JP2009067174A - Control device of electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an electric power steering device capable of continuing the steering assist without increasing the size and the cost when any abnormality occurs in a motor driving circuit. <P>SOLUTION: The control device of the electric power steering device comprises a central processing unit (CPU) 11 for generating the control value of the current to drive a motor, a main motor driving circuit 13 and a sub motor driving circuit 14 for generating the driving current of the motor 2 from the PWM signal based on the control value of the current, a pre-driver IC 12 for driving MOSFETQ31-Q36 of driving elements constituting the main motor driving circuit 13, an abnormality detection unit 15 for detecting any abnormality of the main motor driving circuit 13, and a changing switch 16 for changing the path of the motor current. When any abnormality of the main motor driving circuit 13 is detected by the abnormality detection unit 15, the PWM signal is transmitted from the CPU 11 directly to the motor driving circuit 14, the changing switch 16 is changed to connect the sub motor driving circuit 14 to the motor 2, and the motor 2 is driven by the relatively small motor current generated by the sub motor driving circuit 14. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an electric power steering device that applies a steering assist force to a steering handle by a motor, and more particularly, to an electric power steering device that can continue steering assist when an abnormality occurs in a motor drive circuit. The present invention relates to a control device.

  As a steering assist device for a vehicle such as an automobile, an electric power steering device using the rotational force of a motor is often used. The electric power steering apparatus includes a control device (hereinafter also referred to as an ECU) that controls a current supplied to the motor so that the motor generates a desired rotational torque, and rotates at a current controlled by the ECU. The torque of the motor is transmitted to the steering shaft and the rack shaft directly connected to the steering handle via a reduction gear and a transmission mechanism such as a gear or a belt, and the steering handle is urged to assist the steering of the steering wheel.

Here, a general configuration of this type of conventional electric power steering apparatus will be described.
FIG. 3 is a block diagram showing a configuration of a conventional electric power steering apparatus. The electric power steering apparatus as described above generally includes an ECU 6, a motor 7, a torque sensor 8 that detects a steering torque, and a vehicle speed sensor 9 that detects a traveling speed of the vehicle.

  The ECU 6 generates a control value for the current supplied to the motor 7 based on the steering torque and the vehicle speed detected by the torque sensor 8 and the vehicle speed sensor 9, respectively, and determines the control value based on the generated control value for the current. A central processing unit (hereinafter also referred to as CPU) 61 that outputs a PWM (pulse width modulation) signal with a duty ratio to be applied, and a pre-driver that supplies a pulse voltage to each gate of MOSFETs Q61 to Q66 based on this PWM signal The IC 62 includes a motor drive circuit 63 that generates a current to be supplied to the motor 7.

  The motor drive circuit 63 includes N-channel MOSFETs (field effect transistors) Q61 to Q66 constituting an H-bridge circuit, and upper and lower arms connected in series by a pulse voltage supplied from the pre-driver IC 62 for each gate are alternately arranged. The motor 7 is rotationally driven by the pulse current flowing at this time.

  The electric power steering apparatus configured as described above is mounted not only on small passenger cars but also on large automobiles such as ordinary cars and trucks. These large automobiles require a larger steering assist force than a small passenger car because the vehicle weight is large, and a high output motor and a high power motor drive circuit 63 have been used.

  For this reason, for example, when an abnormality such as a short circuit or a disconnection occurs in the motor drive circuit 63 described above during driving of the vehicle, the motor 7 stops and the steering wheel operation becomes suddenly heavy, and the driver feels anxiety or sense of crisis. I hate giving.

  In order to solve this problem, each of the two motor drive circuits and motor windings is provided, and when the motor drive circuit or motor winding of one system is damaged, the motor drive circuit or motor winding of the other system is damaged. There has been proposed an electric power steering device capable of continuing steering assist by switching to (for example, see Patent Document 1).

JP 2003-40123 A

  However, since the conventional electric power steering device described in Patent Document 1 includes two motor drive circuits and motor windings, it requires twice as many parts as usual and the configuration becomes complicated. There has been a problem of increasing the size and cost.

  The present invention has been made in view of the above-described circumstances, and an object thereof is an electric power capable of continuing steering assist without causing an increase in size and cost when an abnormality occurs in a motor drive circuit. An object of the present invention is to provide a control device for a steering device.

  The object of the present invention described above is achieved by the following configuration.

(1) A control device for an electric power steering device that controls a drive current of a motor that applies a steering assist force,
Control means for generating a control value of a current for driving the motor;
A first motor driving unit that forms a bridge circuit by a plurality of driving elements connected between a power supply voltage and a ground potential, and generates a driving current of the motor based on a control value of the current;
A second motor driving unit that forms a bridge circuit by a plurality of driving elements connected between a power supply voltage and a ground potential, and generates a driving current of the motor based on the control value of the current;
An abnormality detecting means for detecting an abnormality of the first motor driving means;
Switch means for switching the connection with the first motor driving means or the connection with the second motor driving means with respect to the motor;
With
The control means includes
When an abnormality of the first motor driving unit is not detected by the abnormality detecting unit,
Controlling the switch means to connect the motor and the first motor drive means;
When an abnormality of the first motor driving unit is detected by the abnormality detection unit,
A control device for an electric power steering apparatus, wherein the switch means is controlled to connect the motor and the second motor driving means.
(2) The driving element of the second motor driving means is
A P-channel MOSFET whose source is connected to the power supply voltage;
An N-channel MOSFET having a source connected to the ground potential;
Are connected in cascade to form a pair of bridge circuits, and the control means includes:
The motor driving current generated by the second motor driving unit is controlled to be smaller than the motor driving current generated by the first motor driving unit. Control device for electric power steering device.
(3) The drive element of the first motor drive means is
An N-channel MOSFET having a drain connected to a power supply voltage;
An N-channel MOSFET having a source connected to the ground potential;
Are connected in cascade to form a pair of bridge circuits, and further, predrive means for driving the drive element of the first motor drive means based on the control value of the current is provided. The control device for the electric power steering device according to the above (1) or (2).
(4) The first motor driving means is mounted on a metal substrate,
Said 2nd motor drive means is mounted on a resin substrate, The control apparatus of the electric power steering apparatus as described in any one of said (1)-(3) characterized by the above-mentioned.

According to the configuration of (1) above, when an abnormality occurs in the first motor driving means driving the motor, the second motor driving means is switched to the second motor driving means by the switch means. Therefore, the steering assist can be continued without increasing the size and cost of the apparatus.
Further, according to the configuration of (2), the driving element of the second motor driving means is constituted by a pair of bridge circuits composed of a P-channel MOSFET and an N-channel MOSFET, and is generated by the second motor driving means. Since the drive current of the motor is controlled to be smaller than the drive current generated by the first motor drive means, it is not necessary to use a high-power drive element for the drive element, and the pre-drive means for driving the gate Can be directly driven by the control means, and an increase in size and cost of the apparatus can be avoided.
Furthermore, according to the configuration of (3) above, since the drive element of the first motor drive means is driven by the predrive means, the current supplied to the motor can be increased, and the steering assist force of the electric power steering device can be increased. Can be improved.
According to the configuration of (4) above, the first motor driving means is mounted on the metal substrate, so that the driving element can be effectively radiated and the second motor driving means can be replaced with the resin substrate. By mounting on top, it is possible to avoid an increase in size and cost of the apparatus.

  ADVANTAGE OF THE INVENTION According to this invention, when abnormality arises in a motor drive circuit, the control apparatus of the electric power steering apparatus which can continue steering assist can be provided, without causing enlargement and a cost increase.

DESCRIPTION OF EMBODIMENTS Hereinafter, a preferred embodiment of a control device for an electric power steering apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of a control device (ECU) of the electric power steering apparatus according to the present embodiment, and FIG. 2 is an operation procedure of the control apparatus of the electric power steering device according to the embodiment of the present invention. It is a flowchart for demonstrating.

  As shown in FIG. 1, the ECU 1 according to this embodiment includes a central processing unit (CPU) 11, a pre-driver IC 12, a main motor drive circuit (first motor drive means) 13, and a sub motor drive circuit (first motor). 2 motor drive means) 14, an abnormality detection unit 15, and a changeover switch 16.

  The CPU 11 is a computer system including a microcomputer, a RAM, a ROM, and the like, and by running a program stored in the ROM, the steering torque detected by the torque sensor 3 and the traveling of the vehicle detected by the vehicle speed sensor 4. Based on the speed or the like, a current command value that is a control target value of the current supplied to the motor 2 is generated, and based on the duty command value determined based on this current command value, the main motor drive circuit 13 will be described later. PWM (pulse width modulation) signals for turning on and off MOSFETs Q31 to Q36 and MOSFETs Q41 to Q46 (to be described later) of the sub motor drive circuit 14 are output.

  The pre-driver IC 12 is an electronic circuit that generates a pulse voltage for driving the gates of the MOSFETs Q31 to Q36 constituting the main motor drive circuit 13 based on the PWM signal output from the CPU 11, and this pre-driver IC is provided. As a result, the current supplied to the motor 2 via the main motor drive circuit 13 can be increased.

  The main motor drive circuit 13 is configured by a bridge circuit including three inverters that respectively drive the three-phase coils of the motor 2. Each of these inverters has a large current, high breakdown voltage N-channel MOSFETs Q31, Q33, Q35 having a drain connected to a power supply voltage, and a large current, high breakdown voltage N channel MOSFETs Q32, Q34, having a source connected to a ground potential, Q36 is connected in cascade, and for example, while a positive-phase pulse voltage is input from the pre-driver IC 12 to the gate of the upper arm MOSFET, a negative-phase pulse voltage is input to the gate of the lower arm MOSFET. The MOSFETs of the upper and lower arms are complementarily operated and alternately turned on and off repeatedly to output a current having a desired pulse width from the middle point of the cascade connection, and the three-phase coil of the motor 2 via the changeover switch 16 To supply.

  MOSFETs Q31 to Q36 are preferably mounted on, for example, a metal substrate and attached to a radiator made of an aluminum alloy or the like in order to effectively dissipate the heat generated with the switching operation.

The sub motor drive circuit 14 is configured by a bridge circuit including three inverters that respectively drive the three-phase coils of the motor 2. Each of these inverters is configured by cascading P-channel MOSFETs Q41, Q43, Q45 whose sources are connected to the power supply voltage and N-channel MOSFETs Q42, Q44, Q46 whose sources are connected to the ground potential. .
When the abnormality detection unit 15 detects an abnormality in the main motor drive circuit 13, the sub motor drive circuit 14 receives a positive-phase pulse voltage from the CPU 11, for example, to the gate of the upper arm MOSFET. In addition, a reverse-phase pulse voltage is input to the gate of the lower arm MOSFET, and the upper and lower arm MOSFETs are complementarily operated to alternately turn on and off repeatedly, thereby having a desired pulse width from the midpoint of the cascade connection. A current is output and supplied to the three-phase coil of the motor 2 via the changeover switch 15.

Here, the MOSFETs Q41 to 46 constituting the sub motor drive circuit 14 are smaller than the MOSFETs Q31 to Q36 of the main motor drive circuit 13, and are constituted by a pair of bridge circuits composed of P channel MOSFETs and N channel MOSFETs. Thus, the MOSFET has a small gate voltage and maximum drain current.
For this reason, it is possible to drive directly by the CPU 11 without using the pre-driver IC 12 for driving. Further, since the heat generated with the switching operation is relatively small, a heat radiator such as an aluminum alloy as described above is not necessary and can be mounted on a substrate such as a glass epoxy resin. For this reason, size reduction and cost reduction are possible.

  The abnormality detection unit 15 detects an abnormality in the main motor drive circuit 13, for example, the MOSFETs Q31 to Q36 are short-circuited or opened due to an ambient temperature, an overload, an overvoltage, or the like exceeding the specifications estimated in advance at the design stage. Detects that the current cannot be supplied to the motor 2 due to disconnection, etc., and a current monitor that detects current when the MOSFETs Q31 to Q36 are turned on, and a drain when the MOSFETs Q31 to Q36 are turned on A voltage monitor that detects the voltage between the sources is used, and the detection result is transmitted to the CPU 11.

  The changeover switch 16 connects the main motor drive circuit 13 and the motor 2 while the main motor drive circuit 13 is operating normally, and when the abnormality detection unit 15 detects an abnormality in the main motor drive circuit 13, The CPU 11 controls the switching of the contacts to connect the sub motor drive circuit 14 and the motor 2 and is composed of, for example, a power relay.

  Next, the operation of the control device for the electric power steering apparatus according to the present embodiment configured as described above will be described with reference to FIG.

  As shown in FIG. 2, when an ignition switch (not shown) is turned on by a driver's operation and a power supply voltage is supplied to the ECU 1 to bring the vehicle into a running state, first, based on a PWM signal output from the pre-driver IC 12. MOSFETs Q31 to Q36 of the motor drive circuit 13 are turned on and off, current is supplied to the motor 2 to generate rotational torque, and assist force is applied to the steering wheel (ie, step S101).

  While the motor 2 is being driven, the main motor drive circuit 13 is constantly monitored by the abnormality detection unit 15, and it is determined whether an abnormality such as a short circuit or open of the MOSFETs Q31 to Q36 or a disconnection of the harness has been detected. (That is, step S102).

  If no abnormality is detected as a result of the determination in the procedure of step S102, the process returns to step S102 and monitoring of the abnormality in the main motor drive circuit 13 is continued (that is, NO in step S102).

  On the other hand, if it is determined in step S102 that an abnormality of the main motor drive circuit 13 has been detected, the changeover switch 16 is operated by the CPU 11, and the contact is switched to connect the sub motor drive circuit 14 and the motor 2. (That is, step S103).

  After step S103, a PWM signal is transmitted from the CPU 11 to the sub motor drive circuit 14, and the sub motor drive circuit 14 generates a smaller motor current than the main motor drive circuit 13 based on the PWM signal. The motor 2 is rotationally driven through (i.e., step S104).

  As described above, according to the control device of the electric power steering apparatus of the embodiment according to the present invention, the central processing unit (CPU) 11, the pre-driver IC 12, the main motor drive circuit 13, and the sub motor The drive circuit 14, the abnormality detection unit 15, and the changeover switch 16 are provided. When the abnormality detection unit 15 detects an abnormality in the main motor drive circuit 13, the CPU 11 switches the changeover switch 16 and the sub motor drive circuit 14. PWM signal is sent to the motor 2 to drive the motor 2 with the motor current generated by the sub motor drive circuit 14.

  As a result, even if an abnormality occurs in the main motor drive circuit 13 during the operation of the vehicle, the motor 2 can be continuously driven by the sub motor drive circuit 14, so that it is possible to avoid suddenly heavy operation of the steering wheel. , Does not give the driver a sense of anxiety or crisis.

  The MOSFETs Q41 to 46 are smaller than the MOSFETs Q31 to Q36 of the main motor drive circuit 13, and are composed of a pair of bridge circuits composed of a P channel MOSFET and an N channel MOSFET, and have a gate voltage and a maximum drain current. Since the motor current of the sub motor drive circuit 14 is limited to be smaller than the motor current of the main motor drive circuit 13 by the control of the CPU 11 as a small MOSFET, the sub motor drive circuit 14 is not driven via the pre-driver IC 12. It can be directly driven by the CPU 11, and an increase in size and cost of the apparatus can be avoided. Further, by adopting such a configuration, it is not necessary to use MOSFETs Q41 to Q46 constituting the sub motor drive circuit 14 for high power, and the manufacturing cost can be suppressed.

  Further, by mounting the MOSFETs Q31 to Q36 of the main motor drive circuit 13 on the metal substrate, the MOSFETs Q31 to Q36 can be effectively dissipated, and the MOSFETs Q41 to 46 of the sub motor drive circuit 14 are mounted on the resin substrate. By mounting, it is possible to avoid an increase in size and cost of the apparatus.

  This is the end of the description of specific embodiments. However, aspects of the present invention are not limited to these embodiments, and modifications, improvements, and the like can be made as appropriate.

It is a block diagram which shows schematic structure of the control apparatus of the electric power steering apparatus which concerns on embodiment of this invention. It is a flowchart for demonstrating the operation | movement procedure of the control apparatus of the electric power steering apparatus which concerns on embodiment of this invention. It is a figure which shows schematic structure of the conventional electric power steering apparatus.

Explanation of symbols

1,6 ECU (control means)
2,7 Motor 3,8 Torque sensor 4,9 Vehicle speed sensor 11,61 Central processing unit (CPU)
12,62 Pre-driver IC
13 Main motor drive circuit (first motor drive means)
14 Sub motor drive circuit (second motor drive means)
15 Abnormality detection unit (abnormality detection means)
16 changeover switch (switch means)
63 Motor drive circuit Q31-Q36, Q41-Q46, Q61-Q66 MOSFET (drive element)

Claims (4)

A control device for an electric power steering device for controlling a drive current of a motor for applying a steering assist force,
Control means for generating a control value of a current for driving the motor;
A first motor driving unit that forms a bridge circuit by a plurality of driving elements connected between a power supply voltage and a ground potential, and generates a driving current of the motor based on a control value of the current;
A second motor driving unit that forms a bridge circuit by a plurality of driving elements connected between a power supply voltage and a ground potential, and generates a driving current of the motor based on the control value of the current;
An abnormality detecting means for detecting an abnormality of the first motor driving means;
Switch means for switching the connection with the first motor driving means or the connection with the second motor driving means with respect to the motor;
With
The control means includes
When an abnormality of the first motor driving unit is not detected by the abnormality detecting unit,
Controlling the switch means to connect the motor and the first motor drive means;
When an abnormality of the first motor driving unit is detected by the abnormality detection unit,
A control device for an electric power steering apparatus, wherein the switch means is controlled to connect the motor and the second motor driving means. The driving element of the second motor driving means is
A P-channel MOSFET whose source is connected to the power supply voltage;
An N-channel MOSFET having a source connected to the ground potential;
Are connected in cascade to form a pair of bridge circuits, and the control means includes:
2. The electric motor according to claim 1, wherein the motor driving current generated by the second motor driving unit is controlled to be smaller than the motor driving current generated by the first motor driving unit. Control device for power steering device. The driving element of the first motor driving means is:
An N-channel MOSFET having a drain connected to a power supply voltage;
An N-channel MOSFET having a source connected to the ground potential;
Are connected in cascade to form a pair of bridge circuits, and further, predrive means for driving the drive element of the first motor drive means based on the control value of the current is provided. The control apparatus of the electric power steering apparatus according to claim 1 or 2. The first motor driving means is mounted on a metal substrate;
The control device for an electric power steering apparatus according to claim 1, wherein the second motor driving unit is mounted on a resin substrate.

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