JP2008105652A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of surely preventing motor overcurrent generated by a motor back electromotive force when a steering mechanism reaches a steering limit state. <P>SOLUTION: The electric power steering device controls an electric motor 8 for generating a steering auxiliary force to a steering system based on a steering torque detected by a steering torque detection part 16. The electric power steering device is equipped with a rotational speed information detection part 20 for detecting the rotational speed information of the electric motor 8, a voltage limiting part 24 which limits a voltage command value generated at a motor control part 23 to a limit value of either a set value for setting the upper limit of the voltage command value or a fixed value when a motor drive current detected by a current detection part 19 exceeds a predetermined value, and a limit value setting part 25 for setting the limit value of the voltage limiting part 24 based on the rotational speed information detected by the rotational speed information detection part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that generates a steering assist force according to a steering torque input to a steering system.

This type of electric power steering apparatus is, for example, a control apparatus for an electric power steering apparatus that controls a motor that applies a steering assist force to a steering mechanism based on a current command value calculated based on a steering torque generated in a steering shaft. Yes, two overcurrent detection circuits with different detection current values are provided, and when overcurrent is detected at the lower detection current value, the duty of PWM for driving the motor is limited within the response time of current control Then, when an overcurrent is detected at a higher detected current value, a control device for an electric power steering device is proposed in which the motor current output is stopped and the relay is opened (for example, Patent Documents). 1).
Japanese Patent Laid-Open No. 11-240459 (first page, FIG. 1)

  However, in the conventional example described in Patent Document 1 described above, an overcurrent is detected when the steering mechanism reaches the rack end or the tire comes into contact with a curb or the like and cannot be steered further. In this case, the PWM duty ratio is limited to prevent the occurrence of motor overcurrent. However, since the motor back electromotive voltage is not taken into consideration, the effect can be sufficiently improved for the reasons described below. It ’s gone.

  That is, in recent years, the demand for higher output has accelerated due to the adoption of electric power steering devices for large vehicles such as sports utility vehicles (SUVs). For example, motors used in electric power steering devices The counter electromotive voltage tends to be larger. Also, because of the large size of the vehicle, the reaction force from the tire when steering the steering wheel increases due to factors such as the tire becoming larger, so it reaches the rack end or the tire touches the curb etc. As a result, when the steering limit state is reached where further steering is not possible, the force that the steering wheel returns is increased, and the motor counter-electromotive voltage generated by the motor rotating speed is increased. Furthermore, the resistance value of motors and electronic control units (ECUs) has been reduced due to the demand for higher output.

  For this reason, in the conventional example of Patent Document 1 described above, when the steering mechanism reaches the rack end and detects an overcurrent, the PWM duty is limited to suppress the occurrence of the motor overcurrent. Due to the above background, when the steering limit is reached and the steering wheel is returned, the motor back electromotive force voltage becomes larger and the resistance value becomes smaller. An overcurrent (due to the power generation state) due to the motor back electromotive voltage that exceeds the determination threshold may occur, and the motor current output may be stopped despite no failure.

  Therefore, the present invention has been made paying attention to the unsolved problems of the conventional example described above, and reliably prevents motor overcurrent generated by the motor back electromotive voltage when the steering mechanism reaches the steering limit state. It is an object of the present invention to provide an electric power steering device that can be used.

  In order to achieve the above object, an electric power steering apparatus according to claim 1 includes an electric motor that generates a steering assist force for a steering system, and a steering torque detector that detects a steering torque transmitted to the steering system. And a current detection unit that detects a drive current of the electric motor, and a motor current command value is generated based on the steering torque detected by the steering torque detection unit, and is detected by the generated motor current command value and the current detection unit. An electric power steering device including a motor control unit that generates a voltage command value for driving the electric motor based on the motor driving current and controls the driving of the electric motor, the rotational speed information of the electric motor A rotation speed information detection unit for detecting the voltage and a voltage command generated by the motor control unit when the motor drive current detected by the current detection unit exceeds a predetermined value. A voltage limiter that limits the limit value to either a set value or a fixed value that sets the upper limit of the voltage command value, and rotation speed information in which the limit value of the voltage limiter is detected by the rotation speed information detector And a limit value setting unit that is set based on the above.

  An electric power steering apparatus according to a second aspect of the present invention includes an electric motor that generates a steering assist force for a steering system, a steering torque detector that detects a steering torque transmitted to the steering system, and an electric motor A current detection unit that detects a drive current, a motor current command value is generated based on the steering torque detected by the steering torque detection unit, and the generated motor current command value and the motor drive current detected by the current detection unit An electric power steering device including a motor control unit that generates a voltage command value for driving the electric motor based on the motor control unit and controls the driving of the electric motor, wherein the motor driving current detected by the current detection unit is a predetermined value. When the value exceeds the voltage command value, the voltage command value generated by the motor control unit is limited to a limit value made up of either a set value or a fixed value that sets the upper limit of the voltage command value. Comprising a pressure limit portion, it is characterized in that by estimating the counter electromotive voltage of the electric motor was set to be added to the voltage command value limited by the voltage limiting unit.

Furthermore, an electric power steering apparatus according to a third aspect of the present invention includes an electric motor that generates a steering assist force for a steering system, a steering torque detection unit that detects a steering torque transmitted to the steering system, and A current detection unit that detects a drive current, a motor current command value is generated based on the steering torque detected by the steering torque detection unit, and the generated motor current command value and the motor drive current detected by the current detection unit An electric power steering apparatus comprising: a motor control unit that generates a voltage command value for driving the electric motor based on the driving control of the electric motor;
A rotation speed information detection unit that detects rotation speed information of the electric motor, and a voltage command value that is generated by the motor control unit when the motor drive current detected by the current detection unit exceeds a predetermined value. A voltage limiter that limits the limit value to either a set value or a fixed value that sets the upper limit of the value, and sets the limit value of the voltage limiter based on the rotational speed information detected by the rotational speed information detector And a limit value setting unit for estimating the back electromotive force of the electric motor and adding the estimated value to the voltage command value limited by the voltage limiting unit.

Furthermore, the electric power steering device according to claim 4 is the invention according to claim 1 or 3, wherein the angular velocity of the electric motor is calculated from the rotation angle information or is estimated from the terminal voltage and current of the motor. It is characterized by being composed.
Still further, according to a fifth aspect of the present invention, the electric power steering apparatus according to any one of the first, third, and fourth aspects further includes a steering direction detection unit that detects a steering direction of the steering system, and the limit value setting unit. Is characterized in that the limit value is varied in accordance with the steering direction detected by the steering direction detector.

  According to a sixth aspect of the present invention, in the electric power steering apparatus according to the fifth aspect of the invention, the limit value setting unit is configured such that the limit value setting unit is set when the steering direction detected by the steering direction detection unit is the additional direction. The limit value is set to a small value, and the limit value of the limit value setting unit is set to a large value as the rotational speed increases when it is determined to be the switchback direction.

Further, according to a seventh aspect of the present invention, in the electric power steering device according to any one of the first, third, and sixth aspects, the limit value setting unit continuously changes the limit value according to the rotation speed information. It is characterized by being configured.
Furthermore, the electric power steering device according to claim 8 is the invention according to any one of claims 1, 3 to 6, wherein the limit value setting unit sets the limit value stepwise according to the rotation speed information. It is characterized by being configured to change.

  According to the present invention, the rotational speed information of the electric motor is detected, and the limit value for limiting the voltage command value for the electric motor is set based on the rotational speed information. Therefore, when the steering mechanism enters the steering limit state. The counter electromotive voltage generated by the reverse drive of the electric motor due to the reaction force of the tire, that is, kickback can be suppressed by limiting the voltage command value, and the occurrence of motor overcurrent can be reliably prevented, The effect that the steering assist control stoppage due to the overcurrent detection can be surely prevented is obtained.

  Further, by adding the estimated back electromotive force of the electric motor to the voltage command value limited by the limit value, when the steering mechanism is in a steering limit state, the electric motor reversely drives by the reaction force of the tire, that is, kickback. This counteracts the back electromotive voltage generated by, so that the occurrence of motor overcurrent can be reliably prevented, and stop of steering assist control due to overcurrent detection can be reliably prevented.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a steering mechanism. The steering mechanism 1 includes a steering shaft 3 on which a steering wheel 2 is mounted, and the steering shaft 3. A rack and pinion mechanism 4 connected to the opposite side of the steering wheel 2 and left and right steered wheels 6 connected to the rack and pinion mechanism 4 via a connecting mechanism 5 such as a tie rod.

An electric motor 8 is connected to the steering shaft 3 via a speed reducer 7. The electric motor 8 is constituted by, for example, a brushless motor driven by three-phase alternating current, and operates as a steering assist force generating motor that generates a steering assist force of the electric power steering apparatus.
The electric motor 8 is driven and controlled by a control device 13 to which a battery voltage Vb output from a battery 11 mounted on the vehicle is supplied via a fuse 12.

A steering torque T input to the steering wheel 2 detected by a steering torque sensor 16 disposed on the steering shaft 3 is input to the control device 13, and a resolver 17 disposed on the electric motor 8. The motor rotation angle θ _M detected in step S3 is input, and the vehicle speed detection value Vs detected by the vehicle speed sensor 18 is input, and the phase currents Ima, Imb, and Imc of the electric motor 8 detected by the motor current detection unit 19 are input. Is entered.

Here, the steering torque sensor 16 detects the steering torque applied to the steering wheel 2 and transmitted to the steering shaft 3. For example, the torsion bar in which the steering torque is interposed between an input shaft and an output shaft (not shown). The torsional angular displacement is converted into an electrical signal, and the torsional angular displacement is detected with a magnetic signal and converted into an electrical signal. As shown in FIG. 2, the steering torque sensor 16 has a predetermined neutral steering torque detection value T ₀ when the input steering torque is zero. The steering torque detection value T is a value that increases from the neutral steering torque detection value T ₀ , and when the steering torque is turned to the left from the zero state, the steering torque detection value T that decreases from the neutral steering torque T ₀ according to the increase of the steering torque is output. ing.

As shown in FIG. 3, the control device 13 is detected by a rotation speed information calculation unit 20 that calculates rotation speed information based on a detection signal of the resolver 17, a steering torque T detected by the steering torque sensor 16, and a vehicle speed sensor 18. The current vehicle speed Vs is input, and based on these, the current command value calculation unit 21 for calculating the three-phase current command values I _Aref , I _Bref and I _Cref for the electric motor 8, and the current command value calculation unit 21 are used. _A subtractor 22 for subtracting the phase currents Ima, Imb and Imc detected by the motor current detector 19 from the current command values I _Aref , I _Bref and I _Cref to calculate current deviations ΔI _A , ΔI _B and ΔI _C ; The current control unit 23 performs current control on the current deviations ΔI _A , ΔI _B and ΔI _C output from the subtracting unit 22 to calculate the voltage command values V _Aref , V _Bref and V _Cref , and the current control unit 23. Or The outputted voltage command value V _Aref, a voltage limiting unit 24 for limiting the V _Bref and V _Cref, the limit value setting unit 25 for setting on the basis of the limit value at the voltage limiting unit 24 to the motor angular velocity .omega.m, voltage limits The motor drive circuit 26 that drives and controls the electric motor 8 by _receiving the limit voltage command values V _LAref , V _LBref, and V _LCref limited by the unit 24, and the motor drive currents Ima to Imc detected by the motor current detection unit 19 Overcurrent detection unit 27 for duty limitation having an overcurrent determination threshold value that any one of which is larger than the rated level, and overcurrent for failure detection having an overcurrent determination threshold value that is larger than the overcurrent determination threshold value of this overcurrent detection unit 27 And a detector 28.

  As shown in FIG. 4, the rotation speed information calculation unit 20 receives the output signal of the resolver 17 and detects a motor rotation angle θm, and a motor detected by the motor rotation angle detection unit 20a. An electrical angle calculation unit 20b that calculates an electrical angle θe based on the rotation angle θm, and a motor angular speed calculation unit 20c that calculates a motor angular velocity ωm by differentiating the motor rotation angle θm detected by the motor rotation angle detection unit 20a. ing.

As shown in FIG. 4, the current command value calculation unit 21 receives the electrical angle θe and the motor angular velocity ωm calculated by the rotation speed information calculation unit 20 and detects the steering torque T and the vehicle speed input from the steering torque sensor 16. The steering assist current command value calculation unit for calculating the steering assist current command value I _M ^* with reference to the steering assist current command value calculation map for calculating the steering assist current command value I _M ^* shown in FIG. 5 based on the value Vs. 31, a three-phase current command value based on the steering assist current command value I _M ^* calculated by the steering assist current command value calculation unit 31, the electrical angle θe and the motor angular velocity ωm input from the rotation speed information calculation unit 20. And a current command value calculation unit 32 for generating.

Here, the steering assist current command value calculation unit 31 refers to the steering assist current command value calculation map shown in FIG. 5 based on the steering torque T and the vehicle speed Vs, and the steering assist current command value I _{M that is a} current command value. ^* Is calculated.
As shown in FIG. 5, the steering assist current command value calculation map has a parabolic shape with the steering torque T on the horizontal axis, the steering assist current command value I _M ^* on the vertical axis, and the vehicle speed Vs as a parameter. It is composed of a characteristic diagram represented by a curve, and the steering assist current command value I _M ^* is maintained at “0” while the steering torque T is between “0” and a set value Ts1 in the vicinity thereof, and the steering torque T is When the set value Ts1 is exceeded, initially, the steering assist command value I _M ^* increases relatively gently with respect to the increase in the steering torque T, but when the steering torque T further increases, the steering assist current command value with respect to the increase. I _M ^* is set so as to increase steeply, and this characteristic curve is set so that the inclination becomes smaller as the vehicle speed increases.

The current command value calculation unit 32 includes a d-axis target current calculation unit 41 that calculates a d-axis target current Id ^* based on the steering assist current command value I _M ^* , the motor angular velocity ωm, and the electrical angle θe, and an electrical angle. An induced voltage model calculation unit 42 that calculates a d-axis EMF component ed (θe) and a q-axis EMF component eq (θe) of a dq-axis induced voltage model EMF (Electromotive Force) based on θe, and the induced voltage model calculation D-axis EMF component ed (θe) and q-axis EMF component eq (θe) output from the unit 42, d-axis target current Id ^* output from the d-axis target current calculation unit 31, and steering assist current command value I _M ^* The q-axis target current Iq ^* is calculated based on the q-axis target current calculation unit 43, the d-axis target current Id ^* output from the d-axis target current calculation unit 41, and the q-axis target current calculation unit 43. that the q-axis target current Iq ^* Phase current command value I _Aref, and a 2-phase / 3-phase conversion unit 44 for converting the I _Bref and I _Cref.
Further, the current control unit 23 performs current feedback control processing such as PI control processing on each of the current deviations ΔI _A , ΔI _B, and ΔI _C input from the subtraction unit 22 to perform voltage command values V _Aref , V _Bref, and V _Cref. Is calculated.

Furthermore, the voltage limiting unit 24, an overcurrent state when any one of the motor current Ima~Imc detected by the motor current detector 19 although overcurrent determination threshold I _MAX is smaller than the overcurrent judgment threshold value I _MAX 'or When an overcurrent state is detected by the overcurrent detection unit 27 that detects the presence and outputs an overcurrent detection signal CD, a pulse width modulation (output from the FET gate drive circuit 52 of the motor drive circuit 26 described later) PWM) signal is set to a voltage limit value that is suppressed to a motor driving current that does not damage the field effect transistor or the relay, that is, a voltage limit value V _LS set by a limit value setting unit 25 described later, current control unit 23 a voltage command value output from the V _Aref, the V _Bref and V _Cref limited by the voltage limit value V _LU during normal not in an overcurrent condition (100%), the overcurrent state der Sometimes it performs voltage limiting process for limiting voltage limit value V _LS.

The limit value setting unit 25 receives the motor angular speed ωm calculated by the motor angular speed calculation unit 20c of the rotation speed information calculation unit 20 described above, and sets the voltage limit value V _LS according to the motor angular speed ωm. As shown in FIG. 6, the limit value V _LS is set to a relatively small value V _LL when the absolute value | ωm | of the motor angular velocity ωm is equal to or less than a predetermined value ωs, and the absolute value | ωm | The absolute value | ωm | of the motor angular velocity ωm is further increased so as to become the voltage limit value V _LU (100%) when the absolute value | ωm | Set to

Further, in the case of the configuration having the steering direction detection unit, the voltage limit value V _LS is set to a relatively small value V _LL when it is determined that the direction is increased, and the motor angular velocity ωm is determined when it is determined that the direction is the return direction. Based on the absolute value of | ωm |, the limit value is set to change as shown in FIG.
As shown in FIG. 7, the motor drive circuit 26 includes a series circuit in which two field effect transistors Qua and Qub are connected in series, and two field effect transistors Qva connected in parallel with the series circuit. And an inverter circuit 51 including a series circuit of Qvb and a series circuit of field effect transistors Qwa and Qwb. In the inverter circuit 51, the connection points of the field effect transistors Qua and Qub, the connection points of the field effect transistors Qva and Qvb, and the connection points of the field effect transistors Qwa and Qwb are connected to the respective excitation coils La, Lb and Motor drive currents Ima to Imc connected to Lc and output from the inverter circuit 51 to the electric motor 8 are detected by the motor current detection circuit 19.

Further, the motor drive circuit 26 includes an FET gate drive circuit 52 that controls the field effect transistors Qua to Qwb of the inverter circuit 51. The FET gate drive circuit 52 uses the duty ratio Da determined by the field effect transistors Qua to Qwb of the inverter circuit 51 based on the voltage command values V _LAref , V _LBref and V _LCref output from the voltage limiting unit 24 described above. The currents Ima, Imb, and Imc that actually flow through the electric motor 8 are controlled by being turned on / off by PWM (pulse width modulation) signals of Db and Dc. Here, the field effect transistors Qua, Qva, and Qwa that constitute the upper arm and the field effect transistors Qub, Qvb, and Qwb that constitute the lower arm according to the sizes of the duty ratios Da, Db, and Dc, respectively, avoid an arm short circuit. PWM drive with a dead time is required.

Furthermore, the motor drive circuit 26 turns off the pulse width modulation signal output from the FET gate drive circuit 52 when the overcurrent detection signal CF is input from the overcurrent detection unit 28 for failure detection. The relay 72 is turned off.
Next, the operation of the above embodiment will be described.
Now, by turning on the ignition switch 71 shown in FIG. 7, the power from the battery 11 is turned on to the control device 13, the steering assist control processing in the control device 13 is started, and the relay 72 is energized. Thus, the battery voltage Vb is supplied to the motor drive circuit 26 and the electric motor 8 can be driven.

At this time, the current command value calculating section 21, reads the steering torque detection value T detected by the steering torque sensor 16, then the actual steering torque T by subtracting the neutral torque T ₀ from I read steering torque detection value T Is calculated with reference to the steering assist current command value calculation map shown in FIG. 5 based on the steering torque T and the vehicle speed Vs input from the vehicle speed sensor 18.
Further, the motor rotation angle θm detected by the motor rotation angle detection circuit 20a is supplied to the motor angular velocity calculation unit 20c, and the motor angular velocity calculation unit 20c performs differentiation processing to calculate the motor angular velocity ωm, and the calculated electrical angle θe and the motor angular velocity ωm are supplied to the current command value calculation unit 32 of the current command value calculation unit 21, and the dq axis command value is based on the steering auxiliary current command value I _M ^* , the electrical angle θe, and the motor angular velocity ωm. An arithmetic process is executed to calculate a target d-axis current Id ^* and a target q-axis current Iq ^* , and the target d-axis current Id ^* and the target q-axis current Iq ^* are subjected to a two-phase / three-phase conversion process to obtain a three-phase Phase current command values I _Aref , I _Bref and I _Cref are calculated.

Then, the calculated phase current command values I _Aref , I _Bref and I _Cref and the motor phase currents Ima, Imb and Imc detected by the motor current detection unit 19 are subtracted by the subtraction unit 22 to obtain current deviations ΔI _A , ΔI _B and ΔI _C is calculated, and these current deviations ΔI _A , ΔI _B and ΔI _WC are supplied to the current control unit 23 to perform PI control processing, and voltage command values V _Aref , V _Bref and V _Cref for each phase are calculated.
The calculated phase voltage command values V _Aref , V _Bref and V _Cref are output to the FET gate drive circuit 52 of the motor drive circuit 26. Therefore, the FET gate drive circuit 52 supplies the three-phase drive current from the motor drive circuit 26 to the electric motor 8 by controlling the pulse width modulation of the field effect transistors Qua to Qwb of the motor drive circuit 26. A steering assist force in a direction corresponding to the steering torque applied to the steering wheel 2 is generated by the motor 8, and this steering assist force is transmitted to the steering shaft 3 via the speed reducer 7.

At this time, in a so-called stationary state in which the steering wheel 2 is steered while the vehicle is stopped, the vehicle speed Vs is zero, and the gradient of the characteristic line of the steering assist current command value calculation map shown in FIG. 5 is large. Thus, a large steering assist command value I _M ^* is calculated with a small steering torque T, so that a large steering assist force can be generated by the electric motor 8 and light steering can be performed.
When the vehicle is started from the stopped state to the traveling state, the gradient of the characteristic line of the steering assist current command value calculation map shown in FIG. 5 is set to become lower as the vehicle speed increases. Further, the steering assist command value I _M ^* is also a small value, and the steering assist torque generated by the electric motor 8 is smaller than the steering assist torque at the time of stationary.

In any steering state, any one of the motor drive currents Ima to Imc becomes equal to or higher than the overcurrent determination threshold I _MAX ′ in the overcurrent detection unit 27, and the overcurrent state is detected, and the overcurrent detection signal CD is generated. When output to the voltage limiter 24, the voltage limiter 24 sets the voltage limit value V _LS . For this reason, the voltage limiting unit 24 limits the voltage command values V _Aref , V _Bref and V _Cref output from the current control unit 23 to the voltage limiting value V _LS , whereby the FET gate driving circuit 52 of the motor driving circuit 26. Then, a pulse width modulation signal having a motor driving current Ima to Imc that does not damage the field effect transistor or the relay is supplied to the inverter 51 to protect the motor driving circuit 26.

Further, when any one of the motor drive current Ima~Imc overcurrent detection unit 28 is an overcurrent condition becomes overcurrent determination threshold I _MAX or more is detected, in a fault condition abnormality in the motor drive circuit 26 has occurred It is determined that the pulse width modulation signal output from the FET gate drive circuit 52 of the motor drive circuit 26 is all turned off, and the relay 72 is turned off to protect the motor drive circuit 26.

However, as shown in FIG. 8, when the steering wheel 2 is steered relatively slowly in the direction in which the steering wheel 2 is increased, that is, in the direction away from the steering neutral position, the state is changed to a state where the steering wheel 2 is steered at a relatively high speed at time t1. Therefore, the steering assist current command value I _M ^* calculated by the current command value calculation unit 21 increases as shown in FIG. 8A.
At this time, as shown in FIG. 8B, the motor angular velocity ωm is still less than the predetermined value ωs, so the limit value V _LS set by the limit value setting unit 25 is as shown in FIG. 8C. A small value V _LL is set.

On the other hand, the amplitude values of the motor drive currents Ima to Imc output from the motor drive circuit 26 in accordance with the steering assist current command value I _M ^* are far greater than the overcurrent detection threshold I _MAX ′, as shown in FIG. since a small value, not that the detection signal CD from the duty limiting overcurrent detection unit 27 is output, the maximum value V _LU limit V _LS representing a 100% in the voltage limiting section 24 is selected Yes.

Therefore, the voltage command values V _{Aref to} V _Cref generated by the current control unit 23 are not limited by the limit value V _LS and are output to the motor drive circuit 26. Therefore, the amplitude values of the motor currents Ima to Imc output from the motor drive circuit 26 gradually increase as the steering torque T increases as shown in FIG.
Thereafter, when the motor angular velocity ωm exceeds the predetermined value ωs at time t2, as shown in FIG. 8B, the voltage limit value V _LS set by the limit value setting unit 25 in response thereto is shown in FIG. Since the steering assist current command value I _M ^* calculated by the current command value calculation unit 21 is gradually increased as shown in (c), the voltage command value V output from the current control unit 23 is also increased. _{Aref to} V _Cref also increase, and accordingly, the amplitude values of the motor drive currents Ima to Imc output from the motor drive circuit 26 increase as shown in FIG.

Thereafter, when the motor angular velocity ωm tends to decrease at time t3, the voltage limit value V _LS set by the limit value setting unit 25 correspondingly decreases as the motor angular velocity ωm decreases. Thereafter, at time t4, maintaining the ^* steering assist current command value I _M calculated by the current command value calculating section 21 reaches the maximum value, the subsequent steering assist current command value I _M ^* is the maximum value, according to this As shown in FIG. 8D, the amplitudes of the motor drive currents Ima to Imc output from the motor drive circuit 26 are maintained at a relatively large constant value, although smaller than the overcurrent detection threshold value I _MAX ′.

  Thereafter, at time t5, when the steering mechanism 1 reaches the rack stroke end or the tire comes into contact with a curb stone or the like and reaches a steering limit state where further steering is not possible, the motor angular velocity ωm becomes as shown in FIG. As shown in the figure, it decreases relatively rapidly to “0”, and then the steered wheels 6 are moved in the back-turning direction by the reaction force of the tires, that is, the kickback force, and this reverse direction driving force is electrically driven via the speed reducer 7. Since the electric motor 8 is transmitted to the motor 8, the electric motor 8 is also reversely driven at a relatively large motor angular velocity −ωm in the direction opposite to the rotation direction so far.

As described above, when the electric motor 8 is in the reverse drive state, the electric motor 8 is in the power generation state, and the electric motor 8 is driven at high speed reverse rotation, whereby the generated current is superimposed on the motor drive currents Ima to Imc. When the amplitude values of the motor drive currents Ima to Imc increase as shown in FIG. 8D, and the amplitude values of the motor drive currents Ima to Imc reach the overcurrent threshold I _MAX ′ at time t7, the duty cycle A detection signal CD is output from the limiting overcurrent detection unit 27 to the voltage limiting unit 24.

For this reason, the voltage limiter 24 selects the voltage limit value _VLS set by the limit value setting unit 25 instead of the maximum value _VLU so far. At this time, when the motor angular velocity ωm falls below −ωs as shown in FIG. 8B, the voltage limit value V _LS set by the limit value setting unit 25 becomes the minimum value V as shown in FIG. 8C. They started to increase _LL, results in the limited voltage command value V _LAref ~V _LCref output from the voltage limiting unit 24 to the motor drive circuit 26 increases accordingly, the voltage command value V _LAref ~V _LCref As a result, the counter electromotive voltage generated in the power generation state of the electric motor 8 due to the kickback phenomenon of the tire can be offset.

As a result, it is possible to reliably prevent the current generated by the counter electromotive voltage generated by the power generation from being superimposed on the motor drive currents Ima to Imc, and the motor drive currents Ima to Imc are overcurrent as shown in FIG. It is maintained in the vicinity of the detection threshold value I _MAX ′, and it is reliably prevented that the overcurrent detection value threshold value I _MAX is reached.
Thereafter, at time t9, the steering assist current command value I _M ^* generated by the current command value calculation unit 21 decreases, so that the voltage command values V _{Aref to} V _Cref output from the current control unit 23 also decrease. The voltage command values V _{LAref to} V _LCref output from the voltage limiter 24 are also reduced, and the motor drive currents Ima to Imc output from the motor drive circuit 26 are also reduced from the overcurrent detection threshold I _MAX ′. It will be.

In this state, since the detection signal CD is not output from the duty limiting overcurrent detection unit 27, the voltage limiting unit 24 returns the voltage limit value from V _LS to the maximum value V _LU and returns to the normal state. To do.
When the tire kickback phenomenon is settled, the motor angular velocity ωm returns to substantially “0” due to the absence of the rotational force of the electric motor 8 in the switchback direction.

When the steering wheel 2 is further steered in the steering limit state in this steering limit state, the steering mechanism 1 has reached the rack stroke end or the tire is in contact with a curb or the like. Since it cannot be performed, when the amplitude value of the motor drive currents Ima to Imc increases and reaches the overcurrent detection threshold value I _MAX ′, the voltage limit value V _LS set by the limit value setting unit 25 by the voltage limit unit 24 is reached. Select. At this time, in the limit value setting unit 25, the motor angular velocity ωm is substantially “0”, and the absolute value | ωm | is less than the predetermined value ωs, so the voltage limit value V _LS is set to the minimum value V _LL. Therefore, the voltage command values V _{Aref to} V _Cref are limited to a small value, and the motor drive currents Ima to Imc output from the motor drive circuit 26 are reduced, so that the motor drive circuit 26 is also damaged by the overcurrent. It can be surely prevented.

In the first embodiment, the case where the limit value V _LS is changed when the absolute value | ωm | of the motor angular velocity ωm is equal to or greater than the predetermined value ωs has been described. However, the present invention is not limited to this. The limit value V _LS may be changed when the steering direction is reversed from the increasing direction to the returning direction. In order to determine whether the steering direction is the direction of increase or return, as shown in FIG. 9, the steering is determined from the sign of the motor angular velocity ωm and the sign of the steering torque T or the current command value I _M ^*. It is possible to determine whether the wheel 2 is in the direction of increasing in the direction away from the steering neutral position or in the direction of returning to return to the steering neutral position, and this determination signal of the steering direction is output to the limit value setting unit 25. Thus, the limit value setting unit 25 fixes the voltage limit value V _LS to the minimum value V _LL when the steering wheel 2 is in the turning-up direction, and sets the voltage limit value V _LS above when the steering wheel 2 is in the turning-back direction. As in the first embodiment, it may be varied based on the motor angular velocity ωm. In this case, there is no increasing unnecessarily the voltage limit value V _LS when steering in the turning-increasing direction of the steering wheel 2, based on the voltage limit value V _LS only upon reaching the steering limit the motor angular velocity ωm Can be varied.

Further, in the first embodiment, the limit value setting unit 25 refers to the voltage limit value calculation map shown in FIG. 6 and determines the voltage limit value V _LS that continuously changes as the motor angular velocity ωm increases. Although the case of calculating has been described, the present invention is not limited to this, and the voltage limit value V _LS may be increased stepwise as the motor angular velocity ωm increases.
Furthermore, although the case where the voltage limit value V _LS is set based on the absolute value | ωm | of the motor angular velocity ωm has been described in the first embodiment, the present invention is not limited to this. ), For example, when the battery voltage Vb of the battery 11 becomes high, the upper limit value V _LU may be changed to an upper limit value V _LU ′ higher than the upper limit value V _LU as shown in the broken line. Furthermore, since the motor back electromotive force voltage decreases at the same motor angular velocity ωm due to the temperature rise of the electric motor 8, the temperature of the electric motor 8 is detected, and the broken line is shown in FIG. 10B based on the detected temperature. As shown in FIG. 5, when the absolute value | ωm | of the motor angular velocity ωm reaches a predetermined value ωs2 ″ larger than the predetermined value ωs2, the voltage limit value V _LS reaches the maximum value V _LU by making the inclination of the characteristic line gentle. Also good.

Next, a second embodiment of the present invention will be described with reference to FIG.
In the second embodiment, the limit value in the voltage limiter 24 is changed to a fixed value that does not depend on the motor angular velocity ωm, thereby preventing the occurrence of overcurrent when the steering mechanism 1 enters the steering limit state. It is what I did.
That is, in the second embodiment, the control device 13 in the first embodiment described above is in the normal state (the state where no overcurrent has occurred) in which the limit value setting unit 25 is omitted in the configuration of FIG. The limit value of the voltage limiting unit 24 is fixed to a relatively low limit value V _LL , and a counter electromotive voltage estimating unit 60 for estimating the counter electromotive voltage of the electric motor 8 is provided instead. The estimated back electromotive force values VAemf, VBemf, and VCemf estimated at 60 are added to the limit voltage command values V _LAref , V _LBref, and V _LCref output from the voltage limiter 24 by the adder 29. Except for the above, the configuration is the same as in FIG. 3, and the same reference numerals are given to the corresponding parts to FIG. 3, and the detailed description thereof is omitted.

Here, the back electromotive force estimation unit 60 uses the following formulas (1) to (3) based on the motor angular velocity ωm and the rotation angle θe output from the motor angular velocity calculation unit 20c of the rotation speed information calculation unit 20 described above. An arithmetic operation is performed to estimate the back electromotive force estimated values VAemf, VBemf, and VCemf of each phase.
VAemf = F (θe) · ωm (1)
VBemf = F (θe + 2π / 3) · ωm (2)
VCemf = F (θe + 4π / 3) · ωm (3)
Here, F (θe) is a counter electromotive voltage at a unit angular velocity.

When the steering mechanism 1 reaches the rack stroke end or the tire comes into contact with a curb stone or the like to enter a steering limit state, and the motor 8 is caused by a power generation state that occurs when the steering shaft is reversely rotated at a high speed by the reaction force of the tire, that is, the kickback force. Since the back electromotive voltages VAemf, VBemf, and VCemf of each phase are large values, the back electromotive force estimation unit 60 estimates the limited voltage commands V _LAref , V _LBref, and V _LCref limited by a relatively small value by the adding unit 29. By adding the estimated back electromotive voltage values VAemf, VBemf, and VCemf of each phase, the final voltage command value output from the adding unit 29 is obtained from the back electromotive voltages VAmemf, VBmemf, and VCmemf of each phase of the motor 8. The voltage command value cancels out.

For this reason, even if a large back electromotive voltage is generated in the electric motor 8 due to the kickback phenomenon after the steering limit state is reached, the total motor drive current can be suppressed below the overcurrent determination threshold I _MAX , Therefore, the detection by the overcurrent detection unit 28 can be reliably prevented.
In the second embodiment, the case where the motor back electromotive force estimation unit 60 estimates the back electromotive force estimated values VAemf, VBemf, and VCemf of each phase based on the motor angular velocity ωm and the rotation angle Θe has been described. However, the present invention is not limited to this. As shown in FIG. 12, a terminal voltage detection unit 61 for detecting each phase terminal voltage of the electric motor 8 is provided, and the terminal voltage and motor current detected by the terminal voltage detection unit 61 are provided. Based on the detected current value detected by the detector 19, the back electromotive force estimation unit 60 can also estimate each phase back electromotive voltage.

That is, when a Y-connection motor is applied as the electric motor 8, the midpoint voltage of the electric motor is detected, and the midpoint voltage is subtracted from the motor terminal voltages Va to Vc to obtain the phase voltage Vih (i = a to c) may be calculated, and the back electromotive force ei of each phase may be calculated by performing the following equation (4) based on the phase voltage Vih.
ei = Vih− (Ri + s · Li) · Ii (4)
The motor midpoint voltage is obtained by calculating the sum of the motor terminal voltages of the electric motor 8 as shown in the following equation (5), and dividing the value by the number of phases of the motor to obtain the motor midpoint voltage Vn. You may make it calculate.

Vn = (Va + Vb + Vc +... + Vx) / number of motor phases (5)
Further, as shown in FIG. 13, the adding unit 29 of the second embodiment is inserted between the voltage limiting unit 24 and the motor driving circuit 26 in the first embodiment described above, and the motor reverse is inserted in the adding unit 29. The electromotive force estimation unit 60 may be connected. In this case, both effects in the first embodiment and the second embodiment can be exhibited.

It is a schematic structure figure showing one embodiment of the present invention. FIG. 6 is a characteristic diagram of a steering torque detection signal output from a steering torque sensor. It is a block diagram which shows the specific structure of the control apparatus of FIG. It is a block which shows the specific structure of the electric current command value calculating part of FIG. It is explanatory drawing which shows the steering assist command value calculation map showing the relationship between the steering torque and steering assist command value which are used in a steering assist current command value calculating part. It is explanatory drawing which shows the voltage limit value calculation map showing the relationship between the absolute value of the motor angular velocity used by a limit value setting part, and a voltage limit value. It is a block diagram which shows a motor drive circuit. It is a wave form diagram with which it uses for description of the operation | movement in 1st Embodiment. It is a steering direction judgment table showing an additional direction and a return direction. It is explanatory drawing which shows the modification of the voltage limiting value calculation map showing the relationship between the absolute value of the motor angular velocity used by a limiting value setting part, and a voltage limiting value. It is a block diagram which shows the 2nd Embodiment of this invention. It is a block diagram which shows the modification of the 2nd Embodiment of this invention. It is a block diagram which shows other embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering mechanism, 2 ... Steering wheel, 3 ... Steering shaft, 7 ... Reduction gear, 8 ... Electric motor, 11 Car-mounted battery, 13 ... Control device, 16 ... Steering torque sensor, 17 ... Resolver, 18 vehicle speed sensor, 19 ... Current detection unit, 20 ... rotational speed information calculation unit, 20a ... motor rotation angle detection unit, 20b ... electrical angle calculation unit, 20c ... motor angular speed calculation unit, calculation 21 ... current command value calculation unit, 22 ... subtraction unit, 23 ... Current control unit, 24 ... voltage limiting unit, 25 ... limit value setting unit, 26 ... motor drive circuit, 60 ... motor back electromotive voltage estimation unit, 61 ... terminal voltage detection unit

Claims (8)

An electric motor that generates a steering assist force for the steering system; a steering torque detector that detects a steering torque transmitted to the steering system; a current detector that detects a drive current of the electric motor; and the steering torque A motor current command value is generated based on the steering torque detected by the detection unit, and a voltage command value for driving the electric motor is generated based on the generated motor current command value and the motor drive current detected by the current detection unit. And an electric power steering device comprising a motor control unit for driving and controlling the electric motor,
A rotation speed information detection unit that detects rotation speed information of the electric motor, and a voltage command value that is generated by the motor control unit when the motor drive current detected by the current detection unit exceeds a predetermined value. A voltage limiter that limits the limit value to either a set value or a fixed value that sets the upper limit of the value, and sets the limit value of the voltage limiter based on the rotational speed information detected by the rotational speed information detector An electric power steering apparatus comprising: a limit value setting unit that performs An electric motor that generates a steering assist force for the steering system; a steering torque detector that detects a steering torque transmitted to the steering system; a current detector that detects a drive current of the electric motor; and the steering torque A motor current command value is generated based on the steering torque detected by the detection unit, and a voltage command value for driving the electric motor is generated based on the generated motor current command value and the motor drive current detected by the current detection unit. And an electric power steering device comprising a motor control unit for driving and controlling the electric motor,
When the motor drive current detected by the current detection unit exceeds a predetermined value, the voltage command value generated by the motor control unit is limited to either a set value or a fixed value that sets the upper limit of the voltage command value An electric power steering apparatus comprising: a voltage limiting unit that limits a value; and estimating a back electromotive voltage of the electric motor and adding the estimated voltage to a voltage command value limited by the voltage limiting unit. An electric motor that generates a steering assist force for the steering system; a steering torque detector that detects a steering torque transmitted to the steering system; a current detector that detects a drive current of the electric motor; and the steering torque A motor current command value is generated based on the steering torque detected by the detection unit, and a voltage command value for driving the electric motor is generated based on the generated motor current command value and the motor drive current detected by the current detection unit. And an electric power steering device comprising a motor control unit for driving and controlling the electric motor,
A rotation speed information detection unit that detects rotation speed information of the electric motor, and a voltage command value that is generated by the motor control unit when the motor drive current detected by the current detection unit exceeds a predetermined value. A voltage limiter that limits the limit value to either a set value or a fixed value that sets the upper limit of the value, and sets the limit value of the voltage limiter based on the rotational speed information detected by the rotational speed information detector An electric power steering apparatus comprising: a limit value setting unit configured to estimate a back electromotive voltage of the electric motor and add the estimated value to a voltage command value limited by the voltage limiting unit.   The said rotation speed information detection part is comprised so that the angular velocity of the said electric motor may be calculated from rotation angle information, or it may be estimated from the terminal voltage and electric current of the said motor. Electric power steering device.   A steering direction detection unit that detects a steering direction of the steering system is provided, and the limit value setting unit is configured to vary the limit value according to the steering direction detected by the steering direction detection unit. The electric power steering apparatus according to any one of claims 1, 3, and 4.   The limit value setting unit sets the limit value of the limit value setting unit to a small value when the steering direction detected by the steering direction detection unit is in the direction to increase the rotation, and the motor rotation speed when it is determined as the return direction. 6. The electric power steering apparatus according to claim 5, wherein the limit value of the limit value setting unit is set to a larger value as the value becomes larger.   The electric power steering according to any one of claims 1 to 3, wherein the limit value setting unit is configured to continuously change the limit value in accordance with rotation speed information. apparatus.   The electric power steering according to any one of claims 1 to 3, wherein the limit value setting unit is configured to change the limit value in a stepwise manner in accordance with rotation speed information. apparatus.

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