JP2598269B2 - Motor control device for electric power steering device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a motor control device of an electric power steering device that applies an auxiliary steering force (power assist) by driving a motor to a steering system of a vehicle.

[Prior art]

As a motor control device of the electric power steering device as described above, a vehicle speed sensor for detecting a vehicle speed and a steering angle sensor for detecting a steering angle are provided in addition to a torsion torque sensor for detecting a torsional torque of a steering system. A command signal based on the output of the torque sensor is corrected so as to decrease as the vehicle speed increases based on the output of the vehicle speed sensor, and a return signal that increases from the output of the steering angle sensor as the steering angle increases increases. An apparatus for controlling the rotation direction and rotation torque of an electric motor has already been proposed by the present applicant (see Japanese Patent Application Laid-Open No. 61-98675).

[Problems to be solved by the invention]

By the way, in the motor control device of the conventional electric power steering device as described above, the range where the steering angle or the torsional torque is small is set as the dead zone of the power assist, since it is recognized that the power assist is unnecessary when the vehicle is traveling straight. For this reason, there is a problem that no power assist can be obtained when the steering is maintained at a small steering angle, such as when traveling on an extremely gentle curve, and the function of the power assist cannot be sufficiently exhibited. The present invention has been made in order to solve the above-described problems, and has a motor control device for an electric power steering device that can obtain appropriate power assist even when steering at a small steering angle. The purpose is to provide.

[Means for solving the problems]

For this purpose, the present invention relates to an electric power steering device in which the drive control unit controls the rotation direction and the rotation torque of the electric motor in accordance with an assist signal based on an output signal of a torsional torque sensor for detecting a torsional torque of a steering system. The torsional torque corresponding additional torque value which does not output within a predetermined small torsional torque based on the output of the torsional torque sensor, but outputs a torsional torque corresponding assist additional signal which becomes a constant value when the value exceeds a predetermined value. An instructing unit, based on the output of a steering angle sensor that detects the steering angle, maintains a predetermined constant value within a small steering angle, and outputs a steering angle corresponding assistance addition signal that gradually decreases when exceeding the small steering angle. The torque value indicating unit compares the torsional torque assist assist signal with the steering angle assist assist signal, and outputs the smaller absolute value of the assist signal. A steering holding command unit comprising a comparing unit for outputting as an additional signal, by adding the assist signal and the assist additional signal, characterized by comprising an addition unit for obtaining an instruction signal of the electric motor.

[Action]

In such a means, an assist addition signal having a characteristic in which the absolute value gradually increases to a predetermined value in accordance with the torsional torque is output from the steering holding command unit by the steering operation with a small steering angle, and the steering is maintained by the assist addition signal. The assist of the operating force is continuously performed from the lick. When the steering angle exceeds the small steering angle, the absolute value of the assist addition signal gradually decreases, so that the steering wheel is not too light, and an appropriate response can be obtained during steering.

【Example】

Hereinafter, an embodiment of the present invention will be specifically described with reference to the drawings. In FIG. 1, reference numeral 1 denotes an electric motor for power assist, which is connected to a pinion shaft of a rack and pinion mechanism of a steering system (not shown) via a reduction gear, a joint, or the like, and can apply an assist force to the steering system. It has become. Such an electric motor 1 includes a positive / negative discriminating unit 21, an absolute value converting unit 22, a duty control unit 23, an armature current detecting unit 24,
By the drive control unit 2 including the electric motor drive unit 25 and the like,
The rotation direction and the rotation torque are controlled based on a command signal described later. That is, the command signal is input to the positive / negative determination unit 21 and the absolute value conversion unit 22, and the determination signal of the positive / negative determination unit 21 is input to the electric motor driving unit 25, whereby the direction of the motor current is switched according to the command signal. Controlled and absolute value converter
The output signal of 22 is input to the duty control unit 23 and the duty ratio is determined. When the duty ratio is input to the electric motor drive unit 25, the rotation torque according to the magnitude of the command signal is set. The rotational torque of the electric motor 1 is converged to a fixed instruction value by the armature current detection unit 24 detecting the armature current of the electric motor 1 and feeding back the detected value to the duty control unit 23. Is controlled. Here, assuming that a command signal is output to the drive unit control 2, in the present embodiment, the assist command unit 3, the return command unit 4,
A phase compensation command section 5, a steering angle phase compensation command section 6, and a steering hold command section 7 are provided. The assist command unit 3 basically generates an assist signal according to the magnitude and direction of the torsional torque of the steering system. The assist command unit 3 is installed on a pinion of the steering system (steering system) to provide the direction and magnitude of the torsional torque. A torsion torque sensor 31 for detecting the force and an output voltage signal (see FIG. 2) of the torsion torque sensor 31, based on which an assist signal having a characteristic shown by a solid line in the graph of FIG. ,
When the magnitude of the torsional torque is less than a predetermined value, it is not output, and when it exceeds the predetermined value, the assist torque value command function unit 32 outputs an assist signal that increases or decreases according to the value of the torsional torque with a polarity corresponding to the direction of the torsional torque. Is provided. The assist command unit 3 is provided with a vehicle speed sensor 33 for detecting the speed of the vehicle, and based on the output voltage signal of the vehicle speed sensor 33, decreases as the vehicle speed increases as shown in the graph of FIG. An addition constant function unit 34 for generating an addition constant signal Sv having a characteristic to be changed, and an addition operation unit 35 for inputting the addition constant signal Sv and the output signal of the torsion torque sensor 31 and outputting the signal to the assist torque value indicating function unit 32. Is provided. The addition operation unit 35 adds and subtracts an addition constant signal Sv to the output signal of the torsion torque sensor 31 in accordance with the polarity of the output signal, whereby the characteristics shown in the graph of FIG. It is designed to be translated. That is, as an example of the characteristic in the case of right turning, as shown in FIG. 5, the output of the assist torque value indicating function unit 32 decreases in absolute value with increasing vehicle speed at the same torsional torque, and at the same vehicle speed, the torsional torque decreases. The absolute value of the output increases with an increase in the absolute value of. A multiplication constant function unit 36 and a multiplication operation unit 37 are provided to correct such output characteristics according to the vehicle speed as shown by the broken line in FIG. The multiplication constant function 36 is a multiplication constant signal having characteristics shown in FIG. 6 based on the output voltage signal of the vehicle speed sensor 33, that is, the multiplication constant is 1 when the vehicle speed is 0, and the constant gradually increases as the vehicle speed increases. This is to generate a multiplication constant signal having a characteristic of decreasing toward zero. The multiplication operation section 37 multiplies the output of the assist torque value indicating function section 32 by the multiplication constant. The assist signal it from the multiplication operation section 37 is provided in accordance with the vehicle speed in FIG. As shown by the broken line. Next, the return command section 4 generates a return signal for returning the steering angle to the neutral (straight) position in accordance with the steering angle of the steering system, and for example, a rack in a rack and pinion mechanism of the steering system. A steering angle sensor 41 for detecting a turning angle based on the amount of movement of the steering wheel, and a return torque value indicating function for outputting a return signal iθ having characteristics shown in the graph of FIG. 7 based on an output voltage signal of the steering angle sensor 41 A part 42 is provided. The phase compensation command section 5 receives the output signal of the torsional torque sensor 31, receives a signal proportional to the differential value of the output signal, and outputs a signal proportional to the differential value. A phase compensation instruction function unit 52 that outputs an assist assist signal ia having characteristics as shown in the graph is provided. In the present embodiment, the output signal of the phase compensation unit 51 is further added to the output signal of the torsional torque sensor 31 to perform an addition operation. It is input to the section 35 and affects the input signal to the assist torque value indicating function section 32. Further, the steering angle phase compensation command section 6 generates an attenuation signal in the direction opposite to the steering direction according to the speed of the steering operation, receives the output signal of the steering angle sensor 41, and obtains a differential value thereof. A steering angle phase compensating unit 61 that generates a signal proportional to the steering angle phase compensating unit 61, and a steering angle phase compensating instruction function that outputs an attenuation signal i having a characteristic shown in a graph of FIG. And a part 62. The steering command unit 7 generates an assist additional signal for assisting the steering in a small steering angle in the vicinity of the straight running in the steering state, and receives the output voltage signal of the steering angle sensor 41 as an input. A torsion-corresponding additional torque value instructing unit 71 to which the output voltage signal of the torsion torque sensor 31 is inputted,
A comparison unit 73 for inputting signals from the first and second 72 and a vehicle speed correction coefficient instruction unit 74 to which the output voltage signal of the vehicle speed sensor 33 is input, and a signal input from the vehicle speed correction coefficient instruction unit 74 and the comparison unit 73 And a vehicle speed correction calculation unit 75 that performs the operation. As shown in the graph of FIG. 10 (a), the steering angle corresponding additional torque instructing unit 71 maintains a predetermined constant value within a small steering angle up to a steering angle of about 10 degrees, and When it exceeds, the assist addition signal corresponding to the steering angle having the characteristic that the output gradually decreases and the output becomes zero when the steering angle is about 60 degrees is output. Further, the torsional torque-corresponding additional torque value indicating section 72 outputs the characteristic as shown in FIG. 10 (b), that is, until the torsional torque reaches a predetermined value corresponding to the steering holding state at a small turning angle. Instead, when the absolute value exceeds a predetermined value, the assist addition signal corresponding to the torsional torque having a characteristic in which the absolute value gradually increases and becomes a constant value is output. Then, the comparing unit 73 compares the assist additional signal corresponding to the steering angle and the assist additional signal corresponding to the torsional torque, and outputs a signal having a smaller absolute value as the assist additional signal ih. Has become. On the other hand, as shown in FIG. 11, the vehicle speed correction coefficient instructing section 74 outputs a vehicle speed correction coefficient having a characteristic that the vehicle speed increases from zero to about 60 km / h, and gradually decreases when the vehicle speed increases more than 0 and approaches zero. It is. Further, the vehicle speed correction calculation unit 75 includes the comparison unit 73
Is multiplied by the vehicle speed correction coefficient.
The output of the assist addition signal ih from the vehicle speed correction calculation unit 75 decreases as the vehicle speed increases at high speed. Further, in this embodiment, a vehicle speed discriminating unit 8 is provided which regulates the output of the return signal iθ from the return command unit 4 and the attenuation signal i from the steering angle phase compensation command unit 6. The vehicle speed discriminating unit 8 inputs an addition signal of the return signal iθ and the attenuation signal i, and outputs the addition signal as it is when the vehicle speed is, for example, 5 km / h or more based on the output signal of the vehicle speed sensor 33, When the vehicle speed is 5km / h or less, the output of the addition signal is regulated. Then, under the control of the vehicle speed discrimination section 8, the assist signal it from the assist command section 3 and the return command section 4
, The assist assist signal ia from the phase compensation command unit 5, the attenuation signal i from the steering angle phase compensation command unit 6, and the assist addition signal ih from the steering command unit 7. It is configured to be output to the drive control unit 2 as a command signal. Note that the assist signal it and the assist additional signal
An addition signal it 'with ih has the same sign (positive or negative) as the assist signal it and has a magnitude of | it | + ih. In the above configuration, when a torsional torque is generated in the steering system in accordance with the turning operation, the torsional torque sensor 31 detects this and generates an output signal. At this time, the vehicle speed sensor 33 and the steering angle sensor 41 output the output signal. Based on the above information, the assist signal it based on the output signal is corrected. Then, the rotation direction and the rotation torque of the electric motor 1 are controlled through the positive / negative determination of the assist signal it and the duty ratio control according to the absolute value. Here, the relationship between the torsional torque and the assist signal it is basically as shown in the graph of FIG. For example, with respect to the torsion torque at the time of turning right, a positive assist signal is output so as to increase as the torsion torque increases. Therefore, the electric motor 1 is rotationally driven in the rotation direction assisting the right turn with the output torque corresponding to the magnitude of the torsional torque, and the steering force at the time of the right turn is reduced. In the case of a left turn, the electric motor 1 is controlled in a rotation direction assisting the left turn based on a negative assist signal,
It works in the same way as right turn. Here, the function characteristic of the torsional torque and the assist signal changes in this embodiment based on the output signal of the vehicle speed sensor 33. For example, in FIG. 5 showing a characteristic graph of an assist signal with respect to a right-turn torsional torque, the state of the vehicle speed 0 is represented by M _0.
As the vehicle speed increases to V ₁ and V ₂ , the characteristic graph is changed to M ₁ and M ₂ and the X-axis direction in FIG. 5 based on the addition processing of the addition constant signal Sv from the addition constant function unit 34. Translate and change. The characteristic graph is obtained by multiplying the multiplication constant signal.
M ₁ to m _1, M ₂ changes so as to reduce the inclination to m _2.
Therefore, when the magnitude of the torsional torque is the same, the magnitude of the assist signal decreases as the vehicle speed increases. This means that the output torque of the electric motor 1 with respect to the same torsional torque decreases as the vehicle speed increases. When the vehicle is running at low speed, sufficient power assist is obtained. There is no excess, and therefore, there is no fear that the steering wheel is too light when turning to feel uneasy. On the other hand, in accordance with the steering operation, the steering angle sensor 41 detects the steering angle, and based on this, the characteristic shown in FIG. 7 is obtained. In the range of right and left steering angles ± θ ₀ , the value increases proportionally, and when it exceeds ± θ ₀ , the value becomes a constant value. In the right steering region, a negative value (left turning direction), and in the left steering region, a positive value. (Return right direction) is output. Also, when the steering speed is fast, such as when the vehicle is running on a curve with a small radius with a sharp steering wheel, the steering angle θ changes rapidly, and this is detected by the steering angle phase compensator 61. An attenuation signal i is output from the steering angle phase compensation indicating function unit 62 based on the signal. This is the characteristic shown in FIG. Here, when the vehicle speed is 5 km / h or more, the return signal iθ and the attenuation signal i are converted to the assist signal it by the operation of the vehicle speed determination unit 8.
Is added to reduce Therefore, the driver does not feel uneasy because the steering wheel is too light at the time of sudden turning.
Further, for example, if you are holding steering in right steering angle theta ₁ is
A positive assist signal it based on the output signal of the twisting torque sensor 31 described above, control of the electric motor 1 is performed by the addition signal of a negative return signal I [theta] ₁ based on the output signal of the steering angle sensor 41. Here, if the graph of the assist signal it is shown by a solid line in FIG. 3, the above-mentioned added signal becomes as shown by a broken line. Therefore, when the steered state of the steered angle θ ₁ is released,
When the torsional torque T sharply decreases, the addition signal immediately becomes a negative value (leftward turning direction) along the broken line in FIG. As a result, a left-turning torque is generated in the electric motor 1 to offset the frictional force of the speed reducer and the like, and the moment of inertia of the motor, so that when the vehicle is running (5 km / h or more), Due to the effects and the like, the steering system can be smoothly restored to the straight traveling state, and the steering wheel returning operation is improved. Then, as the steering angle θ decreases, the magnitude of the return signal iθ gradually decreases to approach 0, and when the steering angle returns to the neutral position,
The torque of the electric motor disappears. On the other hand, when the steering wheel returns from a sharp turn (high G turn), the handle may exceed neutral due to motor inertia. However, when the damping signal i is output from the steering angle phase compensation command unit 6, the damping signal instructs an output torque opposite to the rotation direction of the steering wheel. The convergence from is also improved. Next, a description will be given of the steering operation in the stopped state of the vehicle, that is, the stationary steering. In this case, since the ground resistance is large, the torsional torque sharply increases with the steering operation,
The output voltage of the torsional torque sensor 31 also increases rapidly in proportion thereto. Then, the sudden increase tendency of the torsional torque is detected by the phase compensating unit 51 of the phase compensation command unit 5, and an output signal corresponding to the degree of increase of the torsional torque is added to the output signal of the torsional torque sensor 31. Therefore, even when the torsional torque T is small and the accompanying assist signal it is not yet generated, if the degree of change in the torsional torque is large, the assist signal it
Is output immediately, and the electric motor 1 is started immediately without delay in response to the steering in a stationary state, thereby preventing the occurrence of self-excited vibration. At the time of stationary steering, the vehicle speed is 5 km / h or less, and the return signal iθ of the return command unit 4 and the attenuation signal i from the steering angle phase compensation command unit 6 are regulated by the vehicle speed determination unit 8, so that the energy Light steering is realized without labor costs. When the phase compensator 51 outputs an output signal, the phase compensation instruction function 52 outputs an assist assist signal ia having the characteristics shown in FIG. That is, when the degree of change in the torsional torque increases or decreases within a predetermined value, and when the degree of the change exceeds the predetermined value, the assist assist signal ia having a constant value is immediately output in accordance with the direction of the change in the torsional torque. Therefore, in the case of repeated left and right steering, the assist assist signal
ia is output immediately to absorb the inertial force when the electric motor 1 starts and stops. Now, a description will be given of a case where the vehicle is maintained at a small steering angle such that the vehicle continuously travels on an extremely gentle curve. At this time, since both the steering angle sensor 41 and the torsion torque sensor 31 output, the steering angle corresponding additional torque value indicating unit 71 and the torsional torque corresponding additional torque value indicating unit 72 each output an assist additional signal. The signal value of the smaller absolute value is output from the comparing unit 73 as the assist additional signal ih. In this case, if the vehicle speed is, for example, 60 km / h or less, the vehicle speed correction coefficient is 1, and the vehicle speed correction calculation unit 75 outputs the assist addition signal ih as it is, and this becomes a command signal to assist the steering operation force. Will be Also, when the vehicle speed exceeds 60 km / h and becomes higher, the vehicle speed correction coefficient decreases accordingly,
Since the assist addition signal ih passing through the vehicle speed correction calculation unit 75 gradually decreases, the steering operation force does not become excessive during high-speed running, and the stability of the steering operation is obtained. At the time of traveling at the small steering angle described above, the assist additional signal ih is not output when the torsional torque is equal to or less than a predetermined value, and the assist additional signal ih gradually increases when the torsional torque exceeds the predetermined value. Power assist is performed smoothly without shock. Also, when the steering angle is increased by turning further from the small steering angle holding state, the absolute value of the assist addition signal ih gradually decreases, so the steering wheel is not too light, and an appropriate response when turning is obtained. Can be

【The invention's effect】

As described above, according to the present invention, at the time of steering with a small steering angle, an assist addition signal is output from the steering instruction unit, and the assist operation of the steering operation force is performed by the assist addition signal. It can be driven with a light steering force even during continuous running. Since the absolute value of the assist addition signal gradually increases to a predetermined value at a small steering angle, the assist of the steering operation force is continuous and smooth. When the steering angle exceeds the small steering angle, the absolute value of the assist addition signal gradually decreases. Therefore, when steering, the steering wheel is not too light and an appropriate response can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
Fig. 3 is a characteristic graph of the output signal of the torsion torque sensor, Fig. 3 is a basic characteristic graph of the assist signal, Fig. 4 is a characteristic graph of the addition constant signal, Fig. 5 is a graph showing a characteristic change of the assist signal, Fig. 6. 7 is a characteristic graph of a multiplication constant signal, FIG. 7 is a characteristic graph of a return signal, FIG. 8 is a characteristic graph of an assist auxiliary signal, FIG. 9 is a characteristic graph of an attenuated signal, and FIGS. FIG. 11 is a characteristic graph of the assist addition signal corresponding to the steering angle and the torsional torque, and FIG. 11 is a characteristic graph of the vehicle speed correction coefficient. DESCRIPTION OF SYMBOLS 1 ... Electric motor 2 ... Drive control part 21 ... Positive / negative discriminating part, 22 ... Absolute value conversion part 23 ... Duty control part, 24 ... Armature current detection part 25 ... Electric motor drive part 3 ... Assist command section 31 Torsional torque sensor 32 Assist torque value indicating function section 33 Vehicle speed sensor 34 Addition constant function section 35
... Addition calculation section, 36 Multiplication constant function section, 37 Multiplication calculation section 4 Return command section 41 Steering angle sensor 42 Return torque value indicating function section 5 Phase compensation command section 51 ... Phase compensation section, 52... Phase compensation instruction function section 6... Steering angle phase compensation command section 61... Steering angle phase compensation section 62,... Steering angle phase compensation instruction function section 7. ·········································································································································································································· Department

Claims (2)

(57) [Claims] 1. An electric power steering apparatus in which a drive control unit controls a rotation direction and a rotation torque of an electric motor according to an assist signal based on an output signal of a torsion torque sensor for detecting a torsion torque of a steering system. A torsional torque corresponding additional torque value indicating unit that does not output within a predetermined minute torsional torque based on the output of the torque sensor and outputs a torsional torque corresponding assist additional signal whose absolute value increases and becomes a constant value when exceeding a predetermined value, A steering angle corresponding additional torque value indicating section which outputs a steering angle corresponding assist additional signal which keeps a predetermined constant value within a small steering angle based on an output of a steering angle sensor for detecting a steering angle and gradually decreases when exceeding the small steering angle. And the torsional torque corresponding assist additional signal and the steering angle corresponding assist additional signal are compared, and a signal having a smaller absolute value is determined as an assist additional signal. An electric power steering apparatus, comprising: a steering-holding command section comprising a comparing section for outputting; and an adding section for adding the assist signal and the assist additional signal to obtain a command signal for the electric motor. Motor control device. 2. The electric power steering system according to claim 1, wherein the steering maintenance command section corrects the assist additional signal to decrease as the vehicle speed increases, based on the output signal of the vehicle speed sensor. The motor control of the device.