Technical Field
The present invention relates to an electric power steering
apparatus that has a redundant system configuration, and in
particular to an electric power steering apparatus that is a
configuration of respectively calculating steering angles from
respectively independent two torque sensors and two angle sensors,
performs comparison diagnoses of independent detection signals,
also concurrently performs individual diagnoses of each detection
signal and is capable of continuing functions such as assist etc.
without spoiling reliability.
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
3
a voltage supplied to the motor so that a difference between a
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 PWM (Pulse Width Modulation)
control.
A general configuration of the conventional electric power
steering apparatus (EPS) 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. Further, the column shaft 2 is
provided with a torque sensor 10 for detecting a steering torque
Th 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. Moreover, the column shaft 2
is provided with a steering angle sensor 14 for detecting a steering
angle θ. 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 the steering torque Th detected by the torque sensor
10 and a vehicle speed Vel detected by a vehicle speed sensor 12,
4
and controls a current supplied to the motor 20 on the basis of
a voltage control value Vref obtained by performing compensation
and so on with respect to the calculated current command value.
A CAN (Controller Area Network) 40 for
transmitting/receiving various information about the vehicle is
connected to the control unit 30, and it is also possible to receive
the vehicle speed Vel from the CAN 40. Further, a non-CAN 41 for
transmitting/receiving communications, analog/digital signals,
radio waves, etc. except for the CAN 40 can also be connected to
the control unit 30.
In such an electric power steering apparatus, the control
unit 30 mainly comprises a CPU (also including an MPU, an MCU,
or the like), and for example, 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 from the torque sensor 10 and the vehicle speed Vel from
the vehicle speed sensor 12 are inputted into a current command
value calculating section 31. The current command value
calculating section 31 calculates a current command value Iref1
based on the steering torque Th and the vehicle speed Vel and by
means of an assist map or the like. The calculated current command
value Iref1 is added to a compensation signal CM from a compensating
section 34 for improving characteristics in an adding section 32A,
an added current command value Iref2 is inputted into a current
5
limiting section 33 so that a maximum current is limited. A current
command value Irefm that the maximum current is limited, is inputted
into a subtracting section 32B, and a subtraction of a motor current
detection value Im from the current command value Irefm is
performed.
A subtraction result I(=Irefm-Im) of the subtracting section
32B is PI-controlled in a PI control section 35. The PI-controlled
voltage control value Vref is inputted into a PWM control section
36 and synchronized with a carrier signal CF so that the duty is
calculated. Furthermore, the motor 20 is PWM-driven through an
inverter 37 by a PWM signal that the duty is calculated. The motor
current value Im of the motor 20 is detected by a motor current
detecting means 38 and inputted into the subtracting section 32B
to be fed back.
The compensating section 34 adds a detected or estimated
self-aligning torque (SAT) 343 to an inertia compensation value
342 in an adding section 344, further adds a convergence control
value 341 to an addition result of the adding section 344 in an
adding section 345, and then inputs an addition result of the adding
section 345 into the adding section 32A as the compensation signal
CM to improve the characteristics.
In an electric power steering apparatus comprising a torsion
bar, it is necessary to detect angles at a plurality of positions,
for example, sensors shown in FIG.3 are mounted on the column shaft
2, and various detection signals are outputted. That is to say,
6
a Hall IC sensor 21 as an angle sensor and a 20° rotor sensor 22
as an input side torque sensor are mounted on an input shaft 2A
of a 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 40. Further, a 40° rotor
sensor 24 as an output side torque sensor 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 being an absolute value on the basis of the
AS_IS angle θh, the TS_IS angle θs1 and the TS_OS angle θr1 to
output.
FIG.4 shows one example of signal period of the detection
signal of each sensor. FIG.4(A) shows the signal period (296°)
of the AS_IS angle θh being the detection signal from the Hall
IC sensor 21, FIG.4(B) shows the signal period (20°) of the TS_IS
angle θs1 being the detection signal from the 20° rotor sensor
22, and FIG.4(C) shows the signal period (40°) of the TS_OS angle
θr1 being the detection signal from the 40° rotor sensor 24. “0”
point adjustments of these three sensors are adjusted by performing
7
calibration at assembling.
In such an electric power steering apparatus, recently,
reliability improvement is further required and the redundancy
of apparatuses and parts are carried out. As such a redundancy
apparatus, for example, there is a detection signal processing
method disclosed in Japanese Published unexamined Patent
Application No.H6-32240 A (Patent Document 1), and this detection
signal processing method is applied to a steering system for
automobile. Further, a physical quantity sensor comprising a
second conversion processing section connected to output terminals
for converting a first output signal outputted from a first sensor
element and a second output signal outputted from a second sensor
element into a second physical quantity that the second conversion
processing section is disposed within a second package, is disclosed
in the publication of Japanese Patent No.4863953 (Patent Document
2).
The List of Prior Art Documents
Patent Documents
Patent Document 1: Japanese Published unexamined Patent
Application No.H6-32240 A
Patent Document 2: the publication of Japanese Patent No.4863953
Patent Document 3: Japanese Published unexamined Patent
Application No.2006-76333 A
8
Summary of the Invention
Problems to be Solved by the Invention
However, in the detection signal processing method disclosed
in Patent Document 1, since processes that obey functions in a
redundant system are carried out and then compared in an external
computer, in the case of being applied to an electric power steering
apparatus, it is necessary to secure a communication line of that
purpose. Further, in the physical quantity sensor disclosed in
Patent Document 2, the output terminals are respectively exposed
from the sensor elements, a first conversion processing section
is disposed within a first package, and the second conversion
processing section is disposed within the second package.
Accordingly, the whole apparatus becomes a large size, and the
physical quantity sensor disclosed in Patent Document 2 is not
suitable for the electric power steering apparatus that downsizing
and weight reduction are required. Moreover, although it becomes
a redundant system configuration, a diagnosing method for function
continuation and a function limiting method are not disclosed.
The present invention has been developed in view of the
above-described circumstances, and the object of the present
invention is to provide an electric power steering apparatus that
improves the reliability by means of a redundant system, performs
comparison diagnoses of independent detection signals, also
concurrently performs individual diagnoses of each detection
signal and is capable of continuing functions without spoiling
9
reliability.
Means for Solving the Problems
The present invention relates to an electric power steering
apparatus that calculates a current command value by using at least
a steering torque and performs an assist control of a steering
system by driving a motor based on said current command value,
the above-described object of the present invention is achieved
by that comprising: at least two respectively independent torque
sensors and angle sensors, wherein having a function that
respectively calculates steering angles from said torque sensors
and said angle sensors to utilize, wherein comparison diagnoses
of independent signals are performed and also concurrently
individual diagnoses of each individual signal are performed,
wherein in a case that it is judged that there is an abnormality
in said comparison diagnoses, said angle sensor signals are not
used, wherein in a case that it is judged that at least one of
said individual diagnoses is abnormal, said angle sensor signal
is treated as downgrading, and in a case that it is judged that
two or more of said individual diagnoses are abnormal, said angle
sensor signals are not used.
Further, the above-described object of the present invention
is more effectively achieved by that wherein in said case that
it is judged that at least one of said individual diagnoses is
abnormal, by using only normal side of said angle sensors, even
10
if reliability declines, continuable functions are continued; or
wherein in said case that it is judged that at least one of said
individual diagnoses is abnormal, furthermore, an output limiting
is performed; or wherein said output limiting is an active return
function; or wherein calibration signals for showing a vehicle
neutral position are used in said steering angle calculation; or
wherein after integrating said electric power steering apparatus
into a vehicle, said calibration signals are written into an EEPROM.
Effects of the Invention
An electric power steering apparatus according to the present
invention set a torque sensor system and an angle sensor system
as a redundant system, performs comparison diagnoses of independent
detection signals, also concurrently performs individual
diagnoses of each detection signal, in the case that there are
abnormalities (including failures) in the angle sensor, carries
out a steering angle control (an output limiting) by means of
function continuation by using a normal steering angle of two
calculated steering angles, and in the case that abnormalities
of two angle sensors are judged, makes a steering angle value invalid.
Accordingly, the reliability is improved.
Further, in the case that the abnormality is judged by
diagnoses of the torque sensor system, assist is stopped to secure
safety.
11
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 a relation between a mounting
example of the electric power steering apparatus and sensors, and
those detection signals;
FIGs.4(A), 4(B) and 4(C) are waveform diagrams showing one
example of signal period of each sensor;
FIG.5 is a configuration diagram showing sensors and those
detection systems of the present invention;
FIG.6 is a block diagram showing a configuration example
of a diagnosis processing section of the present invention;
FIG.7 is a block diagram showing a configuration example
of a steering angle calculating section;
FIG.8 is one part of a flowchart showing an operation example
of the present invention; and
FIG.9 is another part of the flowchart showing the operation
example of the present invention.
Mode for Carrying Out the Invention
The present invention is a redundant system that multiplexes
a torque sensor system, an angle sensor system and a steering angle
12
calculating section to improve the reliability of an electric power
steering apparatus, performs comparison diagnoses (a torque sensor
comparison diagnosis, a steering angle comparison diagnosis and
an angle sensor comparison diagnosis) of independent signals and
also concurrently performs individual diagnoses of each detection
signal by a configuration of respectively calculating steering
angles from at least two respectively independent torque sensors
and angle sensors (steering angle sensors).
The steering angle is used in a steering wheel return control
or the like as an active return function for improving running
stability of vehicles and steerability, and in particular the
reliability is required.
In the case that the comparison diagnosis is negative
(abnormality or failure), a steering angle value is treated as
invalidity and the angle sensor signal is not used. In the case
that one of the individual diagnoses is negative, the angle sensor
signal is treated as downgrading, by using only normal side, even
if the reliability declines, continuable functions are continued
and also a processing such as performing an output limiting or
the like (for example, limiting an output of the active return
function to continue) is carried out. However, functions having
a possibility to reach serious events, are stopped. In the case
that two or more of the individual diagnoses are negative
(abnormality or failure), as with the comparison diagnosis, the
angle sensor signal is not used. Further, even in the case that
13
the torque sensor signal is not used in steering angle calculation
(even in the case of an absolute angle sensor), just the structure
changes and it is equal, as examples of the individual diagnoses,
there are abnormalities such as abnormalities of sensor power
supplies, signal abnormalities (such as communication errors,
disconnections or the like) and so on.
Hereinafter, embodiments of the present invention will be
described with reference to the accompanying drawings.
FIG.5 corresponding to FIG.3 shows an installation example
of various sensors and their signal processing example of the
present invention. As shown in FIG.5, an AS_IS angle from a Hall
IC sensor 21 being an angle sensor (a steering angle sensor) is
inputted into angle sensor circuits 102 and 112, an angle sensor
angle θh1 (296° period) is outputted from the angle sensor circuit
102, and an angle sensor angle θh2 (296° period) is outputted from
the angle sensor circuit 112. Further, a TS_IS angle from an input
side’s rotor sensor 22 being a torque sensor is inputted into torque
sensor circuits 101 and 111, and a TS_OS angle from an output side’s
rotor sensor 24 is inputted into the torque sensor circuits 101
and 111. An input side’s torque sensor angle θs1 (20° period)
and an output side’s torque sensor angle θr1 (40° period) are
outputted from the torque sensor circuit 101, and an input side’s
torque sensor angle θs2 (20° period) and an output side’s torque
sensor angle θr2 (40° period) are outputted from the torque sensor
circuit 111.
14
Moreover, electric power is supplied to the torque sensor
circuits 101 and 111 and the angle sensor circuits 102 and 112
from a separate power supply circuit.
FIG.6 shows a configuration example of a signal processing
circuit of the present invention. As shown in FIG.6, the torque
sensor angles θs1 and θr1 from the torque sensor circuit 101 are
inputted into a torque sensor diagnosing section 103, and the torque
sensor angles θs2 and θr2 from the torque sensor circuit 111 are
inputted into a torque sensor diagnosing section 113. The angle
sensor angle θh1 from the angle sensor circuit 102 is inputted
into an angle sensor diagnosing section 104, and the angle sensor
angle θh2 from the angle sensor circuit 112 is inputted into an
angle sensor diagnosing section 114. In the case that there is
no abnormality in each diagnosing section, the inputted signals
are outputted as it is and then inputted into steering angle
calculating sections 100 and 101 respectively.
That is to say, the torque sensor angles θs1 and θr1 from
the torque sensor diagnosing section 103 are inputted into the
steering angle calculating section 100 and concurrently inputted
into a torque sensor comprehensively diagnosing section 121. The
torque sensor angles θs2 and θr2 from the torque sensor diagnosing
section 113 are inputted into the steering angle calculating section
110 and concurrently inputted into the torque sensor
comprehensively diagnosing section 121. Further, the angle sensor
angle θh1 from the angle sensor diagnosing section 104 is inputted
15
into the steering angle calculating section 100 and concurrently
inputted into an angle sensor comprehensively diagnosing section
122. The angle sensor angle θh2 from the angle sensor diagnosing
section 114 is inputted into the steering angle calculating section
110 and concurrently inputted into the angle sensor comprehensively
diagnosing section 122.
A calibration signal CR1 for calibrating a vehicle neutral
position is inputted into the steering angle calculating section
100, and a calibration signal CR2 for calibrating the vehicle
neutral position is inputted into the steering angle calculating
section 110. After integrating the electric power steering
apparatus (EPS) into a vehicle, the calibration signals CR1 and
CR2 are written into an EEPROM or the like to store. A steering
angle θ1 is outputted from the steering angle calculating section
100, a steering angle θ2 is outputted from the steering angle
calculating section 110, and the steering angles θ1 and θ2 are
inputted into a steering angle diagnosing section 120. A diagnosis
result SD is outputted from the steering angle diagnosing section
120, a diagnosis result TD is outputted from the torque sensor
comprehensively diagnosing section 121, and a diagnosis result
AD is outputted from the angle sensor comprehensively diagnosing
section 122.
Further, the steering angle calculating sections 100 and
110 have the same configuration. Here, a configuration example
of the steering angle calculating section 100 will be described
16
with reference to FIG.7.
As shown in FIG.7, the angle sensor angle θh1 is
subtraction-inputted into a subtracting section 132. The torque
sensor angle θr1 is inputted into an angle difference calculating
section 131, a vernier calculating section 133 and a relative
steering angle calculating section 135. The torque sensor angle
θs1 is inputted into the angle difference calculating section 131.
A angle difference θa(=θs1-θr1) calculated in the angle difference
calculating section 131 is addition-inputted into the subtracting
section 132. An angle AS_OS(=θa-θh1) obtained by subtraction in
the subtracting section 132 is inputted into the vernier
calculating section 133. A steering angle θbr (an absolute
steering angle as a sensor reference) calculated in the vernier
calculating section 133 is inputted into an initial steering angle
calculating section 134. A calculated steering angle initial
value θint is outputted from the initial steering angle calculating
section 134. The steering angle initial value θint is inputted
into an adding section 136. A relative steering angle Rel_OS
calculated in the relative steering angle calculating section 135
is also inputted into the adding section 136. A steering angle
θb(=θint+Rel_OS) obtained by addition of the adding section 136
is inputted into a conversion-to-absolute-value section 137, and
an absolute value steering angle θc is addition-inputted into a
subtracting section 138. The calibration signal CR1 is
subtraction-inputted into the subtracting section 138. The
17
calibrated steering angle θ1 is outputted from the steering angle
calculating section 100.
Since the absolute steering angle θc from the
conversion-to-absolute-value section 137 becomes a steering angle
position on EPS column (sensors), in the case of mounting the EPS
column on the vehicle to use, it is necessary to calibrate a steering
angle “0” point on the vehicle (at the vehicle neutral position).
The absolute steering angle θc is calibrated by using the
calibration signal CR1 to output the steering angle θ1 so that
the vehicle neutral position accords with the steering angle “0”
point.
Moreover, vernier calculation is a calculation that obtains
period position “0~36” (the number of rotations counted from the
steering angle 0°) of the rotor sensor 24 in output shaft side
by utilizing a phase difference between sensor signals that are
different in the period (for example, 40° period, 296° period).
Thereby, it is possible to correctly judge which position of a
steering angle region “0~1480°” the rotor sensor 24 is in.
The individual diagnoses of each detection signal (diagnoses
of a torque sensor #1 (the rotor sensor 22 and the torque sensor
circuits 101) and a torque sensor #2 (the rotor sensor 24 and the
torque sensor circuits 111), diagnoses of an angle sensor #1 (the
Hall IC sensor 21 and the angle sensor circuits 102) and an angle
sensor #2 (the Hall IC sensor 21 and the angle sensor circuits
112)) are diagnoses to be capable of being performed independently
18
for every signal of each sensor. Communication abnormalities in
the case of receiving from the torque sensor by communication are
judged by unreceived, CRC errors, frame errors or the like. Further,
errors of the power supply supplied to the sensors, a matter that
the power supply is A/D-converted and the converted value is out
of range, etc. are judged as abnormalities (including failures).
In order to detect sensor value’s offsets/gain failures etc.,
for example, the comparison diagnoses (a torque sensor
comprehensive diagnosis, an angle sensor comprehensive diagnosis
and a steering angle diagnosis) are performed as follows.
(1)the torque sensor comprehensive diagnosis
A case that | a torque value obtained from the torque sensor
#1 - a torque value obtained from the torque sensor #2| > a
predetermined value (for example, 1Nm), is judged as abnormality.
(2)the steering angle diagnosis
A case that | a steering angle obtained from the torque sensor
#1 and the angle sensor #1 - a steering angle obtained from the
torque sensor #2 and the angle sensor #2| > a predetermined value
(for example, 5°), is judged as abnormality.
(3)the angle sensor comprehensive diagnosis
A case that | an angle value obtained from the angle sensor
#1 - an angle value obtained from the angle sensor #2| > a
19
predetermined value (for example, 5°), is judged as abnormality.
In the above diagnoses, the diagnoses of the angle sensors
#1 and #2 can identify in which sensor abnormality (including
failure) occurs. In this case, it is possible to calculate the
steering angle by using data from the remaining sensor and continue
the control. However, it becomes impossible to carry out a
comparison check with high detection coverage. Thereby, since
the reliability declines, a limit is set on the function. As the
function’s limit, for example, it is considered to multiply the
output of the active return function (the steering angle is used
and the steering wheel return is smoothened) by a limit gain so
as to suppress the output. Thereby, although the smoothness of
the steering wheel return declines, there is an advantage capable
of securing comfort compared to stopping the function.
Further, in the case that the comparison diagnoses are
abnormal, since it is impossible to distinguish which sensor has
abnormality (or failure), the function relating to the steering
angle is stopped and the assist is continued. Although the
diagnoses of the torque sensors #1 and #2 can distinguish which
sensor has abnormality or failure, since the assist of EPS is stopped,
it is excluded.
In such a configuration and functions, its operation example
will be described with reference to a flowchart shown in FIG.8
and FIG.9.
20
The steering angle calculating section 100 calculates the
steering angle θ1 based on the torque sensor angles θs1 and θr1,
the angle sensor angle θh1 and the calibration signal CR1, as
described above. The steering angle calculating section 110
calculates the steering angle θ2 based on the torque sensor angles
θs2 and θr2, the angle sensor angle θh2 and the calibration signal
CR2, as described above.
As diagnosis operations, at first, the torque sensor
diagnosing section 103 individually performs the diagnoses of the
rotor sensor 22 and the torque sensor circuit 101 (step S1), the
torque sensor diagnosing section 113 individually performs the
diagnoses of the rotor sensor 24 and the torque sensor circuit
111 (step S2), and the torque sensor comprehensively diagnosing
section 121 performs the comparison diagnosis of the torque sensors
(the rotor sensor 22 and the torque sensor circuits 101, the rotor
sensor 24 and the torque sensor circuits 111) (step S3). Moreover,
the order of individual diagnoses of the torque sensors is optional.
And then, it is judged whether any one of the individual
diagnoses and the comparison diagnosis of the torque sensors is
abnormal or not (step S4), in the case that any one of the individual
diagnoses and the comparison diagnosis of the torque sensors is
abnormal, the assist is stopped (step S5).
In a judgment about the presence or absence of abnormalities
performed in the above step S4, in the case that it is judged that
there is no abnormality, the angle sensor diagnosing section 104
21
individually performs the diagnoses of the Hall IC sensor 21 and
the angle sensor circuit 102 as an angle sensor (step S10), the
angle sensor diagnosing section 114 individually performs the
diagnoses of the Hall IC sensor 21 and the angle sensor circuit
112 as an angle sensor (step S11), and it is judged whether any
one of the individual diagnoses of the angle sensors is abnormal
or not (step S12). Moreover, the order of individual diagnoses
of the angle sensors is optional. In the case that there is no
abnormality in the result of the judgment about the presence or
absence of abnormalities, the angle sensor comprehensively
diagnosing section 122 performs the comparison diagnosis of the
angle sensors (the Hall IC sensor 21 and the angle sensor circuit
102, the Hall IC sensor 21 and the angle sensor circuit 112) (step
S13), and further, the steering angle diagnosing section 120
performs the steering angle diagnosis (step S14).
In the case that there is no abnormality in both the angle
sensor comprehensive diagnosis (step S13) and the steering angle
diagnosis (step S14), i.e. in the case that both the angle sensor
comprehensive diagnosis and the steering angle diagnosis are normal
(step S15), the steering angle θ1 calculated in the steering angle
calculating section 100 is set as the steering angle value (step
S16), and the steering angle control is turned on (step S17).
In the case that it is judged that any one of the individual
diagnoses of the angle sensors is abnormal in the above step S12,
at first, it is judged whether the angle sensor #1 (the Hall IC
22
sensor 21 and the angle sensor circuits 102) is abnormal or not
(step S20), in the case that the angle sensor #1 is not abnormal,
the steering angle θ1 calculated in the steering angle calculating
section 100 is set as the steering angle value (step S21), and
the steering angle control is limited (step S22). In the case
that the angle sensor #1 is abnormal, it is judged whether the
angle sensor #2 (the Hall IC sensor 21 and the angle sensor circuits
112) is abnormal or not (step S30), in the case that the angle
sensor #2 is not abnormal, the steering angle θ2 calculated in
the steering angle calculating section 110 is set as the steering
angle value (step S31), and the steering angle control is limited
(step S22).
In the case that it is judged that any one of the angle sensor
comprehensive diagnosis and the steering angle diagnosis is
abnormal in the above step S15, in the case that it is judged that
the angle sensor #2 is abnormal in the above step S30, the steering
angle value is made invalid (step S32), and the steering angle
control is turned off (step S33).
Moreover, in the above embodiments, although the Hall IC
sensor is used as an angle sensor (a steering angle sensor), it
is also possible to use other sensor as an angle sensor (a steering
angle sensor).
Explanation of Reference Numerals
1 steering wheel (handle)
23
2 column shaft (steering shaft, handle shaft)
10 torque sensor
12 vehicle speed sensor
13 battery
14 steering angle sensor
20 motor
21 Hall IC sensor (angle sensor, steering angle sensor)
22, 24 rotor sensor (torque sensor)
23 torsion bar
30 control unit (ECU)
31 current command value calculating section
35 PI control section
36 PWM control section
100, 110 steering angle calculating section
101, 111 torque sensor circuit
102, 112 angle sensor circuit
103, 113 torque sensor diagnosing section
104, 114 angle sensor diagnosing section
105, 115 calibration signal generating section
120 steering angle diagnosing section
121 torque sensor comprehensively diagnosing section
122 angle sensor comprehensively diagnosing section
131 angle difference calculating section
133 vernier calculating section
135 relative steering angle calculating section.

claims
1. An electric power steering apparatus that calculates a
current command value by using at least a steering torque and
performs an assist control of a steering system by driving a motor
based on said current command value, comprising:
at least two respectively independent torque sensors and angle
sensors,
wherein having a function that respectively calculates
steering angles from said torque sensors and said angle sensors
to utilize,
wherein comparison diagnoses of independent signals are
performed and also concurrently individual diagnoses of each
individual signal are performed,
wherein in a case that it is judged that there is an abnormality
in said comparison diagnoses, said angle sensor signals are not
used,
wherein in a case that it is judged that at least one of said
individual diagnoses is abnormal, said angle sensor signal is
treated as downgrading, and in a case that it is judged that two
or more of said individual diagnoses are abnormal, said angle sensor
signals are not used.
2. The electric power steering apparatus according to claim
1, wherein in said case that it is judged that at least one of
said individual diagnoses is abnormal, by using only normal side
of said angle sensors, even if reliability declines, continuable
functions are continued.
We Claim:
25
3. The electric power steering apparatus according to claim
1 or 2, wherein in said case that it is judged that at least one
of said individual diagnoses is abnormal, furthermore, an output
limiting is performed.
4. The electric power steering apparatus according to claim
3, wherein said output limiting is an active return function.
5. The electric power steering apparatus according to any
one of claims 1 to 4, wherein calibration signals for showing a
vehicle neutral position are used in said steering angle
calculation.
6. The electric power steering apparatus according to claim
5, wherein after integrating said electric power steering apparatus
into a vehicle, said calibration signals are written into an EEPROM.