Working machine

Abstract

To provide a working machine capable of reducing a load of a control part.SOLUTION: For each of the switching elements Q1 to Q6, the calculation unit can have a first energization section that is an energization section corresponding to 120-degree energization and a second energization section that is an energization section set in at least one of the front and rear of the first energization section, and can set the duty ratio of the PWM control in the second energization section to a value different from the duty ratio of the PWM control in the first energization section. The calculation unit 70 changes the duty ratio of the PWM control in the second energization section according to the rotational speed of the motor 20 or the load applied to the motor 20. The calculation unit 70 fixes the electrical angle of the second energization section regardless of the rotational speed of the motor 20 or the load on the motor 20.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a work machine. [Background technology]

[0002] Patent Document 1 discloses a power tool in which the conduction angle is changed according to the load applied to the motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-027710 Summary of the Invention [Problem to be solved by the invention]

[0004] When the conduction angle is set with a resolution of 1 degree (when set in increments of 1 degree), for example, the processing load for calculating the time corresponding to the conduction angle is large, and it has been difficult for inexpensive control units to handle the maximum rotation speed range (for example, 20,000 rpm to 40,000 rpm) of motors used in power tools and other work machines.

[0005] An object of the present invention is to provide a work machine that can reduce the load on the control unit. [Means for solving the problem]

[0006] One aspect of the present invention is a brushless motor having a rotor and a stator having windings of multiple phases; an inverter circuit having a plurality of switching elements connected to the windings of the plurality of phases; a control unit configured to perform commutation control for controlling the inverter circuit to switch energization to the plurality of phases in accordance with a position of the rotor; Equipped with the commutation control may have, for at least one switching element, a first current conduction interval corresponding to a current conduction interval when a current conduction angle is a first current conduction angle, and a second current conduction interval set at least either before or after the first current conduction interval, The duty ratio of the PWM control in the second current conduction interval can be set to a value different from the duty ratio of the PWM control in the first current conduction interval. This is a work machine characterized by the above.

[0007] The present invention may be expressed as an "electric working machine," "electric tool," "electrical equipment," etc., and such expressions are also valid as aspects of the present invention. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a work machine that can reduce the load on the control unit. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a side view of a work machine 1 according to an embodiment. [Figure 2] FIG. 2 is a circuit block diagram of the work machine 1. [Figure 3] 10 is a time chart showing the on / off states of switching elements Q1 to Q6 of a work machine 1 when the switching elements Q1 to Q6 are controlled at a conduction angle of 120 degrees. [Figure 4] 10 is a time chart showing the on / off states of switching elements Q1 to Q6 when switching elements Q1 to Q6 are controlled at a conduction angle of 150 degrees. [Figure 5] 10 is a time chart showing the on / off states of switching elements Q1 to Q6 when switching elements Q1 to Q6 are controlled at a pseudo conduction angle of 120 degrees. [Figure 6] 10 is a time chart showing the on / off states of switching elements Q1 to Q6 when switching elements Q1 to Q6 are controlled at a pseudo conduction angle of 135 degrees. [Figure 7] 4 is a graph showing an example of the change over time in the rotation speed and conduction angle of the tool bit 19 in the work machine 1. [Figure 8]10 is a state transition diagram of the work machine 1 when two types of conduction angles can be set. [Figure 9] 10 is a control flowchart of the work implement 1 when two types of conduction angles can be set. [Figure 10] 10 is a state transition diagram of the work machine 1 when three types of conduction angles can be set. [Figure 11] 10 is a control flowchart of the work implement 1 when three types of conduction angles can be set. [Figure 12] 12 is a flowchart of the light load process (S57) in FIG. 11. [Figure 13] 12 is a flowchart of the no-load process (S65) in FIG. 11. [Figure 14] 4 is a state transition diagram of the work machine 1 when the pseudo conduction angle is continuously changed. [Figure 15] 6 is a control flowchart of the work machine 1 when the pseudo conduction angle is continuously changed. [Figure 16] 3 is a diagram showing an example of a method for calculating a current-carrying section in the work machine 1. FIG. [Figure 17] 10A and 10B are diagrams showing examples of timings for updating energized sections when the calculation intervals of the energized sections are lengthened. [Figure 18] 10 is a graph showing an example of a sudden change in the rotation speed of the tool bit 19. [Figure 19] 19 is a time chart showing the on / off of switching elements Q1 to Q6 when the time of the second current flow interval is calculated only once per period in electrical angle and applied to all of switching elements Q1 to Q6 in a comparative example in which the electrical angle of the second current flow interval is directly controlled, and shows that a sudden change in rotation speed as shown in FIG. 18 causes a short circuit between the upper and lower switching elements. [Figure 20] 19 is a time chart showing the on / off states of switching elements Q1 to Q6 when a second duty ratio is calculated only once per period of the electrical angle and applied to all of switching elements Q1 to Q6 in an embodiment that controls a pseudo conduction angle, and shows that when a sudden fluctuation in rotation speed occurs as in FIG. 18, a short circuit between the upper and lower switching elements is suppressed. DETAILED DESCRIPTION OF THE INVENTION

[0010] 1 is a side view of a work machine 1 according to an embodiment. The work machine 1 is a cordless circular saw powered by a detachably attached battery pack 17, and can perform work such as cutting wood with a saw blade 19 (tool tip) that rotates in response to operation of a trigger switch 15. The mechanical configuration of the work machine 1 is well known, so a description thereof will be omitted here.

[0011] FIG. 2 is a circuit block diagram of the work machine 1. As shown in FIG.

[0012] Motor 20 is, for example, an inner rotor type brushless motor, and includes rotor 23 and windings 25 that form a stator. Windings 25 are provided for each of the three phases U, V, and W. In the illustrated example, three-phase windings 25 are delta-connected, but three-phase windings 25 may also be Y-connected (star-connected). The combination of the number of poles and the number of slots of motor 20 is arbitrary, and one example is 4 poles and 6 slots.

[0013] A capacitor 68 and an inverter circuit 64 are connected in parallel between the output terminals of the battery pack 17. The inverter circuit 64 is made up of six switching elements Q1 to Q6 that are connected in a three-phase bridge configuration to windings 25 of three phases U, V, and W. A resistor 65 is provided in the path of the current that flows through the windings 25 of the motor 20 (hereinafter referred to as "motor current").

[0014] The control power supply circuit 51 converts the output voltage of the battery pack 17 into a power supply voltage for the calculation unit 70 etc. and supplies it to the calculation unit 70 etc. The current detection circuit 52 detects the motor current from the voltage of a resistor 65 and sends it to the calculation unit 70. The switch operation detection circuit 53 detects the operation of the trigger switch 15 and sends it to the calculation unit 70. The voltage detection circuit 55 detects the output voltage of the battery pack 17 and sends it to the calculation unit 70. The temperature detection circuit 67 detects the temperature of the inverter circuit 64 from the output signal of a temperature sensor 66 such as a thermistor provided near the inverter circuit 64 and sends it to the calculation unit 70.

[0015] The control signal circuit 56 outputs control signals that control the on / off of each switching element of the inverter circuit 64 under the control of the calculation unit 70. The rotational position detection circuit 57 detects the position of the rotor 23 (hereinafter referred to as "rotor position") using output signals from three Hall ICs 63 (magnetic sensors) and transmits the detected position to the calculation unit 70. The Hall ICs 63 are an example of a position detection element that outputs a signal according to the rotor position. In this embodiment, as an example, three Hall ICs 63 are arranged circumferentially around the motor 20 at intervals of 60 electrical degrees.

[0016] The rotation speed detection circuit 58 detects the rotation speed of the motor 20 from the output signal of the rotation position detection circuit 57 and sends it to the calculation unit 70. The operation mode detection circuit 59 detects the operation of the operation mode switch 60 by the user and sends it to the calculation unit 70. The illumination LED drive circuit 61 drives the illumination LED 62 under the control of the calculation unit 70.

[0017] The calculation unit 70 is a control unit that includes a microcontroller and the like and controls the overall operation of the work machine 1. When the trigger switch 15 is turned on, the calculation unit 70 drives the motor 20 through control of the inverter circuit 64 (switching control of the switching elements Q1 to Q6). The calculation unit 70 executes commutation control that controls the inverter circuit 64 to switch the supply of current to the three phases U, V, and W according to the rotor position. The calculation unit 70 drives the motor 20 in an operation mode (operation mode) according to the operation of the operation mode switch 60.

[0018] FIG. 3 is a time chart showing the on / off states of the switching elements Q1 to Q6 of the work machine 1 when the switching elements Q1 to Q6 are controlled at a conduction angle of 120 degrees.

[0019] The conduction angle is expressed as the period (angle) during which each of the switching elements Q1 to Q6 is on within one electrical cycle (360 degrees). 120 degrees is the basic conduction angle in square wave control. As shown in FIG. 3, in the case of 120-degree conduction, the switching elements Q1 to Q3, which are the high-side switching elements, are alternately turned on every 120 degrees, with no overlapping on-periods. Similarly, the switching elements Q4 to Q6, which are the low-side switching elements, are alternately turned on every 120 degrees, with no overlapping on-periods. In the case of 120-degree conduction, at any one time within one cycle, no more than two of the switching elements Q1 to Q6 are turned on.

[0020] Switching elements Q1 and Q5 are ON in the range from 0 degrees to 60 degrees, switching elements Q1 and Q6 are ON in the range from 60 degrees to 120 degrees, switching elements Q2 and Q6 are ON in the range from 120 degrees to 180 degrees, Q2 and Q4 are ON in the range from 180 degrees to 240 degrees, switching elements Q3 and Q4 are ON in the range from 240 degrees to 300 degrees, and switching elements Q3 and Q5 are ON in the range from 300 degrees to 360 degrees. The calculation unit 70 controls the rotation speed of the motor 20 by PWM-controlling at least one of the two switching elements that are ON in each range. Hereinafter, the duty ratio of PWM control will be referred to as "duty ratio."

[0021] FIG. 4 is a time chart showing the on / off states of the switching elements Q1 to Q6 when the switching elements Q1 to Q6 are controlled at a conduction angle of 150 degrees.

[0022] In FIG. 4, the conduction section corresponding to the 120-degree conduction shown in FIG. 3 (the conduction section when the conduction angle is set to 120 degrees as the first conduction angle) is referred to as the first conduction section, and the conduction section additionally set to the first conduction section is referred to as the second conduction section, and the second conduction section has an electrical angle of 30 degrees.

[0023] 4, the second current conduction interval is set to follow the first current conduction interval for each of the switching elements Q1 to Q6. As another example, the second current conduction interval may be set to follow the first current conduction interval for each of the switching elements Q1 to Q6. Alternatively, the second current conduction interval may be set 15 degrees before and after the first current conduction interval.

[0024] As shown in FIG. 4, when the duty ratio in the second current conduction interval (hereinafter referred to as the "second duty ratio") is set to the same as the duty ratio in the first current conduction interval (hereinafter referred to as the "first duty ratio"), the conduction angle is the sum of the lengths of the first and second current conduction intervals, i.e., 150 degrees. In the example shown, the first duty ratio is 100%. In this case, the on-intervals of the switching elements Q1 to Q3 and Q4 to Q6 overlap. Note that the first duty ratio does not need to be always 100%; for example, it may be set to less than 100% under no load or low load, and the duty ratio may be increased when the load increases to maintain the previous rotation speed.

[0025] By controlling the second duty ratio to be different from the first duty ratio, the calculation unit 70 can obtain motor characteristics (such as the relationship between torque and rotation speed) similar to those obtained when the conduction angle is set to an intermediate value between 120 degrees and 150 degrees without changing the electrical angle of the second conduction interval. Hereinafter, the conduction angle that is pseudo-realized by setting the second duty ratio to be different from the first duty ratio will be referred to as the "pseudo conduction angle."

[0026] 5 and 6 are time charts of the on / off states of switching elements Q1 to Q6 when the actual conduction angle is fixed at 150 degrees and the duty ratio is controlled to set the pseudo conduction angles to 120 degrees and 135 degrees, respectively. As shown in FIG. 5, calculation unit 70 sets the second duty ratio to, for example, 5% or less (a small value equal to or less than 1 / 20 of the first duty ratio) to set the pseudo conduction angle to 120 degrees, thereby achieving motor characteristics similar to those achieved when the conduction angle is 120 degrees. As shown in FIG. 6, calculation unit 70 sets the second duty ratio to, for example, 50% (approximately 1 / 2 of the first duty ratio) to set the pseudo conduction angle to 135 degrees, thereby achieving motor characteristics similar to those achieved when the conduction angle is 135 degrees.

[0027] FIG. 7 is a graph showing an example of the time variation of the rotation speed of the tool bit 19, which is the rotation speed after the rotation speed of the motor 20 is reduced at a predetermined reduction ratio via a reduction mechanism, and the conduction angle. Hereinafter, the rotation speed of the motor 20 and the rotation speed of the tool bit 19 will be collectively referred to as the "rotation speed." In FIG. 7, the conduction angle between 120 degrees and 150 degrees is a pseudo conduction angle. The actual conduction angle (the sum of the electrical angles of the first and second conduction intervals) is fixed at 150 degrees regardless of the rotation speed or the load applied to the motor 20 (tool bit 19). Hereinafter, the load applied to the motor 20 and the load applied to the tool bit 19 will be collectively referred to as the "load."

[0028] At time t0 (left end of the figure), the calculation unit 70 controls the switching elements Q1 to Q6 at a conduction angle of 150 degrees, i.e., controls the switching elements Q1 to Q6 with the first duty ratio and the second duty ratio set to the same value, and the rotation speed (rotation speed of the tool tip 19) is equal to or greater than 3,500 rpm, which is the high load detection threshold (first threshold).

[0029] As the motor load increases, the rotation speed begins to decrease from time t0, and at time t1, the rotation speed falls below 3,500 rpm. The calculation unit 70 then fixes the conduction angle at 150 degrees and executes a process to artificially reduce the conduction angle. Specifically, the calculation unit 70 gradually or gradually reduces the second duty ratio relative to the first duty ratio, until the second duty ratio is reduced to 5%. This gradually or gradually reduces the artificial conduction angle to 120 degrees over a certain period of time.

[0030] Thereafter, as the motor load decreases, the rotational speed increases, and at time t2, the rotational speed (the rotational speed of the tool bit 19) exceeds 3,900 rpm, which is the low-load detection threshold (second threshold). The calculation unit 70 then executes a process to artificially increase the pseudo conduction angle from 120 degrees while keeping the conduction angle fixed at 150 degrees. Specifically, the calculation unit 70 gradually or gradually increases the second duty ratio relative to the first duty ratio until the second duty ratio reaches the same value as the first duty ratio. As a result, the pseudo conduction angle gradually or gradually increases to 150 degrees over a certain period of time.

[0031] An example of a high load determination condition is when the rotation speed is less than 3,500 rpm. An example of a low load determination condition is when the rotation speed is 3,900 rpm or more. Note that the calculation unit 70 may detect the load using the motor current instead of the rotation speed. In other words, the high load determination condition and the low load determination condition may be conditions related to the motor current.

[0032] FIG. 8 is a state transition diagram of the work machine 1 when two pseudo conduction angles (120 degrees and 150 degrees) can be set.

[0033] When the calculation unit 70 is activated by operating the trigger switch 15 or the like, it enters a 120-degree conduction mode (S1) in which the conduction angle is fixed at 120 degrees. When a certain time (e.g., two seconds) has elapsed since the start of the motor 20 in the 120-degree conduction mode, the calculation unit 70 transitions to a 150-degree conduction mode (S3) in which the conduction angle is fixed at 150 degrees. Note that the calculation unit 70 executes timer processing required to set the conduction angle to 150 degrees within the certain time (e.g., two seconds) since the start of the motor 20. When the rotation speed in the 150-degree conduction mode falls below a high load detection threshold (e.g., 3,500 rpm), the calculation unit 70 transitions to a pseudo 120-degree conduction mode (S5). The pseudo 120-degree conduction mode is a mode in which the conduction angle is fixed at 150 degrees while the second duty ratio is set sufficiently lower (for example, to 5%) than the first duty ratio, thereby creating a pseudo conduction angle of 120 degrees. When the rotation speed in the pseudo 120-degree conduction mode reaches or exceeds a low load detection threshold value (for example, 3,900 rpm), the calculation unit 70 transitions to the 150-degree conduction mode (S3). When the motor 20 stops due to, for example, the release of the trigger switch 15 in either the 150-degree conduction mode or the pseudo 120-degree conduction mode, the calculation unit 70 transitions to the 120-degree conduction mode (S1).

[0034] FIG. 9 is a control flowchart for the work machine 1 when two pseudo conduction angles (120 degrees and 150 degrees) can be set.

[0035] When calculation unit 70 is started, it sets the conduction angle to 120 degrees (S31). This is a step required to measure the time for a conduction angle of 60 degrees and calculate the time for a conduction angle of 30 degrees, and is not related to the load. If motor 20 is being driven (Yes in S33), and a certain amount of time (e.g., 2 seconds) has passed since motor 20 was started (Yes in S35), calculation unit 70 proceeds to S41 if the conduction angle is 150 degrees (Yes in S37), or if the conduction angle is not 150 degrees (No in S37), it switches the conduction angle to 150 degrees (S39) and proceeds to S41.

[0036] If the rotation speed is equal to or less than the high load detection threshold (e.g., 3,500 rpm) (Yes in S41), the calculation unit 70 reduces the second duty ratio to a specified value (e.g., 5%) or maintains the second duty ratio at the specified value (S43), and returns to S33. If the rotation speed is equal to or greater than the high load detection threshold (No in S41) and less than the low load detection threshold (e.g., 3,900 rpm) (No in S45), the calculation unit 70 returns to S33 without changing the second duty ratio. If the rotation speed is equal to or greater than the low load detection threshold (No in S41, Yes in S45), the calculation unit 70 increases the second duty ratio to a specified value (the same value as the first duty ratio) or maintains the second duty ratio at the specified value (S47), and returns to S33. The change in the second duty ratio in S43 and S47 is preferably performed stepwise or gradually (e.g., −0.1% / ms).

[0037] 10 is a state transition diagram of the work machine 1 when three pseudo conduction angles (120 degrees, 135 degrees, and 150 degrees) can be set. The following description will focus on the differences from FIG.

[0038] When the rotation speed in the 150-degree conduction mode (S3) becomes equal to or less than a first light load detection threshold (a threshold for detecting a switch from no load to a light load), the calculation unit 70 transitions to a pseudo 135-degree conduction mode (S4). The pseudo 135-degree conduction mode is a mode in which the conduction angle is fixed at 150 degrees and the second duty ratio is set to about half the first duty ratio, thereby creating a pseudo conduction angle of 135 degrees.

[0039] When the rotation speed in the pseudo 135-degree conduction mode becomes equal to or lower than the high load detection threshold (a threshold for detecting a switch from light load to high load, which is lower than the first light load detection threshold), the calculation unit 70 transitions to the pseudo 120-degree conduction mode (S5).

[0040] When the rotation speed in the pseudo 120-degree conduction mode becomes equal to or greater than the second light load detection threshold (a threshold for detecting a switch from high load to light load, which is higher than the high load detection threshold), the calculation unit 70 transitions to the pseudo 135-degree conduction mode (S4).

[0041] When the rotation speed in the pseudo 135-degree conduction mode becomes equal to or greater than the no-load detection threshold (a threshold for detecting a switch from light load to no load, which is higher than the first light load detection threshold), the calculation unit 70 transitions to the 150-degree conduction mode (S3).

[0042] In either mode, when the motor 20 stops due to, for example, the release of the trigger switch 15, the calculation unit 70 transitions to the 120-degree conduction mode (S1).

[0043] 11 is a control flowchart for the work machine 1 when three pseudo conduction angles (120 degrees, 135 degrees, and 150 degrees) can be set. The following description will focus on the differences from FIG.

[0044] After Yes in S37 or S39, if the rotation speed is equal to or greater than the second light-load detection threshold (Yes in S55) in the high-load state (Yes in S42), the calculation unit 70 detects the light-load state (S57), increases the second duty ratio to a specified value b (e.g., 50%) or maintains the second duty ratio at the specified value b (S59), and returns to S33. If the rotation speed is not equal to or greater than the second light-load detection threshold in S55 (No in S55), the calculation unit 70 returns to S33 without changing the second duty ratio.

[0045] If the load state is not high in S42 (No in S42) but low (Yes in S61), the calculation unit 70 performs low-load processing (S63). If the load state is not low in S61 (No in S61), the calculation unit 70 performs no-load processing (S65).

[0046] 12 is a flowchart of the light-load processing (S63) of FIG. 11. When the rotation speed is equal to or greater than the no-load detection threshold (Yes in S71), the calculation unit 70 detects a no-load state (S73), increases the second duty ratio to a specified value a (the same value as the first duty ratio) or maintains the second duty ratio at the specified value a (S75), and returns to S33. When the rotation speed is less than the no-load detection threshold (No in S71) and equal to or greater than the high-load detection threshold (No in S77), the calculation unit 70 returns to S33 without changing the second duty ratio. When the rotation speed is equal to or less than the high-load detection threshold (No in S71, Yes in S77), the calculation unit 70 detects a high-load state (S79), reduces the second duty ratio to a specified value c (e.g., 5%) or maintains the second duty ratio at the specified value c (S81), and returns to S33.

[0047] Fig. 13 is a flowchart of the no-load processing (S65) of Fig. 11. If the rotation speed is equal to or less than the first light-load detection threshold (Yes in S91), the calculation unit 70 detects a light-load state (S93), reduces the second duty ratio to a specified value b (e.g., 50%) or maintains the second duty ratio at the specified value b (S95), and returns to S33. If the rotation speed is not equal to or less than the first light-load detection threshold in S91 (No in S91), the calculation unit 70 returns to S33 without changing the second duty ratio.

[0048] The second duty ratio is preferably changed in steps S59, S75, S81, and S95 in a stepwise or gradual manner (for example, −0.1% / ms).

[0049] 14 is a state transition diagram of the work machine 1 when the pseudo conduction angle is continuously changed. The following description will focus on the differences from FIG.

[0050] The calculation unit 70 transitions to the 150-degree conduction mode (S9) when a certain time (e.g., 2 seconds) has elapsed since the start of the motor 20 in the 120-degree conduction mode. The 150-degree conduction mode S9 differs from the 150-degree conduction mode (S3) in Fig. 8 in that the second duty ratio is changed relative to the first duty ratio in accordance with the motor load to change the pseudo conduction angle. When the motor 20 stops in the 150-degree conduction mode due to, for example, the release of the trigger switch 15, the calculation unit 70 transitions to the 120-degree conduction mode (S1).

[0051] 15 is a control flowchart for the work machine 1 when the pseudo conduction angle is continuously changed. The following description will focus on the differences from FIG.

[0052] After determining Yes in S37 or S39, the calculation unit 70 calculates a pseudo conduction angle corresponding to the current rotation speed from the current rotation speed (S101), changes the second duty ratio to a value corresponding to the pseudo conduction angle (S103), and returns to S33. An example of calculating the pseudo conduction angle based on the rotation speed (the rotation speed of the motor 20) and an example of calculating the second duty ratio based on the pseudo conduction angle are shown below. [Example of calculating pseudo conduction angle] ·10,000rpm or less: 120 degrees Over 25,000 rpm: 150 degrees 10,000~25,000rpm: ((Motor RPM - 10,000) ÷ 15,000) × 30 + 120 [Calculation example of the second duty ratio] ((Pseudo conduction angle - 120) ÷ 30) × Duty ratio in the first conduction section

[0053] FIG. 16 is a diagram showing an example of a method for calculating a current-carrying section in the work machine 1. In FIG.

[0054] In the work machine 1, the rotor position is detected by the output signals of three Hall ICs 63 arranged at intervals of 60 electrical degrees around the circumference of the motor 20. Every 60 electrical degrees, an edge appears in the output signal of one of the Hall ICs 63, and the rotor position is detected. Each time the rotor position is detected, an interrupt request is input to the calculation unit 70, and the calculation unit 70 calculates the duration of the second current-carrying interval as interrupt processing.

[0055] Taking switching element Q1 as an example, as shown in Figure 16, the calculation unit 70 calculates the duration of the second current conduction interval from the time required for the rotor position to change from 60 degrees to 120 degrees (the most recent interrupt time interval) during interrupt processing at the 120-degree timing. If the second current conduction interval is 30 degrees in electrical angle, the duration of the second current conduction interval is half the most recent interrupt time interval. The calculation unit 70 PWM-controls switching element Q1 at the second duty ratio from the time when the rotor position reaches 120 degrees until the time of the second current conduction interval has elapsed.

[0056] Although not shown in the figures, the calculation unit 70 performs the same process for the switching element Q1 for the switching elements Q2 to Q6. The calculation of the second current conduction interval for the switching element Q2 is performed at the timing of 240 degrees shown in FIGS. 4 to 6. The calculation of the second current conduction interval for the switching element Q3 is performed at the timing of 0 degrees shown in FIGS. 4 to 6. The calculation of the second current conduction interval for the switching element Q4 is performed at the timing of 300 degrees shown in FIGS. 4 to 6. The calculation of the second current conduction interval for the switching element Q5 is performed at the timing of 60 degrees shown in FIGS. 4 to 6. The calculation of the second current conduction interval for the switching element Q6 is performed at the timing of 180 degrees shown in FIGS. 4 to 6.

[0057] In this way, the calculation unit 70 calculates the duration of the second current conduction interval of any of the switching elements Q1 to Q6 during each interrupt process every 60 degrees. Here, if the second current conduction interval is set to 30 electrical degrees, the process of calculating the duration of the second current conduction interval is a process of calculating 1 / 2 the most recent interrupt time interval. This process involves simply shifting the most recent interrupt time interval expressed in binary notation by one bit, so the load on the calculation unit 70 is small. As another example, if the second current conduction interval is set to 15 electrical degrees, the process of calculating the duration of the second current conduction interval is a process of calculating 1 / 4 the most recent interrupt time interval. This process involves simply shifting the most recent interrupt time interval expressed in binary notation by two bits, so the load on the calculation unit 70 is small. Therefore, even if an inexpensive microcontroller is used as the calculation unit 70, it is relatively easy to calculate the duration of the second current conduction interval during each interrupt process every 60 degrees. Note that calculation of the second duty ratio that determines the pseudo conduction angle also places a load on the calculation unit 70. However, it is sufficient to calculate and update the second duty ratio, for example, once per electrical angle period, and the load on the calculation unit 70 can be reduced to the extent that there is more time available.

[0058] As a comparative example, we will explain control in which the electrical angle of the second current conduction interval is directly switched in response to the motor load. When the electrical angle of the second current conduction interval is set, for example, in increments of 1 degree, calculating the duration of the second current conduction interval from the most recent interrupt time interval requires approximately 50 times the processing time of the calculation unit 70 compared to the aforementioned 1-bit shift process. Therefore, if an inexpensive microcontroller is used as the calculation unit 70, it is difficult to complete the calculation before the next interrupt process. As a countermeasure, instead of calculating the duration of the second current conduction interval set at an electrical angle resolution of 1 degree increments at each 60-degree interrupt process, it is possible to calculate it only once per electrical angle period, as shown in FIG. 17, and apply it to all switching elements Q1 to Q6. However, in this case, a problem occurs when the rotation speed suddenly changes, for example, as shown in FIG. 18, due to a sudden drop (elimination) of the motor load. This point will be explained below.

[0059] FIG. 19 is a timing chart of the on / off states of switching elements Q1 to Q6 in a comparative example in which the electrical angle of the second current conduction interval is directly controlled, where the time of the second current conduction interval is calculated only once per electrical angle cycle and applied to all of switching elements Q1 to Q6. This timing chart illustrates the occurrence of an upper-lower short circuit in a switching element due to a sudden change in rotation speed, as shown in FIG. 18. The calculation unit 70 sets the electrical angle of the second current conduction interval to 30 degrees, for example, and calculates the time of the second current conduction interval (the time corresponding to an electrical angle of 30 degrees) at 0 degrees. This calculated time is used over one electrical angle cycle. When a sudden change in rotation speed, as shown in FIG. 18, occurs, the time corresponding to an electrical angle of 30 degrees calculated at 0 degrees may become longer than the time corresponding to an electrical angle of 60 degrees in the latter half of the cycle (the sum of the first and second current conduction intervals may exceed 180 degrees). 19, the time of the second current conduction interval of switching element Q4 starting at the timing of 300 degrees (the time corresponding to an electrical angle of 30 degrees calculated at the timing of 0 degrees) is longer than the time corresponding to an electrical angle of 60 degrees, and switching elements Q1 and Q4 are simultaneously turned on for a short period of time from 360 degrees, causing an upper and lower short circuit (a short circuit between the positive and negative electrodes of battery pack 17). Note that if the program of calculation unit 70 is written to set the second current conduction interval at an electrical angle resolution of 1 degree, multiplication and division will be performed according to the program even when the electrical angle of the second current conduction interval is 30 degrees, and the simple calculation using the 1-bit shift described above will not be possible.

[0060] FIG. 20 is a time chart showing the on / off states of switching elements Q1-Q6 in an embodiment that controls the pseudo conduction angle when the second duty ratio is calculated only once per electrical angle cycle and applied to all of switching elements Q1-Q6. This time chart illustrates how the occurrence of upper and lower short circuits in the switching elements is suppressed when a sudden change in rotation speed occurs, as shown in FIG. 18. The calculation unit 70 sets the second conduction interval to 30 degrees and calculates the second duty ratio at 0 degrees (here, 100% is used as an example). The calculated second duty ratio is used throughout one electrical angle cycle. Meanwhile, the duration of the second conduction interval is calculated at each interruption process every 60 degrees. Therefore, when a sudden change in rotation speed occurs, as shown in FIG. 18, although there may be a delay in changing the second duty ratio, the duration of the second conduction interval is updated every 60 degrees, thereby suppressing the occurrence of upper and lower short circuits in the switching elements. In this embodiment, the electrical angle of the second current conduction section is fixed to 30 degrees, so that the time of the second current conduction section can be calculated by shifting 1 bit as described above, and there is no problem with the load on the calculation unit 70 even if the time of the second current conduction section is updated every 60 degrees.

[0061] This embodiment has the following advantages.

[0062] (1) The calculation unit 70 can define a first conduction interval and a second conduction interval for each of the switching elements Q1 to Q6, and can set the second duty ratio to a value different from the first duty ratio. For example, if the first conduction interval is 120 degrees, the second conduction interval is 30 degrees, and the first duty ratio is 100%, changing the second duty ratio can achieve a pseudo-intermediate conduction angle between 120 degrees and 150 degrees while keeping the electrical angle of the second conduction interval fixed. This results in motor characteristics (e.g., the relationship between torque and rotation speed) similar to those obtained when the conduction angle is set to the intermediate value. Therefore, by changing the second duty ratio while fixing the pseudo-electrical angle of the second conduction interval to a value that can be calculated by bit shifting, such as 30 degrees or 15 degrees, the duration of the second conduction interval can be easily calculated, for example, in interrupt processing every 60 degrees. This reduces the load on the calculation unit 70 compared to when the conduction angle is set with a resolution of 1 degree. Therefore, an inexpensive microcontroller can be used as the computing unit 70.

[0063] (2) The calculation unit 70 changes the second duty ratio according to the rotation speed or load. This allows the pseudo conduction angle to be set according to the rotation speed or load, and appropriate motor characteristics according to the rotation speed or load can be obtained. Specifically, for example, in the low load region, the pseudo conduction angle is increased to approach sinusoidal control, thereby reducing torque ripple and noise and improving rotation speed and efficiency. On the other hand, in the high load region, the pseudo conduction angle is decreased, making it possible to increase the torque relative to the motor current. This improves the usability of the work machine 1.

[0064] (3) The calculation unit 70 fixes the electrical angle of the second current supply interval regardless of the rotation speed or load. Therefore, even if the rotation speed or load changes, calculation of the duration of the second current supply interval does not become complicated, and the load on the calculation unit 70 is reduced.

[0065] (4) When changing the second duty ratio, the calculation unit 70 changes the second duty ratio gradually or gradually. This prevents sudden changes in motor characteristics before and after changing the second duty ratio. This improves the ease of use of the work machine 1. In a configuration in which the electrical angle of the second current conduction interval is directly changed, changing the electrical angle of the second current conduction interval in increments of, for example, one degree requires far more processing steps to calculate the duration of the second current conduction interval than bit shifting. This places a heavy load on the calculation unit 70, making it difficult to use an inexpensive microcontroller as the calculation unit 70. In contrast, changing the second duty ratio at a constant rate, such as 0.1% / ms, does not require multiplication or division, so the load on the calculation unit 70 is light, and the calculation unit 70 can easily be used even with an inexpensive microcontroller.

[0066] 19 and 20 , the change in the second duty ratio has a lower risk of malfunction even when the change in frequency is reduced compared to the change in the electrical angle of the second conduction angle in the comparative example in which the electrical angle of the second conduction interval is directly controlled. Therefore, the change in the second duty ratio can be set arbitrarily so that the load on calculation unit 70 is within an allowable range, and calculation unit 70 can easily be implemented even when an inexpensive microcontroller is used.

[0067] Although the present invention has been described above using the embodiments as examples, the present invention is not limited to the embodiments. Various modifications can be made to the details specifically described in the embodiments within the scope of the claims.

[0068] The working machine of the present invention is not limited to the circular saw exemplified in the embodiment, but may be other types of machine such as a bench circular saw, a grinder, an impact driver, or an impact tool.

[0069] Six Hall ICs 63 may be arranged circumferentially around the motor 20 at intervals of 30 electrical degrees. In this case, the calculation unit 70 can detect the rotor position every 30 degrees. Therefore, the conduction angle can be set to 150 degrees from the start of motor 20 startup without timer processing, and the motor 20 can be controlled at any pseudo conduction angle by setting the second duty ratio. Furthermore, since there is no need to calculate the duration of the second conduction interval, the load on the calculation unit 70 is further reduced, allowing for the use of a less expensive microcontroller as the calculation unit 70. Furthermore, in situations where a sudden fluctuation in rotation speed occurs, the pseudo conduction angle can be controlled more stably than when the duration of the second conduction interval is calculated, resulting in more stable characteristics. This advantage is particularly noticeable in impact tools, which are prone to sudden fluctuations in rotation speed.

[0070] The trigger switch 15 may be an infinitely variable speed trigger switch. In this case, it is desirable that the threshold values ​​related to the rotation speed, such as the high load detection threshold and the low load detection threshold, be different values ​​depending on the pulling amount of the trigger switch 15. The same applies when detecting the load based on the motor current.

[0071] The second current supply interval may be set for only some of the switching elements Q1 to Q6.

[0072] To smoothly perform commutation by overlapping the ON periods of switching elements Q1 to Q3 and Q4 to Q6, i.e., to bring the conduction angle closer to 180 degrees than 150 degrees, the conduction angle may be fixed at 165 degrees. In this case, the increase in the conduction angle of 45 degrees from 120 degrees can be calculated by using the time for the most recent three phases as follows: 60 degrees × 3 phases ÷ 4 (2-bit shift). Even in this case, the time for the second conduction interval can be easily calculated using bit shifts. Alternatively, the time for the most recent one phase can be calculated by adding the electrical angle of 30 degrees (1-bit shift) and the electrical angle of 15 degrees (2-bit shift).

[0073] The conduction angle, rotation speed, duty ratio, and the like, which are given as specific numerical values ​​in the embodiments, do not limit the scope of the invention in any way, and can be changed as desired to suit the required specifications. [Explanation of symbols]

[0074] 1...work machine, 15...trigger switch, 17...battery pack, 19...saw blade (tip tool), 20...motor, 23...rotor, 25...winding, 51...control power supply circuit, 52...current detection circuit, 53...switch operation detection circuit, 55...voltage detection circuit, 56...control signal circuit, 57...rotation position detection circuit, 58...rotation speed detection circuit, 59...operation mode detection circuit, 60...operation mode switch, 61...lighting LED drive circuit, 62...lighting LED, 63...hall IC (position detection element), 64...inverter circuit, 65...resistor, 66...temperature sensor, 67...temperature detection circuit, 68...capacitor, 70...calculation unit (control unit).

Claims

1. a brushless motor having a rotor and a stator having windings of multiple phases; an inverter circuit having a plurality of switching elements connected to the windings of the plurality of phases; a control unit configured to perform commutation control for controlling the inverter circuit to switch energization to the plurality of phases in accordance with a position of the rotor; Equipped with the commutation control may have, for at least one switching element, a first current conduction interval corresponding to a current conduction interval when a current conduction angle is a first current conduction angle, and a second current conduction interval set at least either before or after the first current conduction interval, The duty ratio of the PWM control in the second current supply interval can be set to a value different from the duty ratio of the PWM control in the first current supply interval. A work machine characterized by:

2. The work machine according to claim 1, In the commutation control, the duty ratio in the second current supply interval is changed in accordance with the rotation speed of the brushless motor or the load applied to the brushless motor. A work machine characterized by:

3. The work machine according to claim 1 or 2, In the commutation control, a conduction angle of the second conduction section is fixed regardless of a rotation speed of the brushless motor or a load applied to the brushless motor. A work machine characterized by:

4. The work machine according to claim 1 or 2, The first current conduction section is 120 degrees, and the sum of the first current conduction section and the second current conduction section is 135 degrees, 150 degrees, or 165 degrees. A work machine characterized by:

5. The work machine according to claim 1 or 2, In the commutation control, the duty ratio in the second current supply interval is decreased when a high load determination condition is satisfied, and is increased when a low load determination condition is satisfied. A work machine characterized by:

6. The work machine according to claim 4, a position detection element that outputs a signal according to the position of the rotor; the control unit is configured to be able to detect the position of the rotor every 60 degrees in response to a signal from the position detection element. A work machine characterized by:

7. The work machine according to claim 1 or 2, the duty ratio in the second current-carrying section has three or more set values; A work machine characterized by:

8. The work machine according to claim 1 or 2, In the commutation control, when changing the duty ratio in the second current supply interval, the duty ratio is changed stepwise or gradually. A work machine characterized by:

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