Open type motor

Abstract

The utility model discloses an open type motor, comprising a housing, a through hole penetrating through two ends of the housing is arranged in the housing, and a plurality of positioning grooves are arranged on the inner side wall of one end, close to the housing, in the through hole; the outer side wall of the rubber cover is provided with positioning protrusions corresponding to the positioning grooves, the positioning protrusions are installed in the positioning grooves so that the rubber cover can be fixedly connected with the shell, and the rubber cover is further provided with a plurality of ventilation holes and an installation hole located in the center of the rubber cover. The electric brush assembly comprises a carbon brush plate and a carbon brush, the carbon brush plate is fixedly installed on the rubber cover, a fixing piece is arranged on the carbon brush plate, a fixing hole penetrating through the two ends of the fixing piece is formed in the fixing piece, and the carbon brush penetrates through one end of the fixing hole, extends out of the other end of the fixing hole and then faces the installation hole. By adopting the design of an axial installation mode, the occupied space of the motor in a product can be reduced, the motor is simpler to assemble, and the motor has a mistake-proof structural design, the performance of the motor is more stable, and the production efficiency is higher.

Description

Technical Field

[0001] This utility model relates to the field of motors, and in particular to an open-type motor. Background Technology

[0002] A brushed motor is a rotary electric motor that contains brushes to convert electrical energy into mechanical energy or vice versa. Unlike brushless motors, brushes are used to introduce or extract voltage and current. Brushed motors are the foundation of all motors, characterized by rapid starting, timely braking, smooth speed adjustment over a wide range, and relatively simple control circuitry. Many devices and electrical appliances now use brushed motors, especially DC brushed motors, which are more widely used.

[0003] However, existing DC brushed motors are large in size, and the radial assembly of the housing makes the housing bulky and the installation process complicated, which is not conducive to use. Utility Model Content

[0004] The purpose of this invention is to solve the problems of existing brushed motors, which are bulky and use a radially assembled housing, resulting in a large housing volume, complex installation process, and inconvenience in use. This invention provides an open-type motor, which reduces the space occupied by the motor in the product, simplifies motor assembly, has a fault-proof structural design, more stable motor performance, and higher production efficiency.

[0005] To solve the above-mentioned technical problems, an embodiment of this utility model discloses an open-type motor, comprising:

[0006] The outer shell has through holes extending through both ends, and multiple positioning grooves are formed on the inner sidewall of the through holes near one end of the outer shell.

[0007] The rubber cap has a positioning protrusion on its outer side wall that corresponds to the positioning groove. The positioning protrusion is installed in the positioning groove to fix the rubber cap to the outer shell. The rubber cap also has multiple ventilation holes and an installation hole located in the center of the rubber cap.

[0008] The brush assembly includes a carbon brush plate and a carbon brush. The carbon brush plate is fixedly mounted on a rubber cover. A fixing member is provided on the carbon brush plate. The fixing member has a fixing hole that passes through both ends. The carbon brush passes through one end of the fixing hole and extends out of the other end of the fixing hole and is positioned towards the mounting hole.

[0009] The rotor is disposed in the through hole. The rotor includes a first shaft and a commutator. The first shaft part passes through and extends out of the mounting hole. The commutator is sleeved on the first shaft and disposed close to the mounting hole. The carbon brush abuts against the commutator.

[0010] Multiple magnets are installed in the through hole and assembled into a ring. The magnets and the outer shell form the stator; the first rotating shaft passes through the magnets.

[0011] By adopting the above technical solutions, the space occupied by the motor in the product can be reduced, the motor assembly can be simplified, it has a fault-proof structural design, the motor performance is more stable, and the production efficiency is higher.

[0012] According to another specific embodiment of the present invention, the embodiment discloses that the rubber cover is provided with a protrusion, and a torsion spring is sleeved on the protrusion, with the two ends of the torsion spring respectively abutting against the rubber cover and the end of the carbon brush away from the commutator.

[0013] According to another specific embodiment of the present invention, the embodiment of the present invention discloses that the outer shell includes an arc-shaped first shell and a second shell, the first shell and the second shell forming a cylindrical shell with openings at both ends.

[0014] According to another specific embodiment of the present invention, the embodiment of the present invention also includes a front end cover, the outer side wall of the front end cover is provided with a first threaded hole, the outer shell is provided with a corresponding second threaded hole, and the front end cover and the outer shell are fixedly connected by bolts.

[0015] According to another specific embodiment of the present invention, a bearing is provided at the center of the front cover, and one end of the first rotating shaft extending out of the mounting hole is installed in the bearing and rotatably connected to the bearing.

[0016] According to another specific embodiment of the present invention, the embodiment of the present invention further includes a gear disk disposed in the through hole, the gear disk being rotatably connected to the other end of the first rotating shaft, and the outer side wall of the gear disk abutting against the inner side wall of the through hole.

[0017] According to another specific embodiment of the present invention, an air duct is provided on the inner sidewall of the through hole, and the air duct is located at the contact point between the gear disk and the through hole.

[0018] According to another specific embodiment of the present invention, the embodiment of the present invention further includes a moving impeller, and a second rotating shaft is provided inside the moving impeller. The second rotating shaft is rotatably connected to a gear disk and is driven to rotate by the gear disk.

[0019] According to another specific embodiment of the present invention, the embodiment of the present invention discloses that along the extension direction of the first rotating shaft, a first axial flow fan, a rotor core and a second axial flow fan are sequentially installed on the first rotating shaft, a stator winding is wound on the stator core, and a channel is opened through both ends of the stator core. The first rotating shaft passes through the annular structure composed of magnets and places the rotor core inside the annular structure composed of magnets.

[0020] According to another specific embodiment of the present invention, the embodiment of the present invention discloses that there are two brush assemblies, which are symmetrically arranged on the rubber cover.

[0021] The beneficial effects of this utility model are as follows: by adopting the axial installation method, the space occupied by the motor in the product can be reduced, the motor assembly is simpler, it has a fault-proof structural design, the motor performance is more stable, and the production efficiency is higher. Attached Figure Description

[0022] Figure 1 This diagram shows a structural schematic of the housing of an open-type motor according to an embodiment of the present invention;

[0023] Figure 2 This diagram illustrates the structure of an open-type motor according to an embodiment of the present invention. Figure 1 ;

[0024] Figure 3 This diagram illustrates the structure of an open-type motor according to an embodiment of the present invention. Figure 2 ;

[0025] Figure 4 Show Figure 3 Enlarged view of point A in the middle;

[0026] Figure 5 This diagram illustrates the structure of an open-type motor according to an embodiment of the present invention. Figure 3 ;

[0027] Figure 6 This diagram illustrates the structure of an open-type motor according to an embodiment of the present invention. Figure 4 .

[0028] Reference numerals: 1. Outer shell; 2. Rubber cover; 21. Mounting hole; 22. Ventilation hole; 23. Positioning protrusion; 24. Protrusion; 25. Torsion spring; 26. Lead wire; 3. Rotor; 3. First shaft; 31. Commutator; 32. First axial fan; 33. Rotor core; 34. Second axial fan; 35. Brush assembly; 41. Carbon brush plate; 42. Fixing piece; 43. Carbon brush; 5. Stator; 51. Magnet; 6. Front cover; 61. Bearing; 7. Gear disk; 71. Gear set; 8. Moving impeller; 81. Second shaft; 9. Impeller cover. Detailed Implementation

[0029] The following specific embodiments illustrate the implementation of this utility model. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. Although the description of this utility model will be presented in conjunction with preferred embodiments, this does not mean that the features of this utility model are limited to this embodiment. On the contrary, the purpose of describing the utility model in conjunction with the embodiments is to cover other options or modifications that may be derived based on the claims of this utility model. To provide a deep understanding of this utility model, many specific details will be included in the following description. This utility model may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of this utility model, some specific details will be omitted in the description. It should be noted that, without conflict, the embodiments and features in the embodiments of this utility model can be combined with each other.

[0030] It should be noted that in this specification, similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] In the description of this embodiment, it should be noted that the terms "upper", "lower", "inner", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship that the utility model product is usually placed in during use. They are only for the convenience of describing the utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the utility model.

[0032] The terms “first”, “second”, etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0033] In the description of this embodiment, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set up," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this embodiment based on the specific circumstances.

[0034] To make the objectives, technical solutions, and advantages of this utility model clearer, the embodiments of this utility model will be described in further detail below with reference to the accompanying drawings.

[0035] Reference Figures 1 to 4 This utility model provides an open-type motor, comprising:

[0036] The outer shell 1 has through holes extending through both ends of it, and multiple positioning grooves 11 are provided on the inner side wall of the through holes near one end of the outer shell 1.

[0037] The rubber cap 2 has a positioning protrusion 23 on its outer side wall that corresponds to the positioning groove 11. The positioning protrusion 23 is installed in the positioning groove 11 to fix the rubber cap 2 to the outer shell 1. The rubber cap 2 also has multiple ventilation holes 22 and an installation hole 21 located at the center of the rubber cap 2.

[0038] The brush assembly 4 includes a carbon brush plate 41 and a carbon brush 43. The carbon brush plate 41 is fixedly installed on the rubber cover 2. A fixing member 42 is provided on the carbon brush plate 41. The fixing member 42 has a fixing hole that passes through both ends. The carbon brush 43 passes through one end of the fixing hole and extends out of the other end of the fixing hole and is set towards the mounting hole 21.

[0039] The rotor 3 is disposed in the through hole. The rotor 3 includes a first rotating shaft 31 and a commutator 32. The first rotating shaft 31 partially passes through and extends out of the mounting hole 21. The commutator 32 is sleeved on the first rotating shaft 31 and disposed close to the mounting hole 21. The carbon brush 43 abuts against the commutator 32.

[0040] Multiple magnets 51 are disposed in the through hole, and the multiple magnets 51 are assembled together to form a ring. The magnets 51 and the outer shell form a stator 5; the first rotating shaft 31 passes through the channel and is connected to the magnets 51.

[0041] In this embodiment, the rubber cover 2 and the rotor 3 are sequentially assembled and installed in the housing 1 along the extension direction of the first rotating shaft 31. This reduces the number of parts assembled in the direction perpendicular to the extension direction of the first rotating shaft 31. The rubber cover 2 is detachably connected to the housing 1 via a fitting mechanism, making installation more convenient. The design of the positioning groove 11 and the positioning protrusion 23 facilitates the installation of the rubber cover 2 inside the housing 1, preventing the rubber cover 2 from shifting during installation and reducing assembly efficiency. Furthermore, the design of the positioning groove 11 and the positioning protrusion 23 has an error-prevention function, indicating the correct installation direction of the rubber cover 2 within the housing.

[0042] Reference Figure 3 and Figure 4 The brush assembly 4 is mounted on the rubber cover 2, allowing for convenient and quick removal and replacement along with the removal of the rubber cover 2. The carbon brush 43 is snapped into the fixing component 42 using a suspended fixing method, ensuring that the carbon brush 43 faces the commutator 32 in a fixed direction. This suspended fixing method also facilitates easy removal when the carbon brush 43 needs replacement, improving replacement efficiency. By adopting the above technical solution, the space occupied by the motor in the product can be reduced, motor assembly is simpler, it has a fault-prevention structural design, the motor performance is more stable, and production efficiency is higher.

[0043] Continue to refer to Figure 2In one feasible embodiment, the rubber cover 2 is provided with a protrusion 24, and a torsion spring 25 is sleeved on the protrusion 24. The two ends of the torsion spring 25 abut against the rubber cover 2 and the end of the carbon brush 43 away from the commutator 32, respectively.

[0044] In this embodiment, since the motor will vibrate during use, in order to prevent the carbon brush 43 from shifting due to vibration when it comes into contact with the commutator 32, a torsion spring 25 is provided on the rubber cover 2. The torsion spring 25 is fixedly installed on the rubber cover 2 by the protrusion 24, so that one end of the torsion spring 25 abuts against the rubber cover 2 and the other end of the torsion spring 25 abuts against the end of the carbon brush 43 away from the commutator 32, thus fixing the carbon brush 43 in the fixing member 42. At the same time, as the carbon brush 43 is used, the torsion spring 25 can push the carbon brush 43 towards the commutator 32 so that the carbon brush 43 is fully utilized.

[0045] In one feasible embodiment, the outer casing 1 includes an arc-shaped first casing and a second casing, the first casing and the second casing forming a cylindrical casing with openings at both ends.

[0046] In this embodiment, the outer shell 1 is formed by an arc-shaped first shell and a second shell, which together form a cylindrical shell with openings at both ends. This makes the outer shell 1 easy to assemble and also increases the storage space of the outer shell 1.

[0047] In one feasible embodiment, a front cover 6 is further included. The outer side wall of the front cover 6 has a first threaded hole, and the outer shell 1 has a corresponding second threaded hole. The front cover 6 and the outer shell 1 are fixedly connected by bolts 12. A bearing 61 is provided at the center of the front cover 6, and one end of the first rotating shaft 31 extending out of the mounting hole 21 is installed in the bearing 61 and rotatably connected to the bearing 61.

[0048] In this embodiment, the front cover 6 is connected to the end of the outer shell 1 near the commutator 32. The front cover 6 has a through hole. The front cover 6 of this utility model has an arched support structure. The top of the arch is connected to the arched plane. The outer wall of the arched plane is provided with reinforcing ribs to effectively prevent the arched plane from deforming under stress. The front cover 6 further includes corner reinforcing ribs, which are provided at the upper and lower corners of the arch to improve the support capacity of the front cover 6. The bottom of the arch protrudes outward and is provided with an installation plane. The outer wall of the installation plane forms several protrusions 2. 4. A protrusion is provided on the mounting plane between several protrusions 24. The outer side wall of the protrusion fits against the inner side wall of the outer shell 1, which serves to position the front cover 6. The distance between the two protrusions is the same as the inner diameter of the outer shell 1, so that the front cover 6 and the inner wall of the outer shell 1 are aligned to ensure concentricity. The protrusions 24 are installed in the corresponding grooves, which support the front cover 6. The front cover 6 and the outer shell 1 are fixed by bolts 12, thus completing the installation of the front cover 6. This eliminates the need for complicated and cumbersome procedures, simplifies the assembly of the motor, and improves the production efficiency of the motor.

[0049] Reference Figure 5 and Figure 6 In one feasible embodiment, the system further includes a gear disk 7 disposed within a through hole. The gear disk 7 is rotatably connected to the other end of the first rotating shaft 31, and the outer side wall of the gear disk 7 abuts against the inner side wall of the through hole. An air duct is formed on the inner side wall of the through hole, and the air duct is located at the abutment point between the gear disk 7 and the through hole. The system also includes a moving impeller 8, which has a second rotating shaft disposed inside it. The second rotating shaft is rotatably connected to the gear disk 7 and is driven to rotate by the gear disk 7.

[0050] In this embodiment, the gear disk 7 fixes the rotor 3 and stator 5 within the cavity. The impeller 8 is configured to draw air, enabling the vacuum cleaner to perform its suction function. When the first shaft 31 rotates, it drives the gears within the gear disk 7 to rotate. The second shaft, which is rotatably connected to the gear disk 7, also rotates, causing the impeller 8 on the second shaft to rotate as well, thus enabling the impeller 8 to perform its suction function. The air duct design allows hot air from the motor to enter the impeller 8, which then exhausts the hot air.

[0051] Continue to refer to Figure 5 In one feasible embodiment, along the extension direction of the first rotating shaft 31, a first axial fan 33, a rotor core 34, and a second axial fan 35 are also sequentially installed on the first rotating shaft 31. The magnets 51 form a ring structure, which together with the outer shell 1 forms a stator 5. The first rotating shaft 31 passes through the ring structure formed by the magnets 51 and places the rotor core 34 inside the ring structure formed by the magnets 51.

[0052] In this embodiment, the outer casing 1 is used to house the rotor 3 and the stator 5. The commutator 32, the first axial fan 33, the rotor core 34, the second axial fan 35, and the gear disk 7 rotate together under the drive of the first rotating shaft 31. By employing two axial fans, when the motor is running, the rotation of the first rotating shaft 31 can drive the first axial fan 33 and the second axial fan 35 to rotate simultaneously. The first rotating shaft 31 drives the first axial fan 33 to rotate, and the first axial fan 33 generates axial cooling airflow that flows along the extension direction of the first rotating shaft 31, thereby carrying away the heat generated by the motor. When flowing through the second axial fan 35, the cooling airflow gradually becomes hot air. At this time, the second axial fan 35 throws the hot air out in the circumferential direction. The entire flow process of the cooling airflow can effectively cool the entire motor, ensuring sufficient cooling and avoiding local overheating, greatly improving the cooling effect. Moreover, the overall cooling process does not increase motor vibration and noise, achieving low-noise heat dissipation. The dual-axial-flow fan design accelerates the airflow within the housing 1, effectively reducing heat generated within the motor, resulting in better heat dissipation, longer service life, and higher power. Simultaneously, with the increased motor efficiency, the amount of rotor core 34 used can be reduced, shortening its length by 10mm, thus reducing the amount of rotor core 34 and copper wire required, thereby lowering costs. The dual-axial-flow fan design, with two fans installed within the housing 1—the first axial-flow fan 33 and the second axial-flow fan 35 fixed at opposite ends of the first rotating shaft 31—increases the airflow and speed within the motor. The overall structure is compact, easy to assemble and disassemble, structurally stable, and has a long fan lifespan. This makes the motor lighter, more flexible in installation, and reduces the space it occupies in the product.

[0053] In one feasible embodiment, two brush assemblies 4 are provided, symmetrically arranged on the rubber cover 2.

[0054] In this embodiment, the carbon brush 43 can transfer external current to the rotating rotor 3, and at the same time, it can introduce the static charge on the shaft to the ground, change the direction of the current, and lead the shaft to the protection device for grounding protection of the rotor 3 and measurement of the positive and negative voltages of the rotor 3 to ground. The brush assembly 4 also includes two leads 26, which are respectively connected to the neutral and live wires of the external power supply, and each lead 26 is connected to one brush assembly 4.

[0055] The front cover 6 is used to shield the brush assembly 4 to prevent the brush assembly 4 from being directly exposed to the outside world. At the same time, by opening a through hole on the front cover 6, the first axial fan 33 blows the outside cold air into the motor through the ventilation hole 22.

[0056] In one feasible embodiment, the first axial fan 33 is fitted with an air collector shroud, which is connected to the outer casing 1.

[0057] In this embodiment, the axis of the air collector shroud coincides with the axis of the first axial fan 33. The rotation of the first axial fan 33 will generate a cooling airflow flowing axially along the motor shaft. The air collector shroud and the magnet 51 together form a guide channel inside the channel to guide the cooling airflow generated by the first axial fan 33 to flow axially along the first shaft 31. This can effectively prevent the axial airflow from dissipating in all directions, allowing the axial airflow to flow fully along the extension direction of the first shaft 31, carrying away the heat generated by the motor. When it flows through the second axial fan 35, the second axial fan 35 uses centrifugal force to throw the airflow out in the circumferential direction and finally discharge it. The airflow in the above process can play a good role in cooling and heat dissipation for the motor.

[0058] In one embodiment, a gap is provided between the inner wall of the first air collector shroud and the outer edge (outermost edge of the blade) of the first axial fan 33 to reduce losses caused by backflow of cooling air. A snap-fit ​​component is connected to the air collector shroud, and a mounting base is connected to the magnet 51. The mounting base has a snap-fit ​​groove, and the snap-fit ​​component is inserted into the snap-fit ​​groove.

[0059] In one feasible embodiment, the gear disk 7 includes at least one set of gears 71, in which three planetary gears are meshed.

[0060] In this embodiment, a bearing 61 is provided at the connection between the first rotating shaft 31 and the gear disk 7. The first rotating shaft 31 passes through the bearing 61 and is rotatably connected to the gear disk 7. The gear disk 7 contains at least one set of gears 71. Three planetary gear sets 71 meshing within each gear set 71 form a planetary reducer. The planetary reducer amplifies the torque of the motor, allowing a smaller power motor to achieve a larger torque output. In one feasible embodiment, Figure 6 The diagram shows that the gear disk 7 includes two sets of gears 71, but this application does not limit the number of gear sets 71. The corresponding number of gear sets 71 can be set according to actual needs, such as three gear sets 71.

[0061] In one feasible embodiment, an impeller cover 9 is further fitted over the outside of the moving impeller 8, and the impeller cover 9 is fixedly connected to the outer casing 1. The impeller cover 9 is fitted onto the outer wall of the end cover.

[0062] In this embodiment, the impeller cover 9 can block dust and prevent external dust from falling directly onto the moving impeller 8.

[0063] Although the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the present invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the present invention to these descriptions. Those skilled in the art can make various changes in form and detail, including some simple deductions or substitutions, without departing from the spirit and scope of the present invention.

Claims

1. An open-type motor, characterized in that, include: The outer shell has through holes extending through both ends of it, and multiple positioning grooves are formed on the inner sidewall of the through holes near one end of the outer shell. The rubber cap has a positioning protrusion on its outer side wall that corresponds to the positioning groove. The positioning protrusion is installed in the positioning groove to fix the rubber cap to the outer shell. The rubber cap also has multiple ventilation holes and a mounting hole located at the center of the rubber cap. A brush assembly includes a carbon brush plate and a carbon brush. The carbon brush plate is fixedly mounted on the rubber cover. A fixing member is provided on the carbon brush plate. The fixing member has a fixing hole that passes through both ends of it. The carbon brush passes through one end of the fixing hole and extends out of the other end of the fixing hole and is positioned towards the mounting hole. A rotor is disposed within the through hole. The rotor includes a first rotating shaft and a commutator. The first rotating shaft passes through and extends out of the mounting hole. The commutator is sleeved on the first rotating shaft and disposed close to the mounting hole. The carbon brush abuts against the commutator. Multiple magnets are disposed within the through hole, and the multiple magnets are assembled together to form a ring-shaped structure. The magnets and the outer shell together form a stator. The first rotating shaft passes through the magnet.

2. The open-type motor as described in claim 1, characterized in that, The rubber cap has a protrusion, and a torsion spring is sleeved on the protrusion. The two ends of the torsion spring abut against the rubber cap and the end of the carbon brush away from the commutator, respectively.

3. The open-type motor as described in claim 1, characterized in that, The outer shell includes an arc-shaped first shell and a second shell, which together form a cylindrical shell with openings at both ends.

4. The open-type motor as described in claim 1, characterized in that, It also includes a front cover, the outer side wall of which has a first threaded hole and the outer shell has a corresponding second threaded hole, and the front cover and the outer shell are fixedly connected by bolts.

5. The open-type motor as described in claim 4, characterized in that, A bearing is provided at the center of the front end cover, and one end of the first rotating shaft that extends out of the mounting hole is installed in the bearing and rotatably connected to the bearing.

6. The open-type motor as described in claim 1, characterized in that, It also includes a gear disk disposed in the through hole, the gear disk being rotatably connected to the other end of the first rotating shaft, and the outer side wall of the gear disk abutting against the inner side wall of the through hole.

7. The open-type motor as described in claim 6, characterized in that, An air duct is provided on the inner wall of the through hole, and the air duct is located at the contact point between the gear disk and the through hole.

8. The open-type motor as described in claim 6, characterized in that, It also includes a moving impeller, which has a second rotating shaft inside. The second rotating shaft is rotatably connected to the gear disk and is driven to rotate by the gear disk.

9. The open-type motor as described in claim 1, characterized in that, Along the extension direction of the first rotating shaft, a first axial fan, a rotor core, and a second axial fan are sequentially installed on the first rotating shaft. The first rotating shaft passes through the annular structure composed of magnets and places the rotor core inside the annular structure composed of magnets.

10. The open-type motor as described in claim 1, characterized in that, Two brush assemblies are provided, symmetrically arranged on the rubber cover.

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