Patent Grant
10179603
The present invention relates to an electric power steering apparatus that has functions of an automatic steering control (an automatic operation mode, a parking assist mode, etc.) and a manual steering control and applies an assist force to a steering system of a vehicle by a motor, especially to an electric power steering apparatus that has a function to switch a control system of the motor between a torque control system to control a motor output torque and a position/speed control system to control a steering angle of a steering, and can change a fade processing (a gradual changing time and a gain) sensitive to a steering torque.
In an electric power steering apparatus (EPS) which has a motor control unit and applies a steering assist force to a steering system of a vehicle by a rotational force of a motor, the steering assist force is applied to a steering shaft or a rack shaft by a transmission mechanism such as gears and a belt with driving power of the motor via a reducer. Such the conventional electric power steering apparatus performs a feedback control of a motor current in order to precisely generate a torque of steering assist force. The feedback control is to adjust an applied voltage to the motor such that a difference between a steering assist command value (current commanded value) and a detected value of the motor current becomes small. Adjustment of the applied voltage to the motor is generally performed by adjusting a duty in a pulse width modulation (PWM) control.
Explaining a general configuration of an electric power steering apparatus with illustration in
The control unit 30 is connected with a controller area network (CAN) 40 that receives various information of the vehicle and the vehicle speed Vs can be received from the CAN 40. The control unit 30 may also be connected with a Non-CAN 41 that receives communication, an analog/digital signal, radio waves, or others that are different from those received by the CAN 40.
In such an electric power steering apparatus, the control unit 30 mainly includes a CPU (including an MPU, an MCU, etc.). Functions executed by a program inside the CPU are illustrated as an exemplary configuration as illustrated in
Functions and operations of the control unit 30 are described with reference to
The subtraction result I (=Irefm−Im) at the subtracting section 32B is proportional and integral (PI)-controlled at a PI-control section 35. The PI-controlled voltage control value Vref is inputted into a PWM-control section 36, whereat a duty thereof is calculated. The motor 20 is PWM-driven by an inverter 37 with a PWM signal calculated the duty. The motor current value Im of the motor 20 is detected by a motor current detection means 38 and is inputted into the subtracting section 32B for the feedback.
The compensating section 34 adds a self-aligning torque (SAT) 34-3 detected or estimated and an inertia compensation value 34-2 at an adding section 34-4. The addition result is further added with a convergence control value 34-1 at an adding section 34-5. The addition result is inputted into the adding section 32A as the compensation signal CM, thereby to improve the characteristics.
In such an electric power steering apparatus, vehicles that have an automatic steering assist function (an automatic operation, a parking assist, etc.) and switches between the automatic steering control and the manual steering control have emerged in recent years. The vehicles having the automatic steering assist function perform the automatic steering control to set a target steering angle based on data from a camera (image), a distance sensor, or other apparatus and to cause an actual steering angle to follow the target steering angle.
In the automatic operation, environment surrounding the vehicle is recognized based on information from a radar, a camera, an ultrasonic sensor or the like and a steering angle command value that allows for safely guiding the vehicle is outputted. The electric power steering apparatus is capable of the automatic operation by performing a position control of the actual steering angle in such a manner as to follow the steering angle command value.
In the known electric power steering apparatus having the functions of the automatic steering control and the manual steering control in the related art, a back-in parking or a parallel parking is automatically performed by controlling an actuator (motor) based on relationship between a pre-stored traveling distance of the vehicle and a turning steering angle. That is, an automatic steering control apparatus recognizes a parking space from a positioning sensor such as an around-view monitor or an ultrasonic sensor and outputs a steering angle command value to the EPS-side. The EPS performs a position-control on the actual steering angle in such a manner as to follow the steering angle command value. As a result of this, the vehicle is guided into the parking space.
In this manner, a normal power assist is subjected to a torque control system. Meanwhile, the parking assist and the automatic operation are subjected to a position/speed control system of the steering angle or other parameters. There are problems such as that the control torque varies upon the switching between the torque control and the position/speed control, thereby making the switching over not smooth and that an unintentional self-steer occurs by a trigger due to variations in the torque upon the switching over.
To handle such problems, a conventional method to gradually change (gradual-change) the control torque in the torque control and the position/speed control is used in order to mitigate the torque variations. For example in Japanese Unexamined Patent Publication No. 2004-17881 A (Patent Document 1), when an automatic steering mode is released at a time point t0 as illustrated in
Upon switching between the torque control and the position/speed control, however, the above effect cannot be fully exercised. This reason is because there are cases where assisting in an opposite direction occurs upon switching over to the normal power assist control since the position/speed control assists torque in such a manner as to suppress an external disturbance in a system such as the electric power steering that allows for inputting the external disturbance from the handle.
In this manner, the method to gradually change (gradual-change) the control torque in the torque control and the position/speed control is conventionally used in order to mitigate the torque variations. However, this cannot fully exercise its effect in the case of switching between the torque control and the position/speed control.
The present invention has been devised in consideration to the above circumstances with an object to provide an electric power steering apparatus capable of smoothly switching the control systems without self-steer by gradually changing a control torque of the torque control and a command value of the position/speed control, sensitive to the steering torque, upon fade processing (gradual-change processing) that switches the control systems.
The present invention relates to an electric power steering apparatus including a torque sensor to detect a steering torque and a motor control unit to control a motor that applies an assist torque to a steering system of a vehicle, the above-described object of the present invention is achieved by that comprising: a function to switch a control system of the motor between a torque control system of a torque system to control a motor output torque and a position/speed control system of a steering angle system to control a steering angle of a steering in accordance with a predetermined switching trigger, wherein a first fade processing which switches from the torque control system to the position/speed control system is changeable sensitive to the steering torque; or wherein a second fade processing which switches from the position/speed control system to the torque control system is changeable sensitive to the steering torque.
Further, the above-described object of the present invention is more effectively achieved by that: further comprising a characteristic calculating section to calculate a fade gain signal F1 that applies a fade gain of the torque system in the first fade processing and the second fade processing, and a fade gain signal F2 that applies a fade gain of the steering angle system in the first fade processing and the second fade processing, sensitive to the steering torque, when the predetermined switching trigger is ON/OFF; or wherein, when the predetermined switching trigger is turned ON, the first fade processing is started and a post-gradual change steering-angle command value in a position/speed control is gradually changed from an actual steering angle to a steering angle command value by the fade gain signal F2, and a level of the assist torque in a torque control is gradually changed from 100% to 0% by the fade gain signal F1 and then the position/speed control system is operated; or wherein, when the predetermined switching trigger is turned OFF, the second fade processing is started and a post-gradual change steering-angle command value in a position/speed control is gradually changed from a steering angle command value to an actual steering angle by the fade gain signal F2, and a level of the assist torque in a torque control is gradually changed from 0% to 100% by the fade gain signal F1 and then the torque control system is operated; or wherein, by setting a past value of a fade gain, an exponential gain and a fade rate as FG(Z−1), A1 and FR1, respectively, the fade gain signal F1 is calculated by “A1×FG(Z−1)+FR1”; or wherein, by setting a past value of a fade gain, an exponential gain and a fade rate as FG(Z−1), A2 and FR2, respectively, the fade gain signal F2 is calculated by “A2×FG(Z−1)+FR2”; or wherein the exponential gain A1 or the exponential gain A2 is changed sensitive to the steering torque; or wherein the exponential gain A1 is a constant value A12 where the steering torque is less than a predetermined value T11 of a steering torque, gradually decreases to a value A11 (<A12) where the steering torque is the predetermined value T11 or more and a predetermined value T12 (>T11) or less, and is a constant value A11 in a region where the steering torque is larger than the predetermined value T12; or wherein the exponential gain A2 is a constant value A21 where the steering torque is less than a predetermined value T21 of a steering torque, gradually increases to a value A22 (>A21) where the steering torque is the predetermined value T21 or more and a predetermined value T22 (>T21) or less, and is a constant value A22 in a region where the steering torque is larger than the predetermined value T22; or wherein the predetermined switching trigger is performed by an automatic steering execution judging section; or wherein the automatic steering execution judging section comprises a calculating section to calculate an angular speed and an angular acceleration by inputting a steering angle command value, a map judging section to judge each of the steering angle command value, the angular speed and the angular acceleration with a judging map corresponding to a vehicle speed, and a diagnosing section to diagnose based on a judgement result from the map judging section; or further comprising an external disturbance observer to compensate inertia and friction of a handle; or wherein the external disturbance observer estimates an external-disturbance estimation torque from a difference between an output of a steering inverse model of the steering system and an output of an LPF to limit a band; or wherein values of inertia and friction of the steering system are greater than or equal to values of inertia and friction of the steering inverse model, respectively.
According to the electric power steering apparatus of the present invention, a post-gradual change steering-angle command value is gradually changed from the actual steering angle to the steering angle command value and the actual steering angle is subjected to the position/speed control in such a manner as to follow the post-gradual change steering-angle command value. This allows the torque command value in the position/speed control to be changed automatically and smoothly, thereby providing a soft handling feeling to a driver.
Further, even when excessive variations in the torque occur upon a fade processing of switching from the automatic steering to the torque control, an excessive power assist by the torque control is automatically compensated by the position/speed control since the steering angle command is gradually changed from the command value to the actual steering angle, sensitive to the steering torque. Therefore, it is possible to suppress such a failure as to losing the control of the handle by the driver.
Moreover, according to the electric power steering apparatus of the present invention, the switch between the automatic steering operation which an intention of the driver is respected and the normal steering by the torque control is performed by the smooth operation. In a case that the driver feels a danger in the automatic operation and strongly steers a handle, the automatic operation is immediately stopped and the switch to the normal torque control can be performed. Providing the external disturbance observer can more effectively improve the switch.
In the accompanying drawings:
In a conventional torque gradual-change control in the electric power steering apparatus, there are problems such as that control is not smoothly switched upon switching between a torque control and a position/speed control and that unintentional self-steer occurs. In the present invention, therefore, a processing that smoothly switches the control without the self-steer is implemented by gradually changing (fade processing) a control torque of a torque control and a command value of a position/speed control.
The present invention includes a function to switch control systems of a motor between a torque control system to control a motor output torque and a position/speed control system to control a steering angle upon steering in accordance with a predetermined switching trigger (e.g. an automatic steering command), can change a fade processing (a gradual-changing time and a gain) sensitive to the steering torque, and implements the smooth fade processing without self-steer.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The present invention may be applied to, other than the column system shown in
The actual steering angle θr is inputted into the steering-angle command value gradual-changing section 100 and a position/speed control section 101, and a post-gradual change steering-angle command value θm from the steering-angle command value gradual-changing section 100 is inputted into the position/speed control section 101. Based on the steering torque Ts, a fade gain signal F1 of a torque system, which is calculated at the characteristic calculating section 140, is inputted into the torque gradual-changing section 103, and a fade gain signal F2 of a steering angle system is inputted into the steering-angle command value gradual-changing section 100.
A post-gradual change steering-assist torque command value Tg at the torque gradual-changing section 103 is inputted into an adding section 104, a position/speed control torque command value Tp from the position/speed control section 101 is also inputted into the adding section 104, and an addition result of the adding section 104 is outputted as a motor torque command value. The motor torque command value is inputted into a current control system 130, and a motor 131 is driven and controlled through the current control system 130.
When the automatic steering command is turned ON or OFF by the automatic steering execution judging section 120, the characteristic calculating section 140 calculates the fade gain signal F1 for the torque gradual-change and the fade gain signal F2 for the steering-angle command value gradual-change, and gradual-changes (a time and a gain) sensitive to the steering torque Ts.
The automatic steering execution judging section 120 has a configuration as illustrated in
The characteristic of the judging map #1 with respect to the steering angle command value θtc is at a constant value θtc0 until a vehicle speed Vs1 of a low speed and decreases as the characteristic A1 or B1 in a range more than or equal to the vehicle speed Vs1. The characteristic of the judging map #2 with respect to the angular speed ωtc is at a constant value ωc0 until a vehicle speed Vs2 of a low speed and decreases as the characteristic A2 or B2 in a range more than or equal to the vehicle speed Vs2. Further, the characteristic of the judging map #3 with respect to the angular acceleration αtc is at a constant value αc0 until a vehicle speed Vs3 of a low speed and decreases as the characteristic A3 or B3 in a range more than or equal to the vehicle speed Vs3. Any of the characteristics of the judging maps #1 to #3 can be tuned, and the characteristic may linearly decrease.
The map judging section 122 judges whether the steering angle command value θtc exceeds the range of characteristic values of the judging map #1, whether the angular speed ωtc exceeds the range of characteristic values of the judging map #2, and further whether the angular acceleration αtc exceeds the range of characteristic values of the judging map #3. A judgment result MD is inputted into a diagnosing section 123. The diagnosing section 123 outputs “ON/OFF” of the automatic steering command based on a diagnosis result by time or times (number) and “ON/OFF” of the automatic steering command is also inputted into an output section 124. The output section 124 outputs the steering angle command value et only when the automatic steering command is “ON”.
Although the steering angle command value et is inputted into the steering-angle command value gradual-changing section 100 together with the actual steering angle θr, the actual steering angle θr is calculated in the following manner in the present invention.
In a mechanism including a torsion bar 23, for example a sensor as illustrated in
Although the present invention descriptions are given assuming that the steering angle θr on the column input-side is the actual steering angle, the steering angle θr1 on the column output-side may be used as the actual steering angle.
Exemplary operations in such a configuration will be described with reference to flowcharts in
When the automatic steering command is not “ON” (Step S1), the normal steering with the assist torque level of 100%, that is, the torque control is performed (Step S15). Then, when the automatic steering execution judging section 120 turns “ON” the automatic steering command at a time point t2 (Step S1), a fade processing of the EPS is started from the time point t2 (Step S2). At this time, the fade gain signals F1 and F2 are calculated based on the steering torque Ts at the characteristic calculating section 140, the fade gain signal F1 is inputted into the torque gradual-changing section 103, and the fade gain signal F2 is inputted into the steering-angle command value gradual-changing section 100 (Step S2A). A fade processing time and a fade gain characteristic are set by the fade gain signals F1 and F2, respectively. The characteristic section 140 calculates the fade gain signal F1 in accordance with a following Equation 1, and calculates the fade gain signal F2 in accordance with a following Equation 2.
F1=A1×FG(z−1)+FR1 [Equation 1]
where, FR1 is a fade rate that determines a rate of the fade which varies in a control period, A1 is an exponential gain that determines a gradient of an exponential, and FG (z−1) is a past value of the fade gain.
F2=A2×FG(z31 1)+FR2 [Equation 2]
where, FR2 is the fade rate that determines the rate of the fade which varies in the control period, A2 is the exponential gain that determines the gradient of the exponential, and FG(z−1) is the past value of the fade gain.
In the Equation 1 and the Equation 2, when the exponential gains A1 and A2 are set to “1.0”, the fade characteristics are a linear line. The time of the fade processing and the gain are controlled by changing the exponential gains A1 and A2 sensitive to the steering torque Ts. In the fade processing between a time point t2 and a time point t3, the exponential gain A1 is related to the torque gradual-change, and is a constant value A12 where the steering torque is less than a predetermined value of a steering torque T11, gradually decreases to a value A11 (<A12) where the steering torque is the predetermined value T11 or more and a predetermined value T12 (>T11) or less, and is a constant value A11 in a region where the steering torque is larger than the predetermined value T12, for example as shown in
The steering torques T11 as shown in
The steering-angle command value gradual-changing section 100 gradually changes the post-gradual change steering-angle command value θm of the position/speed control from the actual steering angle θr to the steering angle command value et (Step S3). The torque gradual-changing section 103 gradually changes the torque level from 100% to 0% in accordance with the fade gain signal F1 (Step S4). Thereafter, the above operations are repeated until the fade processing ends (a time point t3) (Step S5).
As well, the command value gradual-change of the position/speed control and the level gradual-change of the torque control in a fade section (a gradual-change time) may be in any order. In the timing chart of
At and after a time point t3 when the fade processing ends, the torque control is switched to the automatic steering (the position/speed control) and then the automatic steering is continued (Step S6).
Thereafter, when the automatic steering command is turned “OFF” by the automatic steering execution judging section 120 (a time point t4), or when a driver steers the handle during the automatic steering such that the steering torque Ts exceeds a certain threshold and the automatic steering command is turned “OFF” (the time point t4), the automatic steering is completed (Step S10) and the fade processing is started (Step S11).
In this case, the fade gain signals F1 and F2 based on the steering torque Ts are calculated in accordance with the above Equations 1 and 2 at the characteristic calculating section 140, the fade gain signal F2 is inputted into the steering-angle command value gradual-changing section 100, and the fade gain signal F1 is inputted into the torque gradual-changing section 103 (Step S11A).
In this way, the steering-angle command value gradual-changing section 100 gradually changes the post-gradual change steering-angle command value θm of the position/speed control from the steering angle command value et to the actual steering angle θr (Step S12) and the torque gradual-changing section 103 gradually changes the torque level from 0% to 100% (Step S13). This fade processing is continued until a time point t5 (Step S14). At and after the time point t5 when the fade processing ends, the automatic steering is switched to the torque control of the normal steering (Step S15).
Even in this fade processing, the fade gain signals F2 and F1 are calculated by the above Equations 1 and 2, respectively. Thus, in this fade processing, the calculations of following Equations 3 and 4 are performed.
F1=A2×FG(Z−1)+FR2 [Equation 3]
F2=A1×FG(Z−1)+FR1 [Equation 4]
In this case, the exponential gain A2 of the fade gain signal F1 has a characteristic as shown in
Note that, a fading characteristic of the steering angle command value in the position/speed control is represented by an exponential curve while the torque gradual-change in the torque control is represented by a linear line in
Exemplary operations of the automatic steering execution judging section 120 is as shown in the flowchart of
Further, when the steering angle command value θtc corresponding to the vehicle speed Vs is not within the range of the characteristic values of the judging map #1 shown in
As well, the order of the aforementioned Steps S23 to S25 may be changed as appropriate.
When the automatic steering command is turned “ON” as shown in
On the other hand, even when the excessive variations in the steering torque occur after a time point t21 upon the fade processing of the switching from the automatic steering to the torque control (a time point t20) as shown in
As described above, the fade gain characteristic is calculated based on the steering torque, and the fade processing (the time and the gain) is changeable in both the fade processing from the torque control to the position/speed control and the fade processing from the position/speed control to the torque control. The above calculation and processing may be performed in at least the fade processing from the position/speed control to the torque control.
In the present invention as further shown in
The position/speed control section 101 in
A steering system 160 subjected to the controlled object comprises an adding section 161 to add an unknown external disturbance torque Td to the position/speed control torque command value Tp, a steering system 162 represented by a transfer function “1/(J1·s+B1)”, and an integral section 163 to integrate (1/s) the angular speed ωr from the steering system 162 and to output the steering angle θr. The steering angular speed ωr is fed back to the position/speed feedback controller 170 and is also inputted into the integral section 163. The steering angle θr is fed back to the position/speed feedback controller 170.
The symbol “J1” in the transfer function represents the inertia in the steering system 162, “B1” represents the friction in the steering system 162, “J2” represents the inertia in the steering inverse model 151, “B2” represents the friction in the steering inverse model 151, and “τ” represents a predetermined time constant. These have relationships represented by the following Equations 5 and 6.
J1≥J2 [Equation 5]
B1≥B2 [Equation 6]
The external disturbance observer 150 estimates the unknown external disturbance torque Td base on a difference between outputs of the steering inverse model 151 and the LPF 152 and obtains the external-disturbance estimation torque Td* as an estimation value. The external-disturbance estimation torque Td* is subtracting-inputted into the subtracting section 154, and it is possible to realize a robust position/speed control by subtracting the external-disturbance estimation torque Td* from an output of the speed controller 174. However, the robust position/speed control results in contradiction that the handle cannot be stopped even with intervention by the driver. In order to improve this point, the inertia J2 and the friction B2 smaller than or equal to the inertia J1 and the friction B1, respectively, which the steering system 162 actually has, are inputted as the steering inverse model 151. As a result of this, the inertia and the friction of the handle that the driver feels becomes seemingly smaller. This allows the driver to easily intervene in the automatic steering by steering.
Moreover, by monitoring the external-disturbance estimation torque Td* in the external disturbance observer 150, it is possible to detect the steering torque of the driver instead of the torque sensor. Especially, when the torque sensor uses digital signals, detection of steering intervention by the driver may be delayed due to influence of communication delay or other reasons. Similarly to the torque sensor, when the external-disturbance estimation torque Td* exceeds a threshold value for a predetermined period of time, the steering intervention may be determined to be performed and the fade processing may be performed.
Providing the external disturbance observer 150 allows for providing a smoother operation feeling, thereby enabling switching control at a high-speed. Smaller inertia and friction facilitate the steering intervention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-244329 | Dec 2014 | JP | national |
This application is a continuation of U.S. application Ser. No. 15/512,348 filed Mar. 17, 2017, which is U.S. National Stage of International Application No. PCT/JP2015/083560 filed Nov. 30, 2015, claiming priority based on Japanese Patent Application No. 2014-244329, filed Dec. 2, 2014, the contents of all of which are incorporated herein by reference in their entirety.
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| Number | Date | Country | |
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| 20180170421 A1 | Jun 2018 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15512348 | US | |
| Child | 15897928 | US |
