Note: Descriptions are shown in the official language in which they were submitted.
CA 02426109 2003-03-20
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. METHOD AND APPARATUS FCirR
PROPtIRT(tINALLY A$StSTED PRfaPULSt4N
CROSS-REFERENCE TO RELATED APPLICATIONS
The application claims priority of Canadian patent application 2;39,9,8413
ftled September 2'1, ~I:100 by Applicant.
FtE~u of THE ttuvENTroN
The invention relates to proportionally assisted propulsion. More
specifically, it relates to vehicles, for example, bicycles, equipped with a
DC
motor and a propc~rtionai assistance circuitry allowing the user of the
vehicle to
be assisted in propelling the vehicle.
BACKGROUND OF THE iNVEN'T14N
Cydlng is a very popular sport and a mode of transportation, In some
cities, more people trove( to work and to school lay bicyde than by car.
Cycling
has the main advantage of being an environmentally-clean mode of
transportation and a very silent and enjoyable way of discovering a country or
~of
traveling. ~ .
The use of electric motors as a motoring force for many types of vehicles
and devices is desirable since such motors are pollution free, very quiet in
operation, light and can be rpade compact. With such features, electric motors
have progressively been given newer applications. Far instance, wheeled
transportation devices such as bicycles, tricycles, maper~$, scooters, and
nautical
transportation devices, s~rch as personal watercrafts and small boats are all
either known to have been propelled by electric motors or have the pdtentia)
to
be.
Electric power has emerged as a popular mofioring force generator for
some transportation vehicles s(nce electric batteries may be recharged during
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use, thereby allowing such vehicles to b$come autonomous for long distances.
For instance, an electric motor mounted to a bicycle may tae recharged when
the
bike is going downhill, or when the bicycle is braked.
in prior art electric bikes, a specific fixed effort is requested from the
electric motor and this effort is used 'to propel the bicyde. These bikes are
therefore useful for traveling at a regular speed without pedaling. These
bikes do
not interact with the user and do not allow a campensative, proportional or
progressive effort to be provided by the motor.
ether prior art eteGtdc bikes have proportional assistance and allow a
7 g compensation of the motor far the efforts of the cydist. They often have
electrical
or eleotricallmechanicat units which provide the assistance. However, the
assistance provided by the motor in those cases is not smooth. The cyclist is
fully
aware of the presence of the motor and of its assistance to the propulsion of
the
bicycle.
1b
~UMMARI~ OF THliw INVI'NTION
Accordingly, an object of the present invention is to provide a system
which provides motorized assistance to the user propelling the vehicle by
proportionally adapting to the effort provided by the user.
20 According to a broad a$pect of the present invention, there is' prswided a
system for proportionally assisting by a DG motor propulsion of a wheeled
vehicle
propelled by a user who provides a user effort, comprising detection and
measurement means for detecting an~i measuring a filexlon of a fixed shaft of
a
wheel of the vehicle on which the DC motor is secured and subjected to the
user
2b effort, the detection and measuring means being mounted on a fiat vertical
surface formed in the fixed shaft; assistance level request means for
requesting a
level of assistance to be provided; digitizing means for digitizing a signal
obtained
from the detection and measurement means; effort calculation means to
calculate, in real time, the user effort provided by the user using the
digitized
30 signal; assistance level calculation means for calculating an appropriate
assistance effort to be provided by a DC motor mounted on the wheel using a
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value of the user effort and a value of the level of assistance requested;
control
means for controlling an assistance effort to be provided by the DC motor
~ mounted on the shat of the wheel and using a value of the appropriate
assistance effort wherein the user effi5rt and the level of assistants
requested
are used to proportionally assist propulsion of the vehicle by the DG motor.
According to another broad aspect of the present invention, there is
provided a method for proportionally assisting a propulsion of a wheeled
vehicle
propelled by a user who provides an user effort, comprising detecting and
measuring a flexion of a fixed shaft of the vehicle subjected to the user
efFort by a
detection and measuring means mounted on a flat vertical surface formed in the
fixed shaft; requesting a level of assistance to be provided; digitizing a
signal
obtained from the detection and measuring means; calculating, in real time,
the
user effort provided by the user using the digitized signal; calculating an
appropriate assistance efFort to ba provided by a DC motor mounted on the
wheel
using a value of the user effort and a value of the level of assistance
requested;
controlling an assistance effort to be provided by the DG motor using a value
of
the appropriate assistance effort; whereto the user effort and the level of
assistance requested are used to proportionally assist propulsion of the
vehicle '
by the DG motor.
2tJ
BRIEF DESCRIPT(4N OF THE DRAWINGS
These and other features, aspects and advantages of the present
invention will become better understood with regard to the following
description
and accompanying drawings wherein:
FIG. 1 is a block diagram of the proportional assistance electmnlc system
of the present invention;
F1G, 2A, FIG. ~B, FIC. ~C, FIG. 2D and F1G. 2E is a set of comparative
curves;
FIG, 3A is a perspective view of the shaft of a wheel of the bicycle on
which is secured the motor stator core which is stationary and wherein the
shaft
is provided with a flat face for mounting a strain gauge and FJG. 3B shows the
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shaft in its secured position between the forks of a bicycle with the strain
gauge
positioned in a vertical plane
Fl~. 4 is a perspective view of the assembled DC motor about the shaft
of FIG. 3 with the motor housing partly fragmented to show the position of the
strain gauge; .
FIG. 5 shows the DC motor assembled on the axle or shaft of Fly, 3
secured to a vehicle frame supporter the rear wheel oaf a bicycle; and
FIG. 6 is a perspective view . of a bicycle equipped with the DC motor
secured on the shaft of axle of the bicycle , and controller components of the
proportional assistance system; .
D~TAtLED DESCI~IPTIfJN DF THE PREFERRED EMEODIMENT
Reference is made to pending PCT application PGTICA89100290 which
describes a DC motor connected to a rear wheel of a bicycle which can propel
fhe rear wheel of the bicycle when the motor is activated. The proportionally
assisted propulsion system of the present invention has been designed to be
used with a DG motor of the type described in that PCT application.
The present invention will now be explained in more details. It is installed
with a DG motor used to propel a bicycle used by a cyclist In other
embodiments, it could be installed on tricycles, carts or other man-propelled
vehicles. The purpose of the present invention is to assist the person
propelling
the vehicle by controlling the DC motor to provide proportional and
progressive
energy for the propelling of the vehicle when necessary or when requested by
the
user. It is designed to help the cyclist in certain conditions such as when
climbing
abrupt hills, when facing the wind, etc. It also allows people with weaker
health
conditions to keep an acceptable rhythm and to enjoy sightseeing on a bicycle.
.
The proportional assistance mode of the system provides a rtyotor effort
proportional to the effort provided by the user. The level of assistance is
determined by the user and is communicated to the control means of the motor
~0 for proper ad)ustment. Examples of assistance Levels are shown in Table 1.
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-5-
Made As$istance Percentage of Remaric~
user
Level effort added by
motor
1 g.25 25 ~ Cancels the weight
of the
bicycle
2 4.50 50 % For climbing smah hilts
or
when facing the wind
3 1.00 "! fl4 % Far climbing big hills
and
4 2.Q0 2Q0 % fighting strong winds
0 Variable Variable To obtain a varying
assistance using a
throttle
sub-system
1 SDi~.' i. GXilffifJlCS V1 /t3231tiLtri114i1G L~VGL'f
Preferably, the motor assists thq cyclist only when the bicycle has reached
a speed superior to 2 krnlhr. This ensures that the motor does not propel the
vehide while the user was stopped or that the bicyde does not react too
abruptly
to effarf required by the user. The assistance level varies with the gear
ratio used
by the cyclist.
Because of safety reasons, it might be preferable to restrict the total ef~Ott
provided by the motor. According to the safety regulations far each country,
maximum speeds are allowable. For example, For Canada, the motor power
available is progressively reduced after the bicyde speed has reached 25 kmlhr
~ '
to become nit at ~2 kmlhr. If the cydist wishes to go faster, the motor will
not be
assisting him.
In the varying assistance mode, a power adjuster is provided to the cyclist ,
~ who can use It as a means to vary the effort prcavidecf by the motor, in a
manner
'15 similar to gas-powered motorcydes. .
The following table describes approximate distances traveled with a fully .
charged battery.
Mode ' Effort by user , EffQrf by motor Approximate .
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pi$tance
tweveied
0 None, user does not Varying 20 krra
pedal
0 Light pedaling Varying 30 km
p Full pedaling None Unlimited
1 Full pedaling 25 % of the effort 45 km
of user
2 Fuil pedaling 50 % of the effort 40 km
of user
3 Full pedaling Sarne effort as 35 km
user
4 Fuli pedaling Twice the effort 30 km
of user
Table 2. Examples of approximate mszances uave~ea on a tun papery.
The effort or energy provided by the cyclist is measured by the strain
gauge 20 located on the shaft 40 of a rear wheel of the bicycle, which is
subjected to a tow, but measuceble horizt~ntal flexion created by the chain
which
is put under tension by the pedal assembly which is operated by the user.
it will be understood fihat the gauge could be located on a shaft of a front
wheel of the bicycle or on any other portion of the bicycle which is subjected
to a
deformation caused by the effort cf the cyclist. For example, the shaft of the
pedal assembly could be used to mount the gauge. Similarly, a portion of the
1 t~ frame of the bicycle could also be used.
In order to prevent signal noise coming from vertical movements of the
cyclist on the bicycle (vertical strains on the shaft ), the strain gauge ~g
is placed
on a vertical surface 41 located on the axed shaft ~-0, as spawn in Figs 3 and
4
The typical range of duration of the rotation of the pedal assembly is~ 0.5 to
2 seconds. Counting two pushes on the pedal assembly per rotation of the pedal
assembly, a quasi-periodical gauge signal is obtained, having a quasi-
sinusoidal
shape, the frequency of which being between 1 and 4 Hz. To minimize hardware
and installation costs, a half bridge strain gauge is preferably used.
The circus and processing response tame should be such that the motor
can progressively assist the cyclist when he begins to pedal. Similarly, the
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propulsion provided by the system should decrease quite rapidly when the
cyclist
stops pedaling. The propulsion drive should be immediately stopped when the
brake is activated. This low response time is preferable to prevent sudden
accelerations of the bicycle or slow decelerations which could result in
injuries for
the user or accidents. It will be understood that the motor could be mounted
on
the front wheel or the rear wheel of the vehicle.
Reference is now made to FIC3. ~i in which a biucfc diagram of fhe system
of the present invention is shown. l'he half bridge strain gauge 20 is powered
by
a 5V pourer source regulated from an electric battery. The power source is
preferably an electric battery mounted on the bicycle which can be charged and
discharged using prior art systems. The battery Can preferably be a 24 volts,
7-8
Ah or 36 volts battery. The gauge sign( Vj is about 2 mVAC superposed to a
2.blJ DC level.
The variation of the gauge signal Vj is very small, and should be
1S considerably ampllfiied for further proCess(ng. The preferred amplification
ratio i&
above a thousand to one. However, in order to prevent amplifying any DC
component which could saturate the amplfier as well as to prevent having to'
make a zero adjustment on the measurement bridge, especially since such a
zero adjustment could be useless in ti~fe case of a temperature deviation or
of
other environmental conditions, an AD coupling Is used between the gauge 20
and the amplifier 22 using a bandpass filter 2~ of the first order having a
passing
band of 1 to 4 Hz.
The amplifiier 22 gain is adjusted so that all of the measurement range of
the analog to digital converter 23 can be used. The oul~ut sigc~at Vm obtained
at
the output of the ampliber 22 is about 3 Vpp centered at the 2,bV DC level
with
an equivalent mass of ~Q Kg on the pedal assembly. This average value Vm is
- calculated fc~r an average gear ratio. As wilt be readily understood, the
peak to
peak voltage will be different for another gear ratio and this is acceptable
since
the exact level of assistance is not critical for this application. A
precision of t 20
% is sufficient in most cases.
The amplifier signal Vm is digitized every 4 msec in order to obtain an
aerate numerical average.
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In order to compensate for any deviation of the arnpi~ier, a digital filter 24
with a time constant of 10 seconds is used to obtain the DC level tabout 2.5
V~ of
the signal at the output of the amplifier ZZ.
In order to obtain a sufficiently rapid response time far the system taking
into account the effort provided by the cyclist, the average value of the
rectified
gauge signal is calculated using a low pass filter 27 with a 2 second time
constant, in reel time, using Vout = ~ ~ Vm - ~Vm> ~ ~. This technique has
shown
to be more simple and rapid than other numerical techniques.
"fhe amplified signal is integrated to 4btaln the mean DC level and is used
to compen$ate for temperature drift over time. Furthermt~re, this integrated
signal
is subtracted from fine digitized amplified signal to obtain a resulting
signal well
centered around zero.
Figures 2A to 2E show the results of these processing steps, in FIG. 2A,
the voltage representing the cyclist effort is shown. In FIG. 2E~, the voltage
measured by the gauge Vm is shown, with a 2.5 V DC level. In FIG. 2C, the
filtered signal ~Vm> is shown, oscillating around 2.5 V. In F1G. 2Q, the-
absolute
value signal Va is shown and is calculated as ~ Vm - ~Vm~ j. In FIC. 2E, the
signal Vc fed to the motor current feedback loop is shown and is calculated as
~i
Vm - ~Vrn~ j~. The motor current feedback loop then uses this voltage as an
input to calculate and produce the propar~onal effcart required from the
motor.
Pending PCr application PCTICA89100290 which describes a DC motor
connected to a rear wheel of a bicycle which can propel the rear wheel of the
bicycle when the motor is activated by the cyclist descrifaes how the input
voltage
Is used to create an adequate and proportional force on the wheel. Preferably,
the DC motor is a maintenance-free DC motor.
For a given effort on the pedal assembly, the i~orizontal micro-flexion of
the rear shaft d.0 will vary according to the gear ratio selected. Therefore,
it is
possible to require a high precision on the amount of assistance being
provided
by the proportional assistance system in any situation, simply by calculating
the
proportional effort required for each gear ratio and efforf/flexion.
If the amount of assistance being requested is high, a tow effort on the
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pedal assembly will produce a great motor torque and it is therefore important
for
proper functioning of the apparatus that the wheel alignment and balancing be
reasonably well done. For example, an extreme behavior of the wheel could
induce non-negligible flexlons on the shaft 41 which the gauge circuit would
interpret as an effort provided by the cyclist. This phenomenon is mast
iilcefy to
appear at high speeds greater than 20 kmlhr) when the frequency of these .
flexlons would fail in the passing band of the analog filter.
' The following table lists typical power and speed characteristics for a
piurafrty of apparatus made according to the invention.
Continuous Peak Maximum Speed Weight trtr the kit including
Power Qower the
motor hut not the battery
' 180 W 450 20 mph ! 32 7 Ib I 3.2 Kg
W Kmfh
240 W 650 20 mph I 32 8 Ib I 3.1 Kg
W Kmlh
3I10W 81UW 10mphllGKmlh 8.8IbI4Kg
Table 3. Typical characteristics
!=or the apparatus having the 1 ~0 W continuous power, the nominal torque
is 7 Nm and the maximum torque is 25 Nm.
Figures 3A and 3B show the shaft 40 is provided with a fifat mounting
surface 41 on which the strain gauge 20 is to be mounted. Threading 41 at
opposed ends of the shaft is used to mount the shaft between the fork arms of
a
frame of a bicycle wheel, as wets known in the art . The core of the motor
stator,
not shown, is mounted press-fit on the shaft 40 over the knurled portion 42..
The
other recessed flat portion 41" is to provide passage for wiring. Fig. 3B
shows
the portion of the shaft when secured to a bicycle wheel with the strain gauge
20
disposed vertically on the flat mounting surface 41: Any flexion of the shaft
41
due to a pedal effort by a user will cause a micro deformation in the surface
41
whlCh will be detected by the strain A2~uge 20 mounted thereon. .
Figure 4 shows the assembled motor about the shaft with the gear'
assembly 46 secured to the side wall 30 of the rotor housing 48 rotating about
2~ th~ stator care secured fixed to the shaft 40. Wires property dispQSed is
used to
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connect the motor 47 and the circuitry to the battery and to the user control
command and interface. The strain gauge 20 is rnounted on the vertical surface
4'I of the shaft 40 and protected by the rotor housing 30.
The Rotes 36 located in the housing sidewall portions 35 and 39 are for
receiving the spokes 37 of the bicycle wheel 38 as shown in Fig. G.
Figure 5 shows a detail of the assembled axle together with the gear
assembly 45 mounted on the side wall 30 of the rotor housing 4.~ rotatable
about
the fixed shaft 40 i.e., the rear shaft 40 of a bicycle. The fork arm of the
frame of
the bicycle is referred to with numeral 56. The pedal assertibly 51 is also
shown.
'l0 Figure 6 shows a complete bicycle equipped with fihe D~ motor system of
the present invention. The motor 47 is assembled about the shaft 40 together
with the gear assembly, . A battery 60 is shown mounted an a portion of the
frame b6 of the bicycle and the user commend interface 64 is sht~wn mounted
near the handles of the bicycle. As will be readily understood, the battery 60
and
the user interface 61 could be mounted anywhere on the bicycle although the
shown mounting locations are preferable.
It will be understood that numerous modifications thereto will appear tn
those skilled tn the art. Accordingly, the above description and accompanying
drawings should be taken as illustrative of the invention and not in a
limiting
sense. it will further be understood that it is intended to cover any
variations,
uses, or adaptations of the invention following, in general, the principles of
the
invention and including such departures from the present disclosure as come
within known or customary practice within the art to which the invention
pertairie
and as may be applied to the essential features herein before set forth, and
as
follows in the scope of the appended claims.
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