JP4759879B2 - Electric motor control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric motor control device used in an electric steering force assisting device that applies a steering assisting force to a vehicle steering system.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an electric steering force assisting device for a vehicle, an electric motor control device that generates a steering assisting force by a motor has been used in order to reduce a steering force by a driver. As such a motor control device, for example, as disclosed in Japanese Patent Laid-Open No. 1-115770, a battery voltage is increased by using a booster circuit in order to improve the quick steering performance at high speed running. Some output the above voltage to improve the efficiency of the motor or generate a larger torque.
[0003]
[Problems to be solved by the invention]
However, in the motor control device, since the voltage is increased only during high-speed traveling, the motor cannot be designed to always assume a high voltage, and there is a problem that a significant improvement in motor efficiency cannot be expected. That is, as an advantage of increasing the drive voltage of the motor, it is conceivable to reduce the motor current by designing the motor for a high voltage. If the current is reduced, the loss in the wiring / power elements will decrease. Thus, the efficiency of the entire motor control device is improved. However, this advantage cannot be obtained unless the motor is always designed with a high voltage.
[0004]
Further, in the motor control apparatus, since the motor boosts the voltage in the same way even when a high voltage is not particularly required, there is a problem that the efficiency becomes poor and the efficiency is poor. For example, even when conditions such as the vehicle speed are met and boosted, depending on the situation, a high voltage may not be necessary. In that case, the inverter unit lowers the duty ratio and performs a substantial step-down operation. Furthermore, there is a problem that even if a situation where boosting is necessary, the time lag of the booster circuit, which cannot respond instantaneously due to the delay of the determination or the rise time of the booster circuit itself, impairs the responsiveness of the motor.
[0005]
SUMMARY OF THE INVENTION
The present invention has been made to address the above-described problems. The purpose of the present invention is to reduce unnecessary boosting by reducing the boosted voltage when a high voltage in a high current region is unnecessary, and to reduce the high voltage. It is an object of the present invention to provide an electric motor control device that can be designed with a low-current motor and that has good responsiveness.
[0006]
In order to achieve the above object, the motor control device according to the present invention is characterized by an electric motor that outputs a steering assist force, electric motor control means that controls the electric motor, and electric power that is supplied to the electric motor via the electric motor control means. Battery for boosting, boosting circuit for boosting the voltage of the battery, current detection means for detecting the current value of the boosting circuit, and boosting circuit control for controlling the boosting circuit so as to reduce the voltage in accordance with an increase in the current of the boosting circuit And means. In this case, it is preferable that the booster circuit control means controls the booster circuit so that the product of the current value and the voltage value of the booster circuit is constant in a region where the current value of the booster circuit exceeds a predetermined value.
[0007]
According to the characteristics of the present invention configured as described above, when the current of the booster circuit becomes large, the boosted voltage can be lowered according to the increase in the current, and unnecessary boosting can be avoided. In this case, the boosted voltage can be appropriately reduced in consideration of the characteristics of the motor, and even if a simple booster circuit is used, a sufficient effect can be obtained. In addition, by controlling the booster circuit so that the product of the current and voltage of the booster circuit is constant, it is possible to perform appropriate control based on a certain tendency corresponding to the characteristics of the motor.
[0008]
Further, other structural features of the present invention include an electric motor that outputs a steering assist force, an electric motor control unit that controls the electric motor, a battery that supplies electric power to the electric motor through the electric motor control unit, and a voltage of the battery. a booster circuit for boosting, the current value becomes larger, an upper limit to the duty ratio determined based on the output characteristics of the current and voltage of the boost circuit which is set so that the voltage decreases, the upper limit of the duty ratio or less And a booster circuit control means for controlling the booster circuit within the above range.
[0009]
According to the characteristics of the present invention configured as described above, the voltage can be lowered by providing an upper limit restriction on the duty ratio. As a result, there is no need to provide a current detection means for detecting the current of the booster circuit, and the cost can be reduced. In this case, appropriate control can be easily performed by setting the upper limit of the duty ratio in consideration of the current / voltage characteristics of the motor.
[0010]
The feature on another structure of the present invention, a motor that outputs a steering assist force, and a motor control means for controlling the electric motive, via the motor control unit, a battery that supplies electric power to the electric motor, the battery includes a booster circuit for boosting the voltage, and a boosting circuit control means for boosting control the voltage of the boost circuit, the steering torque, with obtaining the assist torque from the vehicle speed and the steering angle, obtains a current value for driving the motor from assisting torque , based on the motor rotation speed of the current value and the motor is a voltage of the booster circuit and the boost control child.
[0011]
According to the feature of the present invention configured as described above, the booster circuit is always boosted, and the motor can be designed exclusively for high voltage and low current. Further, by setting the boost voltage based on the steering torque, unnecessary boost can be suppressed and the efficiency of the motor control device can be improved. Furthermore, by controlling the voltage boosting based on the current required for driving the motor and the motor rotation speed of the motor, it is possible to achieve the minimum required boosting.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an electric steering force assisting device 10 for a vehicle provided with a motor control device according to the embodiment, and FIG. 2 is provided in the electric steering force assisting device 10 shown in FIG. It is a functional block diagram of the control apparatus 11 of an electric motor.
[0013]
In the electric steering force assisting device 10, a torque sensor 14 and a motor 15 as an electric motor are attached to an intermediate portion of a steering shaft 13 connected to a handle 12, and a pinion is attached to a lower end portion of the steering shaft 13. 16 is provided. A rack 17 meshes with the pinion 16, and steering wheels 18 a and 18 b are connected to both ends of the rack 17. Therefore, when the handle 11 is rotated, the rotational force is transmitted to the pinion 16 via the steering shaft 13 to rotate the pinion 16. The rotation of the pinion 16 moves the rack 17 in the horizontal direction shown in the figure, and the movement of the rack 17 turns the steering wheels 18a and 18b to change the direction.
[0014]
Further, the torque sensor 14 and the motor 15 are connected to an inverter 20 as electric motor control means included in the control device 19. The torque sensor 14 detects the steering torque by converting the amount of twist generated in the steering shaft 13 into an electric quantity by a variable resistor or the like, and sends the magnitude of the steering torque of the steering shaft 13 to the inverter 20 as a signal. . The motor 15 has a rotational speed controlled by the inverter 20 and applies a steering assist force to the rack 17 via a speed reducer (not shown) and a pinion 16.
[0015]
In addition to the torque sensor 14 and the motor 15, the inverter 20 is connected to a vehicle speed sensor 21 and a steering angle sensor (not shown). The steering torque t from the torque sensor 14, the vehicle longitudinal direction detected by the vehicle speed sensor 21. The rotational speed and torque of the motor 15 are controlled based on information such as the vehicle speed v and the rotational angle θ of the steering shaft 13 detected by the steering angle sensor.
[0016]
In addition to the inverter 20, the control device 19 includes a booster circuit 22, a PWM regulator 23 as a booster circuit control unit, and a current detector 24 (the PWM regulator 23 and the current detector 24 are omitted in FIG. 1). The booster circuit 22 includes a chopper circuit and is connected to the inverter 20 and the battery 25. The booster circuit 22 boosts the voltage of the battery 25 based on the steering assist force that reduces the steering force of the handle 12. In this case, for example, if the voltage of the battery 25 is 12v, the rotation and torque of the motor 15 are optimally controlled by setting the boosted voltage region of the booster circuit 22 in the range of about 12-25v.
[0017]
The PWM regulator 23 modulates the pulse width to determine the duty ratio. Based on the current value of the booster circuit 22 detected by the current detector 24 and the voltage value at the point A of the booster circuit 22. The booster circuit 22 is controlled to reduce the boosted voltage. In this case, judging from the output characteristics of the voltage and current of the booster circuit 22, in the region where the current value exceeds a certain range, the voltage to be boosted is lowered. The relationship is shown by the line a in FIG. Show.
[0018]
That is, the line a of FIG. 3 shows the output characteristics of the voltage and current in the step-up circuit 22, if the current is less than a predetermined value I _1, the voltage is a constant value V _MAX, the constant voltage V _MAX The maximum value of the voltage of the booster circuit 22 is assumed. When the current increases beyond the predetermined value I ₁ , the voltage decreases at a constant rate. This constant ratio is expressed by a relationship in which the voltage value is obtained so that the power value of the voltage value × the current value is constant, and the arc value bulges downward as shown by the curve b in the line a. It will be a proportion. That is, when the current of the booster circuit 22 is a large current, the voltage can be small. In the case of a large current, the boosted voltage is reduced so as not to waste the boost.
[0019]
The basis for setting the voltage and current of the booster circuit 22 to the relationship indicated by the line a in FIG. 3 is based on the current / voltage characteristics of the motor 15 indicated by the region c in FIG. FIG. 4 shows the relationship between the necessary minimum voltage of the motor 15 and the power supply current. In this case, the necessary minimum voltage is the minimum power supply voltage necessary for the inverter 20 to flow a predetermined current through the motor 15. Thus, it varies depending on the rotation speed and load state of the motor 15. Even if a voltage higher than the necessary minimum voltage is applied, the voltage applied to the motor 15 does not change and the voltage is substantially stepped down only by reducing the duty ratio of the inverter 20.
[0020]
The power supply current is an input current of the inverter 20 and corresponds to an output current of the booster circuit 22. The line a in FIG. 3 is obtained in a range where the voltage of the booster circuit 22 is not less than the maximum part of the necessary minimum voltage in the region c shown in FIG. Therefore, the booster circuit 22 can be boosted efficiently without unnecessary boosting. In this case, the booster circuit 22 is always in a boosted state and can secure a voltage required for the motor 15 in all current regions, and therefore has excellent high-speed response. Further, the motor 15 can be designed for high voltage.
[0021]
FIG. 5 shows a functional block diagram of an electric motor control device 30 according to another embodiment of the present invention. In the motor control device 30, the current detector 24 is not provided in the control device 31, and when the PWM regulator 23 a controls the booster circuit 22 a, the duty limit 32 is based on the voltage value at point B. Is supposed to do. The other configuration is the same as that of the motor control device 11 shown in FIG. Therefore, the same reference numerals are given to the same parts.
[0022]
In this motor control device 30, current detection of the booster circuit 22 a is not performed, and the booster control of the booster circuit 22 a is performed by the PWM regulator 23 a performing the duty limit 32 according to the voltage at point B. Yes. That is, when the voltage at point B is high, the duty ratio is controlled to decrease, and when the voltage at point B is low, the duty ratio is controlled to increase.
[0023]
The output characteristics of voltage and current when the duty limit 32 is applied to the booster circuit 22a are as shown by the line d in FIG. In this case, when the current value is equal to or less than the predetermined value I ₁ , the voltage is the same as the constant value V _MAX shown by the line a in FIG. 3, and this constant voltage V _MAX is set as the maximum value of the voltage of the booster circuit 22a. . When the current increases beyond the predetermined value I ₁ , the voltage is set to decrease in proportion to a certain ratio as in the portion of the straight line e in the line d. In this case, the duty limit 32 is set so that the voltage of the booster circuit 22a is equal to or greater than the maximum portion of the necessary minimum voltage in the region c indicating the current / voltage characteristics of the motor 15 and the range exceeding this is as small as possible. ing.
[0024]
The broken line f indicates the portion of the curve b in FIG. 3, and the straight line e in the line d is a region where the current is particularly large, and is smaller than the curve f. Therefore, in this region, the booster circuit 22 of the control device 31 has a lower voltage than the booster circuit 22a of the control device 19. As a result, when the current of the booster circuit 22a is large, the voltage is reduced so that the boosting is not wasted. Further, since it is only necessary to set a limit on the duty ratio, control can be easily performed. Further, since the current detector 24 is not provided, the cost can be reduced and the motor control device 30 can be simplified.
[0025]
As still another embodiment, for example, when the voltage of the battery 25 is 12 v, the boost target voltage region g of the boost circuit 22 is set to 12 v to 12 v based on experimental data as shown in FIG. The rotation and torque of the motor 15 can be optimized by setting the voltage within a range of about 25 V and controlling the motor 15 according to the voltage value in the boost target voltage region g.
[0026]
The boost target voltage region g in FIG. 7 is obtained as follows. That is, first, the assist torque is determined from information such as the steering torque t detected by the torque sensor 14, the vehicle speed v detected by the vehicle speed sensor 21, and the rotation angle θ detected by the steering angle sensor. Next, a current command value is determined based on the assist torque. This current command value is the value of the current that flows to the motor 15 and is proportional to the steering torque to some extent. Data for obtaining the current command value is stored as information on the inverter 20 side, and a current value corresponding to the magnitude of the assist torque is calculated in advance as data.
[0027]
Then, the number of rotations of the motor 15 is calculated from the power supply voltage of the motor 15 and the motor load, and the voltage value necessary for flowing a current based on the current command value to the motor 15 from the number of rotations of the motor 15 and the current command value. , And mapping this, the boost target voltage region g is obtained. Therefore, the required boosted voltage is obtained from the current command value obtained from the rotation speed of the motor 15 and the assist torque, and the inverter 20 controls the booster circuit 22 to boost the voltage. As a result, ideal boosting based on experimental data can be performed.
[0028]
For example, when the current command value is 0 A and the rotational speed is 0 rpm, the boost target voltage is 12 v, and when the current command value is 40 A and the rotational speed is 1200 rpm, the boost target voltage is 25 v. Thus, the optimum boost target voltage is appropriately set within the range of the current command value of 0 to 40 A and the rotational speed of 0 to 1200 rpm.
[0029]
In the present embodiment, the vehicle speed v detected by the vehicle speed sensor 21 is also taken into account, because the vehicle speed v is effective for determining the steering state. For example, when a large current of the predetermined value I ₁ or more shown in FIG. 3 and FIG. FIG. 4 shows the characteristics of current and voltage at the time of sudden steering and when entering a garage. The characteristics of current and voltage at the time of sudden steering are in a region indicated by a sudden steering area h. The voltage characteristic is an area indicated by the garage entry area i. Therefore, such a difference between the sudden steering and the garage entry is determined by the vehicle speed v detected by the vehicle speed sensor 21, and control according to each situation can be performed.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an electric steering assist device including a motor control device according to an embodiment of the present invention.
FIG. 2 is a functional block diagram showing functions in a motor control device.
FIG. 3 is a characteristic diagram showing characteristics of a booster circuit.
FIG. 4 is a characteristic diagram showing characteristics of a motor.
FIG. 5 is a functional block diagram showing functions in a motor control device according to another embodiment of the present invention.
6 is a characteristic diagram showing output characteristics when a duty limit is provided in the booster circuit of the motor control device of FIG. 5; FIG.
FIG. 7 is a graph showing a boost target voltage.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Electric steering force auxiliary device, 11, 30 ... Motor control device, 14 ... Torque sensor, 15 ... Motor, 19, 31 ... Control device, 20 ... Inverter, 21 ... Vehicle speed sensor, 22, 22a ... Booster circuit, 23, 23a ... PWM regulator, 24 ... current detector, 25 ... battery, 32 ... duty limit, a, d ... line, b ... curve, c ... area, e ... straight, g ... boost target voltage region, I ₁ ... predetermined value.

Claims (4)

An electric motor that outputs steering assist force;
Motor control means for controlling the motor;
A battery for supplying electric power to the electric motor via the electric motor control means;
A booster circuit for boosting the voltage of the battery;
Current detection means for detecting a current value of the booster circuit;
Boosting circuit control means for controlling the boosting circuit so as to reduce the voltage in accordance with an increase in current of the boosting circuit;
An electric motor control device comprising:   2. The boost circuit control unit according to claim 1, wherein the boost circuit control unit controls the boost circuit so that a product of a current value and a voltage value of the boost circuit is constant in a region where a current value of the boost circuit exceeds a predetermined value. Electric motor control device. An electric motor that outputs steering assist force;
Motor control means for controlling the motor;
A battery for supplying electric power to the electric motor via the electric motor control means;
A booster circuit for boosting the voltage of the battery;
Set an upper limit to the duty ratio determined based on the output characteristics of the current and the voltage before Symbol booster circuit was set to the voltage when the current value increases decreases, the boost circuit at the upper limit the range of the duty ratio Boost circuit control means for controlling
An electric motor control device comprising: An electric motor that outputs steering assist force;
And motor control means for controlling the pre-Symbol motor,
A battery for supplying electric power to the electric motor via the electric motor control means;
A booster circuit for boosting the voltage of the battery;
A boosting circuit control means for boosting control the voltage before Symbol booster circuit,
Equipped with a,
The assist torque is obtained from the steering torque, the vehicle speed, and the steering angle, the current value for driving the electric motor is obtained from the assist torque, and the voltage of the booster circuit is boosted based on the current value and the motor rotational speed of the electric motor. control unit for an electric motor, characterized that you.

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