JP2005053304A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform steering assistance without determining a target current value of supply current to an electric motor, and to continuously perform steering assistance with the motor even when steering torque in response to a steering operation cannot be acquired. <P>SOLUTION: This electric power steering device comprises first and second sensor sections for outputting signals according to rotation angles of input and output shafts 32 and 33 of a steering shaft 3, respectively, rotation angle detecting sections for responding using detection result of these sensor sections, torque detecting sections using detection result of these rotation angle detecting sections, and a control unit 21 for performing driving control of the electric motor 6 according to the detection results of these detecting sections. The control unit 21 determines a variation of the rotation angle based on the rotation angle from one of the first and second sensor sections when no detected value of the steering torque cannot be acquired, and supplies current to the electric motor 6 for a predetermined period when the determined variation is determined to exceed a predetermined threshold. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric power steering device that is mounted on a vehicle such as an automobile and assists a driver's steering operation using an electric motor.

  For example, an electric power steering device mounted on an automobile includes an electric motor connected to a steering mechanism from a steering member to a steered wheel. By applying the power of this motor to the steering mechanism, It is designed to assist the steering operation by the driver. Further, the steering mechanism of such a steering device is provided with a steering shaft that is connected to a steering member and a steered wheel at one end side and the other end side, respectively, and rotates in accordance with the steering operation of the driver. In a steering apparatus, generally, drive control of the electric motor is performed based on a steering torque generated in a steering shaft in accordance with the steering operation or the like.

  The conventional electric power steering apparatus includes a torque sensor that directly detects the steering torque and outputs a signal corresponding to the rotation angle of the steering shaft on the steering member side and the steered wheel side. And a second sensor unit, and the rotation angles and steering torque are calculated using detection results from these sensor units. In addition, as in the conventional apparatus disclosed in Patent Document 1 below, there is a system in which a steering angle sensor that detects the steering angle of the steered wheels is provided and the steering torque is calculated based on the detection result of the sensor.

Japanese Patent No. 2969701 (pages 2-4, FIG. 2)

  However, in the conventional apparatus as described above, the target current value of the electric motor is determined according to the acquired steering torque, and steering assist is provided by supplying current to the motor by feedback control using the determined target current value. I was going. For this reason, the target current value of the motor cannot be determined if the steering torque according to the steering operation or the like cannot be acquired due to a failure or abnormality in the torque sensor or the steering angle sensor. In order to prevent inappropriate steering assistance from being performed, the current supply to the motor has been stopped. As a result, the steering burden on the driver may increase, or it may become difficult to operate the steering member as the burden increases, and the operability of the automobile may be significantly reduced.

In view of the conventional problems as described above, the present invention provides a new technical means that can easily and quickly perform steering assistance by the motor without determining the target current value of the current supplied to the electric motor. An object of the present invention is to provide an electric power steering apparatus provided.
Further, the present invention is capable of continuously assisting the steering by the electric motor even when the steering torque according to the steering operation or the like cannot be acquired, and thus the electric power capable of suppressing the deterioration of the operability of the vehicle. An object is to provide a steering device.

An electric power steering apparatus according to the present invention is an electric power steering apparatus that assists steering by applying power of an electric motor to a steering mechanism from a steering member to a steered wheel,
A steering angle detector that detects a steering angle of at least one side of the steering member and the steering wheel; and a controller that performs drive control of the electric motor using the steering angle detected by the steering angle detector. ,
The control unit obtains a change amount of the rudder angle based on the rudder angle from the rudder angle detection unit, and determines that the electric motor has a predetermined amount when the obtained change amount exceeds a predetermined threshold value. A current is supplied during the period.

  In the electric power steering apparatus configured as described above, the control unit supplies current to the electric motor for a predetermined period only when it is determined that the amount of change in the steering angle exceeds a predetermined threshold. Therefore, the motor can be driven without determining a target current value for the motor, and steering assistance by motor power can be performed easily and at high speed. Further, since the current is supplied to the motor only when the amount of change in the steering angle is larger than the threshold value, the steering assistance can be performed only when the steering assistance is necessary. In addition, by using the steering angle change amount as a motor drive reference in this way, the control unit can determine whether or not a steering operation that requires steering assistance has been performed, thereby reducing the driver's steering burden. Can be performed appropriately.

Another aspect of the electric power steering apparatus according to the present invention is a steering mechanism including a steering shaft having a steering member and a steering wheel connected to one end side and the other end side, and applies power to the steering mechanism. An electric motor for assisting steering, first and second sensor units for outputting signals corresponding to rotation angles on the steering member side and the steered wheel side of the steering shaft, and the first and second sensor units, respectively. First and second rotation angle detection units for detecting rotation angles on the steering member side and the steered wheel side using output signals from the two sensor units, respectively, and detection of steering torque generated on the steering shaft A torque detection unit that controls the drive of the electric motor using the rotation angle from the first and second rotation angle detection units and the steering torque from the torque detection unit,
When the control unit cannot acquire the detected value of the steering torque, the control unit obtains the change amount of the rotation angle based on the rotation angle from one of the first and second rotation angle detection units, and When it is determined that the obtained change amount exceeds a predetermined threshold value, a current is supplied to the electric motor for a predetermined period.

  In the electric power steering apparatus configured as described above, when the control unit cannot acquire the detected value of the steering torque due to the abnormality of the torque detection unit, the control unit receives from the one rotation angle detection unit. Only when it is determined that the amount of change in the rotation angle has exceeded a predetermined threshold, electric current is supplied to the electric motor for a predetermined period. Thereby, even when the detected value of the steering torque cannot be acquired, the control unit can continue the steering assist by driving the motor, and the operability of the vehicle due to the stop of the steering assist is reduced. Can be suppressed. Further, since the current is supplied to the motor only when the change amount of the rotation angle is larger than the threshold value, the steering assist can be performed only when the steering assist is necessary. In addition, by using the rotation angle change amount as a motor drive reference in this way, the control unit can determine whether or not a steering operation that requires steering assistance has been performed, thereby reducing the driver's steering burden. Can be performed appropriately.

In the electric power steering apparatus, it is preferable that the control unit obtains the change amount of the steering angle or the change amount of the rotation angle for each predetermined period.
In this case, the control unit determines whether or not steering assistance by the electric motor is necessary every predetermined cycle, and can perform steering assistance more appropriately.

In the electric power steering apparatus, the control unit is based on either a change amount of the steering angle from the steering angle detection unit or a change amount of the rotation angle from the first or second rotation angle detection unit. It is preferable to perform steering assistance by driving the electric motor by open loop control.
In this case, since the electric motor is driven by open loop control that is simpler and faster than feedback control, appropriate steering assistance can be quickly performed by a simpler method.

In the electric power steering apparatus, the control unit may set a predetermined duty ratio for the predetermined period and supply current to the electric motor according to an ON time at the duty ratio.
In this case, it becomes possible to suppress the detection angle from becoming excessively large due to the application of power from the electric motor, and more appropriate steering assistance can be performed.

Further, in the electric power steering apparatus, the speed of the vehicle detected by the vehicle speed sensor is input to the control unit, and the control unit applies to the electric motor according to the vehicle speed from the vehicle speed sensor. It is preferable to change the current supply amount.
In this case, since the amount of current supplied to the electric motor is changed according to the vehicle speed, more appropriate steering assistance can be performed with motor power adapted to the speed.

  According to the present invention, only when the change amount of the detected angle such as the rudder angle exceeds the threshold value, the control unit drives the electric motor to assist the steering. Therefore, the motor target current is determined according to the detected value of the steering torque. Unlike the conventional example in which the value has been determined, the control unit can perform the steering assist easily and at high speed, and the steering operation requiring the steering assist is performed even when the steering torque cannot be obtained. Only when the motor can be driven, the vehicle operability can be prevented from deteriorating.

Hereinafter, preferred embodiments showing an electric power steering apparatus of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram schematically showing the structure of an electric power steering apparatus according to an embodiment of the present invention. In the figure, the apparatus is mounted on, for example, an automobile, and a steering shaft 3 is interposed between a steering member (steering wheel) 1 and a pinion 2. The steering shaft 3 includes a torsion bar 31 provided at the center thereof, an input shaft 32 fixed to the input side (upper side) of the torsion bar 31, and an output shaft 33 fixed to the output side (lower side) of the torsion bar 31. And. The input shaft 32 and the output shaft 33 are arranged coaxially with each other, but are not directly connected to each other, but are connected coaxially with the torsion bar 31 interposed.

The steering member 1 is connected to the input shaft 32 so that the rotation of the steering member 1 by the steering operation of the driver is directly transmitted.
The output shaft 33 is attached with a speed reduction mechanism having a worm 5 and a worm wheel 4 meshing with the worm 5 and the worm 5 so as to be integrally rotatable with the output shaft, and is controlled by a control unit (ECU) 21 as a control unit. An electric motor 6 for assisting steering is connected, and the rotation of the motor 6 is decelerated and transmitted to the pinion 2 as steering assist force. The rotation of the pinion 2 is converted into a linear motion of the rack 7, and the steered wheels 9 are steered via the left and right tie rods 8. The deceleration mechanism and the electric motor 6 constitute a steering assist unit that applies a steering assist force to the steering mechanism from the steering member 1 to the steering wheel 9.

  Further, the input shaft 32 and the output shaft 33 are provided with sensors, and each rotation angle of the input / output shafts 32 and 33 that rotates with the steering operation to the steering member 1 is detected. Yes. Specifically, referring also to FIG. 2, a first target plate 34 is attached to the input shaft 32 so as to be integrally rotatable, and the first magnetic sensors A 1, B 1 are disposed outside the outer periphery of the target plate 34. Is arranged. Similarly, the second and third target plates 35 and 36 are attached to the output shaft 33 so as to be integrally rotatable, and the second and third magnetic sensors A2 and A2 are disposed outside the outer periphery of the target plates 35 and 36. B2 and A3, B3 are respectively arranged.

  The first target plate 34 and the first magnetic sensors A1 and B1 constitute a first sensor unit P that outputs a signal corresponding to the rotation angle of the input shaft 32 to the control unit 21, and the second target plate 35 and the second magnetic sensors A2 and B2 constitute a second sensor unit Q that outputs a signal corresponding to the rotation angle of the output shaft 33 to the control unit 21. The third target plate 36 and the third magnetic sensors A3 and B3 constitute a third sensor unit R that outputs a signal corresponding to the rotation angle of the output shaft 33 to the control unit 21. The unit 21 detects the absolute rotational position of the output shaft 33 using the outputs of the second and third sensor portions Q and R.

Each of the target plates 34 to 36 has a spur gear shape in which outer peripheral teeth made of a magnetic material are provided at equal intervals in the circumferential direction, and forms a target having irregularities on the outer periphery. The number of teeth is the same number N (for example, 36) for the first target plate 34 and the second target plate 35, and the third target plate 36 is relatively prime to N (no common divisor other than 1). Is a number (for example, 35).
The first to third magnetic sensors A1, B1, A2, B2, A3, and B3 are arranged so as to oppose the outer peripheral teeth of the corresponding target plates 34 to 36, and these are attached to the sensor box 10. It is stored. The sensor box 10 is fixed at a predetermined position on the vehicle body. The first magnetic sensors A1 and B1 are arranged to face different circumferential positions of the first target plate 34. Similarly, the second magnetic sensors A2 and B2 are arranged to face different circumferential positions of the second target plate 35, and the third magnetic sensors A3 and B3 are mutually connected to the third target plate 36. Opposed to different circumferential positions.

  Each of the magnetic sensors A1 to A3 and B1 to B3 includes an element having a characteristic that the resistance is changed by the action of a magnetic field, for example, a magnetoresistive element (MR element), and the respective target plates 34 to 36 facing each other. The voltage signal which changes periodically according to the unevenness | corrugation of the outer periphery of is output. Specifically, when the first target plate 34 rotates together with the input shaft 32 according to the steering operation of the driver, the output signals of the first magnetic sensors A1 and B1 are caused by the unevenness so that the rotation angle of the input shaft 32 and the target plate 34 is increased. It becomes a periodic signal that periodically changes in accordance with the change (angular displacement). When the second target plate 35 rotates with the output shaft 33, the output signals of the second magnetic sensors A2 and B2 periodically change according to changes in the rotation angle of the output shaft 33 and the target plate 35 due to the unevenness. When the third target plate 36 rotates with the output shaft 33 as a periodic signal, the output signals of the third magnetic sensors A3 and B3 are periodically generated according to changes in the rotation angle of the output shaft 33 and the target plate 36 due to the unevenness. It becomes a changing periodic signal.

  Further, the first magnetic sensors A1 and B1 are opposed to the first target plate 34 so that their output signals generate a phase difference of, for example, π / 2 in electrical angle as shown in FIG. Has been placed. Similarly, the second magnetic sensors A2 and B2 are arranged opposite to the second target plate 35 so that their output signals generate a phase difference of π / 2, and the third magnetic sensors A3 and B3 Are arranged opposite to the third target plate 36 so that their output signals produce a phase difference of π / 2. As described above, by shifting the phases of the output signals from the two magnetic sensors A1 to A3 and B1 to B3 in the first to third sensor portions P, Q, and R, the unevenness of the corresponding target plates 34 to 36 is obtained. Even when a non-linear change appears in the vicinity of the maximum value and the minimum value of the output waveform according to the shape, the control unit 21 can control the other when one signal of the two magnetic sensors A1 to A3 and B1 to B3 is in the non-linear region. Thus, it is possible to prevent the rotation detection accuracy of the input / output shafts 32 and 33 from being lowered.

  Further, since the number of teeth of the third target plate 36 (= 35) is one less than the number of teeth of the second target plate 35 (= 36), the outputs of the third magnetic sensors A3 and B3 are the second Compared with the outputs of the magnetic sensors A2 and B2, a phase shift of ((2π / 36) − (2π / 35)) occurs per rotation amount (2π / 36) of the output shaft 33. Return to the original. Therefore, the absolute rotation position of the output shaft 33 can be determined from the phase shift by examining the relationship between the absolute rotation position of the output shaft 33 and the phase shift in advance and creating a table. Such a table is stored in advance in a data storage unit described later of the control unit 21.

  The control unit 21 controls the drive of the electric motor 6 based on the calculation result of the calculation unit 21a that performs a predetermined calculation using the outputs of the first to third sensor units P, Q, and R, and the calculation unit 21a. And a drive control unit 21b for performing. The control unit 21 is inputted with a signal of the vehicle speed detected by the vehicle speed sensor 22 and determines the power generated by the electric motor 6 in view of the traveling speed of the automobile. In addition, the control unit 21 is provided with a data storage unit (not shown) configured by a non-volatile memory or the like, and in this data storage unit, a program or a table required for driving control of the electric motor 6 is provided. The stored information and the like are stored in advance, and further, information indicating the calculation result in each part of the unit 21 and the vehicle running state from the vehicle speed sensor 22 and the like are appropriately stored.

  The arithmetic unit 21a uses the output signal of the first sensor unit P (magnetic sensors A1 and B1) to detect the rotational angle of the steering member 1 side of the steering shaft 3, that is, the rotational angle of the input shaft 32. Using the function of the detection unit and the output signal of the second sensor unit Q (magnetic sensors A2, B2) or the third sensor unit R (magnetic sensors A3, B3), that is, the steered wheel 9 side of the steering shaft 3, that is, A function of a second rotation angle detection unit that detects the rotation angle of the output shaft 33 is provided. In addition, the calculation unit 21 a uses the rotation angles detected by the first and second rotation angle detection units to use the steering shaft 3 from the member 1 according to the steering operation of the driver to the steering member 1. The steering torque generated in the steering shaft 3 is detected by the input torque input to the vehicle side and the reverse input torque such as disturbance torque input back to the steering shaft 3 side from the steering wheel 9 according to the road surface of the vehicle. And a function of determining a steering assist force to be applied from the steering assisting unit based on the steering torque detected by the torque detecting unit. In addition, the first and second rotation angle detection units provided to the calculation unit 21a function as a steering angle detection unit that detects the steering angle on the steering member 1 side that has responded with the steering operation and the like. It also has.

Specifically, the calculation unit 21a acquires, for example, the outputs of the sensor units P and Q at a predetermined sampling period, obtains the rotation angles of the corresponding input shaft 32 and output shaft 33, and then inputs / outputs shaft 32. , 33 to obtain the absolute value of the relative rotation angle, and obtain the steering torque. And the calculating part 21a determines the command value (target electric current value) to the electric motor 6 based on the acquired steering torque, and instruct | indicates it to the drive control part 21b. Further, the calculation unit 21a can calculate the steering torque by obtaining the absolute value of the absolute rotation angle of the output shaft 33 by using the output of the third sensor unit R, and the direction of the steering wheel 9 can be calculated. More precise control that takes into account can be performed.
The drive control unit 21b drives the motor 6 by supplying current to the electric motor 6 based on the command value instructed from the calculation unit 21a. Thereby, the electric power steering apparatus of this embodiment can detect the steering operation of the driver and can apply the steering assist force according to the operation.

  Further, in the control unit 21, when the calculation unit 21a cannot acquire the normal first assist mode using the steering torque and the steering torque, the outputs of the first to third sensor units P, Q, and R can be obtained. Is used to assist the driver's driving operation by appropriately switching between the second assist mode using the amount of change (Δθ) in the detected angle (detected rudder angle) of any of the rotation angles θ1, θ2, and θ3 obtained using It is configured to be able to. As will be described in detail later, the control unit 21 performs part of the magnetic sensors A1 to A3 and B1 to B3 by performing the second assist mode as the fail mode when the steering torque cannot be acquired. Even when a failure occurs, it is possible to prevent the steering assist by the power of the electric motor 6 from being stopped.

  Here, the operation of the electric power steering apparatus of the present embodiment configured as described above will be specifically described with reference to FIGS. In the following description, for simplification of description, the rotation angles θ1 and θ2 out of the rotation angles θ1 to θ3 detected by the first to third sensor units P, Q, and R are used to describe the above. A case where the first or second assist mode is performed will be described. Further, in the second assist mode, the case where the drive control of the electric motor 6 is performed based on the angle change rate (that is, the angular velocity) in a predetermined time as the angle change amount Δθ will be described as an example.

  In step S1 of FIG. 4, in the control unit 21, the calculation unit 21a determines whether or not the rotation angles θ1 and θ2 obtained from the outputs of the first and second sensor units P and Q are normal values. Specifically, for example, in the first sensor part P, at least one of the pair of magnetic sensors A1 and B1 has a permanent or temporary failure, or each of these sensors A1, If contact failure occurs in the wiring connecting B1 and the control unit 21 or electromagnetic noise adversely affects, the output signals of the pair of sensors A1 and B1 are not output with a phase difference of π / 2 at the electrical angle. In addition, the sensor signal value of the sensor part P does not change and becomes an abnormal value indicating a constant value even though the output of the remaining sensor part Q is fluctuating. Therefore, the calculation unit 21a performs the above-described rotation angle by performing a mutual check of the two magnetic sensors A1, B1; A2, B2 in each of the sensor units P, Q, or comparing the outputs of the sensor units P, Q. It is determined whether θ1 and θ2 are normal values. Further, even when the calculation unit 21a cannot obtain the rotation angle θ1 or θ2 without referring to the table in the data storage unit due to partial data deletion or the like, the rotation angle θ1 or θ2 that cannot be obtained is an abnormal value. It is determined that

  When the calculation unit 21a determines that both the rotation angles θ1 and θ2 are normal values in step S1, the calculation unit 21a performs drive control of the electric motor 6 in the first assist mode using the steering torque ( Step S2). That is, the calculation unit 21a obtains the steering torque by obtaining the absolute value of the relative rotation angle of the input / output shafts 32 and 33 from the rotation angles θ1 and θ2, and in the electric motor 6 according to the detected value of the steering torque. Determine the target current value. Then, the calculation unit 21a performs feedback control using the determined target current value, thereby supplying current to the motor 6 and applying power corresponding to the driver's steering operation or the like from the motor 6 to the steering mechanism. . As a result, in the first assist mode, the steering assist is performed while suppressing the decrease in steering feeling as much as possible.

When the calculation unit 21a determines in step S1 that either the rotation angle θ1 or θ2, for example, the rotation angle θ1 of the input shaft 32 is an abnormal value, the calculation unit 21a performs predetermined diagnosis output processing. Is performed (step S3). Specifically, the calculation unit 21a stores predetermined information related to the rotation angle θ1 determined as an abnormal value, for example, the abnormal value, in a storage area for storing the history information of abnormality / failure set in the data storage unit. The data such as the location of abnormality / failure and the detection date / time are stored in the storage area.
Subsequently, the calculation unit 21a determines that the steering torque cannot be acquired, switches to the second assist mode using the angle change rate Δθ of the rotation angle θ2 of the normal output shaft 33, and performs the electric motor in the assist mode. 6 is controlled (step S4).

Specifically, in the second assist mode, the calculation unit 21a has an angle change rate Δθ2 at the rotation angle θ2 of the output shaft 33 obtained using the output signal of the second sensor unit Q as a predetermined threshold value. Whether or not Δθ2p is exceeded is determined. As shown in FIG. 5, when the calculation unit 21a detects that the absolute value of the angle change rate Δθ2 is equal to or less than the threshold value Δθ2p, the calculation unit 21a provides steering assistance. It is determined that there is no need to carry out, and the drive of the electric motor 6 is stopped.
Further, when the calculation unit 21a detects that the absolute value of the angle change rate Δθ2 is larger than the threshold value Δθ2p, the calculation unit 21a allows the motor 6 to perform a steering assist with the motor power for a predetermined period. Supply current. Specifically, when the angle change rate Δθ2 fluctuates as shown in the waveform of FIG. 6A, for example, the calculation unit 21a rotates the rotation angle θ2 that is equal to the sampling period in the magnetic sensors A2 and B2 of the sensor unit Q. In addition, the rotation angle θ2 and the angle change rate Δθ2 are obtained on the basis of the output signals of the magnetic sensors A2 and B2 of the second sensor unit Q at every detection cycle (cycle indicated by an arrow in the figure) of the change rate Δθ2.

Next, when it is determined that the absolute value of the angle change rate Δθ2 obtained by the calculation unit 21a has exceeded the threshold value Δθ2p, the calculation unit 21a is set, for example, for the detection period as shown in FIG. The drive control of the electric motor 6 is performed according to the predetermined duty ratio. That is, the arithmetic unit 21a applies a voltage from the power source (not shown) to the electric motor 6 during the on time indicated by the shaded portion in FIG. 5B, that is, for a time shorter than the sampling period. After that, in the next detection cycle, the calculation unit 21a determines that the angle change rate Δθ2 continues to exceed the threshold value Δθ2p, that is, the output shaft 33 is continuously rotating in the same direction. During the ON time, voltage application is intermittently performed. As a result, the current supplied to the electric motor 6 has the waveform shown in FIG. 6C, and when the output shaft 33 continuously rotates in one direction, the motor that is defined by the integrated value of the supplied current as a result. Power is applied to the steering mechanism to assist steering.
Also, in the second assist mode, unlike the first assist mode in which the target current value in the electric motor 6 is determined, the motor 6 is controlled by open loop control that supplies current without determining the target current value. Thus, steering assistance by motor power can be performed easily and at high speed.

In addition, the magnitude of the applied voltage in the second assist mode, the ON time of the duty ratio, the supply current value determined by these values, and the threshold are the steering characteristics such as the vehicle characteristics such as the steering characteristics and the type of the motor 6. It is determined in advance according to the configuration of the auxiliary unit and stored in the data storage unit. However, the duty ratio is appropriately changed according to the speed of the vehicle output from the vehicle speed sensor 22 to the calculation unit 21a, and the calculation unit 21a increases with respect to the off time as the vehicle speed increases. By selecting a duty ratio with a small on-time ratio, dangerous driving due to excessive assist force (motor power) being applied to the steering mechanism is prevented from being performed in the vehicle.
In the above description, the configuration has been described in which the ratio of the on-time is reduced as the vehicle speed increases. However, any vehicle can be used as long as the current supply amount to the electric motor 6 can be changed according to the speed. As the speed increases, the voltage applied to the motor 6 may be reduced.

  Further, in the second assist mode, unlike the first assist mode, the driver feels a slightly uncomfortable feeling with respect to the steering operation feeling to the steering member 1 by the driver. Specifically, in the calculation unit 21a, for example, the steering torque according to the driver's steering operation or the like is estimated based on the normal detection value of the rotation angle θ2, and the electric motor 6 performs the same as in the first assist mode. Although it is possible to determine the target current value, in the second assist mode, a relatively smaller power than that in the first assist mode based on the target current value is applied from the motor 6 to the steering mechanism. It makes the driver feel uncomfortable. Thereby, when the control unit 21 selects the second assist mode, an abnormality in the detection mechanism of the rotational angle θ1 of the input shaft 32 is given to the driver, for example, in combination with the point that voltage is intermittently applied to the motor 6 according to the duty ratio. It is made to grasp that the failure of the steering device resulting from this has occurred. In addition to this description, for example, in step S3, when the calculation unit 21a performs a diagnosis output process for storing an abnormality / failure history, for example, notification means using a light or a speaker blinking on the operation panel, for example. It is also possible to notify a passenger of a car such as a driver of the abnormality / failure memorized by.

  In the electric power steering apparatus of the present embodiment configured as described above, when the steering torque cannot be acquired due to an abnormality in one of the rotation angles θ1 and θ2 of the input / output shafts 32 and 33, the control unit ( The control unit 21 supplies current to the electric motor 6 in the second assist mode using the angle change rate (change amount) Δθ of the other detected angle, and performs the assist by the motor power. Unlike the example, even when the steering torque cannot be acquired, the control unit 21 can perform the driving control of the electric motor 6 and continuously perform the steering assist with the power. As a result, it is possible to prevent the steering assist from being stopped even when the steering torque cannot be acquired, and to prevent the operability of the vehicle from being lowered. In addition, the second assist mode is controlled by the open loop control. Since the drive control is performed, it is possible to implement steering assistance that is simpler and faster than the conventional example. Further, since the current is supplied to the motor 6 only when the absolute value of the angle change rate Δθ is larger than the threshold value, the steering assist can be performed only when the steering assist is necessary. In addition, by using the angle change rate Δθ as a drive reference for the motor 6 in this way, the control unit 21 determines whether or not a steering operation that requires steering assistance has been performed, thereby reducing the driver's steering burden. Can be performed appropriately.

  Further, in the present embodiment, as shown in FIG. 5, when the absolute value of the angle change rate Δθ is in a range equal to or smaller than the threshold value, the electric motor 6 is not driven even if the steering operation is performed. It is possible to inform the driver of the occurrence of a failure in the steering apparatus. Moreover, even when the angle change rate Δθ exceeds the threshold value and the current is supplied to the motor 6, the motor 6 is controlled so that the driver feels uncomfortable, so the driver drives the motor 6 in the second assist mode. It is possible to perceive the vehicle at an early stage, and the driver is encouraged to repair at an early stage from the time of the failure when the steering torque cannot be detected. it can.

  In the above description, the first and second rotation angle (steering angle) detection units that detect the corresponding rotation angle of the input / output shaft using the detection result of the magnetic sensor and the torque detection unit that detects the steering torque. In the calculation unit provided with the function, the current supply to the electric motor according to the on-time of the duty ratio has been described. However, the present invention provides a predetermined amount of change in the detected angle that fluctuates due to the steering operation of the driver. There is no limitation as long as the current is supplied to the motor for a predetermined period when the threshold is exceeded. Specifically, the present invention can also be applied to a steering apparatus having a configuration in which a torque sensor and an angle sensor are provided separately. The present invention is also applied to a steering device that detects the movement of the rack in the vehicle width direction with a position sensor or the like, detects the steering angle (so-called tire angle) on the steered wheel side, and controls the drive of the electric motor. be able to.

  In the above description, the configuration in which the duty ratio is set for the same time as the sampling period of the magnetic sensor has been described. However, the present invention is not limited to this, and current is supplied at a time interval different from the sampling period. It may be what performs. However, by setting the duty ratio for each detection cycle that matches the sampling cycle, excessive detection angle increase due to the addition of motor power while assisting steering at a more appropriate timing for the steering operation. It is preferable in that a more appropriate steering assist can be performed with the (divergence phenomenon) suppressed.

Further, in the above description, the case where the angle change rate (angular velocity) at a predetermined time is used as the angle change amount has been described. However, the current supply to the motor is determined based on the change amount such as angular acceleration. But you can.
Further, in the description using the flowchart of FIG. 4, the case where the abnormality of one of the rotation angles θ1 and θ2 is determined and the second assist mode is executed using the other normal rotation angle has been described. However, you may perform 2nd assist mode using rotation angle (theta) 3 obtained from the 3rd sensor part R output.

It is a figure showing typically the structure of the electric power steering device by one embodiment of the present invention. It is the figure which represented typically the torsion bar in the said electric power steering device, an input shaft, an output shaft, each target board, and a magnetic sensor. It is a graph which shows the output signal (voltage) from the magnetic sensor in the said electric power steering device. It is a flowchart figure which shows the main operation examples in the said electric power steering apparatus. 6 is a graph showing a drive control method for the electric motor in the second assist mode shown in FIG. 4. It is a graph which shows the specific example of a drive with respect to the electric motor in the said 2nd assist mode, (a) is a wave form diagram which shows the example of a change of an angle change rate, (b) and (c) are respectively (a). It is a wave form diagram which shows the applied voltage and supply current to an electric motor when detecting the angle change rate shown to (2).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering member 3 Steering shaft 6 Electric motor 9 Steering wheel 21 Control unit (control part)
21a calculation part (steering angle detection part, 1st and 2nd rotation angle detection part, torque detection part)
21b Drive control unit 22 Vehicle speed sensor P First sensor unit Q Second sensor unit R Third sensor unit

Claims (6)

An electric power steering device for assisting steering by applying power of an electric motor to a steering mechanism from a steering member to a steering wheel,
A steering angle detector for detecting a steering angle on at least one side of the steering member and the steering wheel;
A control unit that performs drive control of the electric motor using the steering angle detected by the steering angle detection unit,
The control unit obtains a change amount of the rudder angle based on the rudder angle from the rudder angle detection unit, and determines that the electric motor has a predetermined amount when the obtained change amount exceeds a predetermined threshold value. An electric power steering apparatus characterized by supplying current during a period. A steering mechanism having a steering shaft in which a steering member and a steered wheel are connected to one end side and the other end side, an electric motor for assisting steering by applying power to the steering mechanism, and steering of the steering shaft First and second sensor units that output signals corresponding to rotation angles on the member side and the steered wheel side, respectively, and the steering member using output signals from the first and second sensor units, respectively. First and second rotation angle detection units for detecting rotation angles on the side and the steering wheel side, a torque detection unit for detecting steering torque generated on the steering shaft, and the first and second rotation angles A control unit that performs drive control of the electric motor using a rotation angle from the detection unit and a steering torque from the torque detection unit;
When the control unit cannot acquire the detected value of the steering torque, the control unit obtains the change amount of the rotation angle based on the rotation angle from one of the first and second rotation angle detection units, and An electric power steering apparatus, wherein when it is determined that the obtained change amount exceeds a predetermined threshold, a current is supplied to the electric motor for a predetermined period.   3. The electric power steering apparatus according to claim 1, wherein the control unit obtains a change amount of the steering angle or a change amount of the rotation angle for each predetermined period.   The control unit controls the electric motor by open loop control based on either a change amount of the steering angle from the steering angle detection unit or a change amount of the rotation angle from the first or second rotation angle detection unit. The electric power steering apparatus according to any one of claims 1 to 3, wherein the steering assist is performed by driving.   The said control part sets a predetermined | prescribed duty ratio with respect to the said predetermined period, and supplies an electric current to the said electric motor according to the ON time by this duty ratio. The electric power steering apparatus as described. While the vehicle speed detected by the vehicle speed sensor is input to the control unit,
The electric power steering apparatus according to claim 1, wherein the control unit changes a current supply amount to the electric motor according to a vehicle speed from the vehicle speed sensor.

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