Power tool

A power tool includes a housing, a saw blade for cutting a workpiece, a motor for driving the saw blade to rotate about a first axis, a circuit board for controlling the motor, a heat sink for cooling, and a base plate being formed with a flat surface for contacting with the workpiece during cutting. The housing includes a first containing portion being formed with a first container for containing the motor, a second containing portion extended along a direction substantially parallel to the flat surface from one of the two ends of the first containing portion along a direction substantially perpendicular to the first axis. The second containing portion is formed with a second container which is communicated with the first container. The circuit board and the heat sink are disposed in the second container.

RELATED APPLICATION INFORMATION

This application claims the benefit under 35 U.S.C. § 119(a) of Chinese Patent Application No. CN 201610976748.4, filed on Nov. 7, 2016, Chinese Patent Application No. CN 201720215245.5, filed on Mar. 6, 2017, Chinese Patent Application No. CN 201720212445.5, filed on Mar. 6, 2017, Chinese Patent Application No. CN 201710709777.9, filed on Aug. 18, 2017, each of which is incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to power tools.

BACKGROUND OF THE DISCLOSURE

Tile or circular saws are a kind of power tool which have a high rotational speed and which can be used to cut tiles and stones.

With currently known saws, a housing part or parts for placing the circuit board and the heat sink are arranged in a manner to facilitate gripping and/or operating of the saw by a user and the cooling or heat dissipation effect of a motor is deeply limited by the arrangement of the circuit board and the heat sink.

SUMMARY

In one aspect of the disclosure, a power tool includes a housing, a saw blade for cutting a workpiece, a motor for driving the saw blade to rotate about a first axis, a circuit board for controlling the motor, a heat sink for cooling, and a base plate being formed with a flat surface for contacting with the workpiece during cutting. The housing includes a first containing portion being formed with a first container for containing the motor, a second containing portion extended along a direction substantially parallel to the flat surface from one of the two ends of the first containing portion along a direction substantially perpendicular to the first axis. The second containing portion is formed with a second container which is communicated with the first container, the circuit board and the heat sink are disposed in the second container.

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the scope of the invention hereinafter claimed, its application, or uses.

Referring toFIGS. 1-9, a first example of a power tool, for example an electric saw, is shown. Specifically, the electric saw100is a tile saw for cutting tiles and stones.

Referring toFIGS. 1-7, the electric saw100includes a housing10, a motor51, a transmission assembly52, a saw blade53, a base plate54, a circuit board55and a heat sink20. The motor51is used to drive the saw blade53to rotate about a first axis101. The transmission assembly52is used to transmit power between the motor51and the saw blade53. The base plate54is formed with a flat surface541for contacting with a workpiece. The circuit board55is used to control the motor51. The heat sink20is used to cool the circuit board55, the motor51and other heating elements. When the saw blade53is driven by the motor51to rotate about the first axis101, the saw blade53is able to cut the workpiece contacting with the flat surface541. The motor51of the electric saw100is an inner rotor brushless motor51. The electric saw100has an output power that is greater than 3000 W.

The housing10is configured to form the shape of the electric saw100. The motor51, the transmission assembly52, the saw blade53, the circuit board55and the heat sink20are contained in the housing10. The housing10includes a main body portion11and a handle portion12. The handle portion12is extended outward from the main body portion11. The motor51and the saw blade53are disposed on two sides of the handle portion12.

For illustrating conveniently, a side where the saw blade53is disposed in a direction of the first axis101is defined as a front side, and a side where the motor51is disposed is defined as a rear side. A side where the base plate54is disposed in a direction that is substantially perpendicular to the base plate54is defined as a lower side, and the other side is defined as an upper side.

Specifically, a hole12ais formed through the main body portion11and the handle portion12, which allows a hand of a user to pass from one side to the other side so as to grip the handle portion12. A button12bis disposed at the handle portion12for the user to press so as to operate the electric saw100when his hand grips the handle portion12.

The main body portion11of the housing10includes a first containing portion111which is formed with a first container1111and a second containing portion112which is formed with a second container1121. The first container1111and the second container1121are communicated with each other.

The motor51is disposed in the first container1111. The motor51includes a motor shaft511for outputting power. In is noted that, as long as the main part of the motor51is disposed in the first container1111, the motor51can be understood as being contained in the first container1111. For example, the motor shaft511is protruded out of the first container1111and the other part of the motor51is disposed in the first container1111, which also can be understood as the motor51being contained in the first container1111for the person skilled in the art.

The heat sink20and the circuit board55are disposed in the second container1121. The second containing portion112is extended from the first containing portion111along a direction that is substantially parallel to the flat surface541. The second containing portion112is located on one of the two ends of the first containing portion111in a direction that is substantially perpendicular to the first axis101.

In the direction that is substantially perpendicular to the flat surface541, the second containing portion112is disposed in the center of the motor51and in the center of the first containing portion111. It is noted that the second containing portion112being disposed in the center of the motor51means that the second containing portion112is aligned with the motor shaft511of the motor51in the direction that is substantially perpendicular to the flat surface541. The first containing portion111and the second containing portion112are aligned with each other on their ends which are removed from the saw blade in a direction substantially parallel to the first axis101. So, a whole constituted by the first containing portion111and the second containing portion112is easier to manufacture and an inner space is larger, so that the heat sink20and the circuit board55with a relatively larger size are easy to dispose therein, which is further adapted to provide the electric saw100with high power. The position of the second containing portion112relative to the first containing portion111and the specific structure of the second containing portion112allow the heat sink20to cool the motor more efficiently.

Otherwise, a projection of the second containing portion112in a plane that is substantially perpendicular to the first axis101is located out of a projection of the hole12ain the plane. Thus, the position of the second containing portion112is so arranged that it cannot interfere with the grip to the handle portion12.

Further, in the direction that is substantially perpendicular to the flat surface541, a distance L1from the second containing portion112to the flat surface541is greater than or equal to 8 mm and less than or equal to 30 mm. Thus, when the saw blade53cuts the workpiece, water thrown out from the lower edge of the saw blade53is inhibited from being thrown to the containing portion112.

More specifically, in the plane that is substantially perpendicular to the first axis101, the first containing portion111is a circular structure which can be matched with the shape of the motor51. In this plane, the second containing portion112is a rectangular structure. Further, the whole constituted by the first containing portion111and the second containing portion112is a key-shaped structure.

Referring toFIGS. 2, 6 and 8, the housing10further includes a gear box13. The transmission mechanism52is disposed in the gear box13. The gear box13includes a first connecting element131. The base plate54is connected with a second connecting element542. Through the engagement of the first connecting element131and the second connecting element542, the base plate54is rotatably connected with the housing10about a second axis102that is substantially parallel to the first axis101.

Specifically, the first connecting element131is formed with two grooves131a, and the second connecting element542is formed with two bulges542awhich can be inserted in the grooves131arespectively. In can be understood that the number of the grooves131aand the bulges542acan be more than two.

The first connecting element131includes an inserting portion131band a limiting portion131c. The inserting portion131bcan be inserted in a space formed between the two bulges542aof the second connecting element542. The number of the limiting portion131cis two. The first connecting element131can be limited by the two limiting portions131cfrom two sides of a whole constituted by the two bulges542ain a direction of the second axis102. The first connecting element131is further formed with an axle hole131d. The axle hole131dgoes through the first connecting element131in the direction of the second axis102. The second connecting element542is formed with a through hole which is connected with the axle hole131dwhen it is connected with the first connecting element131. The electric saw100further includes a C-shaped pin56passing through the axle hole131dand the through hole.

Referring toFIGS. 1 and 4, the housing10further includes a guard14which is used to surround the saw blade53partially so as to protect the user. An auxiliary gripping portion15for the user to grip is extended toward a direction that is departed from the saw blade53from one side of the guard14that is removed from the motor51. In the direction that is substantially parallel to the first axis101, the auxiliary gripping portion15is at least partially located on the side of the guard14that is removed from the motor51. Thereby, when the user operates the electric saw100, the user grips the handle portion12with one hand and pinches the auxiliary gripping portion15with their thumb and index finger of the other hand, so that the electric saw100is held steadily. In the direction that is substantially parallel to the first axis101, the auxiliary gripping portion15and the handle portion12are located on two sides of the saw blade53respectively. Further, the auxiliary gripping portion15and the motor51are located on the two sides of the handle portion12, so that the electric saw100can be easier to grip for the user.

The auxiliary gripping portion15has a size L2in the direction that is substantially parallel to the first axis101which is greater than or equal to 10 mm and less than or equal to 30 mm. The auxiliary gripping portion15has a size L3in a direction that is substantially parallel to the flat surface541and perpendicular to the first axis101which is greater than or equal to 10 mm and less than or equal to 40 mm. Thus, the size of the auxiliary gripping portion15is adapted to the thumb of the user, which is not too big and can reduce the block of the user's view. And the size of the auxiliary gripping portion15is not too small, which can avoid the auxiliary gripping portion15from sliding from the thumb or the index finger of the user during operation.

Referring toFIGS. 6-7 and 9, the heat sink20and the circuit board55are arranged in turn in the second container1121along the direction substantially perpendicular to the flat surface541. Further, the heat sink20is disposed above the circuit board55. The electric saw100includes a fan57disposed between the motor51and the saw blade53. The fan57can be driven to rotate by the motor51so as to generate a cooling airflow flowing towards the circuit board55, the heat sink20and the motor51. The second container1121is communicated with the first container1111, so the cooling airflow can be guided by the heat sink20in the second container1121to the first container1111so as to cool the motor51. In order to make the cooling airflow flow to the motor51along the direction substantially parallel to the first axis101, a gap is formed between a rear wall of the first container1111that is removed from the saw blade53in the direction of the first axis101and a rear end of the motor51that is removed from the saw blade53in the direction of the first axis101. The gap allows the cooling airflow to be guided to the motor51. Here, the first container1111is divided into two portions in the direction of the first axis101which are a first portion1111aand a second portion1111b. The first portion1111ais a portion of the first container1111for containing the motor51. The second portion1111bis a portion of the first container1111where the gap is located.

The heat sink20has a size in the direction substantially parallel to the first axis101that is approximately equal to a size of the first container1111in the direction substantially parallel to the first axis101. Specifically, the heat sink20includes a base board21, first-type ribs22and second-type ribs23. In the direction that is substantially parallel to the flat surface541and perpendicular to the first axis101, the second-type ribs23have an end close to the motor51which is shorter than the first-type ribs22. The base board21is extended in the direction that is substantially parallel to the flat surface541. The first-type ribs22and the second-type ribs23are disposed on the base board21. The first-type ribs22have a first-type air outlet221. In the direction that is substantially parallel to the first axis101, the first-type air outlet221is aligned with one side of the motor51that is removed from the saw blade53. That is, the first-type air outlet221is aligned with the second portion1111bof the first container1111in the direction that is substantially parallel to the first axis101. The second-type ribs23have a second-type air outlet231. The second-type air outlet231is aligned with a portion of the first container1111for containing the motor51in the direction that is substantially parallel to the first axis101. That is, the second-type air outlet231is aligned with the first portion1111aof the first container1111. Otherwise, because the end of the second-type ribs23close to the motor51is shorter than the first-type ribs22, a guiding channel24is formed on the base board21. The guiding channel24is formed on one side of the second-type ribs23that is close to the motor51. The cooling airflow flowing out from the second-type air outlet231can be guided by the guiding channel24to the side of the motor51that is removed from the saw blade53, that is flowing to the second portion1111bof the first container1111. So, the cooling airflow flowing out from the second-type air outlet231can flow to the motor along the direction of the first axis101. The first-type ribs22can guide the cooling airflow to flow out of the first-type air outlet221and then flow to the second portion1111bdirectly, so the cooling airflow passing the first-type ribs22have more air volume. In this example, the first-type ribs22and the second-type ribs23are extended along the direction that is substantially perpendicular to the first axis101. Thus, the first-type ribs22and the second-type ribs23can have the same air inlet25. The air inlet25has a size L4in the direction that is substantially parallel to the first axis101which is greater than a size L5of the first-type air outlet221in the direction that is substantially parallel to the first axis101. Referring toFIGS. 2 and 6, an airflow inlet16is formed on a position of the housing10which is corresponded to the air inlet25. The airflow inlet16is communicated with the air inlet25. A labyrinth inlet channel can be formed between the airflow inlet16and the air inlet25so as to prevent dust from entering the second container1121. In can be understood that the first-type ribs22and the second-type ribs23can be extended along a direction that is obliquely intersected with the first axis101, so that a better cooling effect can be obtain. Otherwise, an arcuate guiding portion1112is formed on the rear wall of the first container111that is removed from the motor51in the direction of the first axis101, which is able to guide the cooling airflow of the first container111to the motor51.

The circuit board55is provided with electronic elements which can generate heat so as to raise the temperature during operation of the tool. For electronic elements with high heating power in particular, they is more need for cooling. Specifically, the circuit board55includes a circuit substrate551, a first-type electronic element552and a second-type electronic element553. The circuit substrate551is extended in the direction substantially parallel to the flat surface541. The first-type electronic element552has a heating power which is greater than or equal to a predetermined heating power, and the second-type electronic element553has a heating power which is less than the predetermined heating power. So, the first-type electronic element552is disposed on a first position of the circuit substrate551which corresponds to the first-type ribs22, and the second-type electronic element553is disposed on a second position of the circuit substrate551which corresponds to the second-type ribs23. That is, the first-type electronic element552is disposed right below the first-type ribs22, and the second-type electronic element553is disposed right below the second-type ribs23. Thereby, the first-type electronic element552with a higher heating power can be cooled more efficiently.

Referring toFIGS. 10-14, a second example of a power tool, for example a hand-held tile saw, is shown. The hand-held saw includes a housing10, a handle12, a base plate54, a brushless motor51and a circuit board55including a controller140therein.

The hand-held saw further includes a saw blade, an output shaft101provided with the saw blade, a motor shaft511of the motor51. The base plate54is configured to contact with a workpiece to be cut. The saw blade has a cutting surface which is substantially parallel to a cutting direction. The output shaft101is connected with the motor shaft511through a transmission assembly. In this example, the output shaft101is substantially parallel to the motor shaft511. The transmission assembly can be one stage or more than two stages so as to provide speed down, speed up or constant speed transmission between the output shaft101and the motor shaft511. In other examples, the output shaft101can be set not to be parallel to the motor shaft511. For example, the output shaft101may be perpendicular to the motor shaft511or obliquely intersected with the motor shaft511.

Referring toFIGS. 12-13, the housing10includes a container. The brushless motor51is mounted in the housing10. Specifically, the container of the housing10is divided into a motor housing111and a non-motor housing112. The brushless motor51is mounted within the motor housing111. The motor housing111has a narrow shape which is adapted to the shape of the brushless motor51. The circuit board55and a motor driving circuit106are mounted within the non-motor housing112. The non-motor housing112has a flat box shape which is adapted to the circuit board55and the motor driving circuit106.

In this example, the brushless motor51includes a rotor, a stator having at least a three-phase winding605and the above-described motor shaft511. The rotor is mounted onto the motor shaft511. In the prior art, one or more electromagnetic induction elements or sense magnets are arranged along the motor shaft at a rear end of the motor shaft, or on the rear side of the motor rotor. The one or more sense magnets were affixed to the motor shaft, and a positional sensor board including one or more sensors is disposed adjacent to the one or more sense magnets. The position sensor board or sensors cooperate with the one or more sense magnets or similar sense elements to sense rotational position of the motor shaft or the motor rotor so as to enable the controller to generate a drive signal to drive the rotation of the motor according to the sensed position of the motor shaft or motor rotor.

As shown inFIG. 13, the brushless motor51defines a first end or a front end602which is adjacent to the saw blade arranged along the extending direction of the motor shaft511and a second end or a rear end604which is far away from the saw blade and opposite to the first end602. The brushless motor51further defines a front side609, an area of which is located perpendicular to the extension direction of the motor shaft511and parallel to the cutting direction of the saw blade, and a rear side which is opposite to the front side609. In this example, the saw blade and the base plate54is located on the front end602of the motor51, and the printed circuit board55and the motor driving circuit106are located on the front side609of the motor51. Referring toFIGS. 10-14, the circuit board55is not located on the rear end604of the motor shaft511, but is disposed at the front side609of the motor51. The handle12of the power tool is located on the center or close to the center of the power tool so as to balance the center of gravity of the power tool during operation thereof, so the user will have a better feel when the user operates the power tool by gripping the handle of the power tool.

In this example, the power tool includes a power plug90for connecting with an AC power supply. The plug90can receive AC power input of 85-265V. Compared with DC power of 12-60V, AC power of 85-265V is a high voltage input. The high voltage input requires a high precision about the position detecting of the motor. In the prior art, for example by a sense way, such as the electromagnetic induction element, the photoelectric element, the photoelectric encoder, the position sensing board, the position sensor and/or the other sense elements are used to detect the position of the motor. In one aspect, the detecting accuracy of the prior art is not sufficient, and in the other aspect, the position sensing board, the position sensor or the other sense elements are greatly affected by the temperature and cannot work well at a place having an extreme temperature, for example a temperature of less than 40 degrees. However, in other examples, the power tool does not use the AC power plug, but uses a battery power supply outputting power of at least 56V, preferably 85-265V. For the power tool with a high power output requirement, multiple battery packs are used to supply the power, for example at least two battery packs. The multiple battery packs can output DC current of at least 56V, preferably 85-265V. One handle or two handles of the power tool is disposed close to the center of the power tool so as to balance the position of the center of the power tool during the operation thereof, so the user will have a good feeling when operating the power tool by gripping the handle or handles thereof. As shown inFIG. 13, in this example, the motor driving circuit106includes switch elements1061for actuating or driving the motor. The motor driving circuit106is mounted onto the circuit board55. The circuit board55along the cutting direction is disposed at the front side609, an area of which is located between the motor51and the handle12. In the prior art as described in US2017/0110935A1 employing the sense magnet and/or positional sensor board, the influence of armature reaction thereof can greatly affect the performance of the motor. That is, in this example, there is no sense magnet and/or positional sensor board within 10 mm of the front end and rear end of the rotor of the motor. In an example of the present invention, as shown inFIGS. 13 and 14, the phase windings605of the stator of the motor are linked or wired to the circuit board55by the phase wires or lines as shown inFIGS. 13 and 14to detect the terminal voltage signals and/or current signals from the phase windings605or wires of the motor so as to determine the position of the rotor of the motor. Thus, the influence of armature reaction can be greatly reduced due to having no sense magnet and/or positional sensor board.

The motor51leads out at least three phase wires or lines which are electrically connected with the at least three stator or phase windings605of the stator. The at least three phase wires of the motor51are directly and electrically connected to the circuit board55including the controller140therein. Referring toFIGS. 13-14, in this example, the motor51includes the rotor and the stator having the at least three stator windings605corresponding to at least three phases of the motor. The motor51leads out the at least three phase wires, corresponding to the at least three stator windings, electrically connected with the at least three stator windings605of the stator and contacts or metal pads on the surface of the circuit board55. That is, each of the at least three phase wires has thereof one end electrically connected to each of the at least three stator windings of the stator of the motor, and the other end soldered or electrically connected to the corresponding metal pad of the circuit board55. In other examples, the stator of the BLDC motor or motor51may include fewer than or more than three phases windings. It should be noted that the motor51has no other wires or lines except for the above-described phase wires extending from the corresponding phase windings605of the stator of the motor. Compared with prior power tools that use the sense magnets and/or the positional sensor board, there is provided with a few phase wires for directly and electrically connecting three stator or phase windings605of the motor and the circuit board55with no other wires or lines extending from the motor of the power tool. In other examples, the controller can directly or indirectly obtain the terminal voltage signals and/or current signals from the corresponding phase windings605of the stator to determine the position of the rotor of the motor not via the entity wires or lines. Thus, in the subject example there is no sense magnet and/or the positional sensor board as the prior art described in US2017/0110935A1 or US2017/0126051A1. Without the sense magnet and/or the positional sensor board, the subject example can greatly reduce to the motor the influence of armature reaction, which was mostly generated by the sense magnet and/or the positional sensor board. Further, due to having no sense magnet and/or positional sensor board, the subject example can output a higher voltage by providing a compact structure for the power tool with a lower cost as compared to the prior art.

The circuit board55includes the controller or control chip140embedded therein. The phase wires for carrying the terminal voltage signals and/or current signals directly from the corresponding phase windings605of the stator of the motor will send the terminal voltage signals and/or current signals to the controller140. In other words, the phase wires are configured to output the terminal voltage signals and/or current signals into the controller140. In this embodiment, the controller140includes a position estimation unit141, a control unit143, and a drive unit145. The position estimation unit141is configured to estimate or determine the position of the rotor of the motor based on the outputted terminal voltage signals and/or current signals from the phase wires of the motor. The control unit143is configured to receive the estimated or determined position of the rotor of the motor and accordingly generate a control command to the drive unit145. Upon the receipt of the control command, the drive unit is configured to output a drive signal to the motor driving circuit106so as to drive the motor. That is, the phase wires are configured to directly and electrically connect the stator or phase windings605of the stator of the motor with the circuit board55including the controller140and output the terminal voltage signals and/or current signals from the corresponding phase windings605of the stator of the motor to the controller140, the controller140is configured to obtain the outputted terminal voltage signals and/or current signals to estimate or determine the position of the rotor of the motor and generate a control command to the motor driving circuit106, which is set to drive the motor by producing phase or phase-changing signals to control the motor51. Note that the controller140is to obtain the terminal voltage of the phase line to estimate the position of the rotor of the motor, and the terminal voltage is defined by difference of the phase line voltage and DC-voltage as shown inFIG. 15. The terminal voltage relates to the counter electromotive force, but not equal to the counter electromotive force as defined by the potential of two phase lines, such as the phase line U and the phase line V. That the controller employing the terminal voltage of the phase line but not the counter electromotive force of the phase lines is because of the potential of two phase lines cannot be accurately obtained when the motor runs or rotates. In this example, the position estimation unit141, the control unit143, and the drive unit145are integrated into a common board55, with the motor driving circuit106including six switching elements mounted onto the circuit board55as shown inFIG. 13andFIG. 15.

As shown inFIG. 15, a circuit diagram of the power tool is shown without the sense magnet and/or the positional sensor board as in the prior art. The AC power supply plug of the power tool preferably receives the AC power input of 110-230V and an EMI element101is provided for filtering the AC power. The EMI element101is mainly constituted by a X capacitor, a Y capacitor and a common mode inductor. Then the AC power is converted to DC power through an AC/DC converter120that is a single phase uncontrolled rectifier bridge. The capacitor can filter the DC current. A part of the DC current flows to the motor driving circuit106that is a three-phase power circuit, which outputs a power source to the motor51. The other part of the DC current generates Vcc power via a power conversion circuit130to supply power to the controller140. The motor driving circuit106is a three-phase power circuit which connects with the three-phase DC brushless motor51via the three phase lines U, V, and W.

A control logic for the circuit diagram inFIG. 15is described as below. The controller using an analog-digital conversion module with an AD sampling interface adapted for receipt of the terminal voltage signals and/or current signals from the three phase lines U, V, and W of the brushless motor, is configured to determine the position of the rotor of the motor based on the terminal voltage signals and/or current signals of the phase wires of the motor through a position estimation unit141and output a drive signal to the motor driving circuit106, which then generates the phase signals to the motor. The position estimation unit141is preferably a software program in this example. The control program of the control unit143can generate six logic signals to the driving unit145. The logic signals can be amplified through the driving unit145, which generates six drive signals Q1, Q2, Q3, Q4, Q5, and Q6to drive the motor driving circuit106. That is, the motor driving circuit106includes six switching elements, which are turned on or off to generate the phase signals to control the motor via the three phase lines U, V, and W.

As shown inFIG. 16, a circuit diagram of the EMI element is shown. When the power tool adapted for receipt of the AC power supply of 110-230V works, there are the switching elements with thereof the frequent ON and OFF operation, which can cause a voltage jump or a current jump and generate a common mode interference and a differential mode interference. In order to reduce the influence to the power grid and the electronic devices by the mode interference, it is needed to use the EMI element inFIG. 16. The EMI element comprises a resistor-capacitor unit meets the safety requirements. In the circuit diagram ofFIG. 16, a fuse acts as an over-current protector for the power tool. A piezo resistor acts as a voltage protector, which is able to reduce the influence to the circuit due to the voltage jump of the AC power input. The two Y capacitors C1, C2are able to restrain the common mode interference and guide the signal of the common mode interference to the ground. The two X capacitors are able to restrain the differential mode interference. The common mode inductor can only restrain the common mode interference current, and can't affect the normal working current.

An example of a principle for changing phase of the brushless motor is shown inFIG. 17. The three-phase BLDC is configured to employ six-beat control. That is a 360° electric cycle is divided into six 60° areas. Each area has two phase windings605at work. One phase is connected with positive current, and the other is connected with negative current. Taking the 0-60° area as example, as the motor driving circuit106includes six switch elements or tubes Q1, Q2, Q3, Q4, Q5, and Q6, during this area, the switch elements Q5and Q4are turned on, and the other switch elements are turned off. At this moment, the phase line V does pass the negative current, and the phase line W does pass the positive current. The respective terminal voltages of the three phase lines U, V, and W run as follows: the terminal voltage of the phase line V is 0, the terminal voltage of the phase line W is UDC, the phase line U acts as a floated phase, and the terminal voltage signal and/or the current signal is detected, wherein the terminal voltage is defined by the difference of the corresponding phase line U, V, and W voltage and DC-voltage as shown inFIG. 15. The oblique line (UDC/2+ count EMF of phase U), and UDC/2 is chosen as a key signal position, which is outputted to the position estimation unit141of the controller140. At this moment, the counter voltage of the phase line U is 0, and the phase changing time of the next area can be obtained by delaying 30° electrical angle. When the phase changing time of the next area is reached, the switch elements Q5and Q4of the motor driving circuit106are switched to switch elements Q1and Q4, and the phase lines U and W then work and the terminal voltage signal and/or the current signal of the phase line V is detected so as to obtain the time at which the terminal voltage UDC/2 arises on the phase line V, and the next phase changing time of another area can be obtained by delaying another 30° electrical angle. And so on, the drive of the phase changing of the motor can be realized as described above, and the motor can be driven to rotate as normal.

The power tool in this example employs the alternating current or AC power plug90, which is able to receive the AC input of 85-265V, preferably 110-230V. In other examples, the power tool may use a high voltage DC power, for example a high voltage DC power composed of one or more battery packs which can output the voltage of at least 56V.

The power tool configured to employ such a high voltage brushless motor of the second embodiment has no need of the sense magnet, the position sensor, and/or the position sensor board to obtain the position of the motor. Thus, the detecting accuracy of the position of the motor is improved, and the influence of armature reaction to the motor is greatly reduced due to having no sense magnet and/or position sensors, and the cost is reduced.

The above illustrates and describes basic principles, main features and advantages of the invention hereinafter claimed. Those skilled in the art should appreciate that the above described examples do not limit the claimed invention in any form. Technical solutions obtained by equivalent substitution or equivalent variations all fall within the scope of the claimed invention.