Electric work machine

Abstract

To make it possible for a control unit common to each motor to control power supply to each motor by a PWM signal of different carrier frequency in an electric work machine having two motors.SOLUTION: An electric work machine includes: a first and a second motors; a first and a second switches provided on an energization path from a DC power source to each motor; a first and a second carrier frequency setting units; and a control unit. The first and second carrier frequency setting units set a first and a second carrier frequencies at the time of performing PWM control of power supplied to the first and second motors to a different frequency. The control unit drives the first or the second switch by a PWM signal generated at the first or the second carrier frequency to perform PWM control of the power supplied to the first or second motor.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an electric work machine. [Background technology]

[0002] Patent Document 1 describes a lawnmower as a working machine, which is equipped with a work motor, a travel motor, and a control unit. In this lawnmower, the work motor is a motor that drives the cutting blade, and the travel motor is a motor that causes the lawnmower to travel (self-propel). The control unit is made up of a computer, and the processor executes a program stored in memory to control the rotation speeds of the work motor and the travel motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2019 / 097683 Summary of the Invention [Problem to be solved by the invention]

[0004] The rotational speed of a motor is controlled by turning on and off a switching element in the current path to the motor using a pulse-width modulated (PWM) control signal (PWM signal). For work motors, a low carrier frequency is required to reduce the number of switching operations, as a high carrier frequency, which determines the PWM control cycle, can cause overheating and breakdown of the switching element due to switching loss. On the other hand, for traction motors, torque fluctuations can make the lawnmower unstable and reduce user comfort, so a high carrier frequency is required to stabilize the torque (or in other words, the motor's rotational speed).

[0005] However, the lawnmower described in Patent Document 1 has a single controller that controls the work motor and the travel motor, and because each motor is controlled by a common controller, the carrier frequency used when PWM controlling each motor is the same. Therefore, the lawnmower described in Patent Document 1 has the problem that it is not possible to set an appropriate carrier frequency for each motor and control the rotation speed of each motor.

[0006] One aspect of the present disclosure is to provide an electric work machine having two motors, in which a control unit common to each motor can control the power supplied to each motor using PWM signals with different carrier frequencies. [Means for solving the problem]

[0007] An electric work machine according to one aspect of the present disclosure includes a first motor, a second motor, a first current path, a second current path, a first switch, a second switch, a first carrier frequency setting unit, a second carrier frequency setting unit, and a control unit.

[0008] The first motor is configured to drive a first driven object, and the second motor is configured to drive a second driven object, i.e., the first motor and the second motor drive different driven objects.

[0009] The first current path is configured to connect the DC power supply and the first motor, and the second current path is configured to connect the DC power supply and the second motor, and a first switch is provided on the first current path, and a second switch is provided on the second current path.

[0010] The first carrier frequency setting unit is configured to set a first carrier frequency when the first switch is turned on and off to PWM control the power supplied to the first motor, and the second carrier frequency setting unit is configured to set a second carrier frequency different from the first carrier frequency when the second switch is turned on and off to PWM control the power supplied to the second motor.

[0011] When a drive command for the first motor is input, the control unit generates a first PWM signal at a first carrier frequency and outputs it to the first switch, thereby controlling the power supplied to the first motor. When a drive command for the second motor is input, the control unit generates a second PWM signal at a second carrier frequency and outputs it to the second switch, thereby controlling the power supplied to the second motor.

[0012] In this way, in the above-mentioned electric work machine, the power supplied to the first motor and the second motor is PWM controlled by the first PWM signal and the second PWM signal generated at the different first carrier frequency and second carrier frequency, respectively.

[0013] Therefore, with the above-described electric operating machine, even though the first motor and the second motor are driven by a single controller common to both motors, the carrier frequency used for PWM control of the power supplied to each motor can be set separately for each motor, so that the power supplied to the first motor and the second motor can be PWM controlled at a carrier frequency appropriate for each motor. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view illustrating the appearance of a lawnmower according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing the electrical configuration of the lawnmower. [Figure 3] 10 is a time chart showing control operations when the blade motor and the self-propelled motor are driven. [Figure 4] 4 is a flowchart showing a control process executed in a control unit. [Figure 5] 5 is a flowchart illustrating the motor drive process shown in FIG. 4. [Figure 6] 6 is a flowchart illustrating a blade motor control process shown in FIG. 5. [Figure 7] 6 is a flowchart illustrating the free-running motor control process shown in FIG. 5. [Figure 8] 8 is a flowchart showing the free-running brake control process shown in FIGS. 4, 5, and 7. [Figure 9] 7 is a flowchart showing the blade brake control process shown in FIGS. 4, 5, and 6. [Figure 10] 10 is a time chart showing an operation during brake control of the blade motor. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Summary of the embodiment] In one embodiment, the electric operating machine may include a first motor configured to drive a first driven object. The first motor may include a first current path configured to connect a DC power supply to the first motor. A first switch may be provided on the first current path.

[0016] Additionally / alternatively, the electric operating machine may include a second motor configured to drive a second driven object. The second motor may include a second current path configured to connect the DC power supply and the second motor. A second switch may be provided on the second current path.

[0017] Additionally / alternatively, the electric working machine may include a first carrier frequency setting unit configured to set a first carrier frequency when turning on and off the first switch to PWM control the power supplied to the first motor. Also, the electric working machine may include a second carrier frequency setting unit configured to set a second carrier frequency different from the first carrier frequency when turning on and off the second switch to PWM control the power supplied to the second motor.

[0018] Additionally / alternatively, the electric work machine may include a control unit that controls the power supplied to the first motor by generating a first PWM signal at a first carrier frequency and outputting it to a first switch when a drive command for the first motor is input.

[0019] In addition, the control unit may be configured to control the power supplied to the second motor by generating a second PWM signal at a second carrier frequency and outputting it to a second switch when a drive command for the second motor is input.

[0020] If an electric working machine in one embodiment includes the above-mentioned first motor, second motor, first current path, second current path, first switch, second switch, first carrier frequency setting unit, second carrier frequency setting unit, and control unit, such an electric working machine can set the first carrier frequency for PWM control of the power supplied to the first motor and the second carrier frequency for PWM control of the power supplied to the second motor to carrier frequencies suitable for controlling each motor.

[0021] Therefore, for example, when the load applied to the first motor from the first driven object is large and the power supplied to the first motor is large, the first carrier frequency can be set to a frequency lower than the second carrier frequency. By setting the first carrier frequency in this manner, the switching loss occurring in the first switch can be reduced, and the first switch can be prevented from becoming overheated.

[0022] In this case, since there is no need to increase the withstand voltage of the first switch to protect it from overheating failure, a switching element with a low withstand voltage can be selected as the first switch, thereby reducing the cost of the electric work machine.

[0023] In this case, the second carrier frequency can be set to a frequency higher than the first carrier frequency, thereby suppressing torque fluctuations of the second motor and enabling the second driven object to be driven stably at a desired speed.

[0024] Additionally / alternatively, the electric working machine may have a first carrier frequency set to be lower than the second carrier frequency. The first driven object may be a blade, and the first motor may be configured to rotate the blade. The second driven object may be a wheel that propels the electric working machine, and the second motor may be configured to rotate the wheel.

[0025] In an electric work machine configured in this manner, the load applied to the first motor from the blade increases during operation, and the first switch is prone to heat generation due to switching loss caused by cyclic on / off by PWM control. However, by setting the first carrier frequency lower than the second carrier frequency as described above, heat generation can be suppressed.

[0026] Furthermore, if the carrier frequency of the second motor is low, torque fluctuations (in other words, rotational fluctuations) are likely to occur due to the load applied from the wheels, but by increasing the second carrier frequency, torque fluctuations can be suppressed. As a result, the traveling speed when the electric work machine is self-propelled can be stabilized, and the discomfort felt by the user due to speed fluctuations can be suppressed.

[0027] Additionally / alternatively, the first carrier frequency of the electric operating machine may be set within a range of 100 Hz to 1 kHz, and the second carrier frequency may be set within a range of 8 kHz to 20 kHz.

[0028] With an electric work machine in which the first carrier frequency or the second carrier frequency is set in this manner, when the power supplied to the first motor is PWM controlled or when the power supplied to the second motor is PWM controlled, switching noise can be prevented from being heard by the user.

[0029] In other words, if the carrier frequency of PWM control is set within the frequency range of 1 kHz to 8 kHz, the switching noise generated by the on / off of the switch will become audible noise that can be heard by those around, and may cause discomfort to users, etc.

[0030] However, by setting the first carrier frequency or the second carrier frequency as described above, it is possible to prevent the switching noise that occurs when the power supplied to the motor is PWM controlled from causing discomfort to the user.

[0031] In this case, more preferably, the first carrier frequency may be set within a range of 300 Hz to 700 Hz, and the second carrier frequency may be set within a range of 8 kHz to 10 kHz.

[0032] Additionally / alternatively, the electric work machine may be configured such that the turn-off time for the first switch and / or the second switch to change from an on state to an off state by the first PWM signal or the second PWM signal is longer than the turn-on time for changing from an off state to an on state.

[0033] With this configuration of the electric operating machine, it is possible to suppress the high peak voltage generated by the energy stored in the first motor or the second motor when the first switch or the second switch is turned off, thereby preventing the first switch or the second switch from being deteriorated by the high voltage generated when it is turned off.

[0034] In addition, in some embodiments, the above-described features may be combined in any combination, and in some embodiments, any of the above-described features may be omitted. Specific Exemplary Embodiments An exemplary embodiment of the present disclosure will be described below with reference to the drawings. Note that in this embodiment, a lawn mower 10 will be described as an example of an electric work machine.

[0035] <Overall structure of the lawnmower> As shown in FIG. 1, the lawnmower 10 of this embodiment includes a vehicle body 11. The lawnmower 10 also includes a battery connector 19 on top of the vehicle body 11. The battery connector 19 includes a lid, and is configured so that multiple battery packs 6 (see FIG. 2) can be attached and detached to the inside of the lid. The battery pack 6 includes a battery 8 therein that can be charged and discharged. The battery 8 is an example of a DC power supply of the present disclosure.

[0036] The lawnmower 10 also includes a grass collection box 5. The grass collection box 5 is attached to the rear of the vehicle body 11. The lawnmower 10 includes a handle 12. The handle 12 is U-shaped and attached to the vehicle body 11. The handle 12 is configured to be gripped by a user. The user holds the handle 12 while walking behind the lawnmower 10 and operates the lawnmower 10 via the handle 12.

[0037] The lawnmower 10 is equipped with a first control lever 13 and a second control lever 14 that are operated by the user. These two control levers 13, 14 are formed in a U-shape corresponding to the shape of the handle 12. The first control lever 13 is located on the front side of the handle 12, and the second control lever 14 is located on the rear side of the handle 12.

[0038] The first operating lever 13 is attached to the handle 12 so that the user can pull it toward the handle 12 (i.e., backward). The second operating lever 14 is attached to the handle 12 so that the user can pull it toward the handle 12 (i.e., forward).

[0039] Next, the lawnmower 10 includes a cutting blade 18 (see FIG. 2) provided on the bottom surface of the vehicle body 11. The lawnmower 10 also includes a blade motor 31 (see FIG. 2) provided inside the vehicle body 11. The rotating shaft of the blade motor 31 is physically connected to the cutting blade 18 directly or via a transmission unit.

[0040] That is, the blade motor 31 is a motor for driving the lawnmower blade 18, and the blade 18 rotates by receiving driving force from the blade motor 31. The grass cut by the rotation of the blade 18 is collected in the grass collection box 5.

[0041] The lawnmower 10 also includes a pair of left and right drive wheels 16. These drive wheels 16 are provided at the rear of the vehicle body 11. The lawnmower 10 also includes a pair of left and right driven wheels 15. These driven wheels 15 are provided at the front of the vehicle body 11.

[0042] The lawnmower 10 also includes a self-propelled motor 32 (see FIG. 2) inside the vehicle body 11. The rotating shaft of the self-propelled motor 32 is physically connected to the pair of drive wheels 16 via a transmission unit. In other words, the self-propelled motor 32 is a motor for driving the pair of drive wheels 16, and the pair of drive wheels 16 receive driving force from the self-propelled motor 32 to rotate, causing the lawnmower 10 to self-propel forward.

[0043] The blade motor 31 corresponds to an example of a first motor in the present disclosure, and the cutting blade 18 corresponds to a blade in the present disclosure and an example of a first driven object. The self-propelled motor 32 corresponds to an example of a second motor in the present disclosure, and the drive wheel 16 corresponds to an example of a second driven object in the present disclosure. In this embodiment, the blade motor 31 and the self-propelled motor 32 are brushed motors.

[0044] Of the two operating levers 13, 14 mentioned above, the first operating lever 13 is for driving or stopping the blade motor 31, and the second operating lever 14 is for driving or stopping the self-propelled motor 32.

[0045] For this reason, the first operating lever 13 is provided with a blade switch 21 (see FIG. 2) as a switch for driving the blade motor 31. The blade switch 21 is turned on when the operating lever 13 is pulled toward the handle 12 (i.e., rearward).

[0046] The second operating lever 14 is provided with a self-propelled switch 22 (see FIG. 2) as a switch for driving the self-propelled motor 32. The self-propelled switch 22 is turned on when the second operating lever 14 is pulled toward the handlebar 12 (i.e., forward).

[0047] The first and second operating levers 13, 14 are attached to the handle 12 so that when the user releases them, they return to their original positions before being pulled. Therefore, when the user releases the first operating lever 13 while the first operating lever 13 is being pulled, the blade switch 21 returns to the OFF state. Similarly, when the user releases the second operating lever 14 while the second operating lever 14 is being pulled, the self-propelled switch 22 returns to the OFF state.

[0048] Next, the lawnmower 10 includes an operating unit 17. The operating unit 17 is attached to the handle 12. The operating unit 17 is provided with a main power switch 20. The main power switch 20 is in the form of a tactile switch that is turned on only when operated (pressed) by the user.

[0049] The operation unit 17 is also provided with a display unit 26 that displays the status of the lawnmower 10. The display unit 26 is equipped with LEDs for various displays. The LEDs on the display unit 26 include, for example, a main power LED that is lit when power is being supplied to the controller 30 shown in FIG. 2 by operating the main power switch 20. The LEDs on the display unit 26 also include a remaining capacity indicator LED that displays the amount of power stored in the battery 8 (hereinafter referred to as remaining capacity), and an abnormality indicator LED that is lit when an abnormality occurs in the drive system of each of the motors 31, 32.

[0050] The operating unit 17 is also equipped with the blade switch 21 and self-propelled switch 22 described above, as well as a speed adjustment dial 24 for adjusting the traveling speed of the lawnmower 10. As shown in Figure 2, the speed adjustment dial 24 is equipped with a variable resistor whose resistance value changes depending on the dial position, which is changed by the user's operation, and is configured to command the traveling speed based on the resistance value.

[0051] <Controller configuration> Next, the controller 30 drives the blade motor 31 and the self-propelled motor 32, and also controls the display of various LEDs provided on the display unit 26. The controller 30 is provided on a single circuit board and is housed inside the vehicle body 11. The electrical configuration of the controller 30 will be described below with reference to FIG. 2.

[0052] 2, the controller 30 is electrically connected to the battery 8, the blade motor 31, and the self-propelled motor 32. Therefore, the controller 30 is provided with a first current path 35, a second current path 34, and a third current path 36 that connect the battery 8 and the blade motor 31, and the battery 8 and the self-propelled motor 32, respectively, and supply power from the battery 8 to each of the motors 31 and 32.

[0053] The first and second current paths 35, 36 are respectively connected to two terminals of the blade motor 31 and the self-propelled motor 32, with one terminal connected to the positive terminal of the battery 8 and the other terminal connected to the negative terminal (ground in the figure) of the battery 8. In other words, the first and second current paths 35, 36 are current paths dedicated to each motor 31, 32. Furthermore, the third current path 34 is a current path common to each motor 31, 32, connecting the positive terminal of the battery 8 to the first and second current paths 35, 36.

[0054] A third switching element 40 is provided on the third current path 34 to turn on or off the current path 34. The third switching element 40 is in the form of an n-channel metal oxide semiconductor field effect transistor (hereinafter referred to as MOSFET). Therefore, when a high-level drive signal is input to the gate of the third switching element 40 from the control circuit 50, the third switching element 40 is turned on and turns on the third current path 34.

[0055] In addition, first and second switching elements 41 and 42 are provided on the first and second current paths 35 and 36, respectively, which connect the terminals of each motor 31 and 32 to the negative side of the battery 8, and which turn on and off the current paths 35 and 36.

[0056] The first and second switching elements 41 and 42 are configured with n-channel MOSFETs, similar to the third switching element 40. Therefore, the first and second switching elements 41 and 42 are turned on when a high-level drive signal is input to their gates from the control circuit 50, thereby causing the first and second current paths 35 and 36 to become conductive.

[0057] When driving the blade motor 31 or the self-propelled motor 32, the control circuit 50 generates a PWM signal with a predetermined duty ratio at a carrier frequency set for each motor 31, 32. The control circuit 50 then outputs the generated PWM signal to the first and second switching elements 41, 42 corresponding to each motor 31, 32, thereby turning the first and second switching elements 41, 42 on and off. As a result, the power supplied to the blade motor 31 and the self-propelled motor 32 is PWM controlled.

[0058] The first switching element 41 corresponds to an example of a first switch of the present disclosure, and the PWM signal output from the control circuit 50 to the first switching element 41 corresponds to an example of a first PWM signal of the present disclosure. The second switching element 42 corresponds to an example of a second switch of the present disclosure, and the PWM signal output from the control circuit 50 to the second switching element 42 corresponds to an example of a second PWM signal of the present disclosure.

[0059] Resistors R11 and R21 are provided on the first and second current paths 35 and 36, respectively, between the first and second switching elements 41 and 42 and the negative electrode of the battery 8. These resistors R11 and R21 are current detection resistors for detecting the motor currents flowing through the motors 31 and 32. Each resistor R11 and R21 is provided with a first current detection circuit 43 and a second current detection circuit 44, respectively, which detect the motor currents flowing through the motors 31 and 32 from the voltages across the resistors R11 and R21.

[0060] The detection signals from the first current detection circuit 43 and the second current detection circuit 44 are input to the control circuit 50. The control circuit 50 monitors the motor current flowing through the blade motor 31 or the self-propelled motor 32 based on the detection signal from the first current detection circuit 43 or the second current detection circuit 44 when the blade motor 31 or the self-propelled motor 32 is driven.

[0061] When the motor current being monitored exceeds a preset current threshold, the control circuit 50 determines that an abnormality has occurred in the drive system of the blade motor 31 or the self-propelled motor 32, and switches the third switching element 40 from the on state to the off state, thereby interrupting the third current path 34. As a result, the blade motor 31 and the self-propelled motor 32 are protected from overcurrent.

[0062] Next, a fourth switching element 45 is provided in the first current path 35 so as to be in parallel with the blade motor 31. Also, a fifth switching element 46 is provided in the second current path 36 so as to be in parallel with the self-propelled motor 32.

[0063] The fourth and fifth switching elements 45 and 46 are configured with n-channel MOSFETs, similar to the first to third switching elements 40 to 42. Therefore, the fourth and fifth switching elements 45 and 46 are turned on when a high-level brake signal is input to the gate from the control circuit 50, and both ends of the blade motor 31 and the self-propelled motor 32 are short-circuited.

[0064] Therefore, when the first switching element 41 is in the OFF state and the fourth switching element 45 is in the ON state while the blade motor 31 is rotating, a brake current flows through the fourth switching element 45, generating a braking torque in the blade motor 31. Also, when the second switching element 42 is in the OFF state and the fifth switching element 46 is in the ON state while the self-propelled motor 32 is rotating, a brake current flows through the fifth switching element 46, generating a braking torque in the self-propelled motor 32. In other words, the fourth and fifth switching elements 45 and 46 are short-circuit brake switches that generate a braking force in the blade motor 31 and the self-propelled motor 32, respectively, to stop their rotation.

[0065] Next, a drive switch 21A for the blade motor 31 is provided on a first current path 35 between the blade motor 31 and the fourth switching element 45 and the positive electrode side of the battery 8. The drive switch 21A is turned on and off in conjunction with the blade switch 21. Further, a drive switch 22A for the self-propelled motor 32 is provided on a second current path 36 between the self-propelled motor 32 and the fifth switching element 46 and the positive electrode side of the battery 8. The drive switch 22A is turned on and off in conjunction with the self-propelled switch 22.

[0066] These two drive switches 21A, 22A conduct the current path 35 or 36 when the blade switch 21 or the self-propelled switch 22 is turned on and a drive command for the blade motor 31 or the self-propelled motor 32 is input.

[0067] Therefore, even if the first and second switching elements 41 and 42 have a short-circuit failure, when the blade switch 21 or the self-propelled switch 22 is turned off, the drive switch 21A or 22A is turned off, and the first current path 35 or the second current path 36 is interrupted. Therefore, even if the first and second switching elements 41 and 42 have a short-circuit failure, the user can stop the drive of the blade motor 31 or the self-propelled motor 32 by switching the blade switch 21 or the self-propelled switch 22 to the off state.

[0068] First and second turn-off delay circuits 47 and 48 are provided on the output paths of the PWM signals from the control circuit 50 to the first and second switching elements 41 and 42. The first and second turn-off delay circuits 47 and 48 are provided to make the turn-off time, which is the time it takes for the first and second switching elements 41 and 42 to change from an on state to an off state, longer than the turn-on time, which is the time it takes for the first and second switching elements 41 and 42 to change from an off state to an on state, by the PWM signal.

[0069] That is, the first turn-off delay circuit 47 includes a resistor R12 provided on the output path of the PWM signal from the control circuit 50 to the first switching element 41, and a series circuit of a resistor R13 and a diode D11 connected in parallel to the resistor R12. The diode D11 is provided so that the direction of current flowing from the control circuit 50 to the gate of the first switching element 41 is the forward direction when the PWM signal rises from low level to high level.

[0070] For this reason, the current flowing from the control circuit 50 to the gate of the first switching element 41 when the PWM signal rises to high level is larger than the current flowing from the gate of the first switching element 41 to the control unit when the PWM signal falls to low level. Therefore, the turn-off time, during which the first switching element 41 changes from the on state to the off state when the PWM signal goes to low level, is longer than the turn-on time, during which the first switching element 41 changes from the off state to the on state when the PWM signal goes to high level.

[0071] The second turn-off delay circuit 48 includes a resistor R22 provided on the output path of the PWM signal from the control circuit 50 to the second switching element 42, and a series circuit of a resistor R23 and a diode D21 connected in parallel to the resistor R22. Like the diode D11 of the first turn-off delay circuit 47, the diode D21 is provided so that the direction of current flowing from the control circuit 50 to the gate of the second switching element 42 when the PWM signal rises is forward. Therefore, the turn-off time required for the second switching element 42 to change from the on state to the off state is longer than the turn-on time required for the second switching element 42 to change from the off state to the on state.

[0072] In this way, the turn-off time of the first and second switching elements 41, 42 is made longer than the turn-on time in order to suppress the high peak voltage that occurs when the first and second switching elements 41, 42 are turned off.

[0073] In other words, when the first and second switching elements 41, 42 change from an ON state to an OFF state, a high voltage is generated at the terminals of the motors 31, 32 on the first and second switching elements 41, 42 sides by the energy stored in the motors 31, 32. If the peak voltage of this high voltage exceeds the withstand voltage of the first and second switching elements 41, 42, the first and second switching elements 41, 42 will deteriorate and may even be damaged. Therefore, in this embodiment, the turn-off time of the first and second switching elements 41, 42 is lengthened to lower the peak voltage of the high voltage generated by the energy stored in the motors 31, 32 and protect the first and second switching elements 41, 42 from the high voltage.

[0074] Next, the controller 30 is provided with a capacitor 37 that stabilizes the voltage of a current path 34 that receives power from the battery 8. The controller 30 also has a power supply circuit 38 that receives power from the battery 8 via the current path 34 and generates a power supply voltage Vcc.

[0075] The power supply voltage Vcc generated by the power supply circuit 38 is a constant DC voltage capable of driving the control circuit 50, and is supplied to the control circuit 50. The power supply voltage Vcc is also applied to the main power switch 20, the blade switch 21, and the self-propelled switch 22 via resistors R0, R1, and R2. The power supply voltage Vcc is also applied to the variable resistor of the speed adjustment dial 24.

[0076] The connection points between the main power switch 20, the blade switch 21, and the self-propelled switch 22 and the resistors R0, R1, and R2 are respectively connected to the control circuit 50. The slider of the variable resistor of the speed adjustment dial 24 is also connected to the control circuit 50. Therefore, the control circuit 50 can obtain the on / off states of the main power switch 20, the blade switch 21, and the self-propelled switch 22, and the command value (speed command value) for the travel speed from the speed adjustment dial 24.

[0077] The connection point between the main power switch 20 and resistor R0 is also connected to the power supply circuit 38. As shown in Fig. 3, the power supply circuit 38 is started or stopped each time the main power switch 20 is operated to turn on. In other words, the main power switch 20 is turned on only when operated (pressed) by the user, and therefore the power supply circuit 38 is switched between on and off states each time the main power switch 20 is operated.

[0078] The controller 30 also includes a display circuit 58 that turns on or off various display LEDs provided on the display unit 26. The control circuit 50 controls the display state of the LEDs on the display unit 26 via the display circuit 58.

[0079] <Control circuit functional configuration> Next, the control circuit 50 is in the form of a microcontroller unit (MCU) including a CPU, a ROM, a RAM, etc. In the control circuit 50, the CPU executes a program stored in the ROM, thereby realizing various functions shown in FIG.

[0080] In other embodiments, instead of or in addition to an MCU, control circuitry 50 may include a combination of electronic components, such as discrete elements, an application specific integrated circuit (ASIC), an application specific general purpose processor (ASSP), a programmable logic device, such as a field programmable gate array (FPGA), or a combination thereof.

[0081] Next, the function of the control circuit 50 will be described. As shown in FIG. 2, the control circuit 50 has functions as a speed command determination unit 52, a SW input determination unit 54, a display control unit 56, a clock generation unit 60, a first frequency division unit 61, a second frequency division unit 62, a first PWM generation unit 65, a second PWM generation unit 66, and a motor drive control unit 68.

[0082] Here, the speed command determining unit 52 receives a voltage value obtained by dividing the power supply voltage Vcc by the variable resistor from the slider of the variable resistor of the speed adjusting dial 24, and determines a speed command value for the traveling speed.

[0083] In addition, the SW input determination unit 54 determines the on / off state of each of the switches 20, 21, and 22 from the potential at the connection point between the main power switch 20 and resistor R0, the connection point between the blade switch 21 and resistor R1, and the connection point between the self-propelled switch 22 and resistor R2.

[0084] That is, when the potential of each of the connection points is at a low level, the SW input determination unit 54 determines that the corresponding switch 20, 21, or 22 is in an on state, and when the potential of each of the connection points is at a high level, the corresponding switch 20, 21, or 22 is in an off state. Note that SW represents a switch.

[0085] Next, the clock generating section 60 is a so-called oscillator that generates a reference clock that determines the operation timing of the control circuit 50 . The first frequency dividing unit 61 divides the reference clock output from the clock generating unit 60 to set the period of the first PWM signal for PWM control of the power supplied to the blade motor 31, in other words, the first carrier frequency.

[0086] In addition, the second frequency dividing unit 62 divides the reference clock output from the clock generating unit 60 to set the period of the second PWM signal for PWM control of the power supplied to the self-propelled motor 32, in other words, the second carrier frequency.

[0087] Next, as shown in FIG. 3, when the blade switch 21 is in the on state, the first PWM generating unit 65 generates a first PWM signal for PWM control of the power supplied to the blade motor 31 in synchronization with the clock of the first carrier frequency output from the first frequency dividing unit 61.

[0088] In addition, when the self-propelled switch 22 is in the on state, the second PWM generating unit 66 generates a second PWM signal for PWM control of the power supplied to the self-propelled motor 32 in synchronization with the clock of the second carrier frequency output from the second frequency dividing unit 62.

[0089] The first PWM generating unit 65 and the second PWM generating unit 66 set the duty ratios of the first PWM signal and the second PWM signal to a preset minimum value when starting to drive the blade motor 31 and the self-propelled motor 32. Then, for each cycle of the first PWM signal and the second PWM signal, the duty ratios are gradually increased until the duty ratios of the first PWM signal and the second PWM signal reach the target duty ratios.

[0090] This is to implement a so-called soft start, which gradually increases the rotation speed of the blade motor 31 and the self-propelled motor 32 after drive starts. This soft start allows the rotation speed of the cutting blade 18 and the drive wheel 16 to increase smoothly after drive starts, preventing the user from feeling uncomfortable due to sudden fluctuations in rotation when the speed increases.

[0091] Furthermore, the target duty ratio (DUTY) of the first PWM signal generated by the first PWM generating unit 65 is fixed to 100% as shown in Fig. 3. Therefore, the blade motor 31 is controlled to the maximum rotation speed by the PWM signal with DUTY: 100%.

[0092] In contrast, the target duty ratio (DUTY) of the second PWM signal generated by the second PWM generating unit 66 is set to an arbitrary duty ratio corresponding to the speed command value from the speed adjustment dial 24, with 100% shown in Fig. 3 being the maximum value. Therefore, the rotation speed of the self-propelled motor 32 is controlled to a rotation speed corresponding to the speed command value.

[0093] However, because the blade motor 31 drives the cutting blade 18, the load applied from the cutting blade 18 during lawn mowing is greater than the load applied to the self-propelled motor 32 from the drive wheels 16 when the lawnmower 10 is running. Therefore, the power consumption of the blade motor 31 is greater than the power consumption of the self-propelled motor 32.

[0094] For this reason, the first switching element 41 used to PWM control the power supplied to the blade motor 31 is prone to heat generation, and if the carrier frequency of the PWM control is high, the first switching element 41 may overheat and break down.

[0095] Therefore, the carrier frequency of the first PWM signal generated by the first PWM generating unit 65 is set to a frequency that can protect the first switching element 41 from overheating. Specifically, the first carrier frequency set by the first frequency dividing unit 61 is set to, for example, 500 Hz in order to protect the first switching element 41 from overheating.

[0096] On the other hand, the self-propelled motor 32 is required to have a constant rotational speed in order to ensure stable running of the lawnmower 10. However, if the carrier frequency used for PWM control of the power supplied to the self-propelled motor 32 is set to a low frequency similar to that of the blade motor, the current flowing through the automatic motor 32 is likely to pulsate due to the switching of the second switching element 42. This pulsation is known as ripple, and if a large ripple is superimposed on the current, uneven torque will occur in the self-propelled motor 32, making it impossible to run the lawnmower 10 stably.

[0097] Therefore, the carrier frequency of the second PWM signal generated by the second PWM generating unit 66 is set to a frequency higher than the first carrier frequency so that the lawnmower 10 can be stably driven by the self-propelled motor 32. Specifically, the second carrier frequency set by the second frequency dividing unit 62 is set to, for example, 8 kHz so that the lawnmower 10 can be stably driven.

[0098] Next, the motor drive control unit 68 outputs the first PWM signal and the second PWM signal generated by the first PWM generating unit 65 and the second PWM generating unit 66 as described above as drive signals for the first and second switching elements 41 and 42, respectively.

[0099] As a result, the power supplied to the blade motor 31 and the self-propelled motor 32 is PWM-controlled by the first PWM signal and the second PWM signal, respectively, and the blade motor 31 and the self-propelled motor 32 are driven.

[0100] In addition, when the blade switch 21 or the self-propelled switch 22 is switched from the on state to the off state and the output of the first PWM signal or the second PWM signal is stopped, the motor drive control unit 68 outputs a drive signal (hereinafter referred to as a brake signal) to the fourth and fifth switching elements 45 and 46.

[0101] The fourth and fifth switching elements 45, 46 are turned on by a brake signal to pass a brake current through the blade motor 31 or the self-propelled motor 32, thereby generating a braking force. Therefore, when the blade switch 21 or the self-propelled switch 22 is switched from the on state to the off state, the blade motor 31 or the self-propelled motor 32 can be stopped quickly.

[0102] In this embodiment, the first frequency divider 61 corresponds to an example of a first carrier frequency setting unit of the present disclosure, and the second frequency divider 62 corresponds to an example of a second carrier frequency setting unit of the present disclosure. Also, the first PWM generator 65, the second PWM generator 66, and the motor drive controller 68 correspond to an example of a controller of the present disclosure.

[0103] <Processing> Next, the control processes executed in the control circuit 50 to realize the above-mentioned functions will be described with reference to the flowcharts shown in FIGS.

[0104] This control process is carried out by the CPU executing a program stored in the ROM when the power supply voltage Vcc is supplied from the power supply circuit 38 and the control circuit 50 is operating. When the control process starts, first, in S110, the elapsed time is measured by counting up a counter for measuring the elapsed time. The elapsed time measured in S110 is a control stop time during which no control is being performed to drive or brake the blade motor 31 and the self-propelled motor 32. Note that S represents a step.

[0105] Next, in S120, it is determined whether the drive switch of the blade motor 31 or the self-propelled motor 32, more specifically, the blade switch 21 or the self-propelled switch 22, is in the on state. If it is determined in S120 that the drive switch of the blade motor 31 or the self-propelled motor 32 is in the on state, the process proceeds to S130. In S130, a counter for measuring elapsed time is cleared, and the process proceeds to S140. In S140, the motor drive process shown in Fig. 5 is executed, and the process proceeds to S110. The motor drive process will be described in detail later.

[0106] On the other hand, if it is determined in S120 that the drive switches of the blade motor 31 and the self-propelled motor 32 are both off, the process proceeds to S150. In S150, it is determined whether the blade motor 31 is currently being braked, more specifically, whether a brake signal is being output to the fourth switching element 45.

[0107] If it is determined in S150 that the blade motor 31 is currently being braked, the process proceeds to S160, and if it is determined in S150 that the blade motor 31 is not currently being braked, the process proceeds to S180.

[0108] In S160, the counter for measuring the elapsed time is cleared, and the process proceeds to S170. In S170, the blade brake control process shown in Fig. 9 is executed, and the process proceeds to S180. The blade brake control process will be described in detail later.

[0109] Next, in S180, it is determined whether the self-propelled motor 32 is currently being braked, more specifically, whether a brake signal is being output to the fifth switching element 46. If it is determined in S180 that the self-propelled motor 32 is currently braking, the process proceeds to S190, and if it is determined in S180 that the self-propelled motor 32 is not currently braking, the process proceeds to S210.

[0110] In S190, the counter for measuring the elapsed time is cleared, and the process proceeds to S200. In S200, the self-propelled brake control process shown in Fig. 8 is executed, and the process proceeds to S210. The self-propelled brake control process will be described in detail later.

[0111] In S210, it is determined whether the count value of the counter for measuring elapsed time, which was counted up in S110, has reached a preset threshold value for determining whether time has elapsed. If the count value of the counter for measuring elapsed time has not reached the threshold value, the process proceeds to S110, and the above series of processes are executed again.

[0112] On the other hand, if it is determined in S210 that the count value of the counter for measuring elapsed time has reached the threshold value, the process proceeds to S220, where power-off processing is executed, and the control processing ends. The power-off process is a process for stopping the operation of the control circuit 50 itself when the count value reaches a threshold value, more specifically, when the control stop time during which control to drive or brake the blade motor 31 and the self-propelled motor 32 is not being performed reaches a predetermined waiting time. Therefore, in S220, the operation of the power supply circuit 38 is stopped, and the control process is terminated.

[0113] Next, the motor drive process executed in S140 will be described. As shown in Fig. 5, in the motor drive process, first in S310, it is determined whether or not both the blade switch 21 and the self-propelled switch 22 are in the on state. If both the blade switch 21 and the self-propelled switch 22 are in the on state, the process proceeds to S320, where the blade motor control process shown in Fig. 6 is executed. After executing the process in S320, the process proceeds to S330, where the self-propelled motor control process shown in Fig. 7 is executed, and the motor drive process ends.

[0114] Next, if it is determined in S310 that neither the blade switch 21 nor the self-propelled switch 22 is in the ON state, the process proceeds to S340, where it is determined whether the blade switch 21 is in the ON state.

[0115] If it is determined in S340 that the blade switch 21 is on, the process proceeds to S350, where it is determined whether the self-propelled motor 32 is currently braking. If it is determined in S350 that the self-propelled motor 32 is currently braking, the process proceeds to S360, where the self-propelled brake control process shown in Figure 8 is executed, and then the process proceeds to S370. If it is determined in S350 that the self-propelled motor 32 is not currently braking, the process proceeds to S370. Then, in S370, the blade motor control process shown in Figure 6 is executed, and the motor drive process ends.

[0116] Next, if it is determined in S340 that the blade switch 21 is not in the ON state, in other words, if the self-propelled switch 22 is in the ON state, the process proceeds to S380 to determine whether the blade motor 31 is currently being braked.

[0117] If it is determined in S380 that the blade motor 31 is currently being braked, the process proceeds to S390, where the blade brake control process shown in Fig. 9 is executed, and then the process proceeds to S400. If it is determined in S380 that the blade motor 32 is not currently being braked, the process proceeds to S400. Then, in S400, the self-propelled motor control process shown in Fig. 7 is executed, and then the motor drive process ends.

[0118] Next, the blade motor control process executed in S320 or S370 and the self-propelled motor control process executed in S330 or S400 will be described. As shown in Fig. 6, in the blade motor control process, first, in S410, it is determined whether or not the blade motor 31 is currently being braked. If the blade motor 31 is currently being braked, the process proceeds to S440, where the blade brake control process shown in Fig. 9 is executed, and the blade motor control process ends.

[0119] Next, if it is determined in S410 that the blade motor 31 is not currently being braked, the process proceeds to S420, where the duty ratio of the first PWM signal to be output to the first switching element 41 is set.

[0120] The target duty ratio (DUTY) of the first PWM signal is fixed at 100%, but in S420, in order to realize the soft start described above, the duty ratio is set so that it approaches the target duty ratio for each cycle of the first PWM signal.

[0121] Then, in the next S430, a first PWM signal is generated by pulse width modulation with the duty ratio set in S420, and output to the first switching element 41, thereby executing PWM signal output control, and the blade motor control process ends.

[0122] The period of the first PWM signal is the period of the first carrier frequency generated by dividing the reference clock in the first frequency divider 61, and in S430, a PWM signal with the duty ratio set in S420 is output in synchronization with this period.

[0123] 7, in the self-propelled motor control process, first, in S510, it is determined whether or not the self-propelled motor 32 is currently braking. If the self-propelled motor 32 is currently braking, the process proceeds to S540, where the self-propelled brake control process shown in FIG. 8 is executed, and the self-propelled motor control process ends.

[0124] Next, if it is determined in S510 that the self-propelled motor 32 is not currently being braked, the process proceeds to S520, where the duty ratio of the second PWM signal to be output to the second switching element 42 is set.

[0125] The target duty ratio (DUTY) of the second PWM signal is set in accordance with the speed command value from the speed adjustment dial 24. Then, in S520, in order to realize the soft start described above, the duty ratio is set so that it approaches the target duty ratio for each cycle of the second PWM signal.

[0126] Then, in the next S530, a second PWM signal is generated by pulse width modulation with the duty ratio set in S520, and output to the second switching element 42, thereby executing PWM signal output control, and the free-running motor control process ends.

[0127] The period of the second PWM signal is the period of the second carrier frequency generated by dividing the reference clock in the second frequency divider 62, and in S530, a PWM signal with the duty ratio set in S520 is output in synchronization with this period.

[0128] Next, the self-propelled brake control process executed in S200, S360 or S540, and the blade brake control process executed in S170, S390 or S440 will be described.

[0129] As shown in FIG. 8, in the free-running brake control process, first, in S610, the output of the second PWM signal to the second switching element 42 is stopped, and the second switching element 42 is set to the OFF state.

[0130] Then, in the following S620, a brake signal is output to the fifth switching element 46 for the self-propelled brake, turning on the fifth switching element 46. As a result, a brake current flows through the self-propelled motor 32, generating a braking force.

[0131] Next, in S630, a counter for measuring the free-running brake time is counted up to measure the time during which the brake signal is output to the fifth switching element 46 (hereinafter referred to as the free-running brake time).

[0132] Next, in S640, it is determined whether the self-propelled braking time measured in S630 has reached a preset braking time for determining when self-propelled braking has ended. This braking time is preset to the time required to stop the lawnmower 10 by applying the self-propelled brakes.

[0133] If it is determined in S640 that the self-propelled braking time has not reached the braking time for determining the end of the self-propelled braking, the self-propelled braking control process is terminated. On the other hand, if it is determined in S640 that the self-propelled braking time has reached the braking time for determining the end of self-propelled braking, the process proceeds to S650. In S650, the output of the brake signal to the fifth switching element 46 is stopped, and brake control of the self-propelled motor 32 is terminated. Then, in the following S660, the counter for counting the self-propelled braking time is cleared, and the self-propelled braking control process is terminated.

[0134] In this way, according to the self-propelled brake control process, when the self-propelled switch 22 is turned off and the drive of the self-propelled motor 32 is stopped, a braking force is generated in the self-propelled motor 32 for a fixed time period corresponding to the braking time for determining the end of the self-propelled brake. This ensures that the lawnmower 10 can be stopped reliably.

[0135] Next, as shown in FIG. 9, in the blade brake control process, first in S710, the output of the first PWM signal to the first switching element 41 is stopped, and the first switching element 41 is set to the OFF state.

[0136] Then, in the following S720, a brake signal is output to the fourth switching element 45 for the blade brake to turn on the fourth switching element 45. As a result, a brake current flows through the blade motor 31, and a braking force is generated.

[0137] Next, in S730, a counter for measuring the blade brake time is counted up to measure the time during which the brake signal is output to the fourth switching element 45 (hereinafter referred to as the blade brake time).

[0138] Then, in S740, it is determined whether the blade braking time measured in S730 has reached a preset braking time TA. If it is determined in S740 that the blade braking time has not reached the braking time TA, the blade brake control process is terminated. The braking time TA is set to the time required for the blade brake to reduce the rotation speed of the blade motor 31 and for the brake current to become sufficiently small.

[0139] On the other hand, if it is determined in S740 that the blade braking time has reached the braking time TA, the process proceeds to S750, where it is determined whether the blade switch 21 is in the ON state. If it is determined in S750 that the blade switch 21 is in the ON state, the process proceeds to S770, where the output of the brake signal to the fourth switching element 45 is stopped, thereby terminating the brake control of the blade motor 31. Then, in the following S780, the counter for measuring the blade brake time is cleared, and the blade brake control process is terminated.

[0140] If it is determined in S750 that the blade switch 21 is not in the ON state, the process proceeds to S760, where it is determined whether the blade brake time measured in S730 has reached a preset brake time TB. This brake time TB is a preset time required for the blade brake to stop the rotation of the blade motor 31. Therefore, the brake time TB is longer than the brake time TA.

[0141] If it is determined in S760 that the blade brake time has not reached the brake time TB, the blade brake control process is terminated. If it is determined in S760 that the blade brake time has reached the brake time TB, the brake control for the blade motor 31 is terminated in S770, and the blade brake time counter is cleared in S780, after which the blade brake control process is terminated.

[0142] In this way, in the blade brake control process, as shown in Figure 10, when the blade switch 21 is turned off and the drive of the blade motor 31 is stopped, a brake signal is output to the fourth switching element 45, causing the blade motor 31 to generate a braking force.

[0143] Then, when the blade brake time during which a brake signal is output to the fourth switching element 45 reaches the brake time TB, it is determined that the rotation of the blade motor 31 has stopped, the output of the brake signal is stopped, and the brake control of the blade motor 31 is terminated.

[0144] Furthermore, if the blade switch 21 is turned on before the blade brake time reaches the brake time TB, the output of the brake signal is stopped on the condition that the blade brake time reaches the brake time TA which allows the blade motor 31 to be driven again.

[0145] Therefore, even if the user stops operating the blade switch 21 while operating the blade switch 21 to perform lawn mowing work, the user can resume lawn mowing work by operating the blade switch 21 again before the rotation of the blade motor 31 stops.

[0146] In other words, in the blade brake control process, when a user is operating the blade switch 21 to perform lawn mowing work, if the user stops operating the blade switch 21, a braking force may be applied to the blade motor 31 until the rotation of the blade motor 31 stops. However, this would make the lawnmower 10 less convenient for an operator who wants to resume driving the blade motor 31 to perform lawn mowing work while the blade motor 31 is not stopped.

[0147] In contrast, in this embodiment, even if the blade motor 31 is not stopped by the brake control, as long as the brake control has been in place for the brake time TA or longer, the user can resume driving the blade motor 21 by operating the blade switch 21. Therefore, the lawnmower 10 of this embodiment allows for efficient lawn mowing, improving usability for the user.

[0148] <Effects> As described above, in the lawnmower 10 of this embodiment, the power supplied to the blade motor 31 and the self-propelled motor 32 is PWM controlled by the first and second PWM signals generated at different first and second carrier frequencies, respectively.

[0149] Therefore, although the blade motor 31 and the self-propelled motor 32 are driven and controlled by a common control circuit 50, the carrier frequency for PWM control of the power supplied to each motor can be set separately for each motor. Thus, the power supplied to the blade motor 31 and the self-propelled motor 32 can be PWM controlled at a carrier frequency suitable for each motor.

[0150] In other words, since the load applied to the blade motor 31 from the cutting blade 18 is large, the power supplied to the blade motor 31 is larger than that to the self-propelled motor 32, and the current flowing through the first switching element 41 is larger than the current flowing through the second switching element 42.

[0151] In contrast, according to this embodiment, the first carrier frequency when PWM-controlling the first switching element 41 can be set to a frequency lower than the second carrier frequency, thereby reducing the switching loss occurring in the first switching element 41 and preventing the first switching element 41 from becoming overheated.

[0152] Furthermore, since there is no need to increase the withstand voltage of the first switching element 41 in order to protect the first switching element 41 from overheating failure, an inexpensive element with a low withstand voltage can be used for the first switching element 41, thereby reducing the cost of the lawnmower 10.

[0153] On the other hand, the second carrier frequency can be set to a frequency higher than the first carrier frequency to suppress torque fluctuations in the self-propelled motor 32. Therefore, the lawnmower 10 of this embodiment can be driven stably at a desired speed.

[0154] Furthermore, in the lawnmower 10 of this embodiment, the first and second switching elements 41, 42 used to PWM control the power supplied to the blade motor 31 and the self-propelled motor 32 are configured so that their turn-off times are longer than their turn-on times.

[0155] Therefore, the high peak voltage generated when the first and second switching elements 41 and 42 are turned off can be suppressed, and the first and second switching elements 41 and 42 can be protected from the high voltage. [Other embodiments] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented in various modified forms.

[0156] In the above embodiment, the first carrier frequency when PWM controlling the power supplied to the blade motor 31 is described as 500 Hz, but the first carrier frequency may be set to a frequency within the range of 100 Hz to 1 kHz.

[0157] Furthermore, in the above embodiment, the second carrier frequency when PWM controlling the power supplied to the self-propelled motor 32 is described as being 8 kHz, but the second carrier frequency may be set to a frequency within the range of 8 kHz to 20 kHz.

[0158] In other words, when PWM-controlling the power supplied to the motor, if the carrier frequency is set within the frequency range of 1 kHz to 8 kHz, the switching noise generated by the on / off of the switch may be heard by people nearby, such as the user.

[0159] However, by setting the first carrier frequency and the second carrier frequency within the above frequency range, it is possible to prevent the switching noise generated when the power supplied to the motor is PWM controlled from being heard by users and causing discomfort.

[0160] In particular, the first carrier frequency may be set within a range of 300 Hz to 700 Hz, and the second carrier frequency may be set within a range of 8 kHz to 10 kHz.

[0161] In addition, in the above embodiment, the first carrier frequency and the second carrier frequency are described as being set by dividing the reference clock within the control circuit 50, but they may also be set by multiplying the reference clock.

[0162] Alternatively, an oscillator may be provided that generates a clock signal with a first carrier frequency or a second carrier frequency, and the output from this oscillator may be divided or multiplied to generate a clock signal with a carrier frequency different from that clock signal.

[0163] Next, in the above embodiment, the lawnmower 10 has been described, but the present invention can be applied in the same way to any other electric work machine equipped with multiple motors for different purposes, such as a rebar tying machine equipped with a motor for tying and a motor for feeding the tying wire. The present invention can also be applied in the same way to self-propelled work machines, such as hand trucks, cultivators, and floor cleaners.

[0164] In the above embodiment, both the blade motor 31 and the self-propelled motor 32 are described as brushed motors. However, one or both of the blade motor 31 and the self-propelled motor 32 may be brushless motors. In other words, the two motors of the present disclosure may be motors whose supplied power is PWM controlled.

[0165] In the above embodiments, multiple functions of one component may be realized by multiple components, or one function of one component may be realized by multiple components. Furthermore, 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, part of the configuration of the above embodiments may be omitted. Furthermore, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments.

[0166] In addition to the electric work machine, the present disclosure can also be realized in various forms, such as a system that includes an electric work machine as a component, a program for causing a computer to function as an electric work machine, a non-transient physical recording medium such as a semiconductor memory on which this program is recorded, and a control method. [Explanation of symbols]

[0167] 8...battery, 10...lawn mower, 16...drive wheel, 18...cutting blade, 21...blade switch, 22...self-propelled switch, 31...blade motor, 32...self-propelled motor, 41...first switching element, 42...second switching element, 47...first turn-off delay circuit, 48...second turn-off delay circuit, 50...control circuit, 61...first frequency dividing unit, 62...second frequency dividing unit, 65...first PWM generating unit, 66...second PWM generating unit, 68...motor drive control unit.

Claims

1. a first motor configured to drive a first driven object; a second motor configured to drive a second driven object; a first current path configured to connect a DC power source and the first motor; a second current path configured to connect the DC power supply and the second motor; a first switch provided on the first current path; a second switch provided on the second current path; a first carrier frequency setting unit configured to set a first carrier frequency when turning on and off the first switch to PWM control the power supplied to the first motor; a second carrier frequency setting unit configured to set a second carrier frequency, which is used when turning on and off the second switch to PWM control the power supplied to the second motor, to a frequency different from the first carrier frequency; a control unit configured to, when a drive command for the first motor is input, generate a first PWM signal at the first carrier frequency and output it to the first switch, thereby controlling power supplied to the first motor, and, when a drive command for the second motor is input, generate a second PWM signal at the second carrier frequency and output it to the second switch, thereby controlling power supplied to the second motor; Equipped with The first switch and / or the second switch are a turn-off delay circuit configured to suppress a high peak voltage generated when the first switch and / or the second switch is turned off by the first PWM signal or the second PWM signal by making a turn-off time during which the first switch changes from an on state to an off state longer than a turn-on time during which the second switch changes from an off state to an on state; An electric work machine equipped with:

2. The electric operating machine according to claim 1, The first carrier frequency is set to be lower than the second carrier frequency.

3. The electric operating machine according to claim 2, An electric work machine, wherein the first driven object is a blade, and the first motor is configured to rotate the blade.

4. The electric operating machine according to claim 3, An electric working machine, wherein the second driven object is a wheel that drives the electric working machine, and the second motor is configured to rotate the wheel.

5. The electric operating machine according to claim 4, The electric work machine, wherein the first carrier frequency is set within a range of 100 Hz to 1 kHz.

6. The electric operating machine according to claim 5, The electric work machine, wherein the first carrier frequency is set within a range of 300 Hz to 700 Hz.

7. The electric operating machine according to claim 5 or 6, The electric work machine, wherein the second carrier frequency is set within a range of 8 kHz to 20 kHz.

8. The electric operating machine according to claim 7, The electric work machine, wherein the second carrier frequency is set within a range of 8 kHz to 10 kHz.

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