Electric work machine

Abstract

This technology provides a way to appropriately brake the brushless motor of an electric work machine using two-phase short-circuit control without using a sensing device for detecting rotational position. [Solution] One aspect of the present disclosure provides an electric work machine comprising a brushless motor, a drive circuit, and a control circuit. The control circuit performs a drive operation, a braking operation, and a switching operation. In the drive operation, the brushless motor is rotated based on the induced voltage of the brushless motor. In the braking operation, a pair of switches among six switches in the drive circuit is turned on and the other four are turned off. The switching operation is performed during the braking operation. The switching operation includes switching the switch pair. In the switching operation, the switch to be turned off is turned off based on the current flowing through the switch to be turned off meeting the off requirement.

Description

Technical Field

[0001] The present disclosure relates to a technique for braking a brushless motor in a power-operated tool.

Background Art

[0002] Patent Document 1 discloses a technique for braking a brushless motor using two-phase short-circuit control. In two-phase short-circuit control, two of the three high-side switches or two of the three low-side switches in the switching circuit are turned on. Further, the two switches to be turned on (hereinafter referred to as "switch pair") are sequentially switched according to the rotation of the brushless motor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In two-phase short-circuit control, when the switch pair is switched, one of the two switches that are on (hereinafter referred to as "off-target switch") is turned off. If the timing for turning off the off-target switch is not appropriate, the switching circuit may be affected. Therefore, it is desirable that the off-target switch be turned off at an appropriate timing.

[0005] When the brushless motor includes a sensing device such as a hall sensor, the rotational position can be appropriately detected even during the execution of two-phase short-circuit braking, and thereby the off-target switch can be turned off at an appropriate timing.

[0006] On the other hand, a so-called sensorless method is known that detects the rotational position based on the induced voltage of the brushless motor without installing a sensing device. Even with such a sensorless method, it is desirable that two-phase short-circuit braking can be properly performed.

[0007] One aspect of this disclosure is to provide a technology that enables the brushless motor of an electric work machine to be appropriately braked by two-phase short-circuit control without using a sensing device for detecting rotational position. [Means for solving the problem]

[0008] In this disclosure, terms such as “first,” “second,” etc., are intended merely to distinguish elements from one another and not to limit the order or number of elements. Therefore, the first element may be referred to as the second element, and similarly, the second element may be referred to as the first element. In addition, the first element may be present without the second element, and similarly, the second element may be present without the first element.

[0009] One aspect of this disclosure is the provision of an electric work machine comprising a brushless motor, a drive circuit, and a control circuit. A brushless motor has three terminals configured to receive power.

[0010] The drive circuit supplies power to the brushless motor. The drive circuit comprises three positive-side paths, three negative-side paths, and six switches. The three positive-side paths each electrically connect their three terminals to the positive terminal of the power supply. The three negative-side paths each electrically connect their three terminals to the negative terminal of the power supply.

[0011] The six switches comprise three positive switches and three negative switches. The three positive switches are provided in each of the three positive paths to individually conduct or interrupt the three positive paths. The three negative switches are provided in each of the three negative paths to individually conduct or interrupt the three negative paths.

[0012] The control circuit performs driving, braking, and switching operations. The drive operation controls the drive circuit based on the induced voltage of the brushless motor generated at each of the three terminals, thereby rotating the brushless motor.

[0013] The braking operation is an operation to decelerate and / or stop the rotating brushless motor, and includes turning on a pair of switches from the six switches and turning off the others. A switch pair is any two of the three positive switches or any two of the three negative switches.

[0014] A switching operation is the operation of switching a switch pair while a braking operation is being performed. A switching operation includes turning off one of the current switch pairs, which is a switch to be turned off, based on the fact that the current flowing through that switch meets the off requirement.

[0015] In this configuration of an electric work machine, during the switching operation, the switch to be turned off is turned off based on whether the current flowing through that switch meets the off requirement. Therefore, the brushless motor can be appropriately braked by two-phase short-circuit control without using a sensing device for detecting rotational position (i.e., in a sensorless manner). [Brief explanation of the drawing]

[0016] [Figure 1] This is a perspective view of the electric work machine according to the first embodiment. [Figure 2] This is an explanatory diagram showing the electrical configuration of the electric work machine of the first embodiment. [Figure 3] This is an explanatory diagram showing an example of motor operation during free-running. [Figure 4] This is an explanatory diagram showing an example of motor operation when three-phase short-circuit braking is performed. [Figure 5] This is an explanatory diagram showing a switch pair table. [Figure 6] It is an explanatory diagram showing an operation example of two-phase short-circuit braking. [Figure 7] It is an explanatory diagram showing an operation example when shifting from a driving operation to two-phase short-circuit braking. [Figure 8] It is a flowchart of the main processing of the first embodiment. [Figure 9] It is a flowchart of the motor control processing of the first embodiment. [Figure 10] It is a flowchart of the soft brake start processing of the first embodiment. [Figure 11] It is a flowchart of the comparator interrupt processing of the first embodiment. [Figure 12] It is a flowchart of the commutation timer interrupt processing of the first embodiment. [Figure 13] It is a flowchart of the motor control processing of the second embodiment. [Figure 14] It is an explanatory diagram showing an operation example of two-phase short-circuit braking of the second embodiment. [Figure 15] It is an explanatory diagram showing an operation example of the motor of the third embodiment. [Figure 16] It is an explanatory diagram showing a single-phase pattern table. [Figure 17] It is a flowchart of the motor control processing of the third embodiment. [Figure 18] It is a flowchart of the comparator interrupt processing of the third embodiment. [Figure 19] It is a flowchart of the commutation timer interrupt processing of the third embodiment. [Figure 20] An operation example of the motor when no countermeasure is taken against timer interrupt delay is shown. [Figure 21] An operation example of the motor of the fourth embodiment with a countermeasure taken against timer interrupt delay is shown. [Figure 22] It is a flowchart of the comparator interrupt processing of the fourth embodiment. [Figure 23] It is a flowchart of the commutation timer interrupt processing of the fourth embodiment. [Figure 24] It is an explanatory diagram showing a switch pair table of the fifth embodiment. [Figure 25] This is an explanatory diagram showing an example of operation of the two-phase short-circuit braking of the fifth embodiment. [Figure 26] This is an explanatory diagram showing a switch pair table of the sixth embodiment. [Figure 27] This is an explanatory diagram showing an example of operation of two-phase short-circuit braking according to the sixth embodiment. [Modes for carrying out the invention]

[0017] [1. Summary of Embodiments] One embodiment may provide an electric work machine comprising at least one of the following: Feature 1: Brushless motor. Feature 2: The brushless motor has three terminals configured to receive power. Feature 3: Drive circuit. Feature 4: The drive circuit is configured to supply the aforementioned power to the brushless motor. Feature 5: The drive circuit has three positive electrode paths. Feature 6: The three positive terminal paths electrically connect each of the three terminals to the positive terminal of the power supply. Feature 7: The drive circuit has three negative electrode paths. Feature 8: The three negative terminal paths electrically connect the three terminals to the negative terminal of the power supply. Feature 9: The drive circuit has six switches. Feature 10: The six switches include three positive-side switches. Feature 11: The three positive-side switches are provided in each of the three positive-side paths and are configured to individually conduct or interrupt the three positive-side paths. Feature 12: The six switches include three negative-side switches. Feature 13: The three negative-side switches are provided in each of the three negative-side paths and are configured to individually conduct or interrupt the three negative-side paths. Feature 14: Control circuit. Feature 15: The control circuit is configured to perform the drive operation. Feature 16: The drive operation includes controlling the drive circuit based on the induced voltage of the brushless motor generated at each of the three terminals, thereby rotating the brushless motor. Feature 17: The control circuit is configured to perform braking actions. Feature 18: Braking is an action to slow down and / or stop a rotating brushless motor. Feature 19: The braking action includes turning on a pair of switches from the six switches and turning off the others. Feature 20: A switch pair consists of any two of the three positive-side switches or any two of the three negative-side switches. Feature 21: The control circuit is configured to perform the switching operation. Feature 22: The switching operation is the operation of switching a switch pair while the braking operation is being performed. Feature 23: The switching operation includes turning off the switch to be turned off. Feature 24: The switch to be turned off is one of the current switch pairs. Feature 25: The switching operation includes turning off the switch to be turned off based on whether the current flowing through the switch to be turned off meets the off requirement.

[0018] In electric work machines possessing at least features 1 to 25, during the switching operation, the switch to be turned off is turned off based on whether the current flowing through that switch meets the off requirement. Therefore, the brushless motor can be appropriately braked by two-phase short-circuit control without using a sensing device for detecting rotational position.

[0019] A brushless motor may be configured to be driven by a three-phase power supply. A brushless motor may have three coils delta-connected to each other. A brushless motor may have three coils star-connected to each other. The three coils may be electrically connected to three terminals and configured to receive power from these three terminals.

[0020] The power source may include a battery. The power source may also be a rechargeable secondary battery. The electric work machine may be configured so that a battery pack containing a battery is detachably attached.

[0021] The OFF requirement may be requested to turn off the switch to be turned off. One embodiment may include, in addition to or instead of, at least one of the features 1 to 25 described above, at least one of the following: Feature 26: The off requirement is met on the basis that the value of the current flowing through the switch to be turned off is not an extreme value in the opposite direction to a specific direction. Feature 27: The specific direction is, in the case of the three positive-side switches, the direction from the brushless motor to the positive terminal via the switch to be turned off. Feature 28: The specific direction is, in the case of the three negative-side switches, the direction from the negative terminal through the switch to be turned off towards the brushless motor.

[0022] In electric work machines that possess at least features 1 to 28, it is possible to suppress the flow of regenerative current from the motor to the power supply in response to the off-target switch being turned off. One embodiment may include, in addition to or instead of, at least one of the above-described features 1 to 28: Feature 29: The off requirement is met based on the fact that the direction of the current flowing through the switch to be turned off is in a specific direction.

[0023] In electric work machines that possess at least features 1-25 and 29, it becomes possible to further suppress the flow of regenerative current from the motor to the power supply in response to the off-target switch being turned off.

[0024] One embodiment may include, in addition to or instead of, at least one of the features 1 to 29 described above, at least one of the following: Feature 30: Current information acquisition circuit. Feature 31: The current information acquisition circuit is configured to acquire current information. Feature 32: Current information is information about the current flowing through each of the six switches, at least two of which can be paired in a braking operation. Feature 33: The control circuit is configured to perform switching operations based on current information acquired by the current information acquisition circuit.

[0025] The current information may include information that directly or indirectly indicates the direction of the current flowing through each of the two or more switches. The current information may also include a first voltage, a second voltage, and / or a third voltage.

[0026] The first voltage is the voltage at the first of the three terminals. When current flows through the switch connected to the first terminal, the first voltage may change depending on the magnitude and / or direction of the current. Therefore, based on the first voltage, the magnitude and / or direction of the current flowing through the switch connected to the first terminal can be detected (or estimated).

[0027] The second voltage is the voltage at the second of the three terminals. When current flows through the switch connected to the second terminal, the second voltage may change depending on the magnitude and / or direction of the current. Therefore, based on the second voltage, the magnitude and / or direction of the current flowing through the switch connected to the second terminal can be detected (or estimated).

[0028] The third voltage is the voltage at the third terminal of the three terminals. When current flows through the switch connected to the third terminal, the third voltage may change depending on the magnitude and / or direction of the current. Therefore, based on the third voltage, the magnitude and / or direction of the current flowing through the switch connected to the third terminal can be detected (or estimated).

[0029] Therefore, in electric work machines that have at least features 1-25, 30-33, the switch to be turned off can be turned off at the appropriate time. One embodiment may include, in addition to or instead of, at least one of the features 1 to 33 described above, at least one of the following: Feature 34: The current information acquisition circuit is equipped with a first comparator. Feature 35: The first comparator is configured to receive the aforementioned first voltage and reference voltage. Feature 36: The first comparator is configured to output first comparison information. Feature 37: The first comparison information indicates whether the value of the first voltage is equal to or greater than the value of the reference voltage. Feature 38: The current information acquisition circuit is equipped with a second comparator. Feature 39: The second comparator is configured to receive the aforementioned second voltage and the reference voltage. Feature 40: The second comparator is configured to output second comparison information. Feature 41: The second comparison information indicates whether the value of the second voltage is greater than or equal to the value of the reference voltage. Feature 42: The current information acquisition circuit is equipped with a third comparator. Feature 43: The third comparator is configured to receive the aforementioned third voltage and the reference voltage. Feature 44: The third comparator is configured to output third comparison information. Feature 45: The third comparison information indicates whether the value of the third voltage is equal to or greater than the value of the reference voltage.

[0030] Electric work equipment that possesses at least features 1-25 and 30-45 allows the target switch to be turned off at the appropriate time. One embodiment may include, in addition to or instead of, at least one of the above-described features 1 to 45: Feature 46: The control circuit is configured to perform drive operations based on the first comparison information, second comparison information, and third comparison information output from the current information acquisition circuit.

[0031] In electric work machines possessing at least features 1-25 and 30-46, the first to third comparison information is used for both driving and braking operations. This enables an efficient configuration of the electric work machine.

[0032] One embodiment may include, in addition to or instead of, at least one of the above-described features 1 to 46: Feature 47: The OFF requirement is met based on a change in the first comparison information, second comparison information, and / or third comparison information.

[0033] In electric work machines that possess at least features 1-25, 30-45, and 47, the timing for turning off the target switch can be easily determined with a simple configuration. One embodiment may include, in addition to or instead of, at least one of the above-described features 1 to 47: Feature 48: When any two of the three negative-side switches are in the switch pair, the off requirement is met based on the voltage value of one terminal connected to the switch to be turned off becoming less than the value of the reference voltage.

[0034] When the voltage value at one terminal connected to the switch to be turned off falls below the reference voltage value, it indicates that current is flowing (or may be flowing) through the switch in a specific direction. Furthermore, when the voltage value at one terminal connected to the switch to be turned off falls below the reference voltage value, the comparison information corresponding to that terminal may change. Therefore, based on a change in at least one of the first to third comparison pieces, the appropriate off timing for the switch to be turned off can be determined.

[0035] Therefore, in electric work machines that possess at least features 1-25, 30-45, and 48, the timing for turning off the switch to be turned off can be easily determined with a simple configuration. One embodiment may include, in addition to or instead of, at least one of the features 1 to 48 described above, at least one of the following: Feature 49: The off requirement when any two of the three negative-side switches are in a switch pair is met based on the arrival of the off-capable timing. Feature 50: The timing at which the switch can be turned off is when (i) the voltage value of one of the three terminals connected to the switch to be turned off becomes less than the value of the reference voltage, and (ii) the voltage value of one of the three terminals connected to one of the three negative-side switches other than the switch pair becomes equal to or greater than the value of the reference voltage.

[0036] In electric work machines that possess at least features 1-25, 30-45, and 48-50, the timing for turning off the switch to be turned off can be easily determined with a simple configuration. One embodiment may include, in addition to or instead of, at least one of the above-described features 1 to 50: Feature 51: The off requirement when any two of the three negative-side switches are in a switch pair is met based on a predetermined delay time elapsed after the off-capable timing has arrived.

[0037] The magnitude of the current flowing through a switch in a specific direction may decrease or become zero after a certain period of time has elapsed since the switch became available to be turned off. Therefore, in electric work machines that possess at least features 1-25, 30-45, and 48-51, it is possible to turn off the target switch while reducing the current flowing through that switch.

[0038] One embodiment may include, in addition to or instead of, at least one of the above-described features 1 to 51: Feature 52: The control circuit is configured to set the delay time such that the off requirement is met when the magnitude of the current flowing through the switch to be turned off is decreasing or is zero.

[0039] In electric work machines that possess at least features 1-25, 30-45, and 48-52, it is possible to turn off the target switch while the current flowing through the switch is reduced or zero.

[0040] One embodiment may include, in addition to or instead of, at least one of the above-described features 1 to 52: Feature 53: The control circuit is configured to set a delay time based on the rotational speed of the brushless motor at the time the off-capable timing arrives.

[0041] Electric work machines possessing at least features 1-25, 30-45, 48-51, and 53 allow for the setting of an appropriate delay time according to the rotational speed. Note that rotational speed refers to the number of rotations per unit time (e.g., 1 minute or 1 second). Rotational speed may also be referred to as rotational velocity or angular velocity.

[0042] One embodiment may include, in addition to or instead of, at least one of the above-described features 1 to 53: Feature 54: The control circuit is configured to set the delay time to be longer the lower the rotational speed of the brushless motor when the off-timing occurs. Electric work machines that possess at least features 1-25, 30-45, 48-51, 53, and 54 allow for setting an appropriate delay time according to the rotational speed.

[0043] One embodiment may include, in addition to or instead of, at least one of the features 1 to 54 described above, at least one of the following: Feature 55: Reference voltage generation circuit. Feature 56: The reference voltage generation circuit includes a first resistor. Feature 57: The first resistor has a first end connected to the first terminal of the three terminals, and a second end. Feature 58: The reference voltage generation circuit includes a second resistor. Feature 59: The second resistor has a first end connected to the second of the three terminals, and a second end connected to the second end of the first resistor. Feature 60: The reference voltage generation circuit includes a third resistor. Feature 61: The third resistor has a first end connected to the third terminal of the three terminals, and a second end connected to the second end of the first resistor and the second end of the second resistor. Feature 62: The reference voltage generation circuit is configured to output a first reference voltage. Feature 63: The first reference voltage is the voltage at the second terminal of the first resistor, the voltage at the second terminal of the second resistor, or the voltage at the second terminal of the third resistor. Feature 64: The current information acquisition circuit is configured to receive the first reference voltage from the reference voltage generation circuit as the reference voltage.

[0044] Electric work equipment possessing at least features 1-25, 30-45, and 55-64 can easily generate an appropriate reference voltage. One embodiment may include, in addition to or instead of, at least one of the above-described features 1 to 64: Feature 65: The current information acquisition circuit is configured to receive the voltage at the terminals electrically connected to the negative terminal of the three negative-side switches as a reference voltage when any two of the three negative-side switches are set as a switch pair.

[0045] Electric work equipment possessing at least features 1-25, 30-45, and 65 can easily generate an appropriate reference voltage. One embodiment may include, in addition to or instead of, at least one of the features 1 to 65 described above, at least one of the following: Feature 66: The current information acquisition circuit is configured to receive the voltage at the terminals electrically connected to the positive terminal of the three positive-side switches as a reference voltage when any two of the three positive-side switches are in a switch pair.

[0046] Electric work equipment possessing at least features 1-25, 30-45, and 66 can easily generate an appropriate reference voltage. One embodiment may include, in addition to or instead of, at least one of the features 1 to 66 described above, at least one of the following: Feature 67: Selection circuit. Feature 68: The selection circuit is configured to receive at least two reference voltages from among a first reference voltage, a second reference voltage, and a third reference voltage. Feature 69: The selection circuit is configured to output one of the at least two reference voltages received as a reference voltage. Feature 70: The second reference voltage is the voltage at the terminals electrically connected to the negative terminals of the three negative-side switches. Feature 71: The third reference voltage is the voltage at the terminals electrically connected to the positive terminal of the three positive-side switches. Feature 72: The current information acquisition circuit is configured to receive the reference voltage output from the selection circuit.

[0047] In electric work machines that possess at least features 1-25, 30-45, 55-64, and 67-72, the reference voltage can be selectively set. One embodiment may include, in addition to or instead of, at least one of the features 1 to 72 described above, at least one of the following: Feature 73: 4th resistor. Feature 74: The fourth resistor has a first end connected to the positive terminal and a second end. Feature 75: Fifth resistor. Feature 76: The fifth resistor has a first end connected to the negative terminal and a second end connected to the second end of the fourth resistor. Feature 77: Selection circuit. Feature 78: The selection circuit is configured to receive at least two reference voltages from among the first reference voltage, the second reference voltage, the third reference voltage, and the fourth reference voltage. Feature 79: The selection circuit is configured to output one of the at least two reference voltages received as a reference voltage. Feature 80: The fourth reference voltage is the voltage at the second terminal of the fourth resistor. Feature 81: The current information acquisition circuit is configured to receive the reference voltage output from the selection circuit.

[0048] For electric work equipment that possesses at least features 1-25, 30-45, 55-64, and 73-81, a wider range of reference voltages can be selected. One embodiment may include, in addition to or instead of, at least one of the features 1 to 81 described above, at least one of the following: Feature 82: The selection circuit is configured to output the fourth reference voltage as the reference voltage when the control circuit is performing the drive operation. Feature 83: The selection circuit is configured to output the first reference voltage, second reference voltage, or third reference voltage as the reference voltage when the control circuit is performing a switching operation (and / or braking operation).

[0049] In electric work machines having at least features 1-25, 30-45, 55-64, and 73-83, the reference voltage used in the drive operation, braking operation and / or switching operation can be easily obtained from the selection circuit.

[0050] One embodiment may include, in addition to or instead of, at least one of the features 1 to 83 described above, at least one of the following: Feature 84: Each of the three positive-side switches includes a first rectifier. Feature 85: The first rectifier is connected in parallel to the corresponding positive-side switch. Feature 86: The first rectifier is configured to allow current to flow from the brushless motor through the positive-side switch to the positive electrode, while suppressing or blocking current flowing from the positive electrode through the positive-side switch to the brushless motor.

[0051] In electric work machines having at least features 1-25, 84-86, it is possible to suppress or prevent the flow of regenerative current from the brushless motor to the power supply via the first rectifier during switching operations.

[0052] One embodiment may include, in addition to or instead of, at least one of the features 1 to 86 described above, at least one of the following: Feature 87: Each of the three negative-side switches includes a second rectifier. Feature 88: The second rectifier is connected in parallel to the corresponding negative-side switch. Feature 89: The second rectifier is configured to allow current to flow from the negative electrode through the negative electrode side switch to the brushless motor, while suppressing or blocking current flowing from the brushless motor through the negative electrode side switch to the negative electrode.

[0053] In electric work machines having at least features 1-25, 87-89, it is possible to suppress or prevent the flow of regenerative current from the brushless motor to the power supply via the first rectifier during switching operations.

[0054] In one embodiment, at least one of the six switches may be a semiconductor switch or a mechanical relay. Examples of semiconductor switches include field-effect transistors (FETs), bipolar transistors, insulated-gate bipolar transistors (IGBTs), thyristors, and solid-state relays (SSRs).

[0055] In one embodiment, the control circuit may be integrated into a single electronic unit, a single electronic device, or a single circuit board. In one embodiment, the control circuit may be a combination of two or more electronic circuits, two or more electronic units, or two or more electronic devices, each individually provided on or within the electric work machine.

[0056] In one embodiment, the control circuit may comprise a microcomputer (or microcontroller or microprocessor), wiring logic, application-specific integrated circuits (ASICs), application-specific general-purpose products (ASSPs), programmable logic devices (such as field-programmable gate arrays (FPGAs)), discrete electronic components, and / or combinations thereof.

[0057] The above examples of electric work machines include various types of work machines used in construction, manufacturing, civil engineering, engineering, agriculture, gardening, cleaning, DIY, and other work sites, configured to operate on a brushless motor powered by electricity. Electric work machines may be configured to operate on battery power or on alternating current power. More specific examples of electric work equipment include power tools for masonry, metalworking, and woodworking, gardening equipment, and equipment for preparing the work site environment, more specifically including electric blowers, electric hammers, electric hammer drills, electric drills, electric screwdrivers, electric wrenches, electric grinders, electric circular saws, electric reciprocating saws, electric jigsaws, electric cutters, electric chainsaws, electric planers, electric nail guns (including rivet guns), electric hedge trimmers, electric lawnmowers, electric grass trimmers, electric brush cutters, electric cleaners, electric sprayers, electric sprayers, electric dust collectors, electric trowels, electric vibrators, electric rammers, electric compactors, electric pumps, electric pile drivers, electric concrete saws, electric screeds, electric cut-off saws, coffee machines (or coffee makers, or coffee stills), robotic vacuum cleaners, battery-powered handcarts, battery-powered bicycles, and fan vests.

[0058] In one embodiment, the above features 1 to 89 may be combined in any way. In one embodiment, any of the above features 1 to 89 may be excluded. [2. Specific exemplary embodiments] The following describes four specific exemplary embodiments.

[0059] [2-1. First Embodiment] The first embodiment provides an electric work implement 1 in the form of an electric brush cutter (or electric grass trimmer). However, such an electric work implement 1 is merely an example, and the present disclosure can be applied to any form of electric work implement.

[0060] (2-1-1) Configuration of electric work equipment As shown in Figure 1, the electric work machine 1 is equipped with a main pipe 2. The main pipe 2 has a long, hollow, rod-like shape.

[0061] The electric work machine 1 is equipped with a control unit 3 at the rear end of the main pipe 2. The control unit 3 houses a controller 22 (see Figure 2). The electric work implement 1 is equipped with a drive unit 4 at the front end of the main pipe 2. The drive unit 4 is detachably fitted with a rotating blade 5. The rotating blade 5 is configured to cut materials such as grass and small trees when rotated.

[0062] The drive unit 4 houses a brushless motor (or brushless DC motor; hereinafter abbreviated as "motor") 20 (see Figure 2). The motor 20 rotates by receiving drive power from the controller 22. The drive unit 4 also houses a power transmission mechanism (not shown). The power transmission mechanism transmits the rotation of the motor 20 to the rotating blade 5. As a result, when the motor 20 rotates, the rotating blade 5 rotates. The motor 20 can rotate in either forward or reverse direction. When the motor 20 rotates in forward direction, the rotating blade 5 rotates in a direction that allows it to cut the target material. When the motor 20 rotates in reverse direction, the rotating blade 5 rotates in the opposite direction to when it rotates in forward direction.

[0063] The electric work implement 1 is equipped with a cover 6 at the front end of the main pipe 2. The cover 6 prevents objects to be cut from flying towards the user of the electric work implement 1 due to the rotation of the rotating blade 5. The electric work implement 1 is equipped with a handle 7. The handle 7 is connected to the main pipe 2 near its midpoint in the longitudinal direction of the main pipe 2. The handle 7 is gripped by the user.

[0064] The electric work implement 1 is equipped with an operating unit 8 at the tip of the handle 7. The operating unit 8 is equipped with a trigger switch 10. The trigger switch 10 is operated manually by the user. When the trigger switch 10 is not operated manually, the trigger switch 10 is off. When the trigger switch 10 is operated manually, the trigger switch 10 is on.

[0065] The operating unit 8 includes a lock-off switch 12. The lock-off switch 12 allows or prohibits manual operation of the trigger switch 10. When the lock-off switch 12 is ON, manual operation of the trigger switch 10 is permitted. When the lock-off switch 12 is OFF, manual operation of the trigger switch 10 is prohibited. The user can turn the lock-off switch 12 ON with one hand (for example, the right hand) and manually operate the trigger switch 10 with the same hand.

[0066] The operation unit 8 includes an operation panel 14. The operation panel 14 displays various information such as the operating status and operating mode of the electric work machine 1. The operation panel 14 includes one or more push buttons (not shown). These one or more push buttons are used, for example, to set the rotation direction of the motor 20, set the operating mode of the motor 20, and so on.

[0067] The control unit 3 is configured such that a battery pack 18 is detachably attached to its rear end. The battery pack 18 houses a battery 19 (see Figure 2). The battery 19 is, for example, a rechargeable secondary battery. The battery 19 is an example of a power source in the overall embodiment. The electric work machine 1 operates by receiving battery power from the battery pack 18.

[0068] (2-1-2) Electrical configuration of electric work equipment Referring to Figure 2, the electrical configuration of the electric work implement 1 will be explained. Figure 2 shows the electric work implement 1 with the battery pack 18 attached.

[0069] The electric work machine 1 is equipped with the aforementioned motor 20. As previously stated, the motor 20 is a brushless motor. The motor 20 comprises a permanent magnet type rotor (not shown) and a stator (not shown). The aforementioned drive force transmission mechanism transmits the rotation of the rotor in detail.

[0070] The motor 20 comprises a first coil L1, a second coil L2, and a third coil L3, each wound around a stator. Drive power from the controller 22 is input to these first to third coils L1, L2, and L3. The first to third coils L1, L2, and L3 are delta-connected to each other. However, the first to third coils L1, L2, and L3 may also be star-connected to each other.

[0071] The motor 20 is provided with a first terminal 20u, a second terminal 20v, and a third terminal 20w. The first to third terminals 20u, 20v, and 20w are examples of three terminals in the overall embodiment. The first terminal 20u is connected to the first end of the first coil L1 and the first end of the third coil L3. The second terminal 20v is connected to the second end of the first coil L1 and the first end of the second coil L2. The third terminal 20w is connected to the second end of the second coil L2 and the second end of the third coil L3. The motor 20 receives drive power via these first to third terminals 20u, 20v, and 20w and rotates as a result. The drive power in this embodiment is in the form of three-phase power. The first terminal 20u corresponds to the terminal to which the U-phase voltage in the three-phase power is applied, the second terminal 20v corresponds to the terminal to which the V-phase voltage in the three-phase power is applied, and the third terminal 20w corresponds to the terminal to which the W-phase voltage in the three-phase power is applied.

[0072] The electric work machine 1 is equipped with the aforementioned controller 22. The controller 22 controls the rotation of the motor 20. The controller 22 is electrically connected to the motor 20, the trigger switch 10, and the control panel 14. The controller 22 is electrically connected to the battery 19 and receives battery power from the battery 19.

[0073] The controller 22 includes a drive circuit 24. The drive circuit 24 is electrically connected to the positive and negative terminals of the battery 19 and receives battery power from the battery 19. The drive circuit 24 is connected to the first to third terminals 20u to 20w of the motor 20. The drive circuit 24 generates drive power from battery power and supplies it to the motor 20.

[0074] The drive circuit 24 of this embodiment is in the form of a three-phase full-bridge circuit. That is, the drive circuit 24 comprises a first energizing path 24a, a second energizing path 24b, a third energizing path 24c, a fourth energizing path 24d, a fifth energizing path 24e, and a sixth energizing path 24f. The first to third energizing paths 24a, 24b, and 24c are examples of three positive-side paths in the embodiment. The fourth to sixth energizing paths 24d, 24e, and 24f are examples of three negative-side paths in the embodiment.

[0075] The first power supply path 24a electrically connects the first terminal 20u of the motor 20 to the positive terminal of the battery 19. The second power supply path 24b electrically connects the second terminal 20v of the motor 20 to the positive terminal of the battery 19. The third power supply path 24c electrically connects the third terminal 20w of the motor 20 to the positive terminal of the battery 19. The fourth power supply path 24d electrically connects the first terminal 20u of the motor 20 to the negative terminal of the battery 19. The fifth power supply path 24e electrically connects the second terminal 20v of the motor 20 to the negative terminal of the battery 19. The sixth power supply path 24f electrically connects the third terminal 20w of the motor 20 to the negative terminal of the battery 19.

[0076] The drive circuit 24 includes a first switch Q1, a second switch Q2, a third switch Q3, a fourth switch Q4, a fifth switch Q5, and a sixth switch Q6. Each of the first to sixth switches Q1 to Q6 may take any form. In this embodiment, each of the first to sixth switches Q1 to Q6 is, for example, an n-channel metal oxide semiconductor field-effect transistor (MOSFET).

[0077] Therefore, each of the first to sixth switches Q1 to Q6 includes a so-called body diode (or parasitic diode). That is, the first switch Q1 includes the first body diode D1, the second switch Q2 includes the second body diode D2, the third switch Q3 includes the third body diode D3, the fourth switch Q4 includes the fourth body diode D4, the fifth switch Q5 includes the fifth body diode D5, and the sixth switch Q6 includes the sixth body diode D6. Each of the first to third body diodes D1, D2, and D3 is an example of a first rectifier in the overall embodiment. Each of the fourth to sixth body diodes D4, D5, and D6 is an example of a second rectifier in the overall embodiment.

[0078] The first switch Q1 is located on the first energizing path 24a. Specifically, the first terminal (i.e., drain) of the first switch Q1 is connected to the positive terminal of the battery 19 via the first energizing path 24a. The second terminal (i.e., source) of the first switch Q1 is connected to the first terminal 20u of the motor 20 via the first energizing path 24a.

[0079] The first switch Q1 conducts or disconnects the first current path 24a. When the first switch Q1 is turned on, the first current path 24a is conducted, and when the first switch Q1 is turned off, the first current path 24a is disconnected. However, in this embodiment, even when the first switch Q1 is turned off, current can flow through the first body diode D1. That is, even when the first switch Q1 is turned off, current can flow from the second end to the first end of the first switch Q1 through the first body diode D2. The first switch Q1 is turned on or off based on the first drive signal Sd1 input from the gate circuit 25.

[0080] The second switch Q2 is located on the second energizing path 24b. Specifically, the first terminal (i.e., drain) of the second switch Q2 is connected to the positive terminal of the battery 19 via the second energizing path 24b. The second terminal (i.e., source) of the second switch Q2 is connected to the second terminal 20V of the motor 20 via the second energizing path 24b.

[0081] The second switch Q2 conducts or blocks the second current path 24b. When the second switch Q2 is turned on, the second current path 24b is conducted, and when the second switch Q2 is turned off, the second current path 24b is blocked. However, in this embodiment, even when the second switch Q2 is off, current can flow through the second body diode D2. That is, even when the second switch Q2 is off, current can flow from the second end to the first end of the second switch Q2 through the second body diode D2. The second switch Q2 is turned on or off based on the second drive signal Sd2 input from the gate circuit 25.

[0082] The third switch Q3 is located on the third energizing path 24c. Specifically, the first terminal (i.e., drain) of the third switch Q3 is connected to the positive terminal of the battery 19 via the third energizing path 24c. The second terminal (i.e., source) of the third switch Q3 is connected to the third terminal 20w of the motor 20 via the third energizing path 24c.

[0083] The third switch Q3 conducts or blocks the third current path 24c. When the third switch Q3 is turned on, the third current path 24c is conducted, and when the third switch Q3 is turned off, the third current path 24c is blocked. However, in this embodiment, even when the third switch Q3 is off, current can flow through the third body diode D3. That is, even when the third switch Q3 is off, current can flow from the second end to the first end of the third switch Q3 through the third body diode D3. The third switch Q3 is turned on or off based on the third drive signal Sd3 input from the gate circuit 25.

[0084] The fourth switch Q4 is located on the fourth energizing path 24d. Specifically, the first end (i.e., drain) of the fourth switch Q4 is connected to the first terminal 20u of the motor 20 via the fourth energizing path 24d. The second end (i.e., source) of the fourth switch Q4 is connected to the negative terminal of the battery 19 via the fourth energizing path 24d.

[0085] The fourth switch Q4 conducts or blocks the fourth current path 24d. When the fourth switch Q4 is turned on, the fourth current path 24d is conducted, and when the fourth switch Q4 is turned off, the fourth current path 24d is blocked. However, in this embodiment, even when the fourth switch Q4 is off, current can flow through the fourth body diode D4. That is, even when the fourth switch Q4 is off, current can flow from the second end to the first end of the fourth switch Q4 through the fourth body diode D4. The fourth switch Q4 is turned on or off based on the fourth drive signal Sd4 input from the gate circuit 25.

[0086] The fifth switch Q5 is located on the fifth energizing path 24e. Specifically, the first terminal (i.e., drain) of the fifth switch Q5 is connected to the second terminal 20V of the motor 20 via the fifth energizing path 24e. The second terminal (i.e., source) of the fifth switch Q5 is connected to the negative terminal of the battery 19 via the fifth energizing path 24e.

[0087] The fifth switch Q5 conducts or blocks the fifth current path 24e. When the fifth switch Q5 is turned on, the fifth current path 24e is conducted, and when the fifth switch Q5 is turned off, the fifth current path 24e is blocked. However, in this embodiment, even when the fifth switch Q5 is off, current can flow through the fifth body diode D5. That is, even when the fifth switch Q5 is off, current can flow from the second end to the first end of the fifth switch Q5 through the fifth body diode D5. The fifth switch Q5 is turned on or off based on the fifth drive signal Sd5 input from the gate circuit 25.

[0088] The sixth switch Q6 is located on the sixth energizing path 24f. Specifically, the first end (i.e., drain) of the sixth switch Q6 is connected to the third terminal 20w of the motor 20 via the sixth energizing path 24f. The second end (i.e., source) of the sixth switch Q6 is connected to the negative terminal of the battery 19 via the sixth energizing path 24f.

[0089] The sixth switch Q6 conducts or disconnects the sixth current path 24f. When the sixth switch Q6 is turned on, the sixth current path 24f is conducted, and when the sixth switch Q6 is turned off, the sixth current path 24f is disconnected. However, in this embodiment, even when the sixth switch Q6 is off, current can flow through the sixth body diode D6. That is, even when the sixth switch Q6 is off, current can flow from the second end to the first end of the sixth switch Q6 through the sixth body diode D6. The sixth switch Q6 is turned on or off based on the sixth drive signal Sd6 input from the gate circuit 25.

[0090] Here, we define the U-phase current, V-phase current, and W-phase current. The U-phase current is the current that flows between the drive circuit 24 and the first terminal 20u of the motor 20. In other words, the U-phase current is the current that flows into the first terminal 20u of the motor 20 and the current that flows out of the first terminal 20u of the motor 20. In the following explanation, the direction in which current flows toward the first terminal 20u is defined as the "positive direction" (+), and the direction in which current flows out of the first terminal 20u is defined as the "negative direction" (-).

[0091] The V-phase current is the current that flows between the drive circuit 24 and the second terminal 20V of the motor 20. In other words, the V-phase current is the current that flows into the second terminal 20V of the motor 20, and the current that flows out of the second terminal 20V of the motor 20. In the following explanation, the direction in which current flows toward the second terminal 20V is defined as the "positive direction" (+), and the direction in which current flows out of the second terminal 20V is defined as the "negative direction" (-).

[0092] The W-phase current is the current that flows between the drive circuit 24 and the third terminal 20w of the motor 20. In other words, the W-phase current is the current that flows into the third terminal 20w of the motor 20, and the current that flows out of the third terminal 20w of the motor 20. In the following explanation, the direction in which current flows toward the third terminal 20w is defined as the "positive direction" (+), and the direction in which current flows out of the third terminal 20w is defined as the "negative direction" (-).

[0093] The controller 22 includes a gate circuit 25. The gate circuit 25 receives first to sixth control signals from the control circuit 26. The gate circuit 25 generates a first drive signal Sd1 in response to the first control signal, a second drive signal Sd2 in response to the second control signal, a third drive signal Sd3 in response to the third control signal, a fourth drive signal Sd4 in response to the fourth control signal, a fifth drive signal Sd5 in response to the fifth control signal, and a sixth drive signal Sd6 in response to the sixth control signal. In other words, the first to sixth control signals control the first to sixth switches Q1 to Q6 (and consequently control the motor 20). The first to sixth control signals may include pulse width modulation (PWM) signals.

[0094] The first control signal and the first drive signal Sd1 are in the form of binary signals (digital signals). The logic level of the first drive signal Sd1 is the same as the logic level of the first control signal. The gate circuit 25 outputs the input first control signal to the drive circuit 24 as the first drive signal Sd1, either amplified or at its original level. In this embodiment, the first drive signal Sd1 may be considered equal to (or equivalent to) the first control signal.

[0095] The correspondence between the second to sixth control signals and the second to sixth drive signals Sd2 to Sd6 is the same as the correspondence between the first control signal and the first drive signal Sd1 described above. Note that the gate circuit 25 may be included in the control circuit 26, and the first to sixth drive signals Sd1 to Sd6 may be output from the control circuit 26.

[0096] The controller 22 includes a current detection circuit 27. The current detection circuit 27 is located on the current path from the drive circuit 24 to the negative terminal of the battery 19 and outputs a current detection signal indicating the value of the current flowing through this current path (hereinafter referred to as the "motor current value"). The current detection signal is input to the control circuit 26.

[0097] The controller 22 includes a reference voltage generation circuit 45. The reference voltage generation circuit 45 generates a first reference voltage Vr1. The first reference voltage Vr1 corresponds to the voltage of the virtual neutral point of the motor 20.

[0098] The reference voltage generation circuit 45 comprises a first resistor R1, a second resistor R2, and a third resistor R3. The first terminal of the first resistor R1 is connected to the first terminal 20u of the motor 20. The first terminal of the second resistor R2 is connected to the second terminal 20v of the motor 20. The first terminal of the third resistor R3 is connected to the third terminal 20w of the motor 20. The second terminals of the first resistor R1, the second terminal of the second resistor R2, and the second terminal of the third resistor R3 are connected to each other. The voltages at the second terminals of the first to third resistors R1 to R3 are output as the first reference voltage Vr1. The first reference voltage Vr1 is input to the selection circuit 36.

[0099] The controller 22 includes a fourth resistor R4 and a fifth resistor R5. The fourth resistor R4 and the fifth resistor R5 are connected in series with each other. The first terminal of the fourth resistor R4 is connected to the positive terminal connection line in the drive circuit 24, which is electrically connected to the positive terminal of the battery 19. The first terminals of the first to third switches Q1 to Q3 are connected to the positive terminal connection line. The second terminal of the fourth resistor R4 is connected to the first terminal of the fifth resistor R5. The second terminal of the fifth resistor R5 is connected to the negative terminal connection line in the drive circuit 24, which is electrically connected to the negative terminal of the battery 19. The second terminals of the fourth to sixth switches Q4 to Q6 are connected to the negative terminal connection line.

[0100] The voltage at the second terminal of the fifth resistor R5 (i.e., the voltage of the negative terminal connection line) is input to the selection circuit 36, described later, as the second reference voltage Vr2. The voltage at the first terminal of the fourth resistor R4 (i.e., the voltage of the positive terminal connection line) is input to the selection circuit 36 ​​as the third reference voltage Vr3. The voltage at the second terminal of the fourth resistor R4 is input to the selection circuit 36 ​​as the fourth reference voltage Vr4. The fourth reference voltage Vr4 corresponds to the voltage obtained by dividing the voltage between the positive terminal connection line and the negative terminal connection line by the fourth and fifth resistors R4 and R5. The voltage division ratio can be determined in any way. The voltage division ratio may be, for example, 1 / 2.

[0101] The controller 22 includes a selection circuit 36. The selection circuit 36 ​​receives first to fourth reference voltages Vr1 to Vr4 and outputs one of them as the reference voltage. In this embodiment, the selection circuit 36 ​​is in the form of a multiplexer. The selection circuit 36 ​​selects the reference voltage to be output as the reference voltage according to the switching signal input from the control circuit 26.

[0102] The controller 22 includes a current information acquisition circuit 40. The current information acquisition circuit 40 receives a first voltage Vu, a second voltage Vv, and a third voltage Vw. The first voltage Vu is the voltage at the first terminal 20u of the motor 20. The second voltage Vv is the voltage at the second terminal 20v of the motor 20. The third voltage Vw is the voltage at the third terminal 20w of the motor 20. The first to third voltages Vu, Vv, and Vw are examples of current information in the overall embodiment.

[0103] The current information acquisition circuit 40 generates first comparison information corresponding to the magnitude of the input first voltage Vu and outputs it to the control circuit 26, generates second comparison information corresponding to the magnitude of the input second voltage Vv and outputs it to the control circuit 26, and generates third comparison information corresponding to the magnitude of the input third voltage Vw and outputs it to the control circuit 26.

[0104] The current information acquisition circuit 40 more specifically comprises a first comparator 41, a second comparator 42, and a third comparator 43. The first comparator 41 receives the first voltage Vu and the reference voltage input from the selection circuit 36. The first comparator 41 compares the value of the first voltage Vu with the value of the reference voltage and outputs first comparison information according to the comparison result. The first comparison information is a binary signal. If the value of the first voltage Vu is greater than or equal to the value of the reference voltage, the first comparator 41 outputs first comparison information at the H level (high level). If the value of the first voltage Vu is less than the value of the reference voltage, the first comparator 41 outputs first comparison information at the L level (low level).

[0105] The second comparator 42 receives the second voltage Vv and the reference voltage input from the selection circuit 36. The second comparator 42 compares the value of the second voltage Vv with the value of the reference voltage and outputs second comparison information according to the comparison result. The second comparison information is a binary signal. If the value of the second voltage Vv is greater than or equal to the value of the reference voltage, the second comparator 42 outputs second comparison information at the H level. If the value of the second voltage Vv is less than the value of the reference voltage, the second comparator 42 outputs second comparison information at the L level.

[0106] The third comparator 43 receives the third voltage Vw and the reference voltage input from the selection circuit 36. The third comparator 43 compares the value of the third voltage Vw with the value of the reference voltage and outputs third comparison information according to the comparison result. The third comparison information is a binary signal. If the value of the third voltage Vw is greater than or equal to the value of the reference voltage, the third comparator 43 outputs third comparison information at the H level. If the value of the third voltage Vw is less than the value of the reference voltage, the third comparator 43 outputs third comparison information at the L level.

[0107] The controller 22 includes a control circuit 26. The control circuit 26 in this embodiment includes, for example, a microcomputer including a CPU 31 and a memory 32. The memory 32 may include, for example, semiconductor memory such as ROM, RAM, NVRAM, or flash memory.

[0108] The control circuit 26 implements various functions by executing a program stored in a non-transitional physical recording medium. In this embodiment, the memory 32 corresponds to the non-transitional physical recording medium that stores the program. In this embodiment, the memory 32 stores programs for various processes described later.

[0109] Some or all of the functions implemented by the control circuit 26 may be achieved by program execution (i.e., by software processing) or by one or more hardware components. For example, the control circuit 26 may include a logic circuit (or wired logic connection) containing two or more electronic components instead of, or in addition to, a microcomputer. That is, the logic circuit may achieve some or all of the functions of the control circuit 26. The logic circuit may include an ASIC, ASSP, and / or a programmable logic device. An example of a programmable logic device is an FPGA.

[0110] The control circuit 26 receives a trigger signal from the trigger switch 10. The trigger signal indicates whether the trigger switch 10 is on or off. The trigger signal may also include information indicating the amount of movement of the trigger switch 10.

[0111] The control circuit 26 is electrically connected to the operation panel 14. The control circuit 26 performs various processes based on various signals input from the operation panel 14. The control circuit 26 displays various information such as the operating status and operating mode of the electric work machine 1 on the operation panel 14.

[0112] The control circuit 26 receives a current detection signal from the current detection circuit 27. The control circuit 26 performs various processes based on the motor current value indicated by the current detection signal. The control circuit 26 outputs a switching signal to the selection circuit 36 ​​to specify the reference voltage according to the operating state of the electric work machine 1. In this embodiment, the control circuit 26 basically sets the fourth reference voltage Vr4 as the reference voltage while the motor 20 is being driven. On the other hand, the control circuit 26 sets one of the first to third reference voltages Vr1 to Vr3 as the reference voltage while the motor 20 is being braked.

[0113] The control circuit 26 receives first to third comparison information from the current information acquisition circuit 40. Based on the first to third comparison information, the control circuit 26 performs the aforementioned driving and braking operations. (2-1-3) Motor control by control circuit The driving and braking operations performed by the control circuit 26 will be explained in more detail.

[0114] (2-1-3-1) Drive operation When the drive requirements are met, the control circuit 26 performs a drive operation to rotate the motor 20. The drive requirements include at least turning on the trigger switch 10.

[0115] In order to rotate the motor 20, the control circuit 26 needs to know the electrical angle (in other words, the rotational position) of the motor 20. There are mainly two methods for detecting the electrical angle of the motor 20: one using a Hall sensor and the other using the induced voltage of the motor 20 (so-called sensorless).

[0116] In the electric work machine 1 of this embodiment, the electrical angle is detected without a sensor. The electric work machine 1 of this embodiment does not have a physical detection device such as a Hall sensor for detecting the electrical angle.

[0117] The control circuit 26 detects the electrical angle of the motor 20 based on the induced voltages of the motor 20 generated at the first to third terminals 20u, 20v, and 20w of the motor 20 during driving operation. Then, it controls the drive circuit 24 according to the electrical angle to rotate the motor 20.

[0118] More specifically, the control circuit 26 instructs the selection circuit 36 ​​to set the fourth reference voltage Vr4 as the reference voltage. In other words, the first to third comparison information based on the fourth reference voltage Vr4 is input to the control circuit 26. The control circuit 26 then detects the electrical angle of the motor 20 based on the first to third comparison information. The first to third comparison information includes information about the induced voltage of the motor 20. Therefore, the electrical angle can be detected from the first to third comparison information.

[0119] Furthermore, when the motor 20 is rotating at a low speed below a predetermined rotational speed, the control circuit 26 may control the rotation of the motor 20 using the current detection signal without using the first to third comparison information. Also, in the following explanation, angles may be expressed as, for example, "120°", but in this case, the angle represents the electrical angle of the motor 20.

[0120] (2-1-3-2) Braking operation When the braking requirements are met, the control circuit 26 performs a braking action to decelerate and / or stop the motor 20. The braking requirements include the trigger switch 10 being turned off while the motor 20 is rotating.

[0121] In braking operations, one of the following braking methods is used to decelerate the motor 20: free-run, two-phase short-circuit braking, or three-phase short-circuit braking. In two-phase and three-phase short-circuit braking, a current flows between the motor 20 and the drive circuit 24 due to the induced voltage of the motor 20, thereby braking the motor 20. This current may be referred to as the "braking current" in the following explanation.

[0122] Free-running involves setting all of the first to sixth drive signals Sd1 to Sd6 to the L level, as illustrated in Figure 3, thereby turning off all of the first to sixth switches Q1 to Q6. When free-running is in progress, the U-phase, V-phase, and W-phase currents do not flow. Figure 3 shows an example of free-running operation when the motor 20 is rotating in the forward direction.

[0123] A drive signal at an L level means that the corresponding switch is off, and a drive signal at an H level means that the corresponding switch is on. In addition, in the waveform diagrams from Figure 3 onwards, "1 (U phase)" represents the first comparison information (i.e., the output of the first comparator 41), "2 (V phase)" represents the second comparison information (i.e., the output of the second comparator 42), and "3 (W phase)" represents the third comparison information (i.e., the output of the third comparator 43).

[0124] During free-running, the control circuit 26 sets the reference voltage to the first reference voltage Vr1. Then, it performs free-running while detecting the electrical angle of the motor 20 based on the first to third comparison information.

[0125] Three-phase short-circuit braking includes low-side three-phase short-circuit braking and high-side three-phase short-circuit braking. Low-side three-phase short-circuit braking involves turning on three low-side switches and turning off three high-side switches. The "three low-side switches" refer to switches Q4 to Q6 (the fourth through sixth switches). In low-side three-phase short-circuit braking, a braking current flows between the motor and the three low-side switches.

[0126] High-side three-phase short-circuit braking involves turning on three high-side switches and turning off three low-side switches. The "three high-side switches" refer to the first to third switches Q1 to Q3. In high-side three-phase short-circuit braking, a braking current flows between the motor and the three high-side switches.

[0127] When the control circuit 26 performs three-phase short-circuit braking, it performs either low-side three-phase short-circuit braking or high-side three-phase short-circuit braking. The control circuit 26 may be configured to perform only low-side three-phase short-circuit braking, or only high-side three-phase short-circuit braking, or it may be configured to perform low-side three-phase short-circuit braking and high-side three-phase short-circuit braking selectively (for example, alternately depending on the rotation of the motor 20).

[0128] During low-side three-phase short-circuit braking, the control circuit 26 sets the reference voltage to either the first reference voltage Vr1 or the second reference voltage Vr2. Then, while detecting the electrical angle of the motor 20 based on the first to third comparison information, it performs low-side three-phase short-circuit braking.

[0129] During high-side three-phase short-circuit braking, the control circuit 26 sets the reference voltage to either the first reference voltage Vr1 or the third reference voltage Vr3. Then, while detecting the electrical angle of the motor 20 based on the first to third comparison information, it performs high-side three-phase short-circuit braking.

[0130] Figure 4 shows an example of low-side three-phase short-circuit braking operation when the motor 20 is rotating in the forward direction. In low-side three-phase short-circuit braking, the U-phase current, V-phase current, and W-phase current change according to the rotation angle of the motor 20, as illustrated in Figure 4. In addition, the first to third comparison information changes according to the rotation angle of the motor 20, as illustrated in Figure 4.

[0131] Two-phase short-circuit braking involves electrically short-circuiting any two of the first to third terminals 20u to 20w of the motor 20. Specifically, in two-phase short-circuit braking, two of the first to sixth switches Q1 to Q6 are turned on and the other four are turned off. The two switches that are turned on in two-phase short-circuit braking are called a "switch pair".

[0132] Two-phase short-circuit braking includes low-side two-phase short-circuit braking and high-side two-phase short-circuit braking. Low-side two-phase short-circuit braking involves turning on a pair of three low-side switches and turning off the other one and three high-side switches. High-side two-phase short-circuit braking involves turning on a pair of three high-side switches and turning off the other one and three low-side switches. In two-phase short-circuit braking, a braking current flows between the motor and the switch pair.

[0133] When the control circuit 26 performs two-phase short-circuit braking, it performs either low-side two-phase short-circuit braking or high-side two-phase short-circuit braking. The control circuit 26 may be configured to perform only low-side two-phase short-circuit braking, or only high-side two-phase short-circuit braking, or it may be configured to perform low-side two-phase short-circuit braking and high-side two-phase short-circuit braking alternately (for example, alternately depending on the rotation of the motor 20).

[0134] During low-side two-phase short-circuit braking, the control circuit 26 sets the reference voltage to either the first reference voltage Vr1 or the second reference voltage Vr2. Then, while detecting the electrical angle of the motor 20 based on the first to third comparison information, it performs low-side two-phase short-circuit braking.

[0135] During high-side two-phase short-circuit braking, the control circuit 26 sets the reference voltage to either the first reference voltage Vr1 or the third reference voltage Vr3. Then, while detecting the electrical angle of the motor 20 based on the first to third comparison information, it performs high-side two-phase short-circuit braking.

[0136] The switch pair may be fixed regardless of the electrical angle of the motor 20. However, the control circuit 26 in this embodiment is configured to perform a switching operation while a braking operation is being performed. The switching operation includes switching the switch pair according to the electrical angle of the motor 20.

[0137] In the following explanation, the switch that is to be turned off in the next switching operation, out of the two switches currently set up in a switch pair and turned on, will be referred to as the switch to be turned off.

[0138] During the switching operation, the control circuit 26 switches the switch pair based on whether the current flowing through the switch to be turned off in the switch pair satisfies the off requirement while two-phase short-circuit braking is being performed. In other words, it turns off the switch to be turned off and turns on one of the switches other than the switch pair that is currently turned off.

[0139] The off requirement is satisfied on the condition that, at a minimum, the magnitude of the current flowing through the switch to be turned off is not an extremum in the opposite direction to a specific direction. The specific direction is the direction of flow from source to drain. In other words, the specific direction is the direction corresponding to the forward direction of the body diode. To put it another way, in low-side two-phase short-circuit braking, the specific direction is the direction from the negative terminal of the battery 19 through the switch to be turned off to the motor 20, and in high-side two-phase short-circuit braking, the direction from the motor 20 through the switch to be turned off to the positive terminal of the battery 19.

[0140] In two-phase short-circuit braking, the off requirement is not met at least when current is flowing through the switch to be turned off in the opposite direction to the specific direction (corresponding to the reverse direction of the body diode) and the current value is at an extreme value. The reason is that if the switch to be turned off at such a timing, a large regenerative current may flow from the motor 20 to the battery 19. This regenerative current can flow through the body diode of the currently ON switch and the switch that is in a pair relationship with the switch to be turned off. "Pair relationship" means that they are in series with respect to the battery 19. For example, the first switch Q1 and the fourth switch Q4 are in a pair relationship with each other.

[0141] In this embodiment, the switch pair is switched such that regenerative current is suppressed or prevented when the switch pair is switched. This is one of the most distinctive features of this embodiment. To achieve this, an off requirement is set so that the switch pair is switched at a timing when regenerative current is suppressed or does not occur.

[0142] To further suppress or prevent the generation of regenerative current, it is desirable to turn off the switch to be turned off when a current in a specific direction is flowing through it. In this way, when the switch to be turned off, the brake current that was flowing through the switch to be turned off can continue to flow through the body diode of the switch to be turned off, thereby preventing or significantly suppressing regeneration to the battery 19. Therefore, in this embodiment, the off requirement is more specifically met based on the direction of the current flowing through the switch to be turned off being in a specific direction.

[0143] In this embodiment, switch pairs are switched according to the electrical angle so that the off requirement is met. The control circuit 26 has a switch pair table, as illustrated in Figure 5. The switch pair table may be stored in memory 32.

[0144] The switch pair table shows the relationship between the range of electrical angles and the switch pairs that should be turned on within that range. Figure 5 shows the switch pairs in low-side two-phase short-circuit braking. As shown in Figure 5, the switch pairs in low-side two-phase short-circuit braking differ depending on whether the electrical angle is -30° or more but less than 90°, 90° or more but less than 210°, or 210° or more but less than 330°. A switch pair table for high-side two-phase short-circuit braking is also implemented separately. In Figure 5, "U phase" means the 4th switch Q4, "V phase" means the 5th switch Q5, and "W phase" means the 6th switch Q6. Also, as shown in Figure 5, the switch pairs differ depending on the rotation direction of the motor 20.

[0145] By switching switch pairs according to the switch pair table in Figure 5 based on the electrical angle, the target switch can be turned off when the off requirements are met. In the conventional configuration that uses a Hall sensor to detect the motor's electrical angle, the motor's electrical angle can be appropriately detected based on the signal from the Hall sensor, even while two-phase short-circuit braking is being performed.

[0146] On the other hand, in this embodiment, there is no Hall sensor, and the electrical angle is detected based on the induced voltage. Electrical angle detection based on the induced voltage can be performed properly during driving operation, but it is difficult during braking operation. That is, for example, during two-phase short-circuit braking, two switch pairs are turned on simultaneously, making it difficult to properly detect the two induced voltages connected to at least two of the switch pairs among the first to third terminals 20u, 20v, and 20w of the motor 20.

[0147] However, during braking, the braking current flows through the switched-on switch, creating a potential difference across its terminals due to the switch's internal resistance. Therefore, it is possible to detect the direction of the braking current flowing through the switch from this potential difference. Specifically, by detecting at least the terminal with the higher (or lower) potential, it is possible to determine the direction in which the braking current is flowing through the switch.

[0148] For example, the direction of the braking current flowing through the fourth switch Q4 can be detected by comparing the first voltage Vu with the first reference voltage Vr1 or the second reference voltage Vr2. Similarly, for example, the direction of the braking current flowing through the first switch Q1 can be detected by comparing the first voltage Vu with the first reference voltage Vr1 or the third reference voltage Vr3.

[0149] In other words, even during two-phase short-circuit braking operation, the direction of the braking current flowing through the switch pair can be detected based on the first to third comparison information from the current information acquisition circuit 40. The first to third comparison information changes according to the rotation of the motor 20 (i.e., according to the electrical angle). Therefore, at the timing when at least one change in the first to third comparison information (hereinafter referred to as the "comparator edge") occurs, the electrical angle of the motor 20 at that timing can be detected.

[0150] Therefore, in this embodiment, switching at a timing that satisfies the off requirement is achieved by switching the switch pair based on the first to third comparison information (more specifically, in response to the occurrence of a comparator edge). In other words, by switching the switch pair based on the occurrence of a comparator edge, switching at a timing that satisfies the off requirement is achieved. That is, the occurrence of a comparator edge means that a brake current in a specific direction is flowing through the switch to be turned off (i.e., the off requirement is met). The timing of the occurrence of a comparator edge is an example of an off-possible timing in the summary of the embodiment.

[0151] Figure 6 shows an example of two-phase short-circuit braking operation when the motor 20 is rotating in the forward direction. In Figure 6, for example, 120°, 240°, 360°, 480°, 600°, etc. correspond to the timing of comparator edge generation.

[0152] In Figure 6, "phase voltage" refers to the first to third voltages Vu, Vv, and Vw. Figure 6 illustrates the changes in the first to third voltages Vu, Vv, and Vw relative to the ground potential. In this embodiment, the ground potential is the same as that of the negative terminal of the battery 19. Furthermore, the voltage of the negative terminal line in the drive circuit 24 (i.e., the second reference voltage Vr2) may also be treated as being the same as the ground potential.

[0153] Furthermore, in Figure 6, "virtual neutral point Vr1" refers to the first reference voltage Vr1, that is, the reference voltage in this embodiment. Figure 6 illustrates the change in the first reference voltage Vr1 when the potential of ground is used as the reference.

[0154] Furthermore, in Figure 6, "comparator input" refers to the first to third voltages Vu, Vv, and Vw input to the first to third comparators 41 to 43, respectively. Figure 6 illustrates the changes in the first to third voltages Vu, Vv, and Vw with respect to the potential of the virtual neutral point (i.e., the first reference voltage Vr1).

[0155] Note that, due to the circuit configuration, a comparator edge is generated when the switch pair switches due to the switching operation. However, in this embodiment, the comparator edge at the time of the switching operation is ignored and is not treated as a comparator edge for control purposes. For example, in Figure 6, a switching operation occurs at 210°, and as a result, the first comparison information changes (changes to H level) at 210°. However, this change is due to the switching operation and is not treated as a comparator edge. The same applies to changes in comparison information at 90°, 330°, 450°, 570°, etc.

[0156] At the timing when the comparator edge occurs, the voltage at the motor 20 side terminal of the switch to be turned off is below the reference voltage. This means that a braking current in a specific direction is flowing through the switch to be turned off. For example, at the 240° timing in Figure 6, a braking current in a specific direction is flowing through the fourth switch Q4, which is the switch to be turned off at this time. Therefore, the switch to be turned off can be turned off at this timing.

[0157] Furthermore, the timing of the comparator edge is when the voltage value at the motor 20 side terminal of one switch other than the switch pair reaches the reference voltage value. For example, at the 240° timing in Figure 6, the brake current flowing through the fifth switch Q5, which is one of the switches other than the switch pair at that time, reaches zero, and as a result the second comparison information changes (changes to H level). Therefore, the change in the comparison information corresponding to one switch other than the switch pair indirectly indicates that a brake current is flowing in a specific direction to the switch to be turned off.

[0158] Therefore, a comparator edge occurs when (i) the voltage value at the motor 20 side terminal of the switch to be turned off is less than the reference voltage value, and (ii) the voltage value at the motor 20 side terminal of one of the switches other than the switch pair is equal to or greater than the reference voltage value.

[0159] When a comparator edge occurs, the switch pair may be switched immediately. For example, in Figure 6, the fourth switch Q4 may be turned off and the fifth switch Q5 turned on immediately at a timing of 240°. This is because, at this point, a current in a specific direction (in other words, a positive U-phase current) is already flowing through the fourth switch Q4, which is the switch to be turned off. Even if the fourth switch Q4 is turned off at this point, the brake current can continue to flow through the fourth body diode D4. Therefore, regeneration is blocked or suppressed.

[0160] However, the larger the braking current flowing through the fourth body diode D4, and the longer the duration for which that braking current flows, the greater the burden on the fourth body diode D4. Specifically, for example, the amount of heat generated by the fourth body diode D4 increases. Therefore, it is desirable that the fourth switch Q4 be turned off when the braking current flowing through it in a specific direction is as small as possible or zero.

[0161] Therefore, in this embodiment, after a comparator edge occurs, a delay time is waited, and the switch pair is switched when the delay time has elapsed. In other words, the off requirement is met not only because a comparison edge has occurred, but also because a delay time has elapsed since the occurrence of that comparator edge. The purpose of waiting for the delay time is to wait for the brake current flowing in a specific direction to the switch to be turned off to decrease.

[0162] The delay time is determined such that the delay time elapses when the motor 20 has rotated by a desired delay angle from the generation of the comparator edge. The delay angle is determined such that the magnitude of the brake current flowing to the switch to be turned off is decreasing or becomes zero after the motor has rotated by that delay angle from the generation of the comparator edge.

[0163] In this embodiment, the delay angle is set to 90°. That is, the switch to be turned off (i.e., the switch pair switches) is turned off when it has rotated 90° from the position where the comparator edge was generated.

[0164] However, it is difficult to detect the position 90° rotated from the position where the comparator edge occurred during braking control. Therefore, in this embodiment, when a comparator edge occurs, the angular velocity (in other words, rotational speed) of the motor 20 is estimated based on the elapsed time from the previous comparator edge occurrence to the current comparator edge occurrence and the electrical angle during that time (120° in this embodiment). For example, the angular velocity can be estimated by dividing the elapsed time by the electrical angle. Then, assuming that the motor 20 continues to rotate at the estimated angular velocity, the time required to rotate 90° is calculated. The result of this calculation is set as the delay time. Therefore, the delay time becomes longer as the estimated angular velocity decreases.

[0165] In the example shown in Figure 6, the fourth switch Q4 is turned off at 330°, after the comparator edge occurs at 240° and the delay time has elapsed (i.e., it has rotated by 90°). At 330°, the brake current flowing through the fourth switch Q4 in a specific direction is almost zero. In other words, the off requirement in this embodiment is strictly met as the delay time elapses (i.e., the delay angle rotates) after the comparator edge occurs.

[0166] Furthermore, it is desirable that the delay angle be set so that the switching operation occurs before the braking current in a specific direction flowing through the switch to be turned off becomes zero. For example, in Figure 6, it is desirable that the delay angle from 240° be set before 360°. The reason for this is as follows.

[0167] At 240°, the fourth switch Q4 is newly set as the switch to be turned off. After 240°, the brake current of the fourth switch Q4 gradually increases in accordance with the rotation of the motor 20, then decreases, and becomes almost zero at 360°. If the switching operation does not occur even after 720°, the direction of the brake current of the fourth switch Q4 will change to the opposite direction to the specific direction. Therefore, if the fourth switch Q4 is turned off after 360°, regenerative current may be generated. For this reason, it is desirable to set the delay angle so that the switching operation occurs when a brake current in the specific direction is flowing through the switch to be turned off.

[0168] The two-phase short-circuit braking of this embodiment has the features described above. Therefore, even though a so-called sensorless method is employed that does not have a rotation angle sensing device, it is possible to perform switching operations at an appropriate timing according to the electrical angle in two-phase short-circuit braking.

[0169] Let's provide a supplementary explanation of the operation example shown in Figure 6. In Figure 6, for example, a comparator edge occurs at 360°. At this time, the switch pair is the 5th and 6th switches Q5 and Q6, and the switch to be turned off is the 6th switch Q6. The switching operation could be performed at this 360° timing, but in this embodiment, a delay time is set. Then, the switching operation is performed when that delay time has elapsed (450° or near 450°). Specifically, the switch pair switches to the 4th and 5th switches Q4 and Q5, and the 6th switch Q6 is turned off. At this time, the brake current flowing through the 6th switch Q6 is in a specific direction and is close to zero or almost zero. Therefore, in addition to preventing or suppressing regeneration, the current flowing through the 6th body diode D6 is also suppressed. Thereafter, the same process is performed each time a comparator edge occurs.

[0170] (2-1-4) Example of operation when changing from driving operation to braking operation Referring to Figure 7, an example of the operation of the motor 20 will be described. Figure 7 illustrates a case where low-side two-phase short-circuit braking is performed during braking operation while rotating forward.

[0171] In the example shown in Figure 7, the drive operation is performed up to 360° because the drive requirements are met. At 360°, the trigger switch 10 is turned off. This satisfies the braking requirements.

[0172] When the braking requirements are met, two-phase short-circuit braking may be initiated without performing free-running. However, in this embodiment, the motor 20 is first braked with a weak braking force by free-running for a short time, and then two-phase short-circuit braking is performed.

[0173] In the example shown in Figure 7, braking occurs through free-running from 360° to 570°. Then, two-phase short-circuit braking begins after 570°. In other words, two-phase short-circuit braking begins after two comparator edge events occur following the start of the braking operation.

[0174] Specifically, the first comparator edge occurs at 420° after the trigger is turned off. The measurement timer starts at this point. The measurement timer is used to measure the interval between comparator edge occurrences. The measurement timer is used simply for time measurement and does not generate a timer interrupt like the commutation timer described later.

[0175] Subsequently, a second comparator edge occurs at 480°. Here, a delay time is set, and a commutation timer based on that delay time is started. The commutation timer is used to generate a timer interrupt. That is, after the commutation timer is started, when the timer value of the commutation timer reaches the delay time, a timer interrupt is generated. Specifically, the commutation timer interrupt processing shown in Figure 12, which will be described later, is executed. This causes the switch pair to switch over. The delay time is calculated based on the value of the measurement timer when the 480° comparator edge occurs. The value of the measurement timer at 480° represents the time from the previous comparator edge occurrence (i.e., 420°) to the current comparator edge occurrence (i.e., 480°), i.e., the edge occurrence interval. The angular velocity is calculated based on this edge occurrence interval, and the delay time corresponding to the delay angle is calculated based on that angular velocity. Then, the commutation timer is started, and when the delay time has elapsed (570° or nearby), the switch pair corresponding to 570° is turned on by the commutation timer interrupt. This initiates two-phase short-circuit braking.

[0176] At 570°, switches Q4 and Q6 (the 4th and 6th switches) are turned on. At this point, the next switch pair will be switches Q5 and Q6 (the 5th and 6th switches), so switch Q4 (the 4th switch) will be the switch to be turned off.

[0177] After two-phase short-circuit braking begins at 570°, a comparator edge occurs at 600°. While a switching operation could be performed at this time, a delay time is set in the same manner as when a comparator edge occurs at 480°. Then, after the delay time has elapsed (at or near 690°), the switching operation takes place, the switch pair switches to the 5th and 6th switches Q5 and Q6, and the 4th switch Q4 is turned off. At this point, the braking current flowing through the 4th switch Q4 is in a specific direction and is close to zero or nearly zero. Therefore, regeneration is prevented or suppressed, and the current flowing through the 4th body diode D4 is also suppressed. The same process is repeated each time a comparator edge occurs thereafter.

[0178] (2-1-5) Various processes by the control circuit The processes executed by the control circuit 26 to realize the various operations described above will now be explained. The memory 32 stores the programs for each of the processes described below. The various operations described above are realized by the CPU 31 executing these programs.

[0179] The following explanation is based on the premise that low-side three-phase short-circuit braking is used as three-phase short-circuit braking, and low-side two-phase short-circuit braking is used as two-phase short-circuit braking. (2-1-5-1) Main Processing After startup, the control circuit 26 executes the main process shown in Figure 8. When the control circuit 26 starts the main process, it determines in S110 whether the base time has elapsed. The base time corresponds to the control cycle. In other words, in S110, it determines whether the control cycle has elapsed since the last time it was determined that the base time had elapsed.

[0180] If the base time has elapsed, the control circuit 26 detects the state of the trigger switch 10 (whether it is on or not) based on the trigger signal in S120. In S120, the amount of movement of the trigger switch 10 may also be detected.

[0181] In S130, the control circuit 26 detects the rotational speed of the motor 20 based on the first to third comparison information. In S140, the control circuit 26 executes motor control processing. Details of the motor control processing are shown in Figure 9.

[0182] As shown in Figure 9, when the control circuit 26 moves to the motor control process, it determines in S210 whether the trigger switch 10 is ON or OFF. If the trigger switch 10 is ON, the process moves to S220.

[0183] In S220, the control circuit 26 determines whether the soft brake flag is set to "Stopped". The soft brake flag indicates whether soft braking is being performed. "Soft brake" refers to two-phase short-circuit braking. Therefore, "soft brake" can be interpreted as "two-phase short-circuit braking."

[0184] If the soft brake flag is set to "Stopped", this process proceeds to S230. In S230, the control circuit 26 causes the selection circuit 36 ​​to set the fourth reference voltage Vr4 as the reference voltage based on a switching signal to the selection circuit 36.

[0185] In S240, the control circuit 26 performs the drive operation. Specifically, it controls the drive circuit 24 based on various information such as the amount of movement of the trigger switch 10 acquired in S120, the electrical angle of the motor 20 based on the first to third comparison information, and the motor current value, thereby rotating the motor 20. After processing in S240, this process moves on to S110 (see Figure 8).

[0186] If the soft brake flag is not set to "Stopped" in S220, the process proceeds to S250. In S250, the control circuit 26 disables comparator interrupts. While comparator interrupts are disabled, even if a comparator edge occurs, the comparator interrupt processing described later will not be executed. In other words, comparator edges are ignored.

[0187] In S260, the control circuit 26 stops the commutation timer and resets its value to its initial value (for example, zero). The commutation timer is used to measure the aforementioned delay time. In S270, the control circuit 26 sets the soft brake flag to "Stopped".

[0188] In S280, the control circuit 26 sets the soft brake interrupt flag to "first time". After processing in S280, the process moves on to S110 (see Figure 8). If the trigger switch 10 is off in S210, the process proceeds to S290. In S290, the control circuit 26, based on a switching signal to the selection circuit 36, causes the selection circuit 36 ​​to set the first reference voltage Vr1 (i.e., the voltage of the virtual neutral point) as the reference voltage.

[0189] In S300, the control circuit 26 determines whether the motor 20 is stopped or not. If the motor 20 is stopped, the process proceeds to S310. In S310, the control circuit 26 performs free run, that is, it turns off all of the first to sixth switches Q1 to Q6. After the execution of S310, the process proceeds to S250.

[0190] If the motor 20 is rotating in S300, the control circuit 26 determines in S320 whether the rotational speed of the motor 20 is low. Here, the rotational speed detected in the preceding S130 is used for the determination. In this context, low speed means that the motor 20 is rotating at or below the predetermined rotational speed mentioned above. If the rotational speed of the motor 20 is low, the process proceeds to S330.

[0191] In S330, the control circuit 26 performs three-phase short-circuit braking (specifically, low-side three-phase short-circuit braking). That is, while rotating at a speed higher than the predetermined speed, two-phase short-circuit braking is performed, but during low-speed rotation below the predetermined speed, the braking force is increased by three-phase short-circuit braking. Specifically in S330, three low-side switches are turned on and three high-side switches are turned off. After processing in S330, the process proceeds to S250. Note that high-side three-phase short-circuit braking may also be performed in S330.

[0192] If the rotational speed of motor 20 is not low in S320, the process proceeds to S340. In S340, the control circuit 26 executes the soft brake start process. That is, it starts two-phase short-circuit braking (specifically, low-side two-phase short-circuit braking). Details of the soft brake start process are shown in Figure 10.

[0193] When the control circuit 26 moves to the soft brake start process, in S341 it determines whether the soft brake flag is "Stopped". If the soft brake flag is not "Stopped", this process ends and proceeds to S110. If the soft brake flag is "Stopped", this process proceeds to S342.

[0194] In S342, the control circuit 26 sets the soft brake flag to "running". In S343, the control circuit 26 performs a free run, similar to S310. In other words, instead of immediately performing two-phase short-circuit braking, it first performs a free run.

[0195] In S344, the control circuit 26 sets the comparator interrupt to enable. After the execution of S344, this process proceeds to S110. Figure 7 shows an example where the trigger is turned off when the motor 20 is not rotating at a low speed in a 360° range. Therefore, the soft brake start process shown in Figure 10 is performed at that 360° range, which enables free running and allows the comparator interrupt.

[0196] (2-1-5-2) Comparator Interrupt Processing As mentioned above, when the soft brake interrupt process shown in Figure 10 is performed, the comparator interrupt is enabled. While the comparator interrupt is enabled, the control circuit 26 executes the comparator interrupt process shown in Figure 11 each time a comparator edge occurs. For example, in Figure 7, the comparator interrupt process shown in Figure 11 is executed when comparator edges such as 420°, 480°, 600°, 720°, and 840° occur.

[0197] When the control circuit 26 initiates a comparator interrupt, it temporarily disables the comparator interrupt in S410. In S420, the control circuit 26 updates the rotational position of the motor 20 based on the current first to third comparison information. In other words, it obtains the latest rotational position.

[0198] In S430, the control circuit 26 determines whether the soft brake interrupt flag is set to "first time". If the soft brake interrupt flag is set to "first time", the process proceeds to S440. While the motor is stopped, the soft brake interrupt flag is set to "first time" by S280. This flag setting is maintained even after the drive operation starts. Therefore, in the first comparator interrupt processing after the trigger is turned off, the soft brake interrupt flag is set to "first time". In this case, the process proceeds to S440.

[0199] In S440, the control circuit 26 starts timing using the measurement timer. In S450, the control circuit 26 sets the soft brake interrupt flag to "second time or later". As a result, the subsequent processing in S430 will be judged as negative.

[0200] In S460, the comparator interrupt is enabled. After processing in S460, this comparator interrupt processing is terminated. If the soft brake interrupt flag is not set to "first time" in S430, the process proceeds to S480. In S480, the control circuit 26 obtains the timer value of the measurement timer (i.e., the elapsed time since the start of the measurement timer). The timer value obtained here corresponds to the edge generation interval mentioned above.

[0201] In S500, the control circuit 26 executes timer processing. Timer processing includes the processing in S520 to S580. In timer processing, in S520, the control circuit 26 obtains the edge generation interval based on the timer value obtained in S480. As mentioned above, the timer value obtained in S480 is essentially equal to the edge generation interval. Therefore, that timer value may be obtained as the edge generation interval.

[0202] In S530, the control circuit 26 acquires the switch pair to be turned on and the switch to be turned off in the next switching operation. Specifically, based on the rotation position (electrical angle) acquired in S420, it acquires the electrical angle at which the next switching operation will be performed (hereinafter referred to as the "next switching angle"). In this embodiment, as mentioned above, the delay angle is 90°. Therefore, the electrical angle obtained by adding 90° to the electrical angle acquired in S420 is acquired as the next switching angle. Then, referring to the switch pair table in Figure 5, the control circuit acquires the switch pair and the switch to be turned off corresponding to the next switching angle. For example, if the motor 20 is rotating forward and the current rotation position is 600°, the next switching angle is 690°, so the 5th and 6th switches Q5 and Q6 are acquired as the switch pair, and the 4th switch Q4 is acquired as the switch to be turned off.

[0203] In S540, the control circuit 26 sets the next switch pair and the switch to be turned off (or more specifically, the information indicating these) acquired in S530 into the buffer. In S550, the control circuit 26 calculates the delay time. Specifically, it calculates the delay time from the edge generation interval obtained in S520 and a predetermined delay angle (90° in this embodiment) according to the estimation method described above.

[0204] In S560, the control circuit 26 sets the delay time calculated in S550 into a register. In S570, control circuit 26 starts the commutation timer. As mentioned above, the commutation timer is used to generate a commutation timer interrupt (and thus perform the switching operation) after the delay time has elapsed.

[0205] In S580, the control circuit 26 restarts the measurement timer from its initial value. After the processing of S580 is completed (i.e., after the timer processing of S500 is completed), the control circuit 26 terminates the comparator interrupt processing.

[0206] As mentioned above, it is not mandatory to include a delay time. Therefore, once the next switch pair and the switch to be turned off are acquired by S530, the switching operation may be performed immediately. (2-1-5-3) Commutation Timer Interrupt Processing When the timer value of the commutation timer, which was started in S570 in Figure 11, reaches the delay time, a commutation timer interrupt occurs. When a commutation timer interrupt occurs, the control circuit 26 executes the commutation timer interrupt processing shown in Figure 12.

[0207] In S610, the control circuit 26 performs a switching operation based on the information of the next switch pair and the switch to be turned off that is set in the buffer. In other words, it turns on the set switch pair and turns off the switch to be turned off.

[0208] Note that this switching operation generates comparator edges (for example, comparator edges at 690°, 810°, 930°, etc. in Figure 7). However, at the time the S610 switching operation is performed, comparator interrupts are disabled. Therefore, the comparator edges caused by this switching operation are ignored.

[0209] After the switching operation is performed, the control circuit 26 sets the comparator interrupt to enable in S620. [2-2. Second Embodiment] A second embodiment describes the motor control process when the reference voltage used during braking is different from that of the first embodiment. In this embodiment as well, the main process (Figure 8), soft brake start process (Figure 10), comparator interrupt process (Figure 11), and commutation timer interrupt process (Figure 12) are executed, similar to the first embodiment. However, the motor control process differs from that shown in Figure 9 of the first embodiment.

[0210] In the motor control process of the first embodiment described above, the first reference voltage Vr1 (i.e., the voltage of the virtual neutral point) was used as the reference voltage during braking. In contrast, in the motor control processing of the second embodiment shown in Figure 13, the second reference voltage Vr2 (i.e., the potential on the negative electrode side of the power supply in the drive circuit 24) is used as the reference voltage during low-side three-phase short-circuit braking and low-side two-phase short-circuit braking. Figure 13 shows the motor control processing assuming that low-side three-phase short-circuit braking and low-side two-phase short-circuit braking are performed as the short-circuit braking method.

[0211] In Figure 13, the same reference numerals are used for the motor control process in Figure 9 of the first embodiment as in Figure 9. The following explanation will focus on the differences from Figure 9. In the motor control process of this second embodiment, if the trigger switch 10 is turned off in S210, the process proceeds to S300. Then, if it is determined in S300 that the motor 20 is stopped, the process proceeds to S305.

[0212] In S305, the control circuit 26, via a switching signal to the selection circuit 36, causes the selection circuit 36 ​​to set the first reference voltage Vr1 (i.e., the voltage of the virtual neutral point) as the reference voltage. Then, in S310, free running is performed. In other words, for free running, the first reference voltage Vr1 is used as the reference voltage, as in the first embodiment.

[0213] On the other hand, if the rotational speed of the motor 20 is low in S320, the process proceeds to S325. In S325, the control circuit 26 causes the selection circuit 36 ​​to set the second reference voltage Vr2 to the reference voltage. Then, in S330, low-side three-phase short-circuit braking is performed.

[0214] Furthermore, if the rotational speed of motor 20 is not low in S320, the process proceeds to S335. In S335, the control circuit 26, similar to S325, sets the second reference voltage Vr2 in the selection circuit 36 ​​to the reference voltage. Then, in S330, the soft brake start process (see Figure 10) is executed.

[0215] Figure 14 shows an example of the operation of the motor 20 when two-phase short-circuit braking is performed based on the motor control process in Figure 13. Figure 14 shows an example of operation during forward rotation. In Figure 14, "Ground Vr2" means the second reference voltage Vr2, that is, the reference voltage in this second embodiment. Also, "Comparator Input" refers to the first to third voltages Vu, Vv, and Vw when the second reference voltage Vr2 (i.e., ground or near ground potential) is used as the reference.

[0216] As shown in Figure 14, since the second reference voltage Vr2 is used as the reference voltage, the inputs and outputs of the first to third comparators 41 to 43 differ from those of the first embodiment. However, the switching operation is performed in the same way as in the first embodiment.

[0217] For example, a comparator edge is generated at 360°, and comparator interrupt processing (Figure 11) is executed. In this case, the switch pair is the 5th and 6th switches Q5 and Q6, and the switch to be turned off is the 6th switch Q6. The switching operation may be performed at this 360° timing, but a delay time is also set in this second embodiment. Then, when the delay time has elapsed (450° or near 450°), the commutation timer interrupt processing (Figure 12) is executed and the switching operation is performed. Specifically, the switch pair switches to the 4th and 5th switches Q4 and Q5, and the 6th switch Q6 is turned off. At this time, the brake current flowing through the 6th switch Q6 is in a specific direction and is close to zero or almost zero. Therefore, in addition to preventing or suppressing regeneration, the current flowing through the 6th body diode D6 is also suppressed. Thereafter, the same processing is performed each time a comparator edge occurs, and as a result, the 4th to 6th switches Q4 to Q6 switch in the same way as the two-phase short-circuit braking in the first embodiment.

[0218] Furthermore, if the system is configured to perform high-side three-phase short-circuit braking and high-side two-phase short-circuit braking during short-circuit operation, then in S325 and S335, the third reference voltage Vr3 is set as the reference voltage in the selection circuit 36.

[0219] [2-3. Third Embodiment] In the motor control process of the first embodiment (Figure 9), if the trigger switch 10 is turned on (i.e., retriggered) while two-phase short-circuit braking is being performed (i.e., while the motor 20 is being decelerated), the braking operation is stopped almost immediately and the driving operation is started.

[0220] In contrast, in this third embodiment, if a retrigger occurs while the motor 20 is decelerating, the braking force is gradually reduced and the system transitions to drive operation. Specifically, as illustrated in Figure 15, the system transitions from a two-phase short-circuit brake to a one-phase short-circuit brake, then free-running is performed, and finally the system transitions to drive operation. In this way, by gradually reducing the rotational speed of the motor 20 before starting the drive operation when a retrigger occurs, the behavior of the motor 20 during retriggering can be stabilized, improving the user experience. This will be explained in detail below.

[0221] (2-3-1) Example of operation Referring to Figure 15, an example of the operation of the motor 20 in this third embodiment will be described. Figure 15 illustrates an operation in which the motor is retriggered while rotating forward and performing two-phase short-circuit braking, thereby initiating the drive operation. Figure 15 also shows examples in which low-side two-phase short-circuit braking and low-side single-phase short-circuit braking are performed during braking.

[0222] In the example shown in Figure 15, low-side two-phase short-circuit braking is performed up to approximately 470°, causing the motor 20 to decelerate. Then, near 470°, a retrigger is activated, i.e., the trigger switch 10 is turned on.

[0223] After being retriggered, a comparator edge occurs at 480°. For the first comparator edge after retriggering, a delay time is set to start the commutation timer. Then, at the timing when the delay time has elapsed (570° or in the vicinity thereof in FIG. 15), it switches to single-phase short-circuit braking. That is, only one of the three low-side switches is turned on, and the other two and the three high-side switches are turned off. As a result, the motor 20 is braked with a braking force smaller than that of two-phase short-circuit braking. Note that in single-phase short-circuit braking, one of the three high-side switches may be turned on.

[0224] The one switch to be turned on in single-phase short-circuit braking is determined based on the electrical angle of the motor 20 by referring to the single-phase pattern table illustrated in FIG. 16. As shown in FIG. 16, the switch pairs in single-phase short-circuit braking are different when the electrical angle is 0° or more and less than 120°, when it is 120° or more and less than 240°, and when it is 240° or more and less than 360°. Referring to FIG. 16, during forward rotation and at 570°, the switch of the U phase, that is, the fourth switch Q4, is set as the switch to be turned on (refer to the position of 210°). Therefore, as shown in FIG. 15, at 570°, the fifth switch Q5 is turned off, and only the fourth switch Q1 is maintained in the on state.

[0225] At the start of single-phase short-circuit braking, the commutation timer starts again. Then, at the timing when the set time has elapsed (600° or in the vicinity thereof in FIG. 15), it switches to free run. And after free run, the drive operation is started.

[0226] (2-3-2) Various Processes by the Control Circuit The motor control process, comparator interrupt process, and commutation timer interrupt process executed by the control circuit 26 to realize the above-described operations will be described with reference to FIGS. 17 to 19. Note that in this third embodiment as well, the main process (FIG. 8) and the soft brake start process (FIG. 10) are executed in the same manner as in the first embodiment. However, the motor control process, comparator interrupt process, and commutation timer interrupt process are different from those in the first embodiment.

[0227] (2-3-2-1) Motor control process The motor control process of this third embodiment will be described with reference to FIG. 17. In the motor control process of FIG. 17, the same processes as those in FIG. 9 of the first embodiment are denoted by the same reference numerals as in FIG. 9. Hereinafter, the description will be focused on the parts different from FIG. 9.

[0228] In the motor control process of this third embodiment, when the soft brake flag is not set to "stopping" at S220, the process proceeds to S221. At S221, the control circuit 26 determines whether the brake release flag is set to "completed". The brake release flag is set to "completed" in response to the completion of the above-described single-phase short-circuit braking and the transition to the free run (see S770).

[0229] When the brake release flag is set to "completed", since the braking operation has substantially ended and it is in a state where it can smoothly transition to the driving operation, the process proceeds to S250. As a result, the soft brake flag is set to "stopping" (S270). Thereby, an affirmative determination is made in the next process of S220, and the driving operation is performed at S240.

[0230] Also, after the process of S280, the control circuit 26 clears the brake cancellation request flag at S281. This brake cancellation request flag is set at S223. The setting of the brake cancellation request flag indicates that the current braking operation is being executed and it should be cancelled.

[0231] Also, at S282, the control circuit 26 sets the brake release flag to "before execution". On the other hand, when the brake release flag is not set to "completed" at S221, it is still in a state where two-phase short-circuit braking or single-phase short-circuit braking is being executed. Therefore, in this case, this process proceeds to S222.

[0232] In S222, the control circuit 26 determines whether the brake stop request flag is set. If the brake stop request flag is set, the motor control process ends. If the brake stop request flag is not set, the control circuit 26 sets the brake stop request flag in S223. After processing in S223, the control circuit 26 ends the motor control process.

[0233] (2-3-2-2) Comparator Interrupt Processing The comparator interrupt processing of this third embodiment will be described with reference to Figure 18. In the comparator interrupt processing of Figure 18, the same processes as in the comparator interrupt processing of Figure 11 of the first embodiment are denoted by the same reference numerals as in Figure 11. The following description will focus on the parts that differ from those in Figure 11.

[0234] In the comparator interrupt processing of this third embodiment, if the soft brake interrupt flag is not set to "first time" in S430, the process proceeds to S481. In S481, the control circuit 26 determines whether or not the brake stop request flag is set. If the brake stop request flag is not set, the process proceeds to S480.

[0235] If the brake cancellation request flag is set, this process proceeds to S482. In S482, the control circuit 26 acquires the timer value of the measurement timer, similar to S480. The timer value acquired here corresponds to the edge generation interval mentioned above.

[0236] In S483, the edge generation interval is obtained based on the timer value acquired in S482, using the same procedure as in S520. In S484, the control circuit 26 calculates the delay time. Specifically, it calculates the delay time from the edge generation interval obtained in S483 and a predetermined delay angle (90° in this embodiment) according to the estimation method described above.

[0237] In S485, the control circuit 26 sets the delay time calculated in S484 into a register. In S486, control circuit 26 starts the commutation timer. (2-3-2-3) Commutation Timer Interrupt Processing The commutation timer interrupt processing of this third embodiment will be described with reference to Figure 19. In the commutation timer interrupt processing of Figure 19, the same processes as in the commutation timer interrupt processing of Figure 12 of the first embodiment are denoted by the same reference numerals as in Figure 12. The following description will focus on the parts that differ from those in Figure 12.

[0238] In this third embodiment, the control circuit 26 determines in S710 whether or not the brake cancellation request flag is set. If the brake cancellation request flag is not set, the process proceeds to S610. From S610 onward, the process is the same as in the first embodiment.

[0239] If the brake cancellation request flag is set, this process proceeds to S720. In S720, the control circuit 26 determines whether two-phase short-circuit braking is currently being performed. If two-phase short-circuit braking is being performed, this process proceeds to S730.

[0240] In S730, the control circuit 26 acquires the first to third comparison information. In S740, the control circuit 26 calculates the rotational position of the motor 20 based on the first to third comparison information acquired in S730. Then, referring to the single-phase pattern table (Figure 16), it turns on only the one switch that should be turned on at the current rotational position, and turns off all the others. In other words, it performs single-phase short-circuit braking.

[0241] S750 sets the single-phase short-circuit braking time. The single-phase short-circuit braking time is the time during which single-phase short-circuit braking should be performed. The single-phase short-circuit braking time can be set in any way. For example, the single-phase short-circuit braking time may be the same as the delay time set in the register in S485 of the most recent comparator interrupt processing.

[0242] In S760, control circuit 26 starts the commutation timer. This terminates the main commutation timer interrupt processing. When the commutation timer is started in S760, in response to the value of the commutation timer reaching the single-phase short-circuit braking time set in S750, a commutation timer interrupt occurs again, and the commutation timer interrupt process in FIG. 19 is executed again. In this case, since single-phase short-circuit braking is being performed, in S720, it is determined that two-phase short-circuit braking is not being executed, and the process proceeds to S770.

[0243] In S770, the control circuit 26 executes free run. In S780, the control circuit 26 sets the brake release flag to "completed". As a result, in the next motor control process, the process proceeds from S221 to S250. Then, the soft brake flag is set to "stopping" (S270). Therefore, in the further next motor control process, an affirmative determination is made in S220, and thereby a driving operation (S240) is performed.

[0244] [2-4. Fourth Embodiment] [[ID=I12]]In the first to third embodiments, when a comparator interrupt occurs, the comparator interrupt is temporarily prohibited (S410 in FIG. 11). Therefore, after the commutation timer starts in S570, even if a comparator edge occurs, that comparator edge is ignored. That is, no comparator interrupt occurs. This is done to invalidate the comparator edge that occurs during the switching operation when the delay time elapses.

[0245] However, because the comparator interrupt is temporarily prohibited in this way, if the delay time is not set appropriately, there is a possibility that no comparator interrupt will occur even if a comparator edge occurs. Specifically, if the delay time is set long, after the commutation timer starts, even if the next comparator edge occurs, the delay time still has not elapsed, and thereby that comparator edge may be inadvertently ignored. That is, there is a possibility of timer interrupt delay. Timer interrupt delay means that the commutation timer interrupt (i.e., the elapse of the delay time) is delayed from the timing of the occurrence of the next comparator edge.

[0246] [[ID=I19]] Timer interrupt delays can occur due to various factors. For example, even if the delay time is set appropriately, a timer interrupt delay may occur due to the subsequent behavior of the motor 20 or various characteristics of the motor 20.

[0247] A specific example of timer interrupt delay will be explained with reference to Figure 20. In Figure 20, for example, a comparator edge occurs at 240°. This temporarily disables the comparator interrupt, sets a delay time, and starts the commutation timer. In this case, as shown by the dashed line in Figure 20, the delay time should elapse around 330° (at least before 360°), a commutation timer interrupt should occur, and the switching operation should be performed.

[0248] However, in Figure 20, a timer interrupt delay occurs, and the commutation timer interrupt occurs when the delay time elapses near 370°. In this case, comparator interrupts are prohibited between 240° and near 370°. Therefore, even if a comparator edge occurs at 360°, that comparator edge is ignored. Also, in the example in Figure 20, the switching operation that should have occurred near 330° does not take place, so no comparator edge occurs even when 360° is reached. Therefore, the comparator interrupt that should have occurred does not occur at 360°. The next comparator interrupt occurs at 510°, and as a result, the switching operation is delayed, and the two-phase short-circuit operation is not performed properly.

[0249] Therefore, in this fourth embodiment, when a timer interrupt delay occurs, control is performed to generate the next comparator edge interrupt as quickly as possible. A specific example of operation will be explained with reference to Figure 21. In Figure 20, the operation up to the occurrence of a commutation timer interrupt near 370° is the same as in Figure 20. In other words, in Figure 21 as well, a timer interrupt delay occurs, and the commutation timer interrupt that should occur at 330° occurs at 370°.

[0250] In this fourth embodiment, each time a commutation timer interrupt occurs, it is determined whether a timer interrupt delay has occurred. Specifically, each time a commutation timer interrupt occurs, a determination time corresponding to the determination angle is set and time measurement is started (specifically, the commutation timer is started as described later). In this case, a commutation timer interrupt occurs when the determination time has elapsed.

[0251] In this embodiment, the determination angle is greater than the electrical angle (e.g., 30°) from the timing when the commutation timer interrupt should occur normally until the next comparator edge occurs (e.g., 210° to 240°). The estimated time required to rotate by this determination angle is set as the determination time.

[0252] Because the judgment time is set in this way, under normal circumstances, after a normal commutation timer interrupt occurs at 210°, a comparator edge occurs at 240° before the judgment time has elapsed (i.e., before the judgment angle rotates).

[0253] On the other hand, if a timer interrupt delay occurs, the judgment time elapses before the next comparator edge occurs. In Figure 21, a timer interrupt delay occurs at 370°. Therefore, even if the judgment time elapses from 370°, the comparator edge does not occur. In other words, after 370°, the judgment time elapses before the comparator edge occurs. In Figure 21, the judgment time elapses at 420°.

[0254] Therefore, in such cases, the switching operation is performed at the timing when the judgment time has elapsed (420°). This is one of the most distinctive features of this fourth embodiment. As a result, a comparator interrupt is generated when the next comparator edge occurs at 480°. In contrast, in the example of Figure 20, no comparator interrupt is generated at 480°. Therefore, in this fourth embodiment, even if a timer interrupt delay occurs, the subsequent two-phase short-circuit braking can be performed properly.

[0255] The comparator interrupt processing and commutation timer interrupt processing of this fourth embodiment, which are performed to achieve this operation, will be explained with reference to Figures 22 and 23. In this fourth embodiment, as in the first embodiment, the main processing (Figure 8) and soft brake start processing (Figure 10) are performed.

[0256] (2-4-1) Comparator interrupt handling The comparator interrupt processing of this fourth embodiment will be described with reference to Figure 22. In the comparator interrupt processing of Figure 22, the same processes as in the comparator interrupt processing of Figure 11 of the first embodiment are denoted by the same reference numerals as in Figure 11. The following description will focus on the parts that differ from those in Figure 11.

[0257] In the comparator interrupt processing of this fourth embodiment, if the soft brake interrupt flag is not set to "first time" in S430, the process proceeds to S481. In S481, the control circuit 26 determines whether or not the timer interrupt delay flag is set to "occurred".

[0258] The timer interrupt delay flag is set to "occurred" in S880 of the commutation timer interrupt processing in Figure 23. This S880 process is performed at the 420° timing in the operation example in Figure 21. In other words, in the commutation timer interrupt processing executed at S360°, the timer interrupt delay flag is set to "determining" by the S870 process. Normally, after the execution of the commutation timer interrupt processing, a comparator edge occurs and the comparator interrupt processing is executed before the determination time has elapsed. For example, in Figure 21, a commutation timer interrupt occurs at 210° and a comparator interrupt occurs at 240°. However, if a timer interrupt delay occurs, after the commutation timer interrupt occurs, the determination time elapses and another commutation timer interrupt occurs before a comparator edge occurs. In such cases, the timer interrupt delay flag is set to "occurred" in S880.

[0259] If the timer interrupt delay flag is not set to "occurred" in S481, the process proceeds to S480. In this case, no timer interrupt delay has occurred. Therefore, the control circuit 26 sequentially executes the processes in S480, S520, and S484. These processes from S480 onward are the same as the processes from S480 onward in Figure 11. That is, the commutation preparation process in S484 is the same as the processes in S530 to S580 in Figure 11.

[0260] If the timer interrupt delay flag is set to "occurred" in S481, the process proceeds to S482. In this case, a timer interrupt delay has occurred. Therefore, in S482, the control circuit 26 sets an estimated value as the edge generation interval.

[0261] The estimated value can be calculated in any way. For example, the edge generation interval obtained in the previous comparator interrupt processing may be used as the estimated value. Alternatively, it may be estimated from the current measurement timer value. For example, half of the current measurement timer value may be used as the estimated value. This is because, when a timer interrupt delay occurs, the measurement timer value at the time of S482 is basically the time required for the motor 20 to rotate 240°.

[0262] For example, in the operation example in Figure 21, the timing of 480° is the timing at which S481 determines that the timer interrupt delay flag has been set to "occurred". The value of the measurement timer at 480° is the value of the measurement timer that started at 240°. In other words, in the example in Figure 21, the measurement timer that started at 240° continues without interruption until 480°. Therefore, half of the value of the measurement timer at the timing of 480° can be estimated to be the time required for the rotation from the previous 360° to 480°, or a time very close to it. Also, the edge generation interval obtained at 240°, when the previous comparator interrupt occurred, can be estimated to be the same as or very close to the time required for the rotation from the previous 360° to 480°. Therefore, the edge generation interval obtained in the previous comparator interrupt processing may be calculated as the estimated value.

[0263] After processing in S482, control circuit 26 sets the timer interrupt delay flag to "none" in S483. After executing S483, this process moves on to S484. In other words, control circuit 26 executes S530 to S580 (see Figure 11).

[0264] (2-4-2) Commutation Timer Interrupt Processing The commutation timer interrupt processing of this fourth embodiment will be described with reference to Figure 23. In the commutation timer interrupt processing of Figure 23, the same processes as in the commutation timer interrupt processing of Figure 12 of the first embodiment are denoted by the same reference numerals as in Figure 12. The following description will focus on the parts that differ from those in Figure 12.

[0265] In the commutation timer interrupt processing of this fourth embodiment, the process transitions from S620 to S810. In S810, the control circuit 26 determines whether the timer interrupt delay flag is set to "none". If the timer interrupt delay flag is set to "none", the process transitions to S820.

[0266] In S820, the control circuit 26 obtains the switch pair to be turned on next and the switch to be turned off. For example, this may be obtained by referring to the switch pair table in Figure 5 based on the current rotation position.

[0267] In S830, the control circuit 26 sets the next switch pair and the switch to be turned off (or more specifically, the information indicating these) acquired in S820 into a buffer. In S840, the control circuit 26 calculates the determination time according to the determination angle. Specifically, it calculates the time required for the determination angle to rotate (i.e., the determination time) from the time from the previous comparator interrupt to the current commutation timer interrupt and the determination angle (30° in this embodiment).

[0268] In S850, the control circuit 26 sets the delay time calculated in S840 into a register. In the S860, the control circuit 26 starts a commutation timer based on the determination time. In other words, it starts the commutation timer so that a commutation timer interrupt occurs after the determination time has elapsed.

[0269] In S870, control circuit 26 sets the timer interrupt delay flag to "determining". If the timer interrupt delay flag is not set to "none" in S810, the process proceeds to S880. In S880, the control circuit 26 sets the timer interrupt delay flag to "occurred".

[0270] [2-5. Fifth Embodiment] As mentioned above, when the control circuit 26 performs two-phase short-circuit braking, it may perform only high-side two-phase short-circuit braking. In this fifth embodiment, an example of operation when high-side two-phase short-circuit braking is performed in two-phase short-circuit braking will be described. In high-side two-phase short-circuit braking, the third reference voltage Vr3 is used as the reference voltage.

[0271] In high-side two-phase short-circuit braking, a switch pair table like the one illustrated in Figure 24 is provided. As shown in Figure 24, the switch pairs in high-side two-phase short-circuit braking differ depending on whether the electrical angle is 30° or more but less than 150°, 150° or more but less than 270°, or 270° or more but less than 390°.

[0272] Each time a comparator edge occurs, the control circuit 26 refers to the switch pair table in Figure 24 to obtain the switch pair and the switch to be turned off at the next switching angle, and sets them in the buffer. Then, when a commutation timer interrupt occurs, it performs the switching operation according to the information set in the buffer.

[0273] A specific example of operation is shown in Figure 25. Figure 25 shows an example of high-side two-phase short-circuit braking operation during forward rotation. As shown in Figure 25, for example, a comparator edge occurs at 180°. The switch pair that is turned on at this time are the second and third switches Q2 and Q3. Also, the next switching angle at the 180° timing is 270°.

[0274] Therefore, the control circuit 26 refers to the switch pair table in Figure 25 to obtain the switch pair to be switched at 270° and the switch to be turned off. At 270° during forward rotation, the switch pair is the first switch Q1 (i.e., the U-phase high-side switch) and the second switch Q2 (i.e., the V-phase high-side switch), and the switch to be turned off is the third switch Q3 (i.e., the W-phase high-side switch).

[0275] As a result, at 270° after the delay time has elapsed, a commutation timer interrupt causes the first switch Q1 to turn ON and the third switch Q3 to turn OFF. The second switch Q2 remains ON.

[0276] [2-6. Sixth Embodiment] As described above, when the control circuit 26 performs two-phase short-circuit braking, it may selectively (for example, alternately) perform high-side two-phase short-circuit braking and low-side two-phase short-circuit braking. In this sixth embodiment, an example of operation when high-side two-phase short-circuit braking and low-side two-phase short-circuit braking are performed alternately in two-phase short-circuit braking will be described.

[0277] In this sixth embodiment, a switch pair table as illustrated in Figure 26 is provided. As shown in Figure 26, the switch pairs when high-side two-phase short-circuit braking and low-side two-phase short-circuit braking are performed alternately differ depending on whether the electrical angle is -30° or more and less than 30°, 30° or more and less than 90°, 90° or more and less than 150°, 150° or more and less than 210°, 210° or more and less than 270°, and 270° or more and less than 330°.

[0278] Each time a comparator edge occurs, the control circuit 26 refers to the switch pair table in Figure 26 to obtain the switch pair and the switch to be turned off at the next switching angle, and sets them in the buffer. Then, when a commutation timer interrupt occurs, it performs the switching operation according to the information set in the buffer.

[0279] If high-side two-phase short-circuit braking was in place at this time, it will be switched to low-side two-phase short-circuit braking. Also, the reference voltage will be switched to the second reference voltage Vr2. Conversely, if low-side two-phase short-circuit braking was in place when the comparator edge occurred, it will be switched to high-side two-phase short-circuit braking. Also, the reference voltage will be switched to the third reference voltage Vr3.

[0280] A specific example of operation is shown in Figure 27. Figure 25 shows an example of operation during forward rotation. As shown in Figure 27, for example, a comparator edge occurs at 120°. The switch pair that is turned on at this time is the 4th and 5th switches Q4 and Q5. In other words, low-side two-phase short-circuit braking is being performed. Therefore, in the next switching operation, it will switch to high-side two-phase short-circuit braking.

[0281] Furthermore, in this sixth embodiment, the delay angle is set to, for example, 30°. Therefore, the next switching angle at the 120° timing is 150°. Therefore, the control circuit 26 refers to the switch pair table in Figure 26 to obtain the switch pair and the switch to be turned off in the high-side two-phase short-circuit braking at 150°. According to the switch pair table in Figure 26, at 150° during forward rotation, the V phase and W phase are set as a switch pair. Therefore, the second switch Q2 (i.e., the V phase high-side switch) and the third switch Q3 (i.e., the W phase high-side switch) are obtained as a switch pair. In addition, the currently ON fourth switch Q4 and fifth switch Q5 are set as the switches to be turned off.

[0282] As a result, at 150° after the delay time has elapsed, a commutation timer interrupt causes the second and third switches Q2 and Q3 to turn ON, and the fourth and fifth switches Q4 and Q5 to turn OFF. Note that, as in the embodiments described above, the comparator edge resulting from this 150° commutation timer interrupt processing is ignored.

[0283] Subsequently, a comparator edge occurs at 180°. The switch pair that is turned on at this time is the second and third switches Q2 and Q3. In other words, high-side two-phase short-circuit braking is being performed. Therefore, in the next switching operation, it will switch to low-side two-phase short-circuit braking. Also, since the delay angle is, for example, 30°, the next switching angle at the 180° timing is 210°.

[0284] Therefore, the control circuit 26 refers to the switch pair table in Figure 26 to obtain the switch pair and the switch to be turned off in the low-side two-phase short-circuit braking at 210°. According to the switch pair table in Figure 26, at 210° during forward rotation, the U phase and W phase are set as a switch pair. Therefore, the fourth switch Q4 (i.e., the low-side switch for the U phase) and the sixth switch Q6 (i.e., the low-side switch for the W phase) are obtained as a switch pair. In addition, the second and third switches Q2 and Q3, which are currently on, are set as the switches to be turned off.

[0285] As a result, at 210° after the delay time has elapsed, the 4th and 6th switches Q4 and Q6 are switched on, and the 2nd and 3rd switches Q2 and Q3 are switched off. [2-5. Other Embodiments] Although embodiments of the present disclosure have been described above, the present disclosure is not limited to the embodiments described above and can be implemented in various modified forms.

[0286] (1) The first to third comparators 41 to 43 may be provided in the control circuit 26. In other words, some or all of the first to third comparators 41 to 43 may be built into the microcomputer in the control circuit 26.

[0287] In this case, some or all of the functions of the first to third comparators 41 to 43 may be implemented by software processing in the control circuit 26. For example, the control circuit 26 may include A / D conversion circuits that perform A / D conversion on the first to third voltages Vu, Vv, Vw and the reference voltage, respectively. Based on the output signals from these A / D conversion circuits, the CPU 31 may implement functions equivalent to those of the first to third comparators 41 to 43 by software processing.

[0288] (2) In the first embodiment described above, the first to fourth reference voltages Vr1 to Vr4 were input to the selection circuit 36. However, any number of reference voltages may be input to the selection circuit 36. For example, if the system is configured not to use the second and third reference voltages Vr2 and Vr3 as reference voltages, then input of these second and third reference voltages Vr2 and Vr3 is unnecessary. In other words, only the reference voltages used to control the motor 20 may be input to the selection circuit 36.

[0289] Furthermore, providing the selection circuit 36 ​​is not mandatory. For example, consider a configuration where the fourth reference voltage Vr4 is used as the reference voltage during driving operations, and the first reference voltage Vr1 is used as the reference voltage during braking and switching operations. In this case, three comparators may be provided for driving operations, and separately, three comparators may also be provided for braking operations. In this example, the selection circuit 36 ​​is unnecessary.

[0290] (3) In the braking operation, only a two-phase short-circuit braking operation may be performed. Alternatively, two or more types of braking operations, including a two-phase short-circuit braking operation, may be performed sequentially. For example, in the first embodiment described above, the braking operation was performed in the order of free run, two-phase short-circuit braking operation, and three-phase short-circuit braking operation. However, in the first embodiment, for example, free run may be omitted. Also, for example, instead of the two-phase short-circuit braking operation and the three-phase short-circuit braking operation, two or more of the one-phase short-circuit braking operation, the two-phase short-circuit braking operation, and the three-phase short-circuit braking operation (however, including the two-phase short-circuit braking operation) may be performed. For example, the one-phase short-circuit braking operation, the two-phase short-circuit braking operation, and the three-phase short-circuit braking operation may be performed in this order. Also, for example, the one-phase short-circuit braking operation and the two-phase short-circuit braking operation may be performed in this order. Furthermore, when two or more types of braking operations are performed in order, any braking operation may be performed in any order. For example, contrary to the first embodiment, the three-phase short-circuit braking operation may be performed first, followed by the two-phase short-circuit braking operation.

[0291] (4) In the third embodiment described above, an example of operation when a retrigger occurs during the execution of a two-phase short-circuit braking operation is shown (Figure 15). However, when a retrigger occurs during a braking operation, the system may transition to a driving operation through any process. For example, when a retrigger occurs, the braking operation may be stopped immediately and the driving operation may be started. Alternatively, when a retrigger occurs, one or more of the following may be performed sequentially: free run, three-phase short-circuit braking operation, two-phase short-circuit braking operation, and one-phase short-circuit braking operation, followed by the driving operation. In this case, any number of braking operations may be performed, and the braking operations may be performed in any order. For example, when a retrigger occurs during the execution of a three-phase short-circuit braking operation, the system may sequentially switch from the three-phase short-circuit braking operation to the two-phase short-circuit braking operation, then to the one-phase short-circuit braking operation, and finally to the free run operation. Alternatively, in the third embodiment described above, the system may transition from the two-phase short-circuit braking operation to the driving operation without going through the one-phase short-circuit braking operation and / or free run operation.

[0292] (5) Multiple functions of one component in the above embodiment may be realized by multiple components, or one function of one component may be realized by multiple components. Also, multiple functions of multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Furthermore, some of the configurations of the above embodiment may be omitted. Furthermore, at least some of the configurations of the above embodiment may be added to or replaced with the configurations of other above embodiments. [Explanation of Symbols]

[0293] 1...Electric work machine, 18...Battery pack, 19...Battery, 20...Motor, 20u...First terminal, 20v...Second terminal, 20w...Third terminal, 24...Drive circuit, 24a...First power supply path, 24b...Second power supply path, 24c...Third power supply path, 24d...Fourth power supply path, 24e...Fifth power supply path, 24f...Sixth power supply path, 26...Control circuit, 36...Selection circuit, 40...Current information acquisition circuit, 41...First comparator, 42...Second comparator, 43...Third comparator, 45...Reference voltage generating circuit, D1...First body diode, D2...Second body diode, D3...Third body diode, D4...Fourth body diode, D5...Fifth body diode, D6...Sixth body diode, Q1...Fourth switch, Q2...Second switch, Q3...Third switch, Q4...Fourth switch, Q5...Fifth switch, Q6...Sixth switch, R1...First resistor, R2...Second resistor, R3...Third resistor, R4...Fourth resistor, R5...Fifth resistor.

Claims

1. A brushless motor having three terminals configured to receive power, A drive circuit configured to supply the power to the brush motor, Three positive-side paths electrically connect the three aforementioned terminals to the positive terminal of the power supply, Three negative-side paths electrically connect the three terminals to the negative terminal of the power supply, Six switches, each comprising (i) three positive-side switches provided in each of the three positive-side paths and configured to individually conduct or interrupt the three positive-side paths, and (ii) three negative-side switches provided in each of the three negative-side paths and configured to individually conduct or interrupt the three negative-side paths, A drive circuit having, A control circuit, A drive operation is performed by controlling the drive circuit based on the induced voltage of the brushless motor generated at each of the three terminals, thereby rotating the brushless motor. A braking operation for decelerating and / or stopping the rotating brushless motor, comprising turning on a pair of switches from the six switches and turning off the others, wherein the switch pair is any two of the three positive switches or any two of the three negative switches, A switching operation that switches the switch pair during the execution of the braking operation, which includes turning off the switch to be turned off based on the fact that the current flowing through the switch to be turned off, which is one of the switch pairs currently, satisfies the off requirement. A control circuit configured to perform, An electric work machine equipped with the following features.

2. An electric work machine according to claim 1, The off requirement is satisfied on the condition that the value of the current flowing through the switch to be turned off is not an extreme value in the opposite direction to a specific direction, and the specific direction is the direction from the brushless motor to the positive terminal in the three positive terminal switches, and the direction from the negative terminal to the brushless motor in the three negative terminal switches. Electric work equipment.

3. An electric work machine according to claim 1 or claim 2, The off requirement is satisfied based on the fact that the direction of the current flowing through the switch to be turned off is in the specific direction. Electric work equipment.

4. An electric work machine according to any one of claims 1 to 3, Furthermore, the system includes a current information acquisition circuit configured to acquire current information relating to the current flowing through at least two or more switches that can be made into a switch pair during the braking operation, among the six switches. The control circuit is configured to perform the switching operation based on the current information acquired by the current information acquisition circuit. Electric work equipment.

5. An electric work machine according to claim 4, The current information acquisition circuit is, A first comparator is configured to receive a first voltage, which is the voltage of the first terminal among the three terminals, and a reference voltage, and to output first comparison information indicating whether the value of the first voltage is greater than or equal to the value of the reference voltage. A second comparator is configured to receive a second voltage, which is the voltage of the second terminal among the three terminals, and the reference voltage, and to output second comparison information indicating whether the value of the second voltage is greater than or equal to the value of the reference voltage. A third comparator is configured to receive a third voltage, which is the voltage of the third terminal among the three terminals, and the reference voltage, and to output third comparison information indicating whether the value of the third voltage is greater than or equal to the value of the reference voltage. An electric work machine equipped with the following features.

6. An electric work machine according to claim 5, The control circuit is configured to perform the drive operation based on the first comparison information, the second comparison information, and the third comparison information output from the current information acquisition circuit. Electric work equipment.

7. An electric work machine according to claim 5 or claim 6, The aforementioned off requirement is satisfied based on the first comparison information, the second comparison information and / or the third comparison information having changed. Electric work equipment.

8. An electric work machine according to any one of claims 5 to 7, When any two of the three negative-side switches are in the switch pair, the off requirement is met based on the voltage value of one of the three terminals connected to the switch to be turned off becoming less than the value of the reference voltage. Electric work equipment.

9. An electric work machine according to claim 8, The off requirement in the state where any two of the three negative-side switches are in the switch pair is met based on the arrival of the off-possible timing, which is the timing when (i) the voltage value of one of the three terminals connected to the switch to be turned off becomes less than the value of the reference voltage, and (ii) the voltage value of one of the three terminals connected to one of the three negative-side switches other than the switch pair becomes equal to or greater than the value of the reference voltage. Electric work equipment.

10. An electric work machine according to claim 9, The off requirement in the state where any two of the three negative-side switches are in the switch pair is satisfied based on the arrival of a predetermined delay time after the off-possible timing. Electric work equipment.

11. An electric work machine according to claim 10, The control circuit is configured such that the delay time is set so that the off requirement is met when the magnitude of the current flowing through the switch to be turned off is decreasing or is zero. Electric work equipment.

12. An electric work machine according to claim 10 or claim 11, The control circuit is configured to set the delay time based on the rotational speed of the brushless motor at the time the off-capable timing occurs. Electric work equipment.

13. An electric work machine according to claim 12, The control circuit is configured to set the delay time to be longer the lower the rotational speed of the brushless motor when the off-timing occurs. Electric work equipment.

14. An electric work machine according to any one of claims 5 to 13, moreover, A reference voltage generation circuit, A first resistor having a first end connected to the first terminal of the three terminals, and a second end, A second resistor having a first end connected to the second terminal of the three terminals and a second end connected to the second terminal of the first resistor, A third resistor having a first end connected to the third terminal of the three terminals, and a second end connected to the second end of the first resistor and the second end of the second resistor, A reference voltage generating circuit is provided, which has a first reference voltage that is the voltage at the second terminal of the first resistor, the voltage at the second terminal of the second resistor, or the voltage at the second terminal of the third resistor, The current information acquisition circuit is configured to receive the first reference voltage from the reference voltage generation circuit as the reference voltage. Electric work equipment.

15. An electric work machine according to any one of claims 5 to 13, The current information acquisition circuit is configured to receive the voltage of the terminals electrically connected to the negative terminals of the three negative-side switches as the reference voltage when any two of the three negative-side switches are in the switch pair. Electric work equipment.

16. An electric work machine according to any one of claims 5 to 13, The current information acquisition circuit is configured to receive the voltage of the terminals electrically connected to the positive terminals of the three positive-side switches as the reference voltage when any two of the three positive-side switches are in the switch pair. Electric work equipment.

17. An electric work machine according to claim 14, The system includes a selection circuit configured to receive at least two reference voltages from among the first reference voltage, a second reference voltage which is the voltage at the terminal electrically connected to the negative terminal of the three negative-side switches, and a third reference voltage which is the voltage at the terminal electrically connected to the positive terminal of the three positive-side switches, and to selectively output one of the received at least two reference voltages as the reference voltage, The current information acquisition circuit is configured to receive the reference voltage output from the selection circuit. Electric work equipment.

18. An electric work machine according to claim 14, moreover, A fourth resistor having a first end and a second end connected to the positive electrode, A fifth resistor having a first end connected to the negative electrode and a second end connected to the second end of the fourth resistor, A selection circuit configured to receive at least two reference voltages from among the first reference voltage, a second reference voltage which is the voltage at the terminal electrically connected to the negative terminal of the three negative-side switches, a third reference voltage which is the voltage at the terminal electrically connected to the positive terminal of the three positive-side switches, and a fourth reference voltage which is the voltage at the second terminal of the fourth resistor, and to output one of the received at least two reference voltages as the reference voltage, Equipped with, The current information acquisition circuit is configured to receive the reference voltage output from the selection circuit. Electric work equipment.

19. An electric work machine according to claim 18, The selection circuit is configured to output the fourth reference voltage as the reference voltage when the drive operation is performed by the control circuit, and to output the first reference voltage, the second reference voltage, or the third reference voltage as the reference voltage when the switching operation is performed by the control circuit. Electric work equipment.

20. An electric work machine according to any one of claims 1 to 19, Each of the three positive-side switches includes a first rectifier configured to (i) be connected in parallel to the positive-side switch and (ii) allow current to flow from the brushless motor through the positive-side switch to the positive electrode, and suppress or block current flowing from the positive electrode through the positive-side switch to the brushless motor. Electric work equipment.

21. An electric work machine according to any one of claims 1 to 20, Each of the three negative-side switches includes a second rectifier configured to (i) be connected in parallel to the negative-side switch and (ii) allow current to flow from the negative electrode through the negative-side switch to the brushless motor, and suppress or block current flowing from the brushless motor through the negative-side switch to the negative electrode. Electric work equipment.

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