Patent Publication Number: US-2022231576-A1

Title: Electric powered work machine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This international application claims the benefit of Japanese Patent Application No. 2019-102667 filed on May 31, 2019 with the Japan Patent Office, and the entire disclosure of Japanese Patent Application No. 2019-102667 is incorporated in this international application by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to an electric powered work machine including a brushless motor as a power source. 
     BACKGROUND ART 
     Patent Document 1 describes an electric powered work machine in which a power supply switching element to control power supply to an inverter circuit that drives a motor is connected in series to a motor driver and in which a connection point between the three-phase inverter circuit and the power supply switching element is pulled up to 5 V. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Patent No. 5798134 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the electric powered work machine described in Patent Document 1, a fault diagnosis of the power supply switching element is performed by measuring a voltage at the above-described connection point at the time when the power supply switching element is turned OFF. However, in the electric powered work machine described in Patent Document 1, it cannot be determined whether a short-circuit fault is occurring in switching elements constituting the inverter circuit. If the motor is driven in such a state that a short-circuit fault is occurring in the switching elements constituting the inverter circuit, a power-supply short-circuit current may flow, thus causing a risk of applying stress to a battery. 
     The present disclosure allows for detection of a short-circuit fault in switching elements, in an electric powered work machine. 
     Means for Solving the Problems 
     One aspect of the present disclosure is an electric powered work machine including a brushless motor as a power source, and the electric powered work machine includes an inverter circuit, a power-source-side switching element, a power-source-side resistor, at least one circuit-side resistor, and a fault determiner. 
     The inverter circuit includes semiconductor switching elements arranged on corresponding first current paths between a direct-current power source and the brushless motor, and is configured to control current flow to the brushless motor via the semiconductor switching elements. 
     The power-source-side switching element is arranged on a second current path between the direct-current power source and the inverter circuit. 
     The power-source-side resistor is connected in parallel to the power-source-side switching element. 
     The at least one circuit-side resistor is connected to the inverter circuit in such a state that electrical conduction is possible between a positive side and a negative side of the direct-current power source in the inverter circuit in a case where all of the semiconductor switching elements in the inverter circuit are OFF. 
     The fault determiner is configured to turn OFF the power-source-side switching element and all of the semiconductor switching elements and to determine whether at least one of “the semiconductor switching elements and the power-source-side switching element” is short-circuited based on a connection-point voltage at a connection point between the power-source-side switching element and the inverter circuit. 
     In the thus-configured electric powered work machine of the present disclosure, the at least one circuit-side resistor is connected to the inverter circuit in such a state that electrical conduction is possible between the positive side and the negative side of the direct-current power source in the inverter circuit. Thus, if at least one of the semiconductor switching elements is short-circuited in the inverter circuit, the connection-point voltage changes. On the other hand, the power-source-side resistor is connected in parallel to the power-source-side switching element. Thus, if the power-source-side switching element is short-circuited, the connection-point voltage changes. Further, the connection-point voltage differs between the case in which at least one of the semiconductor switching elements is short-circuited and the case in which the power-source-side switching element is short-circuited. 
     This makes it possible, in the electric powered work machine of the present disclosure, to detect whether at least one of the semiconductor switching elements is short-circuited and whether the power-source-side switching element is short-circuited. 
     In one aspect of the present disclosure, specifically, the at least one circuit-side resistor may be connected in parallel to at least one of high-side switching elements, and may be connected in parallel to at least one of low-side switching elements. From among the semiconductor switching elements, the high-side switching elements are the semiconductor switching elements arranged on the corresponding first current paths between the brushless motor and a positive electrode of the direct-current power source. The low-side switching elements are the semiconductor switching elements arranged on the corresponding first current paths between the brushless motor and a negative electrode of the direct-current power source. 
     In one aspect of the present disclosure, the fault determiner may be configured to determine that at least one of the semiconductor switching elements is short-circuited if the connection-point voltage is smaller than or equal to a fault determination voltage, which is set in advance so as to indicate the connection-point voltage at a time of occurrence of a short-circuit fault in one of the semiconductor switching elements. This makes it possible, in the electric powered work machine of the present disclosure, to determine whether at least one of the semiconductor switching elements is short-circuited by a simple method in which the connection-point voltage is compared with the fault determination voltage. 
     In one aspect of the present disclosure, the fault determiner may be configured to determine that the power-source-side switching element is short-circuited if the connection-point voltage is larger than or equal to a power-source-side fault determination voltage, which is set in advance so as to indicate the connection-point voltage at a time of occurrence of a short-circuit fault in the power-source-side switching element. This makes it possible, in the electric powered work machine of the present disclosure, to determine whether the power-source-side switching element is short-circuited by a simple method in which the connection-point voltage is compared with the power-source-side fault determination voltage. 
     In one aspect of the present disclosure, a short-circuit notifier and a power-supply interrupter may be provided. The short-circuit notifier is configured, if the fault determiner determines that at least one of “the semiconductor switching elements and the power-source-side switching element” is short-circuited, to notify accordingly. The power-supply interrupter is configured to turn OFF all of the semiconductor switching elements and the power-source-side switching element if an operation switch to be operated to activate the electric powered work machine is in an ON state in a case where the fault determiner determines that at least one of “the semiconductor switching elements and the power-source-side switching element” is short-circuited. This makes it possible, in the electric powered work machine of the present disclosure, when at least one of “the semiconductor switching elements and the power-source-side switching element” is short-circuited, to make a user of the electric powered work machine aware of such a situation. In addition, in the electric powered work machine of the present disclosure, when at least one of “the semiconductor switching elements and the power-source-side switching element” is short-circuited, it is possible to inhibit occurrence of a situation in which a short-circuit current flows between the positive electrode and the negative electrode of the direct-current power source. 
     In one aspect of the present disclosure, a parallel switching element and an at-determination controller may be provided. The parallel switching element is connected in series to the power-source-side resistor and also connected in parallel to the power-source-side switching element. The at-determination controller is configured to turn ON the parallel switching element at a start of fault determination by the fault determiner. This makes it possible, in the electric powered work machine of the present disclosure, not to allow a current to flow through the power-source-side resistor except when the fault determiner performs the fault determination, thus reducing power consumption in the electric powered work machine of the present disclosure. 
     In one aspect of the present disclosure, resistance values of the power-source-side resistor and of the at least one circuit-side resistor may be equal to each other. This makes it possible, in the electric powered work machine of the present disclosure, to facilitate calculation of the connection-point voltage in the case where at least one of “the semiconductor switching elements and the power-source-side switching element” is short-circuited. 
     In one aspect of the present disclosure, a prohibitor configured to prohibit the fault determiner from performing the fault determination during rotation of the brushless motor may be provided. This makes it possible, in the electric powered work machine of the present disclosure, to inhibit occurrence of a situation in which the fault determiner performs the fault determination when an induced voltage resulting from rotation of the brushless motor is affecting the connection-point voltage, thus improving accuracy of the fault determination by the fault determiner. 
     In one aspect of the present disclosure, the fault determination voltage may be set to a value between: a normal-state lowest value, which is a lowest value of the connection-point voltage in a case where all of the semiconductor switching elements and the power-source-side switching element are each in a normal state; and a value of the connection-point voltage in a case where one of the semiconductor switching elements is short-circuited. This makes it possible, in the electric powered work machine of the present disclosure, to inhibit occurrence of a situation in which it is determined that at least one of the semiconductor switching elements is short-circuited despite the fact that none of the semiconductor switching elements is short-circuited, thus improving accuracy of the fault determination by the fault determiner. 
     In one aspect of the present disclosure, the normal-state lowest value may be a value in a case where a temperature of a negative-side element is higher than a temperature of a positive-side element. From among the inverter circuit and the power-source-side switching element that are elements constituting the electric powered work machine, the positive-side element is the element arranged closer to the positive electrode of the direct-current power source, on a current path from the positive electrode of the direct-current power source to the negative electrode of the direct-current power source. The negative-side element is the element arranged closer to the negative electrode of the direct-current power source. This makes it possible, in the electric powered work machine of the present disclosure, to inhibit occurrence of the situation in which it is determined that at least one of the semiconductor switching elements is short-circuited despite the fact that none of the semiconductor switching elements is short-circuited, thus further improving accuracy of the fault determination by the fault determiner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing an overall configuration of an electric powered work machine of a first embodiment. 
         FIG. 2  is a block diagram showing an electrical configuration of the electric powered work machine of the first embodiment. 
         FIG. 3  is a flowchart showing a work machine control process. 
         FIG. 4  is a flowchart showing a fault diagnosis process of the first embodiment. 
         FIG. 5  is a flowchart showing a restart prevention process. 
         FIG. 6  is a flowchart showing a power-saving mode process. 
         FIG. 7  is a flowchart showing a motor control process. 
         FIG. 8  is a perspective view showing an electrical configuration of an electric powered work machine of a second embodiment. 
         FIG. 9  is a flowchart showing a fault diagnosis process of the second embodiment. 
         FIG. 10  is a perspective view showing an electrical configuration of an electric powered work machine of a third embodiment. 
         FIG. 11  is a diagram showing an equivalent circuit of a motor driver of the third embodiment. 
         FIG. 12  is a flowchart showing a fault diagnosis process of the third embodiment. 
         FIG. 13  is a graph showing a relationship between a connection-point voltage and a battery voltage. 
     
    
    
     EXPLANATION OF REFERENCE NUMERALS 
       1  . . . electric powered work machine,  11  . . . motor,  12  . . . battery,  21  . . . motor driver,  23  . . . control circuit, Pc . . . connection point, Q 1 -Q 7  . . . switching element, R 1 -R 7 , R 21  . . . resistor 
     MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     A first embodiment of the present disclosure will be described below with reference to the drawings. 
     As shown in  FIG. 1 , an electric powered work machine  1  of the present embodiment is a circular saw used mainly for the purpose of cutting a workpiece. 
     The electric powered work machine  1  includes a base  2  and a main body  3 . The base  2  is a substantially rectangularly-shaped member that is in contact with an upper face of the workpiece to be cut when a workpiece cutting operation is performed. The main body  3  is arranged on an upper-face side of the base  2 . 
     The main body  3  includes a saw blade  4  having a circular shape, a saw blade case  5 , and a cover  6 . The saw blade  4  is arranged on a right side of the main body  3  with respect to a cutting proceeding direction. The saw blade case  5  is formed so as to accommodate therein and cover a circumference of the saw blade  4  in a range of a substantially upper half thereof. 
     The cover  6  is formed so as to cover the circumference of the saw blade  4  in a range of a substantially lower half thereof. The cover  6  is openable and closable, and  FIG. 1  shows a state in which the cover  6  is closed. By moving the electric powered work machine  1  in the cutting proceeding direction when cutting the workpiece, the cover  6  rotates about a center of rotation of the saw blade  4  in a counterclockwise direction viewed in  FIG. 1 , thus being opened gradually. This causes the saw blade  4  to be exposed, and the exposed part thereof cuts into the workpiece. 
     Arranged on a left side of the main body  3  is a motor case  7  having a substantially cylindrical shape. The motor case  7  accommodates therein a motor  11 , which is a drive source for the electric powered work machine  1 . The motor  11  is not shown in  FIG. 1  but shown in  FIG. 2 . 
     A not-shown gear mechanism is accommodated between the motor case  7  and the saw blade  4 . Upon rotation of the motor  11 , the rotation is transmitted to the saw blade  4  via the gear mechanism, thus rotating the saw blade  4 . 
     Arranged on an upper side of the main body  3  is a handle  8  to be gripped by a user of the electric powered work machine  1 . The handle  8  is attached on the upper side of the main body  3  so as to have an arch-like shape. Specifically, one end of the handle  8  is fixed on a rear end side of the main body  3  with respect to the cutting proceeding direction, and the other end is fixed on a more forward side with respect to the cutting proceeding direction than the rear end side. 
     The handle  8  has a trigger switch  9  mounted thereon. The user of the electric powered work machine  1  can perform a pulling operation and a releasing operation to the trigger switch  9  while gripping the handle  8 . The user of the electric powered work machine  1  can pull the trigger switch  9  in such a state that a lock-off lever protruding in left and right directions of the handle  8  in the vicinity of the trigger switch  9  is operated. Specifically, the user of the electric powered work machine  1  is enabled to pull the trigger switch  9  by pressing the lock-off lever from the left side or from the right side. Hereinafter, a state in which the pulling operation is performed to the trigger switch  9  is referred to as an ON state, and a state in which the releasing operation is performed to the trigger switch  9  is referred to as an OFF state. 
     A battery pack  10  containing therein a battery  12  that can be repeatedly charged is attached to a rear end of the main body  3  in an attachable and detachable manner. When the pulling operation is performed to the trigger switch  9  with the battery pack  10  attached to the main body  3 , electric power of the battery  12  causes the motor  11  within the main body  3  to rotate. The battery  12  is not shown in  FIG. 1  but shown in  FIG. 2 . 
     As shown in  FIG. 2 , the electric powered work machine  1  includes a control unit  20 . The control unit  20  includes a power-supply terminal  20   a,  a ground terminal  20   b,  and a communication terminal  20   c.  Upon attachment of the battery pack  10  to the main body  3 , the power-supply terminal  20   a,  the ground terminal  20   b,  and the communication terminal  20   c  are respectively connected to a power-supply terminal  10   a,  a ground terminal  10   b,  and a communication terminal  10   c  of the battery pack  10 . 
     The power-supply terminal  10   a  of the battery pack  10  is connected to a positive electrode of the battery  12 . The ground terminal  10   b  of the battery pack  10  is connected to a negative electrode of the battery  12 . The battery pack  10  outputs a discharge permission signal or a discharge prohibition signal through the communication terminal  10   c.    
     The control unit  20  receives power supply from the battery  12  within the battery pack  10 , and controls drive of the motor  11 . In the present embodiment, the motor  11  is a three-phase brushless motor. 
     The control unit  20  includes a motor driver  21 , a gate driver  22 , a control circuit  23 , and a regulator  24 . 
     The motor driver  21  is a circuit that receives power supply from the battery  12  to flow a current through windings of respective phases of the motor  11 . In the present embodiment, the motor driver  21  is configured as a three-phase full-bridge circuit including six switching elements Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , and Q 6 . In the present embodiment, the switching elements Q 1  to Q 6  are MOSFETs. 
     In the motor driver  21 , the switching elements Q 1 , Q 3 , and Q 5  are arranged on corresponding power-supply lines that connect, respectively, terminals U, V, and W of the motor  11  and the positive electrode of the battery  12 . The switching elements Q 2 , Q 4 , and Q 6  are arranged on corresponding ground lines that connect, respectively, the terminals U, V, and W of the motor  11  and the negative electrode of the battery  12 . 
     The motor driver  21  includes resistors R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 . The resistors R 1 , R 2 , R 3 , R 4 , R 5 , and R 6  are respectively connected in parallel to the switching elements Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , and Q 6 . Resistance values of the resistors R 1 , R 2 , R 3 , R 4 , R 5 , and R 6  are equal to one another. 
     The gate driver  22  is a circuit that turns ON or OFF each of the switching elements Q 1  to Q 6  within the motor driver  21  in accordance with a control signal outputted from the control circuit  23  to thereby flow a current through the windings of respective phases of the motor  11 , thus rotating the motor  11 . 
     The control circuit  23  is configured mainly with a microcomputer including a CPU  23   a,  a ROM  23   b,  a RAM  23   c,  and so on. Various functions of the microcomputer are performed through execution, by the CPU  23   a,  of a program stored in a non-transitory tangible storage medium. In this example, the ROM  23   b  corresponds to the non-transitory tangible storage medium storing the program. Execution of this program causes processes corresponding to the program to be carried out. Part or all of the functions performed by the CPU  23   a  may be configured with hardware, such as one or more than one IC. The number of the microcomputer constituting the control circuit  23  may be one or more than one. 
     The regulator  24  receives power supply from the battery  12  via the power-supply terminal  20   a,  and generates a voltage of 5 V for causing the control circuit  23  to operate. 
     The control unit  20  includes switching elements Q 7 , Q 8 , and Q 9 , a resistor R 7 , and a voltage-dividing circuit  31 . In the present embodiment, the switching elements Q 7  to Q 9  are MOSFETs. 
     A drain of the switching element Q 7  is connected to the power-supply terminal  20   a,  a source thereof is connected to the motor driver  21 , and a gate thereof is connected to the control circuit  23 . The switching element Q 8  is connected in parallel to the switching element Q 7 . One end of the resistor R 7  is connected to a drain of the switching element Q 8 , and the other end is connected to the source of the switching element Q 7 . A resistance value of the resistor R 7  is equal to the resistance values of the resistors R 1  to R 6 . 
     The voltage-dividing circuit  31  outputs, to the control circuit  23 , a divided voltage obtained by dividing a connection-point voltage at a connection point Pc between the switching element Q 7  and the motor driver  21 . 
     The voltage of 5 V from the regulator  24  is applied to a source of the switching element Q 9 , and a drain of the switching element Q 9  is connected to the motor driver  21  and to the gate driver  22 . A gate of the switching element Q 9  is connected to the control circuit  23 , and the switching element Q 9  is turned ON or OFF in accordance with a voltage level of a control signal from the control circuit  23 . When the switching element Q 9  is ON, the voltage of 5 V from the regulator  24  is supplied to the motor driver  21  and to the gate driver  22  as a power-supply voltage Vcc. When the switching element Q 9  is OFF, supply of the power-supply voltage Vcc to the motor driver  21  and to the gate driver  22  is interrupted. 
     The control unit  20  includes a switch  32  and a light emitting diode  33 . The voltage of 5 V from the regulator  24  is applied to one end of the switch  32  via a resistor R 11 , and the other end of the switch  32  is grounded. The switch  32  is turned ON upon the pulling operation to the trigger switch  9  by the user of the electric powered work machine  1 , and is turned OFF upon the releasing operation to the trigger switch  9  by the user of the electric powered work machine  1 . The one end of the switch  32  is connected to the control circuit  23 , and a voltage at the one end of the switch  32  is detected by the control circuit  23 . 
     An anode of the light emitting diode  33  is connected to the control circuit  23 , and a cathode thereof is grounded. The light emitting diode  33  emits light when an error display signal is outputted from the control circuit  23 . 
     Further, the electric powered work machine  1  includes a rotation sensor  13 . The rotation sensor  13  detects a rotational position and a rotational speed of the motor  11 , and outputs a detection signal indicating the result of detection to the control circuit  23 . 
     Next, an explanation will be given of procedures of a work machine control process performed by the CPU  23   a  in the control circuit  23 . The work machine control process is a process started after the voltage of 5 V is supplied to the control circuit  23  to start the control circuit  23 . 
     When performing the work machine control process, as shown in  FIG. 3 , the CPU  23   a  first performs an initial setting in S 10 . Specifically, the CPU  23   a  sets various parameters used in the work machine control process to initial values, and switches the switching element Q 9  from OFF to ON. 
     Subsequently, in S 20 , the CPU  23   a  performs a fault diagnosis process to be described below. Then, in S 30 , the CPU  23   a  determines whether a fault flag F 1  provided in the RAM  23   c  is set. In the descriptions below, setting a flag refers to setting a value of the flag to 1, and clearing a flag refers to setting a value of the flag to 0. 
     Here, if the fault flag F 1  is not set, the CPU  23   a  performs, in S 40 , a restart prevention process to be described below. Then, in S 50 , the CPU  23   a  performs a power-saving mode process to be described below. Further, in S 60 , the CPU  23   a  performs a motor control process to be described below, and shifts to S 50 . 
     If the fault flag F 1  is set in S 30 , the CPU  23   a  outputs, in S 70 , the error display signal to the light emitting diode  33  to cause the light emitting diode  33  to emit light. In this way, the electric powered work machine  1  displays a notification that a fault has occurred in the electric powered work machine  1 . Subsequently, in S 80 , the CPU  23   a  turns OFF the switching elements Q 1  to Q 7 , and ends the work machine control process. 
     Next, an explanation will be given of procedures of the fault diagnosis process performed by the CPU  23   a  in S 20 . 
     When performing the fault diagnosis process, as shown in  FIG. 4 , the CPU  23   a  first turns OFF the switching elements Q 1  to Q 7  in S 110 . 
     Then, in S 120 , the CPU  23   a  determines whether the motor  11  is inertially rotating based on the detection signal from the rotation sensor  13 . Here, if the motor  11  is inertially rotating, the CPU  23   a  ends the fault diagnosis process. By contrast, if the motor  11  is not inertially rotating, the CPU  23   a  turns ON the switching element Q 8  in S 130 . 
     Then, in S 140 , the CPU  23   a  measures the connection-point voltage based on the divided voltage from the voltage-dividing circuit  31 , and stores the value of the measured voltage in a connection-point voltage Vc provided in the RAM  23   c.    
     Further, in S 150 , the CPU  23   a  stores the value stored in the connection-point voltage Vc in a connection-point voltage Vc 1  provided in the RAM  23   c.    
     In S 160 , the CPU  23   a  determines whether the connection-point voltage Vc is larger than 0 V. If an arm short-circuit fault is occurring in the motor driver  21 , the connection-point voltage Vc becomes 0 V. By contrast, if an arm short-circuit fault is not occurring in the motor driver  21  and also the switching elements Q 1  to Q 6  are turned OFF, the connection-point voltage Vc does not become 0 V even when the switching element Q 7  is turned ON. 
     Here, if the connection-point voltage Vc is smaller than or equal to 0 V, the CPU  23   a  shifts to  5220 . By contrast, if the connection-point voltage Vc is larger than 0 V, the CPU  23   a  turns ON the switching element Q 7  in S 170 . Then, in S 180 , the CPU  23   a  measures the connection-point voltage based on the divided voltage from the voltage-dividing circuit  31 , and stores the value of the measured voltage in the connection-point voltage Vc. 
     Further, in S 190 , the CPU  23   a  stores the value stored in the connection-point voltage Vc in a battery voltage Vb provided in the RAM  23   c.  After that, the CPU  23   a  turns OFF the switching element Q 7  in S 200 . 
     Then, in S 210 , the CPU  23   a  determines whether the value stored in the connection-point voltage Vc 1  is larger than one third of the value stored in the battery voltage Vb and also smaller than the value stored in the battery voltage Vb. That is, the CPU  23   a  determines whether (1/3)×Vb&lt;Vc 1 &lt;Vb is satisfied. 
     Given that drain-to-source resistances of the switching elements Q 1  to Q 7  at the time when the switching elements Q 1  to Q 7  are OFF are sufficiently larger than resistances of the resistors R 1  to R 7  and can be ignored, the connection-point voltage in a case of no occurrence of short circuit in the switching elements Q 1  to Q 7  is calculated to be (2/5)×Vb. The connection-point voltage in a case of occurrence of short circuit in any one of the switching elements Q 1  to Q 6  is calculated to be (1/3)×Vb. The connection-point voltage in a case of occurrence of short circuit in the switching element Q 7  is calculated to be Vb. Accordingly, if the connection-point voltage is equal to Vb or is smaller than or equal to (1/3)×Vb, it can be determined that short circuit is occurring in at least one of the switching elements Q 1  to Q 7 . 
     Here, if the value stored in the connection-point voltage Vc 1  is smaller than or equal to one third of the value stored in the battery voltage Vb, or is larger than or equal to the value stored in the battery voltage Vb, the CPU  23   a  shifts to S 220 . 
     Upon shifting to S 220 , the CPU  23   a  sets the fault flag F 1 , and shifts to S 230 . 
     In S 210 , if the value stored in the connection-point voltage Vc 1  is larger than one third of the value stored in the battery voltage Vb and also smaller than the value stored in the battery voltage Vb, the CPU  23   a  shifts to S 230 . 
     Upon shifting to S 230 , the CPU  23   a  turns OFF the switching element Q 8 , and ends the fault diagnosis process. 
     Next, an explanation will be given of procedures of the restart prevention process performed by the CPU  23   a  in S 40 . 
     When performing the restart prevention process, as shown in  FIG. 5 , the CPU  23   a  first turns OFF the switching elements Q 1  to Q 7  in S 310 . 
     Then, in S 320 , the CPU  23   a  determines whether the trigger switch  9  is in the OFF state. Here, if the trigger switch  9  is in the ON state, the CPU  23   a  repeats the procedure of S 320 , thus waiting until the trigger switch  9  enters the OFF state. 
     Upon the trigger switch  9  entering the OFF state, the CPU  23   a  ends the restart prevention process. 
     Next, an explanation will be given of procedures of the power-saving mode process performed by the CPU  23   a  in S 50 . 
     When performing the power-saving mode process, as shown in  FIG. 6 , the CPU  23   a  first determines, in S 410 , whether the OFF state of the trigger switch  9  has continued for a mode determination period set in advance. Here, if the OFF state of the trigger switch  9  has not continued for the mode determination period, the CPU  23   a  ends the power-saving mode process. 
     By contrast, if the OFF state of the trigger switch  9  has continued for the mode determination period, the CPU  23   a  shifts to a sleep mode in S 420 . Upon shifting to the sleep mode, the CPU  23   a  turns OFF the switching element Q 9 . This results in interruption of supply of the power-supply voltage Vcc to the motor driver  21  and to the gate driver  22 . 
     Then, in S 430 , the CPU  23   a  determines whether the trigger switch  9  is in the ON state. Here, if the trigger switch  9  is in the OFF state, the CPU  23   a    
      repeats the procedure of S 430 , thus waiting until the trigger switch  9  enters the ON state. 
     Upon the trigger switch  9  entering the ON state, the CPU  23   a  wakes up and shifts to a normal operation mode in S 440 , and ends the power-saving mode process. Upon shifting to the normal operation mode, the CPU  23   a  turns ON the switching element Q 9 . This results in restart of supply of the power-supply voltage Vcc to the motor driver  21  and to the gate driver  22 . 
     Next, an explanation will be given of procedures of the motor control process performed by the CPU  23   a  in S 60 . 
     When performing the motor control process, as shown in  FIG. 7 , the CPU  23   a  first determines, in S 510 , whether the trigger switch  9  is in the ON state. Here, if the trigger switch  9  is in the OFF state, the CPU  23   a  shifts to S 540 . By contrast, if the trigger switch  9  is in the ON state, the CPU  23   a  determines, in S 520 , whether the battery  12  is in a discharge permitted state. Specifically, the CPU  23   a  determines that the battery  12  is in the discharge permitted state when detecting the discharge permission signal from the battery pack  10 . 
     Here, if the battery  12  is in the discharge permitted state, the CPU  23   a  performs a motor drive process for driving the motor  11  in S 530 , and shifts to S 510 . By contrast, if the battery  12  is not in the discharge permitted state, the CPU  23   a  shifts to S 540 . 
     Upon shifting to S 540 , the CPU  23   a  performs a motor stop process for stopping drive of the motor  11 , and ends the motor control process. 
     The thus-configured electric powered work machine  1  includes the motor  11  as a power source, and further includes the motor driver  21 , the switching element Q 7 , the resistor R 7 , the resistors R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 , and the control circuit  23 . The motor  11  is a brushless motor. 
     The motor driver  21  includes the six switching elements Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , and Q 6 , which are each arranged on the corresponding one of six first current paths between the battery  12  and the motor  11 , and controls current flow to the motor  11  via the switching elements Q 1  to Q 6 . 
     The first current path on which the switching element Q 1  is arranged is a current path between the positive electrode of the battery  12  and the terminal U of the motor  11 . The first current path on which the switching element Q 3  is arranged is a current path between the positive electrode of the battery  12  and the terminal V of the motor  11 . The first current path on which the switching element Q 5  is arranged is a current path between the positive electrode of the battery  12  and the terminal W of the motor  11 . The first current path on which the switching element Q 2  is arranged is a current path between the negative electrode of the battery  12  and the terminal U of the motor  11 . The first current path on which the switching element Q 4  is arranged is a current path between the negative electrode of the battery  12  and the terminal V of the motor  11 . The first current path on which the switching element Q 6  is arranged is a current path between the negative electrode of the battery  12  and the terminal W of the motor  11 . 
     The switching element Q 7  is arranged on a second current path between the battery  12  and the motor driver  21 . The resistor R 7  is connected in parallel to the switching element Q 7 . 
     The resistors R 1 , R 2 , R 3 , R 4 , R 5 , and R 6  are connected to the motor driver  21  in such a state that electrical conduction is possible between a positive side and a negative side of the battery  12  in the motor driver  21  in a case where all of the switching elements Q 1  to Q 6  in the motor driver  21  are OFF. 
     The control circuit  23  turns OFF the switching element Q 7  and all of the switching elements Q 1  to Q 6 , and determines whether at least one of “the switching elements Q 1  to Q 6  and the switching element Q 7 ” is short-circuited based on the connection-point voltage at the connection point Pc between the switching element Q 7  and the motor driver  21 . 
     Specifically, the resistors R 1 , R 3 , and R 5  are respectively connected in parallel to the switching elements Q 1 , Q 3 , and Q 5 , and the resistors R 2 , R 4 , and R 6  are respectively connected in parallel to the switching elements Q 2 , Q 4 , and Q 6 . From among the switching elements Q 1  to Q 6 , the switching elements Q 1 , Q 3 , and Q 5  are arranged on the first current paths between the motor  11  and the positive electrode of the battery  12 . From among the switching elements Q 1  to Q 6 , the switching elements Q 2 , Q 4 , and Q 6  are arranged on the first current paths between the motor  11  and the negative electrode of the battery  12 . 
     In this way, in the electric powered work machine  1 , the resistors R 1  to R 6  are connected to the motor driver  21  in such a state that electrical conduction is possible between the positive side and the negative side of the battery  12  in the motor driver  21 . Thus, if at least one of the switching elements Q 1  to Q 6  is short-circuited in the motor driver  21 , the connection-point voltage changes. On the other hand, the resistor R 7  is connected in parallel to the switching element Q 7 . Thus, if the switching element Q 7  is short-circuited, the connection-point voltage changes. Further, the connection-point voltage differs between the case in which at least one of the switching elements Q 1  to Q 6  is short-circuited and the case in which the switching element Q 7  is short-circuited. 
     This makes it possible, in the electric powered work machine  1 , to detect whether at least one of the switching elements Q 1  to Q 6  is short-circuited and whether the switching element Q 7  is short-circuited. 
     The control circuit  23  determines that at least one of the switching elements Q 1  to Q 6  is short-circuited when the connection-point voltage is smaller than or equal to a fault determination voltage ((1/3)×Vb in the present embodiment), which is set in advance so as to indicate the connection-point voltage at the time of occurrence of a short-circuit fault in one of the switching elements Q 1  to Q 6 . This makes it possible, in the electric powered work machine  1 , to determine whether at least one of the switching elements Q 1  to Q 6  is short-circuited by a simple method in which the connection-point voltage is compared with the fault determination voltage. 
     The control circuit  23  determines that the switching element Q 7  is short-circuited when the connection-point voltage is larger than or equal to a power-source-side fault determination voltage (Vb in the present embodiment), which is set in advance so as to indicate the connection-point voltage at the time of occurrence of a short-circuit fault in the switching element Q 7 . This makes it possible, in the electric powered work machine  1 , to determine whether the switching element Q 7  is short-circuited by a simple method in which the connection-point voltage is compared with the power-source-side fault determination voltage. 
     When the control circuit  23  determines that at least one of “the switching elements Q 1  to Q 6  and the switching element Q 7 ” is short-circuited, the light emitting diode  33  in the electric powered work machine  1  notifies accordingly. In the cases of determining that at least one of “the switching elements Q 1  to Q 6  and the switching element Q 7 ” is short-circuited, if the trigger switch  9  to be operated to activate the electric powered work machine  1  is in the ON state, the control circuit  23  turns OFF all of the switching elements Q 1  to Q 6  and the switching element Q 7 . This makes it possible, in the electric powered work machine  1 , when at least one of “the switching elements Q 1  to Q 6  and the switching element Q 7 ” is short-circuited, to make the user of the electric powered work machine  1  aware of such a situation. In addition, in the electric powered work machine  1 , when at least one of “the switching elements Q 1  to Q 6  and the switching element Q 7 ” is short-circuited, it is possible to inhibit occurrence of a situation in which a short-circuit current flows between the positive electrode and the negative electrode of the battery  12 . 
     The switching element Q 8  is connected in series to the resistor R 7  and also connected in parallel to the switching element Q 7 . When the control circuit  23  starts a fault determination, the control circuit  23  turns ON the switching element Q 8 . This makes it possible, in the electric powered work machine  1 , not to allow a current to flow through the resistor R 7  except when the control circuit  23  performs the fault determination, thus reducing power consumption in the electric powered work machine  1 . 
     The resistance value of the resistor R 7  and the resistance value of each of the resistors R 1  to R 6  are equal to each other. This makes it possible, in the electric powered work machine  1 , to facilitate calculation of the connection-point voltage in the case where at least one of “the switching elements Q 1  to Q 6  and the switching element Q 7 ” is short-circuited. 
     The control circuit  23  prohibits the control circuit  23  from performing the fault determination when the motor  11  is rotating. This makes it possible, in the electric powered work machine  1 , to inhibit occurrence of a situation in which the control circuit  23  performs the fault determination when an induced voltage resulting from the inertial rotation of the motor  11  is affecting the connection-point voltage, thus improving accuracy of the fault determination by the control circuit  23 . 
     In the above-described embodiment, the motor  11  corresponds to a brushless motor, the motor driver  21  corresponds to an inverter circuit, the switching elements Q 1  to Q 6  correspond to semiconductor switching elements, and the switching element Q 7  corresponds to a power-source-side switching element. 
     The battery  12  corresponds to a direct-current power source, the resistor R 7  corresponds to a power-source-side resistor, the resistors R 1  to R 6  correspond to at least one circuit-side resistor, and S 110  to S 230  correspond to procedures as a fault determiner. 
     The switching elements Q 1 , Q 3 , and Q 5  correspond to high-side switching elements, the switching elements Q 2 , Q 4 , and Q 6  correspond to low-side switching elements, the light emitting diode  33  corresponds to a short-circuit notifier, and S 80  corresponds to a procedure as a power-supply interrupter. 
     The switching element Q 8  corresponds to a parallel switching element, S 130  corresponds to a procedure as an at-determination controller, and S 120  corresponds to a procedure as a prohibitor. 
     Second Embodiment 
     A second embodiment of the present disclosure will be described below with reference to the drawings. In the second embodiment, differences from the first embodiment will be described. The same reference numerals are assigned to common configurations. 
     The electric powered work machine  1  of the second embodiment differs from that of the first embodiment in that the electrical configuration of the electric powered work machine  1  is changed and in that the fault diagnosis process is changed. 
     As shown in  FIG. 8 , the electric powered work machine  1  of the second embodiment is different from that of the first embodiment in that the resistors R 1 , R 2 , R 3 , R 4 , R 5 , and R 6  are omitted and in that a resistor R 21  is added. 
     The resistor R 21  is connected in parallel to the motor driver  21 . Specifically, one end of the resistor R 21  is connected to the connection point Pc, and the other end of the resistor R 21  is grounded. 
     Here, an explanation will be given of a method for detecting a short-circuit fault in the switching elements Q 1  to Q 7  in the second embodiment. 
     First, assume that drain-to-source resistances of the switching elements Q 1  to Q 7  at the time when the switching elements Q 1  to Q 7  are OFF are sufficiently larger than resistances of the resistor R 7  and the resistor R 21 , and can be ignored. 
     Also, assume that resistance in each winding of the motor  11  is sufficiently smaller than those of the resistor R 7  and the resistor R 21 , and can be ignored. In such a case, the motor driver  21  can be deemed to equivalently have a wiring in which sources of the switching elements Q 1 , Q 3 , and Q 5  are connected to drains of the switching elements Q 2 , Q 4 , and Q 6 , respectively, as shown with a broken line L 1  and points P 1 , P 2 , and P 3 . 
     Further, assume that the resistor R 7  and the resistor R 21  have the same resistance value. In such conditions, a connection-point voltage at the time when the switching elements Q 1  to Q 7  are OFF (hereinafter referred to as an OFF-state connection-point voltage) is calculated to be (1/2)×Vb, if no short circuit is occurring in the switching elements Q 1  to Q 7 . 
     The OFF-state connection-point voltage in a case where short circuit is occurring in the switching element Q 7  is calculated to be Vb. 
     The connection-point voltage in a case where short circuit is occurring in at least one of the switching elements Q 1 , Q 3 , and Q 5  and also where at least one of the switching elements Q 2 , Q 4 , and Q 6  is turned ON is calculated to be 0 V. 
     The connection-point voltage in a case where short circuit is occurring in at least one of the switching elements Q 2 , Q 4 , and Q 6  and also where at least one of the switching elements Q 1 , Q 3 , and Q 5  is turned ON is calculated to be 0 V. 
     Accordingly, if the connection-point voltage is equal to Vb or 0 V, it can be determined that short circuit is occurring in at least one of the switching elements Q 1  to Q 7 . 
     Next, an explanation will be given of procedures of a fault diagnosis process of the second embodiment. 
     As shown in  FIG. 9 , the fault diagnosis process of the second embodiment differs from that of the first embodiment in that S 210  is omitted and in that S 610  to S 690  are added. 
     Specifically, upon completion of the procedure of S 200 , the CPU  23   a  determines, in S 610 , whether the value stored in the connection-point voltage Vc 1  is smaller than the value stored in the battery voltage Vb. Here, if the value stored in the connection-point voltage Vc 1  is larger than or equal to the value stored in the battery voltage Vb, the CPU  23   a  shifts to S 220 . 
     By contrast, if the value stored in the connection-point voltage Vc 1  is smaller than the value stored in the battery voltage Vb, the CPU  23   a  turns ON the switching elements Q 2 , Q 4 , and Q 6  in S 620 . Then, in S 630 , the CPU  23   a  measures the connection-point voltage based on the divided voltage from the voltage-dividing circuit  31 , and stores the value of the measured voltage in the connection-point voltage Vc. Further, in S 640 , the CPU  23   a  turns OFF the switching elements Q 2 , Q 4 , and Q 6 . 
     Subsequently, in S 650 , the CPU  23   a  determines whether the connection-point voltage Vc is larger than 0 V. Here, if the connection-point voltage Vc is smaller than or equal to 0 V, the CPU  23   a  shifts to S 220 . By contrast, if the connection-point voltage Vc is larger than 0 V, the CPU  23   a  turns ON the switching elements Q 1 , Q 3 , and Q 5  in S 660 . Then, in S 670 , the CPU  23   a  measures the connection-point voltage based on the divided voltage from the voltage-dividing circuit  31 , and stores the value of the measured voltage in the connection-point voltage Vc. Further, in S 680 , the CPU  23   a  turns OFF the switching elements Q 1 , Q 3 , and Q 5 . 
     Next, in S 690 , the CPU  23   a  determines whether the connection-point voltage Vc is larger than 0 V. Here, if the connection-point voltage Vc is smaller than or equal to 0 V, the CPU  23   a  shifts to S 220 . By contrast, if the connection-point voltage Vc is larger than 0 V, the CPU  23   a  shifts to S 230 . 
     The thus-configured electric powered work machine  1  includes the motor  11  as a power source, and further includes the motor driver  21 , the switching element Q 7 , the resistor R 7 , the resistor R 21 , and the control circuit  23 . 
     The resistor R 21  is connected to the motor driver  21  in such a state that electrical conduction is possible between the positive side and the negative side of the battery  12  in the motor driver  21  in a case where all of the switching elements Q 1  to Q 6  in the motor driver  21  are OFF. Specifically, the resistor R 21  is connected in parallel to the motor driver  21 . 
     The control circuit  23  turns OFF all of the switching element Q 7  and the switching elements Q 1  to Q 6 , and determines whether at least one of “the switching elements Q 1  to Q 6  and the switching element Q 7 ” is short-circuited based on the connection-point voltage at the connection point Pc between the switching element Q 7  and the motor driver  21 . 
     In this way, in the electric powered work machine  1 , the resistor R 21  is connected to the motor driver  21  in such a state that electrical conduction is possible between the positive side and the negative side of the battery  12  in the motor driver  21 . Thus, if at least one of the switching elements Q 1  to Q 6  is short-circuited in the motor driver  21 , the connection-point voltage changes. On the other hand, the resistor R 7  is connected in parallel to the switching element Q 7 . Thus, if the switching element Q 7  is short-circuited, the connection-point voltage changes. Further, the connection-point voltage differs between the case in which at least one of the switching elements Q 1  to Q 6  is short-circuited and the case in which the switching element Q 7  is short-circuited. 
     This makes it possible, in the electric powered work machine  1 , to detect whether at least one of the switching elements Q 1  to Q 6  is short-circuited and whether the switching element Q 7  is short-circuited. 
     In the above-described embodiment, the resistor R 21  corresponds to at least one circuit-side resistor, and S 110  to S 200 , S 220 , S 230 , and S 610  to S 690  correspond to procedures as a fault determiner. 
     Third Embodiment 
     A third embodiment of the present disclosure will be described below with reference to the drawings. In the third embodiment, differences from the first embodiment will be described. The same reference numerals are assigned to common configurations. 
     The electric powered work machine  1  of the third embodiment differs from that of the first embodiment in that the electrical configuration of the electric powered work machine  1  is changed and in that the fault diagnosis process is changed. 
     As shown in  FIG. 10 , the electric powered work machine  1  of the third embodiment is different from that of the first embodiment in that the resistors R 3 , R 4 , R 5 , and R 6  are omitted. 
     Here, an explanation will be given of a method for detecting a short-circuit fault in the switching elements Q 1  to Q 7  in the third embodiment. 
     First, assume that drain-to-source resistances of the switching elements Q 1  to Q 7  at the time when the switching elements Q 1  to Q 7  are OFF are sufficiently larger than resistances of the resistors R 1 , R 2 , and R 7 , and can be ignored. 
     Also, assume that resistance in each winding of the motor  11  is sufficiently smaller than those of the resistors R 1 , R 2 , and R 7 , and can be ignored. In such a case, as shown in  FIG. 8 , the motor driver  21  can be deemed to equivalently have a wiring in which the sources of the switching elements Q 1 , Q 3 , and Q 5  are connected to the drains of the switching elements Q 2 , Q 4 , and Q 6 , respectively, as shown with the broken line L 1  and the points P 1 , P 2 , and P 3 . 
     Further, as described above, the drain-to-source resistances of the switching elements Q 1  to Q 7  at the time when the switching elements Q 1  to Q 7  are OFF are sufficiently larger than the resistances of the resistors R 1 , R 2 , and R 7 . Thus, as shown in  FIG. 11 , the motor driver  21  can be deemed to be equivalently a circuit in which the switching element Q 1 , the switching element Q 3 , and the switching element Q 5  are connected in parallel to one another, the switching element Q 2 , the switching element Q 4 , and the switching element Q 6  are connected in parallel to one another, the parallel-connected switching elements Q 1 , Q 3 , and Q 5  and the parallel-connected switching elements Q 2 , Q 4 , and Q 6  are connected in series to each other, the resistor R 1  is further connected in parallel to the parallel-connected switching elements Q 1 , Q 3 , and Q 5 , and the resistor R 2  is further connected in parallel to the parallel-connected switching elements Q 2 , Q 4 , and Q 6 . 
     Further, assume that the resistor R 7  and the resistors R 1  and R 2  have the same resistance value. In such conditions, a connection-point voltage at the time when the switching elements Q 1  to Q 7  are OFF (hereinafter referred to as an OFF-state connection-point voltage) is calculated to be (2/3)×Vb, if no short circuit is occurring in the switching elements Q 1  to Q 7 . 
     The OFF-state connection-point voltage in a case where short circuit is occurring in the switching element Q 7  is calculated to be Vb. 
     The connection-point voltage in a case where short circuit is occurring in any one of the switching elements Q 1  to Q 6  is calculated to be (1/2)×Vb. 
     Accordingly, if the connection-point voltage is equal to Vb or is smaller than or equal to (1/2)×Vb, it can be determined that short circuit is occurring in at least one of the switching elements Q 1  to Q 7 . 
     Next, an explanation will be given of procedures of a fault diagnosis process of the third embodiment. 
     As shown in  FIG. 12 , the fault diagnosis process of the third embodiment differs from that of the first embodiment in that S 210  is omitted and in that S 710  is added. 
     Specifically, upon completion of the procedure of S 200 , the CPU  23   a  determines, in S 710 , whether the value stored in the connection-point voltage Vc 1  is larger than one-half of the value stored in the battery voltage Vb and also smaller than the value stored in the battery voltage Vb. That is, the CPU  23   a  determines whether (1/2)×Vb&lt;Vc 1 &lt;Vb is satisfied. 
     Here, if the value stored in the connection-point voltage Vc 1  is smaller than or equal to one-half of the value stored in the battery voltage Vb, or larger than or equal to the value stored in the battery voltage Vb, the CPU  23   a  shifts to S 220 . 
     By contrast, if the value stored in the connection-point voltage Vc 1  is larger than one-half of the value stored in the battery voltage Vb and also smaller than the value stored in the battery voltage Vb, the CPU  23   a  shifts to S 230 . 
     The thus-configured electric powered work machine  1  includes the motor  11  as a power source, and further includes the motor driver  21 , the switching element Q 7 , the resistor R 7 , the resistors R 1  and R 2 , and the control circuit  23 . 
     The resistors R 1  and R 2  are connected to the motor driver  21  in such a state that electrical conduction is possible between the positive side and the negative side of the battery  12  in the motor driver  21  in a case where all of the switching elements Q 1  to Q 6  in the motor driver  21  are OFF. 
     The control circuit  23  turns OFF all of the switching element Q 7  and the switching elements Q 1  to Q 6 , and determines whether at least one of “the switching elements Q 1  to Q 6  and the switching element Q 7 ” is short-circuited based on the connection-point voltage at the connection point Pc between the switching element Q 7  and the motor driver  21 . 
     Specifically, the resistor R 1  is connected in parallel to the switching element Q 1 , and the resistor R 2  is connected in parallel to the switching element Q 2 . The switching element Q 1  is arranged on the first current path between the motor  11  and the positive electrode of the battery  12 . The switching element Q 2  is arranged on the first current path between the motor  11  and the negative electrode of the battery  12 . 
     In this way, in the electric powered work machine  1 , the resistors R 1  and R 2  are connected to the motor driver  21  in such a state that electrical conduction is possible between the positive side and the negative side of the battery  12  in the motor driver  21 . Thus, if at least one of the switching elements Q 1  to Q 6  is short-circuited in the motor driver  21 , the connection-point voltage changes. On the other hand, the resistor R 7  is connected in parallel to the switching element Q 7 . Thus, if the switching element Q 7  is short-circuited, the connection-point voltage changes. Further, the connection-point voltage differs between the case in which at least one of the switching elements Q 1  to Q 6  is short-circuited and the case in which the switching element Q 7  is short-circuited. 
     This makes it possible, in the electric powered work machine  1 , to detect whether at least one of the switching elements Q 1  to Q 6  is short-circuited and whether the switching element Q 7  is short-circuited. 
     In the above-described embodiment, the resistors R 1  and R 2  correspond to at least one circuit-side resistor, and S 110  to S 200 , S 220 , S 230 , and S 710  correspond to procedures as a fault determiner. 
     Although the embodiments of the present disclosure have been described so far, the present disclosure may be practiced in various modified forms without being limited to the above-described embodiments. 
     For example, the above-described embodiments show the mode in which the switching element Q 7  is arranged on the current path between the positive electrode of the battery  12  and the motor driver  21 ; however, the switching element Q 7  may be arranged on a current path between the negative electrode of the battery  12  and the motor driver  21 . 
     Further, the above-described first embodiment shows the mode in which it is determined that short circuit is occurring in at least one of the switching elements Q 1  to Q 6  if Vc 1 ≤(1/3)×Vb is satisfied (i.e., the mode in which the fault determination voltage is (1/3)×Vb). However, the fault determination voltage may be set to a value between: a normal-state lowest value, which is the lowest value of the connection-point voltage at the time when the switching elements Q 1  to Q 7  are each in a normal state; and the value of the connection-point voltage at the time when one of the switching elements Q 1  to Q 6  is short-circuited. 
       FIG. 13  is a graph showing relationships between: the connection-point voltage at the time when the switching elements Q 1  to Q 7  are each in a normal state, the connection-point voltage at the time when one of the switching elements Q 1  to Q 6  is short-circuited, and the connection-point voltage at the time when the switching element Q 7  is short-circuited; and the battery voltage. 
     A straight line SL 1  in  FIG. 13  shows the connection-point voltage at the time when the switching element Q 7  is short-circuited. A straight line SL 2  in  FIG. 13  shows the connection-point voltage at the time when one of the switching elements Q 1  to Q 6  is short-circuited. A straight line SL 3  in  FIG. 13  shows the connection-point voltage at the time when the switching elements Q 1  to Q 6  are low in temperature and the switching element Q 7  is high in temperature and also is in a normal state. A straight line SL 4  in  FIG. 13  shows the connection-point voltage at the time when the switching elements Q 1  to Q 7  are normal in temperature and also are each in a normal state. A straight line SL 5  in  FIG. 13  shows the connection-point voltage at the time when the switching elements Q 1  to Q 6  are high in temperature, and the switching element Q 7  is low in temperature and also is in a normal state. 
     As shown by the straight lines SL 3 , SL 4 , and SL 5  in  FIG. 13 , the connection-point voltage at the time when the switching elements Q 1  to Q 7  are each in a normal state varies depending on the temperature of the switching elements Q 1  to Q 7 . The connection-point voltage becomes higher as the temperatures of the switching elements Q 1  to Q 6  become lower or as the temperature of the switching element Q 7  becomes higher. 
     Thus, the fault determination voltage may be set to a value between the value of the connection-point voltage at the highest temperature of the switching elements Q 1  to Q 6  and also at the lowest temperature of the switching element Q 7 , which are expected during use of the electric powered work machine  1  (hereinafter referred to as a normal-state lowest value) and the value of the connection-point voltage at the time when one of the switching elements Q 1  to Q 6  is short-circuited. This makes it possible, in the electric powered work machine  1 , to inhibit occurrence of a situation in which it is determined that at least one of the switching elements Q 1  to Q 6  is short-circuited despite the fact that none of the switching elements Q 1  to Q 6  is short-circuited, thus improving accuracy of the fault determination by the control circuit  23 . 
     Even when the switching elements Q 1  to Q 7  are OFF, a minute leakage current flows between the drains and the sources of the switching elements Q 1  to Q 7 , and this leakage current increases with the temperature rise of the switching elements Q 1  to Q 7 . That is, the drain-to-source resistances at the time when the switching elements Q 1  to Q 7  are OFF decrease with the temperature rise of the switching elements Q 1  to Q 7 . 
     In the case where the switching elements Q 1  to Q 7  are short-circuited, the drain-to-source resistances do not necessarily become 0Ω and have a certain degree of impedance. Thus, in order to improve accuracy of the fault diagnosis, it is desirable to set the fault determination voltage to be close to a normal range. 
     Here, since it is necessary to avoid a situation in which determination of a short-circuit fault is made despite the fact that the switching elements Q 1  to Q 7  are each in a normal state, it is necessary to calculate the normal range with variations included and to set the fault determination voltage to be out of this normal range. 
     The biggest factor that causes variations in the circuit configuration in the above-described first embodiment is the temperatures of the switching elements Q 1  to Q 7 . Review on the temperature conditions for the normal-state lowest value founds that the conditions for the widest variations are when the temperature of the motor driver  21  arranged closer to the ground is high (i.e., the drain-to-source resistance is lowest) and the temperature of the switching element Q 7  closer to the battery  12  is low (i.e., the drain-to-source resistance is highest). Thus, the connection-point voltage under such conditions may be set for the normal-state lowest value. This makes it possible, in the electric powered work machine  1 , to inhibit occurrence of the situation in which it is determined that at least one of the switching elements Q 1  to Q 6  is short-circuited despite the fact that none of the switching elements Q 1  to Q 6  is short-circuited, thus further improving accuracy of the fault determination by the control circuit  23 . In this case, the switching element Q 7  corresponds to a positive-side element, and the motor driver  21  corresponds to a negative-side element. 
     The technique of the present disclosure can be applied to various electric powered work machines, such as an electric hammer, an electric hammer drill, an electric drill, an electric screwdriver, an electric wrench, an electric grinder, an electric circular saw, an electric reciprocating saw, an electric jigsaw, an electric cutter, an electric chain saw, an electric planar, an electric nailer (including a tacker), an electric hedge trimmer, an electric lawn mower, an electric lawn trimmer, an electric grass cutter, an electric cleaner, an electric blower, an electric sprayer, an electric spreader, and an electric dust collector. 
     Two or more functions of a single element in the above-described embodiments may be performed by two or more elements, and a single function of a single element may be performed by two or more elements. Two or more functions of two or more elements may be performed by a single element, and a single function performed by two or more elements may be performed by a single element. Part of a configuration in the above-described embodiments may be omitted. At least part of a configuration in the above-described embodiments may be added to or replace another configuration in the above-described embodiments. 
     In addition to the above-described electric powered work machine  1 , the present disclosure may also be implemented in various forms, such as a program for causing a computer to function as the control unit  20 , a non-transitory tangible storage medium, such as a semiconductor memory, in which this program is stored, and a fault diagnosis method.