performance evaluation of electric bicycles

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Performance Evaluation of Electric BicyclesA.MUETZE,Y. C.TAN

Electrical and Computer Engineering DepartmentUniversity of Wisconsin-Madison, WI 53706, USA

E-mail: [email protected], [email protected]

AbstracElectric motor powered bicycles (short: electric

bicycles) have been making their way into the U.S. market for

about two decades. Such electric bicycles can be used for a

large variety of purposes. This paper gives a systematic, com-

prehensive, theoretically and experimentally based characteri-

zation of electric bicycles, and reports on the different perfor-

mance requirements. Thereby, the needs and challenges in de-

signing electric bicycles with improved overall performance are

identified. For example, generally critical issues such as heavy,

bulky batteries and high drive costs can be addressed. Further-

more, the overview can be used for comparison of existing

drives in a thorough, technically meaningful way.

Keywordspower-assisted bicycle, direct drive, battery,

efficiency, performance evaluation

I. INTRODUCTION

Electric motor powered bicycles have been making theirway into the U.S. market for about two decades. In the U.S.such bicycles can be fully powered by a motor. In othercountries such as Japan, electric motor powered bicycles arerequired to operate with 50% human pedal power for up to12 mph, and an even higher percentage of human power isrequired above that speed. Such bicycles are commonly

known as Pedelecs (Pedal electric cycle). In this paper,the term electric bicycle is used to describe electric motorpowered bicycles, including both fully and partially motorpowered bicycles. Electric bicycles can be used for a varietyof purposes, for example, as a vehicle for police or law en-forcers in cities where parking and traffic are a problem, as aguide bicycle during bicycle races, as a park ranger vehicle,and for leisurely rides and commuting purposes. In the U.S.,electric bicycles are currently used most commonly for shorttrips to grocery stores or for leisurely rides.

First, the paper gives a systematic, comprehensiveclassification of electric bicycles that includes an overview oftodays commercially available electric bicycles [e.g. 1-12]

(Section II). The overview is given by means of tables thatconvey the information in a clear manner. Next, usingknowledge from the field of professional bicycling as astarting point, the technical performance requirements onelectric bicycles are identified. The results of the theoreticalapproach are confirmed with measurements that have beencarried out in the context of real-life-applications(Section III). From the results of Sections II and III, the keyparameters, needs and challenges in improving the perfor-mance of electric bicycles are identified. Then, the paper

gives a summary of the different results that can serve as aroadmap for such improvements. This summary includesboth market trends and regulations, and technical-sciencerelated aspects (Section IV). Different paths of further re-search that can build on the presented work are out-lined inthe conclusion (Section V).

II. EVALUATION OF THE STATE-OF-THE-ART

A. Basic configuration of an electric bicycle system

The basic configuration of an electric bicycle driveconsists of a controller that controls the power flow from thebattery to the electric motor. This power flow acts in parallelto the power delivered by the rider via the pedal of the bike(Fig. 1).

Riderinput

Pedals Gears

Motorcontrol

Motor

Drivewheel

BatteryBatterycharger

Vehicleassecoires

Fig. 1: Parallel Hybrid Schematic Diagram [13]

The rider of an E-bike can choose to1. Rely on the motor completely.2. Pedal and use the motor at the same time.3. Pedal only (use as a conventional bicycle).

B. Overview of electric bicycles worldwide

Electric bicycles have been gaining increasing attentionworldwide, especially in China, Europe, Japan, Taiwan, and

the United States. In the following, the most distinguishingaspects of electric bicycles in these countries are summa-rized, based on the authors own studies and Frank Jamer-sonsElectric bikes worldwide 2002 [1].

Today, China is the largest manufacturer of electricbicycles, exporting the majority of the electric bicycles, butalso meeting a strong local demand. According to ChinasElectric Bike General Technical Qualification GB17761-1999 [9], Chinese electric bicycles may not exceed 20 km/h,and may not be heavier than 40 kg.

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In Europe, most electric bicycles are manufactured inGermany and in the Netherlands, and Pedelec-type electricbicycles are more common.

In Japan, most electric bicycles are produced by theautomotive industry, and electric bicycles are required bylaw to be Pedelec-type bicycles. Electric bicycles producedin Taiwan are mostly exported to Europe.

In regard to the United States, electric bicycles are not aspopular as in the other mentioned countries, and most electricbicycles are imported. In some states, the federal law and thestate law for electric bicycles are different.

C. Aspects favoring the use of electric bicycles

A number of different aspects favor the use of electric bi-cycles in different situations. These include lower energycost per distance traveled (1 %2 % of going by car whengoing by electric bicycle) for a single rider, savings in othercosts such as insurances, licenses, registration, parking, im-provement of the traffic flow, environmental friendliness,and the health benefit for the rider (Table I).

TABLE IASPECTS FAVORING THE USE OF ELECTRIC BICYCLES

Energy costs

Averaging, costs*) are

$7.1/100miles = $4.4/100km for going by car,but only

$0.12/100miles = $0.7/100km for going by electricbicycle

Other costsGenerally, no insurance, license, registration, and

parking are needed.

Traffic flowMost states allow electric bicycles on bicycle paths:avoidance of traffic jams

Environmentalfriendliness

Zero-emission vehicle

Health benefitIncorporation of exercise and longer distancecommuting

*) Sample cost calculation for a 100 miles trip on a 2002 Mitsubishi Lancer:

Gas tank capacity: 28 miles/gallon [13]

Approximate gas rate as of November 2004: $2/gallon

Costs for 100 miles: 2 $/gallon / (28 miles/gallon) 100 miles = $7.1

Sample cost calculation for a 100 miles trip on an electric bicycle:

Power to travel at 10 mph: 120 W (experimentally obtained, see Fig. 4)

Duration: 100 miles/10 mph = 10 hours

Energy usage: 1.2 kWh

Madison Gas & Electric rate as of November 2004: $0.1/kWh

Costs for 100 miles: 1.2 kWh 0.1 $/kWh = $0.12

D. Performance range of commercially available electric

bicycles

Table II gives an overview of the performance range ofcommercially available electric bicycles today according tothe authors market research.

The specifications of electric bicycles vary according tothe bicycle design and the riding conditions for which theelectric bicycle is designed. The influence of several factorsand parameters on the different criteria is elaborated inSection III.

TABLE IIPERFORMANCE RANGE OF COMMERCIALLY AVAILABLE ELECTRIC BICYCLES

Speed

Average speed 12 mph 19 km/hMaximum speed**) 20 mph 32 km/hTravel range (Full charge) 10-50 miles 16-80 km

Batteries

Charging time 2-6 hoursCycles of charge/discharge Up to 400

Power

Power consumption(each full charge)

100-500 Wh

On-board power supply 12-36 V

Torque

Hill climbing ability up to 6 % slope

Weight

Electric bicycle kit excludingoriginal bicycle weight

10-50 lbs 4.6-22.8 kg

Price range

Electric bicycle kit only $250-$800Electric bicycle kit and bicycle(Custom built electric bicycles)

$800-$2600

**) Sec. 2085 of the federal law [14] defines a low-speed electric bicycle asa two- or three-wheeled vehicle with fully operable pedals and an electricmotor of less than 750 W, whose maximum speed on a paved level surface,when powered solely by such a motor while ridden by an operator whoweighs 170 pounds, is less than 20 mph.

E. Criteria for classification of electric bicycles

Criteria for classification of electric bicycles have beendetermined such that they are independent of the country andthe purpose of use. These are the bicycle kit type, motortype, motor assembly, assist type, throttle type, motorplacement, and battery type (Table III). The assets anddrawbacks of these criteria are shown for each sub-categoryin Table IV through Table X.

TABLE III

CRITERIA FOR CLASSIFICATION OF ELECTRIC BICYCLES

Bicycle kit type Custom built Add on

Table IV

Motor type***) Brushed DC machine Brushless DC machine

Table V

Motor assembly Gear Hub Friction

Table VI

Assist type Fully assist Half assist

Table VII

Throttle type Thumb throttle Twist throttle Push button

Table VIII

Motor placement Front wheel Rear wheel

Table IX

Battery type

Lead acid

NiMH Others

Table X

***) At large, both brushed and brushless dc motors are used by most electricbicycle or electric bicycle kit manufacturers. As far as the authors know,induction motors and synchronous motors are rarely used in commerciallyavailable electric bicycles, and thus they are not discussed here.

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TABLE IVASSETS AND DRAWBACKS OF DIFFERENT BICYCLE KIT TYPES

BICYCLE KIT TYPE

Custom built Add on

Assets: High end bicycles Good appearance

Safety features Little/no installation required

Assets: Comparatively inexpensive Mounting flexibility

Suitable for different bicycletypes Bicycle can be re-converted to aconventional bicycle

Drawback:

Comparatively high costsDrawbacks:

Installation needed

Connections may not be robust

TABLE VASSETS AND DRAWBACKS OF DIFFERENT MOTOR TYPES

MOTOR TYPE

Brushed DC motor Brushless DC motor

Asset: Simple controller

Assets: Higher efficiency than brushedmotor Reduced size when compared

with brushed motor

Drawbacks:

Lower efficiency than brushless

motor Brushes increase the motor size

and can increase the difficulty of

mounting the motor into the fork of

the bicycle

Drawback:

More complex controller than

brushed DC motor

TABLE VIASSETS AND DRAWBACKS OF DIFFERENT MOTOR ASSEMBLY TYPES

MOTOR ASSEMBLY TYPE

Gear Hub Friction

Asset: Reduced risk of acci-dental acceleration

Asset: Feels like moped/motorcycle

Asset: Inexpensive

Drawback:

May be less comfort-

table than other types

(personal preference)

Drawback:

Throttle can be

turned accidentally

Drawback:

Need of repetitive

pushing of the but-

ton for precise con-trol

TABLE VIIASSETS AND DRAWBACKS OF DIFFERENT ASSIST TYPES

ASSIST TYPE

Full assist Half assist

Choices of modes of operation: Pedaling only Motor operation only Pedaling and motor operation in

parallel

Choices of modes of operations: Motor assistance is only avail-able when the user is pedaling Level of assistance is deter-mined by the user input

Assets: Increased number of choices ofmodes of operation

Assets: Meets the law requirements inmore countries than the full assisttype

Drawbacks:

Not in all countries legally

allowed

Drawbacks:

Rider always has to pedal

TABLE VIIIASSETS AND DRAWBACKS OF DIFFERENT THROTTLE TYPES

THROTTLE TYPE

Thumb throttle Twist throttle Push button

Asset: Reduced risk of acci-dental acceleration

Asset: Feels like moped/motorcycle

Asset: Inexpensive

Drawback: May be less comfort-table than other types

(personal preference)

Drawback: Throttle can beturned accidentally

Drawback: Need to push buttonrepetitively for more

precise control

TABLE IXASSETS AND DRAWBACKS OF DIFFERENT MOTOR PLACEMENT TYPES

MOTOR PLACEMENT TYPE

Front Rear

Assets: Comparatively easy installation Good weight distribution Suitable for lowland and hillyregions with good roads

Assets: Best for light weight vehicles ingeneral, including bicycles Better traction for hill climbing Suitable for mountainous re-gions and poor ground conditions

Drawback:

Front wheel slides are moredangerous than rear wheel slides

Drawback:

Comparatively complex instal-lation

TABLE XASSETS AND DRAWBACKS OF DIFFERENT BATTERY TYPES

BATTERY TYPE

Lead acid NiMH OthersRegenerative

braking

Asset: Inexpensive

Assets: Light Good perfor-mance

Assets anddrawbacks

depend ontype

Assets: Recovered energyincreases the bi-

bicycle performance

Drawback:

Heavy

Drawback:

CostDrawback:

More complexcontroller than non-

re-generative type

F. Performance evaluation of electric bicycles

In a similar way, as with the previously specified criteriafor classification of electric bicycles, criteria have been de-fined to evaluate the performance of electric bicycles. Theseare technical performance, practicability, design, environ-mental friendliness, and cost and economics (Table XI). Thesub-categories of all criteria except for the technical perfor-mance, and cost and economics are commented individuallyin Table XII through Table XIV. The technical performancecharacteristics such as power, torque, and speed have beeninvestigated both theoretically and experimentally and arediscussed in Section III. Cost and economics have beendiscussed above in Table I.

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TABLE XICRITERIA FOR PERFORMACNE EVALUATION OF ELECTRIC BICYCLES

Technicalperformance

Power Torque Speed Efficiency Distance/charge

Section III

Practicability

Technical maturity Battery charging Operating condition Service/maintenance

Table XII

Design Ergonomics Safety Battery

Table XIII

Environment Pollution Noise

Table XIV

Cost & economics Unit price Other costs

Table I

TABLE XIIASPECTS OF THE DIFFERENT PRACTICABILITY CRITERIA

PRACTICABILITY CRITERIA

Technical maturity

Technical performance is improving, yet more work is needed to becompetitive with other vehicles More research is needed on the durability/lifetime of electric bicycles

Battery charging Long charging time: Typically 4 hours compared with 4 minutes for agasoline fueled vehicle Sparse availability of charging stations: Re-charging can often only

be done at home

Operating conditionAssets:

No age limit Generally no license required Easy to operate

Drawbacks:

Weather dependence

Not winter/wet weather/ rain friendly

Service / MaintenanceAsset: Conventional bicycle parts can be serviced by a conventionalbicycle shopDrawback: After sales service and maintenance are not wellestablished today.

TABLE XIIIASPECTS OF THE DIFFERENT DESIGN CRITERIA

DESIGN CRITERIA

Ergonomic Bicycle size is small. Parking is easy when compared with other

bicycles Honks, headlights, and disk breaks can be added for safety purposes

SafetyAsset: Not as explosive as fuel vehicles (accidents)

Drawback: More tests on general road safety and crash tests on

electric bicycles traveling at high speed are requiredBattery Significant component to increase the electric bicycle performancesignificantly. Lighter weight, higher energy density batteries are needed.

TABLE XIVASPECTS OF THE DIFFERENT ENVIRONMENTAL CRITERIA

ENVIRONMENTAL CRITERIA

Pollution No gas emission

Noise 55-60 dB compared with fuel/gas vehicles at 65-70 dB

III. INVESTIGATION OF TECHNICAL PERFORMANCEREQUIREMENTS

A. Theoretical background

The total powerPtotal required to drive the bicycle isgiven by the sum of the power to overcome the air drag Pdrag,the power to overcome the slopePhill, and the power to over-come the frictionPfriction. Equations (1) through (4) show therelationships as discussed in [6] and [8], where the symbolsfor the parameters, their units, along with some remarks aresummarized in Table XV.

frictionthilldragtotal PPPP ++= (1)

( ) gwgddrag vvvADC

P +

=2

2(2)

mvGP ghill = 81.9 (3)

gcfriction vRmP = 81.9 (4)

TABLE XVSYMBOL AND PARAMETER DEFINITION

SYMBOL PARA-METER

UNIT REMARKS

Cd Dragcoefficient

- The drag coefficient is small foraerodynamic bodies. Typicalvalues are: Passenger car: Cd= 0.3,recumbent bicyclist: Cd= 0.77,upright cyclist Cd= 1 [6], and

Cd= 0.5 for a cyclist [3].D Density of

airkg/m3

A Frontal area m2 The frontal area is the area of themass encountered by the air.Typical values are:A = 0.5m2 [3],

A = 0.4m2 [6]vg Ground

speedm/s

vw Head windspeed

m/s

G Slope grade - The slope grade is rise/run.For steep grades, G should beexpressed by arctan(rise/run).

m Weight****) KgRc Rolling

coefficient- The rolling coefficient depends on

friction effects. For example,

compacted gravel and smoothasphalt paths have different rollingcoefficient of 0.004 [3] and 0.014[6] respectively.

9.81 Gravityacceleration

m/s2

****) Rider and bicycle, including accessories

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The three cases that can be distinguished according toWilsonsBicycle Science [8] correspond to the following ri-ding conditions:

Case 1:

At speed greater than 3 m/s ( 6 mph) the majorityof the power is used to overcome the air drag

Flat ground, high speed:

Pdrag,Phill, = 0,Pdrag>Pfriction Case 2:

At speed less than 3 m/s ( 6 mph) and at level sur-faces, the majority of the power is used to overcomethe rolling resistance.

Flat ground, low speed:

Pfriction,Phill, = 0,Pfriction >Pdrag Case 3:

On steep hills, the power required for overcomingair drag and rolling resistance is small when com-pared with the power required to overcome theslope.

Hilly ground, low speed:Phill,Phill>Pdrag,Phill>Pfriction

B. Design of experimental evaluation of the technical per-

formance of electric bicycles

Two types of measurements were designed to experi-mentally evaluate electric bicycle performance during real-life-applications:

(1) The requirements in terms of powerPversus groundspeed vg with respect to the influence of the load m, slopegrade G, and head wind speed vw are experimentallydetermined.

(2) The riding profiles in terms of powerP, torque T, andground speed vg during riding intervals of different riders,where the bicycle is used for a short leisurely ride, groceryshopping, or commuting.

C. Test vehicle description and instrumentation

For the experimental investigation, an electric bicyclewith a brushed dc motor installed in the front hub, acontroller, thumb throttle and battery pack is used (Fig. 2).The hub-motor is not used during the measurements, yet,using this bicycle, the actual set up of an electric bicycle isrepresented. The torque and speed are directly measured inthe hub of the rear wheel of the test bicycle, using a PowerTap hub (Fig. 3) [15]. The measurement information istransmitted to the Power Tap CPU through the receiver.

Furthermore, the relative head-wind speed as seen whileriding is measured by means of an anemometer. The head-wind speed is then obtained from the difference ofanemometer and power tap speed.

Fig. 2: Electric bicycle test set-up used for the experimental investigation

Fig. 3: Power Tap hub used for the experimental investigation

D. Experimental investigation of power requirement as afunction of load, speed, and headwind

For these experiments, different riders rode the testbicycle without using the hub motor (see previous section)under different riding conditions. The experiments wereconducted for speed up to 12 mph (19 km/h) which is typicalfor city rides. The air density is approximated to be constant.Furthermore, based on the theoretical results, rolling anddrag coefficients are assumed to be almost constant and arenot investigated in detail. Three series of measurementswere carried out:

(1) Total powerPtotal versus ground speed vg as a functionof load m (Fig. 4).

(2) Total powerPtotal versus ground speed vg as a functionof slope grade G (Fig. 5).

(3) Total powerPtotal versus ground speed vg as a functionof wind speed vw (Fig. 6).

In the following, the measurement results are discussedsubsequently.

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0

50

100

150

200

250

300

5 6 7 8 9 10 11

154+20 kg

75+20 kg

64+20 kg

61+20 kg

(Rider + bicycle)

Speed (mph)

Power (W)

Fig. 4. Influence of the weight of rider and bicycle influence on the power

versus speed curve; no wind, constant slope G 1%

The series of measurements for total powerPtotal versusground speed vg as a function of load m illustrates equations(3) and (4): For a given ground speed vg, small variations in

load result in small variations in power requirement (20Wdifference of required power for 15 kg load variation). Fordoubled load, twice the power is required, as is illustrated bycomparing the curves for (64+20) kg and (154+20) kg load.Generally, a heavier rider also has a larger effective area Athat increases the power needed to overcome the air drag (2)and accounts for the non-linear increase from the curvesobtained for (64+20) kg and (154+20) kg load.

An addition of 10kg to the bicycle systems requires

additional power of approximately 10 W to 15 W. Thus,

there is not a significantly larger amount of energy needed to

propel the bike if the load difference is less than a few kilo-

grams.

0

50

100

150

200

250

300

350

5 6 7 8 9 10 11

4.0% 3.9%

2.4% 1.0%

Speed (mph)

Power (W)

Fig. 5. Influence of the slope of the path on the power versus speed curve;no wind, weight of rider and bicycle m = 81kg, all slopes taken as average

The series of measurements, total power Ptotal versusground speed vg as a function of the slope grade G, visualizesthe correlation of equation (3): For a given ground speed vg,Pfriction is constant, but Phill is directly proportional to theslope grade G. Thus, neglecting the Pdrag, Ptotal increases

linearly with the slope grade G. For approximately an 80 kgweight of rider and bicycle, 320 W (47 Nm torque) are re-quired to climb up a reasonable slope of 4% at 10 mph.

With electric bicycles rated at the maximum powerallowed by federal law of 750 W, the maximum torque capa-bility at 10 mph is 110 Nm. As a result, the steepest slopeelectric bicycles can climb at 10 mph ground speed is 8% . Itis important to note that unless riding in a hilly terrain, city

rides usually need high torques only for a short period of

time. Therefore, motors designed for city rides can have ra-

ted power below the federal law provisions.

0

10

20

30

40

50

60

70

80

90

100

3 4 5 6 7 8 9 10 11

1 mph3 mph

5 mph

6 mph

Speed (mph)

Power (W)

Fig. 6. Influence of the head wind on the power versus speed curve; nowind, weight of rider and bicycle m = 81kg, all head wind speeds taken asaverage

The measurement results for total power Ptotal versusground speed vg as a function of head-wind vw are in linewith equation (2): With increasing vw, the power require-ment increases. However, due to the very stochastic nature

of wind, this experiment only provides a rough idea of thetrend. Furthermore, crouching or an upright position affectsthe frontal area A. Yet, at the relatively low ground speedthis does significantly effect the power requirement, notablywith flat ground and at small headwind. Future work toobtain accurate results could be done by using wind tunnels.

It is important to note that headwind does not seem to be

a major criterion for city-ride electric bicycles, given the

usual profiles of city rides.

E. Experimental riding interval analysis

For the second group of measurement, four riders rodethe test bicycle around the city of Madison, WI, for 16 to 26

minutes. The average and maximum total power require-mentsPave /Pmax, torques Tave / Tmax, and ground speeds vave /vmax are summarized in Table XVI. For illustration, Figures7 and 8 show exemplarily the power versus time profiles ofthe two rides of Rider 1 and Rider 4. These two ridesrepresent the two extremes in terms of power requirementsthat are covered (Same scales on both figures by intention.).It should be noted that the maximum speed of the ride ofRider 4 exceeds the speed limit for low-speed electricbicycles according to U.S. law of 20 mph (Table II).

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TABLE XVIRESULTS OF INTERVAL RIDING ANALYSIS

Rider 1 Rider 2 Rider 3 Rider 4

Rider weight [kg] 50 75 85 95

Pave[W] 35.6 133.9 66.3 179.0Pmax [W] 204.0 389.1 368.6 857.0

Tave [Nm] 4.7 8.2 5.9 9.9

Tmax [Nm] 27.9 40.8 26.4 50.2vg,av [mph] 5.4 12.7 7.6 13.0vg,max [mph] 9.2 20.9 18.3 24.2

)vg,av [km/h] 8.7 20.4 12.2 20.9vg,max [km/h] 14.8 33.6 29.4 39.0

Interval time [min] 18 16 22 25

Energy [Wh] 11.9 35.7 24.31 77.6) Above the speed limit for low-speed electric bicycles according to U.S.federal law (Table II)

0

100

200

300

400

500

600

700

800

900

0 5 10 15 20 25Time (min)

Power (W)

Fig. 7. Power versus time profile of Rider 1 (Same scales as Fig. 8 by inten-tion)

0

100

200

300

400

500

600

700

800

900

0 5 10 15 20 25Time (min)

Power (W)

Fig. 8. Power versus time profile of Rider 4

The four riding profiles cover a broad spectrum ofPave,Pmax, Tave, Tmax, vave, and vmax. Neglecting the athletic figureof Rider 4, a maximum torque of 30 Nm, along with amaximum power of somewhat less than 400 W and anaverage torque of 6 to 8 Nm, along with an average power inthe order of 100 W, reflects the requirements of an averageride. It is noticeable that the ride of Rider 1 is shorter thanthe ride of Rider 3, and about as long as the ride of Rider 2,

but consumes less than 50% of the energy, because of thelower weight of the rider. Even with assuming an efficiencyof the drive of 50 %, the energy requirement of the rides ofRiders 1 through 3 could be met by a laptop-size battery.Such an energy source could be easily put on and taken offthe bicycle and the bicycle be recharged in a similar way as itis today common with cell phones.

IV. SUMMARY OF PERFORMANCE REQUIREMENTS

Drawing from the previous discussions, the electricbicycle performance evaluation is summarized in terms ofdifferent key parameters. These include market trends andregulations, opportunities for improvement by special-pur-pose-design to attract customers, identification of possiblyover-sized components and reduction of over-sizing, andidentification of areas where further research is needed(Table V). In a similar way as before (Section II), the sub-categories of the different areas are commented individuallyin Table XVIII through Table XXII.

TABLE XVIISUMMARY: ELECTRIC BICYCLE PERFORMANCE EVALUATION

Market trend Demand Publicity

Table XVIII

Regulations On-road law Bicycle assembly

Table XIX

Special-purpose bicycles

City bicycle Hill bicycle Distance bicycle Speedy bicycle

Table XX

Reduction of possibleover-sizing

Motor Battery

Table XXI

Research & Development Battery Technical Regenerative braking

Table XXII

TABLE XVIIICOMMENTS ON MARKET TRENDS

MARKET TREND

DemandThe market demand for electric bicycles might increase if non-greenvehicles are banned. For example, in Beijing, Tianjin, Guangzhoumunicipals banned the sales and operation of fuel-assisted vehicle.As a result, in the first half of 2000, sales of electric bicycles sales inShanghai increased 99.14%, compared with the same period in the

previous years.

PublicityMore publicity is needed to introduce the public to electric bicycles.

TABLE XIXCOMMENTS ON REGULATIONS

REGULATIONS

On-road lawU.S States have different law for electric bicycles, particularly as re-gards to the licensing aspect. Releasing electric bicycles from licen-sing would favor an increase of popularity.

Bicycle assemblyA uniform standard/guideline for designers/manufacturers of electric

bicycles would avoid the quality of electric bicycles to becompromised.

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TABLE XXSPECIAL-PURPOSE DESGIN OF ELECTRIC BICYCLES

SPECIAL-PURPOSE BICYCLES

City bicycleFast acceleration, frequent stopsAverage power 150 WAverage speed 17.6 km/h (11mph)

Hill bicycleHigh torque capability,Maximum power 300 W at 12.8 km/h (8 mph) for a short timecorresponding to a (4 % slope grade)

Distance bicycleDesigned for traveling at constant and comparatively low speed, but fora longer distanceFor example average speed 16 km/h (10 mph) at average power 100 W

Speedy bicycleFast acceleration capabilityHigh speed capability 29km/h (18mph),Average power 200 WFor example: guide bicycle in cycling competitions, vehicle for lawenforcers

TABLE XXICOMMENTS OF OVERSIZING RISK

POSSIBLY OVER-SIZED COMPONENTS

MotorMaximum power according to federal law: 750 W at 20 mph speedThis is much more power than is normal required with electric

bicycles.Electric bikes in the current market generally do not exceed 400 W.Drawing from Fig. 4 and Fig. 5, this value is a good guideline forgeneral design.

BatteryIn a similar way that with the motor, careful selection of the batterycould reduce the heavy battery weight. For example, drawing fromTable XVI, a laptop-size battery that could be easily put on and takenoff the bicycle would be sufficient for short rides up to 30 minutes.Then, the bicycle recharging would be handled in a similar way as it istoday common with cell phones.

TABLE XXIICOMMENTS ON RESEARCH AND DEVELOPMENT

AREAS OF FURTHER RESEARCH AND DEVELOPMENT

Battery Further investigation is needed to examine how improved batterytechnology could improve the performance of electric bicycles Further investigation on the importance and influence of batterydensity and charging time on electric bicycles is needed

Drive The motor should be designed to be most efficient over the operatingcycle. Further investigation is needed on the assets and drawbacks ofdifferent motor types and controllers.

Regenerative brakingRegenerative braking will be more useful in hilly areas or when

braking is used often as in city rides. Future work needs to identify thepercentage recoverable energy, the impact on efficiency, cost, andreduction of dependence on battery technology.

V. CONCLUSIONS

An important criteria for addressing the generallyassumed issues with high electric bicycle costs and weightthat include battery, controller, and motor are the possibilitiesoffered by custom-designed drives that are most efficient

over a given operating cycle. These include city bicycles,hill bicycles, distance bicycles and speedy bicycles.

The results can serve as a platform to improve electric bi-cycle performance if new drive systems are designed byrevealing the key parameters that will result in improvementof the system performance. Furthermore, they can be usedfor comparison of existing drives in a systematical, compre-hensive, and technical way.

REFERENCES

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[5] A. Muetze, A.G. Jack, and B.C. Mecrow, Alternate designs ofbrushless-dc motors using soft magnetic composites, Proceedings ofthe 15th International Conference on Electrical Machines (ICEM), paperno. 237, Bruges, 2002.

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[9]NASA http://gltrs.grc.nasa.gov/reports/2001/TM-2001-210972.pdf[10]United States Code http://www4.law.cornell.edu/uscode/#SECTIONS[11]Extra energy http://extraenergy.org/main.php[12]Chinas Electric Bike General Technical Qualification [in Chinese],

http://www.wxetc.gov.cn/article.php/127

[13]2002 Mitsubishi Lancer mpg obtained from the United States FuelEconomy Guide http://www.fueleconomy.gov/feg/noframes/17596.shtml

[14]United States Code http://www4.law.cornell.edu/uscode/#SECTIONS[15]Power Tap is by Graber Products, Inc., 5253 Verona Road, Madison,

WI USA. www.cycle-ops.com

IAS 2005 2872 0-7803-9208-6/05/$20.00 2005 IEEE

performance evaluation of electric bicycles

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