal fan and to efficiently push out the foreign matter to the wall of the motor cover.

In the work machine prime mover above, the motor cover may have formed therein a cooling passage positioned inside the motor housing; and a foreign matter discharge passage positioned outside of the motor housing and located in parallel with the cooling passage, a throttle member may be provided in the foreign matter discharge passage, and a passage sectional area of the foreign matter discharge passage on the upstream side of the throttle member may be larger than a passage sectional area of the foreign matter discharge passage at a position of the throttle member.

According to the configuration above, the throttle member increases the passage resistance of the foreign matter discharge passage and so the cooling air containing no foreign matter can be efficiently guided into the cooling passage.

In the work machine prime mover above, the throttle member and an inner surface of the motor cover may form an orifice therebetween.

According to the configuration above, the orifice can be formed of a simple structure.

In the work machine prime mover above, the peripheral wall of the motor cover may be formed of a plurality of steps in such a manner that the peripheral wall expands downward in side view, and the throttle member may be disposed at an interval from an inner side of a horizontal surface of a step portion, which is one of the plurality of steps.

According to the configuration above, it is possible to further increase the passage resistance of the foreign matter discharge passage and hence to further efficiently guide the cooling air containing no foreign matter into the cooling passage.

In the work machine prime mover above, the throttle member may be formed like a circular ring.

According to the configuration above, it is possible to effectively increase the passage resistance of the foreign matter discharge passage.

In the work machine prime mover above, the throttle member may include: a projection projecting radially outward from the motor housing; and an extending portion extending downward from a projecting end of the projection, and the orifice may be formed between the extending portion and the inner surface of the motor cover.

According to the configuration above, the orifice can be formed of a simple structure.

In the work machine prime mover above, an upper surface of the projection may be inclined downward in a radially outward direction.

According to the configuration above, it is possible to reduce accumulation of foreign matter on the upper surface of the projection.

The work machine prime mover above may include a housing covering an upper part of the motor cover, and an air intake port directed downward may be formed in the housing.

According to the configuration above, it is possible to reduce the inflow of foreign matter into the housing from the air intake port and into the motor.

In the work machine prime mover above, the outer diameter of the base may be substantially identical to an outer diameter of the motor housing, and an outer circumferential surface of the base may be positioned right above an outer circumferential surface of the motor housing.

The configuration above makes it possible to simplify the structure of the motor cover accommodating the centrifugal fan and the motor and to thereby enable cost reduction. Further, this prevents foreign matter guided from the centrifugal fan from getting caught on the motor housing.

In the work machine prime mover above, the work machine may be a lawn mower.

This configuration can provide a lawn mower that offers the effects recited above.

DESCRIPTION OF EMBODIMENTS

The work machine according to the present invention will be described below referring to the accompanying drawings in conjunction with preferred embodiments.

As shown inFIG. 1, a work machine13is a walk-type lawn mower11for cutting the grass on lawns. Note that the work machine13is not limited to the lawn mower11but may be a grass cutter, snow blower, a cultivator, etc. InFIG. 1, the arrow Fr shows the forward direction of the lawn mower11(the same direction as the forward direction seen from an operator), and the arrow Rr shows the rearward direction of the lawn mower11(the same direction as the rearward direction seen from the operator).

The lawn mower11includes a prime mover10having a housing12, left and right front wheels14disposed in the front part of the housing12, left and right rear wheels16disposed in the rear part of the housing12, an operation handle18extending rearward from the housing12, and a mown grass storage20attached at the rear of the housing12.

The housing12includes a lower housing12aand an upper housing12b. The lower housing12ais a casing that is opened downward only in a part facing the ground (lawn). The lower housing12acontains a mowing cutter blade22. The cutter blade22is coupled to an output shaft26of a motor24through a blade holder not shown. The cutter blade22is a plate-like elongated member (so-called bar blade).

InFIG. 2, the upper housing12bhas an air intake port28formed in its rear part so as to introduce cooling air (outside air) into the upper housing12b. The prime mover10includes the motor24serving as a driving source of the cutter blade22and the rear wheels16, a centrifugal fan30attached to the motor24, and a motor cover32accommodating the motor24and the centrifugal fan30.

The motor24is driven by electric power supplied from a battery not shown. The motor24is constructed as a so-called inner-rotor type motor. The motor24includes a motor rotary shaft34, a rotor36, a stator38, and a motor housing40.

The motor rotary shaft34extends in a substantially vertical direction. The output shaft26projecting below the motor housing40is coupled to the lower end of the motor rotary shaft34. The output shaft26extends into the lower housing12a. The driving force generated by the motor24is transmitted to the left and right rear wheels16as a travel driving force through a travel power transmission mechanism (not shown) coupled to the output shaft26. The driving force generated by the motor24may be transmitted to the left and right front wheels14.

The rotor36has permanent magnets42arranged at the outer circumferential surface of the motor rotary shaft34. The permanent magnets42are arranged such that the N- and S-poles are disposed alternately in the circumferential direction of the motor rotary shaft34.

The stator38includes an iron core44formed of a stack of multiple steel sheets, and a plurality of stator coils46attached to the iron core44through an insulator45. The iron core44has a plurality of salient poles (poles)48protruding radially inward from its outer circumferential portion. The plurality of salient poles48are arranged at equal intervals in the circumferential direction of the stator38. The stator coils46are formed by winding conducting wires around the salient poles48with the insulator45therebetween.

The motor housing40is disposed coaxially with the motor rotary shaft34. The motor housing40is provided in the motor cover32and supports the stator38. The motor housing40includes a bottom wall40apositioned below the stator38, a side wall40bprojecting upward from the bottom wall40aso as to cover the outer circumferential surface of the stator38, and a top wall40cprovided at the top end of the side wall40b. The bottom wall40ahas formed therein a cooling air discharge outlet50for discharging the cooling air in the motor24to the outside.

As shown inFIGS. 2 and 3, a cooling air inlet52for taking the cooling air into the motor24is formed in the top wall40c. The cooling air inlet52has a plurality of (four in the example ofFIG. 3) openings52aformed in the circumferential direction. The openings52aare positioned above the stator38. An outer circumferential part54forming each opening52aextends like a circular arc along the circumferential direction of the motor rotary shaft34. In other words, the outer circumferential parts54are formed of the top end of the side wall40bof the motor housing40.

As shown inFIGS. 2 and 4, the centrifugal fan30is disposed above the motor24and sends cooling air into the motor24. The centrifugal fan30includes a fan rotary shaft56, a hub58, a base60, and blades62. The fan rotary shaft56is rotatably supported by a bearing63(seeFIG. 2) provided in the top wall40cin such a manner that the fan rotary shaft56projects upward from the top end of the motor rotary shaft34. That is, the centrifugal fan30is disposed coaxially with the motor rotary shaft34and rotates integrally with the motor rotary shaft34.

The hub58is shaped like a cylinder and fixed to the fan rotary shaft56. The base60is a plate-like member provided on the outer circumferential surface of the hub58. The base60is formed like a circular ring. The base60covers the entire cooling air inlet52from above. In other words, the base60has an outer diameter D1that is larger than an outer diameter D2of the cooling air inlet52(the diameter of a circle along the outer circumferential parts54: seeFIGS. 2 to 4). In other words, the outer diameter D1of the base60is larger than an outer diameter D3of the stator38. The outer diameter D1of the base60is substantially the same as the outer diameter of the side wall40bof the motor housing40. That is, the outer circumferential surface of the base60is positioned right above the outer circumferential surface of the motor housing40.

The plurality of blades62are provided on the upper surface of the base60. Each blade62extends from the inner circumferential portion of the base60to the outer edge of the base60. Each blade62extends radially outward, curving in the rotating direction of the base60(seeFIG. 4).

As shown inFIG. 2, the upper portion of the motor cover32is covered by the upper housing12b. The motor cover32includes a lower cover32aand an upper cover32b. The lower cover32ais attached to the upper cover32bto cover the motor24from below. The motor housing40is fixed to the lower cover32a. The lower cover32ahas an insertion hole64through which the output shaft26passes, and a bearing66rotatably supporting the output shaft26. The lower cover32ahas formed therein a cooling air exit port68for guiding the cooling air in the motor cover32to the outside.

The upper cover32bincludes a peripheral wall70covering the motor24and the centrifugal fan30from the side, and an outer circumference cover portion72covering the outer circumferential portion of the centrifugal fan30from above. That is, the upper cover32bextends to the top end of the side of the centrifugal fan30. The peripheral wall70is formed to cover the outer circumferential portion of the centrifugal fan30and part of the area above the centrifugal fan30. The peripheral wall70is formed of a plurality of steps such that it expands downward in side view. The peripheral wall70is fixed to the upper housing12b.

The lower cover32ais provided along the entire circumference of the lower end of the upper cover32b. An annular first space S1is formed between the peripheral wall70and the upper end of the side wall40bof the motor housing40(seeFIG. 3). An annular second space S2is formed between the peripheral wall70and the base60of the centrifugal fan30(seeFIG. 4).

The outer circumference cover portion72is provided at the top end of the peripheral wall70. A cooling air introducing port74for introducing cooling air into the motor cover32is formed in the center portion of the outer circumference cover portion72. The diameter of the cooling air introducing port74is smaller than the outer diameter D1of the base60of the centrifugal fan30. In this embodiment, the cooling air introducing port74is formed in the shape of a perfect circle, but the cooling air introducing port74may be formed in other shapes, such as an ellipse, polygon, etc. When the cooling air introducing port74is not a perfect circle, the diameter of the cooling air introducing port74is the length of the widest part of the cooling air introducing port74.

The motor cover32includes a cooling passage76which is located inside the motor housing40and in which cooling air flows, and a foreign matter discharge passage78positioned outside of the motor housing40and located in parallel with the cooling passage76.

A throttle member80forming an orifice84is provided in the foreign matter discharge passage78. The throttle member80is a plate-like member formed like a circular ring and is fixed to the side wall40bof the motor housing40. The throttle member80is located below the first space S1and the second space S2.

As shown inFIG. 5, the throttle member80is positioned at a step portion82of the peripheral wall70. Specifically, an upper surface80aof the throttle member80faces, at an interval, a downward-facing first step inner surface82a(horizontal surface) of the step portion82. That is, an annular first throttle passage84ais formed between the upper surface80aof the throttle member80and the first step inner surface82a. The passage sectional area of the first throttle passage84ais smaller than the passage sectional area of the second space S2. The interval between the upper surface80aof the throttle member80and the first step inner surface82ais sized so that foreign matter, such as mown grass, dirt, dust, rain water, etc., can pass therethrough.

An outer side surface80bof the throttle member80faces, at an interval, a second step inner surface82bof the step portion82that faces the motor24. That is, an annular second throttle passage84bis formed between the outer side surface80bof the throttle member80and the second step inner surface82b. The passage sectional area of the second throttle passage84bis smaller than the passage sectional area of the second space S2, and substantially the same as the passage sectional area of the first throttle passage84a. The interval between the outer side surface80bof the throttle member80and the second step inner surface82bis sized so that foreign matter, such as mown grass, dirt, dust, rain water, etc., can flow therethrough, and the interval is substantially the same as the interval between the upper surface80aof the throttle member80and the first step inner surface82a. The first throttle passage84aand the second throttle passage84bform the orifice84. That is, the passage sectional area of the foreign matter discharge passage78on the upstream side of the throttle member80is larger than the passage sectional area of the foreign matter discharge passage78at the position of the throttle member80.

Next, operations of the lawn mower11constructed as above will be described.

With the lawn mower11shown inFIG. 1, when the cutter blade22rotates clockwise in plan view under the driving action of the motor24, the cutter blade22cuts the grass growing on the lawn right beneath the lawn mower11. At this time, an air current (swirling wind) swirling in the same direction as the cutter blade22is generated inside the lower housing12a. Then, the cut grass (mown grass) is sent into the mown grass storage20by the conveying wind (swirling wind) thus generated.

The centrifugal fan30rotates as the motor rotary shaft34rotates. Then, as shown inFIG. 2, outside air (air) is taken into the upper housing12bthrough the air intake port28, and the air inside the upper housing12bis introduced as cooling air into the motor cover32through the cooling air introducing port74. The cooling air contains foreign matter, such as mown grass, dirt and dust blown up during work, rain water, etc.

The cooling air introduced into the motor cover32is pushed out radially outward by the blades62of the centrifugal fan30, while swirling along the circumferential direction around the fan rotary shaft56. That is, an eddy of cooling air is formed by the centrifugal fan30. The cooling air that has been pushed out outward in the radial direction of the centrifugal fan30hits the inner surface of the peripheral wall70of the motor cover32and flows downward through the second space S2between the peripheral wall70and the centrifugal fan30. At this time, the foreign matter, which has larger mass than air, flows like an eddy along the inner surface of the peripheral wall70by the centrifugal force. The cooling air guided from the second space S2separates off into the cooling passage76and the foreign matter discharge passage78.

The cooling air containing no foreign matter flows in the cooling passage76, and the cooling air containing foreign matter flows in the foreign matter discharge passage78. The cooling air containing foreign matter and guided into the foreign matter discharge passage78flows downward in the first space S1along the inner surface of the side wall, passes through the orifice84(first throttle passage84aand second throttle passage84b), and flows into the bottom space in the motor cover32. At this time, the orifice84increases the passage resistance of the foreign matter discharge passage78. The foreign matter guided to the bottom portion of the motor cover32through the orifice84moves in the housing12while whirling in the eddy of cooling air, and is discharged out of the motor cover32from the cooling air exit port68.

The cooling air containing no foreign matter and guided into the cooling passage76, is guided to the back of the centrifugal fan30by the effect of the orifice84of the foreign matter discharge passage78, and then flows into the motor24from the cooling air inlet52formed in the top wall40cof the motor housing40. The cooling air flowing into the motor24flows downward through the space between the rotor36and the stator38, and the space between the stator coils46, thereby cooling the stator38(stator coils46). The cooling air, which has cooled the stator38, is discharged out of the motor housing40from the cooling air discharge outlet50, meets the cooling air guided from the foreign matter discharge passage78, and flows out of the motor cover32from the cooling air exit port68.

Note that, with the lawn mower11, a battery (not shown) is installed and removed by opening the upper cover32b. In this work, foreign matter flowing into the motor cover32from above through the cooling air introducing port74remains on the top surface of the base60of the centrifugal fan30. Then, when the motor24is driven, the foreign matter remaining on the top surface of the base60moves in the motor cover32while whirling in the eddy of cooling air and is discharged out of the motor cover32from the cooling air exit port68.

In this case, the lawn mower11according to the embodiment offers the effects below.

The cooling air inlet52is formed in the motor housing40, and the outer diameter D1of the base60is larger than the outer diameter D2of the cooling air inlet52. This configuration reduces the inflow of foreign matter into the motor24from above through the cooling air inlet52.

Furthermore, foreign matter is pushed out radially outward by the centrifugal fan30together with the cooling air, to the inner surface of the peripheral wall70of the motor cover32, and therefore cooling air containing no foreign matter can efficiently flow into the cooling air inlet52located under the centrifugal fan30. It is hence possible to prevent the foreign matter from flowing into the motor24and to effectively cool the motor24with a simple structure.

The centrifugal fan30is disposed coaxially with the motor rotary shaft34. It is therefore possible to efficiently cause the cooling air to flow into the motor24from the cooling air inlet52. Further, the centrifugal fan30can effectively reduce the inflow of foreign matter into the motor24from the cooling air inlet52.

The motor24includes the rotor36attached to the motor rotary shaft34, and the stator38provided on the outer circumferential side of the rotor36. The outer diameter D1of the base60is larger than the outer diameter D3of the stator38. This allows the centrifugal fan30to further effectively reduce the inflow of foreign matter into the motor24from the cooling air inlet52.

The peripheral wall70of the motor cover32is formed to cover the outer circumferential portion of the centrifugal fan30and part of the area above the centrifugal fan30. The cooling air introducing port74is formed in a portion of the motor cover32, the portion being above the centrifugal fan30, and the cooling air introducing port74has a diameter that is smaller than the outer diameter D1of the base60. It is thus possible to cause foreign matter entering the motor cover32to flow radially outward together with the cooling air by the action of the centrifugal fan30and to efficiently push out the foreign matter to the peripheral wall70of the motor cover32.

The motor cover32has formed therein the cooling passage76positioned inside the motor housing40, and the foreign matter discharge passage78positioned outside of the motor housing40and located in parallel with the cooling passage76. The throttle member80is provided in the foreign matter discharge passage78, and the passage sectional area of the foreign matter discharge passage78on the upstream side of the throttle member80is larger than the passage sectional area of the foreign matter discharge passage78at the position of the throttle member80. Thus, the throttle member80increases the passage resistance of the foreign matter discharge passage78and so the cooling air containing no foreign matter can be efficiently guided into the cooling passage76.

The throttle member80and the peripheral wall70of the motor cover32form the orifice84therebetween. The orifice84is thus formed of a simple structure. The throttle member80is formed like a circular ring and therefore effectively increases the passage resistance of the foreign matter discharge passage78.

The peripheral wall70of the motor cover32is formed of a plurality of steps in such a manner that the peripheral wall70expands downward in side view, and the throttle member80is disposed at an interval from the inner side of the horizontal surface of the step portion82, which is one of the plurality of steps. This further increases the passage resistance of the foreign matter discharge passage78and makes it possible to further efficiently guide the cooling air containing no foreign matter into the cooling passage76.

The prime mover10of the lawn mower11includes the upper housing12bcovering an upper part of the motor cover32, and the air intake port28directed downward is formed in the upper housing12b. This reduces the inflow of foreign matter into the lower housing12afrom the air intake port28and into the motor24.

The outer diameter D1of the base60is substantially identical to the outer diameter D3of the motor housing40, and the outer circumferential surface of the base60is positioned right above the outer circumferential surface of the motor housing40. This makes it possible to simplify the structure of the motor cover32accommodating the centrifugal fan30and the motor24and to thereby reduce cost. Further, this prevents foreign matter guided from the centrifugal fan30from getting caught on the motor housing40.

The present invention is not limited to the configurations described above. As shown inFIG. 6, the prime mover10of the lawn mower11may include a throttle member90in place of the throttle member80. The throttle member90is provided integrally with the top wall40cof the motor housing40. The throttle member90is shaped in the form of a circular ring. The throttle member90includes a projection90aprojecting radially outward from the outer peripheral surface of the top wall40c, and an extending portion90bextending downward from the projecting end of the projection90a.

The outer circumferential portion of the projection90ais positioned radially outside the base60. The upper surface of the projection90ais inclined downward in the radially outward direction. This reduces accumulation of foreign matter on the top surface of the projection90a. The outer surface of the extending portion90bfaces, at an interval, the inner surface of the peripheral wall70of the motor cover32. That is, an annular throttle passage92is formed between the outer surface of the extending portion90band the inner surface of the peripheral wall70. The throttle passage92forms an orifice94.

The passage sectional area of the throttle passage92is smaller than the passage sectional area of the second space S2. The interval between the outer surface of the extending portion90band the inner surface of the peripheral wall70is sized so that foreign matter, such as mown grass, dirt, dust, rain water, etc., can pass therethrough. That is, the passage sectional area of the foreign matter discharge passage78on the upstream side of the throttle member90is larger than the passage sectional area of the foreign matter discharge passage78at the position of the throttle member90.

The prime mover10with the throttle member90further includes a plurality of fixing parts96for fixing the motor24to the motor cover32. The fixing parts96are positioned at equal intervals along the circumferential direction of the motor housing40, for example. The fixing parts96each include a first supporting portion98, a second supporting portion100, and a bolt102.

The first supporting portion98is provided at the throttle member90. In other words, the first supporting portion98is provided at the top wall40cof the motor housing40. The first supporting portion98has a hole98athrough which the bolt102passes vertically. The second supporting portion100protrudes upward from the inner surface of the lower cover32aof the motor cover32. The second supporting portion100has a threaded hole100ainto which a threaded portion102aof the bolt102is screwed. According to this configuration, the motor24can be firmly fixed to the motor cover32by the fixing parts96.

The motor24is not limited to inner-rotor type but may be of outer-rotor type. The throttle member80may be fixed to the peripheral wall70of the motor cover32at an interval from the side wall40bof the motor housing40. In this case, the orifice84is formed between the throttle member80and the side wall40b. The cooling air inlet52may be formed in the side wall40bof the motor housing40.

The prime mover of a work machine according to the present invention is not limited to the embodiments described above, but can of course adopt various configurations without departing from the essence and gist of the present invention.