MOTOR CONTROL DEVICE AND ELECTRIC POWER STEERING APPARATUS INCLUDING MOTOR CONTROL DEVICE

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

[0001]
The present invention relates to a motor control device and an electric power steering apparatus including the motor control device, and particularly relates to a motor control device that drives a predetermined switching device of a bridge circuit including a plurality of switching devices and being included in a drive device of an electric motor, to determine an abnormality in a relay for interrupting power supply between the bridge circuit and the electric motor, and an electric power steering apparatus including the motor control device,

DESCRIPTION OF THE RELATED ART

[0002]
An electric power steering apparatus for automobile uses driving force of an electric motor controlled by a motor control device to assist a driver in steering. The electric motor used for the electric power steering apparatus starts operation after the automobile is started and a relay for the motor is turned on to enable control by the motor control device.

[0003]
For example, Fig. 12 is a schematic configuration diagram of an electric power steering apparatus for automobile disclosed in JP-A-2010-148274. As shown in Fig. 12, an electric power steering apparatus 10 includes: a steering column 12 provided outside a steering shaft (not shown) coupled to a steering wheel 11; a torque sensor 13 for detecting a steering force applied to the steering wheel 11 by a driver; an electric motor 14 for applying an assistant steering torque to the steering shaft; a reduction gear 15 supplied with power proportional to a gear reduction ratio from the electric motor 14; and a motor control device 16 for controlling the electric motor 14. A vehicle signal 17 such as vehicle speed, the steering force applied to the steering wheel 11 detected by the torque sensor 13 and the like are input to the motor control device 16. A battery 18 is connected to the motor control device 16.

[0004]
Next, the motor control device 16 is described. Fig. 13 is a schematic internal configuration diagram of the motor control device 16. In Fig. 13, a reference sign 19 represents a control unit and the control unit 19 calculates an appropriate assist current for the electric motor 14 from a torque sensor signal (output signal of the torque sensor 13) that varies depending on the steering torque applied by the driver and the vehicle signal 17 to control a drive device 20 of the electric motor 14. The drive device 20 includes a bridge circuit including a plurality of switching devices and provides a previously calculated current to the electric motor 14. When an abnormality occurs in the control unit 19 or the drive device 20, the control unit 19 turns off relays 21a and 21b to interrupt power supply to the electric motor 14,

[0005]
The conventional electric power steering apparatus 10, configured as above, determines at the start-up of the motor control device 16 whether or not an abnormality has occurred in the relays 21a and 21b, and, if determined that no abnormality has occurred, starts to assist the steering force so as to interrupt the output power of the electric motor 14 when an abnormality has occurred in the control unit 19 or the drive device 20.

[0006]
[Patent Document 1] JP-A-2010-148274

[0007]
As described above, for the electric power steering apparatus for using the electric motor to assist the steering force applied by the driver, the technique disclosed in the Patent Document 1 of determining at the start-up of the motor control device whether or not an abnormality has occurred in the relays, and, if determined that no abnormality has occurred, starting to assist the steering force has a problem in which, since the relays are repeatedly turned on and off during the abnormality determination of the relays, the contacts of the relays are worn away and then their lifetimes are shortened.

[0008]
In order to improve the above problem, one method has been proposed in which a predetermined switching device of a bridge circuit is turned on using the voltage across the terminals of an electric motor, that is motor terminal voltage, to determine an abnormality in a relay without repeatedly turning on and off the relay. However, this method has a problem in which, when a driver steers the steering wheel of an automobile at its start-up or when the steering wheel is caused to rotate by a twisted tire or the like, the rotation speed of the steering wheel 11 causes the motor rotation speed to be increased by a factor equal to the reduction ratio through the reduction gear 15 as shown in Fig. 12, then this larger motor rotation speed induces a voltage that prevents abnormality determination of the relays 21a and 21b while the electric motor 14 is rotating.

SUMMARY OF THE INVENTION

[0009]
In order to solve the above problem, it is an object of the present invention to provide a motor control device that, in determining an abnormality in a relay for interrupting the output power of an electric motor, improves the detection capability in the relay abnormality determination while the electric motor is rotating, and an electric power steering apparatus including the motor control device.

[0010]
A motor control device according to the invention includes: a control unit for controlling an electric motor; a drive device for driving the electric motor, the drive device including a bridge circuit including a plurality of switching devices; relays for interrupting power supply between the bridge circuit and the electric motor; and motor terminal voltage monitoring means for monitoring the terminal voltages of the electric motor (14),
wherein the control unit has an abnormality determination means for determining whether or not an abnormality has occurred in the relays, and wherein the abnormality determination means turns on a predetermined switching device of the switching devices for a predetermined period of time so that dynamic braking is applied to the electric motor, then drives another predetermined switching device of the switching devices, and then determines whether or not an abnormality has occurred in the relays, based on monitored voltages detected by the motor terminal voltage monitoring means.

[0011]
According to the motor control device according to the invention, in determining an abnormality in the relay for interrupting the output power of the electric motor, the detection capability in the relay abnormality determination while the electric motor is rotating can be improved.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]

Fig. 1 is a diagram showing a motor control device in accordance with a first embodiment of the invention.

Fig. 2 is a flowchart showing the operation of the motor control device in accordance with the first embodiment of the invention.

Fig. 3 is a diagram showing an equivalent circuit of an electric motor in accordance with
the first embodiment of the invention.

Fig. 4 is a diagram showing a relation between the motor rotation speed and the motor induced voltage of the electric motor in accordance with the first embodiment of the invention.

Fig. 5 is a diagram showing the abnormality determination of a relay included in the motor control device in accordance with the first embodiment of the invention.

Fig. 6 is a flowchart showing the operation of a motor control device in accordance with a second embodiment of the invention.

Fig. 7 is a diagram showing the abnormality determination of a relay included in the motor control device in accordance with a third embodiment of the invention.

Fig. 8 is a diagram showing a relation between the motor rotation speed and the motor induced voltage of the electric motor in accordance with the third embodiment of the invention.

Fig. 9 is a flowchart showing the operation of a motor control device in accordance with the third embodiment of the invention.

Fig. 10 is a flowchart showing the operation of a motor control device in accordance with a fourth embodiment of the invention.

Fig. 11 is a flowchart showing the operation of a motor control device in accordance with a sixth embodiment of the invention.

Fig. 12 is a schematic configuration diagram of a conventional electric power steering apparatus.

Fig. 13 is a schematic internal configuration diagram of the motor control device provided in the conventional electric power steering apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013]
A preferred embodiment of a motor control device and an electric power steering apparatus in accordance with the invention is described below with reference to the drawings,

[0014] First embodiment
Fig. 1 shows a motor control device in accordance with a first embodiment of the invention. For convenience of description, Fig. 1 also shows an electric motor controlled
by the motor control device and a battery connected to the motor control device. The electric power steering apparatus including the motor control device according to the first
embodiment has a configuration similar to that of the electric power steering apparatus described with reference to Fig. 12 except the motor control device. Also, Fig. 1 corresponds to Fig. 13. In Fig. 1, the same part as or the part corresponding to that of Fig. 13 is denoted by the same reference numeral.

[0015]
In Fig. 1, a motor control device 16 includes a control unit 19. The control unit 19 calculates an appropriate assist current for an electric motor (hereinafter simply referred to as a motor) 14 from a torque sensor signal (output signal of a torque sensor 13) that varies depending on the steering torque applied by a driver and a vehicle signal 17 to control a drive device 20 of the motor 14 , The drive device 20 includes a bridge circuit including a plurality of switching devices 20a-20dand provides a previously calculated current to the motor 14 . When an abnormality occurs in the control unit 19 or the drive device 20, the control unit 19 turns off relays 21a and 21b to interrupt power supply to the motor 14.

[0016]
The switching devices 2 0a-20d are switching devices for generating a PWM (pulse width modulation) signal calculated by the control unit 19, for which a commonly-used MOSFET (metal oxide semiconductor field effect transistor) is used, the MOSFET including a parasitic diode. A battery 18 is connected to the drive device 20 that drives the motor 14 for assisting the steering force applied to a steering wheel,

[0017]
The motor control device 16 includes a motor positive terminal voltage monitoring means 22 for monitoring the terminal voltage of the positive terminal M+ side of the motor 14 and a motor negative terminal voltage monitoring means 23 for monitoring the terminal voltage of the negative terminal M- side of the motor 14. For example, as shown in Fig. 1, the motor positive terminal voltage monitoring means 22 includes resistors 22a-22c connected in Y shape. Then a voltage (e.g., 5 V) is applied by connecting a Vcc power supply 24 to one end of the resistor 22a. Also, for example, as shown in Fig, 1, the motor negative terminal voltage monitoring means 23 includes resistors 23a-23c connected in Y shape. Then a voltage (e.g., 5 V) is applied by connecting a Vcc power supply 24 to one end of the resistor 23a. In the description of Fig, 1, an H bridge circuit and a brush motor are used as an example, however, this description is similarly applicable to a brushless multi-phase motor by including relays 21a and 21b, a bridge circuit including switching devices 20a-20d, a motor positive terminal voltage monitoring means 22 and a motor negative terminal voltage monitoring means 23.

[0018]
The motor control device 16 according to the first embodiment is configured as above. Then, the operation of the motor control device 16 is described. First, a method for determining a stuck-off fault,, which is an abnormality of the relays 21a and 21b, is described with reference to a flowchart in Fig. 2. In step SI01, a relay-on instruction is provided to the relays 21a and 21b, This relay-on instruction is issued from the control unit 19. Next, in step S102, the motor positive terminal voltage monitoring means 22 and the motor negative terminal voltage monitoring means 23.monitor the terminal voltage of the positive terminal M+ and negative terminal M- of the motor 14, respectively,

[0019]
Since a coil component of the motor 14 is negligible if it is static, an equivalent circuit of the motor 14 can be written as shown in Fig. 3, as including an induced voltage 14a and an armature resistance 14b of the motor 14. As shown in Fig. 4, the higher the motor rotation speed, the higher the induced voltage 14a of the motor 14 . Since the induced voltage 14a can be calculated from the voltage between the terminals of the motor and the induced voltage is proportional to the rotation speed, the rotation speed of the motor 14 can be determined from the voltage between the terminals of the motor 14.

[0020]
Returning to Fig. 2, instepSl03, as shown by the Equation (1) below, when the absolute value of the voltage between the terminals of the motor is smaller than a predetermined value Vthl, it is determined that the motor 14 has stopped, then the process proceeds to step S105, and when larger than the predetermined value Vthl, it is determined that the motor 14 is rotating, then the process proceeds to step S104. Note that the control unit 19 has an abnormality determination means and the determinations are performed by the abnormality determination means.

(monitored M+ terminal voltage) -* (monitored M- terminal voltage)I < Vthl (1)

[0021]
In step S104, with the switching devices 20a and 20b on the battery 18 side turned on and the switching devices 20c and 20d on the GND side turned off in the drive device 20, short circuit is caused between the positive terminal M+ and negative terminal M- of the motor 14, which allows dynamic braking to be applied to the motor 14. Then the motor 14 is stopped by using a braking torque depending on the rotation speed of the motor 14 at this time,

[0022]
In step Sl05> when the abnormality determination means of the control unit 19 determines that the motor 14 is stopped, with the switching devices 20a, 20b and 20d turned off and the switching device 20c turned on as shown in Fig. 5, since the relay 21a is normally turned on, the monitored terminal voltage of the positive terminal M+ of the motor 14 is as shown by the Equation (2) below:

22b x 22c x Vcc / {22b x 22c + 22a x (22b + 22c)} (2)

[0023]
On the other hand, when the relay 21a has a stuck-off fault, the relay 21a is turned off, so the monitored terminal voltage of the positive terminal M+ of the motor 14 is as shown by the Equation (3) below. The resistances 22a-22c are set such that Eq. (2) < Eq. (3), 22b x Vcc / (22a + 22b) (3)

[0024]
With the switching device 20c set to be driven in the step S105, in step S106, the monitored terminal voltage of the positive terminal M+ of the motor 14 is compared to a threshold Vth2 that satisfies: Eq. (2) < Vth2 < Eq. (3). Thus, it is determined whether or not a fault has occurred in the relay 21b.

[0025]
In step S106, when the monitored M+ terminal voltage is lower than Vth2, it is determined that the relay 21a is in normal state, then the process proceeds to S107 to determine whether or not a fault has occurred in the relay 21b on the negative terminal M- side. On the other hand, in step S106, when the monitored M+ terminal voltage is not lower than Vth2, it is determined that the relay 21a has a stuck-off fault, then the process proceeds to step S120 to stop the assisting.

[0026]
In step S107, with the switching devices 20a, 20b and 20c turned off and the switching device 20d turned on, the monitored motor terminal voltage in normal state of the relay
21b is as shown by the Equation (4) below, similarly -co the S105. On the other hand, the monitored motor terminal voltage when the relay 21b has a fault is as shown by the Equation (5) below.

23b x 23c x Vcc / {23b x 23c + 23a x (23b + 23c)} (4)

23b x Vcc / (23a + 23b) (5)

[0027]
With the resistances set such that 23a = 22a, 23b = 22b and 23c = 22c, in step S108, whether or not a fault has occurred in the relay 21b can be determined similarly to the step S106.

[0028]
In step S108, when the monitored M- terminal voltage is lower than Vth2, it is determined that the relay 21b is in normal state, then the process proceeds to S109 to start the assisting. On the other hand, when the monitored M- terminal voltage is not lower than Vth2, it is determined that the relay 21b has a fault, then the process proceeds to the step S120 to stop the assisting.

[0029]
As described above, the motor control device according to the first embodiment, before determining from the motor terminal voltages whether or not a stuck-off fault has occurred in the relays 21a and 21b, applies dynamic braking to stop the motor 14 by turning on the switching devices 20a and 20b on the battery 18 side, that is, on the upstream side of the motor 14, and turning off the switching devices 20c and 20d on the GND side, that is, on the downstream side of the motor 14 in the bridge circuit included in the drive device 20. This can improve the detection capability in determining a stuck-off fault of the relays 21a and 21b when the motor 14 is rotating at start-up.

[0030]
Second embodiment
Next, a motor control device in accordance with a second embodiment of the invention is described. In the first embodiment, dynamic braking is applied to stop the motor 14 by turning on the switching devices 20a and 20b on the battery 18 side and turning off the switching devices 20c and 20d on the GND side in the bridge circuit of the drive device 20. However, also with the switching devices 20a and 20b on the battery 18 side turned off and the switching devices 20c and 20d on the GND side turned on in the bridge circuit, short circuit is similarly caused between the terminals of the motor 14, providing the same effect as that of the first embodiment.

[0031]
The description is made below with reference to a flowchart shown in Fig* 6. In step S201 in the flowchart of Fig. 6, the setting of the switching devices is changed from that in the step 104 in the flowchart of Fig. 2 such that the switching devices 20a and 20b are turned off and the switching devices 20c and 20d are turned on. Since the motor control device of the second embodiment has the same configuration as shown in Fig. 1 described for the first embodiment, the description will not be repeated.

[0032]
As described above, the motor control device according to the second embodiment, before determining from the motor terminal voltages whether or not a stuck-off fault has occurred in the relays 21a and 21b, applies dynamic braking to stop the motor 14 by turning on the switching devices 20c and 20d on the GND side and turning off the switching devices 20a and 20b on the battery 18 side in the bridge circuit included in the drive device 20. This can improve the detection capability in determining a stuck-off fault of the relays 21a and 21b when the motor 14 is rotating at start-up.

[0033]

Third embodiment

Next, a motor control device in accordance with a third embodiment of the invention is described. In the first embodiment, dynamic braking is applied to stop the motor by turning on the switching devices 20a and 20b and turning off the switching devices 20c and 20d. On the other hand, with one switching device on the GND side (the switching device 20c) turned on and the other switching devices (the switching devices 20a, 20b and 20d) turned off in the bridge circuit included in the drive device 20, the circuit will be as shown in Fig. 7. In this case, the dynamic braking capability will be as shown in Fig. 8 due to a parasitic diode of the switching device 20d, and, in comparison with the case in Fig. 4, the braking capability of the motor 14 is reduced, but dynamic braking is still applied, providing the same effect as that of the first embodiment.

[0034]
The description is made below with reference to a flowchart shown in Fig. 9. Since the motor control device of the third embodiment has the same configuration as shown in Fig. 1 described for the first embodiment, the description will not be repeated. Also, steps S101-S102 in Fig. 9 are the same as those of the first embodiment, so the description will not be repeated.

[0035]
In step S301, the motor terminal voltages monitored in the step S102 are compared. If the monitored terminal voltage of the positive terminal M+ of the motor 14 is higher, in step
S105, the switching device 20c of the bridge circuit is turned on to connect the terminal of the motor 14 having a higher induced voltage to the GND for dynamic braking. Connecting the terminal having a higher motor terminal voltage to the GND to apply dynamic braking is for improving the detection capability of determining whether or not the monitored terminal voltage of the positive terminal M+ of the motor 14 is lower
than Vth2 in next step S106. The reason for this is explained as follows.

[0036]
The motor induced voltage generated by the rotation of the motor 14 causes the monitored value of the motor positive terminal voltage monitoring means 22 to be relatively higher or lower in the rotation direction of the motor 14 with respect to the value monitored when the motor is stopped. The motor terminal voltage influenced by the motor induced voltage is such that, when the M+ terminal voltage becomes relatively higher, the M- terminal voltage becomes relatively lower, and when the M+ terminal voltage becomes relatively lower, the M-terminal voltage becomes relatively higher. When the motor 14 is not completely stopped, it cannot be determined whether the terminal voltage is lower than the threshold Vth2 because of the influence of induced voltage due to the rotation of the motor 14 despite a stuck-off fault of the relay 21a or due to normal state. Due to that, determination with the terminal having a higher motor terminal voltage connected to the GND improves the detection capability.

[0037]
Next, in step S106, if the monitored M+ terminal voltage is lower than Vth2, it is determined that the relay 21a is in normal state, then the process proceeds to step S107. On the other hand, if the monitored M+ terminal voltage is not lower than Vth2, it is determined that the relay 21a has a stuck-open fault, then the process proceeds to step S120 to stop the assisting.

[0038]
In step S107, in order to determine whether or not a fault has occurred in the relay 21b, only the switching device 20d is turned on and the other switching devices 20a, 20b and 20c are turned off, then the process proceeds to step S108.

[0039]
In the step S108, when the monitored M- terminal voltage is lower than Vth2, it is determined that the relay 21b is in normal state, then the process proceeds to S109 to start the assisting. On the other hand, when the monitored M- terminal voltage is not lower than Vth2, it is determined that the relay 21b has a stucic-off fault, then the process proceeds to the step S120 to stop the assisting.

[0040]
In step S301, when the monitored M+ terminal voltage is not higher than the monitored M- terminal voltage, in step S302, the switching device 20d of the bridge circuit is turned on to connect the motor terminal of the motor 14 having a higher induced voltage to the GND for dynamic braking.

[0041]
Next, in step S303, if the monitored M- terminal voltage is lower than Vth2, it is determined that the relay 21b is in normal state, then the process proceeds to step S304. On the other hand, when the monitored M- terminal voltage is not lower than Vth2, it is determined that the relay 21b has a stuck-off fault, then the process proceeds to the step S120 to stop the assisting.

[0042]
Next, in step S304, in order to determine whether or not a fault has occurred in the relay 21a, the switching device 20c is turned on and the other switching devices 20a, 20b and
20d are turned off, then the process proceeds to next step S305»

[0043]
In the step S305, when the monitored M+ terminal voltage is lower than Vth2, it is determined that the relay 21a is in normal state, then the process proceeds to the S109 to start the assisting. On the other hand, when the monitored M+ terminal voltage is not lower than Vth2, it is determined that the relay 21a has a stuck-off fault, then the process proceeds to the step S120 to stop the assisting.

[0044]
As described above, the motor control device according to the third embodiment applies dynamic braking to stop the motor 14 by turning on the switching device (one of 20c and 20d) and turning off the other switching devices (one of 20a, 20b and 20c, 20d) in the bridge circuit included in the drive device 20 so as to connect the motor terminal having a higher motor terminal voltage to the GND., This can improve the detection capability in determining a stuck-off fault of the relays 21a and 21b when the motor 14 is rotating at start-up.

[0045]
Fourth embodiment
Next, a motor control device in accordance with a fourth embodiment of the invention is described. Since the motor control device of the fourth embodiment has the same configuration as shown in Fig. 1 described for the first embodiment, the description will not be repeated. In the first embodiment, dynamic braking is applied to stop the motor 14 by turning on the switching devices 20a and 20b and turning off the switching devices 20c and 20d. However, in comparison between the motor terminal voltages after a predetermined time of dynamic braking, if determined that the motor 14 is not stopped, the intended switching device or devices are driven again to apply dynamic braking, and when it is determined from the motor terminal voltages that the motor 14 is stopped, it may be determined whether or not a fault has occurred in the relay 21a and 21b.

[0046]
The description is made below with reference to a flowchart shown in Fig. 10. The part of the flowchart that is different from the flowchart shown in Fig. 2 is that, in step S104, a predetermined time of dynamic braking is applied, then, the process returns to step S103 to determine again from the motor terminal voltages whether or not the motor 14 is stopped. Since the remaining part is similar to the flowchart of Fig, 2 described for the first embodiment, the description will not be repeated.

[0047]
As described above, the motor control device according to the fourth embodiment, until it is determined from the motor terminal voltages that the motor 14 is stopped, applies dynamic braking to stop the motor 14 by turning on the switching devices 20a and 20b and turning off the switching devices 20c and 20d in the bridge circuit included in the drive device 20. This can improve the detection capability in determining a stuck-of f fault of the relays 21a and 21b when the motor 14 is rotating at start-up.

[0048]
Fifth embodiment
Next, a motor control device in accordance with a fifth embodiment of the invention is described. Since the motor control device of the fifth embodiment has the same configuration as shown in Fig. 1 described for the first embodiment, the description will not be repeated. In the fourth embodiment, in the step S103, after determined the rotation condition of the motor 14, if determined that the motor 14 is rotating, dynamic braking is applied in the step S104. Furthermore, in the step S104, when dynamic braking is applied again, the length of time for dynamic braking may be increased. A flowchart of the fifth embodiment is not shown because it is the same as Fig. 10.

[0049]
As described above, the motor control device according to the fifth embodiment, until it is determined from the motor terminal voltages that the motor 14 is stopped, turns on the switching devices 20a and 20b and turns off the switching devices 20c and 20d in the bridge circuit included in the drive device 20 and then increases the length of time for dynamic braking when the terminal voltages of the motor are checked. This can decrease the number of loops of the motor terminal voltage determination and dynamic braking, resulting in allowing determination of whether or not a fault has occurred in the relays 21a and 21b, in a shorter time,

[0050]

Sixth embodiment

Next, a motor control device in accordance with a sixth embodiment of the invention is described. Since the motor control device of the sixth embodiment has the same configuration as shown in Fig. 1 described for the first embodiment, the description will not be repeated. In the first embodiment, it is determined from the motor terminal voltages after applying dynamic braking to the motor 14 whether or not a stuck-off fault has occurred in the relays 21a and 21b. However, whether or not a stuck-on fault has occurred in the relays 21a and 21b may also be determined.

[0051]
The description is made below with reference to a flowchart shown in Fig. 11. As a difference from the flowchart shown in Fig. 2, after the motor 14 is stopped in step S103 or step S104, the relays 21a and 21b are turned off in step S601. Next, in step S105, in order to determine whether or not a fault has occurred in the relay 21a, an intended switching device is driven. Then, in step S602, it is determined from the motor terminal voltages whether or not a stuck-on fault has occurred in the relay 21a*

[0052]
Since the motor terminal voltage when the relay 21a has a stuck-on fault is as shown by the Equation (2) and the motor terminal voltage in normal state is as shown by the Equation (3), if the monitored M+ terminal voltage is higher than or equal to Vth2, it is determined that the relay 21a is in normal state, then the process proceeds to step S107 . If the monitored M+ terminal voltage is lower than Vth2, it is determined that a stuck-on fault has occurred in the relay 21a, then the process proceeds to step S120*

[0053]
On the other hand, in order to determine whether or not a fault has occurred in the relay 21b, in step S603, if the monitored M+ terminal voltage is higher than or equal to Vth2, it is determined that the relay 21b is in normal state, then the process proceeds to step S109. If the monitored M+ terminal voltage is lower than Vth2, it is determined that a stuck-on fault has occurred in the relay 21b, then the process proceeds to the step S120. Since the part of the flowchart other than the above is similar to the first embodiment, the description will not be repeated.

[0054]
As described above, according to the motor control device according to the sixth embodiment, not only when a stuck-off fault has occurred in the relays 21a and 21b but also when a stuck-on fault has occurred in the relays 21a and 21b, the detection capability in determining a stuck-on fault of the relays 21a and 21b when the motor 14 is rotating at start-up can be improved as shown in the first embodiment.

[0055]
Although the first to sixth embodiments of the invention have been described, the embodiments of the invention may be appropriately modified or omitted within the scope of the invention.

WHAT IS CLAIMED IS:

1. A motor control device comprising:

a control unit (19) for controlling an electric motor (14);

a drive device (20) for driving the electric motor (14), the drive device (20) including a bridge circuit including a plurality of switching devices (20a-20d);

relays (21a, 21b) for interrupting power supply between the bridge circuit and the electric motor (14); and

motor terminal voltage monitoring means (22, 23) for monitoring the terminal voltages of the electric motor (14),

wherein the control unit (19) has an abnormality determination means for determining whether or not an abnormality has occurred in the relays (21a, 21b), and

the abnormality determination means turns on a predetermined switching device of the switching devices (20a-20d) for a predetermined period of time so that dynamic braking is applied to the electric motor (14), then drives another predetermined switching device of the switching devices (20a-20d), and then determines whether or not an abnormality has occurred in the relays (21a, 21b), based on monitored voltages detected by the motor terminal voltage monitoring means (22, 23).

2. The motor control device according to claim 1, wherein the dynamic braking is applied by turning on only a predetermined switching device of the switching devices (20a-20d) on the upstream side of the electric motor (14) or by turning on only a predetermined switching device of the switching devices (20a-20d) on the downstream side.

3. The motor control device according to claim 1 or 2* wherein, if the difference between the monitored voltages is larger than a first predetermined value, the dynamic braking is applied and then it is determined whether or not an abnormality has occurred in the relays (21a, 21b), on the other hand, if the difference between the monitored voltages is smaller than the first predetermined value, the dynamic braking is not applied and it is determined whether or not an abnormality has occurred in the relays (21a, 21b) .

4. The motor control device according to any one of claims 1 to 3, wherein, after applying the dynamic braking, a switching device of the switching devices (20a-20d) is turned on so that the motor terminal having a higher one of the monitored voltages is connected to the ground, then, based on the resulting voltages detected by the motor terminal voltage monitoring means (22, 23), it is determined whether or not an abnormality has occurred in the relays (21a, 21b).

5. The motor control device according to any one of claims 1 to 4, wherein, if the difference between the monitored voltages is larger than or equal to a second predetermined value, the dynamic braking is further applied for a predetermined extra period of time.

6. An electric power steering apparatus comprising: a steering shaft; an electric motor (14) for applying an assistant steering torque to the steering shaft; and the motor control device (16) according to any one of claims 1 to 5.