Content uploaded by Rosen Ivanov
Author content
All content in this area was uploaded by Rosen Ivanov on Feb 08, 2016
Content may be subject to copyright.
TRANSPORT PROBLEMS 201X
PROBLEMY TRANSPORTU Volume X Issue X
electric bicycle, energy efficiency, energy consumption
Ivan EVTIMOV*, Rosen IVANOV, Gergana STANEVA, Georgi KADIKYANOV
University of Ruse, Department Engines and Vehicles
8, Studentska st., 7017 Ruse, Bulgaria
*Corresponding author. E-mail: ievtimov@uni-ruse.bg
A STUDY ON ELECTRIC BICYCLE ENERGY EFFICIENCY
Summary. The paper presents a construction of an experimental electric bicycle for
evaluation of the energy efficiency. The bicycle is equipped with board computer which
can store the information about motion and energy consumption. The result concerning
power, energy consumption, recharging during brake process, etc. are given. Energy
consumption for 3 typical city routes is studied.
1. INTRODUCTION
Moving in urban areas is connected with big intensity, often braking and starting and continuous
working of the engines in idle mode. The increased fuel consumption leads to increased level of the air
pollutions.
The governments in the different countries apply different measures for stimulation the use of
environmentally cleaner vehicles [1, 3, 5, 7] and production of electric energy by renewable energy
sources [1, 3, 6].
Many European and Asian countries encourage the usage of bicycles and special attention is paid
to the bicycle moving infrastructure [3, 4, 7]. One special category of the vehicles is the electric
bicycles. They combine some advantages both from the classic bicycle and the electromobile [1] such
as less costs for self-movement, typical for the two-wheeled vehicles, possibility for electric operation
or help for climbing etc. In the bigger part of the existing ones there is a possibility provided for
generating of energy by charging of the battery during braking or descending.
The aim of the present work is to study the energy efficiency of the electric bicycle and the
possibilities for re-generating of energy in a medium town.
2. DISCRIPTION OF THE ЕXPERIMENTAL ELECTRIC BICYCLE
For the purposes of the research, a team from the Ruse University has worked out an experimental
electric bicycle [2] based on a Bulgarian bicycle and electric elements. The general structure of the
electric bicycle is shown on fig. 1.
The electric bicycle is operated by BLDC electric motor 5 with a nominal power of 500W, built-in
the front wheel. It is operated by lithium ion battery 3. The battery has a working tension of 36V,
capacity 9Ah and a weight of 3,5kg. The battery contains 324Wh electric energy. The total weight of
the electric bicycle is 24,4kg.
The parts for operating and control are assembled on the handlebar (fig. 2, 3, 4). The controller 4
optimizes the working regimes of the electric motor and the regime of regenerative braking.
111 I. Evtimov, R. Ivanov, G. Staneva, G.
Kadikyanov
The autopilot 1 (fig.4) provides a constant speed of the electric bicycle thus giving a possibility to
free the right hand from the speed regulation lever 2 (fig.3). The regenerative stopping is operated by a
separate button 2 (fig. 4) aiming to eliminate the eventual switch on of the mechanical brake system.
Fig. 1. General view of the electric bicycle:
1 – frame; 2 – back wheel with a chain mechanism; 3 – battery;
4 – controller; 5 – electric motor; 6 – handlebar
Fig. 2. General view of the electric bicycle handlebar:
1 – board computer; 2 – right handle; 3 – left handle
Fig. 3. Operating elements on the right handle:
1 – an indicator for the discharge of the battery; 2 – lever for speed regulation; 3 – a button for switching on/of
the electric supply
A study on electric bicycle energy efficiency 112 .
Fig. 4. Operating elements on the left handle:
1 – cruise control; 2 – the button for regenerative stopping
During braking and descending the electric motor works in a generative regime and charges the
battery.
а) b)
c) d)
e) f)
g)
Fig. 5. Registered parameters from the board computer
The board computer can register and show on a display the following parameters (fig. 5):
- the tension in V and the used capacity in Ah of the battery, the power in W of the electric motor and
the speed of movement in km/h (fig. 5 a);
- the tension of the battery, the power of the electric motor the speed of movement and the running
distance in km (fig. 5 b);
113 I. Evtimov, R. Ivanov, G. Staneva, G.
Kadikyanov
- the tension of the battery, the power and the current of the electric motor in A and the used capacity
of the battery (fig. 5 c);
- the total used energy from battery in Wh and the used energy per 1km in Wh/km (fig. 5 d);
-the minimum and maximum current in the electric motor and the minimum tension of the battery (fig.
5 e);
- the maximum and average speed of movement in km/h and the total time for movement in hrs, m and
s (fig. 5 f);
-the total number of charges, the total used capacity of the battery and the total running distance
(fig. 5 g).
3. RESULTS AND ANALYSIS
3.1. Studying the energy consumption
The energy consumption of the electric bicycle has been studied during different working regimes.
There have been made experiments on a horizontal road in two directions with a five time
repeating at a constant speeds from 5 to 30km/h. The total weight of the electric bicycle and the cyclist
99,4 kg.
The power P from the electric motor at different speed V of the electric bicycle is shown at fig. 6.
The energy consumption E per 1km at different constant speeds V is shown at fig. 7.
Fig. 6. Dependence of the used motor power P by the speed V
Fig. 7. Dependence of the energy consumption E by the speed V
A study on electric bicycle energy efficiency 114 .
3.2. Study on the regenerative braking of the electric bicycle
At serial production the electric bicycles and the sets on the market, the regenerating braking is
achieved by the levers for activation the front and the back brake. At the first starting of the lever only
the regenerating braking is switched on and after that depending on the power of pressing of the lever
is achieved the desired brake delay, accordingly from the two braking systems – the electric and the
mechanical.
Due to the fact that the mechanical braking system has a separate operation (the braking system of
each wheel is operated by a separate lever) it is possible the realization of the following ways for using
the braking systems:
1. Regenerative braking through starting of one of the levers for operating of the braking
mechanisms of the wheels (fig. 8).
-regenerative braking and switched on braking mechanism of the front wheel;
-regenerative braking and switched on braking mechanism of the back wheel;
2. Regenerative braking and switched on braking mechanism of both wheels (fig. 9).)
Fig. 8. Forces balance during regenerative braking without braking
Fig. 9. Forces balance during regenerative braking and switched on braking mechanisms of both wheels
At fig. 8 and 9 are indicated the weight G, the rolling resistance force of the front F fп and the rear
Ff3 wheels and the air resistance force Fв during braking process of the electric bicycle on a horizontal
115 I. Evtimov, R. Ivanov, G. Staneva, G.
Kadikyanov
area. The resistance forces Ffп, Ff3 and Fв are directed against the inertia force Fa and it is not possible
to use the entire kinetic energy of the electric bicycle for generating of electric energy.
At present there are no enough researches for the effectiveness of the regenerative braking of the
electric bicycles in urban areas. In [8] it is indicated that depending on the conditions of moving and
the slopes of the streets, the regeneration of energy varies from 6 to 14%. The experiments made in
city of Ruse during a covered distance of 215 km at some of the routes of the public transport a
regeneration of 5,5% is obtained.
The full stop only by electric motor, without using the mechanical brake is impossible. At the
beginning there is only regenerating braking and after that it is necessary to switch on some of the
braking systems to be achieved a full braking.
There have been made experiments at different initial speed and only regenerative braking has been
performed. The results from the studies are presented at fig. 10. Each full braking or speed reduction
through the electric motor increases the run of the electric bicycle and the exploitation time of the
mechanical brake system.
Fig. 10. Dependence of the regenerating capacity in the battery Cрег by the initial speed of braking Vs
Fig. 11. Dependence of the regenerative current Ip by the speed of the electric bicycle V
It is possible in the infrastructure of the urban area to be realized descending with a speed reduction
possibility through the electric motor. With this regard there have been performed experiments of
A study on electric bicycle energy efficiency 116 .
descending at different speed. The results from the experiments are shown at fig. 11. At the different
values of constant speed V is reported the regenerated current Ip which charges the electric battery.
From this characteristics it is seen that upon descending with speed 25km/h in a regenerating
regime for 60s (the slope is 420 m long) in the battery will be regenerated ~0,17Ah. At 9Ah battery
capacity, this regenerated capacity is ~2%.
3.3. Studying the energy consumption for typical routes in the conditions of a medium size town
For the study of the energy efficiency of the electric bicycle there have been chosen three typical
routes in the town of Ruse (population ~150 000) with a different profile but with a heavy traffic.
They are shown at fig. 12…14. For their visualization a virtual map [11] has been used.
Fig. 12. Route 1: Railway Station – Danube Bridge and back
The three routes were passed by two group experiments. Firstly, at the beginning without the help
of the cyclist and starting only by using the electric motor for acceleration. Again the same routes have
been passed also by the help of the cyclist though the bicycle pedals only at staring until reaching a
speed of 5km/h. All the experiments have been started with fully charged battery. The results are
shown at table 1.
117 I. Evtimov, R. Ivanov, G. Staneva, G.
Kadikyanov
Fig. 13. Route 2: Railway Station – Drujba 3 and back
Fig. 14. Route 3: Railway Station – River Station and back
A study on electric bicycle energy efficiency 118 .
Tab. 1
Results from the trials
Parameters
Routes, passed without a help
at starting
Routes, passed with a help at
starting
1 2 3 1 2 3
Passed distance S, km 15,03 5,5 4,34 15,77 5,78 4,33
Energy consumption per 1km
passed way, Wh/km
12,8 16,4 18,4 12,5 13,4 13,1
Regenerated energy, % 4,5 5,2 9,5 7,7 10,4 10,7
Maximum speed on the route V
max, km/h
36,6 35,8 33,1 35,2 39,8 31,6
Average speed on the route Vср,
km/h,
24,5 22,8 18.4 22,4 21,3 20,6
Time for route passing, min, s 36 min,
46 s
15 min,
5 s
14 min,
5 s
42 min,
10 s
16 min,
16 s
12 min,
36 s
There has been made an experiment also for determination the operating range of the bicycle at a
day time period with a less traffic (Sunday morning). The average results from route 1 showed that
with one charge of the battery, the electric bicycle passes a distance of 34,77km in urban conditions,
without using the regenerative braking. The maximum achieved speed was 35,4km/h and the average
speed - 23,8km/h. For the whole pass of the route, the electric bicycle has used 390,49 Wh of energy
and average per km – 11,2Wh/km. For the bicycles designed abroad with working tension of 36V and
similar battery capacity of 9-10 Ah, the operating range for 1 charge of battery is approximately 20 –
25 miles or 32 – 40 km [8, 9, 10]. This fact shows a similar energy consumption of the studied bicycle
and a good fit of the obtained experimental results for the range in this research and from other authors
[8, 9, 10].
4. CONCLUSIONS
From the carried out research and the analyses of the results, the following conclusions could be made:
1. Without regeneration of the energy in urban conditions the range of the electric bicycle is
about 35km.Considering the average value of the regenerating energy in a town of Ruse, the run of the
electric bicycle could be increased from 5 to 10%. At day time periods with not so heavy traffic, the
run of the electric bicycle could be increased with about 11% due to the less number of braking and
accelerations.
2. The studies showed that in a town like Ruse, the use of electric bicycle instead of other
vehicles by one person could reduce the air pollutions up to 10 times compared to the electromobiles
and up to 15 times compared to the conventional cars. Those values concern the air pollutions
generated only due to motion and exclude the other parts like pollutions due to production of the car or
bicycle, due to disassembling of the old machine etc. The effect of air pollutions reduction could not
be so strong because of a parallel replacing a number of conventional bicycles with electric, which
will increase pollutions. At the moment is not possible to predict how significant will be the influence
of that replacing.
3. At speed of 15 to 25km/h the used power of the electric motor is from 100 to 300W and the
energy consumption is from 7 to 12Wh/km which is 6 to 23 times less than the energy consumption of
the electromobiles produced now.
4. There is a bigger effect from the regeneration of energy at the routes including slopes. For
example at the plain route 1 the regeneration is about 5%, but at routes 2 and 3 including slopes the
regeneration reaches about 10%.
119 I. Evtimov, R. Ivanov, G. Staneva, G.
Kadikyanov
5. The level of increasing the effectiveness of the regenerative braking depends on the road
infrastructure for moving of bicycles and electric bicycles and the chosen by the cyclist regimes for
speed reduction and braking.
References
1. Евтимов, И. & Иванов, Р. Електромобили. Русе: Русенски Университет „Ангел Кънчев“.
2011. P. 176 [In Bulgarian: Evtimov, I. & Ivanov, R. Electromobiles. Ruse: Ruse University
„Angel Kanchev”].
2. Евтимов, И. & Иванов, Р. & Вълов, Н. Изследване разхода на енергия на електровелосипед
при различни режими на движение. МНК BulTrans. Созопол. 2012. P. 212-216 [In Bulgarian:
Evtimov, I. & Ivanov, R. & Valov, N. Research on the energy consumption by electric bicycle at
different moving regimes. Proceedings of ISC BULTRANS. Sozopol. 2012].
3. The Netherlands projects for combining the sun energy with bicycle alleys. Available at:
http://credobonum.bg/material/131/label.
4. Bicycling resources. Available at: http://www.metrotransit.org/bike-options.aspx.
5. Bike Safety as Social Justice. Available at:
http://raisethehammer.org/article/1407/bike_safety_as_social_justice.
6. Pi Mobility. Available at: http://picycle.com/sustainability/.
7. Urban Active Travel: More European Bikes. Available at:
http://www.jaunted.com/story/2007/11/8/161753/351/travel/Urban+Active+Travel
%3A+More+European+ Bikes.
8. Watt Hours; Calculating E-bike Range. Available at: https://www.electricbike.com/watt-hours/
9. Energy Efficient Electric Bikes. Available at:
http://www.nycewheels.com/energy-efficient-electric-bike.html
10. Speed, Distance, and Energy Consumption. Available at:
http://electricbikereview.com/community/threads/speed-distance-and-energy-consumption.547/
11. www.bgmaps.com
