JP2007017402A - Failure detection system of direct current motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a failure detection system of a DC motor for detecting the existence of disconnection failure without rotating the DC motor. <P>SOLUTION: The DC motor 5 is driven by an H-bridge circuit composed of switching elements 1-4. The H-bridge circuit receives direct current power from a high potential power source Vh and a low potential power source Vl. Internal resistors of a minute current detection circuits 6 and 7 have high values of several kΩs and are connected between both the power source terminals of the DC motor and the low potential power source Vl. If disconnection exists between both the power source terminals of the DC motor, the switching element 1 is turned on, minute current is made to flow at voltage (Vh-Vl) in the circuit 6 by turning off the other switching elements, and a signal 105 is at an LO level. Since the current does not flow in the circuit 7, the disconnection of the DC motor is detected with a detection circuit 8 since a signal 106 is at an HI level. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to detection of a disconnection failure in a DC motor, and in particular, in an electric steering system for a self-propelled vehicle such as an automobile, the failure of the DC motor suitable for diagnosing the presence or absence of disconnection of the DC motor that functions as a steering assist power source It relates to the detection method.

  In an electric steering system generally used for driving a self-propelled vehicle such as an automobile, a DC motor is used as auxiliary power means for assisting a steering force by human power. FIG. 10 is a diagram showing circuit diagrams of various DC motors classified according to the connection type between the field winding and the armature winding. In FIG. 10, the armature 27 is composed of a winding (armature winding) and a magnetic circuit. As shown in FIG. 10, the DC motor 5 in practical use has a split motor (FIG. 10A) and a series motor (FIG. 10B) depending on the connection form between the field winding and the armature winding. )), An internally divided compound winding motor (FIG. 10C) and an outer divided compound motor (FIG. 10D). In these DC motors, if a disconnection failure including disconnection of field windings and armature windings and missing commutators occurs, the flow of rotational drive current stops, so that DC motor is used as a power source. The electric steering system loses its function.

  For example, in the DC motor shown in FIG. 10B in which the series winding field winding 29 and the armature winding are connected in series, the series winding field winding 29 is disconnected or the commutator 30 is missing. The current circuit between the power terminals 31 and 32 is lost, and the DC motor is broken as viewed from the power terminals 31 and 32. Even in the DC motor of FIG. 10C, the disconnection of the series winding field winding 29 is a disconnection failure of the DC motor as viewed from the power supply terminals 31 and 32. Further, in the DC motor of FIG. 10A, the disconnection between the connection point between the shunt field winding 28 and the commutator 30 and the power supply terminal 31 or 32 is DC power when viewed from the power supply terminals 31 and 32. The motor breaks. Similarly, in the DC motor of FIG. 10D, a disconnection between the connection point between the divided field winding 28 and the series wound field winding 29 and the power supply terminal 31 or the divided field winding 28 and rectification. The disconnection between the connection point with the child 30 and the power supply terminal 32 becomes a disconnection failure of the DC motor as seen from the power supply terminals 31 and 32. When such a disconnection failure occurs in the DC motor in the electric steering system, the function of the electric steering system is lost. Therefore, in the state where the rotation of the DC motor is stopped before starting the traveling of the self-propelled vehicle, it is indispensable to ensure the safety of the traveling of the self-propelled vehicle such as an automobile in order to detect the disconnection failure of the DC motor. is there.

  Conventionally, when diagnosing the presence or absence of a failure due to such disconnection, a voltage is applied between the power terminals 1 and 2 of the DC motor, a required drive current is supplied, a rotor is rotated, and a current sensor and a rotation sensor Thus, the inflow current and the rotation angle are detected, and it is confirmed whether or not the inflow current and the rotation angle of the motor are obtained as expected.

  On the other hand, Patent Document 1 (Japanese Utility Model Laid-Open No. 5-20976) discloses an “electric power steering device” that enables detection of a ground fault in a DC motor. FIG. 9 is a circuit diagram showing a motor drive circuit disclosed in Patent Document 1. As shown in FIG. The motor drive circuit of FIG. 9 includes an H-bridge circuit, and four switching elements formed by NPN transistors in the H-bridge circuit are turned on or off by pulse width control to control the rotation direction of the DC motor 5 and to be turned on. The rotational force is controlled by the ratio of the time width and the OFF time width (duty ratio).

  The H-bridge circuit includes power NPN transistors 19, 20, 21, and 22 that act as switching elements, current detection resistors 23 and 24, and current detection circuits 25 and 25 that correspond to these current detection resistors, respectively. 26, and a high-potential power supply Vh and a low-potential power supply Vl are provided as current supply power supplies. In this electric power steering device, an ON-OFF control corresponding to a steering direction is performed from a control unit (not shown in FIG. 9) included in the device in response to a required steering control action when the vehicle is running. The signal 105, 106, 107 or 108 is selected and output. The ON-OFF control signal 105, 106, 107 or 108 is a PWM signal, and is input to the base of the corresponding NPN transistor 19, 20, 21 or 22 for power. Since the motor drive current flowing into the DC motor 5 is proportional to the voltage drop of the current detection resistors 23 and 24, the current detection circuits 25 and 26 measure the voltage drop and output it as current detection signals 109 and 110. The current detection signals 109 and 110 represent the drive current of the DC motor 5.

For example, when the ON-OFF control signals 105 and 108 are turned ON and the ON-OFF control signals 106 and 107 are turned OFF, the NPN transistors 19 and 22 are turned ON and the NPN transistors 20 and 21 are turned OFF. When the DC motor 5 is rotating in the positive direction, if there is a difference between the current flowing into the DC motor 5 and the current flowing out from the DC motor 5, the control unit detects the current. In response to the input of the signals 109 and 110, a ground fault in the DC motor 5 is detected based on the current difference. This is the same for the ground fault when the DC motor 5 is rotating in the negative direction, and the ground fault in the DC motor 5 is detected by the control unit regardless of the rotational direction. In the example of the apparatus described in Document 1, detection of a ground fault in the DC motor 5 is performed by operating an electric steering system in which a predetermined operating current is supplied to the DC motor 5 and the rotor of the DC motor 5 is rotating. It is performed at the time, and is not performed when the rotation of the DC motor 5 is stopped.
Japanese Utility Model Publication No. 5-20976

  In the conventional DC motor failure detection method disclosed in Patent Document 1, failure detection is performed by placing the DC motor in a rotating state. However, in self-propelled vehicles such as automobiles, it is necessary for the DC motor to make a pre-diagnosis of the disconnection failure in advance each time before traveling to ensure safety during the subsequent driving. . The self-propelled vehicle can run when the engine is started. In an electric steering system for a self-propelled vehicle, drive power is generally supplied to a DC motor when the engine of the self-propelled vehicle is activated. Therefore, it is desirable from the viewpoint of safety that the failure of the DC motor of the electric steering system can be detected before the start of the engine in which the self-propelled vehicle can run, that is, before the drive power is supplied to the DC motor.

  In order to satisfy this requirement, a failure detection method capable of diagnosing the presence or absence of a disconnection failure of the DC motor when the DC motor is stopped is required. However, in the conventional DC motor failure detection method, a voltage drop in a resistor (for example, resistors 23 and 24 in FIG. 9) inserted in series in the DC motor drive current path is measured to determine whether the drive current is a normal value. Therefore, it was impossible to detect a disconnection failure when the rotational operation was stopped. This is because the conventional DC motor failure detection method cannot diagnose the presence or absence of a DC motor disconnection failure before the self-propelled vehicle can travel. In addition, the electric power steering device described in Patent Document 1 cannot detect a DC motor failure when rotation stops, and cannot detect a DC motor disconnection failure.

  An object of the present invention is to provide a failure detection method for a DC motor that can detect the presence or absence of a disconnection failure without turning the DC motor into a rotating state.

  In order to solve the above-mentioned problems, the present invention provides the following means.

(1) First and second switching elements are connected in series between a high potential power supply and a low potential power supply, and third and fourth switching elements are connected between the high potential power supply and the low potential power supply. An H-bridge circuit connected in series and connecting a DC motor to be driven between a connection point of the first and second switching elements and a connection point of the third and fourth switching elements; A first minute current detection circuit connected between one power supply terminal of the DC motor and one of the high potential power supply and the low potential power supply; the other power supply terminal of the DC motor and the one And a disconnection detection circuit for detecting disconnection between the two power supply terminals in the DC motor based on outputs of the first and second minute current detection circuits. And
In the disconnection detection circuit, only one of two switching elements connected to the other power source of the high potential power source or the low potential power source is ON, and the other three switching elements are OFF. A failure detection method for a DC motor, wherein the disconnection is detected based on the output in the detection mode.

  (2) In the disconnection detection mode, a current flowing through a series circuit in which one of the switching element, the DC motor, and the first and second minute current detection circuits that are ON is connected in series is the DC The failure detection method for a DC motor according to (1), wherein the current is smaller than a minimum current for rotating the motor.

  (3) The DC according to (1) or (2), wherein each of the first and second minute current detection circuits includes a series circuit of a resistor having a high resistance value and a photocoupler. Motor failure detection method.

  In the present invention, the disconnection of the DC motor is detected without inserting any current detection element into the drive current path of the DC motor driven by receiving the voltage difference between the high potential power source and the low potential power source. Instead of inserting a current detection element in the drive current path, in the present invention, only one of the two switching elements connected to the other power source of the high potential power source or the low potential power source is ON. In the disconnection detection mode in which the three switching elements are OFF, the circuit is configured such that the current that has flowed through the DC motor flows directly into one of the first and second minute current detection circuits. The presence or absence of disconnection corresponds to the presence or absence of the current on a one-to-one basis. By adopting this configuration, the disconnection detection circuit can reliably detect disconnection of the DC motor.

  During normal operation of the DC motor that rotates the rotating shaft, the two switching elements in the H-bridge circuit are turned on, and the driving current of the DC motor flows through the two ON switching elements. The drive current is a large current (for example, 60 amperes). The first and second minute current detection circuits are connected in parallel to one of the ON switching elements or a series circuit of this switching element and a DC motor [In the circuit of FIG. One minute current detection circuit (6) is connected in parallel to the series circuit of the switching element (4) and the DC motor (5), and the second minute current detection circuit (7) is parallel to the switching element (4). Connected. ]. By adopting this circuit configuration, it is not necessary to pass a large drive current through the first and second minute current detection circuits both during normal operation of the DC motor and when a disconnection failure is detected. It is possible to increase the internal resistance of the first and second minute current detection circuits and limit the current flowing through the first and second minute current detection circuits to a minute value. The lower limit value of the current flowing through the first and second minute current detection circuits at the time of detecting the disconnection failure of the DC motor is a value by which the presence or absence of the disconnection of the DC motor can be determined, and the lower limit drive current at which the DC motor can rotate 1 / 1,000, for example, several milliamperes. In order to detect the disconnection of the DC motor, it is necessary to pass a current to the DC motor. However, when the disconnection is detected by the method of the present invention, the current flowing to the DC motor is the lower limit drive current necessary for the rotation of the DC motor. About 1/1000 of that is enough. Therefore, according to the present invention, it is possible to provide a failure detection method for a DC motor that can detect the presence or absence of a disconnection failure without turning the DC motor into a rotating state.

  Next, an embodiment of the present invention will be described. In order to facilitate understanding of the DC motor failure detection method according to the present invention, the following description will be given with reference to the drawings. The DC motor failure detection method described below is provided as a steering assist power source in an electric steering system mounted on a self-propelled vehicle such as an automobile. In the embodiment of the present invention, a failure of the DC motor 5 is detected while the DC motor 5 is stopped without being rotated.

  FIG. 1 is a block diagram showing a first embodiment of the present invention. The DC motor failure detection method shown in FIG. 1 is connected between the switching elements 1, 2, 3 and 4 forming the H-bridge circuit, and one power supply terminal of the DC motor 5 and the low potential power supply Vl. Disconnection of the DC motor 5 based on the outputs of the minute current detection circuit 6, the minute current detection circuit 7 connected between the other power supply terminal of the DC motor 5 and the low potential power supply Vl, and the minute current detection circuits 6 and 7. And a disconnection detection circuit 8 for detecting a failure. Tables 1 and 2 in FIG. 5 are failure diagnosis tables of the failure detection method of the DC motor in FIG. A method for detecting a disconnection failure of the DC motor 5 according to the first embodiment of the present invention will be described with reference to FIGS.

  The resistance values of the switching elements 1, 2, 3 and 4 are extremely large when OFF, and are almost zero when ON. The internal resistances of the minute current detection circuits 6 and 7 are selected to be high values. The minute current detection circuit 6 uses the minute current detection signal 105 as a low-level voltage signal LO when the minute current flowing through the high internal resistance is equal to or greater than a predetermined value, and the minute current flowing through the high internal resistance is equal to or smaller than the predetermined value. In some cases, the minute current detection signal 105 is set to a high level voltage signal HI. Similarly, when the minute current flowing through the high internal resistance is equal to or greater than a predetermined value, the minute current detection circuit 7 sets the minute current detection signal 106 to the low level voltage signal LO, and the minute current flowing through the high internal resistance is predetermined. When the value is less than or equal to the value, the minute current detection signal 106 is set to a high level voltage signal HI.

  The ON-OFF control signals 101, 102, 103, and 104 are supplied from an auxiliary power control circuit (not shown) in the electric steering system. According to the first embodiment of the present invention, the method for detecting the presence or absence of a disconnection failure of the DC motor 5 at the time of rotation stop is performed by setting the ON-OFF control signals 101, 102, 103 and 104 to the ON level or the OFF level. There are a first disconnection detection method (in the case of Table 1 in FIG. 5) and a second disconnection detection method (in the case of Table 2 in FIG. 5). In the first disconnection detection method, only the ON-OFF control signal 101 of the switching element 1 is set to the ON level, and the ON-OFF control signals 102, 103, and 104 input to the other switching elements are all set to the OFF level. The disconnection detection mode is set. In the second disconnection detection method, the second ON / OFF control signal 103 of the switching element 3 is set to the ON level, and the ON / OFF control signals 101, 102 and 104 input to the other switching elements are all set to the OFF level. The disconnection detection mode is set.

  First, the first disconnection detection method will be described.

  In the first disconnection detection method, an ON level ON-OFF control signal 101 is input to the switching element 1, and an OFF level ON-OFF control signal 102 is input to the other switching elements 2, 3, and 4. , 103 and 104 are respectively input. Therefore, when the first disconnection detection method is executed, the switching element 1 is turned on and the other switching elements are all in the first disconnection detection mode (Table 1 in FIG. 5). The difference voltage (Vh−Vl) between the high potential power source Vh and the low potential power source Vl is applied to the H-bridge circuit. There are a first current path and a second current path as paths of current flowing by the voltage (Vh−Vl). The first current path passes through the switching element 1 and the minute current detection circuit 6, and the second current path passes through the switching element 1, the DC motor 5, and the minute current detection circuit 7.

  When the DC motor 5 is not disconnected, the internal resistance of the DC motor 5 is sufficiently smaller than the internal resistance of the minute current detection circuits 6 and 7 and can be ignored. Now, the switching element 1 is ON and its internal resistance is extremely small. Therefore, a voltage of (Vh−Vl) is applied to the minute current detection circuit 6 through the first current path. The minute current detection circuit 7 is also applied with a voltage of (Vh−Vl) through the second current path. The internal resistance of the minute current detection circuits 6 and 7 is set to a high value, and when a voltage (Vh−Vl) is applied, the current flowing through the minute current detection circuit 6 or 7 is as small as, for example, several milliamperes. Value.

  When the DC motor 5 is not disconnected, the minute current defined by the resistance value of the minute current detection circuit 6 flows through the first current path. The minute current detection signal 105 output from the minute current detection circuit 6 is a voltage signal, and is a LO level voltage value corresponding to the minute current. Since there is no disconnection failure in the DC motor 5 now, a minute current that does not rotate the DC motor 5 defined by the resistance value of the minute current detection circuit 7 flows through the second current path. The minute current detection circuit 7 outputs a minute current detection signal 106 having an LO level (voltage) corresponding to the minute current.

  The disconnection detection circuit 8 receives these LO level minute current detection signals 105 and 106 and refers to the failure diagnosis table of Table 1 in FIG. 5, and the DC motor 5 is normal with no disconnection. Diagnose things. The failure diagnosis table of Table 1 is recorded in advance in the ROM of the disconnection detection circuit 8. Further, the disconnection detection circuit 8 refers to the failure diagnosis table of Table 1 and performs a diagnosis that the switching element 1 itself is normal without disconnection simultaneously with the diagnosis of the DC motor 5 (see Table 1).

  Next, a case where a disconnection failure exists in the DC motor 5 will be described. At this time, since the DC motor 5 is disconnected, the current path that flows by the voltage (Vh−Vl) is only the first current path that passes through the switching element 1 and the minute current detection circuit 6. Therefore, a minute current defined by the resistance value of the minute current detection circuit 6 flows through the current path, and the minute current detection circuit 6 outputs a detection signal 105 of LO level corresponding to the minute current. On the other hand, since no current flows through the minute current detection circuit 7 in the second current path, the minute current detection circuit 7 outputs a HI level minute current detection signal 106 corresponding to zero inflow current. The disconnection detection circuit 8 receives the LO level minute current detection signal 105 and the HI level minute current detection signal 106 and refers to the failure diagnosis table of Table 1 in FIG. Diagnose a failure.

  If the HI level minute current detection signal 105 and the HI level minute current detection signal 106 are input to the disconnection detection circuit 8, the disconnection detection circuit 8 diagnoses that the switching element 1 has a disconnection failure (see Table 1). ).

  Next, a second disconnection detection method will be described. In the second disconnection detection method, as described above, only the ON-OFF control signal 103 of the switching element 3 is set to the ON level, and the ON-OFF control signals 101, 102, and 104 input to the other switching elements are all set to the OFF level. To do.

  In the second disconnection detection method, an ON level ON-OFF control signal 103 is input to the switching element 3, and an OFF level ON-OFF control signal is input to the other switching elements 1, 2, and 4. 101, 102, and 104 are input, respectively. Therefore, when the second disconnection detection method is executed, the switching element 3 is turned on and the other switching elements are all in the second disconnection detection mode (Table 2 in FIG. 5). A difference voltage (Vh−Vl) between the high potential power supply Vh and the low potential power supply Vl is applied to the H-bridge circuit, and the current paths that flow by this voltage (Vh−Vl) are the first current path and the second current path. There is a current path. The first current path passes through the switching element 3 and the minute current detection circuit 7, and the second current path passes through the switching element 3, the DC motor 5, and the minute current detection circuit 6.

  The following operation in the second disconnection detection method is the same as the first disconnection detection method described above in that the ON switching element is the element denoted by reference numeral 3 and the OFF switching elements are the elements denoted by reference numerals 1, 2, and 4. Since only the difference is the same and the others are the same, detailed description will be omitted. The disconnection detection circuit 8 diagnoses the presence or absence of disconnection of the DC motor 5 and disconnection of the switching element 3 in accordance with the failure diagnosis table shown in Table 2 of FIG.

  Next, a second embodiment of the present invention will be described with reference to FIG. 2 and Tables 3 and 4 in the figure. FIG. 2 is a block diagram showing a second embodiment of the present invention. In the DC motor failure detection method shown in FIG. 2, the minute current detection circuit 6 is connected between one power supply terminal of the DC motor 5 and the high potential power supply Vh, and the minute current detection circuit 7 is connected to the other of the DC motor 5. 1 is different from the first embodiment in FIG. 1 in that it is connected between the power supply terminal and the high-potential power supply Vh, and in other respects, it has the same configuration as that of the first embodiment in FIG. Works similarly. Tables 1 and 2 in FIG. 6 are failure diagnosis tables of the failure detection method of the DC motor in FIG. A method for detecting a disconnection failure of the DC motor 5 according to the second embodiment of the present invention will be described with reference to FIGS.

  According to the second embodiment of FIG. 2, the ON-control signals 101, 102, 103, and 104 are set to the ON level or the OFF level in order to detect the presence or absence of the disconnection failure of the DC motor 5 when the rotation is stopped. Accordingly, there is a first disconnection detection method (in the case of Table 3 in FIG. 6) and a second disconnection detection method (in the case of Table 4 in FIG. 6). In the first disconnection detection method, only the ON-OFF control signal 102 of the switching element 1 is set to the ON level, and all the ON-OFF control signals 1014103 and 104 input to the other switching elements are set to the OFF level. In the second disconnection detection method, only the ON-OFF control signal 104 of the switching element 3 is set to the ON level, and all of the ON-OFF control signals 101, 102, and 103 input to the other switching elements are set to the OFF level.

  First, the first disconnection detection method will be described.

  In the first disconnection detection method, the ON level ON-OFF control signal 102 is input to the switching element 2, and the OFF level ON-OFF control signal 101 is input to the other switching elements 1, 3, and 4. , 103 and 104 are respectively input. Therefore, when the first disconnection detection method is executed, the switching element 2 is turned on and all other switching elements are turned off (Table 3 in FIG. 6). The difference voltage (Vh−Vl) between the high potential power source Vh and the low potential power source Vl is applied to the H-bridge circuit. There are a first current path and a second current path as a path of a current flowing by the voltage (Vh−Vl). The first current path passes through the minute current detection circuit 6 and the switching element 2, and the second current path passes through the minute current detection circuit 7, the DC motor 5, and the switching element 2.

  When the DC motor 5 is not disconnected, the operation is as follows. Now, the switching element 2 is ON. Therefore, a voltage of (Vh−Vl) is applied to the minute current detection circuit 6 through the first current path. The minute current detection circuit 7 is also applied with a voltage of (Vh−Vl) through the second current path. The minute current defined by the resistance value of the minute current detection circuit 6 flows through the first current path. The minute current detection signal 105 output from the minute current detection circuit 6 is a LO level voltage value corresponding to the minute current. Since there is no disconnection failure in the DC motor 5 now, a minute current that does not rotate the DC motor 5 defined by the resistance value of the minute current detection circuit 7 flows through the second current path. The minute current detection circuit 7 outputs a minute current detection signal 106 having an LO level (voltage) corresponding to the minute current.

  The disconnection detection circuit 8 receives these LO level minute current detection signals 105 and 106 and refers to the failure diagnosis table of Table 3 in FIG. 6, and the DC motor 5 is normal with no disconnection. Diagnose things. The failure diagnosis table of Table 3 is recorded in advance in the ROM of the disconnection detection circuit 8. In addition, the disconnection detection circuit 8 refers to the failure diagnosis table in Table 3 and performs a diagnosis that the switching element 2 itself is normal without disconnection simultaneously with the diagnosis of the DC motor 5 (see Table 3).

  Next, a case where a disconnection failure exists in the DC motor 5 will be described. At this time, since the DC motor 5 is disconnected, the current path that flows by the voltage (Vh−Vl) is only the first current path that passes through the minute current detection circuit 6 and the switching element 2. Therefore, a minute current defined by the resistance value of the minute current detection circuit 6 flows through the current path, and the minute current detection circuit 6 outputs a detection signal 105 of LO level corresponding to the minute current. On the other hand, since no current flows through the minute current detection circuit 7 in the second current path, the minute current detection circuit 7 outputs a HI level minute current detection signal 106 corresponding to zero inflow current. The disconnection detection circuit 8 receives the LO level minute current detection signal 105 and the HI level minute current detection signal 106 and refers to the failure diagnosis table of Table 3 in FIG. Diagnose a failure.

  If the HI level minute current detection signal 105 and the HI level minute current detection signal 106 are input to the disconnection detection circuit 8, the disconnection detection circuit 8 diagnoses that the switching element 2 has a disconnection failure (see Table 3). ).

  Next, a second disconnection detection method will be described. In the second disconnection detection method, as described above, only the ON-OFF control signal 104 of the switching element 4 is set to the ON level, and the ON-OFF control signals 101, 102, and 103 input to the other switching elements are all set to the OFF level. To do.

  In the second disconnection detection method, an ON-ON control signal 104 of ON level is input to the switching element 4, and an OFF-level ON-OFF control signal is input to the other switching elements 1, 2, and 3. 101, 102, and 103 are input, respectively. Therefore, when the second disconnection detection method is executed, the switching element 4 is turned on and all other switching elements are turned off (Table 4 in FIG. 6). A difference voltage (Vh−Vl) between the high potential power supply Vh and the low potential power supply Vl is applied to the H-bridge circuit, and the current paths that flow by this voltage (Vh−Vl) are the first current path and the second current path. There are current paths. The first current path passes through the minute current detection circuit 7 and the switching element 4, and the second current path passes through the minute current detection circuit 6, the DC motor 5, and the switching element 4.

  The following operation in the second disconnection detection method is the same as the first disconnection detection method described above in that the ON switching element is the element 4 and the OFF switching element is the elements 1, 2 and 3. Since only the differences are the same and the others are the same, detailed description will be omitted. The disconnection detection circuit 8 diagnoses the disconnection of the DC motor 5 and the disconnection of the switching element 4 according to the failure diagnosis table shown in Table 4 of FIG.

  In the DC motor failure detection system of FIG. 1 according to the first embodiment of the present invention, when the DC motor 5 is rotated, the switching element 1 is turned on by the ON-OFF control signals 101, 102, 103, and 104. , 2, 3 and 4 are controlled as follows. To control the rotation of the DC motor 5 in the forward direction, in FIG. 1, ON-OFF control signals 101 and 104 of ON level are input to the switching elements 1 and 4, respectively, and ON-level of OFF level is input to the switching elements 2 and 3. OFF control signals 102 and 103 are input, respectively. When the DC motor 5 is controlled to rotate in the negative direction, ON-OFF control signals 102 and 103 of ON level are input to the switching elements 2 and 3, respectively, and the ON-level of OFF level is applied to the switching elements 1 and 4, respectively. OFF control signals 101 and 104 are input, respectively. Further, the torque of the DC motor 5 is controlled by the duty ratio of ON-OFF control signals 101, 102, 103 and 104 which are PWM signals. Also in the DC motor failure detection method of FIG. 2 which is the second embodiment of the present invention, the rotation control of the DC motor 5 is performed in the same manner as the rotation control in the DC motor failure detection method of FIG.

  FIG. 3 is a circuit diagram showing a first example of the present invention which further embodies the first embodiment (FIG. 1) of the present invention. Tables 5 and 6 in FIG. 7 are failure diagnosis tables applied to the embodiment in FIG. 3 and correspond to Tables 1 and 2 in FIG. 5, respectively.

  In the embodiment of FIG. 3, the switching elements 1, 2, 3, and 4 of FIG. 1 are realized by NMOS transistors 11, 12, 13, and 14, respectively, and the minute current detection circuit 6 is composed of a photocoupler 15, a resistor 16, and a resistor 37. The minute current detection circuit 17 includes a photocoupler 17, a resistor 18, and a resistor 38. The photocoupler includes a light emitting diode (LED) and a phototransistor. The light emitting diode outputs light corresponding to the current, and the phototransistor receives the light and exhibits conductivity according to the intensity of the light. The light emitting diode and the phototransistor are electrically insulated from each other. The light emitting diode in the photocoupler 15 is connected to the resistor 16 in series. One terminal of the phototransistor in the photocoupler 15 is connected to the power supply Vhi through the resistor 37, and the other terminal of the phototransistor is connected to the power supply Vlo. The light emitting diode in the photocoupler 17 is connected in series with the resistor 18. One terminal of the phototransistor in the photocoupler 17 is connected to the power supply Vhi through the resistor 38, and the other terminal of the phototransistor is connected to the power supply Vlo.

  In FIG. 3, the potential Vh is 12 volts, the potential Vl is the ground potential, and the voltage (Vh−Vl) is 12 volts. The resistors 16 and 18 are internal resistances of the minute current detection circuits 6 and 7, respectively, and are 4 kilohms here. The current flowing through the resistors 16 and 18 when a voltage of Vh−Vl = 12 volts is applied is a low value of 3 milliamps here. Even if such a small current is supplied to the DC motor 5, the DC motor 5 does not rotate. Therefore, in this embodiment, it is possible to detect a disconnection failure of the DC motor 5 without rotating the rotor of the DC motor 5.

  In the embodiment of FIG. 3, currents flowing through the resistors 16 and 18 are detected by the photocouplers 15 and 17. The circuit composed of the NMOS transistors 11, 12, 13 and 14 and the DC motor 5 is a so-called power section through which a large current (for example, 60 amperes) flows. Since the DC motor 5 has a commutator, electromagnetic noise due to the power unit is inevitable. On the other hand, the disconnection detection circuit 8 determines whether the minute current detection signals 105 and 106 are either the LO level or the HI level, that is, treats the signals 105 and 106 as logic value signals, and the failure diagnosis table of FIG. Is a logic circuit that makes a logical decision using a truth table, and is made of a semiconductor integrated circuit. Therefore, the disconnection detection circuit 8 is sensitive to noise caused by electromagnetic noise, and is liable to cause a logical operation error due to the noise. However, in the embodiment of FIG. 3, since the photocouplers 15 and 17 block noise due to electromagnetic noise, erroneous diagnosis in the disconnection detection circuit 8 can be prevented.

  FIG. 4 is a circuit diagram showing a second example of the present invention which further embodies the second embodiment (FIG. 2) of the present invention. Tables 7 and 8 in FIG. 8 are failure diagnosis tables applied to the embodiment in FIG. 4 and correspond to Tables 3 and 4 in FIG. 6, respectively.

  In the embodiment of FIG. 4, the switching elements 1, 2, 3 and 4 of FIG. 2 are realized by NMOS transistors 11, 12, 13 and 14, respectively, and the minute current detection circuit 6 is by a photocoupler 15, a resistor 16 and a resistor 37. The minute current detection circuit 17 is composed of a photocoupler 17, a resistor 18, and a resistor 38, one end of the photocoupler 15 is connected to the power source Vhi through the resistor 37, and the other end of the photocoupler 15 is connected to the power source Vlo. In addition, one end of the photocoupler 17 is connected to the power source Vhi through the resistor 38, and the other end of the photocoupler 17 is connected to the power source Vlo. Just as the first embodiment of the present invention in FIG. 3 corresponds to the first embodiment of the present invention in FIG. 1, the second embodiment of the present invention in FIG. Therefore, the detailed operation description of the example of FIG. 4 is omitted.

  Also in the embodiment of FIG. 4, since the photocouplers 15 and 17 block noise due to electromagnetic noise, the erroneous diagnosis in the disconnection detection circuit 8 can be prevented as in the case of the embodiment of FIG.

  Although the present invention has been described in detail with reference to the embodiments and examples, it is needless to say that the present invention is not limited to these examples. For example, in the embodiments of the present invention shown in FIGS. 3 and 4, an NMOS transistor is exemplified as the switching element. However, the switching element used in the present invention is not limited to the NMOS transistor, and may be a bipolar transistor, for example.

It is a block diagram which shows the 1st Embodiment of this invention. It is a block diagram which shows the 2nd Embodiment of this invention. FIG. 2 is a circuit diagram showing a first example of the present invention, which further embodies the first embodiment of the present invention of FIG. 1. FIG. 3 is a circuit diagram showing a second example of the present invention, which further embodies the second embodiment of the present invention of FIG. 2. It is a figure which shows the failure diagnosis table applied to the 1st Embodiment of this invention of FIG. It is a figure which shows the failure-diagnosis table | surface applied to the 2nd Embodiment of this invention of FIG. It is a figure which shows the failure diagnosis table | surface applied to the 1st Example of this invention of FIG. It is a figure which shows the failure diagnosis table | surface applied to the 2nd Example of this invention of FIG. It is a circuit diagram which shows the failure detection system of the conventional DC motor described in patent document 1. FIG. It is a figure which shows the circuit diagram of the various DC motor classified according to the connection type of a field winding and an armature winding.

Explanation of symbols

1 to 4 Switching element 5 DC motor 6, 7 Minute current detection circuit 8 Disconnection detection circuit 11 to 14 NMOS transistor 15, 17 Photocoupler 16, 18, 37, 38 Resistance 19 to 22 NPN transistor 23, 24 Current detection resistance 25 , 26 Current detection circuit 27 Armature 28 Dividing field winding 29 Series winding field winding 30 Commutator 31, 32 DC motor power supply terminal 101-104 ON-OFF control signal 105, 106 Minute current detection signal Vh H -High potential power supply applied to the power supply terminal of the bridge Vl Low potential power supply applied to the power supply terminal of the bridge Vhi High potential power supply of the microcurrent detection circuit Vlo Low potential power supply of the microcurrent detection circuit

Claims (3)

The first and second switching elements are connected in series between the high potential power supply and the low potential power supply, and the third and fourth switching elements are connected in series between the high potential power supply and the low potential power supply. An H-bridge circuit for connecting a DC motor to be driven between a connection point of the first and second switching elements and a connection point of the third and fourth switching elements, and the DC motor A first minute current detection circuit connected between one of the power supply terminals and one of the high potential power supply and the low potential power supply, the other power supply terminal of the DC motor, and the one power supply And a disconnection detection circuit for detecting disconnection between the power supply terminals of the DC motor based on outputs of the first and second minute current detection circuits. ,
In the disconnection detection circuit, only one of two switching elements connected to the other power source of the high potential power source or the low potential power source is ON, and the other three switching elements are OFF. A failure detection method for a DC motor, wherein the disconnection is detected based on the output in the detection mode.   In the disconnection detection mode, the current flowing through the series circuit in which one of the switching element, the DC motor, and the first and second minute current detection circuits that are ON is connected in series rotates the DC motor. The DC motor failure detection method according to claim 1, wherein the current is smaller than a minimum current to be generated.   3. The DC motor failure detection system according to claim 1, wherein each of the first and second minute current detection circuits includes a series circuit of a resistor having a high resistance value and a photocoupler.

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