JP2010111265A - Steering control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering control device performing adequate overheat protection based on the maximum value of an estimated temperature, even when electric conduction to the switching element of each phase is largely changed according to the locking position of a motor. <P>SOLUTION: The steering control device includes a torque sensor for detecting the steering torque, a brushless motor 18 for imparting the assist torque, an assist torque calculation unit 26 for obtaining an assist torque command value, a motor drive unit 30 including a switching circuit, a current sensor 31 for detecting the phase current of the motor 18, and an overheat protection computation unit 25. The overheat protection computation unit 25 estimates the temperature change of the motor 18 based on the maximum value of the absolute value of the phase current value from the current sensor 31. The torque correction according to the temperature change is calculated, and the assist torque command value is corrected with the torque correction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a steering control device for a vehicle, and more particularly to a steering control device suitable for a power steering device in which a steering assist force is obtained by an assist torque generating mechanism using a brushless motor, which is an electric motor, as a power source.

As a control technique for this type of brushless motor, for example, one disclosed in Patent Document 1 has been proposed. In Patent Document 1, a motor protection unit that manages protection of the motor itself or the motor control device is provided. In this motor protection unit, at least the phase winding previously stored in the square value of the q-axis current iq of the motor. When the amount of heat generated by the phase winding is calculated by multiplying the electric resistance value r of the wire, the temperature T of the phase winding is calculated based on the amount of generated heat, and when this temperature T exceeds a predetermined threshold value Tth It is determined that the current is overcurrent or overheat, and a necessary alarm signal or control signal is output, thereby protecting the motor itself or the motor control device.
JP 2003-164185 A

  However, in the technique described in Patent Document 1, since the brushless motor is a three-phase alternating current, the motor is rotating, and the motor is not rotating but a predetermined current flows to generate torque. In the so-called motor lock state, even if the q-axis current or d-axis current is the same, the applied current to each phase may differ greatly, and the application to each phase also depends on the position (electrical angle) at which the motor is locked. The current may be different. In addition, in an inverter that controls a brushless motor, when a large current is continuously applied to a single phase, a power switching element such as a FET of a specific phase may abnormally generate heat.

  A power steering device that obtains steering assist force by an assist torque generation mechanism that uses a brushless motor as a power source may travel with the steering wheel (handle) kept at a predetermined angle. This state is referred to as a steering wheel holding state, and this steering wheel holding state corresponds to the previous motor lock state.

  Therefore, if an attempt is made to perform the overheat protection by estimating the motor winding temperature using only the q-axis current or the d-axis current as described above, the temperature estimation error becomes too large and appropriate overheat protection is performed. It becomes difficult.

  The present invention has been made paying attention to such problems, and even when the energization amount to the switching element of each phase varies greatly depending on the lock position of the motor, the maximum load (heat generation) state of each phase, In other words, a steering control device is provided in which the highest estimated temperature among the phases is identified and appropriate overheat protection can be performed based on the maximum value of the estimated temperature.

  The steering control device of the present invention includes a torque detector that detects a steering torque by a driver, a brushless motor that applies assist torque as a steering assist force to a steering wheel of a vehicle, and the brushless motor based on an output of the torque detector. An assist torque calculation unit for obtaining an assist torque command value to be applied to the motor, a switching circuit that outputs an applied voltage to each phase of the brushless motor based on the assist torque command value, and a phase current flowing through the brushless motor In addition to the current sensor to detect, it has an overheat protection calculation unit.

  And in this overheat protection calculation part, after estimating the temperature change amount of the brushless motor under the phase current value based on the maximum value of the absolute value of the phase current value detected by the current sensor, A torque correction amount corresponding to the temperature change amount is calculated, and the assist torque command value from the assist torque calculation unit is corrected with the torque correction amount.

  According to the present invention, the temperature change amount is estimated based on the maximum value of the phase current value, and the assist torque command value is corrected with the torque correction amount corresponding to the temperature change amount. Appropriate overheat protection can be performed even when the energization amount to the switching elements of each phase varies greatly depending on the lock position of the motor, such as in the steering-holding state.

  FIG. 1 is a schematic explanatory diagram of a power steering apparatus to which a steering control apparatus according to the present invention is applied.

  As shown in the figure, the power steering device generates an assist torque as a steering assisting force with respect to the steering force of the driver and the steering transmission mechanism 1 that transmits the steering force by the steering wheel (handle) 5 of the driver. An assist torque generation mechanism 2, a hydraulic pressure supply mechanism 3 that supplies hydraulic pressure to the assist torque generation mechanism 2, and a control unit 4 that performs overall control of each of the mechanisms are provided.

  The steering transmission mechanism 1 includes a steering wheel 5, a column shaft 6, a universal joint 7, an intermediate shaft 8, a universal joint 9, and an input shaft 10 connected in order, and the input shaft 10 has a torque sensor as a torque detector that detects steering torque. 11 is provided. A pinion 12 is connected to the tip of the input shaft 10.

  The assist torque generating mechanism 2 includes a power cylinder 13 as a main element. The power cylinder 13 is integrated with the cylinder tube 14, a piston 15 that can move in the cylinder tube 14 in the axial direction, and the piston 15. The rack 16 also serves as a movable piston rod. The interior of the cylinder tube 14 is formed by the piston 15 so as to be separated into a first cylinder chamber R1 and a second cylinder chamber R2.

  The hydraulic pressure supply mechanism 3 includes a pump 17 that generates hydraulic pressure, an electric motor that drives the pump 17, that is, a brushless motor 18, and a first oil path 19 and a second oil path 20 that supply hydraulic pressure to the power cylinder 13. The first oil passage 19 connects the first cylinder chamber R 1 of the power cylinder 13 and the pump 17, and the second oil passage 20 connects the second cylinder chamber R 2 of the power cylinder 13 and the pump 17. A normally open fail-safe valve 21 is provided between the first oil passage 19 and the second oil passage 20.

  The control unit 4 is connected to a vehicle speed sensor 22 and a battery 23. The control unit 4 drives the brushless motor 18 according to the vehicle speed information from the vehicle speed sensor 22 to adjust the amount of hydraulic pressure supplied to the assist torque generating mechanism 2, so that the assist torque generating mechanism 2 operates according to the vehicle speed. The assist torque generated is variably controlled.

  The pinion 12 of the steering transmission mechanism 1 and the rack 16 of the assist torque generating mechanism 2 mesh with each other, and the steering force by the driver's steering wheel 5 and the assist torque by the assist torque generating mechanism 2 are transmitted via the tie rod 24. It is transmitted to steered wheels not shown.

  The control unit 4 normally shuts off the normally open type fail-safe valve 21 to prevent the hydraulic pressure from moving between the first oil passage 19 and the second oil passage 20. When the steering wheel 5 is steered and predetermined steering torque information is input from the torque sensor 11, the brush 17 is driven by the brushless motor 18 to generate assist torque corresponding to the steering torque.

  More specifically, when the steering wheel 5 is steered to the left, the hydraulic pressure is supplied to the first cylinder chamber R1 of the power cylinder 13 via the first oil passage 19, and assist torque is generated for steering to the left. . On the other hand, when the steering wheel 5 is steered to the right, the hydraulic pressure is supplied to the second cylinder chamber R2 of the power cylinder 13 via the second oil passage 20, and assist torque is generated for steering to the right.

  At the time of failure such as failure, the normally open type fail-safe valve 21 is opened to allow the hydraulic oil to move between the first cylinder chamber R1 and the second cylinder chamber R2, and the driver's steering wheel 5 Enables steering by.

  FIG. 2 is a control block diagram of the control unit 4.

  The control unit 4 includes an overheat protection calculation unit 25, an assist torque calculation unit 26, a limiter 27, a motor control unit 28, a rotation position calculation unit 29, a motor drive unit 30, a current sensor 31, a rotation sensor 32, and the like, which will be described later. A sensor 33 is provided.

  The temperature sensor 33 is provided in the vicinity of a switching circuit (for example, a power switching element such as an FET) 34 to 39 forming a motor driving unit 30 described later in the control unit 4. The temperature in the vicinity is detected, and the temperature information is output to the overheat protection calculation unit 25.

  Temperature information from the temperature sensor 33 and motor current information (current value supplied for each phase of the brushless motor 18) from a current sensor 31 described later are input to the overheat protection calculation unit 25. The overheat protection calculation unit 25 performs a predetermined calculation according to the temperature information for each phase of the brushless motor 18 calculated based on the motor current from the current sensor 31 in addition to the temperature information from the temperature sensor 33. More specifically, the assist torque generated by the assist torque generating mechanism 2 is set so that the windings of the respective phases of the switching circuits 34 to 39 and the brushless motor 18 are within the normal movable temperature range. In order to limit, an overheat protection torque limit value as a torque correction amount is calculated as described later, and this is output to the limiter 27. The details of the overheat protection unit 25 will be described later.

  The assist torque calculator 26 receives the steering torque information from the torque sensor 11 and the vehicle speed information from the vehicle speed sensor 22 shown in FIG. 1, and inputs the assist torque to be applied to the brushless motor 18 based on the input information. A torque command value is calculated, and this assist torque command value is output to the subsequent limiter 27.

  The limiter 27 receives the overheat protection torque limit value as the torque correction amount from the above-described overheat protection calculation unit 25 and the assist torque command value from the assist torque calculation unit 26, and inputs these pieces of information. Based on this, a motor torque command value to be applied to the subsequent motor control unit 28 is calculated, and this motor torque command value is output to the motor control unit 28.

  The rotation position calculation unit 29 receives the rotation angle information from the rotation angle sensor 32 that detects the rotation angle of the brushless motor 18, calculates the rotation position of the brushless motor 18, and sends the rotation position information to the motor control unit 28. Output.

  In addition to the motor torque command value from the limiter 27, the motor control unit 28 includes the rotational position information of the brushless motor 18 from the rotational position calculation unit 29, and the U phase, V phase and the brushless motor 18 detected by the current sensor 31. Current information (current value) for each phase of the W phase is input. In the motor control unit 28, in addition to the three-phase two-phase conversion for converting the three-phase currents of the U phase, the V phase, and the W phase into the two-phase current, the opposite two-phase three-phase conversion and the PWM conversion, By performing feedback control such as PI control, a drive signal (PWM signal) for the brushless motor 18 is generated, and this signal is output to the motor drive unit 30 at the subsequent stage.

  The current information (current value) for each phase of the U-phase, V-phase, and W-phase of the brushless motor 18 detected by the current sensor 31 is also output to the overheat protection calculation unit 25 at the same time.

  For example, as shown in FIG. 3, the motor drive unit 30 is configured in the form of a three-phase inverter circuit with switching circuits 34 to 39 including power switching elements such as transistors represented by FETs. The switching circuits 34 to 39 are switched in accordance with the motor drive signal input from, and the brushless motor 18 is driven by outputting a predetermined voltage to the brushless motor 18.

  FIG. 4 is a functional block diagram of the overheat protection calculation unit 25 shown in FIG. 2. In this overheat protection calculation unit 25, the temperature information from the temperature sensor 33, the U phase of the brushless motor 18 detected by the current sensor 31, V As described above, the current information (current value) for each phase of the phase and the W phase is input, and the overheat protection torque limit value as the torque correction amount is output.

  In addition to the A / D converter 40 and the temperature change amount estimation unit 41, the overheat protection calculation unit 25 in FIG. 4 includes a first torque limit value calculation unit 42, a second torque limit value calculation unit 43, and a select low calculation unit 44. Have.

  The A / D converter 40 converts an analog signal related to the actually measured temperature information from the temperature sensor 33 into a digital signal, and then outputs this to the first torque limit value calculation unit 42 in the subsequent stage as temperature sensor actually measured temperature information.

  The first torque limit value calculation unit 42 applies the temperature sensor measured temperature information from the A / D converter 40 to a predetermined calculation formula, and sets the first overheat protection torque limit value based on the temperature in the vicinity of the switching circuits 34 to 39 as the first overheat protection torque limit value. 1 Torque limit value is calculated. The first torque limit value is input to the subsequent select low calculation unit 44.

  In the temperature change amount estimation unit 41, motor current information for each phase of the U-phase, V-phase and W-phase of the brushless motor 18 detected by the current sensor 31 is input, and the motor current information is applied to a predetermined arithmetic expression. The temperature change amount is estimated and calculated as the heat generation amount under the motor current information. The calculated temperature change amount is output to the second torque limit value calculation unit 43 at the subsequent stage.

  The second torque limit value calculation unit 43 applies the estimated temperature change amount information from the temperature change amount estimation unit 41 to a predetermined calculation formula, and uses the second torque limit value as an overheat protection torque limit value based on the estimated temperature change amount. Calculate the value. The second torque limit value is input to the subsequent select low calculation unit 44.

  In the select low calculation unit 44, the first torque limit value from the first torque limit value calculation unit 42 and the second torque limit value from the second torque limit value calculation unit 43 are input, and the first and first torque limit values are input. The smaller one of the two torque limit values is selected, and the selected torque limit value is output as an overheat protection torque limit value as a torque correction amount.

  Here, the details of the temperature change amount estimation unit 41 are as shown in FIG. 5, and current information for each of the U-phase, V-phase, and W-phase of the brushless motor 18 detected by the current sensor 31 described above. Is input to the phase current maximum value detection unit 45 to detect the current value of the phase in which the most current flows among the currents of the U phase, V phase and W phase, that is, the maximum current value in absolute value. To do. Then, the square value calculation unit 46 at the subsequent stage of the phase current maximum value detection unit 45 calculates the square value of the maximum current value at the absolute value detected by the phase current maximum value detection unit 45, and this is calculated as the first-order lag function of the subsequent stage. Input to the device 47. The reason why the square value of the maximum current value in absolute value is calculated is that the temperature is proportional to the square value of the current value.

  Further, the output from the first-order lag function unit 47 is input to a subsequent square value-temperature conversion unit 48, and the output from the first-order lag function unit 47 is multiplied by a temperature conversion gain (coefficient) K, and the value is plotted. 4 is an estimated temperature change amount ΔT which is an output from the temperature change amount estimation unit 41.

  6 and 7 are flowcharts showing the processing procedure in the circuit of FIG.

  As shown in FIG. 6, in step S1, the current flowing in each phase of the brushless motor 18, that is, the currents in the U phase, V phase, and W phase are detected by the current sensor 31 in FIG. 2, and the values are read.

  In the subsequent step S2, the temperature in the vicinity of the switching circuits 34 to 39, which is the heat generating part forming the motor driving unit 30 (referred to as “heat generating part temperature” in FIG. 6), is detected by the temperature sensor 33 in FIG. Detect and read the value.

  On the other hand, in step S3, the assist torque is calculated based on the signal from the torque sensor 11 in FIG.

  In step S4, as a function of the phase current maximum value detection unit 45 in FIG. 5, the current value of the U-phase, V-phase, and W-phase detected in step S1 having the maximum absolute value is detected or specified. In S5 and S6, the maximum current value at the absolute value is integrated for a certain period.

  Next, in step S7, the square value of the integrated value of the maximum current value is calculated as a function of the square value calculation unit 46 of FIG. 5, and in step S8, the function of the primary delay function unit 47 of FIG. After the first-order lag function processing is performed on the square value, in the subsequent step S9 in FIG. 7, the square value first-order lag value is multiplied by the temperature conversion gain k as the function of the square value-temperature conversion unit 48 in FIG. Thus, an estimated temperature change amount ΔT is calculated.

  In step S10, as a function of the second torque limit value calculation unit 43 in FIG. 4, a second torque limit value is calculated based on the estimated temperature change amount ΔT obtained previously.

  In parallel with or in series with the series of processes, in step S11, as a function of the first torque limit value calculation unit 42 in FIG. calculate.

  In step S12, the first torque limit value calculated earlier is compared with the second torque limit value as a function of the select low calculation unit 44 in FIG. 4, and the smaller torque limit is processed in steps S13 and S14. Select a value and output the value as an overheat protection torque limit value as a torque correction amount.

  Thereafter, in step S15, the previously calculated assist function is used as a function of the limiter 27 in FIG. 2 to correct the assist torque from the assist torque calculation unit 26 with the overheat protection torque limit value that is the output of the overheat protection calculation unit 25. Based on the torque and the overheat protection torque limit value, an appropriate motor command torque is calculated and applied to the motor control unit 28 (step S16), and the brushless motor 18 is driven.

  As described above, according to the present embodiment, the absolute value of the U-phase, V-phase, and W-phase current values is specified, and the temperature is determined based on the square value of the maximum value of the absolute values. The amount of change is estimated, and the motor command torque is determined according to the estimated value to drive. Therefore, even when the energization amount to the switching circuits 34 to 39 varies greatly depending on the motor lock position as in the steering wheel holding state described above, the temperature in the switching circuit in which the maximum load state, that is, the maximum current value flows is obtained. Appropriate overheat protection according to the amount of change (heat generation amount) can be performed.

  For example, assuming that the motor is locked at the position A in FIG. 8 and the motor is locked at the position B in FIG. 9, the maximum current value of the U phase, V phase and W phase in each case The estimated temperature change of the switching circuits 34 to 39 (here, the power switching element is assumed to be an FET) calculated based on the absolute value of the current and the measured temperature of the switching circuits 34 to 39 by the temperature sensor 33 were compared. . The result is shown in FIG.

  As is clear from the figure, in each case, the estimated temperature change of the switching circuits 34 to 39 calculated based on the absolute value of the maximum current value and the actually measured temperature by the temperature sensor 33 are very close to each other. It can be seen that there is no significant difference between the temperatures. This means that even if the motor lock position changes, there is no difference between the estimated temperature change and the measured temperature, which means that appropriate overheat protection can always be performed regardless of the motor lock position change. Yes.

  On the other hand, when overheat protection is performed based on, for example, the q-axis current as in the conventional example described above, the q-axis current value is not affected by the change in the motor lock position, as is apparent from FIGS. As shown in FIG. 13, a large error occurs between the estimated temperature change calculated based on the q-axis current and the actually measured temperature as shown in FIG. 13, and appropriate overheat protection cannot be performed. Become.

  Here, in the above embodiment, the current values of the U-phase, V-phase, and W-phase are individually detected by the current sensor 31, but the current values of any two phases of the three phases are detected as current. It may be detected by a sensor and the remaining one-phase current value may be obtained by calculation or estimation.

  14 to 16 show a second embodiment of the present invention. In particular, FIG. 14 shows another example of the overheat protection arithmetic unit 25 shown in FIG.

  In the second embodiment, as apparent from a comparison between FIG. 14 and FIG. 4, the temperature actually measured by the temperature sensor 33 after A / D conversion, which is the output of the A / D converter 40, is added to the adder 49. Is different from that of the first embodiment in that it is added to the estimated temperature change amount ΔT which is the output of the temperature change amount estimating unit 41. As a result, the input of the second torque limit value calculation unit A is obtained by adding the estimated temperature change amount ΔT to the actually measured value of the temperature sensor 33, not the change amount per unit time as in the first embodiment. The estimated temperature in the vicinity of the switching circuits 34 to 39 that substantially form the motor drive unit 30 (herein referred to as “substantially estimated temperature”) itself. Accordingly, the second torque limit value calculation unit 43A calculates a second torque limit value corresponding to the actual estimated temperature that is the output of the adder 49.

  And the processing procedure at the time of replacing the overheat protection calculating part 25 of FIG. 2 with the thing of FIG. 14 is shown to the flowchart of FIG. 16 differs from that of the first embodiment in FIGS. 6 and 7 in that the processing of step S30 in FIG. 16 which is a function of the adder 49 in FIG. 14 is added. It is basically the same as that of 6,7.

  According to the second embodiment, the input in the second torque limit value calculation unit 43A in FIG. 14 is different from that in the first embodiment, and the switching circuits 34 to 34 forming the motor driving unit 30 are used. 39, and the second torque limit value is calculated according to the estimated temperature itself. For example, when the temperature of the motor drive unit 30 itself is low as in the initial stage of control start, or the external environment temperature is When the temperature is low, when the overheating protection of the switching circuits 34 to 39 and the brushless motor 18 is performed, more appropriate overheating protection can be performed in consideration of the actual temperature of the motor driving unit 30 and the external environment temperature.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic explanatory drawing of the power steering apparatus with which the steering control apparatus of this invention is applied. The control block diagram of the control unit containing the brushless motor of FIG. Explanatory drawing which shows the detail of the motor drive part of FIG. The block diagram which shows the detail of the overheat protection calculating part of FIG. The block diagram which shows the detail of the temperature variation estimation part of FIG. The flowchart which shows the process sequence in the control unit of FIG. The flowchart which shows the process sequence in the control unit of FIG. Explanatory drawing which shows the relationship between a phase current absolute value and a motor lock position. Explanatory drawing which similarly shows the relationship between a phase current absolute value and a motor lock position. Explanatory drawing which compared the estimated temperature change in the case of FIG. Explanatory drawing which shows the relationship between the phase current absolute value and motor lock position in a prior art example. Explanatory drawing which similarly shows the relationship between the phase current absolute value and motor lock position in a prior art example. Explanatory drawing which compared the estimated temperature change in the case of FIG. The block diagram which shows another example of an overheat protection calculating part in FIG. 2 as the 2nd Embodiment of this invention. The flowchart which shows the process sequence at the time of applying the overheat protection calculating part of FIG. 14 to the block diagram of FIG. The flowchart which shows the process sequence at the time of applying the overheat protection calculating part of FIG. 14 to the block diagram of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Steering transmission mechanism 2 ... Assist torque generation mechanism 3 ... Hydraulic pressure supply mechanism 4 ... Control unit 11 ... Torque sensor (torque detector)
DESCRIPTION OF SYMBOLS 17 ... Pump 18 ... Brushless motor 25 ... Overheat protection calculating part 26 ... Assist torque calculation part 27 ... Limiter 28 ... Motor control part 30 ... Motor drive part 31 ... Current sensor 33 ... Temperature sensor 34-39 ... Switching circuit 41 ... Temperature change Quantity estimation unit 45 ... phase current maximum value detection unit

Claims (4)

A torque detector for detecting steering torque by the driver;
A brushless motor that applies assist torque to the steering wheel of the vehicle as a steering assist force;
An assist torque calculator for obtaining an assist torque command value to be applied to the brushless motor based on an output of the torque detector;
A switching circuit (power switching element) that outputs an applied voltage to each phase of the brushless motor based on the assist torque command value;
A current sensor for detecting a phase current flowing in the brushless motor;
Based on the maximum absolute value of the phase current value detected by the current sensor, the temperature change amount of the brushless motor under the phase current value is estimated, and then torque correction according to the temperature change amount is performed. An overheat protection calculation unit that calculates an amount and corrects the assist torque command value from the assist torque calculation unit with the torque correction amount;
A steering control device comprising:   The overheat protection calculation unit obtains a first-order lag value from the square value of the maximum absolute value of the phase current value detected by the current sensor, and multiplies this by a temperature conversion coefficient to calculate the brushless motor. The steering control device according to claim 1, wherein the steering control device is estimated as a temperature change amount. A temperature sensor for detecting the temperature in the vicinity of the switching circuit;
The overheat protection calculation unit calculates a torque correction amount corresponding to the temperature change amount of the brushless motor as a first torque correction amount, while a second torque correction amount based on the temperature detected by the temperature sensor. To calculate
3. The assist torque command value from the assist torque calculation unit is corrected with a small torque correction amount of any one of the first and second torque correction amounts. The steering control device described. A temperature sensor for detecting the temperature in the vicinity of the switching circuit;
In the overheat protection calculation unit, the temperature detected by the temperature sensor is added to the temperature change amount of the brushless motor, and a torque correction amount corresponding to the added value is calculated as a first torque correction amount. Calculating a second torque correction amount based on the temperature detected by the temperature sensor;
3. The assist torque command value from the assist torque calculation unit is corrected with a small torque correction amount of any one of the first and second torque correction amounts. The steering control device described.

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