JP5527182B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus that assists steering of a steering wheel.

  Conventionally, there is an electric power steering device that assists steering of a steering wheel (see Patent Document 1). The electric power steering apparatus includes a motor that applies torque to a steering wheel, a three-phase inverter circuit that outputs a three-phase driving current to the motor, and a control unit that controls driving of the motor by controlling the three-phase inverter circuit; Is provided. The three-phase inverter circuit is provided with a total of six MOSFETs, two in each phase path, and is switched by the control unit.

JP 2009-035155 A JP 2009-006963 A JP 2009-008239 A JP 2004-282963 A

  By the way, when a large reverse rotation load acts on the motor, such as when riding on a large level difference, the motor acts as a generator and the back electromotive force increases. At this time, an overcurrent due to the back electromotive force is applied to each MOSFET of the three-phase inverter circuit, which may cause a problem in each MOSFET. Here, if a failure occurs in the MOSFET of two or more phases among the three-phase paths, it is not possible to shift to the two-phase drive control mode, and the assist is completely stopped.

  The present invention has been made in view of such problems, and an object thereof is to provide an electric power steering apparatus that protects switching elements arranged in two phases in a three-phase inverter circuit.

In order to solve the above problems, an electric power steering device according to an aspect of the present invention is an electric power steering device that assists steering of a steering wheel, and includes a motor that generates torque for assisting steering, A three-phase inverter circuit that supplies a three-phase drive current to the motor from the path; and a CPU that controls the three-phase inverter circuit. The three-phase inverter circuit includes an active clamp circuit connected to at least six switching elements that are switched by the control of the CPU, a motor, a control terminal of one switching element whose output terminal is grounded, a motor, A relay provided between the active clamp circuit and the active clamp circuit. This active clamp circuit turns on one switching element when the voltage on the motor side exceeds a predetermined voltage. One switching element is provided in the first path among the three paths for supplying the motor. The relay is provided in the first path, and is controlled by the CPU to disconnect the connection between one switching element and the motor based on the detection result indicating the failure of the first path. In the three-phase inverter circuit, a relay that can be disconnected from the motor is not provided in the second path among the three paths.

  According to this aspect, when a large back electromotive force is generated in the motor, the current can be released by turning on the grounded switching element by the active clamp circuit. Further, even in the worst case, the switching elements of phases other than the switching elements that are turned on can be protected.

  According to the electric power steering apparatus of the present invention, the switching elements arranged in two phases in the three-phase inverter circuit can be protected.

It is a figure explaining the functional composition of the control device concerning an embodiment. It is a figure explaining the effect | action of the active clamp circuit which concerns on embodiment. It is a figure which shows the change of an active clamp circuit and the surrounding voltage or electric current. It is a figure which shows the modification of the control apparatus which concerns on embodiment.

  The electric power steering apparatus according to the embodiment drives a motor in accordance with a steering amount by a driver and gives a steering assist force to a steering mechanism of the vehicle. The steering mechanism includes a steering wheel, a steering shaft, a connecting shaft, and a gear device that converts the movement of the steering shaft into the movement of the front wheels. The steering mechanism converts the rotation of the steering wheel as a handle into the steering motion of the front wheels.

  The steering wheel is provided in the vehicle compartment and is turned by the driver. The steering shaft has one end connected to the steering wheel so as to rotate together with the steering wheel, and functions as a rotating shaft that transmits the rotation of the steering wheel to the gear device. The other end of the steering shaft is connected to one end of the connecting shaft via a universal joint. A pinion gear is provided at the other end of the connecting shaft.

  A rack gear is provided on the steering shaft of the gear device. The pinion gear of the connecting shaft meshes with the rack gear of the steering shaft of the gear device, and the rotation of the steering wheel is converted into the movement of the steering shaft in the axial direction. When the steering shaft moves in the axial direction, the front wheels are steered.

  The electric power steering device according to the embodiment includes a motor, a speed reduction mechanism, a rudder angle sensor, a torque sensor, and a control device. The motor shaft of the motor is connected to a speed reduction mechanism. The speed reduction mechanism is provided with a gear and meshes with a gear portion provided on the steering shaft. When the motor operates, the steering shaft is rotationally driven while the rotational motion is decelerated by the speed reduction mechanism.

  The steering angle sensor is provided on the steering shaft and detects the steering angle and steering direction of the steering wheel. The steering angle sensor is connected to the control device, and the detection value of the steering angle sensor is output to the control device.

  The torque sensor is provided on the steering shaft and detects steering torque applied to the steering shaft. The torque sensor is connected to the control device, and the detected value of the torque sensor is output to the control device.

  The control device calculates a target assist torque for driving the steering shaft based on the detected values of the steering angle sensor and the torque sensor, supplies a current for generating the calculated target assist torque to the motor, and drives the motor. In this way, the control device assists the steering of the steering wheel by the driver according to the steering angle and the steering torque.

  FIG. 1 is a diagram illustrating a functional configuration of a control device 10 according to the embodiment. The control device 10 includes a high voltage battery 20, a converter 30, and a control unit 40. The high voltage battery 20 functions as a drive power source for the motor 12 that rotationally drives the steering shaft. The high voltage battery 20 is connected to the converter 30 and supplies current to the converter 30. One end of the high voltage battery 20 is grounded.

  The converter 30 is set so that the output voltage of the high-voltage battery 20 is as high as 200 V or higher, while the motor 12 is used at a low voltage, for example, 30 V to 50 V.

  Converter 30 includes a step-down circuit 32 and a regenerative power consumption circuit 34. The step-down circuit 32 steps down the voltage input from the high voltage battery 20 and outputs it to the drive IC 44 and the three-phase inverter circuit 50 as a DC power supply voltage for driving the motor. The regenerative power consumption circuit 34 converts the regenerative power output from the motor 12 into heat and consumes it. One end of the regenerative power consumption circuit 34 is connected to the output side line of the step-down circuit 32, for example, between the step-down circuit 32, the drive IC 44 and the three-phase inverter circuit 50, and the other end is grounded.

  Specifically, the step-down circuit 32 switches the input voltage from the high-voltage battery 20 to an AC voltage by switching at a constant frequency, and converts the AC voltage by a winding transformer to step down the voltage. The stepped-down AC voltage is rectified and converted to a DC voltage, and further smoothed and output as a DC current.

  The control unit 40 performs control for supplying a three-phase drive current to the motor 12 using a direct current from the converter 30 as a power source of the motor 12. The control unit 40 includes a three-phase inverter circuit 50, a power supply circuit 42, a drive IC 44, a CPU (Central Processing Unit) 46, an I / F circuit 48, a first relay 47 and a second relay 49. The power supply circuit 42 is connected to the in-vehicle battery 41 having a rated output voltage of 12 V, and supplies current to the CPU 46 of the control unit 40. The power supply circuit 42 may step down and supply a voltage lower than 12V when supplying current to the CPU 46. The power circuit relay 43 turns on and off the supply of current from the in-vehicle battery 41 to the power circuit 42.

  The I / F circuit 48 receives the output value of the torque sensor and the output value of the steering angle sensor, and inputs them to the CPU 46. The CPU 46 calculates the target assist torque based on the output value of the torque sensor and the output value of the steering angle sensor, and sends a command signal (PWM signal) corresponding to the target assist torque to the drive IC 44.

  The drive IC 44 outputs the command signal received from the CPU 46 to the three-phase inverter circuit 50. The three-phase inverter circuit 50 supplies a three-phase alternating current to the motor 12 in accordance with an input from the drive IC 44.

  Specifically, the three-phase inverter circuit 50 includes six switching elements including a first MOSFET 52a, a second MOSFET 52b, a third MOSFET 52c, a fourth MOSFET 52d, a fifth MOSFET 52e, and a sixth MOSFET 52f (referred to as “MOSFET 52” if they are not distinguished from each other). .

  The gate of the MOSFET 52, that is, the control terminal is connected to the drive IC 44. The drains, that is, the input terminals of the first MOSFET 52a, the second MOSFET 52b, and the third MOSFET 52c are connected to the converter 30. The first MOSFET 52a, the second MOSFET 52b, and the third MOSFET 52c are turned on when a high voltage pulse is sent from the drive IC 44.

  The sources of the fourth MOSFET 52d, the fifth MOSFET 52e, and the sixth MOSFET 52f, that is, the output terminals, are grounded via the first resistor portion 54a, the second resistor portion 54b, and the third resistor portion 54c.

  The connection point between the output terminal of the first MOSFET 52a and the input terminal of the fourth MOSFET 52d, the connection point of the output terminal of the second MOSFET 52b and the input terminal of the fifth MOSFET 52e, and the connection point of the output terminal of the third MOSFET 52c and the input terminal of the sixth MOSFET 52f Each is connected. The first MOSFET 52a and the fourth MOSFET 52d are provided in the U-phase path, the second MOSFET 52b and the fifth MOSFET 52e are provided in the V-phase path, and the third MOSFET 52c and the sixth MOSFET 52f are provided in the W-phase path.

  A first relay 47 is provided between the connection point between the second MOSFET 52 b and the fifth MOSFET 52 e and the connection with the motor 12. The first relay 47 is provided in the path L of the V-phase drive current to the motor 12. A second relay 49 is provided between the connection point of the third MOSFET 52 c and the sixth MOSFET 52 f and the connection with the motor 12.

  The first relay 47 and the second relay 49 disconnect the respective phases (V phase, W phase) between the three-phase inverter circuit 50 and the motor 12. For example, when detecting a short circuit of the V-phase MOSFET 52, the CPU 46 opens the first relay 47 in order to disconnect the connection between the second MOSFET 52 b and the motor 12. Thereby, it can prevent that the motor 12 stops working.

  The three-phase inverter circuit 50 converts the power from the converter 30 into three-phase power and supplies it to the motor 12 by switching each MOSFET 52 at a predetermined timing under the control of the CPU 46.

  The three-phase inverter circuit 50 is provided with an active clamp circuit 60 that forcibly turns on the fifth MOSFET 52e when a voltage equal to or higher than the Zener voltage is applied. A first terminal of the active clamp circuit 60 is connected to the first relay 47, and a second terminal is connected between the gate of the fifth MOSFET 52e and the drive IC 44.

  The active clamp circuit 60 includes a Zener diode 62 and a diode 64. The Zener diode 62 is disposed on the first relay 47 side, and starts to energize when the first terminal on the first relay 47 side becomes equal to or higher than the Zener voltage. The diode 64 passes a current from the Zener diode 62 toward the fifth MOSFET 52e, and cuts off a current from the fifth MOSFET 52e and the drive IC 44 toward the Zener diode 62.

  By the way, when the rack gear moves and a large reverse rotation load acts on the motor 12 due to an excessive external force such as when riding on a large step, the motor 12 acts as a generator and the back electromotive force increases. At this time, an overcurrent due to the back electromotive force is applied to each MOSFET 52, and there is a possibility that a malfunction occurs in each MOSFET 52.

  Therefore, the three-phase inverter circuit 50 according to the embodiment protects the MOSFET 52 of the other phase by allowing the overcurrent to flow through the MOSFET 52 of one phase among the three phases when an overcurrent flows from the motor 12. To do. In the worst case, even if a failure occurs in the one-phase MOSFET 52 provided with the active clamp circuit 60, the control unit 40 opens the relay of the phase in which the failure has occurred and switches the control to switch the motor 12 from the other two phases. A current can be supplied to the motor 12 to drive the motor 12.

  FIG. 2 is a diagram illustrating the operation of the active clamp circuit 60 according to the embodiment. FIG. 2 shows a part of the control device 10 and the motor 12. FIG. 3 is a diagram showing changes in the active clamp circuit 60 and the voltage or current around it.

  3 shows the V-phase terminal voltage 70 of the first relay 47, the next shows the gate voltage 72 on the gate side of the fifth MOSFET 52e, and the bottom shows the drain current on the drain side of the fifth MOSFET 52e. 74 is shown. The V-phase terminal voltage 70 is a voltage at a point P1 shown in FIG.

  From time t0, the motor 12 begins to act as a generator, and the V-phase terminal voltage 70 increases. When the V-phase terminal voltage 70 becomes the zener voltage V1 at time t1, the zener diode 62 is energized as indicated by the arrow P2 in FIG. 2, and the gate voltage 72 starts to rise. The Zener voltage V1 is set so as to be lower than the breakdown voltage of the other MOSFET 52 and the voltage of the drive IC 44 including variations.

  Next, at time t2, the gate voltage 72 reaches a voltage for turning on the fifth MOSFET 52e, and the fifth MOSFET 52e is turned on. Then, as indicated by an arrow P3 in FIG. 2, the current from the motor 12 passes through the fifth MOSFET 52e, and the drain current 74 shown in FIG. 3 starts to rise. Thereby, the current from the motor 12 can be released to the ground via only the V phase.

  On the other hand, the fourth MOSFET 52d and the sixth MOSFET 52f are off, and the current from the motor 12 does not flow through the fourth MOSFET 52d and the sixth MOSFET 52f.

  When the voltage from the motor 12 exceeds the withstand voltage of the fifth MOSFET 52e, a problem occurs in the fifth MOSFET 52e. When the CPU 46 detects a failure of the fifth MOSFET 52e by a predetermined failure detection means, the CPU 46 opens the first relay 47 and switches to drive control of the motor 12 using the U phase and the W phase. Although no current can be supplied from the V phase to the motor 12, current can be supplied from the U phase and the W phase to the motor 12 even in this case, so that the drive of the motor 12 can be maintained. Conventional control may be used to control the motor 12 in two phases.

  FIG. 4 shows a modification of the control device according to the embodiment. The control device 100 for the motor 12 is different from the control device 10 shown in FIG. Here, the same or equivalent components and members shown in FIG. 1 are denoted by the same reference numerals, and repeated description thereof will be omitted as appropriate.

  The third relay 92 turns on and off the power line to the control system such as the CPU 46. The fourth relay 88 turns on and off the power supply line to the drive system of the booster circuit 80.

  The booster circuit 80 boosts the voltage of the current supplied from the in-vehicle battery 41 to a predetermined voltage and supplies it to the three-phase inverter circuit 50 and the drive IC 44. The step-up circuit 80 includes a step-up coil 82 provided in series with the in-vehicle battery 41, a first step-up switching element 84 provided between the step-up coil 82 and the ground, and a connection point of the first step-up switching element 84. And a second boosting switching element 86 provided in series with the boosting coil 82. The first boost switching element 84 and the second boost switching element 86 are MOSFETs.

  The booster circuit 80 is boosted by the CPU 46. The CPU 46 outputs a pulse signal having a predetermined cycle to the gates of the first boosting switching element 84 and the second boosting switching element 86 via the drive IC 44 to output the first boosting switching element 84 and the second boosting switching element 86. Is turned on and off, and the current supplied from the vehicle-mounted battery 41 is boosted to generate a predetermined output voltage in the three-phase inverter circuit 50. In this case, the first step-up switching element 84 and the second step-up switching element 86 are controlled so that the ON / OFF operation is reversed. The step-up circuit 80 turns on the first step-up switching element 84 and turns off the second step-up switching element 86 so that a current is passed through the step-up coil 82 for a short time to power the step-up coil 82 and immediately thereafter. The first boosting switching element 84 is turned off and the second boosting switching element 86 is turned on so that the power stored in the boosting coil 82 is output.

  The output voltage (boosted voltage) of the booster circuit 80 can be adjusted by duty ratio control of the first boosting switching element 84 and the second boosting switching element 86. Therefore, the boosted voltage can be adjusted by adjusting the duty ratio of the gate signal output from the CPU 46.

  Similar to the three-phase inverter circuit 50 shown in FIG. 1, the three-phase inverter circuit 50 of the control device 100 includes an active clamp circuit 60, and the U-phase and W-phase switching elements are protected by the active clamp circuit 60. As described above, also in the control device 100 including the booster circuit 80 illustrated in FIG. 4, a desired switching element can be protected by the active clamp circuit 60, and driving of the motor 12 can be maintained.

  The present invention is not limited to the above-described embodiments, and various modifications such as design changes can be added based on the knowledge of those skilled in the art. The configuration shown in each figure is for explaining an example, and any configuration that can achieve the same function can be changed as appropriate, and the same effect can be obtained.

  DESCRIPTION OF SYMBOLS 10 Control apparatus, 12 Motor, 20 High voltage battery, 30 Converter, 32 Step-down circuit, 34 Regenerative power consumption circuit, 40 Control part, 41 Vehicle-mounted battery, 42 Power supply circuit, 43 Power supply circuit relay, 44 Drive IC, 46 CPU, 47 1st relay, 48 I / F circuit, 49 2nd relay, 50 3 phase inverter circuit, 52 MOSFET, 54 resistor, 60 active clamp circuit, 62 Zener diode, 64 diode, 70 V phase terminal voltage, 72 gate voltage 74 Drain current.

Claims (1)

An electric power steering device for assisting steering of a steering wheel,
A motor that generates torque for assisting steering;
A three-phase inverter circuit for supplying a three-phase drive current to the motor from three paths;
A CPU for controlling the three-phase inverter circuit,
The three-phase inverter circuit
At least six switching elements that are switched under the control of the CPU;
An active clamp circuit connected to the motor and a control terminal of one switching element whose output terminal is grounded;
A relay provided between the motor and the active clamp circuit,
The active clamp circuit turns on the one switching element when the voltage on the motor side exceeds a predetermined voltage ,
The one switching element is provided in a first path among the three paths for supplying to the motor,
The relay is controlled by the CPU to disconnect the one switching element and the motor based on a detection result indicating a failure of the first path,
The electric power steering apparatus according to claim 2, wherein a relay capable of disconnecting the connection with the motor is not provided on a second path among the three paths .

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