JP2008213643A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of relaxing impact force transmitted to a torque transmission member such as an intermediate shaft without separately adding a steering angle sensor of high accuracy and a torque limiter when it becomes steering limitation such as at the time of end abutment and when a tire is abutted on a curbstone or the like. <P>SOLUTION: The electric power steering device is provided with an electric motor 12 for transmitting steering assistant torque to a steering mechanism; and a controller 15 for driving/controlling the electric motor 12 according to a current instruction value based on the steering torque. The controller 15 has an end abutment determination part 52 for determining the end abutment time or not based on a variation ratio ΔTma of a motor torque. Further, when the motor torque variation ratio ΔTma is not less than a threshold value ΔTma<SB>TH</SB>for determining the steering limitation set according to a steering angle δ, a duty ratio of a pulse width modulation signal is fixed to a predetermined value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention includes a current command value calculation unit that calculates a current command value based on at least a steering torque, an electric motor that applies a steering assist force to a steering mechanism, and a motor control unit that controls the electric motor based on the current command value And an electric power steering apparatus.

2. Description of the Related Art Conventionally, as a steering device, an electric power steering device that applies a steering assist force to a steering mechanism by driving an electric motor in accordance with a steering torque for a driver to steer a steering wheel has been widespread.
Generally, in the steering mechanism, when the steering wheel is continuously steered in the left or right steering direction from the neutral position and the steering wheel operation amount reaches a maximum steering angle corresponding to the maximum value, the steering mechanism is mechanically operated. A steering limit occurs at which the steering wheel cannot contact any further when it comes into contact with the stopper. It is called so-called end pad that such a steering limit is brought into contact with the mechanical stopper.

When the steering wheel is operated quickly, that is, when the steering speed is high, the steering assist force generated by the electric power steering device is also increased, and the impact force generated at the time of end contact is increased, resulting in a steering mechanism. The durability of the vehicle may decrease, or the driver may feel uncomfortable during the steering operation.
For this reason, conventionally, as an electric power steering device configured to relieve impact at the time of end contact, an unloader correction unit that reduces and corrects the steering assist torque of the motor when the rudder angle exceeds a predetermined rudder angle near the maximum rudder angle It is known that the unloader correction unit increases and corrects the reduction correction amount of the auxiliary steering torque as the steering speed increases (see, for example, Patent Document 1).

In addition, when it is detected that the steered wheel approaches the predetermined maximum steering angle and exceeds the attenuation start steering angle, a damping unit that attenuates the driving force of the electric motor, the load on the steering wheel, and the steering wheel steering There is also known an electric power steering device including an attenuation start steering angle setting unit that sets the attenuation start steering angle according to speed (for example, see Patent Document 2).
However, in the conventional example described in Patent Document 1, the reduction correction amount of the steering assist torque is increased and corrected in the vicinity of the maximum steering angle, so that a sensor for detecting the steering angle is required, When the steering speed is high, the impact at the time of the end contact cannot always be sufficiently mitigated due to the inertia of the electric motor.

  Further, in the conventional example described in Patent Document 2, since the attenuation start steering angle is set according to the load on the steered wheel and the steering speed of the steered wheel, the maximum rudder is obtained when the steering speed is high. By increasing the difference between the angle and the attenuation start steering angle (accelerating the time when the driving force of the electric motor is attenuated), it is possible to prevent a large impact from being generated at the time of end contact due to the motor inertia. However, the assist force is insufficient in the vicinity of the maximum steering angle, and when the steering wheel is turned back from the vicinity of the maximum steering angle toward the neutral position, the steering assist force is reduced due to the attenuation of the driving force of the electric motor. The steering wheel feels like the steering wheel sticks near the maximum steering angle, and the steering feeling is deteriorated.

Therefore, it is considered to mechanically reduce the impact of the end pad (see, for example, Patent Document 3).
In the invention described in Patent Document 3, the torque acting on the part reaches the predetermined value in the middle of the steering force transmission system from the electric motor to the steered wheel where the torque transmitted from the electric motor acts. In this case, by providing a torque limiter that limits the transmission of the torque, the rotational energy of the electric motor that increases instantaneously when the steering operation of the steering wheel stops suddenly, such as when the steering wheel reaches the steering end. Is limited by a torque limiter to prevent the generation of a large impact force by preventing electric power to the steering wheel side with a torque of a predetermined value or more.
Japanese Patent Laid-Open No. 2001-253356 (first page, FIG. 2, FIG. 7) JP 2001-30933 A (first page, FIG. 2, FIG. 3) JP 2000-335431 A (first page, FIG. 2, FIG. 3)

By the way, of the effects of impact load when the steering limit is reached, such as when hitting the end or when the tire abuts against the curbstone, as a torque transmission member inserted between the steering shaft and the steering gear The influence on the intermediate shaft is large, and the durability of the intermediate shaft is reduced.
In each of the above conventional examples, the impact can be reduced when the steering mechanism reaches the steering limit, such as when the steering mechanism comes into contact with the mechanical stopper, but the countermeasures as in the first and second conventional examples are possible. Therefore, since the absolute angle information of the steering wheel is used, a highly accurate rudder angle sensor or an absolute rudder angle estimation function is required, and a low accuracy rudder angle sensor for a skid prevention device cannot be diverted and is expensive. Since a rudder angle sensor and an absolute rudder angle estimation function are required, the manufacturing cost increases. In addition, when the tire comes into contact with the curbstone, the impact force transmitted to the torque transmission member such as the intermediate shaft cannot be reduced regardless of the steering angle.

Further, as in the third conventional example, in order to mechanically prevent the impact at the time of end application using the torque limiter, it is necessary to incorporate the torque limiter, which similarly increases the manufacturing cost.
Therefore, the present invention does not add a separate high-precision rudder angle sensor or torque limiter, etc., and transmits torque to the intermediate shaft or the like when the steering limit is reached, such as when the tire is in contact with a curb or the like. An object of the present invention is to provide an electric power steering device that can alleviate an impact force transmitted to a member.

In order to solve the above problems, an electric power steering apparatus according to claim 1 is based on a steering torque detecting means for detecting a steering torque input to a steering mechanism, and at least a steering torque detected by the steering torque detecting means. Current command value calculating means for calculating a current command value, an electric motor for generating a steering assist torque to be applied to the steering shaft of the steering mechanism, and driving control of the electric motor based on the current command value by a pulse width modulation signal An electric power steering device comprising motor control means,
The motor control means includes a steering angle detection means for detecting or estimating a steering angle, a threshold setting means for setting a threshold for judging a steering limit based on the steering angle detected or estimated by the steering angle detection means, and the electric motor Motor torque detecting means for detecting a motor torque generated between the motor and the steering shaft; motor torque change rate detecting means for calculating a rate of change of the motor torque detected by the motor torque detecting means; and the motor torque change When the rate of change of the motor torque calculated by the rate detecting means is equal to or higher than the threshold set by the threshold setting means, it is determined that the duty ratio limiting condition is satisfied, and the duty ratio of the pulse width modulation signal is The torque transmitted to the torque transmission member between the steering shaft and the steered wheels of the steering mechanism is fixed to a predetermined value. It is characterized by having a Yuti ratio limiting means.

According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect of the invention, the threshold value setting means has a rate of change of the motor torque that is greater than the threshold value as the steering angle detected by the steering angle detection means increases. By changing the threshold value in a direction that easily exceeds the steering angle, it is easy to determine the steering limit.
The electric power steering apparatus according to a third aspect is the invention according to the first or second aspect, wherein a driving current detecting unit that detects a driving current of the electric motor and a rotational angle that detects a rotational angular acceleration of the electric motor. Acceleration detecting means, and the motor torque detecting means is configured to determine whether the electric motor and the steering shaft are based on the motor driving current detected by the driving current detecting means and the rotational angular acceleration detected by the rotational angular acceleration detecting means. It is characterized by calculating the torque generated between them.

According to a fourth aspect of the present invention, in the electric power steering apparatus according to the first or second aspect, the motor torque detecting means is disposed on a torque transmission shaft between the output shaft of the electric motor and the steering shaft. It is characterized by comprising a magnetostrictive torque sensor.
Furthermore, the electric power steering apparatus according to a fifth aspect is characterized in that, in the invention according to any one of the first to fourth aspects, the steering angle detecting means comprises a steering angle sensor.

  An electric power steering apparatus according to a sixth aspect is the invention according to any one of the first to fourth aspects, wherein the steering angle detection means relatively detects a steering angle position of the vehicle. And a neutral point specifying means for specifying a neutral point of the steering angle position, and the steering angle is estimated based on the steering angle position detected by the steering angle position detecting means and the neutral point specified by the neutral point specifying means It is characterized by doing.

  According to the electric power steering apparatus of the present invention, when the rate of change of the motor torque is equal to or greater than a threshold value for determining a steering limit set based on the steering angle, it is determined that the duty ratio limiting condition is satisfied. The duty ratio of the pulse width modulation signal is fixed to a predetermined value for suppressing the torque transmitted to the torque transmission member between the steering shaft and the steered wheels of the steering mechanism, so that the intermediate shaft interposed between the steering shaft and the steering gear It is possible to limit the steering assist torque generated by the electric motor before excessive torque is transmitted to the torque transmission member, etc., and at the time of end application without adding a separate high precision rudder angle sensor or torque limiter etc. Or the torque transmitted to the torque transmission member such as the intermediate shaft when the steering limit is reached, such as when the tire contacts the curb There is an advantage that it is possible to relieve the force.

  Also, the duty ratio limiting control in the original rack end application is made easier by determining the steering limit by changing the threshold in such a direction that the rate of change of the motor torque easily exceeds the above threshold as the steering angle increases. The effect that the erroneous detection of the steering limit other than the steering angle end can be prevented without reducing the above effect. Furthermore, since duty ratio restriction control is not deactivated except at the rudder angle end, excessive torque to the torque transmission member needs to be suppressed at other than the rudder angle end, such as when curb bumps occur. In this case, there is an effect that the restriction control can be functioned reliably.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an embodiment of an electric power steering apparatus according to the present invention.
In the figure, symbol SM is a steering mechanism. This steering mechanism SM has a steering shaft 2 having an input shaft 2a to which a steering force applied from a driver is transmitted to the steering wheel 1 and an output shaft 2b connected to the input shaft 2a via a torsion bar (not shown). It has. The steering shaft 2 is rotatably mounted on the steering column 3, one end of the input shaft 2a is connected to the steering wheel 1, and the other end is connected to a torsion bar (not shown).

The steering force transmitted to the output shaft 2b is transmitted to the intermediate shaft 5 via the universal joint 4 composed of the two yokes 4a and 4b and the cross connecting portion 4c for connecting them, It is transmitted to the pinion shaft 7 through a universal joint 6 composed of yokes 6a and 6b and a cross connecting portion 6c for connecting them.
The steering force transmitted to the pinion shaft 7 is transmitted to the left and right tie rods 9 via the steering gear 8, and steered wheels (not shown) are steered by these tie rods 9. Here, the steering gear 8 is configured in a rack and pinion type having a pinion 8b connected to the pinion shaft 7 and a rack shaft 8c meshing with the pinion 8b in the gear housing 8a, and is transmitted to the pinion 8b. The rotational motion is converted into a straight motion by the rack shaft 8c.

A steering assist mechanism 10 for transmitting a steering assist force to the output shaft 2b is connected to the output shaft 2b of the steering shaft 2. The steering assist mechanism 10 includes a reduction gear 11 connected to the output shaft 2b, and an electric motor 12 composed of, for example, a brushless motor as an electric motor that generates a steering assist force connected to the reduction gear 11. .
A steering torque sensor 14 is disposed in a housing 13 connected to the steering wheel 1 side of the reduction gear 11. The steering torque sensor 14 detects a steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a. For example, a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. The torsional angular displacement is converted into a torsional angular displacement, and this torsional angular displacement is detected by a non-contact magnetic sensor.

The steering torque detection value T output from the steering torque sensor 14 is input to the controller 15 as shown in FIG. The controller 15 detects the vehicle speed detection value V detected by the vehicle speed sensor 16 in addition to the torque detection value T, the motor currents Iu to Iw flowing through the electric motor 12, a rotation angle sensor 17 constituted by a resolver, an encoder, and the like. The rotation angle θ of the electric motor 12 and the steering angle δ detected by the steering angle sensor 18 are also input. Then, to calculate the steering assist torque command value I _M to the steering assisting force corresponding to the torque detection value T and the vehicle speed detecting value V is inputted generated by the electric motor 12 ^*, calculated in the steering assist torque command value I _M ^* On the other hand, after performing various compensation processes based on the motor angular velocity ω and the motor angular acceleration α calculated based on the rotation angle θ, they are converted into dq-axis current command values Id ^* and Iq ^* . Further, the motor currents Iu to Iw are converted into three phases / dq to calculate the dq axis motor currents Id and Iq, and the dq axis current command values Id ^* and Iq ^* and the dq axis motor current are calculated. The drive current supplied to the electric motor 12 is feedback-processed based on Id and Iq, the result is dq / 3-phase converted, and motor currents Iu, Iv and Iw for controlling the drive of the electric motor 12 are output. .

That is, the controller 15 compensates the steering assist torque command value I _M ^*, which calculates the steering assist torque command value I _M ^* based on the steering torque T and the vehicle speed V, and the calculated steering assist torque command value I _M ^* . Based on the command value compensation unit 22 and the torque command value Ir compensated by the command value compensation unit 22, dq-axis current command values Id ^* and Iq ^* are calculated, and the motor currents Iu˜ And a motor current control unit 23 that generates Iw.

Further, based on the steering angle δ detected by the steering angle sensor 18, the controller 15 cannot turn any further because the rack shaft 8c of the steering gear 8 reaches the rack stroke end or the tire contacts the curb or the like. A steering angle determination unit 51 that sets a threshold value ΔTma _TH for determining whether or not the steering limit has been reached, and between the electric motor 12 and the steering shaft 2 based on the q-axis current Iq and the motor angular acceleration α. While calculating the generated motor torque Tma, based on the motor torque Tma, it is determined whether or not the rack shaft 8c of the steering gear 8 has reached the steering limit, and an end contact determination unit 52 that outputs a selection signal SL. And. The selection signal SL output from the end contact determination unit 52 is output to a duty ratio calculation unit 65 described later of the motor current control unit 23.

In the steering assist torque command value calculation unit 21, first, the torque command value calculation unit 41 refers to the steering assist torque command value calculation map shown in FIG. 3 based on the steering torque T and the vehicle speed V to obtain a current command value. A steering assist torque command value I _M ^* is calculated.
As shown in FIG. 3, the steering assist torque command value calculation map has a parabolic shape with the steering torque T on the horizontal axis, the steering assist torque command value I _M ^* on the vertical axis, and the vehicle speed V as a parameter. It is composed of a characteristic diagram represented by a curve, and the steering assist torque 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 torque command value I _M ^* increases relatively slowly with respect to the increase in the steering torque T. However, when the steering torque T further increases, the steering assist torque command with respect to the increase. The value 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.

Then, the phase compensator 42 performs phase compensation to the steering assist torque command value I _M ^*, and outputs a steering assist torque command value I _M ^* after phase compensation to the adder 38 to be described later. Further, the torque differentiation circuit 43 calculates a compensation value for the steering torque T based on the steering torque change rate Td obtained by differentiating the steering torque T, and outputs this to an adder 38 described later.
The command value compensator 22 differentiates the motor rotation angle θ detected by the rotation angle sensor 17 to calculate the motor angular velocity ω, and differentiates the motor angular velocity ω calculated by the angular velocity calculator 31. The angular acceleration calculation unit 32 that calculates the motor angular acceleration α, the convergence compensation unit 33 that compensates for the convergence of the yaw rate based on the motor angular velocity ω calculated by the angular velocity calculation unit 31, and the angular acceleration calculation unit 32 Based on the motor angular acceleration α, the inertia compensator 34 that compensates for the torque equivalent generated by the inertia of the electric motor 12 to prevent the deterioration of the feeling of inertia or control responsiveness, and the self-aligning torque (SAT) are estimated. And at least a SAT estimation feedback unit 35.

Here, the convergence compensation unit 33 receives the motor angular velocity ω calculated by the angular velocity calculation unit 31 and applies a brake to the operation in which the steering wheel 1 swings in order to improve the yaw convergence of the vehicle. Thus, the convergence compensation value Ic is calculated.
The SAT estimation feedback unit 35 receives the steering torque T, the motor angular velocity ω, the motor angular acceleration α, and the steering assist torque command value I _M ^* calculated by the steering assist torque command value calculation unit 21, and based on these, the SAT estimation feedback unit 35 The aligning torque SAT is estimated and calculated.

The principle of calculating the self-aligning torque SAT will be described with reference to FIG. 4 showing the state of torque generated between the road surface and the steering.
That is, when the driver steers the steering wheel 1, a steering torque T is generated, and the electric motor 12 generates an assist torque Tm according to the steering torque T. As a result, the wheel W is steered and a self-aligning torque SAT is generated as a reaction force. Further, at that time, torque serving as a steering resistance of the steering wheel 1 is generated by the inertia J and friction (static friction) Fr of the electric motor 12. Considering the balance of these forces, the following equation of motion can be obtained:

J · α + Fr · sign (ω) + SAT = Tm + T (1)
Here, when the above equation (1) is Laplace transformed with the initial value zero and the self-aligning torque SAT is solved, the following equation (2) is obtained.
SAT (s) = Tm (s) + T (s) −J · ω ′ (s) −Fr · sign (ω (s)) (2)
As can be seen from the above equation (2), the inertia J and static friction Fr of the electric motor 12 are obtained in advance as constants, so that the self-aligning torque is obtained from the motor angular velocity ω, rotational angular acceleration α, assist torque Tm, and steering torque T. The SAT can be estimated. Here, the assist torque Tm is proportional to the steering assist torque command value I _M ^*, to apply a steering assist torque command value I _M ^* in place of the assist torque Tm.

Then, the inertia compensation value Ii calculated by the inertia compensation unit 34 and the self-aligning torque SAT calculated by the SAT estimation feedback unit 35 are added by the adder 36, and the addition output of the adder 36 and the convergence compensation unit 33 are added. Is added by the adder 37 to calculate a command compensation value Icom, and this command compensation value Icom is output from the steering assist torque command value calculation unit 21. _The compensated torque command value Ir is calculated by adding to _M ^* by the adder 38, and this compensated torque command value Ir is output to the motor current control unit 23.

The motor current control unit 23 includes a motor current detector 60 that detects the motor currents Iu, Iv, and Iw supplied to the phase coils Lu, Lv, and Lw of the electric motor 12, and a dq from the torque command value Ir after the limit. A current command value calculation unit 61 for calculating shaft current command values Id ^* and Iq ^* , a three-phase / dq conversion unit 62 for converting motor currents Iu, Iv and Iw to dq axis motor currents Id and Iq, and , Dq axis current command values Id ^* , Iq ^* are subtracted separately from dq axis motor currents Id, Iq to obtain respective phase current deviations ΔId, ΔIq, and respective phase current deviations ΔId. , ΔIq to perform proportional integral control to calculate voltage command values Vd, Vq, and the voltage command values Vd, Vq are input, and three-phase voltage command values Vu, Vv, Vw are obtained. Calculated dq / 3-phase converter 6 When the duty ratio of each phase by performing the duty operation on the basis of these voltage command values Vu, Vv and Vw Du, and a duty ratio calculation unit 65 for calculating a Dv and Dw.

Further, the motor current control unit 23 performs pulse width modulation based on the duty ratio output from the duty ratio calculation unit 65 to obtain a pulse width modulation signal, and based on the pulse width modulation signal, the three-phase motor current Iu, An inverter 66 that outputs Iv and Iw to the electric motor 12 is provided.
As shown in FIG. 5, the duty ratio calculation unit 65 calculates the duty ratio of each phase calculated based on the voltage command values Vu, Vv, and Vw in accordance with the selection signal SL output from the end contact determination unit 52. du _B, select a Dv _B and Dw _B, the duty ratio du _B, a predetermined value Dv _B and Dw _B (e.g., 3%) limits the duty ratio is limited to du _L, one Dv _L and Dw _L Tonouchi In addition, duty calculation / limitation calculation units 65u, 65v, and 65w that output the final duty ratios Du, Dv, and Dw of each phase are provided.

Here, the duty calculation / limit calculation unit 65u includes a duty ratio calculation unit 65a for calculating the sign of the duty ratio Du _B based on voltage command value Vu, the duty ratio Du _B calculated by the duty ratio calculation unit 65a And a limiter 65b limited to a predetermined value (for example, 3%).
Further, the duty ratio / limit calculation unit 65u receives the duty ratio Du _B and the limit duty ratio Du _L , and the selection signal SL indicates that the rack shaft 8c of the steering gear 8 reaches the rack stroke end, or the tire is turned into a curb or the like. The duty ratio Du _B is selected when the logical value is “0”, which means that the steering limit has not been reached at which contact cannot be made any further, and the selection signal SL has reached the steering limit. select limit duty ratio Du _L when the logic value "1" which includes a selection switch unit 65c for outputting as the duty ratio Du. The other duty calculation / limit calculation units 65v and 65w have the same configuration as the duty calculation / limit calculation unit 65u.

The steering angle δ detected by the steering angle sensor 18 is input to the steering angle determination unit 51, and the rack shaft 8c of the steering gear 8 is steered based on the steering angle δ with reference to the threshold calculation map shown in FIG. A steering limit detection threshold value ΔTma _TH that is a threshold value for determining whether or not the limit has been reached is calculated.
Here, the steering limit detection threshold value ΔTma _TH is usually generated when the rack shaft 8c of the steering gear 8 reaches the rack stroke end or when the tire comes into contact with a curb or the like and becomes a steering limit at which no further turning is possible. The threshold calculation map is calculated as a threshold ΔTma _TH = TH1 in a region where the steering angle δ is up to a predetermined steering angle δth near the rack end. In a region where the steering angle δ is greater than or equal to the predetermined steering angle δth, the threshold value ΔTma _TH is set to be smaller than the predetermined value TH1 as the steering angle δ increases. Thus, the threshold value ΔTma _TH near the rack end is calculated smaller than the threshold value ΔTma _TH at the steering angle center.

The end contact determination unit 52 calculates the steering limit detection threshold ΔTma _TH calculated by the steering angle determination unit 51, the q-axis current Iq output from the three-phase / dq conversion unit 62, and the angular acceleration calculation unit 32. Is the steering limit at which the rack shaft 8c of the steering gear 8 reaches the rack stroke end or the tire contacts the curb or the like and cannot be steered any more Determine whether or not.

FIG. 7 is a flowchart showing the end contact determination processing procedure executed by the end contact determination unit 52.
First, in step S1, the end contact determination unit 52 reads the steering limit detection threshold value ΔTma _TH calculated by the steering angle determination unit 51, and proceeds to step S2.
In step S2, the end contact determination unit 52 reads the q-axis current Iq output from the three-phase / dq conversion unit 62 and the motor angular acceleration α calculated by the angular acceleration calculation unit 32, and based on these, The motor torque Tma is calculated by calculating the following equation (3).

Tma = Kt · Iq−Jm · α (3)
Here, Kt is the torque constant of the motor, and Jm is the moment of inertia of the rotor portion of the motor.
Next, in step S3, the end contact determination unit 52 differentiates the motor torque Tma calculated in step S2, calculates a motor torque change rate ΔTma, and proceeds to step S4.

In step S4, the end contact determination unit 52 determines whether or not the motor torque change rate ΔTma calculated in step S3 is equal to or greater than the steering limit detection threshold ΔTma _TH read in step S1. When it is determined in this step S4 that ΔTma ≧ ΔTma _TH, it is determined that the steering limit has been reached, and the process proceeds to step S5.
In step S <b> 5, the end contact determination unit 52 outputs the selection signal SL having the logical value “1” to the duty ratio calculation unit 65 and then ends the end contact determination process.

In step S4, when the end contact determination unit 52 determines that ΔTma <ΔTma _TH , the process proceeds to step S6, after the selection signal SL having the logical value “0” is output to the duty ratio calculation unit 65. End contact determination processing ends.
The waveforms of the steering torque T (q-axis current Iq) and the motor angular velocity ω when the rack shaft 8c reaches the steering limit during normal steering are as shown in FIG. As described above, since the electric motor 12 is driven and controlled based on the dq axis current command values Id ^* and Iq ^* calculated based on the steering torque T, the q axis current Iq is equal to the steering torque T. The q-axis current Iq has a waveform equivalent to the steering torque T.

Assuming that the rack shaft 8c reaches the steering limit at time t1, as shown in FIG. 8A, the steering torque T (q-axis current Iq) increases with a large gradient that does not occur in normal steering. The motor torque Tma is calculated based on the above equation (3). Since the motor torque Tma increases as the q-axis current increases, the motor torque waveform is the same as that shown in FIG. Become. For this reason, when ΔTma ≧ ΔTma _TH , it can be determined that the steering limit has been reached reliably.

  Further, the waveforms of the steering torque T (q-axis current Iq) and the motor angular velocity ω when the steering limit is reached when the steering wheel is heavy, such as a stationary steering wheel, are as shown in FIG. Assuming that the rack shaft 8c reaches the steering limit at time t11, as shown in FIG. 9A, the steering torque T (q-axis current Iq) increases, but the steering torque T ( Since the q-axis current Iq) is originally large, the rate of change is small. Also, the change time is short.

However, in this case, the motor angular velocity ω decreases rapidly as shown in FIG. Since the motor torque Tma is calculated based on the equation (3) as described above, the motor torque Tma increases as the motor angular acceleration α increases in the negative direction. Therefore, even in the stationary state, the motor torque waveform is the same as that shown in FIG. 8A, and when ΔTma ≧ ΔTma _TH , it can be determined that the steering limit has been reached reliably.

  In FIG. 2, the steering torque sensor 14 corresponds to the steering torque detection means, the steering angle sensor 18 corresponds to the steering angle detection means, and the steering assist torque command value calculation unit 21 and the command value compensation unit 22 correspond to the current command value. Corresponding to the calculation means, the steering angle determination unit 51 corresponds to the threshold setting means, the end contact determination unit 52 and the duty ratio calculation unit 65 correspond to the duty ratio limiting means, and the motor current control unit 23 corresponds to the motor control means. The angular acceleration calculation unit 32 corresponds to rotational angular acceleration detection means, and the motor current detector 60 corresponds to drive current detection means.

In FIG. 7, the process of step S2 corresponds to the motor torque detecting means, and the process of step S3 corresponds to the motor torque change rate detecting means.
Next, the operation in the embodiment of the present invention will be described.
Assuming that the ignition switch is turned on to start running the vehicle, the controller 15 is turned on to start execution of the steering assist control process, and the steering torque T detected by the steering torque sensor 14 is The controller 15 includes a vehicle speed V detected by the vehicle speed sensor 16, motor current detection values Iu to Iw detected by the motor current detector 60, a motor rotation angle θ detected by the rotation angle sensor 17, and a steering angle δ detected by the steering angle sensor 18. To be supplied.

Therefore, the steering assist torque command value calculation unit 21 calculates the steering assist torque command value I _M ^* based on the steering torque T and the vehicle speed V with reference to the steering assist torque command value calculation map shown in FIG. On the other hand, the motor rotation angle θ detected by the rotation angle sensor 17 is input to the angular velocity calculation unit 31 to calculate the motor angular velocity ω, and the motor angular velocity ω is input to the angular acceleration calculation unit 32 to calculate the motor angular acceleration α. The

Then, the convergence compensation unit 33 calculates the convergence compensation value Ic based on the motor angular velocity ω, the inertia compensation unit 34 calculates the inertia compensation value Ii based on the motor angular acceleration α, and the SAT estimation feedback unit 35 further. The self-aligning torque SAT is calculated based on the motor angular velocity ω and the motor angular acceleration α, and these are added by the adders 36 and 37 to calculate the command value compensation value Icom. The adder 38 calculates the steering assist torque command value. The compensated torque command value Ir is calculated by adding to I _M ^* .

At this time, when the vehicle is stopped and the steering wheel 1 is not steered, the steering torque T detected by the steering torque sensor 14 is “0”, and the vehicle speed V detected by the vehicle speed sensor 16 is also Since it is “0”, the steering assist torque command value I _M ^* calculated by the steering assist torque command value calculation unit 21 is also “0”. The motor angular acceleration α calculated by the angular velocity calculation unit 32 is also “0”.

Since the electric motor 12 is in a stopped state, the motor currents Iu to Iw detected by the motor current detector 60 are also “0”, and the motor currents Iu to Iw are converted by the three-phase / dq axis conversion unit 62. The q-axis current Iq is also “0”. For this reason, the end contact determination part 52 calculates Tma = 0 based on the said (3) Formula by step S2 of FIG.
Since ΔTma <ΔTma _TH , the end contact determination unit 52 determines No in step S4 of FIG. 7, determines that the steering limit has not been reached, moves to step S6, and sets the logical value “0”. The selection signal SL is output to the duty ratio calculation unit 65.

Therefore, the duty ratio calculation unit 65 outputs the duty ratios Du _B , Dv _B and Dw _B of each phase as they are as the duty ratios Du, Dv and Dw, and the electric motor 12 is driven and controlled based on these. At this time, since the duty ratios Du _B , Dv _B and Dw _B are 0%, the motor currents Iu to Iw output from the inverter 66 are also “0”, and the electric motor 12 continues to be stopped.

When the steering wheel 1 is turned to the right (or left) while the electric motor 12 is stopped, the steering torque T corresponding to the steering direction is detected by the steering torque sensor 14, and the steering torque T Is supplied to the controller 15. At this time, since the vehicle speed V is “0”, the steering assist torque command value calculation unit 21 selects the innermost characteristic curve in FIG. 3 and becomes a large value earlier as the steering torque T increases. A steering assist torque command value I _M ^* is calculated, and this steering assist command value I _M ^* is output to the adder 38. Further, the motor angular acceleration α is output by steering.

Then, compensation for the steering assist command value I _M ^* is performed by the command compensation value Icom calculated by the command value compensation unit 22, and a post-compensation torque command value Ir is calculated.
Since the motor torque change rate ΔTma generated in this state is solely due to the motor angular acceleration α, it is smaller than the motor torque change rate when the steering limit is reached, and ΔTma <ΔTma _TH. The output of the selection signal SL of “0” is continued, and the duty ratio calculation unit 65 outputs the duty ratios Du _{B to} Dw _{B as} they are as the duty ratios Du to Dw, and the electric motor 12 is driven based on these. . Thereby, a steering assist torque corresponding to the steering torque T is generated and transmitted to the output shaft 2b of the steering shaft 2 via the reduction gear 11, so that the steering in the stationary state can be performed lightly.

In this embodiment, the steering limit detection threshold value ΔTma _TH is set according to the steering angle δ. If the rack stroke end has not been reached as described above, refer to the threshold value calculation map of FIG. Since the steering limit detection threshold value ΔTma _TH is set to a relatively large TH1 that makes it difficult for the motor torque change rate ΔTma to exceed the threshold value ΔTma _TH , it is difficult to determine that the steering limit is the steering limit. Can be prevented.

Thereafter, when the vehicle is started, the vehicle speed V detected by the vehicle speed sensor 16 increases, so that the steering assist torque command value calculation unit 21 selects the outer characteristic curve as the vehicle speed V increases in the map of FIG. Will be. Therefore, as the amount of increase in the steering assist torque command value I _M ^* corresponding to the increase in the steering torque T decreases, the steering assist torque generated by the electric motor 12 also becomes smaller than that at the time of stationary, and the vehicle speed V It is possible to generate an optimum steering assist torque corresponding to the above.

  By the way, if the steering wheel 1 is steered relatively fast to the steering limit to the right or left in the extremely low speed traveling state such as the stationary state or the garage, the controller 15 until the steering limit is reached as described above. Thus, motor currents Iu to Iw corresponding to the steering torque T detected by the steering torque sensor 14 at that time are formed, and these are supplied to the electric motor 12 so that light steering can be performed.

At this time, since the steering is performed in the stationary state or the extremely low speed traveling state, the steering torque T is large, and the duty ratio of the pulse width modulation signal output from the pulse width modulation unit 63 is approximately 100%. Yes.
In this state, when the steering limit is reached, the movement of the rack shaft 8c is stopped, whereby the pinion 8b, the pinion shaft 7, the universal joint 6, the intermediate shaft 5, the universal joint 4, and the output shaft 2b of the steering shaft 2 are rotated. Stops, and accordingly, the rotation of the electric motor 12 is also stopped via the reduction gear 11.

At this time, in the controller 15, since the duty ratio of the pulse width modulation signal is close to 100%, the motor currents Iu to Iw output from the inverter 66 increase rapidly, and torque due to the moment of inertia of the motor is applied. Accordingly, the motor torque Tma calculated by the end contact determining unit 52 increases in a steep slope, and the motor torque change rate ΔTma is equal to or greater than the threshold value ΔTma _TH . At this time, when the steering angle δ is large and on the steering angle end side, the steering angle determination unit 51 sets the threshold value ΔTma _TH to a relatively small value, so that it is easy to determine the steering limit.

Then, the end contact determination unit 52 determines Yes in step S <b> 4 of FIG. 7, proceeds to step S <b> 5, and outputs a selection signal SL having a logical value “1” to the duty ratio calculation unit 65. Accordingly, the duty ratio calculation unit 65 limits the duty ratios Du _B , Dv _B and Dw _B to a predetermined value (3%), and outputs them as the duty ratios Du, Dv and Dw. As a result, the electric motor 12 is driven and controlled based on the duty ratio fixed at a predetermined value (3%).

  As described above, by limiting the duty ratio, the motor currents Iu to Iw output from the inverter 66 are reduced, and the steering assist torque generated in the electric motor 12 is reduced and transmitted to the intermediate shaft 5. The torque peak value is suppressed as compared with the case where the duty ratio is not limited, and the durability of the torque transmission member such as the intermediate shaft can be improved.

Moreover, the motor torque value Tma is calculated based on the motor currents Iu to Iw detected by the motor current detector 60 and the motor angular acceleration α calculated by the angular acceleration calculation unit 32, and is differentiated to obtain the motor torque change rate ΔTma. By calculating and comparing the calculation result with the threshold value ΔTma _TH , the steering limit of the end-contact state or the state where the tire is in contact with the curb is detected, so a short time (for example, about 10 msec) from when the steering limit is reached. The steering limit state can be detected.

  Further, since the steering assist torque generated by the electric motor 12 can be limited in a short time (for example, about 20 msec) from the detection of the steering limit, the time from when the steering limit is reached until the peak torque is generated in the intermediate shaft 5. The steering assist torque can be limited within (about 30 msec), and the torque generated in the intermediate shaft can be reduced to prevent the durability of the intermediate shaft 5 from being lowered. Moreover, this effect can be exhibited without providing a separate sensor such as a highly accurate rudder angle sensor.

  Thus, in the above embodiment, when the rate of change of the motor torque is equal to or greater than the threshold for determining the steering limit set based on the steering angle, it is determined that the duty ratio limiting condition is satisfied, and the pulse width The duty ratio of the modulation signal is fixed to a predetermined value that suppresses the torque transmitted to the torque transmission member between the steering shaft and the steered wheels of the steering mechanism, so that the torque of the intermediate shaft or the like inserted between the steering shaft and the steering gear The steering assist torque generated by the electric motor before the excessive torque is transmitted to the transmission member can be limited, and without adding a separate high precision rudder angle sensor or torque limiter etc. Reducing the impact force transmitted to the torque transmission member such as the intermediate shaft when the steering limit is reached, such as when it contacts a curb It can be.

  In addition, the greater the steering angle, the easier it is to determine the steering limit by changing the threshold in such a direction that the motor torque change rate is more likely to exceed the steering limit detection threshold. Without reducing the control effect, it is possible to prevent erroneous detection of the steering limit other than at the steering angle end. Also, since duty ratio restriction control is not deactivated except at the rudder angle end, excessive torque to the torque transmission member needs to be suppressed at other than the rudder angle end, such as when a curbstone hit occurs. Therefore, it is possible to ensure that the above limit control functions.

  In addition, since the steering angle detection means is constituted by a steering angle sensor and the steering limit detection threshold is set based on the steering angle detected by the steering angle sensor, the threshold can be set with a relatively simple configuration, and the skid Since it is possible to divert the low-precision steering angle sensor for the prevention device, it is not necessary to provide a high-precision steering angle sensor separately as in the case of detecting the steering limit using the absolute angle information of the steering wheel. The increase in cost can be suppressed.

In the above embodiment, the case where the duty ratio is fixed to a predetermined value as the steering limit when the motor torque change rate ΔTma is equal to or greater than the threshold value ΔTma _TH has been described. However, the motor torque change rate ΔTma is set to the threshold value ΔTma. and the _TH or more, and or it is determined that the steering limit when the motor torque Tma is a predetermined value (e.g. 2.0 Nm) or more, the motor torque change rate DerutaTma is not less threshold DerutaTma _TH or more, and the motor torque Tma It is also possible to determine that the steering limit is reached when a state of a predetermined value (for example, 2.0 Nm) or more continues for a predetermined time (for example, 10 msec).

  Thereby, the steering limit reaching state can be detected accurately. In this case, during normal steering, the vehicle may be braked on, for example, a Belgian road (cobblestone road) or the like, whereby a large vibration load may be input from the tire. If the vibration load is large, the motor of the electric motor 12 Although the current gradient tends to increase, since a large current does not flow continuously with respect to the vibration load from the tire, erroneous detection of this traveling state can be reliably prevented.

Further, since the steering limit occurs only when the steering wheel 1 is steered in the increased direction, the steering limit is the increased state in which the sign of the motor torque Tma and the sign of the motor torque change rate ΔTma match, and It can also be determined that the steering limit is reached when the motor torque change rate ΔTma is equal to or greater than the threshold value ΔTma _TH .
Further, the motor angular velocity ω calculated by the angular velocity calculating unit 31 is further supplied to the end contact determining unit 52, and when the motor angular velocity ω is not less than a predetermined value and the motor torque change rate ΔTma is not less than the threshold value ΔTma _TH , the steering limit It can also be determined. Since the motor angular velocity ω at the time of reaching the steering limit rapidly decreases as shown in FIG. 10, in this case, the motor angular velocity ω immediately before reaching the steering limit (for example, about 20 msec before) becomes the motor angular velocity ω. Motor angular velocity) is used.

  In this way, by putting the motor angular velocity ω into the steering limit detection condition, when the motor angular velocity ω is smaller than a predetermined value, the impact load when the steering limit is reached is small, and the peak value of the transmission torque transmitted to the intermediate shaft 5 is small. Therefore, if it is determined that there is no need to perform steering assist torque limitation using a small fixed duty ratio and the motor angular velocity ω is equal to or greater than a predetermined value, the impact load when the steering limit is reached increases. Since the peak value of the transmission torque transmitted to the intermediate shaft 5 also increases, it is necessary to limit the steering assist torque. Therefore, the steering assist torque limitation is performed, and the peak torque transmitted to the intermediate shaft 5 is surely reduced. be able to.

  Furthermore, in the above embodiment, the duration of the steering assist torque limit for fixing the duty ratio to a predetermined value is set to a predetermined time (for example, about 20 msec), and after the steering assist torque limit state is continued for the predetermined time, You can also remove the restriction. As a result, the steering assist torque limitation is continued for a time sufficient to reduce the peak of the transmission torque generated in the intermediate shaft 5, and the driver's uncomfortable feeling caused by continuing the steering assist torque limitation for a long time is suppressed. can do. At this time, since the impact load is large when the motor angular velocity ω is large, the duration of the steering assist torque limitation is set longer as the motor angular velocity ω is larger.

In the above embodiment, the case where the electric motor 12 is controlled based on the comparatively small limit duty ratios Du _{L to} Dw _L when the steering limit is detected has been described. The duty ratio of the pulse width modulation signal with respect to the three switching elements constituting the part) is 0%, and the duty ratio of the pulse width modulation signal with respect to the three switching elements constituting the lower arm part (or the upper arm part) is 100%. By fixing and making each coil of the electric motor 12 a closed circuit in a short-circuit state, the electromagnetic brake mode can be set so that the inertia force of the rotor of the electric motor 12 is not transmitted to the intermediate shaft 5.

Furthermore, in the above embodiment, the case where the limit duty ratios Du _{L to} Dw _L are set to 3%, for example, has been described. However, any fixed duty ratio can be set in accordance with the characteristics of the electric motor 12.
Furthermore, in the above embodiment, the case where proportional integral control is performed with respect to the deviation between the d-axis current Id and q-axis current Iq and the d-axis target current Id ^* and q-axis target current Iq ^* has been described. A three-phase / two-phase converter is provided on the output side of the value calculator 61 to convert it into current command values Iu ^* , Iv ^*, and Iw ^* , and the current command values Iu ^{* to} Iw ^* and the motor current Iu are converted by three subtractors. Proportional integral control can also be performed for each deviation from ~ Iw.

In the above embodiment, the duty ratio Du _B is calculated by the duty ratio calculation unit 65a, the limit duty ratio Du _L is calculated by the limiter 65b, and these are selected by the selection switch unit 65c. Voltage command values Vu to Vw are limited to predetermined values by a limiter, voltage command values Vu to Vw and limit voltage command values Vu _{L to} Vw _L are selected by a selection switch unit, and a duty ratio is based on the selected command value Du to Dw and D can also be calculated.

Further, in the above embodiment, the case where the motor torque Tma is calculated based on the q-axis current Iq and the motor angular acceleration α has been described. However, the output shaft of the electric motor 12 and the input / output of the reduction gear 11 are described. A torque sensor such as a magnetostrictive torque sensor may be disposed on a torque transmission shaft such as a shaft to directly detect the motor torque Tma.
In the above-described embodiment, the case where the steering angle sensor 18 is applied as the steering angle detection unit has been described. However, instead of the steering angle sensor 18, a steering angle estimation unit that estimates the steering angle δ is provided in the controller 15. You can also. In this case, the steering angle estimation unit includes, for example, a steering angle position detection unit (steering angle position detection unit) that relatively detects the steering angle position of the vehicle, and a neutral point specification unit that specifies a neutral point of the steering angle position ( (Neutral point specifying means) may be provided, and the steering angle may be estimated based on the steering angle position detected by the steering angle position detection unit and the neutral point specified by the neutral point specification unit. At this time, unlike the case where the steering wheel limit is detected using the absolute angle information of the steering wheel, a highly accurate absolute rudder angle estimation function is not required. it can.

  Furthermore, in the above-described embodiment, the case of using the steering angle detected or estimated by the steering angle sensor or the steering angle estimation unit has been described. However, the self-aligning torque SAT ensures a certain amount of grip on the tire and the road surface. In this case, since it can be said that the vehicle running characteristics have a correlation with the steering angle, the self-aligning torque SAT can be applied instead of the steering angle.

  Furthermore, although the case where a brushless motor was applied as an electric motor was demonstrated in the said embodiment, a brush motor system can also be applied. In this case, for example, the motor angular velocity ω may be estimated from the back electromotive force of the motor.

1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of the controller in this embodiment. It is a steering assist torque command value calculation map. It is a schematic diagram with which it uses for description of the self-aligning torque. It is a block diagram which shows the specific structure of a duty ratio calculating part. It is a threshold value calculation map. It is a flowchart which shows a contact determination process procedure. FIG. 6 is a signal waveform diagram showing a change in steering torque and a change in motor angular velocity when the steering limit is reached during normal steering. It is a signal waveform diagram which shows the steering torque change at the time of a steering limit at the time of a stationary stop, and a motor angular velocity change.

Explanation of symbols

  SM ... steering mechanism, 1 ... steering wheel, 2 ... steering shaft, 3 ... steering column, 4, 6 ... universal joint, 5 ... intermediate shaft, 8 ... steering gear, 10 ... steering assist mechanism, 11 ... reduction gear, 12 ... Electric motor, 14 ... steering torque sensor, 15 ... control unit, 16 ... vehicle speed sensor, 17 ... rotation sensor, 18 ... steering angle sensor, 21 ... steering assist torque command value calculation unit, 22 ... command value compensation unit, 23 ... motor Current control unit, 51 ... rudder angle determination unit, 52 ... end contact determination unit

Claims (6)

Steering torque detection means for detecting steering torque input to the steering mechanism, current command value calculation means for calculating a current command value based on at least the steering torque detected by the steering torque detection means, and a steering shaft of the steering mechanism An electric power steering apparatus comprising: an electric motor that generates a steering assist torque to be applied to the motor; and a motor control unit that drives and controls the electric motor by a pulse width modulation signal based on the current command value,
The motor control means includes a steering angle detection means for detecting or estimating a steering angle, a threshold setting means for setting a threshold for judging a steering limit based on the steering angle detected or estimated by the steering angle detection means, and the electric motor Motor torque detecting means for detecting a motor torque generated between the motor and the steering shaft; motor torque change rate detecting means for calculating a rate of change of the motor torque detected by the motor torque detecting means; and the motor torque change When the change rate of the motor torque calculated by the rate detection means is equal to or higher than the threshold set by the threshold setting means, it is determined that the duty ratio restriction condition is satisfied, and the duty ratio of the pulse width modulation signal is The torque transmitted to the torque transmission member between the steering shaft and the steered wheels of the steering mechanism is fixed to a predetermined value. An electric power steering apparatus characterized by having a Yuti ratio limiting means.   The threshold value setting means changes the threshold value in such a direction that the rate of change of the motor torque tends to exceed the threshold value as the steering angle detected by the steering angle detection means increases, thereby making it easier to determine the steering limit. The electric power steering apparatus according to claim 1.   Drive current detection means for detecting the drive current of the electric motor, and rotation angular acceleration detection means for detecting the rotation angular acceleration of the electric motor, wherein the motor torque detection means is detected by the drive current detection means The torque generated between the electric motor and the steering shaft is calculated from a motor driving current and a rotational angular acceleration detected by the rotational angular acceleration detecting means. Electric power steering device.   The said motor torque detection means is comprised by the magnetostriction type torque sensor arrange | positioned at the torque transmission shaft between the output shaft of the said electric motor to the said steering shaft, The Claim 1 or 2 characterized by the above-mentioned. Electric power steering device.   The electric power steering apparatus according to any one of claims 1 to 4, wherein the steering angle detection means is configured by a steering angle sensor.   The steering angle detecting means includes a steering angle position detecting means for relatively detecting a steering angle position of the vehicle, and a neutral point specifying means for specifying a neutral point of the steering angle position, and the steering angle position detecting means The electric power steering apparatus according to any one of claims 1 to 4, wherein the steering angle is estimated based on the detected steering angle position and the neutral point specified by the neutral point specifying means.

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