JP5032277B2 - Booster device for motor drive of electric power steering device - Google Patents

Description

  The present invention relates to a booster that boosts the voltage of an in-vehicle power supply in order to drive an electric motor that constitutes an electric power steering device in an automobile.

In an electric power steering apparatus for an automobile, an electric motor for generating an auxiliary steering force for reducing a manual steering force applied to a steering wheel by a driver is provided, and a high output is required for the electric motor. A booster circuit that boosts the current from the battery and supplies the electric motor to the electric motor is provided (see Patent Document 1), thereby reducing the current in the power supply wiring of the electric motor and avoiding thickening, In addition, since the influence of the voltage change on the input side can be minimized, stable power supply can be achieved and a good steering feel can be obtained.
JP 2003-312522 A

  However, in a motor drive booster of an electric power steering device, if the electric motor stops due to a failure occurring in an element or a control circuit that constitutes the motor, the driver's steering operability is significantly deteriorated. In order to prevent the electric motor from stopping during driving, an advanced self-diagnosis function is provided, or the so-called derating is used to reduce the rating of the elements used, In order to realize the diagnostic function, a high-performance circuit and a CPU are required, and a specification margin is also increased to increase the derating of the elements used, which increases the manufacturing cost.

  The present invention has been devised to solve such problems of the prior art, and its main purpose is to ensure the operation of the electric motor when a failure occurs in a control circuit or a component. An object of the present invention is to provide a step-up device for driving a motor of an electric power steering device configured so that fail-safe can be realized at low cost.

In order to solve such a problem, in the present invention, as shown in claim 1, a coil (23) and a first switching element (first FET 31) provided between the coil and the ground are provided. And a second switching element (second FET 33) provided between the coil and the electric motor (3), wherein the second driving element includes a second switching element (second FET 33). A first power supply means (FET control power supply circuit 41) for supplying power for driving the switching element; a second power supply means (failsafe power supply circuit 42) different from the first power supply means; A control circuit (29) for controlling the switching operation of the second switching element and the power supply by the first power supply means, and the second switch by the control circuit. Switching means (switching section 46) for switching so that the driving power for the second switching element is supplied by the second power supply means when there is an abnormality in which the control of the switching element and the first power supply means cannot be performed. When the control circuit is abnormal, the second switching element is ensured to be conductive by the power supply from the second power supply means .
In particular, as shown in claim 2, when the control circuit is abnormal, the second power supply means supplies the gate driving power to the gate driving circuit (34) for driving the gate of the second switching element. Thus, the second switching element is preferably turned on.
According to a third aspect of the present invention, when the control circuit is abnormal, the input voltage to the booster is output as it is and applied to the electric motor.

  According to this, when a failure occurs in the control circuit and it becomes difficult to drive the second switching element, the driving power for the second switching element is supplied by the second power supply means. Thus, since the conduction of the second switching element is ensured, it becomes possible to supply the power to the motor via the second switching element, thereby realizing fail-safe.

  At this time, it is a condition that the switching element is operable. However, since the frequency of failure of the switching element and its drive circuit is lower than that of the control circuit, it is possible to secure driving of the electric motor by through processing. If possible, reliability equivalent to that of a system having a complicated self-diagnosis function can be realized. Further, the second power supply means does not require the same performance as the first power supply means used in normal times, and it is sufficient to use a relatively simple circuit and a minimum capacity, which increases the manufacturing cost. Can be suppressed.

  In this case, since there is no drive signal from the control circuit, the original step-up operation is not performed, only conduction between the power source and the motor is ensured, and a through process is performed in which the input voltage to the step-up circuit is output as it is. For this reason, the electric motor is operable with the power supply voltage, and the boosting ratio of the boosting circuit, that is, the ratio of the output voltage to the input voltage is relatively low, and is preferably set to, for example, twice or less.

  The first power supply means is controlled by the control circuit, performs power supply to the first and second switching elements in response to an instruction from the control circuit, and supplies power when a failure occurs in the control circuit. To stop. On the other hand, the second power supply means operates independently of the control circuit, and supplies power to the second switching element instead of the first power supply means when the control circuit is abnormal.

  When the switching element is an N-channel FET, a voltage higher than the input voltage is required for driving the gate, and the first and second power supply means include a booster circuit that boosts the power supply voltage. Become.

Moreover, in this invention, as shown in Claim 4 , a coil (23), the 1st switching element (1st FET31) provided between this coil and the ground, the said coil, and an electric motor ( 3) and a second switching element (second FET 33) provided between the first switching element and the motor driving booster of the electric power steering apparatus, wherein the diode is connected in parallel with the second switching element. (51) and overcurrent absorbing means (zener diode 52) provided between the second switching element and the electric motor, and through the diode when the second switching element is abnormal An electric current was passed through the electric motor.

  According to this, when a failure occurs in the second switching element itself or its control system and the second switching element becomes inoperable, the diode performs a rectifying operation instead of the second switching element. Thus, the boosting process is continuously performed, so that fail-safe is realized. And it can suppress that an overvoltage generate | occur | produces in the motor drive circuit which consists of an H bridge circuit etc. by an overcurrent absorption means.

  In this case, a Zener diode is suitable for the overcurrent absorbing means.

  As described above, according to the present invention, the second switching element is secured by the second power supply unit different from the first power supply unit that is normally used, and the second switching element is interposed. The power supply power can be supplied to the motor by the through process, and the diode connected in parallel with the second switching element performs the rectifying operation instead of the second switching element, thereby continuing the boosting process. Thus, fail-safe for ensuring the operation of the electric motor when a failure occurs in the control circuit or the component can be realized at low cost.

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

  FIG. 1 is an overall configuration diagram of an electric power steering apparatus to which the present invention is applied. The electric power steering apparatus is provided with an electric motor 3 that generates an auxiliary steering force for reducing the manual steering force of the steering wheel (operator) 1.

  The electric power steering apparatus is provided with a pinion 4 connected to the steering wheel 1 via a steering shaft 2 so as to be integrally rotatable, and meshed with the pinion 4 so as to be able to reciprocate in the vehicle width direction. A rack-and-pinion mechanism having a rack shaft 5 is provided, and both ends of the rack shaft 5 are connected to knuckle arms 8 of left and right front wheels 7 as steering wheels via tie rods 6 to rotate the steering wheel 1. Accordingly, the left and right front wheels 7 are steered, and the driving force of the electric motor 3 is input to the steering shaft 2 via the worm gear mechanism 11 housed in the gear box 10 together with the pinion 4.

  The electric motor 3 is controlled by a steering control device (EPS-ECU) 13. The steering control device 13 includes output signals from a steering angle sensor 14 that detects the steering angle of the steering wheel 1, a steering torque sensor 15 that detects manual steering torque that acts on the pinion 4, and a vehicle speed sensor 16 that detects vehicle speed. Is input, and the electric motor 3 is controlled based on these signals so that a required auxiliary steering force is generated.

  The steering control device 13 includes a booster circuit 18 that boosts the voltage of the battery (power source) 17 and a motor drive circuit 19 that includes an H bridge circuit that drives the electric motor 3.

  FIG. 2 is a block diagram showing a first example of the booster circuit shown in FIG. FIG. 3 is a flowchart showing a control procedure of the booster circuit shown in FIG. The booster circuit (boost device) 18 includes an input relay 21, a current sensor 22, a booster coil (choke coil) 23, a temperature sensor 24, a booster 25, and a synchronous rectifier 26.

  The input relay 21 is provided for the purpose of protecting each element from, for example, an overcurrent generated on the load side, and is turned on / off according to a drive signal from the control circuit (CPU) 29 or another circuit. The current sensor 22 detects the current of the booster coil 23, the temperature sensor 24 detects the temperature in the booster circuit 18, and the output signals of the current sensor 22 and the temperature sensor 24 are input to the control circuit 29. The control circuit 29 monitors the input voltage and output voltage of the booster circuit 18.

  The step-up unit 25 excites the step-up coil 23 by applying the voltage of the battery 17 to the step-up coil 23 by grounding the other end of the step-up coil 23 connected to the battery 17 at one end. The first FET (first switching element) 31 and a gate drive circuit 32 are included.

  The first FET 31 includes a transistor Tr1 and a parasitic diode D1. In the transistor Tr1, the drain is connected to the load (electric motor 3) side of the booster coil 23, and the source is grounded. The gate of the transistor Tr 1 is connected to the gate drive circuit 32, and a control signal from the control circuit 29 is input to the gate drive circuit 32.

  The synchronous rectification unit 26 releases the stored energy of the boosting coil 23 during the off period of the first FET 31 of the boosting unit 25, and includes an N-channel MOS type second FET (second switching element) 33, And a gate drive circuit 34.

  The second FET 33 includes a transistor Tr2 and a parasitic diode D2. In the transistor Tr2, the source is connected to the step-up coil 23 side, and the drain is connected to the load (electric motor 3) side. The gate of the transistor Tr2 is connected to the gate drive circuit 34, and a control signal from the control circuit 29 is input to the gate drive circuit 34.

  The booster circuit 18 includes an FET control power supply circuit (first power supply means) 41 that supplies gate drive power to the gate drive circuit 32 of the booster 25 and the gate drive circuit 34 of the synchronous rectifier 26, A fail-safe power supply circuit (second power supply means) 42 that supplies gate drive power only to the gate drive circuit 34 of the synchronous rectifier 26 is provided.

  The FET control power supply circuit 41 and the fail-safe power supply circuit 42 are supplied with power from the battery (power supply) 17 via the power supply control circuit 43, and with respect to the input voltage (usually 10 V to 14.5 V) from the battery 17. In addition, a booster circuit for generating a high voltage (for example, 20 V to 30 V) required for driving the gates of the N-channel FETs 31 and 33 is provided.

  The FET control power supply circuit 41 is controlled by the control circuit 29 and supplies power to the gate drive circuits 32 and 34 based on the control signal output from the control circuit 29, and the transistor Tr 1 and the transistor Tr 2 are supplied from the control circuit 29. A switching operation corresponding to the control signal is performed. In the FET control power supply circuit 41, when an abnormality occurs in the control circuit 29, there is no control signal from the control circuit 29 instructing the power supply, so the power supply to the gate drive circuits 32 and 34 is stopped.

  On the other hand, the fail-safe power supply circuit 42 is connected to the FET control power supply circuit 41 by a switching unit 46 including a transistor (FET) that performs switching operation in response to an output signal of a watchdog timer (WDT) 45 that detects an abnormality of the control circuit 29. Instead, power is supplied to the gate drive circuit 34 of the synchronous rectification unit 26.

  The fail-safe power supply circuit 42 may be configured to operate independently of the control circuit 29 in which an abnormality has occurred, and the switching unit 46 that switches the output is configured by a diode OR circuit that selects the high voltage side. Or the fail-safe power circuit 42 is activated to switch the output in response to the abnormality detection signal of the watchdog timer, or the output is switched to the fail-safe power circuit 42 when the system monitoring sub CPU detects an abnormality. Various configurations, such as a configuration, are possible.

  As described above, the fail-safe power supply circuit 42 operates independently from the control circuit 29, and supplies power to the gate drive circuit 34 of the synchronous rectification unit 26 at the time of failure in which the normal operation in the booster circuit 18 is disabled. Supply. As a result, the transistor Tr2 is always turned on, and the boosting circuit 18 executes a through process in which the input voltage is output without being boosted.

  The electric motor 3 is assumed to be operable with the voltage of the battery 17 (normally 10V to 14.5V), and the boosting ratio of the booster circuit 18 is set to 2 times or less, for example, output for an input voltage of 10V to 14.5V. The electric motor 3 can be operated without boosting by the through process of the booster circuit 18 performed at the time of failure by setting the voltage to 16V.

  In the booster circuit 18 configured as described above, as shown in FIG. 3, if boosting is not impossible (No in step 101), normal boosting control is executed (step 102). On the other hand, if a failure occurs in the control circuit 29, boosting becomes impossible (Yes in Step 101), and if through processing is also impossible (No in Step 103), output is stopped (Step 104), and through processing is possible. If so (Yes in Step 103), a through process is performed (Step 105).

  Note that the fail-safe power supply circuit 42 functions as a fail-safe for the failure generated in the control circuit 29 as described above, and can also function as a fail-safe for the failure generated in the FET control power supply circuit 41. is there.

  FIG. 4 is a block diagram showing a second example of the booster circuit shown in FIG. Here, a diode 51 is connected in parallel to the second FET 33 of the synchronous rectification unit 26, and a Zener diode (overcurrent absorbing means) 42 is provided on the load (electric motor 3) side of the synchronous rectification unit 26. Yes. In addition, the same code | symbol is attached | subjected to what is common in the 1st example shown in FIG. 2, and the detailed description is abbreviate | omitted.

  Similarly to the parasitic diode D2 in the second FET 33, the diode 51 has an anode connected to the boosting coil 23 side and a cathode connected to the load (electric motor 3) side. The Zener diode 52 has a cathode connected to the output line of the synchronous rectifier 26 and an anode grounded.

  In this configuration, when a failure occurs in the transistor Tr2 or the control circuit 29 of the synchronous rectification unit 26 and the second switching element becomes inoperable, conduction is ensured by the diode 51, and the voltage is boosted by the diode rectification method. Processing continues.

  The electric motor 3 functions as a generator when operated by an external force acting from the wheel side, and the high voltage current generated at this time flows to the battery 17 side. When Tr2 becomes non-conductive and the path through which the high voltage generated by the electric motor 3 flows is interrupted, the voltage of the motor drive circuit 19 composed of an H bridge circuit or the like becomes abnormally high, and the elements constituting this are damaged. receive.

  In order to deal with such a problem, an overcurrent (surge) of the motor drive circuit 19 is provided by providing a Zener diode 52 whose one end is grounded between the synchronous rectification unit 26 and the motor drive circuit 19 as in this configuration. ) Is absorbed, and damage to the components of the motor drive circuit 19 can be avoided.

  In the electric power steering device of the present invention, the steering handle and the steered wheels are mechanically separated from each other in addition to the configuration in which the driving force of the electric motor is used as an auxiliary steering force for assisting the driver's steering. Also included is a steer-by-wire configuration in which all of the steering force for the steered wheels is generated by an electric motor.

1 is an overall configuration diagram of an electric power steering apparatus to which the present invention is applied. FIG. 2 is a configuration diagram illustrating a first example of a booster circuit illustrated in FIG. 1. FIG. 3 is a flowchart showing a control procedure of the booster circuit shown in FIG. 2. FIG. 3 is a configuration diagram showing a second example of the booster circuit shown in FIG. 1.

Explanation of symbols

3 Electric motor 13 Steering control device 17 Battery (power source)
DESCRIPTION OF SYMBOLS 18 Booster circuit 19 Motor drive circuit 23 Booster coil 25 Booster part 26 Synchronous rectifier 29 Control circuit 31 1st FET (1st switching element)
33 Second FET (second switching element)
32/34 Gate drive circuit 41 FET control power supply circuit (first power supply means)
42 Fail-safe power supply circuit (second power supply means)
51 Diode 52 Zener diode (overcurrent absorption means)
Tr1 / Tr2 Transistors D1 / D2 Parasitic diode

Claims (4)

A motor of an electric power steering apparatus comprising at least a coil, a first switching element provided between the coil and the ground, and a second switching element provided between the coil and the electric motor A booster device for driving,
First power supply means for supplying power for driving the second switching element ;
A second power supply means different from the first power supply means;
A control circuit for controlling the switching operation of the second switching element and the power supply by the first power supply means;
When the control circuit does not allow the control of the second switching element and the first power supply means, switching is performed so that the driving power for the second switching element is supplied by the second power supply means. Switching means,
A booster for driving a motor of an electric power steering apparatus, wherein conduction of the second switching element is ensured by power supply from the second power supply means when the control circuit is abnormal .   When the control circuit is abnormal, the second power supply means supplies gate driving power to a gate drive circuit that drives the gate of the second switching element, so that the second switching element is turned on. The step-up device for driving a motor of an electric power steering device according to claim 1, characterized in that:   The motor of the electric power steering apparatus according to claim 1 or 2, wherein when the control circuit is abnormal, an input voltage to the booster is output as it is and applied to the electric motor. Drive booster. A motor of an electric power steering apparatus comprising at least a coil, a first switching element provided between the coil and the ground, and a second switching element provided between the coil and the electric motor A booster device for driving,
A diode connected in parallel with the second switching element; and overcurrent absorbing means provided between the second switching element and the electric motor; and when the second switching element is abnormal, A step-up device for driving a motor of an electric power steering device, wherein a current is passed through the electric motor via a diode.

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