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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a steering control apparatus, and more specifically, it relates to an electric power steering control apparatus which controls an assisting force applied by a motor to a steering system of a vehicle based on at
least the steering torque of a steering wheel and the speed of the vehicle when the steering wheel is steered to turn by a driver.
2. Description of the Related Art
There have been developed electric power steering apparatuses in which the speed of a vehicle and the steering torque applied to a steering column or shaft are detected, and a driving current determined according to the vehicle speed and the
steering torque thus detected is supplied to a motor which generates an assisting force given to the steering shaft, so that the motor is thereby driven to rotate, thus assisting the force required to steer the vehicle by means of the rotating force of
the motor to provide the driver with a pleasant steering sensation or feeling.
In the past, a DC motor with a brush has been used as a motor which gives an assisting force to a steering shaft of a vehicle, but it is impossible to perform field control with the DC motor and hence conventional electric power steering control
apparatuses are not equipped with any means for generating a target current value used to carry out field control.
Moreover, there can be considered a steering control apparatus which employs a brushless motor in place of such a DC motor, as a motor for applying an assisting force to the steering shaft. In this case, owing to the absence of any brush within
an electric motor, there will take place almost no abnormality or fault in the motor itself, and it also becomes possible to effect field control, which could not been carried out in the past as referred to above.
A brushless motor control apparatus performs a variety of calculations such as the calculation of a dq-axis target current based on an instruction torque, the detection of currents for respective phases (e.g., u phase and v phase) of a motor, the
dq conversion of currents, the calculation of current deviations, the calculation of instruction voltage values, dq inversions, and the output of PWM control patterns. The detected respective phase currents are subjected to dq conversion in such a
manner that they are controlled in a feedback manner to make their d-axis component and q-axis component equal to a d-axis target current and a q-axis target current, respectively. The d-axis component of each current means a wattless or reactive
current, whereas the q-axis component is proportional to the torque of the motor when the motor is a synchronous motor and when the magnitude of the excitation magnetic field is constant. Therefore, the current feedback control for the synchronous motor
is generally carried out in such a manner that the d-axis component of the detected current becomes zero and the q-axis component thereof becomes equal to a target value of the output torque.
In cases where a steering control apparatus is installed on a vehicle with a large weight, a large motor output torque is required, and there will be a problem that in cases where the motor characteristic is of the high-torque and low-rotation
type, the output torque of the motor rapidly decreases upon rapid steering. As a result, in the case of an electric power steering control apparatus, there arises a problem that the steering operation rapidly becomes heavy upon rapid steering, whereas
in the case of a steer-by-wire steering system, there is a problem in that the actual steering angle of the steered wheels does not follow the steering angle of the steering wheel upon rapid steering.
However, where the motor characteristic is of the low-torque and high-speed rotation type, it is necessary to increase the motor current in order to enlarge the motor output torque, and hence a large-sized motor of high power consumption is
required. With a steering apparatus which is to be installed in a limited space, however, it becomes important to suppress the power consumption of a motor used therein and reduce the size thereof.
SUMMARY OF THE INVENTION
The present invention is intended to obviate the various problems as referred to above, and has for its object to provide a steering control apparatus which is capable of alleviating a decrease in the output torque of a motor during high-speed
steering without increasing the size thereof.
Bearing the above object in mind, according to the present invention, there is provided a steering control apparatus including a motor, a motor current instruction value generation section for generating a current instruction value for the motor,
and a motor current detection section for detecting a current flowing through the motor, the motor being driven to operate based on at least the current flowing through the motor and the current instruction value, wherein the motor current instruction
value generation section includes a correction section for correcting a current instruction value which controls a magnetic field of a field magnet of the motor, the correction section being operable to correct the current instruction value for
controlling the magnetic field of the motor field magnet when a steering speed is high,
In a preferred form of the present invention, the steering control apparatus further comprises a motor control section for performing torque control on the motor in accordance with a torque instruction through vector control which is represented
by a two-phase rotating magnetic flux coordinate system having a direction of a field current oriented in a d-axis direction and a direction perpendicular to the d-axis oriented in a q-axis direction, wherein the correction section corrects a d-axis
current instruction value in such a manner that a d-axis current is controlled to such a predetermined value as to weaken the magnetic field of the motor field magnet when a deviation between the q-axis current instruction value and a q-axis current
detection value becomes not less than a predetermined value.
In another preferred form of the present invention, the correction section increases a negative d-axis current instruction value for weakening the magnetic field of the motor field magnet when the q-axis current deviation is not less than a first
predetermined value, and decreases the negative d-axis current instruction value for weakening the magnetic field of the motor field magnet when the q-axis current deviation is not greater than a second predetermined value.
In a further preferred form of the present invention, the d-axis current instruction value is limited within a preset range.
In a still further preferred form of the present invention, the steering control apparatus further comprises a stator phase current instruction value generation section for generating stator respective phase current instruction values from the
q-axis current instruction value, wherein the current instruction value for controlling the magnetic field of the motor field magnet is corrected based on a deviation between at least one of the stator phase current instruction values and an actual
corresponding stator phase current value in place of the q-axis current deviation.
In a yet further preferred form of the present invention, the steering control apparatus further comprises a reference steering torque generation section for generating a reference steering torque which is used to determine whether the magnetic
field of the motor field magnet is to be weakened, wherein when the steering torque becomes not less than the reference steering torque, the correction section corrects the current instruction value to such a prescribed value as to weaken the magnetic
field of the motor field magnet.
In a further preferred form of the present invention, the reference steering torque generation section generates the reference steering torque as a function of at least a vehicle speed.
In a further preferred form of the present invention, the steering control apparatus further comprises a steering speed detection section for detecting a steering speed of a steering wheel, wherein the correction of the current instruction value
for controlling the magnetic field of the motor field magnet is effected such that when the steering speed of the steering wheel becomes not less than a predetermined value, the current instruction value is corrected to such a prescribed value as to
weaken the magnetic field of the motor field magnet.
In a further preferred form of the present invention, the steering control apparatus further comprises: a motor control section for performing torque control on the motor in accordance with a torque instruction through vector control which is
represented by a two-phase rotating magnetic flux coordinate system having a direction of a field current oriented in a d-axis direction and a direction perpendicular to the d-axis direction oriented in a q-axis direction; a speed detection section for
detecting a rotational speed of the motor; and a voltage limitation value generation section for generating a voltage limitation value to a voltage applied to the motor; wherein the correction section determines a d-axis current value for setting a
working point on a voltage limitation circle through calculations based on at least the rotational speed of the motor, a q-axis current instruction value, a stator winding resistance, a stator winding reactance and a motor counter electromotive voltage
constant, and effects correction in such a manner that when the d-axis current value determined through calculations is a current value which weakens the magnetic field of the motor field magnet more than a d-axis current instruction value does, the
d-axis current value determined through calculations becomes equal to the d-axis current instruction value.
In a further preferred form of the present invention, the steering control apparatus further comprises a power supply voltage detection section for detecting a power supply voltage, wherein the voltage limitation value generation section
generates, as a voltage limitation value, a value obtained by multiplying the power supply voltage by a predetermined coefficient.
In a further preferred form of the present invention, the motor comprises a field winding type motor, and the apparatus further comprises a motor control section for performing torque control on the motor in accordance with a torque instruction
in such a manner that a field winding current instruction value is corrected when a deviation between an armature current instruction value and an armature current detection value becomes not less than a predetermined value.
In a further preferred form of the present invention, the field winding current instruction value is corrected in such a manner that it is decreased when the armature current deviation is not less than a first predetermined value, and it is
increased when the armature current deviation is not greater than a second predetermined value.
In a further preferred form of the present invention, the field winding current instruction value is limited to a preset minimum value.
In a further preferred form of the present invention, the correction section corrects the current instruction value with a correction value which is determined through calculations.
In a further preferred form of the present invention, the correction section corrects the current instruction value with a correction value which is obtained by referring to a table prepared in advance.
In a further preferred form of the present invention, the d-axis current instruction value is limited to a value which is obtained by vector subtracting a q-axis current value from a preset maximum current vector value.
In a further preferred form of the present invention, an integrated value of the deviation is used in place of the deviation.
In a further preferred form of the present invention, the correction section corrects the current instruction value for controlling the magnetic field of the motor field magnet only when a vehicle speed is not less than a predetermined value.
In a further preferred form of the present invention, the correction section corrects the current instruction value for controlling the magnetic field of the motor field magnet only when a steering torque is not less than a predetermined value.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a constructional view illustrating a first embodiment of the present invention.
FIG. 2 is a block diagram illustrating functions of the first embodiment of the present invention.
FIG. 3 is a flow chart illustrating d-axis target current correction processing according to the first embodiment of the present invention.
FIG. 4 is a view illustrating examples of waveforms before and after modulation in the first embodiment of the present invention.
FIG. 5 is a block diagram illustrating a second embodiment of the present invention.
FIG. 6 is a flow chart illustrating d-axis target current correction processing in the second embodiment of the present invention.
FIG. 7 is a block diagram illustrating functions of a third embodiment of the present invention.
FIG. 8 is a flow chart illustrating d-axis target current correction processing in the third embodiment of the present invention.
FIG. 9 is a block diagram illustrating functions of a fourth embodiment of the present invention.
FIG. 10 is a flow chart illustrating d-axis target current correction processing in the fourth embodiment of the present invention.
FIG. 11 is a block diagram illustrating functions of a fifth embodiment of the present invention.
FIG. 12 is a flow chart illustrating d-axis target current correction processing in the fifth embodiment of the present invention.
FIG. 13 is a block diagram illustrating functions of a sixth embodiment of the present invention.
FIG. 14 is a flow chart illustrating d-axis target current correction processing in the sixth embodiment of the present invention.
FIG. 15 is a block diagram illustrating functions of a seventh embodiment of the present invention.
FIGS. 16A through 16D are dq-axis vector diagrams for explaining magnetic flux weakening control according to the seventh embodiment of the present invention.
FIG. 17 is a flow chart illustrating d-axis target current correction processing in the seventh embodiment of the present invention.
FIG. 18 is a block diagram illustrating an eighth embodiment of the present invention.
FIG. 19 is a flow chart illustrating field current instruction value correction processing in the eighth embodiment of the present invention.
FIG. 20 is a steering speed vs. steering torque characteristic view illustrating effects of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings by taking, as an example, the case where the present invention is applied to an electric power steering control apparatus.
Embodiment 1
In a first embodiment of the present invention, a d-axis target current is corrected as a function of a deviation in a q-axis current thereby to decrease the magnetic field of a field magnet of a motor upon high-speed steering in which the
deviation in the q-axis current increases due to voltage saturation, thus alleviate an increase in steering torque during such high-speed steering.
FIG. 1 is a constructional view illustrating an electric power steering control apparatus according to this first embodiment of the present invention.
In this figure, a motor 5, which generates steering assisting torque, is connected through a reduction gear 4 with one end of a steering column or shaft 2, the other end of which is connected with a steering wheel 1. Also connected with the
steering shaft 2 is a torque sensor 3 for detecting the steering torque of the steering wheel 1 to generate a corresponding torque detection value.
A controller 100 serves to determine a steering assisting torque based on the torque detection value of the torque sensor 3 and a vehicle speed detection value detected by a vehicle speed sensor 6, and assist the steering operation of the
steering wheel 1 by driving the motor 5 to generate the steering assisting torque thus determined. A battery 7 is connected with an ignition key 8 and the controller 100.
FIG. 2 functionally illustrates an example of the electric power steering control apparatus according to the first embodiment of the present invention in which a PM brushless motor is used as a steering assisting motor.
In FIG. 2, a reference numeral 100 designates a microcomputer which performs steering assisting control with its software configuration being illustrated in a functional block diagram.
In FIG. 2, the microcomputer 100 includes a q-axis target current calculation section 100a, a d-axis target current correction section 100b acting as a correcting section, a position calculation section 100c, a uv to dq transformation section
100d, a current control section 100e, a dq to uvw transformation section 100f acting as a stator phase current instruction value generation section, a voltage utilization efficiency improvement section 100o, a dead band (Td) correction section 100p, an
angular velocity calculation section 100q acting as a speed detection section, a decoupled control section 100r, and a current detection offset correction section 100s. Here, note that the q-axis target current calculation section 100a and the d-axis
target current correction section 100b together constitute a motor current instruction value generation section.
The q-axis target current calculation section 100a performs predetermined calculations based on the torque detection signal of the torque sensor 3, which detects the steering torque of the steering wheel 1, and the vehicle speed detection signal
of the vehicle speed sensor 6, which detects the vehicle speed, determines a q-axis target current value (Iq*) for driving the motor 5 in the form of a PM brushless motor, and supplies the q-axis target current value thus determined to the current
control section 100e.
The position calculation section 100c determines an electrical angle .theta. through calculations based on the positional detection signal of a position sensor 103, and supplies the electrical angle .theta. thus determined to the angular
velocity calculation section 100q, the uv to dq transformation section 100d and the dq to uvw transformation section 100f.
The angular velocity calculation section 100q determines a motor rotational angular velocity .omega. through calculations based on the electrical angle .theta., and supplies it to the decoupled control section 100r.
The current detection offset correction section 100s calculates respective phase detection currents (Iu, Iv) by subtracting the amounts of respective phase offsets from phase current values detected by current sensors 102a, 102b, respectively,
and supplies them to the Td correction section 100p and the uv to dq transformation section 100d.
The uv to dq transformation section 100d performs dq conversion based on the detected phase current values (Iu, Iv) and the electrical angle .theta., and supplies thus converted dq-axis currents (Id, Iq) to the decoupled control section 100r and
the current control section 100e.
FIG. 3 is a flow chart for explaining the processing performed by the d-axis target current correction section 100b.
In step S1, it is determined whether the vehicle speed detected by the vehicle speed sensor 6 is not less than a predetermined value, and when the detected vehicle speed is less than the predetermined value, the d-axis target current (Id*) is
adopted as a corrected d-axis target current (Id**) in step S5, whereas when the detected vehicle speed is not less than the predetermined value, the control process advances to the processing of step S2. Then, in step S2, it is determined whether the
steering torque detected by the torque sensor 3 is not less than a predetermined value, and when the detected steering torque is less than the predetermined value, the d-axis target current (Id*) is adopted as the corrected d-axis target current (Id**)
in step S5, whereas when the detected steering torque is not less than the predetermined value, the control process advances to the processing of step 3. In step S3, it is determined whether a q-axis current deviation (.DELTA.Iq) is not less than a
predetermined value, and when the q-axis current deviation (.DELTA.Iq) is less than the predetermined value, the d-axis target current (Id*) is adopted as the corrected d-axis target current (Id**) in step S5, whereas when the q-axis current deviation
(.DELTA.Iq) is not less than the predetermined value, the control process advances to the processing of step 4. In step 4, the d-axis target current is corrected by subtracting a corrected current value (f(.DELTA.Iq)), which is obtained as a function of
the q-axis current deviation (.DELTA.Iq), from the d-axis target current (Id*), and the thus corrected d-axis target current (Id**) is supplied to the current control section 100e.
The current control section 100e performs proportional and integral (PI) control based on deviations between the dq-axis target currents (Id**, Iq*) and the corresponding detected dq-axis currents (Id, Iq), and generates dq-axis target
application voltages (Vd*, Vq*).
The control section 100r calculates non-interfering voltages based on the dq-axis detection currents (Id, Iq) and the motor angular velocity .omega., and corrects the dq-axis target application voltages (Vd*, Vq*) to generate corrected dq-axis
target application voltages (Vd**, Vq**), which is supplied to the dq to uvw transformation section 100f.
The dq to uvw transformation section 100f performs dq inversion based on the corrected dq-axis target application voltages (Vd**, Vq**) and the electrical angle .theta. to generate three-phase target application voltages (Vu*', Vv*', Vw*'),
which are supplied to the voltage utilization efficiency improvement section 100o.
To improve the voltage efficiency, the voltage utilization efficiency improvement section 100o modulates the three-phase target application voltages (Vu*', Vv*', Vw*') into a spatial voltage vector, and supplies the thus modulated three-phase
target application voltages (Vu*", Vv*", VW*") to the Td correction section 100p. Examples of waveforms before and after such modulation are illustrated in FIG. 4. In FIG. 4, the axis of ordinate represents the values of the three-phase target
application voltages, and the axis of abscissa represents the rotational position of the motor.
The Td correction section 100p performs dead band compensation for the modulated three-phase target application voltages (Vu*", Vv*", Vw*") based on the detected current values (Iu, Iv, Iw), and supplies the thus compensated three-phase target
application voltages (Vu*, Vv*, Vw*) to a driving section 101.
With the electric power steering control apparatus as constructed above, owing to the provision of the d-axis target current correction section 100b, the magnetic field of the motor field magnet is weakened during high-speed steering in which the
q-axis current deviation is increased due to voltage saturation so that a decrease in the output torque of the steering assisting motor upon rapid steering can be alleviated, thus making it possible to reduce the increasing steering torque during such
rapid steering.
Although in the first embodiment, the electric power steering control apparatus has been taken as an example, the present invention may instead be applied to a steer-by-wire steering control apparatus.
In the case of such a steer-by-wire steering control apparatus, owing to the provision of the d-axis target current correction section 100b, the magnetic field of the motor field magnet can be weakened upon high-speed steering in which the q-axis
current deviation is increased due to voltage saturation, whereby a decrease in the motor output torque upon rapid steering can be alleviated, thus improving the followability of the actual steering angle with respect to the operator's induced steering
angle during rapid steering.
Embodiment 2
In a second embodiment of the present invention, the d-axis target current is corrected with a current value which is obtained by referring to a table, which has been prepared in advance using the q-axis current deviation as a parameter, thereby
to decrease the magnetic field of the motor field magnet upon high-speed steering in which the q-axis current deviation increases due to voltage saturation, thus alleviating an increase in steering torque during such high-speed steering.
FIG. 5 functionally illustrates an example of an electric power steering control apparatus according to the second embodiment of the present invention in which an induction motor is used as a steering assisting motor. In FIG. 5, description will
be made with the same or corresponding parts as those in FIG. 2 being identified by the same symbols.
In FIG. 5, there is illustrated a functional block diagram of a microcomputer, generally designated at 100, which performs steering assisting control by executing software incorporated therein. The microcomputer 100 of this second embodiment
includes a dq-axis target current calculation section 100a, a d-axis target current correction section 100b, a slip angle frequency calculation section 100l, a power supply angular frequency calculation section 100m which calculates a power supply
angular frequency from a slip angle frequency .omega.s and a motor rotational speed .omega.r of an induction motor 5a detected by a speed sensor 104, an integrator 100n which calculates an angle .theta. from the power supply angular frequency, a uv to
dq transformation section 100d, a current control section 100e, and a dq to uvw transformation section 100f.
FIG. 6 is a flow chart for explaining the processing performed by the d-axis target current correction section 100b in the electric power steering control apparatus according to the second embodiment of the present invention.
In step S1, it is determined whether the vehicle speed detected by the vehicle speed sensor 6 is not less than a predetermined value, and when the detected vehicle speed is less than the predetermined value, the d-axis target current (Id*) is
adopted as a corrected d-axis target current (Id**) in step S5, whereas when the detected vehicle speed is not less than the predetermined value, the control process advances to the processing of step S2. Then, in step S2, it is determined whether the
steering torque detected by the torque sensor 3 is not less than a predetermined value, and when the detected steering torque is less than the predetermined value, the d-axis target current (Id*) is adopted as the corrected d-axis target current (Id**)
in step S5, whereas when the detected steering torque is not less than the predetermined value, the control process advances to the processing of step S3.
In step S3, it is determined whether the q-axis current deviation (.DELTA.Iq) is not less than a predetermined value, and when the q-axis current deviation (.DELTA.Iq) is less than the predetermined value, the d-axis target current (Id*) is
adopted as the corrected d-axis target current (Id**) in step S5, whereas when the q-axis current deviation (.DELTA.Iq) is not less than the predetermined value, the control process advances to the processing of step S6. In step S6, a corrected current
value (Ida) is determined by referring to a table, which has been prepared in advance using the q-axis current deviation (.DELTA.Iq) as a parameter. In step S4, the d-axis target current is corrected by subtracting the corrected current value (Ida) from
the d-axis target current (Id*), and the thus corrected d-axis target current (Id**) is supplied to the current control section 100e.
Embodiment 3
In a third embodiment of the present invention, the d-axis target current value is corrected in such a manner that it is decreased when an integrated value of the q-axis current deviation is not less than a first predetermined value 1, and
increased when the integrated q-axis current deviation is not greater than a second predetermined value 2, whereby the magnetic field of the motor field magnet is weakened upon high-speed steering in which the q-axis current deviation increases due to
voltage saturation, thus alleviating an increase in the steering torque during such high-speed steering.
FIG. 7 functionally illustrates an example of an electric power steering control apparatus according to the third embodiment of the present invention in which a PM brushless motor is used as a steering assisting motor. In FIG. 7, the same or
corresponding parts as those in FIG. 2 are identified by the same symbols while omitting a detailed description thereof.
FIG. 8 is a flow chart for explaining the processing performed by a dq-axis target current correction section 100g.
In step S10, the q-axis current deviation .DELTA.Iq is integrated, and in step S11, it is determined whether the integrated value of .DELTA.Iq is not less than the first predetermined value 1. When the integrated value of .DELTA.Iq is not less
than the first predetermined value 1, a d-axis current correction amount Ida is increased in step S12, and the correction value is limited to a preset maximum correction value Ida_max in step S13. On the other hand, when the integrated value of
.DELTA.Iq is less than the first predetermined value 1, it is further determined whether the integrated value of .DELTA.Iq is not greater than a second predetermined value 2 in step S14. When the integrated value of .DELTA.Iq is not greater than the
second predetermined value 2, the d-axis current correction amount Ida is decreased in step S15, and the correction value is limited to a preset minimum correction value Ida_min in step S16. Then in step S17, a corrected d-axis target current value
(Id**) is calculated by subtracting the d-axis current correction value (Ida) from the d-axis target current (Id*).
Subsequently, in step S20, a maximum d-axis target current (Id_max) is calculated by subtracting the q-axis target current value (Iq*) from a preset maximum current vector value (Ia). In step S21, it is determined whether the corrected d-axis
target current value (Id**) is greater than the maximum d-axis target current (Id_max). When the corrected d-axis target current value (Id**) is greater than the maximum d-axis target current (Id_max), the maximum d-axis target current (Id_max) is
adopted as the corrected d-axis target current value (Id**) in step S22.
Embodiment 4
In a fourth embodiment of the present invention, when the steering torque exceeds a prescribed torque value, the d-axis target current is corrected in such a manner as to decrease the magnetic field of the motor field magnet, whereby the magnetic
field is weakened upon high-speed steering in which the steering assisting torque is reduced due to voltage saturation, thus alleviating an increase in the steering torque during such high-speed steering.
FIG. 9 functionally illustrates an example of an electric power steering control apparatus according to the fourth embodiment of the present invention in which a PM brushless motor is used as a steering assisting motor. In FIG. 9, the same or
corresponding parts as those in FIG. 2 are identified by the same symbols while omitting a detailed description thereof.
In FIG. 9, a motor angular velocity calculation section 100i determines a motor rotational angular velocity .omega. through calculations based on the electrical angle .theta. from the position calculation section 100c, and supplies it to the
d-axis target current correction section 100b.
FIG. 10 is a flow chart for explaining the processing performed by the d-axis target current correction section 100b in the electric power steering control apparatus according to the fourth embodiment of the present invention.
In step S30, it is determined whether the motor angular velocity .omega. is not less than a predetermined value, and when the motor angular velocity .omega. is less than the predetermined value, the d-axis target current (Id*) is adopted as the
corrected d-axis target current (Id**) in step S36, whereas when the motor angular velocity .omega. is not less than the predetermined value, the control process advances to reference torque Ts_ref calculation processing in step 31. In the reference
torque Ts_ref calculation processing in step S31 (i.e., a reference steering torque generation section), a reference torque Ts_ref is determined by referring to a table, which has been prepared in advance as a function of the vehicle speed detected by
the vehicle speed sensor 6 or by the use of the detected vehicle speed as a parameter, alternatively it is determined as a preset constant value instead of referring to such a table. In step S32, a comparison is made between the torque sensor signal
(Ts) and the reference torque (Ts_ref), and when the torque sensor signal (Ts) is not greater than the reference torque (Ts_ref), the d-axis target current (Id*) is adopted as the corrected d-axis target current (Id**) in step S36, whereas when the
torque sensor signal (Ts) is greater than the reference torque (Ts_ref), the control process advances to the processing in step S33.
In step S33, a difference .DELTA.Ts between the torque sensor signal (Ts) and the reference torque (Ts_ref) is calculated by subtracting the reference torque (Ts_ref) from the torque sensor signal (Ts). Then in the correction current Ida
calculation processing in step S34, a correction current Ida is calculated by referring to a table, which has been prepared in advance as a function of .DELTA.Ts or using .DELTA.Ts as a parameter. In step S35, a corrected d-axis target current (Id**) is
calculated by subtracting the correction current (Ida) from the d-axis target current (Id*), and the thus corrected d-axis target current (Id**) is supplied to the current control section 100e.
Embodiment 5
In a fifth embodiment of the present invention, when the motor rotational speed exceeds a predetermined value, the current instruction value for controlling the magnetic field of the motor field magnet is corrected to such a prescribed value as
to decrease the magnetic field, whereby the magnetic field is weakened upon high-speed steering, thus alleviating an increase in the steering torque during such high-speed steering.
FIG. 11 functionally illustrates an example of an electric power steering control apparatus according to the fifth embodiment of the present invention in which a PM brushless motor is used as a steering assisting motor. In FIG. 11, the same or
corresponding parts as those in FIGS. 2 and 9 are identified by the same symbols while omitting a detailed description thereof.
FIG. 12 is a flow chart for explaining the processing performed by the d-axis target current correction section 100b.
In step S40, it is determined whether the motor angular velocity .omega. is not less than a predetermined value, and when the motor angular velocity .omega. is less than the predetermined value, the d-axis target current (Id*) is adopted as the
corrected d-axis target current (Id**) in step S43, whereas when the motor angular velocity .omega. is not less than the predetermined value, the control process advances to correction current Ida calculation processing in step 41. In the correction
current Ida calculation processing in step S41, a correction current Ida is calculated by referring to a table, which has been prepared in advance as a function of the motor angular velocity .omega. or using the motor angular velocity .omega. as a
parameter. In step S42, a corrected d-axis target current (Id**) is calculated by subtracting the correction current (Ida) from the d-axis target current (Id*), and the thus corrected d-axis target current (Id**) is supplied to the current control
section 100e.
Embodiment 6
In a sixth embodiment of the present invention, when the steering speed exceeds a predetermined value, the current instruction value for controlling the magnetic field of the motor field magnet is corrected to such a prescribed value as to
decrease the magnetic field, whereby the magnetic field is weakened upon high-speed steering, thus alleviating an increase in the steering torque during such high-speed steering.
FIG. 13 functionally illustrates an example of an electric power steering control apparatus according to the sixth embodiment of the present invention in which a field winding type motor is used as a steering assisting motor. In FIG. 13, the
same or corresponding parts as those in FIG. 2 are identified by the same symbols while omitting a detailed description thereof.
In FIG. 13, the electric power steering control apparatus of this sixth embodiment includes a steering angle sensor 9, a steering angular velocity calculation section 100j acting as a steering speed detection section for determining a steering
angular velocity .omega.' based on the output of the steering angle sensor 9, and a target current calculation section 100t for determining a target armature current value (Ia*) and a target field winding current value (If*) to drive a field winding type
motor 5b based on the torque detection signal of t | | |
