Electric tool

Abstract

The present application relates to an electric tool comprising: a drive motor (30); a motor housing (12) including a housing body (32) having a rear end engaging portion (52) and an expansion portion (34) extending rearward from the housing body (32); a rear cover (16) comprising a cover body (62) and a rear end portion (64), the cover body (62) comprising a front end portion (17), the rear end portion (64) having an opening (65); and an end cap (18) including a cap body (66) and a protrusion (68) and configured to pass the protrusion (68) through the opening (65) to be fastened to the extension (34) of the motor housing (12), the front end portion (17) of the rear cap (16) being configured to engage around the rear end engagement portion (52) of the housing body (32) and having a gap (G) between opposing surfaces of the front end portion (17) and the rear end engagement portion (52) in the longitudinal direction (L).

Description

Technical Field

[0001] The present application relates to an electric tool. Background Art

[0002] Power tools including drive motors are very common in industrial applications. Operators hold the power tools in their hands to operate workpieces. During operation, the operation of the power tool drive motor generates vibrations, the moving parts in the power tool generate vibrations during movement, and the power tool also generates these vibrations when it acts on the workpiece. These vibrations make the operator's hand holding the power tool housing very uncomfortable.

[0003] For example, straight grinders are widely used in many fields. They use motors to drive grinding wheels (such as nylon wheels, blade wheels, grinding wheels, polishing wheels, etc.) to rotate at high speed to process molds, fixtures, or complex parts that are not easy to process on grinders or special equipment. When equipped with diamond grinding wheels, straight grinders are also suitable for grinding metal parts and removing burrs.

[0004] Structurally, the straight grinder includes a main handle suitable for an operator to hold and operate, and an auxiliary handle attached to the front end of the main handle and suitable for mounting the grinding wheel. The main handle includes a motor housing accommodating a drive motor, a rear cover accommodating control electronics (e.g., PCB) of the straight grinder and a motor switch of the drive motor, and an end cover mounted to the rear cover. The rear cover is longitudinally sandwiched between the end cover and the motor housing by fastening the end cover to a mounting post extending from the motor housing into the rear cover with screws.

[0005] When the straight grinder is in operation, the vibration generated by the grinding wheel grinding the workpiece, the vibration generated by the operation of the drive motor, and the vibration generated by other moving parts in the straight grinder are first transmitted backward to the end cover through the bolt connection between the motor housing and the end cover. Then, the end cover squeezes the back cover longitudinally forward to the motor housing, thus forming a longitudinal rigid connection between the three and transmitting the vibration longitudinally forward again to the motor housing. The front end excitation of the straight grinder is transmitted to the motor housing in this way, which increases the vibration value on the motor housing or the operator's grip area, and reduces the comfort and experience of the operator operating the straight grinder. Summary of the invention

[0006] The purpose of the present application is to reduce the vibration on the housing by improving the housing structure of the electric tool.

[0007] This object is achieved by the electric tool of the present application. The electric tool comprises: a driving motor, which comprises a motor output shaft extending in the longitudinal direction; a motor housing, which comprises: a housing body extending around the driving motor and comprising a rear end joint; and an extension extending rearward from the housing body; a rear cover, which comprises a cover body extending around the extension and a rear end extending radially inward from the rear end of the cover body, the cover body comprising a front end, the rear end having an opening; and an end cover, which comprises a cover body and a protrusion, and is configured to allow the protrusion to pass through the opening to be fastened to the extension of the motor housing, wherein the front end of the rear cover is configured to engage around the rear end joint of the housing body and there is a gap between the opposing surfaces of the front end and the rear end joint in the longitudinal direction.

[0008] In one embodiment, the electric power tool further includes a spacer which is sandwiched between the protruding portion of the end cover in a longitudinal direction when the protruding portion of the end cover is fastened to the extended portion of the motor housing.

[0009] In one embodiment, the spacer is a flat member made of a hard material or an elastic material.

[0010] In one embodiment, the protruding portion of the end cap includes a groove configured to receive the spacer and an end portion of the extension portion when the protruding portion of the end cap is secured to the extension portion of the motor housing.

[0011] In one embodiment, the end cap includes a through-going through hole allowing a fastener to pass therethrough to fasten the end cap to the extended portion of the motor housing, and the groove is an end section of the through-going through hole having an increased inner diameter.

[0012] In one embodiment, the rear cover includes a positioning surface configured to abut against an opposing surface of the extended portion in a longitudinal direction when the protruding portion of the end cover is fastened to the extended portion of the motor housing.

[0013] In one embodiment, the back cover includes at least one of the following, and the positioning surface is provided by one of the at least one: a convex rib extending inward from the cover body in the longitudinal direction to provide insulation or attachment or guiding function; a reinforcing rib extending inward from the cover body and / or the rear end of the back cover to enhance the strength of the back cover; and a protrusion extending inward from the cover body and / or the rear end of the back cover to provide the positioning surface.

[0014] In one embodiment, the cover body of the end cover defines a channel for passing the power cord, the rear end of the rear cover includes a thickened portion defining a portion of the channel, and the positioning surface is provided by a protrusion extending from the vicinity of the thickened portion.

[0015] In one embodiment, the electric tool also includes a bearing for rotatably supporting the rear end portion of the motor output shaft, and a bearing sleeve arranged around the outer ring of the bearing, and there is a gap between the outer peripheral surface of the bearing sleeve and the inner peripheral surface of the bearing hole formed in the motor housing for receiving the bearing.

[0016] In one embodiment, the power tool is a straight grinder or an angle grinder.

[0017] The power tool of the present application, the main handle includes a motor housing, a rear cover and an end cover, the three together define and contain and enclose a drive assembly consisting of a drive motor and a control electrical device, wherein the end cover is mounted to the rear cover and the protrusion of the end cover is fastened to the extension of the motor housing through an opening formed on the rear cover. Advantageously, a longitudinal gap is formed between the cover body of the rear cover and the housing body of the motor housing. This effectively disconnects the path of the vibration transmitted from the motor housing to the end cover backwards and then transmitted back to the motor housing forward again, reduces the vibration on the motor housing, and improves the user's experience and comfort when operating the straight grinder. Optionally, the rear cover can be slightly moved in the longitudinal direction between the end cover and the motor housing. A specific example of forming the above-mentioned minimum gap is to separate the protrusion of the end cover and the extension of the motor housing in the longitudinal direction by a spacer. More advantageously, in order to accurately control this longitudinal gap, the rear cover is formed with a protrusion protruding inward from the cover body and / or the rear end to provide a positioning surface that abuts against the motor housing longitudinally when the end cover is fastened in place. The position of the protrusion or positioning surface is relatively easy to control during the manufacturing process, so by properly designing the position of the positioning surface, the size of the above-mentioned gap can be accurately controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other features and advantages of the present application are described in detail with reference to the accompanying drawings, so that those skilled in the art can more easily understand the present application. It should be noted that the drawings are only for illustrative purposes and are not drawn to scale. It should also be noted that the drawings are only used to illustrate and explain the inventive points of the present application and do not illustrate the entire structure. Therefore, the components shown in the drawings do not necessarily exist in all embodiments of the present application, and the components not shown in the drawings may be included in certain embodiments of the present application.

[0019] Figure 1 It is a three-dimensional diagram of the straight grinder of the present application.

[0020] Figure 2 It is a part of a longitudinal sectional view of a longitudinal section passing through the central axis of the motor output shaft of the driving motor of the straight grinder.

[0021] Figure 3 For Figure 2 A view with some internal components removed, such as the electrical components and some parts of the drive motor.

[0022] Figure 4 yes Figure 3 Magnified view of area A in FIG.

[0023] Figure 5 It is a three-dimensional view of the end cover of the straight grinder.

[0024] Figure 6 and 7 They are the rear view and stereogram of the rear cover of the straight grinder. DETAILED DESCRIPTION

[0025] The principle of the present application is described in detail below with reference to the accompanying drawings, taking a straight grinder as an example. Those skilled in the art should understand that the present application is not only applicable to straight grinders, but also to any other electric tools including angle grinders.

[0026] Figure 1 2 is a perspective view of the overall structure of a straight grinder 100 as an example of an electric tool. In general, the straight grinder 100 includes a main handle 10 and an auxiliary handle 20, which are connected together by a connecting portion 25. The main handle 10 is used as a portion for an operator to grasp when operating the straight grinder to perform processing operations on a workpiece, and includes a motor housing 12, a drive motor 30 surrounded by the motor housing 12, a rear cover 16, electrical components surrounded by the rear cover 16, and an end cover 18 mounted to the rear cover 16, wherein the motor housing 12, the rear cover 16 and the end cover 18 can each be a housing portion made of plastic, and the three together constitute an entire housing that encloses a drive assembly consisting of the above-mentioned drive motor 30 and the above-mentioned electrical components. At the motor output shaft 15 ( Figure 2 ), the auxiliary handle 20 is attached to the main handle 10 from the front, and the end cover 18 of the main handle 10 is mounted to the rear cover 16 from the rear, for supplying power from an external power source (socket) to a power cord 29 ( Figure 2 ) extends from the straight grinder 100 through the end cap 18, Figure 1 Only the protective cover 26 mounted on the end cover 18 is shown for passing the power cord 29 and providing protection therefor. The transmission shaft 35 passes through the auxiliary housing 22 of the auxiliary handle 20 and is longitudinally connected to the motor output shaft 15, for example, via a coupling, and the front end of the transmission shaft 35 is mounted with a chuck 23 for attaching a grinding wheel (disc grinding wheel, not shown) of a straight grinder.

[0027] In the present application, the term "longitudinal direction" indicating direction can be understood with reference to the drawings and the above related description, and "front" and "rear" are opposite directions in the longitudinal direction L. When the placement orientation of the straight grinder is changed, the understanding of the directional terms should also change accordingly.

[0028] Figure 2FIG. 1 shows a portion of a longitudinal section of a straight grinder 100 along a longitudinal direction L. Figure 3 For Figure 2 A view with some internal parts removed. Figure 2 and 3 The motor housing 12 includes a cylindrical housing body 32 extending around the drive motor 30 and an extension portion 34 extending rearward from the housing body 32 in the longitudinal direction L. The extension portion 34 is offset radially inward from the housing body 32 in a radial direction perpendicular to the longitudinal direction L or extends radially inwardly obliquely while extending rearward in the longitudinal direction L. The extension portion 34 may be referred to as an extension support portion, and is used to attach or fix electrical components for control of the drive motor 30 or for operation control of the straight grinder 100. In some embodiments, the housing body 32 and the extension portion 34 of the motor housing 12 may be integrally formed, or in some embodiments, the two may be separately formed and attached together.

[0029] The drive motor 30 can be any type of drive motor known in the art. Figure 2 1 shows some parts of the drive motor 30: the motor output shaft 15, the commutator 13 arranged at the rear end of the motor output shaft 15, the carbon brush 19 that slides in contact with the outer peripheral surface of the commutator 13 to provide current, etc., the armature that is accommodated in the housing body 32 and rotates together with the motor output shaft 15 and the stator that is fixed to the housing body 32 are not shown. The front end of the motor output shaft 15 is supported by the first bearing (not shown) on the front side, and the rear end is supported by the second bearing 36 on the rear side in the bearing hole 42 formed in the extension part 34 of the motor housing 12, so that the motor output shaft 15 can rotate. A bearing bushing 38 is arranged radially outside the second bearing 36. The bearing bushing 38 is designed to have a size that is tightly fitted on the bearing outer ring of the second bearing 36 and has a gap between its outer peripheral surface and the inner peripheral surface of the motor housing 12 that defines the bearing hole 42. Compared with the structure in the prior art in which the outer peripheral surface of the bearing bushing forms a tight fit with the inner peripheral surface of the bearing hole of the motor housing, the installation and removal of the bearing bushing 38 are easier.

[0030] The housing body 32 of the motor housing 12 includes a rear end engaging portion 52 configured to engage with the rear cover 16. Specifically, the rear end engaging portion 52 is a rear end annular portion of the housing body 32 with a reduced outer diameter to form a stepped surface 31 ( Figure 4 The rear cover 16 is generally configured to surround or enclose the extension 34 of the motor housing 12 and the electrical components supported thereon, and includes a front end portion 17 at the front end, the front end portion 17 being configured to fit over the rear end engagement portion 52 of the housing body 32 so that a gap G is provided between the end surface 33 (of the front end portion 17) of the rear cover 16 and the stepped surface 31 of the rear end engagement portion 52 in the longitudinal direction L (see the enlarged view). Figure 4). Optionally, the rear cover 16 is further designed to have a clearance fit or an overfit between the front end portion 17 of the rear cover 16 and the rear end joint 52 in a radial direction perpendicular to the longitudinal direction L. In the illustrated embodiment, but not necessarily, the outer diameter of the rear cover 16 is larger than the outer diameter of the housing body 32 and the outer diameter of the front end portion 17 is tapered to the outer diameter of the housing body 32 to provide a smooth transition outer profile of the main handle 10. The inner circumferential surface of the front end portion 17 of the rear cover 16 and the outer circumferential surface of the rear end joint 52 of the motor housing 12 may include features that cooperate with each other to prevent the two from rotating relative to each other around the longitudinal direction L, such as concave and convex fitting features, Figure 7 2 shows the concave-convex features 27 on the inner circumferential surface of the front end portion 17 of the rear cover 16.

[0031] Figure 2 Also shown in the figure are electrical components attached to the extension 34 of the motor housing 12 within the rear cover 16, including electrical components for controlling the drive motor 30, and electrical components for controlling the operation of the straight grinder 100. For example, Figure 2 It can be seen that: a circuit board or PCB board 41 for mounting various electrical components for controlling the operation of the straight grinder 100, a control knob 43, a motor switch 47 connected to a trigger (not shown) provided at the front of the motor housing 12 via a pull rod (not shown) so as to establish or disconnect an electrical connection between the drive motor 30 and the power cord 29 when the trigger is triggered, etc. Under the condition of being able to provide this supporting function, the extension portion 34 can have any appropriate mechanical structure, such as a plate-shaped portion, a shell-shaped portion, a columnar portion or any other irregular structure, etc.

[0032] The rear cover 16 includes a cylindrical cover body 62 extending in the longitudinal direction L and a rear end portion 64 extending radially inward from the rear end of the cover body 62, the rear end portion 64 having a through opening 65 and a periphery 67 defining the through opening 65, and the end cover 18 of the main handle 10 is mounted to the opening 65 on the rear end portion 64 of the rear cover 16. Optionally, but not necessarily, as shown, the power cord 29 also extends out of the straight grinder 100 through the same opening 65.

[0033] The extension 34 of the motor housing 12 includes a mounting rear end 50. Specifically, in combination with Figure 5 , the end cover 18 includes a cover body 66 and a protrusion 68 extending from the cover body 66. When the end cover 18 is mounted to the opening 65 on the rear end portion 64 of the rear cover 16, the protrusion 68 is fixed to the mounting rear end 50 of the extension 34 of the motor housing 12, and a portion of the cover body 66 is pushed against a portion of the periphery 67 defining the through opening 65 in the longitudinal direction L ( Figure 6 denoted by reference numeral 69).

[0034] As described above, there is a gap G between the end surface 33 of the front end portion 17 of the rear cover 16 and the step surface 31 of the rear end joint portion 52 of the motor housing 12 in the longitudinal direction L. During the operation of the straight grinder 100, this cuts off the transmission path of the vibration transmitted from the drive assembly (specifically, from the motor output shaft 15 of the drive motor 30) to the motor housing 12, and then transmitted backward from the installation rear end 50 of the expansion portion 34 of the motor housing 12 to the end cover 18 along the longitudinal direction L, and then transmitted from the rear cover 16 back to the motor housing 12 at the longitudinal joint between the front end portion 17 of the rear cover 16 and the rear end joint portion 52 of the motor housing 12. Therefore, the vibration on the motor housing 12 is greatly reduced, providing a high operator experience. Optionally, the rear cover 16 may have micro-motion in the longitudinal direction L between the end cover 18 and the motor housing 12.

[0035] In the specific embodiment shown in the figure, when the end cover 18 is installed and fastened to the rear end 50 of the motor housing 12, a spacer 60 is sandwiched between the end cover 18 and the motor housing 12, specifically, between the protruding portion 68 of the end cover 18 and the opposing surface of the rear end 50 of the motor housing 12. That is, the spacer 60 is clamped between the end cover 18 and the motor housing 12 to separate the end cover 18 from the motor housing 12. Due to the provision of the spacer 60, the position of the end cover 18 is offset backwards while the structure and size of other components remain unchanged, so that the structure in which the front end portion 17 of the rear cover 16 and the rear end joint portion 52 of the motor housing 12 are directly and rigidly abutted in the longitudinal direction L is changed to no longer being in rigid contact between the two and the above-mentioned gap G is generated. The above-mentioned gap G is related to the thickness of the spacer 60. The greater the thickness of the spacer 60, the greater the above-mentioned gap G.

[0036] In the case of being able to provide the above-mentioned spacing function, it can be imagined by those skilled in the art that the spacer 60 can be made of any suitable material. In one embodiment, the spacer 60 can be a flat gasket made of a hard material such as hard plastic or a soft material such as an elastic material. Compared with hard materials, the use of soft materials to form the spacer 60 can provide better vibration absorption function, reduce the vibration transmitted backward from the installation rear end 50 of the motor housing 12 to the end cover 18, and the straight grinder can obtain a better vibration reduction effect. The spacer 60 can have any suitable external shape, such as a circle. Of course, any other shape is also possible.

[0037] In the illustrated straight grinder example, the fastening of the end cap 18 to the rear mounting end 50 of the motor housing 12 can be achieved by any means known in the art, such as by fasteners such as screws. The end cap 18 has a through-hole 72, and accordingly, the rear mounting end 50 of the motor housing 12 can have a threaded hole 74, and a screw 76 extends through the through-hole 72 and through the hole on the spacer 60 to be threadedly fastened into the threaded hole 74. The through-hole 72 can be unthreaded. The threaded hole 74 can be a blind hole configured to terminate in the extension 34 (or the rear mounting end 50) as shown, and optionally, the threaded hole 74 can extend through the extension 34.

[0038] Further, the rear end 50 of the extension 34 of the motor housing 12 may be formed as a cylindrical section or include a cylindrical end 82, which is configured to be partially received in the receiving groove 78 of the protrusion 68 when fastened together with the protrusion 68 of the end cap 18. The spacer 60 is also disposed in the receiving groove 78. As shown, the receiving groove 78 is provided by a front end section with an increased inner diameter through the through hole 72. Inserting the cylindrical end 82 of the rear end 50 into the receiving groove 78 of the protrusion 68 of the end cap 18 plays a guiding role when fastening the protrusion 68 of the end cap 18 to the rear end 50 of the motor housing 12, which is conducive to the alignment of the two in the longitudinal direction L, thereby facilitating the execution of the fastening operation. In some embodiments, the cross-section of the receiving groove 78 and the end 82 perpendicular to the longitudinal direction L may not be circular.

[0039] Figure 5 It is a parts diagram of the end cover 18. Figure 6 and Figure 7 The end cap 18 has a generally rectangular outer contour. Figure 6 As shown, the defined opening 65 of the rear cover 16 and its periphery 67 also have a substantially rectangular outer contour, and two side portions 69 of the periphery 67 symmetrical with respect to the longitudinal section passing through the central axis of the motor output shaft 15 are portions that overlap with the cover body 66 of the end cover 18 in the longitudinal direction L when the end cover 18 is mounted to the opening 65. The passage through which the power cord 29 extends partially passes through the notch 61 ( Figure 5 ) is defined in part by the rear end portion 64 of the rear cover 16 and may be provided as part of the opening 65 as shown or may be provided independently of the opening 65. The ribs 63 are respectively connected to the cover body 66 and the protrusion 68 of the end cover 18 for increasing strength.

[0040] Refer to Figure 7, the rear cover 16 includes an inwardly extending protrusion 92, the protrusion 92 defining a positioning surface 94 facing forward or toward the front end portion 17, the positioning surface 94 being configured to abut against an opposing surface of the extended portion 34 of the motor housing 12 when the end cover 18 is fastened to the mounting rear end 50 of the extended portion 34 of the motor housing 12. When the end cover 18 is fastened to the mounting rear end 50 of the motor housing 12 using the screw 76, the cover body 66 of the end cover 18 abuts against the side portion 69 of the periphery 67 of the rear end portion 64 of the rear cover 16 to push the rear cover 16 forward in the longitudinal direction L until the positioning surface 94 of the protrusion 92 abuts against the opposing surface of the extended portion 34 of the motor housing 12. At this time, the screw 76 is fastened in place, and the value of the longitudinal gap G between the end surface 33 of the front end portion 17 of the rear cover 16 and the step surface 31 of the rear end joint portion 52 of the motor housing 12 no longer changes. Therefore, by properly designing the positioning surface 94 of the protrusion 92, the size of the longitudinal gap G can be accurately controlled, especially when the spacer 60 is made of a soft material.

[0041] The technicians of the present application should understand that the position where the protrusion 92 protrudes from the rear cover 16 can be changed while being able to achieve the above functions. The protrusion 92 can protrude radially inward from the cover body 62 of the rear cover 16, or protrude longitudinally forward from the rear end 64, or protrude inward from the connecting corner of the cover body 62 and the rear end 64. In the illustrated structure, the protrusion 92 extends longitudinally forward from the rear end 64 of the rear cover 16, specifically extending from the vicinity of the thickened portion 81 that defines a portion of the power cord channel. The protrusion 92 can be in the form of a rib or a strip, can be in the form of a solid protrusion or a hollow shell, or in any other structural form. Only one protrusion 92 can be provided, or two (such as Figure 7 The shape, size and specific arrangement of the protrusions 92 are also not limited.

[0042] exist Figure 6 and 7 Also shown in the figure are formed on the rear cover 16: an opening 87 for exposing the operation button 43 for operation by the operator, a heat dissipation hole 91 for allowing external air to enter to cool the internal electrical components and the drive motor 30, one or more convex ribs 93 extending inwardly from the cover body 62 in the longitudinal direction L for attachment, insulation or installation guide, and reinforcing ribs 95 extending inwardly from the cover body 62 and / or the rear end 64 to strengthen the strength of the rear cover 16. In the case where the above functions can be achieved, the specific structure, number and arrangement of the heat dissipation hole 91, the convex rib 93 and the reinforcing rib 95 can be changed as needed. In some embodiments, in the case where all the above functions can be provided, one or more of the convex rib 93, the reinforcing rib 95 and the protrusion 92 can be omitted. In some embodiments, the positioning surface 94 can be provided by the reinforcing rib 95, the convex rib 93 or any other protrusion protruding inwardly from the rear cover 16.

[0043] The principle of the present application is described in detail above with respect to the illustrated straight grinder example. The present application provides a gap in the longitudinal direction L between the front end of the cover body of the rear cover of the main handle and the rear end joint of the housing body of the motor housing to avoid direct rigid abutment between the two, effectively disconnecting the path of the vibration transmitted backward to the end cover and transmitted forward again to the motor housing via the rear cover, reducing the vibration on the motor housing, and improving the user's experience and comfort when operating the straight grinder. One way to achieve this purpose is to provide a spacer between the end cover of the main handle and the extended portion of the motor housing that are fastened together. Optionally, the rear cover can be slightly moved in the longitudinal direction between the end cover and the motor housing. Further, in order to accurately control the longitudinal gap between the cover body of the rear cover and the housing body of the motor housing, the rear cover includes a positioning surface that longitudinally abuts the corresponding surface of the extended portion of the motor housing when the end cover is fastened in place. The position of the positioning surface is relatively easy to control, and the size of the above-mentioned gap can be accurately controlled by reasonably designing the position of the positioning surface that is longitudinally engaged with the motor housing.

[0044] Although this article describes an electric straight grinder as an example, it is obvious that the present invention is also applicable to any other electric tool whose main handle is composed of a motor housing, a rear cover and an end cover and generates vibration during operation, such as an angle grinder. Although this article describes only the exemplary structure shown in the figure, a person of ordinary skill in the art can make several modifications and improvements after reading this article without departing from the principles of this application, and these modifications and improvements fall within the scope of protection of this application. The scope of protection of this application is limited only by the attached claims.

Claims

1. An electric tool comprising: a drive motor (30) comprising a motor output shaft (15) extending in a longitudinal direction (L); A motor housing (12) comprising: a housing body (32) extending around the drive motor (30) and comprising a rear end joint (52); and an expansion portion (34) extending rearward from the housing body (32); a rear cover (16) comprising a cover body (62) extending around the expansion portion (34) and a rear end portion (64) extending radially inward from the rear end of the cover body, wherein the cover body (62) comprises a front end portion (17), and the rear end portion (64) has an opening (65); and an end cover (18) comprising a cover body (66) and a protrusion (68), and configured so that the protrusion (68) passes through the opening (65) to be fastened to the extension (34) of the motor housing (12), The front end portion (17) of the rear cover (16) is configured to engage around a rear end engaging portion (52) of the shell body (32) and a gap (G) exists between relative surfaces of the front end portion (17) and the rear end engaging portion (52) in the longitudinal direction (L).

2. The electric tool according to claim 1, further comprising a spacer (60) which is sandwiched between the protruding portion (68) of the end cover (18) in the longitudinal direction when the protruding portion (68) is fastened to the extended portion (34) of the motor housing.

3. The electric tool according to claim 2, wherein: The spacer (60) is a flat member made of a hard material or an elastic material.

4. The electric tool according to claim 3, wherein: The projection (68) of the end cap (18) includes a groove (78) configured to receive the spacer (60) and an end portion of the extension (34) when the projection (68) of the end cap (18) is secured to the extension (34) of the motor housing.

5. The electric tool according to claim 4, wherein: The end cap (18) includes a through hole (72) that allows a fastener (76) to pass through to fasten the end cap (18) to the expanded portion (34) of the motor housing (12), and the groove (78) is an end section of the through hole (72) with an increased inner diameter.

6. The electric tool according to any one of claims 1 to 5, wherein: The rear cover (16) includes a locating surface (94) configured to abut an opposing surface of the extension (34) in a longitudinal direction (L) when the protrusion (68) of the end cover (18) is secured to the extension (34) of the motor housing.

7. The electric tool according to claim 6, wherein: The rear cover (16) includes at least one of the following, and the positioning surface (94) is provided by one of the at least one: A rib portion (93) extending inwardly from the cover body (62) in the longitudinal direction (L) for providing insulation or attachment or guiding functions; A reinforcing rib (95) extending inward from the cover body (62) and / or the rear end portion (64) of the rear cover (16) to enhance the strength of the rear cover (16); and A protrusion (92) extends inwardly from the cover body (62) and / or the rear end (64) of the rear cover (16) to provide the positioning surface (94).

8. The electric tool according to claim 6, wherein: The cover body (66) of the end cover (18) defines a channel for a power cord to pass through, the rear end portion (64) of the rear cover (16) includes a thickened portion (81) defining a portion of the channel, and the positioning surface (94) is provided by a protrusion (92) extending from near the thickened portion.

9. The electric tool according to any one of claims 1 to 8 further includes a bearing (36) for rotatably supporting the rear end portion of the motor output shaft (15), and a bearing sleeve (38) arranged around the outer ring of the bearing, and there is a gap between the outer peripheral surface of the bearing sleeve (38) and the inner peripheral surface of the bearing hole (42) formed in the motor housing (12) for receiving the bearing (36).

10. The electric tool according to any one of claims 1 to 9, wherein: The electric tool is a straight grinder or an angle grinder.

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