CN113315450A

CN113315450A - Electric tool and output characteristic control method thereof

Info

Publication number: CN113315450A
Application number: CN202110581695.7A
Authority: CN
Inventors: 张扣锅
Original assignee: Jiangsu Dongcheng Tools Technology Co Ltd
Current assignee: Jiangsu Dongcheng Tools Technology Co Ltd
Priority date: 2021-05-27
Filing date: 2021-05-27
Publication date: 2021-08-27

Abstract

The present invention provides an electric tool and an output characteristic control method thereof, which can automatically change the output characteristic of a motor according to the load state of the electric tool, the electric tool comprises: a motor disposed in the housing and including a stator having a plurality of teeth, a rotor rotating relative to the stator, and a plurality of windings wound around the teeth, at least one of the windings including a plurality of coils independent of each other; the control unit is connected with a winding of the motor and controls the rotation of the motor; a load detection unit that detects a load parameter of the electric tool; and a connection changing unit connected in series between the control unit and the winding. The control method of the electric tool comprises the following steps: starting the electric tool, and detecting a load parameter of the electric tool by a load detection unit; the control unit receives the load parameters and determines the load state of the electric tool according to the load parameters; the connection changing unit switches the connection relation between the control unit and the winding according to the load state.

Description

Electric tool and output characteristic control method thereof

[ technical field ]

The invention relates to the field of electric tools, in particular to an electric tool and an output characteristic control method thereof.

[ background art ]

At present, the electric tools are mostly powered by a direct current power supply, and a direct current brushless motor drives a working head to operate. However, most of the stator windings of the conventional dc brushless motors are wound in a concentrated manner, and the coils wound on the individual stator teeth are fixed to the motor driving circuit in a connection manner, so that once the motor is manufactured, the output characteristics of the motor are fixed, and the optimal efficiency point of the motor is fixed, thereby resulting in a single use of the electric tool.

For a cutting tool such as a circular saw, the circular saw is required to cut wood at a low load and a high speed, and the circular saw is required to cut stone at a high load and a low speed. In order to improve the working efficiency, the electric tools with two different output characteristics are required to be used under the two use scenes. Conventionally, this has been solved by changing the transmission ratio of the transmission mechanism in the tool, but this has caused the transmission mechanism of the electric power tool to be complicated and to be heavy, which is disadvantageous for the user's operation.

Accordingly, there is a need for an improved power tool and method for controlling output characteristics thereof to overcome the shortcomings of the prior art.

[ summary of the invention ]

Therefore, there is a need for an electric tool and an output characteristic control method thereof, which can satisfy the use requirements of various working conditions and give consideration to the working efficiency on the premise of not changing the original transmission mechanism.

The present invention provides an electric tool including: a housing; a DC power supply detachably mounted on the housing for supplying power to the power tool; a motor located in the housing and including a stator having a plurality of teeth, a rotor rotating relative to the stator, and a plurality of windings wound around the teeth; the working head is driven by the motor to rotate; a control unit connected to the winding to control rotation of the motor; a load detection unit that detects a load parameter of the electric tool; at least one winding comprises a plurality of mutually independent coils, and the electric tool further comprises a wiring changing unit which is connected between the control unit and the winding in series.

The further improvement scheme is as follows: each winding comprises a plurality of mutually independent coils, and the wiring changing unit is used for selectively connecting one coil of the coils with the control unit or connecting at least two coil combinations of the coils with the control unit in series according to the load state.

The further improvement scheme is as follows: at least one winding includes first coil and second coil, first coil with the number of turns or the line footpath of second coil is different.

The further improvement scheme is as follows: the motor is a three-phase brushless motor, each phase comprises at least two windings, and the three-phase windings of the motor are connected in a star shape or a triangular shape.

The further improvement scheme is as follows: the power tool further includes a display unit for indicating a load state of the power tool.

The further improvement scheme is as follows: when the electric tool is started initially, only one of the plurality of coils is connected with the control unit.

The further improvement scheme is as follows: the load parameter is one or more of working current, working rotating speed, torque and temperature of the motor.

The present invention also provides an output characteristic control method of an electric tool having the above electric tool, the output characteristic control method including: starting an electric tool, wherein the load detection unit detects a load parameter of the electric tool; the control unit receives the load parameters and determines the load state of the electric tool according to the load parameters; the wiring changing unit switches the connection relationship between the control unit and the winding according to a load state.

The further improvement scheme is as follows: each winding comprises a first coil and a second coil, the number of turns of the first coil is smaller than that of the second coil, and when the electric tool is in a first load state, the wiring changing unit connects the first coil with the control unit; when the electric tool is in a second load state, the wire connection changing unit connects the second coil with the control unit; when the electric power tool is in a third load state, the wire connection changing unit connects the first coil and the second coil in series with the control unit.

The further improvement scheme is as follows: each of the windings includes three coils, and the wire connection changing unit connects one of the three coils with the control unit when the electric power tool is in a first load state; when the electric power tool is in a second load state, the wire connection changing unit connects two of the three coils in series with the control unit; when the electric power tool is in a third load state, the wire changing unit connects the three coils in series with the control unit.

Compared with the prior art, the invention has the following beneficial effects: the electric tool and the control method thereof can automatically change the connection relationship between the coils wound on each stator tooth and the control unit according to the load condition, thereby changing the number of turns of the electrified coils of the motor, outputting different motor characteristics under different working conditions on the basis of not changing a transmission mechanism, and ensuring that the electric tool can meet the use requirements of different working conditions and the working efficiency is always kept better.

[ description of the drawings ]

The following detailed description of embodiments of the invention is provided in conjunction with the appended drawings:

FIG. 1 is a schematic view of a power tool of a first embodiment of the present invention;

FIG. 2 is a block diagram of a control circuit configuration within the power tool shown in FIG. 1;

FIG. 3 is a block diagram of a modified configuration of a control circuit in the power tool shown in FIG. 1;

FIG. 4 is a block diagram of a motor in the power tool shown in FIG. 1;

FIG. 5 is a diagram showing the connection of coils in each winding of the motor in different states of the wire varying unit in the power tool shown in FIG. 1;

FIG. 6 is a diagram of the connection of coils in the motor shown in FIG. 4 with the wire altering unit in a different state;

FIG. 7 is a graph of the speed-torque and efficiency-torque characteristics of the motor shown in FIG. 4 with the wire change unit in different states;

FIG. 8 is a graph illustrating the change in motor speed and efficiency during an increase in the load experienced by the power tool according to the first embodiment of the present invention;

fig. 9 is a structural view of a motor in the electric power tool of the second embodiment of the present invention;

fig. 10 is a flowchart of an output characteristic control method of the electric power tool of the first embodiment of the invention;

fig. 11 is a flowchart of an output characteristic control method of an electric power tool of a second embodiment of the present invention.

The meaning of the reference symbols in the figures:

100 electric tool

11 outer cover

12 D.C. power supply

13 working head

14 display unit

15 electric machine

151 stator

152-1 tooth

153-1, 153-2, 153-3, 153-4, 153-5, 153-6 windings

16 control unit 17 motor drive circuit

18 load detection unit

181 current detection circuit

19. 191 wiring changing unit

[ detailed description of the invention ]

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

Referring to fig. 1 and 2, an electric tool 100 according to a first embodiment of the present invention includes a trigger switch, a housing 11, a working head 13, a dc power source 12, and a motor, a power transmission mechanism and a control circuit board located in the housing 11. A dc power supply 12 is detachably mounted on the housing 11 as a power supply of the electric power tool 100, and a working head 13 is mounted on the front end of the housing 11. The dc power supply 12 is a single battery pack, and the battery pack includes at least one battery unit, and each battery unit is formed by connecting a plurality of battery cells in series. Preferably, the dc power source 12 may be composed of a plurality of lithium battery packs connected in series or in parallel. The motor includes a stator having a plurality of teeth, a rotor rotating with respect to the stator, and a plurality of windings wound around the teeth, at least one of the windings including a plurality of coils independent of each other. The motor 15 is a brushless motor and includes three-phase windings U, V, W, each phase winding includes at least two windings, and the three-phase windings of the motor 15 are connected in a tail connection manner. The rotor comprises a plurality of permanent magnets embedded in a rotor core, and when a motor winding is electrified, a magnetic field generated by the winding and a magnetic field generated by the permanent magnets interact to drive the rotor to rotate relative to the stator. The motor also comprises an output shaft, and the rotor and the output shaft are fixed together to form a whole in an interference fit mode. The output shaft is connected with the working head 13 through a power transmission mechanism, and when the rotor rotates, the output shaft drives the working head 13 to rotate through the power transmission mechanism.

The control circuit of the electric tool 100 is disposed on the control circuit board, and the control circuit includes a control unit connected to a winding of the motor for controlling rotation of the motor. The control unit includes a controller 16 and a motor drive circuit 17, the motor drive circuit 17 is configured to supply a drive voltage supplied from the dc power supply 12 to the three-phase windings of the motor 15, and the controller 16 controls the motor drive circuit 17 to control the rotation of the motor. The motor driving circuit 17 comprises an upper bridge arm and a lower bridge arm, the upper bridge arm comprises switching tubes Q1, Q2 and Q3, the lower bridge arm comprises switching tubes Q4, Q5 and Q6, each switching tube is connected with diodes D1-D6 in parallel in a reverse direction, and control electrodes of the switching tubes Q1, Q2, Q3, Q4, Q5 and Q6 are all electrically connected to the controller 16. In this embodiment, the controller 16 is connected to the motor 15 through a zero-cross detection circuit, and is configured to detect a position of a rotor of the motor 15, and control the switching tubes Q1, Q2, Q3, Q4, Q5, and Q6 to switch phases of the motor 15 electronically according to a conduction sequence of the rotor position, so as to control the rotation of the motor 15. The switch tube is a field effect tube or an insulated gate bipolar transistor. As an alternative embodiment, the controller 16 detects the rotor position of the motor by a position detection sensor, and as shown in fig. 3, the controller 16 is connected to the motor 15 by a rotor position detection circuit, which includes hall detection sensors H1, H2, H3 for detecting the rotor position of the motor 15 and generating hall detection signals. The controller 17 determines the position of the rotor of the motor 15 according to the received hall detection signal, and controls the conduction sequence of the switching tubes in the motor driving circuit 17 according to the position of the rotor to electronically phase-change the motor 15, thereby controlling the rotation of the motor 15, and the rotation speed of the motor 15 can be changed by changing the conduction width or frequency of the switching tubes.

When a user presses a trigger switch, the direct current power supply 12 supplies power to a control circuit board and a motor 15 in the tool, after the control unit is electrified, current is controlled to flow into a winding of the motor to drive a motor rotor to generate rotary motion, driving torque generated by the rotary motion of the rotor is transmitted to the power transmission mechanism through an output shaft, the power transmission mechanism transmits the driving torque to the working head 13 at a fixed transmission ratio, the working head 13 generates rotary motion under the action of the driving torque, and therefore the working head 13 can cut materials such as wood, stone and metal under the driving of the motor 15. The electric tool of the present invention may be any electric tool such as an electric drill, a screwdriver, a swing machine, a circular saw, an angle grinder, a grass trimmer, a pruner, a brush cutter, etc., or any electric device that can perform various operations such as drilling, hammering, grinding, cutting, etc., under the action of a driving torque generated by a motor.

Referring to fig. 2, the control circuit in the power tool 100 further includes a load detection unit 18. The load detection unit 18 is configured to detect a load parameter of the power tool 100, which is one or more of an operating current, an operating speed, a torque, and a temperature of the motor, generate a detection signal, and output the detection signal to the controller 16. As an alternative embodiment, as shown in fig. 3, the load detection unit 18 includes a current detection circuit 181. The current detection circuit 181 detects the magnitude of the operating circuit of the motor 15, generates a detection signal and transmits the detection signal to the controller 16, and the controller 16 calculates the magnitude of the operating current of the motor 15 according to the detection signal, and compares the operating current of the motor 15 with a preset current value to determine the load state of the electric tool. Specifically, two preset current values may be set in the controller 16, the load state of the electric tool includes three different load states, and when the working current is greater than the first preset current, the controller 16 determines that the electric tool is in the first load state; when the working current is greater than the second preset current and less than or equal to the first preset current, the controller 16 determines that the electric tool is in the second load state; when the operating current is equal to or less than the second preset current, the controller 16 determines that the power tool is in the third load state. The first preset current is larger than the second preset current.

Referring to fig. 3 to 6, the motor 15 in the power tool according to the first embodiment of the present invention includes a stator 151 having six teeth, and six identical windings 153-1, 153-2, 153-3, 153-4, 153-5, 153-6. The same winding (153-1, 153-2, 153-3, 153-4, 153-5 and 153-6) is composed of a first coil K1 and a second coil K2 which are independent of each other, the first coil K1 and the second coil K2 are respectively formed by winding two metal enameled wires, are insulated and separated from each other and are wound on the same tooth. The motor 15 is a three-phase brushless motor, the windings wound on two opposite teeth are connected in series to form a phase winding of the motor 15, one end of the three-phase winding of the motor 15 is connected to one of the two windings to form a star winding structure, and the other end of the three-phase winding is connected to the motor driving circuit 17.

Referring to fig. 2, the control circuit in the power tool 100 further includes a wiring change unit 19, the wiring change unit 19 is connected in series between the control unit and the winding of the motor 15, and the controller 16 is electrically connected to the wiring change unit 19 and the load detection unit 18. The wiring changing unit 19 comprises six switch units which are respectively connected to the windings 153-1, 153-2, 153-3, 153-4, 153-5 and 153-6, each switch unit comprises 5 switches Q181, Q182, Q183, Q184 and Q185, the switches Q181, Q182, Q183, Q184 and Q185 are correspondingly connected to two ends of the first coil K1 and the second coil K2 in each winding, and one of the coils in each winding is selectively connected with the motor driving circuit 17 individually or a plurality of coil combinations are connected with the motor driving circuit 17 in series by controlling the on-off of the switches 181, 182, 183, 184 and 185. Here, the form of the switching unit is not limited to the relay switch or the electronic switch, and any component that can change the connection relationship between the coil in each winding and the motor driving circuit 17 may be considered.

Referring to fig. 2 to 6, the connection states between the first coil K1 and the second coil K2 and the motor driving circuit 17 in each winding may be correspondingly set by the wire connection changing unit 19, and when the number of turns n1 of the first coil K1 is smaller than the number of turns n2 of the second coil K2, the connection states between the first coil K1 and the second coil K2 and the motor driving circuit 17 have three kinds. As shown in table 1, in the state of one, the first coil K1 corresponding to each winding is individually connected to the motor driving circuit 17, and the number of turns of the energizable coil on each tooth of the motor 15 is n 1; in the second state, the second coil K2 corresponding to each winding is independently connected with the motor driving circuit 17, and the number of turns of the coil which can be electrified on each tooth is n 2; in the third state, the first coil K1 and the second coil K2 corresponding to each winding are connected in series with the motor driving circuit 17, and the number of turns of the energizable coil on each tooth is n1+ n 2.

TABLE 1 three connection states between the first coil K1, the second coil K2 and the motor drive circuit 17

Connection state	State one	State two	State three
				Connection mode	K1	K2	K1 and K2 are connected in series
Number of turns of coil	n1	n2	n1+n2

In the three states, the output characteristic of the motor is as shown in fig. 7, in the first state, the first coil K1 in each winding is individually connected to the motor driving circuit 17, the number of turns of the energized coil on each tooth of the motor 15 is N1, the corresponding speed-torque characteristic curve of the motor 15 at the time is N1, and the efficiency-torque characteristic curve of the motor 15 is E1; in the second state, the second coil K2 in each winding is separately connected with the motor driving circuit 17, the number of turns of the energized coil on each tooth of the motor 15 is N2, the corresponding speed-torque characteristic curve of the motor 15 at this time is N2, and the efficiency-torque characteristic curve of the motor 15 is E2; in the third state, the first coil K1 and the second coil K2 in each winding are connected in series with the motor driving circuit 17, the number of turns of the coil energized on each tooth of the motor 15 is N1+ N2, the corresponding speed-torque characteristic curve of the motor 15 at this time is N3, and the efficiency-torque characteristic curve of the motor 15 is E3.

As can be seen from fig. 7, when the output characteristic of the motor is fixed, the maximum output torque of the electric power tool is fixed. After the tool is started, along with the increase of the load, the speed of the motor is gradually reduced, the output torque of the motor is gradually increased, and the efficiency of the motor is gradually reduced after the efficiency is increased to the optimal efficiency point. When the load born by the motor is further increased, if the load torque born by the motor is larger than the maximum output torque of the current motor, the motor is easy to stall at the moment, so that the electric tool is stopped, and a user cannot finish the operation. The number of turns of the electrified coil of the motor is different, the output characteristic of the motor is different, the more the number of turns of the electrified coil of the motor is, the stronger the output characteristic of the motor is, the larger the maximum output torque of the motor is, and the more the optimal efficiency point of the motor is.

Based on this, referring to fig. 10, the present invention provides an output characteristic control method of an electric power tool of a first embodiment, including the steps of:

step S10, the user presses the trigger switch to start the electric tool to work;

step S11, the current detection circuit 181 detects the magnitude of the operating current of the motor in the electric power tool;

step S12, the controller 16 determines the load state of the electric tool according to the size of the working circuit of the motor;

in step S13, the wire harness change ticket 19 switches the connection state between the first coil K1 and the second coil K2 and the motor drive circuit 17 according to the load state of the electric power tool.

In this embodiment, the controller 16 determines the load state of the electric power tool according to the working current of the motor and the preset current value, the load state of the electric power tool includes a small load state, a medium load state and a large load state, the connection states between the first coil K1 and the second coil K2 and the motor driving circuit 17 include three states (as shown in table 1), and the steps S12 and S13 specifically include:

step S121, judging whether the working current is greater than a first preset current, determining that the electric tool is in a heavy load state when the working current is greater than the first preset current, and turning to step S233; otherwise, go to step S122;

step S122, judging whether the working current is greater than a second preset current, determining that the electric tool is in a medium load state when the working current is less than or equal to the first preset current and greater than the second preset current, and turning to step S132; otherwise, go to step S131;

step S131, connecting a first coil K1 in each winding with the motor driving circuit 17;

step S132, connecting the second coil K2 in each winding with the motor driving circuit 17;

in step S133, the first coil K1 and the second coil K2 in each winding are connected in series with the motor drive circuit 17.

Referring to fig. 8, the variation trend of the rotation speed of the motor 15 and the load borne by the power tool in the present embodiment is shown as a curve N0, and the variation trend of the operating efficiency of the motor and the load borne by the power tool is shown as a curve E0. As can be seen from the above-described control method, the electric power tool according to the first embodiment of the present invention determines the magnitude of the load on the electric power tool from the operating current of the motor, and determines that the greater the operating current, the greater the load on the electric power tool. When the load of the electric power tool increases, the connection relationship between the first coil K1 and the second coil K2 and the motor drive circuit 17 is switched by the wire connection changing unit 19 so that the larger the load is, the more the number of turns of the energizable coil in each winding of the motor is. Along with the increase of the number of turns of the electrified coil of the motor, the output characteristic of the motor is enhanced, the maximum output torque of the motor is increased, so that the bearable load range of the electric tool is widened, the electric tool can meet the use requirements of three working conditions of small load, medium load and large load, and the working efficiency is always kept better in a wider range. The cruising ability of the dc power supply 12 for electric power tools is also effectively improved due to the improvement of the working efficiency.

As shown in fig. 2, the electric power tool 100 further includes a display unit 14 for indicating a load state of the electric power tool or a connection relationship between windings in the motor 15 and the motor drive circuit 17. The display unit 14 includes a plurality of display lamps, and is connected to the controller 16, and the controller 16 controls the number of the display lamps to indicate the load status of the power tool. Preferably, the display unit 14 comprises an LED lamp, or a light emitting diode, or a display screen. As an alternative embodiment, the display unit 14 includes only one display lamp, and the controller 16 controls the brightness or lighting color of the display lamp to indicate the load status of the power tool. Through the display unit 14, when the user uses the electric tool, the user can clearly know the current state of the electric tool, and adjust the related operation of the electric tool, so as to optimize the use experience of the tool.

Referring to fig. 9, each winding of the motor 15 in the electric tool according to the second embodiment of the present invention includes three independent coils K3, K4, and K5, and the coils K3, K4, and K5 are respectively formed by winding 3 wires on the same tooth in parallel, and are insulated and separated from each other. The motor switching circuit 18 is correspondingly connected to each winding, and is connected with the motor driving circuit 17 in series or individually through the combination of the coils K3, K4 and K5, the coils K3, K4 and K5 are connected with the motor driving circuit 17 in various connection modes, and the corresponding motor can have various output characteristics. When the electric tool is set to support the conversion of the output characteristics of the motor in three load states, the connection states between the coils K3, K4, K5 and the motor drive circuit 17 are, as shown in table 2, one of the coils K3, K4, K5 is connected to the motor drive circuit 17 alone in one state; in the second state, any two of the coils K3, K4 and K5 are connected in series and connected with the motor driving circuit 17; in the third state, the coils K3, K4, and K5 are connected in series with each other and connected to the motor drive circuit 17.

TABLE 2 three connection states between the coils K3, K4, K5 and the motor drive circuit 17

Corresponding to the three connection states of the three coils K3, K4 and K5 and the motor driving circuit 17, the electric tool can be set to support the switching of the output characteristics of the motor under three load states, the output characteristic control method of the electric tool meets the requirements that the load is larger, the number of turns of the coil which can be electrified in each winding of the motor is more, and therefore the output characteristics of the motor are stronger, the electric tool can meet the use requirements of various working conditions, and the corresponding working efficiency is better.

As shown in fig. 11, when the load states of the electric power tool include a small load state, a medium load state, and a large load state, the output characteristic control method of the electric power tool of the second embodiment of the present invention includes:

step S20, the user presses the trigger switch to start the electric tool to work;

step S21, the load detection unit detects a load parameter of the electric tool;

step S22, the control unit receives the load parameter and judges the load state of the electric tool according to the load parameter;

step S23, when the electric tool is in a small load state, controlling the connection state between the coils K3, K4 and K5 in each winding and the motor driving circuit 17 to be a state one; when the electric tool is in a medium-load state, controlling the connection state between the coils K3, K4 and K5 in each winding and the motor driving circuit 17 to be a second state; when the electric power tool is in a heavy load state, the connection state between the coils K3, K4, K5 in each winding and the motor drive circuit 17 is controlled to be state three.

According to different combinations, when the coils K3, K4 and K5 have different numbers of turns, the coils K3, K4 and K5 can have 7 connection modes at most, and correspondingly, the motor 15 can have 7 variable output characteristics. Taking the turns of the coils K3, K4 and K5 as n3, n4 and n5, respectively, and n3< n4< n5 as an example, as shown in table 3 below, in a state of one, the coil K3 is connected with the motor driving circuit 17 independently, and the number of turns of the coil which can be energized in each winding is n 3; in the second state, the coil K4 is independently connected with the motor driving circuit 17, and the number of turns of the coil which can be electrified in each winding is n 4; in the third state, the coil K5 is independently connected with the motor driving circuit 17, and the number of turns of the coil which can be electrified in each winding is n 5; in the fourth state, the coils K3 and K4 are connected in series and connected with the motor driving circuit 17, and the number of turns of the coil which can be electrified in each winding is n3+ n 4; in the fifth state, the coils K3 and K5 are connected in series and connected with the motor driving circuit 17, and the number of turns of the coil which can be electrified in each winding is n3+ n 5; in the sixth state, the coils K4 and K5 are independently connected with the motor driving circuit 17, and the number of turns of the coil which can be electrified in each winding is n4+ n 5; in the seven state, the coils K3, K4 and K5 are connected in series and are separately connected with the motor driving circuit 17, and the number of turns of the energizable coil in each winding is n3+ n4+ n 5.

TABLE 3 seven connection modes between the coils K3, K4, K5 and the motor drive circuit 17

Corresponding seven kinds of variable output characteristic of motor, electric tool can set up the switching that supports the output mode of motor under seven kinds of load states, and control strategy satisfies that the load is big more the number of turns that can energize the coil in every winding of motor is more for the output characteristic of motor is stronger, thereby electric tool can satisfy the user demand of multiple operating mode and the equal preferred of work efficiency that corresponds.

In order to avoid the waste of the electric energy from the dc power source 12, the connection changing unit controls only one coil of each winding in the motor to be connected to the control unit when the electric power tool according to the foregoing embodiment of the present invention is initially started. Preferably, the number of turns of the energizable coil of the motor is minimized at initial start-up of the power tool, so that the power tool starts up with the weakest output characteristic.

According to the above embodiments of the present invention, the load state of the electric power tool includes a plurality of levels of loads classified according to the size of the load, and each level of the loads corresponds to a connection mode between a specific motor winding and the motor driving circuit. The number of turns of the energizable coil in each winding of the motor can be changed by changing the connection relationship between the plurality of coils in each winding and the motor driving circuit, thereby changing the output characteristic of the motor. Different electrified turns of the coil correspond to loads of different grades, so that different motor characteristics can be output by the motor under the load states of different grades, the load is larger, the number of electrified turns of the coil of the motor is more, and the motor characteristics are stronger. So that the electric tool can meet the working requirements of a wider range of load states. In addition, through the switching of the motor characteristics, the problem that the motor efficiency is rapidly reduced when the load is increased is solved, when the load is increased to the next level, the motor characteristics are automatically enhanced, the reduction trend of the motor efficiency is weakened, and the electric tool can always maintain the better motor efficiency. For the electric tool provided by the invention, the endurance time of the direct-current power supply is prolonged, the multipurpose requirement of an operator can be met, and the use requirement of the operator is better met.

In addition, the difference between the plurality of coils in the winding of the motor in the electric tool is not limited to the difference of the number of turns of the coils, and optionally, the connection relation between the plurality of coils is changed by setting different wire diameters of the coils, so that the aim of changing the output characteristic of the motor can be achieved. Correspondingly, the electric tool and the output characteristic control method thereof divide the load state of the electric tool into a plurality of grades, and the connection relation among a plurality of coils with different wire diameters in each winding is set under different grades so as to match the proper motor output characteristic. Therefore, the purpose of enabling the electric tool to adapt to the use requirements of multiple working conditions can be achieved, and the detailed description is omitted.

The present invention is not limited to the above-described embodiments. Those skilled in the art will readily appreciate that there are numerous other alternatives to the power tool and power tool control method of the present invention without departing from the spirit and scope of the present invention. The protection scope of the present invention is subject to the content of the claims.

Claims

1. A power tool, comprising:

a housing;

a DC power supply detachably mounted on the housing for supplying power to the power tool;

a motor located in the housing and including a stator having a plurality of teeth, a rotor rotating relative to the stator, and a plurality of windings wound around the teeth;

the working head is driven by the motor to rotate;

a control unit connected to the winding to control rotation of the motor;

a load detection unit that detects a load parameter of the electric tool;

the method is characterized in that: at least one winding comprises a plurality of mutually independent coils, and the electric tool further comprises a wiring changing unit which is connected between the control unit and the winding in series.

2. The power tool of claim 1, wherein: each winding comprises a plurality of mutually independent coils, and the wiring changing unit is used for selectively connecting one coil of the coils with the control unit or connecting at least two coil combinations of the coils with the control unit in series according to the load state.

3. The power tool of claim 1, wherein: at least one winding includes first coil and second coil, first coil with the number of turns or the line footpath of second coil is different.

4. The power tool of claim 1, wherein: the motor is a three-phase brushless motor, each phase comprises at least two windings, and the three-phase windings of the motor are connected in a star shape or a triangular shape.

5. The power tool of claim 1, wherein: the power tool further includes a display unit for indicating a load state of the power tool.

6. The power tool of claim 1, wherein: when the electric tool is started initially, only one of the plurality of coils is connected with the control unit.

7. The power tool of claim 1, wherein: the load parameter is one or more of working current, working rotating speed, torque and temperature of the motor.

8. An output characteristic control method of an electric power tool having the electric power tool according to any one of claims 1 to 7, characterized in that: the output characteristic control method includes:

starting an electric tool, wherein the load detection unit detects a load parameter of the electric tool;

the control unit receives the load parameters and determines the load state of the electric tool according to the load parameters;

the wiring changing unit changes the connection relation between the control unit and the winding according to the load state.

9. The output characteristic control method of an electric power tool according to claim 8, characterized in that: each winding comprises a first coil and a second coil, the number of turns of the first coil is smaller than that of the second coil, and when the electric tool is in a first load state, the wiring changing unit connects the first coil with the control unit; when the electric tool is in a second load state, the wire connection changing unit connects the second coil with the control unit; when the electric power tool is in a third load state, the wire connection changing unit connects the first coil and the second coil in series with the control unit.

10. The output characteristic control method of an electric power tool according to claim 8, characterized in that: each of the windings includes three coils, and the wire connection changing unit connects one of the three coils with the control unit when the electric power tool is in a first load state; when the electric power tool is in a second load state, the wire connection changing unit connects two of the three coils in series with the control unit; when the electric power tool is in a third load state, the wire changing unit connects the three coils in series with the control unit.