Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Drive device and torque sensor and method of producing it
Technical field
The invention relates to a drive device according to the
preamble of Claim 1. Furthermore, the invention relates to a
torque sensor according to the preamble of Claim 18 and to a
method of producing it according to the preamble of Claim 24.
Prior art
Muscle-power drives assisted by electromotive force are
known, in particular in vehicles, e.g. in bicycles driven by
foot pedals. Important factors in such drives are their
spatial requirement and the detection by measurement of the
[lacuna] produced by muscle power and/or of the motor torque.
Known solutions are often too heavy and too large and have an
inadequate torque-measuring range or a resolution which is
too inferior, or only the rotational speed or the angular
velocity is used instead of a real torque measurement.
It is desirable to be able to control the output of the
electric motor in such a way that its torque can be added to
or superimposed on the biological force in real time and
comfortably according to biomechanically optimum
characteristics, so that the auxiliary force is smoothly
connected to the system; this imposes corresponding
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requirements on the accuracy and resolution of the torque
sensory system.
In the already existing muscle-power-amplifying
auxiliary drives of commercially available electric bicycles
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imposes corresponding
requirement a accuracy and resolution of the torque
sensory system.
In the already existing g u's~~"~ower-amplifying
a
in which the auxiliary drive sits in the region of the pedal
bearing, the motor is usually arranged outside the pedal
bearing, so that the motor spindle is parallel to or at right
angles to the pedal spindle. In these known drive concepts,
the problem occurs that they consist of many individual parts
and therefore require a relatively large amount of space.
This results in losses in the overall efficiency, a large
maintenance cost, wear, a high weight, increased
susceptibility to dirt, etc.
DE-A-195 22 419 shows a gearless drive unit which is
arranged coaxially to the pedal spindle and is designed for
retrofitting conventional bicycles and in which a stator of
an electric motor and a rotor combined with the sprocket
wheel are arranged outside the pedal-bearing cartridge in an
exposed position on the bicycle. The electric motor has a low
rotational speed within the range of the pedal rotational
speed. Rotary-measuring [sic] strips at the connecting point
between crank star and sprocket wheel are used as torque
sensors. The retrofit solution shown in this document has
various disadvantages. The conventional bicycle frame offers
little installation space in the pedal-bearing region, so
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that the motor width is greatly restricted as a result . The
torque required for satisfactory and ample motor assistance
can only be achieved by a large diameter in this type of
construction, a factor which reduces the ground clearance in
the pedal-bearing region.
Owing to the fact that the drive is located in the
region of spray water, this results in a correspondingly high
maintenance cost, increased susceptibility to dirt, and wear.
The installation of an effective seal is very complicated,
since the interface of rotor and stator is on a large
diameter. The torque applied by the cyclist, which torque may
be highly pulsating depending on the crank position, is
passed on via the rotor, mounted only on one side, and
transmitted to the bicycle chain via a single transmission
point. This results in large torsional stresses in the motor
region, so that it is difficult to exactly maintain a uniform
air gap between rotor and stator.
EP-A-0743 238 shows a drive unit for a bicycle in
which a motor having a small diameter and higher rotational
speed is used, for which reason transmission gearing is
fitted for adapting the very low pedal-spindle rotational
speed to the higher rotational speed of the motor. Since the
comparatively very high cyclist torque has to be "stepped up"
via this gearing, considerable losses result. Owing to the
fact that the rotational speeds of motor and drive gear are
relatively high, a freewheel clutch is required for
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decoupling the motor during travel operation without motor
assistance, otherwise a large motor braking torque results
during this travel operation. Furthermore, pushing the
vehicle backward is made more difficult.
Since a freewheel is fitted in the train of the
force-transmission flow from pedal spindle to the output
wheel for decoupling the pedals during pure motor travel
operation, a back-pedalling brake can no longer be used
without additional attachments. The torque is detected by a
load cell at the supporting point of the gear housing, which
is arranged in the drive housing.
Furthermore, w0 97/05010 shows a wheelchair having
wheel-hub motors and muscle-power actuation by a handrail, a
sensor being arranged between handrail and the rotor in order
to detect the torque induced via the handrail.
In the most diverse applications, such as, for
example, motor-driven screwdrivers, drilling machines, motor-
operated drives in general and in particular motor-operated
actuators or the abovementioned electromotive auxiliary
drives of vehicles actuated by muscle power, it is desirable
to be able to detect torque. Various mechanical torque
sensors are known, which, however, often have a complicated
construction and their detection principle makes integration
in an fre . d
-7 82 romec
'sted 8 890 shows
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electronic motor control complicated. EP-A-683 093 and
EP-A-700 825 show electromechanical torque sensors in
bicycles assisted by electric motor, in which the torque is
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detected via the stroke of a lever, extending transversely in
the housing, and a stroke sensor. GB-A-2 312 403 shows an
electric bicycle drive in which a motor with gearing and
freewheel is arranged in a housing coaxially to the pedal
spindle. US-A-3 938 890 shows electro-optical torque
detection, which in drives which contain lubricants can
result in problems with the optical detection. EP-A-682 238
shows a torque-measurement device in which a magnetic field
is produced by a coil and is transmitted via two pole-pair
arrangements on either side of a torsion section. The
magnetic coupling of the poles, which are separated by an air
gap, depends on torsion and thus on torque. The magnetic
field passes into and out of the poles via an air gap.
Magnetic-field sensors are provided at the return point in
order to detect the torque- or torsion-dependent change in
the magnetic field. From the signal of the magnetic-field
sensors, an output signal corresponding to the torque is
produced in an analyzing circuit. The production of the
device is expensive, since the poles are designed as pins
which have to be arranged individually in apertures of the
respective non-magnetic carrier, and this has to be done very
precisely in order to keep the air gap between all the
opposite pins as uniformly large as possible. In restricted
installation conditions and with correspondingly small
dimensions, such a device is complicated and expensive to
produce. US-A-4 876 899 shows a torque sensor having
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continuous pole arrangements on either side of a torsion
section, in which pole arrangements introduction is effected
via a central coil and the outputting is effected via two
lateral coils.
The object of the invention, on the one hand, is
therefore to provide a motor-assisted muscle-power drive
which has a simple construction, requires little space and is
insensitive to dirt and spray water for applications in
vehicles and the torque detection of which enables the torque
produced by muscle power to be detected as far as possible
free from delay and with high resolution. This object is
achieved in a drive device of the type mentioned at the
beginning having the characterizing features of Claim 1.
Owing to the fact that the torque-detection unit is
arranged centrally in the housing and can receive the muscle-
power torque directly. [sic] this results in both a compact
drive arrangement and the possibility of detecting the torque
with good resolution and without interference from gear units
or mechanical transmission members. Furthermore, the torque-
detection unit is accommodated in the housing in a protected
manner.
In a preferred embodiment, the torque-detection unit
comprises a sleeve which at least partly accommodates the
spindle and may also be part of the rotor or be connected to
the latter preferably via a transmission ring, to which the
output wheel is also fastened. The torque-detection unit may
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be designed with strain gages; however, it preferably has a
torque sensor having magnet poles, which are arranged on
either side of a torsion section and change their relative
position during torsion of the section, which results in a
change in a magnetic variable, this change corresponding to
the torque. A preferred field of use of the drive is in an
electric bicycle.
On the other hand, the object of the invention is to
provide a torque sensor which is compact and simple in
construction and thus simple and inexpensive to produce and
which nonetheless has a high resolution and good measuring
accuracy for the torque.
The object is achieved by the characterizing features of
Claim 18. The arrangement of an annular coil around the
torsion member, while maintaining a simple construction,
results in the possibility of a radially or axially low
overall height of the sensor, and the magnetic variable is
detected by a further coil arranged around the torsion member
in an annular manner.
Furthermore, the object of the invention is to
provide a method of producing a torque sensor having magnet
poles which permits its simple and cost-effective production
even in the case of a high number of poles and with very
small air-gap tolerances.
This object is achieved by the characterizing features
of Claim 24.
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Owing to the fact that first of all a ring is formed and
connected to the holding parts and that only then are the
poles cut out of the ring, cost-effective production results,
since the poles do not have to be fastened individually to
the holding parts; furthermore, due to the subsequent forming
of the poles in the fitted state, the accuracy of the air
gaps is determined essentially only by the cutting operation,
which is preferably carried out with a laser.
The poles are preferably already preformed at a flat
strip before the latter is rounded to form the ring, a factor
which reduces the number of subsequent cutting operations.
Brief description of the drawings
Exemplary embodiments of the invention are explained in
more detail below with reference to the drawings, in which:
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achieve es
of Claim 24.
Owing to the fact that first of all a ring formed and
connected to the holding parts and that o then are the
poles cut out of the ring, cost-effective roduction results,
since the poles do not have to be f stened individually to
the holding parts; furthermore, d to the subsequent forming
of the poles in the fitted s te, the accuracy of the air
gaps is determined essentia y only by the cutting operation,
which is preferably car ed out with a laser.
The poles are referably already preformed at a flat
strip before the atter is rounded to form the ring, a factor
which reduces he number of subsequent cutting operations.
Brief description of the drawings
Exemplary embodiments of the invention are explained in
--~~ cn
Figure 1 shows a sectional representation of a first
embodiment of the drive device;
Figure 2 shows a sectional representation through a further
embodiment of the drive device;
Figure 3 shows a side view of a bicycle;
Figure 4 shows a schematic diagrammatic magnetic-field torque
sensor;
Figure 5 shows a schematic side view of poles and the
magnetic-field introduction of the sensor of Figure 4;
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Figure 6 shows a schematic plan view of a partial development
of the poles of the sensor of Figure 4;
Figure 7 shows a plan view of a stamping for producing the
poles of the sensor;
Figure 8 shows a ring part pushed onto two holders on a
torsion section and intended for forming the poles;
Figure 9 shows a sectional representation of a drive device
similar to that of Figure 1 having a magnetic-field torque
sensor.
Best way of implementing the invention
Figure 1 shows a drive device according to the invention
in an electric bicycle in section. In this case, the pedal
spindle 1 is mounted as a central spindle inside the rotor 6
of the electric motor 10, the rotor consisting of the
magnetic return ring 7 having the magnets 8, the disk-shaped
rotor body 6a and a sleeve part 6b, which encloses the
central spindle 1 and in which the pedal spindle 1 is guided
axially and radially by suitable means. However, the mounting
of the pedal spindle 1 may also be modified by virtue of the
fact that the pedal spindle 1 may be mounted directly in the
housing 15 or partly in the housing 15 and partly in the
rotor 6. The pedal cranks 4, 5 having the pedals 2, 3 (only
partly shown) are fastened to the ends of the pedal spindle
1. In order to transmit the muscle-power torque, the pedal
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cranks 4, 5 are detachably connected to the pedal spindle 1,
but a fixed connection is also conceivable.
The spindle 1 is firmly connected to the sleeve 6b at
location 18, e.g. by welding. The spindle 1 is rotatably
mounted in the sleeve 6b at location 19 , a . g . by means of a
sliding intermediate layer. In this way, the torque of both
cranks is passed into the sleeve 6b via the spindle 1 at
location 18.
The drive housing 15 is firmly connected to the frame
16; if need be it may be detachably fastened or be designed
as an integral frame part.
The sprocket wheel 11, which in this case serves as
output wheel, is connected to the rotor 6 so as to be fixed
in terms of torque, but is connected to the pedal spindle 1
in a torsionally elastic manner via the sleeve part 6b of the
rotor 6. The sprocket wheel 11 sits on the sleeve part 6b of
the rotor 6 on the outside of the housing 15 and is in
engagement with the rear wheel of the bicycle by means of a
force-transmission means 12, e.g. a chain. However, the
coupling between sprocket wheel 11 and rotor 6 could also be
effected in another way by the sprocket wheel sitting
directly on the radially running disk-shaped rotor body 6a or
by being designed as an integral part of the rotor body. The
rotor 6 is in each case supported via a bearing 13, 13' both
on the side of the output wheel 11 and on the other side of
the pedal spindle 1. Alternatively, the rotor 6 could be
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mounted, for example, both in the housing 15 and on the pedal
spindle 1. Rolling-contact bearings or sliding bearings are
suitable as bearings for both the rotor mounting and the
pedal-spindle mounting, and in the simplest case, in which no
relative movement takes place between rotor and spindle, the
support may be effected as a fixed connection. The bearings
of the pedal spindle and of the rotor advantageously lie in
one plane; but a position of the bearings relative to one
another which differs therefrom is also conceivable. The
electric motor 10, consisting of stator 9 and rotor 6, is
arranged coaxially to the pedal spindle 1. It may
advantageously be designed as a permanently excited
synchronous motor, the stator 9 being firmly connected to the
drive housing 15 or being provided as a housing part. A very
expedient motor configuration is obtained through the use of
an external rotor.
The torque-detection unit 14 is arranged centrally in
the housing coaxially to the pedal spindle 1 and is assigned
directly to the rotor sleeve part 6b. In this case it detects
the torsion of the sleeve 6b on the basis of the muscle-
power-produced torque induced in this sleeve 6b. The
detection is effected, for example, by means of a torque
sensor having a strain-measuring element fastened to the
sleeve or preferably having a magnetic-pole sensor, as will
be explained. The unit 14 is located entirely in the interior
of the drive housing 15 and, in the example shown, can detect
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both torque on the rotor sleeve part 6b and torque on the
disk-shaped rotor body 6a by means of the strain gages 31 and
32 shown. Thus, depending on the design of the motor control,
both the muscle-power torque and the motor torque can be
detected individually or both together by means of the rotor
parts 6a, 6b, which are under torsional stress due to the
torque and serve as measuring section. The torque originating
from the pedal force of the cyclist is detected via the
deformation of the rotor sleeve part 6b as a result of
torsion and is measured and analyzed by an operatively
connected, electronic sensory measuring system. If, for
example, torque is transmitted by the pedals 2, 3, the torque
signal obtained is processed in real time by a motor control
unit 17, which may also be integrated in the drive interior,
and controlled in accordance with the electric motor 10 or
its torque is adapted to the instantaneous power requirement.
In this way, freewheels or clutches may be completely
dispensed with, which leads to a low-wear drive unit and a
correspondingly high efficiency.
Figure 2 shows, in section, a modification of the drive
device integrated in the pedal-bearing region of an electric
bicycle. The pedal spindle 1 is again placed as a central
spindle inside the rotor 6 of the electric motor 10 and is
mounted partly in the housing 15 and partly in the rotor 6.
However, this may also be achieved as in Figure 1.
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The pedal cranks may again be fastened to the ends of
the pedal spindle . The drive housing 15 is firmly connected
to the frame; if need be it may be detachably fastened or
designed as an integral frame part. In this example, the
spindle 1 is provided with an annular part lc in the center,
and this annular part lc is firmly connected to the sleeve 6b
of the rotor 6. Here, too, a sliding intermediate layer 19 is
provided between spindle and rotor. In this design, via the
two torsion sections la, lb, which each form a part of the
pedal spindle 1, two different torques, the torques of both
cranks, are separately detected and analyzed. The sprocket
wheel 11 (output wheel) again sits on the rotor 6 on the
outside of the housing 15 so as to be fixed in terms of
torque and is in engagement with the rear wheel of the
bicycle by means of a force-transmission means 12, e.g. a
chain. However, the coupling between sprocket wheel 11 and
rotor 6 could also be effected in another way by the sprocket
wheel sitting directly on the radially running disk-shaped
rotor body 6a or by being designed as an integral part of the
rotor body. The rotor 6 or respectively the pedal spindle 1
is in each case supported via a bearing 13 , 13' both on the
side of the output wheel 11 and on the other side of the
pedal spindle 1. Alternatively, the rotor 6 could be mounted,
for example, on either side in the housing 15. Rolling-
contact bearings or sliding bearings are suitable as bearings
for both the rotor mounting and the pedal-spindle mounting.
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The electric motor 10, consisting of stator 9 and rotor
6, is arranged coaxially to the pedal spindle 1. It is
preferably designed as a permanently excited synchronous
motor, the stator 9 being firmly connected to the drive
housing 15 or being provided as a housing part. A very
expedient motor configuration is obtained through the use of
an external rotor.
The torque-detection unit is located entirely in the
interior of the drive housing, consists of two parts 14a, 14b
in this case and is arranged coaxially to the pedal spindle
1. Thus, depending on the design of the motor control, the
torques of both cranks may be separately detected and
analyzed. The torques originating from the pedal forces of
the cyclist are detected via the deformation of the pedal-
spindle torsion sections la, 1b, e.g. again via strain gages
or magnetic-pole sensors, and are measured and analyzed by an
operatively connected, electronic sensory measuring system.
By a motor-control unit 17, which is known per se and is not
explained in any more detail here and which may also be
integrated in the drive interior, the torque signals obtained
are processed in real time and controlled in accordance with
the electric motor 10 or its torque is adapted to the
instantaneous power requirement. Freewheels or clutches may
again be completely dispensed with, which leads to a low-wear
drive unit and a correspondingly high efficiency.
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Figure 3, as a side view, shows how, for example, a
complete concept for a fully sprung electric bicycle 30
having the drive device 1 according to the invention may
look. The main frame 25 is connected to the drive link 28 via
pivot 24 and spring/damper element 21. Frame struts 4 connect
the main frame 25 and seat pillar 26. The drive device 1 sits
in the drive link 28. The battery container 18 forms the
actual energy box, in which the charging device, the motor-
control unit, removed from the drive in this example, and
possible displays 23 can be accommodated. The rear wheel hub
22 may be designed with a commercially available hub gear, a
derailleur gear or a combination of both.
Figure 4 shows a torque sensor which has two holding
members 36 and 37, which are fastened separately from one
another on a tors ion member 3 8 , a . g . a shaf t or sleeve . In
this case, that region of the torsion member 38 which lies
between the holding members 36 and 37 forms a torsion
section, the torsion of which is determined by means of the
magnet poles arranged on the holding members 36 and 37. Only
some of the magnet poles 40-45 of the one holding member or
50-56 of the other holding member are shown in Figure 4, said
magnet poles being fastened to the holding parts all around
the torsion member. The magnet poles 40 [lacuna] are arranged
so as to point toward one another, in which case they are
staggered relative to one another in the example of Figure 4.
A magnetic flux is produced in the poles by a coil 48 (only
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intimated in Figure 4) extending in an annular manner around
the holding part 36. In this case, the magnetic flux is fed
from the stationary coil 48 into the poles 40 to 45 of the
holding part 36 via their respective rear end regions 40' to
45'. In this case, in the example of Figure 4, the magnetic
field is fed in via the coil 48 and the torsion-induced
change in the magnetic flux through the poles is detected by
means of a further coil 58, which is directed in an annular
manner around the holding part 37 or around the poles 50-56
with their end regions 51'-55' shown. The magnetic flux is
preferably introduced via an air gap in a non-contact manner,
so that the torsion member 38 with the holding parts 36, 37
fastened thereto or the poles can rotate relative to the
stationary coils. The torque at a rotating shaft or sleeve 38
can therefore be detected, thus, for example, at a shaft of a
drive moved by muscle power or by a motor.
Figure 5 and Figure 6 show schematic representations for
explaining the mode of operation of the torque sensor of
Figure 4. In this case, Figure 5 shows a side view of two
respective magnet poles 42, 43 and 52, 53, and Figure 6 shows
a plan view of such magnet poles for explaining the magnetic
flux. The torsion member 38 is again shown in Figure 5 and
forms a torsion section 39 between the holding parts 36 and
37 intimated, for which purpose the torsion member may also
have a zone of weakening at this location, as shown by the
reduced cross section over the torsion section 39. The
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torsion member is shown in half vertical section above its
center axis D; the other parts of the drawing, however, are
only shown schematically for explaining the mode of operation
together with the likewise schematic view of Figure 6. Thus
the holders 36 and 37 for the magnet poles are only
intimated. The coil, likewise only intimated by a pair of
winding wires 48, is arranged in a yoke 47, the legs 47' of
which point toward the end pieces 43' and 42' respectively of
the magnet poles 42 and 43 shown. When current flows from a
source 60 indicated, which feeds the coil 48, in the
direction of the current-flow symbol 49, a magnetic south
pole S and north pole N respectively are obtained at the yoke
legs 47'. The magnetic flux produced as a result in the
magnet poles 42 and 43 is shown by the broken lines F in
Figure 6. In the idle state of the torque sensor, i.e.
without torsion of the torsion section 39, the magnet poles
42, 43 and 53 and 54 are located opposite one another as
shown in Figure 6. In this figure, the position of the yoke
legs 47' is indicated by broken lines. The annular coil 48
surrounding the holding part, with its annular yoke 47, which
likewise extends around the holding part 36, produces a
magnetic flux F, which essentially passes at the front end of
the magnet pole 42 through the air gap d into the magnet pole
53 and from the latter again into the magnet pole 43 and back
to the yoke 47. A small portion of the flux may also flow in
this position via the magnet pole 53 or its end 53' and via
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the yoke 57 of the coil 58 into the end 54' of the magnet
pole 54 and through the latter back to the magnet pole 43 and
the yoke 47. This small magnetic flux produces an electric
voltage in the coil 58, which in Figure 5 is also only
intimated by a pair of winding wires, and this electric
voltage may be amplified in an amplifier 61 and rectified in
a rectifier 62. In this case, the voltage induced in the coil
58 in the idle state corresponds to the lower value of the
detectable torque, since torsion of the torsion section 39
still does not occur in this idle state. If a torque which
leads to torsion of the torsion section 39 is now
transmitted via the torsion member 38, the holding member 36,
for example, rotates relative to the holding member 37 in
such a way that a movement of the magnet poles 42, 43 in the
direction of arrow B in Figure 6 is obtained. The magnet
poles 42 and 53 and respectively 43 and 54 are displaced
relative to one another in such a way that their end faces
have a slight overlap over the air gap d, a factor which
leads to the magnetic flux passing increasingly via the
magnet poles 53 and 54 and via the yoke 57, so that the
voltage induced in the coil 58 increases . In this case, the
increasing voltage in the coil 58 or after amplification and
rectification at the output of the rectifier 62 is
approximately proportional within the measuring range to the
rotation of the torsion section 39 or to the torque induced
in the torque sensor. Thus, for example, with a torque sensor
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of a few centimeters diameter, a torque of 1 Nm up to 300 Nm
can be measured in this way with good resolution at an
appropriately designed torsion section. In this case, the
value of 300 Nm may produce a rotation of about 1.5° of the
torsion section. If the coil 47 is fed with a voltage signal
of 3.5 V and a frequency of 14 kHz, a useful signal in the
coil 58 of 5 mV, which may be amplified and rectified, is
obtained. The DC voltage delivered at the rectifier 62 may be
delivered as a measured value for the torque to a display
device or an open-loop or closed-loop control, which controls
a drive for example. In a preferred type of use, the muscle-
power torque at a pedal spindle or a sleeve connected to the
latter is detected in said manner and used for the open-loop
or closed-loop control of an electric auxiliary drive. The
essentially band-shaped configuration of the magnet poles
which is shown in Figure 4 permits a small overall height of
the torque sensor, which is advantageous for its use in a
wide variety of drives or for a wide variety of torque-
measuring tasks. The feeding or the measuring of the magnetic
flux by means of ring coils, as likewise shown in Figures 4-
6, likewise permits the design of the torque sensor with a
small diameter or a small overall height.
In this case, the embodiment shown, having a number of
magnet poles completely staggered relative to one another, is
only to be understood as a preferred example. The magnet
poles, pointing toward one another, of the two holding parts
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36 and 37 could also be staggered relative to one another to
a smaller degree in the idle state or could also be exactly
opposite one another. The latter case results in the maximum
magnetic coupling from the coil 48 to the coil 58 when the
torsion section is not rotated. Rotation of the torsion
section then results in less coupling to the coil 58 and thus
a signal decreasing in accordance with the torque. More than
one row of magnet poles, as disclosed by EP-A-0682 238,
could also be used.
The sensor described is produced according to the
invention by a closed ring first of all being formed from the
ferromagnetic material forming the magnet poles, this
ferromagnetic material preferably being in the form of a
band. This ring is now pushed onto the two ends of the non-
magnetic holding parts 36, 37 and fastened there at those
points where the poles are to be fastened to the holding
parts. This may be effected, for example, by spot-like
adhesive bonding of the ring to the holding parts 36 and 37.
The latter are fastened to the torsion member 38 at the same
time or subsequently, e.g. likewise by adhesive bonding or
pinning. The magnet poles are then cut out of the closed ring
by a laser beam, in which case the parts of the ring which
are fastened to the holding parts 36 and 37 form the magnet
poles and the unfastened parts are removed as cut waste. In
this case, a circumferential cut in the center of the ring
separates the poles of the two holding parts from one
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another. The non-fastened parts of the ring which lie between
the poles of each holding part are released from the poles by
cuts along the lateral lines of the cylindrical ring. After
the poles have been formed, they may be fastened to the
holding parts in a more intensive manner by a casting
compound for example. The production method described has the
advantage that the magnet poles do not have to be separately
formed beforehand and fastened individually to the holding
parts, and that, by the fastened ring being cut with the
holding parts already positioned relative to one another on
the torsion member, an air gap which is uniform to an
extremely accurate degree over the circumference of the
torque sensor is produced, which permits corresponding
accuracy and fine resolution of the torque measurement.
A modified, preferred production method is explained
with reference to Figures 7 and 8. In this case, Figure 7
shows a pole strip 65 of ferromagnetic material, which has a
continuous web 66 and legs 67 projecting from the web 66 in a
staggered manner. The legs may also have a different length
from one another. Such a strip may be produced, for example,
by a stamping or cutting operation. The successive legs 67 of
each side of the pole strip are then alternately bent
approximately in such a way as shown schematically in Figure
for the successive pole strips 42 and 43 or 52 and 53
respectively. The pole strip bent in this way is then bent
into a ring, as partly shown as ring 69 in Figure 8. In this
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case, the actual ring is formed by the web 66, and the bent
legs 67 proj ect from this ring on both sides . The pole ring
69 in this case is now pushed with its legs 67 onto the non-
magnetic holding parts 36 and 37 respectively, in which case
the latter, as shown in Figure 8, may be of stepped design
and may be provided with slots 70 and 71, in which the legs
are accommodated. In this case, Figure 8 shows the ring 69
already pushed onto the holding part 36 and shows the holding
part 37 in a position that (sic] it can likewise be joined
together with the ring 39. In addition, the torsion member 38
with the torsion section 39 is inserted into the holding
parts 36 and 37. In this case, the bent legs 67, with their
end regions projecting upward, form the end regions of the
magnet poles still to be formed, as indicated for one leg by
the reference numeral 43' in accordance with that of Figure
5. The legs 67 may be adhesively bonded in the slots 70 and
71 of the respective holding parts. Furthermore, the stepped
part of the holding parts may be covered by a hardening
casting compound after the holding parts have been pushed
together, so that, of the magnet poles, only the angled end
regions project radially from the holding parts 36 and 37 and
the web 66 is exposed between the holding parts. After the
casting compound has hardened, the circumference of the
holding parts 36 and 37 may be turned or ground, so that the
end regions of the magnet poles, e.g. the end region 43' , is
flush with the outer surface of the holding part. After the
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holding parts 36 and 37 have been fixed in place on the
torsion member 38 as described and the magnet-pole legs 67
have been fastened to and in the holding parts, the web 66,
as already mentioned, is now cut in such a way that the
individual magnet poles are formed. Thus the air gap d is
formed between the opposite magnet poles by a circumferential
cutting line L, e.g. by means of a laser. This air gap, for
example, may have a size of 0.3 mm, which remains constant
even after the cutting due to the already fixed bearings
[sic] of all parts relative to one another. Furthermore, the
hatched parts can be cut out by cuts through the web 66 in
the axial direction, so that the magnet-pole arrangement
according to Figure 4 having magnet poles opposite one
another in a staggered manner is obtained. Of course, magnet
poles which are not staggered relative to one another could
also be obtained by appropriate shaping of the strip 65.
Figure 9 shows a drive device of a bicycle having an
electromotive auxiliary drive similar to that of Figure 1,
using a torque sensor as has been described with reference to
Figures 4-8. In this case, the same reference numerals as
used previously describe the same parts. Since the drive
device is symmetrical to the longitudinal axis, essentially
only the part lying above the longitudinal axis is shown and
this part is also truncated toward the top in the figure, so
that only part of the rotor and the housing of the output
wheel can be seen. In the example shown, the pedal spindle 1
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is welded to the sleeve 76 at location 75. That region of the
pedal spindle which lies inside the sleeve is movably mounted
relative to the sleeve by a sliding intermediate layer 19. In
this way, the torque induced in the pedal spindle 1 by the
pedal cranks (not shown) is transmitted to the sleeve at
location 75. The sleeve at the same time forms the torsion
member 38 of a torque sensor having magnet poles. For this
purpose, the sleeve is designed to be thinner in the region
of the torsion section 39 in order to permit torsion there on
account of the muscle power induced. At its other end, the
sleeve 76 is firmly connected, e.g. welded, at location 77 to
a torsion-transmission ring 78. This ring is also mounted so
as to slide relative to the pedal spindle. Engaging on the
torsion-transmission ring 78 in a torsionally rigid manner
is, on the one hand, the rotor 6, and, on the other hand,
the output wheel 11 on the outside of the housing, which is a
sprocket wheel for example. In this case, the ring 78 is
provided with apertures 80, which are separated from one
another by ribs and in which pins 81 and 82 of the rotor and
the output wheel respectively engage in order to ensure the
torque transmission from the torsion-transmission ring 78 to
the rotor and the output wheel respectively. The holding
parts 36 and 37 arranged over the sleeve 76, which serves as
torsion member 38, are fastened to the sleeve, e.g. by
adhesive bonding, at locations 84 and 85. The holding parts
therefore rotate with the torsion member 38 or the pedal
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spindle. The holding parts hold magnet poles, which are
configured as essentially band-shaped strip poles, as has
already been explained for the above torque sensor. In this
case, two magnet poles 43 and 53 are shown in the figure. The
coil 48 or 58 respectively, which is fastened to the housing
in a stationary position and is thus stationary relative to
the rotatable holding parts 36 and 37, is arranged inside an
annular yoke 47 or 57 respectively composed of two parts. In
this case, as in the exemplary embodiments of the torque
sensor already shown, a coil carrier, which is provided if
need be, is not shown in order to simplify the drawing. The
magnet-pole torque sensor works in the way described with
reference to the examples according to Figures 4-6. The
muscle-power torque induced in the drive on the spindle 1
leads to rotation of the sleeve 76 or the torsion section 39
respectively, thus to a shift of the magnet poles relative to
one another and thus to a change in the magnetic flux, which
is detected by the coil 58. An electronic analyzing system or
a part thereof may be arranged on a plate 89 in a stationary
position above the stationary coils. In the torque sensor
shown according to Figure 9, an electromagnetic screen in the
form of a ring 90, e.g. made of copper, is preferably
provided in the radial direction above the magnet poles. A
further electromagnetic screen arranged radially below the
magnet poles in the form of a ring 91 which also rotates is
also preferably provided. Such an electromagnetic screen,
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either with one annular screen element or both annular screen
elements, may also be provided in the case of a sensor
according to Figure 4-8. It has been found that this screen
can screen electromagnetic interference on the sensor, a
factor which facilitates the analysis of the output signal of
the sensor.
Instead of the torque sensor shown on a magnetic basis,
a torque sensor, e.g. with strain gages, may also be used, as
already explained. In this case, too, the introduction and
outputting of the operating voltage or the useful signal to
the strain gage arranged on the sleeve or the pedal spindle
may be effected in each case by means of a stationary coil 48
and 58, which in this case is opposite a coil which rotates
with the strain gage, is likewise provided with a yoke and is
fed or scanned via the air gap present between the yokes. In
an embodiment variant, the torque detection could also be
effected at the abovementioned torque-transmission ring 78,
e.g. by strain gages on its webs.
