JP5108860B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus.

In the electric power steering device, the electric motor generates an auxiliary torque corresponding to the magnitude of the steering torque, and the auxiliary torque is transmitted to the steering system to reduce the driver's steering force. In the electric power steering device, the pinion gear of the pinion shaft and the rack teeth of the rack shaft mesh with each other, or the pinion shaft is linked to the electric motor via the worm chia, so mechanical friction (friction) is generated. .
In Patent Document 1 (Japanese Patent Laid-Open No. 10-31605), in addition to the auxiliary torque, a friction compensation torque is generated in the motor when the steering wheel is turned or returned, so that the friction is canceled or apparently the same quality as the friction. An electric power steering control device that can improve steering feeling by generating the above is disclosed.

Japanese Patent Laid-Open No. 10-316005

  However, according to the method disclosed in Patent Document 1, when the vehicle speed is constant, only a certain amount of friction can be compensated no matter what steering the driver performs. For this reason, there is a problem that the steering feeling at the beginning of turning and returning of the steering wheel is lowered.

  Therefore, an object of the present invention is to provide an electric power steering apparatus that can improve steering feeling.

In order to solve such a problem, the present invention provides an electric power steering apparatus according to claim 1, a steering torque detecting means for detecting a steering torque when a driver steers a steering wheel, and the steering torque detection. A basic assist command value determining means for determining a basic assist command value based on a signal from the means; an electric motor for generating an assist torque for assisting a driver's steering based on the basic assist command value from the basic assist command value determining means; In the electric power steering apparatus comprising: a friction compensation value determining means for determining a friction compensation value for compensating the friction in the basic assist command value determining means; a steering angle detecting means for detecting a steering angle of the steering wheel; And the steering based on a signal from the steering angle detecting means. A steering angular velocity calculating means for calculating the rotational speed of eel, the case where the direction of the rotational speed of the detected steering torque detection means the the direction of the steering torque the said steering wheel calculated by the steering angular velocity calculating means coincides , And a return state when the direction of the steering torque detected by the steering torque detector and the direction of the rotational speed of the steering wheel calculated by the rudder angular velocity calculator are different from each other. The friction compensation value from the friction compensation value determining means in the return state is increased as the steering angle increases , the friction compensation value has an upper limit value, and the upper limit value is greater than the forward state than in the return state. It is characterized by a higher hour .

According to the present invention, since the friction compensation value is changed according to the steering angle between forward and backward, the steering feeling can be improved. Further, by increasing the upper limit value of the forward travel, it is possible to give a firm sense of stability to the steering wheel after reaching the upper limit value.

The electric power steering apparatus according to claim 2 is characterized in that an increase rate in the return state of the friction compensation value until the upper limit value is reached is higher than an increase rate in the forward state .

According to the present invention, it is possible to give a firm sense of stability at the start of turning the steering wheel by increasing the rise of the return friction compensation value. Further, by slowing the rising of the forward friction compensation value, it is possible to give a refreshing feeling at the start of turning the steering wheel .

The electric power steering apparatus according to claim 3 increases a friction compensation value according to a steering torque from the friction compensation value determining means in the forward state and the return state as the steering torque increases, The friction compensation value according to the steering torque has an upper limit value, and the rate of increase in the friction compensation value according to the steering torque until reaching the upper limit value in the forward state is higher than the rate of increase in the return state. It is characterized by that.

According to the present invention, the gain in the forward state is set higher than the gain in the return state, so that the friction at the time of torque input in the return state is lower than that at the time of torque input in the forward state and the operation feeling is refreshed. Can be granted .

  The electric power steering apparatus according to a fourth aspect is characterized in that the electric motor is a synchronous reluctance motor.

  According to the present invention, in the case of the synchronous reluctance motor, since there is no magnet, a lot of friction compensation is required. However, by applying the friction compensation by the method of the invention according to claims 1 to 3, the reluctance motor is provided. The steering feeling can also be improved when using.

  The electric power steering apparatus according to the present invention can improve the steering feeling.

It is a figure which shows the structure of the electric power steering apparatus of this embodiment. It is a figure which shows the function structure of the DUTY signal generation part of the control apparatus in the electric power steering apparatus of 1st Embodiment. It is a figure which shows the function structure of the target electric current production | generation part of the control apparatus in the electric power steering apparatus of 1st Embodiment. It is a figure which shows the characteristic of the base signal calculating part in the electric power steering apparatus of 1st Embodiment. It is a figure which shows the function structure of the damper compensation signal calculating part in the electric power steering apparatus of 1st Embodiment. It is a figure which shows the characteristic of the base friction signal calculating part in the electric power steering apparatus of 1st Embodiment. It is a figure which shows the characteristic of the vehicle speed ratio calculating part in the electric power steering apparatus of 1st Embodiment. It is a figure which shows the characteristic of the steering angle ratio calculating part in the electric power steering apparatus of 1st Embodiment. It is a figure which shows the characteristic of the pinion torque ratio calculating part in the electric power steering device of 1st Embodiment. It is a figure which shows the function structure of the base signal calculating part in the electric power steering apparatus of 2nd Embodiment. It is a flowchart of the forward / backward ratio update which the forward / backward ratio calculating part in the electric power steering device of 2nd Embodiment performs.

(First embodiment)
Hereinafter, modes for carrying out the present invention (hereinafter referred to as “embodiments”) will be described in detail with reference to the drawings as appropriate. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.

≪Configuration of electric power steering device≫
The configuration of the electric power steering apparatus 100 according to the present embodiment will be described with reference to FIG.
FIG. 1 is a diagram illustrating a configuration of an electric power steering apparatus according to the present embodiment.
In the electric power steering apparatus 100, a main steering shaft 3 provided with a steering wheel 2, a shaft 1, and a pinion shaft 5 are connected by two universal joints (universal joints) 4. The pinion gear 7 provided at the lower end of the pinion shaft 5 meshes with the rack teeth 8a of the rack shaft 8 that can reciprocate in the vehicle width direction. The left and right steered wheels 10 are connected. With this configuration, the electric power steering apparatus 100 can change the traveling direction of the vehicle when the steering wheel 2 is steered. Here, the rack shaft 8, the rack teeth 8a, and the tie rods 9 and 9 constitute a turning mechanism. The pinion shaft 5 is supported by the steering gear box 20 through the bearings 6a, 6b, and 6c at its lower, middle, and upper portions.

  The electric power steering apparatus 100 includes an electric motor 11 that supplies an auxiliary steering force for reducing the steering force when the steering wheel 2 is steered. A worm gear 12 provided on the output shaft of the electric motor 11 is It meshes with a worm wheel gear 13 provided on the pinion shaft 5. That is, the worm gear 12 and the worm wheel gear 13 constitute a speed reduction mechanism. Further, the steering system is constituted by the electric motor 11, the worm gear 12, the worm wheel gear 13, the pinion shaft 5, the rack shaft 8, the rack teeth 8a, the tie rods 9 and 9 connected to the rotor (not shown) of the electric motor 11. Composed.

The electric motor 11 is a three-phase brushless motor having a stator (not shown) having a plurality of field coils and a rotor (not shown) that rotates inside the stator. The power is converted into mechanical power (P _M = ω _m T _M ). Here, ω _m is a rotation speed, and T _M is a generated torque (assist torque) of the electric motor 11. Further, the relationship between the generated torque T _M and the output torque T _M ′ that can be actually extracted as output is expressed by the following equation (1). (I: Reduction ratio between the worm gear 12 and the worm wheel gear 13)
T _M ′ = T _M − ( _cm · dθ _m / dt + J _m · d ² θ _m / dt ² ) i ² (1)
From the above equation (1), the relationship between the output torque T _M ′ and the rotation angle θ _m of the electric motor 11 is defined by the inertia moment J _m of the rotor of the electric motor 11 and the viscosity coefficient _cm, and the vehicle characteristics and the vehicle state Is irrelevant.

  Further, the electric power steering device 100 includes a control device 200, electric motor driving means 60 for driving the electric motor 11, a resolver 50, a torque sensor 30 for detecting pinion torque applied to the pinion shaft 5, and an output of the torque sensor 30. Is provided with a differential amplifier circuit 40 and a vehicle speed sensor 35.

  The motor driving means 60 includes a plurality of switching elements such as a three-phase FET bridge circuit, for example, and uses a DUTY (DUTY U, DUTY V, DUTY W) signal output from the control device 200 to generate a rectangular wave voltage. Is generated and the electric motor 11 is driven. The motor driving means 60 has a function of detecting a three-phase armature current I (IU, IV, IW) using a hall element (not shown).

The resolver 50 detects the rotation angle θ _m of the electric motor 11 and outputs a rotation angle signal θ _mS . For example, a sensor for detecting a change in magnetoresistance is provided with a plurality of uneven portions at equal intervals in the circumferential direction. It is close to the magnetic rotating body. The rotation angle signal θ _mS is a detected rotation angle signal of the electric motor 11.
A steering angle sensor (steering angle detection means) 37 is attached to the main steering shaft 3, detects the steering angle θ of the steering wheel 2, and outputs a steering angle signal θ _S. The steering angle signal θ _S is a signal of the detected steering angle θ of the steering wheel 2.
The steering angle sensor 37 according to the present embodiment is described as being configured to be attached to the main steering shaft 3, but is not limited to this, for example, the steering angle θ from a position sensor that detects the position of the rack shaft 8. It is good also as a structure which detects.

The torque sensor (steering torque detection means) 30 detects pinion torque applied to the pinion shaft 5, and a magnetostrictive film is attached to two axial directions of the pinion shaft 5 so as to have anisotropy in the reverse direction. A detection coil is inserted on the surface of each magnetostrictive film so as to be separated from the pinion shaft 5.
Here, the main steering shaft 3 provided with the steering wheel 2, the shaft 1, and the pinion shaft 5 are connected by two universal joints (universal joints) 4, and the pinion torque applied to the pinion shaft 5 is That is, since it is the steering torque T for steering the steering wheel 2, the torque sensor 30 functions as a steering torque detection means for the steering wheel 2.

The differential amplifier circuit 40 is one in which the detection coil by amplifying a difference of magnetic permeability changes in the two magnetostrictive films detected as an inductance change, and outputs a torque signal T _S. Incidentally, the torque signal T _S is a signal indicating a pinion torque level.

The vehicle speed sensor 35 detects the vehicle speed V of the vehicle as the number of pulses per unit time, and outputs a vehicle speed signal V _S.

The control device 200 includes a microcomputer having a CPU, ROM, RAM, and the like, and includes a three-phase current I from the motor driving means 60, a rotation angle signal θ _mS from the resolver 50, a vehicle speed signal V _S from the vehicle speed sensor 35, steering. A DUTY signal for driving the motor 11 is output to the motor driving means 60 with the steering angle signal θ _S from the angle sensor 37 and the generated torque T _M obtained from the torque signal T _S from the differential amplifier circuit 40. . The output of the DUTY signal, the motor drive unit 60 drives the motor 11 by the torque generated T _M.

In addition, the control device 200 includes a target current signal generation unit 201 and a DUTY signal generation unit 202.
Next, the target current signal generation unit 201 and the DUTY signal generation unit 202 will be described with reference to FIGS. 2 and 3.
FIG. 2 is a diagram illustrating a functional configuration of a DUTY signal generation unit of the control device in the electric power steering apparatus according to the first embodiment. FIG. 3 is a diagram illustrating a functional configuration of a target current generation unit of the control device in the electric power steering apparatus according to the first embodiment.

<< Configuration of DUTY signal generator >>
As shown in FIG. 2, the DUTY signal generation unit 202 includes an excitation current generation unit 260, a Q-axis (torque axis) PID control unit 270, a D-axis (magnetic pole axis) PID control unit 275, a 2-axis three-phase conversion unit 280, A three-phase two-axis conversion unit 285, a PWM conversion unit 290, and adders 253 and 254 are provided as functional blocks.

The three-phase two-axis conversion unit 285 uses the three-phase currents IU, IV, and IW of the electric motor 11 (see FIG. 1) detected by the electric motor driving unit 60 (see FIG. 1) as the magnetic pole axis of the rotor of the electric motor 11. A shaft current (ID) is converted into a Q-axis current (IQ) that is an axis electrically rotated 90 degrees with respect to the D-axis. The D-axis current ID is proportional to the excitation current, and Q The shaft current IQ is proportional to the generated torque T _M of the electric motor 11.

  The exciting current generator 260 generates and outputs an exciting current target value for the electric motor 11 (see FIG. 1).

  The D-axis (magnetic pole axis) PID control unit 275 outputs the output signal of the adder 254, that is, the D-axis current ID output from the three-phase two-axis conversion unit 285 and the excitation current target generated by the excitation current generation unit 260. P (proportional) control, I (integral) control, and D (differential) control are performed so as to reduce the difference from the value.

The Q-axis (torque axis) PID control unit 270 outputs the output signal of the adder 253, that is, the difference between the Q-axis current IQ output from the three-phase two-axis conversion unit 285 and the target current IM of the Q-axis current IQ. P (proportional) control, I (integral) control, and D (differential) control are performed so as to decrease the deviation signal IE. The target current IM of the Q-axis current IQ that defines the generated torque T _M of the electric motor 11 (see FIG. 1) is a signal output from the target current signal generation unit 201, and details will be described later.

The 2-axis 3-phase conversion unit 280 converts the 2-axis signal of the output signal VQ of the Q-axis (torque axis) PID control unit 270 and the output signal VD of the D-axis (magnetic pole axis) PID control unit 275 into 3-phase signals UU, UV , Convert to UW and output. The biaxial three-phase converter 280 receives the rotation angle signal θ _{mS of} the electric motor 11 (see FIG. 1) output from the resolver 50 (see FIG. 1) and outputs a signal corresponding to the magnetic pole position of the rotor. Is done.

The PWM converter 290 is an ON / OFF signal [PWM (Pulse Width Modulation) signal] having a pulse width proportional to the magnitude of the three-phase signals UU, UV, UW output from the biaxial three-phase converter 280. Signals (DUTY U, DUTY Y, DUTY W) are generated and output to the motor driving means 60 (see FIG. 1). The PWM converter 290 receives the rotation angle signal θ _{mS of} the electric motor 11 (see FIG. 1) output from the resolver 50 (see FIG. 1) and outputs a signal corresponding to the magnetic pole position of the rotor.

<< Configuration of target current signal generator >>
As shown in FIG. 3, the target current signal generation unit (basic assist command value determination means) 201 includes a base signal calculation unit 210, a damper compensation signal calculation unit 220, an inertia compensation signal calculation unit 230, a steering angular velocity calculation unit 240, and a forward trip. A return state detection unit 245 and adders 251 and 252 are provided as functional blocks.
The generation of the target current IM of the Q-axis current IQ that defines the generated torque T _M of the electric motor 11 (see FIG. 1) will be described below.
The adder 251 subtracts the damper compensation current A2 output from the damper compensation signal calculation unit 220 from the base assist current A1 output from the base signal calculation unit 210, and outputs the result to the adder 252. The adder 252 adds the inertia compensation current A3 output from the inertia compensation signal calculation unit 230 to the output value (A1-A2) from the adder 251 to obtain the DUTY signal as the target current IM (that is, IM = A1-A2 + A3). The data is output to the generation unit 202.
The target current IM corresponds to the “basic assist command value” recited in the claims, and the damper compensation current A2 corresponds to the “friction compensation value” recited in the claims.

<Base signal calculation unit>
Base signal computing part 210 from the torque signal T _S for outputting the differential amplifier circuit 40 (see FIG. 1), a vehicle speed signal V _S of the vehicle speed sensor 35 (see FIG. 1) outputs, a reference of the target current IM The base assist current A1 is generated and output to the adder 251.
The base assist current A1 is performed by referring to a base map 210a that is set in advance by experimental measurement or the like and stored in the base signal calculation unit 210.

The correspondence relationship between the torque signal T _S and the vehicle speed signal V _{S of} the base map 210a stored in the base signal calculation unit 210 and the base assist current A1 will be described with reference to FIG.
FIG. 4 is a diagram illustrating characteristics of the base signal calculation unit in the electric power steering apparatus according to the first embodiment.
In the base map 210a, when the level of the torque signal T _S is small, a non-assist region N1 where the base assist current A1 is set to zero level is provided, and when the level of the torque signal T _S becomes larger than the non-assist region N1. , And has a characteristic of increasing linearly with the gain G1.
In the base map 210a, when the level of the torque signal T _S is equal to or higher than a predetermined level, the gain increases from G1 to G2 (inclination increases), and the level of the torque signal T _S further increases to exceed the predetermined level. It has a characteristic that the level of the base assist current A1 is saturated when it becomes higher than a predetermined level.

  Further, the base map 210a has characteristics that the gains G1 and G2 are reduced and the non-assist region N1 is increased as the vehicle speed V is increased. Because of this characteristic, the load is the heaviest during stationary operation at zero vehicle speed, the load is relatively light at medium and low speeds, and the road surface information is given to the driver by taking up the manual steering area at high speeds. I am doing so.

<Inertia compensation signal calculation unit>
Returning to FIG. 3, the inertia compensation signal calculation unit 230 generates an inertia compensation current A <b> 3 from the torque signal T _S output from the differential amplifier circuit 40 (see FIG. 1), and outputs it to the adder 252.
This inertia compensation current A3 is generated by referring to an inertia map 230a set in advance by experimental measurement or the like and stored in the inertia compensation signal calculation unit 230.

  In addition, the inertia compensation signal calculation unit 230 compensates for a decrease in responsiveness due to the inertia of the rotor of the electric motor 11. In other words, when switching the rotation direction from the normal rotation to the reverse rotation, or from the reverse rotation to the normal rotation, the electric motor 11 tries to maintain the state by inertia, so the rotation direction is not switched immediately. Therefore, the inertia compensation signal calculation unit 230 performs control so that the switching of the rotation direction of the electric motor 11 coincides with the timing at which the rotation direction of the steering wheel 2 is switched. In this manner, the inertia compensation signal calculation unit 230 improves the response delay of the steering due to the inertia of the steering system and provides a clean steering feeling.

<Rudder angular velocity calculation part>
The steering angular speed calculation unit (steering angular speed calculation means) 240 differentially calculates the steering angle θ of the steering wheel 2 (see FIG. 1) based on the steering angle signal θ _S output from the steering angle sensor 37 (see FIG. 1). As a result, the steering angular velocity ω (= dθ / dt) is calculated, and the steering angular velocity signal ω _S is generated and output to the damper compensation signal calculation unit 220 and the forward / backward state detection unit 245.
The steering angular velocity dθ / dt obtained by differentially calculating the steering angle θ is the rotational angular velocity dθ _m / dt obtained by differentially calculating the reduction ratio i and the rotational angle θ _m of the reduction mechanism (worm gear 12 and worm wheel gear 13). ) Is obtained from the relationship of the equation.
dθ / dt = i ⁻¹ · dθ _m / dt (2)
Therefore, the steering angular velocity calculation unit 240 may be configured to obtain the steering angular velocity ω of the steering wheel 2 from the rotation angle θ _m of the motor 11 of the resolver 50 (see FIG. 1) and the reduction ratio i.

<Backward detection unit>
The forward / return state detection unit 245 determines the “forward state” or “return state” from the torque signal T _S output from the differential amplifier circuit 40 (see FIG. 1) and the steering angular velocity signal ω _S output from the steering angular velocity calculation unit 240. ”Is detected. In addition, a state signal J indicating “forward state” or “return state” is generated from the detection result and output to the damper compensation signal calculation unit 220.

The “forward state” is when the direction of the steering torque of the steering wheel 2 (see FIG. 1) and the rotational direction coincide with each other, and the “returned state” is different from the direction of the steering torque of the steering wheel 2 and the rotational direction. Is the time.
This is the “forward state” when the signs (+/−) of the torque signal T _S and the steering angular velocity signal ω _S have the same sign, that is, when T _S · ω _S > 0. On the other hand, the case where the sign (+/−) of the torque signal T _S and the steering angular velocity signal ω _S is opposite, that is, the case where T _S · ω _S <0 is the “return state”.

<Damper compensation signal calculation unit>
The damper compensation signal calculation unit (friction compensation value determining means) 220 includes a torque signal T _S output from the differential amplifier circuit 40 (see FIG. 1) and a vehicle speed signal V _S output from the vehicle speed sensor 35 (see FIG. 1). From the steering angle signal θ _S output from the steering angle sensor 37 (see FIG. 1), the steering angular velocity signal ω _S output from the steering angular velocity calculation unit 240, and the state signal J output from the forward / backward state detection unit 245, the damper A compensation current A2 is generated and output to the adder 251.
The damper compensation signal calculation unit 220 will be described in more detail with reference to FIG.
FIG. 5 is a diagram illustrating a functional configuration of a damper compensation signal calculation unit in the electric power steering apparatus according to the first embodiment.

  As shown in FIG. 5, the damper compensation signal calculation unit 220 includes a base friction signal calculation unit 221, a vehicle speed ratio calculation unit 222, a steering angle ratio calculation unit 223, a pinion torque ratio calculation unit 224, and integrators 225, 226, and 227. Provide as a functional block.

The integrator 225 adds the vehicle speed ratio R _V output from the vehicle speed ratio calculation unit 222 to the base friction output from the base friction signal calculation unit 221, and outputs the result to the integrator 226.
The integrator 226 adds the steering angle ratio R _θ output from the steering angle ratio calculation unit 223 to the output value of the integrator 225 and outputs the result to the integrator 227.
The accumulator 227 integrates the output value of the accumulator 226 with the pinion torque ratio _RT of the pinion torque ratio calculation unit 224 and outputs the result to the adder 251 (see FIG. 3) as a damper compensation current A2.

<Base friction signal calculation unit>
The base friction signal calculation unit 221 generates a base friction signal serving as a reference for the damper compensation current A2 from the steering angular velocity signal ω _S output from the steering angular velocity calculation unit 240 (see FIG. 3), and outputs the base friction signal to the integrator 225.
The base friction signal is generated by referring to a base friction map 221a that is set in advance by experimental measurement or the like and stored in the base friction signal calculation unit 221.

FIG. 6 is a diagram illustrating characteristics of the base friction signal calculation unit in the electric power steering apparatus according to the first embodiment.
In the base friction map 221a, as shown in FIG. 6, the base friction signal is determined by the sign (+/−) of the steering angular velocity signal ω _S.

<Vehicle speed ratio calculation unit>
The vehicle speed ratio calculation unit 222 generates a vehicle speed ratio R _V from the vehicle speed signal V _S output from the vehicle speed sensor 35 (see FIG. 1), and outputs the vehicle speed ratio R _V to the integrator 225.
The vehicle speed ratio R _V is generated by referring to a vehicle speed ratio map 222 a that is preset by experimental measurement or the like and stored in the vehicle speed ratio calculation unit 222.

FIG. 7 is a diagram illustrating characteristics of the vehicle speed ratio calculation unit in the electric power steering apparatus according to the first embodiment.
In the vehicle speed ratio map 222a, as shown in FIG. 7, the vehicle speed ratio R _V is increased so that the friction increases as the vehicle speed V increases, and the vehicle speed ratio R _V decreases so that the friction decreases as the vehicle speed _V decreases. .

<Rudder angle ratio calculation unit>
The steering angle ratio calculation unit 223 generates a steering angle ratio R _θ from the steering angle signal θ _S output by the steering angle sensor 37 (see FIG. 1) and the state signal J output by the forward / backward state detection unit 245, Output to the integrator 226.
This steering angle ratio R _theta, by reference to the steering angle ratio map 223a stored preset the steering angle ratio calculation unit 223 by experimental measurements or the like, is generated.

FIG. 8 is a diagram illustrating characteristics of the steering angle ratio calculation unit in the electric power steering apparatus according to the first embodiment.
In the steering angle ratio map 223a, as shown in FIG. 8, a steering angle theta is also increased steering angle ratio R _theta with increasing large, the steering angle ratio R _theta has an upper limit value.
Here, the upper limit value of the steering angle ratio R _theta is towards the forward state is set higher than that during the return state.
In this way, by setting the upper limit value of the forward state high, it is possible to give a stable and stable operation feeling to the steering wheel 2 after reaching the upper limit value. Further, by setting the upper limit value of the return state lower than the forward state, it is possible to facilitate the return operation of the steering wheel 2 after reaching the upper limit value.

Furthermore, the gain to the steering angle ratio R _theta reaches the upper limit (the slope), the direction of the state returned than forward state is set high.
Thus, by setting the gain in the return state higher than the gain in the forward state, it is possible to impart a clean operation feeling to the start of turning the steering wheel 2 by delaying the rising of the forward state. . In addition, by making the return state rise earlier, it is possible to provide a stable and stable operation feeling at the beginning of turning of the steering wheel 2.

<Pinion torque ratio calculation unit>
The pinion torque ratio calculation unit 224 generates a pinion torque ratio _RT from the torque signal T _S output from the differential amplifier circuit 40 (see FIG. 1) and the state signal J output from the forward / backward state detection unit 245, Output to the integrator 227.
The pinion torque ratio _RT is generated by referring to a pinion torque ratio map 224a that is preset by experimental measurement or the like and stored in the vehicle pinion torque ratio calculation unit 224.

FIG. 9 is a diagram illustrating characteristics of the pinion torque ratio calculation unit in the electric power steering apparatus according to the first embodiment.
In the pinion torque ratio map 224a, as shown in FIG. 9, the pinion torque ratio _RT increases as the pinion torque _T increases, and the pinion torque ratio _RT has an upper limit value.
Here, the gain (slope) until the pinion torque ratio _RT reaches the upper limit value is set higher in the forward state than in the return state.
In this way, by setting the gain in the forward state higher than the gain in the return state, the torque input during the return state is lower than the torque input during the forward state, giving a clean operation feeling. can do.

≪Summary≫
As described above, according to the first embodiment, since the friction can be made variable according to the steering angle θ, the electric power steering apparatus that achieves both disturbance toughness / convergence and good return can be achieved. Can be provided.

(Modification of the first embodiment)
The electric motor 11 according to the first embodiment has been described as a brushless motor, but a synchronous reluctance motor may be used as the electric motor 11.
Since the synchronous reluctance motor does not use a magnet inside, the friction caused by the electric motor 11 is reduced as compared with the case where a brushless motor is used. However, as described in the first embodiment, by providing a friction compensation value, the steering feeling can be improved even when a synchronous reluctance motor is used, as in the case of using a brushless motor. Can do.

(Second Embodiment)
In the first embodiment, the damper compensation current A2 is applied to control the friction. In the second embodiment, the base assist current A1 is controlled. Note that the same elements as those of the first embodiment are denoted by the same reference numerals and description thereof is omitted.

FIG. 10 is a diagram illustrating a functional configuration of a base signal calculation unit in the electric power steering apparatus according to the second embodiment.
In the second embodiment, the base assist current A1 output from the base signal calculation unit 210 is integrated with the forward / return ratio R _J output from the forward / return ratio calculation unit 212 by the integrator 211, and the base assist current A1 ′ (= A1 × R _J ).
Note that description will be made with the damper compensation signal calculation unit 220 (see FIG. 3) and the inertia compensation signal calculation unit 230 (see FIG. 3) omitted.

<Return ratio calculation unit>
The forward / return ratio calculation unit 212 outputs the forward / backward ratio R _J to the integrator 211. Further, the forward / return ratio R _J is updated from the current forward / return ratio R _J and the state signal J output by the forward / backward state detection unit 245 at regular intervals (for example, every 25 ms).

A method for updating the forward / return ratio R _J by the forward / backward ratio calculation unit 212 will be described.
FIG. 11 is a flowchart of the forward / backward ratio update executed by the forward / backward ratio calculator in the electric power steering apparatus according to the second embodiment.
The forward / return ratio calculation unit 212 determines whether or not the state signal J output by the forward / backward state detection unit 245 is a signal indicating the forward state (step S101).

When it is in the forward state (Yes in step S101), the forward / return ratio calculation unit 212 increases the forward / return ratio R _J (step S102).
Next, the forward / return ratio calculation unit 212 determines whether or not the increased forward / return ratio R _J is greater than the upper limit R _max (step S103).

When the return ratio R _J is larger than the upper limit value R _max (Yes in step S103), the return ratio calculation unit 212 updates the return ratio R _J as the upper limit value R _max (step S104). The update process of the return ratio R _J is terminated.
On the other hand, when the return ratio R _J is equal to or less than the upper limit value R _max (No in step S103), the update process of the return ratio R _J is finished as it is.

  In step S101, when it is not the forward state (No in step S101), the forward / return ratio calculation unit 212 determines whether or not the state signal J output from the forward / backward state detection unit 245 is a signal indicating a return state. Determination is made (step S105).

If it is in the return state (Yes in step S105), the forward / return ratio calculation unit 212 decreases the forward / return ratio R _J (step S106).
Next, the forward / return ratio calculation unit 212 determines whether or not the decreased forward / return ratio R _J is smaller than the addition / subtraction value R _min (step S107).

When the return ratio R _J is smaller than the lower limit value R _max (Yes in step S107), the return ratio calculation unit 212 updates the return ratio R _J as the lower limit value R _min (step S108). The update process of the return ratio R _J is terminated.
On the other hand, when the forward / return ratio R _J is equal to or greater than the lower limit value R _min (No in step S107), the forward / backward ratio R _J update process is terminated.

In step S105, when the return state is not set (No in step S105), the forward / return ratio R _J is not updated, and the update process of the forward / return ratio R _J is terminated.

≪Summary≫
In the torque signal T _S output from the differential amplifier circuit 40 (see FIG. 1), the pinion torque T is caused by the driver's steering input or torque generated by the disturbance input (steering inertia and steering angular velocity). It is impossible to determine whether it is caused by (product of ω). Therefore, when the pinion shaft 5 by the input of the disturbance is rotated from the base signal computing part 210 refers to the torque signal T _S, the base assist current A1 to assist in the rotational direction opposite to the direction of the steering wheel 2 is output As a result, the return of the steering wheel 2 becomes worse.
On the other hand, according to the second embodiment, when the return state is determined, the base assist current A1 ′ is decreased by decreasing the forward / return ratio R _J. Accordingly, it is possible to provide an electric power steering device that provides an operation feeling that reduces the influence of return deterioration due to the input of disturbance.

2 Steering wheel 11 Electric motor 30 Torque sensor (steering torque detection means)
35 Vehicle speed sensor 37 Steering angle sensor (steering angle detection means)
40 differential amplifier circuit 50 resolver 60 motor drive means 100 electric power steering device 200 control device 201 target current signal generation unit (basic assist command value determination means)
202 DUTY signal generation unit 210 Base signal calculation unit 210a Base map 212 Forward / return ratio calculation unit 220 Damper compensation signal calculation unit (friction compensation value determination means)
221 Base friction signal calculator 221a Base friction map 222 Vehicle speed ratio calculator 222a Vehicle speed ratio map 223 Steering angle ratio calculator 223a Steering angle ratio map 224 Pinion torque ratio calculator 224a Pinion torque ratio map 230 Inertia compensation signal calculator 230a Inertia map 240 Rudder angular velocity calculation unit (rudder angular velocity calculation means)
245 Forward / return state detector 211, 225, 226, 227 Accumulator 251, 252, 253, 244 Adder

Claims (4)

Steering torque detecting means for detecting a steering torque when the driver steers the steering wheel;
Basic assist command value determining means for determining a basic assist command value based on a signal from the steering torque detecting means;
An electric motor for generating an assist torque for assisting a driver's steering based on a basic assist command value from the basic assist command value determining means;
In an electric power steering apparatus comprising:
Friction compensation value determining means for determining a friction compensation value for compensating friction in the basic assist command value determining means;
Steering angle detecting means for detecting the steering angle of the steering wheel;
Rudder angular velocity calculating means for calculating the rotational speed of the steering wheel based on a signal from the steering angle detecting means;
When the direction of the steering torque detected by the steering torque detecting means and the direction of the rotational speed of the steering wheel calculated by the steering angular speed calculating means coincide with each other,
When the direction of the steering torque detected by the steering torque detecting means is different from the direction of the rotational speed of the steering wheel calculated by the steering angular speed calculating means,
Increasing the friction compensation value from the friction compensation value determining means in the forward state and the returning state as the steering angle increases ,
The friction compensation value has an upper limit value, and the upper limit value is higher in the forward state than in the return state . 2. The electric power steering apparatus according to claim 1 , wherein an increase rate in the return state of the friction compensation value until the upper limit value is reached is higher than an increase rate in the forward state.   Increasing the friction compensation value according to the steering torque from the friction compensation value determining means in the forward state and the return state as the steering torque increases,
  The friction compensation value according to the steering torque has an upper limit value,
  The increase rate in the forward state of the friction compensation value according to the steering torque until reaching the upper limit value is higher than the increase rate in the return state
  The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is provided. The electric power steering apparatus according to any one of claims 1 to 3, wherein the electric motor is a synchronous reluctance motor.

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