DESCRIPTION
Technical Field
The present invention relates to an electric power steering
apparatus that provides a steering system of a vehicle with an
assist force generated by a motor, and in particular to an electric
power steering apparatus that is capable of taking an accurate
synchronization and suppressing an angle error proportional to
a steering speed by attaching (tying) a time stamp to each detection
signal of plural sensors, and raises a steering speed that a steering
angle detection is established.
Background Art
An electric power steering apparatus which provides a
steering mechanism of a vehicle with a steering assist torque (an
assist torque) by means of a rotational torque of a motor, applies
a driving force of the motor as the steering assist torque to a
steering shaft or a rack shaft by means of a transmission mechanism
such as gears or a belt through a reduction mechanism. In order
to accurately generate the steering assist torque, such a
conventional electric power steering apparatus (EPS) performs a
feedback control of a motor current. The feedback control adjusts
a voltage supplied to the motor so that a difference between a
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steering assist command value (a current command value) and a
detected motor current value becomes small, and the adjustment
of the voltage applied to the motor is generally performed by an
adjustment of duty command values of a pulse width modulation (PWM)
control.
A general configuration of the conventional electric power
steering apparatus will be described with reference to FIG.1. As
shown in FIG.1, a column shaft (a steering shaft or a handle shaft)
2 connected to a steering wheel 1, is connected to steered wheels
8L and 8R through reduction gears 3, universal joints 4a and 4b,
a rack and pinion mechanism 5, and tie rods 6a and 6b, further
via hub units 7a and 7b. In addition, the column shaft 2 is provided
with a torque sensor 10 for detecting a steering torque of the
steering wheel 1, and a motor 20 for assisting the steering force
of the steering wheel 1 is connected to the column shaft 2 through
the reduction gears 3. Electric power is supplied to a control
unit (ECU) 30 for controlling the electric power steering apparatus
from a battery 13, and an ignition key signal is inputted into
the control unit 30 through an ignition key 11. The control unit
30 calculates a current command value of an assist (steering assist)
command on the basis of a steering torque Th detected by the torque
sensor 10 and a vehicle speed Vel detected by a vehicle speed sensor
12, and controls a current supplied to the motor 20 on the basis
of a current control value E obtained by performing compensation
and so on with respect to the current command value. Moreover,
4
it is also possible to receive the vehicle speed Vel from a controller
area network (CAN) and so on.
The control unit 30 mainly comprises a CPU (also including
an MPU), and general functions performed by programs within the
CPU are shown in FIG.2.
Functions and operations of the control unit 30 will be
described with reference to FIG.2. As shown in FIG.2, the steering
torque Th detected by the torque sensor 10 and the vehicle speed
Vel detected by the vehicle speed sensor 12 are inputted into a
current command value calculating section 31 for calculating a
current command value Iref1. The current command value
calculating section 31 calculates the current command value Iref1
that is a control target value of a current supplied to the motor
20 based on the steering torque Th being inputted and the vehicle
speed Vel being inputted and by means of an assist map or the like.
The current command value Iref1 is inputted into a current limiting
section 33 through an adding section 32A. A current command value
Irefm that a maximum current is limited, is inputted into a
subtracting section 32B, and a deviation I(=Irefm-Im) between the
current command value Irefm and a motor current value Im being
fed back, is calculated. The deviation I is inputted into a PI
control section 35 for characteristic improvement of steering
operations. A voltage control command value Vref that the
characteristic improvement is performed by the PI control section
35, is inputted into a PWM control section 36. Furthermore, the
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motor 20 is PWM-driven through an inverter circuit 37 serving as
a driving section. The current value Im of the motor 20 is detected
by a motor current detector 38 and fed back to the subtracting
section 32B. The inverter circuit 37 uses EFTs as driving elements
and is comprised of a bridge circuit of FETs.
Further, a compensation signal CM from a compensating
section 34 is added in the adding section 32A, and compensation
of the system is performed by the addition of the compensation
signal CM so as to improve a convergence, an inertia characteristic
and so on. The compensating section 34 adds a self-aligning torque
(SAT) 343 and an inertia 342 in an adding section 344, further
adds the result of addition performed in the adding section 344
and a convergence 341 in an adding section 345, and then outputs
the result of addition performed in the adding section 345 as the
compensation signal CM.
Such an electric power steering apparatus includes various
sensors for detecting the steering angle of the column shaft (the
steering shaft or the handle shaft) and for detecting a motor
rotation angle and so on.
Conventionally, in order to raise a detection accuracy
(detection resolution) of a rotation position by a rotation angle
sensor, a rotation position detecting apparatus that combines
plural sensors having displacement characteristics and detects
the rotation position by a vernier (sub-scale) method, is proposed
(for example, Japanese Published examined Patent Application
6
No.H6-65967 B2: Patent Document 1). That is, the rotation position
detecting apparatus of Patent Document 1 is a configuration that
comprises a sensor having a first pattern of 1-pitch per rotation
and a sensor having a second pattern that divides one circumference
of the first pattern into “n” on the basis of a reference, and
detects an absolute rotation position.
The List of Prior Art Documents
Patent Documents
Patent Document 1: Japanese Published examined Patent
Application No.H6-65967 B2
Summary of the Invention
Problems to be Solved by the Invention
However, in the case of applying the rotation position
detecting apparatus disclosed in Patent Document 1 to the electric
power steering apparatus, when a combination of a steering’s torque
sensor that detects the steering torque via a torsion bar and a
steering angle sensor that detects an absolute steering angle is
used, it is necessary to further combine another sensor with the
apparatus of Patent Document 1 via the torsion bar to constitute
the torque sensor and detect the steering torque.
Further, in general, a steering angle range of the steering
is about 1080° (one side 540°), in the case of performing the steering
angle detection by using a single steering angle sensor, there
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is a problem that angle resolution becomes rough. Therefore, it
is necessary to detect the angle by using the vernier calculation
based on a combination of plural sensors. In this case, it becomes
necessary to synchronize two sensors, and a synchronization
accuracy is strongly requested.
Further, in the case of using the above combination sensors,
since they are respectively independent sensors, there is a problem
that the angle error becomes large depending on the steering speed.
In particular, in the case of digital communication, since an error
due to communication is also included, the angle error becomes
larger.
The present invention has been developed in view of the
above-described circumstances, and the object of the present
invention is to provide a high-function electric power steering
apparatus that is capable of taking an accurate synchronization
and suppressing an angle error proportional to a steering speed
by attaching (tying) a time stamp every time a detection signal
from each sensor is received, and raises the steering speed that
detection of a steering angle is established.
Means for Solving the Problems
The present invention relates to an electric power steering
apparatus that performs an assist control of a steering by driving
a motor by means of a current command value calculated on a basis
of at least a steering torque, comprises at least sensors A and
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B being different in periods, and has a function to detect a steering
speed, the above-described object of the present invention is
achieved by that comprising: a time stamp attaching section that
attaches a time stamp ATi to a detection signal Ai of said sensor
A and attaches a time stamp BTj to a detection signal Bj of said
sensor B; a storing section that stores said detection signal Bj
to which said time stamp BTj is attached; a synchronous signal
searching section that searches said detection signal Bj most
synchronized with said detection signal Ai from said storing section
based on said time stamps ATi and BTj; a vernier calculating section
that performs a calculation of an angle difference between
synchronous signals searched by said synchronous signal searching
section and a vernier calculation and outputs an absolute steering
angle pf a sensor reference; an initial steering angle calculating
section that calculates an initial steering angle value from said
absolute steering angle; and a steering angle output section that
obtains a steering angle on a basis of a relative steering angle
from said sensor B and said initial steering angle value.
Further, the above-described object of the present
invention is more effectively achieved by that wherein comprising
a comparing section that compares said steering speed with a
threshold, and when said steering speed is less than or equal to
said threshold, search of said synchronous signals, said
calculation of said angle difference and said vernier calculation
are performed; or wherein said threshold is a practical steering
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speed; or wherein said search of said synchronous signal searching
section is a binary search.
Effects of the Invention
Since the angle error that the steering angle detection
(vernier) is established depends on the sensor, the angle error
that the steering angle detection (vernier) is established becomes
a constantn value, the angle error of this case becomes the
multiplication value of a steering angle speed and a time error.
According to an electric power steering apparatus of the present
invention, it is possible to reduce the time error and reduce the
angle error proportional to the time error by implementing the
synchronization of the sensor detection signals. Further, since
it is possible to suppress and reduce the angle error, it is possible
to raise the steering speed that the steering angle detection is
possible.
Brief Description of the Drawings
In the accompanying drawings:
FIG.1 is a configuration diagram illustrating a general
outline of an electric power steering apparatus;
FIG.2 is a block diagram showing a configuration example
of a control system of the electric power steering apparatus;
FIG.3 is a diagram showing an error factor of detection
signals of two sensors (A, B) and an improvement method;
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FIG.4 is a block diagram showing a basic configuration
of the present invention;
FIG.5 is a flowchart showing an operation example of
steering angle calculation;
FIG.6 is a flowchart showing a detecting operation example
of the steering angle;
FIG.7 is a diagram showing a relation among the electric
power steering apparatus, a mounting example of sensors and those
detection signals;
FIG.8 is a waveform diagram showing one example of signal
period of each sensor;
FIG.9 is a block diagram showing a configuration example
of a steering angle detecting apparatus;
FIG.10 is a waveform diagram showing angle signals of 40°
period and 296° period; and
FIG.11 is a diagram showing effects of the present invention
(the steering speed that the steering angle detection is established
becomes high by reducing the angle error).
Mode for Carrying Out the Invention
An electric power steering apparatus of the present
invention detects (calculates) a steering angle from angle signals
of respectively independent angle sensors A and B that are mounted
on the electric power steering apparatus by utilizing a principle
of vernier (sub-scale) including a calculation of an angle
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difference. In the present invention, the period of the angle
sensor A is long, and the angle sensor B is a sensor of output
side of the torque sensor and one period of the angle sensor B
becomes small (short). Since the angle sensor A and the angle
sensor B are independent sensors, the synchronization thereof is
not taken. Further, in order to establish the steering angle
detection, in principle of a vernier calculation, it is necessary
that an angle error of the angle sensor A and the angle sensor
B is less than or equal to a constant value (the greatest common
divisor of the detection angle range of each sensor).
In the case that the synchronization of plural sensors
is not taken, the detection timing of each sensor deviates. Further,
when the sensor is rotated (steered), an error occurs in a detected
angle, and the angle error increases in proportion to the number
of rotations (the steering speed). Therefore, a constraint
condition “the steering angle is detectable only in the case of
being less than or equal to a constant steering speed” for steering
in the steering angle detection is brought. Due to the above
constraint condition, startings of a driving support system to
a driver based on the steering angle control or the like and of
the steering angle control (EPS or the like) of vehicle side are
delayed.
In this connection, the present invention attaches a time
stamp at every time when each detection signal from plural sensors
is received, ties the time stamp to the detection signal, and stores
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a predetermined time duration in a buffer memory. Then, the present
invention searches a signal (a synchronous signal) closest to angle
detection timings of the angle sensor A and the angle sensor B
from the buffer memory, and enables the steering angle calculation
with a minimum angle error. Thus, since it becomes possible to
suppress the increasing of the angle error proportional to the
steering angle speed, even in the case of fast steering speed,
the vernier calculation is established.
Hereinafter, embodiments of the present invention will
be described in detail with reference to the accompanying drawings.
FIG.3 is a time chart illustrating the principle of signal
synchronization according to the present invention, and shows error
factors of detection signals from two sensors A and B and an
improvement method thereof. When completing reception of a signal
A1 from the sensor A, in the case of choosing a signal B1 from
the sensor B as a signal used in the vernier calculation, a time
error of angle detection timings of the sensor A and the sensor
B becomes Δt1 and includes a large time error. Accordingly, the
present invention synchronizes a signal Ai (i=1, 2, ---) from the
sensor A and a signal Bj (j=1, 2, ---) from the sensor B by means
of attachment of the time stamp and signal search. In this case,
for example, the present invention searches the signal Bj closest
to the detection timing of the signal A1 from the buffer memory
of the signal Bj. As a result, in this example, with respect to
the signal A1, the signal B7 is chosen. By synchronizing the signal
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A and the signal B, the time error is improved from Δt1 to Δt2.
Hereafter, the present invention performs the vernier calculation
by using the synchronized signals (the signal A1, the signal B7)
and calculates the steering angle.
Furthermore, in FIG.3, “Δt” is a time error of the angle
detection timings of the signal Ai and the signal Bj, “Δt1” is
a time error before the synchronizing, and “Δt2” is a time error
after the synchronizing. Further, “Δai” is “an internal
processing time of the sensor A (the signal Ai) + a communication
time”, and “Δbj” is “an internal processing time of the sensor
B (the signal Bj) + a communication time”.
FIG.4 shows a basic configuration example of the present
invention (a steering angle calculating apparatus). As shown in
FIG.4, a detection signal SN1 of a sensor 201 (the sensor A) of
the vehicle side and a detection signal SN2 of a sensor 202 (the
sensor B) of the vehicle side are inputted into a signal receiving
section 300 of ECU side due to the communication. The detection
signal SN1 of the sensor 201 is attached the time stamp, inputted
into an angle receiving section 301 and received, and then inputted
into a synchronous signal searching section 310. Further, the
detection signal SN2 of the sensor 202 is attached the time stamp,
inputted into an angle receiving section 302 and received, and
then once stored in a buffer memory 303. A stored detection signal
SN2b is read out from the buffer memory 303 and inputted into the
synchronous signal searching section 310. Sensor detection
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signals SN1s and SN2s that are searched by the synchronous signal
searching section 310 as the synchronous signal, are inputted into
a vernier calculating section 320 that performs the calculation
of the angle difference and the vernier calculation. A steering
angle that the vernier calculation is performed by the vernier
calculating section 320 and by using calculation including the
calculation of the angle difference (an absolute steering angle
of the sensor reference (standard)), is outputted from the vernier
calculating section 320. Further, a steering speed ω is inputted
into the ECU.
An operation example of such a steering angle calculating
apparatus will be described with reference to a flowchart shown
in FIG.5.
FIG.5 shows the operation example of the steering angle
calculation. As shown in FIG.5, the detection signal SN1 from
the sensor 201 (the sensor A) is received by the angle receiving
section 301 (Step S10), attached a time stamp A1 by the angle
receiving section 301 and inputted into the synchronous signal
searching section 310 (Step S11). A detection signal Sn1a that
is inputted into the synchronous signal searching section 310,
is “SN1 + the time stamp A1”. Further, the detection signal SN2
from the sensor 202 (the sensor B) is received by the angle receiving
section 302 (Step S12), attached a time stamp B1 by the angle
receiving section 302 (Step S13), in other words, and sequentially
stored in the buffer memory 303 as “SN2 + the time stamp B1” (Step
15
S14). After detection signals SN2a1, SN2a2, SN2a3, --- to which
the time stamps B1, B2, B3, --- are attached, are stored in the
buffer memory 303, detection signals SN2b1(SN2a1 + the time stamp
B1), SN2b2(SN2a2 + the time stamp B2), SN2b3(SN2a3 + the time stamp
B3), --- that are read out from the buffer memory 303, are inputted
into the synchronous signal searching section 310.
Thereafter, the steering speed ω is inputted (Step S15),
whether or not the steering speed ω is less than or equal to a
limiting steering speed ω0 as a threshold, is judged (Step S20).
When the steering speed ω is too fast, the angle error becomes
too large, therefore, the limit is performed in a practical range
of the steering. In the case that the steering speed ω is less
than or equal to the limiting steering speed ω0, reading out of
time stamps (A1, B1, B2, B3, ---) is performed (Step S21), search
of the synchronous signal (the time stamp A1 and the time stamp
Bj) is performed by, for example, a binary search (Step S22). Based
on a search result, the detection signals, i.e. the detection signal
A1 after the synchronizing and the detection signal Bj after the
synchronizing are read out (Step S23), the calculation of the angle
difference is performed (Step S24), further, the vernier
calculating section 320 performs the publicly known vernier
calculation and outputs the absolute steering angle of the sensor
reference (Step S25). Then, based on an absolute steering angle,
a relative steering angle and a vehicle neutral position (stored
in an EEPROM), the calculation of an initial steering angle is
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performed, and an initial steering angle value is outputted (Step
S26).
FIG.6 shows a detecting operation example of the steering
angle. As shown in FIG.6, based on an angle signal TS_OS from
the sensor, the calculation of the relative steering angle is
performed (Step S30), the initial steering angle value obtained
as stated above is added to the relative steering angle (Step S31),
and the steering angle is outputted.
Next, an embodiment that applies the synchronization of
the detection signals A and B, and the steering angle detection
as described above to the electric power steering apparatus will
be described.
In the electric power steering apparatus having the torsion
bar, it is necessary to detect the angle in a plurality of places,
for example, as shown in FIG.7, sensors are mounted on the column
shaft (the handle shaft) 2 and various detection signals are
outputted. That is to say, a Hall-IC sensor 21 as an angle sensor
and a 20°-rotor sensor 22 of a torque sensor input-side’s rotor
are mounted on an input shaft 2A of the steering wheel 1 side of
the handle shaft 2. The Hall-IC sensor 21 outputs an AS_IS angle
θh of 296° period, and the AS_IS angle θh is inputted into a steering
angle calculating section 40. The 20°-rotor sensor 22 that is
mounted on the steering wheel 1 side than a torsion bar 23, outputs
TS_IS angles θs1 (main) and θs2 (sub) of 20° period, and the TS_IS
angle θs1 is inputted into the steering angle calculating section
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40. Further, a 40°-rotor sensor 24 of a torque sensor output-side’s
rotor is mounted on an output shaft 2B of the handle shaft 2, TS_OS
angles θr1 (main) and θr2 (sub) are outputted from the 40°-rotor
sensor 24, and the TS_OS angle θr1 is inputted into the steering
angle calculating section 40. The steering angle calculating
section 40 calculates a steering angle θab of the absolute value
on the basis of the AS_IS angle θh, the TS_IS angle θs1 and the
TS_OS angle θr1 and outputs the steering angle θab.
FIG.8 shows one example of signal periods of the detection
signals of the respective sensors. FIG.8(A) shows the signal
period (296°) of the AS_IS angle θh being the detection signal
from the Hall-IC sensor 21, FIG.8(B) shows the signal period (20°)
of the TS_IS angle θs1 being the detection signal from the 20°-rotor
sensor 22, and FIG.8(C) shows the signal period (40°) of the TS_OS
angle θr1 being the detection signal from the 40°-rotor sensor
24. A “0-point” adjustment of these three sensors is adjusted
by calibration at assembling.
FIG.9 shows a configuration example of the steering angle
calculating section 40. As shown in FIG.9, the steering speed
ω is inputted into an execution judging section 41, and a steering
speed ω1 judged by the execution judging section 41 is inputted
into a calculating section 50. The AS_IS angle θh from the Hall-IC
sensor 21 corresponding to the sensor A is addition-inputted into
a subtracting section 46A within the calculating section 50, the
TS_IS angle θs1 from the 20°-rotor sensor 22 corresponding to the
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sensor B and the TS_OS angle θr1 from the 40°-rotor sensor 24
corresponding to the sensor B are inputted into an angle difference
calculating section 42, and an angle difference (=θs1-θr1) is
calculated by the angle difference calculating section 42 and
subtraction-inputted into the subtracting section 46A. A
subtraction angle AS_OS (=θh-(θs1-θr1)) obtained by the
subtracting section 46A is inputted into a vernier calculating
section 43. A vernier calculating means comprises the angle
difference calculating section 42, the subtracting section 46A
and the vernier calculating section 43. Further, the TS_OS angle
θr1 from the 40°-rotor sensor 24 corresponding to the sensor B
is inputted into the vernier calculating section 43 and also
inputted into a relative steering angle calculating section 45.
A steering angle θbr (the absolute steering angle of the
sensor reference) calculated by the vernier calculating section
43 is inputted into an initial steering angle calculating section
44, and a calculated initial steering angle value θint is outputted.
The calculating section 50 performs the above calculation one time
in the starting time and outputs the initial steering angle value
θint. The initial steering angle value θint from the calculating
section 50 is inputted into an adding section 46B, and a relative
steering angle Re1_OS calculated by the relative steering angle
calculating section 45 is also inputted into the adding section
46B. A steering angle θab (=θint+Re1_OS) obtained by addition
of the adding section 46B is outputted from the adding section
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46B comprising a steering angle output section.
Since the steering angle calculating section 40 constantly
outputs the steering angle θab that sets the vehicle neutral
position as the “0-point”, the steering angle calculating section
40 performs the vernier calculation one time by the vernier
calculating section 43 in the starting time from the subtraction
angle AS_OS and the TS_OS angle θr1, and obtains a correction value
for correcting the relative steering angle of the TS_OS angle θr1
to the absolute steering angle of the sensor reference. Further,
the steering angle calculating section 40 obtains the initial
steering angle value θint from the correction value and the vehicle
neutral position. After obtaining the initial steering angle
value θint, by adding the relative steering angle of the TS_OS
angle θr1 to the initial steering angle value θint, it is possible
to constantly output the steering angle θab of absolute value from
the adding section 46B comprising the steering angle output section.
The vernier calculation is a calculation that obtain period
positions “0~36” (the number of rotations counted from the steering
angle 0°) of the 40°-rotor sensor 24 in output shaft side by utilizing
a phase difference between the sensor signals that are different
in the period (for example, 40° period, 296° period). Thereby,
it is possible to judge which position of a steering angle region
“0~1480°” the 40°-rotor sensor 24 is in. Further, the subtraction
angle AS_OS (an output shaft side’s angle of 296° period) is
generated for the vernier calculation. That is, the amount of
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a torsion angle of the torsion bar 23 (the angle difference between
the TS_IS angle θs1 and the TS_OS angle θr1) is subtracted from
the AS_IS angle θh being the detection signal from the Hall-IC
sensor 21 in an input shaft side.
In general, in the case of performing the vernier
calculation, when a difference between a large period becoming
a reference and a small period is small, the error becomes small.
When the period of a small cycle is too fine (a difference between
a large cycle and the small cycle is large), it is thought to falsely
recognize a neighbor value of the small cycle. Further, since
the EPS apparatus comprises the torsion bar, a rotation angle of
the steering wheel itself and the steering angle of the vehicle
cause a displacement of the amount of torsion characteristics of
the torsion bar.
Therefore, the present invention employs a configuration
that performs the vernier calculation between the sensor (24) of
rack-and-pinion side than the torsion bar (23) and the sensors
(21, 22) of steering wheel side than the torsion bar (23), provides
the sensor (22) of steering wheel side than the torsion bar (23)
and corrects the amount of the torsion by using the sensors at
front/rear of the torsion bar.
FIG.11 shows effects of the present invention, as a
prerequisite, since an angle error Δθ’ that the steering angle
detection (vernier) is established depends on the sensor, the angle
error Δθ’ becomes a constant value. In this case, with respect
21
to the angle error Δθ, the following Expression 1 holds. That
is, the angle error Δθ increases and decreases in proportion to
the steering speed ω.
[Expression 1]
angle error Δθ = steering speed ω × time error Δt
As a countermeasure, by implementing the synchronization
of the signals, the time error Δt of the detection timing between
the signals of the sensor A and the sensor B is reduced. That
is, by synchronizing the detection signals, the angle error becomes
small. As a result, the steering speed ω that the steering angle
detection is established becomes high like “ω1 → ω2”. In this
way, when the steering speed that the steering angle detection
is established is improved from ω1 (for example, 20°/s) to ω2 (for
example, 200°/s), the function of the steering angle detection
is sufficiently established as the EPS.
Moreover, in the above embodiments, although only the
sensor B that the period is small, is searched, if it is possible
to earn the arithmetic capacity of CPU and the capacity of the
buffer memory, similarly, it is also possible to store data with
time stamp and search the sensor A that the period is large.
Explanation of Reference Numerals
1 steering wheel
22
2 column shaft (steering shaft, handle shaft)
10 torque sensor
12 vehicle speed sensor
13 battery
20 motor
21 Hall-IC sensor
22 20°-rotor sensor
23 torsion bar
24 40°-rotor sensor
30 control unit (ECU)
31 current command value calculating section
33 current limiting section
34 compensating section
35 PI control section
36 PWM control section
37 inverter circuit
40 steering angle calculating section
41 execution judging section
42 angle difference calculating section
43 vernier calculating section
44 initial steering angle calculating section
45 relative steering angle calculating section
200 steering angle control section
201 sensor (A)
202 sensor (B)
23
300 signal receiving section
301,302 angle receiving section
303 buffer memory
310 synchronous signal searching section
320 vernier calculating section
24
We Claim
1. An electric power steering apparatus that performs an
assist control of a steering by driving a motor by means of a current
command value calculated on a basis of at least a steering torque,
comprises at least sensors A and B being different in periods,
and has a function to detect a steering speed, comprising:
a time stamp attaching section that attaches a time stamp
ATi to a detection signal Ai of said sensor A and attaches a time
stamp BTj to a detection signal Bj of said sensor B;
a storing section that stores said detection signal Bj
to which said time stamp BTj is attached;
a synchronous signal searching section that searches said
detection signal Bj most synchronized with said detection signal
Ai from said storing section based on said time stamps ATi and
BTj;
a vernier calculating section that performs a calculation
of an angle difference between synchronous signals searched by
said synchronous signal searching section and a vernier calculation
and outputs an absolute steering angle of a sensor reference;
an initial steering angle calculating section that
calculates an initial steering angle value from said absolute
steering angle; and
a steering angle output section that obtains a steering
angle based on a relative steering angle from said sensor B and
said initial steering angle value.
2. An electric power steering apparatus according to claim
1, wherein further including a comparing section that compares
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said steering speed with a threshold, and
when said steering speed is less than or equal to said
threshold, search of said synchronous signals, said calculation
of said angle difference and said vernier calculation are performed.
3. An electric power steering apparatus according to claim
2, wherein said threshold is a practical steering speed.
4. An electric power steering apparatus according to any one
of claims 1 to 3, wherein said search of said synchronous signal
searching section is a binary search.