JP3603736B2 - Electric power steering control device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering control device that reduces a steering force by energizing a torque generated by a motor to a steering torque of a driver, and particularly reduces an electric current when an excessive current flows to the motor. The present invention relates to an electric power steering control device having control.
[0002]
[Prior art]
2. Description of the Related Art A power steering control device that generates an urging torque corresponding to a driver's steering wheel steering force by a motor to reduce the steering force is widely used in vehicles. In a conventional device, a torque sensor for detecting a steering force of a driver is provided on an input side of a steering system, and a motor for generating an urging torque is provided on an output side. The motor is controlled by a drive current from a control unit (hereinafter referred to as an ECU) in accordance with the state of the vehicle such as the steering force and the vehicle speed detected by the torque sensor. A DC motor is generally used as a motor for electric power steering. In a DC motor, the generated torque has a characteristic substantially proportional to the drive current. Therefore, the actual drive current of the motor is controlled by performing feedback control of the drive current of the motor by the ECU with respect to a target current value. An urging (assist) torque can be generated, and operation as a power steering control device is realized.
[0003]
However, when the driver continues to rotate the steering wheel, the steered wheels reach a steering angle position where the steering cannot be structurally steered. When reaching the maximum steering angle position, the steering torque becomes maximum, and as a result, the steering assist by driving the motor also becomes maximum. The maximum assist force means that the motor current becomes maximum. If this state continues, heat is generated around the brush of the motor, the motor coil, and furthermore, the current supply electronic element and the like, which not only imposes a cost and structural burden on the heat dissipation, but also causes a failure. Therefore, it is necessary to reduce this current.
[0004]
For this reason, the steering angle is detected by the steering wheel angle sensor to determine the maximum steering position, or a microswitch is arranged near the maximum steering position to reduce the current supply. However, these conventional devices require a detecting means for detecting the maximum steering position, which is disadvantageous in terms of cost and structure. Further, when the tire cannot be further steered due to a curb, a groove or an obstacle until the maximum steering position, these conventional devices cannot cope with the problem.
[0005]
Further, there is an invention disclosed in Japanese Patent Application Laid-Open No. 11-43059, and this apparatus will be described with reference to FIG. 1 is a torque sensor for detecting a steering torque of a steering wheel, 2 is a vehicle speed sensor for detecting a vehicle speed, 4 is a motor that generates assist torque when steering a tire by rotating the steering wheel, and 5 is a battery that supplies power to the motor. It is. Reference numeral 3a denotes an ECU, which is a control means for inputting the steering torque 1 and the vehicle speed 2 and controlling the current of the motor 4. The ECU 3a includes a target current calculation unit 6, an overload prevention unit 51, a deviation calculation unit 7, a signal generation unit 8a, a drive circuit 9a, a current detection unit 10, a voltage detection unit 11, and a steering speed calculation unit 52. The target current calculation unit 6 calculates a target current IT to be supplied to the motor based on the torque and the vehicle speed. The deviation calculator 7 calculates a deviation between the target current IT and the actual current IM by the current detector 10. Next, the signal generator 8a outputs a drive signal to the drive circuit 9a so as to make this deviation zero. As a result, current flows to the motor, and the assist force can be varied.
[0006]
On the other hand, the motor rotation speed VM is estimated from the motor voltage EM and the actual current IM by the voltage detection unit 11 according to the following equation.
VM = (EM-IM-RM) / Kp (1)
Here, RM is an amateur resistance value of the motor, and Kp is an induced voltage coefficient.
Since the motor rotation speed VM can be considered to be proportional to the steering speed, it is input to the overload prevention unit 51.
[0007]
When the actual current IM> A and the steering speed VM <B (A and B are predetermined values), the overload state detection unit 53 determines an overload. When the overload state continues for a predetermined time, the overload prevention operation start delay unit 54 changes the multiplication coefficient of the multiplier 55 to a value smaller than the normal value of one. In this way, an attempt is made to reduce the motor current when the vehicle stays at the maximum steering position.
[0008]
[Problems to be solved by the invention]
The above-described conventional device estimates the speed based on the voltage and the current without using a special sensor, so that an error always occurs. This speed estimation has a problem that an offset component is generated and cannot be accurately estimated. In particular, as the current is increased, the temperature rises, and the accuracy of the estimated value deteriorates because the temperature dependency of the motor brush voltage and the motor resistance value RM is strong. An object of the present invention is to remove an error in speed estimation due to voltage and current as much as possible, accurately estimate a rotation speed, and thereby reduce a current flow.
[0009]
[Means for Solving the Problems]
The electric power steering control device according to the present invention includes a torque sensor that detects a steering torque of a steering wheel, a motor that assists a steering force of the steering wheel, and a control unit that controls the motor in accordance with the torque information. A target current calculation unit for determining a current value to be supplied to the motor according to the torque information; a current detection unit for detecting a current flowing to the motor; and a difference between the target current value by feeding back the detected current value. And a signal generation unit that calculates a control amount to flow a motor current according to the deviation, and outputs a control signal, and a motor drive unit that drives the motor according to the control signal. A voltage detection unit for detecting a terminal voltage of the motor; and a first steering speed calculated from the motor current and the voltage. A steering speed estimating unit for estimating a second steering speed by adding an offset removing means having an off frequency to the first steering speed; and Has a first mode in which the motor current is reduced with a high gain and a second mode in which the current is substantially maintained, and at least one of each of these modes is combined. And a maximum current corrector for determining a maximum current for limiting the current and correcting the target current based on the maximum current.
[0010]
Further, in the electric power steering control device according to the present invention, the offset removing means to be added is a high-pass filter having a cutoff frequency of about 0.2 Hz or less.
[0012]
Still further, in the electric power steering control device according to the present invention, the maximum current correction unit detects a steering torque of a predetermined value or less during the first or second mode, or provides a target current of a predetermined value or less. In such a case, the maximum value restriction is stopped.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a system configuration block diagram showing an ECU of the electric power steering control device and an input / output device connected thereto. In FIG. 1, reference numeral 1 denotes a steering torque sensor for detecting a driver's steering torque, 2 denotes a vehicle speed sensor, 3 denotes an ECU, and 4 denotes a motor that assists a steering force from a power supply of a battery 5. The ECU 3 calculates an appropriate motor current target value in accordance with the steering torque 1 and the vehicle speed 2, a current detection unit 10 that detects the motor current, and a target current and a detected current (actual current). A deviation calculating unit 7 for calculating a deviation, a signal generating unit 8 for generating a motor current control signal to reduce the deviation to zero, a motor driving unit 9 for receiving the signal and supplying a motor current, and detecting a voltage between motor terminals A voltage detection unit 11, a steering speed calculation unit 12 that estimates a steering speed from the actual current IM and the motor voltage EM, and a maximum current correction unit 13 that acts to limit the target current according to the steering speed. It is configured.
[0014]
Next, the operation of each unit will be briefly described. As shown in FIG. 2, the target current calculator 6 uses a characteristic in which the motor current is determined in advance by the steering torque and the vehicle speed. 15a is a basic current map showing the relationship between torque and current at a vehicle speed of 0 km / h, 15b at a vehicle speed of 20 km / h, and 15c at a vehicle speed of 50 km / h. The signal generator 8 calculates a control amount for performing the PID control in accordance with the magnitude of the deviation between the target current IT and the actual current IM, and causes the drive unit 9 to generate the result as a PWM control signal. . The drive unit 9 includes four FET elements formed of an H bridge circuit. The motor current is controlled by ON / OFF-controlling these FETs. The current detection unit 10 has a method of measuring the current flowing in the motor by the potential difference between both ends of the resistor. The voltage detecting section 11 measures a voltage difference between terminals of the motor.
[0015]
Next, the steering speed calculator 12 will be described. Assuming the motor voltage EM, the actual current IM, the armature resistance RM of the motor, and the drop voltage Eb of the brush of the motor, the voltage EE induced in the motor is:
EE = EM-IM-RM-Eb (2)
It becomes.
[0016]
The motor rotation speed VM is converted from the induced voltage EE by the following equation.
VM = EE / Kp (3)
Here, Kp is an induced voltage coefficient.
The motor rotation speed and the steering speed are in a predetermined relationship by a deceleration gear, a rack and a pinion of a steering wheel and a tire shaft, and the like. In other words, the motor rotation speed is proportional to the steering speed. Therefore, by changing the coefficient Kp, the motor rotation speed can be regarded as the steering speed VM.
[0017]
FIG. 3 shows the result obtained by calculating the motor rotation speed ω using Expressions (2) and (3). In this test, the motor rotation speed ω with respect to the motor current was measured by forcibly fixing the steering wheel or the tire. The greater the motor current, the greater the error. In particular, an error of about 80 deg / sec occurs near 45 A. Therefore, in order to remove this error as much as possible, a high-pass filter (hereinafter referred to as HPF) is inserted. The cut-off frequency of the HPF is set to less than 1 Hz in consideration of the steering wheel angular velocity that can be operated by the driver and the yaw resonance frequency of the vehicle. By inserting the HPF, the error in the motor rotation speed could be reduced. The result is shown in FIG.
[0018]
FIG. 4A shows a state in which current is passed through the motor with the horizontal axis representing time and the vertical axis representing motor current. When such an operation is performed, how the estimated steering speed changes is shown in FIGS. 4B to 4D, and the vertical axis represents the speed in rad / sec. FIG. 4B shows the result without the conventional HPF, FIG. 4C shows the result when the cutoff frequency fc of the HPF is 0.16 Hz, and FIG. 4D shows the result when fc = 1 Hz. Since the power steering control device has a maximum current of 65 A, focusing on the vicinity of t1 to t3 where the 65A current flows in FIG. 4A, a rotational speed of about 40 deg / sec is seen in t1 to t3 in FIG. 4B. FIG. 4C shows that the speed is very low (10 deg / sec or less). In FIG. 4D, the offset is removed because the cutoff frequency is set large. Therefore, experimentally, it is appropriate that the cutoff frequency is 0.1 ≦ fc ≦ 0.2 Hz.
[0019]
By adding an HPF having an appropriate cutoff frequency as described above, the motor rotation speed can be more accurately estimated without adding any sensor. Therefore, it was possible to accurately estimate the steering speed.
[0020]
Next, the maximum current correction unit 13 will be described. When the state where the steering speed VM is a low speed equal to or lower than a predetermined value and the current value IM is equal to or higher than a predetermined value continues for a predetermined time, the target current is corrected so as to reduce the current current value. As a correction method, the current value calculated by the target current calculation unit 6 may be multiplied by a coefficient or may be subtracted, but the target current value may be replaced so as to reduce the current. As a result, the above-described signal generation unit 8 and drive unit 9 operate, and the current IM decreases. For this reason, the heat generation of the motor current is suppressed, so that not only the motor itself but also the driving circuit elements, and furthermore, the harmful effects of the heat of the connecting portions thereof are prevented.
[0021]
Embodiment 2 FIG.
Next, a second embodiment will be described with reference to FIG. When the steering torque changes as indicated by 20 and the motor current 21 is controlled, it is detected that the steering speed has become extremely low from the relationship between the current and the voltage at ta, and the current current exceeds Ia. I have. At tb, the maximum current correction is determined, indicating that the current reduction control has been started. A predetermined value or a predetermined rate current is reduced at a predetermined high gain from tb. At tc, the current reduction is suspended once, and the current value is maintained until td. This period means an observation period, and when input information such that the current still flows through the second maximum current, for example, torque is detected, the current is further reduced again toward te.
[0022]
As described above, there are a plurality of reduction modes in which the current is reduced at the first high gain, held for a certain period of time, and then reduced again at a high gain. Since several seconds are required from ta to td, there is a possibility that the situation of the vehicle changes during this period, and the device cannot respond to the situation of the next vehicle simply by reducing the current. Accordingly, the following control can be performed by temporarily suppressing the heat generation of the motor and comparing the conditions of the vehicle. If there is no change in the state of the vehicle, the second current reduction can be performed to further suppress the current. Note that tc to td need not be kept constant, but may be lowered at an extremely low gain.
[0023]
At tf, since the steering torque once falls below the predetermined value tq1, the control returns to the normal current control depending on the steering torque again. As described above, while the vehicle is running, when the steering wheel is maintained at the maximum steering position, or the motor current is excessively flow for a while due to an obstacle such as a curb, a groove, or the like up to the maximum steering position, the current of the present invention may occur. The reduction not only suppresses unnecessary power consumption and heat generation, but also has the effect of being able to cope with the next vehicle situation. The current reduction may be stepwise reduced, but in order to prevent the driver from feeling a recoil, the smoother the current reduction, the better.
[0024]
When the target current becomes equal to or less than the predetermined value instead of using the steering torque information, the same effect can be obtained even if the maximum current limit is interrupted. The predetermined value is lower than the predetermined value Ia in FIG. Further, these predetermined values may be variable depending on vehicle speed, current driving time, average current value, and the like.
[0025]
【The invention's effect】
Since the electric power steering control device of the present invention is configured as described above, the following effects can be obtained.
[0026]
An electric power steering control device according to the present invention calculates a first steering speed from a terminal voltage of a motor and a motor current in a control unit, and sets an offset removing means having a predetermined cutoff frequency to a first steering speed. A steering speed estimating unit for estimating a second steering speed by adding a second steering speed; and a motor having a high gain when the second steering speed is a low speed below a predetermined value and the motor current is an overcurrent above a predetermined value. And a second mode in which the current is substantially maintained. A maximum current for limiting the motor current is determined by combining at least one of these modes one by one. Since it is composed of a maximum current correction unit that corrects the current, the steering speed can be easily estimated, and the speed estimation can be accurately performed by removing the offset component. Come, heat generation of the motor current for limiting the maximum current is suppressed, further first mode produces the Ru effect can be controlled corresponding to the status change of the vehicle by the second mode.
[0027]
Further, the electric power steering control device according to the present invention has an effect that the steering speed can be easily and accurately estimated because the offset removing means having the cutoff frequency is added.
[0029]
Furthermore, the electric power steering control device according to the present invention operates so as to stop the maximum value limitation when the maximum current correction unit detects a steering torque smaller than a predetermined value during the first or second mode. Thus, an effect that can respond to a change in the situation of the vehicle is achieved.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of an electric power steering control device according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating a relationship between torque and current of the electric power steering control device according to the first embodiment of the present invention.
FIG. 3 is an error diagram of an estimated steering speed without an offset removing unit according to the first embodiment of the present invention.
FIG. 4 is an estimated steering speed diagram according to the first embodiment of the present invention.
FIG. 5 is a diagram illustrating a maximum current limit according to the second embodiment of the present invention.
FIG. 6 is a system configuration diagram of an electric power steering in a conventional device.
[Explanation of symbols]
Reference Signs List 1 torque sensor, 2 vehicle speed sensor, 3 control unit, 4 motor, 6 target current calculation unit, 7 deviation calculation unit, 8 signal generation unit, 9 motor drive unit, 10 current detection unit, 11 voltage detection unit, 12 steering speed calculation Unit, 13 Maximum current correction unit.

Claims (3)

A torque sensor for detecting a steering torque of the steering wheel, a motor for assisting the steering force of the steering wheel, a control unit for controlling the motor according to the torque information,
The control unit includes a target current calculation unit that determines a current value to be supplied to the motor according to the torque information, a current detection unit that detects a current flowing to the motor, and feeds back the detected current value to the target current. A deviation calculation unit for calculating a difference between the control signal and a value, a signal generation unit for calculating a control amount to flow a motor current according to the deviation, and outputting a control signal; and a motor for driving the motor according to the control signal. A drive unit, a voltage detection unit for detecting a terminal voltage of the motor, and a first steering speed calculated from the motor current and voltage, and an offset removing unit having a predetermined cutoff frequency added to the first steering speed. A steering speed estimating unit for estimating a second steering speed by performing a second steering speed when the second steering speed is a low speed equal to or lower than a predetermined value and the motor current is equal to or higher than a predetermined value. , A second mode for holding substantially the first mode and the current of the current to reduce the motor current at a high gain, determines the maximum current which limits the motor current by combining one at least of these modes An electric power steering control device, comprising: a maximum current correction unit that corrects the target current with the maximum current. 2. The electric power steering control device according to claim 1, wherein the offset removing means to be added is a high-pass filter having a cutoff frequency of about 0.2 Hz or less. The maximum current correction unit stops the maximum value limitation when a steering torque of a predetermined value or less is detected during the first or second mode, or when the target current becomes a predetermined value or less. electric power steering control apparatus according to any one of claims 1-2.

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