JP2824926B2 - Electric power steering system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device that assists a steering force by a rotation output of a motor.

Conventional technology and its problems In conventional electric power steering systems,
The steering assist (auxiliary) motor is controlled based on the steering torque detection value and the vehicle speed detection value to generate a steering assist torque. Conventionally, when performing rotational position control, speed control, acceleration control of a steering assist motor to perform inertia compensation, viscosity compensation, etc. in consideration of inertia, viscosity, friction, etc. of a motor and a steering mechanical system, an encoder or a tachogenerator is conventionally used. A signal representing the angular position or the rotational speed was obtained from the detector. Therefore, the conventional electric power steering apparatus has been expensive.

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to obtain at least the acceleration of a steering assist motor without using a rotational position and speed detector such as an encoder and a tachogenerator and to reduce noise of the steering assist motor. I do.

Configuration, operation and effect of the invention The first invention controls a steering assist motor based on a detected steering torque, a detected vehicle speed, and the like.
In an electric power steering apparatus for generating torque, a means for detecting a voltage applied to the steering assist motor, a means for detecting a current flowing to the steering assist motor, and a detection voltage and a good detection current are used. Means for calculating at least the acceleration of the motor, and dead zone means for outputting the acceleration as zero when the calculated acceleration is within a predetermined minute range and outputting a value corresponding to the calculated acceleration when the calculated acceleration is outside the minute range It is characterized by having.

According to the first aspect of the invention, the voltage and current of the steering assist motor are detected, and at least the acceleration of the steering assist motor is calculated using the detected voltage value and detected current value. , No need for a detector such as a tachogenerator. Therefore, the cost can be reduced and the number of wirings can be reduced, so that the occurrence of failure due to disconnection or the like can be prevented.

Further, according to the first aspect, the dead zone means for outputting the acceleration as zero when the calculated acceleration is within the predetermined minute range is provided, so that noise included in the calculated acceleration value can be removed, and acceleration compensation can be performed. , It is possible to significantly reduce or eliminate the minute vibration of the handle and the deterioration of the feeling. When the calculated acceleration is outside the above minute range,
Since a value corresponding to the calculated acceleration (a value almost calculated as it is) is output, the original purpose of the acceleration compensation can be sufficiently achieved even if the above-described dead zone is added.

The second invention controls a steering assist motor based on a steering torque detection value, a vehicle speed detection value, and the like.
In an electric power steering apparatus for generating torque, a means for giving a current command value to the steering assist motor, a means for detecting a current flowing in the steering assist motor, and a method using the current command value and the detected current value, Means for calculating at least the acceleration of the motor, and a dead zone for outputting the acceleration as zero when the calculated acceleration is within a predetermined minute range, and outputting a value corresponding to the calculated acceleration when the calculated acceleration is outside the minute range. Means is provided.

According to the second invention, only the motor current is actually detected, and the detection of the motor current is necessary for the feedback control of the steering assist motor. This eliminates the need for a device, and can further reduce costs and reduce wiring. It goes without saying that also in the second invention, noise included in the calculated acceleration is removed.

FIG. 1 is a block diagram mechanically showing an entire embodiment of an electric power steering apparatus according to the first invention. FIG. 2 is a configuration diagram showing an example of a steering mechanical system to which the power steering device is applied.

First, the power steering mechanical system shown in FIG. 2 will be described.

The turning force of the steering wheel 71 is transmitted to a steering gear 72 including a pinion gear via a handle shaft, further transmitted to a rack shaft 74 by the pinion gear, and the wheel 75 is turned via a knuckle arm or the like. The torque of a steering assist (auxiliary) motor (DC motor) 10 controlled and driven by the control device 11 is transmitted to the rack shaft 74 by meshing the steering gear 73 including a pinion gear with the rack shaft 74, and The steering by 71 will be assisted. The handle 71 and the rotating shaft of the motor 10 are mechanically connected by gears 72, 73 and a rack shaft 74. The steering torque (torsional torque) is detected by the steering torque sensor 21, and the vehicle speed is detected by the vehicle speed sensor 22, and the control device 11 controls the motor 10 based on the detected torque, vehicle speed, and the like as described later. The operating power of the control device 11 and the motor 10 is supplied from a battery 12 mounted on the vehicle.

The control device 11 includes detectors such as a current detector and a voltage detector, a drive circuit that drives the motor 10, a computer (CPU, for example, a microprocessor) that controls the overall control of the motor 10, a memory, a computer, It is composed of an interface circuit with input and output devices. FIG. 1 is a block diagram showing various functions of a computer built in the control device 11 in the form of other input / output devices,
It can be regarded as one drawn with blocks showing various circuits.

In Figure 1, the assist command section 20 is given and the detected vehicle speed V _S of the detected torque V _T and the vehicle speed sensor 22 of the torque sensor 21. Assist torque instruction function section 23 in the assist command section 20 outputs a command value representing the assist torque to be generated by the motor 10 in accordance with the detected torque V _T.
The multiplication constant function unit 24 generates a constant according to the detected vehicle speed V _S , and this constant is used by the multiplication operation unit 25 to calculate the above assist
Multiplied by the torque command value. As a result, the assist torque value output from the multiplication unit 25 (or the motor current command value), as shown in FIG. 3, the value determined by the detected torque V _T and the detected vehicle speed V _S. Figure 3, in accordance with the steering torque V _T, approximately proportional motor current flows (assist torque is generated) in this respect to the steering torque V _T of a range, a constant that exceeds the above range motor current flows (assist torque is generated) manner, and, according to the vehicle speed V _S, to reduce the motor current (assist torque) when the vehicle speed V _S is high, the motor current when the vehicle speed V _S is slow ( To increase the assist torque)
This indicates that an assist command for controlling the motor 10 is generated. Detected torque V _T is given to the phase compensator 26, by which the differential value of the detected torque V _T by the phase compensator 26 is added to the output of the multiplication unit 25, and finally the output of the assist command section 20 (Reference current command value).

After adding (or subtracting) a command value for angle position, velocity, and acceleration control (at least one of which may be described later) to the reference current command value, the current control unit 60 outputs the target current command value as a target current command value. Given. The front part of the current control unit 60 may be constituted by a hardware circuit, or a part thereof may be realized by computer software.

The current control unit 60 is, for example, a PWM (Pulse Width Modul) according to an H-bridge driving method including four switching elements.
ation) Chopper operation using pulse
And performs current feedback control. Armature current i _a of the motor 10 by armature current detector 66 is detected, the current deviation calculation unit 61, the deviation between the target current command value given and the detected current i _a is calculated. The absolute value of the deviation is obtained by the absolute value converter 64, and the duty ratio of the PWM pulse is determined based on the absolute value. On the other hand, the polarity (positive or negative) of the above deviation
It is determined at 62. The generated duty ratio and the determined polarity are given to the motor drive unit 63, and based on these, the motor drive unit 63 controls the four switching elements wired in an H-bridge type on and off to control the motor 10. Drive.

The applied voltage v of the motor 10 is detected by an applied voltage detection unit 51. The detected applied voltage v and the above of the armature current i _a is given low-pass filter means 55 and 56 to the steering angular velocity estimating means 52 via respectively. Low pass
Voltage through the filter means 55 and 56, current is also conveniently identical reference numerals v, represented by i _a. The steering angular velocity estimating means 52 is an observer to a motor voltage given v and the motor current i _a estimated rotational speed of the motor 10. The estimate is ＾
With, for example, Expressed by

FIG. 4 shows an example of a functional configuration when the steering angular velocity estimating means 52 is realized by a minimum-dimensional observer. 4th
The block diagram in the figure realizes the operation of the following operation expression.

The estimation error Then Determine F so that

Here, (t), z (t), F, G, L0, H and J0 are parameters in the observer. In Fig. 4, 1
/ s represents an integral element.

The parameters of the observer use internal parameters of the motor 10, such as armature resistance R, self-inductance L, torque constant K _T , speed induced voltage constant _Ke , motor shaft viscous drag coefficient D, rotor inertia J, and the like. Is calculated.

FIG. 5 shows an example of a functional configuration in the case where the steering angular velocity estimating means 52 is realized by a configuration for obtaining the steering angular velocity from the electrical relational expression of the motor.

The speed electromotive force constant of the motor K _e, the armature resistance of the motor is R following equation is established.

v−K _e = i _a R This gives the following equation.

The operation of the above equation is performed by the configuration of FIG.

The estimated speed obtained from the steering angle speed estimation means 52 in this way Is output through the low pass filter means 57. And the estimated speed (Estimated speed after passing through low pass filter means 57 is the same sign ) Is the estimated acceleration obtained by differentiating the differential operation unit 53. And integrated by the integration operation unit 54 to obtain the estimated angular position. Is converted to Estimated acceleration obtained from differential operation unit 53 Are also filtered by the low pass filter means 58 and output through the dead band scheme 59 (the estimated acceleration after filtering and the estimated acceleration after passing through the dead band ).

Thus, the acceleration, speed, and position of the motor 10 are estimated. Differential operation unit 53, integral operation unit 54
The acceleration and the position can be directly estimated by the observer without using.

Low-pass filter means 55 and 56, detects the motor voltage v, detected motor current i PWM carrier frequency bands contained in _a (a 20KHz longitudinal one example) or in the case of performing control of the discrete value system It removes noise components in the Nyquist frequency band (about 1 KHz in one example) or higher.

Further, the low pass filter means 57, 58 is provided in a relatively low frequency range (for example, based on the torque ripple of the motor).
(About 100 Hz). Incidentally, the estimated speed Estimated acceleration Is about 20 to 30Hz, for example.
The above-described noise can be sufficiently removed.

Thus, a relatively high-frequency noise filter means 55 and 56 included in the detected voltage v and current i _a, the time of calculation of the velocity and acceleration relatively low frequency noise filter means 57 and 58 Therefore, errors in estimated speed and estimated acceleration due to noise are reduced, and highly accurate estimated speed and acceleration can be obtained.

These filter means 55 to 58 are of course realized by software.

Preferably, the estimated steering angular acceleration The low-pass filter means 58 provided in the differential operation unit 53 for calculating the estimated velocity calculated by the steering angular velocity estimation means 52 And the low-pass filter means 58 has a cutoff frequency whose estimated speed is Estimated speed according to , The cutoff frequency increases as the speed increases, and decreases as the speed decreases. The low pass filter means having such a configuration can be easily realized by computer software.

The current ripple, a kind of noise, has a fundamental frequency proportional to the rotation speed of the motor. Using low-pass filter means with a fixed cut-off frequency at a fixed value eliminates noise (particularly noise at frequencies lower than the cut-off frequency) due to low-frequency current ripples generated when the motor rotation speed is low. It is difficult to perform the acceleration estimation calculation. In particular, since the speed estimation value is differentiated, an estimation error occurs due to the noise due to the current ripple, and acceleration compensation (inertial compensation) is performed using the acceleration estimation value including the error. This may lead to deterioration of steering feel.

According to the configuration as described above, the low
Since the cut-off frequency of the pass filter means is changed based on the estimated speed, noise due to current ripple whose frequency changes according to the rotation speed of the motor can be optimally removed, and the current ripple can be reduced. The error of the estimated acceleration value generated due to the above can be reduced. By performing inertia compensation using the acceleration value thus obtained, not only the feeling during steering but also the control performance can be improved.

The cutoff frequency of the low pass filter means 57 is also estimated speed Needless to say, it may be changed in accordance with.

The dead zone means 59 outputs zero as the estimated acceleration when the value of the input estimated acceleration is within a predetermined minute range around zero, and responds to the calculated estimated acceleration when the value is outside the above minute range. A value (a value that gradually increases from zero as shown in the graph in the block 59 and has the same value as the input when the input is somewhat large) is output.

As described above, the command value for controlling the angular position, speed, and acceleration is added to the output of the assist command unit 20. In this case, if noise is included in the output of the torque sensor 21, the command value fluctuates, and high-frequency noise is also superimposed on the detected motor voltage v and motor current i, which slightly fluctuate at high frequency. Due to the fluctuation of the voltage and the current, a minute noise is included in the estimated acceleration. Therefore, if acceleration compensation is performed using this acceleration value, the steering wheel may vibrate minutely or the feeling may be adversely affected due to the mutual adverse effect of the torque sensor noise and the acceleration value noise.

In this embodiment, when the calculated acceleration is within a predetermined minute range, the dead zone means 59 for outputting the acceleration as zero.
The noise included in the calculated acceleration value due to the torque sensor noise can be removed.
When performing acceleration compensation, the handle may vibrate slightly,
Deterioration in feeling can be significantly reduced or eliminated. When the calculated acceleration is outside the above-mentioned minute range, a value corresponding to the calculated acceleration (almost calculated value as it is) is output from the dead zone means 59, so that the dead zone as described above is added. However, the original purpose of acceleration compensation can be sufficiently achieved.

More preferably, limiter means are provided in the steering angular velocity estimating means 52 and the differential calculating section 53 for calculating acceleration, respectively. These limiter means function to suppress the rate of change of the estimated speed and the estimated acceleration beyond the theoretically conceivable ranges. The limiter means can also be realized by software.

The number of motor current ripples per motor rotation is small,
When the amplitude of the ripple is large, this current ripple becomes low frequency noise. If the cut-off frequency is reduced to reduce this noise by the low-pass filter means, the phase lag in the frequency band of velocity and acceleration increases. If speed compensation and acceleration compensation are performed using the speed and acceleration with a delayed phase, oscillation may occur.

By providing the above-mentioned limiter means, it is possible to reduce noise in the estimated value of speed and acceleration due to low-frequency current ripple, and to set a high cut-off frequency of the low-pass filter means 57 and 58. It is possible to minimize the phase lag of the estimated speed and acceleration values. Thereby, oscillation can be suppressed and controllability can be improved.

Estimated location from which noise components have been removed And speed Is the acceleration that has been estimated and noise components have been removed, and that has passed through the dead zone means, Are provided to the inertia compensator 40 for performing positive feedback of the steering angular acceleration, and are used for controlling the position, speed and acceleration of the motor 10. Any one or two of these controls may be performed, or all of them may be performed.

The viscosity command unit 30 basically has a force for returning the steering angle to the neutral position,
That is, a restoring force is generated. Estimated speed Is given to the viscosity compensation value indicating function unit 31, and this function unit 31 Is larger, the absolute value is larger and a command value for generating a torque in the reverse direction is output. On the other hand, the vehicle V _S detected by the vehicle speed sensor 22 is given to the vehicle speed calculating constant function unit 34,
The function unit 34 outputs a large constant as the vehicle V _S is large. The vehicle speed calculation constant is multiplied by a command value output from the function unit 31 in the multiplication calculation unit 32 via a multiplication calculation unit 35 (this will be described later). The result of the multiplication is subtracted from the reference current command value output from the assist command unit 20 via the viscosity command output command unit 33. Thus, the output of the viscosity command unit 30 is the steering angular velocity The greater the is, the more the output of the assist command unit 20 is reduced. Also, the larger the vehicle speed V _{S, the} larger the constant is multiplied, the larger the value, and the greater the effect of viscous braking. This suppresses the instability at the time of returning from the vehicle, which tends to become unstable at higher vehicle speeds, and provides a good handle feeling. Further, at low vehicle speed, compensation for reducing the viscosity works, so that the sense of viscosity of the steering wheel can be reduced and a good feeling can be obtained.

In addition, the estimated steering angle position Is given to the multiplication constant function part 36. The function unit 36 outputs a smaller constant as the absolute value of the steering angle position increases, and the constant is multiplied by the constant output from the function unit 34 in the multiplication operation unit 35, and the result is given to the multiplication operation unit 32. Will be done. On the other hand, the viscosity command output command section 33 indicates that the steering torque _VT is less than a predetermined value and the steering angular velocity Is greater than or equal to a predetermined value, it is determined that the steering system has been released, and only in this case, the output of the multiplication operation unit 32 is subtracted from the output of the assist command unit 20, and otherwise, the output of the viscosity command unit 30 is set to zero. . In this way, the output of the viscosity command unit 30 is output only in the hand-released state, and its magnitude is determined by the steering angle. Is smaller as the absolute value of is smaller. Therefore, it is possible to prevent the steering wheel from becoming unstable near the neutral position by releasing the hand by viscous braking. In addition, at the beginning of the braking effect, the steering angle is relatively large, so the braking force is small at this time. As the vehicle approaches the neutral position, a large braking force can be obtained, so that the convergence to the neutral position becomes natural.

Only the viscosity compensation by the functional blocks 31, 32, 33, and 34 described above may be performed, and the functional blocks 31, 32 (35), 33, and 36 may be used.
May be performed, or all of these may be performed.

The inertia compensator 40 controls the rotor inertia of the motor 10 as if it had become smaller. The inertia compensator 40 eliminates the weight caused by the motor 10 not following the rotation of the steering wheel at the time of sudden steering, and reduces the return speed when releasing. It acts as if to be faster. Estimated steering angle acceleration Is given to an inertia compensation value command function section 41, and a command value obtained by multiplying a command value output from the function section 41 by an appropriate constant in a multiplication operation section 42 is a reference current command of the assist command section 20. Is added to the value.

FIG. 6 shows an embodiment of the second invention. The same components as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In comparison with FIG. 1, the applied voltage detecting section 51 is not provided in FIG. The steering angular velocity estimating unit 52A, the detection armature current i _a described above with given through the low-pass filter means 56, the current command value i _d output from the assist command section 20 is provided. The current command value i _d, not only the value plus the command value of the viscous command section 30 to the reference current command value of an assist command section 20 as illustrated, applied to the reference current command value or the current control unit 60, May be used.

The functional block configuration of the steering angular velocity estimating means 52A is the same as that shown in FIG. 4, but the input and parameter values of each block are different. In this functional block, its parameters are determined according to the above-described internal parameters of the motor 10 so as to perform the next operation.

The estimation error To be Determine F so that

The low-pass filter means 57 and 58 are provided for the steering angular velocity estimating means 52A and the differential calculating unit 53, and the low frequency noise is removed in the speed and acceleration estimating calculation. Same as the example. In addition, a dead zone means 59 is also provided, and the removal of noise components when the estimated acceleration is in a minute range is achieved similarly to the first embodiment of the present invention.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a configuration of an electric power steering apparatus according to an embodiment of the first invention. FIG. 2 is a configuration diagram showing an example of a power steering mechanical system. FIG. 3 is a graph for obtaining a reference current command value based on a steering torque and a vehicle speed. FIG. 4 is a functional block diagram showing the configuration of the steering angular velocity estimating means shown in FIG. FIG. 5 is a functional block diagram showing another configuration example of the steering angular velocity estimating means. FIG. 6 is a functional block diagram showing a configuration of an electric power steering apparatus according to an embodiment of the second invention. 10 ... steering assist motor, 20 ... assist command section, 21 ... torque sensor, 22 ... vehicle speed sensor, 30 ... viscosity command section, 40 ... inertia compensation section, 51 ... applied voltage detection section, 52, 52A: steering angular velocity estimating means, 53: differential operation section, 55, 56, 57, 58 ... low pass filter means, 59 ... dead zone means, 66: armature current detecting section.

Claims (2)

(57) [Claims] An electric power steering device for controlling a steering assist motor based on a detected steering torque value, a detected vehicle speed, and the like to generate a steering assist torque, detects a voltage applied to the steering assist motor. Means for detecting the current flowing through the steering assist motor, means for calculating at least the acceleration of the motor using the detected voltage and the detected current, and when the calculated acceleration is within a predetermined minute range. An electric power steering device, comprising: dead zone means for outputting acceleration as zero and outputting a value corresponding to the calculated acceleration when the acceleration is outside the minute range. 2. An electric power steering system for controlling a steering assist motor based on a detected steering torque value, a detected vehicle speed value, and the like to generate a steering assist torque, wherein a current command value is supplied to the steering assist motor. Providing means, means for detecting a current flowing through the steering assist motor, means for calculating at least the acceleration of the motor using the current command value and the detected current value, and the calculated acceleration is within a predetermined minute range. An electric power steering apparatus, comprising: a dead zone means for outputting an acceleration as zero at times and outputting a value corresponding to the calculated acceleration when the acceleration is outside the minute range.