JP2005247093A - Electric power steering device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device for a vehicle capable of accurately detecting rotational speed of a DC motor with a brush. <P>SOLUTION: This electric power steering device for the vehicle gives steering auxiliary torque to a steering mechanism by supplying electric power to the DC motor with the brush based on steering operation of a driver. This device is provided with an electric current detecting means for detecting motor actual electric current supplied to the DC motor with the brush, a cycle detecting means for detecting a cycle in which a value of the motor actual electric current is varied, and a rotational speed calculating means for estimating the rotational speed of the DC motor with the brush based on the cycle. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric power steering device for a vehicle that assists the operation of a steering wheel with a motor.

  Electric power steering for a vehicle that detects steering torque and controls the rotation of the motor in accordance with the detected steering torque and vehicle speed, thereby applying assist force to the turning operation of the steering wheel. The device is well known.

When using a DC motor with a brush as a motor (hereinafter also abbreviated as a motor), the rotational speed of the motor is based on the back electromotive force of the motor considering the voltage drop between the brush and the commutator (commutator). (See Patent Documents 1 and 2). The conventional formula for estimating the rotational speed is expressed as: rotational speed = (voltage between motor terminals−motor resistance × current amount) / back electromotive force constant.

Japanese Patent Laid-Open No. 11-139339 JP-A-10-109655

  In the above formula, the motor resistance changes in a complex manner depending on the amount of current, the coil temperature, the brush temperature, the contact resistance with the brush and the commutator, and the oxidation state of the brush, and does not show a stable value. FIG. 5 shows the relationship between the current flowing through the motor and the motor resistance. Theoretically, the relationship is as shown by the solid line portion C. However, when the motor state is taken into consideration, the resistance of one of the values enclosed by the shaded portion D and the vertical axis and horizontal axis in the figure becomes a resistance, and the motor rotation speed is accurately determined. Cannot be calculated. Therefore, the controllability may be deteriorated in the electric power steering device for a vehicle.

  As disclosed in Patent Document 2, there is a method of providing a dead zone for the estimated motor angular velocity value. However, when the dead zone is included, the motor angular velocity (that is, the motor rotational speed) is uniformly set to zero. There is a possibility of feeling uncomfortable.

  With the above problem as a background, an object of the present invention is to provide an electric power steering device for a vehicle that can accurately detect the rotational speed of a brushed DC motor.

Means for Solving the Problems and Effects of the Invention

  The present invention provides an electric power steering device for a vehicle for solving the above-described problems. That is, according to the first aspect of the present invention, in the electric power steering control device for a vehicle which applies a steering assist torque to the steering mechanism by energizing and driving the brushed DC motor based on the steering operation of the driver, it flows to the brushed DC motor. Current detection means for detecting the actual motor current, period detection means for detecting a period in which the value of the motor actual current fluctuates, and a rotation speed calculation means for estimating the rotation speed of the brushed DC motor based on the period The vehicle is configured as an electric power steering device for a vehicle.

  The present invention is a rotational speed detection method using current fluctuations resulting from a motor structure. Focusing on the resistance fluctuation per rotation of the motor that the brushed DC motor has in principle (see Fig. 7 and Fig. 8, details will be described later), the rotation speed of the motor is detected by measuring the period of current fluctuation caused by this. To do. The current fluctuation is caused by a predetermined component (for example, a 44th-order component) of the current flowing through the motor. By extracting this with a filter, the rotational speed can be detected.

  FIG. 4 shows a waveform obtained when a fast Fourier transform is performed on the current that flows when the rotational speed (that is, the rotational speed) of the motor is N [rpm]. 4A is the peak value of the 44th-order component of the motor current, and the current fluctuation frequency at this time is F. In FIG. The current fluctuation frequency has a characteristic such as a straight line B that increases as the motor speed approaches zero, decreases as the motor speed increases, and approaches zero. If this characteristic is utilized, it becomes possible to obtain | require the rotational speed (namely, rotation speed) of a motor from an electric current fluctuation frequency.

  With the above configuration, it is possible to obtain an accurate motor rotation speed without adding new sensing means such as a motor rotation angle sensor, that is, without an increase in cost, and the driver feels uncomfortable with steering. It is possible to configure an electric power steering device for a vehicle without a vehicle.

  According to the second aspect of the present invention, the electric power steering apparatus for a vehicle according to the present invention includes command value calculation means for calculating a motor current command value applied to the brushed DC motor, and the period detection means includes the motor current command value and The configuration is such that the cycle is detected based on the deviation from the actual motor current.

  In order to perform the fast Fourier transform, a microprocessor having a very high processing capability is required, which causes an increase in cost. However, with the above configuration, the motor rotation speed can be obtained by simple subtraction without using the fast Fourier transform. Therefore, it is possible to obtain an accurate motor rotation speed without adding an expensive microprocessor and a new sensing means such as a motor rotation angle sensor, that is, without increasing the cost. An electric power steering device for a vehicle that is not received can be configured.

  The object of accurately detecting the rotational speed of a brushed DC motor in an electric power steering apparatus of a vehicle is realized by a method of detecting the rotational speed based on the fluctuation frequency of the current flowing through the motor.

Hereinafter, an electric power steering device for a vehicle according to an embodiment of the present invention (hereinafter simply referred to as an electric power steering device) will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an electric power steering apparatus 1. A steering handle 10 is connected to the steering shaft 12a. Further, the lower end of the steering shaft 12 a is connected to the torque sensor 11, and the upper end of the pinion shaft 12 b is connected to the torque sensor 11. Further, a pinion (not shown) is provided at the lower end of the pinion shaft 12 b, and this pinion is meshed with the rack bar 18 in the steering gear box 16. Further, one end of a tie rod 20 is connected to each end of the rack bar 18, and a steered wheel 24 is connected to the other end of each tie rod 20 via a knuckle arm 22. A motor 15 is attached to the pinion shaft 12b via a gear (not shown) to constitute a so-called column type electric power steering device.

  The mounting position of the motor 15 may be a rack type that is coaxially attached to the rack bar 18 in addition to the configuration of FIG. 1 or a pinion type that is attached to the steering gear box 16 and rotates the pinion shaft 12b. Good.

  The torque sensor 11 detects the movement of the steering handle 10 of the driver, and includes a torsion bar and a well-known torque detection unit such as a pair of resolvers installed apart from each other in the axial direction thereof. When the steering shaft 12a rotates, a torque corresponding to the amount of rotation is detected, and the detected information is sent to the steering control unit 30.

  The steering control unit 30 (period detection means, rotational speed calculation means, command value calculation means of the present invention) includes a well-known CPU 31, RAM 32, ROM 33, I / O 34 which is an input / output interface, and a bus line 35 connecting these components. Is provided. The CPU 31 controls the program and data stored in the ROM 33 and RAM 32. The ROM 33 has a program storage area 33a and a data storage area 33b. A steering control program 33p is stored in the program storage area 33a. The data storage area 33b stores data necessary for the operation of the steering control program 33p.

  Reference numeral 19 denotes a band-pass filter (hereinafter also referred to as BPF) constituted by a known filter circuit. A known digital signal processor (DSP) may be used for the BPF 19, or the steering control program 33p may be configured to include the filter processing.

  The current sensor 8 (current detection means of the present invention) includes a known shunt resistor. The detected information is sent to the steering control unit 30, converted into a digital signal by an AD converter (not shown), and used for processing by the CPU 31.

  Further, a vehicle speed sensor 17 including a rotation detection unit such as a known rotary encoder for measuring the vehicle speed is connected to the steering control unit 30, and the detected vehicle speed is sent to the steering control unit 30. .

  In the steering control unit 30, the CPU 31 executes a steering control program stored in the ROM 33, thereby calculating a driving torque generated by the motor 15 corresponding to the torque detected by the torque sensor 11, and brushing via the motor driver 14. A voltage for generating the calculated driving torque is applied to the motor 15 which is a direct current motor with a motor. The motor 15 is not particularly limited as long as it can be used in the electric power steering apparatus 1 of the present invention.

  FIG. 2 is a block diagram showing an outline of the motor control process performed by the steering control unit 30. This process is repeatedly performed together with other processes of the steering control program 33p while the electric power steering apparatus 1 is operating.

  Based on the result of correcting the steering torque detected by the torque sensor 11 by the phase compensation calculating unit 49 and the vehicle speed detected by the vehicle speed sensor 17, the assist current calculating unit 50 calculates the basic assist current to be applied to the motor 15. To do. Further, based on the rotation speed (that is, the rotation speed) of the motor 15 and the vehicle speed, the correction current calculation unit 51 calculates a correction current for correcting the assist current. The current addition calculation unit 52 adds the assist current and the correction current to calculate a current (motor current command value) to be applied to the motor 15. A method for calculating the rotation speed of the motor 15 will be described later.

  Then, the maximum current calculation unit 53 checks whether or not the command current is within a range of values that can be applied to the motor 15, and if not, the command current uses a predetermined upper limit value. Then, the current control calculation unit 54 obtains a voltage value for generating a command current and applies the voltage value to the motor 15.

  A motor rotation speed calculation process performed by the steering control unit 30 will be described with reference to the flowchart of FIG. First, the motor current command value is calculated by the maximum current calculator 53 (S1). Next, the actual motor current flowing through the motor 15 is detected by the current sensor 8 (S2). Then, the current deviation calculation unit 55 obtains the deviation between the motor current command value and the motor actual current (S3). The obtained deviation is converted back into an analog signal by a DA converter included in the steering control unit 30 and input to the BPF 19.

  The BPF 19 removes the DC component of the input analog signal, extracts a component in a predetermined frequency band (44th-order component in the present invention), and outputs the signal (see FIG. 6) to the CPU 31 (S4). After the AD conversion of the signal, the CPU 31 measures the cycle in the motor rotation speed calculation unit 56. The period is determined by measuring the time between the peak values of the signal. The peak value is when the result of the differentiation of the signal waveform (the slope of the waveform) is zero or a value close to zero, and the time when the signal value is positive and peak (for example, included in the CPU 31). And the time when the previous signal value is positive and peak (the counter value) is a period T (S5).

And the rotational speed of the motor 15 is calculated | required from the calculated | required period T (S6). When using the 44th order component,
(1 / (T × 44)) × 60 [rpm] (1)
It becomes. Here, (T × 44) is a time (second) per rotation of the motor.

  As shown in FIG. 7A (a part of the motor shaft sectional view), the motor used in this embodiment has four brushes (41a to 41d) and a commutator arranged coaxially with the motor shaft. It is a 22-slot lap winding configuration with 22 pieces. The state between the brush 41a-brush 41b-brush 41c at the time of motor rotation is demonstrated below. In the state of FIG. 7B (the view of FIG. 7A viewed from the outside of the brush 41b), the path of the brush 41a to the coil a to the coil b to the coil c to the coil d to the coil e to the brush 41b and the brush A path of 41b-coil g-coil h-coil i-coil j-coil k-brush 41c is generated, and a total of 10 coils are energized.

  In the state of FIG.7 (c), the path | route of brush 41a-coil b-coil c-coil d-coil e-brush 41b, brush 41b-coil g-coil h-coil i-coil j-coil k-brush 41c And a total of nine coils are energized. In the state of FIG. 7D, the path of brush 41a-coil b-coil c-coil d-coil e-coil f-brush 41b, and brush 41b-coil g-coil h-coil i-coil j-coil k. ~ The path of the brush 41c is generated, and a total of 10 coils are energized. In the state of FIG.7 (e), the path | route of brush 41a-coil b-coil c-coil d-coil e-coil f-brush 41b, brush 41b-coil h-coil i-coil j-coil k--brush A path 41c is generated, and a total of nine coils are energized.

  Thus, when the brush moves by one commutator (one segment), the number of energized coils changes twice. The coil includes a resistance component, and considering the contact resistance or wiring resistance between the brush and the commutator in the motor (not all coils have the same length), as shown in FIG. When the brush moves by one segment, the motor resistance value changes corresponding to the change in the number of coils twice. That is, in the state of FIG. 7B, the rotation angle b is in the horizontal axis state. Similarly, in the state of FIG. 7C, the position of the rotation angle c, and in the state of FIG. In the position shown in FIG. 7 (e), the rotation angle e is set. Since nine coils are energized at the positions of the rotation angles c and e and ten coils are energized at the positions of the rotation angles b and d, the resistance value at the positions of the rotation angles c and e is defined as a reference (1 ), The resistance values at the positions of the rotation angles b and d are larger than the reference value (that is, the ratio of the resistance values is increased).

  That is, when the motor rotates once, the resistance value changes 44 (2 × 22) times. Therefore, in this embodiment, the 44th order component is extracted by the BPF 19. Also in the formula (1), the time (second) per rotation of the motor is (T × 44). Therefore, this value “44” varies depending on the structure of the motor, such as the number of slots, because the motor changes the resistance value per revolution. Moreover, you may detect the fluctuation | variation of the electric current component corresponding to peaks other than the point X in Fig.4 (a).

  Although the embodiments of the present invention have been described above, these are merely examples, and the present invention is not limited to these embodiments, and the knowledge of those skilled in the art can be used without departing from the spirit of the claims. Various modifications based on this are possible.

1 is a block diagram showing the overall configuration of an electric power steering device of the present invention. The block diagram for demonstrating steering control. The flowchart for demonstrating the motor rotational speed calculation method. The figure which shows the relationship between the fluctuation frequency of an electric current component, and a motor rotation speed. The figure which shows the relationship between a motor current and a motor resistance value. The figure which shows an example of the fluctuation | variation of an electric current component. The figure which shows the relationship between the brush and commutator at the time of motor rotation. The figure which shows the change of the motor resistance value at the time of motor rotation.

Explanation of symbols

1 Electric power steering device 8 Current sensor (current detection means)
DESCRIPTION OF SYMBOLS 10 Steering handle 11 Torque sensor 15 Motor 17 Vehicle speed sensor 30 Steering control part (Period detection means, rotational speed calculation means, command value calculation means)

Claims (2)

  In the electric power steering control device for a vehicle that applies a steering assist torque to the steering mechanism by energizing and driving the brushed DC motor based on the steering operation of the driver, current detection for detecting the actual motor current flowing in the brushed DC motor Means, a period detecting means for detecting a period in which the value of the actual motor current fluctuates, and a rotational speed estimating means for estimating the rotational speed of the brushed DC motor based on the period. An electric power steering device for a vehicle.   Command value calculation means for calculating a motor current command value to be applied to the brushed DC motor is provided, and the period detection means detects the period based on a deviation between the motor current command value and the motor actual current. The electric power steering device for a vehicle according to claim 1, wherein the electric power steering device is a vehicle.

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