ACTUATOR DRIVING DEVICE AND STEERING SYSTEM PROVIDED WITH THE SAME

When a DC power source fails, the following controls are performed. The normal control is resumed when an inverter input voltage recovers before a standby period elapses after a power failure time. A power source relay is turned off when the standby period elapses without recovery of the voltage. The power source relay is turned on again when a power source relay off period has elapsed from a turn-off time. The normal control is resumed when the inverter input voltage recovers at the turn-on time. The normal control is resumed when the inverter input voltage recovers before the power source relay on period elapses from the turn-on time. The power source relay is turned off, and driving of the actuator is stopped, when the power source relay on period passes without recovery of the voltage.

TECHNICAL FIELD

The present disclosure relates to an actuator driving device and a steering system provided with the same.

BACKGROUND

Conventionally, a device to control an actuator has been employed.

SUMMARY

According to an aspect of the present disclosure, an actuator driving device is configured to supply an electric power to an actuator.

DETAILED DESCRIPTION

Hereinafter, examples of the present disclosure will be described.

According to an example of the present disclosure, a device controls driving of an actuator in the event of a power failure in a steering system of a vehicle. For example, a vehicle control device supplies, in a steer-by-wire vehicle, an electric power from a backup power source in the event of a failure of a main power source, stops a control of a reaction force actuator, and continues a control of a steering with a steering actuator.

A driving device for an actuator of a steering system includes a steer-by-wire system and an electric power steering system. The driving device has a safety function that deactivates a power source relay installed in a power supply line to cut off the power supply, from a perspective of a concern about an overcurrent and prevention of an erroneous output in the event of a failure of a main power source. When a power supply line is switched to the backup power source after a failure of the main power source, both switches are required to be deactivated once. During that time lag, when the power source relay is deactivated due to safety measures, even after switching to the backup power source has been made, an electric power is not supplied unless the power source relay is activated.

This instance occurs, not only when the main power source is switched to the backup power source, but also when recovery from the failure is made after the main power source temporarily fails and an input voltage to an inverter drops. A normal control is a control when the power source is normal. In the above instance, the normal control cannot be resumed properly if the power source relay is deactivated, when the recovery is made in the power source, after the power source fails and the normal control terminates.

According to an example of the present disclosure, an actuator driving device is configured to convert an electric power from a DC power source using an inverter and supply the converted electric power to an actuator. The actuator driving device comprises the inverter, an input voltage detector, a power source relay, and a control unit.

The inverter is configured to be applied with a voltage of the DC power source via a power supply line. The power source relay is provided in the power supply line and configured to, when turned off, cut off an electric current from the DC power source to the inverter. The input voltage detector is configured to detect an inverter input voltage applied to the inverter. The control unit is configured to control an operation of the inverter, detect a failure and a recovery of the DC power source based on a decrease and a recovery of the inverter input voltage, and manipulate the power source relay.

The control unit is configured to, when the DC power source fails, execute a “power failure recovery process” to determine whether to resume a normal control, which is a control when the DC power source is normal. The control unit is configured to perform the following control in the power failure recovery process.

[1] The normal control is resumed when the inverter input voltage recovers in a period from a power failure time before a standby period elapses. The power source relay is turned off at a first turn-off time, which is a time when the standby period has elapsed without recovery of the inverter input voltage.

[2] The power source relay is turned on again at a turn-on time, which is a time when the power source relay off period has elapsed from the turn-off time. The normal control is resumed when the inverter input voltage recovers at the turn-on time.

[3] The normal control is resumed when the inverter input voltage recovers before the power source relay on period elapses from the turn-on time. The power source relay is turned off for the second time at a second turn-off time (t3), which is a time when the power source relay on period has elapsed without recovery of the inverter input voltage.

The control unit is configured to turn off the power source relay for the second time and stop driving of the actuator when a first power source relay off period and a first power source relay on period elapse without recovery of the inverter input voltage. Alternatively, the control unit turns off the power source relay for (N+1)th time and stops driving of the actuator, when the power source relay off period and the power source relay on period are repeated for N times that is two or more times, without recovery of the inverter voltage.

The control unit of the present disclosure alternately repeats, after the DC power fails, a period in which the power source relay is turned on and a period in which the power source relay is turned off, thereby to enable to quickly resume the normal control and to implement safety measures when the inverter input voltage recovers.

To the contrary, the control unit stops driving of the actuator, when a power source relay off period has elapsed once and a power source relay on period has elapsed once, or when the power source relay off period has elapsed for N times (N≥2) and the power source relay on period has elapsed for N times (N≥2), without recovery of the inverter input voltage. In this way, this configuration avoids continuation of unnecessary processing when there is no possibility of the recovery. thus, the present disclosure enables to appropriately determine whether to resume the normal control after the power source fails.

Additionally, the present disclosure is provided as a steering system comprising: a steering assist actuator configured to output a steering assist force, a reaction force actuator configured to output a reaction force against a steering of a driver, or a turning actuator configured to output a turning force to turn a tire; and the above-described actuator drive device. The actuator drive device is configured to drive, as the actuator, at least one of the steering assist actuator, the reaction force actuator, and the turning actuator.

Hereinafter, an actuator driving device according to multiple embodiments will be described with reference to the drawings. The actuator driving device of each embodiment is applied to a steering system of a vehicle, and drives a steering assist actuator, a reaction force actuator, and a steering actuator. The following first to third embodiments are collectively referred to as a “present embodiment”. The actuator driving device of the present embodiment drives a motor as a typical actuator.

With reference toFIGS.1and2, a schematic configuration of an electric power steering system (hereinafter, “EPS system”) and a steer-by-wire system (hereinafter, “SBW system”) will be described as a steering system. InFIGS.1and2, a tire99on only one side is shown, and a tire on the opposite side is not shown. Furthermore, due to a space limitation, an “actuator” will be abbreviated as an “Act” in some parts. Substantially the same configurations inFIGS.1and2are denoted by the same reference numerals, and the description thereof will be omitted.

FIG.1shows an overall configuration of an EPS system901in which a steering mechanism and a turning mechanism are mechanically coupled. AlthoughFIG.1shows a rack-assist type EPS system, the same applies to a column-assist-type EPS system. In the EPS system901, a steering shaft92and a rack97are connected with each other via an intermediate shaft95.

When a driver operates a steering wheel91, a rotational motion of the steering shaft92is transmitted to a pinion gear96via the intermediate shaft95. A rotational motion of the pinion gear96is converted into a linear motion of the rack97, and tie rods98provided at both ends of the rack97reciprocate knuckle arms985to turn the tires99.

The EPS system901includes a steering torque sensor94, an actuator driving device300, a steering assist actuator801, and the like. The steering torque sensor94is provided at an intermediate portion of the steering shaft92to detect a steering torque applied by the driver. The actuator driving device300supplies an electric power to the steering assist actuator801so as to cause the steering assist actuator801to output a desired steering assist force calculated based on the steering torque and the like. The steering assist force output by the steering assist actuator801is transmitted to the rack97via a reduction gear89.

A main power source10and a backup power source device200are connected to the actuator driving device300. Among the lines connecting the main power source10and the actuator driving device300, a thick solid line indicates a power source line, and a thin solid line indicates a control power source line. Hereinafter, unless otherwise specified, power supply means power supply via a power source line. When the main power source10is normal, a DC power of the main power source10is supplied to the actuator driving device300via the backup power source device200. On the other hand, a power supply configuration when the main power source10fails will be described later with reference toFIG.3.

FIG.2shows an overall configuration of an SBW system902in which the steering mechanism and the turning mechanism are mechanically separated. In the SBW system902, the steering shaft92and the rack97are separated. A reaction force actuator802that outputs a reaction force torque with respect to the steering of the driver is provided on the side of the steering shaft92. The reaction force generated by the reaction force actuator802is transmitted to the steering shaft92via a reduction gear79. A turning actuator803that linearly moves the rack97to turn the tires99is provided on the side of the rack97. The steering force output by the turning actuator803is transmitted to the tires99via the reduction gear89.

The actuator driving device300of the SBW system902includes a reaction force actuator driving device302that supplies an electric power to the reaction force actuator802and a steering actuator driving device303that supplies an electric power to the turning actuator803. The reaction force actuator driving device302and the steering actuator driving device303communicate with each other, and operate the reaction force actuator802and the turning actuator803to cooperate with each other.

Similarly toFIG.1, inFIG.2as well, the actuator driving device300is connected to the main power source10and the backup power source device200, which are “DC power sources”. For example, the DC power supplied from the main power source10and the backup power source device200is distributed to the reaction force actuator driving device302and the steering actuator driving device303. Alternatively, two backup power source devices200may be separately provided for the reaction force actuator driving device302and the steering actuator driving device303, respectively.

A three-phase brushless motor is typically used for each of the steering assist actuator801of the EPS system901and the reaction force actuator802and the turning actuator803of the SBW system902. The “actuator” is replaceable with a “motor”. In this case, the steering assist motor801outputs the steering assist torque, the reaction force motor802outputs the reaction torque, and the turning motor803outputs the steering torque. In this specification, the motor is basically referred to as an “actuator” since the specification does not refer to a configuration or a control specific to the motor.

[Power Supply Configuration of System]

Subsequently, with reference toFIGS.3and4, a power supply configuration of a system including the main power source10, the backup power source device200, and the actuator driving device300will be described. The backup power source device200includes a backup power source20, diodes21and22, and a power source switch25. The main power source10is a DC power source with a relatively large capacity. The backup power source20is a DC power source with a relatively small capacity, and is an emergency sub-battery used when the main power source10fails. In this embodiment, “power source” generally means a DC power source.

The main power source10and the backup power source20are connected in parallel to a junction23of an IG line that is for supplying a control power to a microcomputer41of a control unit40. The diodes21and22are provided to a point between the main power source10and the junction23and to a point between the backup power source20and the junction23, respectively, to prevent backflow of a current from the junction23to the power sources10and20. Only a low current flows through the IG line. Therefore, even when the main power source10fails, the backup power source20can supply an electric power without switching the path.

The power source switch25is provided on a power supply line (so-called PIG line) and includes a first switch251connected to the main power source10and a second switch252connected to the backup power source20. Either one of the first switch251and the second switch252is turned on, or both of the first switch251and the second switch252are turned off. In order to prevent a current from flowing from the main power source10to the backup power source20that results in a short circuit, both switches251and252are operated so as not to be turned on at the same time.

As shown inFIG.4, when the main power source10is used, the first switch251is turned on and the second switch252is turned off. When the main power source10is switched to the backup power source20, both switches251and252are once turned off. Subsequently, the second switch252is turned on, and the backup power source20is used. Therefore, a time lag occurs when the power sources are switched.

The actuator driving device300converts an electric power from the main power source10or the backup power source20, which are the “DC power sources” using an inverter50and supplies the converted electric power to an actuator80. The “actuator80”, which is a driven object, includes actuators801,802, and803shown inFIGS.1and2.

The actuator driving device300includes the inverter50, a power source relay31, an input voltage detector34, an inverter relay35, actuator relays38, and the control unit40. A voltage is applied to the inverter50from the main power source10or the backup power source20, which is the “DC power sources”, via a power supply line (so-called PIG line). In the figure, the power supply line is shown by a thick solid line.

The inverter50is composed of a plurality of switching elements51to56with three-phase upper and lower arms connected in a bridge manner. The inverter50converts the DC power as input into an AC power, and supplies the AC power to the actuator80. More specifically, the switching elements51,52, and53are upper arm elements of a U phase, a V phase, and a W phase, respectively. The switching elements54,55, and56are lower arm elements of the U phase, the V phase, and the W phase, respectively. For example, MOSFETs are used for the switching elements51to56. Illustration of a smoothing capacitor provided at an input section of the inverter50is omitted. Further, a shunt resistor for detecting each phase current may be provided, for example, between the lower arm elements54,55, and56and the ground.

The power source relay31is provided midway through the power supply line, that is, between the power sources10and20and the inverter50. The power source relay31cuts off a current from the power sources10and20to the inverter50when turned off. In the example ofFIG.3, the power source relay31is composed of an MOSFET. In this case, even when the power source relay31is turned off, a current may flow from the inverter50to the power sources10and20through a parasitic diode of the MOSFET.

The input voltage detector34is provided between the power source relay31and the inverter50, and detects an inverter input voltage Vinv applied to the inverter50via the power supply line. The inverter input voltage Vinv detected here serves as determination information for performing a power failure recovery process, which will be described later. “Voltage recovery” in the following description means that the inverter input voltage Vinv, which has once decreased, returns to its normal value.

The inverter relay35and the actuator relay38are optional in this embodiment. At least one of the inverter relay35and the actuator relay38is preferably provided within the scope of the function of this embodiment, nevertheless, is not essential for a minimum configuration. The inverter relay35is provided in the power supply line between the power source relay31and the inverter50, and cuts off the current from the inverter50to the power sources10and20when turned off. Even if a back electromotive voltage of the actuator80is reversely inputted via the inverter50in a state where the voltage of the power sources10,20has decreased, a regenerative current is prevented from flowing to the power sources10,20.

Generally, in an actuator driving device of the EPS system or the SBW system, a similar type of relay is provided as a “reverse connection protection relay” between the power source relay31and the inverter50to prevent a current from flowing in the reverse direction in the circuit when positive and negative electrodes of a battery are connected in reverse. However, in this embodiment, a situation is not assumed in which the backup power source20, which is supposed to be used as a substitute when the main power source10fails, is connected in reverse. Therefore, this relay is referred to as an “inverter relay” instead of a “reverse connection protection relay” which has a different purpose.

The actuator relays38are provided between the inverter50and actuator80, and cut off a current from the actuator80to the inverter50when turned off. In the example ofFIG.3, three motor relays are respectively provided in the phase current paths of the three-phase motor and are collectively referred to as “actuator relays38”. By turning off the actuator relay38, the back electromotive force generated by the actuator80is prevented from being reversely input to the inverter50. In a case where the actuator relays38are provided and turned off at an appropriate timing, the above function of the inverter relay35may not be necessary. However, both the inverter relay35and the actuator relay38may be provided for a redundant fail-safe configuration.

The control unit40controls an operation of the inverter50by operating the switching elements51to56of the inverter50. Hereinafter, a control when the DC power source is normal will be referred to as a “normal control.” The normal control includes both a control when the main power source10is normal and a control after switching to the backup power source20is completed. In a case where the actuator80is a three-phase brushless motor, the control unit40performs a current feedback control using a vector control based on a phase current detection value and a motor rotation angle detection value, and generates a drive signal for the inverter50. Since this is a known motor control technique, the explanation is omitted.

The control unit40detects “failure and recovery of the DC power source” based on a decrease and a recovery of the inverter input voltage Vinv acquired from the input voltage detector34. In this embodiment, “failure of DC power source” means a failure of the main power source10. “DC power source recovery” means that the switching of the connection to the backup power source20has been completed and that the power source relay31has been turned on. Furthermore, the control unit40operates the power source relay31, the inverter relay35, and the actuator relay38to perform an on/off control. Inputs and outputs for these functions of the control unit40are indicated by solid arrows.

In addition, as shown by the broken line arrow, the control unit40detects the current Ibt flowing through the power supply line, and turns off the power source relay31when the current Ibt exceeds a predetermined overcurrent threshold to protect the circuit. Although this overcurrent monitoring itself is not a main function of this embodiment, the overcurrent monitoring is related to the background of an issue. That is, in the configuration of this embodiment, when the main power source10fails, an overcurrent abnormality in the power supply line is detected, and the power source relay31is turned off as a safety measure. Therefore, after switching the connection of the power source switch25from the main power source10to the backup power source20in the backup power source device200, it is necessary to turn on the power source relay31at an appropriate timing. Thus, there is a technical significance in executing the “power failure recovery process”.

The control unit40of this embodiment includes the microcomputer41and a custom IC42. The control unit40includes a CPU, a ROM, a RAM, an I/O, a bus line that connects thereamong, and a like (none shown). The control unit40performs a control by executing a software process implemented by the CPU by executing a program stored in advance or by executing a hardware process implemented by a dedicated electronic circuit.

The microcomputer41mainly performs an arithmetic control to generate an inverter driving signal in the normal control. The microcomputer41also communicates with other devices in the vehicle via an in-vehicle network. As described above, the control power for the microcomputer41is input from the main power source10or the backup power source20via an IG line provided with the backflow prevention diodes21and22.

The custom IC42acquires an inverter input voltage Vinv, detects a failure and a recovery of the main power source10, and operates the power source relay31and the like based on the detection result and the monitoring result of an overcurrent abnormality. That is, the power failure recovery process unique to this embodiment is mainly executed by the custom IC42. By performing the power failure recovery process using the dedicated custom IC42, it becomes possible to perform the process quickly, and the safety is further improved.

When the main power source10fails, the control unit40executes the “power failure recovery process” that determines whether to resume the normal control. In the present embodiment, the controller33executes the power failure recovery process, when the main power source10fails, and the DC power source, which is connected to the power supply line, is switched from the main power source10to the backup power source20. The power failure recovery process will be described. Note that, as described in “Other Embodiments”, the power supply failure recovery process may be executed when the main power source10temporarily fails and then returns after a while.

First Embodiment

With reference to the time charts ofFIGS.5to8, the power failure recovery process of the first embodiment will be described for Case1to Case4depending respectively on recovery timings of the inverter input voltage Vinv. Hereinafter, “recovery of inverter input voltage Vinv” will be abbreviated as appropriate and will be referred to as “voltage recovery”.

The vertical axis in the figure shows five items: “main power source status”, “backup power source status”, “power source relay”, “inverter input voltage Vinv”, and “actuator control”. The “main power source state” and the “backup power source state” are valid when the actuator driving device300is supplied with an electric power and are invalid when the actuator driving device300is not supplied with an electric power. The states do not indicate a detected voltage at a specific location. When the main power source10fails, the “main power source state” changes from valid to invalid. When the switching of the connection to the backup power source20is completed, the “backup power source state” changes from invalid to valid.

The horizontal axis in each ofFIGS.5to8shows a power failure time t0, a first turn-off time t1, a first turn-on time t2, and a second turn-off time t3. Notably, t2 and t3 that do not occur in Case1and t3 that does not occur in Case2are shown in parentheses, and the corresponding vertical lines are shown as broken lines. Common to Cases1to4, the main power source10fails at the power failure time t0. The “main power source state” becomes invalid, and the inverter input voltage Vinv drops to 0. Further, the normal control of the main power source10is terminated, and the in-abnormality-detection control starts.

A time period from the power failure time t0 to the first turn-off time t1 is defined as a “standby period Twt”. A time period from the first turn-off time t1 to the first turn-on time t2 is defined as a “first power source relay off period Toff_1.” A time period from the first turn-on time t2 to the second turn-off time t3 is defined as a “first power source relay on period Ton_1”.

Herein, the standby period Twt and the power source relay on period Ton_1 are set to have the same length. Thereby, the function of the custom IC42can be used effectively. Also in the third embodiment described below, the second and subsequent power source relay on periods Ton_2 . . . Ton_N are preferably set to have the same length as the standby period Twt and the first power source relay on period Ton_1.

In Case1shown inFIG.5, switching to the backup power source20is completed before the first turn-off time t1, that is, before the time at which the standby period Twt has elapsed, and the “backup power source state” becomes valid. The power source relay31is on at this point. Therefore, the voltage is restored simultaneously when the “backup power source state” becomes valid. The control unit40resumes the normal control with the backup power source20at the same time when the voltage recovers.

As shown inFIGS.6to8, the standby period Twt elapses without recovery of the voltage. In this case, the control unit40turns off the power source relay31at the first turn-off time t1 when the standby period Twt has elapsed.

In Case2shown inFIG.6, switching to the backup power source20is completed in a period from the first turn-off time t1 to the first turn-on time t2, that is, before the first power source relay off period Toff_1 has elapsed, and the “backup power source state” becomes valid. At this time, the voltage does not return, because the power source relay31is off.

At the first turn-on time t2, which is a time when the first power source relay off period Toff_1 has elapsed from the first turn-off time t1, the control unit40turns on the power source relay31again. In Case2, the voltage recovers at the first turn-on time t2. In this case, the control unit40resumes the normal control with the backup power source20at the same time when the voltage recovers.

In Case3shown inFIG.7, the switching to the backup power source20is completed in a period from the first turn-on time t2 to the second turn-off time t3, that is, before the first power source relay on period Ton_1 has elapsed, and the “backup power source state” becomes valid. The power source relay31is on at this point. Therefore, the voltage is restored simultaneously when the “backup power source state” becomes valid. The control unit40resumes the normal control with the backup power source20at the same time when the voltage recovers.

As shown inFIG.8, the first power source relay on period Ton_1 has elapsed without the voltage recovery. In this case, at the second turn-off time t3, which is a time when the first power source relay on period Ton_1 has elapsed, the control unit40turns off the power source relay31for the second time.

In Case4shown inFIG.8, switching to the backup power source20is completed after the second turn-off time t3. Alternatively, in Case4, the switching to the backup power source20is not completed permanently. For example, a case is assumed in which the backup power source20or the power source switch25of the backup power source device200is abnormal. Therefore, in the first embodiment, when the second turn-off time t3 has been reached, it is considered that time up occurs.

That is, when the a single power source relay off period Toff_1 and the a single power source relay on period Ton_1 have elapsed without recover of the voltage, the control unit40turns off the power source relay31for the second time and terminates the driving of the actuator80. In this way, at the second turn-off time t3, the abnormality detection control is terminated, and the stop control is started.

Subsequently, with reference toFIG.9, an output limitation of the actuator80in the power failure recovery process will be described. The control unit40limits the output of the actuator80to a predetermined output limit value Plim or less in a period between the power supply failure time t0 and the time when the inverter input voltage Vinv recovers. For example, the control unit40may set the output of the actuator80to 0.

The timing, at which the output limit value is reduced, is not limited to the case shown by the solid line where the limitation is completed before the first turn-off time t1. For example, in Case2and Case3, the limitation may be completed before the first turn-on time t2, as shown by the broken line. After the voltage recovers, the control unit40cancels the output limitation of the actuator80. in this way, sudden generation of the output of the actuator80can be suppressed when the normal control is resumed. Preferably, when the control unit40changes the output limit value, the output limit value is changed gradually, in order to avoid a sudden change.

Furthermore, when resuming the normal control using the backup power source20, the control unit40limits the output of the actuator80compared to the output in the normal control with the main power source10. The capacity of the backup power source20is smaller than the capacity of the main power source10. Therefore, by limiting the output, it is possible to extend a time period in which the control is continued. For example, the output limit value of the actuator80may be set according to a charge amount of the backup power source20.

The process in the abnormality detection control will be described with reference to the flowchart inFIG.10. In the description of the flowchart, a symbol “S” indicates a step. In S1, the main power source10fails at time t0, and the control unit40shifts from the normal control to the abnormality detection control. In S2, the control unit40stops the driving of the inverter50and turns off at least one of the inverter relay35and the actuator relay38. “Stopping of the driving of the inverter50” means turning off the upper and lower arm elements51to56of all the phases. This state continues until it is determined in S3that the voltage has been recovered.

When it is determined in S3that the voltage has been recovered, the control unit40cancels the stopping of the driving of the inverter50and turns on the inverter relay35and the actuator relay38in S4. Note that the power source relay31is already turned on at the time when it is determined that the voltage has been recovered. Further, in S5at the same time as S4, the control unit40terminates the abnormality detection control and resumes the normal control.

In this way, the control unit40stops the driving of the inverter50from the time t0 when the power source fails until the time when the voltage has been recovered. This process prevents the voltage generated by the inverter50from being applied to the power sources10and20. In addition, the control unit40turns off at least one of the inverter relay35and the actuator relay38. This process prevents the regenerative current from flowing from the inverter50to the power sources10and20due to a reverse input from the actuator80.

As described above, the control unit40of the first embodiment alternately repeats the period in which the power source relay31is turned on and the period in which the power source relay31is turned off after the main power source10fails. This process enables to quickly restart the normal control and implement safety measures when the inverter input voltage Vinv recovers. On the other hand, when each of the power source relay off period Toff_1 and the power source relay on period Ton_1 elapses once without recovery of the voltage, the control unit40stops driving of the actuator80. In this way, this configuration avoids continuation of unnecessary processing when there is no possibility of the recovery. In this way, the present embodiment enables to appropriately determine whether to resume the normal control after the power source fails.

In particular, the power failure recovery process of this embodiment is executed in the system including the main power source10and the backup power source20, when the main power source10fails and when the DC power source connected to the power supply line is switched from the main power source10to the backup power source20. This configuration enables to efficiently and safely resume the normal control after the main power source10is switched to the backup power source20. This configuration is suitable particularly for the EPS system and the SBW system that require a high reliability.

Second Embodiment

With reference toFIG.11, the power failure recovery process of the second embodiment will be described.FIG.11representatively shows a control according to Case3(FIG.7) of the first embodiment. The control unit40does not turn on the power source relay31all the time but intermittently turns on and off the power source relay31in the standby period Twt, which is from the power failure time t0 to the time when the inverter input voltage Vinv recovers, and the power source relay on period Ton_1.

When the power source relay31is regularly turned on during the abnormality detection control, there is a risk that the inverter elements51to56and the like may be damaged due to heat generated in an overcurrent state. Therefore, in the abnormality detection control, by intermittently turning on and off the power source relay31, it is possible to suppress heat generation due in the overcurrent state. The duty ratio of the intermittent operation may be a fixed value, or may be set variably according to the detected current value or the like.

Third Embodiment

With reference toFIG.12, the power failure recovery process of the third embodiment will be described.FIG.12representatively shows a control according to Case4(FIG.8) of the first embodiment. The third embodiment has the same operation as that of the first embodiment until the second turn-off time t3. However, the third embodiment is different from the second embodiment in the timing at which driving of the actuator80is stopped, in other words, the timing at which the abnormality detection control is shifted to the stop control.

InFIG.12, the “backup power source supply state” continues to be invalid from the power failure time t0 until the time where the final transition to the stop control is made. At the second turn-off time t3, the control unit40turns off the power source relay31, and transitions to a second power source relay off period Toff_2 is made. Subsequently, when the power source relay off period Toff_2 elapses at a second turn-on time t4, the control unit40turns on the power source relay31, and transition to the second power source relay on period Ton_2 is made.

Assuming if switching to the backup power source20is completed during the second power source relay off period Toff_2, the normal control is resumed at the second turn-on time t4, similarly to Case2of the first embodiment. Assuming if switching to the backup power source20is completed during the second power source relay on period Ton_2, the normal control is resumed at the same time as the time where the voltage recovers, similarly to Case3of the first embodiment.

Thereafter, the power source relay off period and the power source relay on period Ton are repeated for N times (N≥2). At an (N−1)th turn off time t(2N−1), the control unit40turns off the power source relay31, and transition to an N-th power source relay off period Toff_N is made. At an N-th turn-on time t(2N), the control unit40turns on the power source relay31, and transition to an N-th power source relay on period Ton_N is made.

Thereafter, at an (N+1)th turn-off time t(2N+1) after the Nth power source relay on period Ton_N has elapsed, the control unit40turns off the power source relay31for the (N+1)th time and stops driving of the actuator80. That is, the control unit40turns off the power source relay31for the (N+1)th time and stops driving of the actuator80, when the power source relay off period and the power source relay on period are repeated for the N times that is two or more times, without recovery of the voltage.

In the third embodiment, it is possible to secure a chance to resume the normal control as long as possible before finally shifting to the stop control. Alternatively, assuming if a total time period until transition to the stop control is made is set to be the same as the time period in the first embodiment, the power source relay off period and the power source relay on period are repeated for many times in a short cycle, thereby to enable to reduce the time lag from the time, at which the switching is completed, to the time at which the normal control is resumed in Case2.

Other Embodiments

(a) The actuator80driven by the actuator driving device300may be another device than the motor that outputs the torque through rotation and may be an electric linear actuator that outputs a linear force or the like. In addition, the “inverter” may include an H-bridge circuit that converts a current direction of the input DC power. The actuator may include a DC actuator such as a DC motor.

(b) One or both of the inverter relay35and the actuator relay38may not be provided. In this case, the item to turn off the relay that does not exist is excluded from the processing in the abnormality detection control shown inFIG.10.

(c) The semiconductor switching elements are illustrated inFIG.3as the power source relay31, the inverter relay35, and the actuator relay38. The present invention is not limited to this, and each of the relays may be composed of a mechanical relay.

(d) The power failure recovery process is not limited to that switches to the backup power source20when the main power source10fails. The power failure recovery process may be executed when the power source temporarily fails and then recovers after a while. In other words, the present disclosure is not limited to the system including the main power source10and the backup power source20. The present disclosure is also applicable to a system equipped with only one DC power source. In this case, when the normal control is resumed, and the actuator output limitation is canceled, the actuator output may be set to a level similar to that before the power source failure.

(e) The present disclosure is not limited to be applied to the EPS or SBW steering systems. The present disclosure may be applied to various actuator driving systems in which an electric power from a DC power source is converted by an inverter and supplied to an actuator.

The present disclosure should not be limited to the embodiment described above. Various other embodiments may be implemented without departing from the scope of the present disclosure.

The control circuit and method described in the present disclosure may be implemented by a special purpose computer which is configured with a memory and a processor programmed to execute one or more particular functions embodied in computer programs of the memory. Alternatively, the control circuit described in the present disclosure and the method thereof may be realized by a dedicated computer configured as a processor with one or more dedicated hardware logic circuits. Alternatively, the control circuit and method described in the present disclosure may be realized by one or more dedicated computer, which is configured as a combination of a processor and a memory, which are programmed to perform one or more functions, and a processor which is configured with one or more hardware logic circuits. The computer programs may be stored, as instructions to be executed by a computer, in a tangible non-transitory computer-readable medium.

The present disclosure has been made in accordance with the embodiments. However, the present disclosure is not limited to such embodiments and configurations. The present disclosure also encompasses various modifications and variations within the scope of equivalents. Furthermore, various combination and formation, and other combination and formation including one, more than one or less than one element may be made in the present disclosure.