JP2005153570A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device relatively easy in steering of a steering wheel, even when any two-phase wiring is short-circuited among three-phase wiring between a switching element UU of a control part ECU and an assist generator 4. <P>SOLUTION: When any two-phase wiring is short-circuited among the three-phase wiring, a controllable state of the assist generator is continued, that is, a state of closing an inter-phase relay 16 is continued. When the two-phase wiring is also short-circuited, duty output by a PWM signal generating part 13 for controlling an electric current supplied to the assist generator 4, is set to a predetermined duty upper limit value or less. When the two-phase wiring is further short-circuited, a warning is displayed, and is informed to a driver. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus.

  Conventionally, as an assist motor constituting an electric power steering apparatus, there is one using a brushless DC motor which is a three-phase motor. In order to supply a current to the brushless DC motor, an inverter circuit composed of a plurality of switching elements is driven. And when the switching element which comprises this inverter short-circuits, the relay connected in series with each phase as a fail safe is cut | disconnected. That is, when the switching element is short-circuited, the connection between the control unit (ECU) and the brushless DC motor is interrupted (see, for example, Patent Document 1).

Similarly to the case where the switching element is short-circuited, the relay is also disconnected when any two-phase wiring is short-circuited among the three-phase wirings connecting between the control unit (ECU) and the brushless DC motor. ing. As a result, it is possible to prevent a failure of the switching elements constituting the inverter.
JP 2003-81099 A

  However, even when the relay is disconnected when the wiring between the relay and the brushless DC motor (interphase wiring) is short-circuited, the closed circuit is closed by the two-phase wiring short-circuited between the brushless DC motor and the short-circuited portion. Is maintained. In a state where the closed circuit is configured in this way, when the rotor of the brushless DC motor rotates and enters a power generation state, the brushless DC motor generates brake torque by the closed circuit.

  That is, when the inter-phase wiring is short-circuited, when the driver steers the steering wheel, brake torque is generated in the brushless DC motor that is an assist electric motor. As a result, the force required for steering the steering wheel has greatly increased, placing a heavy burden on the driver.

  This invention is made in view of such a situation, and when any two-phase wiring is short-circuited among the three-phase wiring between the switching element of the control unit (ECU) and the assist motor. Even if it exists, it aims at providing the electric power steering device with which steering of a steering wheel is comparatively easy.

  The electric power steering apparatus according to the present invention includes an assist motor including a three-phase motor that generates an assist force for assisting a steering force, and a switching element for each phase, and the switching element is duty-driven based on the steering torque to perform the assist. An electric power steering apparatus comprising: an electric motor control unit that controls an electric motor; wherein the electric motor control unit is configured to connect between any two-phase wirings among three-phase wirings that connect between the assist motor and the switching element. An inter-phase short-circuit detecting means for detecting a short-circuit, and an inter-phase short-circuit control means for continuing the controllable state of the assist motor when a short-circuit between the two-phase wirings is detected. Item 1).

  For example, the motor control means further comprises switch means that can be intermittently switched between electrical connection between the assist motor and the switching element by opening and closing between the assist motor and the switching element. The inter-phase short-circuit control means closes the switch means (claim 2).

  That is, according to the electric power steering apparatus of the present invention, even when the two-phase wiring (interphase wiring) is short-circuited among the three-phase wirings between the switching element of the motor control means (ECU) and the assist motor. The assist motor is controlled. Specifically, current is supplied from the motor control means to the assist motor.

  Here, in the conventional electric power steering apparatus, as described above, when the interphase wiring is short-circuited, a relay (switch means) disposed between the motor control means (ECU) and the assist motor is opened. Thus, the motor control means (ECU) and the assist motor are disconnected. This prevents the switching elements constituting the inverter from failing. That is, a short circuit of the interphase wiring prevents a large current from flowing through the switching element. As a result, brake torque is generated in the assist motor, and the steering performance of the steering wheel is deteriorated. Here, the reason for the conventional control will be briefly described. When the interphase wiring is short-circuited, the motor control means must be repaired. Therefore, when the interphase wiring is short-circuited, it is sufficient to stop the vehicle immediately, so it has been considered that there is no problem even if the steering performance is deteriorated. Therefore, in order to protect the switching element that may fail when the interphase wiring is short-circuited, a relay (switch means) is opened to prevent a large current from flowing through the switching element.

  However, if the switching element does not cause a failure, it is not necessary to open the relay. Therefore, if the switching element does not break down, it is better that the steering is not deteriorated by closing the relay and supplying current to the assist motor. Here, when the interphase wiring is short-circuited, whether or not the steering performance of the steering wheel is deteriorated by supplying a current to the assist motor becomes a problem. This is because even if the relay is closed, if the interphase wiring is short-circuited, a closed circuit is formed and the assist motor generates brake torque. Furthermore, since the interphase wiring is short-circuited, an appropriate current cannot be supplied from the motor control means to the assist motor. That is, the assist motor cannot be driven appropriately. Therefore, it is also a problem whether or not the brake torque generated by the assist motor can be resisted by the closed circuit in a state where the assist motor cannot be appropriately driven. However, the inventor has proved that the steering performance is actually improved as compared with the conventional control even when the interphase wiring is short-circuited. The proof that the steering performance has been improved will be described later. That is, as long as the switching element does not cause a failure, by closing the relay, the fail-safe property can be maintained and the steering property can be improved.

  Next, the present invention will be described in more detail with reference to embodiments.

  The inter-phase short-circuit control means may further comprise warning means for warning the driver that the short circuit is detected when a short-circuit between the two-phase wirings is detected. For example, the warning unit may light a warning display (Warning Lamp). Thereby, it can be transmitted to the driver that the electric power steering apparatus is in an abnormal state.

  The phase-to-phase short-circuit detecting unit further includes a short-circuited phase determining unit that determines the short-circuited two phases, and the phase-to-phase short-circuit control unit limits the duty of at least the short-circuited switching elements of the two-phases. (Claim 4). Here, limiting the duty limits the amount of current flowing in the switching element and the wiring of the limited phase. That is, by limiting the duty of the short-circuited two-phase switching element, it is possible to prevent a large current from flowing through the short-circuited two-phase switching element. As a result, failure of the switching element can be prevented.

  The inter-phase short-circuit control means may not limit the duty of the switching element of one phase other than the short-circuited two phases (Claim 5). Here, a large current due to a short circuit does not flow through a single-phase switching element that is not short-circuited. In addition, since the duty of the one-phase switching element that is not short-circuited is not limited, at least one of the three phases of the assist motor has a current close to normal compared to the amount of current supplied to the other two short-circuited phases. Quantity is supplied. As a result, a large assist torque can be generated by the assist motor by one phase in which current is supplied in a state that is close to a certain degree of appropriateness. That is, the assist torque against the brake torque generated by the short circuit can be generated, so that the steering performance can be improved as compared with the conventional case.

  The inter-phase short-circuit control means may set the duty to be equal to or lower than a predetermined duty upper limit value capable of suppressing heat generation of the switching element. A major cause of failure of the switching element is heat generation due to the flow of a large current. That is, by limiting the duty to a value equal to or lower than the duty upper limit value that can suppress the heat generation of the switching element, a failure of the switching element can be reliably prevented.

  Further, the switching element is an upper arm side switching element and a lower arm side switching element constituting a three-phase inverter, and the inter-phase short-circuit control means is configured to control the two-phase upper arm side switching with the duty short-circuited. The duty may be such that the element and the lower arm side switching element are not turned ON at the same time. When the interphase wiring is short-circuited, a large current flows through the switching element when the short-circuited two-phase upper arm side switching element and lower arm side switching element are simultaneously turned on. This is because an assist motor is normally interposed as a load between the upper arm side switching element and the lower arm side switching element, but is directly connected without any load due to a short circuit of the interphase wiring. Therefore, by restricting the duty so that the short-circuited two-phase upper arm side switching element and lower arm side switching element are not simultaneously turned on, a large current does not flow through the switching element. As a result, failure of the switching element can be reliably prevented. The short-circuited two-phase upper arm side switching element and the lower arm side switching element are as follows. For example, when the wiring between the U phase and the V phase is short-circuited, the U-phase upper arm side switching element and the V phase lower arm side switching element, and the U phase lower arm side switching element and the V phase upper arm Side switching element. The upper arm side switching element and the lower arm side switching element of the same phase are originally provided with a dead time so that they are not simultaneously turned on.

  The phase-to-phase short-circuit detection means includes voltage detection means for detecting each voltage of the three-phase wiring without a filter, current detection means for detecting a current flowing through each of the three-phase wiring, and the three-phase wiring. A short circuit that determines that the short circuit occurs when the voltage difference between any two phases of the respective voltages is zero and the current of any one of the currents flowing through the three-phase wirings exceeds a predetermined current threshold. And a determination unit (claim 8).

  Here, in general, when detecting the voltage of each phase for fail-safe use, such as when the switching element is short-circuited, the detection is performed based on a voltage value with a low-pass filter (LPF) interposed. This is because the voltage output from the switching element of the inverter to the assist motor is a pulse waveform voltage, and therefore it is not possible to determine whether the switching element is short-circuited without a low-pass filter. However, in the interphase short-circuit detection in the present invention, it is possible to detect without interposing a filter. This is because the short-circuit determining means described above is used. And by determining by the short circuit determination means mentioned above, the short circuit of the interphase wiring can be reliably detected without erroneously detecting that the switching element is short circuited.

  Next, an Example is given and this invention is demonstrated more concretely.

(Overall configuration of electric power steering device)
FIG. 1 shows a block diagram of the overall configuration of the electric power steering apparatus in the present embodiment. As shown in FIG. 1, the electric power steering apparatus includes an electric power steering control unit 1, a steering torque sensor 2, a vehicle speed sensor 3, an assist motor 4, and a warning display unit 5.

  The steering torque sensor 2 is a sensor that detects a steering torque applied to a steering shaft (not shown) and outputs a steering torque signal to the target current setting unit 11 of the electric power steering control unit 1. Specifically, a steering shaft is connected to the steering wheel, and the steering shaft includes a torsion bar. A steering torque sensor 2 is attached to the torsion bar. When the steering wheel rotates, a rotational force is applied to the torsion bar, and the torsion bar is twisted according to the applied rotational force. The steering torque applied to the steering shaft corresponding to the twist of the torsion bar is detected by the steering torque sensor 2.

  The vehicle speed sensor 3 is a sensor that detects the traveling speed of the vehicle and outputs a vehicle speed signal to the target current setting unit 11 of the electric power steering control unit 1. The vehicle speed sensor 3 is attached to the front wheel of the vehicle. The assist motor 4 generates assist torque when an assist current is supplied from the electric power steering control unit 1. The assist torque is torque that assists the steering force. The assist motor 4 is constituted by a three-phase brushless DC motor. The warning display part 5 is a part for lighting a warning display (Warning Lamp). Specifically, the warning display unit 5 is disposed on an instrument panel (not shown) installed in front of the driver's seat of the vehicle. That is, when the warning display unit 5 is lit, the driver can be notified immediately. The warning display unit 5 is turned on / off based on a warning display instruction of the phase-short-circuit control unit 21 of the electric power steering control unit 1 described later.

  As shown in FIG. 1, the electric power steering control unit 1 includes a target current setting unit 11, a subtractor 12, a PWM signal generation unit 13, an element driving unit 14, an inverter circuit unit 15, and an interphase relay 16. The shunt resistor Rs, the current detection unit 17, the voltage dividing unit 18, the phase short-circuit voltage detection unit 19, the phase-to-phase short-circuit determination unit 20, the phase-to-phase short-circuit control unit 21, the low-pass filter 22, and the fail voltage It comprises a detector 23 and a fail determination controller 24.

  The target current setting unit 11 first performs phase compensation processing of the steering torque input from the steering torque sensor 2. Based on the steering torque signal subjected to the phase compensation process and the vehicle speed signal input from the vehicle speed sensor 3, a target current signal that is a target value of the assist current supplied to the assist motor 4 is set. This target current signal is set based on a target current map indicating the relationship between the steering torque signal and the vehicle speed signal stored in advance and the target value of the assist current.

  The subtractor 12 calculates a so-called deviation current signal (deviation) obtained by subtracting a current signal detected by a current detection unit 17 described later from a target current signal set by the target current setting unit 11.

  The PWM signal generation unit 13 calculates a PWM signal based on the deviation current signal calculated by the subtractor 12 and outputs the PWM signal to the element driving unit 14. This PWM signal is a drive signal for the switching elements UU, UL, VU, VL, WU, WL of the U-phase, V-phase, and W-phase of the inverter circuit unit 15. That is, the PWM signal is a signal having a duty for each phase. Further, the PWM signal generation unit 13 receives a duty upper limit value signal from a PWM upper limit control unit 211 of the phase short-circuit control unit 21 described later. Then, the PWM signal calculated based on the deviation current signal calculated by the subtractor 12 is compared with the duty upper limit value signal input from the PWM upper limit control unit 211, and the one with the smaller duty is adopted and the element driving unit is adopted. 14 is output. That is, when the duty of the PWM signal calculated based on the deviation current signal is larger than the duty of the duty upper limit value signal, the duty of the PWM signal output to the element driving unit 14 becomes the duty of the duty upper limit value signal.

  The element drive unit 14 applies each gate voltage to each switching element UU, UL, VU, VL, WU, WL of the inverter circuit unit 15 based on the PWM signal output from the PWM signal generation unit 13, thereby switching each switching. The elements UU and the like are driven.

  The inverter circuit unit (three-phase inverter) 15 is composed of six switching elements UU, UL, VU, VL, WU, and WL. Specifically, the U-phase upper arm side switching element UU and the U-phase lower arm side switching element UL are connected in series, and the V-phase upper arm side switching element VU and the V-phase lower arm side switching element VL are connected in series. The W-phase upper arm side switching element WU and the W-phase lower arm side switching element WL are connected in series. Furthermore, the switching elements of each phase are connected in parallel. Further, the upper arm side is connected to the positive side of a battery (not shown), and the lower arm side is grounded via a shunt resistor Rs described later. Further, intermediate positions between the upper arm side switching element and the lower arm side switching element of each phase are connected to the windings of the respective phases of the assist motor 4. That is, each switching element UU, UL, VU, VL, WU, WL of the inverter circuit unit 15 is turned on / off based on the drive signal from the element drive unit 14 to assist each phase winding of the assist motor 4. Current is supplied. When assist current is supplied to the assist motor 4, assist torque is generated. The switching elements UU, UL, VU, VL, WU, WL are, for example, MOSFETs, IGBTs, or the like.

  The interphase relay (switch means) 16 includes a V-phase relay 16v and a W-phase relay 16w. One end of the V-phase relay 16v is connected to an intermediate position between the V-phase upper arm side switching element VU and the V-phase lower arm side switching element VL of the inverter circuit unit 15, and the other end is connected to the V-phase winding of the assist motor 4. It is connected. One end side of the W-phase relay 16w is connected to an intermediate position between the W-phase upper arm side switching element WU and the W-phase lower arm side switching element WL of the inverter circuit section 15, and the other end side is connected to the W-phase winding of the assist motor 4. It is connected. These interphase relays 16 perform an opening / closing operation based on an output signal of a failure determination control unit 24 described later. Conventionally, the opening / closing operation is performed based on a portion corresponding to an inter-phase short-circuit control unit 21 described later. However, in the present embodiment, the opening / closing operation is not performed based on the inter-phase short-circuit control unit 21.

  The shunt resistor Rs is disposed between the lower arm side switching elements UL, VL, WL of each phase of the inverter circuit unit 15 and the ground terminal. The shunt resistor Rs is a resistor for detecting a current flowing through each phase. A current detection unit (phase short-circuit detection means, current detection means) 17 inputs voltages at both ends of each phase shunt resistor Rs, and detects currents Iu, Iv, Iw flowing in each phase based on this input voltage. , Generate a current signal for each phase. Then, the generated current signal of each phase is output to the subtractor 12.

  The voltage dividing unit 18 is provided for each phase, and the input side is connected between the inverter circuit unit 15 and the assist motor 4. Then, the voltage dividing unit 18 divides the voltage at the connection portion between the inverter circuit unit 15 and the assist motor 4 to reduce the voltage Vu2, Vv2, Vw2 of each phase that has been stepped down to the voltage detecting unit 19 for interphase short circuit. And output to the low-pass filter 22.

  An inter-phase short-circuit voltage detection unit (inter-phase short-circuit detection unit, voltage detection unit) 19 directly inputs the voltages Vu2, Vv2, and Vw2 of each phase output by the voltage dividing unit 18. In other words, the interphase short-circuit voltage detection unit 19 receives a voltage obtained by stepping down the voltage applied to the assist motor 4 without using a low-pass filter. That is, the voltage obtained by stepping down the PWM output voltage of the inverter circuit unit 15 is input to the inter-phase short-circuit voltage detection unit 19 as it is. Therefore, the voltage input to the interphase short-circuit voltage detector 19 is a pulse waveform voltage. The inter-phase short-circuit voltage detector 19 detects that any two-phase wirings among the three-phase wirings between the switching elements of the inverter circuit unit 15 and the assist motor 4 are short-circuited (hereinafter referred to as “phase-to-phase”). Inter-phase short-circuit voltages Vu2, Vv2, and Vw2 for determining “short circuit” are detected. In addition, although the expression "phase short circuit voltage" is used, this means that the voltage is used for the determination of the phase short circuit, and does not mean the voltage when the phase is shorted.

  The phase-to-phase short-circuit determination unit (phase-to-phase short-circuit detection unit, short-circuit determination unit) 20 includes the currents Iu, Iv, and Iw input from the current detection unit 17 and the phases input from the phase-to-phase short-circuit voltage detection unit 19. Based on the interphase short circuit voltages Vu2, Vv2, and Vw2, it is determined whether or not the interphase short circuit has occurred. Here, the inter-phase short-circuit determination process will be described later.

  When the inter-phase short-circuit control unit 21 determines that the inter-phase short-circuit determination unit 20 determines that the inter-phase short circuit has occurred, the control unit 21 performs a control process during the inter-phase short circuit. Here, a detailed configuration of the inter-phase short-circuit control unit 21 will be described with reference to FIG. As shown in FIG. 2, the inter-phase short-circuit control unit 21 includes a PWM upper limit control unit 211 and a warning display instruction unit 212.

  The PWM upper limit control unit 211 limits the duty of the PWM signal output from the PWM signal generation unit 13 to the element drive unit 14 when it is determined from the phase-to-phase short-circuit determination unit 20 that a phase-to-phase short has occurred. Specifically, for example, the PWM upper limit control unit 211 stores an upper limit value (duty upper limit value) of the duty in advance, and outputs a signal of this duty upper limit value to the PWM signal generation unit 13. As described above, the PWM signal generation unit 13 compares the PWM signal calculated based on the deviation current signal with the duty upper limit value signal.

  The warning display instructing unit 212 outputs a warning display lighting command to the warning display unit 5 when it is determined by the phase-to-phase short-circuit determining unit 20 that the phase has been short-circuited. That is, the warning display unit 5 to which the warning display lighting command is output from the warning display instruction unit 212 lights up the warning display to notify the driver that there is an abnormal state due to a short circuit between phases.

  The low-pass filter 22 receives the voltage of each phase output from the voltage divider 18 and outputs voltages Vu1, Vv1, Vw1 of intermediate potential for each phase. The voltages Vu1, Vv1, and Vw1 output from the low-pass filter 22 are not voltages that are obtained by stepping down the PWM output voltage of the inverter circuit unit 15. That is, the voltages Vu1, Vv1, and Vw1 are not pulse waveform voltages.

  The fail voltage detector 23 receives the voltages Vu1, Vv1, and Vw1 output from the low-pass filter 22 and detects the filtering voltages Vu1, Vv1, and Vw1. The filtering voltages Vu1, Vv1, and Vw1 are used to determine, for example, that the switching element UU of the inverter circuit unit 15 has been short-circuited.

  The fail determination control unit 24 is based on the currents Iu, Iv, Iw of each phase input from the current detection unit 17 and the filtering voltages Vu1, Vv1, Vw1 of each phase input from the failure voltage detection unit 23. For example, it is determined whether or not the switching element UU of the inverter circuit unit 15 is in a failure state such as a short circuit. Here, the determination of various failures such as a motor open failure, a motor short-circuit failure, and a relay open failure is known in, for example, Japanese Patent Laid-Open No. 6-298104. When various failures are determined, the interphase relay 16 (V-phase relay 16v and W-phase relay 16w) is opened, and the control of the assist motor 4 is stopped. Further, a relay (not shown) disposed between a battery (not shown) and the electric power steering control unit 1 is also opened, and driving of the electric power steering control unit 1 is stopped.

(Interphase short-circuit judgment processing)
Next, the inter-phase short-circuit determination process in the inter-phase short-circuit determination unit 20 will be described with reference to the flowchart of FIG.

  First, it is determined whether or not the electric power steering control unit 1 is under control (step S1). This determination can be made based on, for example, a control mode controlled by the electric power steering control unit 1. Since the control mode is well known, detailed description thereof is omitted. And when the electric power steering control part 1 is not controlling (step S1: No), it determines with having not raise | generated the short circuit between phases and returns (step S11).

  On the other hand, when it is determined that the electric power steering control unit 1 is under control (step S1: Yes), the counter i is initialized and set to 1 (step S2). This counter i is used to prevent erroneous determination of a short circuit between phases. Subsequently, it is determined whether or not the absolute value of any of the currents Iu, Iv, and Iw of each phase detected by the current detection unit 17 is greater than 75A (step S3). Specifically, it is determined whether the current Iu flowing in the U phase is larger than 75A, the current Iv flowing in the V phase is larger than 75A, or the current Iw flowing in the W phase is larger than 75A. That is, it is determined whether or not the current flowing through the wiring of each phase is an overcurrent. Here, when a short circuit between phases occurs, a current flowing in any two phases short-circuited among the three phases of the U, V, and W phases becomes an overcurrent.

  Subsequently, when all the absolute values of the currents Iu, Iv, and Iw of each phase are 75 A or less (step S3: No), it is determined whether or not the time T has elapsed since the counter i was set ( Step S4). If the time T has not elapsed since the counter i was set (step S4: No), the process returns to step S3 and is repeated. That is, the currents Iu, Iv, and Iw of each phase are monitored until the elapsed time after the counter i is set passes the time T.

  If the time T has elapsed since the counter i was set (step S4: Yes), it is determined that no interphase short-circuit has occurred, and the process returns (step S11). That is, when the current flowing in each phase during the time T is not an overcurrent, it is determined that no phase short-circuit has occurred.

  On the other hand, when the absolute value of any of the currents Iu, Iv, and Iw of each phase is greater than 75 A (step S3: Yes), the interphase voltage is determined (step S5). This determination is performed by determining whether or not the voltage difference between the phases is zero. This is because a short circuit between the phases is caused when any of the voltage differences between the phases is zero. Specifically, it is determined whether or not the difference between the U-phase voltage Vu2 and the V-phase voltage Vv2 input from the voltage divider 18 without a low-pass filter is zero. Further, it is determined whether or not the difference between the V-phase voltage Vv2 and the W-phase voltage Vw2 input from the voltage divider 18 without a low-pass filter is zero. Further, it is determined whether or not the difference between the W-phase voltage Vw2 and the U-phase voltage Vu2 input from the voltage divider 18 without a low-pass filter is zero.

  If all the voltage differences of the phases are not 0 (step S5: No), it is determined whether or not the time T has elapsed since the counter i was set (step S6). If the time T has not elapsed since the counter i was set (step S6: No), the process returns to step S5 and is repeated. That is, the difference between the voltages Vu2, Vv2, and Vw2 of each phase is monitored until the elapsed time after the counter i is set passes the time T.

  If the time T has elapsed since the counter i was set (step S6: Yes), it is determined that no interphase short-circuit has occurred, and the process returns (step S11). That is, when the difference between the voltages Vu2, Vv2, and Vw2 of the respective phases is not zero during the time T, it is determined that no interphase short-circuit has occurred.

  Subsequently, if any of the voltage differences between the phases is 0 (step S5: Yes), it is determined whether or not the counter i is 5 (step S7). If the counter i is not 5, it is determined whether or not the time T has elapsed since the counter i was set (step S8). If the time T has not elapsed since the counter i was set (step S8: No), the process waits until the time T elapses. If the time T has elapsed since the counter i was set (step S8: Yes), the counter i is set to a value obtained by adding 1, and the process returns to step S3 and is repeated (step S9). On the other hand, if the counter i is 5, it is determined that the phase is short-circuited, and the phase-short-circuit determination process is terminated (step S10).

  In other words, any of the currents flowing in each phase is overcurrent for 5 times every time T since the processing is started (counter i is initialized), and any of the voltage differences in each phase Is determined to be an interphase short circuit. For example, if the time T is 5 seconds, any of the voltage differences between the phases will occur during the first 5 seconds after the start of processing, and during the next 5 seconds in total 5 times. Is determined to be an interphase short circuit. For example, this may be a false detection even if an overcurrent state and any of the voltage differences of each phase become 0 during the first 5 seconds after the start of processing. Judgment is performed continuously. In other words, this is done to prevent erroneous detection of a short circuit between phases.

(Steering performance during short circuit between phases)
Next, the steering property at the time of a short circuit between phases will be described with reference to FIG. FIG. 4 is a diagram showing values of currents Iu, Iv, Iw flowing in each phase with respect to elapsed time (left vertical axis) and steering angle (right vertical axis). The elapsed time is the elapsed time from the start of measuring the current and the steering angle. The steering angle is a positive value when the steering wheel is steered in the right direction, and a negative value when the steering wheel is steered in the left direction. That is, when the steering angle is 0 [deg], the steering wheel is in a neutral state. FIG. 4 shows a case where the steering wheel is turned to the right from the state where the steering wheel is steered to the left. FIG. 4 shows a case where an interphase short-circuit occurs when the elapsed time is about 0.9 sec.

  As shown in FIG. 4, it is in a normal state until the elapsed time is about 0.9 sec. That is, the currents Iu, Iv, and Iw of the respective phases are normal three-phase AC waveforms and change very smoothly. Note that the steering wheel turns from the state where the steering wheel is steered to the left side to the neutral state until the elapsed time is about 0.9 sec.

  When the elapsed time is about 0.9 sec, the U-phase current Iu and the V-phase current Iv increase rapidly, and the absolute values of the U-phase current Iu and the V-phase current Iv at this time exceed about 60A. I understand that. Furthermore, thereafter, the U-phase current Iu and the V-phase current Iv increase rapidly at intervals of about 0.4 sec. This is because the U-phase upper arm side switching element UU and the V-phase lower arm side switching element VL are simultaneously turned on, or the U-phase lower arm side switching element UL and the V-phase upper arm side switching element VU are simultaneously turned on. This is a state. That is, in these cases, when the interphase wiring between the U phase and the V phase is short-circuited, a large current is generated because the upper arm side switching element is directly connected to the lower arm side switching element without passing through the assist motor 4. Flowing.

  In addition, even during the time when the current suddenly increases, the absolute values of the U-phase current Iu and the V-phase current Iv increase to about 20 A, which is a very large value compared to the normal time. Further, the U-phase current Iu and the V-phase current Iv after the elapsed time of about 0.9 sec or more are almost targeted around the current 0A. That is, the U-phase current Iu and the V-phase current Iv have substantially the same absolute value but different signs. Although the W-phase current Iw is slightly disturbed compared to the normal waveform, the magnitude of the current does not change so much.

  As described above, the U-phase current Iu and the V-phase current Iv that are short-circuited with each other are very large currents, and the current waveforms of both phases are very disturbed as compared with the normal state. However, even in this case, the steering angle changes greatly. Specifically, an angle of about 60 deg is steered between the time when the phase short-circuited is about 0.9 sec and 2.0 sec. Here, in the conventional electric power steering apparatus, as described above, the handle is very heavy due to the brake torque of the assist motor 4. Therefore, the driver needs a very large force to steer the steering wheel. Therefore, even if the steering wheel can be turned, only a slight steering angle can be turned over a long time. However, according to the present embodiment, the steering angle of the steering wheel is steered at a large angle in a very short time. That is, even when the phase is short-circuited as in the present embodiment, the steering performance is improved by not opening the phase relay 16. However, since the current of each phase is greatly disturbed, it can be seen that the steering performance is inferior compared to the normal state.

  FIG. 4 is a diagram when the duty output by the PWM signal generation unit 13 is not limited. Therefore, if the duty output from the PWM signal generation unit 13 is limited to a predetermined duty upper limit value or less, the change rate of the steering angle is slightly reduced. Further, the determination in step S3 in the flowchart of FIG. 3 satisfies the determination condition when the elapsed time in FIG. 4 is about 1.3 sec. This is because the absolute values of the U-phase current Iu and the V-phase current Iv are larger than 75A when the elapsed time is about 1.3 sec.

It is a block diagram which shows the whole structure of the electric power steering apparatus in a present Example. It is a block diagram which shows the detailed structure of the control part at the time of a short circuit between phases. It is a flowchart which shows an interphase short circuit determination process. It is a figure explaining the steering nature at the time of a phase short circuit.

Explanation of symbols

1: Electric power steering control unit (ECU) 2: Steering torque sensor 3: Vehicle speed sensor 4: Assist motor 5: Warning display unit 11: Target current setting unit 12: Subtractor 13: PWM signal generation unit , 14: element drive unit, 15: inverter circuit unit, 16: interphase relay, 17: current detection unit, 18: voltage dividing unit, 19: voltage detection unit for interphase short circuit, 20: interphase short circuit determination unit, 21: interphase short circuit Hour control unit, 22: low-pass filter, 23: fail voltage detection unit, 24: fail determination control unit

Claims (8)

An assist motor composed of a three-phase motor that generates assist force for assisting steering force;
Electric motor control means for controlling the assist electric motor by driving the switching element with a duty based on a steering torque having a switching element of each phase;
In the electric power steering apparatus with
The motor control means includes
An inter-phase short-circuit detecting means for detecting a short circuit between any two-phase wirings among the three-phase wirings wiring between the assist motor and the switching element;
A phase short-circuit control means for continuing the controllable state of the assist motor when a short circuit between the two-phase wirings is detected;
An electric power steering apparatus comprising: The motor control means further includes switch means that can be intermittently switched between electrical connection between the assist motor and the switching element by opening and closing between the assist motor and the switching element.
2. The electric power steering apparatus according to claim 1, wherein the inter-phase short-circuit control means closes the switch means.   2. The electric motor according to claim 1, wherein the inter-phase short-circuit control means further comprises warning means for warning a driver that the short circuit is detected when a short-circuit between the two-phase wirings is detected. Power steering device. The phase-to-phase short-circuit detection means further includes a short-circuit phase determination means for determining the short-circuited two phases,
2. The electric power steering apparatus according to claim 1, wherein the inter-phase short-circuit control means limits at least a duty of the short-circuited switching element of the two phases.   5. The electric power steering apparatus according to claim 4, wherein the inter-phase short-circuit control means does not limit a duty of the switching element of one phase other than the short-circuited two phases.   5. The electric power steering apparatus according to claim 4, wherein the inter-phase short-circuit control means sets the duty to be equal to or less than a predetermined duty upper limit value capable of suppressing heat generation of the switching element. The switching element is an upper arm side switching element and a lower arm side switching element constituting a three-phase inverter,
5. The inter-phase short-circuit control means sets the duty so that the short-circuited upper arm side switching element and lower arm side switching element of the two phases are not simultaneously turned on. The electric power steering apparatus as described. The interphase short circuit detecting means is
Voltage detecting means for detecting each voltage of the three-phase wiring without interposing a filter;
Current detection means for detecting a current flowing through each of the three-phase wirings;
The short circuit when the voltage difference between any two phases of the voltages of the three-phase wiring is 0 and the current of any one of the currents flowing through the three-phase wiring exceeds a predetermined current threshold. Short-circuit determining means for determining
The electric power steering apparatus according to claim 1, comprising:

Images