JPH05112245A - Electric type power steering device for vehicle - Google Patents

Abstract

PURPOSE:To perform handle-operation giving a reaction feeling when a vehicle runs approximately straight and perform light handle operation when it runs on a winding, such as a mountain district, without complicating drive operation of a driver. CONSTITUTION:A steering torque sensor 21 detects steering torque T exerted on a steering handle 11. A car speed sensor 22 detects a car speed V. A current sensor 23 detects an armature current I of an electric motor 16. A microcomputer 24 drives the electric motor 16 in a way that an armature 16a is charged with a motor drive current MI responding to the steering torque T and a car speed V. When a vehicle runs on a winding road and an accumulating result IT of the armature current I during a given time is increased, correction to the side where a motor drive current MI is increased is effected according to the increase of the accumulating result IT, and an assist force by the electric motor 16 is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device for a vehicle, which assists a steering operation of a steering wheel by a rotational force of an electric motor.

[0002]

2. Description of the Related Art Conventionally, an apparatus of this type is disclosed in, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Laid-Open Patent Publication No. 1-119466, the steering torque applied to the steering wheel is detected, and a driving current that increases as the detected torque increases is passed through the electric motor. The steering wheel operation is assisted by an assisting force that increases as the size increases. Further, in this device, the driver can select various characteristics of the change in the drive current with respect to the steering torque, and a desired amount of assisting force is applied to the steering wheel operation.

[0003]

In general, vehicle traveling,
In particular, when driving a vehicle at high speed, there is a feeling of resistance when going straight, and light steering operation is expected when driving on a winding road that is often seen in mountains. However, in the above-mentioned conventional device, when the steering wheel operation as described above is expected, the driver needs to switch the change characteristic of the drive current with respect to the steering torque according to the state of the road while the vehicle is running. Operation becomes complicated. The present invention has been made to address the above problems, and its purpose is to automatically detect the state of the traveling path and automatically correct the drive current to the electric motor according to the detection result. The present invention provides an electric power steering device for a vehicle, which realizes the ideal steering wheel operation as described above by a simple driving operation.

[0004]

In order to achieve the above object, a structural feature of the present invention is that a steering mechanism is provided in a steering mechanism that steers front wheels in response to rotation of a steering handle, and the steering handle is provided in response to the rotation. Electric motor for assisting the steering operation of the electric motor, torque detection means for detecting the steering torque applied to the steering wheel, and a drive current that increases as the detected torque increases to flow through the electric motor. In an electric power steering apparatus for a vehicle, which comprises a motor control means for controlling rotation, an accumulating means for accumulating a drive current flowing through the electric motor within a predetermined time, and the accumulating drive current increasing as the accumulated drive current increases. The correction means for correcting the drive current by the motor control means to the larger side is provided.

[0005]

According to the present invention constructed as described above, when the vehicle is traveling substantially straight, the steering wheel is hardly rotated, and the steering torque applied to the steering wheel is almost "0". Therefore, the drive current supplied to the electric motor by the motor control means is also kept small. Therefore, the driving current accumulated by the accumulating means within a predetermined time is also small, and the correcting means does not correct the driving current to the larger side, or the correction amount becomes small. The power is kept small and the steering wheel operation becomes challenging.

On the other hand, when the vehicle is traveling on a winding road such as a mountain, the steering wheel is frequently turned largely left and right, and the steering torque applied to the steering wheel often has a large value. Therefore, the drive current supplied to the electric motor by the motor control means also frequently becomes large. Therefore, the driving current accumulated by the accumulating means within a predetermined time becomes large, and the correction amount of the driving current by the correcting means also becomes large. In this case, the assisting force by the electric motor becomes large and the steering wheel operation becomes light. It will be

[0007]

As described above, according to the present invention, it is automatically detected whether the vehicle is traveling in a straight line or on a winding road, and a special operation by the driver is required. Without having to do it, you can feel the feeling when driving straight ahead, and you can expect light steering wheel operation while traveling on the winding road, so you can realize ideal steering wheel operation with simple driving operation.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows an electric power steering device for a vehicle.

In this power steering system,
The steering wheel 11 is connected to the front wheels FW and FW via a steering shaft 12, a gear box 13 and a tie rod 14, and the front wheels FW and FW are steered according to the rotation of the steering wheel 11. A gear 15 is attached to an intermediate portion of the steering shaft 12, and a driving force from an electric motor 16 is transmitted to the gear 15 via a speed reducer 17 and a gear 18.

The rotation of the electric motor 16 depends on its armature 16a.
Is controlled by the motor drive current MI flowing through the steering torque sensor 21, the vehicle speed sensor 22, the current sensor 23, and the microcomputer 24.
It is controlled by an electric control device including It should be noted that when the motor drive current MI is in the direction of the arrow in the figure, the electric motor 16a rotates normally in response to the clockwise rotation of the steering wheel 11, and when the drive current MI is in the direction opposite to the arrow in the figure, the motor 16a is the same. The handle 11 is rotated counterclockwise in response to left rotation.

The steering torque sensor 21 is mounted on the steering shaft 12, detects the steering torque T applied to the coaxial shaft 12, and outputs a detection signal representing the torque T to the microcomputer 2.
Supply to 4. In this case, the steering torque T becomes positive when the steering handle 11 is rotated rightward, and becomes negative when the steering handle 11 is rotated leftward. Vehicle speed sensor 2
Reference numeral 2 detects the vehicle speed V by measuring the output shaft of the transmission or the rotational speed of the wheels, and supplies a detection signal representing the vehicle speed V to the microcomputer 24. Current sensor 23
Is composed of a resistor connected between the armature 16a and the ground point, detects an armature current I flowing through the armature 16a, and outputs a voltage signal representing the current I. This voltage signal is A /
It is converted into a digital format by the D converter 25 and supplied to the microcomputer 24.

The microcomputer 24 is a ROM, RA
M, CPU, timer, input / output interface (I /
O) and the like, which is stored in the ROM and executes a program corresponding to the flowcharts shown in FIGS. 2 and 3, controls the motor drive current to the armature 16a. Further, the ROM has a table is provided, the same table the absolute value of the steering torque T | T | vehicle speed coefficient for the motor drive current MI (see FIG. 4) and the vehicle speed V relative to K _V (see FIG. 5) is stored Has been done. The microcomputer 24 is connected to one input terminal (+) of a servo amplifier 27 via a D / A converter 26. The current sensor 23 is connected to the other input terminal (-) of the servo amplifier 27.
Is connected to the output terminal of the armature 1
6a is connected, and a current proportional to the difference between the voltages supplied to both input terminals is supplied from the output terminal to the armature 16a.

The operation of the embodiment configured as described above will be described. When an ignition switch (not shown) is turned on, the microcomputer 24 causes the microcomputer 24 to
The program corresponding to the flowcharts shown in FIGS. 2 and 3 is repeatedly executed. The execution of this program is started in step 30, and in step 31, the steering torque T from the steering torque sensor 21, the vehicle speed V from the vehicle speed sensor 22, and the armature current I from the current sensor 23 are read. Next, the absolute value of the armature current I read in step 32 in the last few seconds to several 10 seconds | by calculating the total sum I _T, the absolute value of the armature current I within a predetermined time | | I I | Is accumulated. In this case, a predetermined number of armature currents I read from a predetermined time before to the present by the process of step 31 are stored in the RAM of the microcomputer 24.
All of the absolute values | I | of the predetermined number of armature current values I that are always stored in the memory are added. In addition,
In the initial, the number of the armature current I to be the sum has not reached the predetermined number, the total sum I _T does not indicate an accurate value, after the ignition switch is turned on, a few seconds to several 10 seconds elapsed since the number of the armature current I to be the addition if reaches a predetermined number, no problem in the case of using the sum I _T during vehicle traveling.

After the processing of step 32, step 33
The read vehicle speed V is a predetermined vehicle speed V determined in advance.
_While being compared with ₀ , the total sum I _T of the absolute values | I | of the armature current I calculated in step 34 is compared with a predetermined current I ₀ .

First, the case where the vehicle is traveling at a low speed will be described. In this case, since the detected vehicle speed V is less than the predetermined vehicle speed V _0, it is determined to be “NO” in step 33, and the flag FLG is set to “0” in step 35. Next, in step 37, it is determined to be "NO" based on the flag FLG set to "0", and step 3
At 9 and 40, a table in the microcomputer 24 is referred to based on the steering torque T and the vehicle speed V, and the motor drive current MI and the vehicle speed coefficient K _V corresponding to the steering torque T and the vehicle speed _V (see FIGS. 4 and 5). ) Is determined. In this case, if the steering torque T is positive, the motor drive current MI is set to a positive value, and if the torque T is negative, the drive current MI is set to a negative value.

Next, in step 41, the same as above is performed.
It is determined to be "NO" based on the flag FLG set to 0 ", the motor drive current MI is multiplied by the vehicle speed coefficient K _V by the calculation of the following equation 1 in step 43, and the same is multiplied in step 44. The digital signal representing the motor drive current MI is output to the D / A converter 26, and step 4
At 5, the execution of this program ends.

[0017]

## EQU1 ## MI = K _V · MI The D / A converter 26 converts the supplied digital signal into an analog signal and outputs a voltage signal representing the motor drive current MI to the servo amplifier 27. Servo amplifier 2
7 operates in cooperation with the current sensor 23 to cause a current corresponding to the supplied voltage signal to flow to the armature 16a of the electric motor 16, so that the armature 16a has an electric motor equal to the motor drive current MI. Child current flows. in this case,
If the motor drive current MI is positive, a current flows in the armature 16a in the direction of the arrow (corresponding to the clockwise rotation of the steering wheel 11), and if the motor drive current MI is negative, the armature 16a is indicated by the arrow in the figure. An electric current flows in the opposite direction (corresponding to the left rotation of the steering wheel 11).

As a result, when the steering wheel 11 is rotated and the steering torque T is applied to the steering shaft 12 while the vehicle is traveling at a low speed, the vehicle speed coefficient K _V when the vehicle speed V is low is a large value ( 5), the microcomputer 24
The absolute value of the voltage signal representing the motor drive current MI output from the motor also increases, and a large current also flows through the armature 16a of the electric motor 16. As a result, when the front wheels FW and FW are steered by the turning of the steering wheel 11, a large assisting force is applied to the steering by the electric motor 16, so that the vehicle is turned by a light steering operation. be able to.

Next, the case where the vehicle is traveling at high speed will be described. In this case, if the vehicle is traveling substantially straight (for example, a lane change is performed but there is no sudden turn), “YES” in step 33, that is, the vehicle speed V is equal to or higher than the predetermined vehicle speed V _0. However, it is determined in step 34 that “NO”, that is, the sum I _T of the absolute values | I | of the armature current I is not equal to or greater than the predetermined current I ₀ . This is for the following reasons. In this case, since the steering handle 11 is rotated very rarely and the steering torque T is usually "0", the motor drive current MI determined in step 39 is also usually "0" (see FIG. 4). ). Therefore, the motor drive current MI calculated in step 43 based on the equation 1 is also the motor drive current MI output from the microcomputer 24 in step 44.
Since the voltage signal representing MI is usually "0", step 3
The armature current I read from the current sensor 23 at 1 is also normally “0”. As a result, the absolute value of the armature current I to be accumulated at step 32 | I | sum I _T becomes a small value.

As described above, "NO" in step 34.
If it is determined that the flag FLG is “0” in step 35.
Therefore, as in the case of low speed running, the voltage signal representing the motor drive current MI determined by the processing of steps 39, 40 and 43 is passed through the D / A converter 26 by the processing of step 44. Are supplied to the servo amplifier 27. However, in this case, since the vehicle speed V is a large value, the vehicle speed coefficient K _V is set to a small value (see FIG. 5),
The absolute value | MI | of the motor drive current MI calculated in step 43 also becomes small. Therefore, the steering wheel 1
When 1 is rotated, the armature current flowing through the armature 16a of the electric motor 16 is also reduced, so that the assisting force of the motor 16 for rotating the handle 11 is also reduced.
As a result, when the vehicle is traveling straight at a high speed, the steering wheel operation becomes responsive and the traveling stability of the vehicle becomes good.

On the other hand, even when the vehicle is traveling at a high speed, when the vehicle is traveling on a winding road in mountainous areas, the steering wheel 11 is frequently rotated left and right, and the steering wheel 11 is frequently operated by a large steering wheel. Torque T is applied. as a result,
A current is frequently applied to the armature 16a of the electric motor 16, and the armature current I read from the current sensor 23 in step 31 usually shows a predetermined value other than "0". the absolute value of the armature current I over a predetermined time that is | I | sum I _T becomes a large value. Accordingly, in this case, in both steps 33 and 34, “YES”, that is, the vehicle speed V is equal to or higher than the predetermined vehicle speed V ₀ ,
And the total I _T is determined to be the predetermined current I ₀ or more, the flag FLG at step 36 is set to "1".

Based on the flag FLG set to "1", it is determined to be "YES" in steps 37 and 41, and in the above case, the following equation 2 in step 38 is used.
And the arithmetic processing of the following Expression 3 in step 42 are added.

[0023]

[Equation 2] T = α · T

[0024]

## EQU00003 ## K _V = βK _{V In} this case, the coefficients α and β are both constants larger than "1".

As a result of the addition of these calculation processes, in this case, the absolute value | MI | of the motor drive current MI as the calculation result of the above equation 1 in step 43 becomes a large value,
Therefore, when the steering handle 11 is rotated, the armature current flowing through the armature 16a of the electric motor 16 also becomes large, so that the motor 1 with respect to the rotation operation of the handle 11 is rotated.
6 will also help. As a result, even when the vehicle is traveling at high speed, when traveling on a winding road in the mountainous area, the vehicle can be driven by a light steering wheel operation.

As described above, according to the above-described embodiment, it is automatically detected whether the vehicle is traveling substantially straight or traveling on the winding road, and the driver does not have to perform a selection operation according to the traveling road. Also, when the vehicle is traveling on the winding road, the current to the armature 16a is corrected to the larger side, and there is a feeling of resistance when traveling straight, and a light steering wheel operation is performed while traveling on the winding road. Since you can expect it, you can realize ideal steering wheel operation with simple driving operation.

In the above embodiment, the current I actually flowing through the armature 16a of the electric motor 16 is detected by the current sensor 23, and the absolute value | I | of this current I is accumulated for a predetermined time. However, since the current flowing through the armature 16a is substantially equal to the motor drive current MI calculated by the arithmetic processing in step 43, the absolute value | MI | of this motor drive current MI is accumulated in step 32 over a predetermined time. You may do so. This eliminates the need to input the digital signal representing the current I detected by the current sensor 23 to the microcomputer 24.

In the above embodiment, the motor 16 is controlled by controlling the armature current of the motor 16.
I controlled the rotation of, but instead of the armature current,
Alternatively, additionally, the field current of the electric motor 16 may be controlled to control the rotation of the electric motor 16.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an electric power steering apparatus for a vehicle showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a part of a program executed by the microcomputer of FIG.

3 is a flowchart showing another part of the program executed by the microcomputer of FIG.

FIG. 4 is a change characteristic diagram of a motor drive current with respect to a steering torque.

FIG. 5 is a change characteristic diagram of a vehicle speed coefficient with respect to a vehicle speed.

[Explanation of symbols]

FW ... front wheel, 11 ... steering wheel, 12 ... steering shaft, 13
... Gear box, 16 ... Electric motor, 21 ... Steering torque sensor, 22 ... Vehicle speed sensor, 23 ... Current sensor, 24 ...
Microcomputer, 27 ... Servo amplifier.

Claims (1)

[Claims] 1. An electric motor provided in a steering mechanism for steering front wheels in response to rotation of a steering wheel, for assisting a steering operation of the steering wheel in response to rotation, and a steering torque applied to the steering wheel are detected. Torque detection means,
An electric power steering apparatus for a vehicle, comprising: a motor control unit that controls a rotation of the electric motor by causing a drive current that increases as the detected torque increases to the electric motor within a predetermined time. A vehicle characterized by comprising accumulating means for accumulating the drive current flowing through the motor, and correcting means for correcting the drive current by the motor control means to a larger side as the accumulated drive current increases. Electric power steering device.