Patent Publication Number: US-2021169007-A1

Title: Power head and lawn mower

Description:
CROSS-REFERENCE TO RELATED INVENTIONS 
     This application is based upon and claims the benefit of priority from the prior Chinese Patent Application No. 201911239774.9, filed on Dec. 6, 2019, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The invention relates to a power head and a lawn mower and belongs to the technical field of garden tools. 
     BACKGROUND ART 
     Lawn mowers are used to cutting grass. Due to the increased requirements for the functions of lawn mower, the power requirements for lawn mower have become higher and higher. 
     In the prior art, the heat dissipation of the power head of the lawn mower is using cooling air. It is more common to place the air outlet on the bottom case below the motor near the blade. This design can use the rotation of the blade to draw wind and blow away the grass and dust attached to the blade. However, there are still some insurmountable defects in this design. First, it cannot be applied to lawn mowers with high heat generation such as high power, high current or high torque. Second, it cannot use the high-pressure water to wash the bottom shell and the blade of the lawn mower. 
     In view of this, it is necessary to improve the heat dissipation mechanism of the existing lawn mower to solve the above problems. 
     SUMMARY OF INVENTION 
     The object of the present invention is to provide a power head, which has a good heat dissipation effect. 
     In order to achieve the above object, the present invention provides a power head comprising a motor assembly, an energy device and a housing assembly covering the motor assembly and the energy device. The motor assembly comprises a motor base and a motor fixed on the motor base. The housing assembly comprises a casing that is assembled with the motor base. An air inlet is located on the top of the casing and an air inlet cavity connected to the air inlet. The air inlet and the air inlet cavity are provided with two and arranged on the left and right sides of the casing. The air inlet cavity is a U-shaped structure with an upper opening, and the casing covers the top of the air inlet cavity to form a sealed airflow passage. The bottom of the motor base is sealed and the side of the motor base is provided with an air outlet. The cooling airflow enters the airflow passage from the air inlet and then flows into the motor, and then flows out from the air outlet. 
     As a further improvement of the present invention, a control board close to the energy device is further received in the casing. One end of the air inlet cavity is connected to the air inlet, and the other end extends to the control board, which is configured to guide the cooling airflow from the air inlet to the control board. 
     As a further improvement of the present invention, a cooling fin is provided on the control board, and the other end of the air inlet cavity is disposed close to the cooling fin. 
     As a further improvement of the present invention, the motor is located below the control board, and the motor assembly further comprises a fan provided on top of the motor, and when the motor starts, the fan rotates and drives the cooling airflow at the control board into the motor. 
     As a further improvement of the present invention, the motor assembly further comprises an air collecting cover covering the motor and the fan, and a vent is provided on the top of the air collecting cover so that when the fan rotates, the cooling airflow at the control board is driven into the motor from the vent. 
     As a further improvement of the present invention, the air outlet is provided with at least two which discharge air in different directions, the air outlet of the motor base is provided with an air guide rib, and the air guide rib is deflected and the deflection direction is tangent to the rotation direction of the cooling airflow driven by the fan, so that the airflow direction at the air outlet is consistent with the rotation direction of the fan. 
     As a further improvement of the present invention, when the rotation direction of the cooling airflow driven by the fan is clockwise, the deflection direction of the air guide rib is deflected to the left relative to the rotation direction of the cooling airflow. 
     As a further improvement of the present invention, the air inlet cavity comprises a first ramp provided near the air inlet and a second ramp provided away from the air inlet, and the first ramp facing the air inlet goes downhill, the second ramp goes uphill towards the air inlet. 
     As a further improvement of the present invention, the casing comprises a first casing and a second casing that are assembled and fixed to each other, and an upper casing that cover the top of the first casing and the second casing, the first casing and the second casing both being provided with the air inlet and the air inlet cavity, and the air inlet of the first casing and the air inlet of the second casing being arranged symmetrically with respect to the center line of the power head, the air inlet cavity of the first casing and the air inlet cavity of the second casing being also arranged symmetrical with respect to the center line of the power head, and the air flow passage being defined by the air inlet cavity and the upper casing. 
     The object of the present invention is also to provide a lawn mower, which has a better heat dissipation effect. 
     In order to achieve the above object, the present invention provides a lawn mower comprising a main body, a handle extending upward and rearward from the main body, and a power head mounted on the main body. The air inlet on the power head is disposed near the handle. 
     The beneficial effects of the present invention are as follows. The top of the case is provided with an air inlet that is inclined backward and downward, an air inlet cavity connected to the air inlet, and an air flow passage surrounded by the case and the air inlet cavity. The motor base is designed to have a sealed bottom and an air outlet on the side that communicates with the outside, so that the cooling air can enter from the air inlet and flow into the motor along the airflow passage, and finally flow out from the air outlet, forming a circulating cooling and heat dissipation system to improve the heat dissipation of the power head of the lawn mower. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of the lawn mower according to the present invention. 
         FIG. 2  is a perspective view of the mounting case in  FIG. 1 . 
         FIG. 3  is a perspective view of the power head in  FIG. 1 . 
         FIG. 4  is an exploded view of the power head shown in  FIG. 3 . 
         FIG. 5  is an exploded view of the motor assembly in  FIG. 4 . 
         FIG. 6  is a perspective view of the motor base in  FIG. 5 . 
         FIG. 7  is a sectional view of the lawn mower shown in  FIG. 1 . 
         FIG. 8  is an enlarged view of a circled portion in  FIG. 7 . 
         FIG. 9  is a perspective view of the first casing in  FIG. 4 . 
         FIG. 10  is a perspective view of the second casing in  FIG. 4 . 
         FIG. 11  is a perspective view of the upper casing in  FIG. 4 . 
         FIG. 12  is a perspective view of the housing assembly after assembly. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     In order to make the objectives, technical solutions, and advantages of the present invention clearer, the following describes the present invention in detail with reference to the accompanying drawings and specific embodiment. 
     As shown in  FIG. 1 , the present invention discloses a lawn mower  100  including a main body  1 , a handle  2  extending backward from the rear of the main body  1 , a power head  3  mounted on the main body  1 , and walking wheels  5  disposed at the bottom of the main body  1  and a grass collecting bag  6  provided behind the main body  1  for collecting broken grass leaves. Because the handle  2 , the walking wheels  5  and the grass collecting bag  6  are all existing structures, they will not be described in detail here. The following description will mainly describe the specific structure of the power head  3  and the connecting relationship between the power head  3  and the main body  1  in detail. 
     As shown in  FIG. 2 , the main body  1  includes a mounting shell  10  recessed with a mounting groove  11 . The mounting groove  11  is formed by being recessed downward from the middle position of the mounting shell  10 , and the mounting groove  11  is substantially annular. A receiving hole  111  is defined in a bottom wall  110  of the mounting groove  11 , so that screws can pass through the receiving hole  111  to fix the bottom of the power head  3  to the bottom wall  110  of the mounting groove  11 . 
     A first annular groove  12  is also recessed in the mounting shell  10 . The first annular groove  12  is formed on the periphery of the mounting groove  11  and the recessed depth of the first annular groove  12  is greater than the recessed depth of the mounting groove  11 . A leakage hole  121  is provided in the first annular groove  12 . When the lawn mower  100  is used in a rainy or humid area, the rainwater on the power head  3  will slide into the first annular groove  12 , and then flows out from the leakage hole  121 . 
     In this embodiment, four receiving holes  111  are provided to stably install the power head  3  in the mounting shell  10 . Five leakage holes  121  are provided and evenly distributed in the first annular groove  12  to divide the accumulated water in the first annular groove  12  to ensure that all the accumulated water in the first annular groove  12  is discharged. 
     The power head  3  can be a replaceable component to replace an internal combustion engine. And the power head  3  can be applied to a variety of equipment, such as outdoor power equipment, including lawn mower, snow sweeper, cleaning machine, cultivator, etc. The present invention will take a lawn mower as an example to describe the specific structure and function of the power head  3  in detail, but it should not be limited to this. 
     As shown in  FIG. 3  to  FIG. 8  in combination with  FIG. 2 , the power head  3  includes a motor assembly  30  received in the mounting groove  11 , an energy device (not shown), and a housing assembly  40  for accommodating the motor assembly  30  and the energy device. The energy device is preferred a battery pack which is detachable mounted on the power head. The battery pack can also be used in the other power tools, such as string trimmer, chain saw. The housing assembly  40  includes an air inlet  41  and an air outlet  311 , and the housing assembly  40  also includes an air inlet cavity  42  connected to the air inlet  41 . The motor assembly  30  includes a motor base  31  cooperating with the mounting shell  10 , a motor  32  fixed on the motor base  31 , a fan  33  arranged on the top of the motor  32 , and an air collecting cover  34  for covering the motor  32  and the fan  33 . 
     The bottom of the motor base  31  is sealed, an air outlet  311  is located on the side of the motor base  31  communicated with the outside and a waterproof rib  312  disposed in the air outlet  311  for partial shielding. The waterproof rib  312  makes the motor base  31  and the housing assembly  40  arranged up and down. That is, the installation bottom surface of the housing assembly  40  corresponding to the air outlet  311  is lower than the upper surface of the waterproof rib  312 , so that rainwater can be prevented from splashing into the air outlet  311  and entering the motor  32 . 
     The upper surface of the first annular groove  12  is also lower than the upper surface of the waterproof rib  312 , which can prevent water from entering the motor base  31  from the air outlet  311 . The bottom of the motor base  31  and the bottom wall  110  of the mounting groove  11  are fastened by screws which go through the receiving hole  111 . The first annular groove  12  is distributed around the periphery of the motor base  31 , in other words, the motor base  31  does not block the first annular groove  12 , so the rainwater flowing down from the top of the power head  3  will flow into the first annular groove  12  along the housing assembly  40  of the power head  3 , and finally drain out from the leakage hole  121  in the first annular groove  12 . 
     It should be noted that some air outlets  311  can be provided on the side wall of the motor base  31 . That is, at least two air outlets  311  can be provided. In the embodiment of the present invention, three air outlets  311  are provided to face three directions to let the wind out. Because the air outlet  311  is provided near the bottom of the motor base  31 , and the waterproof rib  312  and the housing component  40  are arranged up and down and have a certain height difference, rainwater will not splash into the air outlet  311 , and the water in the first annular groove  12  will not flow back into the motor base  31  from the air outlet  311 . 
     Since the air inlet  41  and the air outlet  311  of the power head  3  are located above the bottom shell of the lawn mower  100  and the bottom of the motor base  31  is sealed, when the bottom shell and blades of the lawn mower  100  are cleaned with a high-pressure water, the bottom shell can prevent the water from flowing into the motor  32 . 
     An air guide rib  313  is provided at the air outlet  311 , and the air guide rib  313  is deflected and the deflection direction is tangent to the rotation direction of the cooling airflow driven by the fan  33 , so that the airflow direction at the air outlet  311  is consistent with the rotation direction of the fan  33 . Preferably, when the rotation direction of the cooling airflow driven by the fan  33  is clockwise, the deflection direction of the air guide rib  313  is deflected to the left relative to the rotation direction of the cooling airflow. This design will greatly improve the exchange efficiency of the cold and heat air and can efficiently discharge the heat generated by the lawn mower  100  during work. 
     The waterproof rib  312  is formed between two adjacent air guide ribs  313 , and a first inclined slope  3120  inclining downward is formed at one side of the waterproof rib  312  away from the first annular groove  12 , and a second inclined slope  3121  inclining upward is formed at one side of the waterproof rib  312  close to the first annular groove  12 , which guides the airflow inside the motor  32  flowing out smoothly from the air outlet  311 . At the same time, the second inclined slope  3121  can also make the water splashed on the second inclined slope  3121  flow to the first annular groove  12 . 
     The motor  32  is provided with a motor shaft  321 , and the motor shaft  321  is connected to a working assembly (including a blade) of the lawn mower  100  to transmit power to the working assembly. The fan  33  is connected to the rotor of the motor  32 , so that when the motor  32  is started, the fan  33  can be driven to rotate. The external cooling air is brought in from the air inlet  41  during the rotation of the fan  33 . It flows along the air inlet cavity  42 , passes through the motor  32 , and finally flows out from the air outlet  311 . 
     A vent  341  is provided on the top of the air collecting cover  34 , and the cooling air enters the motor  32  through the vent  341 , thereby taking away the heat generated by the motor  32 . The air collecting cover  34  and the motor base  31  are connected and fixed by screws (not shown) to surround the motor  32  and the fan  33 . 
     A groove  314  is recessed on the inner side wall of the bottom of the motor base  31 , and the groove  314  is located below the motor  32 . An opening  3140  is provided at an end of the groove  314  near the air outlet  311 . The opening  3140  is used to drain water entering the groove  314 . That is, even if a small amount of accumulated water enters the inside of the motor base  31 , it will quickly flow to the bottom of the motor base  31  under the action of gravity and collect into the groove  314 , and finally the accumulated water is discharged from the opening  3140 . 
     The opening  3140  is designed as a dark window structure. The direction of the opening  3140  is parallel to the bottom surface of the motor base  31 , when the bottom of the motor base  31  is washed, water can&#39;t enter into the motor base  31 . 
     A perforation  315  and a second annular groove  316  are also provided at the middle of the bottom of the motor base  31 . The perforation  315  is provided at the center of the bottom of the motor base  31  to let the motor shaft  321  go through. The second annular groove  316  is provided at the outside of the perforation  315 . Two clamping walls  318  are respectively provided on the inner and outer sides of the second annular groove  316 . The height of the clamping wall  318  is slightly higher than the bottom surface of the motor base  31 . In other words, the two clamping walls  318  protrude beyond the bottom surface of the motor base  31 , and a second annular groove  316  is formed between the two clamping walls  318 . Four grooves  314  are provided, and they are evenly distributed on the periphery of the second annular groove  316 . 
     The motor  32  is located above the second annular groove  316 , and a wool felt  317  is accommodated in the second annular groove  316 . The height of the wool felt  317  is greater than the recessed depth of the second annular groove  316  (also can be understood as the height of the clamping wall  318 ), so the wool felt  317  will protrude from the second annular groove  316 , and the wool felt  317  will be pressed downward and outward during the installation of the motor  32  to deform the wool felt  317 . At this time, the wool felt  317  can be used to connect the motor  32  and the second annular groove  316  and seal the gap between the motor  32  and the second annular groove  316 . Of course, in other embodiment, the wool felt  317  can also be replaced with other elastic sealing materials, such as rubber rings. 
     The energy device is preferably a battery pack that supplies power to the motor  32  and other electronic components. The power head  3  is provided with a battery compartment  50  for accommodating a battery pack. The battery compartment  50  and the housing assembly  40  are respectively injection-molded and then assembled together, but it should not be limited to this. 
     The battery pack includes a plurality of cells. In this embodiment, the cells are arranged along the longitudinal direction of the battery pack. In other embodiment, the battery pack may have different shapes, and the cells may be arranged along other directions. Depending on the number and combination of cells, the battery pack can output different voltages. In this embodiment, the battery pack is an 80V battery pack. Of course, battery packs with other voltages are still within the protection scope of the present invention. In the present invention, the number of battery packs is at least two, and the two battery packs are arranged side by side along the lateral direction of the power head  3  and are both located in the battery compartment  50 . 
     As shown in  FIG. 9  to  FIG. 12  in combination with  FIG. 3  and  FIG. 4 , the housing assembly  40  includes a casing assembled with the motor base  31 . The casing includes a first casing  43  and a second casing  44  arranged left and right, an upper casing  45  covering the first casing  43  and the second casing  44 , and a flip cover  46  which can be turned relative to the upper casing  45 . Firstly, the first casing  43  and the second casing  44  are assembled with the motor base  31 , and then the upper casing  45  is fixed to the top of the first casing  43  and the second casing  44 . Finally, the flip cover  46  is assembled with the upper casing  45 . 
     The first casing  43  and the second casing  44  are fixed to each other, and a protruding rib  431  is provided on the first casing  43 . A receiving groove  441  is correspondingly recessed on the second casing  44 , and the protruding rib  431  is received in the receiving groove  441 , which not only enables the first casing  43  to be assembled and fixed with the second casing  44  but also seals the installation gap between the first casing  43  and the second casing  44 , which realizes a good stability installment and a good waterproof effect. 
     The top of the first casing  43  and the second casing  44  are provided with the air inlet  41  and the air inlet cavity  42 . Since the air inlet  41  on the first casing  43  and the air inlet  41  on the second casing  44  are arranged symmetrically with respect to the center line of the power head  3 , and the air inlet cavity  42  on the first casing  43  and the air inlet cavity  42  on the second casing  44  are also arranged symmetrically with respect to the center line of the power head  3 , the following description will take the air inlet  41  and the air inlet cavity  42  provided on the first casing  43  as an example for detailed description. 
     The air inlet  41  is disposed at the left rear of the first casing  43  and is inclined backward and downward, so that when the lawn mower  100  placed on the ground, the rainwater cannot enter the inside of the power head  3  from the air inlet  41 . The air inlet cavity  42  includes a first ramp  421  provided near the air inlet  41 , a second ramp  422  provided away from the air inlet  41 , and a guide piece  423  provided beside the first ramp  421  and the second ramp  422 . The first ramp  421 , the second ramp  422 , the guide piece  423 , and the inner side wall of the first casing  43  collectively surround the air inlet cavity  42  into a U-shaped structure with an upper opening. 
     The first ramp  421  goes downhill toward the air inlet  41 , and the second ramp  422  goes uphill toward the air inlet  41 . In this way, even if water droplets splash into the air inlet  41 , the water will still flow downward from the first ramp  421  and flow out from the air inlet  41 . When the upper casing  45  is mounted on the first casing  43  and the second casing  44 , the U-shaped air inlet cavity  42  and the upper casing  45  together form a sealed airflow passage  424  (see  FIG. 12  for details), and the airflow passage  424  extends from the rear end to the front end of the power head  3 . 
     In order to prevent other debris such as grass and dust from entering the inside of the power head  3 , a filter element (not shown) is provided in the air inlet cavity  42 . In this embodiment, the filter element is a sponge. In order to fix the sponge in the air inlet cavity  42 , a fixing bracket  411  is also provided at the air inlet  41  to fix the sponge. 
     The first casing  43  is provided with a first water-retaining portion  432 , the second casing  44  is provided with a second water-retaining portion  442 . The first water-retaining portion  432  and the second water-retaining portion  442  are connected to each other and located around the battery compartment  50 . When the upper casing  45  is mounted on the first casing  43  and the second casing  44 , the two water-retaining portions can fill the gap between the upper casing  45  and the first casing  43  and the second casing  44 . Therefore, rainwater will not infiltrate from the joints of the upper casing  45  and the first casing  43  and the second casing  44 . 
     The motor assembly  30  is housed in the rear portion of the first casing  43  and the second casing  44  and is covered by the rear end of the upper casing  45 . The battery compartment  50  is provided at the front portion of the first casing  43  and the second casing  44  to separate the motor assembly  30  and the battery pack. 
     The air inlet  41  and the air inlet cavity  42  are covered by the rear end of the upper casing  45 . The front end of the upper casing  45  is provided with a through hole  452  that matches the battery compartment  50  for the insertion and removal of the battery pack. The cell is inserted into the battery compartment  50  through the through hole  452 . The flip cover  46  covers the top of the through hole  452  and the battery compartment  50 , and the flip cover  46  can be opened and sealed with respect to the upper casing  45  so as to perform the plugging operation of the battery pack. 
     A third water-retaining portion  451  is provided at the position where the upper casing  45  is connected to the flip cover  46  to seal the gap between the upper casing  45  and the flip cover  46 , so that rainwater does not flow into the battery compartment  50  from the connection between the upper casing  45  and the flip cover  46 . Of course, the flip cover  46  itself can prevent rainwater or other liquids from entering the battery compartment  50 , and the third water-retaining portion  451  makes the waterproof effect better. The first water-retaining portion  432 , the second water-retaining portion  442 , and the third water-retaining portion  451  form a whole water-retaining portion surrounding the through hole  452  to protect the battery compartment  50  and prevent rainwater from entering the battery compartment  50 . 
     A holding cavity  47  is formed at the top and rear ends of the housing assembly  40 , and it is recessed from the bottom to top. The holding cavity  47  is formed at an end of the housing assembly  40  near the handle  2  and it is formed on the center line of the power head  3 . The holding cavity  47  can be used as a rear handle. The front handle  7  and the rear handle (holding cavity)  47  can be directly held by the left and right hands for carrying. The distance between the front and rear handles is designed to be shorter than the length of the arm, so that the arm is most comfortable with the force. In this way, the machine can be balanced, the labor-saving is for transportation, and the strength of the housing assembly  40  can be increased. 
     A first L-shaped cavity  471  is formed at the side of the first casing  43  near the second casing  44  and it is recessed from the bottom to the top, and the first L-shaped cavity  471  is provided near the top of the first casing  43 . A second L-shaped cavity  472  is at the side of the second casing  44  near the first casing  43  and it is recessed from the bottom to the top. The second L-shaped cavity  472  is disposed near the top of the second casing  44 . The holding cavity  47  is formed by combining the first L-shaped cavity  471  and the second L-shaped cavity  472 . 
     Preferably, the first L-shaped cavity  471  and the second L-shaped cavity  472  are symmetrically arranged left and right with respect to the center line of the power head  3 , and the first L-shaped cavity  471  and the second L-shaped cavity  472  are both with rounded corners to ensure grip comfort. The width of the holding cavity  47  is greater than 80 mm. In other words, the sum of the widths of the first L-shaped cavity  471  and the second L-shaped cavity  472  is greater than 80 mm. 
     The protruding rib  431  protrudes from an edge of the first L-shaped cavity  471  of the first casing  43 , and the receiving groove  441  is recessed from an edge of the second L-shaped cavity  472  of the second casing  44 . A fixing post  433  is provided on the top of the first casing  43  near the protruding rib  431 , and a fixing post  433  is also provided on the top of the second casing  44  near the receiving groove  441  side. One of fixing posts is a screw hole and the other is a screw-through hole, so that the first casing  43  and the second casing  44  can be fixed by screws through the two fixing posts  433 . 
     The fixing posts  433  are arranged inside the first casing  43  and the second casing  44 , which not only avoids the screws from being inserted from the outside and affects the waterproof effect of the power head  3 , but also the two fixing posts  433  are wrapped by the upper casing  45 , which makes the appearance of the power head  3  more beautiful. 
     The housing assembly  40  also includes a control board  48  located near the battery pack for controlling the motor. Two control boards  48  are provided to detect and control the self-propelled motor (not shown) and the main blade motor  32  respectively. One end of the air inlet cavity  42  is connected to the air inlet  41  and the other end extends to the corresponding control board  48  so as to guide the cooling air flow entering from the air inlet  41  to the control board  48 . 
     A cooling fin  481  is provided on the control board  48 , and the other end of the air inlet cavity  42  is disposed close to the cooling fin  481 . In other words, the air inlet cavity  42  is as close as possible to the cooling fin  481  to ensure that the cooling fin  481  is sufficiently cooled. Since two air inlets  41  and two air inlet cavity  42  are provided, two airflow passages are formed, and the control board  48  and the cooling fin  481  located at the left and right sides of the rear end of the battery compartment  50  can be cooled respectively. 
     The motor  32  is located below the control board  48 . When the motor  32  starts, the fan  33  rotates and drives the cooling airflow at the control board  48  into the motor  32 , so that the heat generated by the control board  48 , the motor  32 , and the battery pack is blown to the bottom of the motor base  31  and discharged from the air outlet  311 . 
     Cooling process is described as below. The motor  32  starts, the fan  33  rotates and generates suction. The external cooling air flows inside through the air inlet  41  and flows into the power head  3  along the air inlet cavity  42  under the action of suction of the fan  33 . The cooling air entering inside the power head  3  preferentially passes through the control board  48  and the cooling fin  481 , and then the cooling air flows down to the vent  341  of the air collecting cover  34  and enters the inside of the motor  32  from the vent  341 . Finally, the cooling air flows out from the air outlet  311  at the bottom of the motor base  31 . During the flow of the cooling airflow, the heat inside the battery pack, the control board  48  and the motor  32  will be taken away, so that the power head  3  can work at a relatively stable temperature. 
     In summary, the lawn mower  100  of the present invention prevents the water from entering the inside of the motor base  31  through the air outlet  311  when cleaning the bottom of the lawn mower  100  by arranging the motor base  31  with a sealed bottom and an air outlet  311  on the side. Combined with some waterproof structure design (such as waterproof rib  312 , first annular groove  12 , leakage hole  121 , groove  314 , opening  3140 , wool felt  317 , protruding rib  431 , receiving groove  441 , first water-retaining portion  432 , second water-retaining portion  442  and the third water-retaining portion  451 ) make the lawn mower  100  of the present invention have the best waterproof performance. 
     In addition, a holding cavity  47  is provided at the top and rear ends of the power head  3 , and the holding cavity  47  can be used as a rear handle. Therefore, when carrying the lawn mower  100 , it is not necessary to add additional handle parts, and it is sufficient to carry the handle  7  and the rear handle  47  using the front and left hands separately. 
     Furthermore, the air inlet  41  and the air inlet cavity  42  are provided at the top and rear ends of the power head  3  so that external cooling air can enter the power head  3  from the air inlet  41  and the air inlet cavity  42  and take away the heat generated by the battery pack, the control board  48  and the motor  32 , which makes the heat dissipation performance of the lawn mower  100  of the present invention better. 
     The above embodiment is only used to illustrate the technical solution of the present invention and is not limiting. Although the present invention has been described in detail with reference to the preferred embodiment, those skilled in the art should understand that the technical solution of the present invention may be modified or equivalently replaced without departing from the spirit and scope of the technical solution of the present invention.