JPH1149014A - Motor-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a device to supply stabilized steering assist torque from a motor even in case of slowly performing steering operation, also in the case such as steering a steering system is steered to a maximum steering angle position, prevent an excessive current from being supplied to the motor. SOLUTION: In a steering speed arithmetic part 22, based on a motor current IM and motor voltage EM, a rotational speed of a motor is calculated, an arithmetic result is output as a steering speed VM. In an overload preventing control part 51, the motor current IM corresponding to steering force acting in a steering system is a first prescribed value or more, and when the steering speed VM is detected to be a prescribed value or less, for instance, a 0.5 multiplication coefficient is supplied to a multiplier 52, a correction target current ITH supplied to a motor drive part 24 is decreased. In the overload preventing control part 51, when the electric motor current IM is a second prescribed value or more smaller than the first prescribed value, and when a condition of the steering speed VM in a prescribed value or less is continued for a prescribed time, a current supplied to the motor drive part 24 is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for reducing the steering force of a driver by applying the power of an electric motor to a steering system. More specifically, the steering system is steered to a maximum steering angle position. The present invention relates to an electric power steering device that prevents an excessive current from being continuously supplied to an electric motor.

[0002]

2. Description of the Related Art In an electric power steering apparatus that applies a steering assist force (steering assist torque) output by an electric motor to a steering force transmission system, a steering angle, a steering speed, a steering force (steering torque) of a steering wheel, and the like. ) And steering information,
The current supplied to the motor is controlled in accordance with vehicle motion information such as the vehicle speed, and the steering assist force output from the motor is applied to the steered wheels via the steering mechanism together with the manual steering force to rotate the steered wheels. Steer.

For example, in the case of a rack-and-pinion type electric power steering device, a manual steering force and a steering assist force act on the rack to move the rack from a neutral position in the left and right axial directions, thereby controlling the movement of the rack. The steering wheel is steered by transmitting the steering wheel via a tie rod or the like.

In such an electric power steering apparatus, the rack is brought into contact with a gear case or the like at a maximum left and right movement position (hereinafter, referred to as a maximum steering angle position) of the rack, so that the rack is maximized. Moving beyond the steering angle position is prohibited, and operation of the steering wheel in a direction exceeding the maximum steering angle position is disabled.

Therefore, when the rack is located at the maximum steering angle position, it is not necessary to supply the assisting steering force from the electric motor, and it is desirable to reduce the power consumption by limiting the assisting steering force output from the electric motor. .

In Japanese Utility Model Laid-Open Publication No. 60-193868, a micro switch for detecting that the rack has moved to the maximum steering angle position is provided in a gear case, and the steering assist force is reduced based on the output of the micro switch. An electric power steering device is described.

However, the configuration including the microswitch for detecting that the rack has moved to the maximum steering angle position requires that a wiring be provided between the microswitch provided in the gear case and the control device. Since considerable accuracy is required for the mounting position of the microswitch, the number of assembly steps increases.

Accordingly, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 64-906.
In Japanese Patent Laid-Open No. 4 (1993) -1994, a steering force detecting means for detecting a steering force of a steering (steering) system, a steering speed detecting means for detecting a steering speed of a steering system, and a steering force detected by the steering force detecting means satisfy a predetermined value. There is proposed an electric power steering apparatus including overload prevention means for reducing a current flowing to the electric motor when the steering speed exceeds the predetermined value and the steering speed detected by the steering speed detection means is equal to or less than a predetermined value.

FIG. 1 is a schematic structural view showing an example of an electric power steering device. The electric power steering device 1 includes an electric motor 10 in a steering system.
By controlling the power supplied from the control unit 20 using the control device 20, the steering force of the driver is reduced.

[0010] Steering wheel (steering handle) 2
Is connected to a pinion 6 of a rack & pinion mechanism 5 via a connecting shaft 4 having universal joints 4a and 4b. The rack shaft 7 includes rack teeth 7a that mesh with the pinion 6. The rack and pinion mechanism 5 converts the rotation of the pinion 6 into a reciprocating motion of the rack 7 in the axial direction. Tie rods 8 at both ends of rack shaft 7
The right and left front wheels 9 as rolling wheels are connected via the. When the steering wheel 2 is steered, the front wheels (steering wheels) are driven via the rack & pinion mechanism 5 and the tie rods 8.
9 is rocked. Thereby, the direction of the vehicle can be changed.

In order to reduce the steering force, a motor 10 for supplying a steering assist torque (assist torque) is connected to a rack shaft 7.
The rotation output of the electric motor 10 is converted into a thrust through a ball screw mechanism 11 provided substantially parallel to the rack shaft 7 so as to act on the rack shaft 7. Electric motor 1
The drive side helical gear 10a is provided integrally with the rotor 0. The helical gear 11b and the drive-side helical gear 10a provided integrally with the shaft end of the screw shaft 11a of the ball screw mechanism 11 are meshed. The nut 11c of the ball screw mechanism 11 is connected to the rack shaft 7.

A manual steering torque acting on the pinion 6 is detected by a steering torque detector (steering torque sensor) 12 provided in a steering box (not shown).
A steering torque signal Tp corresponding to the detected steering torque is supplied to the control device 20. The control device 20 operates the electric motor 10 using the steering torque signal Tp as a main signal,
The output power (steering assist torque) of the electric motor 10 is controlled.

FIG. 2 is a block diagram showing an example of a conventional control device. The conventional control device 20A includes a target current calculation unit 21, a steering speed detection unit 22, and an overload prevention unit 23.
And a motor drive unit 24. Reference numeral BAT is a battery power supply, reference numeral 25 is a motor current detector that detects a current flowing through the motor 10 and outputs a motor current signal (hereinafter, referred to as a motor current) IM, and reference numeral 26 is a voltage that is supplied to the motor 10. And outputs a motor voltage signal (hereinafter, motor voltage) EM.

The target current calculation unit 21 supplies a basic steering torque to the electric motor 10 based on the steering torque signal Tp output from the steering torque detector 12 so that the electric motor 10 generates a steering assist torque corresponding to the steering torque. A current value is obtained, a basic current value is corrected in accordance with a vehicle speed detected by a vehicle speed sensor (not shown), and further, in accordance with a steering speed signal (hereinafter, referred to as steering speed) VM output from the steering speed detection unit 22. The corrected base current value is corrected, and the corrected current to be supplied to the motor is output as a target current value (hereinafter, referred to as a target current) IT. The target current IT is supplied to the motor drive unit 24 via the overload prevention unit 23.

The steering speed detector 22 calculates the motor speed VM based on the motor current IM and the motor voltage EM based on the equation 1, and outputs the calculated motor speed VM as the steering speed VM.

[0016]

## EQU1 ## where VM = (EM-IM.RM) / Kp where RM is the resistance value of the motor and Kp is the induced voltage coefficient.

Since there is a fixed relationship between the motor speed (rotation speed of the motor) and the steering speed, the motor speed is set to the steering speed V
M can be treated. The steering speed VM is supplied to the target current calculation unit 21 and the overload prevention unit 23.

The motor speed VM is not calculated from the motor current IM and the motor voltage EM.
A configuration may be adopted in which a steering speed detector is provided on a steering shaft or the like to detect the steering speed.

The overload prevention unit 23 detects the overload state of the motor 10 and reduces the target current IT to be supplied to the motor drive unit 24 in the overload state. Reduce the current supplied to the For example, when a manual steering torque is detected in a state where the steering system is steered to the maximum steering angle position or in a state where the front wheels (steered wheels) are caught in a groove or the like and cannot be steered, a steering assist torque corresponding to the manual steering torque is detected. Motor 10
Even if current is supplied to the motor, the rack shaft is in a state where it cannot move any more, so that the motor 10 cannot rotate, so that wasteful power is consumed and the motor 10 is unnecessarily heated. Absent.

The overload prevention unit 23 shown in FIG.
When the overload state detection unit 31 detects the overload state, the correction target current ITH supplied to the motor drive unit 24 is changed by changing the multiplication coefficient K supplied to the multiplier 32 from the normal value 1 to 0.5 or less. Is to be reduced. here,
When the motor current IM is larger than a predetermined value and the steering speed VM is smaller than the preset steering speed, the overload state detection unit 31 determines that the vehicle is in the overload state, and determines a multiplication coefficient K Is changed from the normal value 1 to 0.5 or less.

The motor driving unit 24 includes a deviation calculating unit 41,
It includes a PID control unit 42, a PWM signal generation unit 43, a gate drive circuit unit 44, and a motor drive circuit 45 in which four power field-effect transistors are H-bridge connected.

The deviation calculator 41 calculates the deviation between the correction target current ITH and the motor current IM detected by the motor current detector 25 and outputs a deviation signal 41a. The deviation signal 41a is supplied to the PID control unit 42.

The PID control unit 42 generates a drive control signal 42a for controlling the current supplied to the motor 10 so as to perform processing such as proportionality, integration and differentiation on the deviation signal 41a so that the deviation approaches zero. And output. The drive control signal 42a is supplied to the PWM signal generator 43.

The PWM signal generator 43 outputs the drive control signal 4
PW for performing PWM operation of electric motor 10 based on 2a
An M (pulse width modulation) signal 43a is generated and output. P
The WM signal 43a is supplied to the gate drive circuit unit 44. The gate drive circuit unit 44 drives the gate of each field-effect transistor based on the PWM signal 43a to drive and switch each field-effect transistor.

With the above configuration, the conventional control device 20
A is calculated based on the steering torque Tp detected by the steering torque detector 12 from the battery power BAT to the electric motor 10.
The power supplied to the motor 10 is PWM-controlled to control the output power (steering assist torque) of the electric motor 10, and the operation state of the electric motor 10 may be overloaded by the overload state detection unit 31 in the overload prevention unit 23. When detected, the current supplied to the motor 10 is reduced by reducing the correction target current ITH supplied to the motor drive unit 24.

[0026]

However, the overload prevention section 23 of the conventional control device 20A shown in FIG. 2 has a motor current IM larger than a predetermined value and a steering speed VM set at a predetermined value. When the steering speed is lower than the set steering speed, it is determined that the vehicle is in an overload state, and the current supplied to the electric motor 10 is reduced. Therefore, when the steering (steering) operation is performed slowly, the steering system becomes the maximum steering angle. Even though the vehicle is not steered to the position, it may be erroneously detected that the vehicle is in an overload state, and the current supplied to the electric motor 10 may be reduced. If the current supplied to the motor 10 is reduced due to this erroneous detection, the motor 10
Since the steering assist torque supplied from the steering wheel is reduced, the steering operation becomes heavy (the steering wheel becomes heavy), which may give a feeling of strangeness to the driver.

The present invention has been made to solve such a problem. Even when the steering operation is performed slowly, a stable steering assist torque can be supplied from the electric motor to the steering system. It is an object of the present invention to provide an electric power steering device that prevents an excessive current from being continuously supplied to an electric motor when the vehicle is steered to an angular position.

[0028]

In order to solve the above-mentioned problems, an electric power steering apparatus according to the present invention is an electric power steering apparatus for controlling a current supplied to an electric motor for applying a steering assist torque to a steering system at least according to a manual steering torque. In the power steering apparatus, when the steering speed of the steering system is equal to or less than a predetermined value and the steering force acting on the steering system is equal to or more than a first predetermined value, the current supplied to the electric motor is immediately reduced, and the steering speed of the steering system is reduced. An overload prevention unit that reduces the current supplied to the motor when a state in which the steering force is equal to or less than a predetermined value and the steering force acting on the steering system is equal to or more than a second predetermined value that is smaller than the first predetermined value has continued for a predetermined time. And characterized in that:

It is also possible to provide a motor current detector for detecting a motor current flowing through the motor, and to detect a steering force acting on the steering system based on the motor current detected by the motor current detector.

The motor further comprises a motor current detector for detecting a motor current flowing through the motor and a motor voltage detector for detecting a motor voltage supplied to the motor. The motor current detected by the motor current detector and the motor voltage detector It may be configured to include a steering speed detector that calculates the steering speed based on the electric motor voltage detected in (1).

In the electric power steering apparatus according to the present invention, when the steering speed of the steering system is equal to or less than the predetermined value and the steering force acting on the steering system is equal to or more than the first predetermined value, the current supplied to the electric motor is immediately reduced. When a state in which the steering speed of the steering system is equal to or less than a predetermined value and the steering force acting on the steering system is equal to or more than a second predetermined value smaller than the first predetermined value continues for a predetermined time, the current supplied to the electric motor is increased. When the steering speed is equal to or lower than the predetermined value and the steering force is equal to or higher than the first predetermined value, it is determined that the steering system has reached the maximum steering angle position. When the steering speed is equal to or less than a predetermined value and the steering force is equal to or more than a second predetermined value that is smaller than the first predetermined value, the motor current is reduced when the state continues for a predetermined time. Decrease Therefore, even when the steering operation is performed slowly, the current supplied to the electric motor is immediately reduced before the steering system reaches the maximum steering angle position to prevent the steering operation from becoming heavy, and the steering system is moved to the maximum steering angle position. It is possible to prevent an excessive current from being continuously supplied to the electric motor when the steering is performed.

The provision of the steering speed detecting section for estimating the steering speed of the steering system based on the motor current signal and the motor voltage signal allows the steering speed to be estimated without providing a steering speed detector. . Therefore, the structure of the electric power steering device can be simplified.

Further, the overload prevention unit is configured to determine whether the steering speed is equal to or lower than a predetermined value and the steering force is equal to or higher than a first predetermined value, or that the steering speed is equal to or lower than the predetermined value and the steering force is equal to the first predetermined value. A micro switch for detecting that the steering system has been steered to the maximum steering angle position by reducing the current supplied to the electric motor when a state equal to or greater than a second predetermined value smaller than the second predetermined value continues for a predetermined time. It is possible to detect that the steering system is at the maximum steering angle position and that the steered wheels cannot be steered due to being caught in a groove or the like without providing a mechanical detecting unit such as. Therefore, the structure of the electric power steering device can be simplified.

[0034]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The structure of the electric power steering device is basically the same as that shown in FIG.
Its structure and operation are as described above.

FIG. 3 is a block diagram of a control device of the electric power steering device according to the present invention. The control device 20B shown in FIG. 3 includes a target current calculation unit 21, a steering speed detection unit 22, an overload prevention unit 50, and a motor drive unit 24.
Consists of Reference numeral BAT denotes a battery power supply, reference numeral 25 denotes a motor current detector that detects a current flowing through the motor 10 and outputs a motor current signal (hereinafter, referred to as motor current) IM, and reference numeral 26 denotes a voltage applied to the motor 10. And outputs a motor voltage signal (hereinafter, motor voltage) EM. The control device 20B shown in FIG.
The configuration of the overload prevention unit 50 is different from that of the conventional control device 20A shown in FIG.

The target current calculation section 21 supplies a basic steering torque to the motor 10 in order to generate a steering assist torque corresponding to the steering torque from the motor 10 based on the steering torque signal Tp output from the steering torque detector 12. A current value is obtained, a basic current value is corrected in accordance with a vehicle speed detected by a vehicle speed sensor (not shown), and further, according to a steering speed signal (hereinafter referred to as steering speed) VM output from the steering speed calculation unit 22. And outputs the corrected current to be supplied to the motor as a target current value (hereinafter, referred to as a target current) IT. The target current IT is supplied to the motor drive unit 24 via the overload prevention unit 50.

The steering speed detector 22 calculates the motor speed VM from the motor current IM and the motor voltage EM based on the equation 2, and outputs the calculated motor speed VM as the steering speed VM.

[0038]

## EQU2 ## VM = (EM-IM.RM) / Kp where RM is the resistance value of the motor and Kp is the induced voltage coefficient.

Since there is a fixed relationship between the motor speed (rotation speed of the motor) and the steering speed, the motor speed is set to the steering speed V
M can be treated. The steering speed VM is supplied to the target current calculation unit 21 and the overload prevention unit 50.

The motor speed VM is not calculated from the motor current IM and the motor voltage EM.
A configuration may be adopted in which a steering speed detector is provided on a steering shaft or the like, and the steering speed is directly detected.

The overload prevention unit 50 includes an overload prevention control unit 5
1 and a multiplier 52. The overload prevention unit 50 detects the overload state of the motor 10 and reduces the target current IT supplied to the motor drive unit 24 in the overload state, so that the target current IT is supplied to the motor 10 via the motor drive unit 24. Current. For example, when manual steering torque is detected in a state where the steering system is steered to the maximum steering angle position or in a state where the front wheels (steered wheels) are caught in a groove or the like and cannot be steered,
Even if a current is supplied to the electric motor 10 so as to generate a steering assist torque corresponding to the manual steering torque, the electric motor 10 cannot rotate because the rack shaft cannot move any more, and wasteful power is consumed. And the motor 10 is unnecessarily heated, which is not desirable.

Therefore, the overload prevention unit 50 shown in FIG.
When the overload state is detected by the overload prevention control unit 51, the correction target current ITH supplied to the motor drive unit 24 is changed by changing the multiplication coefficient K supplied to the multiplier 52 from the normal value 1 to, for example, 0.5. Is to be reduced. The reason why the multiplication coefficient K is set to, for example, about 0.5 in the overload state is to supply a steering assist force against a tire reaction force.

FIG. 4 is an explanatory diagram showing an area in which overload prevention control is performed. The overload prevention unit 50 includes the steering speed detection unit 2
2, the steering speed VM and the motor current I obtained from Equation 1
Based on M, invalid electric power is consumed by the electric motor 10 in a state where the steering reaches an end (maximum steering angle position), a steered wheel is caught in a groove or the like, or hits a curb and steering cannot be performed. The state is determined to determine the necessity of overload prevention. Specifically, it is determined that overload prevention control is necessary when the motor current IM is equal to or more than a predetermined value and the steering speed VM estimated by the steering speed detection unit 22 is equal to or less than a predetermined value (substantially 0).

Here, the motor current IM and the motor voltage EM
As for the steering speed (motor speed) VM calculated (estimated) based on the above, the detection accuracy decreases as the steering speed becomes lower. Further, since the resistance value RM and the induced voltage coefficient Kp of the motor have temperature characteristics, the steering speed (estimated) calculated (estimated) based on the motor current IM and the motor voltage EM with the change in the ambient temperature. An error occurs in the (motor speed) VM.

Therefore, the overload prevention control unit 51 determines that the steering speed VM estimated from the steering speed detection unit 22 is equal to or less than a predetermined value (the steering speed VM is close to 0) and the motor current I
If M is equal to or greater than the first predetermined value, for example, the maximum value (hereinafter, referred to as the maximum target current value) output from the target current calculation unit 21 or the maximum target value, it is determined that an overload condition has occurred and the multiplier 5
2 is multiplied from the normal value 1 to, for example, 0.5
, The correction target current ITH supplied to the motor drive unit 24 is immediately reduced.

Further, the overload prevention control unit 51 determines that the steering speed VM estimated from the steering speed detection unit 22 is equal to or less than a predetermined value (the steering speed VM is a value close to 0) and the motor current I
M is a second predetermined value smaller than the first predetermined value, for example, a value lower than the maximum target current value (for example, the maximum target current value 7
If the state of 5% or more continues for a predetermined time (for example, 3 seconds), it is determined that an overload state has occurred, and the multiplication coefficient K supplied to the multiplier 52 is changed from the normal value 1 to, for example, 0.5. Then, the correction target current ITH supplied to the motor drive unit 24 is reduced.

The overload prevention control unit 51 changes the multiplication coefficient K supplied to the multiplier 52 from the normal value 1 to, for example, 0.5 to decrease the correction target current ITH supplied to the motor drive unit 24. In this state, when the steering speed VM is not substantially zero and the vehicle is not overloaded, the multiplication coefficient K is immediately returned to the normal value 1.

The multiplier 52 multiplies the target current IT supplied from the target current calculation unit 21 by a multiplication coefficient K supplied from the overload prevention control unit 51 to obtain a corrected target current ITH. In a state where no overload is detected (normal state), the value of the multiplication coefficient K is 1. For this reason, the overload prevention unit 50 changes the target current IT as it is to the corrected target current ITH
Output as In a state where the overload is detected, the value of the multiplication coefficient K is, for example, 0.5. Therefore, the overload prevention unit 50 detects the target current I when the overload is detected.
For example, a correction target current ITH that is reduced to half the value of T is supplied to the motor drive unit 24.

The motor drive unit 24 includes a deviation calculation unit 41,
It includes a PID control unit 42, a PWM signal generation unit 43, a gate drive circuit unit 44, and a motor drive circuit 45 in which four power field-effect transistors are H-bridge connected.

The deviation calculator 41 calculates a deviation between the correction target current ITH and the motor current IM detected by the motor current detector 25 and outputs a deviation signal 41a. The deviation signal 41a is supplied to the PID control unit 42.

The PID control section 42 generates a drive control signal 42a for controlling the current supplied to the electric motor 10 so that the deviation approaches zero by performing processes such as proportionality, integration and differentiation on the deviation signal 41a. And output. The drive control signal 42a is supplied to the PWM signal generator 43.

The PWM signal generator 43 outputs the drive control signal 4
PW for performing PWM operation of electric motor 10 based on 2a
An M (pulse width modulation) signal 43a is generated and output. P
The WM signal 43a is supplied to the gate drive circuit unit 44. The gate drive circuit unit 44 drives the gate of each field-effect transistor based on the PWM signal 43a to drive and switch each field-effect transistor.

With the above configuration, the control device 20B shown in FIG. 3 performs PWM control of the power supplied from the battery power supply BAT to the motor 10 based on the steering torque Tp detected by the steering torque detector 12, and When the overload prevention control unit 51 in the overload prevention unit 50 detects that the operation state of the motor 10 is overloaded, the output power (steering assist torque) of the motor 10 is controlled. By reducing the correction target current ITH to be supplied, the current supplied to the electric motor 10 is reduced.

FIG. 5 is an explanatory diagram showing a specific example of the operation of detecting the overload state and reducing the motor current. In FIG. 5, the horizontal axis represents time t, and the vertical axis represents motor current IM. When the steering speed (estimated motor speed) VM calculated by the steering speed detection unit 22 based on the motor current IM and the motor voltage EM is equal to or less than a predetermined value (almost 0), the motor current IM is reduced to a first predetermined value ITH1. Is exceeded, the overload prevention control unit 51 immediately changes the multiplication coefficient K to, for example, 0.5 when the motor current IM exceeds the first predetermined value ITH1. As a result, the overload prevention unit 50 switches the motor drive unit 2
The correction target current ITH supplied to the motor 4 is reduced to, for example, １ ／, and the motor current IM supplied to the motor 10 is reduced. Note that the overload prevention unit 50 returns the multiplication coefficient K to 1 when the steering speed (estimated motor speed) VM exceeds a predetermined value (substantially 0). Therefore, the state in which the motor current IM is reduced due to the determination of the overload state is continued until the steering speed (estimated motor speed) VM exceeds a predetermined value (substantially 0).

VM of Equation 2 = (EM−IM · RM) / Kp
In the case where the steering speed VM suddenly becomes 0, the motor voltage IM does not change, so the motor current IM sharply increases, and the motor current IM exceeds the first predetermined value ITH1. For example, the steering speed VM suddenly becomes 0 when the steering wheel vigorously hits the end (maximum steering angle position) of the steering system, or when the steering wheel hits the curb when vigorously steering. , The motor current IM exceeds the first predetermined value ITH1. Therefore, when the motor current IM exceeds the first predetermined value ITH1, it is detected that the end of the steering system (maximum steering angle position) or that the steered wheels have hit the curb and cannot be steered, and are supplied to the motor 10. Current can be reduced.

FIG. 6 is an explanatory diagram showing another specific example of the operation of detecting the overload state and reducing the motor current. 6, the horizontal axis represents time t, and the vertical axis represents motor current IM. When the steering speed (estimated motor speed) VM calculated by the steering speed detector 22 based on the motor current IM and the motor voltage EM is equal to or less than a predetermined value (substantially 0), the motor current IM becomes the second predetermined value ITH2. When the state of exceeding the predetermined time is continued for a predetermined time (for example, 3 seconds), the overload prevention control unit 51
When the state in which the motor current IM exceeds the second predetermined value ITH2 continues for a predetermined time (for example, 3 seconds), the multiplication coefficient K is changed to, for example, 0.5. Thereby, the overload prevention unit 50
Target current ITH supplied to the motor drive unit 24 from the
Is reduced to, for example, １ ／, and the motor current IM supplied to the motor 10 is reduced. The overload prevention unit 50
Returns the multiplication coefficient K to 1 when the steering speed (estimated motor speed) VM exceeds a predetermined value (substantially 0). Therefore, the state in which the motor current IM is reduced due to the determination of the overload state is continued until the steering speed (estimated motor speed) VM exceeds a predetermined value (substantially 0).

Therefore, the steering speed VM detected by the steering speed detection unit 22 when the steering operation is performed slowly.
Is small (almost 0), and the motor current IM
Is a second predetermined value IT smaller than the first predetermined value ITH1.
When the state exceeding H2 continues for a predetermined time (for example, 3 seconds), the overload prevention unit 50 determines that the electric motor 10 is in an overloaded state, and changes the multiplication coefficient K to, for example, 0.5 to change the electric motor 10. Reduce the current supplied to the The overload prevention unit 50 reduces the current supplied to the motor 10 when the motor current IM exceeds the second predetermined value ITH2 for a predetermined time, so that the motor current IM is temporarily reduced to the second current ITH2. The current supplied to the electric motor 10 is immediately reduced just by exceeding the predetermined value ITH2, and the steering assist torque does not decrease.

As described above, when the steering speed VM is equal to or less than the predetermined value (substantially 0) and the motor current IM exceeds the first predetermined value ITH1, the overload prevention unit 50 immediately reduces the current supplied to the motor. Steering speed VM is equal to or less than a predetermined value (almost 0)
When the motor current IM exceeds the second predetermined value ITH2, the current supplied to the motor is reduced when the state continues for a predetermined time (for example, 3 seconds), so that the steering system moves to the maximum steering angle position. Prevents excessive current from being continuously supplied to the motor even when manual steering torque is detected in a steered state or when the front wheels (steered wheels) are caught in grooves or the like and cannot be steered. can do.

FIG. 7 is a block diagram of another control device of the electric power steering device according to the present invention. FIG.
In the control device 20C shown in FIG. 5, the configuration of the overload prevention control unit 61 in the overload prevention unit 60 is different from that shown in FIG. The overload prevention control unit 51 illustrated in FIG. 3 is configured to detect that the steering force acting on the steering system is equal to or greater than a predetermined value based on the motor current IM. Since the control device controls the motor current IM so that the motor 10 generates a steering assist torque corresponding to the steering torque Tp, the motor current IM is a signal corresponding to the steering torque. Therefore, when the motor current IM exceeds the predetermined value, it can be detected that the steering force acting on the steering system is equal to or more than the predetermined value.

On the other hand, the overload prevention control unit 61 shown in FIG. 7 detects that the steering force acting on the steering system is equal to or more than a predetermined value based on the steering torque signal Tp. . The overload prevention control unit 61 shown in FIG. 7 sets the steering torque signal Tp to a predetermined first value (for example, a value that does not occur in normal steering and a value that occurs when the steering reaches the end). Is large and the steering speed VM is smaller than a preset steering speed, it is determined that the vehicle is in an overload condition, the current supplied to the electric motor 10 is immediately reduced, and the steering torque signal Tp is changed to a first predetermined value ( For example, a state in which the steering speed VM exceeds a second predetermined value smaller than the first predetermined value (about 75%) and the steering speed VM is smaller than a preset steering speed for a predetermined time (for example,
If it continues for 3 seconds, it is determined that an overload state is present, and the current supplied to the electric motor 10 is reduced.

In FIGS. 2, 3 and 7, the correction target current IT
Although the configuration including the motor drive unit 24 that performs feedback control of the motor current based on the deviation between H and the motor current IM has been described, when the feedback control based on the motor current is not performed, the motor current detector 25 is used. Need not necessarily be provided. In the configuration without the motor current detector 25, as shown in FIG.
When p is larger than a predetermined value and the steering speed VM is smaller than the preset steering speed, it is determined that an overload state is present, and the overload prevention control for reducing the current supplied to the electric motor 10 is performed. With the configuration using the unit 61, an overload state can be detected and the current flowing through the electric motor 10 can be reduced.

The overload prevention controllers 51 and 61 may be configured to detect that the steering force acting on the steering system is equal to or greater than a predetermined value based on the target current IT.

Further, instead of calculating the motor speed VM by calculation from the motor current IM and the motor voltage EM,
A configuration may be adopted in which a steering speed detector is provided on a steering shaft or the like, and the steering speed is directly detected.

Further, the multiplication coefficient K may be configured to decrease from 1 to 0.5 over time.

[0065]

As described above, in the electric power steering apparatus according to the present invention, when the steering speed of the steering system is equal to or lower than the predetermined value and the steering force acting on the steering system is equal to or higher than the first predetermined value, the electric motor is controlled. The current supplied to the steering system is immediately reduced, and the steering speed of the steering system is equal to or lower than a predetermined value and the steering force acting on the steering system is equal to or higher than a second predetermined value smaller than the first predetermined value for a predetermined time. Then, since the overload prevention unit that reduces the current supplied to the motor is provided, when the steering speed is equal to or less than the predetermined value and the steering force is equal to or more than the first predetermined value, the steering system has reached the maximum steering angle position. The motor current can be reduced immediately by judging that the steering speed is equal to or less than the predetermined value, and if the steering force is equal to or more than the second predetermined value smaller than the first predetermined value, the state is maintained for a predetermined time. Continued Because it reduces the motor current at the point,
Even if the steering operation is performed slowly, the current supplied to the electric motor is immediately reduced before the steering system reaches the maximum steering angle position to prevent the steering operation from becoming heavy, and the steering system is steered to the maximum steering angle position. In such a case, it is possible to prevent an excessive current from being continuously supplied to the electric motor.

By providing the steering speed detecting section for estimating the steering speed of the steering system based on the motor current signal and the motor voltage signal, it is possible to estimate the steering speed without providing a steering speed detector. . Therefore, the structure of the electric power steering device can be simplified.

Further, the overload prevention unit is configured to determine whether the steering speed is equal to or less than a predetermined value and the steering force is equal to or greater than a first predetermined value, or that the steering speed is equal to or less than a predetermined value and the steering force is equal to or smaller than the first predetermined value. A micro switch for detecting that the steering system has been steered to the maximum steering angle position by reducing the current supplied to the electric motor when a state equal to or greater than a second predetermined value smaller than the second predetermined value continues for a predetermined time. It is possible to detect that the steering system is at the maximum steering angle position and that the steered wheels cannot be steered due to being caught in a groove or the like without providing a mechanical detecting unit such as. Therefore, the structure of the electric power steering device can be simplified.

[Brief description of the drawings]

FIG. 1 is a schematic structural view of an electric power steering device.

FIG. 2 is a block diagram of a conventional control device.

FIG. 3 is a block diagram of a control device according to the present invention.

FIG. 4 is an explanatory diagram showing an area in which overload prevention control is performed.

FIG. 5 is an explanatory diagram showing a specific example of an operation of detecting an overload state and reducing an electric motor current.

FIG. 6 is an explanatory diagram showing another specific example of the operation of detecting the overload state and reducing the motor current.

FIG. 7 is a block diagram of another control device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 10 ... Electric motor, 12
... Steering torque detector, 20, 20A, 20B, 20C ...
Control device, 21: target current calculation unit, 22: steering speed calculation unit, 23, 50, 60: overload prevention unit, 24: motor drive unit, 25: motor current detection unit, 26: motor voltage detection unit, 51, 61: overload prevention control unit, 32, 52: multiplier, EM: motor voltage, IM: motor current, IT: target current, ITH: correction target current, K: multiplication coefficient, VM: steering speed.

Claims (3)

[Claims] 1. An electric power steering apparatus for controlling a current supplied to an electric motor for applying a steering assist torque to a steering system at least according to a manual steering torque, wherein a steering speed of the steering system is equal to or less than a predetermined value and the steering system is controlled. When the steering force acting on the steering system is equal to or greater than the first predetermined value, the current supplied to the electric motor is immediately reduced, and the steering speed of the steering system is equal to or less than the predetermined value and the steering force acting on the steering system is increased to the first value. An electric power steering device, comprising: an overload prevention unit that reduces a current supplied to the electric motor when a state of being equal to or more than a second predetermined value smaller than the predetermined value of 1 continues for a predetermined time. 2. An electric power steering apparatus for controlling a current supplied to an electric motor for applying a steering assist torque to a steering system at least according to a manual steering torque, comprising: a steering speed detection unit for detecting a steering speed of the steering system; A motor current detector for detecting a motor current flowing through the motor, wherein the steering speed is equal to or less than a predetermined value and the motor current is a first
If the steering speed is equal to or less than a predetermined value and the motor current is smaller than a first predetermined value, a second current is supplied to the motor.
And an overload prevention unit that reduces an electric current supplied to the electric motor when a state that is equal to or more than a predetermined value continues for a predetermined time. 3. An electric power steering apparatus for controlling a current supplied to a motor for applying a steering assist torque to a steering system at least according to a manual steering torque, wherein a motor voltage detector detects a motor voltage supplied to the motor. A motor current detector that detects a motor current flowing through the motor; a steering speed detection unit that calculates a steering speed of the steering system based on the motor voltage and the motor current; and the steering speed is equal to or less than a predetermined value. And the motor current is the first
If the steering speed is equal to or less than a predetermined value and the motor current is smaller than a first predetermined value, a second current is supplied to the motor.
And an overload prevention unit that reduces an electric current supplied to the electric motor when a state that is equal to or more than a predetermined value continues for a predetermined time.