JP2000128003A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of providing a more stabilized power assist control. SOLUTION: An electric power steering device comprises an electric motor 7 that assists with steering force, one or a plurality of torque sensors 5 that detect torque applied to a steering shaft 2, a steering angle sensor 9 that detects the steering angle speed of a steering wheel, and a control unit 10 that controls power assist of the electric motor 7 based on output signals from the torque sensor 5 and the steering angle sensor 9. In this device, from among the torque sensors 5, the control unit 10 uses the one whose output values fall within a predetermined range with respect to the obtained steering angle speed to tentatively control power assist of the electric motor 7.

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 apparatus, and more particularly to an improvement in the reliability of an electric power steering apparatus.

[0002]

2. Description of the Related Art As an electric power steering apparatus,
A steering angle sensor and a torque sensor are incorporated in the steering shaft, and the steering force and the assisting force of the electric motor mounted on the steering system are used as parameters with the steering angle and steering torque detected by these sensors and the vehicle speed detected by the vehicle speed sensor as parameters. Control techniques are known. Thus, during low-speed traveling, the assisting force is increased to reduce the steering, and during high-speed traveling, the assisting force is decreased to increase the steering.

[0003] In this type of electric power steering apparatus, if an abnormality occurs in the torque sensor, erroneous control can occur, so various types of fail-safe are being studied. The technology disclosed in Japanese Patent Application Laid-Open No. 9-58505 is to perform assisting force control based on a steering angle detected by a steering angle sensor when an abnormality occurs in a torque sensor. It is characterized in that the auxiliary force is prevented from being suddenly cut by gradually lowering it with time.

[0004]

However, in this technique, since the assisting force is controlled based only on the steering angle irrespective of the degree of the abnormality of the torque sensor, the assisting force changes suddenly when the abnormality of the torque sensor is detected. there is a possibility.

Accordingly, the present invention has been made in view of the above problems,
It is an object of the present invention to provide an electric power steering device capable of performing more stable assist force control.

[0006]

In order to solve the above-mentioned problems, an electric power steering apparatus according to the present invention comprises: an electric motor for assisting a steering force; one or more torque sensors for detecting a torque applied to a steering shaft; An electric power steering apparatus comprising: a steering angle sensor that detects a steering angular velocity of a steering; and a control device that controls an assisting force of an electric motor based on a torque sensor and an output signal of the steering angle sensor. It is determined whether or not the output value of the motor is within a predetermined range with respect to the detected steering angular velocity, and controlling the assisting force of the electric motor using the output value of the torque sensor within the predetermined range. Features.

The steering torque generally depends on the steering angular velocity, although it depends on the road surface condition. Then, even when the torque sensor is abnormal, if the torque value that can be said to be within an appropriate range for the steering angular velocity is output, it is considered that the abnormality of the torque sensor is small. Therefore, by performing control using such a torque sensor having a small abnormality,
It is possible to avoid a sudden change in the assisting force control of the electric motor when the torque sensor is abnormal.

It is preferable that two of these torque sensors are arranged. By using a dual system, the probability that at least one of the torque sensors functions normally becomes higher than in the case where the torque sensor is used alone, and fail-safe is realized.

Further, the control device uses only the torque sensor whose output value is within a predetermined range with respect to the steering angular speed when the absolute value of the steering angular speed is equal to or more than a predetermined value, and uses the torque sensor to assist the electric motor. Is preferably controlled.

When the steering angular velocity is small, the correlation between the steering angular velocity and the torque value is small and it is difficult to make a determination. However, since the steering force itself is small and no auxiliary force is required, it is not necessary to perform the auxiliary force control. Conversely, when the steering angular velocity at which the assisting force of the steering force is required is large, the correlation between the steering angular velocity and the torque value is large, so that reliable assist force control can be performed.

Another electric power steering apparatus according to the present invention comprises: an electric motor for assisting a steering force; two torque sensors for detecting a torque applied to a steering shaft;
The electric power steering system and a control device for controlling the assist force of the electric motor based on the output of the torque sensor, the output value when the zero steering torque both torque sensor during normal V _0, and the respective The output values V ₁ and V ₂ are dual-polarity torque sensors of opposite polarities arranged so as to have mutually opposite characteristics with respect to V ₀ . | (V ₁ −V ₀ ) + (V ₂ −V ₀ ) | <max [| V ₁ −V ₀
When |, | V ₂ −V ₀ |] is satisfied, the auxiliary force of the electric motor is provisionally controlled using the direction information obtained from the output voltage of each torque sensor.

Alternatively, when the torque sensor normally operates, the output voltage values V ₁ ,
V ₂ represents the same output value, a same polarity double-system torque sensor output voltage value is arranged to be set to V ₀ when the steering torque 0, controller, any of the torque sensor is abnormal In the case of | V ₁ −V ₂ | <max [| V ₁ −V ₀ |, | V ₂ −V ₀ |], the direction information obtained from the output voltage of each torque sensor is used. Tentatively controlling the auxiliary force of the electric motor.

In this way, even if one of the dual torque sensors is abnormal, if the respective conditional expressions are satisfied, the steering torque direction information obtained from the output value of each torque sensor is accurate. Considered information. By using this direction information, it is possible to reliably control the auxiliary force provisionally.

Further, it is preferable that the control device provisionally controls the auxiliary force of the electric motor using a torque value having a small absolute value among the torque values obtained from the output voltages of the respective torque sensors.

Most of the abnormalities of the torque sensor are reduced in gain,
This is gain increase, offset application, or a combination thereof. When such an abnormality occurs in one of the torque sensors, if the direction information of both torque sensors is correct as described above, if control is performed using a torque value having a smaller absolute value among the output torque values of both torque sensors, This is preferable because control can be performed at least on the safe side.

[0016]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. To facilitate understanding of the description, the same reference numerals are given to the same constituent elements in each drawing as much as possible, and duplicate description will be omitted.

FIG. 1 is a schematic view showing the entire configuration of an electric power steering apparatus according to the present invention, FIG. 2 is a sectional view of a steering shaft portion, and FIG. 3 is an exploded perspective view of a torque sensor portion. It is.

First, the configuration of the entire electric power steering apparatus will be described with reference to FIG. The steering wheel 1 is configured to drive a rack bar 4 via a steering shaft 2 and a pinion gear 3. The steering shaft 2 is provided with a torque sensor 5 and a ring gear 6. A pinion gear 8 attached to an electric motor 7 meshes with the ring gear 6.
The motor 7 is provided with a rotation angle sensor 9. The torque sensor 5 and the rotation angle sensor 9 are connected to an electric power steering computer 10 that adjusts the rotation of the electric motor 7 to control an auxiliary force. A power supply 11 and a vehicle speed sensor 12 are connected to the electric power steering computer 10. Also,
A display signal for notifying the operation state of the entire electric power steering device is output to the meter display system 13. Further, a diagnostic output for outputting a failure status to the diagnostic device in the event of a failure is provided.

Although the steering shaft 2 is driven by the electric motor 7 here, the rack bar 4 is directly driven by the electric motor 7.
May be driven. Since the electric motor 7 is smaller and lighter than a hydraulic assist device, there is an advantage that the degree of freedom of the installation position is high. Further, since the steering system is directly driven by the electric motor 7 at any of the installation positions, an excellent steering feeling can be realized.

The configuration of the steering shaft 2 will be described with reference to FIG. The steering shaft 2 has an upper input shaft 21 connected to the steering wheel 1 and a lower output shaft 22 connected to the steering gear box 3.
And a torsion bar 23 connecting the two. The above-described ring gear 6 is fixed at an upper position 22a of the output shaft 22, and a pinion gear 3 is provided at a lower position 22b. The pinion gear 3 meshes with a gear provided on the rack bar 3 to reduce the steering force. 3 is transmitted. The torque sensor 5 includes a resistor 51 fixed to the input shaft 21 and a contact 52 fixed to the output shaft 22, and outputs a voltage signal according to a displacement of a relative position between the two. .

FIG. 3 shows a specific configuration of the torque sensor 5.
This will be described with reference to FIG. The resistors 51a, 51b and the contacts 52a, 5b constituting the two torque sensors 5a, 5b
2b are attached to the input shaft 21 and the output shaft 22, respectively, to form the dual torque sensor 5. The two torque sensors 5a and 5b are mounted in opposite directions to the displacement direction and have different polarities.

FIG. 4 is a graph showing the characteristics of the output signals of the two torque sensors 5a and 5b. Voltage value V ₂ of the output signal of the voltage value V ₁ and the torque sensor 5b of the output signal of the torque sensor 5a is straight running of the vehicle, i.e., become the same in both V ₀ when the torque is 0, when the left steering, i.e. steering V ₁ > V ₀ > V ₂ when the left-handed torque is applied to the shaft 2, and V ₁ > V ₀ > V ₂ at the time of right steering, that is, when the right-handed torque is applied to the steering shaft 2.
_2> V _0> V ₁ becomes, V _1, V ₂ are both in the torque value and the linear relationship. As a result, when the torque sensor 5a, 5b is both _{normal, V 1 + V 2 = 2V} 0 ... (1) always holds. Thereby, it can be determined that both torque sensors are functioning normally. A torque value T representing the torque at the time of left steering as positive and the torque at the time of right steering as negative.
Can be obtained by using the constant k and T = k (V ₁ −V ₂ ) (2). That is, the direction and magnitude of the torque can be determined based on the output voltage values of both torque sensors.

The operation of the power steering device when both the torque sensors 5a and 5b are functioning normally will be described with reference to FIGS.

When the steering wheel 1 is turned to the right, for example, by rotating the steering wheel 1 in the right direction, the steering shaft 2 is twisted at the torsion bar 23 and the relative position between the input shaft 21 and the output shaft 22 changes. A displacement corresponding to the angle θ occurs according to T. As shown in FIG.
When the input shaft 21 is displaced clockwise relative to the output shaft 22 by an angle θ when viewed from the steering wheel 1 direction, the contact positions of the contacts 52a, 52b with the resistors 51a, 51b change, and the output voltage changes. In this case, the torque sensor 5a side, resistance increases, while the output voltage V ₁ is lowered, the torque sensor 5b side, the output voltage V ₂ resistance is decreased is increased. Double torque sensor 5
The outputs of a and 5b are sent to the electric power steering computer 10.

The computer 10 includes a vehicle speed sensor 1
2 and a rotation angle signal from the rotation angle sensor 9 are input. Here, the electric motor 7 is provided with a pinion gear 8.
Through the ring gear 6 fixed to the output shaft 22 of the steering shaft 2, the rotation angle of the electric motor 7 corresponds to the output steering angle of the steering shaft 2, and the steering angle can be obtained from the rotation angle. it can.

When the equation (1) is substantially satisfied, that is, when the sum V ₁ + V ₂ of the output values of the torque sensors 5a and 5b matches 2V ₀ with an error equal to or less than a predetermined threshold value, It is determined that the torque sensors 5a and 5b are functioning normally, a torque value is obtained from the difference ΔV between the two, and an optimum steering assist force is calculated according to the steering angle and the vehicle speed. An operating current for providing a driving force corresponding to the calculated auxiliary force is transmitted. The motor 7 is rotated in a predetermined direction by the operating current, and the operating force is applied to the output shaft 22 via the pinion gear 8 and the ring gear 6. Output shaft 2
The rotation of 2 is transmitted to the rack bar 4 via the steering gear box 3 and steering is performed.

Next, an operation when one or both of the torque sensors 5a and 5b are malfunctioning will be described. FIG. 5 is a flowchart of the first embodiment of the control.

First, in step 100, the output values V ₁ , V ₂ of the two torque sensors 5a, 5b and the steering angular velocity ω ₁ are input to the computer 10. Here, the steering angular velocity ω ₁
Can be estimated by converting the rotation angle sent from the rotation angle sensor 9 into a steering angle and performing time differentiation.
Next, in step 101, it is determined whether any of the torque sensors 5a and 5b is abnormal. As described above, the determination is made based on whether or not the equation (1) is substantially satisfied, that is, whether or not the sum V ₁ + V ₂ of the outputs of the two sensors is equal to 2V ₀ with an error equal to or less than a predetermined threshold value. Do. If there is no abnormality in both torque sensors, step 102 is performed as described above.
To perform the normal control described above. When the equation (1) is not satisfied with an error larger than the predetermined threshold value, it is determined that at least one of the torque sensors is abnormal,
A signal indicating that the torque sensor has an abnormality is output to the meter display system 13 and the diagnostic output, and the process proceeds to step 103.
It is determined whether the output values of these torque sensors can be used for provisional control. Specifically, the torque sensor 5a, examined the torque value determined from the output value of 5b and the steering angular velocity omega ₁ of the relationship. FIG. 6 is a graph showing the relationship between the torque value and the steering angular velocity. Although the torque value changes depending on the road surface condition, if the road surface condition is the same, the torque value increases almost in proportion to the steering angular velocity. Thus, in a typical road conditions of the friction coefficient, the torque value T for predetermined steering angular velocity omega ₁ is the value between the predetermined range T _a through T _b. Comparing the minimum value T _a and the maximum value T _b of the torque sensor 5a, a torque value corresponding to the steering angular velocity omega ₁ as determined from the time variation of the torque value T and the steering angle determined from the respective 5b, T _a ≦ T ≦ A torque sensor that satisfies T _b (3) is determined to be normal, and a torque sensor that does not hold Tb is determined to be abnormal. Incidentally, when the absolute value of the steering angular velocity from the steering angular velocity minimum value T _a is 0 the corresponding torque value is small, (3) failure determination by a formula, indistinguishable from disconnection or the like of the torque sensor, difficult to determine Therefore, it is preferable not to perform the auxiliary force control. When the absolute value of the steering angular velocity is small as described above, the steering force itself is small, so that there is no inconvenience without the auxiliary force.

If it is determined that both torque sensors 5a and 5b are abnormal, the routine proceeds to step 104, where manual steering is switched or alternative control is performed, but it is preferable to perform alternative control. This is because the driver may feel uncomfortable if the assist power is suddenly lost during traveling. This alternative control includes steering angle, steering angular speed,
Control for calculating the auxiliary force based on the vehicle speed, control for applying a constant auxiliary force, or the like can be used.

If one or both of the torque sensors 5a and 5b are normal, the routine proceeds to step 105, where provisional control is performed.

As a method of the provisional control, a method of obtaining a torque value from a normal output of the torque sensor, and obtaining and controlling an auxiliary force based on the torque value, the steering angle, and the vehicle speed can be used. If the output values of both torque sensors do not satisfy Expression (1) but satisfy Expression (3), the torque values obtained from both torque sensors will be different. Therefore, for this control, an average value of the torque values obtained from both the torque sensors may be used, but it is preferable to use a smaller torque value among the torque values obtained from both of the more secure torque sensors. As a result, provisional control can be continued when an abnormality occurs in only one of the torque sensors, or when an abnormality occurs in at least one of the two torque sensors, and when at least one of the output voltage values fluctuates only a small amount. Since the force application can be continued, the reliability of the power steering device is improved. In particular, if the failure of one of the torque sensors as in the prior art treats the dual torque sensor itself as a failure, the failure rate of the entire system becomes about twice the failure rate of the torque sensor itself, and the failure rate increases. However, according to the technique of the present invention, unless both of them fail, the failure of the entire system does not occur, so that there is a high probability that control can be continued without failure.

Subsequently, a second control operation when the torque sensor is abnormal is described.
An embodiment will be described. FIG. 7 is a flowchart of the control of this embodiment. This control is basically the same as that of the above-described first embodiment, except for the determination of provisional control and the content of provisional control. In the present embodiment, in order to determine whether or not the output value of the torque sensor can be used in step 203, specifically, the absolute value of the sum of the output voltages of both torque sensors and the output voltage value of each torque sensor And the absolute value of. FIG.
(F) is a graph output voltage value V ₂ is shown a normal case, the torque sensor 5a unusual case, the output voltage value 5b and the relationship that the sum of the torque sensor 5b.

When both sensors 5a and 5b are normal,
Since equation (1) is satisfied, the sum of the output voltage values V ₁ + V ₂
Is equal to 2V ₀ as shown in FIG. 6A (specifically, (V ₁ + V ₂ ) / 2 = V ₀ ). At this time, | (V ₁ −V ₀ ) + (V ₂ −V ₀ ) | <max [| V ₁ −V ₀ |, | V ₂ −V ₀ |] (4) is established.

[0034] As shown in FIG. (B), when the gain of the torque sensor 5b is lowered, the difference between V ₂ and V ₀ becomes relatively _{small, (V 1 + V 2)} / 2 and V close to _1. However, as long as the polarities of V ₁ and V ₂ are opposite, equation (4) holds.

As shown in FIG. 4C, even when an offset is applied to the outputs of the two torque sensors 5a and 5b, as long as the polarities of V ₁ and V ₂ are reversed, the equation (4) is satisfied. To establish. However, when the polarity of the torque sensor 5b is reversed, the expression (4) does not hold as shown in FIG.

On the other hand, when the gain of the torque sensor 5b increases, the difference between V ₂ and V ₀ becomes relatively large, and (V
₁ + V ₂₎ / 2 is close to the V _2. However, as long as the polarities of V ₁ and V ₂ are opposite, equation (4) holds. However, when the polarity of the torque sensor 5b is reversed, the expression (4) does not hold, as shown in FIG.

[0037] Thus, the torque sensor 5a, the relationship polarity opposite characteristics across the V ₀ which the output voltage value of 5b Naritate is established (4). In this case, the torque sensor 5
As long as the characteristics of both a and 5b are not inverted, the output of both will be correct with respect to the direction of torque. The probability of occurrence of such a double failure is significantly lower than the probability of failure of either one, but even if a double failure occurs, whether or not it is a double failure based on the steering angle and steering speed Can be determined.

If equation (4) does not hold, step 2
Proceed to 04 and switch to alternative control or manual steering. If equation (4) holds, step 2
Proceeding to 05, provisional control is performed using the torque value of the two torque sensors having the smaller torque value. In this case as well, the provisional control can be continued as long as a failure that the polarity of the output of the torque sensor is reversed does not occur, so that the reliability can be improved as compared with the related art.

Depending on the situation of the offset application, FIG.
As shown in (c), even if Expression (4) is satisfied in some regions, the torque value obtained from the output value of the torque sensor is opposite to the actual torque value, or Expression (4) is not satisfied. It is possible. However, if the offset is not large,
The region of the torque value in which such a phenomenon occurs is limited to the region of the torque value to which the auxiliary force is not normally applied. Therefore, there is little problem in actual assist force control.

In the above description, an example has been described in which the two torque sensors have different polarities. However, the two torque sensors may have the same polarity in which the same torque is output for the same torque. In this case, it can be determined that both sensors are normal when V ₁ −V ₂セ ン サ 0, and instead of equation (4), | V ₁ −V ₂ | <max [| V ₁ −V ₀ |, | V ₂ −V ₀ |] (5) is satisfied, the torque direction information of the output value of each sensor matches.

In the provisional control, the control may be performed based on the steering angular speed, the steering angle, the vehicle speed, etc., using the torque direction information alone, instead of using the torque value itself. In this case, stable control can be performed even if the gain fluctuates.

The steering angular velocity may be obtained by detecting the steering angle using a dedicated sensor, or by calculating from another detected value and time-differentiating it.

[0043]

As described above, according to the present invention,
Even when an abnormality occurs in the torque sensor in the electric power steering having a plurality of torque sensors, the provisional control can be continued by using the torque output or the torque direction output of the normal torque sensor. As a result, the provisional control can be continued even when the degree of abnormality of the torque sensor is small, so that a sudden change in the auxiliary force can be prevented,
The reliability of the electric power steering is improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an electric power steering device according to the present invention.

FIG. 2 is a sectional view showing a steering shaft portion of the apparatus of FIG.

FIG. 3 is an exploded perspective view showing a torque sensor of the device of FIG.

FIG. 4 is a graph showing output characteristics of the torque sensor of FIG.

FIG. 5 is a control flowchart of a first embodiment of torque sensor abnormality control in the apparatus of FIG. 1;

FIG. 6 is a graph showing a relationship between a torque sensor output and a steering speed.

FIG. 7 is a control flowchart of a second embodiment of torque sensor abnormality control in the apparatus of FIG. 1;

FIG. 8 is a graph showing a relationship between outputs of the respective torque sensors, wherein (a) shows a normal state and (b) to (f) show a relationship when one of the torque sensors becomes abnormal.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Steering gear box, 4 ... Rack bar,
5: Torque sensor, 6: Ring gear, 7: Electric motor, 8 ...
Pinion gear, 9: rotation angle sensor, 10: electric power steering computer, 11: power supply, 12: vehicle speed sensor, 13: meter display system, 21: input shaft, 22: output shaft, 23: torsion bar, 51: resistor, 52 ... Contact.

Continuing from the front page (72) Inventor Takashi Iwasaki 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Toru Suzuki 1 Toyota Town Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference 3D032 CC33 CC46 DA03 DA09 DA15 DA23 DA63 DB02 DB03 DC03 DC33 DC34 DC35 DD05 EA01 EB11 EC23 GG01 3D033 CA16 CA17 CA21 CA27 CA28 CA31

Claims (6)

[Claims] 1. An electric motor for assisting a steering force, one or a plurality of torque sensors for detecting a torque applied to a steering shaft, a steering angle sensor for detecting a steering angular velocity of the steering, the torque sensor and the steering angle sensor. A control device that controls the assisting force of the electric motor based on the output of the electric motor, wherein the control device is configured such that the output value of the torque sensor is within a predetermined range with respect to the detected steering angular velocity. An electric power steering apparatus characterized in that it is determined whether or not the torque is within the predetermined range, and the output of the torque sensor within the predetermined range is used to control the assisting force of the electric motor. 2. The electric power steering apparatus according to claim 1, further comprising two torque sensors. 3. The control device according to claim 1, wherein when the absolute value of the steering angular velocity is equal to or more than a predetermined value, only the torque sensor whose output value is within a predetermined range with respect to the steering angular velocity is used. The electric power steering apparatus according to claim 1, wherein the auxiliary power of the electric motor is controlled. 4. An electric motor for assisting a steering force, two torque sensors for detecting a torque applied to a steering shaft, and a control device for controlling an assist force of the electric motor based on an output of the torque sensor. In the electric power steering apparatus provided, the steering torque is zero when all of the torque sensors are normal.
, The output value becomes V ₀ , and the output values V ₁ and V
₂ is a dual-polarity torque sensor of opposite polarity arranged to have opposite characteristics across V ₀ , wherein the control device comprises:
Even if one of the torque sensors is abnormal, | (V ₁ −V ₀ ) + (V ₂ −V ₀ ) | <max [| V ₁ −V ₀
|, | V ₂ −V ₀ |], an auxiliary power of the electric motor is provisionally controlled by using direction information obtained from output voltages of the respective torque sensors. 5. An electric motor for assisting a steering force, two torque sensors for detecting a torque applied to a steering shaft, and a control device for controlling an assist force of the electric motor based on an output of the torque sensor. In the electric power steering device provided, the output voltage value V ₁ and V ₂ indicate the same output value with respect to the steering torque when the torque sensor is normal, and the output voltage value is V ₀ when the steering torque is _0. a same polarity double-system torque sensor disposed so as to be, the control device, even when either of the torque sensor is _{abnormal, | V 1 -V 2 | <} max [| V 1 -V 0 |, | V ₂ -V ₀ | if] is satisfied, the electric characterized by provisional controlling assisting force of the electric motor by using the direction information obtained from the output voltage of the torque sensor Pawasute Ring device. 6. The control device according to claim 4, wherein the control device temporarily controls the auxiliary force of the electric motor using a torque value having a small absolute value among torque values obtained from output voltages of the torque sensors. 6. The electric power steering device according to any one of the above items 5.