JP5034744B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering device that applies a steering assist force to a steering mechanism to reduce a driver's steering burden.

As a conventional electric power steering device, a correction torque necessary for the vehicle to maintain a straight traveling state is obtained from a wheel speed difference, a steering angle, and a vehicle speed of both wheels caused by a decrease in tire air pressure of one of the left and right wheels. Even if the balance between the left and right tire air pressures is lost by calculating the motor drive current based on the result calculated and added to the steering torque detected by the steering torque detection means Is known (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2003-2222

  However, the electric power steering device described in Patent Document 1 aims to correct a large difference in left and right steering torque, such as improving steering feeling when the left and right steering torque becomes unbalanced due to a decrease in tire air pressure. Therefore, it is difficult to correct the left-right difference of the steering torque caused by the hardware offset of the EPS torque sensor, which is frequently regarded as a problem on the steering feeling of the EPS.

  Therefore, an object of the present invention is to provide an electric power steering device that can correct a left-right torque offset on hardware of an EPS torque sensor and improve steering feeling.

In order to solve the above problems, an electric power steering apparatus according to claim 1 is an electric power steering apparatus including an electric motor that applies a steering assist force to reduce a steering burden on a driver to a steering system,
Steering torque detecting means for detecting steering torque, left and right wheel speed difference detecting means for detecting the wheel speed difference between the left and right wheels, and the left and right wheel speed difference are equal to or less than a predetermined value indicating that the vehicle is running straight. Sometimes the torque average value calculating means for calculating the average value of the steering torque detected by the steering torque detecting means, the reliability calculating means for calculating the reliability of the steering torque average value, and the reliability calculating means Torque correction value calculation means for calculating a steering torque correction value based on the reliability and the steering torque average value calculated by the average value calculation means; steering torque detected by the steering torque detection means; and the torque correction value calculation means Current command value calculation means for calculating a current command value based on the steering torque correction value calculated in step, and motor control means for driving and controlling the electric motor based on the current command value It is characterized in that it comprises.

According to a second aspect of the present invention, there is provided the electric power steering apparatus according to the first aspect of the invention, wherein the torque correction value calculating means has the average value when the reliability calculated by the reliability calculating means is a predetermined value or more. The steering torque average value calculated by the calculation means is set as the steering torque correction value.
Furthermore, in the electric power steering apparatus according to claim 3, in the invention according to claim 1, the torque correction value calculation means calculates the steering torque average value calculated by the average value calculation means by the reliability calculation means. A value obtained by multiplying the reliability is set as the steering torque correction value.

  The electric power steering apparatus according to a fourth aspect is the invention according to the first or second aspect, wherein the reliability calculation means calculates a plurality of reliability having different calculation criteria as the reliability. The torque correction value calculating means sets the steering torque average value as a steering torque correction value when the total value of the plurality of reliability is larger than the previous total value.

Still further, in the electric power steering apparatus according to claim 5, in the invention according to claim 4, the torque correction value calculation unit is configured such that the total value of the plurality of reliability is equal to or greater than a predetermined ratio of the previous total value. The steering torque average value is set as a steering torque correction value.
According to a sixth aspect of the present invention, in the electric power steering apparatus according to any one of the first to fifth aspects of the present invention, the electric power steering device includes a vehicle speed detecting unit that detects a vehicle speed, and the reliability calculation unit is configured as the reliability. A vehicle speed sensitive reliability calculating means for calculating a vehicle speed sensitive reliability according to the vehicle speed is provided.

Furthermore, the electric power steering apparatus according to a seventh aspect is the invention according to any one of the first to sixth aspects, wherein the reliability calculating means takes a time required for calculating the steering torque average value as the reliability. And a time-sensitive reliability calculating means for calculating a time-sensitive reliability according to the above.
According to an eighth aspect of the present invention, there is provided the electric power steering apparatus according to any one of the first to seventh aspects, wherein the reliability calculating means takes the time required for calculating the steering torque average value as the reliability. And a variation reliability calculating means for calculating a variation reliability according to the maximum variation amount of the steering torque.

  According to the electric power steering apparatus of the present invention, the average value of the steering torque detected by the steering torque detection means when the difference between the left and right wheel speeds is small enough to determine that the vehicle is traveling straight, and the steering torque Since the steering torque correction value is calculated based on the reliability of the average value, a highly accurate torque correction value can be obtained, and torque correction in a finer region is possible. As a result, the left and right torque offset on the EPS hardware that can be seen in the steering torque detection process can be corrected with high accuracy, and the steering feeling difference can be reduced by reducing the steering torque difference during steering wheel left and right steering. The effect is obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram showing an embodiment of an electric power steering apparatus according to the present invention.
In the figure, reference numeral 1 denotes a steering wheel, and a steering force applied to the steering wheel 1 from a driver is transmitted to a steering shaft 2 having an input shaft 2a and an output shaft 2b. The steering shaft 2 has one end of the input shaft 2a connected to the steering wheel 1 and the other end connected to one end of the output shaft 2b via a torque sensor 3 as steering torque detecting means.

  The steering force transmitted to the output shaft 2 b is transmitted to the lower shaft 5 via the universal joint 4 and further transmitted to the pinion shaft 7 via the universal joint 6. The steering force transmitted to the pinion shaft 7 is transmitted to the tie rod 9 via the steering gear 8 and steers steered wheels (not shown). Here, the steering gear 8 is configured in a rack and pinion type having a pinion 8a connected to the pinion shaft 7 and a rack 8b meshing with the pinion 8a, and the rotational motion transmitted to the pinion 8a is linearly moved by the rack 8b. It has been converted to movement.

A steering assist mechanism 10 for transmitting a steering assist force to the output shaft 2b is connected to the output shaft 2b of the steering shaft 2. The steering assist mechanism 10 includes a reduction gear 11 coupled to the output shaft 2b, and an electric motor 12 coupled to the reduction gear 11 and generating a steering assist force with respect to the steering system.
The torque sensor 3 detects a steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a, and a torsional angle displacement of a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. The torsional angular displacement is detected by, for example, a potentiometer. The torque detection value Ti output from the torque sensor 3 is input to the controller 15.

As shown in FIG. 2, the controller 15 receives the steering torque Ti detected by the torque sensor 3 and the vehicle speed detection value V detected by the vehicle speed sensor 16 as vehicle speed detection means, and the right wheel speed sensor 17. The right wheel speed V _R detected in step _S3 is input, and the left wheel speed V _L detected by the left wheel speed sensor 18 is input.
The steering torque Ti detected by the torque sensor 3 is corrected by the torque offset correction value ΔT by the steering torque correction unit 30, and the corrected steering torque T is input to the motor drive current calculation unit 40.

The steering torque correction unit 30 subtracts the left wheel speed V _L detected by the left wheel speed sensor 18 from the right wheel speed V _R detected by the right wheel speed sensor 17 to calculate the left and right wheel speed difference ΔV. 31, a vehicle speed sensitive reliability coefficient calculating unit 32 that calculates a vehicle speed sensitive reliability coefficient Kv based on the vehicle speed detected value V, and whether to update the torque offset correction value ΔT based on the vehicle speed sensitive reliability Kv Torque offset correction value calculation that outputs a torque offset correction value ΔT by inputting the torque offset correction value update determination unit 33 and the determination result of the torque offset correction value update determination unit 33, the steering torque Ti, and the left and right wheel speed difference ΔV And a steering torque detected by the torque sensor 3 and a torque offset correction value output unit 35 for executing a torque offset correction value calculation process described later. Subtracts the torque offset correction value ΔT from i, and a subtracting unit 36 for outputting a steering torque T is a result to the motor drive current calculating section 40.

In addition to the steering torque T, a vehicle speed detection value V is also input to the motor drive current calculation unit 40, and a current command value It for generating a steering assist force according to these values in the electric motor 12 is given to the motor drive unit 50. Output.
The motor drive unit 50 feedback-processes the drive current supplied to the electric motor 12 based on the current command value It and a motor current detection value detected by a motor current detector (not shown), and controls the drive of the electric motor 12. Output current.

FIG. 3 is a flowchart showing a torque offset correction value calculation processing procedure executed by the torque offset correction value output unit 35. This torque offset correction value calculation process is executed every predetermined time. First, in step S1, the vehicle speed V detected by the vehicle speed sensor 16 and the steering torque Ti detected by the torque sensor 3 are read, and the vehicle speed V is set to the predetermined vehicle speed. It is determined whether V _SET or more and the absolute value | Ti | of the steering torque is less than or equal to a predetermined value Ti _SET . If V ≧ V _SET and | Ti | ≦ Ti _SET , the process proceeds to step S2, and otherwise, the process proceeds to step S4 described later.

In step S2, a right wheel speed V _R detected by the right wheel speed sensor 17, reads the left wheel speed V _L detected by the left wheel speed sensor 18, a left wheel speed V _L from the right wheel speed V _R By subtracting, the left and right wheel speed difference ΔV is calculated and the process proceeds to step S3.
In step S3, it is determined whether or not the absolute value | ΔV | of the left and right wheel speed difference ΔV calculated in step S2 is equal to or _smaller than a predetermined value ΔV _SET . If | ΔV |> ΔV _SET , the process proceeds to step S4. , | ΔV | ≦ ΔV _SET , the process proceeds to step S5. Here, the predetermined value ΔV _SET is set to such a small value that it can be determined that the vehicle is traveling straight.

In step S4, it is determined whether or not the count value N for measuring the duration of the state in which V ≧ V _SET and | Ti | ≦ Ti _SET and | ΔV | ≦ ΔV _SET is “0”. When N ≠ 0, the process proceeds to step S10 described later, and when N = 0, the torque offset correction value calculation process is terminated as it is.
In step S5, the count value N is incremented, and then the process proceeds to step S6. After the vehicle speed V detected by the vehicle speed sensor 16 is read, the process proceeds to step S7.

In step S7, the vehicle speed sum ΣV is calculated by adding the vehicle speed V read in step S6 to the previously calculated vehicle speed sum ΣV, and the process proceeds to step S8.
In step S8, the torque sum ΣT is calculated by adding the steering torque Ti read in step S1 to the previously calculated torque sum ΣT, and the process proceeds to step S9.
In step S9, it is determined whether or not the count value N is equal to or larger than the set value Nmax. When N ≧ Nmax, the process proceeds to step S10 described later, and when N <Nmax, the torque offset correction value calculation process is terminated as it is. To do.

In step S10, based on the torque sum ΣT calculated in step S8 and the current count value N, the torque average value Ta is calculated based on the following equation (1), and the vehicle speed sum ΣV calculated in step S7. Based on the current count value N, the vehicle speed average value Va is calculated based on the following equation (2).
Ta = ΣT / N (1)
Va = ΣV / N (2)
Then, after calculating the torque average value Ta and the vehicle speed average value Va, the count value N is cleared to “0” and the process proceeds to step S11.

  In step S11, the vehicle speed sensitive reliability coefficient Kv is calculated based on the vehicle speed average value Va calculated in step 10 with reference to the vehicle speed sensitive reliability coefficient calculation map shown in FIG. Here, the vehicle speed sensitive reliability coefficient Kv is the reliability of the torque average value Ta according to the vehicle speed, and the vehicle speed sensitive reliability coefficient calculation map shows that the vehicle speed sensitive reliability coefficient Kv is calculated to be larger as the vehicle speed average value Va is higher. Is set to Note that 0 ≦ Kv ≦ 1.

Next, the process proceeds to step S12, where it is determined whether or not the vehicle speed sensitive reliability coefficient Kv calculated in step S11 is greater than or equal to a predetermined value Kv _SET . If Kv ≧ Kv _SET , the torque offset correction value ΔT is determined. When it is determined that the update is to be performed, the process proceeds to step S13. When Kv <Kv _SET , the torque offset correction value calculation process is terminated.
In step S13, the torque average value Ta calculated in step S10 is updated as the torque offset correction value ΔT, and then the torque offset correction value calculation process ends.

  In FIG. 2, the motor drive current calculation unit 40 corresponds to a current command value calculation unit, and the motor drive unit 50 corresponds to a motor control unit. In FIG. 3, the process of step S2 corresponds to the left and right wheel speed difference detecting means, the process of step S10 corresponds to the torque average value calculating means, and the process of step S11 corresponds to the vehicle speed sensitive reliability calculating means. The processing in step S13 corresponds to torque correction value calculation means.

Next, the operation and effect of the first embodiment will be described.
Now, it is assumed that the vehicle is traveling straight ahead without the driver operating the steering wheel 1. Since the vehicle is traveling straight ahead, the left / right wheel speed difference | ΔV | ≦ ΔV _{SET is established} , and in the torque offset correction value calculation process of FIG. 3, the process proceeds from step S3 to step S5, and the count value N is incremented. The process proceeds to step S6. Then, the vehicle speed sum ΣV is calculated using the vehicle speed V at this time, and then the torque sum ΣT is calculated using the steering torque Ti at this time. That is, here, the sum of the vehicle speed V and the steering torque Ti up to the present after the vehicle is in the straight traveling state and | ΔV | ≦ ΔV _SET is calculated. This is continued until N ≧ Nmax.

When N ≧ Nmax, the routine proceeds from step S9 to step S10, where the torque average value Ta and the vehicle speed average value Va are calculated based on the above equations (1) and (2). If it is assumed that the vehicle is traveling at a relatively high speed during the straight traveling, the vehicle speed sensitive reliability coefficient Kv is referred to in FIG. 4 in step S11, and the vehicle speed sensitive reliability coefficient Kv is equal to or greater than a predetermined value Kv _SET. It is calculated to be a relatively large value. Therefore, it determines with Yes by step S12, transfers to step S13, and the torque average value Ta calculated by said step S10 is updated as torque offset correction value (DELTA) T.

  Therefore, the steering torque T obtained by subtracting the torque offset correction value ΔT from the steering torque Ti detected by the torque sensor 3 is input to the motor drive current calculation unit 40. At this time, since the driver does not operate the steering wheel 1 and Ti = 0, the motor drive current calculation unit 40 calculates a current command value It according to the steering torque T (= ΔT), and this is calculated. Input to the motor drive unit 50. As a result, the electric motor 12 is driven and controlled so that a steering assist force according to the torque offset correction value ΔT is applied.

As a result, the left / right difference of the steering torque Ti caused by the hardware offset of the torque sensor 3 can be corrected, and the steering force of the driver during straight traveling can be made substantially zero. Feeling can be improved.
Thereafter, when the driver operates the steering wheel 1 and the vehicle starts turning, the torque sensor 3 detects the steering torque Ti corresponding to the driver's steering operation. The steering torque T (= Ti−ΔT) obtained by subtracting ΔT is input to the motor drive current calculation unit 40. Therefore, the motor drive current calculation unit 40 calculates the current command value It according to the steering torque T, and the motor drive unit 50 controls the driving of the electric motor 12 based on the current command value It. Steering assistance control is performed to reduce the steering burden on the user. At this time, since the steering torque Ti is corrected with the torque offset correction value ΔT, the left and right steering torques can be corrected to be equal, and the steering feeling during turning can be improved. it can.

On the other hand, when the vehicle is traveling straight at a relatively low speed, in the torque offset correction value calculation process of FIG. 3, the vehicle speed sensitivity reliability coefficient calculation map of FIG. Kv is calculated for a predetermined value Kv _SET smaller value. As a result, it is determined No in step S12, and the torque offset correction value calculation process is terminated without updating the torque offset correction value ΔT.

Further, when the vehicle is traveling straight without the steering wheel 1 being operated by the driver, as described above, the sum of the vehicle speed V and the steering torque Ti from when | ΔV | ≦ ΔV _SET to the present time. Is calculated and is continued until N ≧ Nmax. Before N ≧ Nmax, for example, if the vehicle stops or is in an extremely low speed running state and V <V _SET , step S1 is performed. It determines with No and transfers to step S4. At this time, since N ≠ 0, the process proceeds from step S4 to step S10.

As described above, when the determination condition in step S1 is not satisfied before N ≧ Nmax, the torque offset correction value ΔT is updated based on the sum of the vehicle speed V and the steering torque Ti at that time. .
As described above, in the first embodiment, the average value of the steering torque detected by the steering torque detecting means when the difference between the left and right wheel speeds is small enough to determine that the vehicle is traveling straight ahead is calculated. Since the steering torque correction value is calculated based on the steering torque average value and the reliability of the steering torque average value, a highly accurate torque correction value can be obtained, and torque correction in a minute region is possible. As a result, the left and right torque offset on the EPS hardware that can be seen in the steering torque detection process can be corrected with high accuracy, and the steering feeling difference can be reduced by reducing the steering torque difference during steering wheel left and right steering. .

Further, since the steering torque average value is calculated when the vehicle speed is equal to or higher than the predetermined vehicle speed and the absolute value of the steering torque is equal to or lower than the predetermined value, the average steering torque value can be obtained in a region where the left and right wheel speeds are stable. The calculation accuracy of the correction value can be increased.
Further, when the vehicle speed sensitivity is greater than or equal to a predetermined value, the steering torque average value is set as the steering torque correction value. When the vehicle speed sensitivity is smaller than the predetermined value, the steering torque correction value is not updated. The steering torque correction value can be appropriately updated according to the reliability of the average value.

Furthermore, since the vehicle speed sensitivity is set higher as the vehicle speed increases, the steering torque correction value is updated when the vehicle is traveling at a low speed and the stability of the steering torque detected by the steering torque detecting means is low. Thus, a highly accurate steering torque correction value can be obtained.
Next, a second embodiment of the present invention will be described.

In the second embodiment, when the vehicle speed sensitive reliability coefficient Kv is equal to or greater than the predetermined value Kv _SET in the first embodiment, the torque average value Ta is updated as the torque offset correction value ΔT. On the other hand, a value obtained by multiplying the torque average value Ta by the vehicle speed sensitivity reliability coefficient Kv is updated as a torque offset correction value ΔT.
That is, in the torque offset correction value output unit 35 of the second embodiment, the torque offset calculation process shown in FIG. 5 is executed, and instead of steps S12 and S13 of FIG. 3 in the first embodiment, torque average The same processing as in FIG. 3 is executed except that step S21 is added in which a value (Ta × Kv) obtained by multiplying the value Ta by the vehicle speed sensitivity reliability coefficient Kv is updated as the torque offset correction value ΔT.

In FIG. 5, the processing in step S21 corresponds to torque correction value calculation means.
Therefore, when the vehicle is traveling at a high speed, the vehicle speed average value Va calculated in step S10 becomes a relatively large value, and in step S11, the vehicle speed sensitive reliability coefficient Kv is calculated to, for example, “1”. In step S21, the torque average value Ta calculated in step S10 is multiplied by a vehicle speed sensitive reliability coefficient Kv, which is set as a torque offset correction value ΔT. At this time, since the vehicle speed sensitive reliability coefficient Kv = 1, it is equivalent to setting the torque average value Ta as the torque offset correction value ΔT.

On the other hand, when the vehicle is traveling at a low speed and the vehicle speed sensitive reliability coefficient Kv is calculated to a value smaller than 1, in step S21, the torque average value Ta is multiplied by the vehicle speed sensitive reliability coefficient Kv. The torque offset correction value ΔT is set to a value smaller than the torque average value Ta.
As described above, in the second embodiment, a value obtained by multiplying the steering torque average value by the vehicle speed sensitivity is set as the steering torque correction value. Therefore, the steering torque correction is appropriately performed according to the reliability of the steering torque average value. The value can be updated.

  In the first and second embodiments, the case where the torque offset correction value ΔT is updated based on the torque average value Ta and the vehicle speed sensitivity reliability coefficient Kv has been described. Instead, a time sensitive reliability coefficient Kt (0 ≦ Kt ≦ 1), which is the reliability of the steering torque average value corresponding to the time required to calculate the torque average value Ta, can also be used.

  In this case, in step S11 of FIGS. 3 and 5, the time sensitive reliability coefficient calculation map shown in FIG. 6 is referred to, and the time is calculated based on the count value N corresponding to the time required for calculating the torque average value Ta. The sensitive reliability coefficient Kt may be calculated. Here, the time sensitive reliability coefficient calculation map is set such that the greater the count value N, the higher the reliability of the torque average value Ta, and the larger the time sensitive reliability coefficient Kt is calculated.

Further, instead of the vehicle speed sensitivity reliability coefficient Kv, the maximum variation amount ΔTi of the steering torque Ti within the time required to calculate the torque average value Ta (= the maximum value of the steering torque Ti−the minimum value of the steering torque Ti). The variation reliability coefficient Kb (0 ≦ Kb ≦ 1) can also be used.
In this case, the variation reliability coefficient Kb may be calculated based on the maximum variation amount ΔTi in step S11 of FIGS. At this time, the smaller the maximum variation amount ΔTi, the larger the variation reliability coefficient Kb is calculated. That is, assuming that the steering torque Ti within the time required for calculating the torque average value Ta has a variation degree as shown in FIG. 7, the maximum variation amount ΔTi is greater in the case of the bold line than in the thin line. The variation reliability coefficient Kb is calculated to be large assuming that the torque average value Ta is small and the reliability is high.

Next, a third embodiment of the present invention will be described.
In the third embodiment, only the vehicle speed sensitivity reliability is applied as the reliability of the torque average value Ta in the above-described first embodiment, but a plurality of reliability including the vehicle speed sensitivity reliability is provided. It is to be applied.
FIG. 8 is a flowchart illustrating a torque offset correction value calculation processing procedure executed by the torque offset correction value output unit 35 of the third embodiment. As shown in FIG. 8, in the torque offset correction value calculation process shown in FIG. 3 of the first embodiment described above, after step S11, a step S31 for calculating a time sensitive reliability coefficient Kt, and a variation reliability coefficient Step S32 for calculating Kb is added. In step S12, the vehicle speed sensitive reliability coefficient Kv is equal to or greater than a predetermined value Kv _SET , the time sensitive reliability coefficient Kt is equal to or greater than a predetermined value Kt _SET , and the variation reliability coefficient Kb is predetermined. The same processing as that in FIG. 3 is executed except that the step S33 for determining whether or not the value is equal to or larger than the value Kb _SET is replaced.

That is, in step S31, the time sensitive reliability coefficient calculation map shown in FIG. 6 described above is referred to, the time sensitive reliability coefficient Kt is calculated based on the count value N, and then the process proceeds to step S32.
In step S32, based on the above-described maximum variation amount ΔTi, calculation is performed such that the variation reliability coefficient Kb increases as the maximum variation amount ΔTi decreases, and the process proceeds to step S33.

In step S33, it is determined whether or not the vehicle speed sensitive reliability coefficient Kv is greater than or equal to a predetermined value Kv _SET , the time sensitive reliability coefficient Kt is greater than or equal to the predetermined value Kt _SET , and the variation reliability coefficient Kb is greater than or equal to the predetermined value Kb _SET. If Kv ≧ Kv _SET , Kt ≧ Kt _SET , and Kb ≧ Kb _SET, it is determined that the torque offset correction value ΔT is to be updated, and the process proceeds to step S13. The offset correction value calculation process ends.

In FIG. 8, the process of step S31 corresponds to the time sensitive reliability calculation means, and the process of step S32 corresponds to the variation reliability calculation means.
As described above, in the third embodiment, the reliability of the steering torque average value is applied with a plurality of reliability levels having different calculation criteria, and the steering torque average value is steered when each reliability level is equal to or higher than a predetermined value. Since the torque correction value is set, the steering torque correction value can be updated more appropriately.

  In the third embodiment, the case where the steering torque average value is set as the steering torque correction value when each reliability is equal to or higher than a predetermined value has been described. However, the total value (product or When the sum is larger than the previous total value, the steering torque average value can be set as the steering torque correction value. Further, when the total value (product or sum) of the respective reliability is equal to or higher than a predetermined ratio of the previous total value, the steering torque average value can be set as the steering torque correction value. Also in these cases, the steering torque correction value can be appropriately updated according to the reliability.

Next, a fourth embodiment of the present invention will be described.
In the fourth embodiment, only the vehicle speed sensitivity reliability is applied as the reliability of the torque average value Ta in the second embodiment described above, whereas a plurality of reliability including the vehicle speed sensitivity reliability is provided. It is to be applied.
FIG. 9 is a flowchart illustrating a torque offset correction value calculation processing procedure executed by the torque offset correction value output unit 35 of the fourth embodiment. As shown in FIG. 9, in the torque offset correction value calculation process shown in FIG. 5 of the second embodiment described above, after step S11, a step S41 for calculating a time sensitive reliability coefficient Kt, and a variation reliability coefficient Step S42 for calculating Kb is added, and in Step S21, a value obtained by multiplying the torque average value Ta by the vehicle speed sensitive reliability coefficient Kv, the time sensitive reliability coefficient Kt, and the variation reliability coefficient Kb is set as a torque offset correction value ΔT. The same processing as in FIG. 5 is executed except that the step S43 is updated.

In step S41, the same processing as in step S31 of FIG. 8 described above is performed, a time sensitive reliability coefficient Kt is calculated based on the count value N, and then the process proceeds to step S42.
In step S42, the same processing as in step S32 of FIG. 8 described above is performed, and the variation reliability coefficient Kb is calculated based on the maximum variation amount ΔTi, and then the process proceeds to step S43.
In step S43, a value obtained by multiplying the torque average value Ta by the vehicle speed sensitive reliability coefficient Kv, the time sensitive reliability coefficient Kt, and the variation reliability coefficient Kb is updated as a torque offset correction value ΔT (ΔT = Ta × Kv × Kt × Kb), and the torque offset correction value calculation process is terminated.

In FIG. 9, the process of step S41 corresponds to the time sensitive reliability calculation means, and the process of step S42 corresponds to the variation reliability calculation means.
As described above, in the fourth embodiment, a plurality of reliability levels are applied as the reliability of the steering torque average value, and a value obtained by multiplying the reliability of the steering torque average value is set as the steering torque correction value. The steering torque correction value can be updated more appropriately.

In the third and fourth embodiments, the three reliability levels of the vehicle speed sensitivity reliability coefficient Kv, the time sensitivity reliability coefficient Kt, and the variation reliability coefficient Kb are applied as the reliability of the steering torque average value. Although the case has been described, only two of the reliability levels may be applied.
For example, when the vehicle speed sensitivity reliability coefficient Kv and the time sensitivity reliability coefficient Kt are applied, the torque average value Ta is set as the torque offset correction value ΔT when Kv ≧ Kv _SET and Kt ≧ Kt _SET , or the torque average A value (Ta × Kv × Kt) obtained by multiplying the value Ta by the vehicle speed sensitive reliability coefficient Kv and the time sensitive reliability coefficient Kt may be set as the torque offset correction value ΔT.

  In each of the above embodiments, the case where the average value of the steering torque Ti detected by the torque sensor 3 is employed as the torque average value Ta has been described. However, LPF processing for removing noise with respect to the steering torque Ti, etc. The average value of the steering torque value after applying can be adopted as the torque average value Ta. As a result, a more accurate torque offset correction value ΔT can be obtained.

In the embodiments described above, the vehicle speed and the vehicle speed sensor 16 provided as a detecting means, has been described for detecting the vehicle speed V, the right wheel speed sensor 17 and the right wheel speed V _R detected by the left wheel speed sensor 18 The vehicle speed V can also be calculated from the average value of the left wheel speed V _L detected in step (1).

1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of the controller in 1st Embodiment. It is a flowchart which shows the torque offset correction value calculation process procedure performed in the steering torque correction part in 1st Embodiment. It is a vehicle speed sensitivity reliability coefficient calculation map. It is a flowchart which shows the torque offset correction value calculating process procedure performed in the steering torque correction part in 2nd Embodiment. It is a time sensitive reliability coefficient calculation map. It is a figure explaining the calculation method of a variation reliability coefficient. It is a flowchart which shows the torque offset correction value calculating process procedure performed in the steering torque correction part in 3rd Embodiment. It is a flowchart which shows the torque offset correction value calculating process procedure performed in the steering torque correction part in 4th Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Torque sensor, 10 ... Steering assist mechanism, 11 ... Reduction gear, 12 ... Electric motor, 15 ... Controller, 16 ... Vehicle speed sensor, 17 ... Right wheel speed sensor, 18 ... Left Wheel speed sensor, 30 ... steering torque correction unit, 31 ... subtraction unit, 32 ... vehicle speed sensitive reliability coefficient calculation unit, 33 ... torque offset correction value update determination unit, 34 ... torque offset correction value calculation unit, 35 ... torque offset correction Value output unit 36 ... Subtraction unit 40 ... Motor drive current calculation unit 50 ... Motor drive unit

Claims (8)

An electric power steering apparatus including an electric motor that applies a steering assist force to reduce a steering burden on a driver to a steering system,
Steering torque detecting means for detecting steering torque, left and right wheel speed difference detecting means for detecting the wheel speed difference between the left and right wheels, and the left and right wheel speed difference are equal to or less than a predetermined value indicating that the vehicle is running straight. Sometimes the torque average value calculating means for calculating the average value of the steering torque detected by the steering torque detecting means, the reliability calculating means for calculating the reliability of the steering torque average value, and the reliability calculating means Torque correction value calculation means for calculating a steering torque correction value based on the reliability and the steering torque average value calculated by the average value calculation means; steering torque detected by the steering torque detection means; and the torque correction value calculation means Current command value calculation means for calculating a current command value based on the steering torque correction value calculated in step, and motor control means for driving and controlling the electric motor based on the current command value The electric power steering apparatus comprising: a.   The torque correction value calculation means sets the steering torque average value calculated by the average value calculation means as the steering torque correction value when the reliability calculated by the reliability calculation means is a predetermined value or more. The electric power steering apparatus according to claim 1.   The torque correction value calculation means sets a value obtained by multiplying the steering torque average value calculated by the average value calculation means by the reliability calculated by the reliability calculation means as the steering torque correction value. Item 4. The electric power steering device according to Item 1.   The reliability calculation means calculates a plurality of reliability having different calculation criteria as the reliability, and the torque correction value calculation means determines that the total value of the plurality of reliability is greater than the previous total value. 3. The electric power steering apparatus according to claim 1, wherein when it is large, the steering torque average value is set as a steering torque correction value. 4.   The torque correction value calculation means sets the steering torque average value as a steering torque correction value when the total value of the plurality of reliability values is equal to or greater than a predetermined ratio of the previous total value. 4. The electric power steering apparatus according to 4.   The vehicle speed detection means which detects a vehicle speed, The said reliability calculation means is provided with the vehicle speed sensitivity reliability calculation means which calculates the vehicle speed sensitivity reliability according to a vehicle speed as said reliability. The electric power steering device according to any one of 5.   The said reliability calculation means is provided with the time sensitive reliability calculation means which calculates the time sensitive reliability according to the time required for the calculation of the said steering torque average value as said reliability. The electric power steering device according to any one of the above.   The reliability calculation means includes variation reliability calculation means for calculating a variation reliability according to a maximum amount of steering torque variation within a time required for calculating the steering torque average value as the reliability. The electric power steering apparatus according to any one of claims 1 to 7.

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