JP7181833B2 - electric power steering device - Google Patents

Description

The present invention relates to an electric power steering system.

In Patent Document 1, when the steering state is the turning state, a current value during turning calculated based on the steering torque is output as an assist current value, and when the steering state is the returning state, the steering torque is output. A vehicle steering system (electric power steering system) is disclosed which outputs the return current value calculated as an assist current value.

JP 2010-274822 A

However, in the electric power steering apparatus disclosed in Patent Document 1, the assist current value is determined based on the steering torque, and a value related to the steering speed is not taken into account. There is

Here, it is conceivable to determine the assist current value by adding a value related to the steering speed. However, when the assist current value is determined by similarly considering the value related to the steering speed during the turning steering and the returning steering, the variation according to the steering speed is appropriately adjusted for each of the turning steering and the returning steering. It may not be possible to control it. For example, even if it is possible to suppress the variation in steering force according to the steering speed in the turning steering, it may not be possible to suppress the variation in the steering force according to the steering speed in the return steering.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to improve the steering feeling by suppressing the variation in steering force according to the steering speed in each of the turning steering and the returning steering. .

The present invention relates to an electric power steering apparatus, comprising a steering shaft connected to a steering member steered by a driver and rotated as the steering member is steered by the driver, and an electric motor applying rotational torque to the steering shaft. a torque detection unit that detects steering torque input from the steering member; an assist base current calculation unit that calculates an assist base current value based on the steering torque; and a value related to the steering speed of the steering member, A static friction compensation current calculation unit that calculates a static friction compensation current value for compensating the static friction of the steering system, and a control current calculation unit that corrects the assist base current value by the static friction compensation current value and calculates the control current value. a motor control unit for controlling the electric motor based on the control current value; and a steering state determination unit for determining the steering state of the steering member. The static friction compensation current calculation unit is set to increase the value of the assist base current and to decrease the assist base current value when the steering torque decreases. a corrected static friction compensation current calculation unit that calculates a corrected static friction compensation current value; a time change rate determination unit that determines whether or not a value related to the steering speed is equal to or greater than a predetermined threshold value; a setting unit that sets a first threshold to the threshold when the steering state is the turning state, and sets a second threshold smaller than the first threshold to the threshold when the steering state is the return state. However, if the value related to the steering speed is equal to or greater than the threshold value, the corrected static friction compensation current value is added to the reference static friction compensation current value, and the static friction compensation current value is calculated based on the added value. If the speed-related value is less than the threshold value, the static friction compensation current value is calculated based on the reference static friction compensation current value without adding the corrected static friction compensation current value to the reference static friction compensation current value. Characterized by

In this invention, since the control current value is calculated based on the value related to the steering speed, it is possible to suppress variations in the steering force according to the steering speed. In addition, since an appropriate static friction compensation current value can be set for each of the turning steering and the return steering, it is possible to suppress variations in the steering force according to the steering speed in each of the turning steering and the return steering. Rings can be improved. In particular, when returning steering is performed, the corrected static friction compensation current value is taken into account earlier than when turning steering is performed. As a result, it is possible to quickly reduce the control current value during return steering after the steering member has been cut, thereby preventing a sudden decrease in steering torque. As a result, it is possible to suppress the variation in the steering force according to the return steering speed, and improve the steering feeling during the return steering.

In the present invention, the value related to the steering speed is the time rate of change of the steering torque, and the reference static friction compensation current calculation unit is a first vehicle speed coefficient that increases as the vehicle speed detected by the vehicle speed detection unit increases. Then, a reference static friction compensation current value is calculated based on the time rate of change of the steering torque, and a corrected static friction compensation current calculation unit calculates a second vehicle speed coefficient that increases as the vehicle speed detected by the vehicle speed detection unit increases. A corrected static friction compensation current value is calculated based on.

In the present invention, the static friction compensation current value is calculated based on the first vehicle speed coefficient and the second vehicle speed coefficient, which increase as the vehicle speed increases. Steering feeling can be further improved.

The present invention further includes a steering angle detection unit that detects the steering angle of the steering member, and the static friction compensation current calculation unit detects that when the steering angle is equal to or greater than a predetermined angle, compared to when the steering angle is less than the predetermined angle, It is characterized by comprising a processing unit that reduces a static friction compensation current value.

In this invention, when the steering angle is less than a predetermined angle, the variation in the steering force according to the steering speed during return steering is suppressed, and when the steering angle is greater than or equal to the predetermined angle, the driver feels a large reaction force. You can prevent it from becoming too much.

Advantageous Effects of Invention According to the present invention, it is possible to suppress variations in steering force according to the steering speed and improve the steering feeling in each of the turning steering and the returning steering.

1 is a configuration diagram of an electric power steering device according to a first embodiment of the present invention; FIG. 1 is a block diagram of an electric power steering device according to a first embodiment of the invention; FIG. 4 is a functional block diagram of a static friction compensation current calculator according to the first embodiment of the present invention; FIG. 4 is a time chart of steering angles of an electric power steering device according to a comparative example of the present embodiment; 4 is a time chart of steering force of an electric power steering device according to a comparative example of the present embodiment; FIG. 7 is a functional block diagram of a static friction compensation current calculator according to a second embodiment of the present invention;

<First embodiment>
An electric power steering apparatus 100 according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 4B.

FIG. 1 is a configuration diagram of an electric power steering device 100. As shown in FIG. As shown in FIG. 1, an electric power steering device 100 is connected to a steering wheel 1 as a steering member steered by a driver, and is used for steering of the steering wheel 1 by the driver (hereinafter referred to as "steering"). An input shaft 2 that rotates along with a motor, a rack shaft 5 that steers wheels 6, an output shaft 3 that links with the rack shaft 5, and a torsion bar 4 that connects the input shaft 2 and the output shaft 3. A steering shaft 7 is composed of the input shaft 2 , the output shaft 3 , and the torsion bar 4 .

A pinion gear 3 a is formed at the lower portion of the output shaft 3 to mesh with a rack gear 5 a formed on the rack shaft 5 . When the steering wheel 1 is steered, the steering shaft 7 rotates, the rotation is converted into linear motion of the rack shaft 5 by the pinion gear 3a and the rack gear 5a, and the wheels 6 are steered via the knuckle arms 14.

The electric power steering apparatus 100 includes an electric motor 10 as a power source for assisting the steering of the steering wheel 1 by the driver, a speed reducer 11 that reduces the speed of the rotation of the electric motor 10 and transmits it to the output shaft 3, and a driver. It further includes a torque sensor 12 that detects steering torque acting on the torsion bar 4 due to relative rotation between the input shaft 2 and the output shaft 3 accompanying steering by a person, and a controller 30 that controls the electric motor 10 .

The electric motor 10 is provided with a motor rotation angle sensor 10 a that acquires the rotation angle of the electric motor 10 . The motor rotation angle sensor 10a is composed of a resolver.

The reduction gear 11 has a worm shaft 11a connected to the output shaft of the electric motor 10, and a worm wheel 11b connected to the output shaft 3 and meshing with the worm shaft 11a. The torque output by the electric motor 10 is transmitted from the worm shaft 11 a to the worm wheel 11 b and applied to the output shaft 3 .

The torque sensor 12 is a torque detector that detects steering torque input from the steering wheel 1 . Steering torque applied to the input shaft 2 as the driver steers the steering wheel is detected by the torque sensor 12 , and the torque sensor 12 outputs a signal corresponding to the steering torque to the controller 30 . The torque sensor 12 detects steering torque applied to the torsion bar 4 based on relative rotation between the input shaft 2 and the output shaft 3 .

The torque sensor 12 outputs 0 [Nm] as steering torque when there is no relative rotation between the input shaft 2 and the output shaft 3 . When the torsion bar 4 is twisted to the right, a steering torque of + (positive) sign is output, and when the steering wheel 1 is twisted to the left, a steering torque of - (negative) sign is output. do.

As will be described later, the controller 30 calculates a control current value (target current value) for the electric motor 10 based on the detection result from the torque sensor 12, and controls the electric motor 10 to generate a predetermined torque. 10 drives. The electric motor 10 applies rotational torque to the steering shaft 7 via a reduction gear 11 . Thus, the electric power steering device 100 detects the steering torque input from the steering wheel 1 to the input shaft 2 by the torque sensor 12, and the controller 30 drives the electric motor 10 based on the detection result. It assists the steering of the steering wheel 1 by the driver.

The input shaft 2 is provided with a steering angle sensor 15 as a steering angle detector for detecting a steering angle, which is the rotation angle of the steering wheel 1 . The rotation angle of the input shaft 2 and the steering angle of the steering wheel 1 are equal. Therefore, the steering angle of the steering wheel 1 can be obtained by detecting the rotation angle of the input shaft 2 with the steering angle sensor 15 . A detection result of the steering angle sensor 15 is output to the controller 30 .

Although not shown, the steering angle sensor 15 includes, for example, a center gear that rotates together with the input shaft 2 and two outer gears that mesh with the center gear. , the rotation angle of the center gear, that is, the rotation angle of the input shaft 2 is calculated.

The steering angle sensor 15 outputs 0[°] as the steering angle when the steering wheel 1 is in the neutral position. Further, when the steering wheel 1 is steered rightward from the neutral position, a steering angle with a + (positive) sign is output according to the rotation of the steering wheel 1 . On the other hand, when the steering wheel 1 is steered leftward from the neutral position, a steering angle with a minus sign is output according to the rotation of the steering wheel 1 .

The controller 30 receives a detection result from a vehicle speed sensor 16 as a vehicle speed detector that detects the running speed of the host vehicle (hereinafter referred to as vehicle speed).

The controller 30 includes a CPU (Central Processing Unit) as an operation circuit, a storage unit such as a ROM (Read Only Memory), a RAM (Random Access Memory), an input/output interface (I/O interface), and other peripheral circuits. It consists of a microcomputer. The controller 30 can also be composed of a plurality of microcomputers. As the operation circuit, an MPU (Micro Processing Unit), a DSP (Digital Signal Processor), an ASIC (application specific integrated circuit), an FPGA (Field Programmable Gate Array), etc. can be used instead of or together with the CPU. .

The CPU of the controller 30 controls the operation of the electric motor 10, the ROM of the controller 30 stores control programs and setting values necessary for the processing operation of the CPU, and the RAM of the controller 30 stores the torque sensor 12, Information detected by various sensors such as the steering angle sensor 15 and the vehicle speed sensor 16 is temporarily stored.

Control of the electric motor 10 by the controller 30 will be described with reference to FIGS. 2 and 3. FIG. FIG. 2 is a block diagram of the electric power steering device 100, and FIG. 3 is a functional block diagram of the static friction compensation current calculator 130. As shown in FIG.

As shown in FIG. 2, the controller 30 time-differentiates the steering torque T detected by the torque sensor 12 to obtain a time rate of change Tv of the steering torque T, which is a value related to the steering speed of the steering wheel 1 (hereinafter referred to as Tv). a differentiator 111 that calculates a torque change rate Tv);

When the sign of the steering torque T detected by the torque sensor 12 and the sign of the torque change rate Tv calculated by the differentiator 111 are the same, the steering state determination unit 110 determines that the steering state is the turning state. . When the sign of the steering torque T detected by the torque sensor 12 and the sign of the torque change rate Tv calculated by the differentiator 111 are not the same, the steering state determination unit 110 determines that the steering state is the return state. .

The controller 30 also includes an assist base current calculator 121 that calculates an assist base current value Ia based on the steering torque T detected by the torque sensor 12 and the vehicle speed v detected by the vehicle speed sensor 16, a torque change rate Tv and Based on the vehicle speed v, a static friction compensation current calculation unit 130 calculates a static friction compensation current value If for compensating the static friction of the steering system. A control current calculator 180 that corrects the value Ia and calculates a control current value Isum for the electric motor 10, and a current that is supplied to the electric motor 10 so that the detected current value of the electric motor 10 matches the control current value Isum. and a motor control unit 9 that controls the electric motor 10 by controlling. Other various current values include, for example, a Coulomb friction compensation current value, a viscous friction compensation current value, an inertia compensation current value, and a return current value, although not shown.

The static friction compensation current value If can be calculated by, for example, the following equation.
If=If1+If2
If1=f1×Tv
If2=f2×a

If1 is a reference static friction compensation current value, and If2 is a corrected static friction compensation current value. f1 is a first vehicle speed coefficient that increases as the vehicle speed v increases, and f2 is a second vehicle speed coefficient that increases as the vehicle speed v increases. a is the sign coefficient. The sign coefficient a is set to one of an, 0 (zero), and ap based on the torque change rate Tv. An is an arbitrarily determined negative value, which is stored in advance in the storage unit of the controller 30 . ap is an arbitrarily determined positive value and is stored in advance in the storage unit of the controller 30 . The reference static friction compensation current value If1 is a term that compensates for a linear component proportional to the static friction of the steering system, and in this embodiment, it is obtained by multiplying the first vehicle speed coefficient f1 by the torque change rate Tv.

The relationship between the detected current of the electric motor 10 and the motor output torque at the steering shaft 7 becomes non-linear due to the influence of the friction of the electric motor 10 and the reduction gear 11 and the like. Therefore, in the present embodiment, a corrected static friction compensation current value If2 for compensating for the nonlinear component is added to the reference static friction compensation current value If1. The corrected static friction compensation current value If2 is a term that compensates for the nonlinear components of the electric motor 10 and the speed reducer 11, and in this embodiment, it is obtained by multiplying the second vehicle speed coefficient f2 by the sign coefficient a.

As shown in FIG. 3 , the static friction compensation current calculator 130 has a reference static friction compensation current calculator 141 , a corrected static friction compensation current calculator 142 , an adder 143 , and a limiter 149 .

The reference static friction compensation current calculator 141 calculates a reference static friction compensation current value If1 based on the first vehicle speed coefficient f1 and the torque change rate Tv. A corrected static friction compensation current calculation unit 142 calculates a corrected static friction compensation current value If2 based on a second vehicle speed coefficient f2 different from the first vehicle speed coefficient f1 and a sign coefficient a set by the torque change rate Tv.

A reference static friction compensation current calculation unit 141 calculates a first vehicle speed coefficient setting unit 141a for setting a first vehicle speed coefficient f1, and the first vehicle speed coefficient f1 set by the first vehicle speed coefficient setting unit 141a using a differentiator 111. a multiplier 141b that multiplies the calculated torque change rate Tv to calculate a reference static friction compensation current value If1.

The corrected static friction compensation current calculation unit 142 includes a second vehicle speed coefficient setting unit 142a that sets a second vehicle speed coefficient f2, and a setting unit that sets a sign coefficient a for setting the sign of the corrected static friction compensation current value If2. A sign setting unit 142b multiplies the second vehicle speed coefficient f2 set by the second vehicle speed coefficient setting unit 142a by the sign coefficient a set by the sign setting unit 142b to calculate a corrected static friction compensation current value If2. and a multiplier 142c.

The first vehicle speed coefficient f1 and the second vehicle speed coefficient f2 are coefficients that increase as the vehicle speed v detected by the vehicle speed sensor 16 increases. It is calculated based on the vehicle speed characteristic Cv21. The storage unit of the controller 30 stores the first vehicle speed characteristic Cv11 and the second vehicle speed characteristic Cv21 in the form of a table.

The first vehicle speed coefficient setting unit 141a refers to the first vehicle speed characteristic Cv11 and sets the first vehicle speed coefficient f1 based on the vehicle speed v detected by the vehicle speed sensor 16. FIG. The second vehicle speed coefficient setting unit 142a refers to the second vehicle speed characteristic Cv21 and sets the second vehicle speed coefficient f2 based on the vehicle speed v detected by the vehicle speed sensor 16. FIG.

The sign setting unit 142b sets a sign coefficient a to be multiplied by the second vehicle speed coefficient f2 based on the torque change rate Tv, as will be described later. The multiplier 141b multiplies the first vehicle speed coefficient f1 by the torque change rate Tv to calculate a reference static friction compensation current value If1. The multiplier 142c calculates a corrected static friction compensation current value If2 by multiplying the second vehicle speed coefficient f2 by the sign coefficient a.

The addition unit 143 adds the corrected static friction compensation current value If2 calculated by the corrected static friction compensation current calculation unit 142 to the reference static friction compensation current value If1 calculated by the reference static friction compensation current calculation unit 141 . The calculation result of the adder 143 is subjected to upper/lower limit processing by a limiter 149 and output as a static friction compensation current value If.

Since the sign coefficient a is set to 0 (zero) when the absolute value |Tv| of the torque change rate Tv is less than the threshold, the corrected static friction compensation current value If2 is also 0 (zero). That is, the threshold value of the torque change rate Tv is used to determine whether or not the corrected static friction compensation current value If2 is set to 0, and corresponds to a value for setting the dead zone of the corrected static friction compensation current value If2. do. The code setting unit 142b that sets the code coefficient a will be described in detail below.

The sign setting unit 142b also functions as a time change rate determination unit that determines whether or not the absolute value |Tv| of the torque change rate Tv is equal to or greater than a predetermined threshold value _Tn . Specifically, the sign setting unit 142b determines whether or not the torque change rate Tv is equal to or greater than a predetermined positive threshold (+T _n ), and determines whether the torque change rate Tv is equal to or greater than a predetermined negative threshold (- T _n ) or less. In other words, the sign setting unit 142b determines whether or not the torque change rate Tv is within a predetermined range (negative threshold (−T _n ) to positive threshold (+T _n )). . This threshold value T _n will be specifically described below.

The controller 30 has a positive first threshold value (+T ₁ ) and a negative first threshold value (−T 1 ) for turning the steering wheel 1, which are referred to when turning the steering wheel 1, and a negative first threshold (−T ₁ ), which is referred to when turning the steering wheel 1. A positive second threshold value (+T ₂ ) and a negative second threshold value (−T ₂ ) for return steering are stored. The sign setting unit 142b sets the positive first threshold (+T 1 ) to the positive threshold (+T _n ) and sets the negative threshold ( _{−T n )} to a negative value when the steering state is the turning state. Set the first threshold (-T ₁ ) of . Further, when the steering state is the return state, the sign setting unit 142b sets the positive second threshold (+T _n ) to the positive second threshold (+T ₂ ), and sets the negative threshold (−T n ) to the second positive threshold (+T _n ). is set to a negative second threshold (-T ₂ ). The second threshold _T2 is smaller than the first threshold _T1 ( _T2 < _T1 ).

A method of setting the sign coefficient a when the steering state determination unit 110 determines that the steering state of the steering wheel 1 is in the turning state will be described. The sign setting unit 142b sets the sign coefficient a to "0 (zero)" when the torque change rate Tv is greater than the first negative threshold (-T ₁ ) and less than the first positive threshold (+T ₁ ). . The sign setting unit 142b sets the sign coefficient a to "ap (>0)" when the torque change rate Tv is greater than or equal to the positive first threshold (+ _T1 ). The sign setting unit 142b sets the sign coefficient a to "an (<0)" when the torque change rate Tv is less than or equal to the negative first threshold (-T ₁ ).

A method of setting the sign coefficient a when the steering state determination unit 110 determines that the steering state of the steering wheel 1 is in the return state will be described. The sign setting unit 142b sets the sign coefficient a to “0 (zero)” when the torque change rate Tv is greater than the second negative threshold (−T ₂ ) and less than the second positive threshold (+T ₂ ). do. The sign setting unit 142b sets the sign coefficient a to "ap (>0)" when the torque change rate Tv is equal to or greater than the positive second threshold (+T ₂ ). The sign setting unit 142b sets the sign coefficient a to "an (<0)" when the torque change rate Tv is less than or equal to the negative second threshold (-T ₂ ).

Therefore, when the absolute value |Tv| of the torque change rate Tv is equal to or greater than the threshold value (T ₁ in the cutting state and T ₂ in the returning state), the static friction compensation current calculation unit 130 corrects it to the reference static friction compensation current value If1. The static friction compensation current value If2 is added, and the static friction compensation current value If is calculated based on the added value (If1+If2). Further, when the absolute value |Tv| of the torque change rate Tv is less than a threshold value (T ₁ in the cutting state and T ₂ in the returning state), the static friction compensation current calculation unit 130 corrects it to the reference static friction compensation current value If1. The static friction compensation current value If is calculated based on the reference static friction compensation current value If1 without adding the static friction compensation current value If2.

The static friction compensation current value If calculated by the static friction compensation current calculation section 130 is added to the assist base current value Ia together with other various current values to calculate the control current value Isum (see FIG. 2).

Thus, in this embodiment, since the control current value Isum is calculated based on the torque change rate Tv, which is a value related to the steering speed, it is possible to suppress variations in the steering force according to the steering speed. Further, in the present embodiment, a threshold value of the torque change rate Tv is set for determining whether or not to add the corrected static friction compensation current value If2 to the reference static friction compensation current value If1 in the turning state and the returning state. , different values (T ₁ , T ₂ ) were adopted. Here, the same value (T ₁ ) as the threshold value of the torque change rate Tv for determining whether or not to add the corrected static friction compensation current value If2 to the reference static friction compensation current value If1 in the turning state and the returning state. is employed as a comparative example of the present embodiment.

In the comparative example of this embodiment, the threshold _T1 is stored in the storage unit of the controller, but the threshold _T2 is not stored. The controller according to the comparative example of this embodiment sets the code coefficient a based on the threshold value T ₁ regardless of the steering state of the steering wheel 1 .

4A and 4B, in the comparative example of the present embodiment, the steering wheel 1 is turned to one side (to the right) from the neutral position to steer, and after the steering is maintained at a predetermined steering angle θa [°], A change in the steering force when the vehicle is steered back to the other (leftward) will be described. FIG. 4A is a time chart of the steering angle θ of the electric power steering device according to the comparative example of this embodiment, and FIG. 4B is a time chart of the steering force of the electric power steering device according to the comparative example of this embodiment. .

4A and 4B, the characteristics shown by the solid lines are the characteristics when the torque change rate Tv is turned off at Tva and the return steering is performed, and the characteristics shown by the dashed-dotted lines are the characteristics when the torque change rate Tv is turned off at Tvb and the return steering is performed. The characteristic indicated by the dashed line is the characteristic when the torque change rate Tv is turned off at Tvc and the return steering is performed. The magnitude relationship among Tva, Tvb, and Tvc is Tva<Tvb<Tvc.

A case in which the torque change rate Tv is Tva and the turning steering and the return steering are performed will be described. When the steering wheel 1 is turned into the steering wheel (time t0), the steering force increases as the steering angle θ increases. When the steering wheel 1 is turned to a predetermined steering angle θa, the turning steering ends (time t1). When the turning steering is completed, the steering wheel 1 is held at a predetermined steering angle θa (from time t1 to time t2). Here, when the turning steering is completed and the steering shifts to holding, the steering force increases to Fa and then decreases to Fb, and the steering force F is maintained at Fb while the steering is being held.

When the steering wheel 1 is steered back (time t2), the steering force decreases as the steering angle θ decreases. When the steering wheel 1 is turned to a predetermined steering angle θb (θb<θa), the return steering is completed (time t3). When the return steering is completed, the steering wheel 1 is held at the predetermined steering angle θb. Here, when the return steering is completed and the steering shifts to holding, the steering force decreases to Fc1 and then increases to Fd, and the steering force F is maintained at Fd while the steering is being held.

Here, as shown in the figure, the maximum value of the steering force at the time of shifting from steering to steering to holding steering was approximately Fa regardless of the steering speed, and the same results were obtained. On the other hand, the minimum value of the steering force when shifting from the return steering to the holding steering resulted in variations depending on the steering speed. In the comparative example, when the torque change rate Tv is Tva, the minimum value of the steering force is Fc1 [N], and when the torque change rate Tv is Tvb, the minimum value of the steering force is Fc2 [N], which is smaller than Fc1 [N]. ] became. Further, when the torque change rate Tv is Tvc, the minimum value of the steering force is Fc3 [N], which is smaller than Fc2.

The reason why the steering force varies according to the torque change rate Tv is that the return operation of the rack shaft 5 is delayed with respect to the return steering when the return steering is performed. When the return steering is performed, the input shaft 2 rotates so that the torsion of the torsion bar 4 is released. As the steering speed increases, the torsion of the torsion bar 4 is largely eliminated, the difference in torsion angle between the input shaft 2 and the output shaft 3 becomes smaller, and the minimum value of the steering force becomes smaller.

Therefore, in order to suppress the variation in the steering force according to the torque change rate Tv, the responsiveness of the rack shaft 5 to the return steering should be improved when the return steering is performed. In order to improve the responsiveness of the rack shaft 5 to the return steering, when the return steering is performed, the static friction compensation is strongly effective at an earlier stage than when the turning steering is performed, and the control current value Isum of the electric motor 10 is increased. should be reduced quickly.

Therefore, in the present embodiment, as described above, the threshold value set for determining whether or not to correct the reference static friction compensation current value If1 with the corrected static friction compensation current value If2 in the turning state and the return state is used. Different values (a first threshold T ₁ and a second threshold T ₂ smaller than the first threshold) are adopted for the threshold of the torque change rate Tv. Therefore, in the present embodiment, when _the absolute _value |Tv| , the absolute value |If| of the static friction compensation current value If during return steering becomes larger than the absolute value |If| of the static friction compensation current value If during turning steering.

Here, the static friction compensation current value If is set to increase the assist base current value Ia when the steering torque T increases, and is set to decrease the assist base current value Ia when the steering torque T decreases. be.

The assist base current value Ia is a positive value when the steering wheel 1 rotates in one direction (rightward). On the other hand, the static friction compensation current value If is set when the steering wheel 1 rotates in one direction (rightward) and the steering torque T increases (that is, when the torque change rate Tv is a positive value). becomes a positive value, and becomes a negative value when the steering torque T decreases (that is, when the torque change rate Tv is a negative value).

On the other hand, the assist base current value Ia is a negative value when the steering wheel 1 rotates in the other direction (leftward). On the other hand, the static friction compensation current value If is set when the steering wheel 1 rotates to the other side (leftward) and the absolute value |T| of the steering torque T increases (that is, when the torque change rate Tv of the steering torque T decreases (that is, when the torque change rate Tv is a positive value), it becomes a positive value.

For example, if the steering wheel 1, which is held at a predetermined steering angle on one side (right side) of the neutral position, is steered further to one side (right side), the steering torque T increases. Both the current value Ia and the static friction compensation current value If are positive values. That is, the static friction compensation current value If is corrected so as to increase the assist base current value Ia. On the other hand, when the steering wheel 1, which is held at a predetermined steering angle on one side (right side) of the neutral position, is steered to return to the other side (left side), the steering torque T decreases. While the value Ia is a positive value, the static friction compensation current value If is a negative value. That is, the static friction compensation current value If is corrected so as to decrease the assist base current value Ia.

The second threshold _T2 referred to when the steering state is the returning state is smaller than the first threshold _T1 referred to when the steering state is the turning state. Therefore, _the static friction compensation current value when _the absolute value |Tv| The absolute value |If| of If becomes larger than when the steering state is the turning state. In other words, when the absolute value |Tv| of the torque change rate Tv is within the range of the second threshold value T2 _or more and less than the first threshold value _T1 , the static friction compensation current value If is calculated regardless of the steering state. The absolute value |If| of the static friction compensation current value If when the steering state is the return state can be increased, and the control current value Isum can be decreased, as compared with the case where the control current value Isum is in the return state.

As described above, in the present embodiment, when the steering wheel 1 is returned, the static friction compensation is strongly effected at an earlier stage than when the steering is turned, and the control current value Isum of the electric motor 10 is quickly adjusted. can be made smaller. By reducing the control current value Isum before the steering torque T drops sharply, the responsiveness of the rack shaft 5 can be improved and the sharp drop in the steering torque T can be suppressed.

According to the embodiment described above, the following effects are obtained.

(1) The controller 30 calculates the assist base current value Ia based on the steering torque T, and based on the torque change rate Tv related to the steering speed of the steering wheel 1, the static friction for compensating the static friction of the steering system. A friction compensation current value If is calculated, the assist base current value Ia is corrected by the static friction compensation current value If, a control current value Isum is calculated, and the electric motor 10 is controlled based on the control current value Isum. Further, the controller 30 determines the steering state of the steering wheel 1, and determines whether or not to correct the reference static friction compensation current value If1 with the corrected static friction compensation current value If2 when the steering state is the turning state. A first threshold value _T1 is set as the threshold value of the torque change rate Tv used, and a second threshold value _T2 smaller than the first threshold value _T1 is set as the threshold value of the torque change rate Tv when the steering state is the return state. Therefore, the controller 30 sets the static friction compensation current value If so that the absolute value |If| Calculate.

Thus, in this embodiment, since the control current value Isum is calculated based on the torque change rate Tv related to the steering speed, it is possible to suppress variations in the steering force according to the steering speed. Further, in the present embodiment, the torque change rate Tv for determining whether or not to correct the reference static friction compensation current value If1 by the corrected static friction compensation current value If2 is the threshold value _T1 for turning steering. and the threshold value _T2 for return steering is set individually. As a result, an appropriate static friction compensation current value If can be set for each of the turning steering and the returning steering. Therefore, in each of the turning steering and the returning steering, it is possible to suppress variations in the steering force according to the steering speed, thereby improving the steering feeling.

In particular, when the steering state is the return state, the corrected static friction compensation current value If2 is added so that the absolute value |If| of the static friction compensation current value If becomes larger earlier than when the steering state is the turning state. I made it As a result, the control current value Isum can be quickly reduced during return steering after the steering wheel 1 is turned, and a sudden decrease in the steering torque T can be prevented. As a result, it is possible to suppress the variation in the steering force according to the return steering speed, and improve the steering feeling during the return steering.

(2) The static friction compensation current value If is calculated based on the vehicle speed coefficients (the first vehicle speed coefficient f1 and the second vehicle speed coefficient f2) that increase as the vehicle speed v increases. Variation can be suppressed, and steering feeling can be further improved.

<Second embodiment>
An electric power steering apparatus 100 according to a second embodiment of the present invention will be described with reference to FIG. In the following, the points different from the first embodiment will be mainly described, and in the drawings, the same reference numerals will be given to the same or corresponding configurations as those described in the first embodiment, and the description will be omitted. .

In the second embodiment, only when the steering angle θ of the steering wheel 1 is small, the control current value Isum is calculated taking into account the static friction compensation current value If. The control current value Isum is calculated without considering the friction compensation current value If. A detailed description will be given below.

FIG. 5 is a functional block diagram of the static friction compensation current calculator 230 according to the second embodiment of the invention. As shown in FIG. 5, the static friction compensation current calculator 230 according to the second embodiment calculates the absolute value |θ| of the steering angle θ when the absolute value |θ| of the static friction compensation current value If is less than the predetermined angle θ0.

The steering angle gain processing unit 248 includes a steering angle gain computing unit 248a that computes a steering angle gain Ga based on the steering angle θ detected by the steering angle sensor 15, and an output value (If1+If2) output from the adding unit 143. , and a multiplication unit 248b for multiplying the steering angle gain Ga calculated by the steering angle gain calculation unit 248a.

The steering angle gain Ga is a value that decreases as the steering angle θ detected by the steering angle sensor 15 increases. The storage unit of the controller 30 stores the steering angle gain characteristic Gan in the form of a table. In the steering angle gain characteristic Gan, the steering angle gain Ga becomes the maximum gain Ga0 (>0) when the absolute value of the steering angle θ |θ| is greater than or equal to θ0[°] and less than θ1[°], the steering angle gain Ga decreases as the absolute value |θ| of the steering angle θ increases, and the absolute value |θ| °], the characteristic becomes 0 (zero). θ1 is larger than 0, and θ2 is larger than θ1 (0<θ1<θ2).

The steering angle gain calculator 248a refers to the steering angle gain characteristic Gan and calculates the steering angle gain Ga based on the steering angle θ.

According to the second embodiment as described above, when the absolute value |θ| is greater than or equal to the predetermined angle θ0, that is, when the self-aligning torque acts strongly, it is possible to prevent the driver from feeling an excessively large reaction force.

The following modifications are also within the scope of the present invention. It is also possible to combine the configurations described in the modifications.

<Modification 1>
In the above embodiment, an example in which the time rate of change Tv of the steering torque T is used as a value related to the steering speed has been described, but the present invention is not limited to this. For example, the angular velocity of the steering wheel 1 may be used as a value related to steering velocity. The angular velocity of the steering wheel 1 is calculated by time-differentiating the steering angle θ detected by the steering angle sensor 15 with a differentiator.

<Modification 2>
In the above embodiment, the so-called 1-pinion type electric power steering device 100 that imparts the driving force of the electric motor 10 to the output shaft 3 formed with the pinion gear 3a has been described as an example, but the present invention is not limited to this. The present invention can also be applied to a so-called two-pinion type electric power steering device in which a shaft having an assist pinion for transmitting the rotation of the electric motor 10 to the rack shaft 5 is provided separately from the output shaft 3 . The present invention can also be applied to a so-called column-type electric power steering device in which the torque sensor 12 and the assist mechanism are separated from the rack shaft 5 and arranged inside the vehicle.

The configuration, action, and effects of the embodiment of the present invention configured as described above will be collectively described.

The electric power steering apparatus 100 is connected to a steering member (steering wheel 1) steered by a driver, and includes a steering shaft 7 that rotates as the steering member (steering wheel 1) is steered by the driver; An electric motor 10 that imparts rotational torque, a torque sensor (torque sensor 12) that detects a steering torque T input from a steering member (steering wheel 1), and an assist base current value Ia that is calculated based on the steering torque T. The static friction compensation current value If for compensating the static friction of the steering system is calculated based on the assist base current calculation unit 121 and the value (torque change rate Tv) related to the steering speed of the steering member (steering wheel 1). static friction compensation current computing units 130 and 230 that compute, a control current computing unit 180 that corrects the assist base current value Ia by the static friction compensation current value If and computes the control current value Isum, and an electric current computing unit 180 that computes the control current value Isum A motor control unit 9 that controls a motor 10 and a steering state determination unit 110 that determines the steering state of a steering member (steering wheel 1) are provided. The base current value Ia is set to increase, and the assist base current value Ia is set to decrease when the steering torque T decreases. , a corrected static friction compensation current calculation unit 142 that calculates a corrected static friction compensation current value If2, and a value related to the steering speed (torque change rate Tv) that is predetermined A time change rate determination unit (sign setting unit 142b) that determines whether or not the steering state is equal to or _greater than the threshold; and a setting unit (sign setting unit 142b) for setting a second threshold T ₂ smaller than the first threshold T ₁ to the threshold when , and a value related to the steering speed (torque change rate Tv) is equal to or greater than the threshold value, the corrected static friction compensation current value If2 is added to the reference static friction compensation current value If1, the static friction compensation current value If is calculated based on the added value, and a value related to the steering speed If (torque change rate Tv) is less than the threshold, the corrected static friction compensation current value If2 is not added to the reference static friction compensation current value If1. , the static friction compensation current value If is calculated based on the reference static friction compensation current value If1.

In this configuration, since the control current value Isum is calculated based on the value (torque change rate Tv) related to the steering speed, it is possible to suppress variations in the steering force according to the steering speed. In addition, since an appropriate static friction compensation current value If can be set for each of the turning steering and the returning steering, the variation in the steering force according to the steering speed can be suppressed for each of the turning steering and the returning steering. Feeling can be improved. In particular, when the return steering is performed, the corrected static friction compensation current value If2 is added earlier than when the turning steering is performed. As a result, the control current value Isum can be quickly reduced during return steering after the steering member (steering wheel 1) has been cut, and a sudden decrease in the steering torque T can be prevented. As a result, it is possible to suppress the variation in the steering force according to the return steering speed, and improve the steering feeling during the return steering.

In the electric power steering apparatus 100, the value related to the steering speed is the time change rate (torque change rate Tv) of the steering torque T, and the reference static friction compensation current calculation unit 141 is calculated by the vehicle speed detection unit (vehicle speed sensor 16). A reference static friction compensation current value If1 is calculated based on a first vehicle speed coefficient f1, which increases as the detected vehicle speed v increases, and the rate of change over time of the steering torque T (torque rate of change Tv). A friction compensation current calculator 142 calculates a corrected static friction compensation current value If2 based on a second vehicle speed coefficient f2 that increases as the vehicle speed v detected by the vehicle speed detector (vehicle speed sensor 16) increases.

In this configuration, the static friction compensation current value If is calculated based on the first vehicle speed coefficient f1 and the second vehicle speed coefficient f2, which increase as the vehicle speed v increases. It is possible to further improve the steering feeling.

The electric power steering apparatus 100 further includes a steering angle detector (steering angle sensor 15) that detects a steering angle θ of a steering member (steering wheel 1). A processing unit is provided that reduces the static friction compensation current value If when the steering angle θ is greater than or equal to θ0 compared to when the steering angle θ is less than the predetermined angle θ0.

In this configuration, when the steering angle θ is less than the predetermined angle θ0, variations in the steering force according to the steering speed during return steering are suppressed, and when the steering angle θ is greater than or equal to the predetermined angle θ0, the driver is counteracted. It is possible to suppress the feeling of power from becoming too large.

Although the embodiments of the present invention have been described above, the above embodiments merely show a part of application examples of the present invention, and the technical scope of the present invention is not limited to the specific configurations of the above embodiments. do not have.

DESCRIPTION OF SYMBOLS 1... Steering wheel (steering member) 7... Steering shaft 9... Motor control part 10... Electric motor 12... Torque sensor (torque detection part) 15... Steering Angle sensor (steering angle detection unit) 16 Vehicle speed sensor (vehicle speed detection unit) 30 Controller 100 Electric power steering device 110 Steering state determination unit 121 Assist base current calculation unit 130, 230 static friction compensation current calculation unit 141 reference static friction compensation current calculation unit 142 corrected static friction compensation current calculation unit 180 control current calculation unit , 248 Steering angle gain processing unit (processing unit) Ia Assist base current value If Static friction compensation current value If1 Reference static friction compensation current value If2 Correction Static friction compensation current value Isum Control current value T Steering torque f1 First vehicle speed coefficient f2 Second vehicle speed coefficient v Vehicle speed θ Steering Angle, θ0: Predetermined angle

Claims (3)

An electric power steering device,
a steering shaft connected to a steering member steered by a driver and rotated as the steering member is steered by the driver;
an electric motor that imparts rotational torque to the steering shaft;
a torque detection unit that detects a steering torque input from the steering member;
an assist base current calculation unit that calculates an assist base current value based on the steering torque;
a static friction compensation current calculation unit for calculating a static friction compensation current value for compensating static friction of the steering system based on a value related to the steering speed of the steering member;
a control current calculation unit that corrects the assist base current value with the static friction compensation current value and calculates a control current value;
a motor control unit that controls the electric motor based on the control current value;
a steering state determination unit that determines a steering state of the steering member;
The static friction compensation current value is set to increase the assist base current value when the steering torque increases, and is set to decrease the assist base current value when the steering torque decreases,
The static friction compensation current calculation unit
a reference static friction compensation current calculator for calculating a reference static friction compensation current value;
a corrected static friction compensation current calculator for calculating a corrected static friction compensation current value;
a rate-of-change determination unit that determines whether a value related to the steering speed is equal to or greater than a predetermined threshold;
A setting unit that sets a first threshold to the threshold when the steering state is a turning state, and sets a second threshold smaller than the first threshold to the threshold when the steering state is a return state. and
If the value related to the steering speed is equal to or greater than the threshold value, the corrected static friction compensation current value is added to the reference static friction compensation current value, and the static friction compensation current value is calculated based on the added value. and if the value related to the steering speed is less than the threshold value, the static friction compensation is based on the reference static friction compensation current value without adding the corrected static friction compensation current value to the reference static friction compensation current value. An electric power steering device characterized by computing a current value. The electric power steering device according to claim 1,
the value related to the steering speed is the time rate of change of the steering torque;
The reference static friction compensation current calculation unit calculates the reference static friction compensation current value based on a first vehicle speed coefficient that increases as the vehicle speed detected by the vehicle speed detection unit increases and the time rate of change of the steering torque. and
The corrected static friction compensation current calculation unit calculates the corrected static friction compensation current value based on a second vehicle speed coefficient that increases as the vehicle speed detected by the vehicle speed detection unit increases. steering device. The electric power steering device according to claim 1 or claim 2,
further comprising a steering angle detection unit that detects a steering angle of the steering member;
The static friction compensation current calculation unit includes a processing unit that reduces the static friction compensation current value when the steering angle is equal to or greater than a predetermined angle compared to when the steering angle is less than the predetermined angle. and an electric power steering device.

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