JP2005007990A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power steering device capable of achieving stable steering assist control even when the steering torque of a driver is in an extremely low torque range. <P>SOLUTION: The power steering device has a low pass filter of a variable time constant to perform the filtering of an output signal of a second steering control means, and a time constant selection means to select the time constant of the low pass filter. The time constant selection means selects the first time constant when the steering torque detected by a torque detection means is matched with the output direction of a steering speed detected by the steering speed detection means, and selects the second time constant smaller than at least the first time constant when the output direction is different. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power steering apparatus that assists steering by driving an electric motor based on an output of a torque sensor.
[0002]
[Prior art]
Conventionally, in an electric power steering device, when steering is turned, turning steering control for outputting assist torque is executed. Further, at the time of the steering return, the assist torque is output in the return direction, and the return steering control for applying the damping torque for preventing the excessive return in the direction opposite to the return direction is executed. Patent Document 1 discloses a technique in which the switching from the turning steering control to the return steering control is performed when the sign of the steering torque and the steering angular velocity is shifted from the coincidence to the disagreement.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-264833 (see page 3, right middle, FIG. 2).
[0004]
[Problems to be solved by the invention]
However, in the electric power steering device described in Patent Document 1, even when the steering torque is near 0, that is, when the driver does not input the steering torque so much, when the sign is switched, Since the steering control and the return steering control are frequently switched, there is a problem that the driver feels uncomfortable.
[0005]
The present invention has been made paying attention to the above-described problems, and an object of the present invention is to provide a power steering device capable of achieving stable steering assist control even when the driver's steering torque is in an extremely low torque range. To do.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, the time constant variable low-pass filter for filtering the output signal of the second steering control means, the steering speed detecting means for detecting the steering speed, and the low-pass filter are used. A time constant selecting means for selecting a constant, and the time constant selecting means selects the first time constant when the detected steering torque and the output direction of the detected steering speed match, and the output direction is different. Is to select a second time constant that is at least smaller than the first time constant.
[0007]
For example, when the steering is turned in which the sign of the steering torque and the output direction of the steering speed coincide, 0 is output as the damping torque, and the assist torque only from the first steering control means is output. On the other hand, at the time of steering return in which the sign of the steering torque and the output direction of the steering speed are different, in addition to the assist torque by the first steering control means (actually subtracted), a damping torque corresponding to the steering angular speed and vehicle speed is output. At this time, when it is determined that the steering is returning, the calculated damping torque is output with good response by selecting a small second time constant.
[0008]
On the other hand, when the steering is turned off, the first time constant having a cut-off frequency smaller than the second time constant is selected. At this time, even if the damping torque itself is calculated to be 0, the generated damping torque is output while being gradually reduced.
[0009]
Therefore, even if the output direction of the torque signal is frequently switched and the damping torque calculated by the second steering control means vibrates, the output signal is switched smoothly. Therefore, it is possible to output a stable damping torque, and it is possible to realize a stable steering control without causing the driver to feel uncomfortable.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
FIG. 1 is a system diagram showing the overall configuration of a power steering apparatus according to Embodiment 1 of the present invention. First, the configuration will be described. A rack and pinion gear mechanism 3 is provided on the steering shaft 2 connected to the steering wheel 1, and the steering wheel 7 is operated in accordance with the steering of the steering wheel 1. The steering shaft 2 is provided with a power steering mechanism 5 that assists the steering force of the driver.
[0011]
The power steering mechanism 5 transmits the rotation of the electric motor 6 to a speed reduction mechanism provided on the steering shaft 2. When the driver operates the steering wheel 1, the rotation direction of the electric motor 6 is switched according to the operation direction, and assists the driver's steering force.
[0012]
Further, the steering shaft 2 is provided with a torque sensor 12 for detecting the steering torque of the driver.
[0013]
A steering torque signal from the torque sensor 12 is input to the control unit 10. A command signal is output to the electric motor 6 based on the input signal.
[0014]
FIG. 2 is a block diagram showing the configuration inside the control unit 10. A steering control unit 31 that calculates the target current of the electric motor 6 based on the input torque signal, a motor control unit 32 that outputs a command voltage based on the deviation between the actual motor current and the target current, and the commanded voltage It comprises a drive circuit 33 that outputs to the electric motor 6.
[0015]
FIG. 3 is a block diagram illustrating a control configuration of the steering control unit 31.
The basic assist torque calculation unit 101 includes a map for converting the steering torque into a basic command current value for each of a plurality of vehicle speed ranges, and calculates the basic command current value based on the steering torque and the vehicle speed.
[0016]
The differential correction torque calculation unit 102 differentiates the steering torque from the torque sensor 12. Then, an inertia compensation current value for compensating the inertial force of the electric motor 6 with respect to the driver's steering is calculated based on the steering torque differential value and the vehicle speed.
[0017]
The steering wheel return torque calculation unit 103 calculates a steering wheel return current value based on the steering speed and the vehicle speed in order to compensate for returning to the neutral position when turning back the steering.
[0018]
The damping correction torque calculation unit 104 calculates a damping current value acting in the direction opposite to the steering speed based on the steering speed and the vehicle speed in order to compensate for applying resistance to the steering operation.
[0019]
The motor current command value is calculated by adding or subtracting the current value calculated by each calculation unit. The calculated motor current command value limits the motor current command value in the motor current limit processing unit 105 depending on the operating state of the electric power steering apparatus. The limited motor current command value is output to the motor control unit 32 as a final command value.
[0020]
FIG. 4 is a block diagram showing the control contents of the damping correction torque calculation unit 104. The absolute value processing unit 41 converts the steering angular velocity α into an absolute value. The damping calculation unit 42 calculates a damping torque corresponding to the rudder angular velocity converted into an absolute value. The vehicle speed gain calculation unit 43 calculates a gain according to the vehicle speed. The torque code processing unit 44 encodes the value of the torque sensor 12. Here, the sign of the torque sensor 12 represents the output direction of the steering torque, and the positive and negative signs correspond to the right direction and left direction of the steering, respectively. The steering angular velocity code processing unit 45 encodes the value of the steering angular velocity. Here, the sign of the rudder angular speed represents the output direction of the rudder angular speed, and the sign positive and negative correspond to the right direction and left direction of the rudder angular speed, respectively.
[0021]
The return determination unit 46 determines whether or not the codes input from the torque code processing unit 44 and the steering angular velocity code processing unit 45 match, and outputs 1 when they match, and when they do not match. 0 is output. Based on the determination result of the return determination unit 46, the damping torque switching unit 47 switches whether the damping torque value calculated based on the steering angular speed α and the vehicle speed is output as it is or as 0. The time constant selection unit 48 sets a larger time constant (small cut-off frequency) τ1 and a smaller time constant (large cut-off frequency) τ2. A relationship of τ = 1 / 2πf is established between the time constant τ and the cutoff frequency f. An LPF (low-pass filter) processing unit 49 performs filtering based on the time constant set by the damping torque switching unit 47 and the time constant selection unit 48 to determine a final damping correction torque value.
[0022]
With the above-described control configuration, the finally determined damping correction torque value is output as a torque command value in the direction opposite to the actual steering direction.
[0023]
FIG. 5 is a flowchart showing the control content of the damping correction.
In step 201, the steering angular velocity α is read and converted into an absolute value, and the process proceeds to step 202.
[0024]
In step 202, the vehicle speed V is read, and the process proceeds to step 203.
[0025]
In step 203, a damping correction torque is calculated, and the process proceeds to step 204.
[0026]
In step 204, a steering torque encoding process is performed, and the process proceeds to step 205.
[0027]
In step 205, the steering angular velocity is encoded, and the process proceeds to step 206.
[0028]
In step 206, it is determined whether or not the sign of the steering torque is equal to the sign of the steering angular speed. If they are equal, the process proceeds to step 207, and if different, the process proceeds to step 208.
[0029]
If it is determined in step 207 that the cutting state is present, a time constant τ1 (cut-off frequency 1 Hz) is selected, and the process proceeds to step 209.
[0030]
If it is determined in step 208 that the switch-back state has occurred, the time constant τ2 (cut-off frequency 5 Hz) is selected, and the process proceeds to step 209.
[0031]
In step 209, LPF (low-pass filter) processing based on the selected time constant is performed, and this control flow ends.
[0032]
The contents of the control will be described based on the time chart of FIG. FIG. 6A shows the case where the steering state is determined only by the sign of the steering torque and the sign of the steering angular speed (conventional technology), and FIG. 6B shows the case where the steering state is determined by the present embodiment control.
[0033]
(Steering control in the prior art)
Description will be made based on the time chart of FIG.
At time T _1, since the code of the code and the steering angular velocity of the steering torque is different, it is determined that the return condition, control is performed back to impart damping torque.
At time T _2, the driver by damping torque adding felt torque of the steering direction opposite to impart again torque in the same direction as the steering direction. At this time, since the sign of the steering torque coincides with the sign of the steering angular speed, the damping torque becomes zero.
At time T _3, since the granted damping torque becomes suddenly 0, the sign of the steering torque becomes the sign and the discrepancy of the steering speed again, and controls return again.
At time T _4, because again the sign of the steering torque is the same as the sign of the steering speed, performs the normal control. Thus, the control is frequently switched, and the vibration caused by the damping torque gives the driver a feeling of strangeness.
[0034]
(Steering control in the present invention)
A description will be given based on the time chart of FIG.
At time T _1, since the sign of the steering torque is determined to differ from the sign of the steering angular velocity in step 206, the process proceeds to step 208. In step 208, it is determined that the switch-back state exists, and a time constant τ2 (cut-off frequency 5 Hz) is selected. Therefore, the calculated damping torque is output quickly.
[0035]
At time T _2, since the sign of the steering torque is determined to the same as the sign of the steering speed in step 206, the process proceeds to step 207. In step 207, it is determined that the cutting is in progress, and a time constant τ1 (cut-off frequency 1 Hz) is selected. At this time, the damping torque is output as 0, but since the time constant τ1 is set, the damping torque once set gradually decreases. Therefore, the damping torque does not decrease suddenly and the driver does not feel uncomfortable.
[0036]
In this way, when compared with the steering control of the prior art, the vibration caused by the sudden decrease in the damping torque is prevented, so stable steering is realized without frequently switching the sign of the steering torque. You can see that it is made.
[0037]
As described above, in the first embodiment, in the return determination, when the sign of the steering torque is the same as the sign of the steering angular speed, it is determined as the cutting state, and when the sign is different, the returning state is determined. The time constant (cutoff frequency) is variable.
[0038]
For example, if the driver applies torque in the return direction by hand when the damping correction is performed at the initial stage of the return, the damping correction amount is suddenly reduced to a substantially infeed state, and due to a sudden change from the inversion to the infeed. Vibration occurs. This vibration makes the driver feel uncomfortable. On the other hand, when the time constant is variable between the cut-in state and the cut-back state as in this embodiment, a small time constant τ2 (= a large cut-off frequency is required when damping correction is required as in the cut-back state. ) To quickly give a damping torque. In this state, the sign of the steering torque is switched, and even when the cutting torque is determined to be zero and the damping torque becomes zero, a large time constant τ1 (= small cutoff frequency) is selected and the damping torque is gradually reduced. Thus, it is possible to prevent vibration caused by a sudden change in damping torque. Therefore, stable steering control can be achieved.
[0039]
In this embodiment, two types of time constants are provided, and the time constant is selected at the time of control switching. However, the present invention is not limited to this configuration. For example, the time constant can be made variable according to the vehicle speed or the steering speed. Also good.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the overall configuration of a power steering apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration within a control unit in the first embodiment.
FIG. 3 is a diagram illustrating the control content of a torque calculation unit according to the first embodiment.
FIG. 4 is a block diagram showing control details of damping correction in the first embodiment.
FIG. 5 is a flowchart showing control contents of LPF (low-pass filter) processing in the first embodiment.
FIG. 6 is a time chart showing control contents of LPF (low-pass filter) processing in the first embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Gear mechanism 5 Power steering mechanism 6 Electric motor 7 Steering wheel 10 Control unit (SBWCU)
12 Torque sensor

Claims (1)

Torque detecting means for detecting steering torque;
First steering control means for applying assist torque based on at least the detected steering torque signal;
Second steering control means for applying a damping torque against the assist torque at the time of return control to return to the steering neutral position;
Target assist torque calculating means for calculating a desired target assist torque by adding the output of the first steering control means and the output of the second steering control means;
In the power steering device with
A low-pass filter having a variable time constant for filtering the output signal of the second steering control means;
Steering speed detection means for detecting the steering speed;
Time constant selecting means for selecting a time constant of the low-pass filter;
Provided,
The time constant selection means selects the first time constant when the steering torque detected by the torque detection means and the output direction of the steering speed detected by the steering speed detection means match, and the output direction is different. Selects at least a second time constant smaller than the first time constant.

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