JPH06305437A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE:To detect steering torque correctly even with the generation of offset to a torque sensor so as to perform an appropriate power assist continuously according to the actual steering torque. CONSTITUTION:A motor-driven power steering has a first steering torque detecting device M2 and a second steering torque detecting device M3 for outputting detected steering torque substantially with the characteristic of outputting the linear function of the actual steering torque with mutually reverse inclination, and a reference torque computing device M4 for computing the half of the sum of the detected steering torque, detected by the first and second steering torque detecting devices, as the reference torque. A control steering torque computing device M5 then computes control steering torque by subtracting the reference torque from the detected steering torque detected by the first or second steering torque detecting devices, and a control device M6 controls a motor 1 according to at least the control steering torque so as to control steering assist force.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering device for vehicles such as automobiles, and more particularly to an electric power steering device.

[0002]

2. Description of the Related Art An electric power steering apparatus for a vehicle such as an automobile has heretofore generally been a motor for driving a steering linkage member such as a rack bar via a clutch and a steering gear box, and a controller for controlling the rotation of the motor. The control device is configured to generate a required steering assist force by controlling the motor based on the detection results of various sensors such as a steering torque sensor.

As one of such electric power steering devices, for example, as disclosed in Japanese Patent Laid-Open No. 227859/1987, a difference between steering torques detected by two torque sensors provided on a steering shaft is calculated. However, when the difference between the detected steering torques is less than the reference value, the motor is controlled based on the detection result of at least one of the torque sensors, and when the difference between the detected steering torques is equal to or greater than the reference value, the torque sensor detects an offset such as temperature drift. 2. Description of the Related Art An electric power steering device configured to determine that an abnormality has occurred and stop energizing a motor and release a clutch has been conventionally known. According to the power steering device thus configured, it is possible to reliably prevent the power assist from being stopped and to appropriately perform the power assist when an abnormality occurs in one of the torque sensors.

[0004]

However, in the conventional electric power steering apparatus as described above, the power assist is not stopped unless the difference between the steering torques detected by the two torque sensors exceeds the reference value. Therefore, even if an offset due to temperature drift or the like occurs in the two torque sensors, if the offset directions are the same, the difference between the steering torques detected by those torque sensors does not exceed the reference value and the actual steering torque The power assist continues as it is in response to the steering torque that does not correspond exactly, so that even when the vehicle is straight ahead, the assist force is applied to the right or left turning direction, or the assist force varies depending on the turning direction. There is a problem of doing.

In view of the above-mentioned problems in the conventional electric power steering apparatus as described above, the present invention can accurately detect the steering torque even if the steering torque detecting means is offset due to temperature drift or the like. Therefore, it is an object of the present invention to provide an improved electric power steering device capable of continuously performing appropriate power assist according to the actual steering torque.

[0006]

SUMMARY OF THE INVENTION According to the present invention, the above-described object is to realize a motor M1 for generating a steering assist force and a substantially linear function of an actual steering torque as shown in FIG. A first steering torque detecting means M2 that outputs a detected steering torque based on the output characteristic, and a second steering that outputs a detected steering torque based on an output characteristic that is a reverse slope with respect to the output characteristic of the first steering torque detecting means. The torque detecting means M3, a reference torque calculating means M4 for calculating a half of the sum of the detected steering torques detected by the first and second steering torque detecting means as a reference torque, and the first or second The control steering torque calculation means M5 for calculating the control steering torque by subtracting the reference torque from the detected steering torque detected by the steering torque detection means, and at least the control steering torque. It is achieved by an electric power steering apparatus and a control unit M6 for controlling a steering assist force by controlling the motor Flip.

[0007]

The first steering torque detecting means M2 substantially outputs the detected steering torque based on the output characteristic of the linear function of the actual steering torque, and the second steering torque detecting means M3 functions as the first steering torque detecting means. Since the detected steering torque is output with an output characteristic that is a reverse slope with respect to the output characteristic, if an offset due to temperature drift or the like occurs in one steering torque detection means, it will be the same in the other steering torque detection means. When the actual steering torque is zero, the detected steering torques of the first and second steering torque detecting means are always equal to each other, and the first steering torque is not zero when the actual steering torque is zero. And 1/2 of the sum of the steering torques detected by the second steering torque detecting means, that is, the reference torque is 0, the detection operation of the first and second steering torque detecting means when the actual steering torque is zero. Equal to the torque. Further, a reference torque when an offset occurs in the two steering torque detecting means in the same direction and a reference torque when no offset occurs in any of the steering torque detecting means (hereinafter referred to as "origin torque"). ) Is equal to the magnitude of the offset generated in the two steering torque detecting means.

According to the above-mentioned configuration of the present invention, the reference torque calculating means M4 calculates one half of the sum of the detected steering torques detected by the first and second steering torque detecting means as the reference torque. Control steering torque calculation means M
The control steering torque is calculated by subtracting the reference torque from the detected steering torque detected by the first or second steering torque detection means by 5, and the motor is generated by the control means M6 according to at least the control steering torque. Since the steering assist force is controlled by controlling M1, even if two steering torque detecting means have offsets in the same direction due to temperature drift, as long as the offsets are substantially the same, control steering is performed. The torque is calculated in correspondence with the actual steering torque so that the signs will be reversed depending on whether the steering wheel is left-turned or right-turned. This makes it possible to always operate the power steering device appropriately in accordance with the actual steering torque. Even if the vehicle is traveling straight, the assisting force is applied to the right or left turning direction, or the assisting force varies depending on the turning direction. It is not necessary to or.

In the present specification, the "output characteristic of the second steering torque detecting means M3 having an inclination opposite to the output characteristic of the first steering torque detecting means" means the actual steering torque on the horizontal axis. The straight lines of the output characteristics of the first and second steering torque detecting means intersect with each other on the vertical axis in the orthogonal coordinates with the detected steering torque as the vertical axis, and the straight lines of the first and second steering torque detecting means It means that the absolute values of the slopes of the straight lines of the output characteristics are equal to each other. Therefore, the above-mentioned "reference torque" is the steering torque corresponding to the intersection of the straight lines of the two output characteristics, and "origin torque" is the two output characteristics in the case where no offset occurs in any steering torque detecting means. The steering torque corresponds to the intersection of the straight lines.

[0010]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 2 is a schematic configuration diagram showing one embodiment of the electric power steering apparatus according to the present invention, and FIG. 3 is FIG.
3 is a block diagram showing an electronic control device shown in FIG.

In FIG. 2, reference numeral 10 denotes a steering wheel. The steering wheel 10 drives a rack bar 16 via a steering shaft 12 and a steering gear box 14. A power unit 20 is drivingly connected to the steering shaft 12 by a gear reduction mechanism 18. The power unit 20 has a motor 22 and an electromagnetic clutch 24 for selectively drivingly connecting the gear reduction mechanism 18 and the motor 22.

In the illustrated embodiment, a steering angle sensor 26 for detecting a steering angle θ is provided on the steering shaft 12.
The actual steering torque Tr is detected, and the detected steering torques Tm and Tm are substantially determined by the output characteristics of the linear function of the actual steering torque.
A main torque sensor 28 and a sub torque sensor 30 that output s are provided, and the outputs of these sensors are supplied to the electronic control unit 32. A signal indicating the vehicle speed V detected by the vehicle speed sensor 34 is also input to the electronic control unit 32.

Although not shown in detail in the drawing, the main torque sensor 28 and the sub torque sensor 30 are constructed so that the impedance changes due to the torsion of the torsion bar incorporated in the steering shaft, and the windings are arranged in opposite directions. It has a coil wound around it, so that the two torque sensors output the detected steering torques Tm and Ts with the output characteristics that are opposite to each other as shown in FIG.

That is, the main torque sensor 28 outputs the detected steering torque Tm with an output characteristic of a substantially linear function of the actual steering torque so that the detected steering torque Tm gradually increases as the actual steering torque Tr increases in the right turning direction. Then, the sub torque sensor 30 outputs the detected steering torque Ts with the output characteristic of the linear function of the actual steering torque so that the detected steering torque Ts gradually decreases as the actual steering torque Tr increases in the right-turn direction. It is like this. Also, these two torque sensors intersect each other at the point where the straight line of their output characteristics corresponds to the origin torque To on the vertical axis indicating the detected steering torque by the initial setting and the absolute values of the inclinations of the two straight lines mutually. It is set to be the same.

As shown in detail in FIG. 3, the electronic controller 32 includes a microcomputer 38, which is a central processing unit (CPU) 40.
, Read only memory (ROM) 42, random access memory (RAM) 44, and input port device 46
And an output port device 48, which are connected to each other by a bidirectional common bus 50.

The input port device 46 has a steering angle sensor 26.
A signal indicating the steering angle θ detected by the torque sensor 2
A signal indicating the output steering torques Tm and Ts from 8 and 30 and a signal indicating the vehicle speed V detected by the vehicle speed sensor 34 are input. The input port device 46 appropriately processes the signal input thereto, and outputs the processed signal to the CPU and the RAM 44 according to the instruction of the CPU 40 based on the control program stored in the ROM 42.

The ROM 42 stores the control program shown in FIG. 4 and maps corresponding to the graphs shown in FIGS. 5 and 6. The CPU 40 is adapted to perform various calculations and signal processing as will be described later based on the control program shown in FIG. The output port device 48 outputs a control signal to the motor 22 via the drive circuit 52 and a control signal to the electromagnetic clutch 24 via the drive circuit 54 in accordance with an instruction from the CPU 40, and if one of the torque sensors 28 and 30 has an abnormality. When it is determined that the alarm has occurred, the alarm lamp 56 is turned on.

The operation of the illustrated embodiment will now be described with reference to the flow chart shown in FIG. The control by the electronic control unit 32 is started by closing an ignition switch not shown in FIG. Further, in the flowchart shown in FIG. 4, N represents the number of determinations that abnormality has occurred in one of the torque sensors 28 and 30.

First, in step 10, the control signal is output to the electromagnetic clutch 24 through the drive circuit 54 so that the clutch is engaged, and in step 20, the steering angle θ detected by the steering angle sensor 26 is changed. Signals shown, output steering torques Tm and Ts from torque sensors 28 and 30
And a signal indicating the vehicle speed V detected by the vehicle speed sensor 34 are read.

In step 30, the reference torque Tst is calculated according to the following equation 1 based on the output steering torques Tm and Ts read in step 20, and step 4
At 0, the control steering torque T is calculated according to the following equation 2 based on the output steering torque Tm and the reference torque Tst.

[0022]

[Formula 1] Tst = (Tm + Ts) / 2

(2) T = Tm-Tst

In step 50, the basic assist amount Tab is calculated from the map corresponding to the graph shown in FIG. 5 based on the steering torque T calculated in step 40, and in step 60, step 20 The vehicle speed coefficient Kv is calculated from the map corresponding to the graph shown in FIG. 6 on the basis of the vehicle speed V read in, and in step 70, the basic assist amount Tab calculated in step 30 and step 40 The assist amount Ta is calculated as a product of the vehicle speed coefficient Kv calculated in the above.

At step 80, the deviation ΔTst of the reference torque is calculated by subtracting the origin torque To from the reference torque Tst according to the following equation 3.

[Formula 3] ΔTst = Tst−To

In step 90, the deviation Δ of the reference torque
It is determined whether or not the absolute value of Tst exceeds the reference value Tc (a positive constant), and it is determined that | ΔTst |> Tc, that is, the offsets of the two torque sensors 28 and 30 are within the allowable range. If it is determined that the torque sensor abnormality determination count N is reset to 0 in step 100, it is determined that | ΔTst |> Tc, that is, the offsets of the two torque sensors fall within the allowable range. When it is determined that the number of times of exceeding is exceeded, the number N of abnormality determinations is incremented by 1 in step 110.

The reference value Tc for the determination in step 90 described above may be obtained, for example, experimentally so that the determination that the offsets of the two torque sensors are out of the allowable range is properly performed.

In step 120, it is judged whether or not the number of times N is 3, and when it is judged that N = 3 is not satisfied, in step 130, a control signal corresponding to the assist amount Ta. Is output to the motor 22 via the drive circuit 52, the steering assist force is controlled to a value corresponding to the assist amount Ta, and then the process returns to step 20 and N = 3.
If it is determined that the above condition is true, the process proceeds to step 140.

In step 140, the energization of the motor 22 is stopped and the output of the control signal to the electromagnetic clutch 24 is stopped, so that the clutch is released.
In step 150, a warning lamp is turned on by outputting a control signal to the warning lamp 56, thereby issuing a warning to the driver of the vehicle that the motor is locked.

Thus, according to the illustrated embodiment, in step 30, the reference torque T is set as one half of the sum of the steering torques Tm and Ts detected by the two torque sensors 28 and 30.
st is calculated, and the control steering torque T is calculated by subtracting the reference torque Tst from the steering torque Tm detected by the main torque sensor 28 in step 40, and the basic assist amount Tab is calculated in step 50 by the control steering. 6 is calculated from the map corresponding to the graph shown in FIG. 6 based on the torque T, and the vehicle speed coefficient Kv is calculated from the map corresponding to the graph shown in FIG. The assist amount Ta is calculated as the product of the basic assist amount Tab and the vehicle speed coefficient Kv. In step 80, the origin torque To is subtracted from the reference torque Tst to calculate the deviation ΔTst of the reference torque.

When no offset occurs in either of the torque sensors 28 and 30 and they are operating normally, the reference torque Tst is equal to the actual steering torque Tr as shown in FIG. 8 (A). Since it is the same as the origin torque To regardless of the origin, the characteristic straight line of the control steering torque T always passes through the origin as shown in FIG. 8 (B), and the actual steering torque Tr of the control steering torque T is positive. And negative values are positive and negative values, respectively.

When the torque sensors 28 and 30 are offset by the same amount in the same direction within the allowable range due to temperature drift, the reference torque Tst is as shown in FIG. 9A. Although it has a value different from the origin torque To, the control steering torque T is calculated according to the above-described mathematical expression 2, and therefore the characteristic straight line of the control steering torque T is also shown in this case as shown in FIG. 9B. Always passes through the origin, and the control steering torque T takes positive and negative values when the actual steering torque Tr has positive and negative values, respectively. Further, in this case, the deviation between the reference torque Tst and the origin torque To, that is, the deviation ΔTst of the reference torque is constant regardless of the actual steering torque Tr.

Further, when a serious abnormality such as a short circuit occurs in one of the torque sensors 28 and 30, the straight line of the output characteristic in which the abnormality occurs changes as shown in FIG. 10 (A). The control steering torque T calculated according to No. 2 does not exactly correspond to the actual steering torque Tr as shown in FIG. Further, in this case, the deviation between the reference torque Tst and the origin torque To, that is, the deviation ΔTst of the reference torque fluctuates depending on the actual steering torque Tr, and becomes higher as the actual steering torque increases in the right-turn direction.

Therefore, not only when the torque sensors 28 and 30 are not offset and are operating normally, but the two torque sensors are offset by the same amount in the same direction within the allowable range. In this case, a negative determination is made in step 90, and the control signal corresponding to the assist amount Ta is output to the motor 22 in step 130 so that the steering assist force corresponds to the actual steering torque. Since the higher the vehicle speed is, the lower the vehicle speed is controlled. Therefore, the light steering is ensured in the low vehicle speed range and the good steering stability is ensured in the high vehicle speed range.

On the other hand, if one of the torque sensors 28 or 30 has a serious abnormality such as a wire break, a short circuit, or an offset exceeding the allowable range, the absolute value of the deviation ΔTst of the reference torque exceeds the reference value Tc. At that time, the judgment of yes is made. If this determination, that is, the determination that one of the torque sensors has a serious abnormality occurs three times in succession, a yes determination is made in step 120 and the motor 22 is energized in step 140. Is stopped and the output of the control signal to the clutch 24 is stopped, the clutch is released, which ensures that the power steering device is switched to the manual steering device and the inappropriate power assist is continued. The warning lamp 56 is turned on in step 150 to prevent the driver of the vehicle from using the torque sensor 2.
A warning is issued that a serious abnormality has occurred in 8.

Further, according to the embodiment shown in the figure, steps 140 and 150 are not executed unless the determination that a serious abnormality has occurred in one of the torque sensors is made three times in succession, so that the torque sensor has a serious problem. It is erroneously determined that an abnormality has occurred, and based on the determination result, steps 140 and 150 are executed despite the fact that no serious abnormality has occurred in the torque sensor, that is, the alarm lamp 56.
Is surely turned on and the power steering device is surely prevented from being switched to the manual steering device.

Although the present invention has been described above in detail with reference to specific embodiments, the present invention is not limited to such embodiments, and other various embodiments are possible within the scope of the present invention. It will be apparent to those skilled in the art that it is possible.

For example, in the above-described embodiment, the reverse inclination of the output characteristics of the two torque sensors 28 and 30 is achieved by setting the winding directions of their coils to be opposite to each other. The reverse slope of the output characteristics of the two torque sensors is achieved by passing the output from one of the two torque sensors having the same output characteristics through an amplifier or subtracting the output of one torque sensor from a certain constant. Good.

[0038]

As is apparent from the above description, according to the present invention, one half of the sum of the detected steering torques detected by the first and second steering torque detecting means by the reference torque calculating means M4. Is calculated as the reference torque, and the control steering torque is calculated by subtracting the reference torque from the detected steering torque detected by the first or second steering torque detection means by the control steering torque calculation means M5. Since the steering assist force is controlled by controlling the motor M1 according to at least the control steering torque by the means M6, even if an offset in the same direction occurs in the two steering torque detection means due to temperature drift, for example, those steering torque detection means are controlled. As long as the offset is substantially the same, the actual steering torque is adjusted so that the steering torque for control has the opposite sign when left or right turned. Therefore, the power steering device can always operate properly in accordance with the actual steering torque, so that the assisting force in the right-turning or left-turning direction can be obtained even when the vehicle is straight ahead. It is possible to reliably prevent the assist force from being given or different depending on the turning direction.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of an electric power steering device according to the present invention in correspondence with the description of the claims.

FIG. 2 is a schematic configuration diagram showing one embodiment of an electric power steering device according to the present invention.

FIG. 3 is a block diagram showing the electronic control device shown in FIG. 2.

FIG. 4 is a flowchart showing a power assist control routine achieved by the electronic control device shown in FIGS. 2 and 3.

FIG. 5 is a graph showing a relationship between a steering torque T detected by a torque sensor and a basic assist amount Tab.

FIG. 6 is a graph showing a relationship between a vehicle speed V detected by a vehicle speed sensor and a vehicle speed coefficient Kv.

FIG. 7 is a graph showing the relationship between the actual steering torque Tr and the steering torques Tm and Ts detected by the torque sensor.

FIG. 8 is a graph (A) showing the relationship between the actual steering torque Tr and the detected steering torques Tm and Ts of the two torque sensors when the two torque sensors are operating normally.
3 is a graph (B) showing the relationship between the actual steering torque Tr and the control steering torque T.

FIG. 9 is a graph (A) showing the relationship between the actual steering torque Tr and the detected steering torques Tm and Ts of the two torque sensors when the two torque sensors are offset by the same amount in the same direction. ) And the actual steering torque Tr and the control steering torque T are graphs (B).

FIG. 10 is a graph (A) showing the relationship between the actual steering torque Tr and the detected steering torques Tm and Ts of the two torque sensors when one of the two torque sensors is short-circuited, and the actual steering. Torque Tr and control steering torque T
It is a graph (B) which shows the relationship between and.

[Explanation of Codes] 10 ... Steering wheel 12 ... Steering shaft 14 ... Steering gear box 22 ... Motor 24 ... Electromagnetic clutch 26 ... Steering angle sensor 28, 30 ... Torque sensor 32 ... Electronic control unit 34 ... Vehicle speed sensor 56 ... Warning lamp

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaaki Tsuboi, 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor, Tomoyuki Watanabe 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation

Claims (1)

[Claims] 1. A motor for generating a steering assist force, a first steering torque detecting means for outputting a detected steering torque substantially according to an output characteristic of a linear function of an actual steering torque, and the first steering torque detection. 2 of the sum of the detected steering torque detected by the second steering torque detection means and the second steering torque detection means that outputs the detected steering torque with an output characteristic that is the reverse of the output characteristic of the means. A reference torque calculation unit that calculates one-third as a reference torque, and a steering torque for control is calculated by subtracting the reference torque from the detected steering torque detected by the first or second steering torque detection unit. An electric power steering system having a control steering torque calculation means and a control means for controlling the steering assist force by controlling the motor according to at least the control steering torque. Ring device.