Control device for actuator, actuator, valve driving device and control method for actuator

A position sensor mounted in an actuator includes a magnetic detecting element for detecting the position of a shaft, and a temperature detecting element for detecting intra-sensor temperature which is used for correction of the temperature characteristics of the magnetic detecting element, the magnetic detecting element and the temperature detecting element being built therein. A control device for the actuator acquires both the temperature-corrected position of the shaft and the intra-sensor temperature from the position sensor, and uses them for control of the actuator.

TECHNICAL FIELD

The present invention relates to a control device for an actuator that uses a direct-current motor as a driving source, an actuator, a valve driving device and a control method for an actuator.

BACKGROUND ART

In a direct-current motor used as a driving source of an actuator, its performance degrades when the temperature of coils thereof rises due to the passage of currents through the coils. For this reason, conventionally, an independent temperature sensor is disposed in the direct-current motor, to detect the temperature (for example, refer to Patent Literature 1), or the coil temperature is estimated on the basis of the currents passing through the coils and the time period during which the currents pass through the coils, to limit the current passing through the direct-current motor on the basis of the temperature, thereby preventing performance degradation.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2007-45325

SUMMARY OF INVENTION

Technical Problem

However, a problem is that when the detected value provided by the temperature sensor is used for control of the direct-current motor, an independent temperature sensor is needed independently of the actuator.

Further, another problem is that a coil temperature estimated indirectly is less accurate than a temperature directly detected by the temperature sensor.

The present invention is made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a technique for acquiring the internal temperature of an actuator which is more accurate than temperature estimated indirectly, without disposing a temperature sensor independently of the actuator.

Solution to Problem

A control device for an actuator according to the present invention includes: an acquirer to acquire both the position of a shaft which is temperature-corrected by using intra-sensor temperature detected by a temperature detecting element built in a position sensor, and the intra-sensor temperature; and a controller to control the actuator by using both the temperature-corrected position of the shaft and the intra-sensor temperature which are acquired by the acquirer.

Advantageous Effects of Invention

According to the present invention, because the intra-sensor temperature detected by the temperature detecting element built in the position sensor is acquired, the internal temperature of the actuator which is more accurate than the temperature estimated indirectly can be acquired, without mounting a temperature sensor independently of the actuator.

DESCRIPTION OF EMBODIMENTS

Hereafter, in order to explain this invention in greater detail, embodiments of the present invention will be described with reference to accompanying drawings.

A case of using an actuator according to the present invention as a wastegate (hereinafter referred to as WG) actuator that drives a WG valve of a turbocharger that is mounted in a vehicle will be explained as an example.

FIG. 1is a cross-sectional view showing an example of the configuration of a WG actuator1according to Embodiment 1. The turbocharger is configured so as to rotate a turbine by using an exhaust gas from an engine, drive a compressor connected with this turbine on the same axis, compress intake air, and supply this compressed intake air to the engine. A WG valve2for bypassing the exhaust gas from an exhaust passage100to a bypass passage101is disposed on an upstream side of the exhaust passage100with respect to the turbine. The number of rotations of the turbine is controlled by opening or closing the WG valve2to adjust the inflow of the exhaust gas from the exhaust passage100to the bypass passage101by means of the WG actuator1. InFIG. 1, a solid line shows a fully closed state of the WG valve2, and a chain double-dashed line shows a fully opened state of the WG valve2.

The WG actuator1includes a direct-current motor4that serves as a driving source, a shaft13that opens and closes the WG valve2, and a screw mechanism12that converts a rotary motion of the direct-current motor4into a linear motion of the shaft13. The direct-current motor4includes a rotor6having a magnet5magnetized into a plurality of N and S poles, and a stator8on which coils7are wound. Brushes11bare connected with ends of the coils7. The rotor6is rotatably supported by a bearing portion14on one end side thereof, and a commutator9is fixed on the other end side of the rotor6.

When a voltage is applied to an external terminal10, currents flow through commutator bars in contact with brushes11a, among plural commutator bars which configure the commutator9, via the brushes11aconnected with this external terminal10, and currents flow through the coils7via the brushes11belectrically connected with these commutator bars. The stator8is magnetized into an N pole and an S pole by the passage of the currents through the coils7, and the N pole and the S pole of the stator8repel and attract the N pole and the S pole of the magnet5and this causes the rotor6to rotate. As the rotor6rotates, the coils7through which the currents are made to pass are switched and, as a result, the poles of the stator8are also switched and the rotor6continues rotating. When the directions of the currents are reversed, the direction of rotation of the rotor6is also reversed.

Although a DC motor with brushes is used as the direct-current motor4in the example shown inFIG. 1, a brushless DC motor may be used.

A hole used for disposing the shaft13is made inside the rotor6, and a female screw portion12ais formed on an inner circumferential surface of the hole and a male screw portion12bis formed on an outer circumferential surface of the shaft13. This male screw portion12bis screwed into and coupled with the female screw portion12a, and a rotary motion of the rotor6is converted into a linear motion of the shaft13. The screw mechanism12consists of these female screw portion12aand male screw portion12b. One end of the shaft13penetrates the housing15, and is joined to the WG valve2via a linkage mechanism3. A position sensor16for detecting the position of this shaft13in an axial direction, and so on are disposed on the other end side of the shaft13.

The linkage mechanism3has two plates3aand3b. The shaft13is attached on one end side of the plate3a, and one end of the plate3bis attached rotatably to a supporting point3cdisposed on the other end side of the plate3a. The WG valve2is attached on the other end side of this plate3b. When the shaft13moves in a direction in which the shaft13is pushed out from the housing15in response to a rotation in one direction of the rotor6, the plate3aalso moves in the same direction, the plate3band the WG valve2rotate around the supporting point3c, and the WG valve2moves in a valve opening direction. When the shaft13moves in a direction in which the shaft is retracted into the housing15in response to a rotation in a reverse direction of the rotor6, the plate3aalso moves in the same direction, and the plate3band the WG valve2rotate around the supporting point3c, and the WG valve2moves in a valve closing direction.

Two flat surfaces or the likes are formed on the shaft13, and function as a rotation limiting portion13a. Further, on an inner circumferential surface of a hole of the housing15which the shaft13penetrates, a guide portion15a, such as two flat surfaces, is formed in such away as to match the shape of the rotation limiting portion13a. Sliding between the rotation limiting portion13aand the guide portion15aprevents the shaft13from rotating in synchronization with a rotation of the rotor6, to support the shaft13in such away as to cause the shaft to make the linear motion. A stopper15bprojecting toward the shaft13is formed at an end of the guide portion15a. By causing a butting portion13bwhich is shaped so as to project from the shaft13to come into contact with this stopper15b, the shaft13is prevented from further making the linear motion in the valve opening direction. Similarly, a plate that functions as a stopper15cis disposed at an end of the screw mechanism12. By causing an end surface of the shaft13that functions as a butting portion13cto come into contact with the stopper15c, the shaft13is prevented from further moving in the valve closing direction.

FIG. 2is a side view showing an example of the configuration of the position sensor16according to Embodiment 1.

In the plate that functions as the stopper15cfor the shaft13, a hole having a diameter smaller than the outer diameter of the shaft13penetrates, and a shaft for sensor17is made to pass through this hole, and an end surface of the shaft for sensor17is in contact with the end surface of the shaft13. As a result, the shaft for sensor17also reciprocates in synchronization with a reciprocating motion in the axial direction of the shaft13. A magnetic flux of a magnet for sensor18flows through a stator for sensor19mounted around the magnet for sensor, and passes through the position sensor16. This magnet for sensor18is fixed to the shaft for sensor17, and, when the position of the magnet for sensor18with respect to the position sensor16varies due to the reciprocating motion of the shaft13, a flux density passing through the position sensor16also changes.

FIG. 3is a block diagram showing an example of the configuration of a control device20.

A magnetic detecting element16aand a temperature detecting element16bare built in the position sensor16. The magnetic detecting element16ais a Hall element, a magnetoresistive element or the like, and the temperature detecting element16bis a thermistor or the like. The magnetic detecting element16adetects the flux density which varies due to the reciprocating motion of the shaft13, and converts the flux density into an actual stroke position of the shaft13. Because the magnetic detecting element16ahas characteristics that its magnetic sensitivity depends on temperature, the position sensor16detects an intra-sensor temperature by using the temperature detecting element16b, to correct the temperature characteristics of the magnetic detecting element16a. This position sensor16outputs a digital signal showing the actual stroke position after the correction of the temperature characteristics, and a digital signal showing the intra-sensor temperature used for the correction to the control device20by using, for example, a SENT (Single Edge Nibble Transmission) method. The outputs from the position sensor16to the control device20are not limited to the digital signals such as digital signals based on the SENT method, but analog signals may be used.

An engine control unit includes an engine control part21and the control device20, and illustration and explanation of components other than these components will be omitted. The engine control part21outputs a target stroke position of the shaft13to a control unit22.

Although in the example shown inFIG. 3the functions of the control device20are configured so as to be implemented as one function of the engine control unit, the control device20may be configured as an independent electronic control unit or may be incorporated, as a circuit board, into the WG actuator1.

The control device20includes the control unit22, a motor driver23, an acquiring unit24and an abnormality determining unit25.

The acquiring unit24acquires the digital signal showing the actual stroke position of the shaft13and the digital signal showing the intra-sensor temperature from the position sensor16. The acquiring unit24outputs the actual stroke position acquired thereby to the control unit22, and outputs the intra-sensor temperature to the abnormality determining unit25. The actual stroke position which the acquiring unit24has acquired from the position sensor16is the position which has been temperature-corrected by the position sensor16.

The control device20according to Embodiment 1 estimates that the intra-sensor temperature detected by the temperature detecting element16bis equal to the internal temperature of the WG actuator1, and determines an abnormality in the temperature of the WG actuator1on the basis of this intra-sensor temperature, as explained below.

The abnormality determining unit25compares the intra-sensor temperature received from the acquiring unit24with a predetermined temperature threshold. The abnormality determining unit25determines that the WG actuator1has an abnormal temperature when the intra-sensor temperature is higher than the temperature threshold, whereas the abnormality determining unit determines that the WG actuator1has a normal temperature when the intra-sensor temperature is equal to or lower than the temperature threshold, and outputs the result of the determination to the control unit22. The temperature threshold is an upper limit (e.g., 100 degrees) on a temperature range within which the WG actuator1operates normally. For example, the temperature threshold is the temperature below which a situation in which the internal temperature of the WG actuator1rises due to either the passage of a current through the direct-current motor4or the operating environment temperature, and, as a result, it becomes impossible to maintain the performance needed for the WG actuator1or the WG actuator is subjected to melt damage can be prevented from occurring. Further, a hysteresis can be provided for the temperature threshold, and it is determined as an abnormal temperature when the intra-sensor temperature is higher than an upper limit (e.g., 100 degrees) on the temperature threshold, whereas it can be determined as a normal temperature when the intra-sensor temperature is lower than a lower limit (e.g., 50 degrees) on the temperature threshold.

The control unit22receives a notification of the result of the determination showing the abnormal temperature or the normal temperature from the abnormality determining unit25.

When the result of the determination showing the normal temperature is notified from the abnormality determining unit25, the control unit22performs feedback control on the stroke position of the shaft13in such a way that the actual stroke position received from the acquiring unit24gets close to the target stroke position received from the engine control part21. By performing the feedback control on the stroke position of the shaft13, the degree of opening of the WG valve2joined to the shaft13is adjusted. For example, when performing PID control, the control unit22calculates the difference between the target stroke position and the actual stroke position, calculates amounts of operation which are a proportional term, an integral term and a differential term, these terms corresponding to the difference, to calculate a drive duty, generates a PWM (Pulse Width Modulation) control signal corresponding to the drive duty, and outputs the PWM control signal to the motor driver23.

When the result of the determination showing the abnormal temperature is notified from the abnormality determining unit25, the control unit22generates a PWM control signal to limit the passage of the current through the direct-current motor4, and outputs the PWM control signal to the motor driver23. As a temperature protecting control operation of limiting the passage of the current through the direct-current motor4, for example, an operation of limiting the drive duty acquired through the above-mentioned feedback control to duty lower than the drive duty, thereby decreasing the passing current, or an operation of limiting the drive duty to zero, thereby stopping the current passage is performed. Through this temperature protecting control operation, an excessive temperature rise in the WG actuator1is prevented, and degradation in the performance of the WG actuator1is prevented and melt damage or the like is prevented.

The engine control part21can be configured so as to receive a notification of the result of the determination showing the abnormal temperature from the usual state determining unit25, and output an instruction to limit the passage of the current through the direct-current motor4to the control unit22. In the case of this configuration, the control unit22limits the drive duty acquired through the feedback control to the duty lower than the drive duty in accordance with the instruction received from the engine control part21, thereby decreasing the passing current, or limits the drive duty to zero, thereby stopping the current passage, like in the case of the above-mentioned configuration.

The motor driver23performs on/off control on a voltage applied to the direct-current motor4in accordance with the PWM control signal which the motor driver receives from the control unit22, to adjust the current passing through the direct-current motor4.

FIG. 4is a flow chart showing the operation of the control device20.

The acquiring unit24acquires both the actual stroke position of the shaft13and the intra-sensor temperature from the position sensor16(step ST1). The abnormality determining unit25compares the intra-sensor temperature detected by the temperature detecting element16bwith the predetermined temperature threshold (step ST2), and, when the intra-sensor temperature is higher than the temperature threshold (“YES” in step ST2), determines that the WG actuator1has an abnormal temperature and notifies the control unit22of this determination result (step ST3). The control unit22which has received this notification performs the temperature protecting control in such a way as to limit the passage of the current through the direct-current motor4(step ST4).

In contrast, when the intra-sensor temperature is equal to or lower than the temperature threshold (“NO” in step ST2), the abnormality determining unit25determines that the WG actuator1has a normal temperature, and notifies the control unit22of this determination result (step ST5). The control unit22which has received this notification performs the normal feedback control (step ST6).

Next, an example of the hardware configuration of the control device20will be explained usingFIG. 5.

The motor driver23is comprised of a switching element or the like that switches on and off the voltage applied to the direct-current motor4. In a case in which the position sensor16is of a type that outputs digital signals based on the SENT method, the acquiring unit24is a receiving device42that receives digital signals. In a case in which the position sensor16is of a type that outputs analog signals, the acquiring unit24is an A/D converter43. The control device20should just include either the receiving device42or the A/D converter43in accordance with the type of the outputs of the position sensor16.

The control unit22and the abnormality determining unit25are implemented by a processor41that executes a program stored in a memory40. The processor41is a processing circuit such as a CPU or a system LSI. The memory40stores the temperature threshold used for determining whether the internal temperature of the WG actuator1is abnormal or normal, and so on, in addition to the above-mentioned program. Plural processors and plural memories can perform the above-mentioned functions in cooperation with one another.

As mentioned above, according to Embodiment 1, because the control device20is configured so as to include the acquiring unit24that acquires both the position of the shaft which has been temperature-corrected by using the intra-sensor temperature detected by the temperature detecting element16bbuilt in the position sensor16, and the intra-sensor temperature, and the control unit22that controls the WG actuator1by using both the position of the shaft13and the intra-sensor temperature which the acquiring unit24has acquired, the control device can acquire the internal temperature of the actuator which is more accurate than temperature estimated indirectly, without mounting a temperature sensor independently of the actuator. In addition, the actuator can be controlled with a high degree of accuracy by using the highly-accurate internal temperature.

Further, according to Embodiment 1, because the abnormality determining unit25determines that the internal temperature of the WG actuator1is abnormal when the intra-sensor temperature acquired by the acquiring unit24is higher than the temperature threshold, the temperature protecting control on the actuator can be performed with a high degree of accuracy.

FIG. 6is a block diagram showing an example of the configuration of a control device20for a WG actuator1according to Embodiment 2 of the present invention. InFIG. 6, the same components as those shown inFIG. 3or like components are designated by the same reference numerals, and the explanation of the components will be omitted hereafter. Because the WG actuator1which is an object to be controlled by the control device20according to Embodiment 2 has the same configuration as that according to above-mentioned Embodiment 1, the WG actuator will be explained usingFIGS. 1 and 2.

The control device20according to Embodiment 2 includes a coil temperature estimating unit26that estimates the temperature of the coil7of a direct-current motor4. Hereafter, the temperature of the coil7of the direct-current motor4is referred to as the “coil temperature.” As a method of estimating the coil temperature, a well-known method, for example, a method of detecting the value of a current passing from a motor driver23to the coil7of the direct-current motor4, and a time period during which the current passes through the coil7, to estimate the coil temperature. The coil temperature estimating unit26outputs the estimated coil temperature to a temperature correcting unit27.

However, because the coil temperature estimating unit26estimates the coil temperature indirectly without using any measured temperature, the coil temperature is not highly accurate. Therefore, there is a possibility that the difference between the estimated coil temperature and the WG actuator1is too large in terms of practical use. Thus, in Embodiment 2, the coil temperature estimated by the coil temperature estimating unit26is corrected by using intra-sensor temperature detected by a temperature detecting element16bbuilt in a position sensor16, and the accuracy of the estimation is increased. Concretely, the temperature correcting unit27estimates the internal temperature of the WG actuator1by using both the intra-sensor temperature received from an acquiring unit24and the coil temperature received from the coil temperature estimating unit26, and outputs the internal temperature to an abnormality determining unit25a. The temperature correcting unit27calculates, for example, a simple average or a weighted average of the intra-sensor temperature and the coil temperature, and estimates the calculated average to be the internal temperature of the WG actuator1.

The abnormality determining unit25acompares the internal temperature of the WG actuator1received from the temperature correcting unit27with a temperature threshold, to determine whether the WG actuator1has a normal temperature or abnormal temperature.

As mentioned above, according to Embodiment 2, because the control device20is configured so as to include the coil temperature estimating unit26that estimates the temperature of the coil7of the direct-current motor4, and the temperature correcting unit27that corrects the temperature of the coil7estimated by the coil temperature estimating unit26by using the intra-sensor temperature acquired by the acquiring unit24, the control device can improve the accuracy of the estimation greatly compared with the case in which the coil temperature is estimated indirectly.

Next, a variant of the control device20according to Embodiment 2 will be explained.

As mentioned above, because the accuracy of the estimation of the coil temperature by the coil temperature estimating unit26is not high, even if the coil temperature is corrected using the intra-sensor temperature detected by the temperature detecting element16b, the corrected coil temperature is not necessarily equal to the actual internal temperature of the WG actuator1. Thus, in this modified example, when the intra-sensor temperature detected by the temperature detecting element16bis higher than a temperature threshold, it is determined that the WG actuator1has an abnormal temperature even though the internal temperature of the WG actuator1received from the temperature correcting unit27is equal to or lower than its temperature threshold and indicates a normal temperature.

Concretely, the intra-sensor temperature is outputted from the acquiring unit24directly to the abnormality determining unit25a. The abnormality determining unit25acompares the intra-sensor temperature received from the acquiring unit24with the temperature threshold, first, to determine whether the WG actuator1has a normal temperature or abnormal temperature. When, in this determining process, determining that the WG actuator1has an abnormal temperature, the abnormality determining unit25anotifies a control unit22of the result of the determination showing the abnormal temperature. In contrast, when determining that the WG actuator1has a normal temperature, the abnormality determining unit25athen compares the internal temperature of the WG actuator1which the abnormality determining unit has received from the temperature correcting unit27with the temperature threshold, and determines whether the WG actuator1has a normal temperature or abnormal temperature. When, in this determining process, determining that the WG actuator1has an abnormal temperature, the abnormality determining unit25anotifies the control unit22of the result of the determination showing the abnormal temperature.

As mentioned above, because when the intra-sensor temperature which the acquiring unit24has acquired is higher than the temperature threshold, the abnormality determining unit25adetermines that the internal temperature of the WG actuator1is abnormal, without using the estimated coil temperature, the abnormality determining unit can determine an abnormality in the temperature of the WG actuator1more certainly.

It is to be understood that any combination of the above-mentioned embodiments can be freely made, various changes can be made in any component according to any one of the above-mentioned embodiments, and any component according to any one of the above-mentioned embodiments can be omitted within the scope of the invention.

Although in the above-mentioned explanation the WG valve is mentioned as an example of the object to be driven which is driven by the actuator according to the present invention, the present invention is not limited to this example. An exhaust gas recirculation (EGR) valve mounted in the engine, a movable vane mounted in a variable geometry (VG) turbocharger, or the like can be the object to be driven.

Further, although the configuration of joining the shaft of the actuator according to the present invention and the object to be driven by using the linkage mechanism is shown, a configuration of directly joining the shaft and the object to be driven without using the linkage mechanism may be provided.

Further, a valve driving device including the actuator according to the present invention, the valve which is the object to be driven, and the control device may be configured.

Although in the above-mentioned explanation the example of using the intra-sensor temperature detected by the position sensor for the temperature protecting control on the actuator is explained, this embodiment is not limited to this use.

INDUSTRIAL APPLICABILITY

Because the control device for the actuator according to the present invention acquires the highly-accurate internal temperature of the actuator, the control device is suitable for use as a control device for an actuator that uses a direct-current motor as a driving source.

REFERENCE SIGNS LIST