JP5959981B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus and the like, and relates to a technique capable of suppressing abnormalities such as vibrations and abnormal noises that can occur in the shaft of a reduction gear of the electric power steering apparatus.

  A vehicle such as an automobile can be provided with an electric power steering device, and the electric power steering device assists a steering torque in a steering system (steering system) generated by an operation by a driver on a steering handle (steering handle). Auxiliary torque (assist torque) is generated by an electric motor (electric motor). Due to the generation of the assist torque, the electric power steering device can assist the driver's steering and reduce the burden on the driver.

  For example, FIG. 1 of Patent Document 1 discloses an electric power steering apparatus 100, and according to FIG. 2 of Patent Document 1, a DUTY (DUTYU, DUTYV, DUTYW) signal for driving the electric motor 11 at a predetermined duty ratio is controlled. In accordance with at least the torque signal T, the control device 200 sets a base signal DT that serves as a reference for the target signal IM of the output torque TM of the electric motor 11 in the base signal calculation unit 220. Further, the control device 200 of FIG. 2 of Patent Document 1 uses a damper compensation signal calculation unit that generates a damper compensation signal (damper correction signal) for compensating the viscosity of the steering system and correcting the base signal DT according to at least the angular velocity signal ω. 225 can be set. Here, the damper compensation signal is subtracted from the base signal DT, and the base signal DT decreases.

  Further, the control device 200 of FIG. 2 of Patent Document 1 compensates for an inertia compensation signal (inertia correction signal) that compensates for the influence of the inertia of the steering system and corrects the base signal DT according to at least the torque signal T. It can be set by the calculation unit 210. Here, the inertia compensation signal is added to the base signal DT, and the base signal DT increases.

  For example, FIG. 1 of Patent Document 2 also discloses an electric power steering device. According to FIG. 2 of Patent Document 2, a current control signal (output current signal) of a drive circuit 19 that drives the electric motor 9 with a predetermined duty ratio. The steering control unit 17 sets the auxiliary steering torque (assist torque) that serves as a reference for the target current of the electric motor 9 by the auxiliary steering torque determination means 17a according to at least the output of the torque sensor 12. . Further, the auxiliary steering torque determination means 17a of the steering control unit 17 in FIG. 2 of Patent Document 2 is operated according to at least the output of the steering angular velocity sensor 11 as in Patent Document 1 described above or Patent Document 3 described later, for example. A damper correction signal for correcting the auxiliary steering torque by compensating for the viscosity of the system can be set.

  Furthermore, the auxiliary reaction force torque determining means 17b of the steering control unit 17 of FIG. 2 of Patent Document 2 can set the auxiliary reaction force torque T2 that cancels disturbances such as cross winds at least according to the output of the yaw rate sensor 15. . According to FIG. 6 of Patent Document 2, the auxiliary reaction force torque determining means 17b sets the auxiliary reaction force torque T1 for correcting the auxiliary reaction force torque T2 according to at least the output (steering angular velocity ω) of the steering angular velocity sensor 11. can do.

  For example, FIG. 1 of Patent Document 3 also discloses an electric power steering device. According to FIGS. 4 to 7 of Patent Document 3, the motor control signal Do of the motor driving means 16 that drives the motor 10 with the motor driving signal Mo is used. The control means 15, 22, 27, 30 are set by the control means 15, 22, 27, 30. Set with. Further, the control means 15, 22, 27, and 30 of FIG. 4 to FIG. 7 of Patent Document 3 compensate for the viscosity of the steering system and correct the torque control amount DT according to at least the absolute value of the steering rotational speed signal N. The rotational speed control signal DN (damper correction signal) can be set by the rotational speed control amount converter 18. Here, the rotational speed control signal DN is subtracted from the torque control amount DT in the forward state of the steering system, and the torque control amount DT decreases.

JP2011-136696A Japanese Patent No. 3103049 Japanese Patent No. 2825176

  When the inventors made repeated trial manufactures of the electric power steering apparatus, abnormalities such as vibration and abnormal noise occurred in the electric power steering apparatus. As a result of investigating the cause of this abnormality, we recognized the problem that abnormalities such as vibration and abnormal noise occur in the shaft of the prototype reduction gear.

  FIG. 1A shows a frequency characteristic of an evaluation function (a gain characteristic of a transfer function) in an electric power steering apparatus including a prototype reduction gear. Here, the inventors set the transfer function G (s) from the steering torque TH (s) to the angular speed ωWG (s) of the prototype speed reducer as the evaluation function Ev as shown in the following Expression 1. did.

  Ev = G (s) = ωWG (s) / TH (s) Equation 1

  TH means the steering torque at the steering handle and can also be expressed as TH (t), which is a function of time t. TH (s), which is a function of the Laplace variable s in Equation 1, can be obtained by Laplace transforming TH or TH (t). ωWG means the angular velocity of the speed reducer shaft that is a differential (= d (θWG) / dt) of the rotational angle θWG of the speed reducer shaft, and can also be expressed as ωWG (t) as a function of time t. ΩWG (s), which is a function of the Laplace variable s in Equation 1, can be obtained by performing Laplace transform on ωWG or ωWG (t).

When the Laplace variable s is represented by the product of the imaginary number i and the angular velocity ω, the gain [dB] on the vertical axis in FIG. 1A is 20 Log ₁₀ | G (s) | = 20 Log ₁₀ | G (i · ω) | The frequency f [Hz] on the horizontal axis in FIG. 1 (A) is ω / 2π.

  In the example of FIG. 1A, Comparative Example 1 is indicated by a one-dot chain line. The maximum value in Comparative Example 1 in which the frequency f is around 40 [Hz] means that abnormalities such as vibration and abnormal noise occur in Comparative Example 1. In the example of FIG. 1A, Comparative Example 2 is indicated by a two-dot chain line. The maximum value in Comparative Example 2 where the frequency f is around 40 [Hz] is the magnitude of a damper correction signal (or viscosity coefficient CM at the shaft of the motor described later) for correcting the auxiliary torque (base signal) in Comparative Example 2. This means that in the electric power steering apparatus that increases the depth (contribution), the occurrence of abnormalities such as vibration and abnormal noise is suppressed.

  However, in the example of FIG. 1A, the maximum value in the comparative example 2 in which the frequency f is around 1 [Hz] is significantly smaller than the maximum value in the comparative example 1 in which the frequency f is around 1 [Hz]. doing. In other words, the maximum value in the comparative example 1 in which the frequency f is around 1 [Hz] means that smooth steering is performed in the comparative example 1, while the comparison in which the frequency f is around 1 [Hz]. The maximum value in Example 2 means that smooth steering is not executed in Comparative Example 2. This indicates that the steering feeling is deteriorated when steering is normally performed at about 1 [Hz]. FIG. 1B shows an example of a temporal change in the steering torque TH, which is steering at 1 [Hz].

  FIG. 2A shows a model of the electric power steering apparatus necessary for deriving the evaluation function of FIG. 1A, and FIG. 2B shows deceleration when the model of FIG. 2A is simplified. Indicates the resonance frequency of the machine shaft.

  In the example of FIG. 2A, TH, θH, and JH mean steering torque (input torque), steering angle, and moment of inertia at the steering handle, respectively. CC means the viscosity coefficient at the input shaft. K1 means torsional rigidity at the input shaft. KC and KTS mean the torsional rigidity at the steering column and the torsional rigidity at the torque sensor, respectively. Tdet, Tp, and θp mean steering torque (detected torque), composite torque, and rotation angle at the input shaft, respectively. nM means the reduction ratio of the reduction gear. KWG, θWG, and ωWG mean torsional rigidity, rotation angle, and angular velocity at the shaft of the speed reducer. TM, JM, and CM mean auxiliary torque, moment of inertia, and viscosity coefficient at the shaft of the motor, respectively. nG and KW mean the reduction ratio and torsional rigidity in the reduction mechanism. CW, TW, θW and JW mean the viscosity coefficient, composite torque, rotation angle (turning angle of steered wheels) and moment of inertia at the output shaft, respectively.

  As a result of analyzing the model shown in FIG. 2A while paying attention to the resonance frequency fWGR of the shaft of the speed reducer when the electric power steering device is operated and auxiliary torque is generated in the motor, the present inventors It was recognized that the model shown in FIG. 2 (A) can be simplified to the model shown in FIG. 2 (B). The resonance frequency fWGR of the shaft of the speed reducer can be obtained as shown in Equation 2 below.

fWGR = (1 / 2π) · [(nM ² · KWG) · {(JH) + (nM ² · JM)} / {(JH) · (nM ² · JM)}] ^0.5 Equation 2

  When various parameters in the prototype electric power steering apparatus are substituted into Equation 2, the resonance frequency fWGR of the shaft of the speed reducer is approximately 40 [Hz]. This value substantially coincides with the frequency f corresponding to the second maximum value shown in FIG. 1 (A), and the second maximum value shown in FIG. 1 (A) becomes the resonance frequency fWGR of the speed reducer shaft. I can understand that it is caused.

  In the example of FIG. 2A, the equation of motion such as the rotational motion in the electric power steering apparatus can be obtained as the following Equations 3 to 7.

TH = JH · {d ² (θH) / dt ² } + CC · {d (θH) / dt} + K1 · (θH−θP) Equation 3

TW = (JW / nG ² ) · {d ² (θP) / dt ² } + (CW / nG ² ) · {d (θH) / dt} + K1 · (θP−θH) + nM ² · KWG {θP− ( θWG / nM)} Equation 4

TM = JM · {d ² (θWG) / dt ² } + CM · {d (θWG) / dt} + KWG · {θWG− (nM · θP)} Equation 5

  Tdet = K1 · (θH−θP) Equation 6

TW = −KW · θW = −KW · (θP / nG ² ) (7)

  The transfer function G (s) of the above-described expression 1 can be obtained by performing Laplace transform on the expressions 3 to 7.

  In the example of FIG. 2A, the auxiliary torque TM at the motor shaft can be obtained from the detected torque Tdet at the input shaft by the assist control of the electric power steering device. The detected torque Tdet is amplified to the amplified detected torque TB by the amplifier, and the detected torque TB is converted to the auxiliary torque TM by the electric motor controller. At this time, the motor control unit can take into account, for example, the rotation angle θWG and the angular velocity ωWG on the shaft of the speed reducer.

  One object of the present invention is an electric power steering capable of suppressing abnormalities such as vibration and abnormal noise that can occur in the shaft of a reduction gear provided between a steering system and an electric motor while maintaining a good steering feeling. Is to provide a device. Other objects of the present invention will become apparent to those skilled in the art by referring to the aspects and preferred embodiments exemplified below and the accompanying drawings.

  In the following, in order to easily understand the outline of the present invention, embodiments according to the present invention will be exemplified.

According to a first aspect of the present invention, there is provided an electric motor that applies an auxiliary torque to the steering system via a reduction gear;
A base signal calculation unit that calculates a base signal serving as a reference for the target signal of the auxiliary torque according to at least the steering torque of the steering system;
A correction signal calculation unit that calculates a correction signal for correcting the auxiliary torque according to at least the rotation speed of the steering system or the shaft of the speed reducer;
With
The correction signal calculation unit includes a frequency shaping unit that suppresses a low frequency component of the rotation speed, corrects the auxiliary torque with a high frequency component of the rotation speed ,
The frequency shaping unit has a low-pass filter that extracts the low-frequency component, and generates the high-frequency component by subtracting the low-frequency component from the rotation speed. .

Even when giving the driver a good steering feeling based on the base signal, the auxiliary torque is a reduction gear that causes abnormalities such as vibration and abnormal noise that can occur in the shaft of the reduction gear. The resonance frequency component of the axis may be included. In general, since the steering feeling is determined in a frequency region of, for example, 10 [Hz] or less, from a predetermined value of the rotational speed (for example, the rotational speed frequency 10 [Hz] corresponding to the steering frequency 10 [Hz]). In addition, by correcting the auxiliary torque with a high-frequency component, the resonance frequency component of the speed reducer shaft included in the base signal or the auxiliary torque can be suppressed while maintaining the steering feeling. The upper limit of the frequency when the driver steers the steering handle is about 10 [Hz]. In other words, the driver steers the steering handle at a steering frequency higher than 10 [Hz]. Can not do it. Accordingly, it is preferable to correct the auxiliary torque with a high-frequency component having a rotational speed higher than the rotational speed frequency 10 [Hz] corresponding to, for example, 10 [Hz], which is the upper limit of the driver's steering frequency.
The frequency shaping unit includes a low-pass filter that extracts a low-frequency component, and generates a high-frequency component by subtracting the low-frequency component from the rotation speed. That is, a low-pass filter can be used when extracting a high-frequency component of the rotational speed from the rotational speed. In other words, for example, when a high frequency component is extracted using only a high-pass filter, noise can be amplified in the high-frequency component. Therefore, the high-frequency component can be stabilized by using a low-pass filter.

  In the first aspect, the frequency shaping unit may generate the correction signal by multiplying the high frequency component and the absolute value of the rotation speed.

  When extracting a high-frequency component of the rotational speed from the rotational speed, the high-frequency component of the rotational speed is accompanied by a phase change. On the other hand, the absolute value of the rotational speed is not accompanied by a phase change. By multiplying the high-frequency component of the rotational speed and the absolute value of the rotational speed to generate the correction signal, it is possible to reduce the phase change when extracting the high-frequency component. Since the auxiliary torque is generated by such a correction signal, the correction signal can stabilize the auxiliary torque with respect to the input rotational speed.

In the first aspect, the electric power steering device includes:
A damper correction signal calculation unit that calculates a damper correction signal for correcting the base signal according to at least the rotation speed may be further provided.
The auxiliary torque may be corrected by both the high-frequency component of the correction signal and the damper correction signal.

  The damper correction signal can compensate for the viscosity of the steering system, and the high frequency component of the correction signal is independent of the damper correction signal. Therefore, by independently adjusting the high frequency component of the correction signal, the resonance frequency component of the shaft of the reduction gear included in the base signal or the auxiliary torque can be further suppressed.

In the first aspect, in the gain characteristic of the transfer function from the steering torque at the steering handle to the rotational speed of the speed reducer shaft, the maximum value corresponding to the speed reduction ratio of the speed reducer is 10 [Hz]. May exist in a higher frequency range,
The high frequency component may reduce the local maximum value.

  From the steering torque at the steering handle instead of the overall transfer function from the steering torque at the steering handle to the rotation angle at the output shaft (turning angle of the steered wheels) via the speed of the speed reducer shaft By analyzing the transfer function up to the rotational speed of the shaft of the speed reducer, the maximum value on the gain characteristic corresponding to the resonance frequency of the speed reducer shaft can be found. By reducing the maximum value due to the high-frequency component of the correction signal, it is possible to suppress abnormalities such as vibration and abnormal noise that may occur in the shaft of the speed reducer.

In the first aspect, the rotational speed of the steering system or the shaft of the speed reducer may be an angular speed of the shaft of the speed reducer.

  Those skilled in the art will readily understand that the illustrated embodiments according to the present invention can be further modified without departing from the spirit of the present invention.

FIG. 1A shows a frequency characteristic of an evaluation function (a gain characteristic of a transfer function from a steering torque at a steering handle to a rotational speed of a speed reducer shaft) in an electric power steering apparatus including a prototype reduction gear. FIG. 1B shows an example of the time change of the steering torque, which is steering at 1 [Hz]. FIG. 2A shows a model of the electric power steering apparatus necessary for deriving the evaluation function of FIG. 1A, and FIG. 2B shows deceleration when the model of FIG. 2A is simplified. Indicates the resonance frequency of the machine shaft. The specific structural example of the electric power steering apparatus according to this invention is shown. An example of the relationship between the steering torque and the vehicle speed signal and the target signal is shown. FIG. 5A shows a configuration example of the braking signal calculation unit, and FIG. 5B shows an improvement example of the braking signal calculation unit of FIG. FIGS. 6A, 6B, and 6C show the waveforms of the braking signal in FIG. 5B when the angular velocity component of the angular velocity signal (ωWG = 25 [rad / sec]) is changed. A display example is shown. FIGS. 7A, 7B, and 7C show the waveforms of the braking signal in FIG. 5B when the angular velocity component of the angular velocity signal (ωWG = 57 [rad / sec]) is changed. Another display example is shown. The example of a specific structure of the control apparatus of FIG. 3 is shown. 9A shows an example of the relationship between the detected torque amplification signal and the vehicle speed signal and the base signal, and FIG. 9B shows an example of the relationship between the angular velocity and the vehicle speed signal and the damper compensation signal. . The frequency characteristic of the evaluation function in the electric power steering device according to the present invention is shown.

  The preferred embodiments described below are used to facilitate an understanding of the present invention. Accordingly, those skilled in the art should note that the present invention is not unduly limited by the embodiments described below.

  FIG. 3 shows a specific configuration example of the electric power steering apparatus according to the present invention. The present invention is not limited to the example of FIG. 3, and an electric power steering apparatus according to the present invention can be configured with a schematic configuration example. In other words, the present invention need not comprise all of the components shown in the example of FIG.

  In the example of FIG. 3, the electric power steering device 100 includes, as a schematic configuration example, an electric motor 11 that applies an auxiliary torque TM to the steering system (for example, the pinion shaft 5) via the speed reducers 12 and 13, and an electric motor current of the electric motor 11. Motor control units 200 and 60 for controlling I. As will be described later with reference to FIGS. 5 and 8, the electric power steering device 100 or the control device 200 includes a base signal calculation unit 220 and a correction signal calculation unit as the motor control units 200 and 60. The base signal calculation unit 220 calculates a base signal DT that serves as a reference for the target signal IM of the auxiliary torque TM in accordance with at least the steering torque (for example, the detected torque TB) of the steering system. In addition, the correction signal calculation unit (for example, the braking signal calculation unit 226), according to at least the rotation speed of the steering system or the shaft of the speed reducer (the angular speed ωWG that is a differential of the rotation angle θWG of the speed reducers 12 and 13), A correction signal (for example, a braking signal IBRK) for correcting the auxiliary torque TM is calculated.

  Even when assisting the driver with assist torque TM based on the base signal DT, the assist torque TM causes abnormalities such as vibrations and abnormal noises that can occur in the shafts of the speed reducers 12 and 13. The resonance frequency component of the shaft of the reduction gear may be included (see the maximum value in Comparative Examples 1 and 2 where the frequency f in FIG. 1A is around 40 [Hz]). In general, since the steering feeling is determined in a frequency region of, for example, 10 [Hz] or less, from a predetermined value of the rotational speed (for example, the rotational speed frequency 10 [Hz] corresponding to the steering frequency 10 [Hz]). In addition, by correcting the auxiliary torque TM with a high-frequency component, it is possible to suppress the resonance generated in the shafts of the speed reducers 12 and 13 while maintaining the steering feeling. Note that the upper limit of the frequency when the driver steers the steering handle 2 is about 10 [Hz]. In other words, the driver usually operates at a steering frequency higher than 10 [Hz]. Can not steer. Accordingly, it is preferable to correct the auxiliary torque with a high-frequency component having a rotational speed higher than the rotational speed frequency 10 [Hz] corresponding to, for example, 10 [Hz], which is the upper limit of the driver's steering frequency.

  In the example of FIG. 3, the electric power steering apparatus 100 can include components other than the schematic configuration example as follows. A main steering shaft 3 provided with a steering handle 2 (for example, a steering wheel), a shaft 1 and a pinion shaft 5 are connected by two universal joints (universal joints) 4, 4. The pinion gear 7 provided at the lower end meshes with the rack teeth 8a of the rack shaft 8 that can reciprocate in the vehicle width direction, and the left and right steered wheels 10 are connected to both ends of the rack shaft 8 via tie rods 9 and 9, respectively. , 10 (for example, front wheels) are connected. With this configuration, the electric power steering apparatus 100 can change the traveling direction of the vehicle when the steering handle 2 is steered. Here, the rack shaft 8, the rack teeth 8a, and the tie rods 9 and 9 constitute a turning mechanism. The pinion shaft 5 is supported by the steering gear box 20 through the bearings 6a, 6b, and 6c at its lower, middle, and upper portions.

  A worm gear 12 provided on the output shaft of the electric motor 11 is engaged with a worm wheel gear 13 provided on the pinion shaft 5. In the example of FIG. 3, the speed reducers 12 and 13 are constituted by a worm gear 12 and a worm wheel gear 13, but may be constituted by a ball screw mechanism as shown in FIG. The shafts of the speed reducers 12 and 13 are, for example, the output shaft of the electric motor 11 or the shaft of the worm gear 12, the screw shaft of the ball screw mechanism, and the like. In general, when the “worm gear” itself is called a speed reducer, the “worm gear” is composed of a “worm” and a “worm wheel”. In this specification (and claims), The worm gear 12 means a part of the components of the speed reducers 12 and 13 and means a general “worm” gear.

  The steering system (steering system) includes the pinion shaft 5, the rack shaft 8, the rack teeth 8a, the tie rods 9 and 9 and the like and reaches the steered wheels 10 and 10 from the steering handle 2, and an auxiliary torque mechanism (assist torque mechanism) is provided. Does not include. The auxiliary torque mechanism that gives the auxiliary torque TM to the steering system includes the speed reducers 12 and 13, the electric motor 11, the torque sensor 30, the control device 200, and the like. The auxiliary torque mechanism steers the steering handle 2 to steer the steering system. For example, a steering torque (detected torque Tdet) generated in the pinion shaft 5 (input shaft) is detected by a torque detector such as the torque sensor 30 and this detection signal is amplified by an amplifier such as the differential amplifier circuit 40. Based on the amplified signal TB, the control device 200 generates a base signal DT, and on the basis of the base signal DT, an auxiliary torque TM corresponding to the steering torque TH and the detected torque Tdet is generated by the electric motor 11, via the speed reducers 12 and 13. The auxiliary torque TM is transmitted to the pinion shaft 5.

  The electric power steering apparatus 100 can be classified into a pinion assist type, a rack assist type, a column assist type, and the like, depending on the location where the auxiliary torque TM is applied to the steering system. Although the electric power steering device 100 of FIG. 3 shows a pinion assist type, the electric power steering device 100 may be applied to a rack assist type, a column assist type, or the like.

  The auxiliary torque TM is added to, for example, the steering torque TH or the detected torque Tdet on the pinion shaft 5 to generate a composite torque TP. The composite torque TP (combination of the steering torque TH (or Tdet) and the auxiliary torque TM) is transmitted from the pinion shaft 5 to the speed reduction mechanism such as the pinion gear 7, the rack teeth 8a, the tie rods 9 and 9, and the steering handle 2 The steered wheels 10 and 10 are steered by the steering torque TH or the reversing torque TP at the pinion shaft 5, and the turning angle of the steered wheels 10 and 10 changes.

  Preferably, the vehicle speed V is detected by the vehicle speed sensor 35, and the vehicle speed signal VS from the vehicle speed sensor 35 is input to the control device 200 or the base signal calculation unit 220, and serves as a reference for the target signal IM of the auxiliary torque TM. The signal DT is calculated in accordance with, for example, both TB and the vehicle speed V (or the vehicle speed signal VS) that are amplification signals of the detected torque.

  FIG. 4 shows an example of a base map that can determine the target signal IM based on the relationship between the steering torque TH and the vehicle speed signal VS and the target signal IM, that is, both the steering torque TH and the vehicle speed signal VS. In the example of FIG. 4, for example, six curves are shown, and each of the six curves corresponds to the vehicle speed V. When the vehicle speed V indicates 0 [km / h] and the vehicle is stopped, the target signal IM or the motor current is maximum for the same steering torque TH, while the vehicle speed V is the maximum vehicle speed [km / h]. , The target signal IM or the motor current is minimum for the same steering torque TH. By reducing the target signal IM when the vehicle speed signal VS is large, the auxiliary torque TM is reduced in the high speed region, and rapid steering can be suppressed. The maximum vehicle speed depends on vehicle characteristics such as the weight and size of the vehicle, and can be set according to the type of vehicle. The maximum vehicle speed that the vehicle can actually drive may be set in the base map. It may be the maximum vehicle speed.

  In the example of FIG. 4, the base map includes, for example, six curves. However, the number of curves included in the base map may be two, three to five, or seven or more. Good. Furthermore, the curve included in the base map may be changed to one or a plurality of straight lines, for example, and the base map only needs to have characteristics determined for each vehicle speed V. In the example of FIG. 4, the base map may describe, for example, the relationship between the detection torque amplification signal TB and the vehicle speed signal VS and the target signal IM. The control device 200 in FIG. 3 can determine the target signal IM by referring to both the detection torque amplification signal TB and the vehicle speed signal VS in the base map. Specifically, the target signal IM may be calculated or determined by expressing the characteristic as shown in FIG. 4 by a mathematical expression, and substituting the detected torque amplification signal TB and the vehicle speed signal VS into the mathematical expression, or The characteristics as shown in FIG. 4 may be represented by a table, and the target signal IM corresponding to the detected torque amplification signal TB and the vehicle speed signal VS may be extracted or determined from the table.

  The base map shows, for example, the relationship between the steering torque TH (or the detected torque amplification signal TB), the vehicle speed signal VS, and the target signal IM, but instead of the vehicle speed V, a travel parameter that represents the travel state of the vehicle. For example, the base map may be constructed using the engine speed, or the travel parameter such as the vehicle speed V and the engine speed may be omitted, and the base map indicating the relationship between the steering torque TH and the target signal IM, for example. May be constructed.

  The control device 200 or the braking signal calculation unit 226 calculates a correction signal or a braking signal IBRK for correcting the base signal DT or the target signal IM according to the rotational speed of the shafts of the steering system or the speed reducers 12 and 13. In the example of FIG. 3, the electric power steering apparatus 100 includes a rotation speed detection unit such as a resolver 50, and the resolver 50 detects the motor rotation angle θm of the motor 11. The electric motor 11 is, for example, a three-phase brushless motor, and the rotation angle (electric motor rotation angle θm) of the rotor of the three-phase brushless motor coincides with the rotation angle of the worm gear 12. The rotation angle signal θWG of the worm gear 12 that coincides with the motor rotation angle θm is input to the control device 200 or the braking signal calculation unit 226, the rotation angle signal θWG is differentiated, and the correction signal or the braking signal IBRK is, for example, the worm gear 12 Is calculated according to the angular velocity signal ωWG.

  The angular velocity signal ωWG of the worm gear 12 is an example of the rotational speed of the shafts of the speed reducers 12 and 13, and the braking signal IBRK may be calculated, for example, according to the rotational speed signal of the worm gear 12, or the braking signal IBRK May be calculated according to, for example, a rotation speed signal of the pinion shaft 5 which is an example of the rotational speed of the shaft of the steering system.

  The motor driving means 60 includes a plurality of switching elements such as a three-phase FET bridge circuit, for example, and generates, for example, a sine wave voltage using a DUTY (DUTYU, DUTYV, DUTYW) signal from the control device 200, 11 is driven. The motor driving means 60 has a function of detecting a three-phase motor current I (IU, IV, IW) using, for example, a hall element (not shown). For example, the control device 200 can set the DUTY signal so that the motor current I detected by the motor driving means 60 matches the target signal IM.

  FIG. 5A shows a configuration example of the braking signal calculation unit 226, and FIG. 5B shows an improvement example of the braking signal calculation unit 226 of FIG. In the example of FIG. 5A, the braking signal calculation unit 226 or the correction signal calculation unit calculates the braking signal IBRK or the correction signal according to the angular velocity signal ωWG of the worm gear 12, for example, and the low frequency component of the angular velocity signal ωWG. The frequency shaping part which suppresses is provided. When the angular velocity signal ωWG includes a low frequency component equal to or lower than a predetermined value (for example, the frequency 10 [Hz] of the angular velocity signal ωWG corresponding to the steering frequency 10 [Hz]) and a high frequency component higher than the predetermined value, The braking signal IBRK to be output mainly has a high frequency component of the angular velocity signal ωWG. The frequency shaping unit includes a low-pass filter LPF that extracts a low-frequency component from the angular velocity signal ωWG, and subtracts the low-frequency component from the angular velocity signal ωWG to output a signal HPF. When the angular velocity signal ωWG includes a low-frequency component and a high-frequency component, the signal HPF output from the frequency shaping unit includes only high-frequency components other than the low-frequency component, and the frequency shaping unit illustrated in FIG. Corresponds to a high-pass filter.

  The low-pass filter LPF can be expressed by, for example, a first-order low-pass filter type transfer function as shown in the following Expression 8, and the frequency shaping unit is also used as a first-order high-pass filter type transfer function as shown in the following Expression 9, for example. Can be expressed as τ is a time constant.

  Transfer function of low-pass filter LPF = 1 / (1 + τ · s) Expression 8

  Transfer function of frequency shaping unit in FIG. 5A = 1− {1 / (1 + τ · s)} = {τ · s / (1 + τ · s)} Equation 9

  In the example of FIG. 5A, the braking signal calculation unit 226 multiplies {τ · s / (1 + τ · s)} · ωWG, which is the signal HPF output from the frequency shaping unit, by the coefficient KBRK, and sets the limiter. The braking signal IBRK can be generated via It is preferable to adjust or set the time constant τ that defines the transfer function and the coefficient KBRK that defines the gain of the signal HPF so that the resonance frequency component of the worm gear 12 included in the base signal DT or the auxiliary torque TM can be sufficiently suppressed. . Further, it is preferable to install a limiter for limiting the upper limit and the lower limit of the braking signal IBRK so that the motor current I does not exceed the maximum current value that can be passed through the motor 11.

  In the example of FIG. 5B, the frequency shaping unit of the braking signal calculation unit 226 can have a coefficient KBRK ′ for setting the gain of the signal HPF corresponding to the signal output from the high-pass filter, and further, KBRK ′. The absolute value of {τ · s / (1 + τ · s)} · θWG and, for example, the angular velocity signal ωWG of the worm gear 12 can be acquired. The frequency shaping unit includes a multiplier and can calculate the braking signal IBRK before passing through the limiter as shown in Equation 10 below.

  The braking signal IBRK = KBRK ′ · {τ · s / (1 + τ · s)} · ωWG · | ωWG |

  6 (A), 6 (B) and 6 (C) show the waveform of the braking signal IBRK in FIG. 5 (B) when the angular velocity signal ωWG is a sine wave and the frequency of the sine wave is changed. A display example is shown. The frequency of the sine wave in FIGS. 6A, 6B, and 6C is 50 [Hz], 10 [Hz], and 1 [Hz], respectively, and the maximum angular velocity of the angular velocity signal ωWG. (Amplitude) is 25 [rad / sec] (= 2π · 4 [rad / sec]).

  In FIG. 6A, FIG. 6B, and FIG. 6C, the symbol ωWG represents the angular velocity signal ωWG that is a sine wave, and the waveform of the angular velocity signal ωWG is represented by a one-dot chain line. In the example of FIG. 6A, the angular velocity signal ωWG that is a sine wave has, for example, a maximum angular velocity of 25 [rad / sec] as an amplitude, and the amplitude changes or vibrates at 50 [Hz]. In the example of FIG. 6B, the angular velocity signal ωWG that is a sine wave has, for example, a maximum angular velocity of 25 [rad / sec] as an amplitude, and the amplitude changes or vibrates at 10 [Hz]. In the example of FIG. 6C, the angular velocity signal ωWG that is a sine wave has, for example, a maximum angular velocity of 25 [rad / sec] as an amplitude, and the amplitude changes or vibrates at 1 [Hz].

  6A, 6B, and 6C, the symbol HPF indicates the signal HPF input to the coefficient KBRK ′ shown in FIG. 5B, and is shown in FIG. 5A. This corresponds to the signal HPF output from the frequency shaping unit. The waveform of the signal HPF is represented by a two-dot chain line. 6 (A), 6 (B), and 6 (C), symbol IBRK indicates the braking signal IBRK output from the braking signal calculation unit 226 shown in FIG. 5 (B), and the braking signal IBRK The waveform is represented by a solid line.

  Thus, the amplitude of the braking signal IBRK (solid line) is small on the side of FIG. 6C or the low frequency side, while the amplitude of the braking signal IBRK (solid line) is large on the side of FIG. 6A or the high frequency side. Such a characteristic of the braking signal IBRK is caused by a component of {τ · s / (1 + τ · s)} · ωWG in Equation 10 (a component corresponding to a high-pass filter). The phase of the signal HPF (two-dot chain line) is changed with respect to the angular velocity signal ωWG (one-dot chain line) which is a sine wave, while the braking signal IBRK (solid line) is different from the angular velocity signal ωWG (one-dot chain line). Phase change is reduced. Such a characteristic of the braking signal IBRK results from the | ωWG | component (the absolute value component of the angular velocity) in Equation 10.

  FIGS. 7A, 7B, and 7C show waveforms of the braking signal IBRK in FIG. 5B when the angular velocity signal ωWG is a sine wave and the frequency of the sine wave is changed. Another display example is shown. The frequency of the sine wave in FIGS. 7A, 7B, and 7C is 50 [Hz], 10 [Hz], and 1 [Hz], respectively, and the maximum angular velocity of the angular velocity signal ωWG. (Amplitude) is 57 [rad / sec] (= 2π · 9 [rad / sec]).

  In FIGS. 7A, 7B, and 7C, as in FIGS. 6A to 6C, the reference ωWG, the reference HPF, and the reference IBRK are respectively represented by an alternate long and short dash line, Corresponds to the dotted and solid lines. 7A, 7B, and 7C, the symbol | ωWG | indicates the absolute value signal of the angular velocity signal ωWG, and the waveform of the absolute value signal is represented by a dotted line. When the maximum angular velocity (amplitude) of the angular velocity signal ωWG in FIGS. 7A to 7C increases as compared with FIGS. 6A to 6C, the maximum value of | ωWG | also increases. . In other words, when the maximum angular velocity (amplitude) of the angular velocity signal ωWG increases due to the ωWG · | ωWG | component (square component of angular velocity) in Equation 10, the swing or maximum value of the braking signal IBRK increases.

  FIG. 8 shows a specific configuration example of the control device 200 of FIG. The control device 200 of FIG. 3 is not limited to the example of FIG. 8, and the control device 200 according to the present invention can be configured with a schematic configuration example. In other words, the control device 200 does not have to include all of the components shown in the example of FIG.

  In the example of FIG. 8, the control device 200 includes a base signal calculation unit 220 and a correction signal calculation unit or a braking signal calculation unit 226 as a schematic configuration example. The control device 200 can include components other than the schematic configuration example as follows. The control device 200 preferably further includes a damper correction signal calculation unit. Here, the correction signal calculation unit (for example, the damper compensation signal calculation unit 225) generates at least the rotation speed of the steering system or the shaft of the speed reducer (for example, the angular speed ωWG that is a derivative of the rotation angle θWG of the shafts of the speed reducers 12 and 13). Accordingly, a damper correction signal (for example, a damper compensation signal IDMP) for correcting the base signal DT can be calculated. The damper correction signal IDMP can compensate for the viscosity of the steering system.

  Preferably, the vehicle speed signal VS from the vehicle speed sensor 35 is input to the damper compensation signal calculation unit 225, and the damper compensation signal IDMP is, for example, the angular speed ωWG (or angular speed signal) and the vehicle speed V (or vehicle speed signal VS) of the worm gear 12. It is calculated according to both. As described above, the base signal DT is preferably calculated in accordance with both the detection torque amplification signal TB and the vehicle speed V (or the vehicle speed signal VS), for example.

  FIG. 9A shows an example of the relationship between the detected torque amplification signal TB and the vehicle speed signal VS and the base signal DT, and FIG. 9B shows the relationship between the angular speed ωWG, the vehicle speed signal VS, and the damper compensation signal IDMP. An example of the relationship is shown.

  In the example of FIG. 9A, according to the base map represented by the base table 220a of the base signal calculation unit 220, the dead band N1 in which the base signal DT is set to zero when the detected torque amplification signal TB is small is the base map. When the detected torque amplification signal TB is larger than the dead band N1, the base signal DT increases linearly with the gain G1. When the detected torque amplification signal TB becomes larger than the first predetermined value, the base signal DT increases linearly with the gain G2, and when the detected torque amplification signal TB becomes larger than the first predetermined value, the base signal DT is saturated. In addition, the gains G1 and G2 and the dead zone N1 are adjusted by the vehicle speed signal VS. Specifically, when the vehicle speed signal VS increases, the base signal calculation unit 220 can set the gains G1 and G2 low and the dead zone N1 large.

  The detected torque amplification signal TB is positive when the driver operates the steering handle 2 to the left, for example, while the detected torque amplification signal TB is negative when the driver operates the steering handle 2 to the right, for example. In this case, the base map can be set such that the base signal DT is also negative with respect to the negative detection torque amplification signal TB. In other words, the base map shown in FIG. 9A represents the characteristics of the base signal DT in the first quadrant, but the characteristics of the base signal DT in the first quadrant are targeted with respect to the origin 0. With the characteristic of the base signal DT in the third quadrant, it is possible to cope with the detection signal amplification signal TB that is negative.

  In the example of FIG. 9B, according to the damper map represented by the damper table 225a of the damper compensation signal calculation unit 225, when the angular velocity ωWG of the worm gear 12 is large, the damper compensation signal IDMP increases and the vehicle speed signal VS decreases. As a result, the damper compensation signal IDMP decreases. Similar to the base map, a dead zone may be provided in the damper map. Further, the damper map can represent not only the characteristic of the damper compensation signal in the first quadrant but also the characteristic of the damper compensation signal in the third quadrant.

  In the example of FIG. 8, the control device 200 can include an inertia compensation signal calculation unit 210. Here, the inertia compensation signal calculation unit 210 can calculate an inertia compensation signal for correcting the base signal DT in accordance with at least the detected torque amplification signal TB of the steering system. The inertia compensation signal calculation unit 210 compensates for a decrease in responsiveness due to the inertia of the rotor of the electric motor 11. For example, the inertia compensation signal is calculated in accordance with, for example, differentiation of the detected torque amplification signal TB. According to the inertia map represented by the inertia table 215a of the inertia compensation signal calculation unit 210, the inertia compensation signal can be set to be large when the differential of the amplified signal TB of the detected torque becomes large.

  The control device 200 includes a Q-axis (torque axis) PI control unit 240, a D-axis (magnetic pole axis) PI control unit 245, adders 250, 251, 252, and 253, a two-axis three-phase conversion unit 260, a PWM A conversion unit 270, a three-phase two-axis conversion unit 265, an electric motor speed calculation unit 280, and an excitation current generation unit 285 can be further provided.

  The adder 251 adds the base signal DT of the base signal calculation unit 220, the inverted signal of the damper compensation signal IDMP of the damper compensation signal calculation unit 225, and the inverted signal of the braking signal IBRK of the braking signal calculation unit 226. In other words, the adder 251 subtracts both the damper compensation signal IDMP of the damper compensation signal calculation unit 225 and the braking signal IBRK of the braking signal calculation unit 226 from the base signal DT of the base signal calculation unit 220. In this case, since the damper compensation signal IDMP and the braking signal IBRK are generated independently, the compensation of the viscosity of the steering system and the suppression of abnormalities such as vibration of the shaft of the worm gear 12 and abnormal noise are adjusted independently. Is easy.

  Note that the control device 200 may include one correction signal calculation unit by integrating the damper compensation signal calculation unit 225 and the braking signal calculation unit 226. In other words, the control device 200 is arranged between the damper compensation signal calculation unit 225 and the motor speed calculation unit 280 instead of the braking signal calculation unit 226 as shown in FIG. 5A or 5B. A frequency shaping unit may be provided. In this case, it is possible to easily generate one correction signal (combination of the damper compensation signal and the braking signal) that can suppress abnormalities such as vibration of the shaft of the worm gear 12 and abnormal noise, but the adder 251 can generate the correction signal from the base signal DT. Since one correction signal is subtracted, it is not easy to independently adjust the compensation of the viscosity of the steering system and the suppression of abnormalities such as vibration and abnormal noise.

  The adder 250 adds the output signal of the adder 251 and the output signal of the inertia compensation signal calculation unit 210, and the target signal IM is generated by the adder 250. In the example of FIG. 8, the target signal IM is a Q-axis current target signal that defines the auxiliary torque TM in the electric motor 11.

  The adder 252 subtracts the Q-axis current IQ from the target signal IM (target current), and the deviation signal IE is generated by the adder 252. The Q-axis (torque axis) PI control unit 240 performs PI control so that the deviation signal IE decreases. Here, the Q-axis current IQ is an output signal from the three-phase two-axis conversion unit 265, and the three-phase two-axis conversion unit 265 converts the three-phase currents IU, IV, and IW of the motor 11 into the Q-axis current IQ and Convert to D-axis current ID. The D axis is a magnetic pole axis of the rotor of the electric motor 11, and the Q axis is an axis that is electrically rotated 90 degrees with respect to the D axis. The D-axis current ID is input to the adder 253.

  The exciting current generator 285 generates a target signal for the D-axis current ID, and the adder 253 subtracts the D-axis current ID from the output signal (target signal) of the exciting current generator 285. The D axis (magnetic pole axis) PI control unit 245 performs PI feedback control so that the output signal (deviation signal) of the adder 253 decreases.

  The 2-axis 3-phase converter 260 converts the 2-axis signal of the output signal VQ of the Q-axis (torque axis) PI control unit 240 and the output signal VD of the D-axis (magnetic pole axis) PI control unit 245 into 3-phase signals UU, UV , UW. The PWM converter 270 generates a DUTY signal (DUTYU, DUTYV, DUTYW), which is an ON / OFF signal (PWM signal) having a pulse width proportional to the magnitude of the three-phase signals Vu, Vv, Vw. Note that the rotation angle signal θWG of the worm gear 12 that matches the motor rotation angle θm of the motor 11 is input to the two-axis three-phase conversion unit 260, the PWM conversion unit 270, and the motor speed calculation unit 280, and the motor speed calculation unit 280 An angular velocity signal ωWG is generated by differentiating the angle signal θWG.

  FIG. 10 shows the frequency characteristic of the evaluation function (gain characteristic of the transfer function) in the electric power steering apparatus 100 according to the present invention. In the example of FIG. 10, as in FIG. 1A, a transfer function G (s) from the steering torque TH (s) to the angular velocity ωWG (s) of the shaft of the worm gear 12 is set as the evaluation function Ev. Comparative example 1 and comparative example 2 of 1 (A) are also shown. In the example of FIG. 10, Comparative Example 1 and Comparative Example 2 are indicated by a one-dot chain line and a two-dot chain line, respectively, and the example is indicated by a solid line. In the example of FIG. 10, the maximum value corresponding to the reduction ratio nM of the reduction ratios 12 and 13 is the maximum value in the comparative example 1 where the frequency f is around 40 [Hz], and is a frequency range higher than 10 [Hz]. Exists. The presence of the local maximum value in Comparative Example 1 means that the base signal or auxiliary torque that is the source of the angular velocity ωWG of the shaft of the worm gear 12 includes the resonance frequency component of the shaft of the worm gear 12. Therefore, by adding the signal for suppressing the resonance frequency component according to the present invention, the maximum value of the frequency f on the gain characteristic of the transfer function G (s) near 40 [Hz] can be reduced.

  In the embodiment where the frequency f is around 40 [Hz], the maximum value in the embodiment is that of the worm gear 12 in the electric power steering apparatus to which a correction signal (for example, the braking signal IBRK) is added. This means that the occurrence of abnormalities such as shaft vibration and abnormal noise is suppressed. In addition, the maximum value in the example in which the frequency f is around 1 [Hz] is substantially the same as the maximum value in Comparative Example 1 in which the frequency f is around 1 [Hz]. In other words, the maximum value in the embodiment where the frequency f is around 1 [Hz] means that smooth steering is maintained in the embodiment.

  In addition, without using the braking signal IBRK, it is conceivable to change the material of the worm gear 12, the worm wheel gear 13, etc. in Comparative Example 1 to increase the rigidity and suppress the resonance frequency component of the shaft of the worm gear 12. However, the manufacturing cost of the speed reducers 12 and 13 will increase. In the embodiment according to the present invention, this resonance frequency component is suppressed by controlling the output torque TM of the electric motor 11 with the braking signal IBRK without changing the material of the speed reducers 12 and 13. The braking signal IBRK can be calculated using, for example, the square component of the angular velocity signal ωWG as represented by the above-described Expression 10, but may be calculated exponentially, for example.

  For example, the worm wheel 13 is generally made of resin, and the hardness of the worm wheel 13 is likely to change depending on the temperature of the environment such as the engine room. When the hardness of the worm wheel 13 changes, the rigidity of the worm wheel 13 naturally changes, so that the resonance frequency of the shaft of the worm gear 12 may change depending on the temperature. In the embodiment according to the present invention, the braking signal IBRK is applied to all frequencies other than the normal range (that is, 10 [Hz] or more) so as to suppress the resonance frequency component. It is possible. In other words, for example, by allowing the frequency shaping unit shown in FIGS. 5A and 5B to correspond to a high-pass filter, it is possible to increase the resistance of the speed reducers 12 and 13 to environmental temperature changes.

  The present invention is not limited to the above-described exemplary embodiments, and those skilled in the art will be able to easily modify the above-described exemplary embodiments to the extent included in the claims. .

  DESCRIPTION OF SYMBOLS 1 ... Shaft, 2 ... Steering handle, 3 ... Main steering shaft, 4 ... Universal joint, 5 ... Pinion shaft, 6a, 6b, 6c ... Bearing, 7 ... Pinion gear, 8 ... rack shaft, 8a ... rack teeth, 9 ... tie rod, 10 ... steered wheel, 11 ... electric motor, 12 ... worm gear (reduction gear shaft), 13 ... Worm wheel gear, 20 ... steering gear box, 30 ... torque sensor, 35 ... vehicle speed sensor, 40 ... differential amplifier circuit, 50 ... resolver, 60 ... motor drive means, DESCRIPTION OF SYMBOLS 100 ... Electric power steering apparatus, 200 ... Control apparatus, 210 ... Inertia compensation signal calculating part, 210a ... Inertia table, 220 ... Base signal calculating part, 220a Base table, 225 ... Damper compensation signal calculation unit, 225a ... Damper table, 226 ... Brake signal calculation unit (correction signal calculation unit), 240 ... Q axis (torque axis) PI control unit, 245 ... D axis (magnetic pole axis) PI control unit, 250, 251, 252, 253 ... adder, 260 ... 2-axis 3-phase conversion unit, 265 ... 3-phase 2-axis conversion unit, 270 ... PWM converter, 280 ... Motor speed calculator.

Claims (4)

An electric motor for applying auxiliary torque to the steering system via a speed reducer;
A base signal calculation unit that calculates a base signal serving as a reference for the target signal of the auxiliary torque according to at least the steering torque of the steering system;
A correction signal calculation unit that calculates a correction signal for correcting the auxiliary torque according to at least the rotation speed of the steering system or the shaft of the speed reducer;
With
The correction signal calculation unit includes a frequency shaping unit that suppresses a low frequency component of the rotation speed, corrects the auxiliary torque with a high frequency component of the rotation speed,
Wherein the frequency shaping unit, said has a low-pass filter for extracting a low frequency component, wherein the rotational speed by subtracting a low frequency component to generate a pre-Symbol high frequency component, and the high frequency component and the absolute value of the rotational speed Is multiplied to generate the correction signal . A damper correction signal calculation unit for calculating a damper correction signal for correcting the base signal according to at least the rotation speed;
The electric power steering apparatus according to claim 1 , wherein the auxiliary torque is corrected by both the high-frequency component of the correction signal and the damper correction signal. In the gain characteristic of the transfer function from the steering torque at the steering handle to the rotational speed of the speed reducer shaft, the maximum value corresponding to the speed reduction ratio of the speed reducer is in a frequency range higher than 10 [Hz]. Exists,
The high frequency components, the electric power steering apparatus according to claim 1 or 2, characterized in that to reduce the local maximum value. The electric power steering apparatus according to any one of claims 1 to 3 , wherein the rotational speed of the steering system or the shaft of the speed reducer is an angular speed of the shaft of the speed reducer.

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