JP3433713B2 - Electric power steering device for vehicle - Google Patents

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 a vehicle, which assists a steering operation of a steering wheel by rotating an electric motor.

[0002]

2. Description of the Related Art Conventionally, for example, utility model registration publication No. 2
As disclosed in Japanese Patent No. 58620, an electric power for supplying an electric current having a magnitude corresponding to the steering state of the steering wheel to the electric motor to obtain an assisting force for the turning operation of the steering wheel by the rotation of the electric motor. In a steering device, it is known to limit the amount of current flowing through the electric motor according to the amount of drive current of the electric motor in order to protect the electric motor from overheating. And in this case,
The heat generation amount of the electric motor is calculated by squaring the driving current of the electric motor, and a value determined by the first-order delay of the heat generation amount is set as the upper limit value of the current flowing through the electric motor.

[0003]

However, in the above-mentioned conventional device, the limit value changes only depending on the drive current of the electric motor. For example, the limit of the drive current of the electric motor is released. As described above, the method of changing the limit value when the limit value is largely changed is not considered. Therefore, if the limit value changes significantly before the driver notices, that is, if the limit of the drive current of the electric motor is released and the drive current of the motor changes from a small state to a large state, However, there is a problem in that the steering wheel, which has been heavy to some extent, suddenly becomes lighter, and the driver feels uncomfortable when operating the steering wheel.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to make a driver feel as uncomfortable with a steering wheel operation as possible even if a limit value of a drive current for an electric motor changes. An object of the present invention is to provide an electric power steering device that does not feel.

In order to achieve the above-mentioned object, the structural features of the present invention include an electric motor for giving an assisting force to the turning operation of the steering wheel, and a current having a magnitude corresponding to the steering state of the steering wheel. For controlling the rotation of the electric motor by flowing the electric current to the electric motor, and the electric motor.
Current limit value of the electric power steering device
Multiple current limits determined by dynamic environment and operating conditions
The maximum value to determine as the motor current limit value
The small value calculation means and the value of the current flowing to the electric motor are determined as described above.
And a current limiting means for limiting the motor current limit value, the steering torque detection means for detecting a steering torque, an increase in the motor current limit value the detected steering torque is limited by the current limiting means when a predetermined value or more in that a limiting value control means tolerated.

According to the above-mentioned structural feature, the minimum value operator
Is the current limit value for the electric motor and the electric power
-Depending on the operating environment and operating state of the steering system
Motor current is the minimum of the multiple current limit values
Determine as a limit value. Then, the limit value control means controls the motor limited by the current limiting means when the steering torque detected by the steering torque detecting means is equal to or more than a predetermined value.
Allow increase in current limit value. Therefore, even if the motor current limit value changes significantly as when the drive current limit of the electric motor is released, the motor current limit value increases while the driver turns the steering wheel. Therefore, during this steering, the driver hardly feels a change in the steering operation, so that the driver does not feel a big discomfort with the steering wheel operation, and the steering feeling of the driver is improved.

Further, another structural feature of the present invention is that the limit value control means causes the limit value to be gradually increased over time when the increase of the motor current limit value is allowed. I have configured it. According to this, the driver
The feeling of strangeness with respect to the steering wheel operation is further reduced, and the steering feeling of the driver is further improved.

Another structural feature of the present invention is steering.
Electric that gives assisting force to the turning operation of the handle
The electric power of the size corresponding to the steering state of the motor and the steering wheel is
Flow to the electric motor to control the rotation of the electric motor
The motor control means and the value of the current flowing through the electric motor are set to a specified value.
Equipped with current limiting means for limiting the limit value according to the
In an electric power steering system for a
Steering torque detecting means for detecting the torque, and
When the steering torque is above a specified value, it is controlled by the current limiting means.
The limit value that is limited is gradually increased over time.
With allowing Rukoto is to provided a limiting value control means Ru is dependent rate of increase in the limit value of the vehicle speed. According to this, for example, the increasing speed can be slowed as the vehicle speed becomes higher, or the increasing speed can be increased when the vehicle is stopped and the increasing speed is reduced when the vehicle is traveling. As a result, changes to the steering operation at high vehicle speed are suppressed as much as possible, so that the steering feeling of the driver is improved and the traveling stability of the vehicle is secured.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows an electric power steering apparatus for a vehicle according to the embodiment.

In this electric power steering apparatus, the turning operation of the steering handle 11 is performed by the rack and pinion mechanism 1.
Steering shaft 1 transmitted to the left and right front wheels FW1 and FW2 via 2
3 is equipped with an electric motor 14. The electric motor 14 is composed of a DC motor and applies an assisting force to the turning operation of the steering handle 11 according to the rotation thereof, and the rotation thereof is transmitted to the steering shaft 13 via the reduction mechanism 15. It has become so.

An electric control device 20 is electrically connected to the electric motor 14, and the electric control device 20 rotates the electric motor 14 in accordance with the detection outputs of the steering torque sensor 21, the vehicle speed sensor 22 and the temperature sensor 23. Control. The steering torque sensor 21 is assembled to the steering shaft 13 and is used during steering operation of the steering handle 11 and the steering shaft 1.
The steering torque (steering reaction force) TM acting on No. 3 is detected.
The steering torque TM represents a torque generated by the steering wheel 11 and the steering shaft 13 when the steering wheel 11 is rotated and steered to the right, and the steering wheel 11 is rotated and steered to the left. The torque generated in the steering wheel 11 and the steering shaft 13 is expressed as a negative value. The vehicle speed sensor 22 detects the vehicle speed V. Temperature sensor 23
Detects the temperature Tp of the substrate on which the electric circuit components that constitute the electric control device 20 are assembled.

The electric control unit 20, as shown in FIG.
A drive circuit 30 that drives the electric motor 14 and a control circuit unit 40 that controls the drive circuit 30. The drive circuit 30 includes switching elements 31 to 34 such as FETs.
Is a four-sided bridge circuit, and is connected to a positive voltage terminal (+) of a battery 37 via one of a pair of diagonal positions facing each other via a shunt resistor 35 and a relay switch 36. The relay switch 36 is normally in an ON state, and is controlled by a fail detection unit (not shown) that detects a failure of this electric power steering device, and is turned off when a failure is detected. The negative voltage terminal (-) of the battery 37 is grounded. The other of the pair of diagonal positions is grounded via a shunt resistor 38. Also, at the other diagonal position of the bridge circuit,
Both terminals of the electric motor 14 are connected to each other.

The control circuit unit 40 is composed of a microcomputer and its peripheral circuits, and operates by the voltage from the positive voltage terminal (+) of the battery 37 through the ignition switch IG and the diode 41, and the relay switch 36 and It also operates by the voltage supplied through the diode 42 from the connection point with the shunt resistor 35. The control circuit unit 40 actually realizes various functions by program processing, but in FIG. 2, various functions by the program processing are shown by a functional block diagram.

The control circuit unit 40 includes a voltage detector 4
3, a current detector 44, a steering speed calculator 45, a command current value generator 46, and a drive controller 47.

The voltage detecting section 43 inputs the two terminal voltages of the electric motor 14, respectively, and detects the inter-terminal voltage Vm of the motor 14 by the difference between the both terminal voltages and outputs it.
The current detection unit 44 inputs both terminal voltages of the shunt resistor 38, and based on the both terminal voltages, the drive current Im.
To calculate. The steering speed calculation unit 45 calculates the rotational angular speed ω of the electric motor 14 by executing the calculation of the following Expression 1 using the inter-terminal voltage Vm of the electric motor 14 and the drive current Im.

[0016]

[Equation 1] ω = (Vm-Rm · Im) / K

Equation 1 is an approximate expression for obtaining the rotational angular velocity of a DC motor that does not consider inductance (which can be usually ignored because the inductance is small), and K and Rm are constants determined by the motor. Since the electric motor 14 and the steering wheel 11 rotate integrally, the rotational angular speed ω is equal to the steering speed of the steering wheel 11, and hereinafter, the rotational angular speed ω is also used as the steering speed.

The command current value generator 46 will be described in detail later, but the steering torque TM from the steering torque sensor 21, the vehicle speed V from the vehicle speed sensor 22, the temperature Tp from the temperature sensor 23, and the steering speed calculator 45. The steering control speed ω is input to calculate the output command current value Io * defining the amount of current flowing through the electric motor 14 based on the steering torque TM, the vehicle speed V, the temperature Tp, and the steering speed ω, and the drive control unit is calculated. Four
Output to 7. The command current value generator 46 is also supplied with an ignition off signal IGOF indicating that the ignition switch IG is off and a fail signal FAIL indicating a failure of the electric power steering device.
Both of these signals IGOF and FAIL are supplied from a detector (not shown).

The drive control unit 47 inputs the drive current Im of the motor 14 detected by the current detection unit 44 for feedback control and inputs a difference Io * from the output command current value Io *.
-Im is calculated, and the calculated difference Io * -Im
A control signal is formed by PID control using the. Also,
The drive control unit 47 also has a pulse width modulation (PWM) function, supplies a pulse train signal pulse width modulated according to the control signal to the switching elements 31 to 34, and turns the elements 31 to 34 on and off. Control. As a result, a drive current Im equal to the output command current value Io * is passed through the electric motor 14. The switching elements 31, 34
When the ON / OFF control is performed, the electric motor 14 rotates in the forward direction to assist the steering wheel 11 in the right-side turning steering. When the switching elements 32 and 33 are controlled to be turned on and off, the electric motor 14 is rotated in the reverse direction to assist the steering wheel 11 in the leftward turning steering.

As shown in detail in FIG. 3, the command current value generator 46 includes a command current value calculator 50, a command current limit value calculator 60, and a current limit storage unit 70.

The command current value calculator 50 is provided for the steering wheel 1
In order to generate an assisting force in the electric motor 14 according to the steering state of No. 1, the electric motor 1 corresponding to the assisting force is generated.
The command current value I * for 4 is calculated and includes a basic assist control unit 51, a differentiation unit 52, an inertia compensation control unit 53, a handle return control unit 54, a damping control unit 55, and an addition unit 56.

The basic assist control section 51 has a conversion table for converting the steering torque TM into the basic command current value Ia for each of a plurality of vehicle speed ranges.
Torque TM from the vehicle and vehicle speed V from the vehicle speed sensor 22
Is input to output the basic command current value Ia corresponding to the steering torque TM and the vehicle speed V. As shown in FIG. 4, the basic command current value Ia increases as the steering torque TM increases and decreases as the vehicle speed V increases.

The differentiating section 52 differentiates the steering torque TM from the steering torque sensor 21 to obtain a differential value TM '(= dTM).
/ Dt) is output. The inertia compensation control unit 53 controls the turning operation of the steering handle 11 (in particular, the steering handle 1 at the start of turning).
The inertia compensation current value Ib for compensating the inertial force of the electric motor 14 is calculated with respect to (1 turning operation).
The differential value TM 'of the steering torque TM from the differentiating part 52 and the vehicle speed V from the vehicle speed sensor 22 are input to obtain the differential value TM'.
The inertia compensation current value Ib that increases as the vehicle speed V increases and that decreases as the vehicle speed V increases is output.

The steering wheel return control section 54 calculates a steering wheel return current value Ic for compensating for the steering wheel 11 to quickly return to the neutral position when the steering wheel 11 is turned back. And the vehicle speed V from the vehicle speed sensor 22 are input, and a steering wheel return current value Ic that increases as the steering speed ω increases and decreases as the vehicle speed V increases is output.

The damping control unit 55 has the steering wheel 1
The damping current value Id for compensating the addition of resistance to the turning operation of 1 is calculated, and the steering speed ω from the steering speed calculation unit 45 and the vehicle speed V from the vehicle speed sensor 22 are input. Then, the damping current value Id acts in the opposite direction to the steering speed ω, the absolute value increases as the absolute value | ω | of the steering speed ω increases, and the absolute value increases as the vehicle speed V increases. Is output.

The adder 56 adds the basic command current value Ia, the inertia compensation current value Ib, the handle return current value Ic and the damping current value Id to obtain the basic command current value Ic.
The command current value I * obtained by correcting a by the inertia compensation current value Ib, the handle return current value Ic, and the damping current value Id is output.

The command current limit value calculation unit 60 includes an operating environment (ambient temperature, ambient temperature, etc.) of the electric power steering including the electric motor 14, the electric control device 20, the drive circuit 30, and the like.
The determined command current value I * is limited according to the supply voltage), the operating state (immediately after the start of operation, the occurrence of an abnormality, etc.), and the temperature limit value calculation unit 61 and the motor power supply voltage limit value calculation unit 62 are provided. , Ignition off limit value calculation unit 63, fail limit value calculation unit 64, minimum value calculation unit 65,
The current limit restoring unit 66 and the command current value limiting unit 67 are included.

The temperature limit value calculator 61 is provided for the electric motor 1
4, the upper limit value of the current Im flowing through the electric motor 14 is set in order to prevent overheating due to temperature rise of the drive circuit 30, the control circuit unit 40, etc.
A conversion table is provided for converting the upper limit value of the current Im into a temperature limit value ILt that defines the upper limit value of the current Im based on the temperature Tp detected by. As shown in FIG. 5, the conversion table stores a temperature limit value ILt that decreases as the temperature Tp increases.

When the voltage of the battery 37 drops, the motor power supply voltage limit value calculation unit 62 reduces the influence of the voltage drop on other systems, and supplies an appropriate current to the electric motor 14 as long as it is allowed. In order to set the upper limit value of the current Im flowing through the electric motor 14,
6 is repeatedly executed every predetermined short time to calculate a power supply voltage limit value ILe that defines the upper limit value of the current Im flowing through the electric motor 14. The power supply voltage Em may be any voltage that represents the voltage of the battery 37, such as the voltage on the cathode side of the diodes 41 and 42, the voltage on the positive voltage terminal of the battery 37, and the voltage on the anode side of either of the diodes 41 and 42. Voltage etc. can be used. Further, the motor power supply voltage limit value calculation unit 62
Includes a conversion table for converting the power supply voltage Em into the power supply voltage limit value ILe with the characteristics shown in FIG. 7, and the table is used when the program is executed.

The ignition-off limit value calculation unit 63
Immediately after the ignition switch IG is turned off, the application of an assist force to the steering operation of the driver is ensured, and the upper limit value of the current Im flowing through the electric motor 14 is set in order to cut off the electric power supply to the electric motor 14 thereafter. Then, based on the ignition-off signal IG, the ignition-off limit value ILi that defines the upper limit value of the current Im flowing through the electric motor 14 after the ignition switch IG is turned off is calculated. In this case, the ignition switch-off signal IG is given from a detection unit (not shown) that detects the turning-off of the ignition switch IG, and the ignition-off limit value ILi gradually increases as time passes from the turning-off of the ignition switch IG, as shown in FIG. It decreases to "0". When the ignition switch IG is turned on, the ignition off limit value ILi is set to the maximum allowable current value Imax.

The fail limit value calculation unit 64 ensures the application of the assist force to the steering operation of the driver after the occurrence of the abnormality (fail) of the electric power steering device, and cuts off the power supply to the electric motor 14 thereafter. Therefore, the upper limit value of the current Im flowing through the electric motor 14 is set, and the fail limit value ILf that defines the upper limit value of the current Im flowing through the electric motor 14 at the time of failure is calculated based on the fail signal FAIL. in this case,
The fail signal FAIL is given from a detection unit (not shown) that detects the occurrence of an abnormality (fail) in the electric power steering device, and the fail limit value ILf is immediately set to "0" at the time of fail detection, as shown in FIG. Or (see the solid line in FIG. 9), or set to a small predetermined value after the failure is detected (see the broken line in FIG. 9), or gradually decreases to “0” over time (see the dashed line in FIG. 9). The various restrictions on the fail limit value ILf are due to the type of fail. In this case as well, the fail limit value ILf is set to the maximum allowable current value Imax before the failure occurs.

The minimum value calculator 65 is a temperature limit value calculator 6
1, motor power supply voltage limit value calculation unit 62, ignition off limit value calculation unit 63, and fail limit value calculation unit 64 supplied with respective limit values ILt, ILe, ILi, ILf
The minimum value of the above is determined as the minimum limit value ILmin.

The current limit return unit 66 repeatedly executes the current limit return program of FIG. 10 using the steering torque TM detected by the steering torque sensor 21 and the vehicle speed V detected by the vehicle speed sensor 22 every predetermined short time. By doing so, the change state of the minimum limit value ILmin calculated by the minimum value calculation unit 65 is changed and controlled, and the current limit value I
Output as L *. In addition, the current limit recovery unit 66
Has a table that stores a count-up value CNTup that defines the changing speed of the current limit value IL * in relation to the vehicle speed V. The count-up value CNTup is shown in FIG.
As shown in FIG. 1, the vehicle speed V increases accordingly.

The command current value limiting unit 67 repeatedly executes the command current value limiting program of FIG. 12 every predetermined short time to limit the command current value I * by the current limiting value IL *, and the command current value limiting unit 67 limits the command current value I *. The specified command current value I * is output as the output command current value Io *.

The storage unit 70 repeatedly executes the current limit storage program of FIG. 13 every predetermined short time to store the history of the command current I * when the limit amount of the command current I * is large. To do.

Next, the operation of the embodiment configured as described above will be described. When the driver turns on the ignition IG, the various sensors 21 to 23 and the control circuit unit 40
Etc., and the microcomputer constituting the control circuit unit 40 executes an initial check operation of each part in the initial stage, and in parallel with this initial check, the rotation of the electric motor 14 is controlled to rotate the steering wheel 11. The action of applying the assist force to the dynamic operation is started. The relay switch 36 is in the ON state unless a failure occurs, and is turned off only after a predetermined time has elapsed from the occurrence of the failure.

In this assisting force application operation, the command current value calculation unit 50 calculates the command current value I * according to the turning operation of the steering wheel 11, and the calculated command current value I * is commanded. The output command current value Io * is output to the drive control unit 47 via the current value limiting unit 67. The drive controller 47 cooperates with the current detector 44 to drive the drive circuit 30.
Is controlled to supply a drive current Im equal to the output command current value Io * to the electric motor 14. In response to this, the electric motor 14 starts rotating operation, and the output command current value Io *
The drive torque corresponding to (drive current Im) is applied to the reduction mechanism 15
Is transmitted to the steering shaft 13 via.

In this case, the basic assist control unit 51 inputs the steering torque TM and the vehicle speed V from the steering torque sensor 21 and the vehicle speed sensor 22, respectively, and increases as the steering torque TM increases and as the vehicle speed V increases. The basic command current value Ia that decreases is calculated and output. The differentiation unit 52 and the inertia compensation control unit 53 respectively input the steering torque TM and the vehicle speed V from the steering torque sensor 21 and the vehicle speed sensor 22, and calculate an inertia compensation current value Ib for compensating the inertia force of the electric motor 14. Output.
The steering wheel return control unit 54 inputs the steering torque TM and the vehicle speed V from the steering speed calculation unit 45 and the vehicle speed sensor 22, respectively, and calculates a steering wheel return current value Ic for compensating for returning the steering wheel 11 to the neutral position. Output. The damping control unit 55 inputs the steering torque TM and the vehicle speed V from the steering speed calculation unit 45 and the vehicle speed sensor 22, respectively, and a damping current value for compensating for giving resistance to the turning operation of the steering handle 11. Id is calculated and output.

Then, the adding section 56 makes these current values I
Since a, Ib, Ic, and Id are added and output as the command current value I *, an appropriate assist force is applied to the steering operation by the driver. In this case, in the basic command current value Ia, the vehicle speed V is considered in addition to the steering torque TM, and the inertia force of the electric motor 14, returning the steering handle 11 to the neutral position, and resistance to the turning operation of the steering handle 11. As a result, the driver can obtain a good steering feeling.

The command current value I * output from the adder 56 is restricted by the command current limit value calculator 60. In this case, the temperature limit value calculation unit 61, the motor power supply voltage limit value calculation unit 62, the ignition-off limit value calculation unit 63, and the fail limit value calculation unit 64 are limited to the limit value ILt,
ILe, ILi, ILf are calculated respectively, and the minimum value calculation unit 65 determines these limit values ILt, ILe, ILi, IL.
The minimum value of f is calculated as the minimum limit value ILmin,
The current limit restoration unit 66 changes and controls the change state of the minimum limit value ILmin and outputs it as the current limit value IL *, and the command current value limit unit 67 sets the command current value I * to the current limit value IL *.
Limited by *

The temperature limit value calculation unit 61 includes a temperature sensor 23.
The temperature Tp detected by is input, and the temperature limit value ILt that decreases as the temperature Tp increases is calculated and output. Therefore, the drive circuit 30 and the control circuit unit 4
When the temperature such as 0 rises, the current Im flowing through the electric motor 14 is limited and the temperature rise is suppressed, so that the electric motor 14, the drive circuit 30, the control circuit unit 40, etc. are protected from overheating. become.

The motor power supply voltage limit value calculator 62 is shown in FIG.
Execute the motor power supply voltage limit program of
The power supply voltage limit value ILe corresponding to m is calculated and output.
The execution of this program starts at step 100,
The power supply voltage Em is input in step 102, and step 1
At 04, low-pass filter processing (annealing processing) is performed for noise removal, and it is determined whether the processed power supply voltage Em is equal to or lower than a predetermined voltage value Em1. The predetermined voltage value Em1 is set to be slightly higher than the voltage at which the operation of the microcomputer constituting the control circuit unit 40 becomes unstable, and is set to 7.0 v, for example.

The power supply voltage Em is normal and the predetermined voltage value E
If it is larger than m1, it is determined to be "NO" in step 106, and it is determined in step 108 whether or not the flag F is "1". This flag F sets the power supply voltage limit value ILe to "0" by "1" and sets the same limit value ILe to other values by "0", and is initially set to "0". ing. Therefore, in the initial stage, it is determined to be “NO” in step 108 and step 120
Then, it is judged again whether or not the flag F is "0". In this case, since the flag F is set to "0" as described above, it is determined to be "YES" in step 120 and the program proceeds to step 122 and thereafter.

In step 122, the power supply voltage Em that has been low-pass filtered by the processing of step 104 is subjected to low-pass filtering whose cutoff frequency is much lower than that in the low-pass filtering processing of step 104. Therefore, at the beginning of this low-pass filtering, if the initial value is set low,
The previous value is used as an initial value in order to avoid outputting a low value despite the power supply voltage Em being somewhat high. When calculating for the first time, use the voltage obtained this time as the previous value instead. It should be noted that the lower the cutoff frequency of this low-pass filter processing, the lower the power supply voltage limit value IL.
The change in e (and thus the minimum limit value ILmin) becomes dull,
Suppressing the occurrence of a hunting phenomenon of the power supply voltage Em and the power supply voltage limit value ILe caused by a sharp decrease of the power supply voltage Em due to a large current consumption near the steering end when the steering wheel 11 is stationary and a rapid recovery thereof on the contrary. That is, the vibration of steering of the steering wheel 11 can be suppressed.

After the processing of step 122, step 1
At 24, the power supply voltage limit value ILe is derived by referring to the conversion table (Em-ILe table). In this conversion table, as shown in FIG. 7, the power supply voltage Em is the predetermined voltage value E.
When it is m2 (for example, 10.0 v) or less, it is kept at “0”, and when the power supply voltage Em is larger than the predetermined voltage value Em2 and is less than or equal to the predetermined voltage value Em3, it is “0” according to the increase of the power supply voltage Em3. The power supply voltage limit value ILe that gradually increases from the maximum current value Imax to the allowable maximum current value Imax and reaches the maximum current value Imax when the power supply voltage Em is larger than the predetermined voltage value Em3 is stored. The above-mentioned predetermined voltage value Em1 is smaller than the above-mentioned predetermined voltage value Em2. In this conversion table, the smaller the slope of the power supply voltage limit value ILe between the predetermined voltage values Em2 to Em3 of the power supply voltage Em, the smaller the
Suppressing the occurrence of a hunting phenomenon of the power supply voltage Em and the power supply voltage limit value ILe caused by a sharp decrease of the power supply voltage Em due to a large current consumption near the steering end when the steering wheel 11 is stationary and a rapid recovery thereof on the contrary. That is, the vibration of steering of the steering wheel 11 can be suppressed.

As a result, the power supply voltage Em becomes equal to the predetermined voltage value E.
When it is larger than m1, the power supply voltage limit value ILe is basically set to a value according to the above-mentioned characteristic according to the power supply voltage Em. As a result, when the power supply voltage Em drops due to the rotation of the electric motor 14, the drive current Im for the motor 14 is limited in accordance with the power supply voltage Em, so that the voltage of the battery 37 drops due to the rotation of the motor 14. It is possible to suppress the influence of the rotation of the motor 14 on other systems.

When the power supply voltage Em becomes equal to or lower than the predetermined voltage value Em1, it is determined to be "YES" in step 106, and the state continues for a predetermined time T1 (for example, 20 milliseconds) or more in step 116. Is determined. If the above state has not continued for a predetermined time T1 or more,
In step 116, it is determined to be "NO", and the processing in step 120 and the subsequent steps described above is executed.

On the other hand, if the above state continues for the predetermined time T1 or more, it is determined to be "YES" at step 116, and
In step 118, the flag F is set to "1". When the flag F is thus set to "1", it is determined to be "NO" at step 120, and the power supply voltage limit value ILe is set to "0" at step 126. Then, if the state where the power supply voltage Em is equal to or less than the predetermined voltage value Em1 continues, it is continuously determined as “YES” in steps 106 and 116,
The power supply voltage limit value ILe is continuously set to "0".

Even if the power supply voltage Em becomes larger than the predetermined voltage value Em1 from the above state, steps 108 to 11 are executed.
By the process of 2, the power supply voltage limit value ILe is not immediately restored. That is, the power supply voltage Em is equal to the predetermined voltage value E
If it is larger than m1, it is determined to be "NO" in step 106, but is determined to be "YES" in step 108, that is, the flag F is "1", and the power supply voltage Em is determined to be predetermined in step 110. It is determined whether the voltage value is Em2 or more. If the power supply voltage Em is less than the predetermined voltage value Em2,
In step 110, the determination is “NO” and the program proceeds to step 120 and the subsequent steps. Therefore, in this case, the flag F is maintained at "1" and the power supply voltage limit value ILe is also maintained at "0".

When the power supply voltage Em becomes equal to or higher than the predetermined voltage value Em2, it is determined to be "YES" in step 110, and the state where the power supply voltage Em is equal to or higher than the predetermined voltage value Em2 in step 112 is a predetermined time T2 (for example, , 20 milliseconds) or more. Predetermined time T2
If the above is not continued, “NO” in step 112.
In this case, the flag F is maintained at "1", and the power supply voltage limit value ILe is also maintained at "0".

If the state in which the power supply voltage Em is equal to or higher than the predetermined voltage value Em2 continues for the predetermined time T2 or longer, it is determined to be "YES" in step 112 and the flag F is determined in step 114.
Is set to "0" and the program proceeds to step 120. In step 120, it is determined to be "YES" based on the flag F set to "0", and the processes of steps 122 and 124 described above are executed.
The power supply voltage limit value ILe is set to a value according to the characteristic of FIG. 7 according to the power supply voltage Em. By such processing of steps 106 to 126, the power supply voltage E
A large drop and return of m can be reliably detected, and
Since the power supply voltage limit value ILe is set to a value other than “0” for a predetermined time even if the power supply voltage Em is greatly reduced, the influence of this voltage decrease on other systems is reduced and the electric motor 14 Will be secured as long as it is allowed.

In this embodiment, the flag F
If is changed from "0" to "1", step 1
Although the power supply voltage limit value ILe is suddenly changed to "0" by the process of 26, the power supply voltage limit value ILe is changed.
The e may be gradually changed to "0". In this case, in step 126, the power supply voltage limit value ILe may be gradually changed to "0" over time. As a result, the change of the minimum limit value ILmin becomes dull, and the power supply voltage Em due to a sharp decrease in the power supply voltage Em due to the large current consumption in the vicinity of the steering end when the steering wheel 11 is stationary and the abrupt recovery thereof is reversed. Further, it is possible to suppress the occurrence of the hunting phenomenon of the power supply voltage limit value ILe, that is, the vibration of the steering of the steering wheel 11 can be suppressed.

Further, in the processing of step 124, in the present embodiment, the power supply voltage limit value ILe is determined using the conversion table (Em-ILe table). The power supply voltage limit value ILe may be set to the maximum current value Imax without using it. In this case, the flag F is "
When the value is changed from 0 "to" 1 ", it is necessary to gradually change the power supply voltage limit value ILe to" 0 "in step 126 as described above.
As a result, also in this case, the change in the minimum limit value ILmin becomes dull, and the steering vibration of the steering wheel 11 can be suppressed. Further, in order to improve the steering feeling, the power supply voltage limit value ILe is set to the maximum current value Ima in step 124.
Also in the process of setting to x, the flag F changes from "1" to "
Immediately after being changed to "0", the power supply voltage limit value ILe may be gradually changed to "0" over time.

The ignition-off limit value calculation unit 63
In response to the arrival of an ignition-off signal IGOF, which indicates that the ignition switch IG is off, from a detection unit (not shown), as shown in FIG.
An ignition-off limit value ILi that gradually decreases from x over time is calculated and output. As a result, the application of the assist force to the steering operation of the driver immediately after the ignition switch IG is turned off is secured, and the electric power supply to the electric motor 14 thereafter is cut off.

The fail limit value calculator 64 calculates and outputs the fail limit value ILf having various characteristics as shown in FIG. 9 in response to the fail signal FAIL from the detector (not shown). As a result, the application of the assist force to the steering operation of the driver after the occurrence of the abnormality (failure) in the electric power steering device is ensured, and the electric power supply to the electric motor 14 thereafter is cut off. If a plurality of types of abnormalities are simultaneously generated and detected, the smallest limit value is output as the fail limit value.

By executing the current limit return program of FIG. 10, the current limit return unit 66 allows the change of the minimum limit value ILmin and outputs it as the current limit value IL * in a manner according to the steering torque TM and the vehicle speed V. To do. This current limit recovery program is started in step 200, and it is determined in step 202 whether the microcomputer constituting the control circuit unit 40 is in the initial check. If the initial check is in progress, step 202
In step 226, the current limit value IL * is set to the minimum limit value I supplied from the minimum value calculation unit 65.
Set to Lmin. On the other hand, if the microcomputer finishes the initial check operation, step 202
And the program is judged to be "YES" at step 204.
Continue below.

In step 204, it is determined whether or not the current minimum limit value ILmin supplied from the minimum value calculator 65 is larger than the previous current limit value IL *. If the current minimum limit value ILmin is less than or equal to the previous current limit value IL *, it is determined to be “NO” in step 204, and in step 226, the current limit value IL * is set to the minimum value calculation unit as described above. The minimum limit value ILmin supplied from 65 is set. When the current limit value IL * should be reduced in this way, by immediately responding to this, the electric power steering device can be protected and the influence on other systems can be minimized. .

On the other hand, if the current minimum limit value ILmin is larger than the previous current limit value IL *, that is, if the current limit value IL * should be increased, it is judged "YES" in step 204, The program proceeds to step 206 and thereafter. In step 206, the steering torque TM from the steering torque sensor 21 and the vehicle speed V from the vehicle speed sensor 22 are input. Then, in step 208, it is determined whether or not the absolute value | TM | of the steering torque TM is greater than or equal to a predetermined value TMo. Absolute value of steering torque TM | TM |
Is less than the predetermined value TMo, in step 208 "N
If the current limit value IL * is not changed, that is, the current limit value IL * is maintained at the previous value, the execution of the current limit recovery program is ended in step 228.

If the absolute value | TM | of the steering torque TM is greater than or equal to the predetermined value TMo, it is determined to be "YES" in step 208, and the V-CNTup conversion table is referred to in step 210 to determine the vehicle speed V. Count up value CNTup
To decide. The count-up value CNTup is a time value that determines the increase rate of the current limit value IL * (decreases the increase rate of the current limit value IL * as it increases), and as shown in FIG. It increases as it increases. That is, the count-up value CNTup is a time value for slowly returning the current limit value IL * as the vehicle speed V increases. After the processing in step 210, a predetermined small value ΔCNT is added to the count value CNT in step 212, and the count value CNT is increased by the determination processing in step 214.
The program proceeds to step 220 and thereafter until the above is reached. The count value CNT is initially set to "0".

By the repeated execution of the current limit recovery program, the count value CNT becomes the count-up value CNT.
When it is equal to or more than up, the current limit value IL * is determined in step 216 based on the determination of “YES” in step 214.
To the temporary current limit value IL * '
Is set, the count value CNT is cleared to “0” in step 218, and the program proceeds to step 220 and subsequent steps.

In step 220, the provisional current limit value IL * 'is compared with the minimum limit value ILmin supplied from the minimum value calculator 65. If the provisional current limit value IL * ′ is less than the minimum limit value ILmin, it is determined to be “NO” in the step 220, and the current limit value I is determined in the step 224.
Set L * to the provisional current limit value IL * '. This allows
The current limit value IL * is gradually increased over time. Then, as the current limit value IL * increases, the tentative current limit value IL * ′ calculated in step 216 also increases, and when it becomes the minimum limit value ILmin or more, the current limit value IL
* Is set to the minimum limit value ILmin. As a result, the current limit value IL * does not exceed the minimum limit value ILmin and increase. During the process of returning the current limit value IL * to the minimum limit value ILmin including steps 208 to 224, the vehicle speed V suddenly changes and the count-up value CNTup is increased.
If the value is changed, it may cause an uncomfortable feeling in the return. Therefore, the count-up value CNTup may be held when the return process is started.

In the current limiting recovery section 66 which operates in this way, the steering torque T
The current limit value IL * is not increased unless the absolute value | TM | of M exceeds a predetermined value TMo. This means that the absolute value | TM | of the steering torque TM is the predetermined value TM.
As long as it does not exceed o, it means that the output command current value Io * is not increased, that is, the assist force by the electric motor 14 is not increased, so the minimum limit value ILmin.
(Temperature limit value ILt, motor power supply voltage limit value ILe, ignition off limit value ILi and fail limit value ILf)
Is significantly increased, the driver can
The current limit value IL * increases during the turning operation of the vehicle, and it is difficult for the driver to feel a change in the steering operation during the steering operation, so that the driver does not feel a big discomfort with the steering wheel operation. The steering feeling of the driver is improved.

Even when the increase of the current limit value IL * is detected, the current limit value IL * is gradually increased over time by the processing of steps 212 to 224. Therefore, the driver does not feel more uncomfortable with the operation of the steering wheel, and the steering feeling of the driver is further improved.

Further, in the increase control of the current limit value IL *, the process of step 210 makes the increasing speed of the current limit value IL * dependent on the vehicle speed V and slows it as the vehicle speed V increases. Therefore, a change in the steering operation at a high vehicle speed is suppressed as much as possible, the steering feeling of the driver is improved, and the traveling stability of the vehicle is secured.

In the current limit recovery program, the increasing speed of the current limit value IL * (output command current value Io *) is continuously changed as the vehicle speed V increases. Alternatively, the increasing speed of the current limit value IL * may be switched in two steps, that is, when the vehicle speed V is equal to or lower than the reference vehicle speed Vo with the predetermined reference vehicle speed Vo interposed, and when the vehicle speed V is higher than the reference vehicle speed Vo. As the standard vehicle speed Vo,
If "0" or a predetermined minute value is set, the increase speed of the current limit value IL * is fast only when the vehicle is stopped or running at an extremely low speed, and the increase speed of the current limit value IL * is slow when the vehicle is running normally. Become. Further, the reference vehicle speed Vo is set to 20 km / in order to increase the current limit value IL * at a low vehicle speed.
It may be set to h, 30 km / h. In this case, instead of the process of step 210, the vehicle speed V and the reference vehicle speed Vo are compared, and if the vehicle speed V is less than or equal to the reference vehicle speed Vo, the count-up value CNTup is set to a small value, and the vehicle speed V is increased.
Is greater than the reference vehicle speed Vo, the count-up value CN
A process of setting Tup to a large value may be adopted.

In the current limit recovery program, the count-up value CNTup is increased in step 210 in order to reduce the increasing speed of the current limit value IL * (output command current value Io *) as the vehicle speed V increases. It was changed according to V. However, the predetermined value ΔCNT to which the count value CNT is added in step 212 may be changed according to the vehicle speed V, or the time interval at which the current limit recovery program is executed may be changed according to the vehicle speed V. . In this case, if the predetermined value ΔCNT is made smaller as the vehicle speed V increases, or the time interval is made larger as the vehicle speed increases, the current limit will increase as the vehicle speed V increases, as in the above case. The rate of increase of the value IL * (output command current value Io *) decreases.

The command current value limiting unit 67 limits the absolute value | I * | of the command current value I * to the current limit value IL * or less by executing the command current value limiting program shown in FIG. The final output command current value Io * is output.
This command current value limiting program is started in step 300, and in step 302 it is determined whether or not the command current value I * is less than or equal to the negative current limit value −IL *, and in step 304 the command current value I *. It is determined whether I * is greater than or equal to the positive current limit value IL *.

If the command current value I * is less than or equal to the negative current limit value -IL *, "YES" in step 302.
Then, in step 306, the output command current value Io * is set to the negative current limit value −IL *. If the command current value I * is greater than or equal to the positive current limit value IL *, it is determined to be “YES” in step 304, and the output command current value Io * is set to the positive current limit value IL * in step 308. If the command current value I * is a value between both current limit values-IL *, IL *, it is determined to be "NO" in steps 302 and 304, and the output command current value Io * is set to the command current in step 310. Set to the value I *. As a result, the absolute value | Io * | of the output command current value Io * supplied to the drive control unit 47 is limited within the current limit value IL *, and the electric motor 14 is driven by the limited output command current value Io *. Will be driven.

The current limit storage unit 70 stores the history of the limit when the command current I * is significantly limited by the execution of the current limit storage program of FIG. This current limit storage program is started in step 400, and in step 402 the absolute value | I * of the command current value I *.
The command current I * is increased by determining whether or not the value | I * |-| Io * | that is obtained by subtracting the absolute value | Io * | of the output command current value Io * from | is greater than or equal to the predetermined value Iref. Detect restricted conditions. That is, if the command current I * is greatly restricted and the subtracted value | I * |-| Io * |
S ”, and the current limit information is stored in the non-volatile memory in step 404. As this current limit information,
The subtracted value | I * |-| Io * |, the limited date and time by a program process (not shown), the time from the turning on of the ignition switch IG, and the like are increased. In this case, if the cause of current limitation, that is, the current limitation is caused by one of the temperature limitation value ILt, the motor power supply voltage limitation value ILe, the ignition off limitation value ILi, and the fail limitation value ILf, it is further stored. Good.

Further, when the absolute value | I * | of the command current value I * is subtracted from the absolute value | Io * | of the output command current value Io *, the value | I * |-| Io * | is less than the predetermined value Iref. If there is, it is determined to be “NO” in step 402, and the execution of this current limiting program is ended in step 406.

By storing the history in which the output command current value Io * is greatly limited in this way, it is possible to appropriately perform the analysis of the occurrence and the occurrence of the failure of the electric power steering apparatus even at a later date. be able to.

In the above embodiment, the ignition off limit value ILf calculated by the ignition off limit value calculation unit 63 is output to the minimum value calculation unit 65. However, instead of this, the ignition off limit value ILf is output to the command current value limiter 67, and the limiter 67 changes the command current value IL * from the adder 56 to its absolute value | IL. It is also possible to limit * | to a value which is the smaller of the ignition-off limit value ILf and the current limit value IL * from the current limit reset unit 66, whichever is smaller.

[Brief description of drawings]

FIG. 1 is an overall schematic diagram of an electric power steering device according to an embodiment of the present invention.

2 is a block diagram of the electric control device of FIG. 1. FIG.

FIG. 3 is a detailed block diagram of a command current value generation unit in FIG.

FIG. 4 is a graph showing a relationship between a steering torque and a basic command current value.

FIG. 5 is a graph showing a relationship between temperature and a temperature limit value.

6 is a flowchart of a motor power supply voltage limit program executed by a motor power supply voltage limit value calculation unit in FIG.

FIG. 7 is a graph showing a relationship between a motor power supply voltage and a motor power supply voltage limit value.

FIG. 8 is a graph showing changes in the ignition-off limit value over time.

FIG. 9 is a graph showing changes in the fail limit value over time.

10 is a flowchart of a current limit recovery program executed by the current limit recovery section of FIG.

FIG. 11 is a graph showing the relationship between vehicle speed and count-up value.

12 is a flowchart of a command current value limiting program executed by a command current value limiting unit in FIG.

FIG. 13 is a flowchart of a current limit storage program executed by the current limit storage unit of FIG.

[Explanation of symbols]

FW1, FW2 ... Left and right front wheels, IG ... Ignition switch, 11 ... Steering wheel, 13 ... Steering shaft, 14 ... Electric motor, 20 ... Electric control device, 21 ... Steering torque sensor, 22 ... Vehicle speed sensor, 23 ... Temperature sensor, 30 ... drive circuit, 37 ... battery, 40 ... control circuit unit, 43
... voltage detection unit, 44 ... current detection unit, 45 ... steering speed calculation unit, 46 ... command current value generation unit, 50 ... command current value calculation unit, 51 ... basic assist control unit, 52 ... differentiating unit, 53 ...
Inertia compensation control unit, 54 ... Handle return control unit, 55 ... Damping control unit, 56 ... Addition unit, 60 ... Command current limit value calculation unit, 61 ... Temperature limit value calculation unit, 62 ... Motor power supply voltage limit value calculation unit, 63 ... Ignition-off limit value calculating unit, 64 ... Fail limit value calculating unit, 65 ... Minimum value calculating unit, 66 ... Current limit restoring unit, 67 ... Command current value limiting unit,
70 ... Current limit storage unit.

Continuation of the front page (56) Reference JP-A-5-162651 (JP, A) JP-A-8-207811 (JP, A) JP-A-3-189272 (JP, A) JP-A-4-78664 (JP , A) JP 11-115789 (JP, A) JP 9-290764 (JP, A) JP 2-11470 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) (Name) B62D 6/00-6/06 B62D 5/04

Claims (3)

(57) [Claims] 1. Assisting a turning operation of a steering wheel
An electric motor that applies power, The electric current of a magnitude corresponding to the steering state of the steering wheel is
A motor that is fed to a dynamic motor to control the rotation of the electric motor
Control means,A current limiting value for the electric motor, the electric power
Determined by the operating environment and operating state of the steering system
The minimum value of the multiple current limit values
Minimum value calculating means to determine as a limit value, The value of the current flowing through the electric motorThe determined motor current
Current limiting means to limit to the limit valueWhen, Steering torque detecting means for detecting steering torque, When the detected steering torque is a predetermined value or more, the current
Restricted by restriction meansMotor currentIncrease the limit
Limit value control means to allowPreparedA car characterized by
Both electric power steering devices. 2. The electric power steering apparatus for a vehicle according to claim 1, wherein the limit value control means sets the motor current limit value to a lapse of time when the increase of the motor current limit value is permitted. An electric power steering device for a vehicle, which is characterized by gradually increasing the electric power. 3.Assists in turning the steering wheel
An electric motor that applies power, The electric current of a magnitude corresponding to the steering state of the steering wheel is
A motor that is fed to a dynamic motor to control the rotation of the electric motor
Control means, According to a predetermined condition for the current value to be passed through the electric motor
A vehicle electric power supply equipped with a current limiting means for limiting the electric current to a limit value.
In the word steering device, Steering torque detecting means for detecting steering torque, When the detected steering torque is a predetermined value or more, the current
Although the limit value that is limited by the limiting means has elapsed
And allow the gradual increase Limit
The rate of increase of the value depends on the vehicle speedLimit value control means
DigitAn electric power steering device for a vehicle characterized by
Place