JP4192724B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus for transmitting an assist force from a ball screw nut rotated by a motor to a ball screw groove provided on the rack shaft side via a bearing on a rack shaft of a rack and pinion type steering mechanism. Is.

2. Description of the Related Art Conventionally, there is known an electric power steering apparatus that reduces the steering force by a steering wheel by applying an assist force by a motor to a steering mechanism connected to a steering shaft. In such an electric power steering apparatus, in the column assist type steering mechanism, the driving force from the motor is applied to the column shaft, and in the rack assist type, the driving force of the motor is directly applied to the rack shaft. Here, Patent Document 1 and Patent Document 2 disclose the rack assist type electric power steering apparatus.
Japanese Patent Laid-Open No. 2003-063422 JP 2003-026007 A

  In general, a rack and pinion type steering device can provide a linear steering feeling as compared with a column type, but can easily transmit the influence of a road surface reaction force to a steering wheel. Here, in the rack and pinion type electric power steering apparatus, there is a problem that an impact sound due to rattling is easily generated in a gear assembly incorporating a rack shaft. This is a collision sound between the ball screw nut rotated by the motor and the ball screw groove of the rack shaft, and occurs every time the rack shaft is displaced by the road surface reaction force.

  In order to reduce the impact noise, a certain degree can be dealt with by improving the accuracy of the ball screw groove of the ball screw nut, the ball screw groove of the rack shaft, and the bearing interposed therebetween. However, if the accuracy is increased, the cost increases, and even if the accuracy is increased, a vehicle having a small impact sound and a vehicle having a large impact sound appear due to variations in accuracy. Such collision noise is not a big problem when driving on roads in Japan, but when driving in Europe, where there are many cobblestone roads (Beljan Road), it cannot be denied that it is inferior to European cars, improving accuracy. Only by this means, quietness comparable to that of a hydraulic power steering device could not be realized with an electric power steering device.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electric power steering apparatus that can suppress the generation of an impact sound due to a road surface reaction force.

In order to achieve the above object, the invention of claim 1 assists a ball screw groove provided on the rack shaft side via a bearing from a ball screw nut rotated on a rack shaft of a rack and pinion type steering mechanism. In an electric power steering device that transmits power,
Detection means for detecting rotation of the ball screw nut due to a reciprocating displacement in a lateral direction with respect to a vehicle traveling direction of the rack shaft;
The present invention is characterized by comprising motor control means for controlling the motor in a direction to decrease the rotation speed of the ball screw nut at a predetermined timing from the time point when the reciprocal displacement is zero.

According to the second aspect of the present invention, there is provided an electric power rudder that transmits an assist force to a rack shaft of a rack and pinion type steering mechanism from a ball screw nut rotated by a motor to a ball screw groove provided on the rack shaft side through a bearing. In the taking device,
Detection means for detecting rotation of the ball screw nut due to a reciprocating displacement in a lateral direction with respect to a vehicle traveling direction of the rack shaft;
Frequency judging means for judging whether the frequency of the reciprocating displacement is within a specific range;
Motor control means for controlling the motor in a direction to decrease the rotational speed of the ball screw nut at a predetermined timing from the time when the displacement of the reciprocating displacement is zero when it is determined by the frequency determination means to be within a specific range; It is a technical feature to have.

According to a third aspect of the present invention, there is provided an electric power rudder that transmits an assist force to a rack shaft of a rack and pinion type steering mechanism from a ball screw nut rotated by a motor to a ball screw groove provided on the rack shaft side through a bearing. In the taking device,
Detection means for detecting rotation of the ball screw nut due to a reciprocating displacement in a lateral direction with respect to a vehicle traveling direction of the rack shaft;
Motor control means for calculating the frequency of the reciprocating displacement and controlling the motor in a direction to decrease the rotational speed of the ball screw nut at a predetermined timing from the time point when the displacement of the next reciprocating displacement estimated from the calculated frequency is zero. It is a technical feature to provide.

The electric power steering apparatus according to claim 1 detects the rotation of the ball screw nut due to the reciprocating displacement of the rack shaft, and reduces the rotation speed of the ball screw nut at a predetermined timing from the time when the displacement of the reciprocating displacement is zero. Control the motor in the direction. Therefore, when the rack shaft is displaced by the road surface reaction force, the ball screw nut rotates as the rack shaft fluctuates, and the displacement speed of the rack shaft is attenuated. By controlling and lowering, it is possible to suppress the impact sound caused by the collision between the rack shaft and the ball screw nut.

In the electric power steering apparatus according to the second aspect , the rotation of the ball screw nut due to the reciprocal displacement of the rack shaft is detected. Whether the rack shaft is displaced by the road surface reaction force in a specific situation such as a cobblestone road is determined based on whether the frequency of the reciprocating displacement of the rack shaft is within a specific range. And when it is judged that it is a specific range, that is, when traveling in a specific situation such as a cobblestone road, the rotational speed of the ball screw nut is decreased at a predetermined timing from the time when the displacement of the reciprocating displacement is zero. Control the motor in the direction. Therefore, when the rack shaft is displaced by the road surface reaction force, the ball screw nut rotates as the rack shaft fluctuates, and the displacement speed of the rack shaft is attenuated. By controlling and lowering, it is possible to suppress an impact sound caused by a collision between a rack shaft and a ball screw nut while traveling on a specific road such as a cobblestone road.

The electric power steering apparatus according to claim 3 , wherein the rotation of the ball screw nut due to the reciprocating displacement of the rack shaft is detected, the frequency of the reciprocating displacement is calculated, and the next reciprocating displacement zero estimated from the calculated frequency. Then, at a predetermined timing, the motor is controlled in a direction to decrease the rotation speed of the ball screw nut. For this reason, the rack shaft is displaced by the road surface reaction force, the ball screw nut rotates as the rack shaft fluctuates, and it rotates by inertia at a predetermined timing from the time of zero displacement of the reciprocating displacement at which the displacement speed of the rack shaft attenuates. By controlling the motor to reduce the rotation speed of the ball screw nut that continues, the impact sound caused by the collision between the rack shaft and the ball screw nut can be suppressed.

  Here, if the predetermined timing from the estimated zero point of the next reciprocating displacement is before the zero point of the next reciprocating displacement, even if there is a time lag until the ball screw nut is energized, Thus, it is possible to appropriately suppress the impact sound caused by the collision between the rack shaft and the ball screw nut.

  Here, if the predetermined timing from the estimated time point of zero displacement of the next reciprocating displacement is after the time point of zero displacement of the next reciprocating displacement, by energizing the ball screw nut in a short time, The impact sound due to the collision between the rack shaft and the ball screw nut can be suppressed appropriately.

  By using a motor rotation angle sensor as the detection means, it is not necessary to add a sensor for detecting the rotation of the ball screw nut. In particular, by using the rotation angle sensor for assist control of the electric power steering apparatus, it is possible to realize the control of the collision noise suppression by the assist control interruption process.

Hereinafter, an embodiment of an electric power steering apparatus to which an impact sound reduction process of the present invention is applied will be described with reference to the drawings.
[First embodiment]
First, the main configuration of the electric power steering apparatus 20 according to the first embodiment will be described with reference to FIGS. As shown in FIGS. 1 and 4, the electric power steering apparatus 20 mainly includes a steering wheel 21, a steering shaft 22, a pinion shaft 23, a rack shaft 24, a torque sensor 30, a motor 40, a motor resolver 44, and a ball. It is composed of a screw mechanism 50, an ECU 60, and the like, and detects a steering state by the steering wheel 21 and generates an assist force corresponding to the steering state by the motor 40 to assist steering by the driver. Note that wheels (not shown) are connected to both sides of the rack shaft 24 via tie rods or the like.

  That is, as shown in FIGS. 1 and 2, one end side of a steering shaft 22 is connected to the steering wheel 21, and the other end side of the steering shaft 22 is connected to a pinion shaft 23 accommodated in a pinion housing 25. The input shaft 23 a and the torsion bar 31 are connected by a pin 32. Further, the output shaft 23b of the pinion shaft 23 is connected to the other end 31a of the torsion bar 31 by spline coupling.

  The input shaft 23a of the pinion shaft 23 is rotatably supported in the pinion housing 25 by the bearing 33a, and the output shaft 23b is also rotatably supported by the bearing 33b. Further, between the input shaft 23a and the pinion housing 25, The first resolver 35 and the second resolver 37 are provided between the output shaft 23b and the pinion housing 25, respectively. The first resolver 35 and the second resolver 37 can detect the steering angle by the steering wheel 21 and are electrically connected to the ECU 60 via terminals 39 (see FIG. 4).

  A pinion gear 23c is formed at an end portion of the output shaft 23b of the pinion shaft 23, and a rack groove 24a of the rack shaft 24 is coupled to the pinion gear 23c so as to be meshable. Thus, a rack and pinion mechanism is configured.

  With this configuration, the steering shaft 22 and the pinion shaft 23 can be connected to each other by the torsion bar 31 so as to be relatively rotatable, and the rotation angle of the steering shaft 22, that is, the rotation angle (mechanical angle) of the steering wheel 21. θm can be detected by the first steering angle (electrical angle) θe1 by the first resolver 35 and the second steering angle (electrical angle) θe2 by the second resolver 37. Further, the twist amount (corresponding to the steering torque) of the torsion bar 31 can be detected as the twist angle from the angle difference between the first steering angle θe1 and the second steering angle θe2.

  As shown in FIGS. 1 and 3, the rack shaft 24 is accommodated in a rack housing 26 and a motor housing 27, and a ball screw groove 24 b is formed in a spiral shape at an intermediate portion thereof. A cylindrical motor shaft 43 is provided around the ball screw groove 24 b and is supported by a bearing 29 so as to be rotatable coaxially with the rack shaft 24. This motor shaft 43 constitutes the motor 40 together with the stator 41, the excitation coil 42, etc., and the field generated by the excitation coil 42 wound around the stator 41 is generated on the outer periphery of the motor shaft 43 corresponding to the rotor. By acting on the permanent magnet 45 provided, the motor shaft 43 can be rotated.

  A ball screw nut 52 is attached to the inner periphery of the motor shaft 43, and the ball screw nut 52 is also formed with a ball screw groove 52a in a spiral shape. Therefore, a large number of balls 54 are movably interposed between the ball screw groove 52a of the ball screw nut 52 and the ball screw groove 24b of the rack shaft 24, whereby the rack shaft 24 is pivoted by the rotation of the motor shaft 43. A ball screw mechanism 50 that can move in the direction can be configured.

  In other words, the rotational torque of the motor shaft 43 rotating in the forward and reverse directions can be converted into the reciprocating motion in the axial direction of the rack shaft 24 by the ball screw mechanism 50 including both the ball screw grooves 24b and 52a. As a result, the reciprocating motion becomes an assist force that reduces the steering force of the steering wheel 21 via the pinion shaft 23 that constitutes the rack and pinion mechanism together with the rack shaft 24.

  A motor resolver 44 capable of detecting the rotation angle (electrical angle) θMe of the motor shaft 43 is provided between the motor shaft 43 of the motor 40 and the motor housing 27. The motor resolver 44 is not shown. It is electrically connected to the ECU 60 via a terminal (see FIG. 4).

  FIG. 4 shows a control configuration of the electric power steering apparatus 20 of the first embodiment. When the outputs of the first resolver 35 and the second resolver 37 described above are input to the ECU 60 of the electric power steering apparatus 20, the ECU 60 calculates a steering torque T as will be described later, and performs steering according to the steering torque T. An assist command for assisting the force is output to the motor drive circuit 62 side. The motor drive circuit 62 causes the motor 40 to generate torque according to the assist command. The rotation angle of the motor 40 is detected by the motor resolver 44 and is fed back to the motor drive circuit 62 and also output to the ECU 60. As will be described later, the ECU 60 calculates the steering angle based on the outputs from the first resolver 35, the second resolver 37, and the motor resolver 44, and corrects the assist amount of the steering force described above according to the steering angle. Further, as will be described later, an impact sound reduction process is performed based on the output from the motor resolver 44.

Next, the generation principle of the collision noise during traveling on the cobblestone road in the electric power steering apparatus described above with reference to FIGS. 1 to 3 will be described with reference to FIGS. 9 and 10.
9 schematically shows the motor-side ball screw nut 52, the ball 54, and the rack shaft 24 shown in FIG. Here, FIG. 9A, FIG. 9B, and FIG. 9C show a case where the rack shaft 24 is displaced in the left direction in the figure due to the road surface reaction force during traveling on the cobblestone road. 9 (D), FIG. 9 (E), and FIG. 9 (F) show the rack shaft being displaced in the right direction in the figure. That is, during traveling on the cobblestone road, the rack shaft continues to reciprocate in the lateral direction with respect to the vehicle traveling direction due to the road surface reaction force.

  FIG. 10A is a graph showing the displacement (position) between the rack shaft 24 and the ball screw nut 52 on the motor side. In the drawing, the rack shaft side is represented by a broken line, and the ball screw nut 52 side is represented by a solid line. Among them, the horizontal axis shows time, and the vertical axis shows the amount of displacement to the right side on the plus side from zero displacement, and the minus side shows the amount of displacement to the left side. FIG. 10B is a graph showing the speed of the ball screw nut 52, and FIG. 10C is a graph showing the acceleration (energy) of the ball screw nut 52. The ball screw nut 52 side indicated by a solid line in FIG. 10A is displaced to the left and right in a substantially sine wave shape. On the other hand, the rack shaft 24 indicated by the broken line is swayed back when the displacement exceeds zero, that is, when switching from the right side to the left side, and when switching from the left side to the right side, the rack shaft 24 swings slightly in the reverse direction. I'm back.

  FIG. 9A shows a state in which the rack shaft 24 shown in FIG. 9F has started to be displaced leftward from the rightmost position (corresponding to the point Pa in FIG. 10). ). In the figure, the alternate long and short dash line C represents the position of zero displacement. The ball 54 comes into contact with the side wall of the ball screw groove 24b of the rack shaft 24, the ball 54 presses the side wall of the ball screw groove 52a of the ball screw nut 52, and the ball screw nut 52 rotates clockwise as viewed from the left side in FIG. And displaced to the left of the axis. FIG. 9B shows a state in which the rack shaft 24 has passed the amplitude center (zero displacement) C (corresponding to the point Pb in FIG. 10). Here, the displacement speed of the rack shaft 24 in the left direction is attenuated by mechanical resistance. On the other hand, the ball screw nut 52 is not greatly decelerated due to inertia, and continues to be displaced in the left direction along the axis with rotation in the clockwise direction. Therefore, the side wall of the ball screw groove 52a of the ball screw nut 52 collides with the side wall of the ball screw groove 24b of the rack shaft 24 via the ball 54, and an impact sound is generated. FIG. 9C shows a state in which the rack shaft 24 has reached the left end (corresponding to the point Pc in FIG. 10). The rack shaft 24 gently stops at the left end position shown in FIG. 9C while the displacement speed in the left direction is attenuated by mechanical resistance. As with the rack shaft 24, the ball screw nut 52 stops at the left end position.

  FIG. 9 (D) shows a state in which the rack shaft 24 shown in FIG. 9 (C) has started to be displaced in the right direction from the leftmost position (corresponding to the point Pd in FIG. 10). ). In the figure, the alternate long and short dash line C represents the position of zero displacement. The ball 54 comes into contact with the side wall of the ball screw groove 24b of the rack shaft 24, the ball 54 presses the side wall of the ball screw groove 52a of the ball screw nut 52, and the ball screw nut 52 is counterclockwise as viewed from the left side in FIG. It is rotated and displaced to the right of the axis. FIG. 9E shows a state in which the rack shaft 24 has passed the amplitude center (zero displacement) C (corresponding to the point Pe in FIG. 10). Here, the rack shaft 24 is attenuated in the rightward displacement speed due to mechanical resistance. On the other hand, the ball screw nut 52 is not greatly decelerated due to inertia, and continues to be displaced in the right direction of the axis along with the counterclockwise rotation. Therefore, the side wall of the ball screw groove 52a of the ball screw nut 52 collides with the side wall of the ball screw groove 24b of the rack shaft 24 via the ball 54, and an impact sound is generated. FIG. 9F shows a state in which the rack shaft 24 has reached the right end (corresponding to the point Pf in FIG. 10). Here, the rack shaft 24 and the ball screw nut 52 gently stop at the right end position shown in FIG. 9F while attenuating the displacement speed in the right direction by mechanical resistance. As described above, when the rack shaft 24 swings to the left and right, the ball screw groove 24b of the rack shaft 24 and the ball screw groove 52a of the ball screw nut 52 collide with each other when the displacement slightly exceeds zero, and an impact sound is generated. It has occurred. For this reason, on the cobblestone road, the impact sound due to the amplitude of the rack shaft 24 continues, giving a strong discomfort to the driver.

  For this reason, in the electric power steering apparatus of the first embodiment, the motor is controlled in the direction of decreasing the rotational speed of the ball screw nut 52 from the time when the displacement of the reciprocating displacement of the rack shaft 24 is zero. That is, when the rack shaft is displaced by the road surface reaction force, the ball screw nut 52 rotates as the rack shaft 24 fluctuates, and the rotation of the ball screw nut 52 continues to rotate due to inertia when the displacement speed of the rack shaft 24 attenuates. By controlling the motor 40 to reduce the speed, the impact sound caused by the collision between the rack shaft 24 and the ball screw nut 52 is suppressed.

This principle will be described with reference to FIGS. 5 and 8E.
8E shows the displacement of the rack shaft 24. In FIG. 8E, the plus side of the sine wave shows the displacement amount of the rack shaft 24 to the right side, and the minus side shows the displacement amount of the left side. Yes. FIG. 8E can correspond to FIG. 10A described above. FIG. 5A shows a state in which the rack shaft 24 shown in FIG. 5F has started to be displaced leftward from the rightmost position (point in FIG. 8E). Equivalent to PA). In the figure, the alternate long and short dash line C represents the position of zero displacement. The ball 54 comes into contact with the side wall of the ball screw groove 24b of the rack shaft 24, the ball 54 presses the side wall of the ball screw groove 52a of the ball screw nut 52, and the ball screw nut 52 rotates clockwise as viewed from the left side in FIG. And displaced to the left of the axis. FIG. 5B shows a state in which the rack shaft 24 has passed the amplitude center C (zero displacement {corresponding to the timing t1 in FIG. 8E)) (at a point PB in FIG. 8E). Equivalent). Here, the displacement speed of the rack shaft 24 in the left direction is attenuated by mechanical resistance. On the other hand, since the ball screw nut 52 is not greatly decelerated due to inertia, the rotational speed is reduced (biased counterclockwise) by the motor 40 when it passes through the center of amplitude (zero displacement) C. Thereby, the side wall of the ball screw groove 52a of the ball screw nut 52 does not collide with the side wall of the ball screw groove 24b of the rack shaft 24 via the ball 54, and no impact sound is generated. FIG. 5C shows a state in which the rack shaft 24 has reached the left end (corresponding to the point PC in FIG. 8E). Here, the rack shaft 24 gently stops at the left end position shown in FIG. 5C while the displacement speed in the left direction is attenuated by mechanical resistance. On the other hand, the ball screw nut 52 gently stops rotating similarly to the rack shaft 24.

  FIG. 5 (D) shows a state in which the rack shaft 24 shown in FIG. 5 (C) has started to be displaced in the right direction from the leftmost position (point in FIG. 8 (E)). Equivalent to PD). In the figure, the alternate long and short dash line C represents the position of zero displacement. The ball 54 comes into contact with the side wall of the ball screw groove 24b of the rack shaft 24, the ball 54 presses the side wall of the ball screw groove 52a of the ball screw nut 52, and the ball screw nut 52 is counterclockwise as viewed from the left side in FIG. It is rotated and displaced to the right of the axis. FIG. 5E shows a state where the rack shaft 24 has passed the amplitude center C (zero displacement {corresponding to the timing t2 in FIG. 8E)) (at the point PE in FIG. 8E). Equivalent). Here, the rack shaft 24 is attenuated in the rightward displacement speed due to mechanical resistance. On the other hand, since the ball screw nut 52 is not greatly decelerated due to inertia, when it passes through the center of amplitude (zero displacement) C, the rotational speed in the counterclockwise direction is reduced by the motor 40 (biased in the clockwise direction). ) Thereby, the side wall of the ball screw groove 52a of the ball screw nut 52 does not collide with the side wall of the ball screw groove 24b of the rack shaft 24 via the ball 54, and no impact sound is generated. FIG. 5F shows a state in which the rack shaft 24 has reached the right end (corresponding to the point PF in FIG. 8E). Here, the rack shaft 24 gently stops at the right end position shown in FIG. 5F while the displacement speed in the right direction is attenuated by mechanical resistance. Similarly, the ball screw nut 52 gently stops rotating when the steering is not performed.

Next, the impact sound reduction process for reducing the impact sound described above will be described with reference to the flowchart of FIG.
The ECU 60 of the electric power steering apparatus shown in FIG. 4 detects the rotation of the ball screw nut 52 simultaneously with the rotation angle of the motor 40 based on a signal from the motor resolver 44. First, the frequency of the impact sound generation condition is extracted from the amplitude of the rotation angle (S12). Here, 15 to 25 Hz of the amplitude of the rotation angle is extracted using a bandpass filter. The extracted waveform is shown in FIG. In FIG. 8A, as in FIG. 8E described above, the plus side of the sine wave indicates the amount of displacement to the right side, and the minus side indicates the amount of displacement of the left side. It is determined whether the extracted frequency is a frequency (for example, 17 Hz to 22 Hz) of an impact sound generation condition. Here, the frequency of the impact sound generation condition means, for example, the vibration period of the rack shaft 24 that generates an impact sound while traveling on a cobblestone road at a specific speed (40 to 60 Km / h), and is gradually changed depending on the vehicle. Will be different.

  If the frequency is not the impact sound generation condition (S14: No), the motor current proportional to the steering torque detected by the first resolver 35 and the second resolver 37 is calculated (S24), and the motor current is output. Then, steering is assisted (S22).

  On the other hand, when the frequency of the impact sound generation condition, that is, the period of the amplitude of the rotation angle is 17 Hz to 22 Hz (S14: Yes), it is the amplitude center of the rack shaft 24, that is, the zero cross shown in FIG. It is determined whether the timing is t1, t2, t3, t4, t5, t6, t7) (S16). When the rack shaft 24 is not centered on the amplitude (S16: No), the process proceeds to S24 described above, and normal steering assist processing is performed.

  On the other hand, at the timing of the amplitude center of the rack shaft 24 (S16: Yes), the motor current is corrected in the brake direction (S18), and the corrected motor current is output (S22). For example, when the rack shaft 24 described above with reference to FIG. 5B is displaced from the right side to the left side, at the timing t1 when the rack shaft 24 passes through the amplitude center (zero displacement) C, FIG. ) The motor 40 is controlled as indicated by the hatched lines in the figure, and the speed of rotation in the clockwise direction due to the inertia of the ball screw nut 52 is reduced (energized in the counterclockwise direction at 1 N for 10 ms). As a result, the ball screw nut 52 is rotated clockwise by the motor 40 so as to correspond to the rack shaft 24 that has passed through zero displacement and gently stopped at the left end position while attenuating the displacement speed in the left direction by mechanical resistance. The rotational speed of the is reduced. For this reason, the side wall of the ball screw groove 52a of the ball screw nut 52 does not collide with the side wall of the ball screw groove 24b of the rack shaft 24 via the ball 54, and no impact sound is generated. In the state where the steering is performed, the motor current is corrected so that the motor generating the assist force is urged counterclockwise at 1 N for 10 ms at the timing described above.

  On the other hand, when the rack shaft 24 described above with reference to FIG. 5 (E) is displaced from the left side to the right side, at the timing t2 when the rack shaft 24 passes through the amplitude center (zero displacement) C, FIG. ) The motor 40 is controlled as indicated by the oblique lines in the figure, and the speed of counterclockwise rotation due to the inertia of the ball screw nut 52 is reduced (energized for 10 ms at 1 N in the clockwise direction). Accordingly, the rotational speed of the ball screw nut 52 in the counterclockwise direction is decreased by the motor 40 in correspondence with the rack shaft 24 in which the displacement speed in the right direction is attenuated by mechanical resistance. For this reason, the side wall of the ball screw groove 52a of the ball screw nut 52 does not collide with the side wall of the ball screw groove 24b of the rack shaft 24 via the ball 54, and no impact sound is generated.

[Second Embodiment]
Continuing, with respect to the electric power steering apparatus according to the second embodiment of the present invention, refer to the flowchart of FIG. 7 showing the control in the electric power steering apparatus and the timing chart of FIG. explain. In addition, since it is the same as that of 1st Embodiment mentioned above with reference to FIGS. 1-4, about the mechanical structure of the electric power steering apparatus of 2nd Embodiment, it abbreviate | omits description with reference to the same figure. To do.
In the first embodiment described above, the excitation of the motor is started when the amplitude center (zero displacement) C is passed. On the other hand, in the second embodiment, the excitation of the motor is started before passing through the amplitude center (zero displacement) C. In the second embodiment, since it is necessary to estimate the timing of the amplitude center (zero displacement) C, the period of the amplitude of the rotation angle is obtained, and the timing of the next amplitude center (zero displacement) C is calculated.

FIG. 7 is a flowchart showing impact sound reduction processing of the electric power steering apparatus according to the second embodiment.
Similarly to the first embodiment, the frequency of the impact sound generation condition is extracted from the motor rotation angle (S12), and it is determined whether the frequency is the impact sound generation condition (S14). Here, in the case of the frequency of the impact sound generation condition (S14: Yes), the timing for executing the brake correction is calculated from the calculated cycle (S15). For example, in FIG. 8B, based on one cycle from time 0 to t2, a timing t3 at which the next zero crossing is performed is calculated, and a timing that is 8 ms earlier than the timing t3 is calculated, for example. Then, it is determined whether the calculated correction timing has been reached (S16). When the correction timing is reached (S16: Yes), the motor current is corrected in the brake direction as in the first embodiment described above (S18, S22). Note that the timing 8 ms earlier than the timing t4 is calculated based on the cycle immediately before the timing t1 to t3.

  In this second embodiment, since the predetermined timing from the time point when the next reciprocal displacement is zero is before the time point when the next reciprocal displacement is zero, there is a time lag until the ball screw nut is energized. Even if there is, the impact sound due to the collision between the rack shaft and the ball screw nut can be properly suppressed.

[Third embodiment]
Subsequently, the impact sound reduction processing in the electric power steering apparatus according to the third embodiment of the present invention will be described with reference to the timing chart of FIG.
In the second embodiment, the timing of the next center of amplitude (zero displacement) C is calculated, and brake correction is started before the zero displacement. On the other hand, in the third embodiment, the timing of the next amplitude center (zero displacement) C is calculated, and the brake correction is started after the displacement is zero. For example, in FIG. 8C, based on one cycle from time 0 to t2, a timing t3 at which the next zero crossing is performed is calculated, and a timing 16 ms later than the timing t3 is calculated, for example. When the correction timing comes, the motor current is corrected in the braking direction.

  In the third embodiment, since the predetermined timing from the estimated zero point of the next reciprocating displacement is after the zero point of the next reciprocating displacement, the ball screw nut is urged in a short time. Thus, it is possible to appropriately suppress the impact sound caused by the collision between the rack shaft and the ball screw nut. Further, the control can be realized using a CPU having a slower processing speed as compared with the first embodiment.

[Fourth embodiment]
Next, the impact sound reduction process in the electric power steering apparatus according to the fourth embodiment of the present invention will be described with reference to the timing chart of FIG.
In the second embodiment, the brake correction is started before the displacement is zero, and in the third embodiment, the brake correction is started after the displacement is zero. In contrast, in the fourth embodiment, the brake correction is continued from before to after the zero displacement. For example, in FIG. 8D, based on one cycle from time 0 to t2, timing t3 for the next zero crossing is calculated, for example, timings 8ms before and 16ms after timing t3. When the correction timing is 8 ms before the timing t3, the correction of the motor current in the brake direction is started and continued for 24 ms (that is, until 16 ms after the timing t3).

  It has been found that the electric power steering apparatus of the fourth embodiment can minimize the impact sound when applied to an actual machine. For this reason, the impact sound reduction process of the fourth embodiment is considered optimal. In the fourth embodiment, the energization by the motor is continued for 16 ms from the estimated zero cross timing. However, it is also preferable that this stop timing is performed 16 ms after the actually detected zero cross timing. In this case, even if the periodicity of the displacement of the rack shaft 24 is low, it can be dealt with suitably.

  In the above-described embodiment, an example in which the configuration of the present invention is applied to the impact sound reduction processing when traveling on a cobblestone road with periodicity is given. Needless to say, the configuration of the present invention can also be applied to the reduction of impact noise.

  In the above-described embodiment, the rack assist type electric power steering apparatus is taken as an example, but the impact noise reduction processing of the present invention is further applied to the column assist type and pinion assist type electric power steering apparatus. The present invention can be applied to a variable gear ratio electric power steering apparatus and a steer-by-wire electric power steering apparatus.

It is a lineblock diagram showing the composition of the electric power steering device concerning a 1st embodiment of the present invention. FIG. 2 is an enlarged view inside an ellipse by a one-dot chain line II shown in FIG. 1. It is an enlarged view in the ellipse by the dashed-dotted line III shown in FIG. It is a block diagram which shows the connection structure of ECU and resolver which control the electric power steering device of 1st Embodiment. It is explanatory drawing which shows the displacement of a rack axis | shaft and a ball screw nut. It is a flowchart which shows the impact sound reduction process performed by CPU shown in FIG. It is a flowchart which shows the impact sound reduction process performed with the electric power steering device of 2nd Embodiment. FIG. 8A is a timing chart showing the timing of brake correction in the first embodiment, and FIG. 8B is a timing chart showing the timing of brake correction in the second embodiment. ) Is a timing chart showing the timing of brake correction in the third embodiment, and FIG. 8D is a timing chart showing the timing of brake correction in the fourth embodiment. FIG. 8E shows the displacement of the rack shaft. It is explanatory drawing which shows the collision sound generation | occurrence | production principle of a rack shaft and a ball screw nut in a prior art. FIG. 10A is a graph showing the displacement (position) between the rack shaft and the ball screw nut on the motor side, and FIG. 10B is a graph showing the speed of the ball screw nut. Is a graph showing the acceleration (energy) of the ball screw nut.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Electric power steering device 21 Steering wheel 22 Steering shaft 23 Pinion shaft 23c Pinion gear 24 Rack shaft 24a Rack groove 30 Torque sensor 31 Torsion bar 35 First resolver 37 Second resolver 40 Motor 44 Motor resolver 50 Ball screw mechanism 52 Ball screw Nut 52a Ball screw groove 54 Ball 60 ECU

Claims (5)

In the electric power steering device that transmits the assist force from the ball screw nut rotated by the motor to the ball screw groove provided on the rack shaft side to the rack shaft of the rack and pinion type steering mechanism,
Detection means for detecting rotation of the ball screw nut due to a reciprocating displacement in a lateral direction with respect to a vehicle traveling direction of the rack shaft;
An electric power steering apparatus comprising: motor control means for controlling the motor in a direction to decrease the rotation speed of the ball screw nut at a predetermined timing from the time when the reciprocal displacement is zero. In the electric power steering device that transmits the assist force from the ball screw nut rotated by the motor to the ball screw groove provided on the rack shaft side to the rack shaft of the rack and pinion type steering mechanism,
Detection means for detecting rotation of the ball screw nut due to a reciprocating displacement in a lateral direction with respect to a vehicle traveling direction of the rack shaft;
Frequency judging means for judging whether the frequency of the reciprocating displacement is within a specific range;
Motor control means for controlling the motor in a direction to decrease the rotation speed of the ball screw nut at a predetermined timing from the time when the reciprocation displacement is zero when the frequency judgment means judges that the specific range is reached. An electric power steering apparatus comprising: In the electric power steering device that transmits the assist force from the ball screw nut rotated by the motor to the ball screw groove provided on the rack shaft side to the rack shaft of the rack and pinion type steering mechanism,
Detection means for detecting rotation of the ball screw nut due to a reciprocating displacement in a lateral direction with respect to a vehicle traveling direction of the rack shaft;
Motor control means for calculating the frequency of the reciprocating displacement and controlling the motor in a direction to decrease the rotational speed of the ball screw nut at a predetermined timing from the time point when the displacement of the next reciprocating displacement estimated from the calculated frequency is zero. An electric power steering apparatus comprising: 4. The electric power steering apparatus according to claim 3 , wherein the predetermined timing from the time point when the estimated next reciprocal displacement is zero is before the time point when the next reciprocal displacement is zero. 4. The electric power steering apparatus according to claim 3 , wherein the predetermined timing from the time point when the estimated next reciprocating displacement is zero is after the time point when the next reciprocating displacement is zero.

Images