JP2014208503A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device enabling improvement of shortage of assist force caused in a traveling state where large lateral acceleration is applied to a vehicle.SOLUTION: When a normal sensor signal out of sensor signals in two systems is in one system, a microcomputer reduces an absolute value of basic assist control amount Ias, compared to that before the normal sensor signal is in one system. In this state, the microcomputer increases the absolute value of the basic assist control amount Ias, as lateral acceleration G applied to a vehicle increases. By the increase in the absolute value of basic assist control amount Ias, assist force applied to a steering system increases.

Description

  The present invention relates to an electric power steering apparatus.

  Generally, a control device for an electric power steering device detects a steering torque based on a sensor signal generated by a torque sensor, and applies a motor torque so that an appropriate assist force is applied to the steering system according to the steering torque. Control. For this reason, the electric power steering apparatus is required to stably and accurately detect the steering torque in order to obtain an appropriate assist force. In this regard, for example, the electric power steering apparatus disclosed in Patent Document 1 includes a torque sensor that generates two torque signals. According to the electric power steering apparatus, even when an abnormality occurs in one of the two torque signals, the assist can be continued by using the remaining normal torque signal. Patent Document 1 describes that the maximum assist force is suppressed when assist is continued using the remaining normal torque signals.

Japanese Patent No. 4806694 (paragraphs 0041-0046)

  However, when the assist force is suppressed when the remaining normal torque signal is used to continue the assist, there are the following concerns. For example, on a curved road, it is necessary to hold the steering against the lateral acceleration acting in the direction opposite to the turning direction of the vehicle, and the torque required to hold the steering increases as the lateral acceleration increases. . For this reason, there is a concern that the assist force is insufficient due to the suppression of the assist force.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electric power steering device that can improve shortage of assist force that may occur in a traveling state in which a large lateral acceleration acts on a vehicle. It is to provide.

  An electric power steering apparatus that can achieve the above object is a torque that generates a plurality of sensor signals in accordance with a motor that generates an assist force applied to a steering system of a vehicle and a steering torque that acts on a steering shaft that constitutes the steering system. A sensor; and a control device that calculates a control amount corresponding to an assist force applied to the steering system based on a steering torque obtained from the sensor signal and controls the motor based on the control amount. The control device increases the lateral acceleration acting on the vehicle as the absolute value of the control amount becomes smaller than before the normal sensor signal becomes one system. The absolute value of the control amount is increased.

  According to this configuration, the absolute value of the control amount (in the same steering state and running state) when the normal sensor signal becomes one system is made smaller than before the normal sensor signal becomes one system. The As the control amount decreases, the assist force applied to the steering system decreases. The driver can recognize that the normal sensor signal has become one system by feeling the steering operation heavier than usual.

  However, on the other hand, since the assist force is suppressed, there is a concern that the assist force is insufficient in a traveling state in which a large lateral acceleration acts on the vehicle such as when traveling on a curved road. On a curved road, it is necessary to hold the steering against the lateral acceleration acting in the direction opposite to the turning direction of the vehicle, and the torque required to hold the steering as the lateral acceleration increases (steering torque) ) Becomes larger.

  Therefore, the absolute value of the control amount is increased as the lateral acceleration acting on the vehicle increases as the normal sensor signal becomes one system. The assist force is increased by increasing the control amount in accordance with the lateral acceleration. In other words, the shortage of assist force due to the increase in lateral acceleration is compensated by the assist force corresponding to the increase in control amount. Therefore, the shortage of assist force that can occur in a traveling state where a large lateral acceleration acts on the vehicle is improved.

  In the electric power steering apparatus, when the normal sensor signal becomes one system, the control apparatus executes a limiting process for setting an upper limit value and a lower limit value of the control amount according to a steering angle, and The absolute value of the control amount after the limiting process may be increased as the lateral acceleration increases.

  According to this configuration, when the normal sensor signal becomes one system, the limit processing for setting the upper limit value and the lower limit value of the control amount according to the steering angle is executed, so that the remaining one normal system signal is obtained. Even if an abnormality occurs in the sensor signal, the magnitude of the assist force applied to the steering system is limited to a predetermined range. For this reason, it is suppressed that the assist force which is not intended to a steering system is given. Further, by increasing the absolute value of the control amount after the limiting process as the lateral acceleration increases, the increase in the control amount due to the increase in the lateral acceleration is not limited. For this reason, the assist force can be positively increased in accordance with the increase in lateral acceleration. A suitable steering feel corresponding to the lateral acceleration can also be obtained.

  In the electric power steering apparatus, when the normal sensor signal becomes one system, the control apparatus executes a limiting process for setting an upper limit value and a lower limit value of the control amount according to a steering angle, and The absolute value of the control amount before the limiting process may be increased as the lateral acceleration increases.

  According to this configuration, when the normal sensor signal becomes one system, the limit processing for setting the upper limit value and the lower limit value of the control amount according to the steering angle is executed, so that the remaining one normal system signal is obtained. Even if an abnormality occurs in the sensor signal, the magnitude of the assist force applied to the steering system is limited to a predetermined range. For this reason, it is suppressed that the assist force which is not intended to a steering system is given. Further, by increasing the absolute value of the control amount before the limiting process as the lateral acceleration increases, the increased control amount can be limited through the limiting process. This configuration is suitable when steering safety is prioritized over steering feel.

  In the electric power steering device, the control device stores a map that defines a relationship between the lateral acceleration and a compensation control amount for the lateral acceleration, and when a normal sensor signal becomes one system, You may make it enlarge the absolute value by adding the compensation control amount according to the lateral acceleration obtained based on a map to the said control amount.

  According to this configuration, the compensation control amount corresponding to the lateral acceleration can be easily obtained through map calculation.

  ADVANTAGE OF THE INVENTION According to this invention, the shortage of the assist force which may arise in the driving | running | working state which a big lateral acceleration acts on a vehicle can be improved.

The schematic block diagram of an electric power steering apparatus. The control block diagram of an electric power steering device. The control block diagram of an assist control part. The control block diagram of a basic assist control amount calculating part. The control map which shows the relationship between a lateral acceleration and a compensation control amount. The control block diagram of a control amount restriction | limiting process part. The flowchart which shows the process sequence of the assist control according to the abnormality generation state of a torque sensor. The flowchart which shows the process sequence of assist control. The flowchart which shows the calculation procedure of the basic assist control amount at the time of normal control. The flowchart which shows the calculation procedure of the basic assist control amount at the time of assist continuation control. The control block diagram of the assist control part in other embodiment.

Hereinafter, an embodiment of the electric power steering apparatus will be described.
<Outline of EPS>
As shown in FIG. 1, an electric power steering device (EPS) 10 includes a steering mechanism 20 that steers steered wheels based on a driver's steering operation, a steering assist mechanism 30 that assists the driver's steering operation, and An ECU (electronic control unit) 40 that controls the operation of the steering assist mechanism 30 is provided.

  The steering mechanism 20 includes a steering wheel 21 that is operated by a driver, and a steering shaft 22 that rotates integrally with the steering wheel 21. The steering shaft 22 includes a column shaft 22a connected to the center of the steering wheel 21, an intermediate shaft 22b connected to the lower end portion of the column shaft 22a, and a pinion shaft 22c connected to the lower end portion of the intermediate shaft 22b. . A lower end portion of the pinion shaft 22c is meshed with a rack shaft 23 (more precisely, a portion 23a on which rack teeth are formed) extending in a direction intersecting with the pinion shaft 22c. Therefore, the rotational motion of the steering shaft 22 is converted into the reciprocating linear motion of the rack shaft 23 by the rack and pinion mechanism 24 including the pinion shaft 22 c and the rack shaft 23. The reciprocating linear motion is transmitted to the left and right steered wheels 26 and 26 via tie rods 25 respectively connected to both ends of the rack shaft 23, whereby the steered angle θta of the steered wheels 26 and 26 is changed. The The traveling direction of the vehicle is changed by changing the turning angle θta of the turning wheels 26 and 26.

  The steering assist mechanism 30 includes a motor 31 that is a source of steering assist force. As the motor 31, a brushless motor or the like is employed. The motor 31 is connected to the column shaft 22a via the speed reduction mechanism 32. The reduction mechanism 32 reduces the rotation of the motor 31 and transmits the reduced rotational force to the column shaft 22a. That is, the torque of the motor is applied to the steering shaft 22 as a steering assist force (assist force), thereby assisting the driver's steering operation.

  ECU40 acquires the detection result of the various sensors provided in a vehicle as information which shows a driver | operator's request | requirement or driving | running | working state, and controls motor 31 according to these various information acquired.

Examples of the various sensors include a vehicle speed sensor 51, a steering sensor 52, a torque sensor 53, a rotation angle sensor 54, and a lateral acceleration sensor 55.
The vehicle speed sensor 51 detects a vehicle speed (vehicle traveling speed) V.

The steering sensor 52 is a magnetic rotation angle sensor and is provided on the column shaft 22a to detect the steering angle θs.
A torque sensor 53 is also provided on the column shaft 22a. The torque sensor 53 includes a sensor core (not shown) and two sensor elements 53a and 53b such as a Hall IC. The sensor core generates a magnetic flux that changes based on torsion of a torsion bar 53c provided at an intermediate portion of the column shaft 22a. The two sensor elements 53a and 53b are respectively arranged around the sensor core. When torque is applied to the steering shaft 22 and the torsion bar 53c is twisted, the magnetic flux applied to the two sensor elements 53a and 53b changes. The two sensor elements 53a and 53b generate sensor signals Sa and Sb corresponding to changes in magnetic flux, respectively.

The rotation angle sensor 54 is provided in the motor 31 and detects the rotation angle θm of the motor 31.
The lateral acceleration sensor 55 detects a lateral acceleration G acting on the vehicle. Lateral acceleration refers to acceleration that acts in a direction orthogonal to the traveling direction (front-rear direction) (left-right direction) when the vehicle turns.

  The ECU 40 detects the steering torque τ based on the sensor signals Sa and Sb generated by the two sensor elements 53a and 53b. In addition, the ECU 40 calculates a target assist force based on the vehicle speed V, the steering angle θs, the steering torque τ, the rotation angle θm, and the lateral acceleration G, and generates driving power for causing the steering assist mechanism 30 to generate the target assist force. To supply.

<Configuration of ECU>
Next, the hardware configuration of the ECU will be described.
As shown in FIG. 2, the ECU 40 includes a drive circuit (inverter circuit) 41 and a microcomputer 42.

  The drive circuit 41 converts DC power supplied from a DC power source such as a battery into three-phase AC power based on a motor control signal Sc described later generated by the microcomputer 42. The converted three-phase AC power is supplied to the motor 31 via the power supply path 43 of each phase. A current sensor 44 is provided in the power supply path 43 of each phase. These current sensors 44 detect an actual current value I generated in the power supply path 43 of each phase. In FIG. 2, for convenience of explanation, the power feeding path 43 for each phase and the current sensor 44 for each phase are shown together as one.

  The microcomputer 42 takes in the detection results of the vehicle speed sensor 51, the steering sensor 52, the torque sensor 53, the rotation angle sensor 54, the lateral acceleration sensor 55, and the current sensor 44 at predetermined sampling periods. The microcomputer 42 converts these detected results, that is, the vehicle speed V, the steering angle θs, the steering torque τ (more precisely, the two sensor signals Sa and Sb), the rotation angle θm, the lateral acceleration G, and the actual current value I. Based on this, a motor control signal (PWM drive signal) Sc is generated.

<Microcomputer>
Next, a functional configuration of the microcomputer will be described.
The microcomputer 42 has various arithmetic processing units realized by executing a control program stored in a storage device (not shown).

  As shown in FIG. 2, the microcomputer 42 includes a steering torque calculation unit 61, a current command value calculation unit 62, a motor control signal generation unit 63, and an abnormality determination unit 64 as these calculation processing units.

The steering torque calculator 61 calculates the steering torque τ based on the two sensor signals Sa and Sb generated by the torque sensor 53.
The current command value calculation unit 62 includes an assist control unit 71. The assist control unit 71 calculates a basic assist control amount Ias ^* based on the steering angle θs, the vehicle speed V, the steering torque τ, and the lateral acceleration G. The basic assist control amount Ias ^* is a basic component for generating a target assist force having an appropriate magnitude according to the steering angle θs, the vehicle speed V, the steering torque τ, and the lateral acceleration G. The current command value calculation unit 62 calculates the current command value I ^* of each phase based on the basic assist control amount Ias ^* . The current command value I ^* is a command value indicating a current to be supplied to the motor 31.

The motor control signal generator 63 takes in the current command value I ^* , the actual current value I, and the rotation angle θm of the motor 31, and the actual current value I follows the current command value I ^{* based} on the fetched information. Thus, current feedback control is performed. The motor control signal generation unit 63 obtains a deviation between the current command value I ^* and the actual current value I, and generates a motor control signal Sc so as to eliminate the deviation. When a current corresponding to the motor control signal Sc is supplied to the motor 31 through the drive circuit 41, the motor 31 generates a rotational force corresponding to the target assist force (assist command value).

  The abnormality determination unit 64 detects the presence or absence of abnormality of the two sensor signals Sa and Sb generated by the torque sensor 53 and, by extension, the torque sensor 53. The abnormality determination unit 64 detects the presence / absence of abnormality of the two sensor signals Sa and Sb through the following determination processes (A) and (B), for example.

  (A) A determination process as to whether or not the values of the two sensor signals Sa and Sb deviate from the values that can be taken at normal times. If the values of the two sensor signals Sa and Sb deviate from the values that can be taken at normal times, the deviated sensor signals Sa and Sb are abnormal.

  (B) A process for comparing and determining the values of the two sensor signals Sa and Sb, or a process for comparing and determining the amount of change per unit time of the two sensor signals Sa and Sb. If the values of the two sensor signals Sa and Sb are normal, the values of the two sensor signals Sa and Sb or the amount of change per unit time match. If at least one of the two sensor signals Sa and Sb is abnormal, the values of the two sensor signals Sa and Sb or the amount of change per unit time do not match.

The abnormality determination unit 64 generates an abnormality detection signal Str indicating the abnormality state when the determination result of the presence or absence of abnormality for the two sensor signals Sa and Sb indicates abnormality.
<Aspect control mode>
The microcomputer 42 executes power assist control according to the abnormality occurrence state of the torque sensor 53 detected by the abnormality determination unit 64. There are three types of power assist control: normal power assist control (normal control), assist stop control, and assist continuation control.

The microcomputer 42 executes normal control when the torque sensor 53 is normal, that is, when the two sensor elements 53a and 53b are both normal.
The microcomputer 42 executes assist stop control when both of the two sensor elements 53a and 53b are abnormal. That is, when it is determined that both of the two sensor elements 53a and 53b have failed based on the abnormality detection signal Str, the current command value calculation unit 62 stops outputting the current command value I ^* .

If only one of the two sensor elements 53a and 53b is abnormal, the microcomputer 42 executes assist continuation control as backup control. That is, the steering torque calculation unit 61 continues the calculation of the steering torque τ by using a normal sensor signal generated by the other sensor element in which no failure has occurred. The current command value calculator 62 calculates a current command value I ^* based on the steering torque τ calculated using the remaining normal sensor signal. The power assist control is continuously executed based on the current command value I ^* .

<Assist control unit>
Next, the assist control unit 71 will be described in detail.
As shown in FIG. 3, the assist control unit 71 includes a basic assist control amount calculation unit 81, a compensation control amount calculation unit (lateral G-sensitive control amount calculation unit) 82, an adder 83, and a control amount restriction processing unit 84. Yes.

<Basic assist control amount calculation unit>
The basic assist control amount calculation unit 81 calculates a basic assist control amount Ias ^* , which is a basic component for generating an assist force corresponding to the steering torque τ and the vehicle speed V. In this example, even if the steering torque τ (steering state) and the vehicle speed V (running state) are the same, the assist force applied to the steering system is different during normal control and during assist continuation control.

  Specifically, as shown in FIG. 4, the basic assist control amount calculation unit 81 includes a first assist map 91 for normal control, a second assist map 92 for assist continuation control, and a switching unit 93. ing.

The first and second assist maps 91 and 92 are both vehicle speed sensitive three-dimensional maps for calculating the basic assist control amount Ias ^* based on the steering torque τ and the vehicle speed V. Further, both the first and second assist maps 91 and 92 are configured such that a greater assist force is applied to the steering system as the steering torque τ (absolute value) is larger and the vehicle speed V is smaller. A basic assist control amount Ias ^* having a large value (absolute value) is calculated. However, when the steering torque τ and the vehicle speed V are the same, the basic assist control amount Ias ^* obtained by the first assist map 91 is about 2 of the basic assist control amount Ias ^* obtained by the second assist map 92. It will be more than double the size.

When it is determined that both of the two sensor elements 53a and 53b are normal based on the abnormality detection signal Str, the switching unit 93 connects the contact 93c and the contact 93a and obtains the first assist map 91. supplied to the adder 83 the basic assist control amount Ias ^* to be. Further, when it is determined that only one of the two sensor elements 53a and 53b has failed based on the abnormality detection signal Str, the switching unit 93 connects the contact 93c and the contact 93b, A basic assist control amount Ias ^* obtained by the second assist map 92 is supplied to the adder 83.

The basic assist control amount calculation unit 81 calculates the absolute value of the basic assist control amount Ias ^{* in} the same steering state and traveling state before the normal sensor signal becomes one system. Assist reduction processing is performed to make it smaller. As the absolute value of the basic assist control amount Ias ^* decreases, the assist force applied to the steering system decreases. The driver can recognize that the normal sensor signal has become one system by feeling the steering operation heavier than usual.

<Compensation control amount calculation unit>
The compensation control amount calculation unit 82 takes in the lateral acceleration G and the abnormality detection signal Str, respectively. When it is determined that an abnormality is detected in only one of the two sensor signals Sa and Sb based on the abnormality detection signal Str, the compensation control amount calculation unit 82 compensates for the compensation control amount Ig (lateral acceleration according to the lateral acceleration G). (Sensitive control amount) is calculated.

  As shown in FIG. 5, the compensation control amount calculation unit 82 has a compensation control amount map 94 that defines the relationship between the lateral acceleration G and the compensation control amount Ig. The compensation control amount map 94 is a map in which the horizontal axis is the lateral acceleration G and the vertical axis is the compensation control amount Ig. The compensation control amount calculation unit 82 uses the compensation control amount map 94 to convert the compensation control amount Ig into the lateral acceleration. Calculate according to G.

  The compensation control amount map 94 is set based on the following viewpoint. That is, the reaction torque input from the road surface to the steering system has a correlation with the lateral acceleration G acting on the vehicle. Specifically, the reaction torque increases as the lateral acceleration G acting on the vehicle increases. For this reason, as the lateral acceleration G increases, the driver requires a larger steering torque for steering. Therefore, the compensation control amount map 94 is set so that the absolute value of the compensation control amount Ig increases as the absolute value of the lateral acceleration G increases.

  Precisely, the compensation control amount map 94 indicates that the absolute value of the compensation control amount Ig increases as the absolute value of the lateral acceleration G increases until the absolute value of the lateral acceleration G reaches the specified value Gt. After the absolute value of the acceleration G reaches the specified value Gt, the value of the compensation control amount Ig is set to be constant at the upper limit value Igu regardless of the lateral acceleration G.

  The sign of the compensation control amount Ig is determined according to the sign of the lateral acceleration G. That is, the compensation control amount map 94 is such that when the lateral acceleration G is a positive value, the compensation control amount Ig increases in a positive direction, and when the lateral acceleration G is a negative value, compensation control is performed. The amount Ig is set to increase in the negative direction. Further, since the range of the lateral acceleration G acting on the vehicle during normal traveling can be assumed to some extent, for example, a prescribed value Gt for the lateral acceleration G is set based on the maximum value of the range that the lateral acceleration G can take. Also good. Further, the positive / negative direction of the lateral acceleration G is set to be opposite to the positive / negative direction of the steering torque τ. Therefore, when the vehicle is turned by applying a positive steering torque τ to the steering shaft 22, a positive lateral acceleration G is applied to the vehicle.

  When it is determined that only one of the two sensor elements 53a and 53b has failed based on the abnormality detection signal Str, the compensation control amount calculation unit 82 obtains the compensation control amount Ig obtained from the compensation control amount map 94. Is supplied to the adder 83.

<Adder>
The adder 83 adds the basic assist control amount Ias ^* generated by the basic assist control amount calculation unit 81 and the compensation control amount Ig generated by the compensation control amount calculation unit 82. The adder 83 supplies the basic assist control amount Ias ^* after the compensation control amount Ig is added to the control amount restriction processing unit 84.

<Control amount restriction processing unit>
The control amount restriction processing unit 84 takes in the basic assist control amount Ias ^* , the steering angle θs, and the abnormality detection signal Str from the adder 83. When it is determined that an abnormality is detected in only one of the two sensor signals Sa and Sb based on the abnormality detection signal Str, the control amount restriction processing unit 84 sets the basic assist control amount Ias ^* according to the steering angle θs. Perform restriction processing.

As shown in FIG. 6, the control amount restriction processing unit 84 has a control amount restriction map 95 that defines the relationship between the steering angle θs and the basic assist control amount Ias ^* . The control amount restriction map 95 is a map in which the horizontal axis is the steering angle θs and the vertical axis is the basic assist control amount Ias ^* . The control amount restriction processing unit 84 uses the control amount restriction map 95 to control the basic assist control amount Ias. ^* Is limited within a predetermined range according to the steering angle θs.

The control amount restriction map 95 is set based on the following viewpoint. That is, the reaction force torque that is an external force input from the road surface to the steering system has a correlation with the steering angle θs of the steering wheel 21. Specifically, the reaction force torque increases as the absolute value of the steering angle θs increases. Therefore, as the absolute value of the steering angle θs increases, the driver requires a larger steering torque τ during steering. Therefore, the control amount restriction map 95 is set such that the absolute value of the basic assist control amount Ias ^* increases as the absolute value of the steering angle θs increases. That is, in the control amount restriction map 95, when the steering angle θs is a positive value, the upper limit value of the basic assist control amount Ias ^* increases in the positive direction, and when the steering angle θs is a negative value. The lower limit value of the basic assist control amount Ias ^* is set to increase in the negative direction. It should be noted that the upper limit value and the lower limit value of the basic assist control amount Ias ^* each have a constant value within a certain range near 0 ° which is the steering angle θs when the steering wheel 21 is held at the neutral position.

  The control amount restriction processing unit 84 greatly restricts and reduces the assist force applied to the steering system when the steering angle θs is small so that the assist force applied to the steering system is not so limited when the steering angle θs is large. The restriction process is executed as follows. Even if an abnormality occurs in the remaining one normal sensor signal and the sensor signal is no longer detected, the assist force applied to the steering system is limited to a predetermined range. It is suppressed that an unintended assist force is applied.

<Operation of electric power steering device>
Next, the operation of the electric power steering apparatus configured as described above will be described.
<Assist control procedure>
First, the processing procedure of power assist control by the microcomputer 42 will be described with reference to the flowchart of FIG. Each process according to the flowchart is executed at a predetermined sampling period when the power of the vehicle is turned on.

  Now, as shown in the flowchart of FIG. 7, the microcomputer 42 determines whether or not the two sensor signals Sa and Sb are abnormal through the abnormality determination unit 64 (step S <b> 101).

  When the microcomputer 42 detects an abnormality in at least one of the two sensor signals Sa and Sb through the abnormality determination unit 64 (YES in step S101), the microcomputer 42 proceeds to a process in step S102.

  In step S102, the microcomputer 42 performs failure determination of the sensor elements 53a and 53b, which are output elements of the two sensor signals Sa and Sb, based on the abnormality detection result detected in step S101 (step S103). .

  If it is determined that both of the two sensor elements 53a and 53b have failed (YES in step S103), the microcomputer 42 executes assist stop control (step S104). That is, the microcomputer 42 gradually reduces the assist force applied to the steering system in order to quickly stop the power assist control and achieve failsafe.

  On the other hand, when it is determined in the previous step S103 that only one of the two sensor elements 53a and 53b has failed (NO in step S103), the microcomputer 42 performs the assist continuation control. Is executed (step S105).

  That is, the microcomputer 42 detects the steering torque τ based on the sensor signal (residual sensor signal) generated by the remaining normal sensor elements that have not been determined to fail, and continues the power assist control based on the steering torque τ. To do.

  The microcomputer 42 determines that there is no abnormality in the two sensor signals Sa and Sb in the previous step S101, that is, the two sensor signals Sa and Sb are both normal (step S101). NO), normal power assist control is executed (step S106).

<Procedure for normal control or assist continuation control>
Next, the processing procedure of normal control or assist continuation control by the microcomputer 42 will be described with reference to the flowchart of FIG. Each process according to the flowchart is executed when the process proceeds to step S105 or step S106 in the flowchart of FIG.

  As shown in the flowchart of FIG. 8, the microcomputer 42 first reads signals generated by various sensors such as the vehicle speed sensor 51, the steering sensor 52, and the torque sensor 53 (step S201).

Next, the microcomputer 42 calculates a basic assist control amount Ias ^* based on signals generated by various sensors (step S202).
Next, the microcomputer 42 calculates the current command value I ^* based on the basic assist control amount Ias ^* calculated in step S202 (step S203).

Next, the microcomputer 42 calculates the motor control signal Sc through execution of current feedback control using the current command value I ^* and the actual current value I (step S204).

The microcomputer 42 drives the motor 31 by supplying the motor control signal Sc to the drive circuit 41 (step S205).
<Basic assist control amount calculation processing procedure>
Next, the calculation processing procedure of the basic assist control amount Ias ^* by the microcomputer 42 will be described with reference to the flowcharts of FIGS. Each process according to these flowcharts is executed when the process is shifted to step S202 in the flowchart of FIG. 8 when the normal control and the assist continuation control are executed.

First, a calculation processing procedure at the time of executing normal control will be described.
As shown in the flowchart of FIG. 9, when the normal control is executed, the microcomputer 42 calculates the basic assist control amount Ias ^* based on the first assist map 91 (step S301), and ends the process.

Next, a calculation processing procedure when executing the assist continuation control will be described.
As shown in the flowchart of FIG. 10, when executing the assist continuation control, the microcomputer 42 calculates the basic assist control amount Ias ^* based on the second assist map 92 (step S401).

Next, the microcomputer 42 calculates the compensation control amount Ig based on the compensation control amount map 94 (step S402), and the calculated compensation control amount Ig is used as the basic assist control amount Ias ^* obtained in the previous step S401. Add (step S403).

Finally, the microcomputer 42 executes a limiting process based on the lateral acceleration G with respect to the basic assist control amount Ias ^* after the compensation control amount Ig is added (step S404), and ends the process.

<Operation of compensation control amount calculation unit>
When the assist continuation control is executed, the following operation is obtained by adding the compensation control amount Ig to the basic assist control amount Ias ^* according to the lateral acceleration G.

  When the assist is continued using the remaining one normal torque signal, the second assist map 92 is applied, so that the assist force applied to the steering system is smaller than usual. In this state, for example, when the vehicle travels on a curved road, a large lateral acceleration may act on the vehicle. Since the driver needs to hold the steering against the lateral acceleration acting in the direction opposite to the turning direction of the vehicle, the torque required to hold the steering as the lateral acceleration G increases (steering (Torque) increases. That is, there is a concern that the assist force applied to the steering system may be insufficient because the assist continuation control is being executed, even though a larger assist force is required.

In this regard, in this example, during the execution of the assist continuation control, the basic assist control amount Ias ^* is increased in accordance with the increase in the lateral acceleration G. As the basic assist control amount Ias ^* increases, the torque of the motor 31 and thus the assist force applied to the steering system increases. That is, the shortage (all or a part) of the assist force corresponding to the increase in the lateral acceleration G is compensated by the assist force corresponding to the compensation control amount Ig that is the increase of the basic assist control amount Ias ^* . Accordingly, it is possible to improve the shortage of assist force that may occur in a traveling state in which a large lateral acceleration G acts on the vehicle.

<Effect of Embodiment>
Therefore, according to the present embodiment, the following effects can be obtained.
(1) The microcomputer 42 makes the absolute value of the basic assist control amount Ias ^* smaller than before the normal sensor signal becomes one system, when the normal sensor signal becomes one system. At this time, the microcomputer 42 increases the absolute value of the basic assist control amount Ias ^* as the lateral acceleration G acting on the vehicle increases. The assist force applied to the steering system increases as the absolute value of the basic assist control amount Ias ^* increases. For this reason, the shortage of assist force that may occur in a traveling state in which a large lateral acceleration G acts on the vehicle is improved, and a suitable steering feeling corresponding to the lateral acceleration G is obtained.

(2) The microcomputer 42 executes an assist limiting process for setting the upper limit value and the lower limit value of the basic assist control amount Ias ^* according to the lift and normal steering signal θs in which the normal sensor signal becomes one system. Further, the microcomputer 42 increases the absolute value of the basic assist control amount Ias ^* before the assist limiting process as the lateral acceleration G acting on the vehicle increases. Specifically, the microcomputer 42 adds the compensation control amount Ig corresponding to the lateral acceleration G at that time to the basic assist control amount Ias ^* generated by the basic assist control amount calculation unit 81. Here, it is also conceivable that the basic assist control amount Ias ^* to which the compensation control amount Ig is added exceeds the upper limit value or lower limit value defined by the control amount restriction map 95. In this case, the magnitude of the basic assist control amount Ias ^* to which the compensation control amount Ig is added is limited to a range below the upper limit value and above the lower limit value through the control amount restriction processing unit 84. For this reason, it is possible to prevent an unintended assist force from being applied to the steering system. Steering safety is also ensured.

  (3) The compensation control amount calculation unit 82 calculates the compensation control amount Ig for the lateral acceleration G using the compensation control amount map 94. For this reason, the compensation control amount Ig for the lateral acceleration G can be easily set in accordance with the vehicle specifications and the like.

<Other embodiments>
In addition, you may implement the said embodiment as follows.
In this example, the control amount restriction processing unit 84 may determine whether or not the restriction processing of the basic assist control amount Ias ^* is necessary based on the vehicle speed V. For example, the control amount restriction processing unit 84 executes the restriction process of the basic assist control amount Ias ^* when the vehicle speed V is equal to or higher than the predetermined speed V0, and the basic assist when the vehicle speed V is less than the predetermined speed V0. The restriction process of the control amount Ias ^* is not executed.

In this example, the microcomputer 42 increases the absolute value of the basic assist control amount Ias ^* before the assist limiting process as the lateral acceleration G acting on the vehicle increases, but may be as follows.

That is, as shown in FIG. 11, the microcomputer 42 increases the absolute value of the basic assist control amount Ias ^* after the assist limiting process as the lateral acceleration G acting on the vehicle increases. Specifically, the microcomputer 42 (more precisely, the assist control unit 71) adds the compensation control amount Ig corresponding to the lateral acceleration G at that time to the basic assist control amount Ias ^* that has passed through the control amount restriction processing unit 84. . Even if the basic assist control amount Ias ^* to which the compensation control amount Ig is added exceeds the upper limit value or the lower limit value defined by the control amount restriction map 95, the basic assist control to which the compensation control amount Ig is added. The magnitude of the quantity Ias ^* is not limited. Therefore, the compensation control amount Ig corresponding to the lateral acceleration G can be positively reflected in the assist force.

In this example, the microcomputer 42 sets the upper limit value and the lower limit value of the basic assist control amount Ias ^* according to the lift when the normal sensor signal becomes one system out of the two sensor signals and the steering angle θs. The assist restriction process is executed, but the assist restriction process may not be performed. In this case, it is not necessary to provide the control amount restriction processing unit 84.

In this example, the torque sensor 53 that generates the two sensor signals Sa and Sb is used. However, a sensor that generates three or more sensor signals may be used. Even in this case, when the normal sensor signal among the plurality of sensor signals becomes one system, the absolute value of the basic assist control amount Ias ^* is made smaller than that before the normal sensor signal becomes one system. At this time, the microcomputer 42 increases the absolute value of the basic assist control amount Ias ^* as the lateral acceleration G acting on the vehicle increases.

<Other technical ideas>
Next, the technical idea that can be grasped from the above embodiment will be added below.
(A) When a normal sensor signal is not detected in the sensor signals of the plurality of systems, the control device controls the motor to stop applying the assist force to the steering system. According to this configuration, it is possible to prevent the assist force from being applied based on an abnormal sensor signal.

  DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 22 ... Steering shaft, 31 ... Motor, 42 ... Microcomputer (control apparatus), 53 ... Torque sensor.

Claims (4)

A motor for generating an assist force applied to the steering system of the vehicle;
A torque sensor that generates sensor signals of a plurality of systems in response to a steering torque acting on a steering shaft constituting the steering system;
A control device that calculates a control amount according to the assist force applied to the steering system based on the steering torque obtained from the sensor signal and controls the motor based on the control amount;
The control device increases the lateral acceleration acting on the vehicle as the absolute value of the control amount becomes smaller than before the normal sensor signal becomes one system. An electric power steering device for increasing an absolute value of the control amount. The electric power steering apparatus according to claim 1, wherein
When the normal sensor signal becomes one system, the control device executes a limit process for setting an upper limit value and a lower limit value of the control amount according to a steering angle, and the limit process increases as the lateral acceleration increases. An electric power steering device that increases the absolute value of the subsequent control amount. The electric power steering apparatus according to claim 1, wherein
When the normal sensor signal becomes one system, the control device executes a limit process for setting an upper limit value and a lower limit value of the control amount according to a steering angle, and the limit process increases as the lateral acceleration increases. An electric power steering device that increases the absolute value of the previous control amount. In the electric power steering device according to any one of claims 1 to 3,
The control device stores a map that defines the relationship between the lateral acceleration and the compensation control amount for the lateral acceleration. When the normal sensor signal becomes one system, the lateral acceleration obtained based on the map is calculated. An electric power steering apparatus that increases an absolute value by adding a corresponding compensation control amount to the control amount.