JP2006056474A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of obtaining good steering feeling and high steering stability, even if variation in characteristics of components structuring a steering mechanism exist. <P>SOLUTION: The electric power steering device comprises a steering range estimating means estimating a steering range in which a steering wheel has been started to turn at a not less than predetermined vehicular speed and from a straight-ahead state on the basis of vehicular speed, a torque sensor value, and a rotation angle of an electric motor, without a steering angle sensor; an actual steering stiffness calculating means calculating steering stiffness in the steering range; a deviation calculating means calculating a deviation between the actual steering stiffness and target steering stiffness; and a correcting means correcting an assist gain and an assist staring point of a control map in case that the deviation is not less than a predetermined value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering device, and in particular, drives a steering mechanism by controlling an electric motor so as to achieve a target steering force characteristic based on at least a vehicle speed and a steering torque without having a steering angle sensor. The present invention relates to an electric power steering apparatus.

  Recently, for example, an electric power steering apparatus that uses the power of an electric motor to act on a steering system to reduce the operating force as shown in Japanese Patent Application Laid-Open No. 8-332964 has been used. It is coming. The electric power steering apparatus includes a steering force detection unit that detects the driver's steering force (steering torque) and simultaneously drives the motor to generate a predetermined correction torque based on the vehicle speed. The current is controlled to reduce the driver's steering force.

JP-A-8-332964

In such an electric power steering device, in order to obtain a good steering feeling and high steering performance, the characteristics of the individual components constituting the steering mechanism such as the torsion bar and power assist are tuned to It is necessary to set the characteristic of the steering force (hereinafter referred to as “steering force characteristic”) to be a desired steering force characteristic (target steering force characteristic).
However, even if individual components of the steering mechanism are designed so as to obtain the target steering force characteristics (the target steering force characteristics can be obtained at the time of designing), the individual parts (machine System components and electrical system components), specifically, rubber coupling variations, component friction variations, component itself variations, tightening force variations, motor characteristics variations, etc. The force characteristic is significantly different from the target steering force characteristic, and the steering control performance is deteriorated. As a result, the steering feel may be greatly different from the ideal feel. In addition to variations in the characteristics of the components constituting the steering mechanism, there are also variations in the load (variations in external force received from the tire) and changes over time, and the target steering force characteristics may not be obtained.

On the other hand, if the steering angle is detected by the steering angle sensor and the Fordback control is performed so that the characteristic of the steering force with respect to the steering angle becomes the target steering force characteristic, such a problem of variation in the characteristics of the parts is solved to some extent. However, this requires an expensive steering angle sensor, which is not preferable.
Thus, there is a demand for an electric power steering device that solves the problems caused by variations in the characteristics of the components that constitute the steering mechanism and provides the target steering force characteristics without providing an expensive steering angle sensor.

  Therefore, the present invention has been made to solve the above-described problems, and obtains a good steering feeling and high steering performance even when there are variations in the characteristics of the components constituting the steering mechanism. An object of the present invention is to provide an electric power steering apparatus capable of performing the above.

In order to achieve the above object, the present invention drives a steering mechanism by controlling an electric motor so as to achieve a target steering force characteristic based on at least a vehicle speed and a steering torque without having a steering angle sensor. An electric power steering apparatus for estimating a rotation angular velocity and a rotation angle of an electric motor from a torque sensor for detecting a steering torque, control map means for defining a target steering force characteristic by a control map, and current and voltage of the electric motor Rotational angle estimating means and steering area estimating means for estimating a steering area where the steering wheel is turned from a straight traveling state where the electric motor is controlled at a speed higher than a predetermined vehicle speed from the vehicle speed, the torque sensor value, and the rotational angle of the electric motor And the steering stiffness from the amount of change in the torque sensor value with respect to the change in the rotation angle of the electric motor in this steering region. Actual steering stiffness calculating means to be output, deviation calculating means for calculating a deviation between the calculated actual steering stiffness and a pre-stored target steering stiffness, and if the deviation is a predetermined value or more, the control map is corrected. The control map means determines a target steering force characteristic based on the assist gain and the assist start point, and the control means corrects the assist gain and the assist start point.
In the present invention configured as described above, the steering region estimation means determines the steering region (specific steering region) in which the steering wheel starts to be turned from a straight traveling state that is equal to or higher than a predetermined vehicle speed and the electric motor is not controlled. Estimated from the torque sensor value and the rotation angle of the electric motor, the actual steering stiffness calculation means calculates the steering stiffness from the change amount of the torque sensor value with respect to the change in the rotation angle of the electric motor in the specific steering region, and the deviation calculation means calculates The deviation between the actual steering stiffness and the target steering stiffness stored in advance is calculated, and the correction means corrects the assist gain and the assist start point of the control map when the deviation is a predetermined value or more. Even if there are variations in the components of the steering mechanism, the electric motor is controlled and the target steering force characteristics So that the, it is possible to drive the steering mechanism, as a result, it is possible to obtain a good steering feeling and high driving stability.

In the present invention, preferably, when the actual steering rigidity is larger than the target steering rigidity, the correction means first increases the assist gain to adjust the steering force change rate to the target steering force characteristic, and then the assist start point. Is corrected so that the maximum steering force matches the target steering force characteristic.
In the present invention configured as described above, when the actual steering stiffness is larger than the target steering stiffness, first, the assist gain related to both the steering force change rate and the maximum steering force is increased and corrected. Since the assist start point related to the maximum steering force is corrected to decrease, the steering force change rate and the maximum steering force of the target steering force characteristic can be effectively adjusted based on the actual steering rigidity.

In the present invention, preferably, the control map means sets a lower limit value of the assist start point, and the correction means further increases the assist gain when the assist start point reaches the lower limit value when the assist start point is decreased and corrected. Correction is made so that the maximum steering force matches the target steering force characteristic.
In the present invention configured as described above, since the lower limit value is set at the assist start point, it is possible to prevent the deterioration of the steering feel due to the start of the assist control immediately after the start of the steering.

In the present invention, preferably, the control map means sets an upper limit value of the assist gain, and the correction means increases the assist gain and, as a result, when the assist gain reaches the upper limit value, the assist gain and the assist start are set. Stop point correction.
According to the present invention configured as described above, it is possible to prevent the steering feel from being deteriorated due to excessive assist control.

In the present invention, preferably, when the actual steering rigidity is smaller than the target steering rigidity, the correction means first decreases and corrects the assist gain to match the steering force change rate with the target steering force characteristic, and then the assist start point. Is corrected so that the maximum steering force matches the target steering force characteristic.
In the present invention configured as described above, when the actual steering stiffness is smaller than the target steering stiffness, first, the assist gain related to both the steering force change rate and the maximum steering force is corrected to decrease, and then mainly, Since the assist start point related to the maximum steering force is increased and corrected, the steering force change rate and the maximum steering force of the target steering force characteristic can be effectively adjusted based on the actual steering rigidity.

In the present invention, preferably, the control map means sets an upper limit value of the assist start point, and the correction means increases the assist start point, and when the assist start point reaches the upper limit value when the assist start point is increased, the assist gain and the assist start point are set. Stop point correction.
According to the present invention configured as described above, unnecessary control map correction can be prevented on the steering feel.

  According to the electric steering device of the present invention, it is possible to obtain a good steering feeling and high steering performance even if there are variations in the characteristics of the parts constituting the steering mechanism.

First, an electric power steering apparatus according to a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a perspective view showing an example of an electric power steering apparatus for an automobile to which the present invention is applied. As shown in FIG. 1, an electric power steering apparatus 1 for an automobile includes a handle (steering wheel) 2. The handle 2 is connected to an upper end of a steering shaft 4, and a steering force for operating the handle 2 is used for steering. It is transmitted to the shaft 4. The upper end of the intermediate shaft 6 is connected to the lower end portion of the steering shaft 4 via a universal joint, and the VGR device 8 that is a vehicle response variable mechanism is connected to the lower end portion of the intermediate shaft 6 so that the front wheels with respect to the steering angle of the steering wheel The transmission ratio of steering can be changed. An intermediate shaft 10 is coupled to the lower end portion of the VGR device 8, and a steering gear box 12 is provided at the lower end portion of the intermediate shaft 10. Tie rods 14 are connected to both sides of the steering gear box 12, and tires (wheels) 16 are attached to the tie rods 14.

A rack and pinion mechanism (not shown) is provided in the steering gear box 12 described above, and the lower end of the intermediate shaft 10 is connected to the pinion. On the other hand, tires 16 are connected to both sides of the rack via the tie rods 14 as described above.
The steering gear box 12 is provided with an electric motor 18 that applies force to the pinion side via a reduction gear (not shown), and a torque sensor (not shown) is provided between the reduction gear and the intermediate shaft 10. Is arranged. This torque sensor is for detecting a steering force (steering torque) acting on the intermediate shaft 10.
These VGR device 8, electric motor (DC motor) 18 and torque sensor are each connected to a control unit 20.

Next, the target steering force characteristics obtained by the first embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a diagram showing an example of target steering steering force characteristics (target steering force characteristics in a high vehicle speed range (about 100 km / h)), and FIG. 3 is a basic assist control map for obtaining the target steering force characteristics. Is shown.
First, the target steering force characteristic of the present embodiment represents a characteristic during traveling at a high vehicle speed and substantially straight. Specifically, the high vehicle speed is a speed of about 50 km / h or more, and the almost straight traveling state is a state where the steering wheel is operated slowly, specifically, the steering wheel is repeatedly operated at a frequency of 0.2 Hz or less. A steering state is assumed in which the lateral acceleration (lateral G) is 0.2 G or less, and such a traveling state is referred to as a “center feel sensitive area”.

Next, in the present embodiment, a desired steering feeling (target steering feeling) can be obtained based on the maximum steering force and an index of “disengagement feeling at the time of cutting” that the driver feels with steering. . Here, “feeling of slipping when turning” is a steering feeling that the driver feels that the steering force is released when the steering wheel is cut from the straight traveling state.
As shown in FIG. 2, when the driver cuts the steering wheel from the straight traveling state, the steering force increases from the start of the steering of the steering wheel (region A), and when the steering force becomes a predetermined value (point B) or more (region C). In order to reduce the burden on the driver, the electric motor 18 is driven so that the rate of increase of the steering force is smaller than before, but if the rate of increase of the steering force becomes too small, The driver feels that the cutting amount (steering amount) of the steering wheel is not sufficient, so that the steering wheel is turned too much, or extra correction steering is required without passing the target course. On the other hand, if the amount of decrease in the rate of increase of the steering force is appropriate, the feeling that the steering force is lost becomes good, the safety is improved, and the driver can feel a steering feeling without anxiety.
For this reason, in the present embodiment, “in the region C where the steering force increases more than the predetermined steering force” with respect to “the ratio of the increase in the steering force with respect to the increase in the steering angle in the region A from the start of the turning of the steering wheel to the predetermined steering force”. The ratio of “the ratio of the increase in the steering force to the increase in the steering angle” (referred to as “the steering force change rate”) is set to a predetermined ratio (0.3 to 0.5).
The value of the maximum steering force that the driver feels when the steering wheel turning amount (steering amount) reaches the maximum (point D) is also set to a desired value.

Next, the target steering force characteristic shown in FIG. 2 can be obtained from the basic assist control map shown in FIG. That is, as shown in FIGS. 2 and 3, in the region A where the steering force increases from the start of the turning of the steering wheel, the motor current is not supplied to the electric motor 18 and is a dead zone region, which is a predetermined steering force. At the point B, the supply of the motor current to the electric motor 18 is started. The assist start point (Pas) in FIG. 3 corresponds to the point B in FIG. When the handle is further turned from this point B, the motor current is supplied to the electric motor 18 at a current increase rate determined by the assist gain (Ka).
Here, the steering force change rate described above can be adjusted by correcting the value of the assist gain (Ka).
Further, after adjusting the steering force change rate with the assist gain Ka, the value of the maximum steering force can be adjusted by correcting the value of the assist start point (Pas).

In this embodiment, as will be described in detail later, by correcting the values of the assist gain (Ka) and assist start point (Pas) in this basic assist control map, the components constituting the steering mechanism during mass production of the vehicle Therefore, even when the target steering force characteristic is different from the target steering force characteristic, the target steering force characteristic at the time of design can be obtained.
Note that the steering force characteristic changes not only due to the characteristic variation of the components of the steering mechanism but also due to the variation of the load received from the tire and the change over time. Therefore, it is necessary to correct the steering force characteristic at a predetermined timing instead of being completed once. .

  FIG. 4 is a block diagram showing a control unit according to the first embodiment of the present invention. As shown in FIG. 4, the control unit 20 includes a basic assist control unit 26 that receives a vehicle speed signal from the vehicle speed sensor 22 and a steering torque signal from the torque sensor 24, and a voltage signal and current from the electric motor 18. Motor rotational angular velocity estimation unit 28 that receives signals, ignition (IG) 30, memory unit 32 that stores steering stiffness at the time of design, steering stiffness estimation unit 34, various sensors (navigation device 36, wiper SW 38, engine water temperature sensor 40, a wheel speed sensor 42, a turn SW 44), a determination & correction unit 46 that receives a signal from the steering stiffness estimation unit 34, a damping control unit (Function (A)) 48 for increasing convergence, and a handle return. Friction control section (Function (B)) 50 for improving, and And a motor current control unit 52 for performing PI control.

Here, the target motor current I ₀ is expressed by the following equation.
Target motor current I ₀ = Ka (Ts−Pas) + F (A) + F (B)
Where Ka is the assist gain (rate of change in motor current), Ts is the torque sensor value, Pas is the torque value at the assist start point, F (A) is the current value for performing damping control, and F (B) is the friction control. It is a current value for performing. Note that there is a certain relationship between the motor current and the generated torque due to the characteristics of the electric motor.
As described above, in the present embodiment, the control unit 20 performs basic assist control so that the torque sensor value is decreased based on the torque sensor value (steering torque), the vehicle speed, and the like, and the determination & correction unit 46 performs the steering operation. A change in steering stiffness due to variations in the characteristics of the mechanism components is determined, and the basic assist control map stored in accordance with the change is corrected, whereby the electric motor 18 is controlled. The target steering force characteristic can be realized.

Specifically, based on the vehicle speed signal from the vehicle speed sensor 22 and the steering torque signal from the torque sensor 24, the basic assist control unit 20 controls the electric motor 18 so that the torque sensor value becomes small, and the target steering force characteristics. It is for making it become.
Next, the motor rotation angular velocity estimation unit 28 is for estimating the rotation angular velocity and rotation angle of the electric motor. The electric motor 18 is a direct current motor (DC motor), and its motor rotation angular velocity can be estimated from its electromagnetic model (including electric motor current and voltage as parameters). Get. Here, it may be considered that the motor rotation angle multiplied by the reduction ratio of the motor speed reducer substantially corresponds to the steering angle.

The steering rigidity estimation unit 34 will be described with reference to FIGS. The steering stiffness estimator 34 is for estimating the steering stiffness of the steering mechanism in the region near the steering angle center (region A in FIGS. 2 and 5). In the region near the steering angle center (region A in FIGS. 2 and 5), the assist control by the electric motor is not performed (current is not supplied to the electric motor), so the mechanical steering rigidity of the steering mechanism itself is reduced. Can be detected.
Here, the steering rigidity is represented by a change amount of the steering torque with respect to a change of the steering angle, that is, Δtorque sensor value / Δ (motor rotation angle × reduction ratio).
The steering stiffness estimator 34 determines that the region is in the vicinity of the steering angle center (region A in FIGS. 2 and 5) because no motor current (Io) is supplied, and then determines the motor from the electromagnetic model of the motor. The motor rotation angle is calculated by estimating the rotation angular velocity, and the steering rigidity is estimated from the motor rotation angle and the torque sensor value from the torque sensor.
Specifically, as shown in FIG. 5, the steering stiffness estimator 34 detects a steering stiffness value (estimated value), and in FIG. 5, a value different from the stored value (target value) is detected. It has become.

The determination & correction unit 46 determines that the steering stiffness estimated by the steering stiffness estimation unit 34 is estimated in a stable running state, and the difference from the stored target steering stiffness is equal to or greater than a predetermined value. In this case, the stored basic assist control map is corrected.
The steering rigidity referred to here includes not only variations in the characteristics of the parts constituting the steering mechanism but also the effects of tires and road surfaces. Therefore, the steering rigidity changes depending on the road surface μ, the state of tire pressure, friction, vehicle weight, vehicle speed, aging, and the like.
Therefore, in the present embodiment, the determination & correction unit 46 operates the turn SW (blinker) in a state where the vehicle traveling state is stable, for example, the road surface μ is large (on the dry road surface) and in a predetermined vehicle speed band. The accuracy of the steering stiffness change determination is improved by estimating the estimated steering stiffness under a state where the steering speed of the steering wheel is stable, such as changing the lane. The determination & correction unit 46 further determines whether or not the difference between the estimated steering stiffness and the stored steering stiffness is equal to or greater than a predetermined value. As described above, the values of the assist gain (Ka) and the assist start point (Pas) are corrected so that the target steering force characteristics at the time of design are obtained.

Next, a control flow according to the first embodiment will be described with reference to FIG. In FIG. 6, S indicates each step.
This control flow estimates the steering stiffness, and corrects the control map (Ka, Pas) when there is a significant change compared to the pre-stored target steering stiffness (stored value) at the time of design. Is to do.
Here, the target steering stiffness (memory value) stored in advance is set so that an ideal steering feel is obtained under a predetermined condition (steering amount, steering speed, vehicle speed band, road surface condition, etc.) Therefore, it is necessary to estimate the steering stiffness of the vehicle under substantially the same conditions and compare it with the stored value. Here, all the sensors for determining that these conditions are satisfied are already installed in the vehicle, and it is not necessary to provide a new sensor for the present embodiment.

First, in S1, the input value of the sensor described above is updated, and in S2, the motor rotation angular velocity and the motor rotation angle are estimated. Next, in S3, it is determined whether the vehicle speed and the motor rotation angular velocity are within a predetermined range. Here, the vehicle speed is in a high vehicle speed range (about 100 km / h), and the rotational angular velocity means that the vehicle is slowly steered.
Next, in the case of YES in S3, the process proceeds to S4, and it is determined whether or not the steering is a cut from a straight line. The determination condition is that when the motor rotation angle changes, the torque value changes by a predetermined value or more (condition 1), and the target motor current (Io) = 0 (condition 2). Condition 1 is estimated by a torque sensor and a motor rotation angle. Here, as shown in FIG. 4, Condition 2 is determined from the value of the target motor current input to the steering stiffness estimator 34.

Next, in the case of YES in S4, the process proceeds to S5, and it is determined whether or not the turn SW (blinker) is on. Thereby, the situation where the lane is changed on the expressway is determined.
Next, in the case of YES in S5, the process proceeds to S6, and it is determined whether or not the wiper SW is off. As a result, the road surface condition (μ) is estimated, and when the road surface is wet, the load received by the tire is different from the case of the stored value (set when the road surface is dry). In this case, no correction is performed. It is like that.
Next, in the case of YES in S6, the process proceeds to S7, and it is determined whether or not the fluctuation range of the four-wheel wheel speed sensor is within a predetermined range. This is for determining that the road surface is flat. In the case of an irregular road surface, the fluctuation range of the wheel speeds of the four wheels is increased, so that correction is not performed.

Next, in the case of YES in S7, the process proceeds to S8, and it is determined whether or not the vehicle is traveling on the same road as the previous determination. From the NAVI information, it can be determined whether or not the vehicle is traveling on the same road as the previous determination. This is effective for estimating the steering stiffness after deterioration over time or after tire replacement. When determining the steering stiffness for the first time, the determination at this step is omitted.
Next, in the case of YES in S8, the process proceeds to S9, and it is determined whether or not the engine water temperature is equal to or higher than a predetermined value. This is because the steering rigidity needs to be estimated in a traveling situation where the tire is warmed by traveling a certain distance. Further, although the hardware system of the steering mechanism does not change much with temperature, this situation can also be determined when the hardness of the rubber coupling or the like changes with the ambient temperature due to the heat of the engine.
Next, in the case of YES in S9, the process proceeds to S10, and it is determined whether or not a predetermined time or a predetermined distance has elapsed. This step is executed for the same reason as in S9.

Next, in the case of YES in S10, the process proceeds to S11, and in S11, the steering rigidity (Δtorque sensor value / (Δmotor rotation angle × reduction ratio)) is estimated. This steering rigidity is estimated for each lane change.
Next, in S12, it is determined whether or not the absolute value of the difference between the steering stiffness (stored value) stored in advance and the estimated value of steering stiffness estimated in S11 is greater than a predetermined value.
Next, in the case of YES in S12, the process proceeds to S13, and the basic assist control map (specifically, values of Ka and Pas) are corrected. This correction method will be described later in detail with reference to FIG.
Here, the determination of the steering stiffness is performed a plurality of times, and the difference between the stored value and the estimated value is also a plurality, and these values are temporarily stored, and only when there is little variation in these values, the driver can The control map is corrected at low vehicle speeds or while the vehicle is stopped so as not to feel uncomfortable.
Moreover, you may abbreviate | omit the determination in S5-S10 mentioned above. Moreover, you may perform the determination only of the arbitrary steps of S5-S10.

Next, the control map correction in S13 of FIG. 6 will be described in detail with reference to FIGS. 7 is a control flow showing a subroutine of S13 in FIG. 6, FIG. 8 is a diagram showing a steering force characteristic when the assist gain Ka is increased and corrected, and FIG. 9 is a case where the assist gain Ka is corrected and decreased. It is a diagram which shows the steering force characteristic of. In FIG. 7, S indicates each step.
As described above, in the first embodiment, when the difference between the estimated steering stiffness and the previously stored target steering stiffness (target value, stored value) is large, the “maximum steering force” and the “cutting time” The assist gain Ka and the assist start point Pas are corrected so that the “disengagement feeling” (= steering force change rate) is as similar as possible to the stored target value. As a result, the driver can always obtain a good steering feel (target steering feel).

As shown in FIG. 7, first, in S21, it is determined whether or not “stored value−estimated value” is a negative value, and it is determined whether the assist gain should be increased or decreased.
If the stored value minus the estimated value is a negative value, the estimated steering stiffness is greater than the stored value (target value). In this case, as shown in FIG. The force increases (the handle becomes heavier), and the rate of change in steering force also decreases (α1> α0).
In this case, the process proceeds to S22, and as shown in FIG. 8B, the assist gain Ka is increased and corrected, and the steering force change rate is adjusted to the target value (α1 → α0). The reason why the assist gain Ka is first corrected is that the assist gain Ka affects both the steering force change rate and the maximum steering force.
Next, the process proceeds to S23, where it is determined whether or not the steering force change rate obtained by increasing the assist gain Ka is within the target range. If YES, the process proceeds to S24.

In S24, as shown in FIG. 8C, the assist start point Pas is corrected to decrease, and the maximum steering force is adjusted to the target value.
Next, the process proceeds to S25, where it is determined whether or not the maximum steering force obtained by reducing the assist start point Pas is within the target range. If YES, the process proceeds to S26.
Here, since the influence of the estimated steering rigidity on the steering feel is the same in other vehicle speed ranges, the assist gain Ka and the assist parameters, which are control parameters in the high vehicle speed range (about 100 km / h) obtained here, are provided. The correction amount of the start point Pas is also determined by linear interpolation or the like for the control parameters of the low speed side area (60 km / h to 100 km / h) and the high speed side area (100 km / h to 120 km / h), which are other vehicle speed ranges. Apply.

If it is determined in S25 that the maximum steering force is not within the target range, the process proceeds to S27, in which it is determined whether or not the assist start point Pas has reached the lower limit value. Returns to S24 and further corrects the assist start point to decrease.
If it has reached the lower limit value, the process proceeds to S28, and as shown in FIG. 8D, the assist gain Ka is further corrected for correction (α2 <α0). This is because, when the weight is appropriate, the steering feel is better, and therefore priority is given to matching the maximum steering force to the target value rather than the steering force change rate.
Next, in S29, it is determined whether or not the maximum steering force is within the target range. If it is not within the target range, the process returns to S28, and the assist gain Ka is further corrected for increase.
Here, the reason why the lower limit value is set for the assist start point Pas is that if the assist is started immediately after the start of steering, the vehicle may become unstable, and a good steering feel cannot be obtained. .

Furthermore, if it is determined in S23 that the steering force change rate is not within the target range, the process proceeds to S30, where it is determined whether or not the assist gain Ka has reached the upper limit value. Returns to S22 and further increases the assist gain.
If the upper limit value has been reached, the process proceeds to S31 and the correction is stopped.
Here, the upper limit value is set for the assist gain Ka because if the assist gain Ka is too large, the feeling of slipping during cutting becomes too large, the steering feel deteriorates, and it becomes difficult to drive.
If the assist gain reaches the upper limit, the correction is canceled at the maximum assist gain, and if the assist start point is further decreased, the vehicle may become unstable, and a good steering feel can be obtained. It is because it cannot be obtained.

Further, when it is determined in S21 that “stored value−estimated value” is not a negative value, the estimated steering stiffness is smaller than the stored value (target value). As shown in FIG. 9 (A), the maximum steering force becomes smaller (the handle becomes lighter), and the steering force change rate also becomes larger (α3 <α0).
In this case, the process proceeds to S32, and as shown in FIG. 9B, the assist gain Ka is corrected to decrease, and the steering force change rate is adjusted to the target value (α3 → α0).
Next, in S33, it is determined whether or not the steering force change rate obtained by correcting the assist gain Ka to decrease is within the target range. If not, the process proceeds to S34, where the assist gain Ka is set. It is determined whether or not the lower limit value (Ka = 0). If the answer is NO in S34, the process returns to S32, and the assist gain Ka is corrected to decrease. If YES, the process proceeds to S26.

If YES in S33, the process proceeds to S35, and as shown in FIG. 9C, the assist start point Pas is increased and the maximum steering force is adjusted to the target value.
Next, in S36, it is determined whether or not the maximum steering force obtained by increasing the assist start point Pas is within the target range. If YES, the process proceeds to S26.
If it is determined NO in S36, the process proceeds to S37, in which it is determined whether or not the assist start point Pas has reached the upper limit value. If the upper limit value has not been reached, the process returns to S35, and further , Increase the assist start point. If the upper limit value has been reached, the process proceeds to S31 and the correction is stopped. Here, when the assist start point Pas reaches the upper limit value, the correction is stopped because it is not necessary to adjust the steering feel in the “center feel sensitive area”.

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 10 is a block diagram showing a control unit of the electric power steering apparatus according to the second embodiment of the present invention, FIG. 11 is a diagram showing a target steering force characteristic and a calculated steering force characteristic, and FIG. 12 is a target steering force characteristic. FIG. 13 shows a control flow according to the second embodiment.
In the second embodiment, when the control map is corrected in the first embodiment described above, the assist gain Ka and the assist start point Pas cannot be adjusted under some condition or due to other restrictions, or When only Ka and Pas are adjusted, the friction compensation gain Kc is adjusted when the target steering force characteristic cannot be obtained.
The friction compensation control (adjustment of the friction compensation gain Kc) according to the second embodiment determines the rising value of the steering force when the vehicle is cut straight ahead, and if the rising value is larger than the stored value (target value), the steering is performed. This means that the equivalent friction around the steering wheel of the system is large. Therefore, it is necessary to increase the assist amount of the electric motor. Therefore, the friction compensation gain is corrected to increase, and conversely, the rising value is the stored value (target value). If it is smaller, it is necessary to reduce the assist amount of the electric motor, so the friction compensation gain is corrected to decrease so that the target maximum steering force is felt.

Here, in the control unit shown in FIG. 10, the same parts as those of the control unit 20 of the first embodiment shown in FIG.
As shown in FIG. 10, the control unit 60 includes a basic assist control unit 26 that receives a vehicle speed signal from the vehicle speed sensor 22 and a steering torque signal from the torque sensor 24, and a voltage signal and current from the electric motor 18. Motor rotation angular velocity estimation unit 28 that receives signals, ignition (IG) 30, memory unit 32 that stores steering friction at the time of design, steering force rise value calculation unit 62, turn SW (winker) 44, steering force rise value calculation A determination and correction unit 64 that receives a signal from the unit 62, a damping control unit (Function (A)) 48 for improving convergence, a friction compensation control unit 66 for improving the stability of the steering wheel, and PI A motor current control unit 52 that performs control is provided.

Here, in the second embodiment, the target motor current I ₀ is expressed by the following equation.
Target motor current I ₀ = Ka (Ts−Pas) + F (A) + Kc * sign (θ ′)
Where Ka is the assist gain (motor current change rate), Ts is the torque sensor value, Pas is the torque value at the assist start point, F (A) is the current value for performing damping control, Kc is the friction compensation gain, and θ ′ Is the motor rotation angular velocity. Note that there is a certain relationship between the motor current and the generated torque due to the characteristics of the electric motor.
As described above, in this embodiment, the control unit 60 reduces the detection value of the torque sensor based on the torque sensor value (steering torque), the vehicle speed, and the like, and the determination & correction unit 64 determines the steering mechanism. A change in equivalent friction around the steering wheel of the steering system due to variations in component characteristics is determined, and a friction compensation control map (friction compensation gain Kc) is corrected in accordance with the change amount. As a result, the target steering force characteristic can be realized.

Here, in FIG. 11, the solid line indicates the target steering force characteristic that is the stored target value, and the broken line indicates the steering force characteristic that is the calculated value calculated this time.
The steering force rise value calculation unit 62 will be described with reference to FIG. When the driver cuts the steering wheel from the straight traveling state, the steering force rises as shown in FIG. E and E ′ indicate rising values of the steering force. This rising value is calculated when the torque value changes by a predetermined value or more when the motor rotation angle changes.
The determination & correction unit 64 determines whether or not the calculated steering force rise value E ′ is different from the rise value E of the target value by a predetermined value or more. The gain Kc is corrected to increase, and if it is smaller than the target value E, the friction compensation gain Kc is corrected to decrease.
11 and 12, since the calculated steering force rise value E ′ is larger than the target value E, the friction compensation gain Kc is corrected to increase (Kc1 → Kc2), and the steering force characteristic is the same as the target steering force characteristic. An example is shown.

Next, a control flow according to the second embodiment will be described with reference to FIG. In FIG. 13, S indicates each step.
In this control flow, the steering force rise value is calculated, and when the calculated value and the steering force rise value (stored value) stored in advance are greatly changed, the friction compensation control parameter is used. This is for correcting a certain friction compensation gain Kc.
First, in S41, the input value of the sensor described above is updated, and in S42, it is determined whether or not the turn SW (turn signal) shifts from OFF to ON and the vehicle speed is within a predetermined range. Specifically, a situation in which a lane change is made on an expressway is determined. Here, the vehicle speed is in a high vehicle speed range (about 100 km / h).
Here, in the first embodiment, in S6 to S10 (excluding S5) in FIG. 6, the steering state and the traveling state of the vehicle are determined based on other conditions, but also in the second embodiment, The steering state and the traveling state may be determined under similar conditions or by any combination of these conditions.

Next, the process proceeds to S43, and the rising value of the steering force is calculated. When the steering wheel is turned from the state determined in S42, that is, when the steering wheel is turned straight, when the motor rotation angle changes and the torque value changes by a predetermined value or more, the torque value is calculated as the rising value of the steering force.
Next, in S44, it is determined whether or not the absolute value of the difference between the stored value (target value) of the steering force rise value and the calculated value is greater than a predetermined value.
If larger, the process proceeds to S45, and the friction compensation gain Kc, which is a friction compensation control parameter, is corrected (see FIG. 12). In S45, the stored value of the rising value of the steering force and the magnitude of the calculated value are further determined. If the calculated value is larger than the stored value, the friction compensation gain Kc is corrected to increase, and the calculated value is stored. If it is smaller, the friction compensation gain Kc is corrected to decrease.

Here, the determination of the rising value of the steering force is performed a plurality of times, and there are a plurality of differences between the stored value and the estimated value, and these values are temporarily stored, and only when there is little variation in these values. The friction compensation control map (friction compensation gain Kc) is corrected at low speed or while the vehicle is stopped so that the driver does not feel uncomfortable.
Next, the process proceeds to S46. Since the tendency of the rising value of the steering force calculated in S43 is substantially the same in other vehicle speed ranges, the friction compensation gain Kc corrected for increase in the high vehicle speed range (about 100 km / h) obtained here is The present invention is also applied to other vehicle speed regions, such as a low speed side region (60 km / h to 100 km / h) and a high speed side region (100 km / h to 120 km / h) by linear interpolation or the like.

Next, a third embodiment of the present invention will be described with reference to FIGS. FIG. 14 is a block diagram showing a control unit of an electric power steering apparatus according to a third embodiment of the present invention, FIG. 15 is a diagram showing an example of target steering force characteristics, and FIG. 16 is a friction compensation control according to the third embodiment. A diagram showing a map (friction compensation gain Kc), FIG. 17 is a control flow according to the third embodiment.
In the third embodiment, when the target steering force characteristic cannot be obtained by the correction of the control map of the first embodiment and / or the second embodiment described above, further friction compensation control is executed. It is.
In the friction compensation control according to the third embodiment, a torque sensor value (equivalent friction around the steering system steering wheel at the time of turning back) is calculated when the driver turns back the steering wheel, and this torque sensor value is stored in advance. When the deviation from the torque sensor value (target value) at the time of switching back is large, the friction compensation control map (friction compensation gain Kc) is corrected to obtain the target steering force characteristic.

Here, in the control unit shown in FIG. 14, the same parts as those in the control unit 20 of the first embodiment shown in FIG.
As shown in FIG. 14, the control unit 70 receives the vehicle speed signal from the vehicle speed sensor 22 and the steering torque signal from the torque sensor 24, and the voltage signal and current from the electric motor 18. A motor rotation angular velocity estimation unit 28 that receives signals, an ignition (IG) 30, a memory unit 32 that stores steering friction at the time of steering wheel return at the time of design, various sensors (navigation device 36, wiper SW 38, engine water temperature sensor 40 , Wheel speed sensor 41, turn SW 44), steering friction calculation unit 72, determination & correction unit 74 that receives a signal from the steering friction calculation unit 72, and damping control unit (Function (A)) 48 for increasing convergence. , Friction compensation control unit 76, and motor current control unit 52 for performing PI control. It is.

Here, in the third embodiment, the target motor current I ₀ is expressed by the following equation (the same as the equation in the second embodiment).
Target motor current I ₀ = Ka (Ts−Pas) + F (A) + Kc * sign (θ ′)
Where Ka is the assist gain (motor current change rate), Ts is the torque sensor value, Pas is the torque value at the assist start point, F (A) is the current value for performing damping control, and Kc is the friction compensation gain (torque value). ), Θ ′ is the motor rotation angular velocity. Note that there is a certain relationship between the motor current and the generated torque due to the characteristics of the electric motor.
As described above, in the present embodiment, the control unit 70 reduces the detection value of the torque sensor based on the torque sensor value (steering torque), the vehicle speed, and the like, and the determination & correction unit 74 determines the steering mechanism. A change in the steering friction at the time of turning back the steering wheel due to a variation in the characteristics of the parts is determined, and the friction compensation gain Kc is corrected in accordance with the change amount, whereby the electric motor 18 is controlled, and as a result, the target A steering force characteristic can be realized.

Here, when the driver's handle is turned back (point D and point F in FIG. 15), the motor rotation angle (steering angle) is the same, and the motor current value does not change (region G in FIG. 15). Even when the motor current value is constant, the magnitude of the steering friction (equivalent friction around the steering wheel of the steering system) in the switching region (near point F in FIG. 15) is different.
Therefore, in this embodiment, the steering friction calculation unit 72 determines the steering switchback time point on the condition that “the motor current change≈0” and “the rotation direction of the electric motor is reversed” without providing the steering angle sensor. The steering friction at that time is determined from the torque sensor value, and the determination & correction unit 74 deviates between the calculated steering friction (calculated value) and the previously stored steering friction (design value, stored value). When the deviation is large, the friction compensation gain Kc is corrected.
Further, in the third embodiment, similarly to the first embodiment, the stored value (target value) is set so that an ideal steering feel is obtained under a predetermined condition (vehicle speed, road surface, etc.). The steering friction is calculated under substantially the same conditions, and is compared with values stored in advance (design value, target value, stored value).

Next, a control flow according to the third embodiment will be described with reference to FIG. In FIG. 17, S indicates each step.
In this control flow, the steering friction at the time of turning back the steering wheel is calculated, and when there is a large change compared with the value stored in advance (memory value), the friction compensation control map (friction compensation gain) This is for correcting Kc).
First, in S51, the input value of the sensor described above is updated. In S52, whether the vehicle speed is within a predetermined range, the target motor current change≈0 (the current value is substantially constant), and whether the motor rotation direction is reversed. Determine whether or not. Here, the vehicle speed is in a high vehicle speed range (about 100 km / h).
Next, in the case of YES in S52, the process proceeds to S53, and it is determined whether or not the turn SW (blinker) is on. Thereby, the situation where the lane is changed on the expressway is determined.
Next, in the case of YES in S53, the process proceeds to S54 and it is determined whether or not the wiper SW is off. As a result, the road surface condition μ is estimated, and when the road surface is wet, the load received by the tire is different from the stored value (set when the road surface is dry). In this case, the correction is not performed. It has become.

Next, in the case of YES in S54, the process proceeds to S55, and it is determined whether or not the fluctuation range of the four-wheel wheel speed sensor is within a predetermined range. This is for determining that the road surface is flat. When the road surface is rough, the fluctuation range of the wheel speeds of the four wheels becomes large. Therefore, in such a traveling state, correction is not performed.
Next, in the case of YES in S55, the process proceeds to S56, and it is determined whether or not the vehicle is traveling on the same road as the previous determination. From the NAVI information, it can be determined whether or not the vehicle is traveling on the same road as the previous determination. This is effective when estimating steering friction after deterioration over time or after tire replacement. When the steering friction is determined for the first time, the determination at this step is omitted.
Next, in the case of YES in S56, the process proceeds to S57, and it is determined whether or not the engine water temperature is equal to or higher than a predetermined value. This is because the steering friction needs to be estimated in a traveling state where the tire is warmed by traveling a certain distance. Further, although the hardware system of the steering mechanism does not change much with temperature, this situation can also be determined when the hardness of the rubber coupling or the like changes with the ambient temperature due to the heat of the engine.
Next, in the case of YES in S57, the process proceeds to S58, and it is determined whether or not a predetermined time or a predetermined distance has elapsed. This step is executed for the same reason as S57.

Next, in the case of YES in S58, the process proceeds to S59, and the steering friction (steering torque) at the time of turning back the steering wheel determined in S52 is estimated from the torque sensor value. As this torque sensor value, the torque sensor value when the motor current becomes substantially constant is used. That is, in S59, the steering friction is estimated from the torque sensor value (a decrease amount in the region G in FIG. 15) when the current value of the electric motor is substantially constant (target motor current change≈0). . Note that the difference in torque value between the steering angle and the steering angle when the steering angle is the same (when the motor current is the same) may be estimated as the steering friction. This steering friction is estimated at every lane change.
Next, in S60, it is determined whether or not the absolute value of the difference between the stored value (target value) of steering friction stored in advance and the calculated value of steering friction calculated in S59 is greater than a predetermined value.
Next, in the case of YES in S60, the process proceeds to S61, and the friction compensation gain Kc is corrected.
Specifically, regarding the steering friction, when the calculated value is larger than the stored value, the value of the friction compensation gain Kc shown in FIG. 16 is corrected to be increased. When the calculated value is smaller than the stored value, the friction compensation is performed. The value of the gain Kc is corrected to decrease.

Here, the calculation of the steering friction is performed a plurality of times, and the difference between the stored value and the estimated value becomes a plurality of values. These values are temporarily stored, and only when there is little variation in these values, the vehicle is stopped. During this, the friction compensation control map (friction compensation gain Kc) is corrected. Correcting during traveling is not preferable because the steering force characteristic changes during traveling and the driver feels uncomfortable.
The determinations in S53 to S58 described above may be omitted. Moreover, you may perform determination only of the arbitrary steps of S53-S58.
Here, since the tendency of the steering friction calculated in S59 is the same in other vehicle speed ranges, the correction amount of the friction compensation gain Kc, which is a control parameter in the high vehicle speed range (about 100 km / h) obtained here. Is also applied to control parameters of other vehicle speed ranges, such as a low speed side region (60 km / h to 100 km / h) and a high speed side region (100 km / h to 120 km / h) by linear interpolation or the like.

Next, a fourth embodiment of the present invention will be described with reference to FIGS. 18 is a block diagram showing a control unit of an electric power steering apparatus according to a fourth embodiment of the present invention, FIG. 19 is a diagram showing a steering force characteristic, and FIG. 20 is a basic assist control map for obtaining a target steering force characteristic ( Assist gain Ka, assist start point Pas), FIG. 21 is a friction compensation control map (friction compensation gain Kc) for obtaining target steering force characteristics, FIG. 22 is a control flow according to the fourth embodiment, and FIG. 23 is target steering force characteristics. Another control map for obtaining
In the fourth embodiment, when the vehicle speed is within a predetermined value range (predetermined high vehicle speed region) and a slow lane change is performed, the maximum steering force is obtained from the torque sensor after turning on the turn SW (winker). The steering force change rate is calculated from the relationship between the motor rotation angle and the torque sensor, and the steering force hiss (≈ friction) is calculated from the torque sensor when the turn SW changes from ON to OFF (ON → OFF). When the calculated value has a large deviation from each of the previously stored values (target steering force characteristics), the steering start point is set for the maximum steering force, the assist gain is set for the steering force change rate, and the steering is made in accordance with this deviation. Regarding the force hiss, the friction compensation gain is mainly corrected.

Here, in the control unit shown in FIG. 18, the same parts as those in the control unit 20 of the first embodiment shown in FIG.
As shown in FIG. 18, the control unit 80 includes a basic assist control unit 26 that receives a vehicle speed signal from the vehicle speed sensor 22 and a steering torque signal from the torque sensor 24, and a voltage signal and current from the electric motor 18. Motor rotation angular velocity estimation unit 28 that receives signals, ignition (IG) 30, memory unit 32 that stores target steering force characteristics, turn SW 44, steering force characteristic calculation unit (steering force characteristics: maximum steering force, steering force change rate) , Steering force hiss) 82, a determination & correction unit 84 that receives a signal from the steering force characteristic calculation unit, a damping control unit (Function (A)) 48 for increasing convergence, a friction compensation control unit 86, and A motor current control unit 52 that performs PI control is included.

Here, in the third embodiment, the target motor current I ₀ is expressed by the following equation (the same as the equations in the second and third embodiments).
Target motor current I ₀ = Ka (Ts−Pas) + F (A) + Kc * sign (θ ′)
Where Ka is the assist gain (motor current change rate), Ts is the torque sensor value, Pas is the torque value at the assist start point, F (A) is the current value for performing damping control, and Kc is the friction compensation gain (torque value). ), Θ ′ is the motor rotation angular velocity. Note that there is a certain relationship between the motor current and the generated torque due to the characteristics of the electric motor.
As described above, in the present embodiment, the control unit 80 reduces the torque sensor detection value based on the torque sensor detection value (steering torque), the vehicle speed, and the like. The maximum steering force, the rate of change in steering force, and the value of the steering force hiss that change due to variations in the characteristics of the components of the mechanism are determined, and the assist start point Pas, the assist gain Ka, and the friction compensation gain are determined according to the amount of change. The electric motor 18 is controlled by correcting Kc, and as a result, the target steering force characteristic can be realized.

Here, the steering force change rate, the maximum steering force, and the steering force hiss will be described with reference to FIG. In the fourth embodiment, the “steering force change rate” is the same as that in the first embodiment described above. As shown in FIG. 19, “the region from the start of turning the steering wheel to the predetermined steering force” The ratio of “the increase ratio of the steering force with respect to the increase in the steering angle in the region C where the predetermined steering force is greater than or equal to the ratio of the increase in the steering force with respect to the increase in the steering angle in A”, and a predetermined ratio (0.3 To 0.5).
The “maximum steering force” is the same as that in the first embodiment, and as shown in FIG. 19, the driver feels the steering force felt when the steering wheel turning amount (steering amount) becomes maximum (point D). Yes, the value of the maximum steering force is also set to a desired value.
As shown in FIG. 19, “steering force hiss” is steering friction (equivalent friction around the steering wheel of the steering system) when the driver turns back the steering wheel (region G). When the steering friction is large, the amount of decrease in the steering torque in the region G increases. Therefore, if the steering force hiss is too large (the amount of decrease in the steering torque in the region G is too large), the steering wheel feels bad.

Next, the target steering force characteristics (steering force change rate and maximum steering force) can be obtained from the basic assist control map shown in FIG. That is, as shown in FIG. 19 and FIG. 20, in the region A where the steering force increases from the start of the turning of the steering wheel, the motor current is not supplied to the electric motor 18 and is a dead zone region, resulting in a predetermined steering force. At the point B, the supply of the motor current to the electric motor 18 is started. A point in FIG. 20 corresponding to the point B in FIG. 19 is an assist start point (Pas). When the handle is further turned from this point B, the motor current is supplied to the electric motor 18 at a current increase rate determined by the assist gain (Ka). The steering force change rate can be adjusted by correcting the assist gain (Ka) value.
In addition, after adjusting the steering force change rate with the assist gain Ka, the value of the maximum steering force can be adjusted by correcting the value of the assist start point Pas.

Next, the target steering force characteristic (steering force hiss) can be obtained from the friction compensation control map shown in FIG. That is, when the steering force hiss is larger than the stored value (target value), it is necessary to increase the assist amount of the electric motor. Therefore, the friction compensation gain Kc is corrected to be increased. If the value is smaller than the target value), it is necessary to reduce the assist amount of the electric motor. Therefore, the friction compensation gain is corrected to decrease so that the steering wheel feels good.
The steering force characteristics (maximum steering force, steering force change rate, steering force hiss) change due to load fluctuations and changes over time in addition to variations in the characteristics of the components of the steering mechanism. It is necessary to correct at a predetermined timing.

Next, a control flow according to the fourth embodiment will be described with reference to FIG. In FIG. 22, S indicates each step.
This control flow calculates the maximum steering force, the steering force change rate, and the steering force hiss when the vehicle speed is within a predetermined value range and a slow lane change is performed. When the deviation from the stored target value (stored value) is large, the assist start point Pas, the assist gain Ka, and the friction compensation gain Kc are corrected according to the magnitude of the deviation to obtain the target steering force characteristic. It is.
First, in S71, the input value of the sensor described above is updated, and in S72, it is determined whether or not the vehicle speed is within a predetermined range. Specifically, the vehicle speed is a high vehicle speed range (about 100 km / h).

Next, when the vehicle speed is within the predetermined range, the process proceeds to S73 to determine whether or not the driver's steering state is a slow lane change. Specifically, the turn SW OFF → ON → OFF time is within a predetermined time, the motor rotation angular velocity is a slow steering speed, and the width of the lane change calculated from the total motor rotation angle change amount is within a predetermined value. In this case, it is determined that the lane change is slow.
Next, in the case of YES in S73, the process proceeds to S74, and the maximum steering force, the steering force change rate, and the steering force hiss are calculated. The maximum steering force is calculated from the torque sensor value (torque sensor value at point D in FIG. 19). The steering force change rate is calculated from the motor rotation angle and the torque sensor value (regions A and C in FIG. 19). The steering force hiss is calculated from the torque sensor value (region G in FIG. 19).

Next, in S75, it is determined whether or not the absolute value (| stored value−calculated value |) of the difference between the stored value of the steering force hysteresis and the calculated value is larger than a predetermined value.
If YES in S75, the process proceeds to S76, and the friction compensation gain Kc is proportionally corrected. Specifically, when the calculated value of the steering force hiss is larger than a pre-stored target value (stored value) by a predetermined value or more, the friction compensation gain Kc is increased and corrected to obtain the target steering force hiss. On the other hand, when the calculated value of the steering force hiss is smaller than the target value (stored value) stored in advance by a predetermined value or more, the friction compensation gain Kc is corrected to decrease to obtain the target steering force hiss.

Next, in S77, it is determined whether or not the absolute value (| stored value−calculated value |) of the difference between the stored value of the steering force change rate and the calculated value is greater than a predetermined value.
If YES in S77, the assist gain Ka is corrected in inverse proportion. Specifically, when the calculated value of the steering force change rate is greater than a target value (stored value) stored in advance by a predetermined value or more, the assist gain Ka is corrected to decrease to obtain the target steering force change rate. On the contrary, when the calculated value of the steering force change rate is smaller than the target value (stored value) stored in advance by a predetermined value or more, the assist gain Ka is increased and corrected to obtain the target steering force change rate. Further, an upper limit value is set in advance for the assist gain Ka, and when the assist gain Ka is larger than the upper limit value, the assist gain Ka is not corrected. This is because if the assist gain Ka is too large, the vehicle may become unstable, and a good steering feel cannot be obtained.

Next, in S79, it is determined whether or not the absolute value (| stored value−calculated value |) of the difference between the stored value of the maximum steering force and the calculated value is larger than a predetermined value.
If YES in S79, the assist start point Pas is corrected in inverse proportion. Specifically, when the calculated value of the maximum steering force is greater than a predetermined value (stored value) stored in advance by a predetermined value or more, the assist start point Pas is corrected to decrease to obtain the target maximum steering force. On the other hand, when the calculated value of the maximum steering force is smaller than the target value (stored value) stored in advance by a predetermined value or more, the assist start point Pas is increased and corrected so as to obtain the target maximum steering force. In addition, a lower limit value is set in advance for the assist start point Pas, and when the assist start point Pas is smaller than the lower limit value, the assist start point decrease correction is stopped and the assist gain Ka is increased instead.

Here, the calculation of the steering force hiss, the rate of change of the steering force, and the maximum steering force is performed a plurality of times, and there are also a plurality of differences between the stored value and the estimated value, and these values are temporarily stored. The control map (friction compensation gain Kc, assist gain Ka, assist start point Pas) is corrected during low vehicle speed or when the vehicle is stopped so that the driver does not feel uncomfortable only when there is little variation in values.
Next, it progresses to S81 and the parameter correction of the other vehicle speed area is performed. Since the tendency of the steering force hiss, the steering force change rate, and the maximum steering force calculated in S74 is the same in other vehicle speed ranges, the control parameter (Kc) in the high vehicle speed range (about 100 km / h) obtained here is used. , Ka, Pas), and other vehicle speed regions, such as low speed side region (60 km / h to 100 km / h) and high speed side region (100 km / h to 120 km / h) by linear interpolation, etc. Apply.
Here, in the control flow shown in FIG. 22, the friction compensation gain Kc (steering force hiss), the assist gain Ka (steering force change rate), and the assist start point Pas (maximum steering force) are corrected in this order. You may make it correct | amend in order of the gain Ka (steering force change rate), the friction compensation gain Kc (steering force hiss), and the assist start point Pas (maximum steering force).

Next, a modification of the fourth embodiment will be described with reference to FIG. FIG. 23 is a control map (handle return compensation gain Kw) showing the relationship between the target motor current Io and the torque sensor value according to a modification of the fourth embodiment. In this modification, the control map shown in FIG. 23 is used instead of the control map shown in FIGS.
As shown in FIG. 23, in this control map, the target motor current Io is offset (Kw: steering wheel return compensation gain) when the steering wheel is cut back (region J) and back (region M) (point K and point L). I am letting. With this offset, when the steering wheel is turned back, the target motor current Io being controlled does not become zero, and the steering force hysteresis changes.
Therefore, in this modified example, when the absolute value (| stored value−calculated value |) of the difference between the stored value and the calculated value of the steering force hiss is larger than a predetermined value, the steering wheel return compensation gain Kw is proportionally corrected.
Furthermore, as another modified example of the fourth embodiment, when the steering force hiss is greatly different from the target value, the hysteresis (input processing hiss) is added to the input characteristic of the torque value input from the torque sensor to the control unit 80. The torque sensor hysteresis (input processing hysteresis) may be inversely corrected.

Next, a fifth embodiment of the present invention will be described with reference to FIG. 18, FIG. 24 and FIG. The control unit of the fifth embodiment is the same as the control unit of the fourth embodiment shown in FIG. 24 and 25 show a control flow according to the fifth embodiment.
The fifth embodiment of the present invention first estimates (calculates) a change in the steering force characteristic of the steering mechanism in a factory inspection process at the time of vehicle shipment, and the estimated value and the target steering force characteristic (target value, ie, The control parameters of the control map (assist gain, assist start point, friction compensation gain) are corrected according to the deviation from the design value), and after shipment, the vehicle speed is within a predetermined value range (predetermined high vehicle speed range) When a slow lane change is performed, control parameters (assist gain, assist start point, friction compensation gain) of the control map are set at predetermined timings (vehicles) according to the deviation from the target steering force characteristic (target value). This is corrected when the vehicle is stopped. Here, the actual steering force characteristic is different from the target steering force characteristic (target value) at the time of design due to variations in the characteristics of steering components during mass production of the vehicle, fluctuations in the load acting on the steering mechanism, and changes over time. Although greatly different, according to the fifth embodiment, changes (deviations) due to variations in the characteristics of steering components are mainly corrected in the inspection process, and changes (deviations) due to load fluctuations and changes with time are mainly post-shipment. Thus, the target steering force characteristic at the time of design can be obtained.

  Here, as shown in FIG. 18, the control unit 80 of the fifth embodiment includes a basic assist control unit 26 that receives a vehicle speed signal from the vehicle speed sensor 22 and a steering torque signal from the torque sensor 24, Motor rotation angular velocity estimation unit 28 that receives voltage signal and current signal from motor 18, ignition (IG) 30, memory unit 32 that stores target steering force characteristic, turn SW 44, steering force characteristic calculation unit (steering force characteristic: Maximum steering force, rate of change of steering force, steering force hysteresis) 82, determination & correction unit 84 which receives a signal from the steering force characteristic calculation unit, a damping control unit (Function (A)) 48 for increasing convergence, A friction compensation control unit 86 and a motor current control unit 52 that performs PI control are included.

Here, also in the fifth embodiment, the target motor current I ₀ is expressed by the following equation (the same as the equations in the second to fourth embodiments).
Target motor current I ₀ = Ka (Ts−Pas) + F (A) + Kc * sign (θ ′)
Where Ka is the assist gain (motor current change rate), Ts is the torque sensor value, Pas is the torque value at the assist start point, F (A) is the current value for performing damping control, and Kc is the friction compensation gain (torque value). ), Θ ′ is the motor rotation angular velocity. Note that there is a certain relationship between the motor current and the generated torque due to the characteristics of the electric motor.
As described above, in the present embodiment, the control unit 80 reduces the torque sensor detection value based on the torque sensor detection value (steering torque), the vehicle speed, and the like. The maximum steering force, the rate of change of steering force, and the value of steering force hiss that change due to variations in the characteristics of the mechanical components are determined, and the assist start point Pas, assist gain Ka, and friction compensation gain Kc are corrected. Thus, the electric motor 18 is controlled, and as a result, a target steering force characteristic can be realized.

Next, a control flow according to the first example of the fifth embodiment will be described with reference to FIG. In the first example of the fifth embodiment, the steering force characteristic is calculated in the inspection process of the factory to correct the control map, and the steering force characteristic is calculated by a slow lane change within a predetermined range of the vehicle speed. The control map is corrected when the vehicle stops. In FIG. 24, S indicates each step.
First, in S91, the sensor input value described above is updated, and in S92, it is determined whether or not it is an inspection process at the time of vehicle shipment. This inspection process may be an inspection process at a service station or the like after vehicle shipment, other than at the time of vehicle shipment.
If it is an inspection process, it will progress to S93 and will calculate a steering force characteristic. The calculated steering force characteristics are the steering hysteresis, the steering force change rate, and the maximum steering force described in the fourth embodiment. In the inspection process, an inspection signal is input, and the steering force characteristic is estimated (calculated) from the motor rotation angle and the torque sensor value. Specifically, the maximum steering force is calculated from the torque sensor value (torque sensor value at point D in FIG. 19). The steering force change rate is calculated from the motor rotation angle and the torque sensor value (regions A and C in FIG. 19). The steering force hiss is calculated from the torque sensor value (region G in FIG. 19).

Next, proceeding to S94, the absolute value (| target value−calculated value |) of the deviation between the calculated value calculated in S93 and the target value that is the target steering force characteristic (design value) is equal to or greater than the first predetermined value. 2. It is determined whether or not it is less than a predetermined value. This is because if it is less than the first predetermined value, there is no need for correction, and if it is larger than the second predetermined value, it is necessary to replace the component because the characteristic variation of the component is equal to or greater than the assumed value.
If YES in S94, the process proceeds to S95 to correct the assist gain, assist start point, and friction compensation gain of the control map. This correction method is the same as in the fourth embodiment. In addition, when correcting when the vehicle stops, which will be described later, an upper limit value is defined for the correction amount (see S106), and correction is performed so that one correction amount does not exceed this upper limit value. There is no need to set an upper limit value, and the correction is performed once. Since the correction is performed during the inspection process, even when the correction amount is large, the problem described later (the driver feels uncomfortable when the correction amount at one time is large) does not occur.
In the inspection step of S93 described above, the assist control by the electric motor is stopped by inputting the inspection signal, and the change in the steering rigidity due to the variation in the characteristics of the components of the steering mechanism is determined as in the first embodiment, The basic assist control map (assist gain Ka, assist start point Pas) stored according to the change amount may be corrected.

Next, in S92, in the case of NO, the process proceeds to S96 and it is determined whether or not the ignition is turned on. In the case of YES, since the vehicle is running, the process proceeds to S97, and it is determined whether or not the vehicle speed is within a predetermined range. Specifically, the vehicle speed is a high vehicle speed range (about 100 km / h).
If YES in step S97, the process advances to step S98 to determine whether or not the driver's steering state is a slow lane change. Specifically, the turn SW OFF → ON → OFF time is within a predetermined time, the motor rotation angular velocity is a slow steering speed, and the width of the lane change calculated from the total motor rotation angle change amount is within a predetermined value. In this case, it is determined that the lane change is slow.
When the vehicle speed is within the predetermined range and the lane change is slow, the process proceeds to S99, and steering force characteristics (maximum steering force, steering force change rate, steering force hiss) are calculated. In step S100, the calculated steering force characteristic is stored as a stored value.
Here, S96 to S100 are executed a plurality of times during traveling of the vehicle, and several stored values are stored.

Next, in the case of NO in S96, since the vehicle is stopped, the process proceeds to S101, and it is determined whether or not the variation of the plurality of stored values stored in S100 is equal to or less than a predetermined value. If it is equal to or smaller than the predetermined value, the process proceeds to S102, and an average value of a plurality of stored values is calculated.
Next, the process proceeds to S103, and whether the absolute value (| target value−stored value |) of the deviation between the stored value, which is the average value of the steering force characteristic, and the target value is not less than the first predetermined value and not more than the second predetermined value. Determine whether or not. If it is less than the first predetermined value, there is no need for correction, and if it is larger than the second predetermined value, it is not preferable to correct it because the load fluctuation is greater than the value assumed due to running on an irregular road surface. It is.
If YES in S103, the process proceeds to S104, and the deviation (| previously stored value−stored value) between the previously stored value (the previously corrected control map value) and the stored value (average value of the currently calculated stored value). It is determined whether or not | If the deviation between the two is larger than a predetermined value, the stored value (average value of the stored value calculated this time) may have been calculated in an unexpected driving state. This is because it is considered that the target value cannot be obtained if the correction is made.

In the case of YES in S104, the process proceeds to S105, and the control map change amount is calculated. Specifically, the maximum steering force, the steering force change rate, and the change amount of the steering force hiss, which are control parameters of the steering force characteristic, are calculated.
Next, the process proceeds to S106, where it is determined whether or not the absolute value of the change amount of the control map is equal to or greater than the upper limit value. In the case of YES, the process proceeds to S107, where the upper limit value is applied as the correction amount, and in S109, the control map is corrected by the upper limit value. If NO in S106, the process proceeds to S108, where the calculated value that is the change amount is applied as the correction amount, and the control map is corrected by the change amount in S109. Here, the upper limit value is provided because the driver feels uncomfortable with the steering feel when the correction amount to be corrected at one time is large. Therefore, in order to prevent this, the upper limit value is set so that the driver does not feel uncomfortable. Is set to correct the control parameter of the control map.

Next, a control flow according to the second example of the fifth embodiment will be described with reference to FIG. In the second example of the fifth embodiment, the steering force characteristic is calculated in the inspection process of the factory to correct the control map. Further, the steering force characteristic is calculated by a slow lane change within a predetermined vehicle speed range, and the vehicle travels. The control map is corrected. In FIG. 25, S indicates each step.
In the control flow of FIG. 25, steps related to correction of the control map in the inspection process shown in FIG. 24 are omitted.
First, in S111, the input value of the sensor described above is updated. In S112, it is determined whether or not the vehicle speed is greater than a predetermined value, and it is determined whether or not the vehicle is traveling in a predetermined low vehicle speed range. To do. Here, the predetermined value is 30 km / h.
In S112, when the vehicle speed is higher than the predetermined value, the process proceeds to S113, and it is determined whether or not the vehicle speed is within the predetermined range. Specifically, the vehicle speed is in a high vehicle speed range (100 km / h).
If YES in S113, the process proceeds to S114 to determine whether or not the driver's steering state is a slow lane change by the method described above.
When the vehicle speed is within the predetermined range and the lane change is slow, the process proceeds to S115, and the steering force characteristics (maximum steering force, steering force change rate, steering force hiss) are calculated. In step S116, the calculated steering force characteristic is stored as a stored value. Here, S113 to S116 are executed a plurality of times during traveling of the vehicle, and several stored values are stored.

Next, in the case of NO in S112, since the vehicle is traveling in a predetermined low vehicle speed range, the process proceeds to S117, and it is determined whether or not the variation of the plurality of stored values stored in S116 is equal to or less than a predetermined value. If it is equal to or smaller than the predetermined value, the process proceeds to S118, and an average value of a plurality of stored values is calculated.
Next, in S119, whether the absolute value (| target value-stored value |) of the deviation between the stored value, which is the average value of the steering force characteristic, and the target value is not less than the first predetermined value and not more than the second predetermined value. Determine whether or not.
If YES in S119, the process proceeds to S120, and the deviation (| previous stored value−stored value) between the previously stored value (the value of the previously corrected control map) and the stored value (average value of the stored value calculated this time). It is determined whether or not |
In the case of YES in S120, the process proceeds to S121, and the change amount of the control map is calculated. Next, the process proceeds to S122, in which it is determined whether or not the absolute value of the change amount of the control map is greater than or equal to the upper limit value. In the case of YES, the process proceeds to S123, and the upper limit value is applied as the correction amount. On the other hand, in the case of NO in S122, the process proceeds to S124, and the calculated value that is the change amount is applied as the correction amount.
Next, the process proceeds to S125, where it is determined whether or not the electric power steering device is in a non-control state (whether or not assist control is performed by the electric motor). Is corrected by the upper limit value or the calculated value. Here, when the electric power steering device is in the non-control state, the control map is corrected because when the electric power steering device is in the control state, the control map is corrected to change the steering force characteristic. This is because the change is felt and a sense of incongruity is generated, which is prevented.

  Here, in the first example (S106 to S109) and the second example (S122 to S126) of the fifth embodiment described above, the control map is corrected within a range equal to or lower than the upper limit value, and the correction equal to or lower than the upper limit value. Will be repeated until the target value is reached, but if a new steering force characteristic is calculated in the middle, the deviation between the two will be calculated based on the corrected control map in the middle. The control map is corrected based on the deviation. In the present embodiment, the control map is corrected within a range equal to or lower than the upper limit value, and correction equal to or lower than the upper limit value is repeatedly performed until the target value is reached, and a new steering force characteristic is obtained until this repeated correction is completed. It may not be calculated.

Further, in the first example of the fifth embodiment, in S106 to S109 of FIG. 24, the control map is corrected within the range of the upper limit value or less when the vehicle is stopped, but once the upper limit value is exceeded or You may make it correct | amend several times. In this case, when the vehicle travels after correction, the driver feels uncomfortable at the time of steering, but feels less uncomfortable than when the control map is changed during steering.
Furthermore, in the second example of the fifth embodiment, the control map is corrected when the electric power steering apparatus is in the non-control state (when the assist control by the electric motor is not performed). For this reason, it is preferable that correction is performed every time the driver steers the steering wheel, that is, every time after the steering wheel is turned back and forth. Since the steering force characteristic changes little by little (by performing the correction within the above-described upper limit range) every time the steering is performed, the driver does not feel uncomfortable with the steering feel.

  Here, in the first example and the second example shown in FIG. 24 of the fifth embodiment, both the correction of the steering force characteristic in the inspection process at the factory and the correction of the steering force characteristic during traveling or when stopping are executed. It is like that. However, the correction timing during traveling or stopping in the first example (S91 and S96 to S109 in FIG. 24) and the second example (S111 to S126 in FIG. 25) of the fifth embodiment is the same as in the first to third embodiments. It can be applied as a correction timing when correcting the correction map in the fourth embodiment.

Next, a sixth embodiment of the present invention will be described with reference to FIGS. FIG. 26 shows the control unit of the sixth embodiment, FIG. 27 is an overall configuration diagram showing the VGR device, FIG. 28 is a partial side view taken along line AA of FIG. 27, and FIG. It is the partial side view seen along the BB line of FIG. 27, FIG. 30 shows the control flow by 6th Embodiment.
As a prior art, in a driving state with little visual information, such as during night driving, a steering force characteristic is changed in a stable direction by reducing the assist force and increasing the steering wheel.
However, in a driving state with little visual information (night driving, driving in rainy weather, driving in fog, etc.), the steering force response sensitivity felt by the driver increases and the vehicle response sensitivity decreases. In other words, the phase of the vehicle response to the steering force is delayed and the steering feel is lowered, so that the driver feels uneasy. On the other hand, if the delay in the phase of the vehicle response with respect to the steering force is reduced as opposed to the prior art, the sensitivity of the vehicle response increases, which is generally not preferable. As far as the region (center feel region) is concerned, the steering feel is improved by reducing the phase delay of the vehicle response to the steering force. Therefore, in the sixth embodiment, the assist gain Ka, which is a control parameter of the steering force characteristic, is increased and corrected so that the phase delay of the vehicle response to the steering force is reduced in a driving state with little visual information in a predetermined driving state. In addition, and / or the control gain of the vehicle response variable mechanism is increased and corrected to obtain a good steering feel.

The control unit according to the sixth embodiment will be described with reference to FIG. This control unit 90 includes all of those shown in FIG. 18, and includes a motor rotation angular velocity estimation unit 28, an ignition (IG) 30, a memory unit 32, a steering force characteristic calculation unit 82, a determination & correction unit 84, and a friction compensation control unit 86. Are not shown.
The control unit 90 is further provided with a headlamp SW92, a wiper SW94, and a fog SW96 in order to detect the amount of visual information. The detected information is input to the visual information amount determination unit 98. It has become. Further, a vehicle response variable mechanism 100 is provided so that the vehicle response can be changed.
In this embodiment, the vehicle response variable mechanism 100 uses the VGR device 8 that changes the transmission ratio of the front wheel steering with respect to the steering angle of the steering wheel, but in addition, a 4WS device that changes the transmission ratio of the rear wheel steering angle. SBW (steer-by-wire device) or the like may be used.

Next, the VGR device 8 which is a vehicle response variable mechanism will be described with reference to FIGS. The VGR device 8 is for changing the ratio (transmission ratio: R = θ / θw) between the steering angle (θ) of the steering wheel 2 and the wheel steering angle (θw) of the wheel 16.
The VGR device 8 has an input shaft 134 disposed on the same axis line as the intermediate shaft 10, and rotation of the intermediate shaft 6 is input to the input shaft 134 via integrated input gears 135 and 136. It has become.

A planetary gear mechanism 137 is provided between the input shaft 134 and the intermediate shaft 10. The planetary gear mechanism 137 is disposed on the sun gear 138 and a sun gear 138 fixed on the input shaft 134. A plurality of pinion gears 139, a ring gear 140 disposed outside these pinion gears 139 and fixed to the intermediate shaft 10, and fitted and supported on the input shaft 134 so as to be relatively rotatable, and each pinion gear via the pinion shaft 141. And a carrier 142 supporting 139.
A sector gear 143 is provided integrally with the carrier 142, and a pinion gear 145 fixed to the rotating shaft 130 a of the stepping motor 130 is engaged with the sector gear 143.

  When the steering wheel 2 is steered, the stepping motor 130 is driven to rotate in accordance with the output signal from the control unit 90, so that the sun gear 138 is rotated by an amount corresponding to the steering angle θ in the planetary gear mechanism 137. The carrier 142 is rotated according to the rotation of the stepping motor 130, whereby the amount of rotation of the ring gear 140 or the intermediate shaft 10 corresponding to the wheel steering angle θw is increased or decreased, and the transmission ratio R of the steering angle θ to the wheel steering angle θw is increased. It is variably controlled.

Next, a control flow according to the sixth embodiment will be described with reference to FIG.
First, in S131, the input values of the sensors of the headlamp SW92, wiper SW94, and fog SW96 are updated. In S132, it is determined whether any of the headlamp SW92, wiper SW94, or fog SW96 is turned on. judge. If it is on, the driving state (night driving, driving in rainy weather, driving in fog, etc.) with little visual information is in progress, and the process proceeds to the next S133.
In S133, the assist gain Ka in the high speed range is increased and corrected, and the control gain of the vehicle response variable mechanism is increased and corrected. Only one of the high-speed assist gain Ka and the control gain of the vehicle response variable mechanism may be corrected for increase. Further, the assist start point Pas may be corrected to decrease.
In this way, in the high speed range, the assist gain Ka of the control map is corrected to increase, the assist start point is corrected to decrease, and the control gain of the vehicle response variable mechanism is corrected to increase, thereby reducing the phase delay of the vehicle response to the steering force. As a result, a good steering feel can be obtained.

It is a perspective view which shows an example of the electric power steering device of the motor vehicle to which this invention is applied. It is a diagram showing an example (target steering force characteristic in a high vehicle speed range (about 100 km / h)) according to the first embodiment of the present invention. It is a diagram showing a basic assist control map (assist gain Ka and assist start point Pas) for obtaining a target steering force characteristic according to the first embodiment of the present invention. It is a block diagram which shows the control unit by 1st Embodiment of this invention. It is a diagram for demonstrating the steering rigidity of 1st Embodiment of this invention. It is a control flow by 1st Embodiment of this invention. It is a control flow which shows the subroutine of S13 of FIG. It is a diagram which shows the steering force characteristic in the case of carrying out increase correction of the assist gain Ka by 1st Embodiment of this invention. It is a diagram which shows the steering force characteristic in the case of carrying out decrease correction of the assist gain Ka by 1st Embodiment of this invention. It is a block diagram which shows the control unit by 2nd Embodiment of this invention. It is a diagram which shows the target steering force characteristic and the calculated steering force characteristic in 2nd Embodiment of this invention. FIG. 10 is a diagram showing a friction compensation control map (friction compensation gain Kc) for obtaining a target steering force characteristic according to the second embodiment of the present invention. It is a control flow by 2nd Embodiment of this invention. It is a block diagram which shows the control unit by 3rd Embodiment of this invention. It is a diagram which shows an example of the target steering force characteristic by 3rd Embodiment of this invention. It is a diagram which shows the friction compensation control map (friction compensation gain Kc) for obtaining the target steering force characteristic by 3rd Embodiment of this invention. It is a control flow by 3rd Embodiment of this invention. It is a block diagram which shows the control unit by 4th Embodiment (and 5th Embodiment) of this invention. It is a diagram which shows an example of the target steering force characteristic by 4th Embodiment of this invention. It is a diagram which shows the basic assist control map (assist gain Ka and assist start point Pas) for obtaining the target steering force characteristic by 4th Embodiment of this invention. It is a diagram which shows the friction compensation control map (friction compensation gain Kc) for obtaining the target steering force characteristic by 4th Embodiment of this invention. 10 shows a control flow according to a fourth embodiment of the present invention. It is a diagram which shows the other control map for obtaining the target steering force characteristic by 4th Embodiment of this invention. The control flow by the 1st example of 5th Embodiment of this invention is shown. The control flow by the 2nd example of 5th Embodiment of this invention is shown. It is a block diagram which shows the control unit by 6th Embodiment of this invention. It is a whole lineblock diagram showing the VGR device by a 6th embodiment of the present invention. It is the partial side view of the VGR apparatus seen along the AA line of FIG. It is the fragmentary side view of the VGR apparatus seen along the BB line of FIG. 10 shows a control flow according to a sixth embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering device 2 Handle 4 Steering shaft 8 VGR device 16 Tire (wheel)
DESCRIPTION OF SYMBOLS 18 Electric motor 20, 60, 70, 80, 90 Control unit 22 Vehicle speed sensor 24 Torque sensor 26 Basic assist control part 28 Motor rotational angular velocity estimation part 30 Ignition 32 Memory part 34 Steering rigidity estimation part 36 Navigation apparatus 38 Wiper SW
40 Engine water temperature sensor 42 Wheel speed sensor 44 Turn SW
46, 64, 74, 84 Judgment & Correction Unit 62 Steering Force Rise Value Calculation Unit 66 Friction Compensation Control Unit 72 Steering Friction Calculation Unit 82 Steering Force Characteristic Calculation Unit 92 Headlamp SW
94 Wiper SW
96 Fog SW
98 Visual Information Determination Unit 100 Vehicle Response Variable Mechanism

Claims (6)

An electric power steering device that drives the steering mechanism by controlling the electric motor so as to achieve a target steering force characteristic based on at least the vehicle speed and the steering torque without having a steering angle sensor,
A torque sensor for detecting steering torque;
Control map means for defining a target steering force characteristic by a control map;
Rotation angle estimation means for estimating the rotation angular velocity and rotation angle of the electric motor from the current and voltage of the electric motor;
Steering area estimation means for estimating a steering area starting to turn the steering wheel from a straight traveling state that is equal to or higher than a predetermined vehicle speed and the electric motor is not controlled from the vehicle speed, the torque sensor value, and the rotation angle of the electric motor
An actual steering stiffness calculating means for calculating the steering stiffness from the amount of change of the torque sensor value with respect to the rotation angle change of the electric motor in this steering region;
A deviation calculating means for calculating a deviation between the calculated actual steering stiffness and a pre-stored target steering stiffness;
Correction means for correcting the control map when the deviation is a predetermined value or more,
The control map means determines the target steering force characteristic by an assist gain and an assist start point,
The electric power steering apparatus, wherein the control means corrects the assist gain and the assist start point.   When the actual steering stiffness is greater than the target steering stiffness, the correction means first corrects the assist gain to increase to match the steering force change rate with the target steering force characteristic, and then corrects the assist start point to decrease. The electric power steering apparatus according to claim 1, wherein the maximum steering force is adjusted to a target steering force characteristic.   The control map means sets a lower limit value of the assist start point, and the correction means further increases and corrects the assist gain when the assist start point reaches the lower limit value when the assist start point is decreased. 3. The electric power steering apparatus according to claim 2, wherein the maximum steering force is matched with the target steering force characteristic.   The control map means sets the upper limit value of the assist gain, and the correction means corrects the assist gain and the assist start point when the assist gain reaches the upper limit value as a result of increasing the assist gain. The electric power steering apparatus according to any one of claims 1 to 3, wherein the power is stopped.   When the actual steering stiffness is smaller than the target steering stiffness, the correction means first corrects the assist gain to decrease to match the steering force change rate with the target steering force characteristic, and then increases and corrects the assist start point. The electric power steering apparatus according to claim 1, wherein the maximum steering force is adjusted to a target steering force characteristic.   The control map means sets an upper limit value of the assist start point, and the correction means corrects the assist gain and the assist start point when the assist start point reaches the upper limit value when the assist start point is increased. The electric power steering apparatus according to claim 5, which stops the operation.

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