JP3860104B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus, and more particularly, to an electric power steering apparatus that reduces the steering force of a driver by applying the power of a motor to a steering system.
[0002]
[Prior art]
The electric power steering device includes a motor in a steering system, and controls the power supplied from the motor by using a control device, thereby reducing the driver's steering force.
[0003]
FIG. 5 is a schematic structural diagram of the electric power steering apparatus. In the electric power steering apparatus 100, a steering shaft 102 provided integrally with a steering wheel (handle) 101 is connected to a pinion 105a of a rack and pinion mechanism 105 via a connecting shaft 103 having universal joints 103a and 103b. Thus, a manual steering torque generation mechanism 106 is configured.
[0004]
The rack shaft 107 having rack teeth 107a meshing with the pinion 105a and reciprocatingly converted in the axial direction by the meshing thereof is connected to left and right front wheels 109 as rolling shafts via tie rods 108 at both ends thereof. Yes. By operating the handle 101, the driver can change the direction of the vehicle by swinging the front wheels via the manual steering torque generating mechanism 106 and a normal rack and pinion type steering device.
[0005]
In order to reduce the steering torque generated by the manual steering torque generating mechanism 106, a motor 110 for supplying assist torque (steering assist torque) is disposed coaxially with the rack shaft 107, for example, and substantially parallel to the rack shaft 107. The assist torque supplied by the rotational motion from the motor 110 via the provided ball screw mechanism 111 is converted into a force for linear motion and acts on the rack shaft 107.
[0006]
A driving side helical gear 110 a is integrally provided on the rotor of the motor 110. The helical gear 110a meshes with a helical gear 111b provided integrally with the shaft end of the screw shaft 111a of the ball screw mechanism 111. The nut of the ball screw mechanism 111 is connected to the rack shaft 107.
[0007]
FIG. 6 is a diagram illustrating a control device of the electric power steering device. In FIG. 5, a manual steering torque detector 112 that detects a manual steering torque T acting on the pinion 105a is provided in a steering gear box (not shown). The manual steering torque detector 112 converts the detected manual steering torque T into a manual steering torque detection signal Td, and inputs the converted manual steering torque detection signal Td to the control device 114. The control device 114 operates the motor 110 using the manual steering torque detection signal Td as a main signal, and controls the power (steering assist torque) output by the motor 110.
[0008]
The control device 114 includes a target current determination unit 115 and a control unit 116. The target current determination unit 115 determines a target auxiliary torque based on the manual steering torque detection signal Td, and outputs a target current signal IT necessary for supplying the target auxiliary torque from the motor 110.
[0009]
FIG. 7 is a block configuration diagram of the control device 114. The control device 114 includes a target current determination unit 115 and a control unit 116, and the control unit 116 includes a deviation calculation unit 117, a motor operation control unit 118, a motor drive unit 119, and a current detection unit 120. Deviation calculation unit 117 obtains a deviation between target current signal IT output from target current determination unit 115 and motor current signal IM from current detection unit 120, and outputs the value as deviation signal 117a.
[0010]
The motor operation control unit 118 includes a deviation current control unit 121, a gradual decrease unit 130, and a PWM signal generation unit 122. The deviation current control unit 121 controls the motor current supplied to the motor 110 such that the value of the deviation signal 117a approaches zero by performing processing such as proportionality, integration, and differentiation on the input deviation signal 117a. Drive current signal 121a is generated and output.
[0011]
The gradual decrease unit 130 is a device configured to gradually decrease the drive current signal 121a with time when the ignition switch is turned off. That is, it is a device that multiplies the input drive current signal 121a by a multiplication coefficient k and outputs the result, and at that time, the multiplication coefficient k is gradually reduced with the passage of time.
[0012]
The PWM signal generation unit 122 generates a PWM (pulse width modulation) signal for performing PWM operation of the motor 110 based on the drive current signal 121a, and outputs the generated PWM signal as the motor drive control signal 122a. When the drive current signal 121a is gradually decreased by the gradual decrease unit 130, the motor drive control signal 122a output from the PWM signal generation unit 122 is also gradually decreased.
[0013]
The motor drive unit 119 includes a gate drive circuit unit 123 and a motor drive circuit 124 in which four power field effect transistors are connected in an H-type bridge circuit configuration. Based on the motor drive control signal (PWM signal) 122a, the gate drive circuit unit 123 selects two field effect transistors according to the steering direction of the handle 101, and drives the gates of the two selected field effect transistors. These field effect transistors are switched.
[0014]
The current detection unit 120 detects a motor current (armature current) flowing through the motor 110 and outputs a motor current signal IM.
[0015]
As described above, the control device 114 performs PWM control on the current supplied from the battery power supply 126 to the motor 110 based on the manual steering torque T detected by the manual steering torque detection unit 112, and the power (steering assist torque) output from the motor 110. ) To control.
[0016]
Further, as shown in FIG. 7, the control device 114 detects the motor current that actually flows through the motor 110 as the motor current signal IM in the control unit 116, and performs feedback control based on the motor current signal IM, thereby performing the motor 110. The control characteristics are improved.
[0017]
As described above, the manual steering torque T of the driver is detected by the manual steering torque detecting unit 112 of the manual steering torque generating mechanism 106, and the output of the motor 110 is driven and controlled by the control device 114 to control the steering gear box. Assists the force for the rack shaft 107 to move straight. Several such electric power steering devices have been disclosed (see, for example, Patent Document 1).
[0018]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-34892
[Problems to be solved by the invention]
The control device includes a microcomputer that controls the electric power steering device, and the microcomputer performs current feedback so that the motor current matches the target current signal IT corresponding to the manual steering torque. At the beginning and end of the control, a function of fading in / fade out the assist amount is known so as not to give the steering a sense of incongruity (a sudden change in force, etc.). In addition, the control device has a power drive circuit (H-type bridge circuit) for controlling a large current, and the power supply to the H-type bridge circuit is interrupted between the H-type bridge circuit and the power source when a system failure occurs. A power relay for interrupting dark current is provided. In performing the above-described fading process, it is assumed that the power relay is on as a condition for fading in / out. Therefore, at the time of fade-out, the fade process starts after turning off the ignition switch (during power-down), and the power relay is turned off after a specified time. The event of remaining occurs.
[0020]
In order to solve the above problems, an object of the present invention is to provide an electric power steering apparatus that satisfies the desire to reduce a sense of incongruity due to a relay-off sound when the system is off in a system having variable fade means.
[0021]
[Means and Actions for Solving the Problems]
The electric power steering apparatus according to the present invention is configured as follows to achieve the above object.
[0022]
An electric power steering apparatus according to the present invention (corresponding to claim 1) includes a motor that applies an auxiliary torque to a steering system, a steering torque detector that detects steering torque of the steering system, and a motor based on at least a steering torque signal. A target current determination unit that determines a target current to be supplied to the motor, a current detection unit that detects a current flowing through the motor, a motor operation control unit that outputs a motor drive control signal for driving the motor, a motor operation control unit, and a power source Target power signal output from the target current determining unit when the ignition switch is turned off in the electric power steering apparatus having a power relay that is arranged between the power relay for supplying and shutting off power and a gradually decreasing unit that gradually decreases the motor drive control signal Fade-out process that outputs a no-fade out command signal to the gradual reduction section when It includes a section, decreasing section that received no fade-out instruction signal by the fade-out processing unit to zero without decreasing the motor drive control signal, characterized by turning off the power relay.
[0023]
According to the electric power steering apparatus of the present invention, a motor that applies auxiliary torque to the steering system, a steering torque detection unit that detects steering torque of the steering system, and a target to be supplied to the motor based on at least the steering torque signal A target current determination unit for determining a current; a current detection unit for detecting a current flowing through the motor; a motor operation control unit for outputting a motor drive control signal for driving the motor; and a gradual decrease unit for gradually decreasing the motor drive control signal An electric power steering apparatus having a fade-out processing unit that outputs a no-fade-out command signal to the gradual decrease unit when the target current signal output from the target current determination unit is equal to or less than a predetermined value when the ignition switch is turned off. In response to the no fade-out command signal, Since the control signal is reduced to zero without gradual reduction, the power relay can be turned off immediately without fading when no torque is applied or when fading is not required. The sound can be covered, and the uncomfortable feeling can be reduced.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.
[0025]
The structure of the electric power steering apparatus is basically the same as that shown in FIG. 5, and the structure and operation thereof are as described above.
[0026]
FIG. 1 is a block diagram of a control device for an electric power steering apparatus according to the present invention. The control device 1 shown in FIG. 1 is obtained by adding a fade-out processing unit 10 to the conventional control device 114 shown in FIGS. 6 and 7. Moreover, the function described later is added to the gradual reduction part.
[0027]
The fade-out processing unit 10 interrupts the gradual reduction process of the multiplication coefficient k applied to the drive current signal when the steering torque is small and the target current IT is less than a small torque input of 0 A when fading out. Then, the multiplication coefficient k is set to 0 after the lapse of the specified time.
[0028]
FIG. 2 is a configuration diagram of the fade-out processing unit 10. The fade-out processing unit 10 includes a CPU 11 and a memory 12, and a fade-out processing program 14 is stored in the memory 12. The fade-out processing unit 10 includes an input unit 15 and an output unit 16.
[0029]
The fade-out processing program 14 is a program for judging whether or not to perform the fade-out processing, and for outputting a fade-out command signal for fading out to the gradual reduction unit 30 or a no-fade-out command signal not causing the gradual reduction unit 30 to fade out. Shown in FIG. When the ignition switch is turned off, an ignition switch off signal is input to the fade-out processing unit 10, and at this time, when the target current IT is input from the target current determination unit 115 (step ST10), the CPU 11 sets the target current IT to zero. If the target current IT is not zero, a fade-out command signal is output to the gradual decrease unit (step ST12). If the target current IT is zero, it is determined whether or not the specified time has elapsed by the timer (step ST13). If the specified time has not elapsed, the process returns. A fade-out command signal is output to the gradual reduction unit 30 (step ST14).
[0030]
Next, the gradual reduction unit 30 will be described. The gradual reduction unit 30 includes a CPU, a memory, an input unit, and an output unit (not shown). A processing program is stored in the memory. The flowchart of the processing program in the gradual reduction unit 30 is as shown in FIG. When the ignition switch is turned off and an off signal is input, the program starts. First, it is determined whether the signal from the fade-out processing unit 10 is a fade-out command signal or a non-fade-out command signal (step ST20). If it is a fade-out command signal, fade-out is executed (step ST21). That is, the multiplication coefficient k multiplied by the drive current signal 121a output from the deviation current control unit 121 is set to 1 until the preset time elapses after the fade-out command signal is supplied. A drive current gradual decrease signal is generated by gradually decreasing toward 0 with time. Then, it is determined whether or not the multiplication coefficient k has become zero (step ST22). If the multiplication coefficient k is not zero, the process returns. If the multiplication coefficient k becomes zero, a power relay off signal is output (step ST23). Upon receiving the signal, the power relay 140 is turned off. On the other hand, when the signal from the fade-out processing unit 10 is a no-fade-out command signal, the multiplication coefficient k is set to 0 without fading out, so that the drive current signal becomes zero without fading out (step ST24). In step ST22, the multiplication coefficient k is determined. Since the multiplication coefficient k is zero, the power relay off signal is immediately output to the power relay 140 (step ST23). Thereby, the power relay 140 is turned off.
[0031]
Next, a control method in the control device 1 shown in FIG. 1 will be described.
[0032]
The gradual decrease unit 30 starts its operation when an off signal indicating that the ignition switch is turned off is input. Otherwise, it does not operate and the motor drive signal passes through as it is. When the gradual decrease unit 30 receives the off signal that the ignition switch is turned off, the gradual decrease unit 30 calculates the drive current calculated by the deviation current control unit 121 when the fade-out command signal is supplied from the fade-out processing unit 10. The signal 121a is gradually decreased over time to generate a drive current gradually decreasing signal that is gradually decreased so that the drive current signal finally becomes 0, and the generated drive current gradually decreasing signal is supplied to the PWM signal generating unit 122. To do.
[0033]
The gradual reduction unit 30 sets the coefficient k to be multiplied to the drive current signal calculated by the deviation current control unit 121 corresponding to the deviation to 1 until a preset time elapses from the time when the fade-out command signal is supplied. Then, the multiplication factor k is gradually decreased from 1 to 0 with time to generate a drive current gradual decrease signal. Thereafter, when the multiplication coefficient k becomes zero, a power relay off signal is sent to the power relay, and the power relay is turned off.
[0034]
On the other hand, when a no fade-out command signal is supplied from the fade-out processing unit 10, the multiplication factor k is set to 0 without fading out, the multiplication factor k is multiplied to set the drive current signal to 0, and at the same time, the relay-off command signal And the relay is also cut off. Further, when the target current IT becomes zero during the fade-out, the “fade-out command signal” can be switched to the “no fade-out command signal”.
[0035]
Thus, in this electric power steering apparatus, when the ignition switch is turned off in a minute torque state, the immediate multiplication coefficient k becomes 0 and the power relay is turned off at the same time. Therefore, the power relay off sound is the ignition switch off sound. Because it is closer to, a sense of incongruity can be reduced.
[0036]
In the present embodiment, the gradual reduction unit has been described as being placed in the next stage of the deviation current control unit, but by gradually reducing the target current signal by placing the gradual reduction part in the subsequent stage of the target current determination unit. The motor drive control signal may be gradually decreased, or the motor drive control signal may be gradually decreased by inserting a gradual decrease unit in the next stage of the PWM signal generation unit. In the present embodiment, the CPU of the fade-out processing unit and the CPU of the gradual reduction unit have been described separately. However, one CPU may be used in common by the fade-out processing unit and the gradual reduction unit.
[0037]
【The invention's effect】
As is apparent from the above description, the present invention has the following effects.
[0038]
A motor for applying auxiliary torque to the steering system, a steering torque detection unit for detecting steering torque of the steering system, a target current setting unit for determining a target current to be supplied to the motor based on at least a steering torque signal, and a motor In an electric power steering apparatus having a current detection unit for detecting a flowing current, a motor operation control unit for outputting a motor drive control signal for driving a motor, and a gradual decrease unit for gradually decreasing the motor drive control signal, the ignition switch is turned off. When the target current signal output from the target current determining unit is zero, the gradual decrease unit includes a fade-out processing unit that outputs a no-fade-out command signal. The gradual decrease unit that receives the no-fade-out command signal from the fade-out processing unit is motor drive controlled. Torque is applied to reduce the signal to zero without gradual decrease. Not, when there is no need of a fade, it is possible to turn off the power relay immediately without fading process, it is possible to suffer off sound of the relay off sound of the ignition switch, can reduce the discomfort.
[Brief description of the drawings]
FIG. 1 is a block configuration diagram of a control device for an electric power steering apparatus according to the present invention.
FIG. 2 is a configuration diagram of a fade-out processing unit.
FIG. 3 is a flowchart of fade-out processing in a fade-out processing unit.
FIG. 4 is a processing flowchart in a gradual reduction unit.
FIG. 5 is a schematic structural diagram of an electric power steering apparatus.
FIG. 6 is a diagram showing a control mechanism of a conventional electric power steering apparatus.
FIG. 7 is a block diagram of a conventional control device.
[Explanation of symbols]
10 Fade-out processing unit 11 CPU
12 memory 14 fade-out processing program 15 input unit 16 output unit 30 gradual reduction unit 110 motor 112 manual steering torque detection unit 114 control device 115 target current determination unit 116 control unit 117 deviation calculation unit 118 motor operation control unit 119 motor drive unit 120 current detection Part 130 Gradually decreasing part

Claims (1)

A motor for applying auxiliary torque to the steering system;
A steering torque detector for detecting a steering torque of the steering system;
A target current determination unit for determining a target current to be supplied to the motor based on at least the steering torque signal;
A current detection unit for detecting a current flowing through the motor;
A motor operation control unit for outputting a motor drive control signal for driving the motor;
A power relay disposed between the motor operation control unit and a power source for supplying and shutting off power;
In the electric power steering apparatus having a gradual decrease unit that gradually decreases the motor drive control signal,
When a target current signal output from the target current determining unit when the ignition switch is off is equal to or less than a predetermined value, the gradual decreasing unit includes a fade-out processing unit that outputs a no-fade-out command signal. The electric power steering apparatus according to claim 1, wherein the gradual decrease unit receives the motor drive control signal to zero without gradually decreasing , and turns off the power relay .

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