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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to a power steering apparatus which can be
mounted in any type of vehicle to decrease a steering force needing to be
exerted by a driver.
Light-operated power steering apparatuses have become widespread recently.
Such a conventional power steering apparatus uses electrical energy
supplied from a battery. In this conventional power steering apparatus,
the electrical energy causes a motor to operate an oil pump. Compressed
oil from the pump is supplied to a power steering section to perform
steering with a small force.
However, in this conventional power steering apparatus, a means for
controlling a oil flow rate controlled by motor rotation and for
preventing oil leakage becomes complicated, resulting in high cost and low
reliability.
In order to eliminate the conventional drawbacks, a power steering
apparatus is proposed in Japanese Patent Disclosure No. 55-47,963, wherein
A steering unit is directly driven by a motor. Since the speed of the
motor is high, the motor cannot follow a great change in steering
direction. In particular, when quick turns of a steering wheel for
slalom-like driving are required, the automatic steering apparatus cannot
provide a sufficient performance.
Another conventional power steering apparatus is proposed in Japanese
Patent Disclosure No. 46-33,327, wherein an electromagnetic clutch is
constituted by two main driving members rotated in opposite directions and
one driven member connected to a steering mechanism. The driven member is
coupled to any one of the main driving members, thereby controlling the
steering mechanism. However, the clutch generates large sliding noise,
thereby discomforting the driver. In addition, the clutch is easily worn,
so increasing maintenance operation and degrading reliability.
In a conventional power steering apparatus which does not use oil, the
steering unit must be operated by an amount corresponding to a steering
torque. Although steering torque detection is performed by a strain gauge,
the strain gauge has low reliability and low sensitivity. Thus, the strain
gauge is not suitable in the steering apparatus of a vehicle which
requires high sensitivity.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the conventional problems
and provide a power steering apparatus using a motor rotational force as a
direct steering force.
In order to achieve the above object of the present invention, there is
provided a vehicle power steering apparatus for rotating a motor in
response to a torque signal generated in response to a rotational torque
of input and output steering shafts and for driving a steering direction
control unit using a rotational force of the motor so as to perform power
steering, comprising:
vehicle velocity detecting means for detecting a vehicle velocity;
rotational direction and rotational torque detecting means for detecting a
rotational direction and a rotational torque of the input and output
steering shafts in response to a signal generated by the rotational torque
of the input and output steering shafts;
controlling means for controlling the rotational direction of the motor in
response to a detected rotational direction; and
torque controlling means for decreasing the rotational torque of the motor
in response to a detected vehicle speed signal when the vehicle speed is
increased, and for increasing the rotational torque of the motor in
response to the detected vehicle speed signal when a steering torque is
increased.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a power steering apparatus according to an
embodiment of the present invention;
FIG. 2 is a sectional view of a power steering section 3 in FIG. 1;
FIGS. 3, 4 and 5 are sectional views of the power steering section 3 of
FIG. 2 taken along the lines III--III, IV--IV and V--V, respectively;
FIG. 6 is a circuit diagram of a controller 4 shown in FIG. 1;
FIGS. 7 to 10 are graphs showing output voltages from operational
amplifiers 417 and 418 and a rotational torque detector 410 in a steering
state, and a timing chart showing an output signal from a vehicle speed
signal generator 430 when a vehicle speed changes, respectively;
FIG. 11 is a sectional view showing another embodiment of a power steering
section 3 shown in FIG. 1; and
FIG. 12 is a sectional view of the power steering section 3 taken along the
line XII--XII in FIG. 11.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows an overall system configuration of a power steering apparatus
according to an embodiment of the present invention. Referring to FIG. 1,
reference numeral 1 denotes a steering wheel; 2, a torque sensor; 3, a
power steering section; 4, a controller; 5, a relay; 6, a steering
direction control unit; 7, a battery; 8, an alternator; 9, an engine; and
9a, a vehicle speed sensor.
FIG. 2 is a sectional view of the torque sensor 2 and the steering section
3; FIGS. 3, 4 and 5 are sectional views thereof taken along the lines
III--III, IV--IV and V--V, respectively. Referring to FIGS. 2 to 5,
reference numeral 3a denotes an input steering shaft; 3b, an output
steering shaft; 3c, a torsion bar; and 3d, a fail safe stopper. A
rotational force of the steering wheel 1 is transmitted to the input
steering shaft 3a. A rotational force of the output steering shaft 3b is
transmitted to the steering direction control unit 6. One end of the
torsion bar 3c is fixed by two pins 3e on the input steering shaft 3a, and
the other end thereof is fixed on the output steering shaft 3b. As shown
in FIG. 5, the fail safe stopper 3d is arranged such that the input
steering shaft 3a is not brought into contact with the output steering
shaft 3b. The input and output steering shafts 3a and 3b can be relatively
rotated through the torsion bar 3c within a predetermined steering angle
range. However, when a steering angle exceeds the predetermined range, the
projections of the input and output steering shafts 3a and 3b abut against
each other, so that rotation of one steering shaft is transmitted to the
other steering shaft. Reference numeral 3f denotes a motor. Rotating
shafts 3g of the motor 3f extend from the two ends of the motor 3f,
respectively. Gears 3h and 3i are integrally mounted on the rotating
shafts 3g and are rotated therewith, respectively. The gear 3h meshes with
a gear 3j, and the gear 3i meshes with a gear 3k. The gear 3j is mounted
on the input steering shaft 3a and is rotated therewith, and the gear 3k
is mounted on the output steering shaft 3b and is rotated therewith. The
motor 3f is mounted in a case 3p while the motor 3f is supported by
support shafts 3l and 3m. The support shaft 3l is mounted in the case 3p
while the shaft 3m is slidably inserted in a groove 3n, as shown in FIG.
4. The support shaft 3l is mounted in the case 3p such that the motor 3f
is pivoted. Reference numeral 2a denotes a slider. One end of the slider
2a is pivotally mounted on the support shaft 3m, and the other end thereof
constitutes a free end, so that the slider 2a can be slid on a resistive
element 2b. A groove 2c is formed in the slider 2a at a position in the
vicinity of the support shaft 3m. A support shaft 3q fixed to the case 3p
is slidably inserted in the groove 2c. A change in resistance caused by a
displacement of the slider 2a is transmitted to the controller 4 shown in
FIG. 1. The controller 4 causes the motor 3f to rotate in accordance with
the change in resistance. In this case, the motor 3f is not rotated while
the input and output steering shafts 3a and 3b are located on the same
level (FIG. 4) as the slider 2a. The rotational direction is determined by
a direction in which the slider 2a is deviated from the input and output
steering shafts 3a and 3b, and the rotational torque is determined by a
deviation. The slider 2a and the resistive element 2b constitute a torque
sensor 2.
The operation of the power steering apparatus having the construction
described above will be described hereinafter. When the driver turns the
steering wheel 1, the input steering shaft 3a is rotated. Assume that the
input steering shaft 3a is slightly rotated (e.g., by an angle of about
10.degree.). Since the gear 3j is rotated together with the input steering
shaft 3a, the gear 3j is rotated through the same rotational angle as the
input steering shaft 3a. The rotational force of the gear 3j is
transmitted to the gear 3k through the gear 3i mounted at the opposite
side to the gear 3h and the shaft 3g. The output steering shaft 3b rotated
together with the gear 3i drives the steering direction control unit 6.
Therefore, a large force is required for rotation with a large torque.
When a rotational force exceeding a given value acts on the input steering
shaft 3a, the torsion bar 3c is twisted to rotate the input steering shaft
3a and the gear 3j although the output steering shaft 3b and the gear 3k
are not rotated. As a result, the gear 3h orbits around the input steering
shaft 3a, and thus the motor 3f is pivoted about the support shaft 3l in a
direction (indicated by an arrow in FIG. 4) toward the lower surface of
the drawing.
Upon pivotal movement of the motor 3f, the slider 2a is pivoted about the
support shaft 3q. The slider 2a is slid along the resistive element 2b,
and a resistance change signal is generated from the slider 2a. In this
case, when a distance between the support shafts 3m and 3q is shorter than
that between the support shaft 3q and the resistive element 2b, a
displacement of the slider 2a on the resistive element 2b is magnified as
compared with pivotal movement of the motor 3f.
When the resistance change signal is supplied to the controller 4 shown in
FIG. 1, the controller 4 causes the shaft 3g of the motor 3f to rotate at
a speed corresponding to the resistance change. The gears 3h and 3i are
rotated from the right to left in FIG. 4 (the rotational direction is
viewed from the right side of the drawing, unless otherwise specified).
The rotational force of the gears 3h and 3i is transmitted to the gear 3k,
so that the output steering shaft 3b is rotated in the same direction (the
right-hand direction) as the steering wheel 1. The rotational force of the
output steering shaft 3b is transmitted to the steering direction control
unit 6, and the vehicle can be turned in the direct-hand direction. In
this case, a force required for turning the steering wheel 1 comprises a
force for pivoting the motor 3f about the support shaft 3l. In other
words, only a force for twisting the torsion bar is required. An actual
steering direction force is obtained by the torque from the motor 3f.
When the motor 3f is rotated in the left-hand direction under the control
of the controller 4, the gear 3h is rotated in the same direction as the
motor 3f. Meanwhile, the steering wheel 1 is supported by the driver, and
so the gear 3j will not rotate even if the gear 3h is rotated. For this
reason, a force directed toward the upper surface of the drawing (FIG. 2)
acts on the motor 3f, so that the motor 3f is pivoted about the support
shaft 3l. The slider 2a is then aligned with the input and output steering
shafts 3a and 3b. A portion of the slider 2a which is in contact with the
resistive element 2b is located in the position prior to steering. In this
case, the controller 4 cuts off a current from the motor 3f, so that the
motor 3f is stopped. When the driver further turns the steering wheel 1,
the output steering shaft 3b is rotated in the same direction as that of
the steering wheel 1, so that an angular displacement is increased.
When a vehicle is turned or rotated at a given steering angle in a steady
circular turn or the like, a reaction force acts from the wheels to the
steering wheel. This reaction force causes the output steering shaft 3b to
transmit a rotational force to the gears 3i and 3h. However, since a force
acts from the steering wheel 1 held by the driver to the input steering
wheel 3a, the gear 3j will not rotate. As a result, the torsion bar 3c is
twisted and the gear 3h orbits around the gear 3j. For this reason, an
output is generated from the torque sensor 2, and the motor 3 continuously
generates a torque, thereby continuing power steering. When the driver
releases the force to change turning of the vehicle to straight travel,
the output steering shaft 3b is rotated by a reaction force from the
wheels in an opposite direction. This rotational force is transmitted to
the gears 3k, 3i, 3h and 3j. The input steering shaft 3a is rotated in the
opposite direction, and the steering wheel 1 then returns to the state
prior to steering.
The above description has been made for turning right. However, the same
operation as in turning right is applied to turning left. Even if the
motor 3f or the controller 4 is broken to disable the motor 3f, the
rotational force of the input steering shaft 3a can be transmitted by the
fail safe stopper 3d (FIG. 5) to the output steering wheel 3b.
A maximum rotation speed of the steering shafts 3a and 3b is about two
revolutions/second, and thus the speed of the motor 3f can be four
revolutions/second, i.e., 240 rpm. A series motor is suitable to obtain a
high torque at a low speed. This motor does not employ a permanent magnet
for generating a magnetic field. The rotor can therefore be smoothly
rotated in the OFF time. When the vehicle changes from turning to straight
travel, the steering wheel can be smoothly moved in the same manner as in
conventional power steering. Furthermore, since the speed of the motor 3f
is lowered, the motor can follow quick and repeated turning of the
steering wheel. Unlike the conventional power steering apparatus which is
directly driven by the motor, a response delay will not occur even in
slalom-like driving. In addition, the steering force is detected by the
torsion bar and the electric resistor, resulting in high reliability. If a
noncontact type distortion meter is used in place of the electric
resistor, a still higher reliability can be obtained.
The electric circuit of the power steering section 3 is shown in FIG. 6.
The same reference numerals as in FIG. 6 denote the same parts as in FIGS.
1 to 4. Referring to FIG. 6, the controller 4 comprises a rotational
direction detector 400 for detecting a rotational direction of the input
steering shaft 2a, a rotational torque detector 410 for detecting a
rotational torque of the input steering shaft 2a, a vehicle speed signal
generator 430 for generating a signal which has a smaller magnitude when a
vehicle speed is increased in response to the signal from the vehicle
speed sensor 9a, and a motor control circuit 440 for multiplying signals
from the rotational torque detector 410 and the vehicle signal generator
430 and for controlling to stop the motor 3f when power steering is not
performed and to increase the torque of the motor 3f when a steering
torque becomes higher or a vehicle speed becomes lower. The vehicle speed
signal generator 430 and the motor control circuit 440 constitute a
rotational torque control circuit. The relay 5 constitutes a means for
controlling the rotational direction of the motor 3f in response to an
output signal from the rotational direction detector 400.
The rotational direction detector 400 comprises resistors 401 to 404,
comparators 406 and 407 and a transistor 408. The rotational torque
detector 410 comprises resistors 411 to 416, operational amplifiers (to be
referred to as op amps hereinafter) 417 and 418, diodes 419 and 420, a
Zener diode 421, a transistor 422, and FETs 423 and 424. A Zener voltage
of the Zener diode 421 is selected to be substantially 1/2 of a voltage V
of the battery 7. The vehicle speed signal generator 430 comprises
resistors 431 to 434, a capacitor 435, an op amp 436 and an F-V converter
437 for decreasing an output voltage when the number of pulses of an input
signal is increased. The motor control circuit 40 comprises a resistor
441, a comparator 442, an FET 443 and transistors 444 and 445.
The circuit arranged described above is operated as follows. In the torque
sensor 2, the slider 2a is located at the ground position side when the
the battery 7 is connected across the resistive element 2b and the
steering wheel 1 is rotated in the left-hand direction. However, when the
steering wheel 1 is rotated in the left-hand direction, the slider 2a is
moved to the power supply side. If the rotating angle of the steering
wheel 1 in the right-hand direction is defined to be positive, a voltage
generated from the slider 2a upon rotation of the steering wheel 1 becomes
V/2 in the nonsteering mode as shown in FIG. 7, a voltage which is higher
than the voltage V/2 for turning right, and a voltage which is lower than
the voltage V/2 for turning left.
A voltage generated in accordance with a given steering state is supplied
to a noninverting input terminal of the comparator 406 in the rotational
direction detector 400 and an inverting input terminal of the comparator
407. However, when the nonsteering mode is set, resistances of the
resistors 401 to 404 are selected such that the comparators 406 and 407
generate signals of logic "0". With this arrangement, since the voltage
from the slider 2a in the right steering mode becomes higher than that in
the nonsteering mode, the voltage at the noninverting input terminal of
the comparator 406 becomes higher than that at the inverting input
terminal thereof, so that the comparator 406 generates a signal of logic
"1". In the left steering mode, the voltage at the noninverting input
terminal of the comparator 407 becomes lower than that at the noninverting
input terminal thereof, so that the comparator 407 generates a signal of
logic "1". Output signals from the comparators 406 and 407 are supplied to
the FETs 423 and 424, respectively. The FET 424 is turned on in the right
steering mode, and the FET 423 is turned on in the left steering mode.
The voltage generated from the slider 2a is supplied to the rotational
torque detector 410 as well as the comparators 406 and 407. In the
rotational torque detector 410, when the op amps 417 and 418 are adjusted
to have constants to generate voltages which are 1/2 of the power supply
voltage in the nonsteering mode, the voltage from the torque sensor 2 in
the right steering mode is increased. The op amp 417 increases an output
voltage in accordance with an increase in steering torque, as indicated by
the solid line in FIG. 8. A collector voltage of the transistor 422
decreases in accordance with an increase in base voltage, i.e., an
increase in steering torque. In this case, the op amp 418 generates a
voltage which decreases in response to an increase in steering torque, as
indicated by an alternate long and short dashed line in FIG. 8, so that
the operation of the op amp 417 will not be influenced. In this case, the
comparator 406 in the rotational direction detector 400 generates a signal
of logic "1", so that the FET 424 is kept ON, and a change in collector
voltage of the transistor 422 is applied to the motor control circuit 440.
In the left steering mode, a voltage generated from the torque sensor 2
decreases, and thus the op amp 418 in the rotational torque detector 410
decreases, as indicated by the solid line in FIG. 8. Therefore, the
transistor 422 shows the characteristics shown in FIG. 9. An output signal
from the transistor 422 is supplied to the motor control circuit 440
through the FET 423.
The vehicle sensor 9a generates a signal having a larger number of repeated
pulses when a vehicle speed is increased. The F-V converter 437 generates
a lower voltage when the number of input pulses is increased. The
noninverting input terminal of the op amp 436 receives a signal whose
voltage decreases in accordance with an increase in vehicle speed. A
voltage at the inverting input terminal of the op amp 436 has a triangular
wave having a high amplitude when a vehicle speed is low. However, when a
vehicle speed becomes high, the triangular wave has a low amplitude.
This triangular signal is supplied to the motor control circuit 440
together with the signal which has the characteristic shown in FIG. 9 and
which is generated from the rotational speed detector 410. The FET 443 is
kept OFF in the nonsteering mode, and the motor control circuit 440 does
not generate the output signal. As a result, the motor 3f does not rotate.
When a steering operation of small torque is performed, a voltage supplied
to the noninverting terminal of the comparator 442 is high, as indicated
by the alternate long and short dashed line a in FIG. 10. The comparator
442 generates a pulse having a small duty ratio. However, when the
steering torque becomes large, a voltage applied to the noninverting input
terminal of the comparator 442 becomes low, as indicated by the alternate
long and short dashed line b. In this case, the comparator 442 generates a
signal having a high duty ratio. When the duty ratio is small, i.e., when
the steering torque is small, an average value of output signals from the
comparator 442 becomes small, and the rotational torque of the motor 3f
becomes small. At the same time, the steering force magnification is also
small. However, when the steering torque is large, the rotational torque
of the motor 3f becomes large and the steering force magnification becomes
large. Even if the vehicle speed changes while a predetermined steering
torque is given, the same operation as described above can be performed.
More particularly, when a vehicle speed is low, the rotational torque of
the motor 3f becomes large. However, when the vehicle speed is high, the
rotational torque of the motor 3f becomes small.
The rotational direction of the motor 3f is determined such that the motor
3f is rotated in the left direction upon the steering wheel 1 turning
left. When the steering wheel 1 is turned in the right-hand direction, the
transistor 408 in the rotational direction detector 400 is turned on to
energize the relay 5. The direction of a current flowing through the motor
3f is reversed, and the rotational direction of the motor 3f is reversed
to perform right turning.
FIG. 11 is a sectional view of a power steering section 10 and a torque
sensor 11 of a power steering apparatus according to another embodiment of
the present invention. Referring to FIG. 11, reference numeral 10a denotes
an input steering shaft; 10b, an output steering shaft; 10c, a torsion
bar; and 10d, a fail safe stopper. The rotational force of the steering
wheel 1 is transmitted to the input steering shaft 10a, and a rotational
force of the output steering shaft 10b is transmitted to a steering
direction control unit 6. One end of the torsion bar 10c is fixed by a pin
10e on the input steering shaft 10a, and the other end thereof is urged
and inserted in a recess of the output steering shaft 10b, so that the
torsion bar 10c is rotated together with the output steering shaft 10b.
Reference numeral 10f denotes a motor; and 10g, a rotating shaft. A gear
10h is fixed on the rotating shaft 10g to be rotated together therewith.
The gear 10h drives through the gear 10i a gear 10j rotated together with
the output steering shaft 10b. In the end portion of the output steering
shaft 10b which is located on the side of the torsion bar 10c, a gear 10k
is integrally formed with the output steering shaft 10b. The gear 10k
meshes with a gear 10l. A portion of the gear 10l on the side of the
output steering shaft 10 b is rotatably inserted in a recess of a housing
10m. A gear 10n is formed integrally with the input steering shaft 10a and
meshes with a gear 10o. One end portion of the gear 10o which is located
at the side of the gear 10l is coupled to the gear 10l through an Oldham's
coupling 10p. The other end portion of the gear 10o is rotatably inserted
in a recess of a movable member 10q. A portion of the movable member 10q
which is not engaged with the gear 10o extends away therefrom. A
concave-shaped sensor element 11a is fixed at the distal end thereof. A
portion of the movable member 10q which is engaged with the gear 10o is
rotatably inserted in a support plate 10r, as shown in FIG. 12, which is a
sectional view taken along the line XII--XII in FIG. 11. The support plate
10r is pivotally fitted with the input steering shaft 10a. An elongated
aperture 10s is formed in the housing 10m along the upper-to-lower-surface
direction of the drawing, and the movable member 10q can be moved along
the same direction. Reference numeral 11b denotes a sensor element fixed
on the housing 10m and extending into the recess of a sensor element 11a.
The sensor elements 11a and 11b constitute the torque sensor 11.
The power steering apparatus having the construction described above is
operated in the following manner. When the driver turns the steering wheel
1 in the right-hand direction, the input steering shaft 10a is rotated in
the right-hand direction. A rotational force from the input steering shaft
10a is transmitted to the gear 10k through gears 10n, 10o and 10l. Since
the gear 10k drives the steering direction control unit 6 through the
output steering shaft 10b, the gear 10k has a large load. The torsion bar
10c is twisted to generate a relative rotational displacement of the input
and output steering shafts 10a and 10b. The gears 10n and 10k are
subjected to the same rotational displacement as in the input and output
steering shafts 10a and 10b and are slid along the Oldham's coupling 10p
and pivoted about the input steering shaft 10a in the lower-surface
direction of the drawing. The movable member 10q inserted in the shaft of
the gear 10o is moved together with the gear 10o. The torque sensor 11
generates an electrical signal corresponding to a displacement of the
sensor element 11a. This signal is supplied to the controller 4 and causes
the motor 10f to rotate in response to the sensor output. In this case,
the motor 10f is arranged to rotate from the right to the left when viewed
from the right side of the drawing (rotation is viewed from the right side
of the drawing, unless otherwise specified). A rotational force is
transmitted to the gear 10j through the gear 10i, so that the output
steering shaft 10b is rotated in the right-hand direction. The output
steering shaft 10b is rotated in the same direction as that of the input
steering shaft 10a to control the steering direction control unit 6,
thereby causing of the vehicle to turn right.
When the output steering shaft 10b is rotated in the right-hand direction,
the gear 10k formed integrally therewith is also rotated in the right-hand
direction. The rotational force of the gear 10k is transmitted to the gear
10o through the Oldham's coupling 10p. The gear 10o meshes with the gear
10n rotated together with the input steering shaft 10a. Since the input
steering shaft 10a is supported by a force acting on the steering wheel 1,
the gear 10n will not be rotated by the rotational force transmitted by
the gear 10o. Instead, the gear 10o is moved from the lower surface of the
drawing to the upper surface thereof along the peripheral surface of the
gear 10n. When the axis of the gear 10l is aligned with that of the gear
10o, and the sensor element 11a returns to the initial position, the
torque sensor 11 will not generate a signal. Subsequently, the motor 10f
is stopped, and the respective gears interlocked therewith are also
stopped.
When the vehicle is completely turned, and the force having acted on the
steering wheel 1 is removed, the force having acted on the gear 10n is
removed. The output steering shaft 10b is rotated in the left-hand
direction by the reaction force transmitted from the steering direction
control unit 6. The gear 10l is rotated in the right-hand direction. In
this case, since the axis of the gear 10l is aligned with that of the gear
10o, the gears 10o and 10l are rotated in the same direction. As a result,
the input steering shaft 10a is rotated in the left-hand direction, and
the steering wheel 1 returns to the initial position.
When the steering wheel 1 is rotated in the left-hand direction viewed from
the driver, a left turn is performed in the opposite manner to the above
description. The circuit for the second embodiment is substantially the
same as that shown in FIG. 6, except that the sensor 11 comprises a
noncontact type sensor.
According to the power steering apparatus of the present invention as
described above, the motor is rotated in response to the output signal
from the torque sensor, and the steering direction control apparatus is
operated by the rotatational force of the motor. Unlike the conventional
power steering apparatus, oil need not be used, thus simplifying the
construction and decreasing the power consumption. In the conventional
power steering apparatus, the motor rotation cannot properly follow quick
turning of the steering wheel, a large sliding noise is generated, and
reliability and sensitivity of steering torque detection are degraded.
However, the power steering apparatus of the present invention solves all
these conventional problems.
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