Overload protection method and circuit for an electric tool

Abstract

The present invention discloses an overload protection method and circuit for a power tool, which relates to the field of overload protection of power tools and includes a battery charging management unit, a battery temperature measurement unit, a power management unit, a main control unit, a power-on / off circuit, a motor drive unit, and a current value acquisition unit; the battery charging management unit is connected to the battery temperature measurement unit, the power management unit, and the motor drive unit, the power-on / off circuit is connected to the power management unit, the main control unit is connected to the power management unit, the power-on / off circuit, the motor drive unit, and the current value acquisition unit, and the motor drive unit is connected to the current value acquisition unit. According to the battery voltage, the present invention sets different locked-rotor protection current values, so that the machine system has a low temperature rise, strong single-pack capacity, high system reliability, and comfortable use.

Description

Technical Field

[0001] The present invention relates to the field of overload protection for power tools, and particularly to an overload protection method and circuit for power tools. Background Art

[0002] In the field of overload protection for power tools, especially for electric screwdrivers, the existing technical solutions generally adopt fixed three to four - gear current protection. For example: First gear: 4S protection when the load current > 22A; Second gear: 0.5S protection when the load current > 35A; Third gear: 0.1S protection when the load current > 45A; The highest gear (here it is the third gear) is generally set as the stall protection current. Currently, many portable single - cell - powered screwdrivers have emerged on the market. They are lightweight, compact, can be charged via USB, and the working voltage range is 4.2V - 2.5V, with a relatively large voltage range span. At 4.14V, the motor stall current may be 48A, while at 3.1V, the stall current may drop to 37A. At this time, if the above - mentioned fixed three - gear protection is used, when the voltage is lower than 3.1V, such as Figure 2 As shown, the protection of the controller can only occur in the second gear, and the stall time will increase from 0.1S to 0.5S. The disadvantages brought about are: the motor temperature rises, reducing the reliability of the motor; the temperature of the controller Mos tube rises, reducing the reliability of the power device.

[0003] As Figure 3 As shown is the basic structure of an existing 4V electric screwdriver, including a housing 101. Inside the housing, a machine control board 104, a battery pack 103, a fan 102, a motor 107, a reduction gearbox 105, and a bit 106 are installed. On the machine control board 104, a single - chip microcomputer and related control circuits are installed, which are used to control the operation of the motor 107, the charging and discharging of the battery, etc.; The fan 102 is used to blow air on the motor to dissipate heat from the motor 107. The battery pack 103 is used for charging and discharging and supplying power to electrical equipment. The power output by the motor 107 is decelerated by the reduction gearbox 105 and then output to the bit 106. The bit is installed with a thin wedge - shaped head, so as to tighten or loosen the screw through the thin wedge - shaped head. This structure is small in size. The entire housing of the screwdriver is airtight, and the heat generated inside can only be dissipated through the surface of the housing. Moreover, the motor is relatively close to the housing held by the operator, and the motor temperature is easily transmitted to the holding part of the housing, resulting in a high housing temperature and easily causing discomfort in holding. Therefore, it is necessary to find a way to reduce the temperature rise of the system.

[0004] Due to the above reasons, the temperature of the machine housing rises, resulting in a poor user experience. Especially in summer when the ambient temperature is high, the feel is not good. In addition, due to the high temperature of the machine housing, over-temperature protection will be activated to prevent the machine from failing. If the over-temperature protection is frequently activated, the user will not be able to use it continuously. For example, the 4V screwdriver of BOSCH will continuously activate the over-temperature protection when driving M5x25 screws, resulting in a poor experience. In addition, when the motor is blocked, only ineffective heat is generated and no effective work can be done, which will waste the battery capacity in vain and result in poor single-pack capacity of the machine. For example, originally a 2.0Ah capacity can drive 75 M5x25 screws, but now it can only drive 50. In view of the above defects, the present invention discloses an overload protection method and circuit for an electric tool. Summary of the Invention

[0005] An embodiment of the present invention provides a high-precision acquisition circuit. To have a basic understanding of some aspects of the disclosed embodiments, a simple summary is given below. This summary part is not a general review, nor is it to identify key / important constituent elements or delineate the protection scope of these embodiments. Its sole purpose is to present some concepts in a simple form as a prelude to the subsequent detailed description.

[0006] According to a first aspect provided by an embodiment of the present invention, an overload protection method for an electric tool includes that the current protection value of the electric tool is set with different protection current values according to different battery voltages; for n lithium batteries, when the battery voltage is greater than the full charge voltage V MAX ±0.2V, the locked-rotor protection current value is set to be greater than or equal to I MAX A; when the battery voltage is greater than V M1 =(V MAX -0.5*n)V, the locked-rotor protection current value is set to be greater than or equal to I MAX -5A; when the battery voltage is greater than V M2 =(V MAX -1.0*n)V, the locked-rotor protection current value is set to be greater than or equal to I MAX -10A; when the battery voltage is greater than V MIN =(V MAX -1.4*n)V, the locked-rotor protection current value is set to be greater than or equal to I MAX -15A.

[0007] Preferably, three protection levels are set according to the motor current value of the electric tool. The locked-rotor protection is the highest protection level, the next protection level below the locked-rotor protection is the second protection level, and the next protection level below the second protection level is the third protection level.

[0008] Preferably, after the stall protection gear is activated, the motor of the power tool will stop within 0.1 - 0.3 s; after the second protection gear is activated, the motor of the power tool will stop within 0.4 - 0.6 s; after the third protection gear is activated, the motor of the power tool will stop within 3 - 4 s.

[0009] Preferably, set the current protection value of the second protection gear according to the battery voltage. For n lithium batteries, when the battery voltage is greater than the full charge voltage V MAX ±0.2V, the current protection value of the second protection gear is set to be greater than or equal to I MAX -10 A; when the battery voltage is greater than V MAX -0.5*nV, the current protection value of the second protection gear is set to be greater than or equal to I MAX -15 A; when the battery voltage is greater than V MAX -1.0*nV, the current protection value of the second protection gear is set to be greater than or equal to I MAX -17 A; when the battery voltage is greater than V MAX -1.4*nV, the current protection value of the second protection gear is set to be greater than or equal to I MAX -24 A.

[0010] Preferably, set the current protection value of the third protection gear according to the battery voltage. For n lithium batteries, when the battery voltage is greater than the full charge voltage V MAX ±0.2V, the current protection value of the third protection gear is set to be greater than or equal to I MAX -23 A; when the battery voltage is greater than V MAX -0.5*nV, the current protection value of the third protection gear is set to be greater than or equal to I MAX -23 A; when the battery voltage is greater than V MAX -1.0*nV, the current protection value of the third protection gear is set to be greater than or equal to I MAX -23 A; when the battery voltage is greater than V MAX -1.4*nV, the current protection value of the third protection gear is set to be greater than or equal to I MAX -23 A.

[0011] Preferably, for a single lithium battery, the full charge voltage V MAX is 4.2 V, and the I MAX is set to 45 A.

[0012] Preferably, the battery voltages V MAX 、V M1 、V M2 、V MIN are the voltages of the power tool under no-load conditions.

[0013] According to a second aspect provided by the embodiments of the present invention, an overload protection circuit for a power tool, based on the overload protection method for a power tool according to the above-mentioned invention content, the overload protection circuit of the power tool includes a battery charging management unit, a battery temperature measurement unit, a power management unit, a main control unit, a power-on / off circuit, a motor drive unit, and a current value acquisition unit; the battery charging management unit is connected to the battery temperature measurement unit, the power management unit, and the motor drive unit, the power-on / off circuit is connected to the power management unit, the main control unit is connected to the power management unit, the power-on / off circuit, the motor drive unit, and the current value acquisition unit, and the motor drive unit is connected to the current value acquisition unit.

[0014] Preferably, the motor drive unit is composed of 4 MosFET (Metal-Oxide-Semiconductor Field-Effect Transistor) Q3, Q4, Q5, and Q6. The Metal-Oxide-Semiconductor Field-Effect Transistor Q3 and the Metal-Oxide-Semiconductor Field-Effect Transistor Q6 form a group, and the Metal-Oxide-Semiconductor Field-Effect Transistor Q4 and the Metal-Oxide-Semiconductor Field-Effect Transistor Q5 form a group; when Q3 and Q6 are turned on and Q4 and Q5 are turned off, the motor rotates forward; when Q4 and Q5 are turned on and Q3 and Q6 are turned off, the motor rotates in reverse; when Q3 and Q6 are turned off and Q4 and Q5 are turned off, the motor stops.

[0015] Preferably, the current value acquisition unit is composed of a current sampling resistor Rs and a signal amplification unit, and the current sampling resistor is connected to the signal amplification unit.

[0016] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

[0017] The present invention sets different locked-rotor protection current values according to the battery voltage, making the machine system have a low temperature rise, strong single-pack capacity, high system reliability, and comfortable use.

[0018] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings here are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present invention and used together with the specification to explain the principles of the present invention.

[0020] Figure 1 is an overload protection circuit for a power tool shown according to an exemplary embodiment;

[0021] Figure 2 is the locked-rotor current of the motor under different battery voltages;

[0022] Figure 3 It is a structural schematic diagram of a 4v screwdriver in the prior art.

[0023] In the figure: 1 - Battery charging management unit, 2 - Battery temperature measurement unit, 3 - Power management unit, 4 - Main control unit, 5 - Switching on and off circuit, 6 - Motor drive unit, 7 - Current value acquisition unit. Specific embodiments

[0024] The following description and the accompanying drawings fully illustrate specific embodiments of the present invention so that those skilled in the art can practice them. The examples represent possible variations. Unless explicitly required, individual components and functions are optional, and the order of operations can vary. Parts and features of some embodiments can be included in or substituted for parts and features of other embodiments. The scope of the embodiments of the present invention includes the entire scope of the claims and all available equivalents of the claims. In this document, the embodiments can be individually or collectively referred to by the term "invention" for convenience only, and if in fact more than one invention is disclosed, it is not intended to automatically limit the scope of the application to any single invention or inventive concept. In this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover a non-exclusive inclusion, such that a process, method or device comprising a series of elements includes not only those elements but also other elements not explicitly listed. The various embodiments in this document are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. For the structures, products, etc. disclosed in the embodiments, since they correspond to the parts disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description in the method part.

[0025] The following further describes the present invention with reference to the accompanying drawings and embodiments:

[0026] Embodiment 1:

[0027] The specific embodiment of the present invention discloses an overload protection method for a power tool, including that the current protection value of the power tool is set to different protection current values according to different battery voltages; for n lithium batteries, when the battery voltage is greater than the full charge voltage V MAX ±0.2V, the stall protection current value is set to be greater than or equal to I MAX A; when the battery voltage is greater than V M1 =(V MAXWhen the voltage is (V - 0.5*n)V, the locked-rotor protection current value is set to be greater than or equal to I MAX - 5A; when the battery voltage is greater than V M2 =(V MAX When the voltage is (V - 1.0*n)V, the locked-rotor protection current value is set to be greater than or equal to I MAX - 10A; when the battery voltage is greater than V MIN =(V MAX When the voltage is (V - 1.4*n)V, the locked-rotor protection current value is set to be greater than or equal to I MAX - 15A.

[0028] According to the above solution, further, the motor current value of the electric tool is set with 3 protection levels. The locked-rotor protection is the highest protection level, the next protection level below the locked-rotor protection is the second protection level, and the next protection level below the second protection level is the third protection level.

[0029] According to the above solution, further, after the locked-rotor protection level is activated, the motor of the electric tool will stop within 0.1 - 0.3 s; after the second protection level is activated, the motor of the electric tool will stop within 0.4 - 0.6 s; after the third protection level is activated, the motor of the electric tool will stop within 3 - 4 s.

[0030] According to the above solution, further, the current protection value of the second protection level is set according to the battery voltage. For n lithium batteries, when the battery voltage is greater than the full charge voltage V MAX ±0.2V, the current protection value of the second protection level is set to be greater than or equal to I MAX - 10A; when the battery voltage is greater than V MAX - 0.5*nV, the current protection value of the second protection level is set to be greater than or equal to I MAX - 15A; when the battery voltage is greater than V MAX - 1.0*nV, the current protection value of the second protection level is set to be greater than or equal to I MAX - 17A; when the battery voltage is greater than V MAX - 1.4*nV, the current protection value of the second protection level is set to be greater than or equal to I MAX - 24A.

[0031] According to the above solution, further, the current protection value of the third protection level is set according to the battery voltage. For n lithium batteries, when the battery voltage is greater than the full charge voltage V MAX ±0.2V, the current protection value of the third protection level is set to be greater than or equal to I MAX - 23A; when the battery voltage is greater than V MAX - 0.5*nV, the current protection value of the third protection level is set to be greater than or equal to I MAX-23 A; the battery voltage is greater than V MAX When it is -1.0*nV, the current protection value of the third protection gear is set to be greater than or equal to I MAX -23 A; the battery voltage is greater than V MAX When it is -1.4*nV, the current protection value of the third protection gear is set to be greater than or equal to I MAX -23 A.

[0032] According to the above scheme, further, for a single lithium battery, the full charge voltage V of the battery MAX is 4.2 V, and the I MAX is set to 45 A.

[0033] According to the above scheme, further, the battery voltages V MAX , V M1 , V M2 , V MIN are the voltages of the power tool under no-load conditions.

[0034] Embodiment 2:

[0035] As Figure 1 shown, the present invention also discloses an overload protection circuit for a power tool. According to the overload protection method of the power tool described above, the overload protection circuit of the power tool includes a battery charging management unit 1, a battery temperature measurement unit 2, a power management unit 3, a main control unit 4, a switching on / off circuit 5, a motor drive unit 6, and a current value acquisition unit 7; the battery charging management unit 1 is connected to the battery temperature measurement unit 2, the power management unit 2, and the motor drive unit 6, the switching on / off circuit 5 is connected to the power management unit 3, the main control unit 4 is connected to the power management unit 3, the switching on / off circuit 5, the motor drive unit 6, and the current value acquisition unit 7, and the motor drive unit 6 is connected to the current value acquisition unit 7.

[0036] According to the above scheme, further, the motor drive unit 6 is composed of 4 MosFET (metal-oxide semiconductor field effect transistors) Q3, Q4, Q5, and Q6. The metal-oxide semiconductor field effect transistor Q3 and the metal-oxide semiconductor field effect transistor Q6 form a group, and the metal-oxide semiconductor field effect transistor Q4 and the metal-oxide semiconductor field effect transistor Q5 form a group; when Q3 and Q6 are turned on and Q4 and Q5 are turned off, the motor rotates forward; when Q4 and Q5 are turned on and Q3 and Q6 are turned off, the motor rotates in reverse; when Q3 and Q6 are turned off and Q4 and Q5 are turned off, the motor stops.

[0037] According to the above solution, further, the current value acquisition unit 7 is composed of a current sampling resistor Rs and a signal amplification unit, and the current sampling resistor is connected to the signal amplification unit.

[0038] Embodiment 3:

[0039] This embodiment of the present invention discloses a mini electric screwdriver powered by a single lithium battery built into the device. Its nominal maximum load is capable of driving M5x30 screws in white pine, with a maximum torque of 2.5NS. Due to the relatively high torque requirements, the motor's rated power is 15A, and when the battery is fully charged, the motor's stall current can reach 40A.

[0040] like Figure 2 The schematic diagram of the screwdriver controller is shown. Four MOSFETs are used for motor commutation, although mechanical switches can also be used. The commutation trigger signal is set using two buttons or a toggle switch. When Q3 and Q6 are on and Q4 and Q5 are off, the screw is tightened when the motor rotates forward. When Q4 and Q5 are on and Q3 and Q6 are off, the screw is loosened when the motor rotates reversely.

[0041] The current sampling resistor is used to collect the load current. The sampled signal is then amplifier-amplified to a range of 0 to 5V for AD conversion by the main control unit (MCU). For example, if the sampling resistor is 2 milliohms, the amplifier gain is 40, and the load current is I, then the amplified signal Vc = 0.002*I*40. For a stall current of 40A, then Vc = 3.2V. If the internal AD conversion bit of the main control unit (MCU) is 10 bits and the AD reference voltage is VCC = 5.0V, then the 3.2V analog value is converted to digital value as (3.2 / 5.0)*1024 = 655. If the stall protection time is 100ms, then after 100ms the main control unit (MCU) will turn off the corresponding MOSFET, shutting down the motor. This time is obtained using the main control unit's MCU timer. The following table shows the motor stall current at different battery voltages.

[0042] Battery voltage Locked-rotor current of the motor 4.14V 48A 3.70V 42A 3.10V 37A 2.86V 33A 2.64V 29A

[0043] As can be seen from the table above, as the battery voltage decreases, the motor stall current decreases. This is more clearly shown in a graph, with the battery voltage on the horizontal axis and the stall current on the vertical axis. Stall current Istall = battery voltage Vbat / motor internal resistance R. Since the motor internal resistance is considered constant within a certain temperature range, the stall current is actually proportional to the battery voltage, resulting in an approximate straight line, as shown in Figure 1. Figure 2 shown.

[0044] The key point to be protected by the present invention is that the current protection value is not fixed, but different protection current values, especially the locked-rotor protection current value, are set according to different battery voltages. As in the above embodiments, when the battery voltage > 4.0V, the locked-rotor protection current value can be set > 45A; when the battery voltage > 3.6V, the locked-rotor protection current value can be set > 40A; when the battery voltage > 3.0V, the locked-rotor protection current value can be set > 35A; when the battery voltage > 2.8V, the locked-rotor protection current value can be set > 30A, and then the secondary protection current is adjusted accordingly. Thus, it can achieve that it does not affect the user experience (can tighten large screws), nor will the motor temperature rise too high, that is, the motor efficiency reaches the best state.

[0045] In addition, it should be noted that the measurement of the battery voltage here is also particular. It is necessary to select to measure when the tool is unloaded, because the battery voltage will drop with the load. The greater the load current, the more the battery voltage drops. This is because the internal resistance of a single battery is generally 16 mΩ - 20 mΩ. If the external load current is 20A, then the voltage drop across the battery internal resistance will be 0.32 - 0.4V (0.016 * 20 - 0.020 * 20), and the current of this machine when unloaded is 30mA, so the voltage drop across the internal resistance can be ignored. The specific implementation situation is shown in the following table.

[0046]

[0047] The present invention discloses an overload protection method and circuit for an electric tool. The present invention sets different locked-rotor protection current values according to the battery voltage, making the machine system have a low temperature rise, strong single-pack capacity, high system reliability, and comfortable use. In particular, it solves the problems that the machine shell temperature rises due to the high circuit temperature, especially when the ambient temperature is high in summer, the machine fails and the over-temperature protection is activated, resulting in poor user experience.

[0048] It should be understood that the present invention is not limited to the processes and structures already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. An overload protection method for a power tool, characterized in that, including, the current protection value of the power tool is set with different protection current values according to different battery voltages; for n lithium batteries, when the battery voltage is greater than the full charge voltage (V MAX ±0.2) V, the locked-rotor protection current value is set to be greater than or equal to I MAX A; when the battery voltage is greater than V M1 =(V MAX -0.5*n) V, the locked-rotor protection current value is set to be greater than or equal to (I MAX -5) A; when the battery voltage is greater than V M2 =(V MAX -1.0*n) V, the locked-rotor protection current value is set to be greater than or equal to (I MAX -10) A; when the battery voltage is greater than V MIN =(V MAX -1.4*n) V, the locked-rotor protection current value is set to be greater than or equal to (I MAX -15) A; Three protection levels are set according to the motor current value of the power tool. The stall protection is the highest protection level, the next protection level below the stall protection is the second protection level, and the next protection level below the second protection level is the third protection level; After the stall protection level is activated, the motor of the power tool will stop within 0.1 - 0.3 seconds; after the second protection level is activated, the motor of the power tool will stop within 0.4 - 0.6 seconds; after the third protection level is activated, the motor of the power tool will stop within 3 - 4 seconds; Set the current protection value of the second protection gear according to the battery voltage. For n lithium batteries, when the battery voltage is greater than the full charge voltage (V MAX ±0.2) V, the current protection value of the second protection gear is set to be greater than or equal to (I MAX -10) A; when the battery voltage is greater than (V MAX -0.5*n) V, the current protection value of the second protection gear is set to be greater than or equal to (I MAX -15) A; when the battery voltage is greater than (V MAX -1.0*n) V, the current protection value of the second protection gear is set to be greater than or equal to (I MAX -17) A; when the battery voltage is greater than (V MAX -1.4*n) V, the current protection value of the second protection gear is set to be greater than or equal to (I MAX -24) A.

2. The overload protection method for the power tool according to claim 1, characterized in that, Set the current protection value of the third protection gear according to the battery voltage. For n lithium batteries, when the battery voltage is greater than the full charge voltage (V MAX ±0.2) V, the current protection value of the third protection gear is set to be greater than or equal to (I MAX -23) A; when the battery voltage is greater than (V MAX -0.5*n) V, the current protection value of the third protection gear is set to be greater than or equal to (I MAX -23) A; when the battery voltage is greater than (V MAX -1.0*n) V, the current protection value of the third protection gear is set to be greater than or equal to (I MAX -23) A; when the battery voltage is greater than (V MAX -1.4*n) V, the current protection value of the third protection gear is set to be greater than or equal to (I MAX -23) A.

3. The overload protection method for the power tool according to claim 1, characterized in that, For a single lithium battery, the full charge voltage V of the battery MAX is 4.2V, and the I MAX is set to 45A.

4. The overload protection method of the power tool according to claim 3, characterized in that, The battery voltages V MAX , V M1 , V M2 , V MIN are the voltages of the power tool under no-load conditions.

5. An overload protection circuit for a power tool, according to the overload protection method for a power tool as described in any one of claims 1-4, characterized in that, It includes a battery charging management unit, a battery temperature measurement unit, a power management unit, a main control unit, a power on / off circuit, a motor drive unit, and a current value acquisition unit; the battery charging management unit is connected to the battery temperature measurement unit, the power management unit, and the motor drive unit, the power on / off circuit is connected to the power management unit, the main control unit is connected to the power management unit, the power on / off circuit, the motor drive unit, and the current value acquisition unit, and the motor drive unit is connected to the current value acquisition unit.

6. The overload protection circuit of the power tool according to claim 5, characterized in that, The motor drive unit is composed of 4 MosFET (Metal-Oxide-Semiconductor Field-Effect Transistors) Q3, Q4, Q5, and Q6. Q3 and Q6 are in one group, and Q4 and Q5 are in one group; when Q3 and Q6 are conducting and Q4 and Q5 are off, the motor rotates forward; when Q4 and Q5 are conducting and Q3 and Q6 are off, the motor rotates backward; When Q3 and Q6 are off and Q4 and Q5 are off, the motor stops.

7. The overload protection circuit of the power tool according to claim 5, wherein The current value acquisition unit consists of a current sampling resistor Rs and a signal amplification unit, and the current sampling resistor is connected to the signal amplification unit.

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