Electric power steering device

Abstract

In a control device (4) of an electric power steering device (1), a q-axis current command value calculating unit (31) for calculating a current command value of a motor (8) that generates an assisting torque is provided with a q-axis current limit value calculating unit (42) which calculates a q-axis current limit value such that if an absolute value of a steering angle is equal to or greater than a predetermined first steering angle threshold, the q-axis current limit value decreases as the absolute value of the steering angle increases, thereby regulating the q-axis current command value. As a result, steering to a maximum steering angle θmax is prevented, and impacts caused by end contact can be mitigated.

Description

[Technical field]

[0001] The present application relates to an electric power steering device. [Background technology]

[0002] As a power steering device mounted on a vehicle, an electric power steering (EPS) device using a motor as a drive source is known. Normally, when driving a motor by a semiconductor power converter equipped in an electric power steering device, an AC current is decomposed into a magnetic flux component current and a torque component current by a method called coordinate transformation, and the torque current component corresponding to the assist torque target value of the motor is controlled to a desired value. This makes it possible to make the motor torque a desired assist torque.

[0003] In addition, when using a motor with a permanent magnet in the rotor, as the rotation speed increases, the induced voltage reaches the voltage amplitude that can be applied to the motor. Therefore, by implementing flux-weakening control, which controls the magnetic flux component current to cancel the magnetic flux of the rotor, the increase in induced voltage is suppressed and the motor can be driven at high speed.

[0004] In an EPS, a movable range of the steering angle of the front wheels of the vehicle on which it is installed is set, and steering that would cause the steering angle to exceed either end of this movable range is prevented. Specifically, the movable range of the steering angle is set by the end of the rack shaft (rack end) coming into contact with the rack housing.

[0005] For this reason, when the steering wheel is turned close to the maximum steering angle (steering end position) at which the steering wheel can be turned, if the steering wheel is turned further to increase the absolute value of the steering angle at a large steering angular speed, the rack end collides with the rack housing, causing an impact in the steering system. This type of impact caused by the end hitting is also transmitted to the steering wheel, causing problems such as a worsening of the steering feeling and an increase in hitting noise.

[0006] To address this issue, it is known to mitigate the impact of the end hitting the rack housing by limiting the current command value corresponding to the assist torque target value so that it does not exceed a limit value based on the steering angle before the rack end hits the rack housing (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5962881 (Claim 5, Figure 9, etc.) Summary of the Invention [Problem to be solved by the invention]

[0008] The configuration disclosed in Patent Document 1 reduces only the torque current component, so even if the absolute value of the current command value is limited so as not to exceed the current limit value, steering is possible at a large steering angular velocity due to the assist torque corresponding to the current command value within that range. Therefore, for example, when traveling on a low μ road with a small road reaction force μ, the impact of the end contact cannot be sufficiently alleviated, and as a result, there is a risk that the steering feeling will deteriorate. In response to this, it is desired to realize a better steering feeling by using an electric power steering device, and it is expected to realize a good steering feeling even when traveling on a low μ road.

[0009] The present application discloses technology for solving the above-mentioned problems, and aims to provide an electric power steering device that can reduce the impact caused by end strike even on low μ roads and prevent deterioration of steering feeling. [Means for solving the problem]

[0010] The electric power steering device disclosed in the present application is An electric power steering device comprising: a control device that calculates a current command value based on a steering torque applied by operation of a steering shaft, and calculates a voltage command value based on the current command value; and a power converter that supplies to a motor electric power converted based on the voltage command value output from the control device, the electric power steering device generating an assist torque on the steering shaft by driving the motor, The control device includes: a q-axis current command value calculation unit and a d-axis current command value calculation unit that calculate the current command value; a motor control signal calculation unit that calculates the voltage command value based on the q-axis current command value calculated by the q-axis current command value calculation unit and the d-axis current command value calculated by the d-axis current command value calculation unit; a control steering angle calculation unit that calculates a steering angle of the steering shaft based on a rotational position of the motor, The q-axis current command value calculation unit a base current command value calculation unit that calculates a base q-axis current command value serving as a reference based on the steering torque; When the absolute value of the steering angle calculated by the control steering angle calculation unit is equal to or greater than a first steering angle threshold value set in advance, To make it smaller a q-axis current limit value calculation unit that calculates a q-axis current limit value; the base q-axis current command value calculated by the base current command value calculation unit is input, and the q-axis current limit value calculated by the q-axis current limit value calculation unit is input, When the steering angle is equal to or greater than the first steering angle threshold and the base q-axis current command value is greater than the q-axis current limit value, the q-axis current command value is set based on the q-axis current limit value instead of the base q-axis current command value; When the steering angle is equal to or smaller than -1 x the first steering angle threshold value and the base q-axis current command value is smaller than -1 x the q-axis current limit value, the q-axis current command value is set based on -1 x the q-axis current limit value instead of the base q-axis current command value; and a q-axis current guard processing unit that outputs to the motor control signal calculation unit. Effect of the Invention

[0011] According to the electric power steering device disclosed in the present application, the impact of the end contact can be mitigated even on a low μ road, and deterioration of the steering feeling can be prevented. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram showing a configuration of an electric power steering device according to a first embodiment. [Diagram 2] 1 is a block diagram showing a configuration of a control device for an electric power steering device according to a first embodiment. [Diagram 3] 4 is a diagram showing an example of a q-axis current limit value map provided in a q-axis current limit value calculation unit according to the first embodiment; FIG. [Figure 4A] 7 is a diagram showing another example of the q-axis current limit value map provided in the q-axis current limit value calculation unit according to the first embodiment. FIG. [Figure 4B] 13 is a diagram showing yet another example of the q-axis current limit value map provided in the q-axis current limit value calculation unit according to the first embodiment. FIG. [Diagram 5] 5 is a flowchart showing an operation of a q-axis current guard processor according to the first embodiment. [Figure 6] 4 is a diagram showing an example of a d-axis current limit value map provided in a d-axis current limit value calculation unit according to the first embodiment; FIG. [Figure 7A] 7 is a diagram showing another example of the d-axis current limit value map provided in the d-axis current limit value calculation unit according to the first embodiment. FIG. [Figure 7B] 13 is a diagram showing yet another example of the d-axis current limit value map provided in the d-axis current limit value calculation unit according to the first embodiment. FIG. [Figure 8] 5 is a flowchart showing an operation of a d-axis current limit value calculation unit according to the first embodiment. [Figure 9] 5 is a flowchart showing an operation of a d-axis current guard processor according to the first embodiment. [Figure 10] 4 is a diagram showing an example of a q-axis voltage limit value map provided in a q-axis voltage limit value calculation unit according to the first embodiment; FIG. [Figure 11A]7 is a diagram showing another example of the q-axis voltage limit value map provided in the q-axis voltage limit value calculation unit according to the first embodiment. FIG. [Figure 11B] 13 is a diagram showing yet another example of the q-axis voltage limit value map provided in the q-axis voltage limit value calculation unit according to the first embodiment. FIG. [Figure 12] 5 is a flowchart showing an operation of a q-axis voltage limit value calculation unit according to the first embodiment. [Figure 13] 5 is a flowchart showing an operation of a voltage guard processing unit according to the first embodiment. [Figure 14] FIG. 11 is a block diagram showing a partial configuration of a motor control signal calculation unit of an electric power steering device according to a second embodiment. [Figure 15] 13 is a diagram showing an example of a q-axis voltage limit value map provided in a q-axis voltage limit value calculation unit according to the second embodiment. FIG. [Figure 16] 10 is a flowchart showing an operation of a voltage guard processing unit according to the second embodiment. [Figure 17] 13 is a diagram showing an example of a d-axis current limit value map provided in a d-axis current limit value calculation section according to the third embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, a preferred example of an electric power steering (EPS) device according to the present disclosure will be described. Note that the same reference numerals in each drawing indicate the same or corresponding parts.

[0014] Embodiment 1 The power steering device according to the first embodiment will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of an electric power steering device according to a first embodiment. In FIG. 1, the electric power steering device 1 includes a steering shaft 11 to which a steering wheel 2 is attached, a rack-and-pinion mechanism 12, a rack shaft 13, and a cylindrical rack housing 14 into which the rack shaft 13 is inserted. Thus, the rotation of the steering shaft 11 caused by the operation of the steering wheel 2 is converted into a reciprocating motion in the axial direction of the rack shaft 13 by the rack-and-pinion mechanism 12. The steering shaft 11 is made up of a column shaft 15, an intermediate shaft 16, and a pinion shaft 17, in that order from the steering wheel 2 side. To both ends of the rack shaft 13, in that order from the side closest to the rack shaft 13, a rack end 18 made up of a ball joint, a tie rod 19, a knuckle (not shown), and front wheels 20 are connected.

[0015] When the rack shaft 13 reciprocates, the positions at which it comes into contact with the rack ends 18 at both ends are the maximum steering angles θmax (steering end positions) on the left and right sides at which steering is possible.

[0016] In addition, a torque sensor 3 is provided on the steering shaft 11, and when a steering torque is applied to the steering wheel 2 by the driver's steering, the torque sensor 3 detects the steering torque, and the detected steering torque Ts is output to the control device 4. The control device 4 calculates three-phase voltage commands Vu*, Vv*, Vw* to be applied to the motor 8 based on the steering torque Ts detected by the torque sensor 3, and outputs them to the power converter 9. Note that the steering torque Ts is detected as a positive value when the vehicle is steered in one direction, and as a negative value when the vehicle is steered in the opposite direction.

[0017] The control device 4 is composed of, for example, a CPU (Central Processing Unit) 5 or a processor and a storage device as hardware. The storage device includes a volatile storage device such as a RAM (Random Access Memory) 7, and a ROM (Read Only Memory) 6 which is a non-volatile auxiliary storage device such as a flash memory. Also, instead of the flash memory, a hard disk auxiliary storage device may be included. The CPU 5 sequentially executes the programs input from the ROM 6. In this case, the programs are input from the ROM 6 to the CPU 5 via the RAM 7. The CPU 5 may output data such as the results of calculations to the RAM 7, or may store data in the ROM 6 via the RAM 7. The programs execute the various functions of the control device 4 described below (see FIG. 2).

[0018] The power converter 9 is configured, for example, with switching elements and the like formed from semiconductor devices, and applies three-phase voltages Vu, Vv, Vw, which are voltages converted to predetermined voltages based on the three-phase voltage commands Vu*, Vv*, Vw* output from the control device 4, to the motor 8. The current detection unit 22 detects the three-phase current supplied to the motor 8 by the power converter 9, and outputs the detected current to the control device 4. The current detection unit 22 in this embodiment is shown as detecting the three-phase currents Iu, Iv, Iw, but may also be configured to detect two phases Iu, Iv of the three-phase current.

[0019] The motor 8 generates an assist torque for assisting the steering torque on the steering shaft 11 via the gear 23, and the steering torque and the assist torque are transmitted to the rack shaft 13, thereby changing the steering angle of the front wheels 20, which corresponds to the direction of travel of the vehicle.

[0020] The motor is also provided with a rotational position detector 21, which detects the rotational position θm (electrical angle) of the motor 8 as a relative angle within a range of 360° and outputs it to the control device 4. Although the rotational position detection unit 21 in the present embodiment 1 is a unit that directly detects the rotational position, such as a resolver, the rotational position may be obtained by a known method of calculation based on the voltage applied to the motor 8 and the current detected by the current detection unit 22. Note that, if the rotational position θm is a positive value when the steering is performed in a certain direction, it is detected as a negative value when the steering is performed in the opposite direction.

[0021] Next, the function of the control device 4 will be described. Fig. 2 is a functional block diagram showing the configuration of the control device 4. In Fig. 2, the control device 4 includes a q-axis current command value calculation unit 31 that calculates a q-axis current command value Iq** corresponding to an assist torque target value, a d-axis current command value calculation unit 32 that calculates a d-axis current command value Id** corresponding to a magnetic flux component current target value, and a motor control signal calculation unit 33 that outputs three-phase voltage commands Vu*, Vv*, Vw* based on the q-axis current command value Iq** and the d-axis current command value Id**.

[0022] The q-axis current command value Iq** and the d-axis current command value Id** are target values ​​of the current to be supplied to the motor 8, and respectively indicate the current command value on the d-axis and the current command value on the q-axis in the dq coordinate system. Note that the q-axis current command value Iq** is a positive value when steering is assisted in a certain direction, and is a negative value when steering is assisted in the other direction. The d-axis current command value Id** is always a value of 0 or less, regardless of the direction in which steering is assisted.

[0023] The control device 4 further includes a control steering angle calculation unit 34, a differentiator 35, and a rotational angular velocity axis conversion unit 36, which will be described later. The control steering angle calculation unit 34 calculates a control steering angle θs that corresponds to the rotational angle of the steering shaft 11 and can be converted into the steering angle of the front wheels 20. The control steering angle calculation unit 34 receives an input of the rotational position θm of the motor 8 detected by the rotational position detection unit 21.

[0024] Here, the operation of the control steering angle calculation unit 34 will be described with a specific example. For example, the reference control steering angle θs0 when the vehicle is traveling straight is set as the origin, and the number of rotations of the motor 8, with 360° being one rotation, is counted, and the control steering angle θs is calculated as an absolute steering angle including a range greater than 360° based on the number of rotations of the motor 8 and the rotational position θm of the motor 8. Note that the control steering angle θs is a positive value when it is a rotation angle in a certain direction from the origin, and a negative value when it is a rotation angle in the other direction.

[0025] When the steering wheel 2 is steered to the vicinity of its maximum steering angle θmax (steering end position), that is, when the steering angle of the front wheels 20 is steered to the vicinity of its movable limit, if a turning steering operation for further increasing the absolute value of the control steering angle θs is performed at a large steering angular velocity ωs, the rack end 18 collides with the rack housing 14, and an impact occurs in the steering system. In order to deal with such a problem, for example, a method can be considered in which the absolute value of the assist torque target value is reduced by limiting the q-axis current command value Iq** corresponding to the assist torque target value so that it does not exceed a limit value based on the steering angle. However, as described above, with this configuration, there is a problem that the impact of the end hitting cannot be sufficiently alleviated when traveling on a low μ road with a small road surface reaction force μ.

[0026] Therefore, in this embodiment, the q-axis current command value calculation unit 31, the d-axis current command value calculation unit 32, and the motor control signal calculation unit 33 of the control device 4 respectively calculate the q-axis current command value Iq**, the d-axis current command value Id**, and the q-axis voltage command value Vq** in accordance with the steering angle, thereby enabling the shock caused by the end hit to be sufficiently mitigated.

[0027] First, the q-axis current command value calculation unit 31 will be described. The q-axis current command value calculation unit 31 includes a base current command value calculation unit 41 that calculates a base q-axis current command value Iq* that is the reference for the q-axis current command value Iq**, a q-axis current limit value calculation unit 42 that calculates the q-axis current limit value Iqg, and a q-axis current guard processing unit 43 that calculates the q-axis current command value Iq**.

[0028] The base current command value calculation unit 41 receives the steering torque Ts detected by the torque sensor 3. The base current command value calculation unit 41 calculates a base q-axis current command value Iq* based on the steering torque Ts. As is well known, the base current command value calculation unit 41 may calculate the base q-axis current command value Iq* based on information other than the steering torque Ts, such as a vehicle speed (not shown), in addition to the steering torque Ts. Specifically, the base current command value calculation unit 41 includes a map that defines the relationship between the steering torque Ts and the base q-axis current command value Iq*, and calculates the base q-axis current command value Iq* according to the steering torque Ts by referring to this map. In this map, the base q-axis current command value Iq* is set to be a larger absolute value as the absolute value of the steering torque Ts increases. In this manner, the base q-axis current command value Iq* calculated by the base current command value calculation unit 41 is output to the q-axis current guard processing unit 43.

[0029] The control steering angle θs calculated by the control steering angle calculation unit 34 is input to the q-axis current limit value calculation unit 42. The q-axis current limit value calculation unit 42 has a q-axis current limit value map 44 that indicates the relationship between the absolute value |θs| of the control steering angle θs and the q-axis current limit value Iqg, and calculates the q-axis current limit value Iqg based on this q-axis current limit value map 44.

[0030] Fig. 3 is a diagram showing an example of the q-axis current limit value map 44. As shown in Fig. 3, when the absolute value |θs| of the control steering angle θs is greater than the first steering angle threshold θth1 near the maximum steering angle θmax, the q-axis current limit value Iqg is calculated to be a smaller value as the absolute value |θs| of the control steering angle θs increases, and further, the q-axis current limit value Iqg becomes a negative value between the first steering angle threshold θth1 and the maximum steering angle θmax, and is calculated to be smaller to the q-axis current limit value minimum value IqgMIN, and is output to the q-axis current guard processing unit 43. The minimum value of the q-axis current limit value map 44 is set to be the q-axis current limit value minimum value IqgMIN, and the absolute value of the q-axis current limit value minimum value IqgMIN is a value at which the motor 8 can output a torque greater than the driver torque that a general driver can output.

[0031] In this embodiment, the first steering angle threshold θth1 is set to a value that, for example, when a typical driver steers the steering wheel 2 at the maximum steering angular velocity ωs at which steering is possible, keeps the steering angular velocity ωs below 0 between the first steering angle threshold θth1 and the maximum steering angle θmax, and prevents the control steering angle θs from reaching the maximum steering angle θmax.

[0032] Furthermore, when the control steering angle θs is less than or equal to the first steering angle threshold θth1, the q-axis current limit value Iqg is calculated to be a value IqgMAX greater than the absolute value of the maximum q-axis current value that the motor 8 can output, and is output to the q-axis current guard processing unit 43.

[0033] The q-axis current limit value map 44 is not limited to the example shown in FIG. 3. FIG. 4A is a diagram showing another example of the q-axis current limit value map 44, and FIG. 4B is a diagram showing yet another example of the q-axis current limit value map 44. As shown in FIG. 4A, the q-axis current limit value Iqg can be set to be nonlinearly smaller from IqgMAX to IqgMIN as the absolute value of the control steering angle θs increases. Also, as shown in FIG. 4B, the q-axis current limit value Iqg may be configured to be smaller in a stepwise manner in multiple stages from IqgMAX to IqgMIN as the absolute value of the control steering angle θs increases. Also, when the control steering angle θs is equal to or greater than the first steering angle threshold θth1, the q-axis current limit value Iqg may be set to IqgMIN in one stage from IqgMAX. However, as shown in FIG. 3, it is preferable to gradually decrease the q-axis current limit value Iqg as the control steering angle θs increases in order to suppress shock during steering.

[0034] The q-axis current guard processing unit 43 receives the base q-axis current command value Iq*, the q-axis current limit value Iqg, and the control steering angle θs. Based on these values, the q-axis current guard processing unit 43 outputs the q-axis current command value Iq** shown below to the d-axis current command value calculation unit 32 and the motor control signal calculation unit 33. (1) When the input control steering angle θs is equal to or greater than the first steering angle threshold θth1 and the base q-axis current command value Iq* is greater than the q-axis current limit value Iqg, the base q-axis current command value Iq* is limited to the q-axis current limit value Iqg, and the limited value is output as the q-axis current command value Iq** to the d-axis current command value calculation unit 32 and the motor control signal calculation unit 33.

[0035] (2) When the input control steering angle θs is equal to or greater than the first steering angle threshold θth1 and the base q-axis current command value Iq* is equal to or less than the q-axis current limit value Iqg, the base q-axis current command value Iq* is output as is as the q-axis current command value Iq** to the d-axis current command value calculation unit 32 and the motor control signal calculation unit 33.

[0036] (3) When the input control steering angle θs is less than or equal to -1 × the first steering angle threshold θth1 and the base q-axis current command value Iq* is smaller than -1 × the q-axis current limit value Iqg (i.e., when the absolute value of the base q-axis current command value Iq* is greater than the q-axis current limit value Iqg), the base q-axis current command value Iq* is limited to -1 × the q-axis current limit value Iqg, and the value is output to the d-axis current command value calculation unit 32 and the motor control signal calculation unit 33 as the q-axis current command value Iq**.

[0037] (4) When the input control steering angle θs is equal to or less than -1 × first steering angle threshold θth1 and the base q-axis current command value Iq* is equal to or greater than -1 × q-axis current limit value Iqg (i.e., when the absolute value of the base q-axis current command value Iq* is equal to or less than the q-axis current limit value Iqg), the base q-axis current command value Iq* is output as is as the q-axis current command value Iq** to the d-axis current command value calculation unit 32 and the motor control signal calculation unit 33.

[0038] (5) When the input control steering angle θs is smaller than the first steering angle threshold θth1 and larger than -1 × the first steering angle threshold θth1, the base q-axis current command value Iq* is output as is as the q-axis current command value Iq** to the d-axis current command value calculation unit 32 and the motor control signal calculation unit 33.

[0039] By performing this calculation, when the absolute value of the control steering angle θs becomes equal to or greater than the first steering angle threshold θth1 and steering is performed to approach the maximum steering angle θmax, the upper limit of the absolute value of the q-axis current command value Iq** corresponding to the assist torque target value is reduced, and when the maximum steering angle θmax is approached, the sign of the q-axis current command value Iq** is reversed, so that the q-axis current command value Iq** is output in the opposite direction to the output direction of the steering torque Ts, preventing steering to the maximum steering angle θmax (steering end position) and mitigating the impact of the end hit. In other words, the "guard process" in the q-axis current guard processing unit 43 is to calculate the q-axis current command value Iq** so as to mitigate the impact of the end hit.

[0040] Next, the operation of the above-mentioned q-axis current guard processing unit 43 will be described with reference to the flowchart shown in FIG. First, in step S101, the q-axis current guard processing unit 43 acquires the control steering angle θs, the base q-axis current command value Iq*, and the q-axis current limit value Iqg as each piece of input information.

[0041] Next, in step S102, it is determined whether the control steering angle θs is near the maximum steering angle θmax in the positive direction depending on whether the control steering angle θs is equal to or greater than the first steering angle threshold θth1. If the control steering angle θs is equal to or greater than the first steering angle threshold θth1, it is determined that the control steering angle θs is near the maximum steering angle θmax in the positive direction (Yes in step S102), and the process proceeds to step S103.

[0042] In step S103, it is determined whether the base q-axis current command value Iq* is greater than the q-axis current limit value Iqg. If the base q-axis current command value Iq* is greater than the q-axis current limit value Iqg (Yes in step S103), the process proceeds to step S104, and the q-axis current limit value Iqg is output as the q-axis current command value Iq**.

[0043] In step S103, if the base q-axis current command value Iq* is equal to or less than the q-axis current limit value Iqg (No in step S103), the process proceeds to step S105, and the base q-axis current command value Iq* is output as the q-axis current command value Iq**.

[0044] In step S102, if the control steering angle θs is not near the maximum steering angle θmax in the positive direction, that is, if the control steering angle θs is smaller than the first steering angle threshold θth1 (No in step S102), the process proceeds to step S106. In step S106, it is determined whether the control steering angle θs is near the maximum steering angle θmax in the negative direction depending on whether the control steering angle θs is equal to or smaller than -1 × the first steering angle threshold θth1.

[0045] In step S106, if the control steering angle θs is equal to or smaller than -1 × the first steering angle threshold θth1, it is determined that the control steering angle θs is close to the maximum steering angle θmax in the negative direction (Yes in step S106), and the process proceeds to step S107. In step S107, it is determined whether the base q-axis current command value Iq* is smaller than -1 × the q-axis current limit value Iqg.

[0046] In step S107, if the base q-axis current command value Iq* is smaller than -1 x the q-axis current limit value Iqg (Yes in step S107), the process proceeds to step S108, and -1 x the q-axis current limit value Iqg is output as the q-axis current command value Iq**.

[0047] In step S107, if the base q-axis current command value Iq* is equal to or greater than -1 x the q-axis current limit value Iqg (No in step S107), the process proceeds to step S105, and the base q-axis current command value Iq* is output as the q-axis current command value Iq**.

[0048] In step S106, if the control steering angle θs is greater than −1×the first steering angle threshold θth1 (No in step S106), the process proceeds to step S105, and the base q-axis current command value Iq* is output as the q-axis current command value Iq**.

[0049] As described above, when the control steering angle θs is equal to or greater than the first steering angle threshold θth1, the q-axis current limit value Iqg, which is the upper limit of the base q-axis current command value Iq*, is reduced, and when the control steering angle θs approaches the maximum steering angle θmax in the positive direction, the sign of the q-axis current limit value Iqg is limited to be negative. On the other hand, when the control steering angle θs is equal to or less than -1×the first steering angle threshold θth1, the lower limit of the base q-axis current command value Iq*, -1×the q-axis current limit value Iqg, is increased, and when the control steering angle θs approaches the maximum steering angle -1×θmax in the negative direction, the sign of the -1×the q-axis current limit value Iqg is limited to be positive. By controlling in this manner, steering to the maximum steering angle θmax is prevented, and it is possible to mitigate the impact caused by the end hitting.

[0050] Next, a description will be given of the d-axis current command value calculation unit 32. In Fig. 2, the d-axis current command value calculation unit 32 includes a reference d-axis current command value calculation unit 45 that calculates the d-axis current command value before guard processing, a d-axis current limit value calculation unit 46, and a d-axis current guard processing unit 47.

[0051] The rate of change of the rotational position θm of the motor 8 detected by the rotational position detector 21 is calculated by the differentiator 35, and is output as the rotational speed ωm of the motor 8. The rotational speed ωm and the q-axis current command value Iq** output from the q-axis current guard processor 43 are input to the reference d-axis current command value calculator 45, which calculates the d-axis current command value before guard processing. As described above, when the rotational speed ωm becomes large as an absolute value, the induced voltage reaches a voltage amplitude that can be applied to the motor 8, so the reference d-axis current command value calculator 45 outputs the reference d-axis current command value Id* calculated to a value that cancels the magnetic flux of the rotor so that the motor can be driven at high speed to the d-axis current guard processor 47. When the d-axis current has a negative value, a magnetic flux that cancels the magnetic flux of the rotor is generated in the stator of the motor through which the d-axis current flows.

[0052] The rotational speed ωm output from the differentiator 35 is converted into the rotational speed of the steering shaft in the rotational angular velocity axis conversion unit 36, and is output as the steering angular velocity ωs. The control steering angle θs and the steering angular velocity ωs are input to the d-axis current limit value calculation unit 46. The d-axis current limit value calculation unit 46 has a d-axis current limit value map 48 that indicates the relationship between the absolute value |θs| of the control steering angle θs and the d-axis current limit value Idg, and calculates the d-axis current limit value Idg based on this d-axis current limit value map 48.

[0053] Fig. 6 is a diagram showing an example of the d-axis current limit value map 48. As shown in Fig. 6, when the absolute value |θs| of the control steering angle θs is greater than the second steering angle threshold value θth2 near the maximum steering angle θmax, and the steering state of the steering wheel 2 is in a turning state that satisfies the steering angular velocity ωs>0 when the control steering angle θs>0, or the steering angular velocity ωs<0 when the control steering angle θs<0, the d-axis current limit value Idg is calculated to be a smaller value as the absolute value |θs| of the control steering angle θs increases. The calculation result of the d-axis current limit value calculation unit 46 is output to the d-axis current guard processing unit 47. At this time, the minimum value of the d-axis current limit value map 48 is set to be 0.

[0054] In addition, when the control steering angle θs is equal to or less than the second steering angle threshold θth2, or when the steering state of the steering wheel 2 is not turned, the d-axis current limit value Idg calculated by the d-axis current limit value calculation unit 46 is calculated to be a value IdgMAX greater than the absolute value of the maximum d-axis current value Id that the motor 8 can output, and is output to the d-axis current guard processing unit 47.

[0055] The d-axis current limit value map 48 is not limited to the example shown in FIG. 6. FIG. 7A is a diagram showing another example of the d-axis current limit value map 48, and FIG. 7B is a diagram showing yet another example of the d-axis current limit value map 48. As shown in FIG. 7A, the d-axis current limit value Idg may be set to be nonlinearly smaller from IdgMAX to 0 as the absolute value of the control steering angle θs increases. Also, as shown in FIG. 7B, the d-axis current limit value Idg may be configured to be smaller in a stepwise manner in multiple stages from IdgMAX to 0 as the absolute value of the control steering angle θs increases. Also, when the control steering angle θs is equal to or greater than the second steering angle threshold θth2, the d-axis current limit value Idg may be set to 0 in one stage from IdgMAX. However, as shown in FIG. 6, it is preferable to gradually decrease the d-axis current limit value Idg as the control steering angle θs increases in order to suppress shock during steering.

[0056] The second steering angle threshold θth2 is set to an angle smaller than the first steering angle threshold θth1. In other words, the d-axis current limit value calculation unit 46 of this embodiment calculates the d-axis current limit value Idg so that the absolute value of the d-axis current limit value Idg is smaller than the maximum d-axis current value IdgMAX that the motor 8 can output, in a situation where the absolute value of the control steering angle θs is smaller than the first steering angle threshold θth1.

[0057] Next, the operation of the d-axis current limit value calculation unit 46 will be described with reference to the flowchart shown in FIG. First, in step S201, the d-axis current limit value calculation unit 46 acquires the control steering angle θs and the steering angular velocity ωs as the respective input information.

[0058] In step S202, it is determined whether the control steering angle θs is close to the maximum steering angle θmax depending on whether the control steering angle θs is equal to or greater than the second steering angle threshold θth2. If the control steering angle θs is equal to or greater than the second steering angle threshold θth2, it is determined that the control steering angle θs is close to the maximum steering angle θmax (Yes in step S202), and the process proceeds to step S203.

[0059] In step S203, it is determined whether or not the steering is positive steering, depending on whether the control steering angle θs × the steering angular velocity ωs is greater than 0. If the control steering angle θs × the steering angular velocity ωs is greater than 0, it is determined to be positive steering (Yes in step S203), and the process proceeds to step S204, where a value calculated based on the absolute value |θs| of the control steering angle θs and the d-axis current limit value map 48 is output as the d-axis current limit value Idg.

[0060] In step S203, if the control steering angle θs × steering angular velocity ωs is equal to or less than 0, it is determined that the steering is not a turning steering (No in step S203), and the process proceeds to step S205, where the maximum d-axis current value IdgMAX that the motor 8 can output is output as the d-axis current limit value Idg.

[0061] Also, in step S202, if the control steering angle θs is smaller than the second steering angle threshold θth2 and the control steering angle θs is not near the maximum steering angle θmax (No in step S202), the process proceeds to step S205, and the maximum d-axis current value IdgMAX that the motor 8 can output is output as the d-axis current limit value Idg.

[0062] The d-axis current guard processing unit 47 receives the d-axis current limit value Idg in addition to the reference d-axis current command value Id* before guard processing, and outputs the d-axis current command value Id** shown below based on these values ​​to the motor control signal calculation unit 33. (1) If the absolute value of the input reference d-axis current command value Id* is greater than or equal to the d-axis current limit value Idg and the reference d-axis current command value Id* is greater than or equal to 0, the d-axis current limit value Idg is output to the motor control signal calculation unit 33 as the d-axis current command value Id**.

[0063] (2) If the absolute value of the input reference d-axis current command value Id* is greater than or equal to the d-axis current limit value Idg and the reference d-axis current command value Id* is smaller than 0, -1 x the d-axis current limit value Idg is output to the motor control signal calculation unit 33 as the d-axis current command value Id**.

[0064] (3) When the absolute value of the input reference d-axis current command value Id* is smaller than the d-axis current limit value Idg, the value of the reference d-axis current command value Id* is output as is to the motor control signal calculation unit 33 as the d-axis current command value Id**. That is, the above-mentioned (1) to (3) result in the d-axis current guard processing unit 47 outputting a d-axis current command value Id** whose absolute value does not exceed the d-axis current limit value Idg.

[0065] Next, the operation of the above-mentioned d-axis current guard processor 47 will be described with reference to the flowchart shown in FIG. First, in step S301, the reference d-axis current command value Id* and the d-axis current limit value Idg are obtained as input information.

[0066] In step S302, it is determined whether the absolute value of the reference d-axis current command value Id* is equal to or greater than the d-axis current limit value Idg. If the absolute value of the reference d-axis current command value Id* is equal to or greater than the d-axis current limit value Idg (Yes in step S302), the process proceeds to step S303.

[0067] In step S303, it is determined whether the reference d-axis current command value Id* is greater than or equal to 0. If the reference d-axis current command value Id* is greater than or equal to 0 (Yes in step S303), the process proceeds to step S304, and the d-axis current limit value Idg is output as the d-axis current command value Id**.

[0068] In step S303, if the reference d-axis current command value Id* is smaller than 0 (No in step S303), the process proceeds to step S305, and -1 x the d-axis current limit value Idg is output as the d-axis current command value Id**.

[0069] Furthermore, in step S302, if the absolute value of the reference d-axis current command value Id* is smaller than the d-axis current limit value Idg (No in step S302), the process proceeds to step S306, and the reference d-axis current command value Id* is output as the d-axis current command value Id**.

[0070] As described above, when the absolute value of the control steering angle θs is equal to or greater than the second steering angle threshold θth2 and the steering is in a turning steering state, the d-axis current limit value Idg, which is the upper limit of the absolute value of the reference d-axis current command value Id* before the guard processing, is reduced by the d-axis current limit value calculation unit 46 and the d-axis current guard processing unit 47. This suppresses the function of canceling the magnetic flux of the rotor, and the induced voltage reaches a voltage amplitude that can be applied to the motor 8 at a smaller absolute value of the rotation speed ωm. As a result, it is possible to prevent the driver from steering at high speed near the maximum steering angle and to mitigate the impact caused by the end hit. In other words, the "guard processing" in the d-axis current guard processing unit 47 is to calculate the d-axis current command value Id** so that the impact of the end hit is mitigated.

[0071] Next, the motor control signal calculation unit 33 will be described. In Fig. 2, the motor control signal calculation unit 33 receives the q-axis current command value Iq** output from the q-axis current command value calculation unit 31, the d-axis current command value Id** output from the d-axis current command value calculation unit 32, the control steering angle θs output from the control steering angle calculation unit 34, the steering angular velocity ωs output from the rotational angular velocity axis conversion unit 36, the three-phase currents Iu, Iv, Iw detected by the current detection unit 22, and the rotational position θm of the motor 8 detected by the rotational position detection unit 21. The motor control signal calculation unit 33 then calculates the phase voltage command values ​​Vu*, Vv*, Vw* of the u, v, and w phases, respectively, by executing current feedback control in the dq coordinate system based on the three-phase currents Iu, Iv, Iw and the rotational position θm of the motor 8.

[0072] In the motor control signal calculation unit 33, the three-phase currents Iu, Iv, Iw and the rotational position θm of the motor 8 are input to a three-phase to two-phase conversion unit 49. Then, in the three-phase to two-phase conversion unit 49, the three-phase currents Iu, Iv, Iw are converted into a d-axis current value Id and a q-axis current value Iq, which are actual current values ​​in a dq coordinate system.

[0073] The q-axis current command value Iq** input to the motor control signal calculation unit 33 is input to an adder / subtractor 50a together with the q-axis current value Iq, and the q-axis current deviation ΔIq=Iq**-Iq is calculated. On the other hand, the d-axis current command value Id** is input to an adder / subtractor 50b together with the d-axis current value Id, and the d-axis current deviation ΔId=Id**-Id is calculated. The q-axis current deviation ΔIq and the d-axis current deviation ΔId calculated in this manner are input to the corresponding feedback control units (hereinafter referred to as FB control units) 51, 52, respectively.

[0074] In these FB control units 51 and 52, feedback control is performed to make the q-axis current value and the d-axis current value, which are actual current values, follow the q-axis current command value Iq** and the d-axis current command value Id**, which are their target values. Specifically, the FB control units 51 and 52 multiply the input q-axis current deviation ΔIq and the d-axis current deviation ΔId by a predetermined gain (PI gain) based on the constants of the inductance and induced voltage of the motor, to calculate a reference q-axis voltage command value Vq* and a d-axis voltage command value Vd*, which are references before guard processing.

[0075] In this embodiment, the reference q-axis voltage command value Vq* before guard processing is input to a voltage guard processing unit 55 together with a q-axis voltage limit value Vqg calculated in a q-axis voltage limit value calculation unit 53 described later, and the voltage guard processing unit 55 calculates a q-axis voltage command value Vq**. Then, the q-axis voltage command value Vq** is input to a two-phase to three-phase conversion unit 56 together with a d-axis voltage command value Vd* and a rotational position θm of the motor 8. The two-phase to three-phase conversion unit 56 calculates phase voltage command values ​​Vu*, Vv*, Vw* for the u, v, and w phases, respectively.

[0076] The control steering angle θs and the steering angular velocity ωs are input to the q-axis voltage limit value calculation unit 53. The q-axis voltage limit value calculation unit 53 has a q-axis voltage limit value map 54 indicating the relationship between the absolute value |θs| of the control steering angle θs and the q-axis voltage limit value Vqg, and calculates the q-axis voltage limit value Vqg based on this q-axis voltage limit value map 54.

[0077] FIG. 10 is a diagram showing an example of the q-axis voltage limit value map 54. As shown in FIG. 10, the q-axis voltage limit value map is calculated such that, when the absolute value |θs| of the control steering angle θs is greater than the third steering angle threshold θth3 near the maximum steering angle θmax and the steering state of the steering wheel 2 is in a turning state, the q-axis voltage limit value Vqg becomes smaller as the absolute value of the control steering angle θs becomes greater. Then, the calculation result of the q-axis voltage limit value calculation unit 53 is output to the voltage guard processing unit 55. At this time, the minimum value of the q-axis voltage limit value map 54 is set to VqgMIN. VqgMIN is set to a value equal to or greater than the q-axis voltage value required for the motor 8 to output the rated current when the rotation speed ωm=0.

[0078] In addition, when the absolute value |θs| of the control steering angle θs is equal to or less than the third steering angle threshold θth3, or when the steering state of the steering wheel 2 is in a return state, the q-axis voltage limit value Vqg calculated by the q-axis voltage limit value calculation unit 53 is calculated to be a value VqgMAX greater than the absolute value of the maximum q-axis voltage value Vq that the motor 8 can output, and is output to the voltage guard processing unit 55.

[0079] The q-axis voltage limit value map 54 is not limited to the example shown in FIG. 10. FIG. 11A is a diagram showing another example of the q-axis voltage limit value map 54, and FIG. 11B is a diagram showing yet another example of the q-axis voltage limit value map 54. As shown in FIG. 11A, the q-axis voltage limit value Vqg can be set to be nonlinearly smaller from VqgMAX to VqgMIN as the absolute value of the control steering angle θs increases. Also, as shown in FIG. 11B, the q-axis voltage limit value Vqg may be configured to be smaller in multiple steps from VqgMAX to VqgMIN as the absolute value of the control steering angle θs increases. Also, when the control steering angle θs is equal to or greater than the third steering angle threshold θth3, the q-axis voltage limit value Vqg may be set to VqgMIN in one step from VqgMAX. However, as shown in FIG. 10, it is preferable to gradually decrease the q-axis voltage limit value Vqg as the control steering angle θs increases in order to suppress shock during steering.

[0080] The third steering angle threshold θth3 is set to an angle smaller than the first steering angle threshold θth1 and larger than the second steering angle threshold θth2. In other words, the q-axis voltage limit value calculation unit 53 of this embodiment calculates a q-axis voltage limit value Vqg smaller than the absolute value of the maximum q-axis voltage value Vq that can be output by the motor 8 from a situation in which the absolute value of the control steering angle θs is smaller than the first steering angle threshold θth1 and larger than the second steering angle threshold θth2.

[0081] Next, the operation of the q-axis voltage limit value calculation unit 53 will be described with reference to the flowchart shown in FIG. First, in step S401, the q-axis voltage limit value calculation unit 53 acquires the control steering angle θs and the steering angular velocity ωs as the respective input information.

[0082] In step S402, it is determined whether the control steering angle θs is close to the maximum steering angle θmax depending on whether the control steering angle θs is equal to or greater than the third steering angle threshold θth3. If the control steering angle θs is equal to or greater than the third steering angle threshold θth3, it is determined that the control steering angle θs is close to the maximum steering angle θmax (Yes in step S402), and the process proceeds to step S403.

[0083] In step S403, it is determined whether the steering is positive steering based on whether the control steering angle θs × the steering angular velocity ωs is greater than 0. If the control steering angle θs × the steering angular velocity ωs is greater than 0, it is determined that the steering is positive steering (Yes in step S403), and the process proceeds to step S404, where a value calculated based on the absolute value |θs| of the control steering angle θs and the q-axis voltage limit value map 54 is set as the q-axis voltage limit value Vqg.

[0084] In step S403, if the control steering angle θs × steering angular velocity ωs is equal to or less than 0, it is determined that the steering is not a turning steering (No in step S403), and the process proceeds to step S405, where the maximum q-axis voltage value VqgMAX that the motor 8 can output is set as the q-axis voltage limit value Vqg.

[0085] Also, in step S402, if the control steering angle θs is smaller than the third steering angle threshold θth3 and the control steering angle θs is not near the maximum steering angle θmax (No in step S402), the process proceeds to step S405, and the maximum q-axis voltage value VqgMAX that the motor 8 can output is set as the q-axis voltage limit value Vqg.

[0086] In addition to the reference q-axis voltage command value Vq* before guard processing, the q-axis voltage limit value Vqg is input to the voltage guard processing unit 55, and the voltage guard processing unit 55 outputs the q-axis voltage command value Vq** shown below to the 2-phase to 3-phase conversion unit 56 based on these input values. (1) The absolute value of the reference q-axis voltage command value Vq* before the guard processing is the q-axis voltage limit value Vqg Less than In this case, the value of the reference q-axis voltage command value Vq* before the guard processing is output as it is to the two-phase to three-phase conversion unit 56 as the q-axis voltage command value Vq**.

[0087] (2) The absolute value of the reference q-axis voltage command value Vq* before the guard processing is the q-axis voltage limit value Vqg The above In this case, the absolute value of the reference q-axis voltage command value Vq* before the guard processing is limited to the value of the q-axis voltage limit value Vqg, and the limited value is output to the two-phase to three-phase conversion unit 56 as the q-axis voltage command value Vq**. That is, due to the above-mentioned (1) and (2), the absolute value of the q-axis voltage command value Vq** output from the voltage guard processing unit 55 is output so as not to exceed the value of the q-axis voltage limit value Vqg.

[0088] Next, the operation of the above-mentioned voltage guard processing unit 55 will be described with reference to the flowchart shown in FIG. First, in step S501, the voltage guard processing unit 55 acquires, as input information, the reference q-axis voltage command value Vq* before guard processing and the q-axis voltage limit value Vqg.

[0089] In step S502, it is determined whether the absolute value of the reference q-axis voltage command value Vq* before the guard processing is equal to or greater than the q-axis voltage limit value Vqg. If the absolute value of the reference q-axis voltage command value Vq* before the guard processing is equal to or greater than the q-axis voltage limit value Vqg (Yes in step S502), the process proceeds to step S503.

[0090] In step S503, it is determined whether the reference q-axis voltage command value Vq* before the guard processing is greater than or equal to 0. If the reference q-axis voltage command value Vq* before the guard processing is greater than or equal to 0 (Yes in step S503), the process proceeds to step S504, and the q-axis voltage limit value Vqg is output as the q-axis voltage command value Vq**.

[0091] In step S503, if the reference q-axis voltage command value Vq* before the guard process is smaller than 0 (No in step S503), the process proceeds to step S505, and -1 x the q-axis voltage limit value Vqg is output as the q-axis voltage command value Vq**.

[0092] Also, in step S502, if the absolute value of the reference q-axis voltage command value Vq* before the guard processing is smaller than the q-axis voltage limit value Vqg (No in step S502), proceed to step S506, and output the reference q-axis voltage command value Vq* before the guard processing as the q-axis voltage command value Vq**.

[0093] As described above, when the absolute value of the control steering angle θs is equal to or greater than the third steering angle threshold θth3 and the steering is in a turning steering state, the q-axis voltage limit value Vqg, which is the upper limit of the absolute value of the reference q-axis voltage command value Vq* before the guard processing, is reduced to reduce the voltage amplitude that can be applied to the motor 8 by the q-axis voltage limit value calculation unit 53 and the voltage guard processing unit 55. As a result, the induced voltage reaches the voltage amplitude that can be applied to the motor 8 at a smaller absolute value of the rotation speed ωm, so that it is possible to prevent the driver from steering at high speed near the maximum steering angle and to mitigate the impact of the end hit. In other words, the "guard processing" in the voltage guard processing unit 55 is to calculate the q-axis voltage command value Vq** limited by the q-axis voltage limit value Vqg so that the impact of the end hit is mitigated.

[0094] As described above, according to the electric power steering device of the first embodiment, the control device 4 includes the q-axis current command value calculation unit 31, the d-axis current command value calculation unit 32, and the motor control signal calculation unit 33. The q-axis current command value calculation unit 31 includes the q-axis current guard processing unit 43 that calculates the q-axis current command value Iq** so as to prevent steering to the maximum steering angle θmax (steering end position), so that the impact of end contact can be alleviated. The d-axis current command value calculation unit 32 includes the d-axis current guard processing unit 47 that suppresses the function of canceling the magnetic flux of the rotor and calculates the d-axis current command value Id** so as to prevent the driver from steering at high speed near the maximum steering angle, so that the impact of end contact can be alleviated. Furthermore, the motor control signal calculation unit 33 includes the voltage guard processing unit 55 that calculates the q-axis voltage command value Vq** so as to reduce the voltage amplitude that can be applied to the motor 8 and prevent the driver from steering at high speed near the maximum steering angle, so that the impact of end contact can be alleviated. Therefore, the impact of the end strike can be mitigated even on a low μ road, and deterioration of the steering feeling can be prevented.

[0095] Furthermore, the q-axis current limit value calculation unit 42 that calculates the q-axis current limit value Iqg for limiting the base q-axis current command value Iq* before guard processing previously holds a q-axis current limit value map 44 that indicates the relationship between the absolute value |θs| of the control steering angle θs and the q-axis current limit value Iqg, so it can smoothly calculate the q-axis current limit value Iqg based on the map and output it to the q-axis current guard processing unit 43. The d-axis current limit value calculation unit 46 that calculates the d-axis current limit value Idg for limiting the reference d-axis current command value Id* before guard processing previously holds a d-axis current limit value map 48 that indicates the relationship between the absolute value |θs| of the control steering angle θs and the d-axis current limit value Idg, so it can smoothly calculate the d-axis current limit value Idg based on the map and output it to the d-axis current guard processing unit 47. The q-axis voltage limit value calculation unit 53, which calculates the q-axis voltage limit value Vqg for limiting the reference q-axis voltage command value Vq* before guard processing, previously stores a map showing the relationship between the absolute value |θs| of the control steering angle θs and the q-axis voltage limit value Vqg, so can smoothly calculate the q-axis voltage limit value Vqg based on the map and output it to the voltage guard processing unit 55.

[0096] Embodiment 2 The electric power steering device according to the second embodiment will be described below with reference to FIGS. In the above-mentioned first embodiment, the q-axis voltage limit value Vqg and the q-axis voltage command value Vq** are calculated based on the q-axis voltage limit value calculation unit 53 and the voltage guard processing unit 55, but in the present second embodiment, another method will be described.

[0097] Fig. 14 is a block diagram showing a part of the configuration of the motor control signal calculation unit 33. In Fig. 14, instead of the q axis voltage limit value calculation unit 53, the q axis voltage limit value map 54, and the voltage guard processing unit 55 in Fig. 2, a q axis voltage limit value calculation unit 71, a q axis voltage limit value map 73, and a voltage guard processing unit 72 are provided. The other configuration is the same as in the first embodiment, so the description will be omitted.

[0098] The control steering angle θs is input to the q-axis voltage limit value calculation unit 71. The q-axis voltage limit value calculation unit 71 has a q-axis voltage limit value map 73 that indicates the relationship between the absolute value |θs| of the control steering angle θs and the q-axis voltage limit value Vqg, and calculates the q-axis voltage limit value Vqg based on this q-axis voltage limit value map 73.

[0099] Fig. 15 is a diagram showing an example of the q-axis voltage limit value map 73. As shown in Fig. 15, when the absolute value |θs| of the control steering angle θs is greater than the third steering angle threshold value θth3 near the maximum steering angle θmax, the q-axis voltage limit value Vqg is calculated to be a smaller value as the absolute value of the control steering angle θs increases, and is output to the voltage guard processing unit 72. At this time, the minimum value of the q-axis voltage limit value map 73 is set to VqgMIN. VqgMIN is set to a value equal to or greater than the q-axis voltage value required for the motor 8 to output the rated current when the rotation speed ωm=0.

[0100] In addition, when the absolute value of the control steering angle θs is less than or equal to the third steering angle threshold θth3, the q-axis voltage limit value Vqg calculated by the q-axis voltage limit value calculation unit 71 is calculated to be a value VqgMAX greater than the absolute value of the maximum q-axis voltage value that the motor 8 can output, and is output to the voltage guard processing unit 72.

[0101] The voltage guard processing unit 72 receives the reference q-axis voltage command value Vq* before guard processing, the q-axis voltage limit value Vqg, and the control steering angle θs. Based on these input values, the voltage guard processing unit 72 outputs the q-axis voltage command value Vq** as shown below to the 2-phase to 3-phase conversion unit 56.

[0102] (1) When the input control steering angle θs is equal to or greater than the third steering angle threshold θth3 and the reference q-axis voltage command value Vq* before guard processing is greater than the q-axis voltage limit value Vqg, the reference q-axis voltage command value Vq* before guard processing is limited to the value of the q-axis voltage limit value Vqg, and the value is output to the 2-phase to 3-phase conversion unit 56 as the q-axis voltage command value Vq**.

[0103] (2) When the input control steering angle θs is equal to or greater than the third steering angle threshold θth3 and the reference q-axis voltage command value Vq* before the guard processing is equal to or less than the q-axis voltage limit value Vqg, the reference q-axis voltage command value Vq* before the guard processing is output as is to the two-phase to three-phase conversion unit 56 as the q-axis voltage command value Vq**.

[0104] (3) When the input control steering angle θs is less than or equal to -1 × the third steering angle threshold θth3 and the reference q-axis voltage command value Vq* before guard processing is smaller than -1 × the q-axis voltage limit value Vqg, the reference q-axis voltage command value Vq* before guard processing is limited to the value of -1 × the q-axis voltage limit value Vqg, and the value is output to the 2-phase to 3-phase conversion unit 56 as the q-axis voltage command value Vq**.

[0105] (4) When the input control steering angle θs is equal to or less than -1 × the third steering angle threshold θth3 and the reference q-axis voltage command value Vq* before the guard processing is equal to or greater than -1 × the q-axis voltage limit value Vqg, the reference q-axis voltage command value Vq* before the guard processing is output as is to the 2-phase to 3-phase conversion unit 56 as the q-axis voltage command value Vq**.

[0106] (5) When the input control steering angle θs is smaller than the third steering angle threshold θth3 and larger than -1 × the third steering angle threshold θth3, the reference q-axis voltage command value Vq* before the guard processing is output as the q-axis voltage command value Vq** to the two-phase to three-phase conversion unit 56.

[0107] Next, the operation of the voltage guard processing unit 72 will be described with reference to the flowchart shown in FIG. First, in step S601, the voltage guard processing unit 72 acquires, as input information, the control steering angle θs, the reference q-axis voltage command value Vq* before guard processing, and the q-axis voltage limit value Vqg.

[0108] In step S602, it is determined whether the control steering angle θs is near the maximum steering angle θmax in the positive direction depending on whether the control steering angle θs is equal to or greater than the third steering angle threshold θth3. If the control steering angle θs is equal to or greater than the third steering angle threshold θth3, it is determined that the control steering angle θs is near the maximum steering angle θmax in the positive direction (Yes in step S602), and the process proceeds to step S603.

[0109] In step S603, it is determined whether the reference q-axis voltage command value Vq* before the guard processing is greater than the q-axis voltage limit value Vqg. If the reference q-axis voltage command value Vq* before the guard processing is greater than the q-axis voltage limit value Vqg (Yes in step S603), the process proceeds to step S604, and the q-axis voltage limit value Vqg is set as the q-axis voltage command value Vq**.

[0110] In step S603, if the reference q-axis voltage command value Vq* before the guard processing is equal to or less than the q-axis voltage limit value Vqg (No in step S603), the process proceeds to step S605, where the reference q-axis voltage command value Vq* before the guard processing is set as the q-axis voltage command value Vq**.

[0111] In step S602, if the control steering angle θs is not near the maximum steering angle θmax in the positive direction, that is, if the control steering angle θs is smaller than the third steering angle threshold θth3 (No in step S602), the process proceeds to step S606.

[0112] In step S606, it is determined whether the control steering angle θs is near the maximum steering angle θmax in the negative direction depending on whether the control steering angle θs is equal to or less than -1 × the third steering angle threshold θth3. If the control steering angle θs is equal to or less than -1 × the third steering angle threshold θth3, it is determined that the control steering angle θs is near the maximum steering angle θmax in the negative direction (Yes in step S606), and the process proceeds to step S607.

[0113] In step S607, it is determined whether the reference q-axis voltage command value Vq* before the guard processing is smaller than -1 × the q-axis voltage limit value Vqg. If the reference q-axis voltage command value Vq* before the guard processing is smaller than -1 × the q-axis voltage limit value Vqg (Yes in step S607), the process proceeds to step S608, and -1 × the q-axis voltage limit value Vqg is set as the q-axis voltage command value Vq**.

[0114] In step S607, if the reference q-axis voltage command value Vq* before the guard processing is greater than or equal to -1 x the q-axis voltage limit value Vqg (No in step S607), proceed to step S605, and the reference q-axis voltage command value Vq* before the guard processing is set as the q-axis voltage command value Vq**.

[0115] In step S606, if the control steering angle θs is greater than −1×the third steering angle threshold θth3 (No in step S606), the process proceeds to step S605, and the reference q-axis voltage command value Vq* before the guard process is set as the q-axis voltage command value Vq**.

[0116] As described above, when the control steering angle θs is equal to or greater than the third steering angle threshold θth3, the q-axis voltage limit value calculation unit 71 and the voltage guard processing unit 72 reduce the q-axis voltage limit value Vqg, which is the upper limit value of the reference q-axis voltage command value Vq* before guard processing, and when the control steering angle θs is equal to or less than -1×the third steering angle threshold θth3, increase the -1×the q-axis voltage limit value Vqg, which is the lower limit value of the reference q-axis voltage command value Vq* before guard processing, thereby reducing the voltage amplitude that can be applied to the motor 8. As a result, the induced voltage reaches the voltage amplitude that can be applied to the motor 8 at a small absolute value of the rotation speed ωm, making it possible to prevent the driver from steering at high speed near the maximum steering angle and to mitigate the impact caused by the end hitting.

[0117] The electric power steering device according to the second embodiment has the same effects as those of the first embodiment. Hereinafter, the effect of mitigating the impact caused by the end hit using the control device 4 included in the electric power steering device according to the second embodiment will be described.

[0118] (1) When the absolute value of the control steering angle θs is equal to or greater than the second steering angle threshold θth2 near the maximum steering angle θmax and the steering is in a turning steering state, the d-axis current limit value calculation unit 46 and the d-axis current guard processing unit 47 reduce the d-axis current limit value Idg, which is the upper limit value of the absolute value of the reference d-axis current command value Id* before guard processing, thereby suppressing the function of canceling out the rotor magnetic flux.

[0119] (2) When the absolute value of the control steering angle θs is equal to or greater than the third steering angle threshold θth3 that is greater than the second steering angle threshold θth2 and the steering is in a turning steering state, the q-axis voltage limit value Vqg, which is the upper limit of the absolute value of the reference q-axis voltage command value Vq* before guard processing, is reduced by the q-axis voltage limit value calculation unit 71 and the voltage guard processing unit 72. This allows the induced voltage to reach the voltage amplitude that can be applied to the motor 8 at a smaller absolute value of the rotation speed ωm, making it possible to prevent the driver from steering at high speed near the maximum steering angle θmax.

[0120] (3) When the control steering angle θs is equal to or greater than the first steering angle threshold θth1, the q-axis current limit value Iqg, which is the upper limit of the base q-axis current command value Iq*, is reduced by the q-axis current limit value calculation unit 42 and the q-axis current guard processing unit 43. Furthermore, when the control steering angle θs approaches the maximum steering angle θmax in the positive direction, the sign of the q-axis current limit value Iqg is limited to be negative. On the other hand, when the control steering angle θs is equal to or less than -1×the first steering angle threshold θth1, the -1×q-axis current limit value Iqg, which is the lower limit of the base q-axis current command value Iq*, is increased. Furthermore, when the control steering angle θs approaches the maximum steering angle -1×θmax in the negative direction, the sign of the -1×q-axis current limit value Iqg is limited until it becomes positive. As a result, the q-axis current command value Iq** is output in the direction opposite to the output direction of the steering torque Ts, and steering to the maximum steering angle θmax is prevented, thereby making it possible to mitigate the impact caused by the end contact. Therefore, the impact of the end hitting can be mitigated even on a low μ road, and deterioration of the steering feeling can be prevented.

[0121] In addition, the q-axis current limit value calculation unit 42 and the q-axis current guard processing unit 43, the d-axis current limit value calculation unit 46 and the d-axis current guard processing unit 47, and the q-axis voltage limit value calculation unit 71 and the voltage guard processing unit 72 each achieve the above-mentioned effects even when applied alone.

[0122] In addition, when the control steering angle θs approaches the maximum steering angle θmax, the impact caused by the end contact can be mitigated by reducing the upper limit of the absolute value of the q-axis current command value Iq** without reversing the sign of the q-axis current command value Iq** (IqgMIN>0). However, reversing the sign of the q-axis current command value Iq** generates a torque that cancels the steering force of the driver, making it easier to prevent steering to the maximum steering angle θmax.

[0123] Embodiment 3 The electric power steering device according to the third embodiment will be described below with reference to FIG. In the above-mentioned first embodiment, Idg is calculated based on the d-axis current limit value map 48 shown in Figs. 6, 7A and 7B, but in the present third embodiment, another method will be described.

[0124] Fig. 17 is a diagram showing another example of the d-axis current limit value map 48 held by the d-axis current limit value calculation unit 46. As shown in Fig. 17, when the absolute value |θs| of the control steering angle θs is greater than the second steering angle threshold θth2 near the maximum steering angle θmax, and the steering state of the steering wheel 2 is in a turning state that satisfies the steering angular velocity ωs>0 when the control steering angle θs>0, or the steering angular velocity ωs<0 when the control steering angle θs<0, the d-axis current limit value Idg is calculated to be a smaller value as the absolute value |θs| of the control steering angle θs increases. Furthermore, between the second steering angle threshold θth2 and the maximum steering angle θmax, the d-axis current limit value Idg becomes a negative value, and is calculated to be smaller up to the d-axis current limit value IdgMIN, and is output to the d-axis current guard processing unit 47. At this time, the minimum value of the d-axis current limit value map 48 is set to be the d-axis current limit value minimum value IdgMIN, and the absolute value of the d-axis current limit value minimum value IdgMIN is set to a value equal to or less than the d-axis current value required for the motor 8 to output the rated current.

[0125] When the d-axis current limit value calculation unit 46 calculates the d-axis current limit value Idg as a negative value and the reference d-axis current command value Id* is smaller than 0, the d-axis current guard processing unit 47 outputs the d-axis current command value Id** as a positive value to the motor control signal calculation unit 33. This strengthens the magnetic flux of the rotor, and the induced voltage reaches a voltage amplitude that can be applied to the motor 8 at an absolute value of the rotation speed ωm that is smaller than that in the first embodiment. As a result, it is possible to prevent the driver from steering at high speed near the maximum steering angle and to mitigate the impact caused by end hitting.

[0126] Although the present application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless modifications not exemplified are assumed within the scope of the technology disclosed in the present specification, including, for example, modifying, adding, or omitting at least one component, and further, extracting at least one component and combining it with a component of another embodiment. [Explanation of symbols]

[0127] 1: electric power steering device, 2: steering, 3: torque sensor, 4: control device, 5: CPU, 6: ROM, 7: RAM, 8: motor, 9: power converter, 11: steering shaft, 12: rack and pinion mechanism, 13: rack shaft, 14: rack housing, 15: column shaft, 16: intermediate shaft, 17: pinion shaft, 18: rack end, 19: tie rod, 20: front wheel, 21: rotational position detection section, 22: current detection section, 31: q-axis current command value calculation section, 32: d-axis current command value calculation section, 33: motor control signal calculation section, 34: control steering angle calculation section, 35: differentiator, 36: rotational angular velocity axis conversion section, 41: base current command value calculation section, 42: q-axis current limit value calculation section, 43: q-axis current guard processing section, 44: q-axis current limit value map, 45: reference d-axis current command value calculation unit, 46: d-axis current limit value calculation unit, 47: d-axis current guard processing unit, 48: d-axis current limit value map, 49: 3-phase to 2-phase conversion unit, 50a, 50b: adder / subtractor, 51, 52: FB control unit, 53: q-axis voltage limit value calculation unit, 54: q-axis voltage limit value map, 55: voltage guard processing unit, 56: 2-phase to 3-phase conversion unit, 71: q-axis voltage limit value calculation unit, 72: voltage guard processing unit, 73: q-axis voltage limit value map.

Claims

1. An electric power steering device comprising: a control device that calculates a current command value based on a steering torque applied by operation of a steering shaft, and calculates a voltage command value based on the current command value; and a power converter that supplies to a motor electric power converted based on the voltage command value output from the control device, the electric power steering device generating an assist torque on the steering shaft by driving the motor, The control device includes: a q-axis current command value calculation unit and a d-axis current command value calculation unit that calculate the current command value; a motor control signal calculation unit that calculates the voltage command value based on the q-axis current command value calculated by the q-axis current command value calculation unit and the d-axis current command value calculated by the d-axis current command value calculation unit; a control steering angle calculation unit that calculates a steering angle of the steering shaft based on a rotational position of the motor, The q-axis current command value calculation unit a base current command value calculation unit that calculates a base q-axis current command value serving as a reference based on the steering torque; a q-axis current limit value calculation unit that calculates a q-axis current limit value so as to decrease the q-axis current limit value as the absolute value of the steering angle increases when the absolute value of the steering angle calculated by the control steering angle calculation unit is equal to or greater than a first steering angle threshold value that is set in advance; the base q-axis current command value calculated by the base current command value calculation unit is input, and the q-axis current limit value calculated by the q-axis current limit value calculation unit is input, When the steering angle is equal to or greater than the first steering angle threshold value and the base q-axis current command value is greater than the q-axis current limit value, the q-axis current command value is set based on the q-axis current limit value instead of the base q-axis current command value; When the steering angle is equal to or smaller than −1×the first steering angle threshold value and the base q-axis current command value is smaller than −1×the q-axis current limit value, the q-axis current command value is set based on −1×the q-axis current limit value instead of the base q-axis current command value; and a q-axis current guard processing unit that outputs to the motor control signal calculation unit.

2. An electric power steering device as described in claim 1, wherein the q-axis current limit value calculation unit calculates the q-axis current limit value so that, when the absolute value of the steering angle calculated by the control steering angle calculation unit is equal to or greater than the first steering angle threshold value set in advance, the q-axis current limit value decreases as the absolute value of the steering angle increases, and becomes a negative value toward the maximum steering angle.

3. 3. The electric power steering device according to claim 1, wherein the q-axis current guard processing unit sets the base q-axis current command value as the q-axis current command value when the steering angle is equal to or greater than the first steering angle threshold value and the base q-axis current command value is equal to or less than the q-axis current limit value, or when the steering angle is equal to or less than -1 x the first steering angle threshold value and the base q-axis current command value is equal to or greater than -1 x the q-axis current limit value.

4. An electric power steering device comprising: a control device that calculates a current command value based on a steering torque applied by operation of a steering shaft, and calculates a voltage command value based on the current command value; a power converter that supplies to a motor electric power converted based on the voltage command value output from the control device; and a current detection unit that detects a current supplied to the motor, wherein the electric power steering device generates an assist torque on the steering shaft by driving the motor, The control device includes: a q-axis current command value calculation unit and a d-axis current command value calculation unit that calculate the current command value; a motor control signal calculation unit that calculates the voltage command value based on the q-axis current command value calculated by the q-axis current command value calculation unit and the d-axis current command value calculated by the d-axis current command value calculation unit; a control steering angle calculation unit that calculates a steering angle of the steering shaft based on a rotational position of the motor, The q-axis current command value calculation unit a base current command value calculation unit that calculates a base q-axis current command value serving as a reference based on the steering torque; a q-axis current limit value calculation unit that calculates a q-axis current limit value that decreases as the absolute value of the steering angle increases when the absolute value of the steering angle calculated by the control steering angle calculation unit is equal to or greater than a first steering angle threshold value that is set in advance; the base q-axis current command value calculated by the base current command value calculation unit is input, and the q-axis current limit value calculated by the q-axis current limit value calculation unit is input, When the steering angle is equal to or greater than the first steering angle threshold value and the base q-axis current command value is greater than the q-axis current limit value, the q-axis current command value is set based on the q-axis current limit value instead of the base q-axis current command value; When the steering angle is equal to or smaller than −1×the first steering angle threshold value and the base q-axis current command value is smaller than −1×the q-axis current limit value, the q-axis current command value is set based on −1×the q-axis current limit value instead of the base q-axis current command value; a q-axis current guard processing unit that outputs the motor control signal to the motor control signal calculation unit, The motor control signal calculation unit a feedback control unit that converts the current detected by the current detection unit to obtain an actual q-axis current and an actual d-axis current, and calculates a reference voltage command value that serves as a reference for making the actual q-axis current and the actual d-axis current follow the q-axis current command value input from the q-axis current command value calculation unit and the d-axis current command value input from the d-axis current command value calculation unit, respectively; a voltage limit value calculation unit that calculates a voltage limit value that decreases as the absolute value of the steering angle increases, when the absolute value of the steering angle calculated by the steering angle calculation unit for control is equal to or greater than a second steering angle threshold value that is smaller than a first steering angle threshold value and the product of the angular velocity of the steering shaft and the steering angle is positive, and that calculates a voltage limit value that becomes equal to or greater than a maximum voltage that can be output by the motor, when the absolute value of the steering angle is smaller than the second steering angle threshold value or the product of the angular velocity of the steering shaft and the steering angle is equal to or less than 0; a voltage guard processing unit to which the reference voltage command value calculated by the feedback control unit and the voltage limit value calculated by the voltage limit value calculation unit are input, and which outputs the voltage command value so that an absolute value of the voltage command value does not exceed the voltage limit value.

5. An electric power steering device comprising: a control device that calculates a current command value based on a steering torque applied by operation of a steering shaft, and calculates a voltage command value based on the current command value; a power converter that supplies to a motor electric power converted based on the voltage command value output from the control device; and a current detection unit that detects a current supplied to the motor, wherein the electric power steering device generates an assist torque on the steering shaft by driving the motor, The control device includes: a q-axis current command value calculation unit and a d-axis current command value calculation unit that calculate the current command value; a motor control signal calculation unit that calculates the voltage command value based on the q-axis current command value calculated by the q-axis current command value calculation unit and the d-axis current command value calculated by the d-axis current command value calculation unit; a control steering angle calculation unit that calculates a steering angle of the steering shaft based on a rotational position of the motor, The q-axis current command value calculation unit a base current command value calculation unit that calculates a base q-axis current command value serving as a reference based on the steering torque; a q-axis current limit value calculation unit that calculates a q-axis current limit value that decreases as the absolute value of the steering angle increases when the absolute value of the steering angle calculated by the control steering angle calculation unit is equal to or greater than a first steering angle threshold value that is set in advance; the base q-axis current command value calculated by the base current command value calculation unit is input, and the q-axis current limit value calculated by the q-axis current limit value calculation unit is input, When the steering angle is equal to or greater than the first steering angle threshold value and the base q-axis current command value is greater than the q-axis current limit value, the q-axis current command value is set based on the q-axis current limit value instead of the base q-axis current command value; When the steering angle is equal to or smaller than −1×the first steering angle threshold value and the base q-axis current command value is smaller than −1×the q-axis current limit value, the q-axis current command value is set based on −1×the q-axis current limit value instead of the base q-axis current command value; a q-axis current guard processing unit that outputs the motor control signal to the motor control signal calculation unit, The motor control signal calculation unit a feedback control unit that converts the current detected by the current detection unit to obtain an actual q-axis current and an actual d-axis current, and calculates a reference voltage command value that serves as a reference for making the actual q-axis current and the actual d-axis current follow the q-axis current command value input from the q-axis current command value calculation unit and the d-axis current command value input from the d-axis current command value calculation unit, respectively; a voltage limit value calculation unit that calculates a voltage limit value that decreases as the absolute value of the steering angle increases when the absolute value of the steering angle calculated by the control steering angle calculation unit is equal to or greater than a second steering angle threshold value that is smaller than a first steering angle threshold value that is set in advance; and the reference voltage command value calculated by the feedback control unit and the voltage limit value calculated by the voltage limit value calculation unit are input, When the steering angle is equal to or greater than the second steering angle threshold value and the reference voltage command value is greater than the voltage limit value, the voltage limit value is output as the voltage command value instead of the reference voltage command value; and a voltage guard processing unit that outputs, when the steering angle is equal to or less than -1 x the second steering angle threshold value and the reference voltage command value is smaller than -1 x the voltage limit value, -1 x the voltage limit value instead of the reference voltage command value as the voltage command value. An electric power steering device comprising:

6. An electric power steering device comprising: a control device that calculates a current command value based on a steering torque applied by operation of a steering shaft, and calculates a voltage command value based on the current command value; and a power converter that supplies electric power converted based on the voltage command value output from the control device to a motor, the electric power steering device generating an assist torque on the steering shaft by driving the motor, The control device includes: a q-axis current command value calculation unit and a d-axis current command value calculation unit that calculate the current command value; a motor control signal calculation unit that calculates the voltage command value based on the q-axis current command value calculated by the q-axis current command value calculation unit and the d-axis current command value calculated by the d-axis current command value calculation unit; a control steering angle calculation unit that calculates a steering angle of the steering shaft based on a rotational position of the motor, The q-axis current command value calculation unit a base current command value calculation unit that calculates a base q-axis current command value serving as a reference based on the steering torque; a q-axis current limit value calculation unit that calculates a q-axis current limit value that decreases as the absolute value of the steering angle increases when the absolute value of the steering angle calculated by the control steering angle calculation unit is equal to or greater than a first steering angle threshold value that is set in advance; the base q-axis current command value calculated by the base current command value calculation unit is input, and the q-axis current limit value calculated by the q-axis current limit value calculation unit is input, When the steering angle is equal to or greater than the first steering angle threshold value and the base q-axis current command value is greater than the q-axis current limit value, the q-axis current command value is set based on the q-axis current limit value instead of the base q-axis current command value; When the steering angle is equal to or smaller than −1×the first steering angle threshold value and the base q-axis current command value is smaller than −1×the q-axis current limit value, the q-axis current command value is set based on −1×the q-axis current limit value instead of the base q-axis current command value; a q-axis current guard processing unit that outputs the motor control signal to the motor control signal calculation unit, The d-axis current command value calculation unit a reference d-axis current command value calculation unit that calculates a reference d-axis current command value based on the q-axis current command value output from the q-axis current command value calculation unit and a rotation speed of the motor; a d-axis current limit value calculation unit that calculates a d-axis current limit value that decreases as the absolute value of the steering angle increases, when the absolute value of the steering angle is equal to or greater than a third steering angle threshold value that is set in advance and is smaller than the first steering angle threshold value, and when a product of the angular velocity of the steering shaft and the steering angle is positive, calculates a d-axis current limit value that becomes smaller as the absolute value of the steering angle increases, and that calculates a d-axis current limit value that becomes equal to or greater than the absolute value of a maximum d-axis current value that can be output by the motor, when the absolute value of the steering angle is smaller than the third steering angle threshold value or when a product of the angular velocity of the steering shaft and the steering angle is equal to or smaller than 0; and a d-axis current guard processing unit that sets the d-axis current command value so that the absolute value of the d-axis current command value does not exceed the d-axis current limit value.

7. The d-axis current command value calculation unit a reference d-axis current command value calculation unit that calculates a reference d-axis current command value based on the q-axis current command value output from the q-axis current command value calculation unit and a rotation speed of the motor; a d-axis current limit value calculation unit that calculates a d-axis current limit value that decreases as the absolute value of the steering angle increases, when the absolute value of the steering angle is equal to or greater than a third steering angle threshold value that is set in advance and is smaller than the first steering angle threshold value, and when a product of the angular velocity of the steering shaft and the steering angle is positive, calculates a d-axis current limit value that becomes smaller as the absolute value of the steering angle increases, and that calculates a d-axis current limit value that becomes equal to or greater than the absolute value of a maximum d-axis current value that can be output by the motor, when the absolute value of the steering angle is smaller than the third steering angle threshold value or when a product of the angular velocity of the steering shaft and the steering angle is equal to or smaller than 0; 6. The electric power steering device according to claim 4, further comprising a d-axis current guard processing unit that sets the d-axis current command value so that an absolute value of the d-axis current command value does not exceed the d-axis current limit value.

8. 8. The electric power steering device according to claim 7, wherein the third steering angle threshold is set to be smaller than the first steering angle threshold and the second steering angle threshold.

9. The d-axis current limit value calculation unit 7. The electric power steering device according to claim 6, wherein, when the absolute value of the steering angle is equal to or greater than the third steering angle threshold value which is smaller than the first steering angle threshold value, and when a product of the angular velocity of the steering shaft and the steering angle is positive, the d-axis current limit value is calculated to be smaller as the absolute value of the steering angle increases, and further to be a negative value toward a maximum steering angle.

Images