JP6445900B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering (EPS) device that assists steering force with an electric motor.

  In the EPS apparatus, in order to improve safety and operability, it is desired to continue assisting even if a primary failure occurs. As a redundancy technology that meets this requirement, for example, Patent Document 1 uses a control device for a multi-phase rotating machine that doubles a motor winding of an electric motor and supplies current from the individual inverter circuit to the motor winding. An electric power steering apparatus has been disclosed. In Patent Document 1, when an open failure occurs in a switch element of an inverter circuit, the non-failed switch element is controlled, and the assist is continued while suppressing a decrease in torque by controlling a normal inverter circuit. ing.

Japanese Patent No. 4999836

  However, when the electric motor is driven using a plurality of inverter circuits having the same configuration, switching of a plurality of corresponding switch elements in each inverter circuit is performed simultaneously. When a plurality of switch elements are simultaneously turned on / off, switching noise due to voltage fluctuation is superimposed and increased, and there is a concern that EMC (Electromagnetic Compatibility) performance is deteriorated.

  The present invention has been made in view of the circumstances as described above, and an object of the present invention is to provide electric power that can suppress a decrease in EMC performance when an electric motor is driven using a plurality of inverter circuits having the same configuration. The object is to provide a steering device.

The present invention is an electric power steering device that assists a steering force with an electric motor, wherein the electric motor is driven by selective switching of a first switch element group, and the electric motor is A second motor drive circuit that is driven by selective switching of a second switch element group having the same circuit configuration as the first switch element group, and a control device that controls the first and second motor drive circuits; The control device selectively drives the first switch element group and the second switch element group when the electric power steering apparatus is started by turning on an ignition switch, and a current flowing through the switch element according to a driving state Is detected by the current detection resistor, and an initial diagnosis is performed based on the estimated current and the actual detection signal. When beauty second motor drive circuit is determined that there is no abnormality, by driving the electric motor in the first and second motor drive circuit, corresponding of the second switching element group and the first switching element group The electric motor is driven by switching control of the switch element to be performed with signals of different phases.

  According to the present invention, when the electric motor is driven by the first and second motor drive circuits having the same configuration, the on / off timings of the corresponding switch elements in the first and second switch element groups are shifted simultaneously. It can be prevented from switching. As a result, the switching noise generated from the switch elements in the first and second motor drive circuits can be reduced to take a measure against EMI (Electromagnetic Interference), and the degradation of EMC performance can be suppressed.

1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a circuit diagram of the electric motor and motor control apparatus in FIG. It is a flowchart which shows the operation | movement at the time of starting of the electric power steering apparatus shown in FIG. 2 is a flowchart showing an operation during startup of the electric power steering apparatus shown in FIG. 1. FIG. 3 is a waveform diagram of a drive signal supplied to a drive coil of an electric motor in the circuit shown in FIG. 2. It is a circuit diagram which shows the modification of the motor control apparatus shown in FIG.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a schematic configuration of an EPS device, which includes a steering wheel 10, a steering torque detection sensor 11, an assisting electric motor 12, a motor control device 13, and the like. The steering torque detection sensor 11 and the speed reducer 16 are provided in a steering column 15 that includes the steering shaft 14.

  Then, when the driver of the vehicle performs a steering operation, the steering torque generated in the steering shaft 14 is detected by the steering torque detection sensor 11, and the motor control device 13 based on the steering torque signal S 1 and the vehicle speed signal S 2. By driving and controlling the electric motor 12, a steering assist force corresponding to the traveling state is generated from the electric motor 12. As a result, when the pinion gear 17 provided at the tip of the steering shaft 14 rotates, the rack shaft 18 moves horizontally to the left and right in the traveling direction, so that the driver's steering operation is transmitted to the wheels (tires) 20 and the vehicle. Change direction.

  Next, the assisting electric motor 12 and the motor control device 13 will be described with reference to FIG. The electric motor 12 is a three-phase motor and includes a first system U-phase coil Ua, a V-phase coil Va and a W-phase coil Wa, and a second system U-phase coil Ub, a V-phase coil Vb and a W-phase coil Wb. Each of them is configured to be individually drivable by the first system motor drive circuit 21a and the second system motor drive circuit 21b. The motor drive circuit 21a includes an inverter circuit 22a and a pre-driver 23a, and the motor drive circuit 21b includes an inverter circuit 22b and a pre-driver 23b. Both the motor drive circuits 21a and 21b are controlled by a microcomputer (CPU) 24 that functions as a control device. Is done.

  The inverter circuit 22a has a three-phase bridge circuit configuration including three sets of switch elements that drive the U phase, the V phase, and the W phase of the electric motor 12 for each phase via the drive lines 25U, 25V, and 25W. In this example, each switch element is composed of N-channel MOSFETs 31-36.

In the MOSFETs 31 and 32, the drain and source are connected in series between one end of the power supply line 37 and the current detection resistor 38 connected to the battery BA, and one end of the drive line 25U is connected to a common connection point. In the MOSFETs 33 and 34, the drain and the source are connected in series between one end of the power supply line 37 and the current detection resistor 38, and one end of the drive line 25V is connected to a common connection point. Further, in the MOSFETs 35 and 36, the drain and the source are connected in series between one end of the power supply line 37 and the current detection resistor 38, and one end of the drive line 25W is connected to a common connection point. The other end of the current detection resistor 38 is grounded, detects a current flowing through the current paths of the MOSFETs 31 to 36, and supplies a detection signal S3 to the microcomputer 24.
Here, the diodes D1 to D6 connected in the forward direction between the source and drain in the MOSFETs 31 to 36 are parasitic diodes.

  The pre-driver 23a is connected to the H-side driver corresponding to the MOSFETs 31, 33, and 35 that are upstream drive elements (upper arms) in the inverter circuit 22a, and to the MOSFETs 32, 34, and 36 that are downstream drive elements (lower arms), respectively. A corresponding L-side driver is provided. A power supply voltage is supplied from the battery BA to the H side driver and the L side driver. The gates of MOSFETs 31, 33, and 35 are connected to the output terminals of the H-side drivers, respectively, and are selectively controlled on / off. The gates of MOSFETs 32, 34, and 36 are respectively connected to the output terminals of the L-side drivers. Connected and selectively on / off controlled.

  The inverter circuit 22b has the same circuit configuration as the inverter circuit 22a, and includes three sets of switch elements that drive the U phase, the V phase, and the W phase of the electric motor 12 for each phase via the drive lines 26U, 26V, and 26W. 3 is a three-phase bridge circuit configuration. In this example, each switch element is composed of N-channel MOSFETs 41 to 46.

In the MOSFETs 41 and 42, the drain and source are connected in series between one end of the power supply line 37 and the current detection resistor 48 connected to the battery BA, and one end of the drive line 26U is connected to a common connection point. In the MOSFETs 43 and 44, the drain and the source are connected in series between one end of the power supply line 37 and the current detection resistor 48, and one end of the drive line 26V is connected to a common connection point. The MOSFETs 45 and 46 have a drain and a source connected in series between one end of the power supply line 37 and the current detection resistor 48, and one end of the drive line 26W is connected to a common connection point. The other end of the current detection resistor 48 is grounded, detects the current flowing through the current paths of the MOSFETs 41 to 46, and supplies the detection signal S4 to the microcomputer 24.
Here, the diodes D7 to D12 connected in the forward direction between the source and drain in the MOSFETs 41 to 46 are parasitic diodes.

  The pre-driver 23b is connected to the H-side drivers corresponding to the MOSFETs 41, 43, and 45, which are upstream drive elements (upper arms), and the MOSFETs 42, 44, and 46, which are downstream drive elements (lower arms), respectively, in the inverter circuit 22b. A corresponding L-side driver is provided. A power supply voltage is supplied from the battery BA to the H side driver and the L side driver. The gates of MOSFETs 41, 43, and 45 are connected to the output terminals of the H-side drivers, respectively, and are selectively controlled on / off. The gates of MOSFETs 42, 44, and 46 are respectively connected to the output terminals of the L-side drivers. Connected and selectively on / off controlled.

  The microcomputer 24 receives the steering torque signal S1, the vehicle speed signal S2, and the detection signals S3 and S4 of the current detection resistors 38 and 48, and controls the motor drive circuits 21a and 21b to drive the electric motor 12. The steering assist force corresponding to the traveling state of the vehicle is generated from the electric motor 12.

  Next, the operation of the electric power steering apparatus shown in FIG. 1 will be described with reference to the flowcharts of FIGS. As shown in FIG. 3, when the microcomputer 24 detects that the ignition switch is turned on (S11), the EPS device is activated (S12). First, the microcomputer 24 performs initial diagnosis of the motor drive circuits 21a and 21b (S13), and determines whether or not there is a circuit abnormality (S14). In the initial diagnosis, for example, the MOSFETs 31 to 36 and 41 to 46 are selectively driven, and the currents flowing through the MOSFETs are detected by the current detection resistors 38 and 48 according to the driving state, so that the estimated current and the actual detection signal are detected. Based on S3 and S4, the presence or absence of abnormality is determined. If it is determined that there is no abnormality in the two motor drive circuits 21a and 21b, the motor drive circuits 21a and 21b drive the assisting electric motor 12 to assist the steering force (S15).

  In the normal assist state using the two motor drive circuits 21a and 21b (S16), the microcomputer 24 outputs, for example, a pulse width modulation signal (PWM signal) to the pre-drivers 23a and 23b. Each of the H-side drivers and L-side drivers in the pre-drivers 23a and 23b selectively supplies drive signals based on the PWM signals to the gates of the MOSFETs 31 to 36 in the inverter circuit 22a based on the PWM signals. ON / OFF control. The electric motor 12 is three-phase driven by the motor drive circuit 21a via the drive lines 25U, 25V and 25W, and is three-phase driven by the motor drive circuit 21b via the drive lines 26U, 26V and 26W. Then, the assist force is changed by changing the duty of the PWM signal as necessary and controlling the output torque of the electric motor 12.

  At this time, on / off control is performed by supplying a phase-shifted signal so that the MOSFETs 31 to 36 that are the first switch element group and the corresponding MOSFETs of the MOSFETs 41 to 46 that are the second switch element group do not switch simultaneously. . As shown in FIG. 5A, for example, when a voltage whose phase is shifted by 120 ° is applied to the U-phase coil Ua, the V-phase coil Va, and the W-phase coil Wa of the first system, A voltage having a phase opposite to that of the first phase U-phase coil Ua, V-phase coil Va and W-phase coil Wa as shown in FIG. 5B is applied to the phase coil Ub, V-phase coil Vb and W-phase coil Wb, respectively. Then, the electric motor 12 is driven.

  In this way, when the electric motor 12 is driven by the two motor drive circuits 21a and 21b, the on / off timings of the corresponding MOSFETs in the MOSFETs 31 to 36 and 41 to 46 are shifted and not simultaneously turned on / off. You can Therefore, MOSFET switching noise in the motor drive circuits 21a and 21b can be reduced to take EMI countermeasures, and a decrease in EMC performance can be suppressed.

  On the other hand, if it is determined in step S14 that there is a circuit abnormality, the microcomputer 24 determines whether only one motor drive circuit is abnormal (S17). When a failure is detected in one of the motor drive circuits 21a and 21b, the electric motor 12 is driven by the other motor drive circuit that has not failed to continue assisting the steering force (S18). In this assist limited state, the assist torque is about half (S19).

If it is determined in step S17 that both the motor drive circuits 21a and 21b have a circuit abnormality, the drive of the electric motor 12 is stopped (S20), and the assist stop state is set (S21).
When the assist limit state or the assist stop state is entered, the microcomputer 24 informs the driver of the vehicle that the motor drive circuit 21a or 21b has failed by a warning lamp or a buzzer, etc., and prompts repair. Like that.

  Next, as shown in the flowchart of FIG. 4, when the EPS device is being activated (S31), a diagnosis is always performed instead of the initial diagnosis (S32). In the normal diagnosis, in addition to the detection signals S3 and S4 by the current detection resistors 38 and 48, for example, the steering torque signal S1 and the vehicle speed signal S2 are used, and the assist torque is calculated based on these signals S1 and S2. The motor driving circuits 21a and 21b are controlled so that the calculated assist torque is obtained, and the duty of the PWM signal is varied to drive the electric motor 12, whereby the steering assist force corresponding to the traveling state is obtained from the electric motor 12. generate. The control of each assist state (normal assist state, assist limit state, assist stop state) according to the presence or absence of a circuit abnormality or abnormality of one circuit or two circuits is the same as that at the time of startup described above. . And the operation | movement of step S32 to S40 is repeated until an ignition switch turns off.

  According to the above configuration, during normal operation (when an electric motor is driven using a plurality of inverter circuits), the MOSFETs 31 to 36 having the same circuit configuration and the corresponding MOSFETs in the MOSFETs 41 to 46 are transmitted with signals having different phases. Switching control can be performed to shift the on / off timing of the MOSFET. Further, when a primary failure occurs, the assist can be continued by reducing the torque to approximately half by the motor drive circuit that is not in failure.

  Therefore, it is possible to take measures against EMI by distributing the timings when the MOSFETs in the inverter circuit are turned on / off, and it is possible to suppress a decrease in EMC performance. In addition, when a primary failure occurs, the assist of the EPS device can be prevented from suddenly stopping and the steering operation from becoming suddenly heavy, so that safety and operability can be improved. Moreover, since the electric motor 12 is driven by the two motor drive circuits 21a and 21b during normal operation, the rating of each element constituting the motor drive circuits 21a and 21b may be low, and the cost can be reduced.

  FIG. 6 shows a modification of the motor control device shown in FIG. In FIG. 2, the two motor drive circuits 21 a and 21 b are controlled by one microcomputer 24. On the other hand, in this modification, two systems of microcomputers 24a and 24b are provided as control devices, the pre-driver 23a is controlled by the microcomputer 24a, and the pre-driver 23b is controlled by the microcomputer 24b. The microcomputers 24a and 24b are respectively input with the steering torque signal S1, the vehicle speed signal S2, and the detection signals S3 and S4 of the current detection resistors 38 and 48, exchange data with each other, and cooperate with each other to drive the motor drive circuit. 21a and 21b are controlled.

  Even with such a configuration of the motor control device, basically the same operation as that of the motor control device shown in FIG. 2 can be performed, and substantially the same operational effects can be obtained.

  Note that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. For example, the case where the phases of the signals output from the motor drive circuits of the first system and the second system are opposite in phase (when shifted by 180 °) has been described as an example, but in the first and second switch element groups, Since the corresponding switch elements do not have to be turned on or off at the same time, the signal phase may be shifted.

Although the case where the electric motor is driven by two motor drive circuits has been described, it is needless to say that the present invention can be similarly applied to a motor control device that drives an electric motor by three or more motor drive circuits.
Furthermore, the detection signal of the current detection resistor is input to the microcomputer to control the diagnosis operation of the motor drive circuit. In addition to this, the ambient temperature of the vehicle, the substrate temperature of the motor control device, etc. should be taken into consideration. Anyway.
Furthermore, although the field effect transistor is taken as an example of the switch element, other semiconductor elements such as an IGBT (Insulated Gate Bipolar Transistor) can be similarly applied.

  DESCRIPTION OF SYMBOLS 12 ... Electric motor, 13 ... Motor control device, 21a, 21b ... Motor drive circuit, 22a, 22b ... Inverter circuit, 23a, 23b ... Pre-driver, 24, 24a, 24b ... Microcomputer (control device), 31-36 ... MOSFET (first switch element group), 41 to 46... MOSFET (second switch element group)

Claims (5)

An electric power steering device that assists the steering force with an electric motor,
A first motor driving circuit for driving the electric motor by selective switching of the first switch element group, and a selective switching of the second switch element group having the same circuit configuration as the first switch element group. A second motor drive circuit that is driven by the controller, and a control device that controls the first and second motor drive circuits,
The control device selectively drives the first switch element group and the second switch element group when the electric power steering apparatus is started by turning on an ignition switch, and a current flowing through the switch element according to a driving state Is detected by the current detection resistor, and an initial diagnosis is performed based on the estimated current and the actual detection signal. When the first and second motor drive circuits are determined to be normal, the first and second Driving the electric motor with a second motor drive circuit, and driving the electric motor by switching control the corresponding switch elements of the first switch element group and the second switch element group with signals of different phases; An electric power steering device.   The controller is further characterized in that when one of the first and second motor drive circuits fails, the electric motor is driven by the other motor drive circuit to continue assisting the steering force. The electric power steering apparatus according to claim 1.   The first motor drive circuit includes a first inverter circuit having the first switch element group, and a first pre-driver that selectively controls on / off of the first switch element group. The motor drive circuit includes a second inverter circuit having the second switch element group and a second pre-driver that selectively controls on / off of the second switch element group. 2. The electric power steering apparatus according to 2.   4. The electric power steering apparatus according to claim 3, wherein the control device includes a microcomputer that controls the first and second pre-drivers.   The control device includes: a first microcomputer that controls the first pre-driver; and a second microcomputer that controls the second pre-driver in cooperation with the first microcomputer. 3. The electric power steering device according to 3.