WO2022174284A1 - Electronic clutch for sensorless brushless motors in power tools - Google Patents

Abstract

An electronic clutch for a sensorless brushless DC motor, wherein the clutch does not utilise any rotor position sensors in determining its operation. Preferably the clutch utilises a voltage measurement across a series of power transistors of the DC motor to determine the electronic clutch operation, and operates by means of pulse width modulation of the DC motor. Preferably, the power transistors comprise power MOSFETs and the voltage measurement includes measuring the voltage across the power MOSFET drain-source channel resistance.

Description

Electronic Clutch for Sensorless Brushless Motors in Power Tools

RELATED APPLICATION

[0001] The present disclosure claims benefit of priority to Australian Provisional Patent Application No. 2021900443 filed 19 February 2021, the contents of which are incorporated herein by reference. In jurisdictions where incorporation by reference is not permitted, the applicant reserves the right to add any or the whole of the contents of said Australian Provisional Patent Application No. 2021900443 as an Appendix hereto, forming part of the specification.

FIELD OF THE INVENTION

[0002] The present invention is directed to the area of control of electric brushless DC (BLDC) motors, and, in particular discloses an electronic clutch system and method for sensorless BLDC motor control applications in electric power tools.

References

[0003] [1] Midwest Research Institute, BRUSHLESS DC MOTORS, National Aeronautics and

Space Administration, Washington, D.C., 1975

[0004] [2] Wikipedia, Brushless DC electric motor, http://en.wikipedia.org/wiki/Brushless_DC_electric_motor

[0005] [3] Muhammad Mubeen, Brushless DC Motors Primer, Radford, VA, 2008

[0006] [4] Hendershot J.R. Jr and Miller Tje, Design of Brushless Permanent-Magnet Motors,

Magna Physics Publishing, New York, 1994

[0007] [5] Gamazo-Real J., Vazquez-Sanchez E., Gomez-Gil J., Position and Speed Control of

Brushless DC Motors Using Sensorless Techniques and Application Trends, Open Access, Sensors, 2010

[0008] [6] Bhim Singh and Sanjeev Singh, State of the Art on Permanent Magnet Brushless DC

Motor Drives, Journal of Power Electronics, Vol. 9, No. 1, January 2009 [0009] [7] Hitachi, Instruction Manual and Safety Instructions for Cordless Driver Drill, MODEL

DS 10DV2

[0010] [8] Black & Decker, DIY Basics: How to Use a Drill, March 2018, https://www.blackanddecker.com/ideas-and-inspiration/articles/diy-basics-how-to-use-a-drill

[0011] [9] Texas Instruments, DRV832x 6 to 60-V Three-Phase Smart Gate Driver, SLVSDJ3C -

February 2017

[0012] [10] STMicroelectronics, Current sensing in BLDC motor application, AN5423 - Rev 1

January 2020

BACKGROUND OF THE INVENTION

[0013] Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is widely known or forms part of common general knowledge in the field.

[0014] BLDC Motors: Brushless DC motors are used in a wide variety of market applications, such electric power tools, because they can offer increased energy efficiency and density, power output, compactness, operational reliability and life expectancy. BLDC motors, also known as permanent magnet synchronous motors (PMSM), are classified according to their phase winding configuration, such as wye or delta, and the number of magnetic poles as described in [1], [2], [3], [4]

[0015] Sensored BLDC Motor Control: In today’s global markets, brushless motor applications are dominated by sensored BLDC motor control technologies [5], which utilize rotor position sensors inside the motors, such as Hall effect sensors or encoders. These sensors make it easy to electronically commutate and operate BLDC motors from start to high speeds. However, they increase the size and weight of the motors, and manufacturing costs due to additional components, circuitry and inter-wiring connections that are required. The rotor position sensors can also be subjected to operation at very high temperatures, electric and magnetic interference, and assembly placement errors that can lead to losses in energy efficiency and motor torque. Sensored BLDC motors are also prone to more electrical and mechanical failures which reduce system reliability and increase operating costs compared to alternate brushless motor control technologies that do not employ rotor position sensors. [0016] Sensorless BLDC Motor Control: Instead of using rotor position sensors, sensorless BLDC motor control techniques use only electrical measurements, such as motor phase voltages and currents, obtained directly from the motor in order to ascertain the rotor position during operation. Those skilled in the art of sensorless BLDC motor controller design are familiar with the inherent challenges of operating such motors at and near zero speeds [5], particularly in the presence of demanding dynamic loads, for example such as encountered in power tool fastening and drilling applications with cordless drill drivers. These issues often arise because of the technical difficulties associated with determining accurate rotor position information at zero and low speeds, which is important for robust electronic commutation of sensorless BLDC motors. There exists a significant amount of prior art related to the design of sensorless BLDC motor controllers [5], [6] However, it is evident that no single controller solution, alone, can reliably operate motors from start to high speed under all load conditions. Thus in practice, sensorless BLDC motor controller designs may use a hybrid approach, such as described in PCT Publication WO2019/056072, entitled “System and Method for Controlling a Motor”, to the present applicant, incorporated here by cross reference, which can encompass one or more of the following key areas of controller operation: Initial rotor position detection (IRPD); Sensorless operation at zero and low motor speeds; Sensorless operation at high motor speeds. When designed successfully, sensorless BLDC motor control systems can offer increased energy efficiency, reliability and cost effectiveness compared to sensored BLDC motor control systems.

[0017] Mechanical Clutch: In electric power tool applications, such as a drill driver [7], [8], a mechanical clutch is used to limit the maximum torque transferred to the output spindle during operation. Mechanical clutches used in power tools are commonly referred to as slip or disengagement or torque overload clutches, and their primary function is to decouple the power tool’s motor drive from the output spindle once a set maximum torque is exceeded. In such clutch designs, the transferred torque while the clutch is slipping is generally lower than the maximum torque that the clutch can transfer before starting to slip. An example of a mechanical torque overload clutch in a power tool is described in US Patent US7886841. A mechanical clutch can be used to protect the power tool equipment from damage and the user from potentially harmful injuries. In fastening applications, a mechanical clutch can be used to control the depth of the fastener being driven into a workpiece and thus prevent over-driving the fastener and damaging the workpiece. A mechanical clutch can also be used to prevent damaging the slots on the screw head, for example when fastening set screws into wood using screwdriver bits. Mechanical clutches, however, consist of moving parts which can wear out over time and make the clutch inoperable.

[0018] Electronic Clutch: To reduce manufacturing cost, size, weight and mechanical wear of an electric power tool, an electronic clutch can be used to can emulate the operation of a mechanical clutch by controlling the magnitude of the current flowing through the motor, and thus the motor torque which is proportional to the current. In practise, this is achieved by limiting the maximum motor current and detecting when the motor has stalled due to an overload, before briefly turning-off the power and restarting the motor. The resultant motor torque and rotational speed interruptions create an effect very similar to a mechanical clutch which decouples a power tool’s motor drive from the output spindle once the maximum torque is reached. Since an electronic clutch does not use any moving parts that can wear out, the clutch operating torque can be controlled more accurately and precisely than in a mechanical clutch over the entire lifetime of operation. US Patent US9193055 and US Patent Publication US2016/0354888 are examples of known prior art that disclose electronic clutch operation in power tools using sensored BUDC motors and controllers that require rotor position sensors. These sensors however, increase manufacturing cost, equipment size, weight and reduce system efficiency and reliability. There appears to be very little known prior art that achieves electronic clutch operation in BUDC motor control applications without using rotor position sensors. To those skilled in the art this is apparent for several reasons. Firstly, practical sensorless BUDC motor controllers for power tools, such as described in the aforementioned PCT Publication W02019/056072, are presently rare in the industry because they are difficult to implement, especially for the extremely challenging drill driver applications where clutches are typically used. Secondly, stable electronic clutch operation requires fast, accurate and robust rotor position detection and operation of sensorless BUDC motors at zero and near zero speeds, because in order to successfully emulate a mechanical disengagement clutch operation the motors must be quickly restarted after stalling, typically within a few milliseconds. Such fast and repetitive motor stop-start power interruptions, and the reversed rotor momentum rotations which can ensue in the motor, demand highest performing sensorless BUDC motor control systems that have been designed specifically for these operating conditions. Therefore, it would be desirable if an electronic clutch solution would be provided for the more cost effective, reliable and efficient sensorless BUDC motor control systems in power tool applications, such as drill drivers, which does not use rotor position sensors.

SUMMARY OF THE INVENTION

[0019] It is an object of the invention, in its preferred form to provide for an improved form of electronic clutch for sensorless brushless DC motor control systems in applications such as electric power tools.

[0020] In accordance with a first aspect of the present invention there is provided an electronic clutch for a sensorless brushless DC motor, wherein the clutch does not utilise any rotor position sensors in determining its operation. [0021] In accordance with another aspect of the present invention there is provided an electronic clutch for a sensorless brushless DC motor which utilises the voltage measurement across a series of power transistors of the DC motor to determine the electronic clutch operation.

[0022] In some embodiments, the clutch operates by means of pulse width modulation of the DC motor. Preferably, the power transistors comprise power MOSFETs and said voltage measurement includes measuring the voltage across the power MOSFET drain-source channel resistance.

[0023] In accordance with another aspect of the present invention there is provided a sensorless BLDC motor control system which utilises a series of analog voltage amplifiers to amplify the measured voltage across the power MOSFET drain-source channel to measure the motor current.

[0024] In some embodiments, only one current-shunt resistor sensor is provided between the ground voltage rail and the source terminals of the low-side power transistors, or between the power supply voltage rail and the drain terminals of the high-side power transistors to measure the motor current. In some embodiments, at least two current-shunt resistor sensors are provided between each power transistor’s source terminal and the ground voltage rail, or between each power transistor’s drain terminal and the power supply voltage rail to measure the motor current. In some embodiments, at least two current-shunt resistor sensors are provided in-line between each phase terminal of the BLDC motor and the output of the low-side and high-side power transistors to measure the motor current.

[0025] In accordance with another aspect of the present invention there is provided an electronic clutch for sensorless BLDC motor control systems which limits the pulse width modulation (PWM) duty cycle (D.C.), and thus the motor current and torque, if the measured motor current exceeds a first predetermined set electronic clutch current.

[0026] In some embodiments, the limitation of the PWM includes utilising feedback control techniques such as, but not limited to, PID control or Instantaneously turning -off the power transistors in the same PWM cycle when the maximum electronic clutch current limit threshold is reached.

[0027] In accordance with another aspect of the present invention, there is provided an electronic clutch for sensorless BLDC motor control systems which has an engaged and a disengaged electronic clutch controller state.

[0028] In accordance with another aspect of the present invention, there is provided an electronic clutch for sensorless BLDC motor control systems which detects motor operation errors, such as, but not limited to, a motor stall and a motor commutation timing error, in order to determine when the electronic clutch operation enters the engaged state.

[0029] In accordance with another aspect of the present invention, there is provided an electronic clutch for sensorless BLDC motor control systems which applies a motor brake until the motor has come to a complete standstill to ensure that the motor does not contain any forward or reverse motor rotations, in order to stabilise the operation of the electronic clutch with the sensorless BLDC motor control systems.

[0030] In accordance with another aspect of the present invention, there is provided an electronic clutch for sensorless BLDC motor control systems which utilises an initial rotor position detection pulsing stream with increased on-time pulse duration to create and control the volume of the emitted motor pulsating sound so as to approximate a mechanical clutch.

[0031] In accordance with another aspect of the present invention, there is provided an electronic clutch for sensorless BLDC motor control systems which decreases the electronic clutch current from the user set electronic clutch current (IE-CLUTCH USER) level to an equal or a lower electronic clutch current (IE-CLUTCH ENGAGE), that is IE-CLUTCH ENGAGE <= IE-CLUTCH JJSER, in order to reduce the motor output torque once the clutch is engaged, similar to the operation of a mechanical clutch where the transferred torque while the clutch is slipping is generally lower than the maximum torque that the mechanical clutch can transfer before starting to slip.

[0032] In accordance with another aspect of the present invention, there is an electronic clutch for sensorless BLDC motor control systems which, after the electronic clutch has disengaged, increases the electronic clutch current from the engaged state level (IE-CLUTCH ENGAGE) back to the user electronic clutch level (IE-CLUTCH USER) in a gradual manner at a predefined rate of increase or slope or trajectory, and, or after a time delay in order to improve the stability of the electronic clutch operation with the sensorless BLDC motor control systems.

[0033] In accordance with another aspect of the present invention, there is provided an electronic clutch for sensorless BLDC motor control systems which modulates the BLDC motor driving PWM D.C. between a minimum (PWM_DC_MIN) and maximum (PWM_DC_MAX) PWM duty cycle value, where 0 < PWM_DC_MIN < PWM_DC_MAX, with pulse durations equal to Tpwvi DC MIN and TPWM DC MAX respectively in order to improve the stability and performance of the electronic clutch operation with the sensorless BLDC motor control systems. [0034] In accordance with another aspect of the present invention, there is provided an electronic clutch for sensorless BLDC motor control systems which has a PWM D.C. pulse modulating frequency (F PWM DC MOD) equal to FPWM_DC_MOD = 1 / (TPWM DC_MIN + TPWM_DC_MAX), which is proportional to the command throttle position, that is, by increasing the modulating PWM D.C. pulsing frequency with increasing command throttle value and decreasing the modulating PWM D.C. pulsing frequency with a decreasing command throttle value, in order to create a motor pulsating sound and pitch effect, which is similar to a mechanical clutch operation with a clutch operation frequency proportional to the motor speed and thus the command throttle position that controls the motor speed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0036] Fig. 1 illustrates a block diagram of a disclosed electronic clutch for sensorless BLDC motor control systems in applications such as power tools.

[0037] Fig. 2 illustrates a sensorless BLDC motor controller circuitry (prior art).

[0038] Fig. 3 illustrates an operation block diagram of a sensorless BLDC motor controller (prior art).

[0039] Fig. 4 illustrates an operation flowchart of disclosed electronic clutch controller for sensorless BLDC motor control systems in applications such as power tools.

[0040] Fig. 5 illustrates a practical example of measured motor currents during operation of disclosed electronic clutch with a sensorless BLDC motor controller in a cordless drill driver fastening application.

[0041] Fig. 6 illustrates an initial rotor position detection phase windings voltage pulsing sequence implemented in a sensorless BLDC motor controller (prior art).

[0042] Fig. 7 illustrates a method of power transistor PWM D.C. modulation in disclosed electronic clutch operation for sensorless BLDC motor control systems in applications such as power tools. [0043] Fig. 8 illustrates a method of controlling power transistor PWM D.C. pulse modulating frequency in relation to user command throttle position in disclosed electronic clutch operation for sensorless BLDC motor control systems in applications such as power tools.

DETAILED DESCRIPTION

[0044] The embodiments are directed to the area of electronic clutch control for electric brushless DC (BLDC) motors in power tool applications, such as drill drivers, with a particular focus on the sensorless BLDC motors and control systems. The application and technology relate generally to the challenges of creating an effective electronic clutch for sensorless BLDC motor control systems to operate with such electric motors. A set of challenges for electronic clutch operation with sensorless BLDC motor control systems are apparent, which translate across a large set of applications and realizations, these are: Electronic clutch operation with sensorless BLDC motors without any rotor position sensors, such as Hall effect sensors or encoders; Stability of electronic clutch operation with sensorless BLDC motors; Electronic clutch operation with sensorless BLDC motors with the motor at start, standstill and in motion; Electronic clutch operation with sensorless BLDC motors with the motor with reversed rotor momentum; Electronic clutch operation with sensorless BLDC motors to achieve an operational sound and power feel similar to a mechanical clutch; Electronic clutch operation with sensorless BLDC motors with cost effective current sensing circuitry; Electronic clutch operation with a broad range of sensorless BLDC motors available on the market (salient and non-salient pole, wye and delta winding, asymmetric stator phase winding inductances and resistances); Electronic clutch operation with a broad range of sensorless BLDC motor control applications in power tools, such as drill drivers.

[0045] The embodiments provide an electronic clutch for sensorless BLDC motor control systems that have improved performance, operational behaviour and greater possibility across one or more of these areas of challenge. As such, the disclosure of the embodiments is applicable to a wide area, and more broadly applicable to the application of sensorless BLDC motors across applications, including and not limited to power tools. A general primer of the breadth and applicability of the areas of interest and application of BLDC motors can be found in [1],[2],[3]

[0046] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which does not use any rotor position sensors.

[0047] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which does not require any additional current sensing circuitry to measure the motor current by measuring the voltage across the power MOSFET drain-source channel resistance which is proportional to the motor current.

[0048] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which reduces the size of electronic circuitry by eliminating current-shunt resistor sensors when using analog voltage amplifiers, such as an operational amplifier (OP-AMP) to amplify the measured voltage across MOSFET drain-source channel resistance in order to measure the motor current.

[0049] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which requires only one global current-shunt resistor sensor: between the ground voltage rail and the source terminals of the low-side power transistors, or between the drain terminals of the high-side power transistors and the power supply voltage rail, to measure the motor current.

[0050] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which uses two or three current-shunt resistor sensors between: each power transistor’s source terminal and the ground voltage rail, or between each power transistor’s drain terminal and the power supply voltage rail to measure the motor current.

[0051] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which uses two or three current-shunt resistor sensors in-line between each phase terminal of the BLDC motor and the outputs of the power transistor inverter’s low-side and high-side power transistors to measure the motor current.

[0052] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which limits the PWM D.C., and thus the motor current and torque, if the measured motor current exceeds the set electronic clutch current, using feedback control techniques such as, but not limited to: PID control; or Instantaneously turning-off the MOSFET power transistors in the same PWM cycle when the maximum electronic clutch current limit threshold is reached.

[0053] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which has an engaged and a disengaged electronic clutch controller state.

[0054] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which detects motor operation errors, such as, but not limited to, a motor stall error and a motor commutation timing error, in order to determine when the electronic clutch operation enters the engaged state. [0055] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which applies a motor brake until the motor has come to a complete standstill to ensure that the motor does not contain any forward or reverse motor rotations, in order to stabilise the operation of the electronic clutch with the sensorless BLDC motor control systems.

[0056] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which uses the initial rotor position detection (IRPD) pulsing stream with increased on-time pulse durations to create and control the volume of the emitted motor pulsating sound that is more similar to a mechanical clutch.

[0057] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which decreases the electronic clutch current from the user set electronic clutch current (IE-CLUTCH USER) level to an equal or a lower electronic clutch current (IE-CLUTCH ENGAGE), that is IE-CLUTCH ENGAGE <= IE- CLUTCH USER, in order to reduce the motor output torque once the clutch is engaged, similar to the operation of a mechanical clutch where the transferred torque while the clutch is slipping is generally lower than the maximum torque that the mechanical clutch can transfer before starting to slip.

[0058] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which modulates the BLDC motor driving PWM D.C. between a minimum (PWM DC MIN) and maximum (PWM DC MAX) PWM duty cycle value, where 0 < PWM DC MIN < PWM DC MAX, with pulse durations equal to TPWM DC MIN and TPWM DC MAX respectively in order to improve the stability and performance of the electronic clutch operation with the sensorless BLDC motor control systems.

[0059] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which has a PWM D.C. pulse modulating frequency (FPWM DC MOD) equal to FPWM DC: MOD = 1 / (Tpwvt DC MIN + T pwvi DC MAX), which is proportional to the command throttle position, that is, by increasing the modulating PWM D.C. pulsing frequency with increasing command throttle value and decreasing the modulating PWM D.C. pulsing frequency with a decreasing command throttle value, in order to create a motor pulsating sound and pitch effect, which is similar to a mechanical clutch operation with a clutch operation frequency proportional to the motor speed and thus the command throttle position that controls the motor speed.

[0060] The embodiments provide an electronic clutch for sensorless BLDC motor control systems which, after the electronic clutch has disengaged, increases the electronic clutch current from the engaged state level (IE-CLUTCH ENGAGE) back to the user electronic clutch level (IE-CLUTCH USER) in a gradual manner at a predefined rate of increase or slope or trajectory, and, or after a time delay in order to improve the stability of the electronic clutch operation with the sensorless BLDC motor control systems.

[0061] The embodiments disclose an electronic clutch for sensorless BLDC motor control systems as illustrated in Fig. 1 for applications in electric power tools, which includes: A sensorless BLDC motor controller that also integrates the disclosed electronic clutch controller; A sensorless brushless DC motor which is integrated into a power tool; User control inputs which set the desired user command throttle and electronic clutch current level; A motor current sensing circuitry which is used to measure the motor current during electronic clutch operation.

[0062] To proceed with the description, it is instructive to introduce some sensorless BLDC motor controller background information.

[0063] A Sensorless BLDC Motor Controller Circuit

[0064] The basic equivalent circuit for the control of the sensorless BLDC motor, such as used by the disclosed electronic clutch is illustrated 20 in Fig. 2. This sensorless BLDC motor control circuit is described in greater detail in the aforementioned PCT Publication W02019/056072. The sensorless BLDC motor control system includes:

[0065] A sensorless BLDC motor 21 with a stator consisting of plurality of coil phase windings, wye or delta phase winding configuration (Fig. 2 depicting a delta winding), a rotor which includes a permanent magnet, arranged to rotate in or around the stator of the motor;

[0066] A sensorless BLDC motor switching control circuit, also commonly known as an inverter, consisting of plurality of semiconductor power transistor switches (A_L, A H, B_L, B_H, C L, C_H) 23 such as MOSFETs or IGBTs to control the pulse width modulated (PWM) phase winding currents in a synchronized manner with the rotor position, and includes freewheeling semiconductor diodes e.g. 24 to conduct PWM off-time switching inductive currents;

[0067] A power transistor gate control circuit consisting of plurality of gate drivers (A_L, A H, B_L, B_H, C L, C_H) to optimally control the power transistors during switching operation. Additionally, an analog to digital converter (ADC) circuit 26, converting at high speed, a plurality of analog voltage measurements (Va, Vb, Vc) 29, which can include voltage resistor divider networks to reduce the sampled analog voltages to an acceptable level for measurement with an ADC and capacitors to reduce measured analog voltage bandwidth and filter out electrical noise; [0068] A microcontroller 28 which provides various functionalities. The microcontroller may comprise peripherals such as an integrated high speed ADC circuit, volatile memory such as DRAM, and non-volatile memory such as PROM, EPROM, EEPROM, FLASH, MRAM, PCRAM, and other functionalities such as user input and output interfaces, communication ports, comparator circuits, and operational amplifier circuits etc;

[0069] Electrical voltage source (Vs) such as a battery or a transformer or a switching power supply is also provided (not shown).

[0070] A Sensorless BLDC Motor Controller Operation Block Diagram

[0071] The sensorless BLDC motor controller operation block diagram, such as used by the disclosed electronic clutch is illustrated in Fig. 3. This sensorless BLDC motor controller operation is described in greater detail in the aforementioned PCT Publication W02019/056072. The sensorless BLDC motor controller operation block diagram includes:

[0072] An initial rotor position detection (IRPD) operation which is used to detect the starting rotor position of a sensorless BLDC motor at standstill or in motion, including during reversed rotor momentum rotation, without using rotor position sensors such as Hall effect sensor or encoders;

[0073] A zero to high speed sensorless BLDC motor control operation, which may include a hybrid sensorless BLDC motor control approach as illustrated in Fig. 3, consisting of a zero to high speed sensorless BLDC motor operation and a low to high speed sensorless BLDC motor operation, designed to successfully drive a broader range of BLDC motors from zero speed to high speeds under all motor loading conditions, including during reversed rotor momentum motor operation conditions, without using rotor position sensors such as Hall effect sensor or encoders;

[0074] A sensorless BLDC motor brake operation designed to bring such motors to a standstill. [0075] Electronic Clutch for Sensorless BLDC Motors

[0076] This section discloses the electronic clutch system and methods of operation developed for sensorless BLDC motor control applications such as in power tools. The block diagram of the disclosed electronic clutch for sensorless BLDC motor controllers is illustrated in Fig. 1. The key constituents of the electronic clutch system include: A sensorless BLDC motor controller, such as described in the aforementioned PCT Publication W02019/056072, that integrates the disclosed electronic clutch controller with a method of operation as illustrated in the embodiment of the operation flow chart in Fig. 4; A sensorless brushless DC motor which is integrated into a power tool; User control inputs which set the desired user command throttle and electronic clutch current level; A motor current sensing circuitry which is used to measure the motor current during electronic clutch operation. These are described in greater detail in the proceeding sections.

[0077] (a) User Control Inputs: The user control inputs are used to set the desired command throttle and electronic clutch current level required by the application. In practice, these user control inputs can be implemented with potentiometers, switches and other circuitry, for example as commonly used in power tools. The command throttle is used to control the speed and torque of the motor integrated into a power tool. For example, this can be achieved by setting the PWM duty cycle (D.C.) of the semiconductor power transistors, which are used to drive the BUDC motor, in proportion to the command throttle position. The electronic clutch current user control input is used to set the maximum motor current (I) during electronic clutch operation and thus the maximum motor torque (T) which is directly proportional to the motor current via the motor torque constant (Kt) in the equation below:

T = I . Kt (1)

[0078] The selection of the electronic clutch current level is not limited only to the external user control inputs, for example it may be selected via other sources, such as internally by the program software that implements the electronic clutch controller operation. The user control inputs may also include a forward or reverse motor drive direction selection, and an electronic clutch operation enable or disable selection, which for example are commonly implemented in power tools.

[0079] (b) Motor Current Sensing: The disclosed electronic clutch controller operation senses the motor current and uses this information to control the maximum motor current or torque. The following section discloses the different current sensing circuitries which can be implemented to sense the motor current in order to optimize the disclosed electronic clutch operation with different sensorless BUDC motor control systems that can be realized in practise.

[0080] (i) Motor Current Sensing using MOSFET Drain-Source Resistance Voltage Measurements:

A first disclosed motor current sensing embodiment utilizes the resistance across the MOSFET drain- source channel (Rds) to obtain a motor current measurement (I) which is directly proportional to the voltage across the MOSFET drain-source channel (Yds) via the relationship in the equation below: I = Vds / Rds (2)

[0081] The motor current measurement can be obtained directly from the sensorless BLDC motor controller’s ADC motor phase voltage sensing inputs (Va, Vb, Vc) as illustrated in Fig. 2. This embodiment can offer reduced motor controller size, weight and manufacturing cost which is beneficial in applications such as power tools. This embodiment has the following advantages:

[0082] No additional electronic circuitry, such as current-shunt resistor sensors, is required if the voltages across MOSFET drain-source channel resistances are measured directly by the ADC motor phase voltage sensing inputs;

[0083] Reduced electronic circuitry size when analog voltage amplifiers, such as an operational amplifier (OP-AMP), are used to amplify the measured voltage across MOSFET drain-source channel resistances, without additional current-shunt resistor sensors, in order to sense the motor current with greater resolution and accuracy. This embodiment can also be realized with operational amplifiers that are integrated directly into the peripherals of a microcontroller such as illustrated in Fig. 2;

[0084] Furthermore, power transistor gate drivers as illustrated in Fig. 2, which integrate MOSFET drain-source voltage sensing circuitry with operational amplifiers, such as described in [9], can also be advantageously used to measure the motor current with this cost effective method that does not require any current-shunt resistor sensors.

[0085] (ii) Motor Current Sensing using One Low-Side or High-Side Current-Shunt Resistor Sensor: Another disclosed motor current sensing embodiment utilizes only one global current-shunt resistor sensor to measure the motor current [10], which can be implemented: in the low-side between the ground voltage rail and the common source terminals of the A_L, B_L, C L low-side power transistors; or in the high-side between the power supply voltage rail (Vs) and the common drain terminals of the A H, B_H, C_H high-side power transistors, of the sensorless BLDC motor controller circuitry illustrated in Fig. 2. Together with additional circuitry which may include an operational amplifier and R-C filter circuitry, the motor current can be measured to enable operation of the disclosed electronic clutch.

[0086] (iii) Motor Current Sensing using Two or Three Low-Side or High-Side Current-Shunt Resistor Sensors: Another disclosed motor current sensing embodiment utilizes two or three current- shunt resistor sensors to measure the motor current [10], which can be implemented: in the low-side between the ground voltage rail and the source terminal of each low-side A_L, B_L, C L power transistor; or in the high-side between the power supply voltage rail (Vs) and drain terminal of each high-side A H, B_H, C_H power transistor, of the sensorless BLDC motor controller circuitry illustrated in Fig. 2. Together with additional circuitry which may include operational amplifiers and R- C filter circuitry, these can be used to measure the motor current in each phase of the BLDC motor to enable operation of the disclosed electronic clutch.

[0087] (iv) Motor Current Sensing using Two or Three In-Line Current-Shunt Resistor Sensors: Another disclosed motor current sensing embodiment utilizes two or three current-shunt resistor sensors placed in-line with each phase terminal of the BLDC motor to measure the motor current [10], which can be implemented between each phase terminal of the BLDC motor and the outputs of the low-side and high-side power transistors A_L and A H, B_L and B_H, C L and C_H, of the sensorless BLDC motor controller circuitry illustrated in Fig. 2. Together with additional circuitry which may include operational amplifiers and R-C filter circuitry, these can be used to measure the motor current in each phase of the BLDC motor to enable operation of the disclosed electronic clutch.

[0088] (c) Electronic Clutch Controller: This section discloses the preferred embodiment of the electronic clutch controller operation implemented in a sensorless BLDC motor controller, with reference to the operation flow chart illustrated in Fig. 4. The disclosed electronic clutch controller has an engaged and a disengaged state and is integrated into a sensorless BLDC motor controller, such as disclosed in the aforementioned PCT Publication W02019/056072. A practical example of the measured motor currents of the disclosed electronic clutch operation with a sensorless BLDC motor controller in a cordless drill driver during a fastening application is shown in Fig. 5.

[0089] (i) Motor Startup and Drive Operation: The electronic clutch controller operation starts in the disengaged state by reading the user control inputs, consisting of the command throttle and the desired electronic clutch current value (IE-CLUTCH USER). This maximum electronic clutch current can, for example, be set in the range between 5A to 100A (eg. IE-CLUTCH USER = 45A setting used in the example practical drill driver fastening electronic clutch operation in Fig. 5), however in practise this depends on the type of motor used and the power tool application. The user control inputs may also include other inputs, such as a forward or reverse motor drive direction selection which is commonly used in power tools, in order to allow the user to operate the electronic clutch in both driving direction. If the user engages the command throttle, then the motor controller determines a corresponding proportional PWM D.C. value which is greater than zero (eg. 1% - 100%). This instructs the motor controller to detect the BLDC motor’s startup rotor position using the initial rotor position detection (IRPD) method, such as disclosed in the aforementioned PCT Publication W02019/056072, and then activate the appropriate power transistors, such as illustrated in the sensorless BLDC motor controller circuitry in Fig. 2, in order to create a flow of current through the BLDC motor phase windings and thus drive the motor in either a forward or a reverse direction, as set by the user application. Command throttle slew-rates, throttle mappings (eg. linear, non-linear, piecewise) and time delays may also be applied to the resultant PWM D.C. in order to control the current through the motor in a more specific way that may be advantageous to the operation of the disclosed electronic clutch. For example, a slow throttle slew-rate value (eg. >100ms to increase PWM D.C. from 1% to 100%) may be used to slow down the response of the electronic clutch operation when low maximum electronic clutch current values are used, and a high throttle slew-rate value (eg. <20ms to increase PWM D.C. from 1% to 100%) may be used to increase the response of the electronic clutch operation when high maximum electronic clutch current values are used.

[0090] (ii) Motor Current Limiter: Once the BLDC motor is spinning, the current flowing through the motor’s phase coils is measured at regular timing intervals (eg. every few microseconds) by the motor controller using one of the previously disclosed current sensing methods and compared to the set electronic clutch current level. If the measured motor current exceeds the set electronic clutch current, then the PWM D.C. value is reduced (eg. <100%) by the motor controller in order to limit the maximum motor current, and thus motor torque, to the set electronic clutch current value, as illustrated in the operation flow chart in Fig. 4. The resultant PWM D.C. can be regulated using feedback control techniques such as, but not limited to: PID control; or Instantaneously turning-off the power transistors in the same PWM cycle when the maximum electronic clutch current limit threshold is reached. A practical drill driver fastening application example of the disclosed electronic clutch operation demonstrating this motor current limiting to IE-CLUTCH USER and IE-CLUTCH ENGAGE motor current levels is shown in Fig. 5.

[0091] (iii) Motor Operation Error Detection: An important part of the disclosed electronic clutch operation is the ability of the sensorless BLDC motor controller to accurately detect when an error has occurred during normal motor driving operation. A motor operation error detection can include, but is not limited to: A stalled motor error detection which is activated when the motor has reached a zero or a near zero speed (eg. <200RPM) during operation; A motor commutation timing error detection which is activated when the commutation time between consecutive commutation steps during the sensorless BLDC motor controller operation differs by more than a value (eg. 50%) set by the motor operation error detection controller. In practise, motor operation errors, such as disclosed above, are detected during the disclosed electronic clutch operation when the motor current has reached the maximum set electronic clutch current value and the BLDC motor no longer has sufficient driving torque to continue to turn the motor in the desired direction, thus coming to a stop. When a motor operation error is detected, the electronic clutch operation enters the engaged state, as shown in the operation flow chart in Fig. 4 and in the example practical drill driver electronic clutch operation in Fig. 5.

[0092] (iv) Electronic Clutch Engaged State: Once the electronic clutch has entered the engaged state, a number of important steps are performed in the disclosed invention which have been developed to enable successful and stable electronic clutch operation with the extremely challenging sensorless BLDC motor control systems, and to create an electronic clutch operation with a similar motor pulsating sound and power feel to that of a mechanical clutch operation. These key steps include:

[0093] Applying a motor brake (eg. for < 100ms), as shown in the example practical drill driver electronic clutch operation in Fig. 5, until the motor has come to a complete standstill to ensure that the motor does not contain any forward or reverse motor rotations. This has a stabilising effect on the electronic clutch operation with sensorless BLDC motor control systems and is thus considered an important step in the disclosed electronic clutch operation;

[0094] Increasing the on-time pulse durations of the phase winding measurement pulsing sequence, consisting of on-time and off-time pulses during the initial rotor position detection (IRPD) measurement illustrated in Fig. 6, to on-time pulse durations values greater than the default on-time pulse durations values (eg. >20us), for example as described in the aforementioned PCT publication W02019/056072. The disclosed electronic clutch operation advantageously uses this stream of pulsating motor currents injected into the motor during the initial rotor positon detection to create a distinct pulsating sound in the motor lasting for a short period of time (eg. >0.5ms) that is more similar to the sound of a mechanical clutch. By increasing the on-time pulse durations of the phase winding measurement pulsing sequence during initial rotor positon detection when the electronic clutch is engaged, the audible volume of the pulsating sound emitted from the motor is also proportionally increased during the disclosed electronic clutch operation, and thus more closely simulating the sound produced by a mechanical clutch. The on- time pulse durations of the phase winding measurement pulsing sequence during initial rotor positon detection can for example be increased using fixed values, or in proportion to the command throttle position, or using any other control method that achieves the previously mentioned effect;

[0095] Decreasing the electronic clutch current from the user set electronic clutch current ( I r CLUTCH USER) level to an equal or a lower electronic clutch current (IE-CLUTCH ENGAGE) (eg. 10% - 100% of E-CLUTCH JJSER), that is E-a.utai ENGAGE <= E-CLUTCH USER, which reduces the motor output torque once the electronic clutch is engaged, similar to the operation of a mechanical clutch where the transferred torque while the clutch is slipping is generally lower than the maximum torque that the mechanical clutch can transfer before starting to slip. This reduction in electronic clutch current from IE-CLUTCH USER to IE- CLUTCH ENGAGE level is shown in the example practical drill driver electronic clutch operation in Fig. 5.

[0096] Modulating the BLDC motor driving PWM D.C. during the engaged electronic clutch state between a minimum (PWM_DC_MIN) and maximum (PWM_DC_MAX) PWM duty cycle value, where 0 < PWM_DC_MIN < PWM_DC_MAX, with pulse durations equal to Tpwvi DC MIN (eg. 1ms - 50ms) and Tpwv_t DC MAX (eg. 1ms - 50ms) respectively as illustrated in Fig. 7, and with a pulse modulating frequency (F_P vi DC MOD) equal to:

F PWM DC MOD = 1 / (TpWM DC_MIN + TpwM DC_MAx) (3)

[0097] which is proportional to the command throttle position, that is, by increasing the modulating PWM D.C. pulsing frequency with increasing command throttle value and decreasing the modulating PWM D.C. pulsing frequency with a decreasing command throttle value as illustrated in Fig. 8, thus creating a motor pulsating sound and pitch (eg. 10Hz - 200Hz) effect, which is similar to a mechanical clutch operation with a clutch operation frequency proportional to the motor speed and thus the command throttle position that controls the motor speed. The resultant motor current, and thus motor torque, is modulated as shown in the example practical drill driver electronic clutch operation in Fig. 5. A key aspect of this preferred embodiment for the PWM D.C. modulating scheme is that the minimum PWM duty cycle (PWM_DC_MIN) is limited to a value greater than zero. This is important in the disclosed electronic clutch operation because it ensures that the sensorless BLDC motor drive is always engaged and generating torque in the desired driving direction with minimal motor power interruptions, such as would otherwise occur, for example if the motor PWM D.C. and thus the current are set to zero. In practise this method has been found to reduce reversed rotor momentum rotations in the motor and thus improve the stability and performance of the electronic clutch operation with the challenging sensorless BLDC motor control systems. The minimum PWM duty cycle (PWM DC MIN) can use a fixed value (eg. >1%), and the maximum PWM duty cycle (PWM_DC_MAX) value can be modulated in proportion to the command throttle position (eg. 1% - 100%). The operation of the disclosed electronic clutch is not limited only to this embodiment, for example, the minimum (PWM_DC_MIN) and maximum (PWM_DC_MAX) PWM duty cycle values can also use any other PWM D.C. modulating method that in practise achieves the required electronic clutch performance with the sensorless BLDC motors in applications such as power tools;

[0098] The key steps disclosed above are performed once every time the electronic clutch enters the engaged state. However, the BLDC motor driving PWM D.C. and pulsing frequency continue to be modulated in proportion to the command throttle position as illustrated in Fig. 7 and Fig. 8 for a number of cycles (eg. 1 - 10 cycles) during the engaged state, as set by the electronic clutch controller in order to achieve an electronic clutch operation with sensorless BLDC motors that is stable and similar to a mechanical clutch, until the electronic clutch operation changes back to the disengaged state, as shown in the example practical drill driver electronic clutch operation in Fig. 5.

[0099] (v) Electronic Clutch Disengaged State: When the electronic clutch has entered the disengaged state, the normal motor driving operation is resumed, as illustrated in the operation flow chart in Fig. 4, with the user command throttle value used to calculate the PWM D.C. (eg. 1% - 100%). The electronic clutch current is also increased back to the maximum user electronic clutch level ( I n CLUTCH USER), which is similar to the maximum torque level that a mechanical clutch can transfer before starting to slip. In practise it has been found that best performance is achieved when the electronic clutch current is increased gradually at a predefined rate of increase or slope or trajectory (eg. linear, non linear, piece-wise), and, or after a time delay (eg. 1ms - 1000ms) as in the practical drill driver electronic clutch operation example in Fig. 5, in order to improve the stability of the electronic clutch operation with the challenging sensorless BLDC motor control systems. If the motor current measured during the disengaged state exceeds the set electronic clutch current due to a motor overload, for example during a fastening application with a drill driver, then the motor current and thus torque is limited by the controller and the motor stalls. Consequently, a motor operation error is re-activated and the electronic clutch re-enters the engaged state of operation. Thus in practise, the electronic clutch controller alternates between the disclosed engaged and disengaged states of operation, as shown in the practical drill driver electronic clutch operation example in Fig. 5, until the motor load is removed or the user command throttle is returned to the off position.

Interpretation

[00100] Reference throughout this specification to “one embodiment”, “some embodiments” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment”, “in some embodiments” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[00101] As used herein, unless otherwise specified the use of the ordinal adjectives "first", "second", "third", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.

[00102] In the claims below and the description herein, any one of the terms comprising, comprised of or which comprises is an open term that means including at least the elements/features that follow, but not excluding others. Thus, the term comprising, when used in the claims, should not be interpreted as being limitative to the means or elements or steps listed thereafter. For example, the scope of the expression a device comprising A and B should not be limited to devices consisting only of elements A and B. Any one of the terms including or which includes or that includes as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising.

[00103] As used herein, the term “exemplary” is used in the sense of providing examples, as opposed to indicating quality. That is, an “exemplary embodiment” is an embodiment provided as an example, as opposed to necessarily being an embodiment of exemplary quality.

[00104] It should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.

[00105] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[00106] Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or by other means of carrying out the function. Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the invention.

[00107] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[00108] Similarly, it is to be noticed that the term coupled, when used in the claims, should not be interpreted as being limited to direct connections only. The terms "coupled" and "connected," along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression a device A coupled to a device B should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. "Coupled" may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co operate or interact with each other.

[00109] Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as falling within the scope of the invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.

Claims

We claim:

1. An electronic clutch for a sensorless brushless DC motor, wherein the clutch does not utilise any rotor position sensors in determining its operation.

2. An electronic clutch for a sensorless brushless DC motor which utilises the voltage measurement across a series of power transistors of the DC motor to determine the electronic clutch operation.

3. An electronic clutch for a sensorless brushless DC motor as claimed in any previous claim wherein the clutch operates by means of pulse width modulation of the DC motor.

4. An electronic clutch as claimed in claim 2 wherein said power transistors comprise power MOSFETs and said voltage measurement includes measuring the voltage across the power MOSFET drain-source channel resistance.

5. A sensorless BLDC motor control system which utilises a series of analog voltage amplifiers to amplify the measured voltage across the power MOSFET drain-source channel resistance to measure motor current.

6. A sensorless BLDC motor control system as claimed in claim 5 where only one current-shunt resistor sensor is provided between the ground voltage rail and the source terminals of the low-side power transistors, or between the power supply voltage rail and the drain terminals of the high-side power transistors to measure the motor current.

7. An electronic clutch for a sensorless BLDC motor control systems which uses at least two current-shunt resistor sensors between each low-side power transistor’s source terminal and the ground voltage rail, or between each high-side power transistor’s drain terminal and the power supply voltage rail, or in-line between each phase terminal of the BLDC motor and the output of the low-side and high-side power transistors to measure the motor current.

8. An electronic clutch for sensorless BLDC motor control systems which limits the Pulse Width Modulation Duty Cycle (PWM D.C.), and thus the motor current and torque, if the measured motor current exceeds a first predetermined set electronic clutch current.

9. An electronic clutch as claimed in claim 8 wherein said limitation of the PWM D.C. includes utilising feedback control techniques, such as, but not limited to, PID control or instantaneously turning-off the power transistors in the same PWM cycle when the maximum electronic clutch current limit threshold is reached.

10. An electronic clutch for sensorless BLDC motor control systems which has an engaged and a disengaged electronic clutch controller state.

11. An electronic clutch for sensorless BLDC motor control systems which detects motor operation errors, such as, but not limited to, a motor stall and a motor commutation timing error in order to determine when the electronic clutch operation enters the engaged state.

12. An electronic clutch for sensorless BLDC motor control systems which applies a motor brake until the motor has come to a complete standstill to ensure that the motor does not contain any forward or reverse motor rotations, in order to stabilise the operation of the electronic clutch with the sensorless BLDC motor control system.

13. An electronic clutch for sensorless BLDC motor control systems which utilises an initial rotor position detection pulsing stream with increased on-time pulse duration to create and control the volume of the emitted motor pulsating sound so as to approximate a mechanical clutch.

14. An electronic clutch for sensorless BLDC motor control systems which decreases the electronic clutch current from the user set electronic clutch current (IE-CLUTCH USER) level to an equal or a lower electronic clutch current (IE-CLUTCH ENGAGE), that is IE-CLUTCH ENGAGE ^<= IE-CLUTCH USER, in order to reduce the motor output torque once the clutch is engaged.

15. An electronic clutch for sensorless BLDC motor control systems which modulates a BLDC motor driving Pulse Width Modulation Duty Cycle (PWM D.C.) between a minimum (PWM_DC_MIN) and maximum (PWM_DC_MAX) PWM duty cycle value, where 0 < PWM_DC_MIN < PWM_DC_MAX, with pulse durations equal to TPWM DC MIN and TPWM DC MAX respectively in order to improve the stability and performance of the electronic clutch operation with the sensorless BLDC motor control systems.

16. An electronic clutch for sensorless BLDC motor control systems which has a Pulse Width Modulation Duty Cycle (PWM D.C.) pulse modulating frequency (Fp _\i DC: MOD) equal to Fpwv_t Dt MOD = 1 / (T PWM DC: vii_N + Tpwv_t DC: MAX), which is proportional to a command throttle position, that is, by increasing the modulating PWM D.C. pulsing frequency with increasing command throttle value and decreasing the modulating PWM D.C. pulsing frequency with a decreasing command throttle value, in order to create a motor pulsating sound and pitch effect, which is similar to a mechanical clutch operation.

17. An electronic clutch for sensorless BLDC motor control systems which, after the electronic clutch has disengaged, increases the electronic clutch current from the engaged state level ( I n CLUTCH ENGAGE) back to a user selected electronic clutch level (IE-CLUTCH USER) in a gradual manner at a predefined rate of increase or slope or trajectory, and, or after a time delay in order to improve the stability of the electronic clutch operation with the sensorless BLDC motor control systems.