JP2009274686A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device can surely prevent, in an extremely short time, such an event that a closed circuit is formed when an inverter fails and assisting is stopped and a steering assist force and electromagnetic braking which are not expected by a driver occur by a device which is miniaturized, inexpensive, generates no noise, and consumes small power, and imparting a steering assist force can provide better steering feeling during normal steering. <P>SOLUTION: This electric power steering device includes the inverter which calculates a current command value according to at least steering torque and a vehicle speed and supplies a motor phase current to each phase of a motor which provides a steering assist force to a steering mechanism according to the current command value. The electric power steering device includes a first FET group is installed in each phase supply path for supplying the motor phase current to the motor. The electric power steering device has a function of turning off the second FET group and the first FET group of the inverter when the defect of the inverter is detected. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that applies a steering assist force by a motor to a steering system of a vehicle, and more particularly to an electromagnetic brake when the assist is stopped due to an abnormality of an inverter that supplies a phase current to each phase of the motor. The present invention relates to an electric power steering device that avoids occurrence of the above.

  An electric power steering device that assists a vehicle steering device with an auxiliary load by the rotational force of a motor assists the steering shaft or rack shaft with a transmission mechanism such as a gear or a belt via a speed reducer. The load is energized. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist force). In the feedback control, the motor applied voltage is adjusted so that the difference between the current command value and the motor current detection value becomes small. Generally, the adjustment of the motor applied voltage is a duty of PWM (pulse width modulation) control. This is done by adjusting the tee ratio.

  A general configuration of the electric power steering apparatus will be described with reference to FIG. 4. A column shaft (steering shaft) 2 of the steering wheel 1 is connected to a steering wheel through a reduction gear 3, universal joints 4 a and 4 b, and a pinion rack mechanism 5. It is connected to the tie rod 6. The column shaft 2 is provided with a torque sensor 10 that detects the steering torque of the steering wheel 1, and a motor 20 that assists the steering force of the steering wheel 1 is connected to the column shaft 2 via the reduction gear 3. . The control unit 100 that controls the electric power steering apparatus is supplied with electric power from the battery 13 and also receives an ignition key signal via the ignition key 11. The control unit 100 calculates a steering assist command value (current command value) I of an assist (steering assist) command based on the steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12. Based on the calculated steering assist command value I, the current supplied to the motor 20 is controlled.

  The control unit 100 is mainly composed of a CPU (or MPU or MCU). FIG. 5 shows general functions executed by a program inside the CPU.

  The functions and operations of the control unit 100 will be described with reference to FIG. 5. The steering torque T detected and input by the torque sensor 10 and the vehicle speed V from the vehicle speed sensor 12 are input to the steering assist command value calculation unit 101. Thus, the steering assist command value Iref1 is calculated. The calculated steering assist command value Iref1 is phase compensated by the phase compensator 102 for improving the stability of the steering system, and the phase compensated steering assist command value Iref2 is input to the adder 103. Further, the steering torque T is input to a feedforward differential compensation unit 105 for increasing the response speed, and the differentially compensated steering torque TA is input to the addition unit 103, which adds the steering assist command value Iref2 and the steering Add torque TA. The steering assist command value Iref3 that is the addition result is input to the current limiting unit 106, and the current limiting unit 106 performs steering when the steering assist command value Iref3 is larger than the maximum current value Imax set in the current limiting unit 106. The auxiliary command value Iref3 is limited to the maximum current value Imax. Then, the current command value Iref4, which is the output of the current limiting unit 106, is input to the subtracting unit 104.

  The subtraction unit 104 obtains a deviation Iref5 = (Iref4-i) between the current command value Iref4 and the fed back motor current i. The deviation Iref5 is PI-controlled by the PI control unit 107 and further input to the PWM control unit 108. The duty is calculated and the motor 20 is driven via the motor drive circuit 110. The motor current value i of the motor 20 is detected by a motor current detection means (not shown), and is input to the subtraction unit 104 and fed back.

  A configuration example of the motor drive circuit 110 will be described with reference to FIG. 6. The motor drive circuit 110 determines the gates of the field effect transistors (FETs) FET 1 to FET 6 based on a pulse width modulation (PWM) signal from the PWM control unit 108. It comprises an FET gate drive circuit 111 for driving, an inverter 112 constituted by a three-phase bridge circuit of FET1 to FET6, a boost power supply 113 for driving the high side of FET1, FET2 and FET3. A surge absorbing diode is connected in antiparallel between the source and drain of FET1 to FET6. Power is supplied to the inverter 112 from the battery 13 via the ignition key 11 and the power supply relay RL. The inverter 112 includes FET1 and FET4 connected in series, FET2 and FET5 connected in series, and FET3 and FET6 connected in series, and these FETs connected in series are connected in parallel. Configured. The motor phase current of each phase is supplied to the motor 20 through the supply paths a, b, and c from the connection point of FET1 and FET4, the connection point of FET2 and FET5, and the connection point of FET3 and FET6 of the inverter 112. It has become.

  In the above example, since the motor 20 is a three-phase motor, the inverter 112 uses a three-phase bridge circuit composed of six FET1 to FET6. However, the motor 20 is a two-phase motor. In some cases, inverter 112 uses an H-bridge circuit consisting of four FETs.

  Conventionally, in such an electric power steering device, when a failure is detected in the electric power steering device, the power supply relay RL, which is a mechanical relay, is opened or the two phases of the motor phase current supply path By providing a mechanical relay in the open state and opening the mechanical relay, the power supply to the bridge circuit of the inverter 112 is interrupted to stop driving the motor 20 and stop assisting. Therefore, an unintended steering assist force is avoided.

  However, if a mechanical relay is used, power supply to the bridge circuit cannot be immediately interrupted due to an operation delay. In addition, there is a problem that the mechanical relay becomes large. In order to solve these problems, in the electric power steering apparatus disclosed in Japanese Patent No. 3375502 (Patent Document 1), a switch that opens and closes power supply to the bridge circuit is configured by an FET. When an abnormal state such as an overcurrent is detected, the FET is turned off to cut off the power supply to the bridge circuit in a very short time.

  In addition, an unintended closed circuit is formed due to an abnormality in the bridge circuit that drives the motor, a short circuit or a ground fault between the bridge circuit and the motor, and this causes an unintended steering assist force from the motor, On the contrary, the motor operates as an electromagnetic brake, and there is a risk of acting in a direction that hinders the driver's steering operation. In the motor control device disclosed in Japanese Patent Application Laid-Open No. 2007-295658 (Patent Document 2) and the electric power steering device using the same, between the neutral point of the three-phase brushless motor and the excitation coils Lu to Lw, Field effect transistors FETu to FETw and diodes Du to Dw connected in antiparallel to the field effect transistors FETu to FETw are provided. When an abnormality is detected in the motor control device, the three-phase brushless motor is stopped and the field effect transistors FETu to FETw are opened to avoid the formation of a closed circuit.

Furthermore, in the electric power steering apparatus disclosed in Japanese Patent No. 3427876 (Patent Document 3), a switch means (relay circuit) is provided at the neutral point of the brushless motor. When a failure occurs in the bridge circuit, the closed loop of the motor drive current is interrupted by opening and closing the switch means.
Japanese Patent No. 3375502 JP 2007-295658 A Japanese Patent No. 3427876

  In the case of detecting an abnormality such as an overcurrent, the electric power steering device described in Patent Document 1 turns off the opposing FET (semiconductor relay) instead of the relay to cut off the power supply to the bridge circuit and stop the assist. To do. However, it is not possible to avoid the occurrence of a steering assist force or an electromagnetic brake that is not intended by the driver by interrupting the closed circuit formed when an abnormality such as an inverter occurs.

  Further, in the motor control device described in Patent Document 2 and the electric power steering control device using the motor control device, in order to provide the field effect transistors FETu to FETw inside the motor, it is necessary to mount a substrate inside the motor. There is a problem of increasing the size. Furthermore, in order to control the field effect transistors FETu to FETw, a signal line is required between the motor and the control unit. In addition to the problem of increased reliability of the motor and control unit due to the increase in the size of the connector of the motor and the control unit, Since the inside of the motor becomes high temperature, there is a problem that the parts deteriorate quickly and the reliability deteriorates.

  In the electric power steering device described in Patent Document 3, a relay circuit is used as switch means for opening a closed loop, and there is a problem that the closed loop cannot be opened immediately after detecting an abnormality. In addition, there is a problem that a relay circuit becomes large in a large vehicle or the like that requires a large assist current.

  Further, when a semiconductor relay is provided in two phases of the motor phase current supply path, two FETs are required for each of the two phases, and a total of four FETs are required. Therefore, there exists a problem that a control unit will enlarge.

  The present invention has been made under the circumstances as described above. The object of the present invention is to provide a steering assist force that is not intended by the driver because a closed circuit is formed when an abnormality occurs in the inverter and the assist is stopped. The generation of electromagnetic brakes can be avoided in a very short time with a small, low-cost, low-noise, low-power-consumption device, and the steering assist force provides better steering feeling during normal steering. An object of the present invention is to provide an electric power steering apparatus capable of providing

  The present invention includes an inverter that calculates a current command value based on at least a steering torque and a vehicle speed, and supplies a motor phase current to each phase of a motor that applies a steering assist force to the steering mechanism based on the current command value. Regarding the electric power steering apparatus, the object of the present invention is to provide a first FET group in each phase supply path for supplying the motor phase current to the motor, and to detect the inverter when an abnormality of the inverter is detected. This is achieved by having the function of turning off the second FET group and the first FET group.

  The present invention includes an inverter that calculates a current command value based on at least a steering torque and a vehicle speed, and supplies a motor phase current to each phase of a motor that applies a steering assist force to the steering mechanism based on the current command value. Regarding the electric power steering apparatus, the object of the present invention is to provide a first FET group in each phase supply path for supplying the motor phase current to the motor, and to detect an abnormality of the inverter, An abnormality that turns off the first FET group when the abnormality detection unit detects the abnormality and turns off the second FET group that constitutes the inverter through a gate control circuit provided in the inverter. This is achieved by providing an avoidance unit, or by causing the abnormality to be a short-circuit failure of the FET constituting the inverter.

  According to the electric power steering apparatus of the present invention, an FET is provided in a supply path for supplying motor phase current to the motor, and when an abnormality occurs in the inverter, the FET constituting the inverter and the FET provided in the supply path are provided. I try to turn it off. For this reason, a closed circuit is formed due to the failure of the inverter, and it is possible to reliably avoid the generation of a steering assist force and an electromagnetic brake that are not intended by the driver. Therefore, it is possible to apply a steering assist force that provides a better steering feeling during normal steering.

  In order to avoid the formation of a closed circuit, an FET, which is a high-speed switching element, is used instead of a relay circuit, so that the formation of a closed circuit can be avoided in a very short time, and the electric power steering device can be reduced in size. Can be achieved. In addition, the operation noise due to the driving of the relay circuit can be eliminated, and further, the current flowing through the relay driving coil is not required, so that the power consumption can be kept low.

  In the electric power steering apparatus according to the present invention, an FET is provided in each phase supply path for supplying a motor phase current to the motor, and when an abnormality is detected in the inverter and the assist is stopped, the FET and the supply constituting the inverter By turning off all the FETs provided on the road, the closed circuit is interrupted to avoid the generation of steering assist force and electromagnetic brake that are not intended by the driver.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit connection diagram showing a configuration of a motor drive system for interrupting a closed circuit formed when an abnormality occurs in the inverter 112 and the assist is stopped in the electric power steering apparatus according to the present invention. . In the electric power steering apparatus according to the present invention, FET7, FET8, and FET9 (first FET group) are respectively provided as switching means in the motor phase current supply paths a, b, and c supplied from the inverter 112 to the motor 20. ). A surge absorbing diode is connected in antiparallel between the source and drain of the FET7 to FET9. Furthermore, in the electric power steering apparatus according to the present invention, the abnormality detection unit 121 that detects abnormality such as a short circuit failure of the FET1 to FET6 (second FET group) constituting the inverter 112, and the abnormality detection unit 121 detected abnormality. When the assist stop signal AS is output, the FETs 7 to 9 provided in the supply paths a, b, and c are turned off, and the FET 1 that configures the inverter 112 via the gate control circuit 114 provided in the inverter 112 And an abnormality avoiding unit 122 that turns off FET 6, and a gate control circuit 114 that simultaneously turns off FET 1 to FET 6 when the assist stop signal AS from the abnormality avoiding unit 122 is input to the inverter 112. Is provided. The rest of the configuration of the electric power steering device according to the present invention is the same as the configuration of the electric power steering device shown in FIGS. 4, 5, and 6. Therefore, when the assist stop signal AS is not input to the gate control circuit 114 in the inverter 112, the duty signal from the FET gate drive circuit 111 is input to the FET1 to FET6 through the gate control circuit 114, and further, the FET7 to FET9. Then, the motor 20 is driven.

  According to the electric power steering apparatus according to the present invention, the abnormality detection unit 121 detects an abnormality related to a short circuit failure or the like of the FET1 to FET6 constituting the inverter 112. When the abnormality detection unit 121 detects an abnormality, it outputs an assist stop signal AS, turns off the FETs 7 to 9 provided in the supply paths a, b, and c, and configures the inverter 112 via the gate control circuit 114. ~ Turn off FET6. As a result, the closed circuit formed by the short circuit failure of the FET constituting the inverter 112 can be cut off, and the generation of the steering assist force and the electromagnetic brake not intended by the driver can be avoided.

  When FET1 to FET6 and FET7 to FET9 are turned off by the abnormality avoiding unit 122, the current path flowing through the motor 20 is interrupted, so that no current flows through the motor 20, and the assist is stopped.

  For example, as shown in FIG. 2, when a short circuit failure occurs in the FET 1 of the inverter 112, a closed circuit A is formed along a path that passes through the FET 2, the FET 7, and the FET 8. When the closed circuit A is formed, an electromagnetic brake unintended by the driver may be generated by the induced voltage of the motor 20. However, in the electric power steering apparatus according to the present invention, when the abnormality detection unit 121 detects a short-circuit failure of the FET 1, the abnormality avoidance unit 122 outputs the assist stop signal AS and the FET 7 provided in the supply paths a, b, and c. The FET 9 is turned off, and the FET 1 to FET 6 constituting the inverter 112 are turned off via the gate control circuit 114. This avoids the occurrence of an unintended electromagnetic brake.

  As shown in FIG. 3, when the FET 4 of the inverter 112 causes a short circuit failure, a closed circuit B is formed along a path that passes through the FET 5, FET 7, and FET 8. When the closed circuit B is formed, an electromagnetic brake unintended by the driver may be generated by the induced electric power of the motor 20. However, in the electric power steering apparatus according to the present invention, when the abnormality detection unit 121 detects a short-circuit failure of the FET 4, the abnormality avoidance unit 122 outputs the assist stop signal AS and the FET 7 provided in the supply paths a, b, and c. The FET 9 is turned off and the FET 1 to FET 6 constituting the inverter 112 are turned off via the gate control unit 114. This avoids the occurrence of an unintended electromagnetic brake.

  In the above-described embodiment, since the motor 20 is a three-phase motor, there are three motor phase current supply paths, and one FET is provided in each of the three supply paths. When the motor 20 is a two-phase motor, there are two motor phase current supply paths, and one FET may be provided in each of the two supply paths.

  As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to this, In the range which does not deviate from the meaning, it can change suitably.

It is a circuit connection diagram which shows the structure of the motor drive system for interrupting | blocking the closed circuit formed when abnormality arises in an inverter. It is a circuit connection diagram for demonstrating the closed circuit A formed when FET1 of an inverter raise | generates a short circuit failure. It is a circuit connection diagram for demonstrating the closed circuit B formed when FET4 of an inverter raise | generates a short circuit failure. It is a figure showing an example of composition of a general electric power steering device. It is a block diagram which shows the structural example of the control unit of the conventional electric power steering apparatus. It is a connection diagram which shows the structural example of a motor drive circuit.

Explanation of symbols

20 motor 110 motor drive circuit 111 FET gate drive circuit 112 inverter 113 step-up power supply 114 gate control circuit 121 abnormality detection unit 122 abnormality avoidance unit

Claims (3)

An electric power steering apparatus including an inverter that calculates a current command value based on at least a steering torque and a vehicle speed, and supplies a motor phase current to each phase of a motor that applies a steering assist force to the steering mechanism based on the current command value In
A first FET group is provided in each phase supply path for supplying the motor phase current to the motor, and when an abnormality of the inverter is detected, the second FET group and the first FET constituting the inverter An electric power steering apparatus having a function of turning off the group. An electric power steering apparatus including an inverter that calculates a current command value based on at least a steering torque and a vehicle speed, and supplies a motor phase current to each phase of a motor that applies a steering assist force to the steering mechanism based on the current command value In
A first FET group is provided in each phase supply path for supplying the motor phase current to the motor, an abnormality detection unit for detecting an abnormality of the inverter, and when the abnormality detection unit detects the abnormality, And an abnormality avoiding unit for turning off a second FET group constituting the inverter via a gate control circuit provided in the inverter, and turning off one FET group. Steering device. The electric power steering apparatus according to claim 1 or 2, wherein the abnormality is a short-circuit failure of an FET constituting the inverter.

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