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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a torque detector which detects torque by
converting the torsion of a mechanism for producing an angular
displacement, such as a torsion bar, into a change of voltage and more
particularly, to the type using a strain gage.
2. Description of the Prior Art
Up to now a number of torque detectors have been disclosed, these being
classified roughly into three types.
The first is the magnetic type torque detector which detects a magnetic
change produced on a torsion bar by application of torque. This type of
torque detector is disclosed, for example, in U.S. Pat. No. 4,506,554.
Although the magnetic type torque detector can detect a torque applied to
the torsion bar by the use of a magnetic sensor such as a coil without
making contact with the torsion bar, it has the problem that an electric
circuit becomes complicated.
The second is the electrostatic type torque detector which detects torque
by converting an angular displacement produced on the torsion bar by
application of torque into a change of electrostatic capacity. This type
of torque detector is disclosed, for example, in U.S. Pat. No. 4,522,278.
Although the electrostatic type torque detector can detect a torque
applied to the torsion bar, a change of electrostatic capacity is
generally small, so that there is the problem that it is not only in need
of a precise electronic circuit, but also apt to be influenced by a change
of surroundings such as humidity.
The third is the resistance type torque detector which detects torque by
converting an angular displacement produced on the torsion bary by
application of torque into a change of electric resistance. Torque
detectors of this type are further classified roughly into two types: one
using a potentiometer and the other using a strain gage. The torque
detector using the potentiometer is disclosed, for example, in Japanese
Patent Laid-Open No. 58-177773. The torque detector using the strain gage
is disclosed, for example, in Japanese Patent Laid-Open No. 59-2099644.
The resistance type torque detector has the problem that the durability is
poor because the potentionmeter or strain gage causes a secular change.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a torque detector
devoid of the aforementioned traditional defects.
It is a second object of the present invention to provide a torque detector
using strain gauges on a cantilever which is easily exchangeable.
It is a third object of the present invention to provide a torque detector
of low cost and high reliability.
To achieve the foregoing first through third objects, the present invention
provides a torque detector which comprises a torque-axial displacement
converting mechanism for converting a steering torque appearing between an
input shaft and an output shaft into an axial displacement, a housing for
accommodating the torque-axial displacement converting mechanism, a
cantilever having one end fixed to the housing with the other end
supported by the torque-axial displacement converting mechanism, and at
least one strain gage attached to the cantilever.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of an apparatus using a torque detector
according to the present invention;
FIG. 2 is a sectional view showing the important portion of the torque
detector according to the present invention;
FIG. 3 is a sectional view showing a displacement member according to the
present invention;
FIGS. 4, 5, and 6 are perspective views showing displacement detectors
according to the present invention;
FIGS. 7 and 8 are sectional views each showing the important portion of a
connection section between the displacement detector and the displacement
member according to the present invention;
FIG. 9 is a circuit diagram showing a strain detecting circuit used in the
displacement detector according to the present invention;
FIG. 10 is a characteristic graph showing the characteristic of detection
output voltage of the strain detecting circuit used in the displacement
detector according to the present invention;
FIG. 11 is a perspective view showing the configuration outline of the
mechanical structure of one embodiment according to the present invention;
FIG. 12 is an enlarged sectional view of a reduction gear unit 109 shown in
FIG. 11, taken along line II--II of FIG. 13;
FIG. 13 is a sectional view taken along line III--III of FIG. 12;
FIG. 14 is a plan view showing the outer surface of a sleeve 130 shown in
FIGS. 12 and 13;
FIG. 15 is a block diagram showing the configuration of an electric control
system of the embodiment;
FIG. 16 is a flowchart showing the outline of the control operation of a
micro processor 147 shown in FIG. 15;
FIGS. 17a and 17b are graphs typically showing data stored in an internal
ROM of the micro processor 147;
FIG. 17c is a plan view showing the correlation between the data of
internal registers of the micro processor 147 and ports to which the data
are output; and
FIG. 18 is a flowchart showing the interrupt processing operation of the
micro processor 147.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will now be described with reference
to the drawings.
In FIG. 1, a housing 11 is fixed to a vehicle, which is made up of divided
portions 11a, 11b, 11c, and 11d coupled together by means, for example, of
screw bolts or welded mutually into a single body.
An input shaft 12 provided inside the housing 11 is composed of a hollow
shaft body 13 having a flange 13a formed on the outer periphery of its
lower end and a connection shaft body 15 fitted in the hole of the hollow
shaft body 12 and coupled integrally therewith by means of a
radially-extending coupling pin 14. The upper end portion of the hollow
shaft body 13 is rotatably supported by the housing 11 via a needle
bearing 16. The hollow shaft body 13 has a spline 13b formed in the upper
portion of its inner wall to be coupled with a steering shaft not shown.
An output shaft 17 provided inside the housing 11 has a cylindrical hole
17a formed in its upper end portion into which the lower portion of the
connection shaft body 15 is loosely inserted, the central portion and the
lower end portion of which are rotatably supported by the housing portions
11b and 11c via ball bearings 18 and 19, respectively.
Inside the lower housing portion 11c of the housing 11 is disposed a
reduction gear unit 21 for transmitting the output of an electric motor 20
fixed in the housing portion 11c from a motor output shaft 20a to the
output shaft 17, which reduces the rotation speed of the motor 20 by means
of a required number of gears. This reduction gear unit 21 is composed of
a gear 21a coaxial with the motor output shaft 20a, gears 25 and 26
attached to a shaft 24 rotatably supported by the housing portions 11b and
11c via ball bearings 22 and 23, respectively, and a gear 27 coaxial with
the output shaft 17.
Inside the upper housing portion 11a of the housing 11 is disposed a
torque-axial displacement converting mechanism 28 which produces a
torsional angular displacement corresponding to the torque of the input
shaft 12 between the two shaft bodies thereof. This torque-axial
displacement converting mechanism 28 is composed of a torque balance
detecting section 28A (see FIG. 2) and an axial converting means 28B (see
FIG. 3).
The torque balance detecting section 28A is fundamentally composed of a
spring 29 which is made of a spring wire rod shaped substantially into the
form of a letter "C", a pin 30 fixed to the flange 13a of the hollow shaft
body 13 and pinched between the mutually-parallel end portions 29a and 29b
of the spring 29, and a pin 33 fixed to a plate 32; having a groove 32a in
which a pin 31 fixed to the output shaft 17 is inserted vertically
slidably and rotatable integrally with the output shaft 17; and pinched
between the two end portions 29a and 29b of the spring 29. The plate 32
has a boss portion 32a being guided by the arcuate portion 29c of the
spring 29 between the two end portions thereof. Between the spring 29 and
the lower end surface of the hollow shaft body 13 is interposed a washer
34.
In the torque balance detecting section 28A of the foregoing configuration,
when no torque is applied to the input shaft 12, the spring 29 is restored
to the original state wherein the two end portions pinch the pins 30 and
33 therebetween and are closest to each other, and the input shaft 12 and
the output shaft 17 takes a neutral positional relation where the
torsional angular displacement is zero. If torque is applied to the input
shaft 12, it acts so as to separate the two end portions 29a and 29b of
the spring 29 from each other, and owing to the elastic deformation of the
spring 29 a torsional angular displacement corresponding to the torque of
the input shaft 12 is produced between the input shaft 12 and the output
shaft 17.
Below the torque balance detecting section 28A is disposed the axial
converting means 28B. This axial converting means 28B is, as shown in
FIGS. 1 and 3, composed of a pin 36 fixed to the lower end portion of the
connection shaft body 15 of the input shaft 12 and extending radially
through a spill port 17b formed in the output shaft 17, a slide member 37
slidably fitted on the upper end portion of the output shaft 17 and having
a long hole 37a in which the pin 36 is slidably fitted, and an upper
flange 37b and a lower flange 37c provided at the lower end of the slide
member 37, the slide member 37 having further a slot 37d oriented in the
direction of the output shaft 17 in which a radially-extending pin 43
fixed to the output shaft 17 is slidably fitted.
Apparently, the slide member 37 is shiftable vertically with respect to the
output shaft 17 by means of the pin 43 and the slot 37d, but cannot
rotate. On the slide member 37 is fitted a cylinder body 44 for preventing
the pins 36 and 43 from coming off.
The long hole 37a of the slide member 37 is oriented in the direction of a
spiral, so that when the torsional angular displacement between the input
shaft 12 and the output shaft 17 is zero, the pin 36 is positioned at the
center between the ends of the long hole 37a, whereas when some torsional
angular displacement is produced between the input shaft 12 and the output
shaft 17, owing to contact between the peripheral surface of the pin 36
and the side surface of the long hole 37a, the slide member 37 is
displaced on the output shaft 17 in the direction of the axis thereof in
proportion to the extent of torsional angular displacement by means of the
cam action, and the upper flange 37b and lower flange 37c are displaced.
Between the upper flange 37b and the lower flange 37c is held a cylindrical
shaft 39 provided on the free end of a cantilever 40. The other end of the
cantilever 40 is tightly screwed by a screw bolt 42 to an attaching base
body 45 fixed to the housing portion 11d. As shown in the drawing, the
attaching base body 45 seals up the housing portion 11d by the aid, for
example, of an O-ring, and the cantilever 40 is secured with interposition
of a washer, for example, by means of the screw bolt 42 so that it is
accurately positioned and tightly attached.
As shown in the perspective view of FIG. 4 illustrating the relation
between the cantilever and the cylindrical shaft, on the cantilever 40 are
formed strain gages 41a, 41b, 41c, and 41d forming a resistance bridge
which are provided on either side of the half portion on the side of a
hole for attaching the screw bolt 42, in such a way that when no
displacement is applied to the free end of the cantilever 40 the output of
strain gages 41a, 41b, 41c, and 41d forming the resistance bridge becomes
minimum, whereas when a maximum displacement is applied to the free end of
the cantilever 40 the output of strain gages 41a, 41b, 41c, and 41d
forming the resistance bridge becomes minimum. Of course, the cylindrical
shaft 39 attached to the free end of the cantilever 40 is configured so
that its contact resistance is small with respect to the displacement of
the upper flange 37b and lower flange 37c of the slide member 37. For
reference, in the embodiment, the material of the cantilever 40 is
phosphor bronze, its surface is coated with an insulating layer, on this
insulating layer are formed the strain gages 41a, 41b, 41c, and 41d in the
form of a thin film circuit by, for example, the process of sputtering,
and these gages are connected with lead wires on the side of the fixed
end. The surface of strain gages 41a, 41b, 41c, and 41d is applied with a
dampproofing coating to block an influence of oil or humidity, and further
coated with silicone rubber, for example.
FIG. 5 is a perspective view of another embodiment of the cantilever, in
which a steel ball 39a is provided at the free end of the cantilever 40
and on the opposite side are bonded the strain gages 41a, 41b, 41c, and
41d by the use of an adhesive agent such as thermosetting adhesives. The
surface of strain gages 41a, 41b, 41c, and 41d is treated in a similar
manner to the case of FIG. 4.
FIG. 6 is a perspective view of still another embodiment of the cantilever,
in which a steel ball 39b is held at the free end of the cantilever 40 by
calking and coupling its first base 70a and second base 70b together. The
strain gages 41a, 41b, 41c, and 41d are bonded by the use of an adhesive
agent such as thermosetting adhesives on the side opposite to the free end
of the cantilever 40. The surface of strain gages 41a, 41b, 41c, and 41d
is treated in a similar manner to the case of FIG. 4.
The cantilever shown in FIG. 6 is attached in the manner described below.
As shown in FIG. 7, in a slide groove 37e between the upper flange 37b and
the lower flange 37c is held the steel ball 39 which is held at the free
end of the cantilever 40 by calking and coupling its first base 70a and
second base 70b together, so that the contact resistance of the cantilever
is made small with respect to the displacement of the upper flange 37b and
lower flange 37c of the slide member 37 by means of the steel ball 39.
The other end of the cantilever 40 is tightly screwed to the attaching base
body 45 fixed to the housing portion lld by means of the screw bolt 42. As
shown, the attaching base body 45 seals up the housing portion lld by the
aid, for example, of an O-ring, and the cantilever 40 is accurately
positioned and tightly attached by screwing the screw bolt 42 with
interposition of a washer, for example.
FIG. 8 is a sectional view of another embodiment of the means for holding
the steel ball of the cantilever, in which the steel ball 39 is held by
screwing its first flange 71a and second flange 71b to the free end of the
cantilever 40, and on the opposite side are bonded the strain gages 41a,
41b, 41c, and 41d by the use of an adhesive agent such as thermosetting
adhesives.
Since the cantilever 40 shown in FIG. 4 is configured so that its balance
in the transverse direction is attained by means of the cylindrical shaft
39, it is possible to make uniform the strains of the strain gages 41a,
41b, 41c, and 41d forming the bridge. Since the cantilever 40 shown in
either FIG. 5 or FIG. 6 has the steel ball 39a, 39b, pinched between the
upper flange 37b and the lower flange 37c, its contact resistance can be
made minimum.
FIG. 9 shows a known strain detecting circuit for connecting the strain
gages 41a, 41b, 41c, and 41d into the form of the bridge circuit and
taking out the output thereof.
In FIG. 9, E designates a constant voltage source, and AMP designates an
amplifier circuit. FIG. 10 shows the relation between the torque detection
output voltage pertinent to the input shaft 12 and the extent of vertical
displacement of the slide member 37. Of course, the vertical displacement
of the slide member 37 and the torque detection output voltage can be set
arbitrarily by selecting the amplification factor of the amplifier circuit
AMP, bias voltage, resistance of the strain gage, etc.
In the embodiment described above, the gap between the outer periphery of
the pin 36 fixed to the connection shaft body 15 coupled integrally with
the input shaft 12 via the coupling pin 14 and the long hole 37a of the
slide member 37 may influence the corresponding relation between the
torsional angular displacement between the input shaft 12 and the output
shaft 17 and the axial displacement of the slide member 37. However, such
an influence can be eliminated by interposing a compression spring 60
between the upper flange 37b of the slide member 37 and the plate 32 to
thereby urge the slide member 37 downward so that the outer periphery of
the pin 36 can contact only with the upper side surface of the long hole
37a.
Further, in order to make a vertical relative displacement (backlash)
disappear from between the input shaft 12 and the output shaft 17 and to
prevent the slidability between the pin 36 and the long hole 37a from
becoming worse and the degree of balance between the upper flange 37b and
lower flange 37c of the slide member 37 and the cantilever 40 whose free
end is supported via the steel ball 39 between these flanges also from
becoming worse: these deterioration would result from twisting appearing
between the two shafts 12 and 17 that would be caused owing to the gap
between the fitted portions of these shafts, as shown in FIG. 3, a tapered
recess 15a is formed at the center of the lower end surface of the
connection shaft body 15 coupled integrally with the input shaft 12 via
the coupling pin 14, another tapered recess 17c is formed at the center of
the bottom surface of the fit hole 17a of the output shaft 17, a steel
ball 46 is interposed between these tapered recesses 15a and 17c, and a
compression spring 48 is provided whose upper end is received by the
inside of the housing portion 11a via a needle bearing (a thrust bearing)
47 on the upper side of the flange 13a of the hollow shaft body 13 of the
input shaft with the lower end received by the flange 13a, so that the
input shaft 12 is pushed against the output shaft 17 via the steel ball 46
by means of the compression spring 48.
Additionally, in FIG. 1, 50 designates a stop ring screwed to the housing,
and 51, 52, and 53 designate snap rings.
The operation of the embodiment thus configured of a steering torque
detector according to the present invention will now be described.
First, as a driver applies a steering torque to the input shaft 12, by the
resilient force of the spring 29 forming the torque balance detecting
section 28A there is produced a relative angular displacement
corresponding to the torque of the input shaft 12 between the input shaft
12 and the output shaft 17, this angular displacement causes a
displacement in the axial direction of the slide member 37 forming the
axial converting means 28B, and the displacement of the slide member 37
changes into a displacement of the free end of the cantilever 40, so that
by means of the strain gages 41 of the cantilever 40 there can be obtained
a torque detection signal output indicative of the magnitude and direction
of the torque applied to the input shaft 12.
Therefore, it is possible to use this torque detection signal output as an
output for a controller of an electric power steering system, to supply
power to the motor 20 in accordance with the output of the controller, and
to apply the turning force of the motor 20 via the reduction gear unit 21
to the output shaft 17.
Although the foregoing embodiment uses the torque balance detecting section
and axial converting means as the torque-axial displacement converting
mechanism to convert the steering torque into the axial or vertical
displacement, in practicing the present invention it should not be limited
to the embodiment described herein, and a means is sufficient for
converting the steering torque into a displacement of reciprocating
action, preferably, into an axial displacement proportional to the
steering torque.
Further, since the slide member forming the torque-axial displacement
converting mechanism moves in the axial direction in response to the
torque of the means for converting into the axial displacement, if the
input shaft or output shaft is made in the form of a ball screw and the
torque-axial displacement converting mechanism is made by a mechanism in
which the ball screw rotates in response to torque, the slide member can
take the form of a nut-like member fitting on the ball screw, or of a
member engaging with a ball screw portion.
Furthermore, although the housing of the foregoing embodiment is divided
into four, it should not be limited to such a configuration in practicing
the present invention. Particularly, although the housing portion lld has
the opening portion designed so as to permit the cantilever to be taken
out freely, it may be combined integrally with a different housing portion
of the cantilever is removable freely.
FIG. 11 illustrates the structural outline of the mechanical section of
another embodiment of the present invention. A first steering shaft 102 to
which a steering wheel 101 is fixed is coupled via a first universal joint
104 to a second steering shaft 105. The second steering shaft 105 is
coupled via a second universal joint 106 to a rod 107. This rod 107 is
coupled to the output shaft of a reduction gear unit 109. The input shaft
of the reduction gear unit 109 is coupled to the rotary shaft of an
electric motor 108. The output shaft of the reduction gear unit 109 is in
gear with a rack (111, in FIG. 12) fixed to a toe bar 110. The toe bar 110
is coupled to a steering knuckle arm 116 of a wheel 112. To the axle of
the wheel 112 is coupled a shock absorber 113, and to a suspension upper
support 114 of the shock absorber 113 is coupled a chassis (not shown).
115 designates a vibration buffering coil spring disposed between the
upper support 114 and the wheel, 118 designates a lower suspension arm,
and 119 designates a stabilizer bar.
The internal structure of the reduction gear unit 109 is illustrated in
FIGS. 12 and 13. The upper end of the rod 107 (FIG. 12) is coupled via the
second universal joint 106 (FIG. 11) to the second steering shaft 105
(FIG. 11). To the lower end portion of the rod 107 (FIG. 12) is fixed the
output shaft 121 of the reduction gear unit 109 by means of a pin 120. The
lower end of the output shaft 121 has a pinion gear 122 formed thereon,
and the hollow upper end of the output shaft 121 has an output gear 123
formed thereon. The output shaft 121 is rotatably supported by a reduction
gear unit casing 124. By the casing 124 is rotatably supported an
intermediate gear 125, this gear 125 being in gear with the output gear
123. Another intermediate gear 126 coaxial and integral with the
first-mentioned intermediate gear 125 is in gear with an input shaft gear
127 fixed to the rotary output shaft 128 of the motor 108. As the output
shaft 128 of the motor 108 rotates, the output shaft 121 is rotated by
means of a train of gears 127, 126, 125, and 123, the rack 111 gearing
with the pinion gear 122 formed on the output shaft 121 is driven in the
direction perpendicular to the sheet plane of FIG. 12 (in the extending
direction of the toe board 110 in FIG. 11), and the direction of the wheel
112 (FIG. 11) is changed.
To the upper end portion of the rod 107 (FIG. 12) is fixed a sleeve 130 by
means of a pin 129, this sleeve 130 being rotatably supported by a
reduction gear unit casing 131. The rod 107 passes through the sleeve 130
and comes into the output shaft 121, and is fixed at its lower end to the
output shaft 121 by means of the pin 120. Therefore, as the steering wheel
101 (FIG. 11) rotates, the output shaft 121 is driven and rotated via the
first steering shaft 102, first universal joint 104, second steering shaft
105, second universal joint 106, and rod 107, as a result, the rack 111
gearing with the pinion gear 122 formed on the output shaft 121 is driven
in the direction perpendicular to the sheet plane of FIG. 12 (in the
extending direction of the toe bar 110 in FIG. 11) and the direction of
the wheel 112 (FIG. 11) is changed.
In this way, the direction of the wheel is changed by means of either the
rotation of the output shaft 128 of the motor 108 or the rotation of the
steering wheel 101.
On the sleeve 130 is rotatably mounted a wheel 132. That is, the sleeve 130
passes through the wheel 132. As shown in FIG. 14, in the outer surface of
the sleeve 130 is formed a round-bottom groove 133 obliquely crossing the
center axis of the sleeve 130, and in this round-bottom groove 133 is
fitted a ball 134. This ball 134 is supported by the wheel 132. In the
wheel 132 is formed a narrow groove 135, and in this groove 135 is
inserted the upper end of a pin 136 fixed to the upper end of the output
shaft 121. This pin 136 restricts rotation of the wheel 132.
As the rod 107 rotates, the sleeve 130 and the output shaft 121 are
rotated; but, because the sleeve 130 is fixed to the upper end of the rod
107 and the output shaft 121 to the lower end of the rod 107, the rod 107
is twisted when the load of the output shaft 121 is large. In proportion
to the extent of torsion, the turning angle becomes different between the
sleeve 130 and the output shaft 121, and this difference of turning angle
is transformed into a difference of turning angle between the sleeve 130
and the wheel 132 because the wheel 132 is caused to rotate together with
the output shaft 121 by means of the pin 136. That is, in proportion to
this difference of turning angle the sleeve 130 rotates additionally more
than the wheel 132, the ball 134 is pushed upward or downward by means of
the groove 133 of the sleeve 130 because this groove 133 obliquely crosses
the center axis of the sleeve 130, and the wheel 132 supporting the ball
134 is moved upward or downward. The torsion of the rod 107 corresponds to
the steering torque applied to the steering wheel 101, and the wheel 132
is moved to an up or down position corresponding to the extent of torsion.
Accordingly, the up or down position of the wheel 132 (correctly, the
distance it has moved upward or downward from the steering torque=zero
position) corresponds to the steering torque.
The wheel 132 has a ring-like groove 137. In this groove 137 are inserted a
first ball 139 and a second ball 142. This arrangement is illustrated in
FIG. 13.
The first ball 139 is rotatably supported by one end of a first elastic
plate 138, whereas the second ball 142 is rotatably supported by one end
of a second elastic plate 141 at the symmetrical position with the first
ball 139 about the center axis of the rod 107. The other ends of the first
and second elastic plates 138 and 141 are fixed at respective positions
symmetrical with respect to the center axis of the rod 107.
A first strain gage unit (an electric element whose resistance changes in
response to strain) 140 is bonded to the first elastic plate 138, which
unit is composed of four strain detecting segments provided two on each
side of the first elastic plate 138. Similarly, a second strain gage unit
(an electric element whose resistance changes in response to strain) 143
is bonded to the second elastic plate 141, which unit is composed of four
strain detecting segments provided two on each side of the second elastic
plate 141. A first displacement detecting means composed of the first ball
139, first elastic plate 138, and first strain gage unit 140 is exactly
identical in structure to a second displacement detecting means composed
of the second ball 142, second elastic plate 141, and second strain gage
unit 143, but, differs only in disposition from the former. In either
displacement detecting means, the four strain detecting segments are
connected into the form of a bridge, and a voltage is taken out as a
torque detection signal which corresponds to the difference of resistance
between the segments provided on respective sides (since one side receives
a compressive stress and the other side a tensile stress, and one signal
generated differs in polarity from the other, the difference has a level
which is two times the detected level of one side). Accordingly, as the
wheel 132 moves upward or downward in response to twisting of the rod 107,
the first and second elastic plates 138 and 141 warp upward or downward,
as a result, the first and second displacement detecting means generate
electric signals indicative of the extent of deviation of the wheel 132
(the extent of deviation from the steering torque=zero position), or the
extent of torsion of the rod 107, or the steering torque.
The first and second displacement detecting means are symmetrically
disposed, the wheel 132 is of the form of a ring, and the wheel 132 is of
the center support type and is supported by the first and second elastic
plates, so that the wheel 132 moves up and down smoothly and its posture
leans hardly, thus, variations of the detection value of the first and
second displacement detecting means caused by tolerance or backlash of a
mechanical coupling mechanism provided between the sleeve 130 and the
wheel 132 are small, and the detection value stabilizes. If the wheel 132
inclines, the detection signal level of one of the first and second
displacement detecting means becomes high with the other detection signal
level becoming low. In this case, if the average of these signals is taken
as the torque detection value, a more accurate detection value can be
obtained.
FIG. 15 illustrates the configuration of an electrical control system for
energizing the motor 108 on the basis of the detection signals of the
first and second displacement detecting means.
The motor 108 is connected with switching transistors 163 through 166 of a
motor energizing circuit 180. When both the transistors 163 and 165 are
ON, the motor 108 rotates normally, hence, the output shaft 121 is driven
to rotate clockwise (this corresponds to the clockwise rotation of the
steering wheel 101, or right turn). When both the transistors 164 and 166
are ON, the motor 108 rotates reversely, hence, the output shaft 121 is
driven to rotate counterclockwise (this corresponds to the
counterclockwise rotation of the steering wheel 101, or left turn). The
transistors 165 and 166 are for determining the rotation direction of the
motor 108, and the transistors 163 and 164 are for turning ON/OFF the
energizing current of the motor 108 at a designated duty to control an
effective current value (the time series average of the energizing current
by which the output torque of the motor is determined).
The collectors of the transistors 163 and 164 are connected via a relay 161
to the plus terminal of a car battery. The emitters of the transistors 165
and 166 are connected via a resistor 172 for detection of a current to the
minus terminal of the car battery (the earth of the apparatus).
A switching driver (a transistor ON/OFF-energizing circuit) 167 turns ON
the transistor 165 when an input of high level H is given and keeps the
transistor 165 OFF when the input is at a low level L. A switching driver
168 turns ON the transistor 166 when the input of high level H is given
and keeps the transistor 166 OFF when the input is of the low level L.
A switching driver 170 turns ON the transistor 163 when the output of a
pulse width modulator 171 is H and the input to the driver 167 is H and
keeps the transistor 163 OFF when one of these signals is L. A switching
driver 169 turns ON the transistor 164 when the output of the pulse width
modulator 171 is H and the input to the driver 168 is H and keeps the
transistor 164 OFF when one of these signals is L. A relay driver 160
energizes the relay 161 when the output of an AND gate 159 is H to connect
the collectors of the transistors 163 and 164 with a battery 162. When the
output of the AND gate 159 is L, the relay 161 is deenergized to
disconnect the collectors of the transistors 163 and 164 from the battery
162. To the AND gate 159 are applied a relay-ON (energization: H)/OFF
(deenergization: L) directive signal from a micro processor 147 and a
relay-ON (energization: H)/OFF (deenergization: L) directive signal A from
a stop directing circuit 190 hereinafter described. Accordingly, the relay
161 is energized only when the micro processor 147 is directing relay-ON
and the stop directing circuit 190 is directing relay-ON.
The pulse width modulator 171 is, in the embodiment a digital timer
composed of a preset counter, a clock pulse oscillator, and a controller,
and repeats the steps of loading data Hd into the counter, providing an
output of high level H (a transistor-ON directive) until the counter
generates a carry (count-over of Hd), changing the output to L (a
transistor-OFF directive) and loading Ld into the counter when a carry is
generated, and loading data Hd into the counter and changing the output to
H when the counter generates a carry. That is, the pulse width modulator
171 generates a pulse train of the duty of Hd/(Hd+Ld) in which the level
is H during the time interval indicated by data Hd, L during the time
interval indicated by data Ld, H during the time interval indicated by
data Hd, and so on. For reference, if Hd is zero data, the output of L
continues.
Data Hd and Ld specif | | |
